Mechanisms of provitamin A (carotenoid) and vitamin A (retinol) transport into and out of intestinal Caco-2 cells.
ABSTRACT The purpose of this study was to compare the mechanisms of intestinal retinol (ROL) and carotenoid transport. When differentiated Caco-2 cells were incubated with ROL for varying times, cellular ROL plateaued within 2 h, whereas retinyl ester (RE) formation increased continuously. ROL and RE efflux into basolateral medium (BM) increased linearly with time, ROL in the nonlipoprotein fraction and REs in chylomicrons (CMs). In contrast to carotenoids, ROL uptake was proportional to ROL concentration (0.5-110 microM). ROL efflux into BM occurred via two processes: a) a saturable process at low concentrations (<10 microM) and b) a nonsaturable process at higher concentrations. When ROL-loaded cells were maintained on retinoid-free medium, free ROL, but not REs, was secreted into BM. Glyburide significantly reduced ROL efflux but not ROL uptake. Inhibition of ABCA1 protein expression by small interfering RNAs decreased ROL efflux but not carotenoid efflux. Scavenger receptor class B type I (SR-BI) inhibition did not affect ROL transport but decreased carotenoid uptake. The present data suggest that a) ROL enters intestinal cells by diffusion, b) ROL efflux is partly facilitated, probably by the basolateral transporter ABCA1, and c) newly synthesized REs, but not preformed esters, are incorporated into CM and secreted. In contrast to ROL transport, carotenoid uptake is mediated by the apical transporter SR-BI, and carotenoid efflux occurs exclusively via their secretion in CM.
Article: The Fox and the Rabbits-Environmental Variables and Population Genetics (1) Replication Problems in Association Studies and the Untapped Power of GWAS (2) Vitamin A Deficiency, Herpes Simplex Reactivation and Other Causes of Alzheimer's Disease.[show abstract] [hide abstract]
ABSTRACT: Classical population genetics shows that varying permutations of genes and risk factors permit or disallow the effects of causative agents, depending on circumstance. For example, genes and environment determine whether a fox kills black or white rabbits on snow or black ash covered islands. Risk promoting effects are different on each island, but obscured by meta-analysis or GWAS data from both islands, unless partitioned by different contributory factors. In Alzheimer's disease, the foxes appear to be herpes, borrelia or chlamydial infection, hypercholesterolemia, hyperhomocysteinaemia, diabetes, cerebral hypoperfusion, oestrogen depletion, or vitamin A deficiency, all of which promote beta-amyloid deposition in animal models-without the aid of gene variants. All relate to risk factors and subsets of susceptibility genes, which condition their effects. All are less prevalent in convents, where nuns appear less susceptible to the ravages of ageing. Antagonism of the antimicrobial properties of beta-amyloid by Abeta autoantibodies in the ageing population, likely generated by antibodies raised to beta-amyloid/pathogen protein homologues, may play a role in this scenario. These agents are treatable by diet and drugs, vitamin supplementation, pathogen detection and elimination, and autoantibody removal, although again, the beneficial effects of individual treatments may be tempered by genes and environment.ISRN neurology. 01/2011; 2011:394678.
Article: Divalent minerals decrease micellarization and uptake of carotenoids and digestion products into Caco-2 cells.[show abstract] [hide abstract]
ABSTRACT: Carotenoids are lipophilic, dietary antioxidants with the potential to prevent chronic and age-related diseases. Prior to their availability for physiological functions, carotenoids require micellarization and intestinal uptake, both constituting marginally understood processes. Based on an in vitro digestion model coupled to Caco-2 cells, we assessed the effect of dietary abundant divalent ions on spinach-derived carotenoid micellarization and cellular uptake: Ca and Mg ranging from 7.5 to 25 mmol/L in the digesta and Zn and Fe ranging from 3.8 to 12.5 mmol/L. Both micellarization and uptake were significantly inhibited by minerals in a concentration-dependent manner, with stronger effects for Fe and Zn compared to Ca and Mg. Compared to controls (no mineral addition), fractional micellarization and uptake were decreased to the greatest extent (to 22.5 and 5.0%, respectively; P < 0.001) by 12.5 mmol/L Fe. Effects of Mg were of the least magnitude; at 25 mmol/L, only uptake was decreased significantly to 69.2% of the control value (P < 0.001). Total cellular carotenoid uptake from test meals decreased similarly compared to micellarization; however, decreased β-carotene micellarization was counterbalanced by improved fractional cellular uptakes from the micelles for all ions. Compared to controls, fractional β-carotene uptake from the micelles was greater in samples digested in the presence of Fe, Ca, and Zn, by up to 5-10 times at the highest concentrations of each ion (P < 0.001). Like for the above carotenoids, a high cellular uptake of the epoxycarotenoid conversion products neochrome (from neoxanthin) and luteoxanthin+auroxanthin (from violaxanthin) was also observed. The present results indicate that divalent ions may inhibit carotenoid micellarization and uptake.Journal of Nutrition 08/2011; 141(10):1769-76. · 3.92 Impact Factor
Article: CD36 and SR-BI Are Involved in Cellular Uptake of Provitamin A Carotenoids by Caco-2 and HEK Cells, and Some of Their Genetic Variants Are Associated with Plasma Concentrations of These Micronutrients in Humans.[show abstract] [hide abstract]
ABSTRACT: Scavenger receptor class B type I (SR-BI) and cluster determinant 36 (CD36) have been involved in cellular uptake of some provitamin A carotenoids. However, data are incomplete (e.g., there are no data on α-carotene), and it is not known whether genetic variants in their encoding genes can affect provitamin A carotenoid status. The objectives were 1) to assess the involvement of these scavenger receptors in cellular uptake of the main provitamin A carotenoids (i.e., β-carotene, α-carotene, and β-cryptoxanthin) as well as that of preformed vitamin A (i.e., retinol) and 2) to investigate the contribution of genetic variations in genes encoding these proteins to interindividual variations in plasma concentrations of provitamin A carotenoids. The involvement of SR-BI and CD36 in carotenoids and retinol cellular uptake was investigated in Caco-2 and human embryonic kidney (HEK) cell lines. The involvement of scavenger receptor class B type I (SCARB1) and CD36 genetic variants on plasma concentrations of provitamin A carotenoids was assessed by association studies in 3 independent populations. Cell experiments suggested the involvement of both proteins in cellular uptake of provitamin A carotenoids but not in that of retinol. Association studies showed that several plasma provitamin A carotenoid concentrations were significantly different (P < 0.0083) between participants who bore different genotypes at single nucleotide polymorphisms and haplotypes in CD36 and SCARB1. In conclusion, SR-BI and CD36 are involved in cellular uptake of provitamin A carotenoids, and genetic variations in their encoding genes may modulate plasma concentrations of provitamin A carotenoids at a population level.Journal of Nutrition 02/2013; · 3.92 Impact Factor