Effects of ultraviolet light in vascular cells in vitro and in intact atherosclerotic explants: potential role of apoptosis in vascular biology

Effectiveness of narrow-band ultraviolet-B phototherapy for prevention of intimal hyperplasia in a rat carotid balloon injury model

BACKGROUND AND OBJECTIVE

Narrow-band ultraviolet-B light (NBUVB) (313 nm) is known to have anti-proliferative effects, implying a potential treatment for intimal hyperplasia, but it remains to be ascertained. We assessed the effects of NBUVB irradiation for prevention of intimal hyperplasia.

STUDY DESIGN/MATERIALS AND METHODS

The rat carotid arteries were irradiated with NBUVB after balloon injury (BI), and the degree of intimal hyperplasia was histopathologically assessed. The anti-proliferative effects using cultured human smooth muscle cells were evaluated by flow cytometry and immunoblot analysis.

RESULTS

NBUVB (0.3-4.5 J/cm(2)) irradiation immediately after BI reduced the degree of intimal hyperplasia at 14 and 28 days after BI (P<0.001) without any obvious complications. Neither an increase in the number of medial cells nor upregulation of proliferating cell nuclear antigen was observed in the irradiated arteries. NBUVB irradiation at 2 or 14 days after BI significantly suppressed further intimal hyperplasia (P<0.01). NBUVB-irradiated cultured cells showed inhibited proliferation involved with G(1) and G(2)/M arrests. Increased expression of p53 and inhibition of retinoblastoma protein (pRB) phosphorylation were also seen in the NBUVB-irradiated cells.

CONCLUSIONS

These data suggest that NBUVB irradiation is an effective method for preventing intimal hyperplasia. The anti-proliferative effect is partly due to the cell cycle arrest caused by p53 expression and inhibited pRB phosphorylation.

The clinical and nutritional implications of lipid-lowering drugs that act in the gastrointestinal tract

PURPOSE OF REVIEW

A new class of cholesterol-lowering therapy that reduces intestinal sterol absorption has recently been introduced. This increases the number of classes of lipid-lowering agents that directly affect gastrointestinal function and raises questions concerning the overall effect of these agents on absorption and nutritional status.

RECENT FINDINGS

A recent assessment notes a paucity of information concerning the factors that affect the bioavailability and intestinal absorption of lipophilic nutrients. By contrast, the specificity of the mechanisms of action of new drugs acting on the gastrointestinal tract may circumvent some of the detrimental effects on nutrient and drug bioavailability that have been noted with older forms of treatment.

SUMMARY

The clinical imperative for aggressive control of lipid and metabolic risk factors makes widespread use, alone or in combination, of lipid-lowering agents that affect the gastrointestinal tract seem increasingly likely. Whilst the opportunity for therapeutic synergy is attractive, care will be required to avoid interference with intestinal absorptive function.

Oxidation of LDL, atherogenesis, and apoptosis

A plethora of studies in cultured cells have established that oxidized low-density lipoprotein (oxLDL) may enhance arterial apoptosis that involves both mitochondrial and death receptor pathways (Fas/FasL, TNF receptors I and II), thereby activating caspase cascade and other proteases. When apoptosis is inhibited by Bcl-2 overexpression, oxLDL may trigger necrosis through a calcium-dependent pathway. Despite this effort, the pathophysiological relevance of apoptosis in vivo remains to be elucidated. In principle, apoptosis occurring in atherosclerotic areas could be involved in endothelial cell lining defects, necrotic core formation, and plaque rupture or fissuring. This complex pathogenic framework may favor coronary atherothrombotic events. To date, the pathogenic role of apoptosis in thrombosis is attractive, but a solid evidence is still needed. When the precise role of oxLDL in vascular programmed cell death occurring in vivo is clarified, this may aid in the development of novel therapeutic approaches to adverse atherogenesis and its clinical sequelae.

