Intima-media complex thickness: preliminary workup of comparative evaluation of abdominal aorta and carotid artery of small-for-gestation-age term newborns and normal size term newborns.

BACKGROUND: Increased intima-media thickness (IMT) has shown to be a good predictor of increased incidence of cardiovascular disease. The use of noninvasive measurement of abdominal aortic intima-media thickness (aIMT) and carotid artery intima-media thickness (cIMT) is an attractive modality to further explore and define possible intrauterine factors that may be associated with increased risk of atherosclerosis. PURPOSE: The aim of this study was to compare intima-media thickness of abdominal aorta and carotid artery in small-for-gestation-age (SGA) term newborns with appropriate for gestation age (AGA or normal sized) term newborns. MATERIAL AND METHODS: We measured the intima-media thickness of the abdominal aorta (aIMT) and carotid artery (cIMT) by high resolution ultrasonography of 50 SGA and 50 AGA term newborns. RESULTS: Mean aIMT and cIMT were significantly greaterin the SGA term newborns group as compared to AGA term newborns (0.54 +/- 0.06 mm and 0.44 +/- 0.04 mm in SGA term newborns vs. 0.50 +/- 0.04 mm and 0.40 +/- 0.04 mm in AGA term newborns; P < 0.008 and P < 0.001, respectively). The significance was even more apparent after adjustment for birthweight. A negative correlation of aIMT and cIMT was seen with birthweight, Ponderal index, length and head circumference. CONCLUSION: SGA term newborns have significantly increased aortic and carotid intima-media thickness as compared to AGA term newborns. This might be associated with higher risk for atherosclerosis. Longitudinal studies are required to further enhance the possible correlation between birthweight and intima-media thickness in SGA babies.

Aortic intima media thickness in fetuses and children with intrauterine growth restriction.

OBJECTIVE: To measure aortic intima media thickness and diameter by ultrasonography in fetuses with intrauterine growth restriction (IUGR) and in appropriate for gestational age (AGA) fetuses and in the same children after a mean follow-up of 18 months. METHODS: This was a prospective study performed between January 2006 and August 2008. Fetuses were classified as having IUGR if the estimated fetal weight was below the 10th percentile and umbilical artery pulsatility index was greater than 2 standard deviations; they were classified as AGA if the estimated fetal weight was between the 10th and 90th percentiles. Abdominal aortic intima media thickness and diameter were measured in each fetus with IUGR and in each AGA fetus at a mean gestational age of 32 weeks. The same measurements were taken in the children after a mean follow-up of 18 months. RESULTS: Thirty-eight fetuses with IUGR and 32 AGA fetuses were enrolled in the study. Aortic intima media thickness median values were significantly higher in IUGR than in AGA both in utero (1.9 mm compared with 1.15 mm; P<.001) and after birth (2.4 mm compared with 1.03 mm; P<.001) and were significantly correlated (P=.018, r=0.48). At 32 weeks of gestation, aortic intima media thickness in fetuses with IUGR was inversely correlated with estimated fetal weight (P<.003; r=-0.58). Median diameter of the abdominal aorta and blood-flow velocity at 32 weeks of gestation were significantly higher in fetuses with IUGR compared with AGA fetuses (median diameter 4.5 mm compared with 3.6 mm, P<.001, blood-flow velocity 42.5 cm/s compared with 23.3 cm/s, P<.001). At follow-up, in 25 children who had had IUGR and 25 children who had been AGA, there was no significant difference in median diameter of the abdominal aorta (6.8 mm compared with 7.5 mm, P=.21). CONCLUSION: Aortic wall thickening in fetuses and children with IUGR shows differences with respect to those who were AGA. This may reflect a correlation between impaired growth in utero, Doppler abnormalities, low birth weight, and early signs of vascular dysfunction. LEVEL OF EVIDENCE: II.

Epac1 is upregulated during neointima formation and promotes vascular smooth muscle cell migration.

