Isolated non-naturally occurring, mutant-human islet amyloid polypeptides (hIAPP) are disclosed. These polypeptides can be formulated or co-formulated at physiological pH, which enable the polypeptides of the instant disclosure to be delivered to a subject having an amyloid-based disease in a single injection with an insulin agent. Methods and compositions for treating amyloid-based disease in a subject in need thereof, by administering an effective amount of an isolated, mutant-hIAPP polypeptide, including formulations or co-formulations thereof are also disclosed.