Chemical-induced, nonlethal, developmental model of dissecting aortic aneurysm

Seventy-Day Toxicity Study in Juvenile Sprague-Dawley Rats with Semicarbazide (SEM) from Weaning to Sexual Maturity

The study was conducted to evaluate the toxicological effects, functional observation battery tests, and sexual maturity of semicarbazide oral gavage administration to juvenile Sprague-Dawley rats for 70 days at 0, 15, 30, and 60 mg/kg/day weaning to sexual maturity. At 60 mg/kg/day, there was a delay in mean age at acquisition of balano-preputial and vaginal patency and a decrease in body weight and food consumption in males. Treatment increased reticulocyte count, aspartate aminotransferase, and alanine aminotransferase levels in both sexes and decreased hematocrit and protein in males. Increased absolute and relative liver and spleen weight in both sexes were observed. Male rats had lower thymus and testes weights, whereas female rats had lower uterine weights. Semicarbazide caused significant changes in sperm motility, sperm count, and sperm abnormality. Histopathologically, semicarbazide caused cortical hypertrophy in adrenals and increased extramedullary hematopoiesis in the spleen; hepatocellular hypertrophy, follicular epithelial hypertrophy in the thyroid, and degeneration of seminiferous tubules in the testis were observed at 60 mg/kg/day when compared to control. Results suggest that 60 mg/kg/day of semicarbazide can exert systemic toxicity in juvenile rats. The no observed adverse effect level (NOAEL) of semicarbazide for juvenile Sprague-Dawley rats was estimated to be 30 mg/kg/day.

Establishment and effect evaluation of an aortic dissection model induced by different doses of β-aminopropionitrile in rats

INTRODUCTION

Given the controversy regarding the appropriate dose of β-aminopropionitrile for induction of aortic dissection models in rats, the purpose of this study was to explore the most suitable concentration of β-aminopropionitrile to establish a high-incidence and low-mortality aortic dissection model.

METHODS

Eighty three-week-old male Sprague-Dawley rats were equally divided into four groups: a control group, a 0.06% β-aminopropionitrile group, a 0.08% β-aminopropionitrile group and a 0.1% β-aminopropionitrile group. Initial experiments were performed on the control group, which was not treated with β-aminopropionitrile (and drank water freely), and the other three groups, which were given different concentrations of β-aminopropionitrile solution daily (0.06%, 0.08% and 0.1%). Subsequently, on the 40th day, osmotic minipumps administering 1 μg/kg per min angiotensin II (Ang II) were implanted subcutaneously into the β-aminopropionitrile groups, while the control group was continuously pumped with normal saline. The rats were euthanized 48 h after implantation. All rats that died before the expected end time of the experiment were autopsied immediately, and the aortas were dissected. The rats surviving at the end of the experiment were sacrificed by an overdose of sodium pentobarbital, and tissue samples were harvested for further analyses.

RESULTS

The mean survival days were significantly different among the groups, with 39.1 ± 6.04 days in the 0.08% β-aminopropionitrile group and 32.7 ± 9.85 days in the 0.1% β-aminopropionitrile group (P = 0.0178) at the end of the experiment. Compared with those in the 0.06% β-aminopropionitrile group, the rates of aortic dissection were significantly higher in the 0.08% β-aminopropionitrile group and the 0.1% β-aminopropionitrile group (P = 0.0015 and P = 0.0005, respectively), while there was no significant difference between the 0.08% β-aminopropionitrile group and the 0.1% β-aminopropionitrile group (P = 0.723) at 70% and 75%, respectively. However, the rupture rates were significantly different between the 0.08% β-aminopropionitrile group and the 0.1% β-aminopropionitrile group (55% versus 20%, P = 0.022). Hematoxylin-eosin staining of the aortic tissue sections of the β-aminopropionitrile group showed that red blood cells entered the pseudocavity in the vascular wall, while the vascular wall structure of the control group was intact. Compared with control rats, which were intact and free from fracture, β-aminopropionitrile-treated rats had fewer collagen fibers and exhibited fracture. Magnetic resonance imaging showed that the aortic intimae of the aortic dissection rats showed double lumens and intimal tears.

