Population kinetics of homoarginine and optimized supplementation for cardiovascular risk reduction.

Homoarginine is an endogenous amino acid whose levels are reduced in patients with renal, cardio- and cerebrovascular disease. Moreover, low homoarginine concentrations independently predict morbidity and mortality in these patients. Besides endogenous synthesis, homoarginine is also a constituent of the human diet. The objective of the present study was to analyze the kinetics of orally supplemented homoarginine in human plasma by means of a pharmacometric approach. We developed a pharmacometric model to evaluate different dosing regimens, especially the regimen of 125 mg once weekly, based on a previous clinical study (n = 20). The model was adapted to account for differences in baseline homoarginine plasma concentrations between healthy and diseased individuals. A novel dosing regimen of 25 mg once daily led to higher attainment of homoarginine reference concentrations using clinical trial simulations. With 25 mg/day, the trough concentration of only 6% of the older and 3.8% of the younger population was predicted to be below the target concentration of 2.0-4.1 µmol/L. In synopsis, the new dosing regimen recapitulates the kinetics of homoarginine in healthy individuals optimally.

Oral supplementation with L-homoarginine in young volunteers.

AIMS: Low blood concentrations of the naturally occurring amino acid L-homoarginine (L-hArg) are related to impaired cardiovascular outcome and mortality in humans and animals. L-hArg is a weak substrate of nitric oxide synthase and an inhibitor of arginases in vitro. The aim of our study was to obtain kinetic and dynamic data after oral L-hArg supplementation. METHODS: In a double-blind, randomized, placebo-controlled crossover study, 20 young volunteers received 125 mg L-hArg once daily for 4 weeks. Kinetic parameters (Cmax , Tmax and AUC0-24h ) were calculated after ingestion of single and multiple doses of oral supplementation as primary endpoint. Secondary endpoints that were evaluated were routine laboratory, L-arginine, asymmetric dimethylarginine (ADMA), pulse wave velocity (PWV), augmentation index (AIx), flow-mediated vasodilatation (FMD), corticospinal excitability, i.e. motor threshold (MT), and cortical excitability, i.e. intracortical inhibition (ICI) and facilitation (ICF). RESULTS: One hour after ingestion (Tmax ), L-hArg increased the baseline L-hArg plasma concentration (2.87 ± 0.91 µmol l-1 , mean ± SD) by 8.74 ± 4.46 [95% confidence intervals 6.65; 10.9] and 17.3 ± 4.97 [14.9; 19.6] µmol l-1 (Cmax ), after single and multiple doses, respectively. Once-only and 4 weeks of supplementation resulted in AUCs0-24h of 63.5 ± 28.8 [50.0; 76.9] and 225 ± 78.5 [188; 2624] µmol l-1 *h, for single and multiple doses, respectively. Routine laboratory parameters, L-arginine, ADMA, PWV, AIx, FMD, MT, ICI and ICF did not change by L-hArg supplementation compared to baseline. CONCLUSION: Once daily orally applied 125 mg L-hArg raises plasma L-hArg four- and sevenfold after single dose and 4 weeks of supplementation, respectively, and is safe and well tolerated in young volunteers.

Cognitive performance of 20 healthy humans supplemented with L-homoarginine for 4 weeks.

l-homoarginine (l-hArg) is an endogenous non-proteinogenic amino acid. Low l-hArg concentrations are associated with increased all-cause mortality, fatal strokes, and worse outcome after stroke. On the other hand, oral supplementation with l-hArg in mice improved neurological deficits and preserved cardiac function in experimental models of stroke and heart failure, respectively. Recently, oral supplementation with 125 mg daily l-hArg capsules in healthy volunteers demonstrated increased l-hArg plasma levels. Therefore, oral l-hArg supplementation could represent a potential treatment for patients with cerebrovascular disease. In addition to vascular physiology, animal studies have suggested that l-hArg might play a role in synapse function, neurotransmitter metabolism and cognitive training. However the direct influence of l-hArg on cognitive function has not been studied so far. In this study, cognitive performance in healthy humans was analyzed concerning memory, learning, and attention following supplementation with placebo or l-hArg for 4 weeks. Our results did not reveal any effects on cognition, neither impairment nor improvement, upon l-hArg supplementation. Therefore, potential l-hArg treatment is not expected to cause any acute neurocognitive or behavioral side effects.