Insulin-like growth factor-I prevents development of a vincristine neuropathy in mice

Gait analysis in chemotherapy-induced peripheral neurotoxicity rodent models

Gait analysis could be used in animal models as an indicator of sensory ataxia due to chemotherapy-induced peripheral neurotoxicity (CIPN). Over the years, gait analysis in in vivo studies has evolved from simple observations carried out by a trained operator to computerised systems with machine learning that allow the quantification of any variable of interest and the establishment of algorithms for behavioural classification. However, there is not a consensus on gait analysis use in CIPN animal models; therefore, we carried out a systematic review. Of 987 potentially relevant studies, 14 were included, in which different methods were analysed (observation, footprint and CatWalk™). We presented the state-of-the-art of possible approaches to analyse sensory ataxia in rodent models, addressing advantages and disadvantages of different methods available. Semi-automated methods may be of interest when preventive or therapeutic strategies are evaluated, also considering their methodological simplicity and automaticity; up to now, only CatWalk™ analysis has been tested. Future studies should expect that CIPN-affected animals tend to reduce hind paw support due to pain, allodynia or loss of sensation, and an increase in swing phase could or should be observed. Few available studies documented these impairments at the last time point, and only appeared later on respect to other earlier signs of CIPN (such as altered neurophysiological findings). For that reason, gait impairment could be interpreted as late repercussions of loss of sensory.

Targeting a xenobiotic transporter to ameliorate vincristine-induced sensory neuropathy

Vincristine is a widely used chemotherapeutic drug for the treatment of multiple malignant diseases that causes a dose-limiting peripheral neurotoxicity. There is no clinically effective preventative treatment for vincristine-induced sensory peripheral neurotoxicity (VIPN), and mechanistic details of this side effect remain poorly understood. We hypothesized that VIPN is dependent on transporter-mediated vincristine accumulation in dorsal root ganglion neurons. Using a xenobiotic transporter screen, we identified OATP1B3 as a neuronal transporter regulating the uptake of vincristine. In addition, genetic or pharmacological inhibition of the murine orthologue transporter OATP1B2 protected mice from various hallmarks of VIPN - including mechanical allodynia, thermal hyperalgesia, and changes in digital maximal action potential amplitudes and neuronal morphology - without negatively affecting plasma levels or antitumor effects of vincristine. Finally, we identified α-tocopherol from an untargeted metabolomics analysis as a circulating endogenous biomarker of neuronal OATP1B2 function, and it could serve as a companion diagnostic to guide dose selection of OATP1B-type transport modulators given in combination with vincristine to prevent VIPN. Collectively, our findings shed light on the fundamental basis of VIPN and provide a rationale for the clinical development of transporter inhibitors to prevent this debilitating side effect.

Insulin-like Growth Factor-1 (IGF-1) Related Drugs in Pain Management

Objective. The aim of this review is to explore the role of IGF-1 and IGF-1R inhibitors in pain-related conditions and assess the effectiveness of IGF-1-related drugs in pain management. Specifically, this paper investigates the potential involvement of IGF-1 in nociception, nerve regeneration, and the development of neuropathic pain. Methods. We conducted a search of the PUBMED/MEDLINE database, Scopus, and the Cochrane Library for all reports published in English on IGF-1 in pain management from origination through November 2022. The resulting 545 articles were screened, and 18 articles were found to be relevant after reading abstracts. After further examination of the full text of these articles, ten were included in the analysis and discussion. The levels of clinical evidence and implications for recommendations of all the included human studies were graded. Results. The search yielded 545 articles, of which 316 articles were deemed irrelevant by reading the titles. There were 18 articles deemed relevant after reading abstracts, of which 8 of the reports were excluded due to lack of IGF-1-related drug treatment after reviewing the full text of the articles. All ten articles were retrieved for analysis and discussion. We found that IGF-1 may have several positive effects on pain management, including promoting the resolution of hyperalgesia, preventing chemotherapy-induced neuropathy, reversing neuronal hyperactivity, and elevating the nociceptive threshold. On the other hand, IGF-1R inhibitors may alleviate pain in mice with injury of the sciatic nerve, bone cancer pain, and endometriosis-induced hyperalgesia. While one study showed marked improvement in thyroid-associated ophthalmopathy in humans treated with IGF-1R inhibitor, two other studies did not find any benefits from IGF-1 treatment. Conclusions. This review highlights the potential of IGF-1 and IGF-1R inhibitors in pain management, but further research is needed to fully understand their efficacy and potential side effects.

