Commentary
FIBRIN COMPLEXES IN INTERMEDIARY COAGULATION JOHN R. SHAINOFF, Ph.D. AND HENRY H. ROENIGK, JR., M.D.
from the Research Division and Department of Dermatology, The Cleveland Clinic Foundation, Cleveland^ Ohio
The ease with which pathology can be diagnosed in disease of the integument puts the dermatologist in prime position to assess new concepts of disease mechanisms, especially as they apply to man. Recent advances in the chemistry of fibrin have generated several new concepts of its formation, transport and metabolism within the circulation which have proven useful for the detection and quantification of systemic abnormalities leading to fibrin deposition. By virtue of the derivation of these concepts from intrinsic properties of fibrinogen and fibrin, they should also apply in principle to the highly localized lesion. But their use for diagnosis or investigation of highly localized abnormalities becomes diminished, actually diluted, to varying degrees depending on feasibility of examining blood from the area of the lesion. Fibrin Formation
:
Although detection of fibrin deposits on biopsy can be taken as an indication of fibrin formation, alternative pathways to deposition are known. Questions
may also be posed concerning rates of formation as opposed to removal of fibrin. Ability to detect and quantify specific events involved in the formation and modification of fibrin can aid in establishing mechanism. To that end we have focused on a critical stage in which soluble fibrinogen-fibrin complexes are formed as an intermediary process in coagulation. The complexes can be viewed as critical because the aggregation of fibrin into insoluble strands hinges on formation of saturating levels of the complexes in blood. The level of the complexes therefore serves to define proximity to the coagulative state in the blood being examined. In this commentary we will formulate this perspective and outline details which we believe are important. Examples of the clinical application of this particular perspective, together with citations to other important aspects that are not covered in the present commentary, can be found in a preceding article.' Viewed schematically in step-by-step sequence, fibrin formation involves initially an enzymic attack by thrombin in which certain small segments, the fibrinopeptides, are cleaved from the amino terminal ends of the fibrinogen molecules. The release of fibrinopeptide transforms the fibrinogen into a self-aggregating derivative known as fibrin monomer (1st horizontal arrow, 738
FIBRIN COMPLEXES • Siiainoff and Roenigk
No. 10
\
\
\ \
f
\
•
f(f-f)f
Fibrinogen
Monomer
(f • f ) f ( f • f ) f ( f - f )
/
I / Polymer
\
Fig. 1.
739
\
y
Clot
\\ cjb (f
cj!>
Complex
Fig. 1). These monomers then aggregate (2nd arrow) into threadlike polymers which in turn coalesce to form the fibrous structure of the clot (3rd arrow). Although the aggregation involves fairly weak bonding that is easily broken by concentrated urea or weak acids, virtually none of the fibrin escapes incorporation into the coagulum at the end of the reaction under simulated physiologic conditions. (Under real physiologic conditions^ the reaction seldom goes to completion except in shed blood or the occluded vessel.) In the ongoing reaction, the steps are not temporally separated but are concurrent with the fibrin aggregating as it is produced until the parent fibrinogen is depleted. Small amounts of fibrin may be continually produced within the circulation, and it is reasonable to believe that a balance normally exists between the formation of the fibrin and its destruction. How is this balance maintained? Explanation A partial explanation was found in the observation^ that in the ongoing clotting reaction, the interaction of the fibrin with the parent fibrinogen suppresses its aggregation into insoluble strands. The interaction of fibrinogen with fibrin was confirmed by observation that fibrin, once aggregated into a clot, could be
dissolved again in solutions of fibrinogen, and made to clot again by separating it from the fibrinogen. The soluble combination of fibrinogen with fibrin provides a means for continual transport of fibrin in a dissolved state in blood. Thus, small amounts of fibrin can in principle be continually produced in the peripheral circulation and transported in soluble form to the liver where it is rapidly removed. The absence of fibrin deposits in healthy vascular tissue seems to fit with the experimental observation that critically high threshold concentrations of fibrin appear necessary to predispose its deposition from blood. The threshold varies in proportion to the concentration of fibrinogen. As judged by several investigators, the threshold is reached when the level of fibrin rises to about 8% of the fibrinogen. Above this level, the soluble complexes become unstable, and resultant breakdown of transport serves to disseminate fibrin deposition. Figure 1 attempts to depict the equilibrium. The angular shaped lines can be imagined as a plane projecting through the page at a tilt dependent on the relative amounts of fibrinogen and complex. If the level of complex rises above the perpendicular (the equilibrium plateau) the complexes become unstable, whence the excess breaks down into component fibrinogen and fibrin
