Biliary excretion mechanism of CPT-11 and its metabolites in humans: involvement of primary active transporters

After administration of CTP-11, a camptothecin derivative exhibiting a wide spectrum of antitumor activity, dose-limiting gastrointestinal toxicity with great interpatient variability is observed. Because the biliary excretion is a major elimination pathway for CPT-11 and its metabolites [an active metabolite, 7-ethyl-10-hydroxy-camptothecin (SN-38), and its glucuronide, SN38-Glu], several hypotheses for the toxicity involve biliary excretion. Here, we investigated whether primary active transport is involved in the biliary excretion of anionic forms of CPT-11 and its metabolites in humans using bile canalicular membrane vesicles (cMVs). Uptake of the carboxylate form of CPT-11 and the carboxylate and lactone forms of SN38-Glu by cMVs prepared from five human liver samples was ATP dependent. The concentration dependence of the ATP-dependent uptake of the carboxylate form of CPT-11 and SN38-Glu suggests the involvement of at least two saturable transport components, both with lower affinity and higher capacity than in rats. The ATP-dependent uptake of the carboxylate form of SN-38 showed a single saturable component but was detectable only in one human cMV sample. Both carboxylate and lactone forms of SN38-Glu uptake also showed a large intersample variability, although the variability was less than that observed for the carboxylate form of SN-38. On the other hand, the carboxylate form of CPT-11 exhibited much less variability. The carboxylate forms of SN38-Glu and SN-38 almost completely inhibited the ATP-dependent uptake of leukotriene C4, a well-known substrate of canalicular multispecific organic anion transporter, whereas the inhibition by the carboxylate form of CPT-11 was not as marked. Thus, multiple primary active transport systems are responsible for the biliary excretion of CPT-11 and its metabolites, and the major transport system for CPT-11 differs from that for the other two compounds. A greater degree of inter-cMV variability in the uptake of SN-38 and SN38-Glu may imply that interindividual variability in biliary excretion of these metabolites might contribute to interpatient variability in the toxicity caused by CPT-11.

Prediction of in vivo hepatic metabolic clearance of YM796 from in vitro data by use of human liver microsomes and recombinant P-450 isozymes

The metabolic rate of (S)-(-)-2,8-dimethyl-3-methylene-1-oxa-8-azaspiro [4,5] decane-L-tartarate monohydrate (YM796), an antidementia agent, was determined by use of 12 different human liver microsomal samples. The metabolism of YM796 was shown to consist of three components; one high-affinity (Km1 = 1.67 microM), one low-affinity (Km2 = 654 microM) and a nonsaturable component. Good correlations were observed between the individual CYP3A4 content in 12 different human liver microsomal samples and kinetic parameters such as CL(int, all), the high-affinity component clearance (Vmax1/Km1) and the low-affinity component clearance (Vmax2/Km2). Anti-human CYP3A4/5 antibodies inhibited the metabolism of YM796 at 1 microM by up to 75%. In addition, ketoconazole, an inhibitor of CYP3A4, inhibited YM796 metabolism by >90%. The metabolic clearance of YM796 in each of the 12 human liver microsomal samples was successfully predicted from the kinetic parameters obtained with the recombinant microsomes by taking into consideration the CYP3A4 content in each microsomal sample. Based on the CL(int, all) estimated from the in vitro experiments, the area under the plasma concentration-time curve after oral administration (AUC(oral)) of YM796 was also predicted by taking into account the hepatic blood flow rate (Qh), the unbound fraction of YM796 in human plasma (f(p)) and the fraction absorbed from the gut. In addition, AUC(oral) was determined in six healthy male volunteers. The predicted AUC(oral) was similar to the observed value in vivo, which suggests that the in vitro metabolism data obtained with human liver microsomes are useful for quantitatively predicting human liver metabolism in vivo and that recombinant microsomes are also available when the particular isozyme is almost completely responsible for the metabolism of the drug, the variation in P-450 content of human liver is known and the experimental conditions such as the amount of CYP reductase and cytochrome b5 are carefully optimized to mimic the activity found in native microsomes, as for YM796.

