The inhibition of incorporation of leucine into protein of cell-free systems from rat liver and Escherichia coli by chlortetracycline

A Complementary Mechanism of Bacterial mRNA Translation Inhibition by Tetracyclines

Tetracycline has positively impacted human health as well as the farming and animal industries. Its extensive usage and versatility led to the spread of resistance mechanisms followed by the development of new variants of the antibiotic. Tetracyclines inhibit bacterial growth by impeding the binding of elongator tRNAs to the ribosome. However, a small number of reports indicated that Tetracyclines could also inhibit translation initiation, yet the molecular mechanism remained unknown. Here, we use biochemical and computational methods to study how Oxytetracycline (Otc), Demeclocycline (Dem), and Tigecycline (Tig) affect the translation initiation phase of protein synthesis. Our results show that all three Tetracyclines induce Initiation Factor IF3 to adopt a compact conformation on the 30S ribosomal subunit, similar to that induced by Initiation Factor IF1. This compaction was faster for Tig than Dem or Otc. Furthermore, all three tested tetracyclines affected IF1-bound 30S complexes. The dissociation rate constant of IF1 in early 30S complexes was 14-fold slower for Tig than Dem or Otc. Late 30S initiation complexes (30S pre-IC or IC) exhibited greater IF1 stabilization by Tig than for Dem and Otc. Tig and Otc delayed 50S joining to 30S initiation complexes (30S ICs). Remarkably, the presence of Tig considerably slowed the progression to translation elongation and retained IF1 in the resulting 70S initiation complex (70S IC). Molecular modeling of Tetracyclines bound to the 30S pre-IC and 30S IC indicated that the antibiotics binding site topography fluctuates along the initiation pathway. Mainly, 30S complexes show potential contacts between Dem or Tig with IF1, providing a structural rationale for the enhanced affinity of the antibiotics in the presence of the factor. Altogether, our data indicate that Tetracyclines inhibit translation initiation by allosterically perturbing the IF3 layout on the 30S, retaining IF1 during 70S IC formation, and slowing the transition toward translation elongation. Thus, this study describes a new complementary mechanism by which Tetracyclines may inhibit bacterial protein synthesis.

Biochemical studies with a new cytotoxic immunosuppressive agent, 3-acetyl-5-(4-fluorobenzylidene)-2,5-dihydro-4-hydroxy-2-oxothiophen (I.C.I. 47776)

1. A new cytotoxic agent, 3-acetyl-5-(4-fluorobenzylidene)-2,5-dihydro-4-hydroxy-2-oxothiophen (I.C.I. 47776), strongly inhibits protein and nucleic acid synthesis and, to a smaller extent, respiration in lymph-node cells and Landschütz ascites-tumour cells in vitro. 2. The activity of I.C.I. 47776 in vitro declines as the pH of the medium is increased and is inversely proportional to the concentration of serum in the medium. 3. The compound has no effect on the incorporation of leucine by a cell-free preparation from Landschütz ascites cells containing ATP and phosphoenolpyruvate. 4. I.C.I. 47776 stimulates glycolysis in suspensions of Landschütz ascites cells in the presence of excess of glucose but has no effect on glycolysis in suspensions of rat lymph-node cells. 5. I.C.I. 47776 markedly depresses ATP concentration in ascites cells in the absence of glucose but has no effect on the ATP concentration in the presence of glucose. The inhibition of protein synthesis by I.C.I. 47776 in ascites cells is, however, only partially reversed by the addition of glucose. 6. The ATP concentration of rat lymph-node cells incubated with I.C.I. 47776 in the absence of glucose is also markedly depressed but the addition of glucose increases the ATP concentration only slightly. Further, glucose has no effect on the inhibition of protein synthesis in lymph-node cells by I.C.I. 47776. 7. It is suggested that I.C.I. 47776 inhibits protein and nucleic acid synthesis in cell suspensions indirectly by acting as a mitochondrial poison. 8. The relevance of studies on the activity of I.C.I. 47776 in vitro to its cytotoxic and immunosuppressive action in vivo is discussed.

