Published online Mar 7, 2021. doi: 10.3748/wjg.v27.i9.794
Peer-review started: September 11, 2020
First decision: November 25, 2020
Revised: December 8, 2020
Accepted: January 15, 2021
Article in press: January 15, 2021
Published online: March 7, 2021
Acute pancreatitis (AP) and recurring AP are serious health care problems causing excruciating pain and potentially lethal outcomes due to sepsis. The validated caerulein- (CAE) induced mouse model of acute/recurring AP produces secondary persistent hypersensitivity and anxiety-like behavioral changes for study.
To determine efficacy of acetyl-L-carnitine (ALC) to reduce pain-related behaviors and brain microglial activation along the pain circuitry in CAE-pancreatitis.
Pancreatitis was induced with 6 hly intraperitoneal (i.p.) injections of CAE (50 µg/kg), 3 d a week for 6 wk in male C57BL/6J mice. Starting in week 4, mice received either vehicle or ALC until experiment’s end. Mechanical hyper-sensitivity was assessed with von Frey filaments. Heat hypersensitivity was determined with the hotplate test. Anxiety-like behavior was tested in week 6 using elevated plus maze and open field tests. Microglial activation in brain was quantified histologically by immunostaining for ionized calcium-binding adaptor molecule 1 (Iba1).
Mice with CAE-induced pancreatitis had significantly reduced mechanical withdrawal thresholds and heat response latencies, indicating ongoing pain. Treatment with ALC attenuated inflammation-induced hypersensitivity, but hypersensitivity due to abdominal wall injury caused by repeated intraperitoneal injections persisted. Animals with pancreatitis displayed spontaneous anxiety-like behavior in the elevated plus maze compared to controls. Treatment with ALC resulted in increased numbers of rearing activity events, but time spent in “safety” was not changed. After all the abdominal injections, pancreata were translucent if excised at experiment’s end and opaque if excised on the subsequent day, indicative of spontaneous healing. Post mortem histopathological analysis performed on pancreas sections stained with Sirius Red and Fast Green identified wide-spread fibrosis and acinar cell atrophy in sections from mice with CAE-induced pancreatitis that was not rescued by treatment with ALC. Microglial Iba1 immunostaining was significantly increased in hippocampus, thalamus (intralaminar nuclei), hypothalamus, and amygdala of mice with CAE-induced pancreatitis compared to naïve controls but unchanged in the primary somatosensory cortex compared to naïves.
CAE-induced pancreatitis caused increased pain-related behaviors, pancreatic fibrosis, and brain microglial changes. ALC alleviated CAE-induced mechanical and heat hypersensitivity but not abdominal wall injury-induced hypersensitivity caused by the repeated injections.
Core Tip: The caerulein- (CAE) induced pancreatitis model requiring 6 wk of repeated injections is a model of recurrent acute bouts of pancreatitis that causes pancreatic tissue damage and fibrosis. Control repeated i.p. saline injections alone caused abdominal wall injury and hindpaw secondary mechanical hypersensitivity. Treatment with acetyl-L-carnitine significantly attenuated CAE-induced hypersensitivity without alleviating pancreatic histological disruption. Mice with CAE-induced pancreatitis with secondary mechanical and heat hypersensitivity had elevated plus maze anxiety-like behavior. Post-mortem analysis revealed microglial morphology changes indicative of activation in amygdala, hippocampus, hypothalamus, and thalamus, but not in primary somatosensory cortex. These data suggest that activated microglia in these brain regions contribute to chronic hypersensitivity and anxiety-like behaviors in mice with CAE-induced pancreatitis.