Down-regulation of hypoxia-inducible factor-1alpha by hyperbaric oxygen attenuates the severity of acute pancreatitis in rats

Inhibition of xanthine oxidase alleviated pancreatic necrosis via HIF-1α-regulated LDHA and NLRP3 signaling pathway in acute pancreatitis

Acute pancreatitis (AP) is a potentially fatal condition with no targeted treatment options. Although inhibiting xanthine oxidase (XO) in the treatment of AP has been studied in several experimental models and clinical trials, whether XO is a target of AP and what its the main mechanism of action is remains unclear. Here, we aimed to re-evaluate whether XO is a target aggravating AP other than merely generating reactive oxygen species that trigger AP. We first revealed that XO expression and enzyme activity were significantly elevated in the serum and pancreas of necrotizing AP models. We also found that allopurinol and febuxostat, as purine-like and non-purine XO inhibitors, respectively, exhibited protective effects against pancreatic acinar cell death in vitro and pancreatic damage in vivo at different doses and treatment time points. Moreover, we observed that conditional Xdh overexpression aggravated pancreatic necrosis and severity. Further mechanism analysis showed that XO inhibition restored the hypoxia-inducible factor 1-alpha (HIF-1α)-regulated lactate dehydrogenase A (LDHA) and NOD-like receptor family pyrin domain containing 3 (NLRP3) signaling pathways and reduced the enrichment of 13C6-glucose to 13C3-lactate. Lastly, we observed that clinical circulatory XO activity was significantly elevated in severe cases and correlated with C-reactive protein levels, while pancreatic XO and urate were also increased in severe AP patients. These results together indicated that proper inhibition of XO might be a promising therapeutic strategy for alleviating pancreatic necrosis and preventing progression of severe AP by downregulating HIF-1α-mediated LDHA and NLRP3 signaling pathways.

The Mechanisms of Action of Hyperbaric Oxygen in Restoring Host Homeostasis during Sepsis

The perception of sepsis has shifted over time; however, it remains a leading cause of death worldwide. Sepsis is now recognized as an imbalance in host cellular functions triggered by the invading pathogens, both related to immune cells, endothelial function, glucose and oxygen metabolism, tissue repair and restoration. Many of these key mechanisms in sepsis are also targets of hyperbaric oxygen (HBO2) treatment. HBO2 treatment has been shown to improve survival in clinical studies on patients with necrotizing soft tissue infections as well as experimental sepsis models. High tissue oxygen tension during HBO2 treatment may affect oxidative phosphorylation in mitochondria. Oxygen is converted to energy, and, as a natural byproduct, reactive oxygen species are produced. Reactive oxygen species can act as mediators, and both these and the HBO2-mediated increase in oxygen supply have the potential to influence the cellular processes involved in sepsis. The pathophysiology of sepsis can be explained comprehensively through resistance and tolerance to infection. We argue that HBO2 treatment may protect the host from collateral tissue damage during resistance by reducing neutrophil extracellular traps, inhibiting neutrophil adhesion to vascular endothelium, reducing proinflammatory cytokines, and halting the Warburg effect, while also assisting the host in tolerance to infection by reducing iron-mediated injury and upregulating anti-inflammatory measures. Finally, we show how inflammation and oxygen-sensing pathways are connected on the cellular level in a self-reinforcing and detrimental manner in inflammatory conditions, and with support from a substantial body of studies from the literature, we conclude by demonstrating that HBO2 treatment can intervene to maintain homeostasis.

