LPO | |||||||||||||||||||||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Identifiers | |||||||||||||||||||||||||||||||||||||||||||||||||||
Aliases | LPO , SPO, lactoperoxidase | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | OMIM: 150205 MGI: 1923363 HomoloGene: 21240 GeneCards: LPO | ||||||||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||
Wikidata | |||||||||||||||||||||||||||||||||||||||||||||||||||
|
Lactoperoxidase is a peroxidase enzyme secreted from mammary, salivary and other mucosal glands including the lungs, bronchii and nose [5] that functions as a natural and the first line of defense against bacteria and viruses. [6] Lactoperoxidase is a member of the heme peroxidase family of enzymes. In humans, lactoperoxidase is encoded by the LPO gene. [7] [8]
Lactoperoxidase catalyzes the oxidation of several inorganic and organic substrates by hydrogen peroxide. [9] These substrates include bromide and iodide and therefore lactoperoxidase can be categorised as a haloperoxidase. An other important substrate is thiocyanate. The oxidized products produced through the action of this enzyme have potent and non-specific bactericidal and antiviral activities, including destruction of the influenza virus. Lactoperoxidase together with its inorganic ion substrates, hydrogen peroxide, and oxidized products is known as the lactoperoxidase system. [10] Hence LPO is considered a very important defense against invasive bacteria and viral agents such as influenza and the SARS-CoV-2 virus when sufficient iodine is provided. [11] [12] [13]
The lactoperoxidase system plays an important role in the innate immune system by killing bacteria in milk and mucosal (linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion) secretions hence augmentation of the lactoperoxidase system may have therapeutic applications. Furthermore, addition or augmentation of the lactoperoxidase system has potential applications in controlling bacteria in food and consumer health care products. The lactoperoxidase system does not attack DNA and is not mutagenic. [14] However, under certain conditions, the lactoperoxidase system may contribute to oxidative stress. [15] Furthermore, lactoperoxidase may contribute to the initiation of breast cancer, through its ability to oxidize estrogenic hormones producing free radical intermediates. [16]
The structure of lactoperoxidase consists mainly of alpha-helices plus two short antiparallel beta-strands. [17] Lactoperoxidase belongs to the heme peroxidase family of mammalian enzymes that also includes myeloperoxidase (MPO), eosinophil peroxidase (EPO), thyroid peroxidase (TPO), and prostaglandin H synthase (PGHS). A heme cofactor is bound near the center of the protein. [18]
Lactoperoxidase catalyzes the hydrogen peroxide (H2O2) oxidation of several acceptor molecules: [19]
Specific examples include:
Source of the hydrogen peroxide (H2O2) usually is the reaction of glucose with oxygen in the presence of the enzyme glucose oxidase (EC 1.1.3.4) that also takes place in saliva. Glucose, in turn, can be formed from starch in the presence of the saliva enzyme amyloglucosidase (EC 3.2.1.3).
