Redox-Dependent Modulation of Lipid Synthesis Induced by Oleic Acid in the Human Intestinal Epithelial Cell Line Caco-2

Effects of olive oil and its minor phenolic constituents on obesity-induced cardiac metabolic changes

Background

Olive oil and its minor constituents have been recommended as important dietary therapeutic interventions in preventive medicine. However, a question remains to be addressed: what are the effects of olive oil and its phenolic compounds on obesity-induced cardiac metabolic changes?

Methods

Male Wistar rats were divided into two groups (n = 24/group): (C) receiving standard-chow; (Ob) receiving hypercaloric-chow. After 21 days C and Ob groups were divided into four subgroups (n = 6/group):(C) standard-chow and saline; (C-Olive)standard-chow and olive-oil (3.0 g/kg.day); (C-Oleuropein)standard-chow and oleuropein (0.023 mg/kg/day); (C-Cafeic) standard-chow and cafeic-acid (2.66 mg/kg/day); (Ob)receiving hypercaloric-chow and saline;(Ob-Olive) hypercaloric-chow and olive-oil;(Ob-Oleuropein) hypercaloric-chow and oleuropein;(Ob-Cafeic) hypercaloric-chow and cafeic-acid. Treatments were given twice a week during 21 days.

Results

After 42 days, obesity was evidenced in Ob rats from enhanced body-weight, surface-area, and body-mass-index. Energy-expenditure, oxygen consumption(VO₂) and fat-oxidation were lower in Ob-group than in C. Despite no morphometric changes, Ob-Olive, Ob-Oleuropein and Ob-Cafeic groups had higher VO₂, fat-oxidation, myocardial beta-hydroxyacyl coenzyme-A dehydrogenase and lower respiratory-quotient than Ob. Citrate-synthase was highest in Ob-Olive group. Myocardial lipid-hydroperoxide(LH) and antioxidant enzymes were unaffected by olive-oil and its compounds in obesity condition, whereas LH was lower and total-antioxidant-substances were higher in C-Olive and C-Oleuropein than in C.

Conclusions

The present study demonstrated for the first time that olive-oil, oleuropein and cafeic-acid enhanced fat-oxidation and optimized cardiac energy metabolism in obesity conditions. Olive oil and its phenolic compounds improved myocardial oxidative stress in standard-fed conditions.

Resveratrol toxicity: effects on risk factors for atherosclerosis and hepatic oxidative stress in standard and high-fat diets

The beneficial action of moderate wine consumption is increasingly being attributed to resveratrol (trans-3,4',5-trihydroxystilbene). To test the safety of resveratrol use as a dietary supplement, 24 male Wistar rats were initially divided into three groups: (C, n=6) was given standard chow and water; (R, n=6) received standard chow and 6 mg/l resveratrol in its drinking water (1mg/kg/day), and (HFD, n=12) received high-fat diet and water. In order to more appropriately study the effects of resveratrol on high-fat diet, after 30 days of treatments, HFD-rats were divided into two subgroups (n=6/group):(HFD) remained receiving high-fat diet and water; (HFD-R) given high-fat diet and 6 mg/l resveratrol in its drinking water (1mg/kg/day). The total experimental period was 45 days. The resveratrol dose took into account its average concentration in wine, the time variability of wine ingestion, and so of resveratrol consumption in humans. HFD-rats had hyperglycaemia, dyslipidemia, increased serum oxidized-LDL (ox-LDL) and hepatic oxidative stress. Comparing HFD-R and HFD-rats, resveratrol improved lipid profile and glucose level, enhanced superoxide dismutase, thus reducing ox-LDL and hepatic oxidative stress. Resveratrol, in standard-fed-rats reduced glutathione-antioxidant defense system and enhanced hepatic lipid hydroperoxide. In conclusion, based on the results of this single dose preliminary study with resveratrol in the drinking water of male Wistar rats for 30 days, it may be concluded that resveratrol may have beneficial effects in high-fat diets (e.g. ox-LDL, decreased serum and hepatic oxidativestress), but not in standard-fed diets (effects produced include enhanced hepatic oxidative stress). Further studies are indicated.

