Urolithin-B

Urolithin B (3-hydroxy-6H-dibenzo[b,d]pyran-6-one; CAS 1139-83-9) is one of the two principal terminal metabolites generated by human colonic microflora from dietary ellagitannins and ellagic acid, polyphenolic compounds abundant in pomegranates, walnuts, raspberries, strawberries, and certain tree nuts. Unlike its dihydroxylated isomer urolithin A (3,8-dihydroxyurolithin), which has advanced into human clinical trials primarily on the basis of mitophagy induction and mitochondrial quality control, urolithin B is distinguished by a pharmacological profile centered on skeletal muscle anabolism, neuroprotection through PI3K/Akt survival signaling, anti-inflammatory activity through NF-kappaB and NLRP3 inflammasome suppression, and a unique capacity to attenuate islet amyloid polypeptide (IAPP) proteotoxicity relevant to type 2 diabetes pathogenesis. The skeletal muscle activity, formally characterized by Rodriguez et al. (2017), demonstrated that urolithin B at 15 micromolar enhanced C2C12 myotube protein synthesis by 96.1 percent, increased myotube diameter and fusion index, suppressed the ubiquitin-proteasome degradation pathway, and operated through an androgen receptor to mTORC1 signaling axis independent of Akt phosphorylation. In vivo, 28-day subcutaneous delivery at 10 micrograms in the published literature produced 11.9 percent increases in tibialis anterior muscle fiber cross-sectional area and significant preservation of muscle mass in denervation-induced atrophy models. The neuroprotective profile, characterized by Chen et al. (2021) in D-galactose-induced aging mice, demonstrated dose-dependent rescue of spatial and working memory deficits at oral doses of 50 to 150 mg/kg for 8 weeks, mediated by PI3K/Akt pathway activation, inhibition of JNK/p38 apoptotic signaling, suppression of cytochrome c mitochondrial release, and restoration of hippocampal synaptic density markers PSD95 and synapsin I. Anti-inflammatory mechanisms, characterized in BV2 microglial cells by Lee et al. (2019), include suppression of NF-kappaB activation through reduced IkappaBalpha phosphorylation and degradation, attenuation of JNK, ERK, and Akt phosphorylation, enhancement of AMPK phosphorylation, and upregulation of heme oxygenase-1 through Nrf2/ARE signaling. Anticancer activity has been demonstrated in hepatocellular carcinoma (through Wnt/beta-catenin inactivation), osteosarcoma (G2/M arrest and MMP-2/-9 targeting), bladder cancer, leukemia, triple-negative breast cancer, and esophageal cancer cell lines. Bone-protective activity was reported in ovariectomy-induced osteoporosis models through inhibition of osteoclast formation via ERK/NF-kappaB suppression. The compound is produced endogenously only by individuals with the urolithin metabotype B (UM-B) gut microbiota profile, estimated at approximately 10 to 50 percent of the population depending on ethnicity and dietary pattern. Urolithin B undergoes extensive hepatic phase II conjugation to glucuronide and sulfate metabolites; circulating total urolithin concentrations in UM-B individuals following ellagitannin consumption range from 0.003 to 5.2 micromolar, with urinary excretion reaching up to 50 micromolar. No human clinical trials of exogenous urolithin B supplementation have been completed as of monograph preparation. The compound is available as a research-grade preparation from multiple chemical suppliers at greater than 95 percent purity. This monograph reviews the chemistry, biosynthesis, and structural class of urolithin B; the molecular pharmacology across muscle, neuronal, inflammatory, metabolic, and oncologic systems; the preclinical evidence base; the pharmacokinetic and metabotype considerations; sourcing and quality verification; reconstitution and handling; stack interactions; adverse events and safety signals; and a comparative assessment of five structurally or functionally related compounds against urolithin B on five competency standards.