Considering the heavy impact of childhood diabetes on morbidity and mortality later in life, it is time to refocus efforts and resources for identification of novel diagnostic biomarkers of early silent stages of DKD in this highly vulnerable population that would facilitate the development of more effective monitoring, prevention, and treatment modalities.

In the current study, we explored the diagnostic value of serum Angpt-2 as an early biomarker for DKD in children with T1DM of short duration (3–5 years) before microalbuminuria emerges which appears once significant kidney damage has already occurred and corresponds to DKD stage 3 [10].

The study included two diabetic groups, microalbuminuric and non-albuminuric, who were matched for age, sex, and pubertal status. No significant differences were detected between the two groups as regards age at onset and duration of T1DM, blood pressure, and BMI-Z. Moreover, no significant differences in eGFR-Cr across the study groups were observed. This finding indicating that conventional creatinine-based eGFR method was unable to reflect early renal affection among children with T1DM in the current study. This finding is consistent with the results of prior studies [29,30,31,32,33], supporting the evidence that GFR decline develops over a longer period (10 years to 25 years) after the onset of diabetes [4].

The results of the current study revealed significantly higher serum Angpt-2 values in the microalbuminuric group compared to both non-albuminuric and control groups and in the non-albuminuric group compared to the controls. In addition, serum Angpt-2 level was found to be positively correlated with TGs, LDL-C, Non-HDL-C, HbA1c, and UACR. Among the previous biochemical parameters, Non-HDL-C, HbA1c, and UACR were the predictors for serum Angpt-2 in children with T1DM.

On reviewing the literature, only few studies reported data on Angpt-2 in adults with T1DM [33, 34] and scarce data on Angpt-2 in children with T1DM [22]. However, whether serum Angpt-2 can predict early DKD in children with T1DM has not been explored.

Consistent with our finding, El-Asrar with colleagues reported significantly higher serum Angpt-2 levels in a group of children with T1DM with and without microvascular complications including nephropathy, neuropathy, and retinopathy compared with controls. In addition, serum Angpt-2 was higher in children with microalbuminuria than normoalbuminuric group and positive associations were observed between serum Angpt-2 level and each of fasting blood glucose, HbA1c, serum creatinine, high-sensitivity C-reactive protein (hs-CRP), and with carotid and aortic intima-media thickness [22]. The authors suggested that elevated Angpt-2 levels in children with T1DM reflect inflammation and vascular dysfunction.

In adult patients with T1DM and DKD, Sokolovska and colleagues demonstrated increased concentration of serum Angpt-2 and reported associations between serum Angpt-2 and eGFR and albuminuria that remained significant after adjustment for covariates (age, sex, diabetes duration, arterial hypertension, BMI, smoking, HbA1C, and serum lipids). Therefore, the authors concluded that Angpt-2 is an independent predictor of kidney function and DKD [33]. In a longitudinal study conducted by Khairoun et al., elevated Angpt-2/Angpt-1 ratio was observed in adult patients with T1DM and DKD. Interestingly, the ratio was normalized 1 year after simultaneous kidney-pancreas transplantation [34].

Contrary to the scarce data concerned with Angpt-2 in T1DM in children [22] and in adults [33, 34], Angpt-2 has been extensively studied in adults with T2DM with comparable results. In these studies, serum Angpt-2 levels were higher in patients with T2DM compared to healthy individuals and in diabetic patients with poor glycemic control and those with chronic diabetes-related vascular complications [23, 35,36,37,38,39,40,41,42,43]. Therefore, Angpt-2 has been implicated in the development and progression of DKD in adults with T2DM [20, 21].

It has been postulated that chronic hyperglycemia leads to the accumulation of advanced glycation end products and mitochondrial overproduction of reactive oxygen species that causes the upregulation of Angpt-2 mRNA, which has been reported to promote vascular permeability, destabilization, and sprouting, further inducing microvascular and macrovascular complications [44, 45].

Furthermore, in a large study in Taiwan, Tsai and colleagues found a stepwise increase in serum Angpt-2 levels with urine PCR and reported association of Angpt-2 levels with renal deterioration estimated by eGFR and also demonstrated that Angpt-2 can independently predict adverse clinical outcomes, including commencing dialysis, rapid renal function decline, major adverse cardiovascular events, or all-cause mortality in DKD [46]. Unfortunately, there is no indication on type of diabetes in this study.

