RETURN TO TABLE OF
Corticotropin-Releasing Hormone in
Chronic Fatigue Syndrome
The following is a preliminary report from a study funded by a grant from The
CFIDS Association of America. The Association has issued a new Request for
Applications for studies relating to chronic fatigue syndrome (CFS). For more
ow cortisol and
high interleukin-6 (IL-6) have been associated with the symptoms of chronic
fatigue syndrome (CFS). The purpose of this study is to investigate the role of
endogenous IL-6 in the pathogenesis of all or part of the CFS symptom
Hypocortisolism in CFSOver the past few years increased
emphasis has been placed on the hypothalamic-pituitaryadrenal (HPA) axis
activity in patients with CFS. Adrenal insufficiency shares several symptoms
with CFS (such as flulike symptoms, fatigue, malaise, arthralgias, myalgias,
sleep abnormalities, headaches, dizziness and decreased memory). Given the
similarity of the symptomatology of these two disorders, the HPA axis of CFS
patients has been studied by several investigators.
Hypoactivity of the HPA axis, resulting in low cortisol
production, has been implicated in the pathogenesis of this disorder.
Investigators showed that patients with CFS had subnormal adrenal response to
different doses of ACTH, indicating chronic HPA axis underactivity. These
findings were supported by a subsequent study by Scott et al who
demonstrated that patients with CFS had small adrenal glands compared to normal
controls using computed axial tomography, suggesting adrenal atrophy.
Such findings have led many investigators to believe that CFS
is a state of "functional" hypocortisolism. Patients with CFS showed a normal
cortisol response when "stronger" stimuli of the HPA axis were applied, such as
insulin-hypoglycemia. These data indicate that, while patients with CFS suffer
from chronic hypocortisolism, they do not suffer from Addisons disease, which
is a nearcomplete destruction of the adrenal glands. The chronic
hypocortisolism, though, can have profound effects on several immune and
endocrine systems, further complicating the clinical picture of these patients.
Specifically, hypocortisolism can lead to overproduction of inflammatory
cytokines (such as IL-6), which in turn can further precipitate the symptom
complex of CFS.
Interleukin-6 in CFSGlucocorticoids have
a suppressive effect on the production of inflammatory cytokines, such as IL-6.
Conversely, glucocorticoid deficiency can result in overproduction of
inflammatory cytokines. We have shown that in cases of adrenal insufficiency (a
condition characterized by hypocortisolism) there is significant increase in
IL-6 production. The increased production of inflammatory cytokines is
responsible at least partially for the symptom complex of adrenal
insufficiency, which greatly overlaps with the symptom complex of CFS.
Overproduction of inflammatory cytokines, such as IL-6 has
been reported in states of CFS. However, others have failed to find such
elevation of basal production of inflammatory cytokines in CFS. A possible
explanation for such a disagreement in the literature may be that CFS is an
illness of remission and relapsesand tends to have a fluctuating clinical
Moreover, while patients with CFS may be "functioning" at
baseline, they clearly have difficulty functioning under physical or mental
stress. They typically try to limit their activities and their exposure to
stressful stimuli, so as not to trigger a CFS relapse.
Therefore, evaluation of biological parameters, such as IL-6,
at basal conditions may not be the best way to approach this illness
diagnostically. Rather, a provocative test needs to be applied. Provocative
testing is not uncommon in endocrinology; for example, the diagnosis of adrenal
insufficiency or that of growth hormone insufficiency cannot be made on the
basis of basal sampling, but rather requires the application of a provocative
test, such as an ACTH stimulation test for the former and an insulin-tolerance
test for the latter. Similarly, a stimulation test would be more appropriate for
the diagnosis of CFS. To date such a test does not exist.
The source of circulating IL-6 in humans has been an enigma for some time.
Recent studies have shown that adipose (fat) tissue contributes significantly to
the circulating IL-6 levels in humans. For example, several groups, including
ours, have found that IL-6 is produced by human adipocytes in vitro.
