Advances in Understanding Drug-Induced Neuropathies

Medikamentös-induzierte Polyneuropathien durch Chemotherapeutika und Antiinfektiva

Polyneuropathien können durch zahlreiche Wirkstoffe hervorgerufen oder aggraviert werden. Insbesondere die Chemotherapeutika-induzierte Polyneuropathie (CIPN) ist im Alltag von hoher Relevanz. Jedoch kann auch der Einsatz von Antiinfektiva zu neuropathischen Beschwerden führen. Im Folgenden soll ein Überblick über die wichtigsten mit Polyneuropathien assoziierten Wirkstoffe der Substanzklassen sowie die klinischen Charakteristika gegeben werden.

Grundlagen medikamentös-induzierter Polyneuropathien

Zahlreiche Wirkstoffe können mit dem erstmaligen Auftreten oder dem Fortschreiten neuropathischer Symptome in Verbindung gebracht werden. Insbesondere im Kontext der modernen Polypharmazie kommt medikamentös-induzierten Polyneuropathien eine besondere Bedeutung zu. Die Schädigungsmechanismen und individuellen Risikofaktoren sind vielfältig. In den meisten Fällen resultiert eine längenabhängige, axonale Polyneuropathie mit vorwiegend sensiblen Symptomen. Grundlegende Kenntnisse darüber, welche Arzneimittel mit dem Auftreten einer Polyneuropathie assoziiert sind, können dazu beitragen, das Auftreten dieser Nebenwirkung frühzeitig zu erkennen. Die Verordnung entsprechender Medikamente sollte vermieden werden, wenn das Risiko für den einzelnen Patienten als zu hoch eingeschätzt wird. Unter Therapie sind regelmäßige Kontrolluntersuchungen nötig, um bei neuauftretenden oder zunehmenden Symptomen die Therapie so früh wie möglich anpassen oder absetzen zu können. Die Prognose ist dann meist gut.

Preclinical and Clinical Evidence of Therapeutic Agents for Paclitaxel-Induced Peripheral Neuropathy

Paclitaxel is an essential drug in the chemotherapy of ovarian, non-small cell lung, breast, gastric, endometrial, and pancreatic cancers. However, it frequently causes peripheral neuropathy as a dose-limiting factor. Animal models of paclitaxel-induced peripheral neuropathy (PIPN) have been established. The mechanisms of PIPN development have been elucidated, and many drugs and agents have been proven to have neuroprotective effects in basic studies. In addition, some of these drugs have been validated in clinical studies for their inhibitory PIPN effects. This review summarizes the basic and clinical evidence for therapeutic or prophylactic effects for PIPN. In pre-clinical research, many reports exist of neuropathy inhibitors that target oxidative stress, inflammatory response, ion channels, transient receptor potential (TRP) channels, cannabinoid receptors, and the monoamine nervous system. Alternatively, very few drugs have demonstrated PIPN efficacy in clinical trials. Thus, enhancing translational research to translate pre-clinical research into clinical research is important.

Clinician-rated measures for distal symmetrical axonal polyneuropathy: ACTTION systematic review

Distal symmetrical axonal polyneuropathy (DSP) is due to injury to peripheral sensory, motor, and autonomic nerve fibers, resulting in distal predominant sensory loss, pain, and gait instability. DSP occurs as a complication of multiple medical conditions including diabetes or HIV, or following exposure to various toxins such as chemotherapy. It affects at least 10% of the United States population. Few treatments for DSP are approved by regulatory agencies. Reliable and responsive outcome measures are integral to developing new DSP treatments. Multiple clinician-rated measures that incorporate neuropathy signs exist, however, it is not clear which of these measures performs best for various DSP phenotypes. This systematic review summarizes the content of 18 published measures of DSP identified using PubMed and from personal archives of the authors. The relative percentage of scoring dedicated to motor, reflex, large and small fiber sensory, and autonomic domains varied considerably among measures. The most common neurologic examination items included in the scales were (1) vibration perception (n = 18, 100%), (2) reflexes (n = 16, 89%), (3) pinprick perception (n = 14, 78%), (4) muscle strength (n = 11, 61%), (5) touch-pressure perception (n = 9, 50%), and (6) joint position perception (n = 8, 44%). This review can be used to inform decisions regarding which of the available clinician-rated sign outcome measures would be most appropriate for use in a particular DSP population, based on the domains most affected by that neuropathy or on the domains most likely to be affected by a particular experimental therapy.

