Evaluation of a prototype point-of-care instrument based on monochromatic x-ray fluorescence spectrometry: potential for monitoring trace element status of subjects with neurodegenerative disease.

Assessment of trace elements such as Cu, Zn, and Se in patients with neurodegenerative disease, such as Alzheimer's (AD) and Parkinson's disease (PD), may be useful in etiologic studies and in assessing the risk of developing these conditions. A prototype point-of-care (POC) instrument based on monochromatic x-ray fluorescence (M-XRF) was assembled and evaluated for the determination of Cu, Zn, and Se in whole blood, plasma, and urine. The prototype instrument was validated using certified reference materials for Cu and Zn in serum/plasma, and the reported bias and relative imprecision were <10%. The M-XRF prototype performance was further assessed using human specimens collected from AD and PD subjects, and was found to be satisfactory (<20% bias) for monitoring Cu and Zn levels in plasma and whole blood. However, the prototype M-XRF sensitivity was not sufficient for quantifying Cu, Zn, or Se in urine. Nonetheless, while validating the prototype instrument, body fluids (whole blood, plasma, and urine) were collected from 19 AD patients, 23 PD patients, and 24 controls specifically for trace element analysis using well-validated methods based on inductively coupled plasma mass spectrometry (ICP-MS). This limited biomonitoring study provided robust data for up to 16 elements including Sb, As, Ba, Cd, Cs, Co, Cr, Cu, Hg, Pb, Mo, Se, Tl, Sn, Zn, and U in plasma, whole blood, and urine. The results did not indicate any significant differences in most trace elements studied between AD or PD patients compared to controls, although the sample size is limited. A statistically significant increase in plasma Se was identified for PD patients relative to AD patients, but this could be due to age differences.

Subclinical zinc deficiency in Alzheimer's disease and Parkinson's disease.

To evaluate zinc status in Alzheimer's disease and Parkinson's disease, 29 patients with Alzheimer's disease, 30 patients with Parkinson's disease, and 29 age- and sex-matched controls were studied. All patients and controls were older than age 50, and all zinc and copper supplements were prohibited beginning 30 days prior to study. Patients were diagnosed by standard criteria. Blood zinc and urine zinc were measured. Urine zinc was measured in a casual specimen, standardized for dilution by reference to creatinine content. Results showed a significantly lower blood zinc in patients with Alzheimer's and patients with Parkinson's than in controls. Urine zinc excretion, normalized to urine creatinine excretion, was not significantly different in either patient group compared to controls. These patients are probably zinc deficient because of nutritional inadequacy.

Copper and ceruloplasmin abnormalities in Alzheimer's disease.

The idea that copper may play a role in the pathogenesis of Alzheimer's disease is gaining momentum. Serum copper and ceruloplasmin were measured by both enzymatic (eCp) and immunologic (iCp) methods in 28 patients with Alzheimer's disease and 29 age-matched controls. ''Free copper'' was determined by subtracting copper accounted for in the eCp assay from total serum copper. Percentage free copper, that is the proportion of serum copper not bound to ceruloplasmin, was significantly elevated in patients with Alzheimer's compared to controls. There was significantly more ''defective'' ceruloplasmin, which is apoceruloplamin lacking its copper, in Alzheimer's disease than in normal controls. This abnormality may precede the clinical onset of the disease and help predict risk of disease onset. Increased exposure to environmental copper (eg, the spread of copper plumbing and the use of copper in supplements) and/or defective ceruloplasmin function may play a role in the current epidemic of Alzheimer's disease.