Vascular remodeling after mechanoinjury largely depends on the migration of smooth muscle cells, an initial key step to wound healing. However, the role of the second messenger system, in particular, the cAMP signal, in regulating such remodeling remains controversial. Exchange protein activated by cAMP (Epac) has been identified as a new target molecule of the cAMP signal, which is independent from PKA. We thus examined whether Epac plays a distinct role from PKA in vascular remodeling. To examine the role of Epac and PKA in migration, we used primary culture smooth muscle cells from both the fetal and adult rat aorta. A cAMP analog selective to PKA, 8-(4-parachlorophenylthio)-cAMP (pCPT-cAMP), decreased cell migration, whereas an Epac-selective analog, 8-pCPT-2'-O-Me-cAMP, enhanced migration. Adenovirus-mediated gene transfer of PKA decreased cell migration, whereas that of Epac1 significantly enhanced cell migration. Striking morphological differences were observed between pCPT-cAMP- and 8-pCPT-2'-O-Me-cAMP-treated aortic smooth muscle cells. Furthermore, overexpression of Epac1 enhanced the development of neointimal formation in fetal rat aortic tissues in organ culture. When the mouse femoral artery was injured mechanically in vivo, we found that the expression of Epac1 was upregulated in vascular smooth muscle cells, whereas that of PKA was downregulated with the progress of neointimal thickening. Our findings suggest that Epac1, in opposition to PKA, increases vascular smooth muscle cell migration. Epac may thus play an important role in advancing vascular remodeling and restenosis upon vascular injury.

Endothelial-mesenchymal transition occurs during embryonic pulmonary artery development.

Pulmonary vascular remodeling is a process generally associated with pulmonary hypertension that involves intimal thickening, medial hyperthrophy, and plexiform lesions. Morphological studies during pulmonary hypertension have indicated that intimal thickening consists of immature smooth muscle cells (SMCs) associated with determined extracellular matrix components, suggesting an important role for these cells in vascular lesions. Controversy exists regarding the nature and origin of the cells conforming the intimal thickenings. In this study, the authors characterized the in vivo phenotype of the cells located in the pulmonary artery wall during the advanced stages of chicken embryo development and examined whether intimal thickenings are present in such stages. Immunolabeling of cryosections demonstrated presence of intimal thickenings composed of mesenchymal cells that may arise from the endothelium. These cells persist either as nonmuscle throughout the development, or possibly convert to cells expressing alpha -smooth muscle actin (alpha-SM actin). To determine whether pulmonary endothelial cells undergo a transition to mesenchymal cells, the authors used pulmonary artery explants from 10- to 11-day-old chicken embryos and found that explanted endothelial cells detached from the monolayer and acquired mesenchymal characteristics. Some of these cells maintained immunoreactivity for von Willebrand factor (vWF), whereas other jointly lost vWF and gained alpha -SM actin expression (transitional cells), suggesting conversion to SMCs. Therefore, these findings strongly support the authors' in vivo observations and demonstrate that embryonic pulmonary endothelial cells undergo a transition to mesenchymal cells and participate in intimal thickening formation and pulmonary vascular remodeling.

Intimal thickening involves transdifferentiation of embryonic endothelial cells.

Morphological studies have hypothesized different origins for the precursors of the vascular smooth muscle cells (SMCs). The intriguing possibility that intimal SMCs may arise from the endothelium has newly emerged. As a first step towards understanding of the possible mechanisms involved in the transdifferentiation of endothelium into smooth muscle cells, we characterized the in vivo phenotype of the cells located in the aortic wall (distal to the aortic arches). This was accomplished using advanced stages of chicken embryo development. Furthermore, we investigated whether the cells present at the intimal thickening derive from the endothelial cell transdifferentiation. Immunolabeling of serial cryosections suggested that mesenchymal cells observed in the intimal thickening may arise from the endothelium. These cells may persist either as non-muscle throughout the development or possibly convert to cells expressing smooth muscle alpha-actin (SM alpha-actin). To determine whether endothelial cells may actually transdifferentiate into mesenchymal cells, aortic explants from 14-day-old chicken embryos (stage 40) were used. We found that explanted endothelial cells lose their cobblestone-appearance and migrate toward cell-free area. Some of these cells maintain the vWf immunoreactivity, whereas other cells coordinately lose vWf and gain SM alpha-actin expression (transitional cells). Taken together these findings strongly support the possibility that embryonic aortic endothelial transdifferentiate into mesenchymal cells, some of which express SM alpha-actin. Since TGFbeta-3 is considered an essential factor during epithelial to mesenchymal transitions in earlier chicken heart development, we also investigated the distribution of this growth factor at day 14. Our observations indicated that the immunoreactivity for TGFbeta-3 in this stage may be associated with migrating mesenchymal cells and that this immunoreactivity appears to decrease as cell differentiation advances. Therefore, the present study provides evidence that could help to explain 1) the presence of cells displaying a phenotype reminiscent of fetal-like cells in the normal chicken aorta and in the intimal region of the human aorta; 2) the SM lineage diversity in the chicken embryo reported by others; 3) a subpopulation of immature cells in the subendothelial region of the main pulmonary arteries of fetal, neonatal and adult bovines; and 4) the presence of intimal cushions, intimal pads, eccentric and diffuse intimal thickening that are observed in mammalian and avian vessels at birth.

