Beneficial effects of L-arginine nitric oxide-producing pathway in rats treated with alloxan

Plasma Metabolomics Study on the Impact of Different CRF Levels on MetS Risk Factors

To investigate the metabolomic mechanisms by which changes in cardiorespiratory fitness (CRF) levels affect metabolic syndrome (MetS) risk factors and to provide a theoretical basis for the improvement of body metabolism via CRF in people with MetS risk factors, a comparative blood metabolomics study of individuals with varying levels of CRF and varying degrees of risk factors for MetS was conducted.

METHODS

Ninety subjects between the ages of 40 and 45 were enrolled, and they were categorized into low-MetS (LM ≤ two items) and high MetS (HM > three items) groups, as well as low- and high-CRF (LC, HC) and LCLM, LCLM, LCHM, and HCHM groups. Plasma was taken from the early morning abdominal venous blood. LC-MS was conducted using untargeted metabolomics technology, and the data were statistically and graphically evaluated using SPSS26.0 and R language.

RESULTS

(1) There were eight common differential metabolites in the HC vs. LC group as follows: methionine (↓), γ-aminobutyric acid (↑), 2-oxoglutatic acid (↑), arginine (↑), serine (↑), cis-aconitic acid (↑), glutamine (↓), and valine (↓); the HM vs. LM group are contrast. (2) In the HCHM vs. LCLM group, trends were observed in 2-oxoglutatic acid (↑), arginine (↑), serine (↑), cis-aconitic acid (↑), glutamine (↓), and valine (↓). (3) CRF and MetS risk factors jointly affect biological metabolic pathways such as arginine biosynthesis, TCA cycle, cysteine and methionine metabolism, glycine, serine, and threonine metabolism, arginine and proline metabolism, and alanine, aspartate, and glutamate metabolism.

CONCLUSION

The eight common differential metabolites can serve as potential biomarkers for distinguishing individuals with different CRF levels and varying degrees of MetS risk factors. Increasing CRF levels may potentially mitigate MetS risk factors, as higher CRF levels are associated with reduced MetS risk.

Short-Term l-arginine Treatment Mitigates Early Damage of Dermal Collagen Induced by Diabetes

Changes in the structural properties of the skin due to collagen alterations are an important factor in diabetic skin complications. Using a combination of photonic methods as an optic diagnostic tool, we investigated the structural alteration in rat dermal collagen I in diabetes, and after short-term l-arginine treatment. The multiplex approach shows that in the early phase of diabetes, collagen fibers are partially damaged, resulting in the heterogeneity of fibers, e.g., "patchy patterns" of highly ordered/disordered fibers, while l-arginine treatment counteracts to some extent the conformational changes in collagen-induced by diabetes and mitigates the damage. Raman spectroscopy shows intense collagen conformational changes via amides I and II in diabetes, suggesting that diabetes-induced structural changes in collagen originate predominantly from individual collagen molecules rather than supramolecular structures. There is a clear increase in the amounts of newly synthesized proline and hydroxyproline after treatment with l-arginine, reflecting the changed collagen content. This suggests that it might be useful for treating and stopping collagen damage early on in diabetic skin. Our results demonstrate that l-arginine attenuates the early collagen I alteration caused by diabetes and that it could be used to treat and prevent collagen damage in diabetic skin at a very early stage.

Profiles and diagnostic value of intestinal microbiota in schizophrenia patients with metabolic syndrome

Aims/hypothesis

It is widely thought that the intestinal microbiota plays a significant role in the pathogenesis of metabolic disorders. However, the gut microbiota composition and characteristics of schizophrenia patients with metabolic syndrome (MetS) have been largely understudied. Herein, we investigated the association between the metabolic status of mainland Chinese schizophrenia patients with MetS and the intestinal microbiome.

Methods

Fecal microbiota communities from 115 male schizophrenia patients (57 with MetS and 58 without MetS) were assessed by 16S ribosomal RNA gene sequencing. We assessed the variations of gut microbiome between both groups and explored potential associations between intestinal microbiota and parameters of MetS. In addition, the Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) based on the KEGG database was used to predict the function of intestinal microbiota. We also conducted Decision Tree Analysis to develop a diagnostic model for the MetS in patients with schizophrenia based on the composition of intestinal microbiota.

Results

The fecal microbial diversity significantly differed between groups with or without MetS (α-diversity (Shannon index and Simpson index): p=0.0155, p=0.0089; β-diversity: p=0.001). Moreover, the microbial composition was significantly different between the two groups, involving five phyla and 38 genera (p<0.05). In addition, a significant correlation was observed between the metabolic-related parameters and abundance of altered microbiota including HDL-c (r2 = 0.203, p=0.0005), GLU (r2 = 0.286, p=0.0005) and WC (r2 = 0.061, p=0.037). Furthermore, KEGG pathway analysis showed that 16 signaling pathways were significantly enriched between the two groups (p<0.05). Importantly, our diagnostic model based on five microorganisms established by decision tree analysis could effectively distinguish between patients with and without MetS (AUC = 0.94).

Conclusions/interpretation

Our study established the compositional and functional characteristics of intestinal microbiota in schizophrenia patients with MetS. These new findings provide novel insights into a better understanding of this disease and provide the theoretical basis for implementing new interventional therapies in clinical practice.

L-Arginine in diabetes: clinical and preclinical evidence

L-Arginine (L-Arg), is a semi-essential amino acid involved in the formation of nitric oxide. The functional relevance of L-Arg in diabetes mellitus has been evaluated both in animal models and in human subjects. In the literature there are several lines of evidence indicating that L-Arg has beneficial effects in diabetes and numerous studies advocate its administration to attenuate glucose intolerance in diabetic patients. Here we present a comprehensive overview of the main studies exploring the effects of L-Arg in diabetes, including preclinical and clinical reports on this topic.

Metabolic effects of L-citrulline in type 2 diabetes

The prevalence of type 2 diabetes (T2D) is increasing worldwide. Decreased nitric oxide (NO) bioavailability is involved in the pathophysiology of T2D and its complications. L-citrulline (Cit), a precursor of NO production, has been suggested as a novel therapeutic agent for T2D. Available data from human and animal studies indicate that Cit supplementation in T2D increases circulating levels of Cit and L-arginine while decreasing circulating glucose and free fatty acids and improving dyslipidemia. The underlying mechanisms for these beneficial effects of Cit include increased insulin secretion from the pancreatic β cells, increased glucose uptake by the skeletal muscle, as well as increased lipolysis and β-oxidation, and decreased glyceroneogenesis in the adipose tissue. Thus, Cit has antihyperglycemic, antidyslipidemic, and antioxidant effects and has the potential to be used as a new therapeutic agent in the management of T2D. This review summarizes available literature from human and animal studies to explore the effects of Cit on metabolic parameters in T2D. It also discusses the possible mechanisms underlying Cit-induced improved metabolic parameters in T2D.

