Capture of lipopolysaccharide (endotoxin) by the blood clot: a comparative study

Heparin enables the reliable detection of endotoxin in human serum samples using the Limulus amebocyte lysate assay

The determination of lipopolysaccharide (endotoxin) in serum or plasma samples using Limulus amebocyte lysate (LAL)-based assays is currently not sufficiently reliable in clinical diagnostics due to numerous interfering factors that strongly reduce the recovery of LPS in clinical samples. The specific plasma components responsible for the endotoxin neutralizing capacity of human blood remain to be identified. There are indications that certain endotoxin-neutralizing proteins or peptides, which are part of the host defense peptides/proteins of the innate immune system may be responsible for this effect. Based on our finding that several antimicrobial peptides can be neutralized by the polyanion heparin, we developed a heparin-containing diluent for serum and plasma samples, which enables reliable quantification of LPS measurement in clinical samples using the LAL assay. In a preclinical study involving 40 donors, this improved protocol yielded an over eightfold increase in LPS recovery in serum samples, as compared to the standard protocol. This modified protocol of sample pretreatment could make LPS measurement a valuable tool in medical diagnostics.

The Endotoxin Hypothesis of Parkinson's Disease

The endotoxin hypothesis of Parkinson's disease (PD) is the idea that lipopolysaccharide (LPS) endotoxins contribute to the pathogenesis of this disorder. LPS endotoxins are found in, and released from, the outer membrane of Gram-negative bacteria, for example in the gut. It is proposed that gut dysfunction in early PD leads to elevated LPS levels in the gut wall and blood, which promotes both α-synuclein aggregation in the enteric neurons and a peripheral inflammatory response. Communication to the brain via circulating LPS and cytokines in the blood and/or the gut-brain axis leads to neuroinflammation and spreading of α-synuclein pathology, exacerbating neurodegeneration in brainstem nuclei and loss of dopaminergic neurons in the substantia nigra, and manifesting in the clinical symptoms of PD. The evidence supporting this hypothesis includes: (1) gut dysfunction, permeability, and bacterial changes occur early in PD, (2) serum levels of LPS are increased in a proportion of PD patients, (3) LPS induces α-synuclein expression, aggregation, and neurotoxicity, (4) LPS causes activation of peripheral monocytes leading to inflammatory cytokine production, and (5) blood LPS causes brain inflammation and specific loss of midbrain dopaminergic neurons, mediated by microglia. If the hypothesis is correct, then treatment options might include: (1) changing the gut microbiome, (2) reducing gut permeability, (3) reducing circulating LPS levels, or (4) blocking the response of immune cells and microglia to LPS. However, the hypothesis has a number of limitations and requires further testing, in particular whether reducing LPS levels can reduce PD incidence, progression, or severity. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Post-endotoxin exposure-induced lung inflammation and resolution consequences beneficially impacted by lung-delivered IL-10 therapy

Although lung diseases typically result from long-term exposures, even a robust, one-time exposure can result in long-lasting consequences. Endotoxin is a ubiquitous environmental/occupational inflammatory agent often used to model airway inflammation. Using a murine model, the return to lung homeostasis following high dose inhalant lipopolysaccharide (LPS, 10-100 μg) exposure were delineated over 2 weeks. LPS-induced rapid weight loss, release of proinflammatory mediators, and inflammatory cell influx with prolonged persistence of activated macrophages CD11c⁺CD11b⁺ and recruited/transitioning CD11c^intCD11b⁺ monocyte-macrophages out to 2 weeks. Next, lung-delivered recombinant (r) interleukin (IL)-10 was intratracheally administered for 3 doses initiated 5 h following LPS (10 μg) exposure for 2 days. IL-10 therapy reduced LPS-induced weight loss and increased blood glucose levels. Whereas there was no difference in LPS-induced bronchoalveolar lavage airway fluid cellular influx, total lung cell infiltrates were reduced (37%) with rIL-10 treatment. Post-LPS exposure treatment with rIL-10 strikingly reduced lavage fluid and lung homogenate levels of tumor necrosis factor-α (88% and 93% reduction, respectively), IL-6 (98% and 94% reduction), CXCL1 (66% and 75% reduction), and CXCL2 (47% and 67% reduction). LPS-induced recruited monocyte-macrophages (CD11c^intCD11b⁺) were reduced (68%) with rIL-10. Correspondingly, LPS-induced lung tissue CCR2⁺ inflammatory monocyte-macrophage were reduced with rIL-10. There were also reductions in LPS-induced lung neutrophils, lymphocyte subpopulations, collagen content, and vimentin expression. These findings support the importance of studying resolution processes for the development of treatment after unintended environmental/occupational biohazard exposures. Short-term, lung-delivered rIL-10 favorably hastened inflammatory recovery processes following acute, high dose inhalant LPS exposure.

