Microparticles: Modulators and biomarkers of liver disease
Authors: Miroslaw Kornek, Detlef Schuppan
Journal: Journal of Hepatology (2012)

Microparticles (MP) have gained increasing attention as biomarkers for various diseases. First described as platelet dust, MP were regarded as unspecific debris [[1]Wolf P. The nature and significance of platelet products in human plasma.Br J Haematol. 1967; 13: 269-288Crossref PubMed Scopus (972) Google Scholar]. However, it has become apparent that cell derived MP or ectosomes represent a novel route of horizontal communication between cells. MP are between 100–1000 nm in size and generated through cell membrane shedding (ectocytosis), a process that can be triggered by the activation of the complement C5b-9 complex, as shown for platelet derived MP, or by inhibition of flippase activity through Ca2+ influx, which facilitates collapse of the plasma membrane phospholipids asymmetry [2Sims P.J. Faioni E.M. Wiedmer T. Shattil S.J. Complement proteins C5b-9 cause release of membrane vesicles from the platelet surface that are enriched in the membrane receptor for coagulation factor Va and express prothrombinase activity.J Biol Chem. 1988; 263: 18205-18212Abstract Full Text PDF PubMed Google Scholar, 3Morel O. Jesel L. Freyssinet J.M. Toti F. Cellular mechanisms underlying the formation of circulating microparticles.Arterioscler Thromb Vasc Biol. 2011; 31: 15-26Crossref PubMed Scopus (374) Google Scholar]. This process involves regulated sorting of membrane proteins into the shed MP and flipping of phosphatidylserine from the inner to the outer membrane during cellular activation or early apoptosis [2Sims P.J. Faioni E.M. Wiedmer T. Shattil S.J. Complement proteins C5b-9 cause release of membrane vesicles from the platelet surface that are enriched in the membrane receptor for coagulation factor Va and express prothrombinase activity.J Biol Chem. 1988; 263: 18205-18212Abstract Full Text PDF PubMed Google Scholar, 4Simak J. Gelderman M.P. Cell membrane microparticles in blood and blood products: potentially pathogenic agents and diagnostic markers.Transfus Med Rev. 2006; 20: 1-26Abstract Full Text Full Text PDF PubMed Scopus (261) Google Scholar, 5Beyer C. Pisetsky D.S. The role of microparticles in the pathogenesis of rheumatic diseases.Nat Rev Rheumatol. 2010; 6: 21-29Crossref PubMed Scopus (199) Google Scholar]. MP resemble their parental cells on a smaller scale and share with them many characteristics, such as surface receptors, integral membrane and certain cytosolic proteins, some mRNAs and miRNAs [[5]Beyer C. Pisetsky D.S. The role of microparticles in the pathogenesis of rheumatic diseases.Nat Rev Rheumatol. 2010; 6: 21-29Crossref PubMed Scopus (199) Google Scholar]. Notably, earlier studies focused mostly on platelet MP [1Wolf P. The nature and significance of platelet products in human plasma.Br J Haematol. 1967; 13: 269-288Crossref PubMed Scopus (972) Google Scholar, 2Sims P.J. Faioni E.M. Wiedmer T. Shattil S.J. Complement proteins C5b-9 cause release of membrane vesicles from the platelet surface that are enriched in the membrane receptor for coagulation factor Va and express prothrombinase activity.J Biol Chem. 1988; 263: 18205-18212Abstract Full Text PDF PubMed Google Scholar, 4Simak J. Gelderman M.P. Cell membrane microparticles in blood and blood products: potentially pathogenic agents and diagnostic markers.Transfus Med Rev. 2006; 20: 1-26Abstract Full Text Full Text PDF PubMed Scopus (261) Google Scholar, 5Beyer C. Pisetsky D.S. The role of microparticles in the pathogenesis of rheumatic diseases.Nat Rev Rheumatol. 2010; 6: 21-29Crossref PubMed Scopus (199) Google Scholar, 6Heijnen H.F. Schiel A.E. Fijnheer R. Geuze H.J. Sixma J.J. Activated platelets release two types of membrane vesicles: microvesicles by surface shedding and exosomes derived from exocytosis of multivesicular bodies and alpha-granules.Blood. 1999; 94: 3791-3799Crossref PubMed Google Scholar, 7Rozmyslowicz T. Majka M. Kijowski J. et al.Platelet- and megakaryocyte-derived microparticles transfer CXCR4 receptor to CXCR4-null cells and make them susceptible to infection by X4-HIV.AIDS. 2003; 17: 33-42Crossref PubMed Scopus (230) Google Scholar, 8Boilard E. Nigrovic P.A. Larabee K. et al.Platelets amplify inflammation in arthritis via collagen-dependent microparticle production.Science. 2010; 327: 580-583Crossref PubMed Scopus (776) Google Scholar, 9Corrales-Medina V.F. Simkins J. Chirinos J.A. et al.Increased levels of platelet microparticles in HIV-infected patients with good response to highly active antiretroviral therapy.J Acquir Immune Defic Syndr. 