The effects of the antidepressant mirtazapine on cytosolic Ca2+ concentrations ([Ca2+]i) in human prostate cancer PC3 cells and human osteosarcoma MG63 cells were measured by Ca2+-sensitive fluorescent probe fura-2. In Ca2+-containing medium, mirtazapine induced [Ca2+]i rises in a concentration-dependent manner in both PC3 and MG63 cells. Removal of extracellular Ca2+ inhibited the mirtazapine-induced Ca2+ signal. In Ca2+-free medium, thapsigargin (an inhibitor of the endoplasmic reticulum Ca2+-ATPase pump) induced [Ca2+]i rises by passively depleting the endoplasmic reticulum Ca2+ store, after which the increasing effect of mirtazapine (1.5 mM) on [Ca2+]i was reduced. Conversely, pretreatment with mirtazapine decreased thapsigargin-induced [Ca2+]i rises in PC3 and MG63 cells. When PC3 cells were pretreated with U73122, a phospholipase C inhibitor, mirtazapine-induced [Ca2+]i rises were inhibited by 47%. But in MG63 cells, 2 mM U73122 did not change mirtazapine-induced [Ca2+]i rises. These finding suggest that mirtazapine-induced [Ca2+]i rises were caused both by extracellular Ca2+ influx and intracellular depletion of the endoplasmic reticulum Ca2+ stores. Furthermore, the mechanism of mirtazapine-induced Ca2+ release may be different between PC3 and MG63 cells. Additionally, cell proliferation assays suggest that overnight incubation with higher concentrations of mirtazapine decreased cell viability in a concentration-dependent manner.

Depression is a physiological disorder that may be treated by increasing the body¡¦s amount of one or a few of the following neurotransmitters: serotonin, dopamine and norepinephrine. Although there are seven distinct classes of antidepressants, selective serotonin reuptake inhibitors (SSRIs) and tetracyclic antidepressants are widely prescribed and generally regarded as the first-line drugs in the treatment of depression. However, many physiological roles of some SSRIs appear to be dissociated with the inhibition of serotonin reuptake. For instance, paroxetine, a member of SSRIs and maprotiline, a member of tetracyclic antidepressant, have been shown to induce apoptosis or to prevent other agents from inducing apoptosis in several cell lines. Thus the effects of these two drugs on the apoptosis are still controversial. The aim of this study is to investigate the molecular mechanisms of paroxetine and maprotiline in induction of cell death in human osteosarcoma and murine neuroblastoma cells. First, WST-1 reduction assays and propidium iodide-staining assays were used to determine cell viability and apoptosis in the presence of paroxetine and maprotiline. Then immunoblotting was used to measure the activity of apoptotic markers caspase-3 and mitogen-activated protein kinases (MAPKs) to survey the apoptotic pathways induced by these two antidepressants. The experimental results may be helpful to understand the pharmacological and toxicological effects of these two antidepressants in cells from important organs. Results showed that paroxetine caused apoptosis via the activation of caspase-3 in cultured human osteosarcoma cells (MG63). Although paroxetine could activate the phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun NH2-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK), only SB203580 (a p38 MAPK inhibitor) partially prevented cells from apoptosis. Paroxetine was also found to induce [Ca2+]i increases but pretreatment with BAPTA/AM, a Ca2+ chelator, prevented paroxetine-induced [Ca2+]i increases, and thus did not protect cells from death. These results suggest that paroxetine caused Ca2+-independent apoptosis via the activation of p38 MAPK-associated caspase-3 in MG63 cells. Maprotiline was also found to induce apoptosis through increased caspase-3 activation in murine neuroblastoma Neuro-2a cells. Induction of JNK phosphorylation contributed to the activation of caspase-3 resulting in maprotiline-induced Neuro-2a cell apoptosis. Thus, it appears that maprotiline induced apoptosis via JNK/caspase-3-dependent signaling pathways. Blockage of activation of ERK was found to increase the activation of caspase-3 leading to an enhancement of maprotiline-induced apoptosis. These data suggest that ERK was a survival signal to oppose maprotiline-caused apoptotic effect in Neuro-2a cells. Thus the activation of caspase-3 by maprotiline appears to depend on the activation of JNK and the inactivation of ERK. [Ca2+]i measurement in the presence of maprotiline showed that the antidepressant induced [Ca2+]i increases. Interestingly, pretreatment with BAPTA/AM could suppress maprotiline-induced ERK phosphorylation, enhance caspase-3 activation and increase maprotiline-induced apoptosis. In conclusion, this study demonstrates that maprotiline induced apoptosis in murine neuroblastoma cells through activation of JNK-associated caspase-3 pathways. Maprotiline also evoked an anti-apoptotic response that was both Ca2+- and ERK-dependent. This thesis contains some published data in the journal of Toxicology and Applied Pharmacology and some data were submitted in the journal of Toxicology Letters.

