Plasma Homocysteine and Insulin in Diabetic Nephropathy: Relationship to Body Mass Index

Abstract

The data on plasma homocysteine and endogenous insulin in type 2 diabetes mellitus with nephropathy and relationship to body mass index (BMI) is particularly from the Indian subcontinent. A prospective study was carried out in 50 patients of type 2 diabetes mellitus with overt nephropathy (Group A). The results were compared with 25 diabetics without nephropathy (Group B), and 25 age and sex matched healthy controls (Group C). Microenzyme immunoassay and ELISA estimated the plasma homocysteine and insulin, respectively. The mean values of plasma homocysteine were significantly elevated in diabetic nephropathy (21.3 ± 7.2 µmol/L) and diabetics without nephropathy (19.4 ± 7.1) when compared to healthy control (11.5 ± 2.3). The insulin levels and BMI were significantly higher in diabetics as compared to controls. There was no correlation between homocysteine and insulin, homocysteine and BMI, and homocysteine with the degree of renal failure.

• Homocysteine
• Insulin
• Type 2 diabetes mellitus
• Diabetic nephropathy

Introduction

Homocysteine is a sulfur‐containing amino acid formed in the metabolism of methionine, which is not a normal part of the diet.[1] Hyperhomocysteinemia has been recently acknowledged as an independent risk factor for atherosclerosis.[2], [3] There is substantial evidence that high levels of homocysteine are associated with an increased risk of ischemic heart disease and cerebrovascular accidents.[2], [4] The interpretation of homocysteine concentrations in diabetic disease is complex. Plasma homocysteine levels are reported to be associated with hypertension, hyperuricemia, impaired renal function, and increased risk of development of coronary atherosclerotic disease.[5], [6], [7], [8] Insulin resistance has been hypothesized to play an important role in the development of atherosclerotic disease.[9] Animal studies[10] have shown that insulin is directly involved in the regulation of homocysteine metabolism. There are not much available data on the relationship between plasma homocysteine endogenous insulin and body mass index (BMI) in type 2 diabetes mellitus.[11], [12] The aim of the present study was to assess the plasma homocysteine and insulin levels in type 2 diabetics with overt nephropathy and to find any correlation to body mass index.

Material and Methods

This prospective study was carried out in the department of nephrology at Dayanand Medical College and Hospital, Ludhiana (North India). The study was cleared by the ethical committee of our institute and approved by our medical university. Fifty patients of type 2 diabetes mellitus with overt nephropathy (Group A) and 25 patients of type 2 diabetes mellitus without nephropathy (Group B) were included in the study. The comparison was made with 25 age and sex matched, healthy controls (Group C). Patients with a history of coronary, cerebrovascular, and peripheral vascular disease were not included.

A detailed record of the duration of diabetes mellitus, degree of glycemic control, treatment, and various complications was kept in each case. The diagnosis of diabetes mellitus was based on the World Health Organization (WHO) criteria.[13] Overt diabetic nephropathy was diagnosed by the presence of significant proteinuria and decreased glomerular filtration rate (GFR). Absence of diabetic nephropathy was made from a patient's history, normal creatinine clearance, normal urine examination, and absence of diabetic retinopathy and microalbuminuria. The glycemic status was assessed by HbA1c.

Fasting blood sugar, lipids, homocysteine and insulin levels were estimated in all the patients. Microplate enzyme immunoassay[1] and ELISA estimated plasma homocysteine and serum insulin respectively. Body mass index was calculated as weight (kg) divided by square of height in meters. Statistical methods like standard deviation, Student's t‐test and coefficient of correlation were applied.

Results

The present study included 75 patients of type 2 diabetes mellitus (50 with diabetic nephropathy, 25 without nephropathy) and 25 healthy controls. The age and sex distribution is depicted in Fig. 1. Approximately two‐thirds of the cases were males and the mean age was 53 years.

Figure 1.

The mean values of plasma homocysteine, insulin, and body mass index were significantly elevated in both the diabetic groups when compared to healthy controls. The mean values of plasma homocysteine were insignificantly higher in diabetic nephropathy as compared to diabetics without nephropathy (Table 1).

Table 1. Homocysteine, Insulin, and BMI in Various Groups

Group	Homocysteine (µmol/L)	Insulin (U/L)	BMI
A (diabetic nephropathy), n = 50	21.3 ± 7.2	18.6 ± 7.7,	24.3 ± 4.0,
B (diabetics without nephropathy), n = 25	19.4 ± 7.1	25.0 ± 13.7	26.2 ± 3.8
C (healthy controls), n = 25	11.5 ± 2.3	13.6 ± 3.3	21.5 ± 4.2

Mean ± S.D.

^*P < 0.01 compared to C.

^†P < 0.01 compared to B.

There was no significant correlation between homocysteine and insulin in diabetic nephropathy as well as diabetics without nephropathy (Table 2).

