Antinociceptive effects of combination of tramadol and acetaminophen on painful diabetic neuropathy in streptozotocin-induced diabetic rats

Pharmacological Interaction Between Cannabidiol and Tramadol on Experimental Diabetic Neuropathic Pain: An Isobolographic Analysis

Introduction: Diabetic neuropathies are the most prevalent chronic complications of diabetes, characterized by pain and substantial morbidity. Although many drugs have been approved for the treatment of this type of pain, including gabapentin, tramadol (TMD), and classical opioids, it is common to report short-term results or potentially severe side effects. TMD, recommended as a second-line treatment can lead to unwanted side effects. Cannabidiol (CBD) has been gaining attention recently due to its therapeutic properties, including pain management. This study aimed to characterize the pharmacological interaction between CBD and TMD over the mechanical allodynia associated with experimental diabetes using isobolographic analysis. Materials and Methods: After diabetes induction by streptozotocin (STZ), diabetic rats were systemically treated with CBD or TMD alone or in combination (doses calculated based on linear regression of effective dose 40% [ED40]) and had the mechanical threshold evaluated using the electronic Von Frey apparatus. Both experimental and theoretical additive ED40 values (Zmix and Zadd, respectively) were determined for the combination of CBD plus TMD in this model. Results: Acute treatment with CBD (3 or 10 mg/kg) or TMD (2.5, 5, 10, or 20 mg/kg) alone or in combination (0.38+1.65 or 1.14+4.95 mg/kg) significantly improved the mechanical allodynia in STZ-diabetic rats. Isobolographic analysis revealed that experimental ED40 of the combination (Zmix) was 1.9 mg/kg (95% confidence interval [CI]=1.2-2.9) and did not differ from the theoretical additive ED40 2.0 mg/kg (95% CI=1.5-2.8; Zadd), suggesting an additive antinociceptive effect in this model. Conclusions: Using an isobolographic analysis, these results provide evidence of additive pharmacological interaction between CBD and TMD over the neuropathic pain associated with experimental diabetes induced by STZ.

Oral proniosomal amitriptyline and liraglutide for management of diabetic neuropathy: Exceptional control over hyperglycemia and neuropathic pain

Exploitation of nanocarriers provides a compartment for enclosing drugs to protect them from degradation and potentiate their therapeutic efficiency. In the current study, amitriptyline- and liraglutide-loaded proniosomes were constructed for management of diabetic neuropathy, a serious complication associated with diabetes, that triggers spontaneous pain in patients and results in impaired quality of life. The developed therapeutic proniosomes were extensively characterized via dynamic light scattering, scanning electron microscopy, transmission electron microscopy, and Fourier transform-infrared spectroscopy. High entrapment efficiency could be attained for both drugs in the proniosomes, and the reconstituted amitriptyline- and liraglutide-loaded niosomes possessed spherical morphology and particle sizes of 585.3 nm and 864.4 nm, respectively. In a diabetic neuropathy rat model, oral administration of the developed amitriptyline- and liraglutide-loaded proniosomes significantly controlled blood glucose levels, reduced neuropathic pain, oxidative stress and inflammatory markers, and improved histological structure of the sciatic nerve as compared to the oral and subcutaneous administration of amitriptyline and liraglutide, respectively. Loading of the tricyclic antidepressant amitriptyline and the antidiabetic peptide liraglutide into proniosomes resulted in exceptional control over hyperglycemia and neuropathic pain, and thus could provide an auspicious delivery system for management of neuropathic pain and control of blood glucose levels.

