The mannose receptor on murine liver sinusoidal endothelial cells is the main denatured collagen clearance receptor

The purpose of this study was to identify the receptor responsible for endocytosis of denatured collagen from blood. The major site of clearance of this material (at least 0.5 g/day in humans) is a receptor on liver sinusoidal endothelial cells (LSECs). We have now identified an 180-kDa endocytic receptor on LSECs, peptide mass fingerprinting of which revealed it to be the mannose receptor. Challenge of mannose-receptor knockout mice and their cultured LSECs revealed significantly reduced blood clearance and a complete absence of LSEC endocytosis of denatured collagen. Organ analysis of wild-type versus knockout mice after injection of denatured collagen revealed significantly reduced liver uptake in the knockout mice. Clearance/endocytosis of ligands for other receptors in these animals was as that for wild-type mice, and denatured collagen uptake in wild-type mice was not affected by other ligands of the mannose receptor, namely mannose and mannan. Furthermore, unlike that of mannose and mannan, endocytosis of denatured collagen by the mannose receptor is calcium independent. This suggests that the binding site for denatured collagen is distinct from that for mannose/mannan. Mannose receptors on LSECs appear to have less affinity for circulating triple helical type I collagen.

CONCLUSION

The mannose receptor is the main candidate for being the endocytic denatured collagen receptor on LSECs.

Long-term preservation of high endocytic activity in primary cultures of pig liver sinusoidal endothelial cells

Together with Kupffer cells, liver sinusoidal endothelial cells (LSECs) constitute the most powerful scavenger system in the body. However, studies on LSEC function are hampered by the fact that the cells lose their scavenger ability and start deteriorating after a few days in culture. The purpose of the present study was to improve the conditions of cultivation to prolong the survival of pig LSECs in vitro. We used the high capacity receptor-mediated endocytosis of soluble waste molecules as a marker for functionally intact cells in the cultures. Compared with two commercially-, and two other media specifically designed for use with either SECs or hepatocytes from rat, our newly developed serum-free medium, DM 110/SS, devoid of any components of animal origin, was superior in maintaining the endocytic activity. Of six growth factors studied for their effect on endocytosis, basic fibroblast, and recombinant epidermal, but not vascular endothelial growth factor, were found to be most beneficial. After 8 days in DM 110/SS, LSECs maintained endocytosis via the scavenger receptor, mannose receptor, collagen alpha-chain receptor and the Fc-gamma receptor. All endocytosed ligands, except for aggregated IgG were degraded in 8-day-old cultures. Using the new medium, the cells endocytosed ligands for up to 20 days, and survived for at least an additional 10 days, albeit without the high endocytic activity typical of intact LSECs. Importantly, DNA synthesis in prolonged cultures of LSECs was observed only when maintained in DM 110/SS medium. In conclusion, we describe a protocol for the maintenance of LSECs in culture for the longest period yet reported.

Contractile response of femoral arteries in pigs with acute liver failure

BACKGROUND

Acute liver failure (ALF) is characterized haemodynamically by a progressive hyperdynamic circulation. The pathophysiological mechanism is unknown, but impaired contractility of vascular smooth muscle may play an important role. The aim of this study was to evaluate the vascular response to stimulation with norepinephrine and angiotensin II in endothelium-denuded femoral artery rings.

METHODS

Norwegian Landrace pigs weighing 27.1 +/- 0.5 kg (mean +/- sx (standard error of the mean)) were used. ALF was induced by performing a portacaval shunt followed by ligation of the hepatic arteries (n = 6). Sham-operated animals served as controls (n = 5). Cumulative isometric concentration contraction curves were obtained after in vitro stimulation of the femoral artery rings with either angiotensin II (10(-13) - 10(-5) mol/L) or norepinephrine (10(-13) - 10(-3) mol/L).

RESULTS

Pigs suffering from ALF developed a hyperdynamic circulation with an increased cardiac index (P = 0.017) and decreased systemic vascular resistance index (P = 0.015). Studies of the hind leg revealed a decreased vascular resistance index and increased blood flow compared to sham-operated controls (P = 0.003 and P = 0.01, respectively). Angiotensin II caused a concentration-dependent contraction of the arterial segments, with no significant differences in vascular responses between the two groups. Maximum force generated did not differ (55 +/- 7 versus 56 +/- 7 mN, P = 0.95). Furthermore, there were no differences for norepinephrine in the cumulative concentration-response curves and the maximum contractile force was not significantly different (87 +/- 8 versus 93 +/- 16 mN, P = 0.55).

CONCLUSIONS

This study documents for the first time that there are no signs of endothelium-independent peripheral vascular hyporesponsiveness to angiotensin II and norepinephrine in pigs with ALF.

An experimental large animal model for the assessment of bioartificial liver support systems in fulminant hepatic failure

BACKGROUND

Pre-clinical assessment of bioartificial liver support systems requires a highly reproducible large animal model. The main objective of the present study was to develop a valid large animal model for assessing novel bioartificial liver support systems in fulminant hepatic failure.

METHODS

A complete liver devascularization procedure was performed in 10 female pigs weighing 25-38 kg. Five matched pigs were sham-operated and served as controls.

