Effect of monensin on the enzymes of oxidative stress, thiamine pyrophosphatase and DNA integrity in rat testicular cells in vitro

Effect of cationic ionophore monensin on the lipid composition and fluidity of rat epididymal spermatozoal membrane

The present study was aimed at exploring the effect of monensin, an antibiotic carboxylic polyether ionophore specific for Na(+), on the structural, chemical, and physiological changes of the epididymal sperm of Wistar rats. Animals received monensin at the dose of 3.5 mg/kg body weight daily orally for 70 days, a treatment duration that corresponds to the spermatogenic cycle in rats. At the end of the treatment regime, three regions of the epididymis were separated and the spermatozoa were collected. The plasma membranes of the spermatozoa were isolated and lipid composition, such total lipid, phospholipid, cholesterol, and ganglioside-sialic acid, was studied. Membrane dynamic behavior was investigated by lipid translational fluidity by pyrene excimer formation and rotational diffusion by diphenyl hexatriene polarization and anisotropy parameter. Structural changes in membrane were also evaluated by the dye-binding study with anilino naphthalene sulphonic acid. The results showed marked changes in lipid compositions, fluidity parameters, and kinetics of fluorescent dye binding in the epididymis, and it can be concluded that monensin, by interfering with normal physiological changes in spermatozoal maturation, may provide the basis of certain molecular intervention in the fertilizing capability of the epididymal spermatozoa and thereby may induce antifertility properties in male rats.

The antibiotic monensin causes cell cycle disruption of Toxoplasma gondii mediated through the DNA repair enzyme TgMSH-1

Monensin is a polyether ionophore antibiotic that is widely used in the control of coccidia in animals. Despite its significance in veterinary medicine, little is known about its mode of action and potential mechanisms of resistance in coccidian parasites. Here we show that monensin causes accumulation of the coccidian Toxoplasma gondii at an apparent late-S-phase cell cycle checkpoint. In addition, experiments utilizing a monensin-resistant T. gondii mutant show that this effect of monensin is dependent on the function of a mitochondrial homologue of the MutS DNA damage repair enzyme (TgMSH-1). Furthermore, the same TgMSH-1-dependent cell cycle disruption is observed with the antiparasitic ionophore salinomycin and the DNA alkylating agent methyl nitrosourea. Our results suggest a novel mechanism for the mode of action of monensin and salinomycin on coccidial parasites, in which the drug activates an MSH-1-dependent cell cycle checkpoint by an unknown mechanism, ultimately leading to the death of the parasite. This model would indicate that cell cycle disruption is an important mediator of drug susceptibility and resistance to ionophoric antibiotics in coccidian parasites.

Disruption of a mitochondrial MutS DNA repair enzyme homologue confers drug resistance in the parasite Toxoplasma gondii

MutS homologues (MSHs) are critical components of the eukaryotic mismatch repair machinery. In addition to repairing mismatched DNA, mismatch repair enzymes are known in higher eukaryotes to directly signal cell cycle arrest and apoptosis in response to DNA-damaging agents. Accordingly, mammalian cells lacking certain MSHs are resistant to chemotherapeutic drugs. Interestingly, we have discovered that the disruption of TgMSH-1, an MSH in the pathogenic parasite, Toxoplasma gondii, confers drug resistance. Through a genetic selection for T. gondii mutants resistant to the antiparasitic drug monensin, we have isolated a strain that is resistant not only to monensin but also to salinomycin and the alkylating agent, methylnitrosourea. We have shown that this phenotype is due to the disruption of TgMSH-1 as the multidrug-resistance phenotype is complemented by a wild-type copy of TgMSH-1 and is recapitulated by a directed disruption of this gene in a wild-type strain. We have also shown that, unlike previously described MSHs involved in signalling, TgMSH-1 localizes to the parasite mitochondrion. These results provide the first example of a mitochondrial MSH that is involved in drug sensitivity and implicate the induction of mitochondrial stress as a mode of action of the widely used drug, monensin.

