Protective effect of atorvastatin on oxidative stress in streptozotocin‐induced diabetic rats independently their lipid‐lowering effects

In the present study, we investigate the effects of atorvastatin on the lipid profile, oxidative stress, and liver enzyme markers, and its protective activity against diabetic complications, in streptozotocin (STZ)‐induced diabetic rats. Fasting blood glucose (FBG), triglyceride (TG), total cholesterol (TC), and high‐density lipoprotein (HDL) levels, as well as alanine aminotransferase (ALT) and aspartate aminotransferase (AST) enzyme activities, were measured 7 weeks after the administration of STZ and atorvastatin. Thiobarbituric acid reactive substances (TBARS), non‐protein associated sulfhydryl (NP‐SH), total sulfhydryl (T‐SH), and nitric oxide (NO) levels were measured to evaluate oxidative stress. Atorvastatin was found to inhibit ALT and AST activities and to reduce FBG levels in rats with STZ‐induced diabetes. Moreover, atorvastatin treatment significantly reduced lipid peroxidation in kidney, heart, and eye tissues (P < 0.001, for all), and resulted in a significant increase in NP‐SH levels in brain tissues (P < 0.001). Total NO and nitrate levels increased significantly after atorvastatin treatment (P < 0.01). Our results revealed that atorvastatin has a protective effect against STZ‐induced oxidative damage by reducing TBARS levels and increasing NP‐SH levels, has a hepatoprotective effect by decreasing ALT and AST activities. It also shows the antihyperglycemic activity by lowering FBG levels.     

Charge inversion at position 68 of the glucagon and glucagon‐like peptide‐1 receptors supports selectivity in hormone action

Glucagon and glucagon‐like peptide‐1 (GLP‐1)are two structurally related hormones that acutely regulate glucose control in opposite directions through homologous receptors. The molecular basis for selectivity between these two hormones and their receptors is of physiological and medicinal importance. The application of co‐agonists to enhance body weight reduction and correct multiple abnormalities associated with the metabolic syndrome has recently been reported. Substitution of amino acids 16, 18, and 20 in glucagon with those found in GLP‐1 and exendin‐4 were identified as partial contributors to balanced, high potency receptor action. The amidation of the C‐terminus was an additional glucagon‐based structural change observed to be of seminal importance to discriminate recognition by both receptors. In this work, the molecular basis for receptor selectivity associated with differences in C‐terminal peptide sequence has been determined. A single charge inversion in glucagon and GLP‐1 receptor sequence at position 68* was determined to significantly alter hormone action. Changing E68* in GLP‐1R to the corresponding Lys of GCGR reduced receptor activity for natural GLP‐1 hormones by eightfold. The enhanced C‐terminal positive charges in GLP‐1 peptides favor the native receptor's negative charge at position 68*, while the unfavorable interaction with the C‐terminal acid of native glucagon is minimized by amidation. The extension of these observations to other glucagon‐related hormones such as oxyntomodulin and exendin, as well as other related receptors such as GIPR, should assist in the assembly of additional hormones with broadened pharmacology. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Gender‐dimorphic regulation of DJ1 and its interactions with metabolic proteins in streptozotocin‐induced diabetic rats

Regulation of DJ1 is associated with a number of human diseases. To determine the involvement of DJ1 in progression of diabetes in a gender‐dependent manner, we investigated its tissue‐specific expression in streptozotocin (STZ)‐induced diabetic male and female rats in this study. In animal experiments, females showed greater susceptibility towards developing diabetes because of lower insulin secretion and higher blood glucose levels as compared to male diabetic rats upon exposure to STZ. Immunoblotting confirmed sexually dimorphic regulation of DJ1 in various metabolic tissues such as the liver, pancreas and skeletal muscle. Immunofluorescence analysis revealed the location as well as reinforced the gender‐dependent expression of DJ1 in hepatic tissue. Co‐immunoprecipitation assay identified several interacting proteins with DJ1 whose functions were shown to be involved in various metabolic pathways viz. antioxidative and stress defence system, protein and methionine metabolism, nitrogen metabolism, urea metabolism, etc. Using GeneMANIA, a predictive web interface for gene functions, we showed for the first time that DJ1 may regulate T1DM via the JNK1 pathway, suggesting DJ1 interacts with other proteins from various metabolic pathways. We anticipate that the current data will provide insights into the aetiology of T1DM.     

