Keeping blood clots at bay in sepsis

Thromboprophylaxis with argatroban in critically ill patients with sepsis: a review

During sepsis, an initial prothrombotic shift takes place, in which coagulatory acute-phase proteins are increased, while anticoagulatory factors and platelet count decrease. Further on, the fibrinolytic system becomes impaired, which contributes to disease severity. At a later stage in sepsis, coagulation factors may become depleted, and sepsis patients may shift into a hypo-coagulable state with an increased bleeding risk. During the pro-coagulatory shift, critically ill patients have an increased thrombosis risk that ranges from developing micro-thromboses that impair organ function to life-threatening thromboembolic events. Here, thrombin plays a key role in coagulation as well as in inflammation. For thromboprophylaxis, low molecular weight heparins (LMWH) and unfractionated heparins (UFHs) are recommended. Nevertheless, there are conditions such as heparin resistance or heparin-induced thrombocytopenia (HIT), wherein heparin becomes ineffective or even puts the patient at an increased prothrombotic risk. In these cases, argatroban, a direct thrombin inhibitor (DTI), might be a potential alternative anticoagulatory strategy. Yet, caution is advised with regard to dosing of argatroban especially in sepsis. Therefore, the starting dose of argatroban is recommended to be low and should be titrated to the targeted anticoagulation level and be closely monitored in the further course of treatment. The authors of this review recommend using DTIs such as argatroban as an alternative anticoagulant in critically ill patients suffering from sepsis or COVID-19 with suspected or confirmed HIT, HIT-like conditions, impaired fibrinolysis, in patients on extracorporeal circuits and patients with heparin resistance, when closely monitored.

Silencing Porcine CMAH and GGTA1 Genes Significantly Reduces Xenogeneic Consumption of Human Platelets by Porcine Livers

BACKGROUND

A profound thrombocytopenia limits hepatic xenotransplantation in the pig-to-primate model. Porcine livers also have shown the ability to phagocytose human platelets in the absence of immune-mediated injury. Recently, inactivation of the porcine ASGR1 gene has been shown to decrease this phenomenon. Inactivating GGTA1 and CMAH genes has reduced the antibody-mediated barrier to xenotransplantation; herein, we describe the effect that these modifications have on xenogeneic consumption of human platelets in the absence of immune-mediated graft injury.

METHODS

Wild type (WT), ASGR1, GGTA1, and GGTA1CMAH knockout pigs were compared for their xenogeneic hepatic consumption of human platelets. An in vitro assay was established to measure the association of human platelets with liver sinusoidal endothelial cells (LSECs) by immunohistochemistry. Perfusion models were used to measure human platelet uptake in livers from WT, ASGR1, GGTA1, and GGTA1 CMAH pigs.

RESULTS

GGTA1, CMAH LSECs exhibited reduced levels of human platelet binding in vitro when compared with GGTA1 and WT LSECs. In a continuous perfusion model, GGTA1 CMAH livers consumed fewer human platelets than GGTA1 and WT livers. GGTA1 CMAH livers also consumed fewer human platelets than ASGR1 livers in a single-pass model.

CONCLUSIONS

Silencing the porcine carbohydrate genes necessary to avoid antibody-mediated rejection in a pig-to-human model also reduces the xenogeneic consumption of human platelets by the porcine liver. The combination of these genetic modifications may be an effective strategy to limit the thrombocytopenia associated with pig-to-human hepatic xenotransplantation.

Cell-type-resolved quantitative proteomics of murine liver

Mass spectrometry (MS)-based proteomics provides a powerful approach to globally investigate the biological function of individual cell types in mammalian organs. Here, we applied this technology to the in-depth analysis of purified hepatic cell types from mouse. We quantified 11,520 proteins, making this the most comprehensive proteomic resource of any organ to date. Global protein copy number determination demonstrated that a large proportion of the hepatocyte proteome is dedicated to fatty acid and xenobiotic metabolism. We identified as-yet-unknown components of the TGF-β signaling pathway and extracellular matrix in hepatic stellate cells, uncovering their regulative role in liver physiology. Moreover, our high-resolution proteomic data set enabled us to compare the distinct functional roles of hepatic cell types in cholesterol flux, cellular trafficking, and growth factor receptor signaling. This study provides a comprehensive resource for liver biology and biomedicine.

Glycobiology: progress, problems, and perspectives

This review highlights different aspects of glycobiology with analysis of recent progress in the study of biosynthesis, degradation, and biological role of glycoconjugates and of hereditary diseases related to the metabolism of these compounds. In addition, the review presents some analysis of the papers of other authors who have contributed to this special issue.

Proteomics reveals age-related differences in the host immune response to sepsis

Sepsis is commonly caused by community-acquired pneumonia (CAP) and may develop into severe sepsis, characterized by multiple organ failure. The risk of severe sepsis among CAP patients and subsequent mortality increases sharply after the age of 65. The molecular mechanisms associated with this age-related risk are not fully understood. To better understand factors involved with increased incidence and mortality of severe sepsis in the elderly, we used a nested case-control study of patients enrolled in a multicenter observational cohort of 2320 participants with CAP. We identified a total of 39 CAP patients 50-65 and 70-85 years old who did or did not develop severe sepsis. Plasma samples were obtained on presentation to the emergency department and prior to therapeutic interventions. A semiquantitative plasma proteomics workflow was applied which incorporated tandem immunoaffinity depletion, iTRAQ labeling, strong cation exchange fractionation, and nanoflow liquid chromatography coupled to high-resolution mass spectrometry. In total, 772 proteins were identified, of which 58 proteins exhibit statistically significant differences in expression levels among patients with severe sepsis as a function of age. Differentially expressed proteins are involved in pathways such as acute phase response, coagulation signaling, atherosclerosis signaling, lipid metabolism, and production of nitric oxide and reactive oxygen species. This study provides insight into factors that may explain age-related differences in incidence of severe sepsis in the elderly.

Characterization of Transferrin Glycopeptide Structures in Human Cerebrospinal Fluid

Transferrin in cerebrospinal fluid (CSF) exists as a mixture of silao and asialo glycoforms believed to originate from liver and brain respectively. We have previously shown that alteration in the asialo glycoform pattern could be an indication of certain anomalies in the central nervous system. Additionally, CSF asialo-transferrin has been shown to be a reliable marker to assess cerebrospinal leakage in head trauma. Therefore, the CSF transferrin glycoform pattern could be a useful diagnostic and prognostic tool. In this study we sought to characterize, in-depth, the transferrin glycovariants in cerebrospinal fluid using a combination of two-dimensional gel electrophoresis and high precision mass spectrometry analysis. Cerebrospinal fluid transferrin was detected as multiple spots (seven major spots) with different isoelectric points and slight shift in apparent molecular mass. High resolution (>60,000) and high accuracy (< 3 ppm error) mass spectrometry analysis revealed that each spot had a unique glycopeptide signature. MS(n) analysis enabled characterization of the glycan structure directly from the in-gel digested spots. The multiple spots detected for cerebrospinal fluid transferrin were mainly due to heterogeneity of di-antennary and tri-antennary glycans harboring a varying number of terminal N-acetylneuraminic acids and the existence of a high mannose and high N-acetylhexosamine glycosylated species.

The fate of human platelets perfused through the pig liver: implications for xenotransplantation

BACKGROUND

Pig liver xenotransplantation could offset the shortage of livers available for orthotopic liver transplantation. Studies in pig and baboon liver xenografts revealed the main obstacle to be a lethal thrombocytopenia that occurred within minutes to hours of transplantation.

METHODS

  We have created a model of xenotransplantation-induced thrombocytopenia using ex vivo pig liver perfusion with human platelets. Thrombocytopenia was examined using fluorescently labeled platelets during the ex vivo perfusion and coculture with primary liver sinusoidal endothelial cells (LSEC).

