In tropolone-mkd-jnm-981

BASICSCIENCES
Indium-I11 oxine,a chelateof In-i 11 with 8-hy
droxyquinoline, wasintroducedin 1976 by Thakur and
associates as a label for granulocytes (1 ) and platelets
(2). Since then we and others haveoptimized the various
platelet-labeling parameters, performed comparative
survival studies with Cr-SI-labeled platelets, and used
labeled platelets in thrombosis research (3â€”8).However,
platelet labeling in plasma with In-i I 1 oxine, as rec
ommended by a panel on diagnostic application of ra
dioisotopes in hematology (9), resulted in inconsistent
and low labeling efficiency. Also, because of the poor
solubility of oxine in aqueous solution, a small amount
of ethyl alcohol is needed as a solvent for In-i 11 oxine,
but the probabilityof injuriouseffectsof alcoholon
platelet functions was demonstrated by Haut and Cowan
(JO).
We havedevelopeda newwater-soluble,high-affinity
platelet label that has demonstrated a higher stability
ReceivedApr. 29, 1981; revisionacceptedJuly 20, 1981.
For reprints contact: M. K. Dewanjee,PhD, Mayo Clinic, Roch
ester,MN 55905.
constant and a higher (olive oil/citrate buffer) partition
coefficient than In-i i I oxine. The chelating ability of
tropolone was used by Dyrssen (1 1) in the separation of
metal ionsby solventextraction and by Pitt and Gupta
(12) for iron removal in iron-storage disease. Indium
I 1i-labeled tropolone permits efficient, consistent, and
convenient platelet labeling in either an acid-citrate
dextrose (ACD)-saline or an ACD-plasma medium.
We havealsodevelopeda kit for plateletlabeling,which
may lead to more widespread use of In-i I i-labeled
platelets in investigations of arterial thrombosis and
thrombocytopenia.
MATERIAL AND METHODS
Preparation of sterile ACD anticoagulant kit. Four
grams of anhydrous citric acid, 11.2 g of anhydrous tn
sodium citrate (or i 2.78 g of tnisodium citrate dihy
drate), and 6.0 g of dextrose were dissolved in 500 ml of
distilled water. The solution was membrane filtered (0.22
@.tm),and 8-ml and 25-ml aliquots were stored in sterile
10-mI or 50-ml vials. The former are used for blood
collection, the latter for preparation of the ACD-saline
Volume22,Number ii 981
RADIOCHEMISTRY AND RADIOPHARMACEUTICALS
Indium-i 11 Tropolone, A New High-AffinityPlateletLabel: Preparationand
Evaluationof LabelingParameters
Mrinal K. Dewanjee, Shyam A. Rao, and Paul Didisheim
Mayo Cilnic and MayoFoundation,Rochester, Minnesota
Platelets were labeled with a new neutral, lipid-solublemetal complexof in
dium-ill and tropoione.Unlike oxlne,which mustbe dissolvedIn ethyl alcohol,
tropoloneis solublein isotonicsaline.Platelet labelingwith in-I I I tropoionecan
be performedin bothacid-citrate-dextrose(ACD)-piasma and ACDâ€¢salinemedia
wfthintwo hours'time. Labelingefficiencyhas been 80-90 % in ACD-saIineand
60-70 % inthe ACD-plasmamedium.
Optimumconcentrationsforthe labelingof plateletswfthin-Ill tropoionewere
5 @ig/mlIn ACD-saline and 10 @g/mlin ACD-plasma, using a 15-mm incubation at
roomtemperature.A kit formulationfor convenientroutinepreparationof In-Ill
labeledplateletshasbeendeveloped.Sevenparametersof plateletlabelingwere
studied:concentrationof tropolone,citrate, plasmaproteins,and calcium ions;
alsoplateletdensity,temperature,andpH of Incubationmedium.Theireffectson
the mechanismof plateletlabelingwithlipid-solubletracersare discussed.
J Nuci Med 22: 981â€”987, 1981

DEWANJEE,RAO, AND DIDISHEIM
kit. The pH of the ACD solution was â€œâ€”5.0and osmola
rity was â€˜@300mOsm.
