Ischemic liver cell damage and calcium accumulation in rats

Regulated hepatic reperfusion mitigates ischemia-reperfusion injury and improves survival after prolonged liver warm ischemia: a pilot study on a novel concept of organ resuscitation in a large animal model

BACKGROUND

Ischemia-reperfusion injury (IRI) can occur during hepatic surgery and transplantation. IRI causes hepatic mitochondrial and microcirculatory impairment, resulting in acute liver dysfunction and failure. We proposed a novel strategy of regulated hepatic reperfusion (RHR) to reverse the cellular metabolic deficit that incurred during organ ischemia by using a substrate-enriched, oxygen-saturated, and leukocyte-depleted perfusate delivered under regulated reperfusion pressure, temperature, and pH. We investigate the use of RHR in mitigating IRI after a prolonged period of warm ischemia.

METHODS

Using a 2-hour liver warm ischemia swine model, 2 methods of liver reperfusion were compared. The control group (n = 6) received conventional reperfusion with unmodified portal venous blood under unregulated reperfusion pressure, temperature, and pH. The experimental group (n = 6) received RHR. We analyzed the effects of RHR on post-reperfusion hemodynamic changes, liver function, and 7-day animal survival.

RESULTS

RHR resulted in 100% survival compared with 50% in the control group (p = 0.05). Post-reperfusion syndrome was not observed in the RHR group, but it occurred in 83% of the control group. RHR resulted in a lesser degree of change from baseline serum alanine aminotransferase levels, aspartate aminotransferase, and lactate dehydrogenase after reperfusion compared with the control group. Histopathologic evaluation showed minimal ischemic changes in the RHR group, whereas a considerable degree of coagulative hepatocellular necrosis was observed in the control group.

CONCLUSIONS

Regulated hepatic reperfusion mitigates IRI, facilitates liver function recovery, and improves survival after a prolonged period of hepatic warm ischemia. This novel strategy has potential applicability to clinical hepatic surgery and liver transplantation when marginal grafts are used.

Expression and function of TRP channels in liver cells

The liver plays a central role in whole body homeostasis by mediating the metabolism of carbohydrates, fats, proteins, drugs and xenobiotic compounds, and bile acid and protein secretion. Hepatocytes together with endothelial cells, Kupffer cells, smooth muscle cells, stellate and oval cells comprise the functioning liver. Many members of the TRP family of proteins are expressed in hepatocytes. However, knowledge of their cellular functions is limited. There is some evidence which suggests the involvement of TRPC1 in volume control, TRPV1 and V4 in cell migration, TRPC6 and TRPM7 in cell proliferation, and TRPPM in lysosomal Ca(2+) release. Altered expression of some TRP proteins, including TRPC6, TRPM2 and TRPV1, in tumorigenic cell lines may play roles in the development and progression of hepatocellular carcinoma and metastatic liver cancers. It is likely that future experiments will define important roles for other TRP proteins in the cellular functions of hepatocytes and other cell types of which the liver is composed.

The impact of postreperfusion syndrome on short-term patient and liver allograft outcome in patients undergoing orthotopic liver transplantation

The greatest part of liver allograft injury occurs during reperfusion, not during the cold ischemia phase. The aim of this study, therefore, was to investigate how the severity of postreperfusion syndrome (PRS) influences short-term outcome for the patient and for the liver allograft. Over a 2-year period, 338 consecutive patients who presented for orthotopic liver transplantation (OLT) were included in this retrospective study. They were divided into 2 groups according to the severity of the PRS they experienced. The first group comprised 152 patients with mild or no PRS; the second group comprised 186 patients with significant PRS. Perioperative hemodynamic parameters, coagulation profiles, blood product requirements, incidence of infection, incidence of rejection and outcome data for both groups were collected and analyzed. There was no demographic difference between the groups except for age; group 2 had older patients than group 1 (54.94 +/- 9.07 versus 51.52 +/- 9.91, P = 0.001). Compared to group 1, group 2 patients required more red blood cell transfusions (11.31 +/- 10.90 versus 8.08 +/- 7.89 units, P = 0.002), more fresh frozen plasma transfusions (10.25 +/- 10.96 versus 7.03 +/- 7.64 units, P = 0.002), more cryoprecipitate (1.88 +/- 4.72 units versus 0.61 +/- 1.80 units, P = 0.001), and were more likely to suffer from fibrinolysis (52.7% versus 41.4%, P = 0.041). Interestingly, group 2 had a shorter average warm ischemia time than group 1 (33.19 +/- 8.55 versus 36.21 +/- 11.83 minutes, P = 0.01). Group 2 also required longer, on average, mechanical ventilation (14.95 +/- 29.79 versus 8.55 +/- 17.79 days, P = 0.015), remained in the intensive care unit longer (17.65 +/- 31.00 versus 11.49 +/- 18.67 days, P = 0.025), and had a longer hospital stay (27.29 +/- 32.35 versus 20.85 +/- 21.08 days, P = 0.029). Group 2 was more likely to require retransplantation (8.6% versus 3.3%, P = 0.044). In conclusion, the severity of PRS during OLT appears to be related to the outcome of patient and liver allograft.