Chemotherapy-induced peripheral neurotoxicity (CIPN): what we need and what we know

Chemotherapy-induced peripheral neurotoxicity (CIPN) is one of the most frequent and severe long-term side effects of cancer chemotherapy. Preclinical and clinical studies have extensively investigated CIPN searching for effective strategies to limit its severity or to treat CIPN-related impairment, but the results have been disappointing. Among the reasons for this failure are methodological flaws in both preclinical and clinical investigations. Their successful resolution might provide a brighter perspective for future studies. Among the several neurotoxic chemotherapy drugs, oxaliplatin may offer a clear example of a methodological approach eventually leading to successful clinical trials. However, the same considerations apply to the other neurotoxic agents and, although frequently neglected, also to the new "targeted" agents.

Management of a mixed overdose of calcium channel blockers, β-blockers and statins

We describe a case of extreme mixed overdose of calcium channel blockers, β-blockers and statins. The patient was successfully treated with aggressive resuscitation including cardiac pacing and multiorgan support, glucagon and high-dose insulin for toxicity related to calcium channel blockade and β-blockade, and ubiquinone for treating severe presumed statin-induced rhabdomyolysis and muscle weakness.

Idiopathic small fiber neuropathy: phenotype, etiologies, and the search for fabry disease

Background and Purpose

The etiology of small fiber neuropathy (SFN) often remains unclear. Since SFN may be the only symptom of late-onset Fabry disease, it may be underdiagnosed in patients with idiopathic polyneuropathy. We aimed to uncover the etiological causes of seemingly idiopathic SFN by applying a focused investigatory procedure, to describe the clinical phenotype of true idiopathic SFN, and to elucidate the possible prevalence of late-onset Fabry disease in these patients.

Methods

Forty-seven adults younger than 60 years with seemingly idiopathic pure or predominantly small fiber sensory neuropathy underwent a standardized focused etiological and clinical investigation. The patients deemed to have true idiopathic SFN underwent genetic analysis of the alpha-galactosidase A gene (GLA) that encodes the enzyme alpha-galactosidase A (Fabry disease).

Results

The following etiologies were identified in 12 patients: impaired glucose tolerance (58.3%), diabetes mellitus (16.6%), alcohol abuse (8.3%), mitochondrial disease (8.3%), and hereditary neuropathy (8.3%). Genetic alterations of unknown clinical significance in GLA were detected in 6 of the 29 patients with true idiopathic SFN, but this rate did not differ significantly from that in healthy controls (n=203). None of the patients with genetic alterations in GLA had significant biochemical abnormalities simultaneously in blood, urine, and skin tissue.

Conclusions

A focused investigation may aid in uncovering further etiological factors in patients with seemingly idiopathic SFN, such as impaired glucose tolerance. However, idiopathic SFN in young to middle-aged Swedish patients does not seem to be due to late-onset Fabry disease.

Thalidomide Embryopathy: An Enigmatic Challenge

Thalidomide remains one of the world’s most notorious drugs due to the severe birth defects it induced in children between 1957 and 1962. Yet, to some this drug is a lifesaver, as it now enjoys renaissance in the treatment for a wide range of conditions including leprosy, multiple myeloma, Behcet’s disease, and some cancers. However, thalidomide has also been linked to causing a new generation of thalidomide survivors in Brazil, where the drug is used to treat leprosy. Surprisingly how thalidomide causes birth defects and how it acts in the treatment of clinical conditions are still far from clear. In the past decade great strides in our understanding of the actions of the drug, as well as molecular targets, have been made. The purpose of this review is to look at the recent work carried out into understanding how thalidomide causes birth defects, it’s molecular targets and the challenges that remain to be elucidated. These challenges include identifying clinically relevant but nonteratogenic forms of the drug, and the mechanisms underlying phocomelia and species specificity.

