Does serum kidney injury molecule-1 predict early diabetic nephropathy: A comparative study with microalbuminuria.

Introduction: Diabetic nephropathy (DN) is a multifactorial disease, one of the most common complications of diabetes and a major cause of chronic kidney disease. Kidney injury molecule-1 (KIM-1) is a sensitive and specific marker of kidney injury as well as a predictor of prognosis. Objective: The present study aimed to investigate the usefulness of serum KIM-1 as an early marker of DN. Patients and
Methods: The present study included total 75 participants, among whom 25 nondiabetic participants were chosen as controls. The 50 diabetic participants were divided into two groups according to urine protein/creatinine ratio (UPCR) as participants with normoalbuminuria (T2DM patients without nephropathy) and microalbuminuria (T2DM patients with nephropathy). The complete blood count, blood glucose, HbA1c, serum electrolytes, and creatinine levels were measured using standard laboratory techniques, and serum KIM-1 levels were measured by sandwich enzyme-linked immunosorbent assay.
Results: There was a significant difference in the mean serum KIM-1 between the control and diabetics without microalbuminuria (P = 0.0001). Patients with longer duration of diabetes had a higher serum KIM-1 values (P = 0.05 in DM without microalbuminuria; P = 0.007 for DM with microalbuminuria). Serum KIM-1 did not correlate with UPCR in controls (P = ‒0.167), in diabetics with microalbuminuria (P = 0.487). However, there was a significant correlation observed between UPCR and serum KIM-1 in diabetics without microalbuminuria (P = 0.04).
Conclusion: The present study observed significantly increased levels of serum KIM-1 in both the diabetic groups compared to controls. Moreover, serum KIM-1 positively correlated with the duration of diabetes. Therefore, serum KIM-1 may be used as an early diagnostic marker to predict nephropathy among diabetes in our population.

INTRODUCTION

Diabetic nephropathy (DN) is a multifactorial disease, one of the most common complications of diabetes and a major cause of chronic kidney disease (CKD).[1] Approximately 10%–30% of Type 1 diabetes mellitus and 15%–40% of Type 2 diabetes mellitus patients are estimated to develop DN.[2] Alterations in the renal hemodynamics, activation of protein kinase C, hexosamine biosynthesis, aldose reductase pathway, and the formation of advanced glycation end products are major factors for decline in renal function of DN patients.[3] At present, urine microalbuminuria is used as a standard diagnostic tool for the diagnosis of DN. However, an ethnicity variation of albuminuria in DN was also observed in Asian, Hispanic, and Caucasian populations.[4] Hence, the early diagnosis and prevention of DN are essential which halts the progression of end-stage renal disease. Several studies have assessed the novel biomarkers for DN. The markers specify glomerular injury, tubular injury, inflammation, and oxidative stress pathway which help in early identification of DN.[5] However, most of them still require validation due to the diversity of novel biomarkers.

Kidney injury molecule-1 (KIM-1) is a Type I transmembrane glycoprotein expressed on renal proximal tubule epithelial cells and plays an important role in renal tubulointerstitial damage.[6] Studies indicate that KIM-1 is a sensitive and specific marker of kidney injury as well as a predictor of prognosis.[7] There are many studies that have shown that urinary KIM-1 is an early marker of acute kidney injury (AKI)/CKD, but very few studies have evaluated the usefulness of blood KIM-1 as an early marker of renal damage is inconclusive.[89] Thus, the present study evaluated the usefulness of serum KIM-1 as a marker of DN.

Objectives

This study aimed to evaluate the serum KIM-1 levels and correlate between the diabetic with/without microalbuminuria group and controls.

PATIENTS AND METHODS

This study included a total of 75 participants from the Department of General Medicine and Nephrology of Sri Ramachandra Institute of Higher Education and Research, Chennai, between January 2017 and August 2018. Among the 75 study participants, 25 nondiabetic participants were chosen as controls with fasting blood glucose <110 mg/dl, postprandial blood glucose <140 mg/dl, and HBA1C <6%. The other 50 Type 2 diabetic mellitus participants were divided into two groups according to urine protein/creatinine ratio (UPCR) as participants with normoalbuminuria (UPCR <0.03) and participants with microalbuminuria (UPCR 0.03–0.3) according to WHO criteria.

Laboratory investigations

Blood samples were collected from all participants in the morning after an overnight fast of 8 h, and the serum was separated and stored at −80°C. The complete blood count, blood glucose, HbA1c, serum electrolytes, and creatinine levels were measured using laboratory techniques, and serum KIM-1 levels were measured by sandwich enzyme-linked immunosorbent assay (Elabscience; Cat. NO: E-EL-H6029).

