Biomedical subjects

D K Das

Publications and source records attributed to D K Das.

At least 199 records · Page 11Linked to original sources

PubMed1992

Generation of singlet oxygen and hydroxyl radical from sodium chlorite and lactic acid.

Reperfusion of ischemic tissue is associated with the formation of hydroxyl radical (OH.). In this report, a novel mechanism for (OH.) generation from (1O2) is proposed based on the experimental evidence from the present study. A number of experiments were performed which conclusively demonstrated the formation of 1O2 from the reaction of lactic acid and hypohalite radical. Singlet oxygen attacks the unsaturated olefinic derivatives, which are also formed during reperfusion of ischemic tissue. The reaction between 1O2 and olefinic compounds produces hydroperoxides, which ultimately form OH. radical. The validity of the above mechanism of OH. radical formation is warranted from our experimental results.

Alkenes↗

PubMed1992

Preconditioning of heart by repeated stunning: adaptive modification of myocardial lipid membrane.

Recent studies indicate that preconditioning of a heart by repeated stunning protects it from subsequent ischemic injury. Such myocardial preservation is likely to be due to adaptive modification of lipid composition and dynamic structure of cellular membrane. To test this hypothesis, swine heart was subjected to four episodes of 5 min stunning by LAD occlusion, followed by 10 min of reperfusion after each stunning. Heart was then made regionally ischemic for 60 min by LAD occlusion, followed by 6 h reperfusion. Control heart was perfused for 60 min, followed by 60 min ischemia and 6 h reperfusion. Free fatty acids (FFA) accumulated in control heart during ischemia as expected, which was further enhanced by reperfusion. The FFA level was also enhanced during ischemia in stunned myocardium. However, this FFA level was almost restored during reperfusion. The levels of polyunsaturated fatty acids (PUFA) such as oleate, linoleate, and arachidonate followed a similar pattern. Membrane fluidity, monitored by fluorescence polarization, was decreased during ischemia and reperfusion in the unstunned heart, with the corresponding increase in microviscosity. The increased microviscosity was significantly reduced by stunning. Since FFA are presumably generated from membrane phospholipids, these results suggest that stunning may cause the incorporation of a greater proportion of PUFA in membrane phospholipids, leading to preservation of membrane phospholipids and maintaining the membrane fluidity, which may be at least partially responsible for the attenuation of ischemic reperfusion injury.

Adaptation, Physiological↗

PubMed1992

[Ganglioside protection of the erythrocyte membranes in myocardial ischemia].

Myocardial ischemia was shown to lead to modification of structural and functional organization of rat erythrocyte membranes. Thus, it was found that the activity of Na+, K+-ATP-ase markedly decreased, while accumulation of LPO products and of lysophosphatidylcholine (lyso--PC) took place in erythrocyte membranes of rats subjected to myocardial ischemia. Using nonpenetrating modifier trinitrobenzosulfonic acid, an increase in the content of modified phosphatidylethanolamine in erythrocyte membranes of ischemic rats was revealed as compared to the membranes of control animals. The intravenous administration of gangliosides (30 mg/kg) resulted in partial normalization of Na+, K+(-)ATPase activity, of LPO product and lysoPC content and of transbilayer distribution of lipids.

Animals↗

PubMed1992

Heat shock. A new approach for myocardial preservation in cardiac surgery.

