Intraarterial Infusion of Lidocaine is Superior to the Subcutaneous Injection of Low Molecular Weight Heparin for Improving the Course of Cerulein-Induced Acute Pancreatitis in Rats

Acute pancreatitis (AP) represents one of the most prevalent acute gastrointestinal disorders, with a globally increasing incidence. Most commonly, AP is caused by gallstones and alcohol abuse (Iannuzzi et al. 2022). Pancreatic duct obstruction and increased intraductal pressure trigger the transformation of inactive trypsinogen into trypsin, thus inducing the cascade of biochemical events promoting the course of AP. Damage to the acinar cells as a result of autodigestion processes causes an inflammatory reaction in the damaged pancreatic tissue; infiltration of neutrophils and macrophages; and the release of cytokines, interleukins, and tumor necrosis factor (TNF)-α that eventually result in microcirculatory disturbances in the pancreatic tissue (Antkowiak et al. 2022). The mechanism underlying the disorders of pancreatic micro-circulation and progressive damage to the pancreas consists of early vasoconstriction, with subsequent vascular permeability, and eventually activation of the coagulation system as the result of a local and systemic inflammatory response, which in turn leads to systemic microcirculation disorders and the development of multi-organ failure in the course of AP (Qiu et al. 2019; Tozlu et al. 2019). Therefore, microcirculatory disturbances are considered to be a crucial step in AP development, thus warranting therapeutic approaches to improve pancreatic microcirculation (Antkowiak et al. 2022). Lidocaine is an amide-type anesthetic that, apart from its widely known antiarrhythmic properties, has also been found to have vasoactive and anti-inflammatory properties. It has been found that lidocaine induces vasodilation at concentrations higher than 10–100 µg/mL (Satoh et al. 2015; Arsyad and Dobson 2016). Theoretically, lidocaine may induce vasodilation in pancreatic microcirculation, acting in the early stages of AP development, and thus relieving the severity of AP. The results of our previous study showed that regional, intraarterial infusion of 1% lidocaine solution (acting as a strong vasodilator through the concentration of 10,000 µg/mL) improves the course of cerulein-induced AP in rats (Antkowiak et al. 2020). Although the evidence on the actual efficacy of lidocaine in AP in the clinical settings remains unknown, further research aiming at vasodilation in pancreatic microcirculation needs to be encouraged.

Apart from the microcirculatory vasoconstriction, which is the early pathological mechanism responsible for further AP progression, subsequent vascular disturbances in AP consist of activation of the coagulation system and its consequences. Therefore, much effort has been put into studying the role of low molecular weight heparin (LMWH) for treating AP. LMWH is characterized by its anticoagulatory and anti-inflammatory effects, which are crucial in the later steps of AP development. LMWH reduces the release of cytokines and inflammatory mediators, inhibits leukocyte adhesion to vascular endothelial cells, reduces platelet activation, activates antithrombin III, and inhibits coagulation factors IIa and Xa, ultimately inhibiting the formation of fibrin clots. Moreover, it has been found that a complex of LMWH and antithrombin III reduces trypsin and chymotrypsin activity, thus reducing trypsinogen activation (Qiu et al. 2019; Tozlu et al. 2019). Some studies have shown that LMWH inhibits the development of AP triggered by the ischemia-reperfusion phenomenon (Cuthbertson and Christophi 2006; Podda et al. 2024). Considering complex mechanisms of microcirculatory disturbances, we hypothesized that combined, multi-target therapy with LMWH and lidocaine may positively impact the course of AP, enhancing vasoactive properties. Therefore, the present study aimed to determine the efficacy of LMWH and lidocaine combined with LMWH for improving the course of ceruleininduced experimental AP in rats.

Abnormalities in pancreatic microcirculation constitute the foundation of AP development and progression (Cuthbertson and Christophi 2006; Antkowiak et al. 2022). The pathogenesis of AP begins with activating trypsinogen in the acinar cells, promoting the inflammation process, and consequently, autolysis of the pancreas and peripancreatic adipose tissue (Antkowiak et al. 2022). As a result of the inflammatory process development, platelet-activating factor (PAF) bradykinin and thromboxane A2 are released. The PAF is a strong pro-inflammatory factor that activates monocytes and neutrophils, responsible for thrombus formation and endothelin release (Tozlu et al. 2019). The release of endothelin – serving as a strong vasoconstricting factor – as well as an increase in vascular permeability, leads to an increase in the blood viscosity and reduction of the pancreatic blood flow, increasing the risk of thrombus formation, resulting in the pancreatic tissue swelling and hypoxia. It has already been found that vasoconstriction appears in the early phase of AP development, followed by increased vessel permeability and thrombi formation (Cuthbertson and Christophi 2006). Considering the complexity of mechanisms involved in AP development and progression, vasoactive, anti-thrombotic, and anti-inflammatory approaches are believed to be needed in order to achieve satisfactory control of AP. It has been hypothesized that LMWH, harboring anti-inflammatory, anti-thrombotic, and as a result of those also vasoactive effects, may positively counteract the cascade of AP pathogenesis (Ke et al. 2014; Ning et al. 2015). LMWH activates antithrombin III, leading to the reduction of leukocyte–endothelium interaction and decreases the level of endothelin-1, TNF-α, and interleukin (IL)-6, leading to inhibition of the early inflammatory response.

