Effect of Selegiline Administration on the Urinary Excretion of Dopamine-Derived Tetrahydroisoquinoline Alkaloids in Parkinson’s Disease Patients

It has long been suggested that, in humans, the biosynthesis of salsolinol (Sal), a dopamine (DA)-derived isoquinoline alkaloid, might occur by condensation of DA with acetaldehyde or with pyruvic acid followed by oxidative decarboxylation and reduction (Figure 1). Sal possesses an asymmetric center at C-1 and exists as R and S enantiomers. There is supportive evidence that, at least in healthy subjects under physiological conditions, Sal biosynthesis should result from the condensation of DA with pyruvic acid: 1) 1-carboxysalsolinol and 1,2-dehydrosalsolinol (DSal) have been detected in human brain and urine together with Sal (Sjoquist and Ljungquist, 1985; Ung-Chhun et al., 1985; Dostert et al., 1990a); and 2) the presence of only the R enantiomer of Sal in urine of healthy subjects (Dostert et al., 1991) would not be consistent with this compound arising from the non-enzymic condensation of DA with acetaldehyde.