6-AZACYTIDINE - COMPOUND WITH WIDE SPECTRUM OF ANTIVIRAL ACTIVITY

6-azacytidine demonstrates activity against adenoviruses types 1, 2, 5. It inhibit synthesis of viral DNA and proteins. 6-AC shows antiherpetic and antiinfluenza action during experimental infection in mice. 6-AC is prospective for drug development as an antiviral substance with a wide spectrum of activity.     

Cellular release of [18F]2-fluoro-2-deoxyglucose as a function of the glucose-6-phosphatase enzyme system

[(18)F]-2-Fluoro-2-deoxyglucose (FDG) is a glucose analog currently utilized for positron emission tomography imaging studies in humans. FDG taken up by the liver is rapidly released. This property is attributed to elevated glucose-6-phosphatase (Glc-6-Pase) activity. To characterize this issue we studied the relationship between Glc-6-Pase activity and FDG release kinetics in a cell culture system. We overexpressed the Glc-6-Pase catalytic unit in a Glc-6-Pase-deficient mouse hepatocyte (Ho-15) and in A431 tumor cell lines. Glc-6-Pase enzyme activity and FDG release rates were determined in cells transfected with the Glc-6-Pase gene (Ho-15-D3 and A431-AC3), in mock-transfected cells of both cell lines, and in wild-type mouse hepatocytes (WT10) as control. Although the highest level of Glc-6-Pase activity was measured in A431-AC3, Ho-15-D3 cells showed much faster FDG release rates. The faster FDG release correlated with the level of glucose 6-phosphate transporter (Glc-6-PT) mRNA, which was found to be expressed at higher levels in Ho-15 compared with A431 cells. Overexpression of Glc-6-PT in A431-AC3 produced a dramatic increase in FDG release compared with control cells. This study gives the first direct evidence that activity of the Glc-6-Pase complex can be quantified in vivo by measuring FDG release. Adequate levels of Glc-6-Pase catalytic unit and Glc-6-PT are required for this function. FDG-positron emission tomography may be utilized to evaluate functional status of the Glc-6-Pase complex.     

Metabolism of 6-nitrochrysene by intestinal microflora.

Since bacterial nitroreduction may play a critical role in the activation of nitropolycyclic aromatic hydrocarbons, we have used batch and semicontinuous culture systems to determine the ability of intestinal microflora to metabolize the carcinogen 6-nitrochrysene (6-NC). 6-NC was metabolized by the intestinal microflora present in the semicontinuous culture system to 6-aminochrysene (6-AC), N-formyl-6-aminochrysene (6-FAC), and 6-nitrosochrysene (6-NOC). These metabolites were isolated and identified by high-performance liquid chromatography, mass spectrometry, and UV-visible spectrophotometry and compared with authentic compounds. Almost all of the 6-NC was metabolized after 10 days. Nitroreduction of 6-NC to 6-AC was rapid; the 6-AC concentration reached a maximum at 48 h. The ratio of the formation of 6-AC to 6-FAC to 6-NOC at 48 h was 93.4:6.3:0.3. Interestingly, compared with results in the semicontinuous culture system, the only metabolite detected in the batch studies was 6-AC. The rate of nitroreduction differed among human, rat, and mouse intestinal microflora, with human intestinal microflora metabolizing 6-NC to the greatest extent. Since 6-AC has been shown to be carcinogenic in mice and since nitroso derivatives of other nitropolycyclic aromatic hydrocarbons are biologically active, our results suggest that the intestinal microflora has the enzymatic capacity to generate genotoxic compounds and may play an important role in the carcinogenicity of 6-NC.     

