**2. Copper deficiency**

40 Lipid Metabolism

copper depletion.

**Figure 1. Copper homeostasis and lipid metabolism display functional interactions.** Copper enters circulation via small intestine where copper transporters Ctr1 and ATP7A play the major role in the dietary copper absorption. Dietary copper deficiency is associated with a lower level of ceruloplasmin in the serum and increase in cholesterol and lipoproteins. Copper deficiency also upregulates the copper uptake protein Ctr1 in intestine; this compensatory effects is diminished by high fructose. In the liver, copper deficiency is associated with increased synthesis of cholesterol and higher expression of fatty acid synthase (FAS). Also, in the liver, the copper-transporting ATPase ATP7B mediates copper delivery to ceruloplasmin and copper export into the bile. Genetic inactivation of ATP7B in Wilson's disease is associated with copper overload and marked changes in lipid metabolism. Cholesterol biosynthesis is downregulated and both the serum and hepatic lipid profiles are altered.

The level of expression of copper transporters and their regulation varies between various organs (8). For example, ATP7B is the main transporter in hepatocytes, but it is absent from the adrenal gland, whereas opposite is true for ATP7A (9). Most of the tissues such as heart, brain, lung, placenta and kidneys express both copper-transporting ATPases along with the two copper uptake systems Ctr1 and Ctr2. As a result, the consequences of copper deficiency and copper overload are tissue specific, and certain organs such as heart or liver are more profoundly affected (see below). Recent studies also revealed an important homeostatic cross-talk between different organs in either copper deficiency or copper overload. For example, copper overload in the liver is accompanied by functional copper deficiency in the adrenal gland (9), whereas severe copper deficiency in the heart stimulates copper efflux from the liver (10), presumably to compensate for the deleterious effects of

The analysis of available literature also illustrates that variations in copper levels, either through the diet or as a result of genetic copper misbalance, have a profound effect on lipid

#### **2.1. Copper in western diet**

Copper deficiency has long been known to alter lipid metabolism; consequently, it has been proposed as a significant factor in human diseases associated with dyslipidemia (15). Copper deficiency is rarely diagnosed in humans, with a notable exception of a growing number of reports pointing to copper and other mineral insufficiencies as unintended consequences of bariatric surgeries (16-18). The under-detection of copper deficiency could be due to limitations of screening using serum or urine samples. Although liver is the main homeostatic organ for copper and has a high copper content, copper levels in serum and urine do not correlate well with a hepatic copper concentration (19), possibly masking deficiency in the liver.

Recent work using a categorical regression analysis of copper deficiency and excess shows a U-shaped dose-response curve. Compilation of data on toxicity due to copper excess and deficiency yielded a generalized linear model that was used to estimate adverse responses depending on copper dose or severity of copper limitation, as well as duration of copper misbalance (20). This model indicates that for humans the optimal intake level for Cu is 2.6 mg/day. The current United States Recommended Daily Intake is only 0.9 mg (US Food and Nutrition Board), whereas dietary study indicated that even 1.03 mg of Cu/day may be insufficient for adult men (21). The results of the third National Health and Nutrition Examination Survey (NHANES III, 2003) in the US showed that the mean daily intake of copper, depending on age, was 1.54–1.7 mg*/*day (±0.05 standard deviation (SD)) for men and 1.13-1.18 mg*/*d (±0.05 SD) for women. These results imply that a large portion of the population may have insufficient dietary copper intake and mild copper deficiency.

#### **2.2. Low copper and human disease**

Current data suggest that copper deficiency may be a common contributing factor in cardiovascular disease (CVD) and non-alcoholic fatty-liver disease (NAFLD) (22-24). As described above, surgical obesity treatment has also been strongly implicated in copper deficiency, likely by causing a diminished absorption of copper after a gastric bypass surgery (16-18). In addition, low copper levels were detected in organs, plasma and tissue of patients with several chronic diseases including cardiovascular disease, central nervous system, and musculoskeletal disorders (25). In fact, it was suggested that an ischemic heart disease could be largely attributed to copper deficiency (26), and that Cu deficiency and the high sugar consumption characteristic in the Western diet may interact in CVD (27). In a rat model, copper deficiency that reduces plasma levels of copper and ceruloplasmin also reduces copper content of the heart, liver, and testes. Coincidentally, heart zinc is also reduced, whereas hepatic iron levels rise (28), demonstrating the multifaceted effects of copper depletion on the overall body metal homeostasis.

