6，7-双乙酰化黄芩素在大鼠体内的代谢产物研究

研究6，7-双乙酰化黄芩素在大鼠体内的代谢产物。大鼠灌胃给予6，7-X2K,酰化黄芩素后，采用HPLC—DAD和LC／MS^n方法，检测大鼠肠内和血浆中的代谢产物。6,7-双乙酰化黄芩素在大鼠肠内降解为6-单乙酰黄芩素和黄芩素；在大鼠血浆中检测到4种葡萄糖醛酸苷类代谢产物，初步鉴定为6-O-葡萄糖醛酸黄芩素，6-O-甲基-7-O-葡萄糖醛酸黄芩素，6，7-O-双葡萄糖醛酸黄芩素和6-O-葡萄糖-7-O-葡萄糖醛酸黄芩素。首次报道了6，7-双乙酰化黄芩素在大鼠体内的药物代谢，在肠内和血浆中共鉴定了六个代谢产物。     

汉黄芩素在FVB小鼠体内的磺酸化代谢特征研究

目的探讨汉黄芩素Ⅱ相代谢中主要的磺酸化代谢反应特征。方法采用FVB小鼠肠灌流模型及FVB小鼠肝脏S9体外反应体系,通过采用高效液相色谱-质谱法(HPLC-MS/MS)和高效液相色谱-二极管阵列检测器(HPLC-DAD)测定汉黄芩素及其代谢产物,研究汉黄芩素主要的Ⅱ相代谢反应之一磺酸化代谢反应的特征。结果汉黄芩素在FVB小鼠小肠均发生葡萄糖醛酸化与磺酸化代谢反应,其中磺酸化代谢产物的排出速率为[(3.46±0.16)nmol/30 min/10 cm]。而汉黄芩素在结肠中只检测出磺酸化代谢产物,其排出速率为[(1.40±0.24)nmol/30 min/10 cm]。体外试验显示,汉黄芩素的磺酸化代谢符合双相酶代动力学特征,由两种磺酸化转移酶(Sult)亚型介导。结论汉黄芩素的磺酸化代谢反应是汉黄芩素肠道代谢的重要组成部分,其在肝脏的磺酸化代谢由两种Sult酶催化完成。     

黄芩素在人及不同种属肝微粒体中的UDP-glucuronosyltransferase代谢差异（摘要）

目的：研究黄芩素在不同种属肝微粒体中的UDP-葡萄糖醛酸转移酶（UDP-glucuronosyltransferase, UDPGA）代谢差异特性。方法使用肝微粒体体外代谢孵育法、HPLC-UV分析方法,选用不同种属的肝微粒体进行黄芩素UDPGA体外代谢研究。结果黄芩素在人肝微粒体及不同种属的肝微粒中,加入UDPGA进行37℃恒温孵育,孵育结束后离心,取上清液,经HPLC-UV分离检测得到3个代谢产物,分别是：黄芩素-7-O-β-葡萄糖醛酸结合物、黄芩素-6-O-β-葡萄糖醛酸结合物和黄芩素-6-O-葡萄糖醛酸结合物-7-O-β-葡萄糖醛酸结合物;通过与标准品对照确定黄芩素的三个代谢产物都是葡萄糖醛酸化的代谢产物。同时,不同种属间UGT代谢物的活性表现出较大差异,黄芩素-7-O-β-葡萄糖醛酸结合物在人肝微粒体中的代谢活性最强,Km=1.61,Vmax=0.77（BG在人肝微粒体中的代谢活性是SD雌鼠的25.2倍）;黄芩素-6-O-β-葡萄糖醛酸结合物在比格犬肝微粒体中代谢活性最强,Km=3.05,Vmax=3.51（雄性比格犬肝微粒体的活性是雄性恒河猴肝微粒体的2.6倍）;黄芩素-6-O-葡萄糖醛酸-7-O-β-葡萄糖醛酸结合物在猪肝微粒体中代谢活性最强,Km=5.38, Vmax=0.17（猪肝微粒体的活性是人肝微粒体的13.6倍）,其他依次是犬、恒河猴、鼠和人。结论黄芩素在人及不同种属肝微粒体UGT代谢中均生成上述三种葡萄糖醛酸化代谢产物,但是不同种属间的代谢表现出酶动力学的差异。     

