Oxidative DNA damage in diabetes mellitus: its association with diabetic complications

Cell cycle checkpoints: the role and evaluation for early diagnosis of senescence, cardiovascular, cancer, and neurodegenerative diseases

Maintenance of genomic integrity is critical for prevention of a wide variety of adverse cellular effects including apoptosis, cellular senescence, and malignant cell transformation. Under stress conditions and even during an unperturbed cell cycle, checkpoint proteins play the key role in genome maintenance by and mediating cellular response to DNA damage, and represent an essential part of the "cellular stress response proteome". Intact checkpoint signal transduction cascades check the presence of genome damage, trigger cell cycle arrest, and forward the information to the protein core of cell cycle machinery, replication apparatus, repair, and/or apoptotic protein cores. Genetic checkpoint defects lead to syndromes that demonstrate chromosomal instability, increased sensitivity to genotoxic stress, tissue degeneration, developmental retardation, premature aging, and cancer predisposition that is most extensively studied for the ATM-checkpoint mutated in Ataxia telangiectasia. Tissue specific epigenetic control over the function of cell cycle checkpoints can be, further, misregulated by aberrant DNA methylation status. The consequent checkpoint dysregulation may result in tissue specific degenerative processes such as degeneration and calcification of heart aortic valves, diabetic cardiomyopathy, hyperhomocysteinemic cerebrovascular, peripheral vascular and coronary heart diseases, neurodegenerative disorders (Alzheimer and Parkinson diseases, amyotrophic lateral sclerosis, glaucoma), and accelerated aging frequently accompanied with cancer. This review focuses on the checkpoints shown to be crucial for unperturbed cell cycle regulation, dysregulation of which might be considered as a potential molecular marker for early diagnosis of and therapy efficiency in neurodegenerative, cardiovascular and cancer diseases. An application of the most potent detection technologies such as "Disease Proteomics and Transcriptomics" also considered here, allows a most specific selection of diagnostic markers.

Role of myocardial nitric oxide in diabetic ischemia-reperfusion dysfunction: studies in mice with myocyte-specific overexpression of endothelial nitric-oxide synthase

We investigated the role of nitric oxide (NO) in myocardial ischemia-reperfusion injury of diabetic mice with myocyte-specific overexpression of endothelial NO synthase (NOS). Four weeks after diabetes induction with streptozotocin (blood glucose approximately 29 mM), isolated isovolumic heart function and cellular NO metabolites in response to brief normothermic ischemia-reperfusion were determined. Under normoxic conditions transgenic (TG) hearts from nondiabetic and diabetic animals generated less left-ventricular developed pressure compared with wild-type (WT) control hearts, and this abnormality was unaffected by NOS inhibition. During ischemia, the rise in end-diastolic pressure was less in the TG than WT group of nondiabetic hearts, whereas the transgene had no effect in the diabetic group. Similarly, the transgene also improved reperfusion systolic and diastolic function in nondiabetic but not in diabetic hearts. NOS inhibition worsened reperfusion function in diabetic hearts. Postischemic nitrite and cGMP formation were higher in nondiabetic TG than WT hearts, but in diabetic hearts cGMP was no longer elevated. The formation of reactive oxygen species (superoxide and peroxynitrite) during early reperfusion, measured by electron spin resonance spectroscopy, was similar in nondiabetic WT and TG hearts, but it was significantly higher in diabetic TG hearts. Stimulating endogenous NO production with 10 microM bradykinin more strongly reduced myocardial O(2) consumption in diabetic TG than diabetic WT hearts perfused in normoxia, whereas there was no difference after ischemia-reperfusion. Thus, providing additional endogenous NO is sufficient to protect nondiabetic hearts against ischemia-induced injury, but for a similar protection in diabetic hearts, effective scavenging of reactive oxygen species is also important.

Alleviation of Oxidative Damage in Multiple Tissues in Rats with Streptozotocin-Induced Diabetes by Rice Bran Oil Supplementation

The possibility of 8-hydroxy-2'-deoxyguanosine (8-OHdG) serving as a sensitive biomarker of oxidative DNA damage and oxidative stress was investigated. Reactive oxygen species (ROS) have been reported to be a cause of diabetes induced by chemicals such as streptozotocin (STZ) in experimental animals. In this study, we examined oxidative DNA damage in multiple tissues in rats with STZ-induced diabetes by measuring the levels of 8-OHdG in the liver, kidney, pancreas, brain, and heart. Levels of 8-OHdG in mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) were also determined in multiple tissues of rats treated with rice bran oil. Levels were 0.19 +/- 0.07, 0.88 +/- 0.30, 1.97 +/- 0.05, and 9.79 +/- 3.09 (1/10(5) dG) in the liver of nDNA of normal rats, nDNA of STZ-induced diabetic rats, mtDNA of normal rats, and mtDNA of STZ-induced diabetic rats, respectively. Levels of mtDNA of 8-OHdG were 10 times higher than those of nDNA in multiple tissues. Significant reductions in mtDNA 8-OHdG levels were seen in the liver, kidney, and pancreas of diabetic rats treated with rice bran oil compared with diabetic rats without intervention. Our study demonstrated that oxidative mtDNA damage may occur in multiple tissues of STZ-induced diabetics rats. Intervention with rice bran oil treatment may reverse the increase in the frequency of 8-OHdG.

Oxidative damage in cerebral vessels of diabetic db/db mice

BACKGROUND

Oxidative stress in diabetes mellitus has recently received increasing attention as it has been proven to be associated with the development of diabetic vascular complications. Our aim was to examine whether microvascular changes, including oxidative damage, were induced in the brains of diabetic animals.

METHODS

The expression of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, the binding of cationized ferritin, a marker for evaluating endothelial glycocalyx, to the endothelial cells of capillaries and vascular permeability of intravenously injected horseradish peroxidase were examined in the cortices of 12- and 20-week-old db/db and db/+m mice.

RESULTS

Immunostaining for 8-OHdG was clearly seen in the vessels of the cortex of 20-week-old db/db mice, but was hardly seen in those of mice in the other groups. The immunopositive area of 8-OHdG was significantly increased in the cortex of 20-week-old db/db mice compared with that of 20-week-old db/+m mice. No extravasated leakage of horseradish peroxidase was seen in any groups of mice, while the numbers of cationized ferritin particles binding to the endothelial cells was significantly decreased in 12- and 20-week-old db/db mice compared with that of db/+m mice at the same age, respectively.

CONCLUSION

These findings suggest that changes in endothelial glycocalyx are induced in db/db mice and, in addition, the long-term diabetic condition of these mice induces oxidative DNA damage to the cerebral vessels.

