Stabilization of Natural Antioxidants by Silk Biomaterials

Abstract

The stabilities of three natural antioxidants, vitamin C (VC), (-)-epigallocatechin gallate (EGCG), and curcumin, in silk films were examined and mechanisms of stabilization were elucidated. The antioxidants were physically incorporated into three types of silk films: as-cast, dried from hydrogels, and methanol-treated. Films were stored at 4, 37, and 45 °C for 30 days in phosphate-buffered saline, pH 7.4, along with controls consisting of free antioxidants. Incorporation of antioxidants did not significantly change film morphology or secondary structure. When stored at 4 °C, all samples showed similar antioxidant activities (percent scavenging) at different time points, determined by the colorimetric 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. At higher temperatures, VC in the as-cast film, EGCG in the as-cast and dried hydrogel films, and curcumin in the methanol-treated films retained more than 50% scavenging activity after 14 days of storage, significantly higher than the other samples. Interaction between antioxidants and silk, as well as degradation of the antioxidants, was investigated by fast-performance liquid chromatography (FPLC) and high-pressure liquid chromatography (HPLC), with an aim of understanding the mechanisms of silk-based stabilization. Binding of antioxidant molecules to hydrophobic or to hydrophilic/hydrophilic boundary regions of silk, depending on the chemical properties of the antioxidant, may account for the observed stabilization effects. The data can help guide further engineering of antioxidant-functionalized silk biomaterials.

Epigallocatechin gallate inhibits Streptococcus pneumoniae virulence by simultaneously targeting pneumolysin and sortase A

“…Epigallocatechin gallate (EGCG), a major component of green tea catechins, possesses diverse biological properties, including antioxidant, anti‐inflammatory and anticarcinogenic effects , and has some therapeutic effects for hyperglycaemia‐induced embryopathy, breast tumours and Alzheimer's disease correlated with oestrogen depletion . Zhao et al .…”

“…Epigallocatechin gallate (EGCG), a major component of green tea catechins, possesses diverse biological properties, including antioxidant, anti-inflammatory and anticarcinogenic effects [21,22], and has some therapeutic effects for hyperglycaemia-induced embryopathy, breast tumours and Alzheimer's disease correlated with oestrogen depletion [22][23][24]. Zhao et al [25] have demonstrated that the combination of EGCG with b-lactams revealed a synergistic antibacterial effect on methicillin-resistant S. aureus (MRSA).…”

Comparative Study of Strain‐Dependent Structural Changes of Silkworm Silks: Insight into the Structural Origin of Strain‐Stiffening

“…In contrast to synthetic polymers based on chemical reactions, silkworm silk is a protein‐based material produced by silkworms at ambient conditions in an all‐aqueous reaction environment. Silk is thus produced in an environment‐friendly process, and due to biocompatibility and mechanical features shows potential for developing healthcare products, biomedical devices, and biosensors . The extraordinary mechanical properties of silk originate from the unique highly repetitive sequence in fibroin, along molecular self‐assembly and organization at nanoscale .…”

Recent Advances in Polymer Nanomaterials for Drug Delivery of Adjuvants in Colorectal Cancer Treatment: A Scientific-Technological Analysis and Review

“…For example, Lou et al (2016) used fibroin to stabilize vitamin C, curcumin, and epigallocatechin gallate. The results indicated that these antioxidants presented improved environmental stabilities of up to 14 days due to the binding of antioxidant molecules to the hydrophobic or the hydrophilic/hydrophilic boundary regions of silk [174]. Despite this work not being directly focused on CRC, it is highly relevant because antioxidants can easily react with air and other environmental conditions, losing their ROS -scavenging properties, prior to be consumed by the patient; without stabilization, the antioxidant simply will have little or no effect in the patient.…”