Effects of acute leptin administration on the differences in proton leak rate in liver mitochondria from ob/ob mice compared to lean controls.

In this investigation, the effects on proton leak of leptin administration to ob/ob mice was measured for liver mitochondria. We and others have shown that proton leak is approximately 3 times greater in liver mitochondria from ob/ob mice compared to lean controls at any given membrane potential. The results are consistent with obese mammals having higher lean mass-specific metabolic rates compared to lean controls. The increase in proton leak rate at any given membrane potential cannot be explained by the presence of free fatty acids associated with mitochondria isolated from the obese animals. The difference in proton leak must therefore represent a real difference in inner membrane permeability. Acute leptin (OB protein) administration restores the liver mitochondrial proton leak rate of ob/ob mice to that of lean controls. There was no effect on proton leak rate of liver mitochondria from sham-treated ob/ob mice. These novel results indicate a role for leptin, either directly or indirectly, in regulating the efficiency of oxidative phosphorylation.     

A comparison of the efficiency of G protein activation by ligand-free and light-activated forms of rhodopsin

Activation of the photoreceptor G protein transducin (Gt) by opsin, the ligand-free form of rhodopsin, was measured using rod outer segment membranes with densities of opsin and Gt similar to those found in rod cells. When GTPgammaS was used as the activating nucleotide, opsin catalyzed transducin activation with an exponential time course with a rate constant k(act) on the order of 2 x 10(-3)s(-1). Comparison under these conditions to activation by flash-generated metarhodopsin II (MII) revealed that opsin- and R*-catalyzed activation showed similar kinetics when MII was present at a surface density approximately 10(-6) lower than that of opsin. Thus, in contrast to some previous reports, we find that the catalytic potency of opsin is only approximately 10(-6) that of MII. In the presence of residual retinaldehyde-derived species present in membranes treated with hydroxylamine after bleaching, the apparent k(act) observed was much higher than that for opsin, suggesting a possible explanation for previous reports of more efficient activation by opsin. These results are important for considering the possible role of opsin in the diverse phenomena in which it has been suggested to play a key role, such as bleaching desensitization and retinal degeneration induced by continuous light or vitamin A deprivation.     

High serum vitamin B12 binding capacity as a marker of the fibrolamellar variant of hepatocellular carcinoma.

Ten (9.3%) of 107 patients with hepatocellular carcinoma had considerably increased serum unsaturated vitamin B12 binding capacity. All 10 were young (mean 12 years), had no serum alpha-fetoprotein, and no underlying cirrhosis; all had a longer survival compared with patients without increased serum unsaturated vitamin B12 binding capacity in the study. Seven of the 10 patients had fibrolamellar hepatocellular carcinoma, a recently recognised histological variant, which was found in only one young patient without increased serum unsaturated vitamin B12 binding capacity and no alpha-fetoprotein among the remaining 97. This high degree of correlation between increased serum unsaturated vitamin B12 binding capacity and fibrolamellar hepatocellular carcinoma has not been reported before. Increased serum unsaturated vitamin B12 binding capacity may be of considerable help in diagnosis, prognosis, and monitoring treatment of this well-defined group of patients with hepatocellular carcinoma but no alpha-fetoprotein.     

Inhibition of protein kinase C decreases prostaglandin-induced breakdown of the blood-retinal barrier

Breakdown of the blood-retinal barrier (BRB) occurs in several retinal diseases and is a major cause of visual loss. Vascular endothelial growth factor (VEGF) has been implicated as a cause of BRB breakdown in diabetic retinopathy and other ischemic retinopathies, and there is evidence to suggest that other vasopermeability factors may act indirectly through VEGF. In this study, we investigated the effect of several receptor kinase inhibitors on BRB breakdown resulting from VEGF, tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), insulin-like growth factor-1 (IGF-1), prostaglandin E1 (PGE(1)), or PGE(2). Inhibitors of VEGF receptor kinase, including PKC412, PTK787, and SU1498, decreased VEGF-induced breakdown of the BRB. None of the inhibitors blocked leakage caused by TNF-alpha, IL-1beta, or IGF-1 and only PKC412, an inhibitor of protein kinase C (PKC) as well as VEGF and platelet-derived growth factor (PDGF) receptor kinases, decreased leakage caused by prostaglandins. Since the other inhibitors of VEGF and/or PDGF receptor kinases that do not also inhibit PKC had no effect on prostaglandin-induced breakdown of the BRB, these data implicate PKC in retinal vascular leakage caused by prostaglandins. PKC412 may be useful for treatment of post-operative and inflammatory macular edema, in which prostaglandins play a role, as well as macular edema associated with ischemic retinopathies.     

