Sorbent therapy of the porphyrias. IV. Adsorption of porphyrins by sorbents in vitro.

The adsorption capacities (Qm's) of the ion exchange resin cholestyramine and 8 activated charcoals for uroporphyrin, protoporphyrin and coproporphyrin, porphyrins that accumulate within tissues or vasculature in certain porphyrias, have been determined. Qm's (mg porphyrin/gm dry sorbent) were derived from Langmuir isotherms, which were constructed from experiments that assessed the amount of porphyrin adsorbed after the addition of varying amounts of porphyrin in solution to a constant amount of sorbent. These experiments were carried out at pH 8.2 in 0.5% desoxycholate, to simulate conditions of the small intestine. For uroporphyrin I, the Qm for Amoco Supersorb PX-21 highly activated charcoal was greater than that for cholestyramine (mean +/- SD of 26.5 +/- 12.7 vs. 17.0 +/- 2.6; t'32 = 2.46, P less than 0.025) and highly significantly greater than those of the other charcoals. For protoporphyrin IX, cholestyramine and Amoco Supersorb PX-21 charcoal had the highest Qm's (32.4 +/- 8.6 and 30.9 +/- 9.2), but these were not significantly greater than the Qm's of 5 other charcoals. Little difference was found among sorbents in the rate of adsorption of either porphyrin. For coproporphyrin III, the Qm's of cholestyramine and Amoco Supersorb PX-21 charcoal were not significantly different (39.2 +/- 13.7 vs. 35.1 +/- 4.0) but they were greater than that of Norit USP XX (20.0). Virtually no desorption of porphyrin from either cholestyramine or Amoco Supersorb PX-21 charcoal was detected. Both cholestyramine and Amoco Supersorb PX-21 charcoal appear to be highly avid sorbents for porphyrins of varied states of carboxylation.(ABSTRACT TRUNCATED AT 250 WORDS)