Oxidative DNA damage induced by high glucose and its suppression in human umbilical vein endothelial cells

Effect of Repeated Bolus and Continuous Glucose Infusion on DNA Damage and Oxidative Stress Biomarkers in Healthy Male Volunteers

Glucose variability (GV), which describes fluctuations in blood glucose levels within the day, is a phenomenon that is increasingly becoming the target of scientific attention when it comes to increased risk of coronary heart disease. Effects of GV may contribute to the development of metabolic syndrome and type 2 diabetes. Hyperglycemia can lead to oxidative stress resulting in molecular damage due to accumulation of reactive oxygen species (ROS). To discover more about the immediate effects of GV, continuous vs. bolus intravenous glucose administration was applied to 10 healthy men aged 21-30 years over a time frame of 48 h. Whole blood and plasma were analyzed for DNA damage using a comet assay with 3 different treatments (lysis buffer, H2O2, and the lesion-specific enzyme formamidopyrimidine DNA glycosylase (FPG)) as well as for the oxidative stress markers protein carbonyls (PC), unconjugated bilirubin (UCB), and ferric reducing antioxidant power (FRAP). A significant time effect was found in the three DNA damage treatments as well as in PC and UCB possibly due to circadian changes on oxidative stress, but no intervention group effect was observed for any of the markers. In conclusion, bolus vs. continuous glucose administration had no significant acute effect on DNA damage and markers of oxidative stress in healthy men.

Associations of Dietary Intake With Self-Reported Hearing Loss: Findings From the Survey of the Health of Wisconsin

PURPOSE

The purpose of this study was to evaluate associations of dietary intake components with hearing loss.

METHOD

Participants were from the population-based Survey of the Health of Wisconsin. The Block food frequency questionnaire measured dietary intake of carbohydrates, fiber, protein, free (added) sugars, fruits, vegetables, saturated and trans fats, and glycemic index. Intake was categorized into quintiles (Q). Hearing loss was self-reported. Logistic regression models were used to evaluate associations of dietary determinants with hearing loss. Results are presented as odds ratios (ORs) with corresponding 95% confidence intervals (95% CIs). Final models were adjusted for age, sex, total energy intake, race/ethnicity, education, smoking, and regular physical activity.

RESULTS

There were 2,839 participants (56% women; M_age = 48.2 [SD = 14.5] years) included. Higher consumption of trans fat (Q5: OR = 1.83, 95% CI [1.27, 2.64]) and higher glycemic index (Q5: OR = 1.34, 95% CI [1.00, 1.80]) were associated with increased odds of hearing loss. Hearing loss was associated with fruit, saturated- and trans-fat intake in women, and trans-fat intake and glycemic index in men.

CONCLUSIONS

Dietary intake was associated with self-reported hearing loss. Research on mechanistic pathways of associations and public health interventions to prevent hearing loss is needed.

A Narrative Review of Lifestyle Risk Factors and the Role of Oxidative Stress in Age-Related Hearing Loss

Age-related hearing loss affects a significant proportion of adults aged 60 years and above, with a prevalence of 65%. This condition has a negative impact on both physical and mental well-being, and while hearing interventions can help alleviate the effects of hearing loss, they cannot completely restore normal hearing or halt the progression of age-related hearing loss. Oxidative stress and inflammation have been identified as potential contributors to this condition. By addressing modifiable lifestyle risk factors that exacerbate oxidative stress, there may be an opportunity to prevent hearing loss. Therefore, this narrative review provides an overview of the major modifiable lifestyle risk factors associated with age-related hearing loss, that is, exposure to noise and ototoxic chemicals, smoking, diet, physical activity, and the presence of chronic lifestyle diseases, and offers an overview of the role of oxidative stress in the pathophysiology of this condition.

Bisphenol A and Bisphenol S Induce Endocrine and Chromosomal Alterations in Brown Trout

Bisphenol A is a widely used compound found in large amount of consumer products. As concerns have been raised about its toxicological and public health effect, the use of alternatives to bisphenol A are now increasing. Bisphenol S is one of the analogues being used as a replacement for bisphenol A despite the fact that little is known about the effects of bisphenol S on living organisms. In this study, we investigated the potential endocrine and genotoxic effects of bisphenol A and bisphenol S in juvenile brown trout (Salmo trutta). The fish were exposed to the compounds for either 2 weeks or 8 weeks via sustained-release cholesterol implants containing doses of 2 mg/kg fish or 20 mg/kg fish of the substances. The effects on the thyroid hormone levels and the estrogenic disrupting marker vitellogenin were evaluated, along with the genotoxic markers micronucleated cells and erythrocyte nuclear abnormalities. An increase in plasma vitellogenin was observed in fish exposed to the high dose of bisphenol A for 2 weeks. At this experimental time the level of the thyroid hormone triiodothyronine (T3) in plasma was elevated after bisphenol S exposure at the high concentration, and paralleled by an increase of micronucleated cells. Moreover, bisphenol A induced an increase of micronuclei frequency in fish erythrocytes after the exposure at the lowest dose tested. Taken together the results indicate that both bisphenol A and its alternative bisphenol S cause endocrine disrupting and genotoxic effects in brown trout, although suggesting two different mechanisms of damage underlying bisphenol A and bisphenol S activity.

