Decrease in neuroimmune activation by HSV-mediated gene transfer of TNFα soluble receptor alleviates pain in rats with diabetic neuropathy

Novel Therapies for the Treatment of Neuropathic Pain: Potential and Pitfalls

Neuropathic pain affects more than one million people across the globe. The quality of life of people suffering from neuropathic pain has been considerably declining due to the unavailability of appropriate therapeutics. Currently, available treatment options can only treat patients symptomatically, but they are associated with severe adverse side effects and the development of tolerance over prolonged use. In the past decade, researchers were able to gain a better understanding of the mechanisms involved in neuropathic pain; thus, continuous efforts are evident, aiming to develop novel interventions with better efficacy instead of symptomatic treatment. The current review discusses the latest interventional strategies used in the treatment and management of neuropathic pain. This review also provides insights into the present scenario of pain research, particularly various interventional techniques such as spinal cord stimulation, steroid injection, neural blockade, transcranial/epidural stimulation, deep brain stimulation, percutaneous electrical nerve stimulation, neuroablative procedures, opto/chemogenetics, gene therapy, etc. In a nutshell, most of the above techniques are at preclinical stage and facing difficulty in translation to clinical studies due to the non-availability of appropriate methodologies. Therefore, continuing research on these interventional strategies may help in the development of promising novel therapies that can improve the quality of life of patients suffering from neuropathic pain.

Redefining distal symmetrical polyneuropathy features in type 1 diabetes: a systematic review

Diabetic neuropathy is among the most frequent complications of both type 1 (T1DM) and type 2 diabetes (T2DM) and commonly manifests as a distal symmetrical polyneuropathy (DSPN). Despite evidence that T1DM- and T2DM-related DSPN are separate entities, most of our knowledge on diabetic DSPN derives from studies focused on type 2 diabetes. This systematic review provides an overview of current evidence on DSPN in T1DM, including its epidemiological, pathophysiological and clinical features, along with principal diagnostic tests findings. This review included 182 clinical and preclinical studies. The results indicate that DSPN is a less frequent complication in T1DM compared with T2DM and that distinctive pathophysiological mechanisms underlie T1DM-related DSPN development, with hyperglycemia as a major determinant. T1DM-related DSPN more frequently manifests with non-painful than painful symptoms, with lower neuropathic pain prevalence compared with T2DM-associated DSPN. The overt clinical picture seems characterized by a higher prevalence of large fiber-related clinical signs (e.g., ankle reflexes reduction and vibration hypoesthesia) and to a lesser extent small fiber damage (e.g., thermal or pinprick hypoesthesia). These findings as a whole suggest that large fibers impairment plays a dominant role in the clinical picture of symptomatic T1DM-related DSPN. Nevertheless, small fiber diagnostic testing shows high diagnostic accuracy in detecting early nerve damage and may be an appropriate diagnostic tool for disease monitoring and screening.

The role of dorsal root ganglia alpha-7 nicotinic acetylcholine receptor in complete Freund's adjuvant-induced chronic inflammatory pain

BACKGROUND

Alpha-7 nicotinic acetylcholine receptor (α7 nAChR) was reported to have a critical role in the regulation of pain sensitivity and neuroinflammation. However, the expression level of α7 nAChR in dorsal root ganglion (DRG) and the underlying neuroinflammatory mechanisms associated with hyperalgesia are still unknown.

METHODS

In the present study, the expression and mechanism of α7 nAChR in chronic inflammatory pain was investigated using a complete Freund's adjuvant (CFA)-induced chronic inflammatory pain model. Subsequently, a series of assays including immunohistochemistry, western blotting, and quantitative real-time polymerase chain reaction (qRT-PCR) were performed.

