Potassium Octatitanate Whisker Research Articles

Molten salt synthesis of crystalline photocatalytic potassium octatitanate whiskers from KCl melt

High-quality potassium octatitanate (K2Ti8O17) whiskers were successfully synthesized by reaction of rutile TiO2 with stoichiometric K2CO3 from KCl melt at 760–800°C. The characterization results from X-ray diffraction and Energy dispersive X-ray spectroscopy revealed single-phase K2Ti8O17 whiskers with highly crystalline nanostructure have been obtained. The scanning electron microscopy combined with transmission electron microscopy showed the well dispersive K2Ti8O17 whiskers have a uniform length ranging from 5μm to 10μm with 40–80nm in diameter. Selected area electron diffraction and high-resolution transmission electron microscopy indicated the K2Ti8O17 whiskers have grown preferentially along the [010] direction. According to UV–vis absorption spectrum, the direct band gap of the K2Ti8O17 whiskers was estimated to be 3.31eV. Furthermore, the K2Ti8O17 whiskers have shown good photocatalytic activity in the photodegradation of methyl orange under ultraviolet (UV) light irradiation.

Expression of Heme Oxygenase‐1 in the Lungs of Rats Exposed to Potassium Octatitanate Whiskers

Oxidative stress is thought to be the pathogenesis of pulmonary fibrosis induced by asbestos, and heme oxygenase-1 (HO-1) protects lung tissue against oxidative stress. We hypothesized that HO-1 is also associated with oxidative lung injury caused by exposure to potassium octatitanate whiskers (PT1), which is one of the asbestos substitutes. Male Wistar rats were administered 1 mg or 2 mg PT1 suspended in saline by a single intratracheal instillation and were sacrificed after recovery for 3 days, 1 wk, 1 mo, 3 mo or 6 mo. Gene expression of HO-1 protein and mRNA and immunostaining were investigated in rat lungs. HO-1 protein expression was increased from 3 days to 1 mo and at 6 mo in the 1 or 2 mg PT1-exposed groups, and the gene expression of HO-1 mRNA was also increased at 3 days and from 1 mo to 6 mo. HO-1-positive cells were mainly found in the alveolar macrophages and the bronchial epithelial cells in immunostaining. These findings suggest that HO-1 is involved in lung damage caused by PT1.

Selective Synthesis of Potassium Titanate Whiskers Starting from Metatitanic Acid and Potassium Carbonate

Selective synthesis of potassium titanate whiskers starting from metatitanic acid and potassium carbonate was successfully carried out by a facile calcination method. The mole ratio of potassium carbonate to metatitanic acid and the calcination temperature and time were crucial to the formation of different-structured potassium titanate whiskers. Well-crystallized potassium tetratitanate whiskers were prepared at a calcination temperature of 1000 °C when the mole ratio of potassium carbonate to metatitanic acid was 1:2.5. Potassium hexatitanate whiskers were dominantly formed at 1150 °C when the mole ratios of potassium carbonate to metatitanic acid were in a range of 1:3.5−1:4.5. Well-crystallized potassium octatitanate whiskers were prepared when potassium tetratitanate whiskers were boiled in water and then dried at a high temperature of 400 °C. The growth directions of all the potassium titanate whiskers are along their [010] crystal directions.

Simple Flow‐through Solubility Measurement Apparatus and its Effectiveness for Hazard Assessment of Particles/Fibers

