Purification by HPLC anion-exchange chromatography and some properties of a kinin-releasing enzyme from the venom of Agkistrodon halys ussuriensis

A kinin-releasing enzyme was isolated from the venom of Agkistrodon halys ussuriensis using a very convenient two-step procedure consisting of HPLC anion-exchange chromatography. The relative molecular mass was estimated as 24,000 by SDS gel electrophoresis and an isoelectric point of pH 3.7 was established by gel isoelectric focusing. The kinin-releasing enzyme resembled a typical tissue kallikrein in the values of such physiochemical parameters, in its thermal stability, in its lack of activity towards fibrinogen and casein, and in its behaviour with potential inhibitors. Thus, the enzyme can be classified as a kallikrein-like enzyme.

Purification of a second kallikrein from bovine pancreas

Two kallikreins were identified in a homogenate of bovine pancreas in terms of their differential elution from an anion-exchange chromatography column. The kallikreins were quantified by their ability to release kinin from a partially purified preparation of bovine kininogen. The second kallikrein, designated kallikrein B, was purified by a three-step procedure following anion-exchange chromatography consisting of affinity chromatography on a benzamidine-agarose resin, gel filtration and hydrophobic interaction chromatography. An overall purification factor of 556-fold was achieved with a 58% recovery of enzymatic activity. The final material was shown to be homogeneous by a number of electrophoretic analyses. The relative molecular mass of pro-kallikrein B was found to be 26,700 by gel filtration and that of kallikrein B to be 26,000 by SDS gel electrophoresis. Gel isoelectric focusing revealed the presence of several isoenzymic forms ranging in isoelectric point from pH 4.05 to 4.35.

Carcinogenicity, metabolism and Ki-ras proto-oncogene activation by 7,12-dimethylbenz[a]anthracene in rainbow trout embryos

Field studies suggest that recent epizootics of hepatic neoplasms in some feral fish populations are associated with polycyclic aromatic hydrocarbon (PAH) exposure, but attempts to induce liver tumors in these species under laboratory conditions have been unsuccessful. Several studies have shown hepatic neoplasma to be inducible in laboratory fish species following PAH exposure at the free-swimming life stage. However, neither the susceptibility of the fish embryonic life stage to tumor induction by PAHs nor the potential of these carcinogens to induce oncogenic point mutations analogous to those reported in feral fish hepatic tumors have been clearly established. To address this, rainbow trout embryos were exposed by passive water uptake to 7,12-dimethylbenz[a]anthracene (DMBA), a potent model PAH in many mammalian tumor protocols. DMBA was rapidly absorbed by trout eggs and metabolized. The major non-polar metabolites identified were 12-hydroxymethyl-7-methylbenz[a]anthracene and 3,4-dihydroxy-3,4-dihydro-DMBA, whereas approximately 25% of the water soluble metabolites were identified as glucuronides by beta-glucuronidase treatment. Embryonic DNA adduction increased with time of DMBA exposure (2.2 +/- 0.3 pmol DMBA-equivalents/mg DNA at 24 h). Liver tumor incidence nine months after DMBA treatment was found to increase with DMBA concentration and exposure period (3.8% at 1 p.p.m./2 h; 23% at 5 p.p.m./2 h; 85% at 5 p.p.m./24 h). Stomach adenomas and nephroblastomas also were observed at low incidence in the DMBA-treated trout. Among 11 hepatic tumors examined, nine carried Ki-ras alleles with activating point mutations in codon 12 (4/11 GGA-->AGA; 4/11 GGA-->GTA) or codon 61 (1/11 CAG-->CTG). This spectrum differs substantially from those reported for DMBA-initiated mouse skin papillomas or hepatic tumors. These results may have important environmental implications because they suggest that even a brief exposure to PAHs during a sensitive stage of development may adversely affect some fish populations. They also indicate considerable variation in DMBA ras gene mutations among species and target organs.

Rapid and convenient purification of tonin from rat submandibular gland. Comparison of tonin and tissue kallikrein in their interactions with inhibitors

Tonin was isolated from rat submandibular glands by a very convenient procedure consisting of sequential anion-exchange, hydrophobic interaction and gel filtration chromatographies. The method is superior to earlier purifications as it consists of fewer stages, resulting in a much higher recovery (41%) of tonin. The final preparation was seen to be pure on SDS gel electrophoresis (M(r) 32,800) and on gel isoelectric focusing (pI 6.15). The stability of tonin and its interaction with various inhibitors were investigated, and compared with the corresponding behavior of rat tissue kallikrein.

A 1H-NMR study of the interactions between rat tissue kallikrein and two peptide inhibitors

The 1H-NMR spectra have been obtained for rat submandibular kallikrein in the absence and presence of inhibitors. Two competitive inhibitors were investigated, the tripeptide leupeptin (a potent inhibitor with Ki 0.5 microM) and a hexapeptide (a much weaker, substrate-analogue inhibitor with Ki 380 microM). Analysis of the NMR spectra showed that binding of leupeptin to kallikrein led to a change in the conformation of the enzyme, whereas binding of the substrate analogue to the enzyme produced no such change and may have resulted in a conformational change of the inhibitor.

Tryptase and histamine as markers to evaluate mast cell activation during the responses to nasal challenge with allergen, cold, dry air, and hyperosmolar solutions

We have used assays for histamine and for the specific mast cell enzyme, tryptase, to examine the response of the nasal mucosa to provocation with several different stimuli and to evaluate the reliability of histamine as a marker of mast cell activation. High levels of histamine detected in baseline lavages of some subjects are not associated with any detectable tryptase, suggesting they are not mast cell derived. During pronounced immediate allergic responses, however, mast cell degranulation clearly occurs, and a striking correlation between histamine and tryptase is observed. This correlation is weaker when a more modest allergic response is induced, possibly reflecting differential diffusion of the two mediators across the epithelium. Provocation of susceptible individuals with cold, dry air leads to increased recoveries of both histamine and tryptase, confirming that mast cell degranulation occurs during this reaction. Although hyperosmolarity of the nasal mucosa may contribute to mast cell degranulation induced by cold, dry air, a brief exposure of the nasal cavity to hyperosmolar mannitol was not associated with measurable production of tryptase. The combined use of histamine and tryptase measurements can therefore provide useful evidence regarding the role of mast cell activation in the pathogenesis of inflammatory responses.

Characterization of kallikrein isolated from rat submandibular glands by a simple and rapid purification procedure

Numerous biochemical properties (e.g. Mr, carbohydrate content, pI) were determined for kallikrein isolated from rat submandibular glands by a simple, rapid purification procedure. The kinetic behaviour of the enzyme towards various inhibitors and synthetic substrates was investigated. The effects of different salts and detergents on the esterolytic activity of the rat tissue kallikrein were recorded.

Tissue disposition and excretion of 14C-labelled aflatoxin B1 after oral administration in channel catfish

The pharmacokinetics, tissue distribution and excretion of 14C-labelled aflatoxin B1 (AFB1) were examined after oral administration (250 micrograms/kg body weight) in channel catfish (Ictalurus punctatus). Plasma concentrations of parent AFB1 were best described by a one-compartment pharmacokinetic model, in which peak plasma concentration (503 ppb) occurred at 4.1 hr after dosing. The absorption and elimination half-lives were 1.5 and 3.7 hr, respectively. AFB1 was highly bound (95%) to plasma proteins. Concentrations of 14C (in AFB1 equivalents) measured in the tissues were highest at 4 hr, ranging from 596 ppb in the plasma to 40 ppb in the muscle. AFB1 residues were rapidly depleted; at 24 hr the concentrations in the plasma and muscle were 32 and less than 5 ppb, respectively. Concentrations in the bile exceeded 2000 ppb (at 24 hr), whereas the highest concentration in the urine was 51 ppb (4-6-hr collection interval). Renal and biliary excretion accounted for less than 5% of the administered dose, indicating incomplete absorption. Pharmacokinetic modelling and tissue data demonstrate a very low potential for the accumulation of AFB1 and its metabolites in the edible flesh of channel catfish through the consumption of AFB1-contaminated feed.

Purification of prokallikrein from bovine pancreas

A prokallikrein was isolated from bovine pancreas by a multi-step procedure involving gel filtration, hydrophobic interaction and anion-exchange chromatographies. The purification was initially monitored by measurement of the kinin-releasing activity of the activated zymogen. Later, when the pure prokallikrein had been isolated, a specific radioimmunoassay for the zymogen was set up and that was employed to provide estimates of 323-fold and 28% for the overall degree of purification and percentage recovery of prokallikrein. The relative molecular weight of prokallikrein was found to be 26,900 by SDS gel electrophoresis and its isoelectric point was established as pH 4.55.