RESULTS

α7 nAChR was mostly colocalized with NeuN in DRG and upregulated after CFA injection. Microinjection of α7 nAChR siRNA into ipsilateral L4/5 DRGs aggravated the CFA-induced pain hypersensitivity. Intrathecal α7 nAChR agonist GTS-21 attenuated the development of CFA-induced mechanical and temperature-related pain hypersensitivities. In neuronal the SH-SY5Y cell line, the knockdown of α7 nAChRs triggered the upregulation of TRAF6 and NF-κB under CFA-induced inflammatory conditions, while agitation of α7 nAChR suppressed the TRAF6/NF-κB activation. α7 nAChR siRNA also exacerbated the secretion of pro-inflammatory mediators from LPS-induced SH-SY5Y cells. Conversely, α7 nAChR-specific agonist GTS-21 diminished the release of interleukin-1beta (IL-1β), IL-6, IL-8, and tumor necrosis factor-α (TNFα) in SH-SY5Y cells under inflammatory conditions. Mechanistically, the modulation of pain sensitivity and neuroinflammatory action of α7 nAChR may be mediated by the TRAF6/NF-κB signaling pathway.

CONCLUSIONS

The findings of this study suggest that α7 nAChR may be potentially utilized as a therapeutic target for therapeutics of chronic inflammatory pain.

The Modulatory Effect of Motor Cortex Astrocytes on Diabetic Neuropathic Pain

Diabetic neuropathic pain (DNP) is a common complication of diabetes characterized by persistent pain. Emerging evidence links astrocytes to mechanical nociceptive processing, and the motor cortex (MCx) is a cerebral cortex region that is known to play a key role in pain regulation. However, the association between MCx astrocytes and DNP pathogenesis remains largely unexplored. Here, we studied this association using designer receptors exclusively activated by designer drugs to specifically manipulate MCx astrocytes. We proved that the selective inhibition of MCx astrocytes reduced DNP in streptozocin (STZ)-induced DNP models and discovered a potential mechanism by which astrocytes release cytokines, including TNF-α and IL-1β, to increase neuronal activation in the MCx, thereby regulating pain. Together, these results demonstrate a pivotal role for MCx astrocytes in DNP pathogenesis and provide new insight into DNP treatment strategies.

Cutaneous Neuroimmune Interactions in Peripheral Neuropathic Pain States

Bidirectional interplay between the peripheral immune and nervous systems plays a crucial role in maintaining homeostasis and responding to noxious stimuli. This crosstalk is facilitated by a variety of cytokines, inflammatory mediators and neuropeptides. Dysregulation of this delicate physiological balance is implicated in the pathological mechanisms of various skin disorders and peripheral neuropathies. The skin is a highly complex biological structure within which peripheral sensory nerve terminals and immune cells colocalise. Herein, we provide an overview of the sensory innervation of the skin and immune cells resident to the skin. We discuss modulation of cutaneous immune response by sensory neurons and their mediators (e.g., nociceptor-derived neuropeptides), and sensory neuron regulation by cutaneous immune cells (e.g., nociceptor sensitization by immune-derived mediators). In particular, we discuss recent findings concerning neuroimmune communication in skin infections, psoriasis, allergic contact dermatitis and atopic dermatitis. We then summarize evidence of neuroimmune mechanisms in the skin in the context of peripheral neuropathic pain states, including chemotherapy-induced peripheral neuropathy, diabetic polyneuropathy, post-herpetic neuralgia, HIV-induced neuropathy, as well as entrapment and traumatic neuropathies. Finally, we highlight the future promise of emerging therapies associated with skin neuroimmune crosstalk in neuropathic pain.

Roles of tumor necrosis factor-α and interleukin-6 in regulating bone cancer pain via TRPA1 signal pathway and beneficial effects of inhibition of neuro-inflammation and TRPA1

Background

Pain is one of the most common and distressing symptoms suffered by patients with progression of bone cancer; however, the mechanisms responsible for hyperalgesia are not well understood. The purpose of our current study was to determine contributions of the sensory signaling pathways of inflammatory tumor necrosis factor-α and interleukin-6 and downstream transient receptor potential ankyrin 1 (TRPA1) to neuropathic pain induced by bone cancer. We further determined whether influencing these pathways can improve bone cancer pain.

Methods

Breast sarcocarcinoma Walker 256 cells were implanted into the tibia bone cavity of rats to induce mechanical and thermal hyperalgesia. ELISA and western blot analysis were used to examine (1) the levels of tumor necrosis factor-α and interleukin-6 in dorsal root ganglion and (2) protein expression of tumor necrosis factor-α and interleukin-6 receptors (TNFR1 and IL-6R) and TRPA1 as well as intracellular signals (p38-MAPK and JNK).