Dietary sugars and related endogenous advanced glycation end-products increase chromosomal DNA damage in WIL2-NS cells, measured using cytokinesis-block micronucleus cytome assay

This study investigated the effect of glucose and fructose, and advanced glycation end-products (AGEs) on genome damage in WIL2-NS cells, measured using the cytokinesis-block micronucleus cytome (CBMN-Cyt) assay. The effect of AGEs was investigated using the bovine serum albumin (AGE-BSA) model system induced either with glucose (Glu-BSA) or with fructose (Fru-BSA). Liquid chromatography-mass spectrometry (LC-MS/MS) analysis showed higher Nε-carboxymethyllysine (CML; 26.76 ± 1.09 nmol/mg BSA) levels in the Glu-BSA model. Nε-Carboxyethyllysine (CEL; 7.87 ± 0.19 nmol/mg BSA) and methylglyoxal-derived hydroimidazolone-1 (MG-H1; 69.77 ± 3.74 nmol/mg BSA) levels were higher in the Fru-BSA model. Genotoxic effects were measured using CBMN-Cyt assay biomarkers [binucleated(BN) cells with micronuclei (MNi), BN with nucleoplasmic bridges (NPBs) and BN with nuclear buds (NBuds)] following 9 days of treatment with either glucose, fructose, Glu-BSA or Fru-BSA. Fructose treatment exerted a significant genotoxic dose-response effect including increases of BN with MNi (R2 = 0.7704; P = 0.0031), BN with NPBs (R2 = 0.9311; P < 0.0001) and BN with NBuds (R2 = 0.7118; P = 0.0091) on cells, whereas the DNA damaging effects of glucose were less evident. High concentrations of AGEs (400-600 µg/ml) induced DNA damage; however, there was no effect on cytotoxicity indices (necrosis and apoptosis). In conclusion, this study demonstrates a potential link between physiologically high concentrations of reducing sugars or AGEs with increased chromosomal damage which is an important emerging aspect of the pathology that may be induced by diabetes. Ultimately, loss of genome integrity could accelerate the rate of ageing and increase the risk of age-related diseases over the long term. These findings indicate the need for further research on the effects of glycation on chromosomal instability and to establish whether this effect is replicated in humans in vivo.

Anti-glycation, Carbonyl Trapping and Anti-inflammatory Activities of Chrysin Derivatives

The aim of this study was searching anti-glycation, carbonyl trapping and anti-inflammatory activities of chrysin derivatives. The inhibitory effect of chrysin on advanced glycation end-products (AGEs) was investigated by trapping methylglyoxal (MGO), and MGO-conjugated adducts of chrysin were analyzed using LC-MS/MS. The mono- or di-MGO-conjugated adducts of chrysin were present at 63.86 and 29.69% upon 48 h of incubation at a chrysin:MGO ratio of 1:10. The MGO adducted positions on chrysin were at carbon 6 or 6 & 8 in the A ring by classic aldol condensation. To provide applicable knowledge for developing chrysin derivatives as AGE inhibitors, we synthesized several O-alkyl or ester derivatives of chrysin and compared their AGE formation inhibitory, anti-inflammatory, and water solubility characteristics. The results showed that 5,7-di-O-acetylchrysin possessed higher AGE inhibitory and water solubility qualities than original chrysin, and retained the anti-inflammation activity. These results suggested that 5,7-di-O-acetylchrysin could be a potent functional food ingredient as an AGE inhibitor and anti-inflammatory agent, and promotes the development of the use of chrysin in functional foods.

Impact of obesity and overweight on DNA stability: Few facts and many hypotheses

Health authorities are alarmed worldwide about the increase of obesity and overweight in the last decades which lead to adverse health effects including inflammation, cancer, accelerated aging and infertility. We evaluated the state of knowledge concerning the impact of elevated body mass on genomic instability. Results of investigations with humans (39 studies) in which DNA damage was monitored in lymphocytes and sperm cells, are conflicting and probably as a consequence of heterogeneous study designs and confounding factors (e.g. uncontrolled intake of vitamins and minerals and consumption of different food types). Results of animal studies with defined diets (23 studies) are more consistent and show that excess body fat causes DNA damage in multiple organs including brain, liver, colon and testes. Different molecular mechanisms may cause genetic instability in overweight/obese individuals. ROS formation and lipid peroxidation were found in several investigations and may be caused by increased insulin, fatty acid and glucose levels or indirectly via inflammation. Also reduced DNA repair and formation of advanced glycation end products may play a role but more data are required to draw firm conclusions. Reduction of telomere lengths and hormonal imbalances are characteristic for overweight/obesity but the former effects are delayed and moderate and hormonal effects were not investigated in regard to genomic instability in obese individuals. Increased BMI values affect also the activities of drug metabolizing enzymes which activate/detoxify genotoxic carcinogens, but no studies concerning the impact of these alterations of DNA damage in obese individuals are available. Overall, the knowledge concerning the impact of increased body weight and DNA damage is poor and further research is warranted to shed light on this important issue.

Targeting advanced glycation with pharmaceutical agents: where are we now?

