Effects of phenylbutazone, firocoxib, and dipyrone on the diuretic response to furosemide in horses.

BACKGROUND: Treatment with phenylbutazone (nonselective COX inhibitor) decreases the diuretic and natriuretic effects of furosemide by nearly 30% but the effects of COX-2 specific inhibitors (firocoxib) and atypical NSAIDs (dipyrone) are unknown. HYPOTHESIS: Furosemide-induced diuresis after pretreatment with firocoxib or dipyrone is diminished to a lesser extent than after pretreatment with phenylbutazone. ANIMALS: Eight healthy mares. METHODS: Each mare received 4 treatments in a prospective experimental crossover study using a replicated 4 × 4 Latin Square design: furosemide alone (FU), furosemide and phenylbutazone (PB), furosemide and firocoxib (FX), and furosemide and dipyrone (DP). After 24 hours of NSAID treatment at recommended dosages, ureteral catheters were placed for continual urine collection. After a 30-minute baseline collection period, furosemide (1.0 mg/kg, IV) was administered, and urine and blood samples were collected for 4 hours. Data were assessed by repeated measures ANOVA. RESULTS: Four-hour urine volume was (mean ± SD) ~25% less (P < .001) after pretreatment with all NSAIDs (PB 19.1 ± 2.1 mL/kg, FX 17.7 ± 3.5 mL/kg, DP 19.1 ± 3.9 mL/kg), as compared to FU (23.4 ± 5.1 mL/kg) (P < .001), but there were no differences between PB, FX, or DP. Interindividual variability in furosemide diuresis after pretreatment with different NSAIDs was observed. CONCLUSIONS AND CLINICAL IMPORTANCE: Though COX-2 selective NSAIDs and dipyrone might have less severe or fever gastrointestinal adverse effects in horses, our data suggest minimal differences in effects on furosemide-induced diuresis, and possibly, risk of nephrotoxicosis.

Development of a Lateral Flow Immunoassay Based on a Highly Specific Monoclonal Antibody To Detect 4-Methylaminoantipyrine.

To avoid false-positive results in immunoassays due to cross-reactivity of antibodies with structural analogues, especially metabolites of target compounds, the preparation of highly specific antibodies is crucial. Preserving the characteristic structure of a target compound when designing a hapten is important when preparing highly specific antibodies. Here, we designed a novel hapten, 4-(((1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4yl)amino)methyl)benzoic acid, named AA-BA, to improve the specificity of antibodies for detection of 4-methylaminoantipyrine (MAA), a residual marker of dipyrone, an important antipyretic-analgesic and anti-inflammatory drug. The structural features of the hapten remained almost the same as those of MAA. After experimental validation, monoclonal antibody 6A4 (mAb 6A4) was prepared with the half maximal inhibitory concentration (IC50) value of 4.03 ng/mL and negligible cross-reactivity with dipyrone metabolites and other antibiotics. In addition, a specific lateral flow immunoassay (LFA) strip based on colloidal gold was developed for screening MAA with a cutoff value of 25 ng/mL in milk. The developed LFA is a useful tool for rapid and accurate detection of MAA.

Time course of CYP3A activity during and after metamizole (dipyrone) in healthy volunteers.

