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S Sen

Publications and source records attributed to S Sen.

At least 109 records · Page 6Linked to original sources
PubMed1999

Slow algebraic relaxation in quartic potentials and related results.

We present a detailed report [see S. Sen et al., Phys. Rev. Lett. 77, 4855 (1996)] of our numerical and analytical studies on the relaxation of a classical particle in the potentials V(x)= +/-x(2)/2+x(4)/4. Both of the approaches confirm that at all temperatures, the relaxation functions (e.g., velocity relaxation function and position relaxation function) decay asymptotically in time t as sin(omega(0)t)/t. Numerically calculated power spectra of the relaxation functions show a gradual transition with increasing temperature from a single sharp peak located at the harmonic frequency omega(0) to a broad continuous band. The 1/t relaxation is also found when V(x) is a polynomial in powers of x(2) with a nonvanishing coefficient accompanying the x(4) term in V(x). Numerical calculations show that in the cases in which the leading term in V(x) behaves as x(2n) with integer n, the asymptotic relaxation exhibits 1/t(phi) decay where phi =1/(n-1). We briefly discuss the analytical approaches to relaxation studies in these strongly anharmonic systems using direct solution of the equation of motion and using the continued fraction formalism approach for relaxation studies. We show that the study of the dynamics of strongly anharmonic oscillators poses unique difficulties when studied via the continued fraction or any other time-series construction based approaches. We close with comments on the physical processes in which the insights presented in this work may be applicable.

Journal Article↗
PubMed1999

Diagnostic and prognostic potential of a competitive enzyme-linked immunosorbent assay for leishmaniasis in India.

A Leishmania donovani species-specific monoclonal antibody (monoclonal antibody D2) was evaluated for its diagnostic and prognostic potential by a competitive enzyme-linked immunosorbent assay (C-ELISA) in sera from Indian patients with visceral leishmaniasis (VL) and seven patients with post-kala-azar dermal leishmaniasis (PKDL). These results were compared with those obtained by microscopy with Giemsa-stained tissue smears and a direct enzyme-linked immunosorbent assay (direct ELISA) with crude parasite antigen. Of 121 patients with clinically diagnosed VL examined, 103 (85.1%) were positive and 11 (9.1%) were negative by all three methods. An additional 7 (5.8%) who were negative by microscopy were positive by both C-ELISA and direct ELISA. Seven PKDL patients were also examined and were found to be positive by all three methods. Analysis of the chemotherapeutic response to sodium antimony gluconate of these 110 serologically positive VL patients showed that 57 (51.8%) were drug responsive and 53 (48.2%) were drug resistant. The C-ELISA with sera from 20 longitudinally monitored VL patients before and after chemotherapy showed a significant decrease in percent inhibition of monoclonal antibody D2 in drug-responsive patients. However, in drug-unresponsive patients, the percent inhibition of D2 was unchanged or was slightly increased. Our results therefore indicate (i) the applicability of L. donovani species-specific monoclonal antibody D2 for sensitive and specific serodiagnosis by C-ELISA, (ii) that the C-ELISA is more sensitive than microscopy, especially for early diagnosis, (iii) that L. donovani is still the main causative agent of VL, irrespective of the chemotherapeutic response, and (iv) that the C-ELISA can be used to evaluate the success of drug treatment.

Animals↗
PubMed1999

Animal study on the effects of catalin on aftercataract and posterior capsule opacification.

PURPOSE: To find out the role of Catalin in the prevention of posterior capsular opacification (PCO), we undertook this experimental study in rabbits. METHODS: Twenty rabbits (10 for the Catalin group and 10 for the placebo group) were operated on for extracapsular clear lens extraction in an aseptic environment. In all cases, capsulorrhexis of 8 mm diameter was carried out. Both the test drug and placebo were given at a dose of 4 times/day from the first postoperative day for 8 weeks. Common drugs in both groups were topical corticosteroid, antibiotic and cycloplegic drops. Periodic slitlamp examinations and photographic documentations were carried out to find any evidence of aftercataract. At the end ot 8 weeks, histopathological examination was carried out to document any evidence of aftercataract. RESULT: Overall, evidence of aftercataract was seen in 6 rabbits in the control group and 3 in the Catalin group; the degree of PCO was higher in the placebo group. CONCLUSION: We found that Catalin played some role in preventing PCO.

