Hydrogen sulphide pathway contributes to the enhanced human platelet aggregation in hyperhomocysteinemia

Abstract

Homocysteine is metabolized to methionine by the action of 5,10methylenetetrahydrofolate reductase (MTHFR). Alternatively, by thetransulfuration pathway, homocysteine is transformed to hydrogen sulphide (H2S),through multiple steps involving cystathionine beta-synthase and cystathioninegamma-lyase. Here we have evaluated the involvement of H2S in the thromboticevents associated with hyperhomocysteinemia. To this purpose we have usedplatelets harvested from healthy volunteers or patients newly diagnosed withhyperhomocysteinemia with a C677T polymorphism of the MTHFR gene (MTHFR++). NaHS(0.1-100 microM) or l-cysteine (0.1-100 microM) significantly increased plateletaggregation harvested from healthy volunteers induced by thrombin receptoractivator peptide-6 amide (2 microM) in a concentration-dependent manner. Thisincrease was significantly potentiated in platelets harvested from MTHFR++carriers, and it was reversed by the inhibition of either cystathioninebeta-synthase or cystathionine gamma-lyase. Similarly, in MTHFR++ carriers, thecontent of H2S was significantly higher in either platelets or plasma comparedwith healthy volunteers. Interestingly, thromboxane A2 production was markedlyincreased in response to both NaHS or l-cysteine in platelets of healthyvolunteers. The inhibition of phospholipase A2, cyclooxygenase, or blockade ofthe thromboxane receptor markedly reduced the effects of H2S. Finally,phosphorylated-phospholipase A2 expression was significantly higher in MTHFR++carriers compared with healthy volunteers. In conclusion, the H2S pathway isinvolved in the prothrombotic events occurring in hyperhomocysteinemic patients

Hydrogen Sulfide and Platelets: A Possible Role in Thrombosis

“…In contrast to the above studies, H 2 S generating salts at lower concentrations (0.1-100 μM) have been reported to enhance human platelet aggregation induced by the thrombin receptor activator peptide (TRAP-6) and to contribute to the enhanced platelet aggregation occurring during hyperhomocysteinemia (d'Emmanuele di Villa Bianca R et al 2013). A full causative mechanism was not described to explain the ability of H 2 S to enhance platelet aggregation although the arachidonic acid cascade was shown to be implicated.…”

“…H 2 S is synthesised by CBS and CSE in vascular endothelial cells (Shibuya et al 2009;Whiteman et al 2011) and has been shown to act as a physiologic vasodilator and regulator of blood pressure (Yang et al 2008). Human platelets have been reported to possess both CBS and CSE by western blotting and to generate detectable amounts of H 2 S from L-cysteine (d'Emmanuele di Villa Bianca R et al 2013). In contrast, we have detected robust CBS expression by western blotting but very little or no CSE protein in human platelet lysates using three commercially available antibodies (unpublished data).…”

Regulation of vascular tone homeostasis by NO and H2S: Implications in hypertension

“…Both CBS and CSE are expressed in platelets and generate detectable amounts of H 2 S [258]. Deficiency in H 2 S production stimulates platelets aggregation in a methionine-induced hyperhomocysteinemia rat model [259].…”

“…Deficiency in H 2 S production stimulates platelets aggregation in a methionine-induced hyperhomocysteinemia rat model [259]. H 2 S inhibits platelet activity both in vivo and in vitro [259–266], although controversial [258]. …”

“…However, it has also been reported that H 2 S-induced inhibition of platelet aggregation is not dependent on cAMP/cGMP generation, NO production, or potassium-channels opening [260]. In contrast, a recent report showed that NaSH and L-cysteine dose-dependently enhanced platelet aggregation in hyperhomocysteinemia [258]. This discrepancy may be related to the relative doses of H 2 S employed, which has ranged from mostly high (1–10 mM) to significantly lower doses (0.1–100 µM) [258].…”