Metabolism of 6-nitrochrysene by intestinal microflora

Since bacterial nitroreduction may play a critical role in the activation of nitropolycyclic aromatic hydrocarbons, we have used batch and semicontinuous culture systems to determine the ability of intestinal microflora to metabolize the carcinogen 6-nitrochrysene (6-NC). 6-NC was metabolized by the intestinal microflora present in the semicontinuous culture system to 6-aminochrysene (6-AC), N-formyl-6-aminochrysene (6-FAC), and 6-nitrosochrysene (6-NOC). These metabolites were isolated and identified by high-performance liquid chromatography, mass spectrometry, and UV-visible spectrophotometry and compared with authentic compounds. Almost all of the 6-NC was metabolized after 10 days. Nitroreduction of 6-NC to 6-AC was rapid; the 6-AC concentration reached a maximum at 48 h. The ratio of the formation of 6-AC to 6-FAC to 6-NOC at 48 h was 93.4:6.3:0.3. Interestingly, compared with results in the semicontinuous culture system, the only metabolite detected in the batch studies was 6-AC. The rate of nitroreduction differed among human, rat, and mouse intestinal microflora, with human intestinal microflora metabolizing 6-NC to the greatest extent. Since 6-AC has been shown to be carcinogenic in mice and since nitroso derivatives of other nitropolycyclic aromatic hydrocarbons are biologically active, our results suggest that the intestinal microflora has the enzymatic capacity to generate genotoxic compounds and may play an important role in the carcinogenicity of 6-NC.     

Determination of 4-amino-m-cresol and 5-amino-o-cresol by high performance liquid chromatography and fluorescence derivatization using fluorescamine

For the determination of two oxidation hair dyes, 4-amino-m-cresol (4-AC) and 5-amino-o-cresol (5-AC), a sensitive isocratic high performance liquid chromatography (HPLC) method using the reversed phase mode was developed. The hair dyes were pre-column derivatized with fluorescamine prior to injection. Sensitivity could be improved 10-fold for 4-AC and 50-fold for 5-AC by fluorescence detection compared to UV detection. The limit of detection was 1 ng/injection for 4-AC and 100 pg/injection for 5-AC, respectively. For the determination of both compounds in aqueous biological matrices in order to simulate conditions for penetration studies with pig skin, a solid phase extraction procedure using C18 cartridges and acetonitrile (ACN) for elution could be developed. Average recovery was 83.4% with a coefficient of variation (CV) of 2.64% for intra-day assay and 3.20% for inter-day assay for 5-AC and 2.89% and 3.41% for 4-AC, respectively.     

The production of D-acetoin by a transgenic Escherichia coli

A 6 kbp SphI fragment encoding genes for the enzymes α-acetolactate synthase (ALS), α-acetolactate decarboxylase (ALDC) and meso -2,3-butanediol dehydrogenase ( meso -BDH), involved in the formation of meso -2,3-butanediol ( meso -BD) from pyruvic acid, was cloned into plasmid pUC118. When derivatives of this plasmid were introduced into Escherichia coli JM109, the transformants were able to produce D -acetoin ( D -AC) without contamination with L -acetoin ( L -AC).     

5-azacytidine induces micronuclei in and morphological transformation of Syrian hamster embryo fibroblasts in the absence of unscheduled DNA synthesis.

It is known that 5-azacytidine (5-AC) induces tumors in several organs of rats and mice. The mechanisms of these effects are still poorly understood although it is known that 5-AC can be incorporated into DNA. Furthermore, it can inhibit DNA methylation. The known data on its clastogenic and/or gene mutation-inducing potential are still controversial. Therefore, we have investigated the kinds of genotoxic effects caused by 5-AC in Syrian hamster embryo (SHE) fibroblasts. Three different endpoints (micronucleus formation, unscheduled DNA synthesis (UDS) and cell transformation) were assayed under similar conditions of metabolism and dose at target in this cell system. 5-AC induces morphological transformation of SHE cells, but not UDS. Therefore, 5-AC does not seem to cause repairable DNA lesions. Furthermore, our studies revealed that 5-AC is a potent inducer of micronuclei in the SHE system. Immunocytochemical analysis revealed that a certain percentage of these contain kinetochores indicating that 5-AC may induce both clastogenic events and numerical chromosome changes.     

