Candidate gene analysis of arteriovenous fistula failure in hemodialysis patients

Association of vitamin D receptor gene TaqI, FokI and ApaI variants with arteriovenous fistula failure in hemodialysis patients

PURPOSE

We investigated the influence of the vitamin D receptor gene TaqI (rs731236), ApaI (rs7975232), and FokI (rs2228570) polymorphisms in arteriovenous fistula failure in hemodialysis patients.

METHODS

This study was carried out with 54 patients who experienced two or more fistula failures in the late period after arteriovenous fistula operation and 58 control patients with no history of arteriovenous fistula failure in 3 years or longer. The polymerase chain reaction-restriction fragment length polymorphism method was used to determine the vitamin D receptor TaqI, FokI, and ApaI polymorphisms.

RESULTS

For vitamin D receptor gene TaqI and Fok1 polymorphisms, no significant association was found between the two groups ( p > 0.05). However, a statistically significant association was determined for ApaI polymorphism between the two groups ( p = 0.02). In patients, ApaI AA, AC, and CC genotype frequencies were found as 21 (38.9%), 32 (59.3%), and 1 (1.8%), respectively. However, genotype frequencies of AA, AC, and CC in the control group were 29 (50%), 22 (37.9%), and 7 (12.1%), respectively. In all three polymorphisms, no significant difference was found between the two groups in terms of allele frequencies ( p > 0.05).

CONCLUSION

Vitamin D receptor ApaI AC genotype may be a possible cardiovascular risk factor for the development of arteriovenous fistula failure.

Post-operative arterio-venous fistula blood flow influences primary and secondary patency following access surgery

PURPOSE

Primary arteriovenous fistula arterio venous fistula (AVF) formation has proven to be the best and optimal vascular access for the majority of haemodialysis patients. At present there are limited data to suggest which haemodynamic parameters most correlate with the likelihood of early failure. The aim of this study is to identify the haemodynamic predictors of early failure, hence identify which fistulae may benefit from timely pre-emptive intervention.

MATERIAL AND METHODS

Retrospective analysis of data was performed of 201 patients undergoing native AVF creation over a one year period. Demographic details, co-morbidity, preoperative vessel calibre were collected. Flow was measured by duplex ultrasound post operatively.

RESULTS

Preoperative vein calibre (p = 0.01) and fistula flow (p < 0.001) positively affected primary patency. Age, gender, ethnicity, type of fistula, hypertension and preoperative arterial calibre did not influence outcome. Regression analysis showed that the strength of correlation between early postoperative fistula flow and patency decreased progressively with time. Six week flow predicts early, but not late, failure. ROC analysis identified 300 ml/min flow as the best predictor of patency. Fistulae with flow above 300 ml/min were more likely to remain patent over the next 12 months (p < 0.001, HR = 7.4).

CONCLUSION

Postoperative fistula flow of less than 300 ml/min identifies AVFs at high risk of early failure. These may be candidates for early intervention with balloon assisted maturation. The findings of this retrospective cohort study strongly support the need for a more robust prospectively designed trial identifying haemodynamic factors that can predict mid and long-term AVF patency.

The association of genotype polymorphisms with vascular access patency in hemodialysis patients

Some hemodialysis patients suffer from repeat dysfunction of dialysis vascular access and need procedures of angioplasty, thrombectomy, and even temporary catheter use. Why these patients are vulnerable to vascular access dysfunction and how to improve its patency are imperative to be discovered. Traditional risk factors for vascular access function had been widely investigated but could not fully explain this question. Several genotype polymorphisms were demonstrated to increase the incidence of cardiovascular disease and might also be linked to higher risk of vascular access dysfunction. As the major causes of arteriovenous access thrombosis are hypercoagulable status and arteriovenous access stenosis, the investigated genes mainly focus on the mediators of the coagulation cascade, inflammatory process, and endothelial dysfunction. The reported polymorphisms of genes significantly associated with arteriovenous access dysfunction included genes encoding methylene tetrahydrofolate reductase, coagulation factors, heme oxygenase-1, matrix metalloproteinase, transforming growth factor-β1, tumor necrosis factor-α, vascular endothelial growth factor-A, renin-angiotensin-aldosterone system, and protein methyl transferase. However, further prospective study is indispensable to elucidate the association between the genotype polymorphisms and the outcome of vascular access. More and more therapeutic options that focus on genotype polymorphisms may generate a great benefit to the patency of vascular access of uremic patients.

The molecular mechanisms of hemodialysis vascular access failure

The arteriovenous fistula has been used for more than 50 years to provide vascular access for patients undergoing hemodialysis. More than 1.5 million patients worldwide have end stage renal disease and this population will continue to grow. The arteriovenous fistula is the preferred vascular access for patients, but its patency rate at 1 year is only 60%. The majority of arteriovenous fistulas fail because of intimal hyperplasia. In recent years, there have been many studies investigating the molecular mechanisms responsible for intimal hyperplasia and subsequent thrombosis. These studies have identified common pathways including inflammation, uremia, hypoxia, sheer stress, and increased thrombogenicity. These cellular mechanisms lead to increased proliferation, migration, and eventually stenosis. These pathways work synergistically through shared molecular messengers. In this review, we will examine the literature concerning the molecular basis of hemodialysis vascular access malfunction.

