Cobalt and its compounds: update on genotoxic and carcinogenic activities.

This article summarizes recent experimental and epidemiological data on the genotoxic and carcinogenic activities of cobalt compounds. Emphasis is on the respiratory system, but endogenous exposure from Co-containing alloys used in endoprostheses, and limited data on nanomaterials and oral exposures are also considered. Two groups of cobalt compounds are differentiated on the basis of their mechanisms of toxicity: (1) those essentially involving the solubilization of Co(II) ions, and (2) metallic materials for which both surface corrosion and release of Co(II) ions act in concert. For both groups, identified genotoxic and carcinogenic mechanisms are non-stochastic and thus expected to exhibit a threshold. Cobalt compounds should, therefore, be considered as genotoxic carcinogens with a practical threshold. Accumulating evidence indicates that chronic inhalation of cobalt compounds can induce respiratory tumors locally. No evidence of systemic carcinogenicity upon inhalation, oral or endogenous exposure is available. The scarce data available for Co-based nanosized materials does not allow deriving a specific mode of action or assessment for these species.

Absence of genotoxic impact assessed by micronucleus frequency in circulating lymphocytes of workers exposed to cadmium.

PURPOSE: Cd is considered as a genotoxic carcinogen for which a threshold can be identified. This threshold has, however, not been established and the shape of the relationship between Cd exposure and genotoxic effects is unknown. The aim of the present study was to analyse the shape of the dose-response relationship for the genotoxic effects of Cd in occupational settings. METHODS: The study has a cross-sectional design and includes 60 healthy male and female workers with known Cd exposure selected from two plants manufacturing or recycling nickel-Cd batteries. The frequency of MN was measured in circulating lymphocytes, and related to internal Cd doses (Cd-B, Cd-U). Determinants of MN frequency were traced by multivariate regression analysis. RESULTS: Cd exposure covered a wide range as measured by Cd-B (0.02-1.26 µg/dL), Cd-U (0.26-15.80 µg/g creat) and seniority in the plant (1-42 years). Gender was the only parameter significantly associated with MN frequency, women having on average 8.5 additional MN/1000 BN cells compared to men. Cd-B, Cd-U or Ni-U did not influence MN frequency when adjusted for gender and other potential confounders. CONCLUSION: This finding is consistent with the existing knowledge on the mechanisms governing the genotoxic activity of Cd, which are all non-stochastic and thresholded. The threshold for systemic genotoxic effects of Cd is thus beyond the range of internal exposure considered in the present investigation.

A semi-active milling procedure in view of preparing implantation beds in robot-assisted orthopaedic surgery.

Bone cutting in total joint reconstructions requires a high accuracy to obtain a well-functioning and long-lasting prosthesis. Hence robot assistance can be useful to increase the precision of the surgical actions. A drawback of current robot systems is that they autonomously machine the bone, in that way ignoring the surgeon's experience and introducing a safety risk. This paper presents a semi-active milling procedure to overcome that drawback. In this procedure the surgeon controls robot motion by exerting forces on a force-controlled lever that is attached to the robot end effector. Meanwhile the robot constrains tool motion to the planned motion and generates a tool feed determined by the feed force that the surgeon executes. As a case study the presented milling procedure has been implemented on a laboratory set-up for robot-assisted preparation of the acetabulum in total hip arthroplasty. Two machining methods have been considered. In the first method the surgeon determines both milling trajectory and feed by the forces that he/she executes on the force-controlled lever. In the second method the cavity is machined contour by contour, and the surgeon only provides the feed. Machining experiments have shown that the first method results in large surface irregularities and is not useful. The second method, however, results in accurate cavity preparation and has therefore potential to be implemented in future robot systems.

Evolution of the developmental scores of sixteen morphological features in mouse embryos displaying 0 to 30 somites.

A precise framework of morphological developmental events observed macroscopically in early postimplantation mouse embryos aged 8-10 days (0-30 somites) is established. The quantitative evolution of the developmental score of 16 features as a function of the developmental stage of the embryos (expressed in number of somites) is presented. Thirty-one groups of ten embryos, each with 0 to 30 somites, were scored for each feature according to the previous description of the authors. In addition, the variation of individual structures as a function of embryonic developmental stages is evaluated. It is suggested that the framework of differentiating individual structures at given developmental stages will help to plan experiments in developmental biology of rodents and will facilitate the interpretation of results in developmental toxicity.