The formation of desethyl-piperacillin from piperacillin by human liver S9 in vitro

Piperacillin (PIPC) has been used as one of the most useful beta-lactam antibiotics over the past 10 years. The metabolism of PIPC has been thoroughly investigated and it has been recognized that PIPC gives few metabolites in laboratory species or humans. Recently, an active metabolite, desethyl-piperacillin (DEt-PIPC), was detected in human plasma and urine after PIPC administration. In the current study, human tissues were obtained from organ donors (n = 3) and subcellular fractions (S9) were prepared. The time course of metabolism by S9 mix from liver, kidney cortex, and kidney medulla was then determined using 0.5 mM PIPC. For comparative purposes, rat liver S9 were also prepared and incubated with PIPC under the same conditions. DEt-PIPC was formed by human liver S9 mix from all three specimens studied, with the rate varying approximately eightfold. No DEt-PIPC was detected in any of the incubations with rat liver S9 mix (n = 3) and kidney S9 mix (n = 3) prepared from either the cortex or medulla. In summary, these data suggest that the formation of the unique human metabolite, DEt-PIPC, can be predicted by in vitro studies with human tissues and that this metabolite is formed predominantly by the liver.

Prediction of in vivo drug metabolism in the human liver from in vitro metabolism data

As a new approach to predicting in vivo drug metabolism in humans, scaling of in vivo metabolic clearance from in vitro data obtained using human liver microsomes or hepatocytes is described in this review, based on the large number of literature data. Successful predictions were obtained for verapamil, loxtidine (lavoltidine), diazepam, lidocaine, phenacetin and some other compounds where CLint,in vitro is comparable with CLint,in vivo. On the other hand, for some metabolic reactions, differences in CLint,in vitro and CLint,in vivo greater than 5-fold were observed. The following factors are considered to be the cause of the differences: (1) metabolism in tissues other than liver, (2) incorrect assumption of rapid equilibrium of drugs between blood and hepatocytes, (3) presence of active transport through the sinusoidal membrane, and (4) interindividual variability. Furthermore, the possibility of predicting in vivo drug metabolic clearance from results obtained using a recombinant system of human P450 isozyme was described for a model compound, YM796, where the predicted metabolic clearances obtained from the recombinant system, taking account of the content of the P450 isozyme CYP3A4 in the human microsomes, were comparable with the observed clearances using human liver microsomes containing different amounts of CYP3A4. Even in the case where the first-pass metabolism exhibits nonlinearity, it appears to be possible to predict in vivo metabolic clearance from in vitro metabolic data.

Influence of prior freezing on arylamine acetylation by human liver preparations

Human liver tissue is an important resource for use in xenobiotic metabolism studies. Because of the scarcity of human livers, studies are frequently conducted with subcellular preparations from previously frozen material. The influence of prior freezing on arylamine acetylation with human S-9 was studied and differences were found between S-9 preparations derived from fresh liver and from stored frozen liver. Specifically, the capacity for formation of diacetylated benzidine was lost as a result of tissue freezing, and the rate and extent of monoacetylation appeared to be reduced also, though not as dramatically. These results demonstrate that freezing of human tissue prior to conducting metabolism studies with arylamines may alter metabolite profiles and indicate that, for reliable data, before using frozen human tissue in metabolism studies with arylamines one should check first for this possibility.