Interaction of ionophore and vitamin E in knockdown syndrome of turkeys

Monensin and vitamin E concentrations, as well as histopathology of skeletal muscles and myocardium, were evaluated in broad-breasted white turkeys kept in commercial facilities. Turkeys with knockdown syndrome had myopathy of skeletal muscles, but no lesions in the myocardium. Generally, concentration of monensin in serum was highest in turkeys diagnosed with knockdown syndrome given more than 90 mg/kg of monensin in the diet, followed by turkeys diagnosed with knockdown syndrome given <90 mg/kg of monensin in the diet, healthy turkeys fed a diet that contained <90 mg/kg of monensin, and finally healthy turkeys fed a diet free of monensin (not detectable). However, the concentration of monensin was highly variable within each group, and the median was lower than the average. Vitamin E concentrations in the livers varied from low-normal to below normal and were statistically higher in healthy turkeys fed a diet free of monensin than in the livers of birds from the 3 groups exposed to monensin. This suggests that the concentration of monensin in serum positively correlates to the severity of clinical signs and pathology and to the amount of monensin in the feed. Although the methodology developed to detect serum monensin concentrations is beneficial and accurate for case investigations, it is recommended that several samples from each flock be evaluated because of variation within a flock. The current study also suggests that monensin in the feed could induce lower concentrations of vitamin E in the liver of turkeys and can predispose the turkeys to knockdown syndrome.

Oxidative effects of Na+--specific ionophore monensin on the rat epididymis

The carboxylic antibiotic ionophore monensin is well-known for the Na+/H+ exchanger activity across the biological membranes. The current study has been designed to investigate the effect of monensin on spermatozoal concentration, motility, and oxidative stress-related parameters in the rat epididymis. Monensin was administered orally at a dose of 3.5 mg/kg body weight daily for 70 days, a duration that coincides with the completion of the spermatogenic cycle. At the end of the respective treatment, the epididymis was isolated into three separate regions--the capitum, corpus, and the cauda--successively away from the head of the testis. Marked changes were noted in the body weight, organ (epididymis) weight, sperm concentration and motility, as well as the morphologic observations of the sperm and the histologic architecture of the epididymal epithelium. Significant alterations were also recorded in the oxidative stress parameters such as the lipid peroxidation product, malonyldialdehyde, and the activity of superoxide dismutase, glutathione sulfotransferase, glutathione reductase, and catalase. The nonenzymatic thiol content such as the total, oxidized, and reduced glutathione showed significant changes and the tissue phosphatases such as alkaline and acid phosphatase were increased, indicative of the interference of the drug in lysosomal and Golgi membrane complex. The findings of the current study indicate interactions during the spermatozoal maturational process in the epididymis, and a significant potential use of monensin in male contraception may be suggested.

Rubidium(I) monensinate dihydrate

In the title complex, [Rb(C(36)H(61)O(11))]·2H(2)O, the Rb(+) cation is coordinated by seven O atoms of monensin. Rb-O distances range from 2.7870 (17) to 3.1429 (17) Å. Both O atoms of the carboxyl-ate group are involved in the coordination of Rb. The structure displays inter- and intra-molecular O-H⋯O and C-H⋯O hydrogen-bonding inter-actions.

Methyl parathion induces the formation of symplasts by round spermatid fusion and alters the biochemical parameters in the testis

Methyl parathion (MP: O,O-dimethyl-O-4-nitrophenyl phosphorothioate) is an organophosphate pesticide used in agriculture to protect a variety of crops. Food stuffs such as fruits and vegetables could be contaminated with MP, which may be a potential route of exposure. Previous studies have shown that MP is a reproductive toxicant in animal models. The present study was designed to investigate the mechanism of symplast formation and biochemical changes that occur in the testis, following MP exposure. MP was treated to adult male Wistar rats (N=5/dose/sample time) as follows. Experiment 1 - 0, 0.75 or 1.5mg/kg/d i.p. for 25 days and experiment 2 - 0 or 3.5mg/kg/d p.o. for 25 days and sacrificed on Day 17, after the last exposure. Light microscopic examination of testis was made to evaluate the structural changes and also to establish a process of symplast formation and destruction. Quantitative biochemical estimations were made in the testis for acid phosphatase (ACP), cholesterol, total protein, uric acid, and lactate dehydrogenase (LDH). MP induced structural changes in the testis in consensus with the previous studies. The symplasts were found in the testes in experiment 1. Those cells were formed due to the cell fusion of round spermatids. The symplasts were degenerated by nuclear fragmentation. The nuclear fragments were extruded from the symplasts leaving behind only the eosinophilic cytoplasm. The cell fusion and multinucleated giant cell formation was the reason for MP induced tubular atrophy. Number of tubules with symplasts increased in experiment 1 in a dose-dependent pattern. Johnsen's scores also decreased in a dose-dependent manner in experiment 1 indicating a dose-dependent tubular destruction. The ACP, cholesterol, total protein, and LDH levels decreased in both experiments against their respective controls, whereas the uric acid level decreased in experiment 1 and increased in experiment 2 (P<0.01-0.001). The effects in experiment 1 were dose-dependent. In conclusion, MP induces the formation of symplasts by cell fusion of round spermatids, which is a process involved in tubular atrophy and also induces biochemical changes in the testis.