Results

Tumor necrosis factor-α and interleukin-6 were elevated in the dorsal root ganglion of bone cancer rats, and expression of TNFR1, IL-6R, and TRPA1 was upregulated. In addition, inhibition of TNFR1 and IL-6R alleviated mechanical and thermal hyperalgesia in bone cancer rats, accompanied with downregulated TRPA1 and p38-MAPK and JNK.

Conclusions

We revealed specific signaling pathways leading to neuropathic pain during the development of bone cancer, including tumor necrosis factor-α-TRPA1 and interleukin-6-TRPA1 signal pathways. Overall, our data suggest that blocking these signals is beneficial to alleviate bone cancer pain.

Protein Kinase A Is Involved in Neuropathic Pain by Activating the p38MAPK Pathway to Mediate Spinal Cord Cell Apoptosis

Neuropathic pain is a serious clinical problem to be solved. This study is aimed at investigating protein kinase A (PKA) expression in neuropathic pain and its possible mechanisms of involvement. A neuropathic pain-related gene expression dataset was downloaded from Gene Expression Omnibus, and differentially expressed genes were screened using the R software. cytoHubba was used to screen for hub genes. A spared nerve injury (SNI) rat model was established, and the paw withdrawal threshold was determined using von Frey filaments. Western blotting and immunofluorescence were used to detect the expression and cellular localization, respectively, of key proteins in the spinal cord. Western blot, ELISA, and TUNEL assays were used to detect cell signal transduction, inflammation, and apoptosis, respectively. Pka was identified as a key gene involved in neuropathic pain. After SNI, mechanical allodynia occurred, PKA expression in the spinal cord increased, the p38MAPK pathway was activated, and spinal cord inflammation and apoptosis occurred in rats. PKA colocalized with neurons, astrocytes, and microglia, and apoptotic cells were mainly neurons. Intrathecal injection of a PKA inhibitor not only relieved mechanical hyperalgesia, inflammatory reaction, and apoptosis in SNI rats but also inhibited p38MAPK pathway activation. However, intrathecal injection of a p38MAPK inhibitor attenuated mechanical hyperalgesia, inflammation, and apoptosis, but did not affect PKA expression. In conclusion, PKA is involved in neuropathic pain by activating the p38MAPK pathway to mediate spinal cord cell apoptosis.

TNF-α mediated upregulation of NaV1.7 currents in rat dorsal root ganglion neurons is independent of CRMP2 SUMOylation

Clinical and preclinical studies have shown that patients with Diabetic Neuropathy Pain (DNP) present with increased tumor necrosis factor alpha (TNF-α) serum concentration, whereas studies with diabetic animals have shown that TNF-α induces an increase in Na_V1.7 sodium channel expression. This is expected to result in sensitization of nociceptor neuron terminals, and therefore the development of DNP. For further study of this mechanism, dissociated dorsal root ganglion (DRG) neurons were exposed to TNF-α for 6 h, at a concentration equivalent to that measured in STZ-induced diabetic rats that developed hyperalgesia. Tetrodotoxin sensitive (TTXs), resistant (TTXr) and total sodium current was studied in these DRG neurons. Total sodium current was also studied in DRG neurons expressing the collapsin response mediator protein 2 (CRMP2) SUMO-incompetent mutant protein (CRMP2-K374A), which causes a significant reduction in Na_V1.7 membrane cell expression levels. Our results show that TNF-α exposure increased the density of the total, TTXs and TTXr sodium current in DRG neurons. Furthermore, TNF-α shifted the steady state activation and inactivation curves of the total and TTXs sodium current. DRG neurons expressing the CRMP2-K374A mutant also exhibited total sodium current increases after exposure to TNF-α, indicating that these effects were independent of SUMOylation of CRMP2. In conclusion, TNF-α sensitizes DRG neurons via augmentation of whole cell sodium current. This may underlie the pronociceptive effects of TNF-α and suggests a molecular mechanism responsible for pain hypersensitivity in diabetic neuropathy patients.