Ca(2+) -permeable channels in the hepatocyte plasma membrane and their roles in hepatocyte physiology

Hepatocytes are highly differentiated and spatially polarised cells which conduct a wide range of functions, including intermediary metabolism, protein synthesis and secretion, and the synthesis, transport and secretion of bile acids. Changes in the concentrations of Ca(2+) in the cytoplasmic space, endoplasmic reticulum (ER), mitochondria, and other intracellular organelles make an essential contribution to the regulation of these hepatocyte functions. While not yet fully understood, the spatial and temporal parameters of the cytoplasmic Ca(2+) signals and the entry of Ca(2+) through Ca(2+)-permeable channels in the plasma membrane are critical to the regulation by Ca(2+) of hepatocyte function. Ca(2+) entry across the hepatocyte plasma membrane has been studied in hepatocytes in situ, in isolated hepatocytes and in liver cell lines. The types of Ca(2+)-permeable channels identified are store-operated, ligand-gated, receptor-activated and stretch-activated channels, and these may vary depending on the animal species studied. Rat liver cell store-operated Ca(2+) channels (SOCs) have a high selectivity for Ca(2+) and characteristics similar to those of the Ca(2+) release activated Ca(2+) channels in lymphocytes and mast cells. Liver cell SOCs are activated by a decrease in Ca(2+) in a sub-region of the ER enriched in type1 IP(3) receptors. Activation requires stromal interaction molecule type 1 (STIM1), and G(i2alpha,) F-actin and PLCgamma1 as facilitatory proteins. P(2x) purinergic channels are the only ligand-gated Ca(2+)-permeable channels in the liver cell membrane identified so far. Several types of receptor-activated Ca(2+) channels have been identified, and some partially characterised. It is likely that TRP (transient receptor potential) polypeptides, which can form Ca(2+)- and Na(+)-permeable channels, comprise many hepatocyte receptor-activated Ca(2+)-permeable channels. A number of TRP proteins have been detected in hepatocytes and in liver cell lines. Further experiments are required to characterise the receptor-activated Ca(2+) permeable channels more fully, and to determine the molecular nature, mechanisms of activation, and precise physiological functions of each of the different hepatocyte plasma membrane Ca(2+) permeable channels.

Hepatic ischemia-reperfusion injury: roles of Ca2+ and other intracellular mediators of impaired bile flow and hepatocyte damage

Liver resection and liver transplantation have been successful in the treatment of liver tumors and end-stage liver disease. This success has led to an expansion in the pool of patients potentially treatable by liver surgery and, in the case of transplantation, to a shortage of liver donors. At present, there are significant numbers of potential candidates for liver resection and liver donation who have fatty livers, are aged, or have livers damaged by chemotherapy. All of these are at high risk for ischemic reperfusion (IR) injury. The aims of this review are to assess current knowledge of the clinical effectiveness of ischemic preconditioning and intermittent ischemia in reducing IR damage in liver surgery; to evaluate the use of bile flow as a sensitive indicator of IR liver damage; and to analyze the molecular mechanisms, especially intracellular Ca2+, involved in IR injury and ischemic preconditioning. It is concluded that bile flow is a sensitive indicator of IR injury. Together with reactive oxygen species (ROS) and other extracellular and intracellular signaling molecules, intracellular Ca2+ in hepatocytes plays a key role in the normal regulation of bile flow and in IR-induced injury and cell death. Ischemic preconditioning is an effective strategy to reduce IR injury but there is considerable scope for improvement, especially in patients with fatty and aged livers. The development of effective new strategies to reduce IR injury will depend on improved understanding of the molecular mechanisms involved, especially by gaining a better perspective of the relative importance of the various intrahepatocyte signaling pathways involved.

Elemental composition of anatomically distinct regions of rat liver

Experiments were conducted to test the commonly held assumption that analysis of a portion of rat liver is representative of the elemental concentration of the whole organ. Male Sprague-Dawley rats (initial body weight approximately 250 g) fed a chow diet or weanling male Long-Evans rats (initial body weight approximately 50 g) fed a semipurified diet with or without copper in the mineral premix were sacrificed after 4 wk on their respective diets and livers were dissected into seven portions representing major anatomical divisions of this organ. Elemental analyses by atomic absorption spectroscopy (calcium, magnesium, iron, zinc, copper, manganese), atomic emission spectroscopy (sodium, potassium), or colorimetric assay (phosphorus) demonstrated no statistically significant differences in composition of these nine elements among anatomical regions of liver. Dietary copper deficiency led to equivalently reduced copper concentration in all portions of rat liver and did not cause any other significant alterations in liver composition of these nine elements within the 4 wk of these studies. These results confirm the validity of the common assumption that analysis of a portion of rat liver can be representative of the elemental composition of the whole organ. This conclusion will allow more analyses to be performed on fewer animals, thereby reducing animal use and reagent costs without sacrificing analytical accuracy.

