羟基喜树碱诱导胃癌细胞凋亡的实验研究

目的 研究羟基喜树碱(HCPT)诱导胃癌细胞的凋亡作用,探讨其治疗胃癌的作用机制.方法 应用MTT、TUNEL染色、流式细胞仪技术研究HCPT对胃癌细胞SGC-7901、MKN-45、MKN-28的细胞毒和诱导凋亡的作用.结果 HCPT具有很强的细胞毒作用,对三株不同分化程度胃癌细胞的SGC-7901(中分化)、MKN-45(低分化)、MKN-28(6高分化)的IC50为0.008～0.012mg/ml.HCPT作用于细胞后,可看到较为典型的细胞凋亡的形态学变化:细胞核固缩,染色质凝集,呈新月型紧贴于核膜周边,核碎裂,染色质片断化,凋亡小体形成等.流式细胞仪DNA直方图上出现典型的亚二倍体"凋亡峰".流式细胞仪计数显示,HCPT诱导胃癌细胞SGC-7901、MKN-45、MKN-28的凋亡率分别为21.88%、12.35%、30.26%.HCPT诱导胃癌细胞的凋亡率与胃癌的分化程度有关.TDT染色法显示,细胞凋亡指数在12.35%～30.26%之间.HCPT的作用表现为细胞周期特异性,HCPT主要作用于细胞周期的S期,抑制细胞增殖和诱导细胞凋亡,使细胞阻滞于S期.结论 HCPT对胃癌细胞具有很强的细胞毒作用,诱导凋亡是其主要作用机制之一.     

药物诱导胃癌细胞凋亡的初步探索

目的:了解羟基喜树碱和氧化砷体外诱导胃癌细胞凋亡的能力.探索最佳诱导时间和剂量.并初步阐明其作用机制。方法:利用HE染色法、流式细胞仪和DNA末端原位标记染色法(TUNEL)观察羟基喜树碱和氧化砷在体外对胃癌细胞MKN-28(高分化腺癌)。SGC-7901(中分化腺癌)。MKN-45(低分化腺癌)的作用 结果:药物作用48小时后,羟基喜树碱0.01mg/ml组胃癌细胞MKN-28、SGC-7901、MKN-45的凋亡率分别为30.26％、21.88％和12.35％,氧化砷10μmol/L组胃癌细胞MKN-28、SGC-7901、MKN-45的凋亡率分别为22.52％、13.83％和9.68％其中羟基喜树碱在细胞周期的S期诱导胃癌细胞发生凋亡,而氧化砷则主要作用于G2/M期。     

葡萄糖神经酰胺合成酶基因在人胃癌细胞SGC-7901及SGC-7901/VCR的表达和意义

目的:研究葡萄糖神经酰胺合成酶(glucosyl- ceramide synthase,GCS)基因在人胃癌细胞SGC-7901和SGC-7901/VCR的表达并探讨其对人胃癌发生、发展的意义.方法:体外培养人亲本敏感胃癌细胞SGC-7901和人耐长春新碱胃癌细胞SGC-7901/VCR.采用MTT法检测半数细胞抑制浓度(IC_(50))和SGC-7901/VCR耐药倍数;RT- PCR法检测SGC-7901和SGC-7901/VCR两种细胞GCS mRNA的表达,免疫组化法测定GCS蛋白表达水平.结果:SGC-7901和SGC-7901/VCR的IC_(50)分别为1.40±0.06和86.20±0.50 mg/L.SGC-7091/ VCR细胞耐药指数是亲本细胞SGC-7901的61倍,SGC-7901和SGC-7901/VCR两种细胞均有GCS mRNA表达,且SGC-7901/VCR细胞GCS mRNA表达水平(GCS指数为3.9)较SGC-7901细胞(GCS指数为0.5)有显著升高(P<0.05),耐药细胞GCS蛋白表达阳性率(65%)显著高于亲本细胞(18%)(P<0.05).结论:GCS基因在人胃癌耐药细胞和亲本敏感细胞均有表达,耐药细胞GCS mRNA及蛋白均高表达.GCS可能参与了胃癌的发生过程,且与肿瘤多药耐药有密切关系.     

