Mary U. Snitily

Cirrhosis-induced defects in innate pulmonary defenses against Streptococcus pneumoniae

BackgroundThe risk of mortality from pneumonia caused by Streptococcus pneumoniae is increased in patients with cirrhosis. However, the specific pneumococcal virulence factors and host immune defects responsible for this finding have not been clearly established. This study used a cirrhotic rat model of pneumococcal pneumonia to identify defect(s) in innate pulmonary defenses in the cirrhotic host and to determine the impact of the pneumococcal toxin pneumolysin on these defenses in the setting of severe cirrhosis.ResultsNo cirrhosis-associated defects in mucociliary clearance of pneumococci were found in these studies, but early intrapulmonary killing of the organisms before the arrival of neutrophils was significantly impaired. This defect was exacerbated by pneumolysin production in cirrhotic but not in control rats. Neutrophil-mediated killing of a particularly virulent type 3 pneumococcal strain also was significantly diminished within the lungs of cirrhotic rats with ascites. Levels of lysozyme and complement component C3 were both significantly reduced in bronchoalveolar lavage fluid from cirrhotic rats. Finally, complement deposition was reduced on the surface of pneumococci recovered from the lungs of cirrhotic rats in comparison to organisms recovered from the lungs of control animals.ConclusionIncreased mortality from pneumococcal pneumonia in this cirrhotic host is related to defects in both early pre-neutrophil- and later neutrophil-mediated pulmonary killing of the organisms. The fact that pneumolysin production impaired pre-neutrophil-mediated pneumococcal killing in cirrhotic but not control rats suggests that pneumolysin may be particularly detrimental to this defense mechanism in the severely cirrhotic host. The decrease in neutrophil-mediated killing of pneumococci within the lungs of the cirrhotic host is related to insufficient deposition of host proteins such as complement C3 on their surfaces. Pneumolysin likely plays a role in complement consumption within the lungs. Our studies, however, were unable to determine whether pneumolysin more negatively impacted this defense mechanism in cirrhotic than in control rats. These findings contribute to our understanding of the defects in innate pulmonary defenses that lead to increased mortality from pneumococcal pneumonia in the severely cirrhotic host. They also suggest that pneumolysin may be a particularly potent pneumococcal virulence factor in the setting of cirrhosis.

A Rat Model to Determine the Biomedical Consequences of Concurrent Ethanol Ingestion and Cigarette Smoke Exposure

BACKGROUND Although scientists have used animal models for years to study the effects of ethanol (EtOH) ingestion on humans, the compounding effect of cigarette smoking has been virtually ignored. Because 80 to 95% of human alcoholics smoke, it is imperative to consider the added effects of smoking when trying to determine the consequences of excessive alcohol ingestion. We therefore have developed a rat model for studying the separate and combined results of smoking and drinking on human health. METHODS Male Sprague-Dawley rats were exposed daily for 12 weeks in whole-body chambers to cigarette smoke (smoke-exposed) or room air (sham-exposed). During the final 5 weeks of exposure, the rats were fed liquid diets that contained 0, 16, 26, or 36% EtOH calories. Smoke exposure was quantified by measurement of carboxyhemoglobin, nicotine, and cotinine levels. Body weights, food consumption, blood EtOH concentrations, and various assessments of liver damage and function also were followed. RESULTS Smoke exposure in this rat model approximates that of a moderate to heavy human smoker. Smoke-exposed rats weighed significantly less and ate less food than sham-exposed controls, but both groups ingested equivalent amounts of EtOH for their body weights and had comparable blood EtOH levels. Liver aspartate and alanine aminotransferase levels remained normal. There was an EtOH-induced decrease in asialoglycoprotein receptor binding, but it was not exacerbated by smoke exposure. Alterations in blood cholesterol levels reflected what has been reported for humans, rising with increasing EtOH ingestion and decreasing with smoke exposure. CONCLUSION Our rat model is relevant to what transpires in the vast majority of alcoholics. Both ethanol ingestion and smoke exposure can be manipulated to mimic light to moderate to heavy levels, making it appropriate for studying the separate and combined biomedical consequences of alcohol abuse and cigarette smoking.

Effect of Ethanol on Fluoroquinolone Efficacy in a Rat Model of Pneumococcal Pneumonia

ABSTRACT This investigation compared the effect of ethanol on fluoroquinolone antibiotic efficacy and pharmacodynamics in an ethanol-fed rat model of pneumococcal pneumonia. Male Sprague-Dawley rats received a liquid diet containing 36% of total calories as ethanol. Paired controls (pair-fed controls) were fed a liquid diet without ethanol or received rat chow. Diets began 7 days before and continued for 10 days after transtracheal infections with 10 times the 50% lethal dose of type 3 Streptococcus pneumoniae. Beginning 18 h after infection, the rats received once daily subcutaneous phosphate-buffered saline, levofloxacin, moxifloxacin, or trovafloxacin at 50 or 100 mg/kg of body weight. White blood cell counts were determined, blood samples were collected for culture, and mortality was recorded. Additional rats were killed on day 5 for pharmacodynamic studies and quantitative cultures of bronchoalveolar lavage fluid. Bacteremia occurred by day 3 in 20 of 22 untreated rats. All 22 untreated rats died by day 9. Moxifloxacin treatment was effective in all diet groups at both the 50- and 100-mg/kg doses. In contrast, 50-mg/kg doses of levofloxacin and trovafloxacin improved survival in ethanol-fed rats but were ineffective in chow-fed rats. High-dose trovafloxacin at 100 mg/kg was associated with increased mortality in pair-fed rats. The free-fraction area under the concentration-time curve/MIC ratio exceeded 50 with all antibiotics in the ethanol group but dropped below 30 with levofloxacin and trovafloxacin in the pair- and chow-fed rats, with higher mortality. Achievement of adequate antibiotic-free fraction area under the concentration-time curve/MIC ratios helps overcome ethanol-induced immune defects induced in experimental pneumococcal pneumonia.