Recombinant caprine H-3-[N-acetylglucosamine-6-sulfatase] and human H-3-[N-acetylgalactosamine-4-sulfatase] - Plasma clearance, tissue distribution, and cellular uptake in the rat

The use of recombinant lysosomal enzymes for enzyme replacement therapy (ER T) is likely to be a necessary component of effective treatment regimens fo r lysosomal storage diseases (LSDs). The mechanism and rate of uptake into target cells, rate of disappearance of the enzyme from plasma, and its tiss ue distribution are important factors to assess the need for possible modif ications to the enzyme, particularly for LSDs that affect the central nervo us system (CNS). Two recombinant lysosomal enzymes, caprine N-acetylglucosa mine-6-sulfatase (rc6S) and human N-acetylgalactosamine-4-sulfatase (rh4S), deficient in MPS IIID and MPS VI, respectively, were radiolabeled and puri fied. The major portion (>77%) of each recombinant enzyme contained the man nose-6-phosphate (M6P) recognition marker as demonstrated by their ability to bind to a M6P receptor affinity column. The uptake of H-3-rc6S and H-3-r h4S into cultured rat brain cells was also inhibited by the addition of 5 m M M6P to the culture medium. After iv administration of 0.4-0.5 mg/kg of H- 3-rc6S and 1 mg/kg of H-3-rh4S to the rat, both enzymes were rapidly lost f rom the circulation in a biphasic fashion (t(1/2) for H-3-rc6S = 1.25 +/- 0 .15 min and 37.17 +/- 23.29 min; t(1/2) for H-3-rh4S = 0.41 and 5.3 min). A t this dose, about 6% of H-3-rc6S, but only 0.49% of H-3-rh4S, remained in the plasma 4 h after administration, whereas approx 30% of H-3-rc6S and mor e than 50% of H-3-rh4S was found in the liver. At doses of 1.6-2.9 mg/kg of H-3-rc6S and 1 mg/kg H-3-rh4S, but not at the lower dose of H-3-rc6S, trac e levels of both H-3-rc6S and H-3-rh4S were detected in the brain. The low level of enzyme recovered from the brain suggests that modification of rc6S will be necessary to achieve sufficient enzyme uptake into the CNS for eff ective therapy of MPS IIID.