Oxidative damage to nuclear DNA in streptozotocin-diabetic rat liver

1. Accumulating evidence suggests that oxidative and glycative stress is enhanced in diabetes. Oxidative stress induces DNA damage. In the present study, we assessed the 8-oxo-2'-deoxyguanosine (8-oxodG) content of DNA, an indicator of oxidative DNA damage, in streptozotocin (STZ)-induced diabetic (n = 21) and control rats (n = 18). 2. Rats were rendered diabetic by intraperitoneal administration of STZ at a dose of 65 mg/kg. Glucose was determined by glucose oxidase and glycated haemoglobin (GHb), an indicator of glycative stress, was determined by agarose-boronate affinity chromatography. 8-Oxo-2'-deoxyguanosine within the DNA (ratio of 8-oxodG to deoxyguanosine (dG)) was assessed by HPLC in conjunction with both electrochemical (8-oxodG) and diode array (dG) detection. 3. Glucose, GHb and the extent of oxidative DNA damage in the liver of STZ-diabetic rats were much higher compared with control rats. There was a correlation between GHb and 8-oxodG/10(5) dG levels in control (r = 0.756, P < 0.001) and diabetic groups (r = 0.468, 0.02 < P < 0.05). 4. These results clearly show that oxidative damage to hepatic nuclear DNA increases in the diabetic state and that this increase is correlated with glycative stress.

Inter-relationships between DNA damage, ascorbic acid and glycaemic control in Type 2 diabetes mellitus

AIMS

The onset of complications in Type 2 diabetes mellitus (DM) patients cannot be predicted in individuals. Evidence suggests a link between complications and hyperglycaemia, oxidative stress and antioxidants, but causality is unclear. This study investigated baseline (entry) fasting plasma ascorbic acid, lymphocytic DNA damage and glycaemic control in Type 2 DM as part of a long-term study, the aim of which is to explore a biomarker profiling approach to identify and improve outcome in high-risk subjects.

METHODS

A cross-sectional study, in which DNA damage, glycated haemoglobin (HbA(1c)), fasting plasma glucose (FPG) and ascorbic acid (AA) were measured on fasting blood samples collected from 427 Type 2 DM subjects.

RESULTS

DNA damage was significantly (P < 0.0001) and directly correlated to both FPG (r = 0.540) and HbA(1c) (r = 0.282), and was significantly (P < 0.0001), independently and inversely correlated to plasma AA (r = -0.449). In those subjects with both poor glycaemic control and low AA (< 48 microm, the overall mean value for the study group), DNA damage was significantly (P < 0.005) higher compared with those subjects with a similar degree of hyperglycaemia but with AA above the mean.

CONCLUSIONS

The novel finding of a significant inverse relationship between plasma AA and DNA damage in Type 2 DM indicates that poorly controlled diabetic subjects might benefit from increased dietary vitamin C. The data also have important implications for biomarker profiling to identify those subjects who might benefit most from intensive therapy. Longer-term follow-up is underway.

Nox4 NAD(P)H oxidase mediates hypertrophy and fibronectin expression in the diabetic kidney

Renal hypertrophy and extracellular matrix accumulation are early features of diabetic nephropathy. We investigated the role of the NAD(P)H oxidase Nox4 in generation of reactive oxygen species (ROS), hypertrophy, and fibronectin expression in a rat model of type 1 diabetes induced by streptozotocin. Phosphorothioated antisense (AS) or sense oligonucleotides for Nox4 were administered for 2 weeks with an osmotic minipump 72 h after streptozotocin treatment. Nox4 protein expression was increased in diabetic kidney cortex compared with non-diabetic controls and was down-regulated in AS-treated animals. AS oligonucleotides inhibited NADPH-dependent ROS generation in renal cortical and glomerular homogenates. ROS generation by intact isolated glomeruli from diabetic animals was increased compared with glomeruli isolated from AS-treated animals. AS treatment reduced whole kidney and glomerular hypertrophy. Moreover, the increased expression of fibronectin protein was markedly reduced in renal cortex including glomeruli of AS-treated diabetic rats. Akt/protein kinase B and ERK1/2, two protein kinases critical for cell growth and hypertrophy, were activated in diabetes, and AS treatment almost abolished their activation. In cultured mesangial cells, high glucose increased NADPH oxidase activity and fibronectin expression, effects that were prevented in cells transfected with AS oligonucleotides. These data establish a role for Nox4 as the major source of ROS in the kidneys during early stages of diabetes and establish that Nox4-derived ROS mediate renal hypertrophy and increased fibronectin expression.

Increased gene expression of antioxidant enzymes in KKAy diabetic mice but not in STZ diabetic mice

Oxidative stress and the gene expression at the transcriptional level of antioxidant enzymes were investigated in two models of diabetes in mice. We used KKAy mice as a model of obese insulin-resistant diabetes, and streptozotocin-induced diabetic mice (STZ mice) as a model of insulin-deficient diabetes. C57BL mice and saline-injected ICR mice were used as the respective non-diabetic controls. To assess oxidative damage, plasma malonedialdehyde (MDA), urine 8-isoprostane and 8-hydroxy deoxyguanosine (8-OHdG) were measured. The mRNA expression of antioxidant enzymes, superoxide dismutase 1 (SOD-1) and glutathione peroxidase 1 (GPx-1) in the kidney and heart were quantified using a real-time polymerase chain reaction. The KKAy mice demonstrated moderate hyperglycemia and hyperlipidemia, and the STZ mice showed severe hyperglycemia and hypolipidemia. The KKAy mice, but not the STZ mice, showed elevated plasma MDA relative to the non-diabetic controls. Urine 8-isoprostane and 8-OHdG in both diabetic mouse groups increased significantly. The urine oxidative stress markers in the severely hyperglycemic STZ mice were higher than those in the moderately hyperglycemic KKAy mice. Although GPx-1 and SOD-1 showed elevated mRNA expression in the KKAy mice in the kidney and heart, in the STZ mice they did not increase compared to the controls. The compensatory up-regulation of the mRNA expression of antioxidant enzymes may be impaired in the insulin-deficient severely hyperglycemic state.

Tranilast Prevents the Progression of Experimental Diabetic Nephropathy through Suppression of Enhanced Extracellular Matrix Gene Expression

The present study was performed to investigate the effects of the antiallergic drug tranilast on the development of diabetic nephropathy in streptozotocin (50 mg/kg)-induced diabetic spontaneously hypertensive rats (SHR). Diabetic SHR were given standard chow or chow containing tranilast at a dose of 1400 mg/kg for 24 weeks. The effects of tranilast on urinary albumin excretion, mesangial expansion, expression of transforming growth factor-beta (TGF-beta) and type I collagen mRNAs, number of anionic sites on the glomerular basement membrane (GBM), and urinary TGF-beta and 8-hydroxy-2'-deoxyguanosine (8-OHdG) excretion were assessed. Tranilast did not affect the blood glucose concentration or blood pressure in diabetic SHR. Urinary albumin excretion rate and creatinine clearance were markedly increased in diabetic SHR. Tranilast treatment decreased albuminuria and hyperfiltration. Tranilast inhibited the diabetes-induced expansion of mesangial and tuft areas, as well as the increase in urinary TGF-beta and 8-OHdG excretion, loss of anionic sites of GBM, and overexpression of TGF-beta as determined immunohistochemically. The levels of TGF-beta and type I collagen mRNA expression were increased in the renal cortex in untreated diabetic SHR at 24 weeks, as determined by real-time quantitative polymerase chain reaction. Tranilast treatment inhibited the up-regulation of TGF-beta and type I collagen mRNA expression by 65 and 36%, respectively, in diabetic SHR. In conclusion, tranilast decreased albuminuria by suppressing glomerular hyperfiltration, mesangial expansion, and loss of the charge barrier via regulation of extracellular matrix gene expression and oxidative stress. Tranilast may be clinically useful in the treatment of diabetic nephropathy.

