Biomechanical characterization of the passive porcine stomach

The complex mechanics of the gastric wall facilitates the main digestive tasks of the stomach. However, the interplay between the mechanical properties of the stomach, its microstructure, and its vital functions is not yet fully understood. Importantly, the pig animal model is widely used in biomedical research for preliminary or ethically prohibited studies of the human digestion system. Therefore, this study aims to thoroughly characterize the mechanical behavior and microstructure of the porcine stomach. For this purpose, multiple quasi-static mechanical tests were carried out with three different loading modes, i.e., planar biaxial extension, radial compression, and simple shear. Stress-relaxation tests complemented the quasi-static experiments to evaluate the deformation and strain-dependent viscoelastic properties. Each experiment was conducted on specimens of the complete stomach wall and two separate layers, mucosa and muscularis, from each of the three gastric regions, i.e., fundus, body, and antrum. The significant preconditioning effects and the considerable regional and layer-specific differences in the tissue response were analyzed. Furthermore, the mechanical experiments were complemented with histology to examine the influence of the microstructural composition on the macrostructural mechanical response and vice versa. Importantly, the shear tests showed lower stresses in the complete wall compared to the single layers which the loose network of submucosal collagen might explain. Also, the stratum arrangement of the muscularis might explain mechanical anisotropy during tensile tests. This study shows that gastric tissue is characterized by a highly heterogeneous microstructure with regional variations in layer composition reflecting not only functional differences but also diverse mechanical behavior. STATEMENT OF SIGNIFICANCE: Unfortunately, only few experimental data on gastric tissue are available for an adequate material parameter and model estimation. The present study therefore combines layer- and region-specific stomach wall mechanics obtained under multiple loading conditions with histological insights into the heterogeneous microstructure. On the one hand, the extensive data sets of this study expand our understanding of the interplay between gastric mechanics, motility and functionality, which could help to identify and treat associated pathologies. On the other hand, such data sets are of high relevance for the constitutive modeling of stomach tissue, and its application in the field of medical engineering, e.g., in the development of surgical staplers and the improvement of bariatric surgical interventions.

Western diet-induced obesity results in brain mitochondrial dysfunction in female Ossabaw swine

Diet-induced obesity is implicated in the development of a variety of neurodegenerative disorders. Concurrently, the loss of mitochondrial Complex I protein or function is emerging as a key phenotype across an array of neurodegenerative disorders. Therefore, the objective of this study was to determine if Western diet (WD) feeding in swine [carbohydrate = 40.8% kCal (17.8% of total calories from high fructose corn syrup), protein = 16.2% kcal, fat = 42.9% kCal, and 2% cholesterol] would result in Complex I syndrome pathology. To characterize the effects of WD-induced obesity on brain mitochondria in swine, high resolution respirometry measurements from isolated brain mitochondria, oxidative phosphorylation Complex expression, and indices of oxidative stress and mitochondrial biogenesis were assessed in female Ossabaw swine fed a WD for 6-months. In line with Complex I syndrome, WD feeding severely reduced State 3 Complex I, State 3 Complex I and II, and uncoupled mitochondrial respiration in the hippocampus and prefrontal cortex (PFC). State 3 Complex I mitochondrial respiration in the PFC inversely correlated with serum total cholesterol. WD feeding also significantly reduced protein expression of oxidative phosphorylation Complexes I-V in the PFC. WD feeding significantly increased markers of antioxidant defense and mitochondrial biogenesis in the hippocampi and PFC. These data suggest WD-induced obesity may contribute to Complex I syndrome pathology by increasing oxidative stress, decreasing oxidative phosphorylation Complex protein expression, and reducing brain mitochondrial respiration. Furthermore, these findings provide mechanistic insight into the clinical link between obesity and mitochondrial Complex I related neurodegenerative disorders.

