脂质体槲皮素对食管癌细胞增殖及蛋白表达的影响及机制

目的比较不同脂质体槲皮素对人食管癌Eca109和Eca9706细胞增殖的作用,并初步探讨其作用机制。方法采用旋转蒸发法制备氯仿和甲醇溶解类脂物质的脂质体槲皮素LQ1和按同比例的氯仿和DMSO作为溶剂的脂质体槲皮素LQ2,用DMSO直接溶解槲皮素制备非脂质体槲皮素nLQ,分别作用于Eca109和Eca9706细胞（分别作为LQ1、LQ2及nLQ组）,同时设立对照组。MTT实验检测各组细胞抑制率,免疫组织化学染色和免疫印迹法检测磷酸酶基因（PTEN）和细胞周期素D1（Cychn D1）蛋白表达。结果各组细胞增殖的抑制效应、上调PTEN和下调Cyclin D1蛋白表达的效应呈现同一趋势,即LQ2组〉LQ1组〉nLQ组〉对照组,P〈0．05。结论脂质体槲皮素对食管癌细胞增殖有抑制作用,LQ2的抑制率高于LQ1;上调PTEN表达、下调Cyclin D1表达可能为其作用机制之一。     

rshCD_（40）L、IFN-γ对食管癌Eca109、Eca9706、TE13细胞增殖和凋亡的影响

目的观察可溶性重组人CD40L（rshCD40L）、IFN-γ对食管癌Eca109、Eca 9706、TE13细胞增殖和凋亡的影响。方法取正常培养的食管鳞癌细胞株Eca109、Eca 9706、TE13,分别用PBS、100 U/ml IFN-γ、100 ng/ml rsh-CD40L、100 U/ml IFN-γ＋100 ng/ml rshCD40L培养,分别为A、B、C、D组。用MTT法测算各组细胞增殖抑制率,用TUNEL法检测细胞凋亡率。结果 C组Eca109、Eca9706、TE13细胞增殖抑制率分别为40.6%±4.2%、31.5%±5.7%、44.6%±6.7%,明显高于A、B组（P均〈0.05）;D组分别为56.7%±4.9%、41.2%±6.2%、51.6%±5.2%,均高于C组（P均〈0.05）。C组Eca109、Eca9706、TE13细胞凋亡率分别为33.6%±3.7%、30.5%±2.8%和37.6%±4.9%,明显高于A、B组（P均〈0.05）;D组分别为43.7%±4.7%、34.2%±5.1%、41.5%±5.7%,均高于C组（P均〈0.05）。结论 rshCD40L能促进食管癌Eca109、Eca9706、TE13细胞凋亡,并抑制其增殖。IFN-γ可增强这一作用。     

曲古霉素A对食管癌细胞系EC9706细胞凋亡的作用及机制

目的探讨曲古霉素A（TSA）对食管癌细胞系EC9706细胞凋亡的影响及机制。方法用AnnexinV-FITC和PI进行双染色,流式细胞仪检测细胞凋亡率,Western blot检测TSA对食管癌细胞凋亡相关基因表达的影响。结果 1.0μmol/L的TSA诱导EC9706细胞凋亡率增加（P〈0.05）,且呈浓度依赖性;0.5μmol/L的TSA作用48 h后细胞凋亡率增加（P〈0.05）,呈时间依赖性。TSA处理的EC9706细胞Bax蛋白表达增加,Bcl-2蛋白表达减少;TSA诱导EC9706细胞caspase-8及caspase-9裂解活化,且随作用时间延长逐步升高。结论一定量的TSA可以诱导EC9706细胞凋亡,凋亡原因与Bax表达增强、Bcl-2减少以及凋亡细胞中caspase-8及caspase-9介导的caspase-3活化有关。     

哌立福新对食管癌细胞增殖和凋亡的影响

目的研究不同浓度的哌立福新对食管癌细胞增殖及凋亡的影响,探讨哌立福新阻断蛋白激酶B（Akt）信号通路对食管癌细胞生长的抑制作用。方法将不同浓度的蛋白激酶B抑制剂哌立福新加入到人食管癌细胞Ecal09中,采用M3T法测定细胞毒性,流式细胞仪测定细胞凋亡率,Western Bloting法检测食管癌细胞中蛋白激酶B、mTOR、GSK-3β蛋白表达。结果哌立福新对人食管癌细胞Eca109有明显抑制作用并能诱导食管癌细胞凋亡。MTF结果显示,随着浓度的升高和时间的延长,抑制作用增强,并诱导人食管癌细胞Eca109凋亡,呈剂量一时问效应关系;流式细胞术显示,不同浓度哌立福新作用于人食管癌细胞Eca10924、48、72、96小时后,凋亡率随着时间的延长和浓度的升高而增大,15μmol／L作用48小时后凋亡率最大为51．3％;Western Bloting结果显示,蛋白激酶B、mTOR、GSK-3β在人食管癌细胞Eca109中均有表达,哌立福新作用后表达显著降低。结论哌立福新能显著抑制食管癌细胞增殖并诱导其凋亡。     