assessment, Biopersistence, Inhalation, Intratracheal instillation Biopersistence of respirable particles in the lung is an important indicator for estimating the effects of the particles on the lung 1) , and its relationship with physicochemical properties of particles has been studied 2‐4) . We previously reported that long and insoluble fibers persist in the lung for a long time 5‐7) . International Agency for Research on Cancer summarized that as the solubility per unit surface area of vitreous fibers decreases, the biopersistence of fibers longer than 20 ∝m increases, producing histopathological changes 8) . If the correlation between such physicochemical factors and the biopersistence in the lung is clarified quantitatively, the measurement of these factors is available as a preliminary screening test for the hazard level of new chemical substances prior to conducting animal experiments. Focusing on the solubility among these physicochemical factors, a measurement system for asbestos substitutes was previously proposed 9) , and it indicated a relationship between solubility of long fiber and lung injury. This system is very precise but requires much time and effort because of the simulation of physiological conditions. Respirable dusts needed to be investigated for their health effects in the working environment contain not only long fibers and also small particles and short fibers, therefore it is important to measure the solubility of these small dusts simply and rapidly and to investigate the relation between their solubility and lung injury. In this study, the solubility of 6 types of dust, two respirable particles and three short fibers (>20 ∝m, 20 ∝m, 30%), was determined using a simple apparatus devised by us, in which the solutions surrounding the samples change continuously. In addition, the relationship between the solubility determined in this experiment and the biopersistence in the lung and pathological changes in intratracheal injection and inhalation exposure in our previous rat studies was investigated, in order to determine whether or not solubility has potential as an indicator for estimating the effects of particles and fibers on the lung. Materials and Methods Four types of fibers and 2 types of particle were used as the samples. They were magnesium sulfate whisker (MW; UBE Industries, Japan), calcium silicate fiber (CF; UBE Industries, Japan), magnesium silicate fiber (MF; NICHIAS corporation, Japan), potassium octatitanate whisker (JFM standard reference sample named PT1; Japan Fibrous Materials Research Association (JFMRA)), crystalline silica (CS; US Silica company, USA) and limestone (LS) from a mine in Japan. Electron micrographs of the respective samples are shown in Fig. 1. The abbreviated names, chemical compositions and geometrical configurations of the respective substances are shown in Table 1. The geometric mean diameter and length (geometric standard deviation) of the fibers were determined from their electron micrographs and the geometric mean diameters (geometrical standard deviation) of the particles were determined using a particle size analyzer (Microtrac FRA, Nikkiso, Japan). The outline of the solubility measurement apparatus by the flow-through system is shown in Fig. 2. One milligram of sample was suspended in the solution between the 0.22-∝m membrane filter on the inlet side and the outlet side of a cassette of a 37-mm air sampler. Phosphate buffered saline (0.01 M, pH 7.2) flowed upward from the lower part of this cassette at a rate of 12 ml/h. The effluent passing through the cassette was collected from the upper part at different times to determine the pH and to quantify the ion concentrations of the main components of the sample. The main components in the effluent (magnesium for MW, silicon for CF, MF and CS, titanium for PT1 and calcium for LS) were determined using an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES, SPS-1500R, SII, Japan) and the dissolved amounts of the respective samples were calculated from the contents of the elements by percentage of the samples.

Calcitonin Gene-Related Peptide (CGRP) as Hazard Marker for Lung Injury Induced by Dusts

Calcitonin gene-related peptide (CGRP), which has a function as a growth factor of epithelial cells, is thought to play a role in pulmonary epithelium repair. In order to establish whether or not CGRP is associated with repair in lung damaged by dust, we examined gene expression of CGRP in the lungs of animal models exposed to different dusts. Male Wistar rats were administered 2 mg of crystalline silica, crocidolite, potassium octatitanate whisker (PT-1), and silicon carbide whisker (SiCW) suspended in saline by a single intratracheal instillation and were sacrificed at 3 d, 1 wk, 1 mo, 3 mo, and 6 mo of recovery time. Pathological findings of advanced pulmonary fibrosis were present in the rats exposed to crystalline silica and crocidolite through the experiment, whereas findings of mild or reversible pulmonary fibrosis were present in those exposed to SiCW and PT-1. The expression of CGRP in rat lung was observed by reverse-transcription polymerase chain reaction (RT-PCR) and enzyme immunometric assay (EIA). In RT-PCR, CGRP gene expression was decreased at the interval of 3 d and 1 wk in the case of crystalline silica and crocidolite; on the other hand, it was increased at 3 d and 1 wk in SiCW and at 3 d, 1 wk, and 3 mo in PT-1-exposed rats. CGRP protein level in lungs exposed to PT-1 and SiCW was also higher than that to silica and crocidolite at 3 d of recovery time. These data suggest that CGRP is associated with repair in lung damaged by different dusts, and that CGRP could be used as a sensitive biomarker to indicate the pathogenicity of dusts.

