Adventitial Fibroblasts

Temsirolimus Adventitial Delivery to Improve ANGiographic Outcomes Below the Knee

BACKGROUND

Current endovascular treatments of below the knee (BTK) popliteal or tibial/peroneal arteries including investigational drug-coated balloons have limited long-term efficacy.

OBJECTIVES

This Phase 2 trial assessed the feasibility of adventitial deposition of temsirolimus to reduce neointimal hyperplasia and clinically relevant target lesion failure (CR-TLF) 6 months after BTK arterial revascularization.

METHODS

This prospective, multicenter, double-blinded, comparative, dose-escalation trial enrolled 61 patients with Rutherford 3 to 5 symptoms undergoing endovascular revascularization of ≥1 angiographically significant BTK lesions. Perivascular infusion after completion of arterial revascularization was randomized into control (saline) vs low-dose (0.1 mg/mL) temsirolimus groups for the first 30 patients. In the second part of the trial, patients were randomized to control versus high-dose (0.4 mg/mL) temsirolimus groups. Primary and secondary efficacy endpoints were target lesion (TL) transverse-view vessel area loss percentage (TVAL%) and CR-TLF at 6 months, respectively. CR-TLF was defined as a composite of ischemia-driven major amputation of the target limb, clinically driven target lesion revascularization (CD-TLR), and clinically relevant TL occlusion. The primary safety endpoint was freedom from major adverse limb events or perioperative death (MALE+POD) at 30 days.

RESULTS

There was no discernable difference in effect between temsirolimus doses; therefore, the low- and high-dose cohorts were pooled for the analyses. The principal analysis on the per protocol (PP) group of 53 patients revealed superior primary efficacy of the treatment arm, with reduction in TVAL% of 13.9% absolute (37.3% relative) and the rate of CR-TLF reduced by 27.1% absolute (51.3% relative), at 6 months. Subgroup analysis of all Trans-Atlantic Inter-Society Consensus (TASC) B to D lesions (N=36) revealed TVAL% reduction of 22.3% absolute (48.3% relative) and the rate of CR-TLF reduced by 39.2% absolute (56.6% relative). Freedom from 30-day MALE+POD was 100% in all groups.

CONCLUSIONS

This hypothesis-generating trial suggests that adventitial infusion of temsirolimus in BTK arteries improves TVAL% and CR-TLF with no adverse safety signals through 6 months, supporting the move to a Phase 3 trial.

CLINICAL IMPACT

There remain gaps in the endovascular treatment of patients with atherosclerotic lesions of below-the-knee (BTK) arteries. The TANGO trial evaluated the use of sub-adventitial temsirolimus with the Bullfrog micro-infusion device during BTK interventions. The therapy was safe and effective. Compared with controls, vessel lumen area patency was improved, and target lesion failure was less frequent. The effects were most appreciable in subjects with higher baseline TASC lesions (B, C, or D). Sub-adventitial temsirolimus offers the potential to improve the results of BTK interventions in this challenging patient population.

The anatomical sources of neointimal cells in the arteriovenous fistula

Neointimal cells are an elusive population with ambiguous origins, functions, and states of differentiation. Expansion of the venous intima in arteriovenous fistula (AVF) is one of the most prominent remodeling processes in the wall after access creation. However, most of the current knowledge about neointimal cells in AVFs comes from extrapolations from the arterial neointima in non-AVF systems. Understanding the origin of neointimal cells in fistulas may have important implications for the design and effective delivery of therapies aimed to decrease intimal hyperplasia (IH). In addition, a broader knowledge of cellular dynamics during postoperative remodeling of the AVF may help clarify other transformation processes in the wall that combined with IH determine the successful remodeling or failure of the access. In this review, we discuss the possible anatomical sources of neointimal cells in AVFs and their relative contribution to intimal expansion.

Periadventitial Delivery of Simvastatin-Loaded Microparticles Attenuate Venous Neointimal Hyperplasia Associated With Arteriovenous Fistula

Background

Venous neointimal hyperplasia and venous stenosis (VS) formation can result in a decrease in arteriovenous fistula (AVF) patency in patients with end‐stage renal disease. There are limited therapies that prevent VNH/VS. Systemic delivery of simvastatin has been shown to reduce VNH/VS but local delivery may help decrease the side effects associated with statin use. We determined if microparticles (MP) composed of cyclodextrins loaded with simvastatin (MP‐SV) could reduce VS/VNH using a murine arteriovenous fistula model with chronic kidney disease.

