Response of putative indices of copper status to copper supplementation in human subjects

Dietary copper and human health: Current evidence and unresolved issues

Although copper (Cu) is recognized as an essential trace element, uncertainties remain regarding Cu reference values for humans, as illustrated by discrepancies between recommendations issued by different national authorities. This review examines human studies published since 1990 on relationships between Cu intake, Cu balance, biomarkers of Cu status, and health. It points out several gaps and unresolved issues which make it difficult to assess Cu requirements. Results from balance studies suggest that daily intakes below 0.8 mg/day lead to net Cu losses, while net gains are consistently observed above 2.4 mg/day. However, because of an incomplete collection of losses in all studies, a precise estimation of Cu requirements cannot be derived from available data. Data regarding the relationship between Cu intake and potential biomarkers are either too preliminary or inconclusive because of low specificity or low sensitivity to change in dietary Cu over a wide range of intakes. Results from observation and intervention studies do not support a link between Cu and a risk of cardiovascular disease, cognitive decline, arthritis or cancer for intakes ranging from 0.6 to 3mg/day, and limited evidence exists for impaired immune function in healthy subjects with a very low (0.38 mg/day) Cu intake. However, data from observation studies should be regarded with caution because of uncertainties regarding Cu concentration in various foods and water. Further studies that accurately evaluate Cu exposure based on reliable biomarkers of Cu status are needed.

A randomized trial of copper supplementation effects on blood copper enzyme activities and parameters related to cardiovascular health

Marginal copper deficiency, which may affect cardiovascular disease risk, is proposed to occur in many adults in Western industrialized countries. The present study tested the hypothesis that in a group of USA adults, increased copper intake would alter readings for blood copper enzymes and markers relevant to cardiovascular disease risk. Healthy middle aged adults with moderately high cholesterol, were given either placebo or copper supplementation (2 mg copper/day as copper glycinate) for 8 weeks. Blood samples were taken before and after the 8 weeks. Copper, but not placebo, raised activities for two copper enzymes, erythrocyte superoxide dismutase 1 and plasma ceruloplasmin. In contrast, five cardiovascular health related plasma parameters were not changed significantly by copper: C-reactive protein, homocysteine, and cholesterol (total, LDL and HDL). However, changes in erythrocyte superoxide dismutase 1 correlated positively with changes in plasma HDL and negatively with plasma homocysteine. Also, copper lowered mean oxidized LDL values, a result that was statistically significant, but inconsistent. In this test population, increased copper intake raised copper enzyme activities, but did not consistently improve the cardiovascular health measures studied.

Serum copper as a novel biomarker for resistance to thyroid hormone

Thyroid hormone action is mediated by the thyroid hormone receptors TRα1 and TRβ. Defects in TRβ lead to RTH (resistance to thyroid hormone) β, a syndrome characterized by high levels of thyroid hormone and non-suppressed TSH (thyroid-stimulating hormone). However, a correct diagnosis of RTHβ patients is difficult as the clinical picture varies. A biochemical serum marker indicative of defects in TRβ signalling is needed and could simplify the diagnosis of RTHβ, in particular the differentiation to TSH-secreting pituitary adenomas, which present with clinically similar symptoms. In the present paper we show that serum copper levels are regulated by thyroid hormone, which stimulates the synthesis and the export of the hepatic copper-transport protein ceruloplasmin into the serum. This is accompanied by a concerted reduction in the mRNA levels of other copper-containing proteins such as metallothioneins 1 and 2 or superoxide dismutase 1. The induction of serum copper is abolished in genetically hyperthyroid mice lacking TRβ and human RTHβ patients, demonstrating an important role of TRβ for this process. Together with a previously reported TRα1 specific regulation of serum selenium, we show that the ratio of serum copper and selenium, which is largely independent of thyroid hormone levels, volume changes or sample degradation, can constitute a valuable novel biomarker for RTHβ. Moreover, it could also provide a suitable large-scale screening parameter to identify RTHα patients, which have not been identified to date.

