The pivotal role of intracellular calcium in oxaliplatin-induced inhibition of neurite outgrowth but not cell death in differentiated PC12 cells

The Therapeutic Potential of Antioxidants in Chemotherapy-Induced Peripheral Neuropathy: Evidence from Preclinical and Clinical Studies

As cancer therapies advance and patient survival improves, there has been growing concern about the long-term adverse effects that patients may experience following treatment, and concerns have been raised about such persistent, progressive, and often irreversible adverse effects. Chemotherapy is a potentially life-extending treatment, and chemotherapy-induced peripheral neuropathy (CIPN) is one of its most common long-term toxicities. At present, strategies for the prevention and treatment of CIPN are still an open problem faced by medicine, and there has been a large amount of previous evidence that oxidative damage is involved in the process of CIPN. In this review, we focus on the lines of defense involving antioxidants that exert the effect of inhibiting CIPN. We also provide an update on the targets and clinical prospects of different antioxidants (melatonin, N-acetylcysteine, vitamins, α-lipoic acid, mineral elements, phytochemicals, nutritional antioxidants, cytoprotectants and synthetic compounds) in the treatment of CIPN with the help of preclinical and clinical studies, emphasizing the great potential of antioxidants as adjuvant strategies to mitigate CIPN.

Effects of Oxaliplatin on Facial Sensitivity to Cool Temperatures and TRPM8 Expressing Trigeminal Ganglion Neurons in Mice

The chemotherapeutic agent oxaliplatin is commonly used to treat colorectal cancer. Although effective as a chemotherapeutic, it frequently produces painful peripheral neuropathies. These neuropathies can be divided into an acute sensitivity to cool temperatures in the mouth and face, and chronic neuropathic pain in the limbs and possible numbness. The chronic neuropathy also includes sensitivity to cool temperatures. Neurons that detect cool temperatures are reported to utilize Transient Receptor Potential Cation Channel, Subfamily M, Member 8 (TRPM8). Therefore, we investigated the effects of oxaliplatin on facial nociception to cool temperatures (18°C) in mice and on TRPM8 expressing trigeminal ganglion (TRG) neurons. Paclitaxel, a chemotherapeutic that is used to treat breast cancer, was included for comparison because it produces neuropathies, but acute cool temperature sensitivity in the oral cavity or face is not typically reported. Behavioral testing of facial sensitivity to 18°C indicated no hypersensitivity either acutely or chronically following either chemotherapeutic agent. However, whole cell voltage clamp experiments in TRPM8 expressing TRG neurons indicated that both oxaliplatin and paclitaxel increased Hyperpolarization-Activated Cyclic Nucleotide-Gated channel (HCN), voltage gated sodium channel (Nav), and menthol evoked TRPM8 currents. Voltage gated potassium channel (Kv) currents were not altered. Histological examination of TRPM8 fibers in the skin of the whisker pads demonstrated that the TRPM8 expressing axons and possible Merkel cell-neurite complexes were damaged by oxaliplatin. These findings indicate that oxaliplatin induces a rapid degeneration of TRG neuron axons that express TRPM8, which prevents evoked activation of the sensitized neurons and likely leads to reduced sensitivity to touch and cool temperatures. The changes in HCN, Nav, and TRPM8 currents suggest that spontaneous firing of action potentials may be increased in the deafferented neurons within the ganglion, possibly producing spontaneously induced cooling or nociceptive sensations.

Renin-angiotensin-aldosterone system inhibitors prevent the onset of oxaliplatin-induced peripheral neuropathy: A retrospective multicenter study and in vitro evaluation

