Proteomic analysis of urinary exosomes from patients with lithium-induced nephrogenic diabetes insipidus

: Lithium (Li)-induced Nephrogenic Diabetes Insipidus (NDI) is a large healthcare problem, which affect around 40% of patients with bipolar disorder undergoing Li treatment. NDI is characterized by the inability in the kidney to concentrate urine in response to vasopressin in the kidney collecting duct (CD). In animals, Li causes a downregulation of aquaporin-2 and a cellular remodeling of the CD in rats resulting in a reduced fraction of principal cells relative to intercalated cells. Whether Li has similar effects in the human kidney is, however, not known. Urinary exosomes are extracellular nanovesicles derived from intracellular multivesicular bodies fused with the plasma membrane of epithelial cells lining the kidney tubular system and the urinary tract. The purpose of the first part of this study is to analyze whether the urinary rat proteome reflects the Li-induced changes in the kidney. This is followed by proteomic analyses of urinary exosomes isolated from Li-NDI patients. Rats were divided in three groups; controls (n=8), 2-week Li treatment (40 mmol/kg/food, n=8) and 4-week Li treatment (40 mmol/kg/food, n=8). Treatment with Li showed a significant increase in urine output after 2-weeks (P<0.01) and 4-weeks (P<0.05). Additionally, the rats developed severe polydipsia, with water intake significantly increased after 2-weeks Li treatment (P<0.001) and 4-weeks Li treatment (P<0.0001). Early morning urine samples from the placebo group in a previous published 12-week placebo-controlled pilot trial (Fotso Soh et al, 2021. A double-blind, randomized, placebo-controlled pilot trial of atorvastatin for nephrogenic diabetes insipidus in lithium users. Bipolar Disorders 23, 66-75) involving Li-NDI patients (n=9) were collected. The Li-NDI participants have been on a stable dose of Li (˃2 months) and determined to have a urinary osmolality <600 mOsm/kg at baseline. In addition, urine from random healthy controls (n=6) were collected. Urine samples from the rodent study and human study were subjected to ultracentrifugation for exosome isolation and will be further processed for mass spectrometry analysis (MS/MS).