Administration of high doses of copper to capuchin monkeys does not cause liver damage but induces transcriptional activation of hepatic proliferative responses

Liver cells respond to copper loading upregulating protective mechanisms. However, to date, except for liver content, there are no good indicators that identify individuals with excess liver copper. We hypothesized that administering high doses of copper to young (5.5 mg Cu · kg⁻¹ . d⁻¹) and adult (7.5 mg Cu · kg⁻¹ . d⁻¹) capuchin monkeys would induce detectable liver damage. Study groups included adult monkeys (2 females, 2 males) 3-3.5 y old at enrollment treated with copper for 36 mo (ACu); age-matched controls (1 female, 3 males) that did not receive additional copper (AC); young monkeys (2 female, 2 males) treated from birth with copper for 36 mo (YCu); and young age-matched controls (2 female, 2 males) that did not receive additional copper (YC). We periodically assessed clinical, blood biochemical, and liver histological indicators and at 36 mo the hepatic mRNA abundance of MT2a, APP, DMT1, CTR1, HGF, TGFβ, and NFκΒ only in adult monkeys. After 36 mo, the liver copper concentration was 4-5 times greater in treated monkeys relative to controls. All monkeys remained healthy with normal routine serum biochemical indices and there was no evidence of liver tissue damage. Relative mRNA abundance of HGF, TGFβ and NFκB was significantly greater in ACu than in AC monkeys. In conclusion, capuchin monkeys exposed to copper at doses up to 50 times the current upper level enhanced expression of genes related to inflammation and injury without clinical, blood biochemical, or histological evidence of liver damage.

Searching for specific responses to copper exposure: an in vitro copper challenge in peripheral mononuclear cells

Acute and chronic cellular responses to changes in copper availability are not clear when these changes are mild to moderate, as what often occur in human daily life. The aims of the study were to develop an in vitro copper challenge in peripheral mononuclear cells (PMNCs) obtained from healthy individuals with different preconditioning copper treatments, and measure copper and iron content, and MT2A and TfR mRNA abundance after the copper challenge. (1) Screening using clinical and biochemical indicators defined healthy participants, who received 8 mg Cu/day (copper sulfate) or placebo for 2 months. (2) Mononuclear cells were obtained on days 0, 2 (acute changes), and 60 (chronic changes). (3) Cells were challenged with a 1, 5, and 20 μM Cu-histidine for 20 h, at T0, T2, and T60. Cells from both supplemented and placebo individuals showed a clear trend to increase copper content when there was more copper in the media. Increases were greater in the supplemented group, larger with 20 μM Cu (p < 0.02, one-way ANOVA), and mostly not significant when incubated with 5 μM Cu. By two-way ANOVA, differences were significant by treatment and by time (both p < 0.001). Differences between T0/T2 and T0/T60 were also significant (both p < 0.001). Changes of iron content were significant by treatment and time (two-way ANOVA); mRNA relative abundance of MT2A changed significantly and paralleled those of copper concentration, but TfR transcripts did not change. An in vitro challenge of PMNC showed specific changes of cellular copper and MT2A, while changes of iron content and TfR mRNA abundance were not consistent. PMNCs appear as good candidates to assess changes of cellular copper availability. That results differed after acute (T2) and chronic (T60) supplementation suggests that acute and chronic changes are handled differently by these cells.

Risks and benefits of copper in light of new insights of copper homeostasis

Copper is an essential micronutrient involved in a variety of biological processes indispensable to sustain life. At the same time, it can be toxic when present in excess, the most noticeable chronic effect being liver damage. Potent, efficient regulatory mechanisms control copper absorption in the digestive tract and copper biliary excretion; absorption ranges between 12 and 60% in humans, depending on Cu intake, presence of other factors in the diet that may promote or inhibit its absorption and on the copper status of the individual. Current evidence suggests that copper deficiency may be more prevalent than previously thought, while copper toxicity is uncommon under customary daily life conditions. Menkes syndrome and Wilson disease are genetic conditions associated with severe copper deficiency and severe copper toxicity, respectively. Effects of milder degrees of copper deficiency and excess copper exposure are not well described, mainly due to lack of sensitive and specific indicators; serum copper concentration and ceruloplasmin are the most frequently used indicators, but they only detect rather intense changes of copper status. Of the many proteins assessed as potential markers of copper status the chaperone of Zn-Cu superoxide dismutase (CCS1) has yielded promising results; data on its performance under different conditions are needed to confirm its use as an indicator of early copper deficiency. Defining copper requirements and upper safe limits of consumption (UL) is a complex process since there are adverse health consequences from both copper deficiency and copper excess (U shape curve). The regulatory framework for risk assessment of essential trace elements introduced by the International Programme on Chemical Safety (IPCS) has proposed a homeostatic model to determine the Adequate Range of Oral Intake (AROI) of essential trace elements; the nadir of the resulting U shape curve serves to define the AROI. At this range of intake physiological mechanisms allow for normal homeostasis and basically, there are no detectable adverse effects. At present, Recommended Dietary Intakes (DRIs) and Adequate Intakes (AIs) are used to recommend copper intakes at different ages and life situations. Evidence obtained in humans and non-human primates presented here suggest that current copper UL should be re evaluated. Developing the scientific basis for a copper UL and evaluating the relevance of copper deficiency globally are future key challenges for copper researchers.