BACKGROUND: Recent studies have indicated that heat shock (HS) induces protective genes and HS protein (HSP) expression, which enhances cellular tolerance to ischemic injury. The present study sought to determine if 42 degrees C blood cardioplegia could be used to induce HSP expression and improved myocardial salvage after 2 hours of cardioplegic arrest. METHODS AND RESULTS: To study this, pig hearts (n = 6) on cardiopulmonary bypass were subjected to HS by continuous infusion to the globally arrested heart of warm blood cardioplegia (K+ = 30 meq/l) at 42 degrees C for 15 minutes followed by 2 hours of intermittent hypothermic (4-6 degrees C) hyperkalemic (30 meq/l) crystalloid cardioplegic arrest and 1 hour of reperfusion (heat shock group). The control group (n = 6) was subjected to only 2 hours of hypothermic crystalloid cardioplegic arrest followed by 1 hour of reperfusion without HS. Left ventricular performance, coronary blood flow, and creatine kinase release were determined before arrest and during reperfusion. Prearrest control biopsies were taken in a separate group of pigs (n = 6) for both HSP and superoxide dismutase activity. Additional biopsies were taken for the same measurements in both control and HS groups at the completion of reperfusion. In a single additional pig in both the control and HS groups, biopsies were taken during the study to estimate changes in HSP expression. The cytosolic protein of ventricular tissue was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the HSP70 family protein was examined by Western blot analysis using monoclonal antibodies. HSP was found to be increasingly expressed from control levels after 15 minutes of HS pretreatment, increasing progressively to a level significantly above the non-HS group. Associated with this increased expression of HSP was a significant increase in superoxide dismutase activity in the HS animals and significant improvement in both global and regional functions and reduced creatine kinase release. CONCLUSIONS: The results show that preconditioning the heart with HS improves postischemic ventricular performance and attenuates cellular injury. HS induces a change in cellular metabolism, prompting the expression of HSP and improving antioxidant activity, leading to improved function and reduced tissue injury during ischemia and reperfusion.

Animals↗

PubMed1992

Preconditioning of heart by repeated stunning. Adaptive modification of antioxidative defense system.

Previous studies demonstrated that preconditioning of a heart by repeated stunning can reduce the cellular injury to the heart from subsequent acute ischemic insult. To examine the possible biochemical mechanism for such myocardial preservation afforded by preconditioning, swine heart was subjected to four episodes of 5 min. stunning by occluding the left anterior descending coronary artery (LAD), followed by 10 min. of reperfusion after each stunning. Heart was then made regionally ischemic for 60 min. by LAD occlusion, followed by 6 hrs. reperfusion. Control heart was perfused for 60 min., followed by 60 min. ischemia and 6 hrs. reperfusion. The results of our studies indicated the stimulation of a number of antioxidative enzymes, including Mn-superoxide dismutase (Mn-SOD), catalase, glutathione peroxidase, and glutathione reductase, after repeated stunning and reperfusion. In addition, a number of new proteins were expressed after preconditioning the heart, including some oxidative-stress related proteins and 72 kDa heat-shock protein. These results suggest that preconditioning of a heart by repeated stunning may lead to strengthening of the oxidative defense system of the heart, which is likely to play a role in myocardial preservation during subsequent ischemic and reperfusion injury.

Adaptation, Physiological↗

PubMed1992

Efficacy of a hospital based cytology screening program.

From 1976 to 1986, a total of 117,471 women attending gynecologic outpatient departments of six hospitals in Delhi, India, were screened cytologically. The cytodiagnosis revealed 30,399 (25.9%) normal finding, 84,889 (72.3%) inflammatory changes, 1910 (1.6%) dysplasia of various grades and 213 (0.2%) malignant lesions. Of the 213 cases detected as malignant, clinical suspicion of cervical cancer was not present in 125 women (58.7%). Histologically malignancy was confirmed in 192 women (90.1%) of the 213 cytologically diagnosed malignant cases. The diagnosis revealed 94 (49.0%) as carcinoma in situ and the rest of the cases were invasive lesions. This was in contrast to only 5.2% (10/194) of cases with carcinoma in situ seen at the cancer clinic during 1983-1986 in one of the major collaborating hospitals of Delhi. The analysis of data according to age revealed that median age at detection of mild/moderate, severe dysplasia, carcinoma in situ (CIS) and invasive cancers was 34.0, 37.9, 38.6, and 47.8 years, respectively, indicating a latency period of one and a half decade from the onset of precursor lesions to invasive disease. Mass population screening in our country is not feasible in the near future and this may be true also for other developing countries. In its absence cytological screening of patients attending hospitals and maternity homes can give a large yield of early cervical cancers, which are curable.

