Assessing the role of gene therapy in the treatment of vascular disease

Nonviral gene therapy targeting cardiovascular system

The goal of gene therapy is either to introduce a therapeutic gene into or replace a defective gene in an individual's cells and tissues. Gene therapy has been urged as a potential method to induce therapeutic angiogenesis in ischemic myocardium and peripheral tissues after extensive investigation in recent preclinical and clinical studies. A successful gene therapy mainly relies on the development of the gene delivery vector. Developments in viral and nonviral vector technology including cell-based gene transfer will further improve transgene delivery and expression efficiency. Nonviral approaches as alternative gene delivery vehicles to viral vectors have received significant attention. Recently, a simple and safe approach of gene delivery into target cells using naked DNA has been improved by combining several techniques. Among the physical approaches, ultrasonic microbubble gene delivery, with its high safety profile, low costs, and repeatable applicability, can increase the permeability of cell membrane to macromolecules such as plasmid DNA by its bioeffects and can provide as a feasible tool in gene delivery. On the other hand, among the promising areas for gene therapy in acquired diseases, ischemic cardiovascular diseases have been widely studied. As a result, gene therapy using advanced technology may play an important role in this regard. The aims of this review focus on understanding the cellular and in vivo barriers in gene transfer and provide an overview of currently used chemical vectors and physical tools that are applied in nonviral cardiovascular gene transfer.

Extracorporal shock wave may enhance skin flap survival in an animal model

Several methods have been used in an attempt to increase blood supply and tissue perfusion in ischemic tissues. The authors investigated the effect of extracorporal shock wave (ESW) treatment on compromised skin flaps. For this purpose, the epigastric skin flap model in rats, based solely on the right inferior epigastric vessels was used. Twenty male Sprague-Dawley rats were divided into two groups (ESW-group, Control group) of 10 rats each. The ESW-group was administered 2500 impulses at 0.15 mJ/mm(2) immediately after surgery, whereas, the control group received no treatment. Flap viability was evaluated on day 7 after the operation. Standardised digital pictures of the flaps were taken and transferred to the computer, and necrotic zones relative to total flap surface area were measured and expressed as percentages. Overall, there was a significant reduction in the surface area of the necrotic zones of the flaps in the ESW group compared to the control group (ESW group: 2.2+/-1.9% versus control: 17.4+/-4.4% (p < 0.01). In this study, the authors demonstrated that treatment with ESW enhanced epigastric skin flap survival, as confirmed by the significant reduction of necrotic flap zones. ESW treatment seems to represent a feasible and cost effective method to improve blood supply in ischemic tissue.

Limb salvage after infrainguinal bypass graft failure

OBJECTIVE

The purpose of this study was to examine the outcome of patients in whom an infrainguinal bypass graft failed.

METHODS

This was a retrospective analysis of consecutive patients undergoing infrainguinal bypass grafting in a single institution over 8 years.

RESULTS

Six hundred thirty-one infrainguinal bypass grafts were placed in 578 limbs in 503 patients during the study period. The indication for surgery was limb-threatening ischemia in 533 patients (85%); nonautologous conduits were used in 259 patients (41%), and 144 (23%) were repeat operations. After a mean follow-up of 28 +/- 1 months (median, 23 months; range, 0-99 months), 167 grafts (26%) had failed secondarily. The rate of limb salvage in patients with graft failure was poor, only 50% +/- 5% at 2 years after failure. The 2-year limb salvage rate depended on the initial indication for bypass grafting: 100% in patients with claudication (n = 16), 55% +/- 8% in patients with rest pain (n = 49), and 34% +/- 6% in patients with tissue loss (n = 73; P <.001). The prospect for limb salvage also depended on the duration that the graft remained patent. Early graft failure (<30 days; n = 25) carried a poor prognosis, with 2-year limb salvage of only 25% +/- 10%; limb salvage was 53% +/- 5% after intermediate graft failure (<2 years, n = 110) and 79% +/- 10% after late failure (>2 years, n = 15; P =.04). Multivariate analysis revealed shorter patency interval before failure (P =.006), use of warfarin sodium (Coumadin) postoperatively (P =.006), and infrapopliteal distal anastomosis (P =.01) as significant predictors for ultimate limb loss.

