Vitamin E supplementation counteracts the fish oil-induced increase of blood glucose in humans

The effects of palm oil tocotrienol-rich fraction supplementation on biochemical parameters, oxidative stress and the vascular wall of streptozotocin-induced diabetic rats

OBJECTIVE

This study examined the effects of palm oil tocotrienol-rich fractions on streptozotocin-induced diabetic rats.

METHODS

Animals were divided into three groups: (i) normal non-diabetic (NDM), (ii) diabetic treated (tocotrienol-rich fractions - TRF) and (iii) diabetic untreated (non-TRF). The treatment group received oral administration of tocotrienol-rich fractions (200 mg/kg body weight) daily for eight weeks. The normal non-diabetic and the diabetic untreated groups were fed standard rat feed. Blood glucose and lipid profiles, oxidative stress markers and morphological changes of the thoracic aorta were evaluated.

RESULTS

Tocotrienol-rich fractions treatment reduced serum glucose and glycated hemoglobin concentrations. The tocotrienol-rich fractions group also showed significantly lower levels of plasma total cholesterol, low-density lipoprotein cholesterol, and triglyceride, as compared to the untreated group. The tocotrienol-rich fractions group had higher levels of high-density lipoprotein cholesterol, as compared to the untreated group. Superoxide dismutase activity and levels of vitamin C in plasma were increased in tocotrienol-rich fractions-treated rats. The levels of plasma and aorta malondealdehyde + 4-hydroxynonenal (MDA + 4-HNE) and oxidative DNA damage were significant following tocotrienol-rich fractions treatment. Electron microscopic examination showed that the normal morphology of the thoracic aorta was disrupted in STZ-diabetic rats. Tocotrienol-rich fractions supplementation resulted in a protective effect on the vessel wall.

CONCLUSION

These results show that tocotrienol-rich fractions lowers the blood glucose level and improves dyslipidemia. Levels of oxidative stress markers were also reduced by administration of tocotrienol-rich fractions. Vessel wall integrity was maintained due to the positive effects mediated by tocotrienol-rich fractions.

Effect of fish oils containing different amounts of EPA, DHA, and antioxidants on plasma and brain fatty acids and brain nitric oxide synthase activity in rats

BACKGROUND

The interest in n-3 polyunsaturated fatty acids (PUFAs) has expanded significantly in the last few years, due to their many positive effects described. Consequently, the interest in fish oil supplementation has also increased, and many different types of fish oil supplements can be found on the market. Also, it is well known that these types of fatty acids are very easily oxidized, and that stability among supplements varies greatly.

AIMS OF THE STUDY

In this pilot study we investigated the effects of two different types of natural fish oils containing different amounts of the n-3 PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and antioxidants on plasma and brain fatty acids, blood lipids, vitamin E, and in vivo lipid peroxidation, as well as brain nitric oxide synthase (NOS) activity, an enzyme which has been shown to be important for memory and learning ability.

METHODS

Sprague-Dawley rats were divided into four groups and fed regular rat chow pellets enriched with 5% (w/w) of butter (control group), a natural fish oil (17.4% EPA and 11.7% DHA, referred to as EPA-rich), and a natural fish oil rich in DHA (7.7% EPA and 28.0% DHA, referred to as DHA-rich). Both of the fish oils were stabilized by a commercial antioxidant protection system (Pufanox) at production. The fourth group received the same DHA-rich oil, but without Pufanox stabilization (referred to as unstable). As an index of stability of the oils, their peroxide values were repeatedly measured during 9 weeks. The dietary treatments continued until sacrifice, after 10 days.

