bluuebunny/crossref_metadata_2025 huggingface dataset:
Interleukin‐6‐induced proliferation of pre‐B cells mediated by receptor complexes lacking the SHP2/SOCS3 recruitment sites revisited
Authors: Friederichs Kerstin , Schmitz Jochen , Weissenbach Manuela , Heinrich Peter C. , Schaper Fred
Published: March 2003

Interleukin‐6 (IL‐6) induces B‐cell proliferation by binding to receptor complexes composed of a specific α‐receptor (gp80; CD126) and the signal transducing receptor subunit gp130 (CD130). Immediately after receptor complex activation, signal transducers and activators of transcription (STATs) 1 and 3 and the Src‐homology domain‐containing protein tyrosine phosphatase 2 (SHP2) are recruited to gp130 and subsequently tyrosine phosphorylated. The activated dimerized STATs translocate to the nucleus and bind to enhancer elements of IL‐6‐inducible genes. SHP2 acts as an adapter and links the Jak/STAT pathway to the Ras/Raf/MAPK cascade but it is also involved in signal attenuation. Whereas STAT3 activation appears to be crucial for all biological activities of IL‐6, the requirement of SHP2‐activation depends on the individual biological response analyzed. The requirement of SHP2 activation for the pre‐B cell (Ba/F3) proliferation has been reported previously [Fukada, T., Hibi, M., Yamanaka, Y., Takahashi‐Tezuka, M., Fujitani, Y., Yamaguchi, T., Nakajima, K. & Hirano, T. (1996) Immunity5, 449–460]. In contrast, we have recently demonstrated that the presence of a single STAT‐recruitment site within gp130 is sufficient for IL‐6‐ induced proliferation of Ba/F3 cells [Schmitz, J., Dahmen, H., Grimm, C., Gendo, C., Müller‐Newen, G., Heinrich, P.C. & Schaper, F. (2000) J. Immunol.164, 848–854]. To unravel this discrepancy we analyzed the IL‐6‐induced dose‐dependent proliferation of Ba/F3 cells mediated by receptor complexes lacking SHP2/SOCS3 recruitment sites. Surprisingly, pre‐B cells, after stimulation with low amounts of IL‐6, proliferate much more efficiently in the absence of the activated SHP2 than in the presence of the tyrosine phosphatase. Therefore, SHP2 activation appears to be relevant for IL‐6‐induced proliferation only after stimulation with very large amounts of IL‐6.
The natural silk spinning process
Authors: Li Guiyang , Zhou Ping , Shao Zhengzhong , Xie Xun , Chen Xin , Wang Honghai , Chunyu Lijuan , Yu Tongyin
Published: March 2003

The spinning mechanism of natural silk has been an open issue. In this study, both the conformation transition from random coil to β sheet and the β sheet aggregation growth of silk fibroin are identified in the B. mori regenerated silk fibroin aqueous solution by circular dichroism (CD) spectroscopy. A nucleation‐dependent aggregation mechanism, similar to that found in prion protein, amyloid β (Aβ) protein, and α‐synuclein protein with the conformation transition from a soluble protein to a neurotoxic, insoluble β sheet containing aggregate, is a novel suggestion for the silk spinning process. We present evidence that two steps are involved in this mechanism: (a) nucleation, a rate‐limiting step involving the conversion of the soluble random coil to insoluble β sheet and subsequently a series of thermodynamically unfavorable association of β sheet unit, i.e. the formation of a nucleus or seed; (b) once the nucleus forms, further growth of the β sheet unit becomes thermodynamically favorable, resulting a rapid extension of β sheet aggregation. The aggregation growth follows a first order kinetic process with respect to the random coil fibroin concentration. The increase of temperature accelerates the β sheet aggregation growth if the β sheet seed is introduced into the random coil fibroin solution. This work enhances our understanding of the natural silk spinning process in vivo.
Molecular characterization of the amplified aldehyde oxidase from insecticide resistant Culex quinquefasciatus
Authors: Coleman Michael , Vontas John G. , Hemingway Janet
Published: March 2003

Primary structural information including the complete nucleotide sequence of the first insect aldehyde oxidase (AO) was obtained from the common house mosquito Culex quinquefasciatus (Say) through cloning and sequencing of both genomic DNA and cDNA. The deduced amino‐acid sequence encodes a 150‐kDa protein of 1266 amino‐acid residues, which is consistent with the expected monomeric subunit size of AO. The Culex AO sequence contains a molybdopterin cofactor binding domain and two iron–sulfur centres. A comparison of the partial sequences of AO from insecticide resistant and susceptible strains of C. quinquefasciatus shows two distinct alleles of this enzyme, one of which is amplified in the insecticide resistant strain on a 30‐kb DNA amplicon alongside two resistance‐associated esterases. The amplified AO gene results in elevated AO activity in all life stages, but activity is highest in 3rd instar larvae. The elevated enzyme can be seen as a separate band on polyacrylamide gel electrophoresis. The role of AO in xenobiotic oxidation in mammals and the partial inhibition of elevated AO activity by a range of insecticides in Culex, suggest that this AO may play a role in insecticide resistance.
The processivity and fidelity of DNA synthesis exhibited by the reverse transcriptase of bovine leukemia virus
Authors: Avidan Orna , Entin Meer Michal , Oz Iris , Hizi Amnon
Published: March 2003

