Current status and future directions for diagnostic markers of drug-induced vascular injury

Recently, there has been an increased incidence of vascular toxicity in pre-clinical toxicology studies. This is of concern because of the uncertain relevance and extrapolation of this finding to humans. In dogs, profound heart rate (HR) and mean arterial pressure (MAP) changes were considered surrogate markers for drug-induced vascular injury until the early 1990s when endothelin receptor antagonists (ETRA) did not significantly alter HR or MAP but induced identical lesions in the coronary arteries of dogs. Thus significant alterations in HR and MAP were found not to be a prerequisite for this lesion. Clinically, the potential for vascular injury coupled with the lack of an unequivocal non-invasive diagnostic marker is an issue of concern to pharmaceutical companies and the regulatory authorities. Therefore, qualification and validation of biomarkers as diagnostic tools for drug-induced vascular injury would add great value to risk management and expedite the drug development process. This review focuses on the status, progress and future trends in vascular biology aimed at identification and development of diagnostic markers that are specific, sensitive and possess potential utility in both a pre-clinical and clinical setting.

Biomarkers of drug-induced vascular injury

In pre-clinical safety studies, drug-induced vascular injury is an issue of concern because there are no obvious diagnostic markers for pre-clinical or clinical monitoring and there is an intellectual gap in our understanding of the pathogenesis of this lesion. While vasodilatation and increased shear stress appear to play a role, the exact mechanism(s) of injury to the primary targets, smooth muscle and endothelial cells are unknown. However, evaluation of novel markers for potential clinical monitoring with a mechanistic underpinning would add value in risk assessment and management. This mini review focuses on the progress to identify diagnostic markers of drug-induced vascular injury. Von Willebrand factor (vWF), released upon perturbation of endothelial cells, is transiently increased in plasma prior to morphological evidence of damage in dogs or rats treated with vascular toxicants. Therefore, vWF might be a predictive biomarker of vascular injury. However, vWF is not an appropriate biomarker of lesion progression or severity since levels return to baseline values when there is morphological evidence of injury. A potential mechanistically linked biomarker of vascular injury is caveolin-1. Expression of this protein, localized primarily to smooth muscle and endothelial cells, decreases with the onset of vascular damage. Since vascular injury involves multiple mediators and cell types, evaluation of a panel rather than a single biomarker may be more useful in monitoring early and severe progressive vascular injury.

Pathology and pathophysiology of drug-induced arterial injury in laboratory animals and its implications on the evaluation of novel chemical entities for human clinical trials

In toxicology studies, drug-induced arterial injury in laboratory animals continues to be a pressing issue of concern, particularly to those engaged in the discovery and development of novel therapies intended for human use. The concern is justifiably magnified because, currently, there is no unequivocal biochemical marker of arterial injury and/or toxicity in animals or man. Therefore, in laboratory animals used for toxicology studies a precise description of arterial lesions in terms of location, distribution and morphologic character is necessary so that a correlation can be drawn between structural damage and derangement of specific cardiovascular functions. The critical nature of the latter cannot be over-emphasized because this will provide a basis for understanding the mechanism of toxicity, the pathogenesis of the lesion and assessment of human risk. However, in the decision making process, utilization of pattern recognition must be supported by rigorous scientific investigations aimed at establishing a link, where possible, between the deranged cardiovascular function and alterations in cellular, biochemical and molecular events. Conceivably, engagement of the molecular pharmacology target initiates a series of interactive cascades among cellular and non-cellular arterial components that culminate in organ damage. Therefore, any investigative mechanistic studies aimed at understanding the initiation and development of arterial lesions in laboratory animals must make a conscientious attempt to identify and characterize the molecular target of toxicity.

Differences in time-related cardiopulmonary responses to hypoxia in three rat strains

The cardiopulmonary profile of three rat strains (Sprague-Dawley, Wistar and High altitude-sensitive) was compared upon exposure to hypoxia (9% O2) for 0, 7 or 14 days. No differences were observed among the in vitro contractile (ET-1) and relaxant (carbachol) responses of pulmonary artery isolated from the three strains during normoxia. Chronic hypoxia decreased ET-1 contractile responses and diminished relaxant responses to carbachol similarly in all strains. In Sprague-Dawley, Wistar and High altitude-sensitive rats, pulmonary arterial pressure rose time-dependently and was elevated by 108%, 116% and 167%, respectively, after 14 days of hypoxia compared to normoxic controls. Right ventricular hypertrophy was increased by 51%, 93% and 55%, respectively, at 14 days. Hypoxia-induced hypertrophy and medial thickening in the pulmonary vasculature were more pronounced in High altitude-sensitive rats. Sprague-Dawley exhibited hypoxia-induced airway hyperresponsiveness to intravenous methacholine, but there were no hypoxia- or strain-related differences in in vitro tracheal contractility. Although each strain exhibited greater sensitivity for a particular hypoxia-induced parameter, pulmonary vascular functional and structural changes suggest that High altitude-sensitive rats represent a choice model of hypoxia-induced pulmonary hypertension.

