Nicotine dose-concentration relationship and pregnancy outcomes in rat: biologic plausibility and implications for future research

Cigarette smoke (CS) exposure during pregnancy can lead to profound adverse effects on fetal development. Although CS contains several thousand chemicals, nicotine has been widely used as its surrogate as well as in its own right as a neuroteratogen. The justification for the route and dose of nicotine administration is largely based on inferential data suggesting that nicotine 6 mg/kg/day infused continuously via osmotic mini pumps (OMP) would mimic maternal CS exposure. We provide evidence that 6 mg/kg/day nicotine dose as commonly administered to pregnant rats leads to plasma nicotine concentrations that are 3-10-fold higher than those observed in moderate to heavy smokers and pregnant mothers, respectively. Furthermore, the cumulative daily nicotine dose exceeds by several hundred fold the amount consumed by human heavy smokers. Our study does not support the widely accepted notion that regardless of the nicotine dose, a linear nicotine dose-concentration relationship exists in a steady-state OMP model. We also show that total nicotine clearance increases with advancing pregnancy but no significant change is observed between the 2nd and 3rd trimester. Furthermore, nicotine infusion even at this extremely high dose has little effect on a number of maternal and fetal biologic variables and pregnancy outcome suggesting that CS constituents other than nicotine mediate the fetal growth restriction in infants born to smoking mothers. Our current study has major implications for translational research in developmental toxicology and pharmacotherapy using nicotine replacement treatment as an aid to cessation of cigarette smoking in pregnant mothers.     

Population characteristics and cigarette yield as determinants of smoke exposure

Relationships of population characteristics, smoking history, and cigarette yield with smoke exposure as measured by peripheral blood concentrations of thiocyanate, carboxyhemoglobin, nicotine and cotinine were sought in 170 male smokers. This population of smokers had significant elevations of serum thiocyanate, blood carboxyhemoglobin and plasma nicotine and cotinine concentrations as compared with an equal number of age- and sex-matched nonsmokers and these concentrations correlated significantly with past 24-hour cigarette consumption. Although the nicotine yield of the cigarette correlated significantly with plasma cotinine and marginally with plasma nicotine, the reduction in plasma nicotine and cotinine was not proportionate to the reduced yield of the cigarettes, suggesting that smokers partially compensate for the lower yields of their cigarettes. Blood levels of carboxyhemoglobin, nicotine and cotinine were also significantly associated with the weight of the subjects, presumably due to the relationship between weight and the volume of distribution. Univariate and multiple regression analyses provided evidence that coffee and alcohol consumption and years smoked also may be important determinants of smoke exposure.     

Changes in maternal and fetal nicotine distribution after maternal administration of monoclonal nicotine-specific antibody to rats

Vaccination against nicotine to elicit the production of nicotine-specific antibodies is a potential treatment for tobacco addiction which reduces nicotine distribution from serum to brain. Vaccination of pregnant rats also reduces the distribution of maternally-administered nicotine to the fetal brain. Whether this is due to maternal antibody reducing the transfer of nicotine from mother to fetus, or to fetal antibody altering the distribution of nicotine within the fetus, is not clear. In the current study, passive immunization of rats with the murine monoclonal nicotine-specific antibody Nic311 was used as a surrogate for vaccination because antibody transfer to the fetus was anticipated to be lower than with vaccination. Pregnant rats received nicotine from gestational day (GD) 18-20 as frequent i.v. boluses to simulate nicotine exposure from smoking. Nic311 was administered at doses of 30, 80 or 240 mg/kg on GD 19. Fetal serum Nic311 levels on GD 20 were <3% of concurrent maternal levels, but concentrations of up to 20 ug/ml in fetal serum were obtained owing to the very high levels in maternal serum. Accumulation of the chronically administered nicotine, measured on GD 20, was not changed by Nic311 treatment in either maternal or fetal brain. The early distribution of nicotine to maternal brain, measured 5 min after a dose, was markedly reduced by Nic311, while the early distribution of nicotine to whole fetus and fetal brain was not substantially altered. These data suggest that the limited transfer of Nic311 to the fetus in turn limits the ability of Nic311 to reduce nicotine distribution to the fetal brain.     

