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Unité des Maladies Métaboliques et Micronutriments, INRA de Clermont-Ferrand/Theix and CRNH d’Auvergne, 63122 St-Genes-Champanelle, France
3To whom correspondence should be addressed. E-mail: demigne{at}clermont.inra.fr.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • Zucker rats • apples • cholesterol • lipoproteins • bile acid • antioxidants
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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,2
). As a result, health authorities increasingly recommend eating five to ten portions of fruits and vegetables each day, in the framework of a "prudent" diet. In Western countries, apples represent an important part of fruit consumption and, in some areas, they are the first fruits consumed. This importance of apples can be explained by various factors including their availability in the market throughout the year in a variety of forms (fresh fruit, juice, cider, mashed apples) and also their reputation as a healthy food (3
). The health effects of apples, especially their cholesterol-lowering properties, were first ascribed to the fiber moiety of the fruit (4
,5
). However, the fiber content of apples is not particularly high (2–3%) and soluble fibers, especially pectin, represent < 50% of the fiber in apples. In addition to effects on the circulating lipid levels, plant foods could reduce the atherogenicity of lipoproteins by protecting them from peroxidation. However, apples are poor in lipid-soluble protectants such as tocopherols or carotenoids, but they contain appreciable amounts of vitamin C and of various phenolic compounds (catechins, phenolics acids, quercetin and phloretin), which also have protective effects (6
,7
). In the intact fruit, the fibers and the phenolic compounds are closely associated; they could reciprocally affect digestibility and possibly exert synergistic effects.
Apple effectiveness has been assessed in humans (8
,9
), but more detailed studies on the lipid-lowering effects have generally been conducted in animal models, using either the fruit itself (5
,10
,11
) or specific constituents (4
,12
). Animal models were generally conventional strains of rats (10
), or LDL-species such as hamsters (5
,13
), whereas diabetic or prediabetic models have seldom been used. Yet, the genetically obese Zucker rat is a model of interest for studies of the various aspects of the plurimetabolic syndrome. Homozygous (fa/fa) Zucker rats are characterized by hyperphagy and are subject to obesity, insulin resistance, serum and tissue lipid accumulation (14
, 15
). This rat strain has been frequently used as a model for obesity, noninsulin-dependent mellitus diabetes or type IV hyperlipemia (14
,16
). Therefore, after observing the effects of apples on cholesterol metabolism and on antioxidative protection in cholesterol-fed rats (10
), we decided to investigate these potentialities further in Zucker rats fed semipurified diets containing 20% lyophilized apple, compared with control rats fed a fruit-free diet balanced for simple sugar supply.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Triglycerides and cholesterol were measured using the PAP 150 and RTU BioMérieux kits (Charbonnière-les-Bains, France) respectively; free fatty acids (FFA)4
were estimated using the Wako NEFA-C kit (Biolyon, Dardilly, France) and the creatinine kit (555-A) was from Sigma (St Louis, MO). Apples ["Reinette Canada," a dessert variety particularly rich in polyphenols (17
)] were purchased from a local supplier (Ceyrat, France). Before lyophilization, the core was removed and the rest of the fruit (skin + pulp) was cut into 
10-g pieces, which were frozen at -80°C in aluminum rectified trays. After 24 h of deep-freezing, the samples were transferred into the lyophilizer and freeze-dried for 72 h. The dehydrated apple pieces were then rapidly powdered in a grinder, and the resulting powder was stored desiccated at 4°C in sealed plastic bags.
Animals and diets.
Zucker rats (IFFA CREDO, l’Arbresle, France) were maintained and handled according to the recommendations of the INRA Ethics Committee, in accordance with decree no. 87–848. Male lean (Fa/-) and obese (fa/fa) Zucker rats, weighing 150 g, were housed one per cage (wire bottomed, to limit coprophagy) and fed for 21 d semipurified diets distributed as a moistened powder (Table 1
). Both diets contained a moderate amount of cholesterol (0.25%); the basal vitamin E supply was limited to one third of the recommended value and a fat source (corn oil) that was relatively prone to oxidation was used to increase the antiooxidant response. In addition, the control diet was balanced with the apple diet for mono- and disaccharides (fructose, glucose, and sucrose), which represent the major part of their dry matter, after their enzymatic measurement in microplates (18
). Rats were maintained in temperature-controlled rooms (22°C) with a dark period from 2000 to 0800 h during which they had access to food. Body weight was recorded on d 0, 7, 14, and 21 of the experiment. Food intake determination and collection of feces and urine were performed on 4 consecutive days at the end of the experiment.
