Urinary excretion profile of higenamine in females after oral administration of supplements - Doping scenario

In 2017, higenamine was added to the World Antidoping Agency's (WADA) Prohibited list under group S3: beta-2 agonists and it is banned for athletes both in - and out of competition. Aim of this study was to characterize the urinary excretion profile of higenamine and its metabolite coclaurine after oral administration of multiple doses of higenamine capsules. For this purpose, an administration study including female basketball players was performed. For the detection of higenamine and cocalurine in the collected urine samples, a new, fast, and highly sensitive quantitative on-line SPE LC HRMS method was developed and validated. The method was applied for the quantification of higenamine and cocalurine in urine and their excretion pattern was defined. Results obtained show substantial inter-individual differences in the excretion profile of higenamine and coclaurine. For higenamine, half-lives were estimated to be between 4 and 27 h, and for coclaurine between 5 and 25 h. Furthermore, the data indicate that the elimination of coclaurine is rate-limited by its formation. Higenamine could be detected at a urine concentration above 10 ng/mL for at least 20 h after the last application for all study participants.

[The effects of cycloplegic eyedrops on corneal tomography]

PURPOSE

Whether cycloplegics affect standard keratorefractometric and tomographic measurements is unknown. The purpose of our study was to compare the effects of cycloplegics (cyclopentolate and atropine) on corneal shape and refractive power of the eye.

METHODS

This study was performed on 84 eyes of 49 study participants. Patients were randomized into two groups: atropine 1% (32 eyes) and cyclopentolate 1% (52 eyes). Corneal tomography was performed with the Orbscan IIz. To evaluate the corneal shape, simulated keratometry values, anterior and posterior best-fit sphere, white-to-white and tangential and axial corneal power were performed for the anterior and posterior corneal surfaces before and during cycloplegia. Pupil diameter, anterior chamber depth, corneal thickness at the 3, 5 and 7mm optical zones, thinnest area of the cornea and corneal thickness at the visual axis were examined. Data were analyzed using an SPSS statistical package.

RESULTS

The anterior and posterior BFS (in the atropine 1% group, anterior BFS was P=0.188; anterior BFS in the cyclopentolate group was P=0.227) and tangential and axial corneal power showed no change during cycloplegia in either group. SimK showed no statistical significance. The ACD was deeper when using atropine than cyclopentolate. Corneal thickness remained unchanged during cycloplegia in both groups. Pupil diameter was larger in light-colored irides in the cyclopentolate group than the atropine group. There was no change in W to W before (P=0.473) and during cycloplegia (P=0.287) in either group.

CONCLUSIONS

Our results suggest that usage of atropine or cyclopentolate does not alter corneal shape.

Aleglitazar, a dual peroxisome proliferator-activated receptor-α/γ agonist, improves insulin sensitivity, glucose control and lipid levels in people with type 2 diabetes: findings from a randomized, double-blind trial

The present single-centre, randomized, double-blind, placebo-controlled phase II study investigated the effect of the balanced dual peroxisome proliferator-activated receptor-α/γ agonist aleglitazar on whole-body and liver insulin sensitivity, β-cell function and other components of cardiometabolic syndrome after 16 weeks of treatment in patients with type 2 diabetes inadequately controlled with metformin monotherapy who received once-daily 150 µg aleglitazar or matching placebo as add-on therapy to metformin. Baseline and 16-week assessments included a two-step hyperinsulinaemic-euglycaemic clamp, followed by a hyperglycaemic clamp, as well as evaluation of glycated haemoglobin (HbA1c), lipids and safety variables. The primary endpoint was change in whole-body insulin sensitivity (M-value) from baseline compared with placebo, derived from the second clamp step. M-value improved significantly from baseline with aleglitazar (n = 16) compared with placebo (n = 24; p = 0.05 for difference between arms). We found statistically significant treatment differences with aleglitazar versus placebo in fasting hepatic insulin resistance index (p = 0.01), and in total glucose disposal (p = 0.03) at the second insulin infusion step. Aleglitazar treatment resulted in significant improvements in HbA1c and lipids and was well tolerated.

