Bilirubin Oxidation End Products (BOXes) Induce Neuronal Oxidative Stress Involving the Nrf2 Pathway.

Yinzhong Lu,Wenyi Zhang,Toshinori Hoshi,Bing Zhang,Guangming Zhang,Stefan H Heinemann,Shangwei Hou,Cinzia Signorini

doi:10.1155/2021/8869908

Abstract

Delayed ischemic neurological deficit (DIND) is a severe complication after subarachnoid hemorrhage (SAH). Previous studies have suggested that bilirubin oxidation end products (BOXes) are probably associated with the DIND after SAH, but there is a lack of direct evidence yet even on cellular levels. In the present study, we aim to explore the potential role of BOXes and the involved mechanisms in neuronal function. We synthesized high-purity (>97%) BOX A and BOX B isomers. The pharmacokinetics showed they are permeable to the blood-brain barrier. Exposure of a moderate concentration (10 or 30 μM) of BOX A or BOX B to isolated primary cortical neurons increased the production of reactive oxygen species. In the human neuroblastoma SH-SY5Y cells, BOX A and BOX B decreased the mitochondrial membrane potential and enhanced nuclear accumulation of the protein Nrf2 implicated in oxidative injury repair. In addition, both chemicals increased the mRNA and protein expression levels of multiple antioxidant response genes including Hmox1, Gsta3, Blvrb, Gclm, and Srxn1, indicating that the antioxidant response element (ARE) transcriptional cascade driven by Nrf2 is activated. In conclusion, we demonstrated that primary cortical neurons and neuroblastoma cells undergo an adaptive response against BOX A- and BOX B-mediated oxidative stress by activation of multiple antioxidant responses, in part through the Nrf2 pathway, which provides in-depth insights into the pathophysiological mechanism of DIND after SAH or other neurological dysfunctions related to cerebral hemorrhage.

Highlights

Subarachnoid hemorrhage (SAH) is a serious cerebrovascular complication with complex underlying mechanisms inflicting brain perfusion and function
To address the physiological and pathophysiological role of bilirubin oxidation end products (BOXes) in brain neurons, we synthetized BOX A and BOX B (Figure 1(a) and Supplemental Figure 1) with a predicted mass ~180 Da, which is consistent with the previous reports [14, 19]
These results suggested that BOX A or BOX B derived from the ruptured cerebral artery are permeable through the blood-brain barrier and have the potential to affect neuronal function

Summary

Introduction

Subarachnoid hemorrhage (SAH) is a serious cerebrovascular complication with complex underlying mechanisms inflicting brain perfusion and function. SAH causes early brain injury, which may be followed after 7 to 14 days by delayed ischemic neurological deficit (DIND). DIND is the leading cause of morbidity and mortality in the patients who survive the initial impact of SAH and have had their aneurysm effectively treated [2]. Accumulating evidence has shown that oxidative stress, acute and subsequent consisting immunological response, and other factors collectively cause the severe adverse effects of SAH [3, 4]. Erythrocyte lysis, a major initiator, is the release of heme and its subsequent degradation cascade, which collectively exert a strong effect on the affected neurons and their electrical excitability [5,6,7].

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