Proteinase-Activated rreceptor-2 (PAR 2 ), a G-protein–coupled Receptor, activated by serine proteinases, is reported to have both protective and proinflammatory effects in the airway. Given these opposing actions, both inhibitors and activators of PAR 2 have been proposed for treating asthma. PAR 2 can signal through two independent pathways: a β-arrestin–dependent one that promotes leukocyte migration, and a G-protein/Ca 2+ one that is required for prostaglandin E 2 (PGE 2 ) production and bronchiolar smooth muscle relaxation. We hypothesized that the proinflammatory responses to PAR 2 activation are mediated by β-arrestins, whereas the protective effects are not. Using a mouse ovalbumin model for PAR 2 -modulated airway inflammation, we observed decreased leukocyte recruitment, cytokine production, and mucin production in β-arrestin-2 −/− mice. In contrast, PAR 2 -mediated PGE 2 production, smooth muscle relaxation, and decreased baseline airway resistance (measures of putative PAR 2 “protective” effects) were independent of β-arrestin-2. Flow cytometry and cytospins reveal that lung eosinophil and CD4 T-cell infiltration, and production of IL-4, IL-6, IL-13, and TNFα, were enhanced in wild-type but not β-arrestin-2 −/− mice. Using the forced oscillation technique to measure airway resistance reveals that PAR 2 activation protects against airway hyperresponsiveness by an unknown mechanism, possibly involving smooth muscle relaxation. Our data suggest that the PAR 2 -enhanced inflammatory process is β-arrestin-2 dependent, whereas the protective anticonstrictor effect of bronchial epithelial PAR 2 may be β-arrestin independent.

Preprotachykinin-A (PPT-A) gene products substance P and neurokinin-A have been shown to play an important role in neurogenic inflammation. To investigate the role of PPT-A gene products in lung injury in sepsis, polymicrobial sepsis was induced by cecal ligation and puncture in PPT-A gene-deficient mice (PPT-A−/−) and the wild-type control mice (PPT-A+/+). PPT-A gene deletion significantly protected against mortality, delayed the onset of lethality, and improved the long-term survival following cecal ligation and puncture-induced sepsis. PPT-A−/− mice also had significantly attenuated inflammation and damage in the lungs. The data suggest that deletion of the PPT-A gene may have contributed to the disruption in recruitment of inflammatory cells resulting in protection against tissue damage, as in these mice the sepsis-associated increase in chemokine levels is significantly attenuated.

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Hydrogen sulfide (H2S) has been shown to induce the activation of neurogenic inflammation especially in normal airways and urinary bladder. However, whether endogenous H2S would regulate sepsis-associated lung inflammation via substance P (SP) and its receptors remains unknown. Therefore, the aim of the study was to investigate the effect of H2S on the pulmonary level of SP in cecal ligation and puncture (CLP)-induced sepsis and its relevance to lung injury. Male Swiss mice or male preprotachykinin-A gene knockout (PPT-A−/−) mice and their wild-type (PPT-A+/+) mice were subjected to CLP-induced sepsis. DL-propargylglycine (50 mg/kg i.p.), an inhibitor of H2S formation was administered either 1 h before or 1 h after the induction of sepsis, while NaHS, an H2S donor, was given at the same time as CLP. L703606, an inhibitor of the neurokinin-1 receptor was given 30 min before CLP. DL-propargylglycine pretreatment or posttreatment significantly decreased the PPT-A gene expression and the production of SP in lung whereas administration of NaHS resulted in a further rise in the pulmonary level of SP in sepsis. PPT-A gene deletion and pretreatment with L703606 prevented H2S from aggravating lung inflammation. In addition, septic mice genetically deficient in PPT-A gene or pretreated with L703606 did not exhibit further increase in lung permeability after injection of NaHS. The present findings show for the first time that in sepsis, H2S up-regulates the generation of SP, which contributes to lung inflammation and lung injury mainly via activation of the neurokinin-1 receptor.

Hydrogen sulfide (H(2)S), the gaseous mediator produced by various cells in our body, was recently discovered to play a major role in human physiology despite its toxic nature known for centuries. In addition to its pathophysiological relevance in cardiovascular and neuronal disorders, there is considerable interest in the significance of H(2)S in inflammation. A number of preclinical studies in our laboratory as well as by others, using H(2)S donors and inhibitors of its endogenous synthesis, have provided evidence for both pro- and anti-inflammatory character of H(2)S. But so far, there is a significant lack of support from relevant clinical studies. One of the major contentious issues being variable dose and sampling time, controversies exist on the precise friend or foe nature of this gaseous transmitter. However, it is well accepted that once a clearer picture of the whole story of H(2)S in inflammation emerges, potential for therapeutic manipulations in this field are immense. This review focuses on the intriguing effects of H(2)S in some of the inflammatory conditions such as acute pancreatitis, sepsis, burn injuries and local inflammation of the joints. Active research projects have been undertaken to elucidate the mechanisms of action of H(2)S in inflammation, including neurogenic inflammation and interaction with other biological mediators and pathways. The early and fragmentary evidence obtained holds promise for a successful drug intervention for these inflammatory diseases.