Efficacy, safety and tolerability of aleglitazar in patients with type 2 diabetes: pooled findings from three randomized phase III trials

AIMS

To evaluate the potential efficacy, safety and tolerability of aleglitazar as monotherapy or add-on therapy to metformin or to a sulphonylurea (either alone or in combination with metformin).

METHODS

We conducted a pooled analysis of data from three randomized phase III clinical trials of aleglitazar in patients with type 2 diabetes (n = 591). The three studies focused on: (i) aleglitazar alone; (ii) aleglitazar and metformin; and (iii) aleglitazar and sulphonylurea with or without metformin. Patients were randomized to 26 weeks' treatment with aleglitazar 150 µg/day or placebo. The primary endpoint was change in glycated haemoglobin (HbA1c) concentration from baseline to week 26. Secondary endpoints included changes in lipids, fasting plasma glucose and homeostatic model assessment of insulin resistance (HOMA-IR) at week 26.

RESULTS

Reductions in HbA1c concentration from baseline to week 26 were statistically significantly greater with aleglitazar than with placebo. Aleglitazar treatment was associated with more beneficial changes in lipid profiles and HOMA-IR values than was placebo. Aleglitazar was generally well tolerated, with no reports of congestive heart failure. The incidence of peripheral oedema was similar in both groups. Change in body weight was +1.37 kg with aleglitazar and -0.53 kg with placebo. Hypoglycaemia was more frequently reported with aleglitazar (7.8%) than with placebo (1.7%), a result probably driven by the type of background medication.

CONCLUSIONS

Development of aleglitazar was halted because of a lack of cardiovascular efficacy and peroxisome proliferator-activated receptor-related side effects in patients with type 2 diabetes post-acute coronary syndrome; however, in the present studies, aleglitazar was well tolerated and effective in improving HbA1c, insulin resistance and lipid variables.

Global overview of the risk linked to the Bacillus cereus group in the egg product industry: identification of food safety and food spoilage markers

AIMS

To evaluate the food safety and spoilage risks associated with psychrotrophic Bacillus cereus group bacteria for the egg product industry and to search for relevant risk markers.

METHODS AND RESULTS

A collection of 68 psychrotrophic B. cereus group isolates, coming from pasteurized liquid whole egg products, was analysed through a principal component analysis (PCA) regarding their spoilage and food safety risk potentials. The principal component analysis showed a clear differentiation between two groups within the collection, one half of the isolates representing a safety risk and the other half a spoilage risk.

CONCLUSIONS

Relevant risk markers were highlighted by PCA, that is (i) for the food safety risk, the presence of the specific 16S rDNA-1m genetic signature and the ability to grow at 43°C on solid medium and (ii) for the spoilage risk, the presence of the cspA genetic signature.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work represents a first step in the development of new diagnostic technologies for the assessment of the microbiological quality of foods likely to be contaminated with psychrotrophic B. cereus group bacteria.

Taspoglutide, a once-weekly glucagon-like peptide 1 analogue, vs. insulin glargine titrated to target in patients with Type 2 diabetes: an open-label randomized trial

AIMS

To compare the efficacy and safety of once-weekly taspoglutide with insulin glargine in patients with advanced Type 2 diabetes failing metformin and sulphonylurea combination therapy.

METHODS

This open-label, parallel-group, multi-centre trial randomized 1049 patients continuing metformin 1:1:1 to taspoglutide 10 mg once weekly, taspoglutide 20 mg once weekly or insulin glargine once daily with forced titration to fasting plasma glucose ≤ 6.1 mmol/l. Sulphonylureas were discontinued before randomization. The primary endpoint was change in HbA(1c) after 24 weeks.

RESULTS

After 24 weeks, least-square mean changes from baseline in HbA(1c) in patients receiving taspoglutide 10 mg [-8 mmol/mol (se 1)] [-0.77% (se 0.05)] or taspoglutide 20 mg [-11 mmol/mol (se 1)] [-0.98% (se 0.05)] were non-inferior to insulin glargine [-9 mmol/mol (se 1)] [-0.84% (se 0.05)]; treatment difference of 0.07% (95% CI -0.06 to 0.21) and -0.14% (95% CI -0.28 to -0.01), for taspoglutide 10 and 20 mg, respectively, vs. insulin glargine. Taspoglutide was associated with more adverse events (mainly gastrointestinal) and significantly less hypoglycaemia than insulin glargine.

