Effect of vitamin E supplementation with standard treatment on oxidant-antioxidant status in chronic obstructive pulmonary disease

BACKGROUND & OBJECTIVES

Chronic oxidant burden and depletion of endogenous antioxidants have been proposed to play a key role in the pathogenesis of chronic obstructive pulmonary disease (COPD). Exogenous antioxidants have potential therapeutic implications and their role has not been explored in COPD. The objective of this study was to investigate the effect of supplementation of standard treatment (inhaled long-acting beta(2) agonists, anticholinergics and corticosteroids) with vitamin E on oxidant-antioxidant balance in patients with COPD.

METHODS

The study was carried out in the outpatient setting. Patients were divided into two groups: group A- placebo group (n=14), receiving only standard therapy, and group B- vitamin E-supplemented group (n=10), receiving 400 IU of vitamin E capsules twice daily in addition to standard therapy. Spirometry and clinical assessment were carried out at the start and completion of 8 wk treatment along with measurements of several biochemical parameters of oxidant-antioxidant status in plasma, leukocytes and red cells separated from venous blood.

RESULTS

Leukocyte superoxide generation was decreased in both the groups. Vitamin E-supplemented group had significantly increased levels of plasma sulphydryls and red cell catalase while the placebo group had decreased levels of plasma nitrates and nitrites. No significant differences were observed in red cell superoxide dismutase and glutathione peroxidase activities, total blood glutathione, and plasma total antioxidant capacity, lipid peroxides and glutathione peroxidase activity in either group. There was a similar degree of lung function and clinical improvement in both the groups.

INTERPRETATION & CONCLUSION

Our findings showed that an 8 wk supplementation of standard treatment with 400 IU twice daily of vitamin E did not provide any additional clinical benefit although it augmented certain endogenous antioxidants in patients with COPD.

Targeting protein acetylation for improving cancer therapy

Acetylation is one of the most important post-translational modification of proteins determining the structure, function and intracellular localization that plays an important role in the signal transduction pathways related to diverse cell functions, both during unstimulated and stress conditions. Protein acetylation in cells is regulated by a co-ordinated action of histone acetyl transferases (HAT) and histone deacetylases(HDAC) that ensures the maintenance of homeostasis and execution of activities related to damage response viz. DNA repair, cell cycle delay, apoptosis and senescence. Since inhibition of histone deacetylation, stalls the progress of many nuclear events including proliferation and damage response events on the one hand and the levels of deacetylases are elevated in many tumours on the other. Histone deacetylase has been among the targets for the development of anticancer drugs and adjuvant. The recent observation showing acetylation of proteins by calreticulin (an endoplasmic reticulum resident protein) with a high efficiency when polyphenolic acetates are the acetyl group donating molecules and acetyl CoA as weak substrate extends the realm of protein acetylation beyond HAT/HDAC combination. Elucidation of the relative roles of HAT/HDAC mediated acetylation viz. a calreticulin mediated acetylation in cell function under a variety of stress conditions would hold key to the design of drugs targeting protein acetylation system.

Cell death regulation by B-cell lymphoma protein

Bcl-2 (B Cell Lymphoma) protein is an anti-apoptotic member of Bcl-2 family, which is comprised of pro- and anti-apoptotic members. It regulates cellular proliferation and death by inter- and intra-family interactions. It has a potential to suppress apoptotic cell death under variety of stress conditions by modulating mitochondrial transmembrane potential. However, prevalence of constitutively activated Bcl-2 cellular activity is not always required in cells; a mechanism likely exists in cells, which controls its activity. When expression of Bcl-2 is unregulated, it generates lymphoma like, follicular B-cell lymphoma. This article reviews the structural and functional regulation of Bcl-2 activity at transcriptional, translational, domain, structural and post-translational level, which also accounts for the effects of its deletion and site-directed mutants in the regulation of cellular proliferation and differentiation in vitro and in vivo. This concisely reviewed information on Bcl-2 helps us to update our understanding of cell death and its modulation by Bcl-2 and its mutant's interaction, which has gained therapeutic benefits in cell growth and proliferation, particularly for sensitive human hematopoietic stem cells.

Structural conservation of residues in BH1 and BH2 domains of Bcl-2 family proteins

The sequence of Bcl-2 homology domains, BH1 and BH2, is known to be conserved among anti- and pro-apoptotic members of Bcl-2 family proteins. But structural conservation of these domains with respect to functionally active residues playing role in heterodimerization-mediated regulation of apoptosis has never been elucidated. Here, we have suggested the formation of an active site by structurally conserved residues in BH1 (glycine, arginine) and BH2 (tryptophan) domains of Bcl-2 family members, which also accounts for the functional effect of known mutations in BH1 (G145A, G145E) and BH2 (W188A) domains of Bcl-2.

Effects of Vitamin E on airway responses and biochemical parameters in guinea pigs sensitized to ovalbumin

The effect of dietary supplementation with Vitamin E was studied in sensitized guinea pigs. After measurement of baseline airway reactivity and sensitization with ovalbumin, the animals were randomized into two groups: Group A, on a commercial feed and Group B, on dietary supplementation with oral Vitamin E (0.7 IU/kg). These were challenged with inhaled ovalbumin after 4 weeks. The following outcomes were studied: airway responses to ovalbumin inhalation, airway reactivity, sodium and calcium ion influx in isolated tracheal cells, Na+ K+ ATPase and Ca2+ ATPase activity in tracheal homogenate and plasma malonaldehyde. Sensitization increased airway reactivity in Group A but not in Group B. The tracheal cells of animals in Group B showed significantly lower rates of 45Ca and 22Na influx and lower activities of tracheal Na+ K+ ATPase and Ca2+ ATPase as compared to Group A. Plasma malonaldehyde was similar between two groups. We concluded that Vitamin E suppresses the increase in airway reactivity following sensitization and has membrane stabilizing actions.

Effect of sensitization on membrane ion fluxes & intracellular calcium in guineapigs

BACKGROUND & OBJECTIVES

The biochemical mechanisms underlying the development of sensitization-induced airway hyperresponsiveness (AHR) in asthma are poorly defined. Alterations in the regulation of intracellular calcium may play an important role in its pathogenesis. We carried out this study to see the effect of sensitization with ovalbumin on membrane ion fluxes and intracellular calcium in a guinea pig model.

METHODS

Airway reactivity to inhaled histamine was measured initially and after sensitization with ovalbumin in 28 guineapigs. Intracellular calcium [Ca(2+)]i was measured in tracheal smooth muscle cells and peripheral leukocytes using fluorescent dye FURA 2AM. Calcium and sodium ion influx across the cell membrane was measured in leukocytes. Ouabain-sensitive Rubidium ((86)Rb) influx was measured in tracheal smooth muscles cells. The activities of Na(+), K(+) ATPase and Ca(2+) ATPase were measured in tracheal smooth muscle cells. Lipid peroxides were measured in plasma.

