Antibody-mediated inhibition of EGFR reduces phosphate excretion and induces hyperphosphatemia and mild hypomagnesemia in mice.

Monoclonal antibody therapies targeting the EGF receptor (EGFR) frequently result in hypomagnesemia in human patients. In contrast, EGFR tyrosine kinase inhibitors do not affect Mg2+ balance in patients and only have a mild effect on Mg2+ homeostasis in rodents at elevated doses. EGF has also been shown to affect phosphate (Pi) transport in rat and rabbit proximal convoluted tubules (PCT), but evidence from studies targeting EGFR and looking at Pi excretion in whole animals is still missing. Thus, the role of EGF in regulating reabsorption of Mg2+ and/or Pi in the kidney remains controversial. Here, we inject mice with the anti-EGFR monoclonal antibody ME-1 for 2 weeks and observe a significant increase in serum Pi and mild hypomagnesemia, but no changes in Pi or Mg2+ excretion. In contrast, a single injection of ME-1 resulted in hyperphosphatemia and a significant reduction in Pi excretion 2 days after treatment, while no changes in serum Mg2+ or Mg2+ excretion were observed. Dietary Mg2+ deprivation is known to trigger a rapid Mg2+ conservation response in addition to hyperphosphatemia and hyperphosphaturia. Interestingly, one dose of ME-1 did not significantly modify the response of mice to 2 days of Mg2+ deprivation. These data show that EGFR plays a significant role in regulating Pi reabsorption in the kidney PCT, but suggest only a minor role in long-term regulation of Mg2+ transport in the distal convoluted tubule.

Plasma and urinary levels of cytokines in patients with idiopathic hypercalciuria.

BACKGROUND: Recent studies suggest that cytokines modulate bone turnover. Idiopathic hypercalciuria (IH) seems to be associated with bone mineral loss. Therefore, the aim of this study was to assess cytokines involved in bone turnover in patients with IH. METHODS: Plasma and spot-urine levels of interleukin (IL)-1ß, IL-6, IL-8, tumor necrosis factor alpha (TNF-α), transforming growth factor ß1 (TGF-ß1), and monocyte chemoattractant protein (MCP-1) were measured in 70 children and adolescents with IH and in 37 healthy controls. Patients with IH were subdivided according to their calciuria at the time of sample collection: ≥4 mg/kg/day (persistent IH, n=27) and below 4 mg/kg/day (controlled IH, n=43). Cytokines were determined by enzyme-linked immunoassay. RESULTS: Plasma and urinary concentrations of IL-1ß, IL-6, IL-8, and TNF-α were undetectable in all groups. No differences were found between controlled and persistent hypercalciuria for plasma and urinary levels of MCP-1 and TGF-ß1. On the other hand, MCP-1 levels were significantly higher in both subgroups of IH in comparison to healthy controls. Furthermore, urinary MCP-1 levels of IH patients correlated positively with bone mineral content (p=0.013). CONCLUSION: Although cytokine measurements did not allow the differentiation between persistent and controlled IH, our findings suggest that MCP-1 might play a role in patients with IH.