Answer:
BAPN (beta-amino-proprionitrate) is generally non-toxic and appears to exert a highly selective and significant lathyrogenic effect on the healing wound. A hypothetical basis for control of surface scar in human beings is that lathyrism produces poorly cross-linked collagen in healing wounds. Poorly cross-linked collagen is more susceptible to digestion by tissue collagenase than is normally cross-linked collagen, and colchicine stimulates tissue collagenase activity. (see colchicine)
Proline analogs prevent the development of the helical structure and transport of collagen, however their toxicity limits human testing.
Colchicine: stimulates collagenase activity. In a study, patients with abnormal scar deposition resistant to conventional therapy, have been treated with excision, grafting the defect, inducing lathyrism with BAPN or penicillamine and administering colchicine. No patients developed recurrent keloids while undergoing treatment.
Penicillamine: also induces lathyrism (like BAPN).
Antihistamines: could retard the growth of fibroblasts derived from human skin, scar and keloid. Sixty percent of the fibroblast strains derived from normal skin, scar and keloid reached elevated growth plateaus when cultured in the presence of histamine. A pharmacologic level of the antihistamine diphenhydramine hydrochloride was able to suppress the stimulation in all the keloid strains that were histamine-sensitive.
Tetrahydroquinone: there is no information on this agent in keloid treatment, but hydroquinone is skin lightening agent, used in areas of hyperpigmentation.
Retin A: Retin A reduces collagen metabolism by reducing the production of collagenase. There is a differential modulation of connective tissue metabolism by retinoids in keloid cell culture.
Zinc oxide: no reports on the use of these agents on keloids (based on Medline search).