Methodological Standardization for the Pre-Clinical Evaluation of Renal Sympathetic Denervation

Abstract

Transcatheter ablation of renal autonomic nerves is a viable option for the treatment of resistent arterial hypertension; however, structured preclinical evaluation with standardization of analytical procedures remains a clear gap in this field. Here we discuss the topics relevant to the preclinical model for the evaluation of renal denervation (RDN) devices and report methodologies and criteria towards standardization of the safety and efficacy assessment, including histopathological evaluations of the renal artery, peri-arterial nerves, and associated peri-adventitial tissues. The preclinical swine renal artery model can be used effectively to assess both the safety and efficacy of RDN technologies. Assessment of the efficacy of RDN modalities primarily focuses on the determination of the depth of penetration of treatment-related injury (eg, necrosis) of the peri-arterial tissues and its relationship (ie, location and distance) and affect on the associated renal nerves and the correlation thereof with proxy biomarkers including renal norepinephrine concentrations and nerve-specific immunohistochemical stains (eg, tyrosine hydroxylase). The safety evaluation of RDN technologies involves assessing for adverse effects on tissues local to the site of treatment (ie, on the arterial wall) as well as tissues at a distance (eg, soft tissue, veins, arterial branches, skeletal muscle, adrenal gland, ureters). Increasing experience will help to create a standardized means of examining all arterial beds subject to ablative energy and in doing so enable us to proceed to optimize development and assessment of these emerging technologies.

Comparison of Histopathologic Analysis Following Renal Sympathetic Denervation Over Multiple Time Points

“…These parameters were semiquantified using a scoring system of 0 to 4: 0=none; 1=minimal, 2=mild; 3=moder-ate; and 4=severe. 12 Maximum nerve damage was assessed based on the extent of nerve injury observed histologically. Perineural injury including perineural inflammation or fibrosis and endoneural injury including vacuolization, digestion chambers, pyknotic nuclei, and necrosis were evaluated.…”

“…12 Medial injury was evaluated by the depth and circumferential involvement separately: 0=no media change; grade 1=medial injury involving <25% of media depth/ circumference; grade 2=medial injury, 25% to 50% of media depth/ circumference; grade 3=medial injury 51% to 75% of medial depth/ circumference, and grade 4=media injury >75% of medial depth/circumference. 12 In addition, the presence of arterial medial thinning…”

“…was defined as thickness of media at the site of damage (mm)/unaffected media thickness (mm) <0.5 12 and was assessed as absent (0) or present (1). These changes were the result of severe smooth muscle cell loss/necrosis within the media, accompanied by thinning.…”

“…Arteriolar injury was evaluated using a grading system of 0 to 4, which was applied with respect to inflammation/fibrinoid necrosis: 0=none, 1=minimal, 2=mild, 3=moderate, and 4=severe. 12 Prevalence of denatured collagen, which seems as basophilic staining of collagenous tissue from thermal injury under hematoxylin and eosin stain, was assessed as absent (0) or present (1). To evaluate the extent of tissue damage in a circumferential dimension, the following parameters were assessed after dividing the entire vascular and peri-vascular circumference into 4 equal quadrants: (1) number of quadrants with nerve fascicles; (2) number of quadrants with injured nerve fascicles (grade ≥2); (3) number of quadrants with moderate to severely injured nerve fascicles (grade ≥3); and (4) number of quadrants with injured peri-arterial soft tissue.…”

“…Nevertheless, renovascular anatomy in swine is similar to human, whereas peri-renal nerve distribution in swine is different from that in human. 12,20,21 Also, the life span of swine is dramatically shorter compared with man, 22 and therefore the time course of nerve and vascular regeneration may be substantially prolonged in humans compared with swine. Although a portion of the samples from the 180 days animals were published previously by Rippy et al, 10 scoring in our study was performed independently in a blinded manner without knowledge of previous results.…”