7-ketocholesterol, a specific indicator of lipoprotein oxidation, and malondialdehyde in non-insulin dependent diabetes and peripheral vascular disease

Higher concentration of 25-hydroxycholesterol in treatment-naïve patients with type 2 diabetes compared to healthy individuals

BACKGROUND

Oxysterols are cholesterol oxidation derivatives with diverse biological activities. However, little is known about the oxysterol levels in treatment-naïve patients with type 2 diabetes.

OBJECTIVE

We utilized gas chromatography-mass spectrometry to investigate the potential association between oxysterol concentrations and type 2 diabetes and atherosclerosis in treatment-naïve patients diagnosed with type 2 diabetes.

METHODS

This case-control study enrolled 53 eligible patients with type 2 diabetes and 50 healthy volunteers. We compared serum oxysterol concentrations between the two groups; we examined the correlation between the oxysterol concentrations and the carotid plaque score in the type 2 diabetes group.

RESULTS

Univariate analysis revealed significant differences in the concentrations of oxysterols (i.e., cholesterol-5α, 6α-epoxide; cholesterol-5β, 6β-epoxide; 7β-hydroxycholesterol; and 25-hydroxycholesterol [25-HC]) and other cardiovascular risk factors between the two groups. The 25-HC concentration was almost twofold greater in the type 2 diabetes group than in the healthy volunteers (median [interquartile range]: 8.52 [6.37-11.26] vs. 4.58 [3.45-5.44] ng/mL). After adjusting for multiple covariates, such as age, body mass index, mean arterial pressure, and triglyceride, low-density lipoprotein-cholesterol, and high-density lipoprotein-cholesterol levels, only the concentration of 25-HC showed a significant association with type 2 diabetes. However, the univariate analysis failed to demonstrate any significant correlation between oxysterol concentrations and the carotid plaque score among individuals with type 2 diabetes.

CONCLUSIONS

The levels of various oxysterols differ between treatment-naïve patients with type 2 diabetes and healthy individuals; the 25-HC level differs the most prominently.

A Comprehensive Review on Oxysterols and Related Diseases

The present review aims to provide a complete and comprehensive summary of current literature relevant to oxysterols and related diseases. Oxidation of cholesterol leads to the formation of a large number of oxidized products, generally known as oxysterols. They are intermediates in the biosynthesis of bile acids, steroid hormones, and 1,25- dihydroxyvitamin D3. Although oxysterols are considered as metabolic intermediates, there is a growing body of evidence that many of them are bioactive, and their absence or excess may be part of the cause of a disease phenotype. These compounds derive from either enzymatic or non-enzymatic oxidation of cholesterol. This study provides comprehensive information about the structures, formation, and types of oxysterols even when involved in certain disease states, focusing on their effects on metabolism and linkages with these diseases. The role of specific oxysterols as mediators in various disorders, such as degenerative (age-related) and cancer-related disorders, has now become clearer. Oxysterol levels may be employed as suitable markers for the diagnosis of specific diseases or in predicting the incidence rate of diseases, such as diabetes mellitus, Alzheimer's disease, multiple sclerosis, osteoporosis, lung cancer, breast cancer, and infertility. However, further investigations may be required to confirm these mentioned possibilities.

Hydroxysteroid sulfotransferase 2B1 affects gastric epithelial function and carcinogenesis induced by a carcinogenic agent

Background

A healthy gastric mucosal epithelium exhibits tumor-suppressive properties. Gastric epithelial cell dysfunction contributes to gastric cancer development. Oxysterols provided from food or cholesterol oxidation in the gastric epithelium may be further sulfated by hydroxysteroid sulfotransferase 2B1 (SULT2B1), which is highly abundant in the gastric epithelium. However, the effects of SULT2B1 on gastric epithelial function and gastric carcinogenesis are unclear.

Methods

A mouse gastric tumor model was established using carcinogenic agent 3-methylcholanthrene (3-MCA). A SULT2B1 deletion (SULT2B1^−/−) human gastric epithelial line GES-1 was constructed by CRISPR/CAS9 genome editing system.

Results

The gastric tumor incidence was higher in the SULT2B1^−/− mice than in the wild-type (WT) mice. In gastric epithelial cells, adenovirus-mediated SULT2B1b overexpression reduced the levels of oxysterols, such as 24(R/S),25-epoxycholesterol (24(R/S),25-EC) and 27-hydroxycholesterol (27HC). This condition also increased PI3K/AKT signaling to promote gastric epithelial cell proliferation, epithelization, and epithelial development. However, SULT2B1 deletion or SULT2B1 knockdown suppressed PI3K/AKT signaling, epithelial cell epithelization, and wound healing and induced gastric epithelial cell malignant transition upon 3-MCA induction.

Conclusions

The abundant SULT2B1 expression in normal gastric epithelium might maintain epithelial function via the PI3K/AKT signaling pathway and suppress gastric carcinogenesis induced by a carcinogenic agent.