We have recently expressed in bacteria the enzymatically active reverse transcriptase (RT) of bovine leukemia virus (BLV) [Perach, M. & Hizi, A. (1999) Virology259, 176–189]. In the present study, we have studied in vitro two features of the DNA polymerase activity of BLV RT, the processivity of DNA synthesis and the fidelity of DNA synthesis. These properties were compared with those of the well‐studied RTs of human immunodeficiency virus type 1 (HIV‐1) and murine leukaemia virus (MLV). Both the elongation of the DNA template and the processivity of DNA synthesis exhibited by BLV RT are impaired relative to the other two RTs studied. Two parameters of fidelity were studied, the capacity to incorporate incorrect nucleotides at the 3′ end of the nascent DNA strand and the ability to extend these 3′ end mispairs. BLV RT shows a fidelity of misinsertion higher than that of HIV‐1 RT and lower than that of MLV RT. The pattern of mispair elongation by BLV RT suggests that the in␣vitro error proneness of BLV RT is closer to that of HIV‐1 RT. These fidelity properties are discussed in the context of the various retroviral RTs studied so far.
Interallelic complementation provides genetic evidence for the multimeric organization of the Phycomyces blakesleeanus phytoene dehydrogenase
Authors: Sanz Catalina , Alvarez María I. , Orejas Margarita , Velayos Antonio , Eslava Arturo P. , Benito Ernesto P.
Published: March 2003

The Phycomyces blakesleeanus wild‐type is yellow, because it accumulates β‐carotene as the main carotenoid. A new carotenoid mutant of this fungus (A486) was isolated, after treatment with ethyl methane sulfonate (EMS), showing a whitish coloration. It accumulates large amounts of phytoene, small quantities of phytofluene, ζ‐carotene and neurosporene, in decreasing amounts, and traces of β‐carotene. This phenotype indicates that it carries a leaky mutation affecting the enzyme phytoene dehydrogenase (EC 1.3.‐.‐), which is specified by the gene carB. Biochemical analysis of heterokaryons showed that mutant A486 complements two previously characterized carB mutants, C5 (carB10) and S442 (carB401). Sequence analysis of the carB gene genomic copy from these three strains revealed that they are all altered in the gene carB, giving information about the nature of the mutation in each carB mutant allele. The interallelic complementation provides evidence for the multimeric organization of the P. blakesleeanus phytoene dehydrogenase.
In vivo activation of plasma membrane H+‐ATPase hydrolytic activity by complex lipid‐bound unsaturated fatty acids in Ustilago maydis
Authors: Hernández Agustín , Cooke David T. , Clarkson David T.
Published: March 2003

As an adaptation process to the growth retardation provoked by the presence of nonlethal concentrations of ergosterol biosynthesis inhibitors, Ustilago maydis alters the ratio of linoleic to oleic acid bound to plasma membrane complex lipids [Hernández, A., Cooke, D.T., Lewis, M. & Clarkson, D.T. (1997) Microbiology143, 3165–3174]. This alteration increases plasma membrane H+‐ATPase hydrolytic activity. Activation of H+‐ATPase by the linoleic/oleic acid proportion is noncompetitive, nonessential and only involves changes in the maximum velocity of the pump. Optimum pH, affinity to MgATP and constants for the inhibition by vanadate and erythrosin B remain unchanged. This all indicates that activation of plasma membrane H+‐ATPase by unsaturated fatty acids differs clearly from glucose‐induced activation observed in yeast. Also, it is a physiologically relevant event similar to other, as yet uncharacterized, changes in plasma membrane H+‐ATPase hydrolytic activity observed in plants and fungi, as part of an adaptation process to different stress conditions.
The SK‐N‐MC cell line expresses an orexin binding site different from recombinant orexin 1‐type receptor
Authors: Wieland Heike A. , Söll Richard M. , Doods Henri N. , Stenkamp Dirk , Hurnaus Rudolf , Lämmle Bärbel , Beck‐Sickinger Annette G.
Published: March 2003

Orexin A and B (also known as hypocretins), two recently discovered neuropeptides, play an important role in food intake, sleep/wake cycle and neuroendocrine functions. Orexins are endogenous ligands of two G‐protein‐coupled receptors, termed OX1 and OX2. This work presents the first short orexin A and B analogues, orexin A 23–33 and orexin B 18–28, with high affinity (119 ± 49 and 49 ± 23 nm) for OX1 receptors expressed on SK‐N‐MC cells and indicates the importance of the C‐terminal part of the orexin peptides for this ligand–receptor interaction. However, these C‐terminal fragments of orexin did not displace the 125I‐labelled orexin B from the recombinant orexin 1 receptor stably expressed in Chinese hamster ovary cells. To examine the role of the shortened orexin A 23–33 in feeding, its effects in mimicking or antagonizing the effects of orexin A were studied in rats after administration via the lateral hypothalamus. In contrast with orexin A, which potently induced feeding up to 4 h after administration, orexin A 23–33 neither induced feeding nor inhibited orexin A‐induced feeding. Modafinil (Vigil®), which was shown earlier to activate orexin neurons, displayed binding neither to the orexin receptor expressed on SK‐N‐MC cells nor to the recombinant orexin 1 receptor, which indicates that modafinil displays its antinarcoleptic action via another yet unknown mechanism. PCR and subsequent sequencing revealed expression of the full‐length orexin 1 receptor mRNA in SK‐N‐MC and NT‐2 cells. Interestingly, sequencing of several cDNA clones derived from RNA of both SK‐N‐MC and NT‐2 cells differed from the published nucleotide sequence at position 1375. Amino acid prediction of this A→G change results in an isoleucine→valine substitution at the protein level, which may provide evidence for an editing process.
Rapid caspase‐dependent cell death in cultured human breast cancer cells induced by the polyamine analogue N1,N11‐diethylnorspermine
Authors: Hegardt Cecilia , Johannsson Oskar T. , Oredsson Stina M.
Published: March 2003

