Interactions of the advanced glycation end product inhibitor pyridoxamine and the antioxidant alpha-lipoic acid on insulin resistance in the obese Zucker rat

The effectiveness of antioxidant agents in delaying progression of diabetic nephropathy: A systematic review of randomized controlled trials

Introduction

Oxidative stress plays a central role in the pathophysiology of diabetes mellitus and its complications, including diabetic nephropathy. Excessive production of reactive oxygen species (ROS) alters renal metabolic pathways, leading to inflammation, endothelial dysfunction, and fibrosis, ultimately resulting in end-stage renal disease (ESRD). Studies have shown that exogenous antioxidants can improve the pathophysiological condition of patients with diabetic nephropathy. Objective: This systematic review aims to investigate the types of antioxidant agents that inhibit the development of diabetic nephropathy and the effectiveness of antioxidant agent interventions to repair kidney structure and function.

Methods

A systematic review of randomized controlled trials that examined the role of antioxidants in improving diabetic nephropathy was conducted. The literature search was performed on PubMed, ScienceDirect, and EBSCO. The inclusion criteria covered articles on the antioxidant activity of herbal extracts and compounds that inhibit the progression of diabetic nephropathy in humans. In addition, the articles were written in English and published between 2012 and 2022. The reporting of the systematic review followed the Preferred Reporting Elements for Systematic Review and Meta-Analysis (PRISMA) guideline. The full texts of all potentially relevant systematic reviews were assessed for quality using the Risk of Bias 2 (RoB 2) tool.

Results

A total of 2,367 articles were identified in the three databases, of which only 15 articles met the inclusion criteria. Antioxidant agents that inhibit diabetic nephropathy can be classified as single antioxidants (silymarin, baicalin, epigallocatechin gallate, vitamin E, selenium, curcumin, α-lipoic acid, and tocotrienol-rich vitamin E) and combined antioxidants (α-lipoic acid with vitamin B6, and resveratrol with losartan). Antioxidant agents have been shown to reduce oxidative stress and inflammation, but their role in the progression of fibrosis remains unclear. The oxidative stress marker MDA was significantly reduced by silymarin, curcumin, vitamin E, tocotrienol-rich vitamin E, selenium, ALA, vitamin B, resveratrol and losartan. Silymarin was found to be the most effective (-3.43 µmol/L; 6.02 to 0.83). Compared to silymarin and epigallocatechin gallate, vitamin E was more effective (at -35.4 ng/L; P < 0.001) in reducing inflammation by decreasing TNF-α levels. In addition, tocotrienol-rich vitamin E, silymarin, baicalin, and selenium showed a decrease TGF-β levels, but did not show statistically significant differences between the placebo and intervention groups.

Conclusion

Potential antioxidant agents, such as flavonoids, vitamins, fatty acids, and antioxidant minerals, were examined in this systematic review. These agents contribute to reducing markers of oxidative stress and hyperglycemia-induced inflammation. Although several antioxidants play a role in reducing fibrosis markers, the effect does not appear to be statistically significant.

Vitamin B6 and diabetes and its role in counteracting advanced glycation end products

Naturally occurring forms of vitamin B6 include six interconvertible water-soluble compounds: pyridoxine (PN), pyridoxal (PL), pyridoxamine (PM), and their respective monophosphorylated derivatives (PNP, PLP, and PMP). PLP is the catalytically active form which works as a cofactor in approximately 200 reactions that regulate the metabolism of glucose, lipids, amino acids, DNA, and neurotransmitters. Most of vitamers can counteract the formation of reactive oxygen species and the advanced glycation end-products (AGEs) which are toxic compounds that accumulate in diabetic patients due to prolonged hyperglycemia. Vitamin B6 levels have been inversely associate with diabetes, while vitamin B6 supplementation reduces diabetes onset and its vascular complications. The mechanisms at the basis of the relation between vitamin B6 and diabetes onset are still not completely clarified. In contrast more evidence indicates that vitamin B6 can protect from diabetes complications through its role as scavenger of AGEs. It has been demonstrated that in diabetes AGEs can destroy the functionality of macromolecules such as protein, lipids, and DNA, thus producing tissue damage that result in vascular diseases. AGEs can be in part also responsible for the increased cancer risk associated with diabetes. In this chapter the relationship between vitamin B6, diabetes and AGEs will be discussed by showing the acquired knowledge and questions that are still open.

Matrix viscoelasticity promotes liver cancer progression in the pre-cirrhotic liver

Type 2 diabetes mellitus is a major risk factor for hepatocellular carcinoma (HCC). Changes in extracellular matrix (ECM) mechanics contribute to cancer development1,2, and increased stiffness is known to promote HCC progression in cirrhotic conditions3,4. Type 2 diabetes mellitus is characterized by an accumulation of advanced glycation end-products (AGEs) in the ECM; however, how this affects HCC in non-cirrhotic conditions is unclear. Here we find that, in patients and animal models, AGEs promote changes in collagen architecture and enhance ECM viscoelasticity, with greater viscous dissipation and faster stress relaxation, but not changes in stiffness. High AGEs and viscoelasticity combined with oncogenic β-catenin signalling promote HCC induction, whereas inhibiting AGE production, reconstituting the AGE clearance receptor AGER1 or breaking AGE-mediated collagen cross-links reduces viscoelasticity and HCC growth. Matrix analysis and computational modelling demonstrate that lower interconnectivity of AGE-bundled collagen matrix, marked by shorter fibre length and greater heterogeneity, enhances viscoelasticity. Mechanistically, animal studies and 3D cell cultures show that enhanced viscoelasticity promotes HCC cell proliferation and invasion through an integrin-β1-tensin-1-YAP mechanotransductive pathway. These results reveal that AGE-mediated structural changes enhance ECM viscoelasticity, and that viscoelasticity can promote cancer progression in vivo, independent of stiffness.