Advanced glycation end products (AGEs) are the final products of the Maillard reaction, a complex process that has been studied by food chemists for a century. Over the past 30 years, the biological significance of advanced glycation has also been discovered. There is mounting evidence that advanced glycation plays a homeostatic role within the body and that food-related Maillard products, intermediates such as reactive α-dicarbonyl compounds and AGEs, may influence this process. It remains to be understood, at what point AGEs and their intermediates become pathogenic and contribute to the pathogenesis of chronic diseases that inflict current society. Diabetes and its complications have been a major focus of AGE biology due to the abundance of excess sugar and α-dicarbonyls in this family of diseases. While further temporal information is required, a number of pharmacological agents that inhibit components of the advanced glycation pathway have already showed promising results in preclinical models. These therapies appear to have a wide range of mechanistic actions to reduce AGE load. Some of these agents including Alagebrium, have translated successfully to clinical trials, while others such as aminoguanidine, have had undesirable side-effect profiles. This review will discuss different pharmacological agents that have been used to reduce AGE burden in preclinical models of disease with a focus on diabetes and its complications, compare outcomes of those therapies that have reached clinical trials, and provide further rationale for the use of inhibitors of the glycation pathway in chronic diseases.

Alpha-lipoic acid upregulates antioxidant enzyme gene expression and enzymatic activity in diabetic rat kidneys through an O-GlcNAc-dependent mechanism

PURPOSE

The combined hyperglycemia lowering and antioxidant actions of α-lipoic acid (LA) contribute to its usefulness in preventing renal injury and other diabetic complications. The precise mechanisms by which LA alters diabetic oxidative renal injury are not known. We hypothesized that LA through its hypoglycemic effect lowers O-GlcNAcylation which influences the expression and activities of antioxidant enzymes which assume important roles in preventing diabetes-induced oxidative renal injury.

METHODS

An experimental model of diabetes was induced in rats by the administration of 40 mg/kg streptozotocin (STZ) intraperitoneally (i.p.) for five consecutive days. LA was applied at a dose of 10 mg/kg i.p. for 4 weeks, starting from the last day of STZ administration.

RESULTS

An improved glycemic status of LA-treated diabetic rats was accompanied by a significant suppression of oxidative stress and a reduction of oxidative damage of lipids, proteins and DNA. LA treatment normalized CuZn-superoxide dismutase (SOD) and catalase activities in renal tissue of diabetic rats. These changes were allied with upregulated gene expression and lower levels of O-GlcNA glycosylation. The accompanying increase in MnSOD activity was only linked with upregulated gene expression. The observed antioxidant enzyme gene regulation was accompanied by nuclear translocation of Nuclear factor-erythroid-2-related factor 2 (Nrf2), enhanced expression of heat shock proteins (HSPs) and by reduction in O-GlcNAcylation of HSP90, HSP70, and extracellular regulated kinase and p38.

CONCLUSION

α-Lipoic acid administration activates a coordinated cytoprotective response against diabetes-induced oxidative injury in kidney tissue through an O-GlcNAc-dependent mechanism.

Obestatin and insulin in pancreas of newborn diabetic rats treated with exogenous ghrelin

The aim of the study was to evaluate the effect of ghrelin treatment on obestatin, insulin gene expression and biochemical parameters in the pancreas of newborn-streptozocin (STZ) diabetic rats. Rats were divided into 4 groups. Group I: control rats treated with physiological saline; group II: control rats treated with 100 μg/kg/day ghrelin; group III: two days after birth rats that received 100mg/kg STZ injected as a single dose to induce neonatal diabetes; group IV: neonatal-STZ-diabetic rats treated with ghrelin for four weeks. Sections of the pancreas were examined with immunohistochemistry for the expression of obestatin and insulin and in situ hybridization for the expression of insulin mRNA. The blood glucose levels were measured. Tissue homogenates were used for protein, glutathione, lipid peroxidation and non-enzymatic glycosylation levels and antioxidant enzyme analysis. There was a significant difference in blood glucose levels in newborn-STZ-diabetic rats compared to ghrelin treated diabetic rats at weeks 1, 2 and 4. In group IV, pancreatic non-enzymatic glycosylation and lipid peroxidation levels were decreased, however, glutathione levels and enzymatic activities were increased. Insulin peptide and mRNA (+) signals in islets of Langerhans and obestatin immunopositive cell numbers showed an increase in group IV compared to group III. These results suggest that administration of ghrelin to newborn rats may prevent effects of diabetes.

The impact of thiamine treatment in the diabetes mellitus

Thiamine acts as a coenzyme for transketolase (Tk) and for the pyruvate dehydrogenase and α-ketoglutarate dehydrogenase complexes, enzymes which play a fundamental role for intracellular glucose metabolism. The relationship between thiamine and diabetes mellitus (DM) has been reported in the literature. Thiamine levels and thiamine-dependent enzyme activities have been reduced in DM. Genetic studies provide opportunity to link the relationship between thiamine and DM (such as Tk, SLC19A2 gene, transcription factor Sp1, α-1-antitrypsin, and p53). Thiamine and its derivatives have been demonstrated to prevent the activation of the biochemical pathways (increased flux through the polyol pathway, formation of advanced glycation end-products, activation of protein kinase C, and increased flux through the hexosamine biosynthesis pathway) induced by hyperglycemia in DM.Thiamine definitively has a role in the diabetic endothelial vascular diseases (micro and macroangiopathy), lipid profile, retinopathy, nephropathy, cardiopathy, and neuropathy.

