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Biomedical subjects

M Ramanathan

Publications and source records attributed to M Ramanathan.

At least 37 records · Page 2Linked to original sources
PubMed1999

Oxidative stress increases ubiquitin--protein conjugates in synaptosomes.

Synaptosomes were incubated in the presence of FeSO4 to test the hypothesis that iron-catalyzed oxidative damage causes an increase in the ubiquitination of synaptosomal proteins. Incubation with 10 or 50 microM FeSO4 caused concentration-dependent increases in carbonyl groups (an indication of protein oxidation) and ubiquitinated proteins (determined by probing Western blots with a monoclonal antibody to ubiquitin). Differences in protein ubiquitination occurred within 5 min of incubation, indicating a rapid response to oxidative stress. Results of experiments with MG-132, an inhibitor of the degradation of ubiquitinated proteins, suggested that oxidative damage stimulated ubiquitination rather than inhibited degradation of ubiquitinated proteins. The data are consistent with the hypothesis that synaptic terminals utilize the ubiquitin/proteasome proteolytic pathway to degrade oxidatively damaged proteins.

Animals↗
PubMed1999

Evaluation of an alternative to the Kolmogorov-Smirnov test for flow cytometric histogram comparisons.

BACKGROUND: The Kolmogorov-Smirnov test is a valid statistical test for comparing distributions that has been recommended for flow cytometric histogram analysis. However, this test is frequently found to be too sensitive for flow cytometric histogram comparisons. Here, a parametric alternative to the Kolmogorov-Smirnov test is proposed that is based on fitting suitable models to flow cytometric data. METHODS: Several flow cytometric histograms derived from cell surface immunophenotyping for intercellular adhesion molecule-1 (ICAM-1) on K562 cells were analyzed using numerical modeling. The prediction intervals derived from the modeling were used for decision making. RESULTS: The residuals after peak fitting flow cytometric data are normally distributed and this permits the use of the prediction limit methodology. The usefulness of the approach for analyzing flow cytometry histograms is examined and the method is shown to avoid the "sensitivity" disadvantages associated with the Kolmogorov-Smirnov test. CONCLUSIONS: The prediction limit method is a viable alternative to the Kolmogorov-Smirnov method.

Flow Cytometry↗
PubMed1999

Flow cytometric analysis of in vitro proinflammatory cytokine secretion in peripheral blood from multiple sclerosis patients.

The cytokines, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and interleukin-2 (IL-2) are important endogenous proinflammatory proteins and have been linked to disease activity in multiple sclerosis. In this study, we use flow cytometric methodology to compare the secretion of IFN-gamma, IL-2, and TNF-alpha from peripheral blood-derived T cells of multiple sclerosis patients to the secretion in healthy controls. The percentages of IFN-gamma, IL-2, and TNF-alpha secreting cells are not significantly different between multiple sclerosis patients and controls. However, the TNF-alpha secreting CD3 cell percentage is correlated with the IFN-gamma and IL-2 secreting CD3 cell percentages in multiple sclerosis patients. In the controls, only the TNF-alpha secreting CD3 cell percentage is correlated with IFN-gamma. These findings show that correlated secretion of cytokines occurs in multiple sclerosis and suggest that concerted intercytokine interactions may play an important role in the disease.

Adolescent↗
PubMed1999

Compensatory alveolar growth normalizes gas-exchange function in immature dogs after pneumonectomy.

To determine the extent and sources of adaptive response in gas-exchange to major lung resection during somatic maturation, immature male foxhounds underwent right pneumonectomy (R-Pnx, n = 5) or right thoracotomy without pneumonectomy (Sham, n = 6) at 2 mo of age. One year after surgery, exercise capacity and pulmonary gas-exchange were determined during treadmill exercise. Lung diffusing capacity (DL) and cardiac output were measured by a rebreathing technique. In animals after R-Pnx, maximal O2 uptake, lung volume, arterial blood gases, and DL during exercise were completely normal. Postmortem morphometric analysis 18 mo after R-Pnx (n = 3) showed a vigorous compensatory increase in alveolar septal tissue volume involving all cellular compartments of the septum compared with the control lung; as a result, alveolar-capillary surface areas and DL estimated by morphometry were restored to normal. In both groups, estimates of DL by the morphometric method agreed closely with estimates obtained by the physiological method during peak exercise. These data show that extensive lung resection in immature dogs stimulates a vigorous compensatory growth of alveolar tissue in excess of maturational lung growth, resulting in complete normalization of aerobic capacity and gas-exchange function at maturity.

