The mechanism of elevated alkaline phosphatase activity after bile duct ligation in the rat

Rolling circle transcription/G-quadruplex/QnMorpholine probe for highly selective and sensitive detection of alkaline phosphatase activity

In this study, we combined a rolling circle transcription (RCT) system producing 22AG G-quadruplex RNA with a QnMorpholine (QNM) fluorescent probe for the selective and sensitive detection of alkaline phosphatase (ALP). ALP is involved in various biological functions, with monophosphate cleavage being one of its characteristic properties. Here, we developed a padlock RCT probing system in which a large amount of RCT 22AG RNA G-quadruplex was produced in the absence of ALP, providing a high fluorescence signal. In contrast, no RNA G-quadruplex was produced in the presence of ALP, with minimal fluorescence. This huge deviation in signal intensity allowed us to identify the presence or absence of ALP in a test sample. Under practical conditions, our system allowed the differentiation for ALP even when it was present at an extremely low concentration (0.0085 U/L), along with very high specificity. The simplicity and efficiency of this approach for ALP detection suggest its potential for use as a reliable diagnostic tool.

Postoperative liver function tests can predict anastomotic dysfunction after bile duct injury repair

Liver function tests help in the follow-up of postoperative patients with iatrogenic bile duct injury. There is not clear evidence regarding their predictive role on anastomosis dysfunction. We describe our experience with postoperative liver function tests and a predictive model of long-term patency after repair. This is retrospective cohort study of patients with bilioenteric anastomosis for bile duct injury and their long-term follow-up. A binomial logistic regression model was performed to ascertain the effects of the grade of bile duct injury and liver function test in the postoperative period. A total of 329 patients were considered for the analysis. In the logistic regression model two predictor variables were statistically significant for anastomosis stenosis: type of bilioenteric anastomosis and alkaline phosphatase levels. A ROC curve analysis was made for alkaline phosphatase with an area under the curve of 0.758 (95% CI 0.67-0.84). A threshold of 323 mg/dL was established (OR 6.0, 95% CI 2.60-13.83) with a sensitivity of 75%, specificity of 67%, PPV of 20%, NPV of 96%, PLR of 2.27 and NLR of 0.37. Increased alkaline phosphatase (above 323 mg/dL) after the fourth operative week was found to be a predictor of long-term dysfunction.

Effect of consumption of whole egg and egg fractions on cardiovascular disease factors in adult rats

BACKGROUND

While eggs are a low-cost source of protein, rich in macro- and micronutrients, the association of egg intake and cardiovascular disease (CVD) remains controversial. This study investigated the effect of egg consumption on CVD parameters. Eggs were boiled, separated into four fractions (whole egg, 50% yolk-reduced whole egg, egg yolk and egg white) and then freeze-dried. The different egg fractions or distilled water (control) were orally gavaged to adult male Wistar rats at 1 g kg^-1 rat body weight, each day for 8 weeks, following which basal blood pressure, heart rate, complete blood cell count, blood biochemistry, body fat and liver cell lipid accumulation were determined. The vascular functions of isolated thoracic aorta were studied using classical pharmacological techniques.

RESULTS

In comparison to the control group, none of the egg fractions affected body weight, food intake, plasma glucose or lipid profile. The yolk group experienced increased plasma alkaline phosphatase and creatinine levels, while egg white caused decreased plasma cholesterol and blood urea nitrogen. Whole egg and egg yolk increased blood pressure and mean hemoglobin concentration and the yolk increased liver lipid accumulation. Egg white decreased the white blood cell count and body fat lipids. No changes were found in basal heart rate or vascular functions in any of the groups.

CONCLUSIONS

Consumption of whole egg or egg yolk at the dosage given caused hypertension, with impairment of liver and kidney functions following the intake of yolk alone. However, egg white is beneficial for the cardiovascular system as it decreased plasma cholesterol and body fat accumulation. © 2020 Society of Chemical Industry.

Coenzyme Q 10 supplementation: A potential therapeutic option for the treatment of intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis of pregnancy (ICP) is a pregnancy specific liver disease characterized by pruritus, elevated serum bile acids and abnormal liver function that may be associated with severe adverse pregnancy outcomes. We previously reported that plasma coenzyme Q10 (CoQ10) is decreased in women with ICP as it is its analogue coenzyme Q9 (CoQ9) in rats with ethinyl estradiol (EE)-induced cholestasis. The aim of the present study was to evaluate the possible therapeutic role of CoQ10 in experimental hepatocellular cholestasis and to compare it with ursodeoxycholic acid (UDCA) supplementation. Bile acids, CoQ9, CoQ10, transaminases, alkaline phosphatase, retinol, α-tocopherol, ascorbic acid, thiobarbituric acid reactive substances, carbonyls, glutathione, superoxide dismutase and catalase were assessed in plasma, liver and/or hepatic mitochondria in control and cholestatic rats supplemented with CoQ10 (250 mg/kg) administered alone or combined with UDCA (25 mg/kg). CoQ10 supplementation prevented bile flow decline (P < 0.05) and the increase in serum alkaline phosphatase and bile acids, particularly lithocholic acid (P < 0.05) in cholestatic rats. Furthermore, it also improved oxidative stress parameters in the liver, increased both CoQ10 and CoQ9 plasma levels and partially prevented the fall in α-tocopherol (P < 0.05). UDCA also prevented cholestasis, but it was less efficient than CoQ10 to improve the liver redox environment. Combined administration of CoQ10 and UDCA resulted in additive effects. In conclusion, present findings show that CoQ10 supplementation attenuated EE-induced cholestasis by promoting a favorable redox environment in the liver, and further suggest that it may represent an alternative therapeutic option for ICP.

Liver functions in silica-exposed workers in Egypt: possible role of matrix remodeling and immunological factors

BACKGROUND

Brick manufacturing constitutes an important industrial sector in Egypt with considerable exposure to silica.

OBJECTIVES

We aimed for evaluating hepatic functions in silica-exposed workers in the clay brick industry, and the possible role of matrix remodeling and immunological factors.

METHODS

A case-control study, 87 workers as exposed and 45 as control subjects. Questionnaire, clinical examination, and laboratory investigations: liver functions, matrix metalloproteinase-9, immunoglobulins G and E, and anti-liver kidney microsomal antibody.

RESULTS

In the exposed workers, mean levels of liver functions, matrix metalloproteinase-9 (MMP-9), and IgG and IgE were significantly higher. In the silicotic subgroup the mean level of GGT was almost twice the level in the non-silicotic subjects. Logistic regression showed that abnormal GGT and ALT were associated with production workers.

CONCLUSION

Workers in the clay brick industry showed evidence of liver disease that could be related to matrix remodeling.

The asymptomatic outpatient with abnormal liver function tests

Traditionally, the constellation of biochemistry tests including liver enzymes, total bilirubin, and hepatic synthetic measures (prothrombin time (PT) and serum albumin level) are referred to as liver function tests (LFTs). Abnormal LFTs can be encountered during primary health care visits, routine blood donation, and insurance screening. A reported 1% to 4% of asymptomatic patients exhibit abnormal LFTs, leading to a sizeable number of annual consultations to a gastroenterology and/or hepatology practice. A cost-effective and systematic approach is essential to the interpretation of abnormal LFTs. A review of pattern of abnormal LFTs, detailed medical history, and a comprehensive physical examination help establish a foundation for further individualized testing. Further investigation often involves biochemical testing for disease-specific markers, radiographic imaging, and even consideration of a liver biopsy. In the following account, markers of hepatic injury are reviewed followed by a discussion on an approach to various patterns of abnormal LFTs in an asymptomatic patient.

