Preparation, characterization, and pharmacological application of oral Honokiol-loaded solid lipid nanoparticles for diabetic neuropathy

Honokiol is a phytochemical component with a variety of pharmacological properties. However, the major limitation of Honokiol is its poor solubility and low oral bioavailability. In this study, we formulated and characterized oral Honokiol-loaded solid lipid nanoparticles (SLNs) to enhance bioavailability and then evaluated their effectiveness in experimental diabetic neuropathy (DN). The finalized formulation has a spherical morphology, a particle size (PS) of 121.31 ± 9.051 nm, a polydispersity index (PDI) of 0.249 ± 0.002, a zeta potential (ZP) of -20.8 ± 2.72 mV, and an entrapment efficiency (% EE) of 88.66 ± 2.30 %. In-vitro release data shows, Honokiol-SLNs displayed a sustained release profile at pH (7.4). The oral bioavailability of Honokiol-SLNs was remarkably greater (8-fold) than Honokiol-Pure suspension. The neuroprotective property of Honokiol-SLNs was initially demonstrated against hydrogen peroxide H2O2-stimulated PC12 (pheochromocytoma) cells. Furthermore, results of in-vivo studies demonstrated that treatment with Honokiol-SLNs significantly (p < 0.001) suppressed oxidative stress by inhibition of nuclear factor kappa B (NF-κB) and significant (p < 0.001) upregulation of nuclear factor-erythroid 2-related factor 2 (Nrf2) signaling in the spinal cord. The expression of transient receptor potential melastatin 8(TRPM8) and transient receptor potential vanilloid 1 (TRPV1) was significantly (p < 0.001) downregulated. Honokiol-SLNs inhibited apoptosis by significant (p < 0.001) downregulation of cleaved caspase-3 expression in the spinal cord. These findings demonstrate that Honokiol-SLNs providedbetter neuroprotection in DN because of higher oral bioavailability.

Neuroprotective effects of Bauhinia variegata in ameliorating diabetic neuropathy and neurodegeneration

INTRODUCTION

In diabetic neuropathy with neurodegeneration (DNN), a serious diabetes consequence, extreme hyperglycemia destroys neurons in the brain and limbs. The main therapies for this condition are glucose control and pain management. Phytopharmacology is thought to be more successful in addressing the pain and blood sugar management issues associated with DNN. The objective of this study was to investigate how Bauhinia variegata (BV) could offer protection against streptozotocin (STZ)-induced diabetic neuropathy.

METHODOLOGY

STZ-associated DNN was induced in rats, and these diabetic rats were treated with BV at 200 mg/kg and 400 mg/kg doses for 28 days. Blood glucose (BG), serum nitrite, lipid peroxidation, antioxidants, C-reactive protein, behavioral, and histopathological parameters were assessed.

RESULTS

BV dramatically reduced BG and HbA1c levels in diabetic rats, according to the findings. The levels of superoxide dismutase and catalase both rose significantly. Both lipid peroxidation and serum nitrite levels were drastically decreased with BV treatment. In this study, it was found that BV has anti-hyperglycemic and anti-inflammatory effects on DNN. This was shown by a significant drop in C-reactive protein in diabetic rats, which was a key factor in diabetic neuropathy. Thermal hyperalgesia was significantly alleviated after BV therapy, and diabetic rats' pain thresholds improved.

CONCLUSION

Present study concluded that BV treatment has excellent glycemic control, a high antioxidant status, and relevant pain-relieving potential in diabetic neuropathy with neurodegeneration by reversing thermal hyperalgesia and decreasing hypeglycemia in diabetic rats.

Addition of adipose tissue-derived mesenchymal stem cells improves empagliflozin therapy for alleviating hyperglycemia--induced neuropathy

BACKGROUND

We examined the impact of adipose-derived mesenchymal stem cell (ADMSC)-facilitated empagliflozin (EMPA) therapy for alleviating hyperglycemic induced neuropathy [i.e., diabetic neuropathy (DN)].

METHODS

Study constituted N2a cell culture and rats to be classified into groups 1 (sham-operated-control)/2 (DN)/3 (DN + empagliflozin/20 mg/kg/daily orally for 6 weeks since post-day-7 DN induction)/4 (DN + ADMSCs/1.2 × 106 cells by vein transfusion at time intervals of 1/3/5 weeks after DN induction)/5 (DN + empagliflozin + ADMSCs) and sacrificed by day-42 after DN induction.

RESULTS

In vitro results showed that, compared to N2a cells, the cellular levels of senescence/DNA-damage and protein expressions of oxidative-stress (OS), apoptotic, autophagic and inflammatory biomarkers were significantly higher in N2a + glucose (25 mM) but were significantly reversed in N2a + glucose + ADMSCs, whereas the cellular levels of mitochondrial cytochrome C and protein levels of anti-oxidants displayed an opposite pattern of OS (all P<0.001). The above-mentioned parameters (i.e., OS/apoptosis/fibrosis/autophagy/DNA-damage) were lowest in N2a cells, highest in N2a + glucose and significantly higher in N2a + glucose + EMPA (50 μM) than in N2a + glucose + EMPA (150 μM) (all P<0.001). By days 7/14/21/28/35/42 after DN induction, the values of thermal paw-withdrawal-latency (TPWL)/mechanical-paw-withdrawal-threshold were highest in group 1 and significantly progressively increased from groups 2/4/3/5 (all P<0.0001). The cellular levels of unmyelinated C- and myelinated A-δ fibers, and protein levels of OS/apoptotic/DNA-damaged/fibrotic/autophagic/inflammatory/pain-facilitated/voltage-gated sodium channel biomarkers in L4-L5 levels of dorsal-root-ganglia exhibited an contradictory manner of TPWL among the groups (all P<0.0001).

CONCLUSIONS

Combination of EMPA and ADMSC therapy was superior to either alone for improving outcomes of DN.

Effect of joint limitation and balance control on gait changes in diabetic peripheral neuropathy

Aims

This study analyzed the gait patterns of diabetic peripheral neuropathy (DPN) patients and changes in the center of mass sway to prevent the formation and recurrence of foot ulcers.

Methods

Forty-two subjects were divided into the diabetes mellitus (DM), DPN, and diabetic foot ulcer (DFU) groups. We measured the range of motion (ROM) of the lower limb joints in the resting position and the center of mass sway in the standing position. Joint angles, ROM during walking, and distance factors were evaluated.

Results

In the DFU group, ROM limitation during walking was detected at the knee joint, and functional and ROM limitations were found at the ankle joint. The step length ratio and step width in the DFU group were significantly lower and higher than those in the DM group, respectively. The sway distances in the DFU group were greater than those in the DM and DPN groups.

Conclusions

Functional joint limitations and gait changes due to the decreased ability to maintain the center of gravity were observed in the DFU group. As DPN progressed, the patients' gait became small, wide, and shuffled. Thus, supporting joint movement during walking may help reduce the incidence and recurrence of foot ulcers.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13340-023-00647-9.

Swimming exercise attenuates mechanical hypersensitivity and mitigates peripheral nerve degeneration in rats with painful diabetic neuropathy (PDN)

BACKGROUND

This study aimed to assess the effectiveness of swimming exercise in alleviating mechanical hypersensitivity and peripheral nerve degeneration associated with a pre-clinical model of painful diabetic neuropathy (PDN).

METHODS

This study is a pre-clinical study conducted using the streptozocin (STZ)-induced PDN rat model. Rats were randomly allocated to three groups: a vehicle group of non-diabetic rats (Vehicle, n = 9), a group of rats with PDN (PDN, n = 8), and a group of rats with PDN that performed a swimming exercise program (PDN-SW, n = 10). The swimming exercise program included daily 30-minute swimming exercise, 5 days per week for 4 weeks. Von Frey testing was used to monitor hindpaw mechanical sensitivity over 4 weeks. Assessment of cutaneous peripheral nerve fiber integrity was performed after the 4-week study period via immunohistochemistry for protein gene product 9.5-positive (PGP9.5+) intra-epidermal nerve fiber density (IENFD) in hind-paw skin biopsies by a blinded investigator.

RESULTS

The results showed that swimming exercise mitigated but did not fully reverse mechanical hypersensitivity in rats with PDN. Immunohistochemical testing revealed that the rats in the PDN-SW group retained higher PGP9.5+ IENFD compared to the PDN group but did not reach normal levels of the Vehicle group.

CONCLUSIONS

The results of this study indicate that swimming exercise can mitigate mechanical hypersensitivity and degeneration of peripheral nerve fibers in rats with experimental PDN.

Diabetic neuropathy results in vasomotor dysfunction of medium sized peripheral arteries

BACKGROUND

The effect of the sympathetic nervous system on peripheral arteries causes vasoconstriction when smooth muscle cells in the walls of blood vessels contract, which leads to narrowing of arteries and reduction of the blood flow.

AIM

To compare sympathetic vasomotor activation of the brachial arteries in healthy subjects and patients with painful diabetic neuropathy; and therefore, to assess whether there is significant vasomotor dysfunction of medium sized arteries in diabetic neuropathy.

METHODS

The study included 41 diabetic neuropathy patients and 41 healthy controls. Baseline diameter and flow rate of the brachial arteries were measured. Then, using a bipolar stimulus electrode, a 10 mA, 1 Hz electrical stimulus was administered to the median nerve at the wrist level for 5 s. The brachial artery diameter and blood flow rate were re-measured after stimulation.

