Increased susceptibility to oxidative stress as a proximate cost of reproduction

In iteroparous species high investment in current reproduction is usually paid in terms of reduced future reproduction and increased mortality. However, the proximal mechanisms of these costs remain poorly understood. Free radicals arising as by‐products of normal metabolic activities have deleterious effects on cellular proteins, lipids and DNA, and this phenomenon is known as oxidative stress. Since reproduction is an energetically demanding activity, which increases both basal and field metabolic rates, one could expect that breeding effort generates an oxidative stress whose strength depends on the availability and efficiency of antioxidant defences. In agreement with this prediction, we show here for the first time that reproduction decreases antioxidant defences, illustrating that oxidative stress represents a cost of reproduction. We suggest that increased susceptibility to oxidative stress might be a general proximal connection between reproduction and survival underlying other mechanistic links previously acknowledged.     

Malacofaune et microfaune (foraminifères et ostracodes)d'un milieu estuarien tropical: Le delta de la basse vallée du Sénégal

Molluscs fauna and microfauna (Foraminifera and Ostracoda) from the delta and the lower valley of Senegal river are little various. These ones characterize an estuarian biotope where salinity is very contrasted according to the seasons and level of waters.     

The effects of ouabain in the medullary site of the hypotensive action of clonidine

Blood pressure was studied in pentobarbital anesthetized rats and cats after central administration of ouabain. Intracerebroventricular (i.c.v.) injections caused a classical biphasic effect, a short lasting hypotension followed by a hypertensive phase. When injected directly into the nucleus reticularis lateralis region (NRL), ouabain (0.01–2 μg/kg) caused a dose-dependent pressor effect. In the same region, kryptofix 221, a sodium complexing agent, produced a fall in blood pressure. Moreover, central administration of ouabain prevented the hypotensive effect of i.v. clonidence whereas the central hypotensive effect of muscimol was not affected. It is concluded that sodium movements play an important role in the blood pressure regulation within the NRL region. We also report here that ouabain antagonizes the hypotensive effect of clonidine suggesting that sodium movement might be the essential link of this action.     

Repair of iron-induced DNA oxidation by the flavonoid myricetin in primary rat hepatocyte cultures

Oxidative DNA damage and its repair in primary rat hepatocyte cultures was investigated following 4 h of incubation with the toxic iron chelate, ferric nitrilotriacetate (Fe-NTA), in the presence or absence of the potent protective flavonoid myricetin (25-50-100 microM). Seven DNA base oxidation products were quantified in DNA extracts by gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring mode. Concomitantly, DNA repair capacity of hepatocytes was estimated by the release of oxidized-base products into culture media, using the same GC-MS method. A genotoxic effect of Fe-NTA (100 microM) in hepatocytes was evidenced by a severe increase in DNA oxidation over basal levels, with accumulation in cellular DNA of five oxidation products derived from both purines and pyrimidines. This prooxidant effect of iron was also noted by an induction of lipid peroxidation, estimated by free malondialdehyde production. Addition of increasing concentrations of myricetin (25-50-100 microM) simultaneously with iron prevented both lipid peroxidation and accumulation of oxidation products in DNA. Moreover, as an activation of DNA repair pathways, myricetin stimulated the release of DNA oxidation bases into culture media, especially of purine-derived oxidation products. This removal of highly mutagenic oxidation products from DNA of hepatocytes might correspond to an activation of DNA excision-repair enzymes by myricetin. This was verified by RNA blot analysis of DNA polymerase beta gene expression which was induced by myricetin in a dose-dependent manner. This represented a novel and original mechanism of cytoprotection by myricetin against iron-induced genotoxicity via stimulation of DNA repair processes. Since iron-induced DNA damage and inefficient repair in hepatocytes could be related to genotoxicity and most probably to hepatocarcinogenesis, modulation of these processes in vitro by myricetin might be relevant in further prevention of liver cancer derived from iron overload pathologies.     