Adult↗

PubMed1992

Release of endothelin during reperfusion of ischemic myocardium. ET-1 release from reperfused heart.

Endothelin, the most potent endothelium-derived vasoconstrictor, was found to be released from the isolated ischemic rat heart after a prolonged period of reperfusion. No endothelin release was observed up to 1 hour of reperfusion following 30 minutes of global ischemic arrest. Although most of the endothelin release occurred as a burst after 1 hour of reperfusion, the endothelin release increased progressively at a slower rate up to 2 hours of reperfusion. The calcium slow channel blocker, nifedipine, and the phospholipase inhibitor, mepacrine, but not the free radical scavengers, superoxide dismutase (SOD) and catalase, prevented the endothelin release from the heart. Unlike endothelin release that did not occur until after 1 hour of reperfusion, lipid peroxidation assessed by thiobarbituric acid reactive product formation, and cellular injury as monitored by creatine kinase (CK) release, occurred upon reperfusion, and increased progressively with the duration of reperfusion. All the interventions including nifedipine, mepacrine, and SOD plus catalase, prevented the lipid peroxidation and CK release significantly. Coronary flow was reduced significantly after 1 hour of reperfusion, when endothelin release occurred, an event that also coincided with myocardial endothelial injury as assessed by transmission electron microscopy. These results indicate that endothelin is released only after a prolonged period of reperfusion, and the release process seems to be controlled by calcium and phospholipase, but not by free radicals.

Analysis of Variance↗

PubMed1991

Release of fatty acid-binding protein from ischemic-reperfused rat heart and its prevention by mepacrine.

In an attempt to resolve the issue of whether there is a loss of fatty acid binding protein (H-FABP) from heart during ischemia and reperfusion, and to further examine the role of this protein in ischemic-reperfusion injury, the amount of H-FABP of heart was monitored during ischemia and reperfusion. Excellent correlation was obtained between the loss of H-FABP from heart and its appearance in the perfusate buffer when examined by Western blot using the specific antibody to H-FABP. Further quantitation was achieved by densitometric scanning of the Western blot and rocket electrophoresis. Maximum release of H-FABP was observed within 20 min of reperfusion, the total release being 10% of the H-FABP content of the heart. Mepacrine, a membrane stabilizer and a phospholipase inhibitor, reduced the release of H-FABP from the heart and prevented the accumulation of nonesterified fatty acids in the tissue during ischemia and reperfusion. In view of the established role of H-FABP in the preservation of membrane phospholipids by either scavenging free radicals during ischemia and reperfusion or by modulating the enzymes of phospholipid synthesis, it seems likely that the loss of H-FABP may have some contribution towards the ischemic-reperfusion injury.

Animals↗

PubMed1991

High-performance liquid chromatographic detection of hydroxylated benzoic acids as an indirect measure of hydroxyl radical in heart: its possible link with the myocardial reperfusion injury.

The present report describes a method suitable for the indirect assay of hydroxyl radical (OH.), which is likely to be produced during reperfusion of ischemic myocardium. Isolated rat heart perfused by the Langendorff technique was subjected to 30 min of ischemia, followed by 30 min of reperfusion. Salicylic acid (2 mM) was added to the perfusion circuit to trap any OH. radical generated during the experiment. 2,5- and 2,3-dihydroxybenzoic acids (hydroxylated products of salicylic acid) were identified by authentic standards as well as by pure OH.-generating system using high-performance liquid chromatography with electrochemical detection. In addition to serving as a chemical trap for the detection of OH., salicylate attenuated myocardial reperfusion injury as evidenced by reduced formation of creatine kinase, decreased lipid peroxidation, and improved myocardial contractile functions during reperfusion. These results thus provide direct evidence for the presence of OH. in heart and link it to the myocardial reperfusion injury.

Animals↗

PubMed1991

High-performance liquid chromatographic detection of myocardial prostaglandins and thromboxanes.