Enhanced Angiotensin II type 1 receptor expression in leukocytes of patients with chronic kidney disease

Previously, we demonstrated increased Angiotensin II type I receptor expression in leukocytes from patients with untreated, but not in treated, essential hypertension (essential hypertension). We hypothesized that the Angiotensin II AT1 receptor is also increased in leukocytes from patients with chronic kidney disease, however and can still be corrected with combined anti-hypertensive treatment with renin-angiotensin system (RAS) blockers and statins. Blood pressure, cholesterol, renal function oxidative stress parameters, inflammation, and leukocyte Angiotensin II AT1 receptor mRNA expression were measured both on and (6 weeks) off treatment. Data were compared to data of 10 healthy control subjects. Untreated chronic kidney disease patients (n=20) had higher blood pressure, cholesterol and leukocyte Angiotensin II AT1 receptor mRNA expression, but no different ox-LDL, thiobarbituric acid reactive substances, paraoxonase activity or hs-CRP. OxLDL and Lipoprotein(a) were increased in untreated chronic kidney disease. Angiotensin II AT1 receptor expression inversely correlated with renal function (R(2)=0.15, P<0.03) and Lipoprotein(a) but not with the other parameters. Treatment with RAS blockers and statins normalized blood pressure and cholesterol, however it did not correct enhanced leukocyte Angiotensin II AT1 receptor expression. Leukocyte Angiotensin II AT1 receptor expression is inappropriately high in chronic kidney disease, correlates inversely with renal function and does not depend on antihypertensive and lipid-lowering treatment. The uremic environment seems to dominate over previously reported actions of high blood pressure and cholesterol to enhance leukocyte Angiotensin II AT1 receptor expression.

8-Hydroxy-2-deoxy-guanosine identifies oxidative DNA damage in a rural prediabetes cohort

BACKGROUND

Rising levels of oxidative stress play an important role in the pathogenesis of type 2 diabetes mellitus. Therefore, we investigated the serum level of 8-hydroxy-2-deoxy-guanosine (8-OHdG) as an early oxidative stress marker in patients with prediabetes and with type 2 diabetes mellitus.

SUBJECTS AND METHODS

Convenience sampling from people attending a diabetes screening clinic. Participants at the rural diabetes screening clinic had their medical history recorded as well as body mass index, blood glucose, cholesterol, glutathione, malondialdehyde, fasting blood glucose and 8-OHdG measured. Statistical analysis was performed using ANOVA followed by Sheffe posthoc test for between-group differences.

RESULTS

The 8-OHdG level was significantly greater in the prediabetes (516.5 +/- 260 pg/ml) compared to control group (177.8 +/- 91 pg/ml; P < 0.01). The diabetes group (1926.9 +/- 1197 pg/ml) had the highest level of 8-OHdG, being approximately four times greater compared to the prediabetes group (P < 0.001). No significant change in the cholesterol profile, MDA level indicative of lipid peroxidation and antioxidant activity as measured by erythrocyte reduced glutathione was observed in the prediabetes group compared to the control group (P > 0.05).

CONCLUSIONS

8-OHdG levels in both the prediabetes and diabetes group were increased from control values suggesting a role for 8-OHdG as an early disease marker that may be more sensitive compared to cholesterol, MDA and erythrocyte reduced glutathione levels, which were within normal limits. This is of clinical significance as 8-OHdG is a strong indicator of oxidative stress related DNA damage within blood vessel walls and other tissue that increases the risk of cardiovascular disease.

Cholesterol, Linoleic Acid or/and Tyrosine Yield Different Spectra of Products when Oxidized Alone or in a Mixture: Studies in Various Oxidative Systems

Identification of reliable biomarkers for oxidative stress for the prediction of the early development of pathological conditions is essential. The detection of biomarkers for oxidative stress such as degradation products of polyunsaturated fatty acid (PUFA), oxysterols, and oxidized proteins, as indicators of oxidative stress are in use, but suffers from insufficient specificity, accuracy and reliability. The overall aim of the present study was to develop new markers which will not only provide information about the presence and level of oxidative stress in biological systems but also on the type of reactive oxygen species (ROS) involved and their metabolic consequences. In the first stage of the study, we compared the level and type of oxidized products formed when different ROS were applied onto three major biomolecules, i.e. cholesterol, linoleic acid (LH) and tyrosine, representing sterols, PUFA and protein, when each compounds was exposed alone or in a mixture to the ROS [copper ions, 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH) and hypochlorous acid (HOCl)]. It was found that different types of oxidants resulted in the formation of different types of oxidation products. Furthermore, oxidation pattern differs when the substrates (cholesterol, PUFA or amino acid) were present alone or in a mixture. As biological systems such as lipoproteins and cell membranes are composed of the above studied molecules, the need for simultaneous detection of the major oxidized products is requires for better characterization of the oxidative stress outcome.

