Peripheral nerve exposure to HIV viral envelope protein gp120 induces neuropathic pain and spinal gliosis

P2Y13 receptor involved in HIV-1 gp120 induced neuropathy in superior cervical ganglia through NLRP3 inflammasome activation

Cardiac autonomic neuropathy resulting from human immunodeficiency virus (HIV) infection is common; however, its mechanism remains unknown. The current work attempted to explore the function and mechanism of the P2Y13 receptor in HIV-glycoprotein 120 (gp120)-induced neuropathy in cervical sympathetic ganglion. The superior cervical ganglion (SCG) of the male SD rat was coated with HIV-gp120 to establish a model of autonomic neuropathy. In each group, we measured heart rate, blood pressure, heart rate variability, sympathetic nerve discharge and cardiac function. The expression of P2Y13 mRNA and protein in the SCG was tested by real-time polymerase chain reaction and western blotting. Additionally, this study focused on identifying the protein levels of NOD-like receptor family pyrin domain-containing 3 (NLRP3), Caspase-1, Gasdermin D (GSDMD), interleukin (IL)-1β and IL-18 in the SCG using western blotting and immunofluorescence. In gp120 rats, increased blood pressure, heart rate, cardiac sympathetic nerve activity, P2Y13 receptor levels and decreased cardiac function could be found. P2Y13 shRNA or MRS2211 inhibited the above mentioned changes induced by gp120, suggesting that the P2Y13 receptor may be engaged in gp120-induced sympathetic nerve injury. Moreover, the levels of NLRP3, Caspase-1, GSDMD, IL-1β and IL-18 in the gp120 group were increased, while significantly decreased by P2Y13 shRNA or MRS2211. Therefore, the P2Y13 receptor is involved in gp120-induced sympathetic neuropathy, and its molecular mechanism shows an association with the activation of the NLRP3 inflammasome, followed by GSDMD formation along with the release of inflammatory factors including IL-1β and IL-18. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Progress in Pathological and Therapeutic Research of HIV-Related Neuropathic Pain

HIV-related neuropathic pain (HRNP) is a neurodegeneration that gradually develops during the long-term course of acquired immune deficiency syndrome (AIDS) and manifests as abnormal sock/sleeve-like symmetrical pain and nociceptive hyperalgesia in the extremities, which seriously reduces patient quality of life. To date, the pathogenesis of HRNP is not completely clear. There is a lack of effective clinical treatment for HRNP and it is becoming a challenge and hot spot for medical research. In this study, we conducted a systematic review of the progress of HRNP research in recent years including (1) the etiology, classification and clinical symptoms of HRNP, (2) the establishment of HRNP pathological models, (3) the pathological mechanisms underlying HRNP from three aspects: molecules, signaling pathways and cells, (4) the therapeutic strategies for HRNP, and (5) the limitations of recent HRNP research and the future research directions and prospects of HRNP. This detailed review provides new and systematic insight into the pathological mechanism of HRNP, which establishes a theoretical basis for the future exploitation of novel target drugs. HIV infection, antiretroviral therapy and opioid abuse contribute to the etiology of HRNP with symmetrical pain in both hands and feet, allodynia and hyperalgesia. The pathogenesis involves changes in cytokine expression, activation of signaling pathways and neuronal cell states. The therapy for HRNP should be patient-centered, integrating pharmacologic and nonpharmacologic treatments into multimodal intervention.

Pathogenic mechanisms of human immunodeficiency virus (HIV)-associated pain

Chronic pain is a prevalent neurological complication among individuals living with human immunodeficiency virus (PLHIV) in the post-combination antiretroviral therapy (cART) era. These individuals experience malfunction in various cellular and molecular pathways involved in pain transmission and modulation, including the neuropathology of the peripheral sensory neurons and neurodegeneration and neuroinflammation in the spinal dorsal horn. However, the underlying etiologies and mechanisms leading to pain pathogenesis are complex and not fully understood. In this review, we aim to summarize recent progress in this field. Specifically, we will begin by examining neuropathology in the pain pathways identified in PLHIV and discussing potential causes, including those directly related to HIV-1 infection and comorbidities, such as antiretroviral drug use. We will also explore findings from animal models that may provide insights into the molecular and cellular processes contributing to neuropathology and chronic pain associated with HIV infection. Emerging evidence suggests that viral proteins and/or antiretroviral drugs trigger a complex pathological cascade involving neurons, glia, and potentially non-neural cells, and that interactions between these cells play a critical role in the pathogenesis of HIV-associated pain.

Behavioral Evidence for a Tau and HIV-gp120 Interaction

Despite successful virologic control with combination antiretroviral therapy (cART), about half of people living with the human immunodeficiency virus-1 (HIV) develop an HIV-associated neurocognitive disorder (HAND). It is estimated that 50% of individuals who are HIV-positive in the United States are aged 50 years or older. Therefore, a new challenge looms as individuals living with HIV increase in age. There is concern that Alzheimer’s disease (AD) may become prevalent with an earlier onset of cognitive decline in people living with HIV (PLWH). Clinical data studies reported the presence of AD biomarkers in PLWH. However, the functional significance of the interaction between HIV or HIV viral proteins and AD biomarkers is still not well studied. The main goal of the present study is to address this knowledge gap by determining if the HIV envelope glycoprotein 120 (HIV-gp120) can affect the cognitive functions in the Tau mouse AD model. Male Tau and age-matched, wild-type (WT) control mice were treated intracerebroventricularly (ICV) with HIV-gp120. The animals were evaluated for cognitive function using a Y-maze. We found that HIV-gp120 altered cognitive function in Tau mice. Notably, HIV-gp120 was able to promote a cognitive decline in transgenic Tau (P301L) mice compared to the control (HIV-gp120 and WT). We provide the first in vivo evidence of a cognitive interaction between an HIV viral protein and Tau mice.

Targeting Chemokines and Chemokine GPCRs to Enhance Strong Opioid Efficacy in Neuropathic Pain

Neuropathic pain (NP) originates from an injury or disease of the somatosensory nervous system. This heterogeneous origin and the possible association with other pathologies make the management of NP a real challenge. To date, there are no satisfactory treatments for this type of chronic pain. Even strong opioids, the gold-standard analgesics for nociceptive and cancer pain, display low efficacy and the paradoxical ability to exacerbate pain sensitivity in NP patients. Mounting evidence suggests that chemokine upregulation may be a common mechanism driving NP pathophysiology and chronic opioid use-related consequences (analgesic tolerance and hyperalgesia). Here, we first review preclinical studies on the role of chemokines and chemokine receptors in the development and maintenance of NP. Second, we examine the change in chemokine expression following chronic opioid use and the crosstalk between chemokine and opioid receptors. Then, we examine the effects of inhibiting specific chemokines or chemokine receptors as a strategy to increase opioid efficacy in NP. We conclude that strong opioids, along with drugs that block specific chemokine/chemokine receptor axis, might be the right compromise for a favorable risk/benefit ratio in NP management.

HIV-Proteins-Associated CNS Neurotoxicity, Their Mediators, and Alternative Treatments

Human immunodeficiency virus (HIV)-infected people's livelihoods are gradually being prolonged with the use of combined antiretroviral therapy (ART). Conversely, despite viral suppression by ART, the symptoms of HIV-associated neurocognitive disorder (HAND) endure. HAND persists because ART cannot really permanently confiscate the virus from the body. HAND encompasses a variety of conditions based on clinical presentation and severity level, comprising asymptomatic neurocognitive impairment, moderate neurocognitive disorder, and HIV-associated dementia. During the early stages of HIV infection, inflammation compromises the blood-brain barrier, allowing toxic virus, infected monocytes, macrophages, T-lymphocytes, and cellular products from the bloodstream to enter the brain and eventually the entire central nervous system. Since there are no resident T-lymphocytes in the brain, the virus will live for decades in macrophages and astrocytes, establishing a reservoir of infection. The HIV proteins then inflame neurons both directly and indirectly. The purpose of this review is to provide a synopsis of the effects of these proteins on the central nervous system and conceptualize avenues to be considered in mitigating HAND. We used bioinformatics repositories extensively to simulate the transcription factors that bind to the promoter of the HIV-1 protein and possibly could be used as a target to circumvent HIV-associated neurocognitive disorders. In the same vein, a protein-protein interaction complex was also deduced from a Search Tool for the Retrieval of Interacting Genes. In conclusion, this provides an alternative strategy that could be used to avert HAND.

Neuropathic pain modeling: Focus on synaptic and ion channel mechanisms

Animal models of pain consist of modeling a pain-like state and measuring the consequent behavior. The first animal models of neuropathic pain (NP) were developed in rodents with a total lesion of the sciatic nerve. Later, other models targeting central or peripheral branches of nerves were developed to identify novel mechanisms that contribute to persistent pain conditions in NP. Objective assessment of pain in these different animal models represents a significant challenge for pre-clinical research. Multiple behavioral approaches are used to investigate and to validate pain phenotypes including withdrawal reflex to evoked stimuli, vocalizations, spontaneous pain, but also emotional and affective behaviors. Furthermore, animal models were very useful in investigating the mechanisms of NP. This review will focus on a detailed description of rodent models of NP and provide an overview of the assessment of the sensory and emotional components of pain. A detailed inventory will be made to examine spinal mechanisms involved in NP-induced hyperexcitability and underlying the current pharmacological approaches used in clinics with the possibility to present new avenues for future treatment. The success of pre-clinical studies in this area of research depends on the choice of the relevant model and the appropriate test based on the objectives of the study.

