Collagen production rates following acute lung damage induced by butylated hydroxytoluene

Final report on the safety assessment of BHT(1)

BHT is the recognized name in the cosmetics industry for butylated hydroxytoluene. BHT is used in a wide range of cosmetic formulations as an antioxidant at concentrations from 0.0002% to 0.5%. BHT does penetrate the skin, but the relatively low amount absorbed remains primarily in the skin. Oral studies demonstrate that BHT is metabolized. The major metabolites appear as the carboxylic acid of BHT and its glucuronide in urine. At acute doses of 0.5 to 1.0 g/kg, some renal and hepatic damage was seen in male rats. Short-term repeated exposure to comparable doses produced hepatic toxic effects in male and female rats. Subchronic feeding and intraperitoneal studies in rats with BHT at lower doses produced increased liver weight, and decreased activity of several hepatic enzymes. In addition to liver and kidney effects, BHT applied to the skin was associated with toxic effects in lung tissue. BHT was not a reproductive or developmental toxin in animals. BHT has been found to enhance and to inhibit the humoral immune response in animals. BHT itself was not generally considered genotoxic, although it did modify the genotoxicity of other agents. BHT has been associated with hepatocellular and pulmonary adenomas in animals, but was not considered carcinogenic and actually was associated with a decreased incidence of neoplasms. BHT has been shown to have tumor promotion effects, to be anticarcinogenic, and to have no effect on other carcinogenic agents, depending on the target organ, exposure parameters, the carcinogen, and the animal tested. Various mechanism studies suggested that BHT toxicity is related to an electrophillic metabolite. In a predictive clinical test, 100% BHT was a mild irritant and a moderate sensitizer. In provocative skin tests, BHT (in the 1% to 2% concentration range) produced positive reactions in a small number of patients. Clinical testing did not find any depigmentation associated with dermal exposure to BHT, although a few case reports of depigmentation were found. The Cosmetic Ingredient Review Expert Panel recognized that oral exposure to BHT was associated with toxic effects in some studies and was negative in others. BHT applied to the skin, however, appears to remain in the skin or pass through only slowly and does not produce systemic exposures to BHT or its metabolites seen with oral exposures. Although there were only limited studies that evaluated the effect of BHT on the skin, the available studies, along with the case literature, demonstrate no significant irritation, sensitization, or photosensitization. Recognizing the low concentration at which this ingredient is currently used in cosmetic formulations, it was concluded that BHT is safe as used in cosmetic formulations.

Pirfenidone diminishes cyclophosphamide-induced lung fibrosis in mice

The deposition of excess or abnormal collagen characteristic of pulmonary fibrosis can disrupt gas exchange resulting in severe respiratory impairment. There currently are no effective pharmacologic agents available that inhibit the fibrotic process. Pirfenidone (5-methyl-1-phenyl-2-(1H)-pyridone) is an investigational drug that, when administered at 0.5% (w/w) of the diet, decreases both histologic and biochemical evidence of lung fibrosis in hamsters treated intratracheally with bleomycin. The effectiveness of pirfenidone against lung fibrosis initiated by a systemically administered agent was investigated in mice treated intraperitoneally with 200 mg/kg cyclophosphamide (CP). Control and treated animals were fed a diet containing 0.277% (w/w) pirfenidone beginning 1 day after CP. Despite anorexia in the CP-treated mice the first day after treatment, they ingested a greater average pirfenidone dose over 20 days than saline-treated control mice (717 +/- 44 versus 564 +/- 30 mg/kg per day, respectively). Total lung hydroxyproline content, an index of fibrosis, was significantly lower 21 days after treatment with CP plus pirfenidone as compared to mice treated with CP alone. Although microscopic lung fibrosis scores were not significantly decreased by pirfenidone in CP-treated mice, the overall incidence of fibrosis was significantly decreased. Histologically, mice treated with CP showed fibrosis while mice treated with CP plus pirfenidone exhibited fewer abnormalities. The rate of hydroxyproline synthesis by lung tissue 9 days after treatment with CP was significantly elevated. This rate was not affected by pirfenidone treatment. Overall, these data support an antifibrotic effect of pirfenidone against CP-induced lung fibrosis in mice. The mechanism of its effect is not known, but appears to be unrelated to an inhibition of collagen synthesis.

