Autoxidative and antioxidative potential of simple carbohydrates

Donkey whey protein and peptides regulate gut microbiota community and physiological functions of D-galactose-induced aging mice

The prolongation of life span has attracted more and more attention in the current world. Gut microbiota is considered one of the most critical elements and is essential in regulating life span and quality. The effects of donkey whey protein (DWP) and donkey whey hydrolysate (DWPP) on physiological functions and gut microbiota of D-galactose-induced aging mice were investigated to find new strategies for resisting aging. Our results showed that DWP and DWPP could increase the body weight gain velocity, superoxide dismutase (SOD) activity, and thymus index, whereas decrease the level of reactive oxygen species (ROS) and malondialdehyde (MDA), and improve the aging of the body in the liver congestion, oozy draw focal sclerosis of chronic inflammation. The effects of medium and high concentrations of DWP and low and medium concentrations of DWPP were the same as the vitamin C (Vc)-positive control group. It was found that both DWP and DWPP could change α-diversity; the relative abundance of Lactobacillus increased, whereas the relative abundance of Helicobacter and Stenotrophomonas decreased after being treated with DWP and DWPP. The correlation between intestinal microflora and physiological indexes showed that chao1, ACE, and observed species indexes in the α index were positively correlated with weight gain velocity, SOD activity, and thymus index. The relative abundance of Lactobacillus was positively correlated with SOD and thymus index but negatively correlated with MDA. The relative abundance of Stenotrophomonas was opposite to that of Lactobacillus. The Anaerobiospirillum, Fusobacterium, and Dubosiella had a significant positive correlation with the weight gain velocity. The study provided a deeper more profound understanding of the potential use of DWP and DWPP in senescence delays.

Human Health Effects of Lactose Consumption as a Food and Drug Ingredient

Lactose is a reducing sugar consisting of galactose and glucose, linked by a β (1→4) glycosidic bond, considered as an antioxidant due to its α-hydroxycarbonyl group. Lactose is widely ingested through the milk and other unfermented dairy products and is considered to be one of the primary foods. On the other hand, lactose is also considered as one of the most widely used excipients for the development of pharmaceutical formulations. In this sense, lactose has been related to numerous drug-excipient or drug-food pharmacokinetic interactions. Intolerance, maldigestion and malabsorption of carbohydrates are common disorders in clinical practice, with lactose-intolerance being the most frequently diagnosed, afflicting 10% of the world's population. Four clinical subtypes of lactose intolerance may be distinguished, namely lactase deficiency in premature infants, congenital lactase deficiency, adult-type hypolactasia and secondary lactase intolerance. An overview of the main uses of lactose in human nutrition and in the pharmaceutical industry and the problems derived from this circumstance are described in this review.

Structural analysis and antioxidant activity of an arabinoxylan from Malvastrum coromandelianum L. (Garcke)

Malvastrum coromandelianum L. (Garcke) is extensively used in traditional medicinal systems to treat various ailments. In the present study, an alkali-soluble polysaccharide (MAP) was isolated from the leaves of M. coromandelianum in 1.15% (w/w) yield. MAP was composed of l-rhamnose, l-arabinose, d-xylose, d-glucose and d-galactose in a 1.00 : 6.04 : 19.88 : 1.07 : 3.03 molar ratio along with d-glucuronic acid (1.95). Methylation/linkage analysis revealed a backbone of →4)-β-d-Xylp(1→ (30.09 mol%) with a side chain of →3)-α-l-Araf(1→ (15.21 mol%) residues. The structure of MAP was elucidated by a combination of degradative and derivatization techniques, including hydrolysis, alditol acetate derivatization, methylation, GC-MS, partial hydrolysis, ESI-MS and NMR (1D, 2D) spectral analysis. Based on correlation analysis, MAP was found to be an arabinoxylan comprising a backbone of →4)-β-d-linked Xylp(1→ with branching at O-2 by a →3)-α-l-Araf(1→ and →3)-β-d-Xylp(1→ chain. MAP also exhibited ferric ion reducing activity, with a reducing power of 0.914 ± 0.01 (R 2 = 0.972) at 1 mg mL-1 concentration, which showed dose-dependent behavior. MAP can be utilized as a potential antioxidant.

