17
ABSTRACT
Study of the Antinociceptive activity of Thalidomide, Pentoxifillyne and
Chlorpromazine in Experimental Models. MARIANA LIMA VALE. Thesis submitted
as partial fulfillment of requirement to degree of Doctor in Pharmacology to the post -
graduation Pharmacology course of the Ceará Federal University. Superviser: Dr.
Ronaldo de Albuquerque Ribeiro, Co-Superviser: Dr. Fernando de Queirós Cunha,
Fortaleza 2003.
The release of cyclo-oxygenase products and sympathomimetic amines, the
final mediators of inflammatory pain, is preceded by the generation of pro-inflammatory
and nociceptive cytokines by resident cells. Recently drugs such as thalidomide
(TALD), pentoxifylline (PTX) and chlorpromazine (CLP), despite of other effects, have
been associated with immunomodulatory activity in clinical practice mainly for their
modulatory properties upon cytokine production. Since those drugs are able to inhibit
the production of pro-inflammatory cytokines and the pivotal role of resident cells in the
development of inflammatory pain we have decided to test the possibility of TALD, PTX
and CLP, to modulate inflammatory pain. TALD (5 – 45mg/kg), PTX (0.5 – 45mg/kg) or
CLP (0.1 – 1mg/kgl) was given 30 min before either acetic acid (AAc) or zymosan
(Zym) or iloprost (ILO) administration in the writhing model. TALD, PTX or CLP, at the
same doses were injected, i.p., 30 min before Zym (1 mg/animal; intra-articular) in the
zymosan-induced rat knee joint incapacitation test (JI). Those drugs were also tested
upon hyperalgesic effect of carrageenin (Cg), bradykinin (Bk), tumor necrosis factor
(TNF), interleukin (IL) -1 and prostaglandin E
2
(PGE
2
) on mechanical hyperalgesia test
(HYP). Doses of those drugs that exerted maximum effect in the writhing test were also
injected 30 min before the hot plate test. These same doses were injected ip before
naloxone administration in the AAc-induced writhing model in mice. Cytokines levels
(TNF, IL-1, IL-10 and IL-4) were determined in the supernatant of a macrophage
culture, which were collected from peritoneal fluid of mice treated with Zym and pre-
treated with the drugs under test and in the supernatant of articular fluid of rats pre-
treated with the drugs and stimulated with Zym (TNF, IL-1β, IL-10, IL-6 and CINC-1).
Our results showed that TALD, PTX and CLP inhibited the writhing response in mice
induced by AAc or Zym up to 60.3, 89.8 e 89%, and up to 85.6, 82.9 and 63.7%
respectively (p<0.001), but not the nociceptive response to ILO. Similar results were
observed in the JI induced by Zym: 75, 89 e 99% of inhibition, respectively (p<0.01).
TALD inhibited hyperalgesic effect of Cg (78.6%) and Bk (82.4%), but not the
hyperalgesic effect of TNF or PGE
2
. PTX inhibited Cg, TNF or Bk-induced HYP in 73.3,
55.2 and 45.6% of inhibition respectively, but not IL-1 or PGE
2
hyperalgesic activity.
CLP inhibited a hyperalgesic effect of all stimuli in different levels (68.16, 58.5, 42, 38.8
and 21.1% of inhibition for Cg, Bk, TNF, IL-1 e PGE
2,
respectively). The antinociceptive
activity of TALD, PTX and CLP seems to be peripheral, since these drugs presented no
effect in the reaction time of the animals on hot plate test. This antinociceptive effect
seems to have no relation with endogen opioid release since naloxone (opioid receptor
antagonist) had no effect in reverting the antinociceptive effect of these drugs in the
Zym-induced writhing in mice. The antinociceptive activities seems to be dependent of
the release inhibition of pro-nociceptive cytokines by resident cells since TALD, PTX
and CLP inhibited the release of TNF (100, 85 e 54.4%, respectively - p<0.005) and of
IL-1β (97%, PTX effect - p<0,01) by mice peritoneal resident cells as well as the
production of both TNF (77 e 87.5% by TALD and PTX respectively) and IL-1β (47 e
32.6% by PTX and CLP, respectively) in the articular cavity of ZYM stimulates rats.