Comparison of genomic damage caused by 5-nitrofurantoin in young and adult mice using the in vivo micronucleus assay

The antibiotic 5-nitrofurantoin (5-NF) has been used widely for the treatment of urosepsis in children during the last 20 years. Recent experimentation suggests the need for reevaluating its genotoxic potential. Because of possible differences in the metabolism and clearance of 5-NF in young and adult animals, we conducted a study to determine whether micronuclei caused by 5-NF were age-related. The in vivo micronucleus (MN) assay was performed on 3- and 8-week-old mice given single intraperitoneal injections of 5, 10, and 50 mg/kg 5-NF. Blood samples from the tail vein were taken before injection (baseline) and at 48, 96, 168, and 336 hr (2 weeks) after the treatment. One thousand reticulocytes were analyzed for micronuclei from each animal. Compared to similar baseline values for young and adult mice, 5-NF caused a significant increase in MN frequency in both age groups. The mean MN frequency in the young animals was higher than in the adult animals for each dose and sampling time. MN frequencies remained significantly elevated in young animals even 2 weeks after exposure to 5-NF. The results of the study confirm the genotoxic potential of 5-NF in young and adult animals, and indicate that young animals are more sensitive to the genotoxic effects of 5-NF than adult mice and that the response in young mice persists for a significantly longer time. These findings may be related to poorly developed mechanisms of xenobiotic detoxification and renal elimination in young animals.     

Competitive reactions of L-methionine and 5'-GMP towards platinum (II) complexes

The complex-formation reactions of the platinum(II) complexes, [Pt(dien)H2O]2+, [PtCl(dien)]+ and [PtBr(dien)]+ (dien is diethylenetriamine) with some biologically relevant ligands such as inosine (INO), inosine-5'-monophosphate (5'-IMP), guanosine-5'-monophosphate (5'-GMP), glutathione (GSH) and L-methionine (S-meth), were studied by UV-Vis (UV-Visible) spectrophotometry and 1H NMR spectroscopy. Reactions of the [PtCl(dien)]+ with L-methionine were studied in the presence and absence of 5'-GMP. The rate constants clearly showed a kinetic preference toward L-methionine. However, competitive reactions of [PtCl(dien)]+ with L-methionine and 5'-GMP demonstrated initially rapid formation of [Pt(dien)(S-meth)]2+ followed by displacement of L-methionine by 5'-GMP. In the later stages the concentration of [Pt(dien)(N7-GMP )]2+ is predominant. The results are analyzed in reference to the anti-tumour activity of Pt(II) complexes.     

ACTH-producing cells of 21-day-old rat fetuses after maternal dexamethasone exposure

Adrenocorticotrophic hormone (ACTH) is essential for developmental maturation of numerous organ systems during the fetal period and for adaptation to environmental challenges. Immunocytochemical and stereological methods were used in the present study to examine the effects of dexamethasone (Dx) administration during pregnancy on fetal rat pituitary ACTH-producing cells. Doses of 0.5, 0.5 and 1.0 mg Dx/kg body weight/day were given to the dams on 3 consecutive days starting on day 16 of gestation. Morphometric analysis of the ACTH-producing cells of fetuses at 21 days of gestation revealed significant inhibition by 24% and 27%, respectively, of cell volume and cell number after maternal Dx administration, whereas the volume of cell nuclei and volume density of ACTH-stained cells were insignificantly decreased. Immunocytochemical analysis showed reduced numbers, sizes and immunopositivity of ACTH cells of 21-day-old fetuses from Dx-treated dams as compared with the control group. Maternal Dx treatment in the period of intense differentiation of the hypothalamo-hypophyseal-adrenal system had an inhibitory effect on fetal function and proliferative activity of ACTH-producing cells at 21 days of gestation. Thus, inhibition of activity of fetal ACTH-producing cells may lead to adrenal suppression, modified activity of the hypothalamo-pituitary-adrenal axis and reduced body weight possibly causing lasting functional abnormalities.     