RESULTS

Airway responsiveness was significantly (P<0.001) increased after sensitization along with an increase in [Ca2+]i levels in leukocytes and tracheal smooth muscle cells, higher rates of (45)Ca and (22)Na influx in leukocytes and higher (86)Rb influx rates in tracheal smooth muscle cells, and increased levels of lipid peroxides in plasma.

INTERPRETATION & CONCLUSION

In guineapig model of asthma sensitization to allergen increased the membrane permeability to calcium and sodium, and intracellular calcium levels. These alterations may play a role in the pathogenesis of airway hyper-responsiveness following sensitization.

Suicidal oxidative stress induced by certain antioxidants

Well known antioxidants-coumarins (7,8-dihydroxy-4-methyl coumarin-DHMC and 7,8-diacetoxy-4-methyl coumarin-DAMC) and flavonoids (quercetin-Q and quercetin penta-acetate-QPA) were investigated for their pro-oxidant effects in two human tumor cell lines. The breast carcinoma cell line (MDA-MB-468) was found to be more sensitive to treatment by the drugs-DAMC, Q and QPA at 10 microM than the glioma cell line (U-87MG), while DHMC was non toxic in both cell lines at this concentration. In MDA-MB-468 distinct growth inhibition was observed by 48 hr post treatment. Paradoxically, an increase in the formazan production was revealed by MTT assay at this time indicating an increase in the production of free radicals. An increase in the levels of reactive oxygen species (ROS) was also confirmed by DCFH-DA assay. In cells treated with DAMC, Q and QPA an increase in the percentage of cells with the hypodiploid DNA content was suggestive of apoptotic cell death. Taken together, these results suggest that an increase in oxidative stress caused by the pro-oxidant action of these drugs is responsible for cell death.

Microsomal acetoxy drug: protein transacetylase of placenta: part 1. Characterization of DAMC: GST transacetylase

We have earlier established in tissues of several mammalian animal species the existence of a novel membrane bound enzyme termed 7,8-diacetoxy-4-methylcoumarin (DAMC): protein transacetylase (TAase) that possibly transfers acetyl groups from the model acetoxy drug (DAMC) to certain enzyme protein viz. glutathione S-transferase (GST), cytochrome P-450 and NADPH cytochrome C reductase leading to the drastic modulation of their catalytic activities. We have in this report extended the studies to human tissue and characterized TAase from placenta. For this purpose placental microsomes were preincubated with DAMC along with the receptor protein (cytosolic GST) followed by the addition of the substrates of GST in order to quantify the catalytic activity of GST, the extent of inhibition of GST served as a measure of TAase. Placental TAase was also found to irreversibly activate NADPH cytochrome C reductase by DAMC. Placental enzyme activated the reductase even at very low concentration of DAMC. Iodoacetamide nearly abolished the placental TAase suggesting the presence of active thiol group in the enzyme and the TAase demonstrated hyperbolic kinetics. Kinetic constants obtained by varying the concentrations of either of the substrates DAMC or cytosolic GST characterized TAase catalysed reaction as the bimolecular reaction. Further studies are in progress to delineate the physiological importance of TAase in placenta.

Buffalo plasma fibronectin: a physico-chemical study

Plasma fibronectin (FN) of buffalo (Babulis babulis) was purified to apparent homogeneity, using gelatin-Sepharose and heparin-Sepharose affinity columns. It was found to have two subunits of molecular mass 246 kDa and 228 kDa, on SDS-gel. Its immunological cross-reactivity with anti-human plasma FN was confirmed by Western blotting. The amino acid composition was found to be similar to that of human and bovine plasma FNs. Buffalo plasma FN contained 2.23% neutral hexoses and 1.18% sialic acids. No titrable sulfhydryl group could be detected in the absence of denaturant. Reaction with DTNB indicated 3.4 sulfhydryl groups in the molecule, whereas BDC-OH titration gave a value of 3.8 -SH groups in buffalo plasma FN. Stoke's radius, intrinsic viscosity, diffusion coefficient and frictional ratio indicated that buffalo plasma FN did not have a compact globular conformation at physiological pH and ionic strength. Molecular dimensions (average length, 120 nm; molar mass to length ratio, 3950 nm(-1) and mean diameter, 2.4 nm) as revealed by rotary shadowing electron microscopy further supported the extended conformation of buffalo plasma FN. These results show that buffalo plasma FN has similar properties as that of human plasma FN.

Relationship between intracellular calcium and airway reactivity in guinea pigs

The present study was carried out to examine the relationship between intracellular free calcium ion concentrations and its regulatory enzymes, sodium potassium adenosine triphosphatase (Na(+),K(+)-ATPase) and calcium adenosine triphosphatase (Ca(2+)-ATPase), with airway reactivity to inhaled histamine in guinea pigs. Forty-nine guinea pigs were included in this study. Of these, 34 animals responded to histamine bronchoprovocation challenge in vivo with a greater than 35% fall in specific airways conductance and were labeled as "reactive," and the remaining 15 were "nonreactive." The dose of histamine producing a 35% fall in specific airways conductance was labeled as ED(35) SGaw. The animals were then sacrificed, and the following biochemical measurements were carried out: intracellular free calcium ion concentrations [Ca(2+)](i) in leukocytes and isolated tracheal smooth muscle cells, activities of Na(+),K(+)-ATPase and Ca(2+)-ATPase in tracheal homogenate, and plasma levels of lysophosphatidylcholine (LPC). Reactive guinea pigs showed significantly higher [Ca(2+)](i) and Na(+),K(+)-ATPase and Ca(2+)-ATPase activities. Airway reactivity (ED(35) SGaw) had significant negative correlation with [Ca(2+)](i), with activities of each of the ATPases and with plasma lysophosphatidylcholine. It is concluded that the level of [Ca(2+)](i) is an important determinant of airway reactivity. Intracellular calcium levels modulate airway response to histamine with higher levels being associated with greater reactivity.

