Studies on the metabolism of steroids in the foetus. Biosynthesis of 6α-hydroxytestosterone in the human foetal liver

After incubation of testosterone with 105000g microsomes of human foetal liver, 6alpha-hydroxytestosterone was isolated and identified by t.l.c. and g.l.c.-mass spectrometry. This is the first example of 6alpha-hydroxylation of C(19) steroids in the human liver, and the finding is discussed in relation to earlier reports of 6-oxygenated C(19) and C(18) steroids in pregnant women.     

Ketogenesis in isolated rat liver mitochondria. II. Factors affecting the rate of β-oxidation

1. During fatty acid oxidation by rat liver mitochondria, the rate of β-oxidation is dependent on the relative amounts of substrate and mitochondrial protein, on the energy state of the mitochondria, on the chain length and the number of double bonds of the fatty acid and on the concentration of various compounds in the reaction medium (l-carnitine, CoASH, hexokinase, albumin).2. The rate of β-oxidation of long-chain fatty acids decreases when the ratio of albumin over fatty acid is increased. This effect is most marked in the absence of added carnitine.3. Addition of excess hexokinase decreases the rate of β-oxidation in the presence of added carnitine.4. Maximal rates of β-oxidation are observed with octanoate and decanoate (40–60 nmoles acetyl-CoA/min per mg mitochondrial protein at 25 °C).5. Odd-numbered fatty acids are oxidized at a much lower rate than the even-numbered homologues. In a low-energy state propionyl-CoA accumulates; in a high-energy state in the presence of bicarbonate, Krebs-cycle intermediates accumulate.6. l-Carnitine enhances the rate of β-oxidation of all fatty acids except butyrate. The stimulatory effect is most pronounced with odd-numbered and with long-chain fatty acids.7. In the absence of added carnitine the rate of β-oxidation of long-chain fatty acids decreases with the chain length and increases with the number of double bonds. It is suggested that the solubility of the long-chain fatty acids in the aqueous medium is the rate-limiting factor under these conditions.8. In the presence of carnitine and albumin, palmitate, oleate, linoleate and linolenate are all oxidized at about the same rate (25–30 nmoles/min per mg protein at 25 °C).9. Propionyl-CoA is not formed as an intermediate during oxidation of unsaturated fatty acids.     

Ketogenesis in isolated rat liver mitochondria. III. Relationship with the rate of β-oxidation

The synthesis of ketone bodies has been studied as a function of the rate of acetyl-CoA production during the oxidation of different fatty acids and of pyruvate. In the presence of hexokinase plus glucose and a low concentration of malate, the Krebs cycle has a fixed capacity which is independent of the rate of acetyl-CoA supply. When the rate of acetyl-CoA production increases beyond this capacity, acetyl-CoA is converted to the synthesis of acetoacetate. Under all conditions tested the rate of ketogenesis and the ratio of acetyl-CoA over free CoASH were positively correlated.The relevance of our results for the control of ketogenesis in vivo is discussed.     

Immunological detection of the mitochondrial F1-ATPase alpha subunit in the matrix of rat liver peroxisomes. A protein involved in organelle biogenesis?

Rat liver peroxisomes contain in their matrix the alpha-subunit of the mitochondrial F1-ATPase complex. The identification of this protein in liver peroxisomes has been achieved by immunoelectron microscopy and subcellular fractionation. No beta-subunit of the mitochondrial F1-ATPase complex was detected in the peroxisomal fractions obtained in sucrose gradients or in Nycodenz pelletted peroxisomes. The consensus peroxisomal targeting sequence (Ala-Lys-Leu) is found at the carboxy terminus of the mature alpha-subunit from bovine heart and rat liver mitochondria. Due to the dual subcellular localization of the alpha-subunit and to the structural homologies that exist between this protein and molecular chaperones [(1990) Biol. Chem. 265, 7713-7716] it is suggested that the protein should perform another functional role(s) in both organelles, plus to its characteristic involvement in the regulation of mitochondrial ATPase activity.     