Long-term effects of UV light on contractility of rat arteries in vivo

Several studies have shown that UV irradiation may be effective for preventing vascular restenosis or vasopasm. However, the long-term effects of UV light on the physiological properties of vessels such as arterial tension have not been elucidated. We therefore studied the long-term effects of UV using rat carotid arteries treated with UV-B light (wavelength = 313 nm, total energy = 14 mJ/mm2). The animals were sacrificed at 1, 7 and 14 days after UV light exposure, and the carotid arteries were studied by light microscopy and the contractile responses of isolated arterial rings were recorded under isometric tension. UV treatment had induced a substantial loss of smooth muscle cells (SMC) along the entire circumference of the media on days 7 and 14, whereas loss of SMC on day 1 was negligible. Contractile responses of arteries that had been exposed to UV light were significantly reduced on days, 1, 7 and 14. The susceptibility of UV-treated arteries to phenylephrine and prostaglandin F2 alpha was significantly decreased on days 1 and 7, but decreased susceptibility was not seen on day 14. Acetylcholine-induced relaxations were not altered by UV treatment. These results suggest that the long-term effect of UV light is an attenuation of smooth muscle contractility without impairment of endothelial function.

Oxidation-sensitive mechanisms, vascular apoptosis and atherosclerosis

Increased generation of oxidants, resulting from disruption of aerobic metabolism and from respiratory burst, is an essential defense mechanism against pathogens and aberrant cells. However, oxidative stress can also trigger and enhance deregulated apoptosis or programmed cell death, characteristic of atherosclerotic lesions. Oxidation-sensitive mechanisms also modulate cellular signaling pathways that regulate vascular expression of cytokines and growth factors, and influence atherogenesis, in particular when increased levels of plasma lipoproteins provide ample substrate for lipid peroxidation and lead to increased formation of adducts with lipoprotein amino acids. In some cases, increased oxidation and apoptosis in a group of cells might be beneficial for survival and function of other groups of arterial cells. However, overall, oxidation and apoptosis appear to promote the progression of diseased arteries towards a lesion that is vulnerable to rupture, and to give rise to myocardial infarction and ischemic stroke. Recent rapid advances in our understanding of the interactions between oxidative stress, apoptosis and arterial gene regulation suggest that selective interventions targeting these biological functions have great therapeutic potential.

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.

Progression of atheroma: a struggle between death and procreation

Traditional thinking accorded a major role to deranged cell proliferation as a determinant of the abnormal cellularity of atheroma. However, studies conducted in several laboratories have documented the occurrence of disordered apoptosis during atherogenesis, leading to the death of lipid-rich foam cells (promoting lipid-core formation) and depletion of vascular smooth muscle cells (fostering fragility of the fibrous cap). A complex interplay of environmental factors and endogenous proteins regulates apoptosis and contributes to the struggle between cell death and procreation in atherosclerosis. In addition to a variety of growth factors, chemically modified lipids, reactive oxygen species, proinflammatory cytokines, and Fas ligand produced by activated immune cells may influence cell viability through a diversity of pathways, including the caspase cascade, the Bcl-2 protein family, and the oncogene/antioncogene system. A clarification of the molecular mechanisms responsible for vascular cell death may aid in the development of novel therapeutic strategies to treat atherosclerosis and its complications, including the acute coronary syndromes.

Pancreatic cholesterol esterase, ES-10, and fatty acid ethyl ester synthase III gene expression are increased in the pancreas and liver but not in the brain or heart with long-term ethanol feeding in rats

INTRODUCTION

Chronic alcohol consumption predisposes susceptible individuals to both acute and chronic pancreatitis.

AIMS

Our hypothesis was that alcohol increases the risk of pancreatitis by disrupting defense mechanisms and/or enhancing injury-associated pathways through altered gene expression. Hence, we studied the expression of pancreatic genes in rats chronically exposed to ethanol.

METHODOLOGY

Male Wistar rats were pair-fed liquid diets without and with ethanol for 4 weeks. Total RNA was extracted from rat pancreas and other organs. The mRNA expression patterns among pancreatic samples from ethanol-fed rats and controls were compared with use of mRNA differential display. The differentially expressed cDNA tags were isolated, cloned, and sequenced.