Integrated care pathways for vascular surgery

OBJECTIVES

a trial of the use of integrated care pathways (ICPs) for elective vascular surgical procedures.

DESIGN

a 12-month prospective study, following a multi-disciplinary group construction of current "best practice" ICPs, with changes in practice only occurring following careful audit of results.

MATERIALS

patients admitted to a single vascular unit for "open" repair of abdominal aortic aneurysm, carotid endarterectomy or femoropopliteal bypass grafting.

METHODS

patients followed ICPs on a daily basis with signatures required to confirm that action had been taken and careful recording of variances from the ICPs. Audit of variance data allowed changes in the ICPs and, hence, provision of the best possible nursing and clinical practice.

RESULTS

ICPs were well received by patients and staff. They improved communication, promoted an appreciation of each health group's role in patient care, increased nursing autonomy, reduced calls to junior medical staff, improved patient education and confidence and caused a marked reduction in hospital "length of stay".

CONCLUSIONS

ICPs have clear benefits. This study realises that benefits might be maximal for high throughput, high-cost procedures. Successful use of ICPs depends upon "clinical champions" and effective project management. Sufficient resource and training are essential.

Developmental toxicity and toxicokinetics of two endothelin receptor antagonists in rats and rabbits

Embryo-fetal development studies with toxicokinetic evaluations were conducted in rats and rabbits after oral or intravenous administration of two endothelin receptor antagonists. In the rat studies, females were administered SB-217242 (0.01-300 mg/kg/day) orally or SB-209670 (0.01-50 mg/kg/day) intravenously from days 6-17 postcoitus (pc). External and visceral fetal examinations were performed at necropsy on day 21 pc. Maternal body weight and food consumption were decreased only at 300 mg/kg/day SB-217242. Embryolethality was seen at 300 mg/kg/day SB-217242. Decreased fetal body weight occurred at 300 mg/kg/day SB-217242 and 50 mg/kg/day SB-209670. Dose-dependent increases in the mean percentage of fetuses per litter with malformations were seen at > or = 50 mg/kg/day SB-217242 and > or = 10 mg/kg/day SB-209670. Craniofacial, great vessel, heart, and thyroid were the predominant malformations. In the rabbit studies, females were administered SB-217242 (0.01-50 mg/kg/day) orally or SB-209670 (0.01-25 mg/kg/day) intravenously from days 6-20 pc. There was no drug-related effect on maternal body weight or food consumption. Embryolethality was observed at 50 mg/kg/day of SB-217242. Dose-related increases in the mean percentage of fetuses per litter with malformations were seen at > or = 10 mg/kg/day SB-217242 and > or = 10 mg/kg/day SB-209670. The malformations were similar to those observed in the rat studies, except that craniofacial development was not altered by SB-209670. The malformations observed are consistent with the pattern of endothelin-1 gene expression described in mouse embryonic pharyngeal arches and heart, and with the craniofacial and cardiovascular malformations observed in endothelin-1-deficient mice. Given the known role for endothelins in development, and concordant malformations in rats and rabbits observed in this study, teratogenicity is likely to be a class effect of endothelin receptor antagonists.

Discovery of an imidazopyridine-containing 1,4-benzodiazepine nonpeptide vitronectin receptor (alpha v beta 3) antagonist with efficacy in a restenosis model

In the 3-oxo-1,4-benzodiazepine-2-acetic acid series of vitronectin receptor (alpha v beta 3) antagonists, a compound containing an imidazopyridine arginine mimetic was discovered which had sufficient potency and i.v. pharmacokinetics for demonstration of efficacy in a rat restenosis model.

