Distal Symmetric Polyneuropathy: A Review

Activation of TRPM2 and TRPV1 Channels in Dorsal Root Ganglion by NADPH Oxidase and Protein Kinase C Molecular Pathways: a Patch Clamp Study

Despite considerable research, the mechanisms of neuropathic pain induced by excessive oxidative stress production and overload calcium ion (Ca²⁺) entry in dorsal root ganglion (DRG) remain substantially unidentified. The transient receptor potential melastatin 2 (TRPM2) and vanilloid 1 (TRPV1) channels are activated with different stimuli including oxidative stress. TRPM2 and TRPV1 have been shown to be involved in induction of neuropathic pain. However, the activation mechanisms of TRPM2 and TRPV1 via NADPH oxidase and protein kinase C (PKC) pathways are poorly understood. In this study, I investigated the roles of NADPH oxidase and PKC on Ca²⁺ entry through TRPM2 and TRPV1 channels in in vitro DRG neurons of rats. Rat DRG neurons were used in whole-cell patch clamp experiments. The H₂O₂-induced TRPM2 current densities were decreased by N-(p-amylcinnamoyl)anthranilic acid (ACA), and dose-dependent capsaicin (CAP) and H₂O₂-induced TRPV1 currents were inhibited by capsazepine (CPZ). The TRPV1 channel is activated in the DRG neurons by 0.01 mM capsaicin but not 0.001 mM or 0.05 mM capsaicin. TRPM2 and TRPV1 currents were increased by the PKC activator, phorbol myristate acetate (PMA), although the currents were decreased by ACA, CPZ, and the PKC inhibitor, bisindolylmaleimide I (BIM). Both channel currents were further increased by PMA + H₂O₂ as compared to H₂O₂ only. In the combined presence of PMA + BIM, no TRPM2 or TRPV1 currents were observed. The CAP and H₂O₂-induced TRPM2 current densities were also decreased by the NADPH oxidase inhibitors apocynin and N-Acetylcysteine. In conclusion, these results demonstrate a protective role for NADPH oxidase and PKC inhibitors on Ca²⁺ entry through TRPM2 and TRPV1 channels in DRG neurons. Since excessive oxidative stress production and Ca²⁺ entry are implicated in the pathophysiology of neuropathic pain, the findings may be relevant to the etiology and treatment of neuropathology in DRG neurons.

Peripheral neuropathy in the hands of people with diabetes mellitus

AIMS

Peripheral sensorimotor neuropathy is a recognised complication of diabetes mellitus however little attention has been given to its development in the hands. The aim of this study was to determine the prevalence of sensory impairment in the hands of participants with diabetes, the agreement between two measurement tools for assessing sensation and the association between hand sensibility, age, glycaemic control and end-organ damage.

METHODS

A total of 162 participants were recruited and divided into two cohorts based on a diagnosis of diabetes. Participants were tested for the presence of hand neuropathy using Semmes-Weinstein monofilaments and the AsTex™. Medical records of participants with diabetes were accessed retrospectively to determine glycaemic control and diabetes complications.

RESULTS

A highly statistically significant association was found between neuropathy and diabetes status (P<0.001) on monofilament testing. The prevalence of neuropathy was 64% compared to ∼10% amongst participants without diabetes. Age, male gender and diabetic retinopathy were associated with neuropathy. The AsTex™ identified participants with diminished protective sensation on monofilament testing.

CONCLUSIONS

This study demonstrates a relationship between diabetes and upper limb neuropathy. Age, male gender and retinopathy were associated with diminished hand sensation. The AsTex™ may have a role as a screening tool for identifying clinically significant hand neuropathy.

Targeting the Diabetic Chaperome to Improve Peripheral Neuropathy

The chaperome constitutes a broad family of molecular chaperones and co-chaperones that facilitate the folding, refolding, and degradation of the proteome. Heat shock protein 90 (Hsp90) promotes the folding of numerous oncoproteins to aid survival of malignant phenotypes, and small molecule inhibitors of the Hsp90 chaperone complex offer a viable approach to treat certain cancers. One therapeutic attribute of this approach is the selectivity of these molecules to target high affinity oncogenic Hsp90 complexes present in tumor cells, which are absent in nontransformed cells. This selectivity has given rise to the idea that disease may contribute to forming a stress chaperome that is functionally distinct in its ability to interact with small molecule Hsp90 modulators. Consistent with this premise, modulating Hsp90 improves clinically relevant endpoints of diabetic peripheral neuropathy but has little impact in nondiabetic nerve. The concept of targeting the "diabetic chaperome" to treat diabetes and its complications is discussed.