Animals↗
PubMed1999

Amplification of telomeric DNA directly correlates with metastatic potential of human and murine cancers of various histological origin.

Telomeres, repeated DNA sequences (T2AG3)n that guard the ends of chromosomes, serve as a checkpoint for cell-cycle progression and regulate cell senescence and apoptosis. Loss of the telomeric repeats promotes genomic instability, which is the hallmark of most cancer cells. Whether this loss differs among tumor cells with malignant potential is unknown and was the goal of this study. An all-human telomeric DNA probe was used to perform fluorescence in situ hybridization (FISH) and the telomeric signals in interphase nuclei were quantitated using a computer software package. Southern blot analysis was carried out to measure terminal restriction fragment length (TRFL) in multiple cancer cell lines, including nonmetastatic and metastatic human breast, lung, prostate, colon, brain, and renal carcinomas, as well as human and murine melanoma clones and somatic cell hybrids. The metastatic capability of all cell lines, clones and somatic cell hybrids was evaluated subsequent to orthotopic implantation into nude mice. FISH preparations with telomeric DNA probes showed that the mean percent telomeric area in the metastatic nuclei was significantly greater than their nonmetastatic counterparts and Southern blotting in selected samples confirmed our findings. These data suggest that amplification of telomeres is directly correlated with invasive and metastatic potential of murine or human tumor cells.

Animals↗
PubMed1999

Surgical removal of a free floating cyst of the iris pigment epithelium causing disturbing visual symptoms.

Pigmented cysts in the anterior chamber, fixed or free floating, are considered to be unusual but not very infrequent. However, most of these cases usually do not need any treatment other than a periodic observation. We report the surgical removal of an iris pigment epithelial cyst floating freely in the anterior chamber. The reason for surgical removal was, disturbance in near vision being caused by movement of the cyst across the visual axis. This specific symptom of disturbed near vision, to the best of our knowledge, is a rare indication for surgery that has not been pointed out earlier. Histopathological confirmation of the clinical diagnosis was also obtained.

Adult↗
PubMed1999

Telomere, telomerase, tumorigenesis and therapy: an overview.

The ends of chromosome in higher eukaryote are termed telomere. The DNAs present at that part of chromosome is called telomeric DNA. Telomeric DNA consists of tandemly repeated DNA sequences. The replication of the ends of chromosomes is not controlled by conventional DNA polymerases rather a special kind of enzyme is involved in this process. It is a ribonucleoprotein and known as telomerase. Cells in senescence stage face telomeric crisis that leads to loss of telomeric ends. Surveillance turns to procancer cells with increased telomerase activity which is a later consequence. Based on these facts a key diagnostic approach has been developed for detection of tumour. A novel therapy for tumour repression has been developed using telomerase inhibitors. However, these inhibitors are very much effective for solid tumour therapy and conceptually will not work on hematological malignancies.

Cell Transformation, Neoplastic↗
PubMed1999

Cell death in paclitaxel-dependent chinese hamster ovary cells is initiated by the loss of telomeric DNA repeats.

We have reported earlier that cell death in a metastatic murine melanoma cell line induced by paclitaxel and its water-soluble conjugates is mediated through the extensive erosion of telomeric repeats. The purpose of this study was to investigate if loss of telomeric repeats was also involved in cell death of Tax-18 and Tax-2-4, two paclitaxel-requiring mutant Chinese hamster ovary (CHO) cell lines. Tax-18 and Tax-2-4 cells were grown in paclitaxel-free culture medium for 24, 48, 72, and 96 h at 37 degrees C and then harvested for cytological preparations. Control cultures of both cell lines were grown in paclitaxel-supplemented medium and harvested simultaneously. We found that: 1) the frequency of telomeric associations in metaphase preparations was increased with the duration of paclitaxel-depleted culture; 2) Tax-18 cells showed a higher incidence (33.0%) of endoreduplicated metaphases at 24 h of paclitaxel-depleted culture than did Tax-2-4 cells, in which endoreduplicated metaphases were rare; 3) the frequency of polyploid cells was increased after 48, 72, and 96 h of paclitaxel-depleted culture for Tax-18 relative to that for Tax-2-4 cells; 4) both cell lines showed reductions in telomeric signals at chromosomal termini, but not in the interphase nuclei; and 5) both cell lines had shorter terminal telomeric restriction fragments after culture in paclitaxel-depleted medium. These results support our earlier observations and indicate that reduction of telomeric repeats is involved in G2/M cell arrest (endoreduplication) followed by severe DNA fragmentation, and then cell death of two CHO mutant cell lines that require paclitaxel for cell division.