The antibiotics doxycycline and minocycline inhibit the inflammatory responses to the Lyme disease spirochete Borrelia burgdorferi

Tetracyclines moderate inflammatory responses of various etiologies. We hypothesized that tetracyclines, in addition to their antimicrobial function, could exert control over the inflammation elicited by Borrelia burgdorferi. To model systemic effects, we used the human monocytic cell line THP-1; to model effects in the central nervous system, we used rhesus monkey brain astrocytes and microglia. Cells were stimulated with live or sonicated B. burgdorferi or with the lipoprotein outer surface protein A in the presence of increasing concentrations of doxycycline or minocycline. Both antibiotics significantly reduced the production of tumor necrosis factor-alpha, interleukin (IL)-6, and IL-8 in a dose-dependent manner in all cell types. Microarray analyses of the effect of doxycycline on gene transcription in spirochete-stimulated monocytes revealed that the NFKB and CHUK (alias, IKKA) genes were down-regulated. Functionally, phosphorylation of IkappaBalpha and binding of NF-kappaB to target DNA were both reduced in these cells. Our results suggest that tetracyclines may have a dual therapeutic effect in Lyme disease.

Multi-step resistance to Chloramphenicol in RC-stringent Escherichia coli K12—its effect on the induction of RNA synthesis by antibiotics under amino acid starvation

A multi-step Chloramphenicol (CM)-resistant derivative of an RC-stringent strain of Escherichia coli auxotrophic for threonine and leucine was resistant also to Aureomycin (AM) and Puromycin (PM). All three antibiotics released the repression of RNA synthesis due to amino acid starvation in the CM-sensitive parent strain, their relative activities being about 1:10:100 for AM: CM: PM. High doses of AM and CM failed to induce RNA synthesis. The CM-resistant strain required greater concentrations of each antibiotic than the sensitive strain to induce the same level of RNA synthesis, and appeared to be about one hundred times, ten times and five times more resistant to CM, AM and PM, respectively, than the sensitive strain.

Features of 80S mammalian ribosome and its subunits

It is generally believed that basic features of ribosomal functions are universally valid, but a systematic test still stands out for higher eukaryotic 80S ribosomes. Here we report: (i) differences in tRNA and mRNA binding capabilities of eukaryotic and bacterial ribosomes and their subunits. Eukaryotic 40S subunits bind mRNA exclusively in the presence of cognate tRNA, whereas bacterial 30S do bind mRNA already in the absence of tRNA. 80S ribosomes bind mRNA efficiently in the absence of tRNA. In contrast, bacterial 70S interact with mRNA more productively in the presence rather than in the absence of tRNA. (ii) States of initiation (P_i), pre-translocation (PRE) and post-translocation (POST) of the ribosome were checked and no significant functional differences to the prokaryotic counterpart were observed including the reciprocal linkage between A and E sites. (iii) Eukaryotic ribosomes bind tetracycline with an affinity 15 times lower than that of bacterial ribosomes (K_d 30 μM and 1–2 μM, respectively). The drug does not effect enzymatic A-site occupation of 80S ribosomes in contrast to non-enzymatic tRNA binding to the A-site. Both observations explain the relative resistance of eukaryotic ribosomes to this antibiotic.

The synthesis of ribonucleic acid during inhibition of Escherichia coli by chlortetracycline

1. During inhibition of Escherichia coli by chlortetracycline, protein synthesis was sharply reduced whereas synthesis of RNA was much less affected. 2. Most of the RNA made during inhibition was contained in particles that sedimented more slowly than ribosomes. 3. The particles were more sensitive than ribosomes to degradation by ultrasonic vibrations and ribonuclease and differed from ribosomes in their behaviour during chromatography on DEAE-cellulose. 4. The particles contained two species of RNA that differed slightly in their sedimentation properties from the two RNA components found in ribosomes. 5. The nature of the events taking place during inhibition by chlortetracycline is discussed with particular reference to the status of the particles that accumulate and to the mode of action of this and other antibiotics.

In vitro activities of antibiotics against Plasmodium falciparum are inhibited by iron

The in vitro activities of cyclines (tetracycline, doxycycline, minocycline, oxytetracycline, and rolitetracycline), macrolides (erythromycin, spiramycin, roxithromycin, and lincomycin), quinolones (norfloxacin and ofloxacin), rifampin, thiamphenicol, tobramycin, metronidazole, vancomycin, phosphomycin, and cephalosporins (cephalexin, cefaclor, cefamandole, cefuroxime, ceftriazone, cefotaxime, and cefoxitin) were evaluated on Plasmodium falciparum clones, using an isotopic, micro-drug susceptibility test. Only tetracyclines, macrolides, quinolones, and rifampin demonstrated in vitro activity against P. falciparum, which increased after a prolonged exposure (96 or 144 h). In the presence of iron (FeCl(3)), only the activities of tetracyclines and norfloxacin were decreased. Their in vitro activity against intraerythrocytic stages of multidrug-resistant P. falciparum and their efficacy in vivo favor the use of antibiotics as antimalarial drugs. However, due to their slow antimalarial action and to the fact that they act better after prolonged contact, they probably need to be administered in conjunction with a rapidly acting antimalarial drug, such as a short course of chloroquine or quinine.

RESISTANCE OF ESCHERICHIA COLI TO TETRACYCLINES

1. A strain of Escherichia coli highly resistant to chlortetracycline and partially cross-resistant to tetracycline has been isolated. 2. The nitro-reductase system of the resistant cells was inhibited to a smaller extent by chlortetracycline than was the corresponding enzyme of sensitive cells. 3. The incorporation of leucine in vitro into the ribosomal protein of cell-free preparations from sensitive and resistant cells was equally inhibited by chlortetracycline. 4. Resistant cells accumulated much less chlortetracycline and tetracycline than did sensitive cells when both were cultured in the presence of these drugs. 5. The uptake of tetracycline by both sensitive and resistant E. coli was dependent on the presence of glucose in the medium. 6. Fractionation of cells cultured in medium containing [(14)C]chlortetracycline indicated that the largest proportion of radioactivity in sensitive cells was in the fraction consisting mainly of cell-wall material. There was no concentration of radioactivity in any one fraction of the resistant cells. 7. No evidence could be obtained for a specific tetracycline-excretion system in the resistant cells. 8. The significance of these results in relation to current theories of the antibiotic action of and resistance to the tetracycline drugs is discussed.

CHANGES IN MOUSE PNEUMONITIS AGENT ASSOCIATED WITH DEVELOPMENT OF RESISTANCE TO CHLORTETRACYCLINE

Moulder, James W. (University of Chicago, Chicago, Ill.), Dorothy L. Novosel, and Ilse I. E. Tribby. Changes in mouse pneumonitis agent associated with development of resistance to chlortetracycline. J. Bacteriol. 89:17-22. 1965.-A chlortetracycline-resistant mutant of mouse pneumonitis agent, a member of the psittacosis group of microorganisms, differed in several ways from the susceptible stock from which it had been derived by serial chick-embryo passage in the presence of the antibiotic. It was almost completely resistant to chlortetracycline, had a longer growth cycle, produced many more very large particles, was not neutralized by parent antiserum and vice versa, was 10 times as resistant to d-cycloserine, and was highly lethal to mice when inoculated intracerebrally. These changes probably do not occur independently of one another but are the reflection of some genetically controlled change in the surface structure of the mouse pneumonitis particle which enables the resistant mutant to multiply in the presence of chlortetracycline.

Antimicrobial therapy for rheumatoid arthritis

New interest in the use of antibiotics in the treatment of arthritis was stimulated by two factors: (1) observations that, in some forms of chronic arthritis, microbial antigens persist in the synovial membrane, and (2) the increasing knowledge of the anti-inflammatory and immunosuppressive effects of antibiotics. Recently, several published controlled studies reported a beneficial effect of tetracyclines on RA and reactive arthritis. Whether the anti-arthritic activity of the tetracyclines investigated is mediated by the antimicrobial, anti-inflammatory or immunomodulatory properties remains to be determined. It may be concluded from these studies that tetracyclines have a beneficial effect on RA, especially when laboratory parameters are considered. The effect on the clinical parameters is not unequivocal. The adverse effects seem to be mild but the long-term efficacy and safety of tetracyclines as disease-modifying antirheumatic drugs remain to be demonstrated.

