CLOSING THE GAP FOR PHARMACOLOGICAL TREATMENT OF PAINFUL DIABETIC NEUROPATHY : THE POTENTIAL ROLE OF VITAMIN D

Painful neuropathic pain is a challenging chronic pain to treat. It is heterogeneous in symptoms and could be resistant to the available treatments regimen. Current pharmacological treatments fail to achieve adequate pain relief in a most patients. The previous review showed that only less than 50% of patients can achieve good pain reduction with standard adjuvant treatment. The available adjuvants analgesic only focus in the symptom control, and do not interfere with the progressing damage of the nerve. Vit D insufficiency is quite frequent in type 2 diabetes patients.diabetes, particularly those with symptoms of DPN. The studies also showed that low serum vitamin D levels are an independent predictor of DPN development. Vitamin D supplementation is necessary for diabetic neuropathy patients since it promotes the synthesis of neurotrophins and neurotransmitters. Additional vitamin D therapy have big role in nerve growth factor and the regulation of neurotrophin and Ca2+ homeostasis in neurons, and provides protection for neurons in the peripheral nervous system. In this review, we do systematically search the studies about Vitamin D for the treatment of painful diabetic neuropathic condition. We used PubMed, Cochrane, Clinical Key, and search Google Scholar for papers that used vitamin D phrases. and painful diabetic neuropathy as our major database for this review and we make a systematic table to explain our review. However, there is still an unmet need in the management of neuropathic pain. The unmet needs maybe caused by the gap between pharmacological treatmnet in pain reduction in painful diabetic neuropathy patients. Therefore, in this review we discuss about the potential use of vitamin D as an add-on therapy to closing the gap in the management of neuropathic pain.

Dietary Omega-3 Polyunsaturated Fatty-Acid Supplementation Upregulates Protective Cellular Pathways in Patients with Type 2 Diabetes that reduces Painful Diabetic Neuropathy

Background: Omega-3 polyunsaturated fatty acids (PUFAs) are increasingly reported to improve chronic neuroinflammatory diseases in peripheral and central nervous systems. Specifically, docosahexaenoic acid (DHA) protects nerve cells from noxious stimuli in vitro and in vivo. Recent reports link PUFA supplementation to improving painful diabetic neuropathy (pDN) symptoms. However, the molecular mechanism behind omega-3 PUFAs ameliorating pDN symptoms is lacking. Therefore, we sought to determine the distinct cellular pathways that omega-3 PUFAs dietary supplementation promotes in reducing painful neuropathy in type 2 diabetes mellitus (DM2) patients. Methods: Forty volunteers diagnosed with type 2 diabetes were enrolled in the "En Balance-PLUS" diabetes education study. The volunteers participated in weekly lifestyle/nutrition education and daily supplementation with 1,000 mg DHA and 200 mg eicosapentaenoic acid. The Short-Form McGill Pain Questionnaire validated clinical determination of baseline and post-intervention pain complaints. Laboratory and untargeted metabolomics analyses were conducted using blood plasma collected at baseline and after three months of participation in the dietary regimen. The metabolomics data was analyzed using random forest, hierarchical cluster, ingenuity pathway analysis, and metabolic pathway mapping. Results: We found that metabolites involved in oxidative stress and glutathione production shifted significantly to a more anti-inflammatory state post supplementation. Example of these metabolites include cystathionine (+90%), S-methylmethionine (+9%), glycine cysteine-glutathione disulfide (+157%) cysteinylglycine (+19%), glutamate (-11%), glycine (+11%) and arginine (+13.4%). In addition, the levels of phospholipids associated with improved membrane fluidity such as linoleoyl-docosahexaenoyl-glycerol (18:2/22:6) (+253 %) were significantly increased. Ingenuity pathway analysis suggested several key bio functions associated with omega-3 PUFA supplementation such as formation of reactive oxygen species (p = 4.38 × 10-4, z-score = -1.96), peroxidation of lipids (p = 2.24 × 10-5, z-score = -1.944), Ca2+ transport (p = 1.55 × 10-4, z-score = -1.969), excitation of neurons (p = 1.07 ×10-4, z-score = -1.091), and concentration of glutathione (p = 3.06 × 10-4, z-score = 1.974). Conclusion: The reduction of pro-inflammatory and oxidative stress pathways following omega-3 PUFAS supplementation is consistent with using omega-3 PUFAs as a complementary dietary strategy as part of the overall treatment of painful diabetic neuropathy.

