Search

The amino acid arginine is the sole precursor for nitric oxide (NO) synthesis. We recently demonstrated that an acute reduction of circulating arginine does not compromise basal or LPS-inducible NO production in mice. In the present study, we investigated the importance of citrulline availability in ornithine transcarbamoylase-deficient [spf.sup.ash] (OTCD) mice on NO production, using stable isotope techniques and C57BL6/J (wild-type) mice controls. Plasma amino acids and tracer-to-tracee ratios were measured by LC-MS. NO production was measured as the in vivo conversion of L-[guanidino-[sup.15][N.sub.2]]arginine to L-[guanidine-[sup.15]N]citrulline; de novo arginine production was measured as conversion of L-[ureido-[sup.13]C-5,5-[sup.2][H.sub.2]]citrulline to L-[guanidino-[sup.13]C-5,5-[sup.2][H.sub.2]]arginine. Protein metabolism was measured using L-[ring-[sup.2][H.sub.5]]phenylalanine and L-[ring-[sup.2][H.sub.2]]tyrosine. OTC deficiency caused a reduction of systemic citrulline concentration and production to 30-50% (P < 0.001), reduced de novo arginine production (P < 0.05), reduced whole-body NO production to 50% (P < 0.005), and increased net protein breakdown by a factor of 2-4 (P < 0.001). NO production was twofold higher in female than in male OTCD mice in agreement with the X-linked location of the OTC gene. In response to LPS treatment (10 mg/kg ip), circulating arginine increased in all groups (P < 0.001), and NO production was no longer affected by the OTC deficiency due to increased net protein breakdown as a source for arginine. Our study shows that reduced citrulline availability is related to reduced basal NO production via reduced de novo arginine production. Under basal conditions this is probably cNOS-mediated NO production. When sufficient arginine is available after LPS stimulated net protein breakdown, NO production is unaffected by OTC deficiency. ornithine transcarbamoylase; sepsis; metabolism; protein breakdown

Arginine supplementation is used in several disease states. In arginine-deficient states, supplementation is a logical choice of therapy. However, the definition of an arginine-deficient state is complex. For example, plasma arginine levels could be within normal range but intracellular arginine levels could be reduced because of membrane transport problems. Lysine competes with arginine for transport into the cell. In these situations, arginine supplementation of higher than required levels is proposed. Arginine has several important functions in metabolism as it is a precursor of metabolically active components such as nitric oxide (NO), ornithine, creatine, and polyamines. Supplementing arginine in excess could potentially overstimulate metabolism via enhanced production of NO. NO is a reactive component that, via production of radicals, will inactivate proteins. NO is also a powerful vasodilator, which could lead to severe hemodynamic instability. A good marker for excess supplementation of arginine or lysine could be an increased or reduced production rate of NO. However, NQ production is difficult to measure because NO is a very labile component and is rapidly oxidized in blood. Stable isotope-labeled arginine and citrulline are used to trace the arginine-NO route. During supplementation of arginine in septic pigs or patients in septic shock, NO production, measured with stable isotope technology, is enhanced.

Sepsis is a severe catabolic condition. The loss of skeletal muscle protein mass is characterized by enhanced release of the amino acids glutamine and arginine, which (in)directly affects interorgan arginine and the related nitric oxide (NO) synthesis. To establish whether changes in muscle amino acid and protein kinetics are regulated by NO synthesized by nitric oxide synthase-2 or -3 (NOS2 or NOS3), we studied C57BL6/J wild-type (WT), NOS2-deficient (NOS[2.sup.-/-), and NOS3-deficient (NOS[3.sup-/-) mice under control (unstimulated) and lipopolysaccharide (LPS)-treated conditions. Muscle amino acid metabolism was studied across the hindquarter by infusing the stable isotopes L-[[ring-.sup.2][H.sub.5]]phenylalanine, L-[[ring-.sup.2] [H.sub.2]]tyrosine, L-[[guanidino-.sup.15][N.sub.2]]arginine, and L-[[ureido-.sup.13]C,[sup.2][H.sub.2]]citrulline. Muscle blood flow was measured using radioactive p-aminohippuric acid dilution. Under baseline conditions, muscle blood flow was halved in NOS[2.sup-/-] mice (P < 0.1), with simultaneous reductions in muscle glutamine, glycine, alanine, arginine release and glutamic acid, citrulline, valine, and leucine uptake (P < 0.1). After LPS treatment, (net) muscle protein synthesis increased in WT and NOS[2.sup.-/-] mice [LPS vs. control: 13 [+ or -] 3 vs. 8 [+ or -] 1 (SE) nmol*10 [g.sup.-1]*[min.sup.-1] (WT), 18 [+ or -] 5vs. 7 [+ or -] 2 nmol*10 [g.sup.-1]*[min.sup.-1] (NOS[2.sup.-/-); P < 0.05 for LPS vs. control]. This response was absent in NOS[3.sup.-/-] mice (LPS vs. control: 11 [+ or -] 4vs. 10 [+ or -] 2 nmol*10 [g.sup.-1]*[min.sup.-1]). In agreement, the increase in muscle arginine turnover after LPS was also absent in NOS[3.sup.-/-] mice. In conclusion, disruption of the NOS2 gene compromises muscle glutamine release and muscle blood flow in control mice, but had only minor effects after LPS. NOS3 activity is crucial for the increase in muscle arginine and protein turnover during early endotoxemia. nitric oxide; nitric oxide synthase; metabolism; sepsis

