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Journal of Lipid Research, Vol. 48, 1550-1558, July 2007
Copyright © 2007 by American Society for Biochemistry and Molecular Biology




* Division of Gastroenterology, Robert-Bosch-Hospital Stuttgart, Stuttgart, Germany
Department of Physiology of Nutrition, Hohenheim University, Stuttgart, Germany
Synlab Center of Laboratory Diagnostics, Heidelberg, Germany
** Department of Medicine, University of Freiburg, Freiburg, Germany
Published, JLR Papers in Press, April 12, 2007.
1 To whom correspondence should be addressed. e-mail: christian.schaefer{at}rbk.de
| ABSTRACT |
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Supplementary key words low density lipoprotein very low density lipoprotein high density lipoprotein 2 high density lipoprotein 3 triglycerides beer wine body mass index apolipoprotein
Abbreviations: apoA-I, apolipoprotein A-I; BMI, body mass index; CE, cholesteryl ester; CETP, cholesteryl ester transfer protein; FC, free cholesterol; HDL-CH, high density lipoprotein-cholesterol; LDL-CH, low density lipoprotein-cholesterol; PAL, physical activity level; PL, phospholipid; PLTP, phospholipid transfer protein; SM, sphingomyelin; TG, triglyceride
| INTRODUCTION |
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This cross-sectional study in healthy working men was performed to further examine the effect of various alcohol consumption patterns on the lipid profile. Our working hypothesis was that moderate alcohol consumption induces not only quantitative, but also qualitative, changes of the lipid fractions, in particular HDL. Using extensive fractionation of plasma lipids and measurement of lipid and apolipoprotein components, we show that alcohol consumption is associated with increases of cholesterol and other components of the HDL fraction. In addition, two significant qualitative changes were identified that might affect atherogenicity: a shift from small, dense HDL3 to lipid-rich HDL2 (mainly HDL2a), and a significant phospholipid (PL) enrichment of HDL in all subfractions.
Because not only alcohol consumption but also lifestyle factors, such as nutrition, physical activity, smoking, age, and obesity, may influence lipid metabolism, we performed a thorough interview to characterize the influence of these factors on HDL. Furthermore, it was examined whether consumption patterns (i.e., preference for beer or wine) had differential effects on high density lipoprotein-cholesterol (HDL-CH), because the data from several epidemiological studies had been inconclusive (reviewed in Refs. 6, 7).
| SUBJECTS AND METHODS |
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Of the 290 recruited persons, 11 were excluded for various reasons: self-reported previous myocardial infarction or ischemic stroke (n = 2), heavy (
75 g/day) or highly irregular alcohol consumption (n = 6), unreliable diet history (n = 1), and antihyperlipidemic medication (n = 2).
The remaining 279 individuals were grouped according to their amount of daily alcohol consumption. Group 1 comprised 62 persons with an alcohol consumption of
5 g/day, 172 persons with moderate alcohol consumption of >5 and
30 g/day were assigned to group 2, and 45 males with increased alcohol consumption of >30 and <75 g/day were assigned to group 3. Of group 1, 14 persons were teetotalers. To characterize the consumption patterns of groups 2 and 3, we defined a preference for beer as >80% alcohol calories consumed as beer and, likewise, a preference for wine versus mixed consumption (not meeting any of these criteria).
Evaluation of nutrition and physical activity
To evaluate the nutritional profile of each subject, an experienced interviewer carefully reviewed the intake of food and beverages (including alcoholic beverages) during the past 7 days using a computer-based system, which provided photographs for the assessment of portion sizes. The accuracy of the interview data compared with the actual food intake had been validated previously (8). Nutrient intake was analyzed using the German Nutrient Data Base (Bundeslebensmittelschlüssel), comprising 150 nutritional variables for 11,000 food items. In addition, the physical activity level (PAL) and other lifestyle features were evaluated based on interview data. The plausibility of the total caloric intake was controlled for by calculating the energy demand (ED) for each individual depending on the resting energy level (REE) (9) and PAL: ED = (REE + PAL) x 1.06.