The spermine analogue N1,N11‐diethylnorspermine (DENSPM) efficiently depletes the cellular pools of putrescine, spermidine and spermine by down‐regulating the activity of the polyamine biosynthetic enzymes and␣up‐regulating the activity of the catabolic enzyme spermidine/ spermine N1‐acetyltransferase (SSAT). In the breast cancer cell line L56Br‐C1, treatment with 10 µm DENSPM induced SSAT activity 60 and 240‐fold at 24 and 48 h after seeding, respectively, which resulted in polyamine depletion. Cell proliferation appeared to be totally inhibited and within 48 h of treatment, there was an extensive apoptotic response. Fifty percent of the cells were found in the sub‐G1 region, as determined by flow cytometry, and the presence of apoptotic nuclei was morphologically assessed by fluorescence microscopy. Caspase‐3 and caspase‐9 activities were significantly elevated 24 h after seeding. At 48 h after seeding, caspase‐3 and caspase‐9 activities were further elevated and at this time point a significant activation of caspase‐8 was also found. The DENSPM‐induced cell death was dependent on the activation of the caspases as it was inhibited by the general caspase inhibitor Z‐Val‐Ala‐Asp fluoromethyl ketone. The results are discussed in the light of the L56Br‐C1 cells containing mutated BRCA1 and p53, two genes involved in DNA repair.
DAP kinase activity is critical for C2‐ceramide‐induced apoptosis in PC12 cells
Authors: Yamamoto Mutsuya , Hioki Takeshi , Ishii Takehisa , Nakajima‐Iijima Sadayo , Uchino Shigeo
Published: March 2003

Exposure of PC12 cells to C2‐ceramide results in dose‐dependent apoptosis. Here, we investigate the involvement of death‐associated protein (DAP) kinase, initially identified as a positive mediator of the interferon‐γ‐induced apoptosis of HeLa cells, in the C2‐ceramide‐induced apoptosis of PC12 cells. DAP kinase is endogenously expressed in these cells. On exposure of PC12 cells to 30 µm C2‐ceramide, both the total (assayed in the presence of Ca2+/calmodulin) and Ca2+/calmodulin‐independent (assayed in the presence of EGTA) DAP kinase activities were transiently increased 5.0‐ and 12.2‐fold, respectively, at 10 min, and then decreased to 1.7‐ and 3.4‐fold at 90 min. After 10 min exposure to 30 µm C2‐ceramide, the Ca2+/calmodulin independent activity/ total activity ratio increased from 0.22 to 0.60. These effects were dependent on the C2‐ceramide concentration. C8‐ceramide, another active ceramide analog, also induced apoptosis and activated DAP kinase, while C2‐dihydroceramide, an inactive ceramide analog, failed to induce apoptosis and increase DAP kinase activity. Furthermore, transfection studies revealed that overexpression of wild‐type DAP kinase enhanced the sensitivity to C2‐ and C8‐ceramide, while a catalytically inactive DAP kinase mutant and a construct containing the death domain and C‐terminal tail of DAP kinase, which act in a dominant‐negative manner, rescued cells from C2‐, and C8‐ceramide‐induced apoptosis. These findings demonstrate that DAP kinase is an important component of the apoptotic machinery involved in ceramide‐induced apoptosis, and that the intrinsic DAP kinase activity is critical for ceramide‐induced apoptosis.
SMAP‐29 has two LPS‐binding sites and a central hinge
Authors: Tack Brian F. , Sawai Monali V , Kearney William R. , Robertson Andrew D. , Sherman Mark A. , Wang Wei , Hong Teresa , Boo Lee Ming , Wu Huiyuan , Waring Alan J. , Lehrer Robert I.
Published: March 2003

The CD spectra of SMAP‐29, an antimicrobial peptide from sheep, showed disordered structure in aqueous buffers, and significant helicity in membrane‐like environments, including SDS micelles, lipopolysaccharide (LPS) dispersions, and trifluoroethanol buffer systems. A structure determined by NMR in 40% perdeuterated trifluoroethanol indicated that residues 8–17 were helical, residues 18–19 formed a hinge, and residues 20–28 formed an ordered, hydrophobic segment. SMAP‐29 was flexible in 40% trifluoroethanol, forming two sets of conformers that differed in the relative orientation of the N‐terminal domain. We used a chromogenic Limulus assay to determine the EC50 of the peptide (the concentration that bound 50% of the added LPS). Studies with full‐length and truncated SMAP‐29 molecules revealed that each end of the holopeptide contained an LPS‐binding domain. The higher affinity LPS‐binding domain was situated in the flexible N‐terminal portion. LPS binding to full‐length SMAP‐29 showed positive cooperativity, so the EC50 of the peptide (2.6 µm) was considerably lower than that of the individual LPS‐binding domains. LPS‐binding studies with a mixture of truncated peptides revealed that this cooperativity was primarily intramolecular (i.e. involving the N‐ and C‐terminal LPS‐binding sites of the same peptide molecule). CAP‐18[106−142], an antimicrobial cathelicidin peptide of rabbits, resembled SMAP‐29 in that it contained N‐ and C‐terminal LPS‐binding domains, had an EC50 of 2.5 µm, and bound LPS with positive cooperativity. We conclude that the presence of multiple binding sites that function cooperatively allow peptides such as SMAP‐29 and CAP‐18 to bind LPS with high affinity.
The solution structure of gomesin, an antimicrobial cysteine‐rich peptide from the spider
Authors: Mandard Nicolas , Bulet Philippe , Caille Anita , Daffre Sirlei , Vovelle Françoise
Published: March 2003

