Is Magnetic Resonance Imaging Detection of Kidney Iron Deposition Increased in Haptoglobin 2-2 Genotype Carriers with Type 1 Diabetes?

Abstract

Haptoglobin's (Hp) main role is to bind free hemoglobin (Hb), reducing its oxidative potential. The Hp-Hb complex formed is cleared from the circulation by macrophage receptor CD163. In diabetes, impaired Hp 2-2-Hb CD163 clearance and abnormal glomerular permeability allow the large Hp 2-2-Hb complex to cross the barrier, where its redox active iron leads to cellular toxicity. Although Hp 2-2 predicts renal function decline, whether renal iron deposition differs by Hp is unknown. We used renal quantitative T2∗ magnetic resonance imaging to estimate iron level in the cortex and medullar of type 1 diabetes (T1D) adults [15 Hp 1-1 and 15 Hp 2-2 carriers of similar age (53 years), duration (45 years), and gender]. Total kidney iron level was estimated as the sum of the cortex and medullar iron. Albuminuria was defined as urinary albumin to creatinine ratio >30 mg/g in two of three samples. Total kidney iron did not differ by gender or Hp but was higher in those with albuminuria (p = 0.05), an association confined to Hp 2-2 carriers (p = 0.04 vs. p = 0.51 in Hp 1-1). These data lead to the hypothesis that kidney iron deposition is increased among Hp 2-2 carriers with albuminuria in T1D.