Abstract
Background: Carotenoids are naturally occurring pigments accounting for the brilliant colors of fruits and vegetables. They may display antioxidant and anti-inflammatory properties in humans besides being precursors to vitamin A. There is a gap of knowledge in examining their role within colonic epithelial cells. We proposed to address this research gap by examining the effects of a major dietary carotenoid, β-carotene, in the in vitro epithelial cell model.Methods: We examined the function of β-carotene in the lipopolysaccharide (LPS)/toll-like receptor 4 (TLR4) signaling pathway. We conducted western blotting assays to evaluate expressions of TLR4 and its co-receptor, CD14. We also examined NF-κB p65 subunit protein levels in the model system. Furthermore, we studied the impact of β-carotene on the tight junction proteins, claudin-1, and occludin. We further carried out immunocytochemistry experiments to detect and visualize claudin-1 expression.Results: β-Carotene reduced LPS-induced intestinal inflammation in colonic epithelial cells. β-Carotene also promoted the levels of tight junction proteins, which might lead to enhanced barrier function.Conclusions: β-Carotene could play a role in modulating the LPS-induced TLR4 signaling pathway and in enhancing tight junction proteins. The findings will shed light on the role of β-carotene in colonic inflammation and also potentially in metabolic disorders since higher levels of LPS might induce features of metabolic diseases.
Highlights
Carotenoids are naturally occurring pigments responsible for the brilliant colors of fruits, vegetables, and microalgae [1, 2]
We showed that stimulation of LPS increased toll-like receptor 4 (TLR4) expression within HT-29 whole cell lysates (WCL) (Figure 6A). β-Carotene was subsequently beneficial toward inhibiting this LPS-induced TLR4 activation at higher treatment dosages of 1 and 10 μM
Using the same animal model, the researchers found that β-carotene supplementation resulted in an attenuated jejunal permeability and improved claudin-3, occludin, and zonula occludens protein-1 in the jejunum of piglets that have an increased risk of intestinal stress due to weaning [34]
Summary
Carotenoids are naturally occurring pigments responsible for the brilliant colors of fruits, vegetables, and microalgae [1, 2]. In addition to central (symmetrical) cleavage, eccentric cleavage can take place asymmetrically resulting in the formation of β-apo-10’-carotenal and β-ionone [10]. Within humans, βcarotene is released from the food matrix and incorporated into mixed micelles in order to be absorbed within intestinal cells. This cellular uptake occurs through a mechanism of passive diffusion or facilitated transport via scavenger receptor class B type 1 (SR-B1) [12]. Carotenoids are naturally occurring pigments accounting for the brilliant colors of fruits and vegetables They may display antioxidant and anti-inflammatory properties in humans besides being precursors to vitamin A.
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