Pharmacokinetics, metabolic activation, and lung toxicity of cyclophosphamide in C57/B16 and ICR mice

A single intraperitoneal dose (200 mg/kg) of cyclophosphamide (CP) resulted in significantly less injury to the C57/B16 strain than to the ICR strain of mice. Maximal thymidine incorporation into total lung DNA, an indirect index of lung injury, and pulmonary hydroxyproline content, a marker of fibrosis, were 56 +/- 10% and 69 +/- 9 of ICR mice, respectively. Pharmacokinetics and metabolism of [side chain-3H]CP and [ring-14C]CP were assessed in vivo. In addition, covalent binding and the generation of polar metabolites were determined in hepatic and pulmonary microsomes from both strains. Peak levels and half-lives of radioactivity derived from CP in blood were similar in both strains treated with a 200 mg/kg dose. However, area under curve for total radioactivity over 12 hr was significantly lower (60 and 78% of ICR for 3H and 14C, respectively), and systemic clearance significantly higher (168 and 119% of ICR for 3H and 14C, respectively) in the C57 strain. Total radioactivity derived from CP in lung and liver was similar between strains at all time points examined up to 12 hr, but overall covalent binding of radioactivity, assessed as area under the binding curve, was markedly lower to C57 lungs in vivo (58 and 49% of ICR for 3H and 14C, respectively). In contrast, hepatic binding was not significantly different between strains with either label. No significant differences were evident between strains in hepatic or pulmonary microsomal binding in vitro. Polar CP metabolites in ICR lung were significantly higher than C57 at 2 hr in vivo, but no strain differences were evident at other times nor in the microsomal generation of polar metabolites. These results demonstrate significant differences in the pharmacokinetics of CP between C57 and ICR murine strains. NADPH-mediated activation of CP in vitro was similar between strains suggesting that the increased covalent binding of CP to ICR lung tissue in vivo was due to greater exposure to CP or its reactive metabolites. The relative resistance of C57 mice to CP-induced lung fibrosis may also be influenced by intrinsic differences in response of the lung to reactive CP species, or by differences in activation by other metabolic pathways.

Comparison of lung injury induced in 4 strains of mice by butylated hydroxytoluene

Butylated hydroxytoluene (BHT) is a phenolic antioxidant which induces lung injury in all strains of mice which have been tested, but not in any other species. The mortality of mice treated with BHT is also highly strain-dependent, with LD50s ranging from 138 to 1739 mg/kg. Despite this wide range of toxic doses, the relationship between lung damage and dose has not been well studied. The data presented here demonstrate that BALB/c, ICR and C57BL/6NHsd mice, with LD50s of 1739, 1243 and 917 respectively, exhibit similar time courses of repair (as assessed by the incorporation of radiolabelled thymidine into DNA) and pulmonary fibrosis (as assessed by lung hydroxyproline content) when given a single 400 mg/kg dose of BHT. SSIn mice, with an LD50 of approximately 350 mg/kg, also exhibited a similar time course of repair when given a single dose of 300 mg/kg BHT, although fibrosis did not develop in these animals. These data indicate that all strains of mice develop similar levels of lung injury at equivalent doses and that the extent of lung damage produced in mice does not correlate with the lethal dose.

Collagen synthesis in explants from rat intestine

Collagen is the major structural component of the intestinal wall and its metabolism is of special interest for intestinal strength. We describe collagen synthesis in short-term (3 h) incubations of rat intestinal tissue, as measured in terms of incorporation of [3H]proline in collagenase-digestible protein and percentage relative collagen synthesis. In this time span, incorporation of [3H]proline in collagen increases linearly with time and tissue weight. Addition of unlabeled proline during incubation, in excess of the 0.1 microM [3H]proline always present, strongly increases both total protein and collagen synthesis, suggesting that proline transport is rate limiting. Further experiments have been performed in the presence of labeled proline alone and with the addition of 0.35 mM unlabeled proline. Collagen synthesis is significantly higher in colon than in ileum, comprising 0.37 and 0.21%, respectively, of total protein synthesis. Also, collagen synthesis decreases considerably with age, both in ileum and colon. The results presented here demonstrate that rat intestinal explants synthesize measurable amounts of collagen in vitro and that the system used is able to detect changes in in vivo synthetic capability such as those induced by ageing.

