Improvement in cardiac function of diabetic rats by bosentan is not associated with changes in the activation of PKC isoforms

We previously demonstrated that chronic treatment with the mixed endothelin A and B (ET_A and ET_B) receptor blocker bosentan improved isolated working heart function in streptozotocin (STZ) diabetic rats. Endothelin-1 (ET-1) peptide levels, ET-1 mRNA and ET_A and ET_B receptor mRNA were all increased in diabetic hearts, but were unaffected by bosentan treatment, indicating that the beneficial effects of bosentan on heart appear to be on downstream effectors of ET-1 and ET receptors rather than the ET-1 system itself. Stimulation of ET-1 receptors leads to increased activation of protein kinase C (PKC), which is associated with PKC translocation from the cytosol to the membrane. Persistent activation of specific PKC isoforms has been proposed to contribute to diabetic cardiomyopathy. The purpose of this study was to determine whether chronic treatment with bosentan influences the activation of PKC isoforms in hearts from diabetic rats. Male Wistar rats were divided into four groups: control, bosentan-treated control, diabetic, and bosentan-treated diabetic. Diabetes was induced by the intravenous injection of 60 mg/kg streptozotocin. One week later, treatment with bosentan (100 mg/kg/day) by oral gavage was begun and continued for 10 weeks. The heart was then removed, homogenized, separated into soluble (cytosolic) and particulate (membrane) fractions and PKC isoform content in each fraction was determined by Western blotting. PKC α, β2, δ, ε and ζ were all detected in hearts from both control and diabetic rats. However, no change in the levels or distribution between the soluble and particulate fractions of any of these isoforms could be detected in chronic diabetic hearts compared to control, whether untreated or treated with bosentan. These observations indicate that bosentan does not improve cardiac performance in STZ diabetic rats by affecting the activation of PKC isoforms.     

Chronic estrogen treatment reduces vaso-constrictor responses in insulin resistant rats

Previous experiments have shown that chronic estrogen treatment via subcutaneous implants prevented insulin-induced blood pressure elevation and increased insulin sensitivity in ovariectomized female rats. In vitro vascular studies were performed using isolated mesenteric arteries to determine the effect of chronic estrogen and insulin treatments on vascular responses to vasoconstrictor agents. Female Wistar rats were assigned to the following groups: sham-operated, sham-operated plus insulin, sham-operated plus insulin plus estrogen, ovariectomized, ovariectomized plus insulin, and ovariectomized plus insulin plus estrogen. Chronic insulin and estrogen treatments were initiated with subcutaneous placement of insulin implants (2 U/d) and 17beta-estradiol implants (0.5 mg/pellet, 60 day release) at the back of the neck. After 8 weeks of treatment, mesenteric arteries were isolated for assessment of constrictor responses to norepinephrine and the thromboxane A2 analogue U46619 in the presence or absence of the endothelium. The results show that chronic estrogen treatment attenuated the vascular constrictor responses to norepinephrine and U46619 only in endothelium intact vessels. Incubation with insulin did not significantly affect norepinephrine-induced vascular smooth muscle contraction. The study provides evidence that the mechanism by which estrogen prevents insulin-induced blood pressure elevation in insulin-treated ovariectomized rats is by influencing endothelium-derived vasoactive factors such as thromboxane A2.     

Effects of endothelin receptor blockade on hypervasoreactivity in streptozotocin-diabetic rats: vessel-specific involvement of thromboxane A2

Increased vasoconstrictor response to norepinephrine (NE) and endothelin (ET)-1 in arteries from diabetic animals is ameliorated by chronic endothelin receptor blockade with bosentan and was absent in endothelium-denuded arteries, suggesting the involvement of ET-1 and an endothelium-derived contracting factor such as thromboxane A2 (TxA2). To examine this possibility, we determined the effects of acute blockade of ET receptors or inhibition of TxA2 synthesis on the vascular function of superior mesenteric arteries (SMA) and renal arteries (RA) isolated from nondiabetic and 11-week streptozotocin (STZ) diabetic rats chronically treated with either bosentan or vehicle. Both in vitro incubation with bosentan and a selective ETA receptor blocker, BQ123, eradicated the increase in NE contractile responses in diabetic SMA. Additionally, in vitro incubation with the thromboxane synthase inhibitor, dazmegrel, abrogated the exaggerated NE and ET-1 contractile responses in diabetic SMA. Conversely, in RA, no significant acute effect of bosentan, BQ123, nor dazmegrel on vascular responses to NE was observed. Dazmegrel incubation attenuated the maximum contractile responses to ET-1 in diabetic RA; however, these responses in diabetic RA remained significantly greater than those of other groups. Diabetic RA but not SMA exhibited an enhanced contractile response to the TxA2 analogue U46619, which was corrected by chronic bosentan treatment. Immunohistochemical analyses in diabetic SMA revealed an increase in ETA receptor level that was normalized by chronic bosentan treatment. These data indicate that an interaction between ET-1 and TxA2 may be involved in mediating the exaggerated vasoconstrictor responses in diabetic arteries. Furthermore, the underlying mechanisms appear to be vessel specific.     

