Biomedical subjects

Sanjana Dayal

Publications and source records attributed to Sanjana Dayal.

9 recordsLinked to original sources

PubMed2006

Enhanced susceptibility to arterial thrombosis in a murine model of hyperhomocysteinemia.

Hyperhomocysteinemia is a risk factor for thrombosis, but the mechanisms are not well defined. We tested the hypothesis that hyperhomocysteinemia accelerates arterial thrombosis in mice. Mice heterozygous for a targeted disruption of the cystathionine beta-synthase gene (Cbs+/-) and wild-type littermates (Cbs+/+) were fed either a control diet or a high methionine/low folate (HM/LF) diet for 6 to 8 months to produce graded hyperhomocysteinemia. The time to occlusion of the carotid artery after photochemical injury was shortened by more than 50% in Cbs+/+ or Cbs+/- mice fed the HM/LF diet (P < .001 versus control diet). Carotid artery thrombosis was not accelerated in mice deficient in endothelial nitric oxide synthase (Nos3), which suggests that decreased endothelium-derived nitric oxide is not a sufficient mechanism for enhancement of thrombosis. Cbs+/+ and Cbs+/- mice fed the HM/LF diet had elevated levels of reactive oxygen species in the carotid artery, increased aortic expression of the NADPH oxidase catalytic subunit, Nox4, and decreased activation of anticoagulant protein C in the aorta (P < .05 versus control diet). We conclude that hyperhomocysteinemia enhances susceptibility to arterial thrombosis through a mechanism that is not caused by loss of endothelium-derived nitric oxide but may involve oxidative stress and impairment of the protein C anticoagulant pathway.

Animals↗

PubMed2005

Cerebral vascular dysfunction in methionine synthase-deficient mice.

BACKGROUND: Methionine synthase (MS) catalyzes the folate-dependent remethylation of homocysteine to methionine. We tested the hypothesis that deficiency of MS impairs endothelial function in mice heterozygous for disruption of the Mtr gene, which encodes MS. METHODS AND RESULTS: Plasma total homocysteine was similar in wild-type (Mtr(+/+)) and heterozygous (Mtr(+/-)) mice fed a control diet (4.5+/-0.3 and 5.3+/-0.4 micromol/L, respectively) and mildly elevated in Mtr(+/+) and Mtr(+/-) mice fed a low-folate (LF) diet (7.5+/-0.7 and 9.6+/-1.2 micromol/L, respectively; P<0.001 versus control diet). Dilatation of cerebral arterioles to the endothelium-dependent dilator, acetylcholine (10 micromol/L) was blunted in Mtr(+/-) mice compared with Mtr(+/+) mice fed the control diet (21+/-4 versus 32+/-4%; P<0.05). Both Mtr(+/+) and Mtr(+/-) mice exhibited impaired dilatation of cerebral arterioles to acetylcholine when they were fed the LF diet (12+/-2 and 14+/-2%, respectively; P<0.01 versus Mtr(+/+) mice fed the control diet). Elevated levels of superoxide and hydrogen peroxide were detected by confocal microscopy in cerebral arterioles of Mtr(+/-) mice fed the control diet and in both Mtr(+/+) and Mtr(+/-) mice fed the LF diet. CONCLUSIONS: These findings demonstrate that defective homocysteine remethylation caused by deficiency of either MS or folate produces oxidative stress and endothelial dysfunction in the cerebral microcirculation of mice.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗

PubMed2005

ADMA and hyperhomocysteinemia.

Hyperhomocysteinemia is a risk factor for cardiovascular disease and stroke. Like many other cardiovascular risk factors, hyperhomocysteinemia produces endothelial dysfunction due to impaired bioavailability of endothelium-derived nitric oxide (NO). The molecular mechanisms responsible for decreased NO bioavailability in hyperhomocysteinemia are incompletely understood, but emerging evidence suggests that asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase, may be a key mediator. Homocysteine is produced during the synthesis of ADMA and can alter ADMA metabolism by inhibiting dimethylarginine dimethylaminohydrolase (DDAH). Several animal and clinical studies have demonstrated a strong association between plasma total homocysteine, plasma ADMA, and endothelial dysfunction. These observations suggest a model in which elevation of ADMA may be a unifying mechanism for endothelial dysfunction during hyperhomocysteinemia. The recent development of transgenic mice with altered ADMA metabolism should provide further mechanistic insights into the role of ADMA in hyperhomocysteinemia.

Amidohydrolases↗

PubMed2004

Association of multiple cellular stress pathways with accelerated atherosclerosis in hyperhomocysteinemic apolipoprotein E-deficient mice.