2010; 54: 217-218Crossref PubMed Scopus (39) Google Scholar, 10Pankoui Mfonkeu J.B. Gouado I. Fotso Kuate H. et al.Elevated cell-specific microparticles are a biological marker for cerebral dysfunctions in human severe malaria.PLoS One. 2010; 5: e13415Crossref PubMed Scopus (97) Google Scholar, 11Koiou E. Tziomalos K. Katsikis I. et al.Circulating platelet-derived microparticles are elevated in women with polycystic ovary syndrome diagnosed with the 1990 criteria and correlate with serum testosterone levels.Eur J Endocrinol. 2011; 165: 63-68Crossref PubMed Scopus (21) Google Scholar, 12Ripoche J. Blood platelets and inflammation: their relationship with liver and digestive diseases.Clin Res Hepatol Gastroenterol. 2011; 35: 353-357Crossref PubMed Scopus (45) Google Scholar], except for more recent studies on endothelial cell and leukocyte derived MP in cardiovascular diseases [[13]Mause S.F. Weber C. Microparticles: protagonists of a novel communication network for intercellular information exchange.Circ Res. 2010; 107: 1047-1057Crossref PubMed Scopus (625) Google Scholar]. An elevation of platelet (CD41+) MP in the blood indicates the presence of inflammatory disease or its progression. Thus, an increase of platelet MP in synovial fluid or blood plasma is found in rheumatoid arthritis [[8]Boilard E. Nigrovic P.A. Larabee K. et al.Platelets amplify inflammation in arthritis via collagen-dependent microparticle production.Science. 2010; 327: 580-583Crossref PubMed Scopus (776) Google Scholar], HIV [[9]Corrales-Medina V.F. Simkins J. Chirinos J.A. et al.Increased levels of platelet microparticles in HIV-infected patients with good response to highly active antiretroviral therapy.J Acquir Immune Defic Syndr. 2010; 54: 217-218Crossref PubMed Scopus (39) Google Scholar], the polycystic ovary syndrome [[11]Koiou E. Tziomalos K. Katsikis I. et al.Circulating platelet-derived microparticles are elevated in women with polycystic ovary syndrome diagnosed with the 1990 criteria and correlate with serum testosterone levels.Eur J Endocrinol. 2011; 165: 63-68Crossref PubMed Scopus (21) Google Scholar], malaria [[10]Pankoui Mfonkeu J.B. Gouado I. Fotso Kuate H. et al.Elevated cell-specific microparticles are a biological marker for cerebral dysfunctions in human severe malaria.PLoS One. 2010; 5: e13415Crossref PubMed Scopus (97) Google Scholar] or inflammation in general [[12]Ripoche J. Blood platelets and inflammation: their relationship with liver and digestive diseases.Clin Res Hepatol Gastroenterol. 2011; 35: 353-357Crossref PubMed Scopus (45) Google Scholar]. Importantly, MP are not simply surrogate markers of platelet activation or disease activity, but can also modulate neighbouring cells, e.g., by transferring functional cell surface receptors that may trigger novel pathways in the recipient cell, by exchange of mRNA or miRNA, or by transfer of antigen via MHC class II molecules and other surface molecules [[13]Mause S.F. Weber C. Microparticles: protagonists of a novel communication network for intercellular information exchange.Circ Res. 2010; 107: 1047-1057Crossref PubMed Scopus (625) Google Scholar]. For example, the phenotype of cells deficient in CXCR4 and CD81 was rescued by transfer of MP carrying these surface receptors [5Beyer C. Pisetsky D.S. The role of microparticles in the pathogenesis of rheumatic diseases.Nat Rev Rheumatol. 2010; 6: 21-29Crossref PubMed Scopus (199) Google Scholar, 7Rozmyslowicz T. Majka M. Kijowski J. et al.Platelet- and megakaryocyte-derived microparticles transfer CXCR4 receptor to CXCR4-null cells and make them susceptible to infection by X4-HIV.AIDS. 2003; 17: 33-42Crossref PubMed Scopus (230) Google Scholar, 14Fritzsching B. Schwer B. Kartenbeck J. et al.Release and intercellular transfer of cell surface CD81 via microparticles.J Immunol. 2002; 169: 5531-5537Crossref PubMed Scopus (65) Google Scholar]. Moreover, recent studies have demonstrated that apart from platelets, other cells release functional MP upon activation or early apoptosis, such as from T cells that via transfer of the metalloproteinase inducer CD147 (EMMPRIN) induce fibrolytic activation of hepatic stellate cells [[15]Kornek M. Popov Y. Libermann T.A. Afdhal N.H. Schuppan D. Human T cell microparticles circulate in blood of hepatitis patients and induce fibrolytic activation of hepatic stellate cells.Hepatology. 