Daidzin and its antidipsotropic analogs inhibit serotonin and dopamine metabolism in isolated mitochondria

Abstract

Daidzin, a major active principle of an ancient Chinese herbal treatment (Radix puerariae) for alcohol abuse, selectively suppresses ethanol intake in all rodent models tested. It also inhibits mitochondrial aldehyde dehydrogenase (ALDH-2). Studies on ethanol intake suppression and ALDH-2 inhibition by structural analogs of daidzin established a link between these two activities and suggested that daidzin may suppress ethanol intake by inhibiting ALDH-2. ALDH-2 is a principal enzyme involved in serotonin (5-HT) and dopamine (DA) metabolism. Thus, daidzin may act by inhibiting 5-HT and DA metabolism. To evaluate this possibility, we have studied the effect of daidzin and its analogs on 5-HT and DA metabolism in isolated hamster and rat liver mitochondria. Daidzin potently inhibits the formation of 5-hydroxyindole-3-acetic acid (5-HIAA) and 3,4-dihydroxyphenylacetic acid (DOPAC) from their respective amines in isolated mitochondria. Inhibition is concentration-dependent and is accompanied by a concomitant accumulation of 5-hydroxyindole-3-acetaldehyde and 3, 4-dihydroxyphenylacetaldehyde. Daidzin analogs that suppress hamster ethanol intake also inhibit 5-HIAA and DOPAC formation. Comparing their effects on mitochondria-catalyzed 5-HIAA or DOPAC formation and hamster ethanol intake reveals a positive correlation-the stronger the inhibition on 5-HIAA or DOPAC formation, the greater the ethanol intake suppression. Daidzin and its active analogs, at concentrations that significantly inhibit 5-HIAA formation, have little or no effect on mitochondria-catalyzed 5-HT depletion. It appears that the antidipsotropic action of daidzin is not mediated by 5-HT (or DA) but rather by its reactive intermediates 5-hydroxyindole-3-acetaldehyde and, presumably, 3, 4-dihydroxyphenylacetaldehyde as well, which accumulates in the presence of daidzin.

Figure 1

5-HT metabolism in hamster (A) and rat (B) liver mitochondrial preparations. 5-HT (10 μM) was incubated with freshly prepared hamster or rat liver mitochondria preparations (0.4 mg of mitochondrial protein per milliliter) in a 0.5-ml standard assay medium for 30 min. Concentrations of 5-HT and its metabolic products in the assay media then were analyzed by HPLC as described in Materials and Methods.

Figure 2

Effect of daidzin on 5-HT metabolism in hamster liver mitochondrial preparations. (A) 5-HT metabolized after 30 min of incubation in standard assay media containing 10 μM 5-HT and 0.08 mg/ml hamster liver mitochondrial preparation. (B) Concentrations of 5-HIAA (dotted bars), 5-HIAL (hatched bars), and 5-HTOL (solid bars) in the assay media after 30 min of incubation.

Figure 3

Effect of daidzin and its structural analogs on 5-HT → 5-HIAA metabolism in hamster liver mitochondrial preparations. Daidzin (✶), deczein (▪), hepzein (•), hexzein (⧫), daidzein (◊), puerarin (✠), diCM-daidzein (○), naltrexone (×), and GABA (+).

Figure 4

Effect of puerarin (circles) and daidzin (diamonds) on 5-HT → 5-HIAA metabolism in rat (solid symbols) and hamster (open symbols) liver mitochondrial preparations.

Figure 5

Effect of daidzin and its structural analogs on DA → DOPAC metabolism in hamster liver mitochondrial preparations. Daidzin (✶), deczein (▪), hepzein (•), hexzein (⧫), daidzein (◊), puerarin (✠), diCM-daidzein (○), naltrexone (×), and GABA (+).