Coronary arterial lesions in dogs treated with an endothelin receptor antagonist

Structurally and pharmacologically diverse vasodilators are known to lower blood pressure, increase heart rate, and produce acute injury to right coronary arteries in the dog. Administration of low concentrations of endothelin-1 (ET-1) to anesthetized dogs causes coronary vasoconstriction and reductions in coronary blood flow. Therefore, pharmacologic blockade of endothelin receptors (ETA and ETB) with the mixed ET receptor antagonist SB 209670 could lead to coronary vasodilatation. In toxicology studies, continuous administration of SB 209670 to dogs for 5 days at 50 micrograms/kg/min was associated with minor but sustained increases in heart rate (10-30 beats/min), slight decreases in mean arterial pressure (10-15 mm Hg), and medial hemorrhage and necrosis of extramural coronary arteries in the right atria. Doses of 10 micrograms/kg/min had no effect. The lesions in the right atrium were associated with the highest density of ET receptors, approximately 470 fmol/mg compared to 170-200 fmol/mg in the ventricles and septum. Because changes in systemic cardiovascular parameters are minimal, the coronary arterial lesion is most likely due to a local vasodilatory effect in the coronary bed.

Delayed expression of osteopontin after focal stroke in the rat

Focal brain ischemia induces inflammation, extracellular matrix remodeling, gliosis, and neovascularization. Osteopontin (OPN) is a secreted glycoprotein that has been implicated in vascular injury by promoting cell adhesion, migration, and chemotaxis. To investigate the possible involvement of OPN in brain matrix remodeling after focal stroke, we examined the expression of OPN in ischemic cortex after permanent or temporary occlusion of the middle cerebral artery (MCAO) of the rat. OPN mRNA and protein levels in nonischemic cortex were not detected consistently, although significant induction of OPN was observed in the ischemic cortex. OPN mRNA increased 3.5-fold at 12 hr and reached peak levels 5 d (49.5-fold; p < 0.001) after permanent MCAO. The profile of OPN mRNA induction after transient MCAO (160 min) with reperfusion was essentially the same as that of permanent MCAO. In situ hybridization and immunohistochemical studies demonstrated strong induction of OPN in the ischemic cortex, which was localized primarily in a subset of ED-1-positive macrophages that accumulated in the ischemic zone. Moreover, OPN immunoreactivity was detected in the matrix of ischemic brain, suggesting a functional role of the newly deposited matrix protein in cell-matrix interactions and remodeling. Indeed, using a modified Boyden chamber, we demonstrated a dose-dependent chemotactic activity of OPN in C6 astroglia cells and normal human astrocytes. Taken together, these data suggest that the upregulation of OPN after focal brain ischemia may play a role in cellular (glia, macrophage) migration/activation and matrix remodeling that provides for new matrix-cell interaction.

Possible involvement of stress-activated protein kinase signaling pathway and Fas receptor expression in prevention of ischemia/reperfusion-induced cardiomyocyte apoptosis by carvedilol

Carvedilol, a new vasodilating beta-adrenoceptor antagonist and a potent antioxidant, produces a high degree of cardioprotection in a variety of experimental models of ischemic cardiac injury. Recent clinical studies in patients with heart failure have demonstrated that carvedilol reduces morbidity and mortality and inhibits cardiac remodeling. The present study was designed to explore whether the protective effects of carvedilol on the ischemic myocardium include inhibition of apoptosis of cardiomyocytes and, if so, to determine its mechanism of action. Anesthetized rabbits were subjected to 30 minutes of coronary artery occlusion followed by 4 hours of reperfusion. Detection of apoptosis of cardiomyocytes was based on the presence of nucleosomal DNA fragments on agarose gels (DNA ladder) and in situ nick end labeling. Carvedilol (1 mg/kg IV), administered 5 minutes before reperfusion, reduced the number of apoptotic myocytes in the ischemic area from 14.7 +/- 0.4% to 3.4 +/- 1.8% (77% reduction, P<.001). Propranolol, administered at equipotent beta-blocking dosage, reduced the number of apoptotic myocytes to 8.9 +/- 2.1% (39% reduction, P<.05). DNA ladders were observed in the hearts of all six vehicle-treated rabbits but only one of six carvedilol-treated rabbits (P<.01). Immunocytochemical analysis of rabbit hearts demonstrated an upregulation of Fas protein in ischemic cardiomyocytes, and treatment with carvedilol reduced both the intensity of staining as well as the area stained. Myocardial ischemia/reperfusion led to a rapid activation of stress-activated protein kinase (SAPK) in the ischemic area but not in nonischemic regions. SAPK activity was increased from 2.1 +/- 0.3 mU/mg (basal) to 8.9 +/- 0.8 mU/mg after 30 minutes of ischemia followed by 20 minutes of reperfusion. Carvedilol inhibited the activation of SAPK by 53.4 +/- 6.5% (P<.05). Under the same conditions, propranolol (1 mg/kg) had no effect on SAPK activation. Taken together, these results suggest that carvedilol prevents myocardial ischemia/reperfusion-induced apoptosis in cardiomyocytes possibly by downregulation of the SAPK signaling pathway, by inhibition of Fas receptor expression, and by beta-adrenergic blockade. The former two actions represent novel and important mechanisms that may contribute to the cardioprotective effects of carvedilol.

