Effects of sepiapterin and 6-acetyldihydrohomopterin on the guanosine triphosphate cyclohydrolase I of mouse, rat and the fruit-fly Drosophila.

The regulation of GTP cyclohydrolase I would lead to the regulation of tetrahydrobiopterin, an important cofactor for synthesis of neurotransmitters. In an attempt to extend a previous finding [Bellahsene, Dhondt, & Farriaux (1984) Biochem. J. 217, 59-65] that GTP cyclohydrolase I of rat liver is inhibited by subnanomolar concentrations of reduced biopterin and sepiapterin, we found that this could not be verified with the enzyme from mouse liver, fruit-fly (Drosophila) heads or, indeed, from rat liver. It was shown, however, that 12 microM-sepiapterin inhibited mouse liver GTP cyclohydrolase I. Another compound, namely 6-acetyldihydrohomopterin, was also employed in the present study to explore its effect on enzymes that lead to its synthesis in Drosophila and for effects on mammalian systems; at 2-5 microM this compound was shown to stimulate one form of mouse liver GTP cyclohydrolase I and then to inhibit at higher concentrations (40 microM). Neither sepiapterin nor 6-acetyldihydrohomopterin caused any effect on the Drosophila head enzyme. On the other hand, the sigmoid GTP concentration curve for the Drosophila enzyme may indicate a regulatory characteristic of this enzyme. Another report, on the lower level of GTP cyclohydrolase I in mutant mouse liver [McDonald, Cotton, Jennings, Ledley, Woo & Bode (1988) J. Neurochem. 50, 655-657], was confirmed and extended. Instead of having 10% activity, we find that the hph-1 mouse mutant has less than 2% activity in the liver. These studies demonstrate that micromolar levels of reduced pterins may have regulatory effects on GTP cyclohydrolase I and that a mouse mutant is available that has low enough activity to be considered as a model for human atypical phenylketonuria.     

Rapid Removal of Tissue Culture Monolayers by Collodion for Subsequent Staining

Removing cultures from roller tubes before staining eliminates the destaining which often occurs when the cells are first stained and then removed by embedding in collodion. The cells are fixed in situ, dehydrated, and covered with collodion (Merk's flexible) for 10 min. The collodion is poured off, the fluid residue lining the tube allowed to dry for 10 min, and the tube is filled with tap water. The collodion cast containing the cells is loosened and removed, cut into strips, placed on slides and blotted into firm contact. The collodion is then dehydrated and dissolved with absolute alcohol followed by a 1:1 mixture of alcohol and ether. The slides can then be rehydrated and stained by conventional methods.     

Regulation of apolipoprotein E synthesis and mRNA by diet and hormones

Rats were fasted or fasted and refed simple purified diets so the effects of individual carbohydrates or fats could be studied. Freshly isolated hepatocytes from these animals were used to measure both apoE synthesis and mRNA levels so any changes in apoE synthesis that might occur without changes in its mRNA could be detected. Some of these experiments were done with both sexes. Both fasting and fasting and refeeding a 60% glucose fat-free diet significantly increased spoE synthesis. However, cyclic AMP is not likely to rapidly mediate the effect of fasting since dibutyryl cAMP slightly lowered (rather than increased) apoE synthesis and mRNA when injected into rats for 4.5 h. Dietary fat had no effect either in the absence of carbohydrate or when consumption of carbohydrate was constant in pair-fed rats. ApoE mRNA levels remained normal for 4 days in primary hepatocytes cultured in medium that had only amino acids as an energy source. Added hormones or fructose had no significant effect. Thus, only fasting and fasting and refeeding glucose were able to significantly change apoE synthesis or mRNA levels. Synthesis of apoE may be regulated to increase when apoE is secreted with very low density lipoprotein or when apoE in secreted high density lipoprotein is needed to acquire cholesteryl esters for the synthesis of bile salts and acids by liver.     

mTOR kinase and the regulatory subunit of protein kinase A (PRKAR1A) spatially and functionally interact during autophagosome maturation

The regulatory subunit 1-alpha (RIalpha) of protein kinase A (PKA) and the mTOR kinase are involved in a common pathway regulating mammalian autophagy. RIalpha was found to localize on Rab7-positive late endosomes and on LC3-positive autophagosomal membranes in cultured cells. RIalpha was also shown to physically interact with mTOR kinase and affect its phosphorylation and activity. In this addendum, we further explore the subcellular distribution of mTOR related to RIalpha and LC3. We present experiments showing that mTOR colocalizes with RIalpha-, Rab7- and LC3-positive membranes in cultured cells. Because RIalpha regulates the phosphorylation and activity of mTOR kinase, which we now show localizes on autophagosomal membranes, the possibility emerges that the RIalpha-mTOR complex acts at the level of autophagosome maturation.     

Evaluation of Plasma Trace Elements in Different Stages of Nonalcoholic Fatty Liver Disease

Biological Trace Element Research - Nonalcoholic fatty liver disease (NAFLD) is considered as the hepatic manifestation of metabolic syndrome. Its global prevalence is estimated between 25 and 45%,...     

Solid state and solution studies of a vanadium(III)-L-cysteine compound and demonstration of its antimetastatic, antioxidant and inhibition of neutral endopeptidase activities

Reaction of one equivalent of vanadium(III) chloride with three equivalents of l-cysteine(H2Cys) in methyl alcohol affords a VIII-Cys compound that is formulated as [VIII(Hcys)3].2HCl.2.5H2O 1. The solid state characterization of 1 was performed by microanalysis, circular dichroism (CD) and infrared studies as well as room temperature magnetic susceptibility. These studies have shown coordination of each HCys- ligand to the VIII atom through an amine nitrogen and a carboxylate oxygen atoms. Solution studies of 1 were carried out in water and methanol by UV-visible, CD and electron paramagnetic resonance (EPR) spectroscopies. According to these studies, it was evident that despite the progressive oxidation of 1 to oxovanadium(IV) species, some V(III) species were also present in solution after several hours. Compound 1, VIVOSO4.5H2O and l-cysteine were examined for their total antioxidant capacity (TAC) and lag time. Compound 1 exhibited significantly greater total antioxidant capacity and lag time values than l-cysteine. VIVOSO4.5H2O did not show any total antioxidant capacity or lag time. The inhibition of neutral endopeptidase (NEP) activity caused by 1, VIVOSO4.5H2O and thiorphan was also measured. Compound 1, at a concentration of 10(-3) M, showed inhibition of NEP activity as potent as thiorphan at 10(-6) M, while VIVOSO4.5H2O in the same concentration exhibited less than 50% inhibitory activity than that of thiorphan at 10(-6) M. Moreover, the antimetastatic effects of compound 1, l-cysteine and VIVOSO4.5H2O were examined on Wistar rats, treated with 3,4-benzopyrene. The results revealed that 1 prevents significantly lung metastases (only 9.5% of animals treated with 1 showed metastases), whereas 47-52% of the rats of the control group and those treated with l-cysteine and VIVOSO4.5H2O exhibited metastases.