Lipopolysaccharide, now more commonly known as endotoxin, is a collective term for components of the outermost membrane of the cell envelope of gram-negative bacteria, such as E. coli and Salmonella with a common structural architecture.
Lipopolysaccharides (LPS) are large covalently linked. molecules consisting of three parts: an outer core polysaccharide termed the O-antigen, an inner core oligosaccharide and Lipid A.
Lipid A is where toxicity is largely derived.
The term endotoxin is often used synonymously with LPS, although there are a few endotoxins that are not related to LPS, such as the so-called delta endotoxin proteins produced by Bacillus thuringiensis.
Lipopolysaccharides can impact health, primarily through interactions with the immune system. LPS is a potent activator of the immune system and is a pyrogen.
LPS can trigger host responses and multiple types of acute organ failure which can lead to septic shock.
In lower levels and over a longer time period, endotoxin may play an important and harmful role in autoimmunity, obesity, depression, and cellular senescence.
Endotoxins, which are toxins in the bacterial cell and released only after destruction of the bacterial outer membrane.
The release of LPS from Gram negative microbes does not necessarily require the destruction of the bacterial cell wall, but rather, it is secreted as part of the normal physiological activity of membrane vesicle trafficking in the form of bacterial outer membrane vesicles which may also contain other virulence factors and proteins.
LPS is a major component of the outer cell membrane of gram-negative bacteria, contributing greatly to the structural integrity of the bacteria and protecting the membrane from certain kinds of chemical attack.
LPS is the most abundant antigen on the cell surface of most gram-negative bacteria.
LPS contributes up to 80% of the outer membrane of E. coli and Salmonella.
LPS increases the negative charge of the cell membrane, stabilizing the overall membrane structure.
LPS is nonessential in at least some gram-negative bacteria, such as Neisseria meningitidis, Moraxella catarrhalis, and Acinetobacter baumannii.
It has also been implicated in non-pathogenic aspects of bacterial function including surface adhesion, bacteriophage sensitivity, and interactions with predators such as amoebae.
LPS are amphipathic and composed of three parts: the O antigen (or O polysaccharide) which is hydrophilic, the core oligosaccharide (also hydrophilic), and Lipid A, the hydrophobic domain.
The presence or absence of O chains determines whether the LPS is considered “rough” or “smooth”.
Bacteria with rough LPS usually have more penetrable cell membranes to hydrophobic antibiotics, since a rough LPS is more hydrophobic.
O antigen is exposed on the very outer surface of the bacterial cell, and, as a consequence, is a target for recognition by host antibodies.
Core oligosaccharide domain always contains an oligosaccharide component that attaches directly to lipid A and commonly contains sugars.
The core oligosaccharide is less variable in its structure and composition, a given core structure being common to large groups of bacteria.
Lipid A is a phosphorylated glucosamine disaccharide decorated with multiple fatty acids.
These hydrophobic fatty acid chains anchor the LPS into the bacterial membrane, and the rest of the LPS projects from the cell surface.
The lipid A domain is the most bioactive and responsible for much of the toxicity of Gram-negative bacteria.
When bacterial cells are lysed by the immune system, fragments of membrane containing lipid A may be released into the circulation.
When released it causes fever, diarrhea, and possible fatal endotoxic septic shock.
A form of LPS that has a lower molecular weight due to the absence of the O polysaccharide, is a short oligosaccharide: this form is known as Lipooligosaccharide (LOS), and is a glycolipid found in the outer membrane of some types of Gram-negative bacteria, such as Neisseria spp. and Haemophilus spp.
LOS plays a central role in maintaining the integrity and functionality of the outer membrane of the Gram negative cell envelope, and plays a role in the pathogenesis of certain bacterial infections because they are capable of acting as immunostimulators and immunomodulators.
LOS molecules are responsible for the ability of some bacterial strains to display molecular mimicry and antigenic diversity, aiding in the evasion of host immune defenses and thus contributing to the virulence of these bacterial strains.
A host enzyme called acyloxyacyl hydrolase (AOAH) may detoxify LPS when it enters, or is produced in, animal tissues.
It may also convert LPS in the intestine into an LPS inhibitor.
Neutrophils, macrophages and dendritic cells produce this lipase, which inactivates LPS by removing the two secondary acyl chains from lipid A to produce tetraacyl LPS.
The human body carries endogenous stores of LPS.
The epithelial surfaces are colonized by a complex microbial flora, including gram-negative bacteria, which outnumber human cells by a factor of 10 to 1.
Gram-negative bacterial will shed endotoxins.
There is a host-microbial interaction is a symbiotic relationship which plays a critical role in systemic immunologic homeostasis.
When disrupted, it can lead to disease such as endotoxemia and endotoxic septic shock.
LPS acts as the prototypical endotoxin because it binds the CD14/TLR4/MD2 receptor complex in many cell types, but especially in monocytes, dendritic cells, macrophages and B cells, which promotes the secretion of pro-inflammatory cytokines, nitric oxide, and eicosanoids.
Superoxide is one of the major reactive oxygen species induced by LPS in various cell types that express TLR (toll-like receptor).
LPS is also an exogenous pyrogen.
LPS also produces many types of mediators involved in septic shock.
Humans are much more sensitive to LPS than other primates, and other animals as well.
LPS causes an IL-10-dependent inhibition of CD4 T-cell expansion and function by up-regulating PD-1 levels on monocytes which leads to IL-10 production by monocytes after binding of PD-1 by PD-L1.
Endotoxins are in large part responsible for the dramatic clinical manifestations of infections with pathogenic Gram-negative bacteria, such as Neisseria meningitidis, the pathogens that causes meningococcal disease, including meningococcemia, Waterhouse–Friderichsen syndrome, and meningitis.
Some bacteria have the ability to present molecules on their surface which are chemically identical or similar to the surface molecules of some types of host cells and is termed molecular mimicry.
In addition to acting as a camouflage from the immune system, play a role in the abolishment of immune tolerance when infecting hosts with certain human leukocyte antigen (HLA) genotypes, such as HLA-B35.
LPS can be sensed directly by hematopoietic stem cells (HSCs) through the bonding with TLR4, causing them to proliferate in reaction to a systemic infection.
Toll-like receptors of the innate immune system recognize LPS and trigger an immune response.
O-antigens (the outer carbohydrates) are the most variable portion of the LPS molecule, imparting antigenic specificity.
In contrast, lipid A is the most conserved part.
Normal human blood serum contains anti-LOS antibodies that are bactericidal.
In Neisseria gonorrhoeae the antigenicity of LOS molecules can change during an infection due to the ability of these bacteria to synthesize more than one type of LOS, (phase variation).
Neisseria gonorrhoeae, as well as Neisseria meningitidis and Haemophilus influenzae, are capable of further modifying their LOS, and as a result are able to increase their resistance to complement-mediated killing, down-regulate complement activation or evade the effects of bactericidal antibodies.
Sialylation may also hinder neutrophil attachment and phagocytosis by immune system cells as well as a reduced oxidative burst.
Variations in bacterial surface molecules such as LOS can help the pathogen evade both the humoral antibody and complement-mediated and the cell-mediated host immune defenses.
Lipopolysaccharide makes bacteria harmful, and it helps categorize them into different groups based on their structure and function.
This makes LPS a useful marker for telling apart various Gram-negative bacteria.
The typical detection methods rely on identifying the lipid A part of LPS because Lipid A is very similar among different bacterial species and serotypes.
LPS testing techniques fall into six categories: in vivo tests, in vitro tests, modified immunoassays, biological assays, and chemical assays.
LPS is very difficult to measure in whole blood and most LPS is bound to proteins and complement.
The Endotoxin Activity Assay (EAA™) is a rapid in vitro chemiluminescent immunodiagnostic test that utilizes a specific monoclonal antibody to measure the endotoxin activity in EDTA whole blood specimens.
The Endotoxin Activity Assay uses the biological response of the neutrophils in a patient’s blood to an immunological complex of endotoxin and exogenous antibody – the chemiluminescent reaction formed creates an emission of light.
The amount of chemiluminescence is proportional to the concentration of LPS in the sample and is a measure of the endotoxin activity in the blood.
The assay reacts specifically with the Lipid A moiety of LPS of Gram-negative bacteria and does not cross-react with cell wall constituents of Gram-positive bacteria and other microorganisms.
LPS toxin that, when in the body, triggers inflammation by binding to cell receptors.
Excessive LPS in the blood, endotoxemia, may cause a highly lethal form of sepsis known as endotoxic septic shock.
Sepsis known as endotoxic septic shock includes symptoms that fall along a continuum of pathophysiologic states, starting with a systemic inflammatory response syndrome (SIRS) and ending in multiorgan dysfunction syndrome before death.
Early symptoms of sepsis include rapid heart rate, quick breathing, temperature changes, and blood clotting issues, resulting in blood vessels widening and reduced blood volume, leading to cellular dysfunction.
Even a small exposure to endotoxin is associated with autoimmune diseases and allergies.
High levels of LPS in the blood can lead to metabolic syndrome, increasing the risk of conditions like diabetes, heart disease, and liver problems.
