Impaired hepatocanalicular organic anion transport in endotoxemic rats

Using simulations to explore the potential effect of disease and inflammation on the frequency of violative flunixin residues in cattle

The US Food and Drug Administration (FDA) assigns a tolerance and withdrawal period when evaluating new drugs for use in food-producing species. Because withdrawal periods are determined from data generated in normal, healthy animals, questions have been raised regarding whether disease and inflammation can be a factor associated with some residue violations. We explored this question using flunixin liver concentrations as a model situation. Using data contained in the flunixin FOI Summary (NADA 101-479) and Monte Carlo simulation, we generated sets of residue depletion data. Our mathematical model was simple linear regression containing the terms alpha (the marker residue back-extrapolated to time zero, which equals ln C 0 ) and beta (the elimination rate constant which equals - k e ). By modifying alpha and beta means and variances, we determined the smallest change in these parameters that would result in the presence of violative residues above the statistically determined expected frequency of 1%. The results of this in silico study indicated that the magnitude of change in alpha and beta needed to generate violative residues exceeds that likely to occur due to disease or inflammation when flunixin is used in accordance with the approved product label.

Xenobiotic metabolism capacities of human skin in comparison with a 3D-epidermis model and keratinocyte-based cell culture as in vitro alternatives for chemical testing: phase II enzymes

The 7th Amendment to the EU Cosmetics Directive prohibits the use of animals in cosmetic testing for certain endpoints, such as genotoxicity. Therefore, skin in vitro models have to replace chemical testing in vivo. However, the metabolic competence neither of human skin nor of alternative in vitro models has so far been fully characterized, although skin is the first-pass organ for accidentally or purposely (cosmetics and pharmaceuticals) applied chemicals. Thus, there is an urgent need to understand the xenobiotic-metabolizing capacities of human skin and to compare these activities to models developed to replace animal testing. We have measured the activity of the phase II enzymes glutathione S-transferase, UDP-glucuronosyltransferase and N-acetyltransferase in ex vivo human skin, the 3D epidermal model EpiDerm 200 (EPI-200), immortalized keratinocyte-based cell lines (HaCaT and NCTC 2544) and primary normal human epidermal keratinocytes. We show that all three phase II enzymes are present and highly active in skin as compared to phase I. Human skin, therefore, represents a more detoxifying than activating organ. This work systematically compares the activities of three important phase II enzymes in four different in vitro models directly to human skin. We conclude from our studies that 3D epidermal models, like the EPI-200 employed here, are superior over monolayer cultures in mimicking human skin xenobiotic metabolism and thus better suited for dermatotoxicity testing.

Hepatic expression of multidrug resistance protein 2 in biliary atresia

Background

Biliary atresia (BA) is an idiopathic inflammatory obliterative cholangiopathy of neonates, leading to progressive biliary cirrhosis. Hepatoportoenterostomy (Kasai procedure) can cure jaundice in 30% to 80% of patients. Postoperative clearance of jaundice is one of the most important factors influencing long-term outcomes of BA patients. Multidrug resistance protein 2 (MRP2) is one of the canalicular export pumps located in hepatocytes; it exports organic anions and their conjugates (e.g., bilirubin) into bile canaliculus. Although MRP2 is an essential transporter for the excretion of bilirubin, its role in the clinical course of BA patients is unclear. The present study investigated the relationship between hepatic MRP2 expression and clinical course in BA patients, with particular emphasis in curing jaundice after hepatoportoenterostomy.

