Genetic variants in genes involved in mechanisms of chemoresistance to anticancer drugs

Refractoriness to the pharmacological treatment of cancer is dependent on the expression levels of genes involved in mechanisms of chemoresistance and on the existence of genetic variants that may affect their function. Thus, changes in genes encoding solute carriers may account for considerable inter-individual variability in drug uptake and the lack of sensitivity to the substrates of these transporters. Moreover, changes in proteins involved in drug export can affect their subcellular localization and transport ability and hence may also modify the bioavailability of antitumor agents. Regarding pro-drug activation or drug inactivation, genetic variants are responsible for changes in the activity of drug-metabolizing enzymes, which affect drug clearance and may determine the lack of response to anticancer chemotherapy. The presence of genetic variants may also decrease the sensitivity to pharmacological agents acting through molecular targets or signaling pathways. Recent investigations suggest that changes in genes involved in DNA repair may affect the response to platinum-based drugs. Since most anticancer agents activate cell death pathways, the evasion of apoptosis plays an important role in chemoresistance. Several genetic variants affecting death-receptor pathways, the mitochondrial pathway, downstream caspases and their natural modulators, and the p53 pathway, whose elements are mutated in more than half of tumors, and survival pathways, have been reported. The present review summarizes the available data regarding the role of genetic variants in the different mechanisms of chemoresistance and discusses their potential impact in clinical practice and in the development of tools to predict and overcome chemoresistance.

Genetic variants in genes involved in mechanisms of chemoresistance to anticancer drugs

Refractoriness to the pharmacological treatment of cancer is dependent on the expression levels of genes involved in mechanisms of chemoresistance and on the existence of genetic variants that may affect their function. Thus, changes in genes encoding solute carriers may account for considerable inter-individual variability in drug uptake and the lack of sensitivity to the substrates of these transporters. Moreover, changes in proteins involved in drug export can affect their subcellular localization and transport ability and hence may also modify the bioavailability of antitumor agents. Regarding pro-drug activation or drug inactivation, genetic variants are responsible for changes in the activity of drug-metabolizing enzymes, which affect drug clearance and may determine the lack of response to anticancer chemotherapy. The presence of genetic variants may also decrease the sensitivity to pharmacological agents acting through molecular targets or signaling pathways. Recent investigations suggest that changes in genes involved in DNA repair may affect the response to platinum-based drugs. Since most anticancer agents activate cell death pathways, the evasion of apoptosis plays an important role in chemoresistance. Several genetic variants affecting death-receptor pathways, the mitochondrial pathway, downstream caspases and their natural modulators, and the p53 pathway, whose elements are mutated in more than half of tumors, and survival pathways, have been reported. The present review summarizes the available data regarding the role of genetic variants in the different mechanisms of chemoresistance and discusses their potential impact in clinical practice and in the development of tools to predict and overcome chemoresistance.

Foetal 'flat' bile acids reappear during human liver regeneration after surgery

BACKGROUND

Changes in bile acid (BA) pool, such as the reappearance of typically foetal-type molecular species with a 'flat' structure at the steroid ring, occur during hepatocarcinogenesis, both in humans and rodents. Moreover flat-BAs also appear during rat liver regeneration. These changes can be detected in urine. The aim of the present study was to investigate whether flat-BAs also reappear during human liver regeneration, and whether this change correlates with the magnitude of liver resection.

MATERIALS AND METHODS

Patients undergoing partial hepatectomy were divided in two groups: major hepatectomy group (> 50% of hepatic tissue resection, n = 17) and minor hepatectomy group (< 50%, n = 13). BAs were extracted from serum and urine (collected over 24 h) and analysed by gas chromatography-mass spectrometry. Samples were obtained before surgery (day 0) and on the third and seventh days after hepatectomy.

RESULTS

In serum, total BAs significantly increased on day seven after hepatectomy, but only a moderate increase in flat-BA concentrations was observed. By contrast, urinary excretion of total as well as flat-BAs significantly increased at day three and day seven after hepatectomy. Moreover, the amount of flat-BAs excreted in urine during the first week after partial hepatectomy correlated with the magnitude of the resection.

CONCLUSIONS

Urinary BA output increases and flat-BAs reappear in urine during human liver regeneration. These results suggest that determination of BAs in urine may be an interesting parameter obtained by non-invasive techniques whose actual clinical value during human liver regeneration warrants further evaluation.

Effect of maternal cholestasis and treatment with ursodeoxycholic acid on the expression of genes involved in the secretion of biliary lipids by the neonatal rat liver

In juvenile rats born from mothers with obstructive cholestasis during pregnancy (OCP), transient latent cholestasis together with alterations in the secretion of biliary lipids have been reported. Here we investigated whether the expression of genes involved in this function is already modified at birth and examined the effect of treating pregnant rats with ursodeoxycholic acid (UDCA; i.g., 60 microg/100 g b.w./day). Cholanemia was markedly higher in mothers with OCP, and was further increased by UDCA. In the Control pups, cholanemia increased after birth, whereas in OCP and OCP+UDCA pups, hypercholanemia decreased after birth. Steady-state mRNA levels in neonatal liver were measured by real-time quantitative RT-PCR. The expression of basolateral bile acid transporters was not affected by OCP and was unchanged (Oatp1/1a1 and Oatp4/1b2) or moderately increased (Ntcp and Oatp2/1a4) by UDCA. In both groups, the expression of ABC proteins was either not modified (Bsep, Bcrp and Mrp2) or enhanced (Mrp1 and Mrp3), that of phospholipid flippase Mdr2 was not changed, whereas that of cholesterol transporter Abcg5/Abcg8 was impaired. The expression of the nuclear receptor FXR was not affected by OCP or UDCA, whereas that of SHP and key enzymes in bile acid synthesis (Cyp7a1, Cyp8b1 and Cyp27) was increased in both groups. In conclusion, OCP affects the expression in the neonatal liver of genes involved in hepatobiliary function, which cannot be prevented, at this stage, by treating pregnant rats with UDCA, even though this treatment has been found to partially restore normal lipid secretion later during post-natal development.

Expression in human trophoblast and choriocarcinoma cell lines, BeWo, Jeg-3 and JAr of genes involved in the hepatobiliary-like excretory function of the placenta

Using cytokeratin-7-positive trophoblast cells (hTr) isolated from human term placentas and the choriocarcinoma cell lines (hCC) BeWo, Jeg-3 and JAr, the expression of genes involved in the hepatobiliary excretion of cholephilic compounds was investigated by RT-PCR/sequencing followed by measurement of the absolute abundance of mRNA by real-time RT-PCR. Although mRNA of BSEP was detectable and its expression confirmed by Western blotting, its very low expression (higher in hTr than in whole placenta and hCC) did not permit its detection by immunohistochemistry. In hTr, the expression was high for OATP-B/2B1, OATP-8/1B3, MRP1, MRP3, BCRP, FIC1, RARalpha, FXR and SHP, low for OSTalpha, MRP2, MRP4, MRP8, MDR1, CAR and SXR, very low for OATP-A/1A2 and MDR3, and not detectable for OATP-C/1B1, HNF1alpha and HNF4. Expression patterns in hCC mimicked those in hTr, although some important cell line-specific differences were found. The functionality of transporters expressed in hCC was confirmed by their ability to take up and export estradiol 17beta-d-glucuronide in a self-inhibitable and temperature-sensitive manner. In conclusion, several transporters, export pumps, and nuclear receptors involved in the liver excretory function may play a similar role in the placenta, whose specific aspects can be studied by selectively using BeWo, Jeg-3 or JAr cells.

Chronic renal failure-induced changes in serum and urine bile acid profiles

Although the kidney is believed to play a minor role in bile acid (BA) excretion, chronic renal failure (CRF) has been reported to be accompanied by alterations in the BA balance. The aim of the present work was to evaluate the changes in BA serum concentrations and renal excretion in patients with different stage of CRF or after kidney transplantation and to elucidate whether these might play a role in the development of pruritus, a common symptom in this disease. This study was carried out on 125 patients. None of them had a history or signs of hepatobiliary malfunction. They belonged either to a control group (N = 31) or to one of the three following CRF groups: patients maintained only on a low-protein diet (diet group, N = 23); the same, together with periodic sessions of hemodialysis (dialysis group, N = 42); and patients who had undergone a kidney transplant more than 1 and less than 2 years before (transplanted group, N = 29). Serum and urine BA concentrations were assayed by gas chromatography-mass spectrometry. Pruritus was quantified by means of a questionnaire answered at the time of sample collection. A marked hypercholanemia together with a reduction in BA output into urine and profound alterations in the profiles of these compounds in both serum and urine in patients with CRF were observed. The levels of total BAs in serum, but not the proportions of molecular species, were corrected by hemodialysis. By contrast, kidney transplant reversed BA serum patterns to normality but, due to immunosuppressive therapy with cyclosporin A, total serum BA concentrations were consistently elevated in this group. Pruritus was more frequent in patients with impaired kidney function and hypercholanemia, although no significant correlation between the degree of this symptom and the magnitude of the serum concentrations of total or individual BAs were found. By contrast, in spite of hypercholanemia, once renal function had been restored by kidney transplantation, none of the patients suffered from pruritus. These results suggest that the kidney plays an important role in determining the serum BA pool size and composition and that hypercholanemia may be a contributing factor, but not the only one, determining the development of pruritus in patients with CRF.

