Blood-brain barrier disruption in Long COVIDassociated cognitive impairment
Chris Greene
Trinity College Dublin https://orcid.org/0000-0003-4192-9433
Ruairi Connolly
Trinity College Dublin
Declan Brennan
Trinity College Dublin
Aoife Laffan
St James' Hospital
Eoin O'Keeffe
Trinity College Dublin
Lilia Zaporojan
Trinity College Dublin
Emma Connolly
Trinity College Dublin
Cliona Ni Cheallaigh
Trinity College Dublin
Niall Conlon
St James' Hospital
Colin Doherty
St James's Hospital
Matthew Campbell
Trinity College Dublin https://orcid.org/0000-0003-3325-240X
Article
Keywords: SARS-CoV-2, long COVID, blood-brain barrier, brain fog
Posted Date: January 23rd, 2023
DOI: https://doi.org/10.21203/rs.3.rs-2069710/v2
Page 1/25
License: This work is licensed under a Creative Commons Attribution 4.0 International License.
Read Full License
Additional Declarations: There is NO Competing Interest.
Version of Record: A version of this preprint was published at Nature Neuroscience on February 22nd,
2024. See the published version at https://doi.org/10.1038/s41593-024-01576-9.
Page 2/25
Abstract
Vascular disruption has been heavily implicated in COVID-19 pathogenesis and may predispose the
neurological sequelae associated with the condition now known as long COVID. To date, no studies have
objectively assessed blood-brain barrier (BBB) function in individuals with neurological complications
stemming from prior SARS-CoV-2 infection. Here, we explored the neurobiological effects of SARS-CoV-2
infection in humans with acute infection (n = 76) and those with persistent long COVID with and without
neurological impairment. Following acute infection, patients with neurological impairment had increased
serum S100β, indicative of BBB disruption. Furthermore, using dynamic contrast-enhanced magnetic
resonance imaging (DCE-MRI) in long COVID patients (n = 32), we observed elevated BBB permeability in
distinct neuroanatomical regions including the frontal cortex, occipital lobe and temporal lobes which
correlated with global brain volume and white matter volume de cits in patients with neurological
impairment. Patients with neurological impairment had increased levels of blood-based biomarkers
including GFAP, TGFβ and IL8 with levels of TGFβ that correlated with BBB permeability and structural
brain changes. Peripheral blood mononuclear cells isolated from unaffected and long COVID patients
had persistent upregulation of in ammatory markers including IFNA/G and showed increased adhesion
to human brain endothelial cells in vitro. Finally, exposure of endothelial cells to serum from long COVID
patients induced increases in ICAM-1, VCAM-1 and TNF irrespective of neurological sequelae. Together,
these data suggest that sustained systemic in ammation and persistent localised BBB dysfunction is a
feature of long COVID-associated neurological impairment. Importantly, this may also be therapeutically
relevant in the treatment and clinical management of this patient group.
Introduction
Coronavirus disease 2019 (COVID-19) is a clinical syndrome caused by a novel coronavirus, severe acute
respiratory syndrome coronavirus-2 (SARS-CoV-2). COVID-19 primarily affects the respiratory tract and
can progress to respiratory compromise, severe acute respiratory distress syndrome and death1,2.
Neurological sequelae of COVID-19, colloquially known as “brain fog” are increasingly being reported and
include headache, fatigue, malaise and altered levels of consciousness. Acute respiratory distress
syndrome (ARDS) due to COVID-19 has been associated with encephalopathy, agitation, confusion, and
corticospinal tract dysfunction. Such symptoms however, including anosmia (although not to the extent
seen in the rst wave of COVID-19), may be expected in anyone recovering from a severe viral illness due
to cytokine release, critical illness encephalopathy, or medication3. Clinical observations of neurological
complications in 236,379 patients in the 6 months following a COVID-19 diagnosis have found that
33.62% of patients were estimated to have demonstrated clinically signi cant neurological or psychiatric
dysfunction4. Neurological problems have been reported in other respiratory viral infections including
in uenza, coronavirus and metapneumovirus with febrile or afebrile seizures, status epilepticus,
encephalopathies and encephalitis being the most frequently reported5. However, there is still little
understanding of the pathogenesis and long-term outcome of neurological problems following SARSCoV-2 infection. SARS-CoV-2 gains cellular entry via its receptors ACE2 and TMPRSS2, but it may enter
Page 3/25
via other receptors including neuropilin and vimentin, all of which are enriched in vascular cells6–10. There
are, however, con icting reports regarding the neuro-invasiveness of SARS-CoV-2 and indeed the cellular
expression of the receptors11–15, suggesting that other mechanisms are responsible for the neurological
problems reported. A recent preprint suggests persistence of viral RNA in multiple anatomic sites
including the brain for up to 230 days following symptom onset, though, these data are from postmortem donor tissues which represent the sickest of individuals16.
One hypothesis suggests that breakdown to the integrity of the blood-brain barrier (BBB) and subsequent
brain penetration of serum components is responsible for the neurological manifestations following
SARS-CoV-2 infection. The BBB is formed by endothelial cells lining cerebral blood vessels and supported
by surrounding cells including astrocytes, pericytes, microglia, neurons and the acellular basement
membrane17. The barrier is characterised by an enrichment of interendothelial tight junction proteins, a
variety of luminal and abluminal transporters and luminal e ux transporters which together maintain
separation of the blood and brain and tightly regulate molecular tra cking between the blood and brain
and vice versa18.
There is clear evidence of microvascular injury in the brains of deceased COVID-19 patients, including
brinogen leakage, and thinning of the endothelial cell basal laminae in the olfactory bulb13,19. A more
comprehensive evaluation of the same cohort using spatial transcriptomics revealed more detailed
vascular and immunological features of microvessels in the brain including serum protein extravasation,
platelet accumulation and coagulation system activation20. Numerous studies have also examined BBBrelated changes and responses to SARS-CoV-2 infection or spike protein treatment in post-mortem tissue
and animal models13,14,19,21−35. Indeed, it has been shown that the spike protein can cross the BBB in
rodents which may cause neuroin ammation and cognitive changes32. However, the cerebrovascular
pathology in patients and the underlying mechanisms are still unclear, especially in individuals with long
COVID.
The lack of a speci c neurological signature of the disease is interesting as other zoonotic betacoronaviruses often produce robust and predictable neurological injury36. In humans, data from SARS
and MERS also shows that neurological injury in humans is rare, strongly suggesting that, normally, the
BBB provides robust neuroprotection from viral CNS invasion in the majority of patients37. The clinical
manifestation of SARS-CoV2 induced BBB alterations in patients have not yet been reported.
Here, we hypothesised that the neurological response to COVID may be due to BBB breakdown and
subsequent extravasation of serum components. We show that BBB disruption is evident in acute
neurological COVID patients and that a cohort of patients with persistent “brain fog” have BBB disruption
on neuroimaging which was associated with circulating biomarkers of neuroin ammation and BBB
breakdown. We suggest that measurement of BBB integrity may be a clinically useful biomarker of the
neurological sequelae that is associated with COVID-19 in some patients. Added to this, targeted
Page 4/25
regulation of BBB integrity may also represent a novel method of clinically managing patients with long
COVID.