Neuromodulation in the Treatment of Painful Diabetic Neuropathy: A Review of Evidence for Spinal Cord Stimulation

Background: Neuropathies, the most common complication of diabetes, manifest in various forms, including entrapments, mononeuropathies or, most frequently, a distal symmetric polyneuropathy. Painful diabetic neuropathy (PDN) in the classic “stocking” distribution is a disease of increasing prevalence worldwide and a condition for which standard medical treatment only provides modest relief. Neuromodulation offers a potential alternative to pharmacotherapies given its demonstrated efficacy in other refractory chronic neuropathic pain syndromes. High-quality evidence from randomized controlled trials (RCTs) is available in these other settings for two approaches to spinal cord stimulation (SCS): (1) conventional low-frequency SCS (LF-SCS), which modulates axonal activity in the dorsal column and is paresthesia-dependent, and (2) high-frequency SCS delivered at 10 kilohertz (10 kHz SCS), which targets neurons in the superficial dorsal horn and is paresthesia-independent. Method: This review examines the evidence for SCS from published RCTs as well as prospective studies exploring the safety and effectiveness of treating PDN with neuromodulation. Results: Two RCTs enrolling 60 and 36 participants with PDN showed treatment with LF-SCS reduced daytime pain by 45% to 55% for up to two years. An RCT testing 10 kHz SCS versus conventional medical management (CMM) in 216 participants with PDN revealed 76% mean pain relief after six months of stimulation. None of the studies revealed unexpected safety issues in the use of neuromodulation in this patient population. Conclusion: These well-designed RCTs address the unmet need for improved PDN therapies and provide data on the safety, effectiveness, and durability of SCS therapy.

Contribution of TREM2 Signaling to the Development of Painful Diabetic Neuropathy by Mediating Microglial Polarization in Mice

Background: Painful diabetic neuropathy (PDN) is a common and intractable complication of diabetes mellitus, with little effective treatment. PDN has been associated with spinal neuroinflammation characterized by microglial activation. Recently, the triggering receptor expressed on myeloid cells 2 (TREM2), specifically localized on microglia, has been identified as a vital factor in modulating neuroinflammation and microglial phenotypes in neural diseases. Therefore, we hypothesized that spinal TREM2 might contribute to PDN and neuroinflammation by regulating microglial activity and phenotypes.Methods：Type I diabetes mellitus was elicited by a single intraperitoneal administration of streptozotocin (STZ) in mice. The pain behaviors were reflected by paw mechanical withdrawal thresholds (PMWT) and thermal withdrawal latency (PTWL). Results：We demonstrated that up-regulation of microglial TREM2 and amplification of both microglial M1 and M2 response was along with the presence of diabetes-related mechanical allodynia and thermal hypersensitivity. Moreover, we found that overexpression of TREM2 in microglia aggravated the symptom of PDN, amplified microglia M1 response, and suppressed microglia M2 polarization in the lumbar spinal cord of diabetic mice. However, inhibition of TREM2 with anti-TREM2 neutralizing antibodies attenuated mechanical allodynia and thermal hyperalgesia in diabetic mice. Besides, we identified Galectin-3 (GLT-3) as the potential ligand of the TREM2 receptor in facilitating the progression of PDN.Conclusions: TREM2 could be a critical microglial membrane molecule that modulates microglial phenotypes pain hypersensitivity in PDN. GLT-3 might act as a specific ligand to trigger TREM2 signaling in PDN or other neuropathic pain.