Injury to peripheral nerves often results in a persistent neuropathic pain condition that is characterized by spontaneous pain, allodynia, and hyperalgesia. Nerve injury is accompanied by a local inflammatory reaction in which nerve-associated and immune cells release several pronociceptive mediators. Kinin B 1 receptors are rarely expressed in nontraumatized tissues, but they can be expressed after tissue injury. Because B 1 receptors mediate chronic inflammatory painful processes, we studied their participation in neuropathic pain using receptor gene-deleted mice. In the absence of neuropathy, we found no difference in the paw-withdrawal responses to thermal or mechanical stimulation between B 1 receptor knock-out mice and 129/J wild-type mice. Partial ligation of the sciatic nerve in the wild-type mouse produced a profound and long-lasting decrease in thermal and mechanical thresholds in the paw ipsilateral to nerve lesion.

Kinins, the vasoactive peptides proteolytically liberated from kininogens, were recently recognized as signals alerting the innate immune system. Here we demonstrate that Leishmania donovani and Leishmania chagasi, two etiological agents of visceral leishmaniasis (VL), activate the kinin system. Intravital microscopy in the hamster cheek pouch showed that topically applied promastigotes induced macromolecular leakage (FITC-dextran) through postcapillary venules. Peaking at 15 min, the parasite-induced leakage was drastically enhanced by captopril (Cap), an inhibitor of angiotensin-converting enzyme (ACE), a kinin-degrading metallopeptidase. The enhanced microvascular responses were cancelled by HOE-140, an antagonist of the B2 bradykinin receptor (B2R), or by pre-treatment of promastigotes with the irreversible cysteine proteinase inhibitor N-methylpiperazine-urea-Phe-homoPhe-vinylsulfone-benzene (N-Pip-hF-VSPh). In agreement with the above-mentioned data, the promastigotes vigorously induced edema in the paw of Cap-treated J129 mice, but not Cap-B2R-/- mice. Analysis of parasite-induced breakdown of high molecular weight kininogens (HK), combined with active site-affinity-labeling with biotin-N-Pip-hF-VSPh, identified 35-40 kDa proteins as kinin-releasing cysteine peptidases. We then checked if macrophage infectivity was influenced by interplay between these kinin-releasing parasite proteases, kininogens, and kinin-degrading peptidases (i.e. ACE). Our studies revealed that full-fledged B2R engagement resulted in vigorous increase of L. chagasi uptake by resident macrophages. Evidence that inflammatory macrophages treated with HOE-140 became highly susceptible to amastigote outgrowth, assessed 72 h after initial macrophage interaction, further suggests that the kinin/B2R activation pathway may critically modulate inflammation and innate immunity in visceral leishmaniasis.

Abstract-The bradykinin B 1 receptor (B 1 R) is normally absent under physiological conditions, but is highly inducible during inflammatory conditions or following tissue damage. The present study attempted to determine some of the mechanisms underlying B 1 R upregulation following tissue injury in rat portal vein. Damage induced by tissue isolation and in vitro incubation caused a significant and time-dependent increase in des-Arg 9 -bradykinin (des-Arg 9 -BK) responsiveness that paralleled the B 1 R mRNA expression, as confirmed by real-time quantitative PCR. In vitro incubation of rat portal vein also induced the activation of some members of the mitogen activated protein kinase (MAPK) family, namely, extracellular signal-regulated kinase (ERK), c-Jun NH 2 -terminal kinase (JNK), and p38 MAPK, an effect accompanied by degradation of the inhibitory protein IB␣ and translocation of nuclear transcription factor-B (NF-B) to the nucleus. The blockade of p38 MAPK, JNK or NF-B, but not ERK pathways with selective inhibitors, resulted in a significant reduction of the upregulated contractile response caused by the selective B 1 R agonist des-Arg 9 -BK, and largely prevented the induction of B 1 R mRNA expression in the rat portal vein. Together, these results demonstrate that in vitro tissue damage induces activation of several intracellular signaling pathways that have a key role in the control of B 1 R expression.

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