Interleukin-6 Stimulates the Hypothalamus-Pituitary- Adrenocortical Axis in Man*
ERNST SPÄTH-SCHWALBE, JAN BORN, HUBERT SCHREZENMEIER, STEFAN R. BORNSTEIN, PATRICIA STROMEYER, SABINE DRECHSLER, HORST-LORENZ FEHM, AND FRANZ PORZSOLT
Department of Internal Medicine, University of Ulm, 89081 Ulm; the Departments of Clinical Neuroendocrinology and Internal Medicine, University of Luebeck, 23538 Luebeck; and Sandoz Pharma Ltd., 53113 Bonn, Germany
ABSTRACT
A recent study in humans, animal studies, and in vitro data have suggested that interleukin-6 (IL-6) stimulates the secretory activity of the hypothalamus-pituitary-adrenocortical (HPA) axis. In a phase II study, one female and six male patients with metastatic renal cell carcinoma received IL-6 to evaluate a possible antitumor effect of IL- 6. This offered the possibility of investigating the influence of IL-6 on the HPA axis in man. The subjects were studied 1 day before, on day 1, and on day 21 of IL-6 therapy (150 ug administered sc every day at 0900 h). Blood samples were taken at 0900, 1100, 1300, 1600, and 2000 h the day before, on day 1 of IL-6 therapy, 24 h after the first IL-6 injection, and on day 21 of IL-6 treatment. Plasma ACTH and cortisol levels promptly followed the rise of IL-6, which peaked 4 h after administration. They were significantly (P < 0.05) higher at 1100 and
1300 h on day 1 of IL-6 therapy compared with the corresponding plasma levels the day before IL-6 treatment. Cortisol concentrations remained significantly increased at 1600 and 2000 h after IL-6 admin- istration. Twenty-four hours after the first IL-6 administration, IL-6, ACTH, and cortisol levels had reached preinjection values. Although plasma cortisol levels were similar on days 1 and 21, ACTH levels were lower on day 21 (than on day 1), but significantly elevated at 1100 h compared with levels on the day before the first IL-6 injection. Results confirming the very recent data of another study demonstrate a stim- ulating effect of IL-6 on the HPA axis in man. They support the notion that IL-6 is one of the cytokines involved in the interaction between the immune system and the HPA axis. (J Clin Endocrinol Metab 79: 1212-1214, 1994)
I NTERLEUKIN-6 (IL-6) is a pleiotropic cytokine involved in the regulation of hematopoiesis, immune responses, and acute phase reactions. IL-6 exerts antitumor effects through stimulation of T-cell-mediated antitumor activity (1). Because of its potential as an antitumor agent, IL-6 is cur- rently being investigated in patients with metastatic tumors (2).
Besides IL-1 and tumor necrosis factor, IL-6 appears to be a major factor of the immune system, mediating interactions between the immune and neuroendocrine systems (3). In vitro and in animal experiments, IL-6 has been found to stimulate the secretory activity of the hypothalamus-pitui- tary-adrenocortical (HPA) axis at different levels (4-11). A very recent study provided the first evidence for an activating influence of IL-6 on the HPA axis in humans (12). Here, we further examined the effect of IL-6 on the secretion of ACTH and cortisol in the human.
Subjects and Methods
In a phase II study, one female and six male patients, aged 49-63 yr, with metastatic renal cell carcinoma were treated with human recombi- nant IL-6 (Sandoz, Basel, Switzerland) to evaluate its antitumor effect.
Received December 17, 1993. Revision received April 29, 1994. Accepted June 22, 1994.
Address all correspondence and requests for reprints to: Dr. E. Späth- Schwalbe, Universitätsklinik Ulm, Medizinische Klinik, Abteilung Innere Medizin III, Robert-Koch-Straße 8, 89081 Ulm, Germany.
* This work was supported by Volkswagen-Stiftung.
This offered the possibility of studying the influence of IL-6 on the HPA system in man. The patients had a WHO performance status of 1 or less. They did not receive any medication known to interfere with the secretory activity of the HPA system.
The IL-6 used in this study is a purified nonglycosylated protein product in lyophilized form produced in Escherichia coli using recombi- nant DNA techniques. A dose of 150 µg IL-6 was administered sc daily for 6 weeks at 0900 h. On the day before treatment, on the first day of treatment (day 1), and after 3 weeks of treatment (day 21), blood samples were drawn at 0900, 1100, 1300, 1600, and 2000 h and 24 h after IL-6 injections from an iv forearm catheter, which was introduced 1 h before IL-6 administration. Samples at 0900 h were taken immediately before the administration of IL-6. Plasma ACTH, cortisol, and IL-6 were measured with commercial assays (ACTH, LUMItest, Henning Berlin, Berlin, Germany; cortisol, Enzymun-test Cortisol, Boehringer Mannheim Immundiagnostica, Mannheim, Germany; IL-6, Quantikine, R & D Systems, Minneapolis, MN). The sensitivities of the ACTH and cortisol assays were 1.1 pmol/L and 27.6 nmol/L, respectively. The intra- and interassay coefficients of variation of these assays were all less than 10%. Blood pressure, heart rate, respiration rate, and body temperature were recorded after each blood collection.
