See related article, pages 223–230
Can Tissue Engineering Mend Broken Hearts?
Robert E. Akins
C
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disease, and the possibility that diminished cardiac function
may be recovered through the implantation of tissueengineered, biosynthetic constructs is compelling.
The need for advanced surgical implant materials is not the
only justification for cardiac tissue engineering research,
however. The development of tissue equivalents for use in
vitro could improve the testing of drugs and potential therapeutic agents and could expand our understanding of cardiac
cell biology. Large numbers of animals are used each year in
research, drug testing, drug development, pharmacological
testing, and education (more than 1.2 million in 1998,
excluding rats and mice, according to the USDA). Cell
culture alternatives are also routinely used in research and
testing; however, typical cell culture models confine cells to
a 2-dimensional configuration that does not resemble the
organization of cells within the intact tissue. With evidence
that cellular activities and responses are affected by organization and mechanical activities,6,7 there is an increasing need
to perform studies within the context of the intact cardiac
tissue. In addition, the numerous species differences between
humans and the animal models used for the research, development, and testing often preclude the use of data derived
from animal models to draw specific conclusions about what
may happen in humans. The development of human cardiac
tissue equivalents would alleviate some of the serious problems associated with species-specific effects. By virtue of
being of human origin and organized like tissue, such
constructs would provide superior cell culture models for
research, reduce the number of animals required for testing,
and improve the physiological relevance of in vitro testing.
Clearly, the development of either implantable materials or
tissue equivalents for use in vitro will require a large amount
of concerted effort. Fortunately, substantial groundwork for
this effort has been established over the past decades. The
first demonstration of in vitro cardiac cell culture was
provided by Burrows in the early 1900s.8,9 Ensuing generations of researchers have performed an enormous amount of
research using in vitro culture models. Examples of the many
contributions in this area include work on extracellular
matrix,10,11 studies of 3-dimensional models from suspension
culture,12 and details of mechanical force transduction affecting cardiomyocytes.13,14 Each of these may be especially
significant to tissue engineers. The application of the wealth
of information to potential regenerative therapies has only
recently begun.
Three general tissue-engineering approaches have been
attempted thus far. The first approach involves the implantation of cell suspensions directly into the heart. A number of
cell-implantation studies have been performed in animals15–19
and humans20,21 using a variety of cell types. Results from
these and related studies demonstrate that implanted cells can
incorporate into existing cardiac structures. This approach,
ardiac tissue engineering is an emerging field that
may hold great promise for advancing the treatment
of heart diseases. Cardiac tissue engineering is in its
infancy, and the overall field of tissue engineering, which was
formalized in the late 1980s at conferences and workshops
sponsored by the National Science Foundation, is still new
enough to warrant some description. By broad definition,
tissue engineering involves the construction of tissue equivalents through the manipulation and combination of living
cells and biomaterials. It is a multidisciplinary field combining diverse aspects of the life sciences, engineering, and
clinical medicine. The overall goal of tissue engineering is to
develop tissue equivalents for use in the repair, replacement,
maintenance, or augmentation of tissues or organs. Although
some aspects of cardiac tissue engineering research have been
ongoing for generations, albeit without being known as such,
directed efforts in the field are only beginning.
The main justification for cardiac tissue engineering initiatives is straightforward: congenital and acquired heart diseases are substantial health problems, and there is a limited
amount of donor tissue for use in surgical repairs. Heart
defects are the most common congenital defect and are the
leading cause of death in the first year of life.1,2 Congenital
heart defects may occur in as many as 14 of every 1000 live
births,3 and approximately 25 000 surgical procedures are
performed each year to correct them. Acquired heart diseases
also have a profound effect on the population, and despite
tremendous advances in medical and surgical treatments, it is
estimated that each year 20 000 to 40 000 Americans could
benefit from a heart transplant.4 Unfortunately, fewer than
2500 heart transplants are performed each year.4,5 One of the
principal reasons for the disparity between patient need and
procedures performed is the lack of donor material for
implantation. Furthermore, current treatments short of transplantation are essentially restricted to medical and surgical
approaches that address the sequelae of the primary defect,
and current approaches do not always restore lost structure
and/or function. A large number of patients who are not
necessarily candidates for transplant may benefit from
smaller structures like pieces of muscle, valves, or vessels.
