participation of p2x7 purinergic receptors in the hemorrhagic cystitis

PARTICIPATION OF P2X7 PURINERGIC RECEPTORS IN THE NOCICEPTIVE
RESPONSES ASSOCIATED TO HEMORRHAGIC CYSTITIS INDUCED BY
CYCLOPHOSPHAMIDE IN MICE. 1J.P. Martins, 2R.B.M. Silva, 3R. CoutinhoSilva, 4C.M. Takiya, 5A.M.O. Battastini, 2,6F.B. Morrone, 6,7M.M. Campos
1
Faculdade de Medicina and 2Farmácia, PUCRS, Porto Alegre, RS; 3Instituto de
Biofísica Carlos Chagas Filho and 4Instituto de Ciências Biomédicas, UFRJ, Rio
de Janeiro, RJ; 5Departmento de Bioquímica, ICBS, UFRGS, Porto Alegre, RS;
6
Instituto de Toxicologia, PUCRS , Porto Alegre, RS; 7Faculdade de Odontologia,
PUCRS, Porto Alegre, RS, Brazil.
Introduction: ATP is released in response to cellular damage, and the P2X 7
receptors have an essential role in the onset and maintenance of pathological
changes (Pain, 114, 386, 2005). The hemorrhagic cystitis (HC) is a well known
adverse effect of therapy with cyclophosphamide (CYP) used for the treatment of
many solid tumors (Indian J Urol., 26, 2, 2010). These urotoxic effects are
attributed to the toxic metabolic of the CYP, named acrolein, which can be
partially prevented by sodium 2-mercaptoetanosulfonate (Mesna) (J Cancer Res.
Clin. Oncol., 121, 128, 1995). The present study aimed to determine the role of
P2X7 receptors in the nociceptive changes associated to hemorrhagic cystitis
induced by CYP in mice. Methods and Results: Male Swiss, C57/BL6 mice and
P2X7 receptor knockout mice (n= 4; 25-30 g) were used. HC was induced by a
single administration of CYP (300 mg/kg, i.p.). Immediately after, mice were
housed in individual plastic cages to observe the spontaneous behavior for 4 h,
for 2 min every half-hour. Three behavioral parameters were considered: (i)
activity; (ii) immobility and (iii) indicatives of visceral pain behavior (‘crises’). In
addition, the spontaneous behavior of mice was also scored according to the
scale described before (Eur. J. Pain., 3, 141, 1999). We have also measured the
expression of c-Fos, a known biochemical marker of nociception, in the lumbar
spinal cords and the brains at 6 h. To confirm HC establishment, we performed
bladders gross evaluation (J. Urol., 136, 497, 1986). Swiss mice were treated
with the selective P2X7 receptor antagonist A-438079 (50, 100 and 200 mol/kg)
(Neuroscience., 146, 1817, 2007), given 30 min before and 4 h after the CYP.
Control animals received saline at the same intervals of time. All the
experimental procedures were approved by the Local Ethics Committee
(08/00074, CEUA, PUCRS). The pre-treatment with the selective P2X7 receptor
antagonist A-438079 or genic ablation of P2X7 receptors inhibited the
nociceptive behaviour score induced by CYP. The inhibition percentages using
A-438079 at the doses of 50, 100 and 200 mol/kg were 46 ± 9 %, 47 ± 5 and 48
± 5 % respectively, whereas in knockout animals a reduction of 17 ± 3 % was
observed. The A-438079 treatment also significantly decreased the positive
staining for c-Fos in the lumbar spinal cord (45 ± 13%) and brain cortical areas
(86 ± 5%). Conclusion: In the recent years, the interest in the therapeutic
potential of purinergic receptors has dramatically increased (Pharmacol. Rev.,
58, 58, 2006). Our study revealed the importance of P2X7 receptors in the
nociceptive responses allied to HC induced by CYP. These results confirm and
extend previous evidence suggesting that pharmacological inhibition of P2X7
receptors might represent a new therapeutical approach for treating painful
conditions.
Sources of reaserch support: CNPq, PROBOLSAS-PUCRS.