Oxaliplatin (OXA) is used in chemotherapy for various cancer types and is associated with acute and chronic neurotoxicity. However, a preventive strategy for OXA-induced peripheral neuropathy (OIPN) and its underlying mechanism remain unclear. We examined the effects of renin-angiotensin-aldosterone system inhibitors (RAASIs) on OIPN by performing a retrospective multicenter study and an in vitro assay. We retrospectively evaluated electronic medical records of 976 patients who underwent one or more courses of OXA-containing regimens at Ehime, Okayama, and Tokushima University Hospitals. The primary endpoint was the incidence of OIPN during or after OXA administration. The effects of RAASIs and OXA on the neurite length in PC12 cells were determined. The combined administration of an OXA-containing regimen and RAASI significantly inhibited the cumulative incidence grade-2 or higher OIPN (log-rank test; P=0.0001). RAASIs markedly suppressed the development of both acute and chronic OIPN (multivariate analysis; P=0.017 and P=0.011). In an in vitro assay, 10 µM OXA suppressed the neurite length; treatment with 1 μM aliskiren, spironolactone, 10 μM candesartan, and enalapril significantly restored neurite length to the control level. Moreover, 1 μM SCH772984 (a selective inhibitor of extracellular signal-regulated kinase, ERK1/2) and 500 μM SQ22536 (a cell-permeable adenylate cyclase [AC] inhibitor) markedly abolished neuroprotective effects of candesartan and enalapril. These results indicate that RAASIs possess preventive or therapeutic effects in acute and chronic OIPN, candesartan and enalapril may directly increase in the activity of ERK1/2 and AC in PC12 cells.

Antioxidant Supplementation in the Treatment of Neurotoxicity Induced by Platinum-Based Chemotherapeutics-A Review

Cancer represents one of the most pernicious public health problems with a high mortality rate among patients worldwide. Chemotherapy is one of the major therapeutic approaches for the treatment of various malignancies. Platinum-based drugs (cisplatin, oxaliplatin, carboplatin, etc.) are highly effective chemotherapeutic drugs used for the treatment of several types of malignancies, but their application and dosage are limited by their toxic effects on various systems, including neurotoxicity. Simultaneously, researchers have tried to improve the survival rate and quality of life of cancer patients and decrease the toxicity of platinum-containing drugs by combining them with non-chemotherapy-based drugs, dietary supplements and/or antioxidants. Additionally, recent studies have shown that the root cause for the many side effects of platinum chemotherapeutics involves the production of reactive oxygen species (ROS) in naive cells. Therefore, suppression of ROS generation and their inactivation with antioxidants represents an appropriate approach for platinum drug-induced toxicities. The aim of this paper is to present an updated review of the protective effects of different antioxidant agents (vitamins, dietary antioxidants and supplements, medicaments, medicinal plants and their bioactive compounds) against the neurotoxicity induced by platinum-based chemotherapeutics. This review highlights the high potential of plant antioxidants as adjuvant strategies in chemotherapy with platinum drugs.

Pathogenesis of platinum-induced peripheral neurotoxicity: Insights from preclinical studies

One of the most relevant dose-limiting adverse effects of platinum drugs is the development of a sensory peripheral neuropathy that highly impairs the patients' quality of life. Nowadays there are no available efficacy strategies for the treatment of platinum-induced peripheral neurotoxicity (PIPN), and the only way to prevent its development and progression is by reducing the dose of the cytostatic drug or even withdrawing the chemotherapy regimen. This clinical issue has been the main focus of hundreds of preclinical research works during recent decades. As a consequence, dozens of in vitro and in vivo models of PIPN have been developed to elucidate the molecular mechanisms involved in its development and to find neuroprotective targets. The apoptosis of peripheral neurons has been identified as the main mechanism involved in PIPN pathogenesis. This mechanism of DRG sensory neurons cell death is triggered by the nuclear and mitochondrial DNA platination together with the increase of the oxidative cellular status induced by the depletion of cytoplasmic antioxidant mechanisms. However, since there has been no successful transfer of preclinical results to clinical practise in terms of therapeutic approaches, some mechanisms of PIPN pathogenesis still remain to be elucidated. This review is focused on the pathogenic mechanisms underlying PIPN described up to now, provided by the critical analysis of in vitro and in vivo models.

