Prediction of infant drug exposure through breastfeeding: population PK modeling and simulation of fluoxetine

BACKGROUND: Risks of significant infant drug exposurethrough breastmilk are poorly defined for many drugs, and largescalepopulation data are lacking. We used population pharmacokinetics(PK) modeling to predict fluoxetine exposure levels ofinfants via mother's milk in a simulated population of 1000 motherinfantpairs.METHODS: Using our original data on fluoxetine PK of 25breastfeeding women, a population PK model was developed withNONMEM and parameters, including milk concentrations, wereestimated. An exponential distribution model was used to account forindividual variation. Simulation random and distribution-constrainedassignment of doses, dosing time, feeding intervals and milk volumewas conducted to generate 1000 mother-infant pairs with characteristicssuch as the steady-state serum concentrations (Css) and infantdose relative to the maternal weight-adjusted dose (relative infantdose: RID). Full bioavailability and a conservative point estimate of1-month-old infant CYP2D6 activity to be 20% of the adult value(adjusted by weigth) according to a recent study, were assumed forinfant Css calculations.RESULTS: A linear 2-compartment model was selected as thebest model. Derived parameters, including milk-to-plasma ratios(mean: 0.66; SD: 0.34; range, 0 - 1.1) were consistent with the valuesreported in the literature. The estimated RID was below 10% in >95%of infants. The model predicted median infant-mother Css ratio was0.096 (range 0.035 - 0.25); literature reported mean was 0.07 (range0-0.59). Moreover, the predicted incidence of infant-mother Css ratioof >0.2 was less than 1%.CONCLUSION: Our in silico model prediction is consistent withclinical observations, suggesting that substantial systemic fluoxetineexposure in infants through human milk is rare, but further analysisshould include active metabolites. Our approach may be valid forother drugs. [supported by CIHR and Swiss National Science Foundation(SNSF)]

BAL9141, a novel extended-spectrum cephalosporin active against methicillin-resistant Staphylococcus aureus in treatment of experimental endocarditis.

The therapeutic efficacy of BAL9141 (formerly Ro 63-9141), a novel cephalosporin with broad in vitro activity that also has activity against methicillin-resistant Staphylococcus aureus (MRSA), was investigated in rats with experimental endocarditis. The test organisms were homogeneously methicillin-resistant S. aureus strain COL transformed with the penicillinase-encoding plasmid pI524 (COL Bla+) and homogeneously methicillin-resistant, penicillinase-producing isolate P8-Hom, selected by serial exposure of parent strain P8 to methicillin. The MICs of BAL9141 for these organisms (2 mg/liter) were low, and BAL9141was bactericidal in time-kill curve studies after 24 h of exposure to either two, four, or eight times the MIC. Rats with experimental endocarditis were treated in a three-arm study with a continuous infusion of BAL5788 (formerly Ro 65-5788), a carbamate prodrug of BAL9141, or with amoxicillin-clavulanate or vancomycin. The rats were administered BAL9141 to obtain steady-state target levels of 20, 10, and 5 mg of per liter or were administered either 1.2 g of amoxicillin-clavulanate (ratio 5:1) every 6 h or 1 g of vancomycin every 12 h at changing flow rates to simulate the pharmacokinetics produced in humans by intermittent intravenous treatment. Treatment was started 12 h after bacterial challenge and lasted for 3 days. BAL9141 was successful in the treatment of experimental endocarditis due to either MRSA isolate COL Bla+ or MRSA isolate P8-Hom at the three targeted steady-state concentrations and sterilized >90% of cardiac vegetations (P < 0.005 versus controls; P < 0.05 versus amoxicillin-clavulanate and vancomycin treatment groups). These promising in vivo results with BAL9141 correlated with the high affinity of the drug for PBP 2a and its stability to penicillinase hydrolysis observed in vitro.

Profile order and time-dependent artifacts in contrast-enhanced coronary MR angiography at 3T: origin and prevention.

To enhance the clinical value of coronary magnetic resonance angiography (MRA), high-relaxivity contrast agents have recently been used at 3T. Here we examine a uniform bilateral shadowing artifact observed along the coronary arteries in MRA images collected using such a contrast agent. Simulations were performed to characterize this artifact, including its origin, to determine how best to mitigate this effect, and to optimize a data acquisition/injection scheme. An intraluminal contrast agent concentration model was used to simulate various acquisition strategies with two profile orders for a slow-infusion of a high-relaxivity contrast agent. Filtering effects from temporally variable weighting in k-space are prominent when a centric, radial (CR) profile order is applied during contrast infusion, resulting in decreased signal enhancement and underestimation of vessel width, while both pre- and postinfusion steady-state acquisitions result in overestimation of the vessel width. Acquisition during the brief postinfusion steady-state produces the greatest signal enhancement and minimizes k-space filtering artifacts.