Mechanobiological considerations in colorectal stapling: Implications for technology development

Technological advancements in minimally invasive surgery have led to significant improvements in patient outcomes. One such technology is surgical stapling, which has evolved into a key component of many operating rooms by facilitating ease and efficacy in resection and repair of diseased or otherwise compromised tissue. Despite such advancements, adverse post-operative outcomes such as anastomotic leak remain a persistent problem in surgical stapling and its correlates (i.e., hand-sewing), most notably in low colorectal or coloanal procedures. Many factors may drive anastomotic leaks, including tissue perfusion, microbiome composition, and patient factors such as pre-existing disease. Surgical intervention induces complex acute and chronic changes to the mechanical environment of the tissue; however, roles of mechanical forces in post-operative healing remain poorly characterized. It is well known that cells sense and respond to their local mechanical environment and that dysfunction of this "mechanosensing" phenomenon contributes to a myriad of diseases. Mechanosensing has been investigated in wound healing contexts such as dermal incisional and excisional wounds and development of pressure ulcers; however, reports investigating roles of mechanical forces in adverse post-operative gastrointestinal wound healing are lacking. To understand this relationship well, it is critical to understand: 1) the intraoperative material responses of tissue to surgical intervention, and 2) the post-operative mechanobiological response of the tissue to surgically imposed forces. In this review, we summarize the state of the field in each of these contexts while highlighting areas of opportunity for discovery and innovation which can positively impact patient outcomes in minimally invasive surgery.

Role of Axl in target organ inflammation and damage due to hypertensive aortic remodeling

We have shown that excessive endothelial cell stretch causes release of growth arrest-specific 6 (GAS6), which activates the tyrosine kinase receptor Axl on monocytes and promotes immune activation and inflammation. We hypothesized that GAS6/Axl blockade would reduce renal and vascular inflammation and lessen renal dysfunction in the setting of chronic aortic remodeling. We characterized a model of aortic remodeling in mice following a 2-wk infusion of angiotensin II (ANG II). These mice had chronically increased pulse wave velocity, and their aortas demonstrated increased mural collagen. Mechanical testing revealed a marked loss of Windkessel function that persisted for 6 mo following ANG II infusion. Renal function studies showed a reduced ability to excrete a volume load, a progressive increase in albuminuria, and tubular damage as estimated by periodic acid Schiff staining. Treatment with the Axl inhibitor R428 beginning 2 mo after ANG II infusion had a minimal effect on aortic remodeling 2 mo later but reduced the infiltration of T cells, γ/δ T cells, and macrophages into the aorta and kidney and improved renal excretory capacity, reduced albuminuria, and reduced evidence of renal tubular damage. In humans, circulating Axl+/Siglec6+ dendritic cells and phospho-Axl+ cells correlated with pulse wave velocity and aortic compliance measured by transesophageal echo, confirming chronic activation of the GAS6/Axl pathway. We conclude that brief episodes of hypertension induce chronic aortic remodeling, which is associated with persistent low-grade inflammation of the aorta and kidneys and evidence of renal dysfunction. These events are mediated at least in part by GAS6/Axl signaling and are improved with Axl blockade.NEW & NOTEWORTHY In this study, a brief, 2-wk period of hypertension in mice led to progressive aortic remodeling, an increase in pulse wave velocity, and evidence of renal injury, dysfunction, and albuminuria. This end-organ damage was associated with persistent renal and aortic infiltration of CD8+ and γ/δ T cells. We show that this inflammatory response is likely due to GAS6/Axl signaling and can be ameliorated by blocking this pathway. We propose that the altered microvascular mechanical forces caused by increased pulse wave velocity enhance GAS6 release from the endothelium, which in turn activates Axl on myeloid cells, promoting the end-organ damage associated with aortic stiffening.

Abstract P236: Role Of Axl In Target Organ Inflammation And Damage Due To Hypertensive Aortic Remodeling

Background: Aortic remodeling enhances arterial pulsatility in the microcirculation and we have shown that excessive endothelial stretch increases release of Growth Arrest Specific 6 (GAS6), which activates Axl on monocytes causing immune activation and inflammation.

Hypothesis: GAS6/Axl blockade reduces renal and vascular inflammation and lessens renal dysfunction caused by aortic remodeling.

