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.

Optimization of the hydrolysis of conjugated L-DOPA, dopamine and dihydroxyphenylacetic acid in human urine for assay by high-performance liquid chromatography with electrochemical detection.

Conjugates of the catechol compounds, L-dihydroxyphenylalanine (L-DOPA), dopamine and dihydroxyphenylacetic acid in human urine were analysed using the isocratic ion-pair reversed-phase HPLC method with electrochemical detection. Acid hydrolysis, using 4 mol/l HCl for 60 min, was more effective than treatment with sulphatase for the generation of free catechols. Free (non-conjugated) catechols already present, as well as those produced by either of the hydrolysis procedures, were adsorbed onto aluminium oxide and extracted in acid solution. The repeatability of the technique for within and between-batch urine analysis was less than 2% and 8%, respectively. Free urinary dopamine (and dihydroxyphenylacetic acid) concentrations were much higher in the urine of patients treated with L-DOPA for Parkinson's disease than in healthy volunteers. At high dopamine (and dihydroxyphenylacetic acid) levels the conjugation capacity was apparently exceeded, since the overall percent conjugation of L-DOPA, dopamine and dihydroxyphenylacetic acid was decreased "concentration dependently" where the concentrations of free catechols were increased. Both in the control group and L-DOPA-treated groups, enzymatic hydrolysis was much less effective than acid hydrolysis in generating free catechols. This indicated that there were other, non-sulphated conjugates in the urine, accounting for between 66 and 100% of total conjugates.

Determination of tetrahydropapaveroline in the urine of parkinsonian patients receiving L-dopa-carbidopa (Sinemet) therapy by high-performance liquid chromatography.

Tetrahydropapaveroline (THP) concentrations were measured in the urine of Parkinsonian patients receiving L-dopa-carbidopa (Sinemet) therapy, using a method that employs a separation scheme that selectively isolates THP from urine and utilizes the Pictet-Spengler condensation of THP with formaldehyde combined with high-performance liquid chromatography for identification and determination. The mean (+/- S.D.) recoveries of THP from normal urine with 0.2 pmol/ml added and from Parkinsonian patients' urines with 0.5 pmol/ml added were 48.6 +/- 5.7 and 44.6 +/- 3.1%, respectively. Three Parkinsonian patients who were receiving either 250, 750 or 1000 mg of L-dopa (as Sinemet) daily had 24-h urinary THP excretion levels of 989, 1017 and 1600 pmol, respectively.

In vivo assessment of decarboxylase inhibition or potentiation: urinary dopamine and L-dopa output after L-dopa administration.

In the L-Dopa treated rat, a decreased urinary output of free and conjugated dopamine and an increase in free and conjugated L-Dopa excretion after administration of decarboxylase-inhibiting drugs provide a good in vivo index of Dopa decarboxylase inhibition. With the exception of free dopamine output, which showed an equivocal change, these measurements appear to provide a good yardstick of decarboxylase status in man also. Using this approach, it was not possible to find any evidence of facilitation of decarboxylase action, in L-Dopa-treated parkinsonians given pyridoxine supplements, to account for the ability of this compound to neutralize the beneficial effect of L-Dopa.