Effects of alpha lipoic acid on metabolic syndrome: A comprehensive review

Metabolic syndrome (MetS) is a multifactorial disease with medical conditions such as hypertension, diabetes, obesity, dyslipidemia, and insulin resistance. Alpha-lipoic acid (α-LA) possesses various pharmacological effects, including antidiabetic, antiobesity, hypotensive, and hypolipidemia actions. It exhibits reactive oxygen species scavenger properties against oxidation and age-related inflammation and refines MetS components. Also, α-LA activates the 5' adenosine monophosphate-activated protein kinase and inhibits the NFκb. It can decrease cholesterol biosynthesis, fatty acid β-oxidation, and vascular stiffness. α-LA decreases lipogenesis, cholesterol biosynthesis, low-density lipoprotein and very low-density lipoprotein levels, and atherosclerosis. Moreover, α-LA increases insulin secretion, glucose transport, and insulin sensitivity. These changes occur via PI3K/Akt activation. On the other hand, α-LA treats central obesity by increasing adiponectin levels and mitochondrial biogenesis and can reduce food intake mainly by SIRT1 stimulation. In this review, the most relevant articles have been discussed to determine the effects of α-LA on different components of MetS with a special focus on different molecular mechanisms behind these effects. This review exhibits the potential properties of α-LA in managing MetS; however, high-quality studies are needed to confirm the clinical efficacy of α-LA.

AGER1 downregulation associates with fibrosis in nonalcoholic steatohepatitis and type 2 diabetes

Type 2 diabetes is clinically associated with progressive necroinflammation and fibrosis in nonalcoholic steatohepatitis (NASH). Advanced glycation end-products (AGEs) accumulate during prolonged hyperglycemia, but the mechanistic pathways that lead to accelerated liver fibrosis have not been well defined. In this study, we show that the AGEs clearance receptor AGER1 was downregulated in patients with NASH and diabetes and in our NASH models, whereas the proinflammatory receptor RAGE was induced. These findings were associated with necroinflammatory, fibrogenic, and pro-oxidant activity via the NADPH oxidase 4. Inhibition of AGEs or RAGE deletion in hepatocytes in vivo reversed these effects. We demonstrate that dysregulation of NRF2 by neddylation of cullin 3 was linked to AGER1 downregulation and that induction of NRF2 using an adeno-associated virus-mediated approach in hepatocytes in vivo reversed AGER1 downregulation, lowered the level of AGEs, and improved proinflammatory and fibrogenic responses in mice on a high AGEs diet. In patients with NASH and diabetes or insulin resistance, low AGER1 levels were associated with hepatocyte ballooning degeneration and ductular reaction. Collectively, prolonged exposure to AGEs in the liver promotes an AGER1/RAGE imbalance and consequent redox, inflammatory, and fibrogenic activity in NASH.

Vitamin B6 and Diabetes: Relationship and Molecular Mechanisms

Vitamin B6 is a cofactor for approximately 150 reactions that regulate the metabolism of glucose, lipids, amino acids, DNA, and neurotransmitters. In addition, it plays the role of antioxidant by counteracting the formation of reactive oxygen species (ROS) and advanced glycation end-products (AGEs). Epidemiological and experimental studies indicated an evident inverse association between vitamin B6 levels and diabetes, as well as a clear protective effect of vitamin B6 on diabetic complications. Interestingly, by exploring the mechanisms that govern the relationship between this vitamin and diabetes, vitamin B6 can be considered both a cause and effect of diabetes. This review aims to report the main evidence concerning the role of vitamin B6 in diabetes and to examine the underlying molecular and cellular mechanisms. In addition, the relationship between vitamin B6, genome integrity, and diabetes is examined. The protective role of this vitamin against diabetes and cancer is discussed.

Antioxidant Effects and Mechanisms of Medicinal Plants and Their Bioactive Compounds for the Prevention and Treatment of Type 2 Diabetes: An Updated Review

Diabetes mellitus is a metabolic disorder that majorly affects the endocrine gland, and it is symbolized by hyperglycemia and glucose intolerance owing to deficient insulin secretory responses and beta cell dysfunction. This ailment affects as many as 451 million people worldwide, and it is also one of the leading causes of death. In spite of the immense advances made in the development of orthodox antidiabetic drugs, these drugs are often considered not successful for the management and treatment of T2DM due to the myriad side effects associated with them. Thus, the exploration of medicinal herbs and natural products as therapeutic sources for the treatment of T2DM is promoted because they have little or no side effects. Bioactive molecules isolated from natural sources have been proven to lower blood glucose levels via regulating one or more of the following mechanisms: improvement of beta cell function, insulin resistance, glucose (re)absorption, and glucagon-like peptide-1 homeostasis. In recent times, the mechanisms of action of different bioactive molecules with antidiabetic properties and phytochemistry are gaining a lot of attention in the area of drug discovery. This review article presents an update of the findings from clinical research into medicinal plant therapy for T2DM.

Beneficial Effects of Alpha-Lipoic Acid on Hypertension, Visceral Obesity, UCP-1 Expression and Oxidative Stress in Zucker Diabetic Fatty Rats

Evidence suggests that oxidative stress plays a major role in the development of metabolic syndrome. This study aims to investigate whether α-lipoic acid (LA), a potent antioxidant, could exert beneficial outcomes in Zucker diabetic fatty (ZDF) rats. Male 6-week-old ZDF rats and their lean counterparts (ZL) were fed for six weeks with a standard diet or a chow diet supplemented with LA (1 g/kg feed). At 12 weeks of age, ZDF rats exhibited an increase in systolic blood pressure, epididymal fat weight per body weight, hyperglycemia, hyperinsulinemia, insulin resistance (HOMA index), adipocyte hypertrophy and a rise in basal superoxide anion (O₂•⁻) production in gastrocnemius muscle and a downregulation of epididymal uncoupled protein-1 (UCP-1) protein staining. Treatment with LA prevented the development of hypertension, the rise in whole body weight and O₂•⁻ production in gastrocnemius muscle, but failed to affect insulin resistance, hyperglycemia and hyperinsulinemia in ZDF rats. LA treatment resulted in a noticeable increase of pancreatic weight and a further adipocyte hypertrophy, along with a decrease in epididymal fat weight per body weight ratio associated with an upregulation of epididymal UCP-1 protein staining in ZDF rats. These findings suggest that LA was efficacious in preventing the development of hypertension, which could be related to its antioxidant properties. The anti-visceral obesity effect of LA appears to be mediated by its antioxidant properties and the induction of UCP-1 protein at the adipose tissue level in ZDF rats. Disorders of glucose metabolism appear, however, to be mediated by other unrelated mechanisms in this model of metabolic syndrome.