CONCLUSIONS

An aortic dissection model with a high incidence and low mortality was successfully and stably developed with 0.08% β-aminopropionitrile. This model will enable further studies investigating aortic dissection pathogenesis and drug therapy. Magnetic resonance imaging may be a reliable technique for imaging the aorta in rats.

Endovascular creation and validation of acute in vivo animal model for type A aortic dissection

BACKGROUND

Animal modeling is a prerequisite for clinical transfer of new therapies. This study targets an acute in vivo animal model of type A dissection using endovascular approach with a view to test future stent grafts dedicated to this aortic segment.

METHODS

Experiments were conducted on 13 swine. Two arterial accesses, femoral and percutaneous transapical, were required. Entry tear was created by endovascular instrumental means inserted through transapical access with either Outback catheter (group 1, n = 3) or EchoTip Endoscopic Ultrasound Needle (group 2, n = 10). Afterward, dissection extension was obtained in antegrade direction by looped guidewire technique, and, as often as possible, re-entry tear was created with either looped guidewire or Outback catheter. Finally, entry tear, dissected space, and re-entry tear when existing were dilated with 8-mm balloon. In our acute model, animals were euthanized at the end of the experiment day, and aortas were explanted for macroscopic and histologic examination.

RESULTS

The model was successfully created in 10 out of 13 animals. In group 1, dissection was limited to arch with 23 mm average length and no possibility of achieving re-entry tear. One aortic perforation was observed. In group 2, dissection was extended up to descending thoracic or thoracoabdominal aorta, with 110 mm average length (range 40-165 mm), and re-entry tear was created in seven cases. Histologic examination confirmed the presence of intimo-medial flap.

CONCLUSIONS

The present experiment validates a new type A dissection animal model, which morphologically reproduces human aortic dissection features. As such, it provides an advantageous basis for testing future stent grafts.

Autonomic remodeling may be responsible for decreased incidence of aortic dissection in STZ-induced diabetic rats via down-regulation of matrix metalloprotease 2

Background

Epidemiological studies reported that diabetic patients had a lower incidence of aortic dissection (AD), but the definite mechanism is unknown. We aim to investigate the possible protective effect of diabetes mellitus (DM) on AD formation with an emphasis on autonomic remodeling.

Methods

Streptozotocin (STZ) intraperitoneal injection was applied to induce diabetes, unilateral renal artery stenosis (URAS) together with β-amino propionitrile (BAPN) oral treatment was used to induce AD. Sixty SD rats were equally and randomly divided into four groups (normal group, DM group, URAS + BAPN oral treatment group, DM + URAS + BAPN oral treatment group). Rats were fed for 6 weeks, the number of AD was recorded and remained rats were sacrificed. Thoracic aorta were harvested, morphological changes were assessed. Expression of tyrosine hydroxylase (TH), choline acetylase (ChAT), matrix metalloprotease 2 (MMP2) and matrix metalloprotease 9 (MMP9) were evaluated.

Results

A total of 7 AD was noted in S + B group, DM rats did not develop AD. Diabetic rats had a lower incidence of AD (P < 0.01). In dissected aorta, collagen deposition increased while elastic fiber became fragmented. These pathological changes diminished in diabetic rats. Diabetic rats had a lower expression of ChAT (P < 0.01). URAS + BAPN treatment elevated expression of TH in normal rat and ChAT in diabetic rats (P < 0.001). Expression of MMP2 and MMP9 elevated in all the rats after URAS + BAPN, but the elevation range of MMP2 in diabetic rats was smaller (P < 0.001).

Conclusions

STZ-induced diabetic rats have a lower incidence of AD after URAS and BAPN treatment, this protective effect could be possibly attributed to autonomic innervation modification and possible related down-regulation of MMP2.

