First Observation of the Four-Proton Unbound Nucleus ^{18}Mg

^{18}Mg was observed, for the first time, by the invariant-mass reconstruction of ^{14}O+4p events. The ground-state decay energy and width are E_{T}=4.865(34)  MeV and Γ=115(100)  keV, respectively. The observed momentum correlations between the five particles are consistent with two sequential steps of prompt 2p decay passing through the ground state of ^{16}Ne. The invariant-mass spectrum also provides evidence for an excited state at an excitation energy of 1.84(14) MeV, which is likely the first excited 2^{+} state. As this energy exceeds that for the 2^{+} state in ^{20}Mg, this observation provides an argument for the demise of the N=8 shell closure in nuclei far from stability. However, in open systems this classical argument for shell strength is compromised by Thomas-Ehrman shifts.

Acute mesenteric ischaemia: A case of expedited diagnosis and management using point-of-care ultrasound

INTRODUCTION

The term acute abdomen refers to a clinical syndrome of sudden onset, severe abdominal pain. The differential diagnosis for this presentation is broad, but most cases require emergent medical or surgical management. Especially in cases of ischaemic bowel, time to diagnosis can mean the difference between survival and death. As a result, mortality remains high in resource-limited settings.

CASE REPORT

We describe the case of a 28-year-old male who presented to an urban Ethiopian emergency centre with three days of vomiting, bloody diarrhoea, and abdominal pain. He collapsed in triage with weak pulses and an undetectable blood pressure. Point-of-care ultrasound revealed a hyperechoic, mobile mass in the left ventricle of the heart. Small bowel dilation and thickening was visualised throughout the abdomen. Mesenteric ischaemia was rapidly identified as the working diagnosis, prompting early surgical consultation and aggressive, goal-directed resuscitation.

DISCUSSION

Short of elucidating a definitive diagnosis, ultrasound narrowed the focus of an undifferentiated presentation and supported mobilisation for exploratory laparotomy. Ultimately, this circumvented several hours of time which is conventionally required to obtain computed tomography at this institution. As demonstrated in this case, point-of-care ultrasound can be life-saving in resource-limited settings where acquisition time for definitive imaging is often prohibitive.

Lipid-mediated protein functionalization of electrospun polycaprolactone fibers

In this study, electrospun polycaprolactone (PCL) fibers are plasma-treated and chemically conjugated with cholesteryl succinyl silane (CSS). In addition to Raman spectroscopy, an immobilization study of DiO as a fluorescent probe of lipid membranes provides evidence supporting the CSS coating of plasma-treated PCL fibers. Further, anti-CD20 antibodies are used as a model protein to evaluate the potential of lipid-mediated protein immobilization as a mechanism to functionalize the CSS-PCL fiber scaffolds. Upon anti-CD20 functionalization, the CSS-PCL fiber scaffolds capture Granta-22 cells 2.4 times more than the PCL control does, although the two fiber scaffolds immobilize a comparable amount of anti-CD20. Taken together, results from the present study demonstrate that the CSS coating and CSS-mediated antibody immobilization offers an appealing strategy to functionalize electrospun synthetic polymer fibers and confer cell-specific functions on the fiber scaffolds, which can be mechanically robust but often lack biological functions.

Enterocutaneous fistula as early presentation of Crohn's disease in an adult woman

Crohn's disease is a chronic transmural inflammatory process that primarily affects the gastrointestinal tract, with several extra-intestinal manifestations. Though patients usually present with vague abdominal pain, initial presentation can be at an advanced stage or with extra-intestinal pathology. The authors report the case of a 59-year-old woman, who presented with a tubo-ovarian abscess that resulted in a protracted non-healing enterocutaneous fistula, which was eventually diagnosed as Crohn's disease approximately 2 years after initial presentation. Relevant literature is reviewed, as well as time-points where an earlier diagnosis could have been made thereby underscoring the importance of considering Crohn's Disease in a non-healing enterocutaneous fistula in an otherwise asymptomatic patient.

Endogenous -Carbolines as Clonidine-Displacing Substances

Endogenous beta-carbolines, such as harmane, are known to occur in mammalian species including humans. Radioligand binding studies have revealed that certain beta-carbolines display high affinity for both I(1) and I(2) imidazoline-binding sites (IBS). Functional studies have shown that the beta-carboline harmane elicits many characteristics expected of an endogenous ligand IBS. This article discusses the evidence relating to beta-carbolines as endogenous ligands and presents a case for harmane and related compounds as endogenous ligands for IBS.