Blood molecular biomarkers for chemotherapy-induced peripheral neuropathy: From preclinical models to clinical practice

Chemotherapy-induced peripheral neuropathy (CIPN) has long been recognized as a clinically significant issue in patients treated with antineoplastic drugs. This common long-term toxic side-effect which negatively impacts the outcome of the disease can lead to disability and have detrimental effects on patients' quality of life. Since axonal injury is a prominent feature of CIPN, responsible for several sensory symptoms, including pain, sensory loss and hypersensitivity to mechanical and/or cold stimuli in the hands and feet, neurophysiological assessments remain the gold standard for clinical diagnosis of CIPN. Given the large impact of CIPN on cancer patients, there is increasing emphasis on biomarkers of adverse outcomes in safety assessment and translational research, to prevent permanent neuroaxonal damage. Since the results on reliable blood molecular markers for axonal degeneration are still controversial, here we provide a brief overview of blood molecular biomarkers used for assessing and/or predicting CIPN in preclinical and clinical settings.

Vincristine- and bortezomib-induced neuropathies - from bedside to bench and back

Vincristine and bortezomib are effective chemotherapeutics widely used to treat hematological cancers. Vincristine blocks tubulin polymerization, whereas bortezomib is a proteasome inhibitor. Despite different mechanisms of action, the main non-hematological side effect of both is peripheral neuropathy that can last long after treatment has ended and cause permanent disability. Many different cellular and animal models of various aspects of vincristine and bortezomib-induced neuropathies have been generated to investigate underlying molecular mechanisms and serve as platforms to develop new therapeutics. These models revealed that bortezomib induces several transcriptional programs in dorsal root ganglia that result in the activation of different neuroinflammatory pathways and secondary central sensitization. In contrast, vincristine has direct toxic effects on the axon, which are accompanied by changes similar to those observed after nerve cut. Axon degeneration following both vincristine and bortezomib is mediated by a phylogenetically ancient, genetically encoded axon destruction program that leads to the activation of the Toll-like receptor adaptor SARM1 (sterile alpha and TIR motif containing protein 1) and local decrease of nicotinamide dinucleotide (NAD+). Here, I describe current in vitro and in vivo models of vincristine- and bortezomib induced neuropathies, present discoveries resulting from these models in the context of clinical findings and discuss how increased understanding of molecular mechanisms underlying different aspects of neuropathies can be translated to effective treatments to prevent, attenuate or reverse vincristine- and bortezomib-induced neuropathies. Such treatments could improve the quality of life of patients both during and after cancer therapy and, accordingly, have enormous societal impact.

Depletion of nerve growth factor in chemotherapy-induced peripheral neuropathy associated with hematologic malignancies

Objective

To investigate whether the depletion of nerve growth factor (NGF) is associated with the development of chemotherapy-induced peripheral neuropathy (CIPN) in patients with hematologic malignancy.

Methods

We prospectively enrolled hematologic cancer patients who had a plan to receive bortezomib, thalidomide, or vincristine. Baseline NGF levels were measured within one week before the start date of chemotherapy. Follow-up NGF levels were measured after four months from the start date of chemotherapy or the date when CIPN was initially diagnosed.

Results

Baseline and follow-up NGF pairs were measured in 45 patients (male/female = 27/18, median age = 63 years old). CIPN has developed in 28 patients. In the CIPN group, the level of NGF was significantly decreased after chemotherapy compared to the baseline (△NGF = −3.52 ±5.72; p-value = 0.003), while the NGF level of the no-CIPN group was not changed after chemotherapy. The differences in △NGF levels between the CIPN and no-CIPN group were more profound when analyzed in the subgroup of newly diagnosed multiple myeloma patients (△NGF = −4.14 ± 4.87 pg/ml for the CIPN group and +2.52 ± 8.39 pg/ml for the no-CIPN group; p-value = 0.043).

Conclusions

This study shows that the depletion of NGF occurs during the development of CIPN, suggesting pathogenesis based on the role of NGF and therapeutic implications.

Taxane induced neuropathy in patients affected by breast cancer: Literature review

Taxane induced neuropathy (TIN) is the most limiting side effect of taxane based chemotherapy, relative to the majority of breast cancer patients undergoing therapy with both docetaxel and paclitaxel. The symptoms begin symmetrically from the toes, because the tips of the longest nerves are affected for first. The patients report sensory symptoms such as paresthesia, dysesthesia, numbness, electric shock-like sensation, motor impairment and neuropathic pain. There is a great inter-individual variability among breast cancer women treated with taxanes, in fact 20-30% of them don't develop neurotoxicity. Actually, there is no standard therapy for TIN, although many medications, antioxidants and natural substances have been tested in vitro and in vivo. We will summarize all most recent literature data on TIN prevention and treatment, in order to reach an improvement in TIN management. Further studies are needed to evaluate new therapies that restore neuronal function and improve life quality of patients.

