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S Parthasarathy

Publications and source records attributed to S Parthasarathy.

At least 55 records · Page 3Linked to original sources
PubMed1999

Anti-death properties of TNF against metabolic poisoning: mitochondrial stabilization by MnSOD.

The cytokine tumor necrosis factor (TNF) is toxic to some mitotic cells, but protects cultured neurons from a variety of insults by mechanisms that are unclear. Pretreatment of neurons or astrocytes with TNF caused significant increases in MnSOD activity, and also significantly attenuated 3-nitropropionic acid (3-NP) induced superoxide accumulation and loss of mitochondrial transmembrane potential. In oligodendrocytes, however, MnSOD activity was not increased, and 3-NP toxicity was unaffected by TNF. Genetically engineered PC6 cells that overexpress MnSOD also were resistant to 3-NP-induced damage. TNF pretreatment and MnSOD overexpression prevented 3-NP induced apoptosis, and shifted the mode of death from necrosis to apoptosis in response to high levels of 3-NP. Mitochondria isolated from either MnSOD overexpressing PC6 cells or TNF-treated neurons maintained resistance to 3-NP-induced loss of transmembrane potential and calcium homeostasis, and showed attenuated release of caspase activators. Overall, these results indicate that MnSOD activity directly stabilizes mitochondrial transmembrane potential and calcium buffering ability, thereby increasing the threshold for lethal injury. Additional studies showed that levels of oxidative stress and striatal lesion size following 3-NP administration in vivo are increased in mice lacking TNF receptors.

Adenosine Triphosphate↗
PubMed1999

On the correlation between the main-chain and side-chain atomic displacement parameters (B values) in high-resolution protein structures.

Correlation coefficients (CCs) between the mean atomic displacement parameters (B values) of the main-chain and the side-chain atoms in selected high-resolution protein structures are distributed over a broad range (0.5-1.0). The distribution of CCs is found to be related to the mean difference in B values of Calpha and Cbeta atoms. High CCs are also associated with the frequent occurrence of consecutive Calphaatoms with relatively high B values. The distribution of CCs and its relation to the mean difference between the B values of Calpha and Cbeta atoms shows dependence on the package used for refinement (X-PLOR, PROLSQ or TNT). These observations reflect the differences in the way B-value constraints are handled in these packages. Further differences are discernible in the distributions for proteins refined using the same package. It is likely that these differences are related to the different refinement protocols or weighting schemes followed by investigators. The resolution of these issues is important for evolving correct strategies for the refinement of the atomic displacement parameters in X-ray diffraction studies of proteins. Furthermore, it may be possible to develop refinement-validation tools by observing the features that are invariant in the distribution of atomic displacement parameters.

Animals↗
PubMed1999

Autoantibodies to markers of oxidative stress are elevated in women with endometriosis.

OBJECTIVE: To measure autoantibodies that recognize oxidatively modified proteins in the sera of women with surgically proven endometriosis. DESIGN: Prospective study. SETTING: Tertiary care academic medical center. PATIENT(S): Women undergoing surgery for endometriosis or tubal ligation. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Serum and peritoneal fluid autoantibody titers to malondialdehyde-modified low-density lipoprotein, oxidized low-density lipoprotein, and lipid peroxide-modified rabbit serum albumin determined by ELISA. Correlation of autoantibody titers with revised American Fertility Society staging classification, symptoms, and morphologic type of endometriosis. RESULT(S): Mean (+/-SEM) serum autoantibody titers (in optical density units) to the three antigens were as follows: [1] lipid peroxide-modified rabbit serum albumin, 0.49 +/- 0.12 units in the patients with endometriosis and 0.2 +/- 0.02 units in the controls; [2] oxidized low-density lipoprotein, 0.22 +/- 0.005 units in the patients with endometriosis and 0.18 +/- 0.006 units in the controls; and [3] malondialdehyde-modified low-density lipoprotein, 0.21 +/- 0.005 units in the patients with endometriosis and 0.16 +/- 0.003 units in the controls. There was no correlation between autoantibody titers and revised American Fertility Society stage, symptoms, or morphologic type of endometriosis. Peritoneal fluid did not contain autoantibodies to any of the three antigens. CONCLUSION(S): Autoantibodies to markers of oxidative stress were significantly increased in women with endometriosis. These findings strongly support our data demonstrating that women with endometriosis have enhanced oxidative stress.

