Regulation of hyperglycemia and dyslipidemia by exogenous L-arginine in diabetic rats

Kidney Bean Fermented Broth Alleviates Hyperlipidemic by Regulating Serum Metabolites and Gut Microbiota Composition

Hyperlipidemia with fat accumulation and weight gain causes metabolic diseases and endangers human body health easily which is accompanied by metabolic abnormalities and intestinal flora disorders. In this study, the kidney bean fermented broth (KBF) was used in rats that were fed a high-fat diet to induce hyperlipidemia in order to subsequently analyse the serum metabolomics and gut microbiota modulatoration. The results show that the contents of the total polyphenols and total flavonoids in the KBF were up three and one times, while energy and carbohydrates decreased. In the HFD-induced hyperlipidemic model, body weight, organ weight, and the level of blood lipids (ALT, AST, TG, TC) were lower in rats treated with KBF than in the controls. Metabonomics indicate that there were significant differences in serum metabolomics between the KBF and the HFD. KBF could significantly improve the glycerophospholipids, taurine, and hypotaurine metabolism and amino acid metabolism of hyperlipidemic rats and then improve the symptoms of hypersterol and fat accumulation in rats. The relative abundance of beneficial bacteria increased while pathogenic bacteria decreased after the intervention of KBF. KBF ameliorates dyslipidemia of HFD-induced hyperlipidemic via modulating the blood metabolism and the intestinal microbiota. Collectively, these findings suggest that KBF could be developed as a functional food for anti-hyperlipidemia.

The Potential of L-Arginine in Prevention and Treatment of Disturbed Carbohydrate and Lipid Metabolism—A Review

L-arginine, an endogenous amino acid, is a safe substance that can be found in food. The compound is involved in synthesis of various products responsible for regulatory functions in the body. Particularly noteworthy is, among others, nitric oxide, a signaling molecule regulating carbohydrate and lipid metabolism. The increasing experimental and clinical data indicate that L-arginine supplementation may be helpful in managing disturbed metabolism in obesity, regulate arterial blood pressure or alleviate type 2 diabetes symptoms, but the mechanisms underlying these effects have not been sufficiently elucidated. This review aims to present the up-to-date information regarding the current uses and health-promoting potential of L-arginine, its effects on nitric oxide, carbohydrate and lipid metabolisms, based on the results of in vivo, in vitro studies, and clinical human trials. Available literature suggests that L-arginine may have beneficial effects on human health. However, some studies found that higher dietary L-arginine is associated with worsening of an existing disease or may be potential risk factor for development of some diseases. The mechanisms of regulatory effects of L-arginine on carbohydrate and lipid metabolism have not been fully understood and are currently under investigation.

Anti-cataract effects of coconut water in vivo and in vitro

OBJECTIVE

To determine the anti-cataract effects of coconut water (CW) in vivo and in vitro, and to explore the potential pathogenic mechanism.

METHODS

In this study, 48 male Sprague-Dawley rats were randomly divided into 4 groups: control (CO), diabetic (DM), diabetic treated with CW (DM + CW), and diabetic treated with Glibenclamide (DM + Gli). Except for the CO group, in the other three groups, intraperitoneal injection of STZ (60 mg/kg) was conducted to establish diabetic models. The experiment was conducted for 20 weeks. The slit-lamp examination was undertaken during the period of experiment (20 weeks), and then, all rats were sacrificed. The levels of superoxide dismutase (SOD), malondialdehyde (MDA), and glutathione peroxidase (GSH-Px) in the left lens were measured by using biochemical assays. The right lens was used for pathological analysis. The rat lens epithelial cells (LECs) were cultured in vitro and the subcultured cell were divided into four groups, namely the normal glucose group (5 mmol /L glucose, Group I), the high glucose group (40 mmol/L glucose, Group II), high glucose +5% CW group (Group III), and high glucose +10% CW group (Group IV). LECs were cultured under the conditions as described above for 48 h. Cell proliferation and the morphological changes were observed with interted phase contrast microscope.The level of cell apoptosis was determined by flow cytometry. the level of SOD, MDA and GSH-Px were also detected.

RESULTS

The lens opacity index decreased in diabetic rats, and LECs apoptosis ratio also decreased in high glucose environments that received CW. Under treatment with CW, reduced MDA level and elevated activities of SOD and GSH-Px were detected, both in vivo and in vitro experiments. The increased severity of cataract and LECs apoptosis were noted in diabetic rats that received normal water, while CW markedly mitigated the enhanced cataract severity and the reduction of LECs induced by diabetes mellitus.

CONCLUSION

CW is a functional food that can protect the lens from diabetic cataract. The possible underlying mechanism may be partly explained via the decreased oxidative stress in lens. However, further research needs to be conducted to indicate the pathogenic mechanism of anti-diabetic effects of CW.

Sodium nitroprusside protects HFD induced gut dysfunction via activating AMPKα/SIRT1 signaling

Background

Activation of Adenosine 5′-monophosphate-activated protein kinase/Sirtuin1 (AMPK/SIRT1) exerts an effect in alleviating obesity and gut damage. Sodium nitroprusside (SNP), a nitric oxide (NO) donor, has been reported to activate AMPK. This study was to investigate the effect of SNP on HFD induced gut dysfunction and the mechanism.

Methods

SNP was applied on lipopolysaccharide (LPS) stimulated Caco-2 cell monolayers which mimicked intestinal epithelial barrier dysfunction and HFD-fed mice which were complicated by gut dysfunction. Then AMPKα/SIRT1 pathway and gut barrier indicators were investigated.

Results

SNP rescued the loss of tight junction proteins ZO-1 and occludin, the inhibition of AMPKα/SIRT1 in LPS stimulated Caco-2 cell monolayers, and the effects were not shown when AMPKa1 was knocked-down by siRNA. SNP also alleviated HFD induced obesity and gut dysfunction in mice, as indicated by the decreasing of intestinal permeability, the increasing expression of ZO-1 and occludin, the decreasing levels of pro-inflammatory cytokine IL-6, and the repairing of gut microbiota dysbiosis. These effects were complicated by the increased colonic NO content and the activated AMPKα/SIRT1 signaling.

Conclusions

The results may imply that SNP, as a NO donor, alleviates HFD induced gut dysfunction probably by activating the AMPKα/SIRT1 signaling pathway.

