The first attempt that proved that local delivery of vincristine in a safe concentration is safe and effective and can cause chemical denervation of the sympathetic nervous system of the renal artery was performed in 2011. A dedicated catheter for the local delivery of vincristine in the media layer or the renal artery was created in the laboratory of the First Department of Cardiology of the University of Athens. This catheter consisted of a modified conventional non-compliant balloon angioplasty catheter. Six sideholes of 25 μm diameter were created circumferentially across the balloon in fixed intervals of 60°. The catheter was checked in vitro so that different balloon inflation pressures could create different pressures of vincristine delivery (Fig. 14.2). The experimental model chosen for this protocol were 14 juvenile Landrace swine (3–5 months old, weight 28 ± 0.5 kg). In order to visualize under fluoroscopy the process, a mixture of vincristine was diluted to a final concentration of 25 mg/l in a mixture consisting of 20 ml of sterile 0.9 % NaCl solution and 20 ml of contrast. The mixture used for the placebo procedure, contained 20 ml of sterile 0.9 % NaCl solution and 20 ml of contrast, without the addition of vincristine. The protocol of the procedure was the following: The experiment was performed with the animals under general anesthesia, with continuous monitoring of the vital signs. The trachea was intubated with a 6.5–7.0 mm cuffed tracheal tube and ventilation was performed via a mechanical respirator. General anesthesia was maintained via 1–2 % isoflurane and oxygen. After the insertion of a 6 Fr introducer sheath though the right femoral artery, an initial (reference) angiogram was performed in both renal arteries using a 6 Fr Judkins Right four guiding catheter in order to evaluate the preprocedural anatomy of the arteries and define the desired segment of the renal artery for chemical denervation. The femoral catheter was used to obtain blood samples and to monitor systolic arterial pressure, diastolic arterial pressure mean arterial pressure and heart rate before, immediately after and 28 days after the procedure. The systolic arterial pressure, diastolic arterial pressure, mean arterial pressure and the heart rate, derived from pulsatile arterial pressure, were recorded continuously during the procedure. After the canulation of the renal artery with the JR4 guiding catheter, a guidewire was advanced to the distal segment of the renal artery and the modified balloon catheter was advanced in the main branch of the renal arteries. In order for the modified catheter to produce enough pressure to the media layer of the renal artery, and to cause small dissections so that the agent can pass through the media layer and reach the sympathetic nervous system of the renal artery, the diameter of the balloon for both treated and control segments was selected on a 1:1 ratio according to the diameter of the target vessel. The non-compliant balloon was then inflated at 20 atm to cover the target segment, using the mixture containing vincristine, allowing for delivery of vincristine into the vascular wall. The inflation was interrupted when a total of 4 ml of the mixture, that contained 0.1 mg of vincristine was delivered. The procedure was then repeated in the contralateral renal artery using the placebo mixture for inflation. All angiograms before and after the procedure were recorded on video and blood samples were drawn before, immediately after and 28 days after the procedure in order to determine serum creatinine levels. After the completion of the initial procedures, in all animals delivery of vincristine and placebo mixtures was successful and uncomplicated, with no acute or short-term complications related to the intervention. Moreover the safety for the renal function was proved by the fact that serum creatinine was 1.37 ± 0.12 mg/dl before the procedure, 1.41 ± 0.09 mg/dl after the procedure, and 1.36 ± 0.24 mg/dl 28 days after the procedure (p = NS for all comparisons) [24, 27].

After 28 days all animals were alive for euthanasia and it was previously shown their kidney function was normal. A final renal artery angiography before euthanasia showed that all vincristine and placebo treated renal arteries were angiographically patent at the end of the procedure, without evidence of thrombus formation, abrupt occlusion of the arterial segments or aneurysmal dilatation of the target segments at the post-procedural angiography. Moreover systolic blood pressure showed a significant drop between baseline and follow up at 28 days (132 ± 34.05 versus 125 ± 32.19 mmHg, p = 0.024), although this was beyond the scope of this study.

After euthanasia, both the vincristine and the placebo treated renal arteries were prepared for histology and immunohistology, with neuron specific enolase in order to visualize the sympathetic nerve fibers. It should be noted that during the harvest of the renal arteries, all renal arteries of both groups were patent, with no signs of thrombus. Each renal artery was dissected into 8 equal segments of 2 mm, and the sections of the vincristine treated arteries were compared to the sections of the renal arteries treated with the control mixture. The mean number of intact nerves in all sections was significantly lower in the group of vincristine, (8.6 ± 3.4 versus 11.7 ± 3.1, p < 0.01), showing the effectiveness of renal sympathetic denervation by the local delivery of vincristine [24, 27].

This was actually the first attempt to deliver locally to the renal artery a pharmaceutical agent, although this was performed previously in the coronary arteries, there was not any attempt to perform this on the renal arteries, This first attempt to produce renal artery denervation in an experimental model by vincristine, had the disadvantage that the flow rate of vincristine administration was not checked in vitro, a limitation that however was similar for both groups treated with vincristine or the placebo and therefore had no effect on the conclusions. However this method with the catheter-based chemical renal denervation and had the advantage that vincristine was not only delivered to nerves in the deeper layers of the vascular wall through the injured intima, but it could also exert a direct toxic effect on the sympathetic nerve axons in proximity with the tubular epithelial cells, resulting in an enhancement of its antihypertensive effect. Despite this possible beneficial effect, the spill out of vincristine towards the parenchymal renal tissue de novo raises some issues of safety, although these they were not observed in this preliminary study.

In order to overcome these limitations of the channeled dedicated catheter that delivers vincristine with an uncontrolled flow rate, a new double balloon delivery catheters was tested in vitro and in the same experimental model.

This new catheter was designed and manufactured by Rontis AG Switzerland, and consists of an over the wire triple lumen catheter with two non compliant balloons at its distal tip. It has two differences compared to the previously used channeled dedicated catheter. Firstly it strongly engages the balloon catheter (when the balloon is inflated) in the renal artery allowing all the pharmaceutical mixture to be delivered in the media layer of the renal artery and not spilled out by the circulation, and secondly, it delivers the pharmaceutical agent with a constant flow rate. The outer balloon is channeled and allows the delivery of the drug to the tissues, and the inner balloon, is used for the fixation of the catheter on the arterial wall and the obstruction of the renal artery so that the whole vincristine will be delivered to the arterial wall and not washed out by the blood flow. The third lumen allows the use of a guidewire for the advancement of the catheter. The outer balloon design similarly to the previous catheter consisted of six sideholes of 25 μm diameter, in fixed intervals of 60°. The injected mixture reached the arterial wall by diffusion or as a result of applied hydrostatic pressure. High-pressure inflation of the outer balloon catheter, using normal saline resulted in producing a jet of the solution from the sideholes in jets (Fig. 14.3).

This catheter was checked in vitro in various pressures for both the inner and the outer balloon, in order to assess the optimal inflation pressures in order to achieve a constant flow rate. After calculating the viscosity of the vincristine mixture that was 6.9 cP, the optimal pressures to achieve a constant flow rate of 10.11 cc/min was 2 Atm for the inner balloon and 6 Atm for the outer balloon [26].