X-ray microtomography of biological tissues using laboratory and synchrotron sources

X-ray microradiography is a well established technique for the study of biological structures in which the projected absorption is measured, usually with photographic film or resist. If scanning X-ray microradiography with a 15-μm beam, 2-D scanning, and photon counting is used, more accurate results can be obtained and real-time experiments undertaken. Addition of a rotation axis allows computerized axial tomography to be done at a resolution of 15 μm. This technique overcomes the inherent difficulty of microradiography that all detail perpendicular to the plane of the specimen is superimposed. This method has been applied to the study of the 3-D mineral distribution in a 0.8×0.8 mm column of human cortical bone with a laboratory X-ray source. Calculation of the wavelength dependence of the linear absorption coefficient for liver and bone shows that, for a choice of wavelength in the range of 3–0.4 Å (4–30 keV), the specimen thickness can be from 100μm–2 cm and 10 μm–3 mm, respectively. Synchrotron X-radiation has the potential for better resolution because of the higher intensity, which allows the use of a narrower beam. There is also the possibility of determining individual element 3-D distributions from measurements on either side of the absorption edges because of the continuous nature of the spectrum and also the possibility of doing this from X-ray fluorescence measurements. To investigate these possibilities, a tomographic apparatus has been built based on the availability of accurately ground, tungsten carbide balls. Metrological assessment shows that the specimen remains within <1 μm of the required position during translation and rotation. Preliminary X-ray tomographic studies with a 4-μm diameter beam have been started at the Daresbury laboratory synchrotron source.     

Syringe driver in terminal care.

Continuous subcutaneous infusions of drugs by syringe driver are used often and successfully in the terminal care of patients when drugs cannot be given orally. Diamorphine is the opioid of choice because of its high solubility. If other drugs such as antiemetics, anticholinergics, sedatives, or steroids are required they may also be given by syringe driver. This method is particularly useful for domiciliary care, where the practical difficulties of providing regular parenteral analgesia are otherwise formidable.     

Arabinan-deficient mutants of Corynebacterium glutamicum and the consequent flux in decaprenylmonophosphoryl-D-arabinose metabolism

The arabinogalactan (AG) of Corynebacterianeae is a critical macromolecule that tethers mycolic acids to peptidoglycan, thus forming a highly impermeable cell wall matrix termed the mycolyl-arabinogalactan peptidoglycan complex (mAGP). The front line anti-tuberculosis drug, ethambutol (Emb), targets the Mycobacterium tuberculosis and Corynebacterium glutamicum arabinofuranosyltransferase Mt-EmbA, Mt-EmbB and Cg-Emb enzymes, respectively, which are responsible for the biosynthesis of the arabinan domain of AG. The substrate utilized by these important glycosyltransferases, decaprenylmonophosphoryl-D-arabinose (DPA), is synthesized via a decaprenylphosphoryl-5-phosphoribose (DPPR) synthase (UbiA), which catalyzes the transfer of 5-phospho-ribofuranose-pyrophosphate (pRpp) to decaprenol phosphate to form DPPR. Glycosyl compositional analysis of cell walls extracted from a C. glutamicum::ubiA mutant revealed a galactan core consisting of alternating beta(1-->5)-Galf and beta(1-->6)-Galf residues, completely devoid of arabinan and a concomitant loss of cell-wall-bound mycolic acids. In addition, in vitro assays demonstrated a complete loss of arabinofuranosyltransferase activity and DPA biosynthesis in the C. glutamicum::ubiA mutant when supplemented with p[14C]Rpp, the precursor of DPA. Interestingly, in vitro arabinofuranosyltransferase activity was restored in the C. glutamicum::ubiA mutant when supplemented with exogenous DP[14C]A substrate, and C. glutamicum strains deficient in ubiA, emb, and aftA all exhibited different levels of DPA biosynthesis.     

Sequence and analysis of a plasmid-encoded mercury resistance operon from Mycobacterium marinum identifies MerH, a new mercuric ion transporter

In this study, we report the DNA sequence and biological analysis of a mycobacterial mercury resistance operon encoding a novel Hg²⁺ transporter. MerH was found to transport mercuric ions in Escherichia coli via a pair of essential cysteine residues but only when coexpressed with the mercuric reductase.     

Pesticide exposure: the hormonal function of the female reproductive system disrupted?

Some pesticides may interfere with the female hormonal function, which may lead to negative effects on the reproductive system through disruption of the hormonal balance necessary for proper functioning. Previous studies primarily focused on interference with the estrogen and/or androgen receptor, but the hormonal function may be disrupted in many more ways through pesticide exposure. The aim of this review is to give an overview of the various ways in which pesticides may disrupt the hormonal function of the female reproductive system and in particular the ovarian cycle. Disruption can occur in all stages of hormonal regulation: 1. hormone synthesis; 2. hormone release and storage; 3. hormone transport and clearance; 4. hormone receptor recognition and binding; 5. hormone postreceptor activation; 6. the thyroid function; and 7. the central nervous system. These mechanisms are described for effects of pesticide exposure in vitro and on experimental animals in vivo. For the latter, potential effects of endocrine disrupting pesticides on the female reproductive system, i.e. modulation of hormone concentrations, ovarian cycle irregularities, and impaired fertility, are also reviewed. In epidemiological studies, exposure to pesticides has been associated with menstrual cycle disturbances, reduced fertility, prolonged time-to-pregnancy, spontaneous abortion, stillbirths, and developmental defects, which may or may not be due to disruption of the female hormonal function. Because pesticides comprise a large number of distinct substances with dissimilar structures and diverse toxicity, it is most likely that several of the above-mentioned mechanisms are involved in the pathophysiological pathways explaining the role of pesticide exposure in ovarian cycle disturbances, ultimately leading to fertility problems and other reproductive effects. In future research, information on the ways in which pesticides may disrupt the hormonal function as described in this review, can be used to generate specific hypotheses for studies on the effects of pesticides on the ovarian cycle, both in toxicological and epidemiological settings.