A Chimeric Peptide Inhibits Red Blood Cell Invasion by Plasmodium falciparum with Hundredfold Increased Efficacy.

Inhibiting the formation of a tight junction between two malaria parasite proteins, apical membrane antigen 1 and rhoptry neck protein 2, crucial for red blood cell invasion, prevents progression of the disease. In this work, we have used a unique approach to design a chimeric peptide, prepared by fusion of the best features of two peptide inhibitors, that has displayed parasite growth inhibition ex vivo with nanomolar IC50 , which is 100 times better than any of its parent peptides. Furthermore, to gain structural insights, we computationally modelled the hybrid peptide on its receptor.

Zinc induces iron uptake and DMT1 expression in Caco-2 cells via a PI3K/IRP2 dependent mechanism.

The absorption of iron is influenced by numerous dietary and physiological factors. We have previously demonstrated that zinc treatment of intestinal cells increases iron absorption via induction of the apical membrane iron transporter divalent metal ion transporter-1 (DMT1). To better understand the mechanisms of zinc-induced iron absorption, we have studied the effect of zinc on iron uptake, iron transporter and iron regulatory protein (IRP 1 and 2) expression and the impact of the PI3K pathway in differentiated Caco-2 cells, an intestinal cell culture model. We found that zinc induces DMT1 protein and mRNA expression. Zinc-induced DMT1 expression and iron absorption were inhibited by siRNA silencing of DMT1. Furthermore, zinc treatment led to increased abundance of IRP2 protein in cell lysates and in polysomal fractions, implying its binding to target mRNAs. Zinc treatment induced Akt phosphorylation, indicating the activation of the PI3K pathway. LY294002, a specific inhibitor of PI3K inhibited zinc-induced Akt phosphorylation, iron uptake, DMT1 and IRP2 expression. Furthermore, LY294002 also decreased the basal level of DMT1 mRNA but not protein expression. siRNA silencing of IRP2 led to down-regulation of both basal and zinc-induced DMT1 protein expression, implying possible involvement of post-transcriptional regulatory mechanisms. In agreement with these findings, zinc treatment stabilized DMT1 mRNA levels in actinomycin D-treated cells. Based on these findings, we conclude that zinc-induced iron absorption involves elevation of DMT1 expression by stabilization of its mRNA, by a PI3K/IRP2-dependent mechanism.

ß-Carotene bioaccessibility from biofortified maize (Zea mays) is related to its density and is negatively influenced by lutein and zeaxanthin.

Biofortification of maize with provitamin A (pro-VA) carotenoids has been successful, but the bioavailability of carotenoids needs to be explored. In the present study, we investigated the carotenoid content, micellarization and intestinal cell uptake of carotenoids from 10 maize hybrids [normal maize, quality protein maize (QPM), pro-VA carotenoid and double biofortified QPM + pro-VA maize hybrids] using a simulated in vitro digestion/Caco-2 cell model. The pro-VA carotenoid content of biofortified maize hybrids is 2-10 fold higher compared to that of normal maize. Furthermore, the ratio of non-pro-VA carotenoids lutein (LUT) plus zeaxanthin (ZEA) to the sum of pro-VA carotenoids ß-cryptoxanthin (BCX), α-carotene (AC) and ß-carotene (BC) in biofortified maize was much lower compared to that of normal maize. The consumption of 200 g day-1 of biofortified Pusa-PV-16-3 (BC = 808.4 µg per 100 g; AC = 839.3 µg per 100 g; BCX = 59 µg per 100 g) and Pusa-APQH8 (BC = 345.9 µg per 100 g; AC = 1739 µg per 100 g; BCX = 644.2 µg per 100 g) maize would contribute to 52 and 64% of RDAs for adult Indian men, respectively, after adjusting for cooking losses and conversion factors. The mean efficiency of micellarization of LUT (62.2% ± 5.3), ZEA (65% ± 4.7), and BCX (54% ± 9.5) exceeded that of AC (43% ± 8.9) and BC (49.8% ± 7.8) from all the maize hybrids. Furthermore, the micellarization and uptake in Caco-2 cells during a 4 h incubation period showed high correlation (P < 0.05) with the concentration of carotenoids in the maize digesta and micellar fraction, respectively. However, the LUT + ZEA content in the maize digesta and micellar fraction was inversely (p < 0.05) related to the BC micellarization and intestinal cell uptake, respectively. These results together suggest that the enrichment of pro-VA carotenoids together with decreasing the oxygenated carotenoid metabolites such as LUT and ZEA will further improve the bioavailability of BC from maize hybrids.