Bone is an important organ influenced by mechanical load, hormones, nutrition and disease. During bone remodelling, osteoclasts resorb bone and osteoblasts form new bone. Osteoblasts are derived from mesenchymal stem cells (MSCs) such as adipose-derived stromal cells (ASCs). The mitogen-activated protein kinase (MAPK) pathway has been shown to interfere with osteoblast differentiation from an early stage. Runt related transcription factor 2 (RUNX2) exerts an effect downstream from p38 MAPK. RUNX2 phosphorylation by p38 MAPK may increase osteoblast differentiation markers such as alkaline phosphatase (ALP), osteoprotegerin (OPG) and receptor activator of nuclear factor kB ligand (RANKL). Palmitoleic acid (PLA), an omega-7 monounsaturated fatty acid (MUFA), promotes anti-osteoclastogenic effects, however, the effects of PLA on osteoblasts has not been reported. Osteoporosis is a condition which has debilitating effects in the elderly. Unsaturated fatty acids (UFA) have been studied for their beneficial effects on human health for a number of years. Polyunsaturated fatty acids (PUFA) have been studied as a potential therapeutic agent to prevent and assist in managing the condition. Few studies have been conducted on the effects of MUFA on bone therefore this study aimed to investigate the effects of PLA on osteoblast differentiation using ASCs and MG-63 osteosarcoma cells as an osteoblast model. ASCs and MG-63 osteosarcoma cell lines were exposed to PLA (20-100 μM) in osteogenic media (OM). The effects of PLA on cell viability was evaluated on undifferentiated cells. Thereafter, cells were exposed to PLA for 7, 14 or 21 days. Subsequently ALP activity, calcium mineralisation, gene expression, protein expression and adipogenesis were assessed. In this study, PLA had no significant effects on cell viability in undifferentiated cells. Furthermore, PLA had no significant effects on ALP activity, calcium mineralisation or phosphorylated extracellular signal-regulated kinase (pERK)/extracellular signal-regulated kinase (ERK) expression in differentiating cells, however, ALP activity increased at 7 day in ASCs and 21 days in MG-63 cells. Alizarin Red S staining increased at 21 days in both cell lines with a significant increase in the ASCs, however, calcium nodules were not visible. In the ASCs, PLA significantly increased the gene expression of ALP at 7 and 14 days compared to control (p<0.01 and p<0.05) while RANKL was significantly decreased at 7 days compared to the control (p<0.05). In the MG-63 cells, RUNX2 and OCN were significantly reduced at 7 days compared to control (p<0.05) and ALP, RUNX2, Osx and RANKL were significantly reduced at 14 days compared to control (p<0.001 and p<0.05). In the ASCs, lipid accumulation was not present after 21 days while in MG-63 cells, there was a significant increase in lipid accumulation at a high concentration of PLA after 21 days compared to control (p<0.05). This is the first study to explore the effects of PLA on osteoblast formation using ASCs and MG-63 osteosarcoma cells. Results suggest that PLA exerted changes in the ASCs and MG-63 cells during osteoblast differentiation, however, these changes were not significant. To conclude, PLA showed some significant effects on osteoblast-specific gene expression, however, most of the osteoblast-specific gene expression was downregulated, particularly in the MG-63 cells, after PLA treatment. / Dissertation (MSc)--University of Pretoria, 2020. / Physiology / MSc / Unrestricted