Neuropathic pain: Spotlighting anatomy, experimental models, mechanisms, and therapeutic aspects

The International Association for the Study of Pain defines neuropathic pain as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system". The associated changes can be observed in the peripheral as well as the central nervous system. The available literature discusses a wide variety of causes as predisposing for the development and amplification of neuropathic pain. Further, key interactions within sensory pathways have been discovered, but no common molecular mechanism leading to neuropathic pain has been identified until now. In the first part of this review, the pain mediating lateral spinothalamic tract is described. Different in vivo models are presented that allow studying trauma-, chemotherapy-, virus-, and diabetes-induced neuropathic pain in rodents. We furthermore discuss approaches to assess neuropathic pain in these models. Second, the current knowledge about cellular and molecular mechanisms suggested to underlie the development of neuropathic pain is presented and discussed. A summary of established therapies that are already applied in the clinic and novel, promising approaches closes the paper. In conclusion, the established animal models are able to emulate the diversity of neuropathic pain observed in the clinics. However, the assessment of neuropathic pain in the presented in vivo models should be improved. The determination of common molecular markers with suitable in vitro models would simplify the assessment of neuropathic pain in vivo. This would furthermore provide insights into common molecular mechanisms of the disease and establish a basis to search for satisfying therapeutic approaches.

Large Mitochondrial DNA Deletions in HIV Sensory Neuropathy

OBJECTIVE

The primary objective of this study was to evaluate the correlation of large mitochondrial DNA (mtDNA) deletions in skin samples of people with HIV (PWH) with measures of neuropathy and prior exposure to therapy. We hypothesized that deletions would be associated with neuropathy. As secondary objectives, we determined the correlation of deletion burden with demographic data and neuropathy measures.

METHODS

In this retrospective cohort study, we measured the accumulation of large mtDNA deletions in skin biopsies from PWH recruited as part of the AIDS Clinical Trials Group (ACTG). Our cohort includes individuals with and without sensory neuropathy, as well as individuals with normal or abnormal skin biopsies. Skin biopsies, sural and peroneal nerve conduction studies, total neuropathy score, and deletion burden scores were measured, along with baseline demographic data such as age, CD4+ cell count, viral counts, and prior nucleoside reverse transcriptase inhibitor exposures.

RESULTS

Sixty-seven PWH were enrolled in the study. The mean age of the cohort (n = 67) was 44 years (SD 6.8, range 32-65 years), and 9 participants were female. The mean CD4+ T-cell count was 168 cells/mm³ (SD 97 cells/mm³, range 1-416 cells/mm³) and mean viral load was 51,129 copies/mL (SD 114,586 copies/mL, range 147-657,775 copies/mL). We determined that there was a correlation between the total mtDNA deletion and intraepidermal nerve fiber density (IENFD) (r = -0.344, p = 0.04) and sural nerve amplitude (r = -0.359, p = 0.004).

CONCLUSIONS

Both IENFD and sural nerve amplitude statistically correlate with mitochondrial mutation burden in PWH, specifically in those with HIV-associated sensory neuropathy as assessed by skin biopsy.

Neuroinflammation in HIV-Related Neuropathic Pain

In the management of human immunodeficiency virus (HIV) infection around the world, chronic complications are becoming a new problem along with the prolonged life expectancy. Chronic pain is widespread in HIV infected patients and even affects those with a low viral load undergoing long-term treatment with antiviral drugs, negatively influencing the adherence to disease management and quality of life. A large proportion of chronic pain is neuropathic pain, which defined as chronic pain caused by nervous system lesions or diseases, presenting a series of nervous system symptoms including both positive and negative signs. Injury caused by HIV protein, central and peripheral sensitization, and side effects of antiretroviral therapy lead to neuroinflammation, which is regarded as a maladaptive mechanism originally serving to promote regeneration and healing, constituting the main mechanism of HIV-related neuropathic pain. Gp120, as HIV envelope protein, has been found to be the major toxin that induces neuropathic pain. Particularly, the microglia, releasing numerous pro-inflammatory substances (such as TNFα, IL-1β, and IL-6), not only sensitize the neurons but also are the center part of the crosstalk bridging the astrocytes and oligodendrocytes together forming the central sensitization during HIV infection, which is not discussed detailly in recent reviews. In the meantime, some NRTIs and PIs exacerbate the neuroinflammation response. In this review, we highlight the importance of clarifying the mechanism of HIV-related neuropathic pain, and discuss about the limitation of the related studies as future research directions.

Animal models of pain: Diversity and benefits

Chronic pain is a maladaptive neurological disease that remains a major health problem. A deepening of our knowledge on mechanisms that cause pain is a prerequisite to developing novel treatments. A large variety of animal models of pain has been developed that recapitulate the diverse symptoms of different pain pathologies. These models reproduce different pain phenotypes and remain necessary to examine the multidimensional aspects of pain and understand the cellular and molecular basis underlying pain conditions. In this review, we propose an overview of animal models, from simple organisms to rodents and non-human primates and the specific traits of pain pathologies they model. We present the main behavioral tests for assessing pain and investing the underpinning mechanisms of chronic pathological pain. The validity of animal models is analysed based on their ability to mimic human clinical diseases and to predict treatment outcomes. Refine characterization of pathological phenotypes also requires to consider pain globally using specific procedures dedicated to study emotional comorbidities of pain. We discuss the limitations of pain models when research findings fail to be translated from animal models to human clinics. But we also point to some recent successes in analgesic drug development that highlight strategies for improving the predictive validity of animal models of pain. Finally, we emphasize the importance of using assortments of preclinical pain models to identify pain subtype mechanisms, and to foster the development of better analgesics.

Reactive Oxygen Species (ROS) are Critical for Morphine Exacerbation of HIV-1 gp120-Induced Pain

Many HIV patients develop chronic pain and use opioid-derived medicine as primary analgesics. Emerging clinical evidence suggests that chronic use of opioid analgesics paradoxically heightens pain states in patients. This side effect of opioid analgesics has a significant negative impact on clinical practice, but the underlying pathogenic mechanism remains elusive. Using a mouse model of HIV-associated pain, we simulated the development of morphine exacerbation on pain and investigated potential underlying cellular and molecular pathways. We found that repeated morphine treatment promoted astrocyte activation in the spinal dorsal horn (SDH) and up-regulation of pro-inflammatory cytokines IL-1β and TNF-α. Furthermore, we observed that morphine administration potentiated mitochondrial reactive oxygen species (ROS) in the SDH of the HIV pain model, especially on astrocytes. Systemic application of the ROS scavenger phenyl-N-t-butyl nitrone (PBN) not only blocked the enhancement of gp120-induced hyperalgesia by morphine but also astrocytic activation and cytokine up-regulation. These findings suggest a critical role of ROS in mediating the exacerbation of gp120-induced pain by morphine. Graphical abstract.

Schwann cell-derived CXCL1 contributes to human immunodeficiency virus type 1 gp120-induced neuropathic pain by modulating macrophage infiltration in mice

The neuroinflammatory responses to human immunodeficiency virus type 1 (HIV-1) coat proteins, such as glycoprotein 120 (gp120), are considered to be responsible for the HIV-associated distal sensory neuropathy. Accumulating evidences suggest that T-cell line tropic X4 gp120 increases macrophage infiltration into the peripheral nerves, and thereby induces neuroinflammation leading to pain. However, the mechanisms underlying X4 gp120-induced macrophage recruitment to the peripheral nervous systems remain unclear. Here, we demonstrated that perineural application of X4 gp120 from HIV-1 strains IIIB and MN elicited mechanical hypersensitivity and spontaneous pain-like behaviors in mice. Furthermore, flow cytometry and immunohistochemical studies revealed increased infiltration of bone marrow-derived macrophages into the parenchyma of sciatic nerves and dorsal root ganglia (DRG) 7 days after gp120 IIIB or MN application. Chemical deletion of circulating macrophages using clodronate liposomes markedly suppressed gp120 IIIB-induced pain-like behaviors. In in vitro cell infiltration analysis, RAW 264.7 cell (a murine macrophage cell line) was chemoattracted to conditioned medium from gp120 IIIB- or MN-treated cultured Schwann cells, but not to conditioned medium from these gp120-treated DRG neurons, suggesting possible involvement of Schwann cell-derived soluble factors in macrophage infiltration. We identified using a gene expression array that CXCL1, a chemoattractant of macrophages and neutrophils, was increased in gp120 IIIB-treated cultured Schwann cells. Similar to gp120 IIIB or MN, perineural application of recombinant CXCL1 elicited pain-like behaviors accompanied by macrophage infiltration to the peripheral nerves. Furthermore, the repeated injection of CXCR2 (receptor for CXCL1) antagonist or CXCL1 neutralizing antibody prevented both pain-like behaviors and macrophage infiltration in gp120 IIIB-treated mice. Thus, the present study newly defines that Schwann cell-derived CXCL1, secreted in response to X4 gp120 exposure, is responsible for macrophage infiltration into peripheral nerves, and is thereby associated with pain-like behaviors in mice. We propose herein that communication between Schwann cells and macrophages may play a prominent role in the induction of X4 HIV-1-associated pain.