Naturally occurring rare sugars are free radical scavengers and can ameliorate endoplasmic reticulum stress

Because of potential use of naturally occurring rare sugars as sweeteners, their effect on superoxide (SO), hydroxyl and peroxyl radicals and endoplasmic reticulum (ER) stress was examined in human coronary artery endothelial cells. SO generation was measured using the superoxide-reactive probe 2-methyl-6-(4-methoxyphenyl)-3,7-dihydroimidazo[1,2-A]pyrazin-3-one hydrochloride chemiluminescence. Phycoerythrin fluorescence based assay was used to monitor scavenging activity of sugars in the presence of hydroxyl or peroxyl radical generators [CuSO₄ and azobis (2 amidinopropane) hydrochloride respectively]. Measurements were made in relative light units (RLU). ER stress was measured with an ER stress-sensitive secreted alkaline phosphatase (SAP) assay and by Western blot analysis of the expression and phosphorylation of key proteins in the unfolded protein response, namely CHOP47, eIF2α and JNK1. D-Glucose (27.5 mM) increased SO generation (5536 ± 283 vs. 2963 ± 205 RLU in controls; p < 0.0007) and decreased SAP secretion (73411 ± 3971 vs. 101749 ± 7652 RLU in controls; p < 0.005) indicating ER stress. Treatment of cells with 5.5 or 27.5 mM of D-allulose, D-allose, D-sorbose and D-tagatose reduced SO generation (all p < 0.05). This could not be attributed to inhibition of cellular uptake of dextrose by the rare sugars tested. In a cell free system, all four rare sugars had significantly more SO, hydroxyl and peroxyl radical scavenging activity compared to dextrose (all p < 0.01). Treatment of cells with rare sugars reduced ER stress. However, unlike other three rare sugars, D-sorbose did not inhibit tunicamycin-induced eIF2α phosphorylation. Naturally occurring rare sugars are free radical scavengers and can reduce ER stress.

Strecker Aldehyde Formation in Wine: New Insights into the Role of Gallic Acid, Glucose, and Metals in Phenylacetaldehyde Formation

Strecker degradation (SD) leading to the formation of phenylacetaldehyde (PA) was studied in wine systems. New insights were gained by using two full factorial designs focusing on the effects of (1) pH and (2) temperature. In each design of experiments (DoE) three factors, glucose, gallic acid, and metals at two levels (present or absence), were varied while phenylalanine was kept constant. The obtained results gave a clear indication, with statistical significance, that in wine conditions, the SD occurs in the presence of metals preferentially via the phenolic oxidation independent of the temperature (40 or 80 °C). The reaction of the amino acid with the o-quinone formed by the oxidation of the gallic acid seems to be favored when compared with the SD promoted by the reaction with α-dicarbonyls formed by MR between glucose and phenylalanine. In fact, kinetics results showed that the presence of glucose had an inhibitory effect on PA rate of formation. PA formation was 4 times higher in the control wine when compared to the same wine with 10 g/L glucose added. By gallic acid quinone quantitation it is shown that glucose affects directly the concentration of the quinone. decreasing the rate of quinone formation. This highlights the role of sugar in o-quinone concentration and consequently in the impact on Strecker aldehyde formation, a promising new perspective regarding wine shelf-life understanding.