The Role of Copper as a Modifier of Lipid Metabolism 43

cross-linking of collagen and elastin. Aortas of copper-deficient rats showed deformation and loss of elasticity, though myocardial arteries were normal. Since lysyl oxidase is only one of the copper dependent enzymes required for proper heart functions (others include cytochrome C oxidase, cytosolic superoxide dismutase, dopamine beta-mono-oxygenase) the role of low copper in CVD may be realized through multiple mechanisms in addition to

The development of cholesterolemia in response to copper deficiency has been explored in some detail in rats. Copper deficiency was found to be associated with the increased HDL and LDL levels (30% increase in HDL in one study). In addition, the plasma volume also increases, thus raising the available pool of cholesterol even more (22, 32). In effect, a 60% increase in total cholesterol may be observed (22). Overall, copper deficiency increases the absolute levels of cholesterol, but there is an argument whether the size of plasma cholesterol pool size may be a more powerful measure of cholesterol elevation. For example, the time course study of serum cholesterol in rats kept for 3-7 weeks on a copper deficient diet found that with time the plasma cholesterol concentration leveled off, but the pool size of cholesterol increased due to increases in the plasma volume (33). Curiously, the rates of HDL catabolism also increased, though the liver and the adrenal gland did not take up additional HDL in copper deficiency, suggesting one possible mechanism for dyslipidemia

**2.4. Serum lipoproteins: changes in structure, composition, and degradation** 

Rat models have proven to be especially consistent and valuable in studies of the dyslipidemia resulting from copper deficiency. Despite variations in the age, diet composition, and time on a copper deficient diet, an increase in the cholesterol concentration and/or pool was consistently reported in these animals. The lipids and lipoprotein components were analyzed in detail by al-Othman and co-workers and provided valuable data on changes in plasma pool size along with the composition and concentration of lipoproteins (33). These studies demonstrated no change in plasma phospholipid composition in copper deficient rats when compared to controls. In contrast, triglycerides, phospholipids, and cholesterol in LDL and HDL increased 2-fold or more. The VLDL composition of copper deficient animals changed most significantly with a 6-fold increase in triglycerides, 36% reduction in cholesterol and no change in phospholipid. An increase was observed in the VLDL particle size, but not the number of particles. In contrast, an increase in both size and number was seen for the LDL particles, whereas for the HDL particles an increase in the number of particles was observed, but no

The composition of serum lipoproteins in copper deficient animals may also be influenced by shifts in the expression and distribution of apolipoproteins, linking physiological response in the liver to the observed changes in plasma cholesterol. The plasma levels of apolipoproteins A, B, and E increase in rats fed a copper deficient diet, consistent with the

the altered lipid metabolism.

with respect to the HDL pool (34).

size change.

Numerous studies in the rodent and other animal models (discussed below) provide strong indication of a significant link between copper deficiency and dyslipidemia. Specific studies linking human lipid response to copper deficiency are very limited. The available reports clearly illustrate the need for a better mechanistic insight. For example, studies using healthy male volunteers showed severe copper depletion with a diet containing 0.83 mg Cu/day, which is similar to levels in some contemporary diets. In these individuals, along with the diminished copper, the levels of serum copper-depended enzyme ceruloplasmin were reduced, as was copper-zinc superoxide dismutase activity in erythrocytes. In parallel, changes in lipid metabolism were evident. Cholesterol was elevated in the serum, and changes in the cholesterol levels were found to be more sensitive to copper levels than changes in hematology (29). These observations suggest that the dietary copper levels may be significant modifying factors in the disorders associated with lipid misbalance. Indeed, a role for copper deficiency is emerging in NAFLD (discussed below).

### **2.3. Low copper levels and hypercholesterolemia**

Current data indicate that copper deficiency is associated with specific effects on systemic lipid metabolism. Although copper deficiency affects multiple organs (liver, heart, intestine, brain, adipose tissue), the liver and cardiovascular system appear more profoundly affected compared to other tissues. The effects of copper deficiency are partially reversible. In a middle-aged adult population with cardiovascular disease (CVD), copper supplementation was shown to raise the serum copper enzyme activities, but improvement of CVD measures was inconsistent (30). The same report also showed that copper supplementation reduced levels of oxidized serum LDL with statistical significance, but the results were inconsistent necessitating further research.

