Purpose: The purpose of this study was to characterize the pharmacokinetics (PKs) and pharmacodynamics (PDs) of an oral inositol-stabilized arginine silicate dietary supplement.
Subjects and methods: Ten healthy males, 26.7±5.4 years, took three 500 mg arginine silicate capsules (active product) for 14 days. The subjects attended test visits on Days 1 and 14. Fasting blood and saliva collections were performed predose and at 0.5 hours, 1 hour, 1.5 hours, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours postdose for plasma arginine, serum silicon, and salivary nitric oxide (NO) + nitrite.
Results: Day 1 PK parameters (adjusted for body weight) for arginine were peak serum concentration (C Max) 30.06±7.80 μg/mL, time it takes to reach peak serum concentration (t Max) 1.13±0.52 hours, and time required to reach half its original concentration (t 1/2) 15.93±9.55 hours and for silicon were C Max 2.99±0.63 μg/mL, t Max 2.44±2.05 hours, and t 1/2 34.56±16.56 hours. After Day 1 dose, arginine levels increased at 0.5 hours, 1 hour, 1.5 hours, 2 hours, 3 hours, and 5 hours (P<0.01) and silicon levels increased at 1 hour and 1.5 hours (P<0.05). After Day 14 dose, arginine levels increased at 0.5 hours, 1 hour, and 1.5 hours (P<0.05) and silicon levels increased at 1 hour, 1.5 hours, 2 hours, and 3 hours (P<0.01). After 14 days of use, baseline arginine trended toward being higher than baseline Day 1 (P=0.0645), and 4-hour postdose plasma arginine was significantly higher (P=0.0488) at Day 14 than Day 1. Although not a significant difference, NO, as measured as salivary nitrate, increased in four subjects and stayed the same in six subjects at 0.5 hours after the first dose (P=0.125). After 14 days of use, baseline NO levels increased in six subjects and stayed the same in four subjects; this shift was significant (P=0.031).
Conclusion: The arginine silicate dietary supplement increases blood levels of arginine after a single dose within 30 minutes and blood levels of silicon for up to 1.5 hours. Blood levels of arginine, silicon, and NO (salivary nitrite) were elevated consistently after 14 days of use. The observed increase in baseline salivary nitrite is supporting information that there was some improvement in NO production. Further study on the effect of this supplement on NO production and the resulting physiological effect is warranted. Within the specific protocol of this study, the product was found to be safe.
Keywords: arginine; dietary supplements; nitric oxide; pharmacodynamics; pharmacokinetics; silicon; vasodilation.