Characterization of oxidative stress in blood from diabetic vs. hypercholesterolaemic patients, using a novel synthesized marker

In the present study, we extend our novel concept of designing and using exogenous markers for the characterization of oxidative stress (OS) and OS-associated diseases. The aim was to use such a synthetic compound as a tool for studying OS in blood from diabetic and hypercholesterolaemic (Hc) patients. The marker used N-linoleoyl tyrosine (LT) was constructed from tyrosine and linoleic acid (LA); both components are known to be easily oxidized upon exposure to different types of reactive oxygen/nitrogen species (ROS/RNS), and to generate specific oxidized products, depending on the type of oxidants present in vivo. Using the LT probe, we showed that the ratios of oxidized LT to total LT (Ox-LT/LT) is significantly higher in blood samples obtained from diabetic patients, than in Hc patients or healthy control subjects. LC/MS analysis revealed that blood from diabetic patients oxidizes the marker with predominant formation of Ox-LT hydroperoxide (LT-OOH) and epoxide (epoxy-LT), where the LA moiety is oxidized to hydroperoxide and to epoxide, respectively. Analysis of oxysterol levels in these samples (GC/MS) revealed that the blood of both diabetic and Hc patients contained significantly more oxysterols than blood of control subjects. Consumption of pomegranate juice by diabetic patients for 3 months suppressed their blood capacity to oxidize the LT and similarly also reduced their blood oxysterol/total cholesterol ratio by 93%. The use of an exogenous marker to characterize OS in blood samples yields important information on the extent of OS, and can provide a fingerprint for the early identification of different pathological conditions associated with OS.

An Evaluation of the Clinical Evidence on the Role of Inflammation and Oxidative Stress in Smoking-Mediated Cardiovascular Disease

The number of fatalities due to cardiovascular disease (CVD) continues to be far ahead of loss of human life caused by any other type of disease worldwide. According to the WHO, the annual global tobacco death toll is already 8.4 million and will reach 10 million by the year 2025. However, in contrast to other modifiable primary risk factors for CVD such as obesity, primary prevention strategies for smokers unable to quit are not available to date. This Review, by adopting the principles of evidence-based medicine, summarizes the most recent clinical studies on CVD in smokers, and concludes by suggesting a novel primary prevention strategy for CVD in smokers unable to quit. Evidence gathered from mechanistic studies involving basic research as well as large population-based approaches point to oxidative stress as the major insult imposed by cigarette smoke (CS), and a state of systemic inflammation, as signified by increased hs (high sensitivity) CRP levels in smokers, as the decisive pro-atherogenic response of the body to the initial insult. Since we identified oxidative stress induced by heavy metals as a significant pro-atherogenic activity of CS, strategies aimed at detoxifying heavy metals and combating inflammation appear as plausible approaches to counteract the accelerated onset of CVD in smokers. For this purpose, we discuss metal chelating agents and statins as promising novel primary prevention strategies in smokers unable to quit.

Lack of effect of oral supplementation with antioxidants on cholesterol oxidation product concentration of human plasma, as revealed by an improved gas chromatography method

A gas chromatographic method was successfully applied to determine cholesterol oxidation products (COPs) in human plasma. The linearity, precision, recovery and sensitivity of the method were determined. Oral supplementation with a combination of vitamin E (800 IU), C (1 g) and beta-carotene (24 mg), given for 21 days to 21 patients, did not significantly decrease plasma COP content. No correlations (n = 26) were found between initial plasma COP content and the following parameters: age, body mass index, plasma content of alpha-tocopherol, cholesterol, high-density lipoprotein cholesterol and triglycerides, and fat, natural antioxidant and oxidized lipid intake. Differences in plasma COP content between type 2 diabetic (n = 6) and nondiabetic (n = 20) patients were not statistically significant. The results from this study lead us to hypothesize that the nonenzymatic oxidation of cholesterol in plasma is negligible compared to COPs originating from the diet. This article also includes a comprehensive review of the drawbacks of the analytical methods of COP determination in plasma and serum.

Effects of dietary oxysterols on coronary arteries in hyperlipidaemic hamsters

The aim of this study was to evaluate the effect of dietary oxysterols on coronary atherosclerosis and vasospasm. Golden Syrian hamsters were fed three diets with different lipid contents for 3 months: (1) a normolipidaemic diet containing 25 g corn oil–fish oil (4:1, w/w)/kg (group Low L); (2) a hyperlipidaemic diet composed of the normolipidaemic diet supplemented with 150 g lard+30 g cholesterol/kg (group High L); (3) a third diet, similar to the hyperlipidaemic diet, in which 4 g cholesterol/kg was replaced by a mixture of oxysterols (group High L+OS). The oxysterol mixture contained (g/kg): 5,6α-epoxycholesterol 211, 5,6β-epoxycholesterol 179, 7α-hydroxycholesterol 67, 7β-hydroxycholesterol (7βOH) 185, 7-ketocholesterol (7 K) 235; and trace amounts of 7-hydroperoxycholesterols (approximately 30 g/kg). Atherosclerosis was evaluated by measuring myocardial Ca, oxysterols and acyl-CoA cholesterol acyl transferase (ACAT) activity; furthermore, coronary reactivity to sodium nitroprusside (5×10-6 m) was measured and the morphology of coronary arteries was visualized by transmission electron microscopy. Coronary spasm was determined by evaluating reactivity to serotonin (5×10-6 m). Feeding the high-lipid diet (group High L) increased the plasma level of 7βOH, 7 K and cholestanetriol. The presence of oxysterols in the diet (group High L+OS) further increased the concentrations of 7βOH and 7 K in the plasma. However, as evidenced by myocardial Ca, ACAT activity and coronary reactivity to sodium nitroprusside, severe atherosclerosis did not develop during the 3-month diet. 7 K was increased in myocardial lipids of groups High L and High L+OS. Electron microscopy did not show the development of atherosclerosis in group High L, whereas vascular wall thickening, endothelial damage and smooth muscle cell proliferation and migration occurred when oxysterols were present in the food. Serotonin (5×10-6 m) induced exacerbated coronary vasoconstriction in group High L that was completely reversed by dietary oxysterols. In conclusion, dietary oxysterols exhibit anti-spasmodic properties, but they cannot be used as agents against excess dietary lipid-induced coronary spasm because of their atherogenic properties.

