Histology of Sub-Dermal Remodeling after Collagenase Clostridium Histolyticum (CCH) Subcutaneous Injection: Evidence from Porcine and Human Studies

Goals/Purpose:

In studies of CCH for the treatment of moderate to severe cellulite in the buttocks of adult women, injection site bruising was the most frequently reported adverse event (AE). Histology studies were designed to better characterize the subdermal impact of CCH subcutaneous (sc) injections and investigate injection site bruising. The first study used Yorkshire pigs (domestic swine) as a model due to the similarities to human skin, and the second study, human abdominal tissue.

Methods/Technique:

Porcine Study: Four female Yorkshire pigs (35-45 kg) were to receive CCH (0.07 mg/0.3 mL) or placebo (0.3 mL) sc into 10 sites on the pigs’ left (L) and right (R) ventral side. The dosing schedule was as follows:

	2 Doses/Site		1 Dose/Site
Treatment	Day (s)	Sites	Day (s)	Site
CCH	-42, -21	R1	-21	L1
	-29, -8	R2	-8	L2
	-25, -4	R3	-4	L3
	-23, -2	R4	-2	L4
Placebo	-23, -2	R5	-2	L5

AEs were collected during the study. After euthanization on Day 0, the ventral side with the muscle tissue was excised as a single piece.

Abdominoplasty Study: Prior to abdominoplasty, 8 females, divided into 6 groups (G) will receive 1 or 2 doses of CCH into laterally marked areas of the surgical region (Areas 1 and 2), with the middle region marked as a control. The dosing schedule is as follows:

Groups	Area 1	Area 2
G1, G4; n=2, each	Days -43, -22	Day -14
G2, G5; n=1, each	Days –24, -3	Day -3
G3, G6; n=1, each	Days -22, -1	Day -1

Four subjects, each, will receive either CCH 0.07 mg as 3 x 0.1 mL aliquots (G1, G2, G3) or 0.0653 mg as 14 x 0.1 mL aliquots (G4, G5, G6). AEs will be collected during the study. On the day of abdominoplasty, the tissue incorporating the treatment areas will be excised as a single piece. The pathologist will be blinded to the dosing schedule.

Results/Complications:

Porcine Study: One pig experienced a leg injury unrelated to CCH administration and was euthanized. Histologic findings in the CCH-injected specimens of the three other pigs showed enzyme-induced lysis or disintegration of thick interlobular sub-dermal collagen septae. As collagen support was lost, leakage of blood from the thinner endothelial venules was observed in L3 (Day -4), L4 (Day -2), R3 (Days -25, -4), and R4 (Days -23, -2) injection sites. This correlated with the mild to moderate bruising and edema observed at these sites in all pigs.

Signs of collagen neogenesis and subdermal structural reorganization were evident as early as 4 days after CCH in L3 (Day -4) and R3 (Days -25, -4) and clearly defined in L2 (Day -8) and R2 (Days -29, -8) injection sites. Marked sub-dermal fat and collagen structural reorganization was evident at L1 (Day -21) and R1 (Days -42, -21) injection sites. No histologic changes were observed in sites injected with placebo.

Abdominoplasty Study: Histological findings are pending.

Conclusion:

Histologic findings in the porcine model demonstrate both early and later impacts of CCH-induced subdermal architectural remodeling of the collagenous septae as well as the fat lobules. Early after treatment, CCH induced enzymatic subcision of subdermal collagen macrostructures. Later, enzyme induced collagen neogenesis and marked sub-dermal fat and collagen microstructural reorganization was observed.