Lipopolysaccharide binding protein expression in primary human hepatocytes and HepG2 hepatoma cells

Lipopolysaccharide (LPS)-binding protein (LBP) is a normal plasma protein and an acute phase reactant important for host responses to Gram-negative bacteria and LPS. LBP forms high affinity complexes with LPS which bind to CD14, a monocyte surface protein, to initiate the release of inflammatory mediators. We found that human primary hepatocytes synthesize LBP and that the synthesis is up-regulated by interleukin (IL)-6. To examine this phenomenon in more detail, we evaluated the capacity of IL-6, IL-1, and tumor necrosis factor to induce LBP synthesis in HepG2 cells in the presence or absence of dexamethasone. IL-6 induced LBP synthesis. Dexamethasone, IL-1, and tumor necrosis factor had a synergistic effect when combined with IL-6, but demonstrated minimal effect independently. LBP biosynthesis was evaluated by immunoprecipitation of 35S-labeled LBP from HepG2 supernatants, measurement of steady-state LBP mRNA levels, and analysis of LBP-dependent LPS binding to CD14 positive cells. An 35S-labeled, 60-kDa protein was immunoprecipitated with anti-LBP antibody from IL-6-stimulated HepG2 cell supernatants. Northern blot analysis of cellular RNA revealed an increase in LBP mRNA in IL-6-stimulated cells. CD14 expressing cells bound fluoresceinated LPS in the presence of supernatants from HepG2 cells treated with IL-6. These data provide the first information about specific cytokine and dexamethasone regulation of LBP expression in HepG2 cells. LBP behaves like a Type 1 acute phase protein.

Effects of soya bean flakes and liquorice root extract on enzyme induction and toxicity in B6C3F1 mice

Both soya bean flakes (SBF) and liquorice root extract (LRE) have previously been reported to have anticarcinogenic properties, which have been thought to be related to an increased activity of specific enzymes responsible for the detoxification of chemical carcinogens. 30- and 90-day studies were conducted in male B6C3F1 mice to determine which, if any, of several detoxification enzymes are induced by SBF or LRE. Mice fed 8 and 25% LRE showed a variety of adverse clinical signs, poor weight gain and 30% mortality. Significant increases in liver:body weight ratios were observed in both the SBF and LRE groups. No significant treatment-related gross autopsy findings were observed in any of the SBF groups. A number of abnormalities were observed in the LRE groups, including lesions of the kidney, liver, spleen and thymus. Liver samples from the 90-day study were analysed for 7-ethoxycoumarin O-deethylase (7-ECOD), benzo[a]pyrene hydroxylase (BPH), superoxide dismutase (SOD), glutathione S-transferase (GST) and UDP-glucuronyl transferase (UDPGT) at 90 days, and at an interim 30-day autopsy. No treatment-related increases were observed for BPH or SOD. Both SBF and LRE induced modest increases in UDPGT activity. SBF induced modest increases in GST activity, but LRE decreased this activity. 7-ECOD activity was significantly increased by LRE and decreased by SBF. Samples from a 30-day study in which both LRE and SBF were administered at various dose levels were examined for UDPGT activity; all dose groups showed decreases in UDPGT activity relative to controls. The results suggest that both SBF and LRE may alter the activities of specific enzymes involved in the detoxification of chemical carcinogens; however, the combination of these two foodstuffs may not produce an additive effect in B6C3F1 mice.

Effects of estrogen replacement therapy on serum lipid values and angiographically defined coronary artery disease in postmenopausal women

To examine the effects of estrogen replacement on lipids and angiographically defined coronary artery disease (CAD) in postmenopausal women, lipid profiles were obtained in 90 consecutive postmenopausal women undergoing diagnostic coronary angiography. Eighteen women (20%) were receiving estrogen and 72 (80%) were not. CAD (defined as greater than or equal to 25% luminal diameter narrowing in a major coronary artery) was present in only 22% of women (4 of 18) receiving estrogen and in 68% (49 of 72) who were not (p less than 0.001), with an odds ratio of 0.13. Mean high-density lipoprotein (HDL) cholesterol level was significantly higher (63 +/- 6 vs 48 +/- 2; p less than 0.01) and mean total/HDL cholesterol ratio significantly lower in women receiving estrogen than in those who were not (4.2 +/- 0.5 vs 5.1 +/- 0.2; p less than 0.05). The other lipid values were similar in both groups. On multiple logistic regression analysis, absence of estrogen use was the most powerful independent predictor of the presence of CAD (p less than 0.001), with total/HDL cholesterol ratio as the only other variable selected (p less than 0.01). Thus, among 90 consecutive postmenopausal women undergoing diagnostic coronary angiography, estrogen replacement therapy was associated with an 87% reduction in the prevalence of CAD, and those receiving estrogen had a significantly higher mean HDL cholesterol level and lower mean total/HDL cholesterol ratio.

