CELLULAR BIOLOGICAL EFFECTS AND A SINGLE TRANSTRACHEAL INJECTION TEST IN THREE TYPES OF WHISKER FIBERS

Morphology and structural characteristics of hydroxyapatite whiskers: effect of the initial Ca concentration, Ca/P ratio and pH

Hydrothermal homogeneous precipitation combines the best characteristics of the hydrothermal and homogeneous precipitation methods, and allows long and uniform hydroxyapatite (HA) whiskers, with a high aspect ratio and high crystallinity, to be obtained. Their morphology and structural characteristics depend on the initial Ca/P ratio (iCa/P) and pH (ipH), as well as the initial calcium concentration (i[Ca]). Variation in these values had no effect on constitution, which was crystallographically indistinguishable from HA. Ca/P ratio steadily improved with increases in both ipH and iCa/P, but was independent of i[Ca]. Uniform whiskers were obtained at high iCa/P and low ipH, or at high ipH and low iCa/P. Whiskers with a mean length of 96-140 μm and an aspect ratio of 96-136 were obtained at ipH=2-3 and iCa/P=1.67-2. At a low ipH and low iCa/P, irregular plate-like particles and branch-like whiskers were formed, while a high ipH favoured the formation of lath-like HA at high iCa/P. Preferred growth along the c-axis was more intense at higher iCa/P and ipH as well as at low i[Ca]. However, under these conditions, the crystal growth habit was also changed, showing preferred growth along both the c- and a-axes. The increase in whisker width over the general value obtained was abrupt at low i[Ca] and high iCa/P.

Cytotoxicity and solubility evaluation of two types of whiskers by cell magnetometry

OBJECTIVES

We investigated two types of whiskers, an antimony-containing tin-oxide-coated aluminum borate whisker (CABW) and an aluminum borate whisker (ABW), which are asbestos substitutes, in order to evaluate the safety of these fibers.

METHODS

The cytotoxicity and solubility of CABW and ABW were evaluated by cell magnetometry, LDH assay and solubility test.

RESULTS

ABW was found to be cytotoxic by cell magnetometry and slightly less soluble than CABW. In addition, it was found that the solubility of both fibers was intermediate between that of chrysotile and rock wool, as compared to our previous test results. Regarding the LDH assay, no significant difference was found among the fibers tested. These findings suggested that CABW, the surface of which is coated with antimony-containing tin oxide, had lower cytotoxicity and slightly higher solubility than ABW.

CONCLUSIONS

This study was only a short-term cytotoxicity and solubility study. Therefore, further safety assessment should be carried out in long-term experiments to examine the half-life of these fibers and monitor the potential development of lung carcinoma or mesothelioma after intratracheal instillation of these fibers in rats.

Synthesis and characterization of hydroxyapatite whiskers by hydrothermal homogeneous precipitation using acetamide

Long and uniform HA whiskers with high crystallinity, controlled morphology and high aspect ratio were successfully synthesized by hydrothermal homogeneous precipitation using acetamide. Compared with the additive urea, which is commonly used to raise the pH to drive nucleation and growth of HA crystals, acetamide has a low hydrolysis rate under the required hydrothermal conditions. This allows better and easier control, giving rise to rapid growth of whiskers at a low supersaturation. Whisker length and width were in turn determined by solution conditions, including the concentration of Ca and PO(4). Whiskers had a mean length of 60-116 microm and an aspect ratio of 68-103 for starting solutions containing 42-84 mmolL(-1) Ca and 25-50 mmolL(-1) PO(4) with a fixed Ca/P ratio of 1.67. Such whiskers are favourable for their improved bone bonding and bioactivity, as well as their mechanical properties. Whiskers were slightly Ca-deficient with Ca/P=1.60-1.65, with the preferred direction of growth along the c-axis. Variation of acetamide concentration did not affect the constitution, the crystallinity or the crystal growth habit.

