Biomedical subjects

S Sen

Publications and source records attributed to S Sen.

At least 55 records · Page 3Linked to original sources

PubMed2002

Seasonal effects on the air-water carbon dioxide exchange in the Hooghly estuary, NE coast of Bay of Bengal, India.

Monthly variation of CO2 fugacity (fCO2) in surface water and related atmospheric exchanges were measured in the Hooghly estuary which is one of the most important estuaries, since it is fed by one of the world's largest rivers, the Ganges with a flow of 15,646 m3 s-1 (1.6% of the world's combined river flow). Carbon dioxide fluxes averaged over the entire estuary are in the range of -2.78 to 84.4 mmol m-2 d-1. This estuary acts as a sink for CO2 during monsoon months and seasonal variation of its flux is controlled by dilution of seawater by river water. Since the solubility of CO2 and the disassociation of carbonic acid in estuarine water are controlled by temperature and salinity, the observed variations of CO2 fluxes are compared with those predicted from seasonal changes in temperature, salinity and the ratio of gross primary production to community respiration using empirical equations with an explained variability of 55%.

Air↗

PubMed2002

Review article: the molecular adsorbents recirculating system (MARS) in liver failure.

In recent years different artificial liver support systems are being developed for use in patients with acute decompensation of chronic liver disease or acute liver failure. The molecular adsorbents recirculating system (MARS), a device in which patient's blood is dialysed across an albumin-impregnated membrane against a recirculated albumin-containing solution, seems to be effective in removing albumin-bound toxins, such as fatty acids, bile acids and bilirubin. Although the clinical experience with MARS is scarce, some pilot studies have reported its effectiveness at improving liver function and hepatic encephalopathy in patients with acute decompensation of chronic liver disease, and renal function in patients with hepatorenal syndrome type I. Data regarding MARS experience in acute liver failure and in primary graft dysfunction are encouraging but limited. Its real usefulness in these settings is, at present, under evaluation in randomized controlled clinical trials.

Humans↗

PubMed2002

Effect of amitriptyline on gastric ulceration.

Amitriptyline significantly inhibited alcohol, aspirin, indomethacin and cold-restraint stress-induced ulceration. Secretory studies conducted in pyloric-ligated rats revealed that the drug, at the doses employed, significantly reduced total acidity and protein content. However, significant reductions of the gastric volume were only observed at the highest dose of the drug. In another set of experiments, when 50% alcohol (v/v) was administered to the pyloric-ligated rats pretreated with amitriptyline, it was observed that the drug significantly reduced the pH, total acidity and protein content.

Amitriptyline↗

PubMed2002

Efficacy of a single dose of antenatal steroid in surfactant-treated babies under 31 weeks' gestation.

OBJECTIVES: Antenatal steroids in labor improve the outcome in preterm babies. The objective in this retrospective study was to compare the efficacy of one dose of antenatal steroid against the standard course in surfactant-treated babies. METHODS: A total of 226 babies treated with prophylactic surfactant and under 31 weeks' gestation were divided into three groups: group 1 (n = 89), no antenatal steroids; group 2 (n = 68), one dose of antenatal steroids 4-24 h before delivery; and group 3 (n = 69), two or more doses of antenatal steroids 24 h to 7 days before delivery. The three groups were compared for early clinical well-being and ultimate clinical outcome. RESULTS: Apgar and Clinical risk index for babies (CRIB) scores in groups 2 and 3 were similar and both were significantly better than in group 1. Group 2 babies had a 23.5% reduction in serious intraventricular hemorrhage (IVH) (p < 0.0001, relative risk (RR) 0.2 (95% CI 0.07-0.54), numbers needed to treat (NNT) 4.6) and a 22.9% reduction in death (p < 0.001, RR 0.28 (95% CI 0.12-0.63), NNT 4.4) and group 3 babies had a 21.1% reduction in IVH (p < 0.001, RR 0.25 (95% CI 0.10-0.62), NNT 4.6) and a 24.2% reduction in death (p < 0.001, RR 0.23 (95% CI 0.10-0.57), NNT 4.2) compared to group 1. For these parameters, there was no significant difference between groups 2 and 3. CONCLUSIONS: One dose of antenatal steroids given 4-24 h before delivery was clinically comparable to the recommended schedule of the National Institutes of Health in surfactant-treated preterm infants. Should the findings of this study be confirmed in randomized controlled trials, the dosage regimen could be simplified, steroid administration reduced and the interval from delivery reduced in acute clinical conditions.