A pilot study of copper supplementation effects on plasma F2alpha isoprostanes and urinary collagen crosslinks in young adult women

Marginal copper deficiency has been proposed to occur frequently, but the benefits of correction remain largely uncharacterized. Two benefits could be reduced oxidant stress and better crosslinking of collagen in bone. Copper intake was increased in 8 female university students by supplementation with copper glycinate (2 mg copper/day) for 8 weeks. Supplementation improved copper status based on serum activity of two copper enzymes, ceruloplasmin and diamine oxidase (9% and 75% mean increase, respectively). No effect was seen for erythrocyte copper-zinc superoxide dismutase. Supplementation produced a 39% mean decrease in plasma for F(2alpha)-isoprostanes (a marker of oxidant stress), and gave a 62% increase in the urine ratio of collagen crosslinks to a measure of total collagen. None of the supplementation effects were duplicated for 8 women given placebo. In conclusion, this pilot study found that in young adult women, increased copper intake can alter biochemical parameters relevant to copper function.

Influence of estrogens on copper indicators: in vivo and in vitro studies

Classic copper indicators are not sensitive and specific for detecting excess copper exposure when this is higher than customary but not markedly elevated. Serum copper and ceruloplasmin (Cp) are the most commonly used indicators to assess nutritional status of copper. The objective of this paper was to study the influence of estrogens on these indicators and others used to assess early effects of excess copper exposure in humans and the expression of a set of copper related proteins in a hepatic cellular model. For the studies in humans, 107 healthy participants (18-50 years) were allocated as follows: group 1 (n = 39), women assessed on day 7 of their hormonal cycle; group 2 (n = 34), women assessed on day 21 of their hormonal cycle, and group 3 (n = 34, comparison group), healthy men. Participants received 8 mg Cu/day (as copper sulfate) during 6 months. Serum Cp and Cu, Cu-Zn-superoxide dismutase activity, liver function indicators [aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma glutamyltransferase (GGT)], and serum Fe and Zn concentrations were measured monthly. In addition, the influence of estradiol on intracellular total copper content, hctr1, dmt1 and shbg mRNA abundance and hCTR1, and DMT1 expression was measured in HepG2 cells. Serum Cu, Fe, and Zn and liver aminotransferases but not Cu-Zn-superoxide dismutase varied depending on sex. Fe nutrition indicators, GGT, and ALT activities showed significant differences between the hormonal phases. Cellular experiments showed that estradiol increased cellular Cu concentration and hCTR1 and DMT1 mRNA expression and changed these proteins expression patterns. Estradiols significantly influence the responses to copper at the whole body and the cellular levels, suggesting that they help maintaining copper availability for metabolic needs.

Differential impact of copper deficiency in rats on blood cuproproteins

Sensitive blood biochemical markers of dietary copper status are not yet known. Rat models were used to investigate the response of severe copper deficiency in dams and pups by comparing abundance of several cuproproteins in erythrocytes, white blood cells, and platelets. The hypothesis tested was that copper deficiency would result in changes in abundance of cuproproteins in blood cells. Copper-deficient (CuD) Holtzman dams and pups had signs consistent with severe copper deficiency compared with copper-adequate controls including lower liver copper and hemoglobin levels and near total loss of plasma ceruloplasmin diamine oxidase activity. Copper-deficient erythrocytes had lower copper, zinc superoxide dismutase (SOD1) but higher copper metallochaperone for SOD1 (CCS) compared with copper-adequate, resulting in higher CCS/SOD1 levels. This ratio was more sensitive in CuD erythrocytes than CuD white cells and especially in CuD platelets. However, both white blood cells and platelets from CuD dams and pups had nearly nondetectable levels of cytochrome c oxidase subunit IV. Because isolation of relatively pure populations of erythrocytes and platelets is feasible, and reagents for immunoblot methods are available, determination of CCS/SOD1 and cytochrome c oxidase subunit IV protein levels may be useful to assess copper status of humans.

Methods of assessment of copper status in humans: a systematic review

BACKGROUND

The assessment of dietary adequacy of copper is constrained by the absence of recognized copper status biomarkers.

