Effect of acetyl-L-carnitine on hypersensitivity in acute recurrent caerulein-induced pancreatitis and microglial activation along the brain’s pain circuitry

BACKGROUND 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.AIM To determine efficacy of acetyl-L-carnitine(ALC)to reduce pain-related behaviors and brain microglial activation along the pain circuitry in CAE-pancreatitis.METHODS Pancreatitis was induced with 6 hly intraperitoneal(i.p.)injections of CAE(50μg/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 hypersensitivity 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).RESULTS 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.CONCLUSION 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.

Pharmacological attenuation of chronic alcoholic pancreatitis induced hypersensitivity in rats

AIM:To characterize an alcohol and high fat diet induced chronic pancreatitis rat model that mimics poor human dietary choices.METHODS:Experimental rats were fed a modified Lieber-De Carli alcohol(6%) and high-fat(65%) diet(AHF) for 10 wk while control animals received a regular rodent chow diet.Weekly behavioral tests determinedmechanical and heat sensitivity.In week 10 a fasting glucose tolerance test was performed,measuring blood glucose levels before and after a 2 g/kg bodyweight intraperitoneal(i.p.) injection of glucose.Post mortem histological analysis was performed by staining pancreas and liver tissue sections with hematoxylin and eosin.Pancreas sections were also stained with Sirius red and fast green to quantify collagen content.Insulinexpressing cells were identified immunohistochemically in separate sections.Tissue staining density was quantified using Image J software.After mechanical and heat sensitivity became stable(weeks 6-10) in the AHF-fed animals,three different drugs were tested for their efficacy in attenuating pancreatitis associated hypersensitivity:a Group Ⅱ metabotropic glutamate receptor specific agonist(2R,4R)-4-Aminopyrrolidine-2,4-dicarboxylate(APDC,3 mg/kg,ip; Tocris,Bristol,United Kingdom),nociceptin(20,60,200 nmol/kg,ip; Tocris),and morphine sulfate(3 mg/kg,μ-opioid receptor agonist; Baxter Healthcare,Deerfield,IL,United States).RESULTS:Histological analysis of pancreas and liver determined that unlike control rats,AHF fed animals had pancreatic fibrosis,acinar and beta cell atrophy,with steatosis in both organs.Fat vacuolization was significantly increased in AHF fed rats(6.4% ± 1.1% in controls vs 23.8% ± 4.2%,P < 0.05).Rats fed the AHF diet had reduced fasting glucose tolerance in week 10 when peak blood glucose levels reached significantly higher concentrations than controls(127.4 ± 9.2 mg/d L in controls vs 161.0 ± 8.6 mg/d L,P < 0.05).This concurred with a 3.5 fold higher incidence of single and small 2-10 cell insulin-positive cell clusters(P < 0.05).Insulin expressing islet of Langerhans cells appeared hypertrophied while islet number and area measurements were not different from controls.Weekly behavioral tests determined that mechanical and heat sensitivities were significantly increased by 4 wk on AHF diet compared to controls.Hypersensitivitywas attenuated with efficacy similar to morphine with single dose treatment of either metabotropic glutamate receptor 2/3 agonist APDC,or nociceptin,the endogenous ligand for opioid-receptor-like 1 receptor.CONCLUSION:The AHF diet induces a chronic alcoholic pancreatitis in rats with measurable features resembling clinical patients with chronic pancreatitis and type 3c diabetes mellitus.