Heme–Hemopexin Complex Attenuates Neuronal Cell Death and Stroke Damage

Abstract

Hemoproteins undergo degradation during hypoxic/ischemic conditions, but the pro-oxidant free heme that is released cannot be recycled and must be degraded. The extracellular heme associates with its high-affinity binding protein, hemopexin (HPX). Hemopexin is shown here to be expressed by cortical neurons and it is present in mouse cerebellum, cortex, hippocampus, and striatum. Using the transient ischemia model (90-min middle cerebral artery occlusion followed by 96-h survival), we provide evidence that HPX is protective in the brain, as neurologic deficits and infarct volumes were significantly greater in HPX−/− than in wild-type mice. Addressing the potential protective HPX cellular pathway, we observed that exogenous free heme decreased cell survival in primary mouse cortical neuron cultures, whereas the heme bound to HPX was not toxic. Heme–HPX complexes induce HO1 and, consequently, protect primary neurons against the toxicity of both heme and prooxidant tert-butyl hydroperoxide; such protection was decreased in HO1−/− neuronal cultures. Taken together, these data show that HPX protects against heme-induced toxicity and oxidative stress and that HO1 is required. We propose that the heme–HPX system protects against stroke-related damage by maintaining a tight balance between free and bound heme. Thus, regulating extracellular free heme levels, such as with HPX, could be neuroprotective.

Endothelin-1-mediated vasoconstriction alters cerebral gene expression in iron homeostasis and eicosanoid metabolism

“…6A) (Wagner et al, 2003). Consistent with the literature (Li et al, 2009), we observed inductions of Hpx/hemopexin (2.4 Â at 4 h, 12 Â at 24 h) and Hmox1/HO-1 (3.2 Â at 4 h, 22 Â at 24 h). The gene for heme binding protein Hbp23, also known as peroxiredoxin 1, is induced 2.6 fold at 24 h (Fig.…”

“…As documented in models of stroke and SAH (Li et al, 2009;Wagner et al, 2003;Wang and Dore, 2007), we observed large increases in Hpx/hemopexin and Hmox1/heme oxygenase 1 expression. The uptake and storage of iron is also tightly controlled at the posttranscriptional level by the iron-responsive element binding protein 1 (Ireb1) and 2 (Ireb2) (Pantopoulos, 2004).…”

Kinetics and Specificity of Feline Leukemia Virus Subgroup C Receptor (FLVCR) Export Function and Its Dependence on Hemopexin

“…However, it is also expressed in human neurons (49) and several types of mouse brain cells (26,44,48), implying that this protein is synthesized locally in brain. Interestingly, hemopexin protects the brain of adult mice against ischemic stroke-related damage in murine models (26). In addition to hemopexin, FLVCR is also present in developing mouse neural tissues and human brain tissues and cell lines (1, 2), thus providing a mechanism to remove excess heme iron from this protected site and prevent damaging iron deposits.…”

“…This protein is free of contaminants, binds heme as characterized and quantitated following published procedures and extinction coefficients (25), and is not toxic for cells (26). (27), by preloading for 30 min at 37°C using 5 M ZnMP (Frontier Scientific, Logan, UT) dissolved in cell culture-grade Me 2 SO at a concentration of 4 mM and then diluted to 5 M in working buffer (25 mM HEPES (pH 7.4), 130 mM NaCl, 10 mM KCl, 1 mM CaCl 2 , and 1 mM MgSO 4 ) containing 2.5 M BSA (Sigma).…”

Protection against Heme Toxicity: Hemopexin Rules, OK?

“…4 This is not toxic for cells, even at supraphysiological concentrations, when incubated with primary neurons that are very sensitive to oxidative stress. 76 Heme, but not heme-HPX, produces ROS in human and mouse primary hepatocytes 14 and can induce apoptosis in both. 14 In spite of the data for intact rats with doubly labeled heme-HPX complexes, 43,65 and publications that demonstrate that heme-HPX induces HO1, 8,[77][78][79] the heme transport function of HPX has been disputed.…”