Laboratory analyses
The obtained blood was quickly transported to the laboratory of the Robert-Bosch-Hospital, where analyses of routine parameters were performed using standard equipment. EDTA plasma samples were shipped at ambient temperature to the Department of Clinical Chemistry, University of Freiburg, where lipoprotein metabolism and lipoprotein subfractions were analyzed by sequential preparative ultracentrifugation (10).
Briefly, VLDL (d < 1.006 g/ml), LDL (d = 1.0191.063 g/ml), and HDL (d = 1.0631.21 g/ml) were isolated by sequential preparative ultracentrifugation from 5 ml of plasma (50.3 Ti rotor, L8-55M centrifuge; Beckman Instruments). Analogously, HDL subfractions were obtained: HDL2b (d = 1.0631.100 g/ml), HDL2a (d = 1.1001.150 g/ml), and HDL3 (d = 1.1501.210 g/ml). Lipids in each (sub)fraction were determined as follows (10). Cholesterol and triglycerides (TGs) were determined enzymatically with the cholesterol oxidase-peroxidase amino phenazone phenol and the glycerol-3-phosphate oxidase-peroxidase amino phenazone phenol methods (Roche Diagnostics, Mannheim, Germany), respectively. Free cholesterol (FC) and PLs were determined enzymatically with the cholesterol oxidase-peroxidase amino phenazone phenol method and by phospholipase D, cholinoxidase, and peroxidase, respectively, with commercially available reagents (Wako Chemicals, Osaka, Japan). The concentration of esterified cholesterol was calculated from the difference of total cholesterol and FC. In addition, apolipoproteins A-I and A-II (apoA-I and apoA-II) were determined immunoturbidimetrically [anti-apoA-I from Greiner (Flacht, Germany) and anti-apoA-II from Kamiya Biomedical (Seattle, WA)]. This comprehensive analysis was performed on each individual sample.
Statistics
Unless indicated otherwise, results are reported as means ± SD. The levels of significance between groups 1, 2, and 3 were calculated using ANOVA with Tukey's honestly significant difference test for post hoc analysis. Prerequisites for ANOVA were normal distribution and homogeneity of variances; otherwise, a log transformation of the data was performed. If the conditions were not met, a Kruskal-Wallis test, followed by a Mann-Whitney U-test with Bonferroni correction for post hoc evaluation, was applied.
We also conducted a multivariate analysis of the influence of various factors on HDL components. The multiple linear regression model was calculated according to the formula y = c1x1 + c2x2 + ...cnxn + a (where y is the dependent variable, c1...cn are calculated coefficients, x1...xn are independent variables, and a is the intercept). As independent variables, alcohol consumption, the influence of beer versus wine, anthropometric characteristics, calorie intake, and energy output were chosen. To compare beer versus wine, we determined the percentage of daily beer consumption [RCbeer vs. wine(%)] in relation to the sum of beer and wine consumption, based on alcohol (EtOH) content [EtOHbeer x 100/(EtOHbeer + EtOHwine)]. Drinks other than beer or wine were disregarded, because they were quantitatively unimportant (Table 1 ).
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| RESULTS |
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-glutamyl transferase) became evident.
Overall lipid analysis and lipid fractions
In nonfractionated plasma, plasma cholesterol, PLs, and TGs were similar between groups 1 and 2 (Table 2
). Higher alcohol consumption (group 3) was associated with slightly increased cholesterol levels compared with group 1. TG concentrations exhibited great variability. In group 3, increased TG levels compared with group 2 were measured.
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Changes in the composition of HDL (HDL2 vs. HDL3)
The density of HDL particles is determined mainly by the lipid-to-protein ratio. Within HDL, the dense HDL3 subfraction containing a low percentage of lipids can be separated from HDL2, which contains intermediate HDL2a and buoyant HDL2b. Because the antiatherogenic effect of each of these subfractions may differ, it was of interest to examine the association between alcohol consumption and the cholesterol content of each of these subfractions.