Perspectives on the use of lipoic acid in the support of disease treatment*

Lipoic acid (LA) is a natural compound present in food and used as a dietary supplement. LA is endogenously synthetized in small amounts from octanoid acid in the mitochondria. This compound occurs naturally in vegetables such as spinach, broccoli and in animal tissues, in the kidneys, heart and liver. It has been shown that LA is a cofactor in the multienzyme complexes that are responsible for oxidative decarboxylation of α- ketoacids. LA and its reduced form, dihydrolipoic acid (DHLA), have many biological functions leading to a wide variety of actions such as anti-inflammation and antioxidant protection, scavenging of reactive oxygen species, regenerating other antioxidant agents, such as vitamins C and E, and cytosolic glutathione, chelating the transitional metal ions (e.g. iron and copper), and modulating the signal transduction of nuclear factor. Many authors regard LA as a potentially useful agent in the treatment and/or prevention of many diseases such as diabetes mellitus, overweight, obesity, hypertension, heart diseases, inflammation. This review concentrates on the role of LA in the treatment of diabetes mellitus, obesity, inflammation and blood pressure regulation. LA can be considered as a potentially useful drug in treatment of many diseases, particularly those related to excessive production of free radicals.

RAGE is a Potential Cause of Onset and Progression of Nonalcoholic Fatty Liver Disease

OBJECTIVE

Fatty liver is a rising global health concern, significantly increasing the burden of health care cost. Nonalcoholic fatty liver disease (NAFLD) has a correlation with metabolic syndrome and its complications.

METHOD

We reviewed the literature regarding the mechanisms of developing NAFLD through AGE-RAGE signaling.

RESULTS

NAFLD, metabolic syndrome, and production of advanced glycation end-products (AGEs) share many common risk factors and appear to be connected. AGE induces production of the receptor for AGE (RAGE). AGE-RAGE interaction contributes to fat accumulation in the liver leading to inflammation, fibrosis, insulin resistance, and other complications of the fatty liver disease. The immune system, especially macrophages, has an important defense mechanism against RAGE pathway activities.

CONCLUSION

Soluble form of RAGE (sRAGE) has the capability to reduce inflammation by blocking the interaction of AGE with RAGE. However, sRAGE has some limitations, and the best method of usage is probably autotransplantation of transfected stem cells or monocytes, as a precursor of macrophages and Kupffer cells, with a virus that carries sRAGE to alleviate the harmful effects of AGE-RAGE signaling in the settings of fatty liver disease.

The Gradual and Acute Correction of Equinus Using External Fixation

Equinus is one of the most common deformities noted in foot and ankle biomechanics that, at times, if not identified and managed properly may lead to significant lower extremity pathology. With that being said, this deformity is also one that may be both underdiagnosed and undertreated. Treatment for equinus can range from conservative therapy to more aggressive surgical therapy. The purpose of this article is to review the clinical workup to properly identify the deformity and to explore the various treatment options for its timely management, which include gradual or acute correction of equinus using external fixation.

Protective role of vitamin B6 (PLP) against DNA damage in Drosophila models of type 2 diabetes

Growing evidence shows that improper intake of vitamin B6 increases cancer risk and several studies indicate that diabetic patients have a higher risk of developing tumors. We previously demonstrated that in Drosophila the deficiency of Pyridoxal 5′ phosphate (PLP), the active form of vitamin B6, causes chromosome aberrations (CABs), one of cancer prerequisites, and increases hemolymph glucose content. Starting from these data we asked if it was possible to provide a link between the aforementioned studies. Thus, we tested the effect of low PLP levels on DNA integrity in diabetic cells. To this aim we generated two Drosophila models of type 2 diabetes, the first by impairing insulin signaling and the second by rearing flies in high sugar diet. We showed that glucose treatment induced CABs in diabetic individuals but not in controls. More interestingly, PLP deficiency caused high frequencies of CABs in both diabetic models demonstrating that hyperglycemia, combined to reduced PLP level, impairs DNA integrity. PLP-depleted diabetic cells accumulated Advanced Glycation End products (AGEs) that largely contribute to CABs as α-lipoic acid, an AGE inhibitor, rescued not only AGEs but also CABs. These data, extrapolated to humans, indicate that low PLP levels, impacting on DNA integrity, may be considered one of the possible links between diabetes and cancer.

Attenuation of Glucose-Induced Myoglobin Glycation and the Formation of Advanced Glycation End Products (AGEs) by (R)-α-Lipoic Acid In Vitro

High-carbohydrate containing diets have become a precursor to glucose-mediated protein glycation which has been linked to an increase in diabetic and cardiovascular complications. The aim of the present study was to evaluate the protective effect of (R)-α-lipoic acid (ALA) against glucose-induced myoglobin glycation and the formation of advanced glycation end products (AGEs) in vitro. Methods: The effect of ALA on myoglobin glycation was determined via the formation of AGEs fluorescence intensity, iron released from the heme moiety of myoglobin and the level of fructosamine. The extent of glycation-induced myoglobin oxidation was measured via the levels of protein carbonyl and thiol. Results: The results showed that the co-incubation of ALA (1, 2 and 4 mM) with myoglobin (1 mg/mL) and glucose (1 M) significantly decreased the levels of fructosamine, which is directly associated with the decrease in the formation of AGEs. Furthermore, ALA significantly reduced the release of free iron from myoglobin which is attributed to the protection of myoglobin from glucose-induced glycation. The results also demonstrated a significant protective effect of ALA on myoglobin from oxidative damage, as seen from the decreased protein carbonyls and increased protein thiols. Conclusion: The anti-glycation properties of ALA suggest that ALA supplementation may be beneficial in the prevention of AGEs-mediated diabetic and cardiovascular complications.

Nutrients and Oxidative Stress: Friend or Foe?