RESULTS

In the control group, the median flow rate was 70.0 mL/min prior to stimulation and 35.0 mL/min after stimulation, with a statistically significant decrease (P < 0.001), which is consistent with sympathetic nervous system functioning (vasoconstriction). In the diabetic neuropathy group, median flow rate before the stimulation was 35.0 mL/min. After stimulation, the median flow rate was 77.0 mL/min; thus, no significant decrease in the flow rate was detected. In the control group, the median brachial artery diameter, which was 3.6 mm prior to stimulation, decreased to 3.4 mm after stimulation, and this decrease was also statistically significant (P = 0.046). In the diabetic neuropathy group, the median brachial artery diameter increased from 3.4 mm to 3.6 mm following nerve stimulation. Once again, no narrowing was observed.

CONCLUSION

Our research suggests that diabetic neuropathy results in significant vasomotor dysfunction of medium sized peripheral arteries. Physiological vasoconstriction in response to sympathetic activation is impaired in diabetic neuropathy.

Diabetic neuropathy results in vasomotor dysfunction of medium sized peripheral arteries

BACKGROUND

The effect of the sympathetic nervous system on peripheral arteries causes vasoconstriction when smooth muscle cells in the walls of blood vessels contract, which leads to narrowing of arteries and reduction of the blood flow.

AIM

To compare sympathetic vasomotor activation of the brachial arteries in healthy subjects and patients with painful diabetic neuropathy; and therefore, to assess whether there is significant vasomotor dysfunction of medium sized arteries in diabetic neuropathy.

METHODS

The study included 41 diabetic neuropathy patients and 41 healthy controls. Baseline diameter and flow rate of the brachial arteries were measured. Then, using a bipolar stimulus electrode, a 10 mA, 1 Hz electrical stimulus was administered to the median nerve at the wrist level for 5 s. The brachial artery diameter and blood flow rate were re-measured after stimulation.

RESULTS

In the control group, the median flow rate was 70.0 mL/min prior to stimulation and 35.0 mL/min after stimulation, with a statistically significant decrease (P < 0.001), which is consistent with sympathetic nervous system functioning (vasoconstriction). In the diabetic neuropathy group, median flow rate before the stimulation was 35.0 mL/min. After stimulation, the median flow rate was 77.0 mL/min; thus, no significant decrease in the flow rate was detected. In the control group, the median brachial artery diameter, which was 3.6 mm prior to stimulation, decreased to 3.4 mm after stimulation, and this decrease was also statistically significant (P = 0.046). In the diabetic neuropathy group, the median brachial artery diameter increased from 3.4 mm to 3.6 mm following nerve stimulation. Once again, no narrowing was observed.

CONCLUSION

Our research suggests that diabetic neuropathy results in significant vasomotor dysfunction of medium sized peripheral arteries. Physiological vasoconstriction in response to sympathetic activation is impaired in diabetic neuropathy.

Cucurbita pepo seeds improve peripheral neuropathy in diabetic rats by modulating the inflammation and oxidative stress in rats

BACKGROUND

Cucurbita pepo (C. pepo) is cultivated and used traditionally as vegetable as well as medicine in different parts of the world. The aim of current study was to investigate the potential of C. pepo in attenuation of diabetic neuropathy via using streptozotocin (STZ)-induced diabetes model in male wistar rats.

MATERIALS AND METHODS

Diabetic neuropathy was induced by administration of STZ; 65 mg/kg, i.p. and Nicotinamide (NAD; 230 mg/kg i.p.) and assessed by measuring thermal hyperalgesia, mechanical hyperalgesia and motor nerve conduction velocity (MNCV) in experimental animals. Treatment with different doses of (100, 200 and 400 mg/kg, p.o.) petroleum ether extract of C. pepo (CPE) and hydroethanolic extract of C. pepo (CHE) was started from the 60th day of STZ/NAD administration and continued upto 90th day.

RESULTS

CPE and CHE significantly attenuated the behavioural changes including hyperalgesia, allodynia and MNCV linked to diabetic neuropathy. Moreover, the oxidative stress and level of TNF-α, TGF-β and IL-1β was found to be significantly attenuated in experimental animals.

CONCLUSION

Thus C. pepo might ameliorate the progression of diabetic neuropathy via modulation of chronic hyperglycemia and therefore and have therapeutic potential for treatment of diabetic neuropathic pain.

Aspirin attenuates morphine antinociceptive tolerance in rats with diabetic neuropathy by inhibiting apoptosis in the dorsal root ganglia

Morphine is a drug used in chronic pain such as diabetic neuropathy, but the development of tolerance to its antinociceptive effect is an important clinical problem. Aspirin is an analgesic and antiapoptotic drug used in combination with morphine as an adjuvant in diabetic neuropathy. Our aim in this study was to investigate the effects of aspirin on morphine-induced neuronal apoptosis and analgesic tolerance in rats with diabetic neuropathy. The antinociceptive effects of aspirin (50 mg/kg) and morphine (5 mg/kg) were evaluated by thermal pain tests. Streptozotocin (65 mg/kg) was injected intraperitoneally to induce diabetic neuropathy. To evaluate apoptosis, ELISA kits were used to measure caspase-3, Bax and Bcl-2 levels. Apoptotic cells were detected histologically by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) method. Study results indicate that prior administration of aspirin to diabetic rats significantly increased the antinociceptive efficacy of morphine compared to morphine alone. Thermal pain tests showed that aspirin significantly reduced morphine tolerance in rats with diabetic neuropathy. Biochemical analysis revealed that aspirin significantly decreased the levels of pro-apoptotic proteins, caspase-3 and Bax, while increasing the anti-apoptotic Bcl-2 in DRG neurons. Semiquantitative scoring demonstrated that aspirin provided a significant reduction in apoptotic cell counts in diabetic rats. In conclusion, these data suggested that aspirin attenuated morphine antinociceptive tolerance through anti-apoptotic activity in diabetic rat DRG neurons.

High triglyceride levels increase the risk of diabetic microvascular complications: a cross-sectional study

BACKGROUND

The prevalence of microvascular complications in type 2 diabetes mellitus (T2DM) is increasing. The effect of lipid profiles on diabetic microvascular complications remains debated. This research aimed to study the correlation between lipid profiles and microvascular complications.

METHODS

This retrospective cross-sectional study included 1096 T2DM patients. The patients were divided into the control, diabetic retinopathy (DR), nephropathy (DKD), and peripheral neuropathy (DPN) groups based on the existence of corresponding complications. The lipid profiles were analyzed, and the effect on complications was assessed by logistic regression.

RESULTS

Compared with the control group, the diabetic microvascular complications group had a higher dyslipidemia rate. The rate of high TGs increased significantly with an increasing number of complications. High TG levels contributed to the risk of DKD, DR, and DPN [odds ratios (ORs): 2.447, 2.267, 2.252; 95% confidence interval: 1.648-3.633, 1.406-3.655, 1.472-3.445]. In the age (years) > 55, T2DM duration (years) > 10, and HbA1c (%) ≥ 7 groups, the risk of high TGs was higher for DKD (ORs: 2.193, 2.419, 2.082), DR (ORs: 2.069, 2.317, 1.993), and DPN (ORs: 1.811, 1.405, 1.427).

CONCLUSION

High TG levels increase the risk of diabetic microvascular complications, and patients with older age, longer T2DM duration, and higher HbA1c levels are recommended to keep lipid levels more strictly.

Effects of Photobiomodulation With Two Wavelengths of 630 and 810 nm on Diabetic Neuropathy

Introduction: Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes patients. Among different therapeutic approaches for treating DPN, low-level laser therapy (LLLT) or photobiomodulation (PBM) is a new promising non-invasive technique. This study aims to evaluate the effect of visible and infra-red LLLT on DPN. Methods: Sixty DPN patients enrolled in a randomized-controlled study. The patients were randomly divided into the same population of control and laser groups. The patients in the laser group received LLLT with two wavelengths of 630 and 819 nm and conventional therapy, and those in the control group received conventional therapy alone. Irradiation of the patients lasted 15 minutes per session, and it was performed over the surface of each foot three times a week for 12 sessions. The patients were evaluated at baseline and at the end of the study with the Michigan Neuropathy Screening Instrument (MNSI) and microfilament test. Results: Patients' sensation in the right foot in the monofilament test had increased from 22 (84.6%) to 26 (86.7%) (P=0.000), and in the left foot it had increased from 20 (80%) to 25 (86.2%) (P=0.001). The mean and standard deviation of the scores of section A of the Michigan questionnaire showed a statistically significant difference between the two groups (P<0.05), but the B part scores of the Michigan test did not show a significant difference. Conclusion: This study showed that the visible and infra-red LLLT significantly improved the symptoms of diabetic neuropathy without any side effects.

Tight junction disruption and the pathogenesis of the chronic complications of diabetes mellitus: A narrative review

The chronic complications of diabetes mellitus constitute a major public health problem. For example, diabetic eye diseases are the most important cause of blindness, and diabetic nephropathy is the most frequent cause of chronic kidney disease worldwide. The cellular and molecular mechanisms of these chronic complications are still poorly understood, preventing the development of effective treatment strategies. Tight junctions (TJs) are epithelial intercellular junctions located at the most apical region of cell-cell contacts, and their main function is to restrict the passage of molecules through the paracellular space. The TJs consist of over 40 proteins, and the most important are occludin, claudins and the zonula occludens. Accumulating evidence suggests that TJ disruption in different organs, such as the brain, nerves, retina and kidneys, plays a fundamental pathophysiological role in the development of chronic complications. Increased permeability of the blood-brain barrier and the blood-retinal barrier has been demonstrated in diabetic neuropathy, brain injury and diabetic retinopathy. The consequences of TJ disruption on kidney function or progression of kidney disease are currently unknown. In the present review, we highlighted the molecular events that lead to barrier dysfunction in diabetes. Further investigation of the mechanisms underlying TJ disruption is expected to provide new insights into therapeutic approaches to ameliorate the chronic complications of diabetes mellitus.