Reperfusion of ischemic myocardium is associated with the breakdown of membrane phospholipids and a corresponding increase in arachidonic acid, ultimately resulting in the production of prostaglandins (PGs) and thromboxanes (TXs). However, quantification of these arachidonic acid metabolites has been limited to radioimmunoassay because of their presence in extremely low amounts. In this report, we describe a method suitable to detect sub-picogram levels of 6-keto-PGF1 alpha, PGF1 alpha, PGE2 and TXB2 in myocardial perfusates by high-performance liquid chromatography (HPLC) with a high-gain photomultiplier and a xenon-mercury are lamp. Strong Raleigh scatter of the lamp was eliminated by both interference and long-pass cut-off filters. Improved sample clean-up and HPLC separation were achieved by an HPLC system with an Ultrasphere 3-microns C18 column.

Animals↗

PubMed1991

FNA cytodiagnosis of non-Hodgkin's lymphoma and its subtyping under working formulation of 175 cases.

One hundred thirty-two cases diagnosed as non-Hodgkin's lymphoma (NHL) by fine-needle aspiration cytology (FNAC) and histology, and 43 cases in which there were minor or major discrepancies between cytology and histology for diagnosis of NHL, were reviewed. The diagnostic accuracy of FNAC for NHL was 86.3% at the initial diagnosis. Following review, all the 132 cases initially diagnosed as NHL by cytology and histology remained so with minor changes in subtypes in a few cases. Of the 43 discrepant cases, 28 turned out to be NHL and 6 as Hodgkin's disease (HD); 3 were anaplastic carcinoma; and in 6 cases the discrepancy still persisted. Diagnostic accuracy of FNA for NHL improved to 98.0% following review. Categorization of histologically diagnosed NHL cases under working formulation showed that 10.4%, 21.5%, and 57.7%, respectively, were low, intermediate, and high-grade lymphomas. The corresponding figures were 16.6%, 18.4%, and 60.1%, respectively, in cytology. The diagnostic accuracy of cytology for subtyping was found to be 67.5%.

Adolescent↗

PubMed1991

Working formulation of the non-Hodgkin's lymphomas: a study of cell size and mitotic indices in cytologic subtypes.

Cell size and mitotic indices were studied in 243 non-Hodgkin's lymphomas (NHL) diagnosed cytologically and classified according to the Working Formulation. Low-, intermediate-, and high-grade lymphomas constituted 14.8%, 18.9%, and 61.7% of the cases, respectively. Measurement of the diameter of 100 lymphoid cells in each case showed that in most of the low-grade malignant lymphomas, 50-80% of the cells were small (less than 10 microns). A majority of the cells (an average of 45-60%) in intermediate- and high-grade lymphomas were in the range of 11-15 microns. Only the intermediate-grade large noncleaved and high-grade immunoblastic lymphomas had a majority of their cells (greater than 50%) larger than 15 microns. The mitotic indices (number of mitotic figures per 500 lymphoid cells) showed a highly significant difference between low- (0.7 +/- 1.14), intermediate- (3.0 +/- 2.67), and high-grade (5.4 +/- 3.40) lymphomas using the Wilcoxon's signed rank test (P less than 0.0001). Nearly two-thirds of the cases in each grade were within specific ranges of mitotic indices, i.e., less than 1 for low-, 1-3 for intermediate-, and greater than 3 for high-grade lymphomas.

Adolescent↗

PubMed1991

Protection of ischemic heart from reperfusion injury by myo-inositol hexaphosphate, a natural antioxidant.

