Investigation on Secondary Structure Perturbations of Proteins Embedded in Solid Lipid Matrices as a Novel Indicator of their Biological Activity upon In Vitro Release

Lipid bands of approx. 1740 cm-1 as spectral biomarkers and image of tissue oxidative stress

Studies with the use of FTIR and FTR methods to find spectroscopic biomarkers within the 1740 cm^-1 band of pathological tissues found that oxidative stress, including damage to epidermis and structural changes in pathological amnion and placenta tissue, are associated with the occurrence of products of lipid peroxidation and have impact on fluidity and transport function of membranes. In particular, the findings show that the absence of a marker lipid band of approx. 1743 cm^-1 and the occurrence of a minimum of 1764 cm^-1 (FTIR) and 1734 cm^-1 (FTR) testify to the integrity and absence of damage in the allogeneic dermis, while the presence the 1743 or 1747 cm^-1 bands indicates denaturation of the thermally or electrically burned epidermis. The absence of a marker lipid band of approx. 1736-1740 cm^-1 for a healthy placental and amniotic tissue and the presence of a band of 1740 cm^-1 indicate placental gestosis, while the presence of a band of 1742 cm^-1 indicates hypotrophy. The 1738 cm^-1 bands indicate amniotic macrosomia. Structural changes caused by tissue modification with antioxidants, which were observed on individual samples: the L-ascorbic acid (presence of a lipid band marker at a frequency of 1755 cm^-1), sodium ascorbate (disappearance of the marker band), orthosilicic acid (disappearance or decrease in the intensity of the marker band with a decrease in the concentration of the modifier), as well as graphene oxide (separation of the marker lipid band of 1755 cm^-1), inform us about the effect of modifiers on the tissue repair process. The studies also tracked spectral changes identified in serum. Withing the range of the lipid band and the amide I and II bands (α → β conversion), there are clear differences between normal and pathological serum lyophilisates and a sample analyzed from the solution.

Investigation on Secondary Structure Alterations of Protein Drugs as an Indicator of Their Biological Activity Upon Thermal Exposure

Protein drugs are important therapeutic agents however; they may degrade during formulation processing. The objective of this study was to investigate the correlation between secondary structure alterations and the retentions of biological activity of protein upon the application of thermal stress. Catalase, horseradish peroxidase and α- chymotrypsin were employed as model proteins. Each protein was heated in a solid and solution state at a temperature of 70 °C for 1 h. Attenuated total reflectance Fourier transform infrared spectroscopy, size-exclusion chromatography and biological activity assay were performed. Results showed that heat-exposure of protein solids at 70 °C caused minimum changes in secondary structure and biological activity was almost retained. However, thermal exposure of protein aqueous solution induced significant changes in the secondary structure indicated by area overlap values and caused considerable reduction in the biological activity. The changes in secondary structures were found to be in full alignment with the loss of biological activity for both protein solids as well as aqueous solutions. Catalase lost entire biological activity upon heating in the solution state. In conclusion, the findings of the present study indicate a direct correlation between protein secondary structure alterations and the retention of biological activity which can be taken into account during the development and delivery of protein drugs formulations.