740
INTERNATIONAL JOURNAL OF DERMATOLOGY
until balance is reached again. When left uncombined with fibrJnogen, the excess fjbrin combines vi/Jth itself to form insoluble strands. Shwartzman Reaction ThJs simple concept of the role of the complexes in hemostasis has been shown to apply directly to the problem of fibrjn deposition Jn the generalized Shwartzman reaction. A correspondence was seen between the occurrence of bilateral renal cortJcal necrosis and the formation of threshold concentrations of complex. Fibrinoid formation Jn the Shwartzman reaction has been recognized as being due in large part to reticuloendothelial blockade by endotoxin impairing clearance of mJnute aggregates of fibrin from the blood stream. The steps preceding the precipitation of the fibrJn from blood appear critical. Applicability of the concept of the generalized Shwartzman reaction in rabbits has prompted us to use Jt as a model for study of other disease phenomena with the prospect that exceptions or specific modifications required to explain findings will provide basis for uncovering new reactions or details pertaining to pathology. The model is based in its simplest form on reversibility in the aggregation of fibrin. Irreversible alterations of fibrin occur when it is acted upon by plasmin and fibrin stabilizing factor. Such changes can be detected from physical and chemical characterization of the complexes, and effects on equilibria can be taken into account. For example, fibrin stabilizing factor is known to catalyze crosslinking of fibrin clots and thereby make the clots resistant to dissolution. The equilibrium involved in formation of fibrinogen-fibrin complexes is Jmportant here also. When formation of complexes is favored over
December 1976
Vol. 15
formation of a clot, the fibrin stabilizing factor will crosslink the flbrinogen to the dissolved fibrin within the complex. The permanent linkage of fibrin within the complex in essence inactivates ability of the fibrin to undergo further aggregation until the fibrinogen within the complex is acted upon by thrombin. Plasmin Limited degradation of fibrinogen and fibrin by plasmin appears to displace the equilibrium In the direction of favoring formation of complexes. However, once plasmin destroys ability of fibrin monomer to undergo self-aggregation, it also destroys its ability to form complexes with fibrinogen. It is reasoned that such extensive degradation of fibrin as a complex in plasma is not likely to occur without concurrent destruction of the fibrinogen. Thus, when the noncoagulable forms of fibrin, the "split products," are found in blood in which the fibrinogen is largely intact, it can be inferred that they arise from highly localized breakdown of an existing clot or fibrin deposit. By way of exception to this simplified concept of fibrin deposition, there is growing evidence that alternate pathways to polymerization and deposition of fibrinogen exist which do not depend upon thrombic action.^ Because of this possibility and the importance of complicating factors noted above, we view the distinction between polymers of fibrinogen itself ("macrofibrinogen"), the noncoagulable degradation products ("split products"), the crosslinked and dissociable forms of fibrinogen-fibrin complex ("cryoprofibrin") important, at least for purpose of research. A large repertoire of laboratory methods is available for the detection and quantification of these variant forms which cannot be
No. 10
FIBRIN COMPLEXES • Shainoff and Roenigk
reviewed here. However, the question may be asked whether the effort required for thorough analysis is warranted, particularly when the blood sample gives only an indication of the systemic composition which may differ greatly from that in the highly localized lesion. Systemic Levels Systemic levels of the complexes in man usually comprise only a small fraction of a percentage of the total fibrinogen, and a small increase may reflect formation of substantial amounts in remote regions of the vasculature. Conversely, examples exist^ in which elevated levels of fibrinogen-fibrin complex appeared to be associated with a systemic abnormality while little or no fibrin formation was evident in lesions of the skin. Differentiation between systemic and localized processes is essential to unravelling unique details
741
related to pathology of particular lesions. Thus, knowledge of the systemic levels of the derivatives is important. When the source of the derivatives is questioned, the equilibria and sequence involved in their formation can be taken into account in deciding between alternate possibilities. Apart from providing details to aid In the interpretation of pathology, the information obtained may aid in detection of underlying systemic disorders. References 1. Handel, D. W., Roenigk, H. H., Shainoff, ). R., and Deodhar, S., Necrotizing vasculitis. An evaluation of immunological and coagulopathy aspects of etiology. Arch. Dermatol. 111:847, 1975. 2. Shainoff, J. R., and Page, 1. H., Significance of cryoprofibrin in fibrinogen- fibrin conversion. J. Exp. Med. 116:687, 1962. 3. Kanaide, H., and Shainoff, J. R., Crosslinking of fibrinogen and fibrin by fibrin stabilizing factor (factor Xllla). J. Lab. Clin. Med. 85: 574, 1975.