The effects of voluntary exercise on histological and stereological changes of sciatic nerve, nitric oxide levels, and peripheral neuropathy caused by high-fat diet-induced type 2 diabetes in male rats

This research was conducted to investigate the possible beneficial impacts of voluntary exercise on sciatic tissue, nitric oxide levels, stereological changes, and peripheral neuropathy caused by "high-fat-diet (HFD)"-induced "type 2 diabetes mellitus (T2DM)" in male rats. Rats were put into four experimental groups at random: "healthy control (C), voluntary exercise (VE), diabetic (D), and diabetic rats treated by voluntary exercise (VED)"; each group contain eight animals. Animals in VE and VED groups performed "voluntary exercise (VE)" for ten weeks. Animals in D and VED groups became diabetic after receiving a HFD for four weeks and an intraperitoneal injection (IP) of "streptozotocin (STZ)" (35 mg/kg). In order to evaluate mechanical and thermal algesia, hot plate, tail withdrawal, and von Frey tests were carried out. At the end of this study, serum NOx levels were assessed, and histological and stereological analyses were conducted. Mechanical nociceptive thresholds indicated considerable reduction (p < 0.001) which was followed by a remarkable enhance (p < 0.001) in thermal nociceptive threshold of D group. Tissue changes were also seen in sciatic nerve of D group. Voluntary exercise modified thermal and mechanical sensitivity in diabetic rats. It also improved the damaged sciatic nerve in diabetic animals.

Attenuation of Some Inflammatory Markers by Endurance Training in the Spinal Cord of Rats with Diabetic Neuropathic Pain

Nervous inflammation is an important component of the pathogenesis of neurodegenerative diseases including chronic diabetic neuropathic pain. In order to obtain a decrease in the progression of diabetic neuronal damage, it may be necessary to examine therapeutic options that involve antioxidants and anti-inflammatory agents. The aim of this study was to investigate the attenuation of inflammatory factors with endurance training in the spinal cord of rats with neuropathic pain. Thirty-two 8-week-old male Wistar rats (with a weight range of 204 ± 11.3 g) were randomly divided into 4 groups (n = 8), including (1) diabetic neuropathy (50 mg/kg streptozotocin intraperitoneal injection), (2) diabetic neuropathy training (30 minutes of endurance training at 15 meters per minute, 5 days a week for 6 weeks), (3) healthy training, and (4) healthy control. After confirmation of diabetic neuropathy by behavioral tests, training protocol and supplementation were performed. The NLRP3, P38 MAPK, TNF-α, and IL-1β gene expressions were measured by a real-time technique in the spinal cord tissue. One-way analysis of variance and Tukey's post hoc test were used for statistical analysis. Endurance training reduced the sensitivity of the nervous system to thermal hyperalgesia and mechanical allodynia; also, compared to the diabetic neuropathy group, the gene expressions of NLTP3, P38 MAPK, TNF-α, and IL-1β were significantly reduced by endurance training (P < 0.05). Endurance training modulates NLRP3, P38 MAPK, and TNF-α, IL-1β gene expressions and improves the sensitivity of nociceptors to pain factors. Accordingly, it is recommended to use endurance training to reduce neuropathic pain for diabetics.

Mechanistic approach towards diabetic neuropathy screening techniques and future challenges: A review

Diabetic neuropathy, also called peripheral diabetic neuropathy (PDN), is among the most significant diabetes health consequences, alongside diabetic nephropathy, diabetic cardiomyopathy and diabetic retinopathy. Diabetic neuropathy is the existence of signs and indications of peripheral nerve damage in patients with diabetes after other causes have been governed out. Diabetic neuropathy is a painful and severe complication of diabetes that affects roughly 20% of people. The development of diabetic neuropathy is regulated by blood arteries that nourish the peripheral nerves and metabolic problems such as increased stimulation of polyol pathway, loss of myo-inositol and enhanced non-enzymatic glycation. It's divided into four types based on where neurons are most affected: autonomic, peripheral, proximal, and focal, with each kind presenting different symptoms like numbing, gastrointestinal disorders, and heart concerns. Pharmacotherapy for neuropathic pain is complex and for many patients, effective treatment is lacking; as a result, scientific proof recommendations are crucial. As a result, the current demand is to give the most vital medications or combinations of drugs that work directly on the nerves to help diabetic neuropathy patients feel less pain without causing any adverse effects. In diabetic neuropathy research, animal models are ubiquitous, with rats and mice being the most typically chosen for various reasons. This review covers the epidemiology, clinical features, pathology, clinical symptom, mechanism of diabetic neuropathy development, diagnosis, screening models of animals, diabetic neuropathy pharmacotherapy.

