Role of matrix metalloproteinases 2 and 9, toll-like receptor 4 and platelet-leukocyte aggregate formation in sepsis-associated thrombocytopenia.

BACKGROUND: The development of thrombocytopenia in sepsis is a poor prognostic indicator associated with a significantly increased mortality risk. Mechanisms underlying this phenomenon remain to be clearly elucidated. Matrix metalloproteinases (MMPs) are enzymes that regulate the turnover of the extra-cellular matrix. MMP-2 is recognised as a platelet agonist with MMP-9 proposed as an inhibitor of platelet activation. The existence of MMP-9 in platelets is a subject of debate. There is limited evidence thus far to suggest that toll-like receptor 4 (TLR-4) and platelet-leukocyte aggregate (PLA) formation may be implicated in the development of sepsis-associated thrombocytopenia. OBJECTIVES: To investigate whether MMP -2/-9, toll-like receptor 4 (TLR-4) or platelet-leukocyte aggregate (PLA) formation are implicated in a decline in platelet numbers during septic shock. METHODS: This was an observational study which recruited healthy controls, non-thrombocytopenic septic donors and thrombocytopenic septic donors. MMP-2, MMP-9 and TLR-4 platelet surface expression as well as PLA formation was examined using flow cytometry. In addition MMP-2 and MMP-9 were examined by gelatin zymography and enzyme-linked immunosorbent assay (ELISA) using a 3 compartment model (plasma, intraplatelet and platelet membrane). RESULTS: There was no difference found in MMP-2, MMP-9 or TLR-4 levels between non-thrombocytopenic and thrombocytopenic septic donors. PLA formation was increased in thrombocytopenic patients. MMP-9 was detected in platelets using flow cytometry, gelatin zymography and ELISA techniques. CONCLUSIONS: Platelet consumption into PLAs may account for the development of thrombocytopenia in septic shock. MMP-9 is found in platelets and it is upregulated during septic shock.

Notorious but not understood: How liquid-air interfacial stress triggers protein aggregation.

Protein aggregation is a major challenge in the development of biopharmaceuticals. As the pathways of aggregation are manifold, good understanding of the mechanisms behind is essential. Particularly, the presence of liquid-air interfaces has been identified to trigger the formation of large protein particles. Investigations of two monoclonal antibodies (IgGs) at the liquid-air interface exhibited the formation of a highly compressible film. An inhomogeneous protein distribution across the interface with areas of increased packing density was discovered by Brewster-Angle microscopy. Repeated compression and decompression of the film resulted in a considerable hysteresis and in significantly elevated numbers of particles. Furthermore, the extent and speed of compression directly affected the mechanical properties of the film as well as the number of particles formed. Infrared reflection-absorption spectroscopy did not indicate considerable changes in secondary structure compared to FT-IR spectra in solution. Hence, the IgG remains in a native-like conformation at the interface. Consequently, the physical-chemical methods applied in combination with the newly-designed Mini-trough provided substantial new knowledge of the mechanisms of interface-related protein aggregation and enable testing of different formulations under controlled stress conditions. Pure compression and decompression with a Mini-Trough allows a much more controlled stressing than shaking.

Platelet microaggregation in sepsis examined by quartz crystal microbalance with dissipation technology.

Antiplatelet therapies remain an area of potential interest for the treatment of sepsis; however, studies of platelet aggregation in sepsis have yielded conflicting results. We examined platelet aggregation patterns in patients with septic shock using quartz crystal microbalance with dissipation technology, a microfluidic device capable of measuring platelet microaggregate formation under flow conditions. Platelet aggregation was increased in the washed platelet samples of septic patients. Conversely, these same platelets aggregated less than healthy controls when examined in their plasma.