We are investigating the role of endogenous IL-6 in the
pathogenesis of all or part of the CFS symptom complex. The major advantage of
this approach is that the cytokine under investigation (IL-6) will not be
administered exogenously as a pharmacological agent. Instead, corticotropin-
releasing hormone (CRH) will be administered to the subject. This will lead to a
modest elevation of endogenous IL-6 concentration, which will approximate more
closely than exogenous IL-6 administration the cytokine status of patients with
CRH: a direct stimulant of
IL-6We chose corticotropin- releasing hormone (CRH) as a
stimulus for endogenous IL-6 production. CRH is known primarily for its role as
the major hypothalamic factor stimulating cortisol secretion. During stress
(immunological, physical, or psychological) CRH is secreted from the
hypothalamus, and stimulates the pituitary to secrete ACTH, which in turn
stimulates the adrenal glands to secrete cortisol.
Several lines of evidence suggest that CRH exerts actions independent of its
effects on cortisol secretion: i) CRH participates in the inflammatory response
in a mouse model; ii) in humans it has been shown to interfere with normal sleep,
however, it is unclear whether these effects are due to CRH per se or due to the
concomitant increase in circulating cortisol; iii) recently, CRH was shown to
affect fat metabolism in humans; iv) administration of antalarmin (a CRH
receptor type-1 antagonist) to non-human primates resulted in a decrease in
serum leptin concentration; and v) we recently found that incubation of primary
human adipocytes with CRH for 48 hours resulted in induction of lipolysis and
stimulation of interleukin- 6 (IL-6) and leptin production by these cells. Thus
it appears that fat (one of the major sources of circulating IL-6) is also a
major site of CRH action.
The stimulation of IL-6 secretion by CRH is intriguing and may
be an important link between the HPA axis and the, inflammatory cytokines in the
pathogenesis of CFS-like symptoms. Thus patients with CFS may have an
exaggerated IL-6 response to peripheral CRH, which would in-turn lead to or
exacerbate the symptom complex of this illness.
Our hypothesis is that chronic hypocortisolism leads to
increased production of inflammatory cytokines. Such chronic overproduction of
inflammatory cytokines can subsequently lead to the development of CFS
Study DesignIn the pilot study funded jointly by
the U.S. Centers for Disease Control and Prevention (CDC) and The CFIDS
Association of America, we sought to determine, whether CRH administration
results in increased plasma IL-6 in humans in vivo. To do so we infused CRH to
healthy volunteers in a double-blind, placebocontrolled pilot study. The pilot
study also served to determine the appropriate dose of CRH infusion for future
studies on CFS patients. The study was conducted at the Emory University
Hospital General Clinical Research Center (GCRC). Clinical Research Centers are
designed to provide an inpatient setting in which research protocols are
strictly adhered to by highly trained and experienced staff, minimizing errors
which may compromise study results.
Recruitment of subjects for the pilot study was restricted to
certain groups in order to increase statistical power. To eliminate
genderrelated variability and because CFS affects primarily middle-age women,
only female subjects (age 3050) were included in the pilot study. In addition,
hypothalamic- pituitary-adrenal (HPA) axis physiology varies among races. To
eliminate race-related variability, which would have a negative impact on the
statistical power of the study, only Caucasian subjects were recruited to the
To eliminate the variability due to the effects of the
menstrual cycle on the HPA axis and circulating cytokines, all subjects were
required to have normal menstrual cycles and were studied during the early
follicular phase (Days 47 of the menstrual cycle, Day 1 being the first day of the menstrual bleeding). They
were free of
medical illnesses, had no history of psychiatric illnesses and were on no
medications. In addition, all subjects were off any treatment with
glucocorticoids (oral, topical, or inhaled) for at least one year prior to
entering the study; they were off any treatment with any estrogen or
progesterone-containing medications for at least two months before entering the
study; they were off any non-steroidal antiinflammatory medications for at least
one week prior to entering the study; and acetaminophen-containing medications
if taken were discontinued at least 48 hours prior to entering the study.
Caffeine and alcohol ingestion were discontinued 72 hours
before being admitted for the inpatient part of the protocol. Only non-smokers
were admitted to the study. Because the adipose tissue is one of the major
sources of circulating cytokines and to increase the sensitivity of the study we
studied overweight, but not obese, subjects (BMI: 27- 30 kg/m2). Obese (BMI >
30 kg/m2) subjects were not studied because they were not considered to be
"healthy" volunteers, as obesity is by definition an illness.
administered as a 24-hour intravenous infusion instead of an IV bolus injection.
The 24- hour infusion was preferred over the bolus administration for the
following reasons: i) our preliminary in vitro data using primary
cultures of human adipocytes indicated that a prolonged infusion rather that an
IV bolus administration would be needed for biological effects to occur; ii) a
prolonged infusion would most likely result in a rather prolonged stimulation of
IL-6 production, which would better resemble the chronic characteristics of CFS
and related illness.
