Human β-Glucuronidase. I. Recognition and Uptake by Animal Fibroblasts Suggests Animal Models for Enzyme Replacement Studies (original) (raw)

Summary: As part of an effort to develop an animal model for studies of uptake of human β-glucuronidasc, fibroblasts were established from primary explains of connective tissue from nine different animal species, and examined for their ability to take up human platelet β-glucuronidase. Endogenous fibroblast β-glucuronidase was inactivated by heating extracts to 65° for 30 min. Human β-glucuronidase was stable to this treatment. Uptake of human β-glucuronidase by animal fibroblasts was measured as heat-stable β-glucuronidase present in fibroblasts after exposure to partially purified human platelet β-glucuronidase for 48 hr. Although all animal fibrohlasts examined exhibited some uptake capacity for human β-glucuronidase, the uptake capacity of different animal fihroblasts varied over a 10-fold range. The uptake capacity of bovine fibroblasts was at least 80% that of human fibroblasts. Rat and hamster fibroblasts showed about half the uptake capacity of human fibroblasts. The rat fibroblasls resembled the human fihroblasts in the kinetics of uptake of high uptake (platelet) enzyme, poor uptake of human placental enzyme, and lack of appreciable turnover of enzyme taken up over 4 days. Heating extracts of rat organs containing added human β-glucuronidase at 65° selectively inactivated rat enzyme.

Speculation: These results indicate that uptake of human platelet β-glucuronidase by fibroblasts is a reflection of a general biologic process shared by many animal species. As such, the rat, and probably several other animal species, might serve as animal models for study of that process in the whole animal. Studies in the whole rat should provide information regarding the uptake and metabolic fate of the different forms of human β-glucuronidase that have large differences in uptake activity and corrective potency for human fibrohlasts. This information may prove important in choosing the organ source for purified enzyme, or desirable modifications of purified human enzyme for enzyme replacement therapy.