Sterile ACD-Salinekit for platelet labeling with In-I 11
tropolone. Thirty-six milliliters of ACD solution were
mixed with 250 ml of sterile isotonic saline, and pH was
adjusted to 6.5, with i -ml aliquots transferred to a dis
posable polystyrene tube; 4.0 ml of sterile I N NaOH
was used to titrate. The solution was membrane filtered
(0.22 zm) and aliquots of 10-30 ml were transferred to
sterile vials. This stock solution contained 3.02 mg of
citrate ion per milliliter. We find stainless steel needles
more suitable than aluminum needles in the transfer of
i N NaOH solution. The batches were tested for os
molarity (â€œâ€”â€˜300mOsm), sterility (culture for 7 days with
brain-heart infusion broth with 5% beef extract, and 5
days with blood-agar medium), and apyrogenicity (Li
mulus amebocyte lysate test*).
Preparation of In-I I I tropolone. Eight to ten mg of
tropolone t (weighed by microbalance) was dissolved by
vortexing in sterile isotonic saline in a sterile polystyrene
tube. The volume was adjusted to a concentration of 1
@.ig/@tlof saline. The pH was adjusted to 7.4 with 0.1 N
NaOH and the solutionwassterilizedby membrane
filtration(0.22 @tm).Whenit wascappedat roomtem
perature, we found that this stock solution yielded con
stant labeling efficiency for almost 3 mo.
Twenty microliters of tropolone solution was trans
ferred to a 12-ml polypropylene tube with a sterile mi
cropipette, and 300- 1,200 zCi of In- I 11 chloride was
added dropwise. The solution was mixed for 2 mm, 3.5
ml of ACD-saline was added, and the pH of the solution
was adjusted to 6.5 with sterile 0. 1 N NaOH, using a
precalibrated pH meter. We found this solution of In-i 11
tropolone in ACD-saline suitable up to I wk after
preparation. We also found that the I-ml syringe with
a polypropylene holder (No. 7022D) for the needle (27
gauge, 1/2in. long) introduced minimal aluminum con
tamination in the preparation of ACD-saline. Ten mi
crograms of tropolone were used in the In-i 11tropolone
preparation for platelet labeling in plasma, and the pH
of the final In- 111tropolone solution in a small volume
was adjusted to 7.0 with 0.1 N sterile NaOH. Sterile
stock solutions of 0. 1 N NaOH and 0. 1N HC1 for pH
adjustment were kept in sterile polystyrene tubes in the
refrigerator.
For the determination of optimum conditions of
platelet labeling with In-I 11 tropolone, we studied seven
parameters: plasma proteins, citrate, tropolone, calcium
ion concentration, platelet density, temperature, and pH
of incubation medium. Platelets were obtained from five
healthy mongrel dogs and counted with a commercial
counter.@The details of each of these experiments are
described below.
Tropolone concentration and platelet-labeling effi
ciency. Fifty microcuries of â€˜IIInCl3was added to ali
quots of stock solution of tropolone in saline; the pH was
adjusted to 6.5. Four-milliliter aliquots of ACD-saline
stock (pH = 6.5) were added and 2.2 X iO@plasma-free
platelets were added and incubated for 30 mm at room
temperature. They were then washed with ACD-plasma.
Labeling efficiency was determined after removal of the
small fraction of platelet aggregates (less than 5% of total
radioactivity). For plasma labeling, the platelet pellet
was resuspended in 0.5 ml of plasma and transferred to
In-i I I tropolone in a small volume at pH 7. Labeling
efficiency in percent was then determined by dividing the
radioactivity of In- 111 in the platelet pellet by the total
radioactivity in the platelet pellet and washings, and
multiplying by 100. The radioactivity was measured in
an ionization chamber.
In mostoftheselabelingexperiments,dogbloodwas
collected in ACD-anticoagulant (86 ml of blood/ 16 ml
of ACD) with a 19-gauge needle. Platelet-rich plasma
was obtained by spinning the whole blood in a 40-mI
sterile centrifuge tube (round-bottom polycarbonate,
screw cap) at 200 g for 10 mm. Four to eight milliliters
of platelet-rich plasma was transferred to a 12-mI
polypropylene centrifuge tube with screw cap. (These
caps maintain sterility during labeling and also prevent
loss of carbon dioxide and the consequent increase in
plasma pH, which can adversely affect platelet function.)
