Effects of silymarin on neuropathic pain and formalin-induced nociception in mice.
OBJECTIVE
Based on the previous reports, silymarin can suppress nitric oxide, prostaglandin E2 (PGE2), leukotrienes, cytokines production, and neutrophils infiltration. Regarding the fact that inflammation plays an important role in neuropathic and formalin-induced pain, it was assumed that silymarin could reduce pain. The present study investigates the analgesic effects of silymarin in chemical nociception and a model of neuropathic pain.


METHODS
Chemical nociception was produced by injection of 20 µl of formalin (0.5% formaldehyde in saline) into the plantar region of the right hind paw. A sciatic-nerve ligated mouse was applied as the model of neuropathic pain and the antinociceptive response of silymarin was examined 14 days after unilateral nerve-ligation using the hot plate test.


RESULTS
The intraperitoneal administration of silymarin (25, 50, and, 100 mg/kg) 2 hr prior to the intraplantar formalin injection suppressed the nociceptive response during the late phase of the formalin test significantly, but it was not in a dose-dependent manner. Different doses of silymarin 14 days after unilateral sciatic nerve ligation in hot plate test did not induce obvious antinociception.


CONCLUSIONS
Results of the present study indicated that repeated administration of silymarin prevents the formalin-induced nociceptive behavior. However, it is not effective in the treatment of sciatic neuropathic pain.
School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran.
Faezeh Vahdati
FV
Hassani
Department of Physiology and Pharmacology, School of Medicine, North Khorasan University of Medical Sciences, Bojnurd, Iran.
Ramin
R
Rezaee
School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran.
Hasan
H
Sazegara
Department of Pharmacology and Toxicology, School of Pharmacy, Zabol University of Medical Sciences, Zabol, Iran.
Mahmoud
M
Hashemzaei
School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran.
Kobra
K
Shirani
Medical Toxicology Research Center and Pharmacy School, Mashhad University of Medical Sciences, Mashhad, Iran.
Gholamreza
G
Karimi
Formalin test; Inflammatory pain; Sciatic nerve ligation; Silymarin