External-beam radiation therapy for improved dialysis access patency: feasibility and early safety

Radiation suppresses neointimal hyperplasia through affecting proliferation and apoptosis of vascular smooth muscle cells

PURPOSE

To study the effect of x-ray radiotherapy on vascular smooth muscle cells (VSMCs) and elucidate the mechanisms in preventing neointimal hyperplasia of prosthetic vascular grafts.

MATERIALS AND METHODS

In model I, twelve mongrel dogs underwent revascularization with prosthetic grafts and half the dogs underwent irradiation of the grafts at 28 Gy. In model II, human VSMCs (hVSMCs) were maintained and divided into six groups to which external radiation was applied at six different doses: 0 Gy, 2 Gy, 8 Gy, 16 Gy, 24 Gy and 30 Gy. In both models, specimens were harvested and examined by using morphological, immunological, cellular and molecular methods.

RESULTS

After irradiation, the neointima thickness was significantly lower in irradiated groups (p≤0.01). The radiotherapy could up-regulate p27^kip1, and down-regulate proliferating cell nuclear antigen (PCNA) and S phase kinase associated protein 2 (Skp2). X-ray irradiation inhibits the proliferation of hVSMCs via acting on G1/S phase of cell cycle. The apoptosis of hVSMCs increased significantly with dose and time. The expression of PCNA and Skp2 were decreased after a first increasing trend with dose, but had a significant negative correlation with time. The expression of p27^kip1 had a significant positive correlation with dose and time.

CONCLUSIONS

Postoperative external fractionated irradiation after prosthetic vessel replacement of the abdominal aorta suppressed the development of hyperplasia in the graft neointima in the short term. There was a prominent time- and dose-dependent inhibition of VSMC proliferation by radiation when it was administered.

Radiation therapy for dialysis access stenosis: unfulfilled promise or false expectations

Hemodialysis vascular access dysfunction is a major cause of morbidity and hospitalization in the hemodialysis population at a cost of well over $1 billion per annum. Venous stenosis (due to venous neointimal hyperplasia [VNH]) is the most common cause of polytetrafluroethylene PTFE) dialysis access graft and arteriovenous fistula (AVF) failure. Despite the magnitude of the clinical problem, however, there are currently no effective therapies for this condition. We and others have previously demonstrated that VNH in PTFE dialysis grafts and AVF is composed of smooth muscle cells/myofibroblasts, endothelial cells within neointimal microvessels, and peri-graft macrophages. Radiation therapy blocks the proliferation and activation of all these cell types. The current review will dissect out the available in vitro, experimental, and clinical data on the use of radiation therapy for vascular stenosis in general, and for dialysis access dysfunction in particular. It is important to try and identify whether there is still a role for radiation therapy in this specific clinical setting. We believe that this is a critically important question to answer in view of the huge unmet clinical need that is currently associated with hemodialysis vascular access dysfunction.

High-dose preoperative fractionated radiotherapy does not affect the patency and healing of ePTFE vascular prosthesis after replacement of canine abdominal aorta and inferior vena cava

BACKGROUND

Fractionated radiotherapy allows for the safe administration of larger doses without the development of immediate or late toxicity. The influence of preoperative fractionated radiotherapy on neointima formation for expanded polytetrafluoroethylene (ePTFE) graft has not been determined.

METHODS

Twenty mongrel dogs were randomly divided into radiotherapy group (a total dose of 35 Gy) or control group (no radiation). The infrarenal abdominal aorta and inferior vena cava were replaced by ePTFE grafts at 3 months after irradiation in the radiotherapy group. Grafts were explanted at 4 weeks after surgery. Histopathological techniques were undertaken to evaluate graft neointima formation. The control group was managed the same as the radiotherapy group except for not receiving irradiation.

RESULTS

Four grafts implanted into inferior vena cava in the irradiated group and three in the control group were found to be completely occluded. None of the grafts implanted into abdominal aorta were obstructed. In the case of the inferior vena cava graft, the thickness of the graft neointima did not differ significantly between the irradiated and control groups. However, for the abdominal aorta graft, the neointima thickness in the irradiated groups was significantly thinner than that in the control group.

CONCLUSION

Preoperative fractionated radiotherapy affects vascular healing via suppressing the development of neointima formation in the abdominal aorta graft.