Mechanisms for the Development of Esophageal Atresia
By J. Orford, P. Manglick, D.T. Cass, and P.P.L. Tam
Westmead, Australia and Sydney, Australia
Background:
There is no universally accepted theory to ex-
plain esophageal embryology and the abnormal develop-
ment that produces esophageal atresia.
Methods:
The impact of Adriamycin administration on the
pathogenesis of esophageal atresia was studied in the rat
model of VATER association, from embryonic day (ED) 10 to
ED 13.
Results:
Tissues in the ED10 Adriamycin-exposed embryos
displayed less cell proliferation as shown by the reduced
population of MIB-5–labelled cells. Cell apoptosis that is
characteristic of the normal ED 12 lateral epithelial folds of
the foregut (the prospective site of tracheoesophageal sep-
tation) was absent in the foregut of the Adriamycin-exposed
embryo. Histologic examination of the ED 11-exposed em-
bryo showed the presence of abnormal notochord that was
stretched, split, or tethered to the foregut. This contrasts with
the normal embryo in which the notochord was localized in
close vicinity of the ventral part of the neural tube and
separated from the foregut by ample amount of mesen-
chyme. The abnormal localization of the notochord was
accompanied by the lack of down-regulation of the sonic
hedgehog (Shh) activity in the prospective site of future
tracheoesophageal separation in the exposed ED 12 embryo.
Conclusion:
The authors proposed that the ectopic location
of the notochord leads to the disruption in Shh signalling
that may underpin the development of esophageal atresia.
J Pediatr Surg 36:985-994. Copyright
©
2001 by W.B.
Saunders Company.
INDEX WORDS: Esophageal atresia, tracheoesophageal fis-
tula, notochord, Sonic hedgehog, apoptosis, VATER, Adria-
mycin.
T
HE ADRIAMYCIN rodent model of VATER asso-
ciation
1-18
has presented the opportunity to study
this nongenetic congenital anomaly and associated con-
ditions. We and others have shown that Adriamycin-
exposed rat embryos develop esophageal atresia,
1-4,6,9-17
and that it is accompanied by anomalies in the noto-
chord.
12,15,16,18
Adriamycin is an anthracycline antibiotic
and has multiple mechanisms by which it exerts its
cytotoxic effects. These include inhibition of some im-
portant cellular enzymes: topoisomerase II, RNA poly-
merase, and cytochrome c oxidase.
19-22
Also, it affects
DNA integrity and synthesis by intercalation
21,23
and
produces free radicals and toxic metabolites.
21,24
Our initial approach was to study apoptosis as a
potential mechanism for Adriamycin’s teratogenic effect.
Apoptosis, or programmed cell death, is a gene-directed
cellular process, and during embryogenesis it is impor-
tant for organ differentiation.
25
During our early apopto-
sis analysis
15
we noted that the notochord was abnormal
in the Adriamycin-exposed embryos, prompting us to
further examine the defects of the notochord. In the rat
embryo, the notochord is derived from cells of the node
and forms along most of the cranio-caudal axis underly-
ing the neural tube. Rostrally, the notochord is incorpo-
rated into the roof of the foregut but later is separated
from the foregut by the perinotochordal and splanchnic
mesenchyme.
26
The notochord has been shown in em-
bryologic experiments to play a critical role in the in-
ductive interaction that patterns the tissues in the neural
tube, the paraxial mesoderm, and the endodermal deriv-
atives of the gut. We postulated that a deficiency in the
notochord patterning activity leads to esophageal atresia.
Our results show a possible causal relationship of the
notochord anomalies to failure in tracheoesophageal sep-
aration. Analysis of cell proliferation and apoptosis
points to a possible mechanism for Adriamycin’s terato-
genesis, and this may be mediated by the disruption of
the sonic hedgehog (Shh) signalling activity of the no-
tochord. We propose that a nonspecific teratogenic insult
to the human embryo leads to a common pathway of
disturbed notochordal signalling, and this may account
for the association of esophageal atresia and other con-
genital anomalies.
MATERIALS AND METHODS
Adriamycin Treatment to Induce Esophageal Atresia
Adriamycin (1.75 mg/kg/d) was administered intraperitoneally to
time-mated Sprague Dawley rats on embryonic days (ED) 6, 7, 8, and
9. Control animals were given normal saline. Embryos were harvested
From the Department of Surgical Research, Royal Alexandra Hos-
pital for Children, Westmead, Australia; the Department of Paediatrics
and Child Health, University of Sydney, Sydney, Australia; and the
Embryology Unit, Children’s Medical Research Institute, Westmead,
NSW, Australia.
J.O. was supported by a NHMRC Medical Postgraduate Scholar-
ship, and P.P.L.T. is a NHMRC Principal Research Fellow.
Address reprint requests to J.E. Orford, Surgical Services Depart-
ment, Princess Margaret Hospital for Children, Roberts Rd, Subiaco,
Western Australia, 6008.
Copyright © 2001 by W.B. Saunders Company
0022-3468/01/3607-0004$35.00/0
doi:10.1053/jpsu.2001.24722
985
Journal of Pediatric Surgery,
Vol 36, No 7 (July), 2001: pp 985-994