Tobacco smoke inhalation studies in rats

Heterogeneous deposition of regular and mentholated little cigar smoke in the lungs of Sprague-Dawley rats

BACKGROUND

Quantifying the dose and distribution of tobacco smoke in the respiratory system is critical for understanding its toxicity, addiction potential, and health impacts. Epidemiologic studies indicate that the incidence of lung tumors varies across different lung regions, suggesting there may be a heterogeneous deposition of smoke particles leading to greater health risks in specific regions. Despite this, few studies have examined the lobar spatial distribution of inhaled particles from tobacco smoke. This gap in knowledge, coupled with the growing popularity of little cigars among youth, underscores the need for additional research with little cigars.

RESULTS

In our study, we analyzed the lobar deposition in rat lungs of smoke particles from combusted regular and mentholated Swisher Sweets little cigars. Twelve-week-old male and female Sprague-Dawley rats were exposed to smoke particles at a concentration of 84 ± 5 mg/m3 for 2 h, after which individual lung lobes were examined. We utilized Inductively Coupled Plasma Mass Spectrometry to quantify lobar chromium concentrations, serving as a smoke particle tracer. Our findings demonstrated an overall higher particle deposition from regular little cigars than from the mentholated ones. Higher particle deposition fraction was observed in the left and caudal lobes than other lobes. We also observed sex-based differences in the normalized deposition fractions among lobes. Animal study results were compared with the multi-path particle dosimetry (MPPD) model predictions, which showed that the model overestimated particle deposition in certain lung regions.

CONCLUSIONS

Our findings revealed that the particle deposition varied between different little cigar products. The results demonstrated a heterogenous deposition pattern, with higher particle deposition observed in the left and caudal lobes, especially with the mentholated little cigars. Additionally, we identified disparities between our measurements and the MPPD model. This discrepancy highlights the need to enhance the accuracy of models before extrapolating animal study results to human lung deposition. Overall, our study provides valuable insights for estimating the dose of little cigars during smoking for toxicity research.

Measurement of Respiration and Respiratory Responses During Inhalation Exposures

This report reviews approaches for making measurements of the respiration of subjects during inhalation exposures. Respiration is measured to quantitate the volume of exposure material inhaled, to evaluate the normalcy and steadiness of respiration during exposure, to relate breathing pattern to deposition or uptake of inhaled materials, to detect physiological responses to inhaled materials, and to monitor respiration during controlled breathing. A small number of basic devices are commonly used during exposures, including nonrebreathing valves, pneumotachographs, spirometers, and plethysmographs. Less frequently used devices adaptable for use during exposures include hot wire anemometers, respiratory-inductive plethysmographs, and impedance pneumographs. These devices, some of their potential uses, and their advantages and disadvantages are described and useful references are given. Several useful combinations of respiratory measurement devices are suggested for low-volume, bag-to-bag, and immersion exposure systems.

Preventing negative effects of smoking on microarterial anastomosis

Although microsurgery has rapid expanded, problems related to microarterial anastomosis continue. Cigarette smoking is one of the major risks for anastomosis by increasing platelet adhesion, and its effects on endothelial cells. Aim of this article is to study the negative effects of cigarettes on microarterial anastomosis line, and to investigate the protective effects of recombinant human erythropoietin (rHuEPO).Ninety-six Sprague-Dawley male rats were divided into 3 groups: group 1 was the control. Rats in groups 2 and 3 were exposed to cigarette smoke starting 21 days prior to surgery for 3 times a day. In group 3, additional 150 IU/kg rHuEPO was given via subcutaneously every 48 hours after microvascular anastomosis, femoral arterial samples, and blood samples were taken for assessment at 1st, 3rd, 5th, and 7th day. Intimae/media ratios were calculated for morphologic analyses.On morphologic analysis of femoral arteries there were statistically significant differences for all 3 groups at 1st, 3rd, 5th, and 7th days (P < 0, 05). The group that made differences was group 2, according to one-way analysis of variance within 3 groups in all days.Smoking decreases endothelial cells healing and causes more thromboses. rHuEPO can prevent these negative effects of smoking.

Effects of pentoxyfilline and heparin on reperfusion injury island skin flaps in rats exposed to tobacco

BACKGROUND

Ischemia-reperfusion injury is believed to be a major cause of transferred skin flap failure. Cigarette smoking is known to be associated with endogenous antioxidant depletion, hypercoagulability, and cutaneous vasoconstriction. This investigation was carried out to study possible effects of pentoxyfilline or heparin on rat skin reperfusion injury under tobacco exposure.

