The effects of a comparatively higher dose of 1000 mg/kg/d of oral L- or D-arginine on the L-arginine metabolic pathways in male Sprague-Dawley rats.

Oral L-arginine supplements are popular mainly for their nitric oxide mediated vasodilation, but their physiological impact is not fully known. L-arginine is a substrate of several enzymes including arginase, nitric oxide synthase, arginine decarboxylase, and arginine: glycine amidinotransferase (AGAT). We have published a study on the physiological impact of oral L- and D-arginine at 500 mg/kg/day for 4 wks in male Sprague-Dawley rats. We investigated the effects of oral L-arginine and D-arginine at a higher dose of 1000 mg/kg/d for a longer treatment duration of 16 wks in 9-week-old male Sprague-Dawley rats. We measured the expression and activity of L-arginine metabolizing enzymes, and levels of their metabolites in the plasma and various organs. L-arginine did not affect the levels of L-arginine and L-lysine in the plasma and various organs. L-arginine decreased arginase protein expression in the upper small intestine, and arginase activity in the plasma. It also decreased AGAT protein expression in the liver, and creatinine levels in the urine. L-arginine altered arginine decarboxylase protein expression in the upper small intestine and liver, with increased total polyamines plasma levels. Endothelial nitric oxide synthase protein was increased with D-arginine, the presumed metabolically inert isomer, but not L-arginine. In conclusion, oral L-arginine and D-arginine at a higher dose and longer treatment duration significantly altered various enzymes and metabolites in the arginine metabolic pathways, which differed from alterations produced by a lower dose shorter duration treatment published earlier. Further studies with differing doses and duration would allow for a better understanding of oral L-arginine uses, and evidence based safe and effective dose range and duration.

The effects of oral arginine on its metabolic pathways in Sprague-Dawley rats.

Oral arginine supplements are popular mainly for their presumed vasodilatory benefit. Arginine is a substrate for at least four enzymes including nitric oxide synthase (NOS) and arginase, but the impact of oral supplements on its different metabolic pathways is not clear. Deficiencies of arginine-metabolising enzymes are associated with conditions such as hyperammonaemia, endothelial dysfunction, central nervous system and muscle dysfunction, which complicate the use of oral arginine supplements. We examined the effect of l-arginine (l-Arg) and d-arginine (d-Arg), each at 500 mg/kg per d in drinking water administered for 4 weeks to separate groups of 9-week-old male Sprague-Dawley rats. We quantified the expression of enzymes and plasma, urine and organ levels of various metabolites of arginine. l-Arg significantly decreased cationic transporter-1 expression in the liver and the ileum and increased endothelial NOS expression in the aorta and the kidney and plasma nitrite levels, but did not affect the mean arterial pressure. l-Arg also decreased the expression of arginase II in the ileum, arginine:glycine amidinotransferase in the liver and the kidney and glyoxalase I in the liver, ileum and brain, but increased the expression of arginine decarboxylase and polyamines levels in the liver. d-Arg, the supposedly inert isomer, also unexpectedly affected the expression of some enzymes and metabolites. In conclusion, both l- and d-Arg significantly affected enzymes and metabolites in several pathways that use arginine as a substrate and further studies with different doses and treatment durations are planned to establish their safety or adverse effects to guide their use as oral supplements.

Pharmacological evaluation of novel alagebrium analogs as methylglyoxal scavengers in vitro in cardiac myocytes and in vivo in SD rats.

BACKGROUND: Methylglyoxal (MG) is a byproduct of glucose metabolism and an inducer of advanced glycation end products (AGEs). AGEs are implicated in the pathogenesis of diabetes as well as hypertension. Most of the currently available MG scavengers are non-specific and have other effects as well. Alagebrium (ALA), developed by Alteon Corporation is a MG scavenger. Thus the aim of the present study was to investigate the potential of novel ALA analogs as possible MG scavengers and whether they could prevent any deleterious effects of MG. METHODS AND RESULTS: MG levels were measured by HPLC. The different biochemical and molecular parameters were measured by assay kits, RT-PCR and immunocytochemistry. Out of the 15 ALA analogs tested in vitro, compound no. 13 was found to be an effective inhibitor of MG in a concentration and time dependent manner. Compound no. 13 significantly attenuated the MG levels in vitro in MG treated cultured H9C2 cardiomyocytes as well as in vivo in MG treated SD rats. MG induced oxidative stress and apoptosis were attenuated by pretreatment of H9C2 cardiac myocytes with compound no. 13. MG induced cardiac hypertrophy and apoptosis were also attenuated by treating MG treated SD rats with compound no. 13. CONCLUSION: Our results indicate compound 13 as an effective inhibitor of MG in vitro in cultured cardiomyocytes and in vivo in SD rats and thus it may prove very useful in blocking the multiple deleterious effects of MG, including AGEs and vascular complications of diabetes.