Myo-inositol hexaphosphate (phytic acid), a highly charged antioxidant, has been found to chelate metal ions such as iron and calcium and to scavenge hydroxyl radicals, .OH. This study examined the efficacy of this antioxidant and redox agent in attenuating myocardial reperfusion injury. Sprague-Dawley rats were injected intravenously with three different doses of phytic acid (group 1, saline solution only, control; group 2, 1.5 mg/100 g; group 3, 7.5 mg/100 g; group 4, 15 mg/100 g) 30 minutes before excision of hearts. Isolated hearts were prepared by the Langendorff technique. Global ischemia was induced for 30 minutes, followed by 30 minutes of reperfusion. As expected, in group 1, reperfusion was associated with enhanced creatine kinase release, reduced coronary flow, poor recovery of ventricular function as evidenced by reduced left ventricular developed pressure and the first derivative of left ventricular pressure, and increased lipid peroxidation. Groups 3 and 4, but not group 2, demonstrated myocardial protection as evidenced by reduced creatine kinase release, improved left ventricular function and coronary flow, and decreased lipid peroxidation compared with the control group. These results suggest that potential use of this antioxidant in salvaging the heart from ischemic and reperfusion injury.

Animals↗

PubMed1991

Captopril, an ACE inhibitor, for optimizing reperfusion after acute myocardial infarction.

Captopril is an angiotensin-converting enzyme inhibitor that has been reported to be effective in salvaging post-ischemic reperfused myocardium by its ability to function as a free radical-scavenging agent. A study was performed in the isolated porcine-heart model evaluating the influence of pretreatment with captopril on salvage of myocardium after an induced myocardial infarction. Measurement was carried out of regional and global myocardial function, myocardial high-energy phosphate levels, creatine kinase release, malonaldehyde formation, and 6-keto-prostaglandin F1 alpha generation. In an in vitro preparation, the influence of captopril for scavenging various free radicals was evaluated. A dose-response curve was carried out using this free radical-generating system and differing levels of captopril. Results of the study demonstrate that pretreatment with captopril at a 45-mumol/L level reduced reperfusion injury in the pig heart model. This was manifested by improved cardiac performance, a reduction in creatine kinase release, and reduced malonaldehyde generation. In vitro evaluation of captopril and its free radical-scavenging ability indicated that it is a weak scavenger of superoxide anions (O2-) but behaves as a potent scavenger of hydroxyl radicals (-OH) as well as hypohalite radicals (OCl-). Based on the influence of captopril in reducing lipid peroxidation (decreased malonaldehyde formation) and its documented ability to scavenge -OH as well as OCl-, it is suggested that myocardial preservation in a postinfarction model is due primarily to its free radical-scavenging activity, primarily of the potent free radicals -OH and OCl-.

6-Ketoprostaglandin F1 alpha↗

PubMed1991

Protection from nonfreezing cold injury by quinacrine, a phospholipase inhibitor.

A recent study from our laboratory indicated additional tissue injury during rewarming of a cooled rabbit leg. Oxygen-derived free radicals were believed to play a role in such "rewarming injury." Since free radicals may attack membrane phospholipids, we analyzed the phospholipid composition in the leg tissue during cooling and rewarming. Our results indicated significant breakdown of membrane phospholipids, particularly phosphatidylcholine and phosphatidylethanolamine, with a corresponding accumulation of lysophosphatidylcholine and nonesterified fatty acids. Quinacrine, a phospholipase inhibitor, was able to preserve membrane phospholipids during rewarming of the cooled leg. Rewarming of cooled tissue was also accompanied by additional tissue injury, as evidenced by the increased release of lactic acid dehydrogenase and creatine kinase, as well as enhanced lipid peroxidation, as evidenced by increased malonaldehyde formation. Quinacrine reduced the release of these intracellular enzymes and decreased lipid peroxidation, suggesting its efficacy as a therapeutic agent against hypothermic injury.

Animals↗

PubMed1991

Preservation of membrane phospholipids by propranolol, pindolol, and metoprolol: a novel mechanism of action of beta-blockers.