Arginase: Biological and Therapeutic Implications in Diabetes Mellitus and Its Complications

Arginase is a ubiquitous enzyme in the urea cycle (UC) that hydrolyzes L-arginine to urea and L-ornithine. Two mammalian arginase isoforms, arginase1 (ARG1) and arginase2 (ARG2), play a vital role in the regulation of β-cell functions, insulin resistance (IR), and vascular complications via modulating L-arginine metabolism, nitric oxide (NO) production, and inflammatory responses as well as oxidative stress. Basic and clinical studies reveal that abnormal alterations of arginase expression and activity are strongly associated with the onset and development of diabetes mellitus (DM) and its complications. As a result, targeting arginase may be a novel and promising approach for DM treatment. An increasing number of arginase inhibitors, including chemical and natural inhibitors, have been developed and shown to protect against the development of DM and its complications. In this review, we discuss the fundamental features of arginase. Next, the regulatory roles and underlying mechanisms of arginase in the pathogenesis and progression of DM and its complications are explored. Furthermore, we review the development and discuss the challenges of arginase inhibitors in treating DM and its related pathologies.

Steviol Glycoside, L-Arginine, and Chromium(III) Supplementation Attenuates Abnormalities in Glucose Metabolism in Streptozotocin-Induced Mildly Diabetic Rats Fed a High-Fat Diet

Stevia rebaudiana Bertoni and its glycosides are believed to exhibit several health-promoting properties. Recently, the mechanisms of the anti-diabetic effects of steviol glycosides (SG) have been the subject of intense research. The following study aims to evaluate the results of SG (stevioside (ST) and rebaudioside A (RA)) combined with L-arginine (L-Arg) and chromium(III) (CrIII) supplementation in streptozotocin- (STZ) induced mild type 2 diabetic rats fed a high-fat diet (HFD), with particular emphasis on carbohydrate and lipid metabolisms. The experiment was carried out on 110 male Wistar rats, 100 of which were fed an HFD to induce insulin resistance, followed by an intraperitoneal injection of streptozotocin to induce mild type 2 diabetes. After confirmation of hyperglycemia, the rats were divided into groups. Three groups served as controls: diabetic untreated, diabetic treated with metformin (300 mg/kg BW), and healthy group. Eight groups were fed an HFD enriched with stevioside or rebaudioside A (2500 mg/kg BW) combined with L-arginine (2000 or 4000 mg/kg BW) and Cr(III) (1 or 5 mg/kg BW) for six weeks. The results showed that supplementation with SG (ST and RA) combined with L-arg and Cr(III) could improve blood glucose levels in rats with mild type 2 diabetes. Furthermore, ST was more effective in improving blood glucose levels, insulin resistance indices, and very low-density lipoprotein cholesterol (VLDL-C) concentrations than RA. Although L-arg and Cr(III) supplementation did not independently affect most blood carbohydrate and lipid indices, it further improved some biomarkers when combined, particularly with ST. Notably, the beneficial impact of ST on the homeostatic model assessment–insulin resistance (HOMA-IR) and on the quantitative insulin-sensitivity check index (QUICKI) was strengthened when mixed with a high dose of L-arg, while its impact on antioxidant status was improved when combined with a high dose of Cr(III) in rats with mild type 2 diabetes. In conclusion, these results suggest that supplementary stevioside combined with L-arginine and Cr(III) has therapeutic potential for mild type 2 diabetes. However, further studies are warranted to confirm these effects in other experimental models and humans.

Ferroptosis as a Novel Determinant of β-Cell Death in Diabetic Conditions

The main pathological hallmark of diabetes is the loss of functional β-cells. Among several types of β-cell death in diabetes, the involvement of ferroptosis remains elusive. Therefore, we investigated the potential of diabetes-mimicking factors: high glucose (HG), proinflammatory cytokines, hydrogen peroxide (H₂O₂), or diabetogenic agent streptozotocin (STZ) to induce ferroptosis of β-cells in vitro. Furthermore, we tested the contribution of ferroptosis to injury of pancreatic islets in an STZ-induced in vivo diabetic model. All in vitro treatments increased loss of Rin-5F cells along with the accumulation of reactive oxygen species, lipid peroxides and iron, inactivation of NF-E2-related factor 2 (Nrf2), and decrease in glutathione peroxidase 4 expression and mitochondrial membrane potential (MMP). Ferrostatin 1 (Fer-1), ferroptosis inhibitor, diminished the above-stated effects and rescued cells from death in case of HG, STZ, and H₂O₂ treatments, while failed to increase MMP and to attenuate cell death after the cytokines' treatment. Moreover, Fer-1 protected pancreatic islets from STZ-induced injury in diabetic in vivo model, since it decreased infiltration of macrophages and accumulation of lipid peroxides and increased the population of insulin-positive cells. Such results revealed differences between diabetogenic stimuli in determining the destiny of β-cells, emerging HG, H₂O₂, and STZ, but not cytokines, as contributing factors to ferroptosis and shed new light on an antidiabetic strategy based on Nrf2 activation. Thus, targeting ferroptosis in diabetes might be a promising new approach for preservation of the β-cell population. Our results obtained from in vivo study strongly justify this approach.

Associations of Arginine with Gestational Diabetes Mellitus in a Follow-Up Study

In the reported study we applied the targeted metabolomic profiling employing high pressure liquid chromatography coupled with triple quadrupole tandem mass spectrometry (HPLC–MS/MS) to understand the pathophysiology of gestational diabetes mellitus (GDM), early identification of women who are at risk of developing GDM, and the differences in recovery postpartum between these women and normoglycemic women. We profiled the peripheral blood from patients during the second trimester of pregnancy and three months, and one year postpartum. In the GDM group Arg, Gln, His, Met, Phe and Ser were downregulated with statistical significance in comparison to normoglycemic (NGT) women. From the analysis of the association of all amino acid profiles of GDM and NGT women, several statistical models predicting diabetic status were formulated and compared with the literature, with the arginine-based model as the most promising of the screened ones (area under the curve (AUC) = 0.749). Our research results have shed light on the critical role of arginine in the development of GDM and may help in precisely distinguishing between GDM and NGT and earlier detection of GDM but also in predicting women with the increased type 2 diabetes mellitus (T2DM) risk.