Methods and Results: Three month old male C57Bl/6 mice received osmotic minipumps containing vehicle or ang II for 2 weeks and the pumps removed. Aortas demonstrated increased collagen and an 80% loss of Windkessel function that persisted for 6 months following ang II. Renal function studies showed reduced ability to excrete a volume load, a progressive increase in albuminuria and tubular damage as estimated by Periodic Acid Schiff staining. Treatment with the Axl inhibitor R428 beginning 2 months after ang II had minimal effect on aortic remodeling 2 months later, but reduced aortic and renal infiltration of T cells, gamma/delta T cells and macrophages as measured by flow cytometry (Figure). R428 also improved renal excretory capacity, decreased urinary NGAL, reduced albuminuria, and attenuated renal tubular damage. Interestingly, macrophage/T cell complexes were present in aortas of mice previously exposed to hypertension, and were reduced by R428.

Conclusion: Brief episodes of hypertension induce chronic aortic remodeling which increases Axl signaling and transformation of monocytes to inflammatory antigen presenting cells that activate T cells. Axl blockade might serve as a therapeutic option to improve end-organ damage after an episode of hypertension.

mTOR inhibition prevents angiotensin II-induced aortic rupture and pseudoaneurysm but promotes dissection in Apoe-deficient mice

Aortic dissection and rupture are triggered by decreased vascular wall strength and/or increased mechanical loads. We investigated the role of mTOR signaling in aortopathy using a well-described model of angiotensin II–induced dissection, aneurysm, or rupture of the suprarenal abdominal aorta in Apoe-deficient mice. Although not widely appreciated, nonlethal hemorrhagic lesions present as pseudoaneurysms without significant dissection in this model. Angiotensin II–induced aortic tears result in free rupture, contained rupture with subadventitial hematoma (forming pseudoaneurysms), dilatation, or healing, while the media invariably thickens regardless of mural tears. Medial thickening results from smooth muscle cell hypertrophy and extracellular matrix accumulation, including matricellular proteins. Angiotensin II activates mTOR signaling in vascular wall cells, and inhibition of mTOR signaling by rapamycin prevents aortic rupture but promotes dissection. Decreased aortic rupture correlates with decreased inflammation and metalloproteinase expression, whereas extensive dissection correlates with induction of matricellular proteins that modulate adhesion of vascular cells. Thus, mTOR activation in vascular wall cells determines whether aortic tears progress to dissection or rupture. Previous mechanistic studies of aortic aneurysm and dissection by angiotensin II in Apoe-deficient mice should be reinterpreted as clinically relevant to pseudoaneurysms, and mTOR inhibition for aortic disease should be explored with caution.

Excessive adventitial stress drives inflammation-mediated fibrosis in hypertensive aortic remodelling in mice

Hypertension induces significant aortic remodelling, often adaptive but sometimes not. To identify immuno-mechanical mechanisms responsible for differential remodelling, we studied thoracic aortas from 129S6/SvEvTac and C57BL/6 J mice before and after continuous 14-day angiotensin II infusion, which elevated blood pressure similarly in both strains. Histological and biomechanical assessments of excised vessels were similar at baseline, suggesting a common homeostatic set-point for mean wall stress. Histology further revealed near mechano-adaptive remodelling of the hypertensive 129S6/SvEvTac aortas, but a grossly maladaptive remodelling of C57BL/6 J aortas. Bulk RNA sequencing suggested that increased smooth muscle contractile processes promoted mechano-adaptation of 129S6/SvEvTac aortas while immune processes prevented adaptation of C57BL/6 J aortas. Functional studies confirmed an increased vasoconstrictive capacity of the former while immunohistochemistry demonstrated marked increases in inflammatory cells in the latter. We then used multiple computational biomechanical models to test the hypothesis that excessive adventitial wall stress correlates with inflammatory cell infiltration. These models consistently predicted that increased vasoconstriction against an increased pressure coupled with modest deposition of new matrix thickens the wall appropriately, restoring wall stress towards homeostatic consistent with adaptive remodelling. By contrast, insufficient vasoconstriction permits high wall stresses and exuberant inflammation-driven matrix deposition, especially in the adventitia, reflecting compromised homeostasis and gross maladaptation.