The Interaction between Polynucleotide Kinase Phosphatase and the DNA Repair Protein XRCC1 Is Critical for Repair of DNA Alkylation Damage and Stable Association at DNA Damage Sites

XRCC1 plays a key role in the repair of DNA base damage and single-strand breaks. Although it has no known enzymatic activity, XRCC1 interacts with multiple DNA repair proteins and is a subunit of distinct DNA repair protein complexes. Here we used the yeast two-hybrid genetic assay to identify mutant versions of XRCC1 that are selectively defective in interacting with a single protein partner. One XRCC1 mutant, A482T, that was defective in binding to polynucleotide kinase phosphatase (PNKP) not only retained the ability to interact with partner proteins that bind to different regions of XRCC1 but also with aprataxin and aprataxin-like factor whose binding sites overlap with that of PNKP. Disruption of the interaction between PNKP and XRCC1 did not impact their initial recruitment to localized DNA damage sites but dramatically reduced their retention there. Furthermore, the interaction between PNKP and the DNA ligase IIIα-XRCC1 complex significantly increased the efficiency of reconstituted repair reactions and was required for complementation of the DNA damage sensitivity to DNA alkylation agents of xrcc1 mutant cells. Together our results reveal novel roles for the interaction between PNKP and XRCC1 in the retention of XRCC1 at DNA damage sites and in DNA alkylation damage repair.     

Variation in Galr1 expression determines susceptibility to exocitotoxin-induced cell death in mice

Inbred strains of mice differ in their susceptibility to excitotoxin-induced cell death, but the genetic basis of individual variation in differential susceptibility is unknown. Previously, we identified a highly significant quantitative trait locus (QTL) on chromosome 18 that influenced susceptibility to kainic acid-induced cell death ( Sicd1 ). Comparison of susceptibility to seizure-induced cell death between reciprocal congenic lines for Sicd1 and parental background mice indicates that genes influencing this trait were captured in both strains. Two positional gene candidates, Galr1 and Mbp , map to 55 cM, where the Sicd1 QTL had been previously mapped. Thus, this study was undertaken to determine if Galr1 and/or Mbp could be considered as candidate genes. Genomic sequence comparison of these two functional candidate genes from the C57BL/6J (resistant at Sicd1 ) and the FVB/NJ (susceptible at Sicd1 ) strains showed no single-nucleotide polymorphisms. However, expression studies confirmed that Galr1 shows significant differential expression in the congenic and parental inbred strains. Galr1 expression was downregulated in the hippocampus of C57BL/6J mice and FVB.B6- Sicd1 congenic mice when compared with FVB/NJ or B6.FVB- Sicd1 congenic mice. A survey of Galr1 expression among other inbred strains showed a significant effect such that 'susceptible' strains showed a reduction in Galr1 expression as compared with 'resistant' strains. In contrast, no differences in Mbp expression were observed. In summary, these results suggest that differential expression of Galr1 may contribute to the differences in susceptibility to seizure-induced cell death between cell death-resistant and cell death-susceptible strains.     

An investigation of competitive learning for autonomous cluster identification in embedded systems.

Robust signal processing for embedded systems requires the effective identification and representation of features within raw sensory data. This task is inherently difficult due to unavoidable long-term changes in the sensory systems and/or the sensed environment. In this paper we explore four variations of competitive learning and examine their suitability as an unsupervised technique for the automated identification of data clusters within a given input space. The relative performance of the four techniques is evaluated through their ability to effectively represent the structure underlying artificial and real-world data distributions. As a result of this study it was found that frequency sensitive competitive learning provides both reliable and efficient solutions to complex data distributions. As well, frequency sensitive and soft competitive learning are shown to exhibit properties which may permit the evolution of an appropriate network structure through the use of growing or pruning procedures.     

Sulfate Reduction by a Desulfovibrio Species Isolated from Sheep Rumen

Several dissimilatory, sulfate-reducing bacteria were isolated from the rumen fluid of sheep fed purified diets containing sulfate. One isolate, strain D, was selected for characterization. This organism is a nonsporeforming, obligately anaerobic, mesophilic, nonmotile, gram-negative, straight rod. Cell-free extracts show absorption maxima for cytochrome c(3) and desulfoviridin, characteristic of Desulfovibrio. Carbohydrates, as a sole carbon source, will support growth. Lactate supports growth in the presence of sulfate, not in its absence, whereas glucose or pyruvate support growth either in the presence or absence of sulfate. The isolate has a deoxyribonucleic acid base composition of 61.2% guanine plus cytosine, which is similar to that of several other species of Desulfovibrio; however, it differs from previously described species in morphology, motility, and carbon source utilization. Cell-free extracts of this bacterium exhibit adenosine 5'-triphosphate-sulfurylase, adenosine-5'-phosphosulfate-reductase, and hydrogenase activity. After incubation of cell-free extracts with adenine 5'-triphosphate and (35)SO(4) (2-), adenosine-5'-phosphosulfate rather than 3'-phosphoadenosine-5'-phosphosulfate was shown to be labeled, indicating that the pathway of sulfate reduction in this organism is similar to that of other dissimilatory sulfate reducers. This is the first report of a Desulfovibrio sp. isolated from the rumen.