Impaired Albumin Uptake and Processing Promote Albuminuria in OVE26 Diabetic Mice.

The importance of proximal tubules dysfunction to diabetic albuminuria is uncertain. OVE26 mice have the most severe albuminuria of all diabetic mouse models but it is not known if impaired tubule uptake and processing are contributing factors. In the current study fluorescent albumin was used to follow the fate of albumin in OVE26 and normal mice. Compared to normal urine, OVE26 urine contained at least 23 times more intact fluorescent albumin but only 3-fold more 70 kD fluorescent dextran. This indicated that a function other than size selective glomerular sieving contributed to OVE26 albuminuria. Imaging of albumin was similar in normal and diabetic tubules for 3 hrs after injection. However 3 days after injection a subset of OVE26 tubules retained strong albumin fluorescence, which was never observed in normal mice. OVE26 tubules with prolonged retention of injected albumin lost the capacity to take up albumin and there was a significant correlation between tubules unable to eliminate fluorescent albumin and total albuminuria. TUNEL staining revealed a 76-fold increase in cell death in OVE26 tubules that retained fluorescent albumin. These results indicate that failure to process and dispose of internalized albumin leads to impaired albumin uptake, increased albuminuria, and tubule cell apoptosis.

Tracking Optical Welding through Groove Modes in Plasmonic Nanocavities.

We report the light-induced formation of conductive links across nanometer-wide insulating gaps. These are realized by incorporating spacers of molecules or 2D monolayers inside a gold plasmonic nanoparticle-on-mirror (NPoM) geometry. Laser irradiation of individual NPoMs controllably reshapes and tunes the plasmonic system, in some cases forming conductive bridges between particle and substrate, which shorts the nanometer-wide plasmonic gaps geometrically and electronically. Dark-field spectroscopy monitors the bridge formation in situ, revealing strong plasmonic mode mixing dominated by clear anticrossings. Finite difference time domain simulations confirm this spectral evolution, which gives insights into the metal filament formation. A simple analytic cavity model describes the observed plasmonic mode hybridization between tightly confined plasmonic cavity modes and a radiative antenna mode sustained in the NPoM. Our results show how optics can reveal the properties of electrical transport across well-defined metallic nanogaps to study and develop technologies such as resistive memory devices (memristors).

Covalent binding of acrylonitrile to specific rat liver glutathione S-transferases in vivo.

Acrylonitrile (AN) is an industrial vinyl monomer that is acutely toxic. When administered to rats, AN covalently binds to tissue proteins in a dose-dependent but nonlinear manner [Benz, F. W., Nerland, D. E., Li, J., and Corbett, D. (1997) Fundam. Appl. Toxicol. 36, 149-156]. The nonlinearity in covalent binding stems from the fact that AN rapidly depletes liver glutathione after which the covalent binding to tissue proteins increases disproportionately. The identity of the tissue proteins to which AN covalently binds is unknown. The experiments described here were conducted to begin to answer this question. Male Sprague-Dawley rats were injected subcutaneously with 115 mg/kg (2.2 mmol/kg) [2,3-(14)C]AN. Two hours later, the livers were removed, homogenized, and fractionated into subcellular components, and the radioactively labeled proteins were separated on SDS-PAGE. One set of labeled proteins was found to be glutathione S-transferase (GST). Specific labeling of the mu over the alpha class was observed. Separation of the GST subunits by HPLC followed by scintillation counting showed that AN was selective for subunit rGSTM1. Mass spectral analysis of tryptic digests of the GST subunits indicated that the site of labeling was cysteine 86. The reason for the high reactivity of cysteine 86 in rGSTM1 was hypothesized to be due to its potential interaction with histidine 84, which is unique in this subunit.

Acrylonitrile induces autolysis Bacillus subtilis.

