Frequency of anterolateral ligament tears and ramp lesions in patients with anterior cruciate ligament tears and associated injuries indicative for these lesions-a retrospective MRI analysis

OBJECTIVES

To assess the frequency of anterolateral ligament (ALL) tears and ramp lesions (RL) detected with MRI in patients with anterior cruciate ligament (ACL) tears and to describe associated injuries indicative for these lesions.

METHODS

In this retrospective study, 164 patients with surgically verified ACL tears were included. Preoperative MRI scans were reviewed for ALL tears and different types of RL. All coexisting meniscal tears, tears of the medial (MCL) and lateral collateral band (LCL), and posterior-medial tibial bone marrow edema (BME) were recorded. The frequency of ALL tears and RL was assessed and coexisting injuries were correlated using Pearson's chi-square test. A p < 0.05 was defined as statistically significant. In cases of multiple testing, Bonferroni's correction was applied.

RESULTS

ALL tears and RL combined were detected in 28 patients (17.1%), ALL tears in 48 patients (29.3%), and RL in 54 patients (32.9%) which were significantly associated to each other. ALL tears were significantly associated with tears of the posterior horn of the lateral meniscus (PHLM), BME, and with tears of the LCL and MCL. RL were significantly associated with tears of the posterior horn of the medial (PHMM) and PHLM, with BME, and with tears of the LCL.

CONCLUSIONS

ACL tears are associated with RL or ALL tears in about one-third of cases and with both lesions combined in about one-fifth of cases. ALL tears and RL are significantly associated with additional posttraumatic injuries, which can thus be indicative of these lesions.

KEY POINTS

• ACL tears were associated with ramp lesions or ALL tears in about one-third of the cases. • Ramp lesions and ALL tears were significantly associated with each other, tear in the PHLM, tear in the LCL, and BME. • ALL tears were more frequently associated with instable classified ramp lesion type 4b and type 5.

Field study on bovine paratuberculosis using real-time PCR and liquid culture for testing environmental and individual fecal samples implemented in dairy cow management

Bovine paratuberculosis (Johne's disease) is a bacterial, chronic, and wasting intestinal disease caused by Mycobacterium avium ssp. paratuberculosis (MAP). Johne's disease causes severe losses in dairy farm productivity and is also suspected to be a potential trigger for Crohn's disease in humans. The fecal-oral infection of MAP to neonates is recognized as an important within-herd transmission route. Our objective was to recommend diagnostic methods for herds with suspected paratuberculosis requiring fast results, as well as for herds with breeding programs or others that aim at being nonsuspected of paratuberculosis infection. We determined a period of 8 wk from sampling to diagnostic findings suitable for testing of cows during the dry period. We therefore tested environmental and individual fecal samples with one rapid and one highly sensitive diagnostic method. Environmental samples (boot swabs) were taken as a first step in 3 herds and tested using a DNA extraction protocol for feces and subsequent real-time PCR (referred to as fecal PCR). Additionally, cultivation in liquid medium for 6 wk was performed and verified with real-time PCR (referred to as liquid culture). Automation of DNA extraction based on magnetic beads and the PCR setup was performed with pipetting robots. As a result, we successfully detected MAP in boot swabs of all herds by both methods. In a second step, 245 individual fecal samples from the 3 herds were examined using also fecal PCR and liquid culture. The results obtained by fecal PCR were compared with detection of MAP using cultivation in liquid medium for 6 wk. Testing individual cows, we identified MAP-specific DNA in 53 fecal samples using the liquid culture. Using fecal PCR, we revealed 43 positive samples of which 39 also tested positive in the liquid culture, revealing MAP-positive cows in all 3 herds. The fecal PCR procedure allows rapid detection of MAP-specific DNA with 74% of the sensitivity of liquid culture. For the purpose of testing with maximal sensitivity, cultivation in liquid medium is recommended. Cultivation of MAP in liquid medium M7H9C means a significant time gain in comparison to cultivation on solid media, which requires twice as much time. Thus, this testing fits within the 6- to 8-wk dry period of gravid cows and provides test results before calving, a prerequisite to prevent fecal-oral transmission to newborn calves.

Beneficial effect of the insulin sensitizer (HSP inducer) BGP-15 on olanzapine-induced metabolic disorders

Olanzapine is a widely used atypical antipsychotic, with well known metabolic side effects such as weight gain, insulin resistance and blood glucose abnormalities. It has been previously shown in a phase II clinical trial that BGP-15, an amidoxim derivative has insulin-sensitizing effects. The aim of this study was to investigate the efficacy of BGP-15 for the treatment of olanzapine-induced metabolic side effects, in healthy volunteers. Thirty-seven (37) subjects (ages 18-55 years) with normal glucose metabolism were randomly assigned to 17 days of once-daily treatment with 400mg of BGP-15 or placebo and 5mg of olanzapine for 3 days followed by 10mg for 14 days. Total body and muscle tissue glucose utilization was determined by hyperinsulinemic-euglycemic clamp technique. As expected the 17-day olanzapine treatment provoked insulin resistance and body weight gain (p<0.05) in both groups. Administration of BGP-15 significantly reduced olanzapine-induced insulin resistance. The protective effect of BGP-15 on insulin stimulated glucose utilization had the highest magnitude in the values calculated for the muscle tissue (p=0.002). In healthy individuals BGP-15 was safe and well tolerated during the whole study period. It is suggested that BGP-15 can be a successful insulin sensitizer agent to prevent side effects of olanzapine treatment.

