A Two-Phase Model to Investigate LDL Toxicity in Early Atherosclerosis

Abstract: Atherosclerosis is a chronic inflammatory cardiovascular disease in which fatty plaque is built inside an artery wall. Early atherosclerotic plaque development is typically characterised by inflammatory tissues primarily consisting of foam cells and macrophages. We present a multiphase model that explores early plaque growth to emphasise the role of cytokines (in particular, Monocyte Chemoattractant Protein-1) and oxidised low-density lipoprotein (oxLDL) in monocyte recruitment and foam cell production, respectively. The plaque boundary is assumed to move at the same speed as the inflammatory tissues close to the periphery. This study discusses oxLDL-induced toxic environment towards macrophages and foam cells such that they start to die beyond a threshold limit of oxLDL concentration owing to excessive consumption. Our findings reveal that initially, the plaque evolves rapidly, and the growth rate subsequently reduces with time because of oxLDL-induced toxicity. In addition, it is observed that the saturation of inflammatory cell volume fraction becomes independent of oxLDL concentration beyond the threshold limit, referred to as the oxLDL toxicity limit. Our study manifests that a higher flux of oxLDL leads to plaque growth decay, whereas an increase in cytokines flux is favourable for enhanced plaque growth. Detailed analysis of the model presented in this article unfolds critical insights into the various biochemical and cellular mechanisms behind early plaque development.