Pro-angiogenesis action of arsenic and its reversal by selenium-derived compounds

Inorganic arsenic (arsenite and arsenate) in drinking water hasbeen associated with skin cancers and increased incidence of car-diovascular diseases. Additionally, studies have demonstrated thepro-angiogenic effect of arsenite and its potential promotion oftumor angiogenesis and tumor progression. Furthermore, recentreports demonstrated reversal of skin co-carcinogenesis by anorganoselenium compound. The present study was undertakento determine the effect and mechanism on angiogenesis of arseniteat low level and its potential reversal by various selenium-derivedcompounds. The pro-angiogenesis effects and mechanisms of so-dium arsenite were determined using the chick chorioallantoicmembrane (CAM) model over 3 days and compared with stan-dard pro-angiogenesis factors, such as basic fibroblast growthfactor (b-FGF). Additionally, the potential effect of various sele-nium-derived compounds—such as dimethyl selenone, diphenylselenone, sodium selenite or Se-methyl selenocysteine—in revers-ing the pro-angiogenesis effect of arsenite or b-FGF was alsodetermined in the CAM model. The pro-angiogenesis effect ofarsenite or b-FGF was significantly (P , 0.01) blocked by di-methyl selenone, diphenyl selenone, sodium selenite or Se-methylselenocysteine. The pro-angiogenesis effect of either sodium arse-nite at 33 nM or b-FGF was blocked (P,0.01) by the extracellularsignal-regulated kinases 1 and 2 (ERK1/2) activation inhibitor, PD98059. Additionally, the pro-angiogenic effect of arsenic or b-FGFwas blocked as well (P , 0.01) by the avb3 antagonist, XT199.These data suggest that the pro-angiogenesis effect of arsenic isinitiated at the plasma membrane integrin avb3, involves activa-tion of the ERK1/2 pathway and is effectively reversed by variousselenium-derived compounds.IntroductionArsenic, an element that is found both in native and in combined form,has been used medicinally for over 2400 years. In the 19th century, itwas the mainstay of the materia medica. A solution of potassiumarsenite (Fowler’s solution) was used for a variety of systemic ill-nesses from the 18th until the 20th century. This multipurpose solu-tion was also the primary therapy for the treatment of chronicmyelogenous leukemia until it was replaced by radiation and cyto-toxic chemotherapy. The past 100 years have seen a precipitous de-cline in arsenic use; by the mid-1990s, the only recognized indicationwas the treatment of trypanosomiasis. Much of this decline was due toconcerns about the toxicity and potential carcinogenicity of chronicarsenic administration (1). Chinese physicians had been using arsenic-containing medicines, including arsenic trioxide, as part of a treatmentfor acute promyelocytic leukemia (APL). Their accumulated experi-ence showed that a stable solution of arsenic trioxide given by in-travenous infusion was remarkably effective both in patients withnewly diagnosed APL and in those with refractory and relapsedAPL (2). The mechanisms of action of arsenic derivatives in thisdisease and other malignancies are many and include induction ofapoptosis, inhibition of proliferation and inhibition of angiogenesis(2). Molecular studies and ongoing clinical trials suggest that, asa chemotherapeutic agent, arsenic trioxide shows great promise inthe treatment of malignant diseases (2).Arsenic trioxide can inhibit proliferation and induce apoptosis inmultiple myeloma cells in vitro and in vivo (3). However, low con-centrations of arsenic trioxide stimulate vascular cell proliferation incell culture and angiogenesis in vivo (4,5). Arsenite was shown tocause dose-dependent increase in vessel density in the chick chorio-allantoic membrane (CAM) assay (5). The threshold arsenic trioxideconcentration for this response was 0.033 lM, and inhibition of vesselgrowth was observed at concentrations .1 lM (5). Hence, arsenitemight have carcinogenic effect at low levels of exposure, which mightbe accelerated by its pro-angiogenesis effects.Data supported a potential anti-angiogenic effect of selenium inthe chemoprevention of cancer (6,7). With regard to tumor angio-genesis, the chemopreventive effect of increased selenium intake onchemically induced mammary carcinogenesis has been associatedwith reduced intratumoral microvessel density (6). Control of an-giogenesis is a complex process involving local release of vasculargrowth factors, the extracellular matrix, adhesion molecules andmetabolic factors (7–9). Mechanical forces within blood vesselsmay also play a role (7). The principal endogenous growth factorsimplicated in new blood vessel growth are the fibroblast growthfactor (FGF) family and vascular endothelial growth factor (VEGF)(10). The mitogen-activated protein kinase (MAPK) signal trans-duction cascade (extracellular signal-regulated kinases 1 and 2[ERK1/2]) is known to be involved both in VEGF gene expressionand in control of proliferation of vascular endothelial cells (10). Theavailability of a chick CAM model of angiogenesis (10–14) allowedus to define the effect of low levels of sodium arsenite and its po-tential mechanism of actions.In this report, we describe a pro-angiogenesis effect of arsenic tri-oxide that is comparable with that of basic FGF (b-FGF) or VEGF inthe CAM model. We also provide evidence that representative sele-nium compounds reverse the pro-angiogenesis effect of arsenic,which is initiated at the endothelial cell plasma membrane, involvesa plasma membrane integrin avb3 receptor and is mediated by acti-vation of the ERK1/2 signal transduction pathway.Materials and methods