Cytokines in Pain: Harnessing Endogenous Anti-Inflammatory Signaling for Improved Pain Management

Current pain therapeutics offer inadequate relief to patients with chronic pain. A growing literature supports that pro-inflammatory cytokine signaling between immune, glial, and neural cells is integral to the development of pathological pain. Modulation of these communications may hold the key to improved pain management. In this review we first offer an overview of the relationships between pro-inflammatory cytokine and chemokine signaling and pathological pain, with a focus on the actions of cytokines and chemokines in communication between glia (astrocytes and microglia), immune cells (macrophages and T cells), and neurons. These interactions will be discussed in relation to both peripheral and central nervous system locations. Several novel non-neuronal drug targets for controlling pain are emerging as highly promising, including non-viral IL-10 gene therapy, which offer the potential for substantial pain relief through localized modulation of targeted cytokine pathways. Preclinical investigation of the mechanisms underlying the success of IL-10 gene therapy revealed the unexpected discovery of the powerful anti-nociceptive anti-inflammatory properties of D-mannose, an adjuvant in the non-viral gene therapeutic formulation. This review will include gene therapeutic approaches showing the most promise in controlling pro-inflammatory signaling via increased expression of anti-inflammatory cytokines like interleukin-10 (IL-10) or IL-4, or by directly limiting the bioavailability of specific pro-inflammatory cytokines, as with tumor necrosis factor (TNF) by the TNF soluble receptor (TNFSR). Approaches that increase endogenous anti-inflammatory signaling may offer additional opportunities for pain therapeutic development in patients not candidates for gene therapy. Promising novel avenues discussed here include the disruption of lymphocyte function-associated antigen (LFA-1) activity, antagonism at the cannabinoid 2 receptor (CB2R), and toll-like receptor 4 (TLR4) antagonism. Given the partial efficacy of current drugs, new strategies to manipulate neuroimmune and cytokine interactions hold considerable promise.

The rapidly evolving state of gene therapy

Gene therapy is emerging as a viable option for clinical therapy of monogenic disorders and other genetically defined diseases, with approved gene therapies available in Europe and newly approved gene therapies in the United States. In the past 10 years, gene therapy has moved from a distant possibility, even in the minds of much of the scientific community, to being widely realized as a valuable therapeutic tool with wide-ranging potential. The U.S. Food and Drug Administration has recently approved Luxturna (Spark Therapeutics Inc, Philadelphia, PA, USA), a recombinant adeno-associated virus (rAAV) 2 gene therapy for one type of Leber congenital amaurosis 2 ( 1 , 2 ). The European Medicines Agency (EMA) has approved 3 recombinant viral vector products: Glybera (UniQure, Amsterdam, The Netherlands), an rAAV vector for lipoprotein lipase deficiency; Strimvelis (Glaxo Smith-Kline, Brentford, United Kingdom), an ex vivo gammaretrovirus-based therapy for patients with adenosine deaminase-deficient severe combined immune deficiency (ADA-SCID); and Kymriah (Novartis, Basel, Switzerland), an ex vivo lentivirus-based therapy to engineer autologous chimeric antigen-receptor T (CAR-T) cells targeting CD19-positive cells in acute lymphoblastic leukemia. These examples will be followed by the clinical approval of other gene therapy products as this field matures. In this review we provide an overview of the state of gene therapy by discussing where the field stands with respect to the different gene therapy vector platforms and the types of therapies that are available.-Gruntman, A. M., Flotte, T. R. The rapidly evolving state of gene therapy.

TNF-α and sTNF-RII Are Associated with Pain Following Hip Fracture Surgery in Older Adults

Objective

To explore whether plasma inflammatory mediators on postoperative day 3 (POD3) are associated with pain scores in older adults after hip fracture surgery.

Design

Cross-sectional study.

Setting

Mount Sinai Hospital, New York, New York.

Subjects

Forty patients age 60 years or older who presented with acute hip fracture at Mount Sinai Hospital between November 2011 and April 2013.

