Determination of Domoic Acid Toxins in Shellfish by Biosense ASP ELISAA Direct Competitive Enzyme-Linked Immunosorbent Assay: Collaborative Study

A collaborative study was conducted on the Biosense amnesic shellfish poisoning (ASP) enzyme-linked immunosorbent assay (ELISA) for the determination of domoic acid (DA) toxins in shellfish in order to obtain interlaboratory validation data for the method. In addition, a method comparison study was performed to evaluate the ASP ELISA as an alternative to the current liquid chromatography (LC) reference method for DA determination. The study material comprised 16 shellfish samples, including blue mussels, Pacific oysters, and king scallops, spiked with contaminated mussel homogenates to contain 0.120 mg DA/kg shellfish flesh. The shellfish samples were extracted with 50% aqueous methanol, and the supernatants were directly analyzed. Sixteen participating laboratories in 10 countries reported data from the ASP ELISA, and 4 of these laboratories also reported data from instrumental LC analysis. The participating laboratories achieved interlaboratory precision estimates for the 8 Youden paired shellfish samples in the range of 1020% for RSDr (mean 14.8 4%), and 1329% for RSDR (mean 22.7 6%). The precision estimates for the ELISA data did not show a strong dependence on the DA concentration in the study samples, and the overall precision achieved was within the acceptable range of the Horwitz guideline with HorRat values ranging from 1.1 to 2.4 (mean HorRat 1.7 0.5). The analysis of shellfish samples spiked with certified reference material (CRM)-ASP-MUS-b gave recoveries in the range of 88122%, with an average recovery of 104 10%. The estimate on method accuracy was supported by a correlation slope of 1.015 (R2 = 0.992) for the determined versus the expected DA values. Furthermore, the correlation of the ASP ELISA results with those for the instrumental LC analyses of the same sample extracts gave a correlation slope of 1.29 (R2 = 0.984). This indicates some overestimation of DA levels in shellfish by the ELISA, but it is also a result of apparent low recoveries for the LC methods. This interlaboratory study demonstrates that the ASP ELISA is suitable for the routine determination and monitoring of DA toxins in shellfish, and that it offers a rapid and cost-effective methodology with high sample throughput.

Multiresidue Method for Determination of Algal Toxins in Shellfish: Single-Laboratory Validation and Interlaboratory Study

A method that uses liquid chromatography with tandem mass spectrometry (LC/MS/MS) has been developed for the highly sensitive and specific determination of amnesic shellfish poisoning toxins, diarrhetic shellfish poisoning toxins, and other lipophilic algal toxins and metabolites in shellfish. The method was subjected to a full single-laboratory validation and a limited interlaboratory study. Tissue homogenates are blended with methanol-water (9 + 1), and the centrifuged extract is cleaned up with a hexane wash. LC/MS/MS (triple quadrupole) is used for quantitative analysis with reversed-phase gradient elution (acidic buffer), electrospray ionization (positive and negative ion switching), and multiple-reaction monitoring. Ester forms of dinophysis toxins are detected as the parent toxins after hydrolysis of the methanolic extract. The method is quantitative for 6 key toxins when reference standards are available: azaspiracid-1 (AZA1), domoic acid (DA), gymnodimine (GYM), okadaic acid (OA), pectenotoxin-2 (PTX2), and yessotoxin (YTX). Relative response factors are used to estimate the concentrations of other toxins: azaspiracid-2 and -3 (AZA2 and AZA3), dinophysis toxin-1 and -2 (DTX1 and DTX2), other pectenotoxins (PTX1, PTX6, and PTX11), pectenotoxin secoacid metabolites (PTX2-SA and PTX11-SA) and their 7-epimers, spirolides, and homoYTX and YTX metabolites (45-OHYTX and carboxyYTX). Validation data have been gathered for Greenshell mussel, Pacific oyster, cockle, and scallop roe via fortification and natural contamination. For the 6 key toxins at fortification levels of 0.05–0.20 mg/kg, recoveries were 71–99% and single laboratory reproducibilities, relative standard deviations (RSDs), were 10–24%. Limits of detection were <0.02 mg/kg. Extractability data were also obtained for several toxins by using successive extractions of naturally contaminated mussel samples. A preliminary interlaboratory study was conducted with a set of toxin standards and 4 mussel extracts. The data sets from 8 laboratories for the 6 key toxins plus DTX1 and DTX2 gave within-laboratories repeatability (RSDr) of 8–12%, except for PTX-2. Between-laboratories reproducibility (RSDR) values were compared with the Horwitz criterion and ranged from good to adequate for 7 key toxins (HorRat values of 0.8–2.0).

High prevalence of antibodies to the 2009 pandemic influenza A(H1N1) virus in the Norwegian population following a major epidemic and a large vaccination campaign in autumn 2009

The prevalence of antibodies reactive to the 2009 pandemic influenza A(H1N1) was determined in sera collected before the start of the pandemic, during the early phase, and after the main epidemic wave and nationwide vaccination campaign in Norway. A substantial rise in prevalence of antibodies at protective titres, from 3.2% to 44.9%, was observed between August 2009 and January 2010. The highest prevalence, 65.3%, was seen in the age group of 10-19 year-olds.