Use of the in vivo skin comet assay to evaluate the DNA-damaging potential of chemicals applied to the skin

The aim of the present study was to evaluate both sensitivity and specificity of an in vivo skin comet assay using chemically treated, hairless mouse dorsal skin as a model. N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, 0.0125-0.2%), 4-nitroquinoline-1-oxide (4NQO, 0.01-0.25%), mitomycin C (MMC, 0.0125-0.05%), benzo[a]pyrene (B[a]P, 0.25-2%), and 7,12-dimethylbenz[a]anthracene (DMBA, 0.25-1%) were each applied once to the dorsal skin of hairless male mice; after 3h, epidermal skin cells were isolated, and the alkaline comet assay was performed. The assay was performed after 24h for only the B[a]P and DMBA. Furthermore, B[a]P and DMBA were evaluated by alkaline comet assay using liver cells after both 3 and 24h. The mean percent of DNA (%DNA) in tail in the 0.05-0.2% MNNG and 0.1-0.25% 4NQO treatment groups was markedly higher than in the control group at 3h post-application. Although the mean %DNA values in the tail in the B[a]P and DMBA groups were the same as the controls at 3h post-application, the 2% B[a]P and 1% DMBA groups showed significantly higher values versus controls 24h after application. No significant increases in the mean %DNA in the tail were observed in the MMC group. No clear increases in %DNA in the tail were observed in the B[a]P and DMBA groups at 3 or 24h after application in the liver. These results suggest that the in vivo skin comet assay is able to accurately identify DNA-damaging potential with a skin-specific response and is a useful method to detect the DNA-damaging potential of genotoxic chemicals on the skin.

Protective Effect of Proanthocyanidin against Diabetic Oxidative Stress

We investigated the antidiabetic potential of proanthocyanidin and its oligomeric form in STZ-induced diabetic model rats and db/db type 2 diabetic mice. Proanthocyanidin ameliorated the diabetic condition by significant decreases of serum glucose, glycosylated protein, and serum urea nitrogen as well as decreases of urinary protein and renal-AGE in STZ-induced diabetic rats and decrease of serum glucose as well as significant decrease of glycosylated protein in db/db type 2 diabetic mice. The suppression of ROS generation and elevation of the GSH/GSSG ratio were also observed in the groups administered proanthocyanidin. Moreover, proanthocyanidin, especially its oligomeric form, affected the inflammatory process with the regulation of related protein expression, iNOS, COX-2 and upstream regulators, NF-κB, and the IκB-α. In addition, it had a marked effect on hyperlipidemia through lowering significant levels of triglycerides, total cholesterol, and NEFA. Moreover, expressions in the liver of SREBP-1 and SREBP-2 were downregulated by the administration of proanthocyanidins. The protective effect against hyperglycemia and hyperlipidemia in type 1 and 2 diabetic models was significantly strong in the groups administered the oligomeric rather than polymeric form. This suggests that oligomers act as a regulator in inflammatory reactions caused by oxidative stress in diabetes.

Dietary glycemic load is a predictor of age-related hearing loss in older adults

Age-related hearing loss is a frequent disability in older adults and nutrition could play a role in the development of this condition. Carbohydrate nutrition [including dietary glycemic index (GI) and load (GL)] may be linked to hearing loss. We aimed to determine the association between carbohydrate nutrition (including mean dietary GI and GL, and the dietary intakes of carbohydrate and sugar), starch, cereal and total fiber, and age-related hearing loss. The Blue Mountains Hearing Study is a population-based survey of age-related hearing loss (1997-1999 to 2002-2004). Hearing loss was measured in 2956 participants (aged ≥50 y) and was defined as the pure-tone average of frequencies 0.5, 1.0, 2.0, and 4.0 kHz > 25 dB hearing level. Dietary data were collected in a semiquantitative FFQ. A purpose-built database based on Australian GI values was used to calculate the mean GI. A higher mean dietary GI was associated with an increased prevalence of any hearing loss, comparing quintiles 1 (lowest) and 5 (highest), [multivariable-adjusted odds ratio = 1.41 (95% CI = 1.01-1.97)]. Participants in the highest quartile of mean dietary GL intake compared with those in the lowest quartile had a 76% greater risk of developing incident hearing loss (P-trend = 0.04). Higher carbohydrate and sugar intakes were associated with incident hearing loss (P-trend = 0.03 and P-trend = 0.05, respectively). In summary, a high-GL diet was a predictor of incident hearing loss, as was higher intake of total carbohydrate. Hence, high postprandial glycemia might be a potential underlying biological mechanism in the development of age-related hearing loss.

The effects of combined treatment of antioxidants on the liver injury in STZ diabetic rats

The aim of this study was to examine whether an antioxidant combination of vitamin C, vitamin E, and sodium selenate (Se) has an effect on the liver of diabetic rats. Vitamin C, vitamin E, and Se were administered for 30 days to streptozotocin (STZ)-induced diabetic and control groups. In the STZ diabetic group, blood glucose levels, liver lipid peroxidation (LPO), and nonenzymatic glycosylation (NEG) levels increased, but blood and liver glutathione levels decreased. On the other hand, combined antioxidant treatment reversed these effects. In the diabetic group, some degenerative changes were observed by light and electron microscopic examinations, but the degenerative changes decreased in the diabetic group given antioxidant combination. Proliferating cell nuclear antigen (PCNA) immunohistochemistry showed that the number of proliferative hepatocytes increased significantly with antioxidant treatment. It was concluded that combined treatment with vitamin C, vitamin E, and Se has a curative effect against the hepatotoxicity produced by STZ-induced diabetes.

