International Scholarly Research Network
Volume 2012, Article ID 592648, 6 pages
SerumLevelsof Fetal Antigen 1inExtremeNutritional States
AlinAndries,1AndreasNiemeier,2Rene K.Støving,1Basem M.Abdallah,1
2Department of Orthopedics and Department of Biochemistry and Molecular Cell Biology,
University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
3Department for General, Visceral, and Transplantation Surgery, University Hospital Ulm, 89069 Ulm, Germany
4Stem Cell Unit, Department of Anatomy, College of Medicine, King Saud University, Riyadh 11461, Saudi Arabia
Correspondence should be addressed to Alin Andries, firstname.lastname@example.org
Received 29 April 2012; Accepted 22 May 2012
Academic Editors: G. Garruti, J. A. Rillema, and C. G. Scanes
Copyright © 2012 Alin Andries et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Objective.Recent data suggest that fetal antigen (FA1) is linked to disorders of body weight. Thus,we measured FA1 serum levels in
two extreme nutritional states of morbid obesity (MO) and anorexia nervosa (AN) and monitored its response to weight changes.
Design. FA1 and insulin serum concentrations were assessed in a cross-sectional study design at defined time points after gastric
restrictive surgery for 25 MO patients and 15 women with AN. Results. Absolute FA1 serum levels were within the assay normal
inversely correlated with BMI before and after weight change in AN, but not in MO patients. In addition, MO patients displayed
a significant concomitant decrease of FA1 and insulin with the first 25% of EWL, while in AN patients a significant increase of
FA1 was observed in association with weight gain. Conclusion. FA1 is a sensitive indicator of metabolic adaptation during weight
change. While FA1 serum levels in humans generally do not correlate with BMI, our results suggest that changes in FA1 serum
levels reflect changes in adipose tissue turnover.
Fetal antigen 1 (FA1), also known as preadipocyte factor 1
(pref-1) or Delta-like 1 (Dlk1), was originally isolated from
amniotic fluid . It is a member of the epidermal growth
factor (EGF) superfamily. FA1 refers to the soluble form of
the protein which is released into the circulation and body
fluids after proteolytic cleavage of the larger membrane-
bound Dlk1 . FA1 is a growth and differentiation
factor widely expressed during fetal development and is
progressively downregulated after birth . In adults, FA1
is expressed in neuroendocrine tissues, for example insulin
producing beta cells of the islets of Langerhans, growth
hormone producing cells in the pituitary gland , adrenal
glands, and sex hormone-producing cells of the gonads [3,
5], as well as specific areas in the central nervous system .
for example, adipogenesis , neuroendocrine differentia-
tion , hepatocyte differentiation , hematopoiesis ,
and osteogenesis [9, 10]. FA1 can be measured in serum and
body fluids using ELISA assay, and its levels do not differ
age-related changes beyond adolescence, diurnal variation,
or variations during the menstrual cycle [11, 12].
Recent data from genetically modified mouse models
suggest a role of FA1 in adipose tissue turnover. Dlk1-
deficient mice exhibit an obese phenotype associated with
with high serum levels of FA1 display a decreased fat mass, a
phenotype reminiscent of lipodystrophy, decreased glucose
tolerance, and insulin resistance [14, 15]. Also, recent mouse
studies suggested that Pref-1/FA1 is a factor which may
influence the susceptibility to the metabolic syndrome. FA1
inhibited adipogenesis and prevented diet-induced obesity
. In humans, the relationship between FA1 serum levels
and total body mass or fat mass is less clear. In the human
syndrome of maternal uniparental disomy (matUPD14)
where Dlk1/Pref-1 is silent, the patients exhibit a number of
2 ISRN Endocrinology
developmental abnormalities including obesity, hypotonia,
premature puberty, macrocephaly, short stature, and small
In order to further elucidate the relationship between
we studied two extreme nutritional states, morbid obesity
(MO) and anorexia nervosa (AN), before and after weight
The WHO defines a body-mass index (BMI) above
40kg/m2as class III obesity (or morbid obesity (MO)) and
bariatric surgery is the only effective treatment option for
ensuring weight loss and significant improvement in the
metabolic state [19–22]. On the other extreme of patholog-
ical nutritional states, AN is a psychiatric disorder primarily
characterized by a self-induced weight loss under the WHO
defined lowest normal BMI of 18.5kg/m2. Patients with
AN exhibit complex endocrine and metabolic alterations
occurring in AN in response to undernourishment and
Little is known about serum levels of FA1 in these
extreme nutritional states of MO and AN. Two cross-
sectional studies have been published on the subject, report-
ing elevated FA1 serum levels in both MO patients  and
AN patients  as compared to healthy controls. Thus,
the goals of the current study are to (a) asses FA1 levels of
MO and AN patients and (b) analyze changes of FA1 levels
in response to weight loss of MO and weight gain of AN
patients. As FA1 is produced in pancreatic beta cells, we
also investigated if there was a correlation between FA1 and
changes in insulin levels under these nutritional conditions.
