Secretion and uptake of copper via a small copper carrier in blood fluid

Abstract

Studies with Wilson disease model mice that accumulate excessive copper, due to a dysfunctional ATP7B ‘copper pump’ resulting in decreased biliary excretion, showed that the compensatory increase in urinary copper loss was due to a small copper carrier (∼1kDa) (SCC). We show here that SCC is also present in the blood plasma of normal and Wilson disease model mice and dogs, as determined by ultrafiltration and size exclusion chromatography (SEC). It is secreted by cultured hepatic and enterocytic cells, as determined by pretreatment with 67Cu-NTA or non-radioactive 5-10 µM Cu-nitrilotriacetate, and collecting and examining 3 kDa ultrafiltrates of the conditioned media, where a single major copper peak is detected by SEC. Four different cultured cell types exposed to the radiolabeled SCC all took up the 67Cu at various rates. Rates differed somewhat when uptake was from Cu-NTA. Uptake of SCC-67Cu was inhibited by excess non-radioactive Cu(I) or Ag(I) ions, suggesting competition for uptake by copper transporter 1 (CTR1). Knockout of CTR1 in fibroblasts reduced uptake rates by 60%, confirming its participation, but also involvement of other transporters. Inhibitors of endocytosis, or an excess of metal ions taken up by divalent metal transporter 1 (DMT1), did not decrease SCC-67Cu uptake. The results imply that SCC may play a significant role in copper transport and homeostasis, transferring copper particularly from the liver (but also intestinal cells) to other cells within the mammalian organism, as well as spilling excess into the urine in copper overload—as an alternative means of copper excretion.

A fluorometric assay to determine labile copper(II) ions in serum

“…The metal is distributed throughout the body via the bloodstream, and 0.75–1.4 mg/L Cu 2+ can be found in human serum 3,4 . Approximately 70–90% thereof is contained in ceruloplasmin (CP), while the remaining Cu 2+ , which is typically being referred to as loosely bound Cu 2+ , is associated with albumin (10–15%), α-macroglobulin (5–15%), clotting factors, enzymes (superoxide dismutase (SOD), Oxidases), metallothionein, as well as small Cu 2+ carriers 3 – 5 . The loosely bound Cu 2+ species comprises the whole amount of serum Cu 2+ that is not bound to CP, whereas so-called labile Cu 2+ represents a smaller subset of the loosely bound pool and is defined only to be in equilibrium with low molecular weight (LMW) ligands, e.g., amino acids.…”

Potential Therapeutic Properties of Olea europaea Leaves from Selected Cultivars Based on Their Mineral and Organic Profiles

“…Manganese is implicated in several biological processes, with the literature describing manganese deficiencies as uncommon but holding a concern for the association of cancer susceptibility with low Mn-dependent superoxide dismutase activity. A vegetarian lifestyle prevents Mn deficiency though it might lead to iron deficiency [ 44 ], which in turn may lead to anemia, and copper build-up in the duodenal epithelium and liver [ 45 ]. Copper is predominantly found in the human brain, being absorbed in the intestine and excreted through bile [ 46 ]; moreover, it has been identified as a potential therapeutic target for obesity and nonalcoholic fatty liver disease (NAFLD), Alzheimer’s disease (AD), and Parkinson’s disease (PD), among others [ 39 ].…”

Copper and Diabetes: Current Research and Prospect

“…This process cannot be inhibited by an endocytosis inhibitor or an excess of metal ions taken up by divalent metal transporter 1, indicating alternative pathways to excreting excess Cu. [ 26 ] Furthermore, a recent study showed that a localized lysosome copper transporter, SLC46A3, can modulate intracellular copper levels by sequestering copper in lysosomes, [ 27 ] which demonstrated a new copper‐regulated pathway in cells (Figure 1).…”