Paracetamol for multimodal analgesia

Pain and related disability remain a major social and therapeutic problem. Comorbidities and therapies increase drug interactions and side effects making pain management more compounded especially in the elderly who are the fastest-growing pain population. Multimodal analgesia consists of using two or more drugs and/or techniques that target different sites of pain, increasing the level of analgesia and decreasing adverse events from treatment. Paracetamol enhances multimodal analgesia in experimental and clinical pain states. Strong preclinical evidence supports that paracetamol has additive and synergistic interactions with anti-inflammatory, opioid and anti-neuropathic drugs in rodent models of nociceptive and neuropathic pain. Clinical studies in young and adult elderly patients confirm the utility of paracetamol in multimodal, non-opioid or opioid-sparing, therapies for the treatment of acute and chronic pain.

Spinal cannabinoid CB1 or CB2 receptors activation attenuates mechanical allodynia in streptozotocin-induced diabetic rats

Diabetes is a chronic disease associated with a high number of complications such as peripheral neuropathy, which causes sensorial disturbances and may lead to the development of diabetic neuropathic pain (DNP). The current treatment for DNP is just palliative and the drugs may cause severe adverse effects, leading to discontinuation of treatment. Thus, new therapeutic targets need to be urgently investigated. Studies have shown that cannabinoids have promising effects in the treatment of several pathological conditions, including chronic pain. Thus, we aimed to investigate the acute effect of the intrathecal injection of CB1 or CB2 cannabinoid receptor agonists N-(2-chloroethyl)-5Z, 8Z, 11Z, 14Z-eicosatetraenamide (ACEA) or JWH 133, respectively (10, 30 or 100 μg/rat) on the mechanical allodynia associated with experimental diabetes induced by streptozotocin (60 mg/kg; intraperitoneal) in rats. Cannabinoid receptor antagonists CB1 AM251 or CB2 AM630 (1 mg/kg) were given before treatment with respective agonists to confirm the involvement of cannabinoid CB1 or CB2 receptors. Rats with diabetes exhibited a significant reduction on the paw mechanical threshold 2 weeks after diabetes induction, having the maximum effect observed 4 weeks after the streptozotocin injection. This mechanical allodynia was significantly improved by intrathecal treatment with ACEA or JWH 133 (only at the higher dose of 100 μg). Pre-treatment with AM251 or AM630 significantly reverted the anti-allodynic effect of the ACEA or JWH 133, respectively. Considering the clinical challenge that the treatment of DPN represents, this study showed for the first time, that the intrathecal cannabinoid receptors agonists may represent an alternative for the treatment of DNP.

Synergistic interaction between amitriptyline and paracetamol in persistent and neuropathic pain models: An isobolografic analysis

