Subacute toxicity of piperonyl butoxide in ICR mice

Piperonyl butoxide, alpha-[2-(2-butoxyethoxy)ethoxy]-4,5-methylenedioxy-2-propyltol uene, is a pesticide synergist. ICR mice of both sexes were maintained on diet containing 0, 0.1, 0.3 or 0.9% of piperonyl butoxide for 20 days. At the end of the experimental period, they were necropsied. Selected organs were weighed and serum chemistries were analyzed. In male and female mice of the 0.9% group, body weight, kidney and spleen weight were depressed in comparison to those of control group. Liver weight of the 0.3 and 0.9% group of both sexes were significantly higher than those of control group. Mice of the 0.9% group of both sexes had increased serum levels of cholesterol, total protein, gamma-glutamyl transpeptidase. Histological examination of livers from mice of the 0.9% group by light microscopy showed enlarged hepatocytes, anisonucleosis and single cell necrosis. The results indicated that subacute toxicity of piperonyl butoxide in ICR mice was directed primarily at liver.     

Mechanistic study on liver tumor promoting effects of piperonyl butoxide in rats

Piperonyl butoxide, alpha-[2-(2-butoxyethoxy)ethoxy]-4,5-methylenedioxy-2-propyltol uene, is a widely used pesticide-synergist. Recently, results were reported indicating that piperonyl butoxide is a hepatocarcinogen in rat. Since the underlying mechanism was not elucidated, we examined the effects on rat liver cells in detail. For this purpose male F344 rats were administered piperonyl butoxide mixed in the diet at concentrations of 0 (negative control), 0.05, 0.2 or 2% for 2 days, 1, 2, and 4 weeks. As a positive control, phenobarbital was administered to rats for up to 4 weeks as a 0.1% solution in the drinking water. Increased liver weight, centrilobular hepatocellular hypertrophy due to increased smooth endoplasmic reticulum, decreased numbers and areas of connexin 32-positive spots per hepatocyte, and increased cell proliferation were observed in rats treated with 0.2 and 2% piperonyl butoxide. Similar results were obtained for 0.1% phenobarbital treated rats. Hepatocellular necrosis suggestive of hepatotoxicity was also observed in the 2% piperonyl butoxide group. These results indicate that the promoting mechanism of piperonyl butoxide in hepatocarcinogenesis is similar to that of phenobarbital, involving an ability to induce CYP isoenzymes and inhibit gap junctional intercellular communication. In addition, increased cell proliferation following hepatocellular necrosis may also play a role at high doses.     

Residue levels of pyrethrins and piperonyl butoxide in soil and runoff water

Simultaneous analysis of pyrethrins (Py-I and Py-II) and piperonyl butoxide (PBO) in soil and runoff water samples following field application of a new pyrethrum formulation containing pyrethrins (Py's) and PBO is described. Residues of total Py's and PBO were extracted from soil samples using hexane-acetone (9:1). A solid phase extraction (SPE) column containing C18-octadecyl bonded silica was used to separate Py's and PBO residues from runoff water. Residues in soil and water were quantitated by high performance liquid chromatography (HPLC) equipped with C18-column and a UV detector. Concentration of Py-II in soil was 100 times higher than that of Py-I 1 h following treatment and 9.6 times higher than Py-I in runoff surface water 11 days following treatment. Results indicated that Py's are non-persistent in soil (even though lipophillic) and water when applied at the recommended rate of 6 lbs (5.31 g A.I.) per acre. There was a consistent decrease in total Py's residues as time after spraying increased. Py's residues in soil decreased from 0.91 to 0.11 ppm 4 days following treatment and one month after treatment only 0.002 ppm were detected. The highest concentration of Py's in runoff water was 36.09 ng/liter following the first rainfall (11 days following treatment). PBO initial residues detected in soil samples were low (0.84 microgram/g soil) while no residues of PBO were detected in runoff water.     

Lack of effect of piperonyl butoxide on unscheduled DNA synthesis in precision-cut human liver slices

