Effects of soybean ingestion on pharmacokinetics of levodopa and motor symptoms of Parkinson's disease - In relation to the effects of Mucuna pruriens

Mucuna pruriens is a levodopa-containing legume and its favorable effects on motor complications in Parkinson disease patients have been reported. The aim of this study was to investigate the effects of another legume, soybeans, on the pharmacokinetics and metabolism of levodopa. Seven parkinsonian patients with the wearing-off phenomenon and dyskinesia and five healthy volunteers participated in this study. We conducted a crossover study of the clinical effects on the participants before and after taking either levodopa (100 mg)/carbidopa (10 mg) only (LD/CD) or levodopa/carbidopa with 11 g of ground soybeans (LD/CD/soy). Parkinsonism and dyskinesia before and after ingestion of these substances were evaluated using UPDRS partIII, the modified Abnormal Involuntary Movement Scale (mAIMS) and a self-rating scale. The concentrations of plasma levodopa and its major metabolites were measured by high-performance liquid chromatography. Clinical assessment and blood sampling were conducted before and three hours after the ingestion of ground soybeans. When the patients took LD/CD/soy, they had a significantly longer on-period (p = 0.028) and a lower mAIMS score (p < 0.001). From the comparison of the results of pharmacokinetic study before and after taking LD/CD or LD/CD/soy, the estimated marginal mean (EMM) of HVA after LD/CD/soy increased in the PD group. EMMs of 3-OMD after LD/CD/soy significantly decreased both in PD patients and healthy controls. These results indicate that soy partly increased the bioavailability of levodopa and suppressed levodopa degradation through COMT. Soybeans may have favorable effects on the motor complications occurring under current levodopa therapy. Further investigation to clarify the mechanism underlying such effects is required.