Interpretation of liver enzymes

Abnormalities in liver enzymes are commonly encountered in clinical practice. Knowledgeable assessment requires a full understanding of their pathophysiology and provides an important means of detecting the earliest stage of many serious hepatobiliary disorders. The best interpretations are achieved using an integrated approach, combining historical and physical findings with routine and specialized diagnostic procedures and imaging studies. Information in this article provides the foundation, by example, for understanding the reliability of single time point enzyme measurements, the value of sequential measurements, the importance of interpreting the activity of enzymes in light of their half life and tissue of origin, and the influence of the induction phenomenon.

Evidence for ototopical glucocorticoid-induced decrease in hypothalamic-pituitary-adrenal axis response and liver function

To clarify whether ototopical glucocorticoid treatment is associated with impaired hypothalamic-pituitary-adrenal axis (HPA) activity and altered hepatic metabolism, one commercially available dexamethasone-containing ointment was tested. At present, very little is known about the effects of ototopical glucocorticoid treatment on HPA and liver function. Ten beagle dogs received two daily therapeutic doses of dexamethasone (0.6 mg/ear) in the outer auditory canal for 21 d in a single-blind, placebo-controlled study. Resting cortisol concentrations were assessed before, during, and after treatment using an RIA system. Adrenal function and HPA feedback sensitivity were measured by a standard dose (250 microg) ACTH stimulation test. Serum biochemical and hematological parameters were measured, whether ototopical glucocorticoids affect hepatic function was studied, and blood cell counts were made. Ototopical dexamethasone treatment induced a marked suppression (to about 100%) of resting plasma cortisol concentrations below the placebo effect (P < 0.0001) within the first 11 d, and these remained reduced during the entire treatment period up to d 19. As well, an ACTH stimulation test found a markedly reduced rise in plasma cortisol concentrations (P = 0.0004). Concomitantly, significant increases in serum activities of alkaline phosphatase, gamma-glutamyl transferase, alanine transaminase, and aspartate transaminase were detected. Moreover, we found a significant reduction in differential leukocyte counts of eosinophils and lymphocytes, whereas neutrophils increased. Although cortisol levels and hematological parameters returned to baseline 7 d after treatment cessation, liver enzyme activities remained elevated. In conclusion, these findings suggest that after ototopical application, dexamethasone is sufficiently absorbed from the auditory canal to suppress HPA function as well as to alter metabolic and hemopoietic profiles. Thus, in long-term treatment of otitis externa or media, the systemic adverse suppression of HPA has to be considered in relation to stress exposure, whereas changes in serum enzyme activities may not be interpreted as hepathopathy.

Evaluation of the influence of S-adenosylmethionine on systemic and hepatic effects of prednisolone in dogs

OBJECTIVE

To evaluate the influence of a 1,4-butanedisulfonate stable salt of S-adenosylmethionine (SAMe) administered orally on clinicopathologic and hepatic effects induced by long-term administration of prednisolone in dogs.

ANIMALS

12 healthy dogs.

PROCEDURE

Following a pilot study (4 dogs), 2 groups of 4 dogs received prednisolone (2.2 mg/kg) orally once daily (84-day trial). One group received SAMe (20 mg/kg/d divided in 2 doses) for 42 days and then a placebo for 42 days; the other group received treatments in the reverse order. Before and during the trial, numerous variables were monitored, including serum total alkaline phosphatase (ALP) and glucocorticoid-induced ALP (G-ALP) activities, serum haptoglobin concentration, and total and oxidized glutathione (TGSH and GSSG) and thiobarbiturate-reacting substances (TBARS) concentrations in erythrocytes and liver tissue (days 0, 42, and 84). Hepatic specimens also were examined microscopically.

RESULTS

The stable salt of SAMe was biologically available; plasma concentrations of SAMe or prednisolone were not affected by coadministration. Compared with baseline values, serum ALP and G-ALP activities and haptoglobin concentrations increased and erythrocyte GSSG and TBARS concentrations decreased with both treatments. Erythrocyte TGSH concentration decreased with the prednisolone-placebo treatment. Administration of SAMe appeared to conserve erythrocyte TGSH values and did not inhibit hepatocyte glycogen vacuolation but increased hepatic TGSH concentration and improved the hepatic tissue GSSG:TGSH ratio.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs, administration of 20 mg of SAMe/kg/d may mitigate the apparent pro-oxidant influences of prednisolone but did not block development of classic clinicopathologic or histologic features of vacuolar hepatopathy.

Reversible cholestasis induced by experimental partial obstruction of the bile duct

The aim of this investigation was to reproduce in rats a partial stenosis of the common bile duct to analyze early liver functional and morphometric changes. The hepatic transport kinetics of sulfobromophthalein (organic anion) and rhodamine B (organic cation) was also investigated, and compartmental analysis of both compounds was performed. The humoral parameters of liver function indicated a cholestasis after 2 days of surgery, which reverted to reach normal values on the seventh day. Tumor necrosis factor alpha serum levels showed a tendency to increase on the second day of stenosis (7 out of 14 rats) while white blood cells increased on the second day of stenosis, and turned to normal levels on the seventh day. Histological studies showed increased volume of portal areas and ductular proliferation, which did no revert during the time of the study (up to 7 days post-op). Conversely, a moderate fibrosis and leukocyte infiltrates in portal areas predominated on the second day of stenosis, but normalized on the seventh day. Bile flow was considerably diminished on the second day of partial obstruction as compared to controls. The mean recovery in bile of sulfobromophthalein after 1h of being injected was low on the second day of stenosis, but normalized on the seventh day. Conversely, that of rhodamine B was very low in all animals. Sulfobromophthalein kinetics showed that hepatic uptake and canalicular excretion were impaired during the second but normalized on the seventh day of stenosis. However, rhodamine B kinetics showed that this compound was poorly excreted in all groups although canalicular excretion increased on the second day. The results suggested a model of obstructive cholestasis induced by the experimental stenosis of the bile duct which was not only reversible but also implicates the role of hepatic inflammation.

Serum enzymes associated with cholestasis

Alkaline phosphatase, gamma-glutamyl transferase, and 5' nucleotidase are the most common enzymes used in the evaluation of cholestasis. The present knowledge of these enzymes including their function, activity measurement, biologic variables of enzyme activity in healthy persons and disease states, and clinical significance are reviewed. Usefulness of enzymes patterns for diagnosis of specific cholestatic disorders and future directions in evaluation of cholestasis are also discussed.

Interleukin-1beta enhances retinoic acid-mediated expression of bone-type alkaline phosphatase in rat IEC-6 cells

We previously showed that vitamin A upregulated the expression of bone-type alkaline phosphatase (ALP) in fetal rat small intestine and rat intestinal IEC-6 cells. In this study, we examined interactions between retinoic acid (RA) and several growth factors/cytokines on the isozyme expression in IEC-6 cells. Epidermal growth factor and interleukins (ILs)-2, -4, -5, and -6 completely blocked the RA-mediated increase in ALP activity. In contrast, IL-1beta markedly increased the activity, protein, and mRNA of the bone-type ALP only when RA was present. IL-1beta and/or RA did not change the type 1 IL-1 receptor transcript level, whereas IL-1beta enhanced the RA-induced expressions of retinoic acid receptor-beta (RAR-beta) and retinoid X receptor-beta (RXR-beta) mRNAs and RA-mediated RXR response element binding. The synergism of IL-1beta and RA on ALP activity was completely blocked by protein kinase C (PKC) inhibitors. Our results suggest that IL-1beta may modify the ALP isozyme expression in small intestinal epithelial cells by stimulating PKC-dependent, RAR-beta- and/or RXR-beta-mediated signaling pathways.