High prevalence of antibodies to the 2009 pandemic influenza A(H1N1) virus in the Norwegian population following a major epidemic and a large vaccination campaign in autumn 2009

The prevalence of antibodies reactive to the 2009 pandemic influenza A(H1N1) was determined in sera collected before the start of the pandemic, during the early phase, and after the main epidemic wave and nationwide vaccination campaign in Norway. A substantial rise in prevalence of antibodies at protective titres, from 3.2% to 44.9%, was observed between August 2009 and January 2010. The highest prevalence, 65.3%, was seen in the age group of 10-19 year-olds.

Discovery of localized regions of excess 10-TeV cosmic rays

The 7 year data set of the Milagro TeV observatory contains 2.2 x 10(11) events of which most are due to hadronic cosmic rays. These data are searched for evidence of intermediate scale structure. Excess emission on angular scales of approximately 10 degrees has been found in two localized regions of unknown origin with greater than 12sigma significance. Both regions are inconsistent with pure gamma-ray emission with high confidence. One of the regions has a different energy spectrum than the isotropic cosmic-ray flux at a level of 4.6sigma, and it is consistent with hard spectrum protons with an exponential cutoff, with the most significant excess at approximately 10 TeV. Potential causes of these excesses are explored, but no compelling explanations are found.

Multiresidue method for determination of algal toxins in shellfish: single-laboratory validation and interlaboratory study

A method that uses liquid chromatography with tandem mass spectrometry (LC/MS/MS) has been developed for the highly sensitive and specific determination of amnesic shellfish poisoning toxins, diarrhetic shellfish poisoning toxins, and other lipophilic algal toxins and metabolites in shellfish. The method was subjected to a full single-laboratory validation and a limited interlaboratory study. Tissue homogenates are blended with methanol-water (9 + 1), and the centrifuged extract is cleaned up with a hexane wash. LC/MS/MS (triple quadrupole) is used for quantitative analysis with reversed-phase gradient elution (acidic buffer), electrospray ionization (positive and negative ion switching), and multiple-reaction monitoring. Ester forms of dinophysis toxins are detected as the parent toxins after hydrolysis of the methanolic extract. The method is quantitative for 6 key toxins when reference standards are available: azaspiracid-1 (AZA1), domoic acid (DA), gymnodimine (GYM), okadaic acid (OA), pectenotoxin-2 (PTX2), and yessotoxin (YTX). Relative response factors are used to estimate the concentrations of other toxins: azaspiracid-2 and -3 (AZA2 and AZA3), dinophysis toxin-1 and -2 (DTX1 and DTX2), other pectenotoxins (PTX1, PTX6, and PTX11), pectenotoxin secoacid metabolites (PTX2-SA and PTX11-SA) and their 7-epimers, spirolides, and homoYTX and YTX metabolites (45-OHYTX and carboxyYTX). Validation data have been gathered for Greenshell mussel, Pacific oyster, cockle, and scallop roe via fortification and natural contamination. For the 6 key toxins at fortification levels of 0.05-0.20 mg/kg, recoveries were 71-99% and single laboratory reproducibilities, relative standard deviations (RSDs), were 10-24%. Limits of detection were <0.02 mg/kg. Extractability data were also obtained for several toxins by using successive extractions of naturally contaminated mussel samples. A preliminary interlaboratory study was conducted with a set of toxin standards and 4 mussel extracts. The data sets from 8 laboratories for the 6 key toxins plus DTX1 and DTX2 gave within-laboratories repeatability (RSD(R)) of 8-12%, except for PTX-2. Between-laboratories reproducibility (RSDR) values were compared with the Horwitz criterion and ranged from good to adequate for 7 key toxins (HorRat values of 0.8-2.0).

Analysis of PSP toxins in Norwegian mussels by a post-column derivatization HPLC method

The aim of this study was to investigate the agreement between the AOAC mouse bioassay and an HPLC method for determining Paralytic Shellfish Poisoning (PSP) toxicity in blue mussels from the Norwegian coast. The AOAC mouse bioassay has traditionally been used for determining the toxin levels. Recently, an HPLC method for determining PSP toxins has been implemented and run in parallel with the bioassay. Four hundred mussel extracts from the last six years were analysed with both methods. A highly significant linear correlation between the methods was achieved (r = 0.84). However, the relation between the two methods was best described by a second-degree polynom. Totally, this model explained 87% of the variation in the HPLC method. By agreement analysis, it was possible to establish cut-off levels for the HPLC method related to the AOAC mouse bioassay with kappa values >0.80 for toxicity levels below 500 MU/100 g. The HPLC method could substitute the mouse bioassay in determining PSP toxicity in Norwegian mussels. Additionally, about 70 mussel samples were also analysed by the MIST Alert trade mark test kit. The kit did not give any false negative results compared with the regulatory limit, but 30% of the samples below the cut point were also determined as positive.

