Faculty Bibliography

Occupational exposure to endotoxin-contaminated organic dusts is associated with a variety of adverse pulmonary effects, including chronic bronchitis and sputum production. We have previously demonstrated in F344 rats that inhaled endotoxin rapidly induces an increase in the volume of stored intraepithelial mucosubstances (Vs) in the respiratory tract. The present study examined whether endotoxin-contaminated cotton dust can produce a similar increase in Vs in this animal model. Rats were exposed to air or 1.5 to 15.0 mg/m3 cotton dust for 2 h/d for 3 d. Twenty-four hours after the final exposure, the nasal cavity and lungs were fixed in formalin and the presence of Alcian blue/periodic acid-Schiff-staining mucosubstances determined by morphometry. Exposure to cotton dust produced concentration-dependent changes in Vs in the nasal septum and intrapulmonary airways. Statistically significant increases in Vs were observed in the epithelial lining of the nasal septum of animals exposed to 5.3 and 14.5 mg/m3 cotton dust (equivalent to 2.8 and 8.9 micrograms/m3 endotoxin). Vs in the intrapulmonary airways was also significantly increased at these concentrations. No significant changes were observed in the nasal septum or intrapulmonary airways after exposure to 1.8 mg/m3 cotton dust. These results are consistent with the hypothesis that endotoxin may contribute to the increase in human cases of chronic bronchitis reported in occupational settings in which endotoxin-contaminated dusts are encountered

Components of the complement system are thought to play a role in the respiratory effects of inhaled organic dusts encountered in occupational settings such as grain storage sites and cotton mills. This hypothesis is based upon observations that grain dusts and endotoxin can activate complement in vitro and in vivo and that the complement system appears to contribute to the endotoxin-induced lung injury of septic shock. The present study examined whether the inflammatory effects of inhaled endotoxin and cotton dust were (1) blocked by decomplementing animals with cobra venom factor (CVF) or (2) present in animals genetically deficient in specific components of the complement system. In untreated and sham-treated guinea pigs, inhaled endotoxin produced significant increases in biochemical and cellular indices of pulmonary injury in bronchoalveolar lavage fluid. Treatment of guinea pigs with 200 units CVF/kg at 24 h prior to exposure did not block the biochemical and cellular changes produced by inhaled endotoxin or cotton dust. Guinea pigs deficient in the fourth component of complement (C4) also demonstrated evidence of pulmonary injury roughly equivalent to that of normal guinea pigs exposed to inhaled endotoxin or cotton dust. Finally, mice genetically deficient in the fifth component of complement (C5) did not exhibit a decreased pulmonary response to inhaled endotoxin compared to C5-sufficient mice. These studies suggest that despite in vitro and in vivo evidence of complement activation by endotoxin and extracts of organic dusts, the complement system may not play a major role in the acute respiratory effects of inhaled endotoxin and cotton dust

Increased sputum production and chronic bronchitis are associated with occupational exposure to endotoxin-contaminated organic ducts. The present study examined whether repeated exposure to occupationally relevant concentrations of airborne endotoxin in the F344 rat can alter the volume density of stored intraepithelial mucosubstances (Vs) in the respiratory tract. Rats were exposed to saline or endotoxin aerosols for 3 h/day for 3 days and were killed 24 h after the last exposure. Quantitative histochemistry of Vs in airway epithelium was examined at three distinct levels of the respiratory tract (nose, trachea, and lung). Exposure to endotoxin produced a dose-dependent increase in Vs in the intrapulmonary airways. The quantity of Vs in the intrapulmonary airways was significantly increased in animals exposed to as little as 0.3 micrograms/m3 endotoxin. Significant increases in Vs were observed in the trachea only after exposure to > or = 3.1 micrograms/m3 endotoxin, whereas no significant changes were observed in the nasal airways even at concentrations as high as 52.4 micrograms/m3. These results are consistent with earlier findings in which repeated instillation of endotoxin produced significant increases in Vs in the epithelial lining of the pulmonary airways and demonstrate that inhaled endotoxin may play a role in the increase in sputum and chronic bronchitis reported for workers exposed to organic dusts

