Formation of DHP-DNA Adducts from Rat Liver Microsomal Metabolism of 1,2-Unsaturated Pyrrolizidine Alkaloid-Containing Plant Extracts and Dietary Supplements

An efficient enzymatic system for studying structure-carcinogenicity relationships: metabolism of pyrrolizidine alkaloids by human liver microsomes in the presence of calf thymus DNA, resulting in the formation of DNA adducts

Pyrrolizidine alkaloids (PAs) form a family of toxic and carcinogenic phytochemicals found in plants worldwide. The metabolism of toxic PAs, both in vivo and in vitro, generates four (±)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived DNA adducts, namely, DHP-dG-3, DHP-dG-4, DHP-dA-3, and DHP-dA-4, as documented in previous research. We have proposed that these DHP-DNA adducts play a pivotal role in the induction of liver tumor by PAs in rats and mice, serving as potential common biological biomarkers for PA exposure and carcinogenesis. In this study, we found that the metabolism of PAs and PA N-oxides by human liver microsomes, in the presence of calf thymus DNA, results in the formation of DNA adducts. This process serves as a convenient and biologically significant platform for investigating the structure-carcinogenicity relationships of PAs.

Pyrrolizidine Alkaloids-Pros and Cons for Pharmaceutical and Medical Applications

Heterocyclic organic compounds named pyrrolizidine alkaloids (PAs) belong to a group of alkaloids and are synthesized by either plants or microorganisms. Therefore, they are naturally occurring secondary metabolites. They are found in species applied in the pharmaceutical and food industries, thus a thorough knowledge of their pharmacological properties and toxicology to humans is of great importance for their further safe employment. This review is original because it synthesizes knowledge of plant and microbial PAs, which is unusual in the scientific literature. We have focused on the Boraginaceae family, which is unique due to the exceptional richness and diversity of its PAs in plant species. We have also presented the microbial sources of PAs, both from fungi and bacteria. The structure and metabolism of PAs have been discussed. Our main aim was to summarize the effects of PAs on humans, including both negative, toxic ones, mainly concerning hepatotoxicity and carcinogenicity, as well as potentially positive ones for pharmacological and medical applications. We have collected the results of studies on the anticancer activity of PAs from plant and microbial sources (mainly Streptomyces strains) and on the antimicrobial activity of PAs on different strains of microorganisms (bacteria and fungi). Finally, we have suggested potential applications and future perspectives.