In Vitro and In Vivo Antimicrobial Activities of Gallium Nitrate against Multidrug-Resistant Acinetobacter baumannii

Multidrug-resistant Acinetobacter baumannii poses a tremendous challenge to traditional antibiotic therapy. Due to the crucial role of iron in bacterial physiology and pathogenicity, we investigated iron metabolism as a possible target for anti-A. baumannii chemotherapy using gallium as an iron mimetic. Due to chemical similarity, gallium competes with iron for binding to several redox enzymes, thereby interfering with a number of essential biological reactions. We found that Ga(NO₃)₃, the active component of an FDA-approved drug (Ganite), inhibits the growth of a collection of 58 A. baumannii strains in both chemically defined medium and human serum, at concentrations ranging from 2 to 80 μM and from 4 to 64 μM, respectively. Ga(NO₃)₃ delayed the entry of A. baumannii into the exponential phase and drastically reduced bacterial growth rates. Ga(NO₃)₃ activity was strongly dependent on iron availability in the culture medium, though the mechanism of growth inhibition was independent of dysregulation of gene expression controlled by the ferric uptake regulator Fur. Ga(NO₃)₃ also protected Galleria mellonella larvae from lethal A. baumannii infection, with survival rates of ≥75%. At therapeutic concentrations for humans (28 μM plasma levels), Ga(NO₃)₃ inhibited the growth in human serum of 76% of the multidrug-resistant A. baumannii isolates tested by ≥90%, raising expectations on the therapeutic potential of gallium for the treatment of A. baumannii bloodstream infections. Ga(NO₃)₃ also showed strong synergism with colistin, suggesting that a colistin-gallium combination holds promise as a last-resort therapy for infections caused by pan-resistant A. baumannii.     

Effects of titrated beta blockade (metoprolol) on silent myocardial ischemia in ambulatory patients with coronary artery disease

This study investigates effects of beta-adrenergic blockade on total silent ischemic time assessed by ambulatory electrocardiographic monitoring and its relation to heart rate and time of day in ambulatory men with coronary artery disease. Metoprolol, when titrated to optimal dose in a controlled trial in 9 patients, reduced both total silent ischemic time (from 156 +/- 65 to 20 +/- 15 minutes, p = 0.04) and frequency of silent ischemic episodes (from 8 +/- 2 to 2 +/- 2 episodes, p = 0.03) compared with placebo. Mean daily heart rate was reduced, from 82 +/- 2 beats/min during placebo to 58 +/- 1 beats/min, as was heart rate at onset of 1 mm of ST-segment depression (106 +/- 2 to 74 +/- 4 beats/min, both p less than 0.001). Heart rate increased 10 +/- 1 beats/min during silent ischemia with placebo therapy, but increased only 4 +/- 1 beats/min during metoprolol treatment (p less than 0.03). During placebo administration the largest proportion of silent ischemic time occurred between 0600 and 1200 hours. Metoprolol attenuated this circadian variation in silent ischemia while reducing (p less than 0.05) total silent ischemic time in all periods. Thus, beta-adrenergic blockade reduces the frequency of silent myocardial ischemic episodes and total silent ischemic time, while mean daily heart rate and heart rate at onset of ischemia and maximal ischemia decrease. Metoprolol treatment also attenuates circadian variation of silent ischemia. These data may be interpreted to suggest that beta-adrenergic activation operates in the pathogenesis of silent myocardial ischemia and its circadian variation.     

Low-frequency requirements for recording ischemic ST-segment abnormalities in coronary artery disease

The objective of this investigation was to determine whether extended low-frequency response is required to record ischemic ST-segment abnormalities in humans. Bipolar electrocardiograms (ECGs) were recorded in 5 men with coronary artery disease using a high-fidelity instrumentation amplifier and FM tape recorder before, during and after erect bicycle exercise. In all patients, ischemic ST-segment abnormalities developed during exercise; 3 patients had angina and 2 remained asymptomatic throughout the test. Using a fast-Fourier transform (FFT) and a variable digitizing rate into a 1,024-point input array, FFT spectra were computed with low-frequency content extending to either 0.20, 0.98 or 1.95 Hz for both a rest and exercise ECG. From these spectra, ECGs were resynthesized using the inverse FFT and compared with the original records. Visual inspection of the original and resynthesized ECGs revealed no obvious differences when low-frequency content extended to 0.20, 0.98 or 1.95 Hz. Numerical comparisons were made by calculating the coefficient of determination (R2) between the original and resynthesized ECGs. The R2 (mean +/- standard deviation) for these comparisons was 0.998 +/- 0.001. It is concluded that the amplitude-response characteristics of electrocardiographic recording equipment do not require extended low-frequency range (such as that found in FM systems) to accurately reproduce ischemic ST-segment abnormalities in humans.     

