Phenethyl isothiocyanate activates leptin signaling and decreases food intake.

Obesity, a principal risk factor for the development of diabetes mellitus, heart disease, and hypertension, is a growing and serious health problem all over the world. Leptin is a weight-reducing hormone produced by adipose tissue, which decreases food intake via hypothalamic leptin receptors (Ob-Rb) and the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway. Protein tyrosine phosphatase 1B (PTP1B) negatively regulates leptin signaling by dephosphorylating JAK2, and the increased activity of PTP1B is implicated in the pathogenesis of obesity. Hence, inhibition of PTP1B may help prevent and reduce obesity. In this study, we revealed that phenethyl isothiocyanate (PEITC), a naturally occurring isothiocyanate in certain cruciferous vegetables, potently inhibits recombinant PTP1B by binding to the reactive cysteinyl thiol. Moreover, we found that PEITC causes the ligand-independent phosphorylation of Ob-Rb, JAK2, and STAT3 by inhibiting cellular PTP1B in differentiated human SH-SY5Y neuronal cells. PEITC treatment also induced nuclear accumulation of phosphorylated STAT3, resulting in enhanced anorexigenic POMC expression and suppressed orexigenic NPY/AGRP expression. We demonstrated that oral administration of PEITC to mice significantly reduces food intake, and stimulates hypothalamic leptin signaling. Our results suggest that PEITC might help prevent and improve obesity.

ß-Caryophyllene attenuates palmitate-induced lipid accumulation through AMPK signaling by activating CB2 receptor in human HepG2 hepatocytes.

SCOPE: Nonalcoholic fatty liver disease is currently the most common chronic liver disease worldwide, characterized by excessive hepatic lipid accumulation without significant ethanol consumption. We have performed a screening for medicinal foods that inhibit hepatocytic lipid accumulation through activation of AMP-activated protein kinase (AMPK), which is a critical regulator of the hepatic lipid metabolism. METHODS AND RESULTS: We found that clove (Syzygium aromaticum), which is commonly used as a spice, markedly inhibits palmitate-inducible lipid accumulation in human HepG2 hepatocytes. Analyses of the clove extracts found that ß-caryophyllene, an orally-active cannabinoid, is the principal suppressor of the lipid accumulation, and stimulates the phosphorylation of AMPK and acetyl-CoA carboxylase 1 (ACC1). Our data also showed that ß-caryophyllene prevents the translocation of sterol regulatory element-binding protein-1c (SREBP-1c) into the nucleus and forkhead box protein O1 (FoxO1) into the cytoplasm through AMPK signaling, and consequently, induces a significant downregulation of fatty acid synthase (FAS) and upregulation of adipose triglyceride lipase, respectively. Moreover, we demonstrated that the ß-caryophyllene-induced activation of AMPK could be mediated by the cannabinoid type 2 receptor-dependent Ca2+ signaling pathway. CONCLUSION: Our results suggest that ß-caryophyllene has the potential efficacy in preventing and ameliorating nonalcoholic fatty liver disease and its associated metabolic disorders.

Recent progress in studies on the health benefits of pyrroloquinoline quinone.

Pyrroloquinoline quinone (PQQ), an aromatic tricyclic o-quinone, was identified initially as a redox cofactor for bacterial dehydrogenases. Although PQQ is not biosynthesized in mammals, trace amounts of PQQ have been found in human and rat tissues because of its wide distribution in dietary sources. Importantly, nutritional studies in rodents have revealed that PQQ deficiency exhibits diverse systemic responses, including growth impairment, immune dysfunction, and abnormal reproductive performance. Although PQQ is not currently classified as a vitamin, PQQ has been implicated as an important nutrient in mammals. In recent years, PQQ has been receiving much attention owing to its physiological importance and pharmacological effects. In this article, we review the potential health benefits of PQQ with a focus on its growth-promoting activity, anti-diabetic effect, anti-oxidative action, and neuroprotective function. Additionally, we provide an update of its basic pharmacokinetics and safety information in oral ingestion.