Changes in the pattern of bile acids in the nuclei of rat liver cells during hepatocarcinogenesis

Bile acids reach the nuclei of hepatocytes, where they may play an important role in controlling gene expression by binding to nuclear receptors. In previous studies, changes in the amounts of the different molecular species of bile acids in the hepatocyte nucleus during rat liver regeneration have been reported. The aim of the present work was to investigate whether this also occurs during rat hepatocarcinogenesis. Liver cell nuclei were isolated after homogenization of livers from healthy adult rats (controls) and from rats at different time points during chemically induced hepatocarcinogenesis, corresponding to the stages of foci (12 weeks), hepatoma (20 weeks) and carcinoma (32 weeks). Bile samples from the cannulated common bile duct were collected for 1h from different sets of animals undergoing hepatocarcinogenesis. Bile acids in bile, liver homogenates and isolated nuclei were measured by GC-MS. Because the yield of nuclei isolated changed during the course of hepatocarcinogenesis (control, 20.1%; 12 weeks, 23.6%; 20 weeks, 7.8%; 32 weeks, 5.1%), amounts of bile acids in nuclei were corrected for the amount of DNA in each preparation. During hepatocarcinogenesis, bile acid concentrations in liver homogenates were reduced to approximately half the values obtained in control livers, while the levels of bile acids in both isolated nuclei and bile were not decreased. Hepatocarcinogenesis induced changes in the composition of bile acid pools. These were manifest as an increase in the proportion of cholic acid and a decrease in that of ursodeoxycholic acid in both bile and liver. These modifications differed from the changes seen in the nuclear bile acid pool, where a decrease in the proportion of cholic acid together with an increase in that of ursodeoxycholic acid were the major changes observed during hepatocarcinogenesis. With regard to the 'flat' bile acids (allo-cholic acid plus Delta(5)- or Delta(4)-unsaturated bile acids), a marked hepatocarcinogenesis-induced increase in the output of these species in bile was found. However, these bile acids were only found in liver homogenates at the hepatoma stage, whereas they were not detected in isolated nuclei at any stage of hepatocarcinogenesis. In summary, these results support the existence of a bile acid pool in hepatocyte nuclei whose composition differs from that of the extranuclear bile acid pool. Moreover, they indicate that, during hepatocarcinogenesis, the composition of the nuclear pool undergoes important alterations.

Predominance of human versus rat phenotype in the metabolic pathways for bile acid synthesis by hybrid WIF-B9 cells

The rat hepatoma-human fibroblast hybrid cell line WIF-B9 stably exhibits the structural and functional characteristics of normal differentiated hepatocytes. The abilities of these cells to synthesize bile acids and amidate them with glycine and taurine were investigated. The release of bile acids into the culture media over 72 h was assessed by gas chromatography-mass spectrometry. WIF-B9 cells were able to synthesize bile acids (1.10+/-0.17 nmol/mg protein) but less efficiently than rat hepatocytes in primary culture (2.19+/-0.19 nmol/mg protein; P<0.01). The patterns of major bile acid species produced by both types of cells were also different. Cholic acid (CA; 72%) and beta-muricholic acid (19%) were the major bile acids produced by rat hepatocytes, while chenodeoxycholic acid (CDCA) accounted for only 4.5% of total bile acids. In contrast, muricholic acids were absent, while CA (62%) and CDCA (34%) were the most abundant bile acids synthesized by WIF-B9 cells. Using reverse transcription-polymerase chain reaction and gene- and species-specific primers for key enzymes involved in bile acid synthesis, the expression of human, but not rat, orthologues of CYP7A1, CYP27, CYP8B and CYP7B1 was found in WIF-B9 cells. Induction of cell stress by serum deprivation did not change the amount of total bile acids synthesized by these cells, but an inversion of the CA-to-CDCA ratio from 1.8 to 0.3 together with a marked increase in the proportion of intermediate metabolites related to the acidic pathway was found. Using 500 microM radiolabeled CA and 2 mM of taurine or glycine, the ability to amidate CA over 48 h was determined by high performance liquid chromatography. Rat hepatocytes conjugated more than 90% CA with either amino acid, whereas this ability was very poor (< 2%) in WIF-B9 cells. Regarding the expression of enzymes and the products of bile acid synthesis, it may be concluded that the human phenotype predominates over that of the rat in WIF-B9 cells. Moreover, these cells are almost completely unable to further conjugate primary bile acids, which facilitates the manipulation of these steroids in analytical procedures. These characteristics make WIF-B9 cells a suitable in vitro model to carry out studies on bile acid synthesis by 'human-like' metabolic pathways.

Liver organotropism and biotransformation of a novel platinum-ursodeoxycholate derivative, Bamet-UD2, with enhanced antitumour activity

BACKGROUND/AIMS

Several members of a novel family of bile acid derivatives with cytostatic and virostatic activity have been synthesized and characterized. The aim of this work was to investigate the liver organotropism and biotransformation of two novel compounds with enhanced DNA-reactivity: Bamet-D3, in which a glycine-polyamine tandem was used as a spacer to separate the glycocholic acid moiety from the platinum(II) atom, and Bamet-UD2, in which cisplatin was directly bound to the carboxylate group of two ursodeoxycholic acid moieties.

METHODS

Drug uptake and "in vitro" toxicity were investigated using rat hepatocytes in primary culture. Following i.v. administration of 0.5 mumol cisplatin, Bamet-D3 or Bamet-UD2, bile output, urinary and fecal excretion, organ distribution and pharmacokinetic parameters were determined in short-term (3 h) and long-term (14 days) experiments carried out on anaesthetized and conscious rats, respectively. Liver biotransformation was investigated by HPLC analysis of bile samples. Total platinum was measured by flameless atomic absorption spectroscopy. Using Nude mice, antitumour activity was investigated in subcutaneously implanted Hepa 1-6 mouse hepatoma cells.

RESULTS

Uptake by rat hepatocytes was Bamet-UD2 (11.3 nmol/mg protein) > Bamet-D3 (5.6 nmol/mg protein) > cisplatin (2.1 pmol/mg protein). Bamet-UD2 induced "in vitro" cell toxicity, which was not observed for Bamet-D3 or cisplatin. On the contrary, no toxicity "in vivo" for Bamet-UD2 was found which was observed for cisplatin and Bamet-D3. This may be related with the fact that bile output of Bamet-UD2, which occurs with no major biotransformation, was > 10 fold higher than that of cisplatin and 3-fold higher than that of Bamet-D3, which was previously transformed into at least three different metabolites. Fecal excretion was Bamet-UD2 > Bamet-D3 > cisplatin, whereas urinary output was Bamet-D3 > cisplatin > Bamet-UD2. Accordingly, a marked liver- and a reduced kidney-vectoriality for Bamet-UD2, but not for Bamet-D3, was observed. Bamet-UD2 and cisplatin, but not Bamet-D3, were efficient in inhibiting tumour growth whereas, only Bamet-UD2 significantly prolonged survival time.

CONCLUSIONS

There results indicate that Bamet-UD2 is a cisplatin-ursodeoxycholate derivative with strong antitumour activity, marked hepatobiliary organotropism, and reduced toxic side-effects as compared to the parent drug cisplatin.

Low in vivo toxicity of a novel cisplatin-ursodeoxycholic derivative (Bamet-UD2) with enhanced cytostatic activity versus liver tumors

Cisplatin-bile acid derivatives belonging to the Bamet-family maintain both liver organotropism and cytostatic activity. "In vivo" toxicity and usefulness as chemotherapeutic agent versus liver tumors of a novel drug, Bamet-UD2 [cis-diamminechlorocholylglycinate platinum (II)], with enhanced "in vitro" cytostatic activity was investigated. Using orthotopically implanted mouse Hepa 1-6 hepatoma in the liver of Nude mice, the antitumor effect of Bamet-UD2 was compared with that of a previously characterized compound of this family, Bamet-R2 [cis-diamminebis-ursodeoxycholate platinum(II)], and cisplatin. Life span was significantly prolonged in mice treated with both Bamets (Bamet-UD2 > Bamet-R2), compared with animals receiving saline or cisplatin. All these drugs inhibit tumor growth (Bamet-UD2 = cisplatin > Bamet-R2). However, toxicity-related deaths only occurred under cisplatin treatment. Using rats maintained in metabolic cages, organ-specific toxicity and drug accumulation in tissues were investigated. The amount of both Bamets in the liver was severalfold higher than that of cisplatin. By contrast, a significantly higher amount of cisplatin in kidney and nerve was found. In lung, heart, muscle, brain, and bone marrow the amount of drug was small and also significantly lower in animals receiving Bamets. Signs of neurotoxicity (altered nerve conduction velocity), nephrotoxicity (increased serum urea and creatinine concentrations and decreased creatinine clearance), and bone marrow toxicity (decreased platelet and white blood counts) in animals treated with cisplatin but not with the Bamets were found. These results indicate that, owing to strong antitumor activity together with absence of side effects, Bamet-UD2 may be useful in the treatment of liver tumors.