Role of oxidative stress in diabetic nephropathy

Accumulating research suggests that oxidative stress is a significant contributor to the pathogenesis of diabetic nephropathy. The normal kidney generates a substantial amount of oxidative stress because of its high metabolic activity that is balanced by an extensive antioxidant system. However, in pathologic states such as hyperglycemia, nitroso-oxidant balance shifts toward a pro-oxidant state that accelerates tissue and vascular injury. This oxidative damage progresses concomitant with worsening glucose metabolism, vascular dysfunction, and kidney disease. Accordingly, strategies to reduce oxidative stress in diabetes mellitus may exert favorable effects on the progression of diabetic nephropathy.

Diabetes and chronic nitrate therapy as co-determinants of somatic DNA damage in patients with coronary artery disease

Somatic DNA damage has been linked to coronary artery disease (CAD). However, whether genetic instability is linked to CAD per se or to concomitant potentially genotoxic metabolic and pharmacological factors remains still unclear. The aim of this study was to evaluate the determinants of somatic DNA damage in a large population of patients undergoing coronary angiography. A total of 278 in-hospital patients (215 men, age 61.8+/-0.7 years) were studied by using micronucleus assay (MN) in human lymphocytes, which is one of the most commonly used biomarker for somatic DNA damage. Significant CAD (>50% diameter stenosis) was present in 210 patients (179 men, age 62.3+/-0.7 years). Normal coronary arteries were observed in 68 patients (35 men, age 60.2+/-1.7 years). There were no significant differences between patients with and without CAD, but patients with multivessel disease had the highest MN levels (P=0.01). MN frequency was also found significantly higher in presence of type 2 diabetes (P<0.0001), dyslipidemia (P=0.048) and nitrate therapy (P=0.0002). A significant additive effect was also observed between diabetes and nitrate therapy (P=0.02). On multivariate logistic regression analysis, diabetes [odds ratio=6.8 (95% confidence interval, 3.2-14.5), P<0.0001] and nitrate therapy [odds ratio=2.4 (95% confidence interval, 1.3-4.7), P=0.01] remained the only significant determinants for the 50th percentile of MN (>12 per thousand). These results indicated that diabetes and, to a lesser extent, chronic nitrate therapy are major determinants of somatic DNA instability in patients with CAD. DNA damage might represent an additional pathogenetic dimension and a possible therapeutic target in the still challenging management of coronary artery disease concerning diabetics.

Study of urinary 8-hydroxydeoxyguanosine as a biomarker of oxidative DNA damage in diabetic nephropathy patients

Increased oxidative stress induced by hyperglycemia may contribute to the pathogenesis of diabetic complications. Urinary 8-hydroxydeoxyguanosine (8-OHdG) has been reported to serve as a sensitive biomarker of oxidative DNA damage and also of oxidative stress. This article studied oxidative DNA damage in patients with diabetic nephropathy and in healthy control subjects by urinary 8-OHdG evaluations. Contents of 8-OHdG in urine were analyzed by capillary electrophoresis with end-column amperometric detection (CE-AD) after a single-step solid-phase extraction (SPE). Levels of urinary 8-OHdG in diabetic nephropathy patients with macroalbuminuria was significant higher than in control subjects (5.72 +/- 6.89 micromol/mol creatinine versus 2.33 +/- 2.83 micromol/mol creatinine, P = 0.018). A significant difference of 24 h urinary 8-OHdG excretions exists between the patients with macroalbuminuria and the patients with normoalbuminuria (19.2 +/- 16.8 microg/24 h versus 8.1 +/- 1.7 microg/24 h, P = 0.015). There was a positive correlation between urinary excretion of 8-OHdG and glycosylated hemoglobin (HbA1c) (r = 0.287, P = 0.022). A weak correlation exists between the levels of 8-OHdG and triglyceride (r = 0.230, P = 0.074). However, the urinary 8-OHdG contents are not correlated with blood pressure and total cholesterol. The increased excretion of urinary 8-OHdG is seen as indicating an increased systemic level of oxidative DNA damage in diabetic nephropathy patients.

Repair of cytokine-induced DNA damage in cultured rat islets of Langerhans

Treatment of cultured rat pancreatic islets of Langerhans with the combined cytokines interleukin-1beta (IL-1beta), interferon gamma (IFN gamma) and tumour necrosis factor alpha (TNF alpha) leads to DNA damage including strand breakage. We have investigated the nature of this damage and its repairability. When islets are further incubated for 4 h in fresh medium, the level of cytokine-induced strand breakage remains constant. If the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine (NMMA) is present during cytokine treatment, then strand breakage is prevented. If NMMA is added following, rather than during,the cytokine treatment and islets are incubated for 4 h, further nitric oxide synthesis is prevented and most cytokine-induced strand breaks are no longer seen. To investigate DNA repair following cytokine treatment, cells were transferred to fresh medium and incubated for 4 h in the presence of hydroxyurea (HU) and 1-beta-D-arabinosyl cytosine (AraC), as inhibitors of strand rejoining. In the presence of these inhibitors there was an accumulation of strand breaks that would otherwise have been repaired. However, when further nitric oxide synthesis was inhibited by NMMA, significantly less additional strand breakage was seen in the presence of HU and AraC. We interpret this, as indicating that excision repair of previously induced base damage did not contribute significantly to strand breakage. Levels of oxidised purines, as indicated by formamidopyrimidine glycosylase (Fpg) sensitive sites, were not increased in cytokine-treated islets. We conclude that in these primary insulin-secreting cells: (a) the DNA damage induced by an 18h cytokine treatment is prevented by an inhibitor of nitric oxide synthase, (b) much of the damage is in the form of apparent strand breaks rather than altered bases such as oxidised purines, (c) substantial repair is ongoing during the cytokine treatment and this repair is not inhibited in the presence of nitric oxide.

Effect of I-deprenyl and gliclazide on oxidant stress/antioxidant status and dna damage in a diabetic rat model

BACKGROUND

This study investigates the possible effect of monoamine oxidase inhibitor (MAOI), selegyline (l-deprenyl), in combination with oral antidiabetic-gliclazide (OAD), in preventing oxidative stress in streptozotocin-induced diabetes model in male Swiss Albino rats by measuring oxidant stress/ DNA damage and antioxidant levels.