OBJECTIVES

The objectives were to systematically review the usefulness of copper status biomarkers and identify those that reflected changes in status over > or =4 wk.

DESIGN

The methods included a structured search on Ovid MEDLINE, EMBASE (Ovid), and Cochrane databases to October 2007, followed by the use of formal inclusion/exclusion criteria, data extraction, validity assessment, and meta-analysis.

RESULTS

A total of 16 studies (288 participants) were included in the review, with data on 16 possible copper biomarkers. All of the included studies were small and at high risk of bias. Data for serum copper suggested its value as a biomarker, reflecting changes in status in both depleted and replete individuals, although these changes were smaller in the latter. Total ceruloplasmin protein is related to copper status but reflects changes in highly depleted individuals only. Erythrocyte superoxide dismutase and urinary deoxypyridinoline are not useful biomarkers, but there were insufficient data to draw firm conclusions about plasma, erythrocyte, and platelet copper; leukocyte superoxide dismutase; erythrocyte, platelet, and plasma glutathione peroxidase; platelet and leukocyte cytochrome-c oxidase; total glutathione; diamine oxidase; and urinary pyridinoline. The paucity of data prevented detailed subgroup analysis.

CONCLUSIONS

Despite limited data, serum copper appears to be a useful biomarker of copper status at the population level. Further large studies with low risk of bias are needed to explore the effectiveness of other biomarkers of copper status and the relation between biomarker responsiveness, dose, and period of supplementation.

Present situation of biomarkers for copper status

Serum or plasma copper and ceruloplasmin concentrations are the most widely used laboratory indicators to evaluate copper status. Both indicators are decreased in moderate or severe copper deficiency. The activity of several cuproenzymes is decreased in mild copper deficiency. However, their use is limited by the nonexistence of standardized assays and high interindividual variability and because some of these indicators are affected by other conditions. Recently, it was shown that the protein expression of the copper chaperone for superoxide dismutase (CCS) is increased in erythrocytes of rodents with mild copper deficiency. However, no traditional laboratory indicators have been identified as potential early markers of copper excess. It is possible that the biomarkers studied so far are not sensitive enough to detect an increase in body copper before the appearance of functional or clinical effects or that the homeostatic mechanisms are so strong that no significant changes in body copper occur with mild-to-moderate copper exposure. The identification of appropriate biomarkers for early detection of an increase in body copper represents a major challenge for further research, and the development of new approaches, such as network biology, allows us to search and propose new candidates to be studied. Recently, we found that CCS mRNA abundance in mononuclear blood cells significantly decreased after copper supplementation. The usefulness of this indicator to detect an increase in body copper should be assessed in clinical trials.

Ceruloplasmin as a marker of occupational copper exposure

Estimation of serum copper to indicate copper status in the human system in the context of moderate chronic occupational copper exposure requires a sophisticated and expensive method. Hence, a search for a suitable marker has been made and few studies have found potential in serum ceruloplasmin. In this context, the present study was initiated to explore whether ceruloplasmin could serve as a predictor of occupational copper exposure. An interviewer-administered questionnaire survey (personal, occupational and health-related information) was undertaken involving 185 employees of a copper handling industry. Serum alkaline phosphatase, serum glutamic pyruvic transaminase (SGPT), serum ceruloplasmin and serum copper were estimated in all the subjects. Multivariate analysis was undertaken using a linear regression model to understand the contribution of serum copper on serum ceruloplasmin values adjusting for the role of other confounders. Serum copper and serum ceruloplasmin values were found to have a statistically significant positive correlation (R=0.169, adjusted R(2)=0.024) after adjustment for other predictors like age, nature of job (department), job duration, smoking, serum alkaline phosphatase and SGPT. This study concludes that the serum ceruloplasmin level can act as a reliable indicator of copper status in the human body following copper exposure in cases of chronic moderate occupational exposure to copper.

