Acute methionine loading does not alter arterial stiffness in humans

Hyperhomocystinemia is a risk factor for cardiovascular disease, and acute elevation of plasma homocysteine after methionine loading impairs endothelial function in healthy subjects. Interestingly, pretreatment with vitamin C can ameliorate this effect. We have already shown that acute oral vitamin C administration reduces arterial stiffness in healthy subjects, and the aim of the present study was to investigate the effect of methionine loading on arterial stiffness with and without concomitant vitamin C using the noninvasive technique of pulse wave analysis. Eight healthy male subjects (mean age, 29 years; range, 20-42 years) were studied on three occasions at weekly intervals. In a double-blind, double-dummy, randomized order they received orally either 100 mg/kg methionine, 100 mg/kg methionine plus 2 g of vitamin C, or matching placebos. Peripheral and central blood pressure, heart rate, cardiac index, arterial stiffness, and plasma homocysteine levels were assessed at baseline and 6 hours after dosing. Compared with placebo, there was no significant change in any of the hemodynamic parameters, including arterial stiffness, after oral methionine, although plasma homocysteine did increase from 11.5 ± 1.6 to 28.7 ± 4.4 μM (mean ± SEM; p < 0.001). Combined methionine and vitamin C led to a similar increase in plasma homocysteine but significantly reduced augmentation index by 10.5 ± 3.2% (p = 0.02). Acute hyperhomocystinemia does not significantly alter arterial stiffness, as assessed by pulse wave analysis, whereas a combination of methionine and vitamin C leads to a similar reduction in augmentation index to that previously described after vitamin C alone. These data reinforce evidence that vitamin C reduces arterial stiffness but do not indicate any important interaction with oral methionine.