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Biomedical subjects

A S Gupta

Publications and source records attributed to A S Gupta.

At least 19 recordsLinked to original sources
PubMed2000

TNF-alpha-induced apoptosis in neonatal lymphocytes: TNFRp55 expression and downstream pathways of apoptosis.

Previously we have shown decreased Fas-mediated apoptosis in cord blood lymphocyte subsets. In this study, we compared tumor necrosis factor (TNF)-alpha-induced apoptosis in T lymphocytes and their subsets between cord blood and peripheral blood from healthy young controls. The expression of TNF receptor I (TNFR-I) was assessed by flow cytometry and quantitative RT-PCR. The expression of adapter molecules TNF receptor-associated death domain (TRADD), Fas-associated death domain (FADD) and TNF-associated factor-2 (TRAF-2) and caspase 3 was analyzed by Western blotting. The activity of caspase 3 and caspase 8 was measured by colorimetric assay. The susceptibility of CD4+ and CD8+ T cells to TNF-alpha-induced apoptosis was measured by terminal deoxytidyl transferase-mediated dUTP nick end labelling (TUNEL) assay. Both CD4+ and CD8+ T cell subsets from cord blood demonstrated decreased susceptibility to TNF-alpha-induced apoptosis that was associated with decreased activation of both caspase 8 and caspase 3 as compared to T cell subsets in peripheral blood. Furthermore, expression of TNFR-I, TRADD and caspase 3 was decreased in cord blood lymphocytes as compared to peripheral blood lymphocytes. The significance of these observations is discussed.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Successful treatment of in-transit metastases from Merkel's cell carcinoma with isolated hyperthermic limb perfusion.

Merkel's cell carcinoma is an uncommon neuroendocrine cutaneous neoplasm. An unusual mode of dissemination of this tumor is the phenomenon of in-transit metastases. We report complete resolution of in-transit metastases from a Merkel's cell carcinoma in response to treatment with isolated hyperthermic limb perfusion with melphalan. Limb perfusion appears to be a promising modality for such lesions.

Aged↗
PubMed1993

Increased resistance to oxidative stress in transgenic plants that overexpress chloroplastic Cu/Zn superoxide dismutase.

Transgenic tobacco plants that express a chimeric gene that encodes chloroplast-localized Cu/Zn superoxide dismutase (SOD) from pea have been developed. To investigate whether increased expression of chloroplast-targeted SOD could alter the resistance of photosynthesis to environmental stress, these plants were subjected to chilling temperatures and moderate (500 mumol of quanta per m2 per s) or high (1500 mumol of quanta per m2 per s) light intensity. During exposure to moderate stress, transgenic SOD plants retained rates of photosynthesis approximately 20% higher than untransformed tobacco plants, implicating active oxygen species in the reduction of photosynthesis during chilling. Unlike untransformed plants, transgenic SOD plants were capable of maintaining nearly 90% of their photosynthetic capacity (determined by their photosynthetic rates at 25 degrees C) following exposure to chilling at high light intensity for 4 hr. These plants also showed reduced levels of light-mediated cellular damage from the superoxide-generating herbicide methyl viologen. These results demonstrate that SOD is a critical component of the active-oxygen-scavenging system of plant chloroplasts and indicate that modification of SOD expression in transgenic plants can improve plant stress tolerance.

Base Sequence↗
PubMed1991

Response of photosynthesis and cellular antioxidants to ozone in populus leaves.

Atmospheric ozone causes formation of various highly reactive intermediates (e.g. peroxyl and superoxide radicals, H(2)O(2), etc.) in plant tissues. A plant's productivity in environments with ozone may be related to its ability to scavenge the free radicals formed. The effects of ozone on photosynthesis and some free radical scavengers were measured in the fifth emergent leaf of poplars. Clonal poplars (Populus deltoides x Populus cv caudina) were fumigated with 180 parts per billion ozone for 3 hours. Photosynthesis was measured before, during, and after fumigation. During the first 90 minutes of ozone exposure, photosynthetic rates were unaffected but glutathione levels and superoxide dismutase activity increased. After 90 minutes of ozone exposure, photosynthetic rates began to decline while glutathione and superoxide dismutase continued to increase. Total glutathione (reduced plus oxidized) increased in fumigated leaves throughout the exposure period. The ratio of GSH/GSSG also decreased from 12.8 to 1.2 in ozone exposed trees. Superoxide dismutase levels increased twofold in fumigated plants. After 4 hours of ozone exposure, the photosynthetic rate was approximately half that of controls while glutathione levels and superoxide dismutase activity remained above that of the controls. The elevated antioxidant levels were maintained 21 hours after ozone exposure while photosynthetic rates recovered to about 75% of that of controls. Electron transport and NADPH levels remained unaffected by the treatment. Hence, elevated antioxidant metabolism may protect the photosynthetic apparatus during exposure to ozone.

