Impact on bulk 15N natural isotopic abundance in hair of kidney function in type 2 diabetic nephropathy

• We examine 15N natural isotopic abundance (NIA) in diabetic nephropathy.
• Hair 15N NIA is positively correlated to kidney function in type 2 diabetic patients.
• 15N incorporation into hair protein decreases as renal impairment progresses.
• Hair 15N NIA may provide an index of protein metabolism in type 2 diabetes mellitus.

SummaryBackground and aimsNephropathy is a serious long-term complication in type 2 diabetic patients. Few data are available about nitrogen metabolism in diabetic nephropathy. Bulk 15N natural isotopic abundance (NIA) in hair has been shown modified in different pathologies with altered protein metabolism. We have compared bulk 15N NIA in hair proteins in type 2 diabetic patients to look for differences between groups with or without nephropathy.MethodsCase patients were type 2 diabetic patients with high urinary albumin concentrations (≥20 mg/L or 30 mg/24 h on two of three urine collections) and/or an estimated glomerular filtration rate (eGFR) below 60 mL min−1 1.73 m−2, according to the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula. Control subjects were type 2 diabetic patients of the same geographical origin with long-term diabetes, normo-albuminuria and eGFR above 60 mL min−1 1.73 m−2. The bulk 15N NIA values for hair were measured by isotope ratio measurement mass spectrometry coupled with an elemental analyzer.ResultsThirty-three patients in the nephropathy group and 31 in the control group were included. The mean age of the participants was 69 ± 8 years, and the mean duration of diabetes was 22 ± 8 years. Bulk hair 15N NIA were 8.9 ± 0.7‰ in the nephropathy group and 9.0 ± 0.5‰ in the control group (p = 0.41). Positive correlations were found between bulk hair 15N NIA with eGFR (p < 0.01) and with urinary urea concentration (p < 0.01), and a negative correlation with the urinary albumin-to-creatinine ratio (p < 0.001).ConclusionsBulk hair 15N NIA might be an easily available, non-invasive biomarker of nitrogen metabolism in type 2 diabetic patients.