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60 The pathophysiology and hemodynamics of chronic venous insufficiency of the lower limb
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18. Lurie F, Kistner RL, Eklöf B et al. Mechanism of
venous valve closure and role of the valve in circulation: A new concept. J Vasc Surg 2003;38(5):955–61.
19. Crotty TP. The venous valve agger and plasma
noradrenaline-mediated venodilator feedback.
Phlebology 20 07;22 (3):116 –30.
●
20. van Bemmelen PS, Bedford G, Beach K et al.
Quantitative segmental evaluation of venous valvular
reflux with duplex ultrasound scanning. J Vasc Surg
1989;10(4):425–31.
21. Delis KT, Gloviczki P, Wennberg PW et al.
Hemodynamic impairment, venous segmental disease, and clinical severity scoring in limbs
with Klippel–Trenaunay syndrome. J Vasc Surg
2007;45(3):561–7.
●
22. May R and Thurner J. The cause of the predominantly sinistral occurrence of thrombosis of the
pelvic veins. Angiology 1957;8(5):419–27.
23. Neglen P, Thrasher TL, and Raju S. Venous
outflow obstruction: An underestimated contributor to chronic venous disease. J Vasc Surg
2003;38(5):879–85.
24. Jost CJ, Gloviczki P, Cherry KJ etal. Surgical reconstruction of iliofemoral veins and the inferior vena
cava for nonmalignant occlusive disease. J Vasc Surg
2001;33(2):320–8.
25. Raju S. Treatment of iliac-caval outflow obstruction.
Semin Vasc Surg 2015;28:47–53.
26. Maleti O, Lugli M, and Tripathi RK. Deep
venous reconstructive surgery. Semin Vasc Surg
2015;28:39–46.
27. Glynn JJ, Jones CM, Anderson DEJ et al. In vivo
assessment of two endothelialization approaches
on bioprosthetic valves for the treatment of chronic
deep venous insufficiency. J Biomed Mater Res B
2015, DOI: 10.1002/jbm.b.33507 [Epub ahead of
print].
28. Vogel D, Comerota AJ, Al-Jabouri M et al. Common
femoral endovenectomy with iliocaval endoluminal
recanalization improves symptoms and quality of life
in patients with postthrombotic iliofemoral obstruction. J Vasc Surg 2011;55(1):129–35.
29. Labropoulos N, Mansour MA, Kang SS et al. New
insights into perforator vein incompetence. Eur J
Vasc Endovasc Surg 1999;18(3):228–34.
●
30. Bjordal RI. Circulation patterns in the saphenous system and the perforating veins of the calf in patients
with previous deep vein thrombosis. Vasa Suppl
1974;3:1– 41.
★
31. Comerota A and Lurie F. Pathogenesis of venous
ulcer. Semin Vasc Surg 2015;28:6–14.
●
32. Ludbrook J. The musculovenous pumps of the
human lower limb. Am Heart J 1966;71(5):635 – 41.
●
33. Christopoulos DG, Nicolaides AN, Szendro G etal.
Air-plethysmography and the effect of elastic compression on venous hemodynamics of the leg. JVasc
Surg 1987;5(1):148–59.
34. Browse NL, Burnand KG, and Irvine A. Diseases of
the Veins. London: Arnold, 1999.
35. Meissner MH, Moneta G, Burnand K etal. The
hemodynamics and diagnosis of venous disease.
JVasc Surg 2007;46(Suppl. S):4S–24S.
★
36. Reeder SW, Wolff O, Partsch H etal. Expert consensus document on direct ambulatory venous pressure
measurement. Int Angiol 2013;32(5):453–8.
●
37. Uhl JF and Gillot C. Anatomy of the foot venous
pump: Physiology and influence on chronic venous
disease. Phlebology 2012;27(5):219–30.
38. Scurr JH and Smith PC. The muscular pump of
the foot: Physiological and clinical importance.
Phlebologie 1993;46(2):209–15.
39. White JV, Katz ML, Cisek P et al. J. Venous outflow of the leg: Anatomy and physiologic mechanism of the plantar venous plexus. J Vasc Surg
1996;24(5):819–24.
40. Ibegbuna V, Delis KT, and Nicolaides AN.
Haemodynamic and clinical impact of superficial,
deep and perforator vein incompetence. Eur J Vasc
Endovasc Surg 2006;31(5):535–41.
6
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Pathogenesis of varicose veins and cellular
pathophysiology of chronic venous insufficiency
DEORANIE N. ABDEL-NABY, WALTER N. DURAN, BRAJESH K. LAL,
FRANKT.PADBERGJR.,AND PETER J. PAPPAS
6.1 Introduction 61
6.2 Varicose vein formation (macroscopic alterations) 61
6.3 Microcirulation 64
6.4 ECM alterations 66
6.5 Pathophysiology of stasis dermatitis and
dermal fibrosis 66
6.1 INTRODUCTION
Chronic venous insuciency (CVI) is the seventh leading
cause of chronic debilitating disease in the United States.
In total, 10%–35% of adults in the United States have some
form of CVI, with venous ulcers aecting 4% of people over
the age of 65 years.
United States have varicose veins. Two to six million have
more advanced forms of CVI (swelling and skin changes),
and nearly 500,000 have active venous ulcers. e population-based cost to the U.S. government for CVI treatment
and venous ulcer care has been estimated at over $1 billion
a year. In addition, 4.6 million work days per year are lost to
venous-related illnesses.
eective treatment modalities place a heavy burden on the
healthcare system, underscoring the need for more extensive CVI-related research. Over the past decade, researchers have made strides in dening the roles of genetics and
leukocyte-mediated injury, and have elucidated the role of
inammatory cytokines in lower extremity dermal pathology. In addition, several investigations have been performed
to highlight the pathologic alterations in cellular function
and the molecular regulation of the processes observed in
patients with CVI. is chapter will discuss the pathogenesis and pathophysiology of varicose vein formation and the
molecular regulation of inammatory damage to the lower
extremity dermis caused by persistent ambulatory venous
hypertension.