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At the time of sampling (0900 h), rats were anesthetized with sodium pentobarbital (40 mg/kg) and kept on a plate at 37°C. Blood was drawn from the abdominal aorta into a heparinized syringe and plasma was obtained after centrifugation at 10,000 x g for 2 min. Aliquots of plasma were stored at 4°C for lipid analysis, and other aliquots were kept at -80°C for oxidative protection tests. The cecum with contents was removed and weighed and samples (1 g) of cecal contents were transferred to microfuge tubes and immediately frozen at -20°C. Liver and heart were excised and 3 g of liver and the entire heart were immediately freeze-clamped and stored at -80°C. Urine was collected from the bladder.
Analytical procedures.
Short-chain fatty acids (SCFA) were measured by gas-liquid chromatography on cecal contents, as described by Rémésy and Demigné (19
). Total bile acids were extracted from lyophilized small intestine or feces with 2 x 10 volumes of 0.5 mol/L KOH-ethanol and quantified using the reaction catalyzed by 3
-hydroxysteroid dehydrogenase (EC 1.1.1.50, Sigma). Cholesterol, triglyceride and FFA were determined in plasma using commercial kits. Liver and heart samples were homogenized and lipids were extracted with chloroform/methanol (2:1, v:v). Triglycerides in the lipid residue were saponified by 0.5 mol/L KOH-ethanol at 70°C for 30 min, then 0.15 mol/L MgSO4 was added to neutralize the mixture. After centrifugation (2000 x g, 5 min) the supernatant was assayed for glycerol (BioMérieux). Cholesterol in the lipid residue was measured with an enzymatic procedure as described above. A polyvalent control serum (Biotrol-33-plus, Biotrol, Paris, France) was treated in parallel with samples and served as a control in plasma and tissue lipid analysis.
Plasma insulin concentration was measured by homologous RIA using rat insulin standard (Linco Research, St. Charles, MO) because the assay is 100% cross-reactive with rat and human insulin. The lowest limit of detection was 0.1 µg/L, and the intra- and interassay CV were 2.7 and 3.1%, respectively. RIA of plasma leptin concentration used a homologous assay incorporating anti-rat leptin antibody and rat leptin as the standard (Linco). The lowest limit of sensitivity was 0.5 µg/L, and the intra- and interassay CV were 1.5 and 2.5%, respectively. The glucose concentrations in plasma and urine (sampled from bladder) were determined by an enzymatic procedure (D-glucose kit, Biopharm, Darmstadt, Germany).
Plasma lipoproteins (from arterial blood) were separated on a density gradient by preparative ultracentrifugation. After centrifugation in a TST 41.14 (Kontron, Zurich, Switzerland) swinging-bucket rotor (100,000 x g for 24 h), the gradient was fractionated (500 µL fractions) and cholesterol was determined by the method described above.
The ferric reducing ability of plasma (FRAP) was determined in plasma using the method of Benzie and Strain (20
), which measures the reduction of ferric iron to the ferrous form in the presence of antioxidant components. The colorimetric measurement was performed at 593 nm and the reaction was monitored for up to 8 min on 25-µL samples. Results were calculated from a standard scale of FeSO4. Thiobarbituric acid-reactive substances (TBARS) in urine were measured by the modified procedure of Lee and al. (21
). Malondialdehyde (MDA) calibration standard curves were freshly prepared from 10 nmol/L tetraethoxypropane (TEP) and treated in the same way as the test sample. The amounts of TBARS in urine were expressed as equivalents of MDA and corrected by nmol of urinary creatinine. MDA was also determined in heart homogenates after lipid peroxidation induction with a 2 mmol/L FeSO4/50 mmol/L ascorbate mixture for 30 min in a 37°C water bath in an oxygen-free medium, using TEP as a standard (22
).
Polyphenol analysis.
