Angiogenic Growth Factor Therapy Using Recombinant Platelet-Derived Growth Factor (Regranex) for Lateral Line Disease in Marine Fish
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 well established 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 approved by the Food and Drug Administration 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 were sailfin tangs with fairly extensive HLLE present for more than 14 months with no improvement despite sharp debridement for 3 months of the treatment time. Other background treatments included supplemental oral vitamin C and a broad-spectrum ultraviolet light. Over 10 months of therapy, there was no change in disease progression. Topical angiogenic therapy with Regranex began in June 2002.
Materials and Methods
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 bilateral fairly symmetric 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 proangiogenic wound microenvironment, 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 3-min 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.
Treatment with Regranex led to visible granulation (angiogenesis) in the wound bed within days of application. After 3 weeks of therapy, there was an approximately 50% reduction in size of treated lesions. In contrast, untreated control lesions did not improve. Complete resolution of treated HLLE lesions occurred in 8 weeks, with return of all normal melanophore patterning and no clinically evident scarring. Fish tolerated treatments well. There was no compromise in behavior following treatment.
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 actives 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.
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