Anti-Inflammatory Agents↗

PubMed2002

Twin reversed arterial perfusion (TRAP) syndrome.

Twin reversed arterial perfusion (TRAP) syndrome is an extremely rare manifestation of feto-fetal transfusion syndrome. This condition is seen in monozygotic twin pregnancies, where the affected twin is perfused retrogradely by the healthy twin. The affected twin presents with bizarre malformations such as acardia and acephalus. We present such a case, which was diagnosed prenatally. The pregnancy progressed uneventfully to term.

Abnormalities, Severe Teratoid↗

PubMed2001

Solitary wave dynamics in generalized Hertz chains: an improved solution of the equation of motion.

The equation of motion for a bead in a chain of uncompressed elastic beads in contact that interact via the potential V(delta) approximately delta( n), n>2, delta being overlap, supports solitary waves and does not accommodate sound propagation [V. Nesterenko, J. Appl. Mech. Tech. Phys. 5, 733 (1983)]. We present an iteratively exact solution to describe the solitary wave as a function of material parameters and a universal, infinite set of coefficients, which depend only on n. We compute any arbitrary number of coefficients to desired accuracy and show that only the first few coefficients of our solution significantly improves upon Nesterenko's solution. The improved solution is a necessary step to develop a theoretical understanding of the formation of secondary solitary waves [M. Manciu, et al., Phys. Rev. E 63, 011614 (2001)].

Journal Article↗

PubMed2001

Interaction and feedback regulation between STK15/BTAK/Aurora-A kinase and protein phosphatase 1 through mitotic cell division cycle.

STK15 is an Aurora/Ipl-1 related serine/threonine kinase that is associated with centrosomes and induces aneuploidy when overexpressed in mammalian cells. It is well known that phosphorylation and dephosphorylation of kinases are important for regulation of their activity. But mechanisms by which STK15 activity is regulated have not been elucidated. We report that STK15 contains two functional binding sites for protein phosphatase type 1 (PP1), and the binding of these proteins is cell cycle-regulated peaking at mitosis. Activated STK15 at mitosis phosphorylates PP1 and inhibits PP1 activity in vitro. In vivo, PP1 activity co-immunoprecipitated with STK15 is also reduced. These data indicate that STK15 inhibits PP1 activity during mitosis. Also, PP1 is shown to dephosphorylate active STK15 and abolish its activity in vitro. Furthermore, we show that non-binding mutants of STK15 for PP1 are superphosphorylated, but their kinase activities are markedly reduced. Cells transfected with these non-binding mutants manifest aberrant chromosome alignment during mitosis. Our results suggest that a feedback regulation through phosphorylation/dephosphorylation events between STK15 kinase and PP1 phosphatase operates through the cell cycle. Deregulation of this balance may contribute to anomalous segregation of chromosomes during mitotic progression of cancer cells.

Aurora Kinase A↗

PubMed2001

MD simulations of homomorphous PNA, DNA, and RNA single strands: characterization and comparison of conformations and dynamics.

MD simulations of homomorphous single-stranded PNA, DNA, and RNA with the same base sequence have been performed in aqueous solvent. For each strand two separate simulations were performed starting from a (i) helical conformation and (ii) random coiled state. Comparisons of the simulations with the single-stranded helices (case i) show that the differences in the covalent nature of the backbones cause significant differences in the structural and dynamical properties of the strands. It is found that the PNA strand maintains its nice base-stacked initial helical structure throughout the 1.5-ns MD simulation at 300 K, while DNA/RNA show relatively larger fluctuations in the structures with a few local unstacking events during -ns MD simulation each. It seems that the weak physical coupling between the bases and the backbone in PNA causes a loss of correlation between the dynamics of the bases and the backbone compared to the DNA/RNA and helps maintain the base-stacked helical conformation. The global flexibility of a single-stranded PNA helix was also found to be lowest, while RNA appears to be the most flexible single-stranded helix. The sugar pucker of several nucleotides in single-stranded DNA and RNA was found to adopt both C2'-endo and C3'-endo conformations for significant times. This effect is more pronounced for single strands in completely coiled states. The simulations with single-stranded coils as the initial structure also indicate that a PNA can adopt a more compact globular structure, while DNA/RNA of the same size adopts a more extended coil structure. This allows even a short PNA in the coiled state to form a significantly stable nonsequentially base-stacked globular structure in solution. Due to the hydrophobic nature of the PNA backbone, it interacts with surrounding water rather weakly compared to DNA/RNA.

