Sfrp5 correlates with insulin resistance and oxidative stress

Background Secreted frizzled-related protein 5 (Sfrp5) has been described as novel adipokine in mice with insulin-sensitising and anti-inflammatory properties similar to adiponectin. The aim of this study was to compare serum concentrations and determinants of Sfrp5, its pro-inflammatory antagonist wingless-type MMTV integration site family member (Wnt)5a and adiponectin in humans and their regulation by coffee. Material and methods Serum concentrations of Sfrp5, Wnt5a and adiponectin were measured in 47 individuals who participated in a coffee intervention study. Associations with demographic, metabolic and immunological variables and regulation of serum levels by different amounts of daily coffee intake were analysed. Results At baseline, fasting serum Sfrp5 levels ranged between 96 and 4056ng/mL. Sfrp5 was directly correlated with a surrogate of insulin resistance (homeostasis model assessment of insulin resistance/HOMA-IR; r=0 center dot 32, P<0 center dot 05) and with the oxidative stress markers 8-isoprostane (r=0 center dot 44, P<0 center dot 01) and nitrotyrosine (r=0 center dot 52, P<0 center dot 001). Adiponectin showed inverse correlations with several indices of insulin resistance (e.g. HOMA-IR, Stumvoll index; all P<0 center dot 05) and a direct correlation with the anti-atherogenic apolipoprotein A-I (r=0 center dot 56, P<0 center dot 001). Coffee did not affect serum concentrations of Sfrp5. Serum Wnt5a concentrations were below the detection limit (0 center dot 02ng/mL) in 81% of the study participants. Conclusions In contrast to obese mouse models, serum Sfrp5 was directly related to HOMA-IR and oxidative stress in humans, but not with apolipoproteins, and thus, associations differed from those found for circulating adiponectin. These differences between Sfrp5 and adiponectin might be explained by differences in the investigated species.