Histopathological Changes in Rat Lung Following Intratracheal Instillation of Silicon Carbide Whiskers and Potassium Octatitanate Whiskers

We evaluated the pattern of pulmonary inflammation for the assessment of the biological hazards of two man-made mineral fibers. Rats were exposed by intratracheal instillation to a 2 mg dose of each of two kinds of man-made mineral fibers (PT1, potassium octatitanate whisker; and SiCW, silicon carbide whisker), or three kinds of comparable respirable particles (crystalline silica, crocidolite asbestos, and titanium dioxide, TiO2). The lung tissue was evaluated at 3 day, 1 wk, and 1, 3 and 6 mo after exposure. Digital images taken of the lung sections were examined by morphometric point counting method (PCM). PT1 and SiCW showed a similar inflammatory pattern, which contains temporal inflammation such as moderate alveolitis within 1 wk after the exposure, and in later phase aggregation foci of instilled fibers. Differences in repair patterns of these two man-made mineral fibers showed that the toxicity of these two fibers is less toxic than for crocidolite or crystalline silica. Although SiCW showed a higher inflammation score than TiO2 within 1 mo after instillation, the inflammation scores and fibrotic changes of PT1 and SiCW were not significant as TiO2 at 3 mo and 6 mo in this study. Careful use should be recommended when these materials are used in the workplace.

The Effect of Lung Burden on Biopersistence and Pulmonary Effects in Rats Exposed to Potassium Octatitanate Whiskers by Intratracheal Instillation

In our previous inhalation studies on health effects of the asbestos substitute, potassium octatitanate whiskers (POW), we showed that an excess amount of POW deposition in the rat lung increased biopersistence resulting in fibrotic changes. The critical deposition amount which induced the higher biopersistence was estimated to lie between 1.5 mg and 2.4 mg. In order to find the exact amount, the relationship between the lung POW burden and biopersistence was investigated by the intratracheal instillation method. The chemical formula of POW is K2Ti8O17 and the geometric mean fiber diameter (geometric standard deviation, GSD) and geometric mean fiber length (GSD) are 0.35 microm (1.6) and 4.4 microm (2.7), respectively. Rats were intratracheally instilled with 0.5 mg, 1.0 mg, 2.0 mg or 5.0 mg of POW and sacrificed at 1 day and 1, 3, 6 and 12 months after the instillation. The POW amount in each lung was chemically analyzed by ICP-AES after microwave digestion and the biological half time (BHT) of each POW dose was calculated. The BHTs of each group were 10, 15, 20 and 42 months for 0.5, 1.0, 2.0 and 5.0 mg of POW, respectively, and BHT showed a linear dose-dependent increase, but without a threshold within the range of 0.5 mg to 5.0 mg, which was recognized in our earlier inhalation studies. In the histopathological photograph just after the instillation, many macrophages, which had phagocytized many more fibers, existed around the bronchiole compared with the earlier inhalation study at almost the same deposited amount. The relationship between POW amount and biopersistence in this intratracheal instillation study was different from that of our previous inhalation studies, probably due to the unnatural method of the fiber introduction to the lung, which in turn led to a different fiber distribution. It is suggested that an intratracheal instillation study is not an appropriate method for estimating excess deposition amounts of POW and an inhalation study will be needed. However, this intratracheal instillation study clarified that the clearance of POW was delayed as compared with previous inhalation studies at similar deposition amounts and this result has importance for the hazard assessment of dusts in animal experiments.

