Paul Walter

Bioactive compounds: definition and assessment of activity.

Biomarkers and their role in evaluating efficacy and safety were the topic of the 23rd Hohenheim Consensus Meeting at the University of Hohenheim in Stuttgart. Scientists who had published and reviewed scientific and regulatory papers on the topic were invited, among them basic researchers, toxicologists, clinicians, and nutritionists. The participants were presented with 11 questions (in bold font), which were discussed and answered (in italic font) at the workshop, with the aim of summarizing the current state of knowledge on the subject. The explicatory text accompanying the short answers was produced and agreed on after the conference and was backed up by corresponding references.

Hypothyroidism and thyroxin substitution affect the n−3 fatty acid composition of rat liver mitochondria

The effects of hypothyroidism and of daily treatment for up to 21 days with thyroxin (T4, 0.5 μg/100 g body weight) on the fatty acid composition of total lipid, phosphatidylethanolamine, and phosphatidylcholine of rat liver mitochondria were studied. The fatty acid compositions of hypothyroid and euthyroid (control) rats of similar age were compared. The n−6 and n−3 polyunsaturated fatty acids (PUFA) were affected differently by the hypothyroid state. The levels of linoleic (18∶2n−6), γ-linolenic (18∶3n−6) and dihomo-γ-linolenic acids (20∶3n−6) were higher in hypothyroid rats than in controls, while the level of arachidonic acid (20∶4n−6) was lower, which suggests an impairment of the elongase and desaturase activities. The n−3 polyunsaturated fatty acids, eicosapentaenoic (EPA, 20∶5n−3) and docosapentaenoic (22∶5n−3) acids, were higher in hypothyroid rats, whereas the linolenic acid (18∶3n−3) content remained constant. The level of docosahexaenoic acid (DHA, 22∶6n−3) was dramatically decreased in hypothyroid rats, while the levels of C22 n−6 fatty acids were unchanged. The differences were probably due to the competition between n−3 and n−6 PUFA for desaturases, elongases and acyltransferases. When hypothyroid rats were treated with thyroxin, the changes induced by hypothyroidism in the proportions of n−6 fatty acids were rapidly reversed, while the changes in the n−3 fatty acids were only partially reversed. After 21 days of thyroxin treatments, the DHA content was only half as high in hypothyroid rats than in euthyroid rats. These results suggest that the conversion of 18∶2n−6 to 20∶4n−6 is suppressed in the hypothyroid state which favors the transformation of 18∶3n−3 to 20∶5n−3. The marked decrease in DHA content indicates an impairment of the enzymes involved in the DHA metabolism, possibly the n−3 Δ4 desaturase or the acyltransferases. The increased levels of EPA and 22∶5n−3 is consistent with the inhibition of the n−3 pathway at the Δ4 desaturase step. Observed modifications in the fatty acid composition may significantly alter eicosanoid synthesis and membrane functions in hypothyroidism.

Relation between extra- and intramitochondrial ATPADP ratios in rat liver mitochondria

Changes of the extra- and intramitochondrial ATP/ADP ratios as a function of the respiratory state were measured in incubations with rat liver mitochondria. ATPase or creatine/creatine kinase was used to change the extramitochondrial ATP/ADP ratio; the separation of the mitochondrial pellet was performed by a Millipore filtration technique. Under all conditions tested, the intramitochondrial ratio changed in the same direction as the extramitochondrial one, except in the presence of atractylate where this correlation was not observed. Furthermore, it could be shown that the oxygen uptake and pyruvate carboxylase activity correlated with the intramitochondrial ATP/ADP ratio and not with the extramitochondrial one. These results do not support the proposal that the adenine nucleotide translocase is rate limiting for respiration.

Stereospecific effects of (+)- and (−)-catechin on glycogen metabolism in isolated rat hepatocytes

(+)- and (-)-catechin showed opposite effects on glycogen metabolism in isolated rat hepatocytes. Addition of 0.5 mM catechin to hepatocytes from fasted rats resulted in the case of the (+)-isomer in a 90% stimulation and the case of the (-)-isomer in a 90% inhibition of net glycogen production. When 0.5 mM of the two isomers were added to hepatocytes from fed rats, (+)-catechin inhibited glycogenolysis by 33%, whereas the (-)-isomer stimulated the same process by 42%. At equal concentrations, the effects of (-)-catechin were stronger than those of the (+)-isomer. (-)-Epicatechin acted in a manner similar to (+)-catechin; however, the effect was less pronounced. (+)-Catechin antagonized the inhibitory action of suboptimal doses of glucagon on glycogen production whereby no change in basal or glucagon-elevated cyclic AMP level was observed. The activities of glycogen synthase a and glycogen phosphorylase a were changed by (+)- and (-)-catechin in a way corresponding to the changes in glycogen production and breakdown. (-)-Catechin, however, stimulated the activities of both glycogen synthase a and glycogen phosphorylase a in hepatocytes from fed rats. A possible interaction of the flavonoids or of their metabolites with glycogen phosphorylase is discussed.

Short-term stimulation of net glycogen production by insulin in rat hepatocytes.