Animals↗
PubMed1999

Postpneumonectomy alveolar growth does not normalize hemodynamic and mechanical function.

Immature foxhounds underwent 55% lung resection by right pneumonectomy (n = 5) or thoracotomy without pneumonectomy (Sham, n = 6) at 2 mo of age. Cardiopulmonary function was measured during treadmill exercise on reaching maturity 1 yr later. In pneumonectomized animals compared with Sham animals, maximal oxygen uptake, ventilatory response, and cardiac output during exercise were normal. Arterial and mixed venous blood gases and arteriovenous oxygen extraction during exercise were also normal. Mean pulmonary arterial pressure and resistance were elevated at a given cardiac output. Dynamic ventilatory power requirement was also significantly elevated at a given minute ventilation. These long-term hemodynamic and mechanical abnormalities are in direct contrast to the normal pulmonary gas exchange during exercise in these same pneumonectomized animals reported elsewhere (S. Takeda, C. C. W. Hsia, E. Wagner, M. Ramanathan, A. S. Estrera, and E. R. Weibel. J. Appl. Physiol. 86: 1301-1310, 1999). Functional compensation was superior in animals pneumonectomized as puppies than as adults. These data indicate a limited structural response of conducting airways and extra-alveolar pulmonary blood vessels to pneumonectomy and suggest the development of other sources of adaptation such as those involving the heart and respiratory muscles.

Airway Resistance↗
PubMed1999

Rapid Solubility Determination Using Vapor-Phase Osmometry.

Because of the need for resource-sparing assays of the solubility of new drug candidates, we sought to develop and validate a rapid method for determining the solubility of nonvolatile pharmaceutical solids in water. Vapor-phase osmometry was used to determine the concentration of drugs in saturated solutions prepared by a rapid ultrasound-mediated dissolution protocol. The osmolality of saturated solutions as measured by the vapor-phase osmometer is an excellent predictor of the solubility of pharmaceutical solids in water. Each osmolality measurement requires less than 10 µl of saturated solution and takes less than 2 min to complete. For small-molecule drugs with solubilities greater than 10 g/kg, osmometry may prove to be a rapid and accurate method for determining the water solubilities of drugs.

Journal Article↗
PubMed1999

A method for estimating pharmacokinetic risks of concentration-dependent drug interactions from preclinical data.

This article evaluates a novel approach for estimating the pharmacokinetic risks associated with drug interactions in populations. Preclinical pharmacokinetic and metabolism data are analyzed with a stochastic differential equation-based pharmacokinetic model that recognizes that the risks associated with known drug interactions involve deterministic and stochastic components. Specifically, a Bernoulli jump-diffusion pharmacokinetic model that accounts for the pharmacokinetics, the variability inherent in the pharmacokinetics, and the idiosyncratic nature of the possibility of drug interactions is proposed. In addition, the variability inherent in the extent of drug interaction is explicitly accounted for. The approach provides useful mechanistic insights into the stochastic processes that "drive" drug interactions in populations because it yields analytical results. The validity of the model predictions was tested with experimental data from two previously investigated systems: N-1 and N-3 caffeine demethylation in populations with smokers and in the terfenadine-ketoconazole system.

Dose-Response Relationship, Drug↗
PubMed1999

Experimental methods for evaluation of psychotropic agents in rodents: II-Antidepressants.

Rodent models of clinical depression are extensively used for the evaluation of putative antidepressants. In the present review, the available experimental methods which can be utilized by most laboratories involved in preclinical screening of antidepressants, have been discussed. The methods have been categorized on the basis of induction of the depressive state or on the assumption that monoamine deficiency leads to depression. These methods have been critically validated in terms of efficacy of standard antidepressants in these tests and, in some cases, by the neurochemical basis of depression, namely, the deficient monoaminergic theory of clinical depression.

Animals↗
PubMed1999

Superoxide dismutase, catalase and glutathione peroxidase activities in the brain of streptozotocin induced diabetic rats.

Brain antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) levels were studied in the brains of early diabetic (72 hr) and long term diabetic (one month) rats. Diabetes was induced by injecting streptozotocin (50 mg/kg, i.p.) in citrate buffer. One group of diabetic rats was treated with insulin (1U/day/animal). The results indicate that early diabetic rats exhibit increased SOD and CAT activities with no alteration in the GPX activity. On the contrary, increased CAT decreased GPX activities with no alteration in the SOD activity, was noted in the long-term Diabetic rats. Insulin treatment reversed these alterations in both the groups. It can be concluded that, in diabetic condition antioxidant enzyme levels are elevated and insulin treatment attenuated these changes. Hence, diabetes mellitus, if left untreated, may initiate degenerative processes and other CNS complications due to accumulation of oxidative free radicals.