Glucagon‐like peptide‐1 ameliorates cardiac lipotoxicity in diabetic cardiomyopathy via the PPARα pathway

Lipotoxicity cardiomyopathy is the result of excessive accumulation and oxidation of toxic lipids in the heart. It is a major threat to patients with diabetes. Glucagon‐like peptide‐1 (GLP‐1) has aroused considerable interest as a novel therapeutic target for diabetes mellitus because it stimulates insulin secretion. Here, we investigated the effects and mechanisms of the GLP‐1 analog exendin‐4 and the dipeptidyl peptidase‐4 inhibitor saxagliptin on cardiac lipid metabolism in diabetic mice (DM). The increased myocardial lipid accumulation, oxidative stress, apoptosis, and cardiac remodeling and dysfunction induced in DM by low streptozotocin doses and high‐fat diets were significantly reversed by exendin‐4 and saxagliptin treatments for 8 weeks. We found that exendin‐4 inhibited abnormal activation of the (PPARα)‐CD36 pathway by stimulating protein kinase A (PKA) but suppressing the Rho‐associated protein kinase (ROCK) pathway in DM hearts, palmitic acid (PA)‐treated rat h9c2 cardiomyocytes (CMs), and isolated adult mouse CMs. Cardioprotection in DM mediated by exendin‐4 was abolished by combination therapy with the PPARα agonist wy‐14643 but mimicked by PPARα gene deficiency. Therefore, the PPARα pathway accounted for the effects of exendin‐4. This conclusion was confirmed in cardiac‐restricted overexpression of PPARα mediated by adeno‐associated virus serotype‐9 containing a cardiac troponin T promoter. Our results provide the first direct evidence that GLP‐1 protects cardiac function by inhibiting the ROCK/PPARα pathway, thereby ameliorating lipotoxicity in diabetic cardiomyopathy.     

Neuroprotective effect of mexiletine in the central nervous system of diabetic rats

Both experimental and clinical studies suggests that oxidative stress plays an important role in the pathogenesis of diabetes mellitus type 1 and type 2. Hyperglycaemia leads to free radical generation and causes neural degeneration. In the present study we investigated the possible neuroprotective effect of mexiletine against streptozotocin-induced hyperglycaemia in the rat brain and spinal cord.30 adult male Wistar rats were divided into three groups: control, diabetic, and diabetic-mexiletine treated group. Diabetes mellitus was induced by a single injection of streptozotocin (60 mg/kg body weight). Mexiletine (50 mg/kg) was injected intraperitoneally every day for six weeks. After 6 weeks the brain, brain stem and cervical spinal cord of the rats were removed and the hippocampus, cortex, cerebellum, brain stem and spinal cord were dissected for biochemical analysis (the level of Malondialdehide [MDA], Nitric Oxide [NO], Reduced Glutathione [GSH], and Xanthine Oxidase [XO] activity). MDA, XO and NO levels in the hippocampus, cortex, cerebellum, brain stem and spinal cord of the diabetic group increased significantly, when compared with control and mexiletine groups (P < 0.05). GSH levels in the hippocampus, cortex, cerebellum, brain stem and spinal cord of the diabetic group decreased significantly when compared with control and mexiletine groups (P < 0.05).This study demonstrates that mexiletine protects the neuronal tissue against the diabetic oxidative damage.     