Chemopreventive properties of chlorophyllin: inhibition of aflatoxin B1 (AFB1)-DNA binding in vivo and anti-mutagenic activity against AFB1 and two heterocyclic amines in the Salmonella mutagenicity assay

Chlorophyllin (CHL), a sodium/copper derivative of chlorophyll, has been used to treat a number of human conditions with no toxic effects being reported. Recent studies have described the anti-mutagenic activity of CHL in several short-term genotoxicity assays; however, this compound has not been reported to inhibit carcinogen--DNA binding in vivo, and it has yet to be evaluated as an anti-carcinogen in any species. The chemopreventive properties of CHL were studied in trout using inhibition of aflatoxin B1 (AFB1)--DNA binding as an end-point. Chlorophyllin and AFB1 were coadministered in the diet, and carcinogen--DNA binding levels were determined in liver after 1, 3, 5 and 7 days. Linear increases in AFB1--DNA binding occurred with time of treatment at each CHL dose level (0, 500, 1000 and 2000 p.p.m.). Each increase in CHL dose produced a concomitant decrease in AFB1--DNA binding, resulting in a series of curves of decreasing slope. At the highest CHL dose level of 2000 p.p.m., AFB1--DNA binding was inhibited by 70%. These results suggest that CHL should be a potent inhibitor of AFB1-induced hepatocarcinogenesis in this model. In the Salmonella assay, CHL exhibited potent anti-mutagenic activity against AFB1 and two heterocyclic amines when incubated in the presence of trout liver activation systems. CHL also inhibited the mutagenic activity of AFB1-8,9-epoxide in the absence of a metabolic activation system. Dietary CHL substantially inhibited liver AFB1-DNA binding in vivo, even when AFB1 was given by i.p. injection to avoid direct AFB1--CHL interaction in the diet or gut. Collectively, these studies support a CHL inhibitory mechanism involving complex formation with the carcinogen in the gut coupled with electrophile scavenging or further complexing in the target organ.

Promotion of aflatoxin B1 carcinogenesis by the natural tumor modulator indole-3-carbinol: influence of dose, duration, and intermittent exposure on indole-3-carbinol promotional potency

Indole-3-carbinol (13C), a secondary metabolite from cruciferous vegetables, inhibits aflatoxin B1 (AFB1) hepatocarcinogenesis in trout (Bailey et al., J. Natl. Cancer Inst., 78: 931-934, 1987) and rats (Selivonchick et al., unpublished results) when given prior to and with carcinogen but promotes carcinogenesis in both species when given continuously following AFB1 initiation. Since human 13C intake may not be continuous, and the promotional stimulation may be reversible, we have assessed 13C promotion using delayed and discontinuous exposure protocols. Following initiation with AFB1, 13C was fed to trout for varying periods of time, with varying lengths of delay after initiation and continuous or intermittent patterns of 13C treatment. Promotional enhancement of tumor incidence by 13C was found to be significant when 13C treatment was delayed for several weeks or months after the initial AFB1 challenge. Promotion also was found to increase with length of exposure to 13C treatment and to be decreased but still evident when 13C was given in alternating months or weeks, or twice per week only. These results do not support the idea that promotional stimulation in hepatocarcinogenesis is a reversible phenomenon. To quantify 13C promotional potency in terms of its dietary concentration, a series of AFB1 tumor dose-response curves was established, each with a different level of 13C fed continuously following AFB1 initiation. The resultant tumor dose-response curves, plotted as logit percentage of incidence versus log AFB1 dose, were displaced parallel toward lower AFB1 50% tumor take (TD50) values with increasing 13C concentration. The level of 13C that halves the AFB1 dose for 50% tumor incidence was calculated to be approximately 1000 ppm 13C, fed continuously, with no substantial threshold for promotion. By comparison, 13, when fed before and with AFB1, shows a 50% inhibitory value (13C concentration that doubles the dose of AFB1 for 50% tumor incidence) in trout of 1400 ppm 13C [Dashwood et al., Carcinogenesis (Lond.), 10: 175-181, 1989]. Thus the potential for 13C as a dietary additive to promote prior hepatic initiation events when fed continuously is approximately as great as its potential to inhibit concurrent AFB1 initiation.

Neutralization of kinin-releasing enzymes from viperid venoms by antivenom IgG fragments

The activities of kinin-releasing enzymes in the venoms of Vipera xanthina xanthina, V. lebetina obtusa, V. aspis aspis, V. lebtina schweizeri, V. ammodytes ammodytes and V. berus berus were determined using a specific radioimmunoassay for kinin. The kinin-releasing activities of all the viperid venoms measured in vitro were neutralized, to varying extents, by two commercially available monospecific antivenoms in the form of F(ab')2 (Zagreb) and Fab (TAb) immunoglobin fragments, indicating a high degree of cross-neutralization of those enzymes.

Neutralization of kinin-releasing enzymes of crotalid venoms by monospecific and polyspecific antivenoms

The amounts of kinin-releasing enzymes in the venoms of Crotalus atrox, Crotalus adamanteus, Crotalus scutulatus scutulatus and Agkistrodon piscivorus piscivorus were measured by determining the amounts of kinin released from a sheep kininogen substrate by means of a specific radioimmunoassay. Four monospecific and two commercial polyspecific antivenom IgG samples were tested for their ability to reduce the kinin-releasing activities of the four crotalid venoms measured in vitro. All of the antivenom IgG samples were able to neutralize venom kininogenase activity to varying extents. On of the commercial polyspecific antivenoms was of equal or higher potency than the corresponding monospecific antivenoms for three of the venoms tested, indicating a high degree of cross-neutralization. F(ab')2 and especially Fab fragments of that polyspecific antivenom IgG were also effective in reducing the kinin-releasing activities of the four crotalid venoms.

A simple and rapid purification of kallikrein from rat submandibular gland

Rat submandibular kallikrein was isolated in an 87% yield by a very quick and simple procedure involving hydrophobic interaction chromatography. Furthermore, that purification method was superior to both aprotinin-affinity chromatography and immunoaffinity chromatography for the purification of rat submandibular kallikrein. The kallikrein purified by hydrophobic interaction chromatography consisted of a number of isoenzymes. The major component of Mr 38,000 seen on SDS-gel electrophoresis was found to be the glycosylated kallikrein, whereas the minor component of Mr 26,000 represented the non-glycosylated enzyme.

Tumor dose-response studies with aflatoxin B1 and the ambivalent modulator indole-3-carbinol: inhibitory versus promotional potency

Indole-3-carbinol (I3C), a natural compound from cruciferous vegetables, inhibits aflatoxin B1 (AFB1) carcinogenesis in trout when administered prior to and during carcinogen exposure, but also promotes it in the same species when given after AFB1 initiation. To provide quantitative potency information for these opposing activities, detailed tumor dose-response studies were performed with AFB1 (10-400 ppb) and I3C (0-4,000 ppm). In a plot of (logit) percent tumor response vs log AFB1 exposure, the results generated a series of parallel AFB1 dose-response curves. Increasing I3C doses displaced these curves, respectively, toward higher and lower AFB1 doses in the inhibition and promotion studies. Similar potencies were observed over the dose range 0-1,500 ppm I3C; the 50% promotion and inhibition (P50 and I50) values were 1,000 vs 1,400 ppm I3C, respectively. Differences in the protocols used in the two studies suggest that the inhibitory activity of I3C is more likely to supersede promotion under human exposure conditions.

