Acute pancreatitis (AP) is a serious pancreatic disease, characterised by sudden onset, severe pain, and overall mortality rates of up to 10%. Unlike its acute form, which is potentially reversible, chronic pancreatitis (CP) worsens over time, leading to atrophy of the pancreatic parenchyma and fibrosis mediated by activated pancreatic stellate cells (PSCs). This often results in impaired digestion, diabetes, and increases the risk of pancreatic cancer. Currently, there is no effective and specific treatment for AP or CP.
The hallmark of pancreatitis is premature activation of digestive enzymes stored in pancreatic acinar cells (PACs). Active enzymes damage neighbouring PACs causing necrotic death and triggering the release and activation of other enzymes, thus promoting a self-perpetuating chain reaction of autodigestion and inflammation.
A potential strategy to break the vicious cycle of pancreatic necrosis and mitigate the disease is to direct PACs towards apoptotic death, which is not normally associated with the release of cellular content. Therefore the aim of this study was to test the therapeutic benefit of pharmacological modulation of cell death by Bcl-2 inhibitors in mouse models of acute and chronic pancreatitis.
All animal experiments on C57BL6J mice were approved by our Local Ethics Committee, approval numbers: 106/2020, 312/2021. In both models, the mice were divided into equal groups (n=6). AP was induced by seven hourly intraperitoneal injections of caerulein (50 µg/kg), while control mice were only given saline. In the CP model, mice received caerulein administrations twice a week for eight weeks. In addition, mice received one of the tested Bcl-2 inhibitors or an appropriate vehicle. The efficacy of therapy was evaluated by histological scoring (H/E or Sirius Red staining) and by comparing the extent of necrosis and apoptosis (IHF for cleaved caspase-3) in the pancreata of the experimental animals.
Our results show that 1 h treatment with caerulein induced 20.24±2.43% of necrosis and 9,67±2,35% of apoptosis in freshly isolated mouse PACs; and two Bcl-2 inhibitors reduced caerulein-elicited necrosis to 6.4±1.67% (p<0.001) or 7.44±3.84% (p<0.001), while increasing apoptosis to 15,06±2,67% (p<0.001) or 17,13±1,44% (p<0.001).
Bcl-2 inhibition significantly improved histological score in the AP mouse model. The overall histological severity score for the AP group was 14.25±2.04 points, and Bcl-2 inhibition reduced it to 6.67±2.14 points (p<0.001) and 10.25±2.25 points (p=0.005). The inhibitors not only decreased necrosis from 29.22±11.21% (of the tissue area) in the AP group to 1.75±2.06% (p<0.001) and 10.81±4.24% (p<0.001) in the treatment groups, but also increased apoptosis from 0.7±0.69 (apoptotic cells per mm2 of the tissue) in AP to 26.87±9.63 (p=0.002) and 58.16±41.83 (p=0.0027). In contrast, long-term therapy did not show efficacy in the CP model, and one of the inhibitors exacerbated caerulein-induced fibrosis in the organ.
Short-term Bcl-2 inhibition has the potential to shift acinar cell death from necrosis to apoptosis and thus could find its application as a therapeutic strategy in severe cases of AP. Since one of the Bcl-2 inhibitors is currently approved for the treatment of leukaemia, its use should be carefully considered in patients with concomitant CP.