Molecular Mechanics Simulations and Experimental Investigation of the Effect of Tadalafil on Various Inflammatory Pain Mediators

PURPOSE

Tadalafil's exact analgesic mechanism is still unclear. The current study aimed to elucidate this mechanism in an inflammatory pain model.

METHODS

Computer-assisted simulation docking experiments were carried out to assess the binding of tadalafil to different ligands. The anti-inflammatory and analgesic effects of tadalafil were evaluated using formalin-induced paw edema and a von Frey filament test, respectively. The plantar paw of the mice was then dissected to quantify iNOS, nNOS, COX-2, TNFα, IL1, and IL10 gene expression levels using a real-time polymerase chain reaction. iNOS, TNFα, and COX-2 inhibition was reassessed in vitro using the ELISA technique. One-way analysis of variance followed by post hoc Tukey test or t-test was used to compare the means.

RESULTS

Docking analysis showed a superior binding score of tadalafil to COX-2, iNOS, IL-1, and TNF-α compared to that of indomethacin and morphine and a similar binding score to nNOS and IL-10 relative to that of indomethacin. In the in vivo study, tadalafil, after an hour of formalin administration, inhibited significantly paw edema, similar to indomethacin. Furthermore, it significantly increased the withdrawal force in the von Frey filament test as compared to the negative control, which was similar to the effect observed with indomethacin and morphine. The RT-PCR revealed that tadalafil reduced significantly the iNOS, COX-2, and TNF-α gene expressions but had no effect on nNOS, IL 1, and IL10. In vitro ELISA tests confirmed the inhibition of iNOS, COX-2, and TNF-α.

CONCLUSION

Tadalafil probably exerts its analgesic effect through the simultaneous inhibition of iNOS, COX-2, and TNF-α, which is not the case with other nonsteroidal anti-inflammatory drugs. Nevertheless, further studies are required to confirm its mechanism.

Effects of hydro-ethanolic extract of leaves of Maesa lanceolata (Mursinaceae) on acetic acid-induced ulcerative colitis in rats

Ulcerative colitis is a form of inflammatory bowel disease that is characterized by acute and chronic inflammation. The aim of this work was to evaluate the efficacy of hydroethanolic extract of Maesa lanceolata leaves on acetic acid-induced colitis in rats. Colitis was induced by rectal administration of 1 mL of acetic acid (4%) in 25 male rats except the normal control group which received distilled water after 18 h of fasting followed by Ketamine (50 mg/kg)/Valium (10 mg/kg) anesthesia. Five hours later, the normal control and the negative control received distilled water, the positive control received prednisolone (5 mg/kg) and the three test groups received extract at 100, 200 and 400 mg/kg bw for eight days. During treatment, rectal temperature, the number and quality of the stools, and changes in body weight were assessed. At the end of the treatment, the animals were sacrificed, blood, colon, liver and spleen were collected for evaluation of hematological, inflammatory, antioxidant and histological parameters. Rectal temperature and the number of diarrheal, mucus and bloody stools were significantly reduced (P < 0.01) during treatment in the test and positive control groups with an increase in body weight change. The extract significantly (P < 0.01) reduced myeloperoxidase, TNF-α, interleukin 6, NO and MDA levels and significantly (P < 0.01) increased SOD levels, of GSH and catalase activity in the colon and blood. This extract also increased (P < 0.01) levels of red blood cells, hemoglobin, hematocrit, total white blood cells and blood platelets, prevented leukocyte infiltration in the liver and colon.

cGMP signalling in dorsal root ganglia and the spinal cord: Various functions in development and adulthood

Cyclic GMP (cGMP) is a second messenger that regulates numerous physiological and pathophysiological processes. In recent years, more and more studies have uncovered multiple roles of cGMP signalling pathways in the somatosensory system. Accumulating evidence suggests that cGMP regulates different cellular processes from embryonic development through to adulthood. During embryonic development, a cGMP-dependent signalling cascade in the trunk sensory system is essential for axon bifurcation, a specific form of branching of somatosensory axons. In adulthood, various cGMP signalling pathways in distinct cell populations of sensory neurons and dorsal horn neurons in the spinal cord play an important role in the processing of pain and itch. Some of the involved enzymes might serve as a target for future therapies. In this review, we summarise the knowledge regarding cGMP-dependent signalling pathways in dorsal root ganglia and the spinal cord during embryonic development and adulthood, and the potential of targeting these pathways.