METHODS

Diabetic rats were divided into four groups (n = 10) as (1) diabetic untreated (DM), (2) deprenyl treated (DM + D), (3) gliclazide treated (DM + O), and (4) gliclazide and deprenyl treated (DM + O + D). Controls were divided into two groups (n = 8) (1) untreated (C), and (2) deprenyl treated (C + D). Gliclazide 5 mg/kg and/or MAOI 0.25 mg/kg daily were given orally by gavage for 4 weeks. At the end of the 12th week, catalase and superoxide dismutase (SOD) levels in erythrocyte lysates (EL); total antioxidant status (TAS), 8-hydroxy-deoxyguanosine (8-OHdG), malondialdehyde (MDA), and vitamin A and E levels in plasma, MDA, and MAO in liver homogenates were determined.

RESULTS

Diabetic rats showed a decrease in EL-SOD, plasma TAS, and vitamin E, and an increase in plasma 8-OHdG, plasma, and liver MDA levels (p < 0.05). Gliclazide and/or deprenyl decreased 8OHdG levels and increased antioxidant levels and survival when compared with untreated diabetic rats (p < 0.05). The lowest 8-OHdG levels were determined in the DM +O + D group.

CONCLUSIONS

The combined treatment of deprenyl and gliclazide may contribute to the control of the physiopathological mechanisms underlying both the process of aging and type 2 diabetes by reducing oxidant stress and DNA damage, improving antioxidant status, and increasing survival, and may have implications for further clinical studies.

Oxidative DNA damage and disease: induction, repair and significance

The generation of reactive oxygen species may be both beneficial to cells, performing a function in inter- and intracellular signalling, and detrimental, modifying cellular biomolecules, accumulation of which has been associated with numerous diseases. Of the molecules subject to oxidative modification, DNA has received the greatest attention, with biomarkers of exposure and effect closest to validation. Despite nearly a quarter of a century of study, and a large number of base- and sugar-derived DNA lesions having been identified, the majority of studies have focussed upon the guanine modification, 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-OH-dG). For the most part, the biological significance of other lesions has not, as yet, been investigated. In contrast, the description and characterisation of enzyme systems responsible for repairing oxidative DNA base damage is growing rapidly, being the subject of intense study. However, there remain notable gaps in our knowledge of which repair proteins remove which lesions, plus, as more lesions identified, new processes/substrates need to be determined. There are many reports describing elevated levels of oxidatively modified DNA lesions, in various biological matrices, in a plethora of diseases; however, for the majority of these the association could merely be coincidental, and more detailed studies are required. Nevertheless, even based simply upon reports of studies investigating the potential role of 8-OH-dG in disease, the weight of evidence strongly suggests a link between such damage and the pathogenesis of disease. However, exact roles remain to be elucidated.

Interventions with antioxidants and nutrients in relation to oxidative DNA damage and repair

Cells are constantly exposed to oxidants from metabolic and other biochemical reactions as well as external factors, suggesting that DNA repair systems and nutritional antioxidants are important determinants for low levels of DNA damage and cancer risk. The effects of single antioxidants, as well as various vegetables, fruits and carotenoid- and polyphenolic-rich products, have been assessed with biomarkers, mainly including DNA damage in white blood cells (WBC), urinary excretion of oxidized bases and nucleosides and DNA repair capacity. The basal levels of oxidative DNA damage, and effects of the interventions have been rather variable, possibly reflecting differences in the populations, regimens, and the type of assays. In general, single dose antioxidant interventions have shown protective effects with respect to WBC DNA oxidation. Studies with continuous ingestion of antioxidants show mixed results with respect to effects on oxidative DNA damage in WBC, possibly due to various problems with design, statistical power and period effects. Studies with only male subjects appear to show consistent antioxidant effects in terms of reduced levels of oxidized pyrimidines. Investigations of oxidatively stressed subjects, e.g. HIV-infected patients or diabetics, suggest beneficial outcomes in populations with high initial levels of oxidative DNA damage. Recent research on the effect of antioxidants on DNA repair enzymes suggest effects in terms of increased removal of oxidized purines, whereas mRNA levels of the relevant DNA repair genes appears to be unaffected by an antioxidant-rich diet. In the future, care should be taken with respect to design of intervention studies and considerations of gender effect, genotypes of defence enzymes as well as DNA repair capacity.

Nutrient intakes; biochemical and risk indices associated with Type 2 diabetes and glycosylated haemoglobin, in the British National Diet and Nutrition Survey of people aged 65 years and over

AIMS

To characterize nutritional differences between survey participants diagnosed with Type 2 diabetes; those without diabetes, and those with "undiagnosed diabetes" based on glycosylated haemoglobin (HbA(1c)).

SUBJECTS AND METHODS

The 1994/5 British National Diet and Nutrition Survey, of people aged 65 years and over (mean age 78 years), included 73 respondents with diagnosed Type 2 diabetes [mean (sd) HbA(1c) = 7.06 (2.05)%], and 30 with "undiagnosed diabetes" (defined as HbA(1c) > 6.3%; mean (sd) HbA(1c) = 7.40 (1.66)%], among a representative sample of 1038 with anthropometry; 4-day weighed diet; blood and urine status measurements.

RESULTS

The prevalence of Type 2 diabetes (diagnosed + undiagnosed) was 10%. In subjects without diagnosis of diabetes, those with HbA(1c) > 6.3% had on average a significantly higher body weight (73.6 vs. 67.9 kg), higher waist circumference (99.8 vs. 91.8 cm), higher body mass index (28.6 vs. 25.9 kg/m(2)) and higher white cell counts (7.64 vs. 7.09 x 10(9)/l), than those with mean HbA(1c) < or = 6.3%. Diagnosed diabetic subjects had significantly higher energy-adjusted intakes of protein, fibre, vitamins and minerals than those not in this category (P < 0.01). In contrast, those with undiagnosed diabetes (HbA(1c) > 6.3%) were nutritionally "at risk", having low plasma concentrations of lycopene (0.13 vs. 0.24 micromol/l) and high density lipoprotein cholesterol (0.99 vs. 1.27 micromol/l) and a trend towards low vitamin C (24 vs. 36 micromol/l) which was significant (P < 0.01) for men. HbA(1c) was positively correlated with white cell count, plasma fasting triglycerides, plasma alkaline phosphatase and homocysteine (all P < 0.01 overall), being particularly striking amongst men.

CONCLUSIONS

Among older British citizens, those with diagnosed diabetes had healthier nutritional profiles than those undiagnosed with high HbA(1c). Important health-promoting benefits are therefore predicted following early diagnosis and nutritional advice for people with Type 2 diabetes.