Adolescent↗
PubMed1999

Demonstration of the presence of lipid peroxide-modified proteins in human atherosclerotic lesions using a novel lipid peroxide-modified anti-peptide antibody.

Immunohistochemical demonstration of oxidation-specific epitopes using antibodies developed against oxidized low density lipoprotein (Ox-LDL), LDL modified by products of lipid peroxidation (e.g. malondialdehyde-modified LDL), and lipid peroxide-modified albumin has been considered as strong evidence for the presence of oxidatively modified proteins in atherosclerotic lesions. However, the antigens used in the development of these antibodies were derived from lipoproteins and other proteins that are constituents of both normal and atherosclerotic arteries. In order to demonstrate the unequivocal presence of oxidatively modified proteins, we have used a 15 amino acid synthetic peptide derived from the sequence of human glycodelin. Using an antibody developed against this peptide and the second antibody developed against the lipid peroxide-modified peptide, we immunostained progressive human atherosclerotic lesions. Antibody to the unmodified peptide did not react with antigenic epitopes present in mild, moderate, or severe human atherosclerotic lesions. In contrast, the antibody developed against lipid peroxide-modified peptide highly reacted with tissue samples and provided strong evidence for the presence of lipid peroxide-modified proteins. This study suggests the presence of lipid peroxide-modified proteins in the lesion and that these epitopes are derived by direct interaction of lysine residues with lipid peroxides.

Antibodies, Monoclonal↗
PubMed1999

Characterization of the adduct formed from the reaction between homocysteine thiolactone and low-density lipoprotein: antioxidant implications.

Homocysteine thiolactone is a cyclic thioester that is implicated in the development of atherosclerosis. This molecule will readily acylate primary amines, forming a homocystamide adduct, which contains a primary amine and a thiol. Here, we have characterized and evaluated the antioxidant potential of the homocystamide-low-density lipoprotein (LDL) adduct, a product of the reaction between homocysteine thiolactone and LDL. Treatment of LDL with homocysteine thiolactone resulted in a time-dependent increase in LDL-bound thiols that reached approximately 250 nmol thiol/mg LDL protein. The thiol groups of the homocystamide-LDL adduct were labeled with the thiol-reactive nitroxide, methanethiosulfonate spin label. Using paramagnetic relaxing agents and the electron spin resonance spin labeling technique, we determined that the homocystamide adducts were predominately exposed to the aqueous phase. The homocystamide-LDL adduct was resistant to myoglobin- and Cu2(+)-mediated oxidation (with respect to native LDL), as measured by the formation of conjugated dienes and thiobarbituric acid reactive substances, and the depletion of vitamin E. This antioxidant effect was due to increased thiol content, as the effect was abolished with N-ethylmaleamide pre-treatment. We conclude that the reaction between homocysteine thiolactone and LDL generates an LDL molecule that is more resistant to oxidative modification than native LDL. The potential relationship between the homocystamide-LDL adduct and the development of atherosclerosis is discussed.

Antioxidants↗
PubMed1999

The domain-server: direct prediction of protein domain-homologies from BLAST search.

RESULTS: A WWW server for protein domain homology prediction, based on BLAST search and a simple data-mining algorithm (Hegyi,H. and Pongor,S. (1993) Comput. Appl. Biosci., 9, 371-372), was constructed providing a tabulated list and a graphic plot of similarities. AVAILABILITY: http://www.icgeb.trieste.it/domain. Mirror site is available at http://sbase.abc.hu/domain. A standalone programme will be available on request. SUPPLEMENTARY INFORMATION: A series of help files is available at the above addresses.

