Abstract
PurposeUnder conditions of high ambient temperatures and/or strenuous exercise, humans and animals experience considerable heat stress (HS) leading among others to intestinal epithelial damage through induction of cellular oxidative stress. The aim of this study was to characterize the effects of α-Lipoic Acid (ALA) on HS-induced intestinal epithelial injury using an in vitro Caco-2 cell model.MethodsA confluent monolayer of Caco-2 cells was pre-incubated with ALA (24 h) prior to control (37 °C) or HS conditions (42 °C) for 6 or 24 h and the expression of heat shock protein 70 (HSP70), heat shock factor-1 (HSF1), and the antioxidant Nrf2 were investigated. Intestinal integrity was determined by measuring transepithelial resistance, paracellular permeability, junctional complex reassembly, and E-cadherin expression and localization. Furthermore, cell proliferation was measured in an epithelial wound healing assay and the expression of the inflammatory markers cyclooxygenase-2 (COX-2) and transforming growth Factor-β (TGF-β) was evaluated.ResultsALA pretreatment increased the HSP70 mRNA and protein expression under HS conditions, but did not significantly modulate the HS-induced activation of HSF1. The HS-induced increase in Nrf2 gene expression as well as the Nrf2 nuclear translocation was impeded by ALA. Moreover, ALA prevented the HS-induced impairment of intestinal integrity. Cell proliferation under HS conditions was improved by ALA supplementation as demonstrated in an epithelial wound healing assay and ALA was able to affect the HS-induced inflammatory response by decreasing the COX-2 and TGF-β mRNA expression.ConclusionsALA supplementation could prevent the disruption of intestinal epithelial integrity by enhancing epithelial cell proliferation, and reducing the inflammatory response under HS conditions in an in vitro Caco-2 cell model.
Highlights
Introduction αLipoic acid (ALA, 1,2-dithiolane-3-pentanoic acid) is present in all kinds of pro- and eukaryote cells and is considered to be one of the most potent cellular antioxidants
It has been reported that oxidative stress activates mitogen-activated protein kinase (MAPK) and phosphatidyl inositol 3-kinase (PI3K) signaling pathways, which would lead to a decrease in the expression of tight junction proteins [10,11,12,13]
Thereafter, detached cells were removed by washing with PBS and the cells were incubated with DMEM or DMEM supplemented with ALA under control or heat stress (HS) conditions for 24 h
Summary
Introduction αLipoic acid (ALA, 1,2-dithiolane-3-pentanoic acid) is present in all kinds of pro- and eukaryote cells and is considered to be one of the most potent cellular antioxidants. ALA exhibits free radical scavenging properties, regulates antioxidant enzymes, has metal-chelating capacity, interacts with other antioxidants (vitamin C and E) [1, 2], and maintains its antioxidant function in both oxidized (disulfide, oALA) and reduced (di-thiol; dihydrolipoic acid, DHLA) forms [2]. In vitro and in vivo investigations by Fan et al showed a protective effect of ALA on the intestinal barrier function, which could be related to its antioxidant effect and to the increase in the expression of tight junctions proteins [9]. It seems plausible that ALA prevents the disruption of intestinal integrity by maintaining the expression of tight junction proteins through a suppression of MAPK and PI3K activation [11, 14]
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