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Am J Physiol Heart Circ Physiol 293: H1853–H1860, 2007.
First published July 6, 2007; doi:10.1152/ajpheart.00544.2007.
Deleterious effects of sugar and protective effects of starch on cardiac
remodeling, contractile dysfunction, and mortality in response
to pressure overload
David J. Chess,1 Biao Lei,3 Brian D. Hoit,2 Agnes M. Azimzadeh,4 and William C. Stanley1,3
Departments of 1Physiology and Biophysics and 2Medicine, School of Medicine, Case Western Reserve University, Cleveland,
Ohio; and Division of Cardiology, Departments of 3Medicine and 4Surgery, University of Maryland, Baltimore, Maryland
Submitted 9 May 2007; accepted in final form 3 July 2007
CHRONIC ARTERIAL PRESSURE OVERLOAD is a major cause of left
ventricular (LV) hypertrophy (LVH), which frequently
progresses to heart failure (HF). Even with modern pharmacological treatment, many patients with hypertension still develop LVH and HF (44). Thus, novel therapies are needed to
prevent LVH and/or the development of HF, especially those
that act independently of the neurohormonal axis. Nutritional
approaches are particularly attractive because they could work
additively with medicinal therapies while not exerting negative
hemodynamic effects (37).
While a high-carbohydrate/low-fat diet is recommended for
the prevention of heart disease (21), a recent epidemiological
study (12) found a twofold increase in the risk of coronary
heart disease in women consuming a diet of high glycemic
index (i.e., one containing foods rich in sugars and rapidly
digested polysaccharides) compared with a diet low in sugar.
Diets with a high glycemic load influence the development of
obesity and metabolic syndrome, which have become an epidemic in this country and are positively associated with cardiovascular disease risk (33). The occurrence of such risk
factors is reduced by diets of a lower glycemic load or those
rich in complex carbohydrates (23, 36). Thus, current guidelines
suggest that dietary carbohydrate should be comprised mainly of
complex carbohydrates (starches) rather than sugars (21).
High carbohydrate composition may be associated with
LVH due to activation of the insulin signaling pathway in the
heart (4, 40). Clinical studies (34, 39, 43) have found that
hypertensive patients with a high plasma insulin in the fed state
have a greater occurrence of LVH, suggesting that elevated
insulin may trigger pathological cardiac growth when the heart
is subjected to chronic pressure overload. Recently, we (38)
observed that feeding a high-carbohydrate diet comprised mainly
of fructose to hypertensive Dahl salt-sensitive rats impaired LV
function and increased mortality by 85% over a 13-wk period
compared with a standard laboratory chow. Studies (4, 40) in
transgenic mice have also suggested that the activation of insulin
signaling can lead to LVH and cardiac dysfunction. The main
effector of insulin signaling is the serine/threonine kinase Akt,
whose overexpression results in increased protein synthesis (40),
inhibited protein breakdown (27, 41), and subsequently massive
LVH (22). Insulin also affects the activity of AMP-activated
protein kinase (AMPK), which upregulates glucose and fatty acid
utilization during periods of low energy (1, 19). The effects of diet
on Akt and AMPK expression and activation in mediating structural and metabolic remodeling of the heart during chronic pressure overload are unclear.
Nuclear receptor signaling is also affected by dietary macronutrients. A recent study (10) in transgenic mouse models of metabolic syndrome has suggested that mitochondrial biogenesis is
stimulated by increased lipid availability and activation of peroxisome proliferator-activated receptor-␣ (PPAR-␣) and its coactivators. PPAR-␣, which is suppressed in severe LVH and
HF, is activated by long-chain fatty acids and regulates the
expression of proteins involved in fatty acid metabolism (42).
Dietary fat and carbohydrate intake alters the development of
LVH and the progression toward HF (30, 38); thus, sugar
consumption may accelerate the deactivation of PPAR-␣, resulting in impaired cardiac fatty acid metabolism and mitochondrial function under conditions of pressure overload.
Address for reprint requests and other correspondence: W. C. Stanley, Div. of
Cardiology, Dept. of Medicine, Univ. of Maryland, 20 Penn St., HSF-II, Rm.
S022, Baltimore, MD 21201 (e-mail: [email protected]).
