1Universitätsklinikum Carl Gustav Carus an der TU Dresden Klinik für Viszeral-, Thorax- und Gefäßchirurgie Dresden, Deutschland; 2Universitätsklinikum Carl Gustav Carus an der TU Dresden Institut für klinische Chemie und Laboratoriumsmedizin Dresden, Deutschland; 3Otto-von-Guericke-Universität Magdeburg Medizinische Fakultät, Universitätsklinikum Labor für Experimentelle Kardiologie Magdeburg, Deutschland
Introduction: The majority of abdominal aortic aneurysms (AAA) are covered by an intraluminal thrombus (ILT). Erythrocytes within this ILT release hemoglobin upon hemolysis. Free hemoglobin promotes the formation of reactive oxygen species via the Fenton reaction, thus driving the degeneration of the aortic wall. To reduce its toxicity, hemoglobin is bound to haptoglobin and internalized by the scavenger receptor CD163. CD163 is exclusively found on cells of the monocyte-macrophage lineage. Incorporated heme is degraded by the anti-oxidative enzyme heme oxygenase-1 (HO-1). Further, a soluble form of CD163 (sCD163) is secreted upon pathological conditions e.g. oxidative stress. Increased expression of HO-1 and CD163 is a characteristic feature of the athero-protective MHem macrophages. However, nothing is known yet about the regulation of CD163 and HO-1 in monocyte-derived macrophages from patients with AAA.
Materials and Methods: Primary monocytes were isolated from whole blood of AAA patients and aged-matched controls. To evaluate whether circulating monocytes are already differentially primed, monocytes were differentiated autologously. In another approach, monocytes were differentiated into MHem upon stimulation with hemin. After differentiation, CD163 and HMOX1 mRNA expression was analyzed and compared between AAA and controls. Moreover, cytokines were measured using the cytokine bead array and ELISA. Cell function of differentiated macrophages was evaluated by the measurement of ROS.
Results: Autologously differentiated macrophages showed a 2.5-fold higher CD163 mRNA expression (p=0.04) in AAA patients when compared to controls, whereas HMOX1 mRNA expression did not differ. Accordingly, sCD163 was elevated in cell culture supernatants in AAA patients (p=0.02). However, these differences were absent in monocytes. HMOX1 expression declined during autologous differentiation within the control group (p=0.02). In AAA patients, monocyte-derived macrophages showed a strong positive correlation between the expression of the MHem markers CD163 and HMOX1 (rP = 0.96, p = 0.0001). This correlation was not present within the control group (rP = 0.02, p = 0.96). HMOX1 expression was induced (both p ≤ 0.01) in both groups after differentiation with 50 µM hemin. However, in the control group, hemin-stimulation did not result in a positive correlation of the MHem markers as it was observed in the AAA group. Hemin-treated macrophages in the control group showed decreased IL-6 in the supernatant compared to vehicle (p=0.01), whereas no such difference was observed in AAA patients. Interestingly, hemin-differentiated macrophages from AAA patients were more susceptible towards ROS induction by menadione when compared to controls (p=0.06).
Conclusion: CD163 and HMOX1 expression are closely related in macrophages from patients with AAA. Patients with AAA tended to have an increased expression of MHem markers. Furthermore, differences in autologous and hemin-induced differentiation where observed in AAA when compared to control patients. Future analysis of the interaction of CD163 and HO‑1 could elucidate the therapeutic potential of this system in MHem macrophages.