Serum levels of the myokine irisin in relation to metabolic and renal function.

OBJECTIVE: Irisin has recently been introduced as a novel myokine which reverses visceral obesity and improves glucose metabolism in mice. However, regulation of irisin in humans in relation to renal and metabolic disease has not been comprehensively studied. DESIGN AND METHODS: Serum irisin levels were quantified by ELISA and correlated with anthropometric and biochemical parameters of renal function, glucose and lipid metabolism, as well as inflammation, in 532 patients with stages 1-5 of chronic kidney disease (CKD). RESULTS: Median serum irisin levels adjusted for age, gender, and BMI significantly decreased with increasing CKD stage and lowest concentrations were seen in patients with CKD stage 5. Furthermore, irisin concentrations were associated with facets of the metabolic syndrome including diastolic blood pressure, markers of impaired glucose tolerance, and dyslipidemia in univariate analysis. Moreover, markers of renal function, e.g. glomerular filtration rate, and insulin resistance, e.g. homeostasis model assessment of insulin resistance, remained independently associated with circulating irisin levels in robust multivariate analysis. CONCLUSIONS: We show that irisin serum concentrations decrease with increasing CKD stage and are independently and positively predicted by renal function and insulin resistance. The physiological relevance of our findings, as well as the factors contributing to irisin regulation in humans, needs to be further defined in future experiments.

Serum levels of the adipokine fibroblast growth factor-21 are increased in preeclampsia.

BACKGROUND: Preeclampsia (PE) is a serious cardiovascular complication in pregnancy, which is associated with an increased future metabolic and cardiovascular risk for mother and newborn. Fibroblast growth factor (FGF)-21 was recently introduced as a novel adipokine improving glucose metabolism in vitro and in vivo. MATERIAL AND METHODS: We investigated serum FGF-21 levels in patients with PE (n=51) as compared to healthy, age-matched controls (n=51) during and 6 months after pregnancy. Furthermore, association of FGF-21 with markers of renal function, glucose and lipid metabolism, as well as inflammation, was elucidated in all individuals. RESULTS: Median maternal FGF-21 serum concentrations adjusted for body mass index and gestational age at blood sampling were significantly, almost 3-fold increased in PE patients (309.6 ng/l) as compared to healthy, age-matched pregnant women (105.2 ng/l) (p<0.001). Furthermore, FGF-21 concentrations were independently and positively correlated with triglycerides whereas an independent and negative association was observed with glomerular filtration rate and low density lipoprotein (LDL) cholesterol in pregnant women. Moreover, FGF-21 serum levels significantly decreased in former PE patients 6 months after pregnancy approaching levels found in control patients. CONCLUSIONS: Maternal FGF-21 serum concentrations are significantly increased in PE during pregnancy. Furthermore, triglycerides, glomerular filtration rate, and LDL cholesterol are independent predictors of circulating FGF-21 in pregnant women.

Serum levels of growth arrest specific protein 6 are increased in preeclampsia.

Preeclampsia (PE) contributes to maternal and fetal morbidity and mortality worldwide. Moreover, it is associated with an increased future metabolic and cardiovascular risk for mother and newborn. Recently, growth arrest specific protein (Gas) 6 has been introduced as a novel metabolic risk factor with anti-angiogenic, pro-atherogenic, and pro-adipogenic properties. In the current study, we investigated serum concentrations of Gas6 in patients with PE (n=51) as compared to healthy, age-matched controls (n=51) during and 6 months after pregnancy. Furthermore, association of Gas6 with markers of renal function, glucose and lipid metabolism, as well as inflammation, was assessed in all individuals. Median maternal Gas6 serum levels adjusted for body mass index and gestational age at blood sampling were significantly increased in PE patients (5.7 µg/l) as compared to healthy, age-matched pregnant women (4.6 µg/l) (p<0.05). Furthermore, Gas6 concentrations positively correlated with blood pressure, creatinine, free fatty acids, C-reactive protein, leptin, and adiponectin during pregnancy. Moreover, leptin and adiponectin remained independently associated with Gas6 levels in multivariate analysis. Gas6 serum levels 6 months after pregnancy were not significantly different between former PE and control patients. Taken together, maternal Gas6 serum concentrations are significantly increased in PE during pregnancy. Furthermore, the adipokines leptin and adiponectin are independent predictors of circulating Gas6 in pregnant women.

Fibroblast growth factor-21 serum concentrations are associated with metabolic and hepatic markers in humans.

Rather than a traditional growth factor, fibroblast growth factor-21 (FGF21) is considered to be a metabolic hormone. In the current study, we investigated serum FGF21 levels in the self-contained population of Sorbs. Serum FGF21 concentrations were quantified by ELISA and correlated with IGF1 as well as metabolic, renal, hepatic, inflammatory, and cardiovascular parameters in 913 Sorbs from Germany. Moreover, human IGF1 protein secretion was investigated in FGF21-stimulated HepG2 cells. Median FGF21 serum concentrations were 2.1-fold higher in subjects with type 2 diabetes mellitus (141.8 ng/l) compared with controls (66.7 ng/l). Furthermore, nondiabetic subjects with FGF21 levels below the detection limit of the ELISA showed a more beneficial metabolic profile compared with subjects with measurable FGF21. Moreover, FGF21 was significantly lower in female compared with male subjects after adjustment for age and BMI. In multiple regression analyses, circulating FGF21 concentrations remained independently and positively associated with gender, systolic blood pressure, triglycerides, and γ glutamyl transferase whereas a negative association was observed with IGF1 in nondiabetic subjects. Notably, FGF21 significantly inhibited IGF1 secretion into HepG2 cell culture supernatants in preliminary in vitro experiments. FGF21 serum concentrations are associated with facets of the metabolic syndrome, hepatocellular function, as well as GH status.

Serum levels of the adipokine progranulin depend on renal function.

OBJECTIVE: Progranulin has recently been introduced as a novel adipokine inducing insulin resistance and obesity. In the current study, we investigated renal elimination, as well as association of the adipokine with markers of the metabolic syndrome. RESEARCH DESIGN AND METHODS: Progranulin serum levels were quantified by enzyme-linked immunosorbent assay and correlated to anthropometric and biochemical parameters of renal function and glucose and lipid metabolism, as well as inflammation, in 532 patients with stages 1-5 of chronic kidney disease (CKD). RESULTS: Median serum progranulin levels adjusted for age, sex, and BMI were significantly different between CKD stages with highest values detectable in stage 5 (stage 1, 58.3 µg/L; stage 2, 63.0 µg/L; stage 3, 65.4 µg/L; stage 4, 68.8 µg/L; and stage 5, 90.6 µg/L). Furthermore, CKD stage was the strongest independent predictor of circulating progranulin in our cohort. In addition, high-sensitivity interleukin-6 and adiponectin remained significantly and independently correlated with the adipokine. CONCLUSIONS: We demonstrate that progranulin serum levels increase with deteriorating renal function. These findings are in accordance with the hypothesis that renal clearance is a major elimination route for circulating progranulin. Furthermore, the adipokine is positively and independently associated with markers of inflammation and adiponectin.