Where Art Thou O treatment for diabetic neuropathy: the sequel

INTRODUCTION

Having lived through a pandemic and witnessed how regulatory approval processes can evolve rapidly; it is lamentable how we continue to rely on symptoms/signs and nerve conduction as primary endpoints for clinical trials in DPN.

AREAS COVERED

Small (Aδ and C) fibers are key to the genesis of pain, regulate skin blood flow, and play an integral role in the development of diabetic foot ulceration but continue to be ignored. This article challenges the rationale for the FDA insisting on symptoms/signs and nerve conduction as primary endpoints for clinical trials in DPN.

EXPERT OPINION

Quantitative sensory testing, intraepidermal nerve fiber density, and especially corneal confocal microscopy remain an after-thought, demoted at best to exploratory secondary endpoints in clinical trials of diabetic neuropathy. If pharma are to be given a fighting chance to secure approval for a new therapy for diabetic neuropathy, the FDA needs to reassess the evidence rather than rely on 'opinion' for the most suitable endpoint(s) in clinical trials of diabetic neuropathy.

Effects of exercise therapy on diabetic neuropathy: A systematic review and meta-analysis

OBJECTIVE

To evaluate the effects of exercise therapy on neuropathic symptoms, signs, psychosocial aspects, and physical function in people with diabetic neuropathy (DN).

METHODS

A search in PubMed, Web of Science, Physiotherapy Evidence (PEDro), and Cochrane databases was performed from inception to Invalid Date NaN, . Randomized clinical trials (RCTs) were selected in patients with DN comparing exercise therapy with a control group. The studies' methodological quality was assessed with the PEDro scale. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was used to assess the overall quality.

RESULTS

Eleven RCTs (n = 517 participants) were included. Nine studies showed high methodological quality. Mean (MD) and standardized mean differences (SMD) were observed in favor of exercise therapy for symptoms (MD = -1.05; confidence interval 95% = -1.90 to -0.20), signs (SMD = -0.66; confidence interval 95%= -1 to -0.32), and physical function (SMD = -0.45; confidence interval 95% = -0.66 to -0.24). No changes were found in psychosocial aspects (SMD = -0.37; confidence interval 95% = -0.92 to 0.18). The overall quality of evidence was very low.

CONCLUSION

The quality of evidence suggesting that exercise therapy provides short-term benefits in neuropathic symptoms, signs, and physical function in patients with DN is very low. Furthermore, there were no effects found on psychosocial aspects.

Issues and challenges in diabetic neuropathy management: A narrative review

Diabetic neuropathy (DN) is a devastating disorder with an increasing prevalence globally. This epidemic can pose a critical burden on individuals and com-munities, subsequently affecting the productivity and economic output of a country. With more people living a sedentary lifestyle, the incidence of DN is escalating worldwide. Many researchers have relentlessly worked on ways to combat this devastating disease. Their efforts have given rise to a number of commercially available therapies that can alleviate the symptoms of DN. Unfortunately, most of these therapies are only partially effective. Worse still, some are associated with unfavorable side effects. This narrative review aims to highlight current issues and challenges in the management of DN, especially from the perspective of molecular mechanisms that lead to its progression, with the hope of providing future direction in the management of DN. To improve the approaches to diabetic management, the suggested resolutions in the literature are also discussed in this review. This review will provide an in-depth understanding of the causative mechanisms of DN, apart from the insights to improve the quality and strategic approaches to DN management.

Effects of foot-ankle exercises on foot-ankle kinematics, plantar pressure, and gait kinetics in people with diabetic neuropathy: Secondary outcomes from a randomized controlled trial

BACKGROUND

Follow-up report of secondary outcomes of a randomized, single-blinded, parallel controlled trial that investigated the benefits of a foot-ankle therapeutic exercise program on foot-ankle kinematics, plantar pressure, and lower limb kinetics during gait in individuals with diabetic neuropathy (DPN).

METHODS

Sixty-six participants with DPN were randomly allocated into a control group (CG; n = 31), which received usual care, and an intervention group (IG; n = 35), which received usual care plus a 12-week group-based foot-ankle exercise program. Outcomes were assessed at baseline and 12 weeks by an assessor blinded to group allocation.

RESULTS

The generalized linear mixed model and intention-to-treat analysis revealed a greater hip extensor moment at push-off and greater hallux contact area in the IG than CG after 12 weeks. A within-group analysis revealed a larger arch height during stance and higher peak pressure and pressure-time integral at the central forefoot region in the IG after 12 weeks compared to baseline. There were no other significant group difference or changes over time in foot-ankle kinematics or in any other joint moment related to overall lower limb biomechanics.

CONCLUSION

The increases in hip moment at push-off and hallux surface contact area suggest an improvement in the propulsion phase with greater participation of the toes in foot rollover after 12 weeks of a group-based foot-ankle exercises program for people with DPN. Individual face-to-face, longer-term, and more intensive interventions may be needed to positively influence foot-ankle biomechanics and pressure parameters in other plantar areas.

The role of protein kinases in diabetic neuropathic pain: an update review

Objectives

Diabetic neuropathic pain (DNP) is a debilitating symptom of diabetic neuropathy which seriously impairs patient's quality of life. Currently, there is no specific therapy for DNP except for duloxetine and gabapentin that show limited utility in alleviating DNP. The present review aims to discuss the central role of protein kinases in the pathogenesis of DNP and their therapeutic modulation.

Methods

Scopus, PubMed, and Google scholar were searched up to January 2022 to find relevant studies with English language in which the roles of proteins kinases in DNP were examined.

Results

DNP is associated with hyperactivity in pain sensory neurons and therapies aim to specifically suppress redundant discharges in these neurons without affecting the activity of other sensory and motor neurons. Transient receptor potential vanilloid 1 (TRPV1) and purinergic 2 × 7 receptors (P2 × 7R) are two receptor channels, highly expressed in pain sensory neurons and their blockade produces remarkable analgesic effects in DNP. The activities of receptor channels are mainly regulated by the protein kinases whose modulation provides remarkable analgesic effects in DNP models.

Conclusion

Capsaicin, TRPV1 modulator, is the only agent successfully examined in clinical trials with promising effects in patients with DNP. Current data suggest that blocking calcium calmodulin dependent protein kinase II (CaMKII) is superior to other approaches, considering its pivotal role in regulating the pain neuron potentials. By this means, DNP alleviation is achievable without affecting the activity of other sensory or motor neurons.

Morbidity and mortality of patients with diabetic neuropathy treated with pathogenetically oriented alpha-lipoic acid versus symptomatic pharmacotherapies - a nationwide database analysis from Hungary

AIMS

Diabetic neuropathy is associated with increased risk of morbidity and all-cause mortality. It is unclear whether these outcomes differ in patients with diabetic neuropathy treated with pathogenetically oriented vs symptomatic pharmacotherapies.

METHODS

We performed a retrospective (2009-2019) database analysis of patients treated with pathogenetically oriented alpha-lipoic acid (ALA) or symptomatic pharmacotherapies for diabetic neuropathy. We investigated clinical outcomes in propensity score matched patients in Hungary. Changes in hazard ratios and annualized event rates were assessed and sensitivity analyses performed.

RESULTS

Hazard ratios favored treatment with ALA vs symptomatic pharmacotherapies regarding acute myocardial infarction (HR 0.73, 95%CI: 0.60-0.89, p = 0.0016), stroke (HR 0.71, 95%CI: 0.62-0.82, p<0.0001), hospitalization for heart failure (HR 0.72, 95%CI: 0.66-0.78, p<0.0001), cancer events (HR 0.83, 95% CI: 0.76-0.92, p = 0.0002) and all-cause mortality (HR 0.55, 95% CI: 0.49-0.61, p<0.0001), but not for lower limb amputation (HR 1.05, 95%CI: 0.89-1.25, p = 0.5455). This association was supported by results of evaluating annual event rates and sensitivity analyses.

CONCLUSIONS

This retrospective database analysis revealed a lower occurrence of cardio- and cerebrovascular morbidity, cancer events and all-cause mortality in patients with diabetic neuropathy treated with pathogenetically oriented ALA vs symptomatic pharmacotherapies. This hypothesis-generating result requires further investigations.

CMKLR1 Antagonist Alpha-NETA Protects against Diabetic Nephropathy in Mice

INTRODUCTION

Diabetic nephropathy (DN) is a common complication in diabetic patients. Chemerin, a novel adipokine, has been associated with renal damage in DN. The chemerin chemokine-like receptor 1 (CMKLR1) has been reported to participate in DN. In this study, we aimed to investigate the effect of a CMKLR1 antagonist, 2-(anaphthoyl)ethyltrimethylammonium iodide (α-NETA), on DN.

METHODS

To induce diabetes, 8-week-old male C57BL/6J mice were given a single intraperitoneal injection of 65 mg/kg streptozotocin (STZ). Diabetic mice were randomly assigned to receive daily doses of 0, 5, or 10 mg/kg α-NETA for 4 weeks.

RESULTS

α-NETA dose-dependently induced body weight and reduced fasting blood glucose levels in STZ-induced diabetic mice. Furthermore, α-NETA significantly reduced the expressions of renal injury markers, including serum creatinine, kidney weight/body weight, urine volume, total proteins, and albumin in the urine, and increased creatinine clearance. Periodic acid-Schiff staining also indicated that α-NETA could effectively ameliorate renal injuries in DN mice. In addition, α-NETA inhibited renal inflammation and the expressions of chemerin and CMKLR1 in mice with DN.

