[Effects of four bisphosphonates on macrophage phagocytosis: quantitative measurement by flow cytometry using high-fluorescence particles and human monocytic cell line THP-1].

Impairment of macrophage phagocytosis is a major cause of chronic inflammation. Bisphosphonates (BPs) are widely used as anti-osteoclastic agents. The effects of BPs on monocyte-macrophage lineage cells are being increasingly reported; however, the detailed effects of BPs on macrophage phagocytic activity are still unclear. We examined the effects of four BPs: clodronate as a non-nitrogen containing BP (non-N-BP), and pamidronate, alendronate, and zoledronate as nitrogen-containing BP(N-BP), on macrophage phagocytic activity. The uptake of high fluorescence-labeled polystyrene beads by the human monocytic cell line THP-1 was investigated by flow cytometry. All three N-BPs suppressed the phagocytosis of macrophages more potently than the non-N-BP, clodronate. Pamidronate and zoledronate were more potent than alendronate. BP induced the apoptosis of THP-1. Pamidronate and zoledronate induced apoptosis more effectively than clodronate. The method described to observe phagocytosis was simple and quantitative, and might be useful in screening for the effects of drugs, such as N-BP and non-N-BP, on phagocytic activity.

Conversion of cultured monocytes/macrophages into endothelial-like cells through direct contact with endothelial cells.

When culturing human umbilical vein endothelial cells in a culture medium containing 4% human serum albumin, it was possible to maintain the epithelioid morphology and function for several months without subculturing. When coculturing endothelial cells and labeled monocytes/macrophages (Mo/Phi) that were collected from peripheral blood and allowed to engulf fluorescent latex beads, some Mo/Phi changed their shapes and became epithelioid cells that were indistinguishable from vascular endothelial cells. This transformation started within several hours of coculturing. At 7 days after the start of coculturing, more than half of the labeled cells were identified as endothelial-like cells morphologically. Furthermore, morphologically altered Mo/Phi did not express Mo/Phi-specific antigens, ie, the MHC Class II molecule and CD68, but expressed VE cadherin and vWF, which are specific antigens for endothelial cells, and labeled cells that changed into endothelial-like cells no longer engulfed fluorescent latex beads. This strongly suggests that peripheral blood monocytes differentiate into endothelial-like cells.

PKC pathway and ERK/MAPK pathway are required for induction of cyclin D1 and p21Waf1 during 12-o-tetradecanoylphorbol 13-acetate-induced differentiation of myeloleukemia cells.

Treatment of human promyelocytic leukemia cell HL60 with 12-o-tetradecanoylphorbol 13-acetate (TPA) induces growth arrest, differentiation towards the monocyte/macrophage lineage, and expression of cell cycle-regulating genes cyclin D1 and p21Waf1. First, we demonstrated that p21Waf1 expression was increased by TPA in other leukemia cell lines also, including THP-1, U937, and KG-1, which differentiate into monocytes/macrophages by TPA. Secondly, we demonstrated the signal transduction pathways of cyclin D1 and p21Waf1 expressions in TPA-treated HL60 cells. Induction of cyclin D1 expression in TPA-treated HL60 cells was inhibited with protein kinase C (PKC) inhibitor bisindolylmaleimide I and mitogen activated protein kinase kinase (MEK) inhibitor PD98059. Induction of p21Waf1 expression in TPA-treated HL60 cells was inhibited with PKC inhibitor bisindolylmaleimide I and Gö6976, MEK inhibitor PD98059, and p38 mitogen-actibated protein kinase (MAPK) inhibitor SB202190. Thus, cyclin D1 and p21Waf1 expressions are considered to be induced via PKC and extracellular signal-regulated kinase/mitogen-activated protein kinase (MAPK/ERK) pathways in TPA-treated HL60 cells. The upregulation of p21Waf1 seems to play a critical role in TPA-induced cell differentiation by suppressing cyclin dependent kinase activity , while the upregulation of cyclin D1 seems to be compensated by p21Waf1.