CONCLUSIONS

Compared with insulin glargine, taspoglutide provided non-inferior HbA(1c) reductions associated with less hypoglycaemia, but more gastrointestinal adverse events.

Exposure to domoic acid through shellfish consumption in Belgium

A main known culprit causing amnesic shellfish poisoning in humans is domoic acid (DA). The toxin appearance in sea waters (by counting the toxin producing algae) and consequently in shellfish is closely monitored to prevent acute intoxications with gastrointestinal symptoms and neurological signs. However it is assumed that there might be some chronic problems with repetitive exposures to the toxin in animals. In humans this is greatly unknown and it is mostly assessed by relating reported toxin episodes and representative consumption data. Although in Belgium no alarming outbreaks have been reported in recent years, different concentrations of DA have been found in shellfish samples. In this study the human acute and chronic exposure to DA through shellfish consumption was evaluated by linking the data of DA concentrations in samples collected in the scope of the National Food control program in the period 2004-2009 and consumption data obtained from the National Belgian Food Consumption Survey including 3245 adults. The found level of toxin was highest in scallops while lowest in mussels. The mean usual long-term intake of molluscs such as scallops, mussels and oysters for the whole Belgian population was from 0.10 g/day for scallops to 1.21 g/day for mussels. With average portion size estimated to be 56-108 g/day depending on the shellfish source it was calculated that less than 1% of the population would be at risk of acute intoxication. Using a medium bound approach, 5-6% of the population shows chronic exposure exceeding the tolerable daily intake of 0.075 μg/kg bw per day with scallops being the most probable toxin vector when using lower (68.5%) and medium (45.6%) bound concentrations.

Effect of astaxanthin supplementation on muscle damage and oxidative stress markers in elite young soccer players

AIM

The purpose of the current study was to examine the effect of Astaxanthin (Asx) supplementation on muscle enzymes as indirect markers of muscle damage, oxidative stress markers and antioxidant response in elite young soccer players.

METHODS

Thirty-two male elite soccer players were randomly assigned in a double-blind fashion to Asx and placebo (P) group. After the 90 days of supplementation, the athletes performed a 2 hour acute exercise bout. Blood samples were obtained before and after 90 days of supplementation and after the exercise at the end of observational period for analysis of thiobarbituric acid-reacting substances (TBARS), advanced oxidation protein products (AOPP), superoxide anion (O2•¯), total antioxidative status (TAS), sulphydril groups (SH), superoxide-dismutase (SOD), serum creatine kinase (CK) and aspartate aminotransferase (AST).

RESULTS

TBARS and AOPP levels did not change throughout the study. Regular training significantly increased O2•¯ levels (main training effect, P<0.01). O2•¯ concentrations increased after the soccer exercise (main exercise effect, P<0.01), but these changes reached statistical significance only in the P group (exercise x supplementation effect, P<0.05). TAS levels decreased significantly post- exercise only in P group (P<0.01). Both Asx and P groups experienced increase in total SH groups content (by 21% and 9%, respectively) and supplementation effect was marginally significant (P=0.08). Basal SOD activity significantly decreased both in P and in Asx group by the end of the study (main training effect, P<0.01). All participants showed a significant decrease in basal CK and AST activities after 90 days (main training effect, P<0.01 and P<0.001, respectively). CK and AST activities in serum significantly increased as result of soccer exercise (main exercise effect, P<0.001 and P<0.01, respectively). Postexercise CK and AST levels were significantly lower in Asx group compared to P group (P<0.05)

CONCLUSION

The results of the present study suggest that soccer training and soccer exercise are associated with excessive production of free radicals and oxidative stress, which might diminish antioxidant system efficiency. Supplementation with Asx could prevent exercise induced free radical production and depletion of non-enzymatic antioxidant defense in young soccer players.

Gallbladder emptying in patients with major depression: a case series

INTRODUCTION

Although several adverse effects of antidepressants on the gastrointestinal tract have been described (bleeding, constipation, dolichocolon), their influence on gallbladder motility was not investigated.The aim of our study was to investigate the effects of selected antidepressants on gallbladder emptying in patients with major depression.

