Abstract
The techniques of Inductively Coupled Plasma Mass Spectrometry, (ICP-MS), Instrumental Neutron Activation Analysis, (INAA) and Electrothermal Atomic Absorption Spectrometry, (ETAAS) have been applied to the determination of trace elements in brain tissue. The experimental arrangement and operating conditions have been described for all techniques and the HPGe detector used in INAA has been calibrated. Method development initially was carried out on porcine brain tissue and the homogeneity and precision of the methods is described. Accuracy of the methods was evaluated using NIST Certified Reference Materials and IAEA Animal Blood. Human brain samples from ‘normal’, Alzheimer’s subjects and subjects with Senile Involutive Cortical Changes, (SICC) were sent from the Netherlands Brain Bank. Brain samples were taken from the frontal, parietal and temporal lobes of the cortex, hippocampus and thalamus of both hemispheres. All samples were freeze dried and the Dry to Fresh Weight (DFW) conversion ratios were found to be age related. DFW ratios were increased in the temporal lobe and hippocampus of ‘normal’ subjects, when compared to the Alzheimer’s subjects and DFW ratios were increased in the temporal lobe of the ‘normal’ subjects compared to the subjects with SICC. For elemental concentrations determined by ICP-MS, the ‘normal’ subjects Cu, Zn I and Cd showed positive correlations with age, at significance (p<0.02), (p<0.002) and (p<0.001), respectively. For the Alzheimer’s Disease subjects, negative correlations with disease duration were seen for Cu and Zn, at significance (p<0.001). Cd and Hg in the ‘normal’ subjects and Cd in the Alzheimer’s subjects correlated negatively with the degree of tangles at a high level of significance, (p<0.001). When comparing groups, it was found that Cu, Zn, Hg and Li were found to be increased in ‘normal’ subjects compared to the Alzheimer’s. No significant differences for Fe, Mn, Se, Cd and Pb were found. When comparing the ‘normal’ and the SICC groups, Fe, Zn, Cd and Hg were found to be higher in the ‘normal’ subjects. No significant differences (p>0.1) were found for Mn, Cu, Se and Pb. When comparing the SICC subjects and Alzheimer’s subjects, Fe, Mn, Zn and Cd were found to be increased in the Alzheimer’s subjects and no significant differences were found for Se, Cu and Hg. INAA was carried out on samples taken from the cortex only. Br, Se, Ag and Eu correlated positively with age in the ‘normal’ subjects, at significance (p<0.002), (p<0.02), (p<0.1) and (p<0.1), respectively. Negative correlations with age were found for Fe, at significance (p<0.1) and positive correlations with age for Cs at significance (p<0.05). With disease duration, negative correlations for Zn, K, Rb and Se were seen, at significance (p<0.02), (p<0.02), (p<0.001) and (p<0.1), whereas for Ag and Ba positive correlations were seen, at significance (p<0.05). Positive correlations with the dementia scale was seen for Br, at significance (p<0.02). In the ‘normal’ subjects, tangles correlated positively for Se and Br, at significance (p<0.1) and (p<0.01), respectively and correlated negatively for Cs at significance (p<0.1). In the Alzheimer’s subjects, negative correlations were found for K, Zn, Rb, Se and Cs with the tangles, at significance (p<0.02), (p<0.05), (p<0.001), (p<0.1) and (p<0.001), respectively and a positive correlation was seen for Br, at significance (p<0.1). When comparing ‘normals’ and Alzheimer’s subjects, Br, Na and Fe were found to be increased in the Alzheimer’s subjects and K, Zn, Se, Rb, Ba and Eu showed no significant differences. Cs and Hg were found to be increased in the ‘normal’ subjects. A method intercomparison for ICP-MS and INAA was undertaken for Fe, Se and Zn, no significant differences, (p>0.1) were found between the two methods for the same samples using the Wilcoxon Matched Pairs Test.