Results
Acute COVID-induced brain fog is associated with BBB
dysfunction
We obtained serum samples from 76 in-patients with acute COVID-19 recruited as part of the St James
Hospital STTAR Bioresources collection during the initial wave of COVID-19 in March/April 2020 (Fig.
1a)38. 25 unaffected control samples were collected prior to the COVID-19 pandemic. The mean age of
control and COVID samples was 44 and 44.7 respectively. The most frequent presenting symptoms
included dyspnoea (47), loss of smell and taste (46), cough (45), fatigue (40) and fever (36). As
previously reported, more males than females had severe COVID (***p < 0.001) and more males required
supplemental oxygen (**p = 0.002) (Table 1). Serum samples were screened on a Luminex 10-plex kit for
in ammatory and BBB dysfunction markers. Severity of COVID-19 was determined according to the WHO
Severity Guidelines with 25 unaffected, 43 mild, 10 moderate and 23 severe. We found a signi cant
increase of IL8 (**p = 0.01 vs unaffected) in moderate cases. There was a signi cant increase in TNF
(**p = 0.004 vs unaffected; **p < 0.002 vs mild), IL6 (**p = 0.002 vs unaffected; ***p < 0.001 vs mild) and
IL8 (***p < 0.001 vs unaffected; *p = 0.03 vs mild) cytokines in severe COVID-19 patients (Fig. 1a).
Strati cation of patients according to presence or absence of brain fog revealed a signi cant increase in
serum concentrations of TNF (**p = 0.003), IL6 (***p < 0.001), IL8 (**p = 0.008) and S100β (*p = 0.010) in
brain fog patients after controlling for age, sex and severity of infection (Fig. 1c). There was a signi cant
increase in serum concentrations of TNF (***p < 0.001), IL6 (***p < 0.001) and IL8 (*p = 0.038) in patients
requiring supplemental oxygen (Figure S1a) while there was a signi cant increase in TNF (**p = 0.005),
IL6 (***p < 0.001) and IL8 (*p = 0.046) in patients requiring hospitalisation (Figure S1b). Spearman’s
partial correlation analysis revealed a signi cant correlation between WHO Severity of COVID-19 and
serum concentrations of TNF, IL6 and IL8 (r = 0.367, ***p = 0.002; r = 0.425, ***p < 0.001; and r = 0.231, *p
= 0.047 respectively after adjusting for age and sex) (Figure S2a-c). Of the 76 patients, 36 had a second
blood sample drawn owing to deterioration of clinical symptoms so serum concentrations of all analytes
were assessed between timepoint 1 and 2 (T1 and T2) to monitor disease progression. There was a
signi cant increase in serum concentrations of IL8 (***p < 0.001 Wilcoxon signed-rank test) between T1
and T2 (Figure S3).
Bbb Dysfunction Is Associated With Long COVID-induced Cognitive
Impairment
Given the signi cantly increased serum concentrations of S100β our data indicated that active/acute
SARS-CoV-2 infection is associated with BBB dysfunction in individuals with neurological impairment. To
directly visualise BBB function, we recruited 10 recovered and 22 Long COVID patients who were
Page 5/25
diagnosed with COVID-19 during the rst outbreak of disease in Ireland in April 2020 (Fig. 2a and
Table 2). All participants were recruited from St James Hospital Dublin and were PCR con rmed cases of
COVID-19. None of the patients in this cohort had received a vaccine. We used a quick smell identi cation
test (Q-SIT) based method to determine objective anosmia status in participants and determined a strong
correlation of reported anosmia status and Q-SIT score, providing an excellent readout of the utility of
objective anosmia measurement in prolonged anosmia after COVID-19. Participants were grouped
according to the presence or absence of brain fog (brain fog (-) or brain fog (+)). We hypothesised that
COVID-19 associated cognitive impairment may be a strong predictor of BBB disruption in COVID-19
patients. Brain fog patients reported a mean symptom duration of 222.75 days while non-brain fog
participants had a mean symptom duration of 170.55 days. Participants were scanned an average of 146
days following SARS-CoV-2 infection (Table 2). 16 (50%) participants reported anosmia which was
con rmed by Q-SIT testing (average score 1/3; 159 +/- 88 days duration) at the time of scanning. 6
participants (all brain fog) showed mild-moderate cognitive impairment on the MOCA test (score 18–25)
along with de cits in recall, executive function and word nding (Table 2).
While standard diagnostic MRI scans showed no pathological ndings in any participant, DCE-MRI
imaging revealed signi cantly increased whole brain leakage in COVID-19 patients with brain fog (Fig. 2bd) with increased percentage of brain volume with leaky blood vessels in the brain fog cohort compared
to the cohort without brain fog (***p < 0.001). Stratifying the cohort into recovered, long COVID without
brain fog and long COVID with brain fog revealed signi cantly increased BBB permeability in the brain
fog cohort compared to recovered (*p = 0.014) and long COVID without brain fog (***p < 0.001). Region of
interest analysis identi ed signi cantly increased leakage in the right and left temporal lobes (p***<0.001
and p = 0.005 respectively) and right and left frontal cortex (**p = 0.005 and **p = 0.004 respectively) (Fig.
2e-i). Stratifying the groups according to recovered, long COVID or brain fog revealed signi cantly
increased BBB permeability in the brain fog group only in the right (**p = 0.007 vs recovered; **p = 0.008
vs long COVID) and left (*p = 0.035 vs recovered; p = 0.051 vs long COVID) temporal lobe and right (*p =
0.015 vs long COVID) and left (*p = 0.05 vs recovered; *p = 0.025 vs long COVID) frontal cortex (Figure
S4a-e). There was no association between BBB permeability and anosmia status, duration of anosmia, QSIT or MOCA scores (Figure S5), however regional BBB permeability in the right (r = 0.546, **p = 0.002)
and left (r = 0.532, **p = 0.002) temporal lobes correlated with the duration of anosmia.