TRAIL对人胃癌耐药细胞株SGC-7901/VCR多药耐药基因GST-π表达的影响

背景:肿瘤细胞的多药耐药现象是导致进展期胃癌化疗失败的重要因素之一。肿瘤坏死因子相关凋亡诱导配体(TRAIL)能增强化疗药物对肿瘤细胞的杀伤作用,并逆转耐药细胞株为敏感细胞株,但其确切机制尚不清楚。目的:研究TRAIL对人胃癌耐药细胞株SGC-7901/VCR多药耐药基因谷胱甘肽硫转移酶-π(GST-π)表达的影响,探讨其逆转胃癌细胞多药耐药的可能机制。方法:以不同浓度TRAIL(50、100、200、400μg/L)干预SGC-7901/VCR细胞48 h,采用RT-PCR和ELISA法检测各组SGC-7901/VCR细胞中的GST-πmRNA表达和细胞培养上清液中的GST-π含量。结果:TRAIL干预能抑制SGC7901/VCR细胞的GST-πmRNA表达及其蛋白分泌,抑制作用在一定剂量范围内(≤200μg/L)具有量效关系。50、100、200、400μg/L TRAIL组GST-πmRNA相对表达量分别为0.89±0.04、0.77±0.08、0.65±0.06和0.61±0.03,细胞培养上清液中的GST-π含量分别为(57.56±1.19)ng/m L、(56.30±0.80)ng/m L、(31.41±1.65)ng/m L和(30.80±1.34)ng/m L,均低于对照组的1.01±0.13和(58.62±1.38)ng/m L,差异有统计学意义(P0.05)。结论:TRAIL可能通过下调GST-π表达参与了胃癌细胞多药耐药的逆转。     

洛贝林逆转胃癌细胞SGC7901/VCR多药耐药的作用

目的:探讨哌啶类生物碱洛贝林(Lobeline)能否逆转人胃癌多药耐药细胞株SGC7901/VCR的多药耐药,并进一步探讨洛贝林逆转其多药耐药的机制,评估其有效性.方法:以人胃癌多药耐药细胞株SGC7901/VCR为研究对象,用四氮唑蓝(MTT)法分别测定在无和有洛贝林(细胞无毒浓度10 mol/L)作用下多药耐药细胞株SGC7901/VCR对VCR及5-Fu的半数生长抑制率,并由此求其耐药逆转的倍数;RT-PCR分别检测在无和不同终浓度洛贝林(5、10、20、50、100 mol/L)作用下多药耐药细胞株SGC7901/VCR的多药耐药基因MDR1 mRNA表达情况;Western blot分别检测在无和不同终浓度洛贝林(5、10、20、50、100 mol/L)作用下多药耐药细胞株SGC7901/VCR的P-gp蛋白表达.结果:在洛贝林无毒作用浓度(10 mol/L)作用下,多药耐药细胞株SGC7901/VCR对化疗药的敏感性增加,VCR对耐药细胞株的IC50由原来的16.55 g/L±0.13 g/L变成7.27g/L±0.65 g/L,逆转指数约为2.28;5-Fu对耐药细胞株的IC50由原来的11.01 g/L±0.43 g/L变成9.53 g/L±0.79 g/L,逆转指数约为1.16;RT-PCR检测示多药耐药细胞株SGC7901/VCR呈现MDR1 mRNA高度表达,随洛贝林终作用浓度的增大,MDR1 mRNA表达逐渐下降,各组间差距有统计学意义(P<0.05);Western blot检测表明多药耐药细胞株SGC7901/VCR高度表达P-gp蛋白,随洛贝林作用终浓度依次增加P-gp蛋白表达依次减弱,组间呈浓度依赖性,差别有统计学意义(P<0.05).结论:无细胞毒作用浓度的洛贝林可以逆转胃癌多药耐药细胞株SGC7901/VCR的多药耐药,增强VCR和5-Fu的化疗敏感性.洛贝林对SGC7901/VCR细胞多药耐药的逆转可能机制为抑制P-gp蛋白的表达.     

