J. Pallauf

Nutritional significance of phytic acid and phytase

In the nutrition of monogastric animals phytate-P represents a poorly available source of phosphorus, especially in the case of diets low in phytase activity. Similarly the bioavailability of different minerals and trace elements is considerably reduced by phytate complexes. High concentrations of Ca increase the anti-nutritive effect of phytic acid on mineral and trace element bioavailability and thus impede the action of phytase. This effect can in part be compensated by an increased supply of vitamin D. There is also evidence for protective functions of phytic acid such as the prevention of the formation of free radicals, the delaying of post prandial glucose absorption, the decrease in plasma cholesterol and triglycerides as well as a change in the carry over of heavy metals. The basic mechanisms by which phytic acid may exert these effects are still not clear. In several studies reported in the literature, evidence for the nutritional significance and ecological importance of microbial phytase for pigs and poultry has been given. As the monogastric organism contains no or only negligible amounts of endogenous phytase in the stomach and small intestine, it is therefore dependent on plant or microbial phytase. Plant phytase, e.g. from rye, triticale, wheat or, in smaller amounts from barley, and supplemented Aspergillus-phytase display cumulative effects.

Regulation of cell signalling by vitamin E.

Vitamin E, the most important lipid-soluble antioxidant, was discovered at the University of California at Berkeley in 1922. Since its discovery, studies of the constituent tocopherols and tocotrienols have focused mainly on their antioxidant properties. In 1991 Angelo Azzis group (Boscoboinik et al. 1991a,b) first described non-antioxidant cell signalling functions for alpha-tocopherol, demonstrating that vitamin E regulates protein kinase C activity in smooth muscle cells. At the transcriptional level, alpha-tocopherol modulates the expression of the hepatic alpha-tocopherol transfer protein, as well as the expression of liver collagen alphal gene, collagenase gene and alpha-tropomyosin gene. Recently, a tocopherol-dependent transcription factor (tocopherol-associated protein) has been discovered. In cultured cells it has been demonstrated that vitamin E inhibits inflammation, cell adhesion, platelet aggregation and smooth muscle cell proliferation. Recent advances in molecular biology and genomic techniques have led to the discovery of novel vitamin E-sensitive genes and signal transduction pathways.

Redox Regulation of Protein Tyrosine Phosphatase 1B by Manipulation of Dietary Selenium Affects the Triglyceride Concentration in Rat Liver

Protein tyrosine phosphatase 1B (PTP1B) is a key enzyme in the counter-regulation of insulin signaling and in the stimulation of fatty acid synthesis. Selenium (Se), via the activities of glutathione peroxidase (GPx) and thioredoxin reductase (TrxR), is involved in the removal of H(2)O(2) and organic peroxides, which are critical compounds in the modulation of PTP1B activity via glutathionylation. Our study with growing rats investigated how the manipulation of dietary Se concentration influences the regulation of PTP1B and lipogenic effects mediated by PTP1B. Weanling albino rats were divided into 3 groups of 10. The negative control group (NC) was fed a Se-deficient diet for 8 wk. Rats in groups Se75 and Se150 received diets supplemented with 75 or 150 microg Se/kg. Se supplementation of the rats strongly influenced expression and activity of the selenoenzymes cytosolic GPx, plasma GPx, phospholipidhydroperoxide GPx, and cytosolic TrxR, and liver PTP1B. Liver PTP1B activity was significantly higher in groups Se75 and Se150 than in the NC group and this was attributed to a lowered inhibition of the enzyme by glutathionylation. The increased liver PTP1B activity in groups Se75 and Se150 resulted in 1.1- and 1.4-fold higher liver triglyceride concentrations than in the NC rats. The upregulation of the sterol regulatory element binding protein-1c and of fatty acid synthase, 2 PTP1B targets, provided a possible explanation for the lipogenic effect of PTP1B due to the manipulation of dietary Se. We therefore conclude that redox-regulated proteins, such as PTP1B, represent important interfaces between dietary antioxidants such as Se and the regulation of metabolic processes.

