**3.1. Copper and dietary fat/lipid**

Considering that copper deficiency influences systemic lipid metabolism, it would be interesting to know whether interactions between copper and lipid levels are reciprocal. In other words, it is important to determine whether dietary fat consumption, or changes in the type of fat consumed influences the activity or levels of copper-dependent enzymes. Changes in the ratios of saturated and unsaturated fatty acids have been noted in copper deficiency, and a cardioprotective effect of increasing proportion of polyunsaturated fatty acids was proposed (59). Curiously, feeding saturated fat in a copper deficient rat model increased hepatic copper as well as iron levels to a significant degree. Saturated fat consumption, however, did not change copper deficiency-induced lipid peroxidation, despite recovery of some hepatic copper. Copper-zinc superoxide dismutase (Cu/Zn-SOD) in the liver is less active in copper-deficient rats, whereas other hepatic antioxidant enzymes are unaffected by copper deficiency (56). This observation suggests that proper incorporation of copper in Cu/Zn-SOD may be key to preventing lipid peroxidation.

The effect of fatty acids on copper may also be mediated at the level of intestinal absorption. Experiments with the long chain fatty acids palmitate and stearate showed reduced levels of copper absorption from the jejunum (60) in response to treatment. In another study, direct cholesterol feeding of rabbits was used to model hypercholesterolemia and atherosclerosis. Adding cholesterol to 0.5% of diet triggered the redistribution of copper from the liver to plasma, with a 50% increase in plasma Cu and a 74% reduction in liver copper (61). Interestingly, copper supplementation in cholesterol-fed rabbits reduced atherosclerotic lesions (62). Further support for the importance of copper-lipid interactions in cardiac function is indicated by the observation that cardiomyopathy might be exacerbated by combination of high dietary fat and copper restriction. Specifically, when copper restriction and dietary fat supplementation were tested separately and together, the lowest level of cardiac cytochrome C oxidase activity was observed in copper-deficient rats on a high fat diet (63).

#### **3.2. Fructose, lipids, and copper metabolism**

The influence of dietary sugar consumption on lipid metabolism may be mediated, in part, by exacerbation of copper deficiency. Copper-deficient rats fed a sucrose-based or starchbased diets all had increased plasma cholesterol and lower plasma ceruloplasmin levels, as observed in copper deficiency alone (64). However, feeding sucrose rather than starch greatly enhanced deleterious effects of copper deficiency, such that those animals showed 60% mortality in the 9-week study. The copper deficient sucrose fed rats had a 3-fold lower hepatic copper level compared to starch-fed copper deficient rats. These results suggested a sucrose-dependent change in copper mobilization or retention within the liver (64). Cardiac abnormalities consistent with copper deficiency were also observed. Follow-up work indicated that when diets with fructose, glucose or starch were combined with copper deficiency, both glucose and fructose raised plasma cholesterol levels. However, severity of copper deficiency and mortality were much greater with fructose as opposed to glucose feeding (65), suggesting that the exacerbation of copper deficiency by sucrose was due to the fructose component. More recent work (66) indicates that the effect of fructose may be at the level of absorption, whereby copper deficiency induces upregulation of the copper transporter Ctr1, but this effect is eliminated by high fructose feeding (Figure 1).

46 Lipid Metabolism

diet (63).

**3.2. Fructose, lipids, and copper metabolism** 

**3.1. Copper and dietary fat/lipid** 

**3. Functional interactions between copper, lipid, and other nutrients** 

incorporation of copper in Cu/Zn-SOD may be key to preventing lipid peroxidation.

The effect of fatty acids on copper may also be mediated at the level of intestinal absorption. Experiments with the long chain fatty acids palmitate and stearate showed reduced levels of copper absorption from the jejunum (60) in response to treatment. In another study, direct cholesterol feeding of rabbits was used to model hypercholesterolemia and atherosclerosis. Adding cholesterol to 0.5% of diet triggered the redistribution of copper from the liver to plasma, with a 50% increase in plasma Cu and a 74% reduction in liver copper (61). Interestingly, copper supplementation in cholesterol-fed rabbits reduced atherosclerotic lesions (62). Further support for the importance of copper-lipid interactions in cardiac function is indicated by the observation that cardiomyopathy might be exacerbated by combination of high dietary fat and copper restriction. Specifically, when copper restriction and dietary fat supplementation were tested separately and together, the lowest level of cardiac cytochrome C oxidase activity was observed in copper-deficient rats on a high fat