Innovative tailor made dextran based membranes with excellent non-inflammatory response: In vivo assessment

In this work, dextran based membranes with potential to be used as implantable devices in Tissue Engineering and Regenerative Medicine (TERM) were prepared by a straightforward strategy. Briefly, two polymers approved by the Food and Drug Administration, viz. dextran and poly(ε-caprolactone) (PCL) were functionalized with methacrylate moieties, and subjected to photocrosslinking. Employing different weight ratios of each polymer in the formulations allowed to obtain transparent membranes with tunable physicochemical properties and low adverse host tissue response. Independently of the material, all formulations have shown to be thermally stable up to 300 °C whilst variations in the polymer ratio resulted in membranes with different glass transition temperatures (T_g) and flexibility. The swelling capacity ranged from 50% to 200%. On the other hand, in vitro hydrolytic degradation did not show to be material-dependent and all membranes maintained their structural integrity for more than 30 days, losing only 8-12% of their initial weight. Preliminary in vitro biological tests did not show any cytotoxic effect on seeded human dental pulp stem cells (hDPSCs), suggesting that, in general, all membranes are capable of supporting cell adhesion and viability. The in vivo biocompatibility of membranes implanted subcutaneously in rats' dorsum indicate that M100/0 (100%wt dextran) and M25/75 (25 %wt dextran) formulations can be classified as "slight-irritant" and "non-irritant", respectively. From the histological analysis performed on the main tissue organs it was not possible to detect any signs of fibrosis or necrosis thereby excluding the presence of toxic degradation by-products deposited or accumulated in these tissues. In combination, these results suggest that the newly developed formulations hold great potential as engineered devices for biomedical applications, where the biological response of cells and tissues are greatly dependent on the physical and chemical cues provided by the substrate.

Kamishoyosan and Shakuyakukanzoto promote recovery from paclitaxel-induced neurite retraction in PC12 cells

Background

In chemotherapy, the full round of treatment must be completed as scheduled to achieve the strongest therapeutic effect. However, peripheral neuropathy, a severe side effect of the chemotherapeutic agent paclitaxel, can force the premature discontinuation of treatment. As some kampo practitioners have suggested that it may be possible to counteract such side effects, we analyzed the effects of Kamishoyosan, Shakuyakukanzoto, and Goshajinkigan in an in vitro model of paclitaxel-induced peripheral neuropathy.

Methods

Paclitaxel-treated PC12 cells were assessed for neurite length and performed Western blot analysis for growth-associated protein-43 (GAP-43) and light neurofilament protein (NF-L) levels in the presence of nerve growth factor (NGF); they were re-assessed, with additional testing for acetylcholinesterase levels, after application of one of the kampo. We also compared phosphorylation of extracellular signal-regulated kinase (Erk)1/2 and Akt via Western blot analysis. About effect of kampo to anticancer efficacy, we confirmed cell cytotoxicity in A549 cells using MTT assay.

Results

Addition of Kamishoyosan or Shakuyakukanzoto, but not Goshajinkigan, significantly improved neurite length and GAP-43 and NF-L levels from paclitaxel-treated PC12 cells, relative to those of only NGF-treated PC12 cells. The promoting effect of Kamishoyosan and Shakuyakukanzoto in neurite outgrowth is confirmed when NGF promoted neurite outgrowth, and it was inhibited partially when Erk1/2 and Akt were blocked by Erk1/2 inhibitor or Akt inhibitor alone. Furthermore, neurite outgrowth induced by TJ24 and TJ68 was inhibited more strongly when Erk1/2 inhibitor and Akt inhibitor were treated at the same time. NGF with Kamishoyosan or Shakuyakukanzoto promoted the proportion of phosphorylated Erk1/2 and phosphorylated Akt compare with NGF only. On the other hand, Kamishoyosan or Shakuyakukanzoto didn’t influence cytotoxicity of paclitaxel in A549 cells.

Conclusions

Kamishoyosan or Shakuyakukanzoto promotes neurite outgrowth with NGF via increasing the proportion of phosphorylated Erk1/2 and phosphorylated Akt in PC12 cells. The effect applies to recovery from paclitaxel-induced axonal involvement and might promote recovery from paclitaxel-induced neuropathy without influence of anticancer effect of paclitaxel.

