Molecular and biochemical characterization of therapeutic properties of paeoniae-glycyrrhiza decoction, a Chinese herbal preparation, against antipsychotic-associated hyperprolactinemia

Abstract

Hyperprolactinemia (hyperPRL) is a highly prevalent adverse side effect in antipsychotic therapy as most antipsychotic drugs are dopamine D2 receptor antagonists. Peony-Glycyrrhiza Decoction (PGD, 芍藥甘草湯) is a classic Chinese herbal formula initially used to treat muscle pain and spasm. Our pilot clinical studies have confirmed the effectiveness of PGD in alleviating antipsychotic-induced hyperPRL in patients with schizophrenia. In the present study, we further examined the effects of PGD, its individual herbal preparations and major compounds in suppressing prolactin (PRL) hyperactivity in in vitro and in vivo models and underlying mechanisms. PGD treatment significantly suppressed PRL secretion in MMQ cells, an exemplary model of hyperPRL that is derived from pituitary adenoma cells. PGD also suppressed PRL synthesis of MMQ cells in a dose-dependent manner; however, these suppressive effects were completely abolished by pretreatment with 10 μM haloperidol, a dopamine D2 receptor antagonist. PGD did not affect hyperactive PRL in GH3 cells that lack the D2 receptor expression, but PGD significantly increased the expressions of the D2 receptor and dopamine transporters (DAT) in PC12 cells. In the rat model of hyperPRL produced by repeated injection with the dopamine blocker metoclopramide (MCP), PGD (5 - 10 g/kg daily) treatment for 14 days significantly reduced elevated serum PRL and the reduced magnitude was similar to that of 0.6 mg/kg bromocriptine (BMT), a dopamine D2 receptor agonist used for treating hyperPRL. Both PGD and BMT did not alter serum estradiol, but PGD reversed MCP-induced decreased serum progesterone to control level, whereas BMT did not. Similar to BMT, PGD treatment displayed a great effect in reversing the MCP-induced reduction of the expressions of D2 receptor, DAT and tyrosine hydroxylase in both the pituitary and the hypothalamus, in particular the arcuate nucleus, but both had least effects on the expressions of PRL in the pituitary and hypothalamus. The anti-hyperPRL effects of individual herbal preparation and major compounds of PGD were further examined in cultured cells. The three herbal preparations, Paeoniae Radix (PR) alone, Glycyrrhiza Radix (GR) alone and the pooled PR and GR individual preparation (PR+GR), and the three major constituents 18β-glycyrrhetinic acid (GA), liquiritigenin (LQ) and paeoniflorin (PF), were tested. All these preparations and constituents displayed significant effects in suppressing PRL hyperactivity and enhancing the expressions of dopamine mediators. However, PR had the most robust anti-hyperPRL effects compared to PGD and other preparations and constituents. The present study provides experimental evidence confirming the clinical effects of PGD in suppressing antipsychotic-associated hyperPRL. Not only D2 receptor is involved in the anti-hyperPRL effect of PGD, it is also associated with the modulation of other dopamine mediators and sex hormones. The finding that the magnitudes of the anti-hyperPRL effects of PGD and of combined PR and GR are similar suggests that boiling the herbs together or or separately shows the same effects. Additionally, PR preparation appears to be more efficacious in reducing hyperPRL compared to GR preparation which deserves to be further investigated.