An in vitro study on factors affecting endotoxin neutralization in human plasma using the Limulus amebocyte lysate test

Endotoxin neutralization, caused by plasma components, makes it difficult to detect endotoxins in human blood. In this study, we investigated which factors influence the recovery of endotoxins using limulus ameobocyte lysate (LAL)-based assays. The individual factors that were examined in more detail were lipoprotein content, type of blood anticoagulation, kinetics and serum levels of divalent cations. Furthermore, it was investigated whether there is a direct correlation between LAL activity and monocyte activation. We could show that polyanionic heparin increases endotoxin recovery in blood, while citrate anticoagulation promotes endotoxin neutralization. Furthermore, we could show that the endotoxin activity in human plasma and serum decreases strongly over time. Time-dependent endotoxin neutralization reaches its maximum after 4–6 h incubation. By means of filtration tests we could determine that endotoxins in the plasma bind to lipoproteins but do not influence their activity. Comparative measurements have shown that high LAL activity of endotoxins in plasma simultaneously possesses high monocyte activating properties in whole blood. For the maximum recovery of endotoxins in human blood the physiological calcium and magnesium concentrations are sufficient. In this study, it was shown that the endotoxin neutralizing plasma components have a molecular weight similar to β2-microglobulin (11.7 kDa). For the exact identification of the endotoxin neutralizing plasma components, which caused a modulation of the immunostimulating endotoxin activity, further investigations have to be carried out in the future.

High-Density Lipoproteins Are Bug Scavengers

Lipoproteins were initially defined according to their composition (lipids and proteins) and classified according to their density (from very low- to high-density lipoproteins—HDLs). Whereas their capacity to transport hydrophobic lipids in a hydrophilic environment (plasma) is not questionable, their primitive function of cholesterol transporter could be challenged. All lipoproteins are reported to bind and potentially neutralize bacterial lipopolysaccharides (LPS); this is particularly true for HDL particles. In addition, HDL levels are drastically decreased under infectious conditions such as sepsis, suggesting a potential role in the clearance of bacterial material and, particularly, LPS. Moreover, "omics" technologies have unveiled significant changes in HDL composition in different inflammatory states, ranging from acute inflammation occurring during septic shock to low-grade inflammation associated with moderate endotoxemia such as periodontal disease or obesity. In this review, we will discuss HDL modifications associated with exposure to pathogens including bacteria, viruses and parasites, with a special focus on sepsis and the potential of HDL therapy in this context. Low-grade inflammation associated with atherosclerosis, periodontitis or metabolic syndrome may also highlight the protective role of HDLs in theses pathologies by other mechanisms than the reverse transport of cholesterol.

Understanding Infection-Induced Thrombosis: Lessons Learned From Animal Models

Thrombosis is a common consequence of infection that is associated with poor patient outcome. Nevertheless, the mechanisms by which infection-associated thrombosis is induced, maintained and resolved are poorly understood, as is the contribution thrombosis makes to host control of infection and pathogen spread. The key difference between infection-associated thrombosis and thrombosis in other circumstances is a stronger inflammation-mediated component caused by the presence of the pathogen and its products. This inflammation triggers the activation of platelets, which may accompany damage to the endothelium, resulting in fibrin deposition and thrombus formation. This process is often referred to as thrombo-inflammation. Strikingly, despite its clinical importance and despite thrombi being induced to many different pathogens, it is still unclear whether the mechanisms underlying this process are conserved and how we can best understand this process. This review summarizes thrombosis in a variety of models, including single antigen models such as LPS, and infection models using viruses and bacteria. We provide a specific focus on Salmonella Typhimurium infection as a useful model to address all stages of thrombosis during infection. We highlight how this model has helped us identify how thrombosis can appear in different organs at different times and thrombi be detected for weeks after infection in one site, yet largely be resolved within 24 h in another. Furthermore, we discuss the observation that thrombi induced to Salmonella Typhimurium are largely devoid of bacteria. Finally, we discuss the value of different therapeutic approaches to target thrombosis, the potential importance of timing in their administration and the necessity to maintain normal hemostasis after treatment. Improvements in our understanding of these processes can be used to better target infection-mediated mechanisms of thrombosis.