AIMS: In patients of all ages, metamizole is a frequently used analgesic. Recently, metamizole has been identified as an inducer of, among others, cytochrome P450 (CYP) 3A activity, but the time course of this interaction has not been evaluated. METHODS: Using repeated oral microdoses (30 µg) of the CYP3A index substrate midazolam, we assessed changes in midazolam pharmacokinetics (area under the concentration-time curve from 2-4 h: AUC2-4 and estimated partial metabolic clearance: eClmet ) before, at steady-state, and after discontinuation of 3 × 1000 mg metamizole/day orally for 8 days. RESULTS: Significant changes in pharmacokinetic parameters were detected already 3 days after start of metamizole treatment. At the steady-state of enzyme induction, the geometric mean ratio of midazolam AUC2-4 was substantially reduced to 0.18 (90% confidence interval: 0.14-0.24) with a corresponding 5.43-fold (4.15-7.10) increase of eClmet . After discontinuation of metamizole, the changes slowly recovered, but were still significant at the end of the observation period on the fifth day after discontinuation of metamizole therapy (AUC2-4 reduced to 0.50 [0.41-0.63] and eClmet 1.99-fold increased [1.60-2.47, P < 0.05]). CONCLUSION: Metamizole acts as a strong inducer of CYP3A already few days after start of metamizole administration and, thus, should be avoided in patients using drugs with narrow therapeutic index and major clearance via CYP3A. If their administration is essential, close monitoring and dose adjustment of comedication should be performed as early as the first week after the initiation and after discontinuation of metamizole therapy.

Evaluation of the effect of tramadol, paracetamol and metamizole on the severity of experimental colitis.

Application of dextran sodium sulfate (DSS) is often used to induce experimental colitis. Current state of the art is to refrain from the use of analgesics due to their possible interaction with the model. However, the use of analgesics would be beneficial to reduce the overall constraint imposed on the animals. Here, we analyzed the effect of the analgesics Dafalgan (paracetamol), Tramal (tramadol) and Novalgin (metamizole) on DSS-induced colitis. To study the effect of those analgesics in colitis mouse models, acute and chronic colitis was induced in female C57BL6 mice by DSS administration in the drinking water. Analgesics were added to the drinking water on days four to seven (acute colitis) or on days six to nine of each DSS cycle (chronic colitis). Tramadol and paracetamol had minor effects on colitis severity. Tramadol reduced water uptake and activity levels slightly, while mice receiving paracetamol presented with a better overall appearance. Metamizole, however, significantly reduced water uptake, resulting in pronounced weight loss. In conclusion, our experiments show that tramadol and paracetamol are viable options for the use in DSS-induced colitis models. However, paracetamol seems to be slightly more favorable since it promoted the overall wellbeing of the animals upon DSS administration without interfering with typical readouts of colitis severity.

The effects of metamizole on hematopoietic progenitor cells: Suppression of hematopoiesis stimulation in vitro.

BACKGRAUND: There is evidence that the adverse effects of metamizole occur due to the effect of the drug on the hematopoietic stem/progenitor cells, and therefore, the disruption of hematopoiesis. Therefore, our study aimed to evaluate the effects of metamizole on hematopoietic stem/progenitor cells using cell culture techniques. MATERIAL AND METHODS: In our study, samples were taken from stem cell products of healthy allogeneic stem cell transplant donors. The colony-forming unit (CFU) assay was used for the cells obtained from these samples. In addition, the drug effects on cell proliferation were evaluated with the MTT. Furthermore, the cell colonies were labelled with immunofluorescent antibodies and the effects of metamizole on cell types formed in culture were evaluated. RESULTS: We determined that metamizole negatively affects the proliferation of cells, especially starting from 10 µM. As a result of the evaluation of colonization, we saw that the number of colonies decreased with increasing concentrations. Granulocyte-macrophage colonies were more affected at increasing concentrations than other colonies. As a result of the evaluations of our in vitro study, it was also shown as an important finding that the individual effects of the drug were highly variable. CONCLUSION: CFU method can be used as a suitable method to investigate the effects of drugs and toxic substances on hematopoiesis. We also think it may be suitable for pre-analysing hematopoietic side effects in new drug research. In addition, using stem cell samples in studies may contribute more easily to the in vitro simulation of hematopoietic differentiations (Fig. 7, Ref. 29). Text in PDF www.elis.sk Keywords: metamizole, hematopoietic progenitor cells, hematopoiesis, CFU assay, adverse effect.

The antipyretic effectiveness of dipyrone in the intensive care unit: A retrospective cohort study.