Acetoxy-4-methylcoumarins confer differential protection from aflatoxin B(1)-induced micronuclei and apoptosis in lung and bone marrow cells

The ability of various acetoxy derivatives of 4-methylcoumarins to inhibit the genotoxic changes due to aflatoxin B(1) (AFB(1)) is reported here. Several 4-methylcoumarins (test compounds), such as 7,8-diacetoxy-4-methylcoumarin (DAMC), monoacetoxy-4-methylcoumarin (MAC), 5-N-acetyl-6-acetoxy-4-methylcoumarin (NAMC) and 7,8-dihydroxy-4-methylcoumarin (DHMC) were separately administered intraperitoneally (i.p.) to male wistar rats followed by AFB(1) administration i.p. or intratracheally (i.t.) (2-8 mg/kg b.wt.) and another dose of the test compound. The animals were sacrificed 26h after AFB(1) administration. From animals receiving AFB(1) i.p., bone marrow (BM) cells were isolated and stained with Mayer's haematoxylin and eosin. Micronuclei (MN) in BM were scored by light microscopy. From animals receiving AFB(1) i.t., bronchoalveolar lavage (BAL) was obtained, lung cells (LG) were isolated and stained with fluorochrome 6-diamidino-2-phenylindole (DAPI) for the analysis of MN, apoptotic bodies (AP) and cell cycle variations. Rats were separately treated with the vehicle DMSO to serve as the proper control. AFB(1) caused significant dose-dependent induction of MN in BM as well as LG. AP were observed in LG of rats receiving AFB(1) and was found to correlate with MN induction. DAMC injection caused significant decrease in AP due to AFB(1) in LG and MN in both BM and LG. The effectiveness of MAC was approximately half that of DAMC, thereby indicating that number of acetoxy groups on the coumarin molecule determine the efficacy. The fact that NAMC had no effect either on MN or AP indicate that neither acetoxy group at C-6 nor the N-acetyl group at C-5 facilitate the transfer of acetyl group to P-450 required for inhibition of AFB(1)-epoxidation. DHMC, the deacetylated product of DAMC had no normalizing effect on the induction of MN and AP. These findings confirm our earlier hypothesis that DAMC-mediated acetylation of microsomal P-450 (catalysing epoxidation of AFB(1)) through the action of microsomal transacetylase is responsible for the protective action of DAMC. The relative number and position of acetoxy groups on the coumarin nucleus determine the specificity to the transacetylase necessary for the chemopreventive action.

Chemoprevention of benzene-induced bone marrow and pulmonary genotoxicity

Our earlier studies documented the ability of 7,8-diacetoxy-4-methylcoumarin (DAMC) to cause irreversible inhibition of cytochrome P-450 linked mixed function oxidases (MFO) mediated by membrane bound DAMC: protein transacetylase. Since P-450 catalyzed oxidation of benzene is crucial to its toxic effects, the action of DAMC and related analogues were considered promising in preventing the genotoxicity due to benzene. For this purpose rats were pretreated with various acetoxy-4-methylcoumarins (test compounds), which was followed by the administration of benzene either intratracheally (IT) or intraperitoneally (IP), and sacrificed 26 h after the injection of benzene. The incidence of micronuclei (MN) in bone marrow (BM) and lung (LG) were assessed by light and fluorescent microscopy, respectively. A dose-dependent induction of MN in BM and LG cells was observed in rats administered with benzene. A significant reduction in benzene-induced MN in BM and LG was observed as a result of DAMC administration to rats; a higher dose of DAMC resulted in greater inhibition of clastogenic action of benzene as revealed by MN incidence. 7,8-dihydroxy-4-methylcoumarin (DHMC), the deacetylated product of DAMC, demonstrated relatively lesser potency to inhibit the clastogenic action of benzene. This observation is consistent with the ability of DAMC to inhibit the formation of benzene oxide as well as to scavenge the oxygen radicals formed during the course of benzene metabolism. The fact that DHMC can only scavenge the oxygen radicals and is ineffective in inhibiting benzene oxidation in vivo explains the reduced capability of dihydroxy coumarin to prevent MN due to benzene. 7-Acetoxy-4-methylcoumarin (MAC) inhibits the MN due to benzene being roughly 50% of that produced by DAMC. DAMC is also effective in normalizing the cell cycle alterations produced by benzene in BM and LG. These observations further substantiate our hypothesis that the biological effects of acetoxy coumarins are mediated by the action of membrane bound transacetylase that catalyzes the acetylation of concerned proteins. Teratogenesis Carcinog. Mutagen. 21:181-187, 2001.

Mechanism of biochemical action of substituted benzopyran-2-ones. part 8: acetoxycoumarin: protein transacetylase specificity for aromatic nuclear acetoxy groups in proximity to the oxygen heteroatom

Our earlier work established a convenient assay procedure for acetoxycoumarin (AC): protein transacetylase (TA) by indirectly quantifying the activity of glutathione (GSH)-S-transferase (GST), the extent of inhibition of GST under the conditions of the assay represented TA activity. In this communication, we have probed the specificity for TA with respect to the number and position of acetoxy groups on the benzenoid as well as the pyranone rings of the coumarin system governing the efficient transfer of acetyl groups to the protein(s). For this purpose, coumarins bearing one acetoxy group, separately at C-3 or C-4 position and 4-methylcoumarins bearing single acetoxy group, separately at C-5, C-6 or C-7 position were synthesized and specificities to rat liver microsomal TA were examined. Negligible TA activity was discernible with 3-AC as the substrate, while the substrate efficiency of other AC were in the order 7-acetoxy-4-methylcoumarin (7 AMC)>6 AMC>5 AMC=5 ADMC=4 AC. To achieve a comparable level of GST inhibition which was proportional to the enzymatic transfer of acetyl groups to the protein (GST), the concentrations of 7-AMC, 6-AMC, 5-AMC and 4-AC were in the order 1:2:4:4, respectively. One diacetoxycoumarin, i.e., 7,8-diacetoxy-4-methylcoumarin (DAMC) was also examined and it was found to elicit maximum level of GST inhibition, nearly twice that observed with 7-AMC. These observations lead to the logical conclusion that a high degree of acetyl group transfer capability is conferred when the acetoxy group on the benzenoid ring of the coumarin system is in closer proximity to the oxygen heteroatom, i.e., when the acetoxy groups are at the C-7 and C-8 positions.

Synthetic and biological activity evaluation studies on novel 1,3-diarylpropenones

Fourteen novel C-prenylated and O-allylated 1,3-diarylpropenones (chalcones) were synthesized by Claisen-Schmidt condensation reaction of C-prenylated/O-allylated acetophenones with appropriate aldehydes; twelve of these model chalcones were screened in an assay based on the confrontation of invasive human MCF-7/6 mammary carcinoma cells with fragments of normal embryonic chick heart in vitro. Out of the twelve chalcones tested, three were found to exhibit potent anti-invasive activity. Some of these chalcones and their precursor acetophenones were also tested for inhibition of initiation of lipid peroxidation in rat liver microsomes; a prenylated acetophenone carrying two methoxy groups and two free phenolic hydroxy functions was found to be a potential antioxidant.