The clinical protocol was approved by the ethics committee of the University of Ulm. Written informed consent was obtained from all patients. Differences in body temperature and between hormone and IL-6 concentrations on the day before IL-6 treatment and on days 1 and 21 of IL-6 treatment were statistically assessed by Wilcoxon t tests. Patients served as their own controls to account for interindividual differences in basal parameters. P < 0.05 was considered significant.
Results
Due to disease progression, one patient had to be excluded from the study before day 21.
Endogenous IL-6 levels did not fluctuate substantially
during the day before (day -1) IL-6 treatment. Plasma ACTH and cortisol levels showed normal circadian patterns the day before IL-6 administration, with highest levels in the morning and lowest levels in the evening (Fig. 1).
On days 1 and 21 of treatment, as expected, serum IL-6 levels increased rapidly after administration, reaching the maximum after 4 h at 1300 h. IL-6 levels remained signifi- cantly elevated until 2000 h. Twenty-four hours after the injection of IL-6, serum levels had returned to preinjection values (data not shown).
Plasma ACTH and cortisol concentrations promptly fol- lowed the rise in IL-6 serum levels and were significantly higher 2 and 4 h after injection of IL-6, i.e. at 1100 and 1300 h, than at the same time on the baseline day before the first IL-6 administration (Fig. 1). Although, later on, at 1600 and 2000 h, cortisol concentrations after IL-6 injection remained significantly elevated, ACTH concentrations had returned to values comparable with those during the baseline day. Twenty-four hours after IL-6 injection, cortisol levels had returned to preinjection values. Plasma cortisol levels were similar on days 1 and 21. ACTH levels were lower on day 21 than on day 1, but on day 21, they were still significantly elevated at 1100 h compared with the corresponding value the day before the first IL-6 injection.
Administration of IL-6 was generally well tolerated, and the dose given caused only a few reversible side-effects
ACTH (pmol/L)
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(besides fever, mild anemia, and weakness). Nausea or other gastrointestinal side-effects were not observed. Blood pres- sure, heart rate, and respiration rate did not differ signifi- cantly between the baseline day before IL-6 treatment, the first day and day 21 of treatment (data not shown). Body temperature was significantly higher 2, 4, and 7 h after the first IL-6 injection, i.e. at 1100, 1300, and 1600 h (at 1300, 1600, and 2000 h on day 21) than at the corresponding time points during the baseline day (Fig. 2).
Discussion
This study demonstrates that IL-6 stimulates the pituitary- adrenocortical axis in the human. The finding agrees with in vitro data (4-8) and results from studies in animals (9-11). It also confirms a recent study in humans (12). Whether, after peripheral administration, IL-6 acts centrally on the hypo- thalamus to stimulate CRH release or peripherally at the pituitary or adrenocortical level cannot be decided conclu- sively. In vitro and animal data provided evidence for stim- ulation of the HPA axis by IL-6 at the hypothalamic, median eminence, pituitary, and adrenocortical level (5, 9, 10, 13, 14).
The present data together with previous results (12) indi- cate an acute stimulatory effect of IL-6 at the pituitary or at a higher level. The long-lasting stimulation of cortisol release in the present study, which continued despite declining plasma ACTH levels, may reflect an additional direct, but delayed, stimulatory effect of IL-6 on the adrenal cortex. In vitro, such a direct stimulatory effect on the adrenocortex has been demonstrated after prolonged exposure to IL-6 (6). A direct, but delayed, stimulation of adrenal cortisol secretion by IL-6 could also explain why during chronic treatment with IL-6, i.e. on day 21 of the present study, cortisol re- sponses were preserved, whereas ACTH responses were attenuated, probably due to feedback inhibition by cortisol.
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Comparable observations have been made by Mastorakos et al. (12).
It seems unlikely that the effect of IL-6 on ACTH and cortisol release in our patients was nonspecific, caused, for example, by IL-6-induced fever or the stress of treatment. The aforementioned data from animal and in vitro studies regarding the mechanisms underlying the influence of IL-6 on HPA secretory activity argue strongly against a nonspe- cific mode of action in humans. Furthermore, except for the elevation of body temperature, no significant differences in other vital signs (heart rate, blood pressure, or respiration rate) between the days on IL-6 treatment and the baseline day before treatment were noted. Moreover, the increase in body temperature after IL-6 administration lagged behind the increase in pituitary-adrenocortical secretory activity. Al- though plasma concentrations of ACTH and cortisol reached a maximum 2-4 h after IL-6 injections, the maximum in- crease in body temperature was 7 h after IL-6 injections. Elevated plasma ACTH and cortisol levels after IL-6 treat- ment were also found in two patients who did not show a considerable increase in body temperature (<1 C). These observations exclude a causative role of body temperature for the early increase in ACTH and cortisol secretion after the rise in IL-6 plasma levels.
The increase in plasma ACTH and cortisol during treat- ment with IL-6 in man, as demonstrated here, suggests that IL-6 belongs to the cytokines with an essential regulatory role in the interaction between the immune system and the HPA axis.
Acknowledgments
We thank A. Fischer, A. Otterbein, A. Szmaragowska, and C. Zinke for technical assistance.
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