Application of stem cell derived neuronal cells to evaluate neurotoxic chemotherapy

The generation of induced pluripotent stem cells (iPSCs) and differentiation to cells composing major organs has opened up the possibility for a new model system to study adverse toxicities associated with chemotherapy. Therefore, we used human iPSC-derived neurons to study peripheral neuropathy, one of the most common adverse effects of chemotherapy and cause for dose reduction. To determine the utility of these neurons in investigating the effects of neurotoxic chemotherapy, we measured morphological differences in neurite outgrowth, cell viability as determined by ATP levels and apoptosis through measures of caspase 3/7 activation following treatment with clinically relevant concentrations of platinating agents (cisplatin, oxaliplatin and carboplatin), taxanes (paclitaxel, docetaxel and nab-paclitaxel), a targeted proteasome inhibitor (bortezomib), an antiangiogenic compound (thalidomide), and 5-fluorouracil, a chemotherapeutic that does not cause neuropathy. We demonstrate differential sensitivity of neurons to mechanistically distinct classes of chemotherapeutics. We also show a dose-dependent reduction of electrical activity as measured by mean firing rate of the neurons following treatment with paclitaxel. We compared neurite outgrowth and cell viability of iPSC-derived cortical (iCell® Neurons) and peripheral (Peri.4U) neurons to cisplatin, paclitaxel and vincristine. Goshajinkigan, a Japanese herbal neuroprotectant medicine, was protective against paclitaxel-induced neurotoxicity but not oxaliplatin as measured by morphological phenotypes. Thus, we have demonstrated the utility of human iPSC-derived neurons as a useful model to distinguish drug class differences and for studies of a potential neuroprotectant for the prevention of chemotherapy-induced peripheral neuropathy.

CaMKII-Mediated CREB Phosphorylation Is Involved in Ca2+-Induced BDNF mRNA Transcription and Neurite Outgrowth Promoted by Electrical Stimulation

Electrical stimulation (ES)-triggered up-regulation of brain-derived neurotrophic factor (BDNF) and neurite outgrowth in cultured rat postnatal dorsal root ganglion neurons (DRGNs) is calcium (Ca²⁺)-dependent. The effects of increased Ca²⁺ on BDNF up-regulation and neurite outgrowth remain unclear. We showed here that ES increased phosphorylation of the cAMP-response element binding protein (CREB). Blockade of Ca²⁺ suppressed CREB phosphorylation and neurite outgrowth. Down-regulation of phosphorylated (p)-CREB reduced BDNF transcription and neurite outgrowth triggered by ES. Furthermore, blockade of calmodulin-dependent protein kinase II (CaMKII) using the inhibitors KN93 or KN62 reduced p-CREB, and specific knockdown of the CaMKIIα or CaMKIIβ subunit was sufficient to suppress p-CREB. Recombinant BDNF or hyperforin reversed the effects of Ca²⁺ blockade and CaMKII knockdown. Taken together, these data establish a potential signaling pathway of Ca²⁺-CaMKII-CREB in neuronal activation. To our knowledge, this is the first report of the mechanisms of Ca²⁺-dependent BDNF transcription and neurite outgrowth triggered by ES. These findings might help further investigation of complex molecular signaling networks in ES-triggered nerve regeneration in vivo.

Processed aconite root and its active ingredient neoline may alleviate oxaliplatin-induced peripheral neuropathic pain

ETHNOPHARMACOLOGICAL RELEVANCE

Processed aconite root (PA, the root of Aconitum carmichaeli, Ranunculaceae) is a crude drug used in traditional Chinese or Japanese kampo medicine to generate heat in the body and to treat pain associated with coldness. Oxaliplatin (L-OHP) is a platinum-based anticancer drug that frequently causes acute and chronic peripheral neuropathies, including cold and mechanical hyperalgesia.

AIM OF THE STUDY

We investigated the effects of PA on L-OHP-induced peripheral neuropathies and identified the active ingredient within PA extract.

MATERIALS AND METHODS

L-OHP was intraperitoneally injected into mice, and PA boiled water extract was orally administered. Cold and mechanical hyperalgesia were evaluated using the acetone test and the von Frey filament method, respectively. Dorsal root ganglion (DRG) neurons were isolated from normal mice and cultured with L-OHP with or without PA extract. Cell viability and neurite elongation were evaluated.

