Phenylalanine and indole effects on the pathogenicity of human lysozyme amorphous aggregates

Protein aggregation can affect the stability and function of proteins, and may lead to developing diseases, but reports on the in vivo effect of aggregates are scarce. In the current study, the effect of phenylalanine (Phe) and indole presence was first investigated on the structure and stability of human lysozyme (HLZ) and its aggregation under in vitro condition. Tm measurements, circular dichroism and spectrofluorimetric spectra, as well as and transmission electron microscopy (TEM) were performed in this stage. In the next step, pathogenicity of HLZ amorphous aggregates formed in presence or absence of the additives was investigated in vivo, by subcutaneous injection to adult male Wistar rats. Resulting inflamed tissues were studied by hematoxylin and eosin (HE), Congo red and Sudan black staining. Serum levels of liver enzymes (Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST)), specific inflammatory cytokines (Tumor Necrosis Factor Alpha (TNF-α) and Interleukin 6 (IL-6)) as well as glucose, cholesterol, and triglyceride levels were measured. Amorphous aggregates of HLZ caused inflammation and affected the number of fat cells, macrophages, cytokines, liver enzymes and glucose. Indole, that increases amorphous aggregates amount as shown with CD, fluorescence, and TEM experiments, leads into more severe inflammation. In presence of Phe, (which stabilizes HLZ structure) a markedly milder inflammatory state is observed in histological results and no increase could be detected in the inflammation-related parameters. In conclusion, amorphous aggregates of HLZ may be pathogenic in vivo, and presence of anti-aggregation compounds (such as Phe) can be effective in diminishing their deleterious manifestations.