Tumor necrosis factor-alpha and the early vein graft

The Exacerbating Effects of the Tumor Necrosis Factor in Cardiovascular Stenosis: Intimal Hyperplasia

TNF-α functions as a master regulator of inflammation, and it plays a prominent role in several immunological diseases. By promoting important cellular mechanisms, such as cell proliferation, migration, and phenotype switch, TNF-α induces its exacerbating effects, which are the underlying cause of many proliferative diseases such as cancer and cardiovascular disease. TNF-α primarily alters the immune component of the disease, which subsequently affects normal functioning of the cells. Monoclonal antibodies and synthetic drugs that can target TNF-α and impair its effects have been developed and are currently used in the treatment of a few select human diseases. Vascular restenosis is a proliferative disorder that is initiated by immunological mechanisms. In this review, the role of TNF-α in exacerbating restenosis resulting from neointimal hyperplasia, as well as molecular mechanisms and cellular processes affected or induced by TNF-α, are discussed. As TNF-α-targeting drugs are currently not approved for the treatment of restenosis, the summation of the topics discussed here is anticipated to provide information that can emphasize on the use of TNF-α-targeting drug candidates to prevent vascular restenosis.

Short-term Pre-operative Methionine Restriction Induces Browning of Perivascular Adipose Tissue and Improves Vein Graft Remodeling in Mice

Short-term preoperative methionine restriction (MetR) shows promise as a translatable strategy to modulate the body's response to surgical injury. Its application, however, to improve post-interventional vascular remodeling remains underexplored. Here, we find that MetR protects from arterial intimal hyperplasia in a focal stenosis model and adverse vascular remodeling after vein graft surgery. RNA sequencing reveals that MetR enhances the brown adipose tissue phenotype in arterial perivascular adipose tissue (PVAT) and induces it in venous PVAT. Specifically, PPAR-α was highly upregulated in PVAT-adipocytes. Furthermore, MetR dampens the post-operative pro-inflammatory response to surgery in PVAT-macrophages in vivo and in vitro . This study shows for the first time that the detrimental effects of dysfunctional PVAT on vascular remodeling can be reversed by MetR, and identifies pathways involved in browning of PVAT. Furthermore, we demonstrate the potential of short-term pre-operative MetR as a simple intervention to ameliorate vascular remodeling after vascular surgery.

A hierarchical and collaborative BRD4/CEBPD partnership governs vascular smooth muscle cell inflammation

Bromodomain protein BRD4 reads histone acetylation (H3K27ac), an epigenomic mark of transcription enhancers. CCAAT enhancer binding protein delta (CEBPD) is a transcription factor typically studied in metabolism. While both are potent effectors and potential therapeutic targets, their relationship was previously unknown. Here we investigated their interplay in vascular smooth muscle cell (SMC) inflammation. Chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq) revealed H3K27ac/BRD4 enrichment at Cebpd in injured rat carotid arteries. While genomic deletion of BRD4-associated enhancer in SMCs in vitro decreased Cebpd transcripts, BRD4 gene silencing also diminished Cebpd mRNA and protein, indicative of a BRD4 control over CEBPD expression. Bromodomain-1, but not bromodomain-2, accounted for this BRD4 function. Moreover, endogenous BRD4 protein co-immunoprecipitated with CEBPD, and both proteins co-immunoprecipitated the Cebpd promoter and enhancer DNA fragments. These co-immunoprecipitations (coIPs) were all abolished by the BRD4-bromodomain blocker JQ1, suggesting a BRD4/CEBPD /promoter/enhancer complex. While BRD4 and CEBPD were both upregulated upon tumor necrosis factor alpha (TNF-α) stimulation of SMC inflammation (increased interleukin [IL]-1b, IL-6, and MCP-1), they mediated this stimulation via preferentially elevated expression of platelet-derived growth factor receptor alpha (PDGFRα, versus PDGFRβ), as indicated by loss- and gain-of-function experiments. Taken together, our study unravels a hierarchical yet collaborative BRD4/CEBPD relationship, a previously unrecognized mechanism that prompts SMC inflammation and may underlie other pathophysiological processes as well.

