The investigation of the changes of systemic inflammation on rat brain hippocampus at molecular level

Inflammation, which is necessary for the continuation of life, is the inflammatory reaction by which the immune system manifests to various endo and exo stimuli. If the stimulus exceeds a certain threshold while it is triggering inflammation, systemic inflammation occurs in the organism. It is known that as the systemic inflammation develops, many neurobiological phenomena controlled by the central nervous system take place. Until now, it has been well documented the relationship between inflammation and some diseases such as cancer and obesity. In recent years, inflammation has been related to neurodegenerative diseases, such as Alzheimer's and Parkinson's disease. Although the data regarding the relationship between the inflammation and neuronal and cognitive function loss are increasing, the molecular changes causing this relation are not known exactly. The aim of the study is to reveal the effects of systemic inflammation on the hippocampus, which is well known neurodegenerative diseases-related region of the brain, at molecular level. For this purpose, systemic inflammation was induced by the injection of lipopolysaccharide (LPS), a component of the outer cell wall of gram-negative bacteria, in Wistar albino rats and the hippocampus regions of the brains of these rats were analyzed by FTIR spectroscopy technique. The results showed that systemic inflammation increased the amounts of lipids, proteins and nucleic acids significantly and caused important changes in the structure and conformation of these molecules in hippocampus. When the changes in macromolecular ratios were examined, an increase in the unsaturated/saturated lipid ratio and carbonyl ester/lipid ratio were observed indicating lipid peroxidation presence. A decrease observed in the lipid/protein ratio showed a more dramatic increase in the amount of protein, a decrease observed in the nucleic acid/protein ratio showed an increase in translation rate. Moreover, an increase in the lipid chain lenght, a decrease in membrane order and an increase in membrane dynamics were detected after LPS administration. Furthermore, systemic inflammation altered the secondary structure of proteins by inducing a decrease in turn and an increase in random coil structures. In addition, the control and LPS-treated groups were successfully differentiated by hierarchical cluster analysis which was performed based on the spectral variations. The results revealed that systemic inflammation caused significant structural, conformational and functional changes in the hippocampus.