Dose-dependent smooth muscle cell proliferation induced by thermal injury with pulsed infrared lasers

Mechanisms and Pathways of Pain Photobiomodulation: A Narrative Review

A growing body of evidence supports the modulation of pain by light exposure. As such, phototherapy is being increasingly utilized for the management of a variety of pain conditions. The modes of delivery, and hence applications of phototherapy, vary by wavelength, intensity, and route of exposure. As such, differing mechanisms of action exist depending upon those parameters. Cutaneous application of red light (660 nm) has been shown to reduce pain in neuropathies and complex regional pain syndrome-I, whereas visual application of the same wavelength of red light has been reported to exacerbate migraine headache in patients and lead to the development of functional pain in animal models. Interestingly visual exposure to green light can result in reduction in pain in variety of pain conditions such as migraine and fibromyalgia. Cutaneous application typically requires exposure on the order of minutes, whereas visual application requires exposure on the order of hours. Both routes of exposure elicit changes centrally in the brainstem and spinal cord, and peripherally in the dorsal root ganglia and nociceptors. The mechanisms of photobiomodulation of pain presented in this review provide a foundation in furtherance of exploration of the utility of phototherapy as a tool in the management of pain. PERSPECTIVE: This review synopsizes the pathways and mechanisms through which light modulates pain and the therapeutic utility of different colors and exposure modalities of light on pain. Recent advances in photobiomodulation provide a foundation for understanding this novel treatment for pain on which future translational and clinical studies can build upon.

Preclinical Restenosis Models: Challenges and Successes

Coronary artery disease remains a major problem for Western societies. The advent of percutaneous interventions, including stents has brought clinical care to a new level of efficacy, yet problems remain. Restenosis following stenting in human coronary arteries appears at last to be yielding to therapeutic strategies, especially drug eluting stents. Because therapeutic percutaneous coronary intervention is widely dominated by the intracoronary stent, restenosis therapies must include the stented coronary artery. Animal models and in particular the porcine coronary model seem to represent the human coronary artery reaction to stenting. It mimics several clinical conditions including thrombosis and neointimal formation. A key question in the era of intravascular technologies is how well this and other models can predict clinical events. This paper discusses the models and their application.

Quantification of Adventitial Vasa Vasorum Vascularization in Double-injury Restenotic Arteries

BACKGROUND

Accumulating evidence indicates a potential role of adventitial vasa vasorum (VV) dysfunction in the pathophysiology of restenosis. However, characterization of VV vascularization in restenotic arteries with primary lesions is still missing. In this study, we quantitatively evaluated the response of adventitial VV to vascular injury resulting from balloon angioplasty in diseased arteries.

METHODS

Primary atherosclerotic-like lesions were induced by the placement of an absorbable thread surrounding the carotid artery of New Zealand rabbits. Four weeks following double-injury induced that was induced by secondary balloon dilation, three-dimensional patterns of adventitial VV were reconstructed; the number, density, and endothelial surface of VV were quantified using micro-computed tomography. Histology and immunohistochemistry were performed in order to examine the development of intimal hyperplasia.

RESULTS

Results from our study suggest that double injured arteries have a greater number of VV, increased luminal surface, and an elevation in the intima/media ratio (I/M), along with an accumulation of macrophages and smooth muscle cells in the intima, as compared to sham or single injury arteries. I/M and the number of VV were positively correlated (R2 = 0.82, P < 0.001).

CONCLUSIONS

Extensive adventitial VV neovascularization occurs in injured arteries after balloon angioplasty, which is associated with intimal hyperplasia. Quantitative assessment of adventitial VV response may provide insight into the basic biological process of postangioplasty restenosis.