Pulmonary hydroxyproline content and production following treatment of mice with O,S,S-trimethyl phosphorodithioate

The systemic administration of O,S,S-trimethyl phosphorodithioate (OSS), a contaminant of various organophosphorus insecticides, induces delayed damage to rat and mouse lung tissue. The lesion, particularly in the rat, closely resembles that produced by butylated hydroxytoluene (BHT) in mice. Although the time course of cell damage and repair has been studied in both species, it is not clear whether excess collagen, indicative of fibrosis, is deposited. Changes in pulmonary hydroxyproline content and synthesis, indices of collagen metabolism, were analysed in mice treated with 45 mg/kg OSS. A significant increase in total lung hydroxyproline was evident 21 days after treatment compared to both pair-fed and ad libitum controls. This increase was not augmented by subsequent treatment with 35 mg/kg 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or exposure to 70% oxygen for 7 days. The rate at which lung tissue synthesized hydroxyproline was increased 7-14 days after treatment with OSS. These data demonstrate that treatment of mice with OSS results in changes indicative of pulmonary fibrosis. However, in contrast to some other lung-toxic chemicals, this lesion was not enhanced by subsequent treatment with BCNU or hyperoxia.

O,S,S,-trimethyl phosphorodithioate-induced lung damage in rats and mice

O,S,S,-Trimethyl phosphorodithioate (OSS) is a contaminant of various organophosphorus insecticides which induces delayed damage to rat lung bronchiolar and alveolar epithelial cells. Whether lung damage occurs in mice has not been tested. Changes in DNA synthesis, an index of cell division after the induction of damage, were monitored by measuring thymidine incorporation into pulmonary DNA. Mice, treated with 45 mg/kg OSS, exhibited a significant increase in pulmonary thymidine incorporation on Day 5. Maximal increases occurred on Days 7-10 and were followed by a gradual decline to control levels by Day 15. The labeling index of mouse lung cells, determined following autoradiography, exhibited a similar time course. Differential cell counts indicated that maximal division of type II cells occurred before that of interstitial cells, although interstitial cells were the predominant type labeled at all times. Pulmonary DNA synthesis was significantly increased in rats 2 days after treatment with 90 mg/kg OSS. Maximal thymidine incorporation was measured on Day 3, followed by a decline to control levels on Day 5. Thymidine incorporation into total lung DNA was dose related in both species. Maximal increases appeared after 45 and 90 mg/kg OSS in mice and rats, respectively. The histopathological changes in mouse lung tissue were similar, but somewhat less severe than those seen in rats. Rats exhibited a severe interstitial pneumonitis with type I alveolar cell destruction followed by type II cell proliferation. Mice exhibited a mild to moderate alveolitis with only slight damage to type I cells. Necrosis of bronchiolar Clara cells was evident in both species but was more extensive in rats. SKF 525a and piperonyl butoxide prevented OSS-induced increases in pulmonary DNA synthesis in rat lung suggesting that metabolic activation was necessary to elicit damage. Piperonyl butoxide treatments had no effect, however, on thymidine incorporation after OSS in mouse lung tissue, and the highest dose of SKF 525a had only a moderate inhibitory effect on this parameter while increasing animal mortality. These data indicate that systemic treatment with OSS results in damage to mouse, as well as rat, lung tissue at both the alveolar and bronchiolar levels.