Increased levels of typically fetal bile acid species in patients with hepatocellular carcinoma

The aim of this work was to investigate the reappearance during liver neoplasia of bile acids (BAs) species, which are unusual in healthy adults, but common in fetuses. Serum and urine samples were collected from patients with hepatocellular carcinoma (HCC; n=27), and for comparative purposes, with liver cirrhosis (n=49), liver metastasis (n=19), chronic viral hepatitis (n=11) and healthy volunteer (control group; n=26) groups. BAs were identified and measured by GC--MS. Hypercholanaemia was found in all groups of patients. In HCC, this was characterized by a marked increase in the chenodeoxycholate/cholate ratio in both serum and urine. Although increased levels of BAs, with hydroxylations at unusual positions, and oxo-BAs were found in HCC, these were not significantly different from those observed in other groups. However, BAs with a flat structure, i.e. Delta(4)-unsaturated- and 5 alpha- or allo-BAs, which were almost absent in healthy subjects, were markedly increased in the serum and urine of HCC patients. They were also detected, although in much lower amounts, in liver metastasis and liver cirrhosis, but not in viral hepatitis. Flat-BAs were better detected in urine than in serum. Urinary Delta(4)-unsaturated-BA output was significantly lower in patients with small tumours (<3 cm) compared with those with higher size tumours. No correlation between flat-BA output into urine and serum alpha-fetoprotein or total BAs was found. These results suggest that Delta(4)- and/or allo-BAs are particularly elevated in patients with HCC, which may be a potentially useful complementary, rather than alternative, marker for early detection of liver neoplasia.

Comparison of the effects of bile acids on cell viability and DNA synthesis by rat hepatocytes in primary culture

Bile acid-induced inhibition of DNA synthesis by the regenerating rat liver in the absence of other manifestation of impairment in liver cell viability has been reported. Because in experiments carried out on in vivo models bile acids are rapidly taken up and secreted into bile, it is difficult to establish steady concentrations to which the hepatocytes are exposed. Thus, in this work, a dose-response study was carried out to investigate the in vitro cytotoxic effect of major unconjugated and tauro- (T) or glyco- (G) conjugated bile acids and to compare this as regards their ability to inhibit DNA synthesis. Viability of hepatocytes in primary culture was measured by Neutral red uptake and formazan formation after 6 h exposure of cells to bile acids. The rate of DNA synthesis was determined by radiolabeled thymidine incorporation into DNA. Incubation of hepatocytes with different bile acid species - cholic acid (CA), deoxycholic acid (DCA), chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA), in the range of 10-1000 microM - revealed that toxicity was stronger for the unconjugated forms of CDCA and DCA than for CA and UDCA. Conjugation markedly reduced the effects of bile acids on cell viability. By contrast, the ability to inhibit radiolabeled thymidine incorporation into DNA was only slightly lower for taurodeoxycholic acid (TDCA) and glycodeoxycholic acid (GDCA) than for DCA. When the effect of these bile acids on DNA synthesis and cell viability was compared, a clear dissociation was observed. Radiolabeled thymidine incorporation into DNA was significantly decreased (-50%) at TDCA concentrations at which cell viability was not affected. Lack of a cause-effect relationship between both processes was further supported by the fact that well-known hepatoprotective compounds, such as tauroursodeoxycholic acid (TUDCA) and S-adenosylmethionine (SAMe) failed to prevent the effect of bile acids on DNA synthesis. In summary, our results indicate that bile acid-induced reduction of DNA synthesis does not require previous decreases in hepatocyte viability. This suggests the existence of a high sensitivity to bile acids of cellular mechanisms that may affect the rate of DNA repair and/or proliferation, which is of particular interest regarding the role of bile acids in the etiology of certain types of cancer.

Bile acid secretion during rat liver carcinogenesis

Retro-differentiation of liver parenchyma during neoplastic processes is characterized by the expression of tumor antigens, such as alpha-fetoprotein and the placental isoenzyme of glutathione-S-transferase (GST-P). To investigate whether this may also affect a typical liver function such as bile acid secretion was the aim of this work. Rat hepatocarcinogenesis was induced by diethylnitrosamine (i.p., 200 mg/Kg body weight at day 0) and promoted by two-thirds partial hepatectomy (at day 21) plus 2-acetamidofluorene administration (50 mg/Kg body weight, subcutaneously, twice a week from day 14 to day 35). In order to carry out planimetric measurements of neoplastic tissue after immunohistochemical staining, a novel monoclonal antibody (MAb 14.1.3) against GST-P with no cross-reactivity against the major liver isoform of GST (GST-H) was raised. Analysis of total biliary bile acid output using the 3alpha-hydroxysteroid dehydrogenase method indicated that a significant reduction (-26%) occurred during the formation of GST-P-positive foci (12 wk). This was restored to normal values during adenoma formation (16-20 wk), but decreased again during carcinoma transformation (32 wk). These changes were not parallel to that observed in bile flow, which was progressively but slightly decreased throughout the whole period under study. HPLC analysis of bile samples collected for 1 h at different time points during hepatocarcinogenesis revealed that in contrast to what happens during cholestatic disease, a continuous and progressive increase in the cholic acid-to-chenodeoxycholic acid ratio (from 4.4+/-0.5 in control animals to 15.1+/-1.9 in rats with hepatocellular carcinoma) occurs. A significant and transient increase at 16 wk (+120%) in the proportion of bile acids amidated with glycine as compared to those conjugated with taurine was also observed. These results indicate that the mechanisms accounting for the secretion of major bile acids are modified differently at various steps of rat liver tumor development.

Further evidence of the usefulness of bile acids as molecules for shuttling cytostatic drugs toward liver tumors

BACKGROUND/AIMS

To use bile acids as shuttles for directing cytostatic drugs toward liver tumors, the ability of the tumor to take up these compounds must be maintained. Thus, we investigated whether glycocholate (GC) derivatives such as the fluorescent FITC-GC and the cytostatic Bamet-R2 are taken up by neoplastic tissue at different stages of chemically-induced rat liver carcinogenesis.

METHODS

Placental glutathione-S-transferase (GST-P) was immunohistochemically detected. Uptake studies were carried out on pure GST-P-positive cell cultures, obtained by treatment with ethacrinic acid. FITC-GC, Bamet-R2 or cisplatin was administered (i.v.) to anaesthetized rats. Platinum in culture cells, liver and kidney was measured by flameless atomic absorption.

RESULTS

Co-localization after FITC-GC i.v. administration revealed that only 15% (20 weeks) and 30% (32 weeks) of GST-P-positive tissue was not able to take up FITC-GC. GC uptake was lower in GST-P-positive cells than in normal hepatocytes. Bamet-R2, uptake was lower than that for GC, but similar in both cell types. The amount of Bamet-R2 or cisplatin retained by GST-P-positive tissue after in vivo administration was progressively increased during carcinogenesis. Moreover, this amount was higher for Bamet-R2 than for cisplatin. By contrast, in the kidney, it was higher for cisplatin than for Bamet-R2.

CONCLUSION

These results indicate that at the different stages of rat hepatocarcinogenesis most GST-P-positive tissue is able to take up bile acid derivatives, such as Bamet-R2.

Cholephilic characteristics of a new cytostatic complex of cisplatin with glycocholate (Bamet-R2)

The aim of this work was to investigate both the existence of enterohepatic circulation of cisplatin-cholylglycinate complex, Bamet-R2, and the relevance of biliary versus urinary excretion of this compound. Two experimental models were used: (i) intraluminal perfusion of 'in situ' ileum in anaesthetized rats bearing a biliary catheter that permitted bile sample collection and (ii) conscious rats in which a permanent intraarterial catheter had been implanted to carry out sequential blood sampling after intravenous (i.v.) or intragastric (i.g.) drug administration. Total platinum in serum, bile, ileum, liver, urine and feces was measured by flameless atomic absorption spectroscopy. Serum concentration versus time curves obtained after i.v. administration of 1 micromol Bamet-R2 or cisplatin revealed that the area under the curve was significantly higher for Bamet-R2 than for cisplatin (+48%). Non-ultrafiltrable platinum accounted for 54.8 and 48.4% of serum platinum 168 h after cisplatin and Bamet-R2 i.v. administration, respectively. When the animals received i.g. 1 micromol cisplatin or Bamet-R2, serum concentrations of total platinum were markedly higher (three-fold) after Bamet-R2 than after cisplatin administration. The area under the curve was, also in this case, significantly higher for Bamet-R2 than for cisplatin (+28%). This was in part due to the enhanced intestinal absorption of Bamet-R2, as confirmed in experiments on perfused rat ileum, where a markedly higher amount of the drug was found in ileum tissue and bile after perfusion with media containing Bamet-R2 as compared with experiments where cisplatin instead of Bamet-R2 was added to perfusion media. Moreover, after i.v. administration to conscious rats, excretion of Bamet-R2 by the kidney was three-fold lower than that of cisplatin, while elimination of the former compound into feces was four-fold higher than that of the latter. In summary, these results indicate that in addition to the previously reported cytostatic activity of Bamet-R2, this complex has interesting cholephilic characteristics typical of bile acids, such as low urinary excretion together with enhanced intestinal absorption and biliary secretion, probably endowed by the cholylglycyl moiety included in the Bamet-R2 molecule.