METHODS

The study was set up as an open clinical trial, with the same intervention (ingestion of test meal provoking gallbladder emptying) undertaken in 112 patients with major depression. There were 30 patients not taking antidepressants (the control group), 25 patients taking amitriptyline, 30 patients taking maprotiline, and 27 patients taking fluoxetine. The volume of gallbladder in the study patients was measured by ultrasonography before the test meal, and 15, 30, 45 and 60 min after the meal.

RESULTS

1 h after ingestion of the study meal, the amitriptyline group showed incomplete gallbladder emptying (F=10.829, df=3, p=0.000; mean residual volume 11.0±6.1 mL), while in the control, maprotiline and fluoxetine groups emptying of gallbladder was complete (mean residual volumes 5.0±3.3 mL, 5.6±3.7 mL and 5.7±2.3 mL, respectively).

DISCUSSION

In patients with cholecystitis, it would be wise to use antidepressants which do not impair gallbladder emptying, like maprotiline or fluoxetine, and to avoid amitriptyline.

Estimate of intake of benzoic acid in the Belgian adult population

An exposure assessment was performed to estimate average daily benzoic acid intake for Belgian adults. Food consumption data were retrieved from the national food-consumption survey. As a first step, individual food-consumption data were multiplied with the maximum permitted use levels for benzoic acid per food group (Tier 2). As a second step, a label survey to identify the foods where benzoic acid is effectively used as an additive and a literature review of the possible occurrence of benzoic acid as a natural substance were performed. With this information, a refined list of foods was drafted for the quantification of benzoic acid, which was performed by a high-performance liquid chromatography (HPLC) method, optimized and validated for this purpose. Individual food-consumption data were then multiplied with the actual average concentrations of benzoic acid per food group (Tier 3). Usual intakes were calculated using the Nusser method. The mean benzoic acid intake was 1.58 mg kg(-1) body weight day(-1) (Tier 2) and 1.25 mg kg(-1) body weight day(-1) (Tier 3). In Tier 2, men exceeded the acceptable daily intake (ADI) of 5 mg kg(-1) body weight day(-1) at the 99th percentile. The greatest contributors to the benzoic acid intake were soft drinks. Benzoic acid as a natural substance represents only a small percentage of the total intake. The results show that actual benzoic acid intake is very likely to be below the ADI. However, there is a need to collect national food-consumption data for children as they might be more vulnerable to an excessive intake.

Heat resistance of Bacillus cereus emetic toxin, cereulide

AIMS

The study describes the effects of heating temperature and exposure time on the thermal stability of cereulide under different conditions (pH, presence/absence of oil phase and cereulide concentration).

METHODS AND RESULTS

Cereulide heat inactivation was investigated at 100, 121 and 150 degrees C under different alkaline pH values (8.6-10.6) and in the presence of oil phase (0.6-1.4%). Three different cereulide concentrations (0.5, 5 and 6 microg ml(-1)) were used. Cereulide detection was performed with computer-aided semen analyzer and with HPLC-MS. Highly alkaline pH was needed to achieve inactivation. At lower cereulide concentrations less drastic conditions were needed. Removal of alkaline buffer after the heat treatment resulted in the recovery of toxic activity.

CONCLUSIONS

Heat stability of cereulide has been proved to be remarkable, even at highly alkaline pH values, at all temperatures tested. The loss of activity appeared to be reversible.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study demonstrates the inability of any heat treatment used in the food industry to inactivate cereulide. Food safety has to rely on prevention and cold chain maintenance. Cleaning practices also need to be adapted as cereulide may remain in its active form upon sterilization of used material.

Adaptive significance of amylase polymorphism in Drosophila: XIV. Effect of substrates with different carbohydrate composition on some life-history traits of Drosophila subobscura

The Amy-locus polymorphism of Drosophila subobscura is used as a model-system for an experimental population genetic study of adaptive significance of alpha-amylase activity on substrates of different carbohydrate compositions. So far, fitness components have not commonly been included in ecological-genetic studies of alpha-amylase polymorphism in this species. In the present paper fitness components are analyzed in relation to different amylase activities in D. subobscura individuals homozygous for "slow" and "fast" Amy allele, associated with substrates of different carbohydrate compositions. The results indicate a significant effect of substrate carbohydrate composition on fitness components of the genotypes homozygous for S or F Amy allele in D. subobscura through their enzyme activity.

The effect of lead on fitness components and developmental stability in Drosophila subobscura

We analyzed the developmental time, egg-to-adult viability, and developmental stability (fluctuating wing size asymmetry) in Drosophila subobscura, maintained for six generations on different concentrations of lead. Development time is significantly affected by generation and lead concentration, but interaction of these factors is not a significant source of variability for this fitness component. Generation and the interaction generation x concentration of lead significantly affect egg-to-adult viability. Levene's test of heterogeneity of variance showed that variability of FA is not significant in any of the samples. Within both lead concentrations females showed significantly higher FA indices for the wing width than males. Within sexes, a significantly higher FA was found only in females for wing width FA between the control and the lower concentration of lead. The results show that if strong relationship between FA and the studied fitness components exists, it results in a stronger selection of unstable genotypes under lead as a stress factor and, consequently, FA needs to be used with caution as a biomarker in natural populations under environmental stress.

The effect of different concentrations of lead on inversion polymorphism in Drosophilasubobscura

Drosophila subobscura is a wild Drosophila species that is spread over almost all of Europe. It possesses an uniquely rich inversion polymorphism on all five long chromosomes. This polymorphism is to a certain degree associated with the variation and dynamics of ecological factors in space and time. We analyzed the changes of inversion polymorphism components of Drosophila subobscura flies maintained on media with different concentrations of lead in laboratory conditions. The effects of lead on inversion polymorphism were observed by cytological analysis of gene arrangements on all of the five acrocentric chromosomes, as well as by cytological analysis of karyotypes on all of the four autosomes. The frequencies of particular gene arrangements on the four autosomes changed significantly in the samples maintained on medium not supplemented with lead. The frequencies of some gene arrangements on all of the five acrocentric chromosomes changed significantly in the flies maintained on media supplemented with lead. The length of exposure to different lead concentrations results in a significant change in the frequency of a few gene arrangements on two autosomes. However, the results show that different concentrations of lead, as well as the length of exposure, do not affect major parameters of inversion polymorphism. The results suggest that some gene arrangements could be linked with adaptive processes in evolving heavy metal resistance.

Adaptive significance of amylase polymorphism in Drosophila XIII. Old World obscura species subgroup divergence according to biochemical properties of alpha-amylase

Biochemical properties of enzyme alpha-amylase were surveyed in Drosophila obscura Old world group of species (D. subobscura, D. ambigua, D. obscura and D. tristis) sampled in the same habitat, with the aim to reveal some ecological and evolutionary aspects of amylase polymorphism, which has been studied extensively in D. subobscura, but not compared with other species in the group. The data obtained show that D. subobscura is distinct from the other three species regarding all biochemical amylase properties. Such a divergence also correlates with the niche breadth and relative abundance of these species in the same habitat.

Genetic load and coadaptation of chromosomal inversions. II. O-chromosomes in Drosophila subobscura populations

We have analysed the inversion polymorphism and genetic load of O-chromosomes in three populations of D. subobscura from southeastern Europe. As expected for a central populations the inversion polymorphism was extensive. In a like fashion, the genetic load, in particular the frequency of lethals, was heavy in all three populations. There were significant differences in the frequency of moderately deleterious genes. These differences in viability can be attributed to balancing selection. A comparison of these two kinds of genetic polymorphism indicates that there are differences in mean viability among different gene arrangements of O-chromosomes in the three populations. The differences observed are due to an unequal distribution of various viability classes among O-chromosome gene arrangements. We here show for the first time a specific distribution of lethal genes among these arrangements within the Palearctic distribution area of D. subobscura. The lethal allelism test showed lethals are non-randomly associated with the Ost gene arrangement. The amount of genetic load is heavy in gene arrangements with a high frequency, in comparison with the ones with a low frequency. Lethal genes may be protected in combinations of low and moderate frequency gene arrangements that harbor more lethal genes, as the Ost in the one population. Some arrangements that are less protected against recombination have a higher load than ones that are more protected against recombination. This can be taken as evidence for coadaptation.