There are different types of nutritionally mediated oxidative stress sources that trigger inflammation. Much information indicates that high intakes of macronutrients can promote oxidative stress and subsequently contribute to inflammation via nuclear factor-kappa B- (NF-κB-) mediated cell signaling pathways. Dietary carbohydrates, animal-based proteins, and fats are important to highlight here because they may contribute to the long-term consequences of nutritionally mediated inflammation. Oxidative stress is a central player of metabolic ailments associated with high-carbohydrate and animal-based protein diets and excessive fat consumption. Obesity has become an epidemic and represents the major risk factor for several chronic diseases, including diabetes, cardiovascular disease (CVD), and cancer. However, the molecular mechanisms of nutritionally mediated oxidative stress are complex and poorly understood. Therefore, this review aimed to explore how dietary choices exacerbate or dampen the oxidative stress and inflammation. We also discussed the implications of oxidative stress in the adipocyte and glucose metabolism and obesity-associated noncommunicable diseases (NCDs). Taken together, a better understanding of the role of oxidative stress in obesity and the development of obesity-related NCDs would provide a useful approach. This is because oxidative stress can be mediated by both extrinsic and intrinsic factors, hence providing a plausible means for the prevention of metabolic disorders.

(R)-α-Lipoic acid inhibits fructose-induced myoglobin fructation and the formation of advanced glycation end products (AGEs) in vitro

Background

Fructose-mediated protein glycation (fructation) has been linked to an increase in diabetic and cardiovascular complications due to over consumption of high-fructose containing diets in recent times. The objective of the present study is to evaluate the protective effect of (R)-α-lipoic acid (ALA) against fructose-induced myoglobin fructation and the formation of advanced glycation end products (AGEs) in vitro.

Methods

The anti-glycation activity of ALA was determined using the formation of AGEs fluorescence intensity, iron released from the heme moiety of myoglobin and the level of fructosamine. The fructation-induced myoglobin oxidation was examined using the level of protein carbonyl content and thiol group estimation.

Results

The results showed that co-incubation of myoglobin (1 mg/mL), fructose (1 M) and ALA (1, 2 and 4 mM) significantly inhibited the formation of AGEs during the 30 day study period. ALA markedly decreased the levels of fructosamine, which is directly associated with the reduction of AGEs formation. Furthermore, ALA significantly reduced free iron release from myoglobin which is attributed to the protection of myoglobin from fructose-induced glycation. The results also demonstrated a significant protective effect of ALA on myoglobin oxidative damages, as seen from decreased protein carbonyl content and increased protein thiols.

Conclusion

These findings provide new insights into the anti-glycation properties of ALA and emphasize that ALA supplementation is beneficial in the prevention of AGEs-mediated diabetic and cardiovascular complications.

Elevated cardiac 3-deoxyglucosone, a highly reactive intermediate in glycation reaction, in doxorubicin-induced cardiotoxicity in rats

3-Deoxyglucosone (3-DG) is a highly reactive carbonyl intermediate in glycation reaction (also known as Maillard reaction) and plays an important role in diabetic complications. We investigated the potential involvement of 3-DG in doxorubicin (DXR)-induced cardiotoxicity. Male Crl:CD(SD) rats received intravenous injections of DXR at 2mg/kg, once weekly, for 6 weeks, with/without daily intraperitoneal treatment with 3-DG scavenging agents, i.e., aminoguanidine (AG, 25mg/kg/day) and pyridoxamine (PM, 60mg/kg/day). Cardiac levels of 3-DG, thiobarbituric acid reactive substances (TBARS), fructosamine, and pentosidine, plasma glucose levels and cardiac troponin I (cTnI), echocardiography, and histopathology were assessed at 4 and 6 weeks after treatment. Cardiac 3-DG levels were significantly increased by DXR treatment at 4 and 6 weeks. Cardiac fructosamine levels and plasma glucose were not altered by DXR; however, TBARS levels in the heart were significantly increased at 4 and 6 weeks, suggesting that the enhanced generation of 3-DG is not attributed to any abnormal glycemic status, but may be related to oxidative stress by DXR. An advanced glycation end-product, pentosidine, was significantly increased by DXR treatment at 6 weeks. Intervention by AG and PM ameliorated the DXR-induced echocardiographic abnormalities, increased cTnI in plasma, and histopathological lesion as well as normalizing the elevation of 3-DG and pentosidine levels. These results suggest that 3-DG is generated by DXR and involved, at least in part, in the pathogenesis of DXR-cardiotoxicity through glycation reaction.

Alpha lipoic acid attenuates high-fructose-induced pancreatic toxicity

OBJECTIVES

Chronic consumption of high-fructose corn syrup (HFCS) causes several problems such as insulin resistance. The goal of the study was to investigate pancreatic damage induced by chronic HFCS consumption and the protective effects of alpha lipoic acid (ALA) on pancreatic cells.

METHODS

Wistar Albino, 4-month-old, female rats weighing 250-300 g were randomly distributed into three groups, each containing eight rats. The study included an HFCS group, an HFCS + ALA-administered group and a control group (CON). The prepared 30% solution of HFCS (F30) (24% fructose, 28% dextrose) was added to the drinking water for 10 weeks. ALA treatment was begun 4 weeks after the first HFCS administration (100 mg/kg/oral, last 6 weeks). Rats were anaesthetised and euthanised by cervical dislocation 24 h after the last ALA administration. Blood samples for biochemical tests (amylase, lipase, malondialdehyde (MDA) and catalase (CAT)) and tissue samples for histopathological and immunohistochemical examinations (caspase-3, insulin and glucagon) were collected.

RESULTS

Comparing the control and HFCS groups, serum glucose (150.92 ± 39.77 and 236.50 ± 18.28, respectively, p < 0.05), amylase (2165.00 ± 150.76 and 3027.66 ± 729.19, respectively, p < 0.01), lipase (5.58 ± 2.22 and 11.51 ± 2.74, respectively, p < 0.01) and pancreatic tissue MDA (0.0167 ± 0.004 and 0.0193 ± 0.006, respectively, p < 0.05) levels were increased, whereas tissue CAT (0.0924 ± 0.029 and 0.0359 ± 0.023, respectively, p < 0.05) activity decreased in the HFCS group significantly. Histopathological examination revealed degenerative and necrotic changes in Langerhans islet cells and slight inflammatory cell infiltration in pancreatic tissue in the HFCS group. Immunohistochemically there was a significant decrease in insulin (2.85 ± 0.37 and 0.87 ± 0.64, respectively, p < 0.001) and glucagon (2.71 ± 0.48 and 1.00 ± 0.75, respectively, p < 0.001) secreting cell scores, whereas a greater increase in caspase-3 (0.14 ± 0.37 and 1.00 ± 0.75, respectively, p < 0.05) expression was seen in this group compared with the controls. In the ALA-treated group, all of these pathologic conditions were improved.