Results

No significant differences in hepatic MRP2 expression level were observed between BA and controls groups. There was no correlation between MRP2 expression and age at time of surgery in BA and control groups. In BA patients, MRP2 expression level in the jaundice and jaundice-free group did not differ significantly (2.0 × 10^-4 vs 3.1 × 10^-4, p = 0.094). Although the serum level of total bilirubin just before surgery did not correlate with MRP2 expression level (rs = 0.031, p = 0.914), the serum level of total bilirubin measured at 2 weeks (rs = -0.569, p = 0.034) and 4 weeks after surgery (rs = -0.620, p = 0.018) were significantly correlated with MRP2 expression level. Furthermore, MRP2 expression level was inversely correlated with ratio of change in serum total bilirubin level over 4 weeks (rs = -0.676, p = 0.008), which represents the serum bilirubin level measured at 4 weeks after surgery divided by value just before surgery. There was no correlation between expression level of MRP2 and nuclear receptors, such as retinoid × receptor α, farnesoid × receptor, pregnane × receptor, or constitutive androstane receptor.

Conclusions

Hepatic MRP2 expression level was associated with postoperative clearance of jaundice in BA patients, at least within 1 month after hepatoportoenterostomy. This finding suggests that not only morphological appearance of the liver tissue but also the biological status of hepatocytes is important for BA pathophysiology.

Clinical courses after administration of oral corticosteroids in patients with severely cholestatic acute hepatitis A; three cases

Acute hepatitis A is currently outbreaking in Korea. Although prognosis of acute hepatitis A is generally favorable, a minority of patients are accompanied by fatal complications. Severe cholestasis is one of the important causes of prolonged hospitalization in patients with acute hepatitis A. In such cases, higher chances of additional complications and increased medical costs are inevitable. We report three cases of severely cholestatic hepatitis A, who showed favorable responses to oral corticosteroids. Thirty milligram of prednisolone was initiated and tapered according to the responses. Rapid improvement was observed in all cases without side effects. We suggest that corticosteroid administration can be useful in hepatitis A patients with severe cholestasis who do not show improvement by conservative managements. Clinical trial will be needed to evaluate effectiveness of corticosteroids in these patients.

Effect of adjuvant-induced systemic inflammation in rats on hepatic disposition kinetics of taurocholate

It has been reported that the adjuvant-induced inflammation could affect drug metabolism in liver. Here we further investigated the effect of inflammation on drug transport in liver using taurocholate as a model drug. The hepatic disposition kinetics of [(3)H]taurocholate in perfused normal and adjuvant-treated rat livers were investigated by the multiple indicator dilution technique and data were analyzed by a previously reported hepatobiliary taurocholate transport model. Real-time RT-PCR was also performed to determine the mRNA expression of liver bile salt transporters in normal and diseased livers. The uptake and biliary excretion of taurocholate were impaired in the adjuvant-treated rats as shown by decreased influx rate constant k(in) (0.65 ± 0.09 vs. 2.12 ± 0.30) and elimination rate constant k(be) (0.09 ± 0.02 vs. 0.17 ± 0.04) compared with control rat group, whereas the efflux rate constant k(out) was greatly increased (0.07 ± 0.02 vs. 0.02 ± 0.01). The changes of mRNA expression of liver bile salt transporters were found in adjuvant-treated rats. Hepatic taurocholate extraction ratio in adjuvant-treated rats (0.86 ± 0.05, n = 6) was significantly reduced compared with 0.93 ± 0.05 (n = 6) in normal rats. Hepatic extraction was well correlated with altered hepatic ATP content (r(2) = 0.90). In conclusion, systemic inflammation greatly affects hepatic ATP content/production and associated transporter activities and causes an impairment of transporter-mediated solute trafficking and pharmacokinetics.

Nuclear receptors: mediators and modifiers of inflammation-induced cholestasis

Inflammation-induced cholestasis (IIC) is a frequently occurring phenomenon. A central role in its pathogenesis is played by nuclear receptors (NRs). These ligand-activated transcription factors not only regulate basal expression of hepatobiliary transport systems, but also mediate adaptive responses to inflammation and possess anti-inflammatory characteristics. The latter two functions may be exploited in the search for new treatments for IIC as well as for cholestasis in general. Current knowledge of the pathogenesis of IIC and the dual role NRs in this process are reviewed. Special interest is given to the use of NRs as potential targets for intervention.

