Background

Wound healing in vertebrates is a multi-step process involving a host of molecular and cellular mediators. Angiogenesis, the growth of new capillary blood vessels, is known to be critical for complete healing in acute wounds, and is defective in many chronic wounds.¹ Among the critical mediators of wound angiogenesis are cytokine growth factors, such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF). PDGF is a potent angiogenic stimulator that promotes: 1) endothelial proliferation and migration; 2) vascular tube formation; and 3) vascular stabilization.² Deficiencies in PDGF occur in diabetic chronic wounds, and PDGF knock-out mice exhibit aberrant, dysfunctional wound angiogenesis and delayed healing.^3,4 One iso-form of this growth factor, PDGF-BB, has been developed by recombinant technology and was FDA-approved in 1997 for accelerating wound angiogenesis and healing in human diabetic patients.^5,6

Because the receptor for PDGF-BB is highly conserved among vertebrates, the drug (rhPDGF-BB, becaplermin, tradename: REGRANEX) has been effectively prescribed in extra-label fashion to heal chronic wounds in the exotic veterinary setting, including those occurring in raptors (avian pododermatitis), reptiles (traumatic wound), armadillo (pressure ulcer), and rhinoceros (pressure ulcer). At the New England Aquarium, we hypothesized that rhPDGF-BB would accelerate healing in fish with chronic lesions secondary to Head and Lateral Line disease (HLLE).

The first two cases involved sailfin tangs with fairly extensive HLLE present for > 14 months with no improvement despite sharp debridement for three months of the treatment time. Other background treatments included supplemental oral vitamin C and a broad-spectrum UV light. Over 10 months of therapy, there was no change in progression of disease. Topical angiogenic therapy was begun using REGRANEX in June 2002.

Method

The fish were anesthetized using 90 ppm of MS 222, placed on a padded surface, and maintained with anesthetic water flowing across the gills. One fish had fairly symmetrical bilateral lesions. We initially chose to treat the right-side lesion, and to use the left-side lesion as an untreated, internal control. Both lesions were rinsed with sterile fresh water and surgically debrided by using either a #15 blade or a curette. The rationale for debridement is to remove necrotic tissue and senescent cells, to stimulate a pro-angiogenic wound micro-environment, and to expose endogenous receptors for PDGF-BB. A thin layer of REGRANEX gel (~ 0.1 cc) was then applied using sterile technique directly on the wound with a cotton applicator. A three-minute observation period was strictly enforced following each application to allow the exogenous growth factor to bind to endogenous receptors in the wound bed prior to placing the fish back into water. REGRANEX was applied weekly and the lesion focally debrided on a biweekly basis. The left-side lesion was subsequently treated with REGRANEX after the other lesion had healed completely.

Results

Treatment with REGRANEX led to visible granulation (angiogenesis) in the wound bed within days of application. After three weeks of therapy, treated lesions shrank by approximately 50 percent. In contrast, untreated control lesions did not improve. Complete resolution of treated HLLE lesions occurred in eight weeks, with return of all normal melanophore patterning and no clinically-evident scarring. The fish tolerated the treatments well, and exhibited no compromise in behavior following treatment.

Conclusion

Angiogenic growth factor therapy using REGRANEX can accelerate healing and wound closure in severe HLLE. We speculate that the PDGF-BB receptor is conserved in marine fish, and that stimulation of these receptors by an exogenously applied recombinant growth factor activates signal transduction pathways, leading to granulation and healing. Our results suggest that REGRANEX may be a useful treatment for HLLE in the aquarium setting. Further studies are underway.

References

1.  Tonnesen MG, Feng X, Clark RA. Angiogenesis in wound healing. J Invest Dermatol Symp Proc. 2000;5:40-46.

2.  Thommen R, Humar R, Misevic G, et al. PDGF-BB increases endothelial migration on cord movements during angiogenesis in vitro. J Cell Biochem. 1997;64:403-413.

3.  Doxey DL, Ng MC, Dill RE, Iacopino AM. Platelet-derived growth factor levels in wounds of diabetic rats. Life Sci. 1995;57:1111-1123.

4.  Lindahl P, Johansson BR, Leveen P, Betsholtz C. Pericyte loss and microaneurysm formation in PDGF-B-deficient mice. Science.1997;277:242-245.

5.  Wieman TJ, Smiell JM, Su Y. Efficacy and safety of a topical gel formulation of recombinant human platelet-derived growth factor-BB (becaplermin) in patients with chronic neuropathic diabetic ulcers. A phase III randomized placebo-controlled double-blind study. Diabetes Care.1998;21:822-827.

6.  Steed DL, Donohoe D, Webster MW, Lindsley L. Effect of extensive debridement and treatment on the healing of diabetic foot ulcers. Diabetic Ulcer Study Group. J Am Coll Surg. 1996;183:61-64.