These relatively short lived oxidized intermediates have potent bactericidal effects, hence lactoperoxidase is part of the antimicrobial defense system in tissues that express lactoperoxidase. [10] The lactoperoxidase system is effective in killing a range of aerobic [22] and certain anaerobic microorganisms. [23] Research (1984): "The effect of lactoperoxidase-thiocyanate-hydrogen peroxide mixtures on bacteria is dependent on experimental conditions. If the bacteria are cultured after the exposure to lactoperoxidase-thiocyanate-hydrogen peroxide on nutrient agar under aerobic conditions, they may not grow, whereas they grow readily on blood agar under anaerobic conditions." [24] In its antimicrobial capacity, lactoperoxidase appears to acts synergistically with lactoferrin [25] and lysozyme. [26]
Lactoperoxidase is an effective antimicrobial and antiviral agent. Consequently, applications of lactoperoxidase are being found in preserving food, cosmetics, and ophthalmic solutions. Furthermore, lactoperoxidase have found application in dental and wound treatment. Finally lactoperoxidase may find application as anti-tumor and anti viral agents. [27] Lactoperoxidase has been used with radioactive iodine to selectively label membrane surfaces. [28]
Lactoperoxidase is an effective antimicrobial agent and is used as an antibacterial agent in reducing bacterial microflora in milk and milk products. [29] Activation of the lactoperoxidase system by addition of hydrogen peroxide and thiocyanate extends the shelf life of refrigerated raw milk. [19] [30] [31] [32] It is fairly heat resistant and is used as an indicator of overpasteurization of milk. [33]
A lactoperoxidase system is claimed to appropriate for the treatment of gingivitis and paradentosis. [34] Lactoperoxidase has been used in toothpaste or a mouthrinse to reduce oral bacteria and consequently the acid produced by those bacteria. [35]
A combination of lactoperoxidase, glucose, glucose oxidase (GOD), iodide and thiocyanate is claimed to be effective in the preservations of cosmetics. [36]
Antibody conjugates of glucose oxidase and to lactoperoxidase have been found to effective in killing tumor cells in vitro. [37] In addition, macrophages exposed to lactoperoxidase are stimulated to kill cancer cells. [38] Knockout mice deficient in lactoperoxidase suffer ill-health and develop tumors. [39]
The antibacterial and anti-viral activities of lactoperoxidase play an important role in the mammalian immune defense system; the lactoperoxidase system is considered the first line of defense against airborne bacteria and viral agents. [40] [41] [42] Importantly, lactoperoxidase is also extruded into the lung, bronchii and nasal mucus. [43]
Hypothiocyanite is one of the reactive intermediates produced by the activity of lactoperoxidase on thiocyanate and hydrogen peroxide produced by dual oxidase 2 proteins, also known as Duox2. [44] [45] Thiocyanate secretion [46] in cystic fibrosis patients is decreased, resulting in a reduced production of the antimicrobial hypothiocyanite and consequently contributes to increased risk of airway infection. [47] [48]
Peroxidase-generated hypoiodous acid (HOI), hypoiodite and hypothiocyanite all destroy the herpes simplex virus [49] and human immunodeficiency virus. [50] Both the hypothiocyanite and the hypoiodate ion products are very potent and importantly non-specific antiviral oxidants which are lethal, even in small concentrations, to the influenza virus. [51] The anti-viral activity of lactoperoxidase is enhanced with increasing concentrations of iodide ion. [52] This enzyme has been shown effective against a highly dangerous and tough RNA virus (poliovirus) and a long-lived DNA virus (vaccina). [53]
The duox2-lactoperoxidase system has been shown to offer protection against many dozens of bacteria and mycoplasmas including varieties of the clinically important Staphylococcus and many Streptococcus types. [54] The lactoperoxidase system efficiently inhibits the common helicobacter pylori in buffer; however, in whole human saliva, it seems to have a weaker effect against this microbe. [55] It has been shown that lactoperoxidase in the presence of thiocyanide can catalyze the bactericidal and cytotoxic effects of hydrogen peroxide under specific conditions when hydrogen peroxide is present in excess of thiocyanide. [24] The combination of lactoperoxidase, hydrogen peroxide and thiocyanide is much more effective than hydrogen peroxide alone to inhibit bacterial metabolism and growth. [56]
The oxidation of estradiol by lactoperoxidase is a possible source of oxidative stress in breast cancer. [15] [16] The ability of lactoperoxidase to propagate a chain reaction leading to oxygen consumption and intracellular hydrogen peroxide accumulation could explain the hydroxyl radical-induced DNA base lesions recently reported in female breast cancer tissue. [15] Lactoperoxidase may be involved in breast carcinogenesis, because of its ability to interact with estrogenic hormones and oxidise them through two one-electron reaction steps. [16] Lactoperoxidase reacts with the phenolic A-ring of estrogens to produce reactive free radicals. [57] In addition, lactoperoxidase may activate carcinogenic aromatic and heterocyclic amines and increase binding levels of activated products to DNA, which suggests a potential role of lactoperoxidase-catalyzed activation of carcinogens in the causation of breast cancer. [58]