Expression in promoter variant of the ERα gene in bos taurus liver

Due to the variant functions that estrogens play in the regulation of reproduction, development of the mammary gland, growth and differentiation of cells, estrogen receptors and their genes are considered as a candidates for the markers of production and functional traits in farm animals, including cattle. In the earliest study, a 2853-bp bovine ER gene 5′-region was PCR amplified and sequenced. Moreover, for the first time, a polymorphism was described within 5′ region of the bovine ERα gene—A/G transition lying upstream at position 2591 from acceptor splice site +85, possibly within its promoter—which could be recognized with RFLP-BglI. In other study we are found second polymorphism—A/G transition at position 1213 from acceptor splice site +85, located in promoter for exon B. We have examined the specific mRNA expression of ERα in various genotypes using real-time RT-PCR. We used four animals from each genotype group—AG, GG for BglI and AA, AG for SnaBI—to analyse liver ERα expression at the level of Real-time PCR. Liver samples were taken from the 16 young Friesian bulls of the different ERα genotypes, slaughtered at the local abattoir. As shown by Real-Time PCR, on the livers of animals with different genotype ERα mRNA for BglI polymorphism we didn’t found variability, but for SnaBI we have found variability between AG and AA genotypes.     

Control of the redox state of the nicotinamide–adenine dinucleotide couple in rat liver cytoplasm

1. A study has been made of the ability of rat liver in vivo to maintain equilibrium in the combined glyceraldehyde 3-phosphate dehydrogenase, 3-phosphoglycerate kinase and lactate dehydrogenase reactions, i.e. in the system: [Formula: see text] Attempts were made to upset equilibrium. The [lactate]/[pyruvate] ratio was rapidly changed by injection of ethanol or crotyl alcohol, and the value of [ATP]/[ADP][HPO(4) (2-)] was rapidly changed by injection of ethionine or carbonyl cyanide p-trifluoromethoxy-phenylhydrazone. 2. The concentrations of the metabolites occurring in the above equation were measured in freeze-clamped liver. 3. Although the injected agents caused large changes in the concentrations of the individual components, near-equilibrium in the system was maintained, as indicated by the fact that the value of [ATP]/[ADP][HPO(4) (2-)], referred to as the phosphorylation state of the adenine nucleotides, measured directly agreed with the value calculated for equilibrium conditions from the above equation. 4. The results are discussed and taken to confirm that the order of magnitude of the value of the redox state of the cytoplasmic NAD couple in rat liver is controlled by the phosphorylation state of the adenine nucleotide system.     

Different physiology of interferon-α/-γ in models of liver regeneration in the rat

Liver regeneration may take place after liver injury through replication of hepatocytes or hepatic progenitor cells called oval cells. Interferons (IFN) are natural cytokines with pleiotrophic effects including antiviral and antiproliferative actions. No data are yet available on the physiology and cellular source of natural IFNs during liver regeneration. To address this issue, we have analyzed the levels and biologic activities of IFN-α/IFN-γ in two models of partial hepatectomy. After 2/3rd partial hepatectomy (PH), hepatic levels of IFN-α and IFN-γ declined transiently in contrast to a transient increase of the IFN-γ serum level. After administration of 2-acetylaminofluorene and partial hepatectomy (AAF/PH model), however, both IFN-α and IFN-γ expression were up-regulated in regenerating livers. Again, the IFN-γ serum level was transiently increased. Whereas hepatic IFN-γ was up-regulated early (day 1–5), but not significantly, in the AAF/PH model, IFN-α was significantly up-regulated at later time points in parallel to the peak of oval cell proliferation (days 7–9). Biological activity of IFN-α was shown by activation of IFN-α-specific signal transduction and induction of IFN-α specific-gene expression. We found a significant infiltration of the liver with inflammatory monocyte-like mononuclear phagocytes (MNP) concomitant to the frequency of oval cells. We localized IFN-α production only in MNPs, but not in oval cells. These events were not observed in normal liver regeneration after standard PH. We conclude that IFN-γ functions as an acute-phase cytokine in both models of liver regeneration and may constitute a systemic component of liver regeneration. IFN-α was increased only in the AAF/PH model, and was associated with proliferation of oval cells. However, oval cells seem not to be the source of IFN-α. Instead, inflammatory MNP infiltrating AAF/PH-treated livers produce IFN-α. These inflammatory MNPs may be involved in the regulation of the oval cell compartment through local expression of cytokines, including IFN-α.     