Versatile Nutraceutical Potentials of Watermelon-A Modest Fruit Loaded with Pharmaceutically Valuable Phytochemicals

Watermelon (Citrulus lantus) is an important horticultural crop which belongs to the Curcubitaceae family. The nutraceutical potential of watermelon has been illustrated by several researchers, which makes it a better choice of functional food. Watermelon has been used to treat various ailments, such as cardio-vascular diseases, aging related ailments, obesity, diabetes, ulcers, and various types of cancers. The medicinal properties of watermelon are attributed by the presence of important phytochemicals with pharmaceutical values such as lycopene, citrulline, and other polyphenolic compounds. Watermelon acts as vital source of l-citrulline, a neutral-alpha amino acid which is the precursor of l-arginine, an essential amino acid necessary for protein synthesis. Supplementation of l-citrulline and lycopene displayed numerous health benefits in in vitro and in vivo studies. Similarly, the dietary intake of watermelon has proven benefits as functional food in humans for weight management. Apart from the fruits, the extracts prepared from the seeds, sprouts, and leaves also evidenced medicinal properties. The present review provides a comprehensive overview of benefits of watermelon for the treatment of various ailments.

Effects of intravenous arginine infusion on inflammation and metabolic indices of dairy cows in early lactation

Enhancing the supply of arginine (Arg), a semi-essential amino acid, has positive effects on immune function in dairy cattle experiencing metabolic stress during early lactation. Our objective was to determine the effects of Arg supplementation on biomarkers of liver damage and inflammation in cows during early lactation. Six Chinese Holstein lactating cows with similar BW (508 ± 14 kg), body condition score (3.0), parity (4.0 ± 0), milk yield (30.6 ± 1.8 kg) and days in milk (20 ± days) were randomly assigned to three treatments in a replicated 3 × 3 Latin square design balanced for carryover effects. Each period was 21 days with 7 days for infusion and 14 days for washout. Treatments were (1) Control: saline; (2) Arg group: saline + 0.216 mol/day l-Arg; and (3) Alanine (Ala) group: saline + 0.868 mol/day l-Ala (iso-nitrogenous to the Arg group). Blood and milk samples from the experimental cows were collected on the last day of each infusion period and analyzed for indices of liver damage and inflammation, and the count and composition of somatic cells in milk. Compared with the Control, the infusion of Arg led to greater concentrations of total protein, immunoglobulin M and high density lipoprotein cholesterol coupled with lower concentrations of haptoglobin and tumor necrosis factor-α, and activity of aspartate aminotransferase in serum. Infusion of Ala had no effect on those biomarkers compared with the Control. Although milk somatic cell count was not affected, the concentration of granulocytes was lower in response to Arg infusion compared with the Control or Ala group. Overall, the biomarker analyses indicated that the supplementation of Arg via the jugular vein during early lactation alleviated inflammation and metabolic stress.

Minimization of the Risk of Diabetic Microangiopathy in Rats by Nigella sativa

BACKGROUND

Microangiopathy is a chronic diabetic complication resulting from metabolic derangements, oxidative stress, and increased pro-inflammatory cytokine production. Nigella sativa Linn. is used as an herbal medicine that exerts hypoglycemic, antilipidemic, anti-inflammatory, and antioxidant effects.

OBJECTIVE

To examine the effects of N. sativa extract on cutaneous microvascular changes in diabetic rats.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly assigned into the following four groups: Untreated and N. sativa-treated normal controls and untreated and N. sativa-treated rats with streptozotocin-induced diabetes. A cold-pressed N. sativa extract was then orally administered (1000 mg/kg/day). After 8 weeks of treatment, the glucose, glycosylated hemoglobin (HbA1c), tumor necrosis factor-alpha (TNF-α), insulin levels, and lipid profile were determined in cardiac blood. Dermal capillary wall thickness was measured in tail skin sections stained with periodic acid-Schiff. Endothelial apoptosis was morphologically evaluated by hematoxylin and eosin staining.

RESULTS

Diabetes significantly reduced the circulating insulin and low-density lipoprotein levels and caused elevations in the glucose, HbA1c, and triglyceride levels, accompanied by a slight increase in total cholesterol levels and no change in the high-density lipoprotein and TNF-α levels. Capillary basement membrane thickening and a decreased capillary luminal diameter despite no evidence of endothelial cell apoptosis were also observed. N. sativa treatment of diabetic rats reduced the mean HbA1c concentration by 1.4%, enlarged the capillary lumens, and tended to attenuate dermal capillary basement membrane thickening without affecting the lipid profile or TNF-α level.

CONCLUSION

Our results indicate that N. sativa may be used to minimize the risk of diabetic microangiopathy, potentially due in part to its glycemic control activity.

SUMMARY

Diabetes causes dermal capillary basement membrane thickening and a decreased capillary luminal diameterNigella sativa treatment of diabetic rats enlarged the capillary lumens and tended to attenuate dermal capillary basement membrane thickeningN. sativa treatment of diabetic rats reduced the mean glycosylated hemoglobin concentration by 1.4%, which exceeds the necessary reduction previously described to decrease the risk of diabetic microangiopathy, without affecting the lipid profile or tumor necrosis factor-alpha levelN. sativa improves rat diabetic microangiopathy, potentially due in part to its glycemic control activity. Abbreviations used: H and E: Hematoxylin and eosin, HbA1c: Glycosylated hemoglobin, HDL-C: High-density lipoprotein cholesterol, LDL-C: Low-density lipoprotein cholesterol, PAS: Periodic acid-Schiff, STZ: Streptozotocin.

Effect of sardine proteins on hyperglycaemia, hyperlipidaemia and lecithin:cholesterol acyltransferase activity, in high-fat diet-induced type 2 diabetic rats

Type 2 diabetes (T2D) is a major risk factor of CVD. The effects of purified sardine proteins (SP) were examined on glycaemia, insulin sensitivity and reverse cholesterol transport in T2D rats. Rats fed a high-fat diet (HFD) for 5 weeks, and injected with a low dose of streptozotocin, were used. The diabetic rats were divided into four groups, and they were fed casein (CAS) or SP combined with 30 or 5% lipids, for 4 weeks. HFD-induced hyperglycaemia, insulin resistance and hyperlipidaemia in rats fed HFD, regardless of the consumed protein. In contrast, these parameters lowered in rats fed SP combined with 5 or 30% lipids, and serum insulin values reduced in SP v. CAS. HFD significantly increased total cholesterol and TAG concentrations in the liver and serum, whereas these parameters decreased with SP, regardless of lipid intake. Faecal cholesterol excretion was higher with SP v. CAS, combined with 30 or 5% lipids. Lecithin:cholesterol acyltransferase (LCAT) activity and HDL3-phospholipids (PL) were higher in CAS-HF than in CAS, whereas HDL2-cholesteryl esters (CE) were lower. Otherwise, LCAT activity and HDL2-CE were higher in the SP group than in the CAS group, whereas HDL3-PL and HDL3-unesterified cholesterol were lower. Moreover, LCAT activity lowered in the SP-HF group than in the CAS-HF group, when HDL2-CE was higher. In conclusion, these results indicate the potential effects of SP to improve glycaemia, insulin sensitivity and reverse cholesterol transport, in T2D rats.