Inhibitors of advanced glycation end products (AGEs): potential utility for the treatment of cardiovascular disease

Accelerated atherosclerosis and microvascular complications are the leading causes of coronary heart disease, stroke, blindness, and end-stage renal failure, which could account for disabilities and high mortality rates in patients with diabetes. Recent clinical studies have substantiated the concept of "hyperglycemic memory" in the pathogenesis of cardiovascular disease (CVD) in diabetes. Indeed, the Diabetes Control and Complications Trial-Epidemiology of Diabetes Interventions and Complications (DCCT-EDIC) Research, has revealed that intensive therapy during the DCCT reduces the risk of cardiovascular events by about 50% in type 1 diabetic patients 11 years after the end of the trial. Among various biochemical pathways activated under diabetic conditions, the process of formation and accumulation of advanced glycation end products (AGEs) and their mode of action are most compatible with the theory "hyperglycemic memory." Further, there is a growing body of evidence that AGEs play an important role in CVD in diabetes. These observations suggest that the inhibition of AGEs formation may be a promising target for therapeutic intervention in diabetic vascular complications. Therefore, in this article, we review several agents with inhibitory effects on AGEs formation and their therapeutic implications in CVD in diabetes.

Ameliorative effects of proanthocyanidin on oxidative stress and inflammation in streptozotocin-induced diabetic rats

Recent evidence strongly suggests that oxidative stress due to redox imbalance is causally associated with inflammatory processes and various diseases including diabetes. We examined the effects of proanthocyanidin from persimmon peel, using both oligomers and polymers, against oxidative stress with elucidation of the underlying mechanisms in streptozotocin-induced diabetic rats. The elevation of lipid peroxidation in the kidney and serum under the diabetic condition was decreased by the administration of proanthocyanidin. The suppression of reactive oxygen species generation and elevation of the reduced glutathione/oxidized glutathione ratio were observed in the groups administered proanthocyanidin. These results support the protective role of proanthocyanidin from oxidative stress induced by diabetes. Moreover, proanthocyanidin, especially its oligomeric form, affected the inflammatory process with regulation of related protein expression, inducible nitric oxide synthase, cyclooxygenase-2, and upstream regulators, nuclear factor kappaB, and inhibitor-binding protein kappaB-alpha. Proanthocyanidin ameliorated the diabetic condition by decreases of serum glucose, glycosylated protein, serum urea nitrogen, urinary protein, and renal advanced glycation endproducts. In particular, oligomeric proanthocyanidin exerted a stronger protective activity than the polymeric form. This suggests that the polymerization of proanthocyanidin has an effect on its protective effect against diabetes. The present study supports the beneficial effect of proanthocyanidin against diabetes and oxidative stress-related inflammatory processes.

Molecular action mechanism against apoptosis by aqueous extract from guava budding leaves elucidated with human umbilical vein endothelial cell (HUVEC) model

Chronic cardiovascular and neurodegenerative complications induced by hyperglycemia have been considered to be associated most relevantly with endothelial cell damages (ECD). The protective effects of the aqueous extract of Psidium guajava L. budding leaves (PE) on the ECD in human umbilical vein endothelial cell (HUVEC) model were investigated. Results revealed that glyoxal (GO) and methylglyoxal (MGO) resulting from the glycative and autoxidative reactions of the high blood sugar glucose (G) evoked a huge production of ROS and NO, which in turn increased the production of peroxynitrite, combined with the activation of the nuclear factor kappaB (NFkappaB), leading to cell apoptosis. High plasma glucose activated p38-MAPK, and high GO increased the expressions of p38-MAPK and JNK-MAPK, whereas high MGO levels induced the activity of ERK-MAPK. Glucose and dicarbonyl compounds were all found to be good inducers of intracellular PKCs, which together with MAPK acted as the upstream triggering factor to activate NFkappaB. Conclusively, high plasma glucose together with dicarbonyl compounds can trigger the signaling pathways of MAPK and PKC and induce cell apoptosis through ROS and peroxynitrite stimulation and finally by NFkappaB activation. Such effects of PE were ascribed to its high plant polyphenolic (PPP) contents, the latter being potent ROS inhibitors capable of blocking the glycation of proteins, which otherwise could have brought forth severe detrimental effects to the cells.

High level glucose increases mutagenesis in human lymphoblastoid cells

Epidemiological data have suggested an increased cancer rates in diabetic patients, for which the underlying mechanism is poorly understood. We studied whether high level of glucose (HG) treatment that mimic the hyperglycemic condition in diabetes mellitus is mutagenic. Mutagenesis studies were carried out at both hypoxanthine phosphoribosyltransferase (hprt) and thymidine kinase (tk) loci. Role of p53 in HG-induced mutagenesis was also investigated by using human lymphoblastoid cell lines derived from same donor but differs in p53 statuses; TK6 has wild-type p53, NH32 has null p53, and WTK1 has mutant p53 (ile237). In addition, we studied the influence of antioxidant treatment on HG-induced mutagenesis. Mutation fractions at both loci increased significantly in all three lines at 21 and 28 days after HG treatments. At tk locus, the increase of a class of mutants with normal growth rate is mainly responsible for the overall increased mutant fraction. Compared to TK6 cells, both NH32 and WTK1 cells showed an early onset of mutagenesis. Treatment of cells with antioxidant N-acetyl-L-cysteine partially reduced HG induced mutagenesis. This study is the first to indicate that HG is able to induce gene mutation which may be one of the important mechanisms of diabetes-associated carcinogenesis.

