Biliary excretion and tissue distribution of penta- and hexavalent molybdenum in rats

Accumulation of molybdenum in major organs following repeated oral administration of bis-choline tetrathiomolybdate in the Sprague Dawley rat

Molybdenum is an essential dietary trace element required for several critical enzyme systems. High intake is associated with toxicity in ruminants and animal studies. The proposed therapeutic use of molybdenum based drugs poses a potential risk for accumulation through chronic administration of therapeutic doses of this element. The current experiment was designed to study the effect of daily dosing of a molybdenum compound, bis-choline tetrathiomolybdate (TTM), in Sprague Dawley rats using laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-ToF-MS), and two dosing levels of TTM for up to 3-months. To investigate if molybdenum accumulation was associated with tissue toxicity, histopathology, haematology and clinical biochemistry markers of toxicity were incorporated into the study design. There were no behavioural signs of toxicity to the rats, and no clinical or anatomic pathology associated with treatment. The current data did show a progressive accumulation of molybdenum within the adrenal gland, kidneys, liver, spleen, brain and testes. While this was not associated with tissue toxicity within the three-month study design, greater exposure over a longer period of time has potential for adverse pathophysiological cellular function. Tissue toxicity, as a result of local excessive accumulation of molybdenum over time has clear implications for the therapeutic use of molybdenum in humans and demands sensitive monitoring of tissue molybdenum levels to avoid toxicity. The current study highlights the shortcomings of conventional biomonitoring approaches to detect molybdenum accumulation with the goal of avoiding molybdenum associated toxicity.

Biliary excretion of nickel in rats

Nickel (Ni) concentrations were determined by liquid scintillation spectrometry or electrothermal atomic absorption spectrophotometry in bile and plasma samples obtained from male rats following subcutaneous (s.c.) injection of 63NiCl2 (1.7 mumol/kg) or non-radioactive NiCl2 (125 or 250 mumol/kg). During the intervals from 1-6 or 11-16 h post-injection, the bile:plasma ratios of Ni concentrations ranged from 0.045-0.13, and the excretory clearance of Ni in bile ranged from 0.027-0.055 ml/h. The estimated biliary excretion of Ni in the 24 h post-injection amounted to less than 0.5% of the respective doses of NiCl2. Contrary to previous findings with other divalent metal ions, this study shows that biliary excretion is quantitatively unimportant for the elimination of exogenous Ni(II) in rats.