RESULTS

PA extract significantly attenuated cold and mechanical hyperalgesia induced by L-OHP in mice. In cultured DRG neurons, L-OHP reduced cell viability and neurite elongation in a dose-dependent manner. Treatment with PA extract significantly alleviated the L-OHP-induced reduction of neurite elongation, while the cytotoxicity of L-OHP was not affected. Using activity-guided fractionation, we isolated neoline from PA extract as the active ingredient. Neoline significantly alleviated L-OHP-induced reduction of neurite elongation in cultured DRG neurons in a concentration-dependent manner. Moreover, subcutaneous injection of neoline attenuated cold and mechanical hyperalgesia in L-OHP-treated mice. PA extract and neoline did not show sedation and motor impairment.

CONCLUSIONS

The present study indicates that PA and its active ingredient neoline are promising agents to alleviate L-OHP-induced neuropathic pain.

Chemotherapy-induced peripheral neuropathy: Current status and progress

As there are increasing numbers of cancer survivors, more attention is being paid to the long term unwanted effects patients may experience as a result of their treatment and the impact these side effects can have on their quality of life. Chemotherapy-induced peripheral neuropathy (CIPN) is one of the most common long-term toxicities from chemotherapy. In this review we will briefly review the clinical presentation, evaluation and management of chemotherapy-induced peripheral neuropathy, with a focus on CIPN related to platinum and taxane agents. We will then discuss current clinical models of peripheral neuropathy and ongoing research to better understand CIPN and develop potential treatment options.

Role of transporters in the distribution of platinum-based drugs

Platinum derivatives used as chemotherapeutic drugs such as cisplatin and oxaliplatin have a potent antitumor activity. However, severe side effects such as nephro-, oto-, and neurotoxicity are associated with their use. Effects and side effects of platinum-based drugs are in part caused by their transporter-mediated uptake in target and non target cells. In this mini review, the transport systems involved in cellular handling of platinum derivatives are illustrated, focusing on transporters for cisplatin. The copper transporter 1 seems to be of particular importance for cisplatin uptake in tumor cells, while the organic cation transporter (OCT) 2, due to its specific organ distribution, may play a major role in the development of undesired cisplatin side effects. In polarized cells, e.g., in renal proximal tubule cells, apically expressed transporters, such as multidrug and toxin extrusion protein 1, mediate secretion of cisplatin and in this way contribute to the control of its toxic effects. Specific inhibition of cisplatin uptake transporters such as the OCTs may be an attractive therapeutic option to reduce its toxicity, without impairing its antitumor efficacy.

In vitro models for neurotoxicology research

The nervous system has a highly complex organization, including many cell types with multiple functions, with an intricate anatomy and unique structural and functional characteristics; the study of its (dys)functionality following exposure to xenobiotics, neurotoxicology, constitutes an important issue in neurosciences.

Claulansine F promotes neuritogenesis in PC12 cells via the ERK signaling pathway

AIM

To study the effects of Claulansine F (Clau F), a carbazole alkaloid isolated from the stem of Clausena lansium (Lour) Skeels, on neuritogenesis of PC12 cells, and to elucidate the mechanism of action.

METHODS

Neuritogenesis of PC12 cells was quantified under an inverted microscope. Expression of the neurite outgrowth marker GAP-43 was detected using immunofluorescence. GAP-43 transcription was measured using RT-PCR. Cell viability was evaluated with MTT assay. The levels of phosphor-ERK1/2, phosphor-CREB, phosphor-AKT and acetylate-p53 in the cells were examined using Western blotting analyses.

RESULTS

Clau F (10-100 μmol/L) significantly increased the percentage of PC12 cells bearing neurites. Clau F markedly increased the expression of GAP-43 in the cells. The efficiency of Clau F (10 μmol/L) in increasing neuritogenesis and GAP-43 expression was comparable to that of nerve growth factor (50 ng/mL). In addition, Clau F completely blocked the proliferation of PC12 cells within 7 d of incubation, whereas it did not cause cell death in cultured rat cortical neurons. Treatment of PC12 cells with Clau F activated both ERK and AKT signaling pathways. Co-treatment of PC12 cells with the specific ERK inhibitor PD98059, but not the specific PI3K inhibitor LY294002, blocked Clau F-induced neuritogenesis and GAP-43 upregulation.