L-cysteine down-regulates SREBP-1c-regulated lipogenic enzymes expression via glutathione in HepG2 cells

BACKGROUND/AIM

Protein-associated amino acids are supposed to play a role in sterol regulatory element-binding protein (SREBP)-mediated regulation of lipid metabolism. This study investigates the effects of cysteine on expression of SREBP-regulated hepatic genes.

METHODS

HepG2 cells which are an accepted model for the study of the lipid metabolism were treated with L-cysteine under different conditions.

RESULTS

Exposure of cells to L-cysteine reduced the mRNA concentrations of SREBP-1c (-35 to -43%) and its target genes fatty acid synthase (FAS; -20 to -50%), glucose-6-phosphate-dehydrogenase (G6PDH; -31 to -35%), and stearoyl-coenzyme A desaturase (SCD)1 (-34 to -50%). Cells treated with L-cysteine had 47% higher glutathione and 47% lower triglyceride concentrations than control cells. In cells which were concurrently treated with L-cysteine and L-buthionine-[S,R]-sulfoximine, an inhibitor of enzymatic glutathione synthesis, no down-regulation of the gene expression was observed. Pro-oxidant CuSO(4) up-regulated SREBP-1c (+71%), FAS (+165%), G6PDH (+84%) and SCD1 (+96%) mRNA abundance compared to control cells, but when cells were concurrently treated with L-cysteine, the gene expression remained at control level.

CONCLUSIONS

The results show that L-cysteine rapidly down-regulates the transcription of genes involved in fatty acid biosynthesis via a mechanism that appears to be mediated by an improved glutathione status.

Effects of N-acetylcysteine on sucrose-rich diet-induced hyperglycaemia, dyslipidemia and oxidative stress in rats

This study examined whether sucrose-rich diet (SRD)-induced hyperglycaemia, dyslipidemia and oxidative stress may be inhibited by N-acetylcysteine (C(5)H(9)-NO(3)S), an organosulfur from Allium plants. Male Wistar 40 rats were divided into four groups (n=10): (C) given standard chow and water; (N) receiving standard chow and 2 mg/l N-acetylcysteine in its drinking water; (SRD) given standard chow and 30% sucrose in its drinking water; and (SRD-N) receiving standard chow, 30% sucrose and N-acetylcysteine in its drinking water. After 30 days of treatment, SRD rats had obesity with increased abdominal circumference, hyperglycaemia, dyslipidemia and hepatic triacylglycerol accumulation. These adverse effects were associated with oxidative stress and depressed lipid degradation in hepatic tissue. The SRD adverse effects were not observed in SDR-N rats. N-Acetylcysteine reduced the oxidative stress, enhancing glutathione-peroxidase activity, and normalizing lipid hydroperoxyde, reduced glutathione and superoxide dismutase in hepatic tissue of SRD-N rats. The beta-hydroxyacyl coenzyme-A dehydrogenase and citrate-synthase activities were increased in SRD-N rats, indicating enhanced lipid degradation in hepatic tissue as compared to SRD. SRD-N rats had reduced serum oxidative stress and diminished glucose, triacylglycerol, very-low-density lipoprotein (VLDL), oxidized low-density lipoprotein (ox-LDL) and cholesterol/high-density lipoprotein (HDL) ratio in relation to SRD. In conclusion, NAC offers promising therapeutic values in prevention of dyslipidemic profile and alleviation of hyperglycaemia in high-sucrose intake condition by improving antioxidant defences. N-Acetylcysteine had also effects preventing metabolic shifting in hepatic tissue, thus enhancing fat degradation and reducing body weight gain in conditions of excess sucrose intake. The application of this agent in food system via exogenous addition may be feasible and beneficial for antioxidant protection.

The fatty acid composition of chylomicron remnants influences their propensity to oxidate

BACKGROUND AND AIM

Although the replacement of saturated with unsaturated dietary fat has been advocated as a means of reducing the risk of cardiovascular disease, diets high in polyunsaturated fatty acids (PUFAs) may increase lipid peroxidation, thus contributing to the pathogenesis of atherosclerosis. As the susceptibility of individual fatty acids to oxidation directly depends on their degree of unsaturation, and the oxidative modification of lipoproteins may be an important determinant of atherogenesis, the aim of this study was to evaluate the susceptibility to auto-oxidation and copper-mediated oxidation of chylomicron remnants (CMRs) enriched in n-3 or n-6 PUFA.