Vascular restoration therapy and bioresorbable vascular scaffold

This article describes the evolution of minimally invasive intervention technologies for vascular restoration therapy from early-stage balloon angioplasty in 1970s, metallic bare metal stent and metallic drug-eluting stent technologies in 1990s and 2000s, to bioresorbable vascular scaffold (BVS) technology in large-scale development in recent years. The history, the current stage, the challenges and the future of BVS development are discussed in detail as the best available approach for vascular restoration therapy. The criteria of materials selection, design and processing principles of BVS, and the corresponding clinical trial results are also summarized in this article.

Coronary stents: looking forward

Despite all the benefits of drug-eluting stents (DES), concerns have been raised over their long-term safety, with particular reference to stent thrombosis. In an effort to address these concerns, newer stents have been developed that include: DES with biodegradable polymers, DES that are polymer free, stents with novel coatings, and completely biodegradable stents. Many of these stents are currently undergoing pre-clinical and clinical trials; however, early results seem promising. This paper reviews the current status of this new technology, together with other new coronary devices such as bifurcation stents and drug-eluting balloons, as efforts continue to design the ideal coronary stent.

Next generation drug-eluting stents: focus on bioabsorbable platforms and polymers

The success of drug-eluting stents in preventing restenosis has shifted the focus of new stent development toward enhancing long term safety and efficacy of these devices, while simultaneously eliminating the need for indefinite dual antiplatelet therapy. A technical advance fulfilling these aims would hold tremendous potential to reduce morbidity, mortality and economic costs associated with the percutaneous treatment of coronary artery disease. An attractive approach is the use of bioabsorbable stent designs. These may include stents with different bioabsorbable drugs, bioabsorbable polymers or even bioabsorbable metallic backbones. A device that could achieve excellent acute and long-term results, but disappear completely within months (thereby avoiding the need for prolonged dual antiplatelet therapy), would be a tremendous advance. Too good to be true? We explore here the scientific rationale and prospects for success with this exciting concept.

A new wave in treatment of vascular occlusive disease: biodegradable stents--clinical experience and scientific principles

Stent-based therapies in percutaneous vascular intervention are associated with significant long-term complications related to in-stent restenosis. A growing body of literature demonstrates the feasibility of biodegradable materials for endovascular stents, which may, in theory, circumvent many of the immunologic and inflammatory response issues seen with long-term metallic stent failure in coronary and peripheral applications. This review describes the history of endovascular stents and the challenges encountered with metallic, drug-eluting, and biodegradable stents. A review of the basic engineering principles of biodegradable stents is provided, along with a discussion of the cellular mechanisms of restenosis.

Fully biodegradable coronary stents : progress to date

The limitations of currently available metallic drug-eluting stents have renewed interest in biodegradable stents (BDS). Apart from removing the (offending) foreign material that may potentiate a thrombotic event, BDS have the advantage of avoiding 'full metal jackets,' and thus can preclude subsequent coronary surgery. In addition, they do not interfere with the diagnostic evaluation of non-invasive imaging such as cardiac magnetic resonance and CT. There are now several BDS in development or in clinical trials that incorporate a variety of biodegradable polymer technologies. Two broad categories of materials are generally used: those made from organic biopolymers and those made from corrodible metals. However, to date, none of the materials/stents tested have been able to establish a perfect balance between biocompatibility, the kinetics of degradation needed to maintain mechanical strength to limit recoil, and inflammation. However, studies, such as the ABSORB trial with the everolimus eluting poly-L-lactide stent, which demonstrated comparable restenotic rates with bare metallic stents and a low incidence of major adverse cardiac events (MACE) at 12 months of 3.3%, with only one patient having a non-Q-wave myocardial infarction and no target lesion revascularization, suggest that there has been significant progress with respect to the earlier prototypes. The acute recoil observed could potentially be addressed with the polytyrosine REVA stent currently being evaluated in the RESORB trial, which incorporates a novel locking mechanism within its design. Alternative BDS designs include the combination of an antiproliferative drug with endothelial progenitor cell capturing antibodies to facilitate epithelialization and/or dual eluting having, in addition to the antiproliferative drug, polymeric salicyclic acid to limit inflammation. Compared with biodegradable polymers, there are fewer metals used in the manufacture of BDS. The only metal BDS in trials is the Biotronik absorbable magnesium stent, which showed a MACE of 26.7% at 12 months without deaths, stent thrombosis, or acute myocardial infarction in the PROGRESS-AMS trial. Unlike magnesium stents, there has been little progress with iron stents, which remain in the pre-clinical phase, and this may be partly due to the longer degradation times needed and potential issues related with iron clearance.