N-(2-Aminoethyl) Ethanolamine-Induced Morphological, Biochemical, and Biophysical Alterations in Vascular Matrix Associated With Dissecting Aortic Aneurysm

Dissecting aortic aneurysm (DAA) is an extended tear in the wall of the aorta along the plane of the vascular media. Our previous studies indicated in a developmental animal model, that DAA was related to pathological alteration in collagen, especially collagen type III. Accordingly, in the present studies, neonatal aortic vascular smooth muscle cells (VSMC) and timed pregnant Sprague-Dawley rat dams were treated with N-(2-aminoethyl) ethanolamine (AEEA), which, as shown previously, causes DAA in offspring. Morphological changes in extracellular matrix (ECM) produced by VSMC in vitro were detailed with scanning electron microscopy (SEM), and biochemical changes in cells and ECM produced by VSMCs were defined by Western blotting. Biophysical changes of the collagen extracted from both the ECM produced by VSMC and extracted from fetal rat aortas were studied with atomic force microscopy (AFM). ECM disruption and irregularities were observed in VSMCs treated with AEEA by SEM. Western blotting showed that collagen type I was much more extractable, accompanied by a decrease of the pellet size after urea buffer extraction in the AEEA-treated VSMC when compared with the control. AFM found that collagen samples extracted from the fetal rat aortas of the AEEA-treated dam, and in the in vitro formed ECM prepared by decellularization, became stiffer, or more brittle, indicating that the 3D organization associated with elasticity was altered by AEEA exposure. Our results show that AEEA causes significant morphological, biochemical, and biomechanical alterations in the ECM. These in vitro and in vivo strategies are advantageous in elucidating the underlying mechanisms of DAA.

Dissecting aortic aneurysm induced by N-(2-aminoethyl) ethanolamine in rat: Role of defective collagen during development

BACKGROUND

Dissecting aortic aneurysm (DAA) is a tear in the wall of the aorta that causes blood to flow, or "dissect," between the medial layers of the media.

METHODS

Pregnant rats (dams) were treated with the industrial chemical n-(2-aminoethyl) ethanolamine (AEEA) by intraperitoneal injection or gavage. The histology and pathology of aorta in the thorax from newborn pups were examined. Aortas of fetuses of gestational day 20 from dams exposed to AEEA were harvested for immunohistochemical staining and native Western blot to study the changes of collagen type 1 and type 3 in aorta.

RESULTS

Dissecting aortic aneurysm of newborn rats was induced by treating with AEEA through intraperitoneal injection or gavage. The incidence of DAA reached 100% in live pups at the high dose by means of gavage of AEEA, but without lethality compared with intraperitoneal injection. A grading system for the dose-response of DAA lesions associated with AEEA by gavage was established. Gestational day 20 fetuses from treated dams showed a decreased content and altered distribution of medial and adventitial collagen type 1 and 3 in aorta by immunohistochemistry; this decrease was confirmed by native Western blot.

CONCLUSION

This in vivo model of spontaneous aortic dissection bears striking similarities histologically to human aortic dissection. As such, the model conceivably could contribute to elucidating the mechanisms of DAA formation and to exploring diagnostic and therapeutic strategies. The pathogenesis of AEEA-induced DAA may be related to defects in the normal developmental progression of collagen types 1 and 3 in the vascular wall.

Malformations of the great vessels in the neonatal rat induced by N-(2-aminoethyl)ethanolamine

The reproductive and developmental toxicity of aminoethylethanolamine was evaluated in a standard screening study (OECD, 1995: Organisation for economic co-operation and development. Paris, France), in which groups of Wistar rats (10/sex/group) were administered the test substance by gavage at dosage levels of 50, 250, or 1000 mg/kg/day (groups 2-4, respectively). A control group received the vehicle, doubly distilled water. No live pups were delivered in group 4, and there was a higher incidence of stillborn offspring and reduced postnatal survival in group 3. Macroscopic changes in groups 2 and 3 were primarily related to the great vessels and characterized by dilations, aneurysms, and altered course of the aorta, pulmonary trunk, carotids, and the ductus arteriosus. A follow-up study was conducted to characterize the low dose-response, using dosage levels of 0, 0.2, 1, 5, or 50 mg/kg/day (groups 1-5, respectively). Given the expected scarcity of the lesions in control offspring, each group consisted of 25 animals of each sex. Macroscopic examination revealed a high incidence (18.5%) of aneurysm-bearing offspring in group 5 litters, and single offspring (0.3-0.4%) with aneurysms in groups 3 and 4. Microscopic examination revealed dissecting aneurysms in offspring from all aminoethylethanolamine treatment groups, without a clear dose-response between groups 2 and 4 (0.6%, 1.2%, and 0.3%, respectively), and focal hemorrhages in all groups including the control. In comparison, the background incidence of aneurysms in untreated 4-day old offspring was 0.2% (Treumann et al., 2011: Toxicol Pathol 39:969-974). Consequently, the findings in groups 2-4 cannot be conclusively attributed to treatment.

