Receptor and transporter binding and activity profiles of albiflorin extracted from Radix paeoniae Alba

Abstract

Albiflorin, a traditional Chinese herb, is a main component of Radix paeoniae Alba, which has been used for the treatment of depressive disorders since ancient times. However, the mechanism of the antidepressant effect of albiflorin is poorly understood. Thus, we explored the binding profile of albiflorin at neurotransmitter receptors and transporters. We also characterised the in vivo effect of albiflorin on monoaminergic systems by using microanalysis to determine the extracellular levels of serotonin (5-HT) and norepinephrine (NE) in the hypothalamus of freely moving rats administered albiflorin. We found that albiflorin inhibited the uptake of 5-HT and NE and displayed robust binding affinities for the transporters of both neurotransmitters. By contrast, albiflorin (10 μM) showed no significant affinity to a wide array of central nervous system receptors. The results of our in vivo microdialysis studies showed that administration of albiflorin (3.5, 7.0, 14.0 mg/kg) significantly increased extracellular concentrations of 5-HT and NE in the hypothalamus of freely moving rats. Overall, the current study showed that albiflorin is a novel 5-HT and NE reuptake inhibitor with high selectivity.

Figure 1

Albiflorin competes for the binding of radioligands specific to the rSERT (a) rNET (b) and rDAT (c). For each transporter bioassay, a known comparator was used [fluoxetine (5-HT reuptake inhibitor); desipramine (NE reuptake inhibitor); and nomifensine (DA reuptake inhibitor)]. The IC₅₀ value was generated from each of these curves and used to generate the K_i values. Each data point depicted represents the mean ± S.E.M. of three independent experiments performed in triplicate. The K_i values for albiflorin and the comparators are shown in Table 1.

Figure 2

Albiflorin competes for the binding of radioligands specific to the cloned human SERT (a) NET (b) and DAT (c) expressed in HEK293 cell lines. For each transporter bioassay, a known comparator was used [fluoxetine (5-HT reuptake inhibitor); desipramine (NE reuptake inhibitor); and nomifensine (DA reuptake inhibitor)]. The IC₅₀ value was generated from each of these curves and used to generate the Ki values. Each data point depicted represents the mean ± S.E.M. of three independent experiments performed in triplicate. The K_i values for albiflorin and the comparators are shown in Table 1.

Figure 3

Functional activity of albiflorin demonstrates inhibition of radiolabeled uptake of serotonin (a) norepinephrine (b) and dopamine (c) in rat synaptosomes. For each uptake transporter bioassay, a known comparator was used [fluoxetine (5-HT reuptake inhibitor); desipramine (NE reuptake inhibitor); nomifensine (DA reuptake inhibitor)]. Each data point depicted represents the mean ± S.E.M. of three independent experiments performed in triplicate. The IC₅₀values for albiflorin are shown in Table 2.

Figure 4

Functional activity of albiflorin demonstrates inhibition of radiolabeled uptake of serotonin (a) norepinephrine (b) and dopamine (c) in cloned human transporters expressing in HEK293 cell lines. For each uptake transporter bioassay, a known comparator was used [fluoxetine (5-HT reuptake inhibitor); desipramine (NE reuptake inhibitor); nomifensine (DA reuptake inhibitor)]. Each data point depicted represents the mean ± S.E.M. of three independent experiments performed in triplicate. The IC₅₀ values for albiflorin are shown in Table 2.

Figure 5. Effect of albiflorin on extracellular 5-HT, NE and DA levels in the frontal cortex of rats measured by micro dialysis (n = 6–9 per group).

Data points represent mean ± S.E.M. of 5-HT (a), NE (b) and DA (c) levels expressed relative to basal pretreatment values (define as 100%). Arrow indicates time of drug administration. albiflorin was administered via oral gavage in a volume of 1 ml/kg to rats. *P < 0.05 indicate significant differences compared with saline.