INTRODUCTION: Dipyrone (metamizol) is regularly used in critical care for pain and fever treatment, especially in Germany and Spain. However, indication for antipyretic therapy in critically ill patients is currently unclear and data for both the risk and benefit of dipyrone treatment in the intensive care environment are scarce. We hypothesized that antipyretic efficiency of dipyrone would not exceed antipyretic efficiency of acetaminophen. We therefore aimed to compare temperature courses in critically ill patients receiving either intravenous dipyrone, acetaminophen or no antipyretic medication. MATERIAL AND METHODS: We included 937 intensive care unit (ICU) patients with body temperature recordings of at least 37.5°C. We investigated temperature decrease associated with dipyrone or acetaminophen and additionally compared it to an untreated control group. RESULTS: Within the eight-hour study interval, maximum body temperature decrease in patients without antipyretic medication was -0.6°C (IQR: -1.0 to -0.4°C; n = 315). Maximal decrease in body temperature was higher both with dipyrone (-0.8°C (IQR: -1.2 to -0.4°C); p = 0.016; n = 341) and acetaminophen (-0.9°C (IQR: -1.6 to -0.6°C); p<0.001; n = 71), but did not differ between dipyrone and acetaminophen (p = 0.066). As compared to untreated patients, dipyrone only led to a marginal additional decrease in body temperature of only -0.1°C. Maximum of antipyretic effectiveness was reached four hours after administration. CONCLUSION: Antipyretic effectiveness of dipyrone in ICU patients may be overestimated. Given the lack of prospective data, clinical evidence for antipyretic dipyrone therapy in the ICU is insufficient and warrants further critical evaluation.

Antinociceptive Synergy Between Metamizole and Hesperidin in a Model of Visceral Pain in Mice.

BACKGROUND: Metamizole is used to relieve the visceral pain but its adverse effects limit its use. An alternative to improve its efficacy with lower doses is to combine it with a natural product as hesperidin. AIM OF THE STUDY: The aim of this study was to evaluate the antinociceptive interaction between metamizole and hesperidin in a visceral pain model using an isobolographic analysis. METHODS: Antinociception was evaluated in the writhing model using acetic acid (1%) to induce writhes in mice. Metamizole (1-316 mg/kg), hesperidin (3-300 mg/kg), or combinations with a fixed-dose ratio of 1:1 were administered intraperitoneally 30 min before the acetic acid and the number of writhes was counted for 30 min. Isobolographic analysis was employed to define the nature of the compound interaction. RESULTS: Metamizole and hesperidin in individual administration induced dose-dependent antinociceptive effects, reached an efficacy of 84.2 ± 5.9% and 66.3 ± 7.4%, respectively. The ED50 values calculated from their dose-response curves were 84.5 ± 22.7 and 108.9 ± 17.9 mg/kg, respectively. The analysis of DRC for the metamizole + hesperidin combination, in a ratio 1:1 showed a ED50 COMB value lower than the ED50 ADD estimated from the additivity line from the isobologram (46.7 ± 6.3 vs. 96.7 ± 11.9 mg/kg, respectively). In addition, the pharmacological interaction calculated was of 0.48. These results suggest a synergistic interaction for the antinociceptive activity of metamizole + hesperidin combination. CONCLUSION: These data suggest that metamizole + hesperidin combination could be useful in treating visceral pain as it can interact synergistically using low dose of both drugs with the possibility of reducing the risk of adverse effects.

The PI3Kγ/AKT signaling pathway mediates peripheral antinociceptive action of dipyrone.

