Assessment of Correlation of Oxidative Stress and Insulin Resistance with Glucose-6-Phosphate Dehydrogenase Activity in Type II Diabetes Mellitus Patients.

BACKGROUND: The present study aimed to assess the correlation of oxidative stress glucose-6-phosphate dehydrogenase (G6PD) activity in type II diabetes mellitus (DM) patients.
METHODOLOGY: Forty-eight type II DM patients and healthy subjects were recruited. In all, G6PD activity, protein carbonyl, and total thiol levels were measured.
RESULTS: The mean glycated hemoglobin (HbA1c) was 9.4% in Group I and 5.2% in Group II, G6PD activity was 6.5 U/gHb in Group I and 8.2 U/gHb in Group II, protein carbonyl was 14.2 nmol/mg protein in Group I and 3.5 nmol/mg protein in Group II, and total thiol level was 204.7 μmol/mL in Group I and 318.2 μmol/mL in Group II. In Group I, G6PD activity positively correlated with total thiol (r = 0.62) and negatively correlated with protein carbonyl (r = -0.73) and HbA1C (r = -0.67), protein carbonyl positively correlated with HbA1C (r =0.45) and negatively correlated with total thiol (r = -0.84), and total thiol negatively correlated with HbA1c (r = -0.30).
CONCLUSION: G6PD may be considered a biomarker of oxidative stress and poor glycemic control in diabetic patients. Copyright:

INTRODUCTION

Diabetes is the most prevalent systemic condition occurring all over the world. It is of two types: insulin-dependent diabetes and noninsulin-dependent diabetes. Insulin dependent is also known as juvenile-onset (type I) and noninsulin dependent (type II) as adult-onset diabetes mellitus (DM)[12].

DM occurs as a result of defective insulin metabolism leading to the state of hyperglycemia in the blood. Type I diabetes occurs due to local inflammatory reaction around beta-cells of islet of Langerhans of pancreas, resulting in destruction of cells, whereas type II DM occurs due to impaired insulin secretion or peripheral insulin resistance. It is the leading cause of high mortality and morbidity. It is estimated that the condition affects more than 100 million people worldwide.[34] If it is not managed in time, it can lead to complications such as diabetic foot ulcer, diabetic neuropathy, diabetic nephropathy, retinopathy, cardiovascular accident, and renal failure.

Glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme of the pentose phosphate pathway. It has an essential role in cell metabolism and major source of nicotinamide adenine dinucleotide phosphate (NADPH). G6PD is required for production of NADPH which is helpful in preventing oxidative stress.[5]

There is an alteration of G6PD level in diabetes and cancer patients. With rise of blood glucose level, the concentration and insulin resistance of G6PD decrease. Hence considering this, the present study aimed to assess the correlation of oxidative stress G6PD activity in type II DM patients.[56]

METHODOLOGY

The study enrolled 48 type II DM patients of both genders diagnosed based on the presence of glycosylated hemoglobin level higher than 7%. For better comparison, healthy subjects were also recruited. This study proposal was presented in front of the ethical review committee where after scrutinizing all benefits and drawbacks, it was approved. All subjects (patients and controls) agreed to participate in the study.

Collection of venous blood

Five milliliters of venous blood was obtained from the antecubital vein, after an overnight fasting. Blood samples were divided into two portions: the first portion contained trisodium citrate for the estimation of G6PD activity and the second portion was used for detection of protein carbonyl and total thiol. Along with this, all were also subjected to fasting blood glucose (FBG), random blood glucose, and glycated hemoglobin (HbA1C) estimation. Protein carbonyls were measured based on the method of Reznick and Packer. Thiol group was estimated according to thiol/disulfide reaction of thiol and Ellman's reagent. G6PD activity, protein carbonyl, and total thiol levels were measured. Results were expressed as mean. The level of significance was set below 0.05, and Mann–Whitney U test was performed for all statistical analyses.

RESULTS

Table 1 shows that there were 28 males and 20 females in Group I (diabetics) and 25 males and 23 females (control) in Group II.

Table 1

Patient distribution

Groups	Group I	Group II
Status	Diabetic	Control
Male: female	28:20	25:23

Table 2 and Graph 1 show that the mean body mass index (BMI) was 23.2 kg/m2 in Group I and 23.8 kg/m2 in Group II. FBG was 281.5 mg/dl in Group I and 106.2 mg/dl in Group II, total cholesterol (TC) was 242.6 mg/dl in Group I and 186.2 mg/dl in Group II, high-density lipoprotein (HDL) was 31.2 mg/dl in Group I and 39.5 mg/dl in Group II, low-density lipoprotein (LDL) was 230.5 mg/dl in Group I and 184.2 mg/dl in Group II, and triglyceride (TG) was 180.2 mg/dl in Group I and 172.4 mg/dl in Group II. The difference was significant (P < 0.05).

Table 2

Comparison of parameters

Parameters	Group I	Group II	P
BMI	23.2	23.8	0.91
FBG	281.5	106.2	0.01
TC	242.6	186.2	0.05
HDL	31.2	39.5	0.12
LDL	230.5	184.2	0.02
TG	180.2	172.4	0.94

BMI: Body mass index, FBG: Fasting blood glucose, TC: Total cholesterol, HDL: High-density lipoprotein, LDL: Low-density lipoprotein, TG: Triglyceride

Graph 1

Comparison of parameters

Table 3 and Graph 2 show that the mean HbA1c was 9.4% in Group I and 5.2% in Group II, G6PD activity was 6.5 U/gHb in Group I and 8.2 U/gHb in Group II, protein carbonyl was 14.2 nmol/mg protein in Group I and 3.5 nmol/mg protein in Group II, and total thiol level was 204.7 μmol/mL in Group I and 318.2 μmol/mL in Group II. The difference was significant (P < 0.05).