Alteration of gut microbiota by vancomycin and bacitracin improves insulin resistance via glucagon-like peptide 1 in diet-induced obesity

Firmicutes and Bacteroidetes, 2 major phyla of gut microbiota, are involved in lipid and bile acid metabolism to maintain systemic energy homeostasis in host. Recently, accumulating evidence has suggested that dietary changes promptly induce the alteration of abundance of both Firmicutes and Bacteroidetes in obesity and its related metabolic diseases. Nevertheless, the metabolic roles of Firmicutes and Bacteroidetes on such disease states remain unclear. The aim of this study was to determine the effects of antibiotic-induced depletion of Firmicutes and Bacteroidetes on dysregulation of energy homeostasis in obesity. Treatment of C57BL/6J mice with the antibiotics (vancomycin [V] and bacitracin [B]), in the drinking water, before diet-induced obesity (DIO) greatly decreased both Firmicutes and Bacteroidetes in the gut as revealed by pyrosequencing of the microbial 16S rRNA gene. Concomitantly, systemic glucose intolerance, hyperinsulinemia, and insulin resistance in DIO were ameliorated via augmentation of GLP-1 secretion (active form; 2.03-fold, total form; 5.09-fold) independently of obesity as compared with untreated DIO controls. Furthermore, there were increases in metabolically beneficial metabolites derived from the gut. Together, our data suggest that Firmicutes and Bacteroidetes potentially mediate insulin resistance through modulation of GLP-1 secretion in obesity.

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.

Chronic l-arginine treatment improves metabolic, cardiovascular and liver complications in diet-induced obesity in rats

l-Arginine is an important dietary amino acid in both health and disease, especially of the cardiovascular system. This study has determined whether dietary supplementation with l-arginine attenuates cardiovascular, metabolic, pancreatic and liver changes in a rat model of the human metabolic syndrome. Male Wistar rats (8-9 weeks old) were divided into four groups. Two groups of rats were fed a corn starch-rich diet (C) whereas the other two groups were given a high carbohydrate, high fat diet (H) with 25% fructose in the drinking water, for 16 weeks. One group fed each diet was supplemented with 5% l-arginine in the food for the final 8 weeks of this protocol. The corn starch diet (C) contained ∼68% carbohydrates mainly as polysaccharides, while the high-carbohydrate, high-fat diet contained ∼68% carbohydrates mainly as fructose and sucrose together with 24% fat mainly as saturated and monounsaturated fats from beef tallow. The high-carbohydrate, high-fat diet-fed rats showed the symptoms of metabolic syndrome including obesity and hypertension with heart and liver damage. Supplementation with l-arginine attenuated impairment in left ventricular and liver structure and function, glucose tolerance, and decreased blood pressure, abdominal fat pads, inflammatory cell infiltration, pancreatic cell hypertrophy and oxidative stress. This study indicates that oral supplementation with l-arginine attenuated or normalised obesity-related changes in the heart, liver and pancreas by reducing inflammation and oxidative stress associated with high carbohydrate, high fat feeding in rats.

Red blood cell ATP/ADP & nitric oxide: The best vasodilators in diabetic patients

Background

Diabetes mellitus is a group of metabolic diseases characterized by high blood sugar (glucose) levels that result from defects in insulin secretion, or action, or both. Inspired by previous report the release of ATP from RBCs, which may participate in vessel dilation by stimulating NO production in the endothelium through purinergic receptor signaling and so, the aim of this study is to clearly determined relationship between RBC ATP/ADP ratio with nitric oxide.

Methods

The ATP/ADP ratio of erythrocytes among four groups of normal individuals (young & middle age), athletes’ subjects and diabetic patients were compared and the relationship between ATP/ADP ratio and NO level of plasma was determined with AVOVA test and bioluminescence method.

Results

ATP/ADP level in four groups normal (young & middle age), athletes, diabetes] are measured and analyzed with ANOVA test that show a significant difference between groups (P-value < 0.001). A significant positive correlation was found between RBC ATP/ADP content (r = 0.705; P < 0.001). Plasma NO content is also analyzed with ANOVA test which shows a significant difference between groups.

Conclusion

In this study, a positive relationship between RBC ATP/ADP ratio and NO was found. Based on the obtained result, higher RBC ATP/ADP content may control the ratio of plasma NO in different individuals, also this results show that ATP can activate endothelial cells in NO production and is a main factor in releasing of NO from endothelial cells.

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.

The effect of L-arginine or L-citrulline supplementation on biochemical parameters and the vascular aortic wall in high-fat and high-cholesterol-fed rats

The aim of the present study is to investigate the potential role of L-arginine or L-citrulline in rats fed high-fat and high-cholesterol (HFC) diet. HFC feeding increased significantly serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities, urea and all lipid profiles and decreased significantly serum high-density lipoprotein-cholesterol (HDL-c) and non significantly serum nitric oxide levels. L-arginine or L-citrulline administration reversed the increase in serum AST and ALT activities, urea and all lipid profiles. These effects were associated with a concomitant increase in HDL-c and nitric oxide levels. In general, rats fed HFC diet and orally treated with L-arginine or L-citrulline had higher relative percentage of 18:0, 20:0 and 22:6 and lower 16:0 fatty acids than rats fed HFC diet. Light and transmission electron microscopic findings of the thoracic aorta confirmed the biochemical results and demonstrated structural changes in the endothelial cells of the intimal layer, medial smooth muscle cells as well as in the adventitial layer in HFC fed-animals. However, these findings indicate little structural alterations in animals supplemented with L-arginine or L-citrulline along with HFC feeding. In the present study, L-arginine or L-citrulline was effective hypocholesterolemic and hypolipidemic agents in rats.