Gomesin is the first peptide isolated from spider exhibiting antimicrobial activities. This highly cationic peptide is composed of 18 amino‐acid residues including four cysteines forming two disulfide linkages. The solution structure of gomesin has been determined using proton two‐dimensional NMR (2D‐NMR) and restrained molecular dynamics calculations. The global fold of gomesin consists in a well‐resolved two‐stranded antiparallel β sheet connected by a noncanonical β turn. A comparison between the structures of gomesin and protegrin‐1 from porcine and androctonin from scorpion outlines several common features in the distribution of hydrophobic and hydrophilic residues. The N‐ and C‐termini, the β turn and one face of the β sheet are hydrophilic, but the hydrophobicity of the other face depends on the peptide. The similarities suggest that the molecules interact with membranes in an analogous manner. The importance of the intramolecular disulfide bridges in the biological activity of gomesin is being investigated.
The relationship between airway hyper‐responsiveness, markers of inflammation and lung function depends on the duration of the asthmatic disease
Authors: Grönke L. , Kanniess F. , Holz O. , Jörres R. A. , Magnussen H.
Published: March 2003

Background The combination of airway hyper‐responsiveness, eosinophilic airway inflammation, and lung function impairment is considered as a hallmark of bronchial asthma. Since airway function might change with time in chronic asthma, the association between parameters which are characteristic of asthma could be different in subjects with different durations of the disease.

Objective We assessed whether in patients with asthma the relationship between airway hyper‐responsiveness, non‐invasive markers of airway inflammation, and baseline lung function depended on the duration of the disease.

Methods Sixty‐six non‐smoking patients with mild to moderate allergic asthma without corticosteroids were assigned to two groups, according to a duration of the disease (time interval since doctor's diagnosis) of either ≤ 16 years (median 8 years; mean FEV1, 92.6% pred.; n = 34) or > 16 year (median 25 years; mean FEV1, 87.9% pred.; n = 32).

Results Groups did not differ statistically in PC20FEV1 of methacholine, sputum composition, levels of exhaled nitric oxide (NO), lung function parameters, or history of treatment. There were significant correlations between PC20FEV1, eosinophils and NO in patients with a duration of the disease ≤ 16 year, but no relation to lung function. In contrast, patients with a duration > 16 year showed a correlation between PC20FEV1 of methacholine and lung function but not eosinophils or NO. In both groups, eosinophils and NO were associated with each other. These results were corroborated by the statistical procedure of factor analysis that revealed ‘inflammation’ and ‘lung function’ as major entities and found ‘responsiveness’ to be associated with only one of them in each group.

Conclusion Our data demonstrate that with a shorter duration of the asthmatic disease airway hyper‐responsiveness is associated with airway inflammation, whereas with a longer duration it is associated with impaired lung function, suggesting that in chronic asthma ongoing alterations become the primary determinant of functional characteristics.
Supporting the health and well‐being of people with intellectual disability and high support needs through networking and resource development
Authors: Carlson Glenys
Published: March 2003

The aim of this paper was to describe an innovative network that supports people with intellectual disability in relation to health and well‐being issues. The communication strategies and resources developed by the members of this network are outlined. Occupational therapists have been involved in this network since its inception and some implications for occupational therapists working with people with intellectual disability are identified.
Slow recovery of boreal forest ecosystem following decreased nitrogen input
Authors: Strengbom J. , Nordin A. , Näsholm T. , Ericson L.
Published: March 2003

Ecosystem recovery after decreased input of nitrogen was examined in two different fertilization experiments where the fertilization had been terminated for 9 and 47 years, respectively.

 The species composition of the understorey vegetation showed no signs of recovery 9 years after the fertilization was terminated. Increased sporocarp production of mycorrhizal fungi was seen on formerly fertilized plots compared with plots still receiving N, but the species composition showed large differences compared to control plots.

 In the second experiment, examined 47 years after termination of fertilization, N favoured bryophytes such as Brachythecium reflexum (Starke) Schimp., Plagiothecium denticulatum (Hedw.) Schimp. and the leaf‐parasitic fungus Valdensia heterodoxa Peyronel (attacking Vaccinium myrtillus L.) was more abundant in the formerly N‐treated plots than in controls. The abundance of Hylocomium splendens (Hedw.) Schimp., the most common bryophyte under normal N conditions, showed a contrasting pattern, with less abundance in the formerly N‐treated plots than in controls. Sporocarp production of N‐sensitive mycorrhizal fungi was lower in the formerly N‐treated plots. No difference in plant species composition was noticed for vascular plants.

 These results contrast with other studies that have interpreted reduced N leakage and nutrient levels in trees after decreased N input as a rapid ecosystem recovery. The present study suggests that the time needed for recovery of the ecosystem biota may be substantial in originally N‐limited ecosystems.
A new method of growth analysis for plants that experience periodic losses of leaf mass
Authors: ANTEN N. P. R. , ACKERLY D. D.
Published: March 2003

A new method (the iterative approach) is presented by which growth analyses can be conducted on plants that have been subjected to significant losses in biomass and leaf area between harvests. The method is particularly useful to analyse the effects of defoliation on growth and biomass allocation.

Values for the following parameters can be estimated: absolute growth rate (g day−1), relative growth rate (RGR, g g−1 day−1), net assimilation rate (NAR, g m−2 day−1), leaf area ratio (LAR, m2 g−1), fraction of newly assimilated mass that is allocated to leaf lamina production (flam, g g−1), and daily fractional change in the average specific leaf area of plants (ρ, day−1). These parameters are determined by means of iterations. We defined a number of growth functions, and the values of NAR, flam and the SLA of newly produced leaves were changed until these functions correctly predicted the measured total plant mass, leaf lamina mass and leaf area at the end of the growth period. This avoids having to assume a constant relationship between leaf area and biomass (as in the ‘classical’ approach), and it avoids the use of polynomial functions to fit growth data (as in the ‘functional’ approach) that are unsuitable for fitting data sets exhibiting discontinuities such as abrupt changes in biomass.