Usefulness of the total cholesterol to high-density lipoprotein cholesterol ratio in predicting angiographic coronary artery disease in women

To investigate the relation between lipids and angiographic coronary artery disease (CAD) in women, fasting lipid profiles were obtained on 108 women undergoing coronary angiography (group I). CAD, defined as greater than or equal to 25% luminal diameter narrowing in a major coronary artery, was present in 57 (53%). Neither serum total cholesterol nor triglyceride levels correlated with the presence of CAD. Mean total/high-density lipoprotein (HDL) cholesterol ratio was higher among women with than without CAD (5.5 +/- 0.3 vs 4.2 +/- 0.2, p less than 0.0001). Multiple regression analyses identified a higher total/HDL cholesterol ratio as the variable most predictive of the presence (p less than 0.001), extent (number of narrowed arteries) (p less than 0.0001), and severity (% maximum stenosis) (p less than 0.001) of CAD. Age and lack of estrogen use were also independently associated with the presence of CAD, age and low-density lipoprotein cholesterol level were additional indicators of extent, and age was the only other discriminator of severity of CAD. In 56 women with total cholesterol less than 200 mg/dl (group II), mean total/HDL cholesterol ratio was higher in women with (n = 24) than without CAD (4.3 +/- 0.2 vs 3.5 +/- 0.2, p = 0.01). Higher total/HDL cholesterol ratio was the variable most predictive of the presence of CAD (p = 0.01), and the lone variable associated with severity (p less than 0.001) after adjustment for other risk factors. Age was independently associated with presence and extent, and hypertension was also independently related to extent.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation of stenosis resolution pressure to long-term clinical outcome after successful percutaneous transluminal coronary angioplasty

Variables associated with a poor long-term prognosis after successful percutaneous transluminal coronary angioplasty (PTCA) include a short duration of symptoms before PTCA, unstable angina and the presence of thrombus at the PTCA site. These imply a component of transient or dynamic obstruction as opposed to a pure fixed obstruction. It is postulated that resolution pressure (i.e., the pressure at which complete balloon inflation occurs) may also correlate with prognosis after successful PTCA. In 173 consecutive patients undergoing successful, elective, single-lesion PTCA, 48 (28%) were found to have narrowings that resolved at less than or equal to 2 atm (group 1) and 125 (72%) were found to have narrowings resolved at greater than 2 atm (group 2). There were no significant differences in baseline, anatomic or procedural variables between the 2 groups, except that angiographic coronary dissection occurred in 17% of group 1 patients versus 40% of group 2 patients (p less than 0.007). During a mean follow-up of 12.0 +/- 6.1 months, the incidence of cardiac events (repeat PTCA, coronary artery bypass grafting or myocardial infarction) was 29% in group 1 versus 15% in group 2 (p less than 0.05). The overall incidence of angina was similar between the groups (25 vs 28%), but Canadian Cardiovascular Association class 4 angina occurred significantly more frequently in group 1 than group 2 (21 vs 8%) (p less than 0.04). These data suggest that a low resolution pressure is associated with a higher incidence of unstable angina and recurrent cardiac events during follow-up than higher resolution pressures.

