HIV-associated neuropathic pain: epidemiology, pathophysiology and management

Oxcarbazepine for neuropathic pain

BACKGROUND

Neuropathic pain is difficult to treat. Oxcarbazepine is an anticonvulsant drug closely related to carbamazepine and is reportedly better tolerated. Oxcarbazepine has been reported to be efficacious in the treatment of neuropathic pain.

OBJECTIVES

To determine the benefits and harms of oxcarbazepine for different forms of neuropathic pain.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (30 October 2012), CENTRAL (2012, Issue 10), MEDLINE (January 1966 to October 2012), EMBASE (January 1980 to October 2012) and the Chinese Biomedical Retrieval System (January 1978 to October 2012) for trials. We also searched the National Institutes of Health (NIH) databases and the World Health Organization (WHO) International Clinical Trials Registry Platform for ongoing trials, and wrote to the companies who make oxcarbazepine and to pain experts asking for additional information.

SELECTION CRITERIA

All randomised controlled trials and cross-over studies of oxcarbazepine for the treatment of people of any age or sex with any neuropathic pain were eligible. We planned to include trials of oxcarbazepine compared with placebo or any other intervention, regardless of administration route, dosage or length of treatment.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected the studies for inclusion, assessed their risk of bias, extracted data and typed the data onto forms. The authors resolved any disagreements through discussion.

MAIN RESULTS

Four multicentre, randomised, placebo-controlled, double-blind trials with a total of 779 participants were eligible for inclusion. These were from a series of studies funded by the manufacturer. Three of them investigated oxcarbazepine in people with painful diabetic neuropathy (634 participants) and one was a trial of oxcarbazepine for neuropathic pain due to radiculopathy (145 participants). Although these trials were well designed, the imbalanced and large amount of incomplete outcome data led to a risk of bias in the results. Results for painful diabetic neuropathy showed that compared to the baseline the proportion of participants who reported a 50% or 30% reduction of pain scores after 16 weeks of treatment was significantly higher in the oxcarbazepine group than the placebo group (50% reduction: risk ratio (RR) 1.91, 95% confidence interval (CI) 1.08 to 3.39, number of people needed to treat for an additional beneficial outcome (NNTB) 6.0, 95% CI 3.3 to 41.0; 30% reduction: RR 1.57, 95% CI 1.01 to 2.44, NNTB 6.1, 95% CI 3.1 to 113.6). However, both results were based on data from the single positive trial (146 participants) since the two negative trials did not provide data that could be included in a meta-analysis. For participants with neuropathic pain due to radiculopathy, the trial demonstrated no significant efficacy for oxcarbazepine. Although trial reports stated that most side effects were mild to moderate in severity, the proportion of events leading to withdrawals was statistically higher in the oxcarbazepine group than in the placebo group both for painful diabetic neuropathy (RR 3.86, 95% CI 2.29 to 6.40) and radiculopathy (RR 2.84, 95% CI 1.55 to 5.23).

AUTHORS' CONCLUSIONS

On the basis of moderate quality evidence from one trial in diabetic peripheral neuropathy, oxcarbazepine is effective in reducing pain for this condition. However, this conclusion does not take into account negative results from other trials in diabetic peripheral neuropathy that could not be included in our meta-analysis. We did not find any evidence from randomised controlled trials to determine the efficacy or safety of oxcarbazepine for other kinds of neuropathic pain. Most adverse effects related to oxcarbazepine are rated as mild to moderate in severity, but adverse events leading to discontinuation of drug administration or serious adverse events are not uncommon. More well designed randomised controlled trials investigating oxcarbazepine for various types of neuropathic pain are needed.

A clinically relevant rodent model of the HIV antiretroviral drug stavudine induced painful peripheral neuropathy

HIV-associated sensory neuropathy is the most frequent manifestation of HIV disease, afflicting 40-50% of patients whose HIV disease is otherwise controlled by antiretroviral therapy. It often presents with significant neuropathic pain and is consistently associated with previous exposure to nucleoside reverse transcriptase inhibitors including stavudine (d4T), which is widely used in resource-limited settings. Here we investigated complex pain-related behaviours associated with d4T treatment using ethologically relevant thigmotaxis and burrowing behaviours in adult rats. Detailed neuropathological response was also examined using neurochemistry, electron microscopy, and proteomics. After 2 intravenous injections of d4T (50 mg/kg, 4 days apart), rats developed hind paw mechanical hypersensitivity, which plateaued at 21 days after initial d4T injection, a time that these animals also had significant changes in thigmotaxis and burrowing behaviours when compared to the controls; reductions in hind paw intraepidermal nerve fibre density and CGRP/IB4 immunoreactivity in L5 spinal dorsal horn, suggesting injury to both the peripheral and central terminals of L5 dorsal root ganglion neurons; and increases in myelinated and unmyelinated axon diameters in the sural nerve, suggesting axonal swelling. However, no significant glial and inflammatory cell response to d4T treatment was observed. Sural nerve proteomics at 7 days after initial d4T injection revealed down-regulated proteins associated with mitochondrial function, highlighting distal axons vulnerability to d4T neurotoxicity. In summary, we have reported complex behavioural changes and a distinctive neuropathology in a clinically relevant rat model of d4T-induced sensory neuropathy that is suitable for further pathophysiological investigation and preclinical evaluation of novel analgesics.