Cumulative cultural dynamics and the coevolution of cultural innovation and transmission: an ESS model for panmictic and structured populations.

When individuals in a population can acquire traits through learning, each individual may express a certain number of distinct cultural traits. These traits may have been either invented by the individual himself or acquired from others in the population. Here, we develop a game theoretic model for the accumulation of cultural traits through individual and social learning. We explore how the rates of innovation, decay, and transmission of cultural traits affect the evolutionary stable (ES) levels of individual and social learning and the number of cultural traits expressed by an individual when cultural dynamics are at a steady-state. We explore the evolution of these phenotypes in both panmictic and structured population settings. Our results suggest that in panmictic populations, the ES level of learning and number of traits tend to be independent of the social transmission rate of cultural traits and is mainly affected by the innovation and decay rates. By contrast, in structured populations, where interactions occur between relatives, the ES level of learning and the number of traits per individual can be increased (relative to the panmictic case) and may then markedly depend on the transmission rate of cultural traits. This suggests that kin selection may be one additional solution to Rogers's paradox of nonadaptive culture.

On the number of independent cultural traits carried by individuals and populations.

In species subject to individual and social learning, each individual is likely to express a certain number of different cultural traits acquired during its lifetime. If the process of trait innovation and transmission reaches a steady state in the population, the number of different cultural traits carried by an individual converges to some stationary distribution. We call this the trait-number distribution. In this paper, we derive the trait-number distributions for both individuals and populations when cultural traits are independent of each other. Our results suggest that as the number of cultural traits becomes large, the trait-number distributions approach Poisson distributions so that their means characterize cultural diversity in the population. We then analyse how the mean trait number varies at both the individual and population levels as a function of various demographic features, such as population size and subdivision, and social learning rules, such as conformism and anti-conformism. Diversity at the individual and population levels, as well as at the level of cultural homogeneity within groups, depends critically on the details of population demography and the individual and social learning rules.

Fluoxetine addition to methadone in addicts: pharmacokinetic aspects.

We report nine cases where fluoxetine (FX) (20 mg/day) was added to maintenance treatment with methadone (MTD) (dose range: 30-100 mg) in addicts with affective disorders. MTD plasma levels were measured before and after treatment with FX under steady-state conditions. Among the nine patients, two also received fluvoxamine (FLVX) at different times. Although it is possible that in some patients a moderate FX-MTD interaction occurs, resulting in increased plasma levels of MTD, this interaction is certainly less marked than that between FLVX and MTD and unlikely to have clinical consequences.

Clustering of cardiovascular risk factors mimicking the human metabolic syndrome X in eNOS null mice.

AIMS/HYPOTHESIS: The metabolic syndrome comprises a clustering of cardiovascular risk factors but the underlying mechanism is not known. Mice with targeted disruption of endothelial nitric oxide synthase (eNOS) are hypertensive and insulin resistant. We wondered, whether eNOS deficiency in mice is associated with a phenotype mimicking the human metabolic syndrome. METHODS AND RESULTS: In addition to arterial pressure and insulin sensitivity (euglycaemic hyperinsulinaemic clamp), we measured the plasma concentration of leptin, insulin, cholesterol, triglycerides, free fatty acids, fibrinogen and uric acid in 10 to 12 week old eNOS-/- and wild type mice. We also assessed glucose tolerance under basal conditions and following a metabolic stress with a high fat diet. As expected eNOS-/- mice were hypertensive and insulin resistant, as evidenced by fasting hyperinsulinaemia and a roughly 30 percent lower steady state glucose infusion rate during the clamp. eNOS-/- mice had a 1.5 to 2-fold elevation of the cholesterol, triglyceride and free fatty acid plasma concentration. Even though body weight was comparable, the leptin plasma level was 30% higher in eNOS-/- than in wild type mice. Finally, uric acid and fibrinogen were elevated in the eNOS-/- mice. Whereas under basal conditions, glucose tolerance was comparable in knock out and control mice, on a high fat diet, knock out mice became significantly more glucose intolerant than control mice. CONCLUSIONS: A single gene defect, eNOS deficiency, causes a clustering of cardiovascular risk factors in young mice. We speculate that defective nitric oxide synthesis could trigger many of the abnormalities making up the metabolic syndrome in humans.