The method was applied to a greenhouse experiment in which we analysed the effects of sustained defoliation on growth and biomass allocation in a tropical understorey palm, Chamaedorea elegans Mart.

We showed that C. elegans plants respond to defoliation with a considerable increase in the allocation of new assimilates to lamina growth (flam) and that, despite the repeated loss of leaf area and associated reductions in LAR, they had RGR values that were similar to those of undamaged plants.
Fine root demography and morphology in response to soil resources availability among xeric and mesic sandhill tree species
Authors: Espeleta J. F. , Donovan L. A.
Published: March 2003

Optimality theory suggests that roots should be kept alive until the efficiency of resource acquisition is maximized (i.e. a maximum ratio of benefits to costs). Because root efficiency may vary with environmental conditions, ecological distributions of plant species may be linked to different patterns of root demography.

  In a greenhouse study, we investigated fine root turnover (growth and death) for three woody species from the fall‐line sandhills of the south‐eastern USA. Pinus palustris Mill. is a generalist in this habitat, whereas Quercus marilandica Muenchh. occurs in more fertile, mesic habitats relative to Quercus laevis Walt. Seedlings were grown under four resource treatments (water + nutrients) for 7 months: high resources, low resources, and short‐term exposure (last 2 months of the study) to resource enrichment or depletion.

  Increasing fine root longevity may be optimal in resource‐poor sites because root efficiency may be maximized by less root turnover and resource loss. As expected, fine root death and growth was less in species from xeric habitats (Q. laevis), but greater in species from mesic habitats (Q. marilandica). The generalist species P. palustris exhibited high growth but little death of fine roots.

  When soil resources decrease, less root turnover may reduce resource loss. Fine root growth of all three species decreased at low resources. Fine root death decreased at low resources in Q. marilandica, the only species with significant root death.

  Demographic responses differed between fine roots and leaves. Although leaf and fine root death were greater in Q. marilandica than in Q. laevis, leaf death, unlike root death, did not change with resource availability. Short‐term resource enrichment or depletion affected leaf production but not fine root demography in the Quercus species.

  Given that fine root morphology affects root maintenance and construction costs, we expected greater fine root growth and death in species with thinner roots of high specific root length (SRL) and low density. However, the species with the greatest root turnover, Q. marilandica, had thick and dense roots of low SRL.

  Results from our study with woody species indicate that fine root demography, but not fine root morphology, was linked to ecological distribution in a narrow geographical range. Differences in fine root turnover under different resource availability were consistent with the optimality theory, and may reflect trade‐offs between tolerance and competitive ability below ground: less root turnover of xeric species under low fertility may conserve resources, whereas faster root growth of mesic species potentially maximizes resource uptake in more fertile soils.
Ecosystem respiration in two Mediterranean evergreen Holm Oak forests: drought effects and decomposition dynamics
Authors: Reichstein M. , Tenhunen J. D. , Roupsard O. , Ourcival J.‐M. , Rambal S. , Dore S. , Valentini R.
Published: March 2003

We present ecosystem respiration data from two Mediterranean forest sites in central Italy (Castelporziano) and southern France (Puéchabon) in order to analyse the role of soil drought and decomposition dynamics using different models.

 Ecosystem respiration was derived from continuous eddy covariance measurements. The entire data set was separated into 5‐day periods. For each period a function depending on three parameters was fitted to the scatter of eddy CO2 flux versus photosynthetic photon flux density. The y intercept of each curve was taken as an estimate of the average night‐time ecosystem respiration during the period. The ecosystem respiration was analysed with different regression models as a function of soil water content and temperature.

Ecosystem respiration ranged from 1 to 7 µmol m−2 s−1 and showed a clear seasonality, with low rates during drought periods and in winter. The regression model analysis revealed that in drier soil, ecosystem respiration was more sensitive to soil moisture than is expressed by the often used hyperbolic model.

In contradiction to a simple multiplicative model, the Q10 of ecosystem respiration was not independent of moisture, but increased from nearly 1·0 at low moisture to above 2·0 at field capacity. Several explanations are discussed.

Of the variance in ecosystem respiration, 70–80% was explained with a model where Q10 of ecosystem respiration is a function of soil water content.

 For the Puéchabon site, a soil carbon‐balance model predicted only small changes in litter pool size (max. 7%), which caused only minor changes in soil microbial respiration (0·1 µmol m−2 s−1). In contrast, the contribution of microbial regrowth dynamics to ecosystem respiration is estimated to be substantial (≈1·6 µmol m−2 s−1). The model predicted that soil microbial respiration probably provides the largest contribution to ecosystem respiration (≈50%). The importance of below‐ground processes for ecosystem C balances is thus emphasized.
Inhibin B in boys from birth to adulthood: relationship with age, pubertal stage, FSH and testosterone
Authors: Crofton P. M. , Evans A. E. M. , Groome N. P. , Taylor M. R. H. , Holland C. V. , Kelnar C. J. H.
Published: March 2003

objective Inhibin B in males is produced principally by Sertoli cells under the influence of FSH and is thought to have a role in feedback regulation of FSH. The aims of our study were to investigate how inhibin B changes from birth to late adolescence in boys, to derive reference data and to explore its relation with pubertal stage, FSH and testosterone.