Methods and Results

Male C57BL/6J mice underwent nephrectomy to induce chronic kidney disease. Four weeks later, an arteriovenous fistula was placed and animals were randomized to 3 groups: 20 μL of PBS or 20 μL of PBS with 16.6 mg/mL of either MP or MP‐SV. Animals were euthanized 3 days later and the outflow veins were harvested for quantitative reverse transcriptase–polymerase chain reaction analysis and 28 days later for immunohistochemistical staining with morphometric analysis. Doppler ultrasound was performed weekly. Gene expression of vascular endothelial growth factor‐A (Vegf‐A), matrix metalloproteinase‐9 (Mmp‐9), transforming growth factor beta 1 (Tgf‐β1), and monocyte chemoattractant protein‐1 (Mcp‐1) were significantly decreased in MP‐SV treated vessels compared with controls. There was a significant decrease in the neointimal area, cell proliferation, inflammation, and fibrosis, with an increase in apoptosis and peak velocity in MP‐SV treated outflow veins. MP‐SV treated fibroblasts when exposed to hypoxic injury had decreased gene expression of Vegf‐A and Mmp‐9.

Conclusions

In experimental arteriovenous fistulas, periadventitial delivery of MP‐SV decreased gene expression of Vegf‐A, Mmp‐9, Tgf‐β1 and Mcp‐1, VNH/VS, inflammation, and fibrosis.

Association of atherosclerotic risk factors with carotid adventitial thickness assessed by ultrasonography

PURPOSE

There is increasing evidence that adventitial inflammation may participate in atherosclerosis development. The aim of this study was to investigate which atherosclerotic risk factors correlated with carotid adventitial thickness (AT) and to compare them with those associated with carotid intima-media thickness (IMT). We also set out to test the hypothesis that there is a significant correlation between IMT and AT in the carotid arteries.

METHODS

The far carotid artery wall IMT and AT were measured by high-resolution B-mode ultrasound in 128 persons (mean, 65 +/- 8 years). A number of conventional and novel, clinically and laboratory-derived risk factors were assessed.

RESULTS

Significant correlation (r = 0.35, p < 0.0001) was demonstrated between the IMT and AT. The stepwise forward multiple regression analysis revealed correlations between IMT and leukocyte count, C-reactive protein level, and hypertension, whereas the Chlamydia (C.) pneumoniae IgA antibodies and fibrinogen levels, gender, and smoking correlated merely with AT. The homocysteine/methionine ratio correlated with both IMT and AT.

CONCLUSION

The association between IMT and AT may reflect an interaction between intimal, medial, and adventitial pathology. Different risk factors are associated with the increased AT or IMT. It is possible that inflammation and some chronic infections, such as those induced by C. pneumoniae, could have a marked influence on adventitial cell proliferation.

Urotensin II is an autocrine/paracrine growth factor for aortic adventitia of rat

Urotensin II (UII) is a potent vasoconstrictive peptide; however, its significance in vascular adventitia has not been clearly elucidated. In this study, rat aortic adventitia showed mRNA expression and immunoreactivity of UII and its receptor (UT). Moreover, radioligand-binding assay showed that maximum binding capacity (Bmax) of [(125)I]-UII was higher in adventitia than in media (28.60+/-1.94 vs. 20.21+/-1.11 fmol/mg, P<0.01), with no difference in binding affinity (dissociation constant [Kd] 4.27+/-0.49 vs. 4.60+/-0.40 nM, P>0.05). Furthermore, in cultured adventitial fibroblasts, UII stimulated DNA synthesis, collagen synthesis and secretion in a concentration-dependent manner. These effects were inhibited by the UII receptor antagonist urantide (10(-6) mol/l), Ca(2+) channel blocker nicardipine (10(-5) mol/l), protein kinase C inhibitor H7 (10(-6) mol/l), and mitogen-activated protein kinase inhibitor PD98059 (10(-6) mol/l) but not the phosphatidyl inositol-3 kinase inhibitor wortmannin (10(-7) mol/l). UII may act as an autocrine/paracrine factor through its receptor and the Ca(2+) channel, protein kinase C, and mitogen-activated protein kinase signal transduction pathways, in the pathogenesis of vascular remodeling by activating vascular adventitia.

Increased Migration of Vascular Adventitial Fibroblasts from Spontaneously Hypertensive Rats

Experimental evidence has suggested that vascular adventitial fibroblasts (AFs) may migrate into the neointima of arteries after balloon injury in various animal models. However, the research on migration of AFs has been limited to the effects of acute vascular injury. The role of AFs in chronic vascular injury and hypertension is not yet known. In this study, the migration of spontaneously hypertensive rat (SHR)-AFs and Wistar-Kyoto rat (WKY)-AFs from the thoracic aorta was determined by a transwell technique. Our results showed that fetal calf serum, angiotensin II (Ang II), phorbol ester, basic fibroblast growth factor and platelet-derived growth factor-BB induced migration in a dose-dependent manner, and the migration of SHR-AFs was always greater than that of WKY-AFs. Ang II-induced migration of AFs was considered to have been mediated by Ang II type 1 receptor (AT1-R), because the AT1-R antagonist losartan (10(-7)-10(-5) mol/l) suppressed Ang II-induced migration. Ang II-induced migration was also blocked by the extracellular-regulated protein kinase 1/2 (ERK1/2) inhibitor PD98059 (10(-5) mol/l) and p38 kinase inhibitor SB202190 (10(-5) mol/l), indicating that ERK1/2 and p38 kinase were involved in Ang II-induced migration. Ang II (10(-7) mol/l)-induced ERK1/2 and p38 kinase phosphorylation, both of which peaked after 5 min, were suppressed by PD98059 and SB202190, respectively. The Ang-II induced phosphorylation of both proteins was suppressed by losartan, whereas no effect was observed with PD123319, a specific inhibitor of Ang II type 2 receptor (AT2-R). Thus, in the present study, various factors stimulated the migration of SHR-AFs and, to a leber extent, WKY-AFs from the thoracic aorta, and the ERK1/2 and p38 kinase pathways are involved in Ang II-stimulated migration of fibroblasts.