Testosterone: a specific competitive antagonist of aldosterone in the toad bladder.

Testosterone (100 nM to 40 microM) antagonized the effect of aldosterone (10 nM) on Na+ transport in the toad bladder measured in vitro as short-circuit current (SCC). Half-maximal inhibition occurred at an antagonist-agonist molar ratio of 150:1. The antagonist action of testosterone was reversed by addition of more aldosterone. The antagonism was specific in the sense that testosterone (20 microM) did not inhibit the response of the SCC to oxytocin (50 mU/ml). By itself, testosterone (up to 20 microM) had no agonist activity on base-line SCC. Finally, testosterone (500 nM to 20 microM) specifically displaced [3H]aldosterone (5 nm) from its cytoplasmic and nuclear binding sites in bladders incubated in vitro at 25 or 0 degrees C and labeled at steady state. There was a significant linear correlation between the effect of testosterone on the aldosterone-dependent SCC and its effect on [3H]aldosterone binding sites in the cytoplasm and in the nucleus. We conclude that 1) testosterone is a specific competitive antagonist of aldosterone, and 2) [3H]aldosterone nuclear and cytoplasmic binding sites could be mineralocorticoid receptors, mediating the action of aldosterone on Na+ transport.

Vitamin C requirements in parenteral nutrition.

Some biochemical functions of vitamin C make it an essential component of parenteral nutrition (PN) and an important therapeutic supplement in other acute conditions. Ascorbic acid is a strong aqueous antioxidant and is a cofactor for several enzymes. The average body pool of vitamin C is 1.5 g, of which 3%-4% (40-60 mg) is used daily. Steady state is maintained with 60 mg/d in nonsmokers and 140 mg/d in smokers. Shocked surgical, trauma, and septic patients have a drastic reduction of circulating plasma ascorbate concentrations. These low concentrations require 3-g doses/d to restore normal plasma ascorbate concentrations, questioning the recommended PN dose of 100 mg/d. Determination of intravenous requirements is usually based on plasma concentrations, which are altered during the inflammatory response. There is no clear indicator of deficiency: serum or plasma ascorbate concentrations <0.3 mg/dL (20 micromol/L) indicates inadequate vitamin C status. On the basis of available pharmacokinetic data the 100 mg/d dose for patients receiving home PN and 200 mg/d for stable adult patients receiving PN are adequate, but requirements have been shown to be higher in perioperative, trauma, burn, and critically ill patients, paralleling oxidative stress. One recommendation cannot fit all categories of patients. Large vitamin C supplements may be considered in severe critical illness, major trauma, and burns because of increased requirements resulting from oxidative stress and wound healing. Future research should distinguish therapeutic use of high-dose ascorbic acid antioxidant therapy from nutritional PN requirements.

Inactivation of Notch 1 in immature thymocytes does not perturb CD4 or CD8T cell development.

Notch proteins influence cell-fate decisions in many developing systems. Several gain-of-function studies have suggested a critical role for Notch 1 signaling in CD4-CD8 lineage commitment, maturation and survival in the thymus. However, we show here that tissue-specific inactivation of the gene encoding Notch 1 in immature (CD25+CD44-)T cell precursors does not affect subsequent thymocyte development. Neither steady-state numbers nor the rate of production of CD4+ and CD8+ mature thymocytes is perturbed in the absence of Notch 1. In addition, Notch 1-deficient thymocytes are normally sensitive to spontaneous or glucocorticoid-induced apoptosis. In contrast to earlier reports, these data formally exclude an essential role for Notch 1 in CD4-CD8 lineage commitment, maturation or survival.

The rate-limiting step for glucose transport into the hypothalamus is across the blood-hypothalamus interface.