Comparison of oral and intraperitoneal toxicity of yessotoxin towards mice

Currently, yessotoxin is regulated among the toxins in the diarrhetic shellfish poisoning (DSP) complex. Yessotoxin is equally acutely toxic towards mice upon intraperitoneal injections as those algal toxins giving diarrhea, but is not diarrheagenic. Its presence in mussels may therefore lead to overestimation of risk of DSP in consumers when the standard mouse bioassay is used. Arguments are presented for the use of analytical methods instead of the mouse bioassay for the diarrheagenic DSP toxins and yessotoxin. Yessotoxin was found to be more than ten times less toxic to mice via the oral route, compared with intraperitoneal injections. Even at 10mg/kg body weight, the highest dose ever tested orally, yessotoxin did not kill the mice. By means of light microscopy of several organs, moderate changes were only observed in the heart. Ultrastructural studies revealed swelling of heart muscle cells leading to separation of the organelles. Effects were most pronounced close to the capillaries. The pathological changes were clearly dose dependent, and the lowest oral dose where any effects were seen was 2.5mg yessotoxin per kg.

The validity of two HPLC methods and a colorimetric PP2A assay related to the mouse bioassay in quantification of diarrhetic toxins in blue mussels (Mytilus edulis)

Validity of two HPLC methods and a PP2A assay in relation to the mouse bioassay for diarrhetic shellfish poisoning (DSP) toxins was evaluated. The mouse bioassay for DSP toxins was performed on a total of 177 mussel samples from the Sognefjord, Norway, using diethyl ether in the final step of extraction. For fluorimetric HPLC analyses, either 4-bromomethyl-7-methoxycoumarin (BrMMC) or 9-anthryl diazomethane (ADAM) were used for analysis of 48 and 118 of the samples, respectively. The colorimetric PP2A inhibition assay was performed on all 177 samples that were analysed with the mouse bioassay. When comparing the HPLC-BrMMC, the HPLC-ADAM and the PP2A assays with the mouse bioassay, cut off values of < or =4, 5 and 6 microg okadaic acid (OA) equivalents (eq.)/5 g digestive gland (DG) was used. With reference to the results from the mouse bioassay, the total number of failure and correct classification by HPLC-ADAM and the PP2A method was compared for the three cut off values. No significant differences between the methods were detected. However, all differences were found in favour of HPLC-ADAM. All three methods could replace the mouse bioassay in detecting levels of diarrhetic toxins approved internationally for safe consumption of mussels. However, HPLC-ADAM seems to be the method of choice.

Repeatability and validity of a fluorimetric HPLC method in the quantification of yessotoxin in blue mussels (Mytilus edulis) related to the mouse bioassay

Repeatability and validity of a fluorimetric HPLC method in quantification of yessotoxin (YTX) in mussels related to the mouse bioassay was studied. Blue mussels (Mytilus edulis) from the Sognefjord, Norway were sampled from March to November, 1997, and October to December, 1998. A total of 75 samples were analysed for YTX by HPLC using 4-[2-(6,7-dimethoxy-4-methyl-3-oxo-3, 4-dihydroquinoxalinyl) ethyl]-1,2,4-triazoline-3, 5-dione (DMEQ-TAD) as a fluorimetric derivatization agent. Among these, 28 of the samples were analysed by HPLC in duplicate. All samples were analysed by the mouse bioassay using both chloroform and ether in the final step of extraction. The duplicate measurements using HPLC was found equal and the method repeatable (p<0.05). The absolute difference between the two measurements was found to increase with increasing level of measurements. This significant positive correlation (p<0.05) was mainly due to concentrations of YTX higher than 200 microg/100g mussel meat. However the precision of the results obtained was not found to be less in the upper level than in the lower level. Based on the internal correlation analysis including the mouse bioassay and the HPLC method a cut-off value of < or =10 microg YTX/5 g digestive gland was found preferable. The mouse bioassay of ether extracts often failed to detect high levels of YTX, and as demonstrated by the low kappa-values, the agreement between the mouse bioassay of ether extracts and the HPLC method was very weak. The HPLC method was found to give repeatable results and thereby found to be reliable. Consequently, the HPLC method seems to the method of choice for detection and quantification of YTX in mussels when compared with the mouse bioassay.

Monthly variations in diarrhetic toxins and yessotoxin in shellfish from coast to the inner part of the Sognefjord, Norway

Monthly concentrations of diarrhetic shellfish poisoning (DSP) toxins and yessotoxin (YTX) in mussels from the coast to the inner part of the Sognefjord were determined. Mussels from nine locations were sampled from March to November 1997. The DSP toxins and YTX were analysed by a colorimetric protein phosphatase 2A (PP2A) inhibition assay or fluorometric HPLC, respectively. The mouse bioassay for DSP toxins was performed including either chloroform or diethyl ether in the final step of extraction. Using ether in the final step normally facilitated extraction of the DSP toxins, okadaic acid (OA) and dinophysis toxin-1 (DTX-1), while chloroform extraction included a wider spectrum of toxins, including YTX and a fast acting toxin(s) with neurotoxic effects. The concentrations of DSP toxins and YTX in mussels increased with distance from the coast. The highest concentrations of YTX (574 microg YTX/100 g mussel meat) and diarrhetic toxins (349 microg OA equivalents/100 g mussel meat) were measured in May and August, respectively, at locations in the inner part of the fjord. Since concentrations of DSP toxins and YTX in mussels increased with distance from the coast, the locations for mussel farming in the Sognefjord close to the coast, seem to be preferable.