Pomalidomide is nonteratogenic in chicken and zebrafish embryos and nonneurotoxic in vitro

Thalidomide and its analog, Lenalidomide, are in current use clinically for treatment of multiple myeloma, complications of leprosy and cancers. An additional analog, Pomalidomide, has recently been licensed for treatment of multiple myeloma, and is purported to be clinically more potent than either Thalidomide or Lenalidomide. Using a combination of zebrafish and chicken embryos together with in vitro assays we have determined the relative anti-inflammatory activity of each compound. We demonstrate that in vivo embryonic assays Pomalidomide is a significantly more potent anti-inflammatory agent than either Thalidomide or Lenalidomide. We tested the effect of Pomalidomide and Lenalidomide on angiogenesis, teratogenesis, and neurite outgrowth, known detrimental effects of Thalidomide. We found that Pomalidomide, displays a high degree of cell specificity, and has no detectable teratogenic, antiangiogenic or neurotoxic effects at potent anti-inflammatory concentrations. This is in marked contrast to Thalidomide and Lenalidomide, which had detrimental effects on blood vessels, nerves, and embryonic development at anti-inflammatory concentrations. This work has implications for Pomalidomide as a treatment for conditions Thalidomide and Lenalidomide treat currently.

Association of statin use with peripheral neuropathy in the U.S. population 40 years of age or older

BACKGROUND

Peripheral neuropathy is a serious complication of diabetes and several conditions that may lead to the loss of lower extremity function and even amputations. Since the introduction of statins, their use has increased markedly. Recent reports suggest a role for statins in the development of peripheral neuropathy. The aims of the present study were to assess the association between statin use and peripheral neuropathy, and to determine whether this association varied by diabetes status.

METHODS

Data from the lower extremity examination supplement of the 1999-2004 National Health and Nutrition Examination Survey were used.

RESULTS

The overall prevalence of statin use was 15% and the prevalence of peripheral neuropathy was 14.9%. The prevalence of peripheral neuropathy was significantly higher among those who used statins compared with those who did not (23.5% vs 13.5%, respectively; P < 0.01). Multivariate logistic regression revealed that statin use (adjusted odds ratio 1.3; 95% confidence interval 1.1-1.6; Wald P = 0.04) was significantly associated with peripheral neuropathy, controlling for diabetes status, age, gender, race, height, weight, blood lead levels, poverty, glycohemoglobin, use of vitamin B12 , alcohol abuse, hypertension, and non-high-density lipoprotein-cholesterol. Diabetes status, age, gender, height, weight, blood lead levels, poverty, and glycohemoglobin were also significantly associated with peripheral neuropathy. We found no effect modification between statin use and diabetes status, race, gender, age, vitamin B12 , blood lead levels, or alcohol abuse.

CONCLUSIONS

In the present cross-sectional study, we found a modest association between peripheral neuropathy and statin use. Prospective studies are required to determine the causal direction.

Iatrogenic mitochondriopathies: a recent lesson from nucleoside/nucleotide reverse transcriptase inhibitors

