The effect of low concentrations of chlorampheicol on beating rat-heart cells in tissue culture

Reactions of the nitroso analogue of chloramphenicol with reduced glutathione

Nitroso-chloramphenicol (NOCAP) was synthetized by reduction of chloramphenicol (CAP) with zinc dust in a modification of the procedure published by Corbett and Chipko. The radioactive derivative was similarly prepared from [dichloroacetamido-1-14C]CAP. NOCAP rapidly reacted with GSH with the formation of hydroxylamino-chloramphenicol (NHOHCAP), D-(-)-threo-1-(p-hydroxylaminophenyl)-2-dichloroacetamido-1,3-propanediol and glutathione disulfide (GSSG). In addition, a hydrophilic sulfinamide was formed (GSONHCAP), D-(-)-threo-1-(p-glutathionesulfinamidophenyl)-2-dichloroacetamido-1, 3-propanediol. Free amino-chloramphenicol (NH2CAP), D-(-)-threo-1-(p-aminophenyl)-2-dichloracetamido-1,3-propanediol, was not detected. The proportion of NHOHCAP formed increased with increasing GSH concn, at the expense of GSONHCAP. Analysis by stopped-flow spectroscopy revealed formation of a labile adduct in the reaction of NOCAP with GSH (k = 5500 M-1 sec-1 at 37 degrees, pH 7.4). This reaction was reversible because nearly all NOCAP could be extracted with ether from the labile intermediate. The equilibrium adduct/NOCAP was dependent on GSH concn (K = 4500 M-1 at 37 degrees, pH 7.4). The labile intermediate either isomerized to the sulfinamide, GSONHCAP (favoured by decreasing pH at constant GSH), or it was thiolytically cleaved by another GSH molecule to NHOHCAP and GSSG (favoured by increasing GSH at constant pH). At acid pH, GSONHCAP readily hydrolyzed to NH2CAP and glutathionesulfinic acid. Thus, NOCAP reacts with thiols similar to nitrosobenzene. A scheme is presented for the proposed reaction mechanism. It is concluded that most of the NOCAP, if formed in the intestine or liver, will be rapidly disposed by reactions with GSH. Hence, toxic concns at the sensitive target, i.e. the bone marrow, may usually be prevented.

Effects of mitochondrial inhibition by chloramphenicol on the mitotic cycle of human cell cultures

Chloramphenicol, at concentrations of 500 μg/ml, had a marked inhibitory effect on mitoses in human fibroblasts. Metaphase and G2 appeared to be particularly sensitive to the action of the drug. With concentrations of 1000 μg/ml, or with 500 μg/ml after prolonged exposure, the cells did not reach G2 and no mitoses were seen. The drug required several hours to produce its effect. Studies of oxygen uptake showed no immediate reduction in the respiratory activity of cells at concentrations of 500 μg/ml or 1000 μg/ml but cells which had been in contact with 500 μg/ml of drug for 24 hours showed a marked reduction in respiratory activity. Since the primary effect of chloramphenicol is arrest of mitochondrial protein synthesis, it is concluded that continued synthesis of mitochondrial proteins in the maintenance of the respiratory chain are prerequisites for normal cell division in fibroblasts.

Mitoribosomes from Candida utilis. Morphological, physical, and chemical characterization of the monomer form and of its subunits

Highly purified mitochondrial ribosomes (mitoribosomes) have been obtained from the yeast Candida utilis. Sedimentation analysis in sucrose gradients made in 5 mM MgCl(2), 1 mM Tris, pH 7.4 and 50 mM KCl clearly distinguishes mitoribosomes (72S) from cytoplasmic ribosomes (cytoribosomes) (78S). Mitoribosomes are completely dissociated into 50S and 36S subunits at 10(-4)M MgCl(2) whereas complete dissociation of cytoribosomes into 61S and 37S subunits occurs only at 10(-6)M MgCl(2) Electron microscopy of negatively stained mitoribosomes (72S peak) shows bipartite profiles, about 265 x 210 x 200 A Characteristic views are interpreted as frontal, dorsal, and lateral projections of the particles, the latter is observed in two enantiomorphic forms Mitoribosome 50S subunits display rounded profiles bearing a conspicuous knoblike projection, reminiscent of the large bacterial subunit. The 36S subunits show a variety of angular profiles. Mitoribosomal subunits are subject to artifactual dimerization at high Mg(2+) concentration Under these conditions, a supplementary 80S peak arises. Electron microscopic observation of the 80S peak reveals closely paired particles of the 50S type Buoyant density determinations after glutaraldehyde fixation show a single peak at rho = 1.48 for mitoribosomes and 1.53 for cytoribosomes In the presence of ethylenediaminetetraacetate (EDTA), two species of RNA, 21S and 16S, are obtained from mitoribosomes, while 25S and 17S RNA are obtained from cytoribosomes It is established that the small and large RNA species are derived from the 36S and 50S subunits, respectively, by extraction of the RNA from each subunit The G + C content of the RNA is lower for mitoribosomes (33%) than for cytoribosomes (50%). Incubation of C utilis mitochondria with leucine-(14)C results in the labeling of 72S mitoribosomes. The leucine-(14)C incorporation is inhibited by chloramphenicol and resistant to cycloheximide Puromycin strips the incorporated radioactivity from the 72S mitoribosomes, which is consistent with the view that leucine-(14)C is incorporated into nascent polypeptide chains at the level of mitoribosomes

Respiratory enzymes and mitochondrial morphology of HeLa and L cells treated with chloramphenicol and ethidium bromide

Exposure of HeLa and L cells to chloramphenicol causes a progressive dose-dependent decrease in cytochrome oxidase and succinate-cytochrome c reductase activities, concomitant with an increase in the amount of cytochrome c. At 2-3 days, the specific activities of the enzymes have fallen to about one-half of control values; the mitochondria appear swollen. By day 5, enzyme activities are about one-quarter of control values; the mitochondria are more swollen, with disorientation and disintegration of cristae. By day 6-8, after three generations, growth has stopped, enzyme activities are approximately the same as on day 5, and cytochrome c content has reached 170% of control value. Mitochondria show severe changes, cristae being affected more than peripheral inner membrane. The number of profiles continues to be nearly normal. After 30 days, cytochrome oxidase activity remains low but now there are mitochondria in intermediate and condensed configuration. There is a gradual accumulation in the cytoplasm of smooth membrane elements. If chloramphenicol is removed, cells recover. Ethidium bromide treatment for up to 8 days yields results virtually identical to those obtained with chloramphenicol. Cells treated with 10(-4)M KCN show a decrease in cytochrome oxidase activity to about one-third of control value and an elevated amount of cytochrome c. Only a small number of mitochondria appear damaged. Autochthonous mitochondrial syntheses appear to be essential for the organization of the cristae. When cytochrome oxidase activity is impaired, a regulatory mechanism for cytochrome biosynthesis geared to mitochondrial function may be lacking, resulting in an increase in cytochrome c content.

Differential long-term effects of D-chloramphenicol on the biogenesis of mitochondria in normal and regenerating rat liver

1. Normal and partially hepatectomized rats (150g) were injected daily with d-chloramphenicol (20mg) for a period of 4 weeks, in order to investigate whether defective mitochondria could be induced in vivo in higher organisms as in yeast, and to measure the degree of inhibition of the mitochondrial function thus obtained. 2. The antibiotic did not affect growth and increased the amount of liver protein without changing the mitochondrial yield. 3. The respiration of isolated mitochondria from regenerated liver (regeneration completed) with succinate, alpha-oxo-glutarate, isocitrate and malate, was decreased in the chloramphenicol-treated rats, whereas in normal liver the antibiotic increased the mitochondrial oxygen consumption with succinate and did not significantly change the respiration with other substrates. 4. Mitochondrial cytochromes and respiratory enzymes were also decreased in amount in regenerated liver from the treated rats and enhanced in normal liver. 5. The protein specific radioactivities of most mitochondrial and microsomal subfractions, 30min after an injection of [(14)C]leucine, were decreased in regenerated liver under the action of chloramphenicol. Conversely, the incorporation of [(14)C]leucine into proteins of most subfractions in incubations of liver slices was enhanced in the case of normal rats treated with the antibiotic. 6. It is concluded that in regenerated liver chloramphenicol induces functionally defective mitochondria by inhibiting their biogenesis, whereas in normal liver the stimulation of respiration and protein synthesis is probably a secondary detoxication response.