Molecular differences between arterial and venous grafts in the first year after coronary artery bypass grafting

Despite commonly used for coronary artery bypass surgery, saphenous vein (SV) grafts have significantly lower patency rates in comparison to internal thoracic artery (ITA) grafts, which might be due to the structural characteristics of the vessel wall but also due to differences in oxidative stress adaptation and molecular signaling and regulation. This human post mortem study included a total of 150 human bypass grafts (75 SV grafts and 75 ITA grafts) obtained from 60 patients divided into five groups due to the time period of implantation: group 1: baseline group without grafting; group 2: 1 day; group 3: > 1 day-1 week; group 4: > 1 week-1 month; group 5: > 1 month-1 year. Pieces of 3 mm length were fixed with formaldehyde, dehydrated, wax embedded, cut into sections of 3 µm thickness, and histologically and immunohistochemically examined. Over the whole time period, we observed a lower neointima formation and a better preserved media in ITA grafts with a higher percentage of TNF-α, PDGFR-α, and VEGF-A in nearly all vessel wall layers, a higher amount of MMP-7, MMP-9, EGFR, and bFGF positive cells in SV grafts and a timely different peak not only between ITA and SV grafts but also within the various vessel wall layers of both graft types. Since most of the examined growth factors, growth factor receptors and cytokines are regulated by MAPKs, our results suggest an activation of different pathways in both vessel graft types immediately after bypass grafting.

Smooth muscle cell-specific Tgfbr1 deficiency attenuates neointimal hyperplasia but promotes an undesired vascular phenotype for injured arteries

Neointimal hyperplasia (NIH) and inward wall remodeling cause arterial restenosis and failure of bypass vein grafts. Previous studies from our group suggest that transforming growth factor (TGF) β promotes these pathologies via regulating cell kinetics at the early stage and matrix metabolism at the late stage. Although these temporal TGFβ effects may result from its signaling in different cell groups, the responsible cell type has not been identified. In the current study, we evaluated the effect of smooth muscle cell (SMC)‐specific TGFβ signaling through its type I receptor TGFBR1 on NIH and wall remodeling of the injured femoral arteries (FAs). An inducible Cre/loxP system was employed to delete SMC Tgfbr1 (Tgfbr1^iko). Mice not carrying the Cre allele (Tgfbr1^f/f) served as controls. The injured FAs were evaluated on d3, d7, and d28 postoperatively. Tgfbr1^iko attenuated NIH by 92%, but had insignificant influence on arterial caliber when compared with Tgfbr1^f/f controls on d28. This attenuation correlated with greater cellularity and reduced collagen content. Compared with Tgfbr1^f/fFAs, however, Tgfbr1^ikoFAs exhibited persistent neointimal cell proliferation and cell apoptosis, with both events at a greater rate on d28. Tgfbr1^ikoFAs additionally contained fewer SMCs and more inflammatory infiltrates in the neointima and displayed a thicker adventitia than did Tgfbr1^f/fFAs. More MMP9 proteins were detected in the adventitia of Tgfbr1^ikoFAs than in that of Tgfbr1^f/f controls. Our results suggest that disruption of SMC Tgfbr1 inhibits arterial NIH in the short term, but the overall vascular phenotype may not favor long‐term performance of the injured arteries.

Diet-induced obesity drives negative mouse vein graft wall remodeling

INTRODUCTION

The heightened inflammatory phenotype associated with obesity has been linked to the development of cardiovascular diseases. Short-term high-fat feeding induces a proinflammatory state that may impact the blood vessel wall. CD11c, a significantly increased dendritic cell biomarker during diet-induced obesity (DIO), may have a mechanistic role in this high-fat feeding effect. We hypothesized that the proinflammatory effect of short-term DIO accelerates vein bypass graft failure via CD11c-dependent mechanisms.