Effect of a New Synthetic Peptide Preparation AСTH15-18PGP on the Hemostasis System in Rats

We studied the effect of chronic intranasal and peroral administration of a new peptide preparation AСTH_15-18PGP in a dose of 100 mg/kg body weight on the state of vascular-platelet and plasma hemostasis in animals. It was found that this synthetic regulatory peptide administered intranasally can produce antiplatelet, anticoagulant, and antifibrin-stabilizing effects on the blood plasma in healthy rats. In both administration routes, the peptide induced activation of the anticoagulation system of the hemostasis by increasing enzymatic and non-enzymatic fibrinolysis; after intranasal administration, the fibrinolytic effects were more pronounced.

Protective effects of either C-peptide or l-arginine on pancreatic β-cell function, proliferation, and oxidative stress in streptozotocin-induced diabetic rats

Diabetes and cardiometabolic risk factors including hypertension and dyslipidemia are the major threats to human health in the 21st century. Apoptosis in pancreatic tissue is one of the major causes of diabetes type 1 progression. The aim of this study was to investigate the effects of C-peptide or l-arginine on some cardiometabolic risk factors, pancreatic morphology, function and apoptosis, and the mechanisms of their actions. Forty adult male albino rats were divided into four equal groups: 1-control nondiabetic, 2-diabetic (no treatment), 3-diabetic + C-peptide, and 4-diabetic +  l-arginine. Diabetes was induced by a single intraperitoneal injection of high dose streptozotocin. At the end of the experiment, sera glucose, insulin levels, total antioxidant capacity (TAC), malondialdehyde (MDA), nitric oxide (NO), and pancreatic MDA, TAC, and B-cell lymphoma 2 were measured. The morphology and proliferating activity of the pancreas were examined by hematoxylin and eosin histological stain, proliferative cell nuclear antigen (PCNA), and insulin antibodies. Our results showed that induction of diabetes caused hyperglycemia, dyslipidemia, and oxidative stress. However, administration of C-peptide or l-arginine significantly improved the pancreatic histopathology with a significant increase in the area % of insulin immunoreactivity, the number of PCNA immunopositive cells, the number of islets, and the diameter of islets compared with the diabetic group. C-peptide treatment of the diabetic rats completely corrected these errors, while l-arginine partially antagonized the above diabetic complications. So the administration of C-peptide as an adjuvant therapy in type 1 diabetes can significantly decrease apoptosis of pancreas and subsequent progression of diabetes complication.

[Oxoprolinic short peptides - potential pharmacological means of hypolidemic and antitrombotic actions]

One of the most urgent and important tasks of modern biological and medical research is the search and research of pharmacological agents that combine lipid-lowering and antithrombotic effects in the organism. The unique effects of the regulatory peptides of the oxoproline series (5-oхo-Pro-His-Pro-NH2, 5-oxo-Pro-Trp-Pro and 5-oxo-Pro-Arg-Pro or 5-oхo-Pro-His-Pro-NH2, Pyr-Trp-Pro and Pyr-Arg-Pro) have been found in rats with hypercholesterolemia (metabolic syndrome). Multiple intranasal of these peptides to animals with developed hypercholesterolemia increased anticoagulant, fibrinolytic and antiplatelet potential of the blood and simultaneously lowered increased concentrations of total cholesterol, low-density lipoprotein cholesterol and triglycerides. In addition, they contributed to the normalization of blood glucose levels. A week after the last admistration of these peptides, the hypocholesterolemic, normoglycemic and anticoagulant effects persisted. The relationship between the structure of peptides of the oxoproline series and their functional properties is discussed. A conclusion is made about the prospects of further studies of oxoproline peptides as drugs that combine antithrombotic effects with the improvement of fat metabolism in the body.

Anticoagulant Effects of Arginine-Containing Peptides of the Glyproline Family (His-Phe-Arg-Trp-Pro-Gly-Pro and Thr-Lys-Pro-Arg-Pro-Gly-Pro) Revealed by Thromboelastography

Thromboelastography revealed anticoagulant effects of 3 glyproline oligopeptides (in various concentrations): His-Phe-Arg-Trp-Pro-Gly-Pro, Thr-Lys-Pro-Arg-Pro-Gly-Pro (Selank), and Pro-Gly-Pro. The parameters R, K, MA, S, TMA, and J changed to hypocoagulation direction in comparison to the control. At this, Selank demonstrated the maximal anticoagulation potency.

Decreased diabetes risk over 9 year after 18-month oral L-arginine treatment in middle-aged subjects with impaired glucose tolerance and metabolic syndrome (extension evaluation of L-arginine study)

Purpose

This study aimed to determine whether l-arginine supplementation lasting for 18 months maintained long-lasting effects on diabetes incidence, insulin secretion and sensitivity, oxidative stress, and endothelial function during 108 months among subjects at high risk of developing type 2 diabetes.

Methods

One hundred and forty-four middle-aged subjects with impaired glucose tolerance and metabolic syndrome were randomized in 2006 to an l-arginine supplementation (6.4 g orally/day) or placebo therapy lasting 18 months. This period was followed by a 90-month follow-up. The primary outcome was a diagnosis of diabetes during the 108 month study period. Secondary outcomes included changes in insulin secretion (proinsulin/c-peptide ratio), insulin sensitivity (IGI/HOMA-IR), oxidative stress (AOPPs), and vascular function. After the 18 month participation, subjects that were still free of diabetes and willing to continue their participation (104 subjects) were further followed until diabetes diagnosis, with a time span of about 9 years from baseline.

Results

Although results derived from the 18 month of the intervention study demonstrated no differences in the probability of becoming diabetics, at the end of the study, the cumulative incidence of diabetes was of 40.6% in the l-arginine group and of 57.4% in the placebo group. The adjusted HR for diabetes (l-arginine vs. placebo) was 0.66; 95% CI 0.48, 0.91; p < 0.02). Proinsulin/c-peptide ratio (p < 0.001), IGI/HOMA-IR (p < 0.01), and AOPP (p < 0.05) levels were ameliorated in l-arginine compared to placebo.

Conclusions

These results may suggest that the administration of l-arginine could delay the development of T2DM for a long period. This effect could be mediated, in some extent, by l-arginine-induced reduction in oxidative stress.