CONCLUSIONS

This study indicated HFCS induced pancreatic lesions, but ALA had ameliorative effects.

Effects of Alpha-Lipoic Acid on Oxidative Stress and Kinin Receptor Expression in Obese Zucker Diabetic Fatty Rats

Objective

To investigate the impact of alpha-lipoic acid on superoxide anion production and NADPH oxidase activity as well as on the expression of kinin B1 and B2 receptors in key organs of obese Zucker Diabetic Fatty rats.

Methods

Superoxide anion production was measured by lucigenin chemiluminescence. Kinin B1 and B2 receptors expression was measured at protein and mRNA levels by western blot and qRT-PCR in key organs of Zucker Diabetic Fatty and Zucker lean control rats treated for a period of 6 weeks with a standard diet or a diet containing the antioxidant α-lipoic acid (1 g/kg).

Results

Superoxide anion production and NADPH oxidase activity were significantly enhanced in aorta and adipose tissue of Zucker Diabetic Fatty rats. Kinin B1 and B2 receptors expression levels were also significantly increased in the liver and the gastrocnemius muscle of Zucker Diabetic Fatty rats. Expression of both receptors was not altered in the pancreas of Zucker Diabetic Fatty rats and was undetectable in white retroperitoneal adipose tissue. Alpha-lipoic acid prevented the rise in NADPH oxidase activity in aorta and epididymal adipose tissue of Zucker Diabetic Fatty rats and the upregulation of kinin B1 receptor in liver and gastrocnemius muscle and that of kinin B2 receptor in the liver. Alpha-lipoic acid treatment was found to prevent the final body weight increase without affecting significantly hyperglycemia, hyperinsulinemia and insulin resistance index in Zucker Diabetic Fatty rats.

Conclusion

Findings support the hypothesis that oxidative stress is implicated in the induction of kinin B1 receptor in Zucker Diabetic Fatty rats. The ability of α-lipoic acid to blunt the body weight gain appears to be mediated in part by preventing NADPH oxidase activity rise in adipose tissue and reversing the hepatic upregulation of kinin B1 receptor in Zucker Diabetic Fatty rats.

Exercise training attenuates sympathetic activation and oxidative stress in diet-induced obesity

It is known that excessive sympathetic activity and oxidative stress are enhanced in obesity. This study aimed to clarify whether exercise training (ET) attenuates sympathetic activation and oxidative stress in obesity. The obesity was induced by high-fat diet (HFD) for 12 weeks. Male Sprague-Dawley rats were assigned to four groups: regular diet (RD) plus sedentary (RD-S), RD plus ET (RD-ET), HFD plus sedentary (HFD-S), and HFD plus ET (HFD-ET). The rats in RD-ET and HFD-ET groups were trained on a motorized treadmill for 60 min/day, five days/week for 8 weeks. The sympathetic activity was evaluated by the plasma norepinephrine (NE) level. The superoxide anion, malondialdehyde and F2-isoprostanes levels in serum and muscles were measured to evaluate oxidative stress. The ET prevented the increases in the body weight, arterial pressure and white adipose tissue mass in HFD rats. The NE level in plasma and oxidative stress related parameters got lower in HFD-ET group compared with HFD-S group. We have found decreased mRNA and protein levels of toll-like receptor (TLR)-2 and TLR-4 by ET in HFD rats. These findings suggest that ET may be effective for attenuating sympathetic activation and oxidative stress in diet-induced obesity.

Sugar and chromosome stability: clastogenic effects of sugars in vitamin B6-deficient cells

Pyridoxal 5′-phosphate (PLP), the active form of vitamin B6, has been implicated in preventing human pathologies, such as diabetes and cancer. However, the mechanisms underlying the beneficial effects of PLP are still unclear. Using Drosophila as a model system, we show that PLP deficiency, caused either by mutations in the pyridoxal kinase-coding gene (dPdxk) or by vitamin B6 antagonists, results in chromosome aberrations (CABs). The CAB frequency in PLP-depleted cells was strongly enhanced by sucrose, glucose or fructose treatments, and dPdxk mutant cells consistently displayed higher glucose contents than their wild type counterparts, an effect that is at least in part a consequence of an acquired insulin resistance. Together, our results indicate that a high intracellular level of glucose has a dramatic clastogenic effect if combined with PLP deficiency. This is likely due to an elevated level of Advanced Glycation End-products (AGE) formation. Treatment of dPdxk mutant cells with α-lipoic acid (ALA) lowered both AGE formation and CAB frequency, suggesting a possible AGE-CAB cause-effect relationship. The clastogenic effect of glucose in PLP-depleted cells is evolutionarily conserved. RNAi-mediated silencing of PDXK in human cells or treatments with PLP inhibitors resulted in chromosome breakage, which was potentiated by glucose and reduced by ALA. These results suggest that patients with concomitant hyperglycemia and vitamin B6 deficiency may suffer chromosome damage. This might impact cancer risk, as CABs are a well-known tumorigenic factor.

We show that the active form of vitamin B6 (Pyridoxal 5′-phosphate, PLP) plays an important role in the maintenance of genome integrity. We found, using Drosophila as a model system, that PLP deficiency results in chromosome breaks and rearrangements (collectively dubbed chromosome aberrations, abbreviated with CABs). Most importantly, we observed that in PLP deficient cells, sucrose, glucose, or fructose strongly enhance the frequency of CABs. The mutagenic effects of sugars in the presence of PLP deficiency are evolutionarily conserved, as PLP depletion or inhibition in human cells results in CAB formation, which is potentiated by glucose or fructose. These results suggest that patients with concomitant hyperglycemic crises and vitamin B6 deficiency may suffer genetic damage, which might promote cancer and diabetes complications. Our work further suggests that patients treated with PLP antagonist drugs should keep under control the level of sugar in their blood and compensate their vitamin B6 level.