Dipyrone (DIP), also known as metamizole, is an over-the-counter analgesic used in Europe and Latin America. Evidence suggesting that inflammatory pain attenuation by DIP is associated with a direct impact on peripheral primary nociceptive neurons through the stimulation of nitric oxide signaling pathway. However, the molecular mechanism by which DIP activates this pathway remains unknown. The PI3Kγ/AKT signaling cascade activation is one of the well-known molecular mechanisms that promote nitric oxide production in sensory neurons. Herein, we investigated the role of the PI3Kγ/AKT signaling cascade in the context of peripheral analgesic effect of DIP. DIP was administered into PGE2 pre-sensitized paws of rats and mechanical hyperalgesia was determined using electronic von Frey test after 1 h. Nonselective or selective pharmacological inhibitors of PI3Kγ and AKT were also administered in DIP-treated rats under paws sensitized with PGE2. Intraplantar injection of DIP attenuated PGE2-induced hyperalgesia in a dose-dependent manner. Treatment with nonselective (wortmannin or LY294002) or selective (AS605240) pharmacological inhibitors of PI3Kγ reduced the peripheral antihypernociceptive effect of DIP. Consistently, AKT selective inhibitor also reversed analgesic DIP effects. Corroborating these data, we found that DIP induced AKT phosphorylation in cultured dorsal root ganglion neurons, which was prevented in the presence of PI3Kγ selective inhibitor. Taken together, these findings provide evidence that peripheral analgesic effect of DIP is dependent on the activation of PI3Kγ/AKT signaling pathway.

Metamizole is a Moderate Cytochrome P450 Inducer Via the Constitutive Androstane Receptor and a Weak Inhibitor of CYP1A2.

Metamizole is an analgesic and antipyretic drug used intensively in certain countries. Previous studies have shown that metamizole induces cytochrome (CYP) 2B6 and possibly CYP3A4. So far, it is unknown whether metamizole induces additional CYPs and by which mechanism. Therefore, we assessed the activity of 6 different CYPs in 12 healthy male subjects before and after treatment with 3 g of metamizole per day for 1 week using a phenotyping cocktail approach. In addition, we investigated whether metamizole induces CYPs by an interaction with the constitutive androstane receptor (CAR) or the pregnane X receptor (PXR) in HepaRG cells. In the clinical study, we confirmed a moderate induction of CYP2B6 (decrease in the efavirenz area under the plasma concentration time curve (AUC) by 79%) and 3A4 (decrease in the midazolam AUC by 68%) by metamizole. In addition, metamizole weakly induced CYP2C9 (decrease in the flurbiprofen AUC by 22%) and moderately CYP2C19 (decrease in the omeprazole AUC by 66%) but did not alter CYP2D6 activity. In addition, metamizole weakly inhibited CYP1A2 activity (1.79-fold increase in the caffeine AUC). We confirmed these results in HepaRG cells, where 4-MAA, the principal metabolite of metamizole, induced the mRNA expression of CYP2B6, 2C9, 2C19, and 3A4. In HepaRG cells with a stable knockout of PXR or CAR, we could demonstrate that CYP induction by 4-MAA depends on CAR and not on PXR. In conclusion, metamizole is a broad CYP inducer by an interaction with CAR and an inhibitor of CYP1A2. Regarding the widespread use of metamizole, these findings are of substantial clinical relevance.

Genome-Wide Association Study of Metamizole-Induced Agranulocytosis in European Populations.

Agranulocytosis is a rare yet severe idiosyncratic adverse drug reaction to metamizole, an analgesic widely used in countries such as Switzerland and Germany. Notably, an underlying mechanism has not yet been fully elucidated and no predictive factors are known to identify at-risk patients. With the aim to identify genetic susceptibility variants to metamizole-induced agranulocytosis (MIA) and neutropenia (MIN), we conducted a retrospective multi-center collaboration including cases and controls from three European populations. Association analyses were performed using genome-wide genotyping data from a Swiss cohort (45 cases, 191 controls) followed by replication in two independent European cohorts (41 cases, 273 controls) and a joint discovery meta-analysis. No genome-wide significant associations (p < 1 × 10-7) were observed in the Swiss cohort or in the joint meta-analysis, and no candidate genes suggesting an immune-mediated mechanism were identified. In the joint meta-analysis of MIA cases across all cohorts, two candidate loci on chromosome 9 were identified, rs55898176 (OR = 4.01, 95%CI: 2.41-6.68, p = 1.01 × 10-7) and rs4427239 (OR = 5.47, 95%CI: 2.81-10.65, p = 5.75 × 10-7), of which the latter is located in the SVEP1 gene previously implicated in hematopoiesis. This first genome-wide association study for MIA identified suggestive associations with biological plausibility that may be used as a stepping-stone for post-GWAS analyses to gain further insight into the mechanism underlying MIA.