Cytokine-dependent regulation of hepatic organic anion transporter gene transactivators in mouse liver

Proinflammatory cytokines such as TNF-alpha and IL-1beta lead to downregulation of hepatic organic anion transporters in cholestasis. This adapted response is transcriptionally mediated by nuclear hormone receptors and liver-specific transcription factors. Because little is known in vivo about cytokine-dependent regulatory events, mice were treated with either TNF-alpha or IL-1beta for up to 16 h. Transporter mRNA expression was determined by Northern blot analysis, nuclear activity, and protein-expression of transactivators by EMSA and Western blotting. TNF-alpha induces a sustained decrease in Ntcp, Oatp1/Oatp1a1, and Bsep mRNA expression but exerts only transient [multidrug resistance-associated protein 2 (Mrp2)] or no effects (Mrp3) on Mrps. In addition to Ntcp and Oatp1/Oatp1a1, IL-1beta also downregulates Bsep, Mrp2, and Mrp3 mRNAs to some extent. To study transcriptional regulation, Ntcp and Bsep promoters were first cloned from mice revealing a new distal Ntcp hepatocyte nuclear factor 1 (HNF-1) element but otherwise show a conserved localization to known rat regulatory elements. Changes in transporter-expression are preceeded by a reduction in binding activities at IR-1, ER-8, DR-5, and HNF-1alpha sites after 4 h by either cytokine, which remained more sustained by TNF-alpha in the case of nuclear receptors. Nuclear protein levels of retinoid X receptor (RXR)-alpha are significantly decreased by TNF-alpha but only transiently affected by IL-1beta. Minor reductions of retinoic acid receptor, farnesoid X receptor, pregnane X receptor, and constitutive androstane receptor nuclear proteins are restricted to 4 h after cytokine application and paralleled by a decrease in mRNA levels. Basolateral and canalicular transporter systems are downregulated by both cytokines, TNF-alpha and IL-1beta. Activity of HNF-1alpha as regulator of mNtcp is suppressed by both cytokines. Decreased binding activities of nuclear receptor heterodimers may be explained by a reduction of the ubiquitous heterodimerization partner RXR-alpha.

Jaundice as an early diagnostic sign of urinary tract infection in infancy

OBJECTIVE

Urinary tract infections (UTIs) are a common clinical problem in febrile infants younger than 8 weeks old, with a prevalence between 5% and 11%. Previous studies have noted that jaundice may be one of the first signs of a bacterial infection in infants. Our goal was to determine the incidence of UTIs in asymptomatic, jaundiced infants younger than 8 weeks old and to determine which historical and laboratory parameters are associated with UTIs.

METHODS

We prospectively evaluated asymptomatic, jaundiced infants younger than 8 weeks old for evidence of a UTI (defined as >10 000 colony-forming units per milliliter of a single pathogen, obtained by bladder catheterization). A serum fractionated bilirubin level was obtained on all study patients. Detailed questionnaires were completed, which included demographic information, prenatal, intrapartum, and postnatal events.

RESULTS

Twelve (7.5%) of 160 infants had a UTI (95% confidence interval: 3.9%-12.7%). Isolated organisms included Escherichia coli, Enterobacter cloacae, Enterococcus, Klebsiella pneumoniae, group B Streptococcus, Streptococcus viridans, and Staphylococcus aureus. Patients with the onset of jaundice after 8 days of age had a higher incidence of UTI, 6 (50%) of 12 infants in the positive culture group, versus 15 (10%) of 148 infants in the negative culture group. Abnormal urinalysis and microscopy results were noted in 5 (42%) of 12 infants with a UTI, and 6 (55%) of 11 infants had abnormal renal ultrasound results.

CONCLUSION

A UTI was found in 7.5% of asymptomatic, afebrile, jaundiced infants younger than 8 weeks old. In addition, infants with the onset of jaundice after 8 days of age or patients with an elevated conjugated bilirubin fraction were more likely to have a UTI. Therefore, we recommend that testing for a UTI be included as part of the evaluation in asymptomatic, jaundiced infants presenting to the emergency department.