Comparative characterization of experimental and calculated lipophilicity and anti-tumour activity of isochromanone derivatives

Compound lipophilicity connected to ADME(T)(a) has great importance in drug development and it has to be evaluated by the generally used drug developmental process. In addition to the importance of lipophilicity in ADMET, recently it has been reported that lipophilicity of small molecules correlates with their antiproliferative activity because of certain specific hydrophobic and lipophilic interactions. Due to the complexity of ADME(T) parameters an efficient and fast method is needed to characterize the many promising candidate lead molecules as a preselection in order not to be rejected from the latter phase of drug development. In the present paper we provide an overview of the importance of lipophilicity of drug candidates for biological action and for ADME(T) and describe a novel approach for drug-likeness characterization of a molecular library using correlation study between lipophilicity and biological activity. Lipophilicity and molecular characteristics have been measured, predicted and optimized for a diverse library from which the best members have been selected to describe their biological, chemical and drug-likeness properties. Molecules were selected from the family of alpha,beta-unsaturated ketones and thorough HPLC characterization for lipophilicity and morphological, antiproliferative and flow cytometric studies were carried out on them. Based on the results 17 member isochromanone library including E and Z geometric isomers were selected for further characterization. In this focused library linear correlation has been found between the calculated and measured lipophilicity and significant parabolic correlation was found between the antiproliferative effect and lipophilicity. Using our efficient and fast method, from a diverse library, we identified an outstandingly effective inhibitor of A431 tumour cell growth via a PARP(a) cleavage dependent apoptosis. In summary the optimized HPLC analyses of lipophilicity combined with the cell-culture assay, introduced above, resulted in the determination of an optimal lipophilicity range. This optimized lipophilicity range should be used in designing novel antiproliferative compounds.

Vitamin C: update on physiology and pharmacology

Although ascorbic acid is an important water-soluble antioxidant and enzyme cofactor in plants and animals, humans and some other species do not synthesize ascorbate due to the lack of the enzyme catalyzing the final step of the biosynthetic pathway, and for them it has become a vitamin. This review focuses on the role of ascorbate in various hydroxylation reactions and in the redox homeostasis of subcellular compartments including mitochondria and endoplasmic reticulum. Recently discovered functions of ascorbate in nucleic acid and histone dealkylation and proteoglycan deglycanation are also summarized. These new findings might delineate a role for ascorbate in the modulation of both pro- and anti-carcinogenic mechanisms. Recent advances and perspectives in therapeutic applications are also reviewed. On the basis of new and earlier observations, the advantages of the lost ability to synthesize ascorbate are pondered. The increasing knowledge of the functions of ascorbate and of its molecular sites of action can mechanistically substantiate a place for ascorbate in the treatment of various diseases.

Improvement of insulin sensitivity by a novel drug, BGP-15, in insulin-resistant patients: a proof of concept randomized double-blind clinical trial

The efficacy and safety of the new drug, BGP-15, were compared with placebo in insulin-resistant patients in a 28-day dose-ranging study. Forty-seven nondiabetic patients with impaired glucose tolerance were randomly assigned to 4 weeks of treatment with 200 or 400 mg of BGP-15 or placebo. Insulin resistance was determined by hyperinsulinemic euglycemic clamp technique and homeostasis model assessment method, and beta-cell function was measured by intravenous glucose tolerance test. Each BGP-15 dose significantly increased whole body insulin sensitivity (M-1, p=0.032), total body glucose utilization (M-2, p=0.035), muscle tissue glucose utilization (M-3, p=0.040), and fat-free body mass glucose utilization (M-4, p=0.038) compared to baseline and placebo. No adverse drug effects were observed during treatment. BGP-15 at 200 or 400 mg significantly improved insulin sensitivity in insulin-resistant, nondiabetic patients during treatment compared to placebo and was safe and well-tolerated. This was the first clinical study demonstrating the insulin-sensitizing effect of a molecule, which is considered as a co-inducer of heat shock proteins.

Opposite effect of linearly polarized light on biosynthesis of interleukin-6 in a human B lymphoid cell line and peripheral human monocytes

The effects of linearly polarized light (LPL) and diffuse light (DL) on the in vitro interleukin-6 (IL-6) production in a human B lymphoma cell line (BMNH) and peripheral monocytes of healthy volunteers were compared. Our data show that there was a significant increase of IL-6 and IgM production in BMNH after exposure to LPL. The increase in IgM secretion was a consequence of its autocrine regulation by IL-6, since in the presence of anti-IL-6 and anti-IL-6 receptor antibodies the LPL-induced IgM secretion was abolished. In contrast to the stimulatory effect on B cells, exposure of human mononuclear phagocytes to LPL markedly reduced the production of IL-6 induced by subsequent stimulation of cells with bacterial endotoxin (LPS). The inhibition as most pronounced when suboptimal doses of LPS were applied. Under identical experimental conditions, DL had no effect on the IL-6 and IgM production of either B cells or monocytes.

The regulation of the induction of vascular endothelial growth factor at the onset of diabetes in spontaneously diabetic rats

Early induction of VEGF was studied in liver, kidney and lung of spontaneously diabetic rats. Western blot analysis, northern hybridization were applied to show the expression of VEGF in different organs. Radiolabelled hypoxia responsive element (HRE) and cAMP responsive element (CRE) oligonucleotides were assayed by electrophoretic mobility shift (EMSA) or supershift using anti ARNT and anti CREB-1 monoclonal antibodies. An increase in VEGF expression at the level of protein and mRNA was demonstrated at the beginning of the disease. EMSAs showed: a.) a binding of HIF-1 to HRE and/or CRE, b.) in the same time the binding of CREB- I was detected to both HRE and/or CRE sequences in the liver, kidney and lung of diabetic animals. Based on these in vivo observations it is supposed that HRE and CRE through the interaction between HIF-1 and CREB-1 are equally involved in the regulation of VEGF expression at the onset of diabetes.

Ryanodine receptor channel-dependent glutathione transport in the sarcoplasmic reticulum of skeletal muscle

We found that glutathione transport across endo/sarcoplasmic reticulum membranes correlates with the abundance of ryanodine receptor type 1 (RyR1). The transport was the fastest in muscle terminal cisternae, fast in muscle microsomes and slow in liver, heart, and brain microsomes. Glutathione influx could be inhibited by RyR1 blockers and the inhibitory effect was counteracted by RyR1 agonists. The effect of blockers was specific to glutathione, as the transport of other small molecules was not hindered. Therefore, the glutathione transport activity seems to be associated with RyR1 in sarcoplasmic reticulum.