As described above, plasma cholesterol levels rise in human volunteers consuming a marginally low copper diet (29). In humans, the molecular mechanism behind this phenomenon has not yet been investigated in detail. However, much effort has been made characterizing the influence of copper deficiency on serum cholesterol as well as lipid profiles using animal models. These studies yielded wealth of useful information. Early work feeding rats a copper deficient diet revealed hypercholesterolemia, cardiac hypertrophy, hemorrhage, inflammation, and focal necrosis (31). This work also indicated that some of the cardiac pathology caused by copper deficiency could be linked to the lysyl oxidase deficiency. Lysyl oxidase (LOX) is a copper-dependent enzyme involved in the cross-linking of collagen and elastin. Aortas of copper-deficient rats showed deformation and loss of elasticity, though myocardial arteries were normal. Since lysyl oxidase is only one of the copper dependent enzymes required for proper heart functions (others include cytochrome C oxidase, cytosolic superoxide dismutase, dopamine beta-mono-oxygenase) the role of low copper in CVD may be realized through multiple mechanisms in addition to the altered lipid metabolism.

42 Lipid Metabolism

patients with several chronic diseases including cardiovascular disease, central nervous system, and musculoskeletal disorders (25). In fact, it was suggested that an ischemic heart disease could be largely attributed to copper deficiency (26), and that Cu deficiency and the high sugar consumption characteristic in the Western diet may interact in CVD (27). In a rat model, copper deficiency that reduces plasma levels of copper and ceruloplasmin also reduces copper content of the heart, liver, and testes. Coincidentally, heart zinc is also reduced, whereas hepatic iron levels rise (28), demonstrating the multifaceted effects of

Numerous studies in the rodent and other animal models (discussed below) provide strong indication of a significant link between copper deficiency and dyslipidemia. Specific studies linking human lipid response to copper deficiency are very limited. The available reports clearly illustrate the need for a better mechanistic insight. For example, studies using healthy male volunteers showed severe copper depletion with a diet containing 0.83 mg Cu/day, which is similar to levels in some contemporary diets. In these individuals, along with the diminished copper, the levels of serum copper-depended enzyme ceruloplasmin were reduced, as was copper-zinc superoxide dismutase activity in erythrocytes. In parallel, changes in lipid metabolism were evident. Cholesterol was elevated in the serum, and changes in the cholesterol levels were found to be more sensitive to copper levels than changes in hematology (29). These observations suggest that the dietary copper levels may be significant modifying factors in the disorders associated with lipid misbalance. Indeed, a

Current data indicate that copper deficiency is associated with specific effects on systemic lipid metabolism. Although copper deficiency affects multiple organs (liver, heart, intestine, brain, adipose tissue), the liver and cardiovascular system appear more profoundly affected compared to other tissues. The effects of copper deficiency are partially reversible. In a middle-aged adult population with cardiovascular disease (CVD), copper supplementation was shown to raise the serum copper enzyme activities, but improvement of CVD measures was inconsistent (30). The same report also showed that copper supplementation reduced levels of oxidized serum LDL with statistical significance, but the results were inconsistent

As described above, plasma cholesterol levels rise in human volunteers consuming a marginally low copper diet (29). In humans, the molecular mechanism behind this phenomenon has not yet been investigated in detail. However, much effort has been made characterizing the influence of copper deficiency on serum cholesterol as well as lipid profiles using animal models. These studies yielded wealth of useful information. Early work feeding rats a copper deficient diet revealed hypercholesterolemia, cardiac hypertrophy, hemorrhage, inflammation, and focal necrosis (31). This work also indicated that some of the cardiac pathology caused by copper deficiency could be linked to the lysyl oxidase deficiency. Lysyl oxidase (LOX) is a copper-dependent enzyme involved in the

copper depletion on the overall body metal homeostasis.

role for copper deficiency is emerging in NAFLD (discussed below).

**2.3. Low copper levels and hypercholesterolemia** 

necessitating further research.

The development of cholesterolemia in response to copper deficiency has been explored in some detail in rats. Copper deficiency was found to be associated with the increased HDL and LDL levels (30% increase in HDL in one study). In addition, the plasma volume also increases, thus raising the available pool of cholesterol even more (22, 32). In effect, a 60% increase in total cholesterol may be observed (22). Overall, copper deficiency increases the absolute levels of cholesterol, but there is an argument whether the size of plasma cholesterol pool size may be a more powerful measure of cholesterol elevation. For example, the time course study of serum cholesterol in rats kept for 3-7 weeks on a copper deficient diet found that with time the plasma cholesterol concentration leveled off, but the pool size of cholesterol increased due to increases in the plasma volume (33). Curiously, the rates of HDL catabolism also increased, though the liver and the adrenal gland did not take up additional HDL in copper deficiency, suggesting one possible mechanism for dyslipidemia with respect to the HDL pool (34).

