Mechanical behavior of abdominal aorta aneurysm in rat model treated by cell therapy using mesenchymal stem cells

Promising Novel Therapies in the Treatment of Aortic and Visceral Aneurysms

Aortic and visceral aneurysms affect large arterial vessels, including the thoracic and abdominal aorta, as well as visceral arterial branches, such as the splenic, hepatic, and mesenteric arteries, respectively. Although these clinical entities have not been equally researched, it seems that they might share certain common pathophysiological changes and molecular mechanisms. The yet limited published data, with regard to newly designed, novel therapies, could serve as a nidus for the evaluation and potential implementation of such treatments in large artery aneurysms. In both animal models and clinical trials, various novel treatments have been employed in an attempt to not only reduce the complications of the already implemented modalities, through manufacturing of more durable materials, but also to regenerate or replace affected tissues themselves. Cellular populations like stem and differentiated vascular cell types, large diameter tissue-engineered vascular grafts (TEVGs), and various molecules and biological factors that might target aspects of the pathophysiological process, including cell-adhesion stabilizers, metalloproteinase inhibitors, and miRNAs, could potentially contribute significantly to the treatment of these types of aneurysms. In this narrative review, we sought to collect and present relevant evidence in the literature, in an effort to unveil promising biological therapies, possibly applicable to the treatment of aortic aneurysms, both thoracic and abdominal, as well as visceral aneurysms.

Stem Cell Based Approaches to Modulate the Matrix Milieu in Vascular Disorders

The extracellular matrix (ECM) represents a complex and dynamic framework for cells, characterized by tissue-specific biophysical, mechanical, and biochemical properties. ECM components in vascular tissues provide structural support to vascular cells and modulate their function through interaction with specific cell-surface receptors. ECM–cell interactions, together with neurotransmitters, cytokines, hormones and mechanical forces imposed by blood flow, modulate the structural organization of the vascular wall. Changes in the ECM microenvironment, as in post-injury degradation or remodeling, lead to both altered tissue function and exacerbation of vascular pathologies. Regeneration and repair of the ECM are thus critical toward reinstating vascular homeostasis. The self-renewal and transdifferentiating potential of stem cells (SCs) into other cell lineages represents a potentially useful approach in regenerative medicine, and SC-based approaches hold great promise in the development of novel therapeutics toward ECM repair. Certain adult SCs, including mesenchymal stem cells (MSCs), possess a broader plasticity and differentiation potential, and thus represent a viable option for SC-based therapeutics. However, there are significant challenges to SC therapies including, but not limited to cell processing and scaleup, quality control, phenotypic integrity in a disease milieu in vivo, and inefficient delivery to the site of tissue injury. SC-derived or -inspired strategies as a putative surrogate for conventional cell therapy are thus gaining momentum. In this article, we review current knowledge on the patho-mechanistic roles of ECM components in common vascular disorders and the prospects of developing adult SC based/inspired therapies to modulate the vascular tissue environment and reinstate vessel homeostasis in these disorders.

Therapeutic efficacy of mesenchymal stem cells for abdominal aortic aneurysm: a meta-analysis of preclinical studies

Background

Abdominal aortic aneurysm (AAA) is life-threatening, surgical treatment is currently the only clinically available intervention for the disease. Mesenchymal stem cells (MSCs) have presented eligible immunomodulatory and regenerative abilities which showed favorable therapeutic efficacy in various cardiovascular diseases. However, current evidence summarizing the effectiveness of MSCs for AAA is lacking. Thus, a meta-analysis and systematic review was necessary to be performed to assess the therapeutic efficacy of MSCs for AAA in preclinical studies.

Methods

Comprehensive literature search restricted in English was conducted in PubMed, Cochrane Library, EBSCO, EMBASE and Web of Science from inception to Oct 2021. The primary outcomes were parameters about aortic diameter change during MSCs intervention. The secondary outcomes included elastin content and expression level of inflammatory cytokines, matrix metalloproteinases (MMPs) and their inhibitors (TIMPs). Data were extracted and analyzed independently by two authors. The meta package with random effects model was used to calculate the pooled effect size and 95% confidence intervals in R (version 4.0.2).

Results

Meta-analysis of 18 included studies demonstrated that MSCs intervention has significant therapeutic effects on suppressing aortic diameter enlargement compared with the control group (diameter, SMD = − 1.19, 95% CI [− 1.47, − 0.91]; diameter change ratio, SMD = − 1.36, 95% CI [− 1.72, − 1.00]). Subgroup analysis revealed differences between MSCs and control group regarding to cell type, intervention route and cell compatibility. Moreover, the meta-analysis also showed that MSCs intervention had a significant effect on preserving aortic elastin content, reducing MCP-1, TNF-α, IL-6, MMP-2/9 and increasing TIMP-1/2 expression level compared with control group.