In this study, we examined the effects of three different beta-blockers, propranolol, pindolol, and metoprolol, on membrane phospholipid preservation in the ischemic and reperfused rat heart. Isolated rat hearts were perfused with Krebs-Henseleit bicarbonate buffer by the Langdendorff technique in the presence or absence of propranolol, pindolol, or metroprolol (20 microM each) for 15 mins at 37 degrees C. Hearts where then either made ischemic alone at 37 degrees C for 30 mins, or followed by 30 mins of reperfusion. Coronary flow and perfusate creatine kinase content were monitored during both pre- and post-ischemic periods. At the end of the experiment, hearts were frozen by freeze-clamping at liquid nitrogen temperature. Membrane phospholipids, fatty acid composition of these phospholipids, non-esterified free fatty acids, and myocardial thiobabituric acid (TBA) reactive product were examined in these hearts. The beta-blocker-treated hearts exhibited significantly less lipid peroxidation than the control hearts (P less than 0.05), as indicated by decreased formation of TBA reactive product and the higher percentage of unsaturated fatty acids in the phosphatidylcholine (PC) in heart. In addition, compared to the control group, less accumulation of free fatty acids was observed in the propranolol and pindolol treated groups. Finally, reduced myocardial creatine kinase release and enhanced recovery of coronary flow indicated significant myocardial preservation by these beta-blockers. The efficacy of these beta-blockers were in the following order: propranolol, pindolol, metoprolol. These results suggest that beta-blockers could also protect an ischemic heart from reperfusion injury by preserving the membrane phospholipids.

Adrenergic beta-Antagonists↗

PubMed1991

Squamous metaplasia in hormonally treated prostatic cancer. Significance during follow-up.

A prospective study of 59 hormonally treated prostatic cancer cases was undertaken during follow-up with sequential transrectal palpation and fine-needle aspiration. At initiation of therapy patients' ages ranged from forty-eight to eighty-two years (median, 68 years). The usual follow-up interval was 6 +/- 3 months, and follow-up periods ranged from six months to one hundred twenty months (median 48 months). The cytologic findings were categorized under four cytologic response types and palpation findings under five response grades. Four different degrees of squamous metaplasia (1+, 2+, 3+, 4+) were observed in smears, depending on semiquantitative determination of squamous metaplastic cells in relation to the total amount of benign and malignant epithelial cells in the smear. There were 341 follow-up observations in which both transrectal fine-needle aspiration cytology and palpation were done. In 306 of these, cytologic findings were found to be adequate. Comparison of squamous metaplasia with cytologic response types revealed a highly significant difference between the benign state and recurrence/frank malignancy. This was also true when frequency of squamous metaplasia was compared with palpatory response grades. It was found that squamous metaplasia can be a valuable adjunct to other cytomorphologic changes such as shrinkage of tumor cell size and decrease in size of nucleoli or its disappearance, in determining response to hormonal therapy.

Aged↗

PubMed1991

Capillary gas chromatography for the assessment of cholesterol oxides in the heart.

Recent studies indicated the presence of cholesterol oxides in biological tissues such as heart under pathophysiological conditions. Currently, no suitable method is available to separate and quantitate these oxides in biological tissues. This study was undertaken to develop a method suitable for the quantification of cholesterol oxides in heart. Since under normal conditions cholesterol oxidation does not occur, we exposed isolated perfused rat heart to oxygen-derived free radicals, which are known to oxidize cholesterol in heart. Free radical treated hearts were homogenized and lipids extracted by conventional techniques. The extracted lipids were saponified, and non-saponified portions were extracted with ether. Silyl derivatives of the extracted products were subjected to capillary gas chromatography. One microlitre of the sample was injected onto an SE 54 Supelco capillary column and run by stepwise temperature programming from 230 to 260 degrees C at a rate of 20 degrees C min-1, and then from 260 to 290 degrees C at 6 degrees C min-1. 5-Androsten-3 beta-ol-17-one was used as internal standard. The separated cholesterol oxides were identified by comparing with authentic standards. This method was suitable to separate 7 alpha-hydroxycholesterol, dihydroxycholesterol, 7 beta-hydroxycholesterol, 20 alpha-hydroxycholesterol, cholesterol-5 alpha,6 alpha-epoxide, and 5-cholestene in heart. Since some of these oxides are cytotoxic to the heart, identification of these oxides should be important to understand the pathophysiology of myocardial disease and for the successful therapy to prevent them.

Animals↗