#### **2.4. Serum lipoproteins: changes in structure, composition, and degradation**

Rat models have proven to be especially consistent and valuable in studies of the dyslipidemia resulting from copper deficiency. Despite variations in the age, diet composition, and time on a copper deficient diet, an increase in the cholesterol concentration and/or pool was consistently reported in these animals. The lipids and lipoprotein components were analyzed in detail by al-Othman and co-workers and provided valuable data on changes in plasma pool size along with the composition and concentration of lipoproteins (33). These studies demonstrated no change in plasma phospholipid composition in copper deficient rats when compared to controls. In contrast, triglycerides, phospholipids, and cholesterol in LDL and HDL increased 2-fold or more. The VLDL composition of copper deficient animals changed most significantly with a 6-fold increase in triglycerides, 36% reduction in cholesterol and no change in phospholipid. An increase was observed in the VLDL particle size, but not the number of particles. In contrast, an increase in both size and number was seen for the LDL particles, whereas for the HDL particles an increase in the number of particles was observed, but no size change.

The composition of serum lipoproteins in copper deficient animals may also be influenced by shifts in the expression and distribution of apolipoproteins, linking physiological response in the liver to the observed changes in plasma cholesterol. The plasma levels of apolipoproteins A, B, and E increase in rats fed a copper deficient diet, consistent with the

#### 44 Lipid Metabolism

increased particle numbers and sizes (35-39). Remarkably, hepatic apoA1, ApoE and ApoB mRNA levels remain unchanged, suggesting that the alteration of the apolipoprotein levels is not due to an increase in transcription. Indeed, it was found that hepatic synthesis and secretion rates of apoA1 are upregulated (35), whereas the rates of synthesis of ApoB-48 and ApoB-100 are unchanged, despite an increase in secretion (37). Intestinal secretion of apoA-1 was also observed, providing yet another source for increased circulating apolipoproteins and cholesterol (40).

The Role of Copper as a Modifier of Lipid Metabolism 45

phospholipids in the liver and kidney, as well as lower triacylglycerols in kidneys (51). Lower proportion and total amount of di-homo-γ-linoleic acid was observed in all tissues of these mice, though levels of other lipids varied. Severe copper deficiency also induced hepatomegaly, reduced the brain weight, and reduced serum ceruloplasmin to 0.5% of

The liver is an organ that experiences significant changes in lipid composition and membrane structure in response to copper deficiency. The loss of membrane fluidity in hepatic tissue has been reported and suggested to be caused by changes in the composition of unsaturated fatty acids and triacylglycerols of fatty acids (48). Other observed changes in membrane lipids associated with copper deficiency include a decreased ratio of monounsaturated:saturated C16 and C18 fatty acids in adipose tissue and a decreased fatty acid desaturase activity in liver microsomes (52). Phosphatidylcholine biosynthesis may also be affected, as choline phosphotransferase activity levels are lower both in the heart and

Concurrent with changes in lipid profiles and synthesis, copper deficiency decreases the total amounts of body fat and shifts metabolic fuel use from carbohydrate to fat. Respiratory quotient is reduced, but total energy intake is the same for animals kept on copper deficient and copper adequate diets (54). Young, weanling rats fed on a copper deficient diet for six weeks are leaner than controls, though they have increased serum cholesterol and triglycerides. Metabolically, whole body respiratory quotient decreases, reflected in a reduction of cardiac and adipose lipoprotein lipase, but not the skeletal muscle lipoprotein lipase (55). The change in fuel use may be related to upregulation of fatty acid synthesis. Copper deficiency does, however, decrease levels of hepatic cytochrome C

