The Seven Major Types of Peptides
Polypeptides can generally be divided into two categories: polypeptide drugs and polypeptide health supplements.
1. Traditional polypeptide drugs are mainly peptide hormones. In recent years, the development of peptide drugs has expanded to various fields of disease prevention and treatment, especially showing rapid progress in the following areas:
1.1 Anti-tumor peptides: The occurrence of tumors is the result of multiple factors, but ultimately involves the regulation of oncogene expression. Many genes related to tumors and regulatory factors that affect tumors have been discovered. Screening for peptides that specifically bind to these genes and regulatory factors has become a new hotspot in the search for anti-cancer drugs. For example, somatostatin is already used to treat endocrine tumors of the digestive system; American scholars have discovered a six-peptide that significantly inhibits adenocarcinoma in vivo; Swiss scientists have discovered an eight-peptide that can induce apoptosis in tumor cells.
1.2 Antiviral peptides: Viruses adsorb onto host cells by binding to specific receptors on them and rely on their own specific proteases for protein processing and nucleic acid replication. Therefore, peptides that bind to host cell receptors or interact with active sites of viral proteases can be screened from peptide libraries for antiviral therapy. Currently, Canada, Italy, and other countries have screened out many small peptides with antiviral properties from peptide libraries, some of which have entered clinical trial stages. In June 2004, the Institute of Microbiology of the Chinese Academy of Sciences reported significant progress in the research project "Study on the Cell Fusion Mechanism of SARS Coronavirus and Fusion Inhibitors" conducted collaboratively by the Institute of Microbiology of the Chinese Academy of Sciences and the Modern Virology Research Center of Wuhan University's School of Life Sciences. Experiments showed that the designed HR2 peptide could effectively inhibit the infection of cultured cells by SARS virus at a concentration level of several nanomoles (nmole). Important progress was also made in the viral infection inhibition experiments of synthesized and expressed HR1 peptides and in vitro binding experiments between HR1 and HR2. The developed peptide drug to prevent SARS virus fusion can both prevent viral infection and stop further expansion of the virus in patients who are already infected. This peptide drug has dual functions of prevention and treatment. Researchers from the Fourth Military Medical University's Cell Engineering Research Center have synthesized nine peptides that can effectively block and inhibit the invasion of SARS virus into cells.
1.3 Peptide vaccines: Peptide vaccines and nucleic acid vaccines are one of the more important research aspects currently being emphasized in vaccine studies. Extensive research and development of viral peptide vaccines have been carried out worldwide. For example, in 1999, the NIH in the United States announced the results of clinical trials of two HIV-I virus peptide vaccines on humans; foreign scholars have screened a peptide from the outer membrane protein E2 of hepatitis C virus (HCV) that stimulates the body to produce protective antibodies; the U.S. is developing a multivalent antigen peptide vaccine for malaria; a human papillomavirus (HPV) peptide vaccine for cervical cancer has entered Phase II clinical trials. China has also done a great deal of work in the research of various peptide vaccines.
1.4 Cytokine mimetic peptides: Screening cytokine mimetic peptides using known cytokine receptors from peptide libraries has become a hot topic of research domestically and internationally in recent years. Abroad, mimetic peptides of various growth factors such as human erythropoietin, human thrombopoietin, human growth hormone, human nerve growth factor, and interleukin-1 have been screened. These mimetic peptides have different amino acid sequences from their corresponding cytokines but possess cytokine activity and have advantages such as smaller relative molecular mass. Currently, these cytokine mimetic peptides are in preclinical or clinical study stages.
1.5 Antibacterial active peptides: When insects are stimulated by external environmental factors, they produce large amounts of cationic peptides with antibacterial activity. More than a hundred types of antibacterial peptides have been screened so far. Both in vitro and in vivo experiments have confirmed that many antibacterial peptides not only have strong antibacterial and bactericidal capabilities but can also kill tumor cells.
1.6 Peptides for cardiovascular diseases: Many plants contain substances with effects such as lowering blood pressure, regulating blood lipids, and dissolving blood clots. These substances can be used as drugs or health foods. It has been found that many of these effective components are small molecule peptides. Therefore, discovering new active peptides from plants and conducting research and development has become a hotspot pathway in the study of peptide drugs.
1.7 Diagnostic peptides: The primary use of peptides in diagnostic reagents is as antigens to detect antibodies against corresponding pathogenic organisms. The characteristic of peptide antigens is that they are more specific than natural microbial or parasitic protein antigens and easier to prepare. Currently available antibody detection reagents assembled with peptide antigens include: hepatitis A, B, C, G viruses, HIV, human cytomegalovirus, herpes simplex virus, rubella virus, Treponema pallidum (syphilis), cysticercosis, trypanosomiasis, Lyme disease, rheumatoid arthritis, and others. Most of the peptide antigens used are analyzed and screened from the natural proteins of the corresponding pathogens, while some are newly screened from peptide libraries.