Response to Letter Regarding Article, “Reduction of Circulating Soluble fms-Like Tyrosine Kinase-1 Plays a Significant Role in Renal Dysfunction-Associated Aggravation of Atherosclerosis”
We thank Drs Di Marco and Brand for their comments on our article recently published in Circulation.1 They provided important suggestions on the method used to measure soluble fms-like tyrosine kinase-1 (sFlt-1) levels in both clinical and experimental animal settings.
First, we are confident that there is significant variation in the sFlt-1 plasma levels at the different blood sampling sites, as shown in Figure IA in the online-only Data Supplement available with our article. Although not specifically shown in this Figure, the sFlt-1 plasma levels in the veins were significantly lower than the levels in the arterial blood. We reviewed an article by Drs Di Marco and Brand2 and noticed that this study used the same enzyme-linked immunosorbent assayused in our study and collected blood samples from antecubital veins. Actually, they reported lower levels of sFlt-1 in venous blood than we measured in our subjects’ arterial blood. Although the precise reason for these lower sFlt-1 levels in the veins is currently unclear, sFlt-1 could be trapped or used in the capillaries and/or tissues as it passes through the peripheral circulation, suggesting that the vascular endothelial growth factor/placental growth factor/Flt system has a significant role in regulating peripheral circulation.
Heparin is another important factor that influences the sFlt-1 plasma levels. sFlt-1 plasma levels are immediately and significantly elevated after heparin administration. Drs Di Marco and Brand described in their article that >20% of patients with severe renal dysfunction were treated with heparin. Therefore, it is not possible to compare the sFlt-1 levels in samples with or without heparin.
Regarding the recombinant human sFlt-1 used in our studies, we confirmed that the recombinant sFlt-1 preparations were specific and biologically active against both human and mouse placental growth factor as shown in Figure 3 in our article.1 We agree with Drs Di Marco and Brand that acutely elevated sFlt-1 levels in the plasma could interact with plasma vascular endothelial growth factor and placental growth factor, resulting in elevated peripheral vessel resistance and blood pressure. This interaction and an acute increase in blood pressure have been well documented in patients with preeclampsia.3 When we administered recombinant human sFlt-1, the levels of sFlt-1 in the plasma significantly increased, as shown in Figure 3D in our article,1 but rapidly returned to undetectable levels within 48 hours, so we administered sFlt-1 3 times a week for 10 weeks. We speculate that the nonpersistent increase in plasma sFlt-1 would not significantly affect blood pressure in a mouse model of chronic renal failure.
We also agree that sFlt-1 levels are significantly elevated during the acute phase of cardiovascular disease and that sFlt-1 could be a biomarker of increased morbidity and mortality in patients with acute cardiovascular disease.4 The role of sFlt-1 in the acute or chronic phases of cardiovascular disease seems to differ. However, these divergent biological effects have been frequently observed for several cytokines in patients with cardiovascular disease. Additional large-scale clinical studies should be performed to understand the clinical significance of this important molecule.
Onoue K, Uemura S, Takeda Y, Somekawa S, Iwama H, Imagawa K, Nishida T, Morikawa Y, Takemoto Y, Asai O, Soeda T, Okayama S, Ishigami K, Nakatani K, Kawata H, Horii M, Nakajima T, Akai Y, Iwano M, Saito Y. Reduction of circulating soluble fms-like tyrosine kinase-1 plays a significant role in renal dysfunction associated aggravation of atherosclerosis. Circulation. 2009; 120: 2470–2477.
Di Mario GS, Reuter S, Hillebrand U, Amier AS, Konig M, Larger E, Oberleithner H, Brand E, Pavenstadt H, Brand M. The soluble VEGF receptor sFlt1 contributes to endothelial dysfunction in CKD. J Am Soc Nephrol. 2009; 20: 2235–2245.
Onoue K, Uemura S, Takeda Y, Somekawa S, Iwama H, Nishida T, Morikawa Y, Nakagawa H, Tsutsumi T, Sung JH, Takemoto Y, Soeda T, Okayama S, Ishigami K, Kawata H, Horii M, Nakajima T, Saito Y. Usefulness of soluble fms-like tyrosine kinase-1 as a biomarker of acute severe heart failure in patients with acute myocardial infarction. Am J Cardiol. 2009; 104: 1478–1483.