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Peptides are compounds formed by connecting α-amino acids with peptide bonds (an amide bond). They are intermediate products of protein hydrolysis in organisms and are the direct executors of life activities. Active peptides have all or part of the functions and properties of proteins, and the most important thing is that they can be mass-produced through chemical synthesis. Since the production of peptides by solid-phase synthesis in the 1990s, the industrialization of peptides has progressed rapidly, and their applications in industries such as drugs, health products, and cosmetics have become increasingly widespread. With the development of personalized medical treatment, the peptide industry will usher in a new round of leap-forward development.
Peptides are connected to each other by removing a molecule of water from -NH of one amino acid molecule and -COOH of another amino acid molecule to form -CH-NH. Depending on the number of amino acids (usually 10 to 100), they are called dipeptides, tripeptides, tetrapeptides, pentapeptides, etc. Among them, peptides composed of three or more amino acid molecules are called polypeptides. In addition, with different types and quantities of amino acids, each peptide has a unique composition structure, which determines and produces different functions. Peptides are one of the most complex classes of compounds in terms of type and function. Compared to amino acids, peptides have faster absorption rates, low or no energy consumption, and unsaturation.
Peptides naturally occur in the skin, and the human body can synthesize and degrade peptides according to physiological conditions. Natural peptides come from the enzymatic breakdown products of structural proteins in the epidermis and dermis. They can regulate hormone activity, enhance or inhibit immune responses, regulate cell life cycles, activate aging cells, and comprehensively regulate and promote various major systems of the human body. The effects of peptides on human cells include but are not limited to:
| Peptides Function | Descriptions |
| Improve immunity and enhance disease resistance | Multiple research results have proven that small molecule peptides have powerful killing effects on most bacteria, fungi, protozoa, viruses and cancer cells. In addition, clinical trials have shown that small molecule active peptides can increase the phagocytic activity of macrophages and promote the proliferation of lymphocytes, which can comprehensively and quickly improve human immunity and enhance anti-viral capabilities. |
| Activate cells | Small molecule peptides can activate cell activity, clean up free radicals in the human body, prevent free radicals from damaging cells, so that human cells can function normally and be in a healthy state. |
| Repair cells | Peptides can also repair damaged and diseased cells in the human body and improve cell metabolism. Make cells healthier and more energetic. |
| Remove body toxins | Peptides can promote cell metabolism, provide nutrients and energy to cells, and can also promote the absorption of other nutrients. They can help the body quickly eliminate waste and toxins from the body and maintain normal cell metabolism. |
| Delay and reverse aging | Peptides are considered in the field of cosmetics to inhibit free radical peroxidation. It can accelerate the repair of damaged cells, maintain body vitality, reduce pigmentation, whiten spots, activate cells, promote metabolism, delay cell aging, regulate human growth and development, delay and reverse aging, etc. |
Peptides can be classified in various ways based on their functions, structures, and sources. Below are some common types of peptides:
Hormonal peptides are a class of peptides that play crucial roles in the endocrine system. They are secreted by specific endocrine glands or tissues and transported through the bloodstream to target organs or cells to regulate physiological functions. For example, insulin, a hormonal peptide secreted by the beta cells of the pancreas, regulates blood glucose levels. Growth hormone, secreted by the anterior pituitary, promotes growth and development, while gonadotropins, also secreted by the anterior pituitary, regulate the functions of the reproductive system. Hormonal peptides are characterized by their high specificity and long-range action, making them essential for maintaining homeostasis and regulating physiological processes.
Enzymatic peptides are peptides with catalytic activity. They accelerate chemical reactions and reduce activation energy. These peptides exhibit high specificity and efficiency, enabling them to recognize and bind to substrate molecules selectively. Through catalytic groups in their active sites, they facilitate the transformation of substrate molecules. For example, trypsin, an enzymatic peptide secreted by the pancreas, specifically hydrolyzes peptide bonds involving lysine and arginine residues in proteins, breaking them down into smaller peptides and amino acids to provide nutrients for the body. Enzymatic peptides play vital roles in metabolism, digestion, absorption, and signal transduction in living organisms.
Signal transduction peptides are a type of peptide that plays a critical role in cellular signal transduction processes. They bind to receptors on the cell surface, activating the receptors' signaling functions and converting extracellular signals into intracellular signals, thereby regulating cellular physiological activities. For example, epidermal growth factor (EGF) is a signal transduction peptide that binds to the EGF receptor on the cell surface, activating the receptor's tyrosine kinase activity. This activation initiates a cascade of intracellular signaling pathways, promoting cell proliferation, migration, and differentiation. Signal transduction peptides are crucial for processes such as cell growth, differentiation, apoptosis, and immune responses, serving as essential mediators of intercellular communication and signal transmission.