DNA interaction and cytostatic activity of the new liver organotropic complex of cisplatin with glycocholic acid: Bamet-R2

The aim of this study was to investigate the ability of the new liver organotropic complex of cisplatin with glycocholate (GC), Bamet-R2, to interact with DNA, inhibit its replication and hence reduce tumor-cell proliferation. Changes in the electrophoretic mobility of the open and covalently closed circular forms of the pUC18 plasmid DNA from Escherichia coli, a shift in the denaturation temperature of double-stranded DNA, and ethidium-bromide displacement from DNA binding, were induced by Bamet-R2 and cisplatin, but not by GC. Neutral-red retention was used to measure the number of living cells in culture after long-term (72-hr) exposure to these compounds and to evaluate the effect on cell viability after short-term (6-hr) exposure. Bamet-R2 and cisplatin, but not GC, induced significant inhibition of cell growth. This effect ranged from mild to strong, depending upon the sensitivity of the different cell types as follows: cisplatin, rat hepatocytes in primary culture < rat hepatoma McA-RH7777 cells (rH) < human colon carcinoma LS 174T cells (hCC) < mouse hepatoma Hepa 1-6 cells (mH); Bamet-R2, rat hepatocytes < mH approximately equal to hCC < rH. DNA synthesis was measured by radiolabeled-thymidine incorporation into DNA. Bamet-R2 and cisplatin, but not GC, significantly inhibited the rate of DNA synthesis by these cells. After short-term exposure to Bamet-R2 or GC, no acute cell toxicity was observed, except on hCC cells. By contrast, acute toxicity was induced by cisplatin for all cell types studied. The in vivo anti-tumoral effect was investigated in 3 different strains of mice following s.c. implantation of tumor cells (mouse sarcoma S-18011 cells in Swiss and B6 mice and hCC cells in nude mice). In all 3 models, tumor growth was inhibited by Bamet-R2 and cisplatin to a similar degree. However, signs of toxicity (increases in blood urea concentrations and decreases in packed blood cell volume and in liver, kidney and body weight) and a reduction in survival rate were observed only during cisplatin administration. In sum, these results indicate that this bile-acid derivative can be considered as a cytostatic drug whose potential usefulness deserves further investigation.

Transport and biotransformation of the new cytostatic complex cis-diammineplatinum(II)-chlorocholylglycinate (Bamet-R2) by the rat liver

Rat liver uptake and bile output of the cytostatic complex cis-diammineplatinum(II)-chlorocholylglycinate (Bamet-R2) were studied. Up to 100 microM, Bamet-R2 uptake by rat hepatocytes in primary culture followed saturation kinetics (Vmax = 0.65 +/- 0.12 nmol/5 min per mg protein; K(M) = 45.2 +/- 10.7 microM). Bamet-R2 uptake was lower than that of cholylglycinate (CG) but higher than that of cisplatin. Replacement of 116 mM NaCl by 116 mM choline chloride did not significantly reduce Bamet-R2 uptake. Addition of 500 microM CG, cholic acid, estrone sulfate, or ouabain to 50 microM Bamet-R2-containing incubation media inhibited Bamet-R2 uptake. No liver biotransformation of Bamet-R2 occurred, as indicated by HPLC analysis of bile collected from anesthetized rats after intravenous administration of the drug. Bamet-R2 uptake and secretion into bile by isolated rat livers exceeded those of cisplatin but were lower than those of CG. Differences between Bamet-R2 and CG were more marked for bile output than for liver uptake. Thus, higher Bamet-R2 than CG or cisplatin liver content was found. Co-administration of Bamet-R2 and CG revealed that CG induced a slight reduction in Bamet-R2 uptake and a marked inhibition in Bamet-R2 bile output. By contrast, Bamet-R2 had no effect on CG on either liver uptake or bile output. In sum, the present data indicate that Bamet-R2 is efficiently taken up and secreted into bile by the rat liver by mechanisms shared in part by natural bile acids.

Beneficial effect of ursodeoxycholic acid on alterations induced by cholestasis of pregnancy in bile acid transport across the human placenta

BACKGROUND/AIMS

The existence of impairment in bile acid transport across the placenta during intrahepatic cholestasis of pregnancy and the effect of ursodeoxycholic acid treatment (1 g/day) were investigated.

METHODS

Kinetic parameters were calculated from experiments carried out on membrane vesicles obtained from basal (TPMb, fetal-facing) and apical (TPMa, maternal-facing) trophoblast plasma membranes. Bile acid uptake was measured using varying concentrations of [14C]-glycocholate and a rapid filtration technique.

RESULTS

The maximal velocity of transport (Vmax), the apparent affinity constant (Kt) and the efficiency (Ef) of transport (Vmax/Kt) of the anion:bile acid exchanger located at the TPMb were reduced in intrahepatic cholestasis of pregnancy. Ursodeoxycholic acid induced a reversal of Vmax, Kt and Ef to normal values. Owing to the 3-fold increase in Vmax, with no change in Kt, intrahepatic cholestasis of pregnancy induced an enhancement in Ef of ATP-independent bile acid transport across TPMa. Both Vmax and Ef were restored to normal values by ursodeoxycholic acid. Finally, in ATP-dependent bile acid transport across TPMa, a reduction in the Ef due to an increase in Vmax together with a more pronounced increase in Kt was found. This impairment was also reversed by ursodeoxycholic acid.

CONCLUSIONS

These results suggest that placenta bile acid transport systems are impaired in intrahepatic cholestasis of pregnancy. Moreover, together with the confirmed beneficial effect for intrahepatic cholestasis of pregnancy patients, such as the relief of pruritus and the improvement in biochemical markers of cholestasis, ursodeoxycholic acid treatment restores the ability of the placenta to carry out vectorial bile acid transfer.

In vitro test to determine the effect of cytostatic drugs on co-cultured rat hepatocytes and hepatoma cells

Using uptake of the fluorescent bile acid derivative cholylglycylamido-fluorescein (FITC-GC) as a measurement of liver cell population size and function, the antiproliferative and toxic effects of the well known cytostatic drug, cisplatin was evaluated on rapidly growing rat hepatoma McA-RH7777 cells and rat hepatocytes in primary culture under non-proliferating conditions. Co-culture set up to mimic the in vivo situation of tumour and extratumoural liver tissue exposed to cytostatic chemotherapy does not markedly affect the survival or the growth dynamics of both cell types. FITC-GC uptake as corrected for DNA and protein contents in the dish was significantly lower in hepatoma cells than in rat hepatocytes throughout the experimental period (96 h). Effect of 0.1-100 microM cisplatin exposure from 24 to 96 h of culture on cell population size, as measured by protein and DNA contents in the culture dishes, were consistent with changes observed in total FITC-GC uptake. Cisplatin concentrations lower than 50 microM did not affect FITC-GC uptake by rat hepatocytes. By contrast, a progressively increasing effect on hepatoma cells as from 2 microM cisplatin was observed. Two phases in the decay of FITC-GC uptake versus cisplatin concentrations were found in co-cultures exposed to this drug. The first segment, between 2 microM and 50 microM, was characterized by a slow decay that matched the response of hepatoma cells to cisplatin exposure. This was considered to be due to the antiproliferative effect of cisplatin. The second segment, with a steeper decay, matched the effect of cisplatin on hepatocytes. This was interpreted as being due to non-specific toxicity. These results suggest that FITC-GC uptake by co-culture of hepatocytes and tumour cells provides a useful experimental model to explore the mechanism of action and the size of beneficial effect window for new drugs in vitro.

Rat liver transport and biotransformation of a cytostatic complex of bis-cholylglycinate and platinum (II)

BACKGROUND/AIMS

Bile acids have previously been used as shuttles for directing organic drugs to the liver. The aim of this study was to investigate liver transport and biotransformation of a new cytostatic bioinorganic complex (Bamet-H2), that was obtained by binding platinum(II) to two cholylglycinate moieties.

METHODS

Using rat hepatocytes in primary culture, the kinetics of cholylglycinate, cisplatin and Bamet-H2 uptake were studied. Sodium-dependency of Bamet-H2 uptake was investigated by replacement of 116 mM NaCl by 116 mM choline chloride. Liver biotransformation was investigated by HPLC analysis of bile samples collected from anesthetized rats following intravenous Bamet-H2 administration. Using isolated rat liver preparations, which were perfused with erythrocyte- and albumin-free Krebs-Henseleit solutions for 40 min, measurement of cholylglycinate, cisplatin and Bamet-H2 uptake and bile output was carried out. Interaction between Bamet-H2 and cholylglycinate for liver transport was studied by co-administration of 1 microM Bamet-H2 plus 500 microM cholylglycinate and 1 microM [14C]-cholylglycinate plus 500 microM Bamet-H2.