Postimplantation mouse embryos cultured in vitro. Assessment with whole-mount immunostaining and in situ hybridization.

The postimplantation embryos of rodents have been particularly convenient to study in culture using the whole embryo culture (WEC) system developed by New. Two serious limitations of the method will be illustrated in the present paper and proposals will be made to improve the quality of the information. The first limitation is that the developmental period amenable to culture has not been significantly extended in recent years. In the present paper, we show that the culture of mouse presomitic stages for 48 h leads to poorly reproducible results and frequent dysmorphogenic embryos. We also show that early somite stages cultured for 54 h or less have a normal growth and differentiation. In contrast, the culture of these embryos for 72 h results in subtle abnormalities of the head and the first branchial arch. The second limitation is that the gross morphology and histology are often not informative enough to distinguish between overall toxicity and developmental toxicity. We suggest some improvements by the association of WEC with two specific techniques: 1) whole-mount immunostaining of sensory ganglia and nerves and 2) in situ hybridization on histological sections using molecular probes for some developmental genes. Embryos reaching about the 30 somite stage at the end of the culture were processed for whole-mount immunostaining of sensory ganglia and nerves. We show that these structures are very sensitive to the noxious effects of HgCl2 and valproate. Both developmental retardations and dysmorphogeneses of the cervical ganglia and nerves were observed. Embryos were also exposed in vitro to low concentrations of all-trans-retinoic acid (AT-RA) and processed for in situ hybridization with radiolabeled anti-sense RNA probes for the Hoxb-1 and Hoxb-2 developmental genes. Three-dimensional reconstructions of the expression domains were performed. The data show that AT-RA induces ectopic expression domains of Hoxb-1. Our experiments demonstrate that techniques such as immunostaining and in situ hybridization can significantly expand the information obtained from whole postimplantation embryo culture.

Distraction bone healing versus osteotomy healing: a comparative biochemical analysis.

This study investigates the biochemical changes in a canine tibia lengthening model in comparison with a nonlengthened osteotomy model. The lengthened and the osteotomized callus and a contralateral corresponding segment were analyzed for their mineralization profile, collagen content, osteocalcin, insulin-like growth factor I (IGF-I), and transforming growth factor beta1 (TGF-beta1). Examinations of bone samples were performed using specimens excised at different time intervals (respectively at 3, 5, 7, 9, and 13 weeks postoperatively). Several serum parameters (alkaline phosphatase [ALP], osteocalcin, IGF-I, and TGF-beta1) were also measured during the experimental period. A progressive increase in mineral parameters was noticed in both the lengthened and the osteotomized areas. A higher level of hydroxyproline and TGF-beta1 was observed in the lengthened area compared with the osteotomized area. IGF-I showed a significant increase in both the lengthened and contralateral control area at the later stage of the experimental period in the lengthened group. In serum, a high level of TGF-beta1 and a progressively increasing osteocalcin concentration were observed in the lengthened dogs in comparison with the osteotomized dogs. Serum ALP was significantly increased in both models during the experimental period. Serum IGF-I was increased in the lengthened models during the distraction period and decreased in the osteotomized models at the early stage of the experimental period. These results suggest that the mechanical strain induced by the Ilizarov distraction procedure stimulates osteoblast proliferation and promotes biosynthesis of bone extracellular matrix in distracted callus. Our data furthermore show that this process is different compared with normal fracture healing.

Early neurogenesis and teratogenesis in whole mouse embryo cultures. Histochemical, immunocytological and ultrastructural study of the premigratory neuronal-glial units in normal mouse embryo and in mouse embryos influenced by cocaine and retinoic acid.