MATERIALS AND METHODS

Thirty-six rats were randomized into two major groups: 18 were exposed to cigarette smoke during a 4 wk period prior to surgery; the remaining 18 underwent a sham smoking procedure. Each group was further divided into three equal subgroups: heparin, pentoxyfilline, and saline solution. One identical skin flap was raised in each animal. The vasculature of the flap was clamped for 3 h and reperfused for 5 min. A venous blood sample was obtained from the flap after reperfusion for serum malondialdehyde (MDA) and myeloperoxidase (MPO) analysis. Flap survival was assessed 7 d after the procedure.

RESULTS

The lipid peroxidation levels and flap necrosis were significantly higher in the cigarette-smoking group skin flaps. There was also a decrease of MPO activity in this group compared with the non-smoking group. Heparin-treated rats had significantly lower MDA levels and showed the most viable percent area among smoking rats.

CONCLUSIONS

These data suggest that heparin had a significant beneficial effect both on flap survival and on the lipid peroxidation reduction after smoke exposure in the rat axial-pattern skin flap subjected to ischemia and reperfusion injury. Pharmacologic therapy may represent an alternative way to counteract tobacco effects in flap surgery in emergency situations.

Subchronic inhalation by rats of mainstream smoke from a cigarette that primarily heats tobacco compared to a cigarette that burns tobacco

A subchronic, nose-only inhalation study comparing the potential biological activity of mainstream smoke from a cigarette that primarily heats tobacco (Eclipse) to mainstream smoke from a 1R4F reference cigarette was conducted using Sprague-Dawley rats of each gender. Smoke exposures were for 1 h/day, 5 days/wk for 13 wk, at concentrations of 0, 0.16, 0.32, or 0.64 mg wet total particulate matter (WTPM)/L air. Smoke was generated at the Federal Trade Commission standard of a 2-s puff of 35 ml, taken once per minute. Clinical signs, body and organ weights, clinical chemistry, hematology, carboxyhemoglobin, serum nicotine, plethysmography, gross pathology, and histopathology were determined. Plethysmography indicated that respiratory rate was decreased at all concentrations of 1R4F smoke, but only at the high concentration of Eclipse smoke. Tidal volume was depressed and minute volume was lower for all smoke-exposed rats. Rats exposed to Eclipse smoke inhaled more smoke at the low and mid-concentration exposures than rats exposed to equivalent concentrations 1R4F smoke. Carboxyhemoglobin and serum nicotine were directly related to the exposure concentrations of carbon monoxide (CO) and nicotine in an exposure-dependent manner. Body weights were slightly lower in smoke-exposed rats, while no treatment-related effects were seen in clinical signs, clinical chemistry, hematology, or gross changes at necropsy. The only treatment-related effect seen in organ weights was an increase in heart weight in females in the Eclipse high-concentration exposure group, attributed to higher CO in the Eclipse exposure atmosphere. Higher CO resulted from the lower dilution of Eclipse smoke required to maintain WTPM concentrations equal to those of the 1R4F smoke, and not from a higher CO yield from Eclipse cigarettes. Nasal epithelial hyperplasia and ventral laryngeal squamous metaplasia were noted after exposure to either the 1R4F or Eclipse smoke. The degree of change was less in Eclipse smoke-exposed rats. Lung macrophages were increased to a similar extent in the Eclipse and 1R4F smoke-exposed groups. Brown/gold pigmented macrophages were detected in the lungs of rats exposed to 1R4F smoke, but not those exposed to Eclipse smoke. Subsets of rats from each group were maintained for an additional 13 wk without smoke exposures. Most of the changes noted at the end of the smoke exposures had disappeared, while those that remained were regressing toward normal. Evaluation of these findings indicated the overall biological activity of Eclipse smoke was less than 1R4F smoke at comparable exposure concentrations.

A review of chronic inhalation studies with mainstream cigarette smoke in rats and mice

In this paper, I review the results of a representative selection of chronic inhalation studies with rats and mice exposed to mainstream cigarette smoke and describe the inhalation exposures and the histopathological changes reported by various authors. Many of the studies used nose-only exposure systems, whereas others simply used large whole-body chambers. Smoke-induced epithelial hypertrophy, hyperplasia, and squamous metaplasia were reported in the conducting airways in most of the studies, along with increased numbers of intra-alveolar macrophages that were occasionally associated with alveolar metaplasia. Lung adenomas and adenocarcinomas were reported in only a few of the studies. No statistically significant increase in the incidence of malignant lung tumors was seen in either species as a result of smoke exposure, a finding that does not agree with the results of epidemiological studies in humans. Possible reasons for this lack of correlation are given.