There is a need for new approaches to treat profound heart
The opinions expressed in this editorial are not necessarily those of the
editors or of the American Heart Association.
From the Department of Biomedical Research, A.I. duPont Hospital
for Children, Wilmington, Del.
Correspondence to Robert E. Akins, PhD, Head of Tissue Engineering
and Regenerative Medicine Research, Dept of Biomedical Research, A.I.
duPont Hospital for Children, PO Box 269, Wilmington, DE 19899.
E-mail [email protected]
(Circ Res. 2002;90:120-122.)
© 2002 American Heart Association, Inc.
Circulation Research is available at http://www.circresaha.org
DOI: 10.1161/hh0202.105219
120
Akins
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however, may be of little clinical benefit when the local
cardiac structure cannot support cell seeding because it is
missing or seriously damaged. The second approach is
primarily materials-based and involves culturing cardiac cells
within pre-formed 3-dimensional mesh, foam, or ceramic
scaffolds.22–24 Some of the most promising studies have used
this approach. Shinoka et al25 demonstrated the use of a
biosynthetic pulmonary valve in sheep, and Sodian et al have
constructed trileaflet valves using biodegradable polyhydroxyalkanoate scaffolds.26,27 Li and coworkers28 –30 have
grown small 3-dimensional cardiac grafts and implanted them
into host myocardia and the right ventricular outflow tract.
Two critical observations from this work were the survival of
grafted material and the apparent vascularization of the
implants by the host circulation. Highly engineered scaffolds
could, in theory, direct the gross conformation of a construct,
influence the phenotype of cellular components, or direct
particular cells to specific sites within a construct. This
approach may prove immensely powerful in the eventual
production of large tissue equivalents. The third approach
involves the culture of cells in suspension with31–34 or
without12 orienting surfaces, matrix, or cell adhesion molecules. The establishment of structure through this last approach is apparently directed by the cell population or by the
mechanical and fluid environments of the culture. One
observation from these studies is that tissue architecture can
be formed without extensive 3-dimensional cues form the
matrix. For now, methods of this third type may be best suited
for studying tissue-engineering concepts or for producing
small implants or devices, but in the long-run the technologies will likely converge with the materials-based methods.
In an article in this issue of Circulation Research,35
Eschenhagen’s group uses the third type of approach to
provide one of the most advanced examples of engineered
cardiac tissue to date. The group used a modification of a
previous procedure in which cells were suspended in a
mixture of collagen, basement membrane, and serum then
cast in circular molds. After the mixture coalesced, the
constructs were subjected to unidirectional cyclic stretch. The
application of cyclic stretch resulted in orientation of myocyte contractile activity in a manner previously elaborated by
their group and similar to that described by Vandenburgh’s
group.14 The resulting constructs were characterized in terms
of similarity to tissue, and the investigators report that
oriented bundles of myocytes exhibiting electrical and mechanical coupling were prevalent. The contractile activity of
the constructs was superb, and the method appears to be
highly reproducible. This and related reports by the same
group establish a method for generating engineered heart
tissue (EHT). By virtue of the method’s reproducibility and
the characteristics of the constructs described so far, EHTs
should represent an excellent source of material for in vitro
testing. With some modifications to the procedure, EHTs may
also provide suitable material for implantation studies.
