Application of Pharmacokinetic Modeling to Characterize Hepatobiliary Disposition of Imaging Agents and Alterations due to Liver Injury in Isolated Perfused Rat Livers

BACKGROUND

Understanding the impact of altered hepatic uptake and/or efflux on the hepatobiliary disposition of the imaging agents [99mTc]Mebrofenin (MEB) and [153Gd]Gadobenate dimeglumine (BOPTA) is important for proper estimation of liver function.

METHODS

A multi-compartmental pharmacokinetic (PK) model describing MEB and BOPTA disposition in isolated perfused rat livers (IPRLs) was developed. The PK model was simultaneously fit to MEB and BOPTA concentration-time data in the extracellular space, hepatocytes, bile canaliculi, and sinusoidal efflux in livers from healthy rats, and to BOPTA concentration-time data in rats pretreated with monocrotaline (MCT).

RESULTS

The model adequately described MEB and BOPTA disposition in each compartment. The hepatocyte uptake clearance was much higher for MEB (55.3 mL/min) than BOPTA (6.67 mL/min), whereas the sinusoidal efflux clearance for MEB (0.000831 mL/min) was lower than BOPTA (0.0127 mL/min). The clearance from hepatocytes to bile (CLbc) for MEB (0.658 mL/min) was similar to BOPTA (0.642 mL/min) in healthy rat livers. The BOPTA CLbc was reduced in livers from MCT-pretreated rats (0.496 mL/min), while the sinusoidal efflux clearance was increased (0.0644 mL/min).

CONCLUSION

A PK model developed to characterize MEB and BOPTA disposition in IPRLs was used to quantify changes in the hepatobiliary disposition of BOPTA caused by MCT pretreatment of rats to induce liver toxicity. This PK model could be applied to simulate changes in the hepatobiliary disposition of these imaging agents in rats in response to altered hepatocyte uptake or efflux associated with disease, toxicity, or drug-drug interactions.

Exploration of hypoglycemic effect of an extract from leaves of a plant from Tunisian pharmacopeia: Artemisia campestris (Asteraceae)

Background and objectives

A lot of research has been directed towards medicinal plants which are considered as a source of multiple phytotherapic substances endowed with hypoglycemic activities that could be used to treat diabetes and its complications. Our study was carried out in Wistar rats to investigate the hypoglycemic effect of n-Butanol Fraction from Artemisia campestris leaf Methanolic Extract (BFACME).

Methods

Two experimental models were used in rats: orally induced hyperglycemia (OGTT) and isolated perfused liver (IPRL).

Results

BFACME at 550 mg/kg BW dose significantly reduced fasting glucose level in normal rats as compared to controls. The decrease of glycaemia was 12.6% more significant than that obtained with the standard drug glibenclamide (10 mg/kg BW), an oral antidiabetic preparation belonging to sulfonylurea class. In OGTT model, BFACME at the highest doses of 550 and 400 mg/kg BW significantly reduced the postprandial hyperglycemic peak compared to controls. In the IPRL model, treatment with BFACME significantly decreased glucose concentrations after 30 min of perfusion with 30 mM glucose solely when insulin was present. The higher doses of BFACME lead to glucose concentration at basal level as early as 90 min, while the lowest dose does not restore this concentration even to t = 120min. The best initial glucose concentration retrieval was obtained with 0.7 mg BFACME/mL/g liver. At this dose, BFACME improves the decrease of glucose level caused by only insulin by about 18%.

Conclusion

The BFACME appears to exert a hypoglycemic activity by potentiating the insulin action.

Free radical scavengers improve liver function but not morphological changes induced by reperfusion injury

OBJECTIVE

Reperfusion injury (RI) is associated with high generation of reactive oxygen species (ROS), but the extent of involvement of these agents in the injury remains controversial. The present study aimed to examine the effectiveness of ROS scavengers against hepatic reperfusion injury in the rat.

METHODS

The RI was induced in the liver using an isolated slow-flow, reflow perfused rat liver in both anterograde and retrograde perfusion. The effects of gentisic acid, N-acetyl cysteine, and trolox C on the superoxide production, liver function, and morphological changes were examined using different biochemical and histological assays.

RESULTS

The hepatic RI caused a significant (p < 0.05) increase in superoxide production and enzyme releases and a decrease in bile flow in both directions. Histological changes induced by RI include apoptosis, necrosis, pale cytoplasm, cell vacuolation, and attenuation of cell cords. Although the production of superoxide in retrograde direction was significantly less than the anterograde, the extent of the injury in the retrograde was greater than the anterograde direction. Pretreatment of the livers with each of the test compounds significantly reduced the release of lactate dehydrogenase and aspartate aminotransferase and improved bile flow in the liver exposed to hypoxia/reperfusion. However, they failed to protect the liver against the structural alterations induced by RI.