Attenuation of oxidative stress and alteration of hepatic tissue ultrastructure by D-pinitol in streptozotocin-induced diabetic rats

Abstract

The present study was aimed to investigate the effect of D-pinitol on hyperglycaemia mediated oxidative stress by analysing the hepatic antioxidant competence, pro-inflammatory cytokines and ultrastructural changes in liver tissues of streptozotocin-induced diabetic rats. Oral administration of D-pinitol (50 mg/kg b.w.) resulted in significant (p < 0.05) attenuation in blood glucose, glycosylated haemoglobin and pro-inflammatory markers such as TNF-α, IL-1β, IL-6, NF-κB p65 unit and NO and significant (p < 0.05) elevation in the plasma insulin level. In addition, D-pinitol instigated a significant escalation in the levels of hepatic tissue non-enzymatic antioxidants and the activities enzymatic antioxidants of diabetic rats with significant (p < 0.05) decrease in lipid peroxides and hydroperoxides formation, thus demonstrating the protective role of D-pinitol on the hepatic tissues from oxidative stress-induced liver damage. These biochemical observations were complemented by histological and ultrastructural examination of liver section. Thus, the present study demonstrates the hepatoprotective nature of D-pinitol by attenuating hyperglycaemia-mediated pro-inflammatory cytokines and oxidative stress.     

Rosmarinic acid prevents lipid peroxidation and increase in acetylcholinesterase activity in brain of streptozotocin‐induced diabetic rats

We investigated the efficacy of rosmarinic acid (RA) in preventing lipid peroxidation and increased activity of acetylcholinesterase (AChE) in the brain of streptozotocin‐induced diabetic rats. The animals were divided into six groups (n = 8): control, ethanol, RA 10 mg/kg, diabetic, diabetic/ethanol and diabetic/RA 10 mg/kg. After 21 days of treatment with RA, the cerebral structures (striatum, cortex and hippocampus) were removed for experimental assays. The results demonstrated that the treatment with RA (10 mg/kg) significantly reduced the level of lipid peroxidation in hippocampus (28%), cortex (38%) and striatum (47%) of diabetic rats when compared with the control. In addition, it was found that hyperglycaemia caused significant increased in the activity of AChE in hippocampus (58%), cortex (46%) and striatum (30%) in comparison with the control. On the other hand, the treatment with RA reversed this effect to the level of control after 3 weeks. In conclusion, the present findings showed that treatment with RA prevents the lipid peroxidation and consequently the increase in AChE activity in diabetic rats, demonstrating that this compound can modulate cholinergic neurotransmission and prevent damage oxidative in brain in the diabetic state. Thus, we can suggest that RA could be a promising compound in the complementary therapy in diabetes. Copyright © 2013 John Wiley & Sons, Ltd.     

GUB06‐046, a novel secretin/glucagon‐like peptide 1 co‐agonist,decreases food intake,improves glycemic control,and preserves beta cell mass in diabetic mice

Bariatric surgery is currently the most effective treatment of obesity, which has spurred an interest in developing pharmaceutical mimetics. It is thought that the marked body weight‐lowering effects of bariatric surgery involve stimulated secretion of appetite‐regulating gut hormones, including glucagon‐like peptide 1. We here report that intestinal expression of secretin is markedly upregulated in a rat model of Roux‐en‐Y gastric bypass, suggesting an additional role of secretin in the beneficial metabolic effects of Roux‐en‐Y gastric bypass. We therefore developed novel secretin‐based peptide co‐agonists and identified a lead compound, GUB06‐046, that exhibited potent agonism of both the secretin receptor and glucagon‐like peptide 1 receptor. Semi‐acute administration of GUB06‐046 to lean mice significantly decreased cumulative food intake and improved glucose tolerance. Chronic administration of GUB06‐046 to diabetic db/db mice for 8 weeks improved glycemic control, as indicated by a 39% decrease in fasting blood glucose and 1.6% reduction of plasma HbA1c levels. Stereological analysis of db/db mice pancreata revealed a 78% increase in beta‐cell mass after GUB06‐046 treatment, with no impact on exocrine pancreas mass or pancreatic duct epithelial mass. The data demonstrate beneficial effects of GUB06‐046 on appetite regulation, glucose homeostasis, and beta‐cell mass in db/db mice, without proliferative effects on the exocrine pancreas and the pancreatic duct epithelium. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.     