Enhanced antiparasitic activity of lipophilic tetracyclines: role of uptake

It was previously noted that the inhibitory activities of lipophilic tetracyclines against the growth of Giardia lamblia in vitro were up to 40-fold greater than those of nonlipophilic tetracyclines (50% inhibitory concentration [IC50] = 1.8 to 71 micrograms/ml) (T. D. Edlind, Antimicrob. Agents Chemother. 33:2144-2145, 1989). We have now extended this observation to Trichomonas vaginalis (IC50 = 2.9 to 200 micrograms/ml), Entaoeba histolytica (IC50 = 3.8 to 36 micrograms/ml), and Leishmania major promastigotes (IC50 = 21 to 250 micrograms/ml; one strain only). The basis for these differential tetracycline activities was investigated with G. lamblia. In a cell-free protein synthesis system, lipophilic and nonlipophilic tetracyclines had similar, relatively low activities (IC50 = 170 to 500 micrograms/ml). On the other hand, tetracycline uptake into intact cells after a 1-h incubation varied dramatically: the ratios of intracellular to extracellular drug concentrations were 1.7 to 7.2 for nonlipophilic tetracyclines and 47 to 112 for lipophilic derivatives. Thus, the variable effects of tetracyclines on the growth of G. lamblia can be fully accounted for by differences in uptake. Passive diffusion probably plays a more important role than active transport in uptake of lipophilic tetracyclines, since similar results were obtained with cells rendered nonviable by metronidazole treatment.

Mechanisms that may account for differential antibiotic susceptibilities among Coxiella burnetii isolates

The Nine Mile, S Q217, and Priscilla isolates, representative of the three major genetic groups of Coxiella burnetii, are known to differ in their susceptibilities to antibiotics. Mechanisms potentially responsible for these differences were investigated. Accumulation of antibiotics by infected L929 cells and purified isolates was measured. In addition, C. burnetii plasmid-transformed Escherichia coli HB101 cells were used to study the possibility that different C. burnetii plasmids are responsible for disparate antibiotic susceptibilities of the isolates. L929 cells recently or persistently infected with the Priscilla isolate exhibited a significantly reduced accumulation of [3H]tetracycline as compared with that in L929 cells infected with either the Nine Mile or S Q217 isolates; accumulation of this drug was greater in cells recently infected each isolate. In contrast, L929 cells recently or persistently infected with the different isolates accumulated [3H]norfloxacin to an equivalent extent. [3H]tetracycline accumulation was approximately the same among the purified isolates. However, as measured by both scintillation and spectrofluorometry, norfloxacin accumulation was significantly diminished in the purified Priscilla isolate. pH had no apparent effect upon isolate permeabilities. The presence of C. burnetii QpH1 or QpRS plasmids did not alter the antibiotic susceptibility of E. coli. Collectively, these results indicate that differential susceptibilities to tetracyclines or fluoroquinolones in C. burnetii isolates may be the result of distinct mechanisms involving altered host-cell (tetracyclines) or isolate-specific (fluoroquinolones) permeabilities.

Inosine monophosphate dehydrogenase inhibitors. Probes for investigations of the functions of guanine nucleotide binding proteins in intact cells

Taken together, the above reports indicate that the IMP dehydrogenase inhibitors are valuable probes for investigation of the biological functions of guanine nucleotides in intact cells. While these agents have minor effects on levels of other nucleotides and enzymes, non-specific effects can be monitored by addition of guanine or guanosine to provide substrates for the salvage pathway of guanine nucleotide synthesis. The most important question yet to be resolved in employing these agents is why incomplete depletion of intracellular guanine nucleotides results in such dramatic effects on G-protein function. Since the level of GTP in resting cells is approximately 0.5 mM, even a 90% reduction in GTP levels should leave enough nucleotide to adequately activate most known G-proteins, as the latter display high binding affinities for guanine nucleotides in cell free systems. Several explanations have been proposed to account for this disparity. Much of the intracellular guanine nucleotide may be bound or compartmentalized and therefore unable to interact with certain G-proteins. Possibly, G-proteins in the intracellular environment possess a much lower affinity for GTP that they do in cell free system. It may be to the cells' advantage that relatively minor fluctuations in levels of GTP result in pronounced alterations in the biological function of G-proteins as this effect may provide a physiologically important mechanism for the regulation of G-proteins in vivo. Further studies are necessary to clarify the mechanisms involved in the regulation of the biological function of G-proteins and oncogene products by guanine nucleotides in intact cells.

