Schisandrin B

Schisandrin B (Sch B), also designated gamma-schisandrin, is the most pharmacologically characterized dibenzocyclooctadiene lignan isolated from the dried ripe fruit of Schisandra chinensis (Turcz.) Baill., a climbing vine of the family Schisandraceae with a history of use in traditional Chinese medicine spanning more than two millennia under the name wuweizi (five-flavor berry). Among the more than 30 structurally related lignans present in the Schisandra fruit, Schisandrin B has attracted the greatest research attention owing to a convergence of potent antioxidant, anti-inflammatory, hepatoprotective, cardioprotective, and neuroprotective activities demonstrated across a substantial body of in vitro and in vivo preclinical literature. The compound acts principally through activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor and its downstream antioxidant response element (ARE)-dependent gene program, producing upregulation of glutathione S-transferase, heme oxygenase-1, NAD(P)H:quinone oxidoreductase 1, superoxide dismutase, and catalase. Concurrently, Schisandrin B suppresses NF-kB nuclear translocation and downstream proinflammatory cytokine expression (tumor necrosis factor alpha, interleukin-1 beta, interleukin-6) through inhibition of IkB-alpha degradation and suppression of MAPK cascade phosphorylation at c-Raf, MEK, ERK, JNK, and p38 nodes. Additional characterized mechanisms include enhancement of mitochondrial glutathione antioxidant status and heat shock protein induction, activation of the SIRT1/PI3K/Akt and AMPK/mTOR signaling axes, suppression of ferroptosis through upregulation of SLC7A11, GPX4, and FTH1, and modulation of pregnane X receptor (PXR)-mediated bile acid metabolism. The hepatoprotective activity is the best-validated pharmacological property: Schisandrin B protects against carbon tetrachloride-induced hepatotoxicity, D-galactosamine-induced hepatocyte apoptosis, ischemia-reperfusion liver injury, doxorubicin and pirarubicin-induced hepatotoxicity, acetaminophen hepatotoxicity, cholestatic liver injury, and metabolic-associated fatty liver disease in rodent models, with efficacy demonstrated at oral doses typically in the range of 25 to 100 mg/kg in mice and rats. The compound also exhibits preclinical cardioprotective activity against doxorubicin cardiotoxicity and angiotensin II-induced cardiac fibrosis, and neuroprotective activity against amyloid-beta-induced neuronal dysfunction, scopolamine-induced amnesia, and cisplatin-induced neurotoxicity. Pharmacokinetic characterization in rats demonstrates oral bioavailability of approximately 19 to 55 percent (with sex-dependent variation), extensive hepatic accumulation consistent with its liver-protective profile, a double-peak absorption curve suggestive of enterohepatic circulation, and linear pharmacokinetics across the 10 to 40 mg/kg oral dose range. Schisandrin B is a potent, dose-dependent, noncompetitive inhibitor of CYP3A activity (Ki approximately 16.6 mg/kg in vivo) and inhibits P-glycoprotein-mediated efflux, producing clinically relevant herb-drug interactions with CYP3A substrates including midazolam, tacrolimus, and sirolimus. The compound has not been evaluated in human clinical trials as an isolated entity; all pharmacological and safety characterization derives from preclinical studies and from clinical experience with Schisandra chinensis fruit extracts and the semi-synthetic derivative bifendate (dimethyl-4,4'-dimethoxy-5,6,5',6'-dimethylenedioxybiphenyl-2,2'-dicarboxylate). Preclinical toxicology in dogs has demonstrated dose-dependent plasma accumulation on repeated administration, and in vitro studies at high concentrations have identified paradoxical hepatotoxicity in mouse hepatocytes and macrophages, indicating that the therapeutic window requires careful characterization before clinical translation. This monograph documents the chemistry, stereochemistry, and botanical source of Schisandrin B; the molecular pharmacology across Nrf2, NF-kB, SIRT1, AMPK, and mitochondrial mechanisms; the preclinical pharmacokinetic profile; the comprehensive preclinical evidence base across hepatoprotective, cardioprotective, neuroprotective, anti-inflammatory, and antitumor indications; sourcing and quality verification; reconstitution and handling; stack interactions with emphasis on CYP3A and P-glycoprotein; adverse events and safety signals including dose-dependent hepatotoxicity; and a comparative assessment of five related hepatoprotective or Nrf2-activating compounds against Schisandrin B on five competency standards.