自身酶解法测定黄芩药材中黄芩素和汉黄芩素的含量

目的 探讨一种黄芩药材中黄酮苷元类成分黄芩素和汉黄芩素定量测定方法.方法 通过黄芩自身所含的酶在适宜温度条件下将黄芩药材中的黄芩苷、汉黄芩苷等黄酮苷类成分酶解成黄芩素和汉黄芩素等黄酮苷元,再利用高效液相色谱法进行含量测定.结果 黄芩素酶解完全,色谱峰分离良好,且同一流动相下可同时测定黄芩素和汉黄芩素的含量.黄芩素的平均回收率为96.45%,RSD为1.34%(n=9);汉黄芩素的平均回收率为97.86%,RSD为1.89%(n=9).结论 所用测定方法简便、准确,为黄芩素和汉黄芩素的充分提取、分离提供了真实的基础含量数据.     

HPLC法同时测定黄芩中黄芩苷、黄芩素、汉黄芩素的含量

目的:建立反相高效液相色谱法同时测定黄芩中黄芩苷、黄芩素、汉黄芩素的含量.方法:采用Agilent Eclipse XDB-C18(250 mm×4.6 mm,5μm)色谱柱,以甲醇-乙腈-0.1％磷酸溶液为流动相,梯度洗脱;检测波长为277 nm;流速1.0 ml·min -1;进样量10 μl;柱温35℃.结果:黄芩苷、黄芩素、汉黄芩素的线性范围分别为0.059 ～ 1.175 μg,r=1.000 0(n =7)、0.010～0.204μg,r=1.000 0(n =7)和8.210×10-3～1.642×10-1 μg,r =1.000 0(n =7);提取回收率分别为99.08％,RSD=0.5％(n=6)、98.66％,RSD =0.5％ (n =6)和98.31％,RSD =0.7％ (n =6).结论:本法操作简便、快速、结果准确,可用于黄芩的质量控制.     

基于一测多评法定量的四季三黄片质量评价研究

目的 建立同时测定四季三黄片中黄芩苷、去甲汉黄芩素苷、千层纸素A-7-O-β-D葡萄糖醛酸苷、汉黄芩苷、黄芩素、汉黄芩素、千层纸素A等7种成分的一测多评法。方法 采用HPLC,岛津VP-ODS色谱柱(4.6 mm×250 mm,5μm),以乙腈-0.1%三氟乙酸溶液为流动相,梯度洗脱;流速1.0 mL·min^-1;柱温30℃;检测波长276 nm。以黄芩苷为内参物,建立去甲汉黄芩素苷、千层纸素A-7-O-β-D葡萄糖醛酸苷、汉黄芩苷、黄芩素、汉黄芩素和千层纸素A的相对校正因子,同时采用一测多评法和外标法测定四季三黄片中7个成分的含量,并将2种方法的测定结果进行比较。结果 7种成分在各自范围内线性关系良好(r>0.999 8),平均加样回收率97.0%～102.1%,RSD为1.2%～2.5%。共测定了4个企业29批四季三黄片中7种成分的含量,结果一测多评法与外标法测定结果无明显差异。不同企业样品间各成分含量存在明显差异。结论 建立的含量方法能够反映出投料用黄芩饮片的质量状况,进而全面有效地评价四季三黄片的质量,为其质量标准的提升奠定基础。     

HPLC法测定感冒止咳糖浆中黄芩苷、黄芩素和汉黄芩素的含量

目的：建立HPLC法测定感冒止咳糖浆中黄芩苷、黄芩素和汉黄芩素定量方法。方法：色谱柱：Hypersil ODS C18柱（250mm×4．6mm,5μm）,流动相：甲醇-0．1％磷酸溶液进行梯度洗脱,检测波长：275nm,流速：1．0ml·min^-1,柱温：30℃。结果：黄芩苷在1．54～12．32μg（r=0．9999）,黄芩素在0．10～0．80μg（r=0．9992）及汉黄芩素在0．16～1．28μg范围内均与其峰面积呈良好的线性关系（r=0．9992）;黄芩苷、黄芩素及汉黄芩素的平均回收率分别为99．4％（RSD0．4％）、98．2％（RSD1．2％）及98．8％（RSDI．0％）（n=6）。结论：方法简便,准确,重复性好,可用于感冒止咳糖浆中黄芩苷、黄芩素和汉黄芩素的含量测定。     