Yolk sacs of postimplantation mouse embryos were cultured in a mixture of human and rat sera. The central nervous system of these cultured normal embryos was studied from the stage of 5-9 somites (approximately 8.5 postcoital days) to 20-21 somites (approximately 9.5 postcoital days) and compared with in vivo embryos at the same stages. This developmental period covers most of the neural tube closure, the early premigratory differentiation of the neuroectodermal epithelium, and the glial commitment of a population of germinative cells. The neuronal and glial elements of the in vitro cultivated embryos were found to be identical to the corresponding neural tissue in in vivo embryos (light and electron microscopic comparisons); the morphological identity between the in vivo and in vitro embryos was confirmed by morphometry and by stainings revealing the differentiation of the glial elements and precursors. The study of the neuronal-glial units in this material revealed that the fascicular organization of the radial glial cells occurs before the stage of 20 somites. When submitted to a single low dose of retinoic acid at the 7-somite stage, the expression of the epitope recognized by radial cell 2 (RC2), a glial marker, is delayed in the in vitro embryos 12-16 hours, but the glycogen and the other glial parameters mature in time. The in vitro embryos exposed to cocaine at the 7-somite stage displayed a prosencephalon remaining deprived of almost all glial cytological features during the entire culture period, although the other developmental parameters evolved normally. This in vitro whole embryo model seems to be a powerful tool for studying early neurogenesis and teratogenesis.

Osteogenesis imperfecta phenotypes resulting from serine for glycine substitutions in the alpha2(I) collagen chain.

Clinical and biochemical findings in 5 unrelated patients with osteogenesis imperfecta (OI) with a serine for glycine substitution in the alpha2(I) collagen chain are presented. The data are compared to other serine substitutions in collagen type I. Findings show that the phenotypic severity of serine for glycine substitutions in the alpha2(I) collagen chain is region dependent similar to the observations for the alpha1(I) collagen chain, and that so-called 'lethal' and 'non-lethal' domains in the alpha1 and alpha2 collagen chains do not necessarily correspond.

Physical map of a 1.5 mb region on 12p11.2 harbouring a synpolydactyly associated chromosomal breakpoint.

Synpolydactyly (SPD) is a rare malformation of the distal limbs known to be caused by mutations in HOXD13. We have previously described a complex form of SPD associated with synostoses in three members of a Belgian family, which co-segregates with a t(12;22)(p11.2;q13.3) chromosomal translocation. The chromosome 12 breakpoint of this translocation maps to 12p11.2 between markers D12S1034 and D12S1596. Here we show that a mutation in the HOXD13 gene is not responsible for the phenotype, and present a physical map of the region around the 12p11.2 breakpoint. Starting from D12S1034 and D12S1596, we have established a contig approximately 1.5 Mb in length, containing 13 YAC clones, 16 BAC clones, and 11 cosmid clones. FISH analysis shows that cosmid LL12NCO1-149H4 maps across the breakpoint, and Southern blot experiments using fragments of this cosmid as probes identify a rearranged BamHI fragment in the patients carrying the translocation. A search for expressed sequences within the contig have so far revealed one CpG island, seven anonymous ESTs and three previously characterised genes, DAD-R, KRAG and HT21, all of which were found not to be directly disrupted by the translocation. The gene represented by EST R72964 was found to be disrupted by the translocation. These findings lay the groundwork for further efforts to characterise a gene critical for normal distal limb development that is perturbed by this translocation.

Brief clinical report: the Dubowitz syndrome in a teenager.

The Dubowitz syndrome has been recognized during the past few years as a new, distinct intrauterine growth-retardation syndrome with autosomal recessive inheritance. One new patient is presented, a 10 1/2-year-old slightly mentally retarded girl.

Caffeine-induced disturbances of early neurogenesis in whole mouse embryo cultures.

In toto mouse embryos were cultivated at embryonic day 8.5 for 26 h with 105, 310 or 620 microM caffeine; 105-310 microM correspond to concentrations transferred by the placenta of heavy caffeine consumers. Failure of neural tube closure, excessive proliferation of neuroepithelial cells and premature evagination of telencephalic vesicles were present in 50% of treated embryos. When reaching the embryonic neural tube before neuronal migration, caffeine regionally modifies the schedule and/or rate of neural cell proliferation.

Cranial nerves and ganglia are altered after in vitro treatment of mouse embryos with valproic acid (VPA) and 4-en-VPA.

