Journal of Medical Nutrition and Nutraceuticals

ORIGINAL ARTICLE
Year
: 2012  |  Volume : 1  |  Issue : 2  |  Page : 111--114

Effect of hyperglycemia on LDL oxidation in type 2 diabetic patients


Nivedita Singh1, Neelima Singh1, SK Singh1, Navneet Agarwal2, Deepak Kafle1,  
1 Department of Biochemistry, G.R. Medical College, Gwalior, India
2 Department of Diabetes, Obesity and Thyroid CenterLalitpur Colony, Gwalior, India

Correspondence Address:
Nivedita Singh
Department of Biochemistry, G.R. Medical College, Gwalior, Madhya Pradesh
India

Abstract

Type 2 diabetes is associated with an increased risk for atherosclerosis. Oxidative stress plays a key role in the onset of diabetes and in the development of vascular complications of the disease. Low-density lipoproteins (LDL) are important targets of oxidation, and oxidative modification of LDL is involved in the pathogenesis of atherosclerosis. Hyperglycemia is a major factor in the pathogenesis of atherosclerosis in diabetes. Present study has been carried out to know the sensitivity of LDL to oxidation and assessing whether hyperglycemia in diabetes mellitus is associated with increased LDL oxidation and whether these relationships are related to diabetic complications. The study was carried out in 120 diabetic subjects, classified into two groups with and without complication. LDL from the serum sample was precipitated by heparin-citrate precipitation method. The LDL fractions were exposed to oxidation with CuSO4 to measure its sensitivity to oxidation and its correlation with HbA1c was also evaluated. The present study was demonstrated that sensitivity of LDL oxidation was increased in all diabetic groups and it was positively correlated with HbA1c. In type 2 diabetes increased sensitivity of LDL for oxidation is due to hyperglycemia induced oxidative stress.



How to cite this article:
Singh N, Singh N, Singh S K, Agarwal N, Kafle D. Effect of hyperglycemia on LDL oxidation in type 2 diabetic patients.J Med Nutr Nutraceut 2012;1:111-114


How to cite this URL:
Singh N, Singh N, Singh S K, Agarwal N, Kafle D. Effect of hyperglycemia on LDL oxidation in type 2 diabetic patients. J Med Nutr Nutraceut [serial online] 2012 [cited 2020 Dec 1 ];1:111-114
Available from: https://www.jmnn.org/text.asp?2012/1/2/111/101302


Full Text

 Introduction



Diabetes mellitus is associated with increased oxidative stress and free radical production. [1],[2] Increased production of reactive oxygen species as well as reduced antioxidant defense mechanisms have been suggested to play a role in type 2 diabetic patients. [3] Oxidative stress plays an important role in the etiology of diabetic complications such as atherosclerosis, a major cause of morbidity and mortality in these patients. [4],[5] The following mechanisms are thought to be involved in the increased oxidative stress in diabetes mellitus: Hyperglycemia, oxygen free radical generation due to nonenzymatic protein glycosylation, autooxidation of glucose and glycation products, and changes in antioxidant defense systems. [6],[7] Lipid alterations and oxidizability of lipoproteins have been also considered as contributory factors to oxidative stress in diabetes mellitus. [8],[9] Previous studies have shown an increased susceptibility of LDL to in vitro oxidation in diabetes mellitus. [10] However, other investigators have not confirmed this observation and have reported either unaltered [11] or decreased [12] oxidizability of LDL isolated from diabetic patients. Such discrepancies could be due to the heterogeneity of diabetic populations, glycemic control and the presence or absence of vascular complications. [2] This investigation was aimed at assessing whether glycemic status influenced LDL oxidizability and whether these relationships are related to diabetic complications.Therefore this study has been aimed to know the effect of hyperglycemia on the sensitivity of LDL oxidation in type 2 diabetes.

 Materials and Methods



Regarding the study, type 2 diabetic patients (120) recruited in the Intensive Care Unit (Medicine Department) and Medicine OPD, J.A. Group of Hospitals, Gwalior.Were matched for sex and age to healthy subjects (50). The type 2 diabetic patients were divided into two groups: Group I as diabetic patients without any complications (60 diabetic patients); group II diabetic patients with complications (60 diabetic patients). Complications in the diabetic patients included coronary artery disease, diagnosed by clinical symptoms of angina pectoris, electrocardiogram examination or documented myocardial infarction. All diabetic patients received oral hypoglycemic agents like sulphonylureas or metformin. Diabetic patients with coronary artery disease were treated by calcium antagonists.Exclusion criteria were smoking, antioxidant/vitamin supplementation, anti-aggregatory drugs and insulin treatment. Hypolipidemic drugs (statins and fibrates)treatment was suspended for 7 days before venipuncture. Control subjects were in good health as assessed by medical history andexclusion criteria were any pathology including diabetes. Written informed consent was obtained from all participants and the study was approved by the local ethics committee.

