Public Health Perspectives on Dioxin Risks: Two Decades of Evaluations

The paper provides an overview of approaches to dioxin risk assessment employed by different agencies worldwide over the past 20 years. Our insights regarding understanding of the toxicity of dioxins have advanced tremendously in recent years; however, important data gaps still exist. More information on topics such as mechanism of interaction, effects at low levels of exposure, interspecies differences, and sensitive populations is needed. Some differences exist between USEPA's approach to dioxin assessment and that of other health organizations around the world. The authors conclude that USEPA's reassessment of dioxin and related compounds may place too much confidence in the ability to accurately predict cancer risks at low doses. Further, it is important to derive health-based guidance values for noncancer end points especially in accordance with emerging reports that reproductive and developmental end points are very sensitive to dioxins. A worldwide convergence on the health assessment value being around 1 to 4?pg/kg/day is noted.     

Satellite 2 methylation patterns in normal and ICF syndrome cells and association of hypomethylation with advanced replication

Mutation in the DNMT3B DNA methyltransferase gene is a common cause of ICF (immunodeficiency, centromeric heterochromatin, facial anomalies) immunodeficiency syndrome and leads to hypomethylation of satellites 2 and 3 in pericentric heterochromatin. This hypomethylation is associated with centromeric decondensation and chromosomal rearrangements, suggesting that these satellite repeats have an important structural role. In addition, the satellite regions may have functional roles in modifying gene expression. The extent of satellite hypomethylation in ICF cells is unknown because methylation status has only been determined with restriction enzymes that cut infrequently at these loci. We have therefore developed a bisulfite conversion-based method to determine the detailed cytosine methylation patterns at satellite 2 sequences in a quantitative manner for normal and ICF samples. From our sequence analysis of unmodified DNA, the internal repeat region analyzed for methylation contains an average of 17 CpG sites. The average level of methylation in normal lymphoblasts and fibroblasts is 69% compared with 20% in such cells from ICF patients with DNMT3B mutations and 29% in normal sperm. Although the mean satellite 2 methylation values for these groups do not overlap, there is considerable overlap at the level of individual DNA strands. Our analysis has also revealed a pattern of methylation specificity, suggesting that some CpGs in the repeat are more prone to methylation than other sites. Variation in satellite 2 methylation among lymphoblasts from different ICF patients has prompted us to determine the frequency of cytogenetic abnormalities in these cells. Although our data suggest that some degree of hypomethylation is necessary for pericentromeric decondensation, factors other than DNA methylation appear to play a major role in this phenomenon. Another such factor may be altered replication timing because we have discovered that the hypomethylation of satellite 2 in ICF cultures is associated with advanced replication.     

Highly potent growth hormone secretagogues: hybrids of NN703 and ipamorelin.

A series of NN703 analogues with lysine mimetics combined with naphthyl- or biphenylalanine in the core has been prepared and tested in vitro in a rat pituitary cell based assay and subsequently in vivo in pigs in a single dose at 50 nmol/kg. Re-introduction of certain pharmacophores in the C-terminal of NN703, which were originally removed during optimisation for oral bioavailability, led to unexpectedly potent compounds in vitro as well as in vivo.     

Preparation and use of recombinant protein G-gold complexes as markers in double labelling immunocytochemistry

Summary Recombinant protein G (RPG) was conjugated to colloidal gold particles and used for immunocytochemistry. In this report, the preparation of RPG—gold conjugates (RPGG) and the application of these conjugates in spot blot tests and in double immunolabelling are described. The immunolabelling was performed on ultracryosections of pig small intestine using antibodies directed against aminopeptidase N and sucrase—isomaltase. The labelling efficiency of RPGG was compared to that of protein A—gold conjugates (PAG) in different compartments of the enterocyte. Quantification showed that the labelling intensity was dependent on the size of the marker as well as on the kind of protein used for complex formation. The distributions for RPGG and PAG were respectively: for the 12nm particles, 10.3 and 6.2 particles/µm of length of microvillar membrane, 3.5 and 1.0 particles/µm² of Golgi profile and 5.9 and 2.0 particles/µm² of multivesicular body profile; and for the 6nm particles, 49.6 and 15.7 particles/µm of length of microvillar membrane, 24.4 and 5.0 particles/µm² of Golgi profile and 25.4 and 3.4. particles/µm² of multivesicular body profile. Controls showed very little non-specific gold labelling (<0.02 gold particles/µm² of section).     

Arteriovenous shunting and regional blood flow in myocutaneous island flaps: an experimental study in pigs

In eight pigs, total blood flow, regional capillary blood flow distribution, and arteriovenous (AV) shunting were studied during the first 4 postoperative hours after elevation of a myocutaneous rectus abdominis island flap. Capillary blood flow and AV shunting were measured using radioactive microspheres before flap creation and 1 and 4 hours after surgery. Total blood flow, measured continuously as venous outflow, increased in the first postoperative hour (p less than 0.05). Elevation of the flap caused a slight decrease in skin capillary blood flow (p less than 0.05), whereas muscular capillary blood flow increased (p less than 0.01). AV shunting accounted for 50 percent of the total flap blood flow, whereas it was negligible in the abdominal wall prior to flap elevation. Thus stalk blood flow, skin appearance, and skin temperature may be poor indicators of nutritional capillary perfusion. However, the clinical and nutritional consequences of these findings remain to be established.     

A set of microsatellite primers for the striped possum,Dactylopsila trivirgata (Petauridae: Marsupialia)

The New Guinean endemic dactylopsilines are members of the Petauridae possum family, represented in Australia only by the striped possum Dactylopsila trivirgata. The shy nature and low density of this species have hampered studies of its ecology to date, so we developed nine highly variable polymorphic microsatellite markers to enable molecular genetic analysis of population structure and mating system parameters. This will add substantially to our understanding of the behavioural ecology of this species. The low degree of cross‐amplification of the primers in other petaurid species lends weight to other evidence suggesting that this family underwent a relatively early radiation.     

The Structure of the Hypothalamohypophysial Portal Vascular System in Acipenser ruthenus L. (Chondrostei)

The vascularization of the pituitary region in Acipenser ruthenus L. (Chondrostei) is described. The adenohypophysis has no direct arterial supply but is fed exclusively by a pituitary portal system supplied through a pair of infundibular arteries. Distinct portal vessels connect the lateral part of the primary plexus of the neurohaemal area (the median eminence) with the secondary plexus of the pituitary gland. The primary plexus enters the pars distalis paramedially, apparently without the formation of distinct portal vessels. The neuro-intermediate lobe receives its blood supply exclusively from the primary plexus. The plexus intermedius gives off capillaries to the parenchyma of the intermediate lobe (an intermediate lobe sinus system). The saccus vasculosus receives (1) a “direct” supply, i.e. branches originating directly from the cerebral arteries and (2) an “indirect” supply, i.e. capillaries from the primary plexus. The pars distalis is drained into an unpaired ventral hypophysial vein, while a dorsal hypophysial vein, also unpaired, drains the plexus intermedius. These two veins join to form the unpaired hypophysial vein. The findings are discussed from comparative and functional viewpoints.