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PubMedDate not supplied

Metabolic fate of menthofuran in rats. Novel oxidative pathways.

Metabolic fate of menthofuran (II) in rats was investigated. Menthofuran (II) was administered orally (200 mg/kg of the body weight/day) to rats for 3 days. The following metabolites were isolated from the urine of these animals: p-cresol (VI), 5-methyl-2-cyclohexen-1-one (VII), 3-methylcyclohexanone (VIII), 3-methylcyclohexanol (IX), 4-hydroxy-4-methyl-2-cyclohexen-1-one (V), geranic acid (XI), neronic acid (XII), benzoic acid (XIII), and 2-[2'-keto-4'-methylcyclohexyl]propionic acid (X). Incubation of menthofuran (II) with phenobarbital-induced rat liver microsomes in the presence of NADPH and oxygen resulted in the formation of a metabolite tentatively identified as 2-Z-(2'-keto-4'-methylcyclohexylidene)propanal (III; alpha,beta-unsaturated-gamma-keto-aldehyde). The structure assigned was further supported by trapping this metabolite (III) as a cinnoline derivative. Phenobarbital-induced rat liver microsomes also converted 4-methyl-2-cyclohexenone (IV) to 4-hydroxy-4-methyl-2-cyclohexenone (V) and p-cresol (VI) in the presence of NADPH and oxygen. On the basis of both in vivo and in vitro studies, a possible mechanism for the formation of p-cresol from menthofuran has been proposed.

Animals↗
PubMed2026

Establishment of a CRISPR/Cas9-mediated system for targeted editing of the MFS gene in mint.

The key message of this study is that we established a CRISPR/Cas9-mediated genome-editing system for Mentha haplocalyx "738" by optimizing protoplast transient assay and screening effective regulatory elements. Targeted knockout of the MFS gene generated edited mint plants with reduced menthofuran content, offering a strategy for quality improvement of mint essential oil. The commercial value of mint (Mentha spp.) essential oil is often diminished by the presence of undesirable metabolites, notably menthofuran, which impairs flavor and raises safety concerns. This study aimed to develop a robust CRISPR/Cas9 gene editing system for mint 738 (Mentha haplocalyx "738") and apply it to disrupt the menthofuran synthase (MFS) gene, thereby redirecting metabolic flux to enhance oil quality. We established an optimized system for high-efficiency protoplast isolation and transient transformation from young mint leaves. Key parameters for enzymatic digestion (1.5% cellulase R10, 0.2% macerozyme R-10, 3 h) and PEG-mediated transformation (40% PEG6000, 0.4 M mannitol, 0.4 M CaCl₂) were systematically determined. Using this platform, we screened endogenous regulatory elements, identifying a truncated mint U6 promoter (HmU6.1-3P) and the tomato SlEF1α promoter as the most effective drivers for sgRNA and Cas9 expression, respectively. A CRISPR/Cas9 vector targeting the MFS gene was constructed and used for Agrobacterium-mediated stable transformation. The positive transgenic mint lines were obtained. Sequencing confirmed heritable mutations at the target sites within the MFS gene in multiple independent lines. The results revealed a substantial decrease in menthofuran content in the essential oil of the edited line #10 compared to the wild-type control, thereby demonstrating a viable strategy for improving mint essential oil quality through genome-editing.

CRISPR-Cas Systems↗
PubMedDate not supplied

Investigations of mechanisms of reactive metabolite formation from (R)-(+)-pulegone.

1. (R)-(+)-Pulegone is a monoterpene that is oxidized by cytochromes P-450 to reactive metabolites that initiate events in the pathogenesis of hepatotoxicity in mice, rats and humans. 2. Selective labelling of (R)-(+)-pulegone with deuterium revealed that menthofuran was a proximate hepatotoxic metabolite formed by oxidation of the allylic methyl groups of pulegone. Incubations of pulegone with mouse liver microsomes in an atmosphere of 18O2 resulted in the formation of menthofuran that contained only oxygen-18 in the furan moiety. These results are consistent with oxidation of pulegone to an allylic alcohol that reacts intramolecularly with the ketone moiety to form a hemiketal that subsequently dehydrates to generate menthofuran. 3. Studies on the metabolism of menthofuran revealed that it is oxidized by cytochromes P-450 to an electrophilic gamma-ketoenal that reacts with nucleophilic groups on proteins to form covalent adducts. In addition, diastereomeric mintlactones are formed. Investigations with H2(18)O and 18O2 are indicative of a furan epoxide intermediate, or a precursor, in the formation of the gamma-ketoenal and mintlactones.

Animals↗