Effect of endotoxin on P-glycoprotein-mediated biliary and renal excretion of rhodamine-123 in rats

The effects of Klebsiella pneumoniae endotoxin on the biliary excretion and renal handling of rhodamine-123 were investigated in rats at different times after intraperitoneal injection (1 mg/kg of body weight). The typical substrates for P glycoprotein, i.e., cyclosporine, colchicine, and erythromycin, inhibited the biliary clearance of rhodamine-123, whereas a substrate for organic cation transporter, cimetidine, did not inhibit clearance, suggesting that rhodamine-123 is transported mainly by P glycoprotein. The biliary, renal, and tubular secretory clearances of rhodamine-123 and the glomerular filtration rate significantly decreased 6 h after injection of endotoxin but returned to control levels by 24 h. These results suggest that endotoxin-induced decreases in P-glycoprotein-mediated biliary excretion and renal handling of rhodamine-123 were probably due to impairment of P-glycoprotein-mediated transport ability. Pretreatment with pentoxifylline (50 mg/kg) significantly inhibited endotoxin-induced increases in tumor necrosis factor alpha (TNF-alpha) levels in plasma, which ameliorated the endotoxin-induced reduction of the biliary excretion of rhodamine-123. It is likely that endotoxin-induced impairment of the transport of rhodamine-123 is caused, in part, by overproduction of TNF-alpha. The effect of endotoxin on the expression of P-glycoprotein mRNA in liver and kidneys of rats was investigated by using a reverse transcriptase PCR. The expression of Mdr1a mRNA in both liver and kidney decreased 6 h after endotoxin injection and returned to control levels after 24 h, whereas the expression of Mdr1b mRNA in liver increased at both times and that in kidney decreased at 24 h. These findings suggest that K. pneumoniae endotoxin dramatically decreases P-glycoprotein-mediated biliary and renal excretion of rhodamine-123 probably by decreasing the expression of Mdr1a, which is likely due to increased plasma TNF-alpha levels.

Endotoxin-induced reduction in biliary indocyanine green excretion rate in a chronically catheterized rat model

Using a nonstressed chronically catheterized rat model in which the common bile duct was cannulated, we studied endotoxin-induced alterations in hepatic function by measuring changes in the maximal steady-state biliary excretion rate of the anionic dye indocyanine green (ICG). Biliary excretion of ICG was calculated from direct measurements of biliary ICG concentrations and the bile flow rate during a continuous vascular infusion of ICG. Despite significant elevations in mean peak serum tumor necrosis factor-alpha (TNF-alpha) concentrations (90.9 +/- 16.2 ng/ml), there was no effect on mean rates of bile flow or biliary ICG clearance after administration of 100 microg/kg endotoxin at 6 or 24 h. Significant differences from mean baseline rates of bile flow and biliary ICG excretion did occur after administration of 1,000 microg/kg endotoxin (mean peak TNF-alpha 129.6 +/- 24.4 ng/ml). Furthermore, when rats were treated with up to 16 microg/kg of recombinant TNF-alpha, there was no change in mean rates of bile flow or ICG biliary clearance compared with baseline values. These data suggest that the complex regulation of biliary excretion is not mediated solely by TNF-alpha.

Endotoxin downregulates rat hepatic ntcp gene expression via decreased activity of critical transcription factors

