Calcium-alginate beads for the oral delivery of transforming growth factor-β1 (TGF-β1): stabilization of TGF-β1 by the addition of polyacrylic acid within acid-treated beads

The susceptibility of the gastrointestinal tract to the toxic effects of chemotherapeutic drugs remains a complication in chemotherapy. Recent studies have suggested that transforming growth factor-β₁ (TGF-β₁) can be used as a cytoprotectant against cell cycle specific drugs. This work describes the use of alginate beads as a potential oral delivery system for TGF-β₁ designed to release the drug in the lumen of the small intestine. TGF-β₁ encapsulation and extent of release from alginate beads approached 100% as determined by ¹²⁵I-labelled TGF-β₁. However, when assayed by ELISA and a growth inhibition assay, nearly all immunoreactivity and bioactivity was lost, apparently due to a very high affinity of the alginate for TGF-β₁. This limitation was overcome by two novel methods: (1) incorporation of selected polyanions within the alginate beads to ‘shield’ TGF-β₁ from interaction with alginate and (2) exposure of the alginate beads containing TGF-β₁ to 0.1 N HCl (acid treatment) to simultaneously reduce the molecular weight of the alginate and its ability to interact with TGF- β₁. If the beads were only acid treated, just 8% of the immunoreactivity ofTGF-β₁ was retained. If polyacrylic acid (90 kDa) was added to the beads, 50% of the immunoreactivity of TGF-β₁ was retained. However, when TGF-β₁ was released from acid-treated beads also containing polyacrylic acid, more than 80% of the TGF-β₁ remained immunoreactive and bioactive. The retained TGF-β₁ activity after release from the beads was found to continue to increase with increasing concentrations of polyacrylic acid, until a concentration was reached where beads would not form. The dramatic increase in retained TGF-β₁ activity is attributed to the ability of polyacrylic acid to shield TGF-β₁ from interaction with lower molecular fragments of alginate.