The costs of publication of this article were defrayed in part by the payment
of page charges. The article must therefore be hereby marked “advertisement”
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
glycemic index; ejection fraction; heart failure
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0363-6135/07 $8.00 Copyright © 2007 the American Physiological Society
H1853
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Chess DJ, Lei B, Hoit BD, Azimzadeh AM, Stanley WC. Deleterious effects of sugar and protective effects of starch on cardiac remodeling, contractile dysfunction, and mortality in response to pressure
overload. Am J Physiol Heart Circ Physiol 293: H1853–H1860, 2007.
First published July 6, 2007; doi:10.1152/ajpheart.00544.2007.—Little is
known about the effects of the composition of dietary carbohydrate on the
development of left ventricular (LV) hypertrophy (LVH) and heart failure
(HF) under conditions of pressure overload. The objective of this study
was to determine the effect of carbohydrate composition on LVH, LV
function, and mortality in a mouse model of chronic pressure overload. Male C57BL/6J mice of 6 wk of age (n ⫽ 14 –16 mice/group)
underwent transverse aortic constriction (TAC) or sham surgery and
were fed either standard chow (STD; 32% corn starch, 35% sucrose,
3% maltodextrin, and 10% fat expressed as a percent of the total
energy), high-starch chow (58% corn starch, 12% maltodextrin, and
10% fat), or high-fructose chow (9% corn starch, 61% fructose, and
10% fat). After 16 wk of treatment, mice with TAC fed the STD or
high-fructose diets exhibited increased LV mass, larger end-diastolic
and end-systolic diameters, and decreased ejection fraction compared
with sham. The high-starch diet, in contrast, prevented changes in LV
dimensions and contractile function. Cardiac mRNA for myosin
heavy chain-␤ was increased dramatically in the fructose-fed banded
animals, as was mortality (54% compared with 8% and 29% in the
starch and STD banded groups, respectively). In conclusion, a diet
high in simple sugar was deleterious, resulting in the highest mortality
and expression of molecular markers of cardiac dysfunction in TAC
animals compared with sham, whereas a high-starch diet blunted
mortality, increases in cardiac mass, and contractile dysfunction.
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METHODS
Induction of pressure overload in C57BL/6J mice. Transverse
aortic constriction (TAC) was performed on male C57BL/6J mice at
6 wk of age as previously described (13) using a 26-gauge needle to
induce clinically relevant hypertrophy. The sham procedure was
identical without aortic ligation. This study was conducted according
to the National Institutes of Health Guidelines for the Care and Use
of Laboratory Animals (NIH Pub. No. 85-23) and was approved by
the Institutional Animal Care and Use Committee of Case Western
Reserve University. Animals were maintained on a 12:12-h light-dark
cycle.
Diets. All diets were custom formulated by Research Diets (New
Brunswick, NJ). The macronutrient composition of the diets is shown
in Table 1. Animals were fed institutionally available laboratory chow
(Harlan Teklad 2014, Global 14% Protein Rodent Maintenance Diet)
for 1 wk. Following surgery, animals were randomly assigned to
either the high-starch (starch), standard (STD), or high-fructose (fructose) diet for the remainder of the study.
Echocardiography. LV dimensions and function were measured at
5 and 16 wk postsurgery as previously described (28, 29) using
isoflurane anesthesia. Relative wall thickness (RWT) was approximated using the following formula: RWT ⫽ (LVPWTd ⫹ LVSWTd)/
(LVEDD), where LVPWTd is LV posterior wall thickness at end
diastole, LVSWTd is LV septal wall thickness at end diastole, and
LVEDD is LV end-diastolic diameter. The myocardial performance
index (MPI), a reflection of LV systolic and diastolic function whose
magnitude is inversely related to myocardial performance, was calculated using the following formula: MPI ⫽ (IVCT ⫹ IVRT)/(ET),
where IVCT and IVRT are isovolumic contraction and relaxation
times, respectively, and ET is ejection time. The ejection fraction (EF)
was calculated using the following equation: EF ⫽ [(LVEDV ⫺
LVESV)/(LVEDV)] ⫻ 100, where LVEDV and LVESV are LV
end-diastolic and end-systolic volumes, respectively.
Terminal surgery. Terminal surgeries were performed on fed mice
between 3 and 6 h from the initiation of the dark phase (18:00) on the
light-dark cycle. After 16 wk of treatment, mice were weighed and
anesthetized with 1.5–2.0% isoflurane. The thoracic cavity was
opened by cutting from the xiphoid cartilage around the ventral
portion of the ribs. The heart was removed, weighed, freeze clamped,
and stored at ⫺80°C. Pooled blood was collected from the thoracic
cavity after heart excision for the analysis of plasma and serum
metabolites.