The platelet-rich plasma was then spun at I600 g to
obtain the platelet pellet. For plasma labeling, these
platelets were suspended in 0.5 ml ACD-plasma with a
sterile polyethylene pipette. After incubation for 15 mm
with In-I 11 tropoloneat room temperature, 2.5 ml of
ACD-plasma was added and the platelets were washed
by spinningat I 600 g for 10 mm, then resuspendedand
washed again with 3 ml of ACD-plasma. Finally, any
residual platelet aggregates were removed by spinning
at 100 g for S mm. Residual red blood cells were lysed
by incubation with 5 ml of 0.2% saline for 30 mm. He
moglobin-associated radioactivity was removed by
centrifugation at 1600 g for 10 mm. The platelet-labeling
efficiency was determined by measuring radioactivity
with an ionization chamber in the platelet-pellet wash
ings and platelet aggregates. The only difference in la
beling procedure between In- 111 oxine and In- 111 tro
polone was that with the latter no washing of the platelet
â€¢0
Platelet â€¢Â°
Iab&ing
efficiency(%) @o
20
0 10203040100 200 300 400 S00
Tropoloneconcentration( ,u.g/mI)
FIG. 1. Effect of tropolone concentration on platelet labeling in
plasma and ACD-saline. Dashed line is platelet in-i 11 after eryth
rocytelysis.
.oo
982 THE JOURNAL OF NUCLEAR MEDICINE
--.@ OAcO.S.@
1â€•@ I A@O.

BASICSCIENCES
100
80
60
40
20
of In-i i 1 tropoione solution (50 @tgof tropolone) was
then added and final pH adjustments were made to the
above-mentioned values. Platelets, 2.2 X i0@, from 4 ml
of platelet-rich plasma were incubated in triplicate for
30 mm at room temperature, and platelet-labeling effi
ciency wasdetermined.
Plasma incubation on release of In-i 11 label. In
dium-i 1i-labeled platelets, tagged in ACD-saline or
plasma medium, were resuspended in ACD-plasma and
checked for In-i 1i release during 6 hr at room temper
ature. Aliquots of platelets were centrifuged at 1, 2, 4,
and 6 hr, and radioactivity in plasma and platelets was
determined with the ionization chamber. More than 95%
of the In-i i I was bound to platelets at 6 hr after labeling
in eitherACD-salineor ACD-plasma.
Aggregation of control and In-I I1-labeled platelets.
Blood of conscious, healthy mongrel dogs that had not
received any drugs or participated in any experiments
inthepreviousmonthwascollectedfromajugularvein
into ACD solution. Platelet countst of all tested sus
pensions were adjusted to 300,000/mm3 with autologous
platelet-poor plasma. Platelet aggregation (13) was then
examined at 37Â°C with a single-channel platelet
aggregometer.11The ADP used was from equine muscle.
To control any effect of aging on aggregation, platelet
rich plasma and suspensions prepared from it were tested
alternately and within 4 hr of the time of vene
puncture.
RESULTS
Increasing tropolone concentration decreased plate
let-labeling efficiency, with a peak value of about 5â€”6
@zg/mlin ACD-saline and iO jzg/ml in ACD-plasma
(Fig. I). It is also evident from Fig. i that labeling in
plasma rather than ACD-saline led to lower platelet
labelingefficiency.Increasingtheplasmaproteinsde
creased platelet-labeling efficiency (Fig. 2). Slight loss
of labeling efficiency resulted after red-cell lysis for
platelets labeled in either ACD-saline or ACD-plasma,
but the general shape and peak of tropolone concentra
tion did not change.
The platelet-labeling efficiency increased with both
increasingincubationtimeandincreasingtemperature
(Fig. 3). The rate ofincrease in labeling efficiency with
0
FIG.3. Effectoftemperatureandtimeof incubationonplatelet
labeling efficiency.
Platelet
Labeling
Efficiency
(%)
0 50 100 160 200 260 300
Platelet-poorplasma(pt/mI)
FIG.2.Eftectofplasmaproteinsonplatelet-labelingefficiency.
pellet with ACD-saline was necessary, thus eliminating
one step.
Plasma protein concentration. The effect of plasma
on platelet-labeling efficiency was determined by adding
increasing amounts of plasma to 2.2 X i0@platelets ob
tamed from 4 ml of platelet-rich plasma. Variable
amounts of platelet-poor plasma were added directly to
50 @Ciof In-i 11 tropolone containing 50 @tgof tropolone
in 4 ml of ACD-saline. The platelets were labeled and
washed as before, and platelet-labeling efficiency de
termined.