The current study was designed to evaluate the transient antinociceptive interaction between amitriptyline and paracetamol in the formalin test. In addition, considering other long-term neuroprotective mechanisms of these drugs, we hypothesized that this combination might exert some synergistic effects on neuropathic pain linked with its possible ability to prevent Wallerian degeneration (WD). The effects of individual and fixed-ratio of 1:1 combinations of orally administered amitriptyline and paracetamol were assayed in the two phases of the formalin test and in the chronic constriction injury (CCI) model in rats. Isobolographic analysis was employed to characterize the synergism produced by the combinations. Amitriptyline, paracetamol, and fixed-ratio amitriptyline-paracetamol combinations produced dose-dependent antinociceptive effects mainly on the inflammatory tonic phase. Repeated doses of individual drugs and their combination decreased CCI-induced mechanical allodynia in a dose-dependent manner. ED₃₀ (formalin) and ED₅₀ (CCI) values were estimated for the individual drugs, and isobolograms were constructed. Theoretical ED_30/50 values for the combination estimated from the isobolograms were 16.5 ± 3.9 mg/kg and 26.0 ± 7.2 mg/kg for the single and repeated doses in persistent and neuropathic pain models, respectively. These values were significantly higher than the actually observed ED_30/50 values, which were 0.39 ± 0.1 mg/kg and 8.2 ± 0.8 mg/kg in each model, respectively, indicating a synergistic interaction. Remarkably, CCI-induced sciatic nerve WD-related histopathological changes were prevented by this combination compared to either drug administered alone.

ADME and toxicity considerations for tramadol: from basic research to clinical implications

INTRODUCTION

Tramadol is widely being used in chronic pain management for improving patients' life quality and reducing trauma. Although it is listed in several medicinal guidelines, its use is controversial because of the conflicting results obtained in pharmacokinetic/pharmacodynamic studies. This multi-receptor drug acts as µ₁ opioid receptor agonist, monoamine reuptake inhibitor, and inhibitor of ligand-gated ion channels and some special protein-coupled receptors.

AREAS COVERED

This review provides a comprehensive view on the pharmacokinetic, pharmacodynamic, and toxicity of tramadol with a deep look on its side effects, biochemical and pathological changes, and possible drug interactions. In addition, the main ways of tramadol poisoning management describe according to in vivo and clinical trial studies.

EXPERT OPINION

Given the broad spectrum of targets, increasing the cases of overdoses and toxicity, and probable drugs interaction, it is necessary to take another look at the pharmacology of tramadol. Regarding the adverse effects of tramadol on different tissues, especially the nervous system and liver tissue, more attentions to tramadol metabolites, their interaction with other drugs, and active agents seem critical. Seizure as the most cited effect of tramadol and its destructive effects on tissues would alleviate by co-administration with drugs with antioxidant properties.

Evaluation of ameliorative effect of sodium nitrate in experimental model of streptozotocin-induced diabetic neuropathy in male rats

OBJECTIVE

Diabetes induces sensory symptoms of neuropathy as positive (hyperalgesia), negative (hypoalgesia), or both.

METHODS

In the present study, fifty male Wistar rats were allocated to five groups: control, control+nitrate, diabetes, diabetes+insulin, and diabetes+nitrate. Thirty days after diabetes confirmation, insulin (2-4 U/day) was injected subcutaneously in diabetes+insulin group and nitrate (100 mg/l) was added into drinking water of the control+nitrate and diabetes+nitrate groups for a period of 2 months. In order to assess the mechanical and thermal algesia, tail immersion, hot plate, and von Frey tests were performed. The serum insulin levels were determined with insulin ELISA Kit. Serum level of NOx was determined by the Griess method.

RESULTS

Both thermal and mechanical nociceptive thresholds showed a significant decrease (p<0.05) which was followed by a significant increase (p<0.01) in the thermal nociceptive threshold in the diabetes group. Chronic nitrate or insulin treatment led to a significant decrease (p<0.01) in blood glucose levels, as well as a significant (p<0.05) increase in the body weight and serum NOx. Moreover, nitrate treatment significantly increased serum insulin levels (p<0.001) compared to the other groups.

CONCLUSION

Chronic nitrate treatment modified the thermal and mechanical sensitivities in diabetic animals.

Sodium nitrate preconditioning prevents progression of the neuropathic pain in streptozotocin-induced diabetes Wistar rats

Purpose

The purpose of the study was to evaluate the possible protective effects of low dose sodium nitrate preconditioning on the peripheral neuropathy in streptozotocin (STZ)-induced diabetic model.