CONCLUSION

In summary, our findings suggested that α-NETA has beneficial effects on the management of DN. Specifically, α-NETA effectively ameliorated renal damage and inflammation in a dose-dependent manner in mice with DN. Thus, targeting the chemerin and CMKLR1 axis with α-NETA may be a promising therapeutic strategy for the treatment of DN.

Impact of individual microvascular disease on the risks of macrovascular complications in type 2 diabetes: a nationwide population-based cohort study

BACKGROUND

This study compared the risks of cardiovascular morbidity and mortality between patients with type 2 diabetes (T2D) with and without microvascular diseases, and between matched patients with microvascular diseases.

METHODS

We identified newly diagnosed type 2 diabetes patients from National Health Insurance Research Database in Taiwan from January 1, 2008, to December 31, 2019. Propensity score matching was applied to construct matched pairs of patients with diabetic kidney disease, retinopathy, or neuropathy. Multivariable Cox proportional-hazard models were adopted to compare the risks of cardiovascular morbidity and mortality.

RESULTS

Patients with microvascular disease had a significantly higher risk of cardiovascular morbidities and mortality than those without microvascular disease. Among the matched cohorts, patients with diabetic retinopathy had a significantly higher risk of stroke development than those with diabetic kidney disease (aHR 1.11, 95%CI 1.03-1.2). Diabetic neuropathy showed a significantly higher risk of stroke development than diabetic kidney disease (aHR 1.17, 95%CI 1.1-1.25) and diabetic retinopathy (aHR 1.12, 95%CI 1.03-1.21). Diabetic retinopathy had a significantly higher risk of incident heart failure than diabetic kidney disease (aHR 1.43, 95%CI 1.3-1.57), and diabetic neuropathy had a significantly lower risk of incident heart failure than diabetic retinopathy (aHR 0.79, 95%CI 0.71-0.87).

CONCLUSIONS

T2D patients with microvascular disease have a significantly higher risk of cardiovascular morbidities and mortality than those without microvascular disease. In the matched cohorts, diabetic neuropathy was significantly associated with stroke development, and diabetic retinopathy had a significant association with heart failure compared to other microvascular diseases.

The potential of esculin in ameliorating Type-2 diabetes mellitus induced neuropathy in Wistar rats and probing its inhibitory mechanism of insulin aggregation

Diabetic neuropathy encompasses multiple pathological disturbances, many of which coincide with the pathophysiological mechanisms of neurodegenerative disorders. In the present study, various biophysical techniques like Rayleigh light scattering assay, Thioflavin T assay, far-UV Circular Dichroism spectroscopy, Transmission electron microscopy have unveiled the anti-fibrillatory effect of esculin upon human insulin fibrillation. MTT cytotoxicity assay demonstrated the biocompatibility of esculin and in-vivo studies such as behavioral tests like hot plate test, tail immersion test, acetone drop test, plantar test were performed for validating diabetic neuropathy. Assessment of levels of serum biochemical parameters, oxidative stress parameters, pro-inflammatory cytokines as well as neuron specific markers was done in the current study. Rat brains were subjected to histopathology and their sciatic nerves were subjected to transmission electron microscopy to analyze myelin structure alterations. All these results reveal that esculin ameliorates diabetic neuropathy in experimental diabetic rats. Conclusively, our study demonstrates the anti-amyloidogenic potential of esculin in the form of inhibition of human insulin fibrillation, making it a promising candidate in combating neurodegenerative disorders in the near future and the results of various behavioral, biochemical, and molecular studies reveal that esculin possesses anti-lipidemic, anti-inflammatory, anti-oxidative and neuroprotective properties which help in ameliorating diabetic neuropathy in streptozotocin induced diabetic Wistar rats.

Validity and reliability of the Polish version of the Michigan Neuropathy Screening Instrument

BACKGROUND

Diabetic sensorimotor polyneuropathy is an important risk factor for foot ulceration and amputation. Thus, patients with diabetes should be screened for this disorder according to local guidelines. An obstacle to the diagnosis of this disease may be the lack of unified diagnostic criteria due to the lack of properly validated scales used for assessment.

AIM

To validate both sections (A and B) of the Michigan Neuropathy Screening Instrument (MNSI) in Polish (PL) patients with diabetes.

METHODS

A cross-sectional study using a test (A1, B1) and re-test (A2, B2) formula was performed in 80 patients with diabetes. The gold standard used for neuropathy detection was a nerve conduction study (NCS) which was performed in all participants. Reliability of the MNSI-PL was assessed using the Cronbach’s alpha, Kuder-Richardson formula 20 (KR-20), split-half reliability, the Gottman split-half tests, and correlation between first and second half was accessed. Stability was assessed using an intraclass correlation coefficient (ICC). For external validation, we used simple linear correlation, binomial regression, and agreement between two different tools using a Bland-Altman plot analysis.

RESULTS

The scale was internally consistent (Cronbach’s alpha for the full scale: 0.81 for A and 0.87 for B). MNSI-PL scores in test/retest showed high stability (ICC = 0.73 for A and ICC = 0.97 for B). The statistically important correlations between MNSI-PL and NCS were found for B1, B2, and A1 (P < 0.005). The cut-off points of ≥ 3 for section A (sensitivity of 90%-100%; specificity of 33%-40%) and ≥ 2 for section B (sensitivity of 81%-84%; specificity of 60%-70%) were obtained during neuropathy detection.

CONCLUSION

The MNSI-PL is a reliable and valid instrument in screening for diabetic neuropathy.

Methods for evaluation of corneal nerve fibres in diabetes mellitus by in vivo confocal microscopy: a scoping review protocol

INTRODUCTION

Globally, 422 million people have diabetes. Late complications of diabetes are blindness, kidney failure, heart attack, stroke and lower limb amputation. The prevalence of diabetic peripheral neuropathy and diabetic retinopathy is 50% and 35%, respectively. In vivo confocal microscopy (IVCM) is a rapid, non-invasive method to evaluate subbasal corneal nerve fibres, which are small fibres of the peripheral nervous system. Corneal nerve fibre changes can be a marker of diabetic peripheral neuropathy. There is currently no gold-standard procedure for IVCM imaging, image processing or quantitative analysis of the corneal nerve fibres in the subbasal plexus. This protocol describes a scoping review to map, summarise and critically evaluate current methods used with IVCM evaluation in people with diabetes mellitus.

METHODS

The scoping review will follow Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines for scoping review. A comprehensive search of the literature will be conducted in MEDLINE, Embase, Cochrane, Scopus and Web of Science. The search strategy will include terms related to IVCM, diabetes and corneal nerve fibres. We will set inclusion and exclusion criteria prior to the search, and two reviewers will screen titles and abstracts independently. One reviewer will full text read eligible articles and chart data from the studies. A descriptive summary of the methods used in imaging, image processing and quantitative analysis of peripheral corneal nerve fibres by IVCM will be written.

ETHICS AND DISSEMINATION

Ethical approval is not required since this is a scoping review based on previously published articles. The findings will be published in a scientific peer-reviewed journal.

Nrf2 signaling in diabetic nephropathy, cardiomyopathy and neuropathy: Therapeutic targeting, challenges and future prospective

Western lifestyle contributes to an overt increase in the prevalence of metabolic anomalies including diabetes mellitus (DM) and obesity. Prevalence of DM is rapidly growing worldwide, affecting many individuals in both developing and developed countries. DM is correlated with the onset and development of complications with diabetic nephropathy (DN), diabetic cardiomyopathy (DC) and diabetic neuropathy being the most devastating pathological events. On the other hand, Nrf2 is a regulator for redox balance in cells and accounts for activation of antioxidant enzymes. Dysregulation of Nrf2 signaling has been shown in various human diseases such as DM. This review focuses on the role Nrf2 signaling in major diabetic complications and targeting Nrf2 for treatment of this disease. These three complications share similarities including the presence of oxidative stress, inflammation and fibrosis. Onset and development of fibrosis impairs organ function, while oxidative stress and inflammation can evoke damage to cells. Activation of Nrf2 signaling significantly dampens inflammation and oxidative damage, and is beneficial in retarding interstitial fibrosis in diabetic complications. SIRT1 and AMPK are among the predominant pathways to upregulate Nrf2 expression in the amelioration of DN, DC and diabetic neuropathy. Moreover, certain therapeutic agents such as resveratrol and curcumin, among others, have been employed in promoting Nrf2 expression to upregulate HO-1 and other antioxidant enzymes in the combat of oxidative stress in the face of DM.

Biomarkers in diabetic neuropathy

CONTEXT

The prevalence of diabetic neuropathy is drastically increasing in the world. To halt the progression of diabetic neuropathy, there is an unmet need to have potential biomarkers for the diagnosis and new drug discovery.

OBJECTIVE

To study various biomarkers involved in the pathogenesis of diabetic neuropathy.

METHODS

The literature was searched with the help of various scientific databases and resources like PubMed, ProQuest, Scopus, and Google scholar from the year 1976 to 2020.

RESULTS

Biomarkers of diabetic neuropathy are categorised as inflammatory biomarkers such as MCP-1, VEGF, TRPV1, NF-κB; oxidative biomarkers such as adiponectin, NFE2L2; enzyme biomarkers like NADPH, ceruloplasmin, HO-1, DPP-4, PARP α; miscellaneous biomarkers such as SIRT1, caveolin 1, MALAT1, and microRNA. All biomarkers have a significant role in the pathogenesis of diabetic neuropathy.

CONCLUSION

These biomarkers have a potential role in the progression of diabetic neuropathy and can be considered as potential targets for new drug discovery.

Postural performance assessment in aging people with diabetes and diabetic peripheral neuropathy using a Wii balance board

PURPOSE

To determine the effect of sensory perturbations on static postural control in older people with type 2 diabetes mellitus by comparing postural outcomes of people with and without diabetic neuropathy using a Wii Balance Board (WBB).