Ameliorative potential of montelukast on ischemia-reperfusion injury induced vasculitic neuropathic pain in rat

AIMS

Ischemia-reperfusion (I/R) event in vascular and nervous system has been documented to rising ischemic and vasculitic neuropathic pain, clinically resembles the complex regional pain syndrome (CRPS). The present study evaluated the effect of montelukast, a cysteinyl leukotriene receptor (Cys-LTC(4) and Cys-LTD(4)) antagonist on ischemia -reperfusion (I/R) induced vasculitic neuropathic pain in rats.

MAIN METHODS

Behavioral parameters were assessed at different time intervals (i.e. 0, 1, 7, 14 and 21st day) and biochemical analysis in sciatic nerve tissue samples were also performed along with histopathological studies.

KEY FINDINGS

Behavioral pain assessment has shown increase in paw and tail withdrawal threshold in montelukast treated groups against thermal and mechanical stimuli as compared to I/R control group. We observed a decrease in the total calcium, thiobarbituric acid reactive substance (TBARS) and myeloperoxidase (MPO) activity levels, whereas there is rise in reduced glutathione level in montelukast treated groups as compared to I/R control group. However, significant behavioral and biochemical results were observed only in medium and high dose of treated groups which were comparable to normal control group. Moreover, histopathological study has revealed the reduction of I/R induced neuronal edema and axonal degeneration due to montelukast.

SIGNIFICANCE

Montelukast has ameliorated I/R induced vasculitic neuropathic pain, these effects may be due to inhibition of lipid peroxidation, reduction of oxidative stress, release of inflammatory mediators and neuroprotective actions. Hence, it could be used as a novel therapeutic agent for the management of vasculitic inflammation related neuropathic pain.

Direct effects of HIV-1 Tat on excitability and survival of primary dorsal root ganglion neurons: possible contribution to HIV-1-associated pain

The vast majority of people living with human immunodeficiency virus type 1 (HIV-1) have pain syndrome, which has a significant impact on their quality of life. The underlying causes of HIV-1-associated pain are not likely attributable to direct viral infection of the nervous system due to the lack of evidence of neuronal infection by HIV-1. However, HIV-1 proteins are possibly involved as they have been implicated in neuronal damage and death. The current study assesses the direct effects of HIV-1 Tat, one of potent neurotoxic viral proteins released from HIV-1-infected cells, on the excitability and survival of rat primary dorsal root ganglion (DRG) neurons. We demonstrated that HIV-1 Tat triggered rapid and sustained enhancement of the excitability of small-diameter rat primary DRG neurons, which was accompanied by marked reductions in the rheobase and resting membrane potential (RMP), and an increase in the resistance at threshold (R(Th)). Such Tat-induced DRG hyperexcitability may be a consequence of the inhibition of cyclin-dependent kinase 5 (Cdk5) activity. Tat rapidly inhibited Cdk5 kinase activity and mRNA production, and roscovitine, a well-known Cdk5 inhibitor, induced a very similar pattern of DRG hyperexcitability. Indeed, pre-application of Tat prevented roscovitine from having additional effects on the RMP and action potentials (APs) of DRGs. However, Tat-mediated actions on the rheobase and R(Th) were accelerated by roscovitine. These results suggest that Tat-mediated changes in DRG excitability are partly facilitated by Cdk5 inhibition. In addition, Cdk5 is most abundant in DRG neurons and participates in the regulation of pain signaling. We also demonstrated that HIV-1 Tat markedly induced apoptosis of primary DRG neurons after exposure for longer than 48 h. Together, this work indicates that HIV-1 proteins are capable of producing pain signaling through direct actions on excitability and survival of sensory neurons.

Brain-derived neurotrophic factor modulates antiretroviral-induced mechanical allodynia in the mouse

Nucleoside reverse transcriptase inhibitors (NRTIs) are key components of HIV/AIDS treatment to reduce viral load. However, these drugs can induce chronic neuropathic pain, leading to increased morbidity in HIV patients. This study examines the role of brain-derived neurotrophic factor (BDNF) in the spinal dorsal horn (SDH) in development of mechanical allodynia in male C57BL/6J mice treated with the NRTI stavudine (d4T). After d4T administration, mice developed increased neuronal activity and BDNF expression in the SDH and hind paw mechanical allodynia that was exacerbated by intrathecal BDNF administration. Intrathecal BDNF alone also increased neuronal activity and caused mechanical allodynia. Because excess BDNF amplified d4T-induced mechanical allodynia and neuronal activity, the impact of decreasing BDNF in the SDH was investigated. After d4T, BDNF heterozygous mice were less allodynic than wild-type littermates, which was negated by intrathecal BDNF administration. Finally, pretreatment with intrathecal trkB-Fc chimera prior to d4T or administration of the tyrosine kinase inhibitor K252a 3 days after d4T blocked BDNF-mediated signaling, significantly attenuated the development of mechanical allodynia (trkB-Fc), and decreased neuronal activity (trkB-Fc and K252a). Taken together, these findings provide evidence that BDNF in the SDH contributes to the development of NRTI-induced painful peripheral neuropathy and may represent a new therapeutic opportunity.

Therapeutic potential of matrix metalloprotease inhibitors in neuropathic pain

IMPORTANCE OF THE FIELD

Millions of people suffer from neuropathic pain (NP), but the treatment is empirical and results in transient relief in only a few patients. This is primarily because of the poor understanding of the molecular mechanism underlying NP. Following nerve injury, there is a differential and temporal pattern of MMPs expression that coincides with changes in levels of pro-inflammatory cytokines, suggesting that MMPs not only act as mediators for neuroinflammation but might also be directly involved in pain associated with nerve damage.

AREAS COVERED IN THIS REVIEW

The present review describes the different mechanisms of NP. The main focus of the review is to highlight the importance of MMPs in NP and their inhibition as a novel approach for treating NP.

WHAT THE READER WILL GAIN

A comprehensive overview of the role of MMPs in the pathogenesis of NP and the potential of MMP inhibition as a therapeutic intervention for NP.

TAKE HOME MESSAGE

Targeted therapy using specific MMP inhibitors, siRNAs, peptide inhibitors and monoclonal antibodies can provide a better way of treatment by blocking a single MMP and can reduce the side effects of broad-spectrum MMP inhibitors.

Prevalence, self-care behaviors, and self-care activities for peripheral neuropathy symptoms of HIV/AIDS

As part of a larger randomized controlled trial examining the efficacy of an HIV/AIDS symptom management manual (n = 775), this study examined the prevalence of peripheral neuropathy in HIV-infected individuals at 12 sites in the USA, Puerto Rico, and Africa. Neuropathy was reported by 44% of the sample; however, only 29.4% reported initiating self-care behaviors to address the neuropathy symptoms. Antiretroviral therapy was found to increase the frequency of neuropathy symptoms, with an increased mean intensity of 28%. A principal axis factor analysis with Promax rotation was used to assess the relationships in the frequency of use of the 18 self-care activities for neuropathy, revealing three distinct factors: (i) an interactive self-care factor; (ii) a complementary medicine factor; and (iii) a third factor consisting of the negative health items of smoking, alcohol, and street drugs. The study's results suggest that peripheral neuropathy is a common symptom and the presence of neuropathy is associated with self-care behaviors to ameliorate HIV symptoms. The implications for nursing practice include the assessment and evaluation of nursing interventions related to management strategies for neuropathy.

Oxycodone concentrations are greatly increased by the concomitant use of ritonavir or lopinavir/ritonavir

PURPOSE

this study aimed to investigate the effect of antivirals ritonavir and lopinavir/ritonavir on the pharmacokinetics and pharmacodynamics of oral oxycodone, a widely used opioid receptor agonist used in the treatment of moderate to severe pain.

METHODS

a randomized crossover study design with three phases at intervals of 4 weeks was conducted in 12 healthy volunteers. Ritonavir 300 mg, lopinavir/ritonavir 400/100 mg, or placebo b.i.d. for 4 days was given to the subjects. On day 3, 10 mg oxycodone hydrochloride was administered orally. Plasma concentrations of oxycodone, noroxycodone, oxymorphone, and noroxymorphone were determined for 48 h. Pharmacokinetic parameters were calculated with standard noncompartmental methods. Behavioral effects and experimental cold pain analgesia were assessed for 12 h. ANOVA for repeated measures was used for statistical analysis.

RESULTS

ritonavir and lopinavir/ritonavir increased the area under the plasma concentration-time curve of oral oxycodone by 3.0-fold (range 1.9- to 4.3-fold; P <0.001) and 2.6-fold (range 1.9- to 3.3-fold; P <0.001). The mean (± SD) elimination half-life increased after ritonavir and lopinavir/ritonavir from 3.6 ± 0.6 to 5.6 ± 0.9 h (P <0.001) and 5.7 ± 0.9 h (P <0.001), respectively. Both ritonavir (P <0.001) and lopinavir/ritonavir (P <0.05) increased the self-reported drug effect of oxycodone.

CONCLUSIONS

ritonavir and lopinavir/ritonavir greatly increase the plasma concentrations of oral oxycodone in healthy volunteers and enhance its effect. When oxycodone is used clinically in patients during ritonavir and lopinavir/ritonavir treatment, reductions in oxycodone dose may be needed to avoid opioid-related adverse effects.

Clinical outcomes and immune benefits of anti-epileptic drug therapy in HIV/AIDS

Background

Anti-epileptic drugs (AEDs) are frequently prescribed to persons with HIV/AIDS receiving combination antiretroviral therapy (cART) although the extent of AED use and their interactions with cART are uncertain. Herein, AED usage, associated toxicities and immune consequences were investigated.

Methods

HIV replication was analysed in proliferating human T cells during AED exposure. Patients receiving AEDs in a geographically-based HIV care program were assessed using clinical and laboratory variables in addition to assessing AED indication, type, and cumulative exposures.

Results

Valproate suppressed proliferation in vitro of both HIV-infected and uninfected T cells (p <0.05) but AED exposures did not affect HIV production in vitro. Among 1345 HIV/AIDS persons in active care between 2001 and 2007, 169 individuals were exposed to AEDs for the following indications: peripheral neuropathy/neuropathic pain (60%), seizure/epilepsy (24%), mood disorder (13%) and movement disorder (2%). The most frequently prescribed AEDs were calcium channel blockers (gabapentin/pregabalin), followed by sodium channel blockers (phenytoin, carbamazepine, lamotrigine) and valproate. In a nested cohort of 55 AED-treated patients receiving cART and aviremic, chronic exposure to sodium and calcium channel blocking AEDs was associated with increased CD4+ T cell levels (p <0.05) with no change in CD8+ T cell levels over 12 months from the beginning of AED therapy.

