A new microphotometric method for measurement of cytochrome P-450 in sections of liver

We developed a new microphotometric method for measuring the amounts of cytochrome P-450 (P-450) in fresh frozen sections of liver. Four serial frozen sections cut from the liver were separately incubated in 50 mM Tris-HCl buffer (pH 8.0) alone, in buffer containing sodium dithionite, in buffer saturated with carbon monoxide (CO), and in buffer saturated with CO and containing sodium dithionite. The difference between absorbance at 450 nm and that at 490 nm was measured in these sections with a simple microphotometer system. This method yielded precise amounts of P-450 in sections by measuring the true extinction of P-450 and by minimizing the effect of contaminating hemoproteins. Livers of adult rats contained large amounts of P-450, which was greater in perivenular hepatocytes than in periportal hepatocytes. In livers of newborn rats, however, small amounts of the enzyme were distributed evenly throughout the lobule.     

Protein denaturation during freezing and thawing in phosphate buffer systems: monomeric and tetrameric beta-galactosidase

During freezing in sodium and potassium phosphate (NaP and KP) buffer solutions, changes in pH may impact the stability of proteins. Since the degradation pathways for the model proteins, monomeric and tetrameric beta-galactosidase (beta-gal), chosen for this study are governed by conformational changes (i.e., physical instability) as opposed to chemical transformations, we explored how the stresses of freezing and thawing alter the protein's native structure and if preservation of the native conformation during freeze-thawing is a requisite for optimal recovery of activity. During freezing in NaP buffer, a significant pH decrease from 7.0 to as low as 3.8 was observed due to the selective precipitation of the disodium phosphate; however, the pH during freezing in KP buffer only increased by at most 0.3 pH units. pH-induced inactivation was evident as seen by the lower recovery of activity when freeze-thawing in NaP buffer as compared to KP buffer for both sources of beta-gal. In addition, we investigated the effects of cooling rate and warming rate on the recovery of activity for monomeric and tetrameric beta-gal. Optimal recovery of activity for the NaP samples was obtained when the processing protocol involved a fast cool/fast warm combination, which minimizes exposure to acidic conditions and concentrated solutes. Alterations in the native secondary structure of monomeric beta-gal as measured by infrared spectroscopy were more significant when freezing and thawing in NaP buffer as opposed to KP buffer. Conformational and activity analyses indicate that pH changes during freezing in NaP buffer contribute to denaturation of beta-gal. These results suggest that proteins formulated in NaP buffer should be frozen and thawed rapidly to minimize exposure to low pH and high buffer salts.     

Biochemical studies of the chromaffin granule. III. Redistribution of lipid phosphate,dopamine-β-hydroxylase and chromogranin a after freezing and thawing of the isolated granule membranes

Freezing and thawing a dialysed suspension of lysed chromaffin granules and sedimented membrane preparations resulted in redistribution of lipid phosphate and protein. By this treatment the high ratios of lipid phosphate/protein in the membrane fragments, isolated on sucrose density gradient from the dialysed suspensions and the sedimented membrane preparation, were reduced from 1.56 to 1.03 μmoles/mg and from 1.97 to 0.83 μmoles/mg, respectively.Multilamellar, liposomal structures could be isolated from the frozen and thawed membrane preparations and were found to sediment in the 0.4 M sucrose layer by density gradient centrigugation. This fraction was without morphological resemblance to the intact chromaffin granules or their membranes and was found to account for 53% of the lipid phosphate, 35% of chromogranin A, 21% of dopamine-β-hydroxylase activity and 12% of the protein of the total preparation. The specific activities of chromogranin A and dopamine-β-hydroxylase in the artificially formed liposomal structures closely resembled that of the solubilized protein and was significantly higher than in the lipid phosphate-depleted membrane fragments recovered in the 1.1 M sucrose layers.It is concluded that freezing and thawing as a means of purifying the isolated granule membranes lead not only to the solubilization of chromogranin A, but also to removal of dopamine-β-hydroxylase activity and lipid phosphate from the labile membrane fragments.     

Heat resistance of ileal loop reactive Bacillus cereus strains isolated from commercially canned food.