Targeting Select Cellular Stress Pathways to Prevent Hyperglycemia-Related Complications: Shifting the Paradigm

Despite the advances made in preventing complications of diabetes, there is still substantial residual risk. Hence the need for developing new therapeutic agents that target the various facets of the pathogenesis of complications in people with diabetes. Traditionally four general biochemical pathways had been recognized as major contributors to glucotoxicity. These include the polyol pathway, the protein kinase C (PKC) pathway, glycosylation pathway, and oxidative stress. The latter has been proposed as a common impetus of the other pathways of glucotoxicity. More recently, the cross talk between oxidative stress and other recognized cellular stresses such as endoplasmic reticulum (ER), inflammatory, and mitochondrial stresses has emerged as an important additional mechanism of glucotoxicity. The observation that targeting oxidative stress with antioxidants has been associated with unfavorable clinical outcomes and the recognition that in cell cultures antioxidants may aggravate ER stress, suggests that selective targeting of individual cellular stresses may not be sufficient for preventing glucotoxicity. Future efforts should focus on developing therapeutic agents that can ameliorate cellular stress globally by simultaneously targeting the oxidative, ER, mitochondrial, and inflammatory stresses.

Generation of reactive oxidative species from thermal treatment of sugar solutions

Sugars, prominently fructose, have been shown to accelerate the degradation of food components during thermal treatment. Yet, the mechanism by which this occurs is not well understood. Fructose and glucose have been reported to undergo autoxidation to generate reactive oxidative species (ROS) under physiological conditions; however, information on ROS generation during thermal treatment is limited. We observed that hydrogen peroxide was generated during thermal treatment (up to 70 °C) of aqueous solutions of fructose and glucose (up to 10% w/v), with significantly higher concentrations observed in fructose solutions. The rate of generation of hydrogen peroxide increased with temperature, pH, oxygen concentration and the presence of phosphate buffer. Singlet oxygen was also detected in fructose and glucose solutions prepared in phosphate buffer. Results of this study indicated that fructose and glucose undergo oxidation during thermal treatment resulting in generation of ROS that may have deleterious effects on food components.

EPR spectroscopy as a tool for investigation of differences in radical status in wheat plants of various tolerances to osmotic stress induced by NaCl and PEG-treatment

Two kinds of wheat genotypes with different tolerance to osmotic stress (NaCl and PEG-treatment) were investigated with biochemical analyses, including the measurements of total antioxidant capacity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity, reducing power and starch content. The results were compared with electron paramagnetic resonance (EPR) data concerning the nature and amounts of stable long lived radicals present in the control and stressed plants. In addition, the changes in manganese content upon stress conditions were monitored. Different mechanisms of protection against PEG stress in sensitive and tolerant wheat genotypes were postulated. In sensitive genotypes, electrons were created in excess in stress conditions, and were stabilized by polysaccharide molecules, whereas in tolerant genotypes, protection by antioxidants dominated. Moreover, the quinone-semiquinone balance shifted towards semiquinone, which became the place of electron trapping. NaCl-treatment yielded significant effects mainly in sensitive genotypes and was connected with the changes of water structure, leading to inactivation of reactive oxygen species by water molecules.

Oxygen radical scavenging capacity of phenolic and non-phenolic compounds in red and white wines

The aim of the present study was the evaluation of the antioxidant content in phenolic and non-phenolic extracts of ten wine samples, trying to elucidate the potential role of unusual antioxidant compounds. Samples of wines processed from red and white grapes (Vitis vinifera L.), deprived of the volatile fraction at low temperature and buffered at physiological pH, were fractionated by C18 into two fractions: FR1 and FR2. Non-phenolics, such as tartaric, malic, lactic, and succinic acids; glucose; fructose; and glycerin were mainly found in FR1, while polyphenols were present exclusively in FR2. Peroxyl radical quenching was assayed by the ORAC method, while superoxide and hydroxyl radical scavenging activity were assayed by electron paramagnetic resonance. In the ORAC and superoxide assays, most of the activity was found in FR2, while in hydroxyl radical assay, the activity was found in FR1. Model solutions were used to attribute a role to the single compounds in the evaluation of wine’s ROS scavenging capacity: the ORAC and superoxide anion scavenging effects were mainly attributed to the polyphenols, averaging 94.8%, with some contribution from glycerin, particularly in white wines. Unexpectedly, the main chemical responsible for hydroxyl radical scavenging activity was glycerin (56.1%), with the polyphenols scavenging at 18.1%.

