Plasmin-Induced Proteolysis and the Role of Apoprotein(a), Lysine, and Synthetic
Matthias Rath M.D. and Linus Pauling Ph.D.
Journal of Orthomolecular Medicine 6: 139-143
In recent years the international research community became fascinated
by a unique protein in the human body: apoprotein(a) [apo(a)]. In the
three decades since its discovery apo(a) has been primarily discussed
in relation to its deleterious effects on human health, in particular
on cardiovascular disease (CVD). We did not accept that apo(a) should
have only disadvantageous properties. According to the laws of evolution
apo(a) must have beneficial properties that by far outreach its disadvantages.
Consequently, we discovered that under physiological conditions apo(a)
functions as an adhesive protein, mediating organ differentiation and
growth. Under pathophysiological conditions apo(a) primarily substitutes
for ascorbate deficiency and increases tissue stability by compensating
for impaired collagen metabolism, and by promoting tissue repair (1).
Moreover, we proposed that apo(a) functions as an inhibitor of important
pathomechanisms involved in the proliferation of many diseases. These
pathomechanisms are favored during ascorbate deficiency. One of these
universal pathomechanisms is the damaging effect of oxygen free radicals,
which is attenuated by the antioxidative function of apo(a) as a proteinthiol
Apo(a) also led us to determine the universal importance of another
pathomechanism: the enzymatic degradation of the connective tissue by
the protease plasmin. We recently proposed that apo(a), by virtue of
its homology to plasminogen, functions as a competitive inhibitor of
plasmin- induced proteolysis (3). In this publication we describe the
universal character of this mechanism and the role of apo(a) in more
detail. Plasmin-induced proteolysis had been described as a pathomechanism
for some diseases, e.g. cancer and certain viral diseases (4,5). In cardiovascular
disease, however, this mechanism has received little, if any, attention.
The insufficient understanding of the universal character of this pathomechanism
is further underlined by the absence of a broad therapeutic use of L-lysine
and its synthetic analogs, which are exogenous inhibitors of this pathway.
The lack of this knowledge continues to have detrimental consequences
for human health and it prevents millions of patients from receiving
optimum treatment. It is the aim of this publication to close this gap
and to provide the rationale for a broad introduction of lysine and its
synthetic analogs into clinical therapy.
Plasmin-Induced Proteolysis Under Physiological Conditions
Plasmin-induced proteolysis is a physiological mechanism that occurs
ubiquitously in the human body. The main cellular defense systems, monocytes,
macrophages, and neutrophiles, use this mechanism for their migration
through the body compartments. They secrete plasminogen activators, which
then activate plasminogen to plasmin. This mechanism makes efficient
use of high blood and tissue concentrations of the proenzyme, plasminogen,
which represents a huge reservoir of potential proteolytic activity.
The activated protease plasmin then converts procollagenases into collagenases
(6), and quite possibly also activates other enzymes, leading to a local
degradation of the connective tissue. This local degradation of the connective
tissue paves the way for the migration of macrophages through the body.
The proteolytic effect of plasmin is also involved in increasing vascular
permeability (7). This effect facilitates the infiltration of monocytes
and other blood cells from the circulation to the tissue sites of increased
requirement. Physiological conditions in which plasmin-induced proteolysis
occurs include different forms of tissue formation and reorganization
such as neurogenesis, vascularization, and, quite probably, growth.
Of particular importance is plasmin-induced proteolysis during the remodulation
of female reproductive organs. Under hormonal stimulation mammary and
uterine cells secrete plasminogen activator and thereby initiate the
morphologic changes of the organ during pregnancy and lactation (4).
A particularly striking example for the effectiveness of this mechanism
is ovulation. Luteinizing hormone (LH) and follicle cell stimulating
hormone (FSH) stimulate the secretion of plasminogen activators from
granulosa cells (8). The subsequent degradation of the ovarian connective
tissue is a precondition for ovulation (Figure 1a). Similarly trophoblast
cells use plasmin-induced proteolysis to invade the wall of the uterus
during embryo implantation in early pregnancy. In all these conditions
enzyme production is transient and is precisely regulated by hormones
and other control mechanisms.
