Dipeptidyl peptidase-4 activity might be a link between tumour necrosis factor alpha and insulin resistance in type 1 diabetes.

Abstract

Tumour necrosis factor alpha (TNF α) leads to β cell damage in type 1 diabetes (T1DM) but also causes insulin resistance (IR). It modulates dipeptidyl peptidase-4 (DPP-4) activity, adipokine linked with both IR and T1DM. We were interested if there is an association of TNF α in conjunction with DPP-4 and IR in T1DM. DPP-4 activity, TNF α concentration measurements, and insulin sensitivity calculation using estimated glucose disposal rate (eGDR) equation were performed in 70 T1DM patients. They were divided into two groups according to eGDR median. The group with higher IR had higher value of DPP-4 activity (27.57±1.77 vs. 18.33±1.14, p<0.001) and TNF α concentration (12.91±0.83 vs. 6.72±0.36, p<0.001). TNF α concentration and DPP-4 activity negatively correlated with eGDR (r=-0.616, p<0.001 and r=-0.643, p<0.001) while correlating positively with each other (r=0.422; p=0.001). The linear regression showed that eGDR decreases for 0.166mgkg(-1)min(-1) by TNF α concentration increase of 1pg/mL (p<0.001) and for 0.090mgkg(-1)min(-1) by DPP-4 activity increase of 1 U/L (p=0.001) when adjusted for age, gender disease duration, glycated haemoglobin, body mass index and waist-to-hip ratio. eGDR decreased by additional 0.60mgkg(-1)min(-1) (B=-0.150, p<0.001) when DPP-4 activity was additionally adjusted for TNF α. TNF α concentration is associated with IR, correlates with its severity and increases the drop in insulin sensitivity modulated by DPP-4 activity. Whether TNF α involvement in the insulin signalling pathway is mediated by DPP-4 activity needs to be further evaluated.