RESULTS

Both cholylglycinate and Bamet-H2 uptake by rat hepatocytes followed saturation kinetics. Comparison between the two compounds indicated that the Vmax (22.2 versus 8.5 nmol.5 min(-1).mg protein(-1)), and Kt (365 versus 171 microM) were higher for Bamet-H2 uptake. The efficiency of Bamet-H2 uptake (Vmax/Kt) was significantly reduced (-35%) in the absence of sodium. Cisplatin uptake by rat hepatocytes was approximately 10-fold lower than that for Bamet-H2 at any dose used. Moreover, this was not saturable up to 400 microM cisplatin. Bamet-H2 was not biotransformed during its intrahepatic residence in anesthetized rats. Bamet-H2 uptake and secretion into bile by isolated rat livers exceeded cisplatin but were less than cholylglycinate. Differences between Bamet-H2 and cholylglycinate were more marked for bile output than for liver uptake. Thus, higher drug liver content was found after perfusion with Bamet-H2 than with cholylglycinate or cisplatin. Co-administration of Bamet-H2 and cholylglycinate revealed the existence of partial cross-inhibition in both liver uptake and bile output. Bamet-H2 induced a more profound alteration on cholylglycinate uptake and bile secretion than cholylglycinate on both process for Bamet-H2.

CONCLUSION

These results suggest that in the transfer of Bamet-H2 from the sinusoids to the canaliculi both bile acid and non-bile acid transport systems are involved.

Effect of maternal cholestasis on the kinetics of bile acid transport across the canalicular membrane of infant rat livers

A reversible impairment in the ability of the liver to secrete cholephilic compounds has been reported to exist in infant rats born from mothers with surgically induced complete cholestasis during the last third of the pregnancy. Canalicular plasma membranes (CPM) were purified from livers obtained from 4 and 8 week-old offspring of healthy or cholestatic rats. Using radiolabelled glycocholic acid (GC) and a rapid filtration technique, bile acid transport by CPM vesicles in the presence of 3 mM ATP plus an ATP-regenerating system was measured at varying substrate concentrations. Kinetic parameters were calculated by nonlinear regression analysis. Similar values for the apparent affinity constant (Kt) were found in all experimental groups (approximately 350 microM). The value of the maximal velocity of the transport (Vmax) was similar for CPM obtained from control animals at 4 or 8 weeks of age (approximately 1.5 nmol/20 s/mg protein). In the offspring of cholestatic mothers the Vmax value was not different from that found in control animals as far as 4 week-old rats were concerned. However, Vmax in the 8 week-old group from cholestatic mothers was two-fold higher than that found in the rest of the experimental groups. Thus, the efficiency of transport, defined as Vmax/Kt, was very similar in all experimental groups, except in the group of 8 week-old offspring of cholestatic mothers, where this value was 60% higher. Isolated livers obtained from this group were able to secrete a tracer dose of radiolabelled GC (11.25 nmol) into bile significantly faster than isolated livers obtained from control animals of the same age (8 weeks). In sum, these results indicate that, in young infant rats (4 week-old), in which the maximal secretion rate for bile acids was reduced by maternal cholestasis during pregnancy, the kinetics of ATP-dependent bile acid transport across the canalicular membrane were not affected. By contrast, in older infant rats (8 week-old), in which the overall ability of the liver to secrete bile acids seems to be restored to normality, the efficiency of the canalicular transport system was actually enhanced. This suggests the existence of compensation at the level of the canalicular membrane transfer and thus that there is another hitherto unidentified mechanism involved in bile acid secretion.

Bile acid secretion during synchronized rat liver regeneration

One major difficulty in interpreting the changes occurring during liver regeneration is the co-existence of non-activated cells and proliferating hepatocytes at all stages of differentiation. The aim of this study was to investigate bile acid (BA) secretion into bile during normal (NLR) and synchronized (SLR) liver regeneration in rats. Regeneration was synchronized by reversible inhibition of ribonucleotide reductase by 10 h treatment with hydroxyurea (HU) shortly after two-third partial hepatectomy. Total BA output as measured by GC-MS increased immediately after partial hepatectomy. This was followed by a further transient enhancement during the next day in the NLR. HU treatment did not significantly modify total BA output, but after releasing synchronized regeneration a marked reduction was observed. This was followed by a recovery to reach values close to those of NLR on day 7 of the regenerative process in SLR. Amidated BA output as measured by HPLC analysis revealed an early enhancement in the proportion of non-conjugated BAs in bile in NLR. However, the profile of conjugated BAs, which was not affected by HU treatment, matched that of total BAs during the first stage of SLR. By contrast, the increase in BA output observed on day 3 of the regenerative process in this group was accounted for by an enhancement in non-conjugated BA secretion. On day 7 of the regenerative process, the proportion of conjugated BA in bile was restored to approximately 100% in this group. Most BA molecules were conjugated with taurine rather than with glycine in all experimental groups, during both NLR and SLR. GC-MS determinations indicated that the magnitude of the cholic acid predominance in all bile samples was significantly modified during liver regeneration. This was increased early after partial hepatectomy and declined toward control values after few (2-3) days. Enhancement in the cholic acid predominance was due to a reduction in the proportion of all other major BAs, above all ursocholic acid and omega-muricholic acid. By contrast, minor BAs in normal control rat bile such as allo-cholic acid were increased during both NLR and SLR, and remained at detectable levels up to day 7. Changes in the proportion of secreted BA species were similar in SLR and NLR except that the early reduction in the proportion of BAs other than cholic acid was more pronounced in SLR and the quantitative importance of the diversity in BA species was recovered earlier in SLR than in NLR. In summary, these results indicate that profound changes in BA secretion during rat liver regeneration do occur. Most of them are probably related to the existence of retro-differentiation/re-differentiation processes which are speeded up by hydroxyurea-induced synchronization of the wave of hepatocyte proliferation.

Fluorescent bile acid derivatives: relationship between chemical structure and hepatic and intestinal transport in the rat

Studies were performed to characterize hepatic and intestinal transport, as well as biotransformation during transport, of a spectrum of fluorescent bile acids containing a fluorophore attached to the side chain. The following two classes of compounds were studied: 1) aminofluorescein (amF) coupled directly to the carboxylic group of a bile acid which was cholic, ursodeoxycholic, or cholylglycine; and 2) nitrobenzoxadiazolyl (NBD) coupled to the epsilon-amino group of a lysine conjugated bile acid, which was cholic or ursodeoxycholic. Fluorescein, a cholephilic organic anion, was studied as a control. Fluorescent bile acids were synthesized and their structures confirmed by nuclear magnetic resonance and mass spectrometry. Using the biliary fistula rat, hepatic transport, biotransformation, and choleretic activity were defined; intestinal absorption was assessed by jejunal or ileal perfusion studies. All fluorescent bile acids had hepatic transport maxima about one-sixth that reported for cholyltaurine, but derivatives of cholylglycine were transported best. Bile acids underwent little (<5%) biotransformation during hepatocyte transport. Only the amF conjugate of cholylglycine had normal choleretic activity; other compounds were hypocholeretic or cholestatic. In contrast, fluorescein was well transported, was partly glucuronidated, and had normal choleretic activity. NBD-tagged, but not amF-tagged, bile acids were actively transported by the intestine (ileum > jejunum), and no fluorescent bile acid had passive intestinal permeability; NBD-tagged bile acids were biotransformed during intestinal transport (jejunum > ileum). We conclude that the structure of the fluorophore as well as that of the bile acid influences transport by the hepatocyte and enterocyte. These fluorescent bile acids differ from fluorescein in being impermeable to cell membranes and undergoing little biotransformation during hepatocyte transport. Of these fluorescent bile acids, cholylglycylamF has hepatocyte transport and choleretic properties most closely resembling those of a natural bile acid.

