Dietary L-arginine supplementation reduces fat mass in diet-induced obese rats

This study was conducted to test the hypothesis that dietary arginine supplementation reduces fat mass in diet-induced obese rats. Male Sprague-Dawley rats were fed either low- or high-fat diets for 15 wks (16 rats/diet). Thereafter, lean or obese rats continued to be fed their same respective diets and received drinking water containing either 1.51% L-arginine-HCl or 2.55% alanine (isonitrogenous control) (n=8/treatment group). Twelve weeks after the initiation of the arginine treatment, rats were euthanized to obtain tissues for biochemical analyses. Results were statistically analyzed as a 2x2 factorial experimental design using ANOVA. High-fat diet increased the mass of white adipose tissues at different anatomical locations by 49-96% compared to the low-fat diet. Concentrations of serum cholesterol as well as lipids in skeletal muscle and liver were higher in obese rats than in lean rats. L-Arginine supplementation reduced white adipose tissue mass by 20-40% while increasing brown adipose tissue mass by 15-20%. In addition, arginine treatment decreased adipocyte size, serum concentrations of glucose, triglycerides and leptin, improved glucose tolerance, and enhanced glucose and oleic acid oxidation in skeletal muscles. The mRNA levels for hepatic fatty acid synthase and stearoyl-CoA desaturase were reduced, but mRNA levels for hepatic AMP-activated protein kinase (AMPK), PPAR coactivator-1 and carnitine palmitoyltransferase I (CPT-I) as well as muscle CPT-I were increased in response to the arginine treatment. Subsequent experiments were conducted with cell models to define the direct effects of arginine on energy-substrate metabolism in insulin-sensitive cells. In BNL CL.2 mouse hepatocytes, C2C12 mouse myotubes and 3T3-L1 mouse adipocytes, increasing extracellular concentrations of arginine from 0 to 400 µM increased AMPK expression as well as glucose and oleic acid oxidation. Inhibition of nitric oxide synthesis moderately attenuated the arginine-stimulated increases of substrate oxidation as well as AMPK and ACC phosphorylation in BNL CL.2 cells, but had no effect in C2C12 and 3T3-L1 cells. Collectively, these results suggest that arginine increases AMPK expression and energy-substrate oxidation in a cell-specific manner, thereby reducing fat mass in diet-induced obese rats. The findings have important implications for treating obesity in humans and companion animals as well as decreasing fat deposition in livestock species

Inhibition of the Polyamine Synthesis Pathway Is Synthetically Lethal with Loss of Argininosuccinate Synthase 1

This work was supported by funding from the British Lung Foundation (APG12-10 and MESO15-12), the June Hancock Mesothelioma Research Fund, and Cancer Research UK (C16420/A18066). E.G. acknowledges research funding from the Barry Reed Cancer Research Fund

l-Arginine stimulates proliferation and prevents endotoxin-induced death of intestinal cells

This study tested the hypothesis that l-arginine (Arg) may stimulate cell proliferation and prevent lipopolysaccharide (LPS)-induced death of intestinal cells. Intestinal porcine epithelial cells (IPEC-1) were cultured for 4 days in Arg-free Dulbecco’s modified Eagle’s-F12 Ham medium (DMEM-F12) containing 10, 100 or 350 μM Arg and 0 or 20 ng/ml LPS. Cell numbers, protein concentrations, protein synthesis and degradation, as well as mammalian target of rapamycin (mTOR) and Toll-like receptor 4 (TLR4) signaling pathways were determined. Without LPS, IPEC-1 cells exhibited time- and Arg-dependent growth curves. LPS treatment increased cell death and reduced protein concentrations in IPEC-1 cells. Addition of 100 and 350 μM Arg to culture medium dose-dependently attenuated LPS-induced cell death and reduction of protein concentrations, in comparison with the basal medium containing 10 μM Arg. Furthermore, supplementation of 100 and 350 μM Arg increased protein synthesis and reduced protein degradation in both control and LPS-treated IPEC-1 cells. Consistent with the data on cell growth and protein turnover, addition of 100 or 350 μM Arg to culture medium increased relative protein levels for phosphorylated mTOR and phosphorylated ribosomal protein S6 kinase-1, while reducing the relative levels of TLR4 and phosphorylated levels of nuclear factor-κB in LPS-treated IPEC-1 cells. These results demonstrate a protective effect of Arg against LPS-induced enterocyte damage through mechanisms involving mTOR and TLR4 signaling pathways, as well as intracellular protein turnover

Determination of nitric oxide metabolites, nitrate and nitrite, in Anopheles culicifacies mosquito midgut and haemolymph by anion exchange high-performance liquid chromatography: plausible mechanism of refractoriness

<p>Abstract</p> <p>Background</p> <p>The diverse physiological and pathological role of nitric oxide in innate immune defenses against many intra and extracellular pathogens, have led to the development of various methods for determining nitric oxide (NO) synthesis. NO metabolites, nitrite (NO₂^-) and nitrate (NO₃^-) are produced by the action of an inducible <it>Anopheles culicifacies </it>NO synthase (AcNOS) in mosquito mid-guts and may be central to anti-parasitic arsenal of these mosquitoes.</p> <p>Method</p> <p>While exploring a plausible mechanism of refractoriness based on nitric oxide synthase physiology among the sibling species of <it>An. culicifacies</it>, a sensitive, specific and cost effective high performance liquid chromatography (HPLC) method was developed, which is not influenced by the presence of biogenic amines, for the determination of NO₂^-and NO₃^-from mosquito mid-guts and haemolymph.</p> <p>Results</p> <p>This method is based on extraction, efficiency, assay reproducibility and contaminant minimization. It entails de-proteinization by centrifugal ultra filtration through ultracel 3 K filter and analysis by high performance anion exchange liquid chromatography (Sphereclone, 5 μ SAX column) with UV detection at 214 nm. The lower detection limit of the assay procedure is 50 pmoles in all midgut and haemolymph samples. Retention times for NO₂^-and NO₃^-in standards and in mid-gut samples were 3.42 and 4.53 min. respectively. Assay linearity for standards ranged between 50 n<it>M </it>and 1 m<it>M</it>. Recoveries of NO₂^-and NO₃^-from spiked samples (1–100 μ<it>M</it>) and from the extracted standards (1–100 μ<it>M</it>) were calculated to be 100%. Intra-assay and inter assay variations and relative standard deviations (RSDs) for NO₂^-and NO₃^-in spiked and un-spiked midgut samples were 5.7% or less. Increased levels NO₂^-and NO₃^-in midguts and haemolymph of <it>An. culicifacies </it>sibling species B in comparison to species A reflect towards a mechanism of refractoriness based on AcNOS physiology.</p> <p>Conclusion</p> <p>HPLC is a sensitive and accurate technique for identification and quantifying pmole levels of NO metabolites in mosquito midguts and haemolymph samples that can be useful for clinical investigations of NO biochemistry, physiology and pharmacology in various biological samples.</p