In this study, we have observed that α-CD, when given in the diet at a rate of 10% of the fat (w/w), significantly reduces plasma TC, PL, FC, and CE, primarily in the plasma LDL fraction, while maintaining blood HDL-cholesterol levels in LDLr-KO mice as compared to that of the controls. Milk fat, high in saturated fatty acids and cholesterol content, was used as a fat source in order to induce elevated plasma lipid levels. This goal was achieved as demonstrated by the early onset of significant increases in plasma TC, EC, FC and PL levels between baseline and 2 weeks of feeding (). α-CD also showed its lipid lowering effects as early as 2 weeks of feeding, even though the differences just missed the significance levels (TC, p=0.053, PL, p=0.08). It should be noted that both groups of mice had the same amount of fiber in the diet. The only difference was that 21 g (10% of diet fat, w/w) of α-CD was used to replace 21 g of cellulose in the α-CD group. The difference in the lipid profile therefore couldn’t be attributed to the quantity of the fiber. These results demonstrated that α-CD is efficacious in lowering blood lipid levels not only in normal rats fed a high fat diet (6
), but also in LDL-r KO mice fed a moderate fat diet.
It should be noted that α-CD has been reported to prevent weight gain in high-fat (40% w/w) fed Wistar rats (6
). No difference, however, in body weight and food intake was identified in this 14 week study. In the present study, all mice were fed a milk fat-based diet with 21% fat (w/w). Mice in the α-CD group also ingested 2.1% of α-CD (w/w) in their diet. It is possible that a higher dietary fat content, as was used in the previous rat study (40%, w/w) (6
), is needed to show the weight loss property of α-CD. One may also speculate that mice lacking the LDL receptor may not be an ideal animal model to investigate the effect of a high fat diet on body weight regulation, because of reduced uptake of apoB containing lipoproteins in peripheral cells. However, LDLr-KO mice have the advantage of being susceptible to insulin resistance-linked to diet-induced obesity, an effect that could not be observed in apolipoprotein E-deficient (apoE-KO) mice, another common murine model of atherosclerosis (14
). Further research to investigate the insulin resistance status of these LDLr-KO mice fed the α-CD-containing diet is warranted.
Soluble dietary fibers are known to reduce blood cholesterol levels; however, a meta analysis concluded that soluble fibers reduce total cholesterol by relatively small amounts, approximately 0.045 mmol/L per gram of soluble fiber (4
). For a normal weight subject following the recommended diet of 2000 kcal and 30% fat per day, this amounts to about 4.6% reduction in total cholesterol levels. Another meta analysis of 8 controlled intervention trials reported a 4% reduction in total cholesterol levels after consuming 10.2 g psyllium per day in hypercholesterolemic subjects (15
). In contrast, we have reported that in hypertriglyceridemic obese subjects with type 2 diabetes, 6 g of α-CD (2 g/meal) per day significantly reduced serum total cholesterol by 8% (7
). In a previous rat study, α-CD added to food in the amount of 10% of the fat content reduced total cholesterol by 13.2% in low fat fed rats, whereas a reduction of 8.5% was observed in rats fed the high fat-containing diet. In the present study of LDL-r KO mice, the reduction in the plasma concentration of total cholesterol by α-CD was about 15%, more than 3 times the reduction in TC observed in humans treated with psyllium fibers (15
). Overall, these results consistently demonstrate that α-CD reduces total cholesterol levels by at least 8% when taken in an amount of 6 g/day (humans) or 10% of fat content of animal foods.