Antinociceptive Effect of Lodenafil Carbonate in Rodent Models of Inflammatory Pain and Spinal Nerve Ligation-Induced Neuropathic Pain

Introduction

New therapeutic alternatives for pain relief include the use of phosphodiesterase-5 (PDE5) inhibitors, which could prevent the transmission of painful stimuli by neuron hyperpolarization via nitric oxide (NO)/cyclic 3',5'-guanosine monophosphate (cGMP) pathway. The present work investigated the antinociceptive activity of a new PDE5 inhibitor, lodenafil carbonate, in inflammatory and neuropathic pain models.

Methods and Results

Although no effect was detected on neurogenic phase of formalin test in mice, oral administration of lodenafil carbonate dose-dependently reduced reactivity in the inflammatory phase (200.6 ± 39.1 to 81.9 ± 18.8 s at 10 μmol/kg, p= 0.0172) and this effect was totally blocked by NO synthase inhibitor, L-Nω-nitroarginine methyl ester (L-NAME). Lodenafil carbonate (10 μmol/kg p.o.) significantly reduced nociceptive response as demonstrated by increased paw withdrawal latency to thermal stimulus (from 6.8 ± 0.7 to 10.6 ± 1.3 s, p= 0.0006) and paw withdrawal threshold to compressive force (from 188.0 ± 14.0 to 252.5 ± 5.3 g, p<0.0001) in carrageenan-induced paw inflammation model. In a spinal nerve ligation-induced neuropathic pain, oral lodenafil carbonate (10 μmol/kg) also reversed thermal hyperalgesia and mechanical allodynia by increasing paw withdrawal latency from 17.9 ± 1.5 to 22.8 ± 1.9 s (p= 0.0062) and paw withdrawal threshold from 26.0 ± 2.8 to 41.4 ± 2.9 g (p= 0.0196). These effects were reinforced by the reduced GFAP (3.4 ± 0.5 to 1.4 ± 0.3%, p= 0.0253) and TNF-alpha (1.1 ± 0.1 to 0.4 ± 0.1%, p= 0.0111) stained area densities as detected by immunofluorescence in ipsilateral dorsal horns.

Conclusion

Lodenafil carbonate demonstrates important analgesic activity by promoting presynaptic hyperpolarization and preventing neuroplastic changes, which may perpetuate chronic pain, thus representing a potential treatment for neuropathic pain.

Analgesia additive interaction between tadalafil and morphine in an experimental animal model

Since both morphine and tadalafil have been proven to exert some of their analgesic activity through modulation of the NO-cGMP pathway, the aim of the current study is to evaluate the pharmacologic interaction between tadalafil and morphine to decrease the dose of morphine and subsequently its side effects. The assessment was carried out through isobolographic analysis relative to ED₅₀s of both morphine and tadalafil obtained by tail-flick test on BALB/c mice. Morphine and tadalafil ED₅₀s calculated from the dose-response curves were 8303 and 2080 μg/kg, respectively. The experimental ED₅₀ values of morphine and tadalafil in their mixture were 4800 and 1210 μg/kg, respectively. Those results showed an additive interaction between morphine and tadalafil presented by a total fraction value for the mixture of 1160 μg/kg. This outcome can be interpreted by the fact that both drugs share common pathways, namely, NO-cGMP and opioid receptors. As a conclusion, the morphine and tadalafil combination showed an additive effect against acute pain, which is mediated through the central nervous system, thus providing a rationale for combining them to decrease morphine dose and thus minimizing its side effects.