Serum hepatic biochemical activity in two populations of workers exposed to styrene

OBJECTIVE

To determine whether hepatic biochemical changes, as measured by routinely available tests indicative of hepatocellular necrosis, cholestasis, or altered hepatic clearance of bilirubin, occur in association with low to moderate exposure to styrene commonly experienced in industrial production.

METHODS

Two independent cross sectional studies were performed comparing serum hepatic transaminases (alanine aminotransferase (ALT) and aspartate aminotransferase (AST)), cholestatic enzymes (alkaline phosphatase (AP) and gamma glutamyl transpeptidase (GGT)), and bilirubin in (a) 47 workers of fibreglass reinforced plastics who were exposed to styrene and (b) 21 boat and tank fabricators, with separate referent groups of unexposed workers. Exposure to styrene was assessed in air by dosimetry, and in venous blood by headspace analysis. Hepatic biochemical variables were assessed across strata of exposure to styrene defined as 25 ppm in air, or 0.275 mg/l in blood, adjusting for age, sex, body mass index, and ethanol consumption.

RESULTS

A consistent and significant linear trend for increasing direct bilirubin and direct/total bilirubin ratio was found in association with increasing exposure to styrene, by both air and blood monitoring, in both studies. Mean direct bilirubin concentrations increased from 0.05-0.08 mg% in referents to 0.12-0.19 in workers exposed above 25 ppm, with a significant exposure-response trend (p<0.005). Significantly increased direct/total bilirubin ratios, ranging from 0.22 to 0.35 were associated with exposure to styrene (p<0.001), indicating diminished hepatic clearance of conjugated bilirubin. Also, a significant linear association between the hepatic transaminases ALT and AST and exposure to styrene was found in pooled regression analyses, with an increase in AP of about 10 IU/ml in workers exposed above 25 ppm air or 0.275 mg/l blood styrene in pooled analyses from both studies.

CONCLUSIONS

The consistent finding of increased direct bilirubin and AP concentrations in these two independent studies provides evidence for diminished hepatic clearance of conjugated bilirubin with associated cholestasis in workers exposed to styrene. The finding of a significant linear association between hepatic transaminase concentrations and exposure to styrene in pooled analyses is consistent with mild hepatic injury and associated metabolic dysfunction.

Sodium butyrate induces alkaline phosphatase gene expression in human hepatoma cells

BACKGROUND AND AIMS

Butyrate, a natural product of colonic bacterial flora, has been reported to increase the activities of a number of enzymes, including alkaline phosphatase, (ALP) in several cancer cell lines. However, butyrate-induced ALP gene expression in human hepatoma cells has not been previously demonstrated. In the present study, the effects of sodium butyrate on cell growth and proliferation, cellular activity and expression of ALP gene in human hepatoblastoma-derived HepG2 cells were investigated.

METHODS

The HepG2 cells were treated with sodium butyrate (0-1 mmol/L) and the number of viable cells were counted at 24, 48 and 72 h after treatment. A [3H]-thymidine incorporation study was performed at different concentrations of sodium butyrate for 48 h. The cellular activity of ALP in HepG2 cells by sodium butyrate was measured by a substrate-specific enzymatic assay. To elucidate the effects of sodium butyrate on ALP gene expression, a northern blotting experiment employing hybridization with mouse placental ALP cDNA was performed.

RESULTS

Cell growth and proliferation were dose-dependently inhibited by sodium butyrate. Cellular ALP activity was significantly increased in HepG2 cells in a time- and dose-dependent fashion by treatment with sodium butyrate and a maximum activity was observed at 48 h. These effects were reversible when sodium butyrate was removed from the culture medium. By northern blot analysis, the level of ALP messenger RNA was dose-dependently elevated by sodium butyrate.

CONCLUSION

Butyrate, at a concentration relevant to the normal physiology of the liver, causes augmented expression of ALP mRNA in HepG2 cells. We assume that increased ALP synthesis in HepG2 cells by sodium butyrate results from an enhanced rate of transcription rather than translation of mRNA.

Vitamin A up-regulates expression of bone-type alkaline phosphatase in rat small intestinal crypt cell line and fetal rat small intestine

Vitamin A is a potent inducer for liver/bone/kidney alkaline phosphatase (L/B/K ALP) in a variety of tissues. However, the evidence for induction of L/B/K ALP by vitamin A in small intestine is limited. In this study, we investigated the influence of vitamin A on L/B/K ALP expression in rat small intestinal crypt IEC-6 cells and fetal rat small intestine. Treatment of IEC-6 cells with all-trans retinoic acid (RA) increased the levels of activity, protein and mRNA of L/B/K ALP, whereas enterocyte-specific proteins, including intestinal ALP, sucrase-isomaltase and glucose transporter-2, were not induced. The reverse transcription-polymerase chain reaction technique revealed that this L/B/K ALP transcript had the bone-type but not the liver-type leader exon. IEC-6 cells constitutively expressed mRNAs of all subtypes of retinoic acid receptor (RAR) and retinoid X receptor (RXR) at varied concentrations. Among these receptor mRNAs, RARbeta mRNA quickly responded to RA treatment, and the level was doubled within 4 h. Gel mobility shift assay showed that RA induced an RXRE-binding activity in IEC-6 cells. The L/B/K ALP transcript, expressed in fetal rat small intestine, also contained the bone-type leader exon. Intragastric administration of 10 mg retinyl acetate to pregnant rats from gestational d 7 to 15 increased the levels of this transcript and enzyme in 15-d fetal rat small intestine. Our results suggest that vitamin A may be an important regulator for L/B/K ALP expression in fetal rat small intestine as well as in IEC-6 cells.

Cholestasis and alterations of glutathione metabolism induced by tacrolimus (FK506) in the rat

BACKGROUND

Tacrolimus (FK506) is an immunosuppressive agent used for the prevention of allograft rejection after organ transplantation. The aim of this study was to investigate the effects of chronic tacrolimus treatment on bile secretion in rats.

METHODS

Tacrolimus was administered intraperitoneally at doses of 0.2, 0.5, and 0.8 mg/kg/day for 6 weeks.

RESULTS

Bile flow was significantly reduced at doses of 0.5 mg/kg and 0.8 mg/kg (-25% and -32%, respectively). Bile acid secretion was not significantly modified, but bicarbonate secretion decreased at doses of 0.5 mg/kg and 0.8 mg/kg (-23% and -29%, respectively). Glutathione secretion was significantly reduced at doses of 0.5 mg/kg (-29%) and 0.8 mg/kg (-49%). Liver glutathione concentration was reduced at the higher dose (-17%). Liver gamma-glutamyl-cysteinyl synthetase activity was elevated (+22%, +10, and +15%) and gamma-glutamyl transpeptidase activity was reduced (-18%, -40%, and -25%) at all doses. Dichlorofluorescein and thiobarbituric acid-reactive substance concentrations were not significantly modified. Liver glutathione peroxidase activity increased at doses of 0.5 mg/kg (+65%) and 0.8 mg/kg (+56%). Kidney concentration of thiobarbituric acid-reactive substances was significantly increased at doses of 0.5 mg/kg (+17%) and 0.8 mg/kg (+12%).

CONCLUSIONS

Our data indicate that tacrolimus at high doses induces cholestasis by inhibiting primarily biliary excretion of glutathione and, to a lesser extent, bicarbonate. The decrease in biliary glutathione secretion is not due to a lower synthesis or degradation and could be related to its increased sinusoidal efflux.