Safranal, a novel protein tyrosine phosphatase 1B inhibitor, activates insulin signaling in C2C12 myotubes and improves glucose tolerance in diabetic KK-Ay mice.

SCOPE: Protein tyrosine phosphatase 1B (PTP1B) negatively regulates insulin signaling by tyrosine dephosphorylation of insulin receptor, and its increased activity and expression is implicated in the pathogenesis of insulin resistance. Hence, PTP1B inhibition is anticipated to improve insulin resistance in type 2 diabetic subjects. The aim of this study was to find a novel PTP1B inhibitor from medicinal food and to evaluate its antidiabetic effects. METHODS AND RESULTS: We found that saffron (Crocus sativus L.), which is used both as a spice and as a traditional medicine, potently inhibits PTP1B activity. Analyses of saffron extracts demonstrated that safranal, the saffron's aroma compound, is a principal PTP1B inhibitor, and induces a ligand-independent activation of insulin signaling in cultured myotubes. Our data implied that the molecular mechanism underlying the inactivation of PTP1B could be attributed to the covalent modification of the catalytic cysteinyl thiol by safranal through a Michael addition. Furthermore, safranal significantly enhanced glucose uptake through the translocation of glucose transporter 4. We also demonstrated that 2-wk oral administration of 20 mg/kg/day safranal improved impaired glucose tolerance in type 2 diabetic KK-A(y) mice. CONCLUSION: Our results strongly suggest the usefulness of safranal in antidiabetic treatment for type 2 diabetic subjects.

Cinnamon extract promotes type I collagen biosynthesis via activation of IGF-I signaling in human dermal fibroblasts.

The breakdown of collagenous networks with aging results in hypoactive changes in the skin. Accordingly, reviving stagnant collagen synthesis can help protect dermal homeostasis against aging. We searched for type I collagen biosynthesis-inducing substances in various foods using human dermal fibroblasts and found that cinnamon extract facilitates collagen biosynthesis. Cinnamon extract potently up-regulated both mRNA and protein expression levels of type I collagen without cytotoxicity. We identified cinnamaldehyde as a major active component promoting the expression of collagen by HPLC and NMR analysis. Since insulin-like growth factor-I (IGF-I) is the most potent stimulator of collagen biosynthesis in fibroblasts, we examined the effect of cinnamaldehyde on IGF-I signaling. Treatment with cinnamaldehyde significantly increased the phosphorylation levels of the IGF-I receptor and its downstream signaling molecules such as insulin receptor substrate-1 and Erk1/2 in an IGF-I-independent manner. These results suggested that cinnamon extract is useful in antiaging treatment of skin.

Covalent binding of tea catechins to protein thiols: the relationship between stability and electrophilic reactivity.

In this study, we investigated the relationship between the stability of catechins and their electrophilic reactivity with proteins. The stability of catechins was evaluated by HPLC analysis. Catechol-type catechins were stable in a neutral buffer, but pyrogallol-type catechins, such as (-)-epigallocatechin gallate (EGCg), were unstable. The electrophilic reactivity of catechins with thiol groups in a model peptide and a protein was confirmed by both mass spectrometry and electrophoresis/blotting with redox-cycling staining. In a comparison of several catechins, pyrogallol-type catechins had higher reactivity with protein thiols than catechol-type catechins. The instability and reactivity of EGCg were enhanced in an alkaline pH buffer. The reactivity of EGCg was reduced by antioxidants due to their ability to prevent EGCg autoxidation. These results indicate that the instability against oxidation of catechins is profoundly related to their electrophilic reactivity. Consequently, the difference in these properties of tea catechins can contribute to the magnitude of their biological activities.

Structural characteristics of green tea catechins for formation of protein carbonyl in human serum albumin.

