X-ray fluorescence imaging of the hippocampal formation after manganese exposure.

Manganese (Mn) intoxication results in neurological conditions similar, but not identical, to idiopathic Parkinson's disease. While the mechanism(s) by which Mn exposure leads to neurotoxic effects remains unclear, studies by magnetic resonance imaging demonstrate a high Mn accumulation in the hippocampal formation (HPCf) of the brain. Metal quantification using this method is not possible. Using X-ray fluorescence imaging, we measured the distribution of Mn in the HPCf for a rodent model of chronic Mn exposure and quantitatively compared it with distributions of other biologically relevant metals. We found considerable increases in average Mn concentrations in all analyzed areas and we identified the dentate gyrus (DG) and the cornus ammonis 3 (CA3) layer as areas accumulating the highest Mn content (∼1.2 µg Mn per g tissue). The DG is significantly enriched with iron (Fe), while the CA3 layer has high zinc (Zn) content. Additionally, significant spatial correlations were found for Mn-Zn concentrations across the HPCf substructures and for Mn-Fe concentrations in the DG. Combined results support that at least two mechanisms may be responsible for Mn transport and/or storage in the brain, associated with either Fe or Zn. Subcellular resolution images of metal distribution in cells of the CA3 show diffuse Mn distributions consistent with Mn localization in both the cytoplasm and nucleus. Mn was not increased in localized intracellular Fe or copper accumulations. A consistent Mn-Zn correlation both at the tissue (40 µm × 40 µm) and cellular (0.3 µm × 0.3 µm) levels suggests that a Zn transport/storage mechanism in the HPCf is likely associated with Mn accumulation.

X-ray fluorescence imaging: a new tool for studying manganese neurotoxicity.

The neurotoxic effect of manganese (Mn) establishes itself in a condition known as manganism or Mn induced parkinsonism. While this condition was first diagnosed about 170 years ago, the mechanism of the neurotoxic action of Mn remains unknown. Moreover, the possibility that Mn exposure combined with other genetic and environmental factors can contribute to the development of Parkinson's disease has been discussed in the literature and several epidemiological studies have demonstrated a correlation between Mn exposure and an elevated risk of Parkinson's disease. Here, we introduce X-ray fluorescence imaging as a new quantitative tool for analysis of the Mn distribution in the brain with high spatial resolution. The animal model employed mimics deficits observed in affected human subjects. The obtained maps of Mn distribution in the brain demonstrate the highest Mn content in the globus pallidus, the thalamus, and the substantia nigra pars compacta. To test the hypothesis that Mn transport into/distribution within brain cells mimics that of other biologically relevant metal ions, such as iron, copper, or zinc, their distributions were compared. It was demonstrated that the Mn distribution does not follow the distributions of any of these metals in the brain. The majority of Mn in the brain was shown to occur in the mobile state, confirming the relevance of the chelation therapy currently used to treat Mn intoxication. In cells with accumulated Mn, it can cause neurotoxic action by affecting the mitochondrial respiratory chain. This can result in increased susceptibility of the neurons of the globus pallidus, thalamus, and substantia nigra pars compacta to various environmental or genetic insults. The obtained data is the first demonstration of Mn accumulation in the substantia nigra pars compacta, and thus, can represent a link between Mn exposure and its potential effects for development of Parkinson's disease.