Incubationtemperatureandtime. This was studied by
adding 2.2 X i0@platelets to 50 @Ciof In-i 11 tropolone
(20 @gtropolone) in 4 ml ACD-saline. The platelet Ia
belingwasdeterminedafter incubationat 4Â°C,room
temperature (@-â€œ25Â°C),and 37Â°Cfor periods of 5â€”120
mm.
Numberof platelets. Platelets obtained from i , 2, 3,
5, 8, and 12 ml of platelet-rich plasma were incubated
with In-i i 1 tropolone in 0.5 ml of plasma or 4 ml of
ACD-saline at room temperature for 30 mm, and la
beling efficiency was determined.
Concentration of citrate ion in ACD-saline. Citrate
chelates calcium ion and a host of trace-metal impurities
in the incubation medium, and chelation of free Ca2+
prevents activation of the coagulation cascade. Since
citrate ion is an essential anticoagulant for platelet
harvesting and labeling, we studied the effect of in
creasing amounts of citrate ion on platelet-labeling ef
ficiency. Platelets, 2.2 X iO@,from 4 ml of platelet-rich
plasma were incubated for 30 mm at pH 6.5 with 50 zCi
of In-i i 1 tropolone containing 50 j.ig of tropolone. The
citrate ion concentration varied from 1.5 to 177 mg/ml,
and platelet-labeling efficiency was determined.
Concentration of calcium ion in ACD-saline. Platelets,
1.2 X iOu,from4 ml of platelet-richplasmawerecen
trifuged to form a platelet pellet. Variable amounts of
Ca2@ion were mixed with 50 @Ciof In-i 11tropolone in
4 ml of ACD-saline. These mixtures were added to the
platelet pellet and incubated for 30 mm at room tem
perature, and platelet-labeling efficiency was deter
mined.
Hydrogen ion concentration in ACD-saline. The pH
ofACD-saline was adjusted to 5, 6, 6.5, 7, 8, 9, 10,and
i I with 0.5 N HCI or 0.5 N NaOH. An aliquot of 50 @tCi
100
80
60
40
20
. 25C
. 37C
Platelet
Labeling
Efficiency
(%)
20 40 60 80 100 120
Timeof Incubation(mm)
Volume 22, Number 11 983

100
80
60
40
20
100
80
PlatsIst80
LabelIng
EffIciency
(%) 4o
P@t.I.I
Labeling
Efficiency
(S)
20
0 04 08 12 16 20 24 2.8
Platelet denalty ( 109/ml)
I 2 3 4 5 6
Ca@IonConcentration(mg/mI)
FiG. 4. Effect of platelet densityon platelet-labelingefficiency.
incubation time was higher at 4Â°Cand lower at 37Â°C.
No further gain in labeling efficiency was observed after
60 mm of incubation.
With either ACD-saline or ACD-plasma as incuba
tion medium, the labeling efficiency increased and
reached almost a plateau value at 2.8 X i0@platelets.
ACD-saline labeling led consistently to higher labeling
efficiency (Fig. 4).
Increasing concentration of citrate ion decreased
platelet-labeling efficiency (Fig. 5). If this curve is cx
trapolated to zero citrate concentration, the platelet la
beling increases to its maximum value of about 87%.
When unlabeled In- 111 tropolone was kept for a week
at roomtemperature,dissolvedin ACD-salinewith 3
mg/mi added citrate, there was no loss of platelet-la
beling potential.
Calcium ions at various concentrations did not affect
platelet-labeling efficiency when platelets were labeled
with In-I I I tropolone in ACD-saline (Fig. 6). There is
always excess citrate ion available to chelate excess
calcium ions. The platelet pellets were also easily dis
persed in the ACD-plasma solution, although excess
Ca2+ was available for promoting aggregation.
The highest platelet-labeling efficiency was obtained
at pH 9 (Fig. 7) when platelets were labeled with in- I 11
tropolone in ACD-saline. At this pH the platelet mem
brane may be most permeable because of reversible loss
of phospholipid and cholesterol. At higher or lower pH
values, the platelet-labeling efficiency decreased.
Similar effects of these parameters on platelet-labeling
efficiency have been observed by several investigators
(2â€”6)when platelets were labeled with In-I 11 oxine in
Tyrode buffer, ACD-saline, or ACD-plasma.
Aggregation of platelets to which tropolone was
FIG. 6. Effect of Ca2@ion concentration on platelet-labeling effI-
ciency.
added, in the presence of ACD-plasma or ACD-saline,
was diminished in comparison with the parent platelet
rich plasma (Fig. 8). The reduction was comparable
whether the In-i I 1tropolone was added in the presence
ofACD-plasmaorof ACD-saline.Plateletaggregation
was also comparable when tropolone was used in place
of In-i 11 tropolone.