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS)

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.

Early energy metabolism-related molecular events in skeletal muscle of diabetic rats: The effects of l-arginine and SOD mimic

Considering the vital role of skeletal muscle in control of whole-body metabolism and the severity of long-term diabetic complications, we aimed to reveal the molecular pattern of early diabetes-related skeletal muscle phenotype in terms of energy metabolism, focusing on regulatory mechanisms, and the possibility to improve it using two redox modulators, l-arginine and superoxide dismutase (SOD) mimic. Alloxan-induced diabetic rats (120 mg/kg) were treated with l-arginine or the highly specific SOD mimic, M40403, for 7 days. As appropriate controls, non-diabetic rats received the same treatments. We found that l-arginine and M40403 restored diabetes-induced impairment of phospho-5'-AMP-activated protein kinase α (AMPKα) signaling by upregulating AMPKα protein itself and its downstream effectors, peroxisome proliferator-activated receptor-γ coactivator-1α and nuclear respiratory factor 1. Also, there was a restitution of the protein levels of oxidative phosphorylation components (complex I, complex II and complex IV) and mitofusin 2. Furthermore, l-arginine and M40403 induced translocation of glucose transporter 4 to the membrane and upregulation of protein of phosphofructokinase and acyl coenzyme A dehydrogenase, diminishing negative diabetic effects on limiting factors of glucose and lipid metabolism. Both treatments abolished diabetes-induced downregulation of sarcoplasmic reticulum calcium-ATPase proteins (SERCA 1 and 2). Similar effects of l-arginine and SOD mimic treatments suggest that disturbances in the superoxide/nitric oxide ratio may be responsible for skeletal muscle mitochondrial and metabolic impairment in early diabetes. Our results provide evidence that l-arginine and SOD mimics have potential in preventing and treating metabolic disturbances accompanying this widespread metabolic disease.

Exploring and Enhancing the Anti-Inflammatory Properties of Polymeric Formula

BACKGROUND

Exclusive enteral nutrition (EEN) therapy using a polymeric formula (PF) can substantially attenuate intestinal inflammation in Crohn's disease (CD) patients. However, the mechanism(s) by which EEN suppresses inflammation are not yet fully understood. The aims were to examine cellular mechanism(s) through which EEN may suppress inflammation and investigate potential pathways to enhance anti-inflammatory properties of EEN.

METHODS

Glutamine, arginine, vitamin D3, and α linolenic acid (ALA), present in PF, along with curcumin, were identified as immunoactive nutrient therapies. Tumor necrosis factor (TNF)-α-exposed HT-29 colonic epithelial cells were used to investigate the immunosuppressive activity of the nutrients by assessing their effect on cell viability, cell activity, chemokine response (interleukin-8 [IL-8]), nuclear factor (NF)-κB, P38 mitogen-activated protein kinase, IκB kinase (Iκκ), and nitric oxide (NO).

RESULTS

Cellular viability and activity were maintained with all nutrient treatments. Glutamine, arginine, and vitamin D3, but not ALA, significantly attenuated IL-8 production. Glutamine and arginine led to phosphorylation blockade of the signaling components in NF-κB and P38 pathways, reduction in kinase activity, and enhancement in NO production. Combining glutamine, arginine, and curcumin at optimal concentrations completely abolished the IL-8 response.

CONCLUSIONS

These data indicate that glutamine, arginine, and vitamin D3 can suppress inflammation at concentrations equivalent to those used in PF. The mechanisms of this action were mediated through influencing the NF-κB and P38 cascades. Glutamine and arginine-fortified PF with curcumin might be a promising option to enhance the effectiveness and expand the scope of EEN therapy in CD treatment.

Effect of Nitric Oxide Synthesis Blockade on the Morphology of Langerhans Islets in August and Wistar Rats with Acute Alloxan Diabetes

Alloxan diabetes was modeled in August rats with high activity of the NO system and in Wistar rats, and the effects of NO system blockade (by a course treatment with L-NNA) on Langerhans islet β cells were studied in 15 days. The toxic effects of diabetes on the rat β cells and islets were similar: the content of active β cells in the islets decreased to 15-20%, the number of islets to 24-29% of control. A course of L-NNA reduced the β cell and islet death, in August cells greater than in Wistar: the number of islets in August rats was restored to 81%, in Wistar rats to 60% of initial level; the activity of β cells remained at the control level in the former and 2-fold lower than in the control in the latter. It seems that a less pronounced protective effect of L-NNA in Wistar rats was explained by excessive reduction of NO level essential for β cell regeneration.

Dietary coconut kernel protein beneficially modulates NFκB and RAGE expression in streptozotocin induced diabetes in rats

Previous studies showed that arginine rich coconut kernel protein (CKP) maintains glucose homeostasis in experimental diabetic rats. But the mechanism of this effect was not clear. This study investigated the effect of CKP on the expression of liver receptor for advance glycated end products (RAGE), inducible nitric oxide synthase (iNOS) and NFkB. Diabetes was induced by injecting a single dose of streptozotocin (75 mg/kg body weight) intraperitoneally. After inducing diabetes, CKP was administered to rats orally for 45 days. After the experimental period, serum glucose, insulin, liver glycogen, glucose metabolizing enzyme activities and the expression of liver RAGE, iNOS and NFkB was evaluated. The results showed that CKP beneficially modulated the levels of glucose and insulin as well as the metabolizing enzyme activities. Expression of RAGE and NFkB was found to be over expressed in diabetic rats but was found to be down regulated in CKP fed diabetic rats. iNOS expression was down regulated in diabetic rats, which was expressed normally in CKP fed diabetic rats. These results clearly demonstrated that anti diabetic activity of CKP is mediated through NFkB pathway.

New insights into male (in)fertility: the importance of NO

Infertility is a global problem that is on the rise, especially during the last decade. Currently, infertility affects approximately 10-15% of the population worldwide. The frequency and origin of different forms of infertility varies. It has been shown that reactive oxygen and nitrogen species (ROS and RNS) are involved in the aetiology of infertility, especially male infertility. Various strategies have been designed to remove or decrease the production of ROS and RNS in spermatozoa, in particular during in vitro fertilization. However, in recent years it has been shown that spermatozoa naturally produce a variety of ROS/RNS, including superoxide anion radical (O2 (⋅-)), hydrogen peroxide and NO. These reactive species, in particular NO, are essential in regulating sperm capacitation and the acrosome reaction, two processes that need to be acquired by sperm in order to achieve fertilization potential. In addition, it has recently been shown that mitochondrial function is positively correlated with human sperm fertilization potential and quality and that NO and NO precursors increase sperm motility by increasing energy production in mitochondria. We will review the new link between sperm NO-driven redox regulation and infertility herein. A special emphasis will be placed on the potential implementation of new redox-active substances that modulate the content of NO in spermatozoa to increase fertility and promote conception.