Reduction in excess daytime sleepiness by modafinil in patients with myotonic dystrophy

Patients with myotonic dystrophy frequently suffer from excess daytime sleepiness, which can be a significant cause of disability. Previous studies have indicated that this excess daytime sleepiness is only occasionally due to obstructive sleep apnoea and may be principally of central nervous system origin. Modafinil has been successfully used to treat narcolepsy, a central disorder causing excess daytime sleepiness. We have investigated the use of this drug in myotonic dystrophy patients with excess daytime sleepiness. Patients were recruited from a clinic population on the basis of screening with the Epworth Sleepiness Scale. Patients scoring 10 and above were invited to participate in a randomized double-blind crossover trial of modafinil versus placebo, with four weeks in each arm of the study separated by a 2-week washout period. Patients were assessed by polysomnography at baseline. The primary outcome measures were change in both the Epworth Sleepiness Scale and a modified Maintenance of Wakefulness Test, which were measured at the start of each arm of the trial and in week 3 of each intervention period. In agreement with previous smaller studies, sleepiness is not correlated with CTG expansion size. Treatment with modafinil showed a non-significant reduction in median Epworth Sleepiness Scale. However, the median Maintenance of Wakefulness Test score was prolonged by treatment (31.7-40 min, P=0.006). There were no significant adverse cardiac effects of the drug in this group of patients (resting 12 lead and 24 h ECG monitoring). Selected patients with myotonic dystrophy and excess daytime sleepiness may benefit from modafinil. In this patient group the Epworth Sleepiness Scale may not be the most reliable measure of sleepiness. Despite the potential for cardiac disease in these patients, the drug was well tolerated with no adverse effects.

First in vitro directed biosynthesis of new compounds by a minimal type II polyketide synthase: evidence for the mechanism of chain length determination

The minimal actinorhodin polyketide synthase bearing two point mutations (KSbeta Q161A, ACP C17S) was chemically modified to carry novel C4 to C8 starter units on the ACP: on incubation with an excess of malonyl CoA new 16-carbon polyketides are made, supporting a measuring mechanism.

Evaluation of glucose as a cryoprotectant for boar semen

Fertility parameters of boar spermatozoa were evaluated in vitro, after freeze-thawing the semen in three different extenders containing permeable and non-permeable cryoprotectants: A (111.0 mM Tris, 31.4 mM citric acid, 185.0 mM glucose, 20 per cent egg yolk, 3 per cent glycerol and 100 iu/ml penicillin G); B (200 mM Tris; 70.8 mM citric acid, 55.5 mM glucose, 20 per cent egg yolk, three per cent glycerol and 100 iu/ml penicillin G); C (200 mM Tris, 70.8 mM citric acid, 55.5 mM fructose, 20 per cent egg yolk, 3 per cent glycerol and 100 iu/ml penicillin G). The freeze-thawing techniques were the same for each extender. Eight ejaculates from four boars were obtained; the sperm-rich fraction of each ejaculate was extended in each of the three media at a final concentration of 400 x 106 sperm/ml, loaded into 0.5 ml straws and frozen at a rate of 30 degrees C/minute to -196 degrees C. The straws were thawed at 60 degrees C for eight seconds. Sperm motility, acrosomal integrity and in vitro sperm penetration through the zona pellucida of gilt oocytes matured in vitro were evaluated. The motility of unfrozen spermatozoa was 93.1 per cent compared with 60.7 per cent, 48.2 per cent and 35 per cent for sperm frozen in extenders A, B and C respectively; these values were all significantly different (P<0.05). There was no significant decline in sperm motility after incubation for 30 minutes in extender A, but there were significant decreases in sperm motility after 30 minutes of incubation in B and C. The percentage acrosomal integrities were 97.2 per cent for the control and 45.5 per cent, 30.3 per cent and 16.8 per cent for the frozen-thawed spermatozoa in extenders A, B and C respectively. The results of the in vitro penetration assay were 80.7 per cent when using control spermatozoa, and 42.2 per cent, 18.4 per cent and 3.3 per cent when using frozen-thawed spermatozoa in extenders A, B and C respectively

CD4(+) T cell-dependent airway mucus production occurs in response to IL-5 expression in lung

The potential role of airway interleukin-5 (IL-5) expression in eliciting mucus production was demonstrated in a pulmonary IL-5 transgenic mouse model (NJ.1726) in which naive transgenic mice display comparable levels of airway mucus relative to allergen-sensitized and -challenged wild-type mice. The intrinsic mucus accumulation of NJ.1726 was abolished in compound transgenic-gene knockout mice deficient of either CD4(+) cells [NJ.1726/CD4(-/-)] or alphabeta T cell receptor-positive (TCR(+)) cells [NJ.1726/alