Alterations in the intestinal assimilation of oxidized PUFAs are ameliorated by a polyphenol-rich grape seed extract in an in vitro model and Caco-2 cells

Abstract

The (n-3) PUFAs 20:5 (n-3) (EPA) and 22:6 (n-3) (DHA) are thought to benefit human health. The presence of prooxidant compounds in foods, however, renders them susceptible to oxidation during both storage and digestion. The development of oxidation products during digestion and the potential effects on intestinal PUFA uptake are incompletely understood. In the present studies, we examined: (1) the development and bioaccessibility of lipid oxidation products in the gastrointestinal lumen during active digestion of fatty fish using the in vitro digestive tract TNO Intestinal Model-1 (TIM-1); (2) the mucosal cell uptake and metabolism of oxidized compared with unoxidized PUFAs using Caco-2 intestinal cells; and 3) the potential to limit the development of oxidation products in the intestine by incorporating antioxidant polyphenols in food. We found that during digestion, the development of oxidation products occurs in the stomach compartment, and increased amounts of oxidation products became bioaccessible in the jejunal and ileal compartments. Inclusion of a polyphenol-rich grape seed extract (GSE) during the digestion decreased the amounts of oxidation products in the stomach compartment and intestinal dialysates (P < 0.05). In Caco-2 intestinal cells, the uptake of oxidized (n-3) PUFAs was ~10% of the uptake of unoxidized PUFAs (P < 0.05) and addition of GSE or epigallocatechin gallate protected against the development of oxidation products, resulting in increased uptake of PUFAs (P < 0.05). These results suggest that addition of polyphenols during active digestion can limit the development of (n-3) PUFA oxidation products in the small intestine lumen and thereby promote intestinal uptake of the beneficial, unoxidized, (n-3) PUFAs.

FIGURE 1

Concentrations of CD hydroperoxides in fresh fish and fish stored for 3 d at 4°C in the absence (-) or presence (+) of GSE over time in the TIM-1 stomach compartment. Results are mean ± SD, n = 3. *Different from fresh fish at that time, P < 0.05. CD, conjugated diene; GSE, grape seed extract; TIM-1, TNO Intestinal Model-1.

FIGURE 2

Concentrations of CD hydroperoxides in fresh fish and fish stored for 3 d at 4°C in the absence (-) or presence (+) of GSE over time in the TIM-1 jejunal (A) and ileal (B) dialysates. Results are mean ± SD, n = 3. *Different from fish stored without antioxidant, P < 0.05. CD, conjugated diene; GSE, grape seed extract; TIM-1, TNO Intestinal Model-1.

FIGURE 3

Net uptake of FAs in Caco-2 cells incubated with DHA (A) or PA (B) alone (30 μmol/L) or with antioxidants for 2 or 6 h (100 μmol/L EGCG or 45.8 ppm GSE that contained 47 μmol/L catechin, 46 μmol/L epicatechin, 23 μmol/L EGCG, and 6 μmol/L of procyanidin B2). Results are mean ± SD, n = 3. *Different from FA alone at that time, P < 0.05. EGCG, epigallocatechin gallate; FA, fatty acid; GSE, grape seed extract; PA, palmitic acid.

FIGURE 4

Formation of CD hydroperoxides in the incubation medium of Caco-2 Cells with DHA (30 μmol/L) and GSE (45.8 ppm that contained 47 μmol/L catechin, 46 μmol/L epicatechin, 23 μmol/L EGCG, and 6 μmol/L procyanidin B2) for 2 or 6 h. Results are mean ± SD, n = 3. *Different from DHA+GSE at that time, P < 0.05. CD, conjugated diene; EGCG, epigallocatechin gallate; GSE, grape seed extract.

FIGURE 5

Net uptake of DHA and oxidized DHA by Caco-2 cells incubated with 30 μmol/L FA for 2 or 6 h. Results are mean ± SD, n = 3. *Different from oxidized DHA, P < 0.05. FA, fatty acid.