Sajjad Ahmad

The corneal epithelium is renewed by stem cells located at the limbus, the so-called limbal stem cells (LSCs). Absence, damage or loss of the LSC population leads to the painful and blinding condition of LSC deficiency (LSCD). Ex vivo expansion of LSCs is an increasingly well recognized treatment modality for LSCD. One method of ex vivo expansion of LSCs involves the culture of limbal explants on amniotic membrane (AM). The purpose of this study was to analyze the outgrowths from human cadaveric limbal explants cultured on AM for properties associated with LSCs. In particular, the expression of putative stem cell markers and the colony-forming efficiency of the different zones of the outgrowth were studied. The limbal explants were expanded in the standard way used for clinical transplantation and the outgrowths were divided into three zones depending on proximity to the explant (inner, middle and outer zones). The colony-forming efficiencies (CFEs) of cells from each zone were calculated. In addition, the expression of DeltaNp63, ABCG2 (both putative positive LSC markers) and cytokeratin K3 (marker of corneal differentiation) were assessed using quantitative reverse transcription PCR (RT-PCR). Immunohistochemistry on paraffin-embedded sections was also performed to demonstrate protein localization and allow further confirmation of the quantitative RT-PCR results. Successful cultures for both the explant outgrowths and the CFE calculations were obtained in every case. CFE showed a successive decline in zones further away from the explant (p < 0.00005). Quantitative RT-PCR revealed that the expression of the positive putative LSC markers DeltaNp63 and ABCG2 also showed a steady decrease in the zones furthest from the explant (p < 0.05 and p < 0.005, respectively). The expression of cytokeratin K3 was increased in zones furthest from the explant (p < 0.005). Immunohistochemistry on paraffin-embedded sections of intact ex vivo-expanded limbal epithelium for the putative positive marker p63 and cytokeratin K3 confirmed the findings of the quantitative RT-PCR and CFE results. We demonstrate for the first time that outgrowths from human limbal explants, a widely used technique in ex vivo expansion of LSCs for clinical transplantation, show a steady decline in a wide range of stem cell properties with distance from the central explant. These findings support the importance of proximity of stem cells to their niche environment in maintaining their undifferentiated state. These findings suggest the need for modifications of existing techniques to ensure maximum numbers of LSCs following ex vivo expansion protocols, which will then ensure the success of subsequent engraftment.

This study focuses on the effects of climate variability and climate change on the Colorado River flow as well as on implications for water resources management. A system dynamics model was developed for the Colorado River Basin, operating at a monthly time scale from 1970 to 2035. Changes in streamflow were simulated with a hydrologic model that used outputs from 16 global climate models (GCMs) and 3 emission scenarios. Lake Mead levels–as well as the corresponding probabilities of supply curtailments to the Basin states ...

ABSTRACT In water stressed regions, water managers are exploring new horizons that would help in long‐range streamflow forecasts. Oceanic‐atmospheric oscillations have been shown to influence streamflow variability. In this study, long‐lead time streamflow forecasts are made using a multiclass kernel‐based data‐driven support vector machine (SVM) model. The extended streamflow records based on tree ring reconstructions were used to provide a longer time series data. Reconstructed data were used from 1658 to 1952 and the instrumental record was used from 1953 to 2007. Reconstructions for oceanic‐atmospheric oscillations included the El Niño‐Southern Oscillation, Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation, and North Atlantic Oscillation. Streamflow forecasts using all four oscillations were made with one‐year to five‐year lead times for 21 gages in the western United States. This is the first study that uses both instrumental and reconstructed data of oscillations in SVM model to improve streamflow forecast lead time. SVM model was able to provide “satisfactory” to “very good” forecasts with one‐ to five‐year lead time for the selected gages. The use of all the oscillation indices helped in achieving better predictability compared to using individual oscillations. The SVM modeling results are better when compared with multiple linear regression model forecasts. The findings are statistical in nature and are expected to be useful for long‐term water resources planning and management.

Increasing global warming has led to the incremental retreat of glaciers, which in turn affects the water supply of the rivers dependent on glacier melts. This is further affected by the increases in flooding due to heavy rains during the snowmelt season. An accurate estimation of streamflow is important for water resources planning and management; therefore, this study focuses on improving the streamflow forecast for Kaidu River Basin, situated at the north fringe of Yanqi basin on the south slope of Tianshan Mountains in ...

