Editorial
Vitamin C, Collagen, and Cracks in the Plaque
Peter Libby, MD; Masanori Aikawa, MD, PhD
M
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volves fragility of blood vessels. In 1753, James Lind
described the skin of scorbutics as “. . .covered with several
reddish, bluish. . . spots. . . resembling an effusion of blood.”6
Lind’s discovery that food rich in vitamin C provided a cure
for scurvy spurred England’s subsequent naval supremacy
and putatively changed the course of history. Of course,
chemical characterization of vitamin C as the antiscorbutic
factor did not occur until the 1930s. (Interested readers may
find Albert Szent-Györgi’s dispute with the editor of the
Biochemical Journal regarding publication of the structure of
vitamin C amusing.7 Cardiologists know Szent-Györgi better
for his later discovery of the biochemical basis of muscle
contraction).
Study of vitamin C’s role in vivo has proven challenging.
Unlike humans, usual experimental animals can synthesize
vitamin C and thus cannot be made scorbutic. Maeda’s group
has recently introduced a targeted mutation that makes mice
dependent on dietary vitamin C, allowing manipulation of
ascorbate levels. In this issue of Circulation, Nakata et al8
studied atheroma in hypercholesterolemic and scorbutic mice.
They find no change in lesion size, but they observe decreased collagen content in the lesions. Such changes should
impair the biomechanical strength of the plaque and make it
more prone to rupture. This finding extends the burgeoning
evidence that changes in collagen metabolism can influence
crucial characteristics of the atherosclerotic plaque. Our
recent in vivo studies also showed that alterations in collagen
synthesis and catabolism induced by lipid lowering or statin
treatment influence the collagenous structure of atheroma in
rabbits.9 –11 It would have been of interest to evaluate overall
protein content in these lesions, as we showed almost 2
decades ago that ascorbate can augment noncollagen protein
synthesis by cultured arterial smooth muscle cells.12
We do not know whether scorbutic humans with atherosclerosis would experience increased plaque rupture, a curious but currently clinically irrelevant question. In addition to
its antiscorbutic action, vitamin C has potent antioxidant
properties. Physiological concentrations of ascorbic acid can
inhibit in vitro oxidative modification of LDL, a critical event
during atherogenesis.13 For this reason, many individuals take
this and other antioxidant vitamins in hope that combating
oxidative stress can forestall atherosclerosis and its complications. Vitamin C has other antiinflammatory effects as well,
including decreased leukocyte adhesion to the endothelium
and increased bioavailability of atheroprotective nitric oxide
(NO). Administration of vitamin C for 10 days (2 g/d)
reduces adhesion of monocytes obtained from cigarette
smokers to cultured endothelial cells.14 Vitamin C’s potency
generally exceeds that of vitamin E as an antiinflammatory
and antiatherogenic agent. For example, intake of vitamin C,
but not vitamin E, inhibits oxidized LDL-induced leukocyte
adhesion to endothelium in hamsters.15 Physiological concen-
ost fatal acute myocardial infarctions result from a
fracture of the plaque’s fibrous cap. We proposed
the hypothesis some years ago that the level of
collagen in the fibrous cap depends on a dynamic balance of
synthesis and degradation.1 We further showed that inflammatory cytokines can regulate both the expression of genes
that direct interstitial collagen synthesis in vascular smooth
muscle cells and the interstitial collagenases (matrix metalloproteinases 1, 8, and 13) required to initiate the breakdown
of collagen fibrils.2–5 Given the capital importance of collagen in protecting the plaque from rupture and hence thrombosis, the metabolism of this complex molecule merits
consideration in depth.
See p 1485
The formation of mature fibrillar collagen involves many
steps beyond gene transcription (Figure). The initial translation product, the procollagen peptide chain, undergoes extensive posttranslational modification: an especially noteworthy
point during this period of exploration of the proteome.
Collagen contains unusual amino acids, hydroxyproline and
hydroxylysine, formed by a vitamin C– dependent process
that entails enzymatic transfer of hydroxyl groups to selected
proline and lysine residues in the nascent procollagen chains.
Glycosyl transferases then add sugar moieties to the procollagen chains. The hydroxylated and glycosylated monomers
then self-assemble into helical trimers as they traverse several
intracellular compartments. Trimming the nonhelical tails
(the telopeptides) from both ends of the procollagen molecule
by proteinases yields the mature interstitial collagen triple
helix secreted by smooth muscle cells in arteries. These
building blocks then further self-aggregate into multimers
and form interstitial collagen fibrils, linear structures as
strong as steel wires.
The ascorbate-dependent addition of polar hydroxyl groups
to the side chains of proline and lysine may aid the selfassembly and stability of the collagen fibril by forming
interchain hydrogen bonds. The absence of sufficient ascorbic
acid (vitamin C), a required cofactor for prolylhydroxylase,
thus impairs the formation of stable collagen. The human
phenotype of vitamin C deficiency, scurvy, classically inThe opinions expressed in this editorial are not necessarily those of the
editors or of the American Heart Association.