Sporeformers isolated from a commercially canned food were identified as Bacillus cereus, lactose-positive variants. The thermal resistance of spore crops produced from each of two representative cultures was determined in 0.067 M phosphate buffer at pH 7.0. The D121.1 values for one isolate were approximately 0.03 min (z = 9.9C), whereas the D121.1 values for the other isolate were 2.35 min (z = 7.9 C). Thermal inactivation results for heat-stressed isolates from each strain showed no significant alteration in heat resistance from that of the two parent spore crops. Both isolates were reactive when injected into the ligated rabbit ileum.     

Application of heat-induced antigen retrieval to aldehyde-fixed fresh frozen sections.

We applied the heat-induced antigen retrieval (HIAR) to aldehyde-fixed fresh frozen sections based on a new approach (i.e., a rapid and complete immobilization of antigen followed by heating). Frozen sections were fixed with 10% formalin in 0.1 M cacodylate buffer (pH 7.4) containing 25 mM CaCl(2) for 30 min, or with 0.5% glutaraldehyde in 0.1 M phosphate buffer (pH 7.4) for 1 min at room temperature, and then autoclaved in 20 mM Tris-HCl buffer (pH 9.0) for 10 min at 120 C. Both fixatives yielded good tissue structure after autoclaving. In the sections fixed with formalin containing CaCl(2), 20 of 22 antigens located in the nucleus, cytoplasm, membranes, and extracellular matrix greatly recovered their antigenicity after autoclaving; only two antigens exhibited stronger immunoreaction in acetone-fixed fresh frozen sections than these sections. Heating also retrieved the immunoreactivity of at least 14 antigens in the sections fixed with glutaraldehyde. We used the similar procedures to localize ligand-free estrogen receptor alpha (ERalpha) and glucocorticoid receptors (GR). Mouse uterine cells exhibited almost the same nuclear ERalpha immunostaining regardless of the hormonal status in glutaraldehyde-fixed fresh frozen sections and unliganded GR was localized mainly in the nucleus of mouse hepatocytes in fresh frozen sections fixed with 20% formalin containing 50 or 75 mM CaCl(2) at 40 C, after autoclaving. These results demonstrate that HIAR is useful for the immunohistochemistry of many antigens in aldehyde-fixed fresh frozen sections.     

On the activation of bovine chymotrypsinogen A. Preparation of alanine-neochymotrypsinogen and its activation to alpha-chymotrypsin

Alanine-neochymotrypsinogen was prepared by incubating 20 parts bovine pancreas chymotrypsinogen A with one part alpha-chymotrypsin in a solution containing 1 M (NH4)2SO4, 0.1 M sodium acetate, 0.05 M Tris buffer (pH 8.0) and 0.5 mg/ml soybean trypsin inhibitor. Optimal yields of NH2-terminal alanine were obtained after 60 h incubation at 4 degrees C. Ala-neochymotrypsinogen was isolated from the reaction mixture by affinity chromatography and ion-exchange chromatography on carboxymethyl-cellulose. As expected, the purified preparation was enzymatically inactive and, compared to chymotrypsinogen, had one additional NH2-terminal group identified as alanine. Ala-neochymotrypsinogen was activated by incubating with trypsin at a zymogen : trypsin ratio of 30 : 1 in 0.1 M phosphate buffer, pH 7.6 at 4 degrees C for 1 h. The fully active, stable species was identified as alpha-chymotrypsin.     

