Measurements of blood urea nitrogen and serum creatinine.

Blood samples were collected from the heart at 11:00 AM on the second day of week 24 when mice were euthanized using isofluorane or intraperitoneal injection of ketamine with xylazine (100 mg/kg + 10 mg/kg). Blood was set aside for 45 min at room temperature for clotting and then centrifuged to separate the serum. Serum samples were stored at −80°C in a freezer until assays were conducted. Blood urea nitrogen (BUN) was measured using the QuantiChrom Urea Assay kit (DIUR-100, BioAssay System, Hayward, CA) following the protocol provided by the manufacturer. Serum creatinine levels were measured in the O’Brien Kidney Center at the University of Texas Southwestern Medical Center by the P/ACE MDQ Capillary Electrophoresis System (Beckman Coulter, Fullerton, CA).