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Arsenic Exposure Increases Monocyte Adhesion to the Vascular Endothelium, a Pro-Atherogenic Mechanism.

Lemaire M, Negro Silva LF, Lemarié CA, Bolt AM, Flores Molina M, Krohn RM, Smits JE, Lehoux S, Mann KK - PLoS ONE (2015)

Bottom Line: Hence, no effect of arsenic on platelet activation or platelet/leukocyte interaction was observed.We found that arsenic increases adhesion of mononuclear cells via increased CD29 binding to VCAM-1, an adhesion molecule found on activated endothelial cells.Interestingly, expression of adhesion molecules and increased binding can be inhibited by antioxidants in vitro and in vivo.

View Article: PubMed Central - PubMed

Affiliation: Department of Oncology, Lady Davis Institute for Medical Research, McGill University, Montréal, Québec, Canada.

ABSTRACT
Epidemiological studies have shown that arsenic exposure increases atherosclerosis, but the mechanisms underlying this relationship are unknown. Monocytes, macrophages and platelets play an important role in the initiation of atherosclerosis. Circulating monocytes and macrophages bind to the activated vascular endothelium and migrate into the sub-endothelium, where they become lipid-laden foam cells. This process can be facilitated by platelets, which favour monocyte recruitment to the lesion. Thus, we assessed the effects of low-to-moderate arsenic exposure on monocyte adhesion to endothelial cells, platelet activation and platelet-monocyte interactions. We observed that arsenic induces human monocyte adhesion to endothelial cells in vitro. These findings were confirmed ex vivo using a murine organ culture system at concentrations as low as 10 ppb. We found that both cell types need to be exposed to arsenic to maximize monocyte adhesion to the endothelium. This adhesion process is specific to monocyte/endothelium interactions. Hence, no effect of arsenic on platelet activation or platelet/leukocyte interaction was observed. We found that arsenic increases adhesion of mononuclear cells via increased CD29 binding to VCAM-1, an adhesion molecule found on activated endothelial cells. Similar results were observed in vivo, where arsenic-exposed mice exhibit increased VCAM-1 expression on endothelial cells and increased CD29 on circulating monocytes. Interestingly, expression of adhesion molecules and increased binding can be inhibited by antioxidants in vitro and in vivo. Together, these data suggest that arsenic might enhance atherosclerosis by increasing monocyte adhesion to endothelial cells, a process that is inhibited by antioxidants.

No MeSH data available.


Related in: MedlinePlus

Arsenic increases adhesion of mononuclear cells via increased CD29 binding to VCAM-1.U937 or human PBMC cells (1000 cells/ml) were exposed to arsenic for 72h (0, 10 or 200 ppb) (A). Cells were fluorescently-labelled and incubated on VCAM-1/Fc coated plates. The non-adherent cells were washed away, and adherent fluorescent cells were counted. In B, cellular surface CD29 antigens were detected by flow-cytometry using anti-CD29 antibody. (C-D) CD29 blocking antibody was added to in vitro U937 binding assays to VCAM-1/Fc (C) or to ex vivo organ cultures with primary mononuclear cells (D). Values are expressed as mean ± S.D., n ≥ 3. * p < 0.05: **: p < 0.01; ***: p < 0.001, compared to unexposed controls.
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pone.0136592.g003: Arsenic increases adhesion of mononuclear cells via increased CD29 binding to VCAM-1.U937 or human PBMC cells (1000 cells/ml) were exposed to arsenic for 72h (0, 10 or 200 ppb) (A). Cells were fluorescently-labelled and incubated on VCAM-1/Fc coated plates. The non-adherent cells were washed away, and adherent fluorescent cells were counted. In B, cellular surface CD29 antigens were detected by flow-cytometry using anti-CD29 antibody. (C-D) CD29 blocking antibody was added to in vitro U937 binding assays to VCAM-1/Fc (C) or to ex vivo organ cultures with primary mononuclear cells (D). Values are expressed as mean ± S.D., n ≥ 3. * p < 0.05: **: p < 0.01; ***: p < 0.001, compared to unexposed controls.

Mentions: By binding to VCAM-1, VLA-4 mediates the attachment of circulating cells to the activated vascular endothelium, favoring monocyte migration into the subendothelial space. VLA-4 is composed of CD49d (α4) and CD29 (β1) integrins. Interaction of monocyte VLA-4 with VCAM-1 occurs via inducible interactions between CD49d and CD29, producing changes in affinity (structural) or avidity (number) [37]. We tested whether arsenic exposure of monocytes could increase binding to immobilized VCAM-1. We observed that both human U937 monocytic cells and primary human monocytes adhered more to the VCAM-1/Fc chimera when exposed to arsenic for 72 h, as compared to the non-exposed control (Fig 3A). Furthermore, the presence of arsenic during the monocyte differentiation into macrophages also resulted in greater adhesion to VCAM-1 (Fig 3A). CD29 is constitutively expressed on monocytes [38], but upon activation, adopts an active conformation and its CD49a binding sites (the HUTS epitopes) become available for the antibody. Active-CD29 expression was slightly, but significantly, increased on human primary macrophages, but not monocytes, following arsenic exposure (Fig 3B; *: p < 0.05). We confirmed that CD29 was responsible for arsenic-increased binding to VCAM-1 by the addition of an anti-CD29 blocking antibody. Our results show a significant inhibition of U937 cell adhesion to VCAM-1 when blocking CD29 (Fig 3C; **: p < 0.01). We observed that the CD29 blocking antibody also prevented arsenic-induced binding of leukocytes to vascular endothelium in our ex vivo organ culture model (Fig 3D), supporting an important role for the VCAM-1/CD29 interaction in mediating the initial monocyte/endothelial cell interaction.