From the Leducq Center for Cardiovascular Research, Department of
Medicine, Brigham and Woman’s Hospital, Harvard Medical School,
Boston, Mass.
Correspondence to Peter Libby, MD, Brigham and Woman’s Hospital,
Eugene Braunwald Research Center, 221 Longwood Ave, Room 307,
Boston, MA 02115. E-mail [email protected]
(Circulation 2002;105:1396-1398.)
© 2002 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
DOI: 10.1161/01.CIR.0000012513.58079.EA
1396
Libby and Aikawa
The Collagen Complex
1397
Biosynthetic pathway for interstitial collagen. The text describes the various
steps depicted in this diagram, which
provides particular emphasis on the sites
at which Vitamin C participates in the
process.
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trations of ascorbic acid also increase synthesis and activity
of NO in vitro.16 Vitamin C also inhibits activation of nuclear
factor-␬B (NF-␬B), a key regulator of inflammatory gene
expression.17 Administration of vitamin C can improve endothelial dysfunction in hypercholesterolemic patients.18
Ascorbate’s effect on plaque collagen content adds another
theoretical rationale for using vitamin C in patients at risk for
atherosclerotic events.
Unfortunately, we lack clinical evidence that would permit
us to translate this basic science into practice. The recently
reported (but as yet unpublished) Heart Protection Study
(HPS) administered a cocktail of antioxidant vitamins (vitamin C 250 mg, vitamin E 600 mg, beta-carotene 20 mg/d) to
a large group of individuals at high risk for atherosclerotic
events for a period of 5 years. The vitamins had absolutely no
effect on a variety of end points, including coronary events19
(see also The Heart Protection Study Investigators at http://
www.hpsinfo.org). Brown and colleagues recently reported
acceleration of coronary atherosclerosis in patients treated
with a combination of statins and a cocktail of antioxidant
vitamins (vitamin C 1000 mg, vitamin E 800 IU, betacarotene 25 mg/d) in the HDL-Atherosclerosis Treatment
Study (HATS).20
To what may we attribute this apparent failure of a
plausible and widely used therapeutic approach? First, these
studies may have employed suboptimal doses of the vitamins
used, or interactions among them may have mitigated a
beneficial effect of one or the other supplements. In this
regard, vitamin E monotherapy showed no benefit on atherosclerotic events in both the Heart Outcomes Prevention
Evaluation (HOPE) and GISSI studies.21,22 In these various
studies, the degree of preexisting disease or inadequate
duration of treatment might have limited the benefit of the
antioxidants. Yet, the striking beneficial effects observed in
the statin treatment arms of both the HPS and HATS20 and of
the angiotensin converting enzyme inhibitor in the HOPE
study21 establish the mutability of outcomes measured in
these patient populations in the same trials. Partition of
fat-soluble vitamin E into the lipid phase of plaque or
lipoproteins might shield it from the cooperative antioxidant
effect of water-soluble ascorbate, excluded from these lipid
milieux. Thus, more potent or amphipathic antioxidants
might interrupt oxidative stress during atherogenesis more
effectively than the vitamins. Although vitamin deficiencies
lead to disease, consumption of pharmacological amounts of
these substances in individuals who maintain vitaminsufficient diets may not prevent disease. Indeed, malnutrition
hardly applies to our patients with atherosclerosis. Contemporary developed societies seem at much higher risk of
dietary surfeit than lack.
It is curious indeed that many remain suspicious of
pharmacological lipid-lowering, a strategy now proven un-
1398
Circulation
March 26, 2002
equivocally to prevent myocardial infarction and stroke and
to prolong life as well. Yet, many individuals readily consume costly vitamin supplements devoid of benefit in clinical
trials. This situation may reflect in part a failure of the
medical community to communicate effectively with the
public regarding evidence-based medicine and the life-saving
benefits of preventive strategies. The present results of
Nakata et al8 reinforce the importance of collagen metabolism
in determining the structure of atherosclerotic plaques. However, current clinical and experimental evidence suggests that
the best way to influence favorably the balance of collagen
synthesis and degradation in atheroma at hand today remains
lipid-lowering, not vitamin C.
Acknowledgments
This work was supported in part by grants to Dr Libby from the
National Heart, Lung, and Blood Institute (HL-34636 and
HL-56985).
10.
11.
12.
13.
14.
15.
16.
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KEY WORDS: Editorials
plaque stability
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extracellular matrix
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vitamin C
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collagen
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Vitamin C, Collagen, and Cracks in the Plaque
Peter Libby and Masanori Aikawa
Circulation. 2002;105:1396-1398
doi: 10.1161/01.CIR.0000012513.58079.EA
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