自身酶解水提取黄芩中黄芩素及汉黄芩素的方法

目的建立黄芩中黄芩素及汉黄芩素的绿色环保提取方法。方法在适宜温度下,采用自身酶解法,以水为提取溶剂,借助于苷元类、黄芩药材碎块和黄芩苷的粒度和溶解度之差,分离得到黄芩苷元总提物。结果总提物中黄芩总苷元含量在70％以上,其中黄芩素含量为63％以上,汉黄芩素含量为7％以上。结论所用方法简便、快捷、成本低,是一条绿色的无污染环保提取工艺。     

黄芩药材的高效液相色谱指纹图谱及黄芩苷、黄芩素、汉黄芩素含量的同时测定

目的: 建立黄芩药材的HPLC指纹图谱,并同时测定不同产地商品中黄芩苷、黄芩素和汉黄芩素的含量,全面评价黄芩药材质量。方法: 采用Aglient TC-C₁₈(4.6 mm×250 mm,5 μm)色谱柱。采用梯度洗脱,流速为1.0 ml·min^-1;检测波长280 nm;柱温30℃。指纹图谱共有模式的建立采用国家药典委员会"中药色谱指纹图谱相似度评价系统2004A版"进行处理分析。结果: 在指纹图谱研究中,标定了9个共有峰,建立了对照指纹图谱,10批药材与共有模式之间相似性良好,相似度均在0.9以上;在所建立的分析条件下,黄芩苷、黄芩素、汉黄芩素均达到了基线分离,且在线性范围内线性关系良好,3种成分的加样回收率分别为99.44%,99.71%和99.83%。结论: 本法灵敏、准确、简便,可用于黄芩药材的综合质量评价。     

HPLC法同时测定化痰平喘片中黄芩苷、黄芩素和汉黄芩素的含量

目的:建立同时测定化痰平喘片中黄芩苷、黄芩素和汉黄芩素含量的方法。方法:采用高效液相色谱法。色谱柱为Diamonsil C18,流动相为甲醇-0.1%磷酸(梯度洗脱),流速为1.0 ml/min,检测波长为277 nm,柱温为30℃,进样量为10μl。结果:黄芩苷、黄芩素、汉黄芩素检测进样量线性范围为0.069 04~0.690 4(r=0.999 4)、0.054 56~0.545 6(r=0.999 6)、0.030 36~0.303 6μg(r=0.999 1);精密度、稳定性、重复性试验的RSD<2%;加样回收率分别为97.64%~99.06%(RSD=0.57%,n=6)、98.31%~100.64%(RSD=0.85%,n=6)、97.53%~99.48%(RSD=0.76%,n=6)。结论:该方法操作简便、稳定、重复性好,可用于化痰平喘片中黄芩苷、黄芩素和汉黄芩素含量的同时测定。     

Confirmation of a carboxylic acid metabolite of polychlorotrifluoroethylene and a method for its GC-ECD analysis in biological matrices.

3.1 Oil, referred to as polychlorotrifluoroethylene (pCTFE), is a polymeric mixture consisting primarily of trimers and tetramers of chlorotrifluoroethylene (CTFE) end-capped with chlorine. Inhalation studies have associated dose-related body weight loss, increased organ weights, and abnormal hepatic enzyme activities with exposure to pCTFE. The carboxylic acid metabolites of pCTFE have been shown to cause hepatotoxicity in rats, which is manifested by increased liver weights and the proliferation of hepatic peroxisomes. A method was developed to derivatize these carboxylic acid metabolites. Tissue homogenates and feces were extracted with methanol, and urinary metabolites were extracted on octadecylsilane (ODS) solid-phase extraction columns. Aliquots of the extracts and whole blood were methylated with 3N methanolic HCl to transesterify the carboxylic acid metabolites to volatile methyl esters. The pCTFE methyl esters were analyzed by gas chromatography (GC) with electron capture detection (ECD). The on-column limit of detection was 5 pg for each methyl ester. Solid-phase extraction of spiked urine gave extraction efficiencies of 90.4% for the trimer acid and 84.7% for the tetramer acid. This method was successfully applied to toxicity studies in rats and nonhuman primates. The identities of the derivatized metabolites were confirmed by GC/MS.     

