The antinociceptive effect of acetaminophen in a rat model of neuropathic pain

Effect of Ethanol Extract of Soursop (Annona muricata L.) Stem Bark on Rat Liver Function

<b>Background and Objective:</b> Paracetamol does not cause toxic effects if given in therapeutic doses, namely below 4 g per day. Use of paracetamol at a dose of more than 4 g per day can result in hepatotoxicity. This study aims to compare the hepatoprotector potency of the ethanol extract of soursop stem bark (<i>A. muricata</i>) against the enzyme activity of SGOT and SGPT in rats induced by toxic doses of paracetamol. <b>Materials and Methods:</b> A Completely Randomized Design (CRD) comprised of 6 treatment groups and 3 replications. Total 27 white male rats were induced hepatotoxicity with 1350 mg of paracetamol on the 7th day, except for normal control (K0) which was given aquadest. The tested animals received akuades as the negative control (K-) 11.34 mg kg¹ b.wt., of Hepa-Q as the positive control (K+), ethanol extract stem bark <i>Annona muricata</i> at a dose of 150 mg kg¹ BB (P1), 300 mg kg¹ BB (P2) and 600 mg kg¹ BB (P3). <b>Results:</b> There was a significant difference (p<0.05) in the levels of SGOT and SGPT after giving ethanol extract of soursop (<i>A. muricata</i>) stem bark. The best treatment for reducing SGOT and SGPT levels in rats induced by paracetamol was the administration of ethanol extract of <i>A. muricata</i> stem bark at a dose of 600 mg kg¹ BB. <b>Conclusion:</b> Based on the results of the study, it was concluded that all ethanol extract of <i>Annona muricata</i> L. stem bark (EEAMSB) doses had the potential to reduce the levels of AST and ALT in paracetamol-induced rats.

Synergistic interaction between acetaminophen and L-carnosine improved neuropathic pain via NF-κB pathway and antioxidant properties in chronic constriction injury model

Background

Inflammation is known to underlie the pathogenesis in neuropathic pain. This study investigated the anti-inflammatory and neuroprotective mechanisms involved in antinociceptive effects of co-administration of acetaminophen and L-carnosine in chronic constriction injury (CCI)-induced peripheral neuropathy in male Wistar rats.

Methods

Fifty-six male Wistar rats were randomly divided into seven experimental groups (n = 8) treated with normal saline/acetaminophen/acetaminophen + L-carnosine. CCI was used to induce neuropathic pain in rats. Hyperalgesia and allodynia were assessed using hotplate and von Frey tests, respectively. Investigation of spinal proinflammatory cytokines and antioxidant system were carried out after twenty-one days of treatment.

Results

The results showed that the co-administration of acetaminophen and L-carnosine significantly (P < 0.001) increased the paw withdrawal threshold to thermal and mechanical stimuli in ligated rats compared to the ligated naïve group. There was a significant (P < 0.001) decrease in the levels of nuclear factor kappa light chain enhancer B cell inhibitor, calcium ion, interleukin-1-beta, and tumour necrotic factor-alpha in the spinal cord of the group coadministered with acetaminophen and L-carnosine compared to the ligated control group. Co-administration with acetaminophen and L-carnosine increased the antioxidant enzymatic activities and reduced the lipid peroxidation in the spinal cord.

Conclusions

Co-administration of acetaminophen and L-carnosine has anti-inflammatory effects as a mechanism that mediate its antinociceptive effects in CCI-induced peripheral neuropathy in Wistar rat.

Investigation of the Antinociceptive Activity of the Hydroethanolic Extract of Junglas nigra Leaf by the Tail-Immersion and Formalin Pain Tests in Rats

Background

Juglans (J.) nigra leaf is obtained from a plant that is used in traditional medicine in some countries to alleviate inflammatory diseases.

Aim

The aim of this study was to compare the effects of J. nigra extract on acute nociceptive and inflammatory pain in rats.

Methods

Antinociceptive activity was examined in Wistar rats by the tail-immersion and formalin tests. Motor function was assessed using the rotarod test. Plant extract was administered intraperitoneally.

Results

In the tail-immersion test, the maximal antinociceptive effect of the plant extract (100–330 mg/kg) was about 24–30% and is the result of the effect of a high concentration of ethanol. In the formalin test, the plant extract (41.3–330 mg/kg) significantly and dose-dependently inhibited nociception in both phases of the test with similar maximal effects of about 76% and 85%. Only the plant extract at the dose of 330 mg/kg caused a significant time-dependent reduction in time spent on the rotarod.

Conclusions

In rats, the preventive systemic administration of the hydroethanolic extract of J. nigra leaf reduced chemically but not thermally induced pain. Higher efficacy was obtained in pain associated with inflammation and tissue injury. The antinociceptive effect is dose-dependent and may be limited by motor impairment.