Effects of deoxynivalenol-feed contamination on circulating LPS in pigs

Low concentration of LPS can be detected in healthy mammals without triggering systemic inflammation. Here we analysed the influence of the mycotoxin deoxynivalenol (DON) on very low LPS concentrations and the role of DON in the physiology of pigs challenged with high artificial LPS dosage mimicking septic shock. Pigs were fed for 29 d with DON-contaminated (4.59 mg/kg feed) or control feed. Samples of control animals showed 6.6 ± 13.5 pg/ml LPS in portal and 3.1 ± 7.6 pg/ml LPS in jugular serum samples. In the DON fed group, 3.4 ± 7.2 pg/ml and 0.6 ± 0.8 pg/ml were detected. The differences were statistically not significant, indicating that DON is not a trigger for enhanced LPS transfer into the blood circulation. Next, pigs were challenged with 7.5 µg LPS/kg body mass via portal or jugular route. The application route did not significantly influence the LPS concentration. We expected higher circulating LPS concentrations in the presence of DON due to the additional stress of liver metabolism and reduced liver capacity to remove LPS from circulation. This scenario is supported by tendency. In summary, we found that DON is unlikely to influence LPS transfer in the gut; DON likely reduces the capacity for LPS removal in septic shock conditions.

The clotting system in decapod crustaceans: History, current knowledge and what we need to know beyond the models

Hemolymph coagulation is among the major arms of the humoral immune response in crustaceans. According to the current model, hemolymph clotting in decapod crustacean relies mostly on the polymerization of the plasmatic clotting protein (CP) which is directly promoted by calcium-depended transglutaminase (TGase) released from hemocytes upon microbial stimulus or injury. However, the type of hemocytes containing TGase, and hence how the TGase is released, might vary among species. Thus, we discourse here about possible mechanisms for clotting initiation. On the other hand, the initiation of coagulation reaction in the absence of microbial elicitors is poorly understood and seems to involve hemocytes lability, yet the mechanism remains unknown. A cellular clottable protein called coagulogen, different to the plasma CP, occurs in several species and could be related with the immune response, but the biological relevance of this protein is unknown. It is also demonstrated that the clotting response is actively involved in defense against pathogens. In addition, both TGase and the CP show pleiotropic functions, and although both proteins are relatively conserved, some of their physic-chemical properties vary significantly. The occurrence of differences in the clotting system in crustaceans is conceivable given the high number of species and their diverse ecology. Results from still non-studied decapods may provide explanation for some of the issues presented here from an evolutionary perspective.

A review on recent progress in observations, and health effects of bioaerosols

Bioaerosol is a particulate mixture of solid and semi-solid matter combined with biotic matter like pollens, microbes and their fragments. The present review stresses on a cumulative understanding of sources, components, quantification and distribution of bioaerosols with respect to size, and its significant impacts on human health. The present review will be instrumental in devising strategies to understand and manage bioaerosols and reducing their human exposure and associated health hazards. The present review aims explore the relationship between particle and associated biological agents responsible for behaviours like dispersal, total potential health hazards and toxicology level during exposure to bioaerosol.

Airborne bioaerosols and their impact on human health

Bioaerosols consist of aerosols originated biologically such as metabolites, toxins, or fragments of microorganisms that are present ubiquitously in the environment. International interests in bioaerosols have increased rapidly to broaden the pool of knowledge on their identification, quantification, distribution, and health impacts (e.g., infectious and respiratory diseases, allergies, and cancer). However, risk assessment of bioaerosols based on conventional culture methods has been hampered further by several factors such as: (1) the complexity of microorganisms or derivatives to be investigated; (2) the purpose, techniques, and locations of sampling; and (3) the lack of valid quantitative criteria (e.g., exposure standards and dose/effect relationships). Although exposure to some microbes is considered to be beneficial for health, more research is needed to properly assess their potential health hazards including inter-individual susceptibility, interactions with non-biological agents, and many proven/unproven health effects (e.g., atopy and atopic diseases).

