Effects of Tamoxifen Versus Raloxifene on Retinal Capillary Endothelial Cell Proliferation

Abstract

Purpose: Endothelial cell proliferation in angiogenesis is active in conditions such as cancers and diabetic retinopathy. Tamoxifen (T) and raloxifene (R) have been compared in numerous studies as a prophylaxis for breast cancer, and T is used to treat breast cancer. T, unlike R, has been linked to an increase in uterine cancers, thrombo-embolic events, and cataract. The purpose of our study was to evaluate the efficacies of T and R in reducing estrogen-induced retinal capillary endothelial cell proliferation. Methods: Rhesus monkey retinal capillary endothelial cells (ATCC RF/6A) were used to assay cell proliferation when treated with 0.0, 0.1, 1.0, and 10.0 nM 17 b estradiol (E2) for 24 and 48 h. Viable cells were counted using a Neubauer hemocytometer with a trypan blue exclusion method to determine the number of viable cells. Cell counts were also performed using 1.0 nM E2 with 0.01, 0.1, 1.0, and 10.0 nM concentrations of either T or R. Cell medium, collected at 24 h, was evaluated for vascular endothelial growth factor and pigment epithelium-derived factor. Results: Viable cells were significantly greater in cultures treated with 1.0 or 10.0 nM E2, compared to cells treated with 0.0 or 0.1 nM E2 both at 24 and 48 h. Viable cell counts were reduced significantly in cultures treated with 0.1, 1.0, or 10.0 nM T or R in addition to the 1.0 nM E2. Cell counts were not significantly different when comparing equal concentrations of T and R, that is, 1.0 nM E2 + 1 nM T or R. Vascular endothelial growth factor and pigment epithelium-derived factor protein/10,000 cells was reduced by 1.0 nM E2, but returned to higher levels with the introduction of T and R to growth media. Conclusions: T and R showed similar potency in inhibiting estrogen-induced retinal capillary endothelial cell proliferation. Considering drug safety profiles, our results, when extended to animals and humans, suggest that R is preferable to T in treating angiogenic retinal diseases. Further studies on the signaling mechanism of estrogen-induced endothelial cell proliferation may lead to new treatment strategies in the treatment of ocular angiogenic diseases.

Domain I-IV of β2-glycoprotein I inhibits advanced glycation end product-induced angiogenesis by down-regulating vascular endothelial growth factor 2 signaling

“…The cells demonstrate prolonged expression of VEGF and VEGFRs (19). Due to their ease of culture and rapid transfer, this cell line is widely used in the investigation of PDR and other retina-associated diseases (19)(20)(21)(22).…”

The Role of Sex Hormones in Diabetic Retinopathy

“…Grigsby et al are the first to demonstrate that raloxifene is as effective as tamoxifen in reducing the E2-induced proliferation in a primate retinal endothelial cell line. Results from this cell study on tamoxifen and raloxifene inhibition of E2-induced cell proliferations www.intechopen.com suggest that tamoxifen and raloxifene have similar potency to block estrogen mediated retinal angiogenesis (Grigsby et al 2011).…”

“…At an early stage the proliferation of endothelial cells induced by estradiol may be a benefit as a reparative mechanism; however, at a stage where proliferative retinopathy is threatening vision this increased proliferation and could lead to pathological vessel formation (Espinosa-Heidmann et al 2005;Grigsby et al 2011;Suzuma et al 1999). …”

“…In normoxic conditions Grigsby et al found that, in response to E2, PEDF levels were reduced in RhREC cells. Furthermore, this reduction in response to E2 could be mitigated by concurrent exposure to tamoxifen or raloxifene, but the relative change in PEDF and in VEGF did not exactly correspond to cell growth patterns indicating that additional factors are involved in E2-induced proliferation of RhREC (Grigsby et al 2011). …”

“…Kazi et al have demonstrated in rat uterine luminal cells that E2 required the P13K/AKT pathway to increase VEGF gene expression (Kazi et al 2009). Grigsby et al using a primate cell line of rhesus monkey retinal endothelial cells (RhREC) showed a decrease in VEGF levels with E2 exposure, which only partially recovered with the concurrent use of tamoxifen and raloxifene (Grigsby et al 2011). …”