Association of Pain and Pain Medication Use with Multiple Characteristics of Older People Living with HIV

People living with HIV (PLWH) experience chronic pain that may impact function. Gaps in knowledge exist for factors that impact pain and pain medication use in older (age 50+) PLWH. Data for this study were obtained from the Aging with Dignity, Health, Optimism and Community (ADHOC) cohort, an observational study of older PLWH from 10 clinics across the United States. Participants self-reported socioeconomic, psychosocial, and health factors via an online questionnaire. Of 1,051 participants, 66% reported pain. In a multivariable regression model, multimorbidity and tobacco use were associated with a greater likelihood of experiencing pain, whereas being male, black, and having higher cognitive function were associated with a lower likelihood of experiencing pain. Of the 696 participants who reported pain, 46% reported using pain medication. In a multivariable regression model, pain medication use was associated with multimorbidity and with lower income. Recognition of the factors associated with pain and pain medication use in this vulnerable population may lead to strategies that mitigate negative health outcomes.

Compounds of traditional Chinese medicine and neuropathic pain

Neuropathic pain (NP) has become a serious global health issue and a huge clinical challenge without available effective treatment. P2 receptors family is involved in pain transmission and represents a promising target for pharmacological intervention. Traditional Chinese medicine (TCM) contains multiple components which are effective in targeting different pathological mechanisms involved in NP. Different from traditional analgesics, which target a single pathway, TCMs take the advantage of multiple components and multiple targets, and can significantly improve the efficacy of treatment and contribute to the prediction of the risks of NP. Compounds of TCM acting at nucleotide P2 receptors in neurons and glial cells could be considered as a potential research direction for moderating neuropathic pain. This review summarized the recently published data and highlighted several TCMs that relieved NP by acting at P2 receptors.

The role of CAMKK2 polymorphisms in HIV-associated sensory neuropathy in South Africans

Human immunodeficiency virus-associated sensory neuropathy (HIV-SN) is a common neurological complication of HIV infection. It affected 57% of South African patients whose antiretroviral therapy (ART) included stavudine and was influenced by genotypes of the P2X-block (P2X7R, P2X4R and CAMKK2). We investigate associations between HIV-SN and P2X-block genotypes in patients who never received stavudine. An adjacent gene, ANAPC5, was included. 75 HIV+ individuals were assessed using the Brief Peripheral Neuropathy Screen before treatment and after 6-8 months on stavudine-free regimens. DNA was genotyped for 48 polymorphisms across the four genes using an OpenArray™ platform. Haplotypes were derived using fastPHASE. Associations with HIV-SN were assessed using bivariate and multivariate analyses. Nine individuals (12%) were diagnosed with HIV-SN prior to ART and a further 20 individuals (27%) developed HIV-SN within 6-8 months. Five polymorphisms, rs503720*G (OR = 133) in P2X7R, rs10849861*A (OR = 5.99), rs1653586*T (OR = 67.8) and rs11065504*C (OR = 0.02) in CAMKK2, and rs2089886*A (OR = 6.68) in ANAPC5, associated with HIV-SN after adjusting for body weight, nadir CD4 T-cell counts and prior tuberculosis (model p < 0.0001, n = 69, Pseudo R² = 0.54). Three CAMKK2 haplotypes were associated with HIV-SN (OR = 2.82, 3.42 and 6.85) after adjusting for body weight, nadir CD4 T-cell counts and prior tuberculosis (model p < 0.0005, n = 71, Pseudo R² = 0.26). The results support a role for CAMKK2 in HIV-SN, independent of mechanisms invoked by stavudine. SIGNIFICANCE STATEMENT: HIV-associated sensory neuropathy (HIV-SN) remains a clinically relevant complication of HIV infection and its treatment, affecting 38% of patients treated without neurotoxic stavudine. HIV-SN can impact an individual's ability to work and quality of life, with few effective therapeutic options, so an understanding of the underlying mechanisms would have clinical value. We confirm that CAMKK2 polymorphisms and haplotypes influence susceptibility to HIV-SN in South Africans treated without stavudine. This provides further evidence for a role for the protein encoded by CAMKK2 in the pathogenesis of HIV-SN, independent of mechanisms initiated by stavudine.

Viral Vector-Mediated Gene Transfer of Glutamic Acid Decarboxylase for Chronic Pain Treatment: A Literature Review

Chronic pain is long-lasting nociceptive state, impairing the patient's quality of life. Existing analgesics are generally not effective in the treatment of chronic pain, some of which such as opioids have the risk of tolerance/dependence and overdose death with higher daily opioid doses for increasing analgesic effect. Opioid use disorders have already reached an epidemic level in the United States; therefore, nonopioid analgesic approach and/or use of nonpharmacologic interventions will be employed with increasing frequency. Viral vector-mediated gene therapy is promising in clinical trials in the nervous system diseases. Glutamic acid decarboxylase (GAD) enzyme, a key enzyme in biosynthesis of γ-aminobutyric acid (GABA), plays an important role in analgesic mechanism. In the literature review, we used PubMed and bioRxiv to search the studies, and the eligible criteria include (1) article written in English, (2) use of viral vectors expressing GAD67 or GAD65, and (3) preclinical pain models. We identified 13 eligible original research articles, in which the pain models include nerve injury, HIV-related pain, painful diabetic neuropathy, and formalin test. GAD expressed by the viral vectors from all the reports produced antinociceptive effects. Restoring GABA systems is a promising therapeutic strategy for chronic pain, which provides evidence for the clinical trial of gene therapy for pain in the near future.

HIV-1 gp120 Promotes Lysosomal Exocytosis in Human Schwann Cells

Human immunodeficiency virus type 1 (HIV-1) associated neuropathy is the most common neurological complication of HIV-1, with debilitating pain affecting the quality of life. HIV-1 gp120 plays an important role in the pathogenesis of HIV neuropathy via direct neurotoxic effects or indirect pro-inflammatory responses. Studies have shown that gp120-induced release of mediators from Schwann cells induce CCR5-dependent DRG neurotoxicity, however, CCR5 antagonists failed to improve pain in HIV- infected individuals. Thus, there is an urgent need for a better understanding of neuropathic pain pathogenesis and developing effective therapeutic strategies. Because lysosomal exocytosis in Schwann cells is an indispensable process for regulating myelination and demyelination, we determined the extent to which gp120 affected lysosomal exocytosis in human Schwann cells. We demonstrated that gp120 promoted the movement of lysosomes toward plasma membranes, induced lysosomal exocytosis, and increased the release of ATP into the extracellular media. Mechanistically, we demonstrated lysosome de-acidification, and activation of P2X4 and VNUT to underlie gp120-induced lysosome exocytosis. Functionally, we demonstrated that gp120-induced lysosome exocytosis and release of ATP from Schwann cells leads to increases in intracellular calcium and generation of cytosolic reactive oxygen species in DRG neurons. Our results suggest that gp120-induced lysosome exocytosis and release of ATP from Schwann cells and DRG neurons contribute to the pathogenesis of HIV-1 associated neuropathy.

Mitochondrial dysfunction in HIV-induced peripheral neuropathy

Mitochondria play an essential role in cellular energy production and calcium homeostasis. Abnormalities in mitochondrial homeostasis and function are seen in several acquired as well as genetic neuropathies, emphasizing their prominent role in neuronal cell activities. Chronic infection with HIV, even when appropriately treated, is a risk factor for developing peripheral neuropathy. In this chapter, we discuss the way in which HIV infection, the resultant toxic viral products that are generated, and some of the viral inhibitors used in its treatment may lead to abnormal mitochondrial function. Of importance are the effects on mitochondrial DNA replication and the neurotoxic effects of the viral gp120 protein. One aspect of mitochondrial dysfunction that remains unexplored is the role of the interaction between mitochondria and the endoplasmic reticulum as a possible target of disruption in HIV neuropathy.

Sex Differences in a Rodent Model of HIV-1-Associated Neuropathic Pain

Worldwide, women account for approximately 51% of human immunodeficiency virus-1 (HIV) seropositive individuals. The prevalence of neuropathic pain among individuals with HIV and a lack of preclinical data characterizing sex differences prompted us to address this knowledge gap. C57BL/6 male and female mice received multiple intrathecal injections of HIV-glycoprotein 120 (gp120), followed by determination of mechanical allodynia and thermal hypersensitivity for four weeks. The influence of ovarian hormones in the gp120 pain model was evaluated by comparison of ovariectomized (OVX) mice versus sham control. We found that gp120-induced neuropathic pain-like behaviors are sex-dependent. Female mice showed both increased mechanical allodynia and increased cold sensitivity relative to their male counterparts. The OVX mice showed reduced pain sensitivity compared to sham, suggesting a role of the ovarian hormones in sex differences in pain sensitivity to gp120. Gp120-induced neuropathic pain caused a shift in estrous cycle toward the estrus phase. However, there is a lack of clear correlation between the estrous cycle and the development of neuropathic pain-like behaviors during the four week recording period. This data provided the first evidence for sex differences in a rodent model of HIV-related neuropathic pain, along with a potential role of ovarian hormones.

Plant-derived medicines for neuropathies: a comprehensive review of clinical evidence

Neuropathy is defined as the damage to the peripheral or central nervous system accompanied by pain, numbness, or muscle weakness, which can be due to congenital diseases or environmental factors such as diabetes, trauma, or viral infections. As current treatments are not sufficiently able to control the disease, studies focusing on the identification and discovery of new therapeutic agents are necessary. Natural products have been used for a long time for the management of different neurological problems including neuropathies. The aim of the present study is to review the current clinical data on the beneficial effects of medicinal plants in neuropathy. Electronic databases including PubMed, Scopus, and Cochrane Library were searched with the keywords ‘neuropathy’ in the title/abstract and ‘plant’ or ‘extract’ or ‘herb’ in the whole text from inception until August 2017. From a total of 3679 papers, 22 studies were finally included. Medicinal plants were evaluated clinically in several types of neuropathy, including diabetic neuropathy, chemotherapy-induced peripheral neuropathy, carpal tunnel syndrome, and HIV-associated neuropathy. Some studies reported the improvement in pain, nerve function, nerve conduction velocity, and quality of life. Cannabis sativa (hemp), Linum usitatissimum (linseed oil), capsaicin, and a polyherbal Japanese formulation called Goshajinkigan had the most evidence regarding their clinical efficacy. Other investigated herbal medicines in neuropathy, such as Matricaria chamomilla (chamomile), Curcuma longa (turmeric), and Citrullus colocynthis (colocynth), had only one clinical trial. Thus, future studies are necessary to confirm the safety and efficacy of such natural medicines as a complementary or alternative treatment for neuropathy.

