Introduction: Clodronate liposomes obliterate phagocytic cells such as monocytes and macrophages, and subcutaneous carrageenan injection can provoke acute macrophage-mediated inflammatory reaction. Peripheral blood monocytes were recruited in response to abdominal subcutaneous carrageenan injection in mice, and the process of differentiation from macrophages to foam cells were observed. The objective of our study was to find out the effect of intravenous clodronate liposomes on the macrophage-mediated inflammation provoked by subcutaneous carrageenan injection in mice. Methods: C57/BL6 mice (n=48) were divided into 2 groups (clodronate liposome group, n=24 vs. control liposome group, n=24). With the initiation of clodronate liposome injections, peripheral blood monocytes were counted with FACS analysis after 24 hours, 1 week, and 2 weeks. Either clodronate liposome (0.1 ml/10g) or control liposome (0.1 ml/10g) was injected via tail vein and was followed by subsequent injections every 5 days. Two days after initial clodronate liposome or control liposome injection, 1% carrageenan in saline (0.1ml/10g) was injected into abdominal subcutaneous tissue. Seven and 14 days after subcutaneous carrageenan injection, macrophage infiltrations were compared by using high-power field (HPF) light-microscopy (×40) between two groups (H&E staining and CD68 macrophage antibody immunohistochemistry). Results: FACS analysis showed that more than 75% of peripheral monocytes were depleted 24 hours after intravenous clodronate liposome (22.1 ± 3.4% at baseline and 5.8 ± 2.1% at 24 hours after clodronate liposome injection, p<0.05), and 0.8 ± 0.3% of peripheral monocytes remained one week after clodronate liposome injection. After clodronate liposome injections, macrophage cell count per HPF (×40) at carrageenan granuloma decreased progressively (321 ± 85, 58 ± 31, and 42 ± 23; baseline, 1 week, 2 weeks; respectively (p<0.01)). Conclusion: Macrophage infiltrations at carrageenan granuloma decreased significantly after intravenous clodronate liposome injection, and long-term intravenous injection of clodronate liposomes may influence the macrophage-mediated inflammations such as atherosclerosis.
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