Role of Vitamin E in Ascorbate-Dependent Protein Thiol Oxidation in Rat Liver Endoplasmic Reticulum

Addition of ascorbate or its generation from gulonolactone causes the oxidation of protein thiols and a simultaneous dehydroascorbate formation in rat liver microsomes. The participation of vitamin E in the phenomenon was studied. We measured ascorbate and protein thiol oxidation and lipid peroxidation in vitamin E deficient liver microsomes. Vitamin E deficiency partly uncoupled the two processes: ascorbate oxidation increased, while protein thiol oxidation decreased. These changes were accompanied with an accelerated lipid peroxidation in the vitamin E-deficient microsomes, which indicates the accumulation of reactive oxygen species. All these effects were reduced by the in vitro addition of vitamin E to the deficient microsomes, supporting its direct role in the process. The results demonstrate that vitamin E is a component of the protein thiol oxidizing machinery in the hepatic endoplasmic reticulum transferring electrons from the thiol groups towards oxygen.

Protein-disulfide isomerase- and protein thiol-dependent dehydroascorbate reduction and ascorbate accumulation in the lumen of the endoplasmic reticulum

The transport and intraluminal reduction of dehydroascorbate was investigated in microsomal vesicles from various tissues. The highest rates of transport and intraluminal isotope accumulation (using radiolabeled compound and a rapid filtration technique) were found in hepatic microsomes. These microsomes contain the highest amount of protein-disulfide isomerase, which is known to have a dehydroascorbate reductase activity. The steady-state level of intraluminal isotope accumulation was more than 2-fold higher in hepatic microsomes prepared from spontaneously diabetic BioBreeding/Worcester rats and was very low in fetal hepatic microsomes although the initial rate of transport was not changed. In these microsomes, the amount of protein-disulfide isomerase was similar, but the availability of protein thiols was different and correlated with dehydroascorbate uptake. The increased isotope accumulation was accompanied by a higher rate of dehydroascorbate reduction and increased protein thiol oxidation in microsomes from diabetic animals. The results suggest that both the activity of protein-disulfide isomerase and the availability of protein thiols as reducing equivalents can play a crucial role in the accumulation of ascorbate in the lumen of the endoplasmic reticulum. These findings also support the fact that dehydroascorbate can act as an oxidant in the protein-disulfide isomerase-catalyzed protein disulfide formation.

[Coxiella burnetii infections and infections with bacteria of the genus Chlamydia in dairy cattle]

Comparative studies on the prevalence of infections caused by Coxiella burnetii (C. burnetii) and Chlamydia were carried out with 592 cattle older than 2 years and 234 cattle younger than 2 years. Of these 477 originated from 24 dairy herds with considerable fertility problems (positive herds) and 349 from 14 dairy herds without major fertility problems (control herds). For the direct detection of these pathogens in the genitals capture ELISAs were employed, for the demonstration of antibodies the complement fixation test (CFT). Direct detection of C. burnetii and Chlamydia single as well as mixed infection revealed significant higher values for cattle from positive herds compared with those from the control herds. Animals revealing insemination ratios of > or = 2 showed significantly more frequent excretion of Chlamydia via the genitals and antibodies against C. burnetii than cattle with an insemination ratio of < 2. Investigations of cows which had had an abortion showed no indications of significantly more frequent C. burnetii or chlamydial infections. Inseminated but non-pregnant cows excreted significantly more C. burnetii and Chlamydia than pregnant cows. Clinical signs of endometritis were associated with an enhanced excretion of Chlamydia. Animals younger than 2 years excreted significantly more frequently C. burnetii but not Chlamydia via the genitals than animals older than 2 years. Indirect test showed results vice versa.

Ascorbate oxidation is a prerequisite for its transport into rat liver microsomal vesicles

Oxidation and uptake of ascorbate show similar time courses in rat liver microsomal vesicles: a rapid burst phase is followed by a slower process. Inhibitors of ascorbate oxidation (proadifen, econazole or quercetin) also effectively decreased the uptake of ascorbate. The results show that dehydroascorbate is the transport form of ascorbate at the membrane of the endoplasmic reticulum.

Transcriptional induction of bilirubin UDP-glucuronosyltransrase by ethanol in rat liver

Several drug-metabolizing enzymes including bilirubin UDP-glucuronosyltransferase (UGT1A1) are influenced by long-term ethanol consumption. In the present study, the activity and expression of UGT1A1 were investigated in livers of ethanol-treated rats. Animals were treated daily for 15 days with ethanol or isocaloric amount of glucose solution by gastric intubation. Microsomes and total RNA were prepared from the liver of rats and analyzed by Western blot and Northern hybridization using UGT1A1 specific antibody and cDNA probe. Microsomal bilirubin UGT activity was also measured. The elevation of UGT1A1 mRNA was observed in the liver of ethanol consumer animals with the simultaneous increase in microsomal UGT1A1 protein leading to stimulated bilirubin glucuronidation both in vivo and in microsomal vesicles. These results arise the possibility of the transcriptional induction and/or the mRNA stabilization by ethanol consumption, which can be caused by ethanol itself or the metabolic changes due to the treatment.

Beta-glucuronidase latency in isolated murine hepatocytes

The physiological function of microsomal beta-glucuronidase is unclear. Substrates may be either glucuronides produced in the lumen of endoplasmic reticulum (ER) or those taken up by hepatocytes. In the latter case, efficient inward transport of glucuronides at the plasma membrane and the ER membrane would be required. Therefore, the potential role of beta-glucuronidase in ER was investigated. Isolated mouse hepatocytes and mouse and rat liver microsomal vesicles were used in the experiments. Selective permeabilization of the plasma membrane of isolated hepatocytes with saponin or digitonin resulted in an almost 4-fold elevation in the rate of beta-nitrophenol glucuronide hydrolysis, while the permeabilization of plasma membrane plus ER membrane by Triton X-100 caused a further 2-fold elevation. In microsomal vesicles, the p-nitrophenol glucuronide or phenolphthalein glucuronide beta-glucuronidase activity showed about 50% latency as revealed by alamethicin or Triton X-100 treatment. A light-scattering study indicated that the microsomes are relatively impermeable to both glucuronides and to glucuronate. On the basis of our results, the role of liver microsomal beta-glucuronidase in the deconjugation of glucuronides taken up by the liver seems unlikely. Hydrolysis of the glucuronides produced in the ER lumen may play a role in substrate supply for ascorbate synthesis or in "proofreading" of glucuronidation.