Tannic acid acts as an agonist of the dopamine D2L receptor, regulates immune responses, and ameliorates experimentally induced colitis in mice

Tannic acid (TA) is an herbal polyphenol containing a galloyl group that has been prescribed to treat gastroenteritis, diarrhea, and irritable bowel syndrome. TA has anti-inflammatory, anti-cancer, and anti-viral properties; however, the molecular mechanisms of these potential therapeutic effects are still largely unknown. Here, we examined the ability of TA to induce anti-inflammatory responses. TA was found to be an agonist of the dopamine D2L receptor. TA reduced interferon (IFN)-γ and interleukin (IL)-1β secretion but upregulated tumor necrosis factor α and IL-10 secretion from lipopolysaccharide (LPS)-stimulated mouse splenocytes. TA also reduced IFN-γ secretion but enhanced IL-10 secretion from anti-cluster of differentiation (CD) 3/CD28 antibody-stimulated splenocytes. An immune subset study confirmed that TA regulated cytokine secretion by various types of immune cells in the context of stimulation with LPS or anti-CD3/CD28 antibodies. Administration of TA to mice with experimentally induced colitis strikingly suppressed weight loss, colon shrinkage, and IL-17 secretion from mesenteric lymph node lymphocytes in response to CD3/CD28 stimulation. These data suggest that TA suppresses inflammatory responses in colitis by regulating cytokine secretion by immune cells in the colon.

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Tannic acid is an agonist of the dopamine D2L receptor.

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Tannic acid suppresses IFN-γ secretion by LPS-stimulated splenocytes.

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Tannic acid modulates anti-CD3/CD28 antibody-stimulated cytokine levels in CD4⁺ T cells.

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Tannic acid ameliorates dextran sodium salt (DSS)-induced colitis in C57BL/6 mice.

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Tannic acid reduces production of IL-17 in DSS-induced colitis.

Antinociceptive effect of tadalafil in various pain models: Involvement of opioid receptors and nitric oxide cyclic GMP pathway

Nitric oxide has been proven to play an important role in nociception, accordingly, its promoters, phosphodiesterase inhibitors have been investigated as pain response modulators. Aiming to evaluate the central antinociceptive effect of tadalafil, a phosphodiesterase 5 inhibitor, and to determine its EC50, tail flick and hot plate tests were employed. On the other hand, tadalafil antinociceptive peripheral effect was assessed through acetic acid-induced writhing model. Formalin test was used to appraise both non-inflammatory and inflammatory pain responses. In order to elaborate the involvement of opioid receptors and nitric oxide/cyclic guanosine monophosphate/potassium-ATP pathway in tadalafil-induced analgesia, mice were pretreated with naloxone, l-nitro-arginine-methyl-ester (l-NAME), methylene blue, and glibenclamide. The results illustrated that tadalafil had a significant antinociceptive effect in the tail flick, hot plate, acetic acid-induced writhing and formalin tests indicating the involvement of peripheral and central analgesic mechanisms. Moreover, tadalafil mechanism of action involved several receptors and mediators, specifically NO/cGMP pathway and opioid receptors. In the formalin test, naloxone significantly blocked the effect of tadalafil in the first phase and partially in the second phase which is an inflammatory pain-dependent aspect. l-NAME, methylene blue and glibenclamide partially blocked the effect of tadalafil in the first phase and enhanced its effect in the second phase which is related to nitric oxide role in the inflammatory process. As a conclusion, tadalafil possesses a potential analgesic effect via the involvement of opioid and nitric oxide pathways.

The synthetic peptide PnPP-19 induces peripheral antinociception via activation of NO/cGMP/KATP pathway: Role of eNOS and nNOS

BACKGROUND

and purpose: The peptide PnPP-19, derived from the spider toxin PnTx2-6 (renamed as δ-CNTX-Pn1c), potentiates erectile function by activating the nitrergic system. Since NO has been studied as an antinociceptive molecule and PnPP-19 is known to induce peripheral antinociception, we intended to evaluate whether PnPP-19 could induce peripheral antinociception through activation of this pathway.

EXPERIMENTAL APPROACH

Nociceptive thresholds were measured by paw pressure test. PGE₂ (2 μg/paw) was administered intraplantarly together with PnPP-19 and inhibitors/blockers of NOS, guanylyl cyclase and K_ATP channels. The nitrite concentration was accessed by Griess test. The expression and phosphorylation of eNOS and nNOS were determined by western blot.