RESULTS

One cDNA tag that was overexpressed in the pancreas showed 99% sequence homology to a rat pancreatic cholesterol esterase mRNA (CEL; Enzyme Commission number [EC] 3.1.1.13). The differential expression was confirmed by realtime PCR. Gene expression was also increased in the liver but not in the heart or brain of the alcohol-fed rats. Because CEL has fatty acid ethyl ester (FAEE)-generating activity and FAEEs play a major role in acute alcoholic pancreatitis, we determined the expression of other genes encoding for FAEE-generating enzymes and showed similar organ-specific expression patterns.

CONCLUSION

Our results demonstrate that chronic ethanol consumption induced expression of FAEE-related genes in the pancreas and liver. This upregulation may be a central mechanism leading to acinar cell injury.

Pretreatment with continuous-wave ultraviolet irradiation to prevent the development of delayed vasospasm in the rabbit common carotid artery model

OBJECT

Ultraviolet (UV) light irradiation can lead to immunomodulation. The purpose of this study was to determine the preventive effect of UV light on cerebral vasospasm by using a rabbit common carotid artery (CCA) model.

METHODS

Rabbit CCAs were constricted for a long period by application of autologous blood within a silicon sheath. Before immersion in blood, the CCAs were adventitiously exposed to UV light emitted from a helium-cadmium laser (wavelength 325 nm) yielding an irradiation energy of 10 mJ/mm2. The occurrence of vasospasm was evaluated using angiography 48 hours after blood exposure in this model. The UV light treatment significantly reduced the degree of vasospasm. Compared with luminal diameters measured on Day 0, prior to treatment, the luminal diameters of UV light-treated arteries (six animals) decreased by only 6%, whereas that of the sham-treated arteries (eight animals) significantly decreased by 26% (p<0.001). Histological examination of UV light-treated CCAs revealed no endothelial damage and extended smooth-muscle cells, in which some fragmented nuclei were confirmed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling. Twenty-eight days after blood exposure, examination of UV light-treated CCAs revealed only myointimal proliferation, similar to that of the sham-treated CCAs.

CONCLUSIONS

These results are the first to provide evidence of a prophylactic effect of UV light on vasospasm and are suggestive of involvement of apoptosis in the mechanism of this effect.

Extracellular adenosine induces apoptosis of human arterial smooth muscle cells via A(2b)-purinoceptor

Apoptosis of arterial smooth muscle cells (ASMCs) could play an important role in the pathogenesis of atherosclerosis and restenosis. Recent studies have demonstrated that extracellular adenosine induces apoptosis in various cell types. Our aim was to delineate the capacity of this nucleoside to induce ASMC apoptosis in arterial diseases. We demonstrate that adenosine dose-dependently triggers apoptosis of cultured human ASMCs. Apoptotic cell death was quantified by analysis of nuclear chromatin morphology and characterized by DNA laddering. The involvement of adenosine receptors was suggested, because neither an adenosine deaminase inhibitor, erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride, nor an inhibitor of cellular nucleoside transport, dipyridamole, was able to inhibit adenosine-induced ASMC apoptosis. In contrast, an A(1)/A(2)-adenosine receptor antagonist, xanthine amine congener, totally inhibited adenosine-induced apoptosis. Furthermore, among more selective inhibitors of P(1) purinoceptor subtypes, only alloxazine, an antagonist of A(1)- and A(2)-adenosine receptors, completely inhibited adenosine-induced ASMC apoptosis, suggesting that adenosine triggers ASMC apoptosis via either 1 or both of these receptors. However, 8-cyclopentyl-1,3-dipropylxanthine, 8-(3-chlorostyryl) caffeine, and 3-ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1, 4-(+/-)-dihydropyridine-3,5-dicarboxylate, which are A(1)-, A(2a)-, and A(3)-adenosine receptor antagonists, did not inhibit adenosine-induced apoptosis, suggesting an involvement of the A(2b)-receptor in this process. Moreover, the cAMP increase followed by cAMP-dependent protein kinase activation appears essential to mediate adenosine-induced ASMC apoptosis, thus confirming the previous hypothesis. These results indicate that adenosine-induced apoptosis of ASMCs is essentially mediated via A(2b)-adenosine receptor and involves a cAMP-dependent pathway.