Plasmin-Induced Proteolysis Under Physiological Conditions
Plasmin-induced tissue degradation contributes to the proliferation
of most diseases. Of particular interest is the fact that similar mechanisms
are induced by attacking pathogens as they are used by the defending
host cells, e.g. macrophages. In many pathological conditions macrophages
become 'activated'. This activation reflects a particular state of alert
that is characterized by an abundant release of secretory products. These
products include oxygen metabolites, collagenases, elastases, and a significantly
increased secretion of plasminogen activators. It is immediately obvious
that this mechanism needs to be precisely controlled. Therefore macrophages
also secrete inhibitory products including plasmin inhibitors and a2-macroglobulin
which are able to inactivate plasmin and many other proteases. Any imbalance
in this control system leads to an exacerbation of this mechanism and
to continued tissue degradation. Chronic activation of macrophages and
an exertion of the control mechanisms eventually lead to a sustained
degradation of the connective tissue and to an accelerated proliferation
of the disease. It is, therefore, not unreasonable for us to propose
that plasmin-induced tissue degradation contributes, to a varying degree,
to the proliferation of all diseases.
This mechanism is, however, not limited to macrophages and other defense
cells of the human body. In the following sections we shall discuss this
pathomechanism for the most important diseases in more detail.
Malignant transformation of many cells of the human body leads to an
uncontrolled secretion of plasminogen activators. In this situation the
secretion of plasminogen activators is not a temporary event, but is
rather a characteristic feature of malignant cells. The magnitude of
increase in plasminogen-activator production, between 10 and 100 fold,
renders this enzyme unique among the biochemical changes associated with
oncogenic transformation. Moreover, plasminogen-activator secretion occurs
independently of the induction mechanism and can be found as the result
of oncogenic viruses or chemical carcinogens. Most importantly, the amount
of plasminogen activators secreted was, in general, associated with the
degree of malignancy (4,5). Immunohistological studies showed that the
concentration of plasminogen activators in the vicinity of a tumor is
highest at the sites of its invasive growth (9).
Because of the prominent role of plasmin-induced proteolysis in female
reproductive organs under physiological conditions it is no surprise
that the exacerbation of this mechanism is particularly frequent in malignancies
of the female reproductive organs. Cancer cells of the breast, the uterus,
the ovaries, and other organs continuously secrete increased amounts
of plasminogen activators, destroy the surrounding extracellular matrix,
and thereby pave the way for infiltrative growth. These mechanisms are
also involved in the proliferation of prostatic cancer, one of the most
frequent forms of cancer in males.
Plasmin-induced proteolysis is also critical for the metastatic spread
of cancer. As discussed above, plasmin induces increased permeability
of the blood vessels and thereby facilitates the systemic dissemination
of tumor cells. This pathomechanism is, of course, not limited to reproductive
organs. Plasmin-induced tissue degradation has been reported for tumors
of the ovaries, endometrium, cervix, breast, colon, lung, skin (melanoma,
and many others (4), suggesting that most cancers make use of this mechanism
for their proliferation.
Infectious and inflammatory diseases.
As for transformed cells in malignancies, virally transformed cells
were also found to secrete plasminogen activators (4,5). These cells
activate plasminogen in their vicinity, e.g., the lung tissue, and thereby
facilitate the local spread of the infection. Simultaneously, plasmin
increases the permeability of the local blood vessels and thereby promotes
the systemic spread of the infection.
It is not unreasonable for us to propose that other pathogens may also
make use of this mechanism during the process of infection. Plasminogen
activators play an important role during inflammation in general. Production
of plasminogen activators by macrophages and granulocytes is closely
correlated to different modulators of inflammation. Secretion of the
enzyme is stimulated by asbestos, lymphokines, and interferon and is
inhibited by anti-inflammatory agents such as glucocorticoids. Plasmin-induced
proteolysis has been described for patients with a variety of inflammatory
diseases, including chronic rheumatoid arthritis, allergic vasculitis,
chronic inflamatory bowel disease, chronic sinusitis, demyelinating disease,
and many others (4). Plasmin-induced tissue degradation is therefore
likely to be an important pathomechanism in chronic inflammatory diseases.
