Isabel A Rivera

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BACKGROUND Methylenetetrahydrofolate reductase (MTHFR) is one of the main regulatory enzymes of homocysteine metabolism. Elevated plasma total homocysteine (tHcy) is a major risk for cardiovascular disease. A common 677C-->T mutation in the MTHFR gene results in decreased enzymic activity, and contributes to increased plasma tHcy, in association with low(More)
Hyperhomocysteinemia is a risk factor for atherosclerosis and vascular disease; however, the mechanism underlying this association remains poorly understood. Increased levels of intracellular S-adenosylhomocysteine (AdoHcy), secondary to homocysteine-mediated reversal of the AdoHcy hydrolase reaction, have been associated with reduced DNA methylation(More)
BACKGROUND The pathogenic mechanism of homocysteine's effect on cardiovascular risk is poorly understood. Recent studies show that DNA hypomethylation induced by increases in S-adenosylhomocysteine (AdoHcy), an intermediate of Hcy metabolism and a potent inhibitor of methyltransferases, may be involved in homocysteine-related pathology. METHODS We(More)
Genetic predisposition, environmental toxins and aging contribute to Parkinson's disease (PD) multifactorial etiology. Weak environmental neurotoxic factors may accumulate over time increasing the disease risk in genetically predisposed subjects. Polymorphic genes encoding drug-metabolizing-enzymes (DMEs) are considered to account for PD susceptibility by(More)
In hyperhomocysteinemia (HHcy), an independent risk factor for cardiovascular diseases, endothelial dysfunction due to reduced bioavailability of nitric oxide is a consistent finding. However, the underlying mechanisms remain unknown. Increased levels of the nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) have been associated with HHcy,(More)
OBJECTIVES Vitamin B(12), or B(12), is an essential nutrient for humans, and its deficiency is a public health problem, especially in elderly population. Around 30% of circulating total B(12) levels are attached to transcobalamin II (TCN2), being referred as holotranscobalamin (holo-TC), and representing the biologically active fraction. After cellular(More)
To understand the basis for the clinical heterogeneity of phenylalanine hydroxylase deficiency among Portuguese hyperphenylalaninemic patients, genotype-phenotype correlations were established. A group of 61 patients was completely genotyped, leading to the identification of 20 different mutant alleles in 36 different genotypic combinations, including a(More)
Methyltransferases use S-adenosylmethionine (AdoMet) as methyl group donor, forming S-adenosylhomocysteine (AdoHcy) and methylated substrates, including DNA and proteins. AdoHcy inhibits most methyltransferases. Accumulation of intracellular AdoHcy secondary to Hcy elevation elicits global DNA hypomethylation. We aimed at determining the extent at which(More)