Changes of fast axonal transport by taxol injected subepineurally into the rat sciatic nerve

Paclitaxel Inhibits KCNQ Channels in Primary Sensory Neurons to Initiate the Development of Painful Peripheral Neuropathy

Cancer patients undergoing paclitaxel infusion usually experience peripheral nerve degeneration and serious neuropathic pain termed paclitaxel-induced peripheral neuropathy (PIPN). However, alterations in the dose or treatment schedule for paclitaxel do not eliminate PIPN, and no therapies are available for PIPN, despite numerous studies to uncover the mechanisms underlying the development/maintenance of this condition. Therefore, we aimed to uncover a novel mechanism underlying the pathogenesis of PIPN. Clinical studies suggest that acute over excitation of primary sensory neurons is linked to the pathogenesis of PIPN. We found that paclitaxel-induced acute hyperexcitability of primary sensory neurons results from the paclitaxel-induced inhibition of KCNQ potassium channels (mainly KCNQ2), found abundantly in sensory neurons and axons. We found that repeated application of XE-991, a specific KCNQ channel blocker, induced PIPN-like alterations in rats, including mechanical hypersensitivity and degeneration of peripheral nerves, as detected by both morphological and behavioral assays. In contrast, genetic deletion of KCNQ2 from peripheral sensory neurons in mice significantly attenuated the development of paclitaxel-induced peripheral sensory fiber degeneration and chronic pain. These findings may lead to a better understanding of the causes of PIPN and provide an impetus for developing new classes of KCNQ activators for its therapeutic treatment.

Iridoids isolated from Viticis Fructus inhibit paclitaxel-induced mechanical allodynia in mice

Chemotherapy-induced peripheral neuropathy (CIPN) manifests as mechanical allodynia and hyperalgesia, and is one of the main adverse effects of chemotherapeutic agents. Currently available therapeutic drugs are not sufficiently effective for the management of this adverse effect in the clinic. Therefore, the development of novel therapeutic agents for treating CIPN is necessary. Our previous study suggested the potential of aucubin and pedicularis-lactone (1) as active compounds responsible for the anti-allodynic property of Plantaginis Semen. However, the activity of purified 1 has not been evaluated due to its low content in Plantaginis Semen. In the present study, 1 was isolated from Viticis Fructus, as well as viteoid I (2) and viteoid II (3) during the process of isolation. The purities of isolated 1, 2, and 3 were determined as 67.15%, 92.12%, and 86.72%, respectively, by quantitative ¹H-NMR, using DSS-d₆ as an internal standard. Repeated daily oral administration of these three iridoids at a dose of 15 mg/kg significantly inhibited the PTX-induced mechanical allodynia in mice, suggesting the anti-allodynic activities of 1, 2, and 3. This study provides confirmatory evidence for the anti-allodynic activity of purified 1 and also reveals two additional active iridoids from Viticis Fructus. These three iridoids could be potential candidates for the treatment of CIPN.

Search of anti-allodynic compounds from Plantaginis Semen, a crude drug ingredient of Kampo formula "Goshajinkigan"

Chemotherapy-induced peripheral neuropathy (CIPN) is one of the dose-limiting side effects of cancer chemotherapy. Although the control of CIPN is important, it is difficult to manage with currently available therapeutic drugs. Therefore, there is a need for novel therapeutic agents for treating CIPN. Goshajinkigan (GJG) is a Kampo formula composed of ten crude drugs. While GJG has been used for the treatment of CIPN, the active constituents of GJG and their underlying mechanisms of pharmacological effects are still unknown. Our previous study revealed that repetitive oral administration of the water extract of Plantaginis Semen, a crude drug ingredient of GJG, inhibited the mechanical allodynia induced by an intraperitoneal injection of paclitaxel in mice. To elucidate the active compounds of Plantaginis Semen, activity-guided separation of the water extract of Plantaginis Semen was performed. From the active fraction, four iridoids (1-4) were identified. Repetitive oral administration of aucubin (1) at 100 or 30 mg/kg and 100 mg/kg of the fraction crude 3 [primarily comprised of pedicularis-lactone (3)], showed anti-allodynic activity, suggesting 1 and 3 could be some of the active compounds responsible for the anti-allodynic property of Plantaginis Semen and GJG. Our study establishes that oral administration of 1 has potent anti-allodynic effect in addition to the activity of intraperitoneally administered 1 reported previously. Identification of active anti-allodynic compounds found in Kampo formulations will support the development of novel therapies for the management of CIPN in cancer patients.