Different induction of gulonolactone oxidase in aromatic hydrocarbon-responsive or -unresponsive mouse strains

The role of aromatic hydrocarbon receptor (AhR)-mediated signal transduction pathways was investigated in the regulation of ascorbate synthesis by using Ah-responsive and Ah-unresponsive mouse strains. In vivo 3-methylcholanthrene treatment increased hepatic and plasma ascorbate concentrations only in the Ah-responsive strain. The mRNA level of gulonolactone oxidase and the microsomal ascorbate production from p-nitrophenyl glucuronide, D-glucuronic acid or gulonolactone in the liver of Ah-responsive and Ah-unresponsive mice were compared. In Ah-responsive mice, these parameters were higher originally, and they further increased upon in vivo addition of 3-methylcholanthrene, while in Ah-unresponsive mice the treatment was not effective. These results suggest that the transcription of gulonolactone oxidase gene is regulated by an Ah receptor-dependent signal transduction pathway.

Ascorbate-mediated electron transfer in protein thiol oxidation in the endoplasmic reticulum

Addition of, or gulonolactone oxidase-dependent in situ generation of, ascorbate provoked the oxidation of protein thiols, which was accompanied by ascorbate consumption in liver microsomal vesicles. The maximal rate of protein thiol oxidation was similar upon gulonolactone, ascorbate or dehydroascorbate addition. Cytochrome P450 inhibitors (econazole, proadifen, quercetin) decreased ascorbate consumption and the gulonolactone or ascorbate-stimulated thiol oxidation. The results demonstrate that the ascorbate/dehydroascorbate redox couple plays an important role in electron transfer from protein thiols to oxygen in the hepatic endoplasmic reticulum, even in gulonolactone oxidase deficient species.

Induction and peroxisomal appearance of gulonolactone oxidase upon clofibrate treatment in mouse liver

Various antihyperlipemic peroxisome proliferators are known to be carcinogenic in rodents but not in human, other primates and guinea pig, which species lost their ability to synthesize ascorbate due to mutations in the gulonolactone oxidase gene. Ascorbate synthesis is accompanied by H2O2 production, consequently its induction can be potentially harmful; therefore, the in vivo effect of the peroxisome proliferator clofibrate was investigated on gulonolactone oxidase expression in mouse liver. Liver weights and peroxisomal protein contents were increased upon clofibrate treatment. Elevated plasma ascorbate concentrations were found in clofibrate-treated mice due to the higher microsomal gulonolactone oxidase activities. Remarkable gulonolactone oxidase activity appeared in the peroxisomal fraction upon the treatment. Increased activity of the enzyme was associated with an elevation of its mRNA level. According to the present results the evolutionary loss of gulonolactone oxidase may contribute to the explanation of the missing carcinogenic effect of peroxisome proliferators in humans.

Preferential transport of glutathione versus glutathione disulfide in rat liver microsomal vesicles

A bi-directional, saturable transport of glutathione (GSH) was found in rat liver microsomal vesicles. GSH transport could be inhibited by the anion transport blockers flufenamic acid and 4, 4'-diisothiocyanostilbene-2,2'-disulfonic acid. A part of GSH taken up by the vesicles was metabolized to glutathione disulfide (GSSG) in the lumen. Microsomal membrane was virtually nonpermeable toward GSSG; accordingly, GSSG generated in the microsomal lumen could hardly exit. Therefore, GSH transport, contrary to previous assumptions, is preferred in the endoplasmic reticulum, and GSSG entrapped and accumulated in the lumen creates the oxidized state of its redox buffer.

Conformational change of the catalytic subunit of glucose-6-phosphatase in rat liver during the fetal-to-neonatal transition

The glucose-6-phosphatase system was investigated in fetal rat liver microsomal vesicles. Several observations indicate that the orientation of the catalytic subunit is different in the fetal liver in comparison with the adult form: (i) the phosphohydrolase activity was not latent using glucose-6-phosphate as substrate, and in the case of other phosphoesters it was less latent; (ii) the intravesicular accumulation of glucose upon glucose-6-phosphate hydrolysis was lower; (iii) the size of the intravesicular glucose-6-phosphate pool was independent of the glucose-6-phosphatase activities; (iv) antibody against the loop containing the proposed catalytic site of the enzyme inhibited the phosphohydrolase activity in fetal but not in adult rat liver microsomes. Glucose-6-phosphate, phosphate, and glucose uptake could be detected by both light scattering and/or rapid filtration method in fetal liver microsomes; however, the intravesicular glucose-6-phosphate and glucose accessible spaces were proportionally smaller than in adult rat liver microsomes. These data demonstrate that the components of the glucose-6-phosphatase system are already present, although to a lower extent, in fetal liver, but they are functionally uncoupled by the extravesicular orientation of the catalytic subunit.

Molecular basis of bilirubin UDP-glucuronosyltransferase induction in spontaneously diabetic rats, acetone-treated rats and starved rats

The co-ordinated induction of several hepatic drug-metabolizing enzymes is a common feature in the regulation of drug biotransformation under normal and pathological conditions. In the present study the activity and expression of bilirubin UDP-glucuronosyltransferase (UGT1A1) were investigated in livers of BioBreeding/Worcester diabetic, fasted and acetone-treated rats. Bilirubin glucuronidation was stimulated by all three treatments; this was correlated with an increase in the UGT1A1 protein concentration in hepatic microsomes. Transcriptional induction of UGT1A1 was also observed in diabetes and starvation but not with acetone treatment, which apparently caused translational stabilization of the enzyme protein. The hormonal/metabolic alterations in diabetes and starvation might be a model for postnatal development. The sudden interruption of maternal glucose supply signals the enhanced expression of UGT1A1, giving a novel explanation for the physiological induction of bilirubin glucuronidation in newborn infants.

Prostaglandin-independent stimulation of interleukin-6 production by fibrinogen degradation product D in perfused murine liver

Bacterial endotoxin (LPS) and fibrinogen degradation product D (FDP-D) are both potent stimulators of interleukin-6 (IL-6) production in liver, however, there are differences in their metabolic effects. The aim of the present study was to compare the role of prostaglandins in the enhancement of IL-6 production by LPS or FDP-D in perfused mouse livers. Indomethacin inhibited the effect of LPS significantly but was ineffective in the case of FDP-D. Accordingly, production of prostaglandins D2 and E2 was not elevated following the addition of FDP-D, while their formation was increased several fold by LPS. At the same time interleukin-1 (IL-1) production in perfused liver rose markedly upon the addition of FDP-D. It is suggested that prostaglandins are not involved in the effects of FDP-D on the liver. The stimulatory effect of FDP-P on IL-6 production might be the consequence of elevated IL-1 levels.