The optimal dose of CRH for stimulation of
IL-6 production was unknown. Thus a dose-response study design was implemented.
The study was conducted in a doubleblind fashion. The subjects received a bolus
(over 1 min) injection of placebo (normal saline) or ovine CRH (oCRH) at doses
of 0.01, 0.03, 0.1, 0.3 and 1 mcg/kg, reconstituted in normal saline. This was
followed immediately by an infusion of placebo or oCRH at doses of 0.01, 0.03,
0.1, 0.3 or 1 mcg/kg/hr, respectively for 24 hours. The maximum dose was 100
mcg/hr regardless of body weight (100 mcg is the maximum FDA-approved dose for
this medication). The Baxter Colleague Infusion Pump was used for the infusion.
Five subjects were studied per dose (including saline placebo), totaling 30
subjects., The doses of CRH were selected based on earlier studies showing the
minimum effective dose for the HPA axis to be 0.030.1 mcg/kg, and the maximum
13 mcg/kg. Blood was drawn hourly for 48 hours (24 hours before CRH infusion
and 24 hours during CRH infusion). Study parameters included: hourly
measurements of plasma cortisol, IL-6, tumor necrosis factoralpha (TNF-alpha),
and C-reactive protein.
Results Preliminary data showed that CRH
infusion at the dose of 1 mcg/kg/hr resulted in a significant increase in
plasma IL-6 concentration. C-reactive
protein (C-RP, which is a major index of systemic inflammation and is considered
as a surrogate marker of IL-6 action) increased after 1 mcg/kg/hr infusion
compared to placebo. Plasma TNFalpha (also known to be secreted by adipo-cytes)
was not increased during CRH administration. Plasma cortisol levels and urine
free cortisol excretion were increased in dose-dependent manner as
Study outcomesWe have shown that 24-hour CRH
infusion at 1 mcg/kg/hr results in elevation of circulating IL-6 levels in
healthy volunteers. We have also shown that CRH stimulates IL-6 secretion by
human adipocytes in vitro. We believe
that systemic CRH administration has a dual effect on IL-6: a direct stimulatory
one, and an indirect inhibitory one, the latter through stimulation of cortisol
release, which in turn suppresses IL-6 release.
Low doses of CRH failed to raise IL-6 levels significantly,
most likely due to the antagonistic effects of cortisol, which was stimulated at
the same time. However, CRH exerted its maximum effect on cortisol at the dose
of 0.3 mcg/kg/hr, as 1 mcg/kg/hr did not result in a further increase in
circulating cortisol levels, nor in a further increase in urine free cortisol.
CRH, therefore, had a stimulatory effect on circulating IL-6 and C-reactive
protein at 1 mcg/kg/hr.
We believe that at that dose CRH further stimulated IL-6
release by target organs, such as the adipose tissue, whilst it did not
stimulate cortisol release any further. The fact that the cortisol response to
CRH reached a "plateau" at 0.3 mcg/ kg/hr, whereas the IL-6 response did not,
confers an independent role, of CRH in a net increase in IL-6 release at 1 mcg/
kg/hr. The concomitant increase in circulating C-reactive protein further
demonstrates the physiological significance of the IL-6 increase. The effects of
CRH on IL-6 appear to be specific, since tumor necrosis factor (TNF)-alpha
levels (another inflammatorycytokine produced by fat) were not stimulated at any
CRH dose. In fact, plasma TNF-alpha levels were decreased at the two highest CRH
doses, most likely due to the known suppressive effect of cortisol on TNF-alpha
In summary, these preliminary data suggest that peripheral CRH
administration resulted in an increase in peripheral IL-6 levels. The CRH effect
on systemic IL-6 concentration may have resulted from a direct CRH effect on
IL-6 release by adipose cells.Our next study should help clarify the role of
CRH-IL-6 interaction in the pathophysiology of CFS. Our long-term objective is
to develop a diagnostic tool for CFS and design new treatment strategies,
targeting the HPA-cytokine axis.
Dimitris Papanicolaou, MD, is Assistant Professor of Medicine at Emory
This study was supported by The CFIDS Association of America through gifts
made by Howard and Margaret Arvey and the New Jersey Chronic Fatigue Syndrome