Prophylactic Administration of Aucubin Inhibits Paclitaxel-Induced Mechanical Allodynia via the Inhibition of Endoplasmic Reticulum Stress in Peripheral Schwann Cells

Paclitaxel is a chemotherapeutic agent that causes peripheral neuropathy as its major dose-limiting side effect. However, the peripheral neuropathy is difficult to manage. A study we recently conducted showed that repetitive administration of aucubin as a prophylactic inhibits paclitaxel-induced mechanical allodynia. However, the mechanisms underlying the anti-allodynic activity of aucubin, which is a major component of Plantaginis Semen, was unclear. In addition to mechanical allodynia, aucubin inhibited spontaneous and mechanical stimuli-induced firing in spinal dorsal horn neurons; however, catalpol, a metabolite of aucubin, did not show these effects. Furthermore, paclitaxel induced the expression of CCAAT/enhancer-binding protein homologous protein, a marker of endoplasmic reticulum (ER) stress, in the sciatic nerve and a Schwann cell line (LY-PPB6 cells); however, this effect was inhibited by aucubin. These results suggest that aucubin inhibits paclitaxel-induced mechanical allodynia through the inhibition of ER stress in peripheral Schwann cells.

Prophylactic topical paeoniflorin prevents mechanical allodynia caused by paclitaxel in mice through adenosine A1 receptors

BACKGROUND

The chemotherapeutic agent paclitaxel (PTX) causes refractory peripheral neuropathy as a side effect. Prophylactic oral administration of the traditional herbal medicine Shakuyakukanzoto containing Paeoniae Radix and Glycyrrhizae Radix prevents the development of PTX-induced mechanical allodynia in mice via peripheral effects, mostly due to Paeoniae Radix. However, the bioactive component responsible for the prevention of PTX-induced neuropathic pain remains unknown.

PURPOSE

To determine whether a monoterpene glycoside paeoniflorin (PF), which is the principal bioactive constituent of Paeoniae Radix, has inhibitory effects on PTX-induced mechanical allodynia and investigate the underlying mechanisms.

METHODS

C57BL/6NCr mice received a single intraperitoneal injection of PTX and then were topically administered PF to the planar surface twice daily for 13 days. Mechanical allodynia was evaluated by the von Frey filament test, peripheral nerve activity was recorded using bipolar electrodes, and demyelination in peripheral nerves was analysed by electron microscopy. Schwann cell line LY-PPB6 pre-treated with PF and then treated with PTX was used to analyse the expression of the transcription factor CHOP, a marker of endoplasmic reticulum (ER) stress, by western blotting.

RESULTS

PTX caused mechanical allodynia and increased both spontaneous and mechanical stimuli-evoked peripheral nerve activities, whereas repetitive topical application of PF significantly attenuated PTX-induced allodynia, suppressed saphenous nerve firing, and inhibited demyelination in the plantar nerve. Moreover, in cultured Schwann cells, PF downregulated PTX-induced expression of CHOP, indicating the inhibition of ER stress. The attenuation of mechanical allodynia in mice and downregulation of CHOP levels in cell cultures was inhibited by adenosine A₁ receptor (A1R) antagonist 8-cyclopentyl-1,3-diprooylxanrhine, suggesting the involvement of A1R in PF-associated analgesic effects.

CONCLUSION

These results suggest that prophylactic topical application of PF is effective in alleviating PTX-induced mechanical allodynia by protecting sensory nerves from demyelination via activation of the A1R.