The antioxidant paradox in diabetes mellitus

There is ample empiric evidence to indicate that oxidative stress contributes to the pathogenesis of coronary artery disease and has a key role in the onset and progression of diabetes and its complications. Diabetes leads to depletion of the cellular antioxidant defense system and is associated with an increase in the production of free radicals. Oxidative stress can be the result of multiple pathways. Some of these are related to substrate-driven overproduction of mitochondrial reactive oxygen species, advanced glycation end product formation, glucose autoxidation, and depletion of micronutrients and cellular elements with antioxidative properties. There are numerous observational studies in the literature showing a beneficial outcome of the consumption of antioxidant vitamins. However, the interventional trials portray a different picture. The divide between the robust experimental evidence of the pathogenetic role of increased oxidative load in diabetes and the overwhelming failure of antioxidants to show any health benefits in clinical trials may well be characterized as the "antioxidant paradox."

Sugars comparable to glutathione as hemoglobin oxidation protectants during vacuum drying

One of the most significant challenges to stabilization of blood in the dry state is mitigation of hemoglobin oxidation. Here, oxidation of free hemoglobin vacuum desiccated in phosphate-buffered saline alone reached 65%±5%. Arabinose, glucose, sucrose, trehalose, and raffinose at 100 mM were shown to reduce oxidation to 24%±2%, 23%±2%, 3%±1%, 8%±3%, and 7%±2%, respectively. For comparison, 100 mM glutathione allowed 5%±2% hemoglobin oxidation. Oxidation protection provided by glucose, sucrose, and trehalose was shown to increase with concentration between 5 and 100 mM, plateauing thereafter. Oxidation of hemoglobin dried in the presence of 100 mM trehalose was shown to increase with decreasing initial pH.

Malondialdehyde, a lipoperoxidation-derived aldehyde, can bring about secondary oxidative damage to proteins

Lipoperoxidation-derived aldehydes, for example malondialdehyde (MDA), can damage proteins by generating covalent adducts whose accumulation probably participates in tissue damage during aging. However, the mechanisms of adduct formation and their stability are scarcely known. This article investigates whether oxidative steps are involved in the process. As a model of the process, the interaction between MDA and bovine serum albumin (BSA) was analyzed. Incubation of BSA with MDA resulted in rapid quenching of tryptophan fluorescence and appearance of MDA protein adduct fluorescence; transition metal ion traces interfered with the latter process. MDA induced generation of peroxides in BSA, which was preventable with the antioxidant 2,6,-di-tert-butyl-4-methylphenol (BHT). MDA-exposed BSA underwent aggregation, degradation, and BHT-sensitive "gel retardation" effects. Phycoerythrin fluorescence disappearance, a marker of damage mediated by reactive oxygen species, indicated synergism between MDA and metal ions. The interaction between reactive aldehydes and proteins is likely to occur in several steps, some of them oxidative in nature, giving rise to advanced lipoperoxidation end-products, which could participate, with advanced glycation end-products, in the generation of tissue damage during aging.

