Human Serum Albumin and its N-Terminal Tetrapeptide (DAHK) Block Oxidant-Induced Neuronal Death

Abstract

Background and Purpose-Studies using animal models of stroke have shown that human serum albumin (HSA) significantly ameliorates cerebral ischemic injury after both transient and permanent ischemia, even when administered after the onset of ischemia or reperfusion. The mechanism of this effect remains uncertain, and prior studies suggest both indirect hemodynamic and direct cytoprotective effects. HSA is a potent antioxidant, in part because of its strong copper-binding capacity. Here we examined the effect of HSA on oxidant-induced neuronal death in a cortical cell culture system. Methods-Murine cortical cultures were exposed to oxidative stress generated by hydrogen peroxide and by a mixture of copper plus ascorbic acid. We examined the ability of HSA and a tetrapeptide occupying its N-terminus (DAHK) to prevent neuronal death after these challenges. Results-H 2 O 2 and CuCl 2 /ascorbic acid were used at concentrations that, in the absence of HSA, killed Ͼ90% of the neurons. HSA provided complete protection at a concentration of 37.5 mol/L and 50% protection at 3.75 mol/L. The copper-binding tetrapeptide DAHK had nearly identical potency and efficacy. HSA and DAHK were also equally effective in preventing neuronal death induced by CuCl 2 /ascorbic acid. Conclusions-HSA has potent antioxidant properties, probably due to binding of copper and other transition metals. HSA extravasation into ischemic brain may provide neuroprotection by limiting metal-catalyzed oxidant stress. The tetrapeptide DAHK may be an effective, small-molecular-weight alternative to HSA as a therapeutic agent for stroke. Key Words: albumins Ⅲ antioxidants Ⅲ copper Ⅲ ischemia Ⅲ neurons A recent series of studies has explored the efficacy of human serum albumin (HSA) as a therapeutic agent in experimental models of stroke. 1-7 HSA was administered intravenously to treat permanent or transient cerebral ischemia and was more effective in transient ischemia. HSA significantly reduced infarct size, edema, and sodium accumulation and improved neurological outcome, even when administered up to 2 hours after onset of ischemia. While these studies demonstrated significant efficacy for HSA in the treatment of stroke, the mechanism for this robust neuroprotection remains undetermined. A number of possible mechanisms have been examined, including the effect of HSA on local cerebral perfusion, blood-brain barrier disruption, systemic fatty acid responses, and microvascular patency. While many of these mechanisms probably contribute, none appear robust enough to account for the large neuroprotective effect of HSA. [2][3][4][5]8,9 HSA is a unique molecule. It maintains colloidal osmotic pressure in the vasculature and has a number of important functional properties. 10 It strongly binds fatty acids, some drugs, and drug metabolites, and it has a number of cation and anion binding sites. 8,10 HSA is also a potent antioxidant, acting both as a free radical scavenger and as a chelator of transition metals and heme. 10 A metal binding site on HSA, the 4 -ami...

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