Author(s): IWAGUCHI , K., NISHIKAWA, T., KUROSE, S., INOUE, K., FUJIE, S., MIYAUCHI, T., SANADA, K., KIMURA, Y., IEMITSU, M., Institution: RITSUMEIKAN UNIVERSITY , Country: JAPAN, Abstract-ID: 2438

INTRODUCTION:
High cardiorespiratory fitness achieved through regular aerobic exercise is associated with reduced cardiometabolic risk [1]. Complement component 1q (C1q), a key initiator of the classical complement pathway, has been implicated in vascular remodeling and cardiometabolic disorders, including hypertension and arteriosclerosis [2] [3]. However, the associations among serum C1q levels, cardiorespiratory fitness, and cardiometabolic risk remain unclear. Therefore, this study aimed to clarify the relationships among serum C1q levels, cardiorespiratory fitness, and cardiometabolic risk factors.
METHODS:
This cross-sectional study included 508 Japanese adults aged 18 to 88 years. Serum C1q levels were measured using enzyme-linked immunosorbent assay (ELISA). Maximal oxygen uptake (VO₂peak) was assessed using a breath-by-breath gas analysis system as an indicator of cardiorespiratory fitness. Body fat percentage and blood pressure were assessed, and blood triglycerides, hemoglobin A1c (HbA1c), and HDL cholesterol were measured as cardiometabolic risk factors. A cardiometabolic risk score was calculated from standardized z-scores of these variables (HDL inversely coded). Participants were stratified by sex (men, n = 201; women, n = 307) and age group (<40 years, n = 230; ≥40 years, n = 278), and further categorized into quintiles based on serum C1q levels and VO₂peak. Differences among VO₂peak quintiles were analyzed using one-way ANOVA with Bonferroni correction. Associations were assessed by Pearson’s correlation. Significance was set at p<0.05.
RESULTS:
VO₂peak quintiles showed progressively lower cardiometabolic risk scores and serum C1q levels, with significant reductions observed from the fourth and subsequent quintiles (p<0.05). C1q quintiles showed progressively higher cardiometabolic risk scores and progressive lower VO2peak, with significant differences observed from the second and subsequent quintiles (p<0.05). VO₂peak was negatively correlated with cardiometabolic risk score (r=-0.686, p<0.05) and serum C1q levels (r=-0.602, p<0.05), whereas serum C1q levels were positively correlated with cardiometabolic risk score (r=0.569, p<0.05). Similar association patterns were observed after stratification by sex and age group, indicating consistency across subgroups (each p<0.05).
CONCLUSION:
Higher cardiorespiratory fitness was associated with lower serum C1q levels and a more favorable cardiometabolic profile. Serum C1q levels were positively associated with cardiometabolic risk score. These findings suggest that C1q may represent a potential biomarker linking cardiorespiratory fitness and cardiometabolic health.

References:
[1] Sports Med. 44:487-499. 2014.
[2] Exp Gerontol. 124:110650. 2019.
[3] Nat Commun. 6:6241. 2015.