1,2
An estimated 25 million people in the
3,4
e chronicity of CVI and lack of
6.6 Cytokine regulation and tissue fibrosis 66
6.7 Dermal fibroblast function 68
6.8 Regulation of venous ulcer formation and healing 68
6.9 Role of MMPs and their inhibitors in CVI 69
6.10 Summary 69
References 70
6.2 VARICOSE VEIN FORMATION
(MACROSCOPIC ALTERATIONS)
6.2.1 Genetics and the role of
deepvenousthrombosis
Unlike arteries, veins are thin-walled, low-pressure conduits whose function is to return blood from the periphery
to the heart. Muscular contractions in the upper and lower
extremities propel blood towards the heart and a series
of intraluminal valves prevent retrograde ow or reux.
Venous reux is observed when valvular destruction or dysfunction occurs in association with varicose vein formation.
Valvular reux causes an increase in ambulatory venous
pressure and a cascade of pathologic events that manifest
themselves clinically as lower extremity edema, pain, itching, skin discoloration, varicose veins, venous ulceration,
and, in its severest form, limb loss. ese clinical symptoms collectively refer to the disorder known as CVI.
gender, pregnancy, weight, height, race, diet, bowel habits,
occupation, posture, previous deep venous thrombosis
(DVT), and genetics have all been proposed as predisposing
factors for the formation of varicose veins. However, except
for a history of previous DVT and genetics, there is poor
evidence to suggest a causal relationship between these predisposing factors and varicose vein formation.
ere are a few reported epidemiologic investigations
that suggest a relationship between varicose vein formation
5
Age,
61
62 Pathogenesis of varicose veins and cellular pathophysiology of chronic venous insufficiency
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and a genetic predisposition.
6,7
Historically, it was thought
that axial destruction of venous valves led to the transmission of ambulatory venous hypertension, causing reux and
varix formation.6 However, a publication by Labropoulos
etal.8 indicated that the most frequent location for initial
varicose vein formation was in the below-knee great saphenous vein (GSV) and its tributaries, followed by the aboveknee GSV and the saphenofemoral junction, respectively.
e results of this study suggest that reux appears to be
a local or multifocal process. Vein wall degeneration with
subsequent varix formation can occur in any segment of the
supercial and deep systems, suggesting a genetic component to the disease.
In 1969, Gunderson and Hauge9 reported on the epidemiology of varicose veins observed in a vein clinic in
Malmo, Sweden. In this investigation, 154 female and
24 male patients provided complete survey information
on their parents and siblings. Although biased by the predominance of women and dependence on survey data, this
report suggested that patients with varicose veins had a
higher likelihood of developing varicosities if their father
had varicose veins. Furthermore, the risk of developing
varicose veins increases if both parents had varicosities.
To further support the genetic predisposition theory,
Cornu-enard etal.7 prospectively examined 67 patients
and their parents. e non-aected spouses and parents of
patients were used as controls, giving a total of 402 subjects. ese investigators reported that the risk of developing varicose veins was 90% when both parents were
aected, 25% for males and 62% for females if one parent
was aected, and 20% when neither parent was aected.
ese data suggest an autosomal dominant mode of transmission with variable penetrance. e decreased incidence
in males with an aected parent and the spontaneous
development in patients without aected parents suggest
that males are more resistant to varix formation and that
other multifactorial etiologies, such as environmental factors and hormones, in patients with predispositions to the
disease must exist.
Ng etal.10 demonstrated that varicose veins in the normal
population were linked to the candidate marker D16S520
on chromosome 16q24. A likely candidate gene within close
proximity to the marker D16S520 is the forkhead box C2
(FOXC2). FOXC2 encodes a regulatory forkhead transcription factor and is expressed in the paraxial mesoderm and
somites of the early vertebrate embryo. In later stages, its
expression is noted in the heart and blood vessels.
11
FOXC2
is noted to play an important part in the development of
the lymphatic system, demonstrating its importance in the
development of lymphedema distichiasis.12 Since venous
reux is associated with valve abnormalities, FOXC2 may
play a role in the development of both venous and lymphatic
valvular dysfunction.
13
Serra etal.14 reported that in nine families with varicose
veins, the gene D16S520 on chromosome 16q24, which is
located near the gene FOXC2, was associated with varix
formation. e authors determined that in families with
aected members carrying the D16S520 marker, there
was evidence of saphenofemoral junction reux. Linkage
to the candidate marker for the FOXC2 gene suggests
that there is a functional variant within, or in the vicinity of, the FOXC2 gene, which predisposes to varicose vein
development.
An injury to the venous endothelium or local procoagulant environmental factors leads to thrombus formation in the venous system. It is currently well accepted
that a venous thrombus initiates a cascade of inammatory events that contributes to or causes vein wall
brosis.15 rombus formation at venous conuences
and valve pockets leads to activation of neutrophils and
platelets. Activation of these cells leads to the formation
of inammatory cytokines, pro-coagulants and chemokines, causing thrombin activation and further clot formation. Production of inammatory mediators creates
a cytokine/chemokine gradient, leading to leukocyte
invasion of the vein wall at the thrombus wall interface
and from the surrounding adventitia. Upregulation of
adhesion molecules perpetuates this process, eventually
leading to vein wall brosis, valvular destruction, and
alteration of the vein wall architecture.
15,16
Although the
mechanisms associated with vein wall damage secondary
to venous thrombosis are beginning to be unraveled, the
majority of varicose veins occur in patients with no prior
history of DVT.
