Lovastatin induces synthesis of cholesterol, which acts as a secretagogue of biliary phospholipids in rats

The effects of treatment with lovastatin (LS), a hypocholesterolemic drug, on hepatic metabolism of cholesterol (CH) and phosphatidylcholine (PC) were studied in rats. Hepatic synthesis of CH was increased, as previously reported by our laboratory. Total plasma CH was increased, and biliary secretion of CH was raised fourfold, but biliary secretion of bile salts was not affected. Because CH is practically insoluble in an aqueous milieu, we tested the hypothesis that excessive CH is solubilized and secreted into bile as cholesterol-phospholipid (CH-PL) vesicles. The effects of LS-induced increase in CH synthesis on hepatic metabolism of PC after 7 days of oral LS treatment (17.5 mg/day) were studied. Our results showed accelerated synthesis of PC and increased biliary secretion of newly formed PC into bile, as evidenced by the following. 1) Phosphocholine cytidylyltransferase (EC 2.7.7.15) activity, the rate limiting enzyme in the synthesis of PC, increased 2.5-fold in the hepatic microsomes of the hepatocytes. 2) After intravenous administration of [14C]choline, a precursor of PC, [14C]PC increased significantly in bile. 3) Biliary output of PC increased twofold. 4) Quasi-elastic light scattering measurements of bile showed a 3.5-fold increase in intensity of the CH-PL vesicles, indicating higher concentrations of CH-PL vesicles, but there was no change in the intensity of the micelles. These observations support the hypothesis that PC synthesis was enhanced as a transport mechanism for secretion of the excessive amounts of cholesterol from the hepatocytes into bile as CH-PC vesicles.

Download Full-text

Intestinal absorption, hepatic synthesis, and biliary secretion of cholesterol: Where are we for cholesterol gallstone formation?

Hepatology ◽

10.1002/hep.25604 ◽

2012 ◽

Vol 55 (5) ◽

pp. 1313-1316 ◽

Cited By ~ 24

Author(s):

Piero Portincasa ◽

David Q.-H. Wang

Keyword(s):

Intestinal Absorption ◽

Cholesterol Gallstone ◽

Gallstone Formation ◽

Biliary Secretion ◽

Hepatic Synthesis

Download Full-text

Ceramide Levels and Covid-19 Respiratory Distress, a Causal Relationship

10.21203/rs.3.rs-443020/v2 ◽

2021 ◽

Author(s):

Mehran Khodadoust

Keyword(s):

Respiratory Distress ◽

Causal Relationship ◽

Fold Increase ◽

Plasma Samples ◽

Total Plasma ◽

Lipidomic Analysis ◽

Distress Symptoms ◽

Concentration Dependency ◽

Ceramide Synthesis ◽

Total Plasma Concentration

Abstract A causal relationship between plasma ceramide concentration and Covid-19 patients with respiratory distress symptoms is presented. In this study, plasma samples of 52 individuals infected with Covid-19 were utilized in a lipidomic analysis. Lipids belonging to ceramide class exhibited a 400-fold increase in total plasma concentration in infected patients. Further analysis lead to demonstration of concentration dependency, for severe Covid-19 respiratory symptoms, in a subclass of ceramides. The subclasses Cer(d18:0/24:1), Cer(d18:1/24:1), and Cer(d18:1/22:0) are shown to be increased by 48, 40, and 33–folds respectively in infected plasma samples, and to 116, 91 and 50-folds in plasma samples with respiratory distress. Hence, monitoring of plasma ceramide concentration, targeting ceramide synthesis, its salvage and its regulatory mechanisms, are validated approach towards enhancing survival from Covid-19 respiratory distress.

