Comparative analysis of the triplicate proathocyanidin regulators in Lotus japonicus.

Proanthocyanidins (PAs), which are flavonoid compounds widely distributed in the plant kingdom, protect against environmental stress. The accumulation of PAs is regulated by a ternary transcriptional complex comprising the R2R3-MYB transcription factor, a basic helix-loop-helix (bHLH) transcription factor and a WD40 repeat (WDR) protein. Recently, multigene families of the R2R3-MYB-type PA regulators from Lotus japonicus, LjTT2a, b and c, were isolated and characterized. Although their roles as transcription factors that up-regulate PA biosynthetic genes have been elucidated, the significance of their redundancies and functions in planta is unknown. In this study, we characterized LjTT2a, b and c to elucidate their functions in planta and determine differences in transcriptional activation properties. Transgenic studies demonstrated that LjTT2a could induce ectopic PA accumulation in Arabidopsis. Further analysis of the LjTT2 multigene family using a transient expression system revealed differences in transcriptional activities in cooperation with WDR and bHLH proteins isolated from L. japonicus. In-depth characterization of chimeric constructs of three LjTT2s, as well as site-directed mutagenesis in R2-MYB domains, identified the amino acid residues that affect the level of transcriptional activation of LjTT2.

The frequency of magnesium consumption directly influences its serum concentration and the amount of elutable bone magnesium in rats.

We investigated the influence of Mg feeding frequency on the variation in serum Mg concentration and tissue Mg levels in Mg-deficient rats. Sprague-Dawley rats, which had been fed a Mg-deficient diet for 14 d, were divided into 3 groups that were kept on 3 diets differing in their Mg content. The rats were fed 0.5-fold (Mg250 group), 1-fold (Mg500 group), or 1.5-fold (Mg750 group) the amounts of recommended Mg in their standard AIN-93G diet (Mg: 478 mg/kg diet) during the recovery period (12 d). The Mg500 and Mg750 groups were intermittently fed (Mg500, every 2 d; Mg750, every 3 d) so that their total intake of Mg during the recovery period could equal the Mg intake of the Mg250 group. The serum Mg concentrations increased in the 3 groups after feeding with a Mg-containing diet. However, serum Mg levels were only maintained within the normal range in the Mg250 group. After feeding on the Mg-deficient diet, in the intermittently fed groups, serum Mg concentrations decreased. Urinary Mg excretion was higher and Mg retention was lower in the Mg500 and Mg750 groups than in the Mg250 group. Moreover, bone Mg, especially elutable bone Mg, was lower in the Mg500 and Mg750 groups than in the Mg250 group. The elutable fraction of bone Mg correlated to the coefficient of variation of serum Mg concentration. In conclusion, for the maintenance of serum Mg concentration, it is important to increase the amount of elutable bone Mg by frequent Mg consumption.

Hypoglycemic and hypolipidemic effects of hesperidin and cyclodextrin-clathrated hesperetin in Goto-Kakizaki rats with type 2 diabetes.

We investigated the hypoglycemic and hypolipidemic effects of two hesperertin glycosides, namely, hesperidin and cyclodextrin (CD)-clathrated hesperetin, in Goto-Kakizaki (GK) weanling rats with type 2 diabetes. We demonstrated that hesperidin and CD-hesperetin normalized glucose metabolism by altering the activities of glucose-regulating enzymes and reducing the levels of lipids in the serum and liver of the GK rats. These effects of hesperidin glycosides were partly produced by altering the expression of genes encoding the peroxisome proliferator-activated receptors, 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, and the low-density lipoprotein receptor.

Absence of negative feedback on intestinal magnesium absorption on excessive magnesium administration in rats.

This study aimed to clarify the regulatory mechanism of Mg homeostasis on administration of excessive Mg in rats. Six-week-old male Wistar rats (n=30) were fed a Mg-deficient diet (D) or a control diet (M) in addition to which they received subcutaneous injections of saline (S) or additional Mg (M) for 14 d. Feces and urine were collected from the rats for 4 d every week. Between the MS and MM rats and the DS and DM rats, the injection of additional Mg increased Mg retention, but intestinal Mg absorption did not differ. Urinary Mg excretion in the MM rats was significantly greater than that in the MS rats, but fecal Mg excretion did not increase. Mg retention in the DM rats was approximately 30% of that in the MS rats, and urinary Mg excretion did not differ between the 2 groups, although the serum Mg in DM rats was low. There was no significant difference in the femoral Mg between the MM and MS groups. The physiological Mg pool in the bone appears to be limited. Therefore, there is no physiological Mg pool for the storage of excessive Mg, and there appears to be no negative feedback mechanism on intestinal Mg absorption upon administration of excessive Mg in the rats. In conclusion, it appears that the kidney is the only organ that regulates Mg in the body; apart from this, regulatory mechanisms corresponding to the physiological Mg requirement do not exist or are weak.

Dietary calcium and phosphorus ratio regulates bone mineralization and turnover in vitamin D receptor knockout mice by affecting intestinal calcium and phosphorus absorption.

UNLABELLED: The effects of the dietary Ca and P ratio, independent of any vitamin D effects, on bone mineralization and turnover was examined in 60 VDRKO mice fed different Ca/P ratio diets. High dietary Ca/P ratio promoted bone mineralization and turnover with adequate intestinal Ca and P transports in VDRKO mice. INTRODUCTION: To clarify the effects of the dietary calcium (Ca) and phosphorus (P) ratio (Ca/P ratio) on bone mineralization and turnover in null-vitamin D signal condition, vitamin D receptor knockout (VDRKO) mice were given diets containing different Ca/P ratios. MATERIALS AND METHODS: Five groups of 4-week-old VDRKO mice, 10 animals each, were fed diets for 4 weeks. Group 1 was wild-type littermate mice, fed the diet containing 0.5% Ca and P (Ca/P = 1). Group 2 was the control and was fed a similar diet (Ca/P = 1). Groups 3, 4, 5, and 6 were fed the following diets: 0.5% Ca and 1.0% P (Ca/P = 0.5), 1.0% Ca and 1.0% P (Ca/P = 1), 1.0% Ca and 0.5% P (Ca/P = 2), and 0.5% Ca and 0.25% P (Ca/P = 2). RESULTS AND CONCLUSIONS: Compared with group 2, serum calcium and phosphorus levels in groups 4-6 significantly increased. Serum parathyroid hormone levels increased in group 3 and decreased in group 5. The amounts of intestinal calcium absorption decreased in groups 3 and 4. Phosphorus absorption increased in group 3 and decreased in groups 4-6. Bone mineral content (BMC) and bone mineral density (BMD) of the femur in group 3 significantly decreased and increased in group 5. In the primary spongiosa of the proximal tibia, the trabecular bone volume (BV/TV) and osteoid thickness (O.Th) in group 3 significantly increased, and decreased in group 6. In groups 5 and 6, the numbers of the trabecular osteoclasts increased. In groups 2 and 4, and the secondary spongiosa was identified in 5 of 10 mice. In group 3, there was no secondary spongiosa in either mouse. Osteoid maturation time (OMT) significantly decreased, and bone formation rate (BFR/BS) increased in groups 4-6. These data indicate that the dietary Ca/P ratio regulates bone mineralization and turnover by affecting the intestinal calcium and phosphorus transports in VDRKO mice. They may suggest the existence of Ca/P ratio-dependent, vitamin D-independent calcium and phosphorus transport system in the intestine.