Journal Article↗
PubMed1989

Development and use of chlorotetracycline fluorescence as a measurement assay of chloroplast envelope-bound mg.

Experiments were conducted to develop chlorotetracycline (CTC) fluorescence as an assay of Mg(2+) bound to the envelope of the intact chloroplast. This assay technique has been widely used to measure envelope associated divalent cations in animal cell and subcellular systems, but has not been used with chloroplasts. Chloroplast envelope-associated Mg(2+) was altered by pretreatment with Mg(2+) and divalent cation chelating agents and by additions of Mg(2+) to the CTC assay medium. Results indicated that for a given chloroplast preparation, relative changes in envelope-associated Mg(2+) can be effectively monitored with CTC fluorescence. It was concluded that the limitations of this assay system are: (a) chlorophyll strongly quenches CTC fluorescence signal, so a constant chlorophyll concentration must be maintained, (b) measurements must be made quickly, and (c) use of the technique to compare different chloroplast preparations may not be valid. Studies with (28)Mg(2+) confirmed our interpretation of the fluorescence results, and also suggested that the chloroplast envelope is fairly impermeable to Mg(2+). It was concluded that changes in Mg(2+) associated with the chloroplast due to incubation of plastids in solutions containing up to 5 millimolar Mg(2+) may be exclusively due to increased envelope-associated Mg(2+). The CTC assay was used in experiments to demonstrate that increases in chloroplast envelope-associated Mg(2+) inhibit photosynthetic capacity. This inhibition can be partially overcome by the presence of K(+) in the photosynthetic reaction media.

Journal Article↗
PubMed1989

Maintenance of photosynthesis at low leaf water potential in wheat : role of potassium status and irrigation history.

The interaction of low water potential effects on photosynthesis, and leaf K(+) levels in wheat (Triticum aestivum L.) plants was studied. Plants were grown at three K(+) fertilization levels; 0.2, 2, and 6 millimolar. With well watered plants, 2 millimolar K(+) supported maximal photosynthetic rates; 0.2 millimolar K(+) was inhibitory, and 6 millimolar K(+) was superoptimal (i.e. rates were no greater than at 2 millimolar K(+)). Photosynthesis was monitored at high (930 parts per million) and low (330 parts per million) external CO(2) throughout a series of water stress cycles. Plants subjected to one stress cycle were considered nonacclimated; plants subjected to two successive cycles were considered acclimated during the second cycle. Sensitivity of photosynthesis to declining leaf water potential was affected by K(+) status; 6 millimolar K(+) plants were less sensitive, and 0.2 millimolar K(+) plants were more sensitive than 2 millimolar K(+) plants to declining water potential. This occurred with nonacclimated and acclimated plants at both high and low assay CO(2). It was concluded that the K(+) effect on photosynthesis under stress was not mediated by treatment effects on stomatal resistance. Differences between the K(+) treatments were much less pronounced, however, when photosynthesis of nonacclimated and acclimated plants was plotted at a function of declining relative water content during the stress cycles. These results suggest that K(+) effects on the relationship between relative water content and water potential in stressed plants was primarily responsible for the bulk of the K(+)-protective effect on photosynthesis in stressed plants. In vitro experiments with chloroplasts and protoplasts isolated from 2 millimolar K(+) and 6 millimolar K(+) plants indicated that upon dehydration, K(+) efflux from the chloroplast stroma into the cytoplasm is less pronounced in 6 millimolar K(+) protoplasts.

Journal Article↗
PubMed1988

Chloroplast osmotic adjustment and water stress effects on photosynthesis.