In vivo disposition of the natural anti-carcinogen indole-3-carbinol after po administration to rainbow trout

Indole-3-carbinol (I3C), a compound found naturally as a glucosinolate in cruciferous vegetables such as broccoli and cabbage, has been shown to modulate the carcinogenic process in a number of animal species. The lack of detailed information on the disposition of I3C in vivo provided the main impetus for the study reported here, in which the distribution and metabolic fate of I3C was assessed in selected tissues and excreta after po administration to rainbow trout (Salmo gairdneri). Animals were fasted for 3 days and given [5-3H]I3C either in the diet or by single oral gavage (40 mg/kg body weight; 15 muCi/kg body weight). Following administration, 75% of the initial 3H-dose was detected within the stomach between 0.5 and 12 hr, after which it was released to distal regions of the gut for subsequent uptake, distribution and elimination. At the end of the study (72 hr) 25% of the administered dose was recovered from the water which reflected excretion through the gills and urinary tract. Significant excretion also occurred in the bile, with approximately 5% of the initial 3H-dose recovered from the bile sacs at 72 hr. Further analyses of the radioactive components in the bile indicated that one or more derivatives of I3C, but not the parent compound itself, are excreted as glucuronide conjugates using this route. Radioactivity accumulated in the liver throughout most of the study, reaching levels of 1-1.5% between 48 and 72 hr of the administered dose. High-performance liquid chromatography analyses indicated the presence of four main radiolabelled species in these livers, one of which co-eluted with the parent compound, I3C. The major radiolabelled species recovered from the liver was tentatively identified as the dimer, 3,3'-diindolylmethane (I33'), which comprised 40% of the total hepatic radiolabel. This dimer, I33', was also found to accumulate in the diet containing I3C, which reflected a time-dependent dimerization of the parent compound in vitro. These findings are discussed in view of recent postulates of a role for I3C condensation products such as I33' in the mechanism of I3C anti-carcinogenesis.

Iron resistance of hepatic lesions and nephroblastoma in rainbow trout (Salmo gairdneri) exposed to MNNG

Histochemical markers are important for the early detection of chemically initiated neoplasia in experimental animal studies. The marker, iron resistance, was evaluated in the Shasta strain of rainbow trout (Salmo gairdneri). Twenty-one-day-old trout embryos were exposed to 100 ppm aqueous N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) for 30 min in a static water bath. Fish were fed a semipurified diet, and sampled monthly from the 4th to the 9th month. Two days before sampling, fish were iron-loaded with a single ip dose of 0.30 mg iron dextran/100 g body weight. Livers and kidneys were conventionally processed to paraffin sections for iron, or hematoxylin and eosin (H&E) staining. Normal hepatocytes accumulated iron in pericanalicular locations, but in hepatocytes from carcinogen-altered foci and tumors, iron staining was clearly reduced or absent. Normal renal tubule cells exhibited slight to moderate iron staining, while those from nephroblastoma were iron resistant. These results establish iron resistance as a property of preneoplastic and neoplastic trout hepatocytes and nephroblastoma cells for the first time. Iron resistance may offer a practical histochemical marker in experimental fish models of hepatocellular carcinoma and nephroblastoma.

Metaplastic pancreatic cells in liver tumors induced by diethylnitrosamine

Metaplastic pancreatic cells have been infrequently observed in fish liver tumors induced by chemical carcinogens. An investigation with nitrosamine-exposed trout was undertaken to characterize the relationships of metaplastic pancreatic cells with other cell types. Eight-week-old rainbow trout (Salmo gairdneri) were fed a control diet or diets containing 500 ppm beta-naphthoflavone (BNF), 2000 ppm indole-3-carbinol (13C), or 100 ppm Aroclor 1254 (PCB) for 6 weeks. The fish were then exposed to 250 ppm diethylnitrosamine for 24 hr in an aqueous aquarium bath and reared on control diet for 39 weeks postexposure. Livers were excised, processed to paraffin sections, and stained with hematoxylin and eosin for histological evaluation. Metaplastic pancreatic cells were found only in tumors. Of the tumors with metaplastic pancreatic cells, 100/105 (95.2%) contained neoplastic cholangiolar components. Only 5/105 (4.76%) were hepatocellular carcinomas. 13C pretreatment inhibited the incidence of cholangiolar tumors (cholangioma 3.6% vs 31.3%, cholangiocarcinoma 3.6% vs 13.0%) and metaplastic pancreatic cells (5.1% vs 19.1%), whereas BNF and PCB had no effect. A hepatocellular origin for metaplastic pancreatic cells is supported. Cholangiolar neoplasia is associated with the expression, growth, or survival of metaplastic pancreatic cells in liver tumors. Hepatocarcinogenicity should not be described entirely by hepatocellular events since cholangiolar and metaplastic pancreatic cells can respond associatively to carcinogens and dietary modulators.

Quantitative inter-relationships between aflatoxin B1 carcinogen dose, indole-3-carbinol anti-carcinogen dose, target organ DNA adduction and final tumor response

A number of recent studies have described inhibitor-mediated reductions in the covalent DNA binding and tumorigenicity of various carcinogens, in species such as rats, mice and rainbow trout (Salmo gairdneri). Since inhibitory effects have, in most cases, been reported after testing at one carcinogen and one inhibitor level only, the detailed relationships between carcinogen dose, inhibitor dose, in vivo DNA binding and final tumor response are not well understood in any species. To determine these relationships we have employed the trout model in a combined DNA binding/tumor dose-response protocol using approximately 10,000 animals. Trout were pretreated with one of five different dose-levels of indole-3-carbinol (I3C), a naturally occurring anti-carcinogen found in cruciferous vegetables such as broccoli and cabbage. After 4 weeks, animals received the same dietary level of I3C for a further 2 weeks together with [3H]aflatoxin B1 (AFB1) in the dose-range 10-320 p.p.b. From tanks containing 150 animals (three tanks per I3C-AFB1 dose-point), 15 fish were selected at random in order to assess hepatic AFB1-DNA binding levels. Remaining animals were returned to control diet for determination of tumor response at 12 months. Linear increases in DNA binding occurred with dose of AFB1 at each I3C dose-level. Successive increases in I3C dose gave dose-related decreases in AFB1-DNA binding, resulting in a series of curves of decreasing slope. Shifts in DNA-binding slopes were compared quantitatively with horizontal displacements towards higher carcinogen dose in corresponding tumor dose-response curves. At I3C doses of less than or equal to 2000 p.p.m., the inhibitor-altered tumor response was predicted precisely by changes in dose received (DNA adducts formed) in the target organ. These data constitute the first direct evidence of pure anti-initiating activity by a natural anti-carcinogen found in human diet, where all animals were treated at the same time and under identical conditions of exposure in both DNA binding and tumor studies. The data are discussed further in view of (i) their implications for DNA binding-carcinogenicity correlations and the concept of 'molecular dosimetry', and (ii) limitations in the current database on anti-carcinogenesis as regards in vivo potency information, particularly for 'ambivalent modulators' which exhibit both inhibitory and promotional activity.

Aflatoxin B1 carcinogenesis and its relation to DNA adduct formation and adduct persistence in sensitive and resistant salmonid fish

Rainbow trout (Salmo gairdneri) and coho salmon (oncorhynchus kisutch) were exposed to aflatoxin B1 (AFB1) either by passive embryo uptake or by dietary treatment after hatching and feeding onset. Trout exposed as embryos to an aqueous solution of 0.5 p.p.m. AFB1 for 15 min showed a 62% tumor incidence 12 months later, whereas coho salmon exposed to a similar solution for 30 min showed only a 9% incidence. The difference between salmon and trout response was even greater by dietary AFB1 treatment. Trout exposed for 4 weeks to 20 p.p.b. dietary AFB1 had a 62% tumor response 12 months later, whereas salmon exposed to 40 p.p.b. dietary AFB1 for 4 weeks failed to develop tumors. A 5% tumor incidence was observed in salmon 12 months after 3 weeks exposure to 5000 p.p.b. dietary AFB1, a lethal dose for trout. In addition to a lower tumor incidence when compared to trout, the neoplastic response of salmon to AFB1 is to produce benign hepatic adenomas in contrast to the malignant hepatocellular carcinomas seen in trout. AFB1 metabolism, DNA adduct formation, adduct persistence in vivo and in vitro and cytochrome P-450 isozyme composition were compared in livers of trout and salmon to understand the role of metabolism and initiation in this species difference. AFB1-DNA binding was 7-56 times greater in trout than salmon liver at various times after AFB1 injection, 20 times greater in embryos or in freshly isolated trout hepatocyte preparations after a 1 h incubation with aflatoxin B1, and 18 times greater in trout liver after a three week dietary (80 p.p.b.) exposure. The major AFB1-DNA adduct was 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 in both species. Persistence of AFB1-DNA adducts in vivo in liver was high compared to mammalian systems, implying that active enzymatic removal of bulky DNA adducts is low in both species and probably not a factor in their differential response to aflatoxin. Species differences in other phase I and phase II metabolism pathways and in AFB1 elimination were, overall, much less striking than those previously observed for trout fed inhibitors of aflatoxin carcinogenesis. Rates of bile elimination of AFB1 detoxication products, and total excretion of aflatoxins into water after AFB1 exposure, were not significantly different between trout and salmon. Since detoxication differences were not observed, the species difference in AFB1-DNA binding appears to reflect less efficient cytochrome P-450 metabolism of aflatoxin to the reactive 8,9-epoxide in salmon, compared to trout.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of diethylnitrosamine-induced hepatocarcinogenesis and O6-ethylguanine formation in rainbow trout by indole-3-carbinol, beta-naphthoflavone, and Aroclor 1254