Algorithms↗
PubMed1999

Disulfide engineering at the dimer interface of Lactobacillus casei thymidylate synthase: crystal structure of the T155C/E188C/C244T mutant.

The crystal structure of a covalently cross-linked Lactobacillus casei thymidylate synthase has been determined at 2.8 A resolution. The sites for mutation to achieve the bis-disulfide linked dimer were identified using the disulfide modeling program MODIP. The mutant so obtained was found to be remarkably thermostable. This increase in stability has been reasoned to be entirely a consequence of the covalent gluing between the two subunits.

Crystallography, X-Ray↗
PubMed1999

Modulation of expression of endothelial nitric oxide synthase by nordihydroguaiaretic acid, a phenolic antioxidant in cultured endothelial cells.

Retrospective epidemiological studies have suggested that antioxidant therapy may decrease cardiovascular morbidity and mortality rates, although the mechanisms for this effect remain unclear. In the present study, we demonstrate that selective antioxidants can enhance expression of endothelial nitric oxide synthase (eNOS). We found that the antioxidants nordihydroguaiaretic acid (NDGA), catechol, glutaryl probucol, and N-acetylcysteine increased eNOS expression in cultured bovine aortic endothelial cells (BAECs). NDGA seemed to be the most potent of the phenolic antioxidants, producing a 3-fold increase in eNOS mRNA. This effect of NDGA was enhanced by nonphenolic antioxidants such as N-acetylcysteine and ascorbic acid. Nuclear run-on studies indicated that NDGA increased eNOS transcription. A similar increase in eNOS protein content was observed with Western blot analysis after treating BAECs or human aortic endothelial cells with NDGA. Exposure of BAECs to NDGA enhanced NO production, as measured by electron paramagnetic resonance spin trapping and eNOS activity, as measured by [14C]arginine-to-[14C]citrulline assay. Methylation of the phenolic hydroxyl groups completely inhibited the NDGA effect on eNOS mRNA levels. This effect of NDGA was not due to inhibition of lipoxygenase because cis-5,8,11,14-eicosatetraynoic acid did not alter eNOS expression. We conclude that antioxidants may not only increase the bioactivity of nitric oxide but also enhance expression of the eNOS enzyme. Such an effect may prove useful in conditions such as hypertension and atherosclerosis, in which nitric oxide production and/or biological activity is impaired.

Acetylcysteine↗
PubMed1999

Uptake of 13-hydroperoxylinoleic acid by cultured cells.

Oxidized free fatty acids have profound effects on cultured cells. However, little is known about whether these effects depend on their uptake and metabolism by cells or primarily involve their interaction with cell-surface components. We determined the uptake and metabolism of unoxidized (linoleic or oleic acid) and oxidized linoleic acid (13-hydroperoxyoctadecadienoic acid, 13-HPODE) by endothelial cells, smooth muscle cells, and macrophages. We show that 13-HPODE is poorly taken up by cells. The levels of uptake were dependent on the cell type but were independent of the expression of CD36. 13-HPODE was also poorly used by microsomal lysophosphatidylcholine acyltransferase that is involved in the formation of phosphatidylcholine. Based on these results, we suggest that most of the biological effects of 13-HPODE and other oxidized free fatty acids on cells might involve a direct interaction with cell-surface components. Alternatively, very small amounts of oxidized free fatty acids that enter the cell may have effects, analogous to those of hormones or prostanoids.

Animals↗
PubMed1999

Overexpression of human catalase gene decreases oxidized lipid-induced cytotoxicity in vascular smooth muscle cells.

Reactive oxygen metabolites such as hydrogen peroxide (H(2)O(2)) and oxidized fatty acids are proinflammatory and are involved in the pathophysiology of various diseases including atherosclerosis. The effects of these oxidants could be inhibited by the external addition of an antioxidant, suggesting the promotion or propagation of further oxidation. In this study, we describe the stable overexpression of human catalase in smooth muscle cells and the resistance of these cells to cytotoxicity induced not only by the addition of H(2)O(2) but also by the addition of 13-hydroperoxyoctadecadienoic acid (13-HPODE). The results pose an intriguing possibility of the generation of H(2)O(2) from a peroxidized fatty acid. Accordingly, incubation of cells with both 13-HPODE and 13-hydroxyoctadecadienoic acid resulted in the generation of intracellular H(2)O(2). To explain the observed results by which catalase could overcome the effects of 13-HPODE, we propose that oxidized fatty acids are degraded in the cellular peroxisomes, resulting in the generation of H(2)O(2). In other words, the cellular effects of peroxidized fatty acids could be attributed to the generation of H(2)O(2).

Animals↗
PubMed1999

Oxidants and antioxidants in atherogenesis. An appraisal.

Oxidized low density lipoprotein (Ox-LDL) has a plethora of components that are not present in native LDL. Their presence and quantity depends on the nature, type, and extent of oxidation. Lipids esterified to oxidized fatty acids are the major components formed during the early phase of oxidation and these show a number of proatherogenic properties in in vitro cell culture systems. Recently, evidence has been forthcoming to suggest that some of these oxidized lipids also could elicit "antioxidant;-antiatherogenic" responses from cells. Moreover, some of the cellular effects of Ox-LDL that were previously interpreted as atherogenic could also be reinterpreted to suggest an antiatherogenic cellular response. In addition to the above, the antioxidants that are carried in lipoproteins could have anomalous behavior attributable to their metabolism, ability to be internalized by arterial cells, and the presence of oxidative systems that could render them prooxidants. In conclusion, there are numerous contributing factors that need to be studied and understood before antioxidant therapy becomes an option for the treatment for cardiovascular diseases.

Animals↗
PubMed1998

Oxidized low-density lipoprotein, a two-faced Janus in coronary artery disease?

The word antioxidant has become a household term, and every day we are bombarded with claims of antioxidant protection against a host of diseases. Atherosclerosis, cancer, gastric ulcers, memory loss, rheumatoid arthritis, endometriosis, pregnancy complications, hypertension, stroke, and a host of other diseases have been suggested to be induced by oxidative stress, and antioxidants have been suggested to be beneficial in the prevention and treatment of these disorders. While some of these may be exuberant claims, atherosclerosis is one disease in which the oxidation hypothesis has taken firm roots. The oxidation of low-density lipoprotein (LDL) has been suggested to be a key step in the initiation of the early atherosclerotic lesion. A number of proatherogenic effects have been described for both the protein and lipid components of oxidized low-density lipoprotein. In this commentary, a brief description of the involvement of oxidation and the potential for antioxidant treatment for cardiovascular disease will be provided. However, there are innumerable questions plaguing the hypothesis; this commentary, therefore, will also serve as a devil's advocate and propose that some form of oxidation might actually be beneficial.

Animals↗
PubMed1998

Vascular expression of extracellular superoxide dismutase in atherosclerosis.

We characterized a novel form of extracellular superoxide dismutase (ecSOD) in atherosclerotic vessels. Specific activity and protein expression of ecSOD was increased two- to threefold in apo E-deficient compared with control aortas. RNase protection assays demonstrated that the expected ecSOD transcript was not increased in either apo E-deficient mice or cholesterol-fed LDL receptor-deficient mice, but that a second, lower molecular weight transcript was present and became predominant as atherosclerosis progressed. Sequence analysis revealed that this novel ecSOD has a 10-bp deletion in the 3' untranslated region and an asparagine to aspartic acid mutation at amino acid 21. Studies of isolated macrophages and immunohistochemistry suggested that the truncated ecSOD transcript was expressed by lipid-laden but not control macrophages. Recombinant wild-type and novel ecSODs expressed in Sf9 cells exhibited similar SOD activities. These experiments show that ecSOD expression is increased in atherosclerotic vessels and that this is characterized by an alteration in mRNA and protein structure. Further, the source of this altered ecSOD is likely the lipid-laden macrophage. The enzymatic properties of this novel ecSOD may have important implications for the function of the lipid-laden macrophage and the atherosclerotic process.