MATERIALS AND METHODS

Static postural balance assessments were performed in 31 participants: nine with type 2 diabetes mellitus; 12 with diabetic neuropathy; and 10 non-diabetic controls. Participants stood on the WBB under sensory perturbations (visual and proprioceptive). Body balance was analysed using centre of pressure ellipse area, mean velocity, and sample entropy. The effects of within-participant factors, sensory perturbations and the between-participants factor 'group' on outcomes were analysed using a multivariate analysis of variance model.

RESULTS

Type 2 diabetes mellitus participants with and without neuropathy showed altered postural performance under sensory perturbations compared to non-diabetic participants. Moreover, participants with diabetic neuropathy showed impaired postural performance when one perceptual system was disturbed. Finally, participants with type 2 diabetes mellitus without neuropathy decreased their postural performance when both sensory disturbances were present.

CONCLUSIONS

The Wii Balance Board can be a useful alternative for balance impairment screening related to diabetic neuropathy and contribute as an affordable source of insight in early interventions in integral diabetes care.Implications to rehabilitationOlder people with diabetic peripheral neuropathy depend on visual and somatosensory cues to keep their static postural balance.Static balance assessment using the Wii Balance Board allows the identification of alterations in postural performance in participants with diabetes.This low-cost method used can be considered as a complement to integral diabetes care.

Synergistic role of resveratrol and exercise training in management of diabetic neuropathy and myopathy via SIRT1/NGF/GAP43 linkage

AIMS

Oxidative stress also plays an important role in the pathogenesis of diabetic neuropathy (DN). Both resveratrol (RES) and exercise (EX) have potent anti-oxidative benefits. Low levels of nerve growth factor (NGF) and SIRT1 (a member of sirtuin family) have been reported in patients with DN. The current study has been designed to investigate the role of serum NGF and SIRT1 on DN-induced hyperalgesia and motor incoordination and to evaluate the possible protective role of RES and/or EX.

MAIN METHODS

A total of 40 male adult albino rats divided into five groups; control, DN, DN + RES, DN + EX, and DN + RES and EX. DN was confirmed by sensorimotor disturbance and diminished nerve conduction velocity (NCV). NGF and SIRT1 levels were measured by western blot. Calcitonin gene-related peptide (CGRP) was measured by PCR. Myofibrillar degeneration and inflammation scores were revealed via H&E microscopic analysis of the gastrocnemius muscle. Immunohistochemical evaluation of caspase3 and TNF-α was performed in the lumber segment of spinal cord and gastrocnemius muscle sections. Ultrastructural evaluation of sciatic nerve axonal degeneration has also been assessed.

KEY FINDINGS

DN group showed decreased SIRT1 level, decreased NGF level and correlated with CGRP level and Na+/K+ ATPase. Treatment with RES and/or EX resulted in improvement of sensorimotor disturbance. DN characterized by reduced SOD level, whereas RES and/or EX could limit oxidative damage by up-regulation Bcl2, Akt and GAP-43 and down-regulation of caspase3 and TNF-α. In conclusion, increased level of SIRT1and NGF by incorporation of RES (natural supplementation) and EX (life style modification) could improve the neuroinflammatory state in DN.

Piceatannol promotes neuroprotection by inducing mitophagy and mitobiogenesis in the experimental diabetic peripheral neuropathy and hyperglycemia-induced neurotoxicity

Piceatannol (PCN), a SIRT1 activator, regulates multiple oxidative stress mechanism and has anti-inflammatory potential in various inflammatory conditions. However, its role in Diabetic insulted peripheral neuropathy (DN) remains unknown. Oxidative stress and mitochondrial dysfunction are major contributing factors to DN. Myriad studies have proven that sirtuin1 (SIRT1) stimulation convalesce nerve functions by activating mitochondrial functions like mitochondrial biogenesis and mitophagy. Diabetic neuropathy (DN) was provoked by injecting streptozotocin (STZ) at a dose of 55 mg/kg, i.p to male Sprague Dawley (SD) rats. Mechanical, thermal hyperalgesia was evaluated by using water immersion, Vonfrey Aesthesiometer, and Randall Sellito Calipers. Motor, sensory nerve conduction velocity was measured using Power Lab 4sp system whereas The Laser Doppler system was used to evaluate nerve blood flow. To induce hyperglycemia for the in vitro investigations, high glucose (HG) (30 mM) conditions were applied to Neuro2a cells. At doses of 5 and 10 µM, PCN was examined for its role in SIRT1 and Nrf2 activation. HG-induced N2A cells, reactive oxygen exposure, mitochondrial superoxides and mitochondrial membrane potentials were restored by PCN exposure, and their neurite outgrowth was enhanced. Peroxisome proliferator activated receptor-gamma coactivator-1α (PGC-1α) directed mitochondrial biogenesis was induced by increased SIRT1 activation by piceatannol. SIRT1 activation also enhanced Nrf2-mediated antioxidant signalling. Our study results inferred that PCN administration can counteract the decline in mitochondrial function and antioxidant activity in diabetic rats and HG-exposed N2A cells by increasing the SIRT1 and Nrf2 activities.

Serum neurofilament light chain: a novel biomarker for early diabetic sensorimotor polyneuropathy

AIMS/HYPOTHESIS

No established blood-based biomarker exists to monitor diabetic sensorimotor polyneuropathy (DSPN) and evaluate treatment response. The neurofilament light chain (NFL), a blood biomarker of neuroaxonal damage in several neurodegenerative diseases, represents a potential biomarker for DSPN. We hypothesised that higher serum NFL levels are associated with prevalent DSPN and nerve dysfunction in individuals recently diagnosed with diabetes.

METHODS

This cross-sectional study included 423 adults with type 1 and type 2 diabetes and known diabetes duration of less than 1 year from the prospective observational German Diabetes Study cohort. NFL was measured in serum samples of fasting participants in a multiplex approach using proximity extension assay technology. DSPN was assessed by neurological examination, nerve conduction studies and quantitative sensory testing. Associations of serum NFL with DSPN (defined according to the Toronto Consensus criteria) were estimated using Poisson regression, while multivariable linear and quantile regression models were used to assess associations with nerve function measures. In exploratory analyses, other biomarkers in the multiplex panel were also analysed similarly to NFL.

RESULTS

DSPN was found in 16% of the study sample. Serum NFL levels increased with age. After adjustment for age, sex, waist circumference, height, HbA_1c, known diabetes duration, diabetes type, cholesterol, eGFR, hypertension, CVD, use of lipid-lowering drugs and use of non-steroidal anti-inflammatory drugs, higher serum NFL levels were associated with DSPN (RR [95% CI] per 1-normalised protein expression increase, 1.92 [1.50, 2.45], p<0.0001), slower motor (all p<0.0001) and sensory (all p≤0.03) nerve conduction velocities, lower sural sensory nerve action potential (p=0.0004) and higher thermal detection threshold to warm stimuli (p=0.023 and p=0.004 for hand and foot, respectively). There was no evidence for associations between other neurological biomarkers and DSPN or nerve function measures.

CONCLUSIONS/INTERPRETATION

Our findings in individuals recently diagnosed with diabetes provide new evidence associating higher serum NFL levels with DSPN and peripheral nerve dysfunction. The present study advocates NFL as a potential biomarker for DSPN.

Causal association between vitamin D and diabetic neuropathy: a Mendelian randomization analysis

OBJECTIVES

Vitamin D has been linked to diabetic neuropathy (DN) in previous epidemiological observational studies, however, their findings are inconsistent. The causal relationship between vitamin D and DN remains unknown. In this study we aim to investigate the causal association of serum 25-hydroxyvitamin D (25OHD) and DN.

METHODS

Based on summary statistics from publicly available genome-wide association studies (GWAS) database, we detected the genetic correlation between serum 25OHD levels and DN by a two-sample Mendelian randomization (MR) analysis. The inverse-variance weighted (IVW) method was used as the primary analysis, weighted median and MR-Egger were applied as complementary methods for MR estimates. In addition, we took sensitivity analyses including Cochran's Q test, MR-Pleiotropy Residual Sum and Outlier (MR-PRESSO) and leave-one-out analysis to ensure that we obtained stable and reliable results.

RESULTS

Our MR study showed no significant genetic association between serum 25OHD levels and DN (OR = 1.13, 95% CI = 0.81-1.57, P = 0.46). Furthermore, in the reverse direction analysis, we did not find a significant causal effect of DN and serum 25OHD levels (OR = 0.99, 95% CI = 0.98-1.00, P = 0.09). Results of MR-Egger, Weighted Median were consistent with those of the IVW method. The sensitivity analysis suggesting that no significant heterogeneity and genetic pleiotropy was observed.

CONCLUSIONS

Our results provided no evidence to support the causal association of serum 25OHD levels with DN.

BMP5 ameliorates diabetic peripheral neuropathy by augmenting mitochondrial function and inhibiting apoptosis in Schwann cells

Diabetic peripheral neuropathy is a common and serious complication of diabetes. Bone morphogenetic protein 5 (BMP5) is a multifunctional protein involved in the nervous system. Nevertheless, its effect on diabetic peripheral neuropathy remained uncharacterized. In this study, diabetic neuropathy in mice was induced by a single dose of 150 mg/kg streptozotocin (STZ) via intraperitoneal injection. Lentivirus expressing BMP5 (LV-BMP5) administration improved pain sensitivity, nerve conduction velocities and morphological alterations of the sciatic nerve of diabetic mice. Elevated BMP5 by LV-BMP5 suppressed cell apoptosis in the sciatic nerve, as evidenced by declined TUNEL-positive cells and down-regulated cleaved caspase-3 and cleaved caspase-9 levels. BMP5 enhanced mitochondrial membrane potential and ATP level. BMP5 also increased the phosphorylation of Smad1/5/9. Besides, the role of BMP5 in high glucose (HG)-stimulated Schwann cells was determined. Results of in vitro studies were in line with the in vivo findings. These experimental data seem to imply that BMP5 prevents the development of diabetic neuropathy via the maintenance of Smad1/5/9-mediated mitochondrial function.