Accumulation of somatic mutation in mitochondrial DNA and atherosclerosis in diabetic patients

A point mutation of mitochondrial DNA at nucleotide position 3243 A to G is responsible for the genetic cause of diabetes. Otherwise, this mutation is also reported to occur as a somatic mutation, possibility because of oxidative stress. Because diabetes may cause oxidative stress, we hypothesized that accumulation of the somatic A3243G mutation in mitochondrial DNA may be accelerated by diabetes. DNA was extracted from blood samples of 290 nondiabetic healthy subjects (aged 0-60 years) and from 383 type 2 diabetic patients (aged 18-80 years). Then, the extent of somatic A3243G mutation in total mitochondrial DNA was detected by real-time polymerase chain reaction (PCR) using the TaqMan probe. The genotyping of ACE I/D or p22phox C242T was done by PCR or PCR-restriction fragment length polymorphism. Although the level of the A3243G mutation was negligible in the newborn group, it increased in healthy subjects aged 20-29 and 41-60 years. In diabetic patients, the mutational rate increased along with age and the duration of diabetes. In the middle-aged group (41-60 years old), the A3243G mutation accumulates fourfold higher in the diabetic patients than in the healthy subjects. Moreover, multiple regression analysis revealed that the most critical factor associated with this mutation in diabetic patients was the duration of diabetes. Furthermore, the genotype of DD, DI-CC (ACE-p22phox) has the highest mutational rate and the thickest intima-media thickness of the carotid artery. In conclusion, diabetes accelerates the accumulation of the somatic A3243G mutation in mitochondrial DNA, and this somatic mutation may be a marker for the duration of diabetes and atherosclerosis.

Accumulation of somatic mutation in mitochondrial DNA and atherosclerosis in diabetic patients

A point mutation of mitochondrial DNA at nucleotide position 3243 A to G is responsible for the genetic cause of diabetes. Otherwise, this mutation is also reported to occur as a somatic mutation, possibility because of oxidative stress. Because diabetes may cause oxidative stress, we hypothesized that accumulation of the somatic A3243G mutation in mitochondrial DNA may be accelerated by diabetes. DNA was extracted from blood samples of 290 nondiabetic healthy subjects (aged 0-60 years) and from 383 type 2 diabetic patients (aged 18-80 years). Then, the extent of somatic A3243G mutation in total mitochondrial DNA was detected by real-time polymerase chain reaction (PCR) using the TaqMan probe. The genotyping of ACE I/D or p22phox C242T was done by PCR or PCR-restriction fragment length polymorphism. Although the level of the A3243G mutation was negligible in the newborn group, it increased in healthy subjects aged 20-29 and 41-60 years. In diabetic patients, the mutational rate increased along with age and the duration of diabetes. In the middle-aged group (41-60 years old), the A3243G mutation accumulates fourfold higher in the diabetic patients than in the healthy subjects. Moreover, multiple regression analysis revealed that the most critical factor associated with this mutation in diabetic patients was the duration of diabetes. Furthermore, the genotype of DD, DI-CC (ACE-p22phox) has the highest mutational rate and the thickest intima-media thickness of the carotid artery. In conclusion, diabetes accelerates the accumulation of the somatic A3243G mutation in mitochondrial DNA, and this somatic mutation may be a marker for the duration of diabetes and atherosclerosis.

Cellular Carbonyl Stress Enhances the Expression of Plasminogen Activator Inhibitor-1 in Rat White Adipocytes via Reactive Oxygen Species-dependent Pathway

Carbonyl stress is one of the important mechanisms of tissue damage in vascular complications of diabetes. In the present study, we observed that the plasminogen activator inhibitor-1 (PAI-1) levels in serum and its gene expression in adipose tissue were up-regulated in aged OLETF rats, model animals of obese type 2 diabetes. To study the mechanism of PAI-1 up-regulation, we examined the effect of advanced glycation end products (AGEs) and the product of lipid peroxidation (4-hydroxy-2-nonenal (HNE)), both of which are endogenously generated under carbonyl stress. Stimulation of primary white adipocytes by either AGE or HNE resulted in the elevation of PAI-1 in culture medium and at mRNA levels. The up-regulation of PAI-1 was also observed by incubating the cells in high glucose medium (30 mm, 48 h). The stimulatory effects by AGE or high glucose were inhibited by antioxidant, pyrrolidine dithiocarbamate, and reactive oxygen scavenger, probucol, suggesting a pivotal role of oxidative stress in white adipocytes. We also found that the effect by HNE was inhibited by antioxidant, N-acetylcysteine and that a specific inhibitor of glutathione biosynthesis, l-buthionine-S,R-sulfoximine, augmented the effect of subthreshold effect of HNE. Bioimaging of reactive oxygen species (ROS) by a fluorescent indicator, 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate, revealed ROS production in white adipocytes treated with AGE or HNE. These results suggest that cellular carbonyl stress induced by AGEs or HNE may stimulate PAI-1 synthesis in and release from adipose tissues through ROS formation.

Prevention of diabetic nephropathy by treatment with astaxanthin in diabetic db/db mice

Oxidative stress is implicated as an important mechanism by which diabetes causes nephropathy. Astaxanthin, which is found as a common pigment in algae, fish, and birds, is a carotenoid with significant potential for antioxidative activity. In this study, we examined whether chronic administration of astaxanthin could prevent the progression of diabetic nephropathy induced by oxidative stress in mice. We used female db/db mice, a rodent model of type 2 diabetes, and their non-diabetic db/m littermates. The mice were divided into three groups as follows: non-diabetic db/m, diabetic db/db, and diabetic db/db treated with astaxanthin. Blood glucose level, body weight, urinary albumin, and urinary 8-hydroxydeoxyguanosine (8-OHdG) were measured during the experiments. Histological and 8-OHdG immunohistochemical studies were performed for 12 weeks from the beginning of treatment. After 12 weeks of treatment, the astaxanthin-treated group showed a lower level of blood glucose compared with the non-treated db/db group; however, both groups had a significantly high level compared with the db/m mice. The relative mesangial area calculated by the mesangial area/total glomerular area ratio was significantly ameliorated in the astaxanthin-treated group compared with the non-treated db/db group. The increases in urinary albumin and 8-OHdG at 12 weeks of treatment were significantly inhibited by chronic treatment with astaxanthin. The 8-OHdG immunoreactive cells in glomeruli of non-treated db/db mice were more numerous than in the astaxanthin-treated db/db mice. In this study, treatment with astaxanthin ameliorated the progression and acceleration of diabetic nephropathy in the rodent model of type 2 diabetes. The results suggested that the antioxidative activity of astaxanthin reduced the oxidative stress on the kidneys and prevented renal cell damage. In conclusion, administration of astaxanthin might be a novel approach for the prevention of diabetes nephropathy.

Associations between hyperglycaemia and somatic transversion mutations in mitochondrial DNA of people with diabetes mellitus

AIMS/HYPOTHESIS

Considering that increased oxidative stress induced by hyperglycaemia plays a possible role in the pathogenesis of diabetic complications and that mitochondrial DNA (mDNA) is thought to be more vulnerable than nuclear DNA, we investigated what somatic mutations actually occur in the mDNA of diabetic patients. We also studied the relations between those mutations and urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) which is known to increase considerably in people with diabetes.