Reduction of methylglyoxal-induced glycation by pyridoxamine improves adipose tissue microvascular lesions

Background and Aims. Adipose tissue dysfunction results from many factors, including glycation-induced microvascular damages. We tested the usefulness of inhibiting methylglyoxal-induced glycation to adipose tissue microvasculature in this work, using the antioxidant and dicarbonyl scavenger drug pyridoxamine. Methods. A group of Wistar rats was treated daily with methylglyoxal (MG, 75 mg/Kg/day, 8 weeks). Half of this group was treated with pyridoxamine in the following 4 weeks (Pyr) (100 mg/Kg/day) and the other half did not have any further treatment (MG). A group of Wistar rats without MG treatment was used as control (C). Results. MG group showed decreased HDL cholesterol and increased plasma free fatty acids levels, what was reverted by pyridoxamine. MG also caused an increase of tissue CEL levels (glycation marker), as well as increased staining of PAS and Masson Trichrome-positive components. Pyridoxamine led to CEL and TGF- β levels similar to those observed in control rats and inhibited the accumulation of PAS and Masson Trichrome-positive components. MG caused a decrease of Bcl-2/Bax ratio (marker of apoptosis) and vWF staining (microvascular marker), what was partially reverted by the treatment with pyridoxamine. Conclusions. Preventing methylglyoxal-induced accumulation of glycated and fibrotic materials using pyridoxamine improves the microvascular lesions of the adipose tissue.

Critical evaluation of ayurvedic plants for stimulating intrinsic antioxidant response

Oxidative damage caused by free radicals plays an important role in the causation and progression of many diseases, including aging. Free-radical damage is countered by many mechanisms, including both active antioxidant enzymatic activity in our body and passive antioxidants. Antioxidant response of our body can accommodate increased oxidative damage in diseased states to a level but beyond that level, additional antioxidants are required to combat the increased stress. Apart from the regular dietary sources of antioxidants, many traditional herbal medicines demonstrate a potential to boost antioxidant activity. Rasayana chikitsa that deals with rejuvenation and revitalization is a branch of the Indian traditional medical system of ayurveda. We review some select herbs described in rasayana chikitsa that have been assessed by modern means for stimulating intrinsic antioxidant responses in humans. A critical evaluation of rasayana chikitsa will likely provide urgently needed, actual stimulants of our physiological antioxidant responses and not just more passive antioxidants to add to an already large catalog.

Triglyceride, nonesterified fatty acids, and prediabetic neuropathy: role for oxidative-nitrosative stress

Peripheral neuropathy develops in human subjects with prediabetes and metabolic syndrome before overt hyperglycemia. The contributions of impaired glucose tolerance and insulin signaling, hypertriglyceridemia and/or increased nonesterified fatty acids (NEFA), and hypercholesterolemia to this condition remain unknown. Niacin and its derivatives alleviate dyslipidemia with a minor effect on glucose homeostasis. This study evaluated the roles of impaired glucose tolerance versus dyslipidemia in prediabetic neuropathy using Zucker fatty (fa/fa) rats and the niacin derivative acipimox, as well as the interplay of hypertriglyceridemia, increased NEFA, and oxidative-nitrosative stress. Sixteen-week-old Zucker fatty rats with impaired glucose tolerance, obesity, hyperinsulinemia, hypertriglyceridemia, hypercholesterolemia, and increased NEFA displayed sensory nerve conduction velocity deficit, thermal and mechanical hypoalgesia, and tactile allodynia. Acipimox (100 mg kg(-1) day(-1), 4 weeks) reduced serum insulin, NEFA, and triglyceride concentrations without affecting glucose tolerance and hypercholesterolemia. It alleviated sensory nerve conduction velocity deficit and changes in behavioral measures of sensory function and corrected oxidative-nitrosative stress, but not impaired insulin signaling, in peripheral nerve. Elevated NEFA increased total and mitochondrial superoxide production and NAD(P)H oxidase activity in cultured human Schwann cells. In conclusion, hypertriglyceridemia and/or increased NEFA concentrations cause prediabetic neuropathy through oxidative-nitrosative stress. Lipid-lowering agents and antioxidants may find a use in the management of this condition.

Cellular dysfunction in diabetes as maladaptive response to mitochondrial oxidative stress

Oxidative stress has been implicated in diabetes long-term complications. In this paper, we summarize the growing evidence suggesting that hyperglycemia-induced overproduction of superoxide by mitochondrial electron transport chain triggers a maladaptive response by affecting several metabolic and signaling pathways involved in the pathophysiology of cellular dysfunction and diabetic complications. In particular, it is our goal to describe physiological mechanisms underlying the mitochondrial free radical production and regulation to explain the oxidative stress derived from a high intracellular glucose concentration and the resulting maladaptive response that leads to a cellular dysfunction and pathological state. Finally, we outline potential therapies for diabetes focused to the prevention of mitochondrial oxidative damage.

Oxidative stress and diabetes: what can we learn about insulin resistance from antioxidant mutant mouse models?

The development of metabolic dysfunctions like diabetes and insulin resistance in mammals is regulated by a myriad of factors. Oxidative stress seems to play a central role in this process as recent evidence shows a general increase in oxidative damage and a decrease in oxidative defense associated with several metabolic diseases. These changes in oxidative stress can be directly correlated with increased fat accumulation, obesity, and consumption of high-calorie/high-fat diets. Modulation of oxidant protection through either genetic mutation or treatment with antioxidants can significantly alter oxidative stress resistance and accumulation of oxidative damage in laboratory rodents. Antioxidant mutant mice have previously been utilized to examine the role of oxidative stress in other disease models, but have been relatively unexplored as models to study the regulation of glucose metabolism. In this review, we will discuss the evidence for oxidative stress as a primary mechanism linking obesity and metabolic disorders and whether alteration of antioxidant status in laboratory rodents can significantly alter the development of insulin resistance or diabetes.

AGE formation blockade with aminoguanidine does not ameliorate chronic allograft nephropathy

AIMS

Advanced glycation end products (AGEs) are produced by glycoxidation and lipid peroxidation. AGEs induce oxidative stress and inflammation, and accumulate in tubular cells after kidney transplantation. We hypothesize that the AGE formation blocker aminoguanidine (AG) reduces AGE formation and improves renal transplant function.

