Hormonal regulation of the alpha-ketoglutarate dehydrogenase complex in the isolated perfused rat liver

The metabolic flux through the alpha-ketoglutarate dehydrogenase reaction in perfused livers was monitored by measuring the rate of 14CO2 production from [1-14C]alpha-ketoglutarate. The rates of 14CO2 production and glucose production from [1-14C]alpha-ketoglutarate were increased with increasing perfusate alpha-ketoglutarate concentrations. Vasopressin, angiotensin II, and the alpha 1-adrenergic agonist phenylephrine stimulated transiently by 2.5-fold the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction in the presence and absence of Ca2+ in the perfusion medium. High concentrations of glucagon (1 x 10(-8) M) and 8-p-chlorophenylthio-cAMP (100 microM) (data not shown) also stimulated transiently the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction. However, lower glucagon concentrations (1 x 10(-9) M) stimulated the rate of 14CO2 production from [1-14C]alpha-ketoglutarate only under conditions optimized to fix the cellular oxidation-reduction state at an intermediate level, when glucagon (1 x 10(-9) M)-mediated elevation of cAMP content was greater than that observed under highly oxidizing and reducing conditions. These data indicate that agonists which increase cytosolic free Ca2+ levels stimulate the metabolic flux through the alpha-ketoglutarate dehydrogenase complex. Furthermore, the data presented here demonstrate for the first time that physiological glucagon concentrations stimulate the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction only under conditions known to be optimal for glucagon-mediated Ca2+ mobilization in the isolated perfused rat liver.     

Oxidative metabolism of spironolactone: evidence for the involvement of electrophilic thiosteroid species in drug-mediated destruction of rat hepatic cytochrome P450

In a preliminary paper [Decker et al. (1986) Biochem. Biophys. Res. Commun. 136, 1162] we have shown that the antimineralocorticoid spironolactone (SPL) preferentially inactivates dexamethasone (DEX) inducible rat hepatic cytochrome P450p isozymes in a suicidal manner. These findings are now confirmed, and the kinetic characteristics of such a process are detailed. In an effort to elucidate the mechanism of SPL-mediated inactivation of cytochrome P450, we have examined the metabolism of SPL in vitro. Incubation of [14C]SPL and NADPH with liver microsomes prepared from DEX-pretreated rats results in the formation of several polar metabolites separable by HPLC with UV detection. This process is found to be dependent on NADPH, O2, SPL, and enzyme concentration, as well as temperature. Furthermore, metabolite formation was significantly attenuated by P450 inhibitors CO and n-octylamine. Mass spectral analysis (thermospray LC/MS, FAB/MS, and FAB/MS/MS) of the two most prominent polar metabolites indicated that these compounds had molecular weights that corresponded to the sulfinic and sulfonic acid derivatives of deacetyl-SPL (SPL-SH). These findings document the formation of previously unreported polar metabolites of SPL by rat liver microsomes enriched in cytochrome P450p and implicate a role for this isozyme in the oxidation of the thiol moiety of deacetyl-SPL. The detection of such metabolites also implicates a catalytic trajectory that includes the thiyl radical and/or sulfenic acid species as a plausible protagonist in drug-mediated inactivation of cytochrome P450p.     

Increase in the number of atrial natriuretic hormone receptors in regenerating rat liver.

Forty-eight hours after partial (approximately 67%) hepatectomy the activity of the particulate guanylate cyclase was increased by 2-fold in the regenerating rat liver. This increase was not an artifact of membrane isolation procedures, and as determined by 125I-labeled Tyr-28 atrial natriuretic hormone-(1-28) ANF binding, was accompanied by a 2-fold increase in the number of ANF receptors. The Kd of the receptors in membranes of regenerating livers was not significantly different from the Kd of the receptors in livers of sham-operated rats. The linear synthetic descysteine analog of ANF, analog I, which binds only to the 66-kDa receptors, displaced approximately 40% of the specifically bound 125I-ANF in liver membranes from both hepatectomized and sham-operated (control) animals. Affinity cross-linking studies with 125I-ANF confirmed the increase in the 116-kDa ANF receptor in membranes of regenerating livers. In perfused livers derived from control and hepatectomized animals, the basal rates of cGMP production were not significantly different. However, atriopeptin II-stimulated cGMP production was twice as great in regenerating livers as compared with controls. These data demonstrate that the increase in particulate guanylate cyclase activity observed during liver regeneration is due to an increase in the 116-kDa ANF receptor-associated activity. Additionally, our data demonstrate that the regenerating rat liver may be a valuable model with which to study the role of the hepatic ANF receptor/particulate guanylate cyclase.     