β-榄香烯对胃癌及胃癌耐药细胞杀伤作用的实验研究

目的 研究β-榄香烯联合或不联合化学治疗药物5-氟尿嘧啶(5-FU)对人胃癌细胞株SGC-7901和相应耐药细胞株SGC-7901/5-FU的杀伤作用及机制.方法 用不同剂量β-榄香烯(20、40或80μg/ml)联合或不联合5-FU (100 μg/ml)作用于SGC-7901和SGC-7901/5-FU细胞,采用四甲基偶氮唑盐实验、透射电镜观察、流式细胞仪和DNA原位末端标记(TUNEL)法检测药物对细胞的杀伤作用及其诱导细胞凋亡的情况.通过建立SGC-7901和SGC-7901/5-FU细胞裸鼠移植瘤模型观察β-榄香烯对这两种细胞的体内杀伤作用.结果 β-榄香烯在体内、外均具有抑制SCA3-7901和SGC-7901/5-FU细胞生长的作用(P值均<0.05),一定剂量范围内具量效关系(P=0.02).透射电镜、流式细胞仪和TUNEL实验均显示β-榄香烯抑制两种胃癌细胞生长的作用与其诱导细胞凋亡有关.结论 β-榄香烯在体内外对SGC-7901和SGC-7901/5-FU细胞均具杀伤作用,该作用可能与其诱导细胞凋亡有关.     

人端粒酶反义寡核苷酸抑制三种不同分化程度胃癌细胞生长及作用机制研究

目的 研究特定序列人端粒酶反义寡核苷酸(AS-0DN)抑制三种分化程度不同的胃癌细胞(MKN-45、SGC-7901、MKN-28)生长的可能性，并阐述其抑制胃癌细胞生长的作用与胃癌细胞分化程度的相关性。方法 在指定的作用时问和浓度等条件下，以AS-0DN作用于不同分化程度的三种胃癌细胞，用改良端粒酶活性定量检测法测定AS-0DN片段作用前后胃癌细胞的端粒酶活性；用锥虫蓝染色法观察细胞活力；用倒置显微镜、电镜、流式细胞仪和原位末端标记(TUNEL)法观察细胞凋亡情况。结果以指定浓度的AS-ODN作用后，MKN-45和SGC-7901细胞出现明显的端粒酶活性和细胞生长抑制(P＜0．05)，但在同样浓度条件下，MKN-28胃癌细胞只出现端粒酶活性抑制。错义序列对照组则无明显变化。以10 μmol／L的AS-ODN连续作用三种胃癌细胞96h后，光镜、电镜和TUNEL法检测均发现MKN-45和SGC-7901细胞表现出特有的凋亡征象，流式细胞仪检测证实MKN-45和SGG-7901细胞的平均凋亡率在44．75％和33．56％，错义序列对照组则无明显变化(P＜0．05)。结论 AS-0DN能有效抑制胃癌细胞生长，其作用机制主要是抑制端粒酶活性和诱导细胞凋亡。AS-0DN对中分化胃癌细胞的生长抑制最显著，对低分化胃癌细胞的抑制作用略强于高分化胃癌细胞，提示端粒酶反义核酸的抑制作用不依赖于胃癌细胞的分化程度。     

β-榄香烯对不同分化程度胃癌细胞株端粒酶活性及细胞凋亡的影响

目的:探讨β-榄香烯治疗胃癌的作用机制.方法:应用四唑蓝(MTT)比色法、端粒重复扩增(TRAP)-微孔板杂交法、光镜检查和DNA末端原位标记染色法(TUNEL)研究β-榄香烯对胃癌细胞株SGC-7901(中分化)、MKN-45(低分化)和MKN-28(高分化)的细胞毒作用及其对端粒酶活性、细胞形态学变化和细胞凋亡的影响.结果:β-榄香烯对不同分化程度的胃癌细胞均具有较强的细胞毒作用;其抗癌作用与抑制端粒酶活性和诱导凋亡有关.β-榄香烯抑制端粒酶活性及诱导凋亡的效果与作用时间、浓度及细胞分化程度相关.结论:β-榄香烯对胃癌细胞具有很强的细胞毒作用,这一作用与抑制端粒酶活性和诱导凋亡有关.     

