Lipid peroxidation in type 2 diabetes: relationship with macrovascular disease?

Evaluation of lipid damage related to pathological and physiological conditions

Several diseases and xenobiotics are known to generate reactive species that may trigger oxidative stress when not properly scavenged by the antioxidant defenses and result in tissue damage. We investigated lipid peroxidation (LPO) as a possible mechanism for tissue damage in some pathologies, in the normal aging process, and in subjects exposed to organic solvents. Plasmatic malondialdehyde (MDA) was quantified by high-performance liquid chromatography with visible wavelength detection in 239 subjects and divided into the following: acute myocardium infarction (AMI), diabetes without complications (D) and hemodialysis (HD) patients; into healthy children, adults, and elderly, all nonexposed to xenobiotics; and into painters occupationally exposed to organic solvents (P). Troponin, glycated hemoglobin, and transminases [aspartate aminotransferase (AST) and alanine aminotransferase] were analyzed. An increase in LPO was observed in AMI, D, HD, and P groups, when compared to healthy adults. No correlation between MDA and age was found. Further, we found positive correlations between MDA versus troponin (r = 0.47), MDA versus HbA1c (r = 0.56), and MDA versus AST (r = 0.41) in AMI, diabetics, and painters, respectively. This work has demonstrated increased lipid and protein damages in myocardium and blood, along with an alteration of hepatic transaminase activities and induction of LPO, suggesting that MDA levels are important to evaluate the extent of tissue alterations and development of acute and chronic conditions.

Pathological aspects of lipid peroxidation

Lipid peroxidation (LPO) product accumulation in human tissues is a major cause of tissular and cellular dysfunction that plays a major role in ageing and most age-related and oxidative stress-related diseases. The current evidence for the implication of LPO in pathological processes is discussed in this review. New data and literature review are provided evaluating the role of LPO in the pathophysiology of ageing and classically oxidative stress-linked diseases, such as neurodegenerative diseases, diabetes and atherosclerosis (the main cause of cardiovascular complications). Striking evidences implicating LPO in foetal vascular dysfunction occurring in pre-eclampsia, in renal and liver diseases, as well as their role as cause and consequence to cancer development are addressed.

Effect of insulin treatment on plasma oxidized LDL/LDL-cholesterol ratio in type 2 diabetic patients

OBJECTIVE

In type 2 diabetes mellitus, oxidized LDL/LDL-Cholesterol ratio, an accurate estimation of in vivo LDL oxidation, has been reported elevated and associated with macrovascular disease. Because insulin therapy induces significant modification of lipid metabolism, in type 2 diabetes, we evaluated the effect of insulin treatment on oxidized LDL/LDL-C ratio in type 2 diabetic patients and analyzed the results in comparison with the modifications induced by insulin on glycaemia, plasma lipids and LDL receptors.

RESEARCH DESIGN AND METHODS

Plasma oxidized LDL concentrations were measured by sandwich ELISA in 21 type 2 diabetic patients before and 3 months after the introduction of insulin therapy, and in 27 age-matched controls.

RESULTS

Type 2 diabetic patients had, compared to controls, significantly increased oxidized LDL/LDL-C ratio (P<0.0001). Three months after insulin treatment, oxidized LDL/LDL-C ratio was significantly reduced (21.1+/-4.7 vs. 24.0+/-5.8 U/mmol, P<0.01). This reduction was strongly associated, in multivariate analysis, with reduction of LDL(TG/cholesterol ratio) (P=0.008), and to a lesser extent with the decrease of LDL fructosamine (P=0.034), but not with the increase of the number of LDL receptors.

CONCLUSIONS

In the present study we demonstrate for the first time a lowering effect of insulin therapy on oxidized LDL/LDL-C ratio in type 2 diabetic patients. This decrease is mainly associated with the reduction of LDL TG-enrichment, and to a lesser extent with the decrease of LDL glycation, but not with the insulin-induced increase in number of LDL receptors.

Differences in LDL oxidizability by glycemic status: the insulin resistance atherosclerosis study

OBJECTIVE

To investigate differences in LDL oxidizability by glycemic status within the Insulin Resistance Atherosclerosis Study cohort.

RESEARCH DESIGN AND METHODS

LDL oxidizability (lag time and oxidation rate) after exposure to copper was compared among 352 subjects with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), newly diagnosed type 2 diabetes, and known type 2 diabetes.