Lyophilized apple (500 mg) was extracted with 30 mL of methanol/H2O (70:30) and ground with a polytron for 1 min followed by 15 min centrifugation at 3100 x g, 4°C. The supernatant was recovered and the pellet was extracted twice with 15 mL of methanol/H2O (70:30) followed by a 15-min centrifugation at 3100 x g, 4°C. Supernatants were pooled and 20 µL of a diluted extract was injected into a HPLC system with an 8-electrode coulometric detection (ESA CoulArray, Eurosep, France). HPLC was performed using gradient conditions (column oven temperature, 35°C) 150 x 4.6 mm Hypersil BDS C18–5 µm column (Life Sciences International, Cergy, France). The mobile phases consisted of 30 mmol/L NaH2PO4 buffer, pH 3, containing 5% acetonitrile (A) and 50% acetonitrile (B). The gradient was: 0 -3 min: 100% (A); 3–73 min: from 100% (A) to 100% (B); 73–75 min: 100% (B); 75–95 min: 100% (A), with a flow rate of 0.8 mL/min. The autosampler was at 4°C. The potentials were set at 0, 120, 240, 360, 480, 600, 720 and 840 mV (Fig. 1
).
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Values are given as the means ± SEM; where appropriate, data were tested by two-way ANOVA using the general linear models procedure of the SuperANOVA package (Abacus, Berkley, CA). Individual comparisons were made by least-squares means. Differences of P < 0.05 were considered significant.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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At the beginning of the experiment, the fa/fa Zucker rats were marginally heavier than the Fa/- rats; they were slightly hyperphagic (+15%) and showed a markedly greater weight gain during the experiment (+150 g vs. +105 g, respectively, P < 0.0001) as reflected by differences in food conversion efficiency (Table 2
). Dietary lyophilized apple did not affect food consumption or weight gain. Absolute heart weight did not differ among groups, but relative heart weight was 0.35 g/100 g body in lean rats and < 0.30 g/100 g in obese rats (P < 0.001). The liver represented 4.7–4.8% of the body weight of lean rats; it was markedly heavier both in absolute value (P < 0.0001) and in percentage (6% of body weight) in obese Zucker rats. Absolute liver weight was 10% lower in obese rats fed lyophilized apple than in controls. The cecal weight did not differ between lean and obese Zucker rats fed the control diet, whereas the apple diet elicited an enlargement of the cecum in both phenotypes. This corresponded chiefly with an accumulation of digesta in the cecum (60–90%) and to a slight hypertrophy of the cecal wall itself. The cecal SCFA pool was markedly enhanced due to apple diet consumption in both lean and obese Zucker rats (P < 0.05). In addition, there were qualitative changes in the SCFA molar ratio because the percentage of butyric acid was strongly elevated in rats fed the apple diet (up to 17% of total SCFA instead of 8–9% in rats fed the control diet).
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Plasma levels of cholesterol and triglycerides were 2.0 and 1.0 mmol/L, respectively, in lean Zucker rats (Table 3
). In contrast, obese fa/fa rats had higher plasma cholesterol concentrations, ranging from 4 to 5 mmol/L, but plasma triglycerides did not differ from lean rats. The apple diet did not affect plasma cholesterol or triglycerides in lean rats, but it tended to lower (P = 0.013) circulating FFA. Cholesterolemia of obese Zucker rats was substantially reduced in the apple-fed group (-22%), whereas plasma triglycerides and FFA were not altered. Analysis of cholesterol distribution in various lipoprotein density classes (Fig. 2
) indicated that most of the plasma cholesterol in lean Zucker rats was present in the d > 1.060 kg/L fraction (essentially HDL) and in the d < 1.006 kg/L fraction (referred to as triglyceride-rich lipoproteins, TGRLP). In contrast, there was no significant effect of the apple diet on the lipoprotein profile of lean rats. Obese hypercholesterolemic rats showed a clearly different profile of lipoprotein cholesterol, i.e., the major part of cholesterol (85%) was present in the d >1.006 kg/L lipoproteins together with a noticeable amount in the 1.006 < d < 1.060 kg/L fraction (density range of LDL) shouldering the large peak of d >1.060 kg/L lipoproteins. This HDL peak was 1.8-fold greater than in lean rats, whereas the quantities of cholesterol present in the TGRLP were not different from lean rats. Obese Zucker rats fed the apple diet showed moderately reduced HDL cholesterol (HDL-C; -26%) but drastically lowered LDL cholesterol (LDL-C; -70%). The LDL-C/HDL-C ratio was particularly high in obese Zucker rats fed the control diet (0.47) compared with lean Zucker rats, and it was strongly depressed in rats fed the apple diet to 0.19, a value relatively close to that in lean Zucker rats (0.15).