Animals↗
PubMed1998

Does acute exercise affect the susceptibility of low density lipoprotein to oxidation?

This study describes the effect of an acute exercise bout on the susceptibility of isolated low density lipoprotein (LDL) to in vitro oxidation. LDL was isolated from 23 subjects (exercisers, n = 11; sedentary, n = 12) immediately before and after a single bout of exercise (30 min of treadmill work at 55% & 70% peak oxygen consumption (VO2 peak) for exercisers and sedentary, respectively). A statistically significant decrease in lag time for LDL oxidation was observed following exercise compared to baseline (96.1+/-23.5 min vs. 92.1+/-23.3 minutes; n = 23, p < or = .03) using a 5 microM copper system. There was a statistically significant increase in plasma myeloperoxidase (MPO) levels following exercise compared to baseline values ( 1.58+/-.91 ng/dl versus 2.08+/-1.2 ng/dl; n = 12, p < or = .03). These results suggest that the 30 min exercise bout at a moderate intensity and duration was a sufficient oxidative stress to increase the susceptibility of LDL to in vitro oxidation. Additionally, the exercise bout appeared to activate neutrophils, subsequently releasing MPO protein.

Adult↗
PubMed1998

Catecholamines potentiate amyloid beta-peptide neurotoxicity: involvement of oxidative stress, mitochondrial dysfunction, and perturbed calcium homeostasis.

Oxidative stress and mitochondrial dysfunction are implicated in the neuronal cell death that occurs in physiological settings and in neurodegenerative disorders. In Alzheimer's disease (AD) degenerating neurons are associated with deposits of amyloid beta-peptide (A beta), and there is evidence for increased membrane lipid peroxidation and protein oxidation in the degenerating neurons. Cell culture studies have shown that A beta can disrupt calcium homeostasis and induce apoptosis in neurons by a mechanism involving oxidative stress. We now report that catecholamines (norepinephrine, epinephrine, and dopamine) increase the vulnerability of cultured hippocampal neurons to A beta toxicity. The catecholamines were effective in potentiating A beta toxicity at concentrations of 10-200 microM, with the higher concentrations (100-200 microM) themselves inducing cell death. Serotonin and acetylcholine were not neurotoxic and did not modify A beta toxicity. Levels of membrane lipid peroxidation, and cytoplasmic and mitochondrial reactive oxygen species, were increased following exposure to neurons to A beta, and catecholamines exacerbated the oxidative stress. Subtoxic concentrations of catecholamines exacerbated decreases in mitochondrial energy charge and transmembrane potential caused by A beta, and higher concentrations of catecholamines alone induced mitochondrial dysfunction. Antioxidants (vitamin E, glutathione, and propyl gallate) protected neurons against the damaging effects of A beta and catecholamines, whereas the beta-adrenergic receptor antagonist propanolol and the dopamine (D1) receptor antagonist SCH23390 were ineffective. Measurements of intracellular free Ca2+ ([Ca2+]i) showed that A beta induced a slow elevation of [Ca2+]i which was greatly enhanced in cultures cotreated with catecholamines. Collectively, these data indicate a role for catecholamines in exacerbating A beta-mediated neuronal degeneration in AD and, when taken together with previous findings, suggest roles for oxidative stress induced by catecholamines in several different neurodegenerative conditions.

Amyloid beta-Peptides↗
PubMed1998

Regulation of monocyte to macrophage differentiation by antiglucocorticoids and antioxidants.