Regulation of the insulin antagonistic protein tyrosine phosphatase 1B by dietary Se studied in growing rats

Protein tyrosine phosphatase 1B (PTP1B) is a key enzyme in the counterregulation of insulin signaling, and its physiological modulation depends on H2O2 and glutathione (GSH). Se via GSH peroxidases (GPxs) and its specific metabolism is involved in the removal of H2O2 and in the regulation of GSH metabolism. Recent results from animal trials and epidemiological studies with humans have shown that a high GPx1 activity or a permanent surplus of Se may promote the development of obesity and diabetes. Our nutrition physiological study with 7 x 7 growing rats was carried out to examine if PTP1B is modulated by Se supplements and, thus, may represent one trigger mediating these undesirable metabolic effects of Se. One group of rats was fed an Se-deficient diet for 8 weeks. The diets of the other six groups contained Se as selenite or selenate according to the recommendations (0.20 mg/kg diet) and at two supranutritional levels (1.00 and 2.00 mg/kg diet). All Se-supplemented animals featured a significantly higher body weight (6-14%) compared to their Se-deficient companions. Expression and activity of GPx1 in the liver of Se supplemented animals was 10- and 70-fold higher compared to Se deficiency. The detailed study of PTP1B regulation using an enzymatic assay and Western Blot analysis with an antibody against protein glutathionylation revealed that PTP1B was significantly up-regulated by both a maximization of GPx1 activity and by increasing dietary Se supply, reducing its inhibition via glutathionylation. Selenate effected a stronger PTP activation compared to selenite. In conclusion, our results suggest that the modulation of PTP1B activity may represent one plausible mechanism by which a long-term intake of Se supplements exceeding the requirements can promote the development of obesity and diabetes and needs further intensive investigation.

Selenium and diabetes: an enigma?

In recent years diabetes has become one of the most common metabolic diseases in developed countries and it is closely related to supernutrition and obesity. Since untreated diabetes produces oxidative stress responsible for secondary complications of the disease, antioxidant supplements were considered as being favourable for the therapy of diabetes. However, the situation has changed recently, since large cross-sectional and interventional trials revealed a positive correlation between a high Se status and diabetes incidence in humans. Thus, currently available data on the role of Se in diabetes are inconsistent and an enigma appears to exist for the relation between selenium and diabetes. This review summarizes selected human and animal studies, pointing to beneficial and critical virtues of Se in diabetes. Moreover, the review discusses possible underlying mechanisms how Se may influence diabetes in both directions. From the current literature, the following information can be extracted: (1) In populations with a high Se status, with the single exception of pregnant women, Se supplements cannot be recommended for the prevention of diabetes; (2) Anti-diabetic effects of Se seem to be restricted to high and nearly toxic doses which cannot be used in humans; and (3) Future investigations should consider the stage of the disease.

Exercise affects tissue lymphocyte apoptosis via redox-sensitive and Fas-dependent signaling pathways

Intensive and exhaustive exercise induces an activation of blood T-lymphocytes, which seems to be terminated by apoptotic processes in the postexercise period. Here, we report that exercise-induced T-lymphocyte apoptosis is a systemic phenomenon occurring in various lymphoid and nonlymphoid tissues. The apoptosis rate could be related to exercise intensity and type. Although in some tissues, such as the spleen and Peyers patches, an early start of apoptosis (1-3 h postexercise) could be detected, a delayed apoptosis (24 h postexercise) was observed in lung, bone marrow, and lymph nodes. Further analysis showed a similar apoptosis distribution among lymphocyte subpopulations. We tested whether components of the extrinsic or the intrinsic apoptotic pathways or both were involved in these processes. Elevated levels of lipid peroxidation-product malondialdehyde (MDA), indicating an increased production of reactive oxygen species (ROS), were found after exercise in Peyers patches, lung, and spleen, but not in lymph nodes. Application of N-acetyl-cysteine (NAC) prevented exercise-induced T-cell apoptosis completely in spleen and bone marrow, partially in lung and Peyers patches, while it was ineffective in lymph nodes. Additionally, exercise addressed the Fas-mediated apoptosis. The percentage of Fas-receptor (Fas+) and Fas-ligand positive (FasL+) lymphocytes was enhanced in Peyers patches after exercise. Moreover, FasL+ T cells were increased in the lung, while in lymph nodes Fas+ cells were increased. The critical role of Fas signaling in exercise-induced apoptosis was supported by using Fas-deficient MRL/lpr-mice. In Fas-deficient mice, exercise-induced T-lymphocyte apoptosis was prevented in spleen, lung, bone marrow, and lymph nodes, but not in Peyers patches. These data demonstrate that exercise-induced lymphocyte apoptosis is a transient systemic process with tissue-type specific apoptosis-inducing mechanisms, whose relevance for the adaptive immune competence remains to be shown.

Dietary effect of phytogenic phytase and an addition of microbial phytase to a diet based on field beans, wheat, peas and barley on the utilization of phosphorus, calcium, magnesium, zinc and protein in piglets

SummaryThe effect of the addition of microbial phytase to a diet based on field beans (30 %), wheat (28 %), peas (25 %), and barley (14 %) was studied in a 2-week experiment with 3×8 castrated male, individually housed, hybrid piglets (live weight range 12–16 kg). All diets contained about 4.7 g Ca, 4.2 g P (77 % present as phytate phosphorus), 1.0 g Mg, 60 mg Zn per kg diet, and 17 % crude protein. Group I was fed the basal diet with a native phytase-activity of about 260 U per kg diet. In group II, 350 U, in group III, 700 U of microbial phytase per kg diet were added. The addition of microbial phytase improved the apparent P absorption (% of intake) from 48 % (group I) to 66 % (group II) and 71 % (group III). Comparable positive effects from the phytase treatment were obtained for the calcium utilization. The phytase supplementation also enhanced plasma zinc concentration significantly. The concentration of inorganic phosphorus in plasma, the zinc digestibility, and the magnesium balance were improved in tendency. The utilization of nitrogen remained unchanged.ZusammenfassungIn einem zweiwöchigen Stoffwechselversuch mit 3×8 männlichen kastrierten Hybridferkeln (Lebendmassebereich 12–16 kg) wurde die Wirkung einer Zulage an mikrobieller Phytase zu einer Diät auf der Basis von Ackerbohnen (30 %), Weizen (28 %), Futtererbsen (25 %) und Gerste (14 %) untersucht. Die Diäten enthielten je kg Diät ca. 4,7 g Ca, 4,2 g P (davon ca. 77 % Phytin-P), 1,0 g Mg, 60 mg Zn sowie 17 % Rohprotein. Zum nativen Phytasegehalt von ca. 260 U/kg Diät (Gruppe I) wurden in den Gruppen II und III 350 bzw. 700 U mikrobieller Phytase/kg Diät supplementiert. Durch die Zulage von 350 und 700 U mikrobieller Phytase je kg Diät wurde die scheinbare P-Absorption (in % der Aufnahme) von 48 % in der Kontrollgruppe (Gruppe I) auf 66 % (Gruppe II) und 71 % (Gruppe III) gesteigert. Ähnlich positive Effekte traten bei der Ca-Verwertung auf. Auch die Plasma-Zn-Konzentration wurde durch die Phytasesupplementierung signifikant gesteigert. Die Gehalte an anorganischem Phosphat des Blutplasmas, die scheinbare Zn-Absorption und die Magnesiumverwertung wurden durch die Phytasezulage in der Tendenz erhöht, während die N-Bilanz unbeeinflußt blieb.

APOE ε4 is associated with higher vitamin D levels in targeted replacement mice and humans

The allele ε4 of apolipoprotein E (APOE), which is a key regulator of lipid metabolism, represents a risk factor for cardiovascular diseases and Alzheimers disease. Despite its adverse effects, the allele is common and shows a nonrandom global distribution that is thought to be the result of evolutionary adaptation. One hypothesis proposes that the APOE ε4 allele protects against vitamin D deficiency. Here we present, for the first time, experimental and epidemiological evidence that the APOE ε4 allele is indeed associated with higher serum vitamin D [25(OH)D] levels. In APOE4 targeted replacement mice, significantly higher 25(OH)D levels were found compared with those in APOE2 and APOE3 mice (70.9 vs. 41.8 and 27.8 nM, P<0.05). Furthermore, multivariate adjusted models show a positive association of the APOE ε4 allele with 25(OH)D levels in a small collective of human subjects (n=93; P=0.072) and a general population sample (n=699; P=0.003). The novel link suggests ε4 as a modulator of vitamin D status. Although this result agrees well with evolutionary aspects, it appears contradictory with regard to chronic diseases, especially cardiovascular disease. Large prospective cohort studies are now needed to investigate the potential implications of this finding for chronic disease risks.—Huebbe, P., Nebel, A., Siegert, S., Moehring, J., Boesch‐Saadatmandi, C., Most, E., Pallauf, J., Egert, S., Müller, M. J., Schreiber, S., Nöthlings, U., Rimbach, G. APOE ε4 is associated with higher vitamin D levels in targeted replacement mice and humans. FASEB J. 25, 3262‐3270 (2011). www.fasebj.org

Antidiabetic effects of bitter gourd extracts in insulin-resistant db/db mice.