miR-29通过调节抗凋亡蛋白Mcl-1表达参与胃癌细胞多药耐药的发生

目的研究miR-29在胃癌多药耐药细胞株[SGC7901/长春新碱(vincristine,VCR)及SGC7901/阿霉素(adriamycin,ADR)]及其亲本细胞(SGC7901)中的表达差异,探讨其在胃癌多药耐药发生中的作用及可能机制.方法 qRT-PCR检测miR-29在不同胃癌细胞系中的表达差异,通过细胞转染调控miR-29的表达水平,MTT法检测不同化疗药物对转染后胃癌细胞的IC50值变化;流式细胞术检测细胞凋亡及周期变化;并应用Western blot、双荧光素酶报告基因实验等方法探讨其可能机制.结果 SGC7901/VCR及SGC7901/ADR细胞中miR-29家族(miR-29a/b/c)相对表达量均显著低于其亲本细胞SGC7901(P0.05);MTT实验表明,下调miR-29表达后SGC7901细胞对不同化疗药物的IC50值显著增高(P0.05);而上调miR-29表达后SGC7901/VCR及SGC7901/ADR细胞对不同化疗药物的IC50值则显著降低(P0.05);流式细胞术检测结果显示,miR-29表达变化可显著改变5-氟尿嘧啶诱导胃癌细胞的凋亡水平(P0.05);Western blot、双荧光素酶报告基因实验等证实髓细胞白血病因子-1(myeloid cell leukemia-1,Mcl-1)是miR-29直接调控靶基因.结论 miR-29表达下调是人胃癌细胞多药耐药发生的机制之一,其可能与负性调控抗凋亡蛋白Mcl-1表达有关.     

曲古抑菌素A对胃癌细胞生长的抑制作用

目的: 研究组蛋白去乙酰化酶抑制剂-曲古抑菌素A(trichostatin A, TSA)对胃癌细胞系SGC-7901的生长抑制作用, 证实该作用是通过促使细胞凋亡而实现的.方法: 用不同浓度(0.2、0.4和0.8 mg/L)和不同作用时间(24、48和72 h)的TSA作用于SGC-7901细胞, 采用MTT法观察TSA对SGC-7901细胞增殖的抑制作用;通过流式细胞仪检测细胞周期和凋亡率的变化;通过透射电镜观察细胞超微结构的变化.结果: TSA可抑制胃癌SGC-7901细胞的生长,且这种作用呈时间和剂量依赖关系. 当TSA作用浓度分别为0.2、0.4和0.8 mg/L时, 与SGC-7901细胞均作用72 h, TSA对SGC-7901细胞生长的抑制率分别为25%±1.2%, 45%±1.4%和73%±1.7%, 各组均与TSA 0.2 mg/L组比较, 差异显著( P<0.05). 当0.8 mg/L TSA分别与SGC-7901细胞作用24、48和72 h, TSA对SGC-7901细胞生长的抑制率分别为21%±1.1%, 37%±2.0%和73%±1.7%, 各组均与TSA作用24 h组比较, 差异显著( P<0.05). TSA可延缓细胞周期, 具有明显的诱导细胞凋亡作用. 电镜下见细胞染色质凝聚成段片状, 细胞核固缩断裂, 核膜破裂, 细胞器及胞膜自溶, 凋亡小体形成.结论: TSA通过诱导细胞周期阻止和凋亡来抑制胃癌细胞系SGC-7901的生长, 且这种作用呈时间和剂量依赖性, 为TSA用于胃癌的治疗提供理论依据.     