During the last decades, several clinical studies describing the clinical efficacy of the lactoperoxidase system in a variety of oral care products (tooth pastes, mouth rinses) have been published. After showing indirectly, by means of measuring experimental gingivitis and caries parameters, that mouth rinses [59] [60] containing amyloglucosidase (γ-amylase) and glucose oxidase activate the lactoperoxidase system, the protective mechanism of the enzymes in oral care products has been partially elucidated. Enzymes such as lysozyme, lactoperoxidase and glucose oxidase are transferred from the tooth pastes to the pellicle. Being components of the pellicle, these enzymes are catalytically highly active. [61] [62] Also, as part of tooth pastes, the lactoperoxidase system has a beneficial influence to avoid early childhood caries [63] by reducing the number of colonies formed by the cariogenic microflora while increasing the thiocyanate concentration. With xerostomia patients, tooth pastes with the lactoperoxidase system are seemingly superior to fluoride-containing tooth pastes with respect to plaque formation and gingivitis. [64] More studies are required [62] to examine further the protective mechanisms. [65]
The application of lactoperoxidase is not restricted to caries, gingivitis, and periodontitis. [66] A combination of lysozyme and lactoperoxidase can be applied to support the treatment of the burning mouth syndrome (glossodynia). In combination with lactoferrin, lactoperoxidase combats halitosis; [67] in combination with lactoferrin and lysozyme, lactoperoxidase helps to improve symptoms of xerostomia. [68] Furthermore, gels with lactoperoxidase help to improve symptoms of oral cancer when saliva production is compromised due to irradiation. In this case, also the oral bacterial flora are influenced favorably. [69] [70] [71]
Mouthwash, mouth rinse, oral rinse, or mouth bath is a liquid which is held in the mouth passively or swirled around the mouth by contraction of the perioral muscles and/or movement of the head, and may be gargled, where the head is tilted back and the liquid bubbled at the back of the mouth.
Catalase is a common enzyme found in nearly all living organisms exposed to oxygen which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting the cell from oxidative damage by reactive oxygen species (ROS). Catalase has one of the highest turnover numbers of all enzymes; one catalase molecule can convert millions of hydrogen peroxide molecules to water and oxygen each second.
Heme, or haem, is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver.
Lactic acid is an organic acid. It has a molecular formula CH3CH(OH)COOH. It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natural sources. Lactic acid is an alpha-hydroxy acid (AHA) due to the presence of a hydroxyl group adjacent to the carboxyl group. It is used as a synthetic intermediate in many organic synthesis industries and in various biochemical industries. The conjugate base of lactic acid is called lactate. The name of the derived acyl group is lactoyl.
Glutathione peroxidase (GPx) is the general name of an enzyme family with peroxidase activity whose main biological role is to protect the organism from oxidative damage. The biochemical function of glutathione peroxidase is to reduce lipid hydroperoxides to their corresponding alcohols and to reduce free hydrogen peroxide to water.
Saliva is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells, enzymes, antimicrobial agents.
Cytochrome c peroxidase, or CCP, is a water-soluble heme-containing enzyme of the peroxidase family that takes reducing equivalents from cytochrome c and reduces hydrogen peroxide to water:
Lactoferrin (LF), also known as lactotransferrin (LTF), is a multifunctional protein of the transferrin family. Lactoferrin is a globular glycoprotein with a molecular mass of about 80 kDa that is widely represented in various secretory fluids, such as milk, saliva, tears, and nasal secretions. Lactoferrin is also present in secondary granules of PMNs and is secreted by some acinar cells. Lactoferrin can be purified from milk or produced recombinantly. Human colostrum has the highest concentration, followed by human milk, then cow milk (150 mg/L).
The glucose oxidase enzyme also known as notatin is an oxidoreductase that catalyses the oxidation of glucose to hydrogen peroxide and D-glucono-δ-lactone. This enzyme is produced by certain species of fungi and insects and displays antibacterial activity when oxygen and glucose are present.