Dietary fat composition, food matrix and relative polarity modulate the micellarization and intestinal uptake of carotenoids from vegetables and fruits.

Dietary fat increases carotenoid bioavailability by facilitating their transfer to the aqueous micellar fraction during digestion. However, the specific effect of both quantity and type of dietary fat required for optimal carotenoid absorption remained unexplored. In the present study, the effect of amount and type of vegetable oils on carotenoid micellarization from carrot, spinach, drumstick leaves and papaya using in vitro digestion/Caco-2 cell model have been assessed. Although, dietary fat (0.5-10% w/w) significantly increased the micellarization of carotenoids from all the test foods, the extent of increase was determined by the food matrix (papaya > drumstick = spinach > carrot) and polarity of carotenoids (lutein > ß-carotene = α-carotene > lycopene). Among the dietary fats tested the carotenoid micellarization was twofold to threefold higher with dietary fat rich in unsaturated fatty acids (olive oil = soybean oil = sunflower oil) compared to saturated fatty acids (peanut oil = palm oil > coconut oil). Intestinal cell uptake of lutein exceeded that of ß-carotene from micellar fraction of spinach leaves digested with various oils. However, cellular uptake of ß-carotene is depended on the carotenoid content in micellar fraction rather than the type of fat used. Together these results suggest that food matrix, polarity of carotenoids and type of dietary fat determines the extent of carotenoid micellarization from vegetables and fruits.

Eicosapentaenoic acid inhibits intestinal ß-carotene absorption by downregulation of lipid transporter expression via PPAR-α dependent mechanism.

The involvement of lipid transporters, the scavenger receptor class B, type I (SR-BI) and Niemann-Pick type C1 Like 1 protein (NPC1L1) in carotenoid absorption is demonstrated in intestinal cells and animal models. Dietary ω-3 fatty acids are known to possess antilipidemic properties, which could be mediated by activation of PPAR family transcription factors. The present study was conducted to determine the effect of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), on intestinal ß-carotene absorption. ß-carotene uptake in Caco-2/TC7 cells was inhibited by EPA (p < 0.01) and PPARα agonist (P < 0.01), but not by DHA, PPARγ or PPARδ agonists. Despite unaltered ß-carotene uptake, both DHA and PPARδ agonists inhibited the NPC1L1 expression. Further, EPA also induced the expression of carnitine palmitoyl transferase 1A (CPT1A) expression, a PPARα target gene. Interestingly, EPA induced inhibition of ß-carotene uptake and SR B1 expression were abrogated by specific PPARα antagonist, but not by PPARδ antagonist. EPA and PPARα agonist also inhibited the basolateral secretion of ß-carotene from Caco-2 cells grown on permeable supports. These results suggest that EPA inhibits intestinal ß-carotene absorption by down regulation of SR B1 expression via PPARα dependent mechanism and provide an evidence for dietary modulation of intestinal ß-carotene absorption.

Citric acid mediates the iron absorption from low molecular weight human milk fractions.

Previously, we have demonstrated increased iron absorption from low molecular weight (LMW) human milk whey fractions. In the present study, we investigated the effect of heat denaturation, zinc (a competitor of iron), duodenal cytochrome b (DcytB) antibody neutralization and citrate lyase treatment on LMW human milk fraction (>5 kDa referred as 5kF) induced ferric iron reduction, solubilization, and uptake in Caco-2 cells. Heat denaturation and zinc inhibited the 5kF fraction induced ferric iron reduction. In contrast, zinc but not heat denaturation abrogated the ferric iron solubilization activity. Despite inhibition of ferric iron reduction, iron uptake in Caco-2 cells was similar from both native and heat denatured 5kF fractions. However, iron uptake was higher from native compared to heat denatured 5kF fractions in the cells preincubated with the DcytB antibody. Citrate lyase treatment inhibited the ferric iron reduction, solubilization, and uptake in Caco-2 cells. These findings demonstrate that citric acid present in human milk solubilizes the ferric iron which could be reduced by other heat labile components leading to increased uptake in intestinal cells.