6.2.2 Vein wall anatomy, histopathology,
and functional alterations
Whatever the initiating event, several unique anatomic and
biochemical abnormalities have been observed in patients
with varicose veins. Normal and varicose GSVs are characterized by three distinct muscle layers within their walls.
e inner layer is referred to as the intima. It is one cell
layer thick and is composed of endothelial cells. e media
contains an inner longitudinal and an outer circular layer,
and the adventitia contains a loosely organized extracellular matrix (ECM) in the outer longitudinal layer.
normal GSVs, muscular layers in the media are composed
of smooth muscle cells (SMCs) that appear spindle shaped
(contractile phenotype) when examined with electron
microscopy (Figure 6.1).
20
ese cells lie in close proximity
to each other, are in parallel arrays, and are surrounded by
bundles of regularly arranged collagen bers. In varicose
veins, the orderly appearance of the muscle layers of the
media is replaced by an intense and disorganized deposition of collagen.
20–22
Collagen deposits separate the normally closely opposed SMCs, and are particularly striking
in the media. SMCs appear elliptical rather than spindle
shaped, and demonstrate numerous collagen-containing
vacuoles, imparting a secretory phenotype (Figure 6.2).15
What causes SMCs to dedierentiate from a contractile
to a secretory phenotype is currently unknown. Ascher
23,24
et al.
theorized that SMC dedierentiation may be
related to dysregulation of apoptosis. ese investigators
17–19
In
Figure 6.1 Electron micrograph of a normal vein demon-
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strating a contractile smooth muscle phenotype.
reported a decrease in the pro-apoptotic mediators bax
and poly-ADP-ribose polymerase in the adventitia of varicose veins compared with normal veins. Although no difference in these mediators was observed in the media or
intima of varicose veins, a decrease in SMC turnover was
postulated as a possible cause of the increase in the secretory phenotype. Increased phosphorylation of the retinoblastoma protein, an intracellular regulator of cellular
proliferation and dierentiation, has been observed in varicose veins, and may similarly contribute to this process.
18
Vein wall remodeling has been consistently observed in
histologic varicose vein specimens.
17,19–22,25
Gandhi etal.25
quantitatively demonstrated an increase in collagen content and a decrease in elastin content compared to normal
GSVs. e net increase in the collagen/elastin ratio suggested an imbalance in connective tissue matrix regulation.
Figure 6.2 Electron micrograph of a varicose vein wall
demonstrating a secretory phenotype of smooth muscle
cells.
6.2 Varicose vein formation (macroscopic alterations) 63
As a result, several investigators have observed alterations
in matrix metalloproteinase (MMP) and brinolytic activity in varicose veins. TIMP-1 and MMP-1 protein levels are
increased at the saphenofemoral junction compared with
26
normal controls, whereas MMP-2 levels are decreased.
No
overall dierences in MMP-9 protein or activity levels have
been identied; however, the number of cells expressing
MMP-9 by immunohistochemistry has been reported to be
elevated in varicose veins compared with normal veins.
27, 28
ere are conicting reports regarding the role of plasmin
activators and their inhibitors. Shireman et al.29 reported
that urokinase plasminogen activator (uPA) levels are
increased by three to ve times compared with normal controls in the media of vein specimens cultured in an organ
bath system. No dierences were noted in tissue plasminogen activator (tPA) or plasmin activator inhibitor 1 levels.
However, other investigations have reported a decrease in
uPA and tPA activity as assessed by enzyme zymography
in varicose veins.
27, 30
ese data suggest that the plasminogen activators may play a role in MMP activation, leading
to vein wall brosis and varix formation; however, further
research into the mechanisms regulating vein wall brosis
are clearly needed.
What eect vein wall brosis has on venous function
needs further elucidation. e contractile responses of varicose and normal GSV rings to noradrenaline, potassium
chloride, endothelin, calcium ionophore A23187, angiotensin II, and nitric oxide have been evaluated by several investigators.
31,3 2
ese studies have demonstrated decreased
contractility of varicose veins when stimulated by noradrenaline, endothelin, and potassium chloride. Similarly,
endothelium-dependent and -independent relaxations aer
A23187 or nitric oxide administration, respectively, were
diminished compared with normal GSVs. e mechanisms responsible for decreased varicose vein contractility
appear to be receptor mediated.
32,33
By utilizing sarafotoxin S6c (a selective pharmacologic inhibitor of endothelin B) and competitive inhibition receptor assays with
131
[
I]-endothelin-1, a decrease in endothelin B receptors
has been observed in varicose veins compared with normal
33
GSVs.
Feedback inhibition of receptor production secondary to increased endothelin-1 is postulated to mediate the
decreased receptor content in varicose vein walls. Other
possible mechanisms of decreased contractility appear to be
related to cyclic adenosine monophosphate (cAMP) levels
and the ratio of prostacyclin to thromboxane-A2.34 cAMP
is increased in varicose vein specimens compared with normal GSVs. In addition, the ratio of prostacyclin to throboxane-A2 is increased, even though absolute protein levels do
not dier between normal veins and varicosities. Whether
venodilation of varicosities is caused by diminished endothelin receptor levels and responsiveness to cAMP or is a
secondary eect of varix formation is not known. However,
it is clear that with the development of vein wall brosis,
varicose veins demonstrate decreased contractile properties
that probably exacerbate the development of ambulatory
venous hypertension.
64 Pathogenesis of varicose veins and cellular pathophysiology of chronic venous insufficiency
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6.3 MICROCIRULATION
6.3.1 Leukocyte activation
Dissatisfaction with the brin cu theory and subsequent
observations of decreased circulating leukocytes in blood
samples obtained from the GSVs in patients with CVI led
Coleridge Smith and colleagues35 to propose the leukocyte-trapping theory. is theory proposes that circulating neutrophils are trapped in the venous microcirculation
secondary to venous hypertension. e subsequent sluggish
capillary blood ow leads to hypoxia and neutrophil activation. Neutrophil activation leads to degranulation of toxic
metabolites with subsequent endothelial cell damage. e
ensuing heterogeneous capillary perfusion causes alterations in skin blood ow and eventual skin damage. e
problem with the leukocyte-trapping theory is that neutrophils have never been directly observed to obstruct capillary ow, therefore casting doubt on its validity. However,
there is signicant evidence that leukocyte activation plays
a major role in the pathophysiology of CVI.