Spinal bromodomain-containing protein 4 contributes to neuropathic pain induced by HIV glycoprotein 120 with morphine in rats

The symptoms of HIV-sensory neuropathy are dominated by neuropathic pain. Recent data show that repeated use of opiates enhances the chronic pain states in HIV patients. Limited attention has so far been devoted to exploring the exact pathogenesis of HIV painful disorder and opiate abuse in vivo, for which there is no effective treatment. Bromodomain-containing protein 4 (Brd4) is a member of the bromodomain and extraterminal domain protein (BET) family and functions as a chromatin 'reader' that binds acetylated lysines in histones in brain neurons to mediate the transcriptional regulation underlying learning and memory. Here, we established a neuropathic pain model of interaction of intrathecal HIV envelope glycoprotein 120 (gp120) and chronic morphine in rats. The combination of gp120 and morphine (gp120/M, for 5 days) induced persistent mechanical allodynia compared with either gp120 or morphine alone. Mechanical allodynia reached the lowest values at day 10 from gp120/M application, beginning to recover from day 21. In the model, gp120/M induced overexpression of Brd4 mRNA and protein at day 10 using RT-qPCR and western blots, respectively. Immunohistochemical studies showed that Brd4 at day 10 was expressed in the neurons of spinal cord dorsal horn. BET inhibitor I-BET762 dose-dependently increased the mechanical threshold in the gp120/M pain state. The present study provides preclinical evidence for treating HIV neuropathic pain with opioids using the BET inhibitor.

Resveratrol-decreased hyperalgesia mediated by the P2X7 receptor in gp120-treated rats

Background

Chronic pain is a common symptom in human immunodeficiency virus (HIV)-1 infection/acquired immunodeficiency syndrome patients. The literature shows that the HIV envelope glycoprotein 120 (gp120) can directly cause hyperalgesia by stimulating primary sensory afferent nerves. The P2X₇ receptor in the dorsal root ganglia (DRG) is closely related to neuropathic and inflammatory pain. In this study, we aimed to explore the effect of resveratrol (RES) on gp120-induced neuropathic pain that is mediated by the P2X₇ receptor in the rat DRG.

Results

Mechanical hyperalgesia in rats treated with gp120 was increased compared with that in the sham group. The P2X₇ expression levels in rats treated with gp120 were higher than those in the sham group. Co-localization of the P2X₇ receptor and glial fibrillary acidic protein (GFAP, a marker of satellite glial cells [SGCs]) in the DRG SGCs of the gp120 group exhibited more intense staining than that of the sham group. RES decreased the mechanical hyperalgesia and P2X₇ expression levels in gp120 treatment rats. Co-localization of the P2X₇ receptor and GFAP in the gp120+ RES group was significantly decreased compared to the gp120 group. RES decreased the IL-1β and TNF-α receptor (R) expression levels and ERK1/2 phosphorylation levels as well as increased IL-10 expression in the DRG of gp120-treated rats. Whole cell clamping demonstrated that RES significantly inhibited adenosine triphosphate-activated currents in HEK293 cells that were transfected with the P2X₇ plasmid.

Conclusions

RES relieved mechanical hyperalgesia in gp120-treated rats by inhibiting the P2X₇ receptor.

Nitrosative damage during retrovirus infection-induced neuropathic pain

BACKGROUND

Peripheral neuropathy is currently the most common neurological complication in HIV-infected individuals, occurring in 35-50% of patients undergoing combination anti-retroviral therapy. Data have shown that distal symmetric polyneuropathy develops in mice by 6 weeks following infection with the LP-BM5 retrovirus mixture. Previous work from our laboratory has demonstrated that glial cells modulate antiviral T-cell effector responses through the programmed death (PD)-1: PD-L1 pathway, thereby limiting the deleterious consequences of unrestrained neuroinflammation.

METHODS

Using the MouseMet electronic von Frey system, we assessed hind-paw mechanical hypersensitivity in LP-BM5-infected wild-type (WT) and PD-1 KO animals. Using multi-color flow cytometry, we quantitatively assessed cellular infiltration and microglial activation. Using real-time RT-PCR, we assessed viral load, expression of IFN-γ, iNOS, and MHC class II. Using western blotting, we measured protein nitrosylation within the lumbar spinal cord (LSC) and dorsal root ganglion (DRG). Histochemical staining was performed to analyze the presence of CD3, ionized calcium binding adaptor molecule (Iba)-1, MHCII, nitrotyrosine, isolectin B4 (IB4) binding, and neurofilament 200 (NF200). Statistical analyses were carried out using graphpad prism.

RESULTS

Hind-paw mechanical hypersensitivity observed in LP-BM5-infected animals was associated with significantly increased lymphocyte infiltration into the spinal cord and DRG. We also observed elevated expression of IFN-γ (in LSC and DRG) and MHC II (on resident microglia in LSC). We detected elevated levels of 3-nitrotyrosine within the LSC and DRG of LP-BM5-infected animals, an indicator of nitric oxide (NO)-induced protein damage. Moreover, we observed 3-nitrotyrosine in both small (IB4+) and large (NF200+) DRG sensory neurons. Additionally, infected PD-1 KO animals displayed significantly greater mechanical hypersensitivity than WT or uninfected mice at 4 weeks post-infection (p.i.). Accelerated onset of hind-paw hypersensitivity in PD-1 KO animals was associated with significantly increased infiltration of CD4+ and CD8+ T lymphocytes, macrophages, and microglial activation at early time points. Importantly, we also observed elevated levels of 3-nitrotyrosine and iNOS in infected PD-1 KO animals when compared with WT animals.

CONCLUSIONS

Results reported here connect peripheral immune cell infiltration and reactive gliosis with nitrosative damage. These data may help elucidate how retroviral infection-induced neuroinflammatory networks contribute to nerve damage and neuropathic pain.

Ex-vivo expression of chemokine receptors on cells surrounding cutaneous nerves in patients with HIV-associated sensory neuropathy

OBJECTIVE

HIV-associated sensory neuropathy (HIV-SN) remains common in HIV+ individuals receiving antiretroviral therapy (ART), even though neurotoxic antiretroviral drugs (e.g. stavudine) have been phased out of use. Accumulating evidence indicates that the neuropathy is immune-mediated. We hypothesize that chemokines produced locally in the skin promote migration of macrophages and T cells into the tissue, damaging cutaneous nerves causing HIV-SN.

DESIGN

We assessed chemokine receptor expression on infiltrating CD14 and CD3 cells around cutaneous nerves in standardized skin biopsies from HIV-SN+ patients (n = 5), HIV-SN- patients (n = 9) and healthy controls (n = 4).

METHODS

The AIDS Clinical Trials Group Brief Peripheral Neuropathy Screen was used to assess Indonesian HIV+ patients receiving ART without stavudine (case definition: bilateral presence of at least one symptom and at least one sign of neuropathy). Distal leg skin biopsies were stained to visualize chemokine receptors (CCR2, CCR5, CXCR3, CXCR4, CX3CR1), infiltrating CD3 and CD14 cells, and protein-gene-product 9.5 on nerves, using immunohistochemistry and 4-colour confocal microscopy.

RESULTS

Intraepidermal nerve fibre density was variable in patients without HIV-SN and generally lower in those with HIV-SN. CX3CR1 was more evident on CD14 cells whereas CCR2, CCR5, CXCR3 and CXCR4 were more common on CD3 cells. Expression of CX3CR1, CCR2 and CCR5 was more common in HIV-SN+ patients than those without HIV-SN. CXCR3 and CXCR4 were upregulated in all HIV+ patients, compared with healthy controls.

CONCLUSION

Inflammatory macrophages expressing CX3CR1 and T cells expressing CCR2 and CCR5 may participate in peripheral nerve damage leading to HIV-SN in HIV+ patients treated without stavudine. Further characterization of these cells is warranted.