The use of nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) has revolutionized the treatment of infection by human immunodeficiency virus (HIV) and hepatitis-B virus. NRTIs can suppress viral replication in the long-term, but possess significant toxicity that can seriously compromise treatment effectiveness. The major toxicity of NRTIs is mitochondrial toxicity. This manifests as serious side effects such as myopathy, peripheral neuropathy and lactic acidosis. In general, it is believed that the mitochondrial pathogenesis is closely related to the effect of NRTIs on mitochondrial DNA polymerase-γ. Depletion and mutation of mitochondrial DNA during chronic NRTI therapy may lead to cellular respiratory dysfunction and release of reactive oxidative species, resulting in cellular damage. It is now apparent that the etiology is far more complex than originally thought. It appears to involve multiple mechanisms as well as host factors such as HIV per se, inborn mitochondrial mutation, and sex. Management of mitochondrial toxicity during NRTI therapy remains a challenge. Interruption of NRTI therapy and substitution of the causative agents with alternative better-tolerated NRTIs represents the mainstay of management for mitochondrial toxicity and its clinical manifestations. A range of pharmacological approaches has been proposed as treatments and prophylaxes.

Muscle pain in models of chemotherapy-induced and alcohol-induced peripheral neuropathy

OBJECTIVE

While inflammatory pain is well described in skeletal muscle, neuropathic muscle pain remains to be clarified. We used 3 well-established rodent models of peripheral neuropathy to evaluate for muscle pain.

METHODS

In rats exposed to either of 2 neurotoxic cancer chemotherapies, paclitaxel or oxaliplatin, or to alcohol consumption, we assessed the evolution of mechanical hyperalgesia in skeletal muscle and skin, in the same animal. To explore the involvement of protein kinase C epsilon (PKCε), a second messenger implicated in some forms of neuropathic pain, antisense oligodeoxynucleotides (AS-ODNs) or mismatch ODNs (MM-ODNs) for PKCε were administered intrathecally.

RESULTS

Rats submitted to models of chemotherapy-induced and alcohol-induced neuropathy developed persistent muscle hyperalgesia, which evolved in parallel in muscle and skin. The administration of PKCε AS, which has been shown to mediate cutaneous hyperalgesia in paclitaxel and ethanol models of neuropathic pain, also inhibited muscle hyperalgesia induced by these agents. Stopping AS-ODN was associated with the reappearance of hyperalgesia at both sites. The AS-ODN to PKCε treatment was devoid of effect in both muscle and skin in the oxaliplatin neuropathy model.

INTERPRETATION

Our results support the suggestion that neuropathic muscle pain may be a greater clinical problem than generally appreciated.

Cardiovascular event reduction and adverse events among subjects attaining low-density lipoprotein cholesterol <50 mg/dl with rosuvastatin. The JUPITER trial (Justification for the Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin)

OBJECTIVES

The purpose of this study was to assess the impact on cardiovascular and adverse events of attaining low-density lipoprotein cholesterol (LDL-C) levels <50 mg/dl with rosuvastatin in apparently healthy adults in the JUPITER (Justification for the Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin) trial.

BACKGROUND

The safety and magnitude of cardiovascular risk reduction conferred by treatment to LDL-C levels below current recommended targets remain uncertain.

METHODS

A cohort of 17,802 apparently healthy men and women with high-sensitivity C-reactive protein ≥2 mg/l and LDL-C <130 mg/dl were randomly allocated to rosuvastatin 20 mg daily or placebo, and followed up for all-cause mortality, major cardiovascular events, and adverse events. In a post-hoc analysis, participants allocated to rosuvastatin were categorized as to whether or not they had a follow-up LDL-C level <50 mg/dl.

RESULTS

During a median follow-up of 2 years (range up to 5 years), rates of the primary trial endpoint were 1.18, 0.86, and 0.44 per 100 person-years in the placebo group (n = 8,150) and rosuvastatin groups without LDL-C <50 mg/dl (n = 4,000) or with LDL-C <50 mg/dl (n = 4,154), respectively (fully-adjusted hazard ratio: 0.76; 95% confidence interval: 0.57 to 1.00 for subjects with no LDL-C <50 mg/dl vs. placebo and 0.35, 95% confidence interval: 0.25 to 0.49 for subjects attaining LDL-C <50 mg/dl; p for trend <0.0001). For all-cause mortality, corresponding event rates were 0.67, 0.65, and 0.39 (p for trend = 0.004). Rates of myalgia, muscle weakness, neuropsychiatric conditions, cancer, and diabetes mellitus were not significantly different among rosuvastatin-allocated participants with and without LDL-C <50 mg/dl.