A novel technique for mapping the lipid composition of atherosclerotic fatty streaks by en face fluorescence microscopy

We introduce here a new fluorescence microscopy technique for en face analysis of the atherosclerotic fatty streaks (FS). This technique is semiquantitative and has the sensitivity and resolution to map lipids to individual cells in FS less than 100 microns in diameter. New Zealand White rabbits were fed an atherogenic diet for up to 26 weeks. Aortas were fixed in formalin and stained en bloc with the fluorescent dyes Nile red and filipin. Fluorescent staining was validated by correlating microfluorimetric and biochemical measurements of the lipid content in FS. To determine the cell types associated with the different staining patterns, FS were also evaluated by transmission electron microscopy (TEM) and immunohistochemistry (IH). Correlation of microfluorimetry, TEM, IH, and biochemical data indicated that regions rich in non-esterified cholesterol stained with filipin and fluoresced blue owing to accumulations of lipid vesicles and/or cholesterol crystals. Regions rich in neutral and polar lipids stained with Nile red and fluoresced yellow or orange, respectively, owing to accumulations of lipids in both macrophages and smooth muscle cells (SMC). Digital overlays of the filipin and Nile red images revealed that larger lesions (> 0.5 mm diameter) had a "nested" distribution of lipids, with a blue (filipin) fringe surrounding an orange (Nile red) fringe surrounding a yellow (Nile red) center.

Osteopontin expression in platelet-derived growth factor-stimulated vascular smooth muscle cells and carotid artery after balloon angioplasty

Osteopontin (OPN), an arginine-glycine-aspartate (RGD)-containing adhesive glycoprotein, is constitutively expressed in rat aorta and carotid arteries and is markedly elevated in response to vascular injury. OPN is chemotactic for vascular smooth muscle cells (SMCs), suggesting a role in vascular remodeling. However, the mechanism for the regulation of OPN expression is poorly understood. In the present study, the effect of platelet-derived growth factor (PDGF) on OPN mRNA expression was investigated in cultured rat aortic SMCs (RASMCs). When RASMCs were stimulated with 1 nmol/L PDGF, a 2.4-fold increase in OPN mRNA expression was observed at 3 hours (P < .05) that peaked at 14 hours with a 6.7-fold increase (P < .001). This induction was blocked by a monoclonal anti PDGF antibody. Further studies revealed that OPN mRNA expression was induced by PDGF-AB or PDGF-BB but not by PDGF-AA, indicating that only the beta-type PDGF receptor mediates this response. Compared with basic fibroblast growth factor, epidermal growth factor, transforming growth factor-beta, and interleukin-1 beta, PDGF was the most potent factor studied to induce OPN mRNA expression in RASMCs. Immunohistochemical studies demonstrated the elevation of OPN protein in PDGF-stimulated RASMCs. The temporal expression of OPN mRNA after rat carotid artery balloon angioplasty as assessed by both reverse transcription-polymerase chain reaction and Northern blot analysis revealed a 1.5-fold increase at 6 hours (P < .01) that peaked at 1 and 3 days with a 3.1-fold increase (P < .001). Immunohistochemical studies of carotid artery after angioplasty localized OPN expression in the medical SMCs at 1 day, ie. at a time of significant platelet adherence to the injured vessel, and thereafter to the intimal lesion during neointimal formation. These data suggest that OPN expression in vascular SMCs is regulated by PDGF through the beta-type PDGF receptor in vitro, and possibly in vivo in situations that involve PDGF released from platelets or other cellular sources, such as blood vessels after angioplasty injury.

