Health risk of chrysotile revisited

This review provides a basis for substantiating both kinetically and pathologically the differences between chrysotile and amphibole asbestos. Chrysotile, which is rapidly attacked by the acid environment of the macrophage, falls apart in the lung into short fibers and particles, while the amphibole asbestos persist creating a response to the fibrous structure of this mineral. Inhalation toxicity studies of chrysotile at non-lung overload conditions demonstrate that the long (>20 µm) fibers are rapidly cleared from the lung, are not translocated to the pleural cavity and do not initiate fibrogenic response. In contrast, long amphibole asbestos fibers persist, are quickly (within 7 d) translocated to the pleural cavity and result in interstitial fibrosis and pleural inflammation. Quantitative reviews of epidemiological studies of mineral fibers have determined the potency of chrysotile and amphibole asbestos for causing lung cancer and mesothelioma in relation to fiber type and have also differentiated between these two minerals. These studies have been reviewed in light of the frequent use of amphibole asbestos. As with other respirable particulates, there is evidence that heavy and prolonged exposure to chrysotile can produce lung cancer. The importance of the present and other similar reviews is that the studies they report show that low exposures to chrysotile do not present a detectable risk to health. Since total dose over time decides the likelihood of disease occurrence and progression, they also suggest that the risk of an adverse outcome may be low with even high exposures experienced over a short duration.

Cytotoxicity of respirable dusts from industrial minerals: comparison of two naturally occurring and two man-made silicates

The membranolytic and cytotoxic properties of two naturally occurring (chrysotile asbestos; attapulgite clay) and two man-made (Fiberfrax, an aluminium-silicate, and xonotlite, a calcium silicate) industrial minerals were compared. "Short" fiber fractions of chrysotile and Fiberfrax were obtained by sedimentation in demineralized water, while the attapulgite and xonotlite samples were used as obtained. The aluminium silicate fibers were found to be non- hemolytic, while for the other three silicates, chrysotile had the strongest hemolysis potential, followed very closely by xonotlite; attapulgite was less hemolytic than the former two silicates, but was nevertheless highly hemolytic to the rat erythrocytes. Using rat pulmonary alveolar macrophages, the in vitro cytotoxicity assays showed that with fresh cell monolayers, all four silicates were equivalent in causing cell damages at a dose of 250 micrograms; at a lower dose (50 micrograms), the intensity of the cytotoxic effect was in the decreasing order: Fiberfrax greater than attapulgite greater than chrysotile greater than xonotlite. With one day-old cultured cell monolayers, a dose of 250 micrograms of the silicates fibers was less cytotoxic, with the exception of the attapulgite fibers which remained essentially as cytotoxic as with the fresh cell monolayers. The reduced cytotoxic response was especially noticeable with the chrysotile fibers. At 50 micrograms, the cytotoxicity scale of the mineral dusts with one day-old cell monolayers was essentially the same as the one obtained with the fresh cell monolayers, that is: Fiberfrax approximately equal to attapulgite greater than chrysotile greater than or equal to xonotlite. Overall, these in vitro tests imply: 1) that all four industrial silicates tested can be considered to be "biologically active"; 2) that on the basis of their different reactivities with the two types of cell culture conditions used, their biological reactivity in vivo might be quite distinct. This might be especially true for at least the chrysotile, attapulgite and xonotlite short fibers, considering that these three types of silicate dusts have very similar dimensions. Moreover, for the chrysotile and attapulgite samples, fiber numbers is probably not an important factor, since the density of the two silicates is roughly the same. The unaltered cytotoxic responses of the American attapulgite fibers in the two macrophage assays correlate well with the fact that short attapulgite fibers seems to have a stronger in vivo reactivity than short chrysotile fibers. In fact, it might be the strongest of the four industrial silicates tested.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytotoxic effects of aramid fibres on rat pulmonary macrophages: comparison with chrysotile asbestos

Aramid fibres have been proposed as a substitute for many asbestos uses. Although dimensional characteristics of aramid fibres vary with the type of application, some of the commercial grades proposed contain fibres whose geometry is clearly in a range where biological reactivities have been reported for other natural or man-made fibres. We wish to report that short aramid fibres, when tested on cultures of rat pulmonary alveolar macrophages (PAMs), induce the commonly recognized signs of a cytotoxic effect, that is: leakage of cytoplasmic and lysosomal marker enzymes, concomittant with a decreased ATP cell content.

Effect of age and glucocorticoid administration on the proteolytic activity of gastric mucosa: a comparative study in the young rat, calf and piglet

The proteolytic activity of gastric mucosa markedly increased from 2 to 4 wk of age in rats and from birth to 8 wk in pigs. In calves it was at adult level at birth, then decreased until d 14 and remained at a relatively low level up to d 56 of age. Early postnatal glucocorticoid injections increased (P less than .05) the proteolytic activity of gastric mucosa in rats, decreased (P less than .05) the abomasal proteolytic activity in calves and had no significant effect in pigs. The high levels of proteolytic activity observed in the rat at earlier ages after glucocorticoid treatment suggested a precocious maturation of the gastric mucosa. Injections of different doses of hydrocortisone acetate and dexamethasone to calves and rats indicated that proteolytic activity of gastric mucosa is only sensitive to high doses (i.e., nonphysiological) of glucocorticoids. The response of gastric mucosa to glucocorticoid injections depended on the animal's age; maximum response was obtained in the early postnatal period while minimal response was observed after weaning.

