Aging-induced elevation in circulating complement C1q level is associated with arterial stiffness

Inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) are candidate blood biomarkers of cardiovascular disease (CVD). However, no consensus has been reached on the relationships between aging-induced secretion of cytokines and CVD risk. Complement C1q (C1q) secretion increases with aging, and C1q induces proliferation of vascular smooth muscle cells. Therefore, the secretion of C1q with aging may be a risk factor of CVD and reflect arterial stiffening and blood pressures. This study aimed to clarify whether aging-induced increase in serum C1q, TNF-α, and IL-6 levels are associated with arterial stiffness. One hundred twenty-seven healthy subjects participated in this study. Serum C1q, TNF-α, and IL-6 levels and carotid-femoral pulse wave velocity (cfPWV; arterial stiffness index) in middle-aged and older subjects (≥40 years) were significantly increased as compared with those in young subjects (<40 years; P < 0.05). The serum C1q, TNF-α, and IL-6 levels positively correlated with cfPWV (P < 0.05). Furthermore, C1q level contributed independently to the cfPWV variation after adjustment for 11 confounders. Moreover, serum C1q level is associated with cfPWV regardless of sex, but these relationships with TNF-α or IL-6 differed between sex. Importantly, cfPWV gradually increased from the age of 30 years, with simultaneous increase in circulating C1q level. However, TNF-α and IL-6 levels increased after age 50 years, later than the increase in C1q. These results suggest that serum C1q level may reflect the elevation of arterial stiffness that occurs with advancing age and has a potential as a novel biomarker of arterial stiffness.