Phosphorylated CCAAT/Enhancer Binding Protein β Contributes to Rat HIV-Related Neuropathic Pain: In Vitro and In Vivo Studies

Chronic pain is increasingly recognized as an important comorbidity of HIV-infected patients, however, the exact molecular mechanisms of HIV-related pain are still elusive. CCAAT/enhancer binding proteins (C/EBPs) are expressed in various tissues, including the CNS. C/EBPβ, one of the C/EBPs, is involved in the progression of HIV/AIDS, but the exact role of C/EBPβ and its upstream factors are not clear in HIV pain state. Here, we used a neuropathic pain model of perineural HIV envelope glycoprotein gp120 application onto the rat sciatic nerve to test the role of phosphorylated C/EBPβ (pC/EBPβ) and its upstream pathway in the spinal cord dorsal horn (SCDH). HIV gp120 induced overexpression of pC/EBPβ in the ipsilateral SCDH compared with contralateral SCDH. Inhibition of C/EBPβ using siRNA against C/EBPβ reduced mechanical allodynia. HIV gp120 also increased TNFα, TNFRI, mitochondrial superoxide (mtO₂^·-), and pCREB in the ipsilateral SCDH. ChIP-qPCR assay showed that pCREB enrichment on the C/EBPβ gene promoter regions in rats with gp120 was higher than that in sham rats. Intrathecal TNF soluble receptor I (functionally blocking TNFα bioactivity) or knockdown of TNFRI using antisense oligodeoxynucleotide against TNFRI reduced mechanical allodynia, and decreased mtO₂^·-, pCREB and pC/EBPβ. Intrathecal Mito-tempol (a mitochondria-targeted O₂^·-scavenger) reduced mechanical allodynia and decreased pCREB and pC/EBPβ. Knockdown of CREB with antisense oligodeoxynucleotide against CREB reduced mechanical allodynia and lowered pC/EBPβ. These results suggested that the pathway of TNFα/TNFRI-mtO₂^·--pCREB triggers pC/EBPβ in the HIV gp120-induced neuropathic pain state. Furthermore, we confirmed the pathway using both cultured neurons treated with recombinant TNFα in vitro and repeated intrathecal injection of recombinant TNFα in naive rats. This finding provides new insights in the understanding of the HIV neuropathic pain mechanisms and treatment.SIGNIFICANCE STATEMENT Painful HIV-associated sensory neuropathy is a neurological complication of HIV infection. Phosphorylated C/EBPβ (pC/EBPβ) influences AIDS progression, but it is still not clear about the exact role of pC/EBPβ and the detailed upstream factors of pC/EBPβ in HIV-related pain. In a neuropathic pain model of perineural HIV gp120 application onto the sciatic nerve, we found that pC/EBPβ was triggered by TNFα/TNFRI-mtO₂^·--pCREB signaling pathway. The pathway was confirmed by using cultured neurons treated with recombinant TNFα in vitro, and by repeated intrathecal injection of recombinant TNFα in naive rats. The present results revealed the functional significance of TNFα/TNFRI-mtO₂^·--pCREB-pC/EBPβ signaling in HIV neuropathic pain, and should help in the development of more specific treatments for neuropathic pain.

P2Y12 receptor upregulation in satellite glial cells is involved in neuropathic pain induced by HIV glycoprotein 120 and 2',3'-dideoxycytidine

The direct neurotoxicity of HIV and neurotoxicity of combination antiretroviral therapy medications both contribute to the development of neuropathic pain. Activation of satellite glial cells (SGCs) in the dorsal root ganglia (DRG) plays a crucial role in mechanical and thermal hyperalgesia. The P2Y₁₂ receptor expressed in SGCs of the DRG is involved in pain transmission. In this study, we explored the role of the P2Y₁₂ receptor in neuropathic pain induced by HIV envelope glycoprotein 120 (gp120) combined with ddC (2',3'-dideoxycytidine). A rat model of gp120+ddC-induced neuropathic pain was used. Peripheral nerve exposure to HIV-gp120+ddC increased mechanical and thermal hyperalgesia in gp120+ddC-treated model rats. The gp120+ddC treatment increased expression of P2Y₁₂ receptor mRNA and protein in DRG SGCs. In primary cultured DRG SGCs treated with gp120+ddC, the levels of [Ca²⁺]_i activated by the P2Y₁₂ receptor agonist 2-(Methylthio) adenosine 5'-diphosphate trisodium salt (2-MeSADP) were significantly increased. P2Y₁₂ receptor shRNA treatment inhibited 2-MeSADP-induced [Ca²⁺]_i in primary cultured DRG SGCs treated with gp120+ddC. Intrathecal treatment with a shRNA against P2Y₁₂ receptor in DRG SGCs reduced the release of pro-inflammatory cytokines, decreased phosphorylation of p38 MAPK in the DRG of gp120+ddC-treated rats. Thus, downregulating the P2Y₁₂ receptor relieved mechanical and thermal hyperalgesia in gp120+ddC-treated rats.

A rodent model of HIV protease inhibitor indinavir induced peripheral neuropathy

HIV-associated sensory neuropathy (HIV-SN) is the most frequent manifestation of HIV disease. It often presents with significant neuropathic pain and is associated with previous exposure to neurotoxic nucleoside reverse transcriptase inhibitors. However, HIV-SN prevalence remains high even in resource-rich settings where these drugs are no longer used. Previous evidence suggests that exposure to indinavir, a protease inhibitor commonly used in antiretroviral therapy, may link to elevated HIV-SN risk. Here, we investigated whether indinavir treatment was associated with the development of a "dying back" axonal neuropathy and changes in pain-relevant limb withdrawal and thigmotactic behaviours. After 2 intravenous injections of indinavir (50 mg/kg, 4 days apart), adult rats developed hind paw mechanical hypersensitivity, which peaked around 2 weeks post first injection (44% reduction from baseline). At this time, animals also had (1) significantly changed thigmotactic behaviour (62% reduction in central zone entries) comparing with the controls and (2) a significant reduction (45%) in hind paw intraepidermal nerve fibre density. Treatment with gabapentin, but not amitriptyline, was associated with a complete attenuation of hind paw mechanical hypersensitivity observed with indinavir treatment. Furthermore, we found a small but significant increase in microglia with the effector morphology in the lumbar spinal dorsal horn in indinavir-treated animals, coupled with significantly increased expression of phospho-p38 in microglia. In summary, we have reported neuropathic pain-related sensory and behavioural changes accompanied by a significant loss of hind paw skin sensory innervation in a rat model of indinavir-induced peripheral neuropathy that is suitable for further pathophysiological investigation and preclinical evaluation of novel analgesics.

Effects of nanoparticle-encapsulated curcumin on HIV-gp120-associated neuropathic pain induced by the P2X3 receptor in dorsal root ganglia

HIV-1 envelope glycoprotein (Glycoprotein 120, gp120) can directly stimulate primary sensory afferent neurons and cause chronic neuropathic pain. The P2X₃ receptor in the dorsal root ganglia (DRG) is associated with the transmission of neuropathic pain. Curcumin isolated from the herb Curcuma rhizome has anti-inflammatory and anti-tumor effects. The water solubility, targeting and bioavailability of curcumin can be improved by nanoparticle encapsulation. In this study, we sought to explore the effects of nanoparticle-encapsulated curcumin (nano curcumin) on HIV-gp120-induced neuropathic pain mediated by the P2X₃ receptor in DRG neurons. The results showed that mechanical and thermal hyperalgesia in rats treated with gp120 were increased compared to those in the control group. The expression levels of P2X₃ mRNA and protein in rats treated with gp120 were higher than those in the control group. Nano curcumin treatment decreased mechanical hyperalgesia and thermal hyperalgesia and upregulated the expression levels of P2X₃ mRNA and protein in rats treated with gp120. Nano curcumin treatment also reduced the ERK1/2 phosphorylation levels in gp120-treated rat DRG. In addition, P2X₃ agonist α,β-methylene ATP (α,β-meATP)-induced currents in DRG neurons cultured with gp120 significantly decreased after co-treatment with nano curcumin. Therefore, nano curcumin treatment may inhibit P2X₃ activation, decrease the sensitizing DRG primary afferents and relieve mechanical hyperalgesia and thermal hyperalgesia in gp120-treated rats.

The P2X7 receptor in dorsal root ganglia is involved in HIV gp120-associated neuropathic pain

Human immunodeficiency virus (HIV)-associated neuropathic pain is common, and studies have shown that HIV envelope glycoprotein 120 (gp120) can directly stimulate primary sensory afferent neurons causing hyperalgesia. The P2X₇ receptor in the dorsal root ganglia (DRG) is involved in pain transmission and is closely related to the inflammatory and immune response. In this study, we aimed to explore the role of the P2X₇ receptor in gp120-induced neuropathic pain using a rat model specific for this type of pain. The results showed that mechanical hyperalgesia, thermal hyperalgesia and P2X₇ expression levels were increased in rats treated with gp120. The P2X₇ antagonist, brilliant blue G (BBG), decreased hyperalgesia and P2X₇ expression levels in rats treated with gp120. BBG also decreased IL-1β and TNF-α receptor expression and ERK1/2 phosphorylation levels and increased IL-10 expression in the gp120-treated rat DRG. In addition, P2X₇ agonist (BzATP)-activated currents in DRG neurons cultured with gp120 were larger than those in control neurons, and the inhibitory effect of BBG on BzATP-induced currents in gp120-treated DRG neurons was larger than that in control neurons. Therefore, inhibition of the P2X₇ receptor in rat DRG relieved gp120-induced mechanical hyperalgesia and thermal hyperalgesia.

Brief Report: IL-1β Levels Are Associated With Chronic Multisite Pain in People Living With HIV

BACKGROUND

The pathophysiology of chronic pain experienced by people living with HIV (PLWH) in the current antiretroviral treatment era is poorly understood. We sought to investigate the relationship between inflammation and chronic pain in PLWH. We hypothesized that, among PLWH who have undetectable HIV viral loads, those with chronic multisite pain (CMP) would have higher levels of circulating pain-related inflammatory markers than those without chronic pain.

SETTING

This study was conducted at the University of Alabama at Birmingham's Center for AIDS Research Network of Integrated Clinical System site.

METHODS

We compared inflammatory markers in 70 PLWH with CMP and 70 PLWH without chronic pain. Custom multiplex human inflammatory assays were completed on banked plasma specimens to measure cytokines commonly associated with chronic inflammatory pain: interleukin 1β (IL-1β), eotaxin, IL-15, IL-6, tumor necrosis factor α, and leptin. Logistic regression models were built using group status (CMP vs no pain) as the outcome variable, with each cytokine as independent variables and age, sex, substance use, and prescribed opioid medications as covariates.