CONCLUSIONS

Among adults with LDL-C <130 mg/dl and high-sensitivity C-reactive protein ≥2 mg/l, rosuvastatin-allocated participants attaining LDL-C <50 mg/dl had a lower risk of cardiovascular events without a systematic increase in reported adverse events.

The double crush syndrome revisited--a Delphi study to reveal current expert views on mechanisms underlying dual nerve disorders

A high prevalence of dual nerve disorders is frequently reported. How a secondary nerve disorder may develop following a primary nerve disorder remains largely unknown. Although still frequently cited, most explanatory theories were formulated many years ago. Considering recent advances in neuroscience, it is uncertain whether these theories still reflect current expert opinion. A Delphi study was conducted to update views on potential mechanisms underlying dual nerve disorders. In three rounds, seventeen international experts in the field of peripheral nerve disorders were asked to list possible mechanisms and rate their plausibility. Mechanisms with a median plausibility rating of ≥7 out of 10 were considered highly plausible. The experts identified fourteen mechanisms associated with a first nerve disorder that may predispose to the development of another nerve disorder. Of these fourteen mechanisms, nine have not previously been linked to double crush. Four mechanisms were considered highly plausible (impaired axonal transport, ion channel up or downregulation, inflammation in the dorsal root ganglia and neuroma-in-continuity). Eight additional mechanisms were listed which are not triggered by a primary nerve disorder, but may render the nervous system more vulnerable to multiple nerve disorders, such as systemic diseases and neurotoxic medication. Even though many mechanisms were classified as plausible or highly plausible, overall plausibility ratings varied widely. Experts indicated that a wide range of mechanisms has to be considered to better understand dual nerve disorders. Previously listed theories cannot be discarded, but may be insufficient to explain the high prevalence of dual nerve disorders.

Abnormal muscle afferent function in a model of Taxol chemotherapy-induced painful neuropathy

Despite muscle pain being a well-described symptom in patients with diverse forms of peripheral neuropathy, the role of neuropathic mechanisms in muscle pain have received remarkably little attention. We have recently demonstrated in a well-established model of chemotherapy-induced painful neuropathy (CIPN) that the anti-tumor drug paclitaxel (Taxol) produces mechanical hyperalgesia in skeletal muscle, of similar time course to and with shared mechanism with cutaneous symptoms. In the present study, we evaluated muscle afferent neuron function in this rat model of CIPN. The mechanical threshold of muscle afferents in rats exposed to paclitaxel was not significantly different from the mechanical threshold of muscle afferents in control animals (P = 0.07). However, paclitaxel did produce a marked increase in the number of action potentials elicited by prolonged suprathreshold fixed intensity mechanical stimulation and a marked increase in the conduction velocity. In addition, the interspike interval (ISI) analysis (to evaluate the temporal characteristics of the response of afferents to sustained mechanical stimulation) showed a significant difference in rats treated with paclitaxel; there was a significantly greater ISI percentage of paclitaxel-treated muscle afferents with 0.01- and 0.02-s ISI. In contrast, an analysis of variability of neuronal firing over time (CV2 analysis) showed no effect of paclitaxel administration. These effects of paclitaxel on muscle afferent function contrast with the previously reported effects of paclitaxel on the function of cutaneous nociceptors.

My legs are getting old: sinvastatin-induced polyneuropathy

Axonal degeneration is the most common type of neuropathy induced by medication. The literature describes isolated cases in which polyneuropathy of the lower limb was observed during treatment with statins. The authors present a case of polyneuropathy associated with the use of a statin. An 82-year-old female patient presented with a complaint of weakness and discomfort in her lower limbs after 7 years of therapy with simvastatin. The results of an electromyographic study were compatible with polyneuropathy (sensorimotor axonal neuropathy--moderate to severe). One month after the therapy with simvastatin was discontinued, the symptoms were reduced.