Cholesterol oxides as biomarkers of oxidative stress in type 1 and type 2 diabetes mellitus

BACKGROUND

Oxidative stress plays an important role in the pathophysiology of diabetes mellitus. The aim of this study was to evaluate the formation of cholesterol oxides (ChOx) as biomarkers of oxidative stress in subjects with impaired glucose tolerance (IGT) and diabetes.

METHODS

Blood plasma levels of cholesterol oxidation products were determined in the following groups: type 1 diabetes mellitus (DM1), type 2 diabetes (DM2), impaired glucose tolerance (IGT), children without diabetes (C1) and adults without diabetes (C2). The serum levels of cholest-5-ene-3alpha,7alpha-diol (7alpha-hydroxycholesterol, 7alpha-OH), cholest-5-ene-3beta,7beta-diol (7beta-hydroxycholesterol, 7beta-OH), 3beta-hydroxycholest-5-7-one (7-ketocholesterol, 7-K), 5alpha-cholestane-3beta,5,6beta-triol (cholestanetriol), 5,6alpha-epoxy-5alpha-cholestan-3alpha-ol (cholesterol-5alpha,6alpha-epoxide,), 5,6beta-epoxy-5beta-cholestan-3beta-ol (cholesterol-5beta,6beta-epoxide) and cholest-5-eno-3beta,25-diol (25-hydroxycholesterol, 25-OH) (trivial name and abbreviations indicated in parentheses) were quantified by gas chromatography using flame ionization detection.

RESULTS

The levels of total ChOx were elevated in the DM1 and DM2 groups compared to age-matched subjects without diabetes (p < 0.05). The concentrations of 7beta-hydroxycholesterol, cholesterol-alpha-epoxide and cholesterol-beta-epoxide were higher in the blood plasma of subjects in the DM2 group than in the blood plasma of subjects in the C2 and IGT groups (p < 0.05). Treatment of type 2 diabetic patients with oral hypoglycemic drugs associated with insulin resulted in lower concentrations of nitrotyrosine in the blood plasma without significant changes in the concentrations of glucose and glycated hemoglobin. Moreover, combination with statins in both treatments decreased the concentrations of ChOx.

CONCLUSIONS

ChOx are suitable biomarkers of oxidative stress and may be useful in clinical studies to follow drug effects on lipid oxidative modifications in diabetic patients.

Orange juice ingestion and supplemental vitamin C are equally effective at reducing plasma lipid peroxidation in healthy adult women

OBJECTIVE

To directly examine the contribution of vitamin C to the antioxidant potential of fruits and vegetables, the antioxidant effect of orange juice consumption (8 and 16 fl. oz.) was compared to the antioxidant effect of supplemental vitamin C (dosage equivalent to that supplied by 8 fl. oz. of orange juice).

METHODS

Subjects (n = 11; 28.6 +/- 2.1 years) received each treatment in a 3 x 3 randomized crossover design, and each two-week treatment was preceded by a two-week washout. During the entire trial, subjects restricted fruit and vegetable consumption to < or =3 servings per day except the vitamin C-rich foods (items containing >20 mg/serving), which were restricted to < or =3 servings per week. A fasting blood sample was collected at the end of each washout and each treatment period.

RESULTS

Following washouts, plasma vitamin C and lipid peroxidation (plasma TBARS) were similar by treatment group and averaged 25.4 +/- 3.6 micromol/L and 3.82 +/- 0.10 nmol/mL respectively. Plasma vitamin C concentrations were similar following each treatment period, 37.9 +/- 8.1, 45.8 +/- 9.4, and 38.3 +/- 12.4 micromol/L for the 8 and 16 fl. oz. orange juice treatments and the supplement treatment, respectively. All intervention treatments reduced plasma TBARS as compared to pretreatment values: -47% (p = 0.013), -40% (p = 0.083), and -46% (p = 0.015) for the 8 and 16 fl. oz. orange juice treatments and supplement treatment respectively.

CONCLUSIONS

These data indicate that the regular consumption of 8 fl. oz. orange juice or supplemental vitamin C ( approximately 70 mg/day) effectively reduced a marker of lipid peroxidation in plasma.

Activation of microglial poly(ADP-ribose)-polymerase-1 by cholesterol breakdown products during neuroinflammation: a link between demyelination and neuronal damage

Multiple sclerosis (MS) is a chronic demyelinating disease in which it has only recently been suggested that damage to neuronal structures plays a key role. Here, we uncovered a link between the release of lipid breakdown products, found in the brain and cerebrospinal fluid (CSF) of MS patients as well as in experimental autoimmune encephalomyelitis, and neuronal damage mediated by microglial activation. The concentrations of the breakdown product 7-ketocholesterol detected in the CSF of MS patients were capable of inducing neuronal damage via the activation and migration of microglial cells in living brain tissue. 7-ketocholesterol rapidly entered the nucleus and activated poly(ADP-ribose)-polymerase (PARP)-1, followed by the expression of migration-regulating integrins CD11a and intercellular adhesion molecule 1. These findings reveal a novel mechanism linking demyelination and progressive neuronal damage, which might represent an underlying insidious process driving disease beyond a primary white matter phenomenon and rendering the microglial PARP-1 a possible antiinflammatory therapeutic target.

