Enrique Piña

Plasma triglyceride/HDL-cholesterol ratio, insulin resistance, and cardiometabolic risk in young adults

Studies in mature adults suggest that the plasma concentration ratio of triglyceride (TG)/HDL-cholesterol (HDL-C) provides a simple way to identify apparently healthy individuals who are insulin resistant (IR) and at increased cardiometabolic risk. This study extends these observations by examining the clinical utility of the TG/HDL-C ratio and the metabolic syndrome (MetS) in 2,244 healthy college students (17–24 years old) of Mexican Mestizo ancestry. The TG/HDL-C ratio separating the 25% with the highest value was used to identify IR and increased cardiometabolic risk. Cardiometabolic risk factors were more adverse in men and women whose TG/HDL-C ratios exceeded 3.5 and 2.5, respectively, and approximately one third were identified as being IR. The MetS identified fewer individuals as being IR, but their risk profile was accentuated. In conclusion, both a higher TG/HDL-C ratio and a diagnosis of the MetS identify young IR individuals with an increased cardiometabolic risk profile. The TG/HDL-C ratio identified a somewhat greater number of “high risk” subjects, whereas the MetS found a group whose risk profile was somewhat magnified. These findings suggest that the TG/HDL-C ratio may serve as a simple and clinically useful approach to identify apparently healthy, young individuals who are IR and at increased cardiometabolic risk.

In vivo modification of the energy charge in the liver cell

Summary The energy charge of the adenylate system increases in the liver cells of normal rats 30–120 minutes after the intra — peritoneal injection of adenosine (200 mg/Kg body weight). Simultaneously, in the liver there is an enhancement of glycogen biosynthesis and a diminution in fatty acid catabolism. These metabolic changes correspond to what could be expected from an increase in the energy charge. Thus, a regulatory role of the adenylate system under in vivo conditions is substantiated.

Regulation of glycogen metabolism in hepatocytes through adenosine receptors. Role of Ca2+ and cAMP.

The objective of this work is to identify the adenosine receptor subtype and the triggered events involved in the regulation of hepatic glycogen metabolism. Glycogenolysis, gluconeogenesis, cAMP, and cytosolic Ca2+ ([Ca2+](cyt)) were measured in isolated hepatocytes challenged with adenosine A1, A2A, and A3 receptor-selective agonists. Stimulation of adenosine receptor subtypes with selective agonists in Ca2+ media produced a dose-dependent increase in [Ca2+]cyt with A1>A2=A3, cAMP with A2A, glycogenolysis with A1>A2A>A3, and gluconeogenesis with A2A>A1>A3, in addition, a decrease in cAMP was observed with A1=A3. Comparatively, in Ca2+-free media or with a cell membrane-permeant Ca2+ chelator, activation of these adenosine receptors with the same selective agonists produced a smaller and transient rise in [Ca2+]cyt with A1=A3>A2, no rise in glycogenolysis and gluconeogenesis with A3>A1, but a full rise with A2A. Thus, in isolated rat hepatocytes activation of the adenosine A1 receptor triggered Ca2+-mediated glycogenolysis, activation of the adenosine A2A receptor stimulated cAMP-mediated gluconeogenesis, and activation of the adenosine A3 receptor increased [Ca2+]cyt and decreased cAMP with minor changes in glycogen metabolism.

A novel method for the rapid preparation of coupled yeast mitochondria

Different methods have been developed for the preparation of yeast mitochondria [l-3] . In the methods described, two main techniques for the breakage of the yeast cells are used; in one of them, enzymes are used first to digest the cell wall, and then a rather gentle method is used for the breakage itself. In the other method, no treatment of the cell wall is used, and the cells are broken directly in the MSK cell homogenizer. The first technique is long and tedious, and the integrity of the mitochondria obtained is variable. With the use of the MSK homogenizer, although the procedure is faster, the mitochondria obtained are usually uncoupled. The Ribi cell fractionator (Ivan Sorvall, Inc.) has been used successfully for the breakage of different kinds of cells; this method of disintegration has been claimed to be adequate for the preparation of forespores; these fragile structures are obtained intact after breaking bacteria with this instrument [4] . Dr Anthony .I. Andreoli, who has used this method widely, suggested its use for the preparation of yeast mitochondria, provided the instructions are followed to polish the valve needle and seat, as recommended by the manufacturers. This paper describes the results of using the Ribi cell fractionator as an adequate disruption method for the reproducible preparation of coupled yeast mitochondria by means of a procedure that takes approximately two hours. 2. Materials and methods