Insulin-stimulated protein kinase B phosphorylation on Ser-473 is independent of its activity and occurs through a staurosporine-insensitive kinase

Full activation of protein kinase B (PKB, also called Akt) requires phosphorylation on two regulatory sites, Thr-308 in the activation loop and Ser-473 in the hydrophobic C-terminal regulatory domain (numbering for PKB alpha/Akt-1). Although 3'-phosphoinositide-dependent protein kinase 1 (PDK1) has now been identified as the Thr-308 kinase, the mechanism of the Ser-473 phosphorylation remains controversial. As a step to further characterize the Ser-473 kinase, we examined the effects of a range of protein kinase inhibitors on the activation and phosphorylation of PKB. We found that staurosporine, a broad-specificity kinase inhibitor and inducer of cell apoptosis, attenuated PKB activation exclusively through the inhibition of Thr-308 phosphorylation, with Ser-473 phosphorylation unaffected. The increase in Thr-308 phosphorylation because of overexpression of PDK1 was also inhibited by staurosporine. We further show that staurosporine (CGP 39360) potently inhibited PDK1 activity in vitro with an IC(50) of approximately 0.22 microm. These data indicate that agonist-induced phosphorylation of Ser-473 of PKB is independent of PDK1 or PKB activity and occurs through a distinct Ser-473 kinase that is not inhibited by staurosporine. Moreover, our results suggest that inhibition of PKB signaling is involved in the proapoptotic action of staurosporine.

Activation of protein kinase B induced by H(2)O(2) and heat shock through distinct mechanisms dependent and independent of phosphatidylinositol 3-kinase

Protein kinase B (PKB) is a downstream target of phosphatidylinositol (PI) 3-kinase in the signaling pathway of growth factors, and is activated by cellular stress such as H(2)O(2) and heat shock. To study the mechanism of the stress-induced activation of PKB, PI 3-kinase products were measured in stress-stimulated cells. Both PI 3,4-bisphosphate and PI 3,4, 5-trisphosphate increased in H(2)O(2)-treated cells, and the elevation of these phospholipids and activation of PKB were concurrently blocked by wortmannin, a potent inhibitor of PI 3-kinase. In heat-shocked cells, the level of PI 3,4-bisphosphate did not change while that of PI 3,4,5-trisphosphate increased slightly, and an association between PKB molecules was observed. Two active PKB fractions, presumably monomeric and oligomeric forms, were resolved from heat-shocked cells by gel filtration column chromatography. Activation of the former was suppressed by pretreatment with wortmannin, whereas the generation and activation of the latter were not blocked by the PI 3-kinase inhibitor. Only the monomeric form, but not the oligomeric form, was recovered from H(2)O(2)-treated cells, and its activation was prevented by wortmannin. These results indicate that PKB is activated by two distinct mechanisms that are dependent and independent of PI 3-kinase in stress-stimulated cells.

Protein kinase B localization and activation differentially affect S6 kinase 1 activity and eukaryotic translation initiation factor 4E-binding protein 1 phosphorylation

Recent studies indicate that phosphatidylinositide-3OH kinase (PI3K)-induced S6 kinase (S6K1) activation is mediated by protein kinase B (PKB). Support for this hypothesis has largely relied on results obtained with highly active, constitutively membrane-localized alleles of wild-type PKB, whose activity is independent of PI3K. Here we set out to examine the importance of PKB signaling in S6K1 activation. In parallel, glycogen synthase kinase 3beta (GSK-3beta) inactivation and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) phosphorylation were monitored as markers of the rapamycin-insensitive and -sensitive branches of the PI3K signaling pathway, respectively. The results demonstrate that two activated PKBalpha mutants, whose basal activity is equivalent to that of insulin-induced wild-type PKB, inhibit GSK-3beta to the same extent as a highly active, constitutively membrane-targeted wild-type PKB allele. However, of these two mutants, only the constitutively membrane-targeted allele of PKB induces S6K1 activation. Furthermore, an interfering mutant of PKB, which blocks insulin-induced PKB activation and GSK-3beta inactivation, has no effect on S6K1 activation. Surprisingly, all the activated PKB mutants, regardless of constitutive membrane localization, induce 4E-BP1 phosphorylation and the interfering PKB mutant blocks insulin-induced 4E-BP1 phosphorylation. The results demonstrate that PKB mediates S6K1 activation only as a function of constitutive membrane localization, whereas the activation of PKB appears both necessary and sufficient to induce 4E-BP1 phosphorylation independently of its intracellular location.

Mechanism of protein kinase B activation by insulin/insulin-like growth factor-1 revealed by specific inhibitors of phosphoinositide 3-kinase--significance for diabetes and cancer

Protein kinase B (PKB) is a member of the second messenger subfamily of protein kinases. The three isoforms of PKB identified have an amino-terminal pleckstrin homology domain, a central kinase domain, and a carboxy-terminal regulatory domain. PKB is the major downstream target of receptor tyrosine kinases that signal via the phosphoinositide (PI) 3-kinase. The crucial role of lipid second messengers in PKB activation has been dissected through the use of the PI 3-kinase-specific inhibitors wortmannin and LY294002. Receptor-activated PI 3-kinase synthesises the lipid second messenger PI-3,4,5-trisphosphate, leading to the recruitment of PKB to the membrane. Membrane attachment of PKB is mediated by its pleckstrin homology domain binding to PI-3,4,5-trisphosphate or PI-3,4-bisphosphate with high affinity. Activation of PKB alpha and beta is then achieved at the plasma membrane by phosphorylation of Thr308/309 in the A-loop of the kinase domain and Ser473/474 in the carboxy-terminal regulatory region, respectively. The upstream kinase that phosphorylates PKB on Thr308, termed PI-dependent protein kinase-1, has been identified and extensively characterised. A candidate for the Ser473/474 kinase, termed the integrin-linked kinase, has been identified recently. Activated PKB is implicated in glucose metabolism, transcriptional control, and in the regulation of apoptosis in many different cell types. Stimulation of PKB activity protects cells from apoptosis by phosphorylation and inactivation of the pro-apoptotic protein BAD. These results could explain why PKB is overexpressed in some ovarian, breast, and pancreatic carcinomas.

Phosphorylation and activation of p70s6k by PDK1

Activation of the protein p70s6k by mitogens leads to increased translation of a family of messenger RNAs that encode essential components of the protein synthetic apparatus. Activation of the kinase requires hierarchical phosphorylation at multiple sites, culminating in the phosphorylation of the threonine in position 229 (Thr229), in the catalytic domain. The homologous site in protein kinase B (PKB), Thr308, has been shown to be phosphorylated by the phosphoinositide-dependent protein kinase PDK1. A regulatory link between p70s6k and PKB was demonstrated, as PDK1 was found to selectively phosphorylate p70s6k at Thr229. More importantly, PDK1 activated p70s6k in vitro and in vivo, whereas the catalytically inactive PDK1 blocked insulin-induced activation of p70s6k.

G-Protein-coupled receptors and Fcgamma-receptors mediate activation of Akt/protein kinase B in human phagocytes

Activation of the serine/threonine kinase Akt, also called protein kinase B (PKB), was investigated in human neutrophils. Stimulation of the cells with the chemoattractant fMet-Leu-Phe or the chemokines IL-8 and GROalpha leads to the rapid and transient activation of PKB. Maximum PKB activation correlates with the well documented kinetics of respiratory burst and exocytosis. Wortmannin, a selective inhibitor of phosphoinositide 3-kinases (PI 3-kinases) in neutrophils, abrogates PKB activation. Similarly homo and heterotypic cross-linking of FcgammaIIA and FcgammaIIIB causes a transient activation of PKB that is sensitive to wortmannin treatment. Kinase activity measurements in immunoprecipitates from lysates of the myelocytic GM-1 cells or GM-1/CXCR1 cells, which are transfected with the IL-8 receptor 1, confirmed the transient activation of PKB observed in neutrophils. Stimulation of human monocytes with the CC chemokine RANTES (regulated on activation normal T cell expressed and secreted) also results in the activation of PKB. Preincubation of monocytes and neutrophils with Bordetella pertussis toxin inhibits fMet-Leu-Phe and RANTES-stimulated PKB activation, demonstrating that coupling of the receptors to heterotrimeric Gi-protein is required. The data show, that activation of PKB by Gi-protein-coupled receptors is mediated by PI 3-kinase and suggest that PKB is a constituent of neutrophil activating pathways.