Histological study of cell death in digital malformations induced by 5-azacytidine: suppressive effect of caffeine

The present study investigated microscopically the process of 5-azacytidine (5-AC)-induced digital teratogenesis and caffeine's suppressive effect on this process. Three distinct zones of programmed cell death were observed in control and caffeine-treated embryos 3 hours after 5-AC injection: the preaxial and postaxial ectodermal regions and the central part of the mesodermal regions. 5-AC temporarily suppressed programmed cell death in the ectoderm and mesoderm 3 hours after it was injected. However, caffeine promoted programmed cell death; normal programmed cell death was observed in the limb buds of embryos whose dams were treated with 5-AC and caffeine. The percentage of total cell death in hindlimb buds of embryos treated with 5-AC and caffeine was higher than that from embryos treated with 5-AC, whereas 5-AC-induced digital malformations were reduced by post-treatment with caffeine. Cell death reached a maximum 12 hours after the injection in limb buds from 5-AC and caffeine-treated embryos and at 24 hours in the 5-AC treated embryos. Furthermore, in the 5-AC and caffeine-treated embryos, the frequency of cell deaths at 12 hours increased almost linearly with the doses of caffeine in parallel with the reduction of 5-AC-induced malformation frequency by caffeine. These results suggest that although induced cell death may be one of the factors leading to digital malformations produced by 5-AC, it is not essential, and the existence of other factors affecting the pattern formation of the limb bud is proposed.     

Anthracene-9-carboxylic acid inhibits an apical membrane,chloride conductance in canine tracheal epithelium

Summary Canine tracheal epithelium secretes Cl from the submucosal to the mucosal surface via an electrogenic transport process that appears to apply to a wide variety of secretory epithelia. Cl exit across the apical membrane is thought to be a passive, electrically conductive process. To examine the cellular mechanism of Cl secretion we studied the effect of anthracene-9-carboxylic acid (9-AC), an agent known to inhibit the Cl conductance of muscle membrane. When added to the mucosal solution, 9-AC rapidly and reversibly decreases short-circuit current and transepithelial conductance, reflecting a reduction in electrogenic Cl secretion. The inhibition is concentration-dependent and 9-AC does not appear to compete with Cl for the transport process. The decrease in current and conductance results from a decrease in the net and both unidirectional transepithelial Cl fluxes without substantial alterations of Na fluxes. Furthermore, 9-AC specifically inhibits a Cl conductance: tissues bathed in Cl-free solutions showed no response to 9-AC. Likewise, when the rate of secretion and Cl conductance were minimized with indomethacin, addition of 9-AC did not alter transepithelial conductance. In contrast, neither removal of Na from the media nor blockade of the apical Na conductance with amiloride prevented a 9-AC-induced decrease in transepithelial conductance. We also found that the effect of 9-AC is independent of transepithelial transport: 9-AC decreases transepithelial conductance despite inhibition of Cl secretion with ouabain or furosemide. Intracellular electrophysiologic techniques were used to localize the effect of 9-AC to a reduction of the electrical conductance of the apical cell membrane: 9-AC hyperpolarizes the electrical potential difference across the apical membrane and decreases its relative conductance. 9-AC also prevents the characteristic changes in the cellular electrical potential profile, transepithelial conductance, and the ratio of membrane conductances produced by a reduction in mucosal bathing solution Cl concentration. These results indicate that 9-AC inhibits Cl secretion in tracheal epithelium by blocking an electrically conductive Cl exit step in the apical cell membrane. Thus, they support a cellular model of Cl secretion in which Cl leaves the cell across a Cl permeable apical membrane driven by its electrochemical gradient.     

