Hydroxyapatite nanoparticles (HAP) have been widely used in various fields because of their natural biological origin and functional properties. The emerging evidence on their toxicities has attracted research interest. HAP-induced vascular smooth muscle cell (VSMC) damage is a key step in vascular calcification (VC), particularly in patients with chronic kidney disease. However, the injury effects and mechanism of action of HAP on VSMCs have not been extensively investigated. This study comprehensively characterized commercially available HAP and investigated its adverse biological effects in cultured A7R5 cells. In vitro experiments revealed that internalized HAP was localized in lysosomes, followed by the release of Ca2+ owing to the low pH microenvironment. Upon Ca2+ homeostasis, Ca2+ enters the mitochondria, leading to the simultaneous generation of reactive oxygen species (ROS). ROS subsequently attack mitochondrial transmembrane potentials, promote mitochondrial ROS production, and oxidize mitochondrial DNA (Ox-mtDNA). Mitochondrial permeability-transition pores open, followed by the release of more Ox-mtDNA from the mitochondria into the cytosol due to the redox imbalance. This activates NLRP3/caspase-1/gasdermin D-dependent pyroptosis and finally excretes inflammatory factors to induce VC; an antioxidant could rescue this process. It has been suggested that HAP could induce an imbalance in intracellular Ca2+ homeostasis in A7R5 cells, followed by the promotion of mitochondrial dysfunction and cell pyroptosis, finally enhancing VC. To detect the in vivo toxicity of HAP, mice were treated with Cy7-labelled HAP NPs for 24 h. In vivo results also demonstrated that HAP accumulated in the kidneys, accompined with increased Ca concentration, upregulated oxidative stress-related factor and kidney damage. Overall, our research elucidates the mechanism of calcium homeostasis and redox imbalance, providing insights into the prevention of HAP-induced cell death.

Unusual clinical course Background:Lupus nephritis (LN) is the most common and serious complication of systemic lupus erythematosus (SLE). Minimal change disease (MCD) and primary membranous nephropathy (PMN) are the 2 most common causes of primary nephrotic syndrome. Our purpose in publishing this case report is to introduce an unusual clinical course and initial renal biopsy revealed MCD and then PMN in second renal biopsy. Subsequently, a third renal biopsy resulted in a final diagnosis of LN. To the best of our knowledge, this is the first such report. Case Report:The 31-year-old male patient was initially diagnosed with MCD after the first renal biopsy in 2004. He improved with initial management and had a complete remission for 9 years. After 9 years, the patient again presented with heavy proteinuria without systemic lupus erythematous finding and he was diagnosed with MN following the second renal biopsy. Seven years later, he again developed proteinuria alone with concurrent systemic symptoms of systemic lupus erythematosus, and a third biopsy was performed, leading to final diagnosis as LN. He was well managed with the methylprednisolone and cyclophosphamide (CTX) regimen, which improved renal function and spared the patient from continuous hemodialysis. Conclusions:In rare case, MCD may represent an early phase of lupus nephritis, which may subsequently develop into severe lupus nephritis.