The molecular mechanisms for these changes in lipid metabolism due to copper deficiency are understudied; as a result, current knowledge is limited. Increases in expression of specific apolipoproteins and increased transcription of gene for fatty acid synthase in the liver have been reported (see above), providing first insights into molecular players that are involved in response to low copper. Some key information has also been gained in one gene expression study. A transriptome analysis in the small intestine of copper deficient rats revealed upregulation of mRNA for proteins involved in cholesterol transport including apolipoprotein E and the lecithin:cholesterol acyltransferase providing mechanism for enhanced intestinal cholesterol secretion (57). The study also reported down-regulation of genes in the pathway for fatty acid beta-oxidation (both mitochondrial and peroxisomal). The results suggested a change in cell metabolism that reduced fatty acid oxidation, perhaps as a feedback to the decreased cytochrome C oxidase activity. The specific effects of copper deficiency may differ in tissues and serum. For example, in contrast to intestine, the activity of plasma lecithin:cholesterol acyltransferase (a risk factor for ischemic heart disease) is

control, indicating profound systemic effects.

liver tissue in copper deficient rats (53).

decreased in rats fed a copper deficient diet (58).

oxidase (56).

In copper deficiency, plasma HDL rich in apolipoprotein E (ApoE) accumulates and total ApoE binding to liver plasma membranes increases (also reported as a reduction in ApoEfree HDL binding). Interestingly, the cholesterol levels in the liver decrease with copper deficiency, despite an overall increase in hepatic cholesterol synthesis (41, 42). These changes in synthesis, binding properties, and redistribution of lipoproteins suggest some mechanisms through which copper deficiency affects serum cholesterol levels. Thus far, molecular investigations of copper deficiency have identified increased hepatic expression of SREBP1-responsive fatty-acid synthase, along with the increased nuclear localization of the mature SREBP1 transcriptional activator (24). Changes in the expression of other genes involved in the fatty acid synthesis have not been explored in any significant detail, although the mRNA levels for cholesterol 7-alpha hydroxylase were found decreased by 80%.

Changes in the plasma lipoprotein composition and structure are expected to influence the lipid content of red blood cells (RBC) through lipid exchange. Consequently, in copper deficiency changes in the RBC lipid composition are likely (43-45). Studies of the lipid profile of plasma and membranes of RBCs in copper deficiency support this view. Both cholesterol and phospholipid levels increase in the RBCs plasma membranes in Cu deficient rats, whereas the molar ratios of cholesterol:phospholipids and cholesterol:membrane protein are reduced (46). The phospholipid profiles change as well, with the increased stearic and docosadienoic acid content, and the lower levels of oleic and linolenic acid (47). A study assessing structural characteristics of the RBC membranes demonstrated a decrease in membrane fluidity and speculated that this could be the cause of hemolysis and anemia (48). Intriguingly, another study reported an increase in the RBC plasma membrane fluidity in copper deficient rats (49). This discrepancy may be due to experimental conditions. Motta and colleagues found that in copper deficiency, increased fluidity in RBCs plasma membrane can be seen alongside with higher rigidity due to enhanced susceptibility of triacylglycerol-rich lipoproteins to lipid peroxidation (50).

#### **2.5. Copper-dependent lipid alteration in tissues**

Given significant changes induced by copper deficiency in the serum and the liver, it is not surprising that the lipid and fatty-acid composition of other organs is also affected. Severe copper deficiency can be induced in C57BL mice by feeding dams a copper deficient diet and subsequently weaning pups to the same diet. These animals had lower levels of phospholipids in the liver and kidney, as well as lower triacylglycerols in kidneys (51). Lower proportion and total amount of di-homo-γ-linoleic acid was observed in all tissues of these mice, though levels of other lipids varied. Severe copper deficiency also induced hepatomegaly, reduced the brain weight, and reduced serum ceruloplasmin to 0.5% of control, indicating profound systemic effects.

44 Lipid Metabolism

and cholesterol (40).

80%.

increased particle numbers and sizes (35-39). Remarkably, hepatic apoA1, ApoE and ApoB mRNA levels remain unchanged, suggesting that the alteration of the apolipoprotein levels is not due to an increase in transcription. Indeed, it was found that hepatic synthesis and secretion rates of apoA1 are upregulated (35), whereas the rates of synthesis of ApoB-48 and ApoB-100 are unchanged, despite an increase in secretion (37). Intestinal secretion of apoA-1 was also observed, providing yet another source for increased circulating apolipoproteins