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. Triglyceride accumulation in liver of lean Zucker rats was quite limited and also unresponsive to the apple diet, whereas obese Zucker rats exhibited a marked steatosis (9 g triglycerides/100 g fresh liver; 36 g/100 g dry matter). In obese Zucker rats fed the apple diet, this triglyceride accumulation was less pronounced (-50%), but still substantially greater than in lean rats. Heart cholesterol concentrations were unaffected by obesity and diet in the present experiment. However, there was also an accumulation of triglyceride in heart tissues of obese rats which was markedly counteracted by consumption of the apple diet. Cholesterol intake and digestive balance of bile acids.
Due to hyperphagia, obese Zucker rats consumed 15% more cholesterol than Zucker lean rats (Table 4
). The small intestinal pool of bile acids, representative of the major part of the rat bile acid pool, was 40 µmol in lean and obese Zucker rats fed the control diet. Consumption of the apple diet led to a marked enlargement of this pool, up to 61 µmol in lean Zucker rats and 77 µmol in obese Zucker rats. In rats fed the control diet, fecal excretion of bile acids was 1.2% of cholesterol intake in lean Zucker rats but only 0.8% in obese Zucker rats. There was a considerable increase in bile acid elimination in the feces in rats fed the apple diet (+56% in lean and +30% in obese), which comprised a greater proportion of cholesterol intake in lean than in obese Zucker rats (2.8 and 2.4%, respectively).
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The FRAP value, which reflects the antioxidative capacity of protection of plasma, was markedly higher in obese than in lean Zucker rats (Table 5
). The apple diet did not affect the FRAP value in lean or obese rats. The heart MDA was similar in lean and obese rats fed the control diet; it was markedly lower in rats fed the apple diet, and obese rats were the most responsive to this diet. Urine MDA excretion was roughly consistent with changes in tissue MDA, i.e., MDA excretion was similar in rats fed the control diet, and it was markedly reduced in both lean and obese rats fed the apple diet.
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). In parallel, protein elimination was markedly greater in obese rats than in lean rats fed the control diet. Consumption of the apple diet did not change glucosuria or proteinuria in lean rats, but it markedly reduced both elimination processes in obese rats, to the values observed in lean rats fed the control diet.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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100 g fruit dry matter per day for humans (i.e., 4–5 apples). This represents a high intake of only one type of fruit, but this is not disproportionate if allocated among various type of fruits (Rosacae, Citrus and other tropical fruits, berries). The present apple diet contained only 2.4% fiber (like fresh apple), which is a relatively low level for a rat experimental diet; furthermore only 40% of the fiber fraction was soluble, essentially pectin. The effect of pectin on lipid metabolism has been studied in both humans and animal models (23
), but apple pectin has not been examined (4
,12
) as the fraction responsible for the hypocholesterolemic effect of apples (4
). In the present work, obese Zucker rats exhibited a greater response to dietary cholesterol (up to 4.6 mmol/L in obese controls) compared with either the lean rats or Wistar rats fed the same diet (9
). The apple diet showed an unequivocal plasma cholesterol–lowering effect in obese rats (-22%), whereas no effect was found in lean rats. In male Wistar rats, using a very similar diet, a small but significant effect on plasma cholesterol (-10%) was observed, together with changes in the lipoprotein profile (10
). In the present work, the lipoprotein profile of lean rats was typically that of an "HDL" species, with a substantial part of cholesterol in the d >1.060 kg/L fraction, and this profile was not altered by the apple diet. In the obese rats, much of the cholesterol was actually present in the HDL fraction, but noticeable amounts were also present in a lighter fraction with a density similar to LDL, as previously reported (24
, 25
). Recently, Blay et al. (24
) demonstrated a considerable increase in the mean volume of LDL and HDL particles (9- to 12-fold) and argued that altered lipoprotein size and apoprotein distribution in obese rats could seriously disturb cholesterol interchange and result in hypercholesterolemia. The apple diet effects in obese rats were observed mainly in the 1.006 < d < 1.060 fraction (LDL), which was drastically depressed (-70%). The HDL fraction was also lowered, but to a lesser extent (-28%). This difference in responsiveness to dietary factors between LDL and HDL cholesterol has been identified in Zucker rats fed fibers, especially pectin (25
). Although the rat is not an optimal model for atherogenesis, the changes in the (1.006 < d < 1.060)/(d > 1.060) cholesterol ratio are reminiscent of the LDL-C/HDL-C ratio measured in humans to evaluate the cardiovascular disease risk. The ratio observed in obese rats fed the apple diet (0.19 vs. 0.47 in obese rats fed the control diet) suggests interesting health effects of apples. The actual effectiveness of apples (3 apples/d) for plasma cholesterol–lowering in humans has been estimated to be -6 to -10% (8
), which warrants further investigation using polyphenol-rich cultivars.
