Flow-cytometric Analysis of Reactive Oxygen Species in Blood Cells: A Potential Tool for Predicting Restenosis - Insights from a Cohort Study.

Introduction: In-stent restenosis (ISR) is a recurrence of a blockage in a section of the coronary artery that has previously been treated with a stent. Molecular/biochemical pathways underlying ISR are not fully understood, but inflammation and reactive oxygen species (ROS) induced oxidative stress play a significant role in the pathogenesis of restenosis. As blood cells are highly sensitive to oxidative stress and blood is readily accessible compared to other tissues, the current study flow cytometrically investigated intracellular ROS and cytokine profile of blood cells as possible markers of restenosis. Flow cytometry is commonly used for detecting ROS and analyzing oxidative stress but so far, it has not been utilized for prediction of ISR. So, the aim of the study was to explore the potential of flow cytometric assessment of ROS levels in the blood cells as predictor of ISR.

Methods: The study was carried out in a total of 60 patients who had previously undergone coronary artery stent implantation. They were categorized as Group I - Coronary stent implanted patients without restenosis (n=30) and Group II - Coronary stent implanted patients with restenosis (n=30). Sociodemographics, biochemical and angiographic characteristics were assessed. Intracellular ROS and cytokine estimation in blood cells was done by using flow cytometric analysis.

Results: Flow cytometric measurements demonstrated a 1.3-fold increase in ROS levels in red blood cells (RBCs) and 2-fold increase in ROS levels in leucocytes in group II as compared to group I. Mean serum concentrations of pro-inflammatory cytokines: tumor necrosis factor-α (33.54 ± 6.48 vs. 20.10 ± 5.61, p <0.001***), interferon-gamma (21.76 ± 4.46 vs. 20.10 ± 5.61, p <0.001***), interleukin 6 (152.56 ± 30.67 vs. 113.95 ± 23.38, p <0.001***) were found to be higher in restenotic patients as compared to the non-restenotic patients. Correlation analysis showed that intracellular ROS levels of RBCs exhibited a significant positive correlation with late lumen loss in restenotic (r=0.71, p <0.01) as well as non-restenotic patients (r=0.59, p <0.01). Similarly, intracellular ROS levels of WBCs exhibited a significant positive correlation with late lumen loss in restenotic (r=0.72, p <0.01) as well as non-restenotic patients (r=0.61, p <0.01).

Conclusion: This study highlights the role of increased levels of intracellular ROS in blood cells in the subsequent development of ISR, which can be detected flow cytometrically. The study suggests that intracellular ROS estimation in blood cells may serve as a potential marker for restenosis and their flow cytometric analysis may facilitate the prediction of ISR.