METHODS

We identified somatic mutations by subcloning and sequencing two segments of mDNA [control region (nt 15996-16401) and the segment encompassing t-RNA(Leu(UUR))(nt 3149-3404)] in the peripheral blood cells of six diabetic women and control subjects matched for age and sex. This was done in 20 colonies each. In each case we also assayed urinary 8-OHdG.

RESULTS

No difference in the aggregate somatic mutational burden of mDNA was found between patients and control subjects. However, the incidence of somatic transversion mutations in mDNA was significantly higher in diabetic patients than in control subjects (13.93+/-4.57 x 10(-5) vs 1.27+/-1.27 x 10(-5) mutations per base pair; p=0.031, according to Mann-Whitney U-test). There was no significant difference in transition mutations. A correlation was found between the transversion mutational burden and HbA(1)c values, but not between it and 8-OHdG content in the urine.

CONCLUSIONS/INTERPRETATION

We showed that somatic transversion point mutations of mDNA increase in diabetic patients. Such transversion mutations can become a new biomarker for mDNA damage associated with hyperglycaemia and possibly caused by oxidative stress but not reflected by urinary 8-OHdG.

The contribution of mitochondria to common disorders

Mitochondrial dysfunction secondary to mitochondrial and nuclear DNA mutations has been associated with energy deficiency in multiple organ systems and a variety of severe, often fatal, clinical syndromes. Although the production of energy is indeed the primary function of mitochondria, attention has also been directed toward their role producing reactive oxygen and nitrogen species and the subsequent widespread deleterious effects of these intermediates. The generation of toxic reactive intermediates has been implicated in a number of relatively common disorders, including neurodegenerative diseases, diabetes, and cancer. Understanding the role mitochondrial dysfunction plays in the pathogenesis of common disorders has provided unique insights into a number of diseases and offers hope for potential new therapies.

Oxidative DNA damage in peripheral blood cells in type 2 diabetes mellitus: higher vulnerability of polymorphonuclear leukocytes

Since oxidative stress is thought to play an important role in the pathogenesis and complications of diabetes, we used the comet assay (single cell alkaline gel electrophoresis) to evaluate DNA strand breaks and DNA base oxidation, measured as FPG (formamidopyrimidine DNA glycosylase)-sensitive sites, in peripheral blood cells (PBC) from type 2 diabetes patients and healthy controls. Oxidative DNA damage in leukocytes was increased in diabetic compared to normal subjects. However, no differences in the levels of DNA damage in isolated lymphocytes were found between the two groups. These data indicate a higher vulnerability to oxidative damage of polymorphonuclear as compared to mononuclear leukocytes in type 2 diabetes. Thus, the measurement of oxidative DNA damage in leukocytes by means of the comet assay is a suitable marker for the evaluation of systemic oxidative stress in diabetic patients.

Astaxanthin protects beta-cells against glucose toxicity in diabetic db/db mice

Oxidative stress induced by hyperglycemia possibly causes the dysfunction of pancreatic beta-cells and various forms of tissue damage in patients with diabetes mellitus. Astaxanthin, a carotenoid of marine microalgae, is reported as a strong anti-oxidant inhibiting lipid peroxidation and scavenging reactive oxygen species. The aim of the present study was to examine whether astaxanthin can elicit beneficial effects on the progressive destruction of pancreatic beta-cells in db/db mice--a well-known obese model of type 2 diabetes. We used diabetic C57BL/KsJ-db/db mice and db/m for the control. Astaxanthin treatment was started at 6 weeks of age and its effects were evaluated at 10, 14, and 18 weeks of age by non-fasting blood glucose levels, intraperitoneal glucose tolerance test including insulin secretion, and beta-cell histology. The non-fasting blood glucose level in db/db mice was significantly higher than that of db/m mice, and the higher level of blood glucose in db/db mice was significantly decreased after treatment with astaxanthin. The ability of islet cells to secrete insulin, as determined by the intraperitoneal glucose tolerance test, was preserved in the astaxanthin-treated group. Histology of the pancreas revealed no significant differences in the beta-cell mass between astaxanthin-treated and -untreated db/db mice. In conclusion, these results indicate that astaxanthin can exert beneficial effects in diabetes, with preservation of beta-cell function. This finding suggests that anti-oxidants may be potentially useful for reducing glucose toxicity.

DNA damage and expression of checkpoint genes p21(WAF1/CIP1) and 14-3-3 sigma in taurine-deficient cardiomyocytes

OBJECTIVE

Taurine depletion is associated with development of cardiomyopathy. Further, oxidative stress is advanced as a critical factor mediating the effect of taurine deficiency on target organs. However, the molecular mechanism(s) linking taurine deficiency with the development of cardiomyopathy remains elusive. Since transition between apoptotic degeneration and cell proliferation in stress conditions is regulated at cell cycle checkpoints, we determined the expression of two such genes, namely p21(WAF1/CIP1) and 14-3-3 sigma as well as p53 that are responsible for oxidative stress and DNA damage. We also carried out quantitative determination of DNA damage.

METHODS

Cardiomyocytes from beta-alanine-induced taurine-depleted (TD) rats were used for this investigation. Single- and double-stranded DNA damage was quantified using comet assay analysis. Western blot and two-dimensional polyacrylamide gel electrophoresis with immunoblotting analysis were applied for protein analysis.

RESULTS

Comet assay analysis indicated that the extent of double-stranded DNA damage was greater in TD than in control cardiomyocytes. Whereas only traces of both p53 and p21(WAF1/CIP1) and no detectable expression of 14-3-3 sigma were found in cardiomyocytes of control animals, the TD cardiomyocytes expressed all three genes.

CONCLUSIONS

DNA damage and the consequent up-regulation of checkpoint proteins observed in TD cardiomyocytes indicate the involvement of cell cycle control mechanisms in the effect of taurine deficiency on cardiomyocytes. Single- and double-stranded DNA damage and the consequent arrest of cell proliferation in both G(1) and G(2) phases of the cell cycle induced by checkpoint proteins may trigger the cardiomyopathy that is associated with taurine deficiency.

Protein kinase C-dependent increase in reactive oxygen species (ROS) production in vascular tissues of diabetes: role of vascular NAD(P)H oxidase

Hyperglycemia seems to be an important causative factor in the development of micro- and macrovascular complications in patients with diabetes. Several hypotheses have been proposed to explain the adverse effects of hyperglycemia on vascular cells. Both protein kinase C (PKC) activation and oxidative stress theories have increasingly received attention in recent years. This article shows a PKC-dependent increase in oxidative stress in diabetic vascular tissues. High glucose level stimulated reactive oxygen species (ROS) production via a PKC-dependent activation of NAD(P)H oxidase in cultured aortic endothelial cells, smooth muscle cells, and renal mesangial cells. In addition, expression of NAD(P)H oxidase components were shown to be upregulated in vascular tissues and kidney from animal models of diabetes. Furthermore, several agents that were expected to block the mechanism of a PKC-dependent activation of NAD(P)H oxidase clearly inhibited the increased oxidative stress in diabetic animals, as assessed by in vivo electron spin resonance method. Taken together, these findings strongly suggest that the PKC-dependent activation of NAD(P)H oxidase may be an essential mechanism responsible for increased oxidative stress in diabetes.