Relation of serum lipoprotein cholesterol levels to presence and severity of angiographic coronary artery disease

To assess the relation of lipid levels to angiographic coronary artery disease (CAD), lipid profiles were obtained on 125 men and 72 women undergoing diagnostic coronary angiography. CAD, defined as greater than or equal to 25% diameter narrowing in a major coronary artery, was present in 106 men (85%) and 54 women (75%). Multiple regression analyses revealed that only high-density lipoprotein (HDL) cholesterol level in men, and age and total/HDL cholesterol ratio in women, were independently associated with the presence of CAD after adjustment for other risk factors. HDL cholesterol level and age were significantly correlated with both extent (number of diseased vessels) and severity (percent maximum stenosis) of CAD in men. In women, age was the only independent variable related to severity, whereas age and total/HDL cholesterol ratio were related to extent. Of 71 patients with total cholesterol less than 200 mg/dl, 79% had CAD. With multiple regression analyses, HDL cholesterol was the only variable independently related to the presence and severity of CAD in these patients after adjustment for age and gender; extent was significantly associated with age and male gender, and was unrelated to any of the lipid parameters. With use of multiple logistic and linear regression analyses of the group of 197 patients, HDL cholesterol was the most powerful independent variable associated with the presence and severity of CAD after adjustment for age and gender. HDL cholesterol was also an independent predictor of extent. Age was independently associated with each of the end points examined, and was the variable most significantly related to extent. These data add to the growing body of information demonstrating an important association between HDL and CAD.

Binding of anti-acetaldehyde IgG antibodies to hepatocytes with an acetaldehyde-phosphatidylethanolamine adduct on their surface

We have previously shown that antibodies raised against acetaldehyde adducts of protein cross-react with an acetaldehyde adduct of dioleoylphosphatidylethanolamine, N-ethyl-dioleoylphosphatidylethanolamine, when the latter is incorporated into hexagonal phase phospholipid micelles. In the present study we demonstrate that these same IgG antibodies cross-react with N-ethyl-dioleoylphosphatidylethanolamine when this adduct is incorporated into the surface of hepatocytes. Hapten-specific IgG antibodies were purified from the sera of rabbits sensitized to an albumin-acetaldehyde conjugate that had been reduced with sodium cyanoborohydride (N-ethyl-RSA). The N-ethyl-RSA was coupled to an Affi-Gel-10 column to affinity purify the IgG. Liposomes containing N-ethyl-dioleoylphosphatidylethanolamine were fused with isolated hepatocytes, the affinity purified primary IgG antibodies were added, then fluorescein-conjugated second antibodies were added, and antibody binding to hepatocytes was measured by flow cytometry. The fluorescence of these hepatocytes was significantly greater (p less than 0.01) than control hepatocytes prepared with (1) pre-immune primary IgG antibodies with fluorescein-conjugated second antibodies, (2) no primary antibody but with fluorescein-conjugated second antibodies, and (3) no fluorescein-conjugated second antibodies.

Structure-activity relationship for the intrinsic hepatotoxicity of dinitrotoluenes

The relation of various structural parameters to hepatotoxic potential was investigated by using six dinitrotoluene (DNT) isomers and isolated rat hepatocyte suspensions as the biological test system. DNT-induced hepatotoxicity was found to correlate with an inhibition of protein synthesis and an increase in lactate dehydrogenase (LDH) release but not with lipid peroxidation. With each isomer, protein synthesis inhibition was the most sensitive indicator of cytotoxicity. Regardless of the indicator, ortho- and para-substituted isomers were more hepatotoxic at the same concentration than meta-substituted isomers. High-performance liquid chromatograms (HPLC) on samples at 4 h revealed significant quantities of reduced metabolites in the medium. However, increased lipid peroxidation (formation of thiobarbituric acid reactants or evolution of ethane) in the cells was not consistently demonstrated. log EC50 for protein synthesis inhibition and log EC20 for LDH release were linearly correlated with the C atomic charge on the ring carbons bearing the nitro substituents by using molecular orbital (MNDO calculations) theory. The relation was used to predict the hepatotoxic potentials of untested nitrotoluenes, and the predictions were verified to a first approximation by using three trinitrotoluene isomers.