CONCLUSION

Clau F promotes neuritogenesis in PC12 cells specifically via activation of the ERK signaling pathway.

An animal model of oxaliplatin-induced cold allodynia reveals a crucial role for Nav1.6 in peripheral pain pathways

Cold allodynia, pain in response to cooling, occurs during or within hours of oxaliplatin infusion and is thought to arise from a direct effect of oxaliplatin on peripheral sensory neurons. To characterize the pathophysiological mechanisms underlying acute oxaliplatin-induced cold allodynia, we established a new intraplantar oxaliplatin mouse model that rapidly developed long-lasting cold allodynia mediated entirely through tetrodotoxin-sensitive Nav pathways. Using selective inhibitors and knockout animals, we found that Nav1.6 was the key isoform involved, while thermosensitive transient receptor potential channels were not involved. Consistent with a crucial role for delayed-rectifier potassium channels in excitability in response to cold, intraplantar administration of the K(+)-channel blocker 4-aminopyridine mimicked oxaliplatin-induced cold allodynia and was also inhibited by Nav1.6 blockers. Intraplantar injection of the Nav1.6 activator Cn2 elicited spontaneous pain, mechanical allodynia, and enhanced 4-aminopyridine-induced cold allodynia. These findings provide behavioural evidence for a crucial role of Nav1.6 in multiple peripheral pain pathways including cold allodynia.

Membrane transporters as mediators of Cisplatin effects and side effects

Transporters are important mediators of specific cellular uptake and thus, not only for effects, but also for side effects, metabolism, and excretion of many drugs such as cisplatin. Cisplatin is a potent cytostatic drug, whose use is limited by its severe acute and chronic nephro-, oto-, and peripheral neurotoxicity. For this reason, other platinum derivatives, such as carboplatin and oxaliplatin, with less toxicity but still with antitumoral action have been developed. Several transporters, which are expressed on the cell membranes, have been associated with cisplatin transport across the plasma membrane and across the cell: the copper transporter 1 (Ctr1), the copper transporter 2 (Ctr2), the P-type copper-transporting ATPases ATP7A and ATP7B, the organic cation transporter 2 (OCT2), and the multidrug extrusion transporter 1 (MATE1). Some of these transporters are also able to accept other platinum derivatives as substrate. Since membrane transporters display a specific tissue distribution, they can be important molecules that mediate the entry of platinum derivatives in target and also nontarget cells possibly mediating specific effects and side effects of the chemotherapeutic drug. This paper summarizes the literature on toxicities of cisplatin compared to that of carboplatin and oxaliplatin and the interaction of these platinum derivatives with membrane transporters.

Curcumin reduces cisplatin-induced neurotoxicity in NGF-differentiated PC12 cells

The potential neuroprotective benefits of curcumin against cisplatin neurotoxicity were investigated. Curcumin is a polyphenol derived from the rhizome of Curcuma longa whose pharmacological effects include antioxidant, anti-inflammatory and anti-cancer properties. Cisplatin is a potent chemotherapeutic drug with activity against a wide variety of tumors, although it has notorious side effects. Cisplatin neurotoxicity is clinically evident in patients that have undergone a full course of chemotherapy and develop a peripheral neuropathy that may affect the treatment regimen and the patient's qualify of life. In this study, we examined whether curcumin can protect against cisplatin neurite outgrowth inhibition in PC12 cells, which is an indicator of the protective potential against neuropathy. We also investigated whether curcumin affects cisplatin effectiveness by analyzing the modulation of p53 gene expression and its effect on cisplatin cytotoxicity in HepG2 tumor cells. Non-cytotoxic concentrations of curcumin reduced in vitro neurotoxicity of cisplatin in PC12 cells. The treatment of PC12 cells with cisplatin (10μg/mL) significantly reduced neurite outgrowth. The tested concentration of curcumin (1.0 and 10μg/mL) did not result in neurite toxicity but nevertheless diminished cisplatin-induced inhibition of neurite outgrowth by up to 50% (p<0.05). Our results indicate that curcumin does not compromise cisplatin's anticancer activity. Curcumin neither suppressed p53 mRNA transcription nor protected tumor cells against cisplatin cytotoxicity. These results indicate that curcumin may reduce cisplatin-induced neurotoxicity, and clinical studies should potentially be considered.

