Biochemical biomarkers at the site of inflammation and in peripheral blood

Abstract

Biochemical biomarkers are small molecular species, naturally varying or experimentally induced, which are measurable in body fluids and which may provide alternative or complementary tools to describe disease processes or to assess responses to pharmacological treatment. The focus of this thesis is inflammatory biomarkers, mediators, chemokines and cytokines that attract immune cells and that regulate the course of the inflammatory process at the site of inflammation. A major objective was to evaluate the behavior of these molecules in blood.

In the first study we used two established animal models, the Freund´s Complete Adjuvant (FCA) model and the Carrageenan model, to induce experimental inflammation in rats and could demonstrate a significant decrease of prostaglandin E2 (PGE2) in synovial fluid following treatment with two COX-inhibitors, naproxen and rofecoxib, despite the drugs having limited efficacy on overall joint swelling. L(+)-lactate, the end product of glycolysis, reflects cell activity and was therefore hypothesized to be a suitable novel indicator of experimental inflammation. We found that L(+)-lactate levels were unaffected by COX-inhibitors in this study, indicating that L(+)-lactate might be used as a biochemical biomarker for on-going inflammation in individuals being treated with COX-inhibitors. In the next study we therefore assessed levels of L(+)-lactate, as well as chemokines and cytokines, in joint fluids from human osteoarthritis patients and in an additional animal model, the monoiodo acetate (MIA) model, which primarily induces cartilage degradation, osteophyte formation and mild synovitis. MIA induced distinct inflammatory biomarkers in a biphasic manner, but in considerably lower amounts than FCA, suggesting that the underlying pathology in these two models is significantly different. As expected, L(+)-lactate was readily detectable in synovial fluid in the MIA model and in humans, correlating with the levels of cytokines and chemokines, and thereby indicating the presence of inflammatory cells in the joint cavity. We also observed two common findings between the MIA model and in humans, namely the presence of IL-6 in joint and serum and the lack of IL-1β and TNF in the same matrices. Nevertheless, we found it difficult to identify a single systemic biochemical biomarker that specifically reflects an ongoing local inflammatory process in osteoarthritis, and nor was it possible to identify a specific translational biomarker between the animal models and OA individuals.

In the third study, in rats subjected to spinal cord injury, the main findings were changes in inflammatory biomarkers in serum during the time of treatment with the drug imatinib, a tyrosine kinase inhibitor. Although serum levels of MCP-1 and MIP-3α were increased at day 1 following injury or sham injury, levels remained similar or lower throughout the study up to 7 days whereas MCP-1 and MIP-3α were further increased at 7 days following injury in the imatinib group. It is plausible that our findings will translate to humans and that the SCI individual could be its own control. Nerve Growth Factor (NGF) is released following tissue injury and therefore the aim was to determine whether NGF is released into the synovial fluid in the FCA model. In the last study we reported the successful development of an assay for the measurement of rat NGF in synovial fluid in rats exposed to FCA. We conclude that the usage of biochemical biomarkers has wide application, and may be used as a complementary tool to other readouts for the analysis of inflammatory conditions.