Bitter gourd (BG, Momordica charantia) exerts proven blood glucose- and body weight-lowering effects. To develop an effective and safe application, it is necessary to identify the bioactive compounds and biochemical mechanisms responsible for these effects in type 2 diabetes. A total of forty-five 4-week-old male db/db mice were assigned to five groups of nine each. The mice were given sterile tap water as a control, a whole fruit powder, the lipid fraction, the saponin fraction or the hydrophilic residue of BG at a daily oral dosage of 150 mg/kg body weight for 5 weeks, respectively. Weight gain was significantly decreased in all the BG-treated groups (P ≤ 0.05). Glycated Hb levels were the highest in the control mice compared with all the four BG-treated mice (P = 0.02). The lipid fraction had the strongest effect, and it tended (P = 0.075) to reduce glycated Hb levels from 9.3 % (control mice) to 8.0 % (lipid fraction-treated mice). The lipid and saponin fractions reduced lipid peroxidation of adipose tissue significantly (P ≤ 0.01). Additionally, the saponin fraction and the lipid fraction reduced protein tyrosine phosphatase 1B (PTP 1B) activity in skeletal muscle cytosol by 25 % (P = 0.05) and 23 % (P = 0.07), respectively. PTP 1B is the physiological antagonist of the insulin signalling pathway. Inhibition of PTP 1B increases insulin sensitivity. This is the first study to demonstrate that BG is involved in PTP 1B regulation, and thus explains one possible biochemical mechanism underlying the antidiabetic effects of BG in insulin resistance and type 2 diabetes.

Enhancement of zinc utilization from phytate-rich soy protein isolate by microbial phytase

SummaryA study with three groups, each with 11 male, individually housed albino rats (initial average weight=50 g) was undertaken to examine the effect of microbial phytase (added to a diet containing phytate) on the availability of zinc. The rats were fed diets on the basis of soy protein isolate and corn starch over a 3-week period. All diets contained 15–16 mg Zn/kg diet and 0.40 % PA. Thus, molar PA: Zn-ratios of 26 : 1 were obtained. Group I (control) was fed the phytase-free basal diet. In groups II (pair-fed to group I) and III, 1 000 U of microbial phytase (Aspergillus niger var. van tighem) per kg diet were added.Some rats fed the phytase-free basal diet (control) showed typical symptoms of zinc deficiency, including cyclic changes in food intake, anorexia and partial alopecia.By the addition of 1 000 U microbial phytase the apparent absorption of zinc (percent of intake) significantly increased from 33 % (control) to 63 % (1 000 U, pair-fed) and 66 % (1 000 U, ad lib.). Similar positive effects of the phytase-supplementation were observed for three zinc status parameters in plasma, zinc-concentration, percent unsaturated zinc-binding capacity, activity of alkaline phosphatase and the zinc-concentration in femur and testes. The present study shows that an addition of microbial phytase to phytate-rich diets based on soy protein isolate considerably improves the availability of zinc in growing rats.ZusammenfassungIn einem 3wöchigen Stoffwechselexperiment mit 3 × 11 männlichen, einzeln gehaltenen Albinoratten (Anfangsmasse=50 g) wurde geprüft, ob eine Zulage an mikrobieller Phytase die Bioverfügbarkeit von Zink aus einer phytathaltigen Diät verbessert. Den Ratten wurden Diäten auf der Basis von Sojaproteinisolat und Maisstärke verabreicht. Der native Zn-Gehalt aller Diäten betrug 15–16 mg Zn/kg Diät, die PA-Konzentration 0,40 %. Daraus resultierten molare PA: Zn-Quotienten von 26 : 1. Gruppe I (Kontrolle) erhielt die phytasefreie Basisdiät. In den Gruppen II (pair-fed zu I) und III (ad libitum) wurden jeweils 1 000 U mikrobieller Phytase (Aspergillus niger var. van tighem) pro kg Diät supplementiert.Einige Ratten der Kontrollgruppe, die die phytasefreie Basisdiät erhielten, zeigten typische Zinkmangelsymptome wie Anorexie, partielle Alopezie und zyklische Schwankungen der Futteraufnahme. Durch die Phytasezulage wurde die scheinbare Absorption des Zinks (in % der Aufnahme) signifikant auf 63 % (1 000 U, pair-fed) und 66 % (1 000 U, ad lib.) gegenüber 33 % (phytasefreie Kontrollgruppe) erhöht. Ein vergleichbar positiver Effekt der Phytasesupplementierung wurde bezüglich verschiedener Zinkstatusparameter des Blutplasmas (Zinkkonzentration, freie Zinkbindungskapazität, Aktivität der Alkalischen Phosphatase) und der Zinkeinlagerung in Femur und Testes festgestellt. In der vorliegenden Untersuchung konnte gezeigt werden, daß bei der wachsenden Ratte durch eine Zulage mikrobieller Phytase die Bioverfügbarkeit des Zinks in phytatreichen Diäten auf Sojaproteinisolatbasis sehr deutlich gesteigert werden kann.