Developmental sensitivity to the induction of great vessel malformations by N-(2-aminoethyl)ethanolamine

N-(2-Aminoethyl)ethanolamine (AEEA) induced malformations of the great vessels in the offspring of rats treated during gestation and early lactation (Schneider et al., 2012. Birth Defects Res B Dev Reprod Toxicol [in press]). The aim of this study was to determine if in utero exposure alone was sufficient to induce these malformations or whether a peri-postnatal exposure or physiological component was required. Three groups of five time-mated female Wistar Han rats were administered AEEA (250 mg/kg/day) by gavage from gestation day (GD) 6 to GD 19 (groups 1 and 2) or from GD 6 to postnatal day 3 (group 3). Animals were euthanized on GD 21 (group 1) or postnatal day 4 (groups 2 and 3), and the hearts of the offspring were examined for changes to the great vessels. The incidence of malformations in group 1 was 91.1%, and primarily consisted of high aortic arch and abnormal carotid course. One fetus had an aortic aneurysm. All fetuses in groups 2 and 3 were malformed, primarily exhibiting abnormal carotid course and aneurysms, which mainly affected the aorta, ductus arteriosus, and pulmonary trunk. The incidence of high aortic arch was lower relative to group 1. Aneurysms were more prevalent in group 3 compared to group 2. These findings indicate that exposure to AEEA during gestation alone was sufficient to induce malformations of the great vessels and aneurysms, which may be triggered by physiological changes that occur during or after birth, but that the critical period of susceptibility to AEEA-induced aneurysms in the rat extends beyond gestation into the early postnatal period.

Spontaneous Occurrence of Dissecting Aneurysms in the Region of the Ductus Arteriosus in Four-Day-Old Wistar Rat Pups

Dissecting aortic aneurysms, generally involving the thoracic aorta, have been shown to be caused by specific aliphatic amines in developing rats. Whether such lesions might occur spontaneously in control rats is not known. Therefore, in this study, 1,016 four-day-old, untreated rats culled from ongoing scheduled breeding studies were subjected to gross and histopathological examination in order to create a background control data base on the incidence of spontaneous aortic dissecting aneurysms. Two animals (0.2%) were found to have small dissecting aortic aneurysms, and an additional 2 (0.2%) had only hemorrhagic lesions. All of these lesions were limited to the region of the ductus arteriosus. An additional 18 findings were judged to be artifacts. These findings suggest that small vascular dissections may rarely occur in the aortic arch adjacent to the ductus arteriosus. Special attention should be paid in experimental studies to avoid confusing these small spontaneous lesions with treatment-induced lesions or artifacts.

Age-related Susceptibility to Induction of Osteochondral and Vascular Lesions by Semicarbazide Hydrochloride in Rats

To compare the susceptibility to toxicity of semicarbazide hydrochloride (SEM-HCl) between young and adult rats, 3- and 20-week-old female SD rats were given a diet containing SEM-HCl at 0, 500, or 1,000 ppm and 0 or 1,000 ppm, respectively, for 4 weeks. Half of the animals were then maintained on basal diet for a further 2 weeks as recovery groups. Only in young rats was deformation of the knee joints as well as thorax and tail observed at 500 and 1,000 ppm. Histopathologically, severe osteochondral lesions, such as disarrangement and thickening of the epiphyseal cartilage and deformation of articular cartilage, were observed, but the severity of these lesions became reduced during the recovery period. In adult rats, osteochondral lesions were relatively mild. Fissures in the cartilage matrix of the tibia were characteristic of adult rats, and in these, reduction of severity was not obvious in the recovery group. In the thoracic aorta, the appearance of elastic laminae was altered only in young rats in both the 4-week treatment and recovery groups. These results suggest that growing animals are more susceptible to toxicity of SEM-HCl than adults are. Effects and the induced lesions link to the developing stage of the target organs.

