In a fuel injection system for an internal combustion engine, in which fuel at at least two differently high fuel pressures can be injected via injectors into the combustion chamber of the engine, parallel to a bypass line a hydraulic pressure booster is provided for generating the higher fuel pressure; the pressure booster is actuatable and deactuatable via a valve unit. The proton conductor is produced typically by compacting a powder of the carbonaceous material derivative. Moreover, matching of ligand with GPR2 receptor in mammals provides methods of use.