In this study the effect of piperonyl butoxide (PBO) on unscheduled DNA synthesis in precision-cut human liver slices has been examined. Liver slices prepared from tissue samples from five human donors were cultured in medium containing [3H]thymidine and 0-2.5 mM PBO using a dynamic organ culture system. After 24 h the liver slices were processed for autoradiographic examination of UDS. As positive controls, liver slices were also cultured with three known genotoxic agents, namely 2-acetylaminofluorene (2-AAF), aflatoxin B1 (AFB1) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). UDS was quantified as the net grain count in centrilobular hepatocytes and as the percentage of centrilobular hepatocyte nuclei with > 5 and > 10 net grains. Compared to control liver slice cultures PBO had no effect on UDS. In contrast, treatment with 0.02 and 0.05 mM 2-AAF, 0.002 and 0.02 mM AFB1 and 0.005 and 0.05 mM PhIP produced significant increases in net grain counts of centrilobular hepatocytes. The greatest induction of UDS was observed in liver slices treated with 0.05 mM PhIP. Treatment with 2-AAF, AFB1 and PhIP also produced increases in the number of centrilobular hepatocyte nuclei with > 5 and > 10 net grains. At the concentrations examined neither PBO, 2-AAF nor PhIP had any significant effect on replicative DNA synthesis in 24 h cultured human liver slices. In cultured liver slices treated with 0.02, but not 0.002, mM AFB1 a significant reduction in the rate of replicative DNA synthesis was observed. These results demonstrate that PBO does not induce UDS in cultured human liver slices. However, all three positive control compounds produced marked significant increases in UDS, thus confirming the functional viability of the human liver slice preparations used in this study. In conclusion, these results provide further evidence that PBO is a non-genotoxic agent which does not damage DNA in human liver.     

Oncogenicity testing of 2-ethylhexanol in Fischer 344 rats and B6C3F1 mice

An increasing number of studies, both experimental and epidemiologic, have provided evidence that filtering glaucoma surgery may be less effective than initially described. Of a number of risk factors for failure, duration and number of antiglaucoma drugs prior to surgery seem to play a critical role and highly accumulated antiglaucoma topical treatments significantly reduce success rates. Histopathological studies have confirmed that topically applied drugs may exert toxic effects to the corneoconjunctival surface, and induce chronic infraclinical inflammation, as shown by the presence of immune and inflammatory infiltrates in multitreated eyes. The origin of topical inflammation has not yet been clearly determined, but a common component of ophthalmic drugs, the benzalkonium chloride used as preservative in almost all antiglaucoma preparations, has shown strong evidence of toxicity. A number of questions remain to be investigated, but suppression of preservatives from chronically applied drugs should be a critical issue in the near future.     

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.     

Considerations in the design of studies of dietary influences on mammary carcinogenesis in rats and mice

Design of diets for the study of dietary influences in mammary gland carcinogenesis requires attention to several questions: (1) Do the diets satisfy the nutritional needs of the animal under the conditions of the experiment, and are they palatable? (2) Does the protocol include determination of feed intake (if indicated) and of achievement of the desired level of nutrient deficiency, adequacy, or excess? (3) Are there potentially confounding nutrient interactions or nutrient effects or physiological or pathological responses that must be considered? The particular sensitivity of mammary gland tumorigenesis to intake of fat and calories and to body weight gain must be considered and controlled for in all experiments.     

Some pharmacologic and toxicologic studies on Rhazya stricta decne in rats, mice and rabbits

1. This work examines some in vivo and in vitro pharmacologic and toxicologic effects of extracts of Rhazya stricta, a medicinal plant in the United Arab Emirates. 2. R. stricta extracts at doses of 0.1-10 mg reduced the mean arterial blood pressure (MBP) of anesthetized rats in a dose-dependent manner. The depressor effect was partially sensitive to atropine (5 microM). Although the MBP was reduced by 50% by both doses of extracts, the normal electrocardiogram pattern and the heart rate remained unaltered. 3. Acute treatment of rats with the lyophilized extract at doses of 4 g/kg produced a significant rise in insulin concentration. In streptozotocin-diabetic rats loaded orally with glucose (1 g/kg), R. stricta at doses of 8 g/kg produced significant decreases in plasma glucose concentration at 0.5 and 1 h after treatment. 4. Chronic treatment of rats and mice for 28 days with the lyophilized extract of R. stricta did not affect the plasma glucose or insulin concentration or any of the hematological or biochemical indices measured. 5. The extracts of R. stricta (0.5-4 g/kg) dose-dependently decreased the gastrointestinal transit time in mice by 4-50%. 6. The butanolic extract of R. stricta (1 and 2 g/kg) significantly reduced the carrageenan-induced increase in raw paw edema 3 and 4 h after the extract administration. 7. The rectal temperatures of normothermic and pyrexic rats were reduced significantly 0.5 and 1 h after administration of butanolic R. stricta at doses of 1 and 2 g/kg. 8. The butanolic extract of R. stricta at doses of 1 and 2 g/kg significantly increased the reaction time on the hot plate 30 and 60 min after administration to rats. 9. At concentration < 0.05 mg/ml (bath concentration), lyophilized water and butanol extracts of R. stricta potentiated the twitch responses induced by indirect electrical stimulation in the rat phrenic nerve diaphragm preparation. The responses were inhibited by concentrations > 0.05 mg/ml. Neostigmine (2 x 10(-4)M) did not alter these effects of the extracts. 10. R. stricta extracts dose-dependently decreased the force of contraction and heart rate of the isolated rabbit heart. Atropine (1 x 10(-5)M) had no effect on the inhibitory activity of these extracts. The lyophilized water extract (> 10 mg) and butanol extract (> 5 mg) produced irreversible inhibition and disturbances in the force of contraction and heart rate.     