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 7: Assay and characterization of 7,8-diacetoxy-4-methylcoumarin:protein transacetylase from rat liver microsomes based on the irreversible inhibition of cytosolic glutathione S-transferase

The enzymatic transfer of acetyl groups from acetylated xenobiotics to specific proteins is a relatively grey area in the evergreen field of biotransformation of foreign compounds. In this paper, we have documented evidence for the existence of a transacetylase in liver microsomes that catalyses the transfer of acetyl groups from 7,8-diacetoxy-4-methylcoumarin (DAMC) to glutathione S-transferase (GST), either purified or present in cytosol leading to the irreversible inhibition of GST. A simple procedure is described for the assay of transacetylase by preincubation of DAMC with liver microsomes and pure GST/liver cytosol, followed by the addition of 1-chloro-2,4-dinitrobenzene (CDNB) and reduced glutathione (GSH) in order to quantify GST activity by the conventional procedure. The extent of inhibition of GST by DAMC under the conditions of the assay is indicative of DAMC:protein transacetylase activity. Following the assay procedure described here, the transacetylase was shown to exhibit hyperbolic kinetics. The bimolecular nature of the transacetylase reaction was apparent by the demonstration of Km and vmax values. 7,8-Dihydroxy-4-methylcoumarin (DHMC), one of the products of transacetylase reaction was identified and quantified using the partially purified enzyme. The fact that p-hydroxymercuribenzoate (PHMB) and iodoacetamide abolished irreversible inhibition of GST upon the action of transacetylase on DAMC strongly characterized transacetylase as a protein containing thiol group at the active site. In addition, the relative specificities of acetoxy 4-methylcoumarins to transacetylase have been demonstrated.

Aflatoxin B1-induced micronuclei and cell cycle alterations in lung and bone marrow cells and their modulation by Piper argyrophyllum extract

Aflatoxin B, (AFB1) is a clastogen that causes cellular damage by covalent modification of nucleic acids. In this investigation, male rats were injected i.p. with AFB1 (8 mg/kg b.w.) in DMSO and the same dose of AFB1 was also administered intratracheally (i.t.) to the animals separately. The animals were killed after 26 h of the carcinogen treatment, femur bone was removed, and bone marrow cells were isolated and stained with Mayer's hematoxylin and eosin. Micronuclei (Mn) were scored by using light microscopy. Bronchoalveolar lavage (BAL) was prepared from rats administered AFB1 i.t. A part of BAL was fixed with 70% ethanol, stained with the fluorochrome DAPI, and analysed for cell cycle variations; the other part of the lavage was used for making slides to record Mn with a fluorescent microscope. A significantly greater proportion of lung cells were found to enter cell cycle with extended S-phase due to AFB1 treatment. Mn were induced in polychromatic erythrocytes (PCE) as compared to normochromatic erythrocytes (NCE) in the bone marrow of AFB1-treated rats, where there was nearly a three-fold increase in the number of Mn of bone marrow cells. The administration of AFB1 resulted in a two-fold rise in the Mn in the lung cells. The effect of BSO, DEM, and PB, the modulators of AFB1 metabolism, was studied on AFB1-induced Mn formation. A significant increase in the Mn score in PCEs of BSO- and DEM-treated rats was noted, while a slight reduction in the Mn score was noted in the case of PB-treated rats. The administration of the methanol extract of the leaves of Piper argyrophyllum (taken up in DMSO) to rats for a week exhibited normalising effect on AFB1-induced Mn in bone marrow cells. These observations record the induction of Mn in lung cells due to AFB1 for the first time. We propose the utility of AFB1-induced Mn as a model for screening plant extracts as inhibitors of genotoxicity. Prevention of genotoxic changes described above by phytochemicals is being pursued in our Laboratories.

Long-term stability of bronchial reactivity in guinea pigs

Measurement of lung function and bronchial reactivity are widely used as outcome parameters to assess the efficacy of therapeutic interventions. In order to interpret the results correctly, it is necessary that the outcome parameters are themselves stable over time so that any significant changes measured may be attributed to the interventions. Specific airway conductance (SGaw) and airway reactivity to histamine are two commonly used parameters in animal models such as guinea pigs. Although short-term variability of these parameters has been investigated, there has been no study of long-term stability. In the present paper, SGaw and bronchial reactivity to histamine were measured in 111 conscious guinea pigs using a non-invasive, whole body plethysmograph. Baseline values of SGaw and ED35 histamine were measured and followed for eight weeks at weekly intervals. At baseline, mean SGaw in guinea pigs was 0.17 +/- 0.055 sec-1 cm H2O-1 and ED35 histamine ranged from 0.064 to more than 10 mg/ml. The distribution of ED35 histamine values was gaussian. We observed that the changes in SGaw and ED35 histamine recorded using this technique are highly reproducible over eight weeks. The reactivity varied by less than a doubling dose of histamine over any two consecutive weeks. Thus, the technique described in this paper is quick, easily learned, reproducible, independent of temperature-humidity artifact and highly suitable for studies of repeated measurements as in the study of dietary interventions and evaluation of effect of drugs.

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 5: Pulse radiolysis studies on the antioxidant action of 7,8-diacetoxy-4-methylcoumarin

7,8-Dihydroxy-4-methylcoumarin (1, DHMC) and 7,8-diacetoxy-4-methylcoumarin (2, DAMC) were shown to possess radical scavenging property and strongly inhibit membrane lipid peroxidation. Although free polyphenolic compounds are known to be antioxidants, the antioxidant action of the acetoxy compound DAMC was intriguing. Hence, pulse radiolysis studies were undertaken to explain the antioxidant action of DAMC. Accordingly, DAMC and DHMC were separately reacted with the system generating azide radicals and the resulting transient spectra were recorded. The spectra so obtained in both the cases demonstrated peak at 410 nm, characteristic of phenoxyl radical. The rate constants for the formation of phenoxyl radical from DHMC and DAMC were 34 x 10(8) M(-1) s(-1) and 6.2 x 10(8) M(-1) s(-1), respectively. We propose that the free radical mediated oxidation of DAMC initially produces a radical cation that loses an acetyl carbocation to yield the phenoxyl radical. It is possible to conclude that the mechanism of the antioxidant action of DAMC follows the pathway similar to that of DHMC involving the formation of a stable phenoxyl radical.

Synthesis of E- and Z-pyrazolylacrylonitriles and their evaluation as novel antioxidants

A facile synthesis of (Z)- and (E)-2-(5-arylpyrazol-3-yl)-3-(pyrrol-2-yl)acrylonitriles and (Z)-2-(1,3-diarylpyrazol-5-yl)-3-pyrrol-2-yl)acrylonitriles, and isomerisation of (Z)-2-(5-arylpyrazolyl)acrylonitriles to (E)-2-(5-arylpyrazolyl)acrylonitriles under basic conditions have been reported. (Z)-2-(1,3-Diarylpyrazolyl)acrylonitriles did not undergo isomerisation under the similar conditions. New compounds were identified on the basis of their spectral data (1H-, 13C-, 1H-1H COSY, NOESY, NOE, HMQC NMR, IR, UV and EI mass). The structures of one acrylonitrile and five of their precursor 6-arylpyran-2-ones and cyanomnethylpyrazoles were confirmed by X-ray crystallographic studies. Effects of pyrazolylacrylonitriles and their precursors on rat liver-microsomal lipid peroxidation were evaluated in vitro with a view to establish structure activity relationship and to identify a lead compound.

