Cellular Source Of Serum Vascular Endothelial Growth Factor And Mechanism Of Its Production In Patients With POEMS Syndrome

Backgroud and ObjectivesPOEMS syndrome is a rare paraneoplastic disorder, characterized by polyneuropathy, organomegaly, osteosclerosis and extravascular volume overload, due to an underlying plasma cell dyscrasia. Vascular endothelial growth factor (VEGF), a potent angiogenic cytokine that can increase vascular permeability, plays a critical role in its pathogenesis. Despite extensive studies concerning the diagnostic, disease monitoring and response assessment performance of VEGF, little is known about its cellular source in POEMS patients, as well as the mechanism governing its production.Methods and MaterialsPatients with POEMS syndrome,62 newly diagnosed and 46 of them finished treatment, seen at Peking Union Medical College Hospital between Feburary 2014 and April 2015, were included in the current study. Clinical information, serum and bone marrow samples were collected with the Institutional approval. Serum levels of VEGF were measured by ELISA. VEGF levels in bone marrow plasma cells were quantified via real-time quantitative PCR and multiparameter flow cytometry, respectively. And the correlation of VEGF levels measured in serum and bone marrow plasma cells were analyzed. Taking advantage of the multiparameter flow cytometry, we further pinpointed plasma cell subgroups, concerning its phenotype, clonality and intracellular VEGF and interleukin-6 expression. Moreover, immunohistochemical staining was performed to analyze the plasma cell distribution, clonality and expression of VEGF, IL-6 and hypoxia-inducible factor-la (HIF-la). Statistical analyses were conducted using SPSS 22, and a p< 0.05 was considered as significant.ResultsSerum levels of VEGF were dramatically elevated in patients with newly diagnosed POEMS syndrome (median 5958 pg/mL), significantly higher than both disease and healthy controls (p< 0.001), and can be used as a diagnostic marker (area under curve 0.988, p< 0.001). A cut-off value of 2000 pg/mL had a specificity of 97.7% with a sensitivity of 91.9% in support of the diagnosis. After treatment, VEGF levels decreased gradually (6-cycle after therapy, median 1184 pg/mL, p< 0.001; 12-cycle after therapy, median 832 pg/mL, p< 0.001). Multiparameter flow cytometry revealed that plasma cells in the bone marrow of POEMS patients were mainly polyclonal, and could express VEGF intracellularly, which levels also decreased in response to therapy. More importantly, a statistically linear correlation was observed between serum and bone marrow plasma cell VEGF levels (newly diagnosed patients, rho=0.33, p=0.01; post-therapeutic patients, rho= 0.53, p< 0.001). When we re-analyzed the plasma cells in multiparameter flow cytometry, we found two subpopulations, namely monoclonal and polyclonal, in 11 patients (18%). Their relative amounts were similar (41% vs.59%) and showed comparable levels of VEGF expression (mean fluorescent intensity,2009 vs. 2367, p=0.594). However, monoclonal plasma cells had significantly higher intracellular IL-6 levels (mean fluorescent intensity,1635 vs.865, p= 0.006). In bone marrow biopsies of newly diagnosed patients (n=46), plasma cells were typically distributed in a scattered manner, with focal aggregates observed in 21 cases (46%). The background scattered plasma cells were polyclonal, while both monoclonal and polyclonal fractions were observed in the focal area. Further immunohistochemical staining showed general VEGF and HIF-1α expression in focal plasma cells. In contrast, IL-6 was mainly stained in λ-restricted plasma cells.ConclusionBone marrow plasma cells are potential source of VEGF production in patients with POEMS syndrome. Monoclonal plasma cells, aggregates focally in the bone marrow, may secret IL-6 to stimulate polyclonal plasma cells proliferation, and consequently regulate VEGF production.