It has been known that LOX is the
It has been known that 5-LOX is the rate-limiting enzyme for the products of LTs, and LTs actively participate in the activation of neutrophils . In our study, we determined whether 5-LOX was upregulated in pancreatic tissues during ANP. Moreover, we investigated whether the inhibition of expression levels of 5-LOX with zileuton treatment could repress the activation of neutrophils in pancreatic tissue during ANP. Our results clearly show that 5-LOX is not expressed in pancreatic tissues under the normal condition. When ANP was induced, we observed a significant upregulation of neutrophils and zileuton treatment is shown to repress the activation of neutrophils. Our current observations are consistent with other studies showing that 5-LOX is a critical factor regulating the activation of neutrophils [10,11]. In addition, our results, for the first, report that inhibition of 5-LOX with the treatment of zileuton can decrease the releasing of inflammatory factors into blood and attenuate pancreatic tissue pathology during ANP.
Molecular mechanisms that modulate the severity of acute pancreatitis are still largely unknown. It is generally believed that acinar cell damage is the primary event and other cellular processes, such as activation of neutrophils and the releasing of inflammatory factors, are suggested to be “downstream” events following acinar cell damage . Indeed, previous studies demonstrated that the acinar cell damage is highly associated with the severity of acute pancreatitis disease [14,15]. Specifically, it is found that mild types of acute pancreatitis are associated with upregulation of apoptotic factors in acinar ccr5 antagonist . In contrast, a severe type of acute pancreatitis is found to be relevant with an extensive activation of necrosis and very low levels of apoptosis were observed in acinar cells . These observations suggest that the activation of apoptotic pathways could be an advantageous response to acute pancreatitis-induced cell damages and the introduction of apoptotic factors, in opposition to necrosis, might attenuate the severity of acute pancreatitis .
Apoptosis, also named programmed cell death, is characterized as a mild way of cell deletion . During this process, very little damaged cellular content is released to extracellular spaces. In terms of the disease of acute pancreatitis, little is known about the activation of apoptosis of in pancreatic tissues. A previous study showed that the deletion of 5-LOX repressed pancreatic cancer cell proliferation and activated apoptosis and it is suggested that inhibitors of 5-LOX could be used as potential agents to treat pancreatic cancer . In another study, LOX-5 inhibitors were shown to induce apoptosis via mitochondria-mediated pathway including the activation of Bcl-2 protein family and cytochrome c releasing . On the basis of the above evidence, we investigated the molecular behavior of an LOX-5 inhibitor-induced apoptosis in pancreatic tissues during ANP. Our experiments show that zileuton treatment upregulates the mRNA levels of caspase-3 and downregulates Bcl-2. In addition, TUNEL assay analysis shows that zileuton treatment activates apoptosis in pancreatic tissues during ANP. Our observations are consistent with previous studies showing that 5-LOX is responsible for the activation of apoptosis and the repression of 5-LOX induces apoptosis [17,18]. Most importantly, our results, for the first time, demonstrate that a 5-LOX inhibitor, zileuton, has the capacity to induce apoptosis in vivo and can be used as a potential agent to treat pancreatic tissue pathology during ANP.
Conflicts of interest
Introduction Leukotrienes (LT) are pro-inflammatory lipid mediators derived from arachidonic acid (AA) and formed via the 5-lipoxygenase (5-LO) pathway . Upon activation of leukocytes, AA is released by cytosolic phospholipase (cPLA2) and converted to 5(S)-hydroperoxy-6-trans-8,11,14-cis-eicosatetraenoic acid (5-HPETE) in a first-step catalysis of 5-LO. In a second 5-LO-mediated reaction, 5-HPETE is then converted to the unstable epoxide LTA4, a common precursor that can be transformed by LTC4 synthases to the bronchoconstrictive cysteinyl-leukotrienes (cysLTs) or by LTA4 hydrolase to the chemoattractant LTB4. Due to the pro-inflammatory action of LTs, inhibitors against the enzymes in the LT biosynthetic pathway (i.e., 5-LO, LTA4 hydrolase, LTC4 synthases) , ,  or compounds that act as antagonists at LT receptors  have been developed. However, besides CysLT1 receptor antagonists such as montelukast or pranlukast that are clinically used to treat (childhood) asthma, inhibitors against biosynthetic enzymes within the 5-LO pathway are not widely used in the clinics, certainly due also to significant side effects like liver toxicity . As a consequence, an unmet need to develop new anti-LT compounds remains.