Systematic Review of Systemic and Neuraxial Effects of Acetaminophen in Preclinical Models of Nociceptive Processing

Acetaminophen (APAP) in humans has robust effects with a high therapeutic index in altering postoperative and inflammatory pain states in clinical and experimental pain paradigms with no known abuse potential. This review considers the literature reflecting the preclinical actions of acetaminophen in a variety of pain models. Significant observations arising from this review are as follows: 1) acetaminophen has little effect upon acute nociceptive thresholds; 2) acetaminophen robustly reduces facilitated states as generated by mechanical and thermal hyperalgesic end points in mouse and rat models of carrageenan and complete Freund’s adjuvant evoked inflammation; 3) an antihyperalgesic effect is observed in models of facilitated processing with minimal inflammation (eg, phase II intraplantar formalin); and 4) potent anti-hyperpathic effects on the thermal hyperalgesia, mechanical and cold allodynia, allodynic thresholds in rat and mouse models of polyneuropathy and mononeuropathies and bone cancer pain. These results reflect a surprisingly robust drug effect upon a variety of facilitated states that clearly translate into a wide range of efficacy in preclinical models and to important end points in human therapy. The specific systems upon which acetaminophen may act based on targeted delivery suggest both a spinal and a supraspinal action. Review of current targets for this molecule excludes a role of cyclooxygenase inhibitor but includes effects that may be mediated through metabolites acting on the TRPV1 channel, or by effect upon cannabinoid and serotonin signaling. These findings suggest that the mode of action of acetaminophen, a drug with a long therapeutic history of utilization, has surprisingly robust effects on a variety of pain states in clinical patients and in preclinical models with a good therapeutic index, but in spite of its extensive use, its mechanisms of action are yet poorly understood.

Chronic Polypharmacy with Increasing Drug Burden Index Exacerbates Frailty and Impairs Physical Function, with Effects Attenuated by Deprescribing, in Aged Mice

Polypharmacy (use of ≥5 medications) and increasing Drug Burden Index (DBI) score (measure of person's total exposure to anticholinergic/sedative medications) are associated with impaired physical function in observational studies of older adults. Deprescribing, the supervised withdrawal of medications for which harms outweigh benefits for an individual, may be a useful intervention. Current knowledge is limited to clinical observational studies that are unable to determine causality. Here, we establish a preclinical model that investigates the effects of chronic polypharmacy, increasing DBI, and deprescribing on global health outcomes in aging. In a longitudinal study, middle-aged (12 months) male C57BL/6J (B6) mice were administered control feed or feed and/or water containing polypharmacy or monotherapy with different DBI scores. At 21 months, each treatment group was subdivided (stratified by frailty at 21 months) to either continue on treatment for life or to have treatment withdrawn (deprescribed). Frailty and physical function were evaluated at 12, 15, 18, and 24 months, and were analyzed using a mixed modeling approach. Polypharmacy with increasing DBI and monotherapy with citalopram caused mice to become frailer, less mobile, and impaired their strength and functional activities. Critically, deprescribing in old age reversed a number of these outcomes. This is the first preclinical study to demonstrate that chronic polypharmacy with increasing DBI augments frailty and impairs function in old age, and that drug withdrawal in old age reversed these outcomes. It was not the number of drugs (polypharmacy) but the type and dose of drugs (DBI) that caused adverse geriatric outcomes.

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.

Evaluation of KP-1199: a novel acetaminophen analog for hemostatic function and antinociceptive effects

BACKGROUND

Acetaminophen (APAP) is a widely self-prescribed analgesic for mild to moderate pain, but overdose or repeat doses can lead to liver injury and death. Kalyra Pharmaceuticals has developed a novel APAP analog, KP-1199, currently in Phase 1 clinical studies, which lacks hepatotoxicity. In this study, the authors evaluated the antinociceptive effect of KP-1199 on thermal injury-induced nociceptive behaviors as well as hemostatic parameters using human blood samples.

METHODS

Full-thickness thermal injury was induced in anesthetized adult male Sprague-Dawley rats. On day 7 post-injury, KP-1199 (30 and 60 mg/kg) or APAP (60 mg/kg) was administered orally. Antinociception of KP-1199 and APAP were assessed at multiple time points using Hargreaves' test. In separate experiments, human whole blood was collected and treated with either KP-1199, APAP, or Vehicle (citrate buffer) at 1× (214 μg/ml) and 10× (2140 μg/ml) concentrations. The treated blood samples were assessed for: clotting function, thrombin generation, and platelet activation.

RESULTS

APAP did not produce antinociceptive activity. KP-1199 treatment significantly increased the nociceptive threshold, and the antinociceptive activity persisted up to 3 h post-treatment. In human samples, 10× APAP caused significantly prolonged clotting times and increased platelet activation, whereas KP-1199 had caused no negative effects on either parameter tested.