Glycemic profile variability: An independent risk factor for diabetic neuropathy in patients with type 2 diabetes

BACKGROUND

Impaired glycemic control is a potential predictor for macro- and microvascular complications of diabetes, which could be recognized by glycemic variability. The aim of this 10-year prospective cohort study presented here is to gain a better understanding of the correlation between GV and diabetic peripheral neuropathy (DPN) as one of the most common complications of T2DM.

METHODS

Since February 2010, 1152 adult patients with T2DM have been followed-up. Baseline features, anthropometric measurements, and laboratory findings were collected and documented during ten years. The association between DPN incidence and glycemic profile variability was evaluated using cox regression analysis. The coefficient of variation of glycemic indices within subjects was calculated and compared using an independent sample t-test.

RESULTS

Individuals who developed neuropathy had significantly higher mean levels of glycemic indices (HbA1c, FBS, and 2hpp), urinary albumin excretion, mean creatinine levels, and a longer duration of diabetes. A significant positive correlation between incidence of DPN and glycemic profile variability (cv-FBS10 %, cv-FBS20 %, cv-2hpp20 %, cv-HbA1c5 % and cv-HbA1c10 %) was revealed. Results also showed that higher variability of FBS was associated with the higher risk of neuropathy incidence (HR: 12.29, p-value: 0.045), which indicates that glycemic profile variability is an independent risk factor for DPN in patients with T2DM.

CONCLUSION

Variability of glycemic profiles from a visit to visit, regardless of sustained hyperglycemia, was indeed a significant risk factor for DPN in diabetic type 2 patients. CV-FBS was the most critical glycemic variability indices for DPN development.

Hesperidin inhibits NOX4 mediated oxidative stress and inflammation by upregulating SIRT1 in experimental diabetic neuropathy

Hesperidin possesses myriads of pharmacological benefits, including anti-inflammatory and antioxidant properties. Herein, we speculated that the described pharmacological benefits of hesperidin might be due to its potentiating action on SIRT1; thereby, inhibition of NOX4. We developed diabetic neuropathy in Sprague-Dawley rats by feeding them a high-fat diet (HFD) for 12 weeks. We checked the effect of hesperidin on the level of oxidative stress, inflammatory markers, NOX4, and SIRT1 by biochemical analysis, histopathology, immunoblotting, immunocytochemistry, and real-time qPCR in HFD-fed rats and Palmitate encountered rat glial C6 cells. Hesperidin administration improved mechanical, thermal allodynia, and glucose homeostasis. There was a decrease in oxidative stress and inflammation and an enhanced level of antioxidant enzymes. Besides, the expression of NOX4 was down-regulated, while SIRT1 was upregulated. Interestingly, hesperidin treatment protected them from oxidative and inflammatory damage by upregulating SIRT1 and inhibiting NOX4 expression.

Blockade of receptor for advanced glycation end-products with azeliragon ameliorates streptozotocin-induced diabetic neuropathy

Treatment options for diabetic neuropathy are suboptimal, so development of a new therapeutic strategy is urgent. We focused on the role of receptor for advanced glycation end-products (RAGE) in diabetic neuropathy. We elaborated the effects of azeliragon (orally available small-molecule antagonist of RAGE) on streptozotocin (STZ)-induced mechanical hypersensitivity in mice. A reduction in mechanical nociceptive threshold observed 28 days after STZ treatment was improved by single administration of azeliragon (10 and 30 mg/kg) at 3 h, but this effect disappeared at 24 h. Conversely, repeat administration (three times; days 28, 30, and 32) of azeliragon (30 mg/kg) enhanced the antinociceptive effect significantly compared with that obtained upon single administration, and this effect persisted at least up to 24 h. The antinociceptive effect of azeliragon (30 mg/kg) was almost comparable with that of pregabalin (30 mg/kg). These drug treatments had no effect on blood glucose levels. Our findings suggest that RAGE might be an effective target for diabetic neuropathy treatment.

Diabetic Neuropathy: Review on Molecular Mechanisms

Diabetic mellitus is a worldwide endocrine and metabolic disorder with insulin insensitivity or deficiency or both whose prevalence could rise up to 592 million by 2035. Consistent hyperglycemia leads to one of the most common comorbidities like Diabetic Peripheral Neuropathy (DPN). DPN is underlined with unpleasant sensory experience, such as tingling and burning sensation, hyperalgesia, numbness, etc. Globally, 50-60% of the diabetic population is suffering from such symptoms as microvascular complications. Consistent hyperglycemia during DM causes activation/inhibition of various pathways playing important role in the homeostasis of neurons and other cells. Disruption of these pathways results into apoptosis and mitochondrial dysfunctions, causing neuropathy. Among these, pathways like Polyol and PARP are some of the most intensively studied ones whereas those like Wnt pathway, Mitogen activated protein kinase (MAPK), mTOR pathway are comparatively newly discovered. Understanding of these pathways and their role in pathophysiology of DN underlines a few molecules of immense therapeutic value. The inhibitors or activators of these molecules can be of therapeutic importance in the management of DPN. This review, hence, focuses on these underlying molecular mechanisms intending to provide therapeutically effective molecular targets for the treatment of DPN.

Nanoformulations of flavonoids for diabetes and microvascular diabetic complications

Diabetes is a chronic metabolic disease characterized by an excess of glucose in the blood. If the constant sugar level is not managed correctly in diabetic patients, it may lead to microvascular complications such as diabetic retinopathy, neuropathy, and nephropathy. There are several synthetic drugs for the management of diabetes; however, these drugs produce immense adverse effects in long-term use. Flavonoids are naturally occurring substances categorized in various classes. They are known for their diverse pharmacological actions, and one of them is prominent antihyperglycemic action and their activities in diabetic complications. In the last few decades, many research studies emphasized the potential of flavonoids in diabetes management. Nevertheless, most flavonoids are insoluble in water and cannot produce desired therapeutic action when administered in conventional dosage forms. To overcome this issue, flavonoids were formulated into different nanoformulations to enhance solubility, absorption, and therapeutic efficacy. This review article focuses on flavonoid nanoformulations and in vitro and in vivo studies reported to overcome diabetes mellitus and its complications.

[Diabetic neuropathy and diabetic foot syndrome (update 2023)]

These are the guidelines for diagnosis and treatment of diabetic neuropathy and diabetic foot.The position statement summarizes characteristic clinical symptoms and techniques for diagnostic assessment of diabetic neuropathy, including the complex situation of the diabetic foot syndrome. Recommendations for the therapeutic management of diabetic neuropathy, especially for the control of pain in sensorimotor neuropathy, are provided. The needs to prevent and treat diabetic foot syndrome are summarized.

miRNAs as cornerstones in diabetic microvascular complications

Diabetes mellitus is usually accompanied by nephropathy, retinopathy, and neuropathy as microvascular complications. MicroRNAs (miRNAs) can affect the kidney, retina, and peripheral neurons through their implication in pathways involved in angiogenesis, inflammation, apoptosis, as well as fibrosis within these tissues and hence, play a crucial role in the pathogenesis of microvascular complications. In this review, the updated knowledge of the role of miRNAs in the pathogenesis of diabetic microvascular complications was summarized. PubMed Central was searched extensively to retrieve data from a wide range of reputable biomedical reports/articles published after the year 2000 to systematically collect and present a review of the key molecular pathways mediating the hyperglycemia-induced adverse effects on vascular tissues, particularly in persons with T2DM. In the present review, miR-126, miR-29b, and miR-125a are implicated in diabetes-induced microvascular complications, while miR-146a is found to be connected to all these complications. Also, vascular endothelial growth factors are noted to be the most impacted targets by miRNAs in all diabetic microvascular problems.

Multidimensional pain profiling in people living with obesity and attending weight management services: a protocol for a longitudinal cohort study

INTRODUCTION

Pain is prevalent in people living with overweight and obesity. Obesity is associated with increased self-reported pain intensity and pain-related disability, reductions in physical functioning and poorer psychological well-being. People living with obesity tend to respond less well to pain treatments or management compared with people living without obesity. Mechanisms linking obesity and pain are complex and may include contributions from and interactions between physiological, behavioural, psychological, sociocultural, biomechanical and genetic factors. Our aim is to study the multidimensional pain profiles of people living with obesity, over time, in an attempt to better understand the relationship between obesity and pain.

METHODS AND ANALYSIS

This longitudinal observational cohort study will recruit (n=216) people living with obesity and who are newly attending three weight management services in Ireland. Participants will complete questionnaires that assess their multidimensional biopsychosocial pain experience at baseline and at 3, 6, 12 and 18 months post-recruitment. Quantitative analyses will characterise the multidimensional pain experiences and trajectories of the cohort as a whole and in defined subgroups.

ETHICS AND DISSEMINATION

The study protocol has been approved by the Ethics and Medical Research Committee of St Vincent's Healthcare Group, Dublin, Ireland (reference no: RS21-059) and the University College Dublin Human Research Ethics Committee (reference no: LS-E-22-41-Hinwood-Smart). Findings will be disseminated through peer-reviewed journals, conference presentations, public and patient advocacy groups, and social media.

STUDY REGISTRATION

Open Science Framework Registration DOI: https://doi.org/10.17605/OSF.IO/QCWUE.