Tuftsin ameliorates splenic inflammatory injury by promoting neuropilin-1 in severe acute pancreatitis

Severe acute pancreatitis (SAP)-associated spleen injury causing immune disturbances aggravates organs injuries, which contributes to higher mortality rate. However, there are no effective drugs to cure SAP-induced spleen injury. Here, we found that Tuftsin (TN) is effective for ameliorating SAP-induced pathological damage and inflammation of spleen, mainly via alleviating mitochondrial dysfunction, oxidative stress, ATP depletion and the expression of pro-inflammatory factors. We further found that TN promoted anti-inflammatory macrophage phenotype M2 via up-regulating NRP1 on macrophage in spleen during SAP. Meanwhile, EG00229 (an inhibitor of NRP1 bound to TN) weakened TN's therapeutic effect in SAP-associated spleen injury. And EG00229 also inhibited M2 macrophage, leading to increasing inflammasome formation. Additionally, EG00229 reduced the protective efficiency of TN on mitochondrial dysfunction, and inflammation injury via NRP1 in spleen caused by SAP. Similarly, siRNA-Nrp1 into macrophage also prevented TN's inhibition on apoptosis. These findings reveal that TN alleviates SAP-induced spleen injury by promoting NRP1.

Hyperbaric Oxygen Ameliorates Bleomycin-Induced Pulmonary Fibrosis in Mice

The prevalence of pulmonary fibrosis is increasing with an aging population and its burden is likely to increase following COVID-19, with large financial and medical implications. As approved therapies in pulmonary fibrosis only slow disease progression, there is a significant unmet medical need. Hyperbaric oxygen (HBO) is the inhaling of pure oxygen, under the pressure of greater than one atmosphere absolute, and it has been reported to improve pulmonary function in patients with pulmonary fibrosis. Our recent study suggested that repetitive HBO exposure may affect biological processes in mice lungs such as response to wounding and extracellular matrix. To extend these findings, a bleomycin-induced pulmonary fibrosis mouse model was used to evaluate the effect of repetitive HBO exposure on pulmonary fibrosis. Building on our previous findings, we provide evidence that HBO exposure attenuates bleomycin-induced pulmonary fibrosis in mice. In vitro, HBO exposure could reverse, at least partially, transforming growth factor (TGF)-β-induced fibroblast activation, and this effect may be mediated by downregulating TGF-β-induced expression of hypoxia inducible factor (HIF)-1α. These findings support HBO as a potentially life-changing therapy for patients with pulmonary fibrosis, although further research is needed to fully evaluate this.

Hyperbaric Oxygen Ameliorated Acute Pancreatitis in Rats via the Mitochondrial Pathway

BACKGROUND

Acute pancreatitis (AP) is a common disease of the digestive system. The mechanism of hyperbaric oxygen (HBO) therapy for AP is not completely clear.

AIMS

This study investigated the effects of HBO in AP and whether it acts through the mitochondria-mediated apoptosis pathway.

METHODS

Eighty male Sprague-Dawley rats were randomly assigned to four groups: control (8 rats), sham (24 rats), AP (24 rats), or AP + HBO (24 rats). AP was induced by ligating the pancreatic duct. The AP + HBO group was given HBO therapy starting at 6 h postinduction. Eight rats in each group were killed on days 1, 2, and 3 postinduction to assess pancreatic injury, mitochondrial membrane potential, ATP level, and expression levels of BAX, Bcl-2, caspase-3, caspase-9, and PARP in pancreatic tissue and blood levels of amylase, lipase, and pro-inflammatory cytokines.

RESULTS

HBO therapy alleviated the severity of AP and decreased histopathological scores and levels of serum amylase, lipase, and pro-inflammatory cytokines. Compared to AP induction alone, HBO therapy increased expression of the apoptotic protein BAX, caspase-3, caspase-9, and PARP and ATP levels in tissues and decreased antiapoptotic protein Bcl-2 expression levels and the mitochondrial membrane potential on the first day; the results on the second day were partly consistent with those on the first day, while there was no obvious difference on the third day.

CONCLUSIONS

HBO therapy could induce caspase-dependent apoptosis in AP rats to alleviate pancreatitis, which was possibly triggered by mitochondrial apoptosis pathway regulation of Bcl-2 family members.

