ABSTRACT
Tetracyclines are a class of antibiotics that exhibited potent activity against a wide range of Gram-positive and Gram-negative bacteria, yet only five members were isolated from actinobacteria, with two of them approved as clinical drugs. In this work, we developed a genome mining strategy using a TetR/MarR-transporter, a pair of common resistance enzymes in tetracycline biosynthesis, as probes to find the potential tetracycline gene clusters in the actinobacteria genome database. Further refinement using the phylogenetic analysis of chain length factors resulted in the discovery of 25 distinct tetracycline gene clusters, which finally resulted in the isolation and characterization of a novel tetracycline, hainancycline (1). Through genetic and biochemical studies, we elucidated the biosynthetic pathway of 1, which involves a complex glycosylation process. Our work discloses nature's huge capacity to generate diverse tetracyclines and expands the chemical diversity of tetracyclines.
ABSTRACT
<p><b>BACKGROUND</b>Lidocaine and ropivacaine are often combined in clinical practice to obtain a rapid onset and a prolonged duration of action. However, the systemic toxicity of their mixture at different concentrations is unclear. This study aimed to compare the systemic toxicity of the mixture of ropivacaine and lidocaine at different concentrations when administered intravenously in rats.</p><p><b>METHODS</b>Forty-eight male Wistar rats were randomly divided into 4 groups (n = 12 each): 0.5% ropivacaine (group I); 1.0% ropivacaine and 1.0% lidocaine mixture (group II); 1.0% ropivacaine and 2.0% lidocaine mixture (group III); and 1.0% lidocaine (group IV). Local anesthetics were infused at a constant rate until cardiac arrest. Electrocardiogram, electroencephalogram and arterial blood pressure were continuously monitored. The onset of toxic manifestations (seizure, dysrhythmia, and cardiac arrest) was recorded, and then the doses of local anesthetics were calculated. Arterial blood samples were drawn for the determination of local anesthetics concentrations by high-performance liquid chromatography.</p><p><b>RESULTS</b>The onset of dysrhythmia was later significantly in group IV than in group I, group II, and group III (P < 0.01), but there was no significant difference in these groups (P > 0.05). The onset of seizure, cardiac arrest in group I ((9.2 + or - 1.0) min, (37.0 + or - 3.0) min) was similar to that in group II ((9.1 + or - 0.9) min, (35.0 + or - 4.0) min) (P > 0.05), but both were later in group III ((7.5 + or - 0.7) min, (28.0 + or - 3.0) min) (P < 0.05). The onset of each toxic manifestation was significantly later in group IV than in group I (P < 0.01). The plasma concentrations of the lidocaine-alone group at the onset of dysrhythmia (DYS), cardiac arrest (CA) ((41.2 + or - 6.8) min, (59.0 + or - 9.0) min) were higher than those of the ropivacaine alone group ((20.5 + or - 3.8) min, (38.0 + or - 8.0) min) (P < 0.05). The plasma concentrations of ropivacaine inducing toxic manifestation were not significantly different among groups I, II, and III (P > 0.05).</p><p><b>CONCLUSIONS</b>The systemic toxicity of the mixture of 1.0% ropivacaine and 2.0% lidocaine is the greatest while that of 1.0% lidocaine is the least. However, the systemic toxicity of the mixture of 1.0% ropivacaine and 1.0% lidocaine is similar to that of 0.5% ropivacaine alone.</p>