In each of the HDL subfractions, the cholesterol content was increased in alcohol consumers (groups 2 and 3) compared with group 1 (Table 3 ). However, differences between the dose responses of the HDL subfractions were observed. Comparing group 2 and group 1, HDL2b-CH was increased by 24% and HDL2a-CH was increased by 25%, whereas HDL3-CH showed an increase of only 10%. In group 3, this dissociation was even more pronounced (HDL2b-CH, 28%; HDL2a-CH, 37%; HDL3-CH, 11% increase vs. group 1).
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Increase of the PL component
Because PLs, along with apoA-I, apoA-II, and FC, constitute the outer shell of HDL, presumably interacting with other receptors or soluble enzymes, it was of particular interest to study the ratios between these components in total HDL and its subfractions (Table 4
). We found a stepwise increase of PL versus apoA-I in the alcohol-consuming groups, whereas the ratios between other surface components (i.e., FC, apoA-I, and apoA-II) remained constant. Consequently, the PL/FC ratio was increased. Analysis of the subfractions indicates that in dense HDL3 and intermediate HDL2a, the alcohol-associated increase of the PL portion was attributable to an increase of PL (compared with apoA-I), without major changes of the ratio of FC to apoA-I, as opposed to HDL2b, in which the relative enrichment of PL obviously results from both a depletion of FC and an increase of PL.
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Multivariate analysis: influence of various factors on HDL components
We defined a multivariate model describing HDL components as a linear function of various nutritional, anthropometric, and lifestyle variables (Table 5
). Parameters that significantly increased cholesterol, PL, and apoA-I in HDL were alcohol consumption and PAL, whereas BMI was negatively related to HDL-CH. Alcohol consumption was the only parameter increasing TG and apoA-II concentrations in the HDL fraction. No significant effects of the type of beverage (beer vs. wine), age, or smoking were observed. Calorie intake significantly decreased PL and apoA-I content, whereas PAL was associated with an increase of these variables. In an extended analysis, the influence of carbohydrate, fat, protein, and fiber uptake was examined, but none of these parameters had any statistical effect on each of the HDL components (data not shown).
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| DISCUSSION |
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Several case-control and epidemiological studies indicate that moderate alcohol consumption reduces cardiovascular mortality and that this effect is associated with the increase of HDL-CH (5, 11). In their meta-analysis, Rimm et al. (5) calculated an increase of HDL-CH of 0.134 mg/dl per gram of alcohol of daily consumption for men (for women, it was 0.095 mg/dl per gram of alcohol). In our study, the coefficient reached 0.24 mg/dl per gram of alcohol of daily consumption for healthy male persons. Several factors may account for this difference. Rimm et al. (5) did not adjust their model for BMI and smoking, both of which have decreasing effects on HDL-CH. Also, we could not find evidence for their statement that the effect of alcohol on HDL-CH was more pronounced in subjects with a sedentary lifestyle. In our multivariate analysis, physical activity had an independent and significantly positive influence on HDL-CH levels.
The quantitative change of HDL-CH is thought to be the result of increased hepatic production or an increased transport rate of apoA-I and apoA-II (1214). Other data indicate that alcohol might interfere with the activity of the cholesteryl ester transfer protein (CETP), which mediates cholesterol transfer from HDL to LDL (15). Additionally, it has been shown by ex vivo experiments that moderate alcohol consumption increases the efflux of FC from macrophages to HDL, mainly via the ATP binding cassette transporter 1 (16). Large amounts of alcohol, on the other hand, may result in impaired cholesterol efflux (17).
One of the major findings of our study is the divergence of the dose relationships between the HDL subclasses. Compared with controls, the alcohol-related increase of cholesterol, PL, and TG in HDL2a was more than twice that of the increase in the HDL3 subclass. The changes in HDL2b were similar to those in HDL2a, but somewhat less pronounced. The shift toward HDL2 indicates a higher HDL lipid load in alcohol consumers (Table 3). This phenomenon is confirmed by other examinations (1821), whereas some groups found a predominant increase of HDL3 (22, 23) or no relevant change in the relation of HDL2 to HDL3 components (11, 24). These discrepancies might be explained by variant study design and the disregard of powerful confounders, such as obesity and smoking.