Evaluation of injectable metamizole utilization in children and adults in primary care.

OBJECTIVE: Use of injectable metamizole in the outpatient setting is controversial due to safety concerns. We aimed to compare injectable metamizole prescribing patterns for children and adults with further evaluation of nationwide metamizole consumption trend. MATERIALS AND METHODS: In this retrospective cross-sectional study, 100 injectable drug-containing prescriptions written in each month of 2010 in 32 provinces of Turkey were selected. Drug utilization patterns on injectable metamizole-containing prescriptions (n = 1,270) were analyzed and compared by "pediatric" and "adult" groups. Additionally, nationwide outpatient consumption data from 2010 to 2018 were obtained, and the utilization trend was examined. RESULTS: Children received 12.4% of injectable metamizole-containing prescriptions. Male predominance was observed in children (62.7%), as opposed to female predominance in adults (55.2%, p < 0.05). The most frequent diagnoses were "acute tonsillopharyngitis" and "acute bronchitis" in both groups. Single-diagnosis prescriptions constituted 79.1% of the pediatric group and 53.1% of the adult group (p < 0.05). Diagnoses, drugs, and injectable analgesics per prescription were significantly higher in adults (1.68 ± 0.86, 3.45 ± 0.90, and 1.06 ± 0.23, respectively) than in children (1.22 ± 0.43, 3.25 ± 0.88, and 1.00, respectively) (p < 0.05). The percentage of prescriptions containing injectable antibiotics was higher in children (83.6%) than in adults (64.9%). Outpatient injectable metamizole consumption showed a decreasing trend in 2010 - 2018. CONCLUSION: Despite recent downward trend, prescribing of injectable metamizole in primary care was considerably prevalent. This study, which highlights fundamental differences among metamizole utilization patterns in children and adults, addresses the inadequacy of rational use of the drug in terms of preferred indications and accompanying drugs.

Metamizole relieves pain by influencing cytokine levels in dorsal root ganglia in a rat model of neuropathic pain.

BACKGROUND: Treatment of neuropathic pain is still challenging. Recent studies have suggested that dorsal root ganglia (DRG), which carry sensory neural signals from the peripheral nervous system to the central nervous system, are important for pathological nociception. A proper understanding of the significance and function of DRG and their role in pharmacotherapy can help to improve the treatment of neuropathic pain. Metamizole, also known as sulpyrine or dipyrone, is a non-opioid analgesic commonly used in clinical practice, but it is not used for neuropathic pain treatment. METHODS: Chronic constriction injury (CCI) of the sciatic nerve was induced in Wistar rats. Metamizole was administered intraperitoneally (ip) preemptively at 16 and 1 h before CCI and then twice a day for 7 days. To evaluate tactile and thermal hypersensitivity, von Frey and cold plate tests were conducted, respectively. RESULTS: Our behavioral results provide evidence that repeated intraperitoneal administration of metamizole diminishes the development of neuropathic pain symptoms in rats. Simultaneously, our findings provide evidence that metamizole diminishes the expression of pronociceptive interleukins (IL-1beta, IL-6, and IL-18) and chemokines (CCL2, CCL4, and CCL7) in DRG measured 7 days after sciatic nerve injury. These assays indicate, for the first time, that metamizole exerts antinociceptive effects on nerve injury-induced neuropathic pain at the DRG level. CONCLUSIONS: Finally, we indicate that metamizole-induced analgesia in neuropathy is associated with silencing of a broad spectrum of cytokines in DRG. Our results also suggest that metamizole is likely to be an effective medication for neuropathic pain.