Rodent models of chemotherapy-induced peripheral neuropathy

Peripheral neuropathy is a common and dose-limiting side effect of many chemotherapeutic drugs. These include platinum compounds, taxanes, vinca alkaloids, proteasome inhibitors, and others such as thalidomide and suramin. Although many rodent models have been developed using either mice or rats, there is limited consistency in the dose or mode of delivery of the drug; the sex, age, and genetic background of the animal used in the study; and the outcome measures used in evaluation of the peripheral neuropathy. Behavioral assays are commonly used to evaluate evoked sensory responses but are unlikely to be a good representation of the spontaneous sensory paresthesias that the patients experience. Electrophysiologic tests evaluate the integrity of large myelinated populations and are useful in drugs that cause either demyelination or degeneration of large myelinated axons but are insensitive to degeneration of unmyelinated axons in early stages of neuropathy. Histopathologic tools offer an unbiased way to evaluate the degree of axonal degeneration or changes in neuronal cell body but are often time consuming and require processing of the tissue after the study is completed. Nevertheless, use of drug doses and mode of delivery that are relevant to the clinical protocols and use of outcome measures that are both sensitive and objective in evaluation of the length-dependent distal axonal degeneration seen in most chemotherapy-induced peripheral neuropathies may improve the translational utility of these rodent models.

Levo-tetrahydropalmatine attenuates oxaliplatin-induced mechanical hyperalgesia in mice

Common chemotherapeutic agents such as oxaliplatin often cause neuropathic pain during cancer treatment in patients. Such neuropathic pain is difficult to treat and responds poorly to common analgesics, which represents a challenging clinical issue. Corydalis yanhusuo is an old traditional Chinese medicine with demonstrated analgesic efficacy in humans. However, the potential analgesic effect of its active component, levo-tetrahydropalmatine (l-THP), has not been reported in conditions of neuropathic pain. This study found that l-THP (1–4 mg/kg, i.p.) produced a dose-dependent anti-hyperalgesic effect in a mouse model of chemotherapeutic agent oxaliplatin-induced neuropathic pain. In addition, we found that the anti-hyperalgesic effect of l-THP was significantly blocked by a dopamine D₁ receptor antagonist SCH23390 (0.02 mg/kg), suggesting a dopamine D₁ receptor mechanism. In contrast, l-THP did not significantly alter the general locomotor activity in mice at the dose that produced significant anti-hyperalgesic action. In summary, this study reported that l-THP possesses robust analgesic efficacy in mice with neuropathic pain and may be a useful analgesic in the management of neuropathic pain.

Plant polyphenols in the treatment of age-associated diseases: revealing the pleiotropic effects of icariin by network analysis

Polyphenols are a broad class of compounds. Some are ingested in substantial quantities from nutritional sources, more are produced by medicinal plants, and some of them are taken as drugs. It is becoming clear, that a single polyphenol is impacting several cellular pathways. Thus, a network approach is becoming feasible, describing the interaction of a single polyphenol with cellular networks. Here we have selected icariin to draw a prototypic network of icariin activities. Icariin appears to be a promising drug to treat major age-related diseases, like neurodegeneration, memory and depressive disorders, chronic inflammation, diabetes, and osteoporosis. It interacts with several relevant pathways, like PDE, TGF-ß, MAPK, PPAR, NOS, IGF, Sirtuin, and others. Such networks will be useful to future comparative studies of complex effects of polyphenols.

Auraptenol attenuates vincristine-induced mechanical hyperalgesia through serotonin 5-HT1A receptors

Common chemotherapeutic agents such as vincristine often cause neuropathic pain during cancer treatment in patients. Such neuropathic pain is refractory to common analgesics and represents a challenging clinical issue. Angelicae dahuricae radix is an old traditional Chinese medicine with demonstrated analgesic efficacy in humans. However, the active component(s) that attribute to the analgesic action have not been identified. This work described the anti-hyperalgesic effect of one coumarin component, auraptenol, in a mouse model of chemotherapeutic agent vincristine-induced neuropathic pain. We reported that auraptenol dose-dependently reverted the mechanical hyperalgesia in mice within the dose range of 0.05–0.8 mg/kg. In addition, the anti-hyperalgesic effect of auraptenol was significantly blocked by a selective serotonin 5-HT_1A receptor antagonist WAY100635 (1 mg/kg). Within the dose range studied, auraptenol did not significantly alter the general locomotor activity in mice. Taken together, this study for the first time identified an active component from the herbal medicine angelicae dahuricae radix that possesses robust analgesic efficacy in mice. These data support further studies to assess the potential of auraptenol as a novel analgesic for the management of neuropathic pain.