Stress initiated during isolation of rat renal proximal tubules limits in vitro survival

The effects of oxidative damage were assessed in rat proximal tubule fragments (isolated by collagenase perfusion) by monitoring lactate dehydrogenase release (LDH-R) to measure cell viability and thiobarbituric acid (TBA) reactive material to follow oxidative damage. Increasing the oxygen content in the incubation atmosphere from 10 to 95% significantly increased LDH-R and TBA reactants. Addition of butylated hydroxytoluene or deferoxamine (DF) to the medium prevented these changes, but ascorbic acid or mannitol had no positive effect. Lima bean trypsin inhibitor also reduced LDH leakage significantly when added to the medium, but not when added to the perfusion buffers. In contrast, adding DF to the perfusate during tubule isolation produced the most pronounced benefit; net LDH-R after 4 hr was about 10% in tubules prepared this way compared to 20% when DF was omitted. Basal oxygen consumption declined to approximately the same extent as LDH-R increased. Maintenance of nystatin-stimulated respiration, ATP/ADP, GSH content and total adenine nucleotides indicated good cell function. These results suggest that oxidative damage initiated during the tubule isolation procedure limits cell survival but this effect can be counteracted substantially by the addition of DF to the perfusion buffer.

Polymorphic N-acetylation of sulfamethazine and benzidine by human liver: implication for cancer risk?

Extensive epidemiologic studies have indicated a relationship between bladder cancer in populations exposed to arylamines and the slow phenotype for acetylation of arylamines (e.g., sulfamethazine) and aryl hydrazides (e.g., isoniazid). In human liver preparations, we have examined the association between the capability for sulfamethazine acetylation and that for the human bladder arylamine carcinogen, benzidine. By the usual criteria for polymorphic acetylation, we classified the 10 donor subjects as four rapid and six slow acetylators of sulfamethazine. Concurrent tests of benzidine acetylation in the same liver preparations yielded capacities to acetylate benzidine that were directly and significantly correlated with those for sulfamethazine acetylation (r = 0.672; P less than 0.05). We suggest that acetylation of these two compounds is directly related and knowledge of the human acetylator phenotype may be a useful indicator of possible risk for bladder cancer due to exposure of certain arylamines and, perhaps for other cancers in man.

Recurrent ischemia more than 1 year after successful percutaneous transluminal coronary angioplasty. An analysis of the extent and anatomic pattern of coronary disease

Of 1,181 consecutive patients who underwent successful percutaneous transluminal coronary angioplasty (PTCA) as an initial revascularization procedure and who had at least 1 year of asymptomatic follow-up, 66 (6%) underwent repeat angiography because of recurrent symptoms or evidence of exercise-induced ischemia. Patients who had revascularization procedures within 1 year of PTCA were not included in the analysis. Mean time to recurrent ischemia was 30.8 +/- 17.4 months (range 12-89 months). At follow-up, 47 patients had angina, 13 had atypical chest pain, two had acute myocardial infarction, and four had positive exercise tests without symptoms. No patient showed spontaneous regression in the extent of coronary artery disease (CAD). As compared with the extent of CAD immediately after PTCA, the extent of CAD at follow-up did not change in 26 patients (39%); it increased by one vessel in 30 (45%), by two vessels in seven (11%), and by three vessels in three (5%). The pattern of CAD seen at follow-up compared with that seen after PTCA was as follows: 18 patients (27%), no change; seven (11%), restenosis only; 30 (45%), progression of CAD at other sites only; and 11 (17%), a combination of restenosis and progression of CAD at other sites. The time to recurrence of ischemia was significantly different between those with restenosis only versus those with progression only (20.1 +/- 9.2 vs. 38.3 +/- 18.5 months) (p less than 0.009). Progression of CAD was equally distributed between dilated and nondilated vessels; however, when progression occurred in the PTCA vessel, it was significantly more likely to be distal to the PTCA site (p less than 0.008).