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 4: hyperbolic activation of rat liver microsomal NADPH-cytochrome C reductase by the novel acetylator 7,8-diacetoxy-4-methylcoumarin

The effect of 7,8-diacetoxy-4-methylcoumarin (DAMC) has been studied on hepatic NADPH cytochrome C reductase-- an enzyme participating in the microsomal electron transport. The preincubation of liver microsomes with DAMC resulted in a time-dependent activation of NADPH cytochrome C reductase. The catalytic activity of the enzyme enhanced nearly 600% by 25 microM concentration of DAMC after 10 min of preincubation. The action of DAMC on the reductase resulted in enhanced v(max) while Km remained constant. A plot of 1/v(max) as a function of DAMC concentration resulted in a non-linear, but rectangular hyperbola indicative of hyperbolic activation. DAMC was also proved to be effective in significantly enhancing the activity of NADPH cytochrome C reductase in vivo. 7,8-Dihydroxy-4-methylcoumarin (DHMC), the deacetylated product of DAMC failed to irreversibly activate the enzyme. The activation effect of DAMC upon the enzyme was abolished by p-hydroxymercury benzoate. The role of a transacetylase in transferring the acetyl group of DAMC to the amino acid(s) of the active site of NADPH cytochrome C reductase causing irreversible enzyme activation is enunciated.

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 3: A novel mechanism for the inhibition of biological membrane lipid peroxidation by dioxygenated 4-methylcoumarins mediated by the formation of a stable ADP-Fe-inhibitor mixed ligand complex

7,8-Dihydroxy-4-methylcoumarin (DHMC) and 7,8-diacetoxy-4-methylcoumarin (DAMC) have been reported to effectively inhibit in-vivo lipid peroxidation in rat tissues induced by CCl4 and paraquat. DHMC was found to readily impart green colour to the lipid peroxidation incubation mixture containing ADP and Fe3+, whereas DAMC formed green complex only upon incubation with liver microsomes, confirming our earlier observation that liver microsomal deacetylase hydrolyses DAMC to DHMC. Sensitive pH metric technique revealed the formation of ADP-Fe-DHMC ternary complex with highest stability, while Fe-DHMC and ADP-DHMC had negligible stabilities concluding that ADP-perferryl ion formation is prevented by DHMC resulting in the production of stable ternary mixed ligand complex (ADP-Fe-DHMC), thereby inhibiting the formation of O2-, and eventually other reactive oxygen species (ROS) responsible for membrane lipid peroxidation.

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part II: Mechanism-based inhibition of rat liver microsome-mediated aflatoxin B1-DNA binding by the candidate antimutagen 7,8-diacetoxy-4-methylcoumarin

7,8-Diacetoxy-4-methylcoumarin (DAMC), with no prerequisite for oxidative biotransformation has been reported to produce suicide inactivation of microsomal cytochrome P-450-catalysed formation of aflatoxin B1-8,9-oxide that binds to DNA. Parenteral administration of DAMC to rats caused significant inhibition of AFB1 binding to hepatic DNA in vivo as well as AFB1-induced micronuclei formation in bone marrow cells. These results highlight the antimutagenic potential of DAMC.

Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part I: Dioxygenated 4-methyl coumarins as superb antioxidant and radical scavenging agents

Twenty-three 4-methylcoumarins bearing different functionalities have been examined for the first time for their effect on NADPH-catalysed liver-microsomal lipid peroxidation with a view to establish structure-activity relationship. Dihydroxy- and diacetoxy-4-methylcoumarins produced dramatic inhibition of lipid peroxidation. 7,8-Diacetoxy-4-methylcoumarin and 7,8-dihydroxy-4-methylcoumarin were found to possess superb antioxidant and radical scavenging activities.

Antibody against synthetic rat PTH peptide (1-34) blocks PTH-mediated cAMP formation and phosphate transport in opossum kidney cells

A novel antibody against synthetic rat parathyroid hormone (rPTH(1-34)) was successfully produced in rabbits at a titer of 1:3,000. The ability of this antibody to block PTH was studied utilizing the hormone-sensitive cAMP formation and Na(+)-dependent phosphate transport in the opossum kidney (OK) cells. rPTH peptide(1-34) stimulated cAMP formation and inhibited Na(+)-dependent phosphate transport in OK cells in a dose-dependent manner. Treatment of OK cells with the antisera significantly decreased the level of cAMP and attenuated the inhibition of Na(+)-dependent phosphate transport in response to rPTH(1-34) at a dilution of 1:1,000. Nonimmune rabbit sera at the same dilution did not influence these hormone-sensitive effects. We conclude that antibody against synthetic PTH peptide can be used to study the biological activities of this hormone.

Chemoprevention of carcinogen-DNA binding: the relative role of different oxygenated substituents on 4-methylcoumarins in the inhibition of aflatoxin B1-DNA binding in vitro

Eighteen 4-methylcoumarins bearing methoxy/hydroxy/acetoxy functionalities have been reported to effectively inhibit the rat liver microsome-mediated aflatoxin B1-DNA binding in vitro. The contribution of functionality on coumarin nucleus towards the inhibition of AFB1-DNA binding is in the order acetoxy > hydroxy > methoxy. The results illustrate the structure-activity relationship.

Use of sodium hetastarch (Hespan) solution for reduction of postoperative adhesion formation in rabbits

A study was conducted to determine the effect of sodium hydroxy ethyl starch (Hespan) on primary adhesion formation in a rabbit model. Hespan is a readily available volume expander. This was a randomized, double-blinded animal model in which New Zealand white rabbits were subjected to midline celiotomy. Adhesions were created by abrasion in both uterine horns, adjacent bowel, and peritoneum. Necropsies were performed at the 2-week interval and adhesions were graded. Significant decreases in type II and type III adhesions (p = .032 and p = .020, respectively) were demonstrated in Hespan-treated animals. Sodium hetastarch appears to decrease significant adhesion formation in treated animals and may have a role as an adjunct for postsurgical prevention.