RESULTS

Participants were mostly men (71%); 53% were 50 years or older. The most common sites of pain were low back (86%), hands/feet (81%), and knee (66%). Median CD4 T-cell count was 676 cells per milliliter. IL-1β was significantly higher in the CMP group than in the individuals without chronic pain (odds ratio: 1.35, 95% confidence interval: 1.01 to 1.82, P < 0.05). Eotaxin, IL-15, IL-6, tumor necrosis factor α, and leptin were not significantly different between groups.

CONCLUSIONS

We found that PLWH who also have CMP have significantly higher levels of IL-1β than PLWH who do not have any pain. Future work on the role of IL-1β on chronic pain pathogenesis in this population may inform novel approaches to chronic pain management.

A317491 relieved HIV gp120-associated neuropathic pain involved in P2X3 receptor in dorsal root ganglia

Glycoprotein 120 (gp120) is an HIV envelope glycoprotein. Gp120 can directly stimulate the primary sensory afferent neurons and cause hyperalgesia. The P2X₃ receptor in dorsal root ganglia (DRG) is involved in the transmission of pain. In this study, we aimed to explore the role of the P2X₃ receptor in gp120-induced neuropathic pain. Our data showed that mechanical and thermal hyperalgesia in rats treated with gp120 were increased compared to those in the control group. The expression levels of the P2X₃ mRNA and protein in rats treated with gp120 were higher than those in the control group. The P2X₃ antagonist A317491 decreased mechanical hyperalgesia and thermal hyperalgesia and the up-regulated expression levels of P2X₃ mRNA and protein in rats treated with gp120. A317491 decreased ERK1/2 phosphorylation levels in the gp120-treated rat DRG. In addition, P2X₃ agonist α,β-methylene ATP (α,β-meATP)-activated currents in DRG neurons cultured with gp120 were higher than those in control neurons. The inhibitory effect of A317491 on α,βme-ATP-induced currents in DRG neurons from the gp120-treated neurons was larger than that for control neurons. Molecular docking data showed that A317491 may be acted in the gp120 protein to inhibit the gp120 initiated the P2X₃ activation, decrease the sensitizing DRG primary afferents and reduce the signal transmission of neuropathic pain in gp120-treated rats. Therefore, the inhibition of the P2X₃ receptor in rat DRG neurons relieved gp120-induced mechanical hyperalgesia.

HIV Glycoprotein Gp120 Impairs Fast Axonal Transport by Activating Tak1 Signaling Pathways

Sensory neuropathies are the most common neurological complication of HIV. Of these, distal sensory polyneuropathy (DSP) is directly caused by HIV infection and characterized by length-dependent axonal degeneration of dorsal root ganglion (DRG) neurons. Mechanisms for axonal degeneration in DSP remain unclear, but recent experiments revealed that the HIV glycoprotein gp120 is internalized and localized within axons of DRG neurons. Based on these findings, we investigated whether intra-axonal gp120 might impair fast axonal transport (FAT), a cellular process critical for appropriate maintenance of the axonal compartment. Significantly, we found that gp120 severely impaired both anterograde and retrograde FAT. Providing a mechanistic basis for these effects, pharmacological experiments revealed an involvement of various phosphotransferases in this toxic effect, including members of mitogen-activated protein kinase pathways (Tak-1, p38, and c-Jun N-terminal Kinase (JNK)), inhibitor of kappa-B-kinase 2 (IKK2), and PP1. Biochemical experiments and axonal outgrowth assays in cell lines and primary cultures extended these findings. Impairments in neurite outgrowth in DRG neurons by gp120 were rescued using a Tak-1 inhibitor, implicating a Tak-1 mitogen-activated protein kinase pathway in gp120 neurotoxicity. Taken together, these observations indicate that kinase-based impairments in FAT represent a novel mechanism underlying gp120 neurotoxicity consistent with the dying-back degeneration seen in DSP. Targeting gp120-based impairments in FAT with specific kinase inhibitors might provide a novel therapeutic strategy to prevent axonal degeneration in DSP.

TNF Block Gene Variants Associate With Pain Intensity in Black Southern Africans With HIV-associated Sensory Neuropathy

OBJECTIVES

HIV-associated sensory neuropathy (HIV-SN) is a common neurological complication of HIV infection, and it is often painful. Tumor necrosis factor (TNF)-α is implicated in neuropathic pain, but associations between neuropathic pain and polymorphisms in the TNFA gene have not been identified. The "TNF block" is a region of high linkage disequilibrium within the central major histocompatability complex that contains several genes involved in the regulation of inflammation, including TNFA. Polymorphisms in the block have been associated with an altered risk of HIV-SN, but no investigations into whether this region is associated with the painful symptoms of neuropathy have been undertaken. Therefore, we investigated whether polymorphisms in the TNF block are associated with pain intensity in black Southern Africans with HIV-SN.

METHODS

Single-nucleotide polymorphisms (SNPs) defining TNF block haplotypes and African-specific tagSNPs were genotyped in samples from 150 black Southern Africans with HIV-SN.

RESULTS

One SNP allele, rs28445017*A, was significantly associated with an increased pain intensity after correction for age, sex, and the CD4 T-cell count. A common 3-SNP haplotype containing rs28445017*G remained associated with a reduced pain intensity after correction for covariates and multiple comparisons.

DISCUSSION

We identified a novel genetic association between polymorphisms in the TNF block and the pain intensity in black Southern Africans with HIV-SN. Our study implicates rs28445017 in painful HIV-SN, although its precise role and whether it may be causative is unclear. rs28445017 was not associated with the risk for HIV-SN as such, highlighting potential differences between the pathophysiology of the neuropathy and the painful features of the neuropathy.

Antinociceptive effects of topical mepivacaine in a rat model of HIV-associated peripheral neuropathic pain

Background

A consequence of HIV infection is sensory neuropathy, a debilitating condition that degrades the quality of life of HIV patients. Furthermore, life-extending antiretroviral treatment may exacerbate HIV sensory neuropathy. Analgesics that relieve other neuropathic pains show little or no efficacy in ameliorating HIV sensory neuropathy. Thus, there is a need for analgesics for people with this particular pain. While lidocaine is used in the management of painful peripheral neuropathies, another local anesthetic mepivacaine, with a potentially improved bioavailability, could be utilized for the management of HIV neuropathic pain.

Methods

The efficacy of topical anesthetics was evaluated in a preclinical rodent model of painful peripheral neuropathy induced by epineural administration of the HIV envelope protein gp120 delivered using saturated oxidized cellulose implanted around the sciatic nerve. Beginning at 2 weeks following gp120 administration, the effects of local anesthetics topically applied via gauze pads were tested on heat and mechanical hyperalgesia in the hind paw. Rats were tested using several concentrations of mepivacaine or lidocaine during the following 2 weeks.

Results

By 2 weeks following epineural gp120 implantation, the ipsilateral hind paw developed significant hypersensitivity to noxious pressure and heat hyperalgesia. A short-lasting, concentration-dependent amelioration of pressure and heat hyperalgesia was observed following topical application of mepivacaine to the ipsilateral plantar hind paw. By contrast, topical lidocaine ameliorated heat hyperalgesia in a concentration-dependent manner but not pressure hyperalgesia. Equipotent concentrations of mepivacaine and lidocaine applied topically to the tail of mice significantly increased tail withdrawal latencies in the tail flick test, demonstrating that both local anesthetics attenuate responding to a brief noxious stimulus.

Conclusion

These findings showed that mepivacaine, rather than lidocaine, consistently attenuated two distinct symptoms of neuropathic pain and suggest that topical formulations of this local anesthetic could have utility in the alleviation of clinical HIV neuropathic pain.

Spinal CPEB-mtROS-CBP signaling pathway contributes to perineural HIV gp120 with ddC-related neuropathic pain in rats

Human immunodeficiency virus (HIV) patients treated with nucleoside reverse transcriptase inhibitors (NRTIs), have been known to develop neuropathic pain. While there has been a major shift away from some neurotoxic NRTIs in current antiretroviral therapy, a large number of HIV patients alive today have previously received them, and many have developed painful peripheral neuropathy. The exact mechanisms by which HIV with NRTIs contribute to the development of neuropathic pain are not known. Previous studies suggest that cytoplasmic polyadenylation element-binding protein (CPEB), reactive oxygen species (ROS), and cAMP-response element-binding protein (CREB)-binding protein (CBP), are involved in the neuroimmunological diseases including inflammatory/neuropathic pain. In this study, we investigated the role of CPEB, mitochondrial ROS (mtROS), or CBP in neuropathic pain induced by HIV envelope protein gp120 combined with antiretroviral drug. The application of recombinant gp120 into the sciatic nerve plus systemic ddC (one of NRTIs) induced mechanical allodynia. Knockdown of CPEB or CBP using intrathecal antisense oligodeoxynucleotide (AS-ODN) reduced mechanical allodynia. Intrathecal mitochondrial superoxide scavenger mito-tempol (Mito-T) increased mechanical withdrawal threshold. Knockdown of CPEB using intrathecal AS-ODN, reduced the up-regulated mitochondrial superoxide in the spinal dorsal horn in rats with gp120 combined with ddC. Intrathecal Mito-T lowered the increased expression of CBP in the spinal dorsal horn. Immunostaining studies showed that neuronal CPEB positive cells were co-localized with MitoSox positive profiles, and that MitoSox positive profiles were co-localized with neuronal CBP. Our studies suggest that neuronal CPEB-mtROS-CBP pathway in the spinal dorsal horn, plays an important role in the gp120/ddC-induced neuropathic pain in rats.