DISCUSSION
The structures of the three chelating agents, oxine,
acetylacetone, and tropolone, are shown in Fig. 9. Both
oxine and tropolone molecules form five-membered oc
tahedral and neutral complexes with In-i 11and a variety
of other divalent and trivalent cations (1J) and are used
for the analytic separation of metal ions by solvent cx
traction. Acetylacetone forms a six-membered ring with
metal ions. Most of these complexes are efficiently cx
tracted at low pH in chloroform and other lipid-solu
bilizing organic solvents. The structure of the I :3 com
plex of In- I I I(tropolone)3 is shown in Fig. 10; indium
ion loses its ionic characteristics as it is buried in the
organic envelope of tropolone. It may then diffuse
through a lipid membrane like a neutral ionophore. Our
preliminary studies indicate that In-i I I tropolone has
a higher lipid solubility than In-i I I oxine and in-I I I
acetylacetone. The partition coefficient for olive oil/
ACD-saline was found to be 3.54 Â±0.28 for In-I I I
oxine, 7.93 Â±I .04 for In- 111acetylacetone,and I 8.I 8
Â±I.79fortheIn-I I 1tropolonecomplexes.Thisfive-fold
increase in lipid solubility permits more efficient cellular
extraction of In-i I 1 tropolone from both ACD-saline
and ACD-plasma. Tropolone has been evaluated for the
sequestration of ferric ion in iron-storage disease (12).
100
80
80
40
20
100
80
Labeling
Efficiency 60
(3@)
40
20
Platelst
Labeling
Efficiency
(3@)
0 40 80 120 160
Citrate IonConcentration(mg/mI)
FIG.5. Effect of citrate ion concentrationon platelet-labelingeffI-
ciency.
0 2 4 6 8 10 12
pH of C@nTr@p..j@5in
FIG.7. Effectof pHonplateletlabelingwithIn-i11tropolonein
ACD-salinesolution.
/â€œTT

BASICSCIENCES
RADIOCHEMISTRYAND RADIOPHARMACEUTICALS
H2
H3C C CH3 (V@
@ cii
0 0 HO 0
Oxine Acetylacetone Tropolon
FIG.9. Structuresofthreechelatingagentsthatformneutrallipid
soluble complexes with In-i 11 cation.
The results of platelet labeling with excess citrate ion
(Fig. 5) indicate that when platelets are labeled in
ACD-saline, the labeling efficiency will not be affected
by the metal-ion contaminantsâ€”for example, traces of
Cd2+ ion from@ IIInC13;A13+ion from the aluminum
needle; or Ca2+, Mg2+, or Fe3+ from the saline solution
or the glass vial or residual plasma. The kinetics of re
verse exchange leading to the formation of In-I I I citrate
may be slow, but excess citrate might increase intracel
lular citrate ion. This might lead to the formation of
In-i I i citrate, which could diffuse out again during
washing (11).
Although several investigators (1â€”3)have suggested
chloroform extraction of In- 111 oxine, with removal of
chloroform by evaporation and redissolution in ethyl
alcohol before platelet labeling, we found this step un
necessary. Because In-i 11 ion is carrier-free, the for
mation of In-i i 1 oxine in the presence of excess oxine
is assured. Although 75â€”95%of the In- 111 complex is
extracted with chloroform, it is not known how much of
the oxine is extracted along with the corresponding In
i 1i complexes, for we also found that most of these
lipid-soluble tracers were absorbed to glass and polymer
surfaces. Solvent extraction of In-i I I oxine or In- 1i 1
tropolone and other manipulations thus introduce an
unknown parameter about the level of oxine or tropolone,
and these levels are of critical importance in platelet
labeling (Fig. 1).
Aggregation of platelets by ADP was reduced by the
handling procedures required to label the platelets with
In-i I 1 tropolone. The presence or absence of plasma
duringthelabelingproceduredidnotaffectthedegree
of reduction of platelet aggregation. Neither the In-i 11
radioactivity nor the tropolone appeared to affect platelet
function, inasmuch as the reductions of platelet aggre
U
C
C
EI,
C
C
I-.