Metabolic measurements. Plasma glucose, insulin, free fatty acids,
and triglycerides were determined using commercially available kits.
Serum leptin and total plasma adiponectin (individual adiponectin
isoforms were not assessed) were measured with colorimetric enzyme-linked immunosorbent assays. MCAD and citrate synthase (CS)
activities were analyzed from tissue homogenates as previously described (31).
mRNA expression analysis. Powdered heart tissue was disrupted
and homogenized by being shaken in solution with 5-mm stainless
steel beads for 3 min at 30 s⫺1 (Mixermill 300, Qiagen) followed by
RNA isolation (RNeasy Mini Kit, Qiagen). RNA samples were eluted
in 50 ␮l of nuclease-free water and stored at ⫺80°C. For cDNA
synthesis, RNA (1 ␮g) was mixed with 2 ␮L oligo(dT)16 (Applied
Biosystems) and 0.5 ␮l random primers (Invitrogen) and brought to
15 ␮l of total volume. The sample/primer mix was heated to 70°C for
10 min and then placed immediately on ice for 2 min followed by the
addition of the RT reaction mix containing 5⫻ buffer (5 ␮l) and 0.1
M DTT (2.5 ␮l, Superscript II RT, Invitrogen), 10 mM dNTP (1.25
␮l, Invitrogen), and RNase inhibitor (0.25 ␮l, Applied Biosystems).
The reaction mix was incubated for 2 min at 42°C, 1 ␮l reverse
transcriptase was added, and the incubation was continued at 42°C for
1 h. The reaction mix was then incubated at 70°C for 10 min and
placed on ice for 2 min. The resulting cDNA samples were stored at
⫺20°C. Quantitative RT-PCR (qRT-PCR) was performed using an
ABI 7900 and the following protocol: 2 min at 50°C, 10 min at 95°C,
and 40 cycles at 95°C for 15 s and 1 min at 60°C. Each reaction was
25 ␮l, consisting of 1.0 ␮l cDNA sample, 1.25 ␮l TaqMan Gene
Expression Assay, 12.5 ␮l of 2⫻ TaqMan PCR master mix, and 10.25
␮l nuclease-free water. Expressions of atrial natriuretic peptide, myosin heavy chain (MHC)-␣, MHC-␤, MCAD, CS, PPAR-␣, carnitine
palmitoyl transferase I, pyruvate dehydrogenase kinase 4, uncoupling
protein 3, and peptidylprolyl isomerase A (internal control) were
determined by qRT-PCR using Assays-On-Demand probes (Applied
Biosystems). mRNA concentrations were normalized to the fold
increase relative to the STD sham group.
Western blot analysis. Protein was extracted from frozen cardiac
tissue, separated by electrophoresis in 10% SDS-PAGE gels, transferred onto nitrocellulose membranes, and incubated with specific
antibodies to either phosphorylated Akt (Ser473) or phosphorylated
AMPK (Thr172 of the ␣-subunit) (all at 1:1,000, from Cell Signaling
Technology). Fluorescence-conjugated secondary antibodies (IRDye
680/800, 1:5,000, LI-COR Bioscience) were used for incubation
before the membranes were scanned and analyzed with the Odyssey
infrared imaging system (LI-COR Bioscience). Membranes were then
stripped (Pierce Restore stripping buffer) and reprobed for total Akt
and AMPK (1:1,000, Cell Signaling).
Statistical analysis. All analysis was performed with the investigator(s) blinded. Two-way ANOVA with Bonferroni post hoc adjustment was used to compare all dietary groups with and without aortic
constriction. Differences in mortality were assessed by a Kaplan-
Table 1. Macronutrient composition of the diets used in this study
Fat
Carbohydrate
Protein
Diet
Soy Oil
Cocoa Butter
Cornstarch
Fructose
Sucrose
Maltodextrin
Casein
Total
STD
Starch
Fructose
3
3
3
7
7
7
32
58
9
0
0
61
35
0
0
3
12
0
20
20
20
100
100
100
Values are the contributions of fats, carbohydrates, and proteins to the total energy content of the diet (% of total). Diets were matched for vitamin and mineral
content and were all on a low-sodium background (⬃0.26% by mass). STD, standard diet; starch, high-starch diet; fructose, high-fructose diet.