Role of NKT cells in the digestive system. I. Invariant NKT cells and liver diseases: is there strength in numbers?

Information regarding the functional role of the innate immune T cell, invariant natural killer T (iNKT) cells, in the pathophysiology of liver diseases continues to emerge. Results from animal studies suggest that iNKT cells can have divergent roles by specifically promoting the development of proinflammatory or anti-inflammatory responses in liver diseases. In this themes article, I discuss the critical evidence from animal models that demonstrate a vital role for iNKT cells in the pathophysiology of liver diseases with emphasis on viral, autoimmune, and toxin-induced liver diseases. Furthermore, I discuss the controversial issues (including iNKT cell apoptosis) that typify some of these studies. Finally, I highlight areas that require additional investigation.     

Is there a gloxylate cycle in the liver of the fetal guinea pig?

Studies on the effect of the inhibitor of fatty acid oxidation (+)-octanoylcarnitine on the perfused liver of the 48–51 days fetal guinea pig indicate that the oxidation of endogenous fatty acids is a major source of carbon for the citric acid cycle and for synthesis of hexose. Consistent with this the liver can convert isocitrate to glyoxylate and glyoxylate to malate and may therefore operate a glyoxylate cycle allowing the net production of sugars from acetyl-CoA.     

Investigate of AQP gene expression in the liver of mice after ischemia–reperfusion

Ischemia–reperfusion (IR) injury usually occurs during liver transplantation. Aquaporins (AQPs) are transmembrane channels that facilitate water permeability through cell membranes and are essential for the regulation of water homeostasis. Changes in the AQPs expression have been correlated with several inflammatory diseases. Less is known about AQPs expression in hepatic ischemia reperfusion injury. To clarify the roles of AQPs in IR injury, in this current study we examined the gene expression patterns of AQP1, 8 and 9 in the liver after IR injury. Male balb/c mice were exposed to partial (70%) hepatic ischemia for 65 min and then randomized into five groups of reperfusion [0 h (A), 8 h (B), 1 day (C), 3 days (D), and 7 days (E)]. A surgical group was also selected as the sham group. Serum and liver tissue samples were collected for evaluation of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and liver histopathology. Real time PCR was performed to evaluate the AQPs expression. I/R injury resulted in a significant increase in ALT and AST (p?<?0.05) compared to sham mice in each group. The gene expression of AQPs was significantly increased in the IR group compared with the sham group (p?<?0.05). AQP8 and AQP1 after 8 h (group B) showed the highest gene expression in comparison with other groups, but the highest level of AQP9 gene expression was observed after 1 day (group C). Pathologic changes in the liver after reperfusion were confirmed the IR. In the IR group cytoplasmic vacuolization, inflammatory cell infiltration and focal necrosis were detected. In conclusion, our findings indicated that the damage caused by ischemia–reperfusion in the liver can change the expression of AQP genes, which can interfere with hepatocellular homeostasis and their function. Upregulation of AQP1, 8 and 9 could contribute to the development of hepatocellular swelling after hepatic IR injury.     

Incorporation of cytosol δ-aminolevulinate synthase of rat liver into the mitochondria in vitro

When ¹²⁵I-labeled cytosol δ-aminolevulinate synthase was incubated in suspensions of rat liver mitochondria, the enzyme was incorporated into the mitochondira at the rate that was linear with time and with the [¹²⁵I]enzyme added. Subfractionation of the mitochondria using a digitonin technique revealed that the [¹²⁵I]enzyme was incorporated into the innermembrane-matrix fraction where endogeneous δ-aminolevulinate synthase is located.     