Expression of endothelin-1, endothelin-3, endothelin-converting enzyme-1, and endothelin-A and endothelin-B receptor mRNA after angioplasty-induced neointimal formation in the rat

Endothelins (ETs) are potent vasoconstrictors known to play a role in tissue remodeling after vascular wall injury. The molecular mechanisms for the expression and functions of ETs and their receptors after carotid artery angioplasty are not fully understood. Using quantitative reverse transcription and polymerase chain reaction, the present study demonstrates the temporal mRNA expression of ET-converting enzyme-1 (ECE-1), preproET-1, preproET-3, and both ETA and ETB receptors after rat carotid artery balloon angioplasty. A significant increase in ECE-1 mRNA was observed at 6 hours (1.8-fold increase over control, P < .01) and 24 hours (1.7-fold increase, P < .01) in carotid arteries after angioplasty. In contrast, a significant increase in preproET-1 mRNA levels was not observed until 3 days (1.9-fold increase, P < .05) and 7 days (2.1-fold increase, P < .05). A similarly delayed increase in preproET-3 mRNA was observed at 7 days (2.8-fold increase, P < .05) and 14 days (2.6-fold increase, P < .05) after angioplasty. A parallel but marked increase in ETA and ETB receptor mRNAs compared with preproET-1 and -3 messages was observed after angioplasty. The levels of ETA receptor mRNA were elevated 29.3-fold (P < .001) and 24.3-fold (P < .01) at 3 and 7 days, respectively, after angioplasty. The increase in ETB receptor mRNA occurred slightly earlier than the increase in ETA receptor mRNA, showing 15.1-fold increase at 1 day (P < .001) and 11.3-fold increase at 3 days (P < .01) after angioplasty. Immunohistochemical studies using anti-ET antibodies demonstrated a corresponding increase in ET immunoactivity, which was distributed mainly in the neointimal cells 14 days after angioplasty. The increases in ECE-1, ET-1, and ET-3 and their receptor expression after balloon angioplasty suggest that these proteins play an active role in the pathogenesis of neointimal formation.

Selective ETA receptor antagonism with BQ-123 is insufficient to inhibit angioplasty induced neointima formation in the rat

OBJECTIVE

The aim was to assess whether or not the endothelin ETA receptor selective antagonist BQ-123 could inhibit neointima formation in vivo following balloon angioplasty.

METHODS

The effect of either acute administration of BQ-123 (0.1 mg.kg-1.min-1 intra-arterial infusion for 1 h before and 1 h after angioplasty) or chronic administration (bolus intraperitoneal injection, 2.5 mg.kg-1 twice daily; continuous intraperitoneal infusion, 0.8 and 8 mg.kg-1.d-1) on neointima formation was examined in rats which had undergone left common carotid artery balloon angioplasty.

RESULTS

Neither acute intra-arterial infusion nor either mode of chronic intraperitoneal administration of BQ-123 had a significant effect on the degree of neointima formation observed following balloon angioplasty.

CONCLUSIONS

Neither acute nor chronic ETA receptor blockade is sufficient to inhibit angioplasty induced neointima formation in the rat. Since it was previously shown that the ETA/B antagonist SB 209670 was effective in this model, while the ETA selective antagonist BQ-123 is now found to be ineffective, the data implicate the ETB receptor subtype in the pathogenesis of neointima formation.

A role for endogenous endothelin-1 in neointimal formation after rat carotid artery balloon angioplasty. Protective effects of the novel nonpeptide endothelin receptor antagonist SB 209670

The observation that levels of the mitogenic peptide endothelin-1 are elevated in the human coronary sinus after percutaneous transluminal coronary angioplasty (PTCA) has implicated endothelin-1 in the etiology of vascular restenosis. The present study examined this hypothesis in both an in vitro and an in vivo rat model of neointimal formation by using the novel nonpeptide endothelin receptor antagonist SB 209670. In vitro, endothelin-1 (1 nmol/L) induced a ninefold increase in rat aortic vascular smooth muscle [3H]thymidine incorporation. This endothelin A receptor-mediated effect was completely inhibited by SB 209670 (IC50, 6.2 +/- 2.2 nmol/L). In vivo, acute intra-arterial administration of exogenous endothelin-1 (5 to 500 pmol/kg over a 30-minute period immediately after angioplasty) dose-dependently augmented the degree of neointimal formation (by up to 150% when assessed 14 days after surgery). This response was evident as early as 7 days after angioplasty. Hemodynamic studies indicated that this action was unrelated to a systemic pressor action of the peptide. Administration of SB 209670 (2.5 mg/kg IP, twice a day for 3 days before and for 2 weeks after surgery) reduced neointimal formation by approximately 50% relative to control animals. Thus, the data indicate for the first time that (1) endothelin-1 promotes neointimal formation in vivo and (2) endogenous endothelin-1 is involved in the pathogenesis of angioplasty-induced lesion formation in the rat. Endothelin receptor antagonists such as SB 209670 may therefore serve as useful adjuncts to PTCA, attenuating the degree of vascular restenosis observed after vascular wall injury.