胰岛素瘤的解剖分布特点分析

目的胰岛素瘤是最常见的胰腺神经内分泌肿瘤，因其临床表现多样，导致诊断困难。影像学诊断尤其是超声内镜(EUS)在胰岛素瘤的诊断中起着重要作用，拥有较高的敏感性和特异性。本研究拟通过明确胰岛素瘤的解剖分布特点，以期有助于提高影像学的诊断准确率和降低漏诊率，尤其是在教育和培训实践中对于EUS的学习者更具有指导价值。 方法回顾性分析解放军总医院第一医学中心病案资料数据库1993年1月至2019年11月经外科手术、病理确诊为胰岛素瘤的患者的临床资料，检索方法采取搜索术后病理诊断为"胰岛素瘤"的病例，通过查阅病例的方法，提取出胰岛素瘤的大小和解剖分布等数据，进一步分析其特点。 结果共检索到确诊为胰岛素瘤的患者116例，其中，男45例、女71例，年龄13～76岁，平均年龄(44.4±14.85)岁。胰岛素瘤单发110例(94.8%)、多发6例(5.2%)。位置分布：头颈部46例(39.7%)，单发45例、多发1例；体尾部68例(58.6%)，单发65例、多发3例；全胰腺多发2例(1.7%)。病变大小特点：最大径0.4～3.4 cm，平均大小(1.53±0.58)cm。≤1 cm 29例、>1 cm而≤1.5 cm41例、>1.5 cm而≤2.0 cm28例，≤3 cm 15例，>3 cm 3例。年龄与肿瘤的大小相关，≤44岁患者肿瘤平均大小为(1.36±0.51)cm、>44岁患者肿瘤平均大小为(1.70±0.60)cm，P<0.05。头颈部的肿瘤大于体尾部的肿瘤，头颈部肿瘤平均大小(1.66±0.63)cm，体尾部(1.42±0.52)cm，P<0.05。 结论胰岛素瘤在胰腺体尾部较头颈部更好发；绝大多数单发，但可以全胰腺多发；多数小于1.5 cm，肿瘤的大小与患者年龄和肿瘤的解剖分布相关。     

Pathogenesis of carcinoma of the papilla of Vater

Most adenomas and carcinomas of the small intestine and extrahepatic bile ducts arise in the region of the papilla of Vater. In familial adenomatous polyposis (FAP) it is the main location for carcinomas after proctocolectomy. In many cases symptoms due to stenosis lead to diagnosis at an early tumor stage. In about 80%, curative intended resection is possible. Operability is the most relevant prognostic factor. Most ampullary carcinomas resp. carcinomas of the papilla of Vater develop from adenomatous or flat dysplastic precursor lesions. They can be sited in the ampulloduodenal part of the papilla of Vater, which is lined by intestinal mucosa. They also can develop in deeper parts of the ampulla, which are lined by pancreaticobiliary duct mucosa. Intestinal-type adenocarcinoma and pancreaticobiliary-type adenocarcinoma represent the main histological types of ampullary carcinoma. Furthermore, there exist unusual types and undifferentiated carcinomas. Many carcinomas of intestinal type express the immunohistochemical marker profile of intestinal mucosa (keratin 7?, keratin 20+, MUC2+). Carcinomas of pancreaticobiliary type usually show the immunohistochemical profile of pancreaticobiliary duct mucosa (keratin 7+, keratin 20?, MUC2?). Even poorly differentiated carcinomas, as well as unusual histological types, may conserve the marker profile of the mucosa they developed from. These findings underline the concept of histogenetically different carcinomas of the papilla of Vater which develop either from intestinal- or from pancreaticobiliary-type mucosa of the papilla of Vater. Molecular alterations in ampullary carcinomas are similar to those of colorectal as well as pancreatic carcinomas, although they appear at different frequencies. In future studies, molecular alterations in ampullary carcinomas should be correlated closely with the different histologic tumor types. Consequently, the histologic classification should reflect the histogenesis of ampullary tumors from the two different types of papillary mucosa.     