Dl
-.1
Dl
C
I,
C
C
U
â€˜a
FIG. 8. Typical aggregationtracing of control and labeledcanine
platelets with ADP.As platelets aggregate,light transmittance in
creases. Left: normalplatelet-richplasma(PRP).Center(controls):
platelet suspensions containing tropolone. Right (labeled): platelet
suspensionscontaining In-i 11tropolone. Top:tropolone addedin
presence of plasma. Bottom: tropolone added in presence of
AGO-saline. Time and concentration of ADP additions are mdi
cated.
Its toxicity is minimal in the microgram amounts used
for platelet labeling. The LD50of tropolone in mice by
intraperitoneal administration was in the range 15â€”200
mg/kg, and that of oxine by subcutaneous and intra
peritoneal administration 30 mg/kg and 88.8 mg/kg,
respectively (14). This toxicity is of no significance,
because most of the tropolone carrier, like oxine, is
probably released as a result of ligand exchange inside
the platelets and is thus removed from them during
washing with ACD-plasma solution.
The major advantage of In-i 1i tropolone is its solu
bility in isotonic saline; hence, no solvent that could ad
versely affect platelet functionâ€”such as ethyl alcohol
in the case of oxine and HEPES or Tris buffer in the case
of acetylacetoneâ€”is necessary for cell labeling.
The decrease in labeling efficiency at low tempera
tures (Fig. 3) may be due to freezing of cholesterol and
reduction of permeability at lower temperature. When
platelets are suspendedin ACD-saline, there is a rapid
loss of cholesterol and phospholipid from the platelet
membrane (15â€”17).The enhancement of membrane
permeability increases incorporation of In-i I 1 tropolone,
and therefore labeling efficiency, when platelets are in
cubated in ACD-saline rather than plasma. Similar
observations were made by Scheffel and associates (3)
when human platelets were incubated with In-i 1i oxine
in plasma. For an investigator with minimal experience
in cell labeling, the ACD-saline medium might be more
suitable than ACD-plasma, because the former could
provide higher labeling efficiency and viability and could
tolerate trace metals better than the plasma medium.
t1lndium@ (Tropolone)3
FIG.10.StructureofIn-ii i tropolone.Threemoleculesofmono
valent tropolone anion combine with one central trivalent In-i I 1
ion to form an octahedral complex of In-i 1i(tropolone)3.
Volume 22, Number 11 985

gation of control and labeled platelets were comparable.
Thus the reduction in platelet aggregation appears to be
totally explicable by physical handling (for example,
centrifugation, resuspension) and not by the labeling
itself. During labeling manipulationsâ€”especiallycen
trifugation, pelleting, and dispersionâ€”platelets might
lose some ADP and require more exogenous ADP for
their aggregation. This loss of ADP from platelet or
ganelles is a reversible process. Reimers and associates
(15) pointed out that a partial degranulation process
does not affect platelet survival. These observations are
in agreement with our preliminary platelet-survival
studies.
The intracellular ligand exchange between In-l 1i
oxine and cytoplasmic protein was studied by Hwang
(16) and by Pandian and associates (17). The time
integrated perturbation factors can be related to the
rotational correlation time of the environment of the
In-i I I nucleus. Indium-I I 1 platelets showed rotational
correlation times of half to a third of that for In-i I i
oxine. This suggests that, inside the platelet, the envi
ronment of the In-I 11 nucleus changes from that of
oxine to that of a large molecule. Our work on In-i 11
oxine and In-I i I tropolone with red bloodcellssuggested
that red-cell membrane retained 50-60% of the total
In-l I I inside the red cell (18). This result suggests that
an equilibrium is established inside the cell whereby the
phospholipid and proteins of membranes of cell and or
ganelles share In-i I I along with cytoplasmic proteins.
Perturbed angular correlation studies (16,17) of dif
ferent In-i I I oxineand In-i I i-labeled plateletsalso
support this hypothesis. It is only after lysis of the cell
that these In-I I 1-bound protein and in-i I 1-labeled
organelle fragments are released into the circulation and
sequestered mainly by the reticuloendothelial system.
Our preliminary work suggests that both lipoproteins
and transferrin sequester the neutral In-I 11complexes.
As we increase the amount of plasma proteins, more
In-I i I complex is incorporated into lipoproteins and
transferrin, and less is available for cellular uptake. Also,
the variability ofcell labeling in plasma within the same
species of animals could easily be accounted for by
variationsintheamountof lipoproteins,transferrin,and
metal ions in plasma.
