Abstract. Circulating microRNAs (miRNAs) have been proposed as promising biomarkers for multiple diseases. miR-126 is reported to be associated with type 2 diabetes mellitus (T2D), diabetic nephropathy (DN) and end stage renal disease. The aim of this study was to investigate the expression of circulating miR-126 and to assess its potential as a blood-based biomarker for DN in T2D patients. In 52 patients with T2D without history of DN (with noromoalbuminuria), 50 patients with T2D and DN (29 with microalbuminuria and 21 with macroalbuminuria), and 50 non-diabetic healthy controls, the expression of circulating miR-126 in peripheral whole blood was evaluated by quantitative polymerase chain reaction. The expression levels of circulating miR-126 were significantly decreased in T2D patients and further decreased in DN patients compared with those in the controls. Multivariate logistic regression analysis confirmed the independent association of lower miR-126 levels with T2D [adjusted odds ratio (OR), 0.797; 95% confidence interval (CI), 0.613-0.960] and DN (adjusted OR, 0.513; 95% CI, 0.371-0.708). miR-126 levels were associated with the degree of albuminuria and showed significantly low expression in DN patients with microalbuminuria (adjusted OR, 0.781; 95% CI; 0.698-0.952) and further lower expression in DN patients with macroalbuminuria (adjusted OR, 0.433; 95% CI, 0.299-0.701), respectively compared with T2D patients with normoalbuminuria. miR-126 levels negatively correlated with albuminuria positively with glomerular filtration rate (P<0.05), and in addition, negatively correlated with fasting glucose, glycated hemoglobin, triglyceride and LDL (P<0.05). Stepwise multiple regression analysis identified albuminuria as a significant predictor of miR-126 (P<0.001). miR-126 in peripheral blood yielded area under the receiver operating characteristic curves of 0.854 (95% CI, 0.779-0.929) and 0.959 (95% CI, 0.916-1.000) in the differentiation of DN patients from T2D patients and DN patients from non-diabetic controls respectively. These data suggest that decreased expression of circulating miR-126 is associated with the development of DN in T2D patients, and may be a promising blood-based biomarker for DN risk estimation.

Circulating microRNAs (miRNAs) have been shown as promising biomarkers for various diseases. We investigated the predictive potential of circulating endothelium-enriched miR-126 in type 2 diabetes patients (T2D) without chronic complications and T2D patients with coronary artery diseases (CAD). The expression levels of circulating miR-126, determined by quantitative real time PCR, were decrease in peripheral blood of T2D patients and T2D with CAD compared with healthy controls. MiR-126 strongly associated with T2D and CAD, negatively correlated with LDL in CAD patients and differentiated between T2D patients, T2D patients with CAD and healthy subjects. Circulating miR-126 may serve as a biomarker for predicting patients with T2D and diabetic CAD.

The increased incidence of diabetic nephropathy (DN) in type 2 diabetes (T2D) requires novel markers for the early detection of DN. Previously, microRNAs (miRs) have been demonstrated to be promising disease biomarkers. The present study evaluated the biomarker potential of DN‑associated miR‑377 and miR‑192 in the early stages of DN. The study included 85 participants: 55 patients with T2D (30 without DN and 25 with DN) and 30 healthy controls. The patients with T2D were classified according to albumin‑to‑creatinine ratio and were split into three groups: Normoalbuminuric group (n=30), microalbuminuric group (n=15) and macroalbuminuric group (n=10). Reverse transcription‑quantitative polymerase chain reaction analysis was used to evaluate blood miR expression. It was observed that there was higher miR‑377 expression and lower miR‑192 expression in T2D patients with and without DN compared with healthy controls (P<0.05). miR‑377 was higher in the normoalbuminuric group and gradually increased in the microalbuminuric and macroalbuminuric groups (P<0.05), whereas miR‑192 was lower in the macroalbuminuric group compared with the normoalbuminuric group (P<0.05). Regression analysis revealed direct associations between the two miRs and albuminuria (P<0.05). miR‑377 was independently associated with DN risk, even following multivariable adjustment, and albuminuria was the only predictor of miR‑377 (P<0.001). In discriminating overall patients from healthy subjects, ROC analysis revealed areas under the curve (AUCs) of 0.851 for miR377 and 0.774 for miR‑192 (P<0.001). In discriminating the normoalbuminuric group from the microalbuminuric/macroalbuminuric groups, the AUCs were 0.711 (P=0.008) and 0.70 (P=0.049) for miR‑377 and miR‑192, respectively. In patients with microalbuminuria and macroalbuminuria, miR‑377 correlated positively with albuminuria and negatively with renal function, whereas miR‑192 correlated negatively with albuminuria and positively with renal function (P=0.001), and the two miRs were correlated with known risk factors of DN (P<0.05). The results suggested that blood‑based miR‑377 and miR‑192 may serve as potential biomarkers for early detection of DN. Further validation studies are required with larger sample sizes.

Pre-diabetes represents an intermediate state of altered glucose metabolism between normal glucose levels and type 2 diabetes mellitus (T2D), and is considered a significant risk factor for the development of T2D and related complications. Early detection of pre-diabetes may allow for the use of timely and effective treatment strategies to prevent its progression. Circulating microRNAs (miRNAs/miRs) that reflect changes in diabetes-related tissues, including the pancreas, liver, skeletal and heart muscle, and adipose tissue are promising biomarkers of disease progression. In our previous study, it was demonstrated that the cardiac and skeletal muscle specific miR-1 and miR-133 are upregulated in the blood of patients with T2D and cardiovascular disease. Since both miRNAs have been shown to be implicated in insulin resistance, an important feature of pre-diabetes, we hypothesised that their expression may be increased prior to clinical diagnosis of T2D, and may thus serve as biomarkers for pre-diabetes. The expression levels of circulating miRNAs were evaluated by reverse transcription-quantitative PCR in whole blood samples from 55 subjects, including 28 pre-diabetes individuals with impaired fasting glucose (FG) and impaired glucose tolerance, and 27 healthy controls. The individuals with pre-diabetes exhibited significantly higher expression levels of miR-1 and miR-133 compared with the controls (P<0.05). Target prediction search revealed that both miR-1 and miR-133 target several pathways involved in the pathophysiology of diabetes. Pearson's correlation analysis revealed that the two miRNAs were positively correlated with blood glucose parameters, including FG, 2-h oral glucose tolerance test and glycated haemoglobin A1c levels, as well as with insulin resistance (P<0.05). Multivariate logistic regression analysis revealed that the two miRNAs were significantly and directly associated with pre-diabetes, and this association remained significant after adjustment for several confounding variables (P<0.05). Moreover, linear regression analysis showed that the Homeostatic Model Assessment-Insulin Resistance was the only significant predictor to be significantly associated with both miRNAs (P<0.05). In discriminating pre-diabetes individuals from healthy controls, the area under the curves (AUCs) of the receiver operating characteristic curves (ROCs) were 0.813 and 0.810 for miR-1 and miR-133 respectively (P<0.05). Despite the relatively small number of participants, the present study showed for the first time that circulating levels of miR-1 and miR-133 were increased in individuals with pre-diabetes, and they were associated with important features of pre-diabetes. Thus, they may serve as clinical biomarkers for the early-stages of T2D.

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