2.1. Obese Subjects. Twenty-five obese subjects, 17 women
and 8 men, with a median age of 40 (range 24–56) and
median BMI of 48kg/m2(range 41–70kg/m2) underwent
Germany. To qualify for the study, patients fulfilled the
criteria established by the American Society for Bariatric
Surgery . The bariatric surgery (gastroplasty) was per-
formed according to the standards for laparoscopic and
open surgical treatment of morbid obesity. In all the
MO patients, anthropometrics and metabolic indices were
measured preoperatively and at defined points of excess
weight loss (EWL) of 25%, 50%, and 75% after surgery.
FA1 was measured in all patients before and in 21 patients
fasting, while at the follow-up consultations patients did not
strictly adhere to this recommendation.
2.2. AN Patients. Fifteen women with AN were studied
at the specialized unit for Eating Disorders at Odense
University Hospital, Denmark. The diagnosis of AN was
based on the criteria from DSM-IV . Mean age was
23.4 years (range 16–41 years). Median BMI was 15.30kg/m2
(range 12.0–17.0kg/m2). All patients were outpatients. None
of the patients suffered from primary endocrine diseases,
nor were they taking any medication known to influence
fat metabolism or the nutritional state. All patients were
amenorrheic and none were taking oral contraceptives. The
local scientific ethical committee approved the study. All
participants signed written informed consent.
In the AN group, body weight and height were measured
and BMI was calculated at the study start and after 2–6
months in all subjects. The BMI changes were rather small
(median increase of 3.45% from baseline) but statistically
significant (P < 0.01) corresponding to an approximate
weight gain of more than 10%. Serum FA1 and insulin were
followup. FA1 was measured in all 15 AN patients. In the AN
group fasting blood glucose and insulin were measured for
11 out of 15 patients before weight change and 10 patients
after weight change.
2.3. Biochemical Analysis. Serum FA1 was quantified using a
sandwich ELISA employing polyclonal anti-FA1 antibodies
purified by immunospecific affinity chromatography. The
in detail . The reference interval for serum (s)-FA1
was 12.3–46.6ng/mL (age 19–60 years) . Glucose was
determined by the glucose dehydrogenase method (Merck,
patients it was determined by a double-antibody RIA (Kabi,
Pharmacia Diagnostics, Uppsala, Sweden).
2.4. Statistics. The statistical analyses were performed using
SPSS version 15.0 (SPSS, Chicago, IL, USA) and STATA/IC
12.0 (StataCorp, College Station, TX, USA). Comparisons
between groups were performed using the Mann-Whitney
U test. Mean ± SD and paired t-test were performed for
testing statistical t-changes within the same group. A natural
non-normal distribution. Bivariate correlations were esti-
mated using Pearson and Spearman’s coefficients. Statistical
significance in all analyses was P < 0.05.
of the patients are shown in Table 1. We found no significant
differences regarding FA1 levels in the two subgroups at
baseline (Table 1 and Figure 1). While FA1 did not correlate
with BMI at individual time points, we observed a slight
inverse correlation with BMI both before (r = 0.4; P =
0.012) and after (r = 0.45; P = 0.006) weight change in the
AN subgroup (Figure 2)
Upon weight loss in MO patients, FA1 decreased signif-
icantly at all time points of EWL as compared to baseline.
On the other hand, we observed a significant increase in FA1
levels in AN patients upon weight gain. Figure 3(a) shows
and after weight change.
In order to estimate the contribution of fat tissue to
the serum level of FA1, we calculated the amount of FA1
expressed per BMI unit. The FA1/BMI ratio was significantly
Table 1: Anthropometric and biochemical characteristics at baseline.
Overall (n = 40)
Obese (n = 25)
AN (n = 15)
Numbers indicate median (min-max).
¶n = 10;
∗P < 0.001.
Figure 1: Similar FA1 levels in MO and AN at baseline. Serum
levels of FA1 were similar at baseline in both MO (n = 25) and
AN (n = 15) patients. The error bars represent standard deviations
and confidence limits.
lower in the MO group (Figure 3(b)). In addition, we
observed that FA1/BMI ratio did not change significantly
(Figure 3(b)), while in MO it changed significantly at inter-
mediary EWL points. We also observed a significant, parallel
drop in both FA1 and insulin in MO during weight loss (data
not shown), while in AN insulin correlated significantly with
FA1 only before weight change (r = 0.65; P = 0.031).
By fitting our data to a multiple linear regression model,
we tested the effect of different covariates on the random
variation of the serum level of FA1. Both BMI (r = 0.39,
P < 0.001) and age (r = 0.34, P = 0.04) were found to have
a significantly negative effect on FA1. Interestingly, we found
same age and BMI, but this effect was not above the chosen
level of statistic significance (P = 0.09).
