hCT (Calcitonin), Human

Irreversible aggregation greatly limits the bioavailability and therapeutic activity of peptide-based drugs, so preventing protein or peptide aggregation is a common issue in drug formulation. Human calcitonin (hCT), a peptide hormone secreted by thyroidal parafollicular cells, can regulate blood calcium levels and maintain bone structure. Hence, it can be used as a treatment for metabolic bone diseases, such as osteoporosis and Paget's disease. However, hCT has a relatively high propensity to form amyloid fibrils that hinder its biological function and limit its pharmaceutical potential. In previous studies, we demonstrated, along with other research groups, that modifying specific residues of hCT is sufficient to prevent hCT aggregation. We proceeded to find the key residues that regulate the aggregation of hCT for a better understanding of the mechanism of hCT aggregation. In this work, we used amyloid propensity prediction software and found that Tyr12 may play a key role in regulating hCT aggregation. Thus, we propose three human calcitonin variants (Y12E, Y12P, Y12R) for hCT non-amyloidogenic substituents and examined the aggregation characteristics of variants using multiple biophysical techniques. Y12E showed the best anti-aggregation propensity and can work as inhibitor of hCT aggregation. We also found this residue is crucial for membrane binding and receptor binding. The data presented herein provides an overview of Tyr12 that should be carefully considered in peptide design.

Irreversible aggregation can extremely limit the bioavailability and therapeutic activity of peptide-based drugs. There is therefore an urgent demand of effective strategy to control peptide aggregation. Recently, we found that tyrosine nitration at certain sites of peptide can effectively inhibit its aggregation. This minor modification may be an ideal strategy to the rational design of peptide-based drugs with low aggregation propensity yet without loss of bioactivity. Human calcitonin (hCT) is such a peptide hormone known for its hypocalcaemic effect but has limited pharmaceutical potential due to a high tendency to aggregate. In this study, by using multiple techniques including Fluorescence, TEM, Nu-PAGE and CD, we demonstrated that Y12 nitration of hCT would significantly inhibit its self-assembles, and we also found that this modification would not only reduce the cytotoxicity induced by peptide aggregation, but also had little effect on its potency. This finding may provide a novel strategy for clinically application of hCT instead of sCT.

The development of biocompatible nanomaterials has become a new trend in the treatment and prevention of human amyloidosis. Human calcitonin (hCT), a hormone peptide secreted from parafollicular cells, plays a major role in calcium-phosphorus metabolism. Moreover, it can be used in the treatment of osteoporosis and Paget's disease. Unfortunately, it tends to form amyloid fibrils irreversibly in an aqueous solution, resulting in a reduction of its bioavailability and therapeutic activity. Salmon calcitonin is the replacement of hCT as a widely therapeutic agent due to its lower propensity in aggregation and better bioactivity. Herein, we used citric acid to synthesize carbon dots (CDs) and modified their surface properties by a variety of chemical conjugations to provide different functionalized CDs. It was found that dopamine-conjugated CDs can effectively inhibit hCT aggregation especially in the fibril growth phase and dissociate preformed hCT amyloids. Although the decomposition mechanism of dopamine-conjugated CDs is not clear, it seems to be specific to hCT amyloids. In addition, we also tested dopamine-conjugated mesoporous silica nanoparticles in preventing hCT fibrillization. They also can work as inhibitors but are much less effective than CDs. Our studies emphasized the importance of the size and surface functionalization of core materials in the development of nanomaterials as emerging treatments for amyloidosis. On the other hand, proper functionalized CDs would be useful in hCT formulation.