Conclusions

AEDs were prescribed for multiple indications without major adverse effects in this population but immune status in patients receiving sodium or calcium channel blocking drugs was improved.

Neurologic presentations of AIDS

The human immunodeficiency virus (HIV), the cause of AIDS, has infected an estimated 33 million individuals worldwide. HIV is associated with immunodeficiency, neoplasia, and neurologic disease. The continuing evolution of the HIV epidemic has spurred an intense interest in a hitherto neglected area of medicine, neuroinfectious diseases and their consequences. This work has broad applications for the study of central nervous system (CNS) tumors, dementias, neuropathies, and CNS disease in other immunosuppressed individuals. HIV is neuroinvasive (can enter the CNS), neurotrophic (can live in neural tissues), and neurovirulent (causes disease of the nervous system). This article reviews the HIV-associated neurologic syndromes, which can be classified as primary HIV neurologic disease (in which HIV is both necessary and sufficient to cause the illness), secondary or opportunistic neurologic disease (in which HIV interacts with other pathogens, resulting in opportunistic infections and tumors), and treatment-related neurologic disease (such as immune reconstitution inflammatory syndrome).

Acetyl-l-carnitine and nucleoside reverse transcriptase inhibitor-associated neuropathy in HIV infection

OBJECTIVES

Antiretroviral toxic neuropathy (ATN) is associated with dideoxynucleoside reverse transcriptase inhibitor use in patients infected with HIV, possibly as a result of mitochondrial toxicity. Acetyl-l-carnitine (ALC) has been linked to symptomatic improvement in ATN. We present an open-label single-arm pilot study to evaluate changes in intra-epidermal nerve fibre (IENF) density and mitochondrial DNA (mtDNA) copies/cell among subjects treated with 3000 mg ALC daily.

METHODS

Punch skin biopsies were examined at baseline and after 24 weeks of therapy. Participants reported neuropathic symptoms using the Gracely Pain Intensity Score. Neurological examinations were completed.

RESULTS

Twenty-one subjects completed the study. ALC was generally well tolerated. The IENF density did not change in cases completing 24 weeks of ALC therapy, with median (90% confidence interval) IENF changes of -1.70 (-3.50, infinity) (P=0.98) and 2.15 (-0.10, infinity) (P=0.11) for the distal leg and proximal thigh, respectively. Fat mtDNA copies/cell did not change with therapy. Improvements in neuropathic pain (P<0.01), paresthesias (P=0.01), and symptoms of numbness (P<0.01) were noted. Similarly, improvement was noted on the Gracely Pain Intensity Score.

CONCLUSIONS

ALC therapy coincided with improvements in subjective measures of pain in this open-label single-arm study. However, changes were not observed in objective measures of IENF density or mtDNA levels, providing little objective support for use of ALC in this setting.

Comparison of dorsal root ganglion gene expression in rat models of traumatic and HIV-associated neuropathic pain

To elucidate the mechanisms underlying peripheral neuropathic pain in the context of HIV infection and antiretroviral therapy, we measured gene expression in dorsal root ganglia (DRG) of rats subjected to systemic treatment with the anti-retroviral agent, ddC (Zalcitabine) and concomitant delivery of HIV-gp120 to the rat sciatic nerve. L4 and L5 DRGs were collected at day 14 (time of peak behavioural change) and changes in gene expression were measured using Affymetrix whole genome rat arrays. Conventional analysis of this data set and Gene Set Enrichment Analysis (GSEA) was performed to discover biological processes altered in this model. Transcripts associated with G protein coupled receptor signalling and cell adhesion were enriched in the treated animals, while ribosomal proteins and proteasome pathways were associated with gene down-regulation. To identify genes that are directly relevant to neuropathic mechanical hypersensitivity, as opposed to epiphenomena associated with other aspects of the response to a sciatic nerve lesion, we compared the gp120 + ddC-evoked gene expression with that observed in a model of traumatic neuropathic pain (L5 spinal nerve transection), where hypersensitivity to a static mechanical stimulus is also observed. We identified 39 genes/expressed sequence tags that are differentially expressed in the same direction in both models. Most of these have not previously been implicated in mechanical hypersensitivity and may represent novel targets for therapeutic intervention. As an external control, the RNA expression of three genes was examined by RT-PCR, while the protein levels of two were studied using western blot analysis.

[Treatment of neuropathic pain in HIV-infected patients]

Neuropathic pain of various etiologies is a frequent symptom in HIV-infected patients that is underdiagnosed and inadequately treated. It requires a multidisciplinary pain approach based on psychosocial factors, diet and exercise, etiologic treatment whenever possible, symptomatic medical treatment, and sometimes, interventional techniques. Medical treatment should be individualized and introduced gradually, with a mind to potential drug interactions. Neuropathic pain responds poorly to conventional analgesics, such as nonsteroidal antiinflammatory drugs and opiates; tricyclic antidepressants and anticonvulsants are the drugs of choice. Before establishing an analgesic treatment, possible drug interactions should be ruled out, mainly those occurring with antiretroviral agents.