Characterization of a New Double-Injury Restenosis Model in the Rat Aorta

PURPOSE

To characterize a new rat model of restenosis for evaluation of local or systemic drug strategies.

METHODS

Arterial lesions were induced by placement of silicone cuffs around the aorta of Lewis rats. After 21 days, the cuffs were removed, and a subgroup of rat aortas was subjected to secondary balloon injury. Remodeling of wall compartments and cell kinetics were assessed morphometrically at 3, 7, 14, 21, and 28 days after the single and double-injury approaches. Immunohistochemistry was used to assess the distribution of macrophages, smooth muscle cells, and proliferating cells within the layers of the arterial wall in the experimental groups versus sham-operated and untreated controls.

RESULTS

After cuff placement, the adventitia initially undergoes significant enlargement, while the media shows a reduction in relative thickness. Accumulation of cells within the adventitia at 3 and 7 days is followed by a marked decline in cell density at 14 days, with simultaneously increasing cell numbers in the intima. At this time, activated macrophages are detected in the adventitia, indicating chronic inflammation. Following cuff placement, mild intimal hyperplasia develops. In the double-injury model, extensive neointimal hyperplasia forms rapidly, with a peak at 14 days.

CONCLUSIONS

This new double-injury model is technically easy, and multiple experiments can be accrued in short periods of time. It provides an additional platform to identify new targets and strategies for the prophylaxis of postangioplasty restenosis.

Effects of endothelial injury on the rate of thrombus organization in canine carotid arteries occluded with microcoils

SUMMARY

Thrombus organization in canine carotid arteries occluded with platinum microcoils was studied to determine if endothelial injury created with a Xenon Chloride Excimer Laser (XEL) could acclerate endovascular fibrosis. Ten common carotid artery stumps were created in ten dogs. Each of four stumps were schematically divided into four longitudinally contiguous injury zones (thermal ablation injury, non-ablative injury, proximal and distal non-injury zones) to test the effects of ablative and non-ablative injury and to establish a set of internal controls that would account for proximity to circulating blood at the ostium of the occluded artery. Following XEL irradiation of the endothelium through an arteriotomy, each stump was embolized with microcoils. Four control stumps were subjected to sham laser procedures, and embolized in an identical fashion. Two additional stumps were embolized in the absence of sham surgery. Angiographic, gross and histologic analysis was performed after four weeks. Specimens of freshly clotted whole blood mixed with microcoils were used as an additional control. In irradiated stumps and non-irradiated stumps (sham and embolization only), angiography revealed no evidence of coil compaction or recanalization. In all irradiated stumps the thermal ablation zone contained fibrous tissue and neovascularity without unorganized thrombus. The other zones in the irradiated stumps were indistingnishable from each other and from all zones in the non-irradiated sham stumps, containing primarily unorganized thrombus. Stumps embolized in the absence of sham surgery were filled with material that was grossly and microscopically identical to specimens of freshly clotted whole blood containing microcoils. The results indicate that thermal ablation injury of the endothelium accelerates thrombus organization in canine carotid arteries occluded with platinum microcoils.