Gulonolactone oxidase activity-dependent intravesicular glutathione oxidation in rat liver microsomes

The orientation of gulonolactone oxidase activity was investigated in rat liver microsomes. Ascorbate formation upon gulonolactone addition resulted in higher intravesicular than extravesicular ascorbate concentrations in native microsomal vesicles. The intraluminal ascorbate accumulation could be prevented or the accumulated ascorbate could be released by permeabilising the vesicles with the pore-forming alamethicin. The formation of the other product of the enzyme, hydrogen peroxide caused the preferential oxidation of intraluminal glutathione in glutathione-loaded microsomes. In conclusion, these results suggest that the orientation of the active site of gulonolactone oxidase is intraluminal and/or the enzyme releases its products towards the lumen of the endoplasmic reticulum.

Dehydroascorbate and ascorbate transport in rat liver microsomal vesicles

Ascorbate and dehydroascorbate transport was investigated in rat liver microsomal vesicles using radiolabeled compounds and a rapid filtration method. The uptake of both compounds was time- and temperature-dependent, and saturable. Ascorbate uptake did not reach complete equilibrium, it had low affinity and high capacity. Ascorbate influx could not be inhibited by glucose, dehydroascorbate, or glucose transport inhibitors (phloretin, cytochalasin B) but it was reduced by the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and by the alkylating agent N-ethylmaleimide. Ascorbate uptake could be stimulated by ferric iron and could be diminished by reducing agents (dithiothreitol, reduced glutathione). In contrast, dehydroascorbate uptake exceeded the level of passive equilibrium, it had high affinity and low capacity. Glucose cis inhibited and trans stimulated the uptake. Glucose transport inhibitors were also effective. The presence of intravesicular reducing compounds increased, while extravesicular reducing environment decreased dehydroascorbate influx. Our results suggest that dehydroascorbate transport is preferred in hepatic endoplasmic reticulum and it is mediated by a GLUT-type transporter. The intravesicular reduction of dehydroascorbate leads to the accumulation of ascorbate and contributes to the low intraluminal reduced/oxidized glutathione ratio.

Regulation of glucuronidation by glutathione redox state through the alteration of UDP-glucose supply originating from glycogen metabolism

The effect of altered redox state of glutathione was investigated on p-nitrophenol glucuronidation in isolated mouse hepatocytes. Decrease of GSH/GSSG ratio provoked by various agents caused increased glucuronidation which was accompanied by stimulated glycogenolysis and elevated UDP-glucose content. The stimulation of glycogenolysis and glucuronidation by glutathione consumption could be prevented by the reduction of oxidized glutathione with dithiothreitol and by the glycogenolysis inhibitor fructose. In permeabilized hepatocytes glycogen metabolism, bypassed by the addition of UDP-glucose, stimulated glucuronidation which was insensitive to glutathione depletion. In liver microsomes either UDP-glucuronosyltransferase activity or UDP-glucuronic acid transport was not influenced by GSH/GSSG ratio. These results suggest that alteration of the GSH/GSSG ratio regulates glucuronidation by affecting enzymes of the glycogen metabolism via the modification of UDP-glucuronate supply.

Ascorbate as a substrate for glycolysis or gluconeogenesis: evidence for an interorgan ascorbate cycle

Ascorbate catabolism was investigated in murine and human cells unable to synthesize ascorbate due to the missing gulonolactone oxidase activity. In HepG2 cells the addition of ascorbate or dehydroascorbate resulted in high glucose production, while human erythrocytes, MCF7 cells and the cellular elements of the murine blood were able to metabolize ascorbate or dehydroascorbate to lactate. The oxidative agent menadione stimulated, while the transketolase inhibitor oxythiamine inhibited, the metabolism of dehydroascorbate in each of these three cell types. Our results suggest that ascorbate breakdown through the pentose phosphate pathway can reach the glycolytic/gluconeogenic route in different cells. In ascorbate synthesizing species the ascorbate-lactate route in peripheral cells may form a catabolic branch of an interorgan ascorbate cycle, where hepatocytes are responsible for ascorbate synthesis. The catabolic part of this cycle using exogenous ascorbate could be demonstrated even in humans cells.

Ascorbate metabolism and its regulation in animals

This article provides a comprehensive review on ascorbate metabolism in animal cells, especially in hepatocytes. The authors deal with the synthesis and the breakdown of ascorbate as a part of the antioxidant and carbohydrate metabolism. Hepatocellular and interorgan cycles with the participation of ascorbate are proposed, based on experiments with murine and human cells; reactions of hexuronic acid pathway, non-oxidative branch of the pentose phosphate cycle, glycolysis and gluconeogenesis are involved. Besides the well-known redox coupling between the two major water-soluble antioxidants (glutathione and ascorbate), their metabolic links have been also outlined. Glycogenolysis as a major source of UDP-glucuronic acid determines the rate of hexuronic acid pathway leading to ascorbate synthesis. Glycogenolysis is regulated by oxidized and reduced glutathione; therefore, glycogen, ascorbate and glutathione metabolism are related to each other. Hydrogen peroxide formation, due to the activity of gulonolactone oxidase catalyzing the last step of ascorbate synthesis, also affects the antioxidant status in hepatocytes. Based on new observations a complex metabolic regulation is supposed. Its element might be present also in humans who lost gulonolactone oxidase but they need and metabolize ascorbate. Finally, the obvious disadvantages and the possible advantages of the lost ascorbate synthesizing ability in humans are considered.

Inhibition of glucuronidation by an acyl-CoA-mediated indirect mechanism

The mechanism of the inhibition of glucuronidation by long-chain fatty acyl-CoAs was studied in rat liver microsomal membranes and in isolated hepatocytes. Palmitoyl- and oleoyl-CoA did not affect p-nitrophenol UDP-glucuronosyltransferase activity in native microsomes but were inhibitory in permeabilised vesicles. The extent of inhibition was dependent on the effectiveness of permeabilisation and was constant in time in fully permeabilised microsomes. Fatty acyl-CoAs mobilised calcium from calcium-loaded microsomes. Elevation of the intracellular acyl-CoA level by the addition of palmitate or oleate inhibited the glucuronidation of p-nitrophenol in isolated hepatocytes. This effect could be abolished by emptying the intracellular calcium stores. Therefore, it is concluded that fatty acyl-CoAs inhibit glucuronidation indirectly, presumably via calcium mobilisation.