Concentration, biosynthesis and degradation of collagen in idiopathic pulmonary fibrosis

Despite several studies both in vitro and in vivo, the pathogenesis of pulmonary fibrosis is unclear and some findings related to the biochemistry of collagen are controversial. Collagen metabolism was studied in 11 patients with idiopathic pulmonary fibrosis and in six control subjects. There was an increase in collagen concentration (mean 327 (SD 76) compared with control values of 185 (18) micrograms/mg dry weight, p less than 0.001), normal values for biosynthesis (mean 2.2% (0.8%) v 2.08% (0.5%), and a noteworthy decrease in collagenolytic activity (mean 0.07 (0.04) v 0.23 (0.04) micrograms of collagen degraded per mg of collagen incubated, p less than 0.001). These results suggest that an alteration in enzymatic breakdown of collagen plays an important role in the maintenance and progression of interstitial fibrosis in this disease.

Comparison of in vitro and in vivo rates of collagen synthesis in normal and damaged lung tissue

The rate of collagen synthesis was measured in vivo and in vitro in both normal and damaged mouse lung tissue. Acute lung damage was induced by the administration of butylated hydroxytoluene (BHT). The production of labeled hydroxyproline, following the administration of labeled proline, was used as an index of collagen production. Total and labeled hydroxyproline in normal and damaged lung tissue were solubilized equally following digestion with purified collagenase. Assuming that the extent of hydroxylation was not altered, this indicated that hydroxyproline was an accurate index of collagen content and production in damaged as well as normal lung tissue. The quantities of hydroxyproline formed at various times both in vivo and in vitro were calculated from the specific activity of free proline in lung tissue. The specific activity of free proline in normal and damaged lung tissue remained constant in vivo for at least 90 minutes after the intravenous injection of labeled proline. Hydroxyproline production was a linear function of time for up to 90 minutes in vivo and three hours in vitro. The in vivo rate of hydroxyproline production was significantly greater than the in vitro rate in lung tissue from similarly treated mice. The difference ranged from five-fold in normal lung tissue to eight-fold in lung tissue damaged by the administration of BHT. Comparable differences were seen between the in vivo and in vitro rates of non-collagen protein synthesis. Despite these differences in rates, the percentage of total protein synthesis committed to collagen in vivo was the same as in vitro in normal lung, and identical increases were seen in damaged lung. These data show that in vivo rates of both collagen and non-collagen protein synthesis are significantly higher than those measured in mouse lung tissue in vitro. Although the relative increases in collagen synthesis that occur in response to lung damage are larger in vivo, measurements of collagen synthesis in vitro do accurately reflect the general changes that accompany acute lung damage.

Collagen synthesis and degradation in acutely damaged mouse lung tissue following treatment with prednisolone

Corticosteroids are widely used to treat patients with acute lung damage. Recent work has shown that the administration of 30 mg/kg prednisolone to mice, twice daily on days 1-5 after the induction of lung damage with butylated hydroxytoluene (BHT), results in the development of a more severe fibrotic lesion [J.P. Kehrer, A.J.P. Klein-Szanto, E. M. B. Sorensen, R. Pearlman and M. H. Rosner, Am. Rev. resp. Dis. 130, 256 (1984)]. In the present study, the rate of collagen synthesis in lung tissue from BHT-saline-treated mice was greater than that in lung tissue from oil-treated controls at all days examined. During prednisolone treatment, the rate of pulmonary collagen synthesis was significantly less in tissue from BHT-prednisolone-treated mice compared to BHT-saline controls. Two days after steroid treatment was stopped (day 7 after BHT), there was a significant increase in the rate of collagen synthesis in lung tissue from BHT-prednisolone-treated mice compared to tissue from both BHT- and oil-treated controls. This increase reached a maximum on day 11 and persisted to day 14 after BHT. The rate of pulmonary non-collagen protein synthesis was inconsistently increased in response to treatments with BHT and/or prednisolone. There was, therefore, a relatively greater increase in the synthesis of collagen. The percentage of total protein synthesis committed to collagen increased from 2% in oil-treated controls to 5% on day 7 after BHT alone and reached a maximum of 7.1% on day 11 in lung tissue from BHT-prednisolone-treated mice. The percentage of newly synthesized collagen that was degraded in lung tissue from BHT-prednisolone-treated mice was significantly lower than BHT-saline on days 7 and 11, and lower than oil-prednisolone on day 14. These results show that collagen synthesis was decreased in BHT-damaged mouse lung tissue during short-term, high-dose steroid therapy. There was, however, an increase in collagen synthesis and a decrease in the degradation of newly synthesized collagen after steroid therapy was stopped. These changes in collagen metabolism may contribute to the steroid-induced enhancement of fibrosis seen in BHT-treated mice.