Long COVID Associated Brain Fog Induces Structural Changes In The
Brain
To explore if there were structural brain changes accompanying increased BBB permeability in our
cohorts, we conducted volume and thickness measurements on recovered, long COVID and 60 agematched healthy controls from the publicly available IXI dataset (Table 2) and examined global brain
volume, cerebrospinal uid (CSF) volume and right and left volumes of cerebral and cerebellar white and
grey matter and brainstem, hippocampus, and amygdala. Comparing individuals with prior COVID
infection to unaffected revealed volumetric de cits predominantly in the frontal and temporal lobes and
Page 6/25
increases in the lateral ventricles and occipital lobes (Fig. 3a) while groupwise comparisons of
macrostructures revealed decreased global brain volume in brain fog patients (**p = 0.001) along with
signi cantly reduced cerebral white matter volume in both hemispheres in the recovered (***p < 0.001)
and brain fog (***p < 0.001) cohorts along with reduced cerebellar white matter volume in recovered (***p
< 0.001, right; **p = 0.006, left), long COVID (**p = 0.01, right; *p = 0.049, left) and brain fog (***p < 0.001,
right and left) cohorts (Fig. 3b-e and Table 3). There was signi cantly increased CSF volume in the brain
fog cohort only (**p = 0.005) (Fig. 3f and Table 3). Cortical thinning was also evident predominantly in the
temporal and frontal lobes when looking at all patients with prior SARS-CoV-2 infection compared to
unaffected controls (Fig. 3g). When comparing groups, there was reduced thickness in the fontal pole in
recovered (**p = 003), long COVID (**p = 0.002) and brain fog (***p < 0.001); superior frontal gyrus in long
COVID (**p = 0.003) and brain fog (**p = 0.002); middle temporal gyrus in brain fog only (*p = 0.016); and
superior temporal gyrus (***p < 0.001) in brain fog only. Spearman partial correlations revealed signi cant
negative associations between the number of BBB disrupted voxels with global brain volume (r=-0.528,
**p = 0.002), right (r=-0.424, *p = 0.022) and left (r=-0.466, *p = 0.011) white matter volume, and right
(r=-0.503, **p = 0.005) and left (r=-0.493, **p = 0.007) cerebral volume and was positively associated with
CSF volume (r = 0.532, **p = 0.002) (Fig. 4a-g).
Immunovascular Dysregulation In Long COVID Blood Samples
Finally, we analysed blood-based biomarkers of neuroin ammation and BBB dysfunction in the long
COVID cohort. We selected markers previously associated with BBB dysfunction, neuroin ammation and
chronic fatigue syndrome including S100β, GFAP, TGFβ, IL6, IL8 and CCL2. Individuals with brain fog had
signi cantly increased GFAP (*p = 0.022), TGFβ (**p = 0.004) and IL8 (*p = 0.0427) compared to
unaffected, recovered, and long COVID without brain fog. Levels of phosphorylated TAU, sICAM1 and
S100β were comparable between groups (Fig. 5a-e). This differs from the blood analysis of the patients
with acute COVID and suggests a temporal change in the utility of these markers for prognosis and
clinical management. Next, we performed Spearman partial correlation analysis adjusting for age and
sex to identify any associations between neuroin ammatory/BBB dysfunction markers with BBB
permeability assessed by DCE-MRI. Levels of TGFβ were signi cantly associated with the percentage of
brain volume displaying leaky blood vessels (r = 0.501, **p = 0.008) as well as with global brain volume
(r=-0.394, *p = 0.042), CSF volume (r = 0.438, *p = 0.020), brainstem volume (r=-0.656, p < 0.001) and
amygdala volume (r=-0.402, *p = 0.038) (Fig. 5f-j and Figure S6).
White Blood Cells From COVID Patients Activate Brain Endothelial
Cells
Given the prevalence of circulating markers indicative of BBB dysfunction and immune cell activation, we
examined gene expression changes in PBMCs isolated from long COVID patients which revealed
increased expression of interferon signalling components and in ammatory markers independent of
neurological impairment indicating sustained in ammatory responses in all groups including recovered
Page 7/25
individuals (Fig. 6a-f). We next examined immunovascular interactions in PBMCs isolated from patients
with COVID and found increased adhesion of PBMCs to human brain endothelial cells in the long COVID
group compared to unaffected (***p < 0.001) which was heightened in the presence of TNF (**p = 0.0031
vs control) (Fig. 6g, h). Furthermore, exposure of human brain endothelial cells to 10% serum from
recovered, and long COVID groups resulted in the upregulation of ICAM1 (**p = 0.0081), VCAM1 (*p =
0.0127) and TNF (**p = 0.004) transcripts compared to unaffected sera (Fig. 6i-l). Exposure of human
brain endothelial cells to S1 spike protein had similar effects with dose-dependent increases in TNF (*p =
0.045), TGFβ (*p = 0.017), ICAM1 (p = 0.057) and VCAM1 (***p < 0.001) (Figure S7) following 72 hours
treatment with 0-400 nM S1 spike protein.
Discussion
Overall, our results suggest that long COVID “brain fog” is associated with impairment of BBB function
and increased expression of systemic in ammatory and BBB dysfunction markers including GFAP, TGFβ
and IL8. BBB dysfunction was unique to the brain fog cohort in our study with sustained dysfunction up
to one year following recovery from active infection with dysfunction evident in multiple neuroanatomical
regions including the temporal lobes and frontal cortex. We found no evidence of BBB dysfunction in
patients with anosmia without accompanying brain fog suggesting that cerebrovascular dysfunction in
the olfactory bulb does not clearly drive this condition. It has been shown instead that accumulation of
in ltrating T-cells expressing interferon-gamma results in reduction of olfactory sensory neurons relative
to support cells in patients with long COVID associated anosmia39. It is possible that this sustained
in ammatory response in the olfactory epithelium results in cerebrovascular damage in the olfactory
bulbs and higher resolution MRI could help to tease out these changes. We did observe a signi cant
correlation between BBB disruption in the temporal lobes with the duration of anosmia. The temporal
lobe contains important regions that form part of the primary olfactory cortex including the piriform
cortex, amygdala and entorhinal cortex with direct connections from and to the olfactory bulb
encompassing regions of the piriform cortex, parahippocampal gyrus and entorhinal cortex along with
orbitofrontal areas40–42. The hippocampus is also important for odour recognition memory and it is
possible that BBB dysfunction in these regions contributes to anosmia or hyposmia41. In the brain fog
cohort, we found evidence of reduced global brain volume along with reductions in white matter in
cortical and cerebellar tissue that was also apparent in individuals who had recovered from infection
suggesting that these changes do not drive the fatigue and cognitive slowing associated with brain fog in
this condition. Other groups have also found changes on neuroimaging following mild infection. Initial
systemic neuropathological changes in patients with COVID-19 appeared to be mild, with marked
brainstem neuroin ammation the most common nding43. In a three-month follow up MRI study of
COVID-19 patients, higher grey matter volumes were found in several cerebral territories, including the
olfactory cortices, hippocampi, and cingulate gyri which may be a marker of acute or sub-acute
in ammation43. A recent large cohort study revealed longitudinal changes in brain volume and cortical
thinning following mild SARS-CoV-2 infection42. Neuroimaging has also been used to detect other
Page 8/25
cerebrovascular changes in the brain following SARS-CoV-2 infection. Abnormalities detected include
cerebral microbleeds, hypometabolism and cerebral hypoperfusion in several brain regions29,44−47.
BBB dysfunction was evident in individuals suffering acute neurological impairment during the active
phase of SARS-CoV-2 infection with increased serum levels of the astrocytic protein S100β together with
increased expression of TNF and IL6 after adjusting for age, sex, and severity of infection. This suggests
that a heightened in ammatory response in this neurological cohort may drive BBB dysfunction. Serum
levels of S100β have previously been found elevated in several neurological disorders including epilepsy,
traumatic brain injury and schizophrenia48–50. However, longitudinal studies will be required to determine
if BBB disrupted acute COVID patients are more likely to develop long COVID-associated brain fog.
