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Biomedical subjects

S Kumar

Publications and source records attributed to S Kumar.

At least 667 records · Page 37Linked to original sources
PubMed2000

Design and synthesis of curcumin-bioconjugates to improve systemic delivery.

Di-O-glycinoyl curcumin (I), di-O-glycinoyl-C4-glycyl-curcumin (II), 5'-deoxy-5'-curcuminyl thymidine (5'-cur-T) (III) and 2'-deoxy-2'-curcuminyl uridine (2'-cur-U) (IV) have been synthesized and characeterised by elemental analysis & 1H NMR. The antibacterial activities of these four bioconjugates has been tested particularly for multiresistant micro-organisms. Best results are shown by I & IV. These bioconjugates serve dual purpose of systemic delivery as well as therapeutic agents against viral diseases.

Anti-Infective Agents↗
PubMed2000

Expansion and molecular evolution of the interferon-induced 2'-5' oligoadenylate synthetase gene family.

The mammalian 2'-5' oligoadenylate synthetases (2'-5'OASs) are enzymes that are crucial in the interferon-induced antiviral response. They catalyze the polymerization of ATP into 2'-5'-linked oligoadenylates which activate a constitutively expressed latent endonuclease, RNaseL, to block viral replication at the level of mRNA degradation. A molecular evolutionary analysis of available OAS sequences suggests that the vertebrate genes are members of a multigene family with its roots in the early history of tetrapods. The modern mammalian 2'-5'OAS genes underwent successive gene duplication events resulting in three size classes of enzymes, containing one, two, or three homologous domains. Expansion of the OAS gene family occurred by whole-gene duplications to increase gene content and by domain couplings to produce the multidomain genes. Evolutionary analyses show that the 2'-5'OAS genes in rodents underwent gene duplications as recently as 11 MYA and predict the existence of additional undiscovered OAS genes in mammals.

2',5'-Oligoadenylate Synthetase↗
PubMed2000

Factors enhancing protein thermostability.

Several sequence and structural factors have been proposed to contribute toward greater stability of thermophilic proteins. Here we present a statistical examination of structural and sequence parameters in representatives of 18 non-redundant families of thermophilic and mesophilic proteins. Our aim was to look for systematic differences among thermophilic and mesophilic proteins across the families. We observe that both thermophilic and mesophilic proteins have similar hydrophobicities, compactness, oligomeric states, polar and non-polar contribution to surface areas, main-chain and side-chain hydrogen bonds. Insertions/deletions and proline substitutions do not show consistent trends between the thermophilic and mesophilic members of the families. On the other hand, salt bridges and side chain-side chain hydrogen bonds increase in the majority of the thermophilic proteins. Additionally, comparisons of the sequences of the thermophile-mesophile homologous protein pairs indicate that Arg and Tyr are significantly more frequent, while Cys and Ser are less frequent in thermophilic proteins. Thermophiles both have a larger fraction of their residues in the alpha-helical conformation, and they avoid Pro in their alpha-helices to a greater extent than the mesophiles. These results indicate that thermostable proteins adapt dual strategies to withstand high temperatures. Our intention has been to explore factors contributing to the stability of proteins from thermophiles with respect to the melting temperatures (T(m)), the best descriptor of thermal stability. Unfortunately, T(m) values are available only for a few proteins in our high resolution dataset. Currently, this limits our ability to examine correlations in a meaningful way.

Animals↗
PubMed2000

CD105 antagonizes the inhibitory signaling of transforming growth factor beta1 on human vascular endothelial cells.

CD105 (endoglin), a receptor for transforming growth factor beta (TGFbeta), is highly expressed in tissue-cultured, activated endothelial cells in vitro and in tissues undergoing angiogenesis in vivo. The absence of CD105 in knockout mice leads to their death from defective vascular development, but the role of CD105 in the modulation of angiogenesis has not been elucidated. TGFbeta1 is a well-recognized regulator of angiogenesis. Using an antisense approach, we have shown that inhibition of CD105 protein translation in cultured human endothelial cells enhances the ability of TGFbeta1 to suppress growth and migration in these cells. The ability of endothelial cells to form capillary tubes was evaluated by the use of a 3-dimensional collagen matrix system where TGFbeta1 not only reduced the length of capillary-like structures, but also caused massive mortality in CD105-deficient cells compared to control cultures. These results provide direct evidence that CD105 antagonizes the inhibitory effects of TGFbeta1 on human vascular endothelial cells and that normal cellular levels of CD105 are required for the formation of new blood vessels.

