Abstract
BackgroundElevated homocysteine is a cardiovascular risk factor in hyperlipidemia. Transsulfuration pathway provides an endogenous pathway for homocysteine conversion to antioxidant glutathione (GSH). Salvianolic acid A (Sal A) contains two molecules of caffeic acid and one molecule of danshensu that is capable of enhancing homocysteine transsulfuration, which led to the hypothesis that Sal A has activatory effect on transsulfuration pathway and this effect may have beneficial effects on both homocysteine and redox status in hyperlipidemia.Methods and resultsTo test this hypothesis, we developed a rat model of hyperlipidemia induced by high-fat diet for 16 weeks, during which rats were treated with 1 mg/kg salvianolic acid A (Sal A) for the final 4 weeks. Activities of key enzymes and metabolite profiling in the transsulfuration pathway revealed that hyperlipidemia led to elevated plasma homocysteine levels after 16-week dietary treatment, which was associated with reduced activities of homocysteine transsulfuration enzymes, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). The impaired transsulfuration pathway prevented homocysteine transsulfuration to cysteine, resulting in cysteine deficiency and subsequent reduction in GSH pool size. The redox status was altered in the setting of hyperlipidemia as indicated by GSH/GSSG ratio. Sal A treatment increased hepatic CBS and CSE activities, which was associated with reduced accumulation in circulating homocysteine levels and attenuated decline in hepatic cysteine content in hyperlipidemic rats. Sal A also led to an increase in GSH pool size, which subsequently caused a restored GSH/GSSG ratio. The activatory effect of Sal A on CBS was also observed in normal rats and in in vitro experiment.ConclusionOur results suggest that activation of transsulfuration pathway by Sal A is a promising homocysteine-lowering approach that has beneficial effects on redox homeostasis in hyperlipidemic settings.
Highlights
Elevated homocysteine is a cardiovascular risk factor in hyperlipidemia
Homocysteine is a thiol-containing amino acid, which suffers two major metabolic fates: remethylation catalyzed by methionine synthase (MS), methylenetetrahydrofolate reductase (MTHFR) or betaine-homocysteine methyltransferases (BHMT) and transsulfuration catalyzed by cystathionine β-synthase (CBS) leading to cystathionine [3] (Figure 1)
The enzyme activity profiling for homocysteine transsulfuration in the liver where the lipid metabolism and homocysteine metabolism take place showed that hyperlipidemia led to a significant decrease in Cystathionine β-synthase (CBS) activity (−44% vs. control group, p < 0.01) (Figure 2B) and cystathionine γ-lyase (CSE) activity (−19% vs. control group, p < 0.001) (Figure 2C) in the liver, indicating impaired homocysteine transsulfuration to cysteine
Summary
Elevated homocysteine is a cardiovascular risk factor in hyperlipidemia. Hypercholesterolemia and hypertriglyceridemia are welldocumented risk factors for the development of cardiovascular disease [1]. Homocysteine levels are elevated and considered as important indicators of atherosclerosis in hypercholesterolemia and hypertriglyceridemia [2]. Most of the current homocysteine-lowering therapies are based on the supplementation of folic acid that can facilitate the remethylation of homocysteine [4]. It is necessary to develop a non-folic acid homocysteine-lowering approach for hyperlipidemia, because the lack of benefit of homocysteine-lowering therapy suggests that folic acid-based treatment that is still most widely used may increase the cardiovascular risk that has already been elevated in the hyperlipidemic setting
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