Diabetes mellitus has severe effects on the quality of life and the functioning of various body organs, such as the increased risk of cardiovascular diseases, nephropathy, and reduced kidney function and even failure, ocular retinopathy, blindness, neuropathy, loss of sensation in 4 limbs. Therefore, prevention of onset, identification of factors influencing the development of the disease and their control, and treatment of patients with diabetes have always been one of the top priorities of the medical community [27]. Nephropathy is one of the most important complications of diabetes, which begins with a decrease in kidney function due to vascular damage to the renal vessels and eventually leads to many complications in patients [28].
In this study, 37 patients with diabetic nephropathy, 17 men and 20 women, and 30 diabetic non-nephropathy patients, 14 men and 16 women, were investigated. The differences in age and gender were not significant between the two groups.
The mean BMI in the control group was significantly elevated compared to the case group. The results showed that only the mean diastolic blood pressure in the case group was significantly elevated compared to the control group. High blood pressure is prevalent in people with diabetes, especially in type 2 diabetes. However, blood pressure depends on several factors, including obesity, and according to studies, high blood pressure plays a significant role in the development diabetic nephropathy by glomerular hyperfiltration. Although in some studies, this difference between the diabetic nephropathy group and control group was not found, neither in systolic pressure (as in our study results) nor diastolic pressure (contrary to our study results), but in our study, this difference could be due to a significant difference in BMI and duration of diabetes between the two groups. Increased duration of diabetes is seriously associated with complications of diabetes, especially renal complications and nephropathy.
The incidence of diabetic nephropathy affects the level of vitamin D by reducing vitamin D in the patient's serum. Diabetic nephropathy, separately from diabetes, affects glomerular filtration of the kidneys and increases serum uric acid.
Also, in this study, serum levels of FBS and HbA1c in the control group were significantly lower than in the case group.
The results showed that the mean insulin resistance obtained according to the HOMA-IR formula was insignificant between the two groups. However, in terms of insulin level, the difference was significant, with a higher value in the control group compared to the case group.
Also, the mean levels of cholesterol, triglycerides, and LDL in our study were higher in the DNP group compared to the control group. Still, only the difference in LDL levels between the two groups was significant. Evidence suggests that hyperlipidemia may contribute to the onset and progression of kidney disease, as well as diabetes.
The results showed that the mean creatinine level in the DNP group was significantly higher than in the control group. Still, the mean of GFR (mL per minute per 1.73 cubic meters) in the control group was significantly higher than in the case group. In a study by Luo et al. in China, the mean GFR of diabetic patients with nephropathy was significantly lower than that of the diabetic group without nephropathy [29], which is in line with our results.
In addition, in our study, the mean serum level of uric acid in the case group was significantly higher than the control group. A study conducted by Razi et al. in 2018 in Iran, which examined the relationship between serum uric acid levels and nephropathy in patients with type 2 diabetes, is in line with our results. This study showed that serum uric acid is associated with decreased GFR, and albuminuria can be used as an indicator for diabetic nephropathy [30].
Our results showed that the mean level of vitamin D in the case group was significantly lower than that of the control group. These results are consistent with the Balla et al. [31] study. In this study conducted in 2018, Balla et al. investigated the relationship between serum vitamin D levels with glucose control and complications of nephropathy in patients with type 2 diabetes, 40 diabetic nephropathy patients with 40 diabetic patients without nephropathy, and 40 healthy individuals were compared for the main variables. They concluded that the complications of nephropathy and FBS were inversely related to the level of vitamin D in patients.
In our study in the DNP group, vitamin D has a significant direct relationship with HbA1c, and a significant inverse relationship with HDL. These results may indicate that this decrease in vitamin D levels is significantly associated with the incidence of complications of diabetes, especially nephropathy. The study conducted by Xiao et al. in 2016 also showed that with the progression of kidney disease in diabetic patients, the average level of vitamin D decreases significantly [32].