METHODS AND RESULTS

The remnants were prepared in vitro from chylomicrons obtained from rats given an oral dose of fish or corn oil, using rat plasma containing lipoprotein lipase. Their propensity to oxidate and the extent of the oxidation were estimated by measuring the formation of conjugated dienes and the detrimental products of lipid peroxidation. The results showed that: 1) the corn oil CMRs contained a relatively high proportion of n-6 PUFA (mainly linoleic acid), whereas the fish oil CMRs contained more n-3 PUFA, mainly eicosapentanoic and docosahexaenoic acids; 2) n-3-rich CMRs have a significantly lower propensity to oxidate than n-6-rich CMRs despite their 50% lower alpha-tocopherol content and 40% higher unsaturation index.

CONCLUSION

Our data indicate that the precise allocation of n-3 PUFA within the lipid core of CMRs may play a pivotal role in lowering the susceptibility to oxidation of fish CMRs by overcoming the effects of unfavourable alpha-tocopherol concentration. Eating n-3 rather than n-6 PUFAs seems to make CMRs more resistant against free radical attack, which may contribute to attenuating their potential atherogenic properties.

Regulation of the Aldo-Keto Reductase Gene akr1b7 by the Nuclear Oxysterol Receptor LXRα (Liver X Receptor-α) in the Mouse Intestine: Putative Role of LXRs in Lipid Detoxification Processes

Liver X receptors (LXRs) regulate the expression of a number of genes involved in cholesterol and lipid metabolism after activation by their cognate oxysterol ligands. AKR1-B7 (aldo-keto reductase 1-B7) is expressed in LXR target tissues such as intestine, and because of its known role in detoxifying lipid peroxides, we investigated whether the AKR1-B7 detoxification pathway was regulated by LXRs. Here we show that synthetic LXR agonists increase the accumulation of AKR1-B7 mRNA and protein levels in mouse intestine in wild-type but not lxr−/− mice. Regulation of akr1b7 by retinoic X receptor/LXR heterodimers is dependent on three response elements in the proximal murine akr1b7 promoter. Two of these cis-acting elements are specific for regulation by the LXRα isoform. In addition, in duodenum of wild-type mice fed a synthetic LXR agonist, we observed an LXR-dependent decrease in lipid peroxidation. Our results demonstrate that akr1b7 is a direct target of LXRs throughout the small intestine, and that LXR activation plays a protective role by decreasing the deleterious effects of lipid peroxides in duodenum. Taken together, these data suggest a new role for LXRs in lipid detoxification.

Influence of thiol balance on micellar cholesterol handling by polarized Caco-2 intestinal cells

The in vitro thiol redox modulation of cholesterol homeostasis was investigated in polarized Caco-2 intestinal cells. Cells were pre-incubated with the pro-oxidant compound CuSO4 or with the antioxidant N-acetylcysteine (NAC), to induce a mild shift of the intracellular redox potential toward, respectively, a more oxidizing or a more reducing equilibrium, via a manipulation of intracellular soluble thiols (glutathione). Then, monolayers were exposed to micellar cholesterol and both the cholesterol uptake and export, as well as the cholesteryl ester cycle, were analyzed. We found that pro-oxidizing conditions induced a significant cholesterol retention within the cells, particularly in the unesterified form (FC), as a result of an augmented sterol incorporation coupled with a reduced rate of FC esterification. A reduction in FC export was also evident. Furthermore, the combination of FC retention and the oxidative imbalance leads to significant alterations of the monolayer integrity, evidenced by both the enhanced tight junction permeability and the lactate dehydrogenase release into the basolateral medium. In contrast, a more reducing environment generated by NAC pre-treatment favors the limitation of the resident time of FC into the cells, via a reduced cholesterol uptake and a concomitant increased cholesterol esterification. In addition, a significant higher FC extrusion into the basolateral medium was also appreciable. Our results indicate that the thiol balance of intestinal cells may be critical for the regulation of cholesterol homeostasis at the intestinal level, influencing the lipid transport throughout the intestinal barrier.