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.

The sensory symptoms of diabetic polyneuropathy are improved with alpha-lipoic acid: the SYDNEY trial

OBJECTIVE

Because alpha-lipoic acid (ALA), a potent antioxidant, prevents or improves nerve conduction attributes, endoneurial blood flow, and nerve (Na(+) K(+) ATPase activity in experimental diabetes and in humans and may improve positive neuropathic sensory symptoms, in this report we further assess the safety and efficacy of ALA on the Total Symptom Score (TSS), a measure of positive neuropathic sensory symptoms.

RESEARCH DESIGN AND METHODS

Metabolically stable diabetic patients with symptomatic (stage 2) diabetic sensorimotor polyneuropathy (DSPN) were randomized to a parallel, double-blind study of ALA (600 mg) (n = 60) or placebo (n = 60) infused daily intravenously for 5 days/week for 14 treatments. The primary end point was change of the sum score of daily assessments of severity and duration of TSS. Secondary end points were sum scores of neuropathy signs (NIS), symptoms (NSC), attributes of nerve conduction, quantitative sensation tests (QSTs), and an autonomic test.

RESULTS

At randomization, the groups were not significantly different by the criteria of metabolic control or neuropathic end points. After 14 treatments, the TSS of the ALA group had improved from baseline by an average of 5.7 points and the placebo group by an average of 1.8 points (P < 0.001). Statistically significant improvement from baseline of the ALA, as compared with the placebo group, was also found for each item of the TSS (lancinating and burning pain, asleep numbness and prickling), NIS, one attribute of nerve conduction, and global assessment of efficacy.

CONCLUSIONS

Intravenous racemic ALA, a potent antioxidant, rapidly and to a significant and meaningful degree, improved such positive neuropathic sensory symptoms as pain and several other neuropathic end points. This improvement of symptoms was attributed to improved nerve pathophysiology, not to increased nerve fiber degeneration. Because of its safety profile and its effect on positive neuropathic sensory symptoms and other neuropathic end points, this drug appears to be a useful ancillary treatment for the symptoms of diabetic polyneuropathy.

Polyol pathway and diabetic peripheral neuropathy

This chapter critically examines the concept of the polyol pathway and how it relates to the pathogenesis of diabetic peripheral neuropathy. The two enzymes of the polyol pathway, aldose reductase and sorbitol dehydrogenase, are reviewed. The structure, biochemistry, physiological role, tissue distribution, and localization in peripheral nerve of each enzyme are summarized, along with current informaiton about the location and structure of their genes, their alleles, and the possible links of each enzyme and its alleles to diabetic neuropathy. Inhibitors of pathway enzyme and results obtained to date with pathway inhibitors in experimental models and human neuropathy trials are updated and discussed. Experimental and clinical data are analyzed in the context of a newly developed metabolic odel of the in vivo relationship between nerve sorbitol concentration and metabolic flux through aldose reuctase. Overall, the data will be interpreted as supporting the hypothesis that metabolic flux through the polyol pathway, rather than nerve concentration of sorbitol, is the predominant polyol pathway-linked pathogeneic factor in diabetic preipheral nerve. Finally, key questions and future directions for bsic and clinical research in this area are considered. It is concluded that robust inhibition of metabolic flux through the polyol pathway in peripheral nerve will likely result in substantial clinical benefit in treating and preventing the currently intractable condition of diabetic peripheral neuropathy. To accomplish this, it is imperative to develop and test a new generation of "super-potent" polyol pathway inhibitors.

Oxidative Stress in Diabetes

Increasing evidence in both experimental and clinical studies suggests that there is a close link between hyperglycemia, oxidative stress and diabetic complications. High blood glucose level determines overproduction of reactive oxygen species (ROS) by the mitochondria electron transport chain. High reactivity of ROS determines chemical changes in virtually all cellular components, leading to DNA and protein modification and lipid peroxidation. Measurement of biomarkers such 8-hydroxy-2'deoxyguanosine (8-OHdG), isoprostanes, malondialdehyde (MDA) and nitrotyrosine is a useful tool to assess the oxidative stress of the organism. Knowledge of the mechanisms of ROS damage of is the first step for development of new therapeutic molecules and for rationalizing the use of existing drugs.

Oxidative injury and apoptosis of dorsal root ganglion neurons in chronic experimental diabetic neuropathy

We evaluated the effects of chronic hyperglycemia on L5 dorsal root ganglion (DRG) neurons using immunohistochemical and electrophysiologic techniques for evidence of oxidative injury. Experimental diabetic neuropathy was induced by streptozotocin. To evaluate the pathogenesis of the neuropathy, we studied peripheral nerve after 1, 3, and 12 months of diabetes. Electrophysiologic abnormalities were present from the first month and persisted over 12 months. 8-Hydroxy-2'-deoxyguanosine labeling was significantly increased at all time points in DRG neurons, indicating oxidative injury. Caspase-3 labeling was significantly increased at all three time points, indicating commitment to the efferent limb of the apoptotic pathway. Apoptosis was confirmed by a significant increase in the percentage of neurons undergoing apoptosis at 1 month (8%), 3 months (7%), and 12 months (11%). These findings support the concept that oxidative stress leads to oxidative injury of DRG neurons, with mitochondrium as a specific target, leading to impaired mitochondrial function and apoptosis, manifested clinically as a predominantly sensory neuropathy.

Coronary atherosclerosis and somatic mutations: an overview of the contributive factors for oxidative DNA damage

Coronary artery disease (CAD) is a multifactorial process that appears to be caused by the interaction of environmental risk factors with multiple predisposing genes. Genetic research on CAD has traditionally focused on investigation aimed at identifying disease-susceptibility genes. Recent evidence suggests that somatically acquired DNA mutations may also contribute significantly to the pathogenesis of the disease, underlining the similarity between atherosclerotic and carcinogenic processes. The generation of oxidative stress has been emphasized as an important cause of DNA damage in atherosclerosis. This review highlights some of the major atherogenic risk factors as likely mediators in the oxidative modification of DNA. It also examines the hypothesis that an increase in oxidative stress may derive from "oxidatively" damaged mitochondria. Accordingly, further research in this field should be given high priority, since increased somatic DNA damage could be an important pathogenic factor and an additional prognostic predictor, as well as a potential target for therapeutic strategies in coronary artery disease.

