Assessment and characterization of tomato lipophilic electrophiles and their potential contribution to nutraceutical properties via SKN-1/Nrf2 signaling activation.

Phytochemical electrophiles are drawing significant attention due to their properties to modulate signaling pathways related to cellular homeostasis. The aim of this study was to develop new tools to examine the electrophilic activity in food and predict their beneficial effects on health. We developed a spectrophotometric assay based on the nitrobenzenethiol (NBT) reactivity, as a thiol-reactive nucleophile, to screen electrophiles in tomato fruits. The method is robust, simple, inexpensive, and could be applied to other types of food. We quantified the electrophile activity in a tomato collection and associated this activity with the pigment composition. Thus, we identified lycopene, ß- and γ-carotenes, 16 by-products of carotenoid oxidation and 18 unknown compounds as NBT-reactive by HPLC-MS/MS. The potential benefits of NBT-reactive compounds on health were evaluated in the in vivo model of C. elegans where they activated the SKN-1/Nrf2 pathway, evidencing the ability of electrophilic compounds to induce a biological response.

Effects of chlorogenic acid on thermal stress tolerance in C. elegans via HIF-1, HSF-1 and autophagy.

BACKGROUND: Chlorogenic acid (CGA) is a polyphenol widely distributed in plants and plant-derived food with antioxidant and protective activities against cell stress. Caenorhabditis elegans is a model organism particularly useful for understanding the molecular and biochemical mechanisms associated with aging and stress in mammals. In C. elegans, CGA was shown to improve resistance to thermal, while the underlying mechanisms that lead to this effect require further understanding. PURPOSE: The present study was conducted to investigate the underlying molecular mechanisms behind CGA response conferring thermotolerance to C. elegans. METHODS AND RESULTS: Signaling pathways that could be involved in the CGA-induced thermotolerance were evaluated in C. elegans strains with loss-of-function mutation. CGA-induced thermotolerance required hypoxia-inducible factor HIF-1 but no insulin pathway. CGA exposition (1.4 µM CGA for 18 h) before thermal stress treatment increased HIF-1 levels and activity. HIF-1 activation could be partly attributed to an increase in radical oxygen species and a decrease in superoxide dismutase activity. In addition, CGA exposition before thermal stress also increased autophagy just as hormetic heat condition (HHC), worms incubated at 36 °C for 1 h. RNAi experiments evidenced that autophagy was increased by CGA via HIF-1, heat-shock transcription factor HSF-1 and heat-shock protein HSP-16 and HSP-70. In contrast, autophagy induced by HHC only required HSF-1 and HSP-70. Moreover, suppression of autophagy induction showed the significance of this process for adapting C. elegans to cope with thermal stress. CONCLUSION: This study demonstrates that CGA-induced thermotolerance in C. elegans is mediated by HIF-1 and downstream, by HSF-1, HSPs and autophagy resembling HHC.

Genetic dissection of vitamin E biosynthesis in tomato.

Vegetables are critical for human health as they are a source of multiple vitamins including vitamin E (VTE). In plants, the synthesis of VTE compounds, tocopherol and tocotrienol, derives from precursors of the shikimate and methylerythritol phosphate pathways. Quantitative trait loci (QTL) for α-tocopherol content in ripe fruit have previously been determined in an Solanum pennellii tomato introgression line population. In this work, variations of tocopherol isoforms (α, ß, γ, and δ) in ripe fruits of these lines were studied. In parallel all tomato genes structurally associated with VTE biosynthesis were identified and mapped. Previously identified VTE QTL on chromosomes 6 and 9 were confirmed whilst novel ones were identified on chromosomes 7 and 8. Integrated analysis at the metabolic, genetic and genomic levels allowed us to propose 16 candidate loci putatively affecting tocopherol content in tomato. A comparative analysis revealed polymorphisms at nucleotide and amino acid levels between Solanum lycopersicum and S. pennellii candidate alleles. Moreover, evolutionary analyses showed the presence of codons evolving under both neutral and positive selection, which may explain the phenotypic differences between species. These data represent an important step in understanding the genetic determinants of VTE natural variation in tomato fruit and as such in the ability to improve the content of this important nutriceutical.