Animals↗
PubMed2000

Epstein-Barr virus-positive primary gastrointestinal Hodgkin's disease: association with inflammatory bowel disease and immunosuppression.

Inflammatory bowel disease (IBD) is associated with an increased risk of lymphoma, which is usually extraintestinal but sometimes may involve the diseased bowel itself. Most lymphomas described in this setting are of non-Hodgkin's type, but rare cases of Hodgkin's disease (HD) have been reported. We describe the clinicopathologic and molecular features of four patients with primary gastrointestinal HD. Three patients had preexistent Crohn's disease (CD), for which two of them had received immunosuppressive therapy. The fourth patient had a longstanding history of diverticulitis and myasthenia gravis and was receiving immunosuppressive therapy for the latter. Multifocal involvement of the bowel by HD was noted in all four cases. Disease was staged as IVA in one patient, IIIB in one patient, and IE in one patient, and the fourth patient died in the postoperative period before further workup. Two patients received chemotherapy, one of whom was dead at 9 months, whereas the other has no evidence of disease at 25 months' follow-up. The patient with IE disease did not receive any therapy because only a few microscopic foci of disease were present and is also without any evidence of disease at 17 months. The Reed-Sternberg (RS) cells in all four cases expressed CD30, CD15, EBER-1, and LMP-1; two of four were focally CD20-positive. VJ-polymerase chain reaction for immunoglobulin heavy chain (IgH) rearrangement showed a polyclonal pattern in all four cases. In two cases, laser capture microdissection was used to isolate individual RS and Hodgkin's cells, which contained rearranged immunoglobulin genes, confirming a B-cell genotype. Whereas one case showed a dominant clonal band present in all isolates, cells from the patient with stage IE disease clearly showed a polyclonal population of RS cells. Our findings indicate that HD arising in the setting of IBD or chronic inflammation is the result of an Epstein-Barr virus-driven lymphoproliferation, analogous to that found in other immunodeficient states. Disordered immunoregulation inherent to CD and immunosuppressive therapy for the latter may contribute to its development. The finding of polyclonal RS cells in a patient with early stage disease and apparent cure by surgical resection versus monoclonal RS cells in the patient with disseminated disease suggests that HD in the setting of immunodeficiency also may show molecular progression, in a manner similar to that occurring in conventional B-cell lymphoproliferative disorders arising in the same setting.

Adult↗
PubMed2000

Afferent loop syndrome: the role of Tc-99m mebrofenin hepatobiliary scintigraphy.

Afferent loop syndrome is caused by intermittent mechanical obstruction of the afferent loop of a gastrojejunostomy and may present early as an acute type or late as a chronic type. The authors describe two patients who were examined for a history of bilious vomiting after gastrojejunostomy, and who were thought to have afferent loop syndrome (chronic type) based on clinical findings. Results of routine investigations, such as upper gastrointestinal endoscopy, and ultrasonography were inconclusive. Findings from the barium meal follow-through studies were normal in the first patient and revealed a dilated duodenum in the second patient. Tc-99m bromotriethyl-iminodiacetic acid has been used to identify afferent loop obstruction as represented in these studies.

Adult↗
PubMed2000

Deep vein thrombosis prophylaxis in hip fractures: a comparison of the arteriovenous impulse system and aspirin.

BACKGROUND: A prospective, randomized controlled trial was used to compare the efficacy of the arteriovenous (AV) impulse system and aspirin in reducing venous thrombosis after fracture to the femoral neck. METHODS: A total of 143 patients underwent hemiarthroplasty, after which 70 patients were treated with the AV pump and a second group of 73 patients were commenced on 325 mg of aspirin. Duplex ultrasound was used to assess both proximal and distal venous thrombi on days 7 to 10. Calf and thigh circumferences were also measured. RESULTS: Thrombi developed in seven of the patients treated with aspirin and in four patients treated with the AV pump. No statistically significant difference could be established (p = 0.109). There was a significant reduction in both calf (p = 0.003) and thigh (p = 0.002) swelling in the group treated with the AV pump. Neither treatment group was a significant predictor of a poorer outcome by using logistical regression analysis (p = 0.258). CONCLUSIONS: Both aspirin and the AV pump are effective in reducing thromboembolic events after hemiarthroplasty of the hip.