We also found increased expression of IL8 in individuals with deteriorating clinical symptoms. In the long
COVID cohort, levels of IL8, GFAP and TGFβ were elevated in the brain fog group only. GFAP is a marker
of cerebrovascular damage and has previously been shown to be elevated following repetitive head
trauma, re ecting BBB disruption, as seen in contact sport athletes24,51. Interestingly, TGFβ was strongly
associated with the number of BBB disrupted blood vessels along with global brain volume and white
matter volume changes. TGFβ has been implicated in the pathogenesis of chronic fatigue syndrome, a
condition noted for its overlap of brain fog with COVID 52–54.
Several studies have examined BBB function in animal models of SARS-CoV-2 infection and in postmortem tissue to understand the impact of acute infection on BBB integrity. The spike protein of SARSCoV-2 was shown to cross the BBB while direct intrahippocampal injection induced cognitive de cits and
anxiety-like behaviour in mice32,55. In samples from patients who died during the initial wave of COVID in
2020, Lee et al. showed brinogen extravasation and evidence of overactivation of the coagulation
system19,20 while Wenzel et al. found string vessels, pathological blood vessels without endothelial
cells25. A few studies have also examined changes in systemic markers in convalescent COVID patients
and pinpoint to strong upregulation of biomarkers of in ammation and innate immunity and
downregulation of platelet-related pathways56. Persistent immune activation has also been reported in
individuals with long COVID up to 8 months post infection57.
Long COVID is a signi cant burden in many patients post recovery from COVID-19. Patients describe
fatigue, memory loss, dyspnoea as some of the key symptoms of long COVID, while another subset of
patients describe “brain fog” like that commonly reported in post-concussive syndrome and chronic
fatigue syndrome58,59. In this study, we assessed BBB integrity in a series of patients who had recovered
from infection but had symptoms persisting up to 1 year following infection. Our data suggest that BBB
disruption is strongly associated with long COVID-associated cognitive impairment with regional
differences in BBB integrity in long COVID patients displaying brain fog. Our biomarker analysis in acute
COVID patients suggests that a subset of infected individuals with acute cognitive impairment have a
disrupted BBB as determined by serum presence of the astrocytic protein S100β. This study is the rst to
focus on long COVID patients with or without neurological impairment and compare them to individuals
Page 9/25
who recovered from a previous SARS-CoV-2 infection. Individuals with brain fog have persistent BBB
dysfunction which could be detected by DCE-MRI and plasma assessment of circulating biomarkers. This
provides the rst objective evidence for a link between BBB disruption and cognitive impairment within a
cohort of patients with long COVID. Further longitudinal studies will be required to examine changes in
BBB permeability over time, however, targeted regulation of BBB integrity could now potentially be
considered for the treatment of patients with brain fog associated with long COVID.
Methods
Study participants
Participants included recovered COVID-19 patients, male or female aged 18 and above with and without
neurological symptoms. Participants with long COVID, with symptom persistence over 12 weeks from
infection were also recruited. Candidates were excluded if they had a history of a neurological disorder
that may better explain the results of the study such as epilepsy, brain trauma, neuropsychiatric disorder,
or mild cognitive impairment. Suitable candidates proceeded to assessment with DCE-MRI imaging, Q-SIT
olfactory testing and a review of pulmonary imaging and haematological parameters at the time of
COVID-19 diagnosis. The Joint Research Ethics Committee (JREC) of St James’s and Tallaght Hospital’s
approved the study and informed consent was obtained from all participants. Research was performed
according to the principles of the Declaration of Helsinki. The legal basis for the Study was consent
according to GDPR principles.
Olfactory Testing
Participants olfactory function was assessed using the quick smell identi cation test (Q-SIT). The Q-SIT
is a standardised and validated three item odour identi cation screen60. A score of 2 or more is a normal
test and cut-off score of 1 or less is an abnormal test for anosmia. Q-SIT has displayed high positive and
negative predictive value in detecting olfactory dysfunction in COVID-19 patients. In addition, the Q-SIT is
a tear-off card test is disposable so there is no concern about contamination and transmission of disease
form COVID-19 patients61.
Dynamic Contrast-enhanced Magnetic Resonance Imaging
BBB permeability maps were created using the slope of contrast agent concentration in each voxel over
time, calculated by a linear t model as previously described62,63. Thresholds of high permeability was
de ned by the 95th percentile of all slopes in a previously examined control group. Imaging was
performed with a 3T Philips Achieva scanner. Sequences included a T1- weighted anatomical scan (3D
gradient echo, TE/TR = 3/6.7 ms, acquisition matrix 268x266, voxel size: 0.83x0.83x.9mm), T2-weighted
imaging (TE/TR = 80/3000 ms, voxel size: 0.45x0.45x.4mm), FLAIR (TE/TR = 125/11000 ms, voxel
size:0.45x0.45x4mm). For the calculation of pre-contrast longitudinal relaxation time (T10), the variable
Page 10/25
ip angle (VFA) method was used (3D T1w-FFE, TE/TR = 2.78/5.67 ms, acquisition matrix: 240x184,
voxel size: 0.68x0.68x5 mm, ip angles: 2, 10, 16 and 24°). Dynamic contrast enhanced (DCE) sequence
was then acquired (Axial, 3D T1w-FFE, TE/TR = 2.78/5.6 ms, acquisition matrix: 240x184, voxel size:
0.68x0.68x5 mm, ip angle: 6°, Tt = 6.5 Sec, temporal repetitions: 61, total scan length: 22.6 minutes). An
intravenous bolus injection of the contrast agent gadobenate dimeglumine (Gd-BOPTA, Bracco
Diagnostics Inc., Milan, Italy) was administered using an automatic injector after the rst three DCE
repetitions. To control for interindividual variabilities due to heart rate, blood ow or rate of contrast
injection, each voxel’s leakage rate was normalised to that of the superior sagittal sinus. The percent of
suprathreshold voxels was used as a measure re ecting global BBB leakage.
Volumetric And Thickness Measurements
T1-weighted anatomical images were uploaded to the VolBrain online brain volumetry software
(https://volbrain.upv.es)64, and analysed with vol2brain 1.0 which is an online pipeline that registers
images to the Montreal Neurological Institute (MNI) space, and reports the volumes of expert-labelled
anatomical structures as percentage of total intracranial volume. We analysed the volume of the
right/left cerebral and cerebellar grey/white matter, frontal, temporal, parietal and occipital and CSF along
with thickness of the frontal, parietal, occipital and temporal lobes. All volume data was normalised to
total intracranial volume (TIV) which is the sum of grey matter, white matter and CSF. Volumes were
expressed as a percentage of TIV. 60 age and sex matched healthy control scans were randomly selected
from the IXI dataset (https://brain-development.org/ixi-dataset/) which represents 10% of the entire
dataset. All scans were performed on the same Philips 3T system at Hammersmith Hospital. Volumetric
maps for comparisons between COVID positive and negative groups were generated in xjview following
automatic brain segmentation in the CAT12 toolbox with default parameters and subsequent smoothing
with an 8 mm kernel. Thickness maps for comparisons between COVID positive and negative groups
were generated in CAT12 toolbox run in SPM12 in MATLAB R2021a following brain segmentation as
above and smoothing with a 15 mm kernel. Two-sample t-test was used for statistical analysis with age,
sex and TIV as covariates.