Hydrogen sulfide (H2S), a novel gaseous messenger, is synthesized endogenously from L-cysteine by two pyridoxal-5′-phosphate-dependent enzymes, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). S-propargyl-cysteine (SPRC) is a slow H2S releasing drug that provides cysteine, a substrate of CSE. The present study was aimed to investigate the effects of SPRC in an in vivo model of acute pancreatitis (AP) in mice. AP was induced in mice by hourly caerulein injections (50 µg/kg) for 10 hours. Mice were treated with SPRC (10 mg/kg) or vehicle (distilled water). SPRC was administered either 12 h before or 3 h before the induction of pancreatitis. Mice were sacrificed 1 h after the last caerulein injection. Blood, pancreas and lung tissues were collected and processed to measure the plasma amylase, plasma H2S, myeloperoxidase (MPO) activities and cytokine levels in pancreas and lung. The results revealed that significant reduction of inflammation, both in pancreas and lung was associated with SPRC given 3 h prior to the induction of AP. Furthermore, the beneficial effects of SPRC were associated with reduction of pancreatic and pulmonary pro-inflammatory cytokines and increase of anti-inflammatory cytokine. SPRC administered 12 h before AP induction did not cause significant improvement in pancreatic and lung inflammation. Plasma H2S concentration showed significant difference in H2S levels between control, vehicle and SPRC (administered 3 h before AP) treatment groups. In conclusion, these data provide evidence for protective effects of SPRC in AP possibly by virtue of its slow release of endogenous H2S.

ß-arrestins are multifunctional proteins that modulate heptahelical 7 transmembrane receptors, also known as G protein-coupled receptors (GPCRs), a superfamily of receptors that regulate most physiological processes. ß-arrestin modulation of GPCR function includes termination of G protein-dependent signaling, initiation of ß-arrestin-dependent signaling, receptor trafficking to degradative or recycling pathways, receptor transactivation, transcriptional regulation, and localization of second messenger regulators. The pleiotropic influence ß-arrestins exert on these receptors regulates a breadth of physiological functions, and additionally, ß-arrestins are involved in the pathophysiology of numerous and wide-ranging diseases, making them prime therapeutic targets. In this review, we briefly describe the mechanisms by which ß-arrestins regulate GPCR signaling, including the functional cellular mechanisms modulated by ß-arrestins and relate this to observed pathophysiological responses associated with ß-arrestins. We focus on the role for ß-arrestins in transducing cell signaling; a pathway that is complementary to the classical G protein-coupling pathway. The existence of these GPCR dual signaling pathways offers an immense therapeutic opportunity through selective targeting of one signaling pathway over the other. Finally, we will consider several mechanisms by which the potential of dual signaling pathway regulation can be harnessed and the implications for improved disease treatments.

Earlier work from our laboratory has suggested a role for the neuropeptide substance P (SP) in inducing lung injury in sepsis. In that study, mice lacking the preprotachykinin-A gene, which encodes for SP, were protected against lung injury in sepsis. To further substantiate the role of SP in sepsis and to study its mechanism, we have evaluated the effect of SR140333, a SP receptor antagonist, on lung injury in sepsis, which was induced in male Swiss mice by cecal ligation and puncture (CLP). Sham-operated animals received the same surgical procedure, except CLP. Vehicle or SR140333 (1 mg/kg, s.c.) was administered to CLP mice 30 min before or 1 h after the CLP. Eight hours after surgery, lung tissue was collected and analyzed for myeloperoxidase (MPO) activity, chemokines, cytokines, and adhesion molecules. The CLP procedure alone caused a significant increase in the lung levels of MIP-2, MCP-1, IL-1beta, IL-6, ICAM-1, E- and P-selectin, and MPO activity when compared with sham-operated mice. SR140333 injected 30 min before or 1 h after CLP significantly attenuated the increased lung MPO activity and levels of MIP-2, MCP-1, IL-1beta, IL-6, ICAM-1, and E- and P-selectin compared with CLP-operated mice injected with the vehicle. Histological evaluation of the lung sections further supported the beneficial effect of SR140333 on lung inflammation. Therefore, SP receptor antagonism can be a potential therapeutic target in polymicrobial sepsis, and this effect is brought about via reduction in leukocyte recruitment.