Beneficial effects of L-arginine on reducing obesity: potential mechanisms and important implications for human health

Over the past 20 years, growing interest in the biochemistry, nutrition, and pharmacology of L-arginine has led to extensive studies to explore its nutritional and therapeutic roles in treating and preventing human metabolic disorders. Emerging evidence shows that dietary L-arginine supplementation reduces adiposity in genetically obese rats, diet-induced obese rats, finishing pigs, and obese human subjects with Type-2 diabetes mellitus. The mechanisms responsible for the beneficial effects of L-arginine are likely complex, but ultimately involve altering the balance of energy intake and expenditure in favor of fat loss or reduced growth of white adipose tissue. Recent studies indicate that L-arginine supplementation stimulates mitochondrial biogenesis and brown adipose tissue development possibly through the enhanced synthesis of cell-signaling molecules (e.g., nitric oxide, carbon monoxide, polyamines, cGMP, and cAMP) as well as the increased expression of genes that promote whole-body oxidation of energy substrates (e.g., glucose and fatty acids) Thus, L-arginine holds great promise as a safe and cost-effective nutrient to reduce adiposity, increase muscle mass, and improve the metabolic profile in animals and humans.

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.

L-Arginine prevents metabolic effects of high glucose in diabetic mice

We tested the hypothesis that activation of the polyol pathway and protein kinase C (PKC) during diabetes is due to loss of NO. Our results show that after 4 weeks of streptozotocin-induced diabetes, treatment with L-arginine restored NO levels and prevented tissue accumulation of sorbitol in mice, which was accompanied by an increase in glutathiolation of aldose reductase. L-Arginine treatment decreased superoxide generation in the aorta, total PKC activity and PKC-beta(II) phosphorylation in the heart, and the plasma levels of triglycerides and soluble ICAM. These data suggest that increasing NO bioavailability by L-arginine corrects the major biochemical abnormalities of diabetes.

Dietary supplementation with watermelon pomace juice enhances arginine availability and ameliorates the metabolic syndrome in Zucker diabetic fatty rats

Watermelon is rich in L-citrulline, an effective precursor of L-arginine. This study was conducted to determine whether dietary supplementation with watermelon pomace juice could ameliorate the metabolic syndrome in the Zucker diabetic fatty (ZDF) rat, an animal model of noninsulin-dependent diabetes mellitus. Nine-week-old ZDF rats were assigned randomly to receive drinking water containing 0% (control) or 0.2% L-arginine (as 0.24% L-arginine-HCl), 63% watermelon pomace juice, 0.01% lycopene, or 0.05% citrus pectin (n = 6 per treatment). At the end of the 4-wk supplementation period, blood samples, aortic rings, and hearts were obtained for biochemical and physiological analyses. Feed or energy intakes did not differ among the 5 groups of rats. However, dietary supplementation with watermelon pomace juice or L-arginine increased serum concentrations of arginine; reduced fat accretion; lowered serum concentrations of glucose, free fatty acids, homocysteine, and dimethylarginines; enhanced GTP cyclohydrolase-I activity and tetrahydrobiopterin concentrations in the heart; and improved acetylcholine-induced vascular relaxation. Compared with the control, dietary supplementation with lycopene or citrus pectin did not affect any measured parameter. These results provide the first evidence to our knowledge for a beneficial effect of watermelon pomace juice as a functional food for increasing arginine availability, reducing serum concentrations of cardiovascular risk factors, improving glycemic control, and ameliorating vascular dysfunction in obese animals with type-II diabetes.

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

In an attempt to elucidate molecular mechanisms and factors involved in beta cell regeneration, we evaluated a possible role of the L-arginine-nitric oxide (NO)-producing pathway in alloxan-induced diabetes mellitus. Diabetes was induced in male Mill Hill rats with a single alloxan dose (120 mg kg(-1)). Both non-diabetic and diabetic groups were additionally separated into three subgroups: (i) receiving L-arginine . HCl (2.25%), (ii) receiving L-NAME . HCl (0.01%) for 12 days as drinking liquids, and (iii) control. Treatment of diabetic animals started after diabetes induction (glucose level > or = 12 mmol l(-1)). We found that disturbed glucose homeostasis, i.e. blood insulin and glucose levels in diabetic rats was restored after L-arginine treatment. Immunohistochemical findings revealed that L-arginine had a favourable effect on beta cell neogenesis, i.e. it increased the area of insulin-immunopositive cells. Moreover, confocal microscopy showed colocalization of insulin and pancreas duodenum homeobox-1 (PDX-1) in both endocrine and exocrine pancreas. This increase in insulin-expressing cells was accompanied by increased cell proliferation (observed by proliferating cell nuclear antigen-PCNA immunopositivity) which occurred in a regulated manner since it was associated with increased apoptosis (detected by the TUNEL method). Furthermore, L-arginine enhanced both nuclear factor-kB (NF-kB) and neuronal nitric oxide synthase (nNOS) immunopositivities. The effect of L-arginine on antioxidative defence was observed especially in restoring to control level the diabetes-induced increase in glutathione peroxidase activity. In contrast to L-arginine, diabetic pancreas was not affected by L-NAME supplementation. In conclusion, the results suggest beneficial L-arginine effects on alloxan-induced diabetes resulting from the stimulation of beta cell neogenesis, including complex mechanisms of transcriptional and redox regulation.

CAN NITRIC OXIDE-GENERATING COMPOUNDS IMPROVE THE OXIDATIVE STRESS RESPONSE IN EXPERIMENTALLY DIABETIC RATS?