Delayed redistribution in thallium 201 SPECT myocardial perfusion studies

Stress 201Tl myocardial perfusion studies are useful in differentiating viable, reversibly ischemic from infarcted myocardium. A perfusion defect that shows redistribution 2 to 4 h after 201Tl injection is diagnostic of ischemia, while a fixed defect suggests infarction. However, occasional patients with a fixed defect at 4 h have redistribution at 24 h. This study evaluates the frequency and significance of this delayed redistribution with SPECT 201Tl. Patients with either no or incomplete redistribution at 4 h had repeat imaging 18 to 48 h later. Delayed redistribution was seen in 8/26 (31 percent). Four had incomplete and four had no redistribution at 4 h. Delayed redistribution with SPECT 201Tl is more common than generally appreciated, and we recommend delayed images in patients with fixed perfusion defects or incomplete redistribution at 4-h imaging, particularly in patients with previous infarctions for whom a revascularization procedure is being considered.

Intervention in acute myocardial infarction

The role of thrombolytic therapy in decreasing mortality and improving left ventricular function has been well established. The role of secondary PTCA is still being defined. Current data support a strategy of performing coronary angiography and elective PTCA only in patients with evidence of ischemia after thrombolytic therapy. Despite the trend away from routine early invasive therapy for acute myocardial infarction, accurate definition of coronary anatomy and assessment of left ventricular function will continue to be vital in the management of these patients and provide a continuing challenge for the cardiac radiographer.

Cervical cytology in a community laboratory

A retrospective analysis of the results of 27,801 cervical smears from one year in a community laboratory was undertaken. This represented 23,820 individual patients. Abnormalities were seen in 9.3% of patients. Three point seven percent of patients had benign abnormalities, 5.5% had cervical intraepithelial neoplasia and 0.1% had major abnormalities. The incidence of cervical epithelial abnormality was highest in the 15-34 age group but major abnormalities were seen most often in the 55+ age group. Human papillomavirus was more commonly seen in the youngest age group. The presence of inflammation was reported in 65% of the smears. Thirty percent of smears had no endocervical cells and 0.6% were grossly inadequate. Fifteen percent of patients had repeat smears and 3% of total smears were judged unnecessary. Forty two point six percent of patients less than 55 years of age in the laboratory population base had a smear but only 7.9% of those over 55.

Induction of unscheduled DNA synthesis in primary cultures of rat, mouse, hamster, monkey, and human hepatocytes

Variation in hepatic metabolism between species may be an important factor in the differences observed in chemical carcinogenesis. We examined 6 chemicals representative of 4 chemical classes in the in vitro hepatocyte DNA repair assay using cells isolated from the Fischer-344 rat, B6C3F1 mouse, Syrian golden hamster, cynomolgus monkey and from human liver. Hepatocytes were isolated by in situ or biopsy liver perfusion and incubated with [3H]-thymidine and the test chemical. Unscheduled DNA synthesis (UDS) was measured as net grains/nucleus (NG) by quantitative autoradiography. Qualitative and quantitative differences in UDS responses were observed for every chemical. Liver cultures isolated from the rat, mouse, hamster, human, and monkey and treated with aflatoxin B1 or dimethylnitrosamine all yielded dose-related increases in NG. Human, rat, and hamster hepatocyte cultures yielded positive responses following exposure to the aromatic amines 2-acetylaminofluorene, 4-aminobiphenyl, and benzidine, whereas cultures isolated from the monkey and mouse yielded less than 0 NG. Treatment with benzo[a]pyrene (BAP) produced strong positive responses in monkey and human hepatocyte cultures, weak positive responses in hamster cultures, and equivocal or negative responses in rat and mouse hepatocyte cultures. Hepatocyte function was assessed by measurement of DNA content, glutathione content, BAP hydroxylase activity, p-nitroanisole-O-demethylase activity, p-nitrophenol conjugation, and urea synthesis rates. The functional capabilities of isolated hamster, monkey, and human hepatocyte cultures do not appear to correlate with UDS responses observed for any compound; however, they indicate that the cultures were metabolically competent at the time of chemical exposure. These studies suggest that rat hepatocytes are a suitable model for human hepatocytes, whereas mouse and male monkey hepatocytes may be insensitive to aromatic amines.