Silent myocardial ischemia during daily activities: studies in asymptomatic patients and those with various forms of angina

Asymptomatic subjects with proven coronary artery disease, including those with no previous manifestations of coronary heart disease and those with previous myocardial infarction, have silent ischemic episodes during daily activity. Patients with all forms of angina, stable effort and unstable rest angina, and those with coronary artery spasm have very frequent episodes of silent myocardial ischemia during ordinary activity. Characteristics of these episodes and evidence for these findings are reviewed.     

Application of time series analysis to circadian rhythms: effect of beta-adrenergic blockade upon heart rate and transient myocardial ischemia

Circadian variations of transient myocardial ischemia and heart rate have been identified, but the rhythms and their response to beta blockade have not been fully characterized. Time-series analysis, a mathematical technique to describe oscillatory activity occurring within a continuous data set was used, to address these issues. Nine men with coronary artery disease underwent 72 hours of ambulatory electrocardiographic monitoring during therapy with placebo or metoprolol. During administration of placebo, ischemic time and heart rate showed a primary peak with a periodicity of approximately 24 hours with a tight coupling between the 2 variables and a secondary peak with a periodicity of 5 to 8 hours. During metoprolol therapy, heart rate and ischemic variation were reduced and the 24-hour periodicity for heart rate only remained. The 24-hour periodicity for ischemia was eliminated, but the data with 5- to 8-hour periodicity became the major component of the signal.     

Cumulative effects of quinidine and aspirin on bleeding time and platelet alpha 2-adrenoceptors: potential mechanism of bleeding diathesis in patients receiving this combination

We observed quinidine-induced prolongation of bleeding time without thrombocytopenia in three subjects. In addition, we noticed a cumulative prolongation of bleeding time by a combination of quinidine and aspirin. We postulated that because both quinidine and aspirin inhibit epinephrine-induced platelet aggregation, a cumulative effect of the two drugs might be responsible for the hemostatic defect. In studies using normal human platelets, we confirmed a marked reduction in epinephrine-induced platelet aggregation by the combination of these two agents. To further study the potential mechanism of this cumulative effect, platelet lysates were incubated with the alpha 2-adrenoceptor antagonist tritiated yohimbine in the presence of quinidine and aspirin. On the basis of the radioligand binding data, the dissociation constant (KD) of alpha 2-adrenoceptors was observed to increase in the presence of quinidine as well as aspirin. The combination of these two agents caused a marked increase in the KD of platelet alpha 2-adrenoceptors without alteration in the number of receptor sites. These data suggest that the cumulative effects of quinidine and aspirin on platelet alpha 2-adrenoceptor KD may relate to the significant reduction in epinephrine-induced platelet aggregation. This phenomenon, coupled with other well-known effects of aspirin on the platelet release reaction and arachidonate metabolism, may lead to bleeding problems in some patients receiving this combination.     

The detection of human papillomavirus DNA in skin tags

Human papillomavirus (HPV) is associated with benign cutaneous or mucosal lesions and with malignant tumours, but none of the HPV types has so far been related to skin tags. Skin biopsy specimens from 49 Caucasian patients suffering from the presence of multiple soft fibromas were analysed by means of dot blot hybridization and by polymerase chain reaction assays aimed at detecting all known HPV types. The results revealed the presence of HPV DNA type 6/11 in 88% of the skin tags examined. This result supports the hypothesis that HPV plays a part in the progression of cutaneous soft fibromas, as previously reported for laryngeal papillomas.     

Pyoverdine and Proteases Affect the Response of Pseudomonas aeruginosa to Gallium in Human Serum

Gallium is an iron mimetic which has recently been repurposed as an antibacterial agent due to its capability to disrupt bacterial iron metabolism. In this study, the antibacterial activity of gallium nitrate [Ga(NO₃)₃] was investigated in complement-free human serum (HS) on 55 Pseudomonas aeruginosa clinical isolates from cystic fibrosis and non-cystic fibrosis patients. The susceptibility of P. aeruginosa to Ga(NO₃)₃ in HS was dependent on the bacterial ability to acquire iron from serum binding proteins (i.e., transferrin). The extent of serum protein degradation correlated well with P. aeruginosa growth in HS, while pyoverdine production did not. However, pyoverdine-deficient P. aeruginosa strains were unable to grow in HS and overcome iron restriction, albeit capable of releasing proteases. Predigestion of HS with proteinase K promoted the growth of all strains, irrespective of their ability to produce proteases and/or pyoverdine. The MICs of Ga(NO₃)₃ were higher in HS than in an iron-poor Casamino Acids medium, where proteolysis does not affect iron availability. Coherently, strains displaying high proteolytic activity were less susceptible to Ga(NO₃)₃ in HS. Our data support a model in which both pyoverdine and proteases affect the response of P. aeruginosa to Ga(NO₃)₃ in HS. The relatively high Ga(NO₃)₃ concentration required to inhibit the growth of highly proteolytic P. aeruginosa isolates in HS poses a limitation to the potential of Ga(NO₃)₃ in the treatment of P. aeruginosa bloodstream infections.