Disulfide cross-linked micelles for the targeted delivery of vincristine to B-cell lymphoma

Vincristine (VCR) is a potent anticancer drug, but its clinical efficacy is limited by neurotoxicity. The field of drug delivery may provide an opportunity to increase the therapeutic index of VCR by delivering the drug specifically to tumor sites while sparing normal tissue. We have recently developed a telodendrimer (PEG(5k)-Cys(4)-L(8)-CA(8)) capable of forming disulfide cross-linked micelles (DCMs) which can encapsulate a variety of chemotherapeutics. In the present study, we encapsulated VCR into these micelles (DCM-VCR) and used them to treat lymphoma bearing mice. DCM-VCR particles have a size of 16 nm, which has been shown to be optimal for their accumulation into tumor via the enhanced permeability and retention (EPR) effect. Compared to our first-generation non-cross-linked micelles (NCMs), DCM-VCR demonstrated greater stability and slower drug release under physiological conditions. In addition, DCM-VCR exhibited a maximum tolerated dose (MTD) of 3.5 mg/kg while the MTD for conventional VCR was only 1.5 mg/kg. Using a near-infrared cyanine dye (DiD) as the surrogate drug, we showed that DCM-VCR accumulated at the tumor site starting 1 h after injection and persisted up to 72 h in lymphoma xenografted nude mice. In an in vivo efficacy study, high dose (2.5 mg/kg) DCM-VCR produced the greatest reduction in tumor volume. High dose DCM-VCR was well tolerated with no significant changes in complete blood count, serum chemistry and histology of the sciatic nerve. Mice treated with an equivalent dose (1 mg/kg) of conventional VCR and DCM-VCR controlled tumor growth equally; however, in combination with on-demand addition of the reducing agent N-acetylcysteine, DCM-VCR exhibited a superior antitumor effect compared to conventional VCR.

Objective evaluation of the alleviating effects of Goshajinkigan on peripheral neuropathy induced by paclitaxel/carboplatin therapy: A multicenter collaborative study

Paclitaxel/carboplatin chemotherapy for cancer (TC therapy) exhibits neurotoxicity and causes peripheral neuropathy at a high frequency, which is difficult to cope with. In this study, we investigated the efficacy of Goshajinkigan, a traditional Japanese herbal medicine, for TC therapy-induced peripheral neuropathy. The subjects included in our study were patients with ovarian or endometrial cancer who underwent TC therapy and developed peripheral neuropathy. The patients were randomly divided into Group A, comprising of 14 patients (vitamin B12 treatment), and Group B, comprising of 15 patients (vitamin B12 + Goshajinkigan treatment). The observation period was 6 weeks following treatment initiation, and the evaluation items were as follows: i) the current perception threshold (CPT value) of the peripheral nerve, ii) visual analogue scale for numbness, iii) National Cancer Institute Common Terminology Criteria for Adverse Events v3.0 grade of neurotoxicity, and iv) a questionnaire on the subjective symptoms of peripheral neuropathy (functional assessment of cancer therapy-taxane). These were compared between the groups and no significant differences were noted in any item. However, CTCAE grade 3 neurotoxicity developed in 2 patients (14.3%) after 6 weeks of administration in Group A, whereas no neurotoxicity was observed in Group B. When the change in the frequency of abnormal CPT ratio at 6 weeks of administration from that before treatment was compared between the groups, the frequency of abnormal value was significantly lower in Group B than in Group A (p<0.05). This suggests that Goshajinkigan inhibits the progression of peripheral neuropathy.

Follow-up psychophysical studies in bortezomib-related chemoneuropathy patients

Many frontline chemotherapeutic agents produce robust neuropathy as a dose-limiting side effect; however, the persistence of chemotherapy-related sensory disturbances and pain are not well documented. We have previously investigated the qualities of bortezomib-induced pain, and now seek to determine the ongoing nature of this pain. Twenty-six control subjects and 11 patients who had previously been treated with bortezomib and who were experiencing ongoing pain consented to recurring quantitative sensory testing. A pilot immunohistochemistry study of skin innervation was also performed on patient-obtained biopsies. Psychophysical testing in patients revealed persistent changes including decreased skin temperature in the area of pain, diminished touch and sharpness detection, increased pegboard completion times, and decreased sensitivity to skin heating. Additionally, the intensity of pain, as captured by the use of a visual analog scale and pain descriptors, was reported by patients to be unchanged during the retest despite similar morphine equivalent daily doses. The patient skin biopsies displayed a marked decrease in the density of epidermal nerve fibers and Meissner's corpuscles. These results signify a persistent and severe impairment of Aβ, Aδ, and C fibers in patients with chronic bortezomib-induced chemoneuropathy. Further, this study reports a loss of both epidermal nerve fibers and Meissner's corpuscles.

PERSPECTIVE

The results of this article indicate a persistent, painful peripheral neuropathy in patients treated with bortezomib. Pilot data indicates a loss of nerve fibers innervating the area of pain. This is the first paper to address the persistence, and potential contributing factors, of bortezomib chemoneuropathy.

Differential expression of microRNAs in mouse pain models

BACKGROUND

MicroRNAs (miRNAs) are short non-coding RNAs that inhibit translation of target genes by binding to their mRNAs. The expression of numerous brain-specific miRNAs with a high degree of temporal and spatial specificity suggests that miRNAs play an important role in gene regulation in health and disease. Here we investigate the time course gene expression profile of miR-1, -16, and -206 in mouse dorsal root ganglion (DRG), and spinal cord dorsal horn under inflammatory and neuropathic pain conditions as well as following acute noxious stimulation.