Comparative kinetic studies on aflatoxin B1 binding to pulmonary and hepatic DNA of rat and hamster receiving the carcinogen intratracheally

Several epidemiological studies have discussed the outcome of inhalation of airborne aflatoxins by humans. Metabolism of aflatoxin B1 (AFB1) by lung parenchyma leading to DNA binding is reported here. The tissue distribution pattern of [3H]AFB1 radioactivity revealed the lungs to be the second most important organ after the liver to retain a considerable amount of the radioactivity (66%). The lung indicated a selective activation of AFB1 as it showed only 7.7% binding of [3H]AFB1 to pulmonary DNA. Rats and hamsters were dosed with [3H]AFB1 (2 microCi containing 40 micrograms AFB1/100 g body wt.) intratracheally (i.t.) and sacrificed at different intervals after toxin treatment. Peak binding occurred at 0.5, 1, and 2 h in case of hamster lung, rat lung, and alveolar macrophages of both the species, respectively. At the end of 24 h, the relative AFB1-DNA binding (percentage of peak binding) in hamster lung was 72% while that in rat was 24%. The relative binding in rat lung alveolar macrophages (AMs) was generally higher than that of the hamster. AFB1 binding to hepatic DNA of both the species approached the peak at 1 h after the toxin administration i.t. Under these conditions, binding of AFB1 (or its metabolites translocated to liver) to hepatic DNA of both the species progressively diminished with time in contrast to lung, as revealed by the relative binding values at 12 h for rat and hamster lung, which were 48 and 67%, respectively, while for the rat and hamster liver they were 28 and 24%, respectively. Binding of i.t. administered [3H]AFB1 to rat liver DNA is only marginally higher than that observed with hamster liver, in contrast to the wide difference observed in animals receiving AFB1 intraperitoneally. These results highlight the persistence of AFB1 binding to pulmonary DNA, and the extent of translocated AFB1 binding to hepatic DNA presents an interesting difference from that observed when the toxin was administered through a gastrointestinal route. It is worth concluding that AMs unlike many other xenobiotics, possess specific mixed function oxidase activity to epoxidize AFB1.

Piperine, a plant alkaloid of the piper species, enhances the bioavailability of aflatoxin B1 in rat tissues

Piperine is known to modify the biotransformation of drugs. The effect of piperine on the metabolic activation and distribution of [3H]-aflatoxin B1 (AFB1) in rats has been described. Piperine markedly inhibited liver microsome-catalysed [3H]AFB1 binding to calf thymus DNA in vitro, in a dose dependent manner. Rats pretreated with piperine accumulated considerable [3H]AFB1 radioactivity in plasma and in the tissues examined as compared to the controls. However, piperine had no influence on hepatic [3H]AFB1-DNA binding in vivo, which could possibly be due to the null effect of piperine on liver cytosolic glutathione (GSH) 5-transferase activity. Piperine-treated rat liver microsomes demonstrated a tendency to enhance [3H]AFB1 binding to calf thymus DNA in vivo. The effect of piperine on AFB1 metabolism thus closely resembles the mode of action of SKF 525-A on biotransformation of foreign compounds.

Epoxidation of aflatoxin B1 by Aspergillus flavus microsomes in vitro: interaction with DNA and formation of aflatoxin B1-glutathione conjugate

Metabolism of aflatoxin B1 (AFB1) by subcellular preparations of Aspergillus flavus is least understood. The results reported here have demonstrated for the first time the epoxidation of AFB1 and subsequent conjugation with glutathione (GSH). Microsomes prepared from toxigenic mycelia catalysed [3H]AFB1 to calf thymus DNA to a greater extent (approximately 2-fold) as compared to that of non-toxigenic. The binding of [3H]AFB1 to exogenous and A. flavus nuclear DNA catalyzed by A. flavus microsomes was found to be comparable with that of mammalian extrahepatic tissue such as lung. Addition of phenobarbitone to the growing cultures resulted in 1.5-fold increase in [3H]AFB1-DNA binding mediated by microsomes prepared from either of the two strains. Tolnaftate, an inhibitor of aflatoxin synthesis enhanced the epoxidation rate in a dose-related manner. The binding of [3H]AFB1 to DNA catalyzed by A. flavus microsomes was significantly reduced (50% of control) upon addition of hamster liver cytosol, thereby substantiating the formation of the carcinogen adduct with DNA as reported in mammalian tissues. The metabolite formed by subcellular preparation of A. flavus was found to be AFB1-GSH having Rf value (6.5) similar to that obtained for mammalian liver preparations.

Interaction of aflatoxin B1 metabolites with cellular macromolecules in neonatal rats receiving carcinogen through mother's milk

A single dose of 2 microCi [3H] aflatoxin B1 (AFB1) containing 20 micrograms AFB1 was administered to the lactating rat. This resulted in the excretion of AFB1-metabolites in the milk, which were transferred and distributed in many tissues of the offspring consuming milk for 48 h. An equal distribution of radioactivity in liver and lung of suckling rats as well as in their sub-cellular fractions was observed. No AFB1 metabolite binding was apparent with tissue DNA. However, considerable binding of aflatoxin residues was observed with protein followed by RNA. Three metabolites have been detected in the milk sample derived from the stomach of the suckling rats on thin layer chromatogram with Rf values of 0.2, 0.4 and 0.8. Pretreatment of lactating rats with phenobarbitone (PB: 80 mg/kg/3 days) prior to the administration of [3H]AFB1 caused an overall decrease in the radioactivity in the neonatal tissues, particularly lung and intestine (P less than 0.05). The fluorescent bands with Rf values of 0.2 and 0.4 were not visualized in the milk sample from the PB group. Subsequently, the binding of AFB1 residues to cellular macromolecules of neonatal tissues was decreased. PB treatment further resulted in lowering the glucuronide/sulphate conjugates of AFB1 in the milk consumed by suckling rats; AFB1-glutathione (GSH) conjugates were slightly increased. These results point out the possibility that aflatoxin metabolites bind to the tissues of offspring fed by mothers consuming aflatoxin contaminated diets thus leading to chronic effects.

A mechanism of inhibition of aflatoxin B1-DNA binding in the liver by phenobarbital pretreatment of rats

The effect of phenobarbital (PB) pretreatment of rats on both hepatic aflatoxin B1 (AFB1)-DNA binding and AFB1-glutathione (AFB1-SG) conjugation have been examined in studies in vivo and in vitro. Male Sprague-Dawley rats fed a commercial diet with 0.1% PB in their drinking water for 1 week had total wet liver weight and microsomal protein content about 27% and 38% higher, respectively, than controls. Hepatic cytochrome P-450 content, microsomal cytochrome P-450 mediated AFB1 binding to exogenous DNA and formation of hydroxy metabolites of AFB1 were also about threefold higher in PB-treated rats and cytosolic reduced glutathione S-transferase activities were about doubled. Microsome-mediated AFB1-DNA binding, when examined at 2 microM and 10 microM levels of AFB1, was inhibited two-to threefold more by cytosols of treated rats whereas AFB1-SG conjugation was two- to threefold higher by cytosols of treated rats. In reconstitution experiments with 2 microM AFB1, with intact nuclei serving as a source of endogenous DNA, addition of microsomes from either group generated a large amount of AFB1-DNA binding (68-105 pmol) and a smaller amount of AFB1-SG conjugate (12-21 pmol). The presence of cytosol from the controls reduced AFB1-DNA binding to a much lesser extent than the cytosol from the treated group whereas AFB1-SG conjugation was much higher with the cytosol from the treated group. These results are in agreement with the studies in vivo. In isolated hepatocytes at 33 nM, 2 microM and 10 microM AFB1 levels, AFB1-DNA binding was decreased 50 to 70% by prior PB-treatment whereas AFB1-SG conjugation was two- to threefold higher in treated compared to control hepatocytes. In hepatocytes, addition of 1 mM diethylmaleate increased DNA binding two- to threefold with a corresponding decrease in AFB1-SG conjugation. Addition of 1 mM styrene oxide caused 5- to 10-fold increases in AFB1-DNA binding at levels of AFB1 of 33 nM and 2 microM; but at 10 microM AFB1, increases in AFB1-DNA binding were two- to threefold. In intact rats, PB treatment reduced hepatic AFB1-DNA binding to 30% of controls with concomitant increase in biliary excretion of AFB1-SG conjugate. It appears that the induced cytosolic GSH S-transferases after PB treatment of rats plays a significant role in inhibiting hepatic AFB1-DNA binding and hepatocarcinogenesis presumably by inactivation of the reactive AFB1-epoxide.(ABSTRACT TRUNCATED AT 400 WORDS)

