Preparation and characterization of a [14C]cellulose suitable for human metabolic studies

In six normal subjects administered 5 microCi of an oral dose of a commercially available 14C-labelled cellulose, significant amounts of 14CO2 were detected in expired air within 30 min, suggesting that other 14C-labelled non-cellulosic material was present. Chemical and microscopical examination confirmed that starch was the principal contaminant. The commercial preparation was purified using amyloglucosidase (EC 3.2.1.3) digestion following gelatinization of the starch by autoclaving. Subsequent administration of the purified cellulose to a further six normal subjects decreased the expired air 14CO2 during the subsequent 10 h from 13.0 (SD 4.0) to 4.1 (SD 1.9)%. Administration of the purified product to a further group of four normal subjects, before and after a regimen of increased dietary fibre, showed a cumulative increase in expired 14CO2 over 24 h from 7.9 (SD 1.1) to 12.1 (SD 2.6)% on fibre. In six ileostomy subjects the cumulative excretion of 14CO2 was greatly decreased compared with normal controls (3.0 (SD 1.14) and 10.5 (SD 3.9)% respectively). In constipated subjects expired 14CO2 continued beyond 48 h, in contrast to normal subjects where expired 14CO2 at this time was negligible.