Murine model of surgically induced acute aortic dissection type A

OBJECTIVES

This study aimed at developing a murine model of surgically induced acute aortic dissection type A for investigation of the formation and progression of acute aortic dissection and to test whether this system could be used for biomarker discovery.

METHODS

Adult fibrillin-1 deficient, Fbn1(C1039G/+) mice and wild-type mice were anesthetized, ventilated, and the ascending aorta exposed via hemisternotomy. We hypothesized that acute aortic dissection could be induced either by injecting autologous blood into the aortic wall or by injury to the wall with aortic clamping. Echocardiography was done preoperatively, and serum samples were collected before and 30 minutes after the operation and analyzed by enzyme-linked immunosorbent assay.

RESULTS

Echocardiography revealed larger aortic root diameters in Fbn1(C1039G/+) compared with wild-type mice (P = .001). Histologic examination showed that aortic clamp injury but not injection of blood leads to large intimal tears, disruption of aortic wall structures, and localized dissection of the aortic media in Fbn1(C1039G/+) mice. Acute aortic dissection developed in 4 of 5 Fbn1(C1039G/+) mice versus 0 of 5 wild-type mice after aortic clamping (P < .01). Elastin staining showed higher elastic fiber fragmentation and disarray in Fbn1(C1039G/+) compared with wild-type mice. Enzyme-linked immunosorbent assay analysis revealed elevated circulating transforming growth factor beta1 concentrations after induction of acute aortic dissection in Fbn1(C1039G/+) mice (P = .02, 150 +/- 61 ng/mL vs 456 +/- 97 ng/mL), but not in wild-type or sham-operated mice.

CONCLUSIONS

Aortic clamp injury can induce AAD in Fbn1(C1039G/+), but not in wild-type mice. This murine model of surgically induced acute aortic dissection is highly reproducible and nonlethal in the short term. Using this system, we revealed that circulating transforming growth factor beta1 is a promising biomarker for acute aortic dissection.

A ninety-day toxicity study of semicarbazide hydrochloride in Wistar Hannover GALAS rats

A ninety-day toxicity study of semicarbazide hydrochloride (SEM-HCl) was conducted in male and female Wistar Hannover GALAS rats fed diet containing the compound at concentration of 0, 250, 500 and 1000 ppm. Suppression of body weight gain and food consumption was found in both sexes at 1000 ppm throughout the study. Enlargement and deformation of knee joints were obvious at 500 and 1000 ppm from week 3, together with deformation of the thorax and tail. Histopathologically, disarrangement of chondrocytes and fissures in the cartilage matrix were apparent at all doses tested in epiphyseal and articular cartilage. The severity of these lesions increased dose-dependently, accompanied by increased connective tissues and bone deformation at high doses. Additionally, compact bones at 1000 ppm became thin, suggesting loss of bone mass. In the thoracic aorta, the edges of elastic laminae became rough and the interlaminar spaces were altered from a fibrillar to a rod or globular appearance. No abnormalities were detected in any other organs. Taken together, toxicological effects of subchronic exposure to SEM-HCI were mainly observed in bone, cartilage and the aorta, with the no-observed-adverse-effect-level estimated from the present histopathological examination of less than 250 ppm in both sexes.

The role of amine oxidases in xenobiotic metabolism

The amine oxidases of mammalian tissues are a heterogeneous family of enzymes that metabolise various monoamines, diamines and polyamines produced endogenously, or being absorbed as dietary or xenobiotic substances. The heterogeneous class of amine oxidases can be divided on an arbitrary basis of the chemical nature of their cofactors into two types. Monoamine oxidase (MAO) and an intracellular form of polyamine oxidase (PAO) contain flavin adenine dinucleotide (FAD) as their cofactor, whereas a second group of amine oxidases without FAD contain a cofactor possessing one or more carbonyl groups, making them sensitive to inhibition by carbonyl reagents such as semicarbazide; this group includes semicarbazide-sensitive amine oxidase (SSAO) and the connective tissue enzyme, lysyl oxidase. This article focuses on the general aspects of MAO's contribution to the metabolism of foreign toxic substances including toxins and illegal drugs. Another main objective of this review is to discuss the properties of PAO and SSAO and their involvement in the metabolism of xenobiotics.