Synthesis of cholesterol esterase by monocyte-derived macrophages: a potential role in the biodegradation of poly(urethane)s

Many studies have described the role of monocyte-derived macrophages (MDM) in inflammation leading to atherosclerosis, a process in which alterations in the metabolism of cholesterol esters is well established. On the other hand, the mechanism of MDM activation in response to biomaterial surfaces is still not well understood. Several studies have described the different degrees of activation of monocytes on poly(urethane) surfaces by measuring the release of early markers of differentiation, such as cytokines. It has been possible to decrease MDM activation in contact with materials by modifying the material surface with antioxidants. Therefore, it has been proposed that it is the reactive oxygen species provided by MDM which are responsible for deleterious effects observed in material-derived inflammation. A recent study has shown that one of the markers of the degree of differentiation of MDM is the synthesis of cholesterol esterase (CE), an enzyme demonstrated as causing biodegradation of polyester(urethane)s and more recently polyether- and polycarbonate-poly(urethane)s as well. In this review article, markers used to assess MDM differentiation on material surfaces will be described and related to the activation of MDM. In particular, the CE accumulation in MDM which is associated with atherosclerosis will be related to its degradative potential during chronic inflammation. How this may impact on the biostability of implanted poly(urethane) medical devices is discussed.