MAIN METHODS

Fisher 344 kidneys were orthotopically transplanted into Lewis recipients. Recipients were treated with AG (100 mg/kg/day), candesartan (CAND; 5mg/kg/day), or vehicle (VEH) for 24 weeks. The major non-cross linking AGE N(ε)-carboxymethyllysine (CML) was measured post-transplantation with gas chromatography-tandem mass spectrometry or immunohistochemistry. As a marker of systemic lipid peroxidation 8-isoprostane was measured by ELISA. We determined intra-arterial blood pressure, heart weight/body weight ratio, size of cardiomyocytes and cardiac hypertrophy as assessed by echocardiography. For biochemical evaluation of cardiac and renal fibrosis we measured hydroxyproline content.

KEY FINDINGS

AG significantly reduced serum CML and 8-isoprostane, but did not reduce signs of chronic allograft nephropathy (CAN) or blood pressure. AG did not alter tubular AGE accumulation. AG reduced heart weight/body weight ratio (AG: 2.7 ± 0.1g/kg; CAND: 2.2 ± 0.1, VEH: 3.0 ± 0.4 g/kg), size of cardiomyocytes (P < 0.05) and showed a tendency to reduce cardiac hypertrophy (wall volume average radial AG 7.072 ± 0.83 cm(3) vs. CAND 6.841 ± 0.66 cm(3) vs. VEH 7.839 ± 0.74 cm(3)).

SIGNIFICANCE

Despite effective reduction of serum CML and 8-isoprostane, AG did not ameliorate CAN or reduce renal AGE accumulation. On the other hand AG reduced cardiac size suggesting a supportive cardio-protective action which is blood pressure independent.

Oxidative stress and the etiology of insulin resistance and type 2 diabetes

The condition of oxidative stress arises when oxidant production exceeds antioxidant activity in cells and plasma. The overabundance of oxidants is mechanistically connected to the multifactorial etiology of insulin resistance, primarily in skeletal muscle tissue, and the subsequent development of type 2 diabetes. Two important mechanisms for this oxidant excess are (1) the mitochondrial overproduction of hydrogen peroxide and superoxide ion under conditions of energy surplus and (2) the enhanced activation of cellular NADPH oxidase via angiotensin II receptors. Several recent studies are reviewed that support the concept that direct exposure of mammalian skeletal muscle to an oxidant stress (including hydrogen peroxide) results in stimulation of the serine kinase p38 mitogen-activated protein kinase (p38 MAPK), and that the engagement of this stress-activated p38 MAPK signaling is mechanistically associated with diminished insulin-dependent stimulation of insulin signaling elements and glucose transport activity. The beneficial interactions between the antioxidant α-lipoic acid and the advanced glycation end-product inhibitor pyridoxamine that ameliorate oxidant stress-associated defects in whole-body and skeletal-muscle insulin action in the obese Zucker rat, a model of prediabetes, are also addressed. Overall, this review highlights the importance of oxidative stress in the development of insulin resistance in mammalian skeletal muscle tissue, at least in part via a p38-MAPK-dependent mechanism, and indicates that interventions that reduce this oxidative stress and oxidative damage can improve insulin action in insulin-resistant animal models. Strategies to prevent and ameliorate oxidative stress remain important in the overall treatment of insulin resistance and type 2 diabetes.

Amelioration of lipid abnormalities by α-lipoic acid through antioxidative and anti-inflammatory effects

Recent data have revealed that oxidative products and inflammatory mediators are increased in the insulin-resistant states of obesity and type 2 diabetes mellitus (T2DM). Obese patients with impaired glucose tolerance (IGT) are at high risk for developing T2DM and have high incidence of dyslipidemia. α-Lipoic acid (ALA) is a potent antioxidant with insulin sensitizing activity. However, it is not clear whether ALA is effective on lipid parameters in humans. This study has investigated 22 obese subjects with IGT (obese-IGT), 13 of whom underwent 2-week ALA treatment, 600 mg intravenously once daily. Before and after the treatment, euglycemic-hyperinsulinemic clamps were used to measure insulin sensitivity. Meanwhile, plasma lipids, oxidative products, and chronic inflammatory markers were measured. After treatment of ALA in obese-IGT patients, insulin sensitivity was improved, insulin sensitivity index (ISI) impressively enhanced by 41%. Plasma levels of free fatty acids (FFAs), triglyceride (TG), total cholesterol (T-Chol), low density lipoprotein-cholesterol (LDL-Chol), small dense LDL-Chol (sd-LDL), oxidized LDL-Chol (ox-LDL-Chol), very low density lipoprotein-cholesterol (VLDL-Chol) were all significantly decreased (P < 0.01). At the same time, both plasma oxidative products (malondialdehyde (MDA), 8-iso-prostaglandin) and inflammatory markers (tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6)) were remarkably decreased (P < 0.01), while adiponectin was increased (P < 0.01). There are significant negative correlations between ISI and plasma FFAs, sd-LDL-Chol, ox-LDL-Chol, MDA, 8-iso-prostaglandin, TNF-α, and IL-6, and positive correlations with HDL-Chol and adiponectin in obese-IGT patients. The results indicate that short-term treatment with ALA can improve insulin sensitivity and plasma lipid profile possibly through amelioration of oxidative stress and chronic inflammatory reaction in obese patients with IGT.

Oxidative stress is associated with migraine and migraine-related metabolic risk in females

BACKGROUND AND PURPOSE

Oxidative stress is discussed to be implicated in the pathophysiology of migraine. However, data are in part controversial and the possible underlying mechanisms remain elusive to date. The aim of this study was to investigate the oxidative stress status of female patients with migraine and its implications on migraine-related metabolic alterations.

METHODS

Oxidative stress markers malondialdehyde (MDA), 4-hydroxy-2-nonenal (HNE), carbonylated proteins, parameters of associated nitric oxide stress, inflammation, lipid- and glucose-metabolism were determined in the interictal phase in female patients with migraine and controls.

RESULTS

We found significantly increased HNE levels in female migraineurs compared with controls. Logistic regression analyses of HNE revealed an odds ratio for migraine of 4.55. HNE showed significant correlations with the nitric oxide pathway, the insulin- and the lipid-metabolism.

CONCLUSIONS

We show here that increased oxidative stress is associated with migraine and contributes to migraine-related metabolic risk like nitrosative stress, an atherogenic lipid profile and hyperinsulinemia. Our data suggest that oxidative stress may represent a key event in the pathophysiology of migraine and a suitable therapeutic target.

