Analysis of amino acids in Mucuna pruriens supplements using hydrophilic interaction liquid chromatography-tandem mass spectrometry

Mucuna pruriens (MP), or velvet bean, has been used as an alternative medicine in India for over 4500 years, predominantly due to the natural abundance of the non-protein amino acid L-3,4-dihydroxyphenylalanine (L-DOPA). L-DOPA (levodopa) is used to treat Parkinson's disease (PD), a condition in which the progressive loss of dopaminergic neurons causes dopamine deficiency and impaired motor function. Although L-DOPA increases dopamine synthesis in the remaining dopaminergic neurones in the PD brain, the rate of disease progression appears to remain unchanged. Some studies have demonstrated improved outcomes in patients taking MP preparations compared to those undergoing traditional L-DOPA therapy. There is evidence that the canonical amino acids and L-DOPA precursors L-phenylalanine (L-Phe) and L-tyrosine (L-Tyr) can increase dopamine synthesis and also protect against the mistaken incorporation of L-DOPA into proteins during protein synthesis. The current study developed and validated a sensitive HILIC-TQMS method for the quantification of L-DOPA and related amino acids in MP preparations. Analysis revealed that L-DOPA levels were 66.2% to 82.7% of the values reported by manufacturers. Tyr and Phe were present in both free and protein bound forms in all 5 preparations analysed, potentially offering protection against the mistaken incorporation of L-DOPA into proteins and promoting increased dopamine synthesis. These findings suggest that the additional reported benefits of MP supplements for PD treatment might, in part, be attributable to the presence of these amino acids, further supporting the need to investigate the administration of L-DOPA and its cognate amino acid in symptomatic treatment of PD.