Table 3

Comparison of parameters in both groups

Parameters	Group I	Group II	P
HbA1c (%)	9.4	5.2	0.05
G6PD activity (U/gHb)	6.5	8.2	0.04
Protein carbonyl (nmol/mg protein)	14.2	3.5	0.02
Total thiol (µmol/mL)	204.7	318.2	0.01

G6PD: Glucose-6-phosphate dehydrogenase, HbA1c: Glycated hemoglobin

Graph 2

Comparison of parameters in both groups

Table 4 shows that in Group I, G6PD activity positively correlated with total thiol (r = 0.62) and negatively correlated with protein carbonyl (r = −0.73) and HbA1C (r = −0.67), protein carbonyl positively correlated with HbA1C (r =0.45) and negatively correlated with total thiol (r = −0.84), and total thiol negatively correlated with HbA1c (r = −0.30). In Group II, G6PD activity positively correlated with total thiol (r =0.51) and negatively correlated with protein carbonyl (r = −0.054) and HbA1C (r = −0.052), protein carbonyl positively correlated with HbA1C (r =0.64) and negatively correlated with total thiol (r = −0.47), and total thiol negatively correlated with HbA1c (r = −0.67).

Table 4

Assessment of Pearson’s correlation

	Group I	Group II
G6PD activity and total thiol	0.62	0.51
G6PD activity and HbA1C	−0.67	−0.052
G6PD activity and protein carbonyl	−0.73	−0.054
Protein carbonyl and HbA1c	0.45	0.64
Protein carbonyl and total thiol	−0.84	−0.47
Total thiol and HbA1c	−0.30	−0.67

G6PD: Glucose-6-phosphate dehydrogenase, HbA1c: Glycated hemoglobin

DISCUSSION

DM has spread to involve 100 million people universally. It is an estimate that up to 2030 years, it will affect 552 million subjects.[7] The level of glucose in blood determines the G6PD activity. G6PD plays a central role in cell metabolism and was found to play pathophysiologic roles in many diseases such as diabetes, aldosterone-induced endothelial dysfunction, and cancer.[8] The present study aimed to assess the correlation of oxidative stress G6PD activity in type II DM patients.

In the present study, Group I were diabetics and Group II were healthy subjects. There were 28 males and 20 females in Group I and 25 males and 23 females in Group II. Mahmoud and Nor El-Din[9] found that in diabetics, G6PD activity negatively correlated with protein carbonyl and HbA1C and positively correlated with total thiol, and protein carbonyl negatively correlated with total thiol and positively correlated with HbA1C.

We observed that the mean BMI was 23.2 kg/m2 in Group I and 23.8 kg/m2 in Group II. FBG was 281.5 mg/dl in Group I and 106.2 mg/dl in Group II, TC was 242.6 mg/dl in Group I and 186.2 mg/dl in Group II, HDL was 31.2 mg/dl in Group I and 39.5 mg/dl in Group II, LDL was 230.5 mg/dl in Group I and 184.2 mg/dl in Group II, and TG was 180.2 mg/dl in Group I and 172.4 mg/dl in Group II.

It is a well-established fact that increased blood glucose level may increase oxidative stress, affecting normal function of cellular proteins and enzymes. Hyperglycemia activates adenylate cyclase leading to increase in cAMP levels which, in turn, activates protein kinase A which is an inhibitor of G6PD. G6PD is the major source of NADPH, the main intracellular reductant; hence, the decrease in its activity increases the oxidative stress.[10]

We found that the mean HbA1c was 9.4% in Group I and 5.2% in Group II, G6PD activity was 6.5 U/gHb in Group I and 8.2 U/gHb in Group II, protein carbonyl was 14.2 nmol/mg protein in Group I and 3.5 nmol/mg protein in Group II, and total thiol level was 204.7 μmol/mL in Group I and 318.2 μmol/mL in Group II. A research stated that hyperglycemia induces effects within the cell nucleus through reactive oxygen species (ROS). Transcription events are started causing changes in the levels of NO, cytokines, acute-phase reactants, and cellular adhesion molecules. Generation of ROS can be reduced by avoiding hyperglycemia and by minimizing fluctuations in blood glucose levels.[11]

We observed that in Group I, G6PD activity positively correlated with total thiol and negatively correlated with protein carbonyl and HbA1C. We also found that protein carbonyl positively correlated with HbA1C and negatively correlated with total thiol, and total thiol negatively correlated with HbA1c. In Group II, G6PD activity positively correlated with total thiol and negatively correlated with protein carbonyl and HbA1C, protein carbonyl positively correlated with HbA1C and negatively correlated with total thiol, and total thiol negatively correlated with HbA1C. The study of Zhang et al.[12] in the year 2000 stated that high glucose level inhibited G6PD activity via cAMP in aortic endothelial cells and observed that the culture of bovine endothelial aortic cells at high glucose concentration caused activation of protein kinase A which led to the phosphorylation of G6PD and to a decrease in its activity.

CONCLUSION

The authors found that G6PD may be considered a biomarker of oxidative stress and poor glycemic control in diabetic patients.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.