Ileal bile acid transporter inhibition in Cyp2c70 KO mice ameliorates cholestatic liver injury

Cyp2c70 is the liver enzyme in rodents responsible for synthesis of the primary 6-hydroxylated muricholate bile acid (BA) species. Cyp2c70 KO mice are devoid of protective, hydrophilic muricholic acids, leading to a more human-like BA composition and subsequent cholestatic liver injury. Pharmacological inhibition of the ileal BA transporter (IBAT) has been shown to be therapeutic in cholestatic models. Here, we aimed to determine if IBAT inhibition with SC-435 is protective in Cyp2c70 KO mice. As compared to WT mice, we found male and female Cyp2c70 KO mice exhibited increased levels of serum liver injury markers, and our evaluation of liver histology revealed increased hepatic inflammation, macrophage infiltration, and biliary cell proliferation. We demonstrate serum and histologic markers of liver damage were markedly reduced with SC-435 treatment. Additionally, we show hepatic gene expression in pathways related to immune cell activation and inflammation were significantly upregulated in Cyp2c70 KO mice and reduced to levels indistinguishable from WT with IBAT inhibition. In Cyp2c70 KO mice, the liver BA content was significantly increased, enriched in chenodeoxycholic acid, and more hydrophobic, exhibiting a hydrophobicity index value and red blood cell lysis properties similar to human liver BAs. Furthermore, we determined IBAT inhibition reduced the total hepatic BA levels but did not affect overall hydrophobicity of the liver BAs. These findings suggest that there may be a threshold in the liver for pathological accretion of hydrophobic BAs and reducing hepatic BA accumulation can be sufficient to alleviate liver injury, independent of BA pool hydrophobicity.

Early trypsin activation develops independently of autophagy in caerulein-induced pancreatitis in mice

Premature intrapancreatic trypsinogen activation is widely regarded as an initiating event for acute pancreatitis. Previous studies have alternatively implicated secretory vesicles, endosomes, lysosomes, or autophagosomes/autophagolysosomes as the primary site of trypsinogen activation, from which a cell-damaging proteolytic cascade originates. To identify the subcellular compartment of initial trypsinogen activation we performed a time-resolution analysis of the first 12 h of caerulein-induced pancreatitis in transgenic light chain 3 (LC3)-GFP autophagy reporter mice. Intrapancreatic trypsin activity increased within 60 min and serum amylase within 2 h, but fluorescent autophagosome formation only by 4 h of pancreatitis in parallel with a shift from cytosolic LC3-I to membranous LC3-II on Western blots. At 60 min, activated trypsin in heavier subcellular fractions was co-distributed with cathepsin B, but not with the autophagy markers LC3 or autophagy protein 16 (ATG16). Supramaximal caerulein stimulation of primary pancreatic acini derived from LC3-GFP mice revealed that trypsinogen activation is independent of autophagolysosome formation already during the first 15 min of exposure to caerulein. Co-localization studies (with GFP-LC3 autophagosomes versus Ile-Pro-Arg-AMC trypsin activity and immunogold-labelling of lysosomal-associated membrane protein 2 [LAMP-2] versus trypsinogen activation peptide [TAP]) indicated active trypsin in autophagolysosomes only at the later timepoints. In conclusion, during the initiating phase of caerulein-induced pancreatitis, premature protease activation develops independently of autophagolysosome formation and in vesicles arising from the secretory pathway. However, autophagy is likely to regulate overall intracellular trypsin activity during the later stages of this disease.

Exosomes, Their Biogenesis and Role in Inter-Cellular Communication, Tumor Microenvironment and Cancer Immunotherapy

Exosomes are extracellular vesicles ranging from 30 to 150 nm in diameter that contain molecular constituents of their host cells. They are released from different types of cells ranging from immune to tumor cells and play an important role in intercellular communication. Exosomes can be manipulated by altering their host cells and can be loaded with products of interest such as specific drugs, proteins, DNA and RNA species. Due to their small size and the unique composition of their lipid bilayer, exosomes are capable of reaching different cell types where they alter the pathophysiological conditions of the recipient cells. There is growing evidence that exosomes are used as vehicles that can modulate the immune system and play an important role in cancer progression. The cross communication between the tumors and the cells of the immune system has gained attention in various immunotherapeutic approaches for several cancer types. In this review, we discuss the exosome biogenesis, their role in inter-cellular communication, and their capacity to modulate the immune system as a part of future cancer immunotherapeutic approaches and their potential to serve as biomarkers of therapy response.