LPS also plays a role in symptoms caused by infections from harmful bacteria like Waterhouse-Friderichsen syndrome, meningococcemia, and meningitis.
Bacteria can adapt their LPS to cause long-lasting infections in the respiratory and digestive systems.
Recent studies have shown that LPS disrupts cell membrane lipids, affecting cholesterol and metabolism, potentially leading to high cholesterol, abnormal blood lipid levels, and non-alcoholic fatty liver disease. In some cases, LPS can interfere with toxin clearance, which may be linked to neurological issues.[58]
LPS is a potent activator and modulator of the immune system, especially its inducement of inflammation.
LPS is directly cytoxic and is highly immunostimulatory as host immune cells’ complement are strongly activated.
Complement activation and a rising anti-inflammatory response can lead to immune cell dysfunction, immunosuppression, widespread coagulopathy, and serious tissue damage, and can progress to multi-system organ failure and death.
High level of endotoxemia can lead to septic shock, or more specifically endotoxic septic shock, while lower concentration of endotoxins in the bloodstream is called metabolic endotoxemia.
Endotoxemia is associated with obesity, diet, cardiovascular diseases,and diabetes, while also host genetics might have an effect.
Moreover, endotoxemia of intestinal origin, especially, at the host-pathogen interface, is considered to be an important factor in the development of alcoholic hepatitis, which is likely to develop on the basis of the small bowel bacterial overgrowth syndrome and an increased intestinal permeability.
Lipid A may cause uncontrolled activation of immune systems with production of inflammatory mediators that may lead to endotoxic septic shock.
The lipid inflammatory reaction is primarily mediated by Toll-like receptor 4 which is responsible for immune system cell activation.
Damage to the endothelial layer of blood vessels caused by these inflammatory mediators can lead to capillary leak syndrome, dilation of blood vessels and a decrease in cardiac function and can further worsen shock.
LPS is also a potent activator of complement, which may trigger destructive endothelial damage leading to disseminated intravascular coagulation (DIC), or atypical hemolytic uremic syndrome (aHUS) with injury to various organs such as including kidneys and lungs.
LPS skin effects cause vascular damage often coupled with depletion of coagulation factors in the form of petechiae, purpura and ecchymoses.
The limbs can also be affected with LPS such as the development of gangrene, requiring subsequent amputation.
Loss of function of the adrenal glands can cause adrenal insufficiency.
Hemorrhage into the adrenals causes Waterhouse-Friderichsen syndrome, both of which can be life-threatening.
Toraymyxin is a widely used extracorporeal endotoxin removal therapy through direct hemoperfusion).
Toraymyxin Is a polystyrene-derived cartridge with molecules of polymyxin B (PMX-B) covalently bound to mesh fibers contained within it.
The extracorporeal use of the Toraymyxin cartridge allows PMX-B to bind lipid A with a very stable interaction with its hydrophobic residues thereby neutralizing endotoxins as the blood is filtered through the extracorporeal circuit inside the cartridge, thus reversing endotoxemia and avoiding its toxic systemic effects.
The molecular mimicry of some LOS molecules is thought to cause autoimmune-based host responses, such as flareups seen with multiple sclerosis.
Bacterial mimicry of host structures via LOS are found with the bacteria Helicobacter pylori and Campylobacter jejuni, organisms which cause gastrointestinal disease in humans, and Haemophilus ducreyi which causes chancroid.
C. jejuni LPS serotypes have also been implicated with Guillain–Barré syndrome and a variant of Guillain–Barré called Miller-Fisher syndrome.
An increased endotoxin load, which can be a result of increased populations of endotoxin-producing bacteria in the intestinal tract, is associated with certain obesity-related patient groups.
The association of endotoxin with obesity is that endotoxin induces an inflammation-mediated pathway accounting for the observed obesity and insulin resistance.
Bacterial genera associated with endotoxin-related obesity effects include Escherichia and Enterobacter.
LPS may play a role in depression: there seems to be elevated levels of LPS in some people with depression. Inflammation may sometimes play a role in the development of depression, and LPS is pro-inflammatory.
Inflammation induced by LPS can induce cellular senescence.
LPS induced cellular senescence has been shown for the lung epithelial cells and microglial cells the lead to neurodegeneration
Lipopolysaccharides are frequent contaminants in plasmid DNA prepared from bacteria or proteins expressed from bacteria, and must be removed from the DNA or protein to avoid contaminating experiments?
In pharmaceutical production, it is necessary to remove all traces of endotoxin from drug product containers, as even small amounts of endotoxin will cause illness in humans.