Demonstration of the mechanism of action of biguanides

Summary Palmitic acid oxidation in rat diaphragm homogenate is depressed by biguanide concentrations that are still incapable of inhibiting oxidative phosphorylation. Glucose oxidation is not directly effected by the same biguanide concentrations: however, the inhibitory effect of palmitic acid on glucose oxidation is partly removed by biguanides. Inhibition of fatty acid oxidation, which accounts for most of the metabolic effects caused by these drugs, can be regarded as the fundamental mechanism of action of biguanides. There is some evidence suggesting that these drugs might interact with carnitine, thus preventing long-chain fatty acids from being transported across the mitochondrial membrane to the site of oxidation. Traduzione a cura degli AA.     

Lack of correlation of degree of villous atrophy with severity of clinical presentation of coeliac disease

BACKGROUND AND AIM: Both the clinical presentation and the degree of mucosal damage in coeliac disease vary greatly. In view of conflicting information as to whether the mode of presentation correlates with the degree of villous atrophy, we reviewed a large cohort of patients with coeliac disease. PATIENTS AND METHODS: We correlated mode of presentation (classical, diarrhoea predominant or atypical/silent) with histology of duodenal biopsies and examined their trends over time. RESULTS: The cohort consisted of 499 adults, mean age 44.1 years, 68% females. The majority had silent coeliac disease (56%) and total villous atrophy (65%). There was no correlation of mode of presentation with the degree of villous atrophy (p=0.25). Sixty-eight percent of females and 58% of males had a severe villous atrophy (p=0.052). There was a significant trend over time for a greater proportion of patients presenting as atypical/silent coeliac disease and having partial villous atrophy, though the majority still had total villous atrophy. CONCLUSIONS: Among our patients the degree of villous atrophy in duodenal biopsies did not correlate with the mode of presentation, indicating that factors other than the degree of villous atrophy must account for diarrhoea in coeliac disease.     

血吸虫童虫生长发育及其机制的研究进展

血吸虫童虫是宿主免疫系统攻击的重要靶标,包括皮肤型、肺型和肝门型童虫。宿主分子对童虫生长发育具有重要作用。童虫生长发育机制包括免疫调节、信号转导、性别发育及凋亡等。肌动蛋白、组织蛋白酶、烯醇化酶和葡萄糖基转移酶等分子为血吸虫童虫生长发育的重要分子。本文对血吸虫童虫生长发育及其机制的研究进展做一综述。     

氯硝柳胺悬浮剂的毒性评价

目的评价氯硝柳胺悬浮剂的毒性，为现场大规模应用灭螺提供依据。方法按照中华人民共和国国家标准GB 15670-1995《农药登记毒理学试验方法》和鱼类毒性试验方法进行。结果经口、经皮肤的LDso雌、雄性大鼠均>5 000 mg/kg，经呼吸道的LCso雌、雄性大鼠均>5 000mg/m3，该药经口、经皮肤、经呼吸道毒性均属微毒类药物；兔眼用药后，观察期内无不良反应，对眼无刺激性；皮肤用药后对皮肤无刺激性。与氯硝柳胺原药、氯硝柳胺乙醇胺盐原药和氯硝柳胺乙醇胺盐可湿性粉剂相比，氯硝柳胺悬浮剂对鱼急性毒性最低。结论氯硝柳胺悬浮剂属微毒类药物，对鱼的毒性低于其乙醇胺盐可湿性粉剂，适合于现场应用。     