Mitochondrial Dysfunction, Through Impaired Autophagy, Leads to Endoplasmic Reticulum Stress, Deregulated Lipid Metabolism, and Pancreatitis in Animal Models

BACKGROUND & AIMS

Little is known about the signaling pathways that initiate and promote acute pancreatitis (AP). The pathogenesis of AP has been associated with abnormal increases in cytosolic Ca2+, mitochondrial dysfunction, impaired autophagy, and endoplasmic reticulum (ER) stress. We analyzed the mechanisms of these dysfunctions and their relationships, and how these contribute to development of AP in mice and rats.

METHODS

Pancreatitis was induced in C57BL/6J mice (control) and mice deficient in peptidylprolyl isomerase D (cyclophilin D, encoded by Ppid) by administration of L-arginine (also in rats), caerulein, bile acid, or an AP-inducing diet. Parameters of pancreatitis, mitochondrial function, autophagy, ER stress, and lipid metabolism were measured in pancreatic tissue, acinar cells, and isolated mitochondria. Some mice with AP were given trehalose to enhance autophagic efficiency. Human pancreatitis tissues were analyzed by immunofluorescence.

RESULTS

Mitochondrial dysfunction in pancreas of mice with AP was induced by either mitochondrial Ca2+ overload or through a Ca2+ overload-independent pathway that involved reduced activity of ATP synthase (80% inhibition in pancreatic mitochondria isolated from rats or mice given L-arginine). Both pathways were mediated by cyclophilin D and led to mitochondrial depolarization and fragmentation. Mitochondrial dysfunction caused pancreatic ER stress, impaired autophagy, and deregulation of lipid metabolism. These pathologic responses were abrogated in cyclophilin D-knockout mice. Administration of trehalose largely prevented trypsinogen activation, necrosis, and other parameters of pancreatic injury in mice with L-arginine AP. Tissues from patients with pancreatitis had markers of mitochondrial damage and impaired autophagy, compared with normal pancreas.

CONCLUSIONS

In different animal models, we find a central role for mitochondrial dysfunction, and for impaired autophagy as its principal downstream effector, in development of AP. In particular, the pathway involving enhanced interaction of cyclophilin D with ATP synthase mediates L-arginine-induced pancreatitis, a model of severe AP the pathogenesis of which has remained unknown. Strategies to restore mitochondrial and/or autophagic function might be developed for treatment of AP.

Effect of oral administration of AZD8309, a CXCR2 antagonist, on the severity of experimental pancreatitis

INTRODUCTION

Acute pancreatitis is a common gastrointestinal disorder burdened with a high mortality. Two pathophysiological events during experimental pancreatitis are thought to determine the clinical course: premature digestive protease activation and tissue infiltration by inflammatory cells. We have investigated the effect of AZD8309, a potent and orally bioavailable antagonist of the chemokine receptor CXCR2, which has been proposed to regulate the transmigration of neutrophils.

METHODS

Male C57BL6 mice (25-30 g) received gavage feeding of AZD8309 (50 mg/kg/BW) or mannitol (controls) twice daily starting 3 h prior to pancreatitis induction. Mild pancreatitis was induced by i.p. caerulein administration (50 μg/kg BW), severe pancreatitis by intraductal taurocholate (2%). Pancreas, lung, and serum was harvested up to 48 h after pancreatitis induction and used for histopathology, amylase, lipase, cathepsin B, trypsin, and elastase activity measurements, myeloperoxidase (MPO) content and cytokine concentrations.

RESULTS

Oral administration of AZD8309 significantly reduced MPO in the pancreas and lungs (8 h & 24 h) and reduced intrapancreatic trypsin and elastase activity (8 h) in caerulein-pancreatitis. In taurocholate-pancreatitis AZD8309 reduced cathepsin B activity and MPO. Serum cytokine levels were reduced by AZD8309 as well as histopathological damage.

CONCLUSION

The CXCR2 antagonist AZD8309 reduced the transmigration of neutrophils as well as intrapancreatic protease activation in experimental pancreatitis. This effect was sufficient to reduce the overall severity of the disease. CXCR2 may therefore be a viable therapeutic target and AZD8309 a suitable agent for the treatment of acute pancreatitis.