The "Three-Stage Leap" of Caffeine Metabolism in Humans: Paraxanthine as a Terminal Active Metabolite

Caffeine is among the most widely consumed psychoactive substances globally, yet its metabolic fate in the human body follows a distinctive "three-stage leap" pattern. This article systematically describes the first-stage transition in which caffeine undergoes N-3 demethylation catalyzed primarily by hepatic cytochrome P450 1A2 (CYP1A2), generating paraxanthine (1,7-dimethylxanthine, approximately 70–84% of total metabolism).

Berberine–Ascorbate Salt: A “Chemical Key” Unlocking the Absorption Bottleneck of a Millennia-Old Remedy

Berberine, the principal bioactive constituent of Coptis chinensis (Huanglian) and Phellodendron amurense (Huangbai), exhibits a broad spectrum of pharmacological activities including hypoglycemic, hypolipidemic, and anti-inflammatory effects. However, its clinical utility has been severely constrained by an oral bioavailability of less than 1%. This article introduces berberine–ascorbate salt, a novel salt form engineered via counterion substitution, in which L-ascorbic acid (vitamin C) serves as the counterion. Driven by a favorable ΔpKa of 7.33, the proton-transfer reaction yields a highly water-soluble ion pair, increasing aqueous solubility approximately 100-fold at 37 °C and elevating the plasma peak concentration (Cmax) by 5–7-fold in rat pharmacokinetic studies. We systematically review the molecular mechanism, solubility characteristics, in vivo absorption pathway, and prospective health applications of this salt-form engineering breakthrough, and discuss how it overcomes the century-old absorption barrier of berberine. Keywords: berberine; ascorbic acid; salt formation; bioavailability; solubility; pharmaceutical solid-state chemistry; P-glycoprotein

2026 HNC Shanghai & Youyou