METHODS

Male 9-week-old DIO mice (n = 13, C57BL/6J recipients; n = 6, CD11c(-/-) recipients) and normal chow controls (n = 15, C57BL/6J recipients; n = 6, CD11c(-/-) recipients) underwent unilateral carotid interposition vein isografting (inferior vena cava from the same diet and genetic background donor), with a midgraft or outflow focal stenosis. Vein grafts were harvested at either 1 week (immunohistochemical staining for early CD11c expression) or 4 weeks later (morphometric analyses and CD11c evaluation).

RESULTS

Despite a 40% larger body size, C57BL/6J DIO mice had 44% smaller poststenosis vein graft lumens (P = .03) than their controls via an acceleration of overall negative vein graft wall remodeling in the day-28 midgraft focal stenosis model but not in the outflow stenosis model. Higher CD11c expression occurred in DIO midgraft-stenosis vein graft walls, both at postoperative days 7 and 28. In contrast, with in vivo CD11c deficiency, DIO did not elicit this poststenotic negative remodeling but attenuated intimal hyperplasia.

CONCLUSIONS

These findings highlight negative wall remodeling as a potential factor leading to vein graft failure and provide direct evidence that short-term dietary alterations in the mammalian metabolic milieu can have lasting implications related to acute vascular interventions. DIO induces negative mouse vein graft wall remodeling via CD11c-depedent pathways.

Rule-based model of vein graft remodeling

When vein segments are implanted into the arterial system for use in arterial bypass grafting, adaptation to the higher pressure and flow of the arterial system is accomplished thorough wall thickening and expansion. These early remodeling events have been found to be closely coupled to the local hemodynamic forces, such as shear stress and wall tension, and are believed to be the foundation for later vein graft failure. To further our mechanistic understanding of the cellular and extracellular interactions that lead to global changes in tissue architecture, a rule-based modeling method is developed through the application of basic rules of behaviors for these molecular and cellular activities. In the current method, smooth muscle cell (SMC), extracellular matrix (ECM), and monocytes are selected as the three components that occupy the elements of a grid system that comprise the developing vein graft intima. The probabilities of the cellular behaviors are developed based on data extracted from in vivo experiments. At each time step, the various probabilities are computed and applied to the SMC and ECM elements to determine their next physical state and behavior. One- and two-dimensional models are developed to test and validate the computational approach. The importance of monocyte infiltration, and the associated effect in augmenting extracellular matrix deposition, was evaluated and found to be an important component in model development. Final model validation is performed using an independent set of experiments, where model predictions of intimal growth are evaluated against experimental data obtained from the complex geometry and shear stress patterns offered by a mid-graft focal stenosis, where simulation results show good agreements with the experimental data.

Perivascular innate immune events modulate early murine vein graft adaptations

OBJECTIVE

Innate immunity drives numerous cardiovascular pathologies. Vein bypass grafting procedures are frequently accompanied by low-grade wound contamination. We hypothesized that a peri-graft innate immune challenge, via an outside-in route, augments inflammatory responses, which subsequently drive a component of negative vein graft wall adaptations; moreover, adipose tissue mediates this immune response.

METHODS

The inferior vena cava from a donor mouse was implanted into the common carotid artery of a recipient mouse utilizing a validated cuff technique (9-week-old male C57BL/6J mice). Slow-release low-dose (5 μg) lipopolysaccharide (LPS) (n = 9) or vehicle (n = 9) was applied peri-graft; morphologic analysis was completed (day 28). In parallel, vein-grafted mice received peri-graft LPS (n = 12), distant subcutaneous LPS (n = 6), or vehicle (n = 12), then day-1 and -3 harvest of grafts and adipose tissue for cytokines and toll-like receptor (TLR) signaling mRNA expression (qRT-PCR).

RESULTS

All recipient mice survived, and all vein grafts were patent. Acute low-dose local LPS challenge enhanced vein graft lumen loss (P = .04) and tended to augment intimal hyperplasia (P = .06). The surgical trauma of vein grafting universally upregulated key pro- and anti-inflammatory mediators within the day-1 graft wall, but varied on TLR signaling gene expression. Local and distant LPS accentuated these patterns until at least postoperative day 3. LPS challenge enhanced the inflammatory response in adipose tissue (locally > distantly); local LPS upregulated adipose TLR-4 dramatically.