Trapping reactions of reactive carbonyl species with tea polyphenols in simulated physiological conditions

The carbonyl stress that leads to the formation of advanced glycation end products (AGEs) in diabetes mellitus has drawn much attention recently. Reactive alpha-dicarbonyl compounds, such as glyoxal (GO) and methylglyoxal (MGO), have been shown to be a high potential glycation agent in vitro and in vivo. In this study, epicatechins in green tea and theaflavins in black tea were found to be able to reduce the concentration of MGO in physiological phosphate buffer conditions. Modified MGO derivatization for GC/flame ionization detector (FID) method in quantification was systematically conducted. In molar ratio of 3 (MGO/polyphenol), theaflavin-3,3'-digallate (TF3) in theaflavins and (-)-epigallocatechin (EGC) in epicatechins showed the highest MGO reduction at 66.65 and 45.74%, respectively, after 1 h of incubation. In kinetic study (molar ratio of MGO/polyphenol = 1:1), rapid MGO reduction occurred within 10 min. Identities of primary adducts between (-)-epigallocatechin gallate (EGCG) and MGO were determined. Newly generated stereoisomers at the C8 position of EGCG A-ring were isolated with a chiral column, and structurally confirmed by 2-D NMR analyses.

Effects of in vitro maturation of monkey oocytes on their developmental capacity

The study of in vitro maturation (IVM) of rhesus monkey oocytes has important implications for biomedical research and human infertility treatment. In vitro-matured rhesus monkey oocytes show much less developmental potential than IVM oocytes of other species. Since about 1980 when rhesus monkey IVM, in vitro fertilization (IVF) and in vitro embryo culture (IVC) systems were established, numerous efforts have been made to improve the developmental competence of oocytes and to understand the mechanisms regulating oocyte maturation. This review describes recent progress in this area, particularly the effects of factors such as steroid hormones, energy substrates, amino acids, ovarian follicle status, maternal age and breeding season on the developmental competence, gene expression patterns and genome integrity of rhesus IVM oocytes.

Saturated, unsaturated, and trans-fatty acids modulate oxidative burst induced by high dextrose in human umbilical vein endothelial cells

OBJECTIVE

We determined whether hyperglycemia-induced oxidative burst is augmented in the presence of saturated, unsaturated, and trans-fatty acids (FAs).

METHODS

The time course of superoxide (O2-) production in human umbilical vein endothelial cells treated with 5.5 mM (D100) or 27.5 mM (D500) of dextrose and select FAs were measured using the hydroethidene fluorescence method.

RESULTS

The rate of O2- production in cells treated with D500 was significantly higher (55% to 125% increase) than the rate observed in control cells treated with D100 (P < 0.001). The rate of O2- production (mean +/- standard deviation, in arbitrary units) was increased when cells were treated with 250, 500, and 1000 muM of myristic acid (C14; 0.189 +/- 0.04, 0.240 +/- 0.04, 0.234 +/- 0.02, respectively; P > 0.1, P < 0.05, P < 0.05, respectively), palmitate (C16; 0.151 +/- 0.03, 0.218 +/- 0.01, 0.289 +/- 0.07; P > 0.1, P < 0.05, P < 0.01), and stearic acid (C18; 0.321 +/- 0.03, 0.259 +/- 0.02, 0.341 +/- 0.03; P < 0.01 for all comparisons) compared with control cells treated with D100 only (0.184 +/- 0.01). In the presence of D500, myristic acid did not significantly augment O2- production, whereas stearic acid caused a significant further increase in O2- production. The cis unsaturated FA (oleic, C18:1; linoleic, C18:2; or linolenic acid, C18:3) stimulated O2- production significantly more than did saturated FA or trans-unsaturated FA such as elaidic, linolelaidic, or linolenelaidic acid.

CONCLUSIONS

Fatty acids have the ability to modulate oxidative load in hyperglycemia and this effect may be related to the length, saturation, and possibly cis/trans orientation of the FA.

Pyridoxamine: The Many Virtues of a Maillard Reaction Inhibitor

Pyridoxamine (PM) is one of three natural forms of vitamin B6. It is a critical transient intermediate in catalysis of transamination reactions by vitamin B6-dependent enzymes. The discovery eight years ago that PM can inhibit the Maillard reaction stimulated new interest in this B6 vitamer as a prospective pharmacological agent for treatment of complications of diabetes. PM application in diabetic nephropathy has now progressed to a phase III clinical trial. Investigation of the PM mechanism of action demonstrated that PM inhibits post-Amadori steps of the Maillard reaction by sequestering catalytic metal ions and blocking oxidative degradation of Amadori intermediate. PM also has the capacity to scavenge toxic carbonyl products of sugar and lipid degradation, and to inhibit reactive oxygen species. These multiple activities position PM as a promising drug candidate for treatment of multifactorial chronic conditions in which oxidative reactions and/or carbonyl compounds confer pathogenicity.