Conclusion

Our results suggested that MSC intervention is effective in AAA by suppressing aortic diameter enlargement, reducing elastin degradation, and modulating local immunoinflammatory reactions. These results are important for the systemic application of MSCs as a potential treatment candidate for AAA in further animal experiments and clinical trials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02755-w.

Three-dimensional analysis of the thoracic aorta microscopic deformation during intraluminal pressurization

The aorta is composed of various constituents with different mechanical properties. This heterogeneous structure implies non-uniform deformation in the aorta, which could affect local cell functions. The present study investigates 3D strains of the aorta at a cell scale induced by intraluminal pressurization. After resected mouse, thoracic aortas were stretched to their in vivo length, and the aortas were pressurized at 15, 40, 80, 120, and 160 mmHg. Images of autofluorescent light of elastin were captured under a two-photon microscope. From the movement of markers in elastic laminas (ELs) created by photo-bleaching, 3D strains (ε_θθ, ε_zz, ε_rr, ε_rθ, ε_rz, ε_θz) between two neighboring ELs in the circumferential (θ), longitudinal (z), and radial (r) directions with reference to the dimensions at 15 mmHg were calculated. The results demonstrated that the average of shear strain ε_rθ was almost 0 in a physiological pressure range (from 80 to 120 mmHg) with an absolute value |ε_rθ| changing approximately by 5%. This indicates that ELs experience radial–circumferential shear at the cell scale, but not at the whole tissue scale. The normal strains in the circumferential ε_θθ and longitudinal direction ε_zz were positive but that in the radial direction ε_rr was almost 0, which demonstrates that aortic tissue is not an incompressible material. The first principal direction in the radial–circumferential plane was 29° ± 13° from the circumferential direction. We show that the aorta is not simply stretched in the circumferential direction during pressurization and that cells in the aorta undergo complex deformations by nature.

Three-dimensional modeling of Marfan syndrome with elastic and hyperelastic materials assumptions using fluid-structure interaction

BACKGROUND

Marfan syndrome (MFS) is a genetic disorder of the connective tissue. It most prominently influences the skeletal, cardiovascular, and ocular systems, but all fibrous connective tissue throughout the body can be affected as well.

OBJECTIVE

This study aims to investigate a realistic three-dimensional model of an aorta of a specific patient suffering from MFS by considering elastic and hyperelastic materials for the tissue using fluid-structure interaction (FSI).

METHODS

Isotropic linear elastic and Mooney-Rivlin hyperelastic assumptions are implemented. Linear and nonlinear mechanical properties of the aneurysmal MFS aortic tissue are derived from an uniaxial experimental test.

RESULTS

Vortex generation in the vicinity of the aneurysm region in both elastic and hyperelastic models and the maximum blood velocity at peak flow time is calculated as 0.517 and 0.533 m/s for the two materials, respectively. The blood pressure is not significantly different between the two models (±8 Pa) and the blood pressure difference between the points in the horizontal plane of the aneurysm region is obtained as ±10 Pa for both models. The maximum von Mises stress for the hyperelastic model (2.19 MPa) is 27% more than the elastic one (1.72 MPa) and takes place at the inner curvature and upper part of the aorta and somehow far from the aneurysm region. The wall shear stress (WSS) is also considered for the elastic and hyperelastic assumptions, which is 36.7 Pa for both elastic and hyperelastic models.

CONCLUSION

The aneurysm region in the MFS affects the blood flow and causes the vortex to be generated which consequently affects the blood flow in the downstream by adding some perturbations to the blood flow. The WSS is obtained to be lower in the aneurysm region compared to other regions which indicated vascular remodeling.

Loss of anisotropic properties in abdominal aorta aneurysm obtained from the xenograft rat model

BACKGROUND

Cellular treatments using mesenchymal stem cells (MSCs) cultured in 3D conditions constitute a solution to the classical surgery in treating abdominal aortic aneurysm (AAA). The recurrent question is: how this type of biotherapy changes the mechanical behavior of artery?

METHODS

Experiments measurements based on xenograft rat model showed that the proposed cellular treatment leads to a decreasing radius and length of the AAA during its growth. An inverse finite element method was used to investigate the mechanical hyperelastic behavior of the AAA in the untreated case compared to the treated one.

RESULTS

Although AAA leads a loss anisotropy while the cellular treatment does not restore it, it was shown that the stiffness of the arterial wall was improved. The numerical analysis of the stress distributions permitted to localize the stress concentration through the arterial wall and the probable zone of the rupture of the aneurysm developed from the xenograft rat model.

CONCLUSIONS

The treatment of AAA with MSCs cultured in a 3D conditions constitutes a new challenge. Based on xenograft rat model, this study shows the potential of this cellular treatment to reduce the variation of the growth, the stiffness and the stress distributions.