Download Full-text

The effect of increased absorption of ammonia and aroinine on splanchnic metabolism of beef steers

Proceedings of the British Society of Animal Production (1972) ◽

10.1017/s0308229600024958 ◽

1993 ◽

Vol 1993 ◽

pp. 173-173

Author(s):

S A Maltby ◽

C K Reynolds ◽

M A Lomax ◽

D E Beever

Keyword(s):

Amino Acids ◽

Urea Cycle ◽

Beef Steers ◽

Carbamoyl Phosphate ◽

Lower Efficiency ◽

Dietary Nitrogen ◽

Rate Limiting Step ◽

Ammonia Conversion ◽

Rate Limiting ◽

Hepatic Synthesis

Cattle fed forage based diets often absorb a high proportion of dietary N as ammonia (NH3N) and this must be detoxified in the liver to urea. It has been suggested that this process utilises both energy and amino acids and may contribute to the lower efficiency of utilisation of dietary nitrogen and energy observed in forage fed ruminants (Fitch et al, 1989). However it is not known to what extent ammonia conversion to urea requires simultaneous deamination of amino acids. We report an experiment which examined hepatic nitrogen and energy metabolism at two different rates of NH3 arrival at the liver, in response an infusion of arginine to increase urea cycle flux. Arginine stimulates the hepatic synthesis of N-acetyl glutamate which is an activator of carbamoyl-phosphate synthase, the rate limiting step of the urea cycle (Meijer et al, 1990).

Download Full-text

Effects of controlled RAD52 expression on repair and recombination in Saccharomyces cerevisiae.

Molecular and Cellular Biology ◽

10.1128/mcb.11.4.2013 ◽

1991 ◽

Vol 11 (4) ◽

pp. 2013-2017 ◽

Cited By ~ 22

Author(s):

K J Dornfeld ◽

D M Livingston

Keyword(s):

Fold Increase ◽

Mitotic Recombination ◽

Protein Product ◽

Wild Type ◽

Recombination Rates ◽

Plasmid Recombination ◽

Gal1 Promoter ◽

High Level ◽

Rate Limiting ◽

Mutant Cells

We have examined the effects of RAD52 overexpression on methyl methanesulfonate (MMS) sensitivity and spontaneous mitotic recombination rates. Cells expressing a 10-fold excess of RAD52 mRNA from the ENO1 promoter are no more resistant to MMS than are wild-type cells. Similarly, under the same conditions, the rate of mitotic recombination within a reporter plasmid does not exceed that measured in wild-type cells. This high level of expression is capable of correcting the defects of rad52 mutant cells in carrying out repair and recombination. From these observations, we conclude that wild-type amounts of Rad52 are not rate limiting for repair of MMS-induced lesions or plasmid recombination. By placing RAD52 under the control of the inducible GAL1 promoter, we find that induction results in a 12-fold increase in the fraction of recombinants within 4 h. After this time, the fraction increases less rapidly. When RAD52 expression is quickly repressed during induction, the amount of RAD52 mRNA decreases rapidly and no nascent recombinants are formed. This result suggests a short active half-life for the protein product. Induction of RAD52 in G1-arrested mutant cells also causes a rapid increase in recombinants, suggesting that replication is not necessary for plasmid recombination.

Download Full-text

A new method for the assay of tissue. S-adenosylhomocysteine and S-adenosylmethione. Effect of pyridoxine deficiency on the metabolism of S-adenosylhomocysteine, S-adenosylmethionine and polyamines in rat liver

Biochemical Journal ◽

10.1042/bj1600287 ◽

1976 ◽

Vol 160 (2) ◽

pp. 287-294 ◽

Cited By ~ 75

Author(s):

T O Eloranta ◽

E O Kajander ◽

A M Raina

Keyword(s):

Fold Increase ◽

Major Effect ◽

Albino Rats ◽

Vitamin B ◽

Deficient Diet ◽

Tissue Samples ◽

Adenosylmethionine Decarboxylase ◽

Pyridoxine Deficiency ◽

Hepatic Synthesis

The hepatic synthesis and accumulation of S-adenosylhomocysteine, S-adenosylmethionine and polyamines were studied in normal and vitamin B-6-deficient male albino rats. A method involving a single chromatography on a phosphocellulose column was developed for the determination of S-adenosylhomocysteine and S-adenosylmethionine from tissue samples. Feeding the rat with pyridoxine-deficient diet for 3 or 6 weeks resulted in a four- to five-fold increase in the concentration of S-adenosylhomocysteine, whereas that of S-adenosylmethionine was only slighly elevated. The concentration of putrescine was decreased to half, that of spermidine was somewhat decreased and that of spermine remained fairly constant. The activities of L-ornithine decarboxylase, S-adenosyl-L-methionine decarboxylase, L-methionine adenosyltransferase and S-adenosyl-L-homocysteine hydrolase were moderately increased. S-Adenosylmethionine decarboxylase showed no requirement for pyridoxal 5′-phosphate. The major effect of pyridoxine deficiency of S-adenosylmethionine metabolism seems to be a block in the utilization of S-adenosylhomocysteine, resulting in the accumulation of this metabolite to a concentration that may inhibit biological methylation reactions.