Depression of Plasmodium falciparum dihydroorotate dehydrogenase activity in in vitro culture by tetracycline

The activity of Plasmodium falciparum dihydroorotate dehydrogenase, a particulate, electron transport-linked enzyme involved in de novo pyrimidine synthesis, was depressed when the parasite was cultured in the presence of a therapeutic concentration of tetracycline over a 96 h period. There was no direct inhibitory effect of the antibiotic on the enzyme activity. The activity of glutamate dehydrogenase, which is cytoplasmic in the parasite, was unaffected by tetracycline over the same period. Dihydroorotate dehydrogenase activity was substantially recovered when electron acceptors were added. It is suggested that the effect of tetracycline is manifested at the level of the dehydrogenase and/or the electron transport chain linked to this enzyme.

Quantitative assessment of the polysome profile of the livers of mice treated with tetracycline or doxycycline

The influence of tetracycline and doxycycline (10-100 micrograms/g i.v.) on the aggregational state of ribosomes from mouse liver was tested. Both drugs caused a disaggregation of the ribosomes as evidenced by a rise of the monosomes + disomes/polysomes ratio. Tetracycline was much more potent than doxycycline, the minimum effective doses for tetracycline being 10 micrograms/g i.v. as compared to 100 micrograms/g for doxycycline. The results show that tetracycline but not doxycycline at therapeutic dose range may interfere with the protein synthesis of the liver.

Fidelity of the eukaryotic codon-anticodon interaction: interference by aminoglycoside antibiotics

A homologous in vitro method was developed from Tetrahymena for ribosomal A-site binding of aminoacyl-tRNA to poly(uridylic acid)-programmed ribosomes with very low error frequency. The reaction mixture pH was the crucial factor in the stable A-site association of aminoacyl-tRNA with high fidelity. At a pH greater than 7.1, endogenous activity translocated A-site-bound aminoacyl-tRNA to the P site. If translocation was allowed to occur, a near-cognate amino-acyl-tRNA, Leu-tRNA, could stably bind to the ribosome by translocation to the ribosomal P site. Near-cognate aminoacyl-tRNA did not stably bind to either site when translocation was blocked. Misreading antibiotics stimulated the stable association of near-cognate aminoacyl-tRNA to the ribosomal A site, thereby increasing the error frequency by several orders of magnitude. Ribosome binding of total aminoacyl-tRNA near equilibrium was not inhibited by misreading antibiotics; however, initial rate kinetics of the binding reaction were dramatically altered such that a 6-fold rate increase was observed with paromomycin or hygromycin B. The rate increase was evident with both cognate and near-cognate aminoacyl-tRNAs. Several antibiotics were tested for misreading potency by the ribosome binding method. We found gentamicin G418 greater than paromomycin greater than neomycin greater than hygromycin B greater than streptomycin in the potentiation of misreading. Tetracycline group antibiotics effectively inhibited A-site aminoacyl-tRNA binding without promoting misreading.

Structural changes induced by tetracycline in secretory ameloblasts in young rats

The effects of tetracycline hydrochloride (TC) on secretory ameloblasts in mandibular incisors and first molars in young rats were investigated. The pathogenesis of the TC-induced changes was examined in light and electron microscopes 6, 12, 24 and 96 h after a single intraperitoneal injection of a high dose of TC (200 mg TC/kg body wt.) into 4-d-old animals. Secretory ameloblasts from non-injected animals served as controls. Cellular changes were observed in all teeth 6 h after injection. The changes increased with the postinjection period and after 96 h they were so severe that they were considered irreversible. The incipient changes of the ameloblasts comprised altered structure and location of the mitochondria, succeeded by dilated cisternae of endoplasmic reticulum arranged in short curled formations. Later on, distorted Golgi complexes were observed. Secretory granules appeared in various numbers in the Golgi zone and in the Tomes' processes. In severely affected ameloblasts the cell nuclei showed an increased content of chromatin. Autophagic vacuoles and extracellular membrane bound fragments with cellular remnants were frequent, indicating death of some of the ameloblasts. Areas of stippled secretory material were observed along the formative enamel front and in extracellular spaces between the ameloblasts. In the 96-h group calcified bodies with a varying content of crystals were scattered between the cells. Incisors and the molars displayed similar patterns of structural changes of the secretory ameloblasts; however, the changes developed earlier and became more severe in the molars.