Progress in the analysis of urinary oxidative DNA damage

Oxidative DNA damage has been implicated to be important in the pathogenesis of many diseases, including cancer and heart disease. The assessment of damage in various biological matrices, such as DNA, serum, and urine, is vital to understanding this role and subsequently devising intervention strategies. Despite the numerous techniques to measure oxidative DNA damage products in urine, it remains unclear what these measurements truly represent. Sources of urinary lesions may include the diet, cell death, and, of most interest, DNA repair. Were it possible to exclude the two former contributions, a noninvasive assay for DNA repair would be invaluable in the study of DNA damage and disease. This review highlights that, although progress has been made, significant work remains. Diet, cell death, and repair need continued examination to further elucidate the kinetics of lesion formation and clearance in vivo. Studies from our laboratory and others are making appreciable progress towards the interpretation of urinary lesion measurements along with the development of urinary assays to evaluate DNA repair. Upon establishment of these details, urinary oxidative DNA damage measurements may become more than a reflection of generalized oxidative stress.

Oxidative DNA damage in human white blood cells in dietary antioxidant intervention studies

Many epidemiologic studies have addressed the possible preventive effects of antioxidants in disease causation and progression. With the use of molecular techniques, it is feasible to investigate specific properties of antioxidants in intervention studies. The most widely used techniques to investigate oxidative DNA damage in white blood cells are the measurement of 7-hydroxy-8-oxo-2'-deoxyguanosine and the comet assay. The types of antioxidant intervention studies include those involving single or multiple supplementations of vitamin C, vitamin E, or carotenoids and those involving various natural food products (eg, carrot juice). In short-term intervention studies (usually weeks or a few months), results have been mixed. Single-dosing studies found that decreased oxidative DNA damage lasted only hours after antioxidant supplementation, suggesting that the preventive effect is relatively short. In addition, many of the positive studies were not placebo-controlled, thus leaving a possibility of false-positive results caused by period effects, eg, seasonal variation, changes in the lifestyles of the subjects, or variation in measurements over time. Because participation in an antioxidant intervention study may cause changes in dietary habits and because seasonal changes may have profound effects, it is recommended that future studies have a placebo-controlled, parallel design rather than a crossover design.

Accumulation of 8-hydroxy-2'-deoxyguanosine and mitochondrial DNA deletion in kidney of diabetic rats

Oxidative stress may contribute to the pathogenesis of diabetic nephropathy. However, the detailed molecular mechanism remains uncertain. Here, we report oxidative mitochondrial DNA (mtDNA) damage and accumulation of mtDNA with a 4,834-bp deletion in kidney of streptozotocin-induced diabetic rats. At 8 weeks after the onset of diabetes, levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), which is a marker of oxidative DNA damage, were significantly increased in mtDNA from kidney of diabetic rats but not in nuclear DNA, suggesting the predominant damage of mtDNA. Semiquantitative analysis using PCR showed that the frequency of 4,834-bp deleted mtDNA was markedly increased in kidney of diabetic rats at 8 weeks, but it did not change at 4 weeks. Intervention by insulin treatment starting at 8 weeks rapidly normalized an increase in renal 8-OHdG levels of diabetic rats, but it did not reverse an increase in the frequency of deleted mtDNA. Our study demonstrated for the first time that oxidative mtDNA damage and subsequent mtDNA deletion may be accumulated in kidney of diabetic rats. This may be involved in the pathogenesis of diabetic nephropathy.

The pathogenesis of diabetic retinopathy: old concepts and new questions

Hyperglycaemia appears to be a critical factor in the aetiology of diabetic retinopathy and initiates downstream events including: basement membrane thickening, pericyte drop out and retinal capillary non-perfusion. More recently, focus has been directed to the molecular basis of the disease process in diabetic retinopathy. Of particular importance in the development and progression of diabetic retinopathy is the role of growth factors (eg vascular endothelial growth factor, placenta growth factor and pigment epithelium-derived factor) together with specific receptors and obligate components of the signal transduction pathway needed to support them. Despite these advances there are still a number of important questions that remain to be answered before we can confidently target pathological signals. How does hyperglycaemia regulate retinal vessels? Which growth factors are most important and at what stage of retinopathy do they operate? What is the preferred point in the growth factor signalling cascade for therapeutic intervention? Answers to these questions will provide the basis for new therapeutic interventions in a debilitating ocular condition.

Oxidative stress in diabetic nephropathy: basic and clinical information

Oxidative stress has been known to play an important role in the development and progression of diabetic nephropathy, but the intracellular signal transduction pathways regulated by reactive oxygen species (ROS) have not been clearly defined. High glucose (HG) induces intracellular ROS directly via glucose metabolism and auto-oxidation and indirectly through the formation of advanced glycation end products and their receptor binding. ROS mimic the stimulatory effects of HG and upregulate transforming growth factor-beta 1, plasminogen activator inhibitor-1, and extracellular matrix (ECM) proteins by glomerular mesangial cells, thus leading to mesangial expansion. ROS activate other signaling molecules, such as protein kinase C and mitogen-activated protein kinases and transcription factors, such as nuclear factor-kappa B, activator protein-1, and specificity protein 1 leading to transcription of genes encoding cytokines, growth factors, and ECM proteins. Finally, various antioxidants inhibit mesangial cell activation by HG and ameliorate features of diabetic nephropathy. These findings qualify ROS as intracellular messengers and as integral glucose-signaling molecules in glomerular mesangial cells in diabetic nephropathy. With this new concept, ROS assume a greater importance in the pathogenesis of diabetic nephropathy. Future studies elucidating other downstream-signaling molecules activated by ROS in mesangial and other renal cells will allow us to understand the final cellular responses to HG, such as proliferation, differentiation, apoptosis, and ECM accumulation. With this new information, we should be able to develop strategies for a more rational treatment of diabetic nephropathy.

No association of glutathione S-transferase M1 gene polymorphism with diabetic nephropathy in Japanese type 2 diabetic patients

Oxidative stress possibly contributes to the development of diabetic nephropathy. Therefore, the levels of endogenous antioxidants may be one of determinants of the susceptibility to diabetic nephropathy. Glutathione S-transferases (GSTs) can work as one of endogenous antioxidants to protect cells from oxidative stress. The M1 member of GST mu class (GSTM1) is polymorphic and only expressed in 55-60% of Caucasians because of the homozygous deletion of the gene (null genotype). Recent studies have provided evidence that the GSTM1 null genotype, i.e. lack of the GSTM1 activity, is associated with an increased susceptibility to lung cancer and colorectal cancer. The present study was conducted to determine whether the genetic polymorphism influences the development of diabetic nephropathy. We examined 105 patients with diabetic nephropathy and 69 patients without diabetic nephropathy in Japanese type 2 diabetic patients with proliferative diabetic retinopathy. GSTM1 genotyping was performed by polymerase chain reaction. The two patient groups were well matched with regard to age, body mass index and HbAlc. GSTM1 null genotype was observed in 48.6% of patients with nephropathy versus 55.1% of patients without nephropathy. The frequency of GSTM1 null genotype was not significantly higher in the patient group with nephropathy than in the patient group without nephropathy. This study is the first to investigate the association of GSTM1 gene polymorphism with the development of diabetic nephropathy. The present results suggest that GSTM1 null genotype does not contribute to the development of diabetic nephropathy in Japanese type 2 diabetic patients.