Sodium-dependent uptake of bile acids across the hepatic basolateral membrane is rapidly and profoundly diminished during sepsis, thus contributing to the pathogenesis of sepsis-associated cholestasis. This effect is mediated by endotoxin or effector cytokines, which reduce expression of several hepatobiliary transporters, including the sodium-dependent bile acid transporter gene, ntcp. We test here the hypothesis that endotoxin treatment leads to impaired binding activity of ntcp promoter trans-acting factors, resulting in reduction of ntcp mRNA expression. After endotoxin administration, ntcp mRNA levels reached their nadir by 16 h, and nuclear run-on assays demonstrated a marked reduction in ntcp gene transcription. At 16 h after treatment, nuclear binding activities of two key factors that transactivate the ntcp promoter, hepatocyte nuclear factor (HNF) 1 and Footprint B binding protein (FpB BP), decreased to 44 and 47% of pretreatment levels, respectively, while levels of the other known ntcp promoter transactivator, signal transducer and activator of transcription 5, were unaffected. In contrast, the universal inflammatory response factors nuclear factor kappaB and activating protein 1 were both upregulated significantly. Examination of nuclear extracts obtained at sequential time points revealed that the maximal decrease in nuclear activities of both HNF1 and FpB BP preceded the nadir of ntcp mRNA expression by 6-10 h. Furthermore, these two nuclear factors returned towards normal levels before the recovery of ntcp mRNA levels observed by 48 h. Since HNF1alpha mRNA levels were unchanged at all time points, HNF1 is likely to be regulated posttranscriptionally by endotoxin. We conclude that the downregulation of ntcp gene expression by endotoxin is mediated at the level of transcription through tandem reductions in the nuclear binding activity of two critical transcription factors. These findings provide new insight into the coordinated downregulation of hepatobiliary transporters during sepsis.

Distribution of heme oxygenase isoforms in rat liver. Topographic basis for carbon monoxide-mediated microvascular relaxation

Carbon monoxide (CO) derived from heme oxygenase has recently been shown to play a role in controlling hepatobiliary function, but intrahepatic distribution of the enzyme is unknown. We examined distribution of two kinds of the heme oxygenase isoforms (HO-1 and HO-2) in rat liver immunohistochemically using monoclonal antibodies. The results showed that distribution of the two isoforms had distinct topographic patterns: HO-1, an inducible isoform, was observed only in Kupffer cells, while HO-2, a constitutive form, distributed to parenchymal cells, but not to Kupffer cells. Both isoforms were undetectable in hepatic stellate cells and sinusoidal endothelial cells. Of the two isoforms, HO-2 in the parenchymal cell rather than HO-1 in the Kupffer cell, appears to play a major role in regulation of microvascular tone. In the perfused liver, administration of HbO2, a CO-trapping reagent that can diffuse across the fenestrated endothelium into the space of Disse, elicited a marked sinusoidal constriction, while administration of a liposome-encapsulated Hb that cannot enter the space had no effect on the microvascular tone. These results suggest that CO evolved by HO-2 in the parenchymal cells, and, released to the extrasinusoidal space, served as the physiological relaxant for hepatic sinusoids.

Hepatobiliary excretion of cysteinyl leukotrienes in three experimental models of acute hepatic injury

The acute phase response to chemically-induced organ damage involves inflammation and the production of leukotrienes. The liver ordinarily takes up, metabolizes and excretes into bile cysteinyl leukotrienes, but the effect of hepatic injury on these processes is unknown. The hepatic uptake and biliary excretion of LTC4 was studied in male Sprague-Dawley rats after exposure to either streptozotocin (45 mg/kg iv 30 days before experimentation), estradiol-17 beta-valerate (1 mg/kg sc once a week for 3 weeks) or lipopolysaccharide/D-galactosamine (33 micrograms/ kg ip; 300 mg/kg ip at 6 h and 3 h, respectively, before experimentation). Acute liver injury is produced by these treatment paradigms. Glucose concentrations and activities of several marker enzymes in plasma were measured to demonstrate hepatic injury. Biliary excretion of 3H-LTC4 was similar to normal control rats in the three types of acute liver injury. Bile flow rates after 3H-LTC4 injection were reduced in lipopolysaccharide-pretreated rats and increased in estradiol-treated animals. Total biliary excretion of leukotrienes was not altered in any disease group. Thus, these models of acute hepatic injury do not appear to influence the hepatobiliary clearance of leukotrienes.