Aged↗
PubMed2000

Phase-separated composite films: experiment and theory

A different phase-separation process is capable of producing a composite system consisting of a very thin layer of liquid crystal in contact with a similarly thin layer of polymer. The morphology of the polymer depends on the composition of the prepolymer-liquid crystal mixture and the rate of polymerization. A simple one-dimensional theory is able to describe the essential features of this process.

Journal Article↗
PubMed2000

Mechanism for the faraday instability in viscous liquids

This report presents a discussion of the wave number selection mechanism in the Faraday instability, which arises when standing waves form on the free surface of a liquid subject to vertical sinusoidal oscillation. The focus is on the case where the viscous effects are strong, i.e., when the wavelength is of the same order of magnitude as the boundary layer thickness at the free surface. We investigate the relationship between the Faraday instability and the Rayleigh-Taylor instability by performing linear stability calculations. In the deep water limit (wavelength << liquid depth), our results indicate that the preferred wave number in the Faraday instability is primarily determined through a Rayleigh-Taylor instability. In the case of shallow water (wavelength approximately liquid depth), the agreement between the Rayleigh-Taylor and Faraday wave numbers does not appear to be as good, probably due to the interaction between the oscillatory motion of the standing waves and the bottom boundary.

Journal Article↗
PubMed2000

Folding and binding cascades: dynamic landscapes and population shifts.

Whereas previously we have successfully utilized the folding funnels concept to rationalize binding mechanisms (Ma B, Kumar S, Tsai CJ, Nussinov R, 1999, Protein Eng 12:713-720) and to describe binding (Tsai CJ, Kumar S, Ma B, Nussinov R, 1999, Protein Sci 8:1181-1190), here we further extend the concept of folding funnels, illustrating its utility in explaining enzyme pathways, multimolecular associations, and allostery. This extension is based on the recognition that funnels are not stationary; rather, they are dynamic, depending on the physical or binding conditions (Tsai CJ, Ma B, Nussinov R, 1999, Proc Natl Acad Sci USA 96:9970-9972). Different binding states change the surrounding environment of proteins. The changed environment is in turn expressed in shifted energy landscapes, with different shapes and distributions of populations of conformers. Hence, the function of a protein and its properties are not only decided by the static folded three-dimensional structure; they are determined by the distribution of its conformational substates, and in particular, by the redistributions of the populations under different environments. That is, protein function derives from its dynamic energy landscape, caused by changes in its surroundings.

Models, Molecular↗
PubMed2000

Chemotherapy in recurrent epithelial ovarian cancer (EOC): an analysis of prognostic factors.