OBJECTIVE: Our purpose was to examine RU 486 and related compounds on monocyte to macrophage differentiation through scavenger receptors and cellular adhesion. STUDY DESIGN: Human monocytes were isolated, cultured, and treated with dexamethasone, levonorgestrel, RU 486, and other structurally related compounds alone or in combination. Macrophage scavenger receptor activity, inhibited by glucocorticoids and associated in the current literature with macrophage cellular adhesion, was determined in this study by counting the number of adherent cells after treatment. In addition, fluorescent-labeled acetyl-low-density lipoprotein uptake was determined as a function of scavenger receptor biologic activity. RESULTS: Dexamethasone, levonorgestrel (antiglucocorticoid only) and RU 486 (antiglucocorticoid and antioxidant) all significantly decreased adherent macrophages (4%, 52%, and 74% of control). Levonorgestrel, however, demonstrated a marked uptake of fluorescent-labeled scavenger receptor ligand. RU 486 and dexamethasone were antagonistic when combined (P < .001); levonorgestrel was less antagonistic but, however, still significant (P < .05). Reduced RU 486 (antioxidant but loses antiglucocortioid activity) decreased cellular adhesion, yet scavenger receptor function was enhanced. Both probucol (extracellular mechanism of action) and probucol analog (intracellular action) markedly up-regulated scavenger function, but once again a separation of adhesion from scavenger activity was noted. Vitamin E (antioxidant) and onapristone (antioxidant and antiglucocorticoid) had virtually little to no effect on adhesion and scavenger receptor activity. Finally, pyrrolidine dithiocarbamate, a potent oxygen-free radical quencher, was toxic to all cells examined. CONCLUSIONS: RU 486 is a known antiglucocorticoid with novel antioxidant properties first demonstrated by our laboratories. Levonorgestrel has antiglucocorticoid but no antioxidant activity. RU 486 antagonized the inhibitory effect of dexamethasone on scavenger receptor development, whereas levonorgestrel was stimulatory. A separation of scavenger receptor-induced cellular adhesion and scavenger receptor internalized ligand was demonstrated by (1) reduced RU 486, which loses its antiglucocorticoid activity but retains its antioxidant activity, and (2) probucol analog, which is chemically altered to allow intracellular entry. Glucocorticoids decrease the development of scavenger receptors, whereas antioxidants regulate inflammatory cytokines by intracellular mechanisms. It is therapeutically important to up-regulate scavenger receptor activity by antiglucocorticoids in the peritoneal cavity of women with endometriosis. However, because these mechanisms also induce inflammatory cytokines, a balance of antioxidants and antiglucocorticoids such as those demonstrated in the above study may prove beneficial.

Antioxidants↗
PubMed1998

Generation and characterization of a polyclonal antipeptide antibody to human glycodelin.

OBJECTIVE: To develop and characterize an antiglycodelin antibody using a 15-amino acid synthetic peptide as antigen, derived from the sequence of human glycodelin. DESIGN: We have developed a chicken antiglycodelin-derived peptide antibody and have characterized the antibody with the use of endometrial and ovarian cell lines. The antibody was also tested for its ability to detect glycodelin by ELISA assay, immunocytochemistry, and by Western blot. SETTING: Various cell lines, cell culture medium, and amniotic fluid were used in the experiments. PATIENT(S): Amniotic fluid was collected from pregnant patients in their first trimester of pregnancy. INTERVENTION(S): No intervention. MAIN OUTCOME MEASURE(S): Detection of glycodelin. RESULT(S): The cell lines RL95-2 (human endometrial carcinoma cells), OVCAR-3 (human ovarian adenocarcinoma cells), HeLa (human cervical epitheloid carcinoma cells), and EM42-D (human endometrial epithelial cells) reacted with the antibody, indicating the presence of glycodelin. A specific 45-kd protein representing glycodelin was detected by Western blot in the amniotic fluid. CONCLUSION(S): Antipeptide antibodies can be successfully used to detect and quantify the presence of glycodelin in cells and fluids.

Adenocarcinoma↗