Background: Type 2 diabetes is associated with a high cardiovascular risk, which is even increased if renal damage is superimposed. Peripheral blood mononuclear cells (PBMCs) and pro-inflammatory cytokines are key factors linking type 2 diabetes and atherosclerosis. We investigated the influence of renal damage on serum, urinary and PBMCs expression behavior of TNF-alpha and IL-6 in these patients.
Methods: PBMCs were isolated by density gradient centrifugation (Ficoll-Paque method) from fasting blood samples of 22 non-diabetic control subjects and 78 diabetic patients with normal renal function and different stages of diabetic nephropathy (18 with normoalbuminuria, 29 with microalbuminuria and 31 with macroalbuminuria). Expression levels of TNF-alpha and IL-6 were analyzed by real-time quantitative RT-PCR. Serum and urinary TNF-alpha and IL-6 concentrations were measured by a solid-phase, chemiluminescent immunometric assay.
Results: The mean percent increases in the serum and urinary levels of TNF-alpha and IL-6 in diabetic patients with respect to control subjects were 176% (P < 0.0001), 250% (P < 0.0001), 114% (P < 0.0001) and 39.6% (P = 0.01), respectively. The mRNA expression level of TNF-alpha was higher by 68.8% (P < 0.001) and IL-6 mRNA levels were higher by 64.1% (P < 0.001) with respect to non-diabetic controls. TNF-alpha mRNA expression in patients with macroalbuminuria was higher by 84.8% with respect to subjects with normalbuminuria (P < 0.001) and by 29% with respect to individuals with microalbuminuria (P < 0.05). Likewise, microalbuminuric patients showed a 44.5% increase in TNF-alpha mRNA expression compared to subjects with normoalbuminuria (P < 0.05). Concerning IL-6, the mRNA expression levels of this cytokine was higher by 63.1% with respect to normoalbuminuric subjects (P < 0.01), and by 23.1% with respect to patients with microalbuminuria (P < 0.05). However, with respect to controls, diabetic patients with normoalbuminuria had similar serum TNF-alpha and urinary excretion of IL-6, without any differences in the mRNA expression levels of these cytokines in PBMCs. Partial correlation and multiple regression analysis using TNF-alpha and IL-6 mRNA levels as the dependent variables showed that urinary albumin excretion (UAE) was direct and independently associated with the expression profile of these pro-inflammatory cytokines in PBMCs.
Conclusions: These data show for the first time the relationship between inflammatory activation of PBMCs (reflected by enhanced mRNA expression of TNF-alpha and IL-6) and renal involvement (reflected by increased UAE) in type 2 diabetic patients. These results provide potential insights for the increased inflammation, accelerated atherosclerosis and cardiovascular risk associated with nephropathy in type 2 diabetes.