Paclitaxel inhibits mRNA transport in axons

Paclitaxel is an integral component of solid tumor treatment. This chemotherapeutic agent provokes an often irreversible peripheral sensory neuropathy with pathological features of distal axonal degeneration. Current pathological concepts assume that polymerization of axonal microtubules and mitochondrial dysfunction contributes to the development of paclitaxel-induced peripheral neuropathy. The relationship, however, between microtubule stabilization, mitotoxicity and axonal degeneration is still not completely understood. To explore the function of axonal mitochondria we treated transgenic mice that harbor cyan fluorescent protein (CFP)-labeled neuronal mitochondria with repeated doses of paclitaxel and assessed neuropathic changes by nerve conduction and histological studies. In addition, mitochondrial content and morphology was determined by ex vivo imaging of axons containing CFP-labeled mitochondria. Using quantitative RT-PCR and fluorescence-labeled mRNA we determined axonal mRNA transport of nuclear encoded mitochondrial proteins. Prolonged treatment with high doses of paclitaxel-induced a predominant sensory neuropathy in mice. Although mitochondrial velocity in axons per se was not altered, we observed significant changes in mitochondrial morphology, suggesting that paclitaxel treatment impairs the dynamics of axonal mitochondria. These changes were caused by decreased levels of nuclear encoded mRNA, including the mitochondrial fusion/fission machinery. Moreover, impaired axonal mRNA transport in vitro resulted in mitochondrial dysfunction and subsequent axonal degeneration. Taken together, our experiments provide evidence that disrupted axonal transport of nuclear derived mRNA plays a crucial role in the pathogenesis of paclitaxel-induced sensory neuropathy.

Alpha-lipoic acid prevents mitochondrial damage and neurotoxicity in experimental chemotherapy neuropathy

The study investigates if alpha-lipoic acid is neuroprotective against chemotherapy induced neurotoxicity, if mitochondrial damage plays a critical role in toxic neurodegenerative cascade, and if neuroprotective effects of alpha-lipoic acid depend on mitochondria protection. We used an in vitro model of chemotherapy induced peripheral neuropathy that closely mimic the in vivo condition by exposing primary cultures of dorsal root ganglion (DRG) sensory neurons to paclitaxel and cisplatin, two widely used and highly effective chemotherapeutic drugs. This approach allowed investigating the efficacy of alpha-lipoic acid in preventing axonal damage and apoptosis and the function and ultrastructural morphology of mitochondria after exposure to toxic agents and alpha-lipoic acid. Our results demonstrate that both cisplatin and paclitaxel cause early mitochondrial impairment with loss of membrane potential and induction of autophagic vacuoles in neurons. Alpha-lipoic acid exerts neuroprotective effects against chemotherapy induced neurotoxicity in sensory neurons: it rescues the mitochondrial toxicity and induces the expression of frataxin, an essential mitochondrial protein with anti-oxidant and chaperone properties. In conclusion mitochondrial toxicity is an early common event both in paclitaxel and cisplatin induced neurotoxicity. Alpha-lipoic acid protects sensory neurons through its anti-oxidant and mitochondrial regulatory functions, possibly inducing the expression of frataxin. These findings suggest that alpha-lipoic acid might reduce the risk of developing peripheral nerve toxicity in patients undergoing chemotherapy and encourage further confirmatory clinical trials.

Erythropoietin protects sensory axons against paclitaxel-induced distal degeneration

Paclitaxel causes a sensory polyneuropathy with characteristic features of distal axonal degeneration. Although the exact mechanisms underlying distal axonal degeneration are unknown, paclitaxel-induced axonal degeneration has been shown to be associated with an increase in detyrosinated tubulin. Here we show that recombinant human erythropoietin prevents axonal degeneration in sensory neurons in vitro and this effect is associated with downregulation of detyrosinated tubulin. Furthermore, in an animal model of paclitaxel-induced distal sensory polyneuropathy, recombinant human erythropoietin protects against distal axonal degeneration. These findings suggest that recombinant human erythropoietin may be useful as a therapy to prevent paclitaxel-induced sensory polyneuropathy in patients undergoing chemotherapy.

