#2009 FGF23 in patients with diabetic kidney disease and atherosclerosis

Abstract

Abstract Background and Aims Diabetes mellitus (DM) and chronic kidney disease (CKD) are risk factors for vascular atherosclerosis, a pathological process with an important inflammatory component. The coexistence of these conditions in patients with diabetic kidney disease (DKD) has additive effects with worst cardiovascular mortality and morbidity rates when compared to non-diabetic CKD patient on cardiovascular outcomes. Accumulating research has shown that increased levels of bone-derived fibroblast growth factor 23 (FGF23), the major phosphate-regulating hormone, constitute a novel predictor of cardiovascular and all-cause mortality in CKD patients, with potential effects on disorders of glucose metabolism as well. The objective of this comparative study is to determine the differences in FGF23 levels in two groups of patients with CKD, with and without DM, matched by age, sex and renal function, all of them with clinical atherosclerotic disease. We also evaluated the relationships of FGF23 with several inflammatory markers and parameters of glucose metabolism. Method Sixty-six patients with CKD stages 3-4 (33 of them with DM) and diagnosed with peripheral vascular disease were included in the study. Whole blood and serum samples were obtained from all participants. CRP values, neutrophil/lymphocyte (N/L) ratio, HbA1c (%), fasting glucose, and Triglycerides and glucose (TyG) index, among other parameters, were obtained using standardized routine methods. Circulating levels of the intact form of FGF23, tumor necrosis factor (TNF) α, interleukin (IL) 6, and IL10 were determined by ELISA immunoassays in both groups. We also performed gene expression analysis for these three cytokines in peripheral blood cells (PBCs) using qPCR. Results The mean values of eGFR, ACR and phosphate were 37.6 ± 11.2 ml/min/1.73 m2; 294.1 ± 271.2 mg/g; 3.8 ± 0.82 mg/dL; respectively without differences between patients with and without DM The median circulating FGF23 values were higher in the DM group (51.59 [37.73-89.68] vs. 38.1 [33-54.14] pg/mL; p<0.001). Likewise, patients with DM presented higher levels of TNFα both in serum concentration (1.78 [0.72-2.47] vs. 1.28 [1.01-1.88] pg/mL; p<0.01) as in the expression of mRNA in PBCs (2.1 ± 1.26 vs. 1.87 ± 1.16 a.u.; p<0.05). No differences were observed for IL6 and IL10 levels, nor for CRP concentration or N/L ratio. As expected, fasting glucose, HbA1c and TyG index were higher in the group of subjects with DM. FGF23 was inversely correlated with eGFR (r=−0.435, p<0.0001), while it showed a positive association with ACR (r=0.416, p<0.001) and, interestingly, with proinflammatory cytokines including circulating TNFα (r=0.44, p<0.001), circulating IL6 (r=0.27, p=0.04), and TNF mRNA expression in PBCs (r=0.245, p=0.047). Furthermore, circulating FGF23 was also direct and significantly correlated with HbA1c (r=0.34, p<0.01). Conclusion These results suggest that FGF23 levels are higher in DKD than in non-DM CKD patients with similar renal function. DKD patients also had higher levels of the proinflammatory cytokine TNFα. Our results also show positive correlations of FGF23 with the inflammatory cytokines TNFα and IL6, as well as with HbA1c. Previous studies, shown that elevated TNFα and glucose promote FGF23 production, which may help to explain the higher levels of FGF23 in patients with DM Future studies should clarify whether FGF23 is simply a marker of atherosclerosis disease severity or a contributing factor to this complication in CKD.