Physiologically based pharmacokinetic modeling of the pregnant rat: a multiroute exposure model for trichloroethylene and its metabolite, trichloroacetic acid

A physiologically based pharmacokinetic (PB-PK) model was developed to describe trichloroethylene (TCE) kinetics in the pregnant rat exposed to TCE by inhalation, by bolus gavage, or by oral ingestion in drinking water. The kinetics of trichloroacetic acid (TCA), an oxidative metabolite of TCE, were described by a classical one-compartment pharmacokinetic model. Among the required model parameters for TCE, partition coefficients (PCs) and kinetic constants for oxidation were determined by vial equilibration and gas uptake methods, respectively. The fat:blood PC was 33.9; the blood:air PC was 13.2; and the fetal tissue:fetal blood PC was 0.51. TCE was readily metabolized with high substrate affinity. In naive and pregnant female rats the maximum velocities of oxidative metabolism were 10.98 +/- 0.155 and 9.18 +/- 0.078 mg/kg/hr, while the estimated Michaelis constant for the two groups of rats was very low, 0.25 mg/liter. The first-order rate constant for oral absorption of TCE from water was 5.4 +/- 0.42/hr-1 in naive rats. With TCA, the volume of distribution (0.618 liter/kg) and the plasma elimination rate constant (0.045 +/- 0.0024/hour) were estimated both from intravenous dosing studies with TCA and from an inhalation study with TCE. By comparison of the two routes of administration, the stoichiometric yield of TCA from TCE was estimated to be 0.12 in pregnant rats. To develop a data base for testing the fidelity of the PB-PK model, inhalation and bolus gavage exposures were conducted from Day 3 to Day 21 of pregnancy and a drinking water exposure from Day 3 to Day 22 of pregnancy. Inhalation exposures with TCE vapor were 4 hr/day at 618 ppm. The TCE concentration in drinking water was 350 micrograms/ml and the gavaged rats received single daily doses of 2.3 mg TCE/kg. Time varying physiological parameters for compartment volumes and blood flows during pregnancy were obtained from the published literature. Using the kinetic parameters determined by experimentation, TCE concentrations in maternal and fetal blood and TCA concentrations in maternal and fetal plasma were predicted from the PB-PK model by computer simulation and compared favorably with limited data obtained at restricted time points during pregnancy for all three routes of exposure. On the basis of the PB-PK model, fetal exposure to TCE, as area-under-the-curve, ranged from 67 to 76% of maternal exposure. For TCA the fetal exposure was 63 to 64% of the maternal exposure. The fetus is clearly at risk both to parent TCE and its TCA metabolite.(ABSTRACT TRUNCATED AT 400 WORDS)     

Vitamin C concentration in plasma and leucocytes of men related to age and smoking habit.

Morning plasma and leucocyte vitamin C concentrations were measured in 178 healthy men aged 17-68 years. In the youngest age group (17-29 years), smokers had significantly lower plasma (P less than 0.01) and leucocyte (P less than 0.001) vitamin C levels than non-smokers. With advancing age plasma and leucocyte vitamin C levels of non-smokers appeared to decline. The lower levels in younger smokers did not significantly alter in the later decades. There was no significant difference between the plasma or leucocyte vitamin C levels of smokers and non-smokers in the decade 60-69 years.     

A 12-month, randomized, controlled study to evaluate exposure and cardiovascular risk factors in adult smokers switching from conventional cigarettes to a second-generation electrically heated cigarette smoking system

This randomized, controlled, forced-switching, open-label, parallel-group study in 97 adult male and female smokers of conventional cigarettes evaluated biomarkers of tobacco smoke exposure and cardiovascular risk factors. After baseline measurements, smokers were either switched to a second-generation electrically heated cigarette smoking system (EHCSS) or continued smoking conventional cigarettes for 12 months. Biomarkers of exposure and cardiovascular risk factors were measured at 0.5, 1, 2, 3, 4, 5, 6, 9, and 12 months. There was a rapid and sustained reduction in all biomarkers of exposure after switching to the EHCSS, with statistically significant reductions from baseline in nicotine equivalents (-18%), plasma cotinine (-16%), total 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (-73%), total 1-hydroxypyrene (-53%), urine mutagenicity (-52%), 4-aminobiphenyl hemoglobin adducts (-43%), carboxyhemoglobin AUC7-23 h (-80%), and 3-hydroxypropylmercapturic acid (-35%). These reductions in exposure in the EHCSS group were associated with statistically significant and pathophysiologically favorable changes in several cardiovascular risk factors, including white blood cell count (-0.78 x 10(3)/microL), hemoglobin (-0.16 g/dL), hematocrit (-0.44%), urine 11-dehydrothromboxane B2 (-374 ng/24 h), and high-density lipoprotein cholesterol (+5 mg/dL).     

