Abstract
Inflammation is an integral part of the immune system’s defence against injury or infection. However, uncontrolled inflammation can contribute to the pathophysiology of many diseases, including sepsis. Despite advances in care, sepsis remains a global health problem and a leading cause of death in clinical and veterinary practice. Currently, the only treatment for sepsis is antibiotic therapy. However, while this treatment may eliminate the pre-sepsis infection, it does not reverse the systemic inflammation or its sequelae. Therefore, it is crucial to understand the mediators, pathways and cells governing the underlying mechanisms of sepsis in order to identify novel targets for therapeutic interventions.
Hydrogen sulfide (H2S) is an inflammatory mediator that has been implicated in the pathogenesis of sepsis. H2S is produced endogenously by the enzymatic activity of cystathionine γ-lyase (CSE), cystathionine β-synthetase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). Alternatively, H2S can also be produced exogenously by H2S-donor compounds. Both endogenous and exogenous H2S have been reported to elicit both pro-inflammatory and anti-inflammatory effects in numerous disease conditions. Therefore, this study investigated the role of H2S in the modulation of the inflammatory response in macrophages and liver sinusoidal endothelial cells (LSECs). Additionally, this study also explored the effect of H2S in feline sepsis to improve veterinary medicine.
Results showed that RAW264.7 macrophages produce H2S and proinflammatory cytokines (namely interleukin-1 beta (IL-1β), interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α)) in response to lipopolysaccharide (LPS) stimulation. However, H2S may not be predominantly exerting an inflammatory response via the src-family of tyrosine kinases (SFKs), a vital signalling network in cytokine production and the development of an inflammatory response.
SK-Hep1 cells, a cell line of liver endothelial origin, were used to study the functional changes of LSECs in inflammation. While we found that SK-Hep1 cells express the CSE gene which implies that they may produce hydrogen sulfide, we also found that these cells do not respond to LPS. Therefore, we were unable to use LPS to establish endotoxin-induced inflammation in SK-Hep1 cells. This implies that SK-Hep1 cells may not be a beneficial model to study the structural and functional changes that occur in LSECs during inflammation
Finally, as H2S has been suggested as a potential biomarker of sepsis in human clinical settings, its relevance in the veterinary setting was investigated, with the purpose of improving veterinary medicine. H2S was present in feline plasma. However, no difference was observed between circulatory levels of H2S in septic and non-septic cat patients. Therefore, H2S may not be a biomarker for inflammation in feline sepsis.
In conclusion, the results presented in this thesis demonstrate that H2S plays a key role in modulating inflammation in macrophages and provides information on why the SK-Hep1 cell line may not be a suitable model for the study of inflammation in LSECs in vitro. This thesis also shows the presence of H2S in feline plasma, although this may not have clinical significance in the inflammatory process of feline sepsis.