Statistical analysis

All statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS) version 16 for windows, Chicago, U.S.A. Comparisons of continuous variables between groups were performed using analysis of variance or Kruskal–Wallis tests. Comparison of nominal variables among these groups was performed using the Chi-squared test. All statistical tests were two-tailed, and P < 0.05 was considered statistically significant.

RESULTS

A total of 75 patients (64% female and 36% male) were included in this study. Among the 75 patients, 25 patients were nondiabetic controls, 25 patients were diabetics without microalbuminuria, and 25 patients were diabetics with microalbuminuria. The baseline characteristics of the study participants were documented in Table 1. The mean age for controls was 49.6 ± 12.01 years, diabetics without microalbuminuria 53.5 ± 13.5 years, and 55.8 ± 47.2 years for diabetics with microalbuminuria. There was no significant difference in the mean age between the groups (P = 0.26).

Table 1

Studied characteristics between the groups (n=25)

Variable	Control	Diabetics without microalbuminuria	Diabetics with microalbuminuria	P*	P**	P***
Age (years)	49.6±12.01	53.58±13.52	55.8±47.25		0.256
Gender male/female (%)	28/72	48/52	36/64		0.339
HB (g/dl)	11.76±2.1	11.99±1.9	11.44±2.1	0.67	0.59	0.33
TC (cells/mcL)	7698±2903	8592±2543	9408±2707	0.25	0.036	0.277
Platelets	2.74±0.69	2.55±0.81	2.86±1.00	0.39	0.62	0.24
FBS (mg/dl)	95.76±10.81	199.16±68.18	242.08±92.02	0.001	0.001	0.07
PPBS (mg/dl)	106.4±28.70	244.32±86.97	329.76±116.47	0.001	0.001	0.005
HBA1C	5.72±0.27	9.70±2.03	10.67±2.40	0.001	0.001	0.131
Creatinine (mg/dl)	0.67±0.17	0.73±0.23	0. 89±0.22	0.28	0.001	0.020
Albumin (mg/dl)	3.91±0.40	3. 89±0.31	3.49±0.57	0.44	0.002	0.001
UPCR	0.16±0.26	0.10±0.04	0.66±0.49	0.272	0.001	0.001
Serum KIM-1 (ng/ml)	8.3±6.1	17.3±7.8	17.3±9.3	0.001	0.001	0.99

*P: Control versus diabetics without microalbuminuria, **P: Control versus diabetics with microalbuminuria, ***P: Diabetics without microalbuminuria versus diabetics with microalbuminuria. SD: Standard deviation, HB: Hemoglobin, FBS: Fasting blood sugar, PPBS: Postprandial blood sugar, HBA1C: Hemoglobin A1c, UPCR: Urine protein/creatinine ratio, KIM: Kidney injury molecule, TC: Total cholesterol

The serum creatinine was significantly higher in diabetes with microalbuminuria versus diabetics without microalbuminuria (P = 0.020) and control versus diabetics with microalbuminuria (P = 0.001). But failed to show significant association for serum creatinine between the control and diabetics without microalbuminuria (P = 0.28) [Table 1]. There was a significant difference in the mean serum KIM-1 between the control and diabetics without microalbuminuria (P = 0.0001). Similarly, a significant difference was observed between control and diabetes with microalbuminuria (P = 0.001). However, there was no significant difference in serum KIM-1 between diabetic patients without microalbuminuria and diabetic patients with microalbuminuria (P = 0.99) [Table 1].

Correlation between serum kidney injury molecule-1 and other studied parameters

Correlation coefficient was done to evaluate the correlation between serum KIM-1 and other parameters between the groups. The statistical data are shown in Figure 1. Patients with longer duration of diabetes had a higher serum KIM-1 value (P = 0.05 in DM without microalbuminuria; P = 0.007 for DM with microalbuminuria). There was no significant correlation observed between serum KIM-1 and serum creatinine levels in all groups. Similarly, serum KIM-1 also did not correlate with UPCR in controls (P = ‒0.167) and in diabetics with microalbuminuria (P = 0.487). However, there was a significant correlation observed between UPCR and serum KIM-1 in diabetics without microalbuminuria (P = 0.04) group. There was no significant correlation between serum KIM-1 and HbA1C in diabetics with microalbuminuria (P = 0.101), diabetics without microalbuminuria (P = 0.09), and control (P = 0.191) groups [Figure 1].