design and subjects Blood samples were collected from (i) 366 boys aged 0–18 years to obtain age‐related reference data; (ii) 195 boys who had full pubertal staging; and (iii) a cohort of 15 boys studied longitudinally as they approached and entered early puberty.

measurements Dimeric inhibin B was measured by double antibody enzyme‐linked immunosorbent assay (ELISA), FSH by immunoradiometric assay (IRA) and testosterone by an extraction radioimmunoassay.

results Inhibin B was high in infant boys, decreased gradually to a nadir at 6–10 years of age, then increased rapidly in early adolescence to reach a new plateau at 12–17 years. It was detectable in all samples. Age‐related reference ranges and data for calculation of SD scores are presented. In prepubertal boys, inhibin B correlated positively with age (P < 0·001), but not with FSH. Inhibin B increased progressively from pubertal stages G1 to G3 but then decreased slightly at stages G4 to G5 (P ≤ 0·01). At stage G2, inhibin B correlated positively with testosterone (P < 0·01) but not with FSH. From stage G3 onwards, inhibin B correlated inversely with FSH (P < 0·01) but lost its relationship with testosterone. In the cohort of boys studied longitudinally, inhibin B increased progressively prior to pubertal onset and further on entry into early clinical puberty (P < 0·05). Testosterone also increased over this period (P < 0·05) but FSH showed no significant change.

conclusions The two peaks of inhibin B during infancy and early puberty appear to reflect the two periods of Sertoli cell proliferation in normal human males. During mid‐childhood, a relatively constant amount of inhibin B is secreted constitutively. The early FSH‐independent increase in inhibin B that precedes clinical puberty and continues to stage G2 may be stimulated by testosterone or other factors from Leydig cells. The inverse relationship between inhibin B and FSH that subsequently develops from mid‐puberty onwards is consistent with the establishment of a negative feedback loop at this time.
Hyperkalaemia and selective hypoaldosteronism in myotonic dystrophy*
Authors: Misra Dolly , DeSilva Shari , Fellerman Herbert , Dufour D. Robert , Streeten David H.P. , Nylen Eric S.
Published: March 2003

Myotonic dystrophy (MyD) is a common genetic neuromuscular disorder in which chromosome 19 gives rise to an abnormal expansion of CTG‐trinucleotide repeats. MyD is a highly variable multisystem disorder with muscular and nonmuscular abnormalities. Increasingly, endocrine abnormalities, such as gonadal, pancreatic, and adrenal dysfunction are being uncovered. Herein we present three unrelated cases with MyD with abnormally elevated serum potassium; 2 of the 3 cases presented clinically with cardiac dysrhythmias. Hyperkalaemic conditions such as renal failure, cortisol deficiency, pseudohyperkalaemia, and hyperkalaemic periodic paralysis were excluded. Further endocrine evaluation revealed baseline hypoaldosteronism associated with elevated renin activity. Perturbation of the renin‐angiotensin‐aldosterone system resulted in appropriately enhanced renin activity but with a subnormal aldosterone response, which appeared to be due to adrenal hyporesponsivness. The treatment of all cases with fludrocortisone was without effect. Whether the apparent mineralocorticoid abnormality in MyD is due to associated hormonal perturbations (i.e. excessive ACTH responsivness. elevated cytokines, elevated atrial natriuretic hormone, etc.), adrenal atrophy, and/or a manifestation of the underlying kinase dysfunction is uncertain, but merits further evaluation in view of the clinical consequence of hyperkalaemia.
Pharmacokinetics of sildenafil after single oral doses in healthy male subjects: absolute bioavailability, food effects and dose proportionality
Authors: Nichols Donald J. , Muirhead Gary J. , Harness Jane A.
Published: March 2003

Aims  To determine the absolute bioavailability, dose proportionality and the effects of food on the pharmacokinetics of single oral doses of sildenafil citrate.

Methods  Three open‐label, randomized crossover studies were conducted in healthy male subjects. Absolute bioavailability was determined by comparing pharmacokinetic data after administration of single oral and intravenous 50‐mg doses of sildenafil (n=12 subjects). Food effects were examined by comparing pharmacokinetic data for sildenafil and its primary circulating metabolite, UK‐103,320, after administration of a single oral 100‐mg dose in the fasted and fed states (n=34 subjects). Dose proportionality was assessed from pharmacokinetic data obtained after administration of four single oral doses of sildenafil (25, 50, 100 and 200 mg) to 32 subjects. The safety and tolerability of sildenafil were also assessed in all of these studies.

Results  The calculated absolute oral bioavailability of sildenafil was 41% (90% CI: 36–47). Food slowed the rate of absorption, delaying mean tmax by approximately 1 h and reducing Cmax by 29% (90% CI: 19–38). Systemic exposure, as assessed by the mean area under the plasma concentration–time curve (AUC), was reduced by 11% (90% CI: 6–16). These food effects were not considered to be of clinical significance. There was statistical evidence of nonproportionality in Cmax and AUC over the dose range 25–200 mg. However the degree of nonproportionality was small, with predicted increases in Cmax and AUC of 2.2‐ and 2.1‐fold, respectively, for a doubling in dose, and was thought to be clinically nonsignificant. Sildenafil was well tolerated in the three studies; the majority of adverse events were mild and transient.

Conclusions  Sildenafil had a mean absolute bioavailability of 41%. Food caused small reductions in the rate and extent of systemic exposure; these reductions are unlikely to be of clinical significance. Across the dose range of 25–200 mg, systemic exposure increased in a slightly greater than dose‐proportional manner.
Comparison of clozapine and haloperidol on some autonomic and psychomotor functions, and on serum prolactin concentration, in healthy subjects
Authors: Pretorius J. L. , Phillips M. , Langley R. W. , Szabadi E. , Bradshaw C. M.
Published: March 2003

Aims
To compare the autonomic, neuroendocrine and psychomotor effects of single doses of the ‘atypical’ antipsychotic clozapine and the ‘classical’ antipsychotic haloperidol, in healthy male volunteers.