Rainbow trout were fed a diet containing indole-3-carbinol (2000 ppm), beta-naphthoflavone (500 ppm), or Aroclor 1254 (100 ppm) for 6 weeks before a single 24-hr exposure to an aqueous solution of 250 ppm diethylnitrosamine (DEN). The fish were killed 42 weeks later to determine the carcinogenic response. DEN exposure produced an 80.2% incidence of liver tumors and an average of 3.47 tumors per tumor-bearing fish, whereas no tumors were detected in the sham-treated control fish. Tumor induction was inhibited by indole-3-carbinol (27.5% incidence, 1.89 tumors per tumor-bearing fish) but enhanced by beta-naphthoflavone (91.8% incidence, 3.60 tumors per tumor-bearing fish). Aroclor 1254 had no effect on DEN-induced hepatocarcinogenesis (80.0% incidence, 3.03 tumors per tumor-bearing fish). The effects of these modulators on O6-ethylguanine and 7-ethylguanine formation (measured by HPLC and fluorescence spectrophotometry) were examined. Liver DNA ethylguanine levels were reduced in indole-3-carbinol-pretreated fish and increased in beta-naphthoflavone-pretreated fish compared to untreated controls after DEN exposure. Aroclor 1254 pretreatment had no significant effect on DNA ethylguanine formation. Similar O6-ethylguanine to 7-ethylguanine ratios were found among the control and treated groups. The results of this study indicate that modulation of DEN hepatocarcinogenesis by indole-3-carbinol and beta-naphthoflavone may be mediated by their effects on O6-ethylguanine formation and, therefore, on the initiation phase of carcinogenesis.

Comparative effect of dietary butylated hydroxyanisole and beta-naphthoflavone on aflatoxin B1 metabolism, DNA adduct formation, and carcinogenesis in rainbow trout

Butylated hydroxyanisole (BHA) and beta-naphthoflavone (BNF), both chemicals with anti-carcinogenic properties in some experimental animals, were compared for effects on aflatoxin B1 (AFB1) metabolism, hepatic DNA adduct formation and carcinogenesis in the rainbow trout. Dietary BHA had no effect on the hepatic tumor incidence when fed at 0.03 or 0.3% 4 weeks prior to and during a 4 week dietary exposure of 10 p.p.b. AFB1. BNF, when fed at 0.005 or 0.05% under similar conditions, significantly reduced tumor response, which confirms previous results in trout (Nixon et al., Carcinogenesis, 5, 615-619, 1984). BHA fed at either 0.03 or 0.3% for 8 weeks had no post-initiation effect on the 52 week hepatic tumor incidence of trout exposed to a 0.5 p.p.m. AFB1 solution as embryos. A similar post-initiation exposure to 0.05% BNF significantly enhanced AFB1 tumor response. The influence of dietary BHA and BNF on AFB1 metabolism and DNA adduct formation and persistence in trout were examined. A 3 week pre-treatment with 0.3% dietary BHA had no effect on in vivo hepatic nuclear AFB1-DNA adduct formation at 0.5, 1, 2 and 7 days after AFB1 i.p. injection. By contrast 0.05% dietary BNF reduced hepatic AFB1-DNA adducts to 33-60% of control levels at 0.5, 1, 2 and 4 days after AFB1 exposure. This was accompanied by significantly lower blood and liver levels of AFB1 during the first 24 h after i.p. injection. Livers of BNF trout also contained 4-fold more of the less carcinogenic metabolite, aflatoxin M1, and 50% less aflatoxicol (AFL), a metabolite with similar carcinogenicity as AFB1. Bile AFL-glucuronide levels were significantly decreased in BNF-fed trout, but total bile glucuronides were significantly increased due to a 15-fold increase in aflatoxicol-M1 glucuronide. Freshly isolated hepatocytes from BHA-fed fish, when incubated with AFB1 for 1 h, showed no difference in levels of AFB1-DNA adducts or ratios of AFB1 metabolites when compared to hepatocytes isolated from fish fed a control diet only. By contrast, dietary BNF has been previously shown to greatly enhance AFM1 production, reduce AFL production, and significantly reduce AFB1-DNA adduct formation in isolated trout hepatocytes (Bailey et al., Natl. Cancer Inst. Monograph, 65, 379-385, 1984). These results indicate that dietary BHA up to 0.3% does not alter AFB1 metabolism or DNA adduction in trout, nor does it inhibit or promote AFB1 hepatocarcinogenesis in this species.(ABSTRACT TRUNCATED AT 400 WORDS)

Formation and persistence of ethylguanines in liver DNA of rainbow trout (Salmo gairdneri) treated with diethylnitrosamine by water exposure

Diethylnitrosamine exposure via the water resulted in the formation of 7-ethylguanine and O6-ethylguanine in rainbow trout liver DNA. The modified bases were quantitated by high-pressure liquid chromatography and fluorescence spectrophotometry. In vivo 7-ethylguanine and O6-ethylguanine levels were directly proportional to DEN concentrations between 62.5 and 250 ppm. 7-Ethylguanine and O6-ethylguanine levels were approximately directly proportional to duration of exposure to DEN between 0 and 6 hr under the conditions used, with less than proportionate increases thereafter. Removal of ethylguanines from liver DNA following a 24-hr exposure to 250 ppm DEN (a known carcinogenic regimen) was biphasic; 24% of the O6-ethylguanine and 32% of the 7-ethylguanine found immediately after exposure were removed in 12 hr but no significant decline was found over the period from 12 to 96 hr after exposure. Alkyl acceptor protein activity in trout liver was examined to assess the role of enzymatic repair in the observed loss of O6-ethylguanine in vivo. Although an O6-alkylguanine repair system similar to the alkyltransferase system reported in rodents was found in trout liver, only 4% of the O6-ethylguanine lost from DNA after exposure to 250 ppm DEN can be accounted for by activity of the alkyl acceptor protein. The high incidence of liver tumours observed in DEN-treated rainbow trout may be related to the rapid formation and substantial persistence of the promutagenic O6-ethylguanine in liver DNA.

Identification of human lung mast cell kininogenase as tryptase and relevance of tryptase kininogenase activity

We have described previously the IgE-mediated release of kininogenase activity from purified human lung mast cells. Using supernatant fractions from mast cells stimulated with anti-IgE in the presence of deuterium oxide, we have purified this kininogenase to homogeneity by gel filtration and heparin-agarose chromatography and have demonstrated that it is identical to tryptase, the major neutral protease of human lung mast cells. Thus, tryptase and kininogenase activities co-chromatographed through both purification steps with equivalent yields. The final purified kininogenase was free of detectable chymotryptic and carboxypeptidase activities and was identified as tryptase on the basis of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), amino acid composition and inhibition profile. Three such preparations of tryptase were all capable of releasing kinin from each of two different preparations of purified, single-chain, human low molecular weight kininogen. Interestingly, kinin generation was optimal at pH 5.5 and was enhanced by heparin, which has been reported to stabilize tryptase. SDS-PAGE analysis of kininogen hydrolysis by tryptase revealed the formation of a diffusely stained region in the molecular weight range of 60,000-65,000, rather than a discrete heavy chain band. Under optimal conditions, the three tryptase preparations released 10-12 micrograms kinin/hr/mg but released only 2 micrograms kinin/hr/mg at pH 7.2. HPLC analysis revealed that the kinin released was bradykinin. We conclude that the kininogenase activity from human lung mast cells is attributable to tryptase. The unique pH optimum of this reaction of a serine protease, however, raises doubts as to the physiologic significance of this activity.