Copper and liver function indicators vary depending on the female hormonal cycle and serum hormone binding globulin (SHBG) concentration in healthy women

Previous studies showed that responses to chronic administration of copper were significantly associated with gender, raising the need to better characterize the relation between the effects observed and stradiols. The objective of this study was to measure copper and liver function indicators and the sex hormone binding globulin (SHBG) serum concentrations in healthy adults exposed to copper, grouped by sex and phase of the female hormonal cycle. Healthy females on day 7 (follicular phase, Group 1, n = 39), on day 21 (secretory phase, Group 2, n = 34) and males (comparison group, Group 3, n = 34) received 8 mg Cu/day (as copper sulfate), orally, for 6 months. On days 0, 30, 60, 120, and 180, the serum concentration of copper, ceruloplasmin, liver aminotransferases, and SHBG were measured. Analysis of results included analysis of variance (ANOVA; repeated measures) and the post hoc Bonferroni correction. Participants remained healthy throughout the study period, including aminotransferases below the cut off in all measures. GGT, AST, and ALT activities were significantly different by group and by time (ANOVA repeated measures P < 0.05). Six-month curves of serum copper and ceruloplasmin concentrations were different by group, by time and interaction group x time (all P < 0.001). SHBG curves were different by group and time (P < 0.01), and interaction group x time (P < 0.009). Serum copper, ceruloplasmin, and liver aminotranferases are influenced by estrogens/progesterone, something that should be considered when these indicators are used as outcomes of effects. Time of sampling was also significantly associated with the indicators and deserves further study.

CCS and SOD1 mRNA are reduced after copper supplementation in peripheral mononuclear cells of individuals with high serum ceruloplasmin concentration

The limits of copper homeostatic regulation in humans are not known, making it difficult to define the milder effects of early copper excess. Furthermore, a robust assay to facilitate the detection of early stages of copper excess is needed. To address these issues, we assessed changes in relative mRNA abundance of methallothionein 2A (MT2A), prion (PrP), amyloid precursor-like protein 2 (APLP2), Cu/Zn superoxide dismutase (SOD1) and its copper chaperone (CCS) in peripheral mononuclear cells (PMNCs) from healthy adults representing the 5% highest and lowest extremes in the distribution curve of serum ceruloplasmin (Cp) concentrations of 800 individuals. The intracellular Cu content was also determined. PMNCs were isolated from individuals before and after exposure to a single daily dose of 10 mg Cu (as CuSO(4)) for 2 months. Results showed that although there were fluctuations in serum Cp values of the samples assessed before copper exposure, no significant differences were observed in cell copper content or in the relative abundance of MT2A, PrP and APLP2 transcripts in PMNCs. Also, these values were not modified after copper supplementation. However, CCS and SOD1 mRNA levels were reduced in PMNCs after copper supplementation in the individuals with the high Cp values, suggesting that they should be further explored as biomarkers of moderate copper overload in humans.

The immune system as a physiological indicator of marginal copper status?

Cu appears to have many important functional roles in the body that apparently relate, among others, to the maintenance of immune function, bone health and haemostasis. Some have suggested a role for long-term marginal Cu deficiency in the aetiology of a number of degenerative diseases. Accurate diagnosis of marginal Cu deficiency, however, has remained elusive despite an increased understanding of the biochemistry of Cu and its physiological roles in the body. Traditional markers of Cu status, such as serum Cu and caeruloplasmin protein concentrations are insensitive to subtle changes in Cu status. Cu-containing enzymes, such as Cu–Zn-superoxide dismutase, cytochromecoxidase and diamine oxidase, may be more reliable but evidence to date is not conclusive. Development of markers sensitive to marginal Cu status is essential before conclusions can be drawn concerning the risks of long-term intake of suboptimal dietary Cu. As Cu appears to be essential for maintenance of immune function, activities of specific immunological markers, altered in Cu deficiency, offer alternatives. This review evaluates a selection of immunological markers that could be considered potentially sensitive markers of marginal Cu status. The indices of immune function reviewed are neutrophil function, interleukin 2 production, blastogenic response to mitogens and lymphocyte subset phenotyping.

Effect of copper supplementation on indices of copper status and certain CVD risk markers in young healthy women

Western diets containing suboptimal Cu concentrations could be widespread. A link between marginal Cu deficiency and CVD has been suggested. The objective of the present study was to investigate the effect of Cu supplementation on both Cu status and CVD risk factors in healthy young women. Sixteen women with a mean age of 24 (sd 2) years participated in a randomised crossover study of three 4-week periods with 3-week washouts between periods. During each intervention period, subjects received 0, 3 or 6 mg elemental Cu/d as CuSO4in addition to their habitual diet. Blood samples were taken to assess the effect of supplementation on putative markers of Cu status. The content of plasma lipids, lipoprotein (a), apo and certain haemostatic factors, as putative indices of CVD, was also analysed. Daily supplementation with 3 mg Cu significantly increased (P<0·05) serum Cu concentration and the activity of erythrocyte superoxide dismutase, although there was no further significant increase after an intake of 6 mg Cu/d. The concentration of the fibrinolytic factor plasminogen activator inhibitor type 1 was significantly reduced (P<0·05) by about 30% after supplementation with 6 mg Cu/d. No other marker of Cu status or CVD risk factor was affected by Cu supplementation. The results indicate that supplementation with 3 or 6 mg Cu/d may improve Cu status in these healthy young women. Increased Cu intake could reduce the risk of CVD and atherosclerosis in man by promoting improved fibrinolytic capacity.