Role of nitric oxide in the pathogenesis of alloxan diabetes

We studied the effects of N(w)-nitro-L-arginine (L-NNA), a nonselective inhibitor of NO synthases, on the severity of type 1 diabetes mellitus induced by subcutaneous injection of 130 mg/kg alloxan in August rats with high activity of NO system and in Wistar rats. Five days after alloxan injection, hyperglycemia levels after overnight fasting in August and Wistar rats were 27.1±3.7 and 22.0±1.1 mmol/liter, respectively (p<0.03). The mortality over 15 days after alloxan injection in August rats was higher than in Wistar rats (36 and 26%, respectively). L-NNA normalized glucose levels in diabetics of both groups. It completely prevented mortality in August and reduced it to 13% in Wistar rats. Body weight loss and polydipsia after L-NNA injection were also less pronounced in August rats. Plasma nitrite/nitrate concentrations in August rats were 32% higher than in Wistar rats, both in intact and diabetic rats. These data attest to an important role of NO in the pathogenesis of alloxan diabetes.

Mitochondrial dysfunction in brain cortex mitochondria of STZ-diabetic rats: effect of l-Arginine

Mitochondrial dysfunction has been implicated in many diseases, including diabetes. It is well known that oxygen free radical species are produced endogenously by mitochondria, and also nitric oxide (NO) by nitric oxide synthases (NOS) associated to mitochondrial membranes, in consequence these organelles constitute main targets for oxidative damage. The aim of this study was to analyze mitochondrial physiology and NO production in brain cortex mitochondria of streptozotocin (STZ) diabetic rats in an early stage of diabetes and the potential effect of L-arginine administration. The diabetic condition was characterized by a clear hyperglycaemic state with loose of body weight after 4 days of STZ injection. This hyperglycaemic state was associated with mitochondrial dysfunction that was evident by an impairment of the respiratory activity, increased production of superoxide anion and a clear mitochondrial depolarization. In addition, the alteration in mitochondrial physiology was associated with a significant decrease in both NO production and nitric oxide synthase type I (NOS I) expression associated to the mitochondrial membranes. An increased level of thiobarbituric acid-reactive substances (TBARS) in brain cortex homogenates from STZ-diabetic rats indicated the presence of lipid peroxidation. L-arginine treatment to diabetic rats did not change blood glucose levels but significantly ameliorated the oxidative stress evidenced by lower TBARS and a lower level of superoxide anion. This effect was paralleled by improvement of mitochondrial respiratory function and a partial mitochondrial repolarization.In addition, the administration of L-arginine to diabetic rats prevented the decrease in NO production and NOSI expression. These results could indicate that exogenously administered L-arginine may have beneficial effects on mitochondrial function, oxidative stress and NO production in brain cortex mitochondria of STZ-diabetic rats.

Molecular basis of hippocampal energy metabolism in diabetic rats: the effects of SOD mimic

Hippocampal structural changes associated with diabetes-related cognitive impairments are well described, but their molecular background remained vague. We examined whether/how diabetes alters molecular basis of energy metabolism in hippocampus readily after diabetes onset, with special emphasis on its redox-sensitivity. To induce diabetes, adult Mill Hill hybrid hooded rats received a single alloxan dose (120 mg/kg). Both non-diabetic and diabetic groups were further divided in two subgroups receiving (i) or not (ii) superoxide dismutase (SOD) mimic, [Mn(II)(pyane)Cl2] for 7 days, i.p. Treatment of the diabetic animals started after blood glucose level ≥12 mM. Diabetes decreased protein levels of oxidative phosphorylation components: complex III and ATP synthase. In contrast, protein amounts of glyceraldehyde-3-phosphate dehydrogenase, pyruvate dehydrogenase, and hypoxia-inducible factor-1α - the key regulator of energy metabolism in stress conditions, were higher in diabetic animals. Treatment with SOD mimic restored/increased the levels of oxidative phosphorylation components and returned hypoxia-inducible factor-1α to control level, while diabetes-induced up-regulation of glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase, was additionally stimulated. To conclude, our results provide insight into the earliest molecular changes of energy-producing pathways in diabetes that may account for structural/functional disturbance of hippocampus, seen during disease progression. Also, data suggest [Mn(II)(pyane)Cl2] as potential therapeutic agent in cutting-edge approaches to threat this widespread metabolic disorder.

Supplementation with apple enriched with L-arginine may improve metabolic control and survival rate in alloxan-induced diabetic rats

Supplementation with L-arginine or fresh food with high content of this amino acid is associated with favorable effects in the metabolic control of diabetes. We aimed to determine whether supplementation with apples enriched with L-arginine offer additional benefits compared to L-arginine by itself in a preclinical study of diabetes. This study combines food-engineer technologies with in vivo and in vitro analysis. In vitro experiments show that cells derived from non-diabetic animals and exposed to high glucose (25 mM, 12 H) and cells isolated from alloxan-induced diabetic animals exhibited a reduction (∼50%) in the L-arginine uptake. This effect was reverted by L-arginine pretreatment (12 H) in both the normal and diabetes-derived cells. In preclinical studies, normoglycemic (n = 25) and diabetic groups (n = 50) were divided into subgroups that received either L-arginine (375 mg/kg per 10 days) or apple enriched with L-arginine or vehicle (control). In a preliminary analysis, supplementation with L-arginine by itself (50%) or apple enriched with L-arginine (100%) improve survival rate in the diabetic group compared to control (0%) at the end of the follow up (17 days). This phenomenon was associated with a partial but sustained high plasma level of L-arginine, as well as plasma concentration of nitrites and insulin in the L-arginine or apple + L-arginine groups after supplementation. Apple + L-arginine supplementation in diabetic animals induced the highest and longest effects in the level of these three markers among the studied groups. Therefore, apple enriched by L-arginine offers more benefits than L-arginine by itself in this preclinical study.