Low-grade inflammation in type 2 diabetes: a cross-sectional study from a Danish diabetes outpatient clinic

OBJECTIVES

To investigate low-grade inflammation in type 2 diabetes and explore associations to clinical aspects as well as microvascular and macrovascular complications.

DESIGN

Cross-sectional analysis.

SETTING

The outpatient diabetes clinic at the Department of Endocrinology at Aalborg University Hospital, Denmark.

PARTICIPANTS

100 participants with type 2 diabetes confirmed by a haemoglobin A1c (HbA1c)≥6.5% for a minimum of 1 year and 21 healthy controls.

OUTCOME MEASURES

Serum levels of 27 inflammation-related biomarkers measured by immunoassay. Associations with microvascular and macrovascular complications, body weight, glycaemic control, medication and sex were investigated in the diabetes cohort.

RESULTS

Serum levels of tumour necrosis factor (TNF)-α and eotaxin were elevated in type 2 diabetes (p<0.05), while interleukin (IL)-7 was decreased (p<0.001). IL-12/IL-23p40, IL-15, macrophage-derived chemokine (MDC) and C reactive protein (CRP) levels were increased with body weight (p<0.05), while eotaxin and TNF-α were increased with elevated HbA1c levels (p<0.04). Dipeptidyl peptidase-4 inhibitor therapy was associated with lower levels of induced protein-10, MDC and thymus and activation regulated chemokine (p<0.02), while females had higher levels of MDC (p=0.027). Individuals with ≥3 diabetic complications had elevated levels of IL-6, IL-10, IL-12/IL-23p40, IL-15 and CRP compared with those with ≤3 (p<0.05).

CONCLUSION

The level of low-grade inflammation in type 2 diabetes is associated with obesity, glycaemic regulation, therapeutical management, sex and complications. Our results underline the importance of addressing inflammatory issues in type 2 diabetes, as these may predispose for crippling comorbidities.

Distal symmetrical polyneuropathy is present in all individuals with diabetes and foot ulcers - and does not associate with healing time

We estimated the occurrence of diabetic neuropathy using six different diagnostic modalities in individuals with newly diagnosed diabetic foot ulcers (DFUs) and assessed the association with DFU healing time. All individuals with DFU had distal symmetrical polyneuropathy. Presence of neuropathy did not associate with ulcer healing time (p ≥ 0.12).

Skin advanced glycation end products as a screening tool of neuropathy in type 2 diabetes mellitus

AIM OF THE STUDY

To examine the diagnostic utility of skin advanced glycation end products (AGEs) as screening tool of neuropathy in type 2 diabetes mellitus (T2DM).

PATIENTS AND METHODS

We included 132 participants (88 men) with a mean age of 64.57 years and median T2DM duration of 14.5 years. Skin AGEs were measured with AGE reader mu connect (Diagnoptics) on the dominant arm and were interpreted as normal vs. elevated. Distal sensorimotor polyneuropathy (DSPN) was diagnosed by the Neuropathy Disability Score. Cardiovascular autonomic neuropathy (CAN), sympathetic and parasympathetic nervous system impairment were diagnosed by cardiovascular autonomic reflex tests.

RESULTS

For DSPN, AGEs yielded high sensitivity (82.8%) and NPV (80.4 %) with moderate specificity (55.4 %). For CAN, they yielded relatively high sensitivity (75.0 %) and NPV (74.5 %) with low specificity (48.7 %). For sympathetic nervous system impairment, AGEs yielded relatively high sensitivity (75.0 %) and high NPV (84.3 %) with low specificity (43.9 %). For parasympathetic nervous system impairment, they yielded high PPV (81.0 %) with moderately high sensitivity (66.7 %) and moderate specificity (55.9 %).

CONCLUSIONS

In a simplified approach, skin AGEs may be used as a screening tool of DSPN and CAN (including sympathetic and parasympathetic nervous system impairment) in T2DM.

Early marker of ocular neurodegeneration in children and adolescents with type 1 diabetes: the contributing role of polymorphisms in mir146a and mir128a genes

BACKGROUND

Early ocular neurodegenerative signs of diabetic neuropathy (DN) can be found in children and adolescents with type 1 diabetes (T1D). No data are available on the potential role of polymorphisms in miRNAs genes in predisposing T1D subjects to these signs.

AIMS

To determine whether MIR146A rs2910164 and MIR128A rs11888095 polymorphisms are associated with early retinal and corneal neurodegenerative changes in pediatric patients with T1D.

METHODS

A total of 140 T1D children/adolescents underwent spectral domain-optical coherence tomography (SD-OCT) and in vivo confocal microscopy (IVCM) with measurement of retinal and corneal nerve fiber parameters. Risk factors for diabetes complications (diabetes duration, blood pressure, HbA1c) were recorded. Genotyping of rs2910164 and rs1188095 SNPs and genotype-phenotype association analysis were performed.

RESULTS

The C allele of rs2910164 in MIR146A was associated with higher values of IVCM parameters and minimum rim width (MRW) of the peripapillary region of optic nerve head measured in the retina, whereas the T allele of rs1188095 in MIR128A was associated with a significant impairment of them. Multiple regression analysis showed that MIR146A and MIR128A polymorphisms were significantly associated with corneal nerve fiber length (beta = 0.225 and - 0.204, respectively) and other IVCM parameters, independently from age, diabetes duration, HbA1c and systolic blood pressure percentile. Similar results were found for MRW (beta = 0.213 and - 0.286, respectively).

CONCLUSIONS

These results provide new insight into the genetic predisposition to DN showing that two polymorphisms in MIR146A and MIR128A genes could significantly contribute to the development of early ocular preclinical signs of DN.

Amputation and mortality frequencies associated with diabetic Charcot foot arthropathy: a meta-analysis

BACKGROUND

Five-year mortality and amputation frequencies after new-onset diabetic ulceration have been reported up to 55% and 74%, respectively. for patients with lower-extremity amputation. Following Charcot arthropathy, these frequencies were reported with wide variations. The aim of this meta-analysis is to provide a quantitative evaluation of amputation and mortality frequencies in a diabetic patient with a Charcot foot arthropathy.

METHODS

Electronic search strategy was applied on Medline, Web of Science, Cochrane Library and Google Scholar since inception to December 2021. Extracted data included study design, sample and patients characteristics, diabetes type and duration, lab results, ulcers at diagnosis, co-morbidities and follow up period. Meta-analysis reporting random-effects values was used to generate the weights results.

RESULTS

A total of 16 studies were included in the quantitative meta-analysis with a pooled sample of 2250 patients with 2272 Charcot feet. Two studies including 255 patients yielded a 1-year mortality frequency of 4% (95% CI = 0.018-0.065). Seven studies including 1706 patients reported a 5-year mortality frequency of 24.5% (95% CI = 0.172-0.326, I² = 88.5%). Four studies including 277 patients yielded a seven plus year mortality frequency of 16% (95% CI = 0.065-0.289, I² = 84.3%). Ten studies including 871 foot yielded an amputation frequency of 15% (95% CI = 0.067-0.258, I² = 93.6%) where 9% where major amputations (95% CI = 0.062-0.127, I² = 60%) and 5% were minor amputations (95% CI = 0.004-0.126, I² = 94.7%) CONCLUSION: Diabetic Charcot arthropathy yields marked risk of amputation and mortality. However, mortality frequencies were unexpectedly lesser compared to those related to the published frequencies associated with diabetic foot ulcers.

INvesTigating the Abnormality of detrusor ConTractility by uroflowmetry in diabetic children (INTACT Trial): protocol of a prospective, observational study

INTRODUCTION

Bladder emptying abnormalities and cardiovascular autonomic dysfunction are manifestations of autonomic dysfunction in people with diabetes mellitus (DM), which are major causes of morbidity and mortality. Since they can reduce the quality of life, they are urgent to be addressed before resulting in complications. As uroflowmetry might determine autonomic neuropathy earlier than cardiovascular autonomic dysfunction symptoms occur, our aim is to detect early abnormalities in bladder muscle function in children with DM. We investigate the diagnostic accuracy of uroflowmetry. As a secondary aim, we compare the prevalence of uroflowmetry abnormalities to the appearance of measures of cardiovascular autonomic neuropathy. Finally, as an ancillary study, we examine the association of uroflowmetry with the appearance of peripheral neuropathy. These three aims, we feel, will put our results regarding uroflowmetry into an overall context of nerve disease early in the course of type 1 DM. To our knowledge, such an approach has heretofore not been performed.

METHODS AND ANALYSIS

This will be a prospective, observational, single-centre clinical study. Patients with DM fulfilling the inclusion criteria and healthy controls will have uroflowmetry examination, cardiovascular autonomic dysfunction tests (heart rate response to deep breathing, to Valsalva manoeuvre, blood pressure and heart rate response to standing up, and to sustained handgrip) and nerve conduction test. The autonomic nervous system function will be examined by the reproducible and standardised cardiovascular reflex tests described by Ewing et al. During the examination, electrocardiogram (ECG) and blood pressure values will be recorded continuously. Heart rate response to deep inspiration will be executed to investigate the parasympathetic nervous system. Peripheral neuropathy will be evaluated by nerve conduction test. After a pilot period, when the first 50 diabetic and 50 healthy children will be assessed, sample size calculation will be carried out. The primary objective of this trial is to evaluate the diagnostic accuracy (sensitivity, specificity, positive and negative predictive value) of uroflowmetry. To do so, we compare uroflowmetry to the gold standard neuropathy tests, which are cardiovascular autonomic dysfunction tests (heart rate response to deep breathing, to Valsalva manoeuvre, blood pressure and heart rate response to standing up and to sustained handgrip).