RESULTS

Stability of the oils varied greatly. It took the two stabilized oils 9 weeks to reach the same peroxide value as the unstable oil reached after only a few days. Both the stabilized EPA- and DHA-rich diets lowered the triacylglycerols and total cholesterol compared to control (-45%, P < 0.05 and -54%, P < 0.001; -31%, P < 0.05 and -25%, P < 0.01) and so did the unstable oil, but less efficiently. Only the unstable oil increased in vivo lipid peroxidation significantly compared to control (+40%, P < 0.001). Most of the fatty acids in the plasma phospholipids were significantly affected by both the EPA- and DHA-rich diets compared to control, reflecting their specific fatty acid pattern. The unstable oil diet resulted in smaller changes, especially in n-3 PUFAs. In the brain phospholipids the changes were less pronounced, and only the diet enriched with the stabilized DHA-rich oil resulted in a significantly greater incorporation of DHA (+13%, P < 0.01), as well as total n-3 PUFAs (+13%, P < 0.01) compared to control. Only the stabilized DHA-rich oil increased the brain NOS activity (+33%, P < 0.01).

CONCLUSIONS

Both the EPA- and DHA-rich diets affected the blood lipids in a similarly positive manner, and they both had a large impact on plasma phospholipid fatty acids. It was only the unstable oil that increased in vivo lipid peroxidation. However, the intake of DHA was more important than that of EPA for brain phospholipid DHA enrichment and brain NOS activity, and the stability of the fish oil was also important for these effects.

Women and Omega-3 Fatty Acids

Omega-3 fatty acids (omega-3 FA) are constituents of the membranes of all cells in the body and are precursors of locally produced hormones, eicosanoids, which are important in the prevention and treatment of various diseases, especially in women. Omega-3 FA are of interest in some of the most common conditions affecting women. One mechanism underlying dysmenorrhea is a disturbed balance between antiinflammatory, vasodilator eicosanoids derived from omega-3 FA and proinflammatory, vasoconstrictor eicosanoids derived from omega-6 FA. Increased intake of omega-3 FA can reverse the symptoms in this condition by decreasing the amount of omega-6 FA in cell membranes. An increased prostacyclin/thromboxane ratio induced by omega-3 FA can facilitate pregnancy in women with infertility problems by increasing uterine blood flow. Supplementation with omega-3 FA during pregnancy lowers the risk of premature birth and can increase the length of pregnancy and birth weight by altering the balance of eicosanoids involved in labor and promote fetal growth by improving placental blood flow. Intake of omega-3 FA during pregnancy and breast feeding may facilitate the child's brain development. There is also some evidence that supplementation with omega-3 FA might help to prevent preeclampsia, postpartum depression, menopausal problems, postmenopausal osteoporosis, and breast cancer. Furthermore, because elevated triglyceride levels are associated with cardiovascular disease, especially in women; and because omega-3 FA have powerful effects on triglycerides, women in particular gain from an increased intake of these fatty acids. This is especially important in women receiving hormone therapy, which can increase triglyceride levels. The quality of the omega-3 FA preparation is important. It should have an appropriate antioxidant content not to induce lipid peroxidation, and its content of dioxin and polychlorinated biphenyls (PCBs) should be well below the established safe limit.

A review of the safety of DHA45-oil

Polyunsaturated fatty acids (PUFAs), such as docosahexaenoic acid (DHA), are natural constituents of the human diet; however, dietary intakes of these fatty acids are below recommended values. The main dietary source of DHA is fatty fish, with lesser amounts provided by shellfish, marine mammals, and organ meats. The addition to traditional food products of refined oils produced by marine microalgae represents potential sources of supplemental dietary DHA. DHA45-oil is manufactured through a multi-step fermentation and refining process using a non-toxigenic and non-pathogenic marine protist. Comprising approximately 45% DHA, and lesser concentrations of palmitic acid and docosapentaenoic acid, DHA45-oil is intended for use in foods as a dietary source of DHA. The safety of DHA45-oil was evaluated in various genotoxicity and acute, subchronic, and reproductive toxicity studies. DHA45-oil produced negative results in genotoxicity assays and demonstrated a low acute oral toxicity in mice and rats. Dietary administration of DHA45-oil to rats in subchronic and one-generation reproductive studies produced results consistent with those observed in oral studies using high concentrations of omega-3 PUFAs from fish or other microalgal-derived oils. The results of these studies, as well as those of various published metabolic, toxicological, and clinical studies with DHA-containing oils, support the safety of DHA45-oil as a potential dietary source of DHA.