Axotomy-induced up-regulation of tumor necrosis factor-alpha in the dorsal root ganglia

OBJECTIVES

Neuropathic pain is a chronic pain syndrome associated with drug, injury or disease-induced damage or destruction of sensory afferent fibers of the dorsal root ganglia (DRG). Although the exact underlying pathologic mechanisms are not known, pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) are recognized as potential modulators of peripheral and central nervous system inflammatory responses. They play a crucial role in injury and the pathologic development of chronic pain syndromes such as neuropathic pain.

METHODS

Twenty-four rats were divided into a naive control (n=6), sham (surgery exposing sciatic nerve, n=6), and peripheral nerve lesion group (unilateral axotomy of sciatic nerve, n=12).

RESULTS

The results of this study demonstrate a transient up-regulation of TNF-alpha expression within ipsi- and contralateral DRG following complete unilateral sciatic nerve axotomy as confirmed by immunohistochemistry, reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time PCR. Elevated expression of TNF-alpha was noted to occur within the first 7 days post-axotomy, which subsequently normalized to baseline levels by day 14. This transient up-regulation was also associated with a switch in cellular source from predominant satellite cell expression at baseline to that involving satellite cells and abundant numbers of sensory neurons.

DISCUSSION

These results support the role of TNF-alpha in the upstream cascade of cellular events involved in the underlying pathogenesis of neuropathic pain. Strategies targeting the early attenuation of TNF-alpha within the DRG during the first week post-injury may have significant clinical impact in preventing the downstream cascade of events involved in the underlying cellular pathology of neuropathic pain.

Unhealthy behaviours for self-management of HIV-related peripheral neuropathy

The prevalence of peripheral neuropathy is frequent in HIV disease and is often associated with antiretroviral therapy. Unhealthy behaviours, particularly substance-use behaviours, are utilized by many HIV-positive individuals to manage neuropathic symptoms. As part of a larger study on self-care for symptoms in HIV disease, this study analyzed the prevalence and characteristics of unhealthy behaviours to self-manage peripheral neuropathy in HIV disease. Sociodemographic and disease-related correlates and unhealthy behaviours were examined in a convenience sample of 1,217 respondents who were recruited from data collection sites in several US cities, Puerto Rico, Colombia, and Taiwan. Results of the study indicated that respondents with peripheral neuropathy (n=450) identified a variety of unhealthy self-care behaviours including injection drug use, oral drug use, smoking cigarettes and alcohol ingestion. Specific unhealthy behaviours that participants reported to alleviate peripheral neuropathy included use of marijuana (n=67), smoking cigarettes (n=139), drinking alcohol (n=81) and street drugs (n=30). A subset of those individuals (n=160), who identified high levels of neuropathy (greater than five on a scale of 1-10), indicated significantly higher use of amphetamines and injection drug use in addition to alcohol use and cigarette smoking. For participants from Norway, substance use (using alcohol: 56%) was one of the most frequent self-management strategies. Implications for clinical practice include assessment and education of persons with HIV for self-care management of the complex symptom of peripheral neuropathy.

An open-label pilot study of high-concentration capsaicin patch in painful HIV neuropathy

Peripheral neuropathy is the most frequent neurological complication of human immunodeficiency virus (HIV)-1 infection and is commonly associated with the development of chronic pain. This open-label, 12-week pilot study assessed the efficacy, tolerability, and safety of a high-concentration capsaicin dermal patch (NGX-4010; capsaicin, 640microg/cm2, 8% w/w) to treat painful HIV-associated distal sensory polyneuropathy (DSP). Eligible patients had moderate-to-severe pain in both feet due to HIV-associated DSP or antiretroviral toxic neuropathy. Patients received a single 60-minute application of the investigational high-concentration capsaicin patch to the affected areas. The primary outcome measure was the mean percent change in numeric pain rating scale (NPRS) during weeks two to 12 postadministration. After a single 60-minute NGX-4010 application, the mean percent change from baseline in "average pain for past 24 hours" NPRS scores during weeks two to 12 was -40% (95% CI: -61%, -19%; P=0.0020). Similar results were observed for "worst pain for past 24 hours" and "pain now" scores. Eight of 12 patients (67%) were treatment responders (> or =30% pain decrease). Four of 12 patients (33%) experienced a > or =50% reduction in pain. Treatment was generally well tolerated. Treatment-associated pain was self-limited and could be managed with short-acting opioids. This study demonstrates that treatment of painful HIV-associated neuropathy with a single application of NGX-4010, a high-concentration capsaicin patch, was feasible, well tolerated, and associated with significant reduction in pain over the 12 weeks studied. No safety concerns were identified. Controlled studies of NGX-4010 for the treatment of painful HIV-associated neuropathy are warranted.

Managing HIV peripheral neuropathy

Peripheral nerve disorders are frequent complications of HIV disease. Distal symmetrical polyneuropathy (DSP) is the most common peripheral nerve disorder associated with HIV and occurs in over one third of infected patients but may occur in up to 67% if asymptomatic patients are included. Risk factors for DSP include increased age, advanced HIV disease, and history of "d-drugs" or other neurotoxic drugs. The primary manifestations of polyneuropathy are slowly progressive numbness and paresthesias, with burning sensations in the feet usually in a symmetrical pattern. The etiology of HIV-associated DSP is unknown, although neurotoxic effects of cytokines, toxicity of HIV proteins, and mitochondrial damage have been implicated. The current treatment for HIV-associated DSP is symptomatic, with pain modifying medications, including anti-inflammatory agents, opioids, antidepressants, antiepileptics, topical anesthetics, and capsaicin. Sustained virologic control may improve DSP. Novel therapies such as -acetyl-l-carnitine or neurotrophic factors are being studied for treatment of DSP.