Ninety-day inhalation study in rats, comparing smoke from cigarettes that heat tobacco with those that burn tobacco

Eight groups of 30 male and 30 female rats were exposed 1 hr per day, 5 days per week for 13 weeks, to smoke from reference (tobacco burned) or test (tobacco only heated) cigarettes, at nicotine concentrations of 5, 15, or 30 micrograms/liter of air. Similar smoke concentrations of wet total particulate matter and carbon monoxide were produced in each of the test/reference comparisons. There was a pronounced depression of minute ventilation of animals in the reference groups, but not in the test animals. Blood carboxyhemoglobin concentrations were similar in animals exposed to smoke from test and reference cigarettes. Plasma concentrations of nicotine and cotinine in the test groups were higher than in the reference groups. There were no differences between the smoke-exposed groups in terms of body weight or feed consumption. At necropsy, an increase in heart weight was noted in both high exposure groups. There were notable differences in histopathology, with fewer and less-pronounced changes in the test groups than in the reference groups. Many of the histopathological responses induced in the reference groups were absent in the test groups. Overall, the study demonstrated a substantial reduction in the biological activity of smoke from the test cigarette when compared with the reference.

The effect of oxygen toxicity and cigarette smoking on the binding of heterologous antibodies to alveolar basement membrane in the rat

It has been suspected that pulmonary lesions of the Goodpasture type may be the result of circulating antibodies to alveolar basement membrane and that environmental factors such as cigarette smoke may influence antibody binding. Carefully designed experiments in this study have shown that exposure to cigarette smoke for 3 weeks or 100% oxygen for 65 h did not influence the binding of heterologous antibodies to alveolar basement membrane in Wistar rats, nor did these regimes increase any pathological changes associated with the antibody binding as detected by light microscopy. The results which are at variance with other reported findings are discussed with reference to reported animal models of antibody mediated pneumonitis and Goodpasture's syndrome in man.

Tobacco smoke inhalation studies: a dosimetric comparison of different cigarette types

As part of a long-term inhalation bioassay study of cigarette smoke in rats, a detailed dosimetric comparison of three groups of rats exposed to smoke from different cigarette types was performed. Groups of 20 female F-344 rats were exposed, in Maddox-ORNL smoking machines, to 14C-dotriacontane-labeled smoke from three types of research cigarettes: high tar-low nicotine, low tar-high nicotine, and high tar-high nicotine. Analyses of lung tissues revealed similar deposition amounts and patterns of particulate matter for all three cigarette types even though the chamber smoke concentrations varied substantially. These results suggested that for rats exposed to different types of cigarette smoke, the amount of particulate material deposited may not be a function of concentration only. The authors conclude that when comparing cigarette smoke inhalation studies of different cigarette types, exposure parameters and smoke composition may both influence the amount of smoke inhaled and deposited in the lung and other organs.

Effect of cigarette smoking on experimental microvascular anastomoses

Cigarette smoking has been shown to cause cutaneous vasoconstriction, a decrease in digital blood flow, impaired wound healing, and it was implicated as a cause of failure of microvascular anastomoses in replanted digits. The subject of the following study was to assess the effect of cigarette smoking on experimental microvascular anastomoses. Twenty Sprague-Dawley male rats weighting 200 to 250 grams were divided into groups of ten. Both the experimental and the control groups were acclimatized to a Maddox/ORNL rat smoke inhalation exposure system for six days prior to operation. At this time they were anesthetized and bilateral femoral artery end to end anastomoses were performed by two surgeons, using standard microsurgical techniques. After a recovery period of 24 hours, both groups were started on a smoking/sham-smoking regime for 12 to 13 days. After this time they were anesthetized again, the femoral artery anastomoses were checked for patency in vivo and excised for histological evaluation. Five cm3 of blood was drawn from each animal to be analyzed for the presence of nicotine and its metabolites, and the rats were sacrificed. All the anastomoses in both groups were patent at the time of exploration and no histological difference could be demonstrated between the two groups. The radioimmunoassay of nicotine and cotinine showed large amounts in the smokers, and none in the nonsmokers.