2011; 53: 230-242Crossref PubMed Scopus (79) Google Scholar], or from leukocytes of cirrhotic patients that affect microvessels by compromising vasoconstrictor responses and decreasing systemic blood pressure [[16]Rautou P.E. Bresson J. Sainte-Marie Y. et al.Abnormal Plasma Microparticles Impair Vasoconstrictor Responses in Patients with Cirrhosis.Gastroenterology. 2012; 143: 166-176.e166Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar] (Fig. 1). As outlined before, platelet MP were considered a shared marker of disease activity, precluding their utility as disease-specific biomarker. Only recently, the concept and technology to quantitate different MP populations from plasma or serum have been established, allowing to assess the presumed extent to which a specific (immune cell) compartment is activated in a given disease. Notably, this is illustrated in chronic hepatitis C (CHC), and non-alcoholic fatty liver (NAFLD) [15Kornek M. Popov Y. Libermann T.A. Afdhal N.H. Schuppan D. Human T cell microparticles circulate in blood of hepatitis patients and induce fibrolytic activation of hepatic stellate cells.Hepatology. 2011; 53: 230-242Crossref PubMed Scopus (79) Google Scholar, 17Kornek M. Lynch M. Mehta S.H. et al.Circulating Microparticles as Disease-Specific Biomarkers of Severity of Inflammation in Patients with Hepatitis C or Nonalcoholic Steatohepatitis.Gastroenterology. 2012; 143: 448-458Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar], which show disease-specific MP profiles/signatures. Thus patients with CHC, a disease that is dominated by CD4+ and CD8+ hepatic T-cell infiltration, have primarily elevated circulating CD4+ and CD8+ T cell MP, whereas patients with NAFLD, a disease that is characterized by invariant NKT (iNKT) cells and CD14+ macrophages, monocytes, and dendritic cells (which play a key role in fatty tissue inflammation and the metabolic syndrome) have a unique signature of circulating iNKT and CD14+ MP [15Kornek M. Popov Y. Libermann T.A. Afdhal N.H. Schuppan D. Human T cell microparticles circulate in blood of hepatitis patients and induce fibrolytic activation of hepatic stellate cells.Hepatology. 2011; 53: 230-242Crossref PubMed Scopus (79) Google Scholar, 17Kornek M. Lynch M. Mehta S.H. et al.Circulating Microparticles as Disease-Specific Biomarkers of Severity of Inflammation in Patients with Hepatitis C or Nonalcoholic Steatohepatitis.Gastroenterology. 2012; 143: 448-458Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar]. Notably, these MP elevations correlate with the extent of histological inflammation in paired biopsies, though this correlation is not perfect, likely due to the biopsy's sampling variability rather than incorrectness of MP diagnostics. However, it must be stressed that exact MP functional studies and diagnostics heavily depend on proper purification and characterization of MP fractions, which have not been done in many prior studies. Several groups showed that MP are annexin V positive on their external surface, since they cannot maintain the phospholipid asymmetry of the plasma membrane, which requires energy and various enzymes such as a phospholipid flippase, which is largely absent or inactive in MP [4Simak J. Gelderman M.P. Cell membrane microparticles in blood and blood products: potentially pathogenic agents and diagnostic markers.Transfus Med Rev. 2006; 20: 1-26Abstract Full Text Full Text PDF PubMed Scopus (261) Google Scholar, 18Leventis P.A. Grinstein S. The distribution and function of phosphatidylserine in cellular membranes.Annu Rev Biophys. 2010; 39: 407-427Crossref PubMed Scopus (591) Google Scholar]. Upon cell activation resulting in increased intracellular Ca2+, the flippase becomes inactivated and a floppase activated, leading to collapse of the energy consuming lipid asymmetry and resulting in membrane budding and release of annexin V positive MP [[4]Simak J. Gelderman M.P. Cell membrane microparticles in blood and blood products: potentially pathogenic agents and diagnostic markers.Transfus Med Rev. 2006; 20: 1-26Abstract Full Text Full Text PDF PubMed Scopus (261) Google Scholar]. Generation of annexin V positive MP during early apoptosis may follow another yet ill-defined mechanism during generation of apoptotic bodies [[4]Simak J. Gelderman M.P. Cell membrane microparticles in blood and blood products: potentially pathogenic agents and diagnostic markers.Transfus Med Rev. 2006; 20: 1-26Abstract Full Text Full Text PDF PubMed Scopus (261) Google Scholar]. However, apoptotic bodies are no MP. They are characterized by a larger diameter (>1000 nm) and contain nuclear material [[4]Simak J. Gelderman M.P. Cell membrane microparticles in blood and blood products: potentially pathogenic agents and diagnostic markers.Transfus Med Rev. 2006; 20: 1-26Abstract Full Text Full Text PDF PubMed Scopus (261) Google Scholar]. Such material sediments at 10,000g as opposed to MP sedimenting between 10,000 and 100,000g [8Boilard E. Nigrovic P.A. Larabee K. et al.Platelets amplify inflammation in arthritis via collagen-dependent microparticle production.Science. 