Regulation of alkaline phosphatase gene expression in human hepatoma cells by bile acids

Bile acid-dependent secretion and the translationally regulated synthesis of alkaline phosphatase (ALP) in rat liver cell culture and by bile duct ligation has already been demonstrated. With the advent of ALP cDNA cloned sequences, the mechanism of the effect of bile acids on ALP activity and the expression of the ALP gene in different hepatoma cells was investigated. The HuH7 and HepG2 cells were treated with taurine-conjugated cholic acid (CA), chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA) at 0-1 mmol/L and the numbers of viable cells were counted at 24, 48 and 72 h after treatment. A [3H]-thymidine incorporation study was performed with different bile acids at a concentration of 1 mmol/L for 48 h. The cellular activity of ALP in HuH7 and HepG2 cells by bile acids was measured by a substrate-specific enzymatic assay. To elucidate the effects of bile acids on ALP gene expression, a northern blotting experiment using hybridization with mouse placental ALP cDNA was performed. Cellular ALP activity was time- and dose-dependently increased in both HuH7 and HepG2 cells treated by CA and CDCA; however, no change in ALP activity was observed following treatment with UDCA compared with controls. Induction of ALP activity was dominant in HepG2 cells and independent of cell growth and proliferation. The addition of UDCA synergistically reduced the increased activity of ALP produced by CA and CDCA in both HuH7 and HepG2 cells. By northern blot analysis, the level of ALP mRNA was elevated by CA and CDCA; however, levels of ALP mRNA were suppressed by UDCA. In conclusion, CA and CDCA cause up-regulation of ALP mRNA and UDCA leads to down-regulation of ALP mRNA by its interaction with either CA or CDCA. We assume that increased ALP synthesis in hepatoma cells after bile acid treatment results from an enhanced rate of transcription rather than translation of mRNA.

Elevation of the serum bilirubin diconjugate fraction provides an early marker for cholestasis in the rat

AIMS/METHODS

During cholestasis, components normally excreted into bile, e.g. bilirubin, accumulate in liver cells and biliary passages. In order to assess the conjugation of bilirubin retained in the hepatocyte during cholestasis, we analyzed the pattern of bilirubin pigments in rat serum and bile, using reversed phase alkaline methanolysis-HPLC. Cholestasis was induced by bile flow interruption for 1 to 2 h.

RESULTS

One hour after initiation of cholestasis, the serum concentration of total bilirubin rose 2-fold due to increases in bilirubin di- (BDC) and monoconjugate (BMC), while unconjugated bilirubin (UCB) decreased by 33%. As a result, the BDC/BMC ratio increased to 1.67+/-0.20 vs 0.60+/-0.10 in controls (p<0.01) and the BMC/UCB ratio to 1.0+/-0.2 vs 0.1+/-0.1 (p<0.01). After relief of biliary obstruction, biliary output rose to 8.0+/-0.5 vs 5.5+/-0.3 micromol x min(-1) x kg (p<0.01), and the biliary BDC/BMC ratio to 4.0+/-0.3 vs 1.5+/-0.2 (p<0.01). In contrast, the biliary BMC/UCB ratio remained unchanged throughout. Increasing the duration of obstruction to 2 h led to a further increase in the serum BMC/UCB ratio to 2.2+/-0.3 (p<0.01), but not in the BDC/BMC ratio. Serum aminotransferase activity and the concentration of total bile acids increased 3- and 100-fold above their respective control values. Alkaline phosphatase activity remained unaltered, and electron microscopical features of cholestasis became apparent only after 2 h of biliary obstruction.

CONCLUSIONS

We suggest that one of the initial events of cholestasis is a more efficient conjugation of bilirubin retained in the hepatocyte. This results in a shift of the equilibrium among bilirubin pigments towards BDC, the end-product of conjugation. Such a shift provides an early marker for cholestasis.

Histological and biochemical changes induced by total bile duct ligation in the rat

The aim of the present investigation was to assess in a correlated biochemical and morphological study the dynamics of fibrogenesis after bile duct ligation and to compare the time course of alterations with those occurring in thioacetamide induced liver fibrosis. The data show that, after bile duct obstruction, the deposition of connective tissue elements and formation of ductular proliferates rapidly set in. The index of fibroplasia correlated well with the changes of the OH-proline concentration of the liver. Comparing the biliary fibrosis with the thioacetamide induced liver fibrosis, the progress of the former occurred more rapidly, even though in both cases only a few necroses were observed. Therefore, we suggest that in biliary fibrosis other mechanisms are responsible for the rapid onset of production of extracellular material and proliferative processes than in thioacetamide-induced liver fibrosis.

Modulation of hepatic content and biliary excretion of P-glycoproteins in hepatocellular and obstructive cholestasis in the rat

BACKGROUND/AIMS

Release into bile of canalicular membrane enzymes, such as alkaline phosphatase and gamma-glutamyl transpeptidase, is significantly increased in rats subjected to experimental models of hepatocellular or obstructive cholestasis. This effect appears to be related to a greater susceptibility of these membrane intrinsic proteins to the solubilizing effects of secreted bile acids. It is not known whether canalicular membrane transport proteins, such as P-glycoprotein isoforms, involved in ATP-dependent xenobiotic biliary excretion and phospholipid secretion, are excreted into bile and whether this process is modified in cholestasis. The aims of this work have been to investigate in the rat: a) whether P-glycoproteins are normally excreted into bile, b) whether their excretion is modified in two experimental models of cholestasis, i.e., hepatocellular cholestasis induced by ethynylestradiol and obstructive cholestasis, and c) whether observed changes correlate with bile acid and phospholipid secretion and enzyme release into bile and with relative P-glycoprotein content in hepatic tissue and isolated and purified canalicular membranes.

METHODS

P-glycoproteins in bile and hepatic tissue were identified and quantitated by Western-blotting and immunohistochemistry using the C219 MAb. Changes in total mdr mRNA were analyzed by Northern-blotting.

RESULTS

Like canalicular membrane enzymes, P-glycoproteins are normally excreted into bile. Ethynylestradiol-induced cholestasis was associated with a 4.9-fold increase in P-glycoprotein excretion compared with controls while, in contrast, the excretion of the carrier decreased markedly in obstructive cholestasis to 2% of control values. P-glycoprotein excretion per nmol of secreted bile acids increased 4.4-fold in ethynylestradiol-induced cholestasis but decreased to 2% of control values in obstructive cholestasis. Total mdr mRNA levels in hepatic tissue were markedly increased (3.4-fold) in rats subjected to obstructive cholestasis and moderately increased (1.6-fold) in the ethynylestradiol group, compared with controls. P-glycoprotein content in isolated canalicular membranes was slightly decreased by 15% in ethynylestradiol-induced cholestasis, while it increased 4.7-fold in obstructive cholestasis. Immunohistochemistry of rat livers showed that P-glycoprotein reaction at the canalicular domain of hepatocytes at acinar zone 1 was decreased in ethynylestradiol-treated rats and markedly increased in obstructive cholestasis.

CONCLUSIONS

Ethynylestradiol-induced cholestasis is associated with increased P-glycoprotein biliary excretion and decreased hepatic content. In contrast, obstructive cholestasis results in decreased P-glycoprotein biliary excretion and increased hepatic content. These results suggest that biliary P-glycoprotein excretion might be a modulating factor in canalicular membrane P-glycoprotein content. Increased P-glycoprotein release into bile in ethynylestradiol-treated rats is apparently not a consequence of cholestasis, but it might be a primary event and play a pathogenetic role in ethynylestradiol-induced cholestasis.