Effect of maternal cholestasis on biliary lipid and bile acid secretion in the infant rat

Partial and reversible impairment of bile formation has been reported to occur in the offspring of rats undergoing common bile duct ligation during the last third of pregnancy. This situation was defined as latent cholestasis of the neonate and was suggested to be related to the multilamellar bodies partially occupying the canalicular lumen. The current study was undertaken to investigate the presence of alterations in the secretion of biliary lipids in these infant rats. Using both high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) analyses, no changes caused by maternal cholestasis were found in either the conjugation pattern, or in the ratio of primary to secondary major bile acids in bile samples collected from 4-week-old and 8-week-old rats. However, a decrease in the proportion of cholate together with an increase in the amount of alpha- and omega-muricholate were found at 4 weeks of age. These changes were different from those observed in the pattern of maternal plasma bile acids, in which beta-, but not alpha-muricholate, concentrations were increased. Moreover, studies performed by labeling the bile acid pool of the cholestatic mother-fetus tandem with [14C]glycocholic acid (GC) at day 16 of pregnancy indicated that only a minor proportion (approximately 10%) of bile acids found in 4-week-old pups was of maternal origin. Changes in the bile acid pool composition were fully reversed by 8 weeks of age. Bile lecithin and cholesterol output were determined by enzymatic techniques, both under basal conditions and during stepwise taurocholate (TC) infusion. At the time when multilamellar bodies were found, i.e., 4 weeks after birth, no change in either nonstimulated or TC-induced cholesterol output was observed. By contrast, both spontaneous and TC-induced lecithin secretion were markedly higher (+200%) in pups of cholestatic mothers as compared with control rats. These differences were abolished at 8 weeks of age. At this time, cholesterol output was significantly lower than that found in younger animals. This reduction was more pronounced in the control than in the cholestatic group. Histological examination of liver samples collected from the cholestatic group at 4 weeks of age revealed the presence of multilamellar bodies not only in the canalicular lumen but also within vesicular structures located in the pericanalicular area or near the Golgi apparatus. Both intracellular and intracanalicular bodies were present before and after TC infusion for 2 hours. These results indicate that maternal cholestasis in rats induces profound alterations in biliary lipids and bile acid secretion in their pups. Because bile acids are important activators of different steps responsible for biliary lipid secretion (intracellular trafficking, releasing into bile, and solubilization), alterations in maternal bile acid pool size and composition may affect the fetal development of biliary lipid secretion mechanisms, which may result in the appearance of multilamellar bodies within bile canaliculi, which in turn may be involved in the reversible latent cholestasis observed in these infants rats.

Synthesis and characterization of the new cytostatic complex cis-diammineplatinum(II)-chlorocholylglycinate

Owing to the high efficiency of hepatocytes to take up bile acids, these endogenous compounds or their analogues can be considered as potential shuttles for delivering drugs to the liver. With the aim of using this strategy to target platinum(II)-related cytostatic drugs toward the hepatobiliary system, a cholylglycinate (CG) derivative of cis-diammineplatinum(II) has been synthesized by treatment of cis-diammineplatinum(II) dichloride with sodium cholylglycinate. The complex, named Bamet-R2, was characterized by spectroscopy and elemental analysis. Results obtained in these studies together with conductivity measurements, which pointed to nonelectrolyte behavior, allowed the structure of the complex to be identified as C26H48N3O6ClPt. The compound was found to be soluble (up to 3 mM) in water and was highly soluble (more than 10 mM) in ethanol, methanol, and dimethyl sulfoxide. Its stability in solution was monitored by HPLC analysis. In deionized water, the compound remains > 90% pure in solution for up to 7 days and > 80% for up to 28 days. However, in 150 mM NaCl it remains as > 90% pure compound in solution for only 1 day. By contrast with the parent compound CG, Bamet-R2 was found to significantly inhibit the growth of rat hepatocytes in primary culture and L1210 murine leukemia cells, although in a less marked way than that observed for cisplatin. The cytostatic effect of Bamet-R2 was particularly strong against human colon adenocarcinoma LS174T cells. The results point to the potential usefulness of Bamet-R2 in the antitumoral therapy of enterohepatic-derived neoplasias.

Bile secretion by the rat liver during synchronized regeneration

Simultaneous coexistence of differentiated, proliferating and redifferentiated hepatocytes occurs during normal liver regeneration (LR). The aim of the present work was to study the time course of the capacity of the liver to form bile during synchronized LR. Following two-thirds partial hepatectomy (PH) in rats, i.v. administration of the ribonucleotide reductase reversible inhibitor hydroxyurea (HU) was used to transiently block liver cells at G1/S boundary. Experiments were performed at 0 and 4 hours, and 1, 3 or 7 days after releasing HU-induced inhibition. Bile acid pool size was determined by collecting bile samples over 24 hours. Initial (first hour) bile flow and bile acid output were increased early on during synchronized LR as compared with the values found in non-hepatectomized control animals. These values were thereafter (1 day) reduced, but increased again at 3 days after halting HU infusion. The time course of bile acid depletion and changes in bile flow were very similar in control and synchronized LR, except that in the latter a more important early reduction in bile flow and bile acid output was found. Shortly after PH, part of the bile acid pool was lost, but this was quickly restored, soon (1 day) reaching a net bile acid pool size very similar to that found in control rats. The highest pool size relative to liver weight was found on day 1, when bile acid output and bile flow reached their lowest values. Additional experiments were performed using in situ perfused regenerating rat livers in which stepwise infusion of taurocholate (TC) was carried out. PH alone modified neither the bile acid-independent (BAIF) nor the bile acid-dependent fraction of bile flow (BADF). However, in normal LR, the BAIF decreased on day 1 and recovered at 7 days, while in synchronized LR it remained depressed up to 7 days. The BADF was only reduced during the early phase of normal LR and did not change significantly in synchronized LR. The maximal secretion rate (SRmax) for TC, as expressed per gram of remaining liver tissue, was not affected immediately after PH, but a marked reduction was observed on day 1 in both normal and synchronized LR. Afterwards, SRmax was quickly restored in both synchronized LR and, although in a slower way, normal LR. These results suggest that synchronization of LR involves changes in the time required to the recovery of specific liver functions such as bile formation.

Effect of bile acids on hepatobiliary transport of cisplatin by perfused rat liver

The liver and kidney collaborate in the excretion of the cytostatic drug, cis-diamminedichloroplatinum(II) (cisplatin) from the body. Enhancement of this process is envisaged as a way of reducing cisplatin toxicity, thus allowing increases in the doses administered. In this sense, using different compounds, several attempts have been made to enhance cisplatin biliary excretion. In this study, the ability of endogenous compounds belonging to the bile acid family to improve cisplatin excretion by the isolated perfused rat liver was investigated. A highly choleretic bile acid (ursodexoycholic acid) and two others bile acids with marked micelle-forming properties (glycocholic acid and chenodeoxycholic acid) were chosen for study. When these drugs were given at concentrations (1 microM) that did not affect the viability of liver preparations, a correlation between the biliary excretion of platinum and bile acid output was found. This was not due to the incorporation of cisplatin into mixed micelles because no correlation between the biliary output of lecithin or cholesterol and platinum was observed. Moreover, a wash-out effect of bile acids was probably not the cause of bile acid-induced platinum output into bile because no correlation between this and bile flow was found. An enhancement in cisplatin transport processes by the hepatocyte or by direct binding of cisplatin to bile acid monomers or aggregates cannot be ruled out. In spite of the biliary induction of cisplatin output, the net excretion of platinum was reduced under bile acid administration. This was related to lower platinum contents in the liver tissue, probably due to an inhibition of the ability of the hepatocyte to take up and/or retain cisplatin while subject to bile acid infusion. In summary, our results indicate that bile acids reduce the net excretion of cisplatin by the liver even though they induce an enhancement in the transport of this compound from the hepatocyte into bile.

Reversible impairment of neonatal hepatobiliary function by maternal cholestasis

The effect of total blockage of maternal biliary excretion during the last third of the pregnancy on the maturation of hepatobiliary function was investigated in neonatal rats. Extrahepatic obstruction of the common bile duct on day 14 of pregnancy induced a marked enhancement in serum bilirubin--mainly conjugated bilirubin--and bile acid concentrations as compared with sham-operated pregnant rats. Excretion of bile acids by the kidney was significantly increased, whereas fecal elimination of these compounds was almost abolished. Most of the cholestatic mothers (CMs) (77%) were able to carry pregnancy to term and lactation until weaning (21 days after birth). The body and liver weights of their offspring were lower than for offspring of control healthy mothers in all postnatal periods considered. Serum bile acid concentrations were higher in the fetuses and neonates of CMs. This difference was evident up to 1 week after weaning and disappeared in young adult animals (8 weeks old). When the bile secretion rate was investigated in these animals at 4 or 8 weeks of age, no significant difference was found as far as nonstimulated bile flow and bile acid output was concerned. However, the biliary response to stepwise sodium taurocholate (TC) intravenous infusion showed that 4-week-old neonates of CMs had impaired bile acid secretion. Moreover, the maximal secretion rate (SRmax) for TC was significantly reduced (-30%), whereas the choleretic ability of taurocholate was not modified. This alteration was not selective for bile acids. The SRmax for bromosulfophthalein (BSP) was also significantly lowered (-40%). These dysfunctions were overcome during subsequent development. No impaired biliary response to either TC or BSP infusion was observed at 8 weeks of age. Morphological abnormalities in the canaliculi were found in animals with impaired biliary function. In summary, these results indicate that maternal cholestasis may profoundly but transiently impair the normal liver maturation. The importance of the implications derived from these findings both in the nutrition and management of human neonates demands further evaluation of the hepatobiliary function of babies born after alterations of fetal-maternal bile acid homeostasis, such as in maternal obstetric cholestasis.