Table 2. Relationship of Homocysteine with Insulin

Group	Homocysteine (µmol/L)	Insulin (U/L)	r‐Value	p‐Value
A	21.3 ± 7.2	18.6 ± 7.7	0.196	> 0.10
B	19.4 ± 7.1	25.0 ± 13.2	− 0.131	> 0.10
C	11.5 ± 2.3	13.6 ± 3.3	− 0.089	> 0.10

The body mass index was significantly higher in diabetics as compared to controls and the BMI was significantly higher in diabetics without nephropathy as compared to diabetic nephropathy. There was no significant correlation of BMI with plasma homocysteine in both diabetic groups. There was significant elevation in insulin levels in diabetic nephropathy as the BMI increased (Table 3).

Table 3. Association with Body Mass Index

BMI	Cases	Homocysteine	Insulin
Group A (diabetic nephropathy)
19–25	32	20.7 ± 7.2	18.0 ± 7.5
25–30	14	23.0 ± 7.5	20.2 ± 8.0
> 30	04	20.3 ± 6.0	20.3 ± 5.2
r‐value		0.124	0.251
p‐value		> 0.10	< 0.10
Group B (diabetics without nephropathy)
19–25	13	19.6 ± 8.2	29.2 ± 12.3
25–30	10	19.6 ± 6.0	22.4 ± 11.9
> 30	02	20.3 ± 6.0	25.9 ± 10.1
r‐value		− 0.036	− 0.342
p‐value		> 0.10	< 0.10

There was no significant correlation of homocysteine, insulin, and BMI in diabetic nephropathy with the degree of renal failure (Table 4).

Table 4. Homocysteine, Insulin, and BMI and the Severity of Diabetic Nephropathy

Group	GFR (ml/min)	Homocysteine (µmol/L)	Insulin (U/L)	BMI
Mild (n = 20)	30–50	20.3 ± 7.0	19.0 ± 7.3	24.7 ± 3.9
Moderate (n = 17)	10–29	23.7 ± 9.6	15.8 ± 7.3	22.2 ± 3.1
Severe (n = 13)	< 10	19.2 ± 4.6	18.7 ± 8.3	23.9 ± 3.52

p > 0.10.

Discussion

There is a controversy concerning plasma homocysteine levels in type 2 diabetes mellitus. Plasma homocysteine in type 2 diabetics are reported to be similar or higher than in healthy subjects. Few data are available on the factors affecting plasma homocysteine concentrations in diabetic patients; even less is known about the link between homocysteine and microvascular complications of diabetes mellitus with the exception of nephropathy.[14] Our study demonstrated a significant elevation in homocysteine, insulin, and body mass index in type 2 diabetics with nephropathy as well as without nephropathy as compared to healthy controls.

Mechanisms for a putative association of homocysteine with diabetes mellitus or insulin resistance are unclear. Homocysteine is elevated in severe diabetic nephropathy as in other forms of chronic renal failure, perhaps due to decreased GFR and pre‐ and intrarenal factors. The mechanism of how renal failure increases plasma homocysteine is not clearly understood. Several potential mechanisms like impaired renal homocysteine metabolism, reduced renal homocysteine elimination, and negative influence of vitamin B₁₂ status have been proposed. No matter what the cause, total homocysteine concentration are closely related to serum creatinine concentration and GFR.[15], [16] Although in our study there was a highly significant increase (p < 0.001) in plasma homocysteine in diabetic nephropathy as compared to healthy controls, the plasma homocysteine levels did not correlate to the degree of renal failure

Evidence has accumulated implicating insulin resistance as a major factor in the pathogenesis of type 2 diabetes mellitus.[9] Few studies have examined the relationship of total serum homocysteine concentration and diabetes, increased serum insulin concentration, and insulin resistance. Some studies report higher homocysteine levels in type 2 and type 1 diabetics than in nondiabetes,[7], [17], [18] while others do not.[4], [19] A positive corelation,[20] no correlation,[21] and a negative correlation[22] have been reported between plasma total homocysteine and insulin levels. In the present study, there is no significant correlation between homocysteine and insulin in diabetic nephropathy. There was no significant correlation between homocysteine and BMI. There was a negative correlation between insulin and BMI in type 2 diabetics without nephropathy, while there was a positive correlation in diabetic nephropathy.

Patients with type 2 diabetes mellitus have a 2‐ to 4‐fold increased risk of coronary artery disease. Plasma homocysteine level was found to be a strong and independent risk factor in a large cohort of patients with type 2 diabetes mellitus.[23] The mechanisms by which homocysteine may exert vascular injury are unclear. Even a minimal concentration reduces endothelial vasodilator response, produces a cascade of inflammatory mediators, and increases the expression of the final products of the enzymatic glycation receptors.[24], [25]

In conclusion, the results of our study show a significant elevation of homocysteine and insulin in diabetic nephropathy and there is no significant correlation of homocysteine with the insulin and body mass index. Thus, large placebo‐controlled, prospective studies of homocysteine‐lowering therapy in these patients are warranted. Until then, the folate, vitamin B₆, and B₁₂ supplement may be used in all patients with diabetes mellitus to reduce the microvascular and macrovascular complications.