Structural transition of kidney cystatin induced by silicon dioxide nanoparticles: An implication for renal diseases

Nanotechnology is one of the fastest growing fields of science owing to use of nanomaterials in industries and medicine across the globe. Currently silicon dioxide nanoparticles (SiO₂ NPs) are one of the most popular nanomaterials owing to their inert toxicity profile and hence exposure to SiO₂ nanoparticles is on the increase. Cystatins are thiol proteinase inhibitors (TPIs) ubiquitously distributed in plants and animals and they are now at the heed of a number of normal and pathological conditions and shouldn't be regarded solely as TPIs. Up till now many studies have targeted the potential toxicity of NPs on pulmonary target; although little focus is given to kidney which is a secondary target organ. The objective of this work is to study the structural changes in buffalo kidney cystatin (BKC) induced by SiO₂ NPs. UV and Fluorescence spectroscopy shows BKC transformation from native to non-native form evident by decreased absorbance and increased fluorescence. FTIR and CD spectroscopy further confirmed secondary structure disruption of BKC. Isothermal titration calorimetry (ITC) and microscopy were resorted to visualize interaction between SiO₂ NPs and BKC. Comet assay and MTT assay were utilized to perceive the toxicity of SiO₂ NPs incubated BKC; decreased cell viability clearly suggesting toxicity of SiO₂ NPs incubated BKC. Our work suggests that SiO₂ NPs have a deteriorating effect on BKC thereby causing a decrease in its ability to inhibit papain and hence less functionality. This study also shows that BKC transforms to a toxic non-native form in presence of SiO₂ NPs.