Specialized glucosensing neurons are present in the hypothalamus, some of which neighbor the median eminence, where the blood-brain barrier has been reported leaky. A leaky blood-brain barrier implies high tissue glucose levels and obviates a role for endothelial glucose transporters in the control of hypothalamic glucose concentration, important in understanding the mechanisms of glucose sensing We therefore addressed the question of blood-brain barrier integrity at the hypothalamus for glucose transport by examining the brain tissue-to-plasma glucose ratio in the hypothalamus relative to other brain regions. We also examined glycogenolysis in hypothalamus because its occurrence is unlikely in the potential absence of a hypothalamus-blood interface. Across all regions the concentration of glucose was comparable at a given plasma glucose concentration and was a near linear function of plasma glucose. At steady-state, hypothalamic glucose concentration was similar to the extracellular hypothalamic glucose concentration reported by others. Hypothalamic glycogen fell at a rate of approximately 1.5 micromol/g/h and remained present in substantial amounts. We conclude for the hypothalamus, a putative primary site of brain glucose sensing that: the rate-limiting step for glucose transport into brain cells is at the blood-hypothalamus interface, and that glycogenolysis is consistent with a substantial blood -to- intracellular glucose concentration gradient.

Two-stage, extreme albitization of A-type granites from Rajasthan, NW India

Albitization is a common process during which hydrothermal fluids convert plagioclase and/or K-feldspar into nearly pure albite; however, its specific mechanism in granitoids is not well understood. The c. 1700 Ma A-type metaluminous ferroan granites in the Khetri complex of Rajasthan, NW India, have been albitized to a large extent by two metasomatic fronts, an initial transformation of oligoclase to nearly pure albite and a subsequent replacement of microcline by albite, with sharp contacts between the microcline-bearing and microcline-free zones. Albitization has bleached the original pinkish grey granite and turned it white. The mineralogical changes include transformation of oligoclase (similar to An(12)) and microcline (similar to Or(95)) to almost pure albite (similar to An(0 center dot 5-2)), amphibole from potassian ferropargasite (X-Fe 0 center dot 84-0 center dot 86) to potassic hastingsite (X-Fe 0 center dot 88-0 center dot 97) and actinolite (X-Fe 0 center dot 32-0 center dot 67), and biotite from annite (X-Fe 0 center dot 71-0 center dot 74) to annite (X-Fe 0 center dot 90-0 center dot 91). Whole-rock isocon diagrams show that, during albitization, the granites experienced major hydration, slight gain in Si and major gain in Na, whereas K, Mg, Fe and Ca were lost along with Rb, Ba, Sr, Zn, light rare earth elements and U. Whole-rock Sm-Nd isotope data plot on an apparent isochron of 1419 +/- 98 Ma and reveal significant disturbance and at least partial resetting of the intrusion age. Severe scatter in the whole-rock Rb-Sr isochron plot reflects the extreme Rb loss in the completely albitized samples, effectively freezing Sr-87/Sr-86 ratios in the albite granites at very high values (0 center dot 725-0 center dot 735). This indicates either infiltration of highly radiogenic Sr from the country rock or, more likely, radiogenic ingrowth during a considerable time lag (estimated to be at least 300 Myr) between original intrusion and albitization. The albitization took place at similar to 350-400 degrees C. It was caused by the infiltration of an ascending hydrothermal fluid that had acquired high Na/K and Na/Ca ratios during migration through metamorphic rocks at even lower temperatures in the periphery of the plutons. Oxygen isotope ratios increase from delta O-18 = 7 parts per thousand in the original granite to values of 9-10 parts per thousand in completely albitized samples, suggesting that the fluid had equilibrated with surrounding metamorphosed crust. A metasomatic model, using chromatographic theory of fluid infiltration, explains the process for generating the observed zonation in terms of a leading metasomatic front where oligoclase of the original granite is converted to albite, and a second, trailing front where microcline is also converted to albite. The temperature gradients driving the fluid infiltration may have been produced by the high heat production of the granites themselves. The confinement of the albitized granites along the NE-SW-trending Khetri lineament and the pervasive nature of the albitization suggest that the albitizing fluids possibly originated during reactivation of the lineament. More generally, steady-state temperature gradients induced by the high internal heat production of A-type granites may provide the driving force for similar metasomatic and ore-forming processes in other highly enriched granitoid bodies.

Interleukin-12p40 overexpression promotes interleukin-12p70 and interleukin-23 formation but does not affect bacille Calmette-Guérin and Mycobacterium tuberculosis clearance.