Methods

Plasma levels of six inflammatory mediators of the nuclear factor kappa B pathway were measured using blood collected on POD3. Self-reported pain scores (i.e., pain with resting, walking, and transferring) were assessed at baseline (prefracture) and on POD3. Linear regression models using log-transformed data were performed to determine associations between inflammatory mediators and postoperative pain.

Results

Interleukin 18 (IL-18) was positively associated with POD3 resting pain score in the unadjusted model (β = 0.66, P = 0.03). Tumor necrosis factor α (TNF-α) and soluble TNF receptor II (sTNF-RII) were positively associated with POD3 resting pain score in the adjusted model (β = 0.99, P = 0.03, and β = 0.86, P = 0.04, respectively). Moreover, TNF-α was positively associated with POD3 walking pain score in the adjusted model (β = 1.59, P = 0.05). Pain with transferring was not associated with these inflammatory mediators.

Conclusions

These findings suggest that TNF-α and its receptors may influence pain following hip fracture. Further study of the TNF-α pathway may inform future clinical applications that monitor and treat pain in the vulnerable elderly who are unable to accurately report pain.

Immune System Involvement in Specific Pain Conditions

Chronic pain is a significant problem worldwide and is the most common disability in the United States. It is well known that the immune system plays a critical role in the development and maintenance of many chronic pain conditions. The involvement of the immune system can be through the release of autoantibodies, in the case of rheumatoid arthritis, or via cytokines, chemokines, and other inflammatory mediators (i.e. substance P, histamine, bradykinin, tumor necrosis factor, interleukins, and prostaglandins). Immune cells, such as T cells, B cells and their antibodies, and microglia are clearly key players in immune-related pain. The purpose of this review is to briefly discuss the immune system involvement in pain and to outline how it relates to rheumatoid arthritis, osteoarthritis, fibromyalgia, complex regional pain syndrome, multiple sclerosis, and diabetic neuropathy. The immune system plays a major role in many debilitating chronic pain conditions and we believe that animal models of disease and their treatments should be more directly focused on these interactions.

Activation of spinal dorsal horn P2Y13 receptors can promote the expression of IL-1β and IL-6 in rats with diabetic neuropathic pain

Objective

The dorsal horn P2Y₁₃ receptor is involved in the development of pain behavior induced by peripheral nerve injury. It is unclear whether the expression of proinflammatory cytokines interleukin (IL)-1β and IL-6 at the spinal dorsal horn are influenced after the activation of P2Y₁₃ receptor in rats with diabetic neuropathic pain (DNP).

Methods

A rat model of type 1 DNP was induced by intraperitoneal injection of streptozotocin (STZ). We examined the expression of P2Y₁₃ receptor, Iba-1, IL-1β, IL-6, JAK2, STAT3, pTyr₁₃₃₆, and pTyr₁₄₇₂ NR2B in rat spinal dorsal horn.

Results

Compared with normal rats, STZ-diabetic rats displayed obvious mechanical allodynia and the increased expression of P2Y₁₃ receptor, Iba-1, IL-1β, and IL-6 in the dorsal spinal cord that was continued for 6 weeks in DNP rats. The data obtained indicated that, in DNP rats, administration of MRS2211 significantly attenuated mechanical allodynia. Compared with DNP rats, after MRS2211 treatment, expression of the P2Y₁₃ receptor, Iba-1, IL-1β, and IL-6 were reduced 4 weeks after the STZ injection. However, MRS2211 treatment did not attenuate the expression of the P2Y₁₃ receptor, Iba-1, IL-1β, and IL-6 at 6 weeks after the STZ injection. MRS2211 suppressed JAK2 and STAT3 expression in the early stage, but not in the later stage. Moreover, pTyr₁₃₃₆ NR2B was significantly decreased, whereas pTyr₁₄₇₂ NR2B was unaffected in the dorsal spinal cord of MRS2211-treated DNP rats.

Conclusion

Intrathecal MRS2211 produces an anti-nociceptive effect in early-stage DNP. A possible mechanism involved in MRS2211-induced analgesia is that blocking the P2Y₁₃ receptor downregulates levels of IL-1β and IL-6, which subsequently inhibit the activation of the JAK2/STAT3 signaling pathway. Furthermore, blocking the activation of the P2Y₁₃ receptor can decrease NR2B-containing NMDAR phosphorylation in dorsal spinal cord neurons, thereby attenuating central sensitization in STZ-induced DNP rats.