Effects of nicotine-specific antibodies, Nic311 and Nic-IgG, on the transfer of nicotine across the human placenta

The adverse effects of smoking during pregnancy on fetal development are, in part, due to nicotine. These effects may be due to the actions of nicotine in fetal circulation or on placental functions. In pregnant rats, vaccination with a nicotine immunogen reduces the transfer of nicotine from the maternal to fetal circulation. However, extrapolation of these results to pregnant women might not be valid due to the well-recognized differences between human and rat placentas. In the current investigation, the effects of nicotine-specific antibodies on the transfer of nicotine from the maternal to fetal circuit of the dually perfused human placental lobule were determined. Two types of nicotine-specific antibodies were investigated; nicotine-specific mouse monoclonal antibody (Nic311, K(d) for nicotine 60nM) and IgG from rabbits vaccinated with a nicotine immunogen (Nic-IgG, K(d) 1.6nM). Transfer of the antibodies from maternal to fetal circuits was negligible. Both rabbit Nic-IgG and, to a lesser extent, mouse monoclonal Nic311 significantly reduced nicotine transfer from the maternal to fetal circuit as well as the retention of the drug by placental tissue. These effects were mediated by a substantial increase in the protein binding of nicotine and a reduction in the unbound nicotine concentration. Therefore, the data cited in this report suggest that the use of nicotine-specific antibodies might reduce fetal exposure to the drug, and that antibody affinity for nicotine is a key determinant of the extent of nicotine transfer.     

The effect of maternally inhaled trichloroethylene,perchloroethylene, methyl chloroform,and methylene chloride on embryonal and fetal development in mice and rats

These studies evaluated the effects of trichloroethylene, perchloroethylene (tetrachloroethylene), methyl chloroform (1,1,1-trichloroethane) and methylene chloride (dichloromethane) on mouse and rat embryonal and fetal development at a concentration two times the maximum allowable excursion limit for human industrial exposure as defined by ACGIH, 1973 (300, 300, 875, 1250 ppm, respectively). Groups of pregnant Sprague-Dawley rats and Swiss Webster mice were exposed to each solvent 7 hr daily on days 6–15 of gestation. None of these solvents caused significant maternal, embryonal or fetal toxicity and none was teratogenic in either species of animal at the concentrations studied. Elevated carboxyhemoglobin content was observed in mice and rats exposed to methylene chloride.     

桂利嗪、尼卡地平对人成纤维细胞胶原合成的影响

为探讨成纤维细胞中Ｃａ２＋的主要来源及其对胶原合成的作用，观察了钙通道阻滞剂桂利嗪和具有胞内Ｃａ２＋拮抗作用的尼卡地平对３Ｈ－Ｌ－脯氨酸参入人成纤维细胞的影响。桂利嗪抑制胶原合成的作用呈浓度依赖性，ＩＤ５０为４１．２μｍｏｌ·Ｌ－１。尼卡地平作用２４ｈ表现为浓度依赖性抑制作用，但在３６，４８和６０ｈ低浓度组（１０，２０μｍｏｌ·Ｌ－１）外，高浓度组（４０，８０μｍｏｌ·Ｌ－１）的抑制作用降低。     

Exposure to low doses of 137cesium and nicotine during postnatal development modifies anxiety levels,learning, and spatial memory performance in mice

Radiation therapy is a major cause of long-term complications observed in survivors of pediatric brain tumors. However, the effects of low-doses of ionizing radiation (IR) to the brain are less studied. On the other hand, tobacco is one of the most heavily abused drugs in the world. Tobacco is not only a health concern for adults. It has also shown to exert deleterious effects on fetuses, newborns, children and adolescents. Exposure to nicotine (Nic) from smoking may potentiate the toxic effects induced by IR on brain development. In this study, we evaluated in mice the cognitive effects of concomitant exposure to low doses of internal radiation (¹³⁷Cs) and Nic during neonatal brain development. On postnatal day 10 (PND10), two groups of C57BL/6J mice were subcutaneously exposed to 137-Cesium (¹³⁷Cs) (4000 and 8000 Bq/kg) and/or Nic (100 μg/ml). At the age of two months, neurobehavior of mice was assessed. Results showed that exposure to IR-alone or in combination with Nic-increased the anxiety-like of the animals without changing the activity levels. Moreover, exposure to IR impaired learning and spatial memory. However, Nic administration was able to reverse this effect, but only at the low dose of ¹³⁷Cs     

Prenatal exposure to escitalopram and/or stress in rats

Rationale

A rigorously investigated model of stress and antidepressant administration during pregnancy is needed to evaluate possible effects on the mother.

Objective

The objective of this study was to develop a model of clinically relevant prenatal exposure to an antidepressant and stress during pregnancy to evaluate the effects on maternal care behavior.