Neonatal intima formation in the human coronary artery.

Intimal masses develop in the human coronary arteries of all humans, becoming atherosclerotic in later life either because of focal accumulation of lipid or the resulting response to injury. We evaluated the time course of formation of the intimal mass in the proximal left anterior descending coronary artery in autopsy specimens from 91 patients between 17 weeks' gestation and 23 months of postnatal age. Intima was rarely found before 30 weeks' gestation; however, the frequency with which at least some intimal cells were observed increased to 35% between 36 weeks' gestation and birth. By 3 months after birth, all patients had an intimal mass at this coronary location. The mean intima/media ratio was 0.1 just after birth and increased continuously to the second postnatal year. Replication of medial smooth muscle cells, indicated by proliferating cell nuclear antigen staining, was high before birth and decreased between birth and 2 years of age. However, the replication index of the intima remained at 2% to 5%. Thus, coronary intimal cells appearing in the perinatal period may arise by migration after replication of medial smooth muscle, as is seen in models of carotid artery balloon injury. In conclusion, formation of the coronary artery intima is a rapid process, beginning in the peripartum or postpartum period. Given the clonality of the adult lesion and the lack of proliferation in later stages of lesion formation, it is intriguing to speculate that this event may form the basis for atherosclerosis in later life.

Intima-like smooth muscle cells: developmental link between endothelium and media?

The presence of non-contractile smooth muscle cells within the arterial wall raises questions as to their origin and function. These cells abound within the aortae of murine and porcine neonates, but are also present within the intimal and medial layers of adult arteries. They are largely devoid of smooth muscle-associated proteins and manifest an epithelioid form. Their morphological resemblance to endothelial cells prompted us to explore this potential relationship and to investigate their angiogenic properties in three-dimensional collagen gels. Using well-characterized smooth muscle cell lines, displaying either the intima-like (epithelioid) or media-like (spindle-shaped) morphology, we were able to show that intima-like cells share several features in common with endothelial ones and can transform into a media-like phenotype, whereby they irreversibly lose their characteristic pattern of protein expression. Intima-like, but not media-like, vascular smooth muscle cells are capable of forming capillary tubes, and, in co-cultures, can induce media-like ones to participate in this process. Such capillaries consist of a randomly-organized, mixed population of endothelial cells with intima-like or media-like smooth muscle ones. The functional significance of this diversity in smooth muscle cell type is not well understood, but phenotypic plasticity could conceivably figure as an important adaptive response to changes in the local environment.

Structural and architectural changes during arterial development and the role of hemodynamics.

Hemodynamics is a major determinant in the anatomical and mural architectural development of the arterial tree. Arterial intimal proliferation commences in utero at specific anatomical sites often appearing eccentric in transverse section and precedes more diffuse concentric thickening. Regarded as an inherent structural component of the wall or an adaptive mural response to increasing hemodynamic stresses concomitant with growth, its occurrence in utero and in lower animals, though generally supportive of this view, ignores qualitative changes. Further doubt derives from the retrogressive destructive nature of structural changes in the arterial wall in the young, individual differences and their continued progression after birth and maturation. It is postulated that concomitantly with arterial development the associated degenerative changes are attributable to hemodynamically induced bioengineering fatigue caused by longitudinal stretching and circumferential distensile effects of the pulse waves and by lesser vibrations generated by flow at sites of predilection for compensatory intimal thickening. This intimal proliferation is the compensatory reparative response to loss of tensile strength of mural constituents and of the vessel wall as a whole.

Formation of the arterial media during vascular development.

