Deficiency of glucagon gene-derived peptides induces peripheral polyneuropathy in mice

Dipeptidyl Peptidase (DPP)-4 Inhibitors and Pituitary Adenylate Cyclase-Activating Polypeptide, a DPP-4 Substrate, Extend Neurite Outgrowth of Mouse Dorsal Root Ganglia Neurons: A Promising Approach in Diabetic Polyneuropathy Treatment

Individuals suffering from diabetic polyneuropathy (DPN) experience debilitating symptoms such as pain, paranesthesia, and sensory disturbances, prompting a quest for effective treatments. Dipeptidyl-peptidase (DPP)-4 inhibitors, recognized for their potential in ameliorating DPN, have sparked interest, yet the precise mechanism underlying their neurotrophic impact on the peripheral nerve system (PNS) remains elusive. Our study delves into the neurotrophic effects of DPP-4 inhibitors, including Diprotin A, linagliptin, and sitagliptin, alongside pituitary adenylate cyclase-activating polypeptide (PACAP), Neuropeptide Y (NPY), and Stromal cell-derived factor (SDF)-1a-known DPP-4 substrates with neurotrophic properties. Utilizing primary culture dorsal root ganglia (DRG) neurons, we meticulously evaluated neurite outgrowth in response to these agents. Remarkably, all DPP-4 inhibitors and PACAP demonstrated a significant elongation of neurite length in DRG neurons (PACAP 0.1 μM: 2221 ± 466 μm, control: 1379 ± 420, p < 0.0001), underscoring their potential in nerve regeneration. Conversely, NPY and SDF-1a failed to induce neurite elongation, accentuating the unique neurotrophic properties of DPP-4 inhibition and PACAP. Our findings suggest that the upregulation of PACAP, facilitated by DPP-4 inhibition, plays a pivotal role in promoting neurite elongation within the PNS, presenting a promising avenue for the development of novel DPN therapies with enhanced neurodegenerative capabilities.

Correlation between islet α cell function and peripheral neuropathy in patients with type 2 diabetes mellitus

BACKGROUND

This study explored the correlation between pancreatic islet α cell function, as reflected by the plasma glucagon levels, and Diabetic Peripheral Neuropathy (DPN) in patients with Type 2 Diabetes Mellitus (T2DM).

METHODS

A total of 358 patients with T2DM were retrospectively enrolled in this study and divided into the Non-DPN (NDPN) group (n = 220) and the DPN group (n = 138). All patients underwent an oral glucose tolerance test to detect levels of blood glucose, insulin and glucagon, and the Area Under the Curve (AUC) for Glucagon (AUCglu) was used to estimate the overall glucagon level. The Peripheral Nerve Conduction Velocity (PNCV), Amplitude (PNCA) and Latency (PNCL) were obtained with electromyography, and their Z scores were calculated.

RESULTS

There were significant differences regarding the age, disease duration, serum levels of alanine aminotransferase, aspartate aminotransferase, urea nitrogen, high-density lipoprotein, and 2h-C peptide between these two groups (p < 0.05). The NDPN group had higher glucagon levels at 30, 60 and 120 min and AUCglu (p < 0.05). The Z-scores of PNCV and PNCA showed an increasing trend (p < 0.05), while the Z-score of PNCL showed a decreasing trend (p < 0.05). The glucagon levels were positively correlated with PNCV and PNCA, but negatively correlated with PNCL, with Gluca30min having the strongest correlation (p < 0.05). Gluca30min was independently related to PNCV, PNCL, PNCA and DPN, respectively (p < 0.05). The function of pancreatic α islet cells, as reflected by the plasma glucagon level, is closely related to the occurrence of DPN in T2DM patients.

CONCLUSION

Gluca30min may be a potentially valuable independent predictor for the occurrence of DPN.