Supplementing copper at the upper level of the adult dietary recommended intake induces detectable but transient changes in healthy adults

The health consequences of mild copper excess in humans are unknown. In a previous study, 2 mo of supplementation with up to 6 mg Cu/L in drinking water did not induce detectable changes. Here we assessed a copper supplement at the upper level of dietary recommendations for "healthy" adults. The study was a prospective controlled trial; participants (women and men, 18-50 y old), represented the upper and lower 5% of the ceruloplasmin distribution curve obtained from a community-based sample of 800 healthy adults (n = 41/group, each approximately 50% men). Individuals received a single daily dose of 10 mg Cu for 60 d. Before and after supplementation, blood [copper, ceruloplasmin protein, homocysteine, liver aminotranferases, Cu-Zn -superoxide dismutase activity in erythrocytes (eSOD), and glutathione in peripheral mononuclear cells] and urine [copper excretion after a 5-h administration of a chelator 2,3-dimercapto-1-propano-sodium sulfonate (DMPS)] analyses were performed. After 2 mo, liver enzyme activities remained below the clinical cutoff value used to diagnose liver dysfunction, but had increased significantly in both groups and genders. These increases were no longer present 12 mo after the copper loading period was completed. Glutathione in mononuclear cells (mmol/g of protein) also increased after the 2-mo copper loading in both groups and in both genders (P = 0.01). eSOD activity, serum homocysteine concentration, and urinary copper excretion 5 h after DMPS administration were not affected. We conclude that copper administered as described induced a transient, mild, but significant elevation of aminotransferases.

The molecular basis of copper and iron interactions

The intimate relationship between Fe and Cu in human nutrition has been recognised for many years. The best-characterised link is provided by caeruloplasmin, a multiCu-binding protein that acts as a serum ferrioxidase and is essential for the mobilisation of Fe from storage tissues. Decreased Cu status has been shown to reduce holo-caeruloplasmin production and impair ferrioxidase activity, leading, in a number of cases, to decreased tissue Fe release and the generation of anaemia that is responsive to dietary supplementation with Cu but not Fe. Dietary Fe absorption also requires the presence of a multiCu ferrioxidase. Hephaestin, a caeruloplasmin homologue, works in concert with the IREG1 transporter to permit Fe efflux from enterocytes for loading onto transferrin. The essential role of hephaestin in this process has been recognised from studies in the sex-linked anaemic (sla) mouse, in which Fe efflux is markedly impaired as a result of a mutation in the hephaestin gene that results in a truncated and non-functional version of the protein. There is emerging evidence that a number of other components of the intestinal Fe transport pathway are also Cu sensitive. Divalent metal transporter 1 (DMT1), the Fe transporter located at the apical membrane of enterocytes, is also a physiologically-relevant Cu transporter, suggesting that these two metals may compete with each other for uptake into the duodenal enterocytes. Furthermore, expression of both DMT1 and the basolateral Fe-efflux transporter IREG1 can be regulated by Cu, suggesting that the Fe-Cu relationship may be more complex than first thought.

Sex and ceruloplasmin modulate the response to copper exposure in healthy individuals

Previous studies indicated that sex might influence the response to copper exposure. Ceruloplasmin (Cp) is an indicator of Cu status, but it is not clear whether and how it reflects changes of Cu status among healthy individuals. In this study, 82 apparently healthy women and men were chosen from 800 individuals because their Cp values belonged to the higher and lower 10% of the group Cp distribution curve. Before and after receiving a supplement of 10mg Cu/day (upper limit of daily intake) for 2 months, we performed blood and urinary biochemical measurement of potential Cu markers. We used principal component analysis and linear discriminant analysis to identify blood and/or urinary Cu indicators that showed a differential response to copper. Results showed that Cp values in serum represent a reliable indicator to differentiate subgroups within the normal population in their response to Cu exposure. The response depends on Cp values and on sex, such that women with higher and men with lower Cp values exhibit the greatest response.