Determination of nonderivatized para-hydroxylated metabolites of diazepam in biological fluids with a GC Megabore column system.

A method was developed using gas chromatography (GC) and a Megabore column system capable of simultaneous detection of diazepam, N-desmethyldiazepam, temazepam, oxazepam, and their para-hydroxylated metabolites. This method does not require derivatization of para-hydroxylated metabolites. Standard curves for pure reference compounds were linear, with the minimum detectable concentration of diazepam and its metabolites as low as 0.13 ng/injection.     

Simultaneous detection and quantification of amphetamines, diazepam and its metabolites, cocaine and its metabolites, and opiates in hair by LC-ESI-MS-MS using a single extraction method

A liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous identification and quantification of amphetamines, diazepam and its metabolites, cocaine and its metabolites, and opiates from hair using a single extraction method. As part of the method development, Gemini C18, Synergi Hydro RP, and Zorbax Stablebond-Phenyl LC columns were tested with three different mobile phases. Analyte recovery and limit of detection were evaluated for two different solid-phase extraction methods that used Bond Elut Certify and Clean Screen cartridges. Phosphate buffer (pH 5.0) was chosen as the optimum hair incubation medium because of the high stability of cocaine and 6-monoacetylmorphine using this method and faster sample preparation. The optimized method was fully validated. Linearity was established over the concentration range 0.2-10 ng/mg hair, and the correlation coefficients were all greater than 0.99. Total extraction recoveries were greater than 76%, detection limits were between 0.02 and 0.09 ng/mg, and the intra- and interday imprecisions were generally less than 20% in spiked hair. The intra- and interbatch imprecision of the method for a pooled authentic hair sample ranged from 1.4 to 23.4% relative standard deviation (RSD) and 8.3 to 25.4% RSD, respectively, for representative analytes from the different drug groups. The percent matrix effect ranged from 63.5 to 135.6%, with most analytes demonstrating ion suppression. Sixteen postmortem samples collected from suspected drug-related deaths were analyzed for the 17 drugs of abuse and metabolites included in the method. The method was sufficiently sensitive and specific for the analysis of drugs and metabolites in postmortem hair samples. There is scope for the inclusion of other target drugs and metabolites in the method.     

Development of a column-switching LC-MS/MS method of tramadol and its metabolites in hair and application to a pharmacogenetic study

Hair is a valuable specimen for monitoring long-term drug use. Tramadol is an effective opioid analgesic but is associated with risks such as drug dependence and unexpected toxicity arising from genetic differences in metabolism. However, few studies have been performed on the distribution of tramadol and its metabolites in hair. In the present study, a column-switching LC-MS/MS method was developed and fully validated for the simultaneous determination of tramadol and its phase I and II metabolites in hair. Furthermore, the distribution of tramadol and its metabolites in hair was investigated in a pharmacogenetic study. Tramadol and its metabolites were extracted from hair using methanol and injected onto LC-MS/MS. The validation results of selectivity, matrix effect, linearity, precision and accuracy were satisfactory. The (mean) concentrations of O-desmethyltramadol (ODMT) and N,O-didesmethyltramadol (NODMT) in the CYP2D6*10/*10 and CYP2D6*5/*5 groups were lower than those in the CYP2D6*wt/*wt group, while the (mean) concentrations of N-desmethyltramadol (NDMT) were higher. Moreover, the ratios of ODMT/tramadol, NDMT/tramadol and NODMT/NDMT were well correlated with the CYP2D6 genotypes. The developed method was successfully applied to the clinical study, which demonstrated that the concentrations of a drug and its metabolites in hair were dependent on the polymorphism of its metabolizing enzyme.     

大鼠肝微粒体温孵体系中（＋）,（—）—黄皮酰胺及其代谢产物的LC—MS分析

目的：建立黄皮酰胺及其代谢产物的ＨＰＬＣ－ＥＳＩ－ＭＳ在线检测分析方法,并对未分离得到的微量代谢产物进行分析确证,探索ＬＣ－ＭＳ在代谢转化研究中的应用。方法：利用柱后补偿技术,采用正离子检测对大鼠肝微体中（＋）,（－）－黄皮酰胺及其代谢产物进行ＨＰＬＣ－ＥＳＩ－ＭＳ分析,根据ＭＳ的碎片信息检测主要的代谢产物,特别是对未分离得到的代谢产物的结构碎片进行分析,确定其结构。结果：除检测出主要已知代谢产物     