Chronic mTOR activation induces a degradative smooth muscle cell phenotype

Smooth muscle cell (SMC) proliferation has been thought to limit the progression of thoracic aortic aneurysm and dissection (TAAD) because loss of medial cells associates with advanced disease. We investigated effects of SMC proliferation in the aortic media by conditional disruption of Tsc1, which hyperactivates mTOR complex 1. Consequent SMC hyperplasia led to progressive medial degeneration and TAAD. In addition to diminished contractile and synthetic functions, fate-mapped SMCs displayed increased proteolysis, endocytosis, phagocytosis, and lysosomal clearance of extracellular matrix and apoptotic cells. SMCs acquired a limited repertoire of macrophage markers and functions via biogenesis of degradative organelles through an mTOR/β-catenin/MITF-dependent pathway, but were distinguishable from conventional macrophages by an absence of hematopoietic lineage markers and certain immune effectors even in the context of hyperlipidemia. Similar mTOR activation and induction of a degradative SMC phenotype in a model of mild TAAD due to Fbn1 mutation greatly worsened disease with near-uniform lethality. The finding of increased lysosomal markers in medial SMCs from clinical TAAD specimens with hyperplasia and matrix degradation further supports the concept that proliferation of degradative SMCs within the media causes aortic disease, thus identifying mTOR-dependent phenotypic modulation as a therapeutic target for combating TAAD.

Paradoxical aortic stiffening and subsequent cardiac dysfunction in Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is an ultra-rare disorder with devastating sequelae resulting in early death, presently thought to stem primarily from cardiovascular events. We analyse novel longitudinal cardiovascular data from a mouse model of HGPS (Lmna^G609G/G609G) using allometric scaling, biomechanical phenotyping, and advanced computational modelling and show that late-stage diastolic dysfunction, with preserved systolic function, emerges with an increase in the pulse wave velocity and an associated loss of aortic function, independent of sex. Specifically, there is a dramatic late-stage loss of smooth muscle function and cells and an excessive accumulation of proteoglycans along the aorta, which result in a loss of biomechanical function (contractility and elastic energy storage) and a marked structural stiffening despite a distinctly low intrinsic material stiffness that is consistent with the lack of functional lamin A. Importantly, the vascular function appears to arise normally from the low-stress environment of development, only to succumb progressively to pressure-related effects of the lamin A mutation and become extreme in the peri-morbid period. Because the dramatic life-threatening aortic phenotype manifests during the last third of life there may be a therapeutic window in maturity that could alleviate concerns with therapies administered during early periods of arterial development.

Smooth Muscle Cell Reprogramming in Aortic Aneurysms

The etiology of aortic aneurysms is poorly understood, but it is associated with atherosclerosis, hypercholesterolemia, and abnormal transforming growth factor β (TGF-β) signaling in smooth muscle. Here, we investigated the interactions between these different factors in aortic aneurysm development and identified a key role for smooth muscle cell (SMC) reprogramming into a mesenchymal stem cell (MSC)-like state. SMC-specific ablation of TGF-β signaling in Apoe-/- mice on a hypercholesterolemic diet led to development of aortic aneurysms exhibiting all the features of human disease, which was associated with transdifferentiation of a subset of contractile SMCs into an MSC-like intermediate state that generated osteoblasts, chondrocytes, adipocytes, and macrophages. This combination of medial SMC loss with marked increases in non-SMC aortic cell mass induced exuberant growth and dilation of the aorta, calcification and ossification of the aortic wall, and inflammation, resulting in aneurysm development.