Animal models for atherosclerosis, restenosis, and endovascular graft research

Animal models have significantly advanced our understanding of the mechanisms of atherosclerosis and restenosis formation and the evaluation of therapeutic options. The current focus of research is on preventive strategies against restenosis and includes pharmacologic and biologic interventions directed primarily against smooth muscle cell proliferation, endovascular devices for recanalization and/or drug delivery, and an integrated approach using both devices and pharmacobiologic agents. Devices aimed at the percutaneous endoluminal exclusion of aortic aneurysms have also generated interest recently. The experience over many decades with animal models in vascular research has established that a single, ideal, naturally available model for atherosclerosis, restenosis, or for that matter aneurysm formation, does not exist. Presently, rabbits and pigs are favored for the former two areas of study, and dogs and sheep appear to provide suitable models for testing devices for endoluminal repair of aneurysms. The development of transgenic variants of currently available models may widen our options in the future. Nevertheless, an appreciation of the individual features of natural or stimulated disease in each species is of the utmost importance for the proper design and execution of relevant experiments.

Acute directional coronary atherectomy prior to stenting in complex coronary lesions: ADAPTS Study

The purpose of this study was to determine the results of directional coronary atherectomy (DCA) combined with stenting in a high-risk patient population. The use of stenting or DCA alone for aorto-ostial lesions, total chronic occlusions, long lesions, and lesions containing thrombus is associated with lowered success and a relatively high restenosis rate. Between July 1993 and October 1996, we treated 89 lesions with the combined approach of DCA and stenting in 60 consecutive patients. Thirty-one (51.7%) patients were treated because of unstable angina, 11 (18.3%) for post-myocardial infarction (MI) angina, 3 (5.0%) for acute MI, and 15 (25.0%) patients for stable angina. A total of 43 (71.7%) patients had multivessel disease, 19 (31.7%) had undergone previous coronary artery bypass graft (CABG), and 17 (28.3%) patients had undergone multivessel revascularization. The procedure was successful in all patients; and no postprocedural deaths or emergent CABG occurred. Two patients (3.3%) had non-Q-wave MI after the procedure and 1 patient (1.7%) experienced Q-wave MI due to subacute stent closure 7 days after the procedure. During follow-up ranging from 6 months to 3 years, 2 (3.3%) patients died, 2 (3.3%) required CABG surgery, 1 (1.7%) patient had an MI, and 6 patients (10.0%) required target vessel revascularization. By the quantitative coronary angiography, the initial minimal luminal diameter (MLD) averaged 0.91+/-0.45 mm (74.7+/-11.8% stenosis) increasing to 3.80+/-0.44 mm (-6.7+/-12.1%) after the combined approach procedure. Thirty patients (50.0%) met criteria for late (> or =6 months) angiographic follow-up. Late MLD loss averaged 1.13+/-1.07 mm, for a mean net gain of 1.61+/-1.23 mm. Available angiographic follow-up evaluation showed a restenosis rate of 13.3%. A combined approach, defined as the use of both DCA and stenting, is safe and yields a low restenosis rate in high-risk patients who have lesions known to respond less favorably to stenting or DCA alone.

Analysis of heat generation during rotational atherectomy using different operational techniques

Rotational atherectomy can generate heat from the friction of the burr as it ablates atherosclerotic plaque. The objective of this study is to correlate Rotablator technique and heat generation using two experimental models. First, 2.0 mm burrs were advanced through a lesion model derived from bovine bone implanted with thermal probes. Intermittent ablation with minimal decelerations resulted in a smaller temperature increase than continuous ablation with maximal decelerations (2.6 +/- 1.3 vs. 13.9 +/- 1.0 degrees C, respectively, P < 0.01). The second model used porcine femoral arteries cradled in constricting polyethylene grafts with thermal probes in contact with the adventitia. As the burr advanced through the segment, RPM decreases of 5-7 k resulted in a temperature rise of 4.1 +/- 1.2 degrees C, whereas decelerations of 10-20 k resulted in a 11.3 +/- 6.2 degrees C temperature increase. We conclude that excessive drops in speed and aggressive advancement of the burr are related to significant increases in temperature and potential thermal injury.