Prenatal valproic acid (VPA) exposure results in neural tube defects and in the fetal valproate syndrome (FVS), associated with developmental delay. In the present study we investigate the alterations induced by VPA and one of its metabolite, 4-en-VPA, on specific neural structures: branchial nerves and ganglia. This study was performed on 8-9 pairs of somites mouse embryos exposed in vitro for 24 h to 0.75 mM of VPA or 1 mM of 4-en-VPA. After an additional culture period of 20 h without drug, the embryos were processed for whole mount immunostaining using the monoclonal antibody 2H3, directed against the 155 kDa neurofilament protein. This technique makes it possible to visualise the branchial nerves/ganglia. VPA and 4-en-VPA induced a delay in the development of the trigeminal (V), glossopharyngeal (IX) and vagus (X) nerves/ganglia. The development of the facial (VII) nerve was delayed to a lesser extend. These treatments also induced defects in the four ganglia. The main abnormalities were a reduced dorsal component of ganglion V, the absence of the dorsal root of ganglion IX, a disorganised dorsal part of ganglion X and diffuse ventral fibres in nerves VII-VIII. In addition, scattered fibres were observed around and between ganglia. In conclusion, VPA and 4-en-VPA deeply altered the differentiation of branchial nerves/ganglia. The dorsal part of the ganglia, arising from the rhombencephalic neural crest, was particularly sensitive. The disorganisation of fibres could possibly be explained by alteration of the extracellular matrix.

Biochemical and density assessment of the new bone in late remodeling after callus distraction.

Biochemical changes in a canine bone-lengthening model were characterized 5 months after surgery. The mineral content and the total amount of EDTA-extractable noncollagenous proteins, insulin-like growth factor-I, and osteocalcin were determined for the lengthened callus, and a gradient density fractionation analysis of bone powder particles was performed. The results were compared with two other areas of the lengthened tibia and one region of the contralateral tibia. The mineral and osteocalcin contents showed significant decreases, whereas the hydroxyproline concentration was significantly increased. Neither the insulin-like growth factor-I content nor the concentration of EDTA-extractable proteins was significantly different in any of the examined regions.

Interlaboratory evaluation of three culture media for postimplantation rodent embryos.

The first aim of the study was to compare the ability of rat serum, human serum, and a mixture of human and rat serum (4:1) to support in vitro development of rodent postimplantation embryos. The comparison was made in three laboratories using rat embryos and in one laboratory using mouse embryos. Batches of sera, initial developmental stage, duration of culture, and endpoints were identical in the laboratories. The second aim of the study was to evaluate if other variables that could not be standardized would significantly influence the results of the laboratories. No reproducible difference was observed among the culture media or among the laboratories except that growth and differentiation were slower in the laboratory using mouse embryos. Further experiments are needed to exclude small differences in performance of the media.

Retinoic acid induces a tissue-specific deletion in the expression domain of Otx2.

The expression domain of Otx2, a gene essential for the development of the fore- and midbrain, has previously been shown to be affected by exposure to all-trans-retinoic acid (AT-RA). However, morphological abnormalities of the fore- and midbrain induced by exposure of early somite-stage embryos to AT-RA were not associated with abnormal Otx2 expression. To identify abnormal expression of developmental genes induced by exposure at early somite-stages, we performed a fine analysis of the expression domains of Otx2, Otx1, Emx2, and Pax-6 by combining in situ hybridization (ISH) with computer-assisted superpositions and three-dimensional reconstructions of these expression domains. No alteration in the relative location of the caudal boundaries of the expression domains of these genes was observed. The only abnormality was a deletion of the most cranial portion of the neural folds (NF).

All-trans-retinoic acid upregulates the expression of COUP-TFI in early-somite mouse embryos cultured in vitro.

Exposure of embryos to an excess of retinoic acid (RA) modifies the spatio-temporal pattern of expression of developmental genes. RA regulates the expression of target genes through binding of the retinoid nuclear receptors (RARs and RXRs), as heterodimers, to regulatory cis-acting elements. COUP-TF factors, which are able to dimerize with the RXRs and to compete with the retinoid receptors for their DNA binding sites, are suspected to modulate the retinoid signal transduction pathway. Therefore, COUP-TF factors may be involved in the regulation of the expression of developmental genes and/or in the modifications induced by an excess of RA in the expression of these genes. The aim of this work is to assess whether RA-induced modifications in the expression of Krox-20 and Hox genes correlate with alterations of the expression of COUP-TF genes. In addition to spatial modifications in the expression patterns of Krox-20 and Hox genes, we report here an upregulation of the expression level of COUP-TFI after RA exposure. However, this abnormality did not spatially overlap with the modifications observed in the expression of Krox-20 and Hox genes. These data suggest an involvement of COUP-TFI in the generation of RA-induced abnormalities, but do not support the hypothesis of an involvement of this factor in the regulation of the expression of Hox or Krox-20 genes.