Dual versus single vessel normothermic ex vivo perfusion of rat liver grafts using metamizole for vasodilatation.

BACKGROUND: Normothermic ex vivo liver perfusion (NEVLP) is a promising strategy to increase the donor pool in liver transplantation. Small animal models are essential to further investigate questions regarding organ preservation and reconditioning by NEVLP. A dual vessel small animal NEVLP (dNEVLP) model was developed using metamizole as a vasodilator and compared to conventional portovenous single vessel NEVLP (sNEVLP). METHODS: Livers of male Wistar rats were perfused with erythrocyte-supplemented culture medium for six hours by either dNEVLP via hepatic artery and portal vein or portovenous sNEVLP. dNEVLP was performed either with or without metamizole treatment. Perfusion pressure and flow rates were constantly monitored. Transaminase levels were determined in the perfusate at the start and after three and six hours of perfusion. Bile secretion was monitored and bile LDH and GGT levels were measured hourly. Histopathological analysis was performed using liver and bile duct tissue samples after perfusion. RESULTS: Hepatic artery pressure was significantly lower in dNEVLP with metamizole administration. Compared to sNEVLP, dNEVLP with metamizole treatment showed higher bile production, lower levels of transaminases during and after perfusion as well as significantly lower necrosis in liver and bile duct tissue. Biochemical markers of bile duct injury showed the same trend. CONCLUSION: Our miniaturized dNEVLP system enables normothermic dual vessel rat liver perfusion. The administration of metamizole effectively ameliorates arterial vasospasm allowing for six hours of dNEVLP, with superior outcome compared to sNEVLP.

Non-opioid Analgesics and the Endocannabinoid System

Non-steroidal anti-inflammatory drugs produce antinociceptive effects mainly through peripheral cyclooxygenase inhibition. In opposition to the classical non-steroidal anti-inflammatory drugs, paracetamol and dipyrone exert weak anti-inflammatory activity, their antinociceptive effects appearing to be mostly due to mechanisms other than peripheral cyclooxygenase inhibition. In this review, we classify classical non-steroidal anti-inflammatory drugs, paracetamol and dipyrone as "non-opioid analgesics" and discuss the mechanisms mediating participation of the endocannabinoid system in their antinociceptive effects. Non-opioid analgesics and their metabolites may activate cannabinoid receptors, as well as elevate endocannabinoid levels through different mechanisms: reduction of endocannabinoid degradation via fatty acid amide hydrolase and/or cyclooxygenase-2 inhibition, mobilization of arachidonic acid for the biosynthesis of endocannabinoids due to cyclooxygenase inhibition, inhibition of endocannabinoid cellular uptake directly or through the inhibition of nitric oxide synthase production, and induction of endocannabinoid release.

CB1 receptor-dependent desensitisation of TRPV1 channels contributes to the analgesic effect of dipyrone in sensitised primary sensory neurons.