Interleukin-8 secretion by fibroblasts induced by low density lipoproteins is p38 MAPK-dependent and leads to cell spreading and wound closure

We have previously reported (Dobreva, I., Waeber, G., Mooser, V., James, R. W., and Widmann, C. (2003) J. Lipid Res. 44, 2382-2390) that low density lipoproteins (LDLs) induce activation of the p38 MAPK pathway, resulting in fibroblast spreading and lamellipodia formation. Here, we show that LDL-stimulated fibroblast spreading and wound sealing are due to secretion of a soluble factor. Using an antibody-based human protein array, interleukin-8 (IL-8) was identified as the main cytokine whose concentration was increased in supernatants from LDL-stimulated cells. Incubation of supernatants from LDL-treated cells with an anti-IL-8 blocking antibody completely abolished their ability to induce cell spreading and mediate wound closure. In addition, fibroblasts treated with recombinant IL-8 spread to the same extent as cells incubated with LDL or supernatants from LDL-treated cells. The ability of LDL and IL-8 to induce fibroblast spreading was mediated by the IL-8 receptor type II (CXCR-2). Furthermore, LDL-induced IL-8 production and subsequent wound closure required the activation of the p38 MAPK pathway, because both processes were abrogated by a specific p38 inhibitor. Therefore, the capacity of LDLs to induce fibroblast spreading and accelerate wound closure relies on their ability to stimulate IL-8 secretion in a p38 MAPK-dependent manner. Regulation of fibroblast shape and migration by lipoproteins may be relevant to atherosclerosis that is characterized by increased LDL cholesterol levels, IL-8 production, and extensive remodeling of the vessel wall.

Antisense basic fibroblast growth factor alters the time course of mitogen-activated protein kinase in arterialized vein graft remodeling

PURPOSE

Neointimal hyperplasia (NIH) is complete by 3 weeks in rabbit vein grafts implanted into the arterial circulation. Activation of the mitogen-activated protein kinase (MAPK) family of protein kinases is thought to be critical in remodeling events such as cellular proliferation, differentiation, and migration, as found in NIH. We previously demonstrated that antisense basic fibroblast growth factor (ASbFGF) inhibited the synthesis of basic fibroblast growth factor (bFGF) in the balloon injury model of NIH. We examined the effect of ASbFGF on NIH and the time course of MAPK, extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal protein kinase (JNK), and p38 kinase activation in arterialized vein grafts.

METHODS

Carotid interposition of a vein bypass graft was performed in 75 New Zealand White rabbits. Segments of the external jugular vein were transfected with a replication-deficient adenovirus containing the messenger RNA sequence for rat ASbFGF at 1 x 10(10) plaque-forming units per milliliter; control animals were given phosphate-buffered saline solution (PBS) alone. Rabbits were killed at 30 minutes, 4 days, 7 days, and 21 days (n = 8). Four grafts in each group were fixed with formalin and embedded in paraffin, then processed with elastin-collagen and hematoxylin-eosin stains. The other four grafts were individually frozen, and total protein was extracted. Phosphorylation of MAPK, ERK1/2, JNK, and p38, was determined with Western blot analysis and immunohistochemistry. Groups were compared with analysis of variance.

RESULTS

The thickness of neointima in the PBS group and the ASbFGF group at 21 days was 60.2 +/- 2.1 and 39.4 +/- 2.1 microm, respectively (P <.01). In both the control and ASbFGF groups, all 3 MAPKs demonstrated activation compared with preimplantation levels. However, when compared with the PBS group the ASbFGF group showed greater than 33% inhibition of all three MAPKs by day 4 and day 7 (P <.05), but no significant difference in any MAPK activation by day 21 (P >.05, all groups). Cells staining positive for activated MAPK were found in the neointima and adventitia of vein grafts in both the PBS and ASbFGF groups.

CONCLUSION

MAPKs are activated during the first week after vein graft implantation. Grafts treated with ASbFGF demonstrated reduced MAPK activation and less neointimal thickening. These results suggest that the process of vein graft adaptation to the arterial circulation, and subsequent NIH, may depend on basic fibroblast growth factor activity, which is mediated, at least in part, by a MAPK-dependent mechanism.