Isolated liver cells from 24 h starved rats were incubated in Krebs-Ringer buffer containing 4% albumin. In the presence of 10, 20 and 30 mM glucose, addition of insulin stimulated net glycogen production by 52, 39 and 20%, respectively. 2 . 10(-9) M insulin was required for half-maximal stimulation. Increases of glycogen production and of glycogen synthase a activity were observed after 15-30 min of incubation with insulin. The stimulatory effect of insulin was additive to that of lithium. In agreement with the literature, insulin antagonized the inhibitory action of suboptimal doses of glucagon on glycogen deposition whereby a decrease of glucagon-elevated cyclic AMP levels was observed. In addition, we found that insulin also decreased the basal cyclic AMP levels in the absence of added glucagon by 22%. It is concluded that physiological concentrations of insulin stimulate net glycogen deposition in hepatocytes from fasted rats; the decrease of basal cyclic AMP levels upon insulin addition may play a role in the mechanism of the hormone action.

Food Pyramid of the Swiss Society for Nutrition

The Swiss Society for Nutrition issued its Food Pyramid in 2005. It was updated according to the latest scientific evidence and is in principal agreement with food-based guidelines of other countries. It has also been officially endorsed by the Swiss government. The food pyramid stands for a balanced diet that guarantees the body a sufficient supply of energy, essential nutrients and protective substances. Food from the lower levels of the pyramid should be eaten in larger quantities, and those from the higher levels in smaller quantities. The six levels from top down represent the following food groups: sweets, salty snacks and sweetened or alcoholic drinks; oils, fats and nuts; milk, dairy products, meat, fish and eggs; whole grain products and pulses, other cereals and potatoes; fruit and vegetables; beverages. A basic principle to be communicated by the food pyramid is that there are no good or bad foods but that the relative amounts to be consumed play a key role for our health. The key message is to eat a diet that is as varied as possible and which considers foods of each pyramid level in the right amounts. The recommendations do not need to be followed every day, but should be observed on a long-term basis, e.g. a whole week. Liquid intake is an exception; liquids should be consumed on a daily basis. It is also very important to keep a healthy body weight by daily exercise as indicated by the icons on the side of the Swiss Food Pyramid.

Funiculosin: an antibiotic with antimycin-like inhibitory properties.

The antibiotic funiculosin mimics the action of antimycin in several ways. It inhibits the oxidation of NADH and succinate, but not TMPD+ascorbate. The titer for maximal inhibition in Mg2+-ATP particles (0.4-0.6 nmol/mg protein) is close to the concentrations of cytochromes b and cc1. Funiculosin also induces the oxidation of cytochromes cc1 and an extra reduction of cytochrome b in the aerobic steady state, and it inhibits duroquinol-cytochrome c reductase activity in isolated Complex III. The location of the funiculosin binding site is clearly similar to that of antimycin. In addition, funiculosin, like antimycin, prevents electron transport from duroquinol to cytochrome b in isolated Complex III if the complex is pre-reduced with ascorbate. Funiculosin and antimycin differ, however, in the manner in which they modulate the reduction of cytochrome b by ascorbate+TMPD.

Bioactive compounds: safety and efficacy.

The efficacy and safety of bioactive compounds depend on a few known and unknown parameters. What is a physiologic dose and how can that dose be defined in cases of bioactive compounds with a poor knowledge of supply and distribution? What safety sets are needed? How can individual aspects such as polymorphisms or differences in absorption be considered? A group of experts tried to answer these and related questions during the 23rd Hohenheim Consensus Meeting at the University of Hohenheim in Stuttgart.

Effect of hypothyroidism and thyroid hormone replacement on the level of protein kinase C and protein kinase A in rat liver

We investigated the influence of the thyroid hormone status on the levels of protein kinase C (PKC) and A (PKA) in the soluble fraction of rat liver. The immunodetectable PKC level in hypothyroid liver was elevated 7.7‐fold, whereas the phorbol‐ester binding capacity and the immunodetectable α‐PKC level were increased 2.4‐ and 2.6‐fold, respectively. Conversely, in hypothyroid livers the abundance of the regulatory type I and the catalytic subunits of PKA were lowered to 42% of the euthyroid level as determined by immonoblotting and by measuring the substrate specific phosphorylation rate of PKA. These changes in the PKC and PKA levels were reversible upon treatment with 0.5 μg T4/100 g body weight for 2–21 days. The thyroid state dependent alterations in hepatic PKC and PKA levels may be responsible for the Known changes in the response of hepatocytes to other hormonal stimuli in hypothyroidism.

Towards ensuring the safety of vitamins and minerals.

Today, there is a clear need for a risk assessment for vitamins and minerals because the total daily intake for nutrients through regular food, fortified products (Functional Food) and supplements may very well reach critical levels for an individual consumer. Several expert panels of the European Union, the UK, Japan and China will publish their reports on this issue in the near future. The Food and Nutrition Board of the Institute of Medicine of the US/Canada has already published a new standard. The board has defined the so-called Tolerable Upper Intake Level (UL) as the highest level of daily intake that is likely to pose no risk of adverse health effects to almost all individuals in the general population. Their determination involves a multi-step risk assessment procedure on the basis of mainly human data. Several daily UL values that have already been published are of special interest, e.g. 1 mg folic acid, 50 microg vitamin D, 1 g vitamin E, 2 g vitamin C, 2.5 g calcium, 350 mg magnesium.