Simultaneous determination of loxoprofen and its diastereomeric alcohol metabolites in human plasma and urine by a simple HPLC-UV detection method

A simple, reliable HPLC-UV detection method was developed for the simultaneous determination of loxoprofen and its metabolites (i.e. trans- and cis-alcohol metabolites), in human plasma and urine samples. The method involves the addition of a ketoprofen (internal standard) solution in methanol, zinc sulfate solution and acetonitrile to plasma and urine samples, followed by centrifugation. An aliquot of the supernatant was evaporated to dryness, and the residue reconstituted in a mobile phase (acetonitrile:water=35:65 v/v, pH 3.0). An aliquot of the solution was then directly injected into the HPLC system. Separations were performed on octadecylsilica column (250x4.5 mm, 5 microm) with a guard column (3.2x1.5 cm, 7 microm) at ambient temperature. Loxoprofen and the metabolites in the eluent were monitored at 220 nm (a.u.f.s. 0.005). Coefficients of variations (CV%) and recoveries for loxoprofen and its metabolites were below 10 and over 96%, respectively, in the 200 approximately 15000 ng ml(-1) range for plasma and 500 approximately 50000 ng ml(-1) range for urine. Calibration curves for all the compounds in the plasma and urine were linear over the above-mentioned concentration ranges with a common correlation coefficient of 0.999. The detection limit of the present method was 100 ng for all the compounds. These results indicate that the present method is very simple and readily applicable to routine bioavailability studies of these compounds with an acceptable sensitivity.     

Simultaneous determination of an active metabolite and open-ring metabolites by high performance liquid chromatography and pharmacokinetic studies of a penem antibiotic,FCE22891, in dogs

A sensitive high performance liquid chromatographic method for the simultaneous determination of an active metabolite (FCE22101) and open-ring metabolites (P1, P2) of a penem antibiotic, FCE22891, in dog plasma was developed. Plasma samples were pretreated only by ultrafiltration for the determination of the metabolites. The filtrates were directly analyzed by a reversed-phase high-performance liquid chromatographic system using a two-sided bracketing injection technique. The quantitation limits of FCE22101, P1 and P2 were 0.03, 0.1 and 0.15 μg ml⁻¹, respectively. Analysis of the spiked plasma samples demonstrated the good accuracy and precision of the method.The proposed method was applied to the pharmacokinetic studies of an active metabolite and open-ring metabolites after oral administration of a penem antibiotic, FCE22891, in dogs. In addition, the plasma levels of unchanged FCE22891 and the possible changes of formaldehyde and acyl-l-carnitine levels in plasma, which will be generated from the ester group of FCE22891, were also investigated.     

Analysis of topiramate and its metabolites in plasma and urine of healthy subjects and patients with epilepsy by use of a novel liquid chromatography-mass spectrometry assay