RESULTS

Quantitative real-time polymerase chain reaction analyses showed that the mature form of miR-1, -16 and -206, is expressed in DRG and the dorsal horn of the spinal cord. Moreover, CFA-induced inflammation significantly reduced miRs-1 and -16 expression in DRG whereas miR-206 was downregulated in a time dependent manner. Conversely, in the spinal dorsal horn all three miRNAs monitored were upregulated. After sciatic nerve partial ligation, miR-1 and -206 were downregulated in DRG with no change in the spinal dorsal horn. On the other hand, axotomy increases the relative expression of miR-1, -16, and 206 in a time-dependent fashion while in the dorsal horn there was a significant downregulation of miR-1. Acute noxious stimulation with capsaicin also increased the expression of miR-1 and -16 in DRG cells but, on the other hand, in the spinal dorsal horn only a high dose of capsaicin was able to downregulate miR-206 expression.

CONCLUSIONS

Our results indicate that miRNAs may participate in the regulatory mechanisms of genes associated with the pathophysiology of chronic pain as well as the nociceptive processing following acute noxious stimulation. We found substantial evidence that miRNAs are differentially regulated in DRG and the dorsal horn of the spinal cord under different pain states. Therefore, miRNA expression in the nociceptive system shows not only temporal and spatial specificity but is also stimulus-dependent.

Animal models of chemotherapy-evoked painful peripheral neuropathies

This review examines recent preclinical research on toxic peripheral neuropathy and potential therapeutic developments. Chemotherapy-induced peripheral neurotoxicity is a major clinical problem because it represents the dose-limiting side effects of a significant number of antineoplastic drugs. Patients are unable to complete full or optimal treatment schedules. The incidence of chemotherapy-induced peripheral neuropathy varies depending on the drugs and schedules used, and this can be quite high, particularly when neurophysiological methods are used to make a diagnosis. However, even when chemotherapy-induced peripheral neuropathy is not a dose-limiting side effect, its onset may severely affect the quality of life of cancer patients and cause chronic discomfort. As such, improved understanding of the pathophysiology of chemotherapy-induced neurotoxicity need for animal models is clinically relevant and will assist in the development of future neuroprotective strategies and also in the design of novel chemotherapies with improved toxicity profiles. In this review, the features of animal models of chemotherapy-induced painful neuropathy developed for 20 years, due to the administration of the most widely used drugs, such as platinum drugs, taxanes, and vinca alkaloids, will be discussed. In a second part, data available on neuroprotectants and treatment strategies, evaluated using these previous animal models in the attempt to prevent neuropathic pain, will be summarized.

Phenoxodiol protects against Cisplatin induced neurite toxicity in a PC-12 cell model

BACKGROUND

Many commonly used chemotherapeutic agents, such as Cisplatin, are restricted in their potential anti-neoplastic effectiveness by their side effects, with one of the most problematic being induction of peripheral neuropathy. Although a number of different neurotrophic, neuroprotective or anti-oxidant treatments have been tried in order to prevent or treat the neuropathies, to date they have met with limited success. Phenoxodiol is a new chemotherapeutic agent that has anti-proliferative and apoptotic effects on a range of cancer cells. PC12 cells are a commonly used neuronal cell model for examination of neurite outgrowth. In this study we examined whether phenoxodiol could protect against Cisplatin induced neurite inhibition in PC12 cells as an indication of the potential to protect against neuropathy.

RESULTS

Using the PC12 neuronal cell line, concentrations of Cisplatin were chosen that induced moderate or strong neurite toxicity within 24 hrs but were not cytotoxic. The effect of Phenoxodiol on Cisplatin induced neurite toxicity was assessed by measurement of neurite outgrowth. Addition of phenoxodiol at 100 nM or 1 microM showed no cytotoxicity and blocked the Cisplatin induced neurite toxicity, while phenoxodiol at 10 microM was cytotoxic and enhanced neurite toxicity of Cisplatin. When Cisplatin was added for 24 hrs, then washed out and the cells allowed to recover for 48 hrs, neurite outgrowth was not restored and addition of phenoxodiol did not further promote recovery or restore the Cisplatin treated cells.

CONCLUSION

In addition to its potential as a chemotherapeutic agent Phenoxodiol may thus also have the potential to be used in conjunction with Cisplatin chemotherapy to prevent induction of neuropathy.