Download Full-text

A drug-resistant β-lactamase variant changes the conformation of its active-site proton shuttle to alter substrate specificity and inhibitor potency

Journal of Biological Chemistry ◽

10.1074/jbc.ra120.016103 ◽

2020 ◽

Vol 295 (52) ◽

pp. 18239-18255

Author(s):

Victoria Soeung ◽

Shuo Lu ◽

Liya Hu ◽

Allison Judge ◽

Banumathi Sankaran ◽

...

Keyword(s):

Substrate Specificity ◽

Clavulanic Acid ◽

Fold Increase ◽

Antibiotic Use ◽

Resistance Mutations ◽

Evolution Of Resistance ◽

Inhibitor Resistance ◽

Inhibition Potency ◽

Rate Limiting ◽

Hydrolysis Of

Lys234 is one of the residues present in class A β-lactamases that is under selective pressure due to antibiotic use. Located adjacent to proton shuttle residue Ser130, it is suggested to play a role in proton transfer during catalysis of the antibiotics. The mechanism underpinning how substitutions in this position modulate inhibitor efficiency and substrate specificity leading to drug resistance is unclear. The K234R substitution identified in several inhibitor-resistant β-lactamase variants is associated with decreased potency of the inhibitor clavulanic acid, which is used in combination with amoxicillin to overcome β-lactamase–mediated antibiotic resistance. Here we show that for CTX-M-14 β-lactamase, whereas Lys234 is required for hydrolysis of cephalosporins such as cefotaxime, either lysine or arginine is sufficient for hydrolysis of ampicillin. Further, by determining the acylation and deacylation rates for cefotaxime hydrolysis, we show that both rates are fast, and neither is rate-limiting. The K234R substitution causes a 1500-fold decrease in the cefotaxime acylation rate but a 5-fold increase in kcat for ampicillin, suggesting that the K234R enzyme is a good penicillinase but a poor cephalosporinase due to slow acylation. Structural results suggest that the slow acylation by the K234R enzyme is due to a conformational change in Ser130, and this change also leads to decreased inhibition potency of clavulanic acid. Because other inhibitor resistance mutations also act through changes at Ser130 and such changes drastically reduce cephalosporin but not penicillin hydrolysis, we suggest that clavulanic acid paired with an oxyimino-cephalosporin rather than penicillin would impede the evolution of resistance.

Download Full-text

Over-expression of the brassinosteroid gene TaDWF4 increases wheat productivity under low and sufficient nitrogen through enhanced carbon assimilation

10.1101/2021.09.21.461226 ◽

2021 ◽

Author(s):

Matthew John Milner ◽

Stéphanie M. Swarbreck ◽

Melanie Craze ◽

Sarah Bowden ◽

Howard Griffiths ◽

...

Keyword(s):

Crop Yields ◽

Agronomic Traits ◽

Carbon Assimilation ◽

Fold Increase ◽

Operating Efficiency ◽

Over Expression ◽

Rate Limiting Step ◽

Marginal Soils ◽

Use Efficiency ◽

Rate Limiting

There is a strong pressure to reduce nitrogen (N) fertiliser inputs while maintaining or increasing current cereal crop yields. Brassinosteroids, (BR), are a group of phytohormones essential for plant growth and development, that have been demonstrated to regulate several agronomic traits. DWF4 encodes a cytochrome P450 that catalyses a rate-limiting step in BR synthesis. We show that overexpression of the dominant shoot expressed homoeologue TaDWF4-B in wheat can increase plant productivity by up to 105% under a range of N levels on marginal soils, resulting in increased N use efficiency (NUE). We show that a two to four-fold increase in TaDWF4 transcript levels enhances the responsiveness of genes regulated by N. The productivity increases seen were primarily due to the maintenance of photosystem II operating efficiency and carbon assimilation in plants when grown under limiting N conditions and not an overall increase in photosynthesis capacity. The increased biomass production and yield per plant in TaDWF4 OE lines could be linked to modified carbon partitioning and changes in expression pattern of the growth regulator Target Of Rapamycin, offering a route towards breeding for sustained yield and lower N inputs.