Methods

Male Wistar rats were randomly divided into five groups: control (no intervention), control treated sodium nitrate (100 mg/L in drinking water), diabetic (no intervention), diabetic treated NPH insulin (2-4 U), and diabetic treated sodium nitrate (100 mg/L in drinking water). Diabetes was induced by intraperitoneal injection of STZ (60 mg/kg). All interventions were done for 60 days immediately following diabetes confirmation. Thermal and mechanical algesia thresholds were measured by means of hot-plate test, von Frey test, and tail-withdrawal test before the diabetic induction and after diabetes confirmation. At the end of the experiment, serum NOx level and serum insulin level were assessed. Blood glucose concentration and body weight have recorded at the base and duration of the experiment.

Results

Both hypoalgesia, hyperalgesia along with allodynia developed in diabetic rats. Significant alterations including, decrease in tail withdrawal latency (30th day), decreased mechanical threshold (60th day), and an increase in hot plate latency (61st day) were displayed in diabetic rats compared to control rats. Nitrate and insulin preconditioning produced protective effects against diabetes-induced peripheral neuropathy. Data analysis also showed a significant increase in glucose level as well as a considerable reduction in serum insulin and body weight of diabetic rats, which restored by both insulin and nitrate preconditioning.

Conclusion

Sodium nitrate preconditioning produces a protective effect in diabetic neuropathy, which may be mediated by its antihyperglycemic effects and increased serum insulin level.

Revisiting Tramadol: A Multi-Modal Agent for Pain Management

Tramadol-an atypical opioid analgesic-has a unique pharmacokinetic and pharmacodynamic profile, with opioidergic, noradrenergic, and serotonergic actions. Tramadol has long been used as a well-tolerated alternative to other drugs in moderate pain because of its opioidergic and monoaminergic activities. However, cumulative evidence has been gathered over the last few years that supports other likely mechanisms and uses of tramadol in pain management. Tramadol has modulatory effects on several mediators involved in pain signaling, such as voltage-gated sodium ion channels, transient receptor potential V1 channels, glutamate receptors, α₂-adrenoceptors, adenosine receptors, and mechanisms involving substance P, calcitonin gene-related peptide, prostaglandin E₂, and proinflammatory cytokines. Tramadol also modifies the crosstalk between neuronal and non-neuronal cells in peripheral and central sites. Through these molecular effects, tramadol could modulate peripheral and central neuronal hyperexcitability. Given the broad spectrum of molecular targets, tramadol as a unimodal analgesic relieves a broad range of pain types, such as postoperative, low back, and neuropathic pain and that associated with labor, osteoarthritis, fibromyalgia, and cancer. Moreover, tramadol has anxiolytic, antidepressant, and anti-shivering activities that could improve pain management outcomes. The aim of this review was to address these issues in the context of maladaptive physiological and psychological processes that are associated with different pain types.

Involvement of 5-HT1A/1B receptors in the antinociceptive effect of paracetamol in the rat formalin test

The mechanism of analgesic action of paracetamol (acetominophen) remains still unknown. However, a relationship between serotonergic system and the effect of paracetamol has been previously demonstrated. The serotonin activity in the brainstem is primarily under the control of 5-HT_1A somatodendritic receptors, although some data also suggest the involvement of 5-HT_1B receptors. To determine whether the 5-HT_1A and 5-HT_1B receptors are involved in the antinociceptive effect of paracetamol, we evaluated the effect of paracetamol (0.125-1 g/kg i.p.) followed by different antagonists [WAY 100,635 (0.8 mg/kg s.c.) and SB 216,641 (0.8 mg/kg s.c.)] or agonists [8-OH-DPAT (0.125 mg/kg s.c.) and CP 93,129 (0.125 mg/kg s.c.)] of 5-HT_1A and 5-HT_1B receptors, respectively, in the rat model of formalin-induced pain. We demonstrated that paracetamol administration showed a dose-dependent antinociceptive effect in the formalin test. WAY 100,635 (5-HT_1A antagonist) induced an increase in the antinociceptive effect of paracetamol at 250 mg/kg doses. Conversely, 8-OH-DPAT (5-HT_1A agonist) decreased the antinociceptive effect of paracetamol at 500-1000 mg/kg doses. However, SB216641 (5-HT_1B antagonist) modified weakly the antinociceptive effect of paracetamol at 250 mg/kg doses and CP 93,129 (5-HT_1B agonist) not produce a clear effect in the antinociceptive effect of paracetamol. These results suggest that the antinociceptive effect of paracetamol can be enhanced mainly by compounds having 5-HT_1A antagonist properties in the formalin test and maybe by 5-HT_1B receptors antagonists.