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This study evaluated the effect of carbohydrate composition
on the development of structural, functional, and metabolic
abnormalities in response to pressure overload. We hypothesized that a high-sugar diet would exacerbate cardiac remodeling and dysfunction and increase mortality in mice with
aortic constriction. A top-down approach was taken, with the
effects of carbohydrate composition assessed by mortality,
echocardiographic measurements of LV chamber dimensions
and function, and quantification of hormones and metabolites
in blood, activity of key metabolic enzymes, gene expression, and
hypertrophic signaling pathways. The activation of PPAR-␣ was
assessed through measurements of transcript levels of established PPAR-␣ target genes and the activity of the fatty acid
␤-oxidation enzyme medium-chain acyl-CoA dehydrogenase
(MCAD).
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CARBOHYDRATE INTAKE AND CARDIAC HYPERTROPHY
Fig. 1. Percent survival in sham (A) and transverse aortic constriction (TAC;
B) mice displayed graphically over the 16-wk duration of the study. Starch,
high-starch diet; fructose, high-fructose diet; STD, standard diet. *P ⬍ 0.05
compared with TAC mice on the starch diet. Each group contained 14 –16
animals at the onset of dietary treatment.
Meier survival curve with ␹2-analysis (SPSS Base 15.0, SPSS, Chicago, IL). All data are presented as means ⫾ SE. P ⬍ 0.05 was
accepted as statistically significant.
RESULTS
Survival. All sham-operated mice on the STD and starch
diets survived the 16-wk duration of the study. Mortality was
observed in mice with TAC on STD and starch diets (29% and
8%, respectively; Fig. 1B). The fructose diet had the most
obvious effect on survival, inducing mortality rates in both
sham (21%; Fig. 1A) and TAC (54%; Fig. 1B) mice. The
mortality observed in TAC mice on the fructose diet was
significantly greater than starch diet-fed TAC mice. However,
TAC-induced mortality was not different between fructose
diet- and STD diet-fed mice compared with sham mice (Fig. 1,
A and B).
Body and heart mass. No significant differences in body
mass were observed in either sham or TAC animals fed the
three diets (Table 2). Average daily food consumption was also
not different among groups (data not shown). TAC increased
heart weight (normalized to tibia length) by 38.7% in STD
diet-fed mice and 25.3% in fructose diet-fed mice compared
with sham animals on the same diets (Fig. 2). The starch diet
completely prevented the increase in heart weight in mice with
TAC. TAC led to a significant reduction in epididymal fat pad
mass in fructose diet-fed mice compared with mice on the
starch diet (Table 2).
LV dimensions and performance. There were no differences
in echocardiographic measurements among dietary and/or surgical groups at 5 wk (data not shown). After 16 wk of
treatment, LVEDD and LVESD were increased significantly
by TAC in the fructose diet-fed group compared with its
respective sham group, but there were no differences between
TAC and sham animals in the STD or starch diet groups
(Fig. 3, A and B). TAC reduced EF (Fig. 3C) in both STD dietand fructose diet-fed mice compared with sham mice; however, there was no difference between sham and TAC mice in
the starch diet group. The MPI, whose magnitude is inversely
related to myocardial performance, was increased significantly in TAC animals on the STD and fructose diets
compared with their respective shams; however, there were
no differences in MPI between sham and TAC animals on
the starch diet (Fig. 3D).
Table 2. Body measurements taken at terminal procedure following 16 wk of dietary treatment
Starch
STD
Fructose
Measurements
Sham (n ⫽ 16)
TAC (n ⫽ 14)
Sham (n ⫽ 14)
TAC (n ⫽ 11)
Sham (n ⫽ 10)
TAC (n ⫽ 8)
Body weight, g
Heart weight, mg
Tibia length, mm
Epididymal fat, mg
28⫾1
153.4⫾3.7
17.05⫾0.20
518.0⫾36.6
28⫾1
160.5⫾12.9
16.97⫾0.14
613.1⫾63.1
28⫾1
154.3⫾5.5
16.77⫾0.21
541.7⫾40.6
27⫾1
214.0⫾21.8*
17.11⫾0.13
412.7⫾71.9
27⫾1
147.2⫾4.7
17.12⫾0.29
467.1⫾24.4
26⫾1
184.4⫾21.6*
17.14⫾0.14
383.0⫾27.2*†
Values are means ⫾ SE; n, no. of animals. TAC, transverse aortic constriction. *P ⬍ 0.05 vs. sham animals on the same diet; †P ⬍ 0.05 vs. TAC animals
on the starch diet.