Inhibition of Mitochondrial Fission Protein Reduced Mechanical Allodynia and Suppressed Spinal Mitochondrial Superoxide Induced by Perineural Human Immunodeficiency Virus gp120 in Rats

BACKGROUND

Mitochondria play an important role in many cellular and physiologic functions. Mitochondria are dynamic organelles, and their fusion and fission regulate cellular signaling, development, and mitochondrial homeostasis. The most common complaint of human immunodeficiency virus (HIV)-sensory neuropathy is pain on the soles in patients with HIV, but the exact molecular mechanisms of HIV neuropathic pain are not clear. In the present study, we investigated the role of mitochondrial dynamin-related protein 1 (Drp1, a GTPase that mediates mitochondrial fission) in the perineural HIV coat glycoprotein gp120-induced neuropathic pain state.

METHODS

Neuropathic pain was induced by the application of recombinant HIV-1 envelope protein gp120 into the sciatic nerve. Mechanical threshold was tested using von Frey filaments. The mechanical threshold response was assessed over time using the area under curves. Intrathecal administration of antisense oligodeoxynucleotide (ODN) against Drp1, mitochondrial division inhibitor-1 (mdivi-1), or phenyl-N-tert-butylnitrone (a reactive oxygen species scavenger) was given. The expression of spinal Drp1 was examined using western blots. The expression of mitochondrial superoxide in the spinal dorsal horn was examined using MitoSox imaging.

RESULTS

Intrathecal administration of either antisense ODN against Drp1 or mdivi-1 decreased mechanical allodynia (a sensation of pain evoked by nonpainful stimuli) in the gp120 model. Intrathecal ODN or mdivi-1 did not change basic mechanical threshold in sham surgery rats. Intrathecal Drp1 antisense ODN decreased the spinal expression of increased Drp1 protein induced by peripheral gp120 application. Intrathecal phenyl-N-tert-butylnitrone reduced mechanical allodynia. Furthermore, both intrathecal Drp1 antisense ODN and mdivi-1 reversed the upregulation of mitochondrial superoxide in the spinal dorsal horn in the gp120 neuropathic pain state.

CONCLUSIONS

These data suggest that mitochondrial division plays a substantial role in the HIV gp120-related neuropathic pain state through mitochondrial reactive oxygen species and provides evidence for a novel approach to treating chronic pain in patients with HIV.

A Wnt5a signaling pathway in the pathogenesis of HIV-1 gp120-induced pain

Pathological pain is one of the most common neurological complications in patients with HIV-1/AIDS. However, the pathogenic process is unclear. Our recent studies show that Wnt5a is upregulated in the spinal cord dorsal horn (SDH) of the patients with HIV who develop pain and that HIV-1 gp120, a potential causal factor of the HIV-associated pain, rapidly upregulates Wnt5a in the mouse SDH. Using a mouse model, we show here that a specific Wnt5a antagonist, Box-5, attenuated gp120-induced mechanical allodynia. Conversely, a Wnt5a agonist, Foxy5, facilitated the allodynia. To elucidate the molecular mechanism by which Wnt5a regulates gp120-induced allodynia, we tested the role of the JNK/TNF-α pathway. We observed that the JNK-specific inhibitor SP600125 blocked either gp120- or Foxy5-induced allodynia. Similarly, the TNF-α-specific antagonist Enbrel also reversed either gp120- or Foxy5-induced allodynia. These data suggest that JNK and TNF-α mediate the biological effects of Wnt5a in regulating gp120-induced allodynia. To investigate the cellular mechanism, we performed extracellular single-unit recording from SDH neurons in anesthetized mice. Both Box-5 and SP600125 negated gp120-induced potentiation of SDH neuron spiking evoked by mechanical stimulation of the hind paw. Furthermore, while Foxy5 potentiated spike frequency of SDH neurons, either SP600125 or Enbrel blocked the potentiation. The data indicate that Wnt5a potentiates the activity of SDH neurons through the JNK-TNF-α pathway. Collectively, our findings suggest that Wnt5a regulates the pathogenesis of gp120-induced pain, likely by sensitizing pain-processing SDH neurons through JNK/TNF-α signaling.

Interactions of Opioids and HIV Infection in the Pathogenesis of Chronic Pain

Over 50% of HIV-1/AIDS patients suffer chronic pain. Currently, opioids are the cornerstone medications for treating severe pain in these patients. Ironically, emerging clinical data indicates that repeated use of opiate pain medicines might in fact heighten the chronic pain states in HIV patients. Both laboratory-based and clinical studies strongly suggest that opioids exacerbate the detrimental effects of HIV-1 infection on the nervous system, both on neurons and glia. The combination of opioids and HIV-1infection may promote the damage of neurons, including those in the pain sensory and transmission pathway, by activating both caspase-dependent and caspase-independent pro-apoptotic pathways. In addition, the opiate-HIV-1 interaction may also cause widespread disturbance of glial function and elicit glial-derived pro-inflammatory responses that dysregulate neuronal function. The deregulation of neuron-glia cross-talk that occurs with the combination of HIV-1 and opioids appears to play an important role in the development of the pathological pain state. In this article, we wish to provide an overview of the potential molecular and cellular mechanisms by which opioids may interact with HIV-1 to cause neurological problems, especially in the context of HIV-associated pathological pain. Elucidating the underlying mechanisms will help researchers and clinicians to understand how chronic use of opioids for analgesia enhances HIV-associated pain. It will also assist in optimizing therapeutic approaches to prevent or minimize this significant side effect of opiate analgesics in pain management for HIV patients.

HSV vector-mediated GAD67 suppresses neuropathic pain induced by perineural HIV gp120 in rats through inhibition of ROS and Wnt5a

Human immunodeficiency virus (HIV)-related neuropathic pain is a debilitating chronic condition that is severe and unrelenting. Despite the extensive research, the exact neuropathological mechanisms remain unknown, which hinders our ability to develop effective treatments. Loss of GABAergic tone may play an important role in the neuropathic pain state. Glutamic acid decarboxylase 67 (GAD67) is one of isoforms that catalyze GABA synthesis. Here, we used recombinant herpes simplex virus (HSV-1) vectors that encode gad1 gene to evaluate the therapeutic potential of GAD67 in peripheral HIV gp120-induced neuropathic pain in rats. We found that 1) subcutaneous inoculation of the HSV vectors expressing GAD67 attenuated mechanical allodynia in the model of HIV gp120-induced neuropathic pain, 2) the anti-allodynic effect of GAD67 was reduced by GABA-A and-B receptors antagonists, 3) HSV vectors expressing GAD67 reversed the lowered GABA-IR expression, and 4) the HSV vectors expressing GAD67 suppressed the upregulated mitochondrial superoxide and Wnt5a in the spinal dorsal horn. Taken together, our studies support the concept that recovering GABAergic tone by the HSV vectors may reverse HIV-associated neuropathic pain through suppressing mitochondrial superoxide and Wnt5a. Our studies provide validation of HSV-mediated GAD67 gene therapy in the treatment of HIV-related neuropathic pain.

Gene Transfer of Glutamic Acid Decarboxylase 67 by Herpes Simplex Virus Vectors Suppresses Neuropathic Pain Induced by Human Immunodeficiency Virus gp120 Combined with ddC in Rats

BACKGROUND

Human immunodeficiency virus (HIV)-related painful sensory neuropathies primarily consist of the HIV infection-related distal sensory polyneuropathy and antiretroviral toxic neuropathies. Pharmacotherapy provides only partial relief of pain in patients with HIV/acquired immune deficiency syndrome because little is known about the exact neuropathological mechanisms for HIV-associated neuropathic pain (NP). Hypofunction of γ-aminobutyric acid (GABA) GABAergic inhibitory mechanisms has been reported after peripheral nerve injury. In this study, we tested the hypothesis that HIV gp120 combined with antiretroviral therapy reduces spinal GABAergic inhibitory tone and that restoration of GABAergic inhibitory tone will reduce HIV-related NP in a rat model.

METHODS

The application of recombinant HIV-1 envelope protein gp120 into the sciatic nerve plus systemic ddC (one antiretroviral drug) induced mechanical allodynia. The hind paws of rats were inoculated with replication-defective herpes simplex virus (HSV) vectors genetically encoding gad1 gene to express glutamic acid decarboxylase 67 (GAD67), an enzyme that catalyzes the decarboxylation of glutamate to GABA. Mechanical threshold was tested using von Frey filaments before and after treatments with the vectors. The expression of GAD67 in both the lumbar spinal cord and the L4-5 dorsal root ganglia was examined using western blots. The expression of mitochondrial superoxide in the spinal dorsal horn was examined using MitoSox imaging. The immunoreactivity of spinal GABA, pCREB, and pC/EBPβ was tested using immunohistochemistry.

RESULTS

In the gp120 with ddC-induced neuropathic pain model, GAD67 expression mediated by the HSV vector caused an elevation of mechanical threshold that was apparent on day 3 after vector inoculation. The antiallodynic effect of the single HSV vector inoculation expressing GAD67 lasted >28 days. The area under the time-effect curves in the HSV vector expressing GAD67 was increased compared with that in the control vectors (P = 0.0005). Intrathecal GABA-A/B agonists elevated mechanical threshold in the pain model. The HSV vectors expressing GAD67 reversed the lowered GABA immunoreactivity in the spinal dorsal horn in the neuropathic rats. HSV vectors expressing GAD67 in the neuropathic rats reversed the increased signals of mitochondrial superoxide in the spinal dorsal horn. The vectors expressing GAD67 reversed the upregulated immunoreactivity expression of pCREB and pC/EBPβ in the spinal dorsal horn in rats exhibiting NP.