Methods
Clozapine (50 mg), haloperidol (3 mg) and placebo were administered to 12 healthy male volunteers at weekly intervals, according to a balanced double‐blind design. Resting pupil diameter, salivary output, heart rate, blood pressure, plasma prolactin concentration, critical flicker fusion frequency and subjective ‘alertness’, ‘contentedness’ and ‘anxiety’ were measured at baseline and 2, 3, 4 and 5 h after drug ingestion. Data were analysed by analysis of variance with individual comparisons (Dunnett's test) with a significance criterion of P < 0.05.

Results
Significant treatment effects (difference from placebo [mean, 95% CI] 5 h after drug ingestion) were as follows: clozapine reduced pupil diameter (mm; −3.02 [−3.56, −2.47]), salivary output (g; −0.34 [−0.60, −0.08]), mean arterial blood pressure (mm Hg; −8.7 [−14.3, −3.1]), critical flicker fusion frequency (Hz; −3.26 [−3.94, −2.58]), and subjectively‐rated ‘alertness’ (mm; −20.94 [−29.21, −12.67]) and ‘contentedness’ (mm; −12.98 [−17.90, −8.06]), whereas haloperidol increased prolactin concentration (mU l−1; 301.3 [196.7, 405.8]) and caused small reductions in pupil diameter (mm; −0.68 [−1.23, −0.14]), mean arterial blood pressure (mm Hg; −7.0 [−12.6, −1.4]) and critical flicker fusion frequency (Hz; −1.15 [−1.83, −0.47]).

Conclusions
The effects of the antipsychotics are in agreement with their receptor binding profiles: α1‐adrenoceptor blockade by clozapine may contribute to reductions in pupil diameter, salivation, mean arterial blood pressure and sedation, and muscarinic cholinoceptor blockade by the drug may underlie the reduction in salivation. Conversely, D2 dopamine receptor blockade by haloperidol is likely to be responsible for the increase in prolactin secretion evoked by the drug.
Effect of local hyperthermia of the bladder on mitomycin C pharmacokinetics during intravesical chemotherapy for the treatment of superficial transitional cell carcinoma
Authors: Paroni Rita , Salonia Andrea , Lev Avigdor , Da Pozzo Luigi Filippo , Cighetti Giuliana , Montorsi Francesco , Rigatti Patrizio , Colombo Renzo
Published: March 2003

Aims  To assess the effect of local hyperthermia on the systemic absorption of mitomycin C (MMC) during intravesical chemotherapy for the treatment of superficial transitional cell carcinoma of the bladder, and to establish the likely safety of this procedure.

Methods  Group 1 (n = 12) received 20 mg intravesical MMC plus local hyperthermia, group 2 (n = 13) 20 mg MMC alone, group 3 (n = 16) 40 mg MMC plus local hyperthermia and group 4 (n = 10) 40 mg MMC alone. Patients in groups 1, 2, and 4 underwent post‐tumour resection adjuvant treatment, whereas those in group 3 still had tumour present and were treated to eradicate it. Intravesical instillation lasted 60 min, with the solution (50 ml) being replaced after the first 30 min. Blood samples were taken before, and every 15 min during instillation. MMC concentrations in plasma and in urine were determined by h.p.l.c.

Results  The highest MMC plasma concentration (67.9 ng ml−1) occurred in a patient in group 3. This value was well below the threshold concentration (400 ng ml−1) for myelosuppression. Local hyperthermia associated with the intravesical chemotherapy enhanced plasma MMC concentrations at 30, 45 and 60 min compared with chemotherapy alone (Group 1 vs 2, P ≤ 0.008). Systemic exposure to MMC was not significantly increased by doubling the intravesical dose when intravesical chemotherapy alone was administered. Patients in group 3 displayed the highest degree of MMC absorption and the greatest variability in pharmacokinetics between patients.

Conclusions  Local hyperthermia enhances the systemic absorption of MMC during intravesical chemotherapy for bladder cancer. In the doses used, plasma MMC concentrations were always more than six times lower than those shown to cause toxicity.
Saquinavir and ritonavir pharmacokinetics following combined ritonavir and saquinavir (soft gelatin capsules) administration
Authors: Buss Neil , Snell Paul , Bock Jürgen , Hsu Ann , Jorga Karin
Published: March 2003

Aims  To investigate the influence of combined ritonavir (RTV) and saquinavir (soft‐gelatin capsule formulation; SQV) on systemic exposure to SQV with a view to optimizing the dosing regimen of combined RTV and SQV antiretroviral therapy.

Methods  In this open labelled, randomized, parallel group study, SQV and RTV were administered twice daily for 14 days to groups of eight healthy subjects. The two antiretrovirals were either administered alone (800 mg SQV, regimen A, and 400 mg RTV, B) or in combination at various dose levels (RTV : SQV: 400 : 400 mg, C; 300 : 600 mg, D; 200 : 800 mg, E; 300 : 800 mg, F; 400 : 800 mg, G; and 400 : 600 mg, H). Pharmacokinetic parameters of saquinavir and ritonavir were determined and adverse events, vital signs, and clinical laboratory variables recorded.