1. The present study was designed to evaluate the protective effects of the nitric oxide (NO)-generating compounds L-arginine (L-Arg) and sodium nitroprusside (SNP) on oxidative stress markers in streptozotocin (STZ)-diabetic rats. 2. Diabetes was induced after a single intraperitoneal injection of STZ (60 mg/kg). Rats were divided into non-diabetic (control), diabetic and treated diabetic groups. The treated diabetic groups were supplemented with L-Arg (300 mg/kg), SNP (3 mg/kg per day) or glibenclamide (0.6 mg/kg per day) orally for 4 weeks. 3. At the end of the experiment, fasted rats were killed by cervical decapitation. Blood was collected for estimation of glucose, haemoglobin, glycosylated haemoglobin (HbA(1c)), total cholesterol, high-density lipoprotein-cholesterol and triglycerides. Thiobarbituric acid-reactive substances (TBARS; an index of lipid peroxidation), superoxide dismutase, glutathione peroxidase, catalase, nitrate/nitrite (NO(x)) and reduced glutathione (GSH) were estimated in liver and kidney homogenates. 4. A significant increase was observed in plasma glucose levels and HbA(1c), with a concomitant decrease in haemoglobin levels, in diabetic rats. These alterations reverted back to near normal after treatment with the NO-generating compounds. A loss of bodyweight, polydipsia, polyphagia and elevated levels of serum cholesterol and triglycerides were observed in diabetic rats. Hyperglycaemia was accompanied by a significant increase in tissue TBARS and a decrease in NO(x), GSH and anti-oxidant enzymes, whereas, supplementation with L-Arg and SNP significantly reduced TBARS levels and increased GSH and anti-oxidant enzyme activities. Linear regression analysis indicated that blood glucose and TBARS had a significant positive correlation with HbA(1c), whereas a negative correlation was observed between GSH and NO(x). 5. It is concluded that NO-generating compounds improve most of the biochemical abnormalities and anti-oxidant levels in diabetic rats. The beneficial effects of NO-generating compounds can be attributed to the generation of NO and/or enhanced anti-oxidant enzyme activities.

Succinic acid monoethyl ester, a novel insulinotropic agent: effect on lipid composition and lipid peroxidation in streptozotocin-nicotin-amide induced type 2 diabetic rats

Succinic acid monoethyl ester (EMS) is recently proposed as an insulinotropic agent for the treatment of non-insulin dependent diabetes mellitus. Oxidative stress has been suggested to be a contributory factor in the development and complications of diabetes. In the present study the effect of EMS and Metformin on plasma glucose, insulin, serum and tissue lipid profile, lipoproteins and lipid peroxidation in streptozotocin-nicotinamide induced type 2 diabetic model was investigated. The carboxylic nutrient EMS was administered intraperitonially (8 micromol/g body weight) to streptozotocin diabetic rats for 30 days. The levels of thiobarbituric acid reactive substances (TBARS) and hydroperoxides in liver and kidney and serum and tissue lipids [cholesterol, triglycerides, phospholipids and free fatty acids] and very low density lipoprotein-cholesterol (VLDL-C) and low density lipoprotein-cholesterol (LDL-C), were significantly increased in diabetic rats, whereas the levels of high-density lipoprotein-cholesterol (HDL-C) and antiatherogenic index (AAI) (ratio of HDL to total cholesterol) were significantly decreased. The effect of EMS was compared with metformin, a reference drug. Treatment with EMS and metformin resulted in a significant reduction of plasma glucose with increase plasma insulin in diabetic rats. EMS also resulted in a significant decrease in serum and tissue lipids and lipid peroxidation products. These biochemical observations were supplemented by histopathological examination of liver and kidney section. Our results suggest the possible antihyperlipidemic and antiperoxidative effect of EMS apart from its antidiabetic effect.

Regulatory role for the arginine–nitric oxide pathway in metabolism of energy substrates

Nitric oxide (NO) is synthesized from L-arginine by NO synthase in virtually all cell types. Emerging evidence shows that NO regulates the metabolism of glucose, fatty acids and amino acids in mammals. As an oxidant, pathological levels of NO inhibit nearly all enzyme-catalyzed reactions through protein oxidation. However, as a signaling molecule, physiological levels of NO stimulate glucose uptake as well as glucose and fatty acid oxidation in skeletal muscle, heart, liver and adipose tissue; inhibit the synthesis of glucose, glycogen, and fat in target tissues (e.g., liver and adipose); and enhance lipolysis in adipocytes. Thus, an inhibition of NO synthesis causes hyperlipidemia and fat accretion in rats, whereas dietary arginine supplementation reduces fat mass in diabetic fatty rats. The putative underlying mechanisms may involve multiple cyclic guanosine-3',5'-monophosphate-dependent pathways. First, NO stimulates the phosphorylation of adenosine-3',5'-monophosphate-activated protein kinase, resulting in (1) a decreased level of malonyl-CoA via inhibition of acetyl-CoA carboxylase and activation of malonyl-CoA decarboxylase and (2) a decreased expression of genes related to lipogenesis and gluconeogenesis (glycerol-3-phosphate acyltransferase, sterol regulatory element binding protein-1c and phosphoenolpyruvate carboxykinase). Second, NO increases the phosphorylation of hormone-sensitive lipase and perilipins, leading to the translocation of the lipase to the neutral lipid droplets and, hence, the stimulation of lipolysis. Third, NO activates expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha, thereby enhancing mitochondrial biogenesis and oxidative phosphorylation. Fourth, NO increases blood flow to insulin-sensitive tissues, promoting substrate uptake and product removal via the circulation. Modulation of the arginine-NO pathway through dietary supplementation with L-arginine or L-citrulline may aid in the prevention and treatment of the metabolic syndrome in obese humans and companion animals, and in reducing unfavorable fat mass in animals of agricultural importance.

Role of dietary l-arginine supplementation on serum parameters and intestinal enzyme activities in rats fed an excess-fat diet

We investigated whether dietary supplementation with L-arginine, the endogenous precursor of nitric oxide, might affect serum parameter levels body weight, food intake and activities of intestinal mucosa enzymes in animals fed with a standard diet or a diet high in saturated fat for 4 weeks. Body weight and food intake were not affected by diet but relative liver weight was higher in animals receiving a high-fat diet. Total cholesterol, LDL-cholesterol and triglyceride levels were higher in both groups fed high-fat diet and dietary L-arginine did not affect these parameters but produced an increase in serum protein levels and a slight decrease in glycaemia. Regarding the intestinal enzyme activities, rats fed a high-fat diet plus arginine showed the lowest intestinal disaccharidase activities.

