Stimulation of endogenous antioxidant enzymes

The common mechanism involved is based on the formation of reactive chemical species. But this is also the principal mechanism in normal, chronological skin ageing because the energy metabolism in mitochondria continuously produces reactive chemical byproducts. Reactive chemical species are free radicals containing unpaired electrons such as superoxide, hydroxyl or nitric oxide but also non-radical derivatives of oxygen and nitrogen such as hydrogen peroxide. These reactive chemical species finally lead to DNA damage and the formation of oxidised lipids and proteins. The cells in our tissues normally react with antioxidant molecules and an up-regulated expression of antioxidant and detoxification enzymes. This cellular protection system can however not cope with an excess of detrimental chemical species related to unhealthy lifestyle factors. In addition, there is an age-related decline in cellular protection.

Topically applied antioxidants like vitamins C and E can neutralise reactive chemical species but the vitamins are consumed after one reaction only. The better strategy would be to up-regulate the expression of antioxidant and detoxification enzymes which neutralise electrophiles and replenish used cellular antioxidants such as glutathione. The induction of protective enzymes in response to reactive chemical stress is regulated at the transcriptional level (Fig. 1). These cytoprotective enzymes are characterised by a specific gene sequence, called antioxidant response element (ARE). The expression of these proteins is regulated by the transcription factor Nrf2 that binds to the ARE site in the promoter regulatory sequence.^1,2 Nrf2 induces the expression of a number of genes involved in protecting cells against free radicals and oxidative stress- comprising genes involved in glutathione synthesis, protein thiol homeostasis and phase II antioxidant enzymes such as heme oxygenase 1(HO-1) and NAD(P)H dehydrogenase quinone 1 (NQO1).³

Under basal conditions, Nrf2 is repressed in the cytoplasm by binding to Keap1 (Fig. 1). In response to toxic chemicals and oxidative stress, the Nrf2- Keap1 complex is disrupted and Nrf2 translocates into the cellular nucleus to activate gene expression. When bound to Keap1, Nrf2 is constantly degraded because Keap1 targets Nrf2 for ubiquitination and degradation by the proteasome.⁴ Disruption of the Nrf2-Keap1 complex to avoid proteasomal degradation allows nuclear translocation and expression of ARE-regulated genes. Figure 2 shows the interaction between Nrf2 and Keap1 at the molecular level. The ‘ETGE’ amino acid motif in the Neh2 domain of Nrf2 is responsible for high-affinity interaction with the Kelch-repeat domain of the Keap1 protein.⁵ Responsible for binding are salt bridges between glutamic and aspartic acid residues in the Neh2 domain and arginine residues in the Kelch-repeat domain. The peptide acetyl-DEETGEF corresponding to a Neh2 sequence containing the ‘ETGE’ motif was developed to compete with Nrf2 for binding to Keap1. The heptapeptide was incorporated into solid lipid nanoparticles for stabilisation and for better penetration into the skin and increased cellular uptake. The size of the peptide (868 Dalton) and its hydrophilic nature would otherwise not allow significant penetration into the skin. Solid lipid nanoparticles were originally developed as drug delivery systems for intravenous and parenteral applications. They make possible a controlled release, protection of unstable ingredients and intracellular traffic. The acetyl-DEETGEF peptide in solid lipid nanoparticles (PerfectionPeptide P7; INCI: Acetyl sh- Heptapeptide-1, Glycerin, Butyrospermum Parkii (Shea) Butter, Lecithin, Phenethyl Alcohol, Ethylhexylglycerin, Tocopherol and Water) was tested in cell culture assays and clinical studies for stimulation of the skin’s own defence systems against toxic reactive chemicals.