Glucose formation from methylglyoxal in hepatocytes from streptozotocin-induced diabetic mice: the effect of insulin

Acetol and methylglyoxal are intermediates of the intrahepatic metabolism of acetone leading to pyruvate formation. In hepatocytes prepared from fasted streptozotocin-induced diabetic mice, net glucose production could be measured from methylglyoxal but not from acetone or acetol. Insulin increased glucose formation from methylglyoxal in a concentration-dependent manner, whereas it was ineffective when pyruvate was used as substrate. Drug oxidation, as evidenced by p-aminophenol formation from aniline, was enhanced by methylglyoxal, and insulin proved to be stimulatory in this case as well. It is concluded that insulin might be involved in the regulation of glucose formation from methylglyoxal, but its mode of action is not yet clear.

Gluconeogenesis from ascorbic acid: ascorbate recycling in isolated murine hepatocytes

Ascorbic acid synthesis and breakdown were investigated in isolated hepatocytes prepared from fasted mice. Stimulation of gluconeogenesis by alanine or xylitol led to ascorbate synthesis. On the other hand, ascorbate or dehydroascorbate addition resulted in concentration-dependent glucose production and elevation of the pentose phosphate pathway intermediate xylulose 5-phosphate. Stimulation of ascorbate oxidation and/or the inhibition of dehydroascorbate reduction increased glucose formation. Inhibition of the pentose phosphate pathway decreased glucose production from dehydroascorbate with increased accumulation of xylulose 5-phosphate. These results suggest that ascorbate can be recycled by a novel way involving intermediates of the pentose phosphate pathway, gluconeogenesis and hexuronic acid pathway.

Glutathione depletion induces glycogenolysis dependent ascorbate synthesis in isolated murine hepatocytes

The relationship between glutathione deficiency, glycogen metabolism and ascorbate synthesis was investigated in isolated murine hepatocytes. Glutathione deficiency caused by various agents increased ascorbate synthesis with a stimulation of glycogen breakdown. Increased ascorbate synthesis from UDP-glucose or gulonolactone could not be further affected by glutathione depletion. Fructose prevented the stimulated glycogenolysis and ascorbate synthesis caused by glutathione consumption. Reduction of oxidised glutathione by dithiothreitol decreased the elevated glycogenolysis and ascorbate synthesis in diamide or menadione treated hepatocytes. Our results suggest that a change in GSH/GSSG ratio seems to be a sufficient precondition of altering glycogenolysis and a consequent ascorbate synthesis.

Evidence for an UDP-glucuronic acid/phenol glucuronide antiport in rat liver microsomal vesicles

The transport of glucuronides synthesized in the luminal compartment of the endoplasmic reticulum by UDP-glucuronosyltransferase isoenzymes was studied in rat liver microsomal vesicles. Microsomal vesicles were loaded with p-nitrophenol glucuronide (5 mM), phenolphthalein glucuronide or UDP-glucuronic acid, by a freeze-thawing method. In was shown that: (i) the loading procedure resulted in millimolar intravesicular concentrations of the different loading compounds; (ii) addition of UDP-glucuronic acid (5 mM) to the vesicles released both intravesicular glucuronides within 1 min; (iii) glucuronides stimulated the release of UDP-glucuronic acid from UDP acid-loaded microsomal vesicles; (iv) trans-stimulation of UDP-glucuronic acid entry by loading of microsomal vesicles with p-nitrophenol glucuronide, phenolphthalein glucuronide, UDP-glucuronic acid and UDP-N-acetyl-glucosamine almost completely abolished the latency of UDP-glucuronosyltransferase, although mannose 6-phosphatase latency remained unaltered; (v) the loading compounds by themselves did not stimulate UDP-glucuronosyltransferase activity. This study indicates that glucuronides synthesized in the lumen of endoplasmic reticulum can leave by an antiport, which concurrently transports USP-glucuronic acid into the lumen of the endoplasmic reticulum.

Ascorbate synthesis-dependent glutathione consumption in mouse liver

Ascorbate synthesis causes glutathione consumption in the liver. Addition of gulonolactone resulted in an increase of ascorbate production in isolated murine hepatocytes. At the same time, a decrease in reduced glutathione (GSH) level was observed. In hepatic microsomal membranes, ascorbate synthesis stimulated by gulonolactone caused an almost equimolar consumption of GSH. This effect could be counteracted by the addition of catalase or mercaptosuccinate, indicating the role of hydrogen peroxide formed during ascorbate synthesis in the depletion of GSH. The observed phenomenon may be one of the reasons why the evolutionary loss of ascorbate synthesis could be advantageous.

Endotoxin and fibrinogen degradation product-D have different actions on carbohydrate metabolism: role of Kupffer cells

The effect of endotoxin-derived lipopolysaccharide (LPS) and fibrinogen degradation product D (FDPD) on oxygen consumption and glycogenolysis in the perfused rat liver was investigated. 1. Infusion of LPS (100 micrograms/ml) or FDPD (7 micrograms/ml) caused a rapid stimulation of oxygen uptake by the perfused liver of 10-12 mumol/g/h. 2. LPS also caused a transient increase in glucose and lactate release into the perfusion medium from endogenous glycogen; however, FDPD was without effect. 3. Destruction of Kupffer cells by GdCl3 pretreatment blocked the effects of LPS and FDPD on oxygen uptake and glycogenolysis. Further, LPS and FDPD had no effect on oxygen consumption by isolated hepatocytes. Therefore, it is concluded that Kupffer cells are involved in the increase of hepatic oxygen consumption and carbohydrate release caused by LPS, most likely via release of PGE2 and PGD2. Since FDPD increased oxygen but not carbohydrate release, it is concluded that it acts via stimulating the release of mediators distinct from those released following LPS infusion.