Inhibition by L-arginine and spermidine of hemoglobin glycation and lipid peroxidation in rats with induced diabetes

The effect of L-arginine and spermidine on hemoglobin glycation and lipid peroxidation in serum of normal and diabetic rats was studied. Five groups of 40 rats were studied during 20 days and compared with a control group (Group I) that consisted of normal rats (N = 6) not treated with L-arginine or spermidine. Group II, diabetic rats (alloxan 120 mg/kg, i.p. at the day 0 and alloxan 60 mg/kg, i.p. at the day 10) were considered as diabetic control. Group III, diabetic rats treated with 10 mM L-arginine (i.p.). Group IV, diabetic rats treated with 10 microM spermidine (i.p.). Group V, normal rats treated with 10 mM L-arginine (i.p.). Group VI, normal rats treated with 10 microM spermidine (i.p.). The rats of each group were divided in subgroups of four each. Rats were anesthetized and blood was taken from aorta to determine glucose, triglycerides (TGs), total cholesterol (TC), low- and high-density lipoproteins (LDL and HDL), glycated hemoglobin (HbA(1C)), and thiobarbituric acid-reactive substances (TBARS). We observed that the alloxan concentrations used in this study reproduced the clinical manifestations of disease including hyperglycemia (from 116 +/- 7 mg/dl to 435 +/- 80 mg/dl) in 96 hours. As a consequence the levels of TGs, TC, LDL, TBARS, and HbA(1C) were increased, whereas HDL diminished. HbA(1C) concentration was significantly correlated with the concentration of TBARS. The L-arginine and spermidine injection tended to normalize the glycemia from 24 hours, similarly, hyperlipidemia, TBARS, and HbA(1C). From these results, we conclude that l-arginine and spermidine exerted an inhibitory effect of hemoglobin glycation and lipid peroxidation in vivo, which may be relevant in preventing diabetic complications.

l-Arginine and polyamine administration protect β-cells against alloxan diabetogenic effect in Sprague–Dawley rats

In the searching for new substances with the capacity to protect beta-cells from the toxic effects of alloxan, we evaluated the effect of L-arginine and the polyamines putrescine, spermidine and spermine in a murine experimental model of diabetes. Diabetes was induced by the i.p. injection of either 200 mg/kg (24-h experiments) or 120 mg/kg (12 days experiments) body weight. L-Arginine and polyamines were administered 10 min before or 10 min after alloxan administration, once its half-life had elapsed, respectively. In the 24-h study, serum glucose (199.8+/-27.6 mg/dl) and triglyceride (54.6+/-4.9 mg/dl) concentrations showed a protective effect of spermine, as these parameters were not too high (P < or = 0.05), compared to the alloxan-treated group (415.4+/-47.8 and 90.2+/-11.6 mg/dl, respectively), and were closer to glucose (132.3+/-6.0 mg/dl) and similar to triglycerides (63.8+/-7.1 mg/dl) of the control group. A similar pattern was observed on the parameters measured when L-arginine and polyamines were administered daily for 12 days, starting 10 min after a single alloxan administration, which provides evidence that L-arginine and polyamines are effective in impeding the increase in serum glucose, triglyceride and cholesterol concentration showed on day 3 by the alloxan-treated group, as well as a higher acinar cell regenerative capacity as determined by immunohistochemical techniques. Spermine turning out to be more effective than L-arginine, putrescine or spermidine in counteracting the marked hyperglycemia and triglyceridemia showed by the alloxan-treated group and similar in effect when evaluating cholesterolemia. These results show a clear protective role of L-arginine and polyamines over the pancreatic beta-cell, in addition to the induction of neogenesis from both ductal and acinar cells that leads to the recovery of endocrine pancreatic function in rats with experimental diabetes.

Effect of supplemental l-arginine on the function of T lymphocytes and the formation of advanced glycosylated end products in rats with streptozotocin-induced diabetes

OBJECTIVE

We investigated the effect of supplemental L-arginine on lymphocyte function in diabetes and its association with suppressed formation of advanced glycosylated end products (AGEs).

METHODS

For the in vivo study, rats with streptozotocin-induced (65 mg/kg of body weight, intravenously) diabetes were treated with or without 2% L-arginine or glycine (as a positive control) in drinking water for 8 wk. We then measured serum fructosamine concentrations and concanavalin A-induced proliferative ability of lymphocytes from these animals. For the in vitro study, AGEs derived from albumin were prepared by incubating D-glucose (200 mmol/L) and bovine serum albumin (100 mg/mL) at 37 degrees C for 2 wk in the presence or absence of L-arginine (0.1-10 mmol/L). These preparations were quantified for their bovine serum albumin--derived AGE content, and their effect on concanavalin A-induced proliferative activity of T lymphocyte from normal rats was measured.

RESULTS

Serum fructosamine concentrations were significantly higher in the diabetic rats than in the control rats (P<0.05) but were significantly lowered with L-arginine supplementation (P<0.05). The lower lymphocyte proliferation rate found in the diabetic rats was reversed by supplemental L-arginine (P<0.05). During the course of incubation of bovine serum albumin with D-glucose, the presence of L-arginine prevented the formation of bovine serum albumin-derived AGEs and attenuated their inhibitory effect on the rate of lymphocyte proliferation in a dose-dependent manner.

CONCLUSION

Supplemental L-arginine improved the function of T lymphocytes in diabetic rats in association with decreased formation of AGEs.

Dietary L-arginine supplementation reduces fat mass in Zucker diabetic fatty rats

This study was conducted to test the hypothesis that dietary supplementation of arginine, the physiologic precursor of nitric oxide (NO), reduces fat mass in the Zucker diabetic fatty (ZDF) rat, a genetically obese animal model of type-II diabetes mellitus. Male ZDF rats, 9 wk old, were pair-fed Purina 5008 diet and received drinking water containing arginine-HCl (1.51%) or alanine (2.55%, isonitrogenous control) for 10 wk. Serum concentrations of arginine and NO(x) (oxidation products of NO) were 261 and 70% higher, respectively, in arginine-supplemented rats than in control rats. The body weights of arginine-treated rats were 6, 10, and 16% lower at wk 4, 7, and 10 after the treatment initiation, respectively, compared with control rats. Arginine supplementation reduced the weight of abdominal (retroperitoneal) and epididymal adipose tissues (45 and 25%, respectively) as well as serum concentrations of glucose (25%), triglycerides (23%), FFA (27%), homocysteine (26%), dimethylarginines (18-21%), and leptin (32%). The arginine treatment enhanced NO production (71-85%), lipolysis (22-24%), and the oxidation of glucose (34-36%) and octanoate (40-43%) in abdominal and epididymal adipose tissues. Results of the microarray analysis indicated that arginine supplementation increased adipose tissue expression of key genes responsible for fatty acid and glucose oxidation: NO synthase-1 (145%), heme oxygenase-3 (789%), AMP-activated protein kinase (123%), and peroxisome proliferator-activated receptor gamma coactivator-1alpha (500%). The induction of these genes was verified by real-time RT-PCR analysis. In sum, arginine treatment may provide a potentially novel and useful means to enhance NO synthesis and reduce fat mass in obese subjects with type-II diabetes mellitus.