Comparative metabolism and DNA binding of aflatoxin B1, aflatoxin M1, aflatoxicol and aflatoxicol-M1 in hepatocytes from rainbow trout (Salmo gairdneri)

DNA binding and metabolism patterns of 3H-labeled aflatoxin B1 (AFB1) and its phase I metabolites, aflatoxicol (AFL), aflatoxin M1 (AFM1), and aflatoxicol-M1 (AFL-M1), were compared in freshly prepared rainbow trout (Salmo gairdneri) hepatocytes. Aflatoxins were incubated with hepatocytes for periods up to 1 h, cellular DNA was isolated and specific activities determined by scintillation counting and Burton analysis. Data for (pmol bound aflatoxin/micrograms DNA)/(mumol dose) versus time fit a linear function (P less than 0.002) passing nearly through the origin for each aflatoxin. DNA binding at 1 h relative to AFB1 was: AFL, 0.53 +/- 0.07; AFM1, 0.81 +/- 0.20 AFL-M1, 0.83 +/- 0.24. Statistical analysis indicated that binding of AFL, AFM1 and AFL-M1 were significantly less than that of AFB1. HPLC analysis of the cellular supernatants indicated that the major metabolites were AFL, AFB1, AFL-M1, and AFM1 from AFB1, AFL, AFM1 and AFL-M1 substrates, respectively. Small quantities of hydroxylated metabolites and glucuronides also were detected in some of the incubations. The time-course data suggested that initial formation of major metabolites was rapid and that, by 20-30 min, net changes in metabolite levels decreased or approached zero. Because the four compounds possess a 8,9-double bond, DNA binding could be due to activation of the parent substrates as well as of their phase I metabolites. Based on current mutagenicity data and limited carcinogenicity studies, AFM1 and AFL-M1 have binding levels which are higher than expected compared to AFB1 and AFL.

Mechanisms of anti-carcinogenesis by indole-3-carbinol: detailed in vivo DNA binding dose-response studies after dietary administration with aflatoxin B1

Several recent reports have described inhibitor-mediated reductions in the covalent binding of various carcinogens to DNA in vivo. The majority of these studies show inhibitory effects after testing at one inhibitor and one carcinogen dose level only. Consequently, the detailed relationships between inhibitor dose, carcinogen dose, and in vivo inhibitory potency have not been clearly delineated in any species. To systematically determine these relationships in vivo, rainbow trout (Salmo gairdneri) were exposed to a range of carcinogen (aflatoxin B1, AFB1) and inhibitor (indole-3-carbinol, I3C) doses by concomitant dietary exposure. Inhibitory potencies were then assessed using in vivo covalent binding of AFB1 to hepatic DNA as an end-point. Linear increases in DNA binding occurred with increasing dose of AFB1 and with time of inhibitor/carcinogen co-treatment, at each I3C dose level. Successive increases in inhibitor dose resulted in corresponding dose-related decreases in AFB1--DNA binding such that a series of curves of decreasing slope was produced. AFB1--DNA binding was suppressed by almost 95% at the highest I3C dose tested. These studies describe for the first time such a degree of inhibition by I3C on covalent binding of AFB1 to DNA in vivo, where inhibitor and carcinogen are covariables administered repeatedly in the diet. Moreover, the linear inhibitory response observed at low I3C doses indicates the possible absence of any significant threshold for I3C protection against AFB1--DNA binding. Thus, even at low levels I3C may offer some protection against chemically-induced neoplasia.

The significance of glutathione conjugation for aflatoxin B1 metabolism in rainbow trout and coho salmon

Rainbow trout are known to be more susceptible to aflatoxin B1 (AFB1) hepatocarcinogenesis than coho salmon, or trout pre-fed the carcinogenesis inhibitors beta-naphthoflavone (beta NF), Aroclor 1254 or indole-3-carbinol. The study reported here examined the relationship between AFB1-glutathione (GSH) conjugation and AFB1 carcinogenesis in salmon, trout and trout pre-fed the three inhibitors. The AFB1-glutathione (AFB1-SG) conjugate was not detected in salmon bile and was present in trout bile in amounts representing less than 0.2% of the administered dose 24 hr after injection of [3H]AFB1. The major conjugates were glucuronides of aflatoxicol and aflatoxicol M1. In incubations of isolated liver cell fractions, less than 0.5% of the original AFB1 dose was recovered as AFB1-SG in salmon and trout preparations, compared to 25% in mouse-liver cell preparations. The GSH concentration in livers of the control trout was higher than that for coho salmon but lower than that for trout pre-fed beta NF. Liver GSH-transferase activity in control trout livers was much higher than in the control salmon livers, but was only 62% of that found for trout fed beta NF. There was no apparent relationship among the various groups between liver GSH concentrations, liver GSH-transferase activity, or biliary GSH conjugate, and the degree of carcinogenic response of AFB1. Thus current evidence does not indicate a major role for aflatoxin B1 epoxide-GSH detoxification in coho salmon, or rainbow trout fed any of the three anticarcinogens tested. These results in salmonid fish are contrary to those which suggest AFB1-SG conjugation as a major determinant of AFB1 carcinogenesis and its dietary modulation in rodent models.

Abnormal regulation of renal kallikrein in experimental diabetes. Effects of insulin on prokallikrein synthesis and activation

The effects of streptozotocin (STZ) diabetes and insulin on regulation of renal kallikrein were studied in the rat. 1 and 2 wk after STZ injection, diabetic rats had reduced renal levels and urinary excretion of active kallikrein. Tissue and urinary prokallikrein levels were unchanged, but the rate of renal prokallikrein synthesis relative to total protein synthesis was reduced 30-45% in diabetic rats. Treatment of diabetic rats with insulin prevented or reversed the fall in tissue level and excretion rate of active kallikrein and normalized prokallikrein synthesis rate. To further examine insulin's effects, nondiabetic rats were treated with escalating insulin doses to produce hyperinsulinemia. In these rats, renal active kallikrein increased. Although renal prokallikrein was not increased significantly by hyperinsulinemia, its synthesis was increased. As this was accompanied by proportionally increased total protein synthesis, relative kallikrein synthesis rate was not changed. Excretion of active kallikrein was unchanged, but prokallikrein excretion was markedly reduced. Therefore, increased tissue active kallikrein seen with hyperinsulinemia can be explained not only by increased synthesis but also by retention and increased activation of renal prokallikrein. These studies show that STZ diabetes produces an impairment in renal kallikrein synthesis and suggest that this disease state also impairs renal prokallikrein activation. The findings also suggest that insulin modulates renal kallikrein production, activation, and excretion.

Metabolism and DNA binding of aflatoxicol and aflatoxin B1 in vivo and in isolated hepatocytes from rainbow trout (Salmo gairdneri)

The purpose of this study was to compare the metabolism and DNA binding of aflatoxicol (AFL) with that of aflatoxin B1 (AFB1) in vivo and in isolated hepatocytes from Mt Shasta strain rainbow trout (Salmo gairdneri). Maximum total binding of [3H]AFL to liver DNA from trout exposed by intraperitoneal injection was 38-47% of that of [3H]AFB1 over a 1-7 day period. The average AFL/AFB1 DNA binding ratio in 1-h incubations with isolated hepatocytes was 0.67 +/- 0.36 (n = 13). In freshly isolated hepatocytes, substantial interconversion between AFB1 and AFL via reductase and dehydrogenase enzymes was observed. Total in vivo excretion of conjugates in bile over 4 days was greater for [3H]AFL substrate than for [3H]AFB1. To determine if AFL binding was due to direct activation or to prior metabolism to AFB1 followed by activation, AFL with a tritium atom on the carbon containing the cyclopentenol function [1-3H]AFL, was synthesized and incubated with hepatocytes. Binding of [1-3H]AFL was 3% that of [3H]AFB1 and represents only direct binding of the intact cyclopentenol epoxide molecule before transformation to AFB1 and consequent loss of 3H. H.p.l.c. analysis of DNA hydrolyzed after incubation with [1-3H]AFL resulted primarily in production of non-radioactive 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 (AFB1-N7-guanine). A radioactive peak estimated to be 1% as abundant as the AFB1-N7-guanine was also observed. The overall binding of generally labeled [3H]AFL to trout liver DNA in vivo and in freshly prepared hepatocytes correlates well with available tumor incidence and mutagenicity data. Conclusions from these findings are that direct interaction of AFL-8,9-epoxide with DNA is of relatively minor quantitative importance in rainbow trout hepatocytes and that the major adduct results from conversion of AFL to AFB1 prior to epoxide formation.

Enhancement of carcinogenesis by the natural anticarcinogen indole-3-carbinol

Indole-3-carbinol (I3C), a natural constituent of cruciferous vegetables, is an inhibitor in several experimental animal models of carcinogenesis by polynuclear aromatic hydrocarbons or aflatoxin B1 (AFB1) when administered prior to or during carcinogen exposure. For assessment of the postinitiation effects of I3C, rainbow trout were exposed to dietary I3C in two different protocols--before and during AFB1 exposure or after AFB1 exposure only. Preinitiation exposure to I3C reduced AFB1-initiated hepatocellular carcinomas in trout as previously reported, but post-initiation I3C exposure strongly enhanced the tumor incidence above the positive AFB1 control. These results reveal the need for additional research to elucidate the overall effect of I3C on chemical carcinogenesis.