Systematically applied chemicals that damage lung tissue

A large, and increasing number of drugs and chemicals have been found which are toxic to lung following systemic administration. These agents damage lung tissue specifically, or in addition to damage to other tissues. Mechanisms explaining the pulmonary damage produced by some lung toxins have been uncovered. These include concentration of the agent within lung, the absence of adequate pulmonary detoxication systems, and bioactivation to a toxic species within specific lung cells or at distant sites followed by transport to the lung. The basic biochemical lesions underlying lung damage, responses of individual lung cells and pulmonary repair processes to the toxic agent, and species and age differences in susceptibility to lung damage have not, however, been well defined for most lung toxins. This review describes the information available on pulmonary biochemical and pathological changes associated with some of these lung-toxic agents. In addition, mechanisms proposed to explain the lung damage are discussed. The agents covered include: paraquat, the thioureas, butylated hydroxytoluene, the trialkylphosphorothioates, various lung-toxic furans and antineoplastic agents, the pyrrolizidine alkaloids, metals and organometallic compounds, amphiphilic agents, hydrocarbons, oleic acid, 3-methylindole, and diabetogenic agents. Detailed reviews on the overall toxicity of many of these agents have been published elsewhere. This review concentrates on their pulmonary toxicity. Information is presented as an overview to illustrate both the extensive literature that is available and the important questions that remain to be answered about systemic chemicals that damage lung tissue.

Increased pulmonary collagen synthesis in mice treated with cyclophosphamide

Cyclophosphamide is a widely used anticancer drug which damages lung tissue and elicits a progressive fibrotic lesion in mice. The early time course of collagen accumulation and the changes in collagen synthesis which may accompany this lung damage and fibrosis have not been reported. The total lung concentration of hydroxyproline, an index of collagen content and the extent of pulmonary fibrosis, was not significantly increased in mice until 12 days after treatment with 200 mg/kg cyclophosphamide. The change in total lung hydroxyproline content was preceded, on Day 6, by an increase in the rate of acid-insoluble hydroxyproline synthesis. This rate remained elevated to Day 21, but was no longer significantly increased by Day 28. The percentage of total protein synthesis devoted to the production of collagen was significantly increased 9 and 12 days after cyclophosphamide, compared to saline-treated controls. The rate of pulmonary non-collagen protein synthesis was significantly decreased 3 days after cyclophosphamide, and increased 6 and 15 days after this treatment. These data indicate that cyclophosphamide-induced increases in pulmonary collagen synthesis precede the accumulation of this protein. Increased collagen synthesis may occur in the absence of changes in overall protein synthesis although cyclophosphamide also alters non-collagen protein synthesis.

Synthetic antioxidants: biochemical actions and interference with radiation, toxic compounds, chemical mutagens and chemical carcinogens

Biological actions of 4 commonly used synthetic antioxidants--butylated hydroxyanisole, butylated hydroxytoluene, ethoxyquin and propyl gallate--on the molecular, cellular and organ level are complied. Such actions may be divided into modulation of growth, macromolecule synthesis and differentiation, modulation of immune response, interference with oxygen activation and miscellaneous. Moreover, an overview of beneficial and adverse interactions of these antioxidants with exogenous noxae is given. Beneficial interactions include radioprotection, protection against acute toxicity of chemicals, antimutagenic activity and antitumorigenic action. Possible mechanisms of the antitumorigenic action of antioxidants are discussed. This discussion is centered around antioxidant properties which may contribute to a modulation of initiation-related events, especially their ability to interfere with carcinogen metabolism. The beneficial interactions of antioxidants with physical and chemical noxae are contrasted to those leading to unfavorable effects. These include radiosensitization, increased toxicity of other chemicals, increased mutagen activity and increased tumor yield from chemical carcinogens. At present, the latter one can most adequately be characterized as tumor promotion at least in the case of butylated hydroxytoluene. It is concluded that current information is insufficient to promote expectations as to the use of antioxidants in the prevention of human cancer.