RESULTS

After adjustment for age, clinic, ethnicity, sex, and smoking status, LDL oxidation rates differed by glycemic status (P = 0.001), with a strong trend (P = 0.0001) for reduced LDL oxidation rate with increasing extent and duration of glucose intolerance (2,378 +/- 54, 2,208 +/- 65, 2,145 +/- 71, and 2,115 +/- 48 arbitrary units [mean +/- SE] for NGT, IGT, newly diagnosed type 2 diabetes, and known type 2 diabetes, respectively). Differences in LDL oxidation rate among groups were relatively unaltered by adjustment for lipids and lipoproteins, hypertension, BMI, and waist-to-hip ratio (WHR) and remained significant even after further adjustment for dietary antioxidants and fatty acids, as well as medications. LDL lag times differed marginally by glycemic status (P = 0.058), with similar values for NGT, IGT, and newly diagnosed type 2 diabetes (57-60 min) but higher values for known type 2 diabetes (65 +/- 2). These differences were eliminated by further adjustment for lipids and lipoproteins, hypertension, BMI, and WHR.

CONCLUSIONS

We found that glycemic status influenced LDL oxidizability, with a paradoxical reduction in LDL oxidizability, as indicated by a lower LDL oxidation rate with increased extent and duration of glucose intolerance. This difference was only slightly attenuated by adjustment for relevant demographic, metabolic, dietary, and pharmacological factors that potentially influence LDL oxidation.

Selective neuromicrovascular endothelial cell death by 8-Iso-prostaglandin F2alpha: possible role in ischemic brain injury

BACKGROUND AND PURPOSE

Free radical-induced peroxidation is an important factor in the genesis of hypoxic-ischemic encephalopathy, including that of the preterm infant. Isoprostanes are major peroxidation products. Since microvascular dysfunction seems to contribute to ischemic encephalopathies, we studied the cytotoxicity of 8-iso-prostaglandin F2alpha (PGF2alpha) on cerebral microvascular cells.

METHODS

Microvascular endothelial, astroglial, and smooth muscle cells from newborn brain were cultured. The cytotoxicity of 8-iso-PGF2alpha on these cells was determined by MTT assays and lactate dehydrogenase (LDH) release, propidium iodide incorporation, and DNA fragmentation (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling [TUNEL]). In addition, effects of intraventricular injections of 8-iso-PGF2alpha and possible involvement of thromboxane in 8-iso-PGF2alpha-induced cytotoxicity were determined.

RESULTS

8-Iso-PGF2alpha induced time- and concentration-dependent endothelial cell death (EC50=0.1 nmol/L) but exerted little effect on smooth muscle and astroglial cells; endothelial cell death seemed mostly of oncotic nature (propidium iodide incorporation and LDH release). Cell death was associated with increased endothelial thromboxane A2 (TXA2) formation and was prevented by TXA2 synthase inhibitors (CGS12970 and U63557A); TXA2 mimetics U46619 and I-BOP also caused endothelial cell death. Intraventricular injection of 8-iso-PGF2alpha induced periventricular damage, which was attenuated by CGS12970 pretreatment.

CONCLUSIONS

These data disclose a novel action of 8-iso-PGF2alpha involving TXA2 in oxidant stress-induced cerebral microvascular injury and brain damage.

Effect of atorvastatin on LDL oxidation and antioxidants in normocholesterolemic type 2 diabetic patients

BACKGROUND

Oxidative stress in diabetes increases lipid peroxidation, which stimulates the development of atherosclerosis.

METHODS

We investigated in a 3-month placebo-controlled study with 19 normocholesterolemic type 2 diabetic patients whether treatment with 10-mg atorvastatin influenced antioxidants and reduced LDL oxidizability, assessed by in vitro production of conjugated dienes after copper-induced LDL oxidation.

RESULTS

The lag phase, as a measure of the resistance of LDL to oxidation, did not change (62.8+/-8.2 respectively 59.6+/-9.7 min, p=n.s.), while conjugated dienes decreased (512+/-74 respectively 487+/-50 nmol, p=0.012). Plasma alpha-tocopherol and ubiquinol levels decreased, while their ratios to LDL cholesterol remained stable.

CONCLUSIONS

Atorvastatin favourably influences some parameters of LDL oxidation. Whether this effect is clinically relevant remains to be determined.

Radicals and oxidative stress in diabetes

Recent evidence is reviewed indicating increased oxidative damage in Type 1 and Type 2 diabetes mellitus as well as deficits in antioxidant defence enzymes and vitamins. Mechanisms are considered whereby hyperglycaemia can increase oxidative stress, and change the redox potential of glutathione and whereby reactive oxygen species can cause hyperglycaemia. It is argued that oxygen, antioxidant defences, and cellular redox status should now be regarded as central players in diabetes and the metabolic syndrome.