P3001 細胞磁界測定法を用いたチタン酸カリウムウィスカの細胞毒性評価(一般演題:ポスター,地方の時代の産業保健,第79回日本産業衛生学会)

P3001 細胞磁界測定法を用いたチタン酸カリウムウィスカの細胞毒性評価(一般演題:ポスター,地方の時代の産業保健,第79回日本産業衛生学会)

The Effect of Lung Burden on Biopersistence and Pulmonary Effects in Rats Exposed to Potassium Octatitanate Whiskers by Inhalation

The effect of lung burden on biopersistence and histopathological changes caused by potassium octatitanate whiskers (POW) which is one of the asbestos substitutes were investigated for 1-yr and 4-wk inhalation periods. In the 1-yr inhalation experiment, male Wistar rats were exposed to POW (TW) for 6 h/d, 5 d/wk under the same conditions as a previous study of POW (PT1, JFM fiber) which is made by different manufacturer. The exposure concentration was 1.9 +/- 0.7 mg/m(3) and the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) in the chamber were 1.6 microm and 2.9. Rats were sacrificed at 3 d and 1 yr after the inhalation experiment and TW deposits in the lungs were determined by ICP-AES. Lung burden at 3 d and 1 yr after the inhalation was 2.39 +/- 0.50 mg and 1.37 +/- 0.96 mg, respectively, the deposition fraction was 8.1% and biological half time (BHT) was 15 months. Aggregated dust cells and mild fibrotic changes around these dust cells were observed in the exposed rat lung. These results were almost the same as those obtained in the previous 1-yr PT1 study. In the 4-wk inhalation experiment, to investigate the effect of lung burden on biopersistence and histopathological change, male Wistar rats were exposed to PT1. The exposure concentration was 102 +/- 21 mg/m(3), MMAD (GSD), the geometiric mean length and diameter (GSD) of the PT1 in the chamber were 1.6 microm (3.0), 2.2 microm (1.8) and 0.33 microm (1.5), respectively. Rats were sacrificed at 3 d, 1 wk, and 1, 3, 6 and 12 months after the inhalation experiment. The lung burden of POW at 3 d after 4 wk inhalation was 1.49 +/- 0.19 mg, which was close to the estimated amount of overload. The BHT of the total mass (4.1 months) was not prolonged, but aggregated dust cells were observed in the subpleural region and around the bronchioles and mild fibrotic changes were observed only around the dust cells at one year after the 4-wk inhalation. It is considered that the excessive exposure which impairs the function of alveolar macrophage mediated clearance may cause the aggregation of dust cells and fibrotic changes.

Pulmonary Effects and Clearance After Long-Term Inhalation of Potassium Octatitanate Whiskers in Rats

The pulmonary effects of long-term inhalation of potassium octatitanate whisker (PT1), one of the durable man-made fibers (MMFs), were examined in rats. Male Wistar rats were exposed to PT1 by inhalation for 6 h/day, 5 days/wk for 1 yr. The daily average exposure concentration of PT1 aerosol was 2.2 ± 0.7 mg/m3 (111 ± 34 fiber/ml) during the exposure. Rats were sacrificed at 3 days, 6 mo, and 12 mo after 1 yr of inhalation exposure. The amount of deposited PT1 in rat lungs (lung burden) was 2.4 ± 0.7 mg and the deposition fraction was 7.2% at 3 days after 1 yr. The clearance of inhaled PT1 after 1-yr inhalation was prolonged so that the biological half-life time (BHT) was difficult to estimate. The histopathological findings showed that mild fibrotic changes were observed around the macrophages that had engulfed the PT1 in the 3-day, 6-mo, and 12-mo rat sacrifice groups. As for pulmonary tumors, no malignant tumors were observed, although 2 adenomas at 6 mo and 1 adenoma and 1 squamous metaplasia at 12 mo after the exposure were found in the rat lungs.