Animals↗
PubMed1998

Analysis of intracellular Th1 cytokine secretion data using parametric methodology.

Flow cytometric methods are widely used for analyzing cytokine release from immune cell populations. However, difficulties are frequently encountered in the analysis of flow cytometric data from intracellular cytokine staining because the cytokine positive and cytokine negative histograms overlap considerably. This study compares models containing Gaussian, Giddings, Haarhoff-van der Linde (HVL) and Weibull distributions for fitting flow cytometric intracellular cytokine histogram peaks. The results show that flow cytometric data for the Th1 cytokines, interferon-gamma and interleukin-2, in peripheral blood are well described by a model consisting of the sum of two log-normal distributions but the other distributions tested also showed satisfactory fits. The model-based approach may potentially eliminate the need to use markers derived from isotype control staining. The results obtained using peak fitting were also compared to the widely practised 99% division line or marker method. The percent positive calculated using the 99% division line or marker methods correlates poorly with the percent area under the cytokine-positive peak. However, when the model is used to calculate a cytokine-positive percentage analogous to that determined by the 99% division line or marker method, the two methods correlate well.

Flow Cytometry↗
PubMed1998

Smart X-ray beam position monitor system using artificial-intelligence methods for the Advanced Photon Source insertion-device beamlines.

At the Advanced Photon Source (APS), each insertion-device (ID) beamline front end has two X-ray beam position monitors (XBPMs) to monitor the X-ray beam position for both vertical and horizontal directions. Performance challenges for a conventional photoemission-type XBPM during operations are contamination of the signal from the neighbouring bending-magnet sources and the sensitivity of the XBPM to the insertion-device gap variations. Problems are exacerbated because users change the ID gap during their operations, and hence the percentage level of the contamination in the front-end XBPM signals varies. A smart XBPM system with a high-speed digital signal processor has been built at the Advanced Photon Source for the ID beamline front ends. The new version of the software, which uses an artificial-intelligence method, provides a self-learning and self-calibration capability to the smart XBPM system. The structure of and recent test results with the system are presented in this paper.

Journal Article↗
PubMed1998

Differential effects of diazepam on anxiety in streptozotocin induced diabetic and non-diabetic rats.

The anxiolytic activity of diazepam (DZP) (0.25-1 mg/kg) was investigated in streptozotocin (STZ)-induced diabetic adult Charles Foster albino rats of either sex. Diabetes was induced by injecting STZ IP (50 mg/kg; in citrate buffer, pH 4.5). Experiments were performed 72 h later. The rats were subjected to various anxiety paradigms, including the open-field exploratory behaviour, elevated plus maze and elevated zero maze behaviours and the social interaction tests. In addition, rat brain tribulin activity was also assessed as a biochemical marker of anxiety. The results indicate that diabetic rats showed significantly more anxiogenic activity in comparison to non-diabetic rats on open-field, elevated plus maze, zero maze and social interaction tests. In diabetic rats, brain tribulin activity (MAO-A inhibitory component) was significantly increased. DZP dose dependently produced anxiolytic activity on the various behavioural parameters in non-diabetic rats. DZP (0.5 and 1 mg/kg) partially reversed the anxiogenic behaviour of STZ diabetic rats in elevated plus maze and zero maze tests. However, in open field behaviour and social interaction tests significant anxiolytic activity was observed only at a higher dose of DZP (1 mg/kg). The findings indicate that STZ-induced diabetic rats exhibited augmented anxiety on various experimental paradigms and that the anxiolytic effect of diazepam was less marked in diabetic rats as compared to their euglycaemic counterparts.

Animals↗
PubMed1998

Fixed maximal stroke index in patients after pneumonectomy.