Distal sensory polyneuropathy in the context of HIV/AIDS

Peripheral neuropathy, or distal sensory polyneuropathy (DSPN), is the most common neurological problem in HIV disease. DSPN also represents a complex symptom that occurs because of peripheral nerve damage related to advanced HIV disease and in association with the use of antiretroviral therapy-particularly in individuals treated with dideoxynucleosides. Although DSPN is a frequent symptom, the specific pathophysiology is not well understood. The HIV-related neuropathies are commonly categorized as distal sensory polyneuropathies, although antiretroviral toxic neuropathies are described in the literature. Recently, mitochondrial toxicity has been identified as a possible etiology of DSPN. As individuals with HIV/AIDS survive longer, often living for decades with the disease, chronic symptoms like DSPN must be addressed. Pharmacologic approaches, complementary therapies, and self-care behaviors that may improve quality of life and limit symptoms of DSPN are important interventions for clinicians and those living with HIV/AIDS to consider in the management of peripheral neuropathy.

Characterization of rodent models of HIV-gp120 and anti-retroviral-associated neuropathic pain

A distal symmetrical sensory peripheral neuropathy is frequently observed in people living with Human Immunodeficiency Virus Type 1 (HIV-1). This neuropathy can be associated with viral infection alone, probably involving a role for the envelope glycoprotein gp120; or a drug-induced toxic neuropathy associated with the use of nucleoside analogue reverse transcriptase inhibitors as a component of highly active anti-retroviral therapy. In order to elucidate the mechanisms underlying drug-induced neuropathy in the context of HIV infection, we have characterized pathological events in the peripheral and central nervous system following systemic treatment with the anti-retroviral agent, ddC (Zalcitabine) with or without the concomitant delivery of HIV-gp120 to the rat sciatic nerve (gp120+ddC). Systemic ddC treatment alone is associated with a persistent mechanical hypersensitivity (33% decrease in limb withdrawal threshold) that when combined with perineural HIV-gp120 is exacerbated (48% decrease in threshold) and both treatments result in thigmotactic (anxiety-like) behaviour. Immunohistochemical studies revealed little ddC-associated alteration in DRG phenotype, as compared with known changes following perineural HIV-gp120. However, the chemokine CCL2 is significantly expressed in the DRG of rats treated with perineural HIV-gp120 and/or ddC and there is a reduction in intraepidermal nerve fibre density, comparable to that seen in herpes zoster infection. Moreover, a spinal gliosis is apparent at times of peak behavioural sensitivity that is exacerbated in gp120+ddC as compared to either treatment alone. Treatment with the microglial inhibitor, minocycline, is associated with delayed onset of hypersensitivity to mechanical stimuli in the gp120+ddC model and reversal of some measures of thigmotaxis. Finally, the hypersensitivity to mechanical stimuli was sensitive to systemic treatment with gabapentin, morphine and the cannabinoid WIN 55,212-2, but not with amitriptyline. These data suggests that both neuropathic pain models display many features of HIV- and anti-retroviral-related peripheral neuropathy. They therefore merit further investigation for the elucidation of underlying mechanisms and may prove useful for preclinical assessment of drugs for the treatment of HIV-related peripheral neuropathic pain.

Combination therapy reduces self-injurious behavior in a chimpanzee (Pan Troglodytes Troglodytes): a case report

Self-injurious behavior (SIB) remains a severe and intractable abnormal behavior for nonhuman primates in diverse settings and is a significant concern for veterinarians and behavioral scientists. To date, no single pharmacological, behavioral, social, or environmental intervention method has emerged as a reliable permanent cure for treating SIB in all, or even most, individuals. Implementation and evaluation of a combination therapeutic approach to treating SIB for nonhuman primates is rare. In May 2004, a 25-year-old male chimpanzee with severe SIB (M = 2.09 episodes/day, range = 1-4 episodes/day) underwent intensive behavioral intervention that utilized a combination of techniques. The combination therapy approach entailed the following: (a) pharmacological intervention with a gamma-aminobutyric acid (GABA) analogue to treat suspected HIV-related sensory neuropathic pain, (b) positive reinforcement training, and (c) environmental enrichment, as well as social and environmental modification. The severity of SIB warranted immediate implementation of intensive combination therapy rather than a systematic evaluation of the individual treatment options. The individually tailored, multifaceted combination therapy resulted in the virtual elimination of SIB in this chimpanzee over a 2-year period.