Effect of nonsteroidal anti-inflammatory drugs on colorectal distension-induced visceral pain

Objectives:

To investigate nonsteroidal anti-inflammatory drugs effectiveness in colorectal distension (CRD)-induced visceral pain model.

Materials and Methods:

Male Sprague–Dawley (250–300 g) rats were anesthetized with ketamine (50 mg/kg, intraperitoneally [i.p.]) and chlorpromazine (25 mg/kg, i.p.). Two bipolar Teflon-coated Ni/Cr wire electrodes (80-M diameter) were placed in the abdominal external oblique muscle for the recording of electromyography. Jugular vein catheter was placed for the administration of drugs. CRD method was applied to evaluate of visceral pain. All drugs (paracetamol, meloxicam, metamizole, and dexketoprofen) administered intravenously.

Results:

Paracetamol 200, 400, and 600 mg/kg did not change the visceromotor response (VMR) when compare with the control group. Meloxicam 2 and 4 mg/kg showed no effect but at doses of 6 mg/kg meloxicam significantly ([51.9 ± 6.4%] [P < 0.001]) decreased VMR compared with the control group. Metamizole 200 mg/kg did not change responses but dose of 400 and 600 mg/kg metamizole reduced VMR. Dexketoprofen 2 and 4 mg/kg did not cause a change in VMR but 6 mg/kg dose significantly reduced response compared with the control group ([43.9 ± 3.9%, 36.8 ± 2.8%, 34.8 ± 2.5%, 42.1 ± 4.8%, 40.7 ± 3.5%, 36.4 ± 2.7%, and 26.1 ± 2.2%]; from 10 min to 70 min, respectively, [P < 0.05]).

Conclusion:

Metamizole, dexketoprofen and meloxicam show antinociceptive effect with different duration of action on CRD-induced visceral pain model. This condition can be explained due to different chemical structures and different mechanisms which play a role in modulation of pain.

Levetiracetam synergises with common analgesics in producing antinociception in a mouse model of painful diabetic neuropathy

Painful diabetic neuropathy is difficult to treat. Single analgesics often have insufficient efficacy and poor tolerability. Combination therapy may therefore be of particular benefit, because it might provide optimal analgesia with fewer adverse effects. This study aimed to examine the type of interaction between levetiracetam, a novel anticonvulsant with analgesic properties, and commonly used analgesics (ibuprofen, aspirin and paracetamol) in a mouse model of painful diabetic neuropathy. Diabetes was induced in C57BL/6 mice with a single high dose of streptozotocin, applied intraperitoneally (150 mg/kg). Thermal (tail-flick test) and mechanical (electronic von Frey test) nociceptive thresholds were measured before and three weeks after diabetes induction. The antinociceptive effects of orally administered levetiracetam, analgesics, and their combinations were examined in diabetic mice that developed thermal/mechanical hypersensitivity. In combination experiments, the drugs were co-administered in fixed-dose fractions of single drug ED50 and the type of interaction was determined by isobolographic analysis. Levetiracetam (10-100 mg/kg), ibuprofen (2-50 mg/kg), aspirin (5-75 mg/kg), paracetamol (5-100 mg/kg), and levetiracetam-analgesic combinations produced significant, dose-dependent antinociceptive effects in diabetic mice in both tests. In the tail-flick test, isobolographic analysis revealed 15-, and 19-fold reduction of doses of both drugs in the combination of levetiracetam with aspirin/ibuprofen, and paracetamol, respectively. In the von Frey test, approximately 7- and 9-fold reduction of doses of both drugs was detected in levetiracetam-ibuprofen and levetiracetam-aspirin/levetiracetam-paracetamol combinations, respectively. These results show synergism between levetiracetam and ibuprofen/aspirin/paracetamol in a model of painful diabetic neuropathy and might provide a useful approach to the treatment of patients suffering from painful diabetic neuropathy.