Characterization of the antioxidant activity of sugars and polyhydric alcohols in fish oil emulsions

Polyols have been incorporated into fish oil emulsions as a means for the inhibition of lipid oxidation and suppression of fishy flavor. However, the role of sugars and polyhydric alcohols as antioxidants has not been clearly established. Selected polyols were evaluated for their performance as antioxidants and modifiers of oxidation pathways in a model system. Oil/water (O/W) emulsions were prepared with freshly steam-deodorized menhaden oil. A layer of emulsion in aluminum pans held at 5 degrees C was exposed to 2550 lx fluorescent lights for 24 h before peroxide values and volatile flavor compounds were analyzed by GC headspace entrainment procedure. Antioxidant activity was confirmed for fructose, sucrose, raffinose, sorbitol, or mannitol when incorporated at 16% of the aqueous phase into model fish oil-in-water emulsions. Peroxide values were suppressed 10-18% in treated samples compared to control samples. Viscosity data did not exclude possible contributions from a restricted oxygen diffusion mechanism in the antioxidant activity, but revealed that emulsion viscosity did not govern fish oil oxidation rates. Combining polyols with phenolic antioxidants (alpha-tocopherol, BHT, or TBHQ) frequently diminished the antioxidant activity compared to that for individual phenolic antioxidants, which was interpreted as indicating that the H-donating activity of phenolic antioxidants was hindered by the H-bonding activity of polyols. A viscosity-based inhibition of the retroaldol conversion of (E,Z)-2,6-nonadienal to (Z)-4-heptenal with a high fructose concentration (67%) was attributed to a restriction of molecular mobility of reactants, but the conversion was only slightly inhibited by the concentration of fructose (16%) used in experimental emulsions. The data supported a hypothesis that either or both free radical scavenging and transition state metal chelation activities were provided by polyols in fish oil emulsions. Also, polyols retarded the water-requiring retroaldol decomposition of (E,Z)-2,6-nonadienal to (Z)-4-heptenal in the model systems and the reaction may be involved in some suppression of fishy flavors in emulsions.

Fenton-dependent damage to carbohydrates: free radical scavenging activity of some simple sugars

The antioxidant properties of simple carbohydrates were studied in a chemical system. Hydroxyl radicals generated by a Fenton reaction induce damage on simple carbohydrates with a consequent free radical scavenging activity. Carbohydrate activities were measured by different methods as spin-trapping of hydroxyl radical and electron paramagnetic resonance detection and 1,1-diphenyl-2-picrylhydrazyl quenching. Carbohydrate damage was evaluated in a Fenton system by measuring the reactive substances to thiobarbituric acid, by their decreased detection with an HPLC test, and by a gas chromatographic determination of formic acid from sugar oxidation. Different intensities of damage and scavenging were found according to molecular structure, and some hyphotheses on the carbohydrate action against free radicals were attempted. The assayed disaccharides were shown to be more active toward and less damaged by hydroxyl radical than monosaccharides.

Antioxidant vitamins and their influence in diabetes mellitus

Diabetes mellitus is a chronic disease associated with serious complications. A number of studies have suggested that enhanced oxidation is the underlying abnormality responsible for some of the complications of diabetes. It is not known whether the ingestion of antioxidant vitamins could retard or perhaps reverse the oxidative damage. The information regarding the benefit of antioxidant vitamin supplementation is conflicting some trials have demonstrated adverse effects of excessive consumption of vitamin supplements. In this article, we review the available literature on the association of cardiovascular events and ingestion of vitamins with antioxidant properties. Given the lack of data to substantiate the benefit and safety of ingestion of antioxidant vitamins in excess of the recommended dietary allowance, physicians should avoid the recommendation of vitamin supplementation to their patients.