Following biochemical parameters were taken for this study:



Glycosylated hemoglobin (HbA1c) level was determined. [13] Fasting blood sugar and lipid profile were measured by standard kits on autoanalyser (Biosystem).Isolation of LDL

LDL was isolated byheparin citrate method. [14] Briefly 5 ml 0.064M Na citrate buffer, pH 5.04 with 50, 000 IU/l heparin was mixed with 0.5 ml of serum, vertexed and centrifuge at 1000 g for 10 minute. The supernatant was removed and LDL precipitate was dissolved in 1 ml 1% triton ×100.

Determination of LDL oxidation sensitivity

The LDL oxidation was determined by measuring MDA (malondialdehyde) in isolated LDL. [15] This is basal MDA level. Then again MDA was determined by using same method in copper induced LDL samples. For this LDL samples were incubated at 37°C with CuSO 4 (1 mM). MDA levels were used as an indicator of free radical generation which was increased at the end of lipid peroxidation. The difference between induced and basal MDA levels were used to evaluate sensitivity to oxidation of the samples and results were expressed as nmol/ml. [16]

Statistical analysis

Significance of values was calculated with SPSS 16.0 softwareusing one way analysis of variance (ANOVA). The Pearson's correlation coefficient test was performed by PASW 18.0 (SPSS) software to determine correlation among risk factors.

 Results



In the present study significant differences were found between diabetic groups and controls group in which fasting blood glucose and HbA1c levels were higher (P < 0.001)in both diabetic groups regardless to complications [Table 1]. HDL-C was significantly decreased (P < 0.001) only in group II as compared to group I and control subjects [Table 1]. TG level was also significantly changed in both diabetic groups as compared to control group [Table 1]. LDL-C level was significantly higher (P < 0.001) only in group II diabetic subjects [Table 1]. In this study the sensitivity of LDL to oxidation was significantly increased (P<0.05) in group I and highly significantly increased (P < 0.001)in group IIdiabetic subjects as compared to control subjects [Table 2].Positive correlation of Hba1c with LDL oxidation sensitivity was found significantly (P < 0.05) in group I diabetic subjects and highly significantly (P < 0.01)in group IIdiabetic subjects [Table 3].{Table 1}{Table 2}{Table 3}

 Discussion



Recent evidences suggest that diabetic patients are under oxidative stress and that complications of diabetes seem to be mediated by oxidative stress. [17] However, the relationships between free radical production, antioxidant levels, lipoprotein oxidation, glycemic control and the presence or absence of diabetic complications are still unclear. In our study, increased LDL oxidizability was observed in type 2 diabetic patients, regardless any complications, in favor of an oxidative stress in such patients. [18],[19] Previous data have demonstrated a strong association between poor glycemic control and the depletion of protective antioxidant defense in diabetes mellitus. [20],[21] In our study, all diabetic patients were poorly controlled, as indicated by their high glucose and HbA1C levels. The positive correlation between HbA1C and LDL oxidizability was consistent with the idea that persistent hyperglycemia may increase oxidation of LDL. Previous studies provide evidence for the role of LDL glycation in its increased in vitro oxidation. [2] It is then possible that poor glycemic control may account for the elevated LDL oxidation sensitivity in our diabetic patients. However, our findings show that in diabetes, even in the absence of complications, depletion in antioxidant defenses due to hyperglycemia induced oxidative stress might also be responsible for increased sensitivity to LDL oxidation. In the presence of complications, lipid alterations were seen and could influence the susceptibility of LDL to oxidation. Diabetic patients with complications had higher TG, LDL-C, and lower HDL-C concentrations than those without complications and controls, in agreement with previous reports. [22] Oxidation of LDL induces LDL-C accumulation. [23],[24] High levels of cholesterol activate thrombocytes and cause the release of substances that activate phospholipase A2. Hence, accumulated arachidonic acid may be metabolized to leukotrienes, thromboxanes, prostaglandins and malonaldehyde. During this metabolism, oxygen radicals may be produced, and under insufficient antioxidant capacity, these radicals may also trigger lipid peroxidation, increasing susceptibility of LDL to oxidation. Hypertriglyceridemia induced changes in LDL size and LDL oxidizability. [25] As HDL inhibits the oxidative modification of LDL, [26] its reduction in diabetic patients could influence the susceptibility of LDL to oxidation.

In conclusion, the present study demonstrated that patients with diabetes had increased sensitivity to LDL oxidation and it was closely related to poor glycemic control. Improvement of glycemic control is then a beneficial factor to decrease oxidative stress and LDL atherogenicity in diabetic patients. The clinical approach of this study is that determination of LDL oxidation sensitivity help in prevention of vascular complications in diabetic subjects. Therefore, regular diet, improvement of glycemic control and antioxidant intake in diabetic patient could maintain antioxidant defense and reduce oxidative stress.