Long-term high copper intake: effects on indexes of copper status, antioxidant status, and immune function in young men

BACKGROUND

Short-term high copper intake does not appear to affect indexes of copper status or functions related to copper status, but the effects of long-term high copper intake are unknown.

OBJECTIVE

A study was conducted in men to determine the effect of long-term high copper intake on indexes of copper status, oxidant damage, and immune function.

DESIGN

Nine men were confined to a metabolic research unit (MRU) for 18 d and were fed a 3-d rotating menu providing an average of 1.6 mg Cu/d. The men continued the study under free-living conditions for 129 d and supplemented their usual diets with 7 mg Cu/d. The men then returned to the MRU for 18 d of the same diet as during the first period, except that copper intake was 7.8 mg/d. Plasma copper, ceruloplasmin activity, ceruloplasmin protein, plasma malondialdehyde, benzylamine oxidase activity, erythrocyte superoxide dismutase, hair copper, urinary copper, and urinary thiobarbituric acid-reactive substances were measured during each MRU period.

RESULTS

Ceruloplasmin activity, benzylamine oxidase, and superoxide dismutase were significantly higher at the end of the second MRU period than at the end of the first. Urinary copper excretion, hair copper concentrations, and urinary thiobarbituric acid-reactive substances were significantly higher during the second MRU period than during the first. Polymorphonuclear cell count, the percentage of white blood cells, lymphocyte count, and interleukin 2R were affected by copper supplementation. Antibody titer for the Beijing strain of influenza virus was significantly lower in supplemented subjects after immunization than in unsupplemented control subjects.

CONCLUSIONS

Under highly controlled conditions, long-term high copper intake results in increases in some indexes of copper status, alters an index of oxidant stress, and affects several indexes of immune function. The physiologic implications of these changes are unknown.

Copper enzyme activities in cystic fibrosis before and after copper supplementation plus or minus zinc

One laboratory reports low activities for 2 blood copper enzymes in subjects with cystic fibrosis (CF), which suggests that moderate copper deficiency is common in this state. The present study attempted to confirm this proposition in 3 ways: repeat the measures for 1 of the 2 copper enzymes (superoxide dismutase) in a new group of CF patients (males and females, N = 38), add another copper enzyme measure (plasma diamine oxidase) that has high sensitivity to copper status, and test if copper enzyme activities in CF patients rise by copper supplementation. The last test was performed plus or minus zinc supplementation since poor zinc status may contribute to poor copper status. The results for the first 2 aims supported the idea of poor copper status, as low activities were found for CF subjects for 2 copper enzyme activities, erythrocyte superoxide dismutase and plasma diamine oxidase (although normal activities were obtained for another copper enzyme, plasma ceruloplasmin, both as U/mL plasma or U/mg ceruloplasmin immunoreactive protein). For the last aim, copper enzyme activities were not altered by copper supplementation (6 weeks, 3 mg copper/d as copper-glycinate), plus or minus concurrent zinc supplementation (30 mg zinc/d as zinc-glycinate). Therefore, CF may cause a tendency to moderate copper deficiency, which may be due to abnormal copper metabolism not easily corrected by increased copper and/or zinc intake.

Hohenheim consensus workshop: copper

Copper (Cu) is an essential trace element with many physiological functions. Homeostatic mechanisms exist to allow Cu to act as a cofactor in enzymatic processes and to prevent accumulation of Cu to toxic levels. The aim of this commentary is to better understand the role of dietary Cu supply in deficiency and under physiological and pathological conditions. The essentiality of Cu can be attributed to its role as a cofactor in a number of enzymes that are involved in the defence against oxidative stress. Cu, however, has a second face, that of a toxic compound as it is observed with accumulating evidence in hepatic, neurodegenerative and cardiovascular diseases. The destructive potential of Cu can be attributed to inherent physico-chemical properties. The main property is its ability to take part in Fenton-like reactions in which the highly reactive and extremely deleterious hydroxyl radical is formed. Diseases caused by dietary Cu overload could be based on a genetic predisposition. Thus, an assessment of risk-groups, such as infants with impaired mechanisms of Cu homeostasis regarding detoxification, is of special interest, as their Cu intake with resuspended formula milk may be very high. This implies the need for reliable diagnostic markers to determine the Cu status. These topics were introduced at the workshop by the participants followed by extensive group discussion. The consensus statements were agreed on by all members. One of the conclusions is that a re-assessment of published data is necessary and future research is required.