Alterations of mouse embryonic branchial nerves and ganglia induced by ethanol.

An immunostaining technique using monoclonal antibodies to a neurofilament protein has allowed us to visualize defects in the development of cranial nerves and ganglia of 10 to 10.5 days mouse embryos following exposure to ethanol in whole embryo culture. Reference patterns for development of cranial nerves and ganglia of control mouse embryos explanted and examined when they had 25 to 34 pairs of somites were established. Additionally, control mouse embryos were grown in whole embryo culture for 48 h, with culture being initiated in embryos having 6 to 7 somite pairs. At the end of the culture period, only minor differences were observed between the control groups. An experimental group of embryos was cultured in the presence of increasing doses (1.6, 3.2, 4, and 4.8 g/l) of ethanol. Defects were observed in the development of the glossopharyngeal and vagus nerves. These abnormalities included absence of the dorsal root (superior ganglion) of IX, star-like shape of inferior ganglion IX, disorganization of the rootlets of nerve X and abnormal fibers between the two nerves and ganglia. These results suggest that the migration and patterning of neural crest cells derived from r6 and r7 may be particularly affected by ethanol. The results also demonstrate the usefulness of this approach in evaluating the susceptibility of the developing cranial nerves to toxicant exposure.

In vitro neuroteratogenicity of valproic acid and 4-en-VPA.

Mouse embryos displaying 8 to 9 pairs of somites were cultured during 26 h in presence of 0.75 mM of VPA, or of 1 mM of 4-en-VPA. These concentrations induced approximately 50% of dysmorphogenic embryos. Irregular suture of caudal neural tube, abnormal head shape, cranial neural tube defects, and deformed optic vesicles were the most common defects observed with both compounds. The main differences in the types of dysmorphogeneses detected between the two compounds concerned the suture of the caudal neural tube and the telencephalic region. Other macroscopic effects induced by the two compounds were similar. Several of the observed abnormalities can be correlated with defects reported after in vivo exposure. The major alteration of the histological structure of the neural tube concerned a specific area in the hindbrain : VPA and 4-en-VPA induced an abnormal and irregular budding of the neuroepithelium at this level. Immunohistology with an antibody specific for radial glial fibers (RC-2) as well as SEM analysis showed a moderate effect on glial development, mainly after exposure to VPA.

Developmental table of the early mouse post-implantation embryo.

The developmental tables of early somite mouse embryos that are presently available from the literature give clear and useful descriptions of the differentiation at successive stages. However, they provide no easy access to the correlation between the growth of the embryo and its differentiation. In the present study, quantitative data concerning normal mouse embryonic development as well as the major developmental events occurring between 0 and 30 pairs of somites were established. Measurements of growth (crown-rump length, head length, absorbancy at 280 nm) and differentiation parameters (morphological score) of 168 to 310 explanted mouse embryos were recorded for each developmental stage (number of pairs of somites). A short description of the major events occurring at the corresponding stages is also presented. The table is more detailed than those presently available and provides a rapid and practical overview of the timing of the appearance of developmental events and differentiation in correlation to the progressive growth of the embryo. It could, therefore, be useful for embryologists and toxicologists. In addition, the development of 67 post-implantation mouse embryos cultured in vitro was compared with the reference table established from in vivo embryos. Our results confirm and extend previous reports showing that embryos cultured in vitro grow and differentiate at a pace very similar to that of embryos developed in vivo.

Whole embryo culture of presomitic mouse embryos.

Rat embryos explanted at the presomite stage and cultured through limb bud stages develop to well formed embryos and exhibit growth and differentiation which mimic those observed in vivo at corresponding stages. In contrast, the culture of presomite stage mouse embryos has proven to be much less successful. In the present study presomitic and 3-4 somite stage mouse embryos were cultured for 48 hr. Four stages of presomitic mouse embryos corresponding to late primitive streak, early neural plate, mid neural plate and late neural plate were cultured for 24 hr in a mixture of mouse serum (12.5%), rat serum (25%) and human serum (62.5%) and during a further period of 24 hr in a mixture of human (80%) and rat (20%) serum. Two explantation procedures were used. Embryos of 3-4 somites, cultured as a reference, developed in quite a similar way to embryos in vivo and in this group very few dysmorphogeneses were observed. In contrast, the development of earlier embryos was not reproducible and the two explantation procedures led to similar results.