The therapeutic potential of gene transfer for the treatment of peripheral neuropathies

Peripheral neuropathy is a common medical problem with numerous aetiologies. Unfortunately, for the majority of cases there is no available medical solution for the underlying cause, and the only option is to try to treat the resulting symptoms. Treatment options exist when neuropathy results in positive symptoms such as pain, but there is a significant lack of treatments for negative symptoms such as numbness and weakness. Systemic application of growth factor peptides has shown promise in protecting nerves from neuropathic insults in preclinical animal studies, but translation into human trials has been problematic and disappointing. Significant advancements have been made in the past few years in utilising gene therapy approaches to treat peripheral neuropathy by expressing neuroprotective gene products either systemically or in specific nervous tissues. For example, plasmids expressing vascular endothelial growth factor injected into muscle, or herpes-simplex-virus-based vectors expressing neurotrophin gene products delivered to dorsal root ganglion neurons, have been used to protect peripheral nerve function in animal models of diabetes-associated peripheral neuropathy. Many published studies support the feasibility of this approach, although several questions still need to be addressed as gene therapy to treat peripheral neuropathy moves out of the laboratory and into the clinic.

Neurotrophic factors in peripheral neuropathies: therapeutic implications

Neurotrophic factors are proteins which promote the survival of specific neuronal populations. Many have other physiological effects on neurons such as inducing morphological differentiation, enhancing nerve regeneration, stimulating neurotransmitter expression, and otherwise altering the physiological characteristics of neurons. These properties suggest that neurotrophic factors are highly promising as potential therapeutic agents for neurological disease. Neurotrophic factors will most likely be applied to the peripheral nervous system initially, since there are fewer problems for large proteins to gain access to peripheral neurons. Many of the most intensively studied factors are active in the peripheral nervous system. These include the neurotrophins (nerve growth factor, brain derived neurotrophic factor, neurotrophin-3, neurotrophin-4/5), the insulin like growth factors, ciliary neurotrophic factor, and glial cell derived neurotrophic factor and its related proteins. The biology of these factors and their receptors in the peripheral nervous system is reviewed here. We also review data suggesting that abnormal availability of some factors may contribute towards the pathogenesis of certain types of peripheral neuropathy. Finally, the pre-clinical data suggesting that individual factors might be effective in treating neuropathy is reviewed, along with data relating to possible side effects of neurotrophic factor therapy. Several factors have already entered clinical trials with variable success. The data from these trials is reviewed as well.

The insulin-like growth factor system and its pleiotropic functions in brain

In recent years, much interest has been devoted to defining the role of the IGF system in the nervous system. The ubiquitous IGFs, their cell membrane receptors, and their carrier binding proteins, the IGFBPs, are expressed early in the development of the nervous system and are therefore considered to play a key role in these processes. In vitro studies have demonstrated that the IGF system promotes differentiation and proliferation and sustains survival, preventing apoptosis of neuronal and brain derived cells. Furthermore, studies of transgenic mice overexpressing components of the IGF system or mice with disruptions of the same genes have clearly shown that the IGF system plays a key role in vivo.

Taxol-induced sensory disturbance is characterized by preferential impairment of myelinated fiber function in cancer patients

Taxol produces neuropathic pain with three distinct zones of involvement in the extremities. Most distally is an area of on-going pain and proximal to this is a zone of sensory disturbance but not overt pain. These two areas were confined in all but one case to the glabrous skin of the hands and/or feet. More proximal is an area not recognized by the patients as involved with pain or sensory disturbance yet wherein quantitative sensory tests nevertheless reveal altered sensibility. Impairment of perception to light touch, normally conveyed by myelinated fibers, was dramatically altered in all three areas, being approximately 50-fold greater than normal in areas of pain and sensory disturbance as well as in areas of skin perceived by the patients as not affected. Impairment of perception to sharpness, normally conveyed by small myelinated fibers, was most pronounced in areas of on-going pain, intermediate in areas of sensory disturbance and near baseline in more proximal skin of chemotherapy patients. In contrast to mechanical sensibility, thermal thresholds for warm and heat pain detection were normal throughout. Finally, chemotherapy patients showed paradoxical burning pain to skin cooling that was most pronounced in proximal areas of skin thought to be unaffected by the patients, intermediate in the border zone of altered sensibility and least pronounced in areas of on-going pain. These data suggest that taxol produces a neuropathy characterized by pronounced impairment of function in A-beta myelinated fibers, intermediate impairment of A-delta myelinated fibers, and a relative sparing of C-fibers.

Insulin-like growth factor-I improves cerebellar dysfunction but does not prevent cerebellar neurodegeneration in the calcium channel mutant mouse, leaner

The effects of insulin-like growth factor-I (IGF-I) on cerebellar dysfunction and neurodegeneration were investigated in leaner mice, which exhibit cerebellar ataxia and neurodegeneration related to P/Q-type calcium channel mutations. Leaner mice showed significantly reduced serum and cerebellar IGF-I concentrations compared to wild-type mice at postnatal day 30. Behavioral assessment of leaner mice injected with IGF-I subcutaneously for 4 weeks showed partially improved cerebellar function. Histological analysis of IGF-I treated leaner cerebella showed no difference in the number of dying Purkinje cells compared to control leaner cerebella. These results further support potential use of IGF-I as a therapeutic aid for cerebellar ataxia related to calcium channel mutations. Nonetheless, IGF-I administration does not rescue dying cerebellar neurons, which suggests that the beneficial effects of IGF-I may have been achieved through surviving cerebellar neurons.

