Aging increases circulating BH₂ without modifying BH₄ levels and impairs peripheral vascular function in healthy...

Little is known about the mechanisms of aging on vascular beds and its relationship with tetra and di-hydrobiopterin (BH₄ and BH₂) levels. This observational clinical study analyzed the impact of aging on plasma and platelet biopterins, cutaneous blood flow (CBF), and coronary flow reserve (CFR) in healthy adults. The study enrolled healthy adults in 3 age groups: 18-30, 50-59, and 60-70 years (n = 25/group). Biopterins were assessed by LC-MS/MS using newly defined pre-analytical conditions limiting BH₄ oxidation and improving long-term stability. CBF was measured by Laser Speckle Contrast Imaging coupled with acetylcholine-iontophoresis and CFR by adenosine stress cardiac magnetic resonance. In healthy adults, aging (60-70 years vs 18-30 years) significantly increased platelet BH₂ (+75%, P = 0.033) and BH₂ + BH₄ (+31%, P = 0.033), and to a lesser extent plasma BH₂ (+29%, P = 0.009) without affecting BH₄ and BH₄/BH₂. Simultaneously, CBF was decreased (-23%, P = 0.004) but not CFR, CBF being inversely correlated with platelet BH₂ (r = -0.42, P = 0.001) and BH₂ + BH₄ (r = -0.41, P = 0.002). The proportion of adults with abnormal platelet BH₂ increased with age (+28% in 60-70y). These abnormal BH₂ levels were significantly associated with reduced CBF and CFR (-16%, P = 0.03 and -26%, P = 0.02). In conclusion, our study showed that age-related peripheral endothelial dysfunction was associated with an increase in circulating BH₂ without decreasing BH₄, the effect being more marked in platelets, the most relevant blood compartment to assess biopterin bioavailability. Peripheral but not coronary vascular function is progressively impaired with aging in healthy adults. All these findings support biopterins as therapeutic targets to improve vascular function.