Arsenic Exposure Increases Monocyte Adhesion to the Vascular Endothelium, a Pro-Atherogenic Mechanism.

Lemaire M, Negro Silva LF, Lemarié CA, Bolt AM, Flores Molina M, Krohn RM, Smits JE, Lehoux S, Mann KK - PLoS ONE (2015)

Arsenic increases adhesion of mononuclear cells via increased CD29 binding to VCAM-1.U937 or human PBMC cells (1000 cells/ml) were exposed to arsenic for 72h (0, 10 or 200 ppb) (A). Cells were fluorescently-labelled and incubated on VCAM-1/Fc coated plates. The non-adherent cells were washed away, and adherent fluorescent cells were counted. In B, cellular surface CD29 antigens were detected by flow-cytometry using anti-CD29 antibody. (C-D) CD29 blocking antibody was added to in vitro U937 binding assays to VCAM-1/Fc (C) or to ex vivo organ cultures with primary mononuclear cells (D). Values are expressed as mean ± S.D., n ≥ 3. * p < 0.05: **: p < 0.01; ***: p < 0.001, compared to unexposed controls.
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Related In: Results  -  Collection

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pone.0136592.g003: Arsenic increases adhesion of mononuclear cells via increased CD29 binding to VCAM-1.U937 or human PBMC cells (1000 cells/ml) were exposed to arsenic for 72h (0, 10 or 200 ppb) (A). Cells were fluorescently-labelled and incubated on VCAM-1/Fc coated plates. The non-adherent cells were washed away, and adherent fluorescent cells were counted. In B, cellular surface CD29 antigens were detected by flow-cytometry using anti-CD29 antibody. (C-D) CD29 blocking antibody was added to in vitro U937 binding assays to VCAM-1/Fc (C) or to ex vivo organ cultures with primary mononuclear cells (D). Values are expressed as mean ± S.D., n ≥ 3. * p < 0.05: **: p < 0.01; ***: p < 0.001, compared to unexposed controls.
Mentions: By binding to VCAM-1, VLA-4 mediates the attachment of circulating cells to the activated vascular endothelium, favoring monocyte migration into the subendothelial space. VLA-4 is composed of CD49d (α4) and CD29 (β1) integrins. Interaction of monocyte VLA-4 with VCAM-1 occurs via inducible interactions between CD49d and CD29, producing changes in affinity (structural) or avidity (number) [37]. We tested whether arsenic exposure of monocytes could increase binding to immobilized VCAM-1. We observed that both human U937 monocytic cells and primary human monocytes adhered more to the VCAM-1/Fc chimera when exposed to arsenic for 72 h, as compared to the non-exposed control (Fig 3A). Furthermore, the presence of arsenic during the monocyte differentiation into macrophages also resulted in greater adhesion to VCAM-1 (Fig 3A). CD29 is constitutively expressed on monocytes [38], but upon activation, adopts an active conformation and its CD49a binding sites (the HUTS epitopes) become available for the antibody. Active-CD29 expression was slightly, but significantly, increased on human primary macrophages, but not monocytes, following arsenic exposure (Fig 3B; *: p < 0.05). We confirmed that CD29 was responsible for arsenic-increased binding to VCAM-1 by the addition of an anti-CD29 blocking antibody. Our results show a significant inhibition of U937 cell adhesion to VCAM-1 when blocking CD29 (Fig 3C; **: p < 0.01). We observed that the CD29 blocking antibody also prevented arsenic-induced binding of leukocytes to vascular endothelium in our ex vivo organ culture model (Fig 3D), supporting an important role for the VCAM-1/CD29 interaction in mediating the initial monocyte/endothelial cell interaction.

Bottom Line: Hence, no effect of arsenic on platelet activation or platelet/leukocyte interaction was observed.We found that arsenic increases adhesion of mononuclear cells via increased CD29 binding to VCAM-1, an adhesion molecule found on activated endothelial cells.Interestingly, expression of adhesion molecules and increased binding can be inhibited by antioxidants in vitro and in vivo.

View Article: PubMed Central - PubMed

Affiliation: Department of Oncology, Lady Davis Institute for Medical Research, McGill University, Montréal, Québec, Canada.

ABSTRACT
Epidemiological studies have shown that arsenic exposure increases atherosclerosis, but the mechanisms underlying this relationship are unknown. Monocytes, macrophages and platelets play an important role in the initiation of atherosclerosis. Circulating monocytes and macrophages bind to the activated vascular endothelium and migrate into the sub-endothelium, where they become lipid-laden foam cells. This process can be facilitated by platelets, which favour monocyte recruitment to the lesion. Thus, we assessed the effects of low-to-moderate arsenic exposure on monocyte adhesion to endothelial cells, platelet activation and platelet-monocyte interactions. We observed that arsenic induces human monocyte adhesion to endothelial cells in vitro. These findings were confirmed ex vivo using a murine organ culture system at concentrations as low as 10 ppb. We found that both cell types need to be exposed to arsenic to maximize monocyte adhesion to the endothelium. This adhesion process is specific to monocyte/endothelium interactions. Hence, no effect of arsenic on platelet activation or platelet/leukocyte interaction was observed. We found that arsenic increases adhesion of mononuclear cells via increased CD29 binding to VCAM-1, an adhesion molecule found on activated endothelial cells. Similar results were observed in vivo, where arsenic-exposed mice exhibit increased VCAM-1 expression on endothelial cells and increased CD29 on circulating monocytes. Interestingly, expression of adhesion molecules and increased binding can be inhibited by antioxidants in vitro and in vivo. Together, these data suggest that arsenic might enhance atherosclerosis by increasing monocyte adhesion to endothelial cells, a process that is inhibited by antioxidants.

No MeSH data available.


Related in: MedlinePlus