Impaired arterial neointima formation in mice with disruption of the plasminogen gene

To define the role of plasminogen (Plg) in the smooth muscle cell response after arterial wall injury, neointima formation was evaluated after electric injury of the femoral artery in plasminogen-deficient (Plg-/-) mice. The injury destroyed all medial smooth muscle cells, denuded the injured segment of intact endothelium, and induced transient platelet-rich mural thrombosis. In wild-type (Plg+/+) mice, vascular wound healing was characterized by lysis of the thrombus, transient infiltration of inflammatory cells, and progressive removal of necrotic debris and thrombosis. Topographic analysis revealed repopulation of the media and accumulation in the neointima of smooth muscle cells originating from the noninjured borders, which progressed into the necrotic center. In Plg-/- mice, wound healing was significantly impaired with delayed removal of necrotic debris, reduced leucocyte infiltration and smooth muscle cell accumulation, and decreased neointima formation. Smooth muscle cells accumulated at the uninjured borders, but failed to migrate into the necrotic center. Proliferation of smooth muscle cells was not affected by Plg deficiency. Evans blue staining revealed no genotypic differences in reendothelialization. Thus, Plg plays a significant role in vascular wound healing and arterial neointima formation after injury, most likely by affecting cellular migration.

Differential modulation of vascular endothelial and smooth muscle cell function by photodynamic therapy of extracellular matrix: novel insights into radical-mediated prevention of intimal hyperplasia

PURPOSE

Photodynamic therapy (PDT) has been demonstrated to inhibit experimental intimal hyperplasia and to lead to expedient reendothelialization but negligible repopulation of the vessel media. The mechanism that underlies the differential ingrowth of cells into PDT-treated vessel segments is not understood. Because the extracellular matrix (ECM) is known to modulate specific cell functions, this study was designed to determine whether PDT of isolated ECM affects the function of endothelial cells (ECs) and smooth muscle cells (SMCs).

METHODS

PDT of bovine aortic EC-ECM was performed with chloroaluminum sulfonated phthalocyanine and 675-nm laser light. Control specimens included untreated ECM, ECM-free plates, and ECM exposed to either light or photosensitizer only. Cell function was characterized by attachment, proliferation, and migration of ECs or SMCs that were plated onto identically treated matrixes.

RESULTS

SMC attachment (86% +/- 0.4% vs 95% +/- 0.4%), proliferation (46% +/- 0.5% vs 100% +/- 1.4%), and migration (40% +/- 1.0% vs 100% +/- 0.9%) were significantly inhibited after PDT of ECM when compared with untreated ECM (all p < 0.001). In contrast, PDT of ECM significantly enhanced EC proliferation (129% +/- 6.2% vs 100% +/- 6.2%; p < 0.03) and migration (118% +/- 2% vs 100% +/- 0.8; p < 0.01), but did not affect attachment.

CONCLUSIONS

This report establishes PDT-induced changes in the ECM with a result of inhibition of SMCs and stimulation of EC functions. It provides insight into how PDT-treated arteries can develop favorable EC repopulation without SMC-derived intimal hyperplasia. These findings may help provide a better understanding of the interactions between cells and their immediate environment in vascular remodeling.

Effect of midinfrared holmium: YAG laser angioplasty with and without balloon angioplasty on acute outcome and restenosis in atherosclerotic femoral arteries in rabbits

BACKGROUND AND OBJECTIVE

Pulsed laser may lessen vascular damage and reduce restenosis. This study examined the acute and chronic effects of midinfrared laser angioplasty with and without balloon angioplasty in atherosclerotic femoral arteries in rabbits.

STUDY DESIGN/MATERIALS AND METHODS

Atherosclerosis was induced in arteries by air desiccation and cholesterol feeding. Arteries were assigned to one of four groups: (1) laser angioplasty with a Thullium/Holmium/Chromium:YAG infrared laser (Eclipse), (2) balloon angioplasty, (3) laser followed by balloon angioplasty, and (4) no intervention. Arteries were examined angiographically and histologically at 2 hours and 28 days.