Parathyroid carcinoma is a very rare cause of primary hyperparathyroidism and these tumors are usually hyper-functioning as compared to other malignant endocrine tumors. Surgery is the only effective primary treatment. We report a patient, who presented with pathological fracture of femur, hypercalcemia, bilateral renal stones, markedly raised Parathormone levels and palpable mass in the neck. Parathyroid adenoma was initially diagnosed and localized at left lower gland by Sestamibi scan and ultrasonography. She underwent surgery and enlarged parathyroid gland was removed. Intra operatively there was no evidence of local invasion or lymph nodes involvement but biopsy report suggested malignancy.

Human embryonic stem cells (hESCs) are pluripotent cells capable of differentiating into any cell type of the body. It has long been known that the adult stem cell niche is vital for the maintenance of adult stem cells. The cornea at the front of the eye is covered by a stratified epithelium that is renewed by stem cells located at its periphery in a region known as the limbus. These so-called limbal stem cells are maintained by factors within the limbal microenvironment, including collagen IV in basement membrane and limbal fibroblasts in the stroma. Because this niche is very specific to the stem cells (rather than to the more differentiated cells) of the corneal epithelium, it was hypothesized that replication of these factors in vitro would result in hESC differentiation into corneal epithelial-like cells. Indeed, here we show that culturing of hESC on collagen IV using medium conditioned by the limbal fibroblasts results in the loss of pluripotency and differentiation into epit...

Hydatid cysts in the neck and breast are rare and are incidental finding in neck and breast specimens. It is a zoonotic disease which is due to infectivity with larval stage of Echinococcus granulosus. The disease is chronic and cysts can be lodged in different organs. It has cosmopolitan distribution and impact health and economical challenges for many countries throughout the world. Therefore, accurate information on the distribution of the disease is first step for the control and prevention. We present two unusual cases of hydatid cyst found in the posterior cervical region and in the breast.

A new synthetic approach has been developed for the preparation of 7-deoxypancratistatin analogues bearing a syn-(4aS,10bS)-phenanthridone ring junction. A one-pot tandem process involving a substrate-directed Overman rearrangement and ring closing metathesis reaction was developed for the stereoselective synthesis of a carbocyclic allylic trichloroacetamide. Conversion to a 6-bromopiperonyl amide, followed by a Heck reaction generated a homoallylic alcohol and completed the syn-(4aS,10bS)-phenanthridone carbon skeleton. Stereoselective epoxidation and dihydroxylation of the syn-(4aS,10bS)-phenanthridone framework was then investigated leading to the preparation of new analogues of 7-deoxypancratistatin.

A multi-bond forming, three-step tandem process involving a palladium(II)-catalysed Overman rearrangement and a ring closing metathesis reaction has been utilised for the efficient synthesis of a 2,3,6,7-tetrahydro-3-amidoazepine. Substrate directed epoxidation or dihydroxylation of this synthetic intermediate has allowed the diastereoselective synthesis of hydroxylated 3-aminoazepanes including the syn-diastereomer of the balanol core. Asymmetric synthesis of the 2,3,6,7-tetrahydro-3-amidoazepine motif was also achieved using a chiral palladium(II)-catalyst during the Overman rearrangement.

To investigate graft survival and surgical experience on clinical outcome following deep anterior lamellar keratoplasty (DALK). Multicenter cohort study. The United Kingdom Transplant Database was used to identify patients who had undergone a first DALK or penetrating keratoplasty (PKP) for keratoconus. Data were collected at the time of surgery and at 1, 2, and 5 years postoperatively. Graft survival, best-corrected visual acuity, and refractive error were analyzed for 3 consecutive time periods. DALK outcomes were analyzed according to surgeon experience. A total of 4521 patients were included. Graft survival was 92% (95% CI: 90-92) for PKP and 90% (95% CI: 88-92) for DALK (P = .09). For corneal transplants undertaken in the periods 1999-2002, 2002-2005, and 2005-2007, graft survival was 90%, 92%, and 88% following DALK, and 93%, 91%, and 92% following PKP, respectively. There was no evidence of a difference between surgeons in terms of case mix (P = .4) or outcome (P = .2). Surge...

Abstract Conceptual models are considered to be the best choice for describing the runoff process in a watershed. However, enormous requirements for topographic, hydrologic and meteorological data and extensive time commitment for calibration of conceptual models (both physically based and lumped) are often prohibitive factors in considering this option. Artificial neural networks (ANN) can be an efficient way of modeling the runoff process in situations where explicit knowledge of the internal hydrologic processes is not required. ...