CONCLUSIONS

Based on our results, we suggest that GAD67 mediated by HSV vectors acting through the suppression of mitochondrial reactive oxygen species and transcriptional factors in the spinal cord decreases pain in the HIV-related neuropathic pain model, providing preclinical evidence for gene therapy applications in patients with HIV-related pain states.

HIV-gp120 and physical dependence to buprenorphine

BACKGROUND

Opioids are among the most effective and commonly used analgesics in clinical practice for severe pain. However, the use of opioid medications is clinically limited by several adverse properties including dependence. While opioid dependence is a complex health condition, the treatment of HIV-infected individuals with opioid dependence presents additional challenges. The goal of this study was to examine the physical dependence to buprenorphine in the context of HIV.

METHODS

Young adult male rats (Sprague-Dawley) were pretreated with HIV-1 envelope glycoprotein 120 (gp120) injected into the periaqueductal gray area (PAG) and we examined the impact on physical dependence to opioid.

RESULTS

It was found that the physical dependence to methadone occurred earlier than that to buprenorphine, and that gp120 did not enhance or precipitate the buprenorphine withdrawal.

CONCLUSION

The results suggest that buprenorphine could be the better therapeutic option to manage opioid dependence in HIV.

Microglial content-dependent inhibitory effects of calcitonin gene-related peptide (CGRP) on murine retroviral infection of glial cells

C57BL/6 (B6) mice develop peripheral neuropathy post-LP-BM5 infection, a murine model of HIV-1 infection, along with the up-regulation of select spinal cord cytokines. We investigated if calcitonin gene-related peptide (CGRP) contributed to the development of peripheral neuropathy by stimulating glial responses. An increased expression of lumbar spinal cord CGRP was observed in vivo, post-LP-BM5 infection. Consequently, in vitro CGRP co-treatments led to a microglial content-dependent attenuation of viral loads in spinal cord mixed glia infected with selected doses of LP-BM5. This inhibition was neither caused by the loss of glia nor induced via the direct inhibition of LP-BM5 by CGRP.

Internalization and axonal transport of the HIV glycoprotein gp120

The HIV glycoprotein gp120, a neurotoxic HIV glycoprotein that is overproduced and shed by HIV-infected macrophages, is associated with neurological complications of HIV such as distal sensory polyneuropathy, but interactions of gp120 in the peripheral nervous system remain to be characterized. Here, we demonstrate internalization of extracellular gp120 in a manner partially independent of binding to its coreceptor CXCR4 by F11 neuroblastoma cells and cultured dorsal root ganglion neurons. Immunocytochemical and pharmacological experiments indicate that gp120 does not undergo trafficking through the endolysosomal pathway. Instead, gp120 is mainly internalized through lipid rafts in a cholesterol-dependent manner, with a minor fraction being internalized by fluid phase pinocytosis. Experiments using compartmentalized microfluidic chambers further indicate that, after internalization, endocytosed gp120 selectively undergoes retrograde but not anterograde axonal transport from axons to neuronal cell bodies. Collectively, these studies illuminate mechanisms of gp120 internalization and axonal transport in peripheral nervous system neurons, providing a novel framework for mechanisms for gp120 neurotoxicity.

Peripheral neuropathy in primary HIV infection associates with systemic and central nervous system immune activation

BACKGROUND

Peripheral neuropathy (PN) is a frequent complication of chronic HIV infection. We prospectively studied individuals with primary HIV infection (<1 year after transmission) to assess the presence of and laboratory associations with PN in this early stage.

METHODS

Standardized examination and analysis of blood and cerebrospinal fluid (CSF) was performed in participants with laboratory-confirmed primary HIV infection. PN was defined as ≥1 of the following unilateral or bilateral signs: decreased distal limb position, vibration, or temperature sense or hyporeflexia; symptomatic PN (SPN) was defined as the presence of these signs with symptoms. Analysis used nonparametric statistics.

RESULTS

Overall, 20 (35%) of 58 antiretroviral-naive male subjects without diabetes evaluated at a median of 107 days post HIV transmission met criteria for PN. Thirteen (65%) of 20 PN subjects met criteria for SPN; 6 (30%) of 20 had bilateral findings. PN subjects and no PN subjects (NPN) did not differ in median age, days post HIV transmission, blood CD4 or CD8 counts, CSF or plasma HIV RNA levels, CSF white blood cell counts, or CSF to blood albumin ratio. PN and SPN subjects had elevated CSF neopterin (P = 0.003 and P = 0.0005), CSF monocyte chemoattractant protein-1 (P = 0.006 and P = 0.01), and blood neopterin (P = 0.006 and P = 0.009) compared with NPN subjects. PN subjects had a higher percentage of activated phenotype CSF CD8 T lymphocytes than NPN subjects (P = 0.009).

CONCLUSIONS

Signs of PN were detected by detailed neurologic examination in 35% of men enrolled in a neurological study at a median of 3.5 months after HIV transmission. PN during this early period may be mediated by systemic and nervous system immune responses to HIV.

Attenuation of persistent pain-related behavior by fatty acid amide hydrolase (FAAH) inhibitors in a rat model of HIV sensory neuropathy

Distal sensory neuropathies are a hallmark of HIV infections and can result in persistent and disabling pain despite advances in antiretroviral therapies. HIV-sensory neuropathic (HIV-SN) pain may be amenable to cannabinoid treatment, but currently available agonist treatments are limited by untoward side effects and potential for abuse in this patient population. Fatty acid amide hydrolase (FAAH) inhibitors may offer an alternative approach by inhibiting the degradation of endocannabinoids with purportedly fewer untoward CNS side effects. In order to evaluate this potential approach in the management of HIV-SN pain, the recombinant HIV envelope protein gp120 was applied epineurally to the rat sciatic nerve to induce an HIV-SN-like pain syndrome. Two distinct FAAH inhibitory compounds, URB597 and PF-3845 were tested, and contrasted with standard antinociceptive gabapentin or vehicle treatment, for attenuation of tactile allodynia, cold allodynia, and mechanical hyperalgesia. Both FAAH inhibitors markedly reduced cold and tactile allodynia with limited anti-hyperalgesic effects. Peak antinociceptive effects produced by both agents were more modest than gabapentin in reducing tactile allodynia with similar potency ranges. URB597 produced comparable cold anti-allodynic effects to gabapentin, and the effects of both FAAH inhibitors were longer lasting than gabapentin. To assess the contribution of cannabinoid receptors in these antinociceptive effects, CB1 antagonist AM251 or CB2 antagonist SR144528 were tested in conjunction with FAAH inhibitors. Results suggested a contribution of both CB1- and CB2-mediated effects, particularly in reducing tactile allodynia. In summary, these findings support inhibition of endocannabinoid degradation as a promising target for management of disabling persistent HIV-SN pain syndromes.

Interleukin 10 mediated by herpes simplex virus vectors suppresses neuropathic pain induced by human immunodeficiency virus gp120 in rats

BACKGROUND

Human immunodeficiency virus (HIV)-associated sensory neuropathy is a common neurological complication of HIV infection affecting up to 30% of HIV-positive individuals. However, the exact neuropathological mechanisms remain unknown, which hinders our ability to develop effective treatments for HIV-related neuropathic pain (NP). In this study, we tested the hypothesis that inhibition of proinflammatory factors with overexpression of interleukin (IL)-10 reduces HIV-related NP in a rat model.

METHODS

NP was induced by the application of recombinant HIV-1 envelope protein gp120 into the sciatic nerve. The hindpaws of rats were inoculated with nonreplicating herpes simplex virus (HSV) vectors expressing anti-inflammatory cytokine IL-10 or control vector. Mechanical threshold was tested using von Frey filaments before and after treatments with the vectors. The mechanical threshold response was assessed over time using the area under curves. The expression of phosphorylated p38 mitogen-activated kinase, tumor necrosis factor-α, stromal cell-derived factor-1α, and C-X-C chemokine receptor type 4 in both the lumbar spinal cord and the L4/5 dorsal root ganglia (DRG), was examined at 14 and 28 days after vector inoculation using Western blots.

RESULTS

We found that in the gp120-induced NP model, IL-10 overexpression mediated by the HSV vector resulted in a significant elevation of the mechanical threshold that was apparent on day 3 after vector inoculation compared with the control vector (P < 0.001). The antiallodynic effect of the single HSV vector inoculation expressing IL-10 lasted >28 days. The area under curve in the HSV vector expressing IL-10 was increased compared with that in the control vector (P < 0.0001). HSV vectors expressing IL-10 reversed the upregulation of phosphorylated p38 mitogen-activated kinase, tumor necrosis factor-α, stromal cell-derived factor-1α, and C-X-C chemokine receptor type 4 expression at 14 and/or 28 days in the DRG and/or the spinal dorsal horn.

CONCLUSIONS

Our studies demonstrate that blocking the signaling of these proinflammatory molecules in the DRG and/or the spinal cord using the HSV vector expressing IL-10 is able to reduce HIV-related NP. These results provide new insights on the potential mechanisms of HIV-associated NP and a proof of concept for treating painful HIV sensory neuropathy with this type of gene therapy.