The increased lipidation of HDL, which may be attributable to an increased cholesterol efflux from peripheral cells (16), could indicate an augmentation of reverse cholesterol transport. This can be inferred from studies showing that risk factors such as obesity or hypertriglyceridemia are associated with the opposite change (i.e., a decrease of large HDL2 vs. an increase of small preß HDL or HDL3 particles) (25, 26), which has been confirmed for obesity by the multivariate analysis of our study. Interestingly, the influence of alcohol on the HDL2-CH/HDL3-CH balance seems to "override" the opposing influence of high BMI or increased TGs, as subjects with an alcohol consumption of >30 g/day (group 3) exhibited the highest HDL2-CH/HDL3-CH ratios despite the increased BMI and TG values (Tables 13).
It could be argued that an increase of HDL2 cholesterol might be ambiguous, because this fraction is the substrate of cholesterol transfer protein, which shifts CEs to proatherogenic LDL particles. Thus, we examined the balance between CEs and FC in HDL but found no significant change.
From a clinical point of view, the cardioprotective relevance of HDL2 is supported by several population studies, such as the Québec and Kuopio trials (27, 28). In other population studies, such as the Physicians' Health Study (29) and the Caerphilly and Speedwell trials (30), HDL3 was the strongest predictor, but risk reduction was shown for HDL2 as well.
The other qualitative change of HDL apart from the increase in lipid-rich particles is the alcohol-induced relative increase of the PL components compared with the other HDL components (cholesterol, TG, apoA-I, and apoA-II). This change was observed in all HDL subfractions and was most pronounced in persons with increased alcohol consumption. In the current multivariate analysis, a highly significant association between alcohol consumption and an increase of the PL/cholesterol ratio was detected, although other factors (BMI, energy intake, and physical activity) seemed to be involved in the regulation of this balance as well.
The relative increase of the PL component may have important implications concerning the antiatherosclerotic effects of HDL. Because this change occurs in the surface layer of HDL that interacts with cellular receptors or serum components, it may be of particular importance in two respects: the increase of PL may reduce the inflammatory process in the vessel wall, because HDL particles reconstituted with PLs inhibited the cytokine-induced activation of endothelial cells in vitro (31); and PLs are obviously required for an effective cholesterol efflux from peripheral cells to ApoA-I-containing lipoprotein particles (32).
In this context, it could be argued that the PL portion might contain compounds associated with an increased atherogenic risk, such as sphingomyelin (SM). However, it is very unlikely that SM plays such a role, for the following reasons. i) HDL-like LpA1 containing SM may be even more effective at effluxing cholesterol from fibroblasts than LpA1 without SM (33). ii) There is evidence from animal experiments that excess SM induces an increase of VLDL-CH and LDL-CH but a decrease of HDL-CH (33, 34). This situation is contrary to that found in the alcohol consumers of our study, so a general increase of atherogenic SM is unlikely. iii) In alcohol-consuming humans, no change of the SM content in platelets occurred, and even a decrease of SM in erythrocyte membrane occurred (35, 36). Despite this circumstantial evidence, further studies are needed to delineate the influence of alcohol on PL composition in HDL.
The exact mechanisms leading to the increase of the PL/cholesterol ratio remain unclarified. Several transfer enzymes promote the exchange of lipid components between HDL, LDL, and VLDL. High-level alcohol consumption results in depressed CETP activity, which is associated with an increase of HDL3b (medium HDL3) at the expense of HDL2a. In addition, alcohol-induced phospholipid transfer protein (PLTP) activity, which shifts PL from TG-rich lipoproteins to HDL, appears to increase HDL2b at the expense of HDL3a (large HDL3) (37). The reduction of CETP and the increase of PLTP were confirmed by another study, which also observed an increase in the net PL transfer from apoB-containing lipoproteins to HDL in alcoholics (38). However, none of these enzymes seems to be changed in moderate alcohol consumers (3941). In our study, the analysis of HDL2a and HDL3 composition shows an isolated dose-dependent increase of the PLs compared with apoA-I, whereas the ratio of FC to apoA-I remained unchanged, which argues for a role of PLTP in PL enrichment in these HDL subclasses. In lipid-rich HDL2b, the situation is more complex, because both PL enrichment and FC depletion occur.