Hypertriglyceridemia has frequently been described in obese Zucker rats (26
,27
) but not systematically (24
), in keeping with the present work. The regulation of lipid synthesis is profoundly disturbed in obese Zucker rats (28
) and fat accumulation in these rats (2 g/d in excess of lean rats) might create a cholesterol demand that is fulfilled by uptake of TGRLP because in situ cholesterogenesis is likely inactive (29
). In contrast to plasma, there was a massive triglyceride accumulation in the liver of obese Zucker rats, which was effectively reduced by the apple diet (-52%). The triglyceride-lowering effect of apple components in liver and heart in obese rats is likely complex, and could be connected to hormonal changes as shown for unavailable carbohydrates (30
). However, in the present work, hyperinsulinemia was not affected by the diet and circulating leptin was slightly depressed in rats fed the apple diet; this could reflect a metabolic effect on leptin production by adipose cells (31
). The observation that apples can limit liver steatosis is interesting because this syndrome has been recognized with increased frequency for 20 y; its natural course is relatively asymptomatic but liver cirrhosis, together with all its sequelae, may develop (32
). It is noteworthy that there was also an accumulation of triglycerides in the heart of obese rats and this accumulation was practically halved with apple consumption.
In normal Wistar rats, 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol-7-hydroxylase (C7H) are frequently up-regulated by fiber feeding, even when the diet contains cholesterol (33
). However, little is known about the specific regulation of the key enzymes of cholesterol metabolism in obese Zucker rats that are spontaneously hypercholesterolemic (14
,16
,24
–26
). It has been shown that C7H activity is lower in obese than in lean Zucker rats and, in the former, there was little diurnal variation of C7H activity (34
). The marked rise in the bile acid pool elicited by the apple diet, in both lean and obese rats, suggests the existence of dietary factor(s) that may induce bile acid synthesis. The C7H gene (CYP7a) is subjected to an elaborate autoregulatory cascade mediated by nuclear receptors (35
,36
), and it is conceivable that some elements of this regulation may differ between Zucker and conventional rat strains.
The components present in apples may have various effects on the enterohepatic cyling of bile acids, i.e., adsorption of bile acids on cell wall components such as pectins or on complex unabsorbable structures such as polymerized phenolics (37
,38
). Interactions between bile acids and apple constituents are complex (39
), and it is conceivable that maximal trapping might require a synergism between fibers and phenolic compounds. This could explain the enlargement of the bile acid small intestinal pool, the major part of the body pool in rats (40
), in the apple-fed diet groups. Such a change in bile acid (+72 and +79% in lean and obese, respectively) with an apple diet containing 2.5% fiber was found previously when diets contained at least 5% soluble fiber, for example, guar gum (33
,41
). Considering that only 40% of the apple fiber fraction is soluble (chiefly pectin) and likely to have an effect on lipid metabolism (23
,42
), the observed effects seem disproportionate to the soluble fiber level in apples. In fact, cell wall polysaccharides should probably be considered in their totality, as well as the possibility that other plant compounds play a role in the effects of apple on steroid digestive balance. Changes in intestinal passive transfer of bile acids are still poorly understood, whereas data suggest that the apical sodium-dependent transporter (ASBT) in the ileum may be increased in parallel with an enlargement of the intestinal pool by fibers, as shown by arteriovenous differences in the ileum of rats fed guar gum (30
,37
), or by the increased expression of ileal ASBT of rats fed psyllium (43
). This, together with large intestine reabsorption (41
, 33
), could explain why the changes in fecal bile acid excretion are not directly proportional to those of the digestive pool.