Patients who have undergone pneumonectomy (PNX) show limited exercise capacity, partly attributable to an impaired stroke index (SI). To determine whether this limitation is due to deconditioning, we assessed exercise performance and cardiopulmonary function in seven patients after PNX (age: 59 +/- 2 yr, mean +/- SEM) and eight normal, healthy nonsmokers (52 +/- 3 yr) before and after an ergometer exercise training program for 30 min per day, 5 d per week, for 8 wk at 65% of measured maximal O2 uptake. Lung volume, diffusing capacity of carbon dioxide (DL(CO)) and cardiac index (CI) were determined during steady-state exercise by a rebreathing method. Exercise endurance was measured at 80% of maximal power. As compared with normal subjects, patients who had had PNX showed diminished maximal oxygen uptake (VO2max), as well as diminished lung volumes, ventilatory capacities, and maximal cardiac and stroke indexes. After training, VO2max, endurance, and peripheral O2 extraction improved in both groups. However, maximal cardiac and stroke indexes increased only in normal subjects and not in patients. We conclude that an irreversibly fixed maximal SI is a major source of exercise limitation after PNX, probably because of pulmonary arterial hypertension and/or mechanical distortion of the cardiac fossa. Ventilatory impairment after PNX did not prevent a training-induced increase in VO2max. Exercise training confers significant functional benefit on postpneumonectomy patients by enhancing peripheral O2 extraction.

Adult↗
PubMed1998

Hypercalcaemic crisis as the presenting manifestation of abdominal tuberculosis: a case report.

This report deals with a young man having prolonged fever presenting with hypercalcaemic crisis. Subsequent investigations confirmed tuberculosis (TB) peritonitis in the absence of pulmonary involvement as the cause of his symptoms. His hypercalcaemia and fever resolved with anti-TB therapy. Abdominal TB needs to be included in the differential diagnosis of otherwise unexplained hypercalcaemia especially in our region where TB is an endemic problem and is treatable.

Adult↗
PubMed1998

Interferon-gamma-inhibitory oligodeoxynucleotides alter the conformation of interferon-gamma.

The aptamer mechanism of action involves the direct interaction of oligonucleotide with protein and is responsible for the biological effects of many pharmacologically active oligodeoxynucleotides. In the work reported here, we have determined the effects of aptamers on the secondary, tertiary, and quaternary structures of the proteins with which they interact using interferon-gamma and the interferon-gamma-inhibitory aptamer oligonucleotide, 5'-GGG GTT GGT TGT GTT GGG TGT TGT GT, as a model system. CD, fluorescence spectroscopy studies, and antibody binding studies in this system demonstrate that the interferon-gamma-inhibitory aptamer oligonucleotide causes significant changes in secondary and tertiary structures of interferon-gamma. These structural changes do not result in, or resemble, protein denaturation or aggregation, and the results suggest that aptamer oligodeoxynucleotides can significantly alter the structure of the proteins they interact with.

Circular Dichroism↗
PubMed1997

A physicochemical modelling approach for estimating the stability of soluble receptor-bound tumour necrosis factor-alpha.

Soluble receptors (sr) can both inhibit and stimulate cytokine bioactivity. The extent to which sr stabilizes the loss of cytokine bioactivity is an important determinant of whether a sr exerts an agonist-like or antagonist-like pharmacological effect. However, the half-life of sr-bound cytokines can be difficult to determine experimentally because methods that disrupt the sr-cytokine complex can cause loss of cytokine bioactivity. The purpose of this study was to test whether a parsimonious pharmacokinetic model in which the sr stabilizes the decay of short-lived cytokines can be used to determine the half-life of tumour necrosis factor-alpha (TNF-alpha) bound to two human urine-derived sr. A mathematical model which assumes cytokine-sr equilibrium, constant total sr concentration and first-order kinetics for loss of cytokine bioactivity was used. In addition, the model assumes that the experimentally observed bioactivity is related to the free cytokine concentration. The authors fitted experimental data reported by Aderka et al. for two TNF-alpha sr [Aderka D, Engelmann H, Maor Y, Brakebusch C, Wallach D (1992) J Exp Med 175:323-329] and estimated the half-life of sr-bound TNF-alpha. The parameter estimates were plausible and comparable to those obtained by other methods and, additionally, the model predicted the unexpected relationship between sr dose and cytokine-free concentration that is observed after 9 days of TNF-alpha exposure.

Chemical Phenomena↗
PubMed1997

Antihyperglycemic activity of phenolics from Pterocarpus marsupium.

Glucose levels in rats with hyperglycemia induced by streptozotocin were determined after i.p. administration of marsupsin (1), pterosupin (2), and pterostilbene (3), three important phenolic constituents of the heartwood of Pterocarpus marsupium. Marsupsin and pterostilbene significantly lowered the blood glucose level of hyperglycemic rats, and the effect was comparable to that of 1,1-dimethylbiguanide (metformin).

Animals↗