On the mechanism of ethanol-induced fatty liver and its reversibility by adenosine

Abstract The administration of adenosine partially prevented and reverted the ethanol-induced fatty liver. The hepatic α-glycerophosphate concentration and the α-glycerophosphate/dihydroxyacetone phosphate ratio were significantly increased after ethanol administration. The nucleoside decreased with ratio and enhanced the oxidation of ethanol. A strong correlation between the cytoplasmic redox state and the amount of triacylglycerols in the liver was found (8 h after treatments) stressing the paramount importance of the redox state in the pathogenesis of ethanol-induced fatty liver. As previously reported, the nucleoside expanded the adenine nucleotide pool size and the hepatic ATP level. Ethanol potentiated these effects. It is suggested that adenosine ameliorated the ethanol-induced fatty liver through an increased utilization of reducing equivalents by the mitochondria. An interdependence of these effects is proposed and discussed.

Signaling the Signal, Cyclic AMP-dependent Protein Kinase Inhibition by Insulin-formed H2O2 and Reactivation by Thioredoxin

Catecholamines in adipose tissue promote lipolysis via cAMP, whereas insulin stimulates lipogenesis. Here we show that H2O2 generated by insulin in rat adipocytes impaired cAMP-mediated amplification cascade of lipolysis. These micromolar concentrations of H2O2 added before cAMP suppressed cAMP activation of type IIβ cyclic AMP-dependent protein kinase (PKA) holoenzyme, prevented hormone-sensitive lipase translocation from cytosol to storage droplets, and inhibited lipolysis. Similarly, H2O2 impaired activation of type IIα PKA holoenzyme from bovine heart and from that reconstituted with regulatory IIα and catalytic α subunits. H2O2 was ineffective (a) if these PKA holoenzymes were preincubated with cAMP, (b) if added to the catalytic α subunit, which is active independently of cAMP activation, and (c) if the catalytic α subunit was substituted by its C199A mutant in the reconstituted holoenzyme. H2O2 inhibition of PKA activation remained after H2O2 elimination by gel filtration but was reverted with dithiothreitol or with thioredoxin reductase plus thioredoxin. Electrophoresis of holoenzyme in SDS gels showed separation of catalytic and regulatory subunits after cAMP incubation but a single band after H2O2 incubation. These data strongly suggest that H2O2 promotes the formation of an intersubunit disulfide bond, impairing cAMP-dependent PKA activation. Phylogenetic analysis showed that Cys-97 is conserved only in type II regulatory subunits and not in type I regulatory subunits; hence, the redox regulation mechanism described is restricted to type II PKA-expressing tissues. In conclusion, phylogenetic analysis results, selective chemical behavior, and the privileged position in holoenzyme lead us to suggest that Cys-97 in regulatory IIα or IIβ subunits is the residue forming the disulfide bond with Cys-199 in the PKA catalytic α subunit. A new molecular point for cross-talk among heterologous signal transduction pathways is demonstrated.

Role of ischemic preconditioning in liver surgery and hepatic transplantation.

IntroductionThe purpose of this review is to summarize intraoperative surgical strategies available to decrease ischemia–reperfusion injury associated with liver resection and liver transplantation.Material and methodWe conducted a critical review of the literature evaluating the potential applications of hepatic ischemic preconditioning (IPC) for hepatic resection surgery and liver transplantation. In addition, we provide a basic bench-to-bedside summary of the liver physiology and cell signaling mechanisms that account for the protective effects seen with hepatic IPC.