6.3.2 Role of leukocyte activation
andfunctional status in CVI
In 1988, omas etal.36 reported that 24% fewer white cells
le the venous circulation aer a period of recumbence in
patients with CVI compared with normal patients. ey
studied three groups of ten patients each. Group 1 consisted of patients with no signs of venous disease. Group
2 were patients with uncomplicated primary varicose
veins and group 3 were patients with long-standing CVI
as determined by Doppler ultrasonography, strain gauge
plethysmography, and foot volumetry. e GSV was cannulated just above the medial malleolus. Venous samples
were obtained at various time points with patients in the
sitting and supine positions. Samples were then placed in
an automated cell counter and the numbers of leukocytes
and erythrocytes determined. e ratios of white cells to
red cells at the various time points were then compared.
It was reported that with leg dependency, the packed cell
volume signicantly increased in patients with CVI compared with normal control subjects, whereas patients with
primary varicose veins showed no dierence from control
subjects. It was also noted that the relative number of white
cells was signicantly decreased compared with control and
primary varicose vein patients (28% vs. 5%, P < 0.01). It was
concluded that the decrease in white cell number was due to
leukocyte trapping in the venous microcirculation secondary to venous hypertension. It was further speculated that,
while trapped, leukocytes may be activated and release toxic
metabolites, causing damage to the microcirculation and
the overlying skin. ese important observations were the
rst to implicate abnormal leukocyte activity in the pathophysiology of CVI.
e importance of leukocytes in the development of
dermal skin alterations was emphasized by Scott et al.
37
ese authors obtained punch biopsies from patients with
primary varicose veins, patients with lipodermatosclerosis,
and patients with lipodermatosclerosis and healed ulcers,
and they determined the median number of white blood
cells (WBCs) per high-power eld (40× magnication) in
each group. No patients with active ulcers were included
and no attempt to identify the type of leukocytes was made.
It was reported that in patients with primary varicose veins,
lipodermatosclerosis, and healed ulceration, there were
medians of 6, 45, and 217 WBCs per mm2, respectively.
is study demonstrated that with clinical disease progression and increasing severity of CVI, there was a progressive
increase in the number of leukocytes in the dermis of CVI
patients.
e types of leukocytes involved in dermal venous stasis skin changes are controversial. In a study performed
by Wilkinson et al.,38 skin biopsies were obtained from
23 patients who required surgical ligation, stripping, and/
or avulsion for their varicose veins. e condition of the
skin was recorded as liposclerotic, eczematous, or normal. Lipodermatosclerosis was dened clinically as palpable induration of the skin and subcutaneous tissues
and eczema as visible erythema with scaling of the skin.
Immunohistochemical staining for leukocyte-specic cell
surface markers was carried out, and it was reported that
macrophages and lymphocytes were the predominant leukocytes observed in this patient population. Neutrophils
and B-lymphocytes were rarely observed. T-lymphocytes
and macrophages were predominantly observed perivascularly and in the epidermis. However, Pappas etal.39 performed a quantitative morphometric assessment of the
dermal microcirculation using electron microscopy and
reported that macrophages and mast cells were the predominant cells observed in patients with CVI dermal skin
changes. Furthermore, lymphocytes were never observed.
is discrepancy may reect the types of patients that
were studied. Wilkinson etal.38 biopsied patients with erythematous and eczematous skin changes, whereas Pappas
etal.39 predominantly evaluated older patients with dermal
brosis. Patients with eczematous skin changes may have
an autoimmune component to their CVI, whereas patients
with dermal brosis may reect changes that are consistent
with chronic inammation and altered tissue remodeling.
6.3.3 The venous microcirculation
Numerous investigations have attempted to evaluate the
microcirculation of patients with CVI.
these investigations were qualitative descriptions of vascular abnormalities that lacked uniformity of biopsy sites and
patient stratication. Prior to 1997, it was widely accepted
that endothelial cells from the dermal microcirculation
appeared abnormal, contained Weibel–Palade bodies, were
edematous, and demonstrated widened inter-endothelial gap
42
junctions.
Based on these descriptive observations, it was
assumed that the dermal microcirculation of CVI patients
had functional derangements related to permeability and
39–43
e majority of
6.3 Microcirulation 65
Mast cell density: Gaiter PCVs
(b)
https://t.me/med1917
ulcer formation. It was not until 1997 that a quantitative
morphometric analysis of the dermal microcirculation
was reported.39 e objectives of this investigation were to
quantify dierences in endothelial cell structure and local
cell type, with an emphasis on leukocyte cell types and their
relationship to arterioles, capillaries, and post-capillary
venules (PCVs). e variables assessed were the numbers
and types of leukocytes, endothelial cell thickness, endothelial vesicle density, inter-endothelial junctional width, cu
thickness, and ribosome density. irty-ve patients had
two 4-mm punch biopsies obtained from the lower calf (gaiter region) and lower thigh. Patients were separated into one
of four groups according to the 1995 International Society
for Cardiovascular Surgery/Society for Vascular Surgery
(ISCVS/SVS) CEAP classication.5 Group 1 consisted of
ve patients with no evidence of venous disease. Skin biopsies from these patients served as normal controls. Groups
2–4 consisted of patients with CEAP class 4 (n = 11), class 5
(n = 9), and class 6 (n = 10) CVI.