The repeatability of two HPLC methods and the PP2A assay in the quantification of diarrhetic toxins in blue mussels (Mytilus edulis)

Repeatability in the quantification of diarrhetic shellfish toxins was investigated for two fluorometric HPLC methods and a colorimetric PP2A assay, using agreement analysis. Blue mussels (Mytilus edulis) from the Sognefjord on the southwest coast of Norway were sampled during the periods of July to October, 1996, March to November, 1997, and October to December, 1998. The results from the first and the duplicate measurement were found to be very similar for both HPLC methods using two fluorogenic reagents, 4-bromomethyl,7-methoxycoumarin and 9-anthryl diazomethane, and the colorimetric PP2A inhibition assay in detection of diarrhetic shellfish toxins. The levels of agreement between the measurements were satisfactory for all three methods. Significant correlations were found between the level of observation and the absolute difference between the two measurements and were mainly due to concentrations of OA/DTX-1 higher than 100 microg/100 g mussel meat. However, the precision of quantifying DSP toxins in the upper level was not found to be less than in the lower level. Both the HPLC methods and the PP2A assay were found to give repeatable results and thereby found to be reliable.

Structure and fluorometric HPLC determination of 1-desulfoyessotoxin, a new yessotoxin analog isolated from mussels from Norway

A new analog of yessotoxin, 1-desulfoyessotoxin, was isolated from the digestive glands of mussels growing in the Sognefjord, Norway. Its structure was determined by NMR and negative ion CID MS/MS experiments. 1-Desulfoyessotoxin can be detected by the fluorometric HPLC method analogous with other yessotoxins.

Sensitive detection of apoptogenic toxins in suspension cultures of rat and salmon hepatocytes

A number of algal toxins were tested for the ability to induce apoptosis (regulated cell death) in primary hepatocytes from salmon and rat. The tested toxins included the liver targeting substances microcystin-LR and nodularin, substances associated with the diarrhetic shellfish poison complex (okadaic acid, dinophysistoxin-1 and pectenotoxin-1) and calyculin A. All toxins induced apoptosis in both salmon and rat hepatocytes in less than 2 h. The apoptotic changes were evident both by electron and light microscopy and were counteracted by the caspase inhibitor ZVAD-fmk and by the Ca2+/calmodulin dependent kinase II inhibitor KN-93. The salmon hepatocytes were 10-20-fold more sensitive to okadaic acid and dinophysistoxin-1 (EC50=20 nM) than rat hepatocytes and other mammalian cell lines tested. An assay was devised using hepatocyte apoptosis as parameter for detection of algal toxins. This assay was at least as sensitive as HPLC determination for okadaic acid in mussel extracts. It also detected algal toxins which do not inhibit protein phosphatases, like pectenotoxin-1. Subapoptotic concentrations of the toxins inhibited hepatocyte aggregation. Using this parameter, less than 200 pg okadaic acid could be detected. In conclusion, salmon hepatocytes in suspension culture provide a rapid and sensitive system for detection of a broad range of apoptogenic toxins.

Oral toxicity in mice of algal toxins from the diarrheic shellfish toxin (DST) complex and associated toxins

Mussel samples from four locations along the Norweigian coast were extracted by methods for diarrheic shellfish toxins (DST) and tested by chemical and biological methods, including histopathology. All samples had previously been found to be highly toxic in mice, with symptoms indicating the presence of non-diarrheagenic toxins in the mouse bioassay. Chemical analysis revealed that the DST okadaic acid (OA) and dinophysistoxin-1 (DTX1) were present each one in one sample, but only a minor part of the total toxicity could be attributed to these toxions. In the other two samples, OA and DTX1 were absent. Incubation of the mussel extracts from all four samples with freshly prepared hepatocytes indicated the presence of unknown toxin(s) which may not be classified within the DST complex. Purified mussel samples were given to baby mice both via intraperitoneal (i.p.) injections and by oral intubation. Oral toxicity was about 25-50 times lower than toxicity obtained by i.p. injections, a result in accordance with acute toxic properties of many toxins. Risk assessment of the unknown toxin(s) requires chemical identification, but the preliminary results obtained indicate a large margin of safety, based on the large amounts of mussel extracts necessary to yield toxic effects in the intestine and liver in experimental animals upon oral exposure versus human intake.

Tissue distribution of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in two strains of male rats

Albino and hooded male rats were administered 14C-labeled 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) by gavage. The tissue distribution was investigated by means of whole-body autoradiography and liquid scintillation counting. MeIQx was rapidly absorbed from the alimentary tract and distributed to several tissues. The major predilection sites were the liver and kidneys. The amount of radioactivity decreased dramatically within a few days. However, unextractable radioactive material was still detectable in these organs 6 days after the administration.