Sample Collection
Blood samples were collected into serum separator tubes and EDTA-coated tubes for serum and PBMC
isolation respectively. Serum was separated by centrifugation at 2000 rpm for 10 min at room
temperature. PBMCs were separated via layering of blood samples diluted twofold in PBS (ThermoFisher,
#14190) over Lymphoprep™ density gradient medium (Stemcell Technologies, #07851) followed by
centrifugation at 400 rcf for 25 min at room temperature at 0 break and 0 acceleration. Plasma was
collected and PBMC layer was collected into a new 50 ml falcon tube, resuspended to 50 ml with PBS
and centrifuged at 2000 rpm for 5 min at room temperature. PBMCs were resuspended in 50 ml PBS and
centrifuged at 1000 rpm for 10 min at room temperature. PBMCs were resuspended to 2 x 106 cells/ml in
Page 11/25
RPMI 1640 media with L-glutamine (Lonza, #LZBE12-702F) supplemented with 50% fetal bovine serum
(Merck, #F7524) and 10% DMSO (Merck, #D5879) and frozen at -800C overnight before being moved to
liquid nitrogen.
Luminex Assay
A 10-plex Luminex assay (R&D Systems, #LXSAHM-10) was used for cytokine pro ling. Serum samples
were diluted twofold in sample dilution buffer. Then, 50 µl of sample or standard were pipetted in
duplicate into each wall of an assay 96 well plate. 50 µl of diluted Microparticle Cocktail were added to
each well, the plate was covered and incubated for 2 hours at room temperature on a shaker at 300 rpm.
Wells were washed 3 times with Wash Buffer before addition of 50 µl of diluted Biotin-Antibody Cocktail.
The plate was covered and incubated for 1 hour at room temperature on a shaker at 300 rpm. Wells were
washed as above before addition of 50 µl of diluted Streptavidin-PE to each well. The plate was covered
and incubated for 30 min at room temperature on a shaker at 300 rpm. Wells were washed as above
before microparticles were resuspended in 100 µl of Wash Buffer. The plate was incubated for 2 min at
room temperature on a shaker at 300 rpm and was read on a MAGPIX plate reader (Luminex).
Dot Blot
Plasma samples were spotted (2 µl) onto 0.2 µm nitrocellulose membrane (Whatman, #10401391) and
allowed to dry for 30 minutes. Membranes were blocked in 5% bovine serum albumin (BSA, Merck,
#A7906) in phosphate buffered saline supplemented with 0.1% Triton X-100 (PBST) for 1 hour at room
temperature. Membranes were incubated overnight in primary antibody in blocking buffer. Membranes
were washed three times for ve minutes each in PBST, followed by incubation in secondary HRPconjugated antibodies. Membranes were washed three times for ve minutes each in PBST and
incubated with strong ECL substrate (Advansta, #K-12045-D50) for 2 min before being developed on a CDigit (LiCor). Protein bands were quanti ed in ImageJ (National Institutes of Health, Rockville, MD, USA).
Primary antibodies used were mouse anti-GFAP (1/500, Merck, #G3893), rabbit anti-TGFβ (1/500, Abcam,
#ab92486) and mouse anti-Phospho-Tau (1/500, Fisher Scienti c, #10599853). Secondary antibodies
used were anti-mouse HRP (1/5000, Merck, #A4416) and anti-rabbit HRP (1/5000, Merck, #A6154).
RT-qPCR
RNA was isolated from PBMCs and the human brain endothelial cell line hCMEC/d3 (Millipore, #SCC066)
with the Omega RNA isolation kit (Omega, #R6834-02) according to manufacturer’s instructions. cDNA
was reverse transcribed from 500 ng RNA with the High-Capacity cDNA Reverse Transcription Kit (Applied
Biosystems, # 4368814). Transcript levels were quanti ed on a StepOne Plus instrument (Applied
Biosystems) with FastStart Universal SYBR Green Master (ROX) master mix (Roche, #04913914001). RTPCR was performed with the following conditions: 950C x 2 min, (950C x 5s, 600C x 30s) x40, 950C x 15s,
Page 12/25
600C x 1 min, 950C x 15s, 600C x 15s. Primer sequences for RT-PCR experiments are supplied in
Supplementary Table 4. Relative gene expression levels were quanti ed using the comparative CT
method (ΔΔCT). Expression levels of target genes were normalised to β-actin.
Adhesion Assay
hCMEC/d3 cells were cultured in EGM2-MV growth medium (Lonza, #CC-3202) and were stimulated with
10 ng/ml recombinant human TNF-a (Peprotech, #300-01A) for 4 hours and incubated with 1x105
MitoTracker Orange (ThermoFisher, # M7510) labelled PBMCs for 1 hour at 37oC. Cells were washed
three times in PBS to remove unbound PBMCs and xed in 4% formaldehyde (Merck, #F1635) for 10 min
at room temperature. The number of adhered PBMCs was counted with the ImageJ cell counter plugin.
Images were imported and converted to 8-bit and thresholded. Noise was removed with the despeckle
function, and the images were converted to binary. The cell counter plugin was then used for counting
adhered PBMCs. Counts were averaged from 5 images per treatment.
Serum And Spike Protein Treatment
hCMEC/d3 cells were seeded in 12-well plates at 2x105 cells/well and grown to con uence. Media was
replaced with media containing 10% serum from COVID and unaffected controls and incubated for up to
72 hours followed by RNA isolation. hCMEC/d3 cells were cultured in12-well plates as described above
and stimulated with 4, 40 and 400 nM Recombinant SARS-CoV-2 Spike S1 subunit protein (R&D Systems,
#BT10569) for up to 72 hours and RNA was isolated as described above.
Ethical Approval
Informed consent was obtained from each participant. All ethical approvals were in place prior to the
initiation of studies on human subjects. All experiments conformed to the principles set out in the WMA
Declaration of Helsinki and the Department of Health and Human Services Belmont Report. The St
James’ Hospital ethics committee approved these studies.
Statistical analysis
IBM SPSS Statistics V.28 (IBM Corporation, Armonk, New York, USA) and GraphPad Prism V.9.00
(GraphPad Software, La Jolla California, USA) were used for statistical analysis. Prism 9 was used to
generate charts. Categorical variables were compared between groups with x2 tests. Normal and nonnormal data were analysed with Mann-Whitney tests or ANOVA followed by Tukey or Kruskal-Wallis test
respectively with age and sex adjusted p-values reported. A multivariate general linear model with age,
sex and TIV as covariates was used for volumetric MRI analysis. Correlations were assessed with
Pearson or Spearman rho correlation tests using partial correlations to control for age, sex and TIV. For
repeated blood samples, matched samples were compared with Wilcoxon signed-rank test. To control for
multiple comparisons in brain region MRI analysis and correlation analysis, false discovery rate was
Page 13/25
applied using the Benjamini-Hochberg correction. A p-value <0.05 was considered statistically signi cant.
All quantitative PCR, ELISA and adhesion assays were performed in duplicate.