Development of a multispecies periodontal biofilm model within a stirred bioreactor

Abstract

The objective of this work was to develop a subgingival biofilm model using a stirred bioreactor. Discs of bovine teeth were adapted to a stirred bioreactor filled with a culture medium containing bacterial species associated with periodontal health or disease. After anaerobic incubation, the biofilms growing on the substratum surfaces were collected and analyzed. The mean number of Colony-forming Units (CFUs) varied, but with no difference between 3 and 7?days of biofilm formation (p?>?0.05). Scanning Electron Microscopy (SEM) analysis showed a uniform biofilm layer covering the cement layer of the root surface containing bacteria with diverse morphology. In checkerboard DNA-DNA hybridization, bacterial species were identified in both biofilms. In conclusion, a subgingival biofilm model was developed using a stirred bioreactor, allowing the in vitro reproduction of complex microbial communities. This is an advanced model that may be useful to mimic complex clinical periodontal biofilms.     

Biotin biosynthetic pathway in recombinant strains of Escherichia coli overexpressing bio genes: evidence for a limiting step upstream from KAPA

The effect of the overexpression of the bioABFCD operon on the biotin biosynthetic pathway was investigated in an Escherichia coli K12 bioR mutant with a chromosomal deletion for the biotin operon. When transformed with a multicopy number plasmid containing bioABFCD, this strain synthetized 10,000 times more biotin than a wild-type E. coli strain. In order to further increase biotin production, the bioA and bioB operons were subcloned into plasmids with stronger promoters and in some cases optimal ribosome binding sites. The new constructions led to the accumulation of large amounts of soluble Bio proteins (although not BioC) but did not improve biotin production. In all the constructed strains, BioA, BioD, and BioB activities were greatly amplified but these activitie did not correlate with the level of protein syntthesis. These strains accumulated only low levels of vitamers, auggesting that the major limiting step for higher biotin production occurs upstream from the first intermediate of the Bio pathway we assayed (7,keto-8-aminopelargonic acid). As BioC overproduction was shown to impair cell growth, we could not determine if this early step of pathway was limiting. Correspondence to: S. Lévy-Schil     

Determination of the major zinc fractions in human serum by ultrafiltration

In this paper we report a method for measuring ultrafiltrable zinc in human serum by electrothermal atomic absorption spectrophtometry. We show also that ultrafiltration permits to determine alpha-2 macroglobulin bound zinc and losely bound zinc if a strong zinc ligand (EDTA) is added to serum before ultrafiltration. This last fraction, after deduction of ultrafiltrable zinc, represents roughly all albumin bound zinc. In 20 controls we found that ultrafiltrable zinc amounted 0.311 μmol/L (S.D.=0.117 μmol/L), alpha-2 macroglobulin bound zinc 3.08 μmol/L (S.D.=0.221 μmol/L), and albumin bound zinc 12.11 μmol/L (S.D.=1.95 μmol/L). Our method needs only a small volume of serum, it is simple and rapid but also very accurate and reliable. The losely bound fraction is very dynamic and, representing the physiologically active part of serum zinc, it could be a good marker of zinc deficiency.     

In vitro regulation of the innervation pattern of quail muscle fibres by quail and mouse neurons

Myoblasts from rudiments of slow and fast muscle, anterior latissimus dorsi (ALD) and posterior latissimus dorsi (PLD) respectively, of 9-day-old quail embryos were cultured in vitro for a period of up to 60 days in order to give rise to well-differentiated muscle fibres. These fibres were innervated by neurons from either quail or mouse embryo spinal cord and their innervation pattern was examined by the visualization of acetylcholine receptors (ACh-R) and of acetylcholinesterase (ACh-E) activity at the neuromuscular contacts. In the culture system used, quail neurons always innervated muscle fibres at several sites and only when a fast-type activity was imposed on these neurons did a reduction in the number of the previously established neuromuscular contacts take place. In contrast, in the muscle fibres innervated by mouse neurons, a spontaneous reduction in the number of the previously established neuromuscular contacts occurred but this spontaneous reduction depended upon the level of differentiation reached by the muscle fibres in vitro. In the cultures of muscle fibres previously innervated by mouse neurons, the addition of quail neurons did not provoke any modification in the initial innervation pattern, and no quail ACh-R cluster was observed. In contrast, in the muscle fibres previously innervated by quail neurons, the mouse neurons contacted these fibres, resulting in a decrease in the number of quail ACh-R clusters. These results emphasize the part played by neurons in the establishment of the innervation pattern when muscle fibres have reached a high level of differentiation. In vitro, the slow and fast characteristics of the muscle fibres do not influence this pattern.