Arachidonic Acid Metabolites of CYP450 Enzymes and HIF-1α Modulate Endothelium-Dependent Vasorelaxation in Sprague-Dawley Rats under Acute and Intermittent Hyperbaric Oxygenation

Acetylcholine-induced vasorelaxation (AChIR) and responses to reduced pO₂ (hypoxia-induced relaxation (HIR), 0% O₂) were assessed in vitro in aortic rings of healthy male Sprague-Dawley rats (N = 252) under hyperbaric (HBO₂) protocols. The studied groups consisted of the CTRL group (untreated); the A-HBO₂ group (single HBO₂; 120 min of 100% O₂ at 2.0 bars); the 24H-HBO₂ group (examined 24 h after single exposure) and the 4D-HBO₂ group (four consecutive days of single HBO₂). AChIR, sensitivity to ACh and iNOS expression were decreased in the A-HBO₂ group. HIR was prostanoid- and epoxyeicosatrienoic acid (EET)-mediated. HIF-1α expression was increased in the 24H-HBO₂ and 4D-HBO₂ groups. LW6 (HIF-1α inhibitor) decreased HIR in the 24H-HBO₂ group. HBO₂ affected the expression of COX-1 and COX-2. CYP2c11 expression was elevated in the 24H-HBO₂ and 4D-HBO₂ groups. Concentrations of arachidonic acid (AA) metabolites 14(15)-DiHET, 11(12)-DiHET and 8(9)-DiHET were increased in A-HBO₂ and 24H-HBO_2. An increased concentration of 8(9)-EET was observed in the A-HBO₂ and 24h-HBO₂ groups vs. the CTRL and 4D-HBO₂ groups, and an increased concentration of 5(6)-DiHET was observed in the 24H-HBO₂ group vs. the 4D-HBO₂ group. The 20-HETE concentration was increased in the A-HBO₂ group. All were determined by LC-MS/MS of the aorta. The results show that AChIR in all groups is mostly NO-dependent. HIR is undoubtedly mediated by the CYP450 enzymes’ metabolites of AA, whereas HIF-1α contributes to restored HIR. Vasoconstrictor metabolites of CYP450 enzymes contribute to attenuated AChIR and HIR in A-HBO₂.

The Hyperoxic-Hypoxic Paradox

Effective metabolism is highly dependent on a narrow therapeutic range of oxygen. Accordingly, low levels of oxygen, or hypoxia, are one of the most powerful inducers of gene expression, metabolic changes, and regenerative processes, including angiogenesis and stimulation of stem cell proliferation, migration, and differentiation. The sensing of decreased oxygen levels (hypoxia) or increased oxygen levels (hyperoxia), occurs through specialized chemoreceptor cells and metabolic changes at the cellular level, which regulate the response. Interestingly, fluctuations in the free oxygen concentration rather than the absolute level of oxygen can be interpreted at the cellular level as a lack of oxygen. Thus, repeated intermittent hyperoxia can induce many of the mediators and cellular mechanisms that are usually induced during hypoxia. This is called the hyperoxic-hypoxic paradox (HHP). This article reviews oxygen physiology, the main cellular processes triggered by hypoxia, and the cascade of events triggered by the HHP.

The Hyperoxic-Hypoxic Paradox

Effective metabolism is highly dependent on a narrow therapeutic range of oxygen. Accordingly, low levels of oxygen, or hypoxia, are one of the most powerful inducers of gene expression, metabolic changes, and regenerative processes, including angiogenesis and stimulation of stem cell proliferation, migration, and differentiation. The sensing of decreased oxygen levels (hypoxia) or increased oxygen levels (hyperoxia), occurs through specialized chemoreceptor cells and metabolic changes at the cellular level, which regulate the response. Interestingly, fluctuations in the free oxygen concentration rather than the absolute level of oxygen can be interpreted at the cellular level as a lack of oxygen. Thus, repeated intermittent hyperoxia can induce many of the mediators and cellular mechanisms that are usually induced during hypoxia. This is called the hyperoxic-hypoxic paradox (HHP). This article reviews oxygen physiology, the main cellular processes triggered by hypoxia, and the cascade of events triggered by the HHP.