Activated macrophages play an important role in the pathogenesis of
cardiovascular disease. Blood monocytes enter the vascular wall, where
they become macrophages. Their activation inside the vascular wall is
enhanced by oxidatively modified lipoproteins and other challenging mechanisms
(3,10). Once they are activated a similar cascade of events occurs, as
in any other disease: increased secretion of plasminogen activators,
activation of procollagenases by the protease plasmin, and degradation
of the connective tissue in the vascular wall. Simultaneously, plasmin
increases the permeability of the vascular wall, leading to a further
increase in the infiltration of plasma constituents. The perpetuation
of these pathomechanisms leads to the development of atherosclerotic
lesions. This mechanism is particularly effective when the vascular wall
is already destabilized by a deficiency in ascorbate. As described recently
in detail (3), this instability is primarily unmasked at sites of altered
hemodynamic conditions, such as the branching regions of the coronary
arteries. It is therefore no surprise that increased amounts of plasminogen
activators were detected in these branching regions of human arteries.
Moreover, atherosclerotic lesions in general were found to contain significantly
higher amounts of plasminogen activators than grossly normal arterial
wall (11). It is a remarkable fact that these early observations have
not been followed up systematically. This negligence suggests that the
universal character of uncontrolled plasmin-induced proteolysis for disease
proliferation has not yet been fully understood. It is the aim of this
paper to close this gap.
Apoprotein(a) - An Inhibitor of Plasmin-Induced Proteolysis
In identifying the universal importance of plasmin-induced proteolysis
for most diseases we were once again guided by apo(a) and its increased
demand as reflected by the elevated plasma concentrations in many pathological
conditions. As discussed above, apo(a) exerts a multitude of functions
under physiological and pathophysiological conditions. Here we focus
on the role of apo(a) as an endogenous competitive inhibitor of plasmin-induced
proteolysis and tissue degradation.
Apo(a) is a glycoprotein with a unique structure. It is essentially
composed of a repetitive sequence of the kringle structures highly homologous
to the kringle IV of the plasminogen molecule. The gene for apo(a) is
located in the direct vicinity of the plasminogen gene on chromosome
6. It has been proposed that the apo(a) molecule derives from the plasminogen
molecule or that the two genes share a common ancestral gene (12). As
of today no explanation has been offered as to why among all five kringles
of plasminogen it is almost exclusively kringle IV that was chosen by
nature to compose the apo(a) molecule.We do not accept this selective
advantage of kringle IV as a coincidence. We propose that at least one
of the reasons for the repetition of kringle IV in apo(a) is closely
related to the structure/function of kringle IV in the plasminogen molecule.
It is not unreasonable for us to propose that apo(a), by virtue of its
multiple kringle IV structures, is a competitive inhibitor of plasmin-induced
proteolysis. Apo(a) could be involved in the control of this pathway
without interfering with critical functions of plasminogen mediated by
other kringles of the plasminogen molecule. Consequently, the more kringle
IV repeats one apo(a) molecule contains, the more effective this apo(a)
isoform would be as an inhibitor. This concept could not only explain
the selective advantage of kringle IV versus the other kringle structures,
but it could also explain the great variation in genetically determined
plasma Lp(a) concentrations, which largely reflect the inverse relation
between the number of intramolecular kringle IV repeats and the synthesis
rate of apo(a) molecules.
Supportive evidence for a role of apo(a) in the control of plasmin-
induced proteolysis is also provided by a number of observations. Apo(a)
has been shown to attenuate tissue-plasminogen-activator-induced fibrinolysis
and competitively interfere with plasminogen- and plasmin- induced pathways
(review in 14). Moreover, immunohistological studies in various diseases
showed a preferential deposition of apo(a) at the site of increased demand
for a control of plasmin-induced proteolysis. In several hundred vascular
specimens representing various degrees of cardiovascular disease apo(a)
was found primarily to be located in the subendothelium, quite possibly
counteracting the increased endothelial permeability. In advanced atherosclerotic
lesions apo(a) was preferentially found around the lesion core, particularly
at the edges of the lesion (15), the main sites of chronic repair processes.
In a comprehensive morphological study in different forms of cancer apo(a)
was found to be deposited in the vicinity of the cancer process (Dr.
A. Niendorf, personal communication). Both studies were conducted with
the same monoclonal antibodies not cross-reacting with plasminogen. A
preliminary report is also available for the deposition of apo(a) in
the microvasculature of inflammatory processes (16). We predict that
apo(a) will also be found to play an important role in the containment
of infectious diseases, including AIDS. The role of apo(a) as a competitive
inhibitor of plasmin-induced proteolysis is not limited to pathological
conditions. An increased demand of apo(a) was also observed during the
period of uterus transformation in early pregnancy (17).