Fundamental Roles of Axial Stretch in Isometric and Isobaric Evaluations of Vascular Contractility

Vascular smooth muscle cells (VSMCs) can regulate arterial mechanics via contractile activity in response to changing mechanical and chemical signals. Contractility is traditionally evaluated via uniaxial isometric testing of isolated rings despite the in vivo environment being very different. Most blood vessels maintain a locally preferred value of in vivo axial stretch while subjected to changes in distending pressure, but both of these phenomena are obscured in uniaxial isometric testing. Few studies have rigorously analyzed the role of in vivo loading conditions in smooth muscle function. Thus, we evaluated effects of uniaxial versus biaxial deformations on smooth muscle contractility by stimulating two regions of the mouse aorta with different vasoconstrictors using one of three testing protocols: (i) uniaxial isometric testing, (ii) biaxial isometric testing, and (iii) axially isometric plus isobaric testing. Comparison of methods (i) and (ii) revealed increased sensitivity and contractile capacity to potassium chloride and phenylephrine (PE) with biaxial isometric testing, and comparison of methods (ii) and (iii) revealed a further increase in contractile capacity with isometric plus isobaric testing. Importantly, regional differences in estimated in vivo axial stretch suggest locally distinct optimal biaxial configurations for achieving maximal smooth muscle contraction, which can only be revealed with biaxial testing. Such differences highlight the importance of considering in vivo loading and geometric configurations when evaluating smooth muscle function. Given the physiologic relevance of axial extension and luminal pressurization, we submit that, when possible, axially isometric plus isobaric testing should be employed to evaluate vascular smooth muscle contractile function.

Comparison of 10 murine models reveals a distinct biomechanical phenotype in thoracic aortic aneurysms

Thoracic aortic aneurysms are life-threatening lesions that afflict young and old individuals alike. They frequently associate with genetic mutations and are characterized by reduced elastic fibre integrity, dysfunctional smooth muscle cells, improperly remodelled collagen and pooled mucoid material. There is a pressing need to understand better the compromised structural integrity of the aorta that results from these genetic mutations and renders the wall vulnerable to dilatation, dissection or rupture. In this paper, we compare the biaxial mechanical properties of the ascending aorta from 10 murine models: wild-type controls, acute elastase-treated, and eight models with genetic mutations affecting extracellular matrix proteins, transmembrane receptors, cytoskeletal proteins, or intracellular signalling molecules. Collectively, our data for these diverse mouse models suggest that reduced mechanical functionality, as indicated by a decreased elastic energy storage capability or reduced distensibility, does not predispose to aneurysms. Rather, despite normal or lower than normal circumferential and axial wall stresses, it appears that intramural cells in the ascending aorta of mice prone to aneurysms are unable to maintain or restore the intrinsic circumferential material stiffness, which may render the wall biomechanically vulnerable to continued dilatation and possible rupture. This finding is consistent with an underlying dysfunctional mechanosensing or mechanoregulation of the extracellular matrix, which normally endows the wall with both appropriate compliance and sufficient strength.

Biomechanical Phenotyping of the Murine Aorta: What Is the Best Control?

The availability of diverse mouse models is revealing increasingly greater information on arterial mechanics, including homeostatic adaptations and pathologic maladaptations to genetic, pharmacological, and surgical manipulations. Fundamental to understanding such biomechanical changes, however, is reliable information on appropriate control vessels. In this paper, we contrast 15 different geometrical and mechanical metrics of biaxial wall mechanics for the ascending aorta across seven different types of possible control mice. We show that there is a comforting similarity across these multiple controls for most, though not all, metrics. In particular, three potential controls, namely, noninduced conditional mice, exhibit higher values of distensibility, an important clinical metric of structural stiffness, and two of these potential controls also have higher values of intrinsic circumferential material stiffness. There is motivation, therefore, to understand better the biomechanical changes that can arise with noninduced Cre-lox or similar approaches for generating mutations conditionally. In cases of germline mutations generated by breeding heterozygous +/- mice, however, the resulting homozygous +/+ mice tend to exhibit properties similar to traditional (C57BL/6) controls.

Inhibition of the mTOR pathway in abdominal aortic aneurysm: implications of smooth muscle cell contractile phenotype, inflammation, and aneurysm expansion

The development of effective pharmacological treatment of abdominal aortic aneurysm (AAA) potentially offers great benefit to patients with preaneurysmal aortic dilation by slowing the expansion of aneurysms and reducing the need for surgery. To date, therapeutic targets for slowing aortic dilation have had low efficacy. Thus, in this study, we aim to elucidate possible mechanisms driving aneurysm progression to identify potential targets for pharmacological intervention. We demonstrate that mechanistic target of rapamycin (mTOR) signaling is overactivated in aortic smooth muscle cells (SMCs), which contributes to murine AAA. Rapamycin, a typical mTOR pathway inhibitor, dramatically limits the expansion of the abdominal aorta following intraluminal elastase perfusion. Furthermore, reduction of aortic diameter is achieved by inhibition of the mTOR pathway, which preserves and/or restores the contractile phenotype of SMCs and downregulates macrophage infiltration, matrix metalloproteinase expression, and inflammatory cytokine production. Taken together, these results highlight the important role of the mTOR cascade in aneurysm progression and the potential application of rapamycin as a therapeutic candidate for AAA.

NEW & NOTEWORTHY This study provides novel observations that mechanistic target of rapamycin (mTOR) signaling is overactivated in aortic smooth muscle cells and contributes to mouse abdominal aortic aneurysm (AAA) and that rapamycin protects against aneurysm development. Our data highlight the importance of preservation and/or restoration of the smooth muscle cell contractile phenotype and reduction of inflammation by mTOR inhibition in AAA.

Deficient Circumferential Growth Is the Primary Determinant of Aortic Obstruction Attributable to Partial Elastin Deficiency

OBJECTIVE

Williams syndrome is characterized by obstructive aortopathy attributable to heterozygous loss of ELN, the gene encoding elastin. Lesions are thought to result primarily from excessive smooth muscle cell (SMC) proliferation and consequent medial expansion, although an initially smaller caliber and increased stiffness of the aorta may contribute to luminal narrowing. The relative contributions of such abnormalities to the obstructive phenotype had not been defined.

APPROACH AND RESULTS

We quantified determinants of luminal stenosis in thoracic aortas of Eln^-/- mice incompletely rescued by human ELN. Moderate obstruction was largely because of deficient circumferential growth, most prominently of ascending segments, despite increased axial growth. Medial thickening was evident in these smaller diameter elastin-deficient aortas, with medial area similar to that of larger diameter control aortas. There was no difference in cross-sectional SMC number between mutant and wild-type genotypes at multiple stages of postnatal development. Decreased elastin content was associated with medial fibrosis and reduced aortic distensibility because of increased structural stiffness but preserved material stiffness. Elastin-deficient SMCs exhibited greater contractile-to-proliferative phenotypic modulation in vitro than in vivo. We confirmed increased medial collagen without evidence of increased medial area or SMC number in a small ascending aorta with thickened media of a Williams syndrome subject.

CONCLUSIONS

Deficient circumferential growth is the predominant mechanism for moderate obstructive aortic disease resulting from partial elastin deficiency. Our findings suggest that diverse aortic manifestations in Williams syndrome result from graded elastin content, and SMC hyperplasia causing medial expansion requires additional elastin loss superimposed on ELN haploinsufficiency.

A lumped parameter model of mechanically mediated acute and long-term adaptations of contractility and geometry in lymphatics for characterization of lymphedema

A primary purpose of the lymphatic system is to transport fluid from peripheral tissues to the central venous system in order to maintain tissue-fluid balance. Failure to perform this task results in lymphedema marked by swelling of the affected limb as well as geometric remodeling and reduced contractility of the affected lymphatic vessels. The mechanical environment has been implicated in the regulation of lymphatic contractility, but it is unknown how changes in the mechanical environment are related to loss of contractile function and remodeling of the tissue. The purpose of this paper was to introduce a new theoretical framework for acute and long-term adaptations of lymphatic vessels to changes in mechanical loading. This theoretical framework combines a simplified version of a published lumped parameter model for lymphangion function and lymph transport, a published microstructurally motivated constitutive model for the active and passive mechanical behavior of isolated rat thoracic ducts, and novel models for acute mechanically mediated vasoreactive adaptations and long-term volumetric growth to simulate changes in muscle contractility and geometry of a single isolated rat thoracic duct in response to a sustained elevation in afterload. The illustrative examples highlight the potential role of the mechanical environment in the acute maintenance of contractility and long-term geometric remodeling, presumably aimed at meeting fluid flow demands while also maintaining mechanical homeostasis. Results demonstrate that contractility may adapt in response to shear stress to meet fluid flow demands and show that pressure-induced long-term geometric remodeling may attenuate these adaptations and reduce fluid flow. The modeling framework and illustrative simulations help suggest relevant experiments that are necessary to accurately quantify and predict the acute and long-term adaptations of lymphangions to altered mechanical loading.