6.3.4 Endothelial cell characteristics
No signicant dierences were observed in the endothelial cell thickness of arterioles, capillaries, and PCVs from
either gaiter or thigh biopsies.39 Qualitatively, the endothelial cells appeared metabolically active. Many nuclei exhibited a euchromatic appearance, implying active mRNA
transcription. In most instances, ribosome numbers were so
abundant that they exceeded the resolution capacity of the
image analysis system and were unable to be quantied. e
prominence in the ribosome content and the euchromatic
appearance of the endothelial cell nucleus strongly suggested active protein production. No signicant dierences
in vesicle density were observed in gaiter biopsies between
groups. Class 6 patients exhibited an increased number of
vesicles in arterioles and PCV endothelia from thigh biopsies, but did not dier compared to gaiter biopsies. Mean
inter-endothelial junctional width varied within a normal
range of 20–50 nm. Signicantly widened inter-endothelial
gap junctions were not observed and thus conicted with
the reports of Wenner etal.
diered signicantly at the capillary level in both gaiter and
thig h biopsies. Dierences were most pronounced in pat ients
with class 4 disease. ese data indicated that endothelial
cells from the dermal microcirculation of CVI patients were
far from abnormal. ey demonstrated increased metabolic
activity, suggestive of active cellular transcription and protein production. Most surprising was the observation of uniformly tight gap junctions. Previously, these gap junctions
were reported to be as wide as 180 nm, and it was assumed
that these widened junctions were responsible for macromolecule extravasation and edema formation.
et al.39 suggested that alternative causes of tissue edema,
such as increased trans-endothelial vesicle transport, the
formation of trans-endothelial channels, and alterations in
the glycocalyx lining the junctional cle, may be involved in
CVI edema and macromolecule transport.
42
Mean basal lamina thickness
42,44
Pappas
6.3.5 Types and distributions of leukocytes
e most striking dierences in cell type and distribution
were observed with mast cells and macrophages (Figure
6.3). In both gaiter and thigh biopsies, mast cell numbers
were two- to four-times greater than those of controls in
class 4 and 5 patients around arterioles and PCVs (P < 0.05).
Class 6 patients demonstrated no dierence in mast cell
number compared to controls. Mast cell numbers around
capillaries did not dier across groups in either gaiter or
thigh biopsies. Macrophages demonstrated increased numbers in class 5 and 6 patients around arterioles and PCVs,
respectively (P < 0.05). Dierences in macrophage numbers around capillaries were observed primarily in class 4
patients in both gaiter and thigh biopsies. Surprisingly, lymphocytes, plasma cells and neutrophils were not present in
the immediate perivascular space. Fibroblasts were the most
common cells observed in both gaiter and thigh biopsies.
7.5
(a)
5.0
+
venule endotheliumCells/m
3
2.5
Cells/m
0.0
7.5
5.0
venule endothelium
3
2.5
0.0
Figure 6.3 Histograms demonstrating mast cell densities
(a) and macrophage cell densities (b) according to CEAP
disease classification and their proximity to post-capillary
venules (PCVs). Class 4: venous dermatitis only; class 5:
venous dermatitis and a history of healed ulceration; class 6:
active venous stasis ulcer. CVI: chronic venous insufficiency.
*
Controls
*
Controls
+
*
Class 4
CVI by CEAP class
Macrophage cell density:
Gaiter postcapillary venules
+
ass 4
Cl
CVI by CEAP class
*
Class 5
++
+
Class 5
+
Class 6
+
*
Class 6
66 Pathogenesis of varicose veins and cellular pathophysiology of chronic venous insufficiency
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Migrating
Pericapillary
cuff
Fibroblast
Postcapillary
venule
Figure 6.4 Photomicrograph (4300×) of chronic venous
insufficiency dermal microcirculation demonstrating
extracellular matrix changes (pericapillary cuff), migrating
macrophages, a lymphatic vessel, and a fibroblast.
macrophages
Lymphatic
It was speculated that mast cells and macrophages may
function to regulate tissue remodeling, resulting in dermal
brosis.
vator of MMP-1 and -3 (collagenase and stromelysin).
39,45
e mast cell enzyme chymase is a potent acti-
46–48
In an invitro model using the human mast cell line HMC-1,
these cells were reported to spontaneously adhere to bronectin, laminin, and collagen type I and III, all of which
are components of the perivascular cu (see Figure 6.4).48
Chymase also causes the release of latent transforming
growth factor-β1 (TGF-β1), which is secreted by activated
endothelial cells, broblasts, and platelets from extracellular matrices.49 Release and activation of TGF-β1 initiates
a cascade of events in which macrophages and broblasts
are recruited to wound healing sites and are stimulated to
produce broblast mitogens and connective tissue proteins,
respectively.50 Mast cell degranulation leading to TGF-β1
activation and macrophage recruitment may explain why
decreased mast cell and increased macrophage numbers
were observed in class 6 patients. Macrophage migration, as
evidenced by the frequent appearance of cytoplasmic tails
in perivascular macrophages, further substantiates the concept of inammatory cytokine recruitment.
6.4 ECM ALTERATIONS
types I and III, bronectin, vitronectin, laminin, tenascin,
and brin.53 e role of the cu and its cell of origin is not
completely understood. e investigation by Pappas et al.
suggested that the endothelial cells of the dermal microcirculation were responsible for cu formation.39 e cu was
once thought to be a barrier to oxygen and nutrient diusion. However, recent evidence suggests that cu formation
is an attempt to maintain vascular architecture in response
to increased mechanical load.54 Although perivascular cus
may function to preserve microcirculatory architecture,
several pathologic processes may be related to cu formation. Immunohistochemical analyses have demonstrated
TGF-β1 and α2-macroglobulin in the interstices of perivas-
cular cus.55 It has been suggested that these “trapped” molecules are abnormally distributed in the dermis, leading to
altered tissue remodeling and brosis. Cus may also serve
as a lattice for capillary angiogenesis, explaining the capillary tortuosity and increased capillary density observed in
the dermis of CVI patients.