OBJECTIVE: Prognosis of patients with recurrent epithelial ovarian cancer (EOC) is generally poor. Cisplatin is the most effective drug. We used three cisplatin based chemotherapeutic (CT) regimens and retrospectively analyzed the data to determine the response rate, toxicity, survival and the impact of various prognostic factors on the outcome. PATIENTS AND METHODS: Between August, 1989 and September, 1997, 102 patients were diagnosed to have recurrent EOC. Sixty-five of 102 patients received CT every 3 weeks using cisplatin 75 mg/m2 i.v. day 1 plus cyclophosphamide 750 mg/m2 i.v. day 1 (CP, Group A, n = 29), cisplatin 75 mg/m2 i.v. day 1, plus adriamycin 40 mg/m2 i.v. day 1 and cyclophosphamide (CAP, Group B, n = 22) and paclitaxel 135 mg/m2 i.v. day 1 plus cisplatin 75 mg/m2 i.v. day 1 (TP, Group C, n = 14). Twelve patients received single agent CT and were not analyzed. Remaining 25 patients refused CT treatment and were followed for survival. RESULTS: The overall response rate (complete and partial) was 59.2% for patients receiving CP (Group A), 45% for CAP (Group B) and 76.9% for those receiving TP (Group C), p = ns. Response rate was significantly higher for patients with platinum sensitive disease compared to those with platinum resistant disease; 55.76 vs 39%, p < 0.007. CT was generally tolerated well; 2 patients died of CT toxicity, one each in Group A (CP) and C (TP), respectively. The median survival from the date of relapse for patients receiving chemotherapy was 15 months compared to 4 months for those who did not receive chemotherapy, p < 0.001. Chemotherapy responders had a significantly higher median survival than chemotherapy non-responders, 24 months vs 10 months, p < 0.01. The median overall survival was not significantly different in the 3 groups; Group A--15 months, Group B--12 months and 15 months in Group C, p = 0.738. On univariate analysis--time since last CT (< 6 months vs > 6 months, p < 0.037, response to previous CT, p < 0.0183, cisplatinum sensitivity vs resistance, p < 0.032, number of sites (< 2 vs > 2) of recurrence, p < 0.004 and response to salvage CT, p < 0.01 were associated with survival benefit. On multivariate analysis, 2 factors--platinum sensitivity and response to salvage CT attained significance. CONCLUSIONS: Our study confirms the benefit of platinum based chemotherapy in recurrent EOC. Patients with platinum sensitive disease, and those responding to salvage chemotherapy benefit most.

Adult↗
PubMed2000

Immunogenicity and efficacy in aotus monkeys of four recombinant Plasmodium falciparum vaccines in multiple adjuvant formulations based on the 19-kilodalton C terminus of merozoite surface protein 1.

The immunogenicity and protective efficacy of four versions of recombinant C-terminal 19-kDa epidermal growth factor-like region of the major surface protein 1 (rMSP1(19)) of Plasmodium falciparum was studied in Aotus monkeys. Vaccination with each of the four rMSP1(19) constructs elicited high levels of antibodies to MSP1(19) but only one construct, the 19-kDa fragment expressed as a secreted fusion protein from Saccharomyces cerevisiae (yP30P2MSP1(19)), induced a high degree of protective immunity in Aotus nancymai against lethal P. falciparum challenge. Protective formulation required Freund's adjuvant; vaccination with yP30P2MSP1(19) in six other adjuvants that are suitable for human use induced lower levels of antibody response and no protection. These results emphasize the need to continue the search for an adjuvant that is comparable to Freund's adjuvant in potency and is safe for use in humans.

Adjuvants, Immunologic↗
PubMed2000

Activation of MEK kinase 1 by the c-Abl protein tyrosine kinase in response to DNA damage.

The c-Abl protein tyrosine kinase is activated by certain DNA-damaging agents and regulates induction of the stress-activated c-Jun N-terminal protein kinase (SAPK). Here we show that nuclear c-Abl associates with MEK kinase 1 (MEKK-1), an upstream effector of the SEK1-->SAPK pathway, in the response of cells to genotoxic stress. The results demonstrate that the nuclear c-Abl binds to MEKK-1 and that c-Abl phosphorylates MEKK-1 in vitro and in vivo. Transient-transfection studies with wild-type and kinase-inactive c-Abl demonstrate c-Abl kinase-dependent activation of MEKK-1. Moreover, c-Abl activates MEKK-1 in vitro and in response to DNA damage. The results also demonstrate that c-Abl induces MEKK-1-mediated phosphorylation and activation of SEK1-SAPK in coupled kinase assays. These findings indicate that c-Abl functions upstream of MEKK-1-dependent activation of SAPK in the response to genotoxic stress.

Animals↗
PubMed2000

Risperidone implicated in the onset of tardive dyskinesia in a young woman.

The aim of this case report is to highlight that risperidone may cause and ameliorate tardive dyskinesia. A 16 year old white women with a 12 month history of schizophrenia, developed buccolingual masticatory tardive dyskinesia after receiving risperidone 6 mg. She had received small dosages of typical antipsychotics before and during receiving risperidone for short periods. Recommencement of risperidone with 2 mg and increasing to 6 mg resulted in improvement in tardive dyskinesia and up until now she remains free of any abnormal involuntary movements.

Adolescent↗