Oxidative Stress and Antioxidant Supplementation in the Management of Diabetic Cardiovascular Disease

The diabetic state confers an increased propensity to accelerated atherogenesis. In addition to the established risk factors, there is evidence for increased oxidative stress in diabetes. Increased oxidative stress is manifested by increased lipid peroxidation, increased F2-isoprostanes, increased nitrotyrosine, and increased DNA damage. Also, in diabetics, there is increased superoxide release. With regard to diabetes, antioxidants such as α-tocopherol, α-lipoate, and ascorbic acid supplementation have been shown to be beneficial. Most importantly, α-tocopherol therapy, especially at high doses, clearly shows a benefit with regard to low-density lipoprotein oxidation, isoprostanes, and monocyte superoxide release. Thus, it appears that, in diabetes, antioxidant therapy could alleviate the increased attendant oxidative stress and emerge as an additional therapeutic modality.

Hypoxanthine plus xanthine oxidase causes profound natriuresis without affecting renal blood flow autoregulation

BACKGROUND

Enhanced superoxide (O2-.) production by xanthine oxidase in ischemia/reperfusion has been implicated in structural damage. The reperfusion phase is accompanied by decreased tubular sodium reabsorption, which has been partly attributed to enhanced action of O2-. In the present study we assessed whether intrarenal increases of O2-. accomplished by concomitant intrarenal hypoxanthine and intravenous xanthine oxidase (HX/XO) infusion would decrease or increase sodium excretion, and whether HX/XO infusion could be responsible for the diminished efficacy of renal blood flow (RBF) autoregulation in ischemia/reperfusion.

METHODS

In the first group of Sprague-Dawley rats, renal sodium handling was measured before and during O2-. infusion. In the second group, renal hemodynamics and RBF autoregulation were assessed.

RESULTS

Intrarenal O2-. infusion dramatically increased urine flow from 14.5 +/- 2.0 microL/min to 46.3 +/- 4.4 microL/min, urinary excretion of sodium (UNaV) from 1.7 +/- 0.4 micromol/min to 8.6 +/- 0.9 micromol/min, and fractional excretion of sodium FENa from 1.2 +/- 0.4% to 7.6 +/- 1.2%. Urinary excretion of thiobarbituric acid reactive substances (TBARS), a measure of lipid peroxidation, increased during HX/XO infusion. These changes were completely reversible. Glomerular filtration rate (GFR) decreased from 1.12 +/- 0.08 during baseline to 0.79 +/- 0.06 during HX/XO (P < 0.05) and tended to increase toward baseline during recovery (0.84 +/- 0.06 mL/min/g kidney weight). HX/XO did not significantly affect mean arterial pressure (MAP). HX/XO decreased RBF in the second group from 8.4 +/- 0.6 mL/min/g kidney weight to 7.4 +/- 0.5 mL/min/g kidney weight (P < 0.05) and renal vascular resistance (RVR) slightly increased from 13.8 +/- 0.9 units under baseline conditions to 15.1 +/- 1.1 units during HX/XO infusion (P < 0.05). HX/XO did not significantly affect RBF autoregulation. Proteinuria and glucosuria were absent and light microscopy revealed no renal morphologic changes.

CONCLUSION

Intrarenal O2-. infusion (1) dramatically increased sodium and volume excretion and (2) did not affect autoregulation of RBF. Thus, superoxide can markedly affect glomerulotubular balance by diverging actions on renal hemodynamics and reabsorptive function and could mediate the functional tubular consequences of ischemia/reperfusion.

Male gender increases sensitivity to renal injury in response to cholesterol loading

Males are at greater risk for renal injury than females. This may relate to nitric oxide (NO) availability, because female rats have higher renal endothelial NO synthase (NOS) levels. Previously, our laboratory found susceptibility to proteinuria induced by NOS inhibition in male compared with female rats. Dyslipidemia and hypercholesterolemia dose dependently decreased renal NOS activity and caused renal injury in female rats. We hypothesized that exposure of male rats to hypercholesterolemia would lead to more renal injury in male than in female rats due to an a priori lower renal NO system. Female and male rats were fed no, low-dose, or high-dose cholesterol for 24 wk. Cholesterol feeding dose dependently increased proteinuria in both female and male rats, but male rats developed more proteinuria at similar plasma cholesterol (P < 0.001). Control males had lower renal NOS activity than control females (4.44 +/- 0.18 vs. 7.46 +/- 0.37 pmol. min(-1). mg protein(-1); P < 0.05), and cholesterol feeding decreased renal NOS activity in males and in females (P < 0.05). Cholesterol-fed males developed significantly more vascular, glomerular, and tubulointerstitial monocyte/macrophage influx and injury than females. Thus under baseline conditions, male rats have lower renal NOS activity than female rats. This may explain why male rats are more sensitive to renal injury by factors that decrease NO availability, such as hypercholesterolemia.