Download Full-text

Ketogenesis Impact on Liver Metabolism Revealed by Proteomics of Lysine β-hydroxybutyrylation

10.1101/2021.01.21.427645 ◽

2021 ◽

Author(s):

Kevin B. Koronowski ◽

Carolina M. Greco ◽

He Huang ◽

Jin-Kwang Kim ◽

Jennifer L. Fribourgh ◽

...

Keyword(s):

Metabolic Pathways ◽

Ketone Bodies ◽

Hepatic Metabolism ◽

Mass Spectrometry Analysis ◽

Metabolic Enzyme ◽

Spectrometry Analysis ◽

Evolutionarily Conserved ◽

Specific Manner ◽

Rate Limiting

SUMMARYKetone bodies are evolutionarily conserved metabolites that function as energy substrates, signaling molecules and epigenetic regulators. β-hydroxybutyrate (β-OHB) is utilized in lysine β-hydroxybutyrylation (Kbhb) of histones, which associates with starvation-responsive genes, effectively coupling ketogenic metabolism with gene expression. The emerging diversity of the lysine acylation landscape prompted us to investigate the full proteomic impact of Kbhb. Global protein Kbhb is induced in a tissue-specific manner by a variety of interventions that evoke β-OHB. Mass spectrometry analysis of the β-hydroxybutyrylome in mouse liver revealed 891 sites of Kbhb within 267 proteins enriched for fatty acid, amino acid, detoxification and 1-carbon metabolic pathways. Kbhb of S-adenosyl-L-homocysteine hydrolase (AHCY), a rate-limiting enzyme of the methionine cycle, results in inhibition of enzymatic activity. Our results illuminate the role of Kbhb on hepatic metabolism under ketogenic conditions and demonstrate the functional consequence of this modification on a central metabolic enzyme.

Download Full-text

Pharmacokinetic Interaction between Nevirapine and Nortriptyline in Rats: Inhibition of Nevirapine Metabolism by Nortriptyline

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.03312-14 ◽

2014 ◽

Vol 58 (12) ◽

pp. 7041-7048 ◽

Cited By ~ 5

Author(s):

Iris Usach ◽

Virginia Melis ◽

Patricia Gandía ◽

José-Esteban Peris

Keyword(s):

Plasma Concentrations ◽

Pharmacokinetic Interaction ◽

Hepatic Metabolism ◽

Transcriptase Inhibitor ◽

Tricyclic Antidepressant ◽

Pharmacokinetic Parameters ◽

Maximum Plasma ◽

Hepatic Microsomes

ABSTRACTOne of the most frequent comorbidities of HIV infection is depression, with a lifetime prevalence of 22 to 45%. Therefore, it was decided to study a potential pharmacokinetic interaction between the nonnucleoside reverse transcriptase inhibitor nevirapine (NVP) and the tricyclic antidepressant nortriptyline (NT). NVP and NT were administered to rats either orally, intraduodenally, or intravenously, and the changes in plasma levels and pharmacokinetic parameters were analyzed. Experiments with rat and human hepatic microsomes were carried out to evaluate the inhibitory effects of NT on NVP metabolism. NVP plasma concentrations were significantly higher when this drug was coadministered with NT. The maximum plasma concentrations of NVP were increased 2 to 5 times and the total plasma clearance was decreased 7-fold in the presence of NT. However, statistically significant differences in the pharmacokinetic parameters of NT in the absence and presence of NVP were not found.In vitrostudies with rat and human hepatic microsomes confirmed the inhibition of NVP hepatic metabolism by NT in a concentration-dependent way, with the inhibition being more intense in the case of rat microsomes. In conclusion, a pharmacokinetic interaction between NVP and NT was detected. This interaction was a consequence of the inhibition of hepatic metabolism of NVP by NT.In vivohuman studies are required to evaluate the effects of this interaction on the pharmacokinetics of NVP before it can be taken into account for patients receiving NVP.

Download Full-text