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Fig. 2. Terminal heart weight (HW)-to-tibia length ratios of sham (n ⫽ 10 –16
mice/group) and TAC (n ⫽ 8 –14 mice/group) animals. Data are means ⫾ SE.
*P ⬍ 0.05 compared with sham animals on the same diet.
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CARBOHYDRATE INTAKE AND CARDIAC HYPERTROPHY
Metabolic parameters. Plasma glucose was unaffected by
TAC or dietary treatment. No differences were observed in
plasma free fatty acid concentrations among all groups. Plasma
triglycerides, however, were increased significantly in both TAC
and sham mice on the starch diet compared with all other
TAC and sham groups (Table 3). Plasma insulin was similar in
sham and TAC animals fed the STD and starch diets but was
significantly increased in the fructose-fed TAC group compared
with its respective sham (Table 3). Total adiponectin levels were
unchanged with dietary manipulation in either sham or TAC mice.
Serum leptin was significantly elevated in TAC animals compared
with sham animals in the starch diet-fed groups.
Fructose feeding lowered the activity of MCAD in TAC
animals relative to sham animals (Fig. 4A). CS activity, a
marker of mitochondrial density and oxidative capacity, was
reduced in TAC animals consuming STD and fructose diets
compared with their respective sham groups (Fig. 4B). The
ratio of MCAD activity to CS activity was unaffected by TAC
or diet (data not shown), suggesting there was not a preferential
downregulation of fatty acid ␤-oxidation.
mRNA expression. There was a trend toward increases in atrial
natriuretic factor mRNA in animals with TAC (Table 4). TAC
caused a switch in MHC isoform from ␣ to ␤, an effect that was
enhanced dramatically by fructose diet feeding (Fig. 5) due to a
17-fold increase in MHC-␤ (Table 4). TAC also reduced the
mRNA expression of MCAD and PPAR-␣. Within the TAC
groups, PPAR-␣ expression was significantly decreased with the
fructose diet compared with the starch diet (Table 4).
Western blot analysis. There were no significant differences
in total Akt protein levels or the ratio of phosphorylated Akt
(Ser473) to total Akt between any of the treatment groups
(Table 5). Similarly, there were no significant differences in
total AMPK protein levels or the ratio of phosphorylated
AMPK (Thr172 of the ␣-subunit) to total AMPK (Table 5).
DISCUSSION
The primary findings from this study were that compared
with a complex carbohydrate diet, a diet high in sugar increased the mortality and expression of molecular markers of
Table 3. Metabolite and hormone concentrations in plasma or serum in fed animals after 16 wk of treatment
Starch
STD
Fructose
Metabolite or Hormone
Sham (n ⫽ 10)
TAC (n ⫽ 8)
Sham (n ⫽ 9)
TAC (n ⫽ 8)
Sham (n ⫽ 8)
TAC (n ⫽ 7)
Plasma glucose, mM
Plasma free fatty acids, mM
Plasma triglycerides, mg/ml
Plasma insulin, nM
Plasma adiponectin, ␮g/ml
Serum leptin, ng/ml
9.15⫾0.28
0.44⫾0.03
0.52⫾0.06a
0.93⫾0.26
2.02⫾0.17
1.81⫾0.23
8.48⫾0.23
0.51⫾0.06
0.65⫾0.12b
0.81⫾0.14
2.86⫾0.11c
3.12⫾0.34c,e
8.80⫾0.61
0.38⫾0.05
0.36⫾0.04
0.59⫾0.07
2.09⫾0.26
2.13⫾0.30
8.16⫾0.32
0.48⫾0.04
0.33⫾0.04
0.70⫾0.15
2.48⫾0.24
2.34⫾0.27
8.61⫾0.30
0.53⫾0.13
0.31⫾0.04
0.64⫾0.18
2.60⫾0.52
1.71⫾0.34
9.34⫾0.56
0.41⫾0.03
0.33⫾0.09
1.68⫾0.37c,d
2.05⫾0.20
1.84⫾0.20
c
Values are means ⫾ SE; n, no. of animals. aP ⬍ 0.05 vs. sham animals on STD and fructose diets; bP ⬍ 0.05 vs. TAC animals on STD and fructose diets;
P ⬍ 0.05 vs. sham animals on the same diet; dP ⬍ 0.05 vs. TAC animals on STD and starch diets; eP ⬍ 0.05 vs. TAC animals on the fructose diet.