CONCLUSION

These results suggest that KP-1199 possesses antinociceptive activity in a rat model of thermal injury. Since KP-1199 does not induce platelet activation or inhibit coagulation, it presents an attractive alternative to APAP for analgesia, especially for battlefield or surgical scenarios where blood loss and blood clotting are of concern.

Long-term exposure to polypharmacy impairs cognitive functions in young adult female mice

The potential harmful effects of polypharmacy (concurrent use of 5 or more drugs) are difficult to investigate in an experimental design in humans. Moreover, there is a lack of knowledge on sex-specific differences on the outcomes of multiple-drug use. The present study aims to investigate the effects of an eight-week exposure to a regimen of five different medications (metoprolol, paracetamol, aspirin, simvastatin and citalopram) in young adult female mice. Polypharmacy-treated animals showed significant impairment in object recognition and fear associated contextual memory, together with a significant reduction of certain hippocampal proteins involved in pathways necessary for the consolidation of these types of memories, compared to animals with standard diet. The impairments in explorative behavior and spatial memory that we reported previously in young adult male mice administered the same polypharmacy regimen were not observed in females in the current study. Therefore, the same combination of medications induced different negative outcomes in young adult male and female mice, causing a significant deficit in non-spatial memory in female animals. Overall, this study strongly supports the importance of considering sex-specific differences in designing safer and targeted multiple-drug therapies.

N-acetylcysteine dose-dependently improves the analgesic effect of acetaminophen on the rat hot plate test

BACKGROUND

Acetaminophen (APAP) induced hepatotoxicity is a clinically important problem. Up to now, interventive therapy with n-acetylcysteine (NAC) has been considered as a gold-standard treatment for APAP overdose. However, no study has focused on the efficacy of these drugs' concurrent administration on probable enhancing therapeutic outcomes. Thus, this study was aimed to investigate the analgesic effect of co-administration of NAC and acetaminophen in male rats. The NAC-APAP drug formulation may demonstrate the stranger antinociceptive effect.

METHODS

Forty-eight male Sprague-Dawley rats (12-14 weeks) randomly divided into six equal groups; control, APAP (received 300 mg/kg APAP), NAC (received 600 mg/kg NAC) and APAP+ NAC groups that received simultaneously 300 mg/kg APAP with 200-600 mg/kg NAC (AN200, AN400, AN600). All administrations were done orally for once. The antinociceptive effect was recorded by measurement of latency period on a hot plate in 30, 60, and 90 min after administrations.

RESULTS

The results showed that NAC's concurrent administration with APAP, dose-dependently increased APAP analgesic effects (p< 0.0001). Moreover, NAC treatment exhibited an antinociceptive effect in 60 and 90 min, per se. The treatments had no adverse effect on liver enzymes and oxidative stress.

CONCLUSION

Co-administration of NAC with APAP can improve the antinociceptive effect of APAP. It is suggested that this compound can enhance analgesic effects of APAP and eventually lead to a reduction in acetaminophen dose. Further studies are needed to evaluate the molecular mechanism of this hyper analgesic effect.

Affective dimensions of pain and region -specific involvement of nitric oxide in the development of empathic hyperalgesia

Empathy for pain depends on the ability to feel, recognize, comprehend and share painful emotional conditions of others. In this study, we investigated the role of NO in a rat model of empathic pain. Pain was socially transferred from the sibling demonstrator (SD) who experienced five formalin injection to the naïve sibling observer (SO) through observation. SO rats received L-NAME (a nonspecific NO synthase inhibitor) or L-arginine (a precursor of NO) prior to observing the SD. Nociception, and concentrations of NO metabolites (NOx) in the serum, left and right hippocampus, prefrontal cortex, and cerebellum were evaluated. Nociceptive responses were significantly increased in the pain-observing groups. NOx levels measured 24 h after the last pain observation using the Griess method, were indicative of NOx concentration decreases and increases in the left hippocampus and cerebellum, respectively. There was an increase in tissue concentration of NOx in cerebellum and prefrontal cortex in both pain and observer groups 7 days after the fifth formalin injection. Our results suggest that NO is involved in development of empathic hyperalgesia, and observation of sibling’s pain can change NO metabolites in different brain regions in observer rats.

