Molecular mechanisms of crystal-related kidney inflammation and injury. Implications for cholesterol embolism, crystalline nephropathies and kidney stone disease.

Crystals are particles of endogenous inorganic or organic composition that can trigger kidney injury when deposited or formed inside the kidney. While decades of research have focused on the molecular mechanisms of solute supersaturation and crystal formation, the pathomechanisms of crystal-induced renal inflammation remain largely unknown. The recent discovery of the intracellular NLRP3 inflammasome as a pattern recognition platform that translates crystal uptake into innate immune activation via secretion of IL-1ß and IL-18 revised the pathogenesis of gout, silicosis, asbestosis, atherosclerosis and other crystal-related disorders. As a proof of concept, the NLRP3 inflammasome was now shown to trigger inflammation and acute kidney injury (AKI) in oxalate nephropathy. It seems likely that this and potentially other innate immunity mechanisms drive crystalline nephropathies (CNs) that are associated with crystals of calcium phosphate, uric acid, cysteine, adenine, certain drugs or contrast media, and potentially of myoglobin during rhabdomyolysis and of light chains in myeloma. Here, we discuss the proven and potential mechanisms of renal inflammation and kidney injury in crystal-related kidney disorders. In addition, we list topics for further research in that field. This perspective may also provide novel therapeutic options that can help to avoid progressive tissue remodeling and chronic kidney disease in patients with kidney stone disease or other CNs.

Atheroembolic renal disease with rapid progression and fatal outcome.

Atheroembolic renal disease is caused by foreign-body reaction to cholesterol crystals flushed from the atherosclerotic plaques into the small-vessel system of the kidneys. It is an underdiagnosed entity, mostly related to vascular procedures and/or anticoagulation, and prognosis is considered to be poor. Besides the benefit of aggressive medical prevention of further embolic events, use of steroid therapy has been associated with greater survival. Here we report a case of a patient with a multisystemic presentation of the disease days after performance of percutaneous coronary intervention and anticoagulation initiation due to an episode of myocardial infarction. Renal, cutaneous, ophthalmic, neurological, and possibly muscular and mesenteric involvement was diagnosed. Although medical treatment with corticosteroids and avoidance of further anticoagulation was applied, the patient rapidly progressed to end-stage renal disease requiring hemodialysis and died 6 months after diagnosis. This is a case of catastrophic progression of the disease resistant to therapeutic measures. Focus on diagnosis and more efficient preventive and therapeutic protocols are therefore needed.

Systemic cholesterol embolization syndrome associated with myeloperoxidase-anti-neutrophil cytoplasmic antibody.

A 75-year-old man was transferred to our department because of development of severe renal impairment after coronary artery bypass grafting. Hemodialysis was initiated for postsurgical oliguria and lung congestion. On transfer, he showed systemic purpura rashes and diffuse blue mottlings on his toes with marked eosinophilia and an elevated level of C-reactive protein. Cutaneous biopsy revealed cholesterol crystal embolism and leukocytoclastic vasculitis in dermal arterioles. Myeloperoxidase-anti-neutrophil cytoplasmic antibody titer was increased. Upon oral corticosteroid therapy following intravenous pulse steroid therapy, the purpura dramatically diminished, renal function improved, and hemodialysis was discontinued. Active treatment with corticosteroids may be effective for cholesterol embolization syndrome, particularly when clinical and laboratory manifestations mimic systemic vasculitis.