Cosmetics

• Components of human body


  • Water (60-70%)
  • Proteins (20%)
• Skin


  • Largest organ of the human body
  • Stratum corneum (SC) plays the key role of the barrier function
• Amino acids have been used in cosmetics for a long time and the number of products with amino acids or peptides is increasing
• Amino acids


  Natural L-α-amino acids that build proteins, and some other naturally occurring compounds

  
• α-amino acids


  • Molecular structure within which the amino group is attached to the same carbon atom as the carboxyl group
  • This carbon is asymmetric except for glycine
  • All amino acids as constituents of proteins are L-amino acids

  
• β-, γ-amino acids, amino acids with a sulfonate acid group


  Found in living organisms in the form of small peptides or as "free" amino acids
• Zwitterion


  Structure formed when the pH is lowered in an aqueous solution, as a proton is transferred from the acidic carboxy functional group to the amino functional group
• Proteinogenic amino acids found in human proteins

  • Aliphatic amino acids (neutral, basic, acidic and their amides, sulfur-containing)
  • Aromatic amino acids
  • Heterocyclic amino acids
• Peptides


  Polymers of amino acids, consisting of approximately 50 or fewer amino acids, of molecular weight up to 10,000
• Polypeptides


  Peptides of larger size, when there is no need to imply their functions as biopolymers
• Proteins


  Consist of one or more polypeptides or other ligands such as metal cations, coenzymes, etc., and they have to be assembled properly in order to exhibit biochemical functions

  
• Functional groups of the side chain of amino acid residues

  • Have a critical role to form and maintain the structure

  
• Keratin


  • Members of a family of proteins called intermediate filament (IF) proteins
  • A common secondary structure is that IF proteins consist of α-helical domains separated into four blocks via three shorter linkages and nonhelical N- and C-terminals

  
• Keratin


  • Cysteine-rich protein, the cysteine residue content varies from around 3% of SC keratin to over 7% of human hair keratin
  • The major force that keeps the helical structure is considered to be hydrophobic interaction
  • Disulphide bonds play a major part in stabilizing the complex structure when IFs are assembled into higher level of molecular structures

  
• Filaggrin


  Binds to IFs in epithelial cells during the epidermal terminal differentiation process to help them form an insoluble keratin matrix<|>Synthesized as a histidine-rich large precursor protein, profilaggrin, which is the main constituent of the keratohyalin granules within the granular layer of the epidermis<|>The precursor protein is activated by cleavage into 10-12 filaggrin monomers, and after finalization of the epidermal differentiation, filaggrin undergoes subsequent degradation in the SC to release free amino acids, a major component of natural moisturizing factor (NMF)

  
• Collagen


  • Main constituent of the dermis, representing about 75% of the dry weight
  • The collagen fibres form tough networks providing the dermis with strength, tension, and elasticity
  • The triple-helical structure arises from a repeating of gly-X-Y sequence, where X and Y can be any amino acid; often proline (28%) and hydroxyproline (38%), respectively
• Elastin


  • Insoluble extracellular matrix protein in connective tissue, serving a major role in organs where its elastic recoil and resilience are required
  • In the dermis, elastin plays a major role to provide a scaffold along with collagen
  • Cross-linking of collagen and elastin results in wrinkle formation
• Natural Moisturizing Factor (NMF)


  Originally defined as a complex mixture of free amino acids and other low-molecular-weight, water-soluble compounds found in corneocytes<|>The amino acids and PCA are produced within the SC by degradation of filaggrin, and this process is suggested to be triggered by decrease in humidity
• PCA is produced from glutamic acid; citrulline and ornithine are metabolites of arginine, and alanine is a metabolite of aspartic acid
• The amino acid amount found in the SC correlates with the skin moisture and in nonhealthy skin both amino acids and PCA are decreased
• Loss of profilaggrin or filaggrin by genetic mutations leads to a poorly formed SC, which is also prone to dehydration
• Urocanic acid (UCA)


  Trans-UCA is produced as a metabolite from histidine in the SC and is converted to the cis isomer by UV-B (280 - 310 nm)<|>Trans-UCA has been proposed to provide weak endogenic UV protection, and cis-UCA in turn is known to be involved in immunosuppression induced by UV irradiation
• The low concentration of glycine in comparison to the amino acid composition of filaggrin is probably explained by the low recovery rate of this small molecule
• Amino acids composition of NMF

  • Urocanic acid (UCA)
  • PCA
  • Citrulline
  • Ornithine
• Trans-urocanic acid (trans-UCA)


  Produced as a metabolite from histidine in the SC and is converted to the cis isomer by UV-B (280 - 310 nm)
• Trans-urocanic acid


  Provides weak endogenic UV protection
• Cis-UCA


  Involved in immunosuppression induced by UV irradiation
• Carnosine


  A dipeptide of β-alanine and histidine found in muscles and brain tissues
• Carnosine


  • Shows antioxidant activities, acts as a scavenger for reactive oxygen species (ROS) and unsaturated aldehydes formed by peroxidation of cell membrane fatty acids
  • Acts as an antiglycating agent and is speculated to be involved in enhanced aging process caused by diabetes
• Glutathione


  A tripeptide of glutamic acid, cysteine, and glycine with a peptide linkage between the γ-carboxyl group of the glutamate side-chain and the amine group of cysteine
• Glutathione


  • A powerful antioxidant whose efficacy is based on the thiol group of cysteine
• Production of Amino Acids

  1. Hydrolysis of proteins

  2. Chemical synthesis

  3. Biochemical processes
• Humectants


  Amino acids are widely used as ingredients that provide hydration effects as a result of their hygroscopicity
• Proline and PCA


  Have particularly high hygroscopicity and also show a synergistic effect when mixed
• Acidic amino acids


  Glutamic acid and aspartic acid, possess additional carboxylic groups on their carbon backbone
• Basic amino acids


  Lysine, arginine, and histidine, possess additional basic groups

  
• Arginine


  Used in various applications as a neutralizer or a pH adjuster
• Arginine


  • Prevents a decrease of tensile strength and hair surface hydrophobicity caused by oxidative colouring, and prevents undesirable effects of hydrogen peroxide on hair proteins and hair surface lipids
• Cysteine


  A sulfur-containing amino acid, unstable in the air, usually exists as a cystine by forming a disulfide bond between two cysteine residues
• Cysteine


  • A powerful antioxidant and has the potential to trap ROS, promising as an antiaging active
  • Tends to be absorbed into cells where it cannot exhibit its antioxidant property, so N-acetyl cysteine (NAC) is often used instead