Magnetometric Evaluation for Cytotoxicity of Potassium Octatitanate Whisker on Alveolar Macrophages of Fischer 344 Rats

Magnetometric Evaluation for Cytotoxicity of Potassium Octatitanate Whisker on Alveolar Macrophages of Fischer 344 Rats: Mitsuyasu Watanabe, et al. Department of Preventive Medicine and Public Health, Kitasato University School of Medicine—Alveolar macrophages are thought to play a major role in the pathophysiology of lung diseases caused by exposure to various kinds of pathogens and particles. In the present study, the cytotoxic effect of potassium octatitanate whisker (PT) on macrophages was evaluated by means of magnetometry, lactate dehydrogenase (LDH) release measurement, apoptosis measurement and morphological observations. Alveolar macrophages obtained from Fischer rats (F344/N Sic) by bronchoaiveolar lavage were incubated in vitro for 18 h with Fe3O4 as a magnetometric indicator, and PTs as test materials. In the control group and the group exposed to 10 μg/ml of PT, rapid attenuation of the remanent magnetic field (RMF), so called “relaxation,” was observed immediately after cessation of the external magnetic field. In comparison, a delay of relaxation was observed in alveolar macrophages exposed to 20 and 40 μg/ml of PT. The decay constants, which are calculated from decreasing RMF for the first 2 min, in the groups exposed to 20 and 40 μg/ml of PT had significantly lower values than the control. LDH release induced by exposure to 20 and 40 μg/ml of PT increased significantly in a concentration dependent manner in PT‐exposed macrophages, whereas only negligible LDH release was observed in control groups. The level of PT affecting alveolar macrophages was at the same concentration, and in a dose‐dependent manner among relaxation, decay constant and LDH measurement. A DNA ladder detection method and morphological observations detected no apoptosis in PT‐exposed macrophages. Electron microscopic examination revealed vacuolar changes and cell membrane damage in PT‐exposed macrophages, but no significant changes in control macrophages. The results of magnetometry, LDH release, apoptosis measurement and electron microscopic observations suggest concentration dependent cytotoxicity caused by exposure of alveolar macrophages to PT.

Clearance of Inhaled Potassium Octatitanate Whisker from Rat Lungs

Clearance of Inhaled Potassium Octatitanate Whisker from Rat Lungs: Hiroshi Yamato, et al. Department of Environmental Health Engineering, University of Occupational and Environmental Health, Japan—The clearance rate of inhaled man‐made fibers (MMFs) is one of the important factors for predicting health hazards in human. Potassium octatitanate whisker is a newly developed MMF in Japan with strong resistance to heat and chemicals. Two types of commercially sold potassium octatitanate whisker were used in this study. In order to examine the rate of clearance of this whisker, rats were exposed to whisker aerosol for 4 weeks and the rate of clearance of inhaled whiskers from rat lungs was examined in terms of the fiber mass clearance rate and dimensional change in whiskers. The decrease in fiber mass retained in rat lungs was expressed with a two‐compartment model. As for the dimensional change in whiskers, no decrease was observed in diameter and no surface change due to dissolution was detected over the 12‐month observation period. Macrophage mediated clearance was thought to be the main mechanism for the clearance of potassium octatitanate whiskers.

Gene Expression of Clara Cell Secretory Protein, Surfactant Protein‐A and Thyroid Transcription Factor‐1 in the Lungs of Rats Exposed to Potassium Octatitanate Whiskers in vivo