Tars in Eczema
If it were required to name one remedy only for eczema, I would choose tar; if allowed to choose two, tar and lead; and if three, tar, lead, and mercury. Yet for a disease which presents so many phases and varieties both in kind and stage as does eczema, it may seem almost absurd to speak of single remedies. Making, however, allowance for such considerations, I yet hold to a strong belief that tar is the specific for all forms of true eczematous inflammation of the skin. The chief reason that it is not accepted as such is that it is commonly employed far too strong. If weak enough, and used freely enough, tar solutions will, in my experience, almost invariably cure eczema. Common tar water and solutions of carbolic acid are very useful, and come perhaps to nearly the same thing; but the remedy which 1 find most convenient and most certain is the solution of coal tar in alkali sold under the name of Liquor Carbonis Detergens. — Hutchinson, I.: On tar in the treatment of eczema. Arch. Surg. 1:164, 1890.
FIBRIN COMPLEXES IN INTERMEDIARY COAGULATION JOHN R. SHAINOFF, Ph.D. AND HENRY H. ROENIGK, JR., M.D.
from the Research Division and Department of Dermatology, The Cleveland Clinic Foundation, Cleveland^ Ohio
The ease with which pathology can be diagnosed in disease of the integument puts the dermatologist in prime position to assess new concepts of disease mechanisms, especially as they apply to man. Recent advances in the chemistry of fibrin have generated several new concepts of its formation, transport and metabolism within the circulation which have proven useful for the detection and quantification of systemic abnormalities leading to fibrin deposition. By virtue of the derivation of these concepts from intrinsic properties of fibrinogen and fibrin, they should also apply in principle to the highly localized lesion. But their use for diagnosis or investigation of highly localized abnormalities becomes diminished, actually diluted, to varying degrees depending on feasibility of examining blood from the area of the lesion. Fibrin Formation
:
Although detection of fibrin deposits on biopsy can be taken as an indication of fibrin formation, alternative pathways to deposition are known. Questions
may also be posed concerning rates of formation as opposed to removal of fibrin. Ability to detect and quantify specific events involved in the formation and modification of fibrin can aid in establishing mechanism. To that end we have focused on a critical stage in which soluble fibrinogen-fibrin complexes are formed as an intermediary process in coagulation. The complexes can be viewed as critical because the aggregation of fibrin into insoluble strands hinges on formation of saturating levels of the complexes in blood. The level of the complexes therefore serves to define proximity to the coagulative state in the blood being examined. In this commentary we will formulate this perspective and outline details which we believe are important. Examples of the clinical application of this particular perspective, together with citations to other important aspects that are not covered in the present commentary, can be found in a preceding article.' Viewed schematically in step-by-step sequence, fibrin formation involves initially an enzymic attack by thrombin in which certain small segments, the fibrinopeptides, are cleaved from the amino terminal ends of the fibrinogen molecules. The release of fibrinopeptide transforms the fibrinogen into a self-aggregating derivative known as fibrin monomer (1st horizontal arrow, 738
FIBRIN COMPLEXES • Siiainoff and Roenigk
No. 10
\
\
\ \
f
\
•
f(f-f)f
Fibrinogen
Monomer
(f • f ) f ( f • f ) f ( f - f )
/
I / Polymer
\
Fig. 1.
