α1-Microglobulin (A1M) Protects Human Proximal Tubule Epithelial Cells from Heme-Induced Damage In Vitro.

Oxidative stress is associated with many renal disorders, both acute and chronic, and has also been described to contribute to the disease progression. Therefore, oxidative stress is a potential therapeutic target. The human antioxidant α1-microglobulin (A1M) is a plasma and tissue protein with heme-binding, radical-scavenging and reductase activities. A1M can be internalized by cells, localized to the mitochondria and protect mitochondrial function. Due to its small size, A1M is filtered from the blood into the glomeruli, and taken up by the renal tubular epithelial cells. A1M has previously been described to reduce renal damage in animal models of preeclampsia, radiotherapy and rhabdomyolysis, and is proposed as a pharmacological agent for the treatment of kidney damage. In this paper, we examined the in vitro protective effects of recombinant human A1M (rA1M) in human proximal tubule epithelial cells. Moreover, rA1M was found to protect against heme-induced cell-death both in primary cells (RPTEC) and in a cell-line (HK-2). Expression of stress-related genes was upregulated in both cell cultures in response to heme exposure, as measured by qPCR and confirmed with in situ hybridization in HK-2 cells, whereas co-treatment with rA1M counteracted the upregulation. Mitochondrial respiration, analyzed with the Seahorse extracellular flux analyzer, was compromised following exposure to heme, but preserved by co-treatment with rA1M. Finally, heme addition to RPTE cells induced an upregulation of the endogenous cellular expression of A1M, via activation of the nuclear factor erythroid 2-related factor 2 (Nrf2)-pathway. Overall, data suggest that A1M/rA1M protects against stress-induced damage to tubule epithelial cells that, at least partly, can be attributed to maintaining mitochondrial function.

Increased levels of hemoglobin and alpha1-microglobulin in Huntington's disease.

Hemoglobin released from damaged erythrocytes is a major pro-oxidant, generator of free radicals and inflammatory mediator. Huntington's disease is an inherited neurodegenerative disorder characterized by both neurological and systemic abnormalities, in which oxidative stress has been suggested as a possible pathogenic mechanism. In the present work we have investigated levels of hemoglobin and markers of oxidative damage, including the heme- and radical-scavenger alpha1-microglobulin, in plasma and urine samples from two separate sample cohorts, including controls, premanifest gene carriers and subjects at different stages of Huntington's disease. The results show statistically significant increased levels of hemoglobin and alpha1-microglobulin in Huntington's disease urine samples. Interestingly, urine hemoglobin levels correlate with clinical severity. The results suggest that hemolysis may be linked to the pathogenesis of Huntington's disease and that assay of hemoglobin and alpha1-microglobulin may provide biomarkers that are linked to biologically relevant processes.