CONCLUSIONS

Perivascular and distant inflammatory challenges potentiate the magnitude and duration of inflammatory responses in the early vein graft wall, negatively modulating wall adaptations, and thus, potentially contribute to vein graft failure. Furthermore, surgery activates innate immunity in adipose tissue, which is augmented (regionally > systemically) by LPS. Modulation of these local and distant inflammatory signaling networks stands as a potential strategy to enhance the durability of vascular interventions such as vein grafts.

Oral intake of hydrogen-rich water inhibits intimal hyperplasia in arterialized vein grafts in rats

AIMS

Arterialized vein grafts often fail due to intimal hyperplasia. Hydrogen potently protects organs and cells from many insults via its anti-inflammatory and antioxidant properties. We investigated the efficacy of oral administration of hydrogen-rich water (HW) for prevention of intimal hyperplasia.

METHODS AND RESULTS

The inferior vena cava was excised, stored in cold Ringer solution for 2 h, and placed as an interposition graft in the abdominal aorta of syngeneic Lewis rats. HW was generated by immersing a magnesium stick in tap water (Mg + 2H(2)O → Mg (OH)(2) + H(2)). Beginning on the day of graft implantation, recipients were given tap water [regular water (RW)], HW or HW that had been subsequently degassed water (DW). Six weeks after grafting, the grafts in the rats given RW or DW had developed intimal hyperplasia, accompanied by increased oxidative injury. HW significantly suppressed intimal hyperplasia. One week after grafting, the grafts in HW-treated rats exhibited improved endothelial integrity with less platelet and white blood cell aggregation. Up-regulation of the mRNAs for intracellular adhesion molecules was attenuated in the vein grafts of the rats receiving HW. Activation of p38 mitogen-activated protein kinase, matrix metalloproteinase (MMP)-2, and MMP-9 was also significantly inhibited in grafts receiving HW. In rat smooth muscle cell (A7r5) cultures, hydrogen treatment for 24 h reduced smooth muscle cell migration.

CONCLUSION

Drinking HW significantly reduced neointima formation after vein grafting in rats. Drinking HW may have therapeutic value as a novel therapy for intimal hyperplasia and could easily be incorporated into daily life.

Immobilized contrast-enhanced MRI: Gadolinium-based long-term MR contrast enhancement of the vein graft vessel wall

An implantable MR contrast agent that can be covalently immobilized on tissue during surgery has been developed. The rationale is that a durable increase in tissue contrast using an implantable contrast agent can enhance postsurgical tissue differentiation using MRI. For small-vessel (e.g., vein graft) MRI, the direct benefit of such permanent "labeling" of the vessel wall by modification of its relaxation properties is to achieve more efficient imaging. This efficiency can be realized as either increased contrast leading to more accurate delineation of vessel wall and lesion tissue boundaries, or, faster imaging without penalizing contrast-to-noise ratio, or a combination thereof. We demonstrate, for the first time, stable long-term MRI enhancement using such an exogenous contrast mechanism based on immobilizing a modified diethylenetriaminepentaacetic acid gadolinium(3+) dihydrogen complex on a human vein using a covalent amide bond. Signal enhancement due to the covalently immobilized contrast agent is demonstrated for excised human vein specimens imaged at 3 T, and its long-term stability is demonstrated during a 4-month incubation period.

Cytokines and the early vein graft: strategies to enhance durability

This brief review focuses on experimental studies linking the proinflammatory cytokine tumor necrosis factor-alpha to accelerated vein graft failure in the broader historical context of vein graft research. From some perspectives, the field appears ripe for transfer of cytokine knowledge and therapeutic approaches that have evolved in other systems to vascular surgery problems. However, the complexity of vein graft disease suggests that more robust research approaches, such as broadening of the scope beyond focus on single mediators and neointimal hyperplasia, will be necessary to reach translatable strategies to prolong human vein graft durability.