In silico, in vitro, and in vivo evaluation of the toxicity profile of natural phenolic compounds and synthesized bisphenols
Date
2024
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Publisher
University of Delaware
Abstract
Food safety is the priority of the food industry. Natural phenolic compounds are in abundance in plant-based foods, have a wide variety of structures and are known for their potential bioactive benefits; however, the relationship between these biological functionalities and their potential toxicity is not clear. More and more studies have demonstrated potential toxicities of these dietary phenolic components. Bisphenol A (BPA) is an essential building block for many polymeric systems, such as polycarbonates and epoxy resins. Its widespread use in various consumer products and food packaging materials poses significant safety and environmental concerns. Efforts are underway to address the environmental challenges associated with BPA, including regulatory measures and the search for safer alternatives. As society seeks more sustainable, greener and safer alternatives of BPA, it is vital to generate a comprehensive evaluation platform to target its possible toxicity endpoints. The aim of the current project is to investigate the toxicological profile of natural phenolic compounds and synthesized lignin-derivable monomers as BPA alternatives. ☐ In the first study, the developmental toxicity, endocrine disruption effect, and mutagenicity of thymol and carvacrol were investigated at low exposure doses. The results indicated that as phenolic isomers, thymol and carvacrol had different toxicity patterns on the three toxicity endpoints. Carvacrol showed higher binding affinities to two estrogen receptors, had weak estrogenic activity (EA) at 10−12 M, and negatively impacted chicken embryonic growth at 50 μg/kg. ☐ In the second study, toxicity of four common flavonoids: genistein, apigenin, quercetin, and luteolin were evaluated and compared. In agreement with the in silico molecular docking results, genistein and apigenin showed higher EA from the MCF-7 cell proliferation assay than EA of luteolin and quercetin. Moreover, genistein and luteolin demonstrated high developmental toxicity in the chicken embryonic assay (at 45–477 μg/kg) with a mortality rate of up to 50%. Among the tested flavonoids, quercetin (a flavonol) with a 2-hydroxyl substitution in the phenol ring exhibited lower developmental toxicity and EA. ☐ In the third study, we investigated the toxicity of two monolignols: guaiacol (G) and syringol (S), mixtures with varied S/G ratio, and three lignin depolymerization samples from poplar, pine, and miscanthus species. The results revealed that the S/G ratio impacts the mutagenicity and developmental toxicity in chicken embryos caused by lignin monomers. The mutagenicity potential of S/G mixtures and lignin monomers was correlated with the syringol proportion, while the adverse effects observed in the chicken embryonic assay were linked to the guaiacol ratio. ☐ In the last three studies (Study 4-6), we focused on exploring the toxicity of bisphenol A (BPA) and lignin-derivable monomers as potential BPA replacements. In the fourth study, genotoxicity of six lignin-derivable bisguaiacols with varying regioisomer contents and degrees of methoxy substitution was investigated. Results showed that most bisguaiacols except m,p’-BGS did neither show signs of mutagenicity in the Ames test nor induce DNA damage in comparison to BPA in the Comet test. The findings suggest that having at least one methoxy ortho to a phenolic hydroxyl group contributed to the lower oxidative DNA damage than BPA. ☐ In the fifth study, the EA and developmental toxicity on chicken embryo model of lignin-derivable bisguaiacols/bissyringols were investigated. Bissyringol A (BSA) with four methoxy groups showed undetectable EA and lack of estrogenic response in the chicken fetal liver. A comparable developmental toxicity was observed from the in vivo chicken embryonic assay for lignin-derivable monomers and BPA at environmentally relevant test concentrations. In the sixth study, the in vitro metabolism pattern of three lignin-derivable compounds as well as BPA were explored using ultra-performance liquid chromatography-mass spectrometry. Moreover, we conducted the in vivo toxicokinetic study of BPA via a chicken embryo model. Our results, in agreement with the predicted data, demonstrated that three lignin-derivable compounds had identical in vitro metabolite pathways which are similar to that of BPA. ☐ In summary, we found that the two phenolic monoterpenes and four flavonoids tested in the study demonstrated varied level of EA, mutagenicity, and developmental toxicity depending on their structures at a low exposure range. Moreover, the results showed that the methoxy substituents on lignin-derivable bisphenols appear to be a positive factor to reduce genotoxicity and oxidative DNA damage. The number of methoxy groups on lignin-derivable bisguaiacols/bissyringols plays a role on EA level. Additionally, a novel chicken embryo model was developed to target various critical toxicity endpoints, including developmental toxicity, genotoxicity, endocrine disruption, and metabolism, which were closely related to the structure and treatment dose of the natural phenolic compounds and synthesized bisphenols.
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Keywords
Bisphenols, Food safety, Natural phenolic compounds