A novel liquid chromatography-mass spectrometry (LC-MS) method was developed and validated for quantification of topiramate (TPM) and its metabolites 10-hydroxy topiramate (10-OH-TPM), 9-hydroxy topiramate (9-OH-TPM), and 4,5-O-desisopropylidene topiramate (4,5-diol-TPM) in plasma and urine. The method uses 0.5 mL of plasma or 1 mL of urine that is extracted with diethyl ether and analyzed by LC-MS. Positive ion mode detection enables tandem mass spectrometric (MS/MS) identification of the aforementioned four compounds. Calibration curves of TPM, 4,5-diol-TPM, 9-OH-TPM, and 10-OH-TPM in plasma and urine were prepared and validated over the concentration range of 0.625 to 40 microg/mL using TPM-d(12) as an internal standard. Calibration curves were linear over this concentration range for TPM and its metabolites. Accuracy and precision ranged in urine from 83% to 114% and 4% to 13% (%CV), respectively, and in plasma from 82% to 108% and 6% to 13%, respectively. The applicability of the assay was evaluated by analyzing plasma samples from a healthy subject who received a single oral dose of TPM (200 mg) and urine samples from 11 patients with epilepsy treated with TPM (daily dose between 100 to 600 mg) alone or with other antiepileptic drugs. Only TPM was detected and quantified in the plasma samples, and its concentration ranged between 0.7 and 4.3 microg/mL. The concentrations of TPM and 10-OH TPM were quantifiable in all urine samples and ranged from 20 to 300 microg/mL for TPM and from 1 to 50 microg/mL for 10-OH-TPM. The metabolites 4,5-diol-TPM and 9-OH-TPM were also detected in all urine samples, but their concentrations were quantifiable only in 4 patients. An unidentified peak in the chromatograms obtained from patients' urine was attributed to 2,3-O-desisopropylidene topiramate (2,3-diol-TPM). Due to a lack of reference material of 2,3-diol TPM and the similar MS/MS spectrum with 4,5-diol-TPM, the calibration curves of 4,5-diol-TPM were used for the quantification of its isomer 2,3-diol-TPM. Based on these determinations, the apparent 2,3-diol-TPM-to-TPM concentration ratio in patients' urine ranged from 0.05 to 0.51 and the 10-OH-TPM-to-TPM ratio ranged from 0.02 to 0.17. In conclusion, a novel LC-MS method for the assay of TPM and four of its metabolites in plasma and urine was developed. Its utilization for analysis of urine samples from patients with epilepsy showed that the method was suitable for analysis of TPM and its metabolites in clinical samples. Two quantitatively significant TPM metabolites (10-OH-TPM and 2,3-diol-TPM) and two quantitatively minor metabolites (9-OH-TPM and 4,5-diol-TPM) were detected and quantified in urine samples from patients with epilepsy.     

Selective and sensitive determination of an antiallergic agent, emedastine difumarate (KG-2413), in human plasma by the radioreceptor assay combined with a high-performance liquid chromatography

The selective and sensitive method for the determination of a new antiallergic agent, 1-(2-ethoxyethyl)-2-(hexahydro-4-methyl-1H-1,4-diazepin-1-yl)-1H-b enzimidazole difumarate (emedastine difumarate, KG-2413), in the human plasma has been developed. Emedastine was determined by the receptor assay after the separation from its metabolites by the use of high-performance liquid chromatography (HPLC). This combined method (HPLC-radioreceptor assay (RRA) method) allowed us the quantification only of 0.3 ng/ml of emedastine in the human plasma. The intra-assay coefficients of variation for the determination were below 12%. Furthermore, the total pharmacologically active metabolites, including unchanged emedastine, was determined by the extraction of the unconjugated metabolites in the human plasma with chloroform followed by the receptor assay (RRA method). The human plasma concentrations measured by the HPLC-RRA method were in good agreement with those by the RRA method. These results suggested that in human pharmacological activities occurred by unchanged emedastine itself.     

Identification and quantification of 1-nitropyrene metabolites in human urine as a proposed biomarker for exposure to diesel exhaust

1-nitropyrene (1-NP) is one of the most abundant nitrated polycyclic aromatic hydrocarbons (NPAHs) in diesel exhaust particulate matter (DEP) and is a main contributor of direct-acting mutagenicity in DEP. Therefore, the metabolites of 1-NP are expected to be a biomarker for assessment of exposure to DEP. In this study, a highly specific and sensitive analytical method using liquid chromatography with tandem mass spectrometry (LC-MS/MS) was developed to determine urinary 1-NP metabolites. After enzymatic hydrolysis of the conjugated metabolites, the analytes were selectively extracted from the urine matrix with blue rayon. The eluate from the rayon was further purified on an acidic alumina cartridge. Hydroxy-N-acetyl- 1-aminopyrenes (6- and 8-OHNAAP) and hydroxy-1-nitropyrenes (3-, 6-, and 8-OHNP) in human urine were identified by their retention times and MS/MS spectra and quantified by using deuterated internal standards. 1-NP metabolites were quantified in urine from all healthy, nonoccupationally exposed subjects. 6-OHNAAP, 8-OHNAAP, 6-OHNP, and 8-OHNP (means of 117, 109, 203, and 137 pmol/mol creatinine, respectively) were the most abundant isomers in human urine. This report is the first to demonstrate the presence of OHNAAPs and OHNPs in human urine, in agreement with previous in vivo and in vitro studies that predicted that these metabolites should be excreted into human urine. This method for determining urinary 1-NP metabolites should be useful for the surveillance of exposure to NPAHs and DEP and will facilitate the study of cancer risk associated with these exposures.