Determination of 4-amino-m-cresol and 5-amino-o-cresol and metabolites in human keratinocytes (HaCaT) by high-performance liquid chromatography with DAD and MS detection

A multi-step gradient HPLC system combined with DAD and MS detection has been developed for the determination of the oxidation hair dyes 4-amino-m-cresol (4-AC) and 5-amino-o-cresol (5-AC) and their metabolites in the alternative testing system human keratinocytes (HaCaT) cell culture. The culture medium induced by 3-methylcholanthrene (3-MC) was fortified with 4-AC or 5-AC and incubated for 24 h at 37 degrees C in order to produce metabolites. After several pre-cleaning steps, further cleaning was done by solid-phase extraction using C18 phenyl cartridges. Optimizing chromatographic conditions, a hybrid-based RP8 column was most suitable for the separation of the metabolites formed in HaCaT. Only one conjugation product, the N-acetylated derivative, could be identified for both 4-AC and 5-AC by LC/DAD/MS. The ionisation technique used for MS analysis was Atmospheric Pressure Ionization (API).     

Involvement of the TREK-1 channel in human alveolar cell membrane potential and its regulation by inhibitors of the chloride current

K⁺ channels of the alveolar epithelium control the driving force acting on the ionic and solvent flow through the cell membrane contributing to the maintenance of cell volume and the constitution of epithelial lining fluid. In the present work, we analyze the effect of the Cl⁻ channel inhibitors: (4-[(2-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-inden-5-yl)oxy] butanoic acid (DCPIB) and 9-anthracenecarboxylic acid (9-AC) on the total current in a type II pneumocytes (A549 cell line) model by patch clamp, immunocytochemical, and gene knockdown techniques. We noted that DCPIB and 9-AC promote the activation of K conductance. In fact, they significantly increase the intensity of the current and shift its reversal potential to values more negative than the control. By silencing outward rectifier channel in its anoctamin 6 portion, we excluded a direct involvement of Cl⁻ ions in modulation of I_K and, by means of functional tests with its specific inhibitor spadin, we identified the TREK-1 channel as the presumable target of both drugs. As the activity of TREK-1 has a key role for the correct functioning of the alveolar epithelium, the identification of DCPIB and 9-AC molecules as its activators suggests their possible use to build new pharmacological tools for the modulation of this channel.     

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

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

Establishment of glutamine synthetase of Mycobacterium smegmatis as a protein acetyltransferase utilizing polyphenolic acetates as the acetyl group donors

Acetoxy Drug: Protein Transacetylase (TAase) mediating the transfer of acetyl group(s) from polyphenolic acetates (PA) to certain functional proteins in mammalian cells was identified by our earlier investigations. TAase activity was characterized in the cell lysates of Mycobacterium smegmatis and the purified protein was found to have M(r) 58,000. TAase catalysed protein acetylation by a model acetoxy drug 7,8-diacetoxy-4-methylcoumarin (DAMC) was established by the demonstration of immunoreactivity of the acetylated target protein with an anti-acetyllysine antibody. The specificity of the TAase of M. smegmatis (MTAase) to various acetoxycoumarins was found to be in the order DAMC > 7-AMC > 6-AMC > 4-AC > 3-AC > ABP. Also, the N-terminal sequence of purified MTAase was found to perfectly match with glutamine synthetase (GS) of M. smegmatis. The identity of MTAase with GS was confirmed by the observation that the purified MTAase as well as the purified recombinant GS exhibited all the properties of GS. The finding that purified Escherichia coli GS was found to have substantial TAase activity highlighted the TAase function of GS in other bacteria. These results conclusively established for the first time the protein acetyltransferase function of GS of M. smegmatis.     

5-Azacytidine inhibits aflatoxin biosynthesis in Aspergillus flavus

Aflatoxins, mainly produced by Aspergillus flavus and A. parasiticus, are a group of potent mycotoxins with carcinogenic, hepatotoxic, and immunosuppressive properties. Many studies have been devoted to investigating their biosynthesis mechanism since they were discovered half a century ago. 5-Azacytidine (5-AC), a derivative of the nucleoside cytidine and an inactivator of DNA methyltransferase, is widely used for studies in epigenetics and cancer biology, and has also been used for studying secondary metabolism in fungi. In this study, 5-AC was applied to investigate its effect on the development and aflatoxin biosynthesis of A. flavus. The results indicate that 5-AC inhibits the ability to produce aflatoxin and also causes a fluffy aconidial phenotype. Further studies revealed that 5-AC affects gene expression of A. flavus to a limited degree, and the unique homolog of DNA methyltransferase gene (DmtA) expressed constitutively during different developmental stages of A. flavus irrespective of 5-AC. This work may provide some basic data to elucidate the role of 5-AC in aflatoxin biosynthesis and the development of A. flavus.     