Adiponectin: A Promising Target for the Treatment of Diabetes and Its Complications

Diabetes mellitus, a chronic metabolic disorder characterized by hyperglycemia, presents a formidable global health challenge with its associated complications. Adiponectin, an adipocyte-derived hormone, has emerged as a significant player in glucose metabolism and insulin sensitivity. Beyond its metabolic effects, adiponectin exerts anti-inflammatory, anti-oxidative, and vasoprotective properties, making it an appealing therapeutic target for mitigating diabetic complications. The molecular mechanisms by which adiponectin impacts critical pathways implicated in diabetic nephropathy, retinopathy, neuropathy, and cardiovascular problems are thoroughly examined in this study. In addition, we explore possible treatment options for increasing adiponectin levels or improving its downstream signaling. The multifaceted protective roles of adiponectin in diabetic complications suggest its potential as a novel therapeutic avenue. However, further translational studies and clinical trials are warranted to fully harness the therapeutic potential of adiponectin in the management of diabetic complications. This review highlights adiponectin as a promising target for the treatment of diverse diabetic complications and encourages continued research in this pivotal area of diabetes therapeutics.

Stem Cell Therapy in Diabetic Polyneuropathy: Recent Advancements and Future Directions

Diabetic polyneuropathy (DPN) is the most frequent, although neglected, complication of long-term diabetes. Nearly 30% of hospitalized and 20% of community-dwelling patients with diabetes suffer from DPN; the incidence rate is approximately 2% annually. To date, there has been no curable therapy for DPN. Under these circumstances, cell therapy may be a vital candidate for the treatment of DPN. The epidemiology, classification, and treatment options for DPN are disclosed in the current review. Cell-based therapies using bone marrow-derived cells, embryonic stem cells, pluripotent stem cells, endothelial progenitor cells, mesenchymal stem cells, or dental pulp stem cells are our primary concern, which may be a useful treatment option to ease or to stop the progression of DPN. The importance of cryotherapies for treating DPN has been observed in several studies. These findings may help for the future researchers to establish more focused, accurate, effective, alternative, and safe therapy to reduce DPN. Cell-based therapy might be a permanent solution in the treatment and management of diabetes-induced neuropathy.

Thermal gradient ring reveals thermosensory changes in diabetic peripheral neuropathy in mice

Diabetic peripheral neuropathy (DPN) includes symptoms of thermosensory impairment, which are reported to involve changes in the expression or function, or both, of nociceptive TRPV1 and TRPA1 channels in rodents. In the present study, we did not find changes in the expression or function of TRPV1 or TRPA1 in DPN mice caused by STZ, although thermal hypoalgesia was observed in a murine model of DPN or TRPV1^−/− mice with a Plantar test, which specifically detects temperature avoidance. With a Thermal Gradient Ring in which mice can move freely in a temperature gradient, temperature preference can be analyzed, and we clearly discriminated the temperature-dependent phenotype between DPN and TRPV1^−/− mice. Accordingly, we propose approaches with multiple behavioral methods to analyze the progression of DPN by response to thermal stimuli. Attention to both thermal avoidance and preference may provide insight into the symptoms of DPN.

Glucagon Prevents Cytotoxicity Induced by Methylglyoxal in a Rat Neuronal Cell Line Model

Although diabetic polyneuropathy (DPN) is a frequent diabetic complication, no effective therapeutic approach has been established. Glucagon is a crucial hormone for glucose homeostasis but has pleiotropic effects, including neuroprotective effects in the central nervous system. However, the importance of glucagon in the peripheral nervous system (PNS) has not been clarified. Here, we hypothesized that glucagon might have a neuroprotective function in the PNS. The immortalized rat dorsal root ganglion (DRG) neuronal cell line 50B11 was treated with methylglyoxal (MG) to mimic an in vitro DPN model. The cells were cultured with or without glucagon or MG. Neurotoxicity, survival, apoptosis, neurite projection, cyclic adenosine monophosphate (cAMP), and protein kinase A (PKA) were examined. Glucagon had no cytotoxicity and rescued the cells from neurotoxicity. Cell survival was increased by glucagon. The ratio of apoptotic cells, which was increased by MG, was reduced by glucagon. Neurite outgrowth was accelerated in glucagon-treated cells. Cyclic AMP and PKA accumulated in the cells after glucagon stimulation. In conclusion, glucagon protected the DRG neuronal cells from MG-induced cellular stress. The cAMP/PKA pathway may have significant roles in those protective effects of glucagon. Glucagon may be a potential target for the treatment of DPN.