孕烷X受体抗食管癌EC9706细胞凋亡的作用机制

目的 研究孕烷X受体(PXR)抗食管癌EC9706细胞凋亡的作用机制.方法 使用利福平活化食管鳞癌EC9706细胞中的PXR,阿霉素(ADM)诱导高表达PXR的EC9706细胞凋亡,采用流式细胞仪观察细胞的增殖周期,MTT法观察细胞凋亡率,Western印迹和免疫组化法检测Caspase-3,Bcl-2,Bax蛋白表达情况.结果 ADM处理可以明显抑制细胞生长;使细胞呈明显凋亡改变;利福平诱导PXR高表达的EC9706细胞凋亡减少,抑制Caspase-3的蛋白水平,上调蛋白Bcl-2的表达,表明PXR在抗食管鳞癌细胞凋亡中发挥重要的作用.结论 PXR可能是通过降低Caspase-3和升高Bcl-2蛋白的表达抑制食管癌细胞EC9706的凋亡.     

莪术醇联合顺铂对人食管癌109细胞凋亡以及细胞核因子-κB 表达的影响

目的：研究中药莪术醇联合顺铂对食管癌109细胞系的增殖凋亡、核因子（NF）-κB表达的影响,探讨莪术醇抗肿瘤的分子机制。方法将不同浓度莪术醇、顺铂、莪术醇和顺铂联合作用于食管癌109细胞,用噻唑蓝比色法（MTT 法）检测细胞增殖,流式细胞仪检测细胞凋亡, Western blot 法检测作用48小时后细胞 NF-κB 蛋白的表达情况。结果不同浓度莪术醇、顺铂均对食管癌细胞均有抑制增殖、促进凋亡作用,抑制率、凋亡率呈明显浓度依耐性;联合用药后抑制率、凋亡率显著提高,差异有统计学意义（P ＜0．05）;4个浓度的莪术醇与顺铂（2．5 mg／L）作用食管癌48小时后 NF-κB 的表达量随浓度增加而下降,与对照组比较差异有统计学意义（P ＜0．05）。结论中药莪术醇对人食管癌109细胞株有明显抑制增殖,诱导凋亡的作用,其机制可能与下调NF-κB 蛋白的表达有关。     

槲皮素对卵巢癌细胞HO-8910增殖的抑制作用及机制

目的观察槲皮素体外对卵巢癌HO-8910细胞增殖的抑制作用,并探讨其机制。方法将体外培养卵巢癌HO-8910细胞用0、10、20、40、80、160μmol／L的槲皮素处理。用MTF法测定细胞增殖抑制率,流式细胞仪检测细胞周期分布及细胞凋亡率,细胞免疫化学染色法检测细胞内Fas及HSP70的表达,分光光度计法检测细胞内Caspase-3和Csapase-8的活性。结果浓度10～160μmol／L的槲皮素均能抑制人卵巢癌HO-8910细胞的增殖,并有明显的时间和剂量依赖性（P〈0．05）。不同浓度的槲皮素作用48h后各组细胞凋亡率随槲皮素浓度增高,HSP70表达下调,FAS表达增强,Caspase-3、8活性上调,均呈剂量依赖性（P均〈0．05）。结论槲皮素能抑制卵巢癌细胞的增殖。其机制可能与槲皮素通过提高细胞内Fas的表达,降低HSP70的表达及诱导Caspase-3、8的活化及诱导卵巢癌细胞凋亡有关。     