Mechanisms of anti-carcinogenesis by indole-3-carbinol: effect on the distribution and metabolism of aflatoxin B1 in rainbow trout

Indole-3-carbinol (I3C), a component of cruciferous vegetables, was previously shown to inhibit aflatoxin B1 (AFB1) carcinogenesis in trout. The purpose of this study was to examine the effect of I3C on AFB1 metabolism and hepatic DNA adduct formation in vivo and in vitro. When fed at 0.2%, I3C produced a 70% reduction in average in vivo hepatic DNA binding of injected AFB1 over a 21-day period when compared to controls. A 24-h distribution study of injected tritiated AFB1 in I3C fish showed less total radioactivity in the blood and liver at all times examined, compared to controls. These reductions were due primarily to reduced levels of AFB1 bound to red blood cell DNA, reduced plasma levels of the primary metabolite aflatoxicol (AFL), and decreased levels of AFB1 and polar metabolites present in the liver of I3C fish. In contrast to blood, total radioactivity was significantly elevated in the bile of I3C fish resulting from a 7-fold increase in aflatoxicol-M1 glucuronide levels over controls. No difference was observed in concentration of AFL glucuronide, the primary conjugate present in control fish. There was no difference in total radioactivity remaining in the carcass of I3C or control fish. AFB1 metabolism in freshly isolated hepatocytes from I3C fish showed 20% less DNA binding in a 1-h assay, with a 2-fold increase in aflatoxin M1 production. Addition of I3C to control hepatocytes at levels of 1, 10 or 100 microM had no effect on AFB1 DNA binding. These findings indicate that I3C inhibition of AFB1 hepatocarcinogenesis in trout involves substantial changes in the pharmacokinetics of carcinogen distribution, metabolism and elimination, leading to significantly reduced initial hepatic-nuclear DNA damage in vivo.

Mechanisms of anti-carcinogenesis: the distribution and metabolism of aflatoxin B1 in rainbow trout fed aroclor 1254

Polychlorinated biphenyls (PCBs) have previously been shown to be inhibitors of carcinogenesis in trout. The mechanism of this inhibition was investigated by studying the effects of PCBs on aflatoxin B1 (AFB1) distribution, metabolism and DNA adduct formation, both in vivo and in vitro. A 24 h distribution study of injected tritiated AFB1 showed more radioactivity in blood, liver and bile in fish fed PCBs, but less in residual carcass. The metabolites of AFB1 found in vivo in blood plasma and liver homogenates were shifted by PCB pretreatment towards greater production of the polar metabolite aflatoxin M1 (AFM1) and glucuronide conjugates. The major metabolite in bile of PCB fish was the glucuronide of aflatoxicol M1 (AFL-M1), which was enhanced 15-fold over controls. Levels of aflatoxicol (AFL) glucuronide, the major conjugate in controls, were unaltered by PCBs. The pattern of AFB1 metabolism in isolated hepatocytes from PCB-prefed fish was consistent with in vivo metabolism. AFB1--DNA adduct formation in a 1 h assay was similar in hepatocytes from PCB-fed and control fish. However, the total rate of AFB1 metabolism was significantly elevated in hepatocytes from PCB-fed fish such that the degree of AFB1--DNA adduct formed per unit AFB1 metabolized was 42% lower than control. Similarly, adduct formation in vivo during the first 24 h post-AFB1 injection in PCB fish was not significantly different from controls. However, over a longer 21 day period, adduct levels in PCB fish were only 48-69% of controls (P less than 0.005, analysis of variance), once peak adduct formation was reached. Thus, initial rates of adduct formation may be misleading in the absence of further information on rates of carcinogen metabolism in vitro and/or pharmacokinetics of peak adduct formation in vivo. These results indicate that PCB inhibition of AFB1 carcinogenesis in trout involves dramatic initial changes in carcinogen distribution, metabolism and elimination which, over time, results in a net reduction of DNA adduct formation.

A study of glandular kallikrein in experimental diabetes

Very high blood glucose concentrations were seen in rats one day after injection with alloxan or streptozotocin. Those levels fell (compared to day one, p less than 0.005) by the third day after injection and subsequently rose again during the ensuing days. In contrast, no significant differences between treated and control rats in concentrations of submandibular kallikrein were recorded until the tenth day after the initial injection. At that time the submandibular kallikrein concentrations in the alloxanized and streptozotocinized rats were less (p less than 0.01) than those of the untreated rats. A further fall (compared to day ten, p less than 0.005) took place over the next four days. Thus submandibular kallikrein would not seem to have been involved in the early stages of the experimental diabetes. In agreement with that conclusion were the results of a related series of experiments in which exogenous porcine pancreatic kallikrein was administered to alloxanized rats. The kallikrein did not bring about a reduction in the high blood glucose levels.

Initial observations of a kallikrein-like enzyme associated with the plasma membranes of rat adipocytes

Homogenates of rat adipocytes and plasma membranes thereof were shown by radioimmunoassay to contain immunoreactive glandular kallikrein. On the basis of the hydrolysis of D-Val-Leu-Arg-p-nitroanilide, the kallikrein-like enzyme associated with the plasma membranes was found not to be stimulated by prior incubation with melittin or phospholipase A2. However, pre-incubation of the membrane preparation with trypsin did increase the activity of the enzyme. Furthermore, activation could also be achieved by incubating the plasma membranes with insulin at a dose that stimulated glucose uptake into intact adipocytes. On the other hand, incubation with insulin at a dose that did not increase glucose uptake into rat adipocytes was ineffective in activating the kallikrein-like enzyme.

A comparative study of prokallikreins and kallikreins from rat pancreatic tissue and juice

Two zymogens, designated prokallikreins A and B, were isolated from homogenates of rat pancreatic tissue. The two forms of prokallikrein were found to be very similar in size and charge properties. They gave rise to very similar kallikreins on activation with exogenous trypsin. Differences in carbohydrate content of the two zymogens were probably responsible for differences seen in their behaviour on ion-exchange chromatography and immunoelectrophoresis. In contrast, only one form of prokallikrein was isolated from rat pancreatic juice. It showed almost identical behaviour on ion-exchange chromatography and identical mobility on electrophoresis to prokallikrein A. Thus it can be tentatively suggested that it is prokallikrein A which is secreted into the pancreatic juice and represents the physiologically important zymogen.

Studies of the effects of insulin, bradykinin, and captopril on blood glucose levels of alloxan-diabetic rats

Infusion of bradykinin (1 microgram/min) or saline vehicle for 30 minutes into alloxan-diabetic rats produced no change in the very high levels of blood glucose. Furthermore, intravenous injection of captopril (3 mg/Kg body weight) into the diabetic rats did not result in a significant change of glucose concentrations over a period of 60 minutes. However, infusion of bradykinin 15 minutes after intravenous injection of captopril resulted in a marked decrease of glucose levels (p less than 0.01, compared to pretreatment) by 20 minutes after the start of the infusion. Thus, the captopril potentiated the effect of the kinin, possibly by inhibition of kininase II. Using a spectrophotometric assay with Bz-Gly-Gly-Gly as substrate insulin was shown to be an inhibitor of kininase II purified from hog lungs with an I50 of 1.6 X 10(-5)M compared to captopril with I50 of 2.2 X 10(-9)M. Furthermore, it was found that in vivo infusion of as little as 50 mU insulin over a period of 30 minutes, a dose that by itself was ineffective, potentiated the glucose-lowering activity of a bradykinin infusion in alloxanized rats. Interestingly, the infusion of insulin 15 minutes after injection of captopril, at doses of each compound which alone were inactive, did produce a significant fall (p less than 0.005) in glucose concentrations. Overall, the results show that captopril, insulin and bradykinin can interact to promote a reduction in blood glucose of alloxan-diabetic rats.