Metabolism of bromobenzene to glutathione adducts in lung slices from mice treated with pneumotoxicants

Recent studies showing that the bronchiolar Clara cell and alveolar Type II cell are major loci of cytochrome P-450 monooxygenases in the lung suggested that measurement of xenobiotic metabolizing enzyme activity might provide a useful and sensitive index of injury to these cell types. Accordingly, an assay has been developed for quantitating the rate of formation of reactive bromobenzene metabolites in lung slices which is based upon measuring the rate of formation of bromobenzene glutathione adducts. To demonstrate that monitoring adduct formation would yield quantitatively similar data to the traditional covalent binding assay for measuring the formation of reactive bromobenzene intermediates, covalent binding and conjugate formation were assayed in incubations of phenobarbital-induced hepatic microsomes conducted in the presence of various cytochrome P-450 monooxygenase inhibitors. Incubation conditions which decreased the rate of covalent binding (incubations done in the absence of glutathione) resulted in similar decreases in conjugate formation (incubations done in the presence of glutathione). In lung slices, the metabolism of bromobenzene to glutathione conjugates was linear for 20 min and continued to increase with time over the entire 160 min of the study. The formation of bromobenzene glutathione adducts in lung slices from piperonyl butoxide-treated animals occurred at a significantly lower rate than control. Likewise, lung slices from animals treated with butylated hydroxytoluene or carbon tetrachloride, agents known to injure alveolar epithelial cells, metabolized bromobenzene to glutathione conjugates at significantly slower rates than control. In contrast, treatment with naphthalene or dichloroethylene, agents which damage the bronchiolar epithelial cells, had little or no effect on conjugate formation. Similarly, there were no significant differences in the rate of bromobenzene glutathione conjugate formation between lungs of air- and ozone-exposed (1.0 ppm X 4 hr) mice killed 2, 24, 48, 72, or 120 hr after exposure. These studies suggest that monitoring the rate of bromobenzene glutathione conjugate formation in lung slices may be a useful and sensitive biochemical index of injury to certain cells of the lung but that severe damage to the nonciliated bronchiolar epithelial cells has little effect on the rate of metabolic activation of this aromatic hydrocarbon.

Fibrogenic structure-activity study of the bleomycin molecule

In the present study the fibrogenic potential of intact bleomycins as well as their acetyldipeptide and terminal polyamine constituents have been assessed. Administration of Blenoxane, bleomycin A2, or bleomycin B2 to rats produced histopathologic evidence of pulmonary fibrosis when tissues were examined 28 days following a single intratracheal dose. These compounds also produced a readily detectable increase in pulmonary collagen synthesis as evidenced by an approximate twofold increase over control values in the formation of [3H]hydroxyproline in an in vitro lung mince system. Lung collagen synthetic activity remained significantly elevated over control values for up to 2 weeks. However, neither the acetyldipeptides nor the polyamine constituents of bleomycin A2 and B2 produced detectable increases in lung collagen synthesis or in histopathologic evidence of pulmonary injury. Spermine and spermidine, the terminal amine components associated with bleomycin-A6 and with tallysomycin A, tallysomycin B, and bleomycin-A5, respectively, did produce significant pulmonary fibrotic injury in rats following intratracheal administration. Out of an extensive series of polyamines, bleomycin acetyldipeptides and intact bleomycin and tallysomycin analogs, only spermine and spermidine were found to produce hydrogen peroxide and acrolein upon incubation in vitro with amine oxidase, a common pulmonary enzyme. Conclusions regarding the relative toxicity of different bleomycin analogs based solely on the toxicity produced by administration of their terminal amine constituent must therefore be made with caution.