Base Sequence↗

PubMed2001

Genetic analysis of a new mouse model for non-insulin-dependent diabetes.

The TallyHo (TH) mouse strain is a newly established model for non-insulin-dependent diabetes mellitus (NIDDM). TH mice show obesity, hyperinsulinemia, hyperlipidemia, and male-limited hyperglycemia. A genetic dissection of the diabetes syndrome has been carried out using male backcross 1 progeny obtained from crosses between (C57BL/6J x TH)F1 and TH mice or (CAST/Ei x TH)F1 and TH mice. A genome-wide scan reveals three quantitative trait loci (QTLs), Tanidd1-3 (TH-associated NIDDM) linked to hyperglycemia. The major QTL (common in both crosses), Tanidd1, maps to chromosome (Chr) 19. Additionally, gene-gene interactions contributing to hyperglycemia have been observed between Tanidd1 and a locus on Chr 18 as well as between Tanidd2 and a locus on Chr 16. The overt hyperglycemia in TH mice is, therefore, likely due to a mutation in a major diabetes susceptibility locus on Chr 19, which interacts with additional genes to lead to an observable phenotype.

Animals↗

PubMed2001

Real time fluorescence analysis of the RecA filament: implications of base pair fluidity in repeat realignment.

During recombination, when Escherichia coli RecA mediates annealing across DNA repeats, Watson-Crick chemistry can only specify the complementarity of pairing, but not the most optimal frame of alignment. We describe that although stochastic alignments across poly(dA) and poly(dT) can lead to sub-optimally annealed duplexes containing ssDNA gaps/overhangs, the same are realigned into an optimal frame by a putative motor activity of RecA [Sen et al. (2000) Biochemistry 39, 10196-10206]. In the present study, we analyze the nature of realignment intermediates in real time, by employing a fluorescent probe, 2-aminopurine (2AP), which can not only report the status of RecA on the unstacked duplex, but also the fluidity of bases in such a filament. Although known to display a lower affinity for duplex DNA, RecA seems to remain functionally associated with these sub-optimally aligned repeat duplexes, until the realignment approaches completion. Moreover, a comparison of 2AP fluorescence in repeat versus mixed sequences indicates that bases in a RecA repetitive DNA filament exhibit higher degrees of freedom that might mediate a 'non-planar hydrogen bonding cross talk' across the bases on either strand. We discuss a model to explain the mechanistic basis of realignment and its implications in signaling the end of homology maximization, which triggers RecA fall off.

2-Aminopurine↗

PubMed2001

Relaxation of classical particles in two-dimensional anharmonic single-well potentials.

The canonical ensemble relaxation function of a particle in a symmetric anharmonic potential well in D=1 is known to exhibit slow algebraic behavior [S. Sen, R. S. Sinkovits and S. Chakravarti, Phys. Rev. Lett. 77, 4855 (1996); R. S. Sinkovits, S. Sen, J. C. Phillips, and S. Chakravarti, Phys. Rev. E 59, 6497 (1999)]. In the present work, we report a study of relaxation of a particle in symmetric and asymmetric quartic anharmonic potential wells of the form V(x,y)=1 / 2 (x(2)+Cy2)+1 / 4 (x(2)+Cy2)(2) in D=2. The relaxation in the above system is identical to that in D=1 wells when C=0 (since it is then a D=1 system) and C=1. However, for 0 >1, the frequencies associated with well dynamics are strongly affected and hence the power spectra are altered as a function of C. Our calculations suggest that the exponents of the long-time tails associated with the relaxation processes are insensitive to D. In closing, we comment on the consequences of our analysis for the study of slow dynamics in interacting many-particle systems that are connected by harmonic springs with the individual particles in anharmonic potential wells.

