Piezo channels in the intestinal tract

The intestine is the largest mechanosensitive organ in the human body whose epithelial cells, smooth muscle cells, neurons and enteroendocrine cells must sense and respond to various mechanical stimuli such as motility, distension, stretch and shear to regulate physiological processes including digestion, absorption, secretion, motility and immunity. Piezo channels are a newly discovered class of mechanosensitive ion channels consisting of two subtypes, Piezo1 and Piezo2. Piezo channels are widely expressed in the intestine and are involved in physiological and pathological processes. The present review summarizes the current research progress on the expression, function and regulation of Piezo channels in the intestine, with the aim of providing a reference for the future development of therapeutic strategies targeting Piezo channels.

The roles of calcium and ATP in the physiology and pathology of the exocrine pancreas

This review deals with the roles of calcium ions and ATP in the control of the normal functions of the different cell types in the exocrine pancreas as well as the roles of these molecules in the pathophysiology of acute pancreatitis. Repetitive rises in the local cytosolic calcium ion concentration in the apical part of the acinar cells not only activate exocytosis but also, via an increase in the intramitochondrial calcium ion concentration, stimulate the ATP formation that is needed to fuel the energy-requiring secretion process. However, intracellular calcium overload, resulting in a global sustained elevation of the cytosolic calcium ion concentration, has the opposite effect of decreasing mitochondrial ATP production, and this initiates processes that lead to necrosis. In the last few years it has become possible to image calcium signaling events simultaneously in acinar, stellate, and immune cells in intact lobules of the exocrine pancreas. This has disclosed processes by which these cells interact with each other, particularly in relation to the initiation and development of acute pancreatitis. By unraveling the molecular mechanisms underlying this disease, several promising therapeutic intervention sites have been identified. This provides hope that we may soon be able to effectively treat this often fatal disease.

TRPV4 channel opening mediates pressure-induced pancreatitis initiated by Piezo1 activation

Elevated pressure in the pancreatic gland is the central cause of pancreatitis following abdominal trauma, surgery, endoscopic retrograde cholangiopancreatography, and gallstones. In the pancreas, excessive intracellular calcium causes mitochondrial dysfunction, premature zymogen activation, and necrosis, ultimately leading to pancreatitis. Although stimulation of the mechanically activated, calcium-permeable ion channel Piezo1 in the pancreatic acinar cell is the initial step in pressure-induced pancreatitis, activation of Piezo1 produces only transient elevation in intracellular calcium that is insufficient to cause pancreatitis. Therefore, how pressure produces a prolonged calcium elevation necessary to induce pancreatitis is unknown. We demonstrate that Piezo1 activation in pancreatic acinar cells caused a prolonged elevation in intracellular calcium levels, mitochondrial depolarization, intracellular trypsin activation, and cell death. Notably, these effects were dependent on the degree and duration of force applied to the cell. Low or transient force was insufficient to activate these pathological changes, whereas higher and prolonged application of force triggered sustained elevation in intracellular calcium, leading to enzyme activation and cell death. All of these pathological events were rescued in acinar cells treated with a Piezo1 antagonist and in acinar cells from mice with genetic deletion of Piezo1. We discovered that Piezo1 stimulation triggered transient receptor potential vanilloid subfamily 4 (TRPV4) channel opening, which was responsible for the sustained elevation in intracellular calcium that caused intracellular organelle dysfunction. Moreover, TRPV4 gene-KO mice were protected from Piezo1 agonist- and pressure-induced pancreatitis. These studies unveil a calcium signaling pathway in which a Piezo1-induced TRPV4 channel opening causes pancreatitis.

Duodeno-pancreatic and extrahepatic biliary tree trauma: WSES-AAST guidelines

Duodeno-pancreatic and extrahepatic biliary tree injuries are rare in both adult and pediatric trauma patients, and due to their anatomical location, associated injuries are very common. Mortality is primarily related to associated injuries, but morbidity remains high even in isolated injuries. Optimal management of duodeno-bilio-pancreatic injuries is dictated primarily by hemodynamic stability, clinical presentation, and grade of injury. Endoscopic and percutaneous interventions have increased the ability to non-operatively manage these injuries. Late diagnosis and treatment are both associated to increased morbidity and mortality. Sequelae of late presentations of pancreatic injury and complications of severe pancreatic trauma are also increasingly addressed endoscopically and with interventional radiology procedures. However, for moderate and severe extrahepatic biliary and severe duodeno-pancreatic injuries, immediate operative intervention is preferred as associated injuries are frequent and commonly present with hemodynamic instability or peritonitis. The aim of this paper is to present the World Society of Emergency Surgery (WSES) and American Association for the Surgery of Trauma (AAST) duodenal, pancreatic, and extrahepatic biliary tree trauma management guidelines.

An AAST-MITC analysis of pancreatic trauma: Staple or sew? Resect or drain?

INTRODUCTION

Pancreatic trauma results in high morbidity and mortality, in part caused by the delay in diagnosis and subsequent organ dysfunction. Optimal operative management strategies remain unclear. We therefore sought to determine CT accuracy in diagnosing pancreatic injury and the morbidity and mortality associated with varying operative strategies.

METHODS

We created a multicenter, pancreatic trauma registry from 18 Level 1 and 2 trauma centers. Adult, blunt or penetrating injured patients from 2005 to 2012 were analyzed. Sensitivity and specificity of CT scan identification of main pancreatic duct injury was calculated against operative findings. Independent predictors for mortality, adult respiratory distress syndrome (ARDS), and pancreatic fistula and/or pseudocyst were identified through multivariate regression analysis. The association between outcomes and operative management was measured.

RESULTS

We identified 704 pancreatic injury patients of whom 584 (83%) underwent a pancreas-related procedure. CT grade modestly correlated with OR grade (r 0.39) missing 10 ductal injuries (9 grade III, 1 grade IV) providing 78.7% sensitivity and 61.6% specificity. Independent predictors of mortality were age, Injury Severity Score (ISS), lactate, and number of packed red blood cells transfused. Independent predictors of ARDS were ISS, Glasgow Coma Scale score, and pancreatic fistula (OR 5.2, 2.6-10.1). Among grade III injuries (n = 158, 22.4%), the risk of pancreatic fistula/pseudocyst was reduced when the end of the pancreas was stapled (OR 0.21, 95% CI 0.05-0.9) compared with sewn and was not affected by duct stitch placement. Drainage alone in grades IV (n = 25) and V (n = 24) injuries carried increased risk of pancreatic fistula/pseudocyst (OR 8.3, 95% CI 2.2-32.9).

CONCLUSION

CT is insufficiently sensitive to reliably identify pancreatic duct injury. Patients with grade III injuries should have their resection site stapled instead of sewn and a duct stitch is unnecessary. Further study is needed to determine if drainage alone should be employed in grades IV and V injuries.

LEVEL OF EVIDENCE

Epidemiologic/Diagnostic study, level III.

Piezo1 is a mechanically activated ion channel and mediates pressure induced pancreatitis

Merely touching the pancreas can lead to premature zymogen activation and pancreatitis but the mechanism is not completely understood. Here we demonstrate that pancreatic acinar cells express the mechanoreceptor Piezo1 and application of pressure within the gland produces pancreatitis. To determine if this effect is through Piezo1 activation, we induce pancreatitis by intrapancreatic duct instillation of the Piezo1 agonist Yoda1. Pancreatitis induced by pressure within the gland is prevented by a Piezo1 antagonist. In pancreatic acinar cells, Yoda1 stimulates calcium influx and induces calcium-dependent pancreatic injury. Finally, selective acinar cell-specific genetic deletion of Piezo1 protects mice against pressure-induced pancreatitis. Thus, activation of Piezo1 in pancreatic acinar cells is a mechanism for pancreatitis and may explain why pancreatitis develops following pressure on the gland as in abdominal trauma, pancreatic duct obstruction, pancreatography, or pancreatic surgery. Piezo1 blockade may prevent pancreatitis when manipulation of the gland is anticipated.

Manipulation of the pancreas during surgery can induce acute pancreatitis due to zymogen activation. Here the authors show that the mechanoreceptor Piezo1 is activated by pressure and its activation leads to calcium dependent pancreatic injury whereas its inhibition is protective against pancreatitis.

Surgical Management of Solid Organ Injuries

Surgery used to be the treatment of choice in patients with solid organ injuries. This has changed over the past 2 decades secondary to advances in noninvasive diagnostic techniques, increased availability of less invasive procedures, and a better understanding of the natural history of solid organ injuries. Now, nonoperative management (NOM) has become the initial management strategy used for most solid organ injuries. Even though NOM has become the standard of care in patients with solid organ injuries in most trauma centers, surgeons should not hesitate to operate on a patient to control life-threatening hemorrhage.