In vitro hepatic enzyme activity in rats exposed nose-only to cigarette smoke

Adult male Sprague-Dawley rats were exposed nose-only to cigarette smoke for 10 or 20 min/day for up to 17 weeks. Other animals, identified as sham controls, were handled identically except that cigarettes were not placed in the smoking apparatus. A series of in vitro assays were used to monitor the effects of cigarette smoke and stress on hepatic S15 enzyme activities. Smoke exposure had no effect on any of the biotransformation pathways beyond that resulting from stress associated with the smoke procedure. However, smoking did significantly reduce hepatic levels of glutathione after 16 and 17 weeks of exposure. Smoking also caused a dramatic reduction in weight gain over the various exposure periods. This same effect, but to a lesser degree, was also noted in the sham control animals. These results demonstrate the definite need to reduce the obvious trauma caused by restraining rats for forced, nose-only exposure to the smoke. Until this is accomplished, results of studies on the influence of smoking on rat biochemistry and physiology will be difficult to properly interpret.

Pharmacokinetics of nicotine in rats after multiple-cigarette smoke exposure

The pharmacokinetics of nicotine and its major metabolites was evaluated in male rats after multiple-cigarette smoke exposure. A smoke-exposure apparatus was used to deliver cigarette smoke to the exposure chamber. The rats were exposed to smoke from a single cigarette every 8 hr for 14 days and to the smoke of a cigarette spiked with radiolabeled nicotine on the 15th day. Blood and urine samples were collected at timed intervals during the 10-min smoke-exposure period of the last cigarette and up to 48 hr thereafter. Nicotine, cotinine, and other polar metabolites were separated by thin-layer chromatography and quantified by liquid scintillation counting. The data were analyzed by computer fitting, and the derived pharmacokinetic parameters were compared to those observed after a single iv injection of nicotine and after a single-cigarette smoke exposure. The results indicated that the amount of nicotine absorbed from multiple-cigarette smoke was approximately 10-fold greater than that absorbed from a single cigarette. Also, unlike the single-cigarette smoke exposure experiment, nicotine plasma levels did not decay monotonically but increased after the 5th hr, and high plasma concentrations persisted for 30 hr. The rate and extent of the formation of cotinine, the major metabolite of nicotine, were decreased as compared with their values following a single-cigarette smoke exposure. It was concluded that nicotine or a constituent of tobacco smoke inhibits the formation of cotinine and may affect the biotransformation of other metabolites. Urinary excretion tended to support the conclusions that the pharmacokinetic parameters of nicotine and its metabolites were altered upon multiple as compared to single dose exposure.

Cigarette smoking by baboons: in vivo assessment of particulate inhalation using bronchoalveolar lavage to recover [14C]dotriacontane

In order to demonstrate quantitatively that cigarette-smoking baboons inhale particulate matter into the lung, a bronchoalveolar lavage method for recovery of [14C]dotriacontane was developed. First, 9 baboons were exposed to a known dose of [14C]dotriacontane labeled particulate matter delivered in a manner providing extensive deposition of particulates in the lung. The lungs of these passively exposed animals then were lavaged so that the efficiency of recovery of the standardized lavage procedure could be determined. Second, 9 baboons actively smoked labeled cigarettes, and the lungs of these animals were lavaged to recover labeled [14C]dotriacontane. The total amount of particulate matter present in the lungs was estimated using the efficiency factor previously determined. The smoking baboons retained an average of 9% of he total cigarette particulate matter. Differences among animals in retention of particulate matter were considerable, and the inter-animal variability was related to differences in number, volume, duration, and pressure of puffs. The retention of particulate matter by baboons is similar to particulate retention by other animal smoke inhalation models.

Pharmacokinetics of nicotine in rats after single-cigarette smoke inhalation

The amount of nicotine absorbed following cigarette smoke inhalation was evaluated by comparing the area under the plasma concentration--time curve and urinary recovery with those observed after its intravenous injection to rats. Nicotine was adsorbed rapidly, with the maximum plasma concentration occurring immediately after cessation of cigarette smoke exposure. On the average, 68% of the nicotine delivered to the inhalation chamber was absorbed. The absorption and elimination of nicotine, as well as the formation and elimination of its metabolites, followed first-order kinetics, and the derived pharmacokinetic parameters were similar to those observed after the intravenous administration of nicotine.