CONCLUSION

The overall prognosis for limb salvage in patients with failed infrainguinal bypass grafts is poor, particularly in patients with grafts placed because of tissue loss and those with early graft failure.

Gene therapy progress and prospects: therapeutic angiogenesis for limb and myocardial ischemia

After extensive investigation in preclinical studies and recent clinical trials, gene therapy has been established as a potential method to induce therapeutic angiogenesis in ischemic myocardial and limb disease. Advancements in viral and nonviral vector technology including cell-based gene transfer will continue to improve transgene transmission and expression efficiency. An alternative strategy to the use of transgenes encoding angiogenic growth factors is therapy based on transcription factors such as hypoxia-inducible factor-1alpha (HIF-1alpha) that regulate the expression of multiple angiogenic genes. Further understanding of the underlying biology of neovascularization is needed to determine the ability of growth factors to induce functionally significant angiogenesis in patients with atherosclerotic disease and associated comorbid conditions including endothelial dysfunction, which may inhibit blood vessel growth. The safety and tolerability of therapeutic angiogenesis by gene transfer has been demonstrated in phase I clinical trials. However, limited evidence of efficacy resulted from early phase II studies of angiogenic gene therapy for ischemic myocardial and limb disease. The utility of therapeutic angiogenesis by gene transfer as a treatment option for ischemic cardiovascular disease will be determined by adequately powered, randomized, placebo-controlled phase II and III clinical trials.

Effect of transfection time on the survival of epigastric skin flaps pretreated with adenovirus encoding the VEGF gene

An experimental study was conducted to investigate the effect of time of adenovirus-mediated vascular endothelial growth factor (VEGF) gene therapy on the viability of epigastric skin flaps. Eighty-four male Sprague-Dawley rats were used. Skin flaps measuring 8 x 8 cm were marked on the ventral abdominal wall. The upper border of the flap was 1 cm above the costal margin, and the lower border was at the pubis and the inguinal fold. The lateral borders of the flap corresponded to the location of the distinct conversion of the thin ventral skin to the thick dorsal skin. Seven sites in the predicted area of necrosis on the outlined skin flaps were chosen for subdermal injections. All injections were administered by an individual who was blinded to the different treatment groups. The rats received either saline (control group I, N = 28) or adenovirus encoding green fluorescent protein (Ad-GFP; group II, N = 28) or Ad-VEGF (group III, N = 28). The epigastric island skin flaps based solely on the right inferior epigastric vessels were elevated either on the same day of injection (day 0 = 12 hours after transfection, N = 7) or on day 3 (N = 7), day 7 (N = 7), or day 14 (N = 7) after subdermal gene therapy. Flaps were sutured back to their native configuration. Flap viability was evaluated on day 7 after surgery. Sections of the flaps were examined histologically after undergoing hematoxylin-eosin staining. There was a significant reduction in mean percentage of necrotic flap area by 56%, 67%, 70%, and 54% in flaps transfected with Ad-VEGF, 12 hours, 3 days, 7 days, and 14 days before flap elevation, respectively ( < 0.05). There was no evidence that the mean percentage of skin necrosis in the Ad-GFP group was different than in the control group ( = 0.26). There was evidence of mild inflammation in flaps pretreated with Ad-GFP and Ad-VEGF compared with the control group. The authors demonstrated that adenovirus-mediated gene therapy of the abdominal skin after subdermal injections was technically feasible. This was demonstrated by the visualization of GFP expression in control experiments using a fluorescence microscope. In this study, adenovirus-mediated VEGF gene therapy promoted epigastric flap survival, which was not related to the time of transfection. These findings raise the possibility that pretreatment with VEGF gene therapy using an adenovirus vector may be applicable in patients at risk for plastic surgery.