CXCR4 chemokine receptor signaling mediates pain hypersensitivity in association with antiretroviral toxic neuropathy

Nucleoside reverse transcriptase inhibitors (NRTIs) are known to produce painful neuropathies and to enhance states of pain hypersensitivity produced by HIV-1 infection. It has also been observed that in some neuropathic pain models, chemokines and their receptors are upregulated, perhaps contributing to the pain state. In order to understand if chemokines are involved in NRTI-mediated sensory neuropathies, we treated rats with the anti-retroviral drug, 2',3'-dideoxycytidine (ddC), which is known to produce an extended period of hyperalgesia and allodynia. Using in situ hybridization, we observed that under normal conditions, CXCR4 chemokine receptors were widely expressed by satellite glia in the dorsal root ganglia (DRG) and Schwann cells in the sciatic nerve. A limited number of DRG neurons also expressed CXCR4 receptors. The chemokine SDF-1/CXCL12 was similarly expressed in glial cells in the DRG and peripheral nerve. Following a single administration of ddC, expression levels of CXCR4 mRNA in glia and neurons and SDF-1 mRNA in glia increased considerably. The functional nature of increased CXCR4 mRNA expression was confirmed by measuring SDF-1 induced [Ca2+]i increases in acutely isolated DRG neurons and glia. In contrast, the expression of the chemokine receptors CCR2 and CCR5 did not change following ddC treatment. Pain hypersensitivity produced by ddC could be inhibited by treatment with the CXCR4 antagonist, AMD3100. Hence, we postulate that NRTIs produce pain hypersensitivity through the upregulation of CXCR4 signaling in the DRG. Increased numbers of CXCR4 receptors would also explain the synergism observed between NRTI treatment and the proalgesic effects of HIV-1 infection.

Pharmacological, behavioural and mechanistic analysis of HIV-1 gp120 induced painful neuropathy

A painful neuropathy is frequently observed in people living with human immunodeficiency virus type 1 (HIV-1). The HIV coat protein, glycoprotein 120 (gp120), implicated in the pathogenesis of neurological disorders associated with HIV, is capable of initiating neurotoxic cascades via an interaction with the CXCR4 and/or CCR5 chemokine receptors, which may underlie the pathogenesis of HIV-associated peripheral neuropathic pain. In order to elucidate the mechanisms underlying HIV-induced painful peripheral neuropathy, we have characterised pathological events in the peripheral and central nervous system following application of HIV-1 gp120 to the rat sciatic nerve. Perineural HIV-1 gp120 treatment induced a persistent mechanical hypersensitivity (44% decrease from baseline), but no alterations in sensitivity to thermal or cold stimuli, and thigmotactic (anxiety-like) behaviour in the open field. The mechanical hypersensitivity was sensitive to systemic treatment with gabapentin, morphine and the cannabinoid WIN 55,212-2, but not with amitriptyline. Immunohistochemical studies reveal: decreased intraepidermal nerve fibre density, macrophage infiltration into the peripheral nerve at the site of perineural HIV-1 gp120; changes in sensory neuron phenotype including expression of activating transcription factor 3 (ATF3) in 27% of cells, caspase-3 in 25% of cells, neuropeptide Y (NPY) in 12% of cells and galanin in 13% of cells and a spinal gliosis. These novel findings suggest that this model is not only useful for the elucidation of mechanisms underlying HIV-1-related peripheral neuropathy but may prove useful for preclinical assessment of drugs for the treatment of HIV-1 related peripheral neuropathic pain.

Emerging drugs in neuropathic pain

Neuropathic pain is a personally devastating and costly condition affecting 3-8% of the population. Existing treatments have limited effectiveness and produce relatively frequent adverse effects. Preclinical research has identified many promising pharmacological targets; however, reliable predictors of success in humans remain elusive. At least 50 new molecular entities have reached clinical development including: glutamate antagonists, cytokine inhibitors, vanilloid-receptor agonists, catecholamine modulators, ion-channel blockers, anticonvulsants, opioids, cannabinoids, COX inhibitors, acteylcholine modulators, adenosine receptor agonists and several miscellaneous drugs. Eight drugs are in Phase III trials at present. Strategies that may show promise over existing treatments include topical therapies, analgesic combinations and, in future, gene-related therapies. Recent years have heralded an explosion of pharmaceutical development in neuropathic pain, reflecting advanced knowledge of neurobiology and a heightened perception of the commercial value of neuropathic pain therapeutics. In the interest of improving patient care, the authors recommend implementing comparative studies throughout the development process in order to demonstrate the increased value of novel agents.

Neuropathic pain: a practical guide for the clinician

Neuropathic pain, caused by various central and peripheral nerve disorders, is especially problematic because of its severity, chronicity and resistance to simple analgesics. The condition affects 2%-3% of the population, is costly to the health care system and is personally devastating to the people who experience it. The diagnosis of neuropathic pain is based primarily on history (e.g., underlying disorder and distinct pain qualities) and the findings on physical examination (e.g., pattern of sensory disturbance); however, several tests may sometimes be helpful. Important pathophysiologic mechanisms include sodium-and calcium-channel upregulation, spinal hyperexcitability, descending facilitation and aberrant sympathetic-somatic nervous system interactions. Treatments are generally palliative and include conservative nonpharmacologic therapies, drugs and more invasive interventions (e.g., spinal cord stimulation). Individualizing treatment requires consideration of the functional impact of the neuropathic pain (e.g., depression, disability) as well as ongoing evaluation, patient education, reassurance and specialty referral. We propose a primary care algorithm for treatments with the most favourable risk-benefit profile, including topical lidocaine, gabapentin, pregabalin, tricyclic antidepressants, mixed serotonin-norepinephrine reuptake inhibitors, tramadol and opioids. The field of neuropathic pain research and treatment is in the early stages of development, with many unmet goals. In coming years, several advances are expected in the basic and clinical sciences of neuropathic pain, which will provide new and improved therapies for patients who continue to experience this disabling condition.

