Organic acidemias are a class of inborn metabolic disorders which disrupt amino acid metabolism and lead to abnormal accumulation of organic acids detectable in blood, urine and other biomaterials. While individually rare, collectively these disorders have a significant impact on children?s health. Chronic Kidney Disease (CKD) is a cardinal feature of several organic acidemias, and patients require routine monitoring of kidney function to manage their treatment. Methylmalonic Acidemia (MMA) is an organic acidemia with a frequency of 1/50,000 to 1/100,000 caused by mutations in methylmalonyl-CoA mutase (Mut) with a predictable evolution to CKD. In fact, CKD is developed at a median onset age of 6.5 y in MMA patients who are at high risk of developing renal insufficiency. Unfortunately, current methods for monitoring renal health which include measuring blood creatinine and blood nitrogen urea are not reliable for MMA patients. An alternative strategy is to administer MRI contrast agents to acquire functional information on the kidneys. This proposal involves administering well tolerated, organic compounds which create MRI contrast through Chemical Exchange Saturation Transfer (CEST). An attractive feature of this mechanism is that it enables production of pH maps which reflect the environment surrounding the agents and might be particularly useful for the kidneys, organs which control the acid-base balance of the body. We will design CEST pH sensors which can monitor progression towards CKD through changes in pH and perfusion, and will provide a reliable indicator of the overall health of the kidneys.
In Aim 1, we will synthesize a set of imidazole-4,5-dicarboxyamide probes to provide pH sensitive MRI contrast. The proton exchange rates and resulting CEST contrast will be quantified as a function of pH in buffered solutions to determine the performance of these in vitro. We will also optimize our pH and perfusion imaging protocol and characterize the pharmacokinetics using C57BL/6 control mice.
In Aim 2, we will evaluate the sensitivity of our best agents from Aim 1 for detecting the extent of renal disease in the C57BL/6 Mut-/-;TgINS-Alb-Mut mouse model of MMA and validate the pH measurements using ISUCA. C57BL/6 Mut-/-;TgINS-Alb-Mut mice manifest chronic tubulointerstitial nephritis and a decreased glomerular filtration rate (GFR) which is initiated by placing the mice on a high protein (HP) diet for 2 months.
In Aim 3, we will test our best sensor on six groups of mice with three groups treated with sodium citrate through diet supplementation and three more with CoQ10 + Vitamin E supplemented into their diets. The groups will also include three different timings for the high protein challenge which induces kidney injury. We expect our new agents and imaging protocols could provide an earlier detection of CKD without need of invasive kidney biopsy. This is particularly critical in conditions where standard monitoring methods are not feasible, such as MMA.

Public Health Relevance

Chronic Kidney Disease (CKD) is a cardinal feature of several organic acidemias, and patients require routine monitoring of kidney function to manage their treatment. MRI using contrast agents has the potential to revolutionize monitoring children with CKD. We will evaluate MR imaging agents and pulse sequences suitable for producing pH and perfusion maps using these agents and apply these for monitoring progression to CKD in a mouse model of Methylmalonic Acidemia.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Pathobiology of Kidney Disease Study Section (PBKD)
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Gossett, Daniel Robert
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Hugo W. Moser Research Institute Kennedy Krieger
United States
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