Hypoxia-Inducible Factor-1α Knockdown Plus Glutamine Supplementation Attenuates the Predominance of Necrosis over Apoptosis by Relieving Cellular Energy Stress in Acute Pancreatitis

The present study was conducted to investigate the effect and potential mechanism of hypoxia-inducible factor-1α (HIF-1α) genetic inhibition plus glutamine (Gln) supplementation on necrosis-apoptosis imbalance during acute pancreatitis (AP), with a specific focus on the regulations of intracellular energy metabolism status. Wistar rats and AR42J cells were used to establish AP models. When indicated, a HIF-1α knockdown with or without a Gln supplementation was administered. In vivo, local and systemic inflammatory injuries were assessed by serum cytokine measurement, H&E staining, and transmission electron microscope (TEM) observation of pancreatic tissue. In vitro, intracellular energy metabolism status was evaluated by measuring the intracellular adenosine triphosphate (ATP), lactic acid, and Ca²⁺ concentrations and the mitochondrial potential. In addition, changes in the apoptotic activity were analyzed using TUNEL staining in vivo and an apoptosis assay in vitro. HIF-1α knockdown alleviated AP-related inflammatory injury as indicated by the measurements of serum cytokines and examinations of TEM and H&E staining of pancreatic tissues. HIF-1α knockdown played an antioxidative role against AP-related injuries by preventing the increase in the intracellular Ca²⁺ concentration and the decrease in the mitochondrial membrane potential and subsequently by suppressing the glycolysis pathway and increasing energy anabolism in AR42J cells after AP induction. Apoptosis was significantly upregulated when HIF-1α was knocked down before AP induction due to an attenuation of the translocation of nuclear factor-kappa B to the nuclei. Furthermore, these merits of HIF-1α knockdown in the relief of the metabolic stress and upregulation of apoptosis were more significant when Gln was administered concomitantly. In conclusion, Gln-supplemented HIF-1α knockdown might be promising for the future management of AP by relieving the intracellular energy stress, thereby attenuating the predominance of necrosis over apoptosis.

Use of Gases to Treat Cochlear Conditions

Although the cochlear vascular supply (stria vascularis) is designed to block to certain compounds and molecules, it must enable gas exchange to survive. The inner ear capillaries must deliver oxygen and remove carbon dioxide for the cochlea to function. These gases diffuse through tissues across a concentration gradient to reach the desired target. Tight junctions or the endothelial basement membrane do not impede them. Therefore, gases that can diffuse into the inner ear are attractive as therapeutic agents. The two gases most often used in this way are oxygen and hydrogen, although carbon dioxide, ozone, and argon have also been investigated. Typically, oxygen is delivered as hyperbaric oxygen (HBO) (oxygen at pressure higher than atmospheric) to provide increased oxygen levels to the inner ear. This not only relieves hypoxia, but also has anti-inflammatory and other biochemical effects. HBO is used clinically to treat idiopathic sudden sensorineural hearing loss, and both animal and human studies suggest it may also assist recovery after acute acoustic trauma. Laboratory studies suggest hydrogen works as a free radical scavenger and reduces the strong oxidants hydroxyl radicals and peroxynitrite. It also has anti-apoptotic effects. Because of its anti-oxidant and anti-inflammatory effects, it has been studied as a treatment for ototoxicity and shows benefit in an animal model of cisplatinum toxicity. Gas diffusion offers an effective way to provide therapy to the inner ear, particularly since some gases (oxygen, hydrogen, carbon dioxide, ozone, argon) have important therapeutic effects for minimizing cochlear damage.

The diffuse reduction in spleen density: an indicator of severe acute pancreatitis?