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Fig. 3. Echocardiographic parameters. Enddiastolic diameter (EDD; A), end-systolic diameter (ESD; B), ejection fraction (EF; C),
and myocardial performance index (MPI; D)
were measured in the hearts of sham and TAC
animals following 16 wk of treatment. Open
bars represent sham animals; closed bars represent TAC animals. The numbers of animals
used for all echocardiographic measurements
are shown in A. Data are means ⫾ SE. *P ⬍
0.05 compared with sham animals on the same
diet.
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LVH and HF under conditions of pressure overload. The
expression of fetal genes, LV contractile dysfunction, and
mortality in TAC animals increased as a function of the
percentage of calories derived from sugar (Figs. 1–5). These
Table 4. mRNA expression of cardiac genes determined by quantitative RT-PCR
Starch
STD
Fructose
Gene
Product
Sham (n ⫽ 10)
TAC (n ⫽ 8)
Sham (n ⫽ 9)
TAC (n ⫽ 8)
Sham (n ⫽ 8)
TAC (n ⫽ 7)
P Values (TAC vs. sham)
Nppa
Myh6
Myh7
Acadm
Cs
Ppara
Cpt1b
Pdk4
Ucp3
ANF
MHC-␣
MHC-␤
MCAD
CS
PPAR-␣
CPT-I␤
PDK4
UCP3
0.65⫾0.15
1.08⫾0.13
0.91⫾0.14
1.06⫾0.05
1.23⫾0.17
1.18⫾0.14
1.06⫾0.13
0.72⫾0.13
1.21⫾0.33
1.01⫾0.23
1.00⫾0.05
1.60⫾0.18*
0.86⫾0.07
0.97⫾0.10
1.00⫾0.11
0.87⫾0.05
0.67⫾0.11
1.03⫾0.19
1.00⫾0.23
1.00⫾0.09
1.00⫾0.17
1.00⫾0.07
1.00⫾0.13
1.00⫾0.13
1.00⫾0.08
1.00⫾0.20
1.00⫾0.17
1.19⫾0.17
0.91⫾0.18
2.72⫾0.38*
0.90⫾0.09
0.87⫾0.13
0.78⫾0.14
0.86⫾0.07
0.84⫾0.14
1.05⫾0.23
1.27⫾0.31
1.03⫾0.11
1.55⫾0.28
0.93⫾0.09
1.04⫾0.15
0.94⫾0.13
1.00⫾0.09
0.78⫾0.13
1.29⫾0.48
1.50⫾0.27
0.76⫾0.16
16.59⫾3.17*†
0.75⫾0.07
0.78⫾0.14
0.64⫾0.13‡
0.91⫾0.10
0.46⫾0.12
1.15⫾0.41
0.069
NS
⬍0.001
0.015
NS
0.035
NS
NS
NS
Data are presented as means ⫾ SE of fold changes in gene expression relative to the STD diet-fed sham group; n, no. of animals. ANF, atrial natriuretic factor;
MHC, myosin heavy chain; MCAD, medium-chain acyl-CoA dehydrogenase; CS, citrate synthase; PPAR-␣, peroxisome proliferator-activated receptor-␣;
CPT-I␤, carnitine palmitoyl transferase-I␤; PDK4, pyruvate dehydrogenase kinase 4; UCP3, uncoupling protein 3; NS, not significant. *P ⬍ 0.05 vs. sham
animals on the same diet; †P ⬍ 0.05 vs. TAC animals on STD and starch diets; ‡P ⬍ 0.05 vs. TAC animals on the starch diet.
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Fig. 4. Activities of medium-chain acyl-CoA dehydrogenase (MCAD; A) and citrate
synthase (CS; B) in cardiac tissue measured spectrophotometrically. Data are means ⫾
SE. *P ⬍ 0.05 compared with sham animals on the same diet. †Values of the fructose
TAC group were significantly lower than those of the starch TAC group (P ⬍ 0.05).
findings suggest that dietary sugar composition can promote
cardiac remodeling and contractile dysfunction in the presence of
chronic pressure overload.