6.5 PATHOPHYSIOLOGY OF STASIS
DERMATITIS AND DERMAL FIBROSIS
e mechanisms modulating leukocyte activation, broblast function, and dermal ECM alterations were focuses of
investigation in the 1990s. CV I is a disease of chronic inammation due to a persistent and sustained injury secondary
to venous hypertension. It is hypothesized that the primary
injury is extravasation of macromolecules (i.e., brinogen
and α2-macroglobulin) and red blood cells (RBCs) into the
dermal interstitium.
and interstitial protein extravasation are potent chemoattractants and, presumably, represent the initial underlying chronic inammatory signal responsible for leukocyte
recruitment. It has been assumed that these cytochemical
events are responsible for the increased expression of intercellular adhesion molecule 1 (ICAM-1) on the endothelial
cells of the microcirculatory exchange vessels observed in
CVI dermal biopsies.
dent adhesion molecule that is utilized by macrophages,
lymphocytes, and mast cells for diapedesis. As stated above,
all of these cells have been observed by immunohistochemistry and electron microscopy in the interstitium of dermal
biopsies.
38,39
41,42,44,55,56
38,56
RBC degradation products
ICAM-1 is the activation-depen-
Once leukocytes have migrated to the extracellular space,
they localize around capillaries and PCVs. e perivascular space is surrounded by ECM proteins and forms a
perivascular “cu.”
and throughout the dermal interstitium is an intense and
disorganized collagen deposition.
and the accompanying collagen deposition are the sine
qua non of the dermal microcirculation in CVI patients
(Figure 6.4). e perivascular cu was originally thought
to be the result of brinogen extravasation and was erroneously referred to as a “brin cu.”
the cu is a ring of ECM proteins consisting of collagen
51,52
Adjacent to these perivascular cus
39,44
Perivascular cus
5
It is now known that
6.6 CYTOKINE REGULATION
ANDTISSUEFIBROSIS
Leukocyte recruitment, ECM alterations, and tissue brosis are characteristic of chronic inammatory diseases
caused by alterations in TGF-β1 gene expression and protein production. To determine the role of TGF-β1 in CVI,
Pappas and colleagues took dermal biopsies from normal
patients and CEAP class 4, 5, and 6 CVI patients and analyzed them for TGF-β1 gene expression, protein production, and cellular location. TGF-β1 gene expression in class
4 patients was signicantly elevated compared to controls
and class 5 and 6 patients (Figure 6.5; P < 0.05).57 e
TGF-
β
levels in pg/g of tissue
TGF-
β
gene expression
Results: Quantitative
(a)
(b)
https://t.me/med1917
data demonstrated that in areas of clinically active CVI,
increased amounts of active TGF-β1 are present compared
with normal skin. Furthermore, the active TGF-β1 protein concentrations in biopsies from the lower thigh did
not dier from normal skin, demonstrating a regionalized
response to injury.
iments demonstrated intense TGF-β1 staining in perivascular cus, perivascular leukocytes, and broblasts. Many
perivascular leukocytes demonstrated positive staining of
intracellular granules and appeared morphologically similar to previously reported mast cells (Figures 6.3 and 6.6).57
Preliminary TGF-β1 bioactivity assays, however, demonstrated increased active TGF-β1 protein production in all
class 4, 5, and 6 CVI patients compared to normal patients
and skin from ipsilateral thigh biopsies of CVI patients.
Increased bioactive TGF-β1 in areas of stasis dermatitis
alone signies a regional response to venous hypertension.
e increase in protein production with normal gene expression demonstrates either stabilization of the mRNA message
or post-translational modication of the protein.
patients (43 men and 37 women) with chronic leg ulcers and
Figure 6.5 Increased transforming growth factor-β1 (TGF-
β1) mRNA transcripts in class 4 patients only (a); active
TGF-β1 protein is observed in class 4, 5, and 6 patients in
areas of clinically active disease (b). CVI: chronic venous
insufficiency.
57
Immunohistochemistry and immunogold labeling exper-
In 2008, a prospective observational study looked at 80
100
50
25
1
moles/g total RNA
–12
10
100
50
25
1
reverse polymerase chain reaction (RT-PCR)
for TGF-β
0
Controls Class 4 Class 5 Class 6
* Class 4 compared to controls, class 5 and 6
*
0
CON
* Control vs class 4 and 6 (p0.05)
# LC vs LT biopsies within each class (p0.02)
mRNA from CVI skin biopsies
1
*
CVI patients
Results: Active TGF-β1 protein levels
from CVI dermal skin biopsies
#
*,#
#
C4 LC C4 LT C5 LC C5 LT C6 LC C6 LT
CVI patient classication
LC = Lower calf
LT = Lower thigh
*,#
#
#
6.6 Cytokine regulation andtissuefibrosis 67
Figure 6.6 Perivascular cuff demonstrating transforming
growth factor-β1-positive leukocytes. Horizontal arrow
indicates a leukocyte morphologically similar to a mast
cell (575×).
Ankle–Brachial Index scores of greater than 0.85. Gohel
58
etal.
established an inverse relationship between TGF-β1
concentrations and changes in ulcer size, as well as a direct
relationship between basic broblast growth factor (bFGF)
concentrations and ulcer size. Although paired uid analysis could not be performed in 43% of patients in this study,
the results suggested the presence of greater brogenesis,
matrix deposition, and proliferation in the healing ulcer.
