Development and validation of a screening assay for the evaluation of putative neuroprotective agents in the treatment of Parkinson's disease.

Following initial diagnosis of Parkinson's disease, if it were possible to prescribe a treatment that could halt or prevent further neurodegeneration, disease progression could be prevented. The aim of this study was to generate a quick and reliable assay for assessing putative neuroprotective agents for parkinsonian patients. Abnormalities in mitochondria, proteasome and lysosome function, as well as oxidative stress cause cell death in Parkinson's disease. Thus, we exposed neuroblastoma (SH-SY5Y) cells to EC(50) of toxins that mimic these cell death mechanisms (dopamine to induce oxidative stress; naphthazarin to inhibit lysosome function; proteasome inhibitor N-carbobenzyloxy-Ile-Glu(O-t-butyl)-Ala-leucinal (PSI) to inhibit the UPS (ubiquitin proteasome system) and rotenone to inhibit mitochondria function) in the presence of five compounds previously chosen as neuroprotective agents, and assessed cell viability. Coenzyme Q10 (117 µM) significantly protected against four toxins, dopamine: 16.3 ± 3.3%; naphthazarin: 10.8 ± 1.1%; PSI: 16.2 ± 2.9%; rotenone: 53.2 ± 4.2%; whereas caffeine (140 µM), creatine (25 mM), nicotine (1 µM) and deprenyl (10 µM) provided protection against some, but not all toxins. Interestingly, coenzyme Q10 is the only compound out of the five that showed neuroprotective potential in clinical trials. Thus, there is a direct correlation between the success of disease modifying agents in the clinic and their ability to protect against multiple cell death mechanisms in this assay. We propose that exposure of SH-SY5Y cells to different toxins that recapitulate cell death mechanisms in Parkinson's disease serves as a rapid and reliable method to test neuroprotective agents that may succeed in clinical trials.

Protein synthesis in ovine muscle and skin: sequential measurements with three different amino acids based on the large-dose procedure.

1. Protein synthesis has been determined in biopsies from ovine skin and muscle by sequential use of three [13C] amino acids, valine leucine and phenylalanine, as large-dose injections. 2. Leucine and phenylalanine increased plasma insulin concentrations within 40 min of injection. 3. All three amino acids decreased the plasma concentrations of other amino acids. 4. Intracellular free amino acids in muscle decreased while those in skin increased. 5. The fractional rates of protein synthesis were similar, regardless of which amino acid was used, although the rates for muscle were significantly less than for skin (2.1 vs 11.0%/day, P < 0.001).