Abstract Understanding human behavior during disaster, especially in response to evacuation warning, is very vital and makes a significant difference in reducing potential loss of life. Information on human response to disaster is used in formulating disaster management policies. The engineering aspects of disaster management process are better understood then the behavioral aspects. Proper understanding of human behavior in response to a disaster and our ability to capture it in a dynamic model can be of ...

To evaluate graft size on outcome following Descemet stripping automated endothelial keratoplasty (DSAEK) METHODS: Consecutive patients who had undergone a DSAEK for Fuchs endothelial dystrophy (FED) and pseudophakic bullous keratopathy (PBK) with at least 1 year of follow-up. Patients were divided into three groups according to the size of the donor trephine: <9, 9 and 9.5 mm. Main outcomes were postoperative best corrected visual acuity (BCVA) and graft failure. Grafts were prepared using an automated microkeratome. For larger grafts (≥9 mm), a manual dissection of the residual peripheral ring of anterior lamella was performed before trephination. Donor age, endothelial cell density (ECD) and postmortem times; recipient details including risk factors, comorbidity, surgical complications and postoperative BCVA and graft survival were analysed. Of 174 patients, 131 were included: 84 (64%) with FED and 47 (36%) with PBK. Mean preoperative and postoperative BCVA were 1.01±0.76 and ...

... First, it harbours the corneal epithelial stem cells (CESCs), also known as limbal stem cells (LSCs). ... The cells ultimately responsible for the repopulation of the epithelium are the CESCs, which are also known as limbal stem cells (LSCs) due to their anatomi-cal location. ...

The stereoselective synthesis of a series of di- and tri-hydroxylated aminocyclohexane derivatives has been developed. A one-pot, two step tandem process involving an Overman rearrangement and a ring closing metathesis reaction has been utilised for the asymmetric synthesis of (1S)-1-(2',2',2'-trichloromethylcarbonylamino)cyclohexa-2-ene. Oxidation of this cyclohexene derivative was then studied leading to the preparation of two diol analogues in excellent stereoselectivity. (1S)-1-(2',2',2'-trichloromethylcarbonylamino)cyclohexa-2-ene was then converted to a novel allylic alcohol via a 4,5-dihydro-1,3-oxazole. Functionalisation of this allylic alcohol by Upjohn dihydroxylation conditions or by a directed epoxidation/hydrolysis sequence of reactions allowed the synthesis of two dihydroconduramines in excellent stereoselectivity. The stereochemical assignment of all compounds prepared was confirmed by NOE experiments or X-ray structure determination.

A highly efficient one-pot multistep process involving an asymmetric Pd(II)-catalyzed Overman rearrangement and a Ru(II)-catalyzed ring-closing metathesis reaction has been developed for the preparation of (R)- or (S)-aminocyclopenta-2-enes. The rapid strategy employed and the relatively mild conditions of the one-pot process allowed the multigram synthesis of the carbocycles in high enantiomeric excess (92% ee). The synthetic utility of these compounds was demonstrated by the stereoselective incorporation of hydroxyl groups, generating cis-4- and cis-5-aminocyclopenta-2-en-1-ols, important building blocks for medicinal chemistry.

Summary Soil moisture is an important variable in the hydrological cycle and plays a vital role in agronomy, meteorology, and hydrology. It regulates the exchange of water and heat between land surface and atmosphere and thus plays an important role in the development of weather patterns. It is difficult to obtain a comprehensive spatio-temporal map of soil moisture because of expensive installation of soil moisture measuring instruments.

A new approach called spatial system dynamics (SSD) is presented to model feedback based dynamic processes in time and space. This approach is grounded in control theory for distributed parameter systems. System dynamics and geographic information system (GIS) are coupled to develop this modeling approach. The SSD modeling approach offers a single modeling framework for developing conceptually different models. It also provides the much-needed capability to model feedback based complex dynamic processes in time and ...

The cornea is the clear front of the eye and its surface is composed of an epithelium. This is renewed by stem cells located at the limbus, which encircles the periphery of the cornea. These limbal stem cells become lost or deficient in the blinding disease of limbal stem cell deficiency. In this review article, we discuss the historical perspective in managing limbal stem cell deficiency as well as describing the more contemporary treatment options, and in particular the culture and transplantation of human limbal stem cells. This treatment was first proposed 13 years ago and many case series have been presented to date showing promising outcomes of this technique. However, challenges still remain in treating the debilitating disease of limbal stem cell deficiency. Here we discuss some of the questions, which remain to be answered in this field.

