Abstract
Background:
According to our previous findings, the integrity of the blood-brain barrier (BBB) is affected by tobacco smoke (TSe) and electronic cigarette (ECe) exposure, and metformin (MF) can counter these detrimental effects. It is unknown, therefore, if MF protects against neuronal dysfunction after BBB damage caused by either TSe or ECe alone or combined exposure (TSe and ECe) in stroke cases. Additionally, MF's ability to enter the ischemic brain during ischemic stroke is unknown. The purpose of this effort is to address these questions.
Methods:
A well-established bEnd3/astrocyte co-culture in vitro BBB model was utilized to conduct permeability studies. Normoxia and hypoxia using oxygen-glucose deprivation (OGD) conditions were used to mimic the in vitro stroke conditions. Western blot (WB) and immunofluorescence analysis were performed for relevant molecular targets. Additionally, mitochondrial dysfunction was assessed using Seahorse Mito-stress analysis using primary neurons. Also, tMCAO was performed in C57BL/6 J mice to create ischemic injury. To quantify MF in the mouse brain, a highly sensitive LC-MS/MS technique was used.
Results:
According to our findings, a decrease in transendothelial electric resistance (TEER) values and increased permeability coefficient (PC) for sodium fluorescein were observed in the OGD/R condition alone or when combined with TSe, ECe, or mixed exposure compared to the control group. MF pretreatment, however, protected the BBB from losing barrier properties by increasing the TEER and decreasing PC values. Altered expression of tight junction (TJ) proteins was observed following TSe and ECe exposure paired with OGD compared to the control and OGD alone. However, MF was capable of offsetting the majority of these adverse effects by differentially upregulating ZO-1, occludin, and claudin-5 expression. Altered neuronal mitochondrial dynamics and decreased OCR were observed after OGD alone or in combination with TSe or ECe, however, MF pretreatment significantly increased several indices of mitochondrial functions, especially basal respiration, ATP production, and non-mitochondrial O2 consumption.
Conclusion:
Our findings demonstrate that MF pretreatment could be an effective countermeasure following OGD exposure in conjunction with TSe and ECe exposure, which is often linked to the deterioration of the BBB and possibly mitochondrial function.
Keywords:
BBB; Electronic cigarette; Mitochondrial dysfunction; Stroke; Tobacco smoke.