R-factor-mediated resistance to tetracycline in Proteus mirabilis

The expression of R-factor-mediated resistance to tetracycline has been compared in Proteus mirabilis and Escherichia coli. Resistance to a range of concentrations of tetracycline was significantly lower in P. mirabilis than in E. coli in both induced and repressed states. Indirect evidence showed that conditions which result in a marked increase in the level of resistance of P. mirabilis harboring the R factor NR1 to chloramphenicol, streptomycin, and spectinomycin due to an amplification in the number of copies of r-determinants per cell do not detectably increase the level of resistance to tetracycline. Tetracycline resistance was inducible in early stationary-phase P. mirabilis NR1 although not after 5 h in this state. Double isotope labeling of control and tetracycline-induced P. mirabilis NR1 in early stationary phase revealed isotopic enrichment of certain peaks in extracts from induced cells subjected to polyacrylamide gel electrophoresis.

Effect of osmotic shock on tetracycline resistance in Escherichia coli bearing an R-factor

1. Escherichia coli with an R-factor conferring resistance to tetracycline was induced to high-degree resistance by pre-exposure to the antibiotic. The degree of resistance was drastically lowered by subjecting the cells to osmotic shock. 2. Resistance to tetracycline was rapidly restored by incubating the shocked cells in a glucose-salts medium containing shock proteins prepared from tetracycline-sensitive and -resistant cells. Resistance was also restored by incubating the cells in a complex medium without shock protein. 3. The initial recovery of resistance was followed by a secondary fall in resistance when the cells were cultured in complex medium; this secondary fall was largely prevented by the addition of a low concentration (10mug/ml) of tetracycline to cells. The secondary fall was significantly less in shocked E. coli cells harbouring a mutant R-factor in which tetracycline resistance is largely constitutive. 4. Tetracycline resistance was also transiently depressed by treating R-factor-bearing cells with EDTA in tris buffer. 5. The significance of these results in relation to the mechanism of tetracycline resistance in R-factor-bearing cells is discussed.

The inhibition of nucleic acid synthesis by mycophenolic acid

1. Mycophenolic acid, an antibiotic of some antiquity that more recently has been found to have marked activity against a range of tumours in mice and rats, strongly inhibits DNA synthesis in the L strain of fibroblasts in vitro. 2. The extent of the inhibition of DNA synthesis is markedly increased by preincubation of the cells with mycophenolic acid before the addition of [(14)C]thymidine. 3. The inhibition of DNA synthesis by mycophenolic acid in L cells in vitro is reversed by guanine in a non-competitive manner, but not by hypoxanthine, xanthine or adenine. 4. The reversal of inhibition by guanine can be suppressed by hypoxanthine, 6-mercaptopurine and adenine. 5. Mycophenolic acid does not inhibit the incorporation of [(14)C]thymidine into DNA in suspensions of Landschütz and Yoshida ascites cells in vitro. 6. Mycophenolic acid inhibits the conversion of [(14)C]hypoxanthine into cold-acid-soluble and -insoluble guanine nucleotides in Landschütz and Yoshida ascites cells and also in L cells in vitro. There is some increase in the radioactivity of the adenine fraction in the presence of the antibiotic. 7. Mycophenolic acid inhibits the conversion of [(14)C]hypoxanthine into xanthine and guanine fractions in a cell-free system from Landschütz cells capable of converting hypoxanthine into IMP, XMP and GMP. 8. Preparations of IMP dehydrogenase from Landschütz ascites cells, calf thymus and LS cells are strongly inhibited by mycophenolic acid. The inhibition showed mixed type kinetics with K(i) values of between 3.03x10(-8) and 4.5x10(-8)m. 9. Evidence was also obtained for a partial, possibly indirect, inhibition by mycophenolic acid of an early stage of biosynthesis of purine nucleotides as indicated by a decrease in the accumulation of formylglycine amide ribonucleotide induced by the antibiotic azaserine in suspensions of Landschütz and Yoshida ascites cells and L cells in vitro.