HIV peripheral neuropathy: pathophysiology and clinical implications

One of the most debilitating neurological complications of human immunodeficiency virus (HIV), affecting nearly one in three patients, is painful peripheral neuropathy. Although HIV infection can cause distal sensory polyneuropathy (DSP), the advent of highly active antiretroviral therapy (HAART) to treat HIV infection has resulted in a significant number of patients developing a clinically indistinguishable form of toxic neuropathy. The predominant symptom, regardless of etiology, is excruciating unremitting pain, resistant to pharmacological treatments, that leads to a reduction in the ability to conduct activities of daily living and, eventually, inability to ambulate. Since withdrawal from nucleoside therapy is not typically recommended, a more thorough understanding of the etiology and pathophysiology underlying nucleoside-induced peripheral neuropathy, through basic and clinical research endeavors, will aid in the development of new therapeutic treatments aimed at alleviating or ameliorating pain. This article provides the latest information regarding the pathophysiology and clinical implications of HIV peripheral neuropathy.

HIV Infection and Dementia in Older Adults

Human immunodeficiency virus (HIV) infection in older patients is becoming increasingly common as seropositive individuals live longer because of long-term antiretroviral treatment. Simultaneously, the development and expression of dementia among HIV-infected patients is evolving in the era of highly active antiretroviral therapy (HAART) and immune reconstitution. How long-term HAART interacts with chronic HIV infection and advanced age with regard to cognition is not fully understood. This article provides an overview of HIV cognitive impairment as it relates to aging and presents some emerging issues in the field. Particular emphasis is placed on describing the changing landscape of HIV-related cognitive impairment and discussing possible concerns regarding the long-term effects of antiretroviral treatment. A brief discussion of potential adjunctive therapies to reduce cognitive symptoms associated with HIV infection in older individuals is provided.

Spatially distinct and functionally independent mechanisms of axonal degeneration in a model of HIV-associated sensory neuropathy

Sensory polyneuropathies are the most frequent neurological complication of human immunodeficiency virus (HIV) infection. Distal symmetric polyneuropathy (DSP), associated with HIV infection, is characterized by length-dependent axonal degeneration of sensory fibres. In rodent dorsal root ganglia (DRG) cultures, HIV viral envelope protein gp120 results in neurotoxicity and axonal degeneration. Since it is unknown whether the axonal degeneration is a consequence of neuronal death or whether it is due to a direct toxic effect on axons, we investigated gp120-induced axonal toxicity using compartmentalized cultures of sensory neurons. Our results show that gp120 causes neuronal apoptosis and axonal degeneration through two, independent and spatially separated mechanisms of action: (i) an indirect insult to cell bodies, requiring the presence of Schwann cells, results in neuronal apoptotic death and subsequent axonal degeneration; (ii) a direct, local toxicity exerted on axons through activation of mitochondrial caspase pathway that is independent of cell body. This local axonal toxicity is mediated through binding of gp120 to axonal chemokine receptors and can be prevented by chemokine receptor blockers. In conclusion, we propose a novel pathway of axonal degeneration mediated by gp120 that is dependent on local activation of caspases in the axon. This observation suggests that axonal protection is a relevant therapeutic target for HIV-associated sensory neuropathy. Furthermore, chemokine receptor inhibitors, which are currently being developed as HIV entry inhibitor drugs, may also have a therapeutic role in HIV-associated peripheral neuropathies by preventing axonal degeneration.

RANTES, MDC and SDF-1α, prevent the HIVgp120-induced food and water intake decrease in rats

Human immunodeficiency virus (HIV)-wasting syndrome might be facilitated by the HIVgp120 affecting the immunological system. We studied the effect (subchronic administration: 5 days) of HIVgp120, and a few immune-response mediators: regulated upon activation normal T-cell expressed and presumably secreted (RANTES), stromal derived factor-1alpha (SDF-1alpha), macrophage-derived chemokine (MDC), and their combination, on food and water intake in rats, motor control and pain perception. Eighty male adult Wistar rats received an intracerebroventricular (icv) administration of: vehicle 5 microl/day or 0.92 nmol daily of HIVgp120IIIB, RANTES, SDF-1alpha, or MDC, and the combination of RANTES+HIVgp120IIIB, SDF-1alpha+HIVgp120IIIB, or MDC+HIVgp120IIIB. Food and water intake was measured every day during administration, and 24 and 48 h after the last administration. Rats were also weighed the first and the last day of experiment in order to detect the impact of these treatments in the body weight. HIVgp120IIIB significantly decreased food and water intake. These rats gain less weight than the control (vehicle) and chemokines-treated subjects with exception of those treated with SDF-1alpha that also gain less weight. In addition, HIVgp120 deteriorated motor control. HIVgp120IIIB effects on food and water intake, and motor control were prevented by these chemokines. HIVgp120+RANTES, HIVgp120+SDF-1alpha, and SDF-1alpha alone induced hyperalgesia. Results suggest an interaction between HIVgp120 and the chemokine system to generate the HIV-wasting syndrome, the motor abnormalities and changes in pain perception.