Animals↗
PubMed1999

Histoplasmosis of the eyelids--a case report.

Systemic histoplasmosis manifesting as an ulcerative eyelid lesion is rare. We describe a successfully treated case of histoplasmosis who presented with an eroding ulcer in the lid.

Adult↗
PubMed1998

Loss of heterozygosity in squamous cell carcinomas of the head and neck defines a tumor suppressor gene region on 11q13.

Tumor suppressor genes APC, RB1, and DCC, as well as genes localized to 3p and 11q, have been implicated in the development of a number of human tumors. To determine whether allelic deletions occur at these loci in squamous cell carcinomas (SSCs) of the head and neck, 25 primary, 1 metastatic, and 3 recurrent tumors, along with the corresponding constitutional tissues, were analyzed by using a battery of polymorphic DNA markers. For two primary tumors, we also analyzed subsequent metastatic tumors of the lung. Polymerase chain reaction-based restriction fragment length polymorphism studies demonstrated loss of heterozygosity for the APC gene in 2 of 12 (17%), the RB1 gene in 5 of 22 (23%), and the DCC gene in 5 of 13 (38%) informative cases. Alleles on chromosomes 3p, 11q13, and 18q21.1 were lost in 7 of 20 (35%), 9 of 23 (39%), and 4 of 17 (24%) informative cases, respectively. A breakpoint was identified within the chromosomal region 3p13-21.2 in a SCC of the tongue. Breakpoints within 11q13 were identified in 2 additional tumors. Thus, allelic deletions of DCC, 3p, and 11q13 appear to be common in head and neck cancers, suggesting that these genes play a critical and complex role in the development of these tumors. Furthermore, the present study provides definitive evidence for a tumor suppressor gene at chromosome band 11q13 and localizes this gene to the INT2-D11S533 interval for future cloning and sequencing.

Carcinoma, Squamous Cell↗
PubMed1998

Chromosomal fragile sites and DNA amplification in drug-resistant cells.

It has been well established that DNA amplification is one of the important mechanisms by which cultured cells acquire resistance to many cytotoxic compounds. Amplification of important genes including those encoding oncoproteins, growth factors, their receptors and cell-cycle regulators has been reported in human neoplasms. Yet, despite intensive research since the first description of DNA amplification in cultured cells about 20 years ago, the mechanisms of DNA amplification remain largely unknown. Many models have been proposed to account for the diverse manifestations of amplified DNA in many different cell sources. It is not the intention of this commentary to review these many different models. Rather, we wil focus on the recent advances in this area of research, made mainly via the fluorescence in situ hybridization technique, that have revealed a fairly common chromosomal manifestation of amplified DNA in the drug-resistant hamster cell lines and have demonstrated the association of chromosomal fragile site breakage with early events in DNA amplification. These new developments underscore the importance of future research toward understanding the molecular bases of chromosomal fragile sites, including mechanisms involved in DNA strand breakage and repair, chromosomal translocations, and deletions, which may, in turn, provide important new insights into genomic plasticity and neoplastic transformation.

Animals↗
PubMed1998

Evaluation of alternative strategies to prevent Newcastle disease in Cambodia.

Velogenic viscerotropic Newcastle disease (vvNCD), which is endemic in Cambodia, can be prevented in theory by a combination of biosecurity and immunization of broiler flocks. The relative contribution of appropriate biosecurity and effective vaccination was quantified at the farm level, applying realistic projections for capital investment, fixed and variable production costs and losses following infection. Non-protected broiler flocks generate a loss when the probability of vvNCD infection exceeds 0.4. Applying both biosecurity and effective vaccination would sustain profitability up to a probability of exposure of 1.0. The benefit to cost ratios for alternative strategies were evaluated for a range of probabilities of exposure to vvNCD extending from 0.1 to 1.0. The benefit-to-cost ratio for biosecurity exceeded unity at a risk of exposure exceeding 0.1, and 0.2 for vaccination and the combination of vaccination and biosecurity respectively. A sensitivity analysis demonstrated that the efficiency of protection, feed cost, and financial consequences of infection markedly affected the projected benefit-to-cost ratios associated with alternative methods of prevention.

