Monitoring of Serum Hepcidin-25 in Multicentric Castleman’s Disease Patients Treated with Tocilizumab, an Anti-Interleukin-6 Receptor Antibody.
Authors: Kawabata Hiroshi , Tomosugi Naohisa , Kanda Junya , Mizumoto Chisaki , Tanaka Yasuhiro , Ichinohe Tatsuo , Kadowaki Norimitsu , Yoshizaki Kazuyuki , Ishikawa Takayuki , Uchiyama Takashi 
Published: April 2020

Abstract
Multicentric Castleman’s disease (MCD) is a rare lymphoproliferative disorder with systemic manifestations such as lymphadenopathy, fever and microcytic anemia. Over-production of interleukin-6 (IL-6) has been speculated to be a key event in the pathogenesis of this disorder. IL-6 is known to stimulate hepatic expression of hepcidin, a central regulator of body iron homeostasis. We developed a SELDI-TOF mass spectrometry-based semi-quantitative method for serum hepcidin-25 (Tomosugi N, et al. Blood108, 1381–7, 2006). Utilizing this method, we previously reported a rapid decrease in serum hepcidin-25 in two MCD patients after administration of tocilizumab, an anti-IL-6 receptor antibody (Kawabata H, et al. Haematologica92, 857–8, 2007). Recently, by introducing liquid chromatography tandem mass-spectrometry and an isotopic hepcidin as an internal standard, we developed another serum hepcidin quantification system with very small intra- and inter-assay CVs. Utilizing this new method in this study, we further evaluated the clinical relevance of monitoring serum hepcidin in MCD patients treated with tocilizumab. Serum hepcidin-25 was monitored in 5 MCD cases including two previously reported cases (Cases 1 and 2). Tocilizumab (8 mg/kg body weight) was administered intravenously at 2-week intervals. This study was approved by the Ethics Committee of Kyoto University Graduate School and the Faculty of Medicine. Written informed consent was obtained from each patient. The initial levels of serum hepcidin-25 before tocilizumab treatment varied widely, between 14 and 256 ng/ml (normal range, 22 ± 12 ng/ml). In all cases, rapid reduction of serum hepcidin-25 was observed after the initial dose of tocilizumab, followed by decreases of C-reactive protein and gradual improvement of anemia (Table 1). In Case 5, the initial hepcidin level was extremely high (256 ng/ml) and it decreased only slightly after tocilizumab administration. In this case, the serum hepcidin level on day 35 remained considerably elevated (90.5 ng/ml) even after 3 doses of tocilizumab. On the same day, an anti-tocilizumab antibody was detected in the serum, and this medication was discontinued. In the other 4 cases, serum hepcidin levels decreased below the upper normal limit within 2 weeks. After 16 weeks treatment with tocilizumab, Hb increased from 5.7 to 11.2 g/dl in Case 1, from 10.2 to 11.9 g/dl in Case 2, from 6.3 to 11.0 g/dl in Case 3 and from 8.2 to 13.7 g/dl in Case 4. There were no apparent side effects in these 4 cases. These findings imply that inadequate levels of serum hepcidin caused by overproduction of IL-6 are associated with the pathogenesis of microcytic anemia observed in MCD patients. Monitoring of serum hepcidin may be useful to evaluate the efficacy of tocilizumab in MCD cases.
Table 1 Case 1 Case 2 Case 3 Case 4 Case 5 Pre/Day14 Pre/Day14 Pre/Day14 Pre/Day14 Pre/Day14 Hepcidin-25 (ng/ml) 44.8/2.2 55.5/24.6 14/0.8 43.5/1.5 256/166 CRP (mg/dl) 24.3/5.4 11.7/4.1 16.9/3.6 7.6/0.2 11.9/6.8 Hb (g/dl) 5.7/9.2 10.2/11.2 6.3/7.9 8.2/9.4 6.5/7.4