Manganese speciation in paired serum and CSF samples using SEC-DRC-ICP-MS and CE-ICP-DRC-MS.

Occupational manganese (Mn) overexposure leads to accumulation in the brain and has been shown to cause progressive, permanent, neuro-degenerative damage with syndromes similar to idiopathic Parkinsonism. Mn is transported by an active mechanism across neural barriers (NB) finally into the brain; but to date, modes of Mn neurotoxic action are poorly understood. This paper investigates the relevant Mn-carrier species which are responsible for widely uncontrolled transport across NB. Mn speciation in paired serum/cerebrospinal fluid (CSF) samples was performed by size exclusion chromatography-inductively coupled plasma-dynamic reaction cell-mass spectrometry (SEC-ICP-DRC-MS) and capillary zone electrophoresis coupled to ICP-DRC-MS in a 2D approach for clear identification. For additional species verification, electrospray ionization-Fourier transform ion cyclotron resonance-mass spectrometry was used after SEC-ICP-DRC-MS (second 2D approach). The Mn species from the different sample types were interrelated and correlation coefficients were calculated. In serum protein-bound Mn species like Mn-transferrin/albumin (Mn-Tf/HSA) were dominant, which had the main influence on total Mn in serum if Mn(total) was <1.5 μg/L. Above serum Mn(total) concentration of 1.6 μg/L the serum Mn(total) concentration was correlated with increasing Mn-citrate (Mn-Cit) concentration. In parallel Mn(total) and Mn species in CSF were determined. It turned out that Mn(total) from CSF was about half of Mn(total) in serum; Mn-Tf/HSA was only about 10% compared to serum. It turned out that above 1.6 μg/L Mn(total) in serum Mn-Cit was not only the leading Mn species in serum but also was the main influencing factor of both Mn(total) and Mn-Cit concentration in CSF. These results were further investigated using two statistical models (orthogonal partial least squares discriminant analysis, canonical discriminant analysis). Both models discriminated the samples in two groups where CSF samples were either correlated to Mn(total) and Mn-Cit (samples with serum Mn(total) > 1,550 ng/L) or correlated to Mn-Tf/HSA (samples with serum Mn(total) < 1,550 ng/L). We conclude that elevated Mn-Cit(serum) could be a valuable marker for increased total Mn in CSF (and brain), i.e., it could be a marker for elevated risk of Mn-dependent neurological disorders such as manganism in occupational health.