Results

Female rats implanted with 28-day osmotic minipumps delivering the SSRI escitalopram throughout pregnancy had serum escitalopram concentrations in a clinically observed range (17–65 ng/ml). A separate cohort of pregnant females exposed to a chronic unpredictable mild stress paradigm on gestational days 10–20 showed elevated baseline (305 ng/ml), and acute stress-induced (463 ng/ml), plasma corticosterone concentrations compared to unstressed controls (109 ng/ml). A final cohort of pregnant dams were exposed to saline (control), escitalopram, stress, or stress and escitalopram to determine the effects on maternal care. Maternal behavior was continuously monitored over the first 10 days after parturition. A reduction of 35 % in maternal contact and 11 % in nursing behavior was observed due to stress during the light cycle. Licking and grooming behavior was unaffected by stress or drug exposure in either the light or dark cycle.

Conclusions

These data indicate that: (1) clinically relevant antidepressant treatment during human pregnancy can be modeled in rats using escitalopram; (2) chronic mild stress can be delivered in a manner that does not compromise fetal viability; and (3) neither of these prenatal treatments substantially altered maternal care post parturition.     

Estimating the hazards of less hazardous cigarettes. II. Study of cigarette yields of nicotine, carbon monoxide, and hydrogen cyanide in relation to levels of cotinine, carboxyhemoglobin, and thiocyanate in smokers

Yields of chemical constituents such as tar, nicotine, CO, and HCN defined by smoking machines are commonly assumed to provide a reasonable indication of the relative hazard associated with smoking a given brand of cigarette. Results reported here suggest that this assumption should be carefully reexamined. A total of 240 subjects, representing a wide range of smoking and brand characteristics, were recruited for an investigation of possible relations between brand yields and exposure (levels of carboxyhemoglobin, breath CO, plasma cotinine, plasma thiocyanate, and saliva thiocyanate). Exposure was highly correlated with consumption (number of cigarettes per day), but their was no correlation between any estimate of exposure and brand yield when level of consumption was held constant. In addition, a comparison of levels of carboxyhemoglobin and plasma thiocyanate for 16 smokers of "low-hazard" and 15 smokers of "high-hazard" cigarette brands revealed little difference between the two groups, even though average cigarette yields differed as much as 2- to 3-fold. A possible explanation for the results may be that current values for average puff volume, duration, and interval differ significantly from those used in programming smoking machines, particularly in the case of brands with low nicotine delivery.     

Gender, age, smoking behaviour and plasma clozapine concentrations in 193 Chinese inpatients with schizophrenia

AIM: To study the relationship between age, gender, cigarette smoking and plasma concentrations of clozapine (CLZ) and its metabolite, norclozapine (NCLZ) in Chinese patients with schizophrenia. METHODS: Data from a therapeutic drug monitoring programme were analysed retrospectively. One hundred and ninety-three Chinese inpatients with schizophrenia were assessed using clinical data forms. Steady-state plasma concentrations of CLZ and NCLZ were assayed using high-performance liquid chromatography. Comparisons of dosage and plasma CLZ concentrations were undertaken between males (n = 116) and females (n = 77), younger (40 years, n = 111) and current male smokers (n = 50) and nonsmokers (n = 66). RESULTS: (i) Plasma CLZ concentrations demonstrated large interindividual variability, up to eightfold at a given dose; (ii) there were significant effects of gender on plasma CLZ concentrations (relative to dose per kg of body weight) with female patients having significantly higher concentrations than males (30.09 +/- 24.86 vs. 19.87 +/- 3.55 ng ml(-1) mg(-1) day(-1) kg(-1); P < 0.001); (iii) there were no significant differences in plasma CLZ concentrations between those patients 40 years; and (iv) there were no significant differences in plasma CLZ concentrations between male smokers and nonsmokers, despite the CLZ dosage for smokers being significantly higher. CONCLUSIONS: Plasma CLZ concentrations vary up to eightfold in Chinese patients. Among the patient-related factors investigated, only gender was significant in affecting CLZ concentrations in Chinese patients with schizophrenia, with female patients having higher levels.     

Changes of ghrelin and leptin levels in plasma by cigarette smoke in rats

Cigarettes smoke (CS) limits food intake and body weight increase. Ghrelin and leptin are hormones regulating appetite and energy balance. While ghrelin increases food intake and causes a positive energy balance, leptin decreases food intake and enhances a negative energy balance. To investigate the possible role of ghrelin and leptin regarding the negative energy balance caused by CS, 10-week old male Wistar rats (n = 10) were exposed to CS from 30 cigarettes twice a day for 5 days a week for four weeks. In the smoking group, food intake and body weight gain were less than those in the non-smoking group (n = 10) during the entire CS exposure. In the smoking group, the plasma levels of acyl ghrelin were significantly higher (75.9 ± 5.1 fmol/ml versus 46.5 ± 3.3 fmol/ml, p < 0.01), while those of leptin were significantly lower than those in the non-smoking group (434.9 ± 41.1 ng/ml versus 744.0 ± 45.4 ng/ml, p < 0.01) after the final CS exposure. However, the plasma des-acyl ghrelin levels were not affected by CS exposure. These results suggested that acyl ghrelin and leptin levels in plasma may change to compensate for the negative energy balance by CS.     