Evidence for dual effect of bile acids on thymidine anabolism and catabolism by the regenerating rat liver

Bile acids have been reported to modify DNA synthesis by rodent livers in regeneration, which may be due in part to their ability to interact with the machinery responsible for deoxyribonucleotide synthesis. The aim of this work was to gain information on the effect of taurocholate (TC) on both anabolic and catabolic pathways accounting for the fate of [methyl-14C]thymidine in the liver of two-third hepatectomized rats. Using high-pressure liquid chromatography, the soluble fraction of liver homogenate was used to measure the ability of TC to modify both the rate of thymidine monophosphate formation from thymidine - i.e., thymidine kinase (TK) activity - and the rate of thymidine release from thymidine, which is the result of at least three different reactions catalyzed by thymidine phosphorylase, nucleosidase and nucleoside deoxyribosyl transferase. TC was found to induce a dose-dependent inhibition of both processes. The nature of this inhibition seems to be in part competitive. Apparent Ki values were 1.5 mM for TK and 4 mM for thymidine release. These inhibitory effects were mimicked by glycocholate but not by taurine. To investigate the relevance of the TC-induced modification of anabolism and catabolism in the whole organ, experiments on regenerating perfused rat livers were carried out. The donors underwent two-third hepatectomy 24 h before liver isolation. They were either fasted during this period (F) or allowed free access to food (NF). DNA synthesis, as measured by [methyl-14C]thymidine incorporation into DNA, was significantly increased in both groups, as compared with control non-hepatectomized animals. However, enhancement in DNA synthesis in group F was only 50% of the value found in the NF group. Intravenous TC administration before and/or during liver perfusions induced a dose-dependent recovery of DNA synthesis in the F group. This effect was accompanied by opposed modifications in the amount of radiolabelled metabolites contained in the non-DNA fraction of liver homogenate, consistent with a marked inhibition of thymidine catabolism. These results suggest that, in addition to the previously reported effects of TC on thymidine anabolism, bile acids are also able to affect the thymidine catabolism. The overall results of this dual effect on the fate of thymidine in the regenerating rat liver depend on the metabolic situation. Under circumstances of no nutrient restriction, the effect of TC is characterized by inhibition of thymidine incorporation into DNA. By contrast, under depressed DNA synthesis due to fasting, the overall effect of TC is a partial recovery of this process.

Relationship between bile acid transplacental gradients and transport across the fetal-facing plasma membrane of the human trophoblast

Bile acids and bilirubin are synthesized by the fetal liver very early on during intrauterine life. The main fate of these compounds is to be transferred to the mother. This excretory role of the placenta is primarily determined by the ability of the trophoblast to transport them, which is believed to occur mainly by carrier-mediated processes. The aim of this study was to investigate the role of the cholephilic organic anion exchanger located in the fetal-facing plasma membrane of the human trophoblast in placental "biliary-like" function. No relationship between the magnitude of transplacental gradients for total bile acids and bilirubin was found. However, transport studies, which were carried out by using purified plasma membrane vesicles derived from the fetal-facing pole of the human trophoblast, revealed that [14C]taurocholate transport was affected by both another bile acid (taurochenodeoxycholic acid) and a non-bile acid cholephilic organic anion (bromosulfophthalein). On plotting the ability of different major bile acid species to inhibit radiolabeled taurocholate uptake by these vesicles versus their concentrations in fetal serum or the magnitude of their transplacental gradients, inverse relationships were found. Lower fetal serum concentrations and transplacental gradients were found for bile acid species with higher abilities to affect this transport and presumably to interact with the carrier. By contrast, the magnitude of the transplacental gradient for bile acid species was not correlated with their hydrophobic/hydrophilic balance, as would be expected if diffusion across the lipidic structures of the placental barrier would be the major pathway for the flux of bile acid across this organ.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of amidation in bile acid effect on DNA synthesis by regenerating mouse liver

Effect of bile acids on DNA synthesis by the regenerating liver was investigated in mice in vivo after partial hepatectomy (PH). Radioactivity incorporation into DNA after [14C]thymidine intraperitoneal administration peaked at 48 h after PH. At this time a significant taurocholate-induced dose-dependent reduction in DNA synthesis without changes in total liver radioactivity content was found (half-maximal effect at approximately 0.1 mumol/g body wt). Effect of taurocholate (0.5 mumol/g body wt) was mimicked by chocolate, ursodeoxycholate, deoxycholate, dehydrocholate, tauroursodeoxycholate, taurochenodeoxycholate, and taurodeoxycholate. In contrast, chenodeoxycholate, glycocholate, glycochenodeoxycholate, glycoursodeoxycholate, glycodeoxycholate, 5 beta-cholestane, bromosulfophthalein, and free taurine lacked this effect. No relationship between hydrophobic-hydrophilic balance and inhibitory effect was observed. Analysis by high-performance liquid chromatography indicated that inhibition of thymidine incorporation into DNA was not accompanied by an accumulation of phosphorylated DNA precursors in the liver but rather by a parallel increase in nucleotide catabolism. Bile acid-induced modifications in DNA synthesis were observed in vivo even in the absence of changes in toxicity tests, which suggests that the inhibitory effect shared by most unconjugated and tauroconjugated bile acids but not by glycoconjugated bile acids should be accounted for by mechanisms other than nonselective liver cell injury.

Bile acid-induced modifications in DNA synthesis by the regenerating perfused rat liver

Liver cell proliferation is a complex process that can be affected by a large number of factors such as bile acids, which have been reported to be associated to the pathogenesis of liver cancer. In this work, bile acid-induced modifications in DNA synthesis by regenerating perfused rat liver were investigated. Two-thirds hepatectomy was carried out 24 hr before perfusion of liver with recirculating, erythrocyte-free Krebs-Henseleit solution. The viability of the preparations was maintained under all experimental conditions, as indicated by bile flow, oxygen uptake, perfusion pressure, perfusion flow and release of lactate dehydrogenase and potassium into the perfusate. Livers received (min 10 to min 60) bile acid infusion at a rate of 25 nmol/min/gm liver (i.e., maximal secretion rate/2) in regenerating livers as calculated for taurocholate in separate experiments). Trace amounts of [methyl-14C]thymidine were added to the perfusate at min 30. At the end of the experiments (min 60) the livers were washed, removed, weighed and homogenized to determine radioactivity in whole tissue, in DNA and in non-DNA-related fractions. Taurocholate and, to a lesser extent, taurodeoxycholate and dehydrocholate (but not ursodeoxycholate) were found to reduce 14C incorporation into DNA. This was not due to changes in the content of 14C in whole, regenerating liver tissue. Taurocholate, taurodeoxycholate, dehydrocholate and ursodeoxycholate had no effect on thymidine uptake; moreover, the proportion of 14C found in bile was negligible. However, bile acid-induced modification in the fate of intracellular thymidine was observed. In regenerating livers receiving no bile acid, the 14C carried by thymidine metabolites accounted for about 60% of 14C in whole liver tissue. Taurocholate markedly increased this proportion to about 80%. Reverse-phase high-pressure liquid chromatography revealed that most of this 14C (about 80%) was recovered at the elution time, corresponding to thymidine catabolites rather than to DNA precursors. These results suggest that bile acids induce enhancement of thymidine catabolism that reduces its incorporation into DNA; inhibition in the process of DNA synthesis itself, leading to a subsequent increase in the metabolism of DNA precursors; or both. Moreover, from the diversity in this property for bile acid species it might be inferred that changes in the composition and size of the bile acid pool during liver carcinogenesis or regeneration play a role in the modulation of the proliferative process.

Effects of selective zonal injury on bile acid-induced bile flow in the isolated rat liver

The importance of acinar heterogeneity in ursodeoxycholic acid (UDCA)-induced bile flow was assessed in isolated rat livers that underwent restricted acinar damage by antegrade (A; 50 nmol) or retrograde (R; 500 nmol) digitonin infusion, as confirmed by histological evaluation. Stability of reduced (-40%) bile flow and perfusion flow (-25%) at constant pressure and potassium and lactate dehydrogenase release indicated similar viability of A and R preparations. They also showed similar abilities to secrete increasing doses of taurocholate (TC, maximal secretion rate approximately 105 nmol.min-1.g liver-1). TC-induced bile flow was not reduced by digitonin. In contrast, UDCA-induced choleresis was sensitive to zonal injury. Moreover, increases in bile flow and bicarbonate secretion observed under UDCA infusion (1.5 mumol/min) were lower in R than in A (-33 and -51%, respectively). No significant difference was observed in UDCA amidation or glucuronation between A and R preparations. With the use of single-pass perfusion on intact isolated livers that received 1 or 10 mumol UDCA, an early peak in bile acid output was observed to occur before the appearance of the major secretory peak. This was not found when 1 mumol of chenodeoxycholic acid bolus or trace amounts of [14C]TC were given. High-performance liquid chromatographic analysis of the early peak revealed it to be mainly due to unconjugated UDCA. This suggests the existence of a diffusional pathway for protonated bile acids and hence that the exist of lipophilic UDCA from bile during its way through the intra-acinar canaliculi across this pathway is also possible.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a hypercholesterolaemia-inducing diet on biliary electrolytes and lipid secretion in the rat

