Hyperhomocysteinemia increases arterial permeability and stiffness in mice

We have reported that hyperhomocysteinemia (HHcy) evoked by folate depletion increases arterial permeability and stiffness in rats and that low folate without HHcy increases arterial permeability in mice. In this study, we hypothesized that HHcy independently increases arterial permeability and stiffness in mice. C57BL/6J mice that received rodent chow and water [control (Con), n = 12] or water supplemented with 0.5% L-methionine (HHcy, n = 12) for 18 ± 3 wk had plasma homocysteine concentrations of 8 ± 1 and 41 ± 1 μM, respectively (P < 0.05), and similar liver folate (∼12 ± 2 μg folate/g liver). Carotid arterial permeability, assessed as dextran accumulation using quantitative fluorescence microscopy, was greater in HHcy (3.95 ± 0.4 ng·min^-1·cm^-2) versus Con (2.87 ± 0.41·ng·min^-1·cm ^-2) mice (P < 0.05). Stress versus strain curves generated using an elastigraph indicated that 1) maximal stress (N/mm²), 2) physiological stiffness (low-strain Young's modulus, mN/mm), and 3) maximal stiffness (high-strain Young's modulus, N/mm) were higher (P < 0.05) in aortas from HHcy versus Con mice. Thus, chronic HHcy increases arterial permeability and stiffness. Carotid arterial permeability also was assessed in age-matched C57BL/6J mice before and after incubation with 1) xanthine (0.4 mg/ml)/xanthine oxidase (0.2 mg/ml; X/XO) to generate superoxide anion (O ₂ ^-) or 50 μM DL-homocysteine in the presence of 2) vehicle, 3) 300 μM diethylamine-NONOate (DEANO; a nitric oxide donor), or 4) 10^-3 M 4,5-dihydroxy-1,3-benzene disulfonic acid (tiron; a nonenzymatic intracellular O₂ ^- scavenger). Compared with preincubation values, X/XO and DL-homocysteine increased (P < 0.05) permeability by 66 ± 11% and 123 ± 8%, respectively. DL-Homocysteine-induced increases in dextran accumulation were blunted (P < 0.05) by simultaneous incubation with DEANO or tiron. Thus, acute HHcy increases arterial permeability by generating O₂ ^- to an extent whereby nitric oxide bioavailability is reduced.