CONCLUSION

ROS scavengers can reduce superoxide-induced damage and improve the liver function, but they are not able to prevent the structural changes. It shows that ROS are not the sole causative mechanism of hepatic RI and other mechanisms and mediators may be involved.

Reversal of the vasoconstrictor step of hyperacute xenogeneic rejection of the liver by endothelin antagonists

The role of endothelin in the initial vasoconstrictor step of hyperacute xenogeneic rejection was investigated. Isolated rat livers were perfused in recirculation. Perfusion with human sera provided an ex vivo model of hyperacute rejection in a discordant combination. Perfusion of 10% xenogeneic serum induced a marked (70%) and sustained reduction of the liver flow and induced the release of endothelin into the perfusion medium. In contrast, perfusion of 10% allogeneic serum or of 10% decomplemented human serum induced a weak (25%) and transient reduction of the liver flow and induced the release of minimal amounts of endothelin. The simultaneous administration of BQ 123 and BQ 788, the respective antagonists of ET(A) and ET(B) endothelin receptors, or that of bosentan, a mixed ET(A)/ET(B) antagonist, antagonized the vasoconstrictor effect of 10% xenogeneic human serum, as well as that of 10(-9) M endothelin-1. The vasoconstrictor effects of xenogeneic serum on liver circulation are, at least partly, mediated through the release of endothelin by the graft.

Assessment of the effect of malaria infection on hepatic clearance of dihydroartemisinin using rat liver perfusions and microsomes

1. The clearance of dihydroartemisinin (DHA) in control and malaria-infected (MI) rats was investigated using the isolated perfused rat liver (IPRL) model and hepatic microsomal studies. 2. In the recirculating IPRL, clearance of DHA was reduced from a mean (s.d.) of 8.2+/-1.8 ml min(-1) in controls (n=8) to 6.0+/-1.0 ml min(-1) in MI (n=8; P<0.01). Clearance in control livers was similar to the perfusion flow rate, suggesting a high hepatic extraction ratio for DHA. 3. Single-pass IPRL studies in controls (n=8) showed that DHA bioavailability at 1.3, 8 and 38 microm was 0.026+/-0.020, 0.043+/-0.025 and 0.14+/-0.06, respectively (P<0.001 for 8 microM vs 38 microM). In MI livers (n=5), DHA bioavailability at 8 and 38 microM was 0.18+/-0.07 and 0.40+/-0.08, respectively (P=0.002). Bioavailability was higher in the MI group than in controls (P=0.01 at 8 microM and P<0.001 at 38 microM). DHA-glucuronide was the sole biliary metabolite. 4. Hepatic microsomal studies of DHA-glucuronide formation showed a significantly lower Vmax but no significant change in Km, in MI compared to control livers (n=6). Intrinsic metabolic clearance (Vmax/Km) was higher in control than in MI livers (5.2+/-1.3 and 2.5+/-1.4 microl min(-1) mg(-1), respectively; P=0.006). 5. These studies demonstrate that DHA has a high, concentration-dependent hepatic extraction ratio that is reduced by 20-30% in the P. berghei rodent malaria model. The impaired hepatic clearance of DHA in MI is attributable to a reduction in intrinsic metabolic clearance.

Evidence that S-adenosyl-L-methionine diastereoisomers may reduce ischaemia-reperfusion injury by interacting with purinoceptors in isolated rat liver

1. Mechanisms underlying the haemodynamic activity of diastereoisomers of S-adenosyl-L-methionine (SAM) were investigated using inhibitors of purinoceptors and nitric oxide (NO) synthase in perfused rat livers damaged by sequential 24 h cold and 20 min rewarming ischaemia + reperfusion. 2. Stored livers were flushed with 10 ml saline alone (control) or with added (R,S) or (S,S) SAM (100 microM) and reperfused in the absence (control) or presence of 10 microM 8-phenyltheophylline (8-PT) or 100 microM L-N-monomethylarginine (L-NMMA). 3. Both SAM diastereoisomers rapidly increased blood flow and bile production versus controls (P<0.001) but the (R,S) isomer induced greater increases in blood flow and the (S,S) isomer greater increases in bile production: 625 versus 596 versus 518 ml blood flow and 100 versus 119 versus 56 mg bile production per g liver over 3 h in (R,S), (S,S) and control, respectively. 4. 8-PT prevented the enhancement of blood flow by (S,S) SAM (529 versus 596 ml g(-1) liver over 3 h for (S,S) SAM alone, P<0.001), but was without effect in control livers. 8-PT also reduced SAM-enhanced bile production: 51 versus 119 mg g(-1) liver over 3 h, P<0.001. L-NMMA reduced blood flow and bile production similarly in the absence or presence of (S,S) SAM. 5. Thus, SAM may improve liver perfusion after ischaemia-reperfusion injury via stimulation of P, (A2) purinoceptors at which SAM shows activity. The choleretic activity of (S,S) SAM is disproportionately greater than enhanced blood flow and may occur independently of a NO-dependent component of bile production.