The gut microbiota as a novel regulator of cardiovascular function and disease

The gut microbiome has emerged as a critical regulator of human physiology. Deleterious changes to the composition or number of gut bacteria, commonly referred to as gut dysbiosis, has been linked to the development and progression of numerous diet-related diseases, including cardiovascular disease (CVD). Most CVD risk factors, including aging, obesity, certain dietary patterns, and a sedentary lifestyle, have been shown to induce gut dysbiosis. Dysbiosis is associated with intestinal inflammation and reduced integrity of the gut barrier, which in turn increases circulating levels of bacterial structural components and microbial metabolites that may facilitate the development of CVD. The aim of the current review is to summarize the available data regarding the role of the gut microbiome in regulating CVD function and disease processes. Particular emphasis is placed on nutrition-related alterations in the microbiome, as well as the underlying cellular mechanisms by which the microbiome may alter CVD risk.

A Dormant Microbial Component in the Development of Preeclampsia

Preeclampsia (PE) is a complex, multisystem disorder that remains a leading cause of morbidity and mortality in pregnancy. Four main classes of dysregulation accompany PE and are widely considered to contribute to its severity. These are abnormal trophoblast invasion of the placenta, anti-angiogenic responses, oxidative stress, and inflammation. What is lacking, however, is an explanation of how these themselves are caused. We here develop the unifying idea, and the considerable evidence for it, that the originating cause of PE (and of the four classes of dysregulation) is, in fact, microbial infection, that most such microbes are dormant and hence resist detection by conventional (replication-dependent) microbiology, and that by occasional resuscitation and growth it is they that are responsible for all the observable sequelae, including the continuing, chronic inflammation. In particular, bacterial products such as lipopolysaccharide (LPS), also known as endotoxin, are well known as highly inflammagenic and stimulate an innate (and possibly trained) immune response that exacerbates the inflammation further. The known need of microbes for free iron can explain the iron dysregulation that accompanies PE. We describe the main routes of infection (gut, oral, and urinary tract infection) and the regularly observed presence of microbes in placental and other tissues in PE. Every known proteomic biomarker of "preeclampsia" that we assessed has, in fact, also been shown to be raised in response to infection. An infectious component to PE fulfills the Bradford Hill criteria for ascribing a disease to an environmental cause and suggests a number of treatments, some of which have, in fact, been shown to be successful. PE was classically referred to as endotoxemia or toxemia of pregnancy, and it is ironic that it seems that LPS and other microbial endotoxins really are involved. Overall, the recognition of an infectious component in the etiology of PE mirrors that for ulcers and other diseases that were previously considered to lack one.

Generation and characterization of a monoclonal antibody against canine tissue factor

Tissue factor (TF, coagulation factor III) has recently identified roles in innate immunity and cancer. We generated a murine mAb against canine TF (cTF) cloned from Madin-Darby canine kidney cells and expressed in Chinese Hamster Ovarian (CHO) cells, with an equine IL-4 tag. One clone was selected for purification based on initial screening of CHO cell supernatants. The mAb was further characterized with flow cytometry, immunofluorescent microscopy, immunoblotting and immunohistochemical staining of normal and neoplastic canine tissue. The mAb labeled high, but not low, TF-expressing canine breast cancer (CMT25) and osteosarcoma (HMPOS) cells with flow cytometry and immunofluorescent microscopy. Immunoblotting revealed a 42kDa protein with homogenized canine brain and CMT25, but not HMPOS, lysates. The mAb labeled renal tubules and glomeruli, intestinal and dermal epithelium, and arteriolar adventitial cells in frozen tissues. Using immunofluorescent microscopy, increased numbers of labeled PBMCs were observed after LPS stimulation. Our results indicate that the anti-cTF mAb detects a protein with the expected tissue distribution and molecular weight of TF in normal, LPS-stimulated and neoplastic canine cells. This mAb may prove useful for exploring the role of TF in neoplastic and infectious disorders in dogs.

Interaction of pathogenic vibrio bacteria with the blood clot of the pacific white shrimp, Litopenaeus vannamei

In addition to its roles in hemostasis and wound repair, the blood clot plays an underappreciated role in innate immunity, where the established clot serves as a barrier to microbial penetration into the internal milieu and where the early clot entraps and immobilizes microbes that have entered wounds to the integuments. In this report we document the behavior of the pathogenic gram-negative bacterium Vibrio harveyi that has been entrapped in the fabric of the extracellular blood clot of one of its target organisms, the Pacific white shrimp, Litopenaeus vannamei. The freshly entrapped bacteria are held tightly by the clot, losing even Brownian motility, but by 1 h post-entrapment, a fraction of the bacteria have established small domains of fibrinolysis that enlarge progressively, enabling bacteria to escape from the clot's embrace. Escape is dependent on the actions of both serine- and metallo-proteases released from the bacterial cells.