Determination of an acute no-observed-adverse-effect level (NOAEL) for copper in water

A prospective, double-blind controlled study was designed to determine the acute no-observed-adverse-effect level (NOAEL) of nausea in an apparently healthy population of 179 individuals who drank copper-containing water as the sulfate salt. Subjects were recruited at three different international sites and given a blind, randomly selected dose (0, 2, 4, 6, or 8 mg Cu/L) in a bolus of 200 ml (final total copper dose was equivalent to 0, 0.4, 0.8, 1.2, and 1.6 mg) once weekly over a consecutive 5-week period. Gastrointestinal (GI) symptoms of nausea, abdominal pain, vomiting, or diarrhea were screened for a period of up to 24 h. Nausea was the most frequently reported effect and was reported within the first 15 min of ingestion. For the combined trisite population (n=179), 8, 9, 14, 25, and 44 subjects responded positively to one or more GI symptoms at 0, 2, 4, 6, and 8 mg Cu/L, respectively. Analysis of the data demonstrated a clear dose response to the combined positive GI effects and to nausea alone. Statistically significant greater reporting of effects occurred at 6 and 8 mg Cu/L. Therefore, an acute NOAEL and lowest-observed-adverse-effect level of 4 and 6 mg Cu/L (0.8 and 1.2 mg Cu), respectively, were determined in drinking water for a combined international human population.

No effect of copper supplementation on biochemical markers of bone metabolism in healthy young adult females despite apparently improved copper status

OBJECTIVE

To investigate the effects of increasing Cu intakes, above the usual dietary intake, on biomarkers of bone metabolism in healthy young adult females (aged 21-28 y) over a 4 week period.

DESIGN

A double-blind, placebo-controlled randomised repeat crossover Cu supplementation trial.

SETTING

The study was conducted at the Royal Veterinary and Agricultural University (RVAU), Copenhagen, Denmark.

SUBJECTS

Sixteen healthy young adult females aged 20-28 y were recruited from among students at the RVAU.

INTERVENTION

During the 4 week intervention periods in this randomised, crossover trial (3x4 weeks with a minimum 3 week wash-out period), each subject received, in addition to their usual diet, either 3 or 6 mg elemental Cu/day as CuSO4 or a matching placebo. On the last 3 days of each dietary period 24 h urines were collected. In addition, blood was collected on the last day of each dietary period.

RESULTS

Serum Cu and erythrocyte superoxide dismutase (but not caeruloplasmin protein concentration or activity (putative indices of Cu status)) were significantly increased (P<0.05) after daily Cu supplementation with 3 and 6 mg/day for 4 weeks. Serum osteocalcin (biomarker of bone formation), urinary creatinine (Cr) concentration, urinary pyridinoline (Pyr)/Cr or deoxypyridinoline (Dpyr)/Cr excretion, or daily urinary Pyr or Dpyr excretion (biomarkers of bone resorption) were unaffected by Cu supplementation.

CONCLUSION

Copper supplementation of the usual diet in healthy young adult females, while apparently improving Cu status, had no effect on biochemical markers of bone formation or bone resorption over 4 week periods.

SPONSORSHIP

Funding from the European Commission.

Copper supplementation in humans does not affect the susceptibility of low density lipoprotein to in vitro induced oxidation (FOODCUE project)

The oxidative modification of low-density lipoprotein cholesterol (LDL) has been implicated in the pathogenesis of atherosclerosis. Copper (Cu) is essential for antioxidant enzymes in vivo and animal studies show that Cu deficiency is accompanied by increased atherogenesis and LDL susceptibility to oxidation. Nevertheless, Cu has been proposed as a pro-oxidant in vivo and is routinely used to induce lipid peroxidation in vitro. Given the dual role of Cu as an in vivo antioxidant and an in vitro pro-oxidant, a multicenter European study (FOODCUE) was instigated to provide data on the biological effects of increased dietary Cu. Four centers, Northern Ireland (coordinator), England, Denmark, and France, using different experimental protocols, examined the effect of Cu supplementation (3 or 6 mg/d) on top of normal Cu dietary intakes or Cu-controlled diets (0.7/1.6/6.0 mg/d), on Cu-mediated and peroxynitrite-initiated LDL oxidation in apparently healthy volunteers. Each center coordinated its own supplementation regimen and all samples were subsequently transported to Northern Ireland where lipid peroxidation analysis was completed. The results from all centers showed that dietary Cu supplementation had no effect on Cu- or peroxynitrite-induced LDL susceptibility to oxidation. These data show that high intakes (up to 6 mg Cu) for extended periods do not promote LDL susceptibility to in vitro-induced oxidation.