Previous studies have suggested that chloroplast stromal volume reduction may mediate the inhibition of photosynthesis under water stress. In this study, the effects of spinach (Spinacia oleracea, var ;Winter Bloomsdale') plant water deficits on chloroplast photosynthetic capacity, solute concentrations in chloroplasts, and chloroplast volume were studied. In situ (gas exchange) and in vitro measurements indicated that chloroplast photosynthetic capacity was maintained during initial leaf water potential (Psi(w)) and relative water content (RWC) decline. During the latter part of the stress period, photosynthesis dropped precipitously. Chloroplast stromal volume apparently remained constant during the initial period of decline in RWC, but as leaf Psi(w) reached -1.2 megapascals, stromal volume began to decline. The apparent maintenance of stromal volume over the initial RWC decline during a stress cycle suggested that chloroplasts are capable of osmotic adjustment in response to leaf water deficits. This hypothesis was confirmed by measuring chloroplast solute levels, which increased during stress. The results of these experiments suggest that stromal volume reduction in situ may be associated with loss of photosynthetic capacity and that one mechanism of photosynthetic acclimation to low Psi(w) may involve stromal volume maintenance.

Journal Article↗
PubMed1987

Osmotic adjustment, symplast volume, and nonstomatally mediated water stress inhibition of photosynthesis in wheat.

At low water potential (psi(w)), dehydration reduces the symplast volume of leaf tissue. The effect of this reduction on photosynthetic capacity was investigated. The influence of osmotic adjustment on this relationship was also examined. To examine these relationships, comparative studies were undertaken on two wheat cultivars, one that osmotically adjusts in response to water deficits (;Condor'), and one that lacks this capacity (;Capelle Desprez'). During a 9-day stress cycle, when water was withheld from plants grown in a growth chamber, the relative water content of leaves declined by 30% in both cultivars. Leaf osmotic potential (psi(s)) declined to a greater degree in Condor plants. Measuring psi(s) at full turgor indicated that osmotic adjustment occurred in stressed Condor, but not in Capelle plants. Two methods were used to examine the degree of symplast (i.e. protoplast) volume reduction in tissue rapidly equilibrated to increasingly low psi(w). Both techniques gave similar results. With well-watered plants, symplast volume reduction from the maximum (found at high psi(w) for each cultivar) was the same for Condor and Capelle. After a stress cycle, volume was maintained to a greater degree at low psi(w) in Condor leaf tissue than in Capelle. Nonstomatally controlled photosynthesis was inhibited to the same degree at low psi(w) in leaf tissue prepared from well-watered Condor and Capelle plants. However, photosynthetic capacity was maintained to a greater degree at low psi(w) in tissue prepared from stressed Condor plants than in tissue from stressed Capelle plants. Net CO(2) uptake in attached leaves was monitored using an infrared gas analyzer. These studies indicated that in water stressed plants, photosynthesis was 106.5% higher in Condor than Capelle at ambient [CO(2)] and 21.8% higher at elevated external [CO(2)]. The results presented in this report were interpreted as consistent with the hypothesis that there is a causal association between protoplast (and presumably chloroplast) volume reduction at low psi(w) and low psi(w) inhibition of photosynthesis. Also, the data indicate that osmotic adjustment allows for maintenance of relatively greater volume at low psi(w), thus reducing low psi(w) inhibition of chloroplast photosynthetic potential.

Journal Article↗
PubMed1986

Possible role of collagen in transverse myelitis and chymopapain-induced paraplegia.

We studied the effect of nucleus pulposus (NP) on platelet aggregation. Our in vitro experiments showed that NP extract produced platelet aggregation and the addition of collagenase to the NP extract abolished this response. It was further shown that chymopapain did not affect the activity of the extract. We assume that collagen is the active platelet aggregant in the NP extract. Intravascular release of collagen may cause platelet aggregation, vascular obstruction, ischemia, and cord necrosis in a patient with acute transverse myelitis. Intradiskal chymopapain is known to cause transverse myelitis and it is possible that collagen released during the action of the enzyme initiates a similar chain of events.

Cartilage↗
PubMed1979

A second look at Steinach's second procedure: testiculoepididymal occlusion in man and dog.

After advocating vas occlusion as a biological method for rejuvenating aging males, Steinach had suggested that the effect might be more pronounced if the obstruction were placed proximal to the epididymis. This Steinach II procedure has now been studied in 15 dogs and five men. Occlusion was performed at the level of the vasa efferentia, avoiding any vascular trauma. Radiological visualization confirmed a perfect block. There were no untoward reactions, such as orchitis or hydrocele. In dogs, widespread degeneration in the seminiferous tubules was evident, and the total Leydig cell volume showed an increase from 0.7 to 1.0 ml/testis. The changes, however, were not significantly different from conventional vasectomy. In men, there were considerable preexisting senile changes, and the total Leydig cell volume was already as high as 2.8 ml/testis. These changes obscured any possible effect of Steinach II operation.

Animals↗