Thermic transition and glycolytic capacity as critical events in the survival of rat liver slices after overnight cold hypoxic preservation

Metabolic preconditioning with fructose prior to organ recovery attenuates ischemia-reperfusion injury in the isolated perfused rat liver

OBJECTIVE

Ischemia-reperfusion injury is associated with a high rate of primary organ dysfunction and thereby contributes substantially to morbidity and mortality in the course of liver transplantation. In the present study, the impact of metabolic preconditioning with fructose on ischemia-reperfusion injury in the isolated perfused rat liver model is evaluated.

METHODS

Fasted rats received a single intravenous fructose injection to induce metabolic preconditioning (fructose group) or a volume equivalent of normal saline (control group) 10 min before liver explantation. After 26 h of cold storage, livers were reperfused for 90 min at 37°C with Krebs-Henseleit buffer. The parameters used to quantify ischemia-reperfusion injury included hepatic oxygen consumption, enzyme release, and cell viability.

RESULTS

During reperfusion, livers in the fructose group consumed more oxygen than livers in the control group (p < 0.005), indicating ATP synthesis as a result of glycolytic fructose degradation. Moreover, cell injury was reduced by fructose administration, as reflected by a lower enzyme release during both cold ischemia and reperfusion (p < 0.05). Finally, hepatocyte viability at the end of reperfusion was significantly higher in the fructose group (p < 0.01). However, there was no significant difference between the two experimental groups in reference to the viability of endothelial cells.

CONCLUSION

In clinical use, metabolic preconditioning with fructose prior to organ recovery might contribute to a reduction in the incidence of primary organ dysfunction after liver transplantation.

The use of precision-cut liver slices from male Wistar rats as a tool to study age related changes in CYP3A induction and in formation of paracetamol conjugates

Precision-cut liver slices (PCLS) offer a lot of advantages because all heterogeneity and cell-cell interactions within the original tissue matrix are maintained. This in vitro model was used to study the effect of ageing on certain aspects of drug metabolism and liver function in young (3 months), adult (9 months) and old (24 months) Wistar male rats. Protein synthesis, an important liver function, was not modified in young, adult and old rats, suggesting that ageing does not impair liver functionality but it affects some specific targets. Among them, a decrease in total P450 in liver microsomes and the loss of CYP3A23 inducibility in PCLS were clearly observed in old rats as compared to adult rats. Finally, the amount of total paracetamol conjugates was not modified between 9 and 24 months but in old rats, sulfoconjugation of paracetamol, its major route of elimination, was decreased.

Role of temperature on protein and mRNA cytochrome P450 3A (CYP3A) isozymes expression and midazolam oxidation by cultured rat precision-cut liver slices

The cytochrome P450 3A (CYP3A)-mediated midazolam oxidation was studied in rat precision-cut liver slices (PCLS) maintained for 20hr at 4, 20 and 37 degrees, and further incubated for 8hr at 37 degrees. Either at 4 or 20 degrees, midazolam was oxidised by PCLS at similar rates to that observed in freshly cut slices. Moreover, PCLS kept a regioselectivity since 4-hydroxylation was more important than 1'-hydroxylation. Conversely, PCLS totally lost their capacity to oxidise midazolam after 20hr at 37 degrees, and both CYP3A2 protein and mRNA were not detected. CYP3A1 protein was unaffected by a temperature of 37 degrees but its mRNA was totally lost. By blocking transcription with actinomycin D, the decay of both CYP3A mRNAs followed the same profile at either 20 or 37 degrees, indicating that temperature affected the CYP3A2 protein stability. Cell functionality was not involved in such an impairment since the low values of ATP, GSH and protein synthesis rates observed at 4 and 20 degrees were rapidly restored, when PCLS were further incubated at 37 degrees. The use of rat supersomes expressing either CYP3A1 or CYP3A2, strongly supported the hypothesis that 4-hydroxymidazolam was mainly formed by CYP3A2. These results suggest that: (1) CYP3A1 protein is constitutive and largely expressed in rat liver slices; (2) regioselective midazolam oxidation appears to be mainly CYP3A2 dependent; and (3) since CYP3A isoforms have similar half-lives (about 10-14hr), the loss of CYP3A2 protein at 37 degrees might be due to a selective targeting (phosphorylation ?) leading to proteolytic disposal by the proteasome.

Effects of bacterial endotoxin (lipopolysaccharides) on survival and metabolism of cultured precision-cut rat liver slices

The effect of bacterial endotoxin (lipopolysaccharides from Escherichia coli, LPS) on cellular metabolism and drug biotransformation was studied in precision-cut rat liver slices (PCLS). Xenobiotic metabolism by PCLS was assessed by measuring phase I (midazolam hydroxylation) and phase II (paracetamol conjugates) enzyme activities. Nitrites formation was used as an indirect way to assess LPS-mediated activation of nitric oxide synthase (iNOS, type 2). PCLS incubation with various LPS doses results in a dose-dependent formation of nitrites. Such a nitrite formation is decreased by dexamethasone. After incubation of PCLS for 24 h LPS addition did not increase the basal nitrite formation, indicating that cells are not responsive any more. Paracetamol conjugation was unaffected by LPS treatment but midazolam hydroxylation was reduced by more than 50%. Such a loss is not due to cell impairment since neither survival (LDH leakage) nor cellular metabolism (protein synthesis or ATP content) were modified by LPS. Indeed, under defined conditions, namely Williams' medium E and O(2)/CO(2) (95:5), PCLS maintained both ATP and GSH levels and the capacity of hepatocytes to synthesize proteins. In conclusion, the in vitro model of PCLS reproduces the inhibitory effect of LPS on a CYP3A-dependent activity, allowing a mechanistic approach to study cell-cell interactions.

Reoxygenation after cold hypoxic storage of cultured precision-cut rat liver slices: effects on cellular metabolism and drug biotransformation

Cultured rat precision-cut liver slices (PCLS) were used to study the influence of hypothermic preservation and reoxygenation at 37 degrees C on cellular metabolism and drug biotransformation. Cold hypoxic storage caused a depressed metabolism in rat liver slices, but reoxygenation for 8 h at 37 degrees C partially restored the levels of both ATP and GSH and totally restored the capacity to synthesize proteins. Metabolism of midazolam (CYP3A-dependent oxidation) by cold preserved liver slices was decreased by 30% but no further affected by reoxygenation, showing the same profile as freshly cut slices. Such a reoxygenation at 37 degrees C is accompanied by a dramatic loss of CYP3A2 protein while CYP3A1 protein was unaffected. These results suggest that CYP3A2 did not play a major role in midazolam oxidation. Such results are not consistent with a putative reoxygenation injury but rather with cold hypoxic damage. Since cold preserved liver slices did not respond to bacterial endotoxin stimulation (lipopolysaccharides), a minor role of non-parenchymal cells is suggested as mediators for deleterious effects developed during the cold storage.