Declarations
Acknowledgements
This work was supported by grants from Science Foundation Ireland (SFI), (12/YI/B2614 and
11/PI/1080), The Irish Research Council (IRC) and by a research grant from SFI under grant number
16/RC/3948 and co‐funded under the European Regional Development fund by FutureNeuro industry
partners. The Campbell lab is also supported by a European Research Council (ERC) grant, “Retina‐
Rhythm” (864522). We thank Nollaig Bourke and Matt McElheron for assistance with the Luminex
assays.
Author contributions
CG: Designed research, performed experiments, collected, and analysed data, and wrote the manuscript.
RC: Patient recruitment, assessment and data collection. EOK: Sample preparation. DB, AL, LZ: Patient
recruitment and assessment. EC: Data maintenance and statistical analysis. CNC: Sample
collection/recruitment. NC: Sample collection/recruitment. CPD: Conceived project, designed experiments
and edited manuscript. MC: Conceived project, designed experiments and edited manuscript.
Competing interests
The authors declare no competing interests.
References
1. Zhu, N. et al. A Novel Coronavirus from Patients with Pneumonia in China, 2019. N Engl J Med 382,
727-733 (2020). https://doi.org:10.1056/NEJMoa2001017
2. Wu, Z. & McGoogan, J. M. Characteristics of and Important Lessons From the Coronavirus Disease
2019 (COVID-19) Outbreak in China: Summary of a Report of 72 314 Cases From the Chinese Center
for Disease Control and Prevention. Jama 323, 1239-1242 (2020).
https://doi.org:10.1001/jama.2020.2648
3. Helms, J. et al. Neurologic Features in Severe SARS-CoV-2 Infection. N Engl J Med 382, 2268-2270
(2020). https://doi.org:10.1056/NEJMc2008597
4. Taquet, M., Geddes, J. R., Husain, M., Luciano, S. & Harrison, P. J. 6-month neurological and
psychiatric outcomes in 236 379 survivors of COVID-19: a retrospective cohort study using
electronic health records. The Lancet Psychiatry 8, 416-427 (2021). https://doi.org:10.1016/S22150366(21)00084-5
Page 14/25
5. Bohmwald, K., Gálvez, N. M. S., Ríos, M. & Kalergis, A. M. Neurologic Alterations Due to Respiratory
Virus Infections. Front Cell Neurosci 12, 386 (2018). https://doi.org:10.3389/fncel.2018.00386
. Cantuti-Castelvetri, L. et al. Neuropilin-1 facilitates SARS-CoV-2 cell entry and infectivity. Science 370,
856-860 (2020). https://doi.org:10.1126/science.abd2985
7. Amraei, R. et al. Extracellular vimentin is an attachment factor that facilitates SARS-CoV-2 entry into
human endothelial cells. Proceedings of the National Academy of Sciences 119, e2113874119
(2022). https://doi.org:10.1073/pnas.2113874119
. Ni, W. et al. Role of angiotensin-converting enzyme 2 (ACE2) in COVID-19. Critical Care 24, 422
(2020). https://doi.org:10.1186/s13054-020-03120-0
9. Hoffmann, M. et al. SARS-CoV-2 Cell Entry Depends on ACE2 and TMPRSS2 and Is Blocked by a
Clinically Proven Protease Inhibitor. Cell 181, 271-280.e278 (2020).
https://doi.org:https://doi.org/10.1016/j.cell.2020.02.052
10. Vanlandewijck, M. et al. A molecular atlas of cell types and zonation in the brain vasculature. Nature
554, 475-480 (2018). https://doi.org:10.1038/nature25739
11. Schweitzer, F. et al. Cerebrospinal Fluid Analysis Post-COVID-19 Is Not Suggestive of Persistent
Central Nervous System Infection. Ann Neurol 91, 150-157 (2022).
https://doi.org:10.1002/ana.26262
12. Lersy, F. et al. Cerebrospinal Fluid Features in Patients With Coronavirus Disease 2019 and
Neurological Manifestations: Correlation with Brain Magnetic Resonance Imaging Findings in 58
Patients. The Journal of Infectious Diseases 223, 600-609 (2021).
https://doi.org:10.1093/infdis/jiaa745
13. Thakur, K. T. et al. COVID-19 neuropathology at Columbia University Irving Medical Center/New York
Presbyterian Hospital. Brain 144, 2696-2708 (2021). https://doi.org:10.1093/brain/awab148
14. Yang, A. C. et al. Dysregulation of brain and choroid plexus cell types in severe COVID-19. Nature 595,
565-571 (2021). https://doi.org:10.1038/s41586-021-03710-0
15. Iadecola, C., Anrather, J. & Kamel, H. Effects of COVID-19 on the Nervous System. Cell 183, 16-27.e11
(2020). https://doi.org:10.1016/j.cell.2020.08.028
1 . Chertow, D. et al. SARS-CoV-2 infection and persistence throughout the human body and brain.
(2021). https://doi.org:https://doi.org/10.21203/rs.3.rs-1139035/v1
17. Abbott, N. J., Patabendige, A. A., Dolman, D. E., Yusof, S. R. & Begley, D. J. Structure and function of
the blood-brain barrier. Neurobiol Dis 37, 13-25 (2010). https://doi.org:10.1016/j.nbd.2009.07.030
1 . Greene, C., Hanley, N. & Campbell, M. Claudin-5: gatekeeper of neurological function. Fluids and
barriers of the CNS 16, 3 (2019). https://doi.org:10.1186/s12987-019-0123-z
19. Lee, M.-H. et al. Microvascular Injury in the Brains of Patients with Covid-19. The New England
journal of medicine 384, 481-483 (2021). https://doi.org:10.1056/NEJMc2033369
20. Lee, M. H. et al. Neurovascular injury with complement activation and in ammation in COVID-19.
Brain 145, 2555-2568 (2022). https://doi.org:10.1093/brain/awac151
Page 15/25
21. Constant, O. et al. SARS-CoV-2 Poorly Replicates in Cells of the Human Blood-Brain Barrier Without
Associated Deleterious Effects. Front Immunol 12, 697329-697329 (2021).
https://doi.org:10.3389/ mmu.2021.697329
22. DeOre, B. J., Tran, K. A., Andrews, A. M., Ramirez, S. H. & Galie, P. A. SARS-CoV-2 Spike Protein
Disrupts Blood-Brain Barrier Integrity via RhoA Activation. J Neuroimmune Pharmacol 16, 722-728
(2021). https://doi.org:10.1007/s11481-021-10029-0
23. Kim, E. S. et al. Spike Proteins of SARS-CoV-2 Induce Pathological Changes in Molecular Delivery and
Metabolic Function in the Brain Endothelial Cells. Viruses 13, 2021 (2021).
https://doi.org:10.3390/v13102021
24. Savarraj, J. et al. Brain injury, endothelial injury and in ammatory markers are elevated and express
sex-speci c alterations after COVID-19. J Neuroin ammation 18, 277-277 (2021).
https://doi.org:10.1186/s12974-021-02323-8
25. Wenzel, J. et al. The SARS-CoV-2 main protease M(pro) causes microvascular brain pathology by
cleaving NEMO in brain endothelial cells. Nat Neurosci 24, 1522-1533 (2021).