Postprandial Hyperglycemia in Patients with Type 2 Diabetes Mellitus

The role of postprandial hyperglycemia (PPHG) in diabetes mellitus is being increasingly recognized. It is known that PPHG contributes to the increased risk of both micro- and macrovascular complications in patients with diabetes mellitus. This review looks at the clinical significance of PPHG and the currently available therapeutic modalities. The causes of PPHG are influenced by many factors which include a rapid flux of glucose from the gut, impaired insulin release, endogenous glucose production by the liver and peripheral insulin resistance. Knowledge of the pathophysiology of PPHG is essential when adopting treatment options to tackle the problem. Although most oral antihyperglycemic agents and insulins lower both fasting and postprandial blood glucose levels, drugs are now available which specifically act to control PPHG. These drugs may be classified based on the site of their action. alpha-Glucosidase inhibitors like acarbose and miglitol attenuate the rate of absorption of sucrose by acting on the luminal enzymes. Adverse effects of these agents are predominantly gastrointestinal. Newer insulin secretagogues have been developed which attempt to mimic the physiological release of insulin and thus ameliorate PPHG. These include third generation sulfonylureas like glimepiride and nonsulfonylurea secretagogues like repaglinide and nateglinide. Rapid-acting insulin analogs, the amino acid sequences of which have been altered such that they have a faster onset of action, help to specifically target PPHG. Pre-mixed formulations of the analogs have also been developed. Finally, drugs under development which hold promise in the management of patients with PPHG include pramlintide, an amylin analog, and glucagon-like peptide-1 and its analogs.

Total antioxidant capacity as a tool to assess redox status: critical view and experimental data

The measure of antioxidant capacity (AC) considers the cumulative action of all the antioxidants present in plasma and body fluids, thus providing an integrated parameter rather than the simple sum of measurable antioxidants. The capacity of known and unknown antioxidants and their synergistic interaction is therefore assessed, thus giving an insight into the delicate balance in vivo between oxidants and antioxidants. Measuring plasma AC may help in the evaluation of physiological, environmental, and nutritional factors of the redox status in humans. Determining plasma AC may help to identify conditions affecting oxidative status in vivo (e.g., exposure to reactive oxygen species and antioxidant supplementation). Moreover, changes in the plasma AC after supplementation with galenic antioxidants or with antioxidant-rich foods may provide information on the absorption and bioavailability of nutritional compounds. Consequently, this review discusses the rationale, interpretation, confounding factors, measurement limits, and human applications of the measure of plasma AC.

2,4-dinitrophenylhydrazine carbonyl assay in metal-catalysed protein glycoxidation

Using an experimental in vitro glycation model, long-term incubations of bovine serum albumin with glucose (fructose) resulted in a significant increase in protein content of 2,4-dinitrophenylhydrazine (DNPH)-reactive carbonyl groups, which could be strongly inhibited by anaerobiosis and metal chelation. The pattern of yields of the protein-bound DNPH was not in accordance with that of the sugar-derived carbonyls determined as the ketoamine Amadori product. In spite of the fact that the contribution of the final advanced glycation end-products to the total DNPH-reactivity of glycation-altered protein remains unclear, the present results stress the need of oxidative steps in formation of most of the DNPH-reactive carbonyl compounds generated by glycation. The results provide evidence that, in protein glycoxidation, the DNPH assay is selective enough to discriminate between protein-bound carbonyls produced by metal-catalysed oxidations and those formed in the early glycation steps.

Drug therapy of postprandial hyperglycaemia

It is widely accepted that the most challenging goal in the management of patients with diabetes mellitus is to achieve blood glucose levels as close to normal as possible. In general, normalising postprandial blood glucose levels is more difficult than normalising fasting hyperglycaemia. In addition, some epidemiological studies suggest that postprandial hyperglycaemia (PPHG) or hyperinsulinaemia are independent risk factors for the development of macrovascular complications of diabetes mellitus. Recently, several drugs with differing pharmacodynamic profiles have been developed which target PPHG. These include insulin lispro, amylin analogues, alpha-glucosidase inhibitors and meglitinide analogues. Insulin lispro has a more rapid onset of action and shorter duration of efficacy compared with regular human insulin. In clinical trials, the use of insulin lispro was associated with improved control of PPHG and a reduced incidence of hypoglycaemic episodes. Repaglinide, a meglitinide analogue, is a short-acting insulinotropic agent which. when given before meals, stimulates endogenous insulin secretions and lowers postprandial hyperglycaemic excursions. Both insulin lispro and repaglinide are associated with postprandial hyperinsulinaemia. In contrast, amylin analogues reduce PPHG by slowing gastric emptying and delivery of nutrients to the absorbing surface of the gut. Alpha-Glucosidase inhibitors such as acarbose, miglitol and voglibose also reduce PPHG primarily by interfering with the carbohydrate-digesting enzymes and delaying glucose absorption. With the availability of agents which preferentially reduce postprandial blood glucose excursions, it is now possible to achieve glycaemic goals in a larger proportion of individuals with diabetes mellitus.