Dental dysplasia in rats and mice

Malformations of the maxillary incisors, diagnosed as dental dysplasia, were observed as a spontaneous background lesion in 3% (females) to 9% (males) of CD-1 mice and 14.5% (females) to 10.5% (males) of CD (Sprague-Dawley) rats in a chronic inhalation study. Lesions were reported grossly as overgrown, maloccluded, or malformed incisors. Microscopic findings included tooth pulp and periodontal abscesses, fractured and necrotic teeth, periodontal cysts, malformations of the incisor roots, and expansile masses, including odontomas, of the incisor roots. Development of lesions followed a pattern of tooth pulp necrosis and/or traumatic disruption of the epithelial root sheath at the base of the tooth. Feeding a powdered ration, which reduced the normal wearing of the incisors, and repeated clipping of overgrown incisors were believed to contribute to the incidence of disease.     

Toxicokinetics of oxazepam in rats and mice

The comparative toxicokinetics of oxazepam were studied in F344 rats, B6C3F1 mice, and Swiss-Webster mice of both sexes after an i.v. dose of 20 mg/kg and oral gavage doses of 50, 200, and 400 mg/kg. In addition, the toxicokinetics of oxazepam in a 3-week dosed-feed study of male B6C3F1 mice at 125 and 2500 ppm were also investigated. Results indicated that the elimination of oxazepam from plasma after i.v. injection in both rats and mice were first-order and could be best described by a two-compartment model with a terminal elimination half-life of 4-5 h for rats and 5-7 h for mice. After oral gavage dosing the peak oxazepam plasma concentrations in most rodents were reached within 2-3.5 h. At all doses studied, female rodents had significantly higher plasma concentrations than males. Absorption of oxazepam was significantly extended at higher oral doses of 200 and 400 mg/kg. At 50 mg/kg, the bioavailability of oxazepam in rats (< 50%) was lower than in Swiss-Webster mice (> 80%). The bioavailability of oxazepam in both B6C3F1 and Swiss-Webster mice decreased with increasing dose. A dose proportionality of Cmax was not observed in rats and mice after gavage doses of 50, 200, and 400 mg/kg. Plasma concentrations of oxazepam in the dosed-feed study increased with the concentration of oxazepam in the feed, a quasi-steady-state of plasma concentrations of oxazepam was reached after approximately 4 days ad libitum exposure. In B6C3F1 mice, the estimated relative bioavailability of oxazepam from dosed feed (relative to gavage study at 50 mg/kg) was about 43%.     

Chemical and pharmacological studies of Phyllanthus caroliniensis in mice

We studied retrospectively the effect of long-term treatment with an inhaled corticosteroid on bronchial hyperresponsiveness (BHR) and clinical asthma in moderate-severe asthmatic subjects. Fifty-eight patients who had used beclomethasone dipropionate (BDP) over one year, were enrolled in this study. BHR was measured before and after treatment with BDP by the methods recommended by Japanese Society of Allergology. Moreover we examined the clinical factors and the frequency of acute exacerbations. The results as follows: 1) The mean age was 48.8 years and the mean asthma history was 9.2 years. The mean dose and mean time of BDP administration was 801 micrograms/day and 28.1 months, respectively. 2) Patients during BDP treatment over one year showed about 6-fold mean improvements in BHR, but there were many patients who showed no improvements in BHR. 3) We retrospectively divided all the patients into two groups. Namely, the improved group (n = 25) showed more than 4 fold improvement in BHR and unchanged group (n = 33), less than 4-fold. But there were no significant differences in clinical characteristics and %FEV1 during treatment with BDP. 4) The unchanged group had more near fatal episodes in the past than the improved group. 5) There was significant decrease in acute exacerbation during treatment with BDP, but the unchanged group had more acute exacerbations than the improved group during treatment with BDP. These results indicates that there are many patients who had no improvement on BHR with long term BDP treatment and they have more acute exacerbations due to various stimuli. In conclusion, asthma is recognized chronic inflammatory disease and inhaled corticosteroid therapy has been recommended as the first line therapy. We must further study the clinical problems and underlying mechanisms concerning about treatment with an inhaled corticosteroid.     

