Rapid size fractionation of metal species in paired human serum and cerebrospinal fluid samples using ultrafiltration with off-line element selective detection

Abstract

The transport of metal species across the neural barriers, that means from serum into cerebrospinal fluid (CSF) and brain, is a key issue for metal-induced or metal-promoted neurodegenerative effects. The molecular size is an important factor for the permeation of metal species across these barriers. Therefore the accurate determination of the size-distribution of the species of relevant metals in serum and CSF is an important aspect for estimating their permeation behaviour at the neural barriers. Size-exclusion chromatography (SEC) coupled to element selective detection has been reported to be suitable for this application. However, there are several drawbacks including long analysis times, high effort for column cleaning and potential species transformation during separation. Therefore, the current study investigates the use of ultrafiltration as an alternative fractionation technique for paired human CSF and serum samples. Total concentrations of Mn, Fe, Cu, Zn, Mg and Ca in the original samples, in the permeate samples and in the retentate samples were determined by inductively coupled plasma mass spectrometry (ICP-MS). The percentage amount of low molecular mass species in CSF was determined as (70 ± 20)% for Mn, (5 ± 2)% for Fe, (6 ± 4)% for Cu, (20 ± 10)% for Zn, (103 ± 7)% for Mg and (101 ± 7)% for Ca. Much lower percentage amounts of low molecular mass species were found in serum for Fe (0.2 ± 0.2%), Cu (0.3 ± 0.1%), Zn (0.8 ± 0.3%) and Mn (10 ± 10%) while the respective results for Mg (68 ± 5%) and Ca (57 ± 5%) were only slightly lower. For comparison the same paired samples were analysed with SEC-ICP-MS. The applied ultrafiltration method includes pre-cleaning of the filtration units to avoid contamination, and has several advantages compared to SEC-ICP-MS in respect to sample throughput, contamination control, species stability and availability of the undiluted low molecular mass fraction for further characterisation. The procedure may open new possibilities for the investigation of neurodegenerative effects of Mn and further metals.