Neurovascular disease, antioxidants and glycation in diabetes

People with diabetes are ten to fifteen times more likely to have a lower limb amputation (LLA) than non-diabetic individuals. Fifteen percent of people with diabetes will develop a foot ulcer during their lifetime, the rate of major amputation amongst diabetic individuals continues to rise, foot problems remain the commonest reason for diabetes-related hospitalisation and recurrence rates in patients with previous foot ulcers are 50% or more. Hyperglycaemia-induced oxidative stress has been shown to result in decreased nerve conduction velocity, and decreased endoneural blood flow-both precursors for neuropathy. Vitamin antioxidants have been shown to be effective therapy in experimental models in reducing free radical species and inhibiting the oxidative process in diabetes subjects. Little work has been published, however, regarding the dietary use of antioxidants from foods, and their specific effects on neurovascular disease and glycation within the diabetes population. Aetiological and prevention studies with dietary antioxidants from foods aimed at the complex nature of foot problems in diabetes are needed.

Carotid atherosclerosis in type 2 diabetes mellitus: potential role of endothelin-1, lipoperoxides, and prostacyclin

Factors were studied that may initiate macroangiopathy or enhance or aggravate its pathogenesis in patients with type 2 diabetes mellitus. A total of 151 diabetics were compared with healthy controls (n=50); all patients and subjects were normotensive and without renal failure. Plasma endothelin-1 and free radical levels were measured. In addition, plasma prostacyclin levels were assessed by assaying its stable, spontaneous, breakdown product 6-keto-prostaglandin-F1a. Diabetics were divided into three groups: those with clinically evident macroangiopathy and those with early or without atherosclerosis (as determined by the carotid intima-media thickness. Plasma endothelin-1 levels were increased in all diabetics with atherosclerosis. Plasma free radical levels were increased in diabetics with macroangiopathy when compared with control subjects. The plasma levels of 6-keto-prostaglandin-F1a were slightly, but significantly, decreased in the diabetics with macroangiopathy when compared with control subjects. The carotid intima-media thickness was significantly greater in diabetics without macroangiopathy when compared with the controls. Furthermore, the intima-media thickness increased significantly in this group of diabetics but not in the controls over a 30-month follow-up period. Several factors may contribute to atherogenesis in diabetics. These include increased plasma endothelin-1 and free radical levels as well as a deficiency of prostacyclin. These factors may become targets for intervention as well as markers of disease progression.

Concentration of chosen oxycholesterols in plasma of pregnant women with pregnancy-induced hypertension

Solid-phase extraction (SPE) was applied for isolation of oxycholesterols from plasma lipid extract from pregnant women with hypertension and from a control group. Separation of oxycholesterols fraction was performed in an SD II horizontal chamber (Chromdes, Poland) using silica gel and octadecyl RPC18 silica gel TLC plates (Merck and Machery Nagel). Visualization was carried out under UV light after Liebermann-Burchard reaction specific for cholesterol and its derivatives. The oxycholesterols (5-cholestene-3beta-ol-7-one, sum of 5-cholestene-3beta, 7beta-diol and 5-cholestene-3beta, 7alpha-diol and sum of 5alpha,6alpha-epoxycholestan-3beta-ol and 5beta, 6beta-epoxycholestan-3beta-ol) were quantified by chromatograms scanning in reflectance and fluorescence mode using a CS 9301 densitometer (Shimadzu). The total concentration of the investigated oxycholesterols in the plasma of pregnant women was up to 5000 ng/mL and was statistically significantly higher in women with pregnancy induced hypertension (PIH).

Plasma non-cholesterol sterols

Increased levels of plasma sterols other than cholesterol can serve as markers for abnormalities in lipid metabolism associated with clinical disease. Premature atherosclerosis and xanthomatosis occur in two rare lipid storage diseases, Cerebrotendinous xanthomatosis (CTX) and sitosterolemia. In CTX, cholestanol is present in all tissues. In sitosterolemia, dietary campesterol and sitosterol accumulate in plasma and red blood cells. Plasma accumulation of oxo-sterols is associated with inhibition of bile acid synthesis and other abnormalities in plasma lipid metabolism. Inhibition of cholesterol biosynthesis is associated with plasma appearance of precursor sterols. The increases in non-cholesterol sterols, while highly significant, represent only minor changes in plasma sterols, which require capillary gas-liquid chromatography and MS for effective detection, identification and quantification.

Selective distribution of oxysterols in atherosclerotic lesions and human plasma lipoproteins