References

1Maritim AC, Sanders RA, Watkins JB 3 rd . Diabetes, oxidative stress, and antioxidants: A review. J BiochemMolToxicol 2003;17:24-38.
2Bonnefont-Rousselot D, Bastard JP, Jaudon MC, Delattre J. Consequences of the diabetic status on the oxidant/antioxidant balance. Diabetes Metab 2000;26:163-76.
3Gökkusu C, Palanduz S, Ademoðlu E, Tamer S.Oxidant and antioxidant systems in niddm patients: Influence of vitamin E supplementation. Endocr Res 2001;27:377-86.
4Surekha RH, Madhavi G, Ramachandra RV, Sahay VK, Jyothy A. Risk factors for coronary heart disease in Type II diabetes mellitus. IJCB. 2005;20:75-80.
5VanderJagt DJ, Harrison JM, Ratliff DM, Hunsaker LA, Vander Jagt DL. Oxidative stress indices in IDDM subjects with and without long-term diabetic complications. ClinBiochem 2001;34:265-70.
6Ahmed N. Advanced glycationendproducts-role in pathology of diabetic complications. Diabetes Res ClinPract 2005;67:3-21.
7Courderot-Masuyer C, Lahet JJ, Verges B, Brun JM, Rochette L. Ascorbyl free radical release in diabetic patients. Cell MolBiol (Noisy-le-grand) 2000;46:1397-401.
8Vergès B. New insight into the pathophysiology of lipid abnormalities in type 2 diabetes. Diabetes Metab 2005;31:429-39.
9Beckman JA, Creager MA, Libby P. Diabetes and atherosclerosis: Epidemiology, pathophysiology, and management. JAMA 2002;287:2570-81.
10Scheffer PG, Bos G, Volwater HG, Dekker JM, Heine RJ, Teerlink T. Associations of LDL size with in vitro oxidizability and plasma levels of in vivo oxidized LDL in Type 2 diabetic patients. Diabet Med 2003;20:563-7.
11Scheffer PG, Henry RM, Wever EJ, van Rooij GJ, Bos G, Heine RJ, et al. LDL oxidative modifications in well-or moderately controlled type 2 diabetes. Diabetes Metab Res Rev 2004;20:298-304.
12Feillet C, Roche B, Tauveron I, Bayle D, Rock E, Borel P, et al. Susceptibility to oxidation and physicochemical properties of LDL in insulin-dependent diabetics. Atherosclerosis 1998;136:405-7.
13Rai KB, Pattabiraman TN. Glycosylated haemoglobin levels in iron deficiency anaemia. Indian J Med Res 1986;83:234-6.
14Wieland H, Seidel D. A simple specific method for precipitation of low density lipoproteins. J Lipid Res 1983;24:904-9.
15Dousset JC, Trouilh M, Foglietti MJ. Plasma malonaldehyde levels during myocardial infarction. ClinChimActa 1983;129:319-22.
16Scoccia AE, Molinuevo MS, McCarthy AD, Cortizo AM. A simple method to assess the oxidative susceptibility of low density lipoproteins. BMC ClinPathol 2001;1:1472-8.
17West IC. Radicals and oxidative stress in diabetes. Diabet Med 2000;17:171-80.
18Shimada K, Mokuno H, Matsunaga E, Miyazaki T, Sumiyoshi K, Kume A, et al. Predictive value of circulating oxidized LDL for cardiac events in type 2 diabetic patients with coronary artery disease. Diabetes Care 2004;27:843-4.
19Liguori A, Abete P, Hayden JM, Cacciatore F, Rengo F, Ambrosio G, et al. Effect of glycaemic control and age on low-density lipoprotein susceptibility to oxidation in diabetes mellitus type 1. Eur Heart J 2001;22:2075-84.
20Merzouk S, Hichami A, Madani S, Merzouk H, Berrouiguet AY, Prost J, et al. Antioxidant status and levels of different vitamins determined by high performance liquid chromatography in diabetic subjects with multiple complications. Gen PhysiolBiophys 2003;22:15-27.
21Maxwell SR, Thomason H, Sandler D, Leguen C, Baxter MA, Thorpe GH, et al. Antioxidant status in patients with uncomplicated insulin-dependent and non-insulin-dependent diabetes mellitus. Eur J Clin Invest 1997;27:484-90.
22Taskinen MR. Diabetic dyslipidaemia: From basic research to clinical practice. Diabetologia 2003;46:733-49.
23Holvoet P, Collen D. Oxidation of low density lipoproteins in the pathogenesis of atherosclerosis. Atherosclerosis 1998;137Suppl: S33-8.
24Young IS, McEneny J. Lipoprotein oxidation and atherosclerosis. BiochemSoc Trans 2001;29:358-62.
25Kondo A, Muranaka Y, Ohta I, Notsu K, Manabe M, Kotani K, et al. Relationship between triglyceride concentrations and LDL size evaluated by malondialdehyde-modified LDL. ClinChem 2001;47:893-900.
26Sangvanich P, Mackness B, Gaskell SJ, Durrington P, Mackness M. The effect of high-density lipoproteins on the formation of lipid/protein conjugates during in vitro oxidation of low-density lipoprotein. BiochemBiophys Res Commun 2003;300:501-6.