Liquorice Extract and 18β-Glycyrrhetinic Acid Protect Against Experimental Pyrrolizidine Alkaloid-Induced Hepatotoxicity in Rats Through Inhibiting Cytochrome P450-Mediated Metabolic Activation

Abstract

Misuse of pyrrolizidine alkaloid (PA)-containing plants or consumption of PA-contaminated foodstuffs causes numerous poisoning cases in humans yearly, while effective therapeutic strategies are still limited. PA-induced liver injury was initiated by cytochrome P450 (CYP)-mediated metabolic activation and subsequent formation of adducts with cellular proteins. Liquorice, a hepato-protective herbal medicine, is commonly used concurrently with PA-containing herbs in many compound traditional Chinese medicine formulas, and no PA-poisoning cases have been reported with this combination. The present study aimed to investigate hepato-protective effects of liquorice aqueous extract (EX) and 18β-glycyrrhetinic acid (GA, the primary bioactive constituent of liquorice) against PA-induced hepatotoxicity and the underlying mechanism. Histopathological and biochemical analysis demonstrated that both single- and multiple-treatment of EX (500 mg/kg) or GA (50 mg/kg) significantly attenuated liver damage caused by retrorsine (RTS, a representative hepatotoxic PA). The formation of pyrrole-protein adducts was significantly reduced by single- (30.3% reduction in liver; 50.8% reduction in plasma) and multiple- (32.5% reduction in liver; 56.5% reduction in plasma) treatment of GA in rats. Single- and multiple-treatment of EX also decreased the formation of pyrrole-protein adducts, with 30.2 and 31.1% reduction in rat liver and 51.8 and 53.1% reduction in rat plasma, respectively. In addition, in vitro metabolism assay with rat liver microsomes demonstrated that GA reduced the formation of metabolic activation-derived pyrrole-glutathione conjugate in a dose-dependent manner with the estimated IC50 value of 5.07 µM. Further mechanism study showed that GA inhibited activities of CYPs, especially CYP3A1, the major CYP isoform responsible for the metabolic activation of RTS in rats. Enzymatic kinetic study revealed a competitive inhibition of rat CYP3A1 by GA. In conclusion, our findings demonstrated that both EX and GA exhibited significant hepato-protective effects against RTS-induced hepatotoxicity, mainly through the competitive inhibition of CYP-mediated metabolic activation of RTS.

Genome-wide 5-hydroxymethylcytosine (5hmC) reassigned in Pten-depleted mESCs along neural differentiation

“…The immunostaining was performed according to a previous protocol ( Wang et al, 2022 ). Briefly, cells were fixed in 4% formaldehyde and permeabilized with 0.2% Triton X-100.…”

A review of typical biological activities of glycyrrhetinic acid and its derivatives

“…Additionally, other hepatoprotective mechanisms are also discussed, such as the inhibition of the TLR/NF-κB pathway and upregulation of hepatic FXR to facilitate bile acid synthesis, transport, and detoxification, competitive inhibition of cyto P450 (CYP) enzymes responsible for the activation of pyrrolizidine alkaloid (PA) metabolism, particularly C3A1, which protects against liver damage, activation of PXR to regulate autophagy and lysosomal biogenesis, thereby alleviating acute liver injury, inhibition of hepatic stellate cell activation, and direct transcriptional inhibition of α2 (I) collagen gene (COL1A2), as observed in transgenic reporter mice, and other mechanisms. 147–150…”

Update on new trends and progress of natural active ingredients in the intervention of Alzheimer's disease, based on understanding of traditional Chinese and Western relevant theories: A review

“…Natural products, on the other hand, have a more moderate effect, have more targets to work on and have relatively less side effects, which hold great promise for future drug research in the treatment of AD.Natural products are diverse in type and have a wide range of pharmacological activities, which have been an important source for the development of new drugs. It is undeniable that natural is not the same as safe, and certain pharmacologically active molecules in natural products may pose a risk to human health, such as plants containing pyrrolizidine alkaloids that may cause liver toxicity(Wang et al, 2022). At the meantime, natural plants were of varying qualities and difficult to control due to various reasons, such as their different growing environments.…”