Thalidomide-induced limb defects: resolving a 50-year-old puzzle

Despite the recent discovery that thalidomide causes limb defects by targeting highly angiogenic, immature blood vessels, several challenges still remain and new ones have arisen. These include understanding the drug's species specificity, determining molecular target(s) in the endothelial cell, shedding light on the molecular basis of phocomelia and producing a form of the drug that is clinically effective without having side effects. Now that the trigger of thalidomide-induced teratogenesis has been uncovered, a framework is proposed, incorporating and uniting previous models of thalidomide action, explaining how thalidomide causes not just limb defects, but also all the other defects it induces.

Not all neuropathy in diabetes is of diabetic etiology: differential diagnosis of diabetic neuropathy

Diabetic peripheral neuropathy is the most common peripheral neuropathy in the developed world; however, not all patients with diabetes and peripheral nerve disease have a peripheral neuropathy caused by diabetes. Several (although not all) studies have drawn attention to the presence of other potential causes of a neuropathy in individuals with diabetes; 10% to 50% of individuals with diabetes may have an additional potential cause of a peripheral neuropathy and some may have more than one cause. Neurotoxic medications, alcohol abuse, vitamin B(12) deficiency, renal disease, chronic inflammatory demyelinating neuropathy, inherited neuropathy, and vasculitis are the most common additional potential causes of a peripheral neuropathy in these series. The most common disorders in the differential diagnosis of a generalized diabetic peripheral neuropathy are discussed in this article. Prospective studies to investigate the prevalence of other disorders that might be responsible for a peripheral neuropathy in individuals with diabetes are warranted.

Pharmacogenetics of nucleoside reverse-transcriptase inhibitor-associated peripheral neuropathy

Peripheral neuropathy is an important complication of antiretroviral therapy. Nucleoside reverse-transcriptase inhibitor (NRTI)-associated mitochondrial dysfunction, inflammation and nutritional factors are implicated in its pathogenesis. Pharmacogenetic and genomic studies investigating NRTI neurotoxicity have only recently become possible via the linkage of HIV clinical studies to large DNA repositories. Preliminary case-control studies using these resources suggest that host mitochondrial DNA haplogroup polymorphisms in the hemochromatosis gene and proinflammatory cytokine genes may influence the risk of peripheral neuropathy during antiretroviral therapy. These putative risk factors await confirmation in other HIV-infected populations but they have strong biological plausibility. Work to identify underlying mechanisms for these associations is ongoing. Large-scale studies incorporating clearly defined and validated methods of neuropathy assessment and the use of novel laboratory models of NRTI-associated neuropathy to clarify its pathophysiology are now needed. Such investigations may facilitate the development of more effective strategies to predict, prevent and ameliorate this debilitating treatment toxicity in diverse clinical settings.

Endothelin-1-induced pain and hyperalgesia: a review of pathophysiology, clinical manifestations and future therapeutic options

Pain in patients with metastatic cancer contributes to increased suffering in those already burdened by their advancing illness. The causes of this pain are unknown, but are likely to involve the action of tumour-associated mediators and their receptors. In recent years, several chemical mediators have increasingly come to the forefront in the pathophysiology of cancer pain. One such mediator, endothelin-1 (ET-1), is a peptide of 21 amino acids that was initially shown to be a potent vasoconstrictor. Extensive research has revealed that members of the ET family are indeed produced by several epithelial cancerous tumours, in which they act as autocrine and/or paracrine growth factors. Several preclinical and clinical studies of various malignancies have suggested that the ET axis may represent an interesting contributor to tumour progression. In addition, evidence is accumulating to suggest that ET-1 may contribute to pain states both in humans and in other animals. ET-1 both stimulates nociceptors and sensitises them to painful stimuli. Selective stimulation of ET receptors has been implicated as a cause of inflammatory, neuropathic and tumoural pain. ET-1-induced pain-related behaviour seems to be mediated either solely by one receptor type or via both endothelin-A receptors (ETAR) and endothelin-B receptors (ETBR). Whereas stimulation of ETAR on nociceptors always elicits a pain response, stimulation of ETBR may cause analgesia or elicit a pain response, depending on the conditions. The administration of ETAR antagonists in the receptive fields of these nociceptors has been shown to ameliorate pain-related behaviours in animals, as well as in some patients with advanced metastatic prostate cancer. The identification of tumour-associated mediators that might directly or indirectly cause pain in patients with metastatic disease, such as ET-1, should lead to improved, targeted analgesia for patients with advanced cancer. In this review, we will describe the current status of the role of ET-1 in different types of painful syndromes, with special emphasis on its role in the pathophysiology of cancer pain. Finally, potential new treatment options that are based on the role of the ET axis in the pathophysiology of cancer are elaborated.