RESULTS

Ex vivo liver perfusion revealed that 93% of human platelets were removed from circulation after 15 min. Endothelial cells and platelets were not activated based on tissue factor release into the perfusate. Biopsies from the ex vivo perfusion at 15 and 30 min and in vitro analysis indicated that human platelets are phagocytosed by pig LSEC and degraded in phagosomes. Sixty to 120 min after the addition of platelets to the ex vivo perfusion system, we observed platelet fragments and degraded platelets in hepatocytes. Platelet phagocytosis was not mediated by opsonization as Fc blocking had no effect on platelet phagocytosis. In vitro uptake of human platelets by primary LSEC cultures peaked at 15 min followed by a greater than 55% decrease in platelet fluorescence after 3 h. Primary pig LSEC phagosomes containing human platelets were colocalized with lysosomes positive for lysosome-associated membrane protein-1 (LAMP1), indicating the formation of mature phagosomes within pig LSEC.

CONCLUSIONS

Our observation of pig LSEC phagocytosis of human platelets describes a novel mechanism of large-particle uptake in the liver. The creation of a model system to study xenotransplantation-induced thrombocytopenia makes possible the investigation into mechanisms that mediate platelet loss.

Thrombocytopenia from combination treatment with oseltamivir and probenecid: case report, MedWatch data summary, and review of the literature

The possibility of an avian flu pandemic has spurred interest in preventive treatments with antivirals such as oseltamivir. Combining treatment with probenecid to delay excretion may extend limited supplies of oseltamivir. We previously conducted a pharmacokinetic study of oseltamivir plus probenecid among healthy volunteers. In this article, we describe a 68-year-old woman who, during the pharmacokinetic study, developed severe thrombocytopenia 2 weeks after starting oseltamivir plus probenecid. She was receiving no other drug therapy at the time. Her platelet count decreased from 200 to 15 x 10(3)/mm(3), although no clinically evident bleeding abnormalities were noted. The two drugs were discontinued. One week later, without any therapeutic intervention, her platelet count returned to normal. By using the Naranjo adverse drug reaction probability scale to assess the strength of the association between the drugs and the adverse event, a score of 7 was derived for both drugs, indicating that the association was probable. We found no previous literature reports of thrombocytopenia associated with either drug. However, a review of the United States Food and Drug Administration's Adverse Event Reporting System database found 93 cases of thrombocytopenia and/or decreased platelet counts associated with oseltamivir and 24 cases associated with probenecid administration. Signal detection analyses were significant for oseltamivir (p=0.001), but not probenecid. The underlying mechanism of thrombocytopenia with these drugs is unknown. Clinicians should be aware that the use of oseltamivir and probenecid has been reported to be associated with thrombocytopenia.

Molecular biology of inflammation and sepsis: a primer

BACKGROUND

Remarkable progress has been made during the last decade in defining the molecular mechanisms that underlie septic shock. This rapidly expanding field is leading to new therapeutic opportunities in the management of severe sepsis.

AIM

To provide the clinician with a timely summary of the molecular biology of sepsis and to better understand recent advances in sepsis research.

DATA SELECTION

Medline search of relevant publications in basic mechanisms of sepsis/severe sepsis/septic shock, and selected literature review of other manuscripts about the signalosome, inflammasome, apoptosis, or mechanisms of shock. DATA SYNTHESIS AND FINDINGS: The identification of the toll-like receptors and the associated concept of innate immunity based upon pathogen- or damage-associated molecular pattern molecules allowed significant advances in our understanding of the pathophysiology of sepsis. The essential elements of the inflammasome and signal transduction networks responsible for activation of the host response have now been characterized. Apoptosis, mitochondrial dysfunction, sepsis-related immunosuppression, late mediators of systemic inflammation, control mechanisms for coagulation, and reprogramming of immune response genes all have critical roles in the development of sepsis.

CONCLUSIONS

Many of these basic discoveries have direct implications for the clinical management of sepsis. The translation of these "bench-to-bedside" findings into new therapeutic strategies is already underway. This brief review provides the clinician with a primer into the basic mechanisms responsible for the molecular biology of sepsis, severe sepsis, and septic shock.