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Phenolics from Purple Grape, Apple, Purple Grape Juice, and Apple Juice Prevent Early Atherosclerosis Induced by an Atherogenic Diet in Hamsters
Jean-Max Rouanet, Research Team 4188, Human Nutrition, Bioavailability and Atherogenesis, University Montpellier 2, Place E. Bataillon, 34093 Montpellier cedex 05, France, Email: jm.rouanet@univ-montp2.fr
Introduction
The beneficial health effect of high and regular fruit consumption is an important point emphasized by recent epidemiological studies. The protective effect afforded by this dietary supply may be particularly beneficial for pathologies such as coronary heart diseases [1-3] and some cancers [4]. Especially with regard to cardiovascular diseases (CVD), some studies have shown a relationship between a reduced risk of CVD and fruit consumption [2,3], but no indubitable evidence was given. These protective effects could come from micro-nutrients and micro-constituents, some of them being phenolic compounds [5]. Most of these phenolics are powerful antioxidants [6] and they might also offer protection against CVD [7]. When not consumed raw, fruits undergo processing that can modify these antioxidant properties in various ways, inducing antioxidant loss, improvement of antioxidant properties of natural compounds, formation of new compounds having antioxidant activity, formation of compounds having pro-oxidant properties, or interactions between different compounds [8]. Processing can also affect the bioavailability of bioactive compounds. This is an important aspect since only a small quantity of fruits is consumed in the raw state, whereas the major part needs to be treated to preserve quality as well as for safety and financial reasons.
Nowadays, there is limited information on the influence of fruit preservation processes and transforming techniques on the level of phenolics and antioxidant capacity.
The purpose of the present study was i) to determine the phenolic content of apple (A), purple grape (PG), and their juices (AJ and PGJ) and to evaluate their efficacy before and after technological processing, and ii) to assess a possible preventive effect of their administration on early atherosclerosis in hypercholesterolemic hamsters. Indeed, these compounds constitute useful markers allowing recognition and evaluation of nutritional quality in fresh and processed products.
Animal Studies with Apples, Grapes, and Their Juices
Apple juice (AJ) were obtained from apples (A) (Reinette du Vigan) after pressing, clarification with pectinase, and flash pasteurization at
We have designed a study to compare the effects of A, AJ, PG, and PGJ on plasma lipids and lipoprotein, on plasma antioxidant capacity (PAC), liver antioxidant enzyme activities, liver thiobarbituric acid reactive substances, and anti-atherogenic properties in hamsters consuming a hypercholesterolemic diet. We and others have previously reported that hamsters have increased plasma cholesterol levels when fed hypercholesterolemic diets [9,10]. Furthermore, it is well known that hamsters represent a useful model with respect to humans because they exhibit similar cholesterol metabolism and have a lipoprotein profile similar to that found in humans when fed hypercholesterolemic diets. Hamsters were also chosen for their responsiveness to anti-atherogenic interventions. To induce a peroxidative stress, the high cholesterol and high fat diet was rendered deficient in vitamins C, E, and in selenium. The arterial wall responded by fatty streak formation and aortic atherosclerosis emergence after 12 weeks. Then, we looked at the modulation of this effect by apples, purple grapes and their juices. All hamsters additionally received daily by gavage either tap water (control group), apple (group A), apple juice (group AJ), purple grape (group PG), or purple grape juice (group PGJ). Apples (without peel) and grapes were mashed daily using a high pressure cell disrupter. The volume of mashed fruits and fruit juices gavaged was adjusted daily to the weight of the hamsters: it was established by extrapolating 600 g/day average A or PG consumption (i.e. three apples or three bunches of grapes), or 500 mL/day average AJ or PGJ consumption, which is equivalent to about four glasses per day for a 70-kg person, for the daily weight of hamsters.
Results
At the end of the study, total cholesterol levels were significantly reduced in the animals fed the fruit-supplemented diets, by 11% in A group and 24% in the AJ group, and 30% in the PG and 34% in the PGJ group due to the reductions in levels of non-HDL cholesterol. Liver superoxide dismutase and glutathione peroxidase activities and thiobarbituric acid reactive substances were also efficiently reduced by the fruits and their juices compared with controls, whereas plasma antioxidant capacity was increased. The juices also outperformed the fruit for protecting against atherosclerosis, measured by the aortic fatty streak lesion area. This value was reduced by 93% and 78% for the purple grape juice and the fruit, respectively, and by 60% and 48% for apple juice and apple, respectively.
The results show for the first time that long-term consumption of antioxidants supplied by apple and purple grape, especially phenolic compounds, prevents the development of atherosclerosis in hamsters, and that processing can have a major impact on the potential health benefits of a product. The underlying mechanism is related mainly to increased antioxidant status and improved serum lipid profile.
Flavonoids, especially anthocyanins and catechins in purple grape and purple grape juice, generally have more hydroxyl groups than phenolic acids found in apple and apple juice. This could explain why purple grape juice and purple grape displayed a better efficacy than apple and apple juice against early atherosclerosis. Nevertheless, these beneficial effects cannot only be attributed to their phenolic contents, but to the result of the action of different antioxidant compounds present in the fruits (vitamin C, carotenoids, polyphenols) and to possible synergistic and antagonist effects still unknown. These findings are an encouragement that fruit and fruit juices may have a significant clinical and public health relevance.
References