High affinity binding of inositol phosphates and phosphoinositides to the pleckstrin homology domain of RAC/protein kinase B and their influence on kinase activity

The influence of inositol phosphates and phosphoinositides on the alpha isoform of the RAC-protein kinase B (RAC/PKB) was studied using purified wild type and mutant kinase preparations and a recombinant pleckstrin homology (PH) domain. Binding of inositol phosphates and phosphoinositides to the PH domain was measured as the quenching of intrinsic tryptophan fluorescence. Inositol phosphates and D3-phosphorylated phosphoinositides bound with affinities of 1-10 microM and 0.5 microM, respectively. Similar values were obtained using RAC/PKB expressed and purified from baculovirus-infected Sf9 cells in the fluorescence assay. The influence of synthetic dioctanoyl derivatives of phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate on the activity of RAC/PKB purified from transfected COS-1 cells was studied. Phosphatidylinositol 3,4,5-trisphosphate was found to inhibit the RAC/PKB kinase activity with half-maximal inhibition at 2.5 microM. In contrast, phosphatidylinositol 3, 4-bisphosphate stimulated kinase activity (half-maximal stimulation at 2.5 microM). A mutant RAC/PKB protein lacking the PH domain was not affected by D3-phosphorylated phosphoinositides. These results demonstrate that the PH domain of RAC/PKB binds inositol phosphates and phosphoinositides with high affinity, and suggest that the products of the phosphatidylinositide 3-kinase can act as both a membrane anchor and modulator of RAC/PKB activity. The data also provide further evidence for a link between phosphatidylinositide 3-kinase and RAC/PKB regulation.

Molecular basis for the substrate specificity of protein kinase B; comparison with MAPKAP kinase-1 and p70 S6 kinase

The substrate specificity of protein kinase-B alpha (PKBalpha, also known as RAC kinase or Akt) was investigated using synthetic peptide substrates related to the sequence surrounding the phosphorylation site on glycogen synthase kinase-3 (GSK3). The minimum sequence motif required for efficient phosphorylation was Arg-Xaa-Arg-Yaa-Zaa-Ser/Thr-Hyd, where Xaa is any amino acid, Yaa and Zaa are small residues other than glycine and Hyd is a bulky hydrophobic residue (Phe, Leu). The most effective substrate, Arg-Pro-Arg-Thr-Ser-Ser-Phe, was phosphorylated with a Km of 5 microM and Vmax of 260 U/mg. PKBalpha phosphorylated histone H2B (Km 5 microM, Vmax 68 U/mg) specifically at Ser-36 which also lies in an Arg-Xaa-Arg-Xaa-Xaa-Ser-Hyd motif. The peptide Arg-Pro-Arg-Ala-Ala-Thr-Phe may be a relatively specific substrate for PKBalpha because, unlike other substrates, it is not phosphorylated by p70 S6 kinase or MAP kinase activated protein (MAPKAP) kinase-1.

Mechanism of activation of protein kinase B by insulin and IGF-1

Insulin activated endogenous protein kinase B alpha (also known as RAC/Akt kinase) activity 12-fold in L6 myotubes, while after transfection into 293 cells PKBalpha was activated 20- and 50-fold in response to insulin and IGF-1 respectively. In both cells, the activation of PKBalpha was accompanied by its phosphorylation at Thr308 and Ser473 and, like activation, phosphorylation of both of these residues was prevented by the phosphatidylinositol 3-kinase inhibitor wortmannin. Thr308 and/or Ser473 were mutated to Ala or Asp and activities of mutant PKBalpha molecules were analysed after transfection into 293 cells. The activity of wild-type and mutant PKBalpha was also measured in vitro after stoichiometric phosphorylation of Ser473 by MAPKAP kinase-2. These experiments demonstrated that activation of PKBalpha by insulin or insulin-like growth factor-1 (IGF-1) results from phosphorylation of both Thr308 and Ser473, that phosphorylation of both residues is critical to generate a high level of PKBalpha activity and that the phosphorylation of Thr308 in vivo is not dependent on phosphorylation of Ser473 or vice versa. We propose a model whereby PKBalpha becomes phosphorylated and activated in insulin/IGF-1-stimulated cells by an upstream kinase(s).