Short-Term Supplementation of Sodium Nitrate vs. Sodium Chloride Increases Homoarginine Synthesis in Young Men Independent of Exercise

Abstract

The aim of the study was to investigate the effects of short-term oral administration of inorganic nitrate (NaNO3; n = 8) or placebo (NaCl; n = 9) (each 0.1 mmol/kg body weight/d for 9 days) on plasma amino acids, creatinine, and oxidative stress in healthy young men. At baseline, the plasma concentrations of amino acids did not differ between the groups. At the end of the study, the plasma concentrations of homoarginine (hArg; by 24%, p = 0.0001), citrulline and ornithine (Cit/Orn; by 16%, p = 0.015), and glutamine/glutamate (Gln/Glu; by 6%, p = 0.0003) were higher in the NaNO3 group compared to the NaCl group. The plasma concentrations of sarcosine (Sarc; by 28%, p < 0.0001), tyrosine (by 14%, p = 0.0051), phenylalanine (by 8%, p = 0.0026), and tryptophan (by 8%, p = 0.0047) were lower in the NaNO3 group compared to the NaCl group. These results suggest that nitrate administration affects amino-acid metabolism. The arginine/glycine amidinotransferase (AGAT) catalyzes two reactions: (1) the formation of l-homoarginine (hArg) and l-ornithine (Orn) from l-arginine (Arg) and l-lysine (Lys): Arg + Lys <−> hArg + Orn, with equilibrium constant Kharg; (2) the formation of guanidinoacetate (GAA) and Orn from Arg and glycine (Gly): Arg + Gly <−> GAA + Orn, with equilibrium constant Kgaa. The plasma Kgaa/KhArg ratio was lower in the NaNO3 group compared to the NaCl group (1.57 vs. 2.02, p = 0.0034). Our study suggests that supplementation of inorganic nitrate increases the AGAT-catalyzed synthesis of hArg and decreases the N-methyltransferase-catalyzed synthesis of GAA, the precursor of creatine. To our knowledge, this is the first study to demonstrate elevation of hArg synthesis by inorganic nitrate supplementation. Remarkably, an increase of 24% corresponds to the synthesis capacity of one kidney in healthy humans. Differences in the association between plasma concentrations of amino acids in the NaNO3 and NaCl groups suggest changes in amino-acid homeostasis. Plasma concentrations of the oxidative stress marker malondialdehyde (MDA) did not change after supplementation of NaNO3 or NaCl over the whole exercise time range. Plasma nitrite concentration turned out to be a more discriminant marker of NaNO3 ingestion than plasma nitrate (area under the receiver operating characteristic curve: 0.951 vs. 0.866, p < 0.0001 each).

Homoarginine in the cardiovascular system: Pathophysiology and recent developments

“…However, creatine at presumably high concentrations may inhibit AGAT‐mediated L‐hArg formation as demonstrated in AGAT +/+ mice and previously published work using tissues from chicken and rats 4,26–28 . Contrary, the administration of sodium nitrate (NaNO 3 ) has been shown to influence the homeostasis of L‐hArg with remarkably higher plasma concentrations compared to placebo‐treated healthy volunteers 29 . It seems to shift AGAT‐mediated reactions toward L‐hArg synthesis by decreasing N‐methyltransferase‐catalyzed synthesis of guanidinoacetic acid (GAA) and subsequently creatine.…”

“…4,[26][27][28] Contrary, the administration of sodium nitrate (NaNO 3 ) has been shown to influence the homeostasis of L-hArg with remarkably higher plasma concentrations compared to placebo-treated healthy volunteers. 29 It seems to shift AGAT-mediated reactions toward L-hArg synthesis by decreasing N-methyltransferase-catalyzed synthesis of guanidinoacetic acid (GAA) and subsequently creatine.…”

Mass Sportrometry: An annual look back at applications of mass spectrometry in sport and exercise science

“…In 2022, targeted analyses were the most commonly applied approach for MS‐based research in SES, with 52 human participant studies published. These experiments were predominantly performed in plasma 6,16–35 or serum, 36–50 with other biosamples mediums utilized such as urine, 51–55 fecal matter, 56,57 breath gases, 58–63 red blood cells, 64 cerebrospinal fluid, 25 hair, 65 and whole blood via microsampling 66 . This excludes the use of IR and elemental MS to target specific isotope/elemental signatures, which are discussed individually within section 3.5.…”

“…In 2022, targeted analyses were the most commonly applied approach for MS-based research in SES, with 52 human participant studies published. These experiments were predominantly performed in plasma 6,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] or serum, [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] with other biosamples mediums utilized such as urine, [51][52][53][54][55] fecal matter, 56,57 breath gases, [58][59][60][61][62][63] red blood cells, …”

Homoarginine in health and disease

“…Inorganic nitrate, which is the major metabolite of nitric oxide, is currently investigated as an ergogenic supplement [59]. Very recently, short-term supplementation of inorganic nitrate at a dose of 0.1 mmol/kg body weight/d for 9 days to young men resulted in elevation of hArg synthesis in the volunteers independent of physical exercise [60 ▪▪ ] (Table 1). The increase in plasma hArg concentration was of the same order of the contribution as the synthetic capacity of one kidney in healthy humans [41].…”