The presence of oxidized sterols (oxysterols) in human serum and lesions has been linked to the initiation and progression of atherosclerosis. Data concerning the origin, identity and quantity of oxysterols in biological samples are controversial and inconsistent. This inconsistency may arise from different analytical methods or handling conditions used by different investigators. In the present study, oxysterol levels and distribution were analyzed by an optimized GC-MS method, in human atherosclerotic coronary and carotid lesions, in atherosclerotic apolipoprotein E deficient mice (E degrees mice) and in native and in vitro oxidized human low and high density lipoproteins. Oxysterol levels were analyzed with a limit of detection of 0.06 - 0.24 ng, with 25-hydroxycholesterol (25-OH) being the least sensitive. In human coronary and carotid lesions, obtained from endatherectomic samples, 27-hydroxycholesterol (27-OH) was the major oxysterol, with about 85% as sterols esterified to fatty acids. While total cholesterol and oxysterols levels were similar in both kinds of human lesions, oxysterol distribution was significantly different. In coronary lesions the mean levels of 27-OH and 7beta-hydroxycholesterol (7beta-OH) were 38% and 20% of total oxysterols, whereas in carotid lesions their mean levels were 66% and 5%, respectively. Unlike in human aortic lesions, 27-OH was entirely absent in E degrees mice, whereas the level of 7alpha-hydroxycholesterol (7alpha-OH) was 28% of the total oxysterols, vs. 5% in human coronary lesions. As 27-OH is an enzymatic product of cholesterol oxidation, this finding may indicate that such an enzymatic process does not take place in E degrees mice.

The role of oxidative stress in the onset and progression of diabetes and its complications: a summary of a Congress Series sponsored by UNESCO-MCBN, the American Diabetes Association and the German Diabetes Society

This review summarises the results and discussions of an UNESCO-MCBN supported symposium on oxidative stress and its role in the onset and progression of diabetes. There is convincing experimental and clinical evidence that the generation of reactive oxygen species (ROI) is increased in both types of diabetes and that the onset of diabetes is closely associated with oxidative stress. Nevertheless there is controversy about which markers of oxidative stress are most reliable and suitable for clinical practice. There are various mechanisms that contribute to the formation of ROI. It is generally accepted that vascular cells and especially the endothelium become one major source of ROI. An important role of oxidative stress for the development of vascular and neurological complications is suggested by experimental and clinical studies. The precise mechanisms by which oxidative stress may accelerate the development of complications in diabetes are only partly known. There is however evidence for a role of protein kinase C, advanced glycation end products (AGE) and activation of transcription factors such as NF kappa B, but the exact signalling pathways and the interactions with ROI remain a matter of discussion. Additionally, results of very recent studies suggest a role for ROI in the development of insulin resistance. ROI interfere with insulin signalling at various levels and are able to inhibit the translocation of GLUT4 in the plasma membrane. Evidence for a protective effect of antioxidants has been presented in experimental studies, but conclusive evidence from patient studies is missing. Large-scale clinical trials such as the DCCT Study or the UKPDS Study are needed to evaluate the long-term effects of antioxidants in diabetic patients and their potential to reduce the medical and socio-economic burden of diabetes and its complications.

7-Ketocholesterol delivered to mice in chylomicron remnant-like particles is rapidly metabolised, excreted and does not accumulate in aorta

Cholesterol oxidation products (oxysterols) have been implicated in atherogenesis due to their presence in atherosclerotic tissue and their potent effects in vitro. One of the major oxysterols currently of interest is 7-ketocholesterol (7K) and it has been suggested that the diet is an important source of this oxysterol. This investigation tested the hypothesis that 7K, delivered in a physiologically relevant vehicle, chylomicron remnant-like emulsion (CMR), would be metabolised and excreted by mice in a similar manner and to a similar extent as previously observed in rats when delivered in a chemically modified lipoprotein, acetylated low-density lipoprotein (acLDL). Indeed, the metabolism of 14C-7K delivered in CMR mirrored that of acLDL and was much more rapid than (3)H-cholesterol delivered simultaneously. The 7K-derived (14)C was cleared from the liver, appeared in the intestine and was excreted in the faeces. A substantial proportion of the 7K-derived (14)C in the intestine and faeces was aqueous-soluble, indicating metabolism to polar products, presumably bile acids. Moreover, while cholesterol-derived (3)H increased in the aorta, (14)C appeared transiently and there was no observable accumulation within 24 h. The data confirm our previous findings of rapid hepatic metabolism of 7K when delivered in acLDL and demonstrate that 7K delivered in a vehicle of dietary significance is similarly metabolised and excreted. Indeed, the data encourage further investigation into the contribution that dietary oxysterols may or may not make to atherogenesis.

Comparative analysis of plasma and erythrocyte 7-ketocholesterol as a marker for oxidative stress in patients with diabetes mellitus

OBJECTIVES

To reveal increased lipid peroxidation in diabetics by quantification of cholesterol oxidation products (COPs) not only in plasma, but also in erythrocytes.

DESIGN AND METHODS

We quantified 7-ketocholesterol (7-kCho) by gas chromatography-mass spectrometry as a surrogate measure for COPs. These assays were performed on both plasma and erythrocytes in 20 control subjects and 20 treated patients with relatively poorly controlled Type 2 diabetes.

RESULTS

Both plasma and erythrocyte 7-kCho levels in diabetics were significantly higher than those in control subjects. Although neither plasma nor erythrocyte 7-kCho levels were associated with markers for glucose tolerance in diabetics, a negative correlation of serum HDL-cholesterol levels with erythrocyte, but not plasma, 7-kCho levels was found.

CONCLUSION

Increased oxidative stress in diabetics affects oxidation of cholesterol. Assays of COPs not only in plasma, but also in erythrocytes, may yield complementary information in lipid peroxidation.