Dietary modulations in the prevention of coronary artery disease: a special emphasis on vitamins and fish oil

Coronary artery disease (CAD) is the most common cause of death in most countries. The etiology of CAD is complex, and many risk factors have been described. Traditional risk factors for CAD can only explain about half of the clinical events; therefore, interest in nutritional factors, such as vitamins and fish oil, has been maintained.

Fish oil supplementation with and without added vitamin E differentially modulates plasma antioxidant concentrations in healthy women

The purpose of this study was to assess the effect of fish oil with or without vitamin E on plasma vitamin antioxidants. Thirty-three apparently healthy women aged 18-28 yr were recruited from the university environs, and 30 completed the double-blinded, parallel design supplementation trial. Blood samples were collected at baseline (week 0) and following 28 d of supplementation with three capsules/d (0.8 g x 3) of either fish oil (FO) or FO with vitamin E (3 IU/g) (FOE). An additional blood sample was taken at day 91 (washout). Plasma antioxidant vitamins, fatty acid composition, and lipid peroxides were measured. Plasma alpha-tocopherol concentrations were increased significantly in both groups postsupplementation FO (P = 0.018) and FOE (P = 0.003) compared with baseline and washout values. Plasma retinol concentration was significantly increased (P = 0.034) compared with baseline and washout values following supplementation with FOE but not FO, while plasma beta-carotene was significantly increased (P = 0.036), compared with baseline and washout values, following supplementation with FO but not FOE. There was a trend (P = 0.059) toward decreased plasma ascorbic acid following FO supplementation compared with baseline and washout. Plasma lipid peroxides did not change following either supplementation. Results suggest that low-dose FO feeding with and without vitamin E differentially modulates plasma antioxidant vitamins but has no significant effect on lipid peroxidation.

Effect of in vitro stability of dietary fish oil on lipid peroxidation and prostanoids in vivo

Dietary supplementation of rats with fish oil for 18 days resulted in signs of lipid peroxidation, with increased malondialdehyde production in plasma and myocardium. This increase in malondialdehyde could be completely prevented by supplementing the fish oil with a new natural antioxidant mixture (Pufanox) which is known to markedly increase the in vitro stability of fish oils. Addition of Pufanox to fish oil also tended to increase the ratio between the vasodilator prostacyclin and the vasoconstrictor thromboxane A2. The concentration of vitamin E decreased, both in plasma and in the heart after the period of fish oil ingestion, indicating that the fish oil used contained too little vitamin E. Plasma cholesterol and triglyceride levels decreased markedly after fish oil supplementation but with no apparent difference between fish oil with or without Pufanox, probably due to the insufficient content of vitamin E. The results obtained emphasize the importance both of the in vitro stability of the fish oil given and of the amount of vitamin E added.

Whole blood production of thromboxane, prostacyclin and leukotriene B4 after dietary fish oil supplementation in man: effect of vitamin E

12 subjects were given 30 ml/day of a fish oil already stabilized with vitamin E (1.5 IU/g) and other natural antioxidants (fish oil, FO), and the same fish oil supplemented with extra vitamin E (to total 4.5 IU/g) (FO+E), in a randomized double-blind cross-over study. The whole blood production of thromboxane B2, measured in serum, was reduced after 4 weeks of ingestion of both FO+E (by 47%, P < 0.01) and of FO (by 40%, P < 0.05) whereas 6-keto-PGF1 alpha increased slightly in both cases, by 4% and 5% respectively, both NS. Leukotriene B4 production decreased on both FO+E (by 20%, NS) and FO (by 17%, P < 0.05). This study thus showed that a stabilized fish oil had marked effects on eicosanoid production, which may be important for its cardiovascular effect. Further supplementation with vitamin E had no additional effect, indicating that the vitamin E content (1.5 IU/g) in this stabilized fish oil might have been optimal.