Regulatory role of PGC-1α/PPAR signaling in skeletal muscle metabolic recruitment during cold acclimation

This study examined the molecular basis of energy-related regulatory mechanisms underlying metabolic recruitment of skeletal muscle during cold acclimation and possible involvement of the l-arginine/nitric oxide-producing pathway. Rats exposed to cold (4±1°C) for periods of 1, 3, 7, 12, 21 and 45 days were divided into three groups: untreated, l-arginine treated and N(ω)-nitro-l-arginine methyl ester (l-NAME) treated. Compared with controls (22±1°C), there was an initial increase in the protein level of 5'-AMP-activated protein kinase α (day 1), followed by an increase in peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and peroxisome proliferator-activated receptors (PPARs): PPARα and PPARγ from day 1 and PPARδ from day 7 of cold acclimation. Activation of the PGC-1α/PPAR transcription program was accompanied by increased protein expression of the key metabolic enzymes in β-oxidation, the tricarboxylic acid cycle and oxidative phosphorylation, with the exceptions in complex I (no changes) and ATP synthase (decreased at day 1). Cold did not affect hexokinase and GAPDH protein levels, but increased lactate dehydrogenase activity compared with controls (1-45 days). l-arginine sustained, accelerated and/or intensified cold-induced molecular remodeling throughout cold acclimation. l-NAME exerted phase-dependent effects: similar to l-arginine in early cold acclimation and opposite after prolonged cold exposure (from day 21). It seems that upregulation of the PGC-1α/PPAR transcription program early during cold acclimation triggers the molecular recruitment of skeletal muscle underlying the shift to more oxidative metabolism during prolonged cold acclimation. Our results suggest that nitric oxide has a role in maintaining the skeletal muscle oxidative phenotype in late cold acclimation but question its role early in cold acclimation.

Nitric oxide is a mediator of antiproliferative effects induced by proinflammatory cytokines on pancreatic beta cells

Nitric oxide (NO) is involved in several biological processes. In type 1 diabetes mellitus (T1DM), proinflammatory cytokines activate an inducible isoform of NOS (iNOS) in β cells, thus increasing NO levels and inducing apoptosis. The aim of the current study is to determine the role of NO (1) in the antiproliferative effect of proinflammatory cytokines IL-1β, IFN-γ, and TNF-α on cultured islet β cells and (2) during the insulitis stage prior to diabetes onset using the Biobreeding (BB) rat strain as T1DM model. Our results indicate that NO donors exert an antiproliferative effect on β cell obtained from cultured pancreatic islets, similar to that induced by proinflammatory cytokines. This cytokine-induced antiproliferative effect can be reversed by L-NMMA, a general NOS inhibitor, and is independent of guanylate cyclase pathway. Assays using NOS isoform specific inhibitors suggest that the NO implicated in the antiproliferative effect of proinflammatory cytokines is produced by inducible NOS, although not in an exclusive way. In BB rats, early treatment with L-NMMA improves the initial stage of insulitis. We conclude that NO is an important mediator of antiproliferative effect induced by proinflammatory cytokines on cultured β cell and is implicated in β-cell proliferation impairment observed early from initial stage of insulitis.

L-arginine enriched biscuits improve endothelial function and glucose metabolism: a pilot study in healthy subjects and a cross-over study in subjects with impaired glucose tolerance and metabolic syndrome

OBJECTIVE

The aim of this study was to evaluate the effects of a new L-arginine-enriched biscuit on endothelial function, insulin sensitivity/secretion and body composition.

MATERIALS/METHODS

The project was composed of two studies. The first study was an acute pilot postprandial study in 7 healthy subjects that evaluated bio-availability and vascular effects of L-arginine-enriched biscuits that contained 6.6 gL-arginine, 21.9 g carbohydrates, 3.6 g protein, 7.5 g fat and 4.3 g dietary fiber compared with placebo biscuits and 6.6 g powdered L-arginine. Subjects underwent the tests in random order, in at least 14-day intervals. The second study was a double-blind crossover study in 15 obese subjects with IGT and MS. These subjects consumed 6.6 g of L-arginine-enriched biscuits or placebo biscuits in a 1600 kcal diet. Each study period lasted 2 weeks with a 2-week washout in between. Endothelial function, glucose tolerance, insulin sensitivity and insulin secretion were evaluated at the end of each intervention period.

RESULTS

In the first study, the groups that received the L-arginine-enriched biscuits and the powdered L-arginine had similarly increased L-arginine, NOx and cGMP levels and post-ischemic blood flow (PI-BF). In both cases, these levels were significantly higher than those in the placebo biscuit recipient group. In the second study, the L-arginine-enriched biscuit recipient group displayed increased L-arginine, NOx, cGMP, PI-BF, and Matsuda index levels, whereas their circulating glucose, proinsulin/insulin ratio and fat mass were decreased compared with the placebo biscuit recipient group.

CONCLUSIONS

L-Arginine-enriched biscuits with low sugar and protein content enhance endothelial function and improve glucose metabolism, insulin sensitivity and insulin secretion in subjects with IGT and MS.

L-Arginine ameliorates cardiac left ventricular oxidative stress by upregulating eNOS and Nrf2 target genes in alloxan-induced hyperglycemic rats

Hyperglycemia is independently related with excessive morbidity and mortality in cardiovascular disorders. L-Arginine-nitric oxide (NO) pathway and the involvement of NO in modulating nuclear factor-E2-related factor-2 (Nrf2) signaling were well established. In the present study we investigated, whether L-arginine supplementation would improve the myocardial antioxidant defense under hyperglycemia through activation of Nrf2 signaling. Diabetes was induced by alloxan monohydrate (90 mg kg(-1) body weight) in rats. Both non-diabetic and diabetic group of rats were divided into three subgroups and they were administered either with L-arginine (2.25%) or L-NAME (0.01%) in drinking water for 12 days. Results showed that L-arginine treatment reduced the metabolic disturbances in diabetic rats. Antioxidant enzymes and glutathione levels were found to be increased in heart left ventricles, thereby reduction of lipid peroxidation by L-arginine treatment. Heart histopathological analysis further validates the reversal of typical diabetic characteristics consisting of alterations in myofibers and myofibrillary degeneration. qRT-PCR studies revealed that L-arginine treatment upregulated the transcription of Akt and downregulated NF-κB. Notably, transcription of eNOS and Nrf2 target genes was also upregulated, which were accompanied by enhanced expression of Nrf2 in left ventricular tissue from diabetic and control rats. Under these findings, we suggest that targeting of eNOS and Nrf2 signaling by L-arginine supplementation could be used as a potential treatment method to alleviate the late diabetic complications.