739
\
y
Clot
\\ cjb (f
cj!>
Complex
Fig. 1). These monomers then aggregate (2nd arrow) into threadlike polymers which in turn coalesce to form the fibrous structure of the clot (3rd arrow). Although the aggregation involves fairly weak bonding that is easily broken by concentrated urea or weak acids, virtually none of the fibrin escapes incorporation into the coagulum at the end of the reaction under simulated physiologic conditions. (Under real physiologic conditions^ the reaction seldom goes to completion except in shed blood or the occluded vessel.) In the ongoing reaction, the steps are not temporally separated but are concurrent with the fibrin aggregating as it is produced until the parent fibrinogen is depleted. Small amounts of fibrin may be continually produced within the circulation, and it is reasonable to believe that a balance normally exists between the formation of the fibrin and its destruction. How is this balance maintained? Explanation A partial explanation was found in the observation^ that in the ongoing clotting reaction, the interaction of the fibrin with the parent fibrinogen suppresses its aggregation into insoluble strands. The interaction of fibrinogen with fibrin was confirmed by observation that fibrin, once aggregated into a clot, could be
dissolved again in solutions of fibrinogen, and made to clot again by separating it from the fibrinogen. The soluble combination of fibrinogen with fibrin provides a means for continual transport of fibrin in a dissolved state in blood. Thus, small amounts of fibrin can in principle be continually produced in the peripheral circulation and transported in soluble form to the liver where it is rapidly removed. The absence of fibrin deposits in healthy vascular tissue seems to fit with the experimental observation that critically high threshold concentrations of fibrin appear necessary to predispose its deposition from blood. The threshold varies in proportion to the concentration of fibrinogen. As judged by several investigators, the threshold is reached when the level of fibrin rises to about 8% of the fibrinogen. Above this level, the soluble complexes become unstable, and resultant breakdown of transport serves to disseminate fibrin deposition. Figure 1 attempts to depict the equilibrium. The angular shaped lines can be imagined as a plane projecting through the page at a tilt dependent on the relative amounts of fibrinogen and complex. If the level of complex rises above the perpendicular (the equilibrium plateau) the complexes become unstable, whence the excess breaks down into component fibrinogen and fibrin
740
INTERNATIONAL JOURNAL OF DERMATOLOGY
until balance is reached again. When left uncombined with fibrJnogen, the excess fjbrin combines vi/Jth itself to form insoluble strands. Shwartzman Reaction ThJs simple concept of the role of the complexes in hemostasis has been shown to apply directly to the problem of fibrjn deposition Jn the generalized Shwartzman reaction. A correspondence was seen between the occurrence of bilateral renal cortJcal necrosis and the formation of threshold concentrations of complex. Fibrinoid formation Jn the Shwartzman reaction has been recognized as being due in large part to reticuloendothelial blockade by endotoxin impairing clearance of mJnute aggregates of fibrin from the blood stream. The steps preceding the precipitation of the fibrJn from blood appear critical. Applicability of the concept of the generalized Shwartzman reaction in rabbits has prompted us to use Jt as a model for study of other disease phenomena with the prospect that exceptions or specific modifications required to explain findings will provide basis for uncovering new reactions or details pertaining to pathology. The model is based in its simplest form on reversibility in the aggregation of fibrin. Irreversible alterations of fibrin occur when it is acted upon by plasmin and fibrin stabilizing factor. Such changes can be detected from physical and chemical characterization of the complexes, and effects on equilibria can be taken into account. For example, fibrin stabilizing factor is known to catalyze crosslinking of fibrin clots and thereby make the clots resistant to dissolution. The equilibrium involved in formation of fibrinogen-fibrin complexes is Jmportant here also. When formation of complexes is favored over
December 1976
Vol. 15
