The impact of paclitaxel-DCB treatment on late lumen enlargement of coronary vessels

Local delivery of paclitaxel (PTX) via drug eluting stents (DES) or drug coated balloons (DCB) reduces restenosis. While after DES treatment some loss of lumen over time occurs, DCB treatment appears to reduce lumen loss and may promote lumen enlargement. The mechanism leading to the positive remodeling phenomenon remains elusive. Since paclitaxel is known to be neurotoxic, we hypothesize that paclitaxel might affect the sympathetic nerve fibers innervating the coronary arteries, and thereby promotes late lumen enlargement (LLE).

In twelve pigs, 32 arteries (CX, LAD, RCA), were randomized to treatment with uncoated balloons (POBA, control), balloons coated with 3µg PTX/mm² (3), 6 µg PTX/mm² 6 and treatment with two balloons coated with 6µg PTX/mm² each (12). After four weeks, the pigs were sacrificed and the balloon treated vessel and a part of the proximal untreated vessel were dissected and embedded. HE-staining was performed for histomorphometry. Neuronal tissue was visualized by immunohistology using S100 staining. For assessment of efferent sympathetic nerves an anti-tyrosine hydroxylase (TH) antibody was used. Nerve count, nerve area and the distance to the luminal intima (LEI) were investigated.

DCB treatment resulted in a lumen enlargement compared to POBA (POBA: 0.83±0.11mm; 3: 1.01±0.11mm; 6: 1.13±0.25mm; 12: 1.08±0.29mm; p vs POBA: 6 = 0.0277, 12 ns, 3 ns). Likewise, a decreasing neointima thickness was recognized with increasing PTX content (POBA: 0.52 ±0.24mm, 3: 0.49 ±0.08mm; 6: 0.49±0.20mm; 12: 0.40±0.15mm; p vs POBA: ns). Because of the missing lumen stabilization by the stent, the lumen in the balloon area was smaller than in the stented part of the vessel. The untreated vessel sections showed similar nerve sizes and nerve counts. In the treated vessel section, the nerve area of the POBA group were comparable to the proximal part (1941.3±1171.3 µm²). The area increased with increasing PTX amount (3: 5223.47±4103.8µm²; 6: 4182.8±3711.6. µm²; 12: 5517.3±5215.7µm²; p vs POBA = ns). The distance to the LEI was larger than in the untreated vessels, but similar in-between the groups. After treatment with PTX, the nerve count was diminished (POBA: 647.8±497.3 n./cm²; 3: 455.6±257.3 n./cm²; 6: 318.7±164.6 n./cm²; 12: 350.1.2±169.1 n./cm²; p vs POBA = ns). In addition, more sympathetic nerves were counted within the POBA group (POBA: 328.5±289.9 n./cm²; 

3: 177.1±130.4 n./cm²; 6: 142.3±61.7 n./cm²; 12: 176.5±103.5 n./cm²; p vs POBA = ns). In the untreated vessel sections the TH positive nerve count was similar (POBA: 386.5±169.1 n./cm²; 3: 540.9±216.2 n./cm²; 6: 546.5±226.8 n./cm²; 

12: 498.6±404.0 n./cm²; p vs POBA = ns). 

Next, we compared the treated and untreated area of the same treatment group to investigate if the balloon treatment itself has an impact of the vessel innervation. The S100 nerve count was comparable, but the TH positive nerves decreased in the PTX treated vessel part. Also, the TH/S100 ratio decreased after balloon treatment, most pronounced in the PTX groups. Interestingly, the ratio itself was similar in all four groups (fig.).

Angioplasty with a PTX-DCB leads to a decrease of sympathetic nerves. Our results indicate, that not only the drug, but also the combination with the balloon induced overstretch, supports nervous remodeling and LLE.