Enhanced biliary excretion of canalicular membrane enzymes in ethynylestradiol-induced cholestasis. Effects of ursodeoxycholic acid administration

Cholestasis is associated with a marked increase in the release of canalicular membrane enzymes into bile. This phenomenon has been related to an increased lability of these canalicular membrane integral proteins to the solubilizing effects of secreted bile salts. To further characterize the effects of oral ursodeoxycholic acid (UDCA) administration on ethynylestradiol (EE)-induced cholestasis, the influence of this bile acid on changes in biliary excretion of membrane-bound enzymes was investigated. Bile flow, basal bile salt and biliary lipid secretory rates, the maximum secretory rate of taurocholate (TC SRm), and the biliary excretion of the canalicular membrane-bound ectoenzymes alkaline phosphatase (ALP) and gamma-glutamyl transpeptidase (GGT) were measured in rats after EE and/or UDCA administration. The activities of ALP, GGT and Na+,K(+)-ATPase in purified isolated canalicular and sinusoidal membrane fractions and the ultrastructure of hepatic acinus, including histochemical studies of ALP distribution, were also examined. EE significantly reduced bile flow, bile salt and biliary lipid secretory rates, and TC SRm, and caused dilatation and loss of microvilli at the canalicular pole of hepatocytes. Biliary excretion of ALP increased 2-fold, whereas biliary excretion of GGT was unchanged. The relationship between biliary excretion of ALP or GGT and bile salt secretion (units of enzyme activity secreted per nanomole of bile salt) was greater in EE-treated rats compared with controls (2.1- and 1.5-fold greater for ALP and GGT, respectively), indicating that in EE-induced cholestasis more enzyme was released into bile per nanomole of bile salt. Na+,K(+)-ATPase activity in sinusoidal membrane fraction was reduced significantly, whereas ALP activity increased in both membrane fractions in EE-treated rats. The histochemical distribution of ALP in the acinus showed a strong reaction in acinar zone 3 and at both the canalicular and sinusoidal membranes. Oral administration of UDCA prevented EE-induced bile secretory failure by normalizing bile flow, bile salt and biliary phospholipid secretory rates, and TC SRm. UDCA also prevented the EE-induced changes in the biliary excretion of enzymes. On the contrary, UDCA did not modify either the enzyme activity in isolated membrane fractions or the morphological or ALP histochemical changes associated with EE administration. These data indicate that in EE-induced cholestasis changes occur at the canalicular membrane, enabling this portion of the plasma membrane to be more susceptible to the solubilizing effect of bile salt, and that oral administration of UDCA prevents bile secretory failure and changes in the biliary excretion of ALP and GGT in EE-treated rats.

Redistribution and fate of colchicine-induced alkaline phosphatase in rat hepatocytes: possible formation of autophagosomes whose membrane is derived from excess plasma membrane

The redistribution and fate of colchicine-induced alkaline phosphatase (ALPase) in rat hepatocytes were investigated by electron microscopic enzyme cytochemistry and biochemistry. ALPase activity markedly increased in rat hepatocytes after colchicine treatment (2.0 mg/kg body weight, intraperitoneal injection). At 20-24 h after colchicine treatment, the liver showed the highest activity of ALPase. Thereafter, ALPase activity decreased and returned to normal levels at 48 h. In normal hepatocytes from control rats, ALPase activity was seen only on the bile canalicular membrane. However, at 20-24 h after colchicine treatment, colchicine-induced ALPase was redistributed in the sinusoidal and lateral (basolateral) membranes as well as in the bile canalicular membrane. At 30-36 h after colchicine treatment, ALPase activity on the basolateral membrane gradually decreased. In contrast, ALPase in the bile canalicular membrane increased along with the enlargement of bile canaliculi, suggesting that ALPase in the basolateral membrane had been transported to the bile canalicular membrane. Furthermore, ALPase-positive vesicles, cisternae and autophagosome-like structures were frequently seen in the cytoplasm. ALPase was also positive in some lysosomal membranes. ALPase in hepatocytes at 48 h after colchicine treatment returned to almost the same location as in control hepatocytes. Altogether, it is suggested that excessively induced ALPase is at least partially retrieved by invagination of the bile canalicular membrane and then transported to lysosomes for degradation. In addition, this study indicates that excess plasma membrane might be a possible origin of autophagosomal membrane.

Enhanced biliary excretion of canalicular membrane enzymes in estrogen-induced and obstructive cholestasis, and effects of different bile acids in the isolated perfused rat liver

BACKGROUNDS/AIMS

Canalicular membrane enzymes are normally released into bile by partially known processes. This study was undertaken to investigate whether hepatocellular cholestatis induced in rats by ethynylestradiol or obstructive cholestasis produced by complete biliary obstruction for 24 h is associated with an increased release of alkaline phosphatase and gamma-glutamyl transpeptidase into bile, and to clarify how this process is affected by different bile acids.

METHODS

The studies were performed in the isolated perfused liver during infusion of sodium taurocholate, taurochenodeoxycholate and tauroursodeoxycholate at increasing rates.

RESULTS

Maximum sodium taurocholate, taurochenodeoxycholate and tauroursodeoxycholate secretory rates were decreased in both cholestatic groups (complete biliary obstruction > ethynylestradiol) compared with controls. Maximum biliary outputs of alkaline phosphatase and gamma-glutamyl transpeptidase were significantly increased in the ethynylestradiol group during infusion of sodium taurocholate and taurochenodeoxycholate, but not of tauroursodeoxycholate, and were increased in the complete biliary obstruction group during the infusion of sodium taurocholate and tauroursodeoxycholate but not of taurochenodeoxycholate. The biliary outputs of alkaline phosphatase and gamma-glutamyl transpeptidase showed a significant and direct linear relationship with sodium taurocholate and taurochenodeoxycholate secretory rates in both cholestatic groups. However, only in the complete biliary obstruction group did alkaline phosphatase and gamma-glutamyl transpeptidase excretion show a significant correlation with tauroursodeoxycholate secretory rates. The slope of the line, which indicated the mU of enzyme activity secreted per nmol of sodium taurocholate or taurochenodeoxycholate, was greater for gamma-glutamyl transpeptidase and alkaline phosphatase in both cholestatic groups (ethynylestradiol > complete biliary obstruction) than in the control group. Alkaline phosphatase activity in purified isolated canalicular and sinusoidal membranes was significantly increased in both cholestatic groups (complete biliary obstruction > ethynylestradiol), while gamma-glutamyl transpeptidase activity was unchanged compared with controls.

CONCLUSION

The marked increase in sodium taurocholate and taurochenodeoxycholate-mediated release of alkaline phosphatase and gamma-glutamyl transpeptidase into bile in cholestatic rats suggests an increased lability of these intrinsic membrane proteins to the detergent effects of secreted bile acids. It remains to be elucidated whether this phenomenon, which was particularly intense in ethynylestradiol induced cholestasis, is important in the pathogenesis and perpetuation of bile secretory failure. In contrast, tauroursodeoxycholate administration did not result in enhanced biliary excretion of these membrane enzymes, in either the control group or the ethynylestradiol group, supporting the concept that this bile salt lacks the membrane toxicity of common bile acids.

