Therapeutic Nonresponsiveness in Major Depression
Gideon Goldstein, Maurizio Fava, Michael Culler, Alan Fisher, Karl Rickels,
R. Bruce Lydiard, and Jerrold Rosenbaum
Background:
Stress predisposes to major depression, and
hyperactivity of the stress-activated
hypothalamic-pitu-itary-adrenal (HPA) axis occurs in this disease.
Thymo-pentin, an active fragment of thymopoietin (TP), reduces
endocrine and behavioral responses to experimental
stress, possibly by lowering plasma TP (pTP) levels.
Methods:
Plasma TP and the HPA hormones arginine
vasopressin (pAVP), adrenocorticotropic hormone (pACTH),
and plasma cortisol (pCORT) were measured in 21
un-treated depressed patients and 21 matched control
sub-jects. Clinical responses to antidepressants were
evalu-ated in 17 depressed patients.
Results:
Plasma TP was elevated in depression (
p
,
.002), with in 8 out of 21 (38%) depressed patients having
significant elevations (
p
,
.03). For 17 patients whose
antidepressant responses were evaluated,
nonresponsive-ness occurred in 6 out of 7 (86%) with elevated pTP (
.
7.5
pg/mL) versus 3 out of 10 (30%) with normal pTP (
p
,
.05).
Conclusions:
The significant association of elevated
pTP with nonresponsiveness to antidepressant drugs
may signify a distinct pathogenesis for the depression of
patients with elevated pTP.
Biol Psychiatry 2000;48:
65– 69 ©
2000 Society of Biological Psychiatry
Key Words:
Major depression, plasma thymopoietin,
plasma arginine vasopressin, pulsatile secretion,
therapeu-tic response, stress
Introduction
E
arly adverse life events and chronic stress predispose
to major depression (Heim et al 1997), a highly
prevalent disease causing extensive morbidity (Kessler et
al 1994; Lopez and Murray 1998). The synthetic
thymo-poietin (TP)-derived peptide thymopentin (Goldstein et al
1979) and its analog IRI-514 attenuate experimental stress
responses in rats (Klusa et al 1990; Menzaghi et al 1996)
and also appear to lower levels of pTP (unpublished data).
Thus, plasma thymopoietin (pTP), which circulates as a 20
kd protein corresponding to the N-terminal 187 amino
acids of larger intracellular forms of TP (Berger et al 1996;
Harris et al 1994), may be involved in stress responses
associated with depression.
Corticotropin releasing factor (CRF) is a critical
medi-ator of behavioral stress responses within the brain (Koob
et al 1993), and activation of the
hypothalamic-pituitary-adrenal (HPA) axis is a peripheral manifestation of CRF
hypersecretion in major depression (Owens and Nemeroff
1993). Although antidepressant drugs are widely used and
effective, nonresponse to antidepressant treatment of
ade-quate dose and duration is observed in 19% to 34% of
patients (Fava and Davidson 1996; Keller et al 1995). We
studied the plasma levels of TP and of the HPA hormones
arginine vasopressin (AVP), adrenocorticotropic hormone
(ACTH), and cortisol as possible biologic correlates of
depression or responsiveness to antidepressant drugs.
Methods and Materials
Study Population
Twenty-one untreated outpatients (11 men, 10 women) fulfilling the DSM-III-R criteria for a current major depressive episode lasting at least 1 month were studied along with 21 age-matched (within 2 years) and gender-matched normal control subjects. Depressed patients were free of antidepressant drugs for 1 month before obtaining the plasma samples. Routine hematology, blood chemistry, and urinalysis tests were performed. A medical history, complete physical exam, and psychiatric evaluation with the structured clinical interview for DSM-III-R (SCID-P) were obtained for all subjects plus the 17-point Hamilton Depression Rating Scale (HDRS). A depression rating greater than 16 was required at entry. The protocol was approved by Institutional Review Boards, and all subjects signed Informed Consent forms. The 17 depressed study subjects from the Depression Clinical and Research Program of the Massachusetts General Hospital were entered into one of two trials involving open treatment for 8 weeks with fluoxetine 20 mg daily or nortryptiline 50 –150 mg
From Thymon, L.L.C., Short Hills, New Jersey (GG); Massachusetts General Hospital, Boston (MF, JR) and Biomeasure, Inc., Milford (MC), Massachu-setts; R W Johnson Pharmaceutical Research Institute, Raritan, New Jersey (AF); Psychopharmacology Unit, University of Pennsylvania, Philadelphia (KR); and Psychopharmacology Unit, Medical University of South Carolina, Charleston (RBL).
Address reprint requests to Gideon Goldstein, M.D., Thymon, L.L.C., 30 Dorison Drive, Short Hills NJ 07078-1701.
Received August 4, 1999; revised December 21, 1999; accepted January 3, 2000.
daily to maintain a therapeutic plasma range of 50 –150 ng/mL. Response data from these patients was utilized to determine, in a blinded fashion, the clinical responses to drug treatment, using an intent-to-treat analysis. A full response required a decline of the HDRS.50% to #7 and a partial response required a 25% to 50% decline in depression rating (Fava et al 1994).