RESULTS

Pigs with fulminant hepatic failure developed a hyperdynamic circulation, with increased cardiac index (P(GT) < .0001), decreased systemic vascular resistance index (P(GT) < .0001) and mean arterial pressure (P(GT) = .001). Furthermore, intracranial hypertension developed (P(GT) < .0001). with increased common carotid artery flow (P(GT) < .0001) and decreased common carotid resistance (P(G) = .003). Femoral artery flow increased (P = .036). while hindleg resistance (P < .001) and renal artery resistance decreased (P = .019). Oxygen consumption (P(GT) = .050) and oxygen extraction ratio (P(GT) = .001) increased compared to controls. Arterial ammonia, venous aspartate aminotransferase and bilirubin levels increased (P(GT) < .0001, respectively). Abnormal haemostasis developed with significant loss of platelets (P(GT) = .010), decreasing fibrinogen levels (P(G) = .001) and increasing international normalized ratio (P(GT) = .012) and activated clotting time (PGT < .001). Urine became hypo-osmotic (P < .001. P(G) = .011), with decreased sodium levels (P = .08) and increased potassium levels (P(G) = .025).

CONCLUSIONS

This study characterizes a reproducible large animal model for fulminant hepatic failure that seems suitable for the assessment of bioartificial liver support systems.

N-acetylcysteine increases cerebral perfusion pressure in pigs with fulminant hepatic failure

OBJECTIVE

Intravenous administration of N-acetylcysteine beyond 15 hrs reduces mortality rates in patients suffering from paracetamol-induced fulminant hepatic failure, although the mechanism of the therapeutic benefit remains unclear. We hypothesized increased survival to be caused by improved hemodynamic performance. The main objective for the study was to explore the effect of N-acetylcysteine on hemodynamics, oxygen transport, and regional blood flow in pigs with fulminant hepatic failure.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Surgical research laboratory in a university hospital.

SUBJECTS

Female Norwegian Landrace pigs.

INTERVENTIONS

Fulminant hepatic failure was induced by a total liver devascularization procedure. Five hours later, the pigs were allocated to N-acetylcysteine treatment (150 mg.kg-1 in 100 mL of 0.9% saline over 15 mins, followed by 50 mg.kg-1 in 500 mL of 0.9% saline over a period of 4 hrs) or placebo.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure stabilized in the N-acetylcysteine group and increased slightly during the last 2 hrs (pGT =.009). Thus, mean arterial pressure was significantly higher compared with placebo after 3 hrs (p =.01). Cerebral perfusion pressure was significantly higher during the last 2 hrs in the N-acetylcysteine group (pGT =.033). Common carotid artery flow also increased and was maintained at a higher level compared with placebo (pG =.027). Systemic vascular resistance index initially decreased but then gradually increased (pGT <.001). Cardiac index increased after 15 mins of N-acetylcysteine infusion, causing a significant interaction (pGT =.038), but did not differ after 3 hrs. No significant differences in hindleg and mesentery hemodynamics were found. A short-lived increase in oxygen delivery caused by a temporary increase in cardiac index was observed but without any corresponding increase in oxygen consumption.

CONCLUSIONS

Intravenous N-acetylcysteine infusion increases cerebral perfusion pressure in pigs with fulminant hepatic failure. Earlier reported effects on oxygen transport and uptake could not be confirmed.

Renal elimination of protein S-100beta in pigs with acute encephalopathy

BACKGROUND

Protein S-100beta is an established biochemical marker for cerebral injury in serum. For the further interpretation and possible use of S-100beta serum measurements in acute hepatic encephalopathy, renal elimination of S-100beta was measured in pigs with elevated S-100beta levels due to hepatic encephalopathy.

METHODS

Eighteen female Norwegian Landrace pigs were randomly allocated to either hepatic devascularization (n=13) or sham operation (n=5). Repeated samples from the common carotid artery, right renal vein, and urine were simultaneously drawn for S-100beta analysis, using the Sangtec100 Liamat immunoassay.

RESULTS

In hepatic devascularized pigs, arterial serum levels of S-100beta increased from 0.96+/-0.04 microg/L (mean +/- SEM) at t = 0h to 1.74+/-0.11 microg/L (mean +/- SEM) at t = 5 h. Urinary excretion increased simultaneously from 8.48+/-3.66 ng/h (mean +/- SEM) to 20.4+/-9.54 ng/h (mean +/- SEM), while renal arterial-venous fluxes for both kidneys increased from 1022+/-404 ng/h (mean +/- SEM) to 2444+/-590 ng/h (mean +/- SEM).

CONCLUSIONS

Increased arterial S-100beta levels in pigs with acute hepatic encephalopathy are not a result of decreased renal elimination. The large difference between the renal arterial venous S-100beta concentrations and the urinary excretion of S-100beta indicate that renal metabolism is the major route of elimination.

Protein S-100beta: a biochemical marker for increased intracranial pressure in pigs with acute hepatic failure

BACKGROUND

Acute hepatic failure (AHF) may cause encephalopathy. Intracranial pressure (ICP) is frequently monitored to guide therapy, but such monitoring may cause intracerebral haemorrhagic complications. We hypothesize that determination of serum levels of S-100beta, a protein synthesized in astroglial cells, will provide useful clinical information on the presence and extent of intracranial hypertension in AHF.

METHODS

Continuous intraparenchymatous ICP monitoring and serial S-100beta measurements in serum were performed in 11 Norwegian Landrace pigs with surgically induced AHF and in 4 sham-operated controls.

RESULTS

ICP increased hour by hour in the devascularized pigs in parallel with increased serum levels of protein S-100beta. In the sham-operated controls S-100beta was not detectable at any time point.

CONCLUSIONS

Serum levels of S-100beta are increased early in experimental AHF. Determination of protein S-100beta may provide useful information on the presence and extent of intracranial hypertension in AHF.