Hepatocarcinogenicity of benzo[a]pyrene to rainbow trout by dietary exposure and intraperitoneal injection

The influence of benzo[a]pyrene [(BP) CAS: 50-32-8] on the induction of certain enzymes within the hepatic mixed-function oxidase (MFO) system and its potential carcinogenicity were examined in rainbow trout (Salmo gairdneri). Nine-week feeding trials were performed with 500 and 1,000 ppm BP to determine trout tolerance to BP. Levels of MFO enzymes, including ethoxyresorufin-O-deethylase (EROD), ethoxycoumarin-O-deethylase (ECOD), benzo[a]pyrene monooxygenase (BPMO), and cytochrome P450 were measured during this time. An 18-month feeding trial of a 1,000-ppm BP dose was initiated in duplicate groups of 100 fingerling rainbow trout. Samples of trout were killed at 6, 12, and 18 months for gross and histologic examination of the internal organs for neoplasms. A group of fifty 10-month-old rainbow trout were given 12 monthly ip injections of 1 mg BP in 0.4 ml propylene glycol (PG), and comparable controls were given PG injections only. The trout were held for an additional 6 months, killed at age 28 months, and examined as in the dietary study. Mean MFO enzyme levels of EROD, ECOD, BPMO, and cytochrome P450 were significantly (P less than .001) elevated, showing dose- and time-response relationships when compared to MFO enzyme levels in control fish. Twelve months after BP exposure was initiated, 15% of the BP-fed fish had histologically confirmed neoplasms of the liver. After 18 months the incidence increased to 25%. No evidence of neoplasia was observed in control fish. BP injected ip resulted in a 50% incidence of hepatocellular neoplasms and in a fibrosarcoma of the liver and papillary adenomas of the swim bladder in 1 fish. These results indicate that BP is a potent inducer of selected hepatic MFO enzymes and establish, for the first time, the hepatocarcinogenicity of BP in an aquatic species.

Urinary and renal tissue kallikrein in the streptozocin-diabetic rat

The renal kallikrein-kinin system is thought to participate in blood pressure regulation and displays abnormalities in human hypertension, as well as in many animal models of hypertension. Urinary excretion and tissue levels of renal kallikrein were measured in streptozocin (STZ)-diabetic rats in relation to blood pressure, glycemia, and insulin treatment. In study 1, STZ-diabetic rats with marked hyperglycemia showed reduced kallikrein-like esterase excretion, compared with control rats, when first measured after 7 days of diabetes (9.9 +/- 2.5 versus 17.5 +/- 2.4 EU/24 h, P less than 0.05). This difference increased with time and, after 210 days, urinary esterase excretion in diabetic and control rats was 6.7 +/- 2.1 and 39.0 +/- 6.0 EU/24 h, respectively (P less than 0.001). Urine kallikrein, measured by radioimmunoassay, was similarly reduced in diabetic rats (40.4 +/- 8.0 versus 88.0 +/- 6.5 micrograms/24 h, at 30 days, P less than 0.001). At 120 days, systolic blood pressures were elevated in diabetic rats (P less than 0.05), and at 180 days over 60% of the diabetic rats had pressures above the highest pressures of control rats. In study 2, STZ-diabetic rats were treated with insulin for 2 wk (2 U NPH at 0800 h, or 2 U NPH at 0800 and 1600 h). In the single-dose group, with hyperglycemia similar to that of diabetic rats in study 1, kallikrein excretion was reduced as early as day 2, compared with nondiabetic rats (56.0 +/- 6.1 versus 109 +/- 9.4 micrograms/24 h, respectively, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

A time-course study of submandibular kallikrein, blood glucose and insulin of alloxan-diabetic and streptozotocin-diabetic rats

A time-course study was carried out of the levels of submandibular kallikrein, serum insulin and blood glucose of rats rendered diabetic by alloxan or streptozotocin. The permanent hyperglycemia seen one day after treatment and the subsequent relative changes in the levels of blood glucose recorded over the following nine days were in agreement with previous observations. A significant reduction in the concentration of submandibular kallikrein did not become apparent until ten days following the injection of alloxan or streptozotocin. Thus the enzyme would not appear to have played either a causal or a preventative role in the production of the hyperglycemic state. Furthermore, in disagreement with previous speculation, the submandibular gland had not compensated for the deficiency of insulin with an increase in production of kallikrein. The fall in the level of serum insulin had preceded the decrease in submandibular kallikrein. However, administration of exogenous insulin over a period of three days did not bring about an increase in the concentration of submandibular kallikrein of the diabetic rats. Thus insulin would not seem to be involved in controlling the level of kallikrein in the submandibular gland.

The hepatocarcinogenicity of diethylnitrosamine to rainbow trout and its enhancement by Aroclors 1242 and 1254

Rainbow trout (Salmo gairdneri) were fed diets containing 100 ppm Aroclor 1242 (AC42) or Aroclor 1254 (AC54) in combination with 1100 ppm diethylnitrosamine (DEN) for one year. The incidence of hepatocarcinomas was determined and compared with the incidence in trout fed 1100 ppm DEN alone. The two Aroclors dramatically enhanced tumor incidence from 10.2% in the positive controls (DEN alone) to 40.2% for AC42 and 21.6% for AC54. This is in contrast to previous results obtained when AC54 was fed concomitantly with aflatoxin B1 (AFB1), where a substantial inhibition of carcinogenesis was observed. The alteration of chemical carcinogenesis in trout by PCB, therefore, depends upon the carcinogen involved and is not a generalized effect.

Inhibition of aflatoxin B1 carcinogenesis in rainbow trout by flavone and indole compounds

Several compounds such as flavonoids, selenium, antioxidants and retinoids reportedly reduce the induction of cancer in experimental animals, and some have been suggested to function by affecting the mixed-function oxidase (MFO) system. The following compounds: 50 and 500 p.p.m. beta-naphthoflavone (BNF), 1000 p.p.m. flavone, 1000 p.p.m. of a tangeretin - nobilitin mixture, 1000 p.p.m. beta- ionone , 1000 p.p.m. indole-3-carbinol ( I3C ) and 2000 p.p.m. quercetin were examined for protection against aflatoxin B1 (AFB1) hepatocarcinogenesis, induction of the MFO system and metabolism of AFB1 in rainbow trout. These compounds were fed to fingerling rainbow trout for 8 weeks. At that time the activity of several MFO enzymes and cytochrome P450 content were measured and the trout were exposed for 2 weeks to 20 p.p.b. AFB1 in the same diets. After feeding the test diets without AFB1 for another 6 weeks and basal diet for another 52 weeks, the tumor incidence was determined. The effect of BNF and I3C on in vivo binding of AFB1 to DNA was also measured in separate groups of trout. BNF induced the trout MFO system in a dose-dependent manner, tangeretin - nobilitin was less effective and I3C did not induce. BNF showed significant alterations in the metabolism of AFB1 to aflatoxicol and aflatoxin M1 using cell fractions from pretreated fish. None of the other compounds, including I3C showed such an effect. Despite the apparent lack of in vitro effect of I3C , both BNF and I3C reduced AFB1 - DNA binding in vivo. I3C and BNF provided marked protection against AFB1-induced hepatocarcinogenesis, while the other compounds were less effective. The 58 weeks tumor incidences were 4% for 1000 p.p.m. I3C , 6% for 500 p.p.m. BNF and 18% for 50 p.p.m. BNF, compared to 38% for the AFB1-positive control. These data demonstrate that gross induction of the MFO system was not necessarily required for alterations in DNA adduct formation in vivo or protection against AFB1 carcinogenesis. Both BNF and I3C provided marked protection but only BNF induced the MFO system.

Dietary modification of aflatoxin B1 carcinogenesis: mechanism studies with isolated hepatocytes from rainbow trout

Hepatocytes were prepared from rainbow trout by perfusion in situ with collagenase and hyaluronidase. Preparations normally showed high initial viability (95 +/- 5% dye exclusion, 92 +/- 5% lactate dehydrogenase retention) and gradually decreased in viability and glutathione concentration over 5 hours. Cellular metabolism of aflatoxin B1 (AFB1), a potent hepatocarcinogen, was characterized by an investigation of the following parameters: kinetics of AFB1 metabolism and DNA adduct formation, dose response, viabilities of detoxication and activation pathways with time, influence of organic solvents, and effect of variation in cell concentration. The AFB1 metabolites and DNA adducts were resolved and quantitated by high-performance liquid chromatography. From these results a standardized assay procedure was derived which we used to examine AFB1 metabolism and DNA adduct formation in hepatocytes from fish fed dietary substances known to alter the carcinogenic response to this mycotoxin. Dietary beta-naphthoflavone, which strongly inhibits AFB1 carcinogenesis in rainbow trout, dramatically and reproducibly altered AFB1 binding and metabolism in isolated hepatocytes. Overall rate of AFB1 metabolism and rates of detoxication reactions increased, whereas DNA binding decreased. Dietary cyclopropenoid fatty acids, powerful synergists and promoters of AFB1 carcinogenesis in trout, also repressed AFB1-DNA binding. Both dietary factors appeared to depress initial DNA damage by AFB1 but operated through different metabolic pathways to do so.