ETHICS AND DISSEMINATION

Ethics approval was obtained from the Scientific and Research Ethics Committee of the Heim Pál National Paediatric Institute in Budapest, Hungary (registration number KUT-37/2021). Results will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NCT05247840.

Mosaic vs. Single Image Analysis with Confocal Microscopy of the Corneal Nerve Plexus for Diagnosis of Early Diabetic Peripheral Neuropathy

INTRODUCTION

The assessment of the corneal nerve fibre plexus with corneal confocal microscopy (CCM) is an upcoming but still experimental method in the diagnosis of early stage diabetic peripheral neuropathy (DPN). Using an innovative imaging technique-Heidelberg Retina Tomograph equipped with the Rostock Cornea Module (HRT-RCM) and EyeGuidance module (EG)-we were able to look at greater areas of subbasal nerve plexus (SNP) in order to increase the diagnostic accuracy. The aim of our study was to evaluate the usefulness of EG instead of single image analysis in diagnosis of early stage DPN.

METHODS

This prospective study was performed on 60 patients with type 2 diabetes mellitus, classified equally into two subgroups based on neuropathy deficient score (NDS): patients without DPN (group 1) or with mild DPN (group 2). The following parameters were analysed in the two subgroups: corneal nerve fibre length (CNFL; mm/mm²), corneal nerve fibre density (CNFD; no./mm²), corneal nerve branch density (CNBD; no./mm²). Furthermore, we compared the data calculated with the novel mosaic, EG-based method with those received from single image analysis using different quantification tools.

RESULTS

Using EG we did not find a significant difference between group 1 and group 2: CNFL (16.81 ± 5.87 mm/mm² vs. 17.19 ± 7.19 mm/mm², p = 0.895), CNFD (254.05 ± 115.36 no./mm² vs. 265.91 ± 161.63 no./mm², p = 0.732) and CNBD (102.68 ± 62.28 no./mm² vs. 115.38 ± 96.91 no./mm², p = 0.541). No significant difference between the EG method of analysing the SNP and the single image analysis of 10 images per patient was detected.

CONCLUSION

On the basis of our results it was not possible to differentiate between early stages of large nerve fibre DPN in patients with type 2 diabetes mellitus via SNP analysis. To improve sensitivity and specificity of this method newer technologies are under current evaluation.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT05326958.

Rolipram and pentoxifylline combination ameliorates experimental diabetic neuropathy through inhibition of oxidative stress and inflammatory pathways in the dorsal root ganglion neurons

Diabetic neuropathy (DN) is the most challenging microvascular complication of diabetes and there is no suitable treatment for it, so the development of new agents to relieve DN is urgently needed. Since oxidative stress and inflammation play an essential role in the development of DN, clearance of these factors are good strategies for the treatment of this disease. According to key role of cyclic adenosine monophosphate (cAMP) in the regulation of oxidative stress and inflammatory pathways, it seems that phosphodiesterase inhibitors (PDEIs) can be as novel drug targets for improving DN through enhancement of cAMP level. The aim of this study was to evaluate the effects of rolipram, a selective PDE4 inhibitor, and pentoxifylline, a general PDE inhibitor on experimental model of DN and also to determine the possible mechanisms involved in the effectiveness of these agents. We investigated the effects of rolipram (1 mg/kg) and pentoxifylline (100 mg/kg) and also combination of rolipram (0.5 mg/kg) and pentoxifylline (50 mg/kg), orally for five weeks in rats that became diabetic by STZ (55 mg/kg, i.p.). After treatments, motor function was evaluated by open-field test, then rats were anesthetized and dorsal root ganglion (DRG) neurons isolated. Next, oxidative stress biomarkers and inflammatory factors were assessed by biochemical and ELISA methods, and RT-PCR analysis in DRG neurons. Rolipram and/or pentoxifylline treatment significantly attenuated DN - induced motor function deficiency by modulating distance moved and velocity. Rolipram and/or pentoxifylline treatment dramatically increased the cAMP level, as well as suppressed DN - induced oxidative stress which was associated with decrease in LPO and ROS and increase in TAC, total thiol, CAT and SOD in DRG neurons. On the other hand, the level of inflammatory factors (TNF-α, NF-kB and COX2) significantly decreased following rolipram and/or pentoxifylline administration. The maximum effectiveness was with rolipram and/or pentoxifylline combination on mentioned factors. These findings provide novel experimental evidence for further clinical investigations on rolipram and pentoxifylline combination for the treatment of DN.

Low level light therapy/photobiomodulation for diabetic peripheral neuropathy: protocol of a systematic review and meta-analysis

INTRODUCTION

Diabetic peripheral neuropathy (DPN) is one of the most common complications of diabetes that strongly impact the patients' quality of life and working ability. Evidence indicated that low level light therapy (LLLT)/photobiomodulation might be effective for neuropathy. However, the effect of LLLT for DPN is not clear. The objective of this systematic review and meta-analysis is to determine the effects and safety of LLLT/photobiomodulation for DPN, in comparison with other methods such as sham light, no treatment, other active treatment and LLLT as an additional treatment compared with another treatment alone.

METHODS AND ANALYSIS

We will search eight databases from their inception to the date before the review submission. Randomised controlled trials (RCTs) will be included. Two reviewers will independently extract data using a structured data extraction method and assess the risk of bias in the included studies. Data will be synthesised using standardised mean difference or risk ratio with 95% CIs for continuous and dichotomous data, respectively. The primary outcome will be change in pain and secondary outcomes will include global symptom improvement, functional impairment and disability, impairment of sensation, quality of life, nerve conduction, and adverse events. Sensitivity and subgroup analysis will be employed to explore the influence of possible clinical and methodological characteristics. Publication bias will be assessed using funnel plot. We will conduct meta-analysis with RevMan V.5.4 and evaluate quality of the evidence using GRADE approach.

ETHICS AND DISSEMINATION

This study does not require ethics approval. Our findings will be disseminated in the peer-reviewed publications.

PROSPERO REGISTRATION NUMBER

CRD42021276056.

A randomized controlled trial assessing the safety and efficacy of palmitoylethanolamide for treating diabetic-related peripheral neuropathic pain

Background

Peripheral neuropathy is a common complication of diabetes. The management of the associated neuropathic pain remains difficult to treat.

Objective

This study explored the safety, tolerability and efficacy of a palmitoylethanolamide (PEA) formulation in treating diabetic-related peripheral neuropathic pain (PNP). Secondary outcomes included systemic inflammation, sleep and mood changes in patients diagnosed with type 1 and type 2 diabetes and PNP.

Design

This study was a single-centre, quadruple-blinded, placebo-controlled trial with 70 participants receiving 600 mg of PEA or placebo daily, for 8 weeks, with a 94% rate of study participation completion. Primary outcomes were neuropathic pain and specific pain types (the BPI-DPN and NPSI). The secondary outcomes were sleep quality (MOS sleep scale), mood (DASS-21), glucose metabolism and inflammation.

Results

There was a significant reduction (P ≤ 0.001) in BPI-DPN total pain and pain interference, NPSI total score and sub-scores, except for evoked pain (P = 0.09) in the PEA group compared with the placebo group. The MOS sleep problem index and sub-scores significantly improved (P ≤ 0.001). DASS-21 depression scores significantly reduced (P = 0.03), but not anxiety or stress scores. Interleukin-6 and elevated C-reactive protein levels significantly reduced in the PEA group (P = 0.05), with no differences in fibrinogen between groups (P = 0.78) at treatment completion. There were no changes in safety pathology parameters, and the treatment was well tolerated.

Conclusions

The study demonstrated that the PEA formulation reduced diabetic peripheral neuropathic pain and inflammation along with improving mood and sleep. Further studies on the mechanistic effectiveness of PEA as an adjunct medicine and as a monotherapy pain analgesic are warranted.

Clinical Trial Registration

Registry name: Australian New Zealand Clinical Trials Registry (ANZCTR), Registration number: ACTRN12620001302943, Registration link: https://anzctr.org.au/Trial/Registration/TrialReview.aspx?id=380826, Actual study start date: 20 November 2020.

Metformin prevents morphine-induced apoptosis in rats with diabetic neuropathy: a possible mechanism for attenuating morphine tolerance

Morphine is a drug of choice for the treatment of severe and chronic pain, but tolerance to the antinociceptive effect limits its use. The development of tolerance to morphine has recently been associated with neuronal apoptosis. In this study, our aim was to investigate the effects of metformin on morphine-induced neuronal apoptosis and antinociceptive tolerance in diabetic rats. Three days of cumulative dosing were administered to establish morphine tolerance in rats. The antinociceptive effects of metformin (50 mg/kg) and test dose of morphine (5 mg/kg) were considered at 30-min intervals by thermal antinociceptive tests. To induce diabetic neuropathy, streptozotocin (STZ, 65 mg/kg) was injected intraperitoneally. ELISA kits were used to measure caspase-3, bax, and bcl-2 levels from dorsal root ganglion (DRG) tissue. Semi-quantitative scoring system was used to evaluate apoptotic cells with the the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) method. The findings suggest that co-administration of metformin with morphine to diabetic rats showed a significant increase in antinociceptive effect compared to morphine alone. The antinociceptive tests indicated that metformin significantly attenuated morphine antinociceptive tolerance in diabetic rats. In addition, metformin decreased the levels of apoptotic proteins caspase 3 and Bax in DRG neurons, while significantly increased the levels of antiapoptotic Bcl-2. Semi-quantitative scoring showed that metformin provided a significant reduction in apoptotic cell counts in diabetic rats. These data revealed that metformin demonstrated antiapoptotic activity in diabetic rat DRG neurons and attenuated morphine tolerance. The antiapoptotic activity of metformin probably plays a significant role in reducing morphine tolerance.