Outcomes after Distal Pancreatectomy for Trauma in the Modern Era

Multiple stump closure techniques after distal pancreatectomy (DP) for trauma have been described, and all are associated with a significant fistula rate. With increasing emphasis on abbreviated laparotomy, stapled pancreatectomy has become more common. This study describes the outcomes of patients with different closure techniques of the pancreatic stump after resection following pancreatic trauma. Retrospective analysis of 50 trauma patients, who sustained grade III pancreatic injuries with subsequent DP and stapled stump closure, were conducted from 1995 to 2011. Demographic, operative, and outcome data were analyzed to characterize patients, and to directly compare closure techniques. After 12 patients were excluded because of early death (<72 hours), final analyses included 38 patients: 19 (50%) had stapled closure alone and 19 (50%) had stapling with adjunct, including additional closure with sutures, fibrin sealants, or a combination of sutures with fibrin sealants/omental coverage. Twenty-four patients (63%) had postoperative complications, most commonly pancreatic fistula (n = 11, 29%). There were no significant differences with regard to pancreatic fistula or other abdominal complications between closure groups, or were any factors associated with increased likelihood of complications. DP remains a morbid operation after trauma regardless of closure technique. Stapled closure alone is perhaps the method of choice in this setting due to the time constraints directly related to outcomes.

Morbidity and mortality after distal pancreatectomy for trauma: a critical appraisal of 107 consecutive patients undergoing resection at a Level 1 Trauma Centre

BACKGROUND

This study evaluated 30-day morbidity and mortality and assessed pancreas-specific complications in patients with major pancreatic injuries who underwent a distal pancreatectomy.

STUDY DESIGN

Records of 107 consecutive patients who underwent a distal pancreatectomy at a Level 1 Trauma Centre in Cape Town between January 1982 and December 2011 were reviewed. Primary endpoints were postoperative morbidity and death. Complications were graded according to the Clavien-Dindo severity classification and the International Study Group of Pancreatic Surgery (ISGPS) definitions.

RESULTS

A total of 107 patients [94 men, median age 26, median RTS 7.8, 69 penetrating injuries (63 gunshot wounds, 6 stabs wounds), 38 blunt injuries] underwent distal pancreatectomy. Overall mortality was 12%, 16% for gunshot injuries, 8% for blunt trauma and 0% in patients who had stab wounds. Eighty patients had a post-operative complication. A pancreatic leak (n=26) was the most common pancreatic related complication. Median postoperative stay in 28 patients with no or grade I complications was 9 days; in 11 patients with grade II complications was 18 days; in 14 grade IIIa, 31 days; in 19 grade IIIb, 38 days; in 8 grade IVa, 33 days in 14 grade IVb, and in 13 grade V the duration of postoperative stay was 14±39.4 days.

CONCLUSIONS

Overall mortality for distal pancreatectomy was 12%. Pancreatic leak was a common cause of morbidity. Length of hospitalisation increased with increasing Clavien-Dindo severity grading. There was a significant difference in the duration of hospitalisation in patients with no or grade I complications compared to those with grade II-IV injuries (p<0.05).

Evaluation of blunt pancreatic injury with contrast-enhanced ultrasonography in comparison with contrast-enhanced computed tomography

The aim of the present study was to evaluate acute blunt pancreatic injury using contrast-enhanced ultrasonography (CEUS) in comparison with contrast-enhanced computed tomography (CECT). Superficial and deep lesions were established by blunt pancreatic injury in 40 Chinese Guangxi Bama miniature pigs. Conventional ultrasound (US), CEUS and CECT were performed to detect traumatic lesions in the pancreas. A total of 40 lesions were established, including 20 deep lesions and 20 superficial lesions. US identified 21 of the 40 lesions, including 7 of the 20 superficial and 14 of the 20 deep lesions. CEUS identified 34 of the 40 lesions, including 14 of the 20 superficial and 20 of the 20 deep lesions. CECT identified 33 of the 40 lesions, including 13 of the 20 superficial and 20 of the 20 deep lesions. The detection rate of acute blunt pancreatic injury using CEUS was significantly higher compared with that using US (85 vs. 52.5%, P<0.05), however there was no significant difference in the detection rate of pancreatic lesions between CEUS and CECT (85 vs. 82.5%, P>0.05). CEUS improves the diagnostic levels of conventional US and is comparable with CECT scans in the diagnosis of blunt pancreatic injury.