Thiocyanate is the anion [SCN]−, a salt or an ester of thiocyanic acid. It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Mercury(II) thiocyanate was formerly used in pyrotechnics.
Streptococcus mutans is a facultatively anaerobic, gram-positive coccus commonly found in the human oral cavity and is a significant contributor to tooth decay. It is part of the "streptococci", an informal general name for all species in the genus Streptococcus. The microbe was first described by James Kilian Clarke in 1924.
Iron-binding proteins are carrier proteins and metalloproteins that are important in iron metabolism and the immune response. Iron is required for life.
Animal heme-dependent peroxidases is a family of peroxidases. Peroxidases are found in bacteria, fungi, plants and animals. On the basis of sequence similarity, a number of animal heme peroxidases can be categorized as members of a superfamily: myeloperoxidase (MPO); eosinophil peroxidase (EPO); lactoperoxidase (LPO); thyroid peroxidase (TPO); prostaglandin H synthase (PGHS); and peroxidasin.
Haloperoxidases are peroxidases that are able to mediate the oxidation of halides by hydrogen peroxide. Both halides and hydrogen peroxide are widely available in the environment.
Biotene is an over-the-counter dental hygiene product currently marketed by GlaxoSmithKline (GSK). It comes in a number of forms, including toothpaste, mouthwash and gel.
Hypothiocyanite is the anion [OSCN]− and the conjugate base of hypothiocyanous acid (HOSCN). It is an organic compound part of the thiocyanates as it contains the functional group SCN. It is formed when an oxygen is singly bonded to the thiocyanate group. Hypothiocyanous acid is a fairly weak acid; its acid dissociation constant (pKa) is 5.3.
The respiratory tract antimicrobial defense system is a layered defense mechanism which relies on components of both the innate and adaptive immune systems to protect the lungs and the rest of the respiratory tract against inhaled microorganisms.
Haem peroxidases (or heme peroxidases) are haem-containing enzymes that use hydrogen peroxide as the electron acceptor to catalyse a number of oxidative reactions. Most haem peroxidases follow the reaction scheme:
Eosinophil peroxidase is an enzyme found within the eosinophil granulocytes, innate immune cells of humans and mammals. This oxidoreductase protein is encoded by the gene EPX, expressed within these myeloid cells. EPO shares many similarities with its orthologous peroxidases, myeloperoxidase (MPO), lactoperoxidase (LPO), and thyroid peroxidase (TPO). The protein is concentrated in secretory granules within eosinophils. Eosinophil peroxidase is a heme peroxidase, its activities including the oxidation of halide ions to bacteriocidal reactive oxygen species, the cationic disruption of bacterial cell walls, and the post-translational modification of protein amino acid residues.
Sujata Sharma is an Indian structural biologist, biophysicist, writer and a professor at the Department of Biophysics of the All India Institute of Medical Sciences, Delhi. She is known for her studies in the fields of protein structure, drug design and drug resistance of bacteria. Her studies have been documented by way of a number of articles and ResearchGate, an online repository of scientific articles has listed 167 of them. She is also the author of the books, "Warriors in White", an autobiographical account of some COVID-19 Warriors at All India Institute of Medical Sciences, Delhi and other leading hospitals of India, including Prof Randeep Guleria, using a combination of modern medicine, astronomy and Vedic astrology, "The Secret of the Red Crystals", an autobiographical account of her days in AIIMS Delhi. and "A Dragonfly's purpose", which is an autobiographical account of her recovery from an autoimmune disease, Guillain Barre Syndrome. The Department of Biotechnology of the Government of India awarded her the National Bioscience Award for Career Development, one of the highest Indian science awards, for her contributions to biosciences, in 2011. She is also a recipient of the Woman Scientist Award of the Biotech Research Society of India and the National Young Woman Bioscientist Award of the Department of Biotechnology which she received in 2006 and 2007 respectively. In 2020, she was awarded the Kalpana Chawla Excellence award, for her contributions in science. This award is instituted in the memory of the first Indian woman astronaut, Kalpana Chawla to go on space missions.