The effect of passive and active exposure to tobacco smoke on lipid profile parameters and the activity of certain membrane enzymes in the blood of women in the first trimester of pregnancy

The effect of tobacco smoke on lipid peroxidation, the lipid profile and membrane-bound enzymatic activity in the first trimester of pregnancy was investigated.In the plasma of women with active exposure to tobacco smoke, we have found increased lipid peroxidation and higher total concentrations of cholesterol, triglycerides and low-density lipoproteins in the blood, as well as a decreased concentration of high-density lipoproteins. A higher concentration of low-density lipoproteins and a lower concentration of high-density lipoproteins were also found in the plasma of passive smokers. In contrast, women who smoked before pregnancy had only a higher low-density lipoprotein concentration. In the group of active and passive smoking women, lower arylesterase and phosphotriesterase activities of paraoxonase were observed, while the lactonase activity of paraoxonase decreased only in the group of active smoking women. In women with active exposure to tobacco smoke, a higher activity level of alanine aminopeptidase and γ-glutamyltransferase in the plasma was found.It is important to monitor the lipid profile during pregnancy, especially when exposure to tobacco smoke occurs.     

Long‐term exposure to extremely low‐dose of nicotine and 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK) induce non‐malignant breast epithelial cell transformation through activation of the a9‐nicotinic acetylcholine receptor‐mediated signaling pathway

Breast cancer (BC) is the most common cancer affecting women worldwide and has been associated with active tobacco smoking. Low levels of nicotine (Nic) and 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK), have been detected in cases of second‐hand smoke (SHS). However, the correlation between SHS and BC risk remains controversial. In this study, we investigated whether the physiological SHS achievable dose of Nic and tobacco specific nitrosamine, NNK act together to induce breast carcinogenesis using an in vitro breast cell carcinogenesis model. Immortalized non‐tumorigenic breast epithelial cell line, HBL‐100 used for a time‐course assay, was exposed to very low levels of either Nic or NNK, or both. The time‐course assay consisted of 23 cycles of nitrosamines treatment. In each cycle, HBL‐100 cells were exposed to 1pM of Nic and/or 100 femtM of NNK for 48 hours. Cells were passaged every 3 days and harvested after 10, 15, and 23 cycles. Our results demonstrated that the tumorigenicity of HBL‐100, defined by soft agar colony forming, proliferation, migration and invasion abilities, was enhanced by co‐exposure to physiologically SHS achievable doses of Nic and NNK. In addition, α9‐nAChR signaling activation, which plays an important role in cellular proliferation and cell survival, was also observed. Importantly, an increase in stemness properties including the prevalence of CD44+/CD24? cells, increase Nanog expression and mammosphere‐forming ability were also observed. Our results indicate that chronic and long term exposure to environmental tobacco smoke, may induce breast cell carcinogenesis even at extremely low doses.     

Carbon disulphide intrauterine sensitization

This study was designed to evaluate the effect of carbon disulphide (CS2) exposure during pregnancy in two subsequent generations. Albino rats (F1), which had been prenatally exposed by maternal inhalation to teratogenic (200 and 100 mg m-3) and subteratogenic (10 and 0.03 mg m-3) concentrations of CS2, were reared until maturity and mated to produce an F2 generation. During pregnancy the F1 females were again subjected to CS2 exposure at the same concentrations as the F0 females throughout gestation. Pre- and postnatal development of F1 and F2 generations, as well as the corresponding maternal effects, were studied. Embryonic lethality, weight, congenital malformations, indices of lipid and energy metabolism, DNA and some liver drug metabolizing enzymes in maternal and fetal tissues were studied at term. Postnatal viability, physical and behavioral development, and hexobarbital sleeping time of the progeny were evaluated. Comparisons of CS2 effect on F1 and F2 generations were performed. A marked increase in CS2-induced teratogenicity was found in the F2 generation, together with retarded development of MFO system and increased postnatal behavioral effects. The results point to intrauterine sensitization of progeny to CS2. This effect is discussed in the light of possible interference of the agent with the hormonal programming of intrauterine development.