Analysis of 7-ketocholesterol in low density lipoprotein and fatty acid composition in erythrocyte membranes of patients on maintenance hemodialysis and healthy controls

We established a method to quantify 7-ketocholesterol (7-KC) in low density lipoprotein by using the heparin-citrate method and gas chromatography-mass spectrometry. We examined the concentration of 7-ketocholesterol in LDL using this method to assess the pathological conditions in uremic patients with hemodialysis and healthy controls. We also examined the fatty acid composition in erythrocyte membranes to estimate the modification of biological membranes. We showed that the concentrations of 7-KC/cholesterol in LDL were significantly increased in hemodialysis patients compared to healthy controls (3.68+/-0.45 vs. 2.41+/-0.19, P<0.05) and the ratio of polyunsaturated fatty acids to saturated fatty acids in erythrocyte membranes was significantly decreased in hemodialysis patients compared to healthy controls (0.499+/-0.014 vs. 0.655+/-0. 017, P<0.001). There was no significant difference in 7-KC concentration in LDL or fatty acid composition in erythrocyte membranes between pre- and post-intervention of hemodialysis. We concluded that hemodialysis patients are under oxidative stress, which modifies LDL and erythrocyte membranes and we speculated these modifications may participate in the process of atherosclerosis. We believe that the method to quantify 7-KC in this study is concise and reliable and may be used to investigate various diseases.

Oxidized monocyte-derived macrophages in aortic atherosclerotic lesion from apolipoprotein E-deficient mice and from human carotid artery contain lipid peroxides and oxysterols

Oxidative stress is thought to play an important role in atherogenesis. The present study demonstrated, for the first time, that macrophages (originally derived from blood monocytes) isolated from aortas of the atherosclerotic apolipoprotein E deficient (E degrees ) mice or from human carotid artery, are oxidized as they contain lipid peroxides and oxysterols. The major oxysterol in arterial macrophages was found to be 7-ketocholesterol (51% of total oxysterols). To find out whether lipid peroxidation of monocytes occurs in vivo already in the blood, we analyzed the oxidative state of monocytes derived from E degrees mice in comparison to monocytes from control mice. Cellular lipid peroxides and total oxysterols were four and sevenfold higher respectively, in monocytes derived from E degrees mice in comparison to monocytes from control mice. The results of the present study thus demonstrated the presence of lipid-peroxidized monocytes already in the blood, which are further oxidized in the arterial wall after their conversion into macrophages. The arterial oxidized macrophages could be considered key contributors to foam cell formation, the hallmark of early atherosclerosis.

alpha-crystallin protects glucose 6-phosphate dehydrogenase against inactivation by malondialdehyde

The present work investigates the effect of malondialdehyde (MDA) binding on the enzymic activity and on some structural properties of glucose 6-phosphate dehydrogenase (G6PD). We studied whether alpha-crystallin could protect the enzyme against MDA damage, and if so, by what mechanism. We also studied whether alpha-crystallin could renature G6PD denatured by MDA. alpha-Crystallin was prepared from bovine lenses by gel chromatography. MDA was freshly prepared and incubated with G6PD with or without alpha-crystallin. The results show that MDA reacted with G6PD non-enzymically causing inactivation at concentrations lower than those used previously on structural proteins. The modified enzyme became fluorescent. alpha-Crystallin, acting as a molecular chaperone, specifically protected the enzyme against inactivation by MDA. The enzyme was not reactivated by alpha-crystallin, but it was stabilised and protected against further denaturation. Complex formation between alpha-crystallin and the modified enzyme was demonstrated by immunoprecipitation. G6PD was very susceptible to MDA and we have shown for the first time that alpha-crystallin is able to protect the enzyme against this damage.

Oxysterols and atherosclerosis

Oxysterols are present in human atherosclerotic plaque and are suggested to play an active role in plaque development. Moreover, the oxysterol:cholesterol ratio in plaque is much higher than in normal tissues or plasma. Oxysterols in plaque are derived both non-enzymically, either from the diet and/or from in vivo oxidation, or (e.g. 27-hydroxycholesterol) are formed enzymically during cholesterol catabolism. While undergoing many of the same reactions as cholesterol, such as being esterified by cells and in plasma, certain oxysterols in some animal and in vitro models exhibit far more potent effects than cholesterol per se. In vitro, oxysterols perturb several aspects of cellular cholesterol homeostasis (including cholesterol biosynthesis, esterification, and efflux), impair vascular reactivity and are cytotoxic and/or induce apoptosis. Injection of relatively large doses of oxysterols into animals causes acute angiotoxicity whereas oxysterol-feeding experiments have yielded contrary results as far as their atherogenicity is concerned. There is no direct evidence yet in humans that oxysterols contribute to atherogenesis. However, oxysterol levels are elevated in human low-density lipoprotein (LDL) subfractions that are considered potentially atherogenic and two recent studies have indicated that raised plasma levels of a specific oxysterol (7beta-hydroxycholesterol) may be associated with an increased risk of atherosclerosis. At the present time there are a number of significant and quite widespread problems with current literature which preclude more than a tentative suggestion that oxysterols have a causal role in atherogenesis. Further studies are necessary to definitively determine the role of oxysterols in atherosclerosis, and considering the wide-ranging tissue levels reported in the literature, special emphasis is needed on their accurate analysis, especially in view of the susceptibility of the parent cholesterol to artifactual oxidation.