In summary, apo(a) is suggested to be an important element in the endogenous
control system of plasmin-induced proteolysis. Apo(a) may back-up antiplasmin
and other endogenous inhibitors of this pathway particularly during chronic
activation of this mechanism. Beside endogenous inhibitors of plasmin-induced
tissue degradation there are also exogenous inhibitors. The universal
importance of the pathomechanism described here immediately suggests the
great value of these exogenous inhibitors in the therapy of many diseases.
The Therapeutic Use of Lysine and Synthetic Lysine Analogs
Lysine, an essential amino acid, is the most important naturally- occurring
inhibitor of this pathway. As opposed to the competitive inhibition by
apo(a), lysine inhibits plasmin-induced proteolysis in a direct way.
Lysine attenuates an overshooting activation of plasmin, at least in
part, by occupying the lysine binding sites in the plasminogen molecule.
Since lysine is an essential amino acid, its availability is not regulated
endogenously. Insufficient dietary lysine intake invariably leads to
a deficiency of this amino acid and thereby weakens the natural defense
against this pathomechanism. Moreover, chronic activation of plasminogen
by cancer cells, virally transformed cells, or macrophages leads to an
additional relative lysine deficiency and thereby to an acceleration
of the underlying disease. The therapeutic value of lysine has been documented
for a variety of diseases, including viral diseases (18), and recently
in combination with ascorbate for cardiovascular disease (19).
Synthetic lysine analogs such as epsilon-aminocaproic acid, para-aminomethylbenzoic
acid and trans-aminocyclohexanoic acid (tranexamic acid) are potent inhibitors
of plasmin-induced proteolysis. These substances, in particular tranexamic
acid, have been successfully used in the treatment of a variety of pathological
conditions, such as angiohematoma, colitis ulcerosa, and others. Most
remarkable results were reported from the treatment of patients with
late-stage cancer of the breast (20) and the ovaries (21) and also for
cancer of other origins (22). We have recently suggested the therapeutic
use of synthetic lysine analogs for the reduction of atherosclerotic
On the basis of the work presented here, comprehensive clinical studies
should be initiated to establish the critical role of lysine in the prevention
and treatment of various diseases without delay. A daily intake of 5
grams of lysine and more (19,23) has been described to be without side
effects. On the basis of the encouraging therapeutic results with tranexamic
acid, particularly in inhibiting and reducing late-stage cancer, these
substances should now be extensively tested for a broad introduction
into clinical therapy, particularly for advanced forms of cancer, CVD,
and AIDS. A possible explanation of why this has not happened long ago
may be the argument that these substances may induce coagulative complications.
They are , however, protease inhibitors and inhibit not only fibrinolysis
but also coagulation (24). Moreover, tranexamic acid has been given for
more than 10 years without clinical complications (25). We have proposed
that the risk of any hemostatic complication will be further reduced
by a combination of these compounds with ascorbate and other vitamins
with anticoagulative properties (3). This medical consideration is, however,
not the only factor why these compounds are not used much more frequently
and why thousands of patients are still deprived of optimum therapy.
There is also an economic factor. Patent protection is a guiding principle
of any pharmaceutical company in developing or marketing a drug. Lysine,
like many other nutrients, is not patentable and the patents for the
clinically approved synthetic lysine analogs, including tranexamic acid,
have expired. The negligence of these substances may be explainable from
the economic point of view; from the perspective of human health there
is no justification for this delay.
Here we have described plasmin-induced proteolysis as a universal pathomechanism
propagating cancer, and cardiovascular, inflammatory, and many other
diseases. Plasmin-induced tissue degradation under pathological conditions
is an exacerbation of a physiological mechanism. Apo(a) is suggested
to function as a competitive endogenous inhibitor of this pathway. On
the basis of the selective advantage of apo(a) in the evolution of man
it comes as no surprise that apo(a) should lead us on the way to recognize
the universal importance of this pathomechanisms. Further clinical confirmation
of the therapeutic value of lysine and its synthetic analogs may provide
new options for an effective therapy for millions of people. We predict
that the use of lysine and synthetic lysine analogs, particularly in
combination with ascorbate, will lead to a breakthrough in the control
of many forms of cancer and infectious diseases, including AIDS, as well
as many other diseases.
We thank Dr. Alexandra Niedzwiecki for helpful discussions, Rosemary
Babcock for library services, Jolanta Walechiewicz for graphical assistance,
Martha Best and Dorothy Munro for secretarial help.
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