Peripheral neuropathy: A persisting challenge in paclitaxel-based regimes

Cumulative peripheral neuropathy (PNP) still remains a limitation to optimal treatment with paclitaxel (PAC), especially in more dose-dense schedules. This primary sensory PNP may affect the majority of patients after administration of certain cumulative dosages of PAC, while the exact mechanisms of PAC-induced PNP are not known. While a number of preclinical models revealed its vehicle Cremophor EL (CrEL) to be mainly responsible for ganglionopathy, axonopathy and demyelination, clinical data also supports a strong and independent effect of PAC itself, which is most likely based on disturbances in the microtubules in perikaryons, axons and glia cells. Indeed, clinical trials of CrEL-free formulations of PAC still report grade III neurotoxicity as dose-limiting. As treatment options of PAC-induced PNP are rare the use of specific scoring systems for screening purposes is strongly encouraged. In this report we review and discuss the pathogenesis, incidence, risk factors, diagnosis, pharmacodynamics and treatment options for PAC-induced PNP.

A painful peripheral neuropathy in the rat produced by the chemotherapeutic drug, paclitaxel

Paclitaxel, an effective anti-neoplastic agent in the treatment of solid tumors, produces a dose-limiting painful peripheral neuropathy in a clinically significant number of cancer patients. Prior work has demonstrated paclitaxel-induced neurodegeneration and sensory loss in laboratory rodents. We describe here an experimental paclitaxel-induced painful peripheral neuropathy. Adult male rats were given four intraperitoneal injections on alternate days of vehicle or 0.5, 1.0, or 2.0 mg/kg of paclitaxel (Taxol). Behavioral tests for pain using mechanical and thermal stimuli applied to the tail and hind paws, and tests for motor performance, were taken before, during and after dosing for 22-35 days. All three doses of paclitaxel caused heat-hyperalgesia, mechano-allodynia, mechano-hyperalgesia, and cold-allodynia, but had no effect on motor performance. Neuropathic pain began within days and lasted for several weeks. We did not detect any dose-response relationship. Tests at the distal, mid, and proximal tail failed to show evidence of a length-dependent neuropathy. Vehicle control injections had no effect on any measure. No significant systemic toxicities were noted in the paclitaxel-treated animals. Light-microscopic inspection of the sciatic nerve (mid-thigh level), L4-L5 dorsal root ganglia, and dorsal and ventral roots, and the gray and white matter of the L4-L5 spinal cord, showed no structural abnormalities. Electron microscopic examination of the sciatic nerve (mid-thigh level) and the L4-L5 dorsal root ganglia and dorsal horns demonstrated no degeneration of myelinated and unmyelinated axons in the sciatic nerve and roots, but revealed endoneurial edema. This model may be useful in understanding a significant source of pain in cancer patients, and in finding ways to avoid the neurotoxicity that limits paclitaxel therapy.

Carotid artery stenosis: who should undergo surgery and who should undergo stenting?

Carotid angioplasty and stent implantation is a rapidly evolving treatment option currently under evaluation in several randomized trials. Although this technique needs some special technical skills and knowledge, it is technically simpler than many other interventional procedures. Current data indicate that the results regarding success rate and complication rate may be similar to surgery. It will take years to get the results of the randomized trials that are currently planed or have already started. Unfortunately, the results of these studies will not reflect the state-of-the-art because new stents and new protection devices will become available during these studies. Therefore, in clinical practice the decision has to be made depending on individual patient and lesion characteristics. Patients with concomitant diseases considered to be a risk factor for surgical procedures and patients with contralateral occlusion may be better candidates for angioplasty and stenting. However, patients with diffuse disease of the common carotid artery and patients with difficult vascular access may be better candidates for surgery.

Morphological evidence of the inhibitory effect of taxol on the fast axonal transport

The short term effects of taxol, a stabilizing drug of microtubules, on the peripheral nerves in the rat was investigated using a new chamber system which can be applied to incubate a sciatic nerve with various solutions in vivo. A functional analysis of retrograde axonal transport using rhodamine-labeled wheat germ agglutinin (WGA-rhodamine) showed the inhibitory effect of the drug. An electron microscopic study also revealed that a variety of vesicles were observed to accumulate on both the proximal and the distal sides of the chamber, however, no significant increase in the number of microtubules in the axons, based on the pharmacological effect of the drug, was observed even though one had been expected. These findings support the inhibitory effect of taxol on the fast axonal transport of the neurons. Furthermore, the accumulated vesicles were morphologically different from those accumulated by ligation. These results suggest that a special component of the fast axonal transport was thus selectively blocked by the drug.