https://doi.org:10.1038/s41593-021-00926-1
2 . Zhang, L. et al. SARS-CoV-2 crosses the blood-brain barrier accompanied with basement membrane
disruption without tight junctions alteration. Signal Transduct Target Ther 6, 337-337 (2021).
https://doi.org:10.1038/s41392-021-00719-9
27. Zhou, Y. et al. Network medicine links SARS-CoV-2/COVID-19 infection to brain microvascular injury
and neuroin ammation in dementia-like cognitive impairment. Alzheimers Res Ther 13, 110-110
(2021). https://doi.org:10.1186/s13195-021-00850-3
2 . Bocci, M. et al. Infection of Brain Pericytes Underlying Neuropathology of COVID-19 Patients. Int J
Mol Sci 22, 11622 (2021). https://doi.org:10.3390/ijms222111622
29. Fitsiori, A., Pugin, D., Thieffry, C., Lalive, P. & Vargas, M. I. COVID-19 is Associated with an Unusual
Pattern of Brain Microbleeds in Critically Ill Patients. J Neuroimaging 30, 593-597 (2020).
https://doi.org:10.1111/jon.12755
30. Krasemann, S. et al. The blood-brain barrier is dysregulated in COVID-19 and serves as a CNS entry
route for SARS-CoV-2. Stem Cell Reports 17, 307-320 (2022).
https://doi.org:10.1016/j.stemcr.2021.12.011
31. Pellegrini, L. et al. SARS-CoV-2 Infects the Brain Choroid Plexus and Disrupts the Blood-CSF Barrier in
Human Brain Organoids. Cell Stem Cell 27, 951-961.e955 (2020).
https://doi.org:10.1016/j.stem.2020.10.001
32. Rhea, E. M. et al. The S1 protein of SARS-CoV-2 crosses the blood-brain barrier in mice. Nat Neurosci
24, 368-378 (2021). https://doi.org:10.1038/s41593-020-00771-8
33. Schwabenland, M. et al. Deep spatial pro ling of human COVID-19 brains reveals neuroin ammation
with distinct microanatomical microglia-T-cell interactions. Immunity 54, 1594-1610.e1511 (2021).
https://doi.org:10.1016/j.immuni.2021.06.002
Page 16/25
34. Yang, R. C. et al. SARS-CoV-2 productively infects human brain microvascular endothelial cells. J
Neuroin ammation 19, 149 (2022). https://doi.org:10.1186/s12974-022-02514-x
35. Buzhdygan, T. P. et al. The SARS-CoV-2 spike protein alters barrier function in 2D static and 3D
micro uidic in-vitro models of the human blood-brain barrier. Neurobiology of disease 146, 105131105131 (2020). https://doi.org:10.1016/j.nbd.2020.105131
3 . Montalvan, V., Lee, J., Bueso, T., De Toledo, J. & Rivas, K. Neurological manifestations of COVID-19
and other coronavirus infections: A systematic review. Clin Neurol Neurosurg 194, 105921 (2020).
https://doi.org:10.1016/j.clineuro.2020.105921
37. Ng Kee Kwong, K. C., Mehta, P. R., Shukla, G. & Mehta, A. R. COVID-19, SARS and MERS: A
neurological perspective. J Clin Neurosci 77, 13-16 (2020).
https://doi.org:10.1016/j.jocn.2020.04.124
3 . O'Doherty, L. et al. Study protocol for the St James's Hospital, Tallaght University Hospital, Trinity
College Dublin Allied Researchers' (STTAR) Bioresource for COVID-19. HRB Open Res 5, 20 (2022).
https://doi.org:10.12688/hrbopenres.13498.1
39. Finlay, J. B. et al. Persistent post-COVID-19 smell loss is associated with in ammatory in ltration
and altered olfactory epithelial gene expression. bioRxiv, 2022.2004.2017.488474 (2022).
https://doi.org:10.1101/2022.04.17.488474
40. Zhou, G., Lane, G., Cooper, S. L., Kahnt, T. & Zelano, C. Characterizing functional pathways of the
human olfactory system. eLife 8, e47177 (2019). https://doi.org:10.7554/eLife.47177
41. Saive, A. L., Royet, J. P. & Plailly, J. A review on the neural bases of episodic odor memory: from
laboratory-based to autobiographical approaches. Front Behav Neurosci 8, 240 (2014).
https://doi.org:10.3389/fnbeh.2014.00240
42. Douaud, G. et al. SARS-CoV-2 is associated with changes in brain structure in UK Biobank. Nature
604, 697-707 (2022). https://doi.org:10.1038/s41586-022-04569-5
43. Sudre, C. H. et al. Attributes and predictors of long COVID. Nature Medicine 27, 626-631 (2021).
https://doi.org:10.1038/s41591-021-01292-y
44. Qin, Y. et al. Long-term microstructure and cerebral blood ow changes in patients recovered from
COVID-19 without neurological manifestations. J Clin Invest 131 (2021).
https://doi.org:10.1172/jci147329
45. Tian, T. et al. Long-term follow-up of dynamic brain changes in patients recovered from COVID-19
without neurological manifestations. JCI Insight 7 (2022). https://doi.org:10.1172/jci.insight.155827
4 . Donegani, M. I. et al. Brain Metabolic Correlates of Persistent Olfactory Dysfunction after SARS-Cov2
Infection. Biomedicines 9 (2021). https://doi.org:10.3390/biomedicines9030287
47. Guedj, E. et al. (18)F-FDG brain PET hypometabolism in patients with long COVID. Eur J Nucl Med
Mol Imaging 48, 2823-2833 (2021). https://doi.org:10.1007/s00259-021-05215-4
4 . Greene, C. et al. Microvascular stabilization via blood-brain barrier regulation prevents seizure
activity. Nat Commun 13, 2003 (2022). https://doi.org:10.1038/s41467-022-29657-y
Page 17/25
49. Aleksovska, K. et al. Systematic Review and Meta-Analysis of Circulating S100B Blood Levels in
Schizophrenia. PLOS ONE 9, e106342 (2014). https://doi.org:10.1371/journal.pone.0106342
50. Thelin, E. P., Nelson, D. W. & Bellander, B.-M. A review of the clinical utility of serum S100B protein
levels in the assessment of traumatic brain injury. Acta Neurochirurgica 159, 209-225 (2017).
https://doi.org:10.1007/s00701-016-3046-3
51. Abdelhak, A. et al. Blood GFAP as an emerging biomarker in brain and spinal cord disorders. Nature
Reviews Neurology 18, 158-172 (2022). https://doi.org:10.1038/s41582-021-00616-3
52. McCarthy, M. J. Circadian rhythm disruption in Myalgic Encephalomyelitis/Chronic Fatigue
Syndrome: Implications for the post-acute sequelae of COVID-19. Brain, Behavior, & Immunity -
Health 20, 100412 (2022). https://doi.org:https://doi.org/10.1016/j.bbih.2022.100412
53. Montoya, J. G. et al. Cytokine signature associated with disease severity in chronic fatigue syndrome
patients. Proc Natl Acad Sci U S A 114, E7150-e7158 (2017).