In vivo exposure to sulfuric acid aerosols produces profound effects on pulmonary macrophage (PM phi) phagocytic function and cytokine release and perturbs intracellular pH (pHi) homeostasis. Because pHi influences a multitude of cellular processes, we sought to investigate the mechanism by which acid aerosol exposure affects its regulation. Guinea pigs underwent a single or 5 repeated 3-hr exposures to sulfuric acid aerosol (969 and 974 micrograms/m3 for single and repeated exposures, respectively). PM phi harvested immediately after exposure were incubated in HCO3-free media and their pHi recovery from an intracellular acid load was examined. The overall pHi recovery was depressed after single and multiple exposures to sulfuric acid aerosol. delta pHi (the difference between initial pHi and the one measured at 150 sec) decreased by 15.6 and 23.3% (p < 0.05) for single and repeated exposures, respectively. Initial dpHi/dt (maximum pHi recovery rate) after cytoplasmic acidification diminished by 20.3 and 32.2%, which were not statistically significant (p = 0.08 for repeated exposure). To determine whether the activity of the H(+)-ATPase pump the Na(+)-H+ exchanger was specifically altered by the acid exposures, PM phi were first incubated in Na+ and HCO3-free media with NBD-Cl (7-chloro-4-nitrobenz-2-oxa-1,3-diazol, blocking H(+)-ATPase and leaving only the Na(+)-H+ exchanger in effect) and then challenged with 30 mM NaCl. The pHi recovery of PM phi after Na challenge was significantly reduced in acid aerosol exposed guinea pigs (p < 0.05) compared to controls (for delta pHi, 18.2% lower in single exposure and 22.7% in multiple exposure groups; for initial dpHi/dt, 26.9% lower in single exposure and 22.4% in multiple exposure groups). In contrast, the H(+)-ATPase pump was inconsistently affected as indicated by delta pHi and initial dpHi/dt measured in the presence of MIA (amiloride-5-N-methylisobutyl, inhibiting the Na(+)-H+ exchanger and leaving only the H(+)-ATPase pump in effect). These results suggest that in vivo exposure to sulfuric acid aerosols induces alterations in pHi regulation in guinea pig PM phi attributable to changes in Na(+)-H+ exchanger activity

Metal fume fever is an acute self-limited illness induced most commonly by inhalation of zinc oxide fumes. The affected individual characteristically experiences the rapid onset of intense shaking chills, fever, and body aches a few hours after exposure, and symptoms dissipate spontaneously. While the occurrence of metal fume fever appears to be widespread and the current TLV/PEL of 5 mg/m3 and STEL of 10 mg/m3 may not be fully protective, no chronic health sequelae have been documented to date. Nonetheless, as any worker who has experienced a full-blown case will likely testify, metal fume fever remains one of the more noxious short-term illnesses contracted in the workplace, and its prevention deserves serious attention

An important aspect of risk assessment is identification of subpopulations particularly susceptible to the effects of inhaled pollutants. The present study examined whether female rats were more sensitive during lactation to the acute pulmonary injury produced by inhaled endotoxin. Lactating and age-matched virgin female rats were exposed to aerosols of saline or endotoxin for 3 h and lavaged at 24 h after exposure. No significant differences in lactate dehydrogenase, beta-glucuronidase, total protein, and total cell and PMN counts were observed between virgin and lactating rats after exposure to saline. Each marker of pulmonary injury except beta-glucuronidase was 1.5- to 3-fold greater in lactating than in virgin female rats exposed to 29.6 micrograms/m3 endotoxin. PMNs (6-fold), total cell counts, and protein were also significantly increased (p < 0.05) in lactating rats exposed to 1.3 micrograms/m3 endotoxin, a concentration reported to occur in a number of agricultural settings. These results demonstrate that the physiologic state of lactation is associated with an increased sensitivity to the acute pulmonary injury produced by inhaled endotoxin and are consistent with previous work demonstrating a similar increased sensitivity to ozone exposure. The possibility of a similar pattern of enhanced response in analogous groups of humans merits examination

As a cell wall component of gram-negative bacteria, endotoxin is thought to play a significant role in the respiratory effects of inhaled organic dusts which are microbially contaminated. Assessment of occupational survey data and clinical studies suggests that few measureable, acute functional changes occur below 30-50 ng/m3 endotoxin (as sampled in airborne dust with a vertical elutriator). Little information is available on the inflammatory effects of inhaled endotoxin at these low concentrations. The present study examined the dose-response relationship between inhaled endotoxin and functional, biochemical, and histological endpoints in the lungs of guinea pigs. Animals were exposed to 0.03 to 50.5 micrograms/m3 aerosolized endotoxin or the vehicle water for 4 hr. At 2 hr into exposure, significant decreases in specific airway conductance were observed only in animals exposed to 9.6 and 50.5 micrograms/m3 endotoxin (17.3 +/- 1.2 and 35.5 +/- 0.5% decreases from baseline values, respectively (mean +/- SE)). Total cell count and lactate dehydrogenase levels in bronchoalveolar lavage fluid were significantly elevated at 24 hr after exposure in all endotoxin-exposed groups except the lowest dose, 0.03 micrograms/m3 (P < 0.05). Polymorphonuclear leukocyte influx into the alveolar region was also dependent on the concentration of inhaled endotoxin. Thus, LDH activity, a biochemical marker of cell injury, and total cell counts and polymorphonuclear leukocytes, markers of inflammation, were more sensitive indices of adverse pulmonary effects from inhaled endotoxin than a functional measurement. These results suggest that subtle inflammatory changes may occur at airborne endotoxin concentrations which may produce no acute respiratory symptoms

