Analysis of Opuntia ficus-indica triggered cellular mechanisms in the protection against cellular stressor

Abstract

The aim of the study was to analyse the ability, effectiveness, and mechanisms of action of the selected plant extract – prickly pear extract (PPE) – from the fruit of a local cultivar of Opuntia ficus-indica provided by and proprietary to Nutribiotech Services Limited, Malta, as a mode of protection against the cellular damage induced by cellular stressors on human dermal fibroblasts. Specifically, the cellular stressors used were heat stress, oxidative stress and UV irradiation, and these have the potential to exert deleterious effects on the cellular microarchitecture and physiology that may result in pathologies secondary to the effect of these injurious stimuli including but is not limited to, sunburn, cellular aging, and carcinogenesis. A cytoprotective effect was observed on exposure of human dermal fibroblasts to cytotoxic levels of heat stress (44°C for 1 h), menadione induced oxidative stress (25 μM, 12.5 μM and 6.25 μM), UVC (10 µJ/m2) and UVA (5 J/cm2) irradiation by varying degrees instigated by PPE (0.002 %, 0.004 %, 0.01 %, 0.02 %, 0.04 % and 0.08 %) treatment, reaching zenith at PPE (0.04 %) when considering the totality of the results of the Cell Titre Glo / Presto blue viability assay and scratch assay. Mechanistic elucidation was performed by means of transcriptome analysis using RNA sequencing focusing on the effect of PPE (0.04 %) treatment at alleviating the observed deleterious effect of heat stress (44°C for 1 h) and menadione induced oxidative stress (6.25 μM). The results indicate that the Opuntia ficus-indica extract used in this study provided protection against both heat and oxidative stress through the modulation of gene expression primarily related to cell cycle, incorrect/unfolded protein response (UPR), DNA repair and cytokine systems. In heat stress, a TP53 independent downregulation of cell cycle through GADD45G, GADD45A, MDM2 upregulation as well as an increase in cellular response to UPR showed by upregulation of DNAJB9, HSPA5, HSPA1A, HSPA1B. In oxidative stress, upregulated DNA repair and cell cycle pathways characterised by the upregulation of the genes RAD51AP1, ESCO2, POLQ and GINS2 with the concomitant downregulation of pathways related to morphogenesis and differentiation as well as RNA and ribosome processing. The upregulation of SESN2 is further evidence of the antioxidant effects of the PPE. Finally, the downregulation of inflammatory cytokine genes CXCL3, CXCL8, IL33, oxytocin receptor gene OXTR, SOCS cytokine signalling genes as well as the overall downregulation of the JAK-STAT pathway and the genes IL6, JAK3 are also indicative of a protective effect conferred by the PPE against oxidative stress. These findings advance the frontiers of knowledge in plant-based dermatoprotection and possibly open an avenue for the prophylactic application of Opuntia ficus-indica extracts as a defence against the deleterious implications of a plethora of cellular stressors.