Interleukin (IL)-12p40, a subunit of IL-12p70 and IL-23, has previously been shown to inhibit IL-12p70 activity and interferon-gamma (IFN-gamma) production. However, recent evidence has suggested that the role of IL-12p40 is more complex. To study the contribution of IL-12p40 to immune responses against mycobacterial infections, we have used transgenic (tg) mice overexpressing IL-12p40 under the control of a major histocompatibility complex-II promoter. The IL-12p40 transgene was expressed during steady state at concentrations of 129 +/- 25 ng/ml of serum and 75 +/- 13 ng per spleen, while endogenous IL-12p40 was hardly detectable in control littermates. Bacille Calmette-Guérin (BCG) infection strongly induced the expression of IL-12p40 transgene in infected organs, and IL-12p40 monomeric and dimeric forms were identified in spleen of IL-12p40 tg mice. Excessive production of IL-12p40 resulted in a 14-fold increase in IL-12p70 serum levels in tg mice versus non-transgenic mice. IL-23 was also strongly elevated in the serum and spleens of IL-12p40 tg mice through BCG infection. While IFN-gamma and tumour necrosis factor protein levels were similar in IL-12p40 tg and non-transgenic mice, Th2 type immune responses were reduced in IL-12p40 tg mice. The number of BCG granulomas and macrophage expressing inducible nitric oxide synthase were similar in IL-12p40 tg and non-transgenic mice. IL-12p40 tg mice were as resistant as non-transgenic mice to BCG and Mycobacterium tuberculosis infections as they could efficiently control bacillary growth. These data show that high amounts of IL-12p40 promotes IL-12p70 and IL-23 formation, but that does not affect T helper 1 type immune responses and granuloma function, thus leading to normal mycobacterial clearance in infected organs.

c-Myc acts downstream of IL-15 in the regulation of memory CD8 T-cell homeostasis.

A subset of CD8 T cells in normal mice, expressing high levels of activation markers such as CD44, shares many properties with antigen-specific memory CD8 T cells. Homeostasis of CD44(high) CD8 T cells depends upon cytokines such as interleukin-15 (IL-15); however, the downstream signaling pathways regulating IL-15-dependent homeostatic proliferation are poorly defined. Surprisingly, we show here that haploinsufficiency of the protooncogene c-myc leads to a highly selective decrease in CD44(high) CD8 T cells in mice. Although steady-state proliferation and survival of CD44(high) CD8 T cells appeared not to be dependent on c-Myc, homeostatic proliferation of c-myc(+/-) CD44(high) CD8 T cells in lymphopenic hosts was strongly reduced, and the residual homeostatic proliferation of these cells appeared to occur independently of IL-15. Moreover, c-myc(+/-) CD44(high) CD8 T cells responded very poorly to purified IL-15 in vitro. Backcrossing of c-myc(+/-) mice to IL-15(-/-) mice revealed that the number of CD44(high) CD8 T cells decreased in an additive fashion in mice heterozygous for c-myc and IL-15. Finally homeostatic proliferation of antigen-specific memory CD44(high) CD8 T cells was also impaired in c-myc(+/-) mice. Collectively, our data identify c-Myc as a novel downstream component of the IL-15-dependent pathway controlling homeostatic proliferation of memory CD44(high) CD8 T cells.

Artifact-free coronary magnetic resonance angiography and coronary vessel wall imaging in the presence of a new, metallic, coronary magnetic resonance imaging stent.

BACKGROUND: Coronary in-stent restenosis cannot be directly assessed by magnetic resonance angiography (MRA) because of the local signal void of currently used stainless steel stents. The aim of this study was to investigate the potential of a new, dedicated, coronary MR imaging (MRI) stent for artifact-free, coronary MRA and in-stent lumen and vessel wall visualization. METHODS AND RESULTS: Fifteen prototype stents were deployed in coronary arteries of 15 healthy swine and investigated with a double-oblique, navigator-gated, free-breathing, T2-prepared, 3D cartesian gradient-echo sequence; a T2-prepared, 3D spiral gradient-echo sequence; and a T2-prepared, 3D steady-state, free-precession coronary MRA sequence. Furthermore, black-blood vessel wall imaging by a dual-inversion-recovery, turbo spin-echo sequence was performed. Artifacts of the stented vessel segment and signal intensities of the coronary vessel lumen inside and outside the stent were assessed. With all investigated sequences, the vessel lumen and wall could be visualized without artifacts, including the stented vessel segment. No signal intensity alterations inside the stent when compared with the vessel lumen outside the stent were found. CONCLUSIONS: The new, coronary MRI stent allows for completely artifact-free coronary MRA and vessel wall imaging.