Neuropeptides are peptides that play significant roles in the nervous system. They act as neurotransmitters or neuromodulators, participating in the transmission and regulation of neural signals. For instance, substance P is a neuropeptide involved in transmitting pain signals, while vasoactive intestinal peptide (VIP) has multiple functions, including vasodilation and regulation of gastrointestinal motility. Neuropeptides are characterized by their diverse functions and complex regulatory mechanisms, playing important roles in regulating physiological functions and pathological states within the nervous system.
Peptides have diverse sources, primarily including natural peptide extraction, production through bioengineering techniques, and chemical synthesis.
Natural peptides are widely found in animals and plants. In animal tissues, meat and organs are significant sources of peptides. For example, enkephalins can be extracted from pig brains, and hemoglobin peptides can be obtained from bovine blood. These natural peptides are characterized by high bioactivity and minimal side effects, though the extraction process is relatively complex and yields are limited. Plants also contain abundant peptides. Protein-rich seeds from plants such as soybeans and wheat can be processed and extracted to produce bioactive peptides. For instance, soybean peptides exhibit various functions, including antioxidant activity, blood pressure regulation, and immune modulation, and are widely used in food and health products. The extraction of plant peptides typically involves enzymatic hydrolysis, where specific enzymes break down plant proteins into peptides, followed by separation and purification to obtain the target peptides. This method is cost-effective and utilizes abundant raw materials, but the resulting peptides often have lower activity and purity.
With advancements in bioengineering, recombinant peptide production has become an important method for obtaining peptides. Through genetic engineering, the gene encoding the target peptide is inserted into a suitable expression vector, which is then expressed in host cells such as Escherichia coli, yeast, or mammalian cells to produce large quantities of recombinant peptides. For example, recombinant insulin is produced via genetic engineering in E. coli. This method offers high yield, high purity, and low cost, making it suitable for large-scale production and application. Additionally, bioengineering enables the modification and optimization of peptides through protein engineering to enhance their stability and activity. For instance, modifications to insulin molecules can extend their half-life in the body and improve therapeutic efficacy. Peptides produced via bioengineering techniques have broad applications in medicine, cosmetics, and food industries.
Chemical synthesis is a critical method for peptide production, involving the stepwise connection of amino acids through chemical reactions to form peptides with specific sequences. This approach allows for precise control over the sequence of amino acids, ensuring high fidelity in peptide composition. One of the major advantages of chemical synthesis is the ability to rapidly produce peptides, making it an essential tool for research, including the development of small peptide drugs. However, it does come with some drawbacks, including relatively high costs and limitations in the length of peptides that can be synthesized effectively. Despite these challenges, chemical synthesis remains a valuable technique, particularly in the creation of peptides with well-defined structures. As advancements in synthetic methodologies continue, the scope of chemical synthesis in peptide production is expected to expand, potentially lowering costs and enabling the synthesis of longer and more complex peptides for a broader range of applications in both research and therapeutics.
As mentioned above, there are three main sources of active peptides: chemical synthesis, animal and plant extraction, and genetic engineering. Among them, chemical synthesis is the mainstay, and solid-phase synthesis technology has greatly promoted the development of peptides. The content of peptides in animals and plants is low and their purity is not enough. Genetic engineering, also called DNA recombination, refers to the process of exchanging and recombining DNA fragments due to the breakage and connection of different DNA strands, thereby forming new DNA. This method is mainly used for the preparation of long peptides. However, the cost is high, the success rate is low, and the product cannot be extracted in large quantities, so it still needs to be improved.
Chemical synthesis of peptides has become a mainstream synthesis method of peptides, especially in the field of pharmaceuticals, which are basically chemically synthesized peptides. Compared with peptides from other sources, it was found that the production cost of chemically synthesized peptides is controllable and easy for industrial production. Moreover, the amino acid length can be 2-50, the impurity content is predictable, the quality standards are easy to establish, and non-naturally occurring peptide types can be produced. Fully chemical synthesis of peptides can be divided into liquid phase synthesis (LPPS) and solid phase synthesis (SPPS) depending on the synthesis environment.