Various apple constituents are potentially protective against peroxidative attack, chiefly water-soluble compounds such as vitamin C and absorbable polyphenols. The vitamin C concentration of apples is 100 mg/kg; however, this supply is likely not critical because rats can synthesize ascorbic acid. Polyphenols could also play a protective role because they were present in substantial quantities in the "Reinette Canada" cultivar (17
). Previous investigators have reported a potent inhibitory effect of apple juice on human LDL oxidation in vitro (44
) and on oxygen radical absorbance capacity values (7
). Various types of phenolic compounds are present in apples (Fig. 1)
, with different antioxidative potencies and bioavailabilities (6
). For example, polymerized compounds such as proanthocyanidins have been identified as biological antioxidants (45
) but their intestinal absorption is probably very low. Low-molecular-weight phenolics (catechins, phenolic acids, quercetin and phloretin compounds) are absorbable, to different degrees, and are likely to exert protective effects in plasma as well as in tissues (46
,47
). MDA excretion can be considered to be a reflection of the intensity of lipid peroxidation, but it must be noted that only certain lipid peroxidation products yield MDA and there are additional sources of MDA besides this process (48
). The apple diet clearly lowered MDA excretion, suggesting a reduced peroxidation of lipids in plasma and tissues, but confounding factors might also account for reduced MDA production, such as the lowering of plasma and liver lipids by the apple diet in obese Zucker rats. Apples were nearly as effective in lean rats (showing no dyslipemia nor liver steatosis) as in obese rats, which suggests that the partial normalization of lipid variables in the latter had little consequence on reduced MDA production and excretion. A reduction of MDA excretion concomitant with a rise in FRAP value was reported previously in Wistar rats fed an apple diet (10
). In the present experiment, it seems paradoxical that the plasma of obese (prediabetic) rats was less affected than that of controls, but this type of response has already been reported in experimental diabetes (49
) and could stem from changes in vitamin E distribution in the body. The fact that apple constituents had little influence on the FRAP values in Zucker rats, while depressing the overall MDA production and its local tissue production (especially in the heart), supports the view that they could be more effective in tissues. The intracellular effects of flavonoids, against pancreatic damage in experimental diabetes (50
) or through protection of vitamin C and E from consumption by oxidative processes have already been reported (51
). The reduction of heart MDA by apples is interesting because several studies suggest that reactive oxygen species contribute to the physiopathology of heart failure (52
). Some doubts remain concerning the actual source of heart MDA, and the lipid peroxidation it reflects likely has distinct consequences when fatty acids from fat stores or from structural phospholipids in biological membranes are affected.
Glomerulopathy is an early complication of diabetes, leading to proteinuria, which reflects decreased albumin endocytosis with increased lipid peroxidation in the proximal tubule (14
). Compared with lean controls, obese Zucker rats exhibited moderate proteinuria and glucosuria; although these rats were not definitely hyperglycemic at the time of blood sampling, they were apparently at an early stage of the progressive nephropathy that develops spontaneously in this strain. It is noteworthy that the apple diet reduced proteinuria in obese rats to the basal value observed in lean rats. The factors involved in this protective action are complex and could encompass the following: 1) improvement of plasma lipid variables (especially cholesterolemia and FFA) known to aggravate the progression of renal disease in the model (53
); 2) limitation of oxidative damage in kidneys; and 3) various additional factors such as blunted hypertension or favorable alkalinizing effects through K+ malate supply by apple consumption (54
). Additional studies are required to determine whether the apple diet could compensate for the consequences of a preexisting nephropathy or counteract the emergence of this pathology.
In conclusion, apples appear to exert a diversity of interesting effects on a plurimetabolic syndrome model. The specific role of the apple constituents on the various physiologic or metabolic processes, and the possible synergistic effects are yet to be clearly identified. A better knowledge of the health effects of apple consumption would be relevant in human nutrition; for example, Vinson et al. (55
) estimated that apples provide 20–25% of the per capita consumption of fruit polyphenols in the United States. This percentage is probably higher in areas in which the consumption of tropical fruits is less prevalent and/or apples cultivars rich in polyphenols are well represented in markets.
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FOOTNOTES |
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2 O.A. is funded by a Ph.D. scholarship from the scientific committee of the Agency for Promotion of Fresh Fruits and Vegetables (APRIFEL, Paris, France).
4 Abbreviations used: C7H, cholesterol-7-hydroxylase; FFA, free fatty acid; FRAP, ferric reducing ability of plasma; HDL-C, HDL cholesterol; LDL-C, LDL cholesterol; MDA, malondialdehyde; SCFA, short-chain fatty acid; TBARS, thiobarbituric acid-reactive substances; TEP, 1,1,3,3-tetraethoxypropane; TGRLP, triglyceride-rich lipoprotein.
Manuscript received 14 February 2002. Initial review completed 12 March 2002. Revision accepted 8 April 2002.
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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