The Role of Antimicrobial Peptides in Periodontal Disease (Part I): an Overview of Human Defensins and Cathelicidin
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The oral cavity is a warm and moist environment, suitable for microorganisms to colonize and live in harmony as a community, socalled biofilm. In this environment, antimicrobial peptides may play a critical role in maintaining normal oral health and controlling innate and acquired immune systems in response to continuous microbial challenges in periodontal disease. Two major families of antimicrobial peptides, found in the oral cavity, are defensin and cathelicidin. Members of the defensin family are cysteine-rich peptides, synthesized by plants, insects, and mammals. In the oral cavity, four alpha-defensins are synthesized and stored in neutrophil granules, which are converted into active peptides by proteolytic processing, while three human betadefensins (hBDs), hBD-1, hBD-2, and hBD-3, are predominantly produced by oral epithelial cells. The only member of the cathelicidin family found in humans is LL-37, which contains 37 amino acids and begins with two leucines at its N-terminus. Clinically, differential expression of antimicrobial peptides has been reported in different types of periodontal disease, and their presence has been shown in saliva and gingival crevicular fluid. In the first part of our review article, basic knowledge of antimicrobial peptides will be discussed in detail.Keywords:
Cathelicidin
Beta defensin
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Cyclic peptides are receiving significant attention thanks to their antimicrobial activity and high serum stability, which is useful to develop and design novel antimicrobial agents. Antimicrobial peptides appear to be key components of innate defences against bacteria, viruses, and fungi. Among the others, defensins possess a strong microbicidial activity. Defensins are cationic and amphipathic peptides with six cysteine residues connected by three disulfide bonds found in plants, insects, and mammals; they are divided in three families: α-, β-, and θ-defensins. α-Defensins are contained in the primary granules of human neutrophils; β-defensins are expressed in human epithelia; and θ-defensins are pseudo-cyclic defensins not found in humans, but in rhesus macaques. The structural diversities among the three families are reflected in a different antimicrobial action as well as in serum stability. The engineering of these peptides is an exciting opportunity to obtain more functional antimicrobial molecules highlighting their potential as therapeutic agents. The present review reports the most recent advances in the field of cyclic peptides with a specific regard to defensin analogs.
Beta defensin
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Human defensin peptides with antimicrobial properties are classified under antimicrobial peptides (AMPs). They are produced by neutrophils and epithelial cells and involved in innate immunity through killing of microbial pathogens or neutralizing bacterial toxins and adaptive immunity by serving as chemo attractants and activators of immune cells. They all are 29-35 amino acids peptides, invariably cationic in nature and belongs to β sheet structure with two or three intra molecular disulfide bonds. Many of them attack their target cells by permeabilizing the cell membrane. They can be roughly categorized into three main classes according to their structural differences: the α defensins, β defensins and θ defensins. Most of the known human defensin peptides with antimicrobial functions have been identified and studied during the last 15 years. As a result of these studies, new knowledge has been acquired into biology and biochemistry. It has become evident that these peptides may be developed into useful antimicrobial additives and drugs. The use of some defensin mimetic peptide as replacement for clinical antibiotics is promising. This review focuses on the current status of some of the main types of human defensin AMPs produced by neutrophils and epithelial cells and discusses its mode of action, the novel antimicrobial functions, molecular characterization, new developments, e.g. recombinant DNA production of defensins in bacteria and transgenic plants, novel applications related to these peptides, and future research paradigms.
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Defensins are a class of cationic peptides which is widely found in plants and animals,and are a representative sub-clan of antimicrobial peptides family(Antimicrobial peptides are a kind of short-chain peptide of broad-spectrum antimicrobial effects) and a very conservative host defense molecules.So far,a variety of defensins have been found.Human beta defensin(hBD) play an important role in these defensins,and have a strong bactericidal activity,chemotactic activity,regulatory function of phagocytic cells and acquired immune etc.In addition,several researches also found that hBD have an anti-tumor activity,and are closely related with oral carcinoma.Therefore,hBD may provide a new strategy for the prevention and treatment of the tumor.
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Beta defensin
Cathelicidin
Cecropin
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Despite advances in the treatment of oral diseases, dental caries, its complicated forms and diseases of the mucous membranes of the oral cavity are often found in children. Proved a clear link between the state of the oral cavity and the General somatic status of the child, the state of his immunity. One of the neglected components of the innate immune system are antimicrobial peptides (AMP). AMP can be found virtually in all physiological liquids, as well as the epithelium of the skin and mucous membranes. Peptides are important in the oral cavity, where microbial flora is present in high concentration constantly; AMP are natural antibiotics, which provide the first line of defense against a wide range of pathogens. There are three main groups of amino acid composition and the three-dimensional structure: a-helical peptides without cysteine (cathelicidins) peptides with three disulfide bonds (a - and b-defensine), and peptides with a high number of amino acids (histatin). Recent studies show the importance of defensine and cathelicidin as antibacterial agents of the mouth, while histatine has a pronounced anti-fungal and prevents the formation of microbial film on the surface of the tooth.
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Cationic antimicrobial peptides are present throughout the plant and animal kingdoms and bear striking structural and functional similarities across species lines. They provide primitive, nonspecific means of combating a variety of bacteria, fungi, enveloped viruses, and protozoa. Some are also cytotoxic against host cells, including neoplastic cells. Cationic antimicrobial peptides may play various roles in inflammation and tissue repair. Antimicrobial peptides are found in epithelial tissues regularly exposed to microbial attack as well as in cells whose primary function is defense against potential pathogens. They constitute an important part of the nonoxidative antimicrobial arsenal of leukocytes. They are preformed and/or readily synthesized when the cells are stimulated by exposure to pathogens. They exert their effects directly by inserting into membranes of target cells and forming ion channels which increase membrane permeability; however, antimicrobial peptides can also act as opsonins to facilitate phagocytosis. Resistance to defensins is a virulence factor for organisms such as Salmonella sp. The study of cationic antimicrobial peptides is increasing our understanding of innate immunity, inflammation, and the pathogenesis of genetic diseases such as specific granule disease in humans. Therapeutic applications of antimicrobial peptides are currently under investigation.
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Introduction. General Concepts of Antimicrobial Peptides, Past and Future. Section 1. Select Diverse Peptides with Antimicrobial Action in Humans. 1. The Role of Cathelicidins in the Innate Host Defences of Mammals. 2. The Role of Alpha and Beta Defensins in Human Defense. 3. Granulysin. 4. Hepcidin. Section 2 Tissues and their use of Antimicrobial Peptides. 5. Antimicrobial Peptides in Human Blood. 6. The Role of Paneth Cell a-Defensins in Enteric Innate Immunity. 7. Lung. 8. Antimicrobial Peptides in the Oral Environment: Expression and Function in Health and Disease. 9. Natural Antimicrobial Peptides: A Barrier against Human Skin Infection. Section 3 Clinical Concepts. 10. Antimicrobial Peptide Resistance in Human Bacterial Pathogens. 11. A Pediatric Perspective on Antimicrobial Proteins and Peptides: Expression, Function, and Clinical Relevance. 12. Therapeutic Applications of Innate Immunity Peptides.
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