环氧合酶-2选择性抑制剂NS-398诱导食管癌细胞EC 9706凋亡及其机制的探讨

目的 观察环氧合酶-2(COX-2)选择性抑制剂NS一398对食管癌细胞株EC 9706增殖及凋亡的影响,砌究其对凋亡抑制蛋白Survivin和Caspase-3表达的影响,探讨NS-398诱导Ec 9706细胞凋亡的作用机制.方法 NS-398作用EC 9706细胞后,MTT法测定NS-398对人食管癌EC 9706细胞增殖的抑制率;DNA片段分析法和流式细胞仪检测细胞凋亡;免疫细胞化学检测Survivin和Caspase-3蛋白表达变化.结果 NS-398(10～100μmol/L)对EC 9706细胞生长有抑制作用,随浓度升高、时间延长抑制作用增强,并诱导EC 9706细胞凋亡,呈剂量-时间效应关系;NS-398可降佴Survivin蛋白表达,增加Caspase-3蛋白表达.结论 NS-398可诱导人食管癌细胞株EC 9706凋亡,其机制可能与下调Survivin表达及激活Capase-3表达有关.     

玉竹提取物B对人食管癌细胞Eca-109增殖与凋亡的影响

目的观察玉竹提取物B（EB-PAOA）对人食管癌细胞Eca-109增殖与凋亡的影响。方法将体外培养的Eca-109细胞与不同浓度的EB-PAOA共育,采用MTT法检测Eca-109细胞增殖抑制率,采用流式细胞仪检测Eca-109细胞凋亡率。结果随着EB-PAOA浓度增大、作用时间延长,Eca-109细胞的增殖抑制率逐渐升高（P均〈0.05）,呈时间、剂量依赖性;随着EB-PAOA浓度增加,Eca-109细胞凋亡率逐渐增加,呈一定浓度依赖性（P均〈0.05）。结论EB-PAOA能够抑制人食管癌细胞Eca-109的增殖,并诱导其凋亡。     

p38在二硫苏糖醇与顺铂诱导食管癌Eca109细胞凋亡中的作用

将人食管癌Eca109细胞分为七组,其中三组分别加二硫苏糖醇(DTT,Ds)、顺铂(Cs)及二药联合(Ds Cs)处理细胞,另三组则先用磷酸化p38特异性抑制剂SB203580孵育,再分别加Ds、Cs及Ds Cs处理细胞,未加药组作为对照(C′).采用流式细胞仪技术检测细胞凋亡率.结果与C′比较,各组均存在明显差异(P均＜0.01); SB203580孵育细胞后,与相应组别比较,Ds 、Cs 、Ds Cs凋亡率均明显下降(P均＜0.01).证实p38 MAPK在Ds 和Cs诱导食管癌Eca109细胞凋亡中被显著激活,p38 MAPK的激活可能是多种上游凋亡信号传导必经的共同通路.     

槲皮素在机械性创伤导致大鼠心脏继发性损伤中的保护作用

目的 观察槲皮素对机械性创伤（MT）造成大鼠继发性心肌细胞及心脏功能损伤的保护效果,同时探究其作用机制。 方法 实验分为在体实验和离体实验。将120只成年雄性SD大鼠按随机数字表法分为4组,分别为正常组、创伤组、创伤+槲皮素和创伤+溶剂组。先后应用小动物定量创伤仪制备大鼠MT模型;经右颈总动脉向左心室内插管,记录左心室舒缩压力变化,检测大鼠心功能,初步研究槲皮素对心脏的保护作用;通过MTT比色法检测槲皮素对创伤诱导的H9c2细胞存活率的影响,确定槲皮素对心脏的保护效果;在槲皮素的保护机制研究中,TUNEL染色后计算心肌细胞凋亡指数,以评估心肌细胞的凋亡状况;通过酶标仪检测H9c2细胞在加入槲皮素前后产生活性氧(ROS)自由基的量的变化;激光共聚焦显微镜下观察测定经Fluo-4AM标记的心肌细胞内Ca2+的浓度变化,从而初步探讨槲皮素发挥保护作用的机制。结果 ①心功能指标LVDP、+dP/dtmax 、-dP/dtmax显示,创伤组、创伤+溶剂组与正常组比较均明显下降,而创伤+槲皮素组较创伤组升高（P<0.01）。②MTT检测发现,在一定的浓度范围内,槲皮素对H9c2细胞没有细胞毒性作用,并且可明显阻碍创伤血清对H9c2细胞的损伤。③MT后通过对正常组、创伤组、创伤+槲皮素组和创伤+溶剂组心肌细胞凋亡指数的检测,发现创伤+槲皮素组与创伤组比较凋亡指数明显降低(P<0.01)。④通过对H9c2细胞内ROS的检测,发现槲皮素能够减低MT后细胞内ROS的产生。⑤通过对心肌细胞内钙浓度变化的检测,发现MT后Ca2+浓度上升,给予一定浓度槲皮素后Ca2+浓度下降。结论 在一定的浓度范围内,槲皮素能够降低MT后产生的ROS自由基,抑制Ca2+内流,继而降低心肌细胞凋亡,改善MT后心脏功能,发挥心脏保护作用。     

Quercetin inhibits Ca2+ uptake but not Ca2+ release by sarcoplasmic reticulum in skinned muscle fibers.