Inhibition of p-nitrophenol glucuronidation by calcium mobilizing hormones

1. Vasopressin and phenylephrine markedly inhibited the glucuronidation of p-nitrophenol in isolated murine hepatocytes. 2. After longer preincubation of hepatocytes in the presence of vasopressin or phenylephrine the rate of conjugation began to return to the control values indicating the reversibility of the inhibition caused by these agents. 3. The inhibitory effect of both agents was dependent on the Ca2+ filled state of the intracellular stores. 4. The inhibition caused by the alpha 1 receptor agonist phenylephrine was receptor mediated because it could be prevented by the addition of alpha 1 antagonist prazosin. 5. The data support the theory that the maintenance of the intralumenal Ca2+ concentration is necessary for the optimal activity of p-nitrophenol UDP-glucuronosyl-transferase.

Enhancement of interleukin-6 production by fibrinogen degradation product D in human peripheral monocytes and perfused murine liver

The effect of fibrinogen degradation products D and E (FDP-D, FDP-E) on IL-6 production in perfused mouse livers and peripheral monocytes is studied. Similarly to bacterial endotoxin FDP-D is highly potent to augment the IL-6 production measured in perfused mouse livers, while FDP-E is not stimulatory. FDP-D but not FDP-E is able to stimulate the in vitro IL-6 production of human peripheral monocytes, as well. Plasmin alone is almost ineffective on IL-6 production both in perfused livers and monocytes. Our findings suggest a direct positive feedback circuit, among fibrinogen, FDP and IL-6.

Increased oxidation and decreased conjugation of drugs in the liver caused by starvation. Altered metabolism of certain aromatic compounds and acetone

Starvation causes several changes in the various processes of biotransformation. The focus of this review is on biotransformation of various aromatic and other compounds whose metabolism is catalyzed in phase I by isozymes belonging to the CYP2E1 gene subfamily, while in phase II phenol-UDPGT or conjugation with GSH play a dominant role. The other ways of conjugation are beyond the scope of this review. The reason why this aspect has been chosen is that the capacity of these reactions is profoundly altered by nutritional conditions. There is a balance between the two phases of biotransformation. Therefore, under standard circumstances in a well-fed state the intermediate formed in the course of phase I is converted to a conjugated compound rapidly, as a result of phase II. However, in starvation the pattern of drug metabolism is altered and the balance between the two phases is changed. This alteration of drug metabolism upon starvation is partly connected to the changes of cofactor supplies due to the metabolic state.

Endotoxin inhibits glucuronidation in the liver. An effect mediated by intercellular communication

Endotoxin [lipopolysaccharide (LPS) 50 micrograms/mL] added to the perfusion medium increased glucose production and inhibited the glucuronidation of p-nitrophenol in perfused mouse liver both in recirculating and non-recirculating systems, while sulfation of p-nitrophenol was unchanged. The effects of endotoxin could be prevented by the addition of cyclooxygenase inhibitors, while PGD2 and PGE2 also caused a decrease in p-nitrophenol glucuronidation in perfused liver. In isolated hepatocytes endotoxin failed to affect p-nitrophenol conjugation, while PGD2 and PGE2 decreased the rate of it. Our results suggest that endotoxin inhibits glucuronidation through an intercellular communication presumably mediated by eicosanoids.

Ascorbic acid synthesis is stimulated by enhanced glycogenolysis in murine liver

Ascorbic acid synthesis was stimulated by glucagon, dibutyryl cyclic AMP, as well as phenylephrine vasopressin or okadaic acid, in hepatocytes prepared from fed mice. However, no such effect was observed in glycogen-depleted cells from starved animals, either in the presence or absence of glucose. The rate of ascorbate synthesis showed close correlation with the glucose release by hepatocytes. In mice the injection of glucagon increased plasma ascorbate concentration fifteenfold, and caused a sixfold elevation of the ascorbate content of the liver. These results show that hepatic ascorbate synthesis is dependent on glycogenolysis, and indicate a regulatory role of ascorbate released by the liver.

Net glucose production from acetone in isolated murine hepatocytes. The effect of different pretreatments of mice

1. To evaluate the condition under which net glucose production from acetone, added as sole substrate, occurs different pretreatments of mice, in combination with starvation, were used; (i) acetone pretreatment (acetone is a known inducer of cytochrome P-450 isozymes involved in this pathway), (ii) fructose pretreatment (to induce NADPH+H+ generating enzymes) or (iii) their combination. 2. There was net glucose formation from acetone only in that case, when the cells were prepared from 48 hr fasted animals pretreated with both acetone and fructose. However, using 2-14C-acetone, incorporation of 14C-carbon into glucose could be detected in all the cases and, at the same time, acetone was without any effect on protein synthesis. 3. The addition of acetone increased gluconeogenesis from alanine in almost all the cases. The only exception from this general rule was that the case, when hepatocytes were prepared from acetone pretreated 48 hr starved mice where, instead of the elevation of glucose formation, a decrease of that was caused by acetone. 4. Acetone decreased 14C-carbon incorporation into glucose from 14C-(U)-alanine added at saturating concentration in hepatocytes prepared from starved mice. 5. Similarly to acetone there was no net glucose formation from acetone either when added alone, however, it enhanced gluconeogenesis from alanine at non-saturating concentrations of the amino acid. 6. Methylglyoxal proved gluconeogenic in all the cases. 7. It is concluded that net glucose formation from acetone as sole substrate occurs only under those conditions which are far from a physiological situation, however, when gluconeogenesis from another substrate takes place, acetone can contribute to net glucose formation in hepatocytes prepared from fasted mice.

Methylglyoxal and cell viability

Methylglyoxal by depleting glutathione stores increased Trypan-blue uptake by the cells incubated in glucose, pyruvate and amino acids free medium. Only a transient fall of glutathione concentration without any effect on cell viability was caused by methylglyoxal when the medium was supplemented with above-mentioned compounds. The role of gamma-glutamyl-transpeptidase is discussed.