Low-Cost Method to Monitor Patient Adherence to HIV Antiretroviral Therapy Using Multiplex Cathepsin Zymography

Monitoring patient adherence to HIV antiretroviral therapy (ART) by patient survey is inherently error prone, justifying a need for objective, biological measures affordable in low-resource settings where HIV/AIDS epidemic is highest. In preliminary studies conducted in Ethiopia and South Africa, we observed loss of cysteine cathepsin activity in peripheral blood mononuclear cells of HIV-positive patients on ART. We optimized a rapid protocol for multiplex cathepsin zymography to quantify cysteine cathepsins, and prospectively enrolled 350 HIV-positive, ART-naïve adults attending the Themba Lethu Clinic, Johannesburg, South Africa, to test if suppressed cathepsin activity could be a biomarker of ART adherence (103 patients were included in final analysis). Poor adherence was defined as detectable viral load (>400 copies/ml) or simplified medication adherence questionnaire, 4-6 months after ART initiation. 86 % of patients with undetectable viral loads after 6 months were cathepsin negative, and cathepsin-positive patients were twice as likely to have detectable viral loads (RR 2.32 95 % CI 1.26-4.29). Together, this demonstrates proof of concept that multiplex cathepsin zymography may be an inexpensive, objective method to monitor patient adherence to ART. Low cost of this electrophoresis-based assay makes it a prime candidate for implementation in resource-limited settings.

Efavirenz and ritonavir-boosted lopinavir use exhibited elevated markers of atherosclerosis across age groups in people living with HIV in Ethiopia

BACKGROUND

HIV patients on highly-active antiretroviral therapy (HAART) have shown elevated incidence of dyslipidemia, lipodystrophy, and markers of cardiovascular disease. Evidence is beginning to emerge that implicates efavirenz (EFV) as a potential mediator of early on-set cardiovascular disease.

METHODS

Pediatric and adult HIV-infected HAART-naïve, EFV-treated, nevirapine (NVP)-treated, and ritonavir-boosted lopinavir (LPV/r)-treated subjects were recruited from Black Lion Hospital in Addis Ababa, Ethiopia. Pulse wave velocity (PWV), carotid intima-media thickness (cIMT), carotid arterial stiffness, brachial artery flow-mediated dilation (FMD), body mass index, waist-to-hip circumference ratio, and skinfold thickness were measured. CD4+ cell count, fasting glucose, lipoprotein profiles and triglycerides were also determined. Results were segmented into pediatric (6-17 years of age), young adults (25-39 years old) and older adults (40-60 years old).

RESULTS

PWV was generally elevated in EFV- and LPV/r-treated subjects compared to NVP-treated subjects across age groups. cIMT was elevated in EFV- and LPV/r-treated compared to NVP-treated older adults and in EFV-treated compared to HAART-naïve older adults. FMD was impaired in EFV- and LPV/r-treated compared to HAART-naïve younger adults, in EFV-treated compared to NVP-treated young and older adults, and in LPV/r-treated compared to NVP-treated older adults. Differences in lipoprotein profiles and skinfold thickness with HAART regimen were observed in pediatric and young adults, but less so in older adults.

CONCLUSIONS

Whereas LPV/r and other protease inhibitors have long been recognized as mediators of HIV/HAART-associated atherosclerosis, this report supports the emerging evidence that EFV may also mediate cardiovascular disease in people living with HIV on HAART.