Our preliminary studies with Sephadex gel chroma
tography indicate that the cytoplasmic protein carrier
of In-I I I has a molecular weight of 50,000â€”55,000
daltons. A similar molecular weight for In-I I 1-bound
platelet protein was reported by Hudson and associates
(19) for platelets labeled with In-l I I oxine. Variations
of intraplatelet distribution of In- 111 were observed by
Eakins and associates (20) when platelets were labeled
in ACD-saline and ACD-plasma. As long as In-I I I is
bound to platelet organelles or cytoplasmic platelet
proteins,and the membrane integrity is intact, platelet
recovery, survival, and imaging may not be affected
whether the platelets are labeled in an ACD-saline or an
ACD-plasma medium. The present knowledge of sim
plified platelet labeling with In-i 11, and the acceptable
radiation dose (21 ) for platelet-survival and imaging
studies, should lead to more widespread use of In-i 1i
labeled platelets in the future.
FOOTNOTES
S Microbiological Associates.
t Aldrich Chemical Co.
2Coulter ZBI or S-Plus counter.
I Model 330,Chrono-LogCorp.
ACKNOWLEDGMENTS
The authorsgreatly appreciatethe encouragementof Heinz W.
Wahner, M.D., and the expert technical assistanceof Mr. Sushital
Chowdhury,Mr. JamesA. Rosemark,and Mr. JohnQ. Stropp.
This investigationwassupportedin part by GrantsHL-24602 and
HV-929I5 from the National Institutes of Health, Public Health
Service.
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2. THAKUR ML, WELCH MJ, JOIST JH, et al: Indium-hI
labeled platelets: studies on preparation and evaluation of in
vitro and in vivo functions. Thromb Res 9:345â€”357,1976
3. SCHEFFEL U, TSAN M-F, MCINTYRE PA: Labeling of
humanplateletswith [I Iâ€˜In]8-hydroxyquinoline.J Nuci Med
20:524â€”531,1979
4. HEATON WA, DAvis HH, WELCH Mi, et al: Indium-ill:
a newradionuclidelabel for studying humanplatelet kinetics.
Br J Haema:ol 42:613-622, 1979
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Volume 22, Number 1i 987
RADIOPHARMACEUTICAL SCIENCE COUNCIL
WORKSHOP ON
The Choice of the Appropriate AnImal Model in Radlotracer Design
January 28, 1982 PhoenIx Hilton Phoenix, Arizona
The Radiopharmaceutical Science Council will hold a one-dayworkshop held in conjunction with the midwinter meet
in9 of the Society of Nuclear Medicine. The program for the workshop will include the following invited papers as
well as contributed papers.
Edward A. Carr, M.D. â€œAnimalModels for Study of Radiopharmaceuticals that are Substrates for
(Catecholamine) Uptakei and Uptake2â€•
Brian M. Gallagher, Ph.D. â€œMonoclonalAntibodies: The Design of the Appropriate Carrier and
Evaluation Systemâ€•
Adrian Nunn, Ph.D. â€œSpeciesDifferences and the Need for Multiple Animal Models for Hepatobiliary Agentsâ€•
Michael J. Welch, Ph.D. â€œLabeledCellsâ€•
Leonard I. Wiebe, Ph.D. â€œOncologicalModels for Screening Potential Diagnostic Radiopharmaceuticalsâ€•
Participants are encouraged to make hotel reservations at the meeting site by contacting the Registrar, SNM, 475 Park
Ave. So., New York, NY iOOi6. A registration fee of $35.00will be collected at the entrance to the meeting room.
For further information contact the Co-Organizers: William Eckelman, President, RPSC, or Richard M. Lambrecht,
President-Elect, RPSC, do the National Office.
Abstracts should be sent to Richard M. Lambrecht, Ph.D., Dept. of Chemistry, Brookhaven National Laboratory,
Upton, NY 11973.
DeadlineforthereceiptofabstractsIsJanuary2,1982.
SNM REFERRALSERVICE
The SNM Referral Service is accepting applications from employers and job applicants. The Service lists positions
wanted and positions available in the following nuclear medicine fields: Physician, Technologist, Scientist, Commer
cial, and Other.
The fee forjob applicants is $5.00 for SNM members and $50.00 for nonmembers. For employers, thefee is $50.00for
each position listed.
To obtain more information and an application form, please write to:
Referral Service
SocietyofNuclearMedicine
475ParkAvenueSouth
NewYork,NY 10016

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