Cu metabolism in the liver

The Role of Fe, Zn, and Cu in Pregnancy

Iron (Fe), copper (Cu), and zinc (Zn) are microelements essential for the proper functioning of living organisms. These elements participatein many processes, including cellular metabolism and antioxidant and anti-inflammatory defenses, and also influence enzyme activity, regulate gene expression, and take part in protein synthesis. Fe, Cu, and Zn have a significant impact on the health of pregnant women and in the development of the fetus, as well as on the health of the newborn. A proper concentration of these elements in the body of women during pregnancy reduces the risk of complications such as anemia, induced hypertension, low birth weight, preeclampsia, and postnatal complications. The interactions between Fe, Cu, and Zn influence their availability due to their similar physicochemical properties. This most often occurs during intestinal absorption, where metal ions compete for binding sites with transport compounds. Additionally, the relationships between these ions have a great influence on the course of reactions in the tissues, as well as on their excretion, which can be stimulated or delayed. This review aims to summarize reports on the influence of Fe, Cu, and Zn on the course of single and multiple pregnancies, and to discuss the interdependencies and mechanisms occurring between Fe, Cu, and Zn.

Metal-cation regulation of enzyme dynamics is a key factor influencing the activity of S-adenosyl-L-homocysteine hydrolase from Pseudomonas aeruginosa

S-adenosyl-l-homocysteine hydrolase from Pseudomonas aeruginosa (PaSAHase) coordinates one K⁺ ion and one Zn²⁺ ion in the substrate binding area. The cations affect the enzymatic activity and substrate binding but the molecular mechanisms of their action are unknown. Enzymatic and isothermal titration calorimetry studies demonstrated that the K⁺ ions stimulate the highest activity and strongest ligand binding in comparison to other alkali cations, while the Zn²⁺ ions inhibit the enzyme activity. PaSAHase was crystallized in the presence of adenine nucleosides and K⁺ or Rb⁺ ions. The crystal structures show that the alkali ion is coordinated in close proximity of the purine ring and a ²³Na NMR study showed that the monovalent cation coordination site is formed upon ligand binding. The cation, bound in the area of a molecular hinge, orders and accurately positions the amide group of Q65 residue to allow its interaction with the ligand. Moreover, binding of potassium is required to enable unique dynamic properties of the enzyme that ensure its maximum catalytic activity. The Zn²⁺ ion is bound in the area of a molecular gate that regulates access to the active site. Zn²⁺ coordination switches the gate to a shut state and arrests the enzyme in its closed, inactive conformation.

[64Cu]NOTA-pentixather enables high resolution PET imaging of CXCR4 expression in a preclinical lymphoma model

BACKGROUND

The chemokine receptor 4 (CXCR4) is an important molecular target for both visualization and therapy of tumors. The aim of the present study was the synthesis and preclinical evaluation of a 64Cu-labeled, CXCR4-targeting peptide for positron emission tomography (PET) imaging of CXCR4 expression in vivo.

METHODS

For this purpose, 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA), or 1,4,7-triazacyclononane-triacetic acid (NOTA) was conjugated to the highly affine CXCR4-targeting pentixather scaffold. Affinities were determined using Jurkat T-lymphocytes in competitive binding assays employing [125I]FC131 as the radioligand. Internalization and efflux studies of [64Cu]NOTA-pentixather were performed in chem-1 cells, stably transfected with hCXCR4. The stability of the tracer was evaluated in vitro and in vivo. Small-animal PET and biodistribution studies at different time points were performed in Daudi lymphoma-bearing severe combined immunodeficiency (SCID) mice.

RESULTS

[64Cu]NOTA-pentixather was rapidly radiolabeled at 60 °C with high radiochemical yields ≥90% and purities >99%. [64Cu]NOTA-pentixather offered the highest affinity of the evaluated peptides in this study (IC50 = 14.9 ± 2.1 nM), showed efficient CXCR4-targeting in vitro and was stable in blood and urine with high resistance to transchelation in ethylenediaminetetraacetic acid (EDTA) challenge studies. Due to the enhanced lipophilicity of [64Cu]NOTA-pentixather (logP = -1.2), biodistribution studies showed some nonspecific accumulation in the liver and intestines. However, tumor accumulation (13.1 ± 1.5% ID/g, 1.5 h p.i.) was CXCR4-specific and higher than in all other organs and resulted in high resolution delineation of Daudi tumors in PET/CT images in vivo.

CONCLUSIONS

[64Cu]NOTA-pentixather was fast and efficiently radiolabeled, showed effective CXCR4-targeting, high stability in vitro and in vivo and resulted in high resolution PET/CT images accompanied with a suitable biodistribution profile, making [64Cu]NOTA-pentixather a promising tracer for future application in humans.

