Monitoring mitochondrial disease related nephropathy and subclinical redox stress of the brain in the kd/kd murine model

Objectives The homozygous kidney recessive disease (kd) mutation in CBA mice causes a defect in CoQ9 synthesis resulting in nephropathy from chronic mitochondrial oxidative stress. Here we apply Tc99m-HMPAO, a tracer with redox sensitive properties, to the monitoring of renal disease and redox stress to the brain of kd/kd mice.

Methods The kidneys and brain of kd/kd and wild type (Wt) CBA mice were imaged with Tc99m-HMPAO SPECT imaging from the age of 9 to 21 weeks. 30 minutes after injection of 5 to 7 mCi of Tc99m-HMPAO the brain and then at 3 hours the kidneys, were imaged with the following parameters: 15 sec/step x 64 steps, 0.5 mm pinhole collimator, 2 cm ROR, 64x64 matrix with a single head small animal SPECT unit (A-SPECT, Gamma Medica). ROI histographic analyses were performed to calculate renal uptake (upper 33% counts / mCi) and brain uptake (upper 95% counts / soft tissue BKG, adjusted for ROI volume) of Tc99m-HMPAO.

Results Renal uptake in kd/kd mice decreased to 59% of Wt controls at week 14 at which time there was the first significant increase (*p= 0.0121) in urine output due to disease as shown in Table I. Renal uptake continued fall with worsening renal failure down to 15% of control by 18-21 weeks. While all mice demonstrated no neurologic signs of encephalopathy kd/kd mice showed falling brain uptake from 69% of control at 13 weeks to 34% at 21 weeks. At 21 weeks there was also significantly lower (*p = 0.0152) blood levels of reduced glutathione in kd/kd mice (787 ± 29 μmol/L) compared to control (1009 ± 90 μmol/L).

Conclusions Tc99m-HMPAO SPECT can monitor chronic oxidative stress and its progression in the kidneys and brain of kd/kd mice. Serial Tc99m-HMPAO SPECT imaging may prove to be useful in monitoring nephropathy induced by chronic oxidative stress in patients with genetic mitochondrial disease.

Research Support Supported in part by Edison Pharmaceuticals and the Stanford Mitochondrial Disease Institute.