Adrenaline stimulates H2O2 generation in liver via NADPH oxidase

It is known that adrenaline promotes hydroxyl radical generation in isolated rat hepatocytes. The aim of this work was to investigate a potential role of NADPH oxidase (Nox) isoforms for an oxidative stress signal in response to adrenaline in hepatocytes. Enriched plasma membranes from isolated rat liver cells were prepared for this purpose. These membranes showed catalytic activity of Nox isoforms, probably Nox 2 based on its complete inhibition with specific antibodies. NADPH was oxidized to convert O2 into superoxide radical, later transformed into H2O2. This enzymatic activity requires previous activation with either 3 mM Mn2+ or guanosine 5′-0-(3-thiotriphosphate) (GTPγS) plus adrenaline. Experimental conditions for activation and catalytic steps were set up: ATP was not required; S0.5 for NADPH was 44 μM; S0.5 for FAD was 8 μM; NADH up to 1 mM was not substrate, and diphenyleneiodonium was inhibitory. Activation with GTPγS plus adrenaline was dose- and Ca2+-dependent and proceeded through α1-adrenergic receptors (AR), whereas β-AR stimulation resulted in inhibition of Nox activity. These results lead us to propose H2O2 as additional transduction signal for adrenaline response in hepatic cells.

Natural alcohol exposure: is ethanol the main substrate for alcohol dehydrogenases in animals?

Alcohol dehydrogenase (ADH) activity is widely distributed in all phyla. In animals, three non-homologous NAD(P)(+)-dependent ADH protein families are reported. These arose independently throughout evolution and possess different structures and mechanisms of reaction: type I (medium-chain) ADHs are zinc-containing enzymes and comprise the most studied group in vertebrates; type II (short-chain) ADHs lack metal cofactor and have been extensively studied in Drosophila; and type III ADHs are iron-dependent/-activated enzymes that were initially identified only in microorganisms. The presence of these different ADHs in animals has been assumed to be a consequence of chronic exposure to ethanol. By far the most common natural source of ethanol is fermentation of fruit sugars by yeast, and available data support that this fruit trait evolved in concert with the characteristics of their frugivorous seed dispersers. Therefore, if the presence of ADHs in animals evolved as an adaptive response to dietary ethanol exposure, then it can be expected that the enzymogenesis of these enzymes began after the appearance of angiosperms with fleshy fruits, because substrate availability must precede enzyme selection. In this work, available evidence supporting this possibility is discussed. Phylogenetic analyses reveal that type II ADHs suffered several duplications, all of these restricted to flies (order Diptera). Induction of type II Adh by ethanol exposure, a positive correlation between ADH activity and ethanol resistance, and the fact that flies and type II Adh diversification occurred in concert with angiosperm diversification, strongly suggest that type II ADHs were recruited to allow larval flies to exploit new restricted niches with high ethanol content. In contrast, phyletic distribution of types I and III ADHs in animals showed that these appeared before angiosperms and land plants, independently of ethanol availability. Because these enzymes are not induced by ethanol exposure and possess a high affinity and/or catalytic efficiency for non-ethanol endogenous substrates, it can be concluded that the participation of types I and III ADHs in ethanol metabolism can be considered as incidental, and not adaptive.

SOME CHARACTERISTICS OF THE D‐GLUCOSE‐6‐PHOSPHATE: CYCLOALDOLASE (NAD+ DEPENDENT) FROM Neurospora crassa *

The biosynthesis of myo-inositol? seems to be very similar in all species investigated, including yeast (Chen & Charalampous, 1963), mammals (Eisenberg & Bolden, 1963), higher plants (Kind1 & Hoffmann-Ostenhof, 1964), and Neurospora (Piiia & Tatum, 1967). A single enzyme, with an absolute requirement for nicotinamide adenine dinucleotide (NAD+) , catalyzes the formation of inositol-phosphate (inositol-P) from glucose-6-phosphate (glucose-6-P) . Eisenberg and Bolden (1965) and Chen and Charalampous (1966) have demonstrated for the mammal and yeast enzyme, respectively, that L-myoinositol1-phosphate is the enzymatically formed isomer. The present paper deals with some properties of the enzyme, isolated from Neurospora crassa, which is responsible for this reaction.