Figure 1

Correlation between serum KIM-1 and other parameters in controls and other groups. (a) KIM 1 with urine PCR; (b) KIM 1 with creatinine; (c) KIM1 with HbA1C.

DISCUSSION

This present study was done to analyze the role of serum KIM-1 as an early marker for DN. In our study, both groups DM with microalbuminuria and DM without microalbuminuria had higher serum KIM-1 values with longer duration of diabetes. However, no significant correlation was observed between serum KIM-1 and serum creatinine. A recent follow-up study (which included 85 participants from the diabetic clinic of Jinnah Postgraduate Medical Center) revealed that KIM-1 was independently associated with BUN (r = 0.727; P < 0.001), creatinine (r = 0.510; P < 0.001), and HbA1c (r = 0.401; P = 0.008) in all groups.[10] The other study (which included 80 Egyptian patients with diabetic with nephropathy) found that urinary KIM-1 levels were increased with the progression of nephropathy and also revealed that urinary KIM-1 levels were independent risk factor of estimated glomerular filtration rate (eGFR) and albuminuria in diabetic patients.[11] Further, study with 482 Type 1 diabetic patients measured both plasma KIM-1 and urinary KIM-1 concentrations, which revealed an early renal decline with a doubling of plasma KIM-1 in normoalbuminuria and microalbuminuria.[12] Even in our study, both serum KIM-1 and UPCR were elevated in both diabetic groups when compared to the controls, but there was no correlation between serum KIM-1 and UPCR.

A study conducted by El Ashmawy et al.,[13] in Egypt (60 T2D patients), revealed that microalbuminuria positively correlated (P < 0.001) with age, duration of diabetes, fasting blood glucose, HbA1C, BUN, and creatinine. However, this study measured urinary KIM-1 but not serum KIM-1. Urinary KIM-1 also positively correlated (P < 0.001) with age, duration of diabetes, fasting blood glucose, HBA1C, BUN, creatinine, and microalbuminuria and negatively correlated with eGFR (P < 0.001). In our study, serum KIM-1 correlated well with the duration of diabetes. However, serum KIM-1 did not correlate with creatinine, UPCR, and HbA1C. Patients with longer duration of diabetes had higher serum KIM-1 values (P = 0.05 in DM without microalbuminuria, P = 0.007 in DM with microalbuminuria group). The mean creatinine in nondiabetic controls was 0.67 mg/dl, in diabetes without microalbuminuria was 0.732 mg/dl, and in diabetes with microalbuminuria was 0.89 mg/dl. The difference between the groups was statistically significant (P = 0.002). However, there was no correlation between serum KIM-1 and creatinine in all groups. Serum KIM-1 positively correlated with UPCR only in diabetes without microalbuminuria group, when compared to the other two groups, which showed a negative correlation with serum KIM-1.

Studies have shown that urinary KIM-1 is a sensitive marker of kidney injury in both rodents and humans with AKI.[141516] However, studies evaluating the role of urinary KIM-1 as a marker of DN have been inconclusive.[8917] Furthermore, when compared to serum KIM-1, urinary KIM-1 had a lower association with early renal decline. However, a study observed that prolonged KIM-1 expression was associated with severe renal failure in experimental animals.[18]

CONCLUSION

The present study revealed that serum KIM-1 concentrations were significantly elevated in both diabetic groups (with and without microalbuminuria) when compared to the controls. Furthermore, serum KIM-1 positively correlated with the duration of diabetes. Furthermore, larger multicentric studies are warranted to assess the usefulness of serum KIM-1 as an early marker of DN.

Limitations of the study

The study has some limitations; first, this study is from a single center with a limited number of patients. Second, the urine KIM-1 level was not measured to compare with serum KIM-1. Third, we have not followed up the patients to observe the decline in renal status. Finally, the environmental and lifestyle characteristics which can alter the disease progression were not included to compare with KIM-1 and between the groups.

Highlights of the study

This study clearly shows that patients with longer duration of diabetes had higher serum KIM-1 values. It also showed that elevated serum KIM-1 concentrations were observed in both diabetic with and without microalbuminuria groups. There is also a significant correlation observed between UPCR and serum KIM-1 in diabetes without microalbuminuria group.

Ethics committee approval

The study was approved by the Institutional Ethical Committee of Sri Ramachandra Institute of Higher Education and Research, Chennai, India. Written Informed consent was obtained from all study participants before recruiting the study (IEC.no: CSP-MED/16/NOV/32/181).

Ethical considerations

Ethical issues (including plagiarism and double publication) have been completely considered by the authors.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.