124例耐多药结核分枝杆菌基因突变特征分析

目的对临床分离的耐多药结核分枝杆菌相关基因的突变特征进行分析。方法对124例耐多药结核分枝杆菌以及50株敏感株的耐药相关基因(包括异烟肼inh A、kat G、oxyR-ahp C间隔区以及利福平rpo B)进行序列测定,分析其基因突变情况。结果异烟肼耐药inh A基因突变率为14.5%;kat G基因突变率为70.2%(87/124),主要位于315位;oxyR-ahp C间隔区突变率为15.3%;inh A、kat G两种基因同时突变率75.0%,三种基因同时突变率为89.5%。利福平rpo B基因突变的检出率高达95.2%,突变主要发生在531、526、516位点。结论我省耐多药菌异烟肼耐药相关基因最常见突变为kat G 315、inh A C-T(-15)、axyR-ahp C间隔区(-10)C-T,利福平为rpo B531、526、516。结合MDR-TB耐药相关基因的特征分析,可以建立一种快速、准确、特异的适合于我省的检测结核菌耐多药性的新方法。     

Assessment of quality of life of parents of children with juvenile chronic arthritis

The aim of the study was to assess the quality of life (QOL) and the psychological status of parents of children with juvenile chronic arthritis (JCA). The QOL, anxiety and depression of the parents of 28 children with JCA were evaluated and compared to those of the parents of 28 healthy children. Mothers of JCA children and mothers of healthy children reported similar QOL. The reported anxiety and depression levels were similar for mothers and fathers in both groups. The parents of children with pauciarticular-type JCA reported lower QOL and higher levels of anxiety and depression than the parents of children with other types, namely polyarticular and systemic JCA. These findings may be explained by the fact that the pauciarticular patients had shorter disease duration and were less frequently seen in the outpatient clinic. The QOL of mothers of children with JCA was found to be slightly impaired in the group of children with pauciarticular JCA. Future larger studies are needed to confirm these results, as the number of subjects in the three groups was rather low. Received: 26 September 2001 / Accepted: 8 February 2002     

Numerical Simulation of the Effect of Rate of Change of Glucose on Measurement Error of Continuous Glucose Monitors

Background

A 5-day in-patient study designed to assess the accuracy of the FreeStyle Navigator® Continuous Glucose Monitoring System revealed that the level of accuracy of the continuous sensor measurements was dependent on the rate of glucose change. When the absolute rate of change was less than 1 mg•dl⁻¹•min⁻¹ (75% of the time), the median absolute relative difference (ARD) was 8.5%, with 85% of all points falling within the A zone of the Clarke error grid. When the absolute rate of change was greater than 2 mg•dl⁻¹•min⁻¹ (8% of the time), the median ARD was 17.5%, with 59% of all points falling within the Clarke A zone.

Method

Numerical simulations were performed to investigate effects of the rate of change of glucose on sensor measurement error. This approach enabled physiologically relevant distributions of glucose values to be reordered to explore the effect of different glucose rate-of-change distributions on apparent sensor accuracy.

Results

The physiological lag between blood and interstitial fluid glucose levels is sufficient to account for the observed difference in sensor accuracy between periods of stable glucose and periods of rapidly changing glucose.

Conclusions

The role of physiological lag on the apparent decrease in sensor accuracy at high glucose rates of change has implications for clinical study design, regulatory review of continuous glucose sensors, and development of performance standards for this new technology. This work demonstrates the difficulty in comparing accuracy measures between different clinical studies and highlights the need for studies to include both relevant glucose distributions and relevant glucose rate-of-change distributions.     

Study of constancy of hydrogen-consuming flora of human colon

The constancy of the hydrogen consuming flora of the human colon was studied in 15 healthy subjects via two measurements obtained 18 to 36 months apart. Hydrogen disappearance rate and the major products of H₂-consuming bacteria, methane and sulfide, were measured during incubation of fecal homogenates with excess hydrogen and sulfate. In 11/15, the hydrogen consumption rate and the predominant hydrogen-consuming pathway (methanogenesis, sulfate reduction, or neither) remained constant. However, major shifts in these pathways were observed in four subjects, with two losing and two gaining the ability to produce methane. Methanogenesis was associated with the highest hydrogen consumption rate. This study demonstrates that clinically unrecognizable, major alterations of the colonic flora occur in healthy subjects. Understanding of the factors responsible for these alterations might allow for therapeutic manipulation of the colonic flora.Supported in part by the Department of Veterans Affairs and NIDDKD RO1 DK 13309-25.