Activation of ephrinB-EphB receptor signalling in rat spinal cord contributes to maintenance of diabetic neuropathic pain

BACKGROUND

Diabetic neuropathic pain (DNP) is severe and intractable in clinic. The specific cellular and molecular mechanisms underlying DNP remain elusive and its treatment are limited. We investigated roles of EphB1 receptor in the development of DNP.

METHODS

Diabetic neuropathic pain was produced in male, adult, Sprague-Dawley rats by a single i.p. streptozotocin (STZ) or alloxan. Western blot analysis and immunohistochemistry were used to analyse expression of EphB1 receptor as well as the activation of the glial cells and the pro-inflammatory cytokines in the spinal cord. DNP manifested as mechanical allodynia, which was determined by measuring incidence of foot withdrawal in response to mechanical indentation of the hind paw by an electro von Frey filament.

RESULTS

Diabetic neuropathic pain and high blood glucose were exhibited simultaneously in around 70% of animals that received i.p. STZ or alloxan. Phosphorylation of EphB1, activation of the astrocytes and microglial cells, and level of tumour necrosis factor (TNF)-α and interleukin (IL)-1β in the spinal cord were significantly increased in rats with DNP. Spinal blocking EphB1 receptor activation in the late phase after STZ injection significantly suppressed the established mechanical allodynia as well as activation of the astrocytes and microglial cells and activity of TNF-α and IL-1β. However, spinal treatment of EphB1-Fc in the early phase after STZ injection did not prevent the induction of DNP.

CONCLUSIONS

EphB1 receptor activation in the spinal cord is critical to the maintenance, but not induction of diabetic pain. EphB1 receptor may be a potential target for relieving the established diabetic pain.

SIGNIFICANCE

Activation of EphB1 receptor in the spinal cord is critical to maintaining the established diabetic neuropathic pain, but not to diabetic pain induction. Spinal blocking EphB1 receptor activation suppresses ongoing diabetic neuropathic pain.

Viral vector mediated continuous expression of interleukin-10 in DRG alleviates pain in type 1 diabetic animals

Painful diabetic neuropathy is a common and difficult to treat complication of diabetes. A growing body of evidence implicates the role of inflammatory mediators in the damage to the peripheral axons and in the pathogenesis of neuropathic pain. Increased expression of pro-inflammatory cytokines such as interleukin (IL)-1β and tumor necrosis factor (TNF)-α in the peripheral nervous system suggests the possibility of change in pain perception in diabetes. In this study we investigated that continuous delivery of IL10 in the nerve fibers achieved by HSV vector mediated transduction of dorsal root ganglion (DRG) in animals with Type 1 diabetes, blocks the nociceptive and stress responses in the DRG neurons by reducing IL1β expression along with inhibition of phosphorylation of p38 MAPK (mitogen-activated protein kinase) and protein kinase C (PKC). The continuous expression of IL10 also alters Toll like receptor (TLR)-4 expression in the DRG with increased expression of heat shock protein (HSP)-70 in conjunction with the reduction of pain. Taken together, this study suggests that macrophage activation in the peripheral nervous system may be involved in the pathogenesis of pain in Type 1 diabetes and therapeutic benefits of HSV mediated local expression of IL10 in the DRG with the reduction of a number of proinflammatory cytokines, subsequently inhibits the development of painful neuropathy along with a decrease in stress associated markers in the DRG. This basic and preclinical study provides an important evidence for a novel treatment strategy that could lead to a clinical trial for what is currently a treatment resistant complication of diabetes.