Journal Article↗

PubMed2001

Estrogen modulates sexually dimorphic contextual fear conditioning and hippocampal long-term potentiation (LTP) in rats(1).

The present study examined the role of ovarian steroids in contextual fear conditioning and hippocampal synaptic plasticity in female rats. In experiment 1, adult female rats were ovariectomized and submitted to contextual fear conditioning, a procedure in which rats received unsignaled footshock in a novel observation chamber; freezing behavior served as the measure of conditional fear. Ovariectomized female rats froze at levels comparable to male rats, both of which froze significantly more than sham-operated female rats. In experiment 2, estrogen replacement in ovariectomized female rats reduced fear conditioning to a level comparable to that of sham-operated females in experiment 1. In experiment 3, the influence of estrogen on the induction of long-term potentiation (LTP) at perforant path-dentate granule cell synapses in ovariectomized female rats was examined. Estrogen decreased both population spike LTP and EPSP-spike potentiation at perforant path synapses. Taken together, these experiments indicate that ovarian steroids regulate both sexually dimorphic behavior and hippocampal plasticity in a fear-conditioning paradigm.

Animals↗

PubMed2001

Local repeat sequence organization of an intergenic spacer in the chloroplast genome of Chlamydomonas reinhardtii leads to DNA expansion and sequence scrambling: a complex mode of "copy-choice replication"?

Parent-specific, randomly amplified polymorphic DNA (RAPD) markers were obtained from total genomic DNA of Chlamydomonas reinhardtii. Such parent-specific RAPD bands (genomic fingerprints) segregated uniparentally (through mt+) in a cross between a pair of polymorphic interfertile strains of Chlamydomonas (C. reinhardtii and C. minnesotti), suggesting that they originated from the chloroplast genome. Southern analysis mapped the RAPD-markers to the chloroplast genome. One of the RAPD-markers, "P2" (1.6 kb) was cloned, sequenced and was fine mapped to the 3 kb region encompassing 3' end of 23S, full 5S and intergenic region between 5S and psbA. This region seems divergent enough between the two parents, such that a specific PCR designed for a parental specific chloroplast sequence within this region, amplified a marker in that parent only and not in the other, indicating the utility of RAPD-scan for locating the genomic regions of sequence divergence. Remarkably, the RAPD-product, "P2" seems to have originated from a PCR-amplification of a much smaller (about 600 bp), but highly repeat-rich (direct and inverted) domain of the 3 kb region in a manner that yielded no linear sequence alignment with its own template sequence. The amplification yielded the same uniquely "sequence-scrambled" product, whether the template used for PCR was total cellular DNA, chloroplast DNA or a plasmid clone DNA corresponding to that region. The PCR product, a "unique" new sequence, had lost the repetitive organization of the template genome where it had originated from and perhaps represented a "complex path" of copy-choice replication.

Animals↗

PubMed2001

Pneumonostomy in the surgical management of bilateral hydatid cysts of the lung.

During the period 1994-1998, three patients with bilateral hydatid cysts of the lung (HCL) underwent operative removal of the cysts. In three of the six lungs operated upon the conventional technique was used: after removal of the cyst and suture closure of bronchial leaks, the chest was closed with an intercostal drainage tube. Two of these patients developed bronchopleural fistulae requiring rethoracotomy and prolonged hospital stays. The other three lungs were operated upon using the pneumonostomy technique: after excision of the cyst a separate catheter is fixed within the residual lung cavity and brought out through the adjacent chest wall, effectively marsupialising the residual cavity to the atmosphere. All these patients had an uneventful postoperative recovery. We conclude that the pneumonostomy technique is a very useful method of treating HCL surgically, especially when the cysts are bilateral and complicated.

Child↗

PubMed2001

Bilateral high loop ureterostomy in the primary management of posterior urethral valves in a developing country.