KEY RESULTS

PnPP-19 (5, 10 and 20 μg/paw) induced peripheral antinociception in rats. Administration of NOS inhibitor (L-NOarg), selective nNOS inhibitor (L-NPA), guanylyl cyclase inhibitor (ODQ) and the blocker of K_ATP (glibenclamide) partially inhibited the antinociceptive effect of PnPP-19 (10 μg/paw). Tissue nitrite concentration increased after PnPP-19 (10 μg/paw) administration. Expression of eNOS and nNOS remained the same in all tested groups, however the phosphorylation of nNOS Ser852 (inactivation site) increased and phosphorylation of eNOS Ser1177 (activation site) decreased after PGE₂ injection. Administration of PnPP-19 reverted this PGE₂-induced effect.

CONCLUSIONS AND IMPLICATIONS

The peripheral antinociceptive effect induced by PnPP-19 is resulting from activation of NO-cGMP-K_ATP pathway. Activation of eNOS and nNOS might be required for such effect. Our results suggest PnPP-19 as a new drug candidate to treat pain and reinforce the importance of nNOS and eNOS activation, as well as endogenous NO release, for induction of peripheral antinociception.

Bioactivity of Polyphenols: Preventive and Adjuvant Strategies toward Reducing Inflammatory Bowel Diseases-Promises, Perspectives, and Pitfalls

Inflammatory bowel diseases (IBDs) are characterized by autoimmune and inflammation-related complications of the large intestine (ulcerative colitis) and additional parts of the digestive tract (Crohn's disease). Complications include pain, diarrhoea, chronic inflammation, and cancer. IBD prevalence has increased during the past decades, especially in Westernized countries, being as high as 1%. As prognosis is poor and medication often ineffective or causing side effects, additional preventive/adjuvant strategies are sought. A possible approach is via diets rich in protective constituents. Polyphenols, the most abundant phytochemicals, have been associated with anti-inflammatory, antioxidant, immunomodulatory, and apoptotic properties. Locally reducing oxidative stress, they can further act on cellular targets, altering gene expression related to inflammation, including NF-κB, Nrf-2, Jak/STAT, and MAPKs, suppressing downstream cytokine formation (e.g., IL-8, IL-1β, and TNF-α), and boosting the bodies' own antioxidant status (HO-1, SOD, and GPx). Moreover, they may promote, as prebiotics, healthy microbiota (e.g., Bifidobacteria, Akkermansia), short-chain fatty acid formation, and reduced gut permeability/improved tight junction stability. However, potential adverse effects such as acting as prooxidants, or perturbations of efflux transporters and phase I/II metabolizing enzymes, with increased uptake of undesired xenobiotics, should also be considered. In this review, we summarize current knowledge around preventive and arbitrary actions of polyphenols targeting IBD.

Sildenafil Treatment Eliminates Pruritogenesis and Thermal Hyperalgesia in Rats with Portacaval Shunts

Pruritus is a common symptom in chronic liver diseases, which may also alter thermal sensitivity. The underlying mechanisms remain unclear and treatments are not satisfactory. Portal-systemic shunting has been proposed to alter thermal sensitivity in cirrhotics. Inflammation-induced enhanced activity of the Transient Receptor Potential Vanilloid 1 (TRPV1) may contribute to pruritus and thermal hyperalgesia. Sildenafil reduces neuroinflammation in portacaval shunt (PCS) rats. The aims were to assess whether: (1) PCS rats show enhanced scratching or thermal sensitivity; (2) TRPV1 activity is enhanced in PCS rats; (3) treatment with sildenafil reduces TRPV1 activation, scratching and thermal hyperalgesia. Rats were treated with sildenafil beginning 3 weeks after surgery. The number of scratches performed were counted. Thermal hyperalgesia was analyzed using the Hargreaves' Plantar Test. TRPV1 activation by measuring the increase in Ca²⁺ induced by capsaicin in dorsal root ganglia neurons. PCS rats show enhanced scratching behavior, reaching 66 ± 5 scratches/h (p < 0.01) at 21 days after surgery, while controls show 37 ± 2 scratches/h. PCS rats show thermal hyperalgesia. Paw withdrawal latency was reduced (p < 0.05) to 10 ± 1 s compared to controls (21 ± 2 s). Capsaicin-induced calcium increase was higher in dorsal root ganglia cultures from PCS rats, indicating TRPV1functional increase. PCS rats show enhanced scratching behavior and thermal sensitivity and are a good model to study these alterations in chronic liver diseases. Enhanced sensitivity and activity of TRPV1 channel underlies these alterations. Treatment with sildenafil reduces TRPV1 channel sensitivity and activity and normalizes scratching behavior and thermal sensitivity.

