title: Antinociception of petroleum ether fraction derived from crude methanol extract of Melastoma malabathricum leaves and its possible mechanisms of action in animal models.
abstract: BACKGROUND
  Melastoma malabathricum L. (family Melastomaceae) has been traditionally used as remedies against various ailments including those related to pain. The methanol extract of M. malabathricum leaves has been proven to show antinociceptive activity. Thus, the present study aimed to determine the most effective fraction among the petroleum ether- (PEMM), ethyl acetate- (EAMM) and aqueous- (AQMM) fractions obtained through successive fractionation of crude, dried methanol extract of M. malabathricum (MEMM) and to elucidate the possible mechanisms of antinociception involved.
  
  
  METHODS
  The effectiveness of fractions (100, 250 and 500 mg/kg; orally) were determine using the acetic acid-induced abdominal constriction test and the most effective extract was further subjected to the hot plate- or formalin-induced paw licking-test to establish its antinociceptive profile. Further elucidation of the role of opioid and vanilloid receptors, glutamatergic system, and nitric oxide/cyclic guanosine phosphate (NO/cGMP) pathway was also performed using the appropriate nociceptive models while the phytoconstituents analyses were performed using the phytochemical screening test and, HPLC-ESI and GCMS analyses.
  
  
  RESULTS
  PEMM, EAMM and AQMM significantly (p < 0.05) attenuated acetic acid-induced nociception with the recorded EC50of 119.5, 125.9 and 352.6 mg/kg. Based on the EC50value, PEMM was further studied and also exerted significant (p < 0.05) antinociception against the hot plate- and formalin-induced paw licking-test. With regards to the mechanisms of antinociception,: i) PEMM significantly (p < 0.05) attenuated the nociceptive action in capsaicin- and glutamate-induced paw licking test.; ii) naloxone (5 mg/kg), a non-selective opioid antagonist, failed to significantly (p < 0.05) inhibit PEMM's antinociception iii) L-arginine (a nitric oxide precursor), but not NG-nitro-L-arginine methyl esters (L-NAME; an inhibitor of NO synthase), methylene blue (MB; an inhibitor of cGMP), or their respective combination, significantly (p < 0.05) reversed the antinociception of PEMM. Phytochemical analyses revealed the presence of several antinociceptive-bearing bioactive compounds, such as triterpenes and volatile compounds like oleoamide and palmitic acid. The presence of low flavonoids, such as gallocatechin and epigallocatechin, saponins and tannins in PEMM might synergistically contribute to enhance the major compounds antinociceptive effect.
  
  
  CONCLUSIONS
  PEMM exerted a non-opioid-mediated antinociceptive activity at the central and peripheral levels via the inhibition of vanilloid receptors and glutamatergic system, and the activation of NO-mediated/cGMP-independent pathway. Triterpenes, as well as volatile oleoamide and palmitic acid, might be responsible for the observed antinociceptive activity of PEMM.
authors.affiliation: Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia (UPM), 43400, Serdang, Selangor D.E, Malaysia. dr_zaz@yahoo.com.|Integrative Pharmacogenomics Institute (iPROMISE), Universiti Teknologi MARA (UiTM), Level 7, FF3 Building, 42300, Puncak Alam, Selangor D.E, Malaysia. dr_zaz@yahoo.com.
authors.forename: Z A
authors.initials: ZA
authors.lastname: Zakaria
authors.affiliation: Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia (UPM), 43400, Serdang, Selangor D.E, Malaysia.
authors.forename: E S
authors.initials: ES
authors.lastname: Jaios
authors.affiliation: Phytochemistry Unit, Herbal Medicine Research Centre, Institute for Medical Research, Jalan, Pahang, 50588, Kuala Lumpur, Malaysia.
authors.forename: M H
authors.initials: MH
authors.lastname: Omar
authors.affiliation: Department of Biomedical Sciences, Kulliyyah of Allied Health Sciences, International Islamic University Malaysia (IIUM), 25200, Kuantan, Pahang D.M, Malaysia.
authors.forename: S
authors.initials: S
authors.lastname: Abd Rahman
authors.affiliation: Medical Technology Division, Malaysian Nuclear Agency, 43000, Bangi, Kajang, Selangor, Malaysia.
authors.forename: S S A
authors.initials: SS
authors.lastname: Hamid
authors.affiliation: Department of Family Medicine, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia (UPM), 43400, Serdang, Selangor D.E, Malaysia.
authors.forename: S M
authors.initials: SM
authors.lastname: Ching
authors.affiliation: Integrative Pharmacogenomics Institute (iPROMISE), Universiti Teknologi MARA (UiTM), Level 7, FF3 Building, 42300, Puncak Alam, Selangor D.E, Malaysia.
authors.forename: L K
authors.initials: LK
authors.lastname: Teh
authors.affiliation: Integrative Pharmacogenomics Institute (iPROMISE), Universiti Teknologi MARA (UiTM), Level 7, FF3 Building, 42300, Puncak Alam, Selangor D.E, Malaysia.
authors.forename: M Z
authors.initials: MZ
authors.lastname: Salleh
authors.affiliation: Department of Chemistry, Kulliyyah of Sciences, International Islamic University Malaysia (IIUM), 25200, Kuantan, Pahang D.M, Malaysia.
authors.forename: S
authors.initials: S
authors.lastname: Deny
authors.affiliation: Department of Pharmaceutical Technology, Kulliyyah of Pharmacy, International Islamic University Malaysia (IIUM), 25200, Kuantan, Pahang D.M, Malaysia.
authors.forename: M
authors.initials: M
authors.lastname: Taher
mesh_terms: D000473:Alkanes; D000700:Analgesics / Q000302:isolation & purification* / Q000494:pharmacology / Q000633:toxicity; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004195:Disease Models, Animal; D008401:Gas Chromatography-Mass Spectrometry; D008297:Male; D035322:Melastomataceae / Q000737:chemistry* / Q000633:toxicity; D000432:Methanol; D051379:Mice; D008813:Mice, Inbred ICR; D010146:Pain / Q000188:drug therapy* / Q000209:etiology; D064209:Phytochemicals; D010936:Plant Extracts / Q000494:pharmacology* / Q000633:toxicity; D018515:Plant Leaves / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D012997:Solvents; D050916:TRPV Cation Channels / Q000037:antagonists & inhibitors
chemical_list: D000473:Alkanes; D000700:Analgesics; D064209:Phytochemicals; D010936:Plant Extracts; D012997:Solvents; D050916:TRPV Cation Channels; C004544:naphtha; D000432:Methanol
keywords: Antinociceptive activity; Crude methanol extract; Fraction; Glutamatergic system; Mechanisms of antinociception; Melastoma malabathricum; NO-mediated/cGMP-independent pathway; Non-opioid system; Vanilloid receptors