Clearly, there are many further characterizations required
to establish EHTs as true tissue equivalents. Some of these
characterizations are straightforward. For example, do EHTs
exhibit the Frank-Starling effect or do inotropic and chronotropic agents affect the muscle as predicted? These assess-
Cardiac Tissue Engineering
121
ments are likely underway. Several issues regarding EHTs,
however, may prove more difficult to address. Some of these
may be crucial in future tissue engineering efforts. Elucidation of the mechanism by which EHTs achieve tissue- or
organ-level functionality would be key to allowing tissue
engineers to manipulate and control the process to produce
desired constructs. A host of comparisons between EHTs and
intact tissue, especially those related to the responsiveness of
EHTs to hormones, cytokines, pharmaceutical compounds,
etc, might be needed. Detailed assessments of the genomic,
proteomic, and/or metabolic profiles of the EHTs will be
needed to establish firmly that EHTs are tissue equivalents.
The applicability of the current method to human heart cells
will be critical. Controlling automaticity, which was apparent
in the rat EHTs described in the paper, may be critical, and
the arrhythmogenic potential of the EHTs in general will need
to be evaluated. Eschenhagen’s group has made a clear step
forward in cardiac tissue engineering, but numerous more
steps need to be taken to realize the potential of cardiac tissue
engineering.
There are also fundamental questions surrounding cardiac
tissue engineering as a field. The recent success of the
AbioCor artificial heart36,37 must be taken into account, and
though it will take some time to evaluate, tissue engineering
a complete heart replacement may not be necessary. The true
value of cardiac tissue engineering in the surgical setting may
be in the provision of implantable constructs short of complete hearts or in small biological interfaces for mechanical
hearts. The development of such small implants has been
emphasized by the NIH. Developing smaller pieces of heart
as waypoints in developing an entire organ is also the
approach being used by the LIFE tissue engineering initiative.38 The development of the AbioCor will be unlikely to
affect tissue-engineering initiatives in the near future but may
factor heavily in the future.
In the nonsurgical setting of the lab, the need for tissueengineered constructs is not affected by the development of
mechanical devices or even by the refinement of xenografting
techniques. In fact, the need for human tissue equivalents
may grow as more effort is placed into verifying the safety
and the arrhythmogenic potential of test drugs. Recent experience has shown that even drugs that are not targeted to the
cardiovascular system may adversely affect the heart, and
tissue engineering may be a desirable approach to assuring
drug actions.
If, as suggested by Zimmermann et al35 and others,
researchers can culture functional constructs with the biological, mechanical, and electrical properties of cardiac tissue, it
may be possible to specifically tissue engineer constructs for
clinical and laboratory use. Autologous or heterologous cells
collected from a variety of sources including biopsies, reductive surgeries, donor organs, or stem cells of some type may
have practical use in the construction of biosynthetic implants. The eventual application of tissue engineering to the
heart will require a profound understanding of varied and
complex topics. Eschenhagen’s group has taken a big first
step toward developing tissue equivalents, and the development of first-generation human tissue equivalents may soon
follow. With concerted effort within the scientific commu-
122
Circulation Research
February 8, 2002
nity, it may be possible to treat diverse diseases of the heart
using tissue engineering sometime in the future.
References
Downloaded from http://circres.ahajournals.org/ by guest on June 17, 2017
1. Hoffman JI. Incidence of congenital heart disease: I, Postnatal incidence.
Pediatr Cardiol. 1995;16:103–113.
2. Hoffman JI. Incidence of congenital heart disease: II, Prenatal incidence.
Pediatr Cardiol. 1995;16:155–165.
3. Gillum RF. Epidemiology of congenital heart disease in the United States.
Am Heart J. 1994;127:919 –927.
4. American Heart Association. 2000 Heart and Stroke Statistical Update.
Dallas, Texas: American Heart Association; 1999.
5. Stevenson LW, Warner SL, Steimle AE, Fonarow GC, Hamilton MA,
Moriguchi JD, Kobashigawa JA, Tillisch JH, Drinkwater DC, Laks H.
The impending crisis awaiting cardiac transplantation: modeling a
solution based on selection. Circulation. 1994;89:450 – 457.
6. Ross RS, Borg TK. Integrins and the myocardium. Circ Res. 2001;88:
1112–1119.
7. Simpson DG, Terracio L, Terracio M, Price RL, Turner DC, Borg TK.
Modulation of cardiac myocyte phenotype in vitro by the composition
and orientation of the extracellular matrix. J Cell Physiol. 1994;161:
89 –105.
8. Burrows MT. The cultivation of tissues of the chick embryo outside the
body. JAMA. 1910;55:2057–2058.
9. Burrows MT. Rhythmical activity of isolated heart muscle cells in vitro.
Science. 1912;36:90 –92.
10. Lundgren E, Terracio L, Borg K. Adhesion of cardiac myocytes to
extracellular matrix components. Basic Res Cardiol. 1985;80(suppl):
69 –74.
11. Carver W, Terracio L, Borg TK. Extracellular matrix maturation and
heart formation. In: Burggren WW, Keller BB, ed. Development of
Cardiovascular Systems. New York, NY: Cambridge University Press;
1997:43–56.
12. Sperelakis N. Cultured heart cell reaggregate model for studying cardiac
toxicology. Environ Health Perspect. 1978;26:243–267.
13. Sadoshima J, Jahn L, Takahashi T, Kulik TJ, Izumo S. Molecular characterization of the stretch-induced adaptation of cultured cardiac cells: an
in vitro model of load-induced cardiac hypertrophy. J Biol Chem. 1992;
267:10551–10560.
14. Samuel JL, Vandenburgh HH. Mechanically induced orientation of adult
rat cardiac myocytes in vitro. In Vitro Cell Dev Biol. 1990;26:905–914.
15. Klug MG, Soonpaa MH, Koh GY, Field LJ. Genetically selected cardiomyocytes from differentiating embronic stem cells form stable intracardiac grafts. J Clin Invest. 1996;98:216 –224.
16. Koh GY, Soonpaa MH, Klug MG, Field LJ. Long-term survival of AT-1
cardiomyocyte grafts in syngeneic myocardium. Am J Physiol. 1993;264:
H1727–H1733.
17. Koh GY, Klug MG, Soonpaa MH, Field LJ. Differentiation and long-term
survival of C2C12 myoblast grafts in heart. J Clin Invest. 1993;92:
1548 –1554.
18. Soonpaa MH, Koh GY, Klug MG, Field LJ. Formation of nascent intercalated disks between grafted fetal cardiomyocytes and host myocardium.
Science. 1994;264:98 –101.
19. Chiu RC, Zibaitis A, Kao RL. Cellular cardiomyoplasty: myocardial
regeneration with satellite cell implantation. Ann Thorac Surg. 1995;60:
12–18.
20. Strauer BE, Brehm M, Zeus T, Gattermann N, Hernandez A, Sorg RV,
Kogler G, Wernet P. [Intracoronary, human autologous stem cell transplantation for myocardial regeneration following myocardial infarction].
Dtsch Med Wochenschr. 2001;126:932–938.
21. Menasche P, Hagege AA, Scorsin M, Pouzet B, Desnos M, Duboc D,
Schwartz K, Vilquin JT, Marolleau JP. Myoblast transplantation for heart
failure. Lancet. 2001;357:279 –280.
22. Li RK, Yau TM, Weisel RD, Mickle DA, Sakai T, Choi A, Jia ZQ.
Construction of a bioengineered cardiac graft. J Thorac Cardiovasc Surg.
2000;119:368 –375.
23. Polonchuk L, Elbel J, Eckert L, Blum J, Wintermantel E, Eppenberger
HM. Titanium dioxide ceramics control the differentiated phenotype of
cardiac muscle cells in culture. Biomaterials. 2000;21:539 –550.