We have conducted exposures in rats to determine pulmonary responses following inhalation of two common components of welding fumes, zinc oxide and ozone. To examine their effects on target-inducible gene expression, we measured mRNA levels of two metal-responsive genes, metallothionein (MT) and heme oxygenase (HO), in lung tissue by RNA slot-blot analysis. A 3-hr exposure to ZnO fume via a combustion furnace caused a substantial elevation in lung MT mRNA at all concentrations tested. Exposures to 5 and 2.5 mg/m3 ZnO resulted in peak 8-fold increases in MT mRNA levels (compared to air-exposed control animal values) immediately after exposure, while 1 mg/m3 ZnO exposure caused a 3.5-fold elevation in MT mRNA. These levels returned to approximate control gene expression values 24 hr after exposure. In addition, ZnO exposure caused an immediate elevation in lung HO gene expression levels, with 8-, 11-, and 5-fold increases observed after the same ZnO exposure levels (p < 0.05). Like MT gene induction, HO mRNA values returned to approximate control levels 24 hr after exposure. In striking contrast to the induction of MT and HO gene expression after ZnO exposures, there was no elevation in gene expression following a 6-hr exposure to 0.5 and 1 ppm ozone, even when lungs were examined as late as 72 hr after exposure. Our results demonstrate the induction of target gene expression following the inhalation of ZnO at concentrations equal to, and below, the current recommended threshold limit value of 5 mg/m3 ZnO. Furthermore, the lack of effect of ozone exposure on MT and HO gene expression suggests no involvement of these genes in the acute respiratory response to this oxidant compound

Occupational exposure to freshly formed zinc oxide (ZnO) particles (less than 1.0 micron aerodynamic diameter) produces a well-characterized response known as metal fume fever. An 8-hr threshold limit value (TLV) of 5 mg/m3 has been established to prevent adverse health effects because of exposure to ZnO fumes. Because animal toxicity studies have demonstrated pulmonary effects near the current TLV, the present study examined the time course and dose-response of the pulmonary injury produced by inhaled ZnO in guinea pigs, rats, rabbits, and human volunteers. The test animals were exposed to 0, 2.5, or 5.0 mg/m3 ZnO for up to 3 hr and their lungs lavaged. Both the lavage fluid and recovered cells were examined for evidence of inflammation or altered cell function. The lavage fluid from guinea pigs and rats exposed to 5 mg/m3 had significant increases in total cells, lactate dehydrogenase, beta-glucuronidase, and protein content. These changes were greatest 24 hr after exposure. Guinea pig alveolar macrophage function was depressed as evidenced by in vitro phagocytosis of opsonized latex beads. Significant changes in lavage fluid parameters were also observed in guinea pigs and rats exposed to 2.5 mg/m3 ZnO. In contrast, rabbits showed no increase in biochemical or cellular parameters following a 2-hr exposure to 5 mg/m3 ZnO. Differences in total lung burden of ZnO, as determined in additional animals by atomic absorption spectroscopy, appeared to account for the observed differences in species responses. Although the lungs of guinea pigs and rats retained approximately 20% and 12% of the inhaled dose, respectively, rabbits retained only 5%.(ABSTRACT TRUNCATED AT 250 WORDS)

Exposure to machining fluid aerosols in the automotive industry is associated with a variety of respiratory symptoms including cross-shift changes in pulmonary function, cough, asthma, and phlegm. Lubricating and cooling fluids used in machining operations are predominantly water and thus are susceptible to microbial growth. In the present study, the role of endotoxin in the acute pulmonary injury produced by machining fluid aerosols was examined in guinea pigs. Animals were exposed to nebulized water, unused machining fluid, or used machining fluid. At the end of a 3-hr exposure, specific airway conductance (SGaw) was not affected by exposure to the vehicle water, but was decreased in a dose-dependent manner by exposure to aerosols of the used machining fluid. SGaw decreased from preexposure baseline values by 0, 7, and 40% in animals exposed to 1, 10, and 100 mg/m3 used machining fluid, respectively. These exposure levels also produced acute lung injury as evidenced by changes in cellular and biochemical indices in lavage fluid. These adverse respiratory effects may have been due to microbial contamination of the used machining fluid as the aerosol exposures were associated with airborne endotoxin concentrations of 0.3, 1.9, and 5.3 micrograms/m3, respectively. Animals exposed to aerosols of the endotoxin-free unused machining fluid had no statistically significant adverse functional, cellular, or biochemical effects except for a fourfold increase in neutrophils at 100 mg/m3. These results suggest that contamination of machining fluid during use or storage may lead to the adverse respiratory effects of aerosolized machining fluids.(ABSTRACT TRUNCATED AT 250 WORDS)