Peripheral nerve damage associated with administration of taxanes in patients with cancer

Peripheral neuropathy is a well recognized toxicity of taxanes, usually resulting to dose modification and changes in the treatment plan. Taxanes produce a symmetric, axonal predominantly sensory distal neuropathy with less prominent motor involvement. A "dying back" process starting from distal nerve endings followed by effects on Schwann cells, neuronal body or axonal transport changes and a disturbed cytoplasmatic flow in the affected neurons is the most widely accepted mechanism of taxanes neurotoxicity. The incidence of taxanes-induced peripheral neuropathy is related to causal factors, such as single dose per course and cumulative dose and risk factors including treatment schedule, prior or concomitant administration of platinum compounds or vinca alcaloids, age and pre-existing peripheral neuropathy of other causes. The most reliable method to assess taxanes neurotoxicity is by clinical examination combined with electrophysiological evaluation. There is currently no effective symptomatic treatment for paclitaxel-associated pain, myalgias and arthralgias. Tricyclic antidepressants and anticonvulsants have been used as symptomatic treatment of neurotoxicity with some measure of success. Therefore, new approaches for prophylaxis against taxanes-induced peripheral neuropathy are needed. Several neuroprotective agents including, thiols, neurotrophic factors, and antioxidants hold promise for their ability to prevent neurotoxicity resulting from taxanes exposure. However, further confirmatory trials are warranted on this important clinical topic. This review critically looks at the pathogenesis, incidence, risk factors, diagnosis, characteristics and management of taxanes-induced peripheral neuropathy. We also highlight areas of future research.

Mutations in PRPS1, which encodes the phosphoribosyl pyrophosphate synthetase enzyme critical for nucleotide biosynthesis, cause hereditary peripheral neuropathy with hearing loss and optic neuropathy (cmtx5)

We have identified missense mutations at conserved amino acids in the PRPS1 gene on Xq22.3 in two families with a syndromic form of inherited peripheral neuropathy, one of Asian and one of European descent. The disease is inherited in an X-linked recessive manner, and the affected male patients invariably develop sensorineural hearing loss of prelingual type followed by gating disturbance and visual loss. The family of European descent was reported in 1967 as having Rosenberg-Chutorian syndrome, and recently a Korean family with the same symptom triad was identified with a novel disease locus CMTX5 on the chromosome band Xq21.32-q24. PRPS1 (phosphoribosyl pyrophosphate synthetase 1) is an isoform of the PRPS gene family and is ubiquitously expressed in human tissues, including cochlea. The enzyme mediates the biochemical step critical for purine metabolism and nucleotide biosynthesis. The mutations identified were E43D, in patients with Rosenberg-Chutorian syndrome, and M115T, in the Korean patients with CMTX5. We also showed decreased enzyme activity in patients with M115T. PRPS1 is the first CMT gene that encodes a metabolic enzyme, shedding a new light on the understanding of peripheral nerve-specific metabolism and also suggesting the potential of PRPS1 as a target for drugs in prevention and treatment of peripheral neuropathy by antimetabolite therapy.

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.