Fructose diet feeding in the TAC mice also decreased the
activities of MCAD and CS, marker enzymes for myocardial
fatty acid oxidation capacity and citric acid cycle flux, respectively. These decreases in enzyme activity occurred despite no
alterations in the mRNA for either MCAD or CS (Table 4).
These findings differ from our previous observations showing
that MCAD activity and protein expression remained unchanged despite reductions in MCAD gene expression (24) and
contrasts with evidence of HF-induced downregulation of fatty
acid oxidation genes (8, 32). These conflicting results reinforce
the notion that there are frequent disconnections between
mRNA and protein levels during LVH and HF (24, 42).
The precise mechanism for increased mortality in the fructose diet-fed TAC group is not known. Previous studies (4, 14,
40) have suggested that enhanced activation of the Akt-insulin
pathway could contribute to LVH and contractile dysfunction
in transgenic animals and isolated cardiomyocytes. In this
study, however, there was no increase in Akt activation in TAC
animals on the fructose diet despite a significant elevation in
plasma insulin. This discrepancy may be attributed to eating
patterns of the mice prior to terminal studies, as it has been
shown that Akt activation is highly dependent on nutritional
status (40).
There were also no changes observed in the expression and
activation of AMPK. To our knowledge, only two studies have
measured the effects of cardiac hypertrophy on the activation
and expression of AMPK. A study (18) in juvenile pigs with
volume overload-induced LVH showed an ⬃30% decrease in
AMPK activity in freeze-clamped myocardial tissue. In contrast, ex vivo perfused hearts from rats subjected to 17–19 wk
of ascending aortic banding exhibited an approximately threefold increase in AMPK activity (45). Thus, at this point, the
role of this protein in the development of LVH remain unclear.
The expression of PPAR-␣ mRNA was reduced in the
TAC mice fed the fructose diet; however, the expression of
PPAR-␣-regulated genes (such as MCAD) was unaffected by
diet among TAC groups. Nonetheless, the activity of MCAD
was suppressed in TAC mice on the fructose diet (Fig. 4). CS
activity was also reduced in the fructose diet group, suggesting
that fructose diet feeding in the setting of pressure overload
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CARBOHYDRATE INTAKE AND CARDIAC HYPERTROPHY
exacerbated the impairment in mitochondrial oxidative metabolism.
The effects of fructose diet feeding may be mediated by the
development of metabolic syndrome (insulin resistance, hyperglycemia, dyslipidemia, hypertension, and/or obesity). The
consumption of dietary fructose, particularly in more developed countries in which many foods are enriched with highfructose corn syrup, has been suggested to contribute to the
development of obesity and its corresponding metabolic abnormalities (3, 5, 11, 16, 25). Fructose diet feeding is a
well-established model of metabolic syndrome, as it leads to
hypertension, hypertriglyceridemia, and insulin resistance in
rats (15). Mild insulin resistance was suggested in fructose
diet-fed TAC animals as they displayed significantly higher
plasma insulin compared with starch diet- and STD diet-fed
TAC animals and also exhibited the highest glycemia (Table
3). Secondary to this modest insulin resistance was impaired
Akt activation, which has been shown previously (9).
It is also possible that the fructose diet increased blood
pressure in TAC mice; thus, a limitation of the present study is
the lack of blood pressure data. Studies (20, 26) have shown
mild decreases in arterial pressure in C57BL/6J mice using the
noninvasive tail-cuff method following 11 wk of TAC. Terminal measurements of ventricular pressure could have been
performed through LV catheterization, but the additional stress
of anesthesia and arterial catheterization likely would have
altered cardiac signaling pathways (e.g., Akt and AMPK acti-
Table 5. Western blot densitometry of Akt, phospho-Akt (Ser473), AMPK, and phospho-AMPK (Thr172) in the heart
Starch
STD
Fructose
Protein
Sham (n ⫽ 8)
TAC (n ⫽ 7)
Sham (n ⫽ 8)
TAC (n ⫽ 7)
Sham (n ⫽ 7)
TAC (n ⫽ 6)
Phospho-Akt
Total Akt
Phospho-Akt/total Akt
Phospho-AMPK
Total AMPK
Phospho-AMPK/total AMPK
0.89⫾0.09
0.97⫾0.09
0.92⫾0.08
0.86⫾0.06
1.10⫾0.18
0.84⫾0.11
0.99⫾0.11
0.89⫾0.06
1.10⫾0.06
0.95⫾0.04
1.04⫾0.09
0.92⫾0.08
1.00⫾0.08
1.00⫾0.06
1.00⫾0.07
1.00⫾0.07
1.00⫾0.06
1.00⫾0.08
0.83⫾0.06
0.99⫾0.06
0.86⫾0.08
0.87⫾0.06
0.99⫾0.09
0.89⫾0.06
0.88⫾0.10
1.09⫾0.12
0.87⫾0.09
0.88⫾0.03
1.06⫾0.07
0.83⫾0.06
0.78⫾0.03
1.11⫾0.12
0.76⫾0.09
0.93⫾0.02
1.17⫾0.10
0.81⫾0.07
Values are means ⫾ SE. Data are presented as fold changes in protein expression relative to the STD diet-fed sham group (in arbitrary units). AMPK,
AMP-activated protein kinase.
