Gender‐based differential infiltration of CRP from the blood into skeletal muscle

We conducted 3 studies to profile C‐reactive protein (CRP), a marker of systemic inflammation, in serum and muscle (vastus lateralis) and its response to endurance exercise in men and women. In study 1, we found serum CRP to be 2.9 fold higher in sedentary lean women (mean ± SD; 1096 ± 1241 ng/mL) vs. men (382 ± 366 ng/mL) (P = 0.006), in contrast to muscle CRP which was 40% higher in men (0.83 ± 0.21 ng/mg protein) vs. women (0.61 ± 0.13 ng/mg protein) (P < 0.001). Sedentary obese women had 3.8 fold higher serum CRP (4147 ± 3452 ng/mL; P = 0.022) and 50% higher muscle CRP (0.88 ± 0.49 ng/mg protein; P = 0.031) vs. sedentary lean women (serum, 1096 ± 1241 mg/mL; muscle, 0.58 ± 0.14 ng/mg protein) in the follicular phase. Serum CRP corrected for protein concentration (6.9 ± 6.2 ng/mg protein) was 9.8 fold higher than muscle CRP (0.7 ± 0.2 ng/mg protein; P < 0.001): men had 7 fold higher (P < 0.001), whereas women had 26 fold higher (P = 0.002), CRP in serum vs muscle. However, serum and muscle CRP values did not correlate. In study 2, plasma CRP decreased by 53% in 8 men eight days following one bout of cycling for 90 min at 65% VO 2 max (344 ± 208ng/mL vs. 164 ± 50 ng/mL, P = 0.07). In study 3, plasma and muscle CRP concentrations were measured prior to and following 12 weeks of progressive endurance exercise training in lean and obese women. There were not significant differences in CRP. We conclude that ‐1‐ lean sedentary men have lower serum, but higher muscle, CRP vs. lean women and ‐2‐ obese women have higher serum and muscle CRP vs. lean women. The discrepancy in fold difference between serum and muscle CRP in men vs. women suggests gender‐based differential infiltration of CRP from the blood into the skeletal muscle. (Supported by CIHR and NSERC Canada)