Magnetometric evaluation of the effects of man-made mineral fibers on the function of macrophages using the macrophage cell line RAW 264.7

The toxic effects of man-made mineral fibers (MMMFs) have been evaluated by cell magnetometry using alveolar macrophages (AMs). Recently, on the other hand, the murine macrophage cell line, RAW 264.7, became available and has been used as an in vitro model of AMs. The objective of this study was to determine whether or not cell magnetometry using RAW 264.7 cells can be used to evaluate the toxic effects of MMMFs. RAW 264.7 cells were exposed to one of the MMMFs, potassium octatitanate (PT) or silicon carbide whisker (SiC) at 0, 20, 40 and 60 microg/ml, or chrysotile as a positive control at 0, 15, 20 and 25 microg/ml. The toxic effects of fibers were evaluated by cell magnetometry and LDH assay. For this comparison, AMs were also exposed to chrysotile fibers (CF). In the RAW 264.7 cells exposed to PT 20, 40, 60 or SiC 20, 40, 60, CF 15, 20 and 25 microg/ml, significant delayed relaxation were observed compared with the respective control. In the LDH assay, significant increases in LDH in the supernatant of the cells exposed to PT 20, 40, 60, SiC 20, 40, 60 and CF 15, 20, 25 microg/ml were observed. In AMs exposed to CF 20, 25 microg/ml significant delayed relaxation and significant increases in LDH compared with the control were observed. The levels of MMMFs that induced significant differences were similar for cell magnetometry and LDH. The levels of CF that induced significant differences in cell magnetometry and LDH were identical for RAW 264.7 cells and AMs. Our results suggest that cell magnetometry using RAW 264.7 cells is adequate to evaluate the cytotoxicity of exposure to MMMFs.

Acute biological effects of intratracheally instilled titanium dioxide whiskers compared with nonfibrous titanium dioxide and amosite in rats

The dimensions of man-made mineral fiber whiskers are similar to those of some kinds of asbestos. Thus these mineral fibers raise the concern for potential health hazard for workers exposed in the occupational environments. This study was designed to define acute biological effects of intratracheally administered titanium dioxide whiskers (TO1) compared with nonfibrous titanium dioxide (TOP) and UICC amosite (Ams), and their relations to acute lung inflammation in rats. The observed geometric mean length (microm) and width (microm) and geometric standard deviation are: TO1(2.1[2.0], 0.14[1. 53]); Ams (4.3[3.3], 0.31[1.9]); and TOP (50 nm, 1-2 microm aggregates). Ten-week-old Wistar-Jcl male rats received a single tracheal injection of test materials at doses between 0.05 and 1.0 mg/rat. Control animals were injected with the same volume of saline. Lung tissue and bronchoalveolar lavage (BAL) fluid were collected from rats on days 1, 3, and 7 after administration. In the group injected with TO1, total protein, cytokine-induced neutrophil chemoattractant (CINC)/growth-regulated gene product (GRO), interleukin (IL) 1beta, and tumor necrosis factor (TNF) alpha increased on day 1. Subsequently, total elastolytic activity and fucose levels in BAL increased by day 3. All parameters, except for fucose in BAL, recovered to the normal levels. Animals in the Ams group showed increased total protein and CINC/GRO and decreased total elastolytic activity in a dose-dependent manner on day 1. The fucose level increased on day 3 in the Ams group. All parameters returned to their control levels on day 7. Animals in the TOP group did not show significant changes any of parameters during the experimental period. Gene expression of TNF-alpha and monocyte chemoattractant protein (MCP) 3 in the lung increased dose-dependently in the animals treated with the three materials. The mRNAs for eotaxin and MIP-1alpha were overexpressed in the lung of animals treated with Ams and TO1, while RANTES mRNA was overexpressed dose-dependently in the lung of animals treated with Ams on day 1. Onset of inflammatory response was more rapid in the Ams group than the TO1 group. Recovery of the fucose level in BAL was slower in the TO1 group than in the Ams group, though we observed similar histopathological changes in the lung of animals with TO1 or Ams. We conclude that whisker-induced acute biological effects in the lung may be related to the shape of the whiskers and not to their chemical composition or surface crystal structure, showing biological effects similar to those of UICC amosite.