Gene Expression of Clara Cell Secretory Protein, Surfactant Protein‐A and Thyroid Transcription Factor‐1 in the Lungs of Rats Exposed to Potassium Octatitanate Whiskers in vivo: Li Ding, et al. Institute of Industrial and Ecological Sciences, University of Occupational and Environmental Health, Japan—Inhalation studies have shown that exposure to potassium octatitanate whiskers (PT1), an asbestos substitute, produces pulmonary fibrotic changes, suggesting that PT1 might have fibrogenic potential. It has been theorized that Clara cell secretion protein (CCSP) and surfactant protein‐A (SP‐A) play a critical role in regulating the acute inflammatory response in the lung. The present study was conducted to investigate the time course (3 days, 1 wk, 1 month, 3 months, and 6 months) of the expression of mRNA of CCSP, SP‐A and thyroid transcription factor‐1 (TTF‐1), a common transcription factor of CCSP and SP‐A, in lungs exposed to PT1in vivo. PT1 suspended in saline was administered to male Wistar rats at a dose of 2 mg or 10 mg by single intratracheal instillation, and RNA was then extracted from the lungs. Expression of CCSP, SP‐A and TTF‐1 mRNA from the lungs was examined by reverse transcription‐polymerase chain reaction. Exposure to 2 mg of PT1 did not increase levels of CCSP, SP‐A or TTF‐1 mRNA. The level of SPA mRNA in PT1‐exposed rats was decreased at 1,3 and 6 months after a single instillation of 10 mg. Levels of CCSP and TTF‐1 mRNA were also decreased at 3 days, 3 and 6 months after a single instillation. These findings suggest that CCSP and SP‐A are involved not only in the acute inflammatory response but also in the chronic response of the lung exposed to PT1.

COMPARISON OF GENE EXPRESSION OF CYTOKINES mRNA IN LUNGS OF RATS INDUCED BY INTRATRACHEAL INSTILLATION AND INHALATION OF MINERAL FIBERS

To investigate whether the results of intratracheal instillation studies on mineral fibers reflect the findings obtained by long-term inhalation data on mineral fibers, we have examined gene expression of cytokines and pathological features in lungs induced by intratracheal instillation and inhalation of mineral fibers. Male Wistar rats were given a single intratracheal instillation of 2 mg alumina silicate refractory fiber (RF1) or potassium octatitanate whisker (PT1), and were sacrificed 4 wk after the fiber instillation. Long-term inhalation studies were also performed. In these, animals were exposed to fiber aerosol of RF1 or PT1 for 5 days/wk for 1 yr, and sacrificed after 1 yr of inhalation. Expression of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and transforming growth factor-beta1 (TGF-beta1) from lungs was observed by reverse-transcription polymerase chain reaction (RT-PCR). The expression of TNF-alpha, IL-6, and TGF-beta1 mRNA in PT1-exposed lung was significantly higher than for those exposed to RF1 in both intratracheal instillation and inhalation studies. Pathological findings revealed that mild pulmonary fibrosis was seen in the lungs after intratracheal instillation and inhalation of PT1 but not RF1. Similarities were observed not only in gene expression of cytokines but in pathological features between both studies. These data suggested that the results of intratracheal instillation reflect the findings obtained from long-term inhalation data.

PT1 気管内注入によるクララ細胞分泌蛋白, サーファクタント蛋白Aと甲状腺転写因子の遺伝子発現変化

PT1 気管内注入によるクララ細胞分泌蛋白, サーファクタント蛋白Aと甲状腺転写因子の遺伝子発現変化

Effects of Mineral Fibers on the Gene Expression of Proinflammatory Cytokines and Inducible Nitric-Oxide Synthase in Alveolar Macrophages.

To determine which parameters are useful for the risk assessment of man-made mineral fibers (MMMFs), we examined the gene expression of interleukin-1 alpha (IL-1 alpha), tumor necrosis factor alpha (TNF alpha), interleukin-6 (IL-6) and inducible nitric-oxide synthase (iNOS) in mineral fiber-exposed alveolar macrophages (AMs). Male Wistar rats were intratracheally exposed to saline or mineral fibers suspended in saline (2 mg of crocidolite, chrysotile, alumina silicate refractory fiber (RF1) or potassium octatitanate whisker (TW)). Bronchoalveolar lavage was performed 4 weeks after the fiber-instillation, and the recovered AMs were stimulated by lipopolysaccharide for 2 or 6 hours. Expression of IL-1 alpha, TNF alpha, IL-6 and iNOS from AMs was observed using reverse transcription-polymerase chain reaction (RT-PCR). The levels of IL-1 alpha and IL-6 mRNA induced by mineral fiber exposure were greatest in AMs exposed to TW, crocidolite, chrysotile and RF1 in that order. However, both gene expression of iNOS and TNF alpha were not elevated in both crocidolite and TW exposure, despite their high pathological potential. These data suggested that IL-1 alpha and IL-6 may be useful indicators for the risk assessment of MMMFs.