Future research directions to improve fistula maturation and reduce access failure

With the increasing prevalence of end-stage renal disease, there is a growing need for hemodialysis. Arteriovenous fistulae (AVF) are the preferred type of vascular access for hemodialysis, but maturation and failure continue to present significant barriers to successful fistula use. AVF maturation integrates outward remodeling with vessel wall thickening in response to drastic hemodynamic changes in the setting of uremia, systemic inflammation, oxidative stress, and pre-existent vascular pathology. AVF can fail due to both failure to mature adequately to support hemodialysis and development of neointimal hyperplasia that narrows the AVF lumen, typically near the fistula anastomosis. Failure due to neointimal hyperplasia involves vascular cell activation and migration and extracellular matrix remodeling with complex interactions of growth factors, adhesion molecules, inflammatory mediators, and chemokines, all of which result in maladaptive remodeling. Different strategies have been proposed to prevent and treat AVF failure based on current understanding of the modes and pathology of access failure; these approaches range from appropriate patient selection and use of alternative surgical strategies for fistula creation, to the use of novel interventional techniques or drugs to treat failing fistulae. Effective treatments to prevent or treat AVF failure require a multidisciplinary approach involving nephrologists, vascular surgeons, and interventional radiologists, careful patient selection, and the use of tailored systemic or localized interventions to improve patient-specific outcomes. This review provides contemporary information on the underlying mechanisms of AVF maturation and failure and discusses the broad spectrum of options that can be tailored for specific therapy.

Candidate Gene Analysis of Mortality in Dialysis Patients

Background

Dialysis patients have high cardiovascular mortality risk. This study aimed to investigate the association between SNPs of genes involved in vascular processes and mortality in dialysis patients.

Methods

Forty two SNPs in 25 genes involved in endothelial function, vascular remodeling, cell proliferation, inflammation, coagulation and calcium/phosphate metabolism were genotyped in 1330 incident dialysis patients. The effect of SNPs on 5-years cardiovascular and non-cardiovascular mortality was investigated.

Results

The mortality rate was 114/1000 person-years and 49.4% of total mortality was cardiovascular. After correction for multiple testing, VEGF rs699947 was associated with all-cause mortality (HR1.48, 95% CI 1.14–1.92). The other SNPs were not associated with mortality.

Conclusions

This study provides further evidence that a SNP in the VEGF gene may contribute to the comorbid conditions of dialysis patients. Future studies should unravel the underlying mechanisms responsible for the increase in mortality in these patients.

Role of pharmacogenomics in dialysis and transplantation

PURPOSE OF REVIEW

Pharmacogenomics is the study of differences in drug response on the basis of individual genetic background. With rapidly advancing genomic technologies and decreased costs of genotyping, the field of pharmacogenomics continues to develop. Application to patients with kidney disease provides growing opportunities for improving drug therapy.

RECENT FINDINGS

Pharmacogenomics studies are lacking in patients with chronic kidney disease and dialysis, but are abundant in the kidney transplant field. A potentially clinically actionable genetic variant exists in the CYP3A5 gene, with the initial tacrolimus dose selection being optimized based on CYP3A5 genotype. Although many pharmacogenomics studies have focused on transplant immunosuppression pharmacokinetics, an expanding literature on pharmacodynamic outcomes, such as calcineurin inhibitor toxicity and new onset diabetes, is providing new information on patients at risk.

SUMMARY

Appropriately powered pharmacogenomics studies with well-defined phenotypes are needed to validate existing studies and unearth new findings in patients with kidney disease, especially the chronic kidney disease and dialysis population.

A Patient with Recurrent Arteriovenous Graft Thrombosis

Arteriovenous grafts (AVGs) are prone to frequent thrombosis that is superimposed on underlying hemodynamically significant stenosis, most commonly at the graft-vein anastomosis. There has been great interest in detecting AVG stenosis in a timely fashion and performing preemptive angioplasty, in the belief that this will prevent AVG thrombosis. Three surveillance methods (static dialysis venous pressure, flow monitoring, and duplex ultrasound) can detect AVG stenosis. Whereas observational studies have reported that surveillance with preemptive angioplasty substantially reduces AVG thrombosis, randomized clinical trials have failed to confirm such a benefit. There is a high frequency of early AVG restenosis after angioplasty caused by aggressive neointimal hyperplasia resulting from vascular injury. Stent grafts prevent AVG restenosis better than balloon angioplasty, but they do not prevent AVG thrombosis. Several pharmacologic interventions to prevent AVG failure have been evaluated in randomized clinical trials. Anticoagulation or aspirin plus clopidogrel do not prevent AVG thrombosis, but increase hemorrhagic events. Treatment of hyperhomocysteinemia does not prevent AVG thrombosis. Dipyridamole plus aspirin modestly decreases AVG stenosis or thrombosis. Fish oil substantially decreases the frequency of AVG stenosis and thrombosis. In patients who have exhausted all options for vascular access in the upper extremities, thigh AVGs are a superior option to tunneled internal jugular vein central vein catheters (CVCs). An immediate-use AVG is a reasonable option in patients with recurrent CVC dysfunction or infection. Tunneled femoral CVCs have much worse survival than internal jugular CVCs.

Novel paradigms for dialysis vascular access: downstream vascular biology--is there a final common pathway?

Vascular access dysfunction is a major cause of morbidity and mortality in hemodialysis patients. The most common cause of vascular access dysfunction is venous stenosis from neointimal hyperplasia within the perianastomotic region of an arteriovenous fistula and at the graft-vein anastomosis of an arteriovenous graft. There have been few, if any, effective treatments for vascular access dysfunction because of the limited understanding of the pathophysiology of venous neointimal hyperplasia formation. This review will (1) describe the histopathologic features of hemodialysis access stenosis; (2) discuss novel concepts in the pathogenesis of neointimal hyperplasia development, focusing on downstream vascular biology; (3) highlight future novel therapies for treating downstream biology; and (4) discuss future research areas to improve our understanding of downstream biology and neointimal hyperplasia development.