An evaluation of the mouse bioassay applied to extracts of 'diarrhoetic' shellfish toxins

The standard mouse bioassay, used to assess 'diarrhoetic shellfish poison' (DSP), is based on intraperitoneal administration of toxic mussel extracts, and monitoring of survival time within a 24-hr period. Toxic effects on mice were examined for extracts of mussel samples from two different regions of south Norway known to possess toxins of specific properties. Both samples revealed an exponential pattern in the dose-response relationship. Whereas the time lag from injection to death was linearly dependent on mouse weight, the effect of weight also increased with decreased sample toxicity. When tested with doses adjusted for weight, a marked individual variation was found within all size groups of mice. The results imply that, regarding prohibition limits for distribution and sale of mussels, a certain degree of variation with regard to time should be accepted in the testing of parallel samples. On the basis of the results, a revised method for the determination of toxicity by mouse bioassay is proposed for DSP testing. The method is based on administration to two mice of size-adjusted doses of extracts, followed by a 4-hr surveillance period and a 1-hr upper limit of acceptable time variation between parallel samples. The method shows advantages regarding savings of time and money, in precision in determination of toxicity level, as well as curtailed exposure to toxin and reduced suffering of laboratory animals.

Impairment of lymphocyte adhesion to cultured fibroblasts and endothelial cells by gamma-irradiation

A critical component of immune responsiveness is the localization of effector cells at sites of inflammatory lesions. Adhesive molecules that may play a role in this process have been described on the surfaces of both lymphocytes and connective tissue cells. Adhesive interactions of T lymphocytes with fibroblasts or endothelial cells can be inhibited by preincubation of the fibroblasts or endothelial cells with antibody to intercellular adhesion molecule 1 (CD54) or by preincubation of the T cells with antibody to lymphocyte function-associated Ag 1 (CD11a/CD18), molecules shown to be important in several other cell-cell adhesive interactions. Here we show that gamma-irradiation of human T lymphocytes impaired their ability to adhere to both fibroblasts and endothelial cells. This impairment was not associated with a loss of cell viability or of cell surface lymphocyte function-associated Ag 1 expression. gamma-Irradiation of T cells is known to result in the activation of ADP-ribosyltransferase, an enzyme involved in DNA strand-break repair, causing subsequent depletion of cellular nicotinamide adenine dinucleotide (NAD) pools by increasing NAD consumption for poly(ADP-ribose) formation. Preincubation of T cells with either nicotinamide or benzamide [corrected], both known inhibitors of ADP-ribosyltransferase, completely reversed the suppressive effects of gamma-irradiation on T cell adhesion. The maintenance of adhesion was accompanied by inhibition of irradiation-induced depletion of cellular NAD. These experiments suggest that the impairment of cellular immune function after irradiation in vivo may be caused, in part, by defective T cell emigration and localization at inflammatory sites.

Impairment of lymphocyte adhesion to cultured fibroblasts and endothelial cells by gamma-irradiation

A critical component of immune responsiveness is the localization of effector cells at sites of inflammatory lesions. Adhesive molecules that may play a role in this process have been described on the surfaces of both lymphocytes and connective tissue cells. Adhesive interactions of T lymphocytes with fibroblasts or endothelial cells can be inhibited by preincubation of the fibroblasts or endothelial cells with antibody to intercellular adhesion molecule 1 (CD54) or by preincubation of the T cells with antibody to lymphocyte function-associated Ag 1 (CD11a/CD18), molecules shown to be important in several other cell-cell adhesive interactions. Here we show that gamma-irradiation of human T lymphocytes impaired their ability to adhere to both fibroblasts and endothelial cells. This impairment was not associated with a loss of cell viability or of cell surface lymphocyte function-associated Ag 1 expression. gamma-Irradiation of T cells is known to result in the activation of ADP-ribosyltransferase, an enzyme involved in DNA strand-break repair, causing subsequent depletion of cellular nicotinamide adenine dinucleotide (NAD) pools by increasing NAD consumption for poly(ADP-ribose) formation. Preincubation of T cells with either nicotinamide or benzamide [corrected], both known inhibitors of ADP-ribosyltransferase, completely reversed the suppressive effects of gamma-irradiation on T cell adhesion. The maintenance of adhesion was accompanied by inhibition of irradiation-induced depletion of cellular NAD. These experiments suggest that the impairment of cellular immune function after irradiation in vivo may be caused, in part, by defective T cell emigration and localization at inflammatory sites.

Metabolic activation of food mutagens by liver and lung enzymes from rats, pigs and oxen

Mutagenic activation of the 3 cooked food mutagens 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was compared in liver and lung enzyme preparations from oxen, pigs and rats. Liver preparations from oxen were the most efficient in activating the mutagens, while the rat enzymes were more active than those from pigs. The different cooking mutagens showed different mutagenic potential. MeIQ was the most potent mutagen, followed by IQ and MeIQx in descending order. In oxen, MeIQx was as potent as IQ. The activation with the lung enzymes was 2-3 orders of magnitude lower than with liver. Furthermore, species differences in mutagenic activation with lung enzymes were small compared with liver enzymes. In lung preparations the differences between IQ and MeIQ were small, but in all 3 animal species the mutagenicity of MeIQx was 1 order of magnitude lower than that of the other 2 mutagens.

