Anti-inflammatory and ethopharmacological effects of an ethanolic leaf extract of Palisota Hirsuta K. Schum. (Commelinaceae)

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Leaves of Palisota hirsuta are used in Ghana and other West African states for various painful and inflammatory conditions. This study is aimed at evaluating the anti-inflammatory and ethopharmacological properties as well as toxicity profile of an ethanolic leaf extract of Palisota hirsuta using animal models. Preliminary phytochemical screening showed that the powdered leaves contained tannins, reducing sugars, flavonoids, steroids and terpenoids with traces of alkaloids. Effect of the extract on acute inflammation was assessed in the carrageenan- induced foot edema in 7-day-old chicks with diclofenac and dexamethasone as reference drugs. Pre treatment with the extract (30-300 mg kg-1; p.o.) significantly, inhibited foot edema in the chicks comparable to the NSAID diclofenac with maximal inhibition of 54.71±11.04%. Diclofenac and dexamethasone also dose- dependently inhibited carrageenan-induced foot edema. The anti-arthritic effect of the ethanolic leaf extract was assessed in the Freund’s adjuvant induced-arthritis model in rats. Palisota hirsuta extract (PHE) as well as dexamethasone and methotrexate, used as positive controls, showed significant dose-dependent anti-arthritic properties when administered prophylactically, curatively and also in combination therapy. PHE (30-300 mg kg-1) significantly reduced the arthritic edema in the ipsilateral paw with the highest dose used giving a maximum inhibition of 13.02±8.77%. PHE (300 mg kg-1) also significantly prevented the spread of the edema from the ipsilateral to the contralateral paw indicating inhibition of systemic spread. Dexamethasone (0.3-3 mg kg-1) and methotrexate (0.1-1.0 mg kg-1) significantly and in a dose dependent manner also inhibited polyarthritis edema. PHE in combination with methotrexate did not show significant effect. However there was a significant inhibition of arthritis in both the acute and the polyarthritic phases when PHE was combined with dexamethasone. Dexamethasone in combination with methotrexate caused the greatest inhibition of both phases with an extreme level of significance as expected. Overall, the present results demonstrate that PHE has anti-arthritic effect which could be similar to that exhibited by methotrexate. P. hirsuta (30-300 mg kg-1; p.o.) also dose-dependently decreased baker’s yeast induced fever in rats when Paracetamol (10-100 mg kg-1; p.o.) was used as the reference drug. The in vitro antioxidant properties of the extract were evaluated using the reducing power test; 2, 2-diphenyl-1-picrylhydrazyl hydrate (DPPH) radical scavenging assay and the lipid peroxidation assay. In all tests, n-propyl gallate was used as the reference antioxidant. The extract (0.1-3.0 mg ml -1) showed a reducing power potential (EC ; 133.7±7.59 mg ml-1) but was less than that of the reference antioxidant n-propyl gallate (EC 3.77±0.07 mg ml-1) in the reducing power test. The relative anti-oxidative activity in the DPPH de-colorization assay (defined by the EC ) was in the order: n-propyl gallate (8.02±0.01 × 10-4) > extract (1.77±0.40 × 10-1). The extract (0.1-1.0 mg ml-1) and n-propyl gallate (0.01-0.1 mg ml-1) exhibited a concentration dependent inhibition of lipid peroxidation. The rank order of potency (defined by ED in mg ml-1) was found to be: n-propyl gallate (1.31±3.00 × 10-2) > extract (4.29±0.95 × 10-1). These findings present the extract with potent antioxidant properties which may account in part for its anti-inflammatory and analgesic activities. In the analgesic assay, the leaf extract of P. hirsuta (PHE) (30, 100 and 300 mg kg-1 p.o) as well as morphine and diclofenac (positive controls), caused significant dose- dependent anti-nociceptive activity in all the pain models used. In the tail withdrawal test, PHE (300 mg kg-1) increased withdrawal latencies significantly by 43.83±11.62%. Also, PHE (300 mg kg-1) completely reversed the inflammatory- induced mechanical hyperalgesia with a maximum percentage effect of 154.79±15.84%. PHE significantly reduced the number of acetic acid induced writhing in mice. In the formalin test, PHE (10–300 mg kg-1, p.o.) caused a marked and dose-related inhibition of both phases of formalin-induced nociception. The anti-nociceptive effect exhibited by PHE in the formalin test was reversed by the systemic administration of the non-selective opioid antagonist, naloxone, the NO synthase inhibitor, NG-nitro-arginine methyl ester (L-NAME) and the ATP- sensitive K+ channel inhibitor, glibenclamide. However, theophylline a non- selective adenosine receptor antagonist did not reverse the effect. PHE, unlike morphine, did not induce tolerance to its anti-nociceptive effect in the formalin test after chronic administration and also morphine tolerance did not cross-generalize to PHE. Overall, the present results demonstrate that the central and peripheral anti-nociceptive of PHE may partially or wholly be due to the stimulation of peripheral and/or central opioid receptors through the activation of the nitric oxide-cyclic GMP- ATP-sensitive K+ (NO/cGMP/K+ATP)-channel pathway. As part of the present study, the ethopharmacological properties of the ethanolic leaf extract, in multiple behavioral paradigms of anxiety and depression— the open field test, the light/dark box, the elevated plus maze (EPM), the forced swimming test (FST) and tail suspension test (TST) was evaluated. P. hirsuta treated mice (30-300 mg kg-1) exhibited anxiolytic activity similar to diazepam in all the anxiety models used. PHE significantly increased the percentage number of center entries and the percentage time spent in the center of the open field. It also significantly increased the time spent in the lit area in relation to the time spent in the dark area of the light/dark box as well as significantly increasing open arm activity in the EPM. These effects were completely reversed in the presence of flumazenil (3 mg kg-1), a specific antagonist of the benzodiazepine site in the GABAA benzodiazepine receptor complex. The extract also dose-dependently reduced the duration of immobility in both the FST (ED50: 114.55±72.69 mg kg ) and TST (70.42±0.06 mg kg-1). Pretreatment with •-methyldopa (400 mg kg-1; 3 h; p.o.), to reduce brain NE and DA tissue content or reserpine (1 mg kg-1; 24 h; s.c.) for the disruption of vesicular storage of brain NE, DA and 5-HT tissue content or a combination of the two drugs to deplete both newly synthesized and vesicular components of NE and DA transmission attenuated the anti-immobility effects of both imipramime and the extract but not fluoxetine. Neither the extract nor the standard drugs used modified motor performance on the rota rod test at all doses tested. Collectively, these results suggest that the extract has anxiolytic and antidepressant-like effects in the models employed possibly by GABAergic activation and/or modification of monoamine transport and/or metabolism. In the toxicological study, there were no significant differences found in almost all of the hematological, serum biochemical parameters and organ/body weight ratio. No abnormality of any organ was found during histopathological examination. The results showed that the no-observed adverse- effect level (NOAEL) of P. hirsuta extract (PHE) was >3000 mg kg-1 body weight per day in rats, which can be regarded as virtually non-toxic. In conclusion, PHE had no overt organ specific toxicity and hence has a high safety profile in rats. Putting all together, these novel findings provide some pharmacological evidence and basis for the traditional use of the leaves of P. hirsuta in traditional medicine to manage various painful and inflammatory conditions.
A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy in the Department Of Pharmacology.