The effects of a high cholesterol/cholate diet on the biliary secretion of bile acids, cholesterol, phospholipid and inorganic electrolytes in the rat were examined. Wistar rats were fed a hypercholesterolaemia-inducing diet (HID) for 20 days prior to the biliary experiments. Rats fed a standard laboratory diet were used as controls. The HID diet increased plasma cholesterol concentrations and the hepatic content of total, free and esterified cholesterol, without changes in ALP*, ALT and AST plasma activities. Bile flow and biliary secretion of bile acids and inorganic electrolytes were markedly increased in the hypercholesterolaemic animals. The stimulated biliary secretion was due to an increase in both the bile acid-dependent and bile acid-independent fractions of bile flow. An increase in the bile acid pool induced by the administration of exogenous cholic acid/cholesterol would account for these changes in bile flow and inorganic electrolyte secretion. Nevertheless, the increase in the bile acid-independent bile flow could be also related, at least to some extent, to a higher efficiency of bicarbonate transport into bile. The HID diet also increased both cholesterol and phospholipid biliary outputs, whereas it did not modify the relationship between lipid and bile acid secretion. The lithogenic index of bile was reduced in the rats after the HID regimen due to a relatively higher increase in the biliary outputs of phospholipids and bile acids than of cholesterol.

Further evaluation of the interrelationship between the hepatocellular transport of bile acids and endocytosed proteins

Experiments on the relationship between the hepatocellular transport of endogenous or exogenously loaded bile acids (sodium taurocholate, TC, 0.5 mumol/min/100 g body wt) and horseradish peroxidase (HRP) or immunoglobulin A (IgA) (0.5 mg/100 g body wt) were carried out on anaesthetized Wistar rats. The time course of HRP excretion into bile (acceleration in the secretory peak), but not the total amount of HRP output, was affected by TC infusion. Administration of HRP was found to have no stimulatory effect on either spontaneous or TC-induced bile flow, bile acid, lecithin or cholesterol output. Spontaneous bile acid output was increased (25 and 67%, respectively) in rats that were treated for 12-h fasting or by oral administration of TC (45 mg/100 g body wt, every 12 h, for 2 days). These manoeuvres did not change the inability of HRP and IgA to increase bile acid output. Exogenous TC load had no stimulatory effect on the hepatocellular transport of endogenous bile acid pool, that was labelled by a combination of fasting and oral administration of 14C-glycocholic acid 12 h before the experiments. Therefore, exogenous bile acid load-induced stimulation of transcytosis had no effect on endogenous bile acid output. Moreover, bile secretion of both endogenous and exogenously loaded bile acids is unaffected by the administration of proteins, irrespective of whether they are endocytosed by a receptor or nonreceptor mediated process.

Inhibition of hepatocytary vesicular transport by cyclosporin A in the rat: relationship with cholestasis and hyperbilirubinemia

In an attempt to understand the hepatotoxicity associated with immunosuppressive therapy with cyclosporin A, we investigated the effects of acute cyclosporin A administration on biliary secretion, serum bile acid and bilirubin levels and the histological changes in the hepatic parenchyma in anesthetized male Wistar rats. The animals were divided into three experimental groups that received equal volumes (1 ml, intravenously) of physiological saline (controls), cyclosporin A vehicle (a fat emulsion, Intralipid, mixed with absolute ethanol) or cyclosporin A dissolved in the aforementioned mixture. In another series of assays, horseradish peroxidase was coinjected with cyclosporin A vehicle or with the solution containing cyclosporin A. Only after cyclosporin A administration was an immediate inhibition in bile flow and in the biliary concentrations and secretion of bile acids and bilirubin found. In addition, a delay in the peak time of the appearance of horseradish peroxidase together with a reduction in the biliary excretion rate and in the total amount of horseradish peroxidase excreted were observed during cholestasis. At 40 to 50 min after drug administration, all biliary parameters evaluated had returned to the pretest values. The relationship between bile flow and bile acid secretion showed that cyclosporin A-induced cholestasis is related to a decrease of both the bile acid-dependent and bile acid-independent fractions of bile flow. At the end of the cyclosporin A assays, the serum bile acid, total bilirubin and conjugated bilirubin concentrations were greater than those observed in the controls and Intralipid-treated animals. These effects were dose-dependent. Light microscopy and transmission electron microscopy studies did not reveal architectural hepatic abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory action of cyclobutyrol on the secretion of biliary cholesterol and phospholipids

A number of organic anions are known to decrease biliary secretion of cholesterol and phospholipid without affecting bile acid secretion. Cyclobutyrol (CB) is a choleretic agent which also inhibits biliary lipid secretion. Using isolated perfused rat liver we have studied this inhibition in relation to possible mechanisms suggested for other anions. Shortly after its administration to the isolated perfused liver, CB decreases biliary outputs of cholesterol and phospholipid, without changes in bile acid secretion, at low (450 nmol/min), high (1350 nmol/min) and nil taurocholate infusion rates. The absolute inhibition does not appear to be decreased by elevated bile acid secretion. There is a differential effect on secretion of cholesterol and phospholipid, more marked at low bile acid secretion rates. Biliary outputs of the canalicular membrane enzymes 5'-nucleotidase and alkaline phosphodiesterase I are also depressed by CB administration, but the anion does not affect the biliary output of bovine serum albumin or the output of rat serum albumin into the perfusion fluid. Since CB does not inhibit intracellular vesicular transport or apparently inhibit intracanalicular events, its effect is different from the effect of several other anions. From these studies it appears that the most likely effect of CB is exerted at the level of the canalicular membrane.

Cholestasis in the rat by means of intravenous administration of cyclosporine vehicle, Cremophor EL

The effect of cyclosporine vehicle, Cremophor EL, on bile flow and biliary bile acids and bilirubin output was studied in anesthetized male Wistar rats. Intravenous administration of Cremophor EL or castor oil as a single bolus reduced bile flow and the biliary output of bile acids and bilirubin. The Cremophor EL-induced cholestasis was an immediate and reversible phenomenon, since at 30-35 min after drug injection all parameters evaluated had returned to control values. A slight increase in serum bilirubin concentrations was observed. Our data indicate that the observed cholestasis is related to a reduction in both bile acid-dependent and bile acid-independent bile flow, probably due to a transitory hepatotoxic effect of Cremophor EL. We conclude that the clinically used vehicle for i.v. administration of cyclosporine, Cremophor EL, has adverse effects on hepatobiliary physiology in the rat and suggest that an alternative vehicle should be used.

Oestradiol 17 beta-glucuronide increases tight-junctional permeability in rat liver

By using rat liver perfusion under one-pass conditions with a single pulse of horseradish peroxidase (HRP), the biliary output of HRP was used as an indicator of paracellular permeability change caused by the cholestatic compound oestradiol 17 beta-glucuronide (E17G). Since E17G reduced bile flow, we have also used, during the assessment of junctional permeability after E17G treatment, the choleretic compound taurodehydrocholate to enhance bile flow back to control levels. At both low and restored bile flow rates, the acute administration of E17G (3.4 mumol) increased the HRP peak height, thereby indicating that one of the hepatotoxic actions of E17G is to increase the permeability of hepatic tight junctions. The action of E17G in affecting bile acid secretion and biliary volume are also explored.

Impairment of bromosulfophthalein hepatic transport and cholestasis induced by diethyl maleate in the rabbit

The present study was designed to investigate the effect of hepatic glutathione depletion induced by intraperitoneal administration of diethyl maleate (DEM) on the maximum biliary transport (Tm) and on the biliary excretion of bromosulfophthalein (BSP) in anaesthetized rabbits when the dye was perfused endovenously at doses exceeding Tm. The Tm of total BSP (BSPt) and that of conjugated BSP (BSPc) were significantly reduced after DEM administration whereas that of unconjugated BSP (BSPu) was markedly increased. A reduction in the biliary excretion of BSPt and BSPc, in the percentage of BSPc, in the cumulative excretion of BSPt and in the percent-dose recovery were also observed. However, no change in hepatic glutathione S-transferase activity was noted after DEM. The cholestasis observed following DEM administration coursed with falls in the biliary secretion of sodium, chloride and bicarbonate.

Biliary bilirubin and biliverdin excretion in rabbits during fasting and feeding

Biliary excretion rate of bilirubin and biliverdin from fasted and fed conscious rabbits has been investigated. The animals were cholecystectomized and fitted with a chronic surgical double recurrent choledoco-choledocal biliary fistula. The enterohepatic circulation of bile salts were maintained by bile administration. Mean bile flow, biliary concentrations and excretion rates of bilirubin and biliverdin remained constant during fasting conditions. After feeding bile flow and biliary output of biliverdin increased whereas that of bilirubin did not. The higher excretion rate of biliverdin after feeding could be explained by the low biliverdin reductase activity in this species and the stimulation of biliverdin formation by postprandial factors.