Seasonal variation in the form of iron in the liver of Spitsbergen reindeer: a Mössbauer spectroscopic study

Mössbauer spectra have been obtained from samples of the liver of Spitsbergen reindeer at different times of the year. Most of the iron is in a very similar form to that of the iron storage materials ferritin and haemosiderin. The data reflect the large differences in the amount of iron found in the liver at different times of the year and also indicate that there are only relatively small differences in the chemical and physical form of the iron found in the liver at different times of the year.     

Quantitative analysis of estradiol-17β-induced changes in the ultrastructure of the liver of the male zebrafish,Brachydanio rerio

Summary Hepatocytes of male zebrafish, Brachydanio rerio, were studied by means of light- and electron-microscopy, following a period of maximally 16 days of in-vivo treatment with estradiol-17. The responsiveness of the male hepatocytes to this female sex steroid was investigated by use of morphometric methods. The results of this investigation show that the responsiveness was most obvious between 2 and 16 days, as revealed by an increase in cell size, accompanied by a proliferation of the granular endoplasmic reticulum and the Golgi complex. In addition, accumulations of glycogen granules, which are characteristic of hepatocytes in untreated males, had disappeared and lipid droplets had accumulated. These experimentally induced changes in the morphology of the male hepatocyte closely resemble those described for the female hepatocyte during the sexual cycle. It is concluded that the hepatocytes of male zebrafish can be stimulated by estradiol-17 to produce vitellogenin and that in female zebrafish this steroid is a key sex hormone responsible for vitellogenin production by the liver during the natural sexual cycle.     

Distribution of ecto-5′-nucleotidase in the rat liver: effect of anaemia

In the kidney a striking parallel exists between the expression of ecto-5-nucleotidase and of erythropoietin by renal fibroblasts. It was therefore hypothesized that the expression of ecto-5-nucleotidase in fibroblasts might be controlled by oxygen tension. In order to test this hypothesis, we examined the distribution of the enzyme in a tissue which displays a defined zonation in respect to oxygen tension, namely in the liver; anaemia was used in order to exaggerate this zonation. The distribution of ecto-5-nucleotidase was investigated by light and electron microscopy using enzyme and immunohistochemical methods in the livers of healthy and of anaemic rats. Anaemia was produced by haemolysis combined with X-ray irradiation. The enzyme was detected in the bile canaliculi, in the connective tissue of the portal triads and of the central veins, and in fat-storing cells probably corresponding to a special form of fibroblasts. In healthy animals the perisinusoidal ecto-5-nucleotidase activity was slightly higher in the pericentral than in the periportal area of the acinus whereas the inverse was observed for the staining of bile canaliculi. Anaemia provoked an increase of ecto-5-nucleotidase in fat-storing cells in the pericentral zone of the acinus and in fibroblasts around the central veins, resulting in steepended gradients along the sinusoids. The intralobular gradient of ecto-5-nucleotidase in perisinusoidal cells and the effect thereon of anaemia suggest that the expression of the ecto-5-nucleotidase might be directly or indirectly controlled by local oxygen tension.     

Insulin resistance in the liver: Deficiency or excess of insulin?

In insulin-resistant states (obesity, pre-diabetes, and type 2 diabetes), hepatic production of glucose and lipid synthesis are heightened in concert, implying that insulin deficiency and insulin excess coexists in this setting. The fact that insulin may be inadequate or excessive at any one point in differing organs and tissues has many biologic ramifications. In this context the concept of metabolic compartmentalization in the liver is offered herein as one perspective of this paradox. In particular, we focus on the hypothesis that insulin resistance accentuates differences in periportal and perivenous hepatocytes, namely periportal glucose production and perivenous lipid synthesis. Subsequently, excessive production of glucose and accumulation of lipids could be expected in the livers of patients with obesity and insulin resistance. Overall, in this review, we provide our integrative perspective regarding how excessive production of glucose in periportal hepatocytes and accumulation of lipids in perivenous hepatocytes interact in insulin resistant states.