Capacity of a low calcium diet to induce the renal vitamin D 1a-hydroxylase is decreased in adult rats

Young animals adapt to a low calcium diet by increasing renal production of 1,25-dihydroxyvitamin D [1,25(OH)2D], the active metabolite of vitamin D. However, the capacity of adult animals to adapt is markedly diminished. With the recent cloning of the cytochrome P450 component (CYP1a) of the renal 1-hydroxylase enzyme complex, it is now possible to determine directly the effect of dietary calcium and maturation on the expression of renal 1-hydroxylase. Using a ribonuclease protection assay, it was found that feeding a low Ca diet markedly increased renal CYP1a mRNA levels in young rats. However, feeding this diet to adult rats produced an increase in CYP1a mRNA that was only 10% that of the young rats. These studies demonstrate that a low calcium diet increases renal 1,25-dihydroxyvitamin D production in young animals but not in adult animals by increasing CYP1a expression. Since the low calcium diet increased plasma parathyroid hormone levels to similar levels in both age groups, this suggests that in the adult there is a renal refractoriness to parathyroid hormone.

Transcriptional regulation of the human carboxyl ester lipase gene in exocrine pancreas. Evidence for a unique tissue-specific enhancer

The human carboxyl ester lipase (CEL) is an important enzyme for the intestinal absorption of dietary lipids. The gene is highly expressed in exocrine pancreas and in the mammary gland during pregnancy and lactation. In this paper, we have focused on its transcriptional regulation in exocrine pancreas. Reporter gene analysis in cell cultures reveals that a high level of tissue-specific expression is established by the proximal 839 base pairs of the 5'-flanking region. This is due to a strong enhancer, located at -672 to -637. Transfections in mammary gland-derived cells reveal that the enhancer is pancreas-specific and does not contribute to the mammary gland expression. This indicates that the expression of the CEL gene in the mammary gland and pancreas, respectively, is due to two different regulatory systems. Further characterizations of the enhancer reveal that it is composed of two closely located cis-elements. The proximal element mediates a positive effect, whereas the distal element exerts a silencing effect on the positive proximal element. The functional enhancer complex is composed of ubiquitously expressed factors, since similar interactions are achieved with nuclear extracts from cells derived from other tissues. However, no enhancer activity is achieved in such cells. Hence, the net enhancer activity is the result of a tissue-specific balance between factors interacting with the two elements. Since none of the described cis-elements show any clear homology to known cis-elements, we propose that the interacting complex is composed of yet unidentified transcription factors.

Biliary cholesterol excretion: a novel mechanism that regulates dietary cholesterol absorption

The regulation of dietary cholesterol absorption was examined in C57BL/6 and transgenic mice with liver overexpression of the scavenger receptor BI (SR-BI Tg). In C57BL/6 animals, feeding 0.02 to 1% (wt/wt) dietary cholesterol resulted in a dose-dependent decrease in the percentage of dietary cholesterol absorbed. A plot of total daily mass of dietary cholesterol absorbed versus the percentage by weight of cholesterol in the diet yielded a curve suggesting a saturable process with a Km of 0.4% (wt/wt) and a Vmax of 0.65 mg cholesterol/g body weight per day. Dietary cholesterol suppressed hepatic 3-hydroxy-3-methylglutaryl CoA reductase activity, stimulated cholesterol 7alpha-hydroxylase activity, and enhanced fecal excretion of bile acids, but none of these changes correlated with the percentage of dietary cholesterol absorption. Dietary cholesterol also caused an increase in biliary cholesterol concentration, and in this case the concentration of biliary cholesterol was strongly and inversely correlated with the percentage dietary cholesterol absorption (r = -0.63, P < 0.0001). Biliary cholesterol concentration was also directly correlated with daily cholesterol intake, dietary cholesterol mass absorption, and liver cholesterol ester content. Transgene-induced overexpression of SR-BI resulted in a stimulation of excretion of cholesterol into the bile and suppressed percentage dietary cholesterol absorption. Furthermore, biliary cholesterol levels in SR-BI Tg mice were strongly and inversely correlated with the percentage of dietary cholesterol absorbed (r = -0.99, P < 0.0008). In summary, these results suggest that the excretion of cholesterol into the bile plays an important role in regulating the percentage absorption of dietary cholesterol.