Integrating cannabis into clinical cancer care

Cannabis species have been used as medicine for thousands of years; only since the 1940s has the plant not been widely available for medical use. However, an increasing number of jurisdictions are making it possible for patients to obtain the botanical for medicinal use. For the cancer patient, cannabis has a number of potential benefits, especially in the management of symptoms. Cannabis is useful in combatting anorexia, chemotherapy-induced nausea and vomiting, pain, insomnia, and depression. Cannabis might be less potent than other available antiemetics, but for some patients, it is the only agent that works, and it is the only antiemetic that also increases appetite. Inhaled cannabis is more effective than placebo in ameliorating peripheral neuropathy in a number of conditions, and it could prove useful in chemotherapy-induced neuropathy. A pharmacokinetic interaction study of vaporized cannabis in patients with chronic pain on stable doses of sustained-release opioids demonstrated no clinically significant change in plasma opiates, while suggesting the possibility of synergistic analgesia. Aside from symptom management, an increasing body of in vitro and animal-model studies supports a possible direct anticancer effect of cannabinoids by way of a number of different mechanisms involving apoptosis, angiogenesis, and inhibition of metastasis. Despite an absence of clinical trials, abundant anecdotal reports that describe patients having remarkable responses to cannabis as an anticancer agent, especially when taken as a high-potency orally ingested concentrate, are circulating. Human studies should be conducted to address critical questions related to the foregoing effects.

Assessment scales for the diagnosis of polyneuropathy

Epidemiological studies that investigate the occurrence and determinants of chronic length-dependent polyneuropathy are scarce. Population-based studies on polyneuropathy require a valid and reliable screening protocol with both good sensitivity and specificity. Several questionnaires and scoring scales have been developed for the detection of polyneuropathy, grading the severity of the disease, or evaluating the clinical course during follow-up. This review summarizes the aims and content of existing diagnostic polyneuropathy screening tools in order to help future studies decide which scale to use for screening in specific situations. We searched the PubMed database and identified 27 scales, 13 are based on symptoms alone, 8 on neurological signs alone, and 6 on a combination of symptoms and signs. Scales that combine questions concerning symptoms and a neurological examination with a focus on sensory alterations seem to have the best discriminatory power. However, all scoring scales were developed for and investigated in prespecified patient populations. Therefore, the generalizability of specific findings to the general population may be limited. We also discuss other limitations of existing scales. Future studies are required to determine which clinimetrically well-developed scales are preferred for use in population-based studies.

Impact of neuropathy on the adherence to diabetes-related self-care activities: a cross-sectional study

PURPOSE

The purpose of this study was to evaluate the impact of the presence and severity of neuropathy and depression on the patient's adherence to diabetes-related self-care activities (DRSCA) in a cohort of patients with type 2 diabetes mellitus (T2DM).

PATIENTS AND METHODS

In this cross-sectional, noninterventional study, 198 patients with T2DM were enrolled according to a population-based, consecutive-case enrollment principle. In all patients, the adherence to DRSCA was evaluated using the Summary of Diabetes Self-Care Activities (SDSCA) questionnaire; a higher SDSCA score is associated with a better adherence. The presence and severity of neuropathy was assessed using the Michigan Neuropathy Screening Instrument (MNSI) and the severity of depression using the Patient Health Questionnaire-9 (PHQ-9).

RESULTS

The presence of neuropathy was associated with a decreased SDSCA score (26 points vs 37 points; P<0.001), an increased severe depression prevalence (24.7% vs 4.3%; P<0.001), and an increased PHQ-9 score (12 points vs 7 points; P<0.001). The MNSI score was reverse correlated with SDSCA score (r=-0.527; P<0.001) and positively correlated with PHQ-9 score (r=0.495; P<0.001). The reverse correlation between MNSI score and SDSCA score was present for all the subcomponents of SDSCA questionnaire (diet, exercise, glycemic monitoring, and foot care).

CONCLUSION

The presence of neuropathy is associated with decreases in the quality of adherence to DRSCA in patients with T2DM and with increases in the symptomatology of depression. The significant, negative association between the severity of T2DM and the quality of disease self-management points to a possible loop-type relationship between these two components, being possible a reciprocal augmentation with negative consequences on the global management of the disease.