Potential role of bile duct collaterals in the recovery of the biliary obstruction: experimental study in rats using microcholangiography, histology, serology and magnetic resonance imaging

Obstructive cholestasis induced in animals at the level of the lobar and common bile ducts is known to be reversible with time. This study was conducted not only to test the hypothesis that formation of bile duct collaterals is responsible for the recovery of biliary obstruction but also to assess the potential of hepatobiliary agent-enhanced magnetic resonance imaging for visualizing cholestasis. A total of 52 rats were divided into three groups with selective biliary obstruction, total biliary obstruction and sham surgery. We studied the evolution of cholestasis by correlating microcholangiographic, histological findings with the results of liver tests and hepatobiliary agent-enhanced magnetic resonance imaging. Lobar cholestasis undetected by liver tests but seen on magnetic resonance imaging as a difference between ligated and unligated lobes, occurred in 15 out of 20 rats subjected to selective biliary obstruction within 48 hr after ligation, and recovered later on as a result of the development of bile duct collaterals. Five rats failed to show local cholestasis as a result of the existence of interlobar accessory bile channels. All 18 total biliary obstruction-treated rats were cholestatic soon after ligation, as confirmed by high serum bilirubin and alkaline phosphatase levels and as documented by poor liver enhancement on magnetic resonance imaging. Cholestasis recovered within 4 wk with normalization of liver enhancement on magnetic resonance imaging as a result of the formation of bile duct collaterals (as demonstrated by microcholangiographic and histological study). Bile duct collateral formation is responsible for the recovery from obstructive cholestasis in rats. A similar mechanism might be present in conditions of bile duct obstruction without cholestasis. Hepatobiliary agent-enhanced magnetic resonance imaging is more sensitive than blood tests in detecting local cholestasis and can be used to monitor noninvasively the evolution of biliary obstruction.

Changes in the blood composition of calves during experimental and natural infections with Eimeria alabamensis

Two trials were carried out to assess the changes in blood composition of calves infected either experimentally or naturally with Eimeria alabamensis. In the first, 12 calves were dosed orally with 10 to 400 million sporulated oocysts and compared with three control calves. The second trial used eight calves turned out to graze a permanent pasture known to induce E alabamensis coccidiosis in calves and eight calves turned out on to a previously ungrazed pasture. In both trials the serum activities of glutamate dehydrogenase (GLDH) and alkaline phosphatase (AP) and the serum concentration of total bile acids decreased in the infected animals while total bilirubin increased. The changes in GLDH, bile acids and bilirubin were most pronounced just before the calves began to excrete oocysts. In the first trial the lowest AP activity was observed 10 days after infection, but in the second its activity continued to decrease throughout the trial. In the first trial haematology, serum fibrinogen, total protein and protein fractions were also investigated. All the significant changes were small and the potential of the investigated blood components as diagnostic markers is therefore minimal.

Effects of bile acids and cholestasis on major histocompatibility complex class I in human and rat hepatocytes

BACKGROUND/AIMS

Major histocompatibility complex (MHC) class I molecules, which are normally poorly expressed on the surface of hepatocytes, are overexpressed during cholestasis. The mechanisms responsible for this overexpression were examined.

METHODS

The expression of class I molecules, assessed by flow cytofluorimetry, and the class I messenger RNA (mRNA) transcripts, assessed by Northern blot analysis, were measured on normal human hepatocytes in primary culture.

RESULTS

Chenodeoxycholic acid induced an overexpression of MHC class I molecules, whereas ursodeoxycholic acid did not. The level of class I mRNA closely reflected that of the membrane protein. Moreover, cholestasis, induced in the rat by ligation-section of the common bile duct, increased the MHC class I mRNA level. Actinomycin D inhibited bile acid-induced class I transcription of rat hepatocytes in primary culture, whereas cycloheximide did not. Finally, class I mRNA expression was induced in hepatocytes by phorbol myristate acetate and by forskolin. This hyperexpression, as well as that observed with chenodeoxycholic acid, was suppressed by an inhibitor of protein kinase C and protein kinase A.

CONCLUSIONS

Taken together, these results suggest that chenodeoxycholic acid, as interferon, activates protein kinase C and protein kinase A, resulting in the induction of MHC class I expression.

Phosphorylcholine as a unique substrate for human intestinal alkaline phosphatase

1. The enzymatic nature of human liver, bone, placental and intestinal alkaline phosphatases (ALPs) were investigated with phosphorylcholine (PC), phosphorylethanolamine, pyridoxal-5'-phosphate and p-nitrophenylphosphate at a weakly alkaline pH. 2. The apparent Km value of the intestinal ALP with PC was the highest of all ALPs tested. Intestinal ALP hydrolyzes PC the most and has higher affinity for choline as a transphosphorylating acceptor than the other ALPs. In addition, the intestinal ALP activity with PC was most susceptible to Na2HPO4, in the tested ALPs. 3. The present results suggest that PC is a unique substrate for human intestinal ALP, which may be related to the metabolism of PC or choline as part of phosphatidylcholine.

Potentiation of butyrate-induced differentiation in human colon tumor cells by deoxycholate

Human colon adenocarcinoma cells, treated with deoxycholate for 24 h prior to exposure to 1 mM butyrate, exhibited dose-dependent increases in the activities of three markers of colonic differentiation (alkaline phosphatase, lactase and CEA). Treatment with deoxycholate alone, for 24 h or longer, did not increase the secretion of CEA or the activities of either of the brush border-associated enzyme activities. Increases in differentiation markers were found to be bile acid-specific. Pretreatment with either dehydrocholic acid or cholic acid, even at cytotoxic concentrations, led to no significant butyrate-induced increases in brush-border associated hydrolase activities. The addition of a bacterial superoxide dismutase decreased the short-term cytotoxicity of deoxycholate and increased the maturation-potentiating effects of the bile acid in HCT-116 DO cells. The results of these studies demonstrate that bile acids, which are commonly thought to have tumor promoting activities in vivo, may also have physiological effects which serve to limit carcinogenic processes in the human colon by potentiating tumor cell differentiation.

Alterations in bilirubin metabolism during extra- and intrahepatic cholestasis

This study was performed to investigate modifications in the serum bilirubin forms, hepatobiliary enzymes, and some glycoproteic substances in patients during the course of extrahepatic cholestasis (stage A) and following its clinical resolution (stage B). The series consisted of 16 patients: 11 had main bile duct stones; two, benign stenosis of the main bile duct; and three, main bile duct cancer. Cholestasis resolved spontaneously in one case, under endoscopy in two, and following surgery in 13. Five patients with liver cirrhosis and a picture of intrahepatic cholestasis following anesthesia were also investigated. Serum bilirubin forms were measured using van den Bergh's method and the alkaline methanolysis-HPLC procedure; the mono- and di-conjugated forms were considered together in the overall evaluation of the results. The hepatobiliary enzymes (ALP, GGT, and AST) were increased at stage A and significantly decreased at stage B. Similar patterns were observed in total (TB), unconjugated (UB), and conjugated bilirubin (CB) and in the percentage of CB out of TB (% CB). In the majority of patients, % CB at stage B was lower than at stage A, whereas in subjects with a high initial UB value, a different % CB pattern was observed. The direct bilirubin percentage (% DB), on the other hand, had a different pattern, and the variations between stages A and B were not significant. The pathophysiological bilirubin pattern was similar in patients with intrahepatic cholestasis. At stage A, in a number of patients the levels of glycoproteic substances (CA 19-9, TPA and ferritin) were raised, but at stage B they tended to decrease towards the normal range.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrahepatic cholestasis: a review of biochemical-pathological mechanisms

