Lipoprotein(a) Reduction by Ascorbate
Matthias Rath M.D. and Linus Pauling Ph.D.
Journal of Orthomolecular Medicine 7: 81-82.
Lipoprotein(a) [Lp(a)] is associated with an increased risk of atherogenesis
and thrombogenesis. Recently it was proposed that Lp(a) is a surrogate
for ascorbate.1 This proposal suggested a role of ascorbate in the
regulation of Lp(a) synthesis: namely, that increased intake of ascorbate,
a strong natural reducing agent, would lower Lp(a) plasma levels. N-Acetylcysteine
(NAC) was then also proposed to lower Lp(a) plasma levels and was reported
to do this to a variable degree.2,3 The effect of ascorbate in lowering
Lp(a) plasma levels was studied in a clinical pilot study with the
results reported here.
Patients, Materials and Methods
Eleven outpatients with coronary heart disease and elevated Lp(a) levels
consented to participate in this study. The patients received 9 grams
of ascorbic acid (Bronson Pharmaceuticals, La Canada, California) per
day for a period of 14 weeks. Plasma Lp(a) levels were determined at
the beginning and at the end of the study. Lp(a) plasma levels were
determined by a sandwich ELISA method with monoclonal capture antibodies
against apo(a) and monoclonal peroxidase-labeled antibodies against
the apoB-100 portion of the Lp(a) molecule. 4 The antibodies were a
gift from Dr. J. C. Fruchart, Lille, France.
In this study ascorbate was found to lower Lp(a) plasma levels on average
by 27% with a median value also of 27% (Table 1). Two of the 11 patients
showed no decrease of Lp(a) during this time period. Lp(a) in the same
plasma samples was also measured with immunological assays using monoclonal
antibodies against the apo(a) portion of the Lp(a) molecule for both,
capturing and revealing (radioimmunoassay[RIA], Pharmacia Diagnostics;
anti-apo(a) sandwich ELISA). Changes in Lp(a) plasma concentrations
were measured for RIA mean +2%, median -7.5 % and for ELISA mean -4%,
median -12%. The mean values for vitamin C plasma levels were 48.6
uM at the beginning and 94.4 uM at the end of the study.
Two factors may account for the differences between the assay including
an antibody against apoB and the assays using exclusively anti-apo(a)
antibodies. One factor could be the variation in epitopes of the apo(a)
molecule as a result of the variation of the molecular size determined
by the genetic isoforms. This factor was largely excluded in this study
by determining the apo(a) isoforms by means of SDS PAGE and subsequent
immunoblotting with anti apo(a) antibodies.
The second possible factor accounting for these differences is the effect
of reducing agents on the intramolecular disulfide bonds of the apo(a)
molecule. This factor is discussed here in more detail. Apo(a) has
been proposed to function as a proteinthiol1 and the disulfide bonds
of the repetitive plasminogen kringle IV structure are known to have
different dissociation constants. Elevated plasma concentrations of
reducing agents such as ascorbate or NAC could alter the epitope constellation
of the apo(a) molecule in vivo by reducing some of the many disulfide
bonds to sulfhydryl groups. Underthis condition, assays using only
anti-apo(a) antibodies could give falsely positive results, dependent
on the specific epitopes they recognize in the repetitive kringle structures
of the apo(a) molecule.
In contrast, an assay measuring the apoB portion of the Lp(a) molecule
should provide more reliable results since apoB contains less disulfide
bonds and in addition has a constant molecular size. This conclusion
could also explain the fact that the only two studies reporting a lowering
of Lp(a) plasma levels with reducing agents included assays using anti-apoB
antibodies for detection (2, and this paper). In contrast, assays exclusively
based on antibodies against apo(a) gave variable results in the presence
of reducing agents. 2,3
From in vitro studies with NAC it was recently concluded that supraphysiological
concentrations of reducing agents above 1 mM decrease the immunoreactivity
for Lp(a). 5 The extrapolation of these results to the in vivo situation
must, of course, be handled with care. The highest molar concentration
of ascorbate measured in the study reported here was 154 uM, a level
that does not decrease the immunoreactivity of apo(a) or Lp(a). The
effect of physiological levels of ascorbate on the reduction of disulfide
bonds of the apo(a) molecule as well as the possible immunological
implications need further investigation
The results of the clinical study reported here, namely that dietary
ascorbate supplementation reduces Lp(a) plasma levels, was supported
by in vitro studies in our laboratory with human liver cells (HepG2,
data not shown). In metabolic studies using S35 methionine increasing
concentrations of ascorbate in the cell culture medium decreased the
amount of Lp(a) secreted by these cells. Ascorbate concentrations up
to 2.25 mM did not reveal any dissociation of apo(a) from apoB. It
is, therefore, concluded that the effect of ascorbate on Lp(a) plasma
levels is the result of a decreased rate of synthesis of Lp(a) particles
in the liver.
In conclusion, ascorbate is a physiological reducing agent involved in
the metabolic regulation of Lp(a) synthesis. Dietary supplementation
of ascorbate, as an adjunct to conventional therapy, should contribute
to reducing elevated Lp(a) plasma levels and the risk of cardiovascular
disease. Prolonged supplementation of ascorbate may be required to
achieve these effects.
1. Rath M, Pauling L. Hypothesis: Lipoprotein(a) is a surrogate for
ascorbate. Proceedings of the National Academy of Sciences USA 1990;
2. Gavish D, Breslow J. Lipoprotein(a) reduction by N-acetylcysteine.
Lancet 1991; 337:203-204.
3. Stalenhoef AFH, Kroon A, Demacker PNM. N-acetylcysteine
and lipoprotein. Lancet 1991; 337: 491.
4. Vu Dac N, Mezdour H, Parra HJ, Luc G, Luyeye I, Fruchart
JC. A selective bi-site immunoenzymatic procedure for human Lp(a) lipoprotein
using monclonal antibodies against apo(a) and apoB. Journal of
Research 1989; 30: 1437-1443.
5. Scanu AM, Pfaffinger D, Fless GM, Makino K, Eisenbart
J, Hinman J. Attenuation of immunologic reactivity of lipoprotein(a) by
thiols and cysteine-containing compounds. Arteriosclerosis and Thrombosis
1992; 12: 424-429