We observed that acute pancreatitis (AP) was associated with diffuse reduction in spleen density (DROSD) in some patients. Furthermore, the condition of these patients was more serious, and the potential relationship between DROSD and structural and functional injury of the spleen remained unclear. Therefore, we performed a preliminary exploration of these factors. We analysed pertinent clinical data for AP patients with normal spleen density (control group) and for those with DROSD (reduction group) at the First Affiliated Hospital of Harbin Medical University (June 2013–June 2015). We measured the immunoglobulin M (IgM) B-cells of the AP patients and examined pancreatic and splenic tissues from AP rats with optical microscopy and TEM. The reduction group had a higher acute physiology and chronic health evaluation II (APACHE II) score, a longer length of stay (LOS) and lower serum calcium than the control group. The levels of triglycerides (TG) and total cholesterol (TC) did not differ significantly between the two groups. The percentage of IgM memory B-cells was significantly lower in the DROSD group than in the control group. TEM revealed that the spleen T-lymphocytes were normal in AP rats, but pyroptotic and necrotic spleen B-cells were observed in the severe AP rats. In AP, DROSD was an independent indicator of more severe conditions. Furthermore, spleen B-lymphocytes showed obvious damage at the cellular level, and the immunological function of the spleen was down-regulated when AP was associated with DROSD.

Hyperbaric oxygen preconditioning: a reliable option for neuroprotection

Brain injury is the leading cause of death and disability worldwide and clinically there is no effective therapy for neuroprotection. Hyperbaric oxygen preconditioning (HBO-PC) has been experimentally demonstrated to be neuroprotective in several models and has shown efficiency in patients undergoing on-pump coronary artery bypass graft (CABG) surgery. Compared with other preconditioning stimuli, HBO is benign and has clinically translational potential. In this review, we will summarize the results in experimental brain injury and clinical studies, elaborate the mechanisms of HBO-PC, and discuss regimes and opinions for future interventions in acute brain injury.

Protective Effects of Hydrogen Gas on Experimental Acute Pancreatitis

Acute pancreatitis (AP) is an inflammatory disease mediated by damage to acinar cells and pancreatic inflammation. In patients with AP, subsequent systemic inflammatory responses and multiple organs dysfunction commonly occur. Interactions between cytokines and oxidative stress greatly contribute to the amplification of uncontrolled inflammatory responses. Molecular hydrogen (H2) is a potent free radical scavenger that not only ameliorates oxidative stress but also lowers cytokine levels. The aim of the present study was to investigate the protective effects of H2 gas on AP both in vitro and in vivo. For the in vitro assessment, AR42J cells were treated with cerulein and then incubated in H2-rich or normal medium for 24 h, and for the in vivo experiment, AP was induced through a retrograde infusion of 5% sodium taurocholate into the pancreatobiliary duct (0.1 mL/100 g body weight). Wistar rats were treated with inhaled air or 2% H2 gas and sacrificed 12 h following the induction of pancreatitis. Specimens were collected and processed to measure the amylase and lipase activity levels; the myeloperoxidase activity and production levels; the cytokine mRNA expression levels; the 8-hydroxydeoxyguanosine, malondialdehyde, and glutathione levels; and the cell survival rate. Histological examinations and immunohistochemical analyses were then conducted. The results revealed significant reductions in inflammation and oxidative stress both in vitro and in vivo. Furthermore, the beneficial effects of H2 gas were associated with reductions in AR42J cell and pancreatic tissue damage. In conclusion, our results suggest that H2 gas is capable of ameliorating damage to the pancreas and AR42J cells and that H2 exerts protective effects both in vitro and in vivo on subjects with AP. Thus, the results obtained indicate that this gas may represent a novel therapy agent in the management of AP.