The hemolytic activity of chrysotile asbestos fibers: a freeze-fracture study

Short asbestos fibers isolated by a sedimentation procedure have a strong hemolytic activity. In the presence of ferritin particles, hemolysis by chrysotile fibers is inhibited at least during the first 10 min. Freeze-fracture studies show that after 20 sec or 2 min of contact between the fibers and the RBC membrane, the intramembranous particles remain randomly distributed over the whole surface of the P-face. On the E-face of the asbestos-treated red blood cell membranes, the number of intramembranous particles is significantly reduced. With the transmission electron microscopy, it is not possible to resolve the trilaminar structure of the ghost membrane around the deeply buried asbestos fibers. It is postulated that the membrane defects brought about by asbestos are caused by the adsorption of one membrane constituent, possibly phospholipids, on the chrysotile fibers.

Effects of administration of glucocorticoids on pancreas and growth of dairy calves

The possibility of reducing calf weaning age by accelerating development of the pancreas of dairy calves with hormone administration was studied. Hydrocortisone acetate or dexamethasone was injected at 3 or 17 days of age to determine their effects on the pancreas. Hydrocortisone acetate injections (50 mg/kg body weight) to 3-day-old calves increased within 4 days the pancreas weight, amylase and chymotrypsin activities, and proteins, ribonucleic acid, and deoxyribonucleic acid contents. However, the glucocorticoid injection had no effect on activities of digestive enzymes of the 21-day-old calves. The pancreas hypertrophied in the 7-day-old calves following hormonal treatment. In the 21-day-old calves administration of glucocorticoids brought about hyperplasia of the pancreas but no hypertrophy of the tissue. This response of the pancreas to injections of glucocorticoids in the 7-day-old calves was interpreted as an acceleration of normal development of the tissue. Hydrocortisone acetate injection to 3-day-old calves had no effect on feed consumption but had a small depressive effect on growth of calves at 14 and 21 days of age.

Isoelectric focusing of pure rat pancreatic juice in polyacrylamide gel : possibility of concomitant estimation of radioactivity incorporated into single identified protein constituents

A method is described for the isoelectric focusing of rat pancreatic juice on columns of polyacrylamide gel containing urea. Twenty-six bands were separated, and 6 were identified. Application of this method of separation to in vivo radioactively labelled pancreatic juice resulted in bands which could be counted with precision. This procedure allowed also the expression of radioactivity of one constituent relative to any single band, or relative to total radioactivity, concomitantly.

Early dissociation of protein synthesis and amylase secretion following hormonal stimulation of the pancreas

The secretion of the various pancreatic enzymes can be increased by hormonal and cholinergic stimulation. However, it is not yet clear among the different investigators if their synthesis remains constant or can be modified according to different metabolic conditions. The secretion and synthesis of the pancreatic proteins were then studied in parallel to evaluate if secretion triggers synthesis or both phenomenons are controlled by separate mechanisms.The approach for these studies consists mainly in a combination of in vivo and in vitro experiments. The stimulants were injected in vivo and the pancreatic secretions were collected for different periods of time. The animals were then sacrificed and protein synthesis was measured in vitro along with the amylase secreted into the incubation medium. The results show that protein synthesis is decreased during the first 15 min after a single injection or infusion of both cholecystokinin–pancreozymin (CCK–PZ) and secretin. This reduction was associated with an increase in amylase secreted into the incubation medium. However, at 30 min after the hormonal stimulation, protein synthesis is increased while secretion into the incubation medium had returned to control levels. This increase in protein synthesis lasts for at least 1 h. These results strongly suggest that pancreatic enzyme secretion and synthesis are dissociated in the early minutes following hormonal stimulation.

Biochemical reactions involved in pancreatic enzyme secretion. I. Activation of the adenylate cyclase complex

Pancreatic amylase secretion was studied using an in vitro system. Secretion was increased by urecholine and cholecystokinin–pancreozymin (CCK–PZ). Addition of tetracaine and dibucaine to the medium abolished secretion stimulated by urecholine and decreased by 75% that stimulated by CCK–PZ. In contrast, an increase in enzyme secretion was observed after dibutyryl cyclic AMP; this was potentiated by tetracaine added to the medium. Oxygen uptake by pieces of pancreatic tissue was not affected by tetracaine. Adenylate cyclase activity, increased in vitro when CCK–PZ was added to a pancreas homogenate, was inhibited by 15% by tetracaine at 2 mM and by 67.5% at the 10 mM concentration.From data known on biochemical reactions associated with the process of secretion and the results described in the present paper, we propose a model for the activation of the pancreatic adenylate cyclase complex. Associated to the depolarization of the acinar cell plasma membrane by urecholine and CCK–PZ and an inward movement of sodium and calcium, there is an immediate rise in adenylate cyclase activity within 10 s which is timed with the initiation of amylase secretion.

Evidence that protein synthesis can be increased in vitro following cholinergic stimulation

These experiments were performed to evaluate secretory and synthetic responses of rat pancreas using in vitro experimental models. With previously described in vitro models, it was impossible to increase pancreatic protein synthesis over control level during or following stimulated enzyme secretion. An in vitro model is proposed combining four different incubation periods: preincubation, stimulation, stabilization, and incorporation. With this model, a 41% increase in protein synthesis has been observed following cholinergic stimulation. This increase occurred only if the previously increased secretion had returned to basal level during the incorporation period. These data would suggest that secretion and synthesis are two separate controlled mechanisms but any increase in synthesis requires a previously increased secretion.

Determination of pancreatic amylase activity by a radial diffusion assay

A technique for assay of amylase content in homogenates of rat pancreas is described. It is based on the measurement of the diameter of a "reaction zone" resulting from the action of the enzyme diffusing through a gel containing the substrate. The method is used to evaluate the amylase content of the pancreas of rats stimulated by feeding and by insulin-hypoglycemia. The results are compared with those obtained by a classic amyloclastic method, using the optical density of the starch-iodine complex.