Oral application of FGF21 for targeted action in the liver

Fibroblast growth factor 21 (FGF21) is a metabolically active peptide hormone that can reduce obesity-associated metabolic disorders in various animal models. Initial clinical trials with FGF21 analogs (administered by injection) confirmed reductions in body weight, blood lipids, and insulin in humans and point to the liver as an important target organ, particularly in patients with fatty liver disease. The liver is also the main producer of FGF21, but direct hepatic effects and mechanisms are still insufficiently understood. The biology of FGF21 is highly complex and only partially understood, and there is also ongoing controversy regarding the target organs and intracellular mechanisms of FGF21. Furthermore, elevated plasma levels can have negative side effects, for example, on bone density. We hypothesize that an oral administration system could achieve positive metabolic effects by targeting the liver while avoiding side effects.

The objectives of this project are (i) to elucidate the liver-specific metabolic effects of FGF21 and (ii) to establish an oral delivery system using edible plants expressing FGF21.

Through transcriptomic and metabolomic analyses of liver tissue and primary hepatocytes from FGF21 knockout mice treated with FGF21, novel molecular mechanisms of FGF21 action in hepatocytes will be identified and validated both in vitro and in vivo. These findings will then be used to specifically investigate the effects of orally administered FGF21.

For oral delivery, a plant-based expression system will be developed. Edible plants are particularly well-suited for this purpose, as plant cells can protect intracellular proteins from degradation in the stomach, allowing them to be released only in the small intestine—a process referred to as in planta bioencapsulation. This leads to a high concentration of FGF21 in the portal vein and its targeted transport to the liver, while maintaining low peripheral exposure due to the rapid degradation of FGF21 in serum.

To improve protection within the plant cell, FGF21 will be fused to an oil-binding domain. For transcytosis from the intestine into the bloodstream, transferrin will be used as an additional fusion partner, which will be cleaved by endogenous proteases in the serum. Initially, the efficacy of various transiently expressed and purified FGF21 variants will be tested in vitro using a simulated intestinal system and a Ussing chamber. The most suitable variants will then be used for stable transformation of edible, oil-rich tobacco varieties. The bioavailability and biological effects, particularly on the liver, will subsequently be evaluated in feeding studies with obese and FGF21 knockout mice.

The Fraunhofer IME contributed its expertise and technologies in Plant Molecular Farming to produce FGF21 in plants and make it available for oral administration.