Complex sentence: Once inside the vessel wall, LDL particles can become more prone to oxidation with resultant responses by the endothelial cells to attract monocyte white blood cells to leave the blood stream, penetrate into the arterial walls and transform into macrophages.
Split into simpler sentences: Once inside the vessel wall, LDL particles can become more prone to oxidation. Endothelial cells respond by attracting monocyte white blood cells, causing them to leave the blood stream, penetrate into the arterial walls and transform into macrophages.