We are still in the earliest stages of studying the molecular biology of vascular development. Key questions, even simple questions, such as the origin of endothelial precursors from the epiblast or the mesoderm, remain largely unanswered. For the smooth muscle cell, we do not even have a satisfactory molecular definition of cell type, because the known cell type-specific markers generally disappear when these cells are placed in vitro, and even in vivo smooth muscle cells identified by location can be very undifferentiated. A few bright spots illuminate this cloudy prospect. We do have endothelial lineage markers, and, given the powerful tools of promoting analysis, it seems likely that we will soon known a lot more about the identification of the endothelial lineage. It is hoped that this will help us understand how patterns of development of the vessel wall are controlled. Similarly, the failure of our early studies to identify molecules responsible for investment by smooth muscle can be seen as an exciting finding. If platelet-derived growth factor, fibroblast growth factor, and transforming growth factor beta are not expressed until after smooth muscle investment, still other as yet unidentified factors must be present to account for this stage of development of the vessel wall.

[A comparative ultrastructural and morphometric analysis of the smooth myocytes in the tunicae intima and media of the human fetal aorta]. / Sravnitel'nyi ul'trastrukturnyi i morfometricheskii analiz gladkikh miotsitov vnutrennei i srednei obolochek aorty ploda cheloveka.

Transmission electron microscopy was used for studying the thoracic part of the aorta of 9 human fetuses of 20-28 weeks of development. In the medial tunic of the human fetus aorta there are smooth myocytes (SM) of the contractile and synthetic phenotypes. The latter are localized mainly in the inner part of the media. In the inner tunic there are also SM of the synthetic phenotype. With the help of processes they make contacts with endotheliocytes and processes of SM of the media. In the gaps between the subendothelial SM and endothelium there are particles of elastin which form the structure resembling an additional elastic membrane. It is reasonable to think that the migration of SM into the intima is a stage of normal development of the vessel associated with the adaptation to local hemodynamic conditions rather than an initial manifestation of atherosclerosis.

Phenotypic changes of human smooth muscle cells during development: late expression of heavy caldesmon and calponin.

Expression of the regulatory contractile proteins, heavy caldesmon (h-caldesmon) and calponin was studied in human aortic smooth muscle cells (SMCs) during development and compared with the expression of alpha-SM-actin and smooth muscle-myosin heavy chain (SM-MHCs). For this study, novel monoclonal antibodies specific to SM-MHCs, h-caldesmon, and calponin were developed and characterized. Aortic SMCs from fetuses of 8-10 and 20-22 weeks of gestation express alpha-SM-actin and SM-MHCs, but neither h-caldesmon nor calponin were expressed as demonstrated by immunoblotting and immunofluorescence techniques. In the adult aortic tunica media, SMCs contain all four markers. Thus, the expression of calponin, similar to the expression of alpha-SM-actin, SM-MHCs, and h-caldesmon, is developmentally regulated in aortic SMCs. In the adult aortic subendothelial (preluminal) part of tunica intima, numerous cells containing SM-MHCs, but lacking h-caldesmon and calponin, were found. These results illustrate the similarity of SMCs from intimal thickenings and immature (fetal) SMCs. Expression of contractile proteins in the developing SMCs is coordinately regulated; however, distinct groups of proteins appear to exist whose expression is regulated differently. Actin and myosin, being major contractile proteins, also play a structural role and appear rather early in development, whereas caldesmon and calponin, being involved in regulation of contraction, can serve as markers of higher SMC differentiation steps. In contrast, h-caldesmon and calponin were already present in visceral SMCs (trachea, esophagus) of the 10-week-old fetus. These results demonstrate that the time course of maturation of visceral SMCs is different from that of vascular SMCs.

[The three-dimensional structure of the tunica intima and tunica media of the human fetal aorta studied by a new method]. / Issledovanie trekhmernoi organizatsii vnutrennei i srednei obolochek aorty ploda cheloveka s pomoshch'iu novogo metoda.

A new method is developed for revealing the latent surfaces in the structure of organs by scanning electronic microscopy. The method is based on the treatment of specimens with potassium ethoxide until cells start to appear in the dissociating solution. Using this method, thoracic aorta of nine human fetuses at the stage of 20-28 weeks was studied. Subendothelial intima and media of human fetal aorta contain smooth muscle cells differing by their arrangement, shape and surface microrelief. The intima cells are arranged in a mosaic pattern formed of single cells or cell clusters. By means of cell processes they are connected with each other, as well as with endothelial and smooth muscle cells of the media. Smooth muscle cells in the inner part of the media also have processes and form an open network. Part of the cells penetrate the intima through pores of the inner elastic membrane. In the deeper layers of the media, laterally adjoining spindle-shaped smooth muscle cells are found. It is suggested that the observed cell polymorphism is due mostly to penetration of the media smooth muscle cells into subendothelium and modification of their shape under the effect of the microenvironment.