BACKGROUND AND PURPOSE: While dipyrone is a widely used analgesic, its mechanism of action is not completely understood. Recently, we have reported that the dipyrone metabolite 4-aminoantipyrine (4-AA) reduces PGE2 -induced pain-related behaviour through cannabinoid CB1 receptors. Here, we ascertained, in naive and PGE2 -induced "inflamed" conditions, both in vivo and in vitro, the molecular mechanisms involved in the 4-AA-induced analgesic effects. EXPERIMENTAL APPROACH: The effect of local administration of 4-AA (160 µg per paw) on capsaicin (0.12 µg per paw) injection-induced pain-related behaviour and 4-AA's effect on 500-nM capsaicin-induced changes in intracellular calcium concentration ([Ca2+ ]i ) in cultured primary sensory neurons were assessed in vivo and in vitro, respectively. KEY RESULTS: 4-AA reduced capsaicin-induced nociceptive behaviour in naive and inflamed conditions through CB1 receptors. 4-AA (100 µM) reduced capsaicin-induced increase in [Ca2+ ]i in a CB1 receptor-dependent manner, when PGE2 was not present. Following PGE2 application, 4-AA (1-50 µM) increased the [Ca2+ ]i . Although 4-AA activated both TRPV1 and TRPA1 channels, increased [Ca2+ ]i was mediated through TRPV1 channels. Activation of TRPV1 channels resulted in their desensitisation. Blocking CB1 receptors reduced both the excitatory and desensitising effects of 4-AA. CONCLUSION AND IMPLICATIONS: CB1 receptor-mediated inhibition of TRPV1 channels and TRPV1-mediated Ca2+ -influx- and CB1 receptor-dependent desensitisation of TRPV1 channels contribute to the anti-nociceptive effect of 4-AA in naive and inflamed conditions respectively. Agonists active at both CB1 receptors and TRPV1 channels might be useful as analgesics, particularly in inflammatory conditions.

Dipyrone is locally hydrolyzed to 4-methylaminoantipyrine and its antihyperalgesic effect depends on CB2 and kappa-opioid receptors activation.

Dipyrone is an analgesic pro-drug used clinically to control moderate pain with a high analgesic efficacy and low toxicity. Dipyrone is hydrolyzed to 4-methylaminoantipyrine (4-MAA), which is metabolized to 4-aminoantipyrine (4-AA). Here, were investigate the involvement of peripheral cannabinoid CB2 and opioid receptor activation in the local antihyperalgesic effect of dipyrone and 4-MAA. The inflammatory agent, carrageenan was administered to the hindpaw of male Wistar rats, and the mechanical nociceptive threshold was quantified by electronic von Frey test. Dipyrone or 4-MAA were locally administered 2.5 h after carrageenan. Following dipyrone injection, hindpaw tissue was harvested and its hydrolysis to 4-MAA was analyzed by mass spectrometry (MS). The selective CB2 receptor antagonist (AM630), naloxone (a non-selective opioid receptor antagonist), nor-BNI (a selective kappa-opioid receptor), CTOP (a selective mu-opioid receptor), or naltrindole (a selective delta-opioid receptor) was administered 30 min prior to 4-MAA. The results demonstrate that carrageenan-induced mechanical hyperalgesia was inhibited by dipyrone or 4-MAA in a dose-dependent manner. Dipyrone administered to the hindpaw was completely hydrolyzed to 4-MAA. The antihyperalgesic effect of 4-MAA was completely reversed by AM630, naloxone and nor-BNI, but not by CTOP or naltrindole. These data suggest that the local analgesic effect of dipyrone is mediated by its hydrolyzed bioactive form, 4-MAA and, at least in part, depends on CB2 receptor and kappa-opioid receptor activation. In conclusion, the analgesic effect of dipyrone may involve a possible interaction between the cannabinoid and opioid system in peripheral tissue.

Peripheral nitric oxide signaling directly blocks inflammatory pain.

Pain is a classical sign of inflammation, and sensitization of primary sensory neurons (PSN) is the most important mediating mechanism. This mechanism involves direct action of inflammatory mediators such as prostaglandins and sympathetic amines. Pharmacologic control of inflammatory pain is based on two principal strategies: (i) non-steroidal anti-inflammatory drugs targeting inhibition of prostaglandin production by cyclooxygenases and preventing nociceptor sensitization in humans and animals; (ii) opioids and dipyrone that directly block nociceptor sensitization via activation of the NO signaling pathway. This review summarizes basic concepts of inflammatory pain that are necessary to understand the mechanisms of peripheral NO signaling that promote peripheral analgesia; we also discuss therapeutic perspectives based on the modulation of the NO pathway.

Nociception in a Progressive Multiple Sclerosis Model in Mice Is Dependent on Spinal TRPA1 Channel Activation.

