Chronic treatment with imipramine inhibits cell growth and enhances serotonin 2C receptor mRNA expression in NG 108-15 cells

γ-Mangostin increases serotonin 2A/2C, muscarinic, histamine and bradykinin receptor mRNA expression

AIM OF THE STUDY

γ-Mangostin is a xanthone found in the fruit hulls of Garcinia mangostana L., which have long been used in Southeast Asia as a traditional medicine for the treatment of abdominal pain, dysentery, wound infections, fever and convulsions. Recent studies have revealed that γ-mangostin exhibits a variety of pharmacological activities, including serotonin 2 (5-HT(2)) receptor antagonism, anti-inflammatory effects and analgesic effects. To explore the mechanism of γ-mangostin responsible for these pharmacological activities, especially its effects on some related receptors, we investigated the effects of γ-mangostin on 5-HT(2), histamine (H(1)) and bradykinin (BK(2)) receptor gene expression in neuroblastoma (NG 108-15) cells in vitro. Additionally, to extend the study of the pharmacological properties, we examined the effect of γ-mangostin on the muscarinic (M(4)) receptor.

MATERIALS AND METHODS

NG 108-15 cells were cultured in vitro and treated with γ-mangostin or a 5-HT(2) receptor antagonist (either imipramine or ketanserin). Then, the levels of mRNA for 5-HT(2A/2C) receptors were evaluated by semi-quantitative RT-PCR. The preventive effect of serotonin on the enhancement effects was also revealed. Additionally, the effects of γ-mangostin on the muscarinic, histamine and bradykinin receptors were determined.

RESULTS

Chronic application of γ-mangostin at a concentration of 0.1 μM induced a significant increase in the level of 5-HT(2A/2C) receptor mRNA. These effects were prevented by serotonin. Moreover, γ-mangostin up-regulated the M(4), H(1) and BK(2) receptors.

CONCLUSION

The ability of γ-mangostin to enhance the expression of 5-HT(2A/2C), muscarinic, histamine and bradykinin receptor mRNA suggests that this compound has antagonistic effects. These pharmacological properties may partly account for the benefits of using mangosteen in the treatment of inflammation, pain and neuropsychiatric symptoms.

Developmental changes in serotonin 2C receptor mRNA editing in the rat cerebral cortex and primary cultured cortical neurons

Serotonin 2C receptor (5-HT2CR) mRNA has been reported to receive editing at 5 nucleotide positions (named sites A-E) which are located inconsecutively on the nucleotide sequence encoding the 2nd intracellular loop of the receptor protein. To clarify the physiological role of 5-HT2CR mRNA editing, we investigated developmental changes in editing frequencies at sites A-E in the rat cerebral cortex and primary cultured cortical neurons. The editing at sites A and B increased in parallel with the rat brain development and reached a plateau of 80-100% frequency at postnatal days 1-3. Although editing frequency at site C was low compared to those detected at other sites except site E during a developmental period, it reached the maximal value of 30% during a first 7-d period after birth and then decreased gradually to the negligible level at PN49. Site D exhibited almost constant susceptibility (about 60%) to editing, while no editing at site E was occurred during rat brain development. Similar changes during development in editing frequencies at these sites were observed in primary cultured cortical cells during the cultivation period. These findings indicated that editing sites A-D on 5-HT2CR mRNA have different susceptibility and that the frequencies at these sites are not always constant during development.

Molecular pathopharmacology of 5-HT2C receptors and the RNA editing in the brain

Among the 14 kinds of serotonin (5-hydroxytryptamine, 5-HT) receptor subtypes (5-HTR), 5-HT(2C) receptor (5-HT2CR) has been intensively investigated because of its physiologically and pathophysiologically important role in the brain. 5-HT2CR has been suggested to be involved in depressive disorders based on findings from pharmacological/neurochemical/behavioral studies using autopsy preparations of humans suffering from depression, animal models of depression, and animals treated with antidepressant drugs. Recently the editing of 5-HT2CR mRNA has been reported to participate in the pathogenesis of depressive disease. The RNA editing of 5-HT2CR induced by the presumable alteration of deaminase during a pathological state in depression causes changes of a base to another base (e.g., adenosine to guanosine, cytidine to uracil (thymidine)), followed by changes in amino acids constituting the second intracellular transmembrane loop that couples G proteins. Thus 5-HT2CR receptor-mediated signal transduction is changed. In the present review, the pathopharmacological significance of 5-HT2CR in special reference to RNA editing of receptors is reviewed and discussed from the aspect of development of novel therapeutics for depression.

The mRNA Expression Differences of RNA Editing Enzymes in Differentiated and Undifferentiated NG108-15 Cells

The alteration of the editing pattern of serotonin 2C receptor (5-HT2CR) mRNA has been reported during cell differentiation. Since editing of 5-HT2CR mRNA is regulated by adenosine deaminases acting on RNA (ADARs), it is of interest to investigate if the expression of these enzymes changes during cell differentiation. The level of ADAR1 mRNA in NG108-15 cells was decreased by cell differentiation. These results suggest that the decrease of ADAR1 expression during cell differentiation may play an important role in the differentiation-induced alteration of the 5-HT2CR editing pattern in NG108-15.