Nitrite Activates 5'AMP-Activated Protein Kinase-Endothelial Nitric Oxide Synthase Pathway in Human Glomerular Endothelial Cells.

Recent studies have shown that orally supplied nitrates, which substantially exist in our daily diets, are reduced into nitrites and become significant sources of nitric oxide (NO) especially in hypoxic tissues. However, physiological significance of nitrites in normal tissues has not been elucidated though our serum concentrations of nitrites reach as high as micromolar levels. We investigated effects of nitrite on endothelial NO synthase (eNOS) using human glomerular endothelial cells to reveal potential glomerular-protective actions of nitrites with its underlying molecular mechanism. Here we demonstrate that nitrite stimulation evokes eNOS activation which is dependent on 5'AMP-activated protein kinase (AMPK) activation in accordance with ATP reduction. Thus, nitrites should facilitate AMPK-eNOS pathway in an energy level-dependent manner in endothelial cells. The activation of AMPK-eNOS signals is suggested to be involved in vascular and renal protective effects of nitrites and nitrates. Nitrites may harbor beneficial effects on metabolic regulations as AMPK activators.

AICAR stimulation metabolome widely mimics electrical contraction in isolated rat epitrochlearis muscle.

Physical exercise has potent therapeutic and preventive effects against metabolic disorders. A number of studies have suggested that 5'-AMP-activated protein kinase (AMPK) plays a pivotal role in regulating carbohydrate and lipid metabolism in contracting skeletal muscles, while several genetically manipulated animal models revealed the significance of AMPK-independent pathways. To elucidate significance of AMPK and AMPK-independent signals in contracting skeletal muscles, we conducted a metabolomic analysis that compared the metabolic effects of 5-aminoimidazole-4-carboxamide-1-ß-D-ribonucleoside (AICAR) stimulation with the electrical contraction ex vivo in isolated rat epitrochlearis muscles, in which both α1- and α2-isoforms of AMPK and glucose uptake were equally activated. The metabolomic analysis using capillary electrophoresis time-of-flight mass spectrometry detected 184 peaks and successfully annotated 132 small molecules. AICAR stimulation exhibited high similarity to the electrical contraction in overall metabolites. Principal component analysis (PCA) demonstrated that the major principal component characterized common effects whereas the minor principal component distinguished the difference. PCA and a factor analysis suggested a substantial change in redox status as a result of AMPK activation. We also found a decrease in reduced glutathione levels in both AICAR-stimulated and contracting muscles. The muscle contraction-evoked influences related to the metabolism of amino acids, in particular, aspartate, alanine, or lysine, are supposed to be independent of AMPK activation. Our results substantiate the significance of AMPK activation in contracting skeletal muscles and provide novel evidence that AICAR stimulation closely mimics the metabolomic changes in the contracting skeletal muscles.

A novel prodrug strategy for extremely hydrophobic agents: conjugation to symmetrically branched glycerol trimer improves pharmacological and pharmacokinetic properties of fenofibrate.

Management of a lipophilic-hydrophilic balance is a key element in drug design to achieve desirable pharmacokinetic characters. Therefore we have created unique modular molecules, symmetrically branched oligoglycerols (BGL), as an alternative way to endow hydrophobic molecules with sufficient hydrophilicity. We have successfully demonstrated amelioration of the water solubility and thermal stability of several hydrophobic agents by covalent conjugation to BGL so far. However, it has not been clarified whether the molecular modification by BGL also improves the pharmacological and/or pharmacokinetic properties indeed. Recently, we synthesized a novel BGL-prodrug derivative of fenofibrate, which is an antihyperlipidemic agent and one of the most hydrophobic medicinal compounds currently used clinically, by conjugating fenofibric acid to symmetrically branched glycerol trimer (BGL003), the simplest BGL. We have previously demonstrated that the hydrophilicity and water solubility of fenofibrate are improved more than 2000 times just by conjugation to the BGL003. To verify our hypothesis that the prodrug strategy with BGL should improve pharmacological efficacy and pharmacokinetic properties of extremely hydrophobic agents such as fenofibrate by the rise in hydrophilicity, we evaluated the BGL003-prodrug derivative of fenofibrate (FF-BGL) using rodent models. Here we demonstrate that the lipid-lowering effects of fenofibrate are much potentiated by chemical conjugation to BGL003 without exhibiting significant toxicity. Plasma concentration of fenofibric acid, an active metabolite of fenofibrate, after single oral administration of FF-BGL was more than 3 times higher than that of fenofibrate, in accordance. In fasting rats, plasma concentration of fenofibric acid after fenofibrate administration was curtailed into less than half of that in ad libitum-fed rats, while FF-BGL showed about the same plasma level even in the starving rats. This is the first report showing that BGL-prodrug improves pharmacological and pharmacokinetic properties as well as hydrophilicity of highly hydrophobic compounds. Furthermore, prodrug strategy using BGL suggests the possibility of diminishing the food-drug interaction effects, which should be advantageous for promoting drug compliance. BGL will be a suitable prodrug strategy to ameliorate physical, pharmacological, and pharmacokinetic characteristics of extremely hydrophobic compounds.

Acute oral toxicity evaluation of symmetrically branched glycerol trimer in ddY mice.

Lipophilic-hydrophilic balance is a quite important determinant of pharmacokinetic properties of pharmaceuticals. Thus it is a key step to successfully manage lipophilic-hydrophilic balance in drug design. We have designed unique modular molecules, symmetrically branched oligoglycerols (BGL) as an alternative means to endow hydrophobic molecules with much hydrophilicity. We have succeeded in improving the water-solubility of several hydrophobic medicinal small molecules and thermal stability of artificial protein by covalent conjugation to BGL. We have also demonstrated that a representative BGL, symmetrically branched glycerol trimer (BGL003) does not exhibit significant cytotoxicity against human hepatocarcinoma HepG2 cells. However, there have been no reports suggesting whether BGL could be used in safety in vivo. Therefore, evaluation of acute oral toxicity of BGL003 in healthy mice was conducted. Here we demonstrate that an oral administration of BGL003 did not exhibit acute lethal toxicity up to 3,000 mg/kg. Body weight, food intake, blood glucose levels and weights of tissues were not affected by a short-term repetitive administration of increasing doses of BGL003. Biochemical indications related to hepatic disorders and tissue damage were unchanged, either. A single administration study revealed that 50% lethal dose of BGL003 should be more than 2,000 mg/kg. BGL003 will be safe and suitable approach to improve hydrophilicity of hydrophobic compounds.