Lack of influence of butylated hydroxytoluene on modification of lung microsome mediated aflatoxin B1-DNA binding: role of pulmonary glutathione S-transferase

Phenolic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are known to inhibit tumor formation due to several chemical carcinogens including aflatoxin B1 (AFB1). Metabolic activation of AFB1 by lung microsomes and possible modification by dietary BHA was reported in an earlier communication (Allameh et al. (1988) Cancer Lett., 40, 49). Here we report the effect of dietary BHA at a high dose (0.75% for 15 days) and a low dose (0.06% for 180 days) on the activation and inactivation of AFB1 by subcellular preparations of lung. BHT at high dose alone induced hepatic cytosolic glutathione (GSH) S-transferases activity while the pulmonary enzyme was unaffected by BHT feeding. This observation was substantiated when the addition of lung cytosol from control and BHT-treated rats showed similar inhibition (50%) in the microsome mediated AFB1-DNA binding. Thus BHT appears to have little influence on the pulmonary metabolism of AFB1.

Positive correlation exists between glutathione S-transferase activity and aflatoxin formation in Aspergillus flavus

The presence of glutathione (GSH) S-transferase activity, using 1-chloro-2, 4-dinitrobenzene (CDNB) as a substrate, has been established in the cytosolic fraction of the toxigenic (aflatoxin producing) and nontoxigenic strains of Aspergillus flavus. Significant differences in the GSH S-transferase activity were observed between the toxigenic and non-toxigenic strains. A positive correlation has been demonstrated for the first time between aflatoxin formation and a biochemical parameter, namely GSH S-transferase activity. The evidence in support of A. flavus GSH S-transferase induction by endogenous aflatoxins is as follows: (i) the age-related production of aflatoxin follows the same pattern as the cytosolic GSH S-transferase activity profile; (ii) significantly higher enzyme activity was associated with mycelia of a toxigenic strain grown in medium supporting high aflatoxin production (sucrose-low-salts medium) while the enzyme activity was low in medium producing less aflatoxin (glucose-ammonium nitrate medium). The GSH S-transferase activity of the non-toxigenic strain was hardly affected by a change in the medium as it produces no aflatoxins; and (iii) the toxigenic strain demonstrated significantly higher apparent Vmax. with no change in Km as compared with the non-toxigenic strain. This indicates that the enzyme induction by endogenous aflatoxins is similar to the action of phenobarbitol and other inducing drugs (Kaplowitz et al., 1975).

Differential effects of butylated hydroxyanisole on metabolism of aflatoxin B1 in vitro by liver and lung microsomes

Growing epidemiological evidence points out the carcinogenic hazard of inhaled aflatoxin B1 (AFB1) to the pulmonary system. Metabolism of AFB1 by lung microsomes and its binding to calf thymus DNA are reported for the first time in this paper. In addition, the ability of dietary butylated hydroxyanisole (BHA) to modulate AFB1 adduct formation with DNA was examined. Lung microsomes from BHA-treated rats unlike those from liver caused a 50% inhibition of AFB1-DNA binding. However, pulmonary cytosolic glutathione (GSH) S-transferase activity remained unaltered. The addition of BHA-treated lung cytosol failed to produce a greater inhibition of AFB1-DNA binding than control cytosol. Microsome mediated AFB1-DNA binding was markedly inhibited (30%) by the addition of GSH alone to the incubation system. Further addition of cytosol contributed much less (10%) to the inhibition of AFB1-DNA binding. These observations together with the induction of microsomal GSH S-transferase strongly implicate the role of microsomal GSH S-transferase in the modulation of AFB1-DNA binding.

Drug metabolism in experimental tuberculosis: II. Modification of monooxygenase activities due to infection by the administration of isonicotinic acid hydrazide

Isonicotinic acid hydrazide (INH) upon administration to tuberculous guinea pigs exhibited curative effect by bringing back the tissue weights to normal. The reduced hepatic content of cytochrome P450 and NADPH-cytochrome C reductase activity of tuberculous guinea-pigs was restored to normal by INH treatment. Also a similar effect of INH was observed in the case of aminopyrine-N-demethylase and benzphetamine-N-demethylase in the liver and lung of tuberculous guinea-pigs. But INH had little effect on the content of cytochrome b5 and NADH-cytochrome b5 reductase activity. The hepatic and pulmonary activities of glutathione-S-transferase exhibited a tendency to come back to normal while UDP-glucuronyl transferase was unaffected by INH administration to the infected animals. The results suggest that the treatment of tuberculous guinea-pigs with INH cause the normalisation of disturbed hepatic and pulmonary metabolism.

Lack of effect of glutathione on the binding of dimethylnitrosamine to DNA in vitro

The possibility that glutathione (GSH) S-transferases may affect microsome-mediated methylation of DNA by dimethylnitrosamine (DMN) in vitro has been investigated using aflatoxin B1 (AFB1) as a positive control. Hamster liver microsomes were incubated with either [14C]DMN or [3H]AFB1 and calf thymus DNA, with or without GSH and hamster cytosol. Although a significant amount of DMN was metabolized, GSH alone or in conjunction with cytosol or purified GSH S-transferases did not affect the binding of 14C to DNA and the amount of 7-methylguanine formed. However with AFB1, a significant reduction in both its binding to DNA and in the formation of AFB1-N7Gua adduct with a concomitant increase in AFB1-GSH conjugation was observed, suggesting that the test system was functioning effectively.

Drug metabolism in experimental tuberculosis: I. Changes in hepatic and pulmonary monooxygenase activities due to infection

Pulmonary and hepatic drug metabolizing enzyme activities of tuberculous guinea pigs were examined in detail. Experimental tuberculosis resulted in enlargement of liver and lung accompanied by decreased microsomal cytosolic protein. The tuberculosis infection resulted in decreased hepatic contents of cytochrome P-450 and cytochrome b5 NADPH-cytochrome C reductase in lung and liver. A parallel decrease in the microsomal mixed function oxidases (MFO) was observed in liver and lung of tuberculous guinea pigs. The hepatic and pulmonary activities of UDP-glucuronyl transferase were elevated in the infected animals. Glutathione S-transferase activity exhibited an increase in liver and decrease in the lung of tuberculous guinea pigs. Some of the changes observed in monooxygenase in tuberculosis were caused by reduced food consumption. In general, tuberculosis infection can be viewed to lower drug metabolizing capacity of the animal, probably due to the damage and disturbed membrane integrity.