Effect of a long-term oral l-arginine supplementation on glucose metabolism: a randomized, double-blind, placebo-controlled trial

AIM

This study assessed the efficacy of long-term l-arginine (l-arg) therapy in preventing or delaying type 2 diabetes mellitus.

METHODS

A mono-centre, randomized, double-blind, parallel-group, placebo-controlled, phase III trial (l-arg trial) was conducted on 144 individuals affected by impaired glucose tolerance (IGT) and metabolic syndrome (MS). l-Arg/placebo was administered (6.4 g/day) on a background structured lifestyle intervention for 18 months plus a 12-month extended follow-up period after study drug termination. Fasting glucose levels and glucose tolerance after oral glucose tolerance test were evaluated throughout the study.

RESULTS

After 18 months, l-arg as compared with placebo did not reduce the cumulative incidence of diabetes [21.4 and 20.8%, respectively, hazard ratio (HR), 1.04; 95% confidence interval (CI), 0.58-1.86] while the cumulative probability to become normal glucose tolerant (NGT) increased (42.4 and 22.1%, respectively, HR, 2.60; 95% CI, 1.51-4.46, p < 0.001). The higher cumulative probability to become of NGT was maintained during the extended period in subjects previously treated with l-arg (HR, 3.21; 95% CI, 1.87-5.51; p < 0.001). At the end of the extended period, the cumulative incidence of diabetes in subjects previously treated with l-arg was reduced as compared with placebo (27.2 and 47.1%, respectively, HR, 0.42; 95% CI, 0.24-0.75, p < 0.05). During both periods, l-arg significantly improved insulin sensitivity and β-cell function.

CONCLUSION

Among persons with IGT and MS, the supplementation of l-arg for 18 months does not significantly reduce the incidence of diabetes but does significantly increase regression to NGT.

Effects of L-arginine supplementation on blood flow, oxidative stress status and exercise responses in young adults with uncomplicated type I diabetes

BACKGROUND AND AIMS

Vascular disease is the principal cause of death and disability in patients with diabetes, and endothelial dysfunction seems to be the major cause in its pathogenesis. Since L-arginine levels are diminished in conditions such as type 1 and type 2 diabetes, in this work we aimed to verify the effects of L-arginine supplementation (7 g/day) over the endothelial function and oxidative stress markers in young male adults with uncomplicated type 1 diabetes. We also investigated the influences of L-arginine administration on vascular/oxidative stress responses to an acute bout of exercise.

METHODS

Ten young adult male subjects with uncomplicated type 1 diabetes and twenty matched controls volunteered for this study. We analysed the influence of L-arginine supplementation (7 g/day during 1 week) over lower limb blood flow (using a venous occlusion plethysmography technique), oxidative stress marker (TBARS, Carbonyls), anti-oxidant parameters (uric acid and TRAP) and total tNOx in rest conditions and after a single bout of submaximal exercise (VO₂ at 10 % below the second ventilatory threshold). Data described as mean ± standard error (SE). Alpha level was P < 0.05.

RESULTS

Glycaemic control parameters were altered in type 1 diabetic subjects, such as HbA1c (5.5 ± 0.03 vs. 8.3 ± 0.4 %) and fasted glycaemia (94.8 ± 1.4 vs. 183 ± 19 mg/dL). Oxidative stress/damage markers (carbonyls and TBARS) were increased in the diabetic group, while uric acid was decreased. Rest lower limb blood flow was lower in type 1 diabetic subjects than in healthy controls (3.53 ± 0.35 vs. 2.66 ± 0.3 ml 100 ml⁻¹ min⁻¹). L-Arginine supplementation completely recovered basal blood flow to normal levels in type 1 diabetics' subjects (2.66 ± 0.3 to 4.74 ± 0.86 ml 100 ml⁻¹ min⁻¹) but did not interfere in any parameter of redox state or exercise.

CONCLUSION

Our findings highlight the importance of L-arginine for the improvement of vascular function in subjects with diabetes, indicating that L-arginine supplementation could be an essential tool for the treatment for the disease complications, at least in non-complicated diabetes. However, based on our data, it is not possible to draw conclusions regarding the mechanisms by which L-arginine therapy is inducing improvements on cardiovascular function, but this important issue requires further investigations.

Arginine-rich coconut kernel diet influences nitric oxide synthase activity in alloxandiabetic rats

BACKGROUND

Coconut kernel protein (CKP) has been reported to contain significant amounts of L-arginine. Its potential effect on glucose homeostasis, possibly through the nitric oxide synthase (NO) pathway, was therefore investigated in alloxan-induced diabetic rats. Diabetes was induced by a single intraperitoneal dose of alloxan (150 mg kg⁻¹ body weight). Experimental rats were grouped as follows: Group I, normal control; Group II, diabetic control; Group III, diabetic + CKP; Group IV, diabetic + L-arginine; Group V, diabetic + L-arginine + L-N(G)-Nitroarginine methyl ester (L-NAME). Purified CKP isolated from dried coconut kernel and L-arginine was administered to rats along with a semi-synthetic diet for 45 days. L-NAME (0.5 mg kg⁻¹ body weight) was given to Group V animals. After the experimental period, serum glucose, insulin, activities of liver nitric oxide synthase and arginase, liver glycogen levels and histopathology of the pancreas were evaluated.

RESULTS

Serum glucose, insulin and antioxidant enzyme activities and liver glycogen levels were found to be restored to basal levels in CKP-fed rats. Decreased arginase and increased nitric oxide synthase (NOS) activities were found in CKP- and arginine-fed rats. L-NAME treatment showed a partial effect on these parameters. Histopathology revealed that CKP and L-arginine feeding reduced the diabetes-related pancreatic damage in treated rats compared to the diabetic control.

CONCLUSION

The results observed in this study indicate that the potential antidiabetic activity of CKP may be through an arginine-NO pathway leading to pancreatic beta cell regeneration.