RESULTS

Intervention groups had significant initial gain, but this gain was less with laser alone than after balloon or after laser plus balloon. At 2 hours, laser alone caused greater arterial damage and thrombosis compared to controls. At 28 days, arteries treated with laser plus balloon had greater narrowing compared with arteries treated with balloon angioplasty. By multivariate regression analysis, the severity of the pre-intervention stenosis (P = 0.001) and intervention with laser plus balloon (P = 0.01) correlated independently with the severity of luminal narrowing at 28 days.

CONCLUSION

Midinfrared Ho:YAG laser angioplasty resulted in substantial acute damage with increased frequency of thrombus formation in this rabbit model. arteries treated with laser alone had suboptimal initial gain and more obstruction by plaque at 28 days compared to nonintervened arteries. The adjunctive use of balloon angioplasty improved initial gain, but correlated with smaller luminal diameters and more severe narrowing by plaque at 28 days.

Initial clinical experiences with rescue unipolar radiofrequency thermal balloon angioplasty after abrupt or threatened vessel closure complicating elective conventional balloon coronary angioplasty

OBJECTIVES

The purpose of this study was to evaluate the effectiveness of radiofrequency thermal balloon angioplasty and rescue procedure after abrupt or threatened vessel closure complicating elective percutaneous transluminal coronary angioplasty.

BACKGROUND

Coronary angioplasty is an established therapy for ischemic heart disease. However, abrupt closure after successful angioplasty remains a serious problem.

METHOD

We utilized a unipolar radiofrequency balloon in which a radiofrequency potential of 13.56 MHz was transmitted between the coil within the balloon and a plate electrode attached to the patient's body. The temperature within the balloon could be monitored through a thermistor within the balloon. From October 1991 through December 1993, 31 patients who had abrupt or threatened vessel closure during 1,005 consecutive elective coronary angioplasty procedures were randomly assigned to radiofrequency balloon angioplasty or to other procedures as rescue

RESULTS

Fifteen patients were assigned to radiofrequency balloon angioplasty (5 with abrupt vessel closure and 10 with threatened closure). The average balloon temperature and inflation time were 62 +/- 9 degrees C and 129 +/- 62 s, respectively. Percent diameter stenosis decreased from 87 +/- 14% to 36 +/- 25% (p < 0.01). The procedure was successful in 14 patients. The rate of restenosis was 67%, but the success rate of repeat conventional coronary angioplasty for restenosed lesions was 86%.

CONCLUSIONS

Radiofrequency balloon angioplasty is effective in the treatment of abrupt or threatened vessel closure complicating elective coronary angioplasty even though the procedure is associated with a relatively high rate of restenosis.

Corticosteroid agents inhibit proliferation of smooth muscle cells from human atherosclerotic arteries in vitro

We studied the in vitro effect of steroid agents on smooth muscle cells from human atherosclerotic arteries. Recent advances in the understanding of the biology of restenosis indicate that restenosis is predominantly caused by a multifactorial stimulation of smooth muscle cell proliferation. Primary stenosing plaque material of 24 patients (aged 63 +/- 14 years) and restenosing plaque material of 7 patients (aged 65 +/- 9 years) was selectively extracted from femoral arteries by the Simpson atherectomy device. Cells were isolated by enzymatic disaggregation and identified as smooth muscle cells by positive reaction with smooth muscle alpha-actin. The steroid agents prednisolone (0.0075-750 micrograms/ml), hydrocortisone (0.0125-1250 micrograms/ml), and dexamethasone (0.0004-40 micrograms/ml) were added to the cultures. Six days after seeding the cells were trypsinized and the cell number was measured by a cell counter. All three steroid agents exhibited a significant antiproliferative effect on smooth muscle cell proliferation. At high concentrations of hydrocortisone, cytoskeletal elements of smooth muscle cells such as actin, microtubules, and vimentin, were largely altered. Our data indicate that the proliferation of smooth muscle cells from human atherosclerotic arteries in vitro can be inhibited by steroid agents and thus may open the way for local post-angioplasty treatment strategies.