Effect of cord factor, a toxic glycolipid from Mycobacterium tuberculosis, on mouse liver drug metabolizing enzymes

Cord factor (a mycobacterial toxin) treatment of mice for 72 hr resulted in decreased activities of hepatic drug metabolizing enzymes. The toxin treated animals exhibited reduced levels of liver cytochrome P-450 and cytochrome b5, accompanied by significant lowering of NADPH-cytochrome c reductase and NADH-cytochrome b5 reductase activities. The hepatic activities of aminopyrine N-demethylase and aniline hydroxylase were diminished, while liver cytosolic glutathione S-transferase activity was inhibited in mice receiving the toxin. Earlier studies from this laboratory (J. K. Batra, Ph.D. Thesis, Delhi University, India, 1982) on the effects of experimental tuberculosis on hepatic drug metabolism revealed changes similar to the presently reported influence of cord factor on mouse liver microsomal monooxygenases. Thus, the action of cord factor (on hepatic drug metabolism) largely mimics the effects of tuberculosis infection.

Changes in liver polyamines due to aflatoxin B1

Changes in liver polyamines of rats and mice of both sexes injected with aflatoxin B1 (AFB1) were determined. AFB1 significantly enhanced liver polyamines of both susceptible and resistant animals, viz. rats and mice, respectively. Sex appears to have little influence on AFB1-mediated stimulation of liver polyamine levels. AFB1 significantly reduced liver polyamine in growing rats reflecting the inhibitory effect of this carcinogen on induced polyamine synthesis.

Effect of purified rat and hamster hepatic glutathione S-transferases on the microsome mediated binding of aflatoxin B1 to DNA

Rat and hamster liver cytosolic glutathione (GSH) S-transferases purified by GSH-affinity chromatography have been examined for their effects on the microsome mediated binding of aflatoxin B1 (AFB1) to DNA and on the conjugation of AFB1-2,3-epoxide with GSH. Like previous studies with cytosolic preparations (Raj et al. (1984) Carcinogenesis 5, 879), our present study with purified GSH S-transferases showed 2-3-fold more inhibitory activity of AFB1-DNA binding with hamster than that with the rat. Concomitant with the inhibition of AFB1-DNA binding, increase in AFB1-GSH conjugation occurred. Subunit compositions of GSH S-transferases indicate preponderance of Yb and Ya subunits in the hamster and rat, respectively. The role of GSH S-transferases in modulating AFB1-DNA binding and AFB1 induced hepatocarcinogenesis is discussed.

Benzo(a)pyrene hydroxylase activity in human bronchial mucus

Sputum collected from patients with respiratory diseases were examined for presence of benzo(a)pyrene hydroxylase (BPH) activity. The human bronchial mucus used in these studies had significant capability to metabolize benzo(a)pyrene. Clarification of the sputum by agents such as N-acetylcysteine or pancreatin in presence of antibiotics was found to be essential for the detection of BPH activity. In vitro incubation of the clarified human bronchial mucus with benzoflavone caused inhibition, while 7,8-dimethyl-benzanthracene induced BPH enzyme activity.

Effects of neutralization of luteinizing hormone on corpus luteum function and cyclicity in Macaca fascicularis

The primate corpus luteum (including the human) is thought to require continuous exposure to LH for normal progesterone production and menstrual cyclicity. Recently, normal luteal function was reported in rhesus monkeys after postovulatory hypophysectomy or treatment with an antagonist to GnRH. We studied the effects of neutralization of LH by specific antiserum in the fascicularis monkey. A potent antiserum to ovine LH, which cross-reacted with monkey pituitary extract, was produced in rabbits; this antiserum was administered daily to cycling monkeys during the midluteal phase. The pretreatment cycle duration was 32.4 +/- 1.7 (+/- SE) days, and luteal length was 16.5 +/- 0.8 days, with a midluteal progestin peak of 15.28 +/- 2.23 ng/ml. LH antiserum treatment resulted in a precipitous fall in serum progestin within 24 h, which remained low for the remainder of the cycle. All treated monkeys had premature menstrual bleeding, with mean cycle length shortened to 22.8 +/- 1.6 days (P less than 0.0005). These results confirm that the continuous presence of LH is essential for maintenance of corpus luteum function in this species of primate.

Comparative kinetic studies on aflatoxin B1-DNA binding and aflatoxin B1-glutathione conjugation with rat and hamster livers in vitro

Inhibition of microsome mediated aflatoxin B1 (AFB1) binding to exogenous or endogenous DNA by cytosolic glutathione (GSH) S-transferases is well established from our earlier studies. Correlation between inhibition of AFB1-DNA binding and AFB1-GSH conjugation in vitro using rat and hamster liver subcellular fractions is elucidated in this report. Even though hamster liver microsomes catalyzed AFB1 binding to exogenous DNA three times as much as the rat, hamster cytosol inhibited AFB1-DNA binding catalyzed by either microsomes severalfold more than the rat cytosol. AFB1-DNA binding is found to be inversely related to AFB1-GSH conjugation at all AFB1 concentrations (2-100 microM) studied. Presence of either styrene oxide or 3,3,3-trichloropropene oxide at 1 mM level diminished AFB1-GSH formation in vitro confirming some competition by these epoxides with AFB1-epoxide for cytosolic GSH S-transferases. In a reconstituted system with endogenous DNA, the ratio of AFB1-GSH to AFB1-DNA binding was found to be 10-15 times higher with the hamster in comparison with the rat indicating enhanced inactivation of the ultimate carcinogenic metabolite in the hamster. These results are discussed in relation to AFB1-DNA binding and AFB1 hepatocarcinogenicity in resistant and sensitive species.

Urinary excretion of thiol conjugates of aflatoxin B1 in rats and hamsters

After intraperitoneal injection of [3H]aflatoxin B1 in rats and hamsters, 24-h urinary excretion of aflatoxin B1 metabolites was examined in these species. Total excretion was 10-15% of the injected dose with hamster excreting 50% more than the rat. In both species, 60% of the total excretion was due to glucuronide and sulfate conjugates of hydroxy metabolites. Striking differences were observed in the excretion of both aflatoxin B1-diol and various thiol conjugates. Aflatoxin B1-glutathione and aflatoxin B1-cysteinylglycine were major thiol conjugates in rats and hamsters, respectively. An unknown metabolite believed to be mercapturic acid (N-acetylcysteine conjugate) of aflatoxin B1 was excreted by both species, hamster excreting twice as much as the rat.