Clinical Pancreatology for Practising Gastroenterologists and Surgeons. Группа авторов

cyclophilin A, it was in clinical development by Novartis as a treatment for hepatitis C. This development has been abandoned, however, and at present DEB025 is not in clinical development. It remains unclear whether nonspecific cyclophilin inhibition will benefit or detract from the treatment of AP, but the high amino acid sequence homology between cyclophilins means the development of novel molecule inhibitors specific to CypD remains a challenge [44]. Non‐immunosuppressive sanglifehrin analogs, which are orally bioavailable and lighter in molecular weight compared to CsA, have also been developed [45] but have not been tested in experimental AP. We are also developing CypD inhibitors, as this strategy holds significant promise for future progression to early phase trials [41,46–48]. As we and others have demonstrated a reduction of ATP from mitochondrial dysfunction to be an important contributor to AP pathogenesis [9,13,36], we look forward to the results of the current GOULASH trial comparing high‐ versus low‐energy nutrition in the early phase of AP [49].

Autophagy

      Autophagy is a cellular degradative process driven by the lysosomal pathway and is an essential mechanism by means of which cells remove dysfunctional components, allowing cellular organelle recycling. The exact role of autophagy in the pathogenesis of AP remains unclear [50], although impaired autophagy (mainly macroautophagy) has been defined as a critical pathological event during the early phase of AP [13,51–53], significantly aided by the recent comprehensive demonstration of methods to identify autophagic structures and to measure autophagic flux using in vitro and in vivo models of pancreatitis [54]. The investigation of autophagy in AP began a decade ago when Yamamura and colleagues [55,56] created a conditional knockout mouse lacking the autophagy‐related gene Atg5 in pancreatic acinar cells and found the severity of cerulein‐induced AP to be significantly alleviated in vivo. Furthermore, isolated acinar cells from these mice showed a greatly reduced level of cerulein‐induced trypsinogen activation. Vitamin K₃ administration can markedly attenuate cerulein‐induced AP by inhibition of microtubule‐associated protein 1A/1B‐light chain 3 (LC3‐II) expression and colocalization of autophagosomes and lysosomes in pancreatic tissue [57]. Blocking autophagic flux with a specific inhibitor, 3‐methyladenine, substantially prevented cell vacuolation and trypsinogen activation induced by CCK hyperstimulation of mouse pancreatic acinar cells [53] and alleviated cerulein plus lipopolysaccharide‐induced pancreatic injury alongside multiple organ failure [58]. Treatment with CYT387, a TBK1‐mediated autophagy inhibitor, significantly suppressed cytokine activation and pancreatic inflammatory cell infiltration in cerulein‐induced mouse AP [59]. Most recently, trehalose, an mTOR‐independent autophagy enhancer, has been demonstrated to alleviate experimental AP in the L‐arginine and cerulein models of AP by reducing the accumulation of LC3‐II, P62 and other ubiquitinated proteins, accumulation of which occurs as a result of impaired autophagic flux [60,61] (see Figure 12.1). Simvastatin may also play a protective role in AP through the modulation of autophagy [62]. Future focus on specific “clean” agents that maintain an efficient and healthy autophagic pathway for pancreatic acinar cells may be of potential use for the treatment of AP.

Acinar Cell Secretion, Serine Proteases, and Serine Protein Kinases

The observation that somatostatin or its analog, octreotide, caused a dose‐dependent reduction in exocrine pancreatic secretions prompted much interest in their consideration as therapeutic options for AP [63] (Figure 12.2). Although a reduction in organ failure was observed from delivery of both agents in clinical trials, detailed assessment found them to have flawed designs with no benefit on overall mortality [64]. Prevention of trypsinogen activation by inhibition of cathepsin B [65] or deletion of the cathepsin B gene [66] has resulted in a decrease in pancreatic injury in experimental AP, stressing the importance of trypsinogen activation for pancreatic damage. A further study in which genetically modified mice expressed an endogenously activated trypsinogen within pancreatic acinar cells found intra‐acinar activation of trypsinogen to initiate AP with rapid induction of acinar cell death via apoptosis, facilitating resolution of inflammation. Nevertheless, serine protease inhibition with ulinastatin, a multifunctional serine protease inhibitor, has shown promise in preclinical and small clinical observational studies [67] (see Figure 12.1). However, larger clinical trials with ulinastatin have not demonstrated benefit [64], possibly due to trial design. Further, well‐planned trials of ulinastatin remain to be conducted.

Protein kinase D (PKD/PKD1) activation is necessary for nuclear factor (NF)‐κB activation in vitro in pancreatic acinar cells [68], which in turn is a crucial early regulator of inflammatory and cell death responses in AP (see Figure 12.1). The novel small molecule PKD inhibitors CID755673 and CRT0066101 have both demonstrated efficacy in in vitro and in vivo models of experimental AP, likely through significant attenuation of NF‐κB activation [69], holding promise for translational drug discovery.

Figure 12.2 Strategies modulating pancreatic secretion. Cystic fibrosis transmembrane conductance regulator (CFTR) is found on the luminal surface of pancreatic ductal cells, contributing chloride and water secretion; defects resulting from CFTR gene mutations are associated with recurrent pancreatitis. CFTR correctors (VX770 and VX809) significantly reduce the number of acute pancreatitis attacks in patients with cystic fibrosis and may hold promise if their use is widened to other indications. Somatostatin and its synthetic analog octreotide inhibit acinar cell enzyme secretion and although not beneficial in reducing mortality in clinical trials, have shown a reduction in organ failure and may benefit from improved future trial design.

Immune Cells/Inflammation

Acinar cell injury induces synthesis and release of proinflammatory cytokines [70,71] and of proinflammatory DAMPs (damage‐associated molecular patterns) including histones, high mobility group box 1 protein (HMGB1), nuclear and mitochondrial DNA, cyclophilin A, heat shock proteins, and ATP [14,72] that act in concert to initiate a cellular inflammatory response consisting primarily of neutrophils and monocytes (Figure 12.3). Nuclear DAMPs can be measured as early as four hours after induction of experimental AP [73,74] and act via common immune sensors, including toll‐like receptors (TLRs), nucleotide‐binding domain (NOD)‐like receptors (NLRs), and receptors for advanced glycation end‐products (RAGE), to initiate sterile inflammation [75]. Targeting these receptors ameliorates experimental AP. Genetic deletion of TLR4 [76] or TLR9 [77] has been shown to reduce disease severity, as has pretreatment with the TLR9‐specific antagonist IRS‐954 [77]. The RAGE ligand S100A9 directly affects pancreatic leukocyte infiltration, which in turn has been shown to limit the degree of intrapancreatic trypsin activation and tissue damage in cerulein‐induced AP [78]. Neutralizing antibodies to HMGB1 or histone H3 have ameliorated experimental AP in two models [79]. While there are no human trials targeting these mechanisms as yet, release and concentration of nuclear DAMPs directly correlates with disease severity in human AP [80,81].

Another approach for targeting inflammatory pathways in AP has derived from a focus on the kynurenine pathway of tryptophan metabolism, pursued by the Mole group at the University of Edinburgh in collaboration with GSK [82,83]. Kynurenine is converted into 3‐hydroxykynurenine and other downstream toxic metabolites that damage organs by the enzyme kynurenine‐3‐monooxygenase (KMO), a pathway that is upregulated in AP and which primes the immune system for the systemic inflammatory response