Acrylonitrile (AN) is an industrial chemical used in the manufacture of plastics and other polymers. AN has been reported to be an acute toxin and is a known carcinogen in rodents. When AN was mixed with suspensions of Bacillus subtilis, the bacteria began autolysis. It was determined that AN is partially converted to cyanide, a strong protonophore in B. subtilis. Autolytic enzymes in B. subtilis become active when the protonmotive force is dissipated. The amount of cyanide produced from AN, however, was not enough to promote autolysis in exponential B. subtilis. This is the first report showing that AN may induce autolytic reactions in bacteria. It is suggested the autolysis of B. subtilis may be useful in the environmental monitoring of AN. In addition, the metabolism of AN by bacilli may be useful in bioremediation.

Biological markers of acute acrylonitrile intoxication in rats as a function of dose and time.

Three markers of acute acrylonitrile (AN) intoxication, namely, tissue glutathione (GSH), tissue cyanide (CN), and covalent binding to tissue protein, were studied as a function of dose and time. Doses administered and responses expected were 20 mg/kg (LD0), 50 mg/kg (LD10), 80 mg/kg (LD50), and 115 mg/kg (LD90). Liver GSH was the most sensitive marker of AN exposure. At 80 mg/kg AN, virtually complete depletion of liver GSH was observed within 30 min with no recovery through 120 min. Kidney GSH showed a similar, but less intense depletion; while blood and brain GSH were more refractory to AN. Whole blood and brain CN rose progressively during the first 60 min in a dose-dependent fashion. At the lowest dose, CN levels decreased thereafter, whereas, at the three higher doses, CN levels were maintained or continued to increase through 120 min. At the highest dose, blood and brain CN remained at acutely toxic levels through 240 min. Covalent binding increased rapidly in all tissues during the first 30 min at all doses. At the lowest dose, little additional covalent binding was observed beyond 30 min, while at the three higher doses, covalent binding increased, although at a slower rate. The data indicate that these three biologic markers of acute AN intoxication respond dramatically in a time-dependent manner in the toxic dosage range. Furthermore, the data provide evidence that AN toxicity is gated by GSH depletion in liver with the resultant termination of AN detoxification.

Dose dependence of covalent binding of acrylonitrile to tissue protein and globin in rats.

The dose dependence of acrylonitrile (AN) covalent binding to tissue protein, following a single acute exposure over a 100-fold range in dose, was measured. Covalent binding was a linear function of AN dose in the lower dose range (0.02-0.95 mmol AN/kg). The slopes of the dose-response curves indicated that tissues varied by nearly 10-fold in their reactivity with AN. The relative order of covalent binding was as follows: blood > > kidney = liver > forestomach = brain > glandular stomach > > muscle. Similar dose-response behavior was observed for globin total covalent binding and for globin N-(2-cyanoethyl) valine (CEValine) adduct formation. The latter adduct was found to represent only 0.2% of the total AN adduction to globin. Regression of tissue protein binding versus globin total covalent binding or globin CEValine adduct indicated that both globin biomarkers could be used as surrogates to estimate the amount of AN bound to tissue protein. At higher AN doses, above approximately 1 mmol/kg, a sharp break in the covalent binding dose-response curve was observed. This knot value is explained by the nearly complete depletion of liver glutathione and the resultant termination of AN detoxification. The toxicity of AN is known to increase sharply above this dose. The data suggest that a comparison of specific tissue proteins labeled by AN above and below this threshold dose may provide some insight into the mechanism of AN-induced toxicity.

Studies on inhibition and induction of metabolism of ethyl carbamate by acetone and related compounds. Evidence for metabolism by cytochromes P-450.

Ethanol and a variety of other compounds previously have been shown to acutely inhibit the metabolism of ethyl carbamate (EC) when given concurrently in mice. On the other hand, ethanol pretreatment (10% in drinking water for the period 48 to 12 hr prior to EC treatment) is known to have the opposite effect and enhance the clearance of EC from blood of mice. In the present work, acetone has been shown to act similarly. Concurrent acetone treatment inhibits the metabolism of EC (11.1 mg/kg po) in male A/JAX mice in a dose-response manner. Blood clearance (Cl) of this po dose of EC from mice following concurrent acetone treatment (50 mg/kg, 0.86 mmol/kg ip) averaged 185 +/- 5.4 (SE) ml hr-1 kg-1 vs. controls of 804 +/- 24.6 ml hr-1 kg-1. Comparing doses that produce equal effects on the blood clearance values of EC, acetone is approximately 50-fold more potent as an inhibitor than ethanol. Pretreatment of mice with acetone (2 g/kg ip) 48 hr and 24 hr before EC administration po increased the clearance of EC approximately 3-fold (CI = 2623 +/- 123 ml hr-1 kg-1). 2-Propanol was found to be at least as potent as inhibitor as acetone, but with a longer duration of inhibition; this longer duration was explained by the longer persistence of acetone in blood from conversion of 2-propanol to acetone.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute acrylonitrile toxicity: studies on the mechanism of the antidotal effect of D- and L-cysteine and their N-acetyl derivatives in the rat.

Thiol-containing antidotes for acute acrylonitrile (AN) toxicity may exert their action by chemically reacting with AN, by replacing critical sulfhydryl groups cyanoethylated by AN, and by detoxifying cyanide produced from AN metabolism. We have evaluated the ability of the optical isomers of cysteine and N-acetylcysteine to act as antidotes against AN toxicity in order to assess the relative importance of each of these three antidotal mechanisms. The toxicity of AN was determined in male Sprague-Dawley rats and compared to the toxicity determined after treatment with 2 mmol/kg of thiol antidote by computing a protective index (median lethal dose with antidote/median lethal dose without antidote). The protective indices of L-cysteine, D-cysteine, N-acetyl-L-cysteine, and N-acetyl-D-cysteine were 2.03, 1.97, 1.76, and 1.25, respectively. Measurements of urinary mercapturates, derived from the non-oxidative pathway of AN metabolism, indicated that none of the antidotes was able to significantly increase the excretion of these metabolites. Blood cyanide generated from the oxidative metabolism of AN and butyronitrile was also determined. All of the antidotes, except N-acetyl-D-cysteine, lowered blood cyanide levels. A comparison of these results with the predicted relative abilities of the enantiomers to participate in each of the three antidotal mechanisms leads to the conclusion that, under these experimental conditions, the best correlation exists with the cyanide detoxification mechanism.

1H NMR studies of the binding of EDTA to bovine pancreatic ribonuclease.

EDTA binds at the active site of ribonuclease causing a selective downfield shift of the C2 proton resonance of His 12 at pH 5.5 (pH denotes an uncorrected glass electrode pH meter reading of a 2H2O solution). A dissociation constant for EDTA binding to ribonuclease of 1.70 mM was calculated from this chemical shift change. The pKa of His 12 increased from 5.79 in ribonuclease alone to 6.73 in the RNAase . EDTA complex. Compared to these effects, the other histidine residues were not significantly affected by EDTA. EDTA was shown to act as a competitive inhibitor of cytidine 2',3'-cyclic phosphate hydrolysis by ribonuclease with a Ki of 1.37 mM at pH 5.5, 25 degrees C. Molecular model building suggests that three of the four carboxyl groups of EDTA could simultaneously interact with histidine 12, lysine 41 and lysine 7. A complex of this type would account for the data described herein.

Enhancement of bovine pancreatic ribonuclease activity by mercaptoethanol.

Incubation of ribonuclease with 0.1M mercaptoethanol at pH 8.5 can increase the enzyme's hydrolytic activity toward cytidine 2',3'-monophosphate (cyclic CMP) under standard assay conditions. Cation-exchange chromatography of the ribonuclease-thiol reaction mixture revealed seven fractions. The fraction with the highest activity had an approximate tenfold decrease in the apparent Michaelis constant for cyclic CMP with respect to native ribonuclease. The enhanced activity is a metastable property since this fraction reverts back to the control activity and chromatographic behavior of native ribonuclease on standing in solution at room temperature.