The pathogenesis of type 2 diabetes (T2D) is associated with a progressive loss of pancreatic beta-cell mass. It is known that miR-146a, miR-34a, and miR-375 are involved in beta-cell functionality. In this work, we evaluated the levels of these miRNAs in normal-glycaemic individuals, pre-diabetic, and T2D patients in relation to beta-cell functionality, insulin resistance, and metabolic parameters. The relative expression of the miRNAs was evaluated in serum samples by real-time polymerase chain reaction. In a principal component analysis, we observed that T2D patients and pre-diabetic individuals were not associated with beta-cell functionality. However, in a correlation matrix analysis, we detected that miR-34a was related to miR-146a and insulin resistance. The relative expression of miR-375 was correlated with cholesterol and low-density lipoprotein levels. A decrease of beta-cell function in pre-diabetic individuals and T2D patients was observed. The insulin resistance was higher in pre-diabetic individuals and T2D patients. The relative expression of miR-146a in pre-diabetic individuals, T2D patients with insulin treatment, and T2D patients with nephropathy and diabetic foot was decreased. In addition, miR-34a was increased in T2D patients who were overweight and obese. The relative expression of miR-375 was increased in T2D patients with poor glycaemic control, while a decrease was seen in T2D patients with nephropathy and diabetic foot. Circulating miR-375, miR-34a, and miR-146a were not associated with beta-cell functionality, but their expression was differentially affected by glycaemia, obesity, insulin treatment, and the presence of nephropathy and diabetic foot.