Quercetin inhibited Ca2+-dependent ATP hydrolysis, ATP-dependent Ca2+ uptake, chelator-induced [ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid] Ca2+ release, and ATP synthesis coupled to Ca2+ release in isolated vesicles of sarcoplasmic reticulum. Use of this inhibitor permitted evaluation of whether Ca2+ release from sarcoplasmic reticulum in situ occurs through a reversal of the uptake pathway. Release of Ca2+ from the sarcoplasmic reticulum of skinned muscle fibers can be detected by the measurement of tension in the fiber. If the sarcoplasmic reticulum of these preparations is first allowed to accumulate Ca2+, tension development may be induced by the addition of Ca2+ itself or of caffeine to the bathing medium or by depolarization with Cl-. The presence of quercetin during the loading phase inhibited Ca2+ uptake by sarcoplasmic reticulum in situ. When quercetin was added together with initiators of tension development, however, the rate of tension development was enhanced 4- to 7-fold and the relaxation rate of the fibers was greatly inhibited. These results suggest that quercetin had no effect on Ca2+ release in skinned fiber; its effect on Ca2+ reuptake could account for the apparent enhancement of the release rate and for the prolonged relaxation time. These observations rule out reversal of the Ca2+ pump as the mechanism of Ca2+ release in situ.     

Antiproliferative activity of quercetin on normal bone marrow and leukaemic progenitors

We used an in vitro clonogenic assay in semi-solid medium to test the sensitivity of normal bone marrow and acute myeloid and lymphoid leukaemia progenitors to the flavonol quercetin. We have studied 14 acute myeloid (AML) and four acute lymphoid (ALL) leukaemias. All ALL and the vast majority of AML (12/14) had a high sensitivity to quercetin with more than 50% growth inhibition at 2 x 10(-6) M quercetin. One M3-AML was partially quercetin-sensitive displaying 60% surviving AML-colony forming units (CFU-AML) at a quercetin concentration of 10(-5) M. One M1-AML was resistant to the growth inhibitory effect of quercetin at a concentration of 2 x 10(-5) M. The clonogenic efficiency of both AML and ALL positively correlated with leukaemic colony-forming unit (CFU-L) sensitivity to quercetin suggesting that this parameter can be useful in predicting quercetin responsiveness of leukaemic cells. We have also studied the effect of various quercetin concentrations on colony formation by normal bone marrow cells. At a quercetin concentration of 10(-5) M, we observed (in five different experiments) a mean recovery of 53% and 65% of erythroid blast-forming units (BFU-E) and granulocyte-macrophage colony-forming units (CFU-GM), respectively. Thus, normal bone marrow appeared partially resistant to quercetin, being inhibited less than 50% by quercetin concentration higher than 2 x 10(-5). When normal bone marrow were deprived in CD34+ haematopoietic progenitors the resultant population became highly sensitive to quercetin, with a mean recovery of BFU-E and CFU-GM of 5% and 12% of controls respectively in the presence of 2 x 10(-5) M quercetin. Furthermore, CD34 progenitors, positively selected, appeared fully resistant to quercetin concentrations as high as 2 x 10(-5) M. Thus, CD34+ progenitors are a quercetin-resistant component in normal bone marrow. In conclusion, our results further provide a biological basis for the therapeutic use of quercetin, considering that this compound could inhibit leukaemic cell growth without suppressing normal haematopoiesis.     