Animal Husbandry↗
PubMed1998

Increased protein kinase C activity in myotrophin-induced myocyte growth.

Myotrophin, a novel protein that has been shown to stimulate myocyte growth, has been isolated, purified, and sequenced from the hearts of spontaneously hypertensive rats and dilated cardiomyopathic human tissue. Recently, the cDNA clones encoding myotrophin have been isolated and expressed in Escherichia coli, and the recombinant myotrophin was found to be as biologically and immunologically active as natural myotrophin. The mechanism by which myotrophin stimulates protein synthesis and initiates myocardial hypertrophy is not known. To evaluate the involvement of protein kinase C (PKC) in myotrophin-induced hypertrophy, PKC activity and its distribution in the subcellular fraction were determined in cultured neonatal and adult myocytes. PKC activity was determined by measuring the incorporation of 32P into histone type III-S and PKCepsilon substrate peptide (epsilon(pep)) from [gamma-32P]ATP in neonatal myocytes. Myotrophin significantly stimulated PKC activity in neonatal myocytes and was associated with a significant increase in protein synthesis. The effect of myotrophin on the stimulation of PKC activity and [3H]leucine incorporation was abolished by pretreatment with either staurosporine or H-7, two selective, pharmacological PKC inhibitors. Pretreatment of myocytes with staurosporine also reduced the myotrophin-induced mRNA levels of c-fos and beta-myosin heavy chain. To evaluate the subcellular events whose occurrence was due to myotrophin and translocation of PKC, we studied the effect of genistein, a tyrosine kinase inhibitor, on myotrophin-induced neonatal myocyte growth. Genistein attenuated the [3H]leucine incorporation induced by myotrophin. To define the specificity of the PKC isoform(s) involved in myotrophin-stimulated myocyte growth, both neonatal and adult myocytes were treated with myotrophin, and Western blot analyses were performed by using the antibodies of different PKC isoforms. Results showed that both PKCalpha and PKCepsilon isoforms participated in the myotrophin-induced neonatal myocyte growth, whereas only the PKCepsilon isoform was involved in myotrophin-induced adult myocyte hypertrophy. PKCdelta and PKCzeta do not seem to participate in either neonatal or adult myocyte growth induced by myotrophin. Treatment with antisense oligonucleotides specific for PKCalpha and PKCepsilon isoforms further supported this result. PKCalpha is the major PKC isoform in neonatal myocytes and needs Ca2+ and phospholipids for its activation, and PKCepsilon (the Ca2+-independent PKC isoform) is present in both neonatal and adult myocytes; the 15-mer antisense oligodeoxynucleotides of each were used for this study. Treatment of neonatal myocytes with the PKCalpha and PKCepsilon antisense oligodeoxynucleotides for 5 days significantly reduced Ca2+-dependent and Ca2+-independent PKC activity, respectively, as well as the [3H]leucine incorporation induced by myotrophin. Furthermore, myotrophin-induced PKC activity was primarily located in the particulate fraction and did not result in a concomitant decrease in the cytosolic fraction. Myotrophin does not change PKC isoform expression (both Ca2+ dependent and independent PKC isoforms used in this study) in rat neonatal cardiac fibroblasts. Our data suggest that myotrophin exerts its action on protein synthesis, possibly through a tyrosine kinase-coupled pathway and translocation of PKC from the cytosol to the cell membrane.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1998

The structural basis of ankyrin-like repeat function as revealed by the solution structure of myotrophin.