BACKGROUND: A causal relation between hyperhomocysteinemia (HHcy) and accelerated atherosclerosis has been established in apolipoprotein E-deficient (apoE-/-) mice. Although several cellular stress mechanisms have been proposed to explain the atherogenic effects of HHcy, including oxidative stress, endoplasmic reticulum (ER) stress, and inflammation, their association with atherogenesis has not been completely elucidated. METHODS AND RESULTS: ApoE-/- mice were fed a control or a high-methionine (HM) diet for 4 (early lesion group) or 18 (advanced lesion group) weeks to induce HHcy. Total plasma homocysteine levels and atherosclerotic lesion size were significantly increased in early and advanced lesion groups fed the HM diet compared with control groups. Markers of ER stress (GRP78/94, phospho-PERK), oxidative stress (HSP70), and inflammation (phospho-IkappaB-alpha) were assessed by immunohistochemical staining of these atherosclerotic lesions. GRP78/94, HSP70, and phospho-IkappaB-alpha immunostaining were significantly increased in the advanced lesion group fed the HM diet compared with the control group. HSP47, an ER-resident molecular chaperone involved in collagen folding and secretion, was also increased in advanced lesions of mice fed the HM diet. GRP78/94 and HSP47 were predominantly localized to the smooth muscle cell-rich fibrous cap, whereas HSP70 and phospho-IkappaB-alpha were observed in the lipid-rich necrotic core. Increased HSP70 and phospho-IkappaB-alpha immunostaining in advanced lesions of mice fed the HM diet are consistent with enhanced carotid artery dihydroethidium staining. Interestingly, GRP78/94 and phospho-PERK were markedly increased in macrophage foam cells from early lesions of mice fed the control or the HM diet. CONCLUSIONS: Multiple cellular stress pathways, including ER stress, are associated with atherosclerotic lesion development in apoE-/- mice.

Animals↗

PubMed2004

Cerebral vascular dysfunction mediated by superoxide in hyperhomocysteinemic mice.

BACKGROUND AND PURPOSE: Hyperhomocysteinemia is an emerging risk factor for stroke, but little is known about effects of hyperhomocysteinemia on cerebral vascular function. We tested the hypothesis that chronic hyperhomocysteinemia in mice causes endothelial dysfunction in cerebral arterioles through a mechanism that involves superoxide. METHODS: Mice heterozygous for a targeted disruption of the cystathionine beta-synthase gene (Cbs+/-) and their wild type littermates (Cbs+/+) were fed either a control diet or a high-methionine diet for 10 to 12 months. RESULTS: Plasma total homocysteine was elevated with the high-methionine diet compared with the control diet for both Cbs+/+ (7.9+/-1.0 versus 5.0+/-0.5 micromol/L; P<0.05) and Cbs+/- (20.5+/-3.1 versus 8.2+/-0.9 micromol/L; P<0.001) mice. Dilatation of cerebral arterioles ( approximately 30 microm baseline diameter) was measured in vivo in response to the endothelium-dependent dilator acetylcholine or the endothelium-independent dilator nitroprusside. Vasodilatation to acetylcholine was impaired with the high-methionine diet compared with the control diet for both Cbs+/+ and Cbs+/- mice (P<0.01). Dilatation of arterioles to acetylcholine was restored toward normal by the superoxide scavenger tiron (P<0.05). Vasodilatation to nitroprusside was not influenced by Cbs genotype or diet. Dihydroethidium (DHE) staining for vascular superoxide was elevated in Cbs+/- mice fed the high-methionine diet and was inhibited by apocynin or Nomega-nitro-l-arginine methyl ester, implicating NAD(P)H oxidase and nitric oxide synthase as potential sources of superoxide. CONCLUSIONS: Superoxide is a key mediator of endothelial dysfunction in the cerebral circulation during diet-induced hyperhomocysteinemia.

1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium ↗

PubMed2004

Perturbations in homocysteine-linked redox homeostasis in a murine model for hyperhomocysteinemia.

Elevated plasma levels of homocysteine are a risk factor for cardiovascular diseases, neural tube defects, and Alzheimer's disease. The transsulfuration pathway converts homocysteine to cysteine, and approximately 50% of the cysteine in glutathione is derived from homocysteine in human liver cells, which suggests the hypothesis that defects in the transsulfuration pathway perturb redox homeostasis. To test this hypothesis, we examined a murine model for hyperhomocysteinemia in which the gene encoding the first enzyme in the transsulfuration pathway, cystathionine beta-synthase (CBS), has been disrupted. Limited metabolite profiling and CBS expression studies in liver, kidney, and brain reveal tissue-specific differences in the response to Cbs disruption. Homozygous disruption of Cbs lowered cysteine concentration in all three organs. Glutathione concentration was diminished in liver and brain, thus affecting the redox buffering capacity in these organs, whereas the approximately twofold higher glutathione synthesis capacity in kidney helped preserve the glutathione pool size despite loss of the transsulfuration pathway in this organ. In contrast, disruption of a single Cbs allele elicited only minor redox perturbations. Furthermore, the Cbs+/- genotype did not confer a significant disadvantage compared with the Cbs+/+ genotype in hepatocytes challenged by oxidative stress from exposure to tertiary butylhydroperoxide. These studies provide evidence that homozygous disruption of Cbs perturbs redox homeostasis and reduces cysteine levels, raising the possibility that these changes may be important in the etiology of the clinical manifestations of CBS deficiency.