Carvedilol, a cardiovascular drug, prevents vascular smooth muscle cell proliferation, migration, and neointimal formation following vascular injury

Carvedilol is a cardiovascular drug currently used for the treatment of hypertension. Clinical studies have recently demonstrated efficacy in angina and congestive heart failure. Recently, carvedilol has been shown to attenuate oxygen free radical-initiated lipid peroxidation and to inhibit vascular smooth muscle mitogenesis induced by a wide variety of growth factors. These findings are of interest since smooth muscle proliferation and abnormal lipid metabolism are proposed to play an important role in the pathogenesis of atherosclerotic plaque formation and in development of stenotic lesions following vascular injury by balloon angioplasty and coronary artery bypass grafting. On the basis of these observations, the antiproliferative actions of carvedilol have been explored in detail. In human cultured pulmonary artery vascular smooth muscle cells, carvedilol (0.1-10 microM) produced a concentration-dependent inhibition of the mitogenesis stimulated by platelet-derived growth factor, epidermal growth factor, thrombin, and serum, with IC50 values ranging from 0.3 to 2.0 microM. Carvedilol also produced a concentration-dependent inhibition of vascular smooth muscle cell migration induced by platelet-derived growth factor, with an IC50 value of 3 microM. The extensive neointimal formation that occurs following balloon angioplasty of rat carotid arteries was markedly attenuated by carvedilol (1 mg/kg, i.p.; twice daily starting 3 days before angioplasty and continuing until 14 days after angioplasty). Quantitative image analysis demonstrated that carvedilol reduced the neointimal growth following angioplasty by 84% without altering either medial or adventitial cross-sectional areas. These observations indicate that carvedilol may also be effective in the treatment of pathological disorders principally associated with abnormal vascular smooth muscle growth, such as atherosclerosis and acute vascular wall injury induced by angioplasty or coronary artery bypass grafting.

Malignant transformation of human fibroblast cell strain MSU-1.1 by (+-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo [a]pyrene

Treatment of MSU-1.1 cells, a near-diploid, karyotypically stable, infinite life-span human fibroblast strain, with (+-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene induced focus formation. Eight independent foci were isolated and the cell strains developed from them were examined for characteristics of malignant cells. Each grew to a higher density in medium containing 1% serum than did the MSU-1.1 cells. Three of the eight grew rapidly in serum-free medium without added growth factors, formed colonies in agarose with diameters of greater than or equal to 120 microns at a frequency of 5-19%, exhibited loss of genetic material, and, when injected into athymic mice, formed sarcomas that reached 6 mm in diameter within 2-3 wk. One produced high-grade sarcomas (progressively growing, invasive tumors exhibiting high mitotic activity); the other two produced low-grade sarcomas (tumors with a lower degree of mitotic activity) that developed focal areas of high-grade malignant cells if left in the animals for greater than 4 wk. A fourth cell strain formed high-grade sarcomas only after 2.5-3 mo, but the tumor-derived cells analyzed showed the same growth properties as the three malignant cell strains described above, exhibited loss of genetic material, and, when reinjected into athymic mice, produced high-grade sarcomas with a short latency period.

Mast cell numbers in normal and glaucomatous canine eyes

Numbers of mast cells in the cornea, sclera, choroid, ciliary body, iris, and retina of sections of globes from 35 clinically normal dogs and 34 dogs with secondary glaucoma was determined. Fixed globes were trimmed along a vertical midsagittal plane and embedded in paraffin. Tissue sections, approximately 6 microns thick, were stained with toluidine blue for identification of mast cells. In normal globes, most of the mast cells were observed in the anterior portion of the uvea, and fewer mast cells were seen in the choroid and sclera. Mast cells were not observed in the retina and were seldom observed in the cornea of dogs with or without glaucoma. In sections of glaucomatous globes, mast cells were distributed evenly in the uvea and sclera, and fewer mast cells were present than in normal globes, regardless of the cause of glaucoma.