BACKGROUND: Myotrophin is a 12.5 kDa protein that appears to have a key role in the initiation of cardiac hypertrophy, a central process in many heart diseases. Myotrophin primarily comprises ankyrin-like (ANK) repeats, the 33 amino acid motifs involved in a wide range of protein-protein interactions. As a first step in the structure-based search for cardiac hypertrophy antagonists and in order to gain insight into the molecular basis of action of the ubiquitous and multifunctional ANK repeat motif, we have determined the solution structure of myotrophin using multidimensional heteronuclear NMR spectroscopy. RESULTS: The myotrophin structure determination was based on 2786 experimental NMR restraints, and the precision of the coordinates for the final 45 simulated-annealing structures is 0.43 A for the backbone atoms and 0.87 A for all atoms. The structure of myotrophin is well defined and is ellipsoidal: approximately 46 A long and 21 A wide. The ANK repeats, which constitute the main part of the myotrophin structure, are characteristic of a hairpin-like protruding tip followed by a helix-turn-helix motif. The V-shaped helix-turn-helix of the ANK repeats stack sequentially in bundles and are stabilized by compact hydrophobic cores, whereas the protruding tips are less ordered. This arrangement is quite different to the continuous beta-sheet topology observed in the corresponding regions of another ANK protein, 53BP2, the structure of which was determined in complex with p53. CONCLUSIONS: The solution structure of myotrophin provides important insights into the structural and dynamic features of the ANK motif, and suggests that the protruding tips with highly variable sequences may be critical to facilitate diverse protein-protein recognition. The present structure also provides a molecular basis for the further functional characterization of myotrophin and the development of therapeutics for hypertrophy-related heart diseases.

Amino Acid Sequence↗
PubMed1998

Alfalfa Saponins and Their Implication in Animal Nutrition.

Alfalfa (Medicago sativa L.) is of immense importance as livestock fodder for both developed and lesser developed countries as it contains a high amount of protein, and yield of dry matter is also very high. The main antinutritional components present in this plant are saponins, and their unfavorable effects on animal performance have restricted the optimum use of this high-protein plant as an animal feed. The occurrence, chemistry, analysis, and consequences of intake of alfalfa saponins are reviewed. The information synthesized may lead to planning of more detailed studies on isolation and characterization of saponins and sapogenins to gain a better understanding of the biological activities of the aglycon and carbohydrate moieties of saponins.

Journal Article↗
PubMed1998

Results of Wilms' tumour management in two tertiary-care hospitals in Asia.

In the period 1985-1995, 87 children underwent surgery for Wilms' tumour; 16 were lost to follow-up. Of the remaining children, 27 presented with stage I disease, 11 with stage II, 12 with stage III, 14 with stage IV, and 6 with stage V. One child was not staged. The histology was favourable Wilms' tumour in 44, anaplastic in 12, unclassified in 8, clear-cell sarcoma in 4, and rhabdoid tumour in 3. Although a total nephrectomy was generally performed, partial renal surgery was performed for 6 bilateral and 4 unilateral tumours, the latter including 2 fused kidneys. Preoperative chemotherapy was employed with benefit in massive tumours, tumour in fused kidneys, bilateral tumours, and preoperatively diagnosed inferior vena caval tumour thrombi. Postoperative chemotherapy, employed in all cases, consisted of actinomycin D and vincristine with the addition of adriamycin in anaplastic and advanced-stage tumours. Ten children underwent second-line chemotherapy for disease unresponsive to the above management, but only 1 of these is currently free of disease. Postoperative tumour-bed radiotherapy, used in selected cases, prevented local recurrence in stage I and II disease. However, 20% of stage I and II patients not receiving radiotherapy developed tumour-bed recurrence. Twenty-three children have died and 5 with advanced disease and incomplete follow-up are presumed to be dead. Nine children are currently on treatment; 34 have successfully completed treatment, the disease-free survival in stages I-V being 81%, 75%, 42%, 14%, and 50%, respectively. Overall disease-free survival was 69% for Wilms' tumour of favourable histology and 50% for anaplastic tumours. The 3 patients with rhabdoid tumours and 3 of 4 with clear-cell sarcomas have died. Wilms' tumour management in the developing world is compromised by cases lost to follow-up and late presentation with massive tumours and advanced stage. Preoperative chemotherapy is advantageous in a number of cases, and postoperative radiotherapy should be deployed more frequently.

Adolescent↗
PubMed1998

Surgical management of complete ureteric duplication abnormalities.

In 2 decades (1974-1993), the senior author (S.A.) managed 148 patients with various abnormalities associated with complete ureteric duplication. Included were 72 patients with primary vesicoureteric reflux, 50 with ureteroceles, and 26 with upper-pole ectopic ureters. The majority of the patients were female, and the common clinical presentations included urinary tract infection (UTI), UTI with septicemia, and urinary incontinence. Ten cases were diagnosed after recognition of a renal abnormality on prenatal ultrasonography, an avenue that has provided new challenges, new opportunities, and new dilemmas. This review article is based on the authors' experience together with an analysis of current emphasis on early diagnosis, minimal surgery, and maximum preservation of renal function.

Female↗