Serum IGF-1 levels correlate negatively to liver damage in diabetic rats

Abstract

Diabetes and insulin resistance frequently cause liver damage. Diabetes also causes reduction in liver and blood IGF-1 levels. We investigated the relation between liver damage and IGF-1 levels in diabetic rats. Fourteen Wistar albino rats were divided into control and diabetic groups. Diabetes was induced by streptozotocin. Rats were sacrificed for biochemical and histologic examinations 2 weeks after streptozotocin injection. Serum and liver IGF-1 levels were decreased, liver malondialdehyde (MDA) levels were increased, glutathione peroxidase (GPx) enzymes activities were decreased and serum alanine aminotransferase (ALT) levels were increased in diabetic group. Microscopic examination of liver revealed that normal tissue organization was disrupted in streptozotocin-induced diabetic rats. There was a strongly positive correlation between blood glucose levels and liver injury, and blood and liver IGF-1 levels. There was a strongly negative correlation between blood IGF-1 levels and hepatic injury. Our results suggest that reduction of blood IGF-1 levels correlates with hepatic injury and circulating IGF-1 levels may have predictive value for determining hepatic damage that results from diabetes. In addition, circulating IGF-1 levels are correlated with glutathione levels and the oxidative stress status of diabetic rat liver.     

Adenoviral vector-mediated glucagon-like peptide 1 gene therapy improves glucose homeostasis in Zucker diabetic fatty rats

BACKGROUND: Glucagon-like peptide-1 (GLP-1) is a gut-derived incretin hormone that plays an important role in glucose homeostasis. Its functions include glucose-stimulated insulin secretion, suppression of glucagon secretion, deceleration of gastric emptying, and reduction in appetite and food intake. Despite the numerous antidiabetic properties of GLP-1, its therapeutic potential is limited by its short biological half-life due to rapid enzymatic degradation by dipeptidyl peptidase IV. The present study aimed to demonstrate the therapeutic effects of constitutively expressed GLP-1 in an overt type 2 diabetic animal model using an adenoviral vector system. METHODS: A novel plasmid (pAAV-ILGLP-1) and recombinant adenoviral vector (Ad-ILGLP-1) were constructed with the cytomegalovirus promoter and insulin leader sequence followed by GLP-1(7-37) cDNA. RESULTS: The results of an enzyme-linked immunosorbent assay showed significantly elevated levels of GLP-1(7-37) secreted by human embryonic kidney cells transfected with the construct containing the leader sequence. A single intravenous administration of Ad-ILGLP-1 into 12-week-old Zucker diabetic fatty (ZDF) rats, which have overt type 2 diabetes mellitus (T2DM), achieved near normoglycemia for 3 weeks and improved utilization of blood glucose in glucose tolerance tests. Circulating plasma levels of GLP-1 increased in GLP-1-treated ZDF rats, but diminished 21 days after treatment. When compared with controls, Ad-ILGLP-1-treated ZDF rats had a lower homeostasis model assessment for insulin resistance score indicating amelioration in insulin resistance. Immunohistochemical staining showed that cells expressing GLP-1 were found in the livers of GLP-1-treated ZDF rats. CONCLUSIONS: These data suggest that GLP-1 gene therapy can improve glucose homeostasis in fully developed diabetic animal models and may be a promising treatment modality for T2DM in humans.     

Lipid peroxidation is essential for α‐synuclein‐induced cell death

Parkinson's disease is the second most common neurodegenerative disease and its pathogenesis is closely associated with oxidative stress. Deposition of aggregated α‐synuclein (α‐Syn) occurs in familial and sporadic forms of Parkinson's disease. Here, we studied the effect of oligomeric α‐Syn on one of the major markers of oxidative stress, lipid peroxidation, in primary co‐cultures of neurons and astrocytes. We found that oligomeric but not monomeric α‐Syn significantly increases the rate of production of reactive oxygen species, subsequently inducing lipid peroxidation in both neurons and astrocytes. Pre‐incubation of cells with isotope‐reinforced polyunsaturated fatty acids (D‐PUFAs) completely prevented the effect of oligomeric α‐Syn on lipid peroxidation. Inhibition of lipid peroxidation with D‐PUFAs further protected cells from cell death induced by oligomeric α‐Syn. Thus, lipid peroxidation induced by misfolding of α‐Syn may play an important role in the cellular mechanism of neuronal cell loss in Parkinson's disease.

