Allyl Isothiocianate Induces Ca2+ Signals and Nitric Oxide Release by Inducing Reactive Oxygen Species Production in the Human Cerebrovascular Endothelial Cell Line hCMEC/D3

Abstract

Nitric oxide (NO) represents a crucial mediator to regulate cerebral blood flow (CBF) in the human brain both under basal conditions and in response to somatosensory stimulation. An increase in intracellular Ca²⁺ concentrations ([Ca²⁺]_i) stimulates the endothelial NO synthase to produce NO in human cerebrovascular endothelial cells. Therefore, targeting the endothelial ion channel machinery could represent a promising strategy to rescue endothelial NO signalling in traumatic brain injury and neurodegenerative disorders. Allyl isothiocyanate (AITC), a major active constituent of cruciferous vegetables, was found to increase CBF in non-human preclinical models, but it is still unknown whether it stimulates NO release in human brain capillary endothelial cells. In the present investigation, we showed that AITC evoked a Ca²⁺-dependent NO release in the human cerebrovascular endothelial cell line, hCMEC/D3. The Ca²⁺ response to AITC was shaped by both intra- and extracellular Ca²⁺ sources, although it was insensitive to the pharmacological blockade of transient receptor potential ankyrin 1, which is regarded to be among the main molecular targets of AITC. In accord, AITC failed to induce transmembrane currents or to elicit membrane hyperpolarization, although NS309, a selective opener of the small- and intermediate-conductance Ca²⁺-activated K⁺ channels, induced a significant membrane hyperpolarization. The AITC-evoked Ca²⁺ signal was triggered by the production of cytosolic, but not mitochondrial, reactive oxygen species (ROS), and was supported by store-operated Ca²⁺ entry (SOCE). Conversely, the Ca²⁺ response to AITC did not require Ca²⁺ mobilization from the endoplasmic reticulum, lysosomes or mitochondria. However, pharmacological manipulation revealed that AITC-dependent ROS generation inhibited plasma membrane Ca²⁺-ATPase (PMCA) activity, thereby attenuating Ca²⁺ removal across the plasma membrane and resulting in a sustained increase in [Ca²⁺]_i. In accord, the AITC-evoked NO release was driven by ROS generation and required ROS-dependent inhibition of PMCA activity. These data suggest that AITC could be exploited to restore NO signalling and restore CBF in brain disorders that feature neurovascular dysfunction.

Keywords: Ca2+ signalling; allyl isothiocianate; hCMEC/D3; nitric oxide; plasma membrane Ca2+-ATPase; reactive oxygen species; store-operated Ca2+ entry.