The neuroprotective benefit from pioglitazone (PIO) addition on the alpha lipoic acid (ALA)-based treatment in experimental diabetic rats

In this study, we investigated the combined effect of pioglitazone (PIO) with alpha lipoic acid (ALA) on the peripheral nerves of diabetic rats. Animals were divided into 8 groups (N = 6-8) and designated according to ALA (100 mg/kg/day) and PIO (10 mg/kg/day) treatment: Normal, Normal + ALA, Normal + PIO, Normal + ALA + PIO, DM, DM + ALA, DM + PIO, and DM + ALA + PIO. After 24 weeks, current perception threshold, mechanical allodynia, oxidative stresses, intraepidermal nerve fiber density (IENFD), and axonal morphology in the sciatic nerve were compared among groups. IENFD in the DM + ALA + PIO group was significantly less reduced than in other DM groups (7.61 ± 0.52 vs. 5.62 ± 0.96, 5.56 ± 0.60, and 7.10 ± 0.70 for DM, DM + ALA, and DM + PIO, respectively P < 0.05). The mean myelinated axonal area in the sciatic nerves was significantly higher in the DM + ALA + PIO group compared with non-treated DM group (70.2 ± 3.46 vs. 61.1 ± 2.91, P < 0.05) although significant differences were not present between combination therapy and monotherapy independent of ALA or PIO. Our results demonstrated that combination therapy using PIO based on ALA can give an additional benefit in peripheral nerve preservation in diabetes. Moreover, PIO can be preferentially considered when additional glucose-lowering agent is required in DPN patients treated with ALA.

Ascorbic Acid interaction with analgesic effect of morphine and tramadol in mice

Background:

Combining different analgesic drugs for improvement of drug efficacy is a recommended strategy intended to achieve the optimal therapeutic effects.

Objectives:

The purpose of the present study was to assess the nature of the interaction between ascorbic acid and two analgesic drugs, morphine and tramadol.

Materials and Methods:

The analgesic activity was assessed by the acetic acid writhing test in male Naval Medical Research Institute (NMRI) mice. The results were obtained using four to six animals in each group. All the drugs were injected intraperitoneally. The effective doses (ED) that produced 20%, 50%, and 65% antinociception (ED₂₀, ED₅₀ and ED₆₅) were calculated from the dose-response curve of each drug alone as well as co-administration of ascorbic acid and tramadol or morphine. The interaction index was calculated as experimental ED/theoretical ED. For each drug combination, ED₅₀, ED₂₀ and ED₆₅ were determined by linear regression analysis of the dose-response curve, and they were compared to theoretical ED₅₀, ED₂₀ and ED₆₅ using t-test.

Results:

The antinociceptive effects of all drugs were dose-dependent (ED₅₀was 206.1 mg/kg for ascorbic acid, 8.33 mg/kg for tramadol, and 0.79 mg/kg for morphine). The interaction index demonstrated additive effects at ED₅₀ and ED₆₅ for co-administration of ascorbic acid and tramadol or morphine. However, at ED₂₀, combination of ascorbic acid and tramadol or morphine showed synergic effects. The interaction index values of the combinations demonstrated the potency ratio of ascorbic acid/morphine to be lower than ascorbic acid/tramadol.