Inhibition of in vitro pyrraline formation by l-arginine and polyamines

Glycation of biomolecules such as proteins, nucleic acids and lipids leading to the formation of advanced glycation end products (AGEs) may be a major contributor to the pathological manifestations of diabetes mellitus. Several studies have shown that the chemical inhibition of AGEs formation results in attenuation of diabetic complications. We tested the in vitro inhibition of pyrraline formation on bovine serum albumin and L-lysine by L-arginine and the polyamines putrescine, cadaverine, spermidine and spermine. Among the inhibitors, L-arginine and spermine potently inhibited pyrraline formation. This effect could be related to the presence of the guanidino group in L-arginine and four amino groups in spermine, but this inhibitory effect was also shown by putrescine, cadaverine and spermidine, suggesting that these natural compounds may have a novel therapeutic potential in preventing diabetic complications. A significant unexpected observation emerged when experiments were carried out with aminoguanidine. It showed increased absorbance produced by a non-identified compound whose peak appears at 285 nm, but this aspect remains to be investigated.

Healing of diabetic foot ulcers in l-arginine-treated patients

Experimentally, we demonstrated the beneficial effects of L-arginine on regulation of hyperglycemia and dyslipidemia in experimental diabetes, in addition to a positive anti-aggregating effect in platelets in animals and humans. Here, the effect of L-arginine on foot ulcers from diabetic patients was studied. Three groups of diabetic patients were included: 11 patients without ulcer received neither treatment and served as controls. Eleven patients with diabetic ulcer received the standard treatment, this group served as diabetic control with diabetic ulcer. Eleven remain patients with diabetic ulcer received 10 mM L-arginine subcutaneously on the site of the wound. Biopsy with punch number 5 on wound site comprising both ulcerative and contiguous undamaged skin were performed in all patients with ulcerative lesions before any treatment. Patients with intact skin had biopsy performed with punch number 5 on external malleolar region of right lower limb. Biopsies were examined by light and confocal microscopy utilizing histochemical and immunohistochemical methods. Initial and final blood samples were collected to determine glucose, triglycerides, total cholesterol, glycated hemoglobin (HbA(1c)), low (LDL), and high density lipoproteins (HDL). Significant differences (P < 0.05) were observed between initial and final serum glucose levels for treated patients, and initial serum glucose levels between treated and control patients without diabetic ulcer. Glycated hemoglobin, triglycerides, cholesterol, and lipoprotein levels showed no significant changes. Eight patients treated with L-arginine reached total wound healing and the remaining three who abandoned the study because of change of residence showed relevant improvement. Histochemistry and immunohistochemistry methods have shown vascular impairment in both patients with diabetic ulcer (prior to treatment) and control patients without diabetic ulcer. Our observations strongly support efficacy of L-arginine for successful wound healing of diabetic ulcers.

Effects of dietary L-arginine supplementation on serum lipids and intestinal enzyme activities in diabetic rats

We investigated whether dietary supplementation with L-arginine, the endogenous precursor of nitric oxide, might affect serum lipid levels and activities of intestinal mucosa enzymes in animals, in which diabetes was induced by administration of streptozotocin. Control and diabetic rats were fed diets with or without 2% L-arginine supplementation for 4 weeks. Diabetic rats had significantly higher concentrations of serum triglycerides and LDL-cholesterol than control rats. These alterations were partially reduced by L-arginine supplementation. Experimental diabetes did not influence the lactase and leucine aminopeptidase activity in the intestine, but the activity of alkaline phosphatase was increased. Furthermore, activities of maltase and sucrase in the intestinal mucosa were elevated in streptozotocin-induced diabetic rats and were restored to control levels after dietary L-arginine supplementation. On the basis of the present experimental evidence, dietary L-arginine supplementation appears to affect the metabolism of lipoproteins and might alleviate some gastrointestinal dysfunctions, commonly seen in diabetes mellitus.

Regeneration of β-cells and neogenesis from small ducts or acinar cells promote recovery of endocrine pancreatic function in alloxan-treated rats

BACKGROUND

We previously showed by using biochemical parameters that male Sprague-Dawley rats receiving a single intraperitoneal (i.p.) administration of alloxan (120 mg/kg body weight) with no further treatment recovered endocrine pancreatic function after 12 days.

METHODS

Male Sprague-Dawley rats received an i.p. injection of alloxan (120 mg/kg body wt), were killed at 3, 6, 9, or 12 days (n=7), and their capacity to recover endocrine function was evaluated by means of a) biochemical parameters, which included glucose, triglyceride, and total cholesterol measurements and b) nuclear incorporation of 5'-bromodeoxyuridine (BrdU) by beta and acinar cells as well as presence of neogenesis from either ductal or acinar cells using double-staining BrdU-insulin immunohistochemical technique.

RESULTS

Three days after receiving a single i.p. administration of alloxan, rats showed increase in serum glucose, triglyceride, and total cholesterol concentrations, reaching levels of 542.4+/-63.1, 907.6+/-154.9, and 106.0+/-2.7 mg/dL (mean+/-standard deviation [SD]), respectively. At this time, increase in beta-cell replication was also observed, although this reached maximum by day 6 (p <0.001). Replication was also present in acinar cells, but these cells showed their maximum at day 3 (p <0.001) and subsequently decreased, as did beta-cells, almost steadily to normal values by day 12. Neogenesis of beta-cells was observed mainly as transdifferentiation from acinar cells at day 3 and from ductal cells at day 6, after which it tended to be normal.

CONCLUSIONS

Male Sprague-Dawley rats receiving a single i.p. alloxan dose tended to normalize their endocrine function by day 12 after alloxan administration. This process included both regeneration and neogenesis of pancreatic beta-cells from either ductal or acinar cells.