Central neuropathic pain is a common untreated symptom in progressive multiple sclerosis (PMS) and is associated with poor quality of life and interference with patients' daily activities. The neuroinflammation process and mitochondrial dysfunction in the PMS lesions generate reactive species. The transient potential receptor ankyrin 1 (TRPA1) has been identified as one of the major mechanisms that contribute to neuropathic pain signaling and can be activated by reactive compounds. Thus, the goal of our study was to evaluate the role of spinal TRPA1 in the central neuropathic pain observed in a PMS model in mice. We used C57BL/6 female mice (20-30 g), and the PMS model was induced by the experimental autoimmune encephalomyelitis (EAE) using mouse myelin oligodendrocyte glycoprotein (MOG35-55) antigen and CFA (complete Freund's adjuvant). Mice developed progressive clinical score, with motor impairment observed after 15 days of induction. This model induced mechanical and cold allodynia and heat hyperalgesia which were measured up to 14 days after induction. The hypersensitivity observed was reduced by the administration of selective TRPA1 antagonists (HC-030031 and A-967079, via intrathecal and intragastric), antioxidants (α-lipoic acid and apocynin, via intrathecal and intragastric), and TRPA1 antisense oligonucleotide (via intrathecal). We also observed an increase in TRPA1 mRNA levels, NADPH oxidase activity, and 4-hydroxinonenal (a TRPA1 agonist) levels in spinal cord samples of PMS-EAE induced animals. In conclusion, these results support the hypothesis of the TRPA1 receptor involvement in nociception observed in a PMS-EAE model in mice.

Development and validation of an LC-MS/MS method for the bioanalysis of the major metamizole metabolites in human plasma.

Aim: Metamizole is a frequently used antipyretic and analgesic prodrug, yet its pharmacokinetics has not been thoroughly studied in infants and with coadministered medications. Thus, an LC-MS/MS method was developed to quantify the four major metamizole metabolites in human plasma. Methodology: Pre- and postcolumn infusion was installed to enable robust analyte retention and electrospray ionization following deproteinization of plasma samples. Results: The method was linear (R > 0.996), accurate (93.1-106.0%) and precise (≤12.7%). Mean recovery was more than 91.8% and ion suppression less than 13.1% for all analytes. Pharmacokinetic profiles were reproducible after 4 years at -80°C except for the formylated metabolite (-22.2%). Conclusion: The method fulfilled pertinent criteria of validation guidelines and required only little sample volume. The method therefore qualifies for metamizole analyses in children.

Identifying inducers of BDNF gene expression from pharmacologically validated compounds; antipyretic drug dipyrone increases BDNF mRNA in neurons.

Low levels of brain-derived neurotrophic factor (BDNF), a key regulator of synaptic plasticity, are associated with neurological diseases, including depression and Alzheimer's disease. Therefore, BDNF is a drug target for these diseases. Here we screened for inducers of neuronal Bdnf expression from a pharmacologically validated compound library using our recently developed screening assay based on luciferase activity in cultured cortical neurons. We identified 18 pharmacologically validated compounds, most of which were inferred to induce Bdnf expression by their validated pharmacological actions, such as Gs-coupled receptor activation or neuronal excitation. Unexpectedly, the screening assay identified the antipyretic drug, dipyrone, to increase Bdnf expression. Dipyrone induced endogenous Bdnf expression by Ca2+ influx evoked via L-type voltage-dependent Ca2+ channels and the N-methyl-d-aspartate receptor, indicating that dipyrone induced activity-regulated Bdnf expression in neurons. However, dipyrone-induced Bdnf expression is independent of validated pharmacological effects. Although our screening assay is difficult to reveal how active compounds induce Bdnf expression, this method is convenient to identify inducers of Bdnf expression in primary neurons. Our screening assay evaluated neuronal BDNF induction and can be used to screen for drug re-positioning, as well as novel candidate drugs, for neurological diseases that have low levels of BDNF in the brain.