Paclitaxel. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic potential in the treatment of cancer

Paclitaxel is a new anticancer agent with a novel mechanism of action. It promotes polymerisation of tubulin dimers to form microtubules and stabilises microtubules by preventing depolymerisation. In noncomparative trials, continuous infusion of paclitaxel 110 to 300 mg/m2 over 3 to 96 hours every 3 to 4 weeks produced a complete or partial response in 16 to 48% of patients with ovarian cancer and 25 to 61.5% of patients with metastatic breast cancer, many of whom were refractory to treatment with cisplatin or doxorubicin, respectively. 23 to 100% of patients with ovarian cancer achieved complete or partial responses with paclitaxel in combination with cisplatin, carboplatin, cyclophosphamide, altretamine and/or doxorubicin. Similarly, response rates of 30 to 100% were observed with paclitaxel plus doxorubicin, cisplatin, mitoxantrone and/or cyclophosphamide in patients with metastatic breast cancer. Comparative trials in patients with advanced ovarian cancer showed paclitaxel therapy to produce greater response rates than treatment with parenteral hydroxyurea (71 vs 0%) or cyclophosphamide (when both agents were combined with cisplatin) [79 vs 63%]. Paclitaxel was also more effective than mitomycin in 50 patients with previously untreated breast cancer (partial response in 20 vs 4% of patients). Paclitaxel therapy also produced promising results in patients with advanced squamous cell carcinoma of the head and neck, malignant melanoma, advanced non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), germ cell cancer, urothelial cancer, oesophageal cancer, non-Hodgkin's lymphoma or multiple myeloma, and was successfully combined with cisplatin, carboplatin and/or etoposide in patients with NSCLC, SCLC or advanced squamous cell carcinoma of the head and neck. Hypersensitivity reactions were initially a concern with administration of paclitaxel, although current dosage regimens have reduced the incidence of these events to less than 5%. The major dose-limiting adverse effects of paclitaxel are leucopenia (neutropenia) and peripheral neuropathy. Other haematological toxicity was generally mild. Cardiac toxicity was reported in small numbers of patients and most patients developed total alopecia. Several aspects of paclitaxel use remain to be clarified, including the optimal treatment schedule and infusion time, confirmation of the tolerability profile and efficacy of combination regimens in an expanded range of malignancies. Long term follow-up of paclitaxel recipients will also allow the effects of the drug on patient survival to be determined. Nevertheless, paclitaxel is a promising addition to the current therapies available, with significant activity reported in patients with advanced ovarian or breast cancer or other types of tumors.(ABSTRACT TRUNCATED AT 400 WORDS)

Image analysis of neuritic regeneration by adult rat dorsal root ganglion neurons in culture: quantification of the neurotoxicity of anticancer agents and of its prevention by nerve growth factor or basic fibroblast growth factor but not brain-derived neurotrophic factor or neurotrophin-3

Peripheral neuropathies are a common side effect of chemotherapeutic agents, particularly antineoplastic drugs such as taxol, cisplatin, or vinca-alkaloids (vincristine, vinblastine, vindesine). Using dissociated cultures of adult rat dorsal root ganglion (DRG) neurons and video image analysis after neurofilament immunostaining, we have designed a system that allows: (i) rapid screening of potential neurotoxic agents, with the establishment of dose-response curves and the calculation of IC50; (ii) quantification of neurotrophic effects; and (iii) demonstration of neuroprotection by trophic factors. In particular, we show that nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) stimulate in vitro neuritic regeneration by adult rat DRG neurons, while brain-derived neurotrophic factor and neurotrophin-3 lack such effects. Furthermore, 24 h of pretreatment by NGF or bFGF drastically decreases the neurotoxic effect of vincristine and cisplatin.