Intrahepatic cholestasis involves impaired excretion of bile via the hepatobiliary system as a consequence of one or more lesions within the liver. In humans, intrahepatic cholestasis most often results as a side-effect of drug therapy and the clinical manifestation of this condition, jaundice, has been estimated to account for hospitalization in 2 to 5% of the cases for the general population and approaches as much as 20% in the elderly. With the aging of the population and the common occurrence of poly-drug therapy in geriatric patients, it is to be expected that jaundice due to drug-induced intrahepatic cholestasis will become even more prevalent, and accordingly the need to understand the basic mechanisms of this disease condition will become more urgent. The list of culprit agents implicated in the induction of intrahepatic cholestasis in humans is continually expanding. These include various steroid hormones, bile acids, drugs and other chemicals. Experimentally, a wide spectrum of agents has been shown to precipitate intrahepatic cholestasis. Over the years, a number of hypotheses on the biochemical and pathological mechanisms of intrahepatic cholestasis has emerged, including the following: impaired sinusoidal membrane function; interference with the distribution and binding of cytoplasmic endogenous carrier proteins; interference with mitochondrial energy supply; defects in the canalicular membrane including altered Na+/K+ -ATP-ase activity; impairment of microfilament and microtubule functions; interference with bile secretion involving bile acid dependent and independent fractions, and altered bile acid metabolism due to "hypoactive hypertrophic smooth endoplasmic reticulum". In partial agreement with the latter hypothesis, our studies indicated that impairment of the endoplasmic reticulum might represent one of the early stages in the development of intrahepatic cholestasis. Various experimental conditions that induce intrahepatic cholestasis to different degrees resulted in an interference of the synthesis of microsomal phospholipids and altered microsomal function. The conditions included the administration of various hepatotoxic compounds or steroids, pregnancy, delayed development of the endoplasmic reticulum in neonates, and dietary methyl donor or choline deficiency. This review reports the biochemical-pathological mechanisms postulated to be involved in the genesis of intrahepatic cholestasis with specific reference to experimental models of drug-induced intrahepatic cholestasis. The important practical implications of cholestasis are also briefly surveyed.

Altered biosynthesis of gangliosides in developing biliary cirrhosis in the rat

The biosynthesis of gangliosides was studied in developing biliary cirrhosis in rats 14, 28, and 42 days after bile duct obstruction. The total content and patterns of gangliosides in livers and sera, and the activity of six hepatic ganglioside synthases in a cell-free system were determined. Up to 7-fold increased synthase activities were strictly correlated in time and extent with increased total contents of gangliosides in liver and serum. In addition, altered patterns of serum gangliosides were observed. The results clearly demonstrate that the liver is the main source of elevated serum gangliosides in biliary cirrhosis in the rat. Increased hepatic biosynthesis and the secretion of gangliosides into the serum appear to be an important pathogenetic event. Alterations of hepatic enzyme activities indicate that GL2 and GM3 synthase regulate total hepatic ganglioside content. However, certain abnormalities in ganglioside patterns which were observed in the liver and sera of cirrhotic animals can not be explained by changes in hepatic enzyme activity. They indicate additional pathobiochemical mechanisms to be involved, e.g., altered hepatocellular processing and/or impaired secretion into bile.

Alkaline phosphatase isoforms in bile and serum and their generation from cells in vitro

Alkaline phosphatase is anchored to cell membranes by a glycosyl-phosphatidylinositol anchor and is present in bile and plasma in various isoforms. The formation of these isoforms depends upon mechanisms of release and subsequent complex formation. Evidence is presented for an enzymatic activity possibly a glycosyl-phosphatidylinositol-specific phospholipase D (GPI-PLD), in serum that releases an isoform incapable of further complex formation, whereas such an activity is absent from bile.

Transient hyperphosphatasaemia in association with acute infection in adults

The causes of raised serum alkaline phosphatase were determined prospectively in a consecutive series of 2884 acute medical admissions. Diagnoses were established by pre-defined clinico-pathological criteria. Two hundred and four patients had hyperphosphatasaemia. Liver and bone disease accounted for only 98 (48%) of the established diagnoses. The diagnosis was not established in 31 (15%). Transient hyperphosphatasaemia occurred in 66 (32.4%) cases. In 25 of these patients (12% of the total) an acute infection was the sole illness identified. In this infected group, the isoenzyme type was predominantly hepatic, although jaundice occurred in only 3 patients. Discriminant analysis revealed that this group was characterized by haematological and biochemical features of an acute phase response. Transient hyperphosphatasaemia is commonly found in acutely ill medical inpatients and is frequently associated with acute extrahepatic infection.

Purification and partial characterization of intestinal-like alkaline phosphatase in rabbit kidney

Two types of alkaline phosphatase (AP) isozymes in rabbit kidney, a major intestinal-like type and a minor tissue-unspecific type, have been identified. The former enzyme was purified from rabbit kidney by immunoaffinity chromatography using monoclonal anti-human intestinal AP antibody. The purified enzyme yielded a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the apparent molecular size of its monomer subunit was found to be 72,000. Three amino acid residues within the first 16 N-terminal amino acid residues were different in purified AP and human intestinal AP. Although the rabbit enzyme possessed some peptide bands identical to those of human adult intestinal AP after Staphylococcus aureus V8 protease digestion, the enzyme did not react with monoclonal antibody against human adult intestinal AP alone, whereas it did react with monoclonal antibody against both human adult and fetal intestinal APs. The affinity of the enzyme for concanavalin A was identical to that of the fetal intestinal AP, but different from that of the adult enzyme. These results indicate that the antigenicity and certain properties of purified rabbit AP are more like those of human fetal intestinal AP or Kasahara isozyme, so-called intestinal-like AP, than like human adult intestinal AP.

Mechanism of gamma-glutamyl transpeptidase release in serum during intrahepatic and extrahepatic cholestasis in the rat: a histochemical, biochemical and molecular approach

The mechanism of the elevation of serum gamma-glutamyl transpeptidase activity in cholestasis is not clear. We therefore analyzed rat gamma-glutamyl transpeptidase activities in liver, bile and serum during intrahepatic cholestasis induced by a single dose of alpha-naphthyl isothiocyanate (20 mg/100 gm body weight) and during extrahepatic cholestasis after bile duct ligation. At days 1 and 2 after alpha-naphthyl isothiocyanate ingestion, we saw a fivefold and a 60-fold increase in serum and bile gamma-glutamyl transpeptidase activities, respectively. These increases were associated with a decrease in hepatic gamma-glutamyl transpeptidase activity and of corresponding mRNA. Simultaneously, necrosis of the biliary epithelium appeared in portal tracts. From day 2 to day 14, gamma-glutamyl transpeptidase activity in bile and serum progressively returned to basal levels; in the liver, cholangiolar proliferation was mild and was associated with moderate elevation of the gamma-glutamyl transpeptidase activity and of its corresponding mRNA. In extrahepatic cholestasis, a 10-fold increase in serum gamma-glutamyl transpeptidase activity was detected between day 0 and day 14. This increase was associated with major cholangiolar proliferation and with a progressive rise in hepatic gamma-glutamyl transpeptidase activity and in specific mRNA; in bile, gamma-glutamyl transpeptidase activity was slightly elevated. In these two models of cholestasis, histochemically detected gamma-glutamyl transpeptidase activity was largely predominant in biliary cells. We found no significant induction of gamma-glutamyl transpeptidase activity in hepatocytes. These results suggest that in these two models of cholestasis, the increase in serum gamma-glutamyl transpeptidase activity is of biliary cell origin and does not originate from hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental changes in the antigenicity and sugar-chain heterogeneity of rabbit alkaline phosphatases

1. Rabbit alkaline phosphatases (APs) clearly fused with the anti-human AP antibodies. In particular, fetal liver and kidney APs reacted slightly less with the anti-intestinal AP antibody as did adult enzymes, suggesting that intestinal AP-like isozyme is expressed at earlier stages of gestation in rabbit liver and kidney. 2. Immunohistochemical data indicated that intestinal AP-like isozyme in the kidney was mainly localized in the distal convoluted tubules and slightly in the proximal straight tubules, whereas liver/bone/kidney AP-like enzyme was found more in the glomeruli and interstitial capillary walls as a major component. 3. The sugar-chain heterogeneity of adult and fetal rabbit APs displayed organ-specificity as did of rat and human APs. Moreover, in fetal development, the expression of high-mannose type or hybrid type sugar chains precedes the expression of complex type sugar chains in fetal development.