A prospective study of 30 non-healing lower extremity
ulcers with edema (CEAP class 6) by Beidler etal.59 investigated the levels of pro-inammatory and anti-inammatory cytokines in chronic venous ulcers before and aer
four weeks of compressive therapy. e authors demonstrated that ulcers with higher levels of the pro-inammatory cytokines interleukin-1α (IL-1α), IL-1β, interferon-γ
(IFN-γ), IL-12p40, and granulocyte–macrophage colony
stimulating factor were more likely to be rapid healers. e
rapid-healing ulcers had very high pre-compression levels
of IFN-γ and were noted to have a signicant reduction
of IFN-γ following compression therapy. IFN-γ is a glyco-
protein with numerous immunologic functions. IFN-γ has
been shown to suppress the cell cycle, DNA replication, and
RNA metabolism of keratinocytes. It is the key mediator
in keratinocyte apoptosis, and it acts synergistically with
IL-1α to produce tumor necrosis factor-α. e data suggest
that the expression of IFN-γ is important during the inam-
matory phase of acute wound healing, but its down-regulation is necessary for wound healing to occur. In addition,
this study indicates that the mechanism of action of compression therapy is the inhibition of the pro-inammatory
signals that prohibit ulcer healing.
e distribution and location of several other growth
factors in the skin of CVI patients has also been inves-
60
tigated. Peschen et al.
investigated the role of plate-
let-derived growth factor receptor-α (PDGFR-α) and
PDGFR-β and vascular endothelial growth factor (VEGF)
using skin biopsies from 30 patients with symptoms of
reticular veins, venous eczema, skin pigmentation, lipodermatosclerosis, and active leg ulcers. e data suggested
that PDGFR-α and -β and VEGF expression was strongly
increased in the stroma of CVI patients with eczema and
68 Pathogenesis of varicose veins and cellular pathophysiology of chronic venous insufficiency
https://t.me/med1917
active ulcers compared with patients with reticular veins
and pigmentation changes only. To a lesser degree, patients
with lipodermatosclerosis also demonstrated immunoreactivity to PDGFR-α and -β and VEGF. PDGFR-α and-β
expression was considerably elevated in the capillaries
and surrounding broblasts and inammatory cells of
venous eczema patients. In addition, immunoreactivity
was increased in dermal broblasts, SMCs, and vascular cells of lipodermatosclerosis patients compared with
patients with reticular veins only. e greatest expression
of PDGFR-α and -β was observed in the mesenchymal
cells and vascular endothelial cells of patients with active
venous ulcers. VEGF immunoreactivity correlated with
disease severity. VEGF-positive capillary endothelial cells
and pericapillary cells were increased in patients with
venous eczema, lipodermatosclerosis, and active venous
ulceration, respectively. Subsequently, these authors
reported that with progression of CVI dermal pathology, there is increased expression of the endothelial cell
adhesion molecules ICAM-1 and vascular adhesion molecule-1 and their corresponding leukocyte ligands LFA-1
and VLA-4.56 ese data suggest that leukocyte recruitment, capillary proliferation, and interstitial edema in
CVI patients may be regulated through PDGF and VEGF
by the up-regulation of adhesion molecules, leading to
leukocyte recruitment, diapedesis, and the release of
chemical mediators.
58
6.7 DERMAL FIBROBLAST FUNCTION
Several studies have reported aberrant phenotypic behavior of broblasts isolated from venous ulcer edges when
compared with broblasts obtained from ipsilateral thigh
biopsies of normal skin in the same patients. Hasan etal.61
compared the ability of venous ulcer broblasts to produce
aI procollagen mRNA and collagen aer stimulation with
TGF-β1. ese authors were not able to demonstrate dier-
ences in aI procollagen mRNA levels aer stimulation with
TGF-β1 between venous ulcer broblasts and normal bro-
blasts (control) from ipsilateral thigh biopsies. However, collagen production was increased by 60% in a dose-dependent
manner in control subjects, whereas venous ulcer broblasts
were unresponsive. is unresponsiveness was associated
with a four-fold decrease in TGF-β1 type II receptors. In a
follow-up report, Kim etal.
TGF-β1 type II receptors was associated with a decrease in
phosphorylation of the TGF-β1 receptor substrates SMAD2
and SMAD3, as well as p42/44 mitogen-activated protein
(MAP) kinases. A similar investigation reported a decrease
in collagen production from venous ulcer broblasts, and
similar amounts of bronectin production when compared
with normal control subjects.
Fibroblast responsiveness to growth factors was further
delineated by Stanley etal.
ized the proliferative responses of venous ulcer broblasts
when stimulated with bFGF, epidermal growth factor
(EGF), and IL-1β. In their initial study, they reported that
62
indicated that the decrease in
63
64
ese investigators character-
venous ulcer broblast growth rates were markedly suppressed when stimulated with bFGF, EGF, and IL-1β. In a
follow-up investigation, these authors noted that the previously observed growth inhibition could be reversed with
bFGF.65 Lal etal.66 reported that the proliferative responses
of CVI broblasts to TGF-β1 correlated with disease severity. Fibroblasts from patients with CEAP class 2–3 disease
retain their agonist-induced proliferative capacity. Class 4
and 5 broblasts demonstrated diminished agonist-induced
proliferation, whereas class 6 (venous ulcer) broblasts
did not proliferate aer TGF-β1 stimulation, conrming the observations made by the previous investigators.
Phenotypically, venous ulcer broblasts appeared large and
polygonal and exhibited varied nuclear morphologic features, whereas normal broblasts appeared compact and
tapered, with well-dened nuclear morphologic features.
Venous ulcer broblasts appeared morphologically similar
to broblasts undergoing cellular senescence. erefore,
the blunted growth response of CVI venous ulcer broblasts appears to be related to the development of cellular
senescence.
