Can homocysteine from one‑carbon metabolism impairment cause endothelial dysfunction and vascular inflammation?

Impairments in the one-carbon metabolic pathway, such as genetic variants in methylenetetrahydrofolate reductase (MTHFR) or deficiencies in B-vitamin cofactors (B6, B9, B12), disrupt the remethylation and transsulfuration pathways, directly leading to systemic homocysteine accumulation.

Cellular mechanisms of oxidative stress and endothelial damage

• Reactive oxygen species (ROS) generation: Homocysteine's reactive sulfhydryl group undergoes auto-oxidation, generating superoxide and hydrogen peroxide. It further upregulates NADPH oxidase (Nox) through protease-activated receptor-4 (PAR-4) activation while downregulating vital antioxidant defenses like thioredoxin and glutathione peroxidase.
• Nitric oxide depletion and eNOS uncoupling: Localized oxidative stress oxidizes tetrahydrobiopterin ($BH_4$), an essential cofactor for endothelial nitric oxide synthase (eNOS). This uncouples eNOS, shifting its function from producing vasodilatory nitric oxide (NO) to generating more superoxide.
• Cellular stress: Homocysteine accumulation increases asymmetric dimethylarginine (ADMA), an endogenous eNOS inhibitor, and induces endoplasmic reticulum (ER) stress, which drives endothelial cell apoptosis and impairs vasodilation.

Induction of vascular inflammation

• NF-κB activation: Homocysteine-induced ROS act as secondary messengers to activate the transcription factor nuclear factor-kappa B (NF-κB).
• Adhesion molecule expression: Activated NF-κB upregulates endothelial adhesion molecules, specifically vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1), which promote leukocyte adhesion and atherogenesis. This cascade correlates clinically with elevations in systemic inflammatory markers, including high-sensitivity C-reactive protein (hs-CRP).

Bottom line

• Key takeaway: Impaired one-carbon metabolism directly causes homocysteine accumulation, which triggers a pathological feedback loop of oxidative stress, eNOS uncoupling, and NF-κB-mediated vascular inflammation, significantly accelerating endothelial dysfunction and cardiovascular risk.