Extrahepatic obstructive cholestasis reverses the bile salt secretory polarity of rat hepatocytes

To elucidate the consequences of extrahepatic cholestasis on the structure and function of hepatocytes, we studied the effects of bile duct ligation on the turnover, surface distribution, and functional activity of the canalicular 100-kD bile salt transport protein (cBSTP). Basolateral (blLPM) and canalicular (cLPM) liver plasma membrane vesicles were purified to the same degree from normal and cholestatic rat livers and the membrane bound cBSTP identified and quantitated using polyclonal anti-cBSTP antibodies. Cholestasis of 50 h resulted in an increased release of cBSTP into bile, thereby decreasing its in vivo half-life from 65 to 25 h. Furthermore, a significant portion of cBSTP accumulated at the basolateral surface and in intracellular vesicles of cholestatic hepatocytes. This redistribution of cBSTP was functionally paralleled by decreased and increased electrogenic taurocholate anion transport in cLPM and blLPM vesicles, respectively. These results demonstrate that biliary obstruction causes a reversal of the bile salt secretory polarity of rat hepatocytes. The resulting increase in basolateral (sinusoidal) bile salt efflux might protect hepatocytes from too high an accumulation of toxic bile salts within the cell interior.

The source of serum alkaline phosphatases in liver-tumour-bearing rats

Patients with hepatic tumours have increased serum activities of alkaline phosphatases. In order to clarify the origin of the increased enzyme activity, two experimental models of rat liver carcinogenesis were studied. In one model, the resistant hepatocyte model, the process was initiated by diethylnitrosamine (DEN, 200 mg/kg), and preneoplastic liver nodules were selected for by 2 weeks of 2-acetylaminofluorene (2-AAF, 0.02%) feeding and partial hepatectomy (PH). High activities of serum alkaline phosphatases were found in these rapidly growing nodules harvested at the peak time of nodular mass expansion. In the other model in which nodules were induced with long-term intermittent feeding of a diet containing 0.05% 2-AAF and harvested in a late stage with a low increase of nodular liver cell mass, no such increase in serum alkaline phosphatase activity was found. A similar difference was also noted when measuring the activities of the enzyme in the nodular tissue. Thus the first model showed high activities of the enzyme in the nodular tissue, while the second model had similar activities to those of the control animals. The serum levels reflected the nodular enzyme activity in both models. The tissue surrounding the nodules did not show increased enzyme activity. No difference was noted in the serum or tissue activity of transaminases. In both models the liver nodules occupied 30-50% of the liver volume. The experimental models were selected to emphasize the importance of the rate of intrahepatic mass expansion for the levels of serum alkaline phosphatase activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat ileal alkaline phosphatase activity and secretion is stimulated by alterations in calcium metabolism

The mechanism of calmodulin-stimulated alkaline phosphatase activity was studied in the rat. In calmodulin-treated rats (2.5 micrograms/animal, intraperitoneally) alkaline phosphatase (ALP) activity was elevated 11-fold in the ileum, 1.5-fold in the duodenum and calvarium, 3-fold in serum, and not at all in liver. The elevated ALP activity was prevented by prior treatment with flunarizine, a calcium channel blocker, and by W-7, a calmodulin antagonist. cAMP content in ileum paralleled the timing and changes in ALP activity, but was not elevated in the duodenum or calvarium. Calcium ionophore A23187 and calcitonin treatment also increased ileal, duodenal, and calvarial ALP activity, but by less than the response to calmodulin. All of these treatments caused a 2-fold elevation in serum 1,25-dihydroxyvitamin D-3 (1,25(OH)2D3) levels. Pretreatment of the animals with parathyroid hormone prevented the rise of both ALP activity and of 1,25(OH)2D3. Administration of 1,25(OH)2D3 alone stimulated a different pattern of increased ALP activity, greater in duodenum than ileum. The uptake of 45Ca by calmodulin was also elevated in ileum and calvarium. These data suggest that shifts in calcium movement, perhaps mediated by vitamin D, can alter ALP activity, and may provide a mechanism for rapid control of the secretion of this enzyme.

High hepatic gamma-glutamyltransferase (gamma-GT) activity with normal serum gamma-GT in children with progressive idiopathic cholestasis

gamma-Glutamyl transferase (gamma-GT) was assayed in the serum and liver biopsies of children affected with either progressive idiopathic cholestasis (PIC, Byler's disease), or other types of cholestatic (biliary atresia, cholestasis of various origins) and non-cholestatic diseases. The mean liver gamma-GT activity was increased significantly only in PIC and biliary atresia. In contrast, the serum gamma-GT activity, raised in children with evident damage to the main bile ducts or to the interlobular bile ducts, was normal in children with PIC. Although the mechanism for such a discrepancy between high liver and normal serum gamma-GT activities in PIC is still speculative, this peculiarity could prove to be of use in leading to a better understanding of the disease.

Clinical use of serum enzymes in liver disease

Some of the many enzymes found in hepatocytes can be measured in the serum and are used as tests of liver function. We now review the current knowledge of their physiology and pathophysiology and outline their clinical usefulness. We divide them into two categories: enzymes that primarily reflect cholestasis, such as the alkaline phosphatase, the 5'-nucleotidase, and the gamma-glutamyl transpeptidase, and those that primarily reflect hepatocellular necrosis, such as the aminotransferases. We also briefly discuss several enzymes of more limited usefulness.

Primary sclerosing cholangitis with normal serum alkaline phosphatase activity

We report 12 cases of primary sclerosing cholangitis (confirmed by cholangiography) in which the serum alkaline phosphatase activity was normal. The enzyme activity remained normal during follow-up in 7 cases and fluctuated in 5 cases (it returned to normal in 4). The presence of advanced histologic stage (fibrosis/cirrhosis) with marked cholangiographic changes in 4 patients establishes that cirrhotic-stage primary sclerosing cholangitis can occur without a concomitant increase in serum alkaline phosphatase activity. Therefore, primary sclerosing cholangitis may exist in an occult state without symptoms or increase in serum alkaline phosphatase activity. Our findings suggest that primary sclerosing cholangitis may be more prevalent than realized, especially in patients who have inflammatory bowel disease. A normal value for serum alkaline phosphatase activity should not preclude further investigation for primary sclerosing cholangitis in patients with inflammatory bowel disease when symptoms or signs suggest liver disease.

Partial characterization of human ileal alkaline phosphatase: differences between human ileal and duodenal enzymes

Properties of human ileal and duodenal alkaline phosphatase (ALP) were compared. The pH optimum, Km values, heat stability, inhibition of activity by amino acids, and antigenicity of ileal and duodenal ALPs were similar. Affinity for DEAE and Tyraminyl derivatives/Sepharose chromatographies, substrate specificity, molecular mass, isoelectric point, and sugar chain structure differed, suggesting two forms of intestinal enzyme. The N-terminal amino acid sequence, or peptide mapping or both suggest that the two major intestinal ALPs are identical, but the minor ALP may be differed from the sequence of major one.