A copper chelating agent suppresses carbonyl stress in diabetic rat lenses

To clarify whether transition metals are involved in carbonyl stress in diabetic tissues, we observed the effects of a metal chelating agent, trientine (TE) hydrochloride on the levels of methylglyoxal (MG), 3-deoxyglucosone (3-DG), advanced glycation end products, 8-hydroxy-2'-deoxyguanosine (8-OHdG), and polyol pathway metabolites along with semicarbazide-sensitive amine oxidase (SSAO) enzyme activity in lenses from streptozotocin-induced diabetic rats. Lens MG and 3-DG levels were significantly higher in diabetic rats than nondiabetic controls, and TE significantly restored the increase of these compounds. Lens argpyrimidine was also increased in diabetic rats as compared with controls and was significantly reduced by TE. Lens SSAO activity and 8-OHdG were also significantly elevated in diabetic rats, and TE suppressed both of them, whereas TE showed no effect on the polyol pathway metabolites. The results indicate that transition metals play a significant role in the formation of MG and 3-DG via oxidative stress and SSAO activity.

Attenuation of hyperglycemia and associated biochemical parameters in STZ-induced diabetic rats by dietary supplementation of potato peel powder

BACKGROUND

Both dietary fiber and polyphenols have been reported to exert antihyperglycemic effect. Potato peel (PP), a waste by product of potato processing, is found to be a good source of both dietary fiber and polyphenols. The current study examined the attenuating influence of dietary potato peel (PP) powder on hyperglycemia and various oxidative stress-associated biochemical parameters in diabetic rats.

METHODS

Streptozotocin (STZ)-induced diabetic male Wistar rats were used as experimental models. The rats were divided into nondiabetic (control), diabetic, potato-peel-supplemented (5% and 10%) and diabetic-PP (5% and 10%)-supplemented groups and were maintained for 4 weeks on the experimental regime. The modulatory role of PP was assessed by determining its effect on blood glucose, urine output, body weight gain, lipid peroxidation, reduced glutathione, serum aminotransferases, lipid profiles, selected antioxidant enzymes in liver/kidney and selected eye lens parameters.

RESULTS

Diabetic rats fed with PP-powder-supplemented diet for 4 weeks showed a significant decrease in blood glucose levels. Incorporation of PP powder reduced significantly the hypertrophy of both liver and kidney of STZ-diabetic rats and also normalized the activities of serum ALT and AST, hepatic and renal MDA and GSH, as well as activities of various antioxidant enzymes in liver and kidney of diabetic rats. Furthermore, PP powder in the diet also appeared to attenuate the eye lens damage associated with the diabetic condition.

CONCLUSION

Potato peel powder supplementation in diet was found to effectively attenuate diabetic alterations in rats.

DNA damage and repair in type 2 diabetes mellitus

DNA damage may be associated with type 2 diabetes mellitus (T2DM) and its complications mainly through oxidative stress. Little is known about DNA repair disturbances potentially contributing to the overall extent of DNA damage in T2DM, which, in turn, may be linked with genomic instability resulting in cancer. To assess whether DNA repair may be perturbed in 2DM we determined: (1) the level of endogenous basal DNA damage, this means damage recognized in the alkaline comet assay (DNA strand breaks and alkali labile sites) as well as endogenous oxidative and alkylative DNA damage (2) the sensitivity to DNA-damaging agents hydrogen peroxide and doxorubicin and the efficacy of removing of DNA damage induced by these agents in peripheral blood lymphocytes of T2DM patients and healthy individuals. The level of DNA damage and the kinetics of DNA repair was evaluated by the alkaline single cell gel electrophoresis (comet assay). Oxidative and alkylative DNA damage were assayed with the use of DNA repair enzymes endonuclease III (Endo III) and formamidopyrimidine-DNA glycosylase (Fpg), recognizing oxidized DNA bases and 3-methyladenine-DNA glycosylase II (AlkA) recognizing alkylated bases. The levels of basal endogenous and oxidative DNA damage in diabetes patients were higher than in control subjects. There was no difference between the level of alkylative DNA in the patients and the controls. Diabetes patients displayed higher susceptibility to hydrogen peroxide and doxorubicin and decreased efficacy of repairing DNA damage induced by these agents than healthy controls. Our results suggest that type 2 diabetes mellitus may be associated not only with the elevated level of oxidative DNA damage but also with the increased susceptibility to mutagens and the decreased efficacy of DNA repair. These features may contribute to a link between diabetes and cancer and metrics of DNA damage and repair, measured by the comet assay, may be markers of risk of cancer in diabetes.

Rapid adaptive down regulation of oxidative burst induced by high dextrose in human umbilical vein endothelial cells

To determine whether hyperglycemia-induced increase in oxidative burst undergoes adaptive changes, the time course of superoxide (SO) production in human umbilical vein endothelial cells treated with 13.75 mM (D250) or 27.5mM dextrose (D500) was measured using the hydroethidine (HE) fluorescence method. The rate of SO production (mean +/- S.D., in arbitrary units) in cells treated with D500 during the first hour (0.758 +/- 0.367) or with D250 (0.618 +/- 0.126) was significantly higher than the rate observed in control cells treated with 100mg/dl dextrose, (D100; 0.474 +/- 0.125) (P < 0.001). However, the rate of SO production during the second, third, fourth, and fifth hour was not significantly different from that measured in control cells. The fluorescence at baseline for control cells was 3.4 +/- 2.3 and for cells treated with D500 for 1, 2, 3, 4, and 5h was 3.4 +/- 1.9, 15.2 +/- 2.5, 21.6 +/- 2.3, 27.4 +/- 3.4, and 31.8 +/- 4.3 respectively (P < 0.001). The increased baseline fluorescence suggests that the antioxidant pool may be depleted within the first hour of exposure to high concentrations of dextrose. The latter possibility is supported by the observation that treatment of cells with varying concentrations of ascorbate (15, 150, and 1500 microM) or alpha-tocopherol (10,100 and 1000 microM) prevents D500 induced increase in SO production. It is concluded that increased oxidative load in sustained chronic hyperglycemia is probably the result of depletion of antioxidant pool rather than secondary to sustained increase in SO production.