Hyperbaric oxygen therapy ameliorates TNBS-induced acute distal colitis in rats

BACKGROUND

This study investigated the therapeutic effects of hyperbaric oxygen in experimental acute distal colitis focusing on its effect on the production of pro-inflammatory cytokines, nitric oxide and hypoxia-inducible factor 1alpha.

METHODS

Colitis was induced with a rectal infusion of 150 mg/kg of TNBS under anesthesia with Ketamine (50 mg/kg) and Xylazine (10 mg/kg). Control animals received only rectal saline. After colitis induction, animals were subjected to two sessions of hyperbaric oxygen and were then euthanized. The distal intestine was resected for macroscopic analysis, determination of myeloperoxidase activity, western-blotting analyses of inducible nitric oxide synthase and cyclooxygenase-2 expression and immunohistochemical analysis of hypoxia-inducible factor 1alpha and cyclooxygenase-2. Cytokines levels in the distal intestine were measured using an enzyme-linked immunosorbent assay.

RESULTS

Hyperbaric oxygen therapy attenuated the severity of acute distal colitis, with reduced macroscopic damage score. This effect was associated with prevention in the increase of pro-inflammatory cytokine production; myeloperoxidase activity, in the expression of inducible nitric oxide synthase and cyclooxygenase-2. Finally, hyperbaric oxygen inhibited the acute distal colitis-induced up-regulation of hypoxia-inducible factor 1alpha.

CONCLUSIONS

The results indicate that hyperbaric oxygen attenuates the severity of acute distal colitis through the down-regulation of pro-inflammatory events.

The apoptosis of peripheral blood lymphocytes promoted by hyperbaric oxygen treatment contributes to attenuate the severity of early stage acute pancreatitis in rats

The aim of this study was to investigate the immunoregulatory effects of hyperbaric oxygen (HBO) via promoting the apoptosis of peripheral blood lymphocytes (PBLs) to attenuate the severity of early stage acute pancreatitis (AP) in rats. Additionally, the persistence of the HBO treatment effects was evaluated. One hundred and twenty male Wistar rats were randomized into four groups: sham, AP, AP + normobaric oxygen (NBO), and AP + HBO. Each group consisted of 30 rats. Four hours after the induction of AP, the 30 rats in the AP + NBO group were given normobaric oxygen treatment with 100 % oxygen at 1 atm for 90 min. The 30 rats in the AP + HBO group received 100 % oxygen at 2.5 atm for 90 min, with a compression/decompression time of 15 min. The 30 rats in the AP group remained untreated. At 6, 12, and 24 h after the induction of AP, surviving rats from each group were sacrificed, and the blood and tissue samples were collected for the following measurements: the partial pressure of oxygen (PaO2) and oxygen saturation (SaO2) of the arterial blood, the levels of serum amylase, lipase, interleukin-2 (IL-2), interferon-γ (IFN-γ), interleukin-10 (IL-10), hepatocyte growth factor (HGF), and reactive oxygen species (ROS), and the mitochondrial membrane potential (∆Ψm) of the PBLs. The expression levels of procaspase-3, caspase-3, procaspase-9, and caspase-9 were also evaluated in the PBLs. Additionally, the apoptosis of PBLs was assessed, and the pancreatic tissues were subjected to a histopathological analysis by pathological grading and scoring. The histopathology of the lung, liver, kidney, duodenum, and heart was also analyzed at 12 h after the induction of AP. Significant differences were found at 6 and 12 h after AP induction. The HBO treatment significantly elevated the PaO2 and SaO2 levels, and the ROS levels in the PBLs. Additionally, HBO downregulated the levels of amylase and lipase. The HBO treatment also reduced the ∆Ψm levels, upregulated the expression of caspase-3 and caspase-9, and increased the apoptosis rate of the PBLs. Moreover, the HBO treatment decreased the serum concentrations of IL-2, IFN-γ and HGF, and reduced the pathological scores of the pancreatic tissue. The histopathological changes of the lung, liver, kidney, duodenum, and heart were also improved. A significant elevation of IL-10 occurred only at the 12-h time point. However, no obvious differences were found at the 24-h time point. This study demonstrated that the HBO treatment can promote the apoptosis of PBLs via a mitochondrial-dependent pathway and inhibit the inflammatory response. These immunoregulatory effects may play an important therapeutic role in attenuating the severity of early stage AP. The repeated administration of HBO or the use of HBO in combination with other approaches may further improve outcomes.