In the present study, we examined the possible use of FA1
as a biomarker for changes in fat mass and investigated the
dynamic changes of its serum levels during weight change in
patients at two extreme nutritional states: MO and AN.
We did not detect any differences in serum levels of
FA1 between MO and AN in our study, and their levels
were within the normal range of our ELISA assay. Previous
studies have shown that serum levels of FA1 in MO 
and AN  were significantly higher compared to lean
controls. In these studies, the absolute values of serum FA1
levels were within the normal range of our assay (12.3–
46.6ng/mL) , but the assays employed in these studies
were different, thus not directly comparable. The absence of
significant changes in serum FA1 levels between MO and
AN is at variance with our findings in rodent models. Our
group has previously studied the effects of circulating FA1
on fat mass in vivo in mice with high serum levels of FA1
(198 ± 74ng/mL)  and found that increased serum level
of FA1 was associated with a significant reduction of total
body weight and fat mass. Also, dlk1/FA1-overexpressing
mice exhibited decreased fat mass [14, 15]. Our results
confirm these findings in humans, showing that the serum
levels of FA1 were significantly inversely correlated with
BMI, independently of the individual nutritional status. The
available data in humans, therefore, suggest that steady state
levels of serum FA1 are not a sensitive biomarker for the
nutritional state of an individual.
The serum level of several adipokines (e.g., leptin) corre-
lates with fat mass. FA1 is produced by adipocyte precursors
and its expression is downregulated in mature adipocytes
. Thus, we expressed FA1 per BMI in order to estimate
the contribution of fat tissue to FA1 serum levels. We found
that the ratio of FA1/BMI in MO was significantly lower than
in the AN group and it changed significantly during weight
loss, suggesting that newly recruited adipocyte precursors
contribute to serum pool of FA1. The presence of an inverse
correlation between FA1 and BMI in AN, but not in MO
patients, suggests that fat tissue undergoes a higher degree
of turnover in AN than in MO. Our findings that a minor
weight gain of 10% in the AN group was accompanied
by a significant increase in serum FA1 levels, while in the
MO group a significant fall in FA1 levels occurred after
bariatric surgery with 25% EW, corroborate this hypothesis
reflect change in fat tissue mass.
A significant correlation between baseline serum levels of
FA1 and insulin levels was found the AN group and not in
the MO. However, the absence of the correlation in the MO
group may have been caused by the inconsistency in obtain-
ing fasting samples in this group. It is not clear whether
changes in serum FA1 was caused by changes in insulin
levels since FA1 is produced in pancreatic beta cells .
In contrast with previous reports, we found that serum FA1
4 ISRN Endocrinology
70 60 5040
38 3634 323028
After weight change (75% EWL)
18 1614 12
After weight change
Figure 2: FA1 correlates with BMI in AN but not in MO. (a) We found no significant correlation between FA1 and BMI in MO, neither at
baseline nor after weight change. (b) In AN, we found that FA1 slightly correlated to BMI both before (FA1 = 90.5−4.6 ∗ BMI, R-squared =
0.4; P = 0.012) and after (FA1 = 122.9−6.3 ∗ BMI, R-squared = 0.45; P = 0.006) weight change.
levels are inversely correlated to age and might be influenced
by sex, sustaining our previously reported reports on the
possible regulation of serum FA1 by systemic hormones, for
example estrogen  and growth hormone . However,
further studies are needed to confirm the relationship
between insulin production and serum levels of FA1.
In conclusion, steady state serum FA1 in human adults is not
a biomarker for fat mass but it can be employed to monitor
acute changes in fat mass. We propose that these changes
in serum FA1 are caused by changes in the pool of FA1-
periods of acute turnover of adipose tissue, a hypothesis
which will have to be confirmed by other studies.
pref-1: preadipocyte factor,
Dlk1:delta-like preadipocyte factor,
EGF: epidermal growth factor,
MO: morbid obesity,
EWL: excess weight loss,
BMI:body mass index,
WHO: World Health Organization,
SOS:Swedish Obese Subjects study.
P < 0.01
P < 0.01
P < 0.01
P = 0.03
P < 0.01
P = 0.01
P = 0.02
P = 0.02
Figure 3: (a) FA1 levels decrease with weight loss in MO and increase with weight gain in AN. FA1 levels changed significantly both during
and after weight change. The error bars represent standard deviations and confidence limits. (b) The FA1/BMI ratio is lower in MO and
remains constant upon weight change. In MO, FA1/BMI ratio was lower than in AN. It decreased significantly at 25% EWL, followed by a
slow ascending course to the initial levels. The error bars represent standard deviations and confidence limits.
Haskell Foundation for Child Mental Health Research of
Copenhagen and Institute of Clinical Research, University of
Southern Denmark. The authors declare that there are no
competing financial interests in relation to this paper.
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