2010; 327: 580-583Crossref PubMed Scopus (776) Google Scholar, 15Kornek M. Popov Y. Libermann T.A. Afdhal N.H. Schuppan D. Human T cell microparticles circulate in blood of hepatitis patients and induce fibrolytic activation of hepatic stellate cells.Hepatology. 2011; 53: 230-242Crossref PubMed Scopus (79) Google Scholar, 17Kornek M. Lynch M. Mehta S.H. et al.Circulating Microparticles as Disease-Specific Biomarkers of Severity of Inflammation in Patients with Hepatitis C or Nonalcoholic Steatohepatitis.Gastroenterology. 2012; 143: 448-458Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar]. Another "contaminant" of shedded vesicles are exosomes, a class of phospholipid bilayer vesicles that are stored intracellularly and are either annexin V negative or only slightly positive [[13]Mause S.F. Weber C. Microparticles: protagonists of a novel communication network for intercellular information exchange.Circ Res. 2010; 107: 1047-1057Crossref PubMed Scopus (625) Google Scholar]. They are smaller in size (<100 nm) and sediment at 100,000g in sucrose gradients [4Simak J. Gelderman M.P. Cell membrane microparticles in blood and blood products: potentially pathogenic agents and diagnostic markers.Transfus Med Rev. 2006; 20: 1-26Abstract Full Text Full Text PDF PubMed Scopus (261) Google Scholar, 6Heijnen H.F. Schiel A.E. Fijnheer R. Geuze H.J. Sixma J.J. Activated platelets release two types of membrane vesicles: microvesicles by surface shedding and exosomes derived from exocytosis of multivesicular bodies and alpha-granules.Blood. 1999; 94: 3791-3799Crossref PubMed Google Scholar]. All these 'undesired' particles have to be removed physically by differential centrifugation or gated out during the process of fluorescent-activated cell sorting (FACS). Only such rigorous separation permits an exact MP quantification [15Kornek M. Popov Y. Libermann T.A. Afdhal N.H. Schuppan D. Human T cell microparticles circulate in blood of hepatitis patients and induce fibrolytic activation of hepatic stellate cells.Hepatology. 2011; 53: 230-242Crossref PubMed Scopus (79) Google Scholar, 16Rautou P.E. Bresson J. Sainte-Marie Y. et al.Abnormal Plasma Microparticles Impair Vasoconstrictor Responses in Patients with Cirrhosis.Gastroenterology. 2012; 143: 166-176.e166Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar, 17Kornek M. Lynch M. Mehta S.H. et al.Circulating Microparticles as Disease-Specific Biomarkers of Severity of Inflammation in Patients with Hepatitis C or Nonalcoholic Steatohepatitis.Gastroenterology. 2012; 143: 448-458Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar]. Based on current knowledge, we suggest that circulating MP will likely become novel, highly attractive biomarkers for cell and disease specific (immune) activation, and that MP promise to become useful markers for diagnosis and especially monitoring of acute and chronic liver diseases. Importantly, MP profiling may allow for a better on-target, e.g., inflammatory cell-specific assessment of therapies directed to subsets of cells that are involved in disease pathogenesis, such as certain T cells in viral or autoimmune hepatitis, endothelial cells in cirrhosis, or iNKT cells and macrophages in NASH. To this aim, state of the art methodology for MP isolation and quantification is mandatory. Finally, the biological properties of MP as cell–cell signaling modalities may be exploited for an improved cell-specific delivery of drugs and biologicals in liver and other diseases. The authors declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript. The underlying research reported in the study was funded by the NIH Institutes of Health. This work was supported by NIDDK Grant R21 DK075857-01A2 to D.S. and DFG fellowship Grant KO4103/1-1 to M.K. Part of this work was presented as oral presentation by M.K. during the EASL annual meeting 2011 in Berlin, Germany, and as poster at DDW 2011, Chicago, USA.