Quercetin transiently increases energy expenditure but persistently decreases circulating markers of inflammation in C57BL/6J mice fed a high-fat diet

Quercetin, a polyphenolic compound and a major bioflavonoid in the human diet, has anti-inflammatory properties and has been postulated to enhance energy expenditure (EE). We sought to determine whether quercetin alters body weight, body composition, EE, and circulating markers of inflammation. At 6 weeks (W) of age, 2 cohorts of C57BL/6J mice (N = 80) were placed on one of 2 diets for 3W or 8W: (1) high fat (HF) (45% kcal fat) or (2) high fat + quercetin (HF + Q) (45% kcal fat + 0.8% quercetin). Quercetin concentrations in the diet and plasma were evaluated using mass spectrometry. Body weight, composition (nuclear magnetic resonance), and food consumption were measured weekly. Energy expenditure was measured by indirect calorimetry at 3 and 8W, and inflammatory markers were measured in plasma obtained at 8W. The presence of quercetin in the HF diet did not alter food consumption over time in the HF + Q group and did not differ from the HF group at any time point. However, circulating plasma quercetin concentrations declined between 3 and 8W. At 3W, EE was higher during both day and night phases (P < .0001) in the HF + Q group compared with the HF group; but this difference was not detected at 8W and did not translate into significant differences between the HF + Q and HF groups with respect to body weight or body composition. During the night phase, concentrations of the inflammatory markers (interferon-γ, interleukin-1α, and interleukin-4) were significantly lower when compared with HF treatment group (P < .05). Dietary supplementation with quercetin produces transient (3W) increases in EE that are not detected after 8W on the diet. A corresponding decrease in circulating quercetin between 3 and 8W suggests that metabolic adaptation may have diminished the impact of quercetin's early effect on EE and diminished its overall effect on nutrient partitioning and adiposity. However, quercetin at the levels provided was effective in reducing circulating markers of inflammation observed in animals on an HF diet at 8W.     

Effects of flavonoids on insulin secretion and 45Ca2+ handling in rat islets of Langerhans

The effects of some flavonoids, a group of naturally occurring pigments one of which has been claimed to possess antidiabetic activities, on insulin release and 45Ca2+ handling have been studied in isolated rat islets of Langerhans. Insulin release was enhanced by approximately 44-70% when islets were exposed to either (-)epicatechin (0.8 mmol/l) or quercetin (0.01-0.1 mmol/l); others such as naringenin (0.1 mmol/l) and chrysin (0.08 mmol/l) inhibited hormone release by approximately 40-60%. These effects were observed only in the presence of 20 mmol glucose/l. Quercetin (0.01 mmol/l) and (-)epicatechin (0.8 mmol/l) both inhibited 45Ca2+ efflux in the presence and absence of extracellular Ca2+. In the presence of 20 mmol glucose/l both the short-term (5 min) and steady-state (30 min) uptake of 45Ca2+ were significantly increased by either quercetin or (-)epicatechin. These results suggest that the stimulatory compounds such as quercetin and (-)epicatechin may, at least in part, exert their effects on insulin release via changes in Ca2+ metabolism.     

Quercetina Melhora o Perfil Lipídico e Apolipoproteico em Ratos Tratados com Glicocorticóides em Altas Doses

BackgroundGlucocorticoids (GCs) are widely prescribed for the treatment of numerous clinical disorders due to their anti-inflammatory and immune-modulatory properties and one of the most common untoward effects of these drugs is dyslipidemia.ObjectiveTo evaluate the effect of quercetin, a plant-derived flavonoid, on the lipid profile of high-dose glucocorticoid treated rats.MethodsA total of 32 Sprague-Dawley rats, were randomly distributed among four groups (8 rats per group) and treated for 6 weeks with one of the following: (i) normal saline; (ii) 40 mg/kg methylprednisolone sodium succinate (MP); (iii) MP + 50 mg/kg quercetin; (iv) MP + 150 mg/kg quercetin. MP was injected subcutaneously, and quercetin was administered by oral gavage 3 days a week. At the end of the study, the animals’ lipid profile was measured by enzymatic kits. Data were analyzed and statistical significance was set at p<0.05.ResultsThe mean serum total cholesterol (TC), triglyceride (TG) and LDL levels were drastically increased in GC-treated animals compared with the control group. Both doses of quercetin (50 and 150 mg/kg) ameliorated TC (43% and 45%), LDL (56% and 56%) and TG (46% and 55% respectively). Apo B/A1 ratio decreased more than 20% following quercetin intake and the decline in TC/HDL, TG/HL, LDL/HDL ratios were significant.ConclusionsThese data suggest that quercetin intake with both doses of 50 and 150 mg/kg could be considered as a protective agent for glucocorticoid-induced dyslipidemia. (Arq Bras Cardiol. 2020; 115(1):102-108.)     