Immunoassay Procedures
Two 90-mL blood samples, the first drawn between 8 and 9AM
and the second between 4 and 6PM, were drawn into prechilled EDTA-vacutainer tubes, centrifuged in the cold, and the plasma aliquoted into chilled polypropylene tubes and stored at270°C to280°C. Commercial radioimmunoassay kits from Diagnostic Systems Laboratories (Webster, TX; AVP) and ICN Biomedicals (Costa Mesa, CA; cortisol) were used in accordance with the manufacturers’ instructions, and ACTH was measured as previously described (Nicholson et al 1984) using reagents from IgG Corp. (Nashville). pTP was measured by ELISA as previously described (Goldstein and Culler 1997). Briefly, plasma was extracted using a C-18 SepPak and assayed with a sandwich ELISA using affinity purified rabbit antibody to synthetic TP1–19for capture
and mouse monoclonal antibody to synthetic TP30 –50(6E10) as
the detector antibody. Synthetic TP1–50was used as a standard.
More recently, a direct high-sensitivity plasma TP assay has been developed in collaboration with R&D Systems (Minneapolis).
Statistical Analyses
Statistical analyses were performed on Prism Version 3.0, GraphPad Software (San Diego) unless otherwise specified. The significance of depression and control subjects and AM/PM
differences was assessed by repeated measures two-way ANOVA using SAS (SAS Institute, Cary, NC). With no signif-icant differences inAM/PM values, the mean AM/PM values in each subject were used for subsequent comparisons. Between-group differences were assessed with a two-tailed t test with Welch’s correction. Correlation of TP and AVP values in depression was assessed with the Spearman correlation coeffi-cient. pTP and pAVP distributions tested as Gaussian and cutoff values of mean 1 1.645 SD in control subjects were used to define significant elevations (p , .05). Fisher’s exact test,
two-tailed, was used to analyze 232 contingency tables;p.
.05 was considered nonsignificant.
Results
Study Subjects
Twenty-one depressed subjects (22 men, 20 women) aged
40
6
12 (mean
6
SD) and 21 matched control subjects
with identical age and gender distributions were entered
into the study. HDRS scores at entry were 23
6
4 in
depressed patients and 1
6
1 in control subjects (mean
6
SD; Table 1).
Comparisons of Depressed and Control Subjects
and
AM/
PMDifferences
Plasma TP (
p
,
.002) and pAVP (
p
,
.002) levels were
significantly elevated in depressed subjects but there were
no significant between-group differences in pACTH or
pCORT levels. None of the hormones showed significant
AM/
PMdifferences nor was there a significant
group-by-time interaction. The mean
AM/
PMvalues for each
param-eter similarly reflected these differences (Table 1).
Incidence of Elevation of pTP and pAVP Levels in
Depression
Using cut-off values of 7.5 pg/mL for pTP and 5.0 pg/mL
for pAVP, pTP was elevated in 8 out of 21 (38%)
depressed subjects versus 1 out of 21 (5%) control subjects
(
p
,
.03; Figure 1), and pAVP was elevated in 6 out of 21
(29%) depressed subjects versus 1 out of 21 (5%) control
subjects (ns).
Figure 1. Scattergram of mean AM/PM plasma thymopoietin (pTP) levels in 21 depressed patients and 21 matched control subjects. The dotted line at 7.5 pg/mL represents the cut-off value (p,.05 for values above this in control subjects). Table 1. HDRS Scores and pTP, pAVP, pACTH, and pCORT
Levels in 21 Depressed Subjects and 21 Matched Healthy Control Subjects
Control subjects (mean6SD)
Depressed subjects
(mean6SD) pvaluea
HDRS 161 2364 ,.0001
pTP (pg/mL) 5.261.4 7.763.0 .002 pAVP (pg/mL 2.961.3 4.962.4 .002
pACTH (pg/mL) 1769 1769 ns
pCORT (pg/mL) 1469 1466 ns
HDRS, Hamilton Depression Rating Scale; pTP, plasma thymopoietin; pAVP, plasma arginine vasopressin; pACTH, plasma adenocorticotropic hormone; pCORT, plasma cortisol.
Decreased Clinical Response Rate in Subjects with
Elevated pTP
Among depressed subjects, 41% (7 out of 17) of those
treated with fluoxetine (13) or nortryptiline (4) had full (5)
or partial (3) responses. 86% (6 out of 7) of patients with
elevated pTP were nonresponders versus 30% (3 out of
10) nonresponders in patients with normal pTP (
p
,
.05;
Figure 2). The response rates for subjects divided on the
basis of pAVP levels did not differ statistically.
Relationship between pAVP and pTP in Depressed
Subjects
Plasma AVP elevations were found in 3 out of 8 (38%)
subjects with elevated pTP versus 3 out of 13 (23%)
subjects with normal pTP (ns). There was no significant
correlation between pTP and pAVP levels in depressed
subjects (Spearman
r
5
.39, ns).
Discussion
Early morning and late afternoon plasma levels of the
HPA hormones ACTH and cortisol did not prove useful
diagnostic measures in major depression. AVP secretion is
pulsatile (Redekopp et al 1986; Wood et al 1994) and HPA
hyperactivity in depression is related to a greater
fre-quency of episodic hormone release (Deuschle et al 1997).