The effect of bile salts and calcium on isolated rat liver mitochondria

Intact mitochondria were incubated with and without calcium in solutions of chenodeoxycholate, ursodeoxycholate, or their conjugates. Glutamate dehydrogenase, protein and phospholipid release were measured. Alterations in membrane and organelle structure were investigated by electron paramagnetic resonance spectroscopy. Chenodeoxycholate enhanced enzyme liberation, solubilized protein and phospholipid, and increased protein spin label mobility and the polarity of the hydrophobic membrane interior, whereas ursodeoxycholate and its conjugates did not damage mitochondria. Preincubation with ursodeoxycholate or its conjugate tauroursodeoxycholate for 20 min partially prevented damage by chenodeoxycholate. Extended preincubation even with 1 mM ursodeoxycholate could no longer prevent structural damage. Calcium (from 0.01 mM upward) augmented the damaging effect of chenodeoxycholate (0.15-0.5 mM). The combined action of 0.01 mM calcium and 0.15 mM chenodeoxycholate was reversed by ursodeoxycholate only, not by its conjugates tauroursodeoxycholate and glycoursodeoxycholate. In conclusion, ursodeoxycholate partially prevents chenodeoxycholate-induced glutamate dehydrogenase release from liver cell mitochondria by membrane stabilization. This holds for shorter times and at concentrations below 0.5 mM only, indicating that the different constitution of protein-rich mitochondrial membranes does not allow optimal stabilization such as has been seen in phospholipid- and cholesterol-rich hepatocyte cell membranes, investigated previously.

The roles of reactive oxygen species and endogenous opioid peptides in ischemia-induced arrhythmia of isolated rat hearts

Although the formation of oxygen-derived free radicals (or reactive oxygen species; ROS) and the release of endogenous opioid peptides (EOP) have been independently reported to be the major arrhythmogenic factors in ischemic hearts, possible relations between these two factors have seldom been investigated. Thus, we studied whether the ROS and EOP were related in the progression of ischemia-induced arrhythmias. Isolated rat hearts perfused in the Langendorff mode were treated with dynorphin A1-13 (kappa EOP receptor agonist), and/or allopurinol (xanthine oxidase inhibitor), before the onset of ischemia induced by ligating the left coronary arteries. Ischemic period lasted for 30 min, during which cardiac rhythms were recorded. At the end of ischemia, hearts were analyzed for the glutathione and ascorbate levels. Allopurinol (100 nmoles/heart) was effective in reducing the severity of arrhythmia (arrhythmia score: Mean +/- SEM 3.00 +/- 0.80 for allopurinol, 5.75 +/- 0.41 for placebo, p < 0.01), while dynorphin (10 micrograms/heart) potentiated the arrhythmia (6.71 +/- 0.52, p < 0.05 vs. placebo). Coadministration of allopurinol and dynorphin was capable of reducing arrhythmia (5.57 +/- 0.65) when compared with the administration of dynorphin alone (6.71 +/- 0.52, p < 0.05). Tissue oxidative stress was evaluated by the concentrations of glutathione (GSH) and ascorbate. Allopurinol did not significantly elevate tissue GSH concentrations (1.46 +/- 0.05 mumoles/g wet wt) in ischemic hearts, while dynorphin alone significantly decreased the GSH concentrations (0.96 +/- 0.08, p < 0.05) when compared with the placebo (1.32 +/- 0.03). The dynorphin-induced GSH decrease cannot be reversed by coadministration with allopurinol (0.90 +/- 0.104). Allopurinol significantly elevated tissue ascorbate levels (0.16 +/- 0.01) when compared with placebo (0.10 +/- 0.01, p < 0.05). Interestingly, dynorphin alone also elevated the tissue ascorbate concentrations (0.16 +/- 0.02). Coadministration of allopurinol and dynorphin further spiked the ascorbate levels (0.28 +/- 0.05, p < 0.01). In conclusion, the results suggested that ischemia-induced arrhythmia mechanisms might involve the formation of superoxide and other ROS, which were probably generated from the release of EOP (or EOP/EOP receptor interactions). Superoxide, the formation of which can be inhibited by allopurinol that exerted antiarrhythmic effect, was probably scavenged by ascorbate in myocardial ischemia. The ROS resulting from EOP/EOP receptor interactions were probably scavenged by glutathione system. Elevated ascorbate levels in dynorphin-treated hearts might result from the compensatory synthesis induced by decreased glutathione levels.

Inhibition of the increase of intrahepatic Ca2+ by diltiazem in rats with liver ischemia

The effects of a continuous infusion of a calcium entry blocker, 1, 5-benzothiazepine derivative (diltiazem), on ischemic liver cell damage were studied using quantitative 45Ca-autoradiographic and liquid scintillation techniques. The drug was administered to male Wistar rats as a continuous infusion for 3 h, beginning 30 min before ischemia. Autoradiographic studies showed that 45Ca accumulated in the liver lobuli after 1 h of liver ischemia and 3 h of reperfusion, but the level of 45Ca accumulation was significantly lower in drug-treated rats than in untreated animals. In addition, liquid scintillation studies showed significant differences in the intrahepatic 45Ca contents. These results suggest that diltiazem may inhibit the rise of intracellular Ca2+ due to the flow of extracellular Ca2+ into the cytosol, and may protect the ischemic liver from damage.