Modulating Molecular Chaperones Improves Mitochondrial Bioenergetics and Decreases the Inflammatory Transcriptome in Diabetic Sensory Neurons

We have previously demonstrated that modulating molecular chaperones with KU-32, a novobiocin derivative, ameliorates physiologic and bioenergetic deficits of diabetic peripheral neuropathy (DPN). Replacing the coumarin core of KU-32 with a meta-fluorinated biphenyl ring system created KU-596, a novobiocin analogue (novologue) that showed neuroprotective activity in a cell-based assay. The current study sought to determine whether KU-596 offers similar therapeutic potential for treating DPN. Administration of 2-20 mg/kg of KU-596 improved diabetes induced hypoalgesia and sensory neuron bioenergetic deficits in a dose-dependent manner. However, the drug could not improve these neuropathic deficits in diabetic heat shock protein 70 knockout (Hsp70 KO) mice. To gain further insight into the mechanisms by which KU-596 improved DPN, we performed transcriptomic analysis of sensory neuron RNA obtained from diabetic wild-type and Hsp70 KO mice using RNA sequencing. Bioinformatic analysis of the differentially expressed genes indicated that diabetes strongly increased inflammatory pathways and that KU-596 therapy effectively reversed these increases independent of Hsp70. In contrast, the effects of KU-596 on decreasing the expression of genes regulating the production of reactive oxygen species were more Hsp70-dependent. These data indicate that modulation of molecular chaperones by novologue therapy offers an effective approach toward correcting nerve dysfunction in DPN but that normalization of inflammatory pathways alone by novologue therapy seems to be insufficient to reverse sensory deficits associated with insensate DPN.

Current gene therapy using viral vectors for chronic pain

The complexity of chronic pain and the challenges of pharmacotherapy highlight the importance of development of new approaches to pain management. Gene therapy approaches may be complementary to pharmacotherapy for several advantages. Gene therapy strategies may target specific chronic pain mechanisms in a tissue-specific manner. The present collection of articles features distinct gene therapy approaches targeting specific mechanisms identified as important in the specific pain conditions. Dr. Fairbanks group describes commonly used gene therapeutics (herpes simplex viral vector (HSV) and adeno-associated viral vector (AAV)), and addresses biodistribution and potential neurotoxicity in pre-clinical models of vector delivery. Dr. Tao group addresses that downregulation of a voltage-gated potassium channel (Kv1.2) contributes to the maintenance of neuropathic pain. Alleviation of chronic pain through restoring Kv1.2 expression in sensory neurons is presented in this review. Drs Goins and Kinchington group describes a strategy to use the replication defective HSV vector to deliver two different gene products (enkephalin and TNF soluble receptor) for the treatment of post-herpetic neuralgia. Dr. Hao group addresses the observation that the pro-inflammatory cytokines are an important shared mechanism underlying both neuropathic pain and the development of opioid analgesic tolerance and withdrawal. The use of gene therapy strategies to enhance expression of the anti-pro-inflammatory cytokines is summarized. Development of multiple gene therapy strategies may have the benefit of targeting specific pathologies associated with distinct chronic pain conditions (by Guest Editors, Drs. C. Fairbanks and S. Hao).

ARA 290, a nonerythropoietic peptide engineered from erythropoietin, improves metabolic control and neuropathic symptoms in patients with type 2 diabetes

Although erythropoietin ameliorates experimental type 2 diabetes with neuropathy, serious side effects limit its potential clinical use. ARA 290, a nonhematopoietic peptide designed from the structure of erythropoietin, interacts selectively with the innate repair receptor that mediates tissue protection. ARA 290 has shown efficacy in preclinical and clinical studies of metabolic control and neuropathy. To evaluate the potential activity of ARA 290 in type 2 diabetes and painful neuropathy, subjects were enrolled in this phase 2 study. ARA 290 (4 mg) or placebo were self-administered subcutaneously daily for 28 d and the subjects followed for an additional month without further treatment. No potential safety issues were identified. Subjects receiving ARA 290 exhibited an improvement in hemoglobin A(1c) (Hb A(1c)) and lipid profiles throughout the 56 d observation period. Neuropathic symptoms as assessed by the PainDetect questionnaire improved significantly in the ARA 290 group. Mean corneal nerve fiber density (CNFD) was reduced significantly compared with normal controls and subjects with a mean CNFD >1 standard deviation from normal showed a significant increase in CNFD compared with no change in the placebo group. These observations suggest that ARA 290 may benefit both metabolic control and neuropathy in subjects with type 2 diabetes and deserves continued clinical evaluation.