Furthermore, heparin prevents microvascular constriction in the pancreas by inhibiting complement system activation and endothelin release from the endothelial cells (Dobosz et al. 2004; Hackert et al. 2004). Perfusion analysis showed that administering heparin significantly improved microcirculation in the pancreas and other organs, which may significantly impact the treatment and prevention of local and systemic complications of AP (Dobosz et al. 2004). Considering the multiplicitous mechanism of LMWH action, we aimed to evaluate the impact of LMWH applied subcutaneously on the pancreatic enzyme levels. Our study showed that LMWH did not significantly reduce the severity of AP compared with untreated controls in terms of pancreatic enzyme levels and pathological changes in the pancreatic tissue.

Given the importance of vasoconstriction of the pancreatic vasculature in the development of AP, we hypothesized that early pharmacologically induced vasodilation may improve the course of AP. Lidocaine, an amide-type anesthetic agent, has been found to have concentration-dependent vasoactive properties, with concentrations of 1 µg/mL inducing vessel contraction, while concentrations of 10–100 µg/mL show vasodilatory effects (Satoh et al. 2015). In our previous experimental study on cerulein-induced AP, we demonstrated that 1% lidocaine solution (lidocaine concentration of 10,000 µg/mL), acting as a strong vasodilating substance, significantly improved the course of AP, reducing the levels of pancreatic enzymes and slightly improving the severity of pathological changes in the pancreatic tissue, as compared with untreated controls. Although that study did not directly evaluate the influence of lidocaine on the microcirculation (through imaging tools like Doppler flowmetry), we hypothesized that given the vasoactive effects of lidocaine, its therapeutic mechanism could have resulted from pancreatic microcirculation dilation.

In the present study, we evaluated the efficacy of subcutaneously injected LMWH combined with intraarterial infusion of 1% lidocaine solution in treating cerulein-induced AP in rats. Consequently, in rats receiving combined treatment, we observed significantly lower amylase values compared with both untreated controls and rats receiving only subcutaneous injection of LMWH without the intraarterial preinfusion of 1% lidocaine solution. Conversely, rats receiving combined treatment with LMWH and lidocaine showed significantly lower lipase levels compared with untreated controls only in the first post-treatment evaluation point (M2). However, rats receiving combined treatment presented significantly lower lipase levels than the heparin group in both the first (M2) and second (M3) post-treatment evaluation points. Lipase is more sensitive than amylase in diagnosing AP (Ismail and Bhayana 2017). It is worth noting that the protocol of our study involved the induction of AP using a total dose of 80 µg/kg cerulein, which led to the development of edematous AP instead of severe AP (Ding et al. 2003; Buyukberber et al. 2009). However, the presented study constituted the continuation of our effort to determine the role of lidocaine in experimentally induced AP (Antkowiak et al. 2020). When designing these studies, we hypothesized that if severe AP was induced, the therapeutical role of lidocaine (which has never been studied in AP before – therefore, its actual impact on AP has been unknown) could have been challenging to observe. Hence, initially, edematous AP was induced in order to detect even subtle changes in pancreatic enzyme levels as a result of lidocaine infusion. However, given that both our studies reflected the efficacy of lidocaine in relieving the course of mild edematous AP, it is our future aim to design an experimental study on severe AP to define further the actual therapeutical role of lidocaine in a more advanced stage of AP. Based on the foregoing results, considering the tendency of pancreatic enzymes to naturally decrease, as observed in the untreated controls, we conclude that the addition of lidocaine may influence the course of AP while lacking the impact on the final AP outcomes. Moreover, the dynamics of pancreatic enzymes stay in line with the histopathological findings, which did not differ significantly between groups. Theoretically, if the severe AP was induced instead of the mild edematous one, the histopathological findings could have shown the differences caused by one treatment, supporting its efficacy.

Lidocaine and LMWH act at different stages of AP. Since vasoconstriction represents an early and crucial event in AP development, followed by vascular permeability and thrombi formation, lidocaine is believed to prevent further progression of AP. On the contrary, LMWH is thought to act at the later stages of AP, when irreversible changes induced by vasoconstriction have occurred. These discrepancies may stand for lack of LMWH efficacy compared with lidocaine. Consequently, it may be hypothesized that the superior efficacy of additional lidocaine infusion to the LMWH compared with LMWH alone stands for the significance of vasoactive (vasodilatory) management in the early phases of AP.

Subcutaneous injection of LMWH does not impact the natural course of AP in an experimental setting. However, the addition of intraarterially administered 1% lidocaine solution significantly reduces the severity of AP. Through the comparison of two drugs acting at different stages of AP development, both targeting pathological cascade occurring in the pancreatic microcirculation, it can be stated that lidocaine-triggered vasodilation appeared as a crucial step in relieving the course of AP.