formation of a clot, the fibrin stabilizing factor will crosslink the flbrinogen to the dissolved fibrin within the complex. The permanent linkage of fibrin within the complex in essence inactivates ability of the fibrin to undergo further aggregation until the fibrinogen within the complex is acted upon by thrombin. Plasmin Limited degradation of fibrinogen and fibrin by plasmin appears to displace the equilibrium In the direction of favoring formation of complexes. However, once plasmin destroys ability of fibrin monomer to undergo self-aggregation, it also destroys its ability to form complexes with fibrinogen. It is reasoned that such extensive degradation of fibrin as a complex in plasma is not likely to occur without concurrent destruction of the fibrinogen. Thus, when the noncoagulable forms of fibrin, the "split products," are found in blood in which the fibrinogen is largely intact, it can be inferred that they arise from highly localized breakdown of an existing clot or fibrin deposit. By way of exception to this simplified concept of fibrin deposition, there is growing evidence that alternate pathways to polymerization and deposition of fibrinogen exist which do not depend upon thrombic action.^ Because of this possibility and the importance of complicating factors noted above, we view the distinction between polymers of fibrinogen itself ("macrofibrinogen"), the noncoagulable degradation products ("split products"), the crosslinked and dissociable forms of fibrinogen-fibrin complex ("cryoprofibrin") important, at least for purpose of research. A large repertoire of laboratory methods is available for the detection and quantification of these variant forms which cannot be
No. 10
FIBRIN COMPLEXES • Shainoff and Roenigk
reviewed here. However, the question may be asked whether the effort required for thorough analysis is warranted, particularly when the blood sample gives only an indication of the systemic composition which may differ greatly from that in the highly localized lesion. Systemic Levels Systemic levels of the complexes in man usually comprise only a small fraction of a percentage of the total fibrinogen, and a small increase may reflect formation of substantial amounts in remote regions of the vasculature. Conversely, examples exist^ in which elevated levels of fibrinogen-fibrin complex appeared to be associated with a systemic abnormality while little or no fibrin formation was evident in lesions of the skin. Differentiation between systemic and localized processes is essential to unravelling unique details
741
related to pathology of particular lesions. Thus, knowledge of the systemic levels of the derivatives is important. When the source of the derivatives is questioned, the equilibria and sequence involved in their formation can be taken into account in deciding between alternate possibilities. Apart from providing details to aid In the interpretation of pathology, the information obtained may aid in detection of underlying systemic disorders. References 1. Handel, D. W., Roenigk, H. H., Shainoff, ). R., and Deodhar, S., Necrotizing vasculitis. An evaluation of immunological and coagulopathy aspects of etiology. Arch. Dermatol. 111:847, 1975. 2. Shainoff, J. R., and Page, 1. H., Significance of cryoprofibrin in fibrinogen- fibrin conversion. J. Exp. Med. 116:687, 1962. 3. Kanaide, H., and Shainoff, J. R., Crosslinking of fibrinogen and fibrin by fibrin stabilizing factor (factor Xllla). J. Lab. Clin. Med. 85: 574, 1975.
Tars in Eczema
If it were required to name one remedy only for eczema, I would choose tar; if allowed to choose two, tar and lead; and if three, tar, lead, and mercury. Yet for a disease which presents so many phases and varieties both in kind and stage as does eczema, it may seem almost absurd to speak of single remedies. Making, however, allowance for such considerations, I yet hold to a strong belief that tar is the specific for all forms of true eczematous inflammation of the skin. The chief reason that it is not accepted as such is that it is commonly employed far too strong. If weak enough, and used freely enough, tar solutions will, in my experience, almost invariably cure eczema. Common tar water and solutions of carbolic acid are very useful, and come perhaps to nearly the same thing; but the remedy which 1 find most convenient and most certain is the solution of coal tar in alkali sold under the name of Liquor Carbonis Detergens. — Hutchinson, I.: On tar in the treatment of eczema. Arch. Surg. 1:164, 1890.