Central nervous system complications of diabetes mellitus--a perspective from the blood-brain barrier

A host of diabetes-related changes in the central nervous system (CNS) has been recognized. The underlying causes of these changes are multiple. An important contributor to the changes in the CNS is the blood-brain barrier (BBB). Diabetes is associated with changes in both the barrier and transport functions of the cerebral microvessels. Structural changes in cerebral microvessels may account for some of the observed changes. Additional mechanisms include alterations in hemodynamic variables such as arteriovenous shunting, changes in biophysical properties and biochemical compositions of the endothelial cells including changes in lipid fluidity and composition, and alterations of neurotransmitter activity in the cerebral microvessels, notably altered beta adrenergic neurotransmission. These observations indicate that the CNS is not immune against the microangiopathic complications commonly found in various tissues of diabetic animals.

The antioxidative potential of cerebral microvessels in experimental diabetes mellitus

To determine if experimental diabetes is associated with decreased antioxidative potential along with increased peroxidation of lipids in cerebral microvessels, streptozotocin-induced diabetic rats were compared with control rats and to diabetic rats treated with insulin. Isolated cerebral microvessels from diabetic rats had significantly higher concentrations of malondialdehyde (MDA; micrograms/mg protein) (0.0283 +/- 0.0017) compared with control (0.0201 +/- 0.0016) or insulin-treated diabetic rats (0.196 +/- 0.0022) P < 0.01. The antioxidative potential was measured in the presence of a peroxy radical generator 2,2'-azobis(2-amidinopropane) (AAPH) and hydroxyl radical generator CuSO4 with monitoring of the fluorescence of phycoerythrin at 37 degrees C. The free radical quenching activity of cerebral microvessels expressed as % inhibition of phycoerythrin oxidation by AAPH was significantly reduced in diabetic rats (38.7 +/- 4.5%) compared with control (54.3 +/- 4.9%) or insulin-treated diabetic rats (57.6 +/- 2.9%) (P < 0.01). The % inhibition of oxidation by cerebral microvessels in the presence of CuSO4 was only 15.7 +/- 3.1% and did not differ significantly in diabetic rats (13.1 +/- 2.1%). The results indicate that antioxidative potential of cerebral microvessels, especially in the presence of peroxy radical generator, is reduced in diabetes along with increased accumulation of lipid peroxidation byproducts. Increased oxidative stress may be one of the many mechanisms underlying the diabetes-related changes in the blood-brain barrier.

Tissue-specific distribution of malondialdehyde modified proteins in diabetes mellitus

A potential mechanism of diabetes-related tissue damage is modification of various proteins by lipid peroxidation by-products such as malondialdehyde (MDA). To determine the extent of MDA derivatization of various proteins in diabetes mellitus, Western blots were carried out using a specific anti-MDA antiserum to study proteins in plasma and various tissues of control and streptozotocin (STZ)-induced diabetic rats. The concentration of MDA-proteins was highest in plasma compared to other tissues tested. Diabetes was associated with a reduction in MDA-protein content of plasma, lung and liver while in the heart, testicle, cerebrum and kidney the MDA-protein concentration was not altered. Insulin treatment of diabetic rats normalized MDA-protein content of plasma but not in the lung or liver. A large interindividual variability in various protein species was observed within a group. This was partly attributed to polymerization of MDA-proteins. It is concluded that although diabetes is associated with increased lipid peroxidation the content of MDA-proteins in plasma and in some tissues is decreased.