Plasmin-Induced Proteolysis and the Role of Apoprotein(a),
Lysine, and Synthetic Lysine Analogs
Matthias Rath M.D. and Linus Pauling Ph.D.
Most human diseases, independent of their individual genetic or exogenous
origin, proliferate via similar pathomechanisms. One of these universal
pathways is propagated by oxygen free radicals. Here we present another
universal pathomechanism: the degradation of the connective tissue by
the protease plasmin. This mechanism had been described for some diseases
but its universal character has still been insufficiently understood.
We propose now that the proliferation of cancer, cardiovascular disease
(CVD), and also inflammatory and many other diseases depends to a varying
degree on this pathomechanism. Activated macrophages, but also cancer
cells, virally transformed cells, and other pathogenic cells secrete considerable
amounts of plasminogen activators, which lead to an activation of plasminogen
to the protease plasmin which activates procollagenase to collagenase.
The resulting degradation of the extracellular matrix is a precondition
for the proliferation and the clinical manifestation of any disease. Most
acute and chronic diseases make use of this pathomechanism. This pathomechanism
is the exacerbation of a mechanism used under physiological conditions
by a variety of cellular systems of the human body. The exacerbation under
pathological conditions is the result of a chronic imbalance between activators
and inhibitors of this pathway. Apoprotein (a), apo(a), by virtue of its
homology to plasminogen is proposed to be a competitive endogenous inhibitor
of plasmin induced proteolysis and tissue degradation. The essential amino
acid L-lysine functions as an exogenous inhibitor of this pathway. Therapeutic
administration of L-lysine and synthetic lysine analogs, such as tranexamic
acid, should lead to an effective control of plasmin- induced tissue degradation.
Comprehensive clinical confirmation of this work will particularly improve
the therapeutic options for advanced forms of CVD, cancer, and inflammatory
and infectious diseases, including AIDS.
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
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
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
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 plaques
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
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
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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