Quercetin protects liver injury induced by bile duct ligation via attenuation of Rac1 and NADPH oxidase1 expression in rats

BACKGROUND:Bile duct ligation (BDL) and subsequent cholestasis are correlated with oxidative stress,hepatocellular injury and fibrosis.Quercetin is a flavonoid with antifibrotic,and hepatoprotective properties.However,the molecular mechanism underlying quercetin-mediated hepatoprotection is not fully understood.The current study was to evaluate mechanisms of hepatoprotective effect of quercetin in BDL rat model.METHODS:We divided male Wistar rats into 4 groups (n=8 for each):sham,sham+quercetin (30 mg/kg per day),BDL,and BDL+quercetin (30 mg/kg per day).Four weeks later,the rats were sacrificed,the blood was collected for liver enzyme measurements and liver for the measurement of Racl,Racl-GTP and NOX1 mRNA and protein levels by quantitative PCR and Western blotting,respectively.RESULTS:Quercetin significantly alleviated liver injury in BDL rats as evidenced by histology and reduced liver enzymes.Furthermore,the mRNA and protein expression of Racl,Racl-GTP and NOX1 were significantly increased in BDL rats compared with those in the sham group (P＜0.05);quercetin treatment reversed these variables back toward normal (P＜0.05).Another interesting finding was that the antioxidant markers e.g.superoxide dismutase and catalase were elevated in quercetin-treated BDL rats compared to BDL rats (P＜0.05).CONCLUSION:Quercetin demonstrated hepatoprotective activity against BDL-induced liver injury through increasing antioxidant capacity of the liver tissue,while preventing the production of Racl,Racl-GTP and NOX1 proteins.     

Enhancing effect of quercetin on 3-methylcholanthrene carcinogenesis in C57Bl/6 mice

We investigated the effect of quercetin on 3-methylcholanthrene (MCA) carcinogenesis in C57Bl/6 mice. We found that quercetin itself was not carcinogenic when administered i.m., even at a dose of 20 mg, throughout an observation period of 420 days. An i.m. administration of various doses of quercetin admixed with 1.0 mg of MCA, however, significantly shortened the mean latency periods for the development of local primary tumors compared with those of the group which had been given MCA alone. The shortening of latency periods was also found in the experiments using 0.1 mg of MCA after the administration of quercetin either admixed with MCA or fed with a diet containing it. Moreover, lung metastasis increased in mice given the mixture of MCA (0.1 mg) and quercetin compared with its occurrence in mice given MCA alone. A simultaneous administration of MCA and quercetin significantly increased the in vivo sister chromatid exchanges (SCE) formation of bone marrow cells when compared with its occurrence in the group given MCA alone. These results suggest that quercetin has an enhancing effect on MCA carcinogenesis and that this enhancement may be associated with such a genetic effect as an increased mutation rate in the host.     

Type II oestrogen binding sites in acute lymphoid and myeloid leukaemias: growth inhibitory effect of oestrogen and flavonoids

The presence of oestrogen receptors (ER) and type II oestrogen binding sites (type II EBS) have been investigated by a whole cell assay in seven cases of acute lymphoid leukaemia (ALL) and 16 cases of acute myeloid leukaemia (AML). ER were detected in 6/7 ALL patients with values ranging between 133 and 2268 sites/cell and in 12/16 AML patients with values ranging between 274 and 4197 sites/cell. The apparent dissociation constant (KD) for ER was 0.6 +/- 0.3 nM (mean + SD of 20 cases). All blasts from ALL and AML patients expressed type II EBS at variable levels ranging between 3109 and 239450 sites/cell. The mean KD value for these sites was 18.3 +/- 5.6 nM (mean +/- SD of 23 cases). Specificity experiments demonstrated that type II EBS are oestrogen specific relative to the class of steroid hormones. In addition, the flavonol quercetin was able to compete for [3H]17 beta-oestradiol (E2) binding to type II EBS, the relative binding affinity (RBA) of quercetin being greater than that of diethylstillboestrol (DES). DES and quercetin exerted a dose-dependent inhibition of ALL and AML blast proliferation in the range of concentrations between 10(-8) and 10(-5) M. The RBA of DES and quercetin for type II EBS correlated well with their potency as cell growth inhibitors. Moreover, the flavonols rutin and hesperidin which compete slightly for [3H]E2 binding to type II EBS, were scarcely effective in inhibiting leukaemic cell proliferation. The inhibitory effect of DES and quercetin was not due to a non-specific cytotoxic action since after a 1 d culture period, cell viability did not vary between control and treated cells, being greater than 80%. Our results suggest that high oestrogen concentrations and the flavonol quercetin may inhibit leukaemic blast proliferation through a common mechanism involving a binding interaction with type II EBS.