Light and scanning electron microscopic studies on effects of marine algal toxins toward freshly prepared hepatocytes

Mussels exposed to dinoflagellates may represent a human health risk due to accumulation of a variety of algal toxins. In several parts of the world, algal toxins leading to diarrhea (diarrhetic shellfish poisons, DSP) are found in mussels for extended periods of the year. Routine monitoring of these toxins involves ip injections in mice. Chemical analytical methods have been developed for only some of the toxins in question, namely, those giving diarrhea. Other toxins in the DSP complex are not easily detected by analytical methods. In this report we show that freshly prepared hepatocytes from rats are a convenient means to differentiate between the toxins that give diarrhea and those that do not. Consequently, hepatocytes can be useful in both screening and as a tool in the process of developing analytical methods. Freshly prepared hepatocytes might be useful in combination either with the mouse bioassay or with chemical analytical methods.

Testing for Algal Toxins In Vitro

Toxic blooms of several strains of blue-green algae are found in both natural and man-made freshwater lakes. Furthermore, mussels may accumulate toxic marine dinoflagellates, rendering them toxic to humans.

Traditionally, the presence of algal toxins is tested by intraperitoneal injections of extracts in mice. However, toxic waterblooms and mussels can both be detected by means of freshly prepared rat hepatocytes in suspension.

Freshly prepared rat hepatocytes used in screening the toxicity of blue-green algal blooms

The acute toxicity of extracts of blue-green algae was tested in freshly prepared rat hepatocytes in suspension. The results were compared with the traditional in vivo mouse bioassay. Sixty samples of natural algal blooms from freshwater lakes in Norway, Sweden, and Finland and 14 samples cultured in the laboratory were tested. The mouse bioassay revealed hepatotoxins in a large number of the algae, while neurotoxins were not found. Acute hepatotoxicity in vitro was scored by measurement of leakage of the enzyme lactate dehydrogenase (LDH) from damaged cells and of morphological changes of the cells. The correlation coefficients between mouse toxicity and LDH, mouse toxicity and morphological cell damage, and between LDH and morphological cell damage were 0.812, 0.735, and 0.882, respectively. Consequently, the rat hepatocyte toxicity test seems to be well suited for screening blooms of blue-green algae for the presence of hepatotoxins.

Nitropyrene-induced DNA repair in Clara cells and alveolar type-II cells isolated from rabbit lung

DNA excision repair, as measured by unscheduled DNA synthesis (UDS), was examined in different cell types of rabbit lung exposed to nitropolycyclic aromatic hydrocarbons (NO-PAH) in vitro. Dose-related increases in UDS were observed. 1,6-Dinitropyrene (1,6-DNP) and 1,8-dinitropyrene (1,8-DNP) induced UDS more effectively in alveolar type-II cells compared with Clara cells. On the other hand, 1-nitropyrene (1-NP) caused a weak UDS response in Clara cells but no DNA repair in alveolar type-II cells.

Use of freshly prepared rat hepatocytes to study toxicity of blooms of the blue-green algae Microcystis aeruginosa and Oscillatoria agardhii

Extracts from blue-green algal blooms (Microcystis aeruginosa and Oscillatoria agardhii) from different lakes in southeastern Norway were tested for toxicity toward freshly prepared rat hepatocytes. The toxicity effects were scored by means of morphological studies of the cells and by measuring leakage of the enzyme lactate dehydrogenase (LDH) from the cells. The results with the hepatocytes correspond well with results from the traditional mouse bioassay, concerning both ability to distinguish between toxic and nontoxic samples and estimation of relative toxicity. Morphological changes due to toxic effects on the plasma membrane appeared earlier than leakage of enzyme from damaged cells. The results indicate that the hepatocyte-toxicity assay system might be well suited for screening purposes concerning water contamination by blue-green algae.

Culture of rabbit pulmonary Clara cells

Rabbit pulmonary Clara cells isolated by centrifugal elutriation have been cultured for several weeks. Clara cells generally adhered poorly to plastic but the cells did attach to coated substrates. A selected medium supported serial subculture of Clara cells for 4-5 passages (1:2 split). The medium consisted of a basal nutrient medium, alpha MEM, supplemented with insulin, transferrin, epidermal growth factor, D-glucose, biotin, alpha-tocopherol, pituitary extract, trace elements and 2% Sephadex G-10-filtered FBS. Freshly prepared Clara cells showed high capacity to activate 2-aminofluorene (AF) to mutagenic products. However, after 6 weeks of culture the mutagenic activation of AF was reduced by 92.5% indicating loss of cytochrome P-450.

Mutagenic activation of IQ and Me-IQ by liver and lung microsomes from rabbit and mouse, and with isolated lung cells from the rabbit

The heterocyclic amines 2-amino-3-methylimidazo-(4,5-f)-quinoline (IQ) and 2-amino-3,4-dimethylimidazo(4,5-f)-quinoline (Me-IQ) which are formed during broiling (grilling) and cooking of protein-rich food, have previously been shown to be both carcinogenic and mutagenic. In this work IQ and Me-IQ were found to be several hundred-fold more mutagenic in liver than in lung microsomal preparations from uninduced mice and rabbits. IQ has already been found to induce tumors at about the same frequency in liver and lung in mice. Obviously, the discrepancy between the data on carcinogenicity in vivo and mutagenicity in vitro with microsomal preparations from the two organs might in part be due to the lack of detoxification mechanisms in the latter system. Freshly isolated lung cells will better mimic the in vivo situation. With the metabolically active Clara cells, IQ was much more mutagenic than Me-IQ. It has previously been shown that the Clara cells have low capacity for DNA repair. It is tempting to speculate whether the situation in the mouse is in correspondence with that described in the rabbit, in which case the cell data fits well with the in vivo carcinogenesis data.