Dietary protein quality is considered to be dependent on the degree and velocity with which protein is digested, absorbed as amino acids, and retained in the gut as newly synthesized protein. Metabolic animal studies suggest that the quality of soy protein is inferior to that of casein protein, but confirmatory studies in humans are lacking. The study objective was to assess the quality of casein and soy protein by comparing their metabolic effects in healthy human subjects. Whole-body protein kinetics, splanchnic leucine extraction, and urea production rates were measured in the postabsorptive state and during 8-h enteral intakes of isonitrogenous [0.42 g protein/(kg body weight. 8 h)] protein-based test meals, which contained either casein (CAPM; n = 12) or soy protein (SOPM; n = 10) in 2 separate groups. Stable isotope techniques were used to study metabolic effects. With enteral food intake, protein metabolism changed from net protein breakdown to net protein synthesis. Net protein synthesis was greater in the CAPM group than in the SOPM group [52 [+ or -] 14 and 17 [+ or -] 14 nmol/(kg fat-free mass (FFM) * min), respectively; P < 0.02]. Urea synthesis rates decreased during consumption of both enteral meals, but the decrease tended to be greater in the subjects that consumed CAPM (P = 0.07). Absolute splanchnic extraction of leucine was higher in the subjects that consumed CAPM [306 [+ or -] 31 nmol/(kg FFM. min)] vs. those that consumed SOPM [235 [+ or -] 29 nmol/(kg FFM * min); P < 0.01]. In conclusion, a significantly larger portion of soy protein is degraded to urea, whereas casein protein likely contributes to splanchnic utilization (probably protein synthesis) to a greater extent. The biological value of soy protein must be considered inferior to that of casein protein in humans. KEY WORDS: * dietary protein * stable isotopes * urea * protein turnover * protein quality

Previously, we observed an enhanced renal protein synthesis and increased de novo arginine production in the early response to endotoxemia in wild-type Swiss mice (Hallemeesch MM, Soeters PB, and Deutz NE. Am J Physiol Renal Physiol 282: F316-F323, 2002). To establish whether these changes are regulated by nitric oxide (NO) synthesized by NO synthase isoforms NOS2 and NOS3, we studied C57BL6/J wild-type (WT), NOS2-deficient ([NOS2.sup.-/-]), and NOS3-deficient ([NOS3.sup.-/-]) mice under baseline (unstimulated) and LPS-treated conditions. The metabolism of renal protein, amino acid, and arginine was studied at the whole body level and across the kidney by infusing the stable isotopes L-[phenyl-[sup.2][H.sub.5]]phenylalanine, L-[phenyl-[sup.2][H.sub.2]]tyrosine, L-guanidino-[[sup.15][N.sub.2]]arginine, and L-[ureido-[sup.13] C,[sup.2][H.sub.2]]citrulline. Renal blood flow was measured using radioactive PAH extraction. Under baseline conditions, renal blood flow was significantly reduced in [NOS2.sup.-/-] mice (0.29 [+ or -] 0.01 vs. 0.48 [+ or -] 0.07 ml x 10 g body [wt.sup.-1] x [min.sup.-l] in WT) (P < 0.05), and de novo arginine production was lower in [NOS2.sup.-/-] mice. After LPS challenge, renal protein turnover and arginine production increased in all three groups (P < 0.05), even though renal de novo arginine synthesis did not increase. The expected increase in renal citrulline production and disposal after LPS was not observed in [NOS2.sup.-/-] mice (P = 0.06). Collectively, these data show that NOS2 is constitutively expressed in the kidney and remarkably functional as it affects renal blood flow and de novo arginine production under baseline conditions and is important for the increase in renal citrulline turnover during endotoxemia. NOS3, in contrast, appears less important for renal metabolism. The increase in renal protein turnover during endotoxemia does not depend on NOS2 or NOS3 activity. kidney; nitric oxide; nitric oxide synthase; sepsis

The significance of gastric or duodenal origin of phase III activity was studied to elucidate the variability of the migrating motor complex (MMC). Findings showed that individual MMC cycle duration and duration of phases I, II and III are dependent on the place of origin of the preceding phase III, which explains in part the within-subject variance. Also, the origin of phase III determines the duration of phase III.

Aims: Safety and tolerability of prolonged supplementation with a vitamin D, calcium and leucine-enriched whey protein medical nutrition drink (WP-MND) was evaluated in sarcopenic older adults. Methods: A 13-week double-blinded, randomized, isocaloric placebo-controlled trial (PROVIDE study; n = 380) was extended with a voluntary 13-week open-label extension (OLE). OLE participants were randomized to receive daily 1 or 2 servings of WP-MND (21 g protein, 3 g leucine, 10 µg vitD and 500 mg calcium per serving). Gastro-intestinal tolerability, kidney function and serum levels of calcidiol, parathyroid hormone (PTH) and calcium were evaluated at week 0, 13 and 26. Results and discussion: In response to the high daily protein intake (median1.5; IQR: 1.3, 1.7 g/kg BW/day), the estimated glomerular filtration rate (eGFR) increased in the test group during the RCT (p = 0.013). The same trend was observed for those participants with moderate chronic kidney disease. During OLE no eGFR change was observed in any of the groups. Serum calcidiol and calcium reached a plateau after 13-week WP-MND supplementation. As expected, PTH significantly changed in the opposite direction, decreasing during RCT in the test group (T vs C: p < 0.001) and during OLE in former control groups. During RCT, 20/366 participants with normal baseline calcidiol reached levels ≥ 100 nmol/L (T: n = 18; C: n = 2) and 6 developed albumin-corrected calcium levels > 2.55 mmol/L (T: n = 3; C: n = 3), without associated adverse events. Conclusion: A 6 months intervention with up to 2 servings of WP-MND did neither result in kidney function deterioration nor symptoms of vitamin D or calcium toxicity. The product was overall well tolerated. [ABSTRACT FROM AUTHOR]