Pyridoxamine, an inhibitor of advanced glycation and lipoxidation reactions: a novel therapy for treatment of diabetic complications

Pyridoxamine (PM), originally described as a post-Amadori inhibitor of formation of advanced glycation end-products (AGEs), also inhibits the formation of advanced lipoxidation end-products (ALEs) on protein during lipid peroxidation reactions. In addition to inhibition of AGE/ALE formation, PM has a strong lipid-lowering effect in streptozotocin (STZ)-induced diabetic and Zucker obese rats, and protects against the development of nephropathy in both animal models. PM also inhibits the development of retinopathy and neuropathy in the STZ-diabetic rat. Several products of reaction of PM with intermediates in lipid autoxidation have been identified in model reactions in vitro and in the urine of diabetic and obese rats, confirming the action of PM as an AGE/ALE inhibitor. PM appears to act by a mechanism analogous to that of AGE-breakers, by reaction with dicarbonyl intermediates in AGE/ALE formation. This review summarizes current knowledge on the mechanism of formation of AGE/ALEs, proposes a mechanism of action of PM, and summarizes the results of animal model studies on the use of PM for inhibiting AGE/ALE formation and development of complications of diabetes and hyperlipidemia.

Use of aminoguanidine (Pimagedine) to prevent the formation of advanced glycation endproducts

Aminoguanidine (AG) is a prototype therapeutic agent for the prevention of formation of advanced glycation endproducts. It reacts rapidly with alpha,beta-dicarbonyl compounds such as methylglyoxal, glyoxal, and 3-deoxyglucosone to prevent the formation of advanced glycation endproducts (AGEs). The adducts formed are substituted 3-amino-1,2,4-triazine derivatives. Inhibition of disease mechanisms, particularly vascular complications in experimental diabetes, by AG has provided evidence that accumulation of AGEs is a risk factor for disease progression. AG has other pharmacological activities, inhibition of nitric oxide synthase and semicarbazide-sensitive amine oxidase (SSAO), at pharmacological concentrations achieved in vivo for which controls are required in anti-glycation studies. AG is a highly reactive nucleophilic reagent that reacts with many biological molecules (pyridoxal phosphate, pyruvate, glucose, malondialdehyde, and others). Use of high concentrations of AG in vitro brings these reactions and related effects into play. It is unadvisable to use concentrations of AG in excess of 500 microM if selective prevention of AGE formation is desired. The peak plasma concentration of AG in clinical therapy was ca. 50 microM. Clinical trial of AG to prevent progression of diabetic nephropathy was terminated early due to safety concerns and apparent lack of efficacy. Pharmacological scavenging of alpha-oxoaldehydes or stimulation of host alpha-oxoaldehyde detoxification remains a worthy therapeutic strategy to prevent diabetic complications and other AGE-related disorders.

Intervention against the Maillard reaction in vivo

The field of Maillard/glycation reactions in vivo has grown enormously during the past 20 years, going from 25 to 500 publications per year. It is now well recognized that many of the "advanced" products form oxidatively or anaerobically and can have deleterious effects on macromolecular and biological function. The feasibility of developing pharmacological agents with beneficial in vivo properties, based on in vitro inhibition of glycation, has been surprisingly successful. This Editorial sets the stage for a series of articles by experts in the field, who have made key contributions to our understanding of the Maillard reaction in vivo.

Insulin and glucose regulate the expression of the DNA repair enzyme XPD

Nucleotide excision repair (NER) of damaged DNA is operated by a complex network of DNA repair enzymes that include a protein termed xeroderma pigmentosum complementation group D (XPD). We have previously reported that the expression of XPD is regulated by activation of the insulin receptor and that mutations of the tyrosine kinase domain of the receptor inhibit the insulin-dependent increase in XPD messenger RNA (mRNA) and protein levels. In the present study, we characterize the insulin-dependent signaling pathway leading to the control of XPD expression. Using Chinese hamster ovary (CHO) cells transfected with the human insulin receptor, we demonstrated that the effect of insulin on XPD mRNA levels was mediated via the RAS-signaling and the p70 S6 kinase pathways. On the other hand, the intracellular level of XPD protein was under the exclusive control of the activation of the RAS-dependent cascade in response to insulin. We also studied the effect of acute and chronic exposures to different concentrations of glucose on the insulin-dependent regulation of intracellular XPD levels. A short-term exposure (48 h) to increasing concentrations of glucose potentiated the insulin-dependent regulation of XPD, and this was associated with an efficient protection against glucose-dependent damage to cellular DNA, as determined by the comet assay. Conversely, in cells that were grown for 3 weeks in the presence of glucose concentration greater than 10 mM, the capability of insulin to regulate the level of XPD was significantly reduced, and this promoted a glucose-dependent accumulation of products of DNA damage. In conclusion, glucose and insulin are important regulators of XPD, and prolonged exposure to toxic levels of glucose reduces the insulin-dependent regulation of DNA repair.