Deacetylation to 2-aminofluorene as a major initial reaction in the microsomal metabolism of 2-acetylaminofluorene to mutagenic products in preparations from rabbit lung and liver

The rabbit pulmonary and hepatic microsomal pathways for the metabolism of 2-acetylaminofluorene (AAF) and 2-aminofluorene (AF) to mutagenic products were investigated by means of high performance liquid chromatography and the Salmonella mutagenicity assay. Mutagenic activity approached a maximum with increasing concentrations of AAF incubated with hepatic microsomal preparations and Salmonella; with pulmonary microsomal preparations, mutagenic activity was proportional to the concentration of AAF over the range examined. The mutagenic activities of AF exhibited typical saturation kinetics with both hepatic and pulmonary microsomal preparations. Approximately 7 times more AF than N-hydroxy-2-acetylaminofluorene (N-hydroxy-AAF) was formed in incubations of AAF (0.5 mM) with hepatic microsomal preparations. When AAF was incubated with pulmonary microsomal preparations, formation of AF, but not N-hydroxy-AAF, was detected. The inclusion of paraoxon in the pulmonary incubations blocked the formation of AF but did not lead to the recovery of any N-hydroxy-AAF. We conclude that the metabolism of AAF to mutagenic products in pulmonary microsomal preparations from rabbits is initiated primarily, if not entirely, by deacetylation of AAF to AF. The mutagenic activity of AAF with the pulmonary microsomal preparations is limited by the deacetylase activity which, like mutagenic activity, exhibits a linear relationship with the concentration of AAF. On the basis of the rates of formation of AF and N-hydroxy-AAF and their mutagenic activities, we estimate that about 60% of the hepatic metabolism of AAF to mutagenic products is dependent upon deacetylation of AAF and subsequent oxidation of the AF formed.

Metabolism of 2-acetylaminofluorene by Clara cells, type II cells and alveolar macrophages isolated from rabbit lung, and use of a new chamber incubation mutagenicity test system

Clara cells, alveolar type II cells and pulmonary alveolar macrophages (PAM) were isolated in high yield from rabbit lung. The purity of the cell fractions was 80-90%, 98% and above 99%, respectively. Cytochrome P-450 total content was determined in microsomes from freshly prepared cells. The Clara cells contained significantly more cytochrome P-450 than was found in whole lung microsomes. Furthermore, the cytochrome content of the Clara cells was 2-fold higher than in the type II cells and 4-fold higher than in the macrophages. 2-aminofluorene (AF) was the major metabolite in all preparations when intact cells were incubated with 2-acetylaminofluorene (AAF). The PAMs produced AF in the highest rates, while the Clara cells showed the largest rates of cytochrome P-450-dependent, ring hydroxylation of AAF. Mutagenic activation of AAF by isolated lung cells was assayed with a chamber-incubation method. The Clara cells were far more active than the type II cells in this respect, while the macrophages were inactive.

Metabolism and mutagenicity of aromatic amines by human fetal liver

Human fetal liver microsomes were found to metabolize the carcinogen 2-acetylaminoflurene (AAF), the major metabolite being the deacetylated product 2-aminofluorene (AF). On the other hand, N-hydroxy-2-acetylaminofluorene (N-OH-AAF), a proximate carcinogenic metabolite, could not be detected. The human fetal liver samples converted AF and N-OH-AAF, but not AAF, to products mutagenic for S. typhimurium TA 98.

Effects of harman and norharman on the metabolism and genotoxicity of 2-acetylaminofluorene in cultured rat hepatocytes

Monolayers of rat hepatocytes metabolize 0.25 mM 2-acetylaminofluorene (AAF) to various ether-extractable, water-soluble as well as covalently bound products. The major ether-extractable metabolite formed is 2-aminofluorene (AF), followed by 7-OH-AAF and 9-OH-AAF. Pretreatment of rats with the inducer Aroclor 1254 (PCB) increased the metabolism of AAF and caused an increased DNA repair synthesis in hepatocytes exposed to AAF or AF. With N-OH-AAF, a decreased genotoxic response in PCB-treated cells compared to control cells was seen. The addition of harman and norharman decreased the metabolism of AAF to ether-extractable metabolites, water-soluble metabolites and metabolites covalently bound to macromolecules. In contrast, the DNA-repair synthesis caused by the same concentrations of AAF was increased by harman. One explanation for this apparent discrepancy could be that the aromatic amines changed the metabolism of harman and norharman in such a way that these compounds were converted into genotoxic metabolites.

