Metabolic activation of furan moiety makes Diosbulbin B hepatotoxic

Abstract

Diosbulbin B (DIOB), a furanoid, is a major constituent of herbal medicine Dioscorea bulbifera L. Exposure to DIOB caused liver injury in humans and experimental animals. The mechanisms of DIOB-induced hepatotoxicities remain unknown. The present study demonstrated that DIOB induced hepatotoxicities in a time- and dose-dependent manner in mice. H&E stained histopathologic image showed the occurrence of necrosis in the liver obtained from the mice treated with DIOB at dose of 200 mg/kg. Pretreatment with KTC protected the animals from hepatotoxicities and hepatic GSH depletion induced by DIOB, increased area under the concentration-time curve of blood DIOB, decreased urinary excretion of GSH conjugates derived from DIOB, and increased urinary excretion of parent drug. Pretreatment with BSO exacerbated DIOB-induced hepatotoxicities. In order to define the role of furan moiety in DIOB-induced liver toxicities, we replaced the furan of DIOB with a tetrahydrofuran group by chemical hydrogenation of the furan ring of DIOB. No liver injury was observed in the animals given the same doses of tetrahydro-DIOB. The furan moiety was essential for DIOB-induced hepatotoxicities. The results implicate the cis-enedial reactive metabolite of DIOB was responsible for the observed toxicities. The observed modest depletion of hepatic GSH in DIOB-treated animals suggests the actions of one or more reactive metabolites, and the hepatic injury observed could be due at least in part to reactions of these metabolites with crucial biomolecules. Cytochrome P450 3A enzymes are implicated in DIOB-induced hepatotoxicities by catalyzing the formation of the reactive metabolite of DIOB.

Chemical Identity of Interaction of Protein with Reactive Metabolite of Diosbulbin B In Vitro and In Vivo

“…The present study characterized the chemical identities of protein adducts resulting from the metabolic activation of DIOB both in vitro and in vivo. cis -Enedial 2 was identified as the reactive intermediate possibly associated with DIOB-induced hepatotoxicity [ 16 , 21 ]. The toxicity is likely triggered by protein covalent binding derived from the reactive metabolite.…”

“…The adduction reached the peak at 12 h after the administration of DIOB. Our recent study demonstrated that the elevation of serum ALT reached the peak at 36 h in mice after a single dose of DIOB [ 16 ]. This indicates that a significant lag time between protein modification and the development of hepatotoxicity is required for the induction of DIOB hepatotoxicity from the onset of protein modification.…”

“…Our early work revealed that inhibition of P450 3A by KTC attenuated the production of the reactive metabolite of DIOB and protected mice from DIOB-induced hepatotoxicity [ 16 , 21 ]. The present study showed that pretreatment with KTC protected hepatic protein from covalent modification by the reactive metabolite of DIOB ( Figure 6 c), consistent with the observed reduction of protein adduction in liver microsomes from mice treated with KTC ( Figure 5 ).…”

“…Our early study showed that administration of DIOB at 100 mg/kg produced acute liver injury by biochemical estimation of serum markers and histopathological examination. In particular, biotransformation of the furan group played an important role in DIOB hepatotoxicity [ 16 ]. Metabolic conversion of toxic furan-containing compounds to cis -enediones, cis -enedials or γ -ketoenals is generally suggested to be a crucial step that initiates the development of the reported toxicities [ 17 , 18 , 19 , 20 ].…”

Metabolic Activation and Covalent Protein Binding of Berberrubine: Insight into the Underlying Mechanism Related to Its Hepatotoxicity

“…6 – 8 Recently, exposure to Dioscorea bulbifera L., a widely used herbal medicine was reported to display hepatotoxicities in human and experimental animals. 9 , 10 The main toxic ingredients were found to be diosbulbin B (DIOB) and 8‑Epidiosbulbin E Acetate (EEA), which both can be metabolized to the cis -enedial intermediate, and the liver injury correlated with the reaction of these electrophilic intermediates with cell protein. 11 – 13 Obviously, metabolic activation often plays a significantly critical role in the pathogenesis of the observed toxicities induced by drugs.…”