MECHANICAL PROPERTIES CHANGE IN THE RAT XENOGRAFT MODEL TREATED BY MESENCHYMAL CELLS CULTURED IN AN HYALURONIC ACID-BASED HYDROGEL

This study investigated the efficiency of a cellular therapy with mesenchymal stem cells (MSCs) cultured in an hyaluronic acid-based hydrogel on growth of abdominal aortic aneurysms (AAA) obtained in the rat xenograft model. The experimental model was devoted to create an AAA at D14 after grafting of a decellularized abdominal aorta obtained from guinea pigs before being transplanted into rats. At D21, geometrical measurements as radius and length of AAA were performed on untreated ([Formula: see text]) and treated ([Formula: see text]) arteries. When compared to different cases, it was shown that the proposed cellular treatment significantly reduced the expansion of radius and length of AAA. Furthermore, to explore the mechanical properties change of the arterial wall, an inverse finite element method was performed where AAA is represented by an elliptical geometry with varying thicknesses. To identify the material parameters, the AAA tissue was assumed to behave isochoric and isotropic undergoing large strains and described by the Yeoh’s strain energy function. Although limitations exist in this study such as the time of the experimental protocol, the isotropic behavior law of the AAA wall and the axisymmetric geometry of the artery, the results revealed that arterial wall stiffness change and the maximum effective stress decreased during expansion of AAA when cellular treatment is applied.

Mechanical behavior of the abdominal aortic aneurysm assessed by biaxial tests in the rat xenograft model

This paper addresses the mechanical biaxial behavior of degraded arteries obtained by the rat xenograft model. For that, a pressure myograph was used to perform extension-inflation tests on abdominal aortic aneurysms (AAAs). Furthermore, residual stresses in the aneurismal wall were assessed by opening angle tests. Thus, the changes in mechanical behavior between native murine aortas, decellularized guinea pig aortas (the grafts) and degraded aortas (AAAs) were investigated. It was shown that decellularized and degraded aortas exhibited a different mechanical behavior than native murine aortas. Indeed, decellularized aortas presented a marked decrease in circumferential stretch and distensibility compared with native aortas. Moreover, we evidenced an exacerbation of these changes in mechanical behavior for AAAs, which showed the lowest distension and distensibility at 100mmHg. The opening angle test also revealed a complete loss of residual stresses in the degraded arterial wall given the non opening of rings extracted from AAAs.

Diameter and thickness-related variations in mechanical properties of degraded arterial wall in the rat xenograft model

The purpose of this study was to evaluate the diameter and thickness-related variations in mechanical properties of degraded arterial wall. To this end, ring tests were performed on 31 samples from the rat xenograft model of abdominal aortic aneurysm (AAA) and failure properties were determined. An inverse finite element method was then employed to identify the material parameters of a hyperelastic and incompressible strain energy function. Correlations with outer diameter and wall thickness of the rings were examined. Furthermore, we investigated the changes in mechanical properties between the grafts, which consist in guinea pig decellularized aortas, native murine aortas and degraded aortas (AAAs). Decellularized aortas presented a significantly lower ultimate strain associated with a higher stiffening rate compared to native aortas. AAAs exhibited a significantly lower ultimate stress than other groups and an extensible-but-stiff behavior. The proposed approach revealed correlations of ultimate stress and material parameters of aneurysmal aortas with outer diameter and thickness. In particular, the negative correlations of the material parameter accounting for the response of the non-collagenous matrix with diameter and thickness (r=-0.67 and r=-0.73, p<0.001) captured the gradual loss of elastin with dilatation observed in histology (r=-0.97, p<0.001). Moreover, it exposed the progressive weakening of the wall with enlargement and thickening (r=-0.64 and r=-0.69, p<0.001), suggesting that wall thickness and diameter may be indicators of rupture risk in the rat xenograft model.

MECHANICAL CHARACTERIZATION OF ABDOMINAL AORTIC ANEURYSM WALL IN RAT MODEL TREATED BY MESENCHYMAL STEM CELLS

In this work, we study the mechanical properties of abdominal aortic aneurysms (AAAs) treated by cell therapy. Based on the xenograft model in rats, we analyze the effects of the injection of bone marrow mesenchymal stem cells (MSCs) on the stiffness of the arterial wall. Uniaxial tests performed on control, treated and untreated samples, have led to the identification of a nonlinear behavior law, using a mechanical model based on a stress-stretch exponential relation. The comparison of the mechanical behavior shows the benefits of the proposed cell therapy which improves the mechanical strength of the aneurysmal vessel wall. A histological study has shown the favorable change expression of elastin and collagen which are involved in the mechanical behavior of repaired arterial tissue. Thus, this work is part of MSCs biological understanding and it contributes to evaluate the approaches used in cell therapy and regenerative medicine to treat AAAs.