S-(N-methylcarbamoyl)glutathione: a reactive S-linked metabolite of methyl isocyanate

S-(N-methylcarbamoyl)glutathione, a chemically-reactive glutathione conjugate, has been isolated from the bile of rats administered methyl isocyanate and characterized, as its N-benzyloxycarbonyl dimethylester derivative, by tandem mass spectrometry. The ability of this glutathione adduct to donate an N-methylcarbamoyl moiety to the free -SH group of cysteine was evaluated in vitro with the aid of a highly specific thermospray LC/MS assay procedure. The glutathione adduct reacted readily with cysteine in buffered aqueous media (pH 7.4, 37 degrees C) and after 2 hr, 42.5% of the substrate existed in the form of S-(N-methylcarbamoyl)cysteine. The reverse reaction, i.e. between the cysteine adduct and free glutathione, also took place readily under these conditions. It is concluded that conjugation of methyl isocyanate with glutathione in vivo affords a reactive S-linked product which displays the potential to carbamoylate nucleophilic amino acids. The various systemic toxicities associated with exposure of animals or humans to methyl isocyanate could therefore be due to release of the isocyanate from its glutathione conjugate, which thus may serve as a vehicle for the transport of methyl isocyanate in vivo.     

Extremely Sensitive Photonic Crystal Fiber–Based Cancer Cell Detector in the Terahertz Regime

A new photonic crystal fiber (PCF)–based, hollow-core, optical waveguide is proposed and numerically investigated to quickly identify numerous species of cancerous cells in the human body. Typical and cancerous cells have different refractive indices (RIs), and via this characteristic, the other important optical parameters are evaluated. The guiding properties of this proposed cancer cell sensor are analyzed in the COMSOL Multiphysics environment which used the finite element method as mathematical tool to solve differential equations. Furthermore, to ensure the highest simulation accuracy, extremely fine mesh elements are introduced. The simulation studies confirm that the proposed sensor, at 2.5 THz, achieves an extremely high relative sensitivity of almost 98% with negligible loss (< 0.025 dB/cm). Furthermore, a high numerical aperture (NA) and spot size, with low modal area, enhance the propagation characteristics of the sensor to a new height. The sensor’s physical structure is very simple so that it can be easily fabricated with modern fabrication technology. Thus, it seems that this sensor will open a new door in the field of detecting and diagnosing different cancer cells.

     

A new species of Polydrusus (Polydrusus) Germar (Coleoptera:Curculionidae) from the Kurdistan region of Iraq

Polydrusus (s. str.) akreanus sp. n. is a new record of Curculionidae found in Iraqi Kurdistan. The new species is described, illustrated and compared with Polydrusus (s. str.) kadleci Borovec & Germann, 2013 known from Turkey and Iran, which is morphologically similar to the new species.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:9FDC3C5B-6854-4DEF-BDF6-EE6809F82DEE     

Hiding in plain sight

Although the principles of disruptive colouration are widely believed to explain a variety of animal colour patterns, there has been no field evidence that it works to reduce the detection rates of natural prey. In a recent paper, Cuthill et al. successfully address this shortfall, separating the benefits of background matching from those of disruptive colouration. Their results provide the first definitive field support for this long-recognized phenomenon and suggest several new avenues of research.     

Synthesis of 2-bromomethyl-3-hydroxy-2-hydroxymethyl-propyl pyrimidine and theophylline nucleosides under microwave irradiation. Evaluation of their activity against hepatitis B virus

Alkylation of 2-methylthiopyrimidin-4(1H)-one (1a) and its 5(6)-alkyl derivatives 1b-d as well as theophylline (7) with 2,2-bis(bromomethyl)-1,3-diacetoxypropane (2) under microwave irradiation gave the corresponding acyclonucleosides 1-[(3-acetoxy-2-acetoxymethyl-2-bromomethyl)prop-1-yl]-2-methyl-thio pyrmidin-4(1H)-ones 3a-d and 7-[(3-acetoxy-2-acetoxymethyl-2-bromomethyl)prop-1-yl]theophylline (8), which upon further irradiation gave the double-headed acyclonucleosides 1,1 '-[(2,2-diacetoxymethyl)-1,3-propylidene]-bis[(2-(methylthio)-pyrimidin-4(1H)-ones] 4a-c, and 7,7 '-[(2,2-diacetoxymethyl)-1,3-propylidene]-bis(theophylline) (9). The deacetylated derivatives were obtained by the action of sodium methoxide. The activity of deacetylated nucleosides against Hepatitis B virus was evaluated. Compound 5b showed moderate inhibition activity against HBV with mild cytotoxicity.