Results  RTV substantially increased the plasma concentration of saquinavir for all dose combinations, compared with SQV alone. Based on the primary statistical analysis there was an overall 17‐, 22‐, and 23‐fold increase in saquinavir AUC(0,24 h) on day 14 with regimens E, F, and G, respectively (with confidence intervals of 10–30, 13–37, and 13–39). The lowest combination dose of RTV (200 : 800 mg; E) significantly increased the saquinavir AUC(0,24 h) from below 5 to 57 µg ml−1 h, which was higher than the exposure obtained with the 400 : 400 mg twice daily regimen (i.e. 36 µg ml−1 h). RTV also reduced intersubject variability in AUC(0,24 h) for saquinavir from 105% to 32–68%, and Cmax(0,24 h) from 124% to 30–49%. In contrast, SQV showed no clinically significant effect on the pharmacokinetics of ritonavir. The combination regimens were well tolerated, with the least number of adverse events recorded for the 200 : 800 mg (RTV : SQV) combination regimen.

Conclusions  RTV significantly increases saquinavir exposure as a consequence of inhibiting SQV metabolism and possibly P‐glycoprotein efflux. Pharmacokinetic and safety profiles obtained in the current study indicate that the use of a combination with a lower dose of RTV and a higher dose of SQV than the 400 : 400 mg combination frequently used in clinical practice should be further explored.
The prevention of migraine: a critical review with special emphasis on β‐adrenoceptor blockers
Authors: Limmroth Volker , Michel Martin C.
Published: March 2003

Migraine is one of the most frequent neurological disorders affecting up to 15% of the general population. Many patients require not only management of individual migraine episodes but also prophylactic treatment. β‐adrenoceptor blockers, flunarizine and valproic acid have been established as first‐line agents for the prophylaxis of migraine attacks. Among the β‐adrenoceptor blockers propranolol and metoprolol are best documented and hence deserve preferential use. On the other hand, it appears that other β‐adrenoceptor blockers, perhaps with the exception of those with intrinsic sympathomimetic activity, can be equally effective. Uncertainties regarding the relative merits of various treatment modalities are largely caused by lack of adherence to specific requirements for clinical trials on migraine prophylaxis. Therefore, this article reviews internationally recommended conditions for reliable studies on migraine prophylaxis and appraises individual agents in the light of these criteria.
Polymorphisms of CYP2A6 and its practical consequences
Authors: Raunio Hannu , Rautio Arja , Gullstén Harriet , Pelkonen Olavi
Published: March 2003

CYP2A6 is an hepatic enzyme predominantly with some expression in specialized extrahepatic cell types. The CYP2A6 enzyme has a somewhat restricted active site, accepting only a few xenobiotics as substrates. Interest in CYP2A6 has risen considerably after nicotine and some tobacco specific nitrosamines were established as high‐affinity substrates for this enzyme. Recently, the organization and structures of the CYP2A gene cluster and several polymorphic alleles of the CYP2A6 gene have been characterized. Two alleles with a point mutation and at least three different types of gene deletion, all leading to deficient gene function, have been found. The frequencies of these alleles vary considerably among different ethnic populations, the deletion alleles being most common in Orientals (up to 20%). The frequency of point mutations are low in all populations studied thus far (< 3%). Several case‐control studies have addressed the relationship between CYP2A6 status and smoking habits as well as the role of CYP2A6 polymorphism in lung cancer risk. Studies in Japanese suggest that CYP2A6 poor metabolizer genotypes result in altered nicotine kinetics and may lower cigarette smoking elicited lung cancer risk, whereas similar studies in Caucasian populations have not revealed any clear associations between variant CYP2A6 genotypes and smoking behaviour or lung cancer predisposition.
Distribution of R‐ and S‐methadone into human milk during multiple, medium to high oral dosing
Authors: Begg Evan J. , Malpas Timothy J. , Hackett L. Peter , Ilett Kenneth F.
Published: March 2003

Aims  To measure the interdose milk to plasma ratio (M/P) of R‐ and S‐methadone during multiple dosing in lactating mothers taking medium to high doses of methadone (> 40 mg daily), and to assess likely infant exposure.

Methods  Eight mother/child pairs were studied, initially during their postpartum hospital stay (immature milk), and where possible again after 15 days (mature milk). The women were on a methadone maintenance programme with daily doses of ≥40 mg day−1. Venous blood was collected at 0, 1, 2, 4, 6, 8, 12, and 24 h and milk was collected from both breasts at 0–4, 4–8, 8–12, 12–16, 16–20, and 20–24 h after dose. R‐ and S‐methadone were quantified by h.p.l.c. The areas under the plasma and milk concentration‐time curves (AUC) were estimated and M/PAUC was calculated. The relative infant dose of both enantiomers was estimated as the product of drug concentration in milk and an average daily milk intake of 0.15 l kg−1.

Results  For immature milk (n = 8) the M/PAUC for R‐methadone was 0.68 (95% CI 0.48, 0.89) and for S‐methadone 0.38 (0.26, 0.50). For mature milk (n = 2) the M/PAUCs for R‐methadone were 0.39 and 0.54 and for S‐methadone 0.24 and 0.30, respectively. The estimated doses of R‐ and S‐methadone that would be received by the infant via immature milk were 3.5% (2.05, 5.03%) and 2.1% (1.3, 2.8%), respectively, of the maternal dose (assuming 50% of each enantiomer in the dose). The relative infant dose for R‐ plus S‐methadone together was 2.8% (1.7, 3.9%).

Conclusions  Breastfeeding during medium to high dose methadone appears to be ‘safe’ according to conventional criteria because the dosage is < 10%. However because the absolute dose received by the infant is dependent on the maternal dose rate, the risk‐benefit ratio should be considered for each individual case. The doses of methadone received via milk are unlikely to be sufficient to prevent the neonatal abstinence syndrome.