Antinociception produced by nonsteroidal anti-inflammatory drugs in female vs male rats

Favorable pharmacokinetic and tolerability profiles make carprofen an attractive analgesic for subcutaneous injection and oral self-administration in rats

As basis for evidence-based analgesia refinement, species-specific pharmacokinetic and tolerability profiles of carprofen were determined in rats for least aversive administration routes and prolonged treatment. Further, potential influence on behavioral pain indicators was evaluated. LC-MS/MS determined plasma concentrations in Sprague-Dawley rats (n = 21/sex) after subcutaneous (s.c.) injection (5 mg/kg) and during a 5-day treatment via the drinking water (d.w., 10 mg/kg/24 h). Irwin test parameters, clinical scoring, body weight, body temperature, fluid and food intake, grimace scale, burrowing, nesting, hematology, and histopathology were investigated. Plasma concentrations early after injection were higher in females, reached a maximum (Cmax) of 39.16 ± 7.38 µg/ml at 3 h after injection and remained above an estimated in-vitro-derived therapeutic threshold (24.3 µg/ml) for at least 6 h with a T1/2 of 7.06 h. Carprofen-medicated d.w. was readily consumed, with constant target dose intake over the 5-day treatment period reaching a Cmax of 38.68 ± 8.67 µg/ml at 24 h. Tolerability and behavioral parameters revealed only minor changes, such as transient sedation (s.c.) and decreased body temperature (females). Gastrointestinal adverse effects were not detected. Carprofen's pharmacokinetic profile allows for a practicable s.c. injection interval. Acceptance and tolerability during prolonged oral treatment with the assessed dose of 10 mg/kg/24 h makes its non-invasive administration promising for analgesia refinement in rats.

Evaluation of gastric tolerability for long-term use of diclofenac and celecoxib in male albino rats and potential gastroprotective benefits of royal jelly: a randomized controlled trial

OBJECTIVES

Nonsteroidal anti-inflammatory drugs (NSAIDs) are used for pain and inflammation relief. Our study aimed to explore the ulcerogenic effect of long-term diclofenac and celecoxib administration on male albino stomachs, focusing on the possible gastroprotective effect of royal jelly (RJ) administration.

METHODS

Five equal groups of 50 male albino rats. The drug dosages were: diclofenac potassium (10 mg/kg/day), celecoxib (50 mg/kg/day), and RJ (300 mg/kg/day), for 4 weeks. Group 1 received no medication. Group 2 received oral diclofenac potassium. Group 3 received oral RJ plus diclofenac potassium. Group 4 received celecoxib orally. Group 4 received oral RJ plus celecoxib. When the experiment was over, rats were euthanized, blood samples were gathered, and stomachs were dissected out. Stomachs were examined for ulcer counts. Serum levels of MDA and SOD were determined. Gastric mucosa contents of MDA, SOD, PGE2, MPO, apoptotic (Bax), and anti-apoptotic (Bcl-2) genes were measured. Gastric tissue was also analyzed histopathologically.

RESULTS

Long-term administration of diclofenac and celecoxib, in such dose and duration, caused each of the aforementioned parameters to significantly deteriorate, with significant improvement with RJ co-administration. Diclofenac developed severe gastric ulcers in group 2, and RJ co-administration significantly reduced the gastric mucosa damage in group 3. Celecoxib developed no gastric ulcer in both groups 4 and 5.

CONCLUSIONS

Long-term use of diclofenac in male albino rats caused severe gastric ulcers with significant gastroprotective effects of RJ. Celecoxib provides preferable GI tolerability; thus, it should be prescribed for patients at increased risk of gastrointestinal bleeding requiring NSAIDs.

Thymoquinone attenuates paw incision-induced spontaneous and evoked pain through anti-oxidative and anti-inflammatory mechanisms in rats

Surgery commonly causes post-operative pain that should be alleviated to prevent complications. In addition to the use of synthetic drugs, there has been a widespread desire to use medicinal plants for surgical pain management. Thymoquinone (TQ), a constituent of Nigella sativa black seeds, exhibits a potent anti-oxidant property. Celecoxib (CLX), a potent non-steroidal anti-inflammatory drug, is widely used in pain management. In the present study, the effects of TQ and CLX on pain caused by hind paw surgical incision were compared. Fifty-six rats were divided into four groups of 14 rats as intact, vehicle, TQ, and CLX groups. In each group, six rats were planned to record pain-related behaviors on days 1 - 10 and eight rats were designed for determination of serum biochemical alterations on days 1 (four rats) and 3 (four rats) after surgery. Oral administrations of TQ and CLX at a same dose of 10.00 mg kg-1 alleviated paw lifting number (spontaneous pain) and paw withdrawal threshold evoked by von Frey filaments on metal mesh floor, improved the decreased contents of serum total anti-oxidant capacity and superoxide dismutase, and restored the increased levels of serum malondialdehyde and tumor necrosis factor-alpha. The results suggested that TQ by employing anti-oxidant and anti-inflammatory mechanisms, might relieve the pain induced by hind paw plantar incision, being comparable with CLX.