A New Animal Model of Vincristine-Induced Nociceptive Peripheral Neuropathy

Using doses close to those used clinically, we have developed an animal model of vincristine-induced nociceptive sensory neuropathy after repeated intravenous injection in male Sprague-Dawley rats. In order to validate the model, three different doses (50, 100 and 150 microg/kg) of vincristine were injected every 2nd day until five injections had been given. The sensory behavioural assessment revealed mechanical hyperalgesia and allodynia associated with cold thermal hyperalgesia and allodynia. With regard to electrophysiological evaluation, we observed a decrease in the nerve conduction velocity in the highest dose group. Morphological studies revealed few degenerated fibers in the sciatic nerve and many degenerated myelinated axons in the fine nerve fibers of the subcutaneous paw tissue. Finally, to develop an animal model, we chose the 150 microg/kg dose because of the good general clinical status of the rats without motor function changes associated with severe sensation disorders like hyperalgesia and allodynia. This model of vincristine-induced painful neuropathy will be used to explore physiopathological mechanisms implied in the genesis of neuropathic pain and also to test new analgesic and neuroprotective drugs.

Selective decrease in axonal nerve growth factor and insulin-like growth factor I immunoreactivity in axonopathies of unknown etiology

In an attempt to approach the mechanisms underlying axonopathies of unknown etiology, we have studied by immunocytochemistry the fate of several growth factors in eight of such cases that we had previously analyzed by morphometry and which were characterized by a decrease in neurofilaments and an increase in beta tubulin immunostaining. Here we establish that, contrary to beta tubulin, growth-associated protein43 (GAP-43) immunolabeling is not up-regulated in theses cases, correlating well with the failure of regeneration. Neurotrophin-3 (NT-3) and its receptor TrkC were not modified compared to controls (five cases). On the contrary, we observed in all cases a pronounced decrease in the number of fibers labeled for nerve growth factor (NGF) and insulin-like growth factor I (IGF-I), which were both approximately half of control values. This decrease could not be ascribed to the reduction in fiber density since it was also present in cases without fiber loss (isolated large fiber atrophy). The fact that only around 50% of fibers were stained, versus all fibers in controls, probably accounted for this decrease. It contrasted also with the normality of NGF and IGF-I immunolabeling in six cases of chronic inflammatory demyelinating neuropathy that were investigated in parallel. These results differ from those reported in experimental diabetic neuropathy, during which NT-3 is also decreased. A deficient supply of specific growth factors delivered by neuronal targets may be responsible for these neuropathies and their associated axonal cytoskeleton abnormalities.

Cytoskeleton abnormalities in axonopathies of unknown aetiology: correlations with morphometry

To determine if specific axonal cytoskeleton abnormalities could be demonstrated in axonopathies without aetiology, nerve biopsies from five controls and nine cases were analyzed by morphometry and immunocytochemistry with anti-neurofilament (NF, subunits L, M, H) and anti-beta tubulin (TUB) antibodies. Morphometry revealed either large fiber atrophy (decrease in large fiber density with increased density in small fibers), degeneration of large fibers (decrease in large fiber density and in total density of fibers) or of all diameter fibers. NF immunostaining density decreased (by 21-89%) only in cases with fiber loss, in parallel to myelinated fiber density as determined by morphometry. On the contrary, the density of fibers labelled for TUB increased significantly in all except two cases by 52-102% over controls. Nevertheless, in these two cases--with a severe loss of fibers--as well as in other cases, the ratio of the density of fibers labelled for TUB and NFL (TUB/NFL) increased by 48-404%. Thus, the total density of myelinated fibers was always inversely correlated with the TUB/NFL ratio. Similar abnormalities have been described only after axotomy; our cases could thus be compared to <<permanent axotomy>>.

In vivo gene therapy for pyridoxine-induced neuropathy by herpes simplex virus-mediated gene transfer of neurotrophin-3

Neurotrophic factors have been demonstrated to prevent the development of peripheral neuropathy in animal models, but the therapeutic use of these factors in human disease has been limited by the short serum half-life and dose-limiting side effects of these potent peptides. We used peripheral subcutaneous inoculation with a replication-incompetent, genomic herpes simplex virus-based vector containing the coding sequence for neurotrophin-3 to transduce sensory neurons of the rat dorsal root ganglion in vivo, and found that expression of neurotrophin-3 from the vector protected peripheral sensory axons from neuropathy induced by intoxication with pyridoxine assessed by electrophysiological (foot sensory response amplitude, and conduction velocity, and H-wave), histological (nerve morphology and morphometry), and behavioral measures of proprioceptive function. In vivo gene transfer using herpes simplex virus vectors provides a unique option for treatment of diseases of the sensory peripheral nervous system.

