The modulating effect of myo-inositol and other antidepressants on the mRNA levels and protein expression of selected subcellular enzymes

Abstract

Myo-lnositol (mIns), a natural component of the human diet and essential precursor of several signalling pathways, including that of G protein-coupled receptors, has also been shown to be effective in the treatment of psychiatric disorders such as depression, obsessive compulsive disorder and panic disorder. Most likely since mlns is a simple isomer of glucose, no serious side effects have been reported with its use, even at high oral doses of mlns. Previous studies suggest that the therapeutic action of mlns may include reduced serotonin 5HTzA and muscarinic acetylcholine receptor function. An important signal transduction system that may possibly be involved in the mechanism of action of antidepressants is phosphoinositide (PI) turnover. In this signalling system PI-phospholipase C (PLCpl), that is implicated in the in the mechanism of action of antidepressants and anxiolytics, is activated. The mechanism of action of mlns, however, still remains elusive and needs further investigation. In this study a possible modulatory role of 24-hour pre-treatment of human neuroblastoma cell line (SH-SY5Y) with mlns on mRNA levels and protein expression of phospholipase C-p1 (PLCP1) and glycogen synthase kinase 3P (GSK3p) was investigated. The effects of mlns were also compared to that of other prototype antidepressants, such as fluoxetine (a selective serotonin reuptake inhibitor), imipramine (a tricyclic antidepressant), lithium and another drug with potential antidepressant effects, sildenafil (phosphodiesterase 5-type (PDE5) inhibitor). Real-time reverse transcription Polymerase Chain Reaction (RTPCR) was performed in order to investigate the mRNA levels, while protein expression in membranes and the cytosol fraction of cells were quantified with Western blots. The expression of PLCPl was decreased after pre-treatments with imipramine or myoinositol in combination with fluoxetine. In addition, sildenafil alone or in combination with myo-inositol, also decreased the expression of membrane-bound PLCp1. However, a 24-hour pre-treatment with lithium did not alter PLCPl expression significantly. Determined mRNA levels for the expression of PLCPl were consistent in these findings, except for the inhibition of the mRNA for the expression of PLCPl also after lithium treatment. The reduced PLCpl mRNA levels after lithium pre-treatment may suggest the involvement of posttranscriptional modification (or delayed translational effects) of PLCpl after lithium treatment. The data from the current study suggest that antidepressant action may include downregulation of PLCPl expression and that modulators of the nitric oxidecGMP pathway (e.g. sildenafil as a PDE5 inhibitor) may exhibit similar properties.