Heme and lithospermic acid synergistically inhibit aggregation of human islet amyloid polypeptide: A novel hIAPP inhibitor for the potential therapy of type 2 diabetes

Amyloid deposition of human islet amyloid polypeptide (hIAPP) is closely linked to the pathogenesis and progression of type 2 diabetes mellitus (T2DM). Developing effective inhibitors to suppress hIAPP aggregation holds significant therapeutic potential for the prevention and treatment of T2DM. Recent researches indicate that both heme and lithospermic acid (LPA) can inhibit hIAPP aggregation. However, heme is prone to induce protein damage under oxidative stress, while LPA exhibits limited inhibitory efficacy despite its antioxidant properties. To overcome these limitations, we aimed to develop a dual-component inhibitor comprising heme and LPA. thioflavin T (ThT) fluorescence, transmission electron microscopy (TEM), circular dichroism (CD) and gel electrophoresis were combined to observe the inhibitory efficacy of heme-LPA co-formulation on hIAPP aggregation. The results demonstrate that LPA and heme can synergistically inhibit hIAPP aggregation. The inhibitory effect of heme-LPA co-formulation on hIAPP aggregation is significantly stronger than that of either component alone. The heme-LPA not only prevents the complete conversion of hIAPP into β-sheet fibrillar structures but also maintains its active monomeric conformation for extended periods. Furthermore, peroxidase activity assays revealed that the presence of LPA significantly reduces the peroxidase activity of heme in a concentration-dependent manner and attenuates peptide nitration damage under H₂O₂-NO₂ − oxidative stress. At a heme-to-LPA ratio of 1:4, peptide nitration bands were virtually undetectable. These findings indicate that the dual-component inhibitor heme-LPA represents an efficient and safe strategy for inhibiting hIAPP aggregation. This research provides an important avenue for developing novel anti-hIAPP aggregation inhibitors for the prevention and treatment of T2DM.