Characterization of porphobilinogen deaminase from rat liver

Porphobilinogen deaminase (porphobilinogen ammonia-lyase, EC 4.3.1.8) was isolated from rat liver. The final preparation was homogeneous according to polyacrylamide gel electrophoresis and immunodiffusion criteria. Electrophoresis of the native enzyme revealed a single band of activity which was distributed into three bands after incubation with porphobilinogen. When electrophoresed under denaturing condition it displayed a single polypeptide band with a molecular weight of 42,000 confirmed by exclusion chromatography and by sucrose density gradient centrifugation. The enzyme showed a pH optimum of 7.5 both in 0.1 M sodium phosphate and 0.05 M Tris-HCl buffer, when assayed at 37 degrees C. An isoelectric point of 4.9 for the native purified protein was found. Hepatic porphobilinogen deaminase was remarkably heat-stable showing maximum activity at 55-60 degrees C with one break in the Arrhenius plot. The kinetic behaviour of the purified enzyme followed the typical Michaelis-Menten kinetics with values of Km = 17 microM and Vmax = 29.4 units power mg in 0.1 M phosphate buffer at 37 degrees C. The amino acid composition was determined, showing that the enzyme had a low content of sulphur-containing amino acids and a considerable number of acidic residues per mol of polypeptide chain. Reagents known to interact with sulphydryl groups have small effect on rat liver enzyme activity.     

Separation of the epithelial and mesenchymal components of the newt limb regenerate with salt.

After incubation of isolated forelimb regenerates of Notophthalmus (Triturus) viridescens at all developmental stages for 60 minutes at 37 degrees C in a salt medium containing 111 mM sodium chloride, 5.6 mM potassium chloride and 100 mM sodium phosphate buffer at pH 7.5, the wound epithelium of each regenerate was removed intact from its underlying mesenchymal component. The suggestion is made that the salt medium is an effective epithelial-mesenchymal separating agent due to a combination of its hypertonicity, high ionic strength and the fact that the medium precipitates calcium as calcium phosphate. Attempts to dissect away the epithelium from the mesenchyme after incubation of isolated regenerates in sodium phosphate containing 1% or 3% Difco 1:250 trypsin, 10 mM EDTA or 150 units collagenase/ml medium were unsuccessful. Epidermis of adult newt forelimb skin was removed only after extended incubation of the forelimbs in the salt medium for three hours at 37 degrees C or after freezing isolated forelimbs in buffer and subsequent thawing.     

Molecular properties of yeast glyceraldehyde-3-phosphate dehydrogenase in the presence of ATP and KCl.

The influence of ATP and KCl on the quaternary structure and the enzymatic activity of D-glyceraldehyde-3-phosphate dehydrogenase from yeast(Y-GAPDH) has been studied by ultracentrifugation, gel chromatography and standard optical tests. In 0.1 M imidazole buffer pH 7.0, at low temperature (0°C) both complete deactivation and dissociation to dimers occur in the presence of 2 mM ATP and 0.1 M 2-mercaptoethanol. In 0.067 M phosphate buffer pH 7.0, containing 2 mM ATP and 1 mM dithiothreitol, only slight deactivation paralleled by minor changes of the native quaternary structure is observed. In this same buffer, increasing temperature leads to stabilization of both the tetrameric state and the catalytic activity of the enzyme. Deactivation and dissociation in the presence of 0.15 M KCl (in 0.2 M glycine buffer 9.1 ≥ pH ≥ 8.0) is a function of pH rather than electrolyte concentration; at neutral pH the enzyme is stabilized in its native state. Contrary to earlier assumptions in the literature, ATP and KCl under the above experimental conditions do not appear to play an important role in the $\text{in vivo}$ regulation of Y-GAPDH.     

The use of pH indicators to identify suitable environments for freezing samples in aqueous and mixed aqueous/nonaqueous solutions

The colours of frozen solutions containing pH indicators are shown to provide a test for changes in pH in the solvent environment which occur on freezing. Yeast alcohol dehydrogenase loses activity on freezing in phosphate buffer (a buffer in which pH indicator colour changes shows a marked decrease in pH on freezing) but when frozen in bis-tris, Hepes, or N-glycylglycine buffers (all of which show little change in the colour of universal pH indicator and hence of pH on freezing) is stable on freezing. The effects of freezing in different buffer systems on the rate of decomposition of NADPH, and on the rate hydrolysis of 4-nitrophenyl acetate, are rationalised in terms of the pH shifts in these buffers which were determined using universal pH indicator. It is proposed that a major reason for the instability of samples on freezing is the pH changes which occur when some systems are frozen. From the results a general scheme for selecting the best environment for safely freezing samples is proposed which is based on the use of pH indicators.     