A clearance model of inhaled man-made fibers in rat lungs.

A clearance model of inhaled man-made fibers (MMFs) was developed, and the calculated fiber numbers and dimensions were compared with the experimental ones using a glass fiber (GF), ceramic fiber (RF1) and two potassium octatitanate whiskers (PT1, TW). If the translocation rate by macrophages is constant and the effect of dissolution and disintegration can be ignored, the fiber number is expected to decrease exponentially with time. In the experimental study, however, the fiber number did not always decrease exponentially. In the case of RF1, the fiber number decreased almost exponentially and the diameter decreased linearly with the time. The clearance rate constant of GF during 3 to 6 months after the end of one-month exposure was greater than that during 1 to 3 months. On the contrary, the clearance rate constants of PT1 and TW during 1 to 6 months were greater than next six months. The diameter and the length of GF did not change significantly. The fiber length of PT1 tends to become longer with time although the diameter did not change significantly. Our theoretical model gives a satisfactory fit to these experimental results.

チタン酸カリウムウィスカ気管内注入ラット肺におけるIL-6発現の経時的変化

チタン酸カリウムウィスカ気管内注入ラット肺におけるIL-6発現の経時的変化

吸入曝露されたチタン酸カリウムウィスカのラット肺からのクリアランスモデル

吸入曝露されたチタン酸カリウムウィスカのラット肺からのクリアランスモデル

Effects of mineral fibers on the expression of genes whose product may play a role in fiber pathogenesis.

To determine which factors are useful for the risk assessment of man-made fibers, we examined the gene expression of proinflammatory cytokines, growth factors, manganese superoxide dismutase (MnSOD), and inducible nitric oxide synthase (iNOS) in mineral fiber-exposed rats by means of reverse transcription-polymerase chain reaction (RT-PCR). Male Wistar rats received a single intratracheal instillation of either saline (control) or two types of fibers (2 mg of Union Internationale Centre le Cancer (UICC) chrysotile or alumina silicate refractory ceramic fiber [RCF]). Expression of interleukin-1 alpha (IL-1 alpha), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-alpha), platelet-deriving growth factor-A, (PDGF-A), platelet-deriving growth factor-B (PDGF-B), transforming growth factor beta 1 (TGF-beta 1), basic fibroblast growth factor (bFGF), MnSOD, and iNOS mRNA from lung and lipopolysaccharide (LPS)-stimulated alveolar macrophages (AM) were assessed by RT-PCR. Among these factors, IL-1 alpha, TNF-alpha, IL-6, bFGF, and iNOS would be the possible parameters for the risk assessment of fibers. In a follow-up study, we investigated the time course (3 days, 1 week, 1 month, and 3 months) of expression of IL-1 alpha and TNF-alpha by LPS-stimulated AM exposed to mineral fibers in vivo. Male Wistar rats were instilled intratracheally with saline or fibers (2 mg of Union Internationale Contre le Cancer UICC crocidolite or potassium octatitanate whisker [TW]). The expression of IL-1 alpha mRNA by fibers was greatest in TW, crocidolite, chrysotile, and RCF-instilled rat AM, in that order. The increase of IL-1 alpha and TNF-alpha mRNA in AM peaked at 1 month and 3 days after exposure to crocidolite or TW, respectively. The expression of IL-1 alpha by fibers (crocidolite, chrysotile, TW, and RCF) may be a good indicator of the pathologic potential of fibers.