Another possible mechanism for the PL enrichment is highlighted by an in vitro study showing that ethanol at concentrations found in heavy drinkers inhibits the incorporation of cholesterol into preß-like particles containing apoA-I and phosphatidylcholine, whereas this phenomenon was not observed in particles without this PL (42). Thus, alcohol, at least at high concentrations, might influence the balance between PL and cholesterol at this very early step of HDL assembly.
In terms of antiatherogenicity, it is also of interest to study the effect of alcohol consumption on a third feature of HDL, the relation of HDL particles containing only apoA-I, termed LpA1, to particles containing apoA-I and apoA-II (LpA1/A2), because LpA1 has a higher potency than LpA1/A2 in effluxing cellular cholesterol (43, 44). In our study, the concentrations of LpA1 and LpA1/A2 were not measured directly. However, comparison between the groups and multivariate analysis showed no influence of alcohol consumption on the ratio of apoA-I to apoA-II (Tables 4, 6), which allows the conclusion that LpA1 and LpA1/A2 are increased in a similar manner. This conclusion is in accordance with two studies directly showing an alcohol-related increase of both lipoprotein species (24, 45). Yet, other data suggest that alcohol consumption mainly increases LpA1/A2 (18, 46).
It is somewhat surprising that the shift from HDL3 to HDL2 does not result in an increase of apoA-I, given the fact that HDL2 consists mainly of LpA1, with most of LpA1/A2 being associated with HDL3. Two phenomena may account for the constancy of the apoA-I/apoA-II ratio despite the relative increase of HDL2 in alcohol consumers (Table 4): i) the ratios of the two apolipoproteins in HDL3 and in HDL2a, the major portion of HDL2, are almost alike; ii) HDL2b, the minor portion of HDL2, showed a slight, although insignificant, decrease in this ratio in group 3, indicating some loss of LpA1 in this subfraction.
Apart from the mere alcohol effect, we examined whether beer or wine consumption had a differential effect on the composition of the HDL fraction. The multivariate analysis showed no significant differences between relative beer and wine consumption on all HDL components and on qualitative changes. Thus, our data are in accordance with the general assumption (5) that the increase of HDL-CH is an effect of the alcohol itself, particularly in the range of moderate alcohol consumption.
The effect of alcohol must be interpreted in the context of other lifestyle and anthropometric parameters. In our multivariate model, obesity and factors predisposing to it, such as high caloric intake and scarce physical activity, are associated with a reduction in essential HDL components; thus, they counteract the influence of alcohol on HDL (Table 4). Beyond this, obesity tilts the balance between apoA-I and apoA-II toward the latter, resulting in a relative increase of LpA1/A2 at the cost of LpA1, which is an additional indication of impaired reverse cholesterol transport (Table 5). Cigarette consumption had no statistically significant effect, probably because of the low percentage of smokers in this study, whereas age, interestingly, is associated with a "favorable" increase of the apoA-I/apoA-II ratio.
In summary, this study supports previous data showing a powerful influence of moderate (530 g/day) and increased (3075 g/day) alcohol consumption on the concentration of HDL-CH. An additional effect, which deserves further research, is the compositional and qualitative change of HDL particles in alcohol-consuming persons, such as PL enrichment, which may inhibit the inflammatory process associated with the formation of atheromatous plaques, and the relative increase of lipid-rich HDL2 versus HDL3, which indicates a more effective reverse cholesterol transport.
| ACKNOWLEDGMENTS |
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Manuscript received May 3, 2006 and in revised form December 4, 2006 and in re-revised form February 28, 2007.
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