Copper is taken up efficiently from albumin and alpha2-macroglobulin by cultured human cells by more than one mechanism

Ionic copper entering blood plasma binds tightly to albumin and the macroglobulin transcuprein. It then goes primarily to the liver and kidney except in lactation, where a large portion goes directly to the mammary gland. Little is known about how this copper is taken up from these plasma proteins. To examine this, the kinetics of uptake from purified human albumin and alpha(2)-macroglobulin, and the effects of inhibitors, were measured using human hepatic (HepG2) and mammary epithelial (PMC42) cell lines. At physiological concentrations (3-6 muM), both cell types took up copper from these proteins independently and at rates similar to each other and to those for Cu-dihistidine or Cu-nitrilotriacetate (NTA). Uptakes from alpha(2)-macroglobulin indicated a single saturable system in each cell type, but with different kinetics, and 65-80% inhibition by Ag(I) in HepG2 cells but not PMC42 cells. Uptake kinetics for Cu-albumin were more complex and also differed with cell type (as was the case for Cu-histidine and NTA), and there was little or no inhibition by Ag(I). High Fe(II) concentrations (100-500 microM) inhibited copper uptake from albumin by 20-30% in both cell types and that from alpha(2)-macroglobulin by 0-30%, and there was no inhibition of the latter by Mn(II) or Zn(II). We conclude that the proteins mainly responsible for the plasma-exchangeable copper pool deliver the metal to mammalian cells efficiently and by several different mechanisms. alpha(2)-Macroglobulin delivers it primarily to copper transporter 1 in hepatic cells but not mammary epithelial cells, and additional as-yet-unidentified copper transporters or systems for uptake from these proteins remain to be identified.

Cellular prion protein regulates intracellular hydrogen peroxide level and prevents copper-induced apoptosis

The function of cellular prion protein (PrPC), which is a copper binding protein, remains unclear. To elucidate the mechanisms in which PrPC is involved in neuroprotection, we compared death signals in prion protein gene-deficient (Prnp-/-) primary cerebellar granular neurons (CGNs) to those with wild-type (WT) CGNs. When copper was exposed to these CGNs, ZrchI, and Rikn Prnp-/- CGNs were more sensitized and underwent apoptotic cell death more readily than WT CGNs. Furthermore, the level of intracellular hydrogen peroxide (H2O2) in WT CGNs increased by copper toxicity, whereas those in ZrchI and Rikn Prnp-/- CGNs did not. These results suggest that PrPC modulates the intracellular H2O2 level as a copper-binding protein to protect CGNs from apoptotic cell death possibly due to inhibiting a Fenton reaction.

Copper transportion of WD protein in hepatocytes from Wilson disease patients in vitro

AIM

To study the effect of copper transporting P-type ATPase in copper metabolism of hepatocyte and pathogenesis of Wilson disease (WD).

METHODS

WD copper transporting properties in some organelles of the cultured hepatocytes were studied from WD patients and normal controls.These cultured hepatocytes were incubated in the media of copper 15 mg x L(-1) only, copper 15 mg x L(-1) with vincristine (agonist of P-type ATPase) 0.5mg x L(-1), or copper 15 mg x L(-1) with vanadate (antagonist of P-type ATPase) 18.39 mg x L(-1) separately. Microsome (endoplasmic reticulum and Golgi apparatus), lysosome, mitochondria, and cytosol were isolated by differential centrifugation. Copper contents in these organelles were measured with atomic absorption spectrophotometer, and the influence in copper transportion of these organelles by vanadate and vincristine were comparatively analyzed between WD patients and controls. WD copper transporting P-type ATPase was detected by SDS-PAGE in conjunction with Western blot in liver samples of WD patients and controls.

RESULTS

The specific WD proteins (M(r)155,000 lanes) were expressed in human hepatocytes, including the control and WD patients. After incubation with medium containing copper for 2 h or 24 h, the microsome copper concentration in WD patients was obviously lower than that of controls, and the addition of vanadate or vincristine would change the copper transporting of microsomes obviously. When incubated with vincristine, levels of copper in microsome were significantly increased, while incubated with vanadate, the copper concentrations in microsome were obviously decreased. The results indicated that there were WD proteins, the copper transportion P-type ATPase in the microsome of hepatocytes. WD patients possessed abnormal copper transporting function of WD protein in the microsome, and the agonist might correct the defect of copper transportion by promoting the activity of copper transportion P-type ATPase.

CONCLUSION

Copper transportion P-type ATPase plays an important role in hepatocytic copper metabolism. Dysfunction of hepatocytic WD protein copper transportion might be one of the most important factors for WD.

The response of neurones and glial cells to elevated copper

Defective copper excretion in Wilson's disease can result in increased neurological copper concentrations. This is thought to occur following exposure to increased circulating copper released from necrotic hepatocytes in a saturated liver. BU17 human glioma cells and SH-SY5Y human neuroblastoma cells were exposed to media supplemented with copper in the range 0-250 microM for periods up to 48 h to investigate this hypothesis. Copper uptake, cell growth, intracellular radical generation, and oxidative stress were measured in copper exposed cells. No increase in copper uptake or inhibition of cell growth could be measured in either cell type at any time point or copper concentration investigated. However, significant increases in radical generation (p < 0.001) could be measured in both BU17 and SH-SY5Y cells. A decreased ability to cope when the cells were exposed to additional pro-oxidants suggested that the cells were under oxidative stress with significant reductions in cell viability following exposure to both copper and ascorbic acid. These data suggest that copper sequestration does not occur in neuronal cells exposed to elevated extracellular copper concentrations.