Theranostic nanoemulsions suppress macrophage-mediated acute inflammation in rats

In inflammatory diseases or following an injury, dysregulated inflammation is a common driver of pain and tissue damage. Macrophages are immune cells that contribute to the initiation, maintenance, and resolution of inflammation due to their phenotypic plasticity in response to signals from inflammatory microenvironments. Macrophages infiltrate and polarize toward a pro-inflammatory phenotype (M1-like), thereby increasing the severity of inflammation. Therefore, we aimed to suppress the pro-inflammatory activity of M1-like macrophages and decrease their infiltration at the site of inflammatory insult to resolve tissue inflammation. To achieve this, we developed a theranostic curcumin-loaded nanoemulsion platform that delivers a low dose of curcumin, a known anti-inflammatory phytochemical, to macrophages and allows in vivo tracking of macrophages by near-infrared fluorescence (NIRF) imaging technique. In vitro, we showed that curcumin-loaded nanoemulsion suppressed polarization of macrophages towards M1-like phenotype, consequently decreasing the release of pro-inflammatory cytokines and mediators like IL-6, IL-[Formula: see text] TNF-[Formula: see text], and nitric oxide (NO). Furthermore, curcumin-loaded nanoemulsion increased the level of IL-10, an anti-inflammatory cytokine, and protected macrophages against ferroptosis compared to drug-free nanoemulsion. In a rodent model of Complete Freund's adjuvant (CFA)-induced inflammation, we demonstrated that infiltrating macrophages sequestered curcumin-loaded nanoemulsion droplets and acted as cellular drug depots at the site of inflammation. This consequently decreased macrophage infiltration at the CFA-induced inflammation site in both sexes compared to drug-free nanoemulsion, as demonstrated by NIRF imaging, H&E staining, and immunofluorescence. Taken together, our results indicated that the anti-inflammatory efficacy of curcumin was significantly improved when directly delivered to pro-inflammatory macrophages via theranostic nanoemulsion. This work opens an avenue for exploring theranostic nanoemulsions as a platform for delivering natural anti-inflammatory products for immune modulation.

Research progress on rat model of drug-induced liver injury established by nonsteroidal anti-inflammatory drug (celecoxib) and royal jelly ameliorative effect

OBJECTIVES

NSAIDs, like celecoxib, are widely used to treat pain, fever, and inflammation, with celecoxib being particularly effective in managing arthritis symptoms and acute or chronic pain especially with its favorable gastrointestinal tolerability. The study aimed at exploring the effect of chronic administration of celecoxib on hepatic tissues in male albino rats. It also examined the royal jelly celecoxib interplay.

METHODS

50 male albino rats in 5 equal groups; Group 1: received no drug. Group 2: received celecoxib (50 mg/kg/day, orally), for 30 successive days. Group 3: received celecoxib plus royal jelly (300 mg/kg/day, orally) for 30 successive days. Group 4: received celecoxib, for 30 days, then were left untreated for another 30 days. Group 5: received celecoxib plus royal jelly for 30 days, then were left untreated for another 30 days.

RESULTS

Chronic celecoxib administration caused hepatotoxicity in male albino rats, with ameliorative effect of royal jelly. Celecoxib discontinuation significantly diminished the celecoxib-induced toxicity, and normal liver enzymes and serum protein levels were regained in the case of dual medications (celecoxib+RJ) discontinuation.

CONCLUSIONS

Long-term celecoxib administration caused hepatotoxicity, with ameliorative effects of royal jelly against celecoxib-induced oxidative and apoptotic stress. In addition, it could be concluded that royal jelly may prove a useful adjunct in patients being prescribed celecoxib.

Identifying therapeutic candidates for endometriosis through a transcriptomics-based drug repositioning approach

Existing medical treatments for endometriosis-related pain are often ineffective, underscoring the need for new therapeutic strategies. In this study, we applied a computational drug repurposing pipeline to stratified and unstratified disease signatures based on endometrial gene expression data to identify potential therapeutics from existing drugs, based on expression reversal. Of 3,131 unique genes differentially expressed by at least one of six endometriosis signatures, only 308 (9.8%) were in common; however, 221 out of 299 drugs identified, (73.9%) were shared. We selected fenoprofen, an uncommonly prescribed NSAID that was the top therapeutic candidate for further investigation. When testing fenoprofen in an established rat model of endometriosis, fenoprofen successfully alleviated endometriosis-associated vaginal hyperalgesia, a surrogate marker for endometriosis-related pain. These findings validate fenoprofen as a therapeutic that could be utilized more frequently for endometriosis and suggest the utility of the aforementioned computational drug repurposing approach for endometriosis.

Interleukin-10-producing monocytes contribute to sex differences in pain resolution in mice and humans

Pain is closely associated with the immune system, which exhibits sexual dimorphism. For these reasons, neuro-immune interactions are suggested to drive sex differences in pain pathophysiology. However, our understanding of peripheral neuro-immune interactions on sex differences in pain resolution remains limited. Here, we have shown, in both a mouse model of inflammatory pain and in humans following traumatic pain, that males had higher levels of interleukin (IL)-10 than females, which were correlated with faster pain resolution. Following injury, we identified monocytes (CD11b+ Ly6C+ Ly6G-F4/80 mid ) as the primary source of IL-10, with IL-10-producing monocytes being more abundant in males than females. In a mouse model, neutralizing IL-10 signaling through antibodies, genetically ablating IL-10R1 in sensory neurons, or depleting monocytes with clodronate all impaired the resolution of pain hypersensitivity in both sexes. Furthermore, manipulating androgen levels in mice reversed the sexual dimorphism of pain resolution and the levels of IL-10-producing monocytes. These results highlight a novel role for androgen-driven peripheral IL-10-producing monocytes in the sexual dimorphism of pain resolution. These findings add to the growing concept that immune cells play a critical role in resolving pain and preventing the transition into chronic pain.

Graphical abstract

Burrowing as an index of inflammatory pain in male vs. female rats

The study objective was to determine whether burrowing behavior is useful as a functional index of pain in both male and female rats, and whether a 'no-training' protocol can be used to increase testing efficiency. Adult Sprague-Dawley rats were injected in one or both hindpaws with oil vehicle or complete Freund's adjuvant (CFA); starting the next day, the amount of gravel each rat burrowed out of a tube in 1 h was measured daily for ≤7 days. Without preliminary training on the burrowing procedure, CFA reliably suppressed burrowing for 2-3 days compared to controls, in both sexes. However, whereas unilateral CFA completely suppressed burrowing 1-day post-CFA in nearly all males, bilateral CFA was required to do so in females. When administered 30 min before testing, once daily for 5 days post-CFA, the nonsteroidal anti-inflammatory drug ketoprofen (0.01-3.2 mg/kg) and the opioid morphine (0.1-3.2 mg/kg) significantly increased CFA-suppressed burrowing, whereas the purported cannabinoid analgesic Δ 9 -tetrahydrocannabinol (0.01-2.0 mg/kg) did not. The benzodiazepine chlordiazepoxide (1.25-10 mg/kg), included as a 'true negative' control, also did not restore CFA-suppressed burrowing in either sex. However, in CFA-treated males only, chlordiazepoxide decreased burrowing, suggesting that anxiety may contribute to burrowing in males but not females that are in pain. Overall these results suggest that burrowing is a valid, functional index of inflammatory pain in both sexes, and training on the burrowing procedure is not necessary. However, females are more avid burrowers than males, which should be considered when both sexes are used in inflammatory pain testing.

Preclinical comparison of antinociceptive effects between ibuprofen, diclofenac, naproxen, and acetaminophen on acid-stimulated body stretching and acid-depressed feeding behaviors in rats

Pain is a major problem that burdens the health and economy of societies worldwide. Nonsteroidal anti-inflammatory drugs (NSAIDs) are over-the-counter medications that are widely indicated for mild to moderate pain conditions. Clinically, the selection of a medication among this class is mainly based according to both patient's and doctor's previous experiences. Herein, we studied differences in therapeutic efficacies among the most commonly prescribed NSAIDs and acetaminophen in inflammatory pain rat model. Body stretching and food consumption behaviors were assessed after intraperitoneal administration of lactic acid. Initially, different concentrations of lactic acid were evaluated in adult male rats in both behavioral models. Acid concentrations of 1.8 and 3.2% were selected to assess the effects of ibuprofen, diclofenac, naproxen, and acetaminophen in body stretching and feeding behaviors, respectively. In the feeding study, food restriction for 1-24 h prior to feeding studies was assessed at first, and 24 h was selected for further tests. Acetaminophen (100 mg/kg), diclofenac (10 mg/kg), ibuprofen (10-32 mg/kg), and naproxen (3.2-10 mg/kg) significantly decreased acid-stimulated body stretching. Likewise, acetaminophen (100 mg/kg), diclofenac (10 mg/kg), and ibuprofen (32 mg/kg) increased food consumption significantly after 3.2% lactic acid. There were no significant differences between different test drugs efficacies in both stretching and feeding behaviors. In conclusion, feeding behavior provides a good appraisal for pain and analgesic drugs in preclinical studies. There were comparable efficacies between all tested medications in both lactic acid-stimulated body stretching and -depressed feeding behaviors.

