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

Abstract

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.

Ferryl Hemoglobin and Heme Induce A1-Microglobulin in Hemorrhaged Atherosclerotic Lesions with Inhibitory Function against Hemoglobin and Lipid Oxidation

“…Therefore, we examined whether Hb or its oxidation products heme and FerrylHb induce A1M expression in the resident cells of atherosclerosis in vitro-those are human aortic endothelial cells (HAoECs), human aortic smooth muscle cells (HAoSMCs) and macrophages. Here we showed that heme induces A1M mRNA expression in cell cultures, supporting previous results in human primary renal proximal tubule epithelial cells [53] and keratinocytes [54]. Whereas A1M protein levels remained below the detection limit when cells were exposed to free heme, FerrylHb induced a significant A1M secretion in all cell types.…”

Binding of the human antioxidation protein α1-microglobulin (A1M) to heparin and heparan sulfate. Mapping of binding site, molecular and functional characterization, and co-localization in vivo and in vitro

“…A1M has previously been shown to be taken up intracellularly by several different human cell types in vitro , e.g., liver cells (HepG2), red blood cells, erythroid cells (K562), kidney cells (primary renal proximal tubule epithelial cells) and keratinocytes [ 25 , 53 , [53] , [58] , [59] , [60] ]. The mechanism behind the uptake, however, remains unknown.…”

177Lu-PSMA-617 Therapy in Mice, with or without the Antioxidant α1-Microglobulin (A1M), Including Kidney Damage Assessment Using 99mTc-MAG3 Imaging

“…It is mainly synthesized in the liver and has a plasma concentration of 20–50 mg/L with a half-life of 2–3 min and clearance via the kidneys [ 18 , 19 , 20 , 21 ]. A1M has been shown to protect against oxidative damage in cells, tissues and organs, including kidneys [ 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. Interestingly, an in vitro study showed reduction in cell death and oxidation markers by A1M in α-particle irradiated cells and bystander cells, emphasizing the role of oxidative stress in radiation damage [ 29 ].…”