It has also been reported that α-CD preferentially binds and reduces the absorption of saturated fatty acids from the diet. Its ability to reduce saturated fatty acid absorption was found to be significantly higher than that of chitosan (16
). Because saturated fatty acids promote the hepatic synthesis of cholesterol and reduce its clearance (17
), and reduction of saturated fat intake lowers blood cholesterol levels (18
), the ability of α-CD to lower plasma cholesterol may be related to its effect on saturated fatty acid absorption. This is supported by the data shown in , showing that α-CD lowers the total level of saturated fatty acids in the plasma. FPLC analysis of the plasma () demonstrated that feeding of the α-CD diet preferentially lowers the pro-atherogenic apoB lipid fractions, leading to a major 29 % decrease in LDL, IDL and VLDL. There was no observed change, however, in the athero-protective HDL cholesterol fractions in the plasma of the studied mice, which is in agreement with the results of previous studies on the effect of fibers on plasma cholesterol levels (4
). The ratio of LDL/HDL was lower (−4.8%) in the α-CD treated mice, suggesting that α-CD treatment may lower the risk for atherosclerosis. In addition, it is now understood that the anti-atherogenic potential of HDL can vary significantly between individuals (20
). HDL from different subjects can vary in its anti-oxidant and anti-inflammatory ability (21
), although the reason for this is still not fully understood. There is evidence that the consumption of saturated fat impairs the anti-inflammatory potential of HDL, while this beneficial property improves after consuming a PUFA-rich diet (22
) Hence, besides its ability to improve the LDL-C/HDL ratio, α-CD may have other potential beneficial effects on lipoprotein metabolism through its ability to modulate the plasma fatty acid profile ().
Analysis of the plasma fatty acid profile revealed that all fatty acid concentrations were reduced in the α-CD treated group relative to the Control group. Considering the reductions in plasma triglyceride, as well as significant reductions in cholesterol ester and phospholipid levels, this finding is not unexpected. However, when the fatty acids were expressed as percent of the total lipids and the difference between the 2 groups were compared, an additional effect of α-CD was observed. α-CD reduced saturated (C16:0, C18:0, and C22:0) and trans fatty acids (C18:1 trans, and C18:2 trans), while polyunsaturated fatty acids such as arachidonic acid (C20:4 ω-6), docosahexanoic acid (C22:6 ω-3) were increased. Gallaher et al.
have reported that α-CD preferentially bound with saturated fats and promoted their excretion into the feces (16
). Our current finding thus is consistent with the fecal fat findings of Gallaher et al.
). The mechanism for this alteration would appear to be related to the higher affinity of α-CD for saturated and trans dietary fat over unsaturated fats.
Trans fatty acids are known to increase the risk of cardiovascular disease and type 2 diabetes (23
). They also cause systemic inflammation and endothelial dysfunctions, and may alter the plasma lipoprotein fractions towards a more pro-atherogenic profile (24
). In addition, a study with monkeys has shown that trans fats increased abdominal fat deposition and impaired glucose tolerance (25
). Abdominal obesity and reduced insulin sensitivity in turn increase the risk of developing type 2 diabetes. Not all trans fatty acids, however, are equally pro-atherogenic. Trans isomers of C18:1 and C18:2 have more detrimental effects than other trans fatty acids, such as C16:1 isomers (26
). A recent finding from The Cardiovascular Health Study showed that elevated plasma phospholipid trans 18:2 was associated with higher risk for fatal ischemic heart disease after adjusting for other risk factors (28
). Although it did not reach statistical significance, perhaps because of the relatively low content of trans fat in the milk fat diet used in this study, the α-CD treated group had a 25% reduction in trans C18:2 compared to the control group. This amount of reduction may have significant clinical importance. In summary, this study demonstrated that in LDLr-KO mice, feeding α-CD as 10% (w/w) of the dietary fat not only improved blood lipid levels, but also improved the fatty acid profile. This improvement was shown in reduced saturated and trans fatty acid levels with concomitant increase in polyunsaturated fatty acid levels. Considering the relative safety and tolerability of α-CD (7
), and the fact that both saturated fats and trans fats are associated with increased risk of CVD, type 2 diabetes, abdominal obesity and inflammation, future clinical studies assessing the benefits of the addition of α-CD to foods or as a food supplement should be performed.