This can be gauged by frequent sampling over 24 hours
(Deuschle et al 1997) or by measuring 24-hour urinary
cortisol secretion (Carroll et al 1976). These methods have
not found widespread acceptance in clinical practice,
however. Using only two samples, we found an increase of
48% in mean pAVP level in depression, a 29% incidence
of patients with elevated pAVP, and no detectable diurnal
rhythm, findings similar to those of van Londen et al
(1997), with a mean pAVP increase of 68%, an incidence
of elevated pAVP of 31% and no detectable diurnal
rhythm. In contrast to our findings of no depression related
changes in pCORT, however, van Londen et al (1997)
found a 20% elevation of mean plasma cortisol in
depres-sion and a statistically detectable diurnal rhythm in their
study of 52 depressed patients and 37 control subjects.
Depression-related or diurnal changes in pCORT appear
small in relation to individual variation and apparently
require large numbers of subjects for statistical detection.
pAVP elevations in depression probably reflect the
in-creased statistical probability of sampling higher levels
during longer and more frequent secretion pulses of AVP,
and patients with elevated pAVP do not appear to
repre-sent a biologically distinct group. Accordingly, there was
no significant correlation of pAVP elevation with the
clinical response status of patients treated with
antidepres-sant drugs.
In contrast, pTP was elevated in 7 out of 17 depressed
subjects whose clinical responses to antidepressant drugs
were evaluated, and most of the subjects with elevated
pTP failed to respond to fluoxetine or nortryptyline.
Nonresponse to antidepressant drugs is found in 19% to
34% of depressed subjects (Fava and Davidson 1996;
Keller et al 1995), and it was interesting that pTP
eleva-tions were present in 6 out of 9 (67%) nonresponders but
only 1 out of 8 (13%) full or partial responders. Fluoxetine
and nortriptyline modify CRF and AVP release by
regu-lating serotonin pathways, catecholamine pathways, or
both (De Bellis et al 1993; Veith et al 1993). Nonetheless,
CRF and AVP release can be triggered through alternative
pathways (Plotsky et al 1988) and, if TP were such a
serotonin- and catecholamine-independent stress mediator,
it could explain our finding of poor therapeutic responses
in depressed patients with elevated pTP.
Animal data provide some additional clues.
Thymopen-tin pretreatment in mice and rats inhibited stress-induced
behavioral changes, alterations in hippocampal GABA,
and benzodiazepine receptor densities and elevations of
plasma corticosterone levels, but it did not affect these
parameters when administered alone (Klusa et al 1990).
IRI-514, an analog of thymopentin, was similarly
stress-protective (Menzaghi et al 1996). IRI-514
dose-depen-dently reversed the behavior induced by social stress if
administered at least 1 day earlier, and the effect lasted for
several days. Because small peptides are eliminated
rap-idly (Adsumali et al 1996), direct action of the peptide
could not account for these long-lasting modulatory
ef-fects on behavior. pTP was measured in normal human
volunteers during a phase I study of an orally active
Figure 2. Column bar graph showing low incidence of responsethymopentin analog, IRI-695 (Adsumali et al 1996), and
statistically significant decreases in pTP were found
start-ing 12 hours after a sstart-ingle oral dose and persiststart-ing through
2 days, the last time point measured (GG, unpublished
observations). Thus the behavioral effects of thymopentin
and its analogs may be mediated via reduction of pTP
levels, and pTP may be a mediator or regulator of
stress-induced behavioral changes.
There is a growing literature on intranuclear proteins
encoded by the thymopoietin gene, which are involved in
cell cycle regulation of nuclear organization (Alsheimer et
al 1998; Berger et al 1996; Harris et al 1995; Weber et al
1999). Nonetheless, the immunoassay described in this report
is novel and the physiological role of pTP awaits elucidation.
The lack of correlation of pTP and pAVP in depression
suggests that pTP is not a component of the HPA system
although the relation of pTP to stress remains to be
eluci-dated. The levels of pTP in the psychiatrically evaluated
control subjects in our study were similar to those of a
randomly selected sample of 40 healthy volunteers, and there
were no detectable age- or gender-related effects on pTP
levels (GG, unpublished observations). There are presently
no systematic studies of pTP levels in other disorders.
Although the high incidence of nonresponders in
sub-jects with elevated pTP was statistically significant, the
finding is not robust because the small sample size
enhances the possibility of a Type I statistical error. If the
present findings prove reproducible, pTP assay could be
useful in the study of depression. Drugs related to
thymo-pentin may offer new therapeutic possibilities for patients
with elevated pTP who are nonresponsive to standard
antidepressant drugs.
This project was supported by funds from Immunobiology Research Institute (IRI), Annandale, New Jersey. Patient and sample acquisitions and performance of immunoassays were carried out while Gideon Goldstein, Michael Culler, and Alan Fisher were at IRI. The authors thank Linda Meyerson and the Clinical Research staff at IRI for their valued support and Meredith Rankin for evaluating the case records of study subjects at the Massachusetts General Hospital.
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