Liquid-phase peptide synthesis (LPPS) remains a widely used method for the synthesis of peptides, especially short peptides and peptide fragments, due to its significant advantages in terms of scalability and cost-effectiveness. One of the key benefits of LPPS is the ability to perform reactions in the liquid phase, which allows for a broader range of reaction conditions to be employed. For example, catalytic hydrogenation, alkaline hydrolysis, and other specific conditions can be utilized, providing greater flexibility compared to solid-phase peptide synthesis (SPPS). In contrast, SPPS may face limitations due to lower reaction efficiency and the potential for side reactions under certain conditions. Two major strategies commonly employed in LPPS are the BOC (tert-butyloxycarbonyl) and Z (benzyloxycarbonyl) methods. These strategies involve the selective protection and deprotection of amino acid side chains, facilitating the stepwise construction of peptide chains in solution. Overall, LPPS remains an essential tool for peptide synthesis, particularly when large-scale production or low-cost synthesis is required.
Solid-phase synthesis has many advantages such as a wide selection of protective groups, low cost, and easy scale-up of synthesis. Compared with solid-phase synthesis, the main disadvantage of liquid-phase synthesis is that the synthesis range is small, and it generally focuses on the synthesis of peptides within 10 amino acids. In addition, intermediates need to be purified during synthesis, which takes a long time and requires a lot of work. There are currently two main strategies used in solid-phase peptide synthesis: BOC and FMOC. In the BOC method, TFA needs to be used repeatedly to remove BOC during the peptide synthesis process, and HF needs to be used to cleave the peptide from the resin at the end. Since HF must be operated using specialized instruments, and side reactions are easy to occur during peptide cleavage, its use is now restricted by experimental conditions and its use is gradually decreasing. The reaction conditions of the FMOC method are mild and peptide synthesis can be carried out under general experimental conditions. Therefore, it has also been widely used.
Research Peptides are short chains of amino acids widely utilized in scientific research, drug development, and the biomedical field. These peptides are prepared through chemical or biological synthesis, allowing them to mimic the functions of natural peptides within the body. This capability provides powerful tools for investigating specific molecular mechanisms or disease pathways. The applications of research peptides span multiple areas, from signal transduction to immune responses, and they hold particular significance in studies on cancer therapies, neurodegenerative diseases, and metabolic disorders. Furthermore, research peptides are often used as model molecules in drug screening to study interactions between drugs and target proteins.
Peptide modification refers to the structural or functional alteration of peptide molecules through chemical or enzymatic methods to enhance their stability, bioactivity, or specific properties. This process has broad applications in the fields of pharmaceuticals, biotechnology, and materials science. Common modification techniques include N-terminal and C-terminal modifications, chemical modification of amino acid residues, glycosylation, PEGylation (polyethylene glycol modification), and lipidation. These modifications can improve the enzymatic degradation resistance, extend the half-life, enhance the targeting ability, or reduce the immunogenicity of peptides. Additionally, site-specific modifications can endow peptide molecules with new functionalities, such as fluorescent labeling for imaging or conjugation with antibodies and small molecule drugs for the development of antibody-drug conjugates (ADCs).
Peptides are showing huge potential in cosmetic industry, exerting multiple functions as skin tightening, rapid wrinkle repair, muscle relaxation and skin comfort, etc. Argireline, also known as acetyl hexapeptide-3 has the main effect of reducing the wrinkles caused by the contraction of facial expression muscles and wrinkles around the forehead or eyes. Besides, it can promote collagen production, which helps to rebuild skin tissue. Palmitoyl tripeptide-5 is a nutritional anti-wrinkle ingredient used by many famous international cosmetic brands. It helps to improve facial elasticity, reduce facial wrinkles, improve skin water content, and enhance skin radiance, etc.
Marketed peptide drugs have been quite widely implemented in treating diseases, including diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection. This field has emerged many blockbuster drugs. These include the GLP-1 receptor agonists Exenatide and Liraglutide for the treatment of diabetes, and the gonadotropin-releasing hormone analogs (GnRHa) Leuprolide and Goserelin for the treatment of cancer. Long-acting, non-injectable formulation will be the focus of research and development in the future.
Peptides showing remarkable characteristics of processing stability, moisturizing property, low viscosity and foaming property endow their extensively applications in food industry. Moreover, they have the advantages of abundant sources, functional diversity and high bioavailability making their applications in functional foods and dietary supplements. Pea peptides are with more nutrients containing 8 essential amino acids required by human body, high water retention, gel formation and good emulsion stability, thus are used as an excellent additive in meat products processing. Due to its foaming properties and other properties, it can be added to pastry products instead of eggs and to noodle products to improve the nutritional value, strength and tenderness of noodles, and the appearance and taste of food.
As plant protectants, peptides can activate plant growth potential, regulate plant metabolism, enhance plant water and fertilizer absorption, promote plant flower bud differentiation, improve crop fruit quality and induce plant resistance to fungal diseases, bacterial diseases, viral diseases and other diseases after being applied on the plant surface. Besides, peptides can be developed into plant immune inducers, fungicides, insecticides and chelated micronutrients, etc.