Nitric oxide is proangiogenic in the retina and choroid

Nitric oxide (NO) has been shown to have proangiogenic or antiangiogenic effects depending upon the setting. In this study, we used mice with targeted deletion of one of the three isoforms of nitric oxide synthase (NOS) to investigate the effects of NO in ocular neovascularization. In transgenic mice with increased expression of vascular endothelial growth factor (VEGF) in photoreceptors, deficiency of any of the three isoforms caused a significant decrease in subretinal neovascularization, but no alteration of VEGF expression. In mice with laser-induced rupture of Bruch's membrane, deficiency of inducible NOS (iNOS) or neuronal NOS (nNOS), but not endothelial NOS (eNOS), caused a significant decrease in choroidal neovascularization. In mice with oxygen-induced ischemic retinopathy, deficiency of eNOS, but not iNOS or nNOS caused a significant decrease in retinal neovascularization and decreased expression of VEGF. These data suggest that NO contributes to both retinal and choroidal neovascularization and that different isoforms of NOS are involved in different settings and different disease processes. A broad spectrum NOS inhibitor may have therapeutic potential for treatment of both retinal and choroidal neovascularization.     

Vascular endothelial growth factor and angiopoietin in liver regeneration

Liver architecture remodeling following partial hepatectomy (PHx) involves the formation of a complex network of liver sinusoids through which the blood flows. The present study examines the involvement of vascular endothelial growth factor (VEGF) and angiopoietin-1 (ang-1) during liver regeneration. Following PHx, VEGF and ang-1 mRNA levels increase, followed by gradual return to baseline levels. RT-PCR analysis of VEGF mRNA reveals three isoforms, VEGF120, VEGF164 and VEGF188. Of the three, VEGF188 is the predominant isoform, VEGF120 being the less abundant. Although VEGF mRNA fluctuates following PHx, the relative expression of each isoform remains the same throughout the recovery process. The level of neuropilin-1, an accessory receptor of VEGF to main receptor corresponds with that of VEGF and ang-1. We have previously demonstrated the capacity of exogenous VEGF165 to stimulate liver cell proliferation following PHx. We now report similar effect using VEGF121, further demonstrating the benefit of manipulating growth factors where such an intervention is required.     

Genomic Models of Short-Term Exposure Accurately Predict Long-Term Chemical Carcinogenicity and Identify Putative Mechanisms of Action

Background

Despite an overall decrease in incidence of and mortality from cancer, about 40% of Americans will be diagnosed with the disease in their lifetime, and around 20% will die of it. Current approaches to test carcinogenic chemicals adopt the 2-year rodent bioassay, which is costly and time-consuming. As a result, fewer than 2% of the chemicals on the market have actually been tested. However, evidence accumulated to date suggests that gene expression profiles from model organisms exposed to chemical compounds reflect underlying mechanisms of action, and that these toxicogenomic models could be used in the prediction of chemical carcinogenicity.

Results

In this study, we used a rat-based microarray dataset from the NTP DrugMatrix Database to test the ability of toxicogenomics to model carcinogenicity. We analyzed 1,221 gene-expression profiles obtained from rats treated with 127 well-characterized compounds, including genotoxic and non-genotoxic carcinogens. We built a classifier that predicts a chemical''s carcinogenic potential with an AUC of 0.78, and validated it on an independent dataset from the Japanese Toxicogenomics Project consisting of 2,065 profiles from 72 compounds. Finally, we identified differentially expressed genes associated with chemical carcinogenesis, and developed novel data-driven approaches for the molecular characterization of the response to chemical stressors.

Conclusion

Here, we validate a toxicogenomic approach to predict carcinogenicity and provide strong evidence that, with a larger set of compounds, we should be able to improve the sensitivity and specificity of the predictions. We found that the prediction of carcinogenicity is tissue-dependent and that the results also confirm and expand upon previous studies implicating DNA damage, the peroxisome proliferator-activated receptor, the aryl hydrocarbon receptor, and regenerative pathology in the response to carcinogen exposure.     

Psychological Factors as Predictors of Suicidal Ideation among Adolescents in Malaysia

Background

There has been a drastic increase in the rate of suicides over the past 45 years in Malaysia. The statistics show that adolescents aged between 16 and 19 years old are at high risk of committing suicide. This could be attributed to issues relating to the developmental stage of adolescents. During this stage, adolescents face challenges and are exposed to various stressful experiences and risk factors relating to suicide.

Method

The present study examined psychological factors (i.e., depression, anxiety and stress) as predictors for suicidal ideation among adolescents. A cross-sectional study was conducted on 190 students (103 males and 87 females), aged 15 to 19 years old from two different schools in Kuala Lumpur. The Depression Anxiety Stress Scale 21-item version (DASS-21) was used to measure depression, anxiety and stress among the students, and the Beck Scale for Suicide Ideation (BSS) to measure suicidal ideation. The data were analysed using Pearson''s correlation and multiple regression analysis.

Results

The results show that 11.10%, 10.00%, and 9.50% of the students reported that they were experiencing severe depression, anxiety and stress, respectively. There were significant correlations between depression, anxiety, and stress with suicidal ideation. However, only depression was identified as a predictor for suicidal ideation.

Conclusion

Hence, this study extends the role of depression in predicting suicidal ideation among adolescents in the Malaysian context. The findings imply that teenagers should be assisted in strengthening their positive coping strategies in managing distress to reduce depression and suicidal ideation.