Neurite outgrowth mediated by the heat shock protein Hsp90α: a novel target for the antipsychotic drug aripiprazole

Aripiprazole is an atypical antipsychotic drug approved for the treatment of psychiatric disorders such as schizophrenia, bipolar disorder, major depressive disorder and autism. The drug shows partial agonistic activity at dopamine D(2) receptors and 5-hydroxytryptamine (5-HT) 5-HT(1A) receptors, and antagonistic activity at 5-HT(2A) receptors. However, the precise mechanistic pathways remain unclear. In this study, we examined the effects of aripiprazole on neurite outgrowth. Aripiprazole significantly potentiated nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells, in a concentration-dependent manner. The 5-HT(1A) receptor antagonist WAY-100635, but not the dopamine D(2) receptor antagonist sulpiride, blocked the effects of aripiprazole, although, only partially. Specific inhibitors of inositol 1,4,5-triphosphate (IP(3)) receptors and BAPTA-AM, a chelator of intracellular Ca(2+), blocked the effects of aripiprazole. Moreover, specific inhibitors of several common signaling pathways phospholipase C-γ (PLC-γ), phosphatidylinositol-3 kinase (PI3K), mammalian target of rapamycin, p38 MAPK, c-Jun N-terminal kinase, Akt, Ras, Raf, ERK, MAPK) also blocked the effects of aripiprazole. Using proteomic analysis, we found that aripiprazole significantly increased levels of the heat shock protein Hsp90α in cultured cells. The effects of aripiprazole on NGF-induced neurite outgrowth were significantly attenuated by treatment with Hsp90α RNA interference, but not by the negative control of Hsp90α. These findings suggest that both 5-HT(1A) receptor activation and Ca(2+) signaling via IP(3) receptors, as well as their downstream cellular signaling pathways play a role in the promotion of aripiprazole-induced neurite outgrowth. Furthermore, aripiprazole-induced increases in Hsp90α protein expression may form part of the therapeutic mechanism for this drug.

Potentiation of nerve growth factor-induced neurite outgrowth in PC12 cells by ifenprodil: the role of sigma-1 and IP3 receptors

In addition to both the α1 adrenergic receptor and N-methyl-D-aspartate (NMDA) receptor antagonists, ifenprodil binds to the sigma receptor subtypes 1 and 2. In this study, we examined the effects of ifenprodil on nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells. Ifenprodil significantly potentiated NGF-induced neurite outgrowth, in a concentration-dependent manner. In contrast, the α1 adrenergic receptor antagonist, prazosin and the NMDA receptor NR2B antagonist, Ro 25-6981 did not alter NGF-induced neurite outgrowth. Potentiation of NGF-induced neurite outgrowth mediated by ifenprodil was significantly antagonized by co-administration of the selective sigma-1 receptor antagonist, NE-100, but not the sigma-2 receptor antagonist, SM-21. Similarly, ifenprodil enhanced NGF-induced neurite outgrowth was again significantly reduced by the inositol 1,4,5-triphosphate (IP(3)) receptor antagonists, xestospongin C and 2-aminoethoxydiphenyl borate (2-APB) treatment. Furthermore, BAPTA-AM, a chelator of intracellular Ca(2+), blocked the effects of ifenprodil on NGF-induced neurite outgrowth, indicating the role of intracellular Ca(2+) in the neurite outgrowth. These findings suggest that activation at sigma-1 receptors and subsequent interaction with IP(3) receptors may mediate the pharmacological effects of ifenprodil on neurite outgrowth.