The noncovalent binding of selected phenolic compounds (chlorogenic-, ferulic-, gallic acid, quercetin, rutin, and isoquercetin) to proteins (HSA, BSA, soy glycinin, and lysozyme) was studied by an indirect method applying the quenching of intrinsic tryptophan fluorescence. From the data obtained, the binding constants were calculated by nonlinear regression (one site binding; y = Bx/k + x). It has been reported that tannins inhibit human salivary amylase and that these complexes may reduce the development of cariogenic plaques. Further, amylase contains two tryptophan residues in its active site. Therefore, in a second part of the study involving 31 human subjects, evidence was sought for noncovalent interactions between the phenols of green tea and saliva proteins as measured by the fluorescence intensity. Amylase activity was determined before and after the addition of green tea to saliva of 31 subjects. Forty percent of the subjects showed an increase in amylase activity contrary to studies reporting only a decrease in activity. The interactions of tannin with amylase result in a decrease of its activity. It still remains to be elucidated why amylase does not react uniformly under conditions of applying green tea to saliva. Further, in terms of using phenols as caries inhibitors this finding should be of importance.

OBJECTIVE-It has been suggested that retinol-binding protein 4 (RBP4) links adiposity, insulin resistance, and type 2 diabetes. However, circulating RBP4 levels are also affected by kidney function. Therefore, the aim of this study was to test whether RBP4 serum levels are primarily associated with kidney function or type 2 diabetes.RESEARCH DESIGN AND METHODS-RBP4 serum concentration was determined by enzyme-linked immunosorbent assay in 126 nondiabetic and 104 type 2 diabetic subjects. The study population was divided according to estimated glomerular filtration rate (eGFR) into the following groups: eGFR Ͼ90 ml/min per 1.73 m 2 (n ϭ 53), 60 -90 ml/min per 1.73 m 2 (n ϭ 90), 30 -60 ml/min per 1.73 m 2 (n ϭ 38), and Ͻ30 ml/min per 1.73 m 2 (n ϭ 49). Each group was subdivided into nondiabetic and type 2 diabetic subjects.RESULTS-RBP4 serum concentration was elevated (2.65 vs. 2.01 mol/l; P Ͻ 0.001) and eGFR was reduced (56 vs. 74 ml/min per 1.73 m 2 ; P Ͻ 0.001) in type 2 diabetic vs. nondiabetic subjects, respectively. By stratifying for eGFR, no more differences in RBP4 serum concentration were detectable between type 2 diabetic and nondiabetic subjects. A linear regression analysis revealed an influence of eGFR (r ϭ Ϫ0.477; P Ͻ 0.001) but not A1C (r ϭ 0.093; P ϭ 0.185) on RBP4 serum concentration.CONCLUSIONS-Existing human data showing elevated RBP4 levels in type 2 diabetic patients may be the result of moderate renal insufficiency rather than support for the suggestion that RBP4 links obesity to type 2 diabetes. Diabetes 57:3323-3326, 2008 R etinol-binding protein 4 (RBP4) is a small visceral protein (ϳ21 kDa), mainly synthesized in the liver and catabolized in the kidneys after glomerular filtration (1). To prevent the renal loss of RBP4 before delivering its ligand retinol to the target tissues, RBP4 is complexed by transthyretin, a homotetrameric protein with a molecular weight of ϳ55 kDa, formerly known as prealbumin (2). RBP4 was recently discussed as a new adipokine that is possibly linked to insulin resistance and type 2 diabetes (3-5). Although it is known that RBP4 serum levels are elevated in states of impaired kidney function (1,6 -8) (which is a common feature of diabetes, metabolic syndrome, and obesity [9,10]), parameters of kidney function have not been reported in most of the studies concerning RBP4 and insulin resistance and/or diabetes (3-5). Therefore, the aim of this study was to determine whether RBP4 serum concentration is associated with kidney function rather than type 2 diabetes. RESEARCH DESIGN AND METHODSSerum samples of 230 age-matched subjects (131 male, including 59 with type 2 diabetes, and 99 female, including 45 with type 2 diabetes) were collected by the Department of Endocrinology, Diabetes and Nutrition and the Department of Nephrology-both of Charité -Universitä tsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany-and by the Department of Clinical Nutrition of the German Institute of Human Nutrition, Potsdam-Rehbruecke, Germany. The study protocol was approved by ...

In recent years, the importance of vitamin A in adipose tissue biology, obesity and type II diabetes has become apparent. This review focuses on recent developments within the area of vitamin A and adipose tissue biology. Adipose tissue has an active vitamin A metabolism as it not only stores vitamin A but retinol is also converted to its active metabolite retinoic acid. Several mouse models point to a relationship between vitamin A metabolism and the development of adiposity. Similarly, in vitro studies provide new molecular mechanisms for the function of different forms of vitamin A and retinol- or retinoic acid-binding proteins in adipose tissue.

Background: The levels of retinol-binding protein 4 (RBP4) -the carrier protein for Vitamin A in plasma -are tightly regulated under healthy circumstances. The kidney, the main site of RBP4 catabolism, contributes to an elevation of RBP4 levels during chronic kidney disease (CKD) whereas during chronic liver disease (CLD) RBP4 levels decrease. Little is known about RBP4 isoforms including apo-RBP4, holo-RBP4 as well as RBP4 truncated at the C-terminus (RBP4-L and RBP4-LL) except that RBP4 isoforms have been reported to be increased in hemodialysis patients. Since it is not known whether CLD influence RBP4 isoforms, we investigated RBP4 levels, apo-and holo-RBP4 as well as RBP4-L and RBP4-LL in plasma of 36 patients suffering from CKD, in 55 CLD patients and in 50 control subjects. RBP4 was determined by ELISA and apo-and holo-RBP4 by native polyacrylamide gel electrophoresis (PAGE). RBP4-L and RBP4-LL were analyzed after immunoprecipitation by mass spectrometry (MALDI-TOF-MS).

Adipogenesis is governed by a well-documented cascade of transcription factors. However, less is known about non-transcription factors that govern early stages of adipogenesis. Here we show that cellular retinolbinding protein type I (CRBP-I), a small cytosolic binding protein for retinol and retinaldehyde, is specifically restricted to preadipocytes in white adipose tissue. The absence of CRBP-I in mice (CRBP-I-KO mice) leads to increased adiposity. Despite increased adiposity, CRBP-I-KO mice remain more glucose tolerant and insulin sensitive during high-fat-diet feeding. 3T3-L1 cells deficient in CRBP-I or mouse embryonic fibroblasts derived from CRBP-I-KO mice had increased adipocyte differentiation and triglyceride (TG) accumulation. This was due to increased expression and activity of PPAR␥, while other transcription factor pathways in early and late differentiation remained unchanged. Conversely, the overexpression of CRBP-I in 3T3-L1 cells results in decreased TG accumulation. In conclusion, CRBP-I is a cytosolic protein specifically expressed in preadipocytes that regulates adipocyte differentiation in part by affecting PPAR␥ activity.