In copper deficiency, plasma HDL rich in apolipoprotein E (ApoE) accumulates and total ApoE binding to liver plasma membranes increases (also reported as a reduction in ApoEfree HDL binding). Interestingly, the cholesterol levels in the liver decrease with copper deficiency, despite an overall increase in hepatic cholesterol synthesis (41, 42). These changes in synthesis, binding properties, and redistribution of lipoproteins suggest some mechanisms through which copper deficiency affects serum cholesterol levels. Thus far, molecular investigations of copper deficiency have identified increased hepatic expression of SREBP1-responsive fatty-acid synthase, along with the increased nuclear localization of the mature SREBP1 transcriptional activator (24). Changes in the expression of other genes involved in the fatty acid synthesis have not been explored in any significant detail, although the mRNA levels for cholesterol 7-alpha hydroxylase were found decreased by

Changes in the plasma lipoprotein composition and structure are expected to influence the lipid content of red blood cells (RBC) through lipid exchange. Consequently, in copper deficiency changes in the RBC lipid composition are likely (43-45). Studies of the lipid profile of plasma and membranes of RBCs in copper deficiency support this view. Both cholesterol and phospholipid levels increase in the RBCs plasma membranes in Cu deficient rats, whereas the molar ratios of cholesterol:phospholipids and cholesterol:membrane protein are reduced (46). The phospholipid profiles change as well, with the increased stearic and docosadienoic acid content, and the lower levels of oleic and linolenic acid (47). A study assessing structural characteristics of the RBC membranes demonstrated a decrease in membrane fluidity and speculated that this could be the cause of hemolysis and anemia (48). Intriguingly, another study reported an increase in the RBC plasma membrane fluidity in copper deficient rats (49). This discrepancy may be due to experimental conditions. Motta and colleagues found that in copper deficiency, increased fluidity in RBCs plasma membrane can be seen alongside with higher rigidity due to enhanced susceptibility of

Given significant changes induced by copper deficiency in the serum and the liver, it is not surprising that the lipid and fatty-acid composition of other organs is also affected. Severe copper deficiency can be induced in C57BL mice by feeding dams a copper deficient diet and subsequently weaning pups to the same diet. These animals had lower levels of

triacylglycerol-rich lipoproteins to lipid peroxidation (50).

**2.5. Copper-dependent lipid alteration in tissues** 

The liver is an organ that experiences significant changes in lipid composition and membrane structure in response to copper deficiency. The loss of membrane fluidity in hepatic tissue has been reported and suggested to be caused by changes in the composition of unsaturated fatty acids and triacylglycerols of fatty acids (48). Other observed changes in membrane lipids associated with copper deficiency include a decreased ratio of monounsaturated:saturated C16 and C18 fatty acids in adipose tissue and a decreased fatty acid desaturase activity in liver microsomes (52). Phosphatidylcholine biosynthesis may also be affected, as choline phosphotransferase activity levels are lower both in the heart and liver tissue in copper deficient rats (53).

Concurrent with changes in lipid profiles and synthesis, copper deficiency decreases the total amounts of body fat and shifts metabolic fuel use from carbohydrate to fat. Respiratory quotient is reduced, but total energy intake is the same for animals kept on copper deficient and copper adequate diets (54). Young, weanling rats fed on a copper deficient diet for six weeks are leaner than controls, though they have increased serum cholesterol and triglycerides. Metabolically, whole body respiratory quotient decreases, reflected in a reduction of cardiac and adipose lipoprotein lipase, but not the skeletal muscle lipoprotein lipase (55). The change in fuel use may be related to upregulation of fatty acid synthesis. Copper deficiency does, however, decrease levels of hepatic cytochrome C oxidase (56).

The molecular mechanisms for these changes in lipid metabolism due to copper deficiency are understudied; as a result, current knowledge is limited. Increases in expression of specific apolipoproteins and increased transcription of gene for fatty acid synthase in the liver have been reported (see above), providing first insights into molecular players that are involved in response to low copper. Some key information has also been gained in one gene expression study. A transriptome analysis in the small intestine of copper deficient rats revealed upregulation of mRNA for proteins involved in cholesterol transport including apolipoprotein E and the lecithin:cholesterol acyltransferase providing mechanism for enhanced intestinal cholesterol secretion (57). The study also reported down-regulation of genes in the pathway for fatty acid beta-oxidation (both mitochondrial and peroxisomal). The results suggested a change in cell metabolism that reduced fatty acid oxidation, perhaps as a feedback to the decreased cytochrome C oxidase activity. The specific effects of copper deficiency may differ in tissues and serum. For example, in contrast to intestine, the activity of plasma lecithin:cholesterol acyltransferase (a risk factor for ischemic heart disease) is decreased in rats fed a copper deficient diet (58).
