Determination of the clearance factor for TSE agents during the manufacturing process of polygeline

Polygeline (a polymer prepared from heat-hydrolyzed gelatine) is a plasma substitute used by infusion as a 3.5% solution in the management of hypovolaemic shock. TSEs (transmissible spongi-form encephalopathies) are a group of fatal neurodegenerative (CNS) diseases affecting humans (e.g. Kuru, CJD) and animals (e.g. ovine, Scrapie, bovine BSE), all caused by a common class of agents, Prions. The link between TSEs and polygeline lies in its precursor, the gelatine which derives from bovine bones; bones may be at risk due to adjacent CNS (skull and vertebrae) contamination. In this experiment the main steps of the manufacturing process of polygeline were validated in order to see if the process is able to reduce the risk of iatrogenic transmission of the infectious agent, if present. It is, the first time that results of a validation study on a gelatine-derived product have been published. Three steps of the process were validated separately: in step 1, gelatine was subjected to three alternative autoclaving schedules (1A:121°C for 1.5 h; 1B: 121°C for 3 h; 1C: 133°C for 40 min). Step 2 was the crosslinking and distillation phase, and Step 3 the final sterilization at 121°C for 45 min. The hamster-adapted 263K strain of Scrapie was used as the TSE model. The ineffective spike was added to each material before being processed and titrated in hamsters. Each assay was performed in duplicate, and animals were monitored for 1 year. The initial hamster-titrated infectivity of the spike resulted in 10^9.0 LD50/2 ml. From the preliminary results of the experiment, only based on symptomatology (histological results of all brains expected till February 1999), the average step-clearance of infectivity (mean of two replicates) was (LU50/2 ml): 10^6.0 (IA), 10^6.9 (1B) and ≥ 10^7.4 (1C), 10^2.4 (2) and 10^4.8 (3). It is clear that heating the gelatine (step 1) was very ineffective in reducing the infectivity of TSE agents. Taking also into account that the initial experimental contamination level adopted was extremely high, that raw materials used in the real production are carefully selected from a BSE-free country (USA) and exclude the skull and spinal cord, that the starting material - gelatine - is already produced by BSE-reducing procedures, and that steps 2 and 3 also contribute to lowering the infectivity, if any, it may be concluded that the polygeline manufacturing process is capable of inactivating BSE agents to a very high extent.