Conclusions:

This study demonstrated the results of interactions between ascorbic acid and tramadol or morphine. The results showed that the interaction effects on antinociception may be synergistic or additive, depending on the level of effect.

Use of natural compounds in the management of diabetic peripheral neuropathy

Nephropathy, retinopathy cardiomyopathy and peripheral neuropathy are all recognized as important complications in about 50% of diabetes mellitus (DM) patients, mostly related to a poor glycemic control or to an improper management of this pathology. In any case, amongst others, diabetic peripheral neuropathy (DPN) seems the leading and most painful complication usually affecting many DM patients. For this reason, this work was conceived to review the large variety of strategies adopted for management of DPN, starting from the most conventional therapies to arrive at alternative approaches. From this perspective, both the most popular pharmacological treatments used to respond to the poorly effect of common analgesics—non-steroidal anti-inflammatory drugs (NSAIDS) and opioids—understood as gabapentin vs. pregabalin clinical use, and the guidelines provided by Oriental Medicine as well as by a long list of natural compounds that many authors identify as possible therapeutic or alternative agents to replace or to combine with the existing therapies will be included. Moreover, in the effort to provide the widest panel of remedies, the most antique techniques of acupuncture and electrostimulation will be considered as alternative, which are useful approaches to take into account in any non-pharmacological strategy for DPN management.

Curcumin ameliorated diabetic neuropathy partially by inhibition of NADPH oxidase mediating oxidative stress in the spinal cord

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases are the main enzymes that produce oxidative stress, which plays an important role in painful diabetic neuropathy. Curcumin has been reported to exert an antinociceptive effect in a rat model of diabetic neuropathy by suppressing oxidative stress in the spinal cord. However, it remains unknown whether the mechanism by which curcumin ameliorates diabetic neuropathy can be attributed to spinal NADPH oxidases. This study was designed to determine the effect of curcumin on diabetic neuropathy and to investigate its precise mechanism in relation to NADPH oxidase-mediating oxidative stress in the spinal cord. Diabetic neuropathy was induced in Sprague-Dawley rats by intraperitoneal injection with 1% streptozotocin (STZ; 60 mg/kg). After the onset of diabetic neuropathy, a subset of the diabetic rats received daily intragastric administrations of curcumin (200mg/kg) or intraperitoneal injections of apocynin (2.5mg/kg) for 14 consecutive days, whereas other diabetic rats received equivalent volumes of normal saline (NS). STZ resulted in diabetic neuropathy with hyperglycemia and a lower paw withdrawal threshold (PWT), accompanied by elevations in the expression of the NADPH oxidase subunits p47(phox) and gp91(phox) and in the levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) and a reduction in superoxide dismutase (SOD) activity (P<0.05) in the spinal cord. Both curcumin and apocynin ameliorated diabetic neuropathy. In conclusion, curcumin attenuated neuropathic pain in diabetic rats, at least partly by inhibiting NADPH oxidase-mediating oxidative stress in the spinal cord.

Venlafaxine and neuropathic pain

The possible mechanisms involved in the antinociceptive effect of venlafaxine (VFX), a selective serotonin and noradrenaline reuptake inhibitor, after a single administration and chronic treatment were investigated in a diabetic neuropathic pain (DNP) model. VFX produced a significant antihyperalgesic effect after a single and repeated administration. This effect was reversed by pretreatment with yohimbine (a relatively selective α(2)-adrenergic antagonist) and p-chloroamphetamine (a neurotoxin which destroys serotonergic neurons). Conversely, naloxone (a nonselective opioid antagonist) did not reverse the effect of VFX in a DNP model. It is concluded that both noradrenergic and serotonergic mechanisms participate in the antinociceptive effect of VFX in the DNP model. However, the noradrenergic mechanism probably plays a more important role.