Differential capacities for DNA repair in Clara cells, alveolar type II cells and macrophages of rabbit lung

The ability to repair damaged DNA was determined in different cell populations of rabbit lung cells isolated by centrifugal elutriation. DNA excision repair, measured as unscheduled DNA synthesis, was examined in in vitro confluent primary cultures. A dose dependent level of DNA excision repair was observed in alveolar type II cells after exposure to the direct acting alkylating agents N-methyl-N'-nitro-N-nitrosoguanidine, N-ethyl-N-nitrosourea and methyl methansesulphonate. Furthermore, O6-alkylguanine-DNA alkyltransferase activity was easily detectable in alveolar type II cells and alveolar macrophages. In contrast, non-ciliated (Clara) cells had 4 to 20-fold lower levels of DNA excision repair and non-detectable levels of O6-alkylguanine-DNA alkyltransferase. Uracil-DNA glycosylase activities in Clara cells and alveolar type II cells were in the same range and had 3-fold lower activity than alveolar macrophages. Our findings indicate that various lung cells differ in DNA repair capacity and may thus differ in sensitivity to some carcinogens.

Studies on mutagenic and carcinogenic N-substituted aryl compounds: cosmetics and drugs

We aimed our studies toward gaining an understanding of some of the reactions and pathways involved in the metabolism and activation of the aromatic diamines used in hair dyes and of phenacetin used in analgesic mixtures. Comparison of the data obtained from human and animal tissues established that animal tissues can serve as suitable models for evaluation of the activity of these compounds in humans.

Genetic differences in dimethylnitrosamine mutagenicity in vitro associated with mouse hepatic aryl hydrocarbon hydroxylase activity induced by 3-methylcholanthrene

The effects of 3-methylcholanthrene (MC) pretreatment on metabolism and mutagenic activation of dimethylnitrosamine (DMN) were studied with liver subfractions from two strains of mice differing genetically with respect to aromatic hydrocarbon responsiveness. Both mutagenic activation and DMN N-demethylase activity segregated with aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity as a dominant trait in appropriate crosses between C57BL/6J (Ahb Ahb) and DBA/2J (Ahd Ahd) mice. DMN metabolism and mutagenicity were increased by MC-pretreatment in responsive Ahb Ahb and Ahb Ahd mice, but not in non-responsive Ahd Ahd mice. This indicates the involvement of the Ah locus in the genetic regulation of these activities in mice. Deuteration of DMN reduced mutagenicity and DMN N-demethylase activity by approximately 90 and 50 percent, respectively.

Developmental pattern of 3-methylcholanthrene-inducible mutagenic activation of N-2-fluorenylacetamide, 2-fluorenamine, and 2,4-diaminoanisole in the rabbit

The effects of 3-methylcholanthrene (MCA) on mutagenic activation of the carcinogenic arylamines N-2-fluorenylacetamide (FAA), 2-fluorenamine (FA), and 2,4-diaminoanisole (2,4-DAA) by liver homogenates were studied postnatally in Dutch rabbits. These effects were compared with the developmental profiles of cytochrome P448 and aryl hydrocarbon hydroxylase (AHH) activity. Mutagenic activation of FA and 2,4-DAA was increased by MCA as early as 2 days after birth, whereas induction of FAA mutagenicity appeared 6 days after birth. Thereafter, induction of all three arylamines closely paralleled induction of cytochrome P448, which was maintained into adulthood. In contrast, induction of AHH activity by MCA was highest at 2 days of age and decreased to control levels 20 days after birth.

Mutagenicity and irreversible binding of the hepatocarcinogen, 2,4-diaminotoluene

Mutagenicity of 2,4-diaminotoluene (DAT) in the Salmonella mutagenicity assay was increased with liver fractions from phenobarbital (PB) or beta-naphthoflavone (BNF) treated rats. Substitutions of the hydrogens in the methyl group of 2,4-DAT with deuterium resulted in a decrease in mutagenicity. Incubation of rat liver microsomes with tritiated 2,4-DAT in the presence of NADPH led to the formation of irreversibly bound products to microsomal protein. The rates of binding were not increased using microsomes from PB or BNF-treated rats and was not altered by deuterium substitution in the methyl group. Addition of superoxide dismutase, glutathione (GSH) or rat liver supernatant reduced 2,4-DAT irreversible binding, whereas 2,4-DAT mutagenicity was unaffected by superoxide dismutase addition. Injection of tritiated 2,4-DAT 100 mg/kg to rats lead to its irreversible binding to liver protein and ribosomal RNA and to kidney protein in vivo, again protein binding was not increased after prior treatment with PB or BNF. No irreversible interaction of tritiated 2,4-DAT with DNA either in vitro or in vivo could be demonstrated.

Covalent binding of 2,4-diaminoanisole and 2,4-diaminotoluene in vivo

We have studied the activation of 2,4-diaminoanisole (2,4-DAA), a mutagenic hair-dye component, and 2,4-diaminotoluene (2,4-DAT), a hepatocarcinogen, to products which blind covalently to tissue macromolecules. Four hours after a dose of 100 mg/kg ring-labeled 3H-2,4-DAA, 0.30 nmol is found covalently bound per mg liver protein. This amount is increased by 83% after phenobarbital pretreatment, and by 43% after beta-naphthoflavone-pretreatment. Almost the same degree of binding is seen in kidneys. Subcellular fractionation of livers shows that most of the bound material is in the microsomal fraction. Similar levels of covalent protein binding is seen after administering ring-labeled 3H-2,4-DAT. No significant binding to DNA in vitro or in vivo could be demonstrated using 3H-2,4-DAA or 3H-2,4-DAT, whereas 3H-2,4-DAT is found to covalently bind to hepatic RNA.