Limbal stem cell deficiency is a blinding disease which affects the cornea at the front of the eye. The definitive cure involves replacing the corneal epithelial (limbal) stem cells, for example by transplanting cultured limbal epithelial cells. One method of performing cultures is to grow a sheet of epithelial cells from a limbal explant on human amniotic membrane. The growth of limbal tissue can be variable. The aim of this study is to investigate how different donor and culture factors influence the ex vivo growth of cadaveric limbal explants. Limbal explant cultures were established from 10 different cadaveric organ cultured corneo-scleral discs. The growth rate and the time taken for growth to be established were determined. Statistical analysis was performed to assess correlation between these factors and donor variables including donor age, sex, time from donor death to enucleation, time from enucleation to organ culture storage and duration in organ culture. Growth curves consistently showed a lag phase followed by a steeper linear growth phase. Donor age, time between death and enucleation, and time between enucleation and organ culture were not correlated to the lag time or the growth rate. Time in organ culture had a significant correlation with the duration of lag time (P = 0.003), but no relationship with the linear growth rate. This study shows that an important factor correlating with growth variation is the duration of corneo-scleral tissue in organ culture. Interestingly, donor age was not correlated with limbal explant growth.

Two major xylanase components, XynC and XynZ from the anaerobic thermophilic bacterium, Clostridium thermocellum cellulosome were cloned and expressed with and without non-catalytic domains in E. coli. Two constructs of XynC, one with its cellulose binding domain and the catalytic domain (pXynC-BC) and the other with only the catalytic domain (pXynC-C) were produced. For XynZ the constructs produced were pXynZ-BDC, which included the dockerin domain, and pXynZ-C, which did not. E. coli cells transformed with pXynC-BC or pXynZ-BDC gave xylanase expression of 30% and 25% total cell proteins, respectively. Transformation of E. coli cells with the constructs carrying only the catalytic domains gave expression levels of approximately 45% in each case. The specific activities of XynC with and without the non-catalytic domains were similar, but for XynZ the specific activity of the enzyme without the non-catalytic domains was approximately 5-fold greater than that of the intact enzyme. The total activity increased from 1925Ul(-1)OD(600)(-1) for XynC-BC to 3050Ul(-1)OD(600)(-1) for XynC-C. However, the overall increase in activity was approximately 9-fold higher for XynZ-C (32,900Ul(-1)OD(600)(-1)) versus XynZ-BDC (3665Ul(-1)OD(600)(-1)). Both the enzymes with and without non-catalytic domains were found to be quite stable over a broad pH range (pH 4-9). XynZ-C was more thermostable than XynZ-BDC as it retained 87% of xylanase activity when incubated at 70 degrees C for 2h as compared to 42% for XynZ-BDC. However, XynC-BC retained 70% activity on incubation at 70 degrees C for 2h but XynC-C lost all activity under the same conditions. K(m) values for XynC-BC and XynC-C determined on soluble xylan were 3.1 and 3.6 mg ml(-1), respectively, whereas these values for XynZ-BDC and XynZ-C were 33.3 and 15.4 mg ml(-1), respectively. Thus the production of xylanase activity by expressing only the catalytic domains of XynC and XynZ is significantly enhanced.

ABSTRACT Participatory irrigation management is gradually being introduced in the canal irrigation system in Pakistan. In this study, performance of a participatory irrigation management system is compared with that of a conventional centrally controlled irrigation system. The study is carried out for canal irrigation systems of Lower Chenab and Jhelum, both located in Punjab, Pakistan. The performance indicators used included: establishment cost, operation and maintenance cost, water fees (abiana) collected and equity of water distribution. The data for performance assessment were collected from various sources, including field measurements, interviews with farmers, interviews with officers of the irrigation department, previous studies, and data from the Punjab Irrigation Department and the Punjab Irrigation and Drainage Authority. The analysis indicates that establishment costs of both public-private partnership management and a centrally controlled irrigation system are more than operational and maintenance costs. The water supply in the main canal is satisfactory in both systems. Water fees (abiana) collected are declining in the case of the participatory management system. Structural change in the participatory management system and extensive work on capacity building are required in order to obtain the benefits of transferring management to farmers' organizations in Pakistan. Copyright (C) 2013 John Wiley & Sons, Ltd.