Deposition and clearance of labeled cigarette smoke particles in rat respiratory and digestive tract

In this investigation 160 8-wk-old Sprague-Dawley rats inhaled smoke from 14C-labeled cigarettes in a Hamburg II smoking machine. The research cigarettes were labeled with [16,17-14C]dotriacontane. Eighty of the rats were acclimatized to smoke from nonlabeled research cigarettes for 21 d before inhaling labeled cigarette smoke. The investigation was divided into four experiments. In experiment I all rats were killed immediately after exposure to the 14C-labeled smoke from 30 cigarettes (10 muCi per cigarette) and the organs of the respiratory and digestive tracts were measured for 14C activity. These animals showed high activity in the apex nasi, fundus nasi, and larynx. The highest activity was found in the lobus dexter caudalis and the lobus sinister of the lung. The lungs contained four-fifths of the condensate inhaled into the respiratory tract. In experiment II three animals were killed immediately after smoking, three after 6 h, and four after 24 h. No activity was found after 6 h in apex, fundus nasi, larynx, and trachea. The lungs showed no clearance at all. The activity in the digestive tract was highest in the stomach and the esophagus immediately after cessation of smoking. These values decreased rapidly after 6 h. In experiment III the animals were killed after 7, 21, and 42 d. Clearance from the upper respiratory tract was fast, whereas clearance from the lungs was slow. Clearance from all lung lobes was faster in the nonacclimatized animals. In experiment IV the rats inhaled the smoke from 14C-labeled cigarettes (2 muCi per cigarette) on 5 successive days. The animals were killed 7, 14, and 21 d after the last smoke inhalation. Clearance from the lungs was slower in acclimatized and non-acclimatized animals than in experiment III.

Cigarette smoke induced pathology of the rat respiratory tract: a comparison of the effects of the particulate and vapour phases

Changes in the rat respiratory tract produced by a 12-week exposure to the particulate or vapour phases of cigarette smoke are described and compared with the changes produced by combined exposure to both phases. The most extensive changge in the upper respiratory tract was a pronounced squamous metaplasia of the laryngeal epithelium, along with extensive deciliation and squame cell production. In the lung, smoke exposure produced marked increase in the numbers of bronchial goblet cells and intra-alveolar brown-gold macrophages. None of the above changes could be directly attributed to exposure to vapour phase alone, and in many cases the lesions produced by whole smoke and by carbon filtered smoke were directly comparable. For lesions to occur in some ciliated areas of the tract both phases of the smoke were required.

Inhalation toxicity studies on cigarette smoke (VIII). 6-week comparative experiments using modified flue-cured cigarettes: general toxicology

Details are given of studies carried out to compare the inhalation toxicity to rats of smoke from cigarettes modified to give a range of deliveries of particulate matter. Dosimetry work showed that under conditions similar to those used for subsequent toxicity experiments, smoke particulates deposited in the lower respiratory system within the approximate dose range of 500--700 microgram TPM/g lung tissue. Respiratory monitoring showed that the response of animals to a range of smoke exposure conditions was similar and did not change during the course of the experiments. This observation was confirmed by monitoring of blood carboxyhaemoglobin levels after exposure to smoke. During exposure to smoke the rate of respiration decreased to approximately 40% of the pre-exposure rate. Tidal volume, after an initial slight decrease, showed a progressive increase throughout the smoke exposure period. Bodyweight gain was reduced in those animals subjected to smoke exposures. True sham-smoked animals showed a body weight gain intermediate between that of smoke and cage control rats. The clear indications of such between-group differences in response to treatment, coupled with the indicators of consistent dosing of animals under the defined exposure conditions, form a sound basis for the interpretation of terminal pathology.

Inhalation toxicity studies on cigarette smoke. V. Deposition of smoke particles in the respiratory system of rats under various exposure conditions

This paper describes a dosimetry experiment on rats which was designed to make a contribution towards the optimisation of exposure conditions for inhalation toxicology studies with smoke aerosols. The main conclusions drawn from the work are: (i) Under continuous exposure conditions the deposition of total particulate matter (TPM) in the respiratory system and carboxyhaemoglobin (COHb) levels in blood were linearly dependent on the concentration of smoke in the exposure chamber. (ii) Intermittent exposure gave relatively lower TPM deposition compared to continuous exposure, even after allowing for differences in actual exposure times. (iii) For arithmetically equivalent exposure levels, short exposure to high concentration gave greater TPM deposition than long exposures to low smoke concentrations. (iv) There was a good correlation between lower respiratory system (LRS) and lung deposition of TPM and blood COHb level for both continuous and intermittent exposure conditions. These findings are discussed in relation to the conduct of inhalation studies with tobacco smoke.