In our study, the mean serum Zinc level was not significant difference between the two groups. But the relationship between serum Zinc levels and other variables in the two groups showed that in the case group, serum Zinc levels had a significant inverse relationship with age and HbA1c. It was also generally shown that zinc had a significant inverse relationship with vitamin D. In a study by Luo et al. in 2015 in China, serum Zinc levels were compared between 271 diabetic patients with specific vascular complications and 141 patients without vascular complications. Serum Zinc levels in patients with diabetic retinopathy, diabetic nephropathy, or diabetic peripheral neuropathy were significantly lower compared to patients without these complications, contrary to our study. The results showed that lower serum Zinc levels in patients with type 2 diabetes are associated with a higher prevalence of diabetic microvascular complications and are shown as an independent risk factor for diabetic nephropathy. Also, patients with lower zinc levels are more likely to have a longer duration of diabetes [29]. In this study, the mean duration of diabetes in diabetic patients with nephropathy was 11 years, and without nephropathy was 7 years in comparison, in our study, the mean was 4.7 and 2.7 years, respectively, which may be one of the reasons for the difference in results of two studies.
In this study, the mean serum Iron level in the case group was significantly higher than that the control group. The relationship between serum Iron levels and other variables in the two groups showed that in diabetic nephropathy patients, serum Iron levels had a significant direct relationship with vitamin D and uric acid and a significant inverse relationship with FBS, HbA1c, and total cholesterol. Also, it was shown that in the case group, serum Iron level has a significant inverse relationship with disease duration.
Excess Iron and oxidative stress play a role in the pathogenesis and increased risk of type 2 diabetes and related problems. It is now known that Iron, even if not in large amounts, affects glucose metabolism. Some studies have shown that the body's Iron stores are involved in developing glucose tolerance in type 2 diabetes and gestational diabetes [33–35]. The oxidative stress and the inflammatory cytokines extend and exacerbate these disorders [36, 37].
Tuleub et al. conducted a study In Iraq that evaluated Serum Iron levels in type 2 diabetic nephropathy patients. 24 healthy individuals as a control group along with 30 diabetic nephropathy patients and 30 patients with type 2 diabetes without nephropathy were selected. The results of this research, Contrary to the results of our study, showed that the amount of iron in patients with type 2 diabetes without nephropathy was significantly higher than in other groups [38]. It has been demonstrated that Iron has an essential role in kidney injury and the progression of kidney disease [39], [40]. Therefore, there is hypothesized that reducing excessive Iron levels might contribute to the prevention of complications of diabetes like nephropathy. According to our results, this is directly related to the amount of vitamin D.
Also, our results showed that the mean serum CD34 and CD133 levels in the control group were significantly higher than in the case group.
The results showed that in the diabetic nephropathy group, CD34 has a significant direct relationship with CD133. In general, CD34 has a significant inverse relationship with HbA1c, FBS, LDL, and Uric acid. Also, it has a significant direct relationship with Insulin, IR, and CD133.
In the study by Rigato et al. [41], the level of CD133 marker was measured and analyzed in patients with nephropathy and patients without nephropathy. However, similar to the results of our study, the level of CD133 in patients without nephropathy was higher than in patients with nephropathy, but this difference was not statistically significant. In the study by Despot et al. [42], the level of CD133 was measured in patients with and without microalbuminuria. Still, its level was not explicitly reported, but the ratio of CD34 to CD133 was reported in two groups of patients, and this ratio was in the group of diabetic patients with microalbuminuria. It was significantly less than the group of diabetic patients without microalbuminuria (P < 0.05). This result also secondarily confirms the results of our study and shows that there is a relationship between the level of CD34 and the level of CD133 with the occurrence of microalbuminuria, and subsequently, nephropathy in diabetic patients.
In the study by Fadini et al. [43], the level of CD34 was measured in patients with diabetes with vascular disease, patients with diabetes without vascular disease, and the control group including healthy individuals, and the results, inconsistent with our results, showed that the level of CD34 in patients with diabetes type 2 with vascular disease. It was significantly less than diabetic patients without vascular disease and control group. Also, in a recent study, we showed that CD34 significantly decreases in diabetic patients compared to the non-diabetic group [12]. A recent study conducted by Boscari et al. [44] in 2021 confirms the decrease hematopoietic stem/progenitor cells in diabetes de type 1. They conclude that the potential for the hypoglycemic stimulatory effect of hematopoietic stem/progenitor cells decreases with long-term diabetes.
In the study of the relationship between the severity of nephropathy with vitamin D, Zinc, Iron, CD34, and CD133 it was shown that Iron, vitamin D, CD34, and CD133 have a significant relationship with the severity of nephropathy. Unfortunately, no similar study was found which measured the relationship between the severity of nephropathy with CD34 and CD133 levels.
Finally, according to the results of this study, we propose that Serum levels of iron, vitamin D, CD34, and CD133 could serve as diagnostic and prognostic biomarkers of diabetic nephropathy.