Chronic polypharmacy impairs explorative behavior and reduces synaptic functions in young adult mice

A major challenge in the health care system is the lack of knowledge about the possible harmful effects of multiple drug treatments in old age. The present study aims to characterize a mouse model of polypharmacy, in order to investigate whether long-term exposure to multiple drugs could lead to adverse outcomes. To this purpose we selected five drugs from the ten most commonly used by older adults in Sweden (metoprolol, paracetamol, aspirin, simvastatin and citalopram). Five-month-old wild type male mice were fed for eight weeks with control or polypharmacy diet. We report for the first time that young adult polypharmacy-treated mice showed a significant decrease in exploration and spatial working memory compared to the control group. This memory impairment was further supported by a significant reduction of synaptic proteins in the hippocampus of treated mice. These novel results suggest that already at young adult age, use of polypharmacy affects explorative behavior and synaptic functions. This study underlines the importance of investigating the potentially negative outcomes from concomitant administration of different drugs, which have been poorly explored until now. The mouse model proposed here has translatable findings and can be applied as a useful tool for future studies on polypharmacy.

Anxiety- and activity-related effects of paracetamol on healthy and neuropathic rats

Paracetamol has recently been suggested to affect emotion processing in addition to alleviating pain in humans. We investigated in adult male Hannover-Wistar rats whether acute intraperitoneally administrated paracetamol affects behavior in tests measuring anxiety, mood, motor activity, and memory. Unoperated rats received saline or a low (50 mg/kg) or high (300 mg/kg) dose of paracetamol, while rats with a spared nerve injury (SNI) model of neuropathy and sham-operated rats received saline or the low dose of paracetamol. Rats were tested on open-field (OFT), elevated plus-maze (EPM), light-dark box (LDB), novel-object recognition (NOR), sucrose preference, rotarod, and monofilament tests. In unoperated rats, both the low and high dose of paracetamol reduced line crossings, and grooming time in the OFT, and novel preference in NOR. The high dose of paracetamol increased the time spent in the closed arm in EPM, reduced the number of rearings and leanings in OFT, the time spent in the light box in LDB, and sucrose preference. Paracetamol had no significant effect on the rotarod test measuring motor activity. The low dose of paracetamol suppressed mechanical pain hypersensitivity in SNI rats, without influencing pain behavior in sham-operated rats. Saline- but not paracetamol-treated SNI rats spent more time than sham-operated rats in the closed arm in the EPM test. Together the results suggest that a high dose of paracetamol increases anxiety-like and anhedonic behavior, and impairs recognition memory in unoperated controls, while in neuropathy, a low dose of paracetamol reduces nerve injury-associated anxiety probably by reducing neuropathic pain.

Role of inducible nitric oxide synthase and interleukin-6 expression in estimation of skin burn age and vitality

Estimation of age and vitality of burn injury both in the living and dead is essential in forensic practice. Nitric oxide and interleukin-6 (IL-6) play an important role in skin burn healing. In this study, the expression of inducible nitric oxide synthase (iNOS) and IL-6 proteins during skin burn healing in rats was studied for purposes of burn dating and to differentiate between ante-mortem and post-mortem burn. Ante-mortem skin burns were created on forty five rats. Normal and burnt skin samples were taken at 1, 3, 5, 7, 9, 11, 13, 15 and 21 days following burn induction (5 rats for each stage). Post-mortem burn was inflicted 6 h after scarification in another five rats. There was a statistically significant difference in both iNOS and IL-6 expression between the different time intervals of the ante-mortem burn. Expression of both iNOS and IL-6 decreased remarkably in the post-mortem burn with a statistically significant difference from ante-mortem intervals. A statistically significant positive association between the two markers was found. These results indicate that both iNOS and IL-6 expression in ante-mortem burnt skin was time dependent and significantly differed from post-mortem burn. Further research on humans is recommended.

Adverse Geriatric Outcomes Secondary to Polypharmacy in a Mouse Model: The Influence of Aging

We aimed to develop a mouse model of polypharmacy, primarily to establish whether short-term exposure to polypharmacy causes adverse geriatric outcomes. We also investigated whether old age increased susceptibility to any adverse geriatric outcomes of polypharmacy. Young (n= 10) and old (n= 21) male C57BL/6 mice were administered control diet or polypharmacy diet containing therapeutic doses of five commonly used medicines (simvastatin, metoprolol, omeprazole, acetaminophen, and citalopram). Mice were assessed before and after the 2- to 4-week intervention. Over the intervention period, we observed no mortality and no change in food intake, body weight, or serum biochemistry in any age or treatment group. In old mice, polypharmacy caused significant declines in locomotor activity (pre minus postintervention values in control 2 ± 13 counts, polypharmacy 32 ± 7 counts,p< .05) and front paw wire holding impulse (control -2.45 ± 1.02 N s, polypharmacy +1.99 ± 1.19 N s,p< .05), loss of improvement in rotarod latency (control -59 ± 11 s, polypharmacy -1.7 ± 17 s,p< .05), and lowered blood pressure (control -0.2 ± 3 mmHg, polypharmacy 11 ± 4 mmHg,p< .05). In young mice, changes in outcomes over the intervention period did not differ between control and polypharmacy groups. This novel model of polypharmacy is feasible. Even short-term polypharmacy impairs mobility, balance, and strength in old male mice.