Intestinal lipid esterification and aging in mice and rats

BACKGROUND AND PURPOSE: The risk of side effects of low activity (i.e. <20 mCi) Iodine-125I (125I) interstitial radiotherapy was analyzed in patients with low-grade gliomas. MATERIALS AND METHODS: Permanent (247 patients) or temporary 125I-implants (268 patients) were used with a median reference dose of 60 Gy and 100 Gy, respectively, which was calculated to the outer rim of the tumour. The mean dose rate for temporary implants was low (median, 10 cGy/h). Risk factors were obtained from the multivariate proportional-hazards model. RESULTS: Radiogenic complications occurred in 39/515 patients (28 patients with transient symptoms and 11 patients with progressive symptoms). The most important risk factor was the volume of the intratumoural 200 Gy isodose. Available experimental data have associated a high dose zone in this range with the size of the treatment induced radionecrosis. Rapid tumour shrinkage (decrease of the tumour volume > or =50%) within the first 6 months with subsequent centripetal movement of non-pathologic tissue into the high dose zone and a reimplantation were additional risk factors. Radiation injury after rapid tumour shrinkage could be better avoided with temporary implants. A 200 Gy isodose volume <4.5 ml corresponded to an estimated risk of radiogenic complications <3%. There was a steep increase of the risk beyond this limit. Translation of the 200 Gy isodose volume in terms of the treatment volume and the reference dose allows rational treatment planning. The estimated risk of a temporary implant with an applied reference dose of 60 Gy and a treatment volume <23 ml was <3%. CONCLUSIONS: The intratumoural necrotizing effect of a low activity 125I implant limits its application to small treatment volumes. Radiation injury outside the treatment volume can be better avoided with temporary implants in the case of rapid tumour shrinkage.     

Metabolism of carvedilol in dogs, rats, and mice

The excretion and biotransformation of carvedilol [1-[carbazolyl-(4)-oxy]-3-[(2-methoxyphenoxyethyl)amino]-2-p ropanol], a new, multiple-action, neurohormonal antagonist that exhibits the combined pharmacological activities of beta-adrenoreceptor antagonism, vasodilation, and antioxidation, were investigated in dogs, rats, and mice. Carvedilol was absorbed well, and biliary secretion was predominant in each species. Carvedilol was metabolized extensively in each species, and elimination of unchanged compound was minor in bile duct-catheterized rats and dogs. In dogs, glucuronidation of the parent compound and hydroxylation of the carbazolyl ring, with subsequent glucuronidation, were the major metabolic pathways. Rats showed the simplest metabolite profile; the primary metabolites were formed by hydroxylation of the carbazolyl ring, with subsequent glucuronidation. Mice displayed the most complicated metabolite profile; glucuronidation of the parent compound and hydroxylation of either the carbazolyl or phenyl ring, with subsequent glucuronidation, were the major metabolic routes. O-Dealkylation was a minor pathway in all species examined.     

Comparative infectivity of Toxoplasma gondii bradyzoites in rats and mice

Infectivity of Toxoplasma gondii bradyzoites was compared in outbred female Sprague Dawley rats and outbred Swiss Webster mice. Rats inoculated subcutaneously with 1-10 bradyzoites of the 2 strains of T. gondii (VEG and GT-1) developed persistent infection, whereas an infective dose by the oral route was 10-1,000 bradyzoites. The infectivity of bradyzoites of the VEG and the GT-1 strains of T. gondii in rats by the subcutaneous route was comparable to that in mice.     

Noncompensation of adipose mass in partially lipectomized mice and rats

The effects of surgical ablation of adipose tissue were studied in normal mice and rats. It was found that: 1) restortation of adipose tissue does not occur locally in epididymal fat pads of young rats. 2) Bilateral epididymal fat pad removal in mice disrupts the testes and causes the other fat depots to accumulate excess lipid, but these effects are not sustained; After a sufficient recovery period, testes appear normal and no excess lipid is found in the remaining depots; 3) Temporary enlargement of remaining depots is probably due specifically to epididymal pad removal. It does not occur in response to inguinal depot removal, nor in response to disruption of the testes alone; 4)The quantity of lipid stored by a rapidly growing mouse depends on the number of intact depots in the mouse. These results suggest that surgical removal of fat does not lead to compensatory growth of fat. Autoregulation of adipose tissue mass, if it occurs, most likely operates through detection of adipocyte size rather than adipocyte number or total fat mass.