Moreover, urinary Angtp-2 level in DKD was explored by many studies. He with colleagues reported that tumor necrosis factor-alpha and 8-hydroxy-2′-deoxyguanosine were associated with elevated urinary Angpt-2 level in adult patients with T2DM and albuminuria [47].

In a study conducted by Chen et al., urinary Angpt-2 levels were increased in a stepwise manner in T2DM patients with various degrees of kidney damage in particular normoalbuminuric group and suggested that Angpt-2 may be an earlier measurable indicator of tubular impairment before the onset of clinical symptoms or signs, such as microalbuminuria [43].

Regarding the associations of Angpt-2 with clinical and biochemical variables in T2DM, Rasul et al. reported significant correlation between levels of Angpt-2 and HOMA-IR index, eGFR, and BMI, but not HbA1C [37]. In contrast, Lim with colleagues reported HbA1C as a predictor of Angpt-2 concentration and observed improvement in Angpt-2 levels in patients with T2DM after multifactorial intervention [35]. In addition, Angpt-2 levels are associated with indexes of endothelial damage/dysfunction in T2DM [35, 39]. Martynov et al. reported a relation between increased Angpt-2 concentration and increased albuminuria as well as reduction of GFR in adults with T2DM [38]. In the study conducted by Chen et al., no significant correlations were found between serum or urinary Angpt-2 and age, HbA1c, blood pressure, in addition to lipid profile [43]. Aly et al. found plasma Angpt-2 levels steadily increased with the progression of albuminuria and renal impairment and identified significant positive correlation of plasma Angpt-2 level with mean arterial pressure, CRP, and HbA1c and negatively correlated with eGFR, but no detected correlations between plasma levels of Angpt-2 with microalbuminuria and UACR [23]. The inconsistency between our findings and previous studies regarding Angpt-2 associations can be attributed to differences in the age of diabetic patients and the type and duration of diabetes; also, diabetic adult patients in previous studies were at advanced stages of DKD, mostly hypertensive or had associated other diabetes-related microvascular or macrovascular complications.

In the current study, we explored for the first time the predictive power of serum Angpt-2 as a biomarker for DKD in children with T1DM through construction of ROC curve. Interestingly, serum Angpt-2 demonstrated excellent diagnostic accuracy in discrimination between the studied groups. The optimal cutoff value for serum Angpt-2 to discriminate between microalbuminuric and non-albuminuric diabetic groups was at 137.4 ng/L with AUC = 0.960, 80% sensitivity, and 96.7% specificity, while the optimal cutoff value for serum Angpt-2 to discriminate between the non-albuminuric diabetic group and the control group was at 115.95 ng/L with AUC = 0.976, 86.7% sensitivity, and 93.3% specificity. This observation highlights the potential role of serum Angpt-2 as promising biomarker in the early detection of DKD prior to the microalbuminuric phase.

In agreement with our results, Aly et al. explored the validity of plasma Angpt-2 as a predictor of different stages of DKD among adult patients with T2DM who were classified into five groups: non-albuminuric, microalbuminuria, macroalbuminuria, macroalbuminuria complicated to renal impairment, and ESRD on top of DKD. The authors demonstrated that plasma Angpt-2 levels have high sensitivity and specificity in prediction of DKD at different cutoff values among studied groups [23].

Taking the results of the current study and all previous studies together, it is quite evident that serum Angpt-2 can serve as a useful diagnostic and prognostic marker for DKD in clinical settings, guiding the physicians to make proper early interference in the near future. Interestingly, manipulation of local and systemic angiopoietins could represent an attractive therapeutic target for patients with diabetic microvascular complications [48, 49]. Early studies in patients with diabetes with macular edema have shown that administration of AKB-9778 (a vascular endothelial protein tyrosine phosphatase that promotes Tie-2 receptor activation) for 4 weeks reduced macular edema and improved vision, without demonstrating any safety concerns [50]. Future studies might address the role of Tie-2 activation in diabetic glomerular disease.