Delayed functional recovery by vincristine after sciatic nerve crush injury: a mouse model of vincristine neurotoxicity

Neuropathy is the dose-limiting side effect of vincristine (VCR) in cancer therapy. However, no simple experimental model has yet been reported. Here, we present a simple experimental model of VCR neurotoxicity using a mouse sciatic nerve crush model, which allows evaluation within a few weeks. VCR administered intravenously once on the day after the crush lesion caused a dose-dependent delay of the recovery of motor and sensory functions. The minimal dose required to cause the delay was 0.25 mg/kg, which corresponded to five times the usual clinical dose for man and was far less than the reported doses required to cause functional impairment in intact animals. The model would be useful not only for the development of new drugs but also for the estimation of the drug interactions in combination cancer therapy.

Survival activity of troglitazone in rat motoneurones

Troglitazone (TGZ), an antidiabetic drug that improves insulin-resistance in the peripheral tissues, was tested for neurotrophic activity in motoneurones and other neurones in culture. In rat motoneurones, TGZ had a remarkable effect on survival, which was comparable or superior to that of brain-derived neurotrophic factor, a known potent neurotrophic factor for rat motoneurones. However, TGZ did not promote the survival of sensory, sympathetic, septal or hippocampal neurones. The effect of TGZ on motoneurones was additive to that of insulin-like growth factor-I and both activities were inhibited by phosphatidylinositol 3-kinase (PI3-kinase) inhibitors, wortmannin and LY294002, suggesting the involvement of the activation of PI3-kinase in the activity of TGZ. Pioglitazone, another antidiabetic drug structurally similar to TGZ, did not show any activity, indicating that the agonistic activity of TGZ for peroxisome proliferator-activated receptor-gamma is not involved in the survival activity. Chromanol, an antioxidant moiety of TGZ, showed little or no survival activity. These results indicate specific neurotrophic activity of TGZ for motoneurones through the activation of PI3-kinase and support the applicability of TGZ for the treatment of motor neurone diseases such as amyotrophic lateral sclerosis.

Actions and interactions of the IGF system in Alzheimer's disease: review and hypotheses

Insulin-like growth factors (IGF) are pleiotrophic polypeptides affecting all aspects of growth and development. The IGF system, including ligands, receptors, binding proteins and proteases is also involved in pathophysiological conditions, such as cancer and degenerative conditions. In this review, the actions and interactions of the IGF system as it relates to Alzheimer's disease will be investigated.

Neurotrophic factors and neuro-muscular disease: II. GDNF, other neurotrophic factors, and future directions

This is the second of two reviews in which we discuss the essential aspects of neurotrophic factor neurobiology, the characteristics of each neurotrophic factor, and their clinical relevance to neuromuscular diseases. The previous paper reviewed the neurotrophin family and neuropoietic cytokines. In the present article, we focus on the GDNF family and other neurotrophic factors and then consider future approaches that may be utilized in neurotrophic factor treatment.

Neuroprotective actions of peripherally administered insulin-like growth factor I in the injured olivo-cerebellar pathway

Exogenous administration of insulin-like growth factor I (IGF-I) restores motor function in rats with neurotoxin-induced cerebellar deafferentation. We first determined that endogenous IGFs are directly involved in the recovery process because infusion of an IGF-I receptor antagonist into the lateral ventricle blocks gradual recovery of limb coordination that spontaneously occurs after partial deafferentation of the olivo-cerebellar circuitry. We then analysed mechanisms whereby exogenous IGF-I restores motor function in rats with complete damage of the olivo-cerebellar pathway. Treatment with IGF-I normalized several markers of cell function in the cerebellum, including calbindin, glutamate receptor 1 (GluR1), gamma-aminobutyric acid (GABA) and glutamate, which are all depressed after 3-acetylpyridine (3AP)-induced deafferentation. IGF-I also promoted functional reinnervation of the cerebellar cortex by inferior olive (IO) axons. In the IO, increased expression of bax in neurons and bcl-X in astrocytes after 3AP was significantly reduced by IGF-I treatment. On the contrary, IGF-I prevented the decrease in poly-sialic-acid neural cell adhesion molecule (PSA-NCAM) and GAP-43 expression induced by 3AP in IO cells. IGF-I also significantly increased the number of neurons expressing bcl-2 in brainstem areas surrounding the IO. Altogether, these results indicate that subcutaneous IGF-I therapy promotes functional recovery of the olivo-cerebellar pathway by acting at two sites within this circuitry: (i) by modulating death- and plasticity-related proteins in IO neurons; and (ii) by impinging on homeostatic mechanisms leading to normalization of cell function in the cerebellum. These results provide insight into the neuroprotective actions of IGF-I and may be of practical consequence in the design of new therapeutic approaches for neurodegenerative diseases.