Antioxidant Peptides

Reactive oxygen species (ROS) play a key role in promoting mitochondrial cytochrome c release and induction of apoptosis. Antioxidant peptides are cell-permeable and are very potent at reducing intracellular ROS and preventing cell death caused by the oxidant.

Discovery

To utilize fish processing waste, tuna backbone protein was hydrolyzed using different proteases (alcalase, α-chymotrypsin, neutrase, papain, pepsin and trypsin) for production of antioxidant peptide. Antioxidant activities of hydrolysates were evaluated by Jae-Young J et al., in 2007 using lipid peroxidation inhibition assay and direct free radical scavenging activity by using electron spin resonance (ESR) spectrometer. Among hydrolysates, peptic hydrolysate exhibited the highest antioxidant activity compared to other hydrolysates 1. Hee-Guk Byun et al., 2009 analyzed protein derived from the rotifer Brachionus rotundiformis using different proteases (Alcalase, α-chymotrypsin, Neutrase, papain, pepsin and trypsin) for production of antioxidant peptide. Antioxidant activities of hydrolysates were evaluated using DPPH radical scavenging activity. Peptic hydrolysate exhibited the highest antioxidative activity compared to other hydrolysates 2. The muscle of the prawn Penaeus japonicus was hydrolyzed by various proteases, and antioxidant activity of the hydrolysates was examined by Suetsuna K in 2000 3.

Structural Characteristics

Peptides corresponding to the region adjacent to His-94 in the small subunit of cytochrome b558 inhibit superoxide generation in a cell-free system from human neutrophils. This peptide is the shortest sequence that shows inhibitory effect. Substitutions of alanine for any of two tyrosine or central valine residues markedly increase inhibition, indicating the importance of these residues 4.

To identify antioxidant peptides, peptic hydrolysate was purified using consecutive chromatographic methods, and antioxidant peptides were identified to be Leu-Leu-Gly-Pro-Gly-Leu-Thr-Asn-His-Ala (1076 Da), and Asp-Leu-Gly-Leu-Gly-Leu-Pro-Gly-Ala-His (1033 Da) by Q-TOF ESI mass spectroscopy 2. The muscle of the prawn Penaeus japonicus was examined and antioxidant activity of the hydrolysates was analyzed. Among the digests, pepsin digest showed the most potent antioxidant activity. Three antioxidant peptides have been isolated from the active peptidic fraction by ion-exchange chromatography, gel filtration, and ODS high-performance liquid chromatography. Their structures were identified as Ile-Lys-Lys, Phe-Lys-Lys, and Phe-Ile-Lys-Lys 3.

Mode of Action

ROS induce dissociation of cytochrome c from cardiolipin on the inner mitochondrial membrane (IMM), and cytochrome c may then be released via mitochondrial permeability transition (MPT)-dependent or MPT-independent mechanisms. We have developed peptide antioxidants that target the IMM, and used them to investigate the role of ROS and MPT in cell death caused by t-butylhydroperoxide (tBHP) and 3-nitropropionic acid (3NP). The structural motif of these peptides centers on alternating aromatic and basic amino acid residues, with dimethyltyrosine (Dmt) providing scavenging properties. These peptide antioxidants are cell-permeable and concentrate 1000-fold in the IMM. They potently reduced intracellular ROS and cell death caused by tBHP in neuronal N2A cells (EC50 ~nM). They also decreased mitochondrial ROS production, inhibited MPT and swelling, and prevented cytochrome c release induced by Ca2+ in isolated mitochondria.

Functions

Aging and diseases, these IMM-targeted antioxidants may be very beneficial in the treatment of aging and diseases associated with oxidative stress 4.

Peroxidation inhibition, antioxidant activities of hydrolysates were evaluated using lipid peroxidation inhibition assay and direct free radical scavenging activity by using electron spin resonance (ESR) spectrometer. Among hydrolysates, peptic hydrolysate exhibits the highest antioxidant activity compared to other hydrolysates 1.

Malondialdehyde level has been used as the oxidation index in many biological systems. GLP showed substantial antioxidant activity in the rat liver tissue homogenates and mitochondrial membrane peroxidation systems. The auto-hemolysis of rat red blood cells was also blocked by GLP in a dose-dependent manner. On the basis of these results, it is concluded that GLP is the major constituent responsible for the antioxidant activity of G. lucidum. GLP could play an important role in the inhibition of lipid peroxidation in biological systems through its antioxidant, metal chelating, and free radical scavenging activities.

References

1. Jae-Young J, Zhong-Ji Qian, Hee-Guk Byun, Se-Kwon Kim (2007). Purification and characterization of an antioxidant peptide obtained from tuna backbone protein by enzymatic hydrolysis. Process Biochemistry, 42(5):840-846.

2. Hee-Guk Byun, Jung Kwon Lee, Heum Gi Park, Joong-Kyun Jeon, Se-Kwon Kim (2009). Antioxidant peptides isolated from the marine rotifer, Brachionus rotundiformis. Process Biochemistry, 44(8):842-846.

3. Suetsuna K (2000). Antioxidant peptides from the protease digest of prawn (Penaeus japonicus) muscle. Journal Marine Biotechnology, 2(1):5-10.

4. Park MY, Imajoh-Ohmi S, Nunoi H, Kanegasaki S (1994). Peptides corresponding to the region adjacent to His-94 in the small subunit of cytochrome b558 inhibit superoxide generation in a cell-free system from human neutrophils. Biochem. Biophys. Res. Commun., 204(2):924-929.