     

Neuroprotective actions of Glucagon‐like peptide‐1 in differentiated human neuroprogenitor cells

Glucagon‐like peptide‐1 (GLP‐1)‐based therapies are currently available for the treatment of type 2 diabetes, based on their actions on pancreatic β cells. GLP‐1 is also known to exert neuroprotective actions. To determine its mechanism of action, we developed a neuron‐rich cell culture system by differentiating human neuroprogenitor cells in the presence of a combination of neurotrophins and retinoic acid. The neuronal nature of these cells was characterized by neurogenesis pathway‐specific array. GLP‐1 receptor expression was seen mainly in the neuronal population. Culture of neurons in the presence of Aβ oligomers resulted in the induction of apoptosis as shown by the activation of caspase‐3 and caspase‐6. Exendin‐4, a long‐acting analog of GLP‐1, protected the neurons from apoptosis induced by Aβ oligomers. Exendin‐4 stimulated cyclic AMP response element binding protein phosphorylation, a regulatory step in its activation. A transient transfection assay showed induction of a reporter linked to CRE site‐containing human brain‐derived neurotrophic factor promoter IV, by the growth factor through multiple signaling pathways. The anti‐apoptotic action of exendin‐4 was lost following down‐regulation of cAMP response element binding protein. Withdrawal of neurotrophins resulted in the loss of neuronal phenotype of differentiated neuroprogenitor cells, which was prevented by incubation in the presence of exendin‐4. Diabetes is a risk factor in the pathogenesis of Alzheimer's disease. Our findings suggest that GLP‐1‐based therapies can decrease the incidence of Alzheimer's disease among aging diabetic population.     

硫化氢对1型糖尿病大鼠肾脏的保护作用

目的：观察硫化氢（H₂S）对1型糖尿病大鼠肾脏的保护作用及其机制。方法：32只雄性SD大鼠随机分为4组：正常对照（NC）组、糖尿病（DM）组、糖尿病治疗（NaHS+DM）组和NaHS对照（NaHS）组（n=8）。DM组和NaHS+DM组大鼠采用链脲佐菌素（STZ）55 mg/kg腹腔注射诱导1型糖尿病模型。造模成功后,NaHS+DM组和NaHS组采用腹腔注射NaHS溶液56 μmol/kg干预治疗。8周后,测定大鼠24 h尿蛋白含量、肾重指数、空腹血糖、尿素氮、肌酐等指标;HE染色观察肾脏组织形态学变化;测定肾脏组织脂质过氧化物丙二醛（MDA）含量、超氧化物歧化酶（SOD）和Caspase-3的活性;Western blot检测肾脏组织Bcl-2和Bax蛋白表达。结果：与NC组相比,NaHS组各项指标均无显著差异,DM组,24 h尿蛋白含量、肾重指数、空腹血糖、尿素氮和肌酐水平均明显升高;HE染色结果显示肾小球基底膜增厚、系膜基质增多;MDA含量、Caspase-3活性和Bax蛋白表达明显增高;SOD活性和Bcl-2蛋白表达显著降低。与DM组相比,NaHS+DM组肾功能损伤明显减轻,肾脏组织形态学变化明显改善,MDA含量、Caspase-3活性和Bax蛋白表达明显下降,SOD活性和Bcl-2蛋白表达显著增高。结论：H₂S对1型糖尿病大鼠肾脏具有保护作用,其机制可能与抑制氧化应激和细胞凋亡有关。     

N‐acetylcysteine improves diabetic associated erectile dysfunction in streptozotocin‐induced diabetic mice by inhibiting oxidative stress

