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Rodent hair is a Poor biomarker for internal manganese exposure
Rekha C Balachandran1, Frank M Yanko2, Pinjing Cheng3
1School of Health Sciences, Purdue University, West Lafayette, IN, USA; Abt Associates, Rockville, MD, USA.
Abstract:
Hair is used as a biomarker of manganese (Mn) exposure, yet there is limited evidence to support its utility to quantify internal vs external Mn exposure. C57BL/6 J mice and Sprague-Dawley rats were exposed in two blocks of 3 subcutaneous injections every 3 days starting on day 0 or 20. The control group received two blocks of saline (vehicle); Treatment A received the first block as Mn (50 mg/kg MnCl2 tetrahydrate), with the second block as either methylmercury (MeHg at 2.6 or 1.3 mg/kg) for mice or vehicle for rats; and Treatment B received Mn for both blocks. Hair was collected on days 0 and 60 from all treatment groups and Mn quantified by inductively coupled plasma-mass spectrometry (ICP-MS) and total Hg by Direct Mercury Analyzer (DMA). No correlation between internal Mn dose and hair Mn was observed, whereas hair Hg was significantly elevated in MeHg exposed vs non-exposed mice. Whole body Mn content at day 60 was quantified postmortem by neutron activation analysis, which detected significantly elevated Mn for Treatment B in mice and rats. Overall, we find no evidence to support the use of hair as a valid biomarker for internal exposure to Mn at a neurotoxic level.
Insights
Hair manganese levels do not reflect internal manganese exposure. This study found no correlation between manganese dose and hair manganese, questioning its use as a biomarker for neurotoxic manganese exposure.
Area of Science:
- Environmental toxicology
- Biomarker research
- Neurotoxicology
Background:
- Hair is a potential biomarker for manganese (Mn) exposure.
- Limited evidence exists to validate hair Mn for quantifying internal versus external exposure.
Purpose of the Study:
- To investigate the utility of hair as a biomarker for internal manganese exposure.
- To assess the correlation between administered manganese dose and hair manganese concentrations.
- To evaluate hair mercury levels as a contrast to manganese exposure.
Main Methods:
- C57BL/6J mice and Sprague-Dawley rats were administered subcutaneous injections of manganese chloride (MnCl2) and/or methylmercury (MeHg).
- Hair and whole-body samples were collected at specified time points (days 0 and 60).
- Manganese was quantified using inductively coupled plasma-mass spectrometry (ICP-MS), and mercury using Direct Mercury Analyzer (DMA); whole-body manganese was analyzed by neutron activation analysis.
Main Results:
- No significant correlation was observed between internal manganese dose and hair manganese concentrations.
- Hair mercury levels were significantly elevated in mice exposed to methylmercury.
- Whole-body manganese content was significantly elevated in both mice and rats treated with manganese in both injection blocks.
Conclusions:
- Hair is not a reliable biomarker for assessing internal manganese exposure at neurotoxic levels.
- The findings question the current use of hair manganese analysis for exposure assessment.
- Further research may be needed to identify valid biomarkers for internal manganese exposure.