Behavioral and inflammatory sex differences revealed by celecoxib nanotherapeutic treatment of peripheral neuroinflammation

Neuropathic pain affects millions of people worldwide, yet the molecular mechanisms of how it develops and persists are poorly understood. Given that males have historically been utilized as the primary sex in preclinical studies, less is known about the female neuroinflammatory response to injury, formation of pain, or response to pain-relieving therapies. Macrophages contribute to the development of neuroinflammatory pain via the activation of their cyclooxygenase-2 (COX-2) enzyme, which leads to the production of prostaglandin E₂ (PGE₂). PGE₂ activates nociception and influences additional leukocyte infiltration. Attenuation of COX-2 activity decreases inflammatory pain, most commonly achieved by nonsteroidal anti-inflammatory drugs (NSAIDs), yet NSAIDs are considered ineffective for neuropathic pain due to off target toxicity. Using chronic constriction injury of the rat sciatic nerve, we show that males and females exhibit quantitatively the same degree of mechanical allodynia post injury. Furthermore, a low-dose nanotherapeutic containing the NSAID celecoxib is phagocytosed by circulating monocytes that then naturally accumulate at sites of injury as macrophages. Using this nanotherapeutic, we show that treated males exhibit complete reversal of hypersensitivity, while the same dose of nanotherapeutic in females provides an attenuated relief. The difference in behavioral response to the nanotherapy is reflected in the reduction of infiltrating macrophages at the site of injury. The observations contained in this study reinforce the notion that female neuroinflammation is different than males.

Acetaminophen Exerts an Analgesic Effect on Muscular Hyperalgesia in Repeated Cold-Stressed Rats through the Enhancement of the Descending Pain Inhibitory System Involving Spinal 5-HT3 and Noradrenergic α2 Receptors

Musculoskeletal and psychological complaints have increased with the widespread use of visual display terminals, and musculoskeletal pain is known to be closely related to stress. One method of experimentally inducing persistent muscle pain is repeated cold stress (RCS), and animals exposed to such stress exhibit a dysfunction in the descending pain inhibitory system. Acetaminophen (N-acetyl-p-aminophenol; APAP) is widely used to relieve several types of pain, including musculoskeletal pain, and is available as an OTC drug. However, the mechanism underlying its analgesic action has not yet been fully elucidated. In this study, we compared the analgesic effect of APAP on RCS-induced muscular hyperalgesia with those of other analgesics to identify its mechanism of action. The daily oral administration of APAP significantly suppressed the decrease in the mechanical withdrawal threshold caused by RCS, similar to the results for neurotropin but not for the cyclooxygenase inhibitor ibuprofen (IBP). Moreover, the intrathecal administration of antagonists of the 5-hydroxytryptamine (5-HT)3 receptor or α2-adrenoceptor significantly abolished the analgesic effect of APAP but not of IBP. These results suggest that the analgesic effect of APAP on RCS-induced muscular pain might be exerted due to the activation of the descending pathways involving the spinal 5-HT3 receptor or α2-adrenoceptor.

Models of Inflammation: Carrageenan- or Complete Freund's Adjuvant (CFA)-Induced Edema and Hypersensitivity in the Rat

Animal models of inflammation are used to assess the production of inflammatory mediators at sites of inflammation, the processing of pain sensation at CNS sites, the anti-inflammatory properties of agents such as nonsteroidal anti-inflammatory drugs (NSAIDs), and the efficacy of putative analgesic compounds in reversing cutaneous hypersensitivity. Detailed in this article are methods to elicit and measure carrageenan- and complete Freund's adjuvant (CFA)-induced cutaneous inflammation. Due to possible differences between the dorsal root sensory system and the trigeminal sensory system, injections into either the footpad or vibrissal pad are described. In this manner, cutaneous inflammation can be assessed in tissue innervated by the lumbar dorsal root ganglion neurons (footpad) or by the trigeminal ganglion neurons (vibrissal pad). © 2021 Wiley Periodicals LLC.