Oxidative stress appears to play a role in the pathogenesis of diabetes mellitus erectile dysfunction (DMED). This study aimed to investigate the effect of N‐acetylcysteine (NAC) on DMED in streptozotocin‐induced diabetic mice and to explore potential mechanisms. In the present study, we show that an erectile dysfunction is present in the streptozotocin‐induced mouse model of diabetes as indicated by decreases in intracavernous pressure responses to electro‐stimulation as well as from results of the apomorphine test of erectile function. After treatment of NAC, the intracavernous pressure was increased. In these DMED mice, oxidative stress and inflammatory responses were significantly reduced within the cavernous microenvironment, while activity of antioxidant enzymes in this cavernous tissue was enhanced after NAC treatment. These changes protected mitochondrial stress damage and a significant decreased in apoptosis within the cavernous tissue of DMED mice. This appears to involve activation of the nuclear factor erythroid 2‐like‐2 (Nrf2) signalling pathway, as well as suppression of the mitogen‐activated protein kinase (MAPK) p38/ NF‐κB pathway within cavernous tissue. In conclusion, NAC can improve erectile function through inhibiting oxidative stress via activating Nrf2 pathways and reducing apoptosis in streptozotocin‐induced diabetic mice. NAC might provide a promising therapeutic strategy for individuals with DMED.     

Functional association of the N‐terminal residues with the central region in glucagon‐related peptides

GLP‐1 is an incretin peptide involved in the regulation of glucose metabolism and the glucose‐dependent stimulation of insulin secretion. Ex‐4 is a paralog of GLP‐1 that has comparable GLP‐1R potency but extended physiological action. GLP‐1 and Ex‐4 are helical peptides that share ～50% sequence homology but differ at several residues, notably the second amino acid which controls susceptibility to DPP‐IV cleavage. This single amino acid difference yields divergent receptor potency when studied in the context of the two hormone sequences. Ex‐4 uniquely tolerates Gly2 through select amino acid differences in the middle region of the peptide that are absent in GLP‐1. We report that substitution of Ex‐4 amino acids Glu16, Leu21, and Glu24 to the GLP‐1 sequence enabled Gly2 tolerance. The coordination of the N‐terminus with these central residues shows an interaction of substantial importance not only to DPP‐IV stability but also to receptor activation. Extension of this observation to glucagon‐based co‐agonist peptides showed different structural requirements for effective communication between the N‐terminus and the mid‐section of these peptides in achieving high potency agonism at the GLP‐1 and GCGRs. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Acquired tolerance of tomato (Lycopersicon esculentum cv. Micro‐Tom) plants to cadmium‐induced stress

The effects of varying concentrations of cadmium (Cd) on the development of Lycopersicon esculentum cv. Micro‐Tom (MT) plants were investigated after 40 days (vegetative growth) and 95 days (fruit production), corresponding to 20 days and 75 days of exposure to CdCl₂, respectively. Inhibition of growth was clearly observed in the leaves after 20 days and was greater after 75 days of growth in 1 mM CdCl₂, whereas the fruits exhibited reduced growth following the exposure to a concentration as low as 0.1 mM CdCl₂. Cd was shown to accumulate in the roots after 75 days of growth but was mainly translocated to the upper parts of the plants accumulating to high concentrations in the fruits. Lipid peroxidation was more pronounced in the roots even at 0.05 mM CdCl₂ after 75 days, whereas in leaves, there was a major increase after 20 days of exposure to 1 mM CdCl₂, but the fruit only exhibited a slight significant increase in lipid peroxidation in plants subjected to 1 mM CdCl₂ when compared with the control. Oxidative stress was also investigated by the analysis of four key antioxidant enzymes, which exhibited changes in response to the increasing concentrations of Cd tested. Catalase (EC 1.11.1.6) activity was shown to increase after 75 days of Cd treatment, but the major increases were observed at 0.1 and 0.2 mM CdCl₂, whereas guaiacol peroxidase (EC 1.11.1.7) did not vary significantly from the control in leaves and roots apart from specific changes at 0.5 and 1 mM CdCl₂. The other two enzymes tested, glutathione reductase (EC 1.6.4.2) and superoxide dismutase (SOD, EC 1.15.1.1), did not exhibit any significant changes in activity, apart from a slight decrease in SOD activity at concentrations above 0.2 mM CdCl₂. However, the most striking results were obtained when an extra treatment was used in which a set of plants was subjected to a stepwise increase in CdCl₂ from 0.05 to 1 mM, leading to tolerance of the Cd applied even at the final highest concentration of 1 mM. This apparent adaptation to the toxic effect of Cd was confirmed by biomass values being similar to the control, indicating a tolerance to Cd acquired by the MT plants.