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Fig. 5. Ratio of myosin heavy chain (MHC)-␤ to MHC-␣ mRNA expression
relative to the STD sham group (dashed line) as determined by quantitative
RT-PCR. Data are means ⫾ SE. *P ⬍ 0.05 compared with sham animals on
the same diet; †P ⬍ 0.05 compared with TAC animals on the STD and starch
diets.
vation). Recently, Joho et al. (17) demonstrated that LV pressure and volume can be measured in conscious, unrestrained
mice. Thus, future studies should investigate the effects of diet
on arterial and LV pressure in sham and TAC animals.
The mechanism for the increased mortality in fructose dietfed sham animals is unclear. No evidence of cardiac-related
death was found based on EF (Fig. 3c) or the expression of
atrial naturietic factor or MHC-␤ (Table 4). A possible explanation for the mortality seen in the fructose diet-fed sham
group is renal damage. It has recently been shown in rats that
60% fructose consumption over 8 wk was associated with
kidney hypertrophy, glomerular hypertension, cortical vasoconstriction, and a decreased glomerular filtration rate (35). In
the present study, 61% fructose diet feeding was maintained
for 16 wk, possibly inducing irreversible renal damage and
subsequent death due to renal failure. Future studies involving
chronic fructose diet feeding should assess structural and
functional aspects of the kidney to provide evidence for this
hypothesis.
An important finding in this study was the cardioprotective
effects of a high-starch diet during chronic pressure overload.
Cornstarch, the primary source of carbohydrate in the starch
diet used in this study, contains mostly amylopectin. Having a
branched-chain configuration, amylopectin is more susceptible
to degradation by ␣-glucosidases compared with straight-chain
amylose, suggesting a relatively high glycemic index for the
starch diet and theoretically greater cardiac growth. However,
TAC animals consuming the starch diet exhibited no increase
in heart mass or contractile dysfunction compared with sham
animals. The beneficial effects of high-starch diet feeding may
be related to overall myocardial oxidative capacity, as the
activities of MCAD and CS were maintained in starch diet-fed
TAC mice compared with fructose diet-fed TAC mice (Fig. 4).
Further studies are needed to determine how dietary manipulation during pressure overload affects substrate preference and
the hypertrophic response.
The blunting of cardiac hypertrophy and contractile dysfunction with high-starch diet feeding may also be species dependent. A concurrent feeding study in our laboratory involving
the rat abdominal aortic constriction model of pressure overload found similar increases cardiac mass, LVESV, and
LVEDV in animals fed either a high-sugar or high-starch diet
(M. K. Duda, K. M. O’Shea, and W. C. Stanley, unpublished
data). However, compared with a high-starch diet, feeding a
high-sugar diet to hypertensive Dahl salt-sensitive rats decreased EF and increased mortality (38), consistent with the
findings of the present investigation. Taken together, those
CARBOHYDRATE INTAKE AND CARDIAC HYPERTROPHY
ACKNOWLEDGMENTS
We acknowledge Karen O’Shea, Kristen King, and Celvie Yuan for the help
with the terminal surgeries, Dr. Willem Kop for the assistance in the survival
analyses, and Dr. Brian Barrows for the technical support with the quantitative
RT-PCR. We thank Dr. Ken Walsh and Dr. Kaori Sato at Boston University for
teaching us the TAC procedure.
GRANTS
This work was supported by National Heart, Lung, and Blood Institute
Grant HL-074237.
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