Effects of hypoxia-inducible factor-1α and matrix metalloproteinase-9 on alveolar-capillary barrier disruption and lung edema in rat models of severe acute pancreatitis-associated lung injury

The aim of this study was to investigate the effects of hypoxia-inducible factor-1α (HIF-1α) and matrix metalloproteinase-9 (MMP-9) on alveolar-capillary barrier disruption and lung edema in rat models of severe acute pancreatitis-associated lung injury (PALI). A total of 40 male Sprague-Dawley rats were randomly divided into a sham surgery group (n=10) and three PALI groups, in which acute pancreatitis was induced by the retrograde infusion of 5% sodium taurocholate (1 ml/kg). The PALI groups were as follows: i) Untreated PALI group (n=10); ii) 2-methoxyestradiol (2ME2) group (5 mg/kg body mass; n=10); and iii) 2ME2 group (15 mg/kg body mass; n=10). In the two 2ME2 groups, the HIF-1α inhibitor 2ME2 was administered intraperitoneally 1 h after the induction of AP. The severity of the pancreatitis was evaluated by the serum amylase levels and pathology. The severity of the lung injury was evaluated by the wet/dry ratio, blood gas analysis and pathology. The alveolar-capillary barrier disruption was assessed by Evans blue dye extravasation. The protein and mRNA expression levels of HIF-1α and MMP-9 were studied using enzyme-linked immunosorbent assays (ELISAs), western blot analysis and reverse transcription-polymerase chain reaction. The active tumor necrosis factor-α levels were measured using an ELISA. The HIF-1α inhibitor 2ME2 attenuated the severity of the pancreatitis and PALI, while the lung edema and alveolar-capillary barrier disruption were significantly ameliorated compared with those in the untreated PALI group. Administration of the higher dose of 2ME2 significantly suppressed the protein expression of MMP-9 in the lung tissues. The results indicate that HIF-1α has a major function in alveolar-capillary barrier disruption and lung edema in PALI via a molecular pathway cascade involving MMP-9. Inhibition of HIF-1α by 2ME2 attenuates alveolar-capillary barrier disruption and lung edema. Pharmacological blockade of this pathway in patients with PALI may provide a novel therapeutic strategy.

From nitric oxide to hyperbaric oxygen: invisible and subtle but nonnegligible gaseous signaling molecules in acute pancreatitis

Nitric oxide (NO), carbon monoxide, and hydrogen sulfide in addition to hydrogen are well established as gaseous signal molecules throughout the body. Although the role of gasotransmitters in acute pancreatitis (AP) has been explored for many years, many details remain to be elucidated. The physiologic effect of NO in AP mainly relies on induced NO synthase, which stimulates the production of cytokines in the blood. Carbon monoxide inhibits nuclear factor-κB activation, which leads to amelioration of the inflammatory response. Hydrogen sulfide displays a dual role in the mechanism of AP according to its concentration in the system. Hydrogen is a newly discovered gaseous signaling molecule, and currently, there is little evidence that it has any function in alleviating inflammation. We discovered that hyperbaric oxygen is a novel gasotransmitter that has potential use in the treatment of AP. The correlation among hyperbaric oxygen, hypoxia inducible factor 1α, and other signaling pathways should be further studied. We also discuss some prospects and issues that remain to be resolved in this review. In summary, the discovery of gaseous signal molecules has established a new platform for deep investigation of the mechanism of AP, and our knowledge of the role of gasotransmitters in AP will increase with further research.