Degradation of dibenzofuran via multiple dioxygenation by a newly isolated Agrobacterium sp. PH-08.

AIMS: To demonstrate the biodegradation of dibenzofuran (DF) and its structural analogs by a newly isolated Agrobacterium sp. PH-08. METHODS AND RESULTS: To assess the biodegradation potential of newly isolated Agrobacterium sp. PH-08, various substrates were evaluated as sole carbon sources in growth and biotransformation experiments. ESI LC-MS/MS analysis revealed the presence of angular degrading by-products as well as lateral dioxygenation metabolites in the upper pathway. The metabolites in the lower pathway also were detected. In addition, the cometabolically degraded daughter compounds of DF-related compounds such as BP and dibenzothiophene (DBT) in dual substrate degradation were observed. Strain PH-08 exhibited the evidence of meta-cleavage pathway as confirmed by the activity and gene expression of catechol-2,3-dioxygenase. CONCLUSIONS: Newly isolated bacterial strain, Agrobacterium sp. PH-08, grew well with and degraded DF via both angular and lateral dioxygenation as demonstrated by metabolites identified through ESI LC-MS/MS and GC-MS analyses. The other heterocyclic pollutants were also cometabolically degraded. SIGNIFICANCE AND IMPACT OF THE STUDY: Few reports have described the complete degradation of DF by a cometabolic lateral pathway. Our study demonstrates the novel results that the newly isolated strain utilized the DF as a sole carbon source and mineralized it via multiple dioxygenation.

Effect of leptin on insulin resistance of muscle--direct or indirect?

We examined the effect of leptin on the insulin resistance in skeletal muscles by measuring glucose transport. Male Wistar rats were fed rat chow or high-fat diets for 30 days. Before sacrifice, rats fed high-fat diet were subcutaneously injected with leptin (1 mg/kg b.w.) for 3 days. The glucose transport in epitrochlearis and soleus muscles did not differ in the experimental groups under basal conditions, however these values decreased significantly in the rats fed high-fat diet under insulin stimulation (p<0.01). Leptin treatment recovered the decreased glucose transport in epitrochlearis (p<0.05) and soleus muscles (p=0.08). Triglyceride concentrations in soleus muscles were increased significantly in the rats fed high-fat diet as compared to rats fed chow diet (p<0.01), and were decreased significantly by leptin treatment (p<0.01). The glucose transport was measured under basal conditions and after 60 microU/ml of insulin treatment with or without 50 ng/ml of leptin. Leptin had no direct stimulatory effect on glucose transport under both basal and insulin-stimulated conditions in vitro. These results demonstrate that leptin injection to rats fed high-fat diet recovered impaired insulin responsiveness of skeletal muscles and muscle triglyceride concentrations. However, there was no direct stimulatory effect of leptin on insulin sensitivity of skeletal muscles in vitro.

Aldosterone directly induces Na, K-ATPase alpha 1-subunit mRNA in the renal cortex of rat.

The change of blood pressure and the induction of Na, K-ATPase alpha 1-subunit mRNA have been investigated in the renal cortex of aldosterone-treated hypertensive rat. The increase of blood pressure by aldosterone-treatment for 25 days was decreased by the treatment of amiloride or spironolactone. The level of Na, K-ATPase alpha 1-subunit mRNA of the renal cortex in aldosterone-treated rat was increased than that in the control, and its increase was repressed by treatment of spironolactone, but not altered by the treatment of amiloride. This result suggests that the increase of Na, K-ATPase alpha 1-subunit mRNA in the renal cortex of aldosterone-treated hypertensive rat may be related with the direct induction of Na, K-ATPase mRNA without the increase of Na-traffic through Na-channel.

Aldosterone stimulates Na,K-ATPase activity in basolateral membrane of rat kidney.

The changes of Na,K-ATPase activity and its regulation have been investigated in the renal cortex and its basolateral membrane of aldosterone-induced hypertensive rat. Ouabain-sensitive Na,K-ATPase activity and [3H]ouabain-binding site (Bmax) in the hypertensive rat were significantly increased than those in the control. The levels of Na,K-ATPase alpha 1- and beta 1-subunit mRNA of the renal cortex in hypertensive rat were more increased than those in the control, and their increases were repressed by actinomycin-D. These results suggest that the increase of Na,K-ATPase activities and ouabain binding sites in aldosterone-induced hypertensive rat may be correlated with transcriptional regulation of Na,K-ATPase gene expression.