Evidence for the intraluminal positioning of p-nitrophenol UDP-glucuronosyltransferase activity in rat liver microsomal vesicles

Addition of p-nitrophenol and UDP-glucuronic acid to rat hepatic microsomes enhanced the MgATP-stimulated Ca2+ sequestration. This stimulatory effect was more explicit in the presence of the activator of glucuronidation, UDP-N-acetylglucosamine. The stimulation of Ca2+ uptake was dependent on the p-nitrophenol concentration and showed a good correlation with the rate of p-nitrophenol glucuronidation. The stimulation of Ca2+ sequestration was probably due to its coaccumulation with the intraluminar Pi originated during glucuronidation. The increase in extravesicular osmolarity due to the addition of UDP-glucuronic acid to microsomes resuspended in an hyposmotic medium caused a rapid and prolonged shrinking as revealed by light-scattering measurements. This indicates a poor permeability of microsomal membrane to UDP-glucuronic acid. The subsequent addition of the pore-forming compound alamethicin resulted in an immediate swelling of vesicles indicating a rapid entry of UDP-glucuronic acid. Alamethicin also caused an about 15-fold increase in p-nitrophenol UDP-glucuronosyltransferase activity. These results support the hypothesis of the intravesicular compartmentation of the microsomal UDP-glucuronosyltransferase catalytic site.

Latency is the major determinant of UDP-glucuronosyltransferase activity in isolated hepatocytes

The glucuronidation of p-nitrophenol was measured in intact, saponin- and alamethicin-treated isolated mouse hepatocytes. In saponin-permeabilized cells the elevation of extrareticular UDP-glucuronic acid concentration enhanced the rate of glucuronidation threefold. When intracellular membranes were also permeabilized by alamethicin, a further tenfold increase in the glucuronidation of p-nitrophenol was present. Parallel measurements of the ER mannose 6-phosphatase activity revealed that saponin selectively permeabilized the plasma membrane, whereas alamethicin permeabilized both plasma membrane and ER membranes. The inhibition of p-nitrophenol glucuronidation by dbcAMP in intact hepatocytes was still present in saponin-treated cells and disappeared in alamethicin-permeabilized hepatocytes. It is suggested that the permeability of the endoplasmic reticulum membrane is a major determinant of glucuronidation not only in microsomes but in isolated hepatocytes as well.

Intraluminal calcium of the liver endoplasmic reticulum stimulates the glucuronidation of p-nitrophenol

The relationship between the intraluminal Ca2+ content of endoplasmic reticulum and the rate of the glucuronidation of p-nitrophenol was investigated in isolated rat hepatocytes. Different agents which decrease the Ca2+ level in the endoplasmic reticulum [calcium ionophores (A23187, ionomycin) or Ca(2+)-ATPase inhibitors(thapsigargin,2,5-di-(t-butyl)-1,4-benzohydroquinone+ ++)] inhibited the conjugation of p-nitrophenol. Depletion of intracellular Ca2+ stores by preincubation of hepatocytes in the absence of free Ca2+ (in the presence of excess EGTA) also decreased the rate of glucuronidation; Ca2+ re-admission to EGTA-treated hepatocytes restored glucuronidation. In intact liver microsomes the p-nitrophenol UDP-glucuronosyl-transferase activity was not modified by varying the external free Ca2+ concentrations within a cytosol-like range. Emptying of the Ca2+ from the lumen of microsomal vesicles by A23187, after MgATP-stimulated Ca2+ sequestration, decreased the glucuronidation of p-nitrophenol. A similar effect was observed in filipin-permeabilized hepatocytes. In native and in detergent-treated microsomes, Ca2+ (1-10 mM) increased the p-nitrophenol UDP-glucuronosyltransferase activity. It is suggested that the physiological concentration of Ca2+ in the lumen of the endoplasmic reticulum is necessary for the optimal activity of p-nitrophenol UDP-glucuronosyltransferase; the depletion of Ca2+ decreases the activity of the enzyme.

Gluconeogenesis from methylglyoxal in isolated murine hepatocytes. Does an alternative pathway exist in which pyruvate is not an intermediate?

1. Gluconeogenesis from alanine can be prevented by the addition of monoiodo acetic acid (an inhibitor of glyceraldehyde 3-phosphate dehydrogenase), while glucose production from methylglyoxal is only partially inhibited by this compound. 2. It is supposed that methylglyoxal can enter gluconeogenic sequence not only at pyruvate.

Accumulation of S-D-lactoylglutathione and transient decrease of glutathione level caused by methylglyoxal load in isolated hepatocytes

Methylglyoxal is converted to D-lactic acid through a conjugation with glutathione and S-D-lactoylglutathione is an intermediate of this pathway. In isolated hepatocytes prepared from fed mice incubated without nutrients (glucose, pyruvate and amino acids) the formation and release of S-D-lactoylglutathione and also a continuous lowering of cellular glutathione were demonstrated upon addition of methylglyoxal (20 mM). Under these incubation conditions, the glutathione content of the cells decreased in the controls. On the other hand, in hepatocytes incubated in a medium supplemented with the above-mentioned compounds an accumulation of S-D-lactoylglutathione and a transient decrease of glutathione were shown after addition of methylglyoxal. Under these experimental circumstances the glutathione content of the cells was preserved. Buthionine sulfoximine--an inhibitor of glutathione synthesis--prevented the restoration of glutathione level in hepatocytes observed in the presence of methylglyoxal; emetine--an inhibitor of protein synthesis--was ineffective. It is suggested that increased methylglyoxal formation may have a role in alterations of glutathione metabolism under conditions when serum acetone is increased and methylglyoxal production from acetone is elevated.

Inhibition of gluconeogenesis, ureogenesis and drug oxidation by redox cycler quinone in isolated mouse hepatocytes

1. The effect of a redox cycler and arylator (menadione) and a pure arylator quinone (benzoquinone) was studied on different NADPH generating and consuming processes in isolated mouse hepatocytes. 2. Menadione inhibited gluconeogenesis from alanine but not from fructose or glycerol. 3. Drug oxidation measured as aniline hydroxylation and aminopyrine N-demethylation could be inhibited by menadione in microsomal membrane and in isolated hepatocytes both from fed or fasted animals. 4. Ureogenesis in isolated hepatocytes from fed mice could not be inhibited even by high concentration of menadione, while in cells from fasted animals menadione was inhibitory at high concentration in the presence of gluconeogenic precursor and at lower concentration in the absence of it. 5. Benzoquinone did not inhibit the above mentioned processes.