Repeated Dosing with NCX1404, a Nitric Oxide-Donating Pregabalin, Re-establishes Normal Nociceptive Responses in Mice with Streptozotocin-Induced Painful Diabetic Neuropathy

NCX1404 [(3S)-5-methyl-3-(((1-(4-(nitrooxy)butanoyloxy)ethoxy)carbonylamino) methyl)hexanoic acid] is a novel nitric oxide (NO)-donating pregabalin that is readily absorbed and processed in vivo to pregabalin and NO. We determined the antiallodynic response of NCX1404 after acute or after 7, 14, and 21 days of repeated daily oral dosing in mice with streptozotocin (STZ)-induced painful diabetic neuropathy (PDN). Pregabalin and its combination with the NO donor isosorbide mononitrate (ISMN) were used for comparison. The blood levels of pregabalin and nitrites, used as surrogate marker of NO release, after NCX1404 or pregabalin dosing were monitored in parallel experiments using liquid chromatography with tandem mass spectrometry (LC-MS/MS). NCX1404 and pregabalin resulted in similar pregabalin levels as it was their antiallodynic activity after acute dosing in STZ mice. However, NCX1404 resulted in disease-modifying properties when administered daily for 21 days, as indicated by the time- and dose-dependent reversal of STZ-induced mechanical allodynia (paw withdrawal threshold [PWT]Veh_21d= 1.3 ± 0.15 g for vehicle; PWTNCX1404_21d= 1.4 ± 0.5 g, 2.9 ± 0.2 g* and 4.1 ± 0.2 g*, respectively for 19, 63, and 190μmol/kg, oral gavage [PO] of NCX1404; *P< 0.05 versus vehicle). This effect was not shared by pregabalin at equimolar doses (190μmol/kg, PO, PWTPregab_21d= 1.4 ± 0.1 g*, *P< 0.05 versus equimolar NCX1404). In addition, the NO donor ISMN (52.3μmol/kg, PO) alone or combined with pregabalin (63μmol/kg) was active at 7 days (PWTVeh_7d= 1.7 ± 0.16 g; PWTISMN_7d= 3.9 ± 0.34 g*; PWTPregab_7d= 1.3 ± 0.07 g; PWTISMN+pregab_7d= 3.8 ± 0.29 g*; *P< 0.05) but not at later time points. The long-term effect of NCX1404 was independent of residual drug exposure and lasted for several days after the treatment was stopped. In summary, like pregabalin, NCX1404 is an effective antiallodynic agent. Differently from pregabalin, repeated dosing of NCX1404 re-established normal nociceptive responses in STZ-induced PDN in mice.

Determination of Elemental Composition of Malabar spinach, Lettuce, Spinach, Hyacinth Bean, and Cauliflower Vegetables Using Proton Induced X-Ray Emission Technique at Savar Subdistrict in Bangladesh

The concentrations of 18 different elements (K, Ca, Fe, Cl, P, Zn, S, Mn, Ti, Cr, Rb, Co, Br, Sr, Ru, Si, Ni, and Cu) were analyzed in five selected vegetables through Proton Induced X-ray Emission (PIXE) technique. The objective of this study was to provide updated information on concentrations of elements in vegetables available in the local markets at Savar subdistrict in Bangladesh. These elements were found in varying concentrations in the studied vegetables. The results also indicated that P, Cl, K, Ca, Mn, Fe, and Zn were found in all vegetables. Overall, K and Ca exhibited the highest concentrations. Cu and Ni exhibited the lowest concentrations in vegetables. The necessity of these elements was also evaluated, based on the established limits of regulatory standards. The findings of this study suggest that the consumption of these vegetables is not completely free of health risks.