Dietary L-arginine supplementation enhances endothelial nitric oxide synthesis in streptozotocin-induced diabetic rats

This study tested the hypothesis that dietary arginine supplementation increases endothelial tetrahydrobiopterin (BH(4)) availability for nitric oxide (NO) synthesis in diabetic rats. Streptozotocin-induced diabetic rats either were given unrestricted access to a casein-based diet (Expt. 1) or were pair-fed the diet on the basis of the food intake per kg of body weight of nondiabetic rats (Expt. 2). Beginning 1 d after vehicle or streptozotocin injection, arginine-HCl (1.51%) or alanine (isonitrogenous control, 2.55%) was added daily to the drinking water for nondiabetic rats, whereas concentrations were adjusted (0.43% arginine-HCl and 0.73% alanine) in the drinking water for diabetic rats (which consumed more water) to ensure isonitrogenous provision. At 2 wk after the initiation of arginine supplementation, coronary endothelial cells and plasma were obtained for the measurement of NO synthesis and metabolites. In both experiments, plasma and endothelial concentrations of N(G)-monomethylarginine, asymmetric dimethylarginine, and symmetric dimethylarginine increased, but those of arginine as well as endothelial BH(4) availability and NO synthesis decreased in diabetic rats, compared with nondiabetic rats. In both diabetic and nondiabetic rats, arginine supplementation increased plasma concentrations of arginine and insulin, endothelial concentrations of arginine and BH(4), and endothelial NO synthesis, but did not affect plasma and endothelial concentrations of methylarginines or plasma concentrations of homocysteine. Dietary arginine supplementation or provision of a BH(4) precursor normalized endothelial NO synthesis in diabetic rats. Arginine supplementation did not affect plasma glucose levels in nondiabetic rats, but reduced body weight loss and plasma glucose levels in diabetic rats. Thus, dietary L-arginine supplementation stimulates endothelial NO synthesis by increasing BH(4) provision, which is beneficial for vascular function and glucose homeostasis in diabetic subjects.

Effects of l-arginine-enriched total enteral nutrition on body weight gain, tumor growth, and in vivo concentrations of blood and tissue metabolites in rats inoculated with Walker tumor in the kidney

OBJECTIVE

We evaluated the effects of l-arginine-enriched total enteral nutrition (LATEN) on tumor-free and right kidney tumor-bearing rats through the determination of in vivo concentrations of metabolites to better understand intermediary metabolism in this model.

METHODS

Rats were individually housed in wire cages within a controlled environment (25 degrees C and 50% relative humidity) and exposed to a 12-h light-and-dark cycle. Rats comprised the following groups: tumor-free on enteral nutrition plus l-amino acid (n = 8); tumor-free on enteral nutrition plus l-arginine (n = 8); tumor bearing on enteral nutrition plus l-amino acids (n = 8); and tumor bearing on enteral nutrition plus l-arginine (n = 8). Rats had their right kidneys inoculated with saline or tumor cells and were subjected to laparotomy or gastrostomy on day 1 and received chow diet for the next 2 days. Gastrostomy with enteral nutrition was performed on days 3 to 9. On day 9, body weight gain, tumor growth as volume, in vivo blood (microM/mL), and tissue (microM/g) metabolite concentrations were determined. The Mann-Whitney U test was used to test significance.

RESULTS

LATEN in tumor-free rats decreased liver (0.25 +/- 0.03 versus 0.13 +/- 0.03 micromol/g, P < 0.05) and right kidney (0.13 +/- 0.1 versus 0.04 +/- 0.00 micromol/g, P < 0.05) ketone body concentrations. LATEN in tumor-bearing rats decreased blood pyruvate (0.17 +/- 0.01 versus 0.10 +/- 0.008 microM/mL, P < 0.005), lactate (5.2 +/- 0.3 versus 2.9 +/- 0.28 microM/mL, P < 0.01), and glucose (6.4 +/- 0.8 versus 3.7 +/- 0.5 microM/mL, P < 0.05). Glucose concentrations decreased in liver (13.9 +/- 2.0 versus 4.89 +/- 0.6 microM/g, P < 0.005) and tumor (3.5 +/- 0.8 versus 1.41 +/- 0.3 microM/g, P < 0.05). There were no changes in body weight gain (21 +/- 2.0 versus 30.3 +/- 3.6 g) or tumor growth (1.53 +/- 0.1 versus 1.26 +/- 0.01 cm(3)).

CONCLUSIONS

LATEN decreased ketone body concentrations in liver and kidney in tumor-free rats, possibly due to lower ketogenesis and decreased kidney uptake. In tumor-bearing rats, LATEN decreased lacticemia and glycemia and pyruvate blood concentrations. LATEN also reduced liver and tumor glucose concentrations in tumor-bearing animals. The possibility of LATEN-induced insulin and insulin-like growth factor-1 liberation signaling these changes is discussed.

The metabolic basis of arginine nutrition and pharmacotherapy

As an essential precursor for the synthesis of proteins and other molecules with enormous biological importance (including nitric oxide, urea, ornithine, proline, polyamines, glutamate, creatine, agmatine, and dimethylarginines), arginine displays remarkable metabolic and regulatory versatility. Evidence available to date provides a sound reason to classify arginine as an essential amino acid for young mammals (including parenterally fed human infants) and as a conditionally essential amino acid for adults under such conditions as trauma, burn injury, massive small-bowel resection, and renal failure. Arginine administration reverses endothelial dysfunction, enhances wound healing, prevents the early stages of tumorigenesis, and improves cardiovascular, reproductive, pulmonary, renal, digestive, and immune functions. Arginine or its effective precursor citrulline may hold great promise as a nutritional or pharmacotherapeutic treatment for a wide array of human diseases.

Effect of L-arginine on arginase activity in male accessory sex glands of alloxan-treated rats

Arginase activity has been identified in the prostate, and may be important in the synthesis of polyamines in accessory sex glands in the male. Polyamines in turn may mediate the action of androgens. Diabetic patients have disordered androgen synthesis. The purpose of this work was to evaluate the effect of L-arginine on arginase activity in accessory sex glands of male rats under normal and diabetic conditions (alloxan 120 mg/kg, i.p.). Normal and diabetic male rats were untreated or were treated with insulin or L-arginine for 96 h, and sacrificed. Arginase activity was measured in serum and in accessory sex glands. Arginase activity in accessory glands did not change significantly with induction of diabetes. Arginase activity was increased in diabetic insulin-treated rats, but there was no arginase response to L-arginine administration in diabetic animals. These findings stand in contrast to beneficial effects of L-arginine previously observed when this amino acid was administered for a long time (at least 10 days). We suspect that altered arginase activity in accessory sex glands may play a role in the reproductive dysfunction caused by diabetes, inasmuch as arginase activity can be increased in experimentally diabetic rats by the administration of insulin.