24. Papadaki M, Bursac N, Langer R, Merok J, Vunjak-Novakovic G, Freed
LE. Tissue engineering of functional cardiac muscle: molecular,
structural, and electrophysiological studies. Am J Physiol Heart Circ
Physiol. 2001;280:H168 –H178.
25. Shinoka T, Breuer CK, Tanel RE, Zund G, Miura T, Ma PX, Langer R,
Vacanti JP, Mayer JE Jr. Tissue engineering heart valves: valve leaflet
replacement study in a lamb model. Ann Thorac Surg. 1995;60:513–516.
26. Sodian R, Sperling JS, Martin DP, Egozy A, Stock U, Mayer JE, Jr.,
Vacanti JP. Fabrication of a trileaflet heart valve scaffold from a polyhydroxyalkanoate biopolyester for use in tissue engineering. Tissue Eng.
2000;6:183–188.
27. Sodian R, Hoerstrup SP, Sperling JS, Daebritz SH, Martin DP, Schoen FJ,
Vacanti JP, Mayer JE Jr. Tissue engineering of heart valves: in vitro
experiences. Ann Thorac Surg. 2000;70:140 –144.
28. Li RK, Yau TM, Weisel RD, Mickle DA, Sakai T, Choi A, Jia ZQ.
Construction of a bioengineered cardiac graft. J Thorac Cardiovasc Surg.
2000;119:368 –375.
29. Li RK, Jia ZQ, Weisel RD, Mickle DA, Choi A, Yau TM. Survival and
function of bioengineered cardiac grafts. Circulation. 1999;100(suppl):
II63–II69.
30. Sakai T, Li RK, Weisel RD, Mickle DA, Kim ET, Jia ZQ, Yau TM. The
fate of a tissue-engineered cardiac graft in the right ventricular outflow
tract of the rat. J Thorac Cardiovasc Surg. 2001;121:932–942.
31. Eschenhagen T, Fink C, Remmers U, Scholz H, Wattchow J, Weil J,
Zimmermann W, Dohmen HH, Schafer H, Bishopric N, Wakatsuki T,
Elson EL. Three-dimensional reconstitution of embryonic cardiomyocytes in a collagen matrix: a new heart muscle model system. FASEB J.
1997;11:683– 694.
32. Zimmermann WH, Fink C, Kralisch D, Remmers U, Weil J, Eschenhagen
T. Three-dimensional engineered heart tissue from neonatal rat cardiac
myocytes. Biotechnol Bioeng. 2000;68:106 –114.
33. Fink C, Ergun S, Kralisch D, Remmers U, Weil J, Eschenhagen T.
Chronic stretch of engineered heart tissue induces hypertrophy and functional improvement. FASEB J. 2000;14:669 – 679.
34. Akins RE, Boyce RA, Madonna ML, Schroedl NA, Gonda SR,
McLaughlin TA, Hartzell CR. Cardiac organogenesis in vitro: reestablishment of three-dimensional tissue architecture by dissociated neonatal
rat ventricular cells. Tissue Eng. 1999;5:103–118.
35. Zimmermann W, Schneiderbanger K, Schubert P, Didié M, Münzel F,
Heubach J, Kostin S, Neuhuber W, Eschenhagen T. Tissue engineering of
a differentiated cardiac muscle construct. Circ Res. 2002;90:223–230.
36. SoRelle R. Cardiovascular news: totally contained AbioCor artificial
heart implanted July 3, 2001. Circulation. 2001;104:E9005–E9006.
37. SoRelle R. Third AbioCor artificial heart implanted in Houston. Circulation. 2001;104:E9033–E9034.
38. Akins RE, Sefton MV. Tissue engineering a heart. New Surgery. 2001;
1:26 –32.
KEY WORDS: heart disease
䡲 cell biology 䡲 surgery
䡲
tissue engineering
䡲
congenital heart defects
Can Tissue Engineering Mend Broken Hearts?
Robert E. Akins
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Circ Res. 2002;90:120-122
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