Transplantation of bone marrow-derived mesenchymal stem cells facilitates epithelial repair and relieves the impairment of gastrointestinal function in a rat model of enteritis

BACKGROUND

To examine whether the bone marrow-derived MSCs (BM-MSCs) could facilitate epithelial repair and thereby reduce impairment of gastrointestinal structure and function in chronic murine enteritis induced by indomethacin (IDM).

METHODS

MSCs were isolated from young Sprague-Dawley rats. After in vitro expansion and characterization, BM-MSCs were labelled with the fluorescent dye PKH26 and transfused, via the tail veins, into rats with enteritis induced by IDM. The controls were infused with sterile saline. The homing and differentiation of the transplanted BM-MSCs were tracked by means of fluorescent staining. The clinical symptoms of the IDM-treated rats were assessed, and the macroscopic and microscopic histological evaluations of the intestines were performed.

RESULTS

Compared to controls that received saline infusion, BM-MSCs treated rats showed lower scores of weight loss, stool consistency, and stool blood. The PKH26-labelled cells resided at the injured intestine, where they co-localize with the proliferating cell nuclear antigen (PCNA), Lgr-5, and Msi-1. The BM-MSCs treated rats showed significantly higher intestinal villi with larger areas relative to the saline-treated rats.

CONCLUSION

The transplanted BM-MSCs are able to recognize the injured intestine, where they proliferate and transdifferentiate into intestinal stem cells which repair the injured intestinal tissues. Therefore, BM-MSCs are able to relieve the impairment of gastrointestinal function in IMD-treated rats.

The in vivo and in vitro study of polysaccharides from a two-herb formula on ulcerative colitis and potential mechanism of action

ETHNOPHARMACOLOGICAL RELEVANCE

Lycium barbarum and Astragalus membranaceus are two traditional medicinal herbs widely used in China for nourishing Yin and reinforcing Qi. The purpose of the study was to investigate the prophylactic and curative effects of crude polysaccharides (QHPS) extracted from a two-herb formula composed of Lycium barbarum and Astragalus membranaceus at a ratio of 2:3 in colitis rats, and to further elucidate the potential mechanism of action in epithelial cell proliferation in vitro.

MATERIALS AND METHODS

An acetic acid (AA)-induced ulcerative colitis rat model was applied in the study. Two independent protocols were used to assess the prophylactic and curative effects of QHPS, respectively, in which rats were either pre-treated with QHPS (0.18g/kg) for 14 days prior to AA induction, or post-treated with QHPS for 7 days after AA induction. The stool consistency and weight loss were used to evaluate disease activity. The morphological changes in intestinal mucosa at the end of the experiments were observed. The serum levels of endotoxin (EDT), diamine oxidase (DAO) and d-lactate (DLA), important biochemical markers for evaluating intestinal mucosal structure and function, were measured. In the in vitro mechanistic studies, rat intestinal epithelial cells (IEC-6) were used to access for epithelium regeneration.

RESULTS

The intra-colonic instillation of AA induced ulcerative colitis in rat, as indicated by diarrhea, weight loss, and colonic mucosal damage. Both prophylactic and curative treatments effectively reduced the weight loss and diarrhea and attenuated the colonic mucosal damage associated with inducible colitis. The significant increase in serum levels of DAO, DLA and EDT was induced by AA and inhibited by QHPS treatment. Moreover, QHPS could significantly stimulate IEC-6 proliferation in a dose-dependent manner (p<0.05).

CONCLUSION

The present study indicated for the first time that polysaccharides extracted from this two-herb formula can protect against experimental ulcerative colitis, presumably by promoting the recovery of the intestinal barrier.