The origin and acceleration mechanism of ultra-high-energy cosmic rays (UHECRs) with energy exceeding the GZK-cutoff remain unknown. It is often speculated that supermassive black holes (SMBHs) located at the centers of many galaxies can serve as possible sources of UHECRs. This is also supported by recent detections of high-energy neutrinos from blazar, as neutrinos are the tracers of UHECRs. In this contribution we explore the capabilities of some SMBHs to accelerate UHECR protons of certain energies by the induced electric field generated due to frame-dragging effect of twisting of magnetic field lines near horizon of rotating SMBHs. In particular, we study the ionization of freely-falling neutral particles, such as the hydrogen ionization or neutron beta-decay in the vicinity of SMBHs immersed into external magnetic field and calculate the energies of escaping protons after the ionization. We choose 25 nearby SMBH candidates (within 100 Mpc) with measured and estimated masses, spins and magnetic fields, for which we present a table with mean proton energy and explore their acceleration capabilities.