Rainbow trout embryos: advantages and limitations for carcinogenesis research

Rainbow trout embryos are sensitive to the initiation of neoplasms in various tissues by brief exposures to solutions of water-soluble carcinogens. This characteristic was first demonstrated with the sparingly soluble liver carcinogen, aflatoxin B1 (AFB1). A 30-minute exposure of 21-day-old embryos (embryos hatch in 24-25 days at 12 degrees C) to a 0.5-ppm aqueous solution of AFB1 will result in approximately 65 of the survivors having at least 1 liver tumor, 1 year after treatment. The embryos are responsive to both AFB1 dose and the length of exposure and become increasingly sensitive with increased embryonic age. We have used rainbow trout embryos to demonstrate the hepatocarcinogenicity of other aflatoxin metabolites and precursors; aflatoxicol, aflatoxin G1, versicolorin A, and sterigmatocystin. In addition to mycotoxins, trout embryos are sensitive to several nitrosamine hepatocarcinogens including: dimethylnitrosamine, diethylnitrosamine, nitrosopyrrolidine, and 2,6-dimethylnitrosomorpholine. However, with the highly water-soluble nitrosamines, longer exposure time (up to 24 hr) are required. It is generally accepted that each of the above-named carcinogens requires metabolic activation to the ultimate carcinogenic form. This provides indirect evidence that the trout embryo is capable of cytochrome P-450-mediated metabolism. Finally, trout embryos are sensitive to the direct-acting carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine. This compound produces tumors of the liver, stomach, kidney, and swim bladder, and a pronounced female-to-male sex reversal. Results to date have shown that the trout embryo is a sensitive, convenient, and economical whole animal model system with many distinct advantages for carcinogen testing and research.(ABSTRACT TRUNCATED AT 250 WORDS)

A quantitative study of the levels of glandular kallikrein in normal and diabetic rats

The concentrations of kallikrein, as measured by specific radioimmunoassay, in pancreatic tissue of normal, alloxan-, and streptozotocin-diabetic rats were found to be essentially the same. In contrast, the levels of kallikrein in the submandibular glands of the diabetic rats were significantly less than that of the normal rats. However, there were no such differences in the levels of acid phosphatase or alpha-amylase. Thus, the experimentally induced diabetic state would seem to involve a specific reduction in submandibular kallikrein.

The sensitivity of rainbow trout and other fish to carcinogens

Systematic design of replacement chemicals with reduced toxicities will require knowledge of mechanisms of action of parent compounds, especially in species which occupy the environment of most likely exposure. For aquatic systems, the rainbow trout has proven a valuable model for studying mechanisms of carcinogenicity. By comparison, small aquarium species show great potential as in situ field monitors of aquatic contamination by toxic chemicals but are less developed for mechanism studies. Fish species, especially rainbow trout, have also proven useful alternatives to traditional rodent models for comparative studies on mechanisms of action of nonaquatic carcinogens. These kinds of comparative studies form an essential basis for extrapolation of animal studies to man. Carcinogenicity testing of individual compounds and their replacements can provide only limited information on the expected impact of such chemicals on natural populations, since these populations are unavoidably exposed to potent modulators of the carcinogenic response. Hence any program which aims at redesign of commercial chemicals with reduced toxicities must have as a prior aim the full understanding of the mechanisms of joint carcinogen-inhibitor-promotor interactions. Because of their high sensitivity, low cost per individual, and low background tumor incidences, fish models such as the rainbow trout may be the only vertebrate models in which it is economically practical to initiate such complex studies.

Effect of dose on the inhibition of carcinogenesis/mutagenesis by Aroclor 1254 in rainbow trout fed aflatoxin B1

Prior studies have shown that Aroclor 1254 (PCB) differentially alters the incidence of aflatoxin B1 (AFB1) induced hepatocellular carcinomas in trout, depending upon the time of PCB administration relative to AFB1 exposure (Shelton et al., 1983). When fed simultaneously with AFB1, PCB inhibits carcinoma incidence. We investigated the effect of AFB1 and PCB dose on this inhibition. Duplicate tanks of 100 rainbow trout were fed AFB1 at concentrations of 1, 4, or 8 ppb, either with or without the addition of 50 ppm PCB. Other groups were fed 4 ppb AFB1 + 5 ppm PCB, 50 ppm PCB alone, or control diet alone. After 9 and 12 mo, 40 and 60 fish per tank, respectively, were sampled to determine the incidence of liver tumors. The results show a parallel inhibition of the AFB1-tumor dose-response curve by the presence of 50 ppm PCB. Fish fed 4 ppb AFB1 + 5 ppm PCB showed slight inhibition in response when compared with 4ppb AFB1 alone. Also, livers from fish fed 50 ppm PCB were used to prepare S20 for use in the Salmonella mutagenesis assay. These livers were less efficient in converting AFB1 to a mutagen, when compared to control S20. The AFB1-mutagenesis dose-response curve was again shifted parallel to the right of the curve generated using control S20. These results suggest that the inhibitory action is at least partly at the level of carcinogen activation. The finding of parallel, as opposed to proportional, inhibition with varying carcinogen exposure for certain classes of inhibitors may have important implications for inhibition of environmental carcinogenesis at low levels of carcinogen exposure.

Comparative activation of aflatoxin B1 to mutagens by isolated hepatocytes from rainbow trout (Salmo gairdneri) and coho salmon (Oncorhynchus kisutch)

Isolated hepatocytes from rainbow trout readily activated aflatoxin B1 (AFB1) to mutagens detectable by S. typhimurium TA 98. Characterization studies demonstrated that activation efficiency was essentially linear with respect to hepatocyte concentration (5 X 10(5)-2 X 10(7) cell/ml) and AFB1 dose (0-10 micrograms/ml). This system was employed to assess possible differences in AFB1 activation in hepatocytes from rainbow trout and coho salmon, two species which have been shown in in vivo studies to differ widely in sensitivity to AFB1 carcinogenesis. Activation efficiency was approximately three times greater in trout hepatocytes compared with salmon hepatocytes. This difference was more marked when S20 liver fractions from the two species were used. Analysis of unbound [3H]AFB1 metabolites performed on supernatants of hepatocyte incubations revealed that under the normal conditions of assay, addition of bacteria does not perturb the various pathways of AFB1 metabolism within hepatocytes. These results support other studies which suggest that the greater sensitivity of trout to AFB1 carcinogenicity resides largely in increased initial DNA damage, compared with coho salmon.

Glucuronides in bile of rainbow trout (Salmo gairdneri) injected with [3H]aflatoxin B1 and the effects of dietary beta-naphthoflavone

Rainbow trout Salmo gairdneri were fed a diet containing the mixed-function oxidase system inducer, beta-naphthoflavone or were fed a control diet. For the two respective diets, as much as 50 and 12% of an i.p.-injected dose of [3H]aflatoxin B1 was recovered in the bile. The major product in the bile of beta-naphthoflavone-fed trout was an aflatoxicol-M1 glucuronide, whereas the major product in the control bile was an aflatoxicol glucuronide.

Identification and mutagenicity of aflatoxicol-M1 produced by metabolism of aflatoxin B1 and aflatoxicol by liver fractions from rainbow trout (Salmo gairdneri) fed beta-naphthoflavone

beta-Naphthoflavone (beta NF) fed to rainbow trout (Salmo gairdneri) at 50 or 500 ppm in the diet, modified the in vitro metabolism of aflatoxin B1 (AFB1) by the postmitochondrial fraction (PMF) of the liver. Production of aflatoxicol (AFL) was significantly less in the 500 ppm beta NF-fed group (33.9 ng/mg protein) than in the control group (45.7 ng/mg protein), aflatoxin M1 production was dependent on the dose of beta NF, being greatest in the 500 ppm beta NF-fed group (48.9 ng/mg protein), intermediate in the 50 ppm beta NF-fed group (3.7 ng/mg protein), and was not detected in controls. A new trout metabolite, 4-hydroxyaflatoxicol (aflatoxicol M1, AFLM1) was also detected in small amounts from in vitro metabolism by liver PMF from beta NF-fed trout. Sufficient quantities of AFLM1 for confirmation of identity by ultraviolet spectra, mass spectra and nuclear magnetic resonance spectra were prepared by biotransformation of AFL using liver microsomes and isolation by HPLC. In a modified Ames mutagen assay with Salmonella typhimurium TA98, ALFM1 was 4.1% as mutagenic as AFB1 in a previous determination. The carcinogenicity of AFLM1 to rainbow trout is expected to be considerably less than that of AFB1.