The influence of dietary sugar consumption on lipid metabolism may be mediated, in part, by exacerbation of copper deficiency. Copper-deficient rats fed a sucrose-based or starchbased diets all had increased plasma cholesterol and lower plasma ceruloplasmin levels, as observed in copper deficiency alone (64). However, feeding sucrose rather than starch greatly enhanced deleterious effects of copper deficiency, such that those animals showed 60% mortality in the 9-week study. The copper deficient sucrose fed rats had a 3-fold lower hepatic copper level compared to starch-fed copper deficient rats. These results suggested a sucrose-dependent change in copper mobilization or retention within the liver (64). Cardiac abnormalities consistent with copper deficiency were also observed. Follow-up work

Considering that copper deficiency influences systemic lipid metabolism, it would be interesting to know whether interactions between copper and lipid levels are reciprocal. In other words, it is important to determine whether dietary fat consumption, or changes in the type of fat consumed influences the activity or levels of copper-dependent enzymes. Changes in the ratios of saturated and unsaturated fatty acids have been noted in copper deficiency, and a cardioprotective effect of increasing proportion of polyunsaturated fatty acids was proposed (59). Curiously, feeding saturated fat in a copper deficient rat model increased hepatic copper as well as iron levels to a significant degree. Saturated fat consumption, however, did not change copper deficiency-induced lipid peroxidation, despite recovery of some hepatic copper. Copper-zinc superoxide dismutase (Cu/Zn-SOD) in the liver is less active in copper-deficient rats, whereas other hepatic antioxidant enzymes are unaffected by copper deficiency (56). This observation suggests that proper

Dietary fructose consumption and dietary copper deficiency independently alter fatty-acid metabolism; in combination, the effect is enhanced (66-69). Feeding weanling rats for three weeks on a diet adequate or deficient in copper along with either fructose or corn starch as a carbohydrate source (62% carbohydrate) revealed that fructose feeding enhanced indicators of copper deficiency, such as enhanced heart/body weight ratio and reduced hepatic copper (70). Analysis of hepatic enzymes involved in the lipid and carbohydrate metabolism also indicated that a diet deficient in copper had greatest metabolic effects in combination with fructose, less with glucose and least with starch (71). Glucose-6-phosphate dehydrogenase, malic enzyme, L-alpha-glycerophosphate dehydrogenase and fructose 1-6-diphosphatase were all unaffected by Cu deficiency, but their activities were enhanced most in combination with fructose, suggesting a complementary rather than direct role for fructose in exacerbating copper deficiency (71).

Copper deficiency in combination with fructose feeding alters the fatty acid composition of triacylglycerol in the heart and the liver. Cardiac phosphatidylinositol and phosphatidylserine were shown to increase nearly two-fold and arachidonic acid and docosapentaenoic acid to be elevated more than two-fold in copper deficient, fructose fed animals (70). A change in cardiac phospholipids may explain the increased mortality observed in copper deficient/fructose fed rats and suggest a potentially significant role for these dietary factors in ischemic heart disease. However, the observed changes in the lipid composition could not be correlated with the extent of copper deficiency, illustrating once again that a detailed mechanistic understanding of these dietary interactions could be highly beneficial.

Western diet is characterized by high fructose and high fat. In combination with a likely mild copper deficiency (see above), it stands to reason that these factors may all interact to induce changes in whole body metabolism, especially lipid metabolism, producing deleterious hepatic and cardiovascular effects. When this idea is tested in rats by combining high fat and fructose, or low fat and fructose with copper deficiency, liver metabolism is most significantly affected by the fat and fructose combination (28). Sugars mobilize copper from the liver to other tissues (64), possibly causing a change in liver physiology. Recent work also indicates that the mobilization of copper from the liver may be driven by heartspecific copper deficiency (10). Thus, in addition to interaction during absorption, an important inter-organ communication exists that jointly modulates levels of copper and lipids in various tissues