Mechanisms of resistance in Enterobacteriaceae towards beta-lactamase antibiotics

Except for Salmonella spp., all Enterobacteriaceae produce intrinsic chromosomal encoded beta-lactamases which, beside their physiologic role in cell-wall synthesis and natural beta-lactam protection, are responsible for intrinsic resistance of individual species among Enterobacteriaceae. E. coli and Shigella spp. produce a small amount of AmpC beta-lactamases and are susceptible to ampicillin and other beta-lactam antibiotic agents. Enterobacter spp, C. freundii, Serratia spp., M. morganii, P. stuarti and P. rettgeri produce small amounts of inducible AmpC beta-lactamases which are not inhibited by beta-lactamases inhibitor, causing intrinsic resistance to ampicillin, co-amoxiclav and first-generation cephalosporins. K. pneumoniae produces small amounts of SHV-1 beta-lactamases, and K. oxytoca chromosomal K1 beta-lactamase, causing resistance to ampicillin, carbencillin, ticarcillin and attenuated zone of inhibition to piperacillin, compared to piperacillin with tazobactam. They are susceptible to beta-lactamase inhibitors. Whereas P. mirabilis shows a minor chromosomal expression of beta-lactamases, P. vulgaris produces chromosomal beta-lactamases of class A (cefuroximases), causing resistance to ampicillin, ticarcillin, and first- and second-generation cephalosporins. Antibiotics have caused the appearance of acquired or secondary beta-lactamases, with the sole function of protecting bacteria from antibiotics. The production of broad-spectrum beta-lactamases (TEM-1, TEM-2, SHV-1, OXA-1) results in resistance to ampicillin, ticarcillin, first-generation cephalosporins and piperacillin. A high level of beta-lactamases leads to resistance to their inhibitors. The plasmid-mediated extended-spectrum beta-lactamases (ESBLs) are of increasing concern. Most are mutants of classic TEM- and SHV-beta-lactamases types. Unlike these parent enzymes, ESBLs hydrolyze oxymino-cephalosporins such as cefuroxime, cefotaxime, ceftriaxone, ceftizoxime, ceftazidime, cefpirome and cefepime, aztreonam, as well as penicillins and other cephalosporins, except for cephamycin (cefoxitin and cefotetan). They are inhibited by beta-lactamase inhibitors. AmpC beta-lactamases are chromosomal and inducible in most Enterobacter spp., C. freundii, Serratia spp., M. morganii and Providentia spp. They are resistant to almost all penicillins and cephalosporins, to beta-lactamase inhibitors and aztreonam, and are susceptible to cefepime and carbapenems as well. Plasmid-mediated AmpC beta-lactamases have arisen through the transfer of chromosomal genes for the inducible AmpC beta-lactamase onto plasmids. All plasmid-mediated AmpC beta-lactamases have similar substrate profiles to the parental enzymes from which they appear to be derived. With one exception, plasmid-mediated AmpCs differ from chromosomal AmpCs in being uninducible. The National Committee for Clinical Laboratory Standards (NCCLS) has issued recommendations for ESBL screening and confirmation for isolates of E. coli, K. pneumoniae and K. oxytoca. No NCCLS recommendations exist for ESBLs detection and reporting for other organisms or for detecting plasmid-mediated AmpC beta-lactamases. High-level expression of AmpC may prevent recognition of an ESBL in species that produce a chromosomally encoded inducible AmpC beta-lactamase. AmpC-inducible species (e. g. Enterobacter spp. and C. freundii) can be recognized by cefoxitin/cefotaxime disk antagonism tests. Since clinical laboratories are first to encounter bacteria with new forms of antibiotic resistance, they need appropriate tools to recognize these bacteria, including trained staff with sufficient time and equipment to follow up important observations. Because bacterial pathogenes are constantly changing, training must be an ongoing process.