Normal ranges of angiogenesis regulatory proteins in human platelets

Abstract

Platelets sequester angiogenesis regulatory proteins early in tumor growth, which suggests a new avenue for monitoring disease. To date, there are no clinically relevant reference ranges for markers of early angiogenesis. We introduce a new ELISA-based method for accurate and reproducible measurement of vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), platelet factor 4 (PF4), thrombospondin-1 (TSP-1), fibroblast growth factor, basic (bFGF), and endostatin in platelets. To facilitate clinical applicability, the platelet levels in isolated samples were determined utilizing a new actin ELISA method. Platelets from healthy donors at single and repetitive time points were used for the assessment of normal ranges of these proteins. The physiological levels in platelets were: VEGF (0.74 ± 0.37 pg/10 6 platelets); PDGF (23 ± 6 pg/10 6 ); PF4 (12 ± 5 ng/10 6 ); TSP-1 (31 ± 12 ng/10 6 ); bFGF (0.44 ± 0.15 pg/10 6 ); and endostatin (5.6 ± 3.0 pg/10 6 ). There was an excellent correlation (R 2 5 0.7) between the platelet levels calculated with the actin ELISA and complete blood count. The levels of the platelets were higher than those in platelet-poor plasma by factors of: VEGF (215-fold); PDGF (914-fold); PF-4 (516-fold); TSP-1 (813-fold); and bFGF (17-fold). The endostatin levels were nearly equivalent. The biovariability of the platelet proteins in eight healthy subjects over a 5-week period was found to be minimal. We describe accurate and direct measurements of the concentrations of VEGF, bFGF, PDGF, TSP-1, endostatin, and PF4 in platelets of healthy human subjects. In contrast to the highly variable levels in plasma and serum, the platelet-derived measurements were accurate and reproducible with minimal biovariability. Am. J. Hematol. 85:487-493, 2010. V

Haematologic Parameters in Metastatic Colorectal Cancer Patients Treated with Capecitabine Combination Therapy

“…It is well-established that platelets carry a multitude of angiogenesis regulatory proteins in their granules, and the normal ranges of angiogenesis regulators have been characterized in human platelets and in the platelets of patients with malignancy (Peterson et al, 2010).…”

Release of angiogenesis regulatory proteins from platelet alpha granules: modulation of physiologic and pathologic angiogenesis

“…It is well-established that platelets carry a multitude of angiogenesis regulatory proteins in their ␣ granules, and the normal ranges of angiogenesis regulators have been characterized in human platelets and in the platelets of patients with malignancy. 17 Our laboratory has shown that platelets store angiogenic factors in distinct ␣ granules and that these granules can be differentially released in the presence of the thrombin agonists; with PAR1 resulting in the release of VEGF and PAR4 resulting in release of endostatin. 18 Others have shown that differential release is not limited to angiogenic factors and also affects known hemostatic factors.…”

A novel and essential role for FcγRIIa in cancer cell–induced platelet activation

“…9 Platelet depletion in tumor-bearing mice triggers intratumor hemorrhage which is rescued by platelet secretome, 1 demonstrating a requirement for platelet secretion to stabilize angiogenesis in tumor metastases. Indeed, platelet a-granules contain large reservoirs of cytokines and growth factors, including transforming growth factor b (TGF-b) and vascular endothelial growth factor (VEGF), 10,11 which are selectively released upon platelet activation. 12,13 Consistent with a role of platelet secretion in tumor metastasis, TGF-b derived from platelet a-granules has been shown to profoundly impact tumor metastasis and survival by enhancing an epithelial mesenchymal-like transition and suppressing tumor cell natural killer-mediated lysis, respectively.…”