Acute oxidative stress can reverse insulin resistance by inactivation of cytoplasmic JNK

Chronic oxidative stress results in decreased responsiveness to insulin, eventually leading to diabetes and cardiovascular disease. Activation of the JNK signaling pathway can mediate many of the effects of stress on insulin resistance through inhibitory phosphorylation of insulin receptor substrate 1. By contrast, exercise, which acutely increases oxidative stress in the muscle, improves insulin sensitivity and glucose tolerance in patients with Type 2 diabetes. To elucidate the mechanism underlying the contrasting effects of acute versus chronic oxidative stress on insulin sensitivity, we used a cellular model of insulin-resistant muscle to induce either chronic or acute oxidative stress and investigate their effects on insulin and JNK signaling. Chronic oxidative stress resulted in increased levels of phosphorylated (activated) JNK in the cytoplasm, whereas acute oxidative stress led to redistribution of JNK-specific phosphatase MKP7 from the nucleus into the cytoplasm, reduction in cytoplasmic phospho-JNK, and a concurrent accumulation of phospho-JNK in the nucleus. Acute oxidative stress restored normal insulin sensitivity and glucose uptake in insulin-resistant muscle cells, and this effect was dependent on MKP7. We propose that the contrasting effects of acute and chronic stress on insulin sensitivity are driven by changes in subcellular distribution of MKP7 and activated JNK.

Infusion fluids contain harmful glucose degradation products

Purpose

Glucose degradation products (GDPs) are precursors of advanced glycation end products (AGEs) that cause cellular damage and inflammation. We examined the content of GDPs in commercially available glucose-containing infusion fluids and investigated whether GDPs are found in patients’ blood.

Methods

The content of GDPs was examined in infusion fluids by high-performance liquid chromatography (HPLC) analysis. To investigate whether GDPs also are found in patients, we included 11 patients who received glucose fluids (standard group) during and after their surgery and 11 control patients receiving buffered saline (control group). Blood samples were analyzed for GDP content and carboxymethyllysine (CML), as a measure of AGE formation. The influence of heat-sterilized fluids on cell viability and cell function upon infection was investigated.

Results

All investigated fluids contained high concentrations of GDPs, such as 3-deoxyglucosone (3-DG). Serum concentration of 3-DG increased rapidly by a factor of eight in patients receiving standard therapy. Serum CML levels increased significantly and showed linear correlation with the amount of infused 3-DG. There was no increase in serum 3-DG or CML concentrations in the control group. The concentration of GDPs in most of the tested fluids damaged neutrophils, reducing their cytokine secretion, and inhibited microbial killing.

Conclusions

These findings indicate that normal standard fluid therapy involves unwanted infusion of GDPs. Reduction of the content of GDPs in commonly used infusion fluids may improve cell function, and possibly also organ function, in intensive-care patients.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-010-1873-x) contains supplementary material, which is available to authorized users.

Maillard reaction, mitochondria and oxidative stress: potential role of antioxidants

Glycation and oxidative stress are two important processes known to play a key role in complications of many disease processes. Oxidative stress, either via increasing reactive oxygen species (ROS), or by depleting the antioxidants may modulate the genesis of early glycated proteins in vivo. Maillard Reactions, occur in vivo as well as in vitro and are associated with the chronic complications of diabetes, aging and age-related diseases. Hyperglycaemia causes the autoxidation of glucose, glycation of proteins, and the activation of polyol metabolism. These changes facilitate the generation of reactive oxygen species and decrease the activity of antioxidant enzymes such as Cu,Zn-superoxide dismutase, resulting in a remarkable increase of oxidative stress. A large body of evidence indicates that mitochondria alteration is involved and plays a central role in various oxidative stress-related diseases. The damaged mitochondria produce more ROS (increase oxidative stress) and less ATP (cellular energy) than normal mitochondria. As they are damaged, they cannot burn or use glucose or lipid and cannot provide cell with ATP. Further, glucose, amino acids and lipid will not be correctly used and will accumulate outside the mitochondria; they will undergo more glycation (as observed in diabetes, obesity, HIV infection and lipodystrophia). The objective of this paper is to discuss how to stop the vicious circle established between oxidative stress, Maillard Reaction and mitochondria. The potential application of some antioxidants to reduce glycation phenomenon and to increase the antioxidant defence system by targeting mitochondria will be discussed. Food and pharmaceutical companies share the same challenge, they must act now, urgently and energetically.

Metabolic interactions of AGE inhibitor pyridoxamine and antioxidant alpha-lipoic acid following 22 weeks of treatment in obese Zucker rats

AIMS

The advanced glycation end product inhibitor pyridoxamine (PYR) and the antioxidant alpha-lipoic acid (LA) interact to ameliorate insulin resistance in obese Zucker rats following short-term (6-week) treatment. This study was designed to ascertain whether these unique interactive effects of PYR and LA remain manifest following longer-term (22-week) treatment.

MAIN METHODS

Female obese Zucker rats received vehicle (OV), PYR (OP, 60 mg/kg body wt), racemic LA (rac-LA; OM, 92 mg/kg), the R-(+)-enantiomer of LA (R-LA; OR, 92 mg/kg), or combined treatments with PYR and rac-LA (OPM) or PYR and R-LA (OPR), daily for 22 weeks.

KEY FINDINGS

Individual and combined treatments with PYR, rac-LA, and R-LA significantly (p<0.05) inhibited skeletal muscle protein carbonyls (28-36%), a marker of oxidative damage, and triglyceride levels (21-51%). Plasma free fatty acids were reduced in OM (9%), OR (11%), and OPM (16%), with the greatest decrease (26%) elicited in OPR. HOMA-IR, an index of fasting insulin resistance, was decreased in OP (14%) and OPM (17%) groups, with the greatest inhibition (22%) in OPR. Insulin resistance (glucose-insulin index) was lowered (20%) only in OPR. Insulin-mediated glucose transport in isolated skeletal muscle was improved in OM (34%), OR (33%), OPM (48%) and OPR (31%) groups.

SIGNIFICANCE

Important interactions between PYR and LA for improvements in glucose and lipid metabolism in the female obese Zucker rat are manifest following a 22-week treatment regimen, providing further evidence for targeting oxidative stress as a strategy for reducing insulin resistance.