The present invention relates to novel particles comprising polyelectrolyte polymers which are transporters of active principle (AP), in particular protein and peptide active principle, and to novel modified-release pharmaceutical formulations comprising said AP microparticles.These novel particles loaded with AP release the AP over a prolonged period of time of several days, or even several weeks.The invention relates, in a first aspect, to particles comprising: a) a first polyelectrolyte polymer (PE1) in a charged state, carrying side hydrophobic groups (GH), wherein said first polyelectrolyte polymer (PE1) can spontaneously form, in water, a colloidal solution of particles at least one pHm value of the pH of between 3 and 8; b) a second polyelectrolyte polymer (PE2) of opposite polarity to the first polyelectrolyte polymer (PE1), wherein said second polyelectrolyte polymer (PE2) forms, in water, a solution or a colloidal solution at said pHm value of the pH; and c) at least one active principle (AP) associated noncovalently with the particles of the colloidal solution of the first polyelectrolyte polymer (PE1); wherein said particles are obtained by mixing, at a pH equal to pHm, the first polyelectrolyte polymer (PE1), in the form of a colloidal solution of particles associated with the active principle (AP), with the second polyelectrolyte polymer (PE2), in the form of a solution or colloidal solution. The invention also relates to the process for the preparation of these particles, to a pharmaceutical formulation comprising such particles and to a process for the preparation of medicaments.