Inhibitory effect of caffeine on 5-azacytidine-induced digital malformations in the rat

The effect of caffeine on 5-azacytidine (5-AC)-induced digital malformations in rat fetuses was investigated. Caffeine suppressed all types of digital defects in the fore- and hindlimbs except for syndactyly induced by 1.0 mg/kg of 5-AC; it was still effective when administered 24 hours after 5-AC treatment. However, fetal mortality increased as the frequency of malformations decreased. While the malformation results support the view that caffeine inhibits the processes leading to malformation expression, the relation between its suppressive effect on malformations and its enhancing effect on fetal mortality is unclear.     

Developmental characterization and chromosomal mapping of the 5-azacytidine-sensitive fluF locus of Aspergillus nidulans.

In Aspergillus nidulans, a fungus that possesses negligible, if any, levels of methylation in its genome, low concentrations of 5-azacytidine (5-AC) convert a high percentage of the cell population to fluffy phenotypic variants through a heritable modification of a single nuclear gene (M. Tamame, F. Antequera, J. R. Villanueva, and T. Santos, Mol. Cell. Biol. 3:2287-2297, 1983). This new 5-AC-altered locus, designated here fluF1, was mapped as the closest marker to the centromere that has been identified so far on the right arm of chromosome VIII. Of all mutagens tested, only 5-AC induced the fluffy phenotype with a significant frequency. Furthermore, we determined that the wild-type, dominant allele of the fluF gene was primarily accessible to modification by 5-AC at the initial stages of fungal vegetative growth. These results indicated that 5-AC does not act through random mutagenic action but, rather, that fluF constitutes a specific target for this drug during a well-defined period of fungal development. Alteration of fluF by 5-AC resulted in a dramatic modification of the developmental program of A. nidulans. The resulting fluffy clones were characterized by massive, uncontrolled proliferation of undifferentiated hyphae, a drastic delay in the onset of asexual differentiation (conidiation), and colonies with an invasive nature. These features are reminiscent of the malignant properties of tumor cells. We propose that the locus fluF plays a primary role in the control of cell proliferation in A. nidulans and that its alteration by 5-AC produces pleiotropic modifications of the developmental program of this fungus.     

On the inhibition of muscle membrane chloride conductance by aromatic carboxylic acids

25 aromatic carboxylic acids which are analogs of benzoic acid were tested in the rat diaphragm preparation for effects on chloride conductance (G(Cl)). Of the 25, 19 were shown to reduce membrane G(Cl) with little effect on other membrane parameters, although their apparent K(i) varied widely. This inhibition was reversible if exposure times were not prolonged. The most effective analog studied was anthracene-9-COOH (9-AC; K(i) = 1.1 x 10(-5) M). Active analogs produced concentration-dependent inhibition of a type consistent with interaction at a single site or group of sites having similar binding affinities, although a correlation could also be shown between lipophilicity and K(i). Structure-activity analysis indicated that hydrophobic ring substitution usually increased inhibitory activity while para polar substitutions reduced effectiveness.

These compounds do not appear to inhibit G(Cl) by altering membrane surface charge and the inhibition produced is not voltage dependent. Qualitative characteristics of the I-V relationship for Cl(-) current are not altered. Conductance to all anions is not uniformly altered by these acids as would be expected from steric occlusion of a common channel. Concentrations of 9-AC reducing G(Cl) by more than 90 percent resulted in slight augmentation of G(I). The complete conductance sequence obtained at high levels of 9-AC was the reverse of that obtained under control conditions. Permeability sequences underwent progressive changes with increasing 9-AC concentration and ultimately inverted at high levels of the analog. Aromatic carboxylic acids appear to inhibit G(Cl) by binding to a specific intramembrane site and altering the selectivity sequence of the membrane anion channel.