Of 200 consecutive cases of posterior urethral valves (PUV) managed in a single institution, 26 underwent bilateral high loop ureterostomy (BU) as their first operative intervention. Indications for BU were persistently raised serum creatinine levels after bladder drainage, severe urosepsis, and urinary ascites, especially in a neonate or infant. After a median period of 1 year of diversion, the serum creatinine fell from a median value of 2.5 to 0.6 mg%. Twelve cases have been fully undiverted without deleterious effects (median serum creatinine level 0.5 mg%). Three patients died. Of the 14 renal units with documented persistent vesicoureteric reflux at the time of undiversion, only 1 has been reimplanted. One child has undergone bladder augmentation.

Child, Preschool↗

PubMed2001

Pulmonary lipoblastoma: a case report.

We report a case of pulmonary lipoblastoma in a 2-year-old child. This pathology has not been previously reported in the English literature.

Child, Preschool↗

PubMed2001

Phenanthrene derivatives from the orchid Coelogyne cristata.

Coeloginanthridin, a 9,10-dihydrophenanthrene derivative, and coeloginanthrin, the corresponding phenanthrene analogue, were isolated from the orchid Coelogyne cristata which earlier afforded coelogin (1a) and coeloginin (1b). The structures of coeloginanthridin and coeloginanthrin were established as 3,5,7-trihydroxy-1,2-dimethoxy-9,10-dihydrophenanthrene (2a) and 3,5,7-trihydroxy-1,2-dimethoxyphenanthrene (2c), respectively, from spectral and chemical evidence including the conversion of coeloginanthridin triacetate (2b) to coeloginanthrin triacetate (2d) by dehydrogenation with DDQ. In the light of earlier reports on structurally similar compounds, 2a and 2c may have biological activities of phytoalexins and endogenous plant growth regulators.

Molecular Structure↗

PubMed2001

A comparative study of telomerase activity in sputum, bronchial washing and biopsy specimens of lung cancer.

The potential of telomerase, the ribonucleoprotein enzyme, as a non-invasive screening marker was studied in pre-bronchoscopy sputum (S), bronchial washings (W) and bronchoscopic biopsy (B) samples from individuals under evaluation for lung cancer. Out of the 52 cases studied, 42 were clinically suspected primary lung cancer patients and 10 had pulmonary disorders but had no clinical evidence of lung cancer. Fifteen (39.5%) S samples, 24 (63.1%) W samples and 32 (84.2%) B samples, which were cytologically/histopathologically positive were also positive for telomerase activity. Interestingly, 16 (42%) S samples, 20 (52.6%) W samples and 20 (52.6%) B samples, initially reported cytologically/histopathologically negative, showed detectable telomerase activity. Lung cancer was finally confirmed in these cases by repeat cytology/histopathology. However, telomerase activity was detected in 31 (81.6%) S, 26 (68.4%) W and 33 (86.8%) B samples of suspected lung cancer patients. Telomerase activity was negative in S, W, and B of four of the suspected cases, which ultimately turned out to be negative for lung cancer. Cytopathology/histopathology alone (including repeat attempts) identified 15 (39.5%) cases of sputum, 24 (63.1%) cases of bronchial washings and 32 (84.2%) bronchoscopic biopsy samples. Out of 10 controls, low telomerase activity was detected in only one (10%) of the bronchial washings, which later turned out to be due to large number of inflammatory cells. Telomerase activity assay of sputum carried sensitivity, specificity and diagnostic accuracy of 81.6, 100 and 86.5%, respectively, while that for bronchial washing was 68.4, 100 and 76.9%, respectively, and for bronchoscopic biopsy samples was 86.8, 100 and 88.1%, respectively. A positive correlation (P<0.01) was seen between age and telomerase activity in sputum, bronchial washing and biopsy samples but no significant correlation was seen between sex and telomerase activity or duration of smoking and telomerase activity. A significant positive correlation was observed between staging and telomerase activity in sputum (P<0.01), bronchial washing (P<0.01) and biopsy samples (P<0.01). Our findings indicate that telomerase is a specific marker for malignant lung disease and can complement cytology/histopathology in the diagnosis of lung cancer. Sputum telomerase assay holds the potential for early and non-invasive diagnosis of lung cancer.

Adult↗