65,66
Other characteristics of senescent cells are an overex-
pression of matrix proteins such as bronectin (cFN) and
enhanced activity of β-galactosidase (SA-β-Gal). In an
evaluation of seven patients with venous stasis ulcers, it
was noted that there was a higher percentage of SA-β-Galpositive cells in patients with venous ulcers than in normal
control subjects (6.3% vs. 0.21%, P ≤ 0.0.6).65 It was also
reported that patients with venous ulcer broblasts produced one- to four-times more cFN by western blot analysis
than control subjects.67 ese data support the hypothesis
that venous ulcer broblasts phenotypically behave like
senescent cells. However, senescence is probably the end
manifestation of a wide spectrum of events that leads to
proliferative resistance and cellular dysfunction. Telomeres
and telomerase activity are the sine qua non of truly senescent cells. To date, there are no reported studies indicating
an abnormality in CVI broblast telomere or telomerase
activity. Despite these investigations, the true role of senescence in CVI remains ill dened.
6.8 REGULATION OF VENOUS ULCER
FORMATION AND HEALING
e primary method of normal wound healing is dependent on broblast-mediated matrix contraction, in association with keratinocyte epithelialization. e progression of
CVI appears to be associated with a concomitant increase in
broblast-mediated contractile properties and the potential
for accelerated wound healing. Pappas and colleagues investigated the eect of TGF-β1 and MAP kinases on broblastmediated matrix contraction in a prospective study using
biopsies from patients with varying degrees of CVI.
was found that treatment with TGF-β1 and inhibition of
MAP kinase promoted gel contraction in a dose-dependent
fashion, and a graded response to treatment was observed
with increasing clinical disease severity using the CEAP
68,69
It
6.10 Summary 69
https://t.me/med1917
classication. is suggests that MAP kinases regulate
TGF-β1-induced intracellular contractile proteins and the
development of a myobroblast phenotype.
Conversely, Ras activation of extracellular signal-reg-
ulated kinase (ERK)-1/2 was shown to irreversibly inhibit
TGF-β1-induced gel contraction, suggesting that ERK-1/2
modulates TGF-β1-induced contraction. e molecular
cross-talk between ERK-1/2 and TGF-β1 was altered
according to the severity of CVI. ere is an increase in
stored kinetic energy and tension in the dermis of CVI that
increases with TGF-β1 and/or ERK inhibition in adaptive
wound healing. While increased broblast contractility is
benecial in the process of wound healing, injury to the
CVI dermal architecture releases stored kinetic energy in
the dermis. is release of energy clinically manifests as
wound separation.
Bacterial contamination and persistent venous hypertension are thought to secondarily aect poor wound healing in the presence of increased matrix contraction. It is
thought that hypertension inuences ulcer wound healing
through a mechanism known as mechanotransduction.
Mechanotransduction is the process of converting physical
forces into biochemical signals and integrating these signals
into a cellular response. It is thought that mechanotransduction of pressure to the CVI dermal broblasts activates
cellular senescence processes and stimulates signaling cascades that inhibit TGF-β1-mediated matrix contraction,
resulting in prolonged wound healing.
Several studies have reported a loss of growth factor
responsiveness in broblasts isolated from patients with
venous ulcers. Senescent broblasts, although they do not
proliferate, remain synthetically active. Increased synthesis and secretion of proteins by these broblasts cause an
alteration in the tissue microenvironment, aecting tissue
structure and function. Campisi has reported that the overexpression of oncogenic Ras stimulates ERK MAP kinase
signaling and the induction of a senescence response in
other broblast strains. Ras signaling might therefore aect
CVI ulcer healing.
70
6.9 ROLE OF MMPS AND THEIR
INHIBITORS IN CVI
Wound healing is an orderly process that involves inammation, re-epithelization, matrix deposition, and tissue
remodeling. MMPs and tissue inhibitors of metalloproteinases (TIMPs) are known for their tissue remodeling properties and their involvement in inammation and wound
repair. ey are oen implicated in the pathogenesis of
CVI. In general, MMPs and TIMPs are not constitutively
expressed. ey are induced temporarily in response to
exogenous signals such as various cytokines or growth factors, cell–matrix interactions, and altered cell–cell contacts.
Fluid from chronic venous ulcers shows a ten-fold increase
in levels of MMP-2 and MMP-9 (gelatinases) and a 116-fold
increase in MMP-1 (collagenase) levels when compared to
uid from acute wounds. TGF-β1 is a potent inducer of
TIMP-1 and an inhibitor of MMP-1. Alterations in MMP
and TIMP production may help modulate the tissue brosis of the lower extremity in CVI patients.
71,72
In patients
with active ulcers, increases in TIMP-1 in keratinocytes
from venous ulcers have been reported. For wound healing to occur, there is a delicate balance between MMPs and
TIMPs, which must be maintained in order to prevent the
uncontrolled ECM degradation by MMPs that is observed
in non-healing ulcers.
73–7 7
6.10 SUMMARY
CVI results from venous hypertension caused by venous
incompetence and/or outow obstruction. Prolonged exposure to venous hypertension in turn causes macromolecule
and RBC extravasation, resulting in the activation of multiple biological processes, such as endothelial activation,
Guidelines 1.5.0 of the American Venous Forum on the pathogenesis of varicose veins and the cellular
pathophysiology of chronic venous insufficiency
No. Guideline
1.5.1 Genetics and deep venous thrombosis are predisposing factors for varicose veins. A
1.5.2 Age, female gender, pregnancy, weight, height, race, diet, bowel habits,
1.5.3 Vein wall remodeling and fibrosis, affected by hemodynamic factors, matrix
1.5.4 In chronic venous insufficiency, the transmission of high venous pressures to the
1.5.5 Transforming growth factor-β1 and matrix metalloproteinases play key roles in the
Grade of evidence
(A:high quality;
B:moderate quality;
C:low or very low
quality)
C
occupation, and posture are predisposing factors for varicose veins.
C
metalloproteinases, and plasminogen activators, lead to varicose vein formation.
A
dermal microcirculation causes extravasation of macromolecules and red blood
cells that serve as the underlying stimulus for inflammatory injury.
B
inflammatory injury that leads to lipodermatosclerosis and chronic skin changes.
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