Urinary tumour necrosis factor-α excretion independently correlates with clinical markers of glomerular and tubulointerstitial injury in type 2 diabetic patients

Background. Inflammation is a potential factor in the development and progression of diabetic nephropathy. The aim of this study was to analyse the relationship between the pro-inflammatory cytokine tumour necrosis factor-alpha (TNF alpha) and clinical markers of glomerular and tubulointerstitial damage [urinary albumin excretion (UAE) and urinary N-acetyl-beta-glucosaminidase (UNAG), respectively] in a large group of type 2 diabetic patients. Methods. A total of 160 diabetic patients and 32 healthy controls were included in the study. High-sensitive C-reactive protein (hs-CRP) as well as serum and urinary levels of TNF alpha were measured. UAE and UNAG were determined by 24-h urine collection. Results. Serum hs-CRP and TNF alpha were significantly higher in diabetic than in control subjects, as well as UAE and UNAG. Diabetic patients had increased urinary TNF alpha compared to non-diabetics [14.5 (2-29) vs 4 (0.8-12), P < 0.001]. Serum hs-CRP and TNF alpha in diabetics with increased UAE were elevated compared to diabetics having normoalbuminuria. Urinary TNF alpha was also higher in diabetic subjects with micro- or macroalbuminuria than in patients with normal UAE [10.5 (4-20) and 18 (9-29) vs 7 (2-18) pg/mg, P < 0.0001, respectively]. Multiple regression analysis showed that urinary TNF alpha (P < 0.0001), hs-CRP (P < 0.0001), serum TNF alpha (P < 0.01) and HbA1c (P < 0.05) were independent of and significantly associated with UAE, whereas duration of diabetes (P < 0.001), urinary TNF alpha (P < 0.01), HbA1c (P = 0.01), hs-CRP (P < 0.05) and serum creatinine (P < 0.05) were associated with UNAG. Conclusions. In patients with type 2 diabetes, urinary TNF alpha excretion is elevated and correlates with severity of renal disease in terms of both glomerular and tubulointerstitial damage, suggesting a significant role for TNF alpha in the pathogenesis and progression of renal injury in diabetes mellitus.