Catechins are polyphenolic antioxidants found in green tea leaves. Recent studies have reported that various polyphenolic compounds, including catechins, cause protein carbonyl formation in proteins via their pro-oxidant actions. In this study, we evaluate the formation of protein carbonyl in human serum albumin (HSA) by tea catechins and investigate the relationship between catechin chemical structure and its pro-oxidant property. To assess the formation of protein carbonyl in HSA, HSA was incubated with four individual catechins under physiological conditions to generate biotin-LC-hydrazide labeled protein carbonyls. Comparison of catechins using Western blotting revealed that the formation of protein carbonyl in HSA was higher for pyrogallol-type catechins than the corresponding catechol-type catechins. In addition, the formation of protein carbonyl was also found to be higher for the catechins having a galloyl group than the corresponding catechins lacking a galloyl group. The importance of the pyrogallol structural motif in the B-ring and the galloyl group was confirmed using methylated catechins and phenolic acids. These results indicate that the most important structural element contributing to the formation of protein carbonyl in HSA by tea catechins is the pyrogallol structural motif in the B-ring, followed by the galloyl group. The oxidation stability and binding affinity of tea catechins with proteins are responsible for the formation of protein carbonyl, and consequently the difference in these properties of each catechin may contribute to the magnitude of their biological activities.

Covalent modification of proteins by green tea polyphenol (-)-epigallocatechin-3-gallate through autoxidation.

Green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) has various beneficial properties including chemopreventive, anticarcinogenic, and antioxidant actions. The interaction with proteins known as EGCG-binding targets may be related to the anticancer effects. However, the binding mechanisms for this activity remain poorly understood. Using mass spectrometry and chemical detection methods, we found that EGCG forms covalent adducts with cysteinyl thiol residues in proteins through autoxidation. To investigate the functional modulation caused by binding of EGCG, we examined the interaction between EGCG and a thiol enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Concentration-dependent covalent binding of EGCG to GAPDH was found to be coupled to the irreversible inhibition of GAPDH activity. Mutation experiments revealed that EGCG is primarily bound to the cysteinyl thiol group of the active center, indicating that the irreversible inhibition of GAPDH is due to the covalent attachment of EGCG to the active-center cysteine. Moreover, using EGCG-treated cancer cells, we identified GAPDH as a target of EGCG covalent binding through specific interactions between catechols and aminophenyl boronate agarose resin. Based on these findings, we propose that the covalent modification of proteins by EGCG may be a novel pathway related to the biological activity of EGCG.

Oxidative deamination of benzylamine and lysine residue in bovine serum albumin by green tea, black tea, and coffee.

Oxidative deamination by various polyphenolic compounds is presumed to be due to the oxidative conversion of polyphenols to the corresponding quinones through autoxidation. Here we examined the oxidative deamination by the polyphenol-rich beverages green tea, black tea, and coffee at a physiological pH and temperature. Green tea, black tea, and coffee extracts oxidatively deaminated benzylamine and the lysine residues of bovine serum albumin to benzaldehyde and alpha-aminoadipic delta-semialdehyde residues, respectively, in sodium phosphate buffer (pH 7.4) at 37 degrees C in both the presence and absence of Cu2+, indicating the occurrence of an amine (lysyl) oxidase-like reaction. We also examined the effects of pH and metal ions on the reaction. The possible biological effects of drinking polyphenol-rich beverages on human are also discussed.

Production of hydrogen peroxide by polyphenols and polyphenol-rich beverages under quasi-physiological conditions.

To investigate the ability of the production of H(2)O(2) by polyphenols, we incubated various phenolic compounds and natural polyphenols under a quasi-physiological pH and temperature (pH 7.4, 37 degrees C), and then measured the formation of H(2)O(2) by the ferrous ion oxidation-xylenol orange assay. Pyrocatechol, hydroquinone, pyrogallol, 1,2,4-benzenetriol, and polyphenols such as catechins yielded a significant amount of H(2)O(2). We also examined the effects of a metal chelator, pH, and O(2) on the H(2)O(2)-generating property, and the generation of H(2)O(2) by the polyphenol-rich beverages, green tea, black tea, and coffee, was determined. The features of the H(2)O(2)-generating property of green tea, black tea, and coffee were in good agreement with that of phenolic compounds, suggesting that polyphenols are responsible for the generation of H(2)O(2) in beverages. From the results, the possible significances of the H(2)O(2)-generating property of polyphenols for biological systems are discussed.