Quantification of the passive and active biaxial mechanical behaviour and microstructural organization of rat thoracic ducts

Mechanical loading conditions are likely to play a key role in passive and active (contractile) behaviour of lymphatic vessels. The development of a microstructurally motivated model of lymphatic tissue is necessary for quantification of mechanically mediated maladaptive remodelling in the lymphatic vasculature. Towards this end, we performed cylindrical biaxial testing of Sprague-Dawley rat thoracic ducts (n = 6) and constitutive modelling to characterize their mechanical behaviour. Spontaneous contraction was quantified at transmural pressures of 3, 6 and 9 cmH2O. Cyclic inflation in calcium-free saline was performed at fixed axial stretches between 1.30 and 1.60, while recording pressure, outer diameter and axial force. A microstructurally motivated four-fibre family constitutive model originally proposed by Holzapfel et al. (Holzapfel et al. 2000 J. Elast. 61, 1-48. (doi:10.1023/A:1010835316564)) was used to quantify the passive mechanical response, and the model of Rachev and Hayashi was used to quantify the active (contractile) mechanical response. The average error between data and theory was 8.9 ± 0.8% for passive data and 6.6 ± 2.6% and 6.8 ± 3.4% for the systolic and basal conditions, respectively, for active data. Multi-photon microscopy was performed to quantify vessel wall thickness (32.2 ± 1.60 µm) and elastin and collagen organization for three loading conditions. Elastin exhibited structural 'fibre families' oriented nearly circumferentially and axially. Sample-to-sample variation was observed in collagen fibre distributions, which were often non-axisymmetric, suggesting material asymmetry. In closure, this paper presents a microstructurally motivated model that accurately captures the biaxial active and passive mechanical behaviour in lymphatics and offers potential for future research to identify parameters contributing to mechanically mediated disease development.

Current Efavirenz (EFV) or ritonavir-boosted lopinavir (LPV/r) use correlates with elevate markers of atherosclerosis in HIV-infected subjects in Addis Ababa, Ethiopia

BACKGROUND

HIV patients on antiretroviral therapy have shown elevated incidence of dyslipidemia, lipodystrophy, and cardiovascular disease (CVD). Most studies, however, focus on cohorts from developed countries, with less data available for these co-morbidities in Ethiopia and sub-Saharan Africa.

METHODS

Adult HIV-negative (n = 36), treatment naïve (n = 51), efavirenz (EFV)-treated (n = 91), nevirapine (NVP)-treated (n = 95), or ritonavir-boosted lopinavir (LPV/r)-treated (n=44) subjects were recruited from Black Lion Hospital in Addis Ababa, Ethiopia. Aortic pressure, augmentation pressure, and pulse wave velocity (PWV) were measured via applanation tonometry and carotid intima-media thickness (cIMT) and carotid arterial stiffness, and brachial artery flow-mediated dilation (FMD) were measured via non-invasive ultrasound. Body mass index, waist-to-hip circumference ratio (WHR), skinfold thickness, and self-reported fat redistribution were used to quantify lipodystrophy. CD4+ cell count, plasma HIV RNA levels, fasting glucose, total-, HDL-, and LDL-cholesterol, triglycerides, hsCRP, sVCAM-1, sICAM-1, leptin and complete blood count were measured.

RESULTS

PWV and normalized cIMT were elevate and FMD impaired in EFV- and LPV/r-treated subjects compared to NVP-treated subjects; normalized cIMT was also elevated and FMD impaired in the EFV- and LPV/r-treated subjects compared to treatment-naïve subjects. cIMT was not statistically different across groups. Treated subjects exhibited elevated markers of dyslipidemia, inflammation, and lipodystrophy. PWV was associated with age, current EFV and LPV/r used, heart rate, blood pressure, triglycerides, LDL, and hsCRP, FMD with age, HIV duration, WHR, and glucose, and cIMT with age, current EFV use, skinfold thickness, and blood pressure.

CONCLUSIONS

Current EFV- or LPV/r-treatment, but not NVP-treatment, correlated with elevated markers of atherosclerosis, which may involve mechanisms distinct from traditional risk factors.