Impact of leukocytes and platelets in mediating hepatocyte apoptosis in a rat model of systemic endotoxemia

Abstract

Apoptotic hepatocytes have been demonstrated to represent an important signal for transmigration of leukocytes sequestered in sinusoids during endotoxemia in vivo. Beside leukocytes, platelets and their adhesion to endothelial cells and leukocytes have been implicated in inflammatory liver injury. Using in vivo multifluorescence microscopy, we examined the possibility that hepatocellular apoptosis causes both leukocytes and platelets to colocalize within the sinusoidal microvasculature of endotoxemic livers. We further addressed the issue whether cellular colocalization with apoptotic hepatocytes is cause or consequence of apoptosis. Intraperitoneal exposure of rats with LPS (5 mg/kg) induced liver injury after 6 and 16 h, as given by nutritive perfusion failure (20 +/- 2 and 21 +/- 2%), intrahepatic leukocyte (60 +/- 10 and 121 +/- 48 cells/mm(2)), and platelet (12 +/- 4 and 34 +/- 4 cells/mm(2)) accumulation as well as parenchymal cell apoptosis (4 +/- 1 and 11 +/- 2 cells/mm(2)) and caspase cleavage (4.7 +/- 2.4- and 7.0 +/- 3.0-fold increase; P < 0.05 vs. saline-exposed controls). Higher doses of LPS (10 mg/kg ip) further increased intrahepatic leukocyte and platelet accumulation but not the extent of parenchymal apoptosis. Detailed spatial analysis revealed colocalization of leukocytes (range 12-24%) but barely of platelets (<6%) with apoptotic hepatocytes in all endotoxemic groups studied. It is of interest, however, that platelets were found at increasing rates in colocalization with leukocytes at 6 and 16 h after LPS exposure (5 mg/kg LPS: 7 +/- 3 and 25 +/- 6%; 10 mg/kg LPS: 11 +/- 4 and 14 +/- 1%). Platelet-leukocyte events significantly correlated with the extent of caspase cleavage as an indicator of tissue apoptosis (P < 0.05; r = 0.82). Blockade of apoptosis by a pan-caspase inhibitor caused a significant reduction of leukocyte adherence and platelet-leukocyte colocalization on LPS exposure. On the other hand, leukocytopenic animals revealed reduced hepatocyte apoptosis, although values still exceeded those of controls, and in leuko- and thrombocytopenic animals, hepatocyte apoptosis was found reduced to control values. Taken together, LPS-associated hepatocyte apoptosis seems to be initiated by circulating blood cells that become adherent within the liver but might also contribute to further sustain the inflammatory cell-cell response.

Role of cysteinyl-leukotrienes for portal pressure regulation and liver damage in cholestatic rat livers

“…16 Microcirculatory disturbances and liver injury have been shown to be interrelated in animal studies and human studies in the setting of ischemia reperfusion, endotoxin-induced liver injury, or druginduced liver injury. [17][18][19][20] Accordingly, in the current study, LDH efflux from isolated perfused livers increased to a higher degree in cholestatic livers than in sham-operated livers following KC activation. The good correlation between LDH efflux and transaminases has been shown in different earlier studies.…”

Urinary trypsin inhibitor protects against liver injury and coagulation pathway dysregulation induced by lipopolysaccharide/D-galactosamine in mice

“…Liver cell apoptosis represents not only a crucial step in acute hepatic failure, but also functions as a signal for leukocyte infiltration in parenchymal cells, 29,30 thereby establishing a vicious circle with the augmentation of leukocyte inflammation and cell death, although necrosis is also likely to markedly contribute to the liver injury in view of the elevation of serum liver transaminase levels and histological findings (see Leonis et al 25 and Figures 1 and 4 in this study). Consistent with this, preventing apoptosis in hepatocytes by caspase inhibition reportedly suppresses leukocyte transmigration and leukocyte-dependent liver cell necrosis accompanied by apoptosis.…”

Attenuation of Inflammation and Apoptosis by Pre- and Posttreatment of Darbepoetin-α in Acute Liver Failure of Mice

“…Using a Zeiss fluorescence microscope equipped with a 100 W mercury lamp and different filter sets for blue, green, and UV epi-illumination (Axiotech Vario; Zeiss, Jena, Germany), microscopic images were taken by water immersion objectives (ϫ20/0.50W, ϫ40/0.8W; Zeiss), televised using a charge-coupled device video camera (FK 6990A-IQ; Pieper, Berlin, Germany), and recorded on videotape for subsequent off-line evaluation. 9 Blood perfusion within individual sinusoids was studied after tissue contrast enhancement by sodium fluorescein (2 mol/kg body weight i.v. ; Merck, Darmstadt, Germany) and blue light epi-illumination (450 to 490/Ͼ520 nm, excitation/emission wavelength).…”

“…6 Within the extremely complex cascade of pathophysiological events, representing the systemic inflammatory response, great attention has recently been brought to the contribution of apoptosis in organ dysfunction and failure. 7,8 Hepatocellular apoptosis represents not only a crucial step in ALF but functions also as a signal for leukocyte migration and attack on parenchymal cells, 9,10 thereby establishing a vicious circle with aggravation of leukocytic inflammation and final cell death. It has been shown that preventing apoptosis in hepatocytes by caspase inhibition suppresses leukocyte transmigration and leukocyte-dependent liver cell necrosis.…”