Effect of dietary arginine on growth, intestinal enzyme activities and gene expression in muscle, hepatopancreas and intestine of juvenile Jian carp (Cyprinus carpio var. Jian)

The present study was conducted to test the hypothesis that dietary arginine promotes digestion and absorption capacity, and, thus, enhances fish growth. This improvement might be related to the target of rapamycin (TOR) and eIF4E-binding protein (4E-BP). A total of 1200 juvenile Jian carp, Cyprinus carpio var. Jian, with an average initial weight of 6.33 (SE 0.03) g, were fed with diets containing graded concentrations of arginine, namely, 9.8 (control), 12.7, 16.1, 18.5, 21.9 and 24.5 g arginine/kg diet for 9 weeks. An real-time quantitative PCR analysis was performed to determine the relative expression of TOR and 4E-BP in fish muscle, hepatopancreas and intestine. Dietary arginine increased (P < 0.05): (1) glutamate-oxaloacetate transaminase and glutamate-pyruvate transaminase activities in muscle and hepatopancreas; (2) intestine and hepatopancreas protein content, folds height, and trypsin, chymotrypsin, lipase, Na⁺/K⁺-ATPase, alkaline phosphatase, γ-glutamyl transpeptidase and creatine kinase activities in intestine; (3) Lactobacillus counts; (4) relative expression of TOR in the muscle, hepatopancreas and distal intestine (DI); (5) relative expression of 4E-BP in proximal intestine (PI) and mid-intestine (MI), as compared with the control group. In contrast, dietary arginine reduced (P < 0.05): (1) plasma ammonia content; (2) Aeromonas hydrophila and Escherichia coli counts; (3) relative expression of TOR in PI and MI; (4) relative expression of 4E-BP in the muscle, hepatopancreas and DI. The arginine requirement estimated by specific growth rate using quadratic regression analysis was found to be 18.0 g/kg diet. These results indicate that arginine improved fish growth, digestive and absorptive ability and regulated the expression of TOR and 4E-BP genes.

L-arginine is essential for pancreatic β-cell functional integrity, metabolism and defense from inflammatory challenge

In this work, our aim was to determine whether L-arginine (a known insulinotropic amino acid) can promote a shift of β-cell intermediary metabolism favoring glutathione (GSH) and glutathione disulfide (GSSG) antioxidant responses, stimulus-secretion coupling and functional integrity. Clonal BRIN-BD11 β-cells and mouse islets were cultured for 24 h at various L-arginine concentrations (0-1.15  mmol/l) in the absence or presence of a proinflammatory cytokine cocktail (interleukin 1β, tumour necrosis factor α and interferon γ). Cells were assessed for viability, insulin secretion, GSH, GSSG, glutamate, nitric oxide (NO), superoxide, urea, lactate and for the consumption of glucose and glutamine. Protein levels of NO synthase-2, AMP-activated protein kinase (AMPK) and the heat shock protein 72 (HSP72) were also evaluated. We found that L-arginine at 1.15  mmol/l attenuated the loss of β-cell viability observed in the presence of proinflammatory cytokines. L-arginine increased total cellular GSH and glutamate levels but reduced the GSSG/GSH ratio and glutamate release. The amino acid stimulated glucose consumption in the presence of cytokines while also stimulating AMPK phosphorylation and HSP72 expression. Proinflammatory cytokines reduced, by at least 50%, chronic (24 h) insulin secretion, an effect partially attenuated by L-arginine. Acute insulin secretion was robustly stimulated by L-arginine but this effect was abolished in the presence of cytokines. We conclude that L-arginine can stimulate β-cell insulin secretion, antioxidant and protective responses, enabling increased functional integrity of β-cells and islets in the presence of proinflammatory cytokines. Glucose consumption and intermediary metabolism were increased by L-arginine. These results highlight the importance of L-arginine availability for β-cells during inflammatory challenge.

Rapamycin impairs proliferation of transplanted islet β cells

BACKGROUND

The cause for a progressive attrition of islet graft function observed over the years after islet transplantation is not well defined but may be in part the result of adverse effects of immunosuppressive agents. In this study, we examined the effect of rapamycin, a key component of the immunosuppressive regimen, on β-cell replication of transplanted islets.

METHODS

Mice transplanted with rat islets under kidney capsule received bromodeoxyuridine for 7 days. Mice were treated with rapamycin or appropriate vehicle. β-cell replication was determined by double immunofluorescence staining for insulin and bromodeoxyuridine. For in vitro studies, apoptosis, glucose-stimulated insulin secretion, and proliferation were determined in islet cells incubated with EdU in the presence or absence of rapamycin.

RESULTS

In our islet transplant model, rapamycin impaired glucose tolerance and β-cell proliferation of transplanted and host islets. In vitro, rapamycin reduced glucose-stimulated insulin secretion and reversibly decreased β-cell replication. The inhibitory effect of rapamycin on β-cell proliferation was not due to the decrease in insulin release. Additionally, in islet cells, expression of cell cycle proteins was significantly modified by rapamycin, suggesting a blockade of cell cycle progression. Inhibition of p38MAPK partially reverted rapamycin effect on β-cell proliferation.

CONCLUSION

Rapamycin, at concentration usually used to prevent islet graft rejection, is able to reduce the rate of β-cell proliferation in transplanted rat islets but also in host murine islets. These data suggest that the progressive islet graft dysfunction observed under immunosuppressive therapy may result in part from an impairment of β-cell regeneration.

Exercise and possible molecular mechanisms of protection from vascular disease and diabetes: the central role of ROS and nitric oxide

It is now widely accepted that hypertension and endothelial dysfunction are associated with an insulin-resistant state and thus with the development of T2DM (Type 2 diabetes mellitus). Insulin signalling is impaired in target cells and tissues, indicating that common molecular signals are involved. The free radical NO* regulates cell metabolism, insulin signalling and secretion, vascular tone, neurotransmission and immune system function. NO* synthesis is essential for vasodilation, the maintenance of blood pressure and glucose uptake and, thus, if levels of NO* are decreased, insulin resistance and hypertension will result. Decreased blood levels of insulin, increased AngII (angiotensin II), hyperhomocysteinaemia, increased ADMA (asymmetric omega-NG,NG-dimethylarginine) and low plasma L-arginine are all conditions likely to decrease NO* production and which are associated with diabetes and cardiovascular disease. We suggest in the present article that the widely reported beneficial effects of exercise in the improvement of metabolic and cardiovascular health are mediated by enhancing the flux of muscle- and kidney-derived amino acids to pancreatic and vascular endothelial cells aiding the intracellular production of NO*, therefore resulting in normalization of insulin secretion, vascular tone and insulin sensitivity. Exercise may also have an impact on AngII and ADMA signalling and the production of pro- and anti-inflammatory cytokines in muscle, so reducing the progression and development of vascular disease and diabetes. NO* synthesis will be increased during exercise in the vascular endothelial cells so promoting blood flow. We suggest that exercise may promote improvements in health due to positive metabolic and cytokine-mediated effects.