Animals↗

PubMed2003

Hyperhomocysteinemia, endothelial dysfunction, and cardiovascular risk: the potential role of ADMA.

Hyperhomocysteinemia is an emerging risk factor for cardiovascular disease and stroke. The mechanisms underlying the pathophysiology of hyperhomocysteinemia are not completely defined, but endothelial dysfunction resulting from impaired bioavailability of nitric oxide is a consistent finding in experimental models. One potential mechanism for decreased nitric oxide bioavailability is inhibition of endothelial nitric oxide synthase by its endogenous inhibitor, asymmetric dimethylarginine (ADMA). Elevated plasma levels of ADMA have been found in association with hyperhomocysteinemia and endothelial dysfunction in both animals and humans. Additional studies are required to determine the mechanisms by which ADMA accumulates in hyperhomocysteinemia and to define the importance of ADMA in the endothelial dysfunction of hyperhomocysteinemia in vivo.

Animals↗

PubMed2002

Deficiency of glutathione peroxidase-1 sensitizes hyperhomocysteinemic mice to endothelial dysfunction.

OBJECTIVE: We tested the hypothesis that deficiency of cellular glutathione peroxidase (GPx-1) enhances susceptibility to endothelial dysfunction in mice with moderate hyperhomocysteinemia. METHODS AND RESULTS: Mice that were wild type (Gpx1+/+), heterozygous (Gpx1+/-), or homozygous (Gpx1-/-) for the mutated Gpx1 allele were fed a control diet or a high-methionine diet for 17 weeks. Plasma total homocysteine was elevated in mice on the high-methionine diet compared with mice on the control diet (23+/-3 versus 6+/-0.3 micromol/L, respectively; P<0.001) and was not influenced by Gpx1 genotype. In mice fed the control diet, maximal relaxation of the aorta in response to the endothelium-dependent dilator acetylcholine (10(-5) mol/L) was similar in Gpx1+/+, Gpx1+/-, and Gpx1-/- mice, but relaxation to lower concentrations of acetylcholine was selectively impaired in Gpx1-/- mice (P<0.05 versus Gpx1+/+ mice). In mice fed the high-methionine diet, relaxation to low and high concentrations of acetylcholine was impaired in Gpx1-/- mice (maximal relaxation 73+/-6% in Gpx1-/- mice versus 90+/-2% in Gpx1+/+ mice, P<0.05). No differences in vasorelaxation to nitroprusside or papaverine were observed between Gpx1+/+ and Gpx1-/- mice fed either diet. Dihydroethidium fluorescence, a marker of superoxide, was elevated in Gpx1-/- mice fed the high-methionine diet (P<0.05 versus Gpx1+/+ mice fed the control diet). CONCLUSIONS: These findings demonstrate that deficiency of GPx-1 exacerbates endothelial dysfunction in hyperhomocysteinemic mice and provide support for the hypothesis that hyperhomocysteinemia contributes to endothelial dysfunction through a peroxide-dependent oxidative mechanism.

Animals↗

PubMedDate not supplied

Spectrum of hemostatic derangements, in Budd-Chiari syndrome.

BACKGROUND: Hemostatic abnormalities have been reported in various hepatocellular diseases. We evaluated the hemostatic functions in patients with Budd-Chiari syndrome. METHODS: Biochemical liver function tests, and measurement of prothrombin time, activated partial thromboplastin time, and plasma levels of anti-thrombin III (antigen) and activity of protein C were done in 36 patients with Budd-Chiari syndrome. RESULTS: Liver biochemistry was abnormal in 34 patients. Plasma prothrombin time and activated partial thromboplastin time were prolonged in 17 (47%) and 23 (64%) patients, respectively. Antithrombin III antigen levels and protein C activity were reduced in 15 (50%) and 25 (83%) patients, respectively, among the 30 patients studied. Albumin levels showed significant correlation with coagulation test results, levels of anti-thrombin-III, and protein C activity. CONCLUSION: Hepatic synthesis of coagulation factors and anticoagulants is reduced in Budd-Chiari syndrome; this may play a role in recurrence of thrombosis.

Budd-Chiari Syndrome↗