     

Production of (2S,3S)-2,3-butanediol and (3S)-acetoin from glucose using resting cells of Klebsiella pneumonia and Bacillus subtilis

Production of highly pure (2S,3S)-2,3-butanediol ((2S,3S)-2,3-BD) and (3S)-acetoin ((3S)-AC) in high concentrations is desirable but difficult to achieve. In the present study, glucose was first transformed to a mixture of (2S,3S)-2,3-BD and meso-2,3-BD by resting cells of Klebsiella pneumoniae CICC 10011, followed by biocatalytic resolution of the mixture by resting cells of Bacillus subtilis 168. meso-2,3-BD was transformed to (3S)-AC, leaving (2S,3S)-2,3-BD in the reaction medium. Using this approach, 12.5 g l(-1) (2S,3S)-2,3-BD and 56.7 g l(-1) (3S)-AC were produced. Stereoisomeric purity of (2S,3S)-2,3-BD and enantiomeric excess of (3S)-AC was 96.9 and 96.2%, respectively.     

5-氮杂胞苷对桦褐孔菌多酚积累的影响

本文旨在研究DNA甲基转移酶抑制剂5-氮杂胞苷对桦褐孔菌多酚合成的调控。以液体摇瓶法培养桦褐孔菌,并在培养液中添加5-氮杂胞苷。采用荧光定量PCR测定与多酚合成相关的编码苯丙氨酸解氨酶（pal）、4-香豆酸辅酶A连接酶（4cl）和硬毛素合成酶（sps）基因表达水平,染色质免疫沉淀技术对编码硬毛素合成酶基因启动子区的组蛋白甲基化修饰进行检测,Folin-Ciocalteu法测定桦褐孔菌细胞内和发酵液中多酚的含量。结果显示,5-氮杂胞苷的添加提高了桦褐孔菌体内pal、4cl和sps基因的表达水平,改变了sps启动子区的组蛋白甲基化修饰,即降低了H3K9三甲基化修饰水平,提高了H3K4和H3K36三甲基化修饰水平,显著提高了桦褐孔菌细胞内和发酵液中多酚的积累量。5-氮杂胞苷诱导下桦褐孔菌细胞内多酚积累量达(46.6±2.8)mg/g,明显高于对照组多酚积累量(28.7±1.0)mg/g,并且胞外多酚的含量由对照组的(66.9±1.3)mg/L提高至(92.3±2.3)mg/L。此外,经5-氮杂胞苷处理后胞内多酚清除DPPH自由基、超氧阴离子和羟自由基的能力显著提高。可见,5-氮杂胞苷可以作为调节因子激发桦褐孔菌液体培养条件下多酚的合成,可以成为进一步提高桦褐孔菌液体发酵产物中多酚产量的技术手段之一。     

Determination of 9-nitrocamptothecin by precolumn derivatization and its metabolite 9-aminocamptothecin in a biological fluid using reversed-phase high-performance liquid chromatography with fluorescence detection

A novel insoluble topoisomerase I inhibitor, 9-nitrocamptothecin (9-NC), is in advanced stages of clinical development and has been used to treat a diverse array of tumor types, including breast, ovarian, pancreatic and haematological malignancies. We have established a sensitive high-performance liquid chromatography method using fluorescence detection for the quantitation of 9-NC. Non-fluorescent 9-NC is converted to fluorescent 9-aminocamptothecin (9-AC) via a one-step pre-column derivative reaction. The quantitative limit of 9-NC was 1 ng/ml and the method was reproducible with the respective intra- and inter-day variability falling below 5.0 and 9.0%. The determination of both 9-NC and its metabolite 9-AC in dog plasma was also achieved using the same chromatographic and detection conditions. In dog plasma, the quantitative limits of 9-AC and 9-NC were 0.25 and 1 ng/ml, respectively. The presence of 9-AC in the samples yielded no interference with the determination of 9-NC. However, individual matrices can affect the conversion efficiency of 9-NC, thus indicating that standard samples should be run for each matrix.