https://doi.org:10.1073/pnas.1710519114
54. Lee, W. K. et al. Exogenous Transforming Growth Factor-β in Brain-Induced Symptoms of Central
Fatigue and Suppressed Dopamine Production in Mice. Int J Mol Sci 22 (2021).
https://doi.org:10.3390/ijms22052580
55. Oh, J. et al. SARS-CoV-2 spike protein induces cognitive de cit and anxiety-like behavior in mouse via
non-cell autonomous hippocampal neuronal death. Scienti c Reports 12, 5496 (2022).
https://doi.org:10.1038/s41598-022-09410-7
5 . Ryan, F. J. et al. Long-term perturbation of the peripheral immune system months after SARS-CoV-2
infection. BMC Medicine 20, 26 (2022). https://doi.org:10.1186/s12916-021-02228-6
57. Phetsouphanh, C. et al. Immunological dysfunction persists for 8 months following initial mild-tomoderate SARS-CoV-2 infection. Nature Immunology 23, 210-216 (2022).
https://doi.org:10.1038/s41590-021-01113-x
5 . Rass, V. et al. Neurological outcomes one year after COVID-19 diagnosis: a prospective longitudinal
cohort study. Eur J Neurol (2022). https://doi.org:10.1111/ene.15307
59. Whitaker, M. et al. Persistent COVID-19 symptoms in a community study of 606,434 people in
England. Nature Communications 13, 1957 (2022). https://doi.org:10.1038/s41467-022-29521-z
0. Jackman, A. H. & Doty, R. L. Utility of a three-item smell identi cation test in detecting olfactory
dysfunction. Laryngoscope 115, 2209-2212 (2005).
https://doi.org:10.1097/01.mlg.0000183194.17484.bb
1. Lechien, J. R. et al. Olfactory and gustatory dysfunctions as a clinical presentation of mild-tomoderate forms of the coronavirus disease (COVID-19): a multicenter European study. Eur Arch
Otorhinolaryngol 277, 2251-2261 (2020). https://doi.org:10.1007/s00405-020-05965-1
2. O'Keeffe, E. et al. Dynamic Blood-Brain Barrier Regulation in Mild Traumatic Brain Injury. Journal of
neurotrauma 37, 347-356 (2020). https://doi.org:10.1089/neu.2019.6483
3. Weissberg, I. et al. Imaging Blood-Brain Barrier Dysfunction in Football Players. JAMA Neurology 71,
1453-1455 (2014). https://doi.org:10.1001/jamaneurol.2014.2682
Page 18/25
4. Manjón, J. V. & Coupé, P. volBrain: An Online MRI Brain Volumetry System. Frontiers in
Neuroinformatics 10 (2016). https://doi.org:10.3389/fninf.2016.00030
Tables
Tables 1 to 4 are available in the Supplementary Files section.
Figures
Page 19/25
Figure 1
In ammation and blood-brain barrier (BBB) permeability in acute COVID-19 infected cases. a) TNF, IL6,
IL8, S100β and CCL2 serum concentrations in unaffected, mild, moderate, and severe SARS-CoV-2
infected patients. b) TNF, IL6, IL8, S100β and CCL2 serum concentrations in neurological SARS-CoV-2
infected patients. Data represent means with 95% con dence intervals; each datapoint represents one
Page 20/25
patient. Data analysed by MANCOVA with age, sex and WHO severity as covariates. *p<0.05; **p<0.01;
***p<0.001.
Figure 2
BBB disruption in Long COVID-associated cognitive impairment. a) Patient cohort for dynamic contrastenhanced magnetic resonance imaging (DCE-MRI). b) Averaged BBB permeability maps in non-brain fog
and brain fog cases. c) There were signi cantly increased percentage of brain volume with leaky blood
vessels in the brain fog cohort compared to recovered and non-brain fog cases. d) Frequency distribution
of the percentage of BBB disrupted voxels in the non-brain fog and brain fog cases. e) Representative
BBB permeability maps at the level of the temporal lobe, frontal lobe and occipital lobe showing
enhanced BBB permeability in brain fog cases. f-i) Quanti cation of regional BBB permeability in the right
and left temporal lobe and right and left frontal cortex. Data represent means ± s.e.m.; each datapoint
represents one patient. Data analysed by ANCOVA with age and sex as covariates. *p<0.05; **p<0.01;
***p<0.001.
Page 21/25
Figure 3
COVID-associated brain changes. a) Voxel-based morphometry map indicating brain regions with
reduced volume in patients with prior SARS-CoV-2 infection. b-e) Group-wise comparison of brain volume
in unaffected, recovered, long COVID and brain fog groups. f) Surface-based morphometry map
indicating brain regions with reduced cortical thickness in patients with prior SARS-CoV-2 infection. g-j)
Group-wise comparison of cortical thinning in unaffected, recovered, long COVID and brain fog groups.
Maps generated with CAT12 toolbox in SPM12 running on MATLAB 2021a. Groups compared with
unpaired t-test with family-wise error <0.05, adjusted for age, sex and TIV. Volumetric and thickness
region of interest measurements were obtained from VolBrain. Groups were compared with ANCOVA
adjusted for age and sex. Data represents means ± s.e.m.; each datapoint represents one patient.
*p<0.05, **p<0.01, ***p<0.001.
Page 22/25
Figure 4
BBB permeability is associated with structural brain changes. a-f) Spearman partial correlation between
the percentage of BBB disrupted voxels and white matter volume and global brain volume. g) Heat-map
of Spearman correlations between BBB permeability and global brain volume. Each datapoint represents
one patient. Spearman partial correlation analysis for all panels adjusted for age, sex and TIV. *p<0.05;
**p<0.01.
Page 23/25
Figure 5
Plasma TGFβ is associated with increased BBB permeability. a-e) Serum and plasma analysis of GFAP,
TGFβ, P-TAU, IL8 and CCL2 in recovered, non-brain fog and brain fog cohort. f) Spearman partial
correlations between analyte levels and BBB permeability and global brain volume measurements. g-i)
Spearman correlation between levels of TGFβ and percentage BBB disruption, percentage CSF volume,
brainstem volume and amygdala volume. Data represent means ± s.e.m.; each datapoint represents one
patient. Kruskal Wallis test for a-e, Spearman partial correlation analysis controlling for age, sex and TIV
for f-j. *p<0.05; **p<0.01.
Page 24/25
Figure 6
Immunovascular dysfunction in long COVID blood samples. a-f) Gene expression changes in unaffected
and long COVID PBMCs. g-h) PBMC adhesion assay on human brain endothelial cells (hCMEC/d3) in the
presence or absence of 10 ng/ml TNF. i-l) Gene expression changes in hCMEC/d3 cells exposed to control
or long COVID serum. Data represent means ± s.e.m.; each datapoint represents one patient. Unpaired ttest for gene expression data, two-way ANOVA for adhesion assay. *p<0.05; **p<0.01; ***p<0.001.
Supplementary Files
This is a list of supplementary les associated with this preprint. Click to download.
Tables.pdf
SupplementaryFigures.pdf
Page 25/25