Nontoxic Carbon Dots Potently Inhibit Human Insulin Fibrillation

Abstract

One prevention and therapeutic strategy for diseases associated with peptide or protein fibrillation is to inhibit or delay the fibrillation process. Carbon dots (C–Dots) have recently emerged as benign nanoparticles to replace toxic quantum dots and have attracted great attention because of their unique optical properties and potential applications in biological systems. However, the effect of C-Dots on peptide or protein fibrillation has not been explored. In this in vitro study, human insulin was selected as a model to investigate the effect of C-Dots on insulin fibrillation. Water-soluble fluorescent C-Dots with sizes less than 6 nm were prepared from carbon powder and characterized by UV–vis spectroscopy, fluorescence, Fourier transform infrared spectrophotometry, X-ray photoelectron spectrometry, transmission electron microscopy, and atomic force microscopy. These C-Dots were able to efficiently inhibit insulin fibrillation in a concentration-dependent manner. The inhibiting effect of C-Dots was even observed at 0.2 μg/mL. Importantly, 40 μg/mL of C-Dots prevent 0.2 mg/mL of human insulin from fibrillation for 5 days under 65 °C, whereas insulin denatures in 3 h under the same conditions without C-Dots. The inhibiting effect is likely due to the interaction between C-Dots and insulin species before elongation. Cytotoxicity study shows that these C-Dots have very low cytotoxicity. Therefore, these C-Dots have the potential to inhibit insulin fibrillation in biological systems and in the pharmaceutical industry for the processing and formulation of insulin.

Dihydrolipoic Acid Conjugated Carbon Dots Accelerate Human Insulin Fibrillation

“…Our experiments demonstrated that these CDs strongly inhibit human insulin fibrillation in a concentration-dependent manner [21]. Increasing the concentration of CDs enhances the inhibiting effect.…”

“…On the contrary, the presence of the DHLA-CDs in this study promotes human insulin fibrillation in a concentration-dependent manner. One has to point out that the DHLA-CDs have completely different nature in terms of size, surface property and component from those we reported in Reference [21]. As displayed in Figure 2D and 2E, the size of the DHLA-CDs is much larger (i.e.…”

“…The formation of the nucleation species (also called lag phase) is the key rate-determining ISSN: 2376-922X step, as it is a thermodynamically unfavored process during protein fibrillation. It has been known recently that the presence of nanoparticles can significantly affect protein conformation as a result of the interactions between nanoparticles and proteins [12,14,15,21]. Therefore, it is not unexpected that the presence of nanoparticles may accelerate or inhibit protein fibrillation.…”

“…In this study, human insulin was chosen to study the effects of CDs on its fibrillation. It is worth noting that the CDs used in this study have completely different nature from those we reported most recently [21] in terms of size, surface properties and components. The CDs in the present study have a hydrophobic core capped by dihydrolipoic acid (DHLA-CDs) to increase their water…”

“…For any application of CDs in a biological system, they are inevitably interacting with proteins which may undergo conformational changes to form fibrils due to the presence of CDs. However, the effect of CDs on protein fibrillation has not been reported until most recently (March 2015) from our group [21]. In that study, water soluble CDs with size less than 6 nm are prepared by oxidizing carbon nano powder and these CDs are demonstrated to inhibit human insulin fibrillation in vitro in a concentration-dependent manner.…”