A rapid and gentle method for the salt extraction of chromatin core histones H2A,H2B,H3 and H4 from rat liver nuclei

A complex of histones H2A, H2B, H3 and H4 has been isolated from purified rat liver nuclei by a method which is both gentle and rapid. Nuclei were homogenised in 0.25 M sucrose and the residual nuclear material obtained after centrifligation was adsorbed on calcium phosphate gel. After removing histone H1 from the adsorbed material by washing with 1M NaCl in 25 mM sodium phosphate buffer, pH 6.0, histones H2A, H2B, H3 and H4 were eluted together, with 2 M NaCl in 25 mM sodium phosphate buffer, pH 7.0. The core histones so obtained migrated as a single sharp band on polyacrylamide gel electrophoresis under non-denaturing conditions. Fractionation of the freshly prepared core histones on a Sephadex G-100 column yielded two major protein peaks. The peak having the larger elution volume contained histones H2A and H2B in equal amounts while the peak with the smaller elution volume contained all the four histones. Histones H3 and H4 were present in larger proportions in the second peak.     

Determination of telithromycin in human plasma and microdialysates by high-performance liquid chromatography

A high-performance liquid chromatography method for the quantitative determination of telithromycin in biological fluids is described. The method is suitable for plasma and microdialysates from the interstitial space fluid of skeletal muscle and subcutaneous adipose tissue. Plasma samples were deproteinised with trichloroacetic acid and neutralised with sodium hydroxide. Microdialysates were analysed without further preparation step. Telithromycin was separated isocratically on a reverse-phase column using acetonitrile-0.03 M ammonium acetate, pH 5.2 (43:57, v/v) at a flow rate of 0.8 mlmin(-1), and fluorescence detection (excitation 263 nm, emission 460 nm). The calibration curve was linear from 0.01 to 5 microgml(-1). Within- and between-day imprecision and inaccuracy was < or =10%. The limits of quantification were 0.02 and 0.015 microgml(-1) for plasma and microdialysates, respectively. Since telithromycin is decomposed in aqueous solution at ambient temperature, it is strongly recommended to store samples frozen at -80 degrees C, to maintain the temperature at 4 degrees C during all preparation steps, and to analyse samples within 120 min after thawing.     

A multi-laboratory evaluation of cryopreserved monkey hepatocyte functions for use in pharmaco-toxicology.

Ethical, economic and technical reasons hinder regular supply of freshly isolated hepatocytes from higher mammals such as monkey for preclinical evaluation of drugs. Hence, we aimed at developing optimal and reproducible protocols to cryopreserve and thaw parenchymal liver cells from this major toxicological species. Before the routine use of these protocols, we validated them through a multi-laboratory study. Dissociation of the whole animal liver resulted in obtaining 1-5 billion parenchymal cells with a viability of about 86%. An appropriate fraction (around 20%) of the freshly isolated cells was immediately set in primary culture and various hepato-specific tests were performed to examine their metabolic, biochemical and toxicological functions as well as their ultrastructural characteristics. The major part of the hepatocytes was frozen and their functionality checked using the same parameters after thawing. The characterization of fresh and thawed monkey hepatocytes demonstrated the maintenance of various hepato-specific functions. Indeed, cryopreserved hepatocytes were able to survive and to function in culture as well as their fresh counterparts. The ability for synthesis (proteins, ATP, GSH) and conjugation and secretion of biliary acids was preserved after deep freeze storage. A better stability of drug metabolizing activities than in rodent hepatocytes was observed in monkey. After thawing, Phase I and Phase II activities (cytochrome P450, ethoxycoumarin-O-deethylase, aldrin epoxidase, epoxide hydrolase, glutathione transferase, glutathione reductase and glutathione peroxidase) were well preserved. The metabolic patterns of several drugs were qualitatively and quantitatively similar before and after cryopreservation. Lastly, cytotoxicity tests suggested that the freezing/thawing steps did not change cell sensitivity to toxic compounds.     

Hepatic zonation of drug metabolizing enzymes. Studies on hepatocytes isolated from the periportal or perivenous region of the liver acinus

Models of hepatic intraacinar zonation have been proposed previously; in most models, direct visualization of the acinar destruction is not possible while intact hepatocyte recovery-viability often presents a problem for subsequent metabolic studies. In the present studies, the liver is isolated in situ and perfused with Krebs-Henseleit buffer, pH 7.4. A 1.5-mL intrahepatic volume of a 7 mM digitonin solution is then injected at a flow rate of 6 mL/min for 15 s via the portal vein or via the vena cava for selective destruction of the periportal (PP) or perivenous (PV) region of the acinus. To avoid diffusion of the detergent throughout the acinus, the liver is then immediately perfused with oxygenated Hanks buffer in the direction opposite to that of digitonin injection. The preparation can then be used for histological evaluation, for studies on isolated-perfused liver, or for isolation of hepatocytes. Direct visualization of the acinar destruction can be achieved by coloring the permeabilized cells with 0.2 mM trypan blue; the liver is then fixed in situ by a 10-min perfusion with paraformaldehyde and histological evaluation is achieved by eosine staining of liver slices. Following isolation of hepatocytes by collagenase perfusion, a highly significant PV localization was found for the synthesis of glutamine, the N-demethylation of aminopyrine, and the glucuronidation of p-nitrophenol, whereas a highly significant PP zonation was found for alanine aminotransferase. By contrast, no specific acinar zonation was found for the enzymes 7-ethoxycoumarin O-deethylase and aniline p-hydroxylase. Total cytochrome P-450 was 0.42 +/- 0.006 and 0.4 +/- 0.03 nmol/10(6) hepatocytes in PV and PP, respectively (nonsignificant).(ABSTRACT TRUNCATED AT 250 WORDS)     

High-performance liquid chromatography method for the simultaneous determination of sulfamethoxazole and trimethoprim in bovine milk using an on-line clean-up column

A bidimensional HPLC method for the simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) in bovine milk has been developed and validated. After centrifugation, aliquots (150 microl) of milk samples were directly injected to a column-switching HPLC system. At the first step a RAM octyl-BSA column was employed to automatically remove proteins that otherwise would interfere with milk analysis. The mobile phase 0.01 M phosphate buffer pH 6.0:acetonitrile (95:5, v/v) was used in the first 5 min for the elution of milk proteins and then 0.01 M phosphate buffer pH 6.0:acetonitrile (83:17, v/v) for transfer SMX and TMP to the analytical column. The separation of SMX and TMP from one another and from other remaining milk components was performed on an octyl column using the mobile phase 0.01 M phosphate buffer pH 5.0:acetonitrile (82:18, v/v), which were detected by UV at 265 nm. The calibration graphs were linear in the concentration ranges of 25-800 ng/ml and 50-400 ng/ml for SMX and TMP, respectively. The intra- and inter-assay coefficients of variation were less than 15% for both drugs. The validated method was applied to the analysis of milk samples of twelve (two groups of six) cows after administration (intramuscular or subcutaneous) of a single recommended therapeutic dose of the SMX-TMP combination.     

Thermal inactivation of ileal loop-reactive Clostridium perfringens type A strains in phosphate buffer and beef gravy.

The thermal resistance of spore crops produced from each of two ileal loop-reactive strains of Clostridium perfringens type A was determined in two suspending vehicles consisting of 0.067 M (pH 7.0) phosphate buffer and a commercial beef gravy. D115.6 values obtained in buffer and enumerated after pretreatment with sodium ethylenediaminetetraacetate and recovery in plating medium containing lysozyme were two- to threefold greater than those obtained without this treatment. D115.6 values obtained with beef gravy were less than those obtained in buffer with or without lysozyme; however, the D98.9 and D104.4 values were 1.3 to 2 times greater than those obtained in buffer with lysozyme. The z values were within the ranges reported by previous investigators.     

Solubilization of 3-hydroxy-3-methylglutaryl coenzyme A reductase from rat and chicken liver microsomes

A simple, efficient, freeze-thaw procedure for the solubilization of liver 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase has been developed. Microsomes of chicken or rat liver were prepared by homogenization in buffer containing 100 mm sucrose, 50 mm KCl, 40 mm KH₂PO₄, 30 mm EDTA, and 2 mm DTT, pH 7.2 (buffer A). The homogenate was centrifuged at 12,000g (15 min), and the microsomes were separated from the supernatant by centrifugation at 100,000g (60 min). The isolated microsomes were frozen, either by dry ice-acetone or by storage in a freezer at ?20°C. The frozen microsomes were permitted to thaw at room temperature, homogenized in buffer A, and centrifuged at 100,000g (60 min). The extraction was repeated and the combined supernatants contained 70 to 90% of the microsomal HMG-CoA reductase activity. The yield of enzyme activity by the freeze-thaw technique is equal to or greater than previously reported methodologies and is significantly easier to perform. This procedure is particularly suited to the preparation of large quantities of solubilized enzyme for isolation and characterization of HMG-CoA reductase. In addition, this method does not require the use of detergents, sonification, or other procedures which might partially inactivate or alter the molecular properties of the enzyme.     

Antigen retrieval trial for post-embedding immunoelectron microscopy by heating with several unmasking solutions.

A novel antigen retrieval procedure was carried out in the post-embedding immunogold electron microscopy method to improve the stainability of the samples. This was done by weakly fixing cultured Helicobacter pylori (ATCC43504) and embedding in Lowicryl K4M. Before staining with the anti-H. pylori antibody, the ultrathin sections were mounted on a nickel grid and heated at 121C for 15 min, 99C for 40 min, and 65C for 24 hr in distilled water, 0.1 M phosphate buffer (pH 7.4), 0.01 M EDTA (pH 7.2), 0.05 M Tris buffer (pH 10.0), 0.8 M urea (pH 7.2), 0.01 M citric acid (pH 6.0), or a commercially available target unmasking fluid (S1699; pH 6.0). Antigen retrieval in the Tris buffer solution generally showed better stainability than the classical post-embedding method without any antigen retrieval. At 65C for 24 hr, better stainability of the ultrasections was observed for each of the solutions used except for the phosphate buffer compared to the control. We suggest that the antigen retrieval method should be applied for routine use even by in post-embedding immunogold electron microscopy.     

Hormonal regulation of mitochondrial function. Description of a system capable of mimicking several effects of glucagon

Isolated rat liver mitochondria were incubated at 0 degrees C in a medium consisting of 225 mM sucrose, 10 mM KCl, 1 mM EDTA, 10 mM KH2PO4, 5 mM MgCl2 and 10 mM Tris-HCl, pH 7.4 (buffer 1) for 10 min, centrifuged and resuspended in 0.3 M sucrose. This treatment resulted in a stimulation of mitochondrial functions, mimicking several of the effects that follow glucagon treatment of the intact rat or isolated hepatocytes. Both phosphate and potassium are required for this effect; the addition of magnesium serves to enhance it. Mitochondrial respiration is essential for the development of the activated state as the stimulation is blocked by increasing concentrations of rotenone in the incubation. The intramitochondrial ATP/ADP ratio is increased, but when this increase was prevented by including low levels of rotenone or oligomycin in buffer 1, the stimulation of mitochondrial function was not diminished, thus demonstrating that an increased ATP/ADP ratio is not essential for activation. The rate of citrulline formation was unaffected by buffer 1 treatment unless glutamate was also included in the medium, indicating that control of this mitochondrial function differs from other functions studied.     

Thermal inactivation of ileal loop-reactive Clostridium perfringens type A strains in phosphate buffer and beef gravy.

The thermal resistance of spore crops produced from each of two ileal loop-reactive strains of Clostridium perfringens type A was determined in two suspending vehicles consisting of 0.067 M (pH 7.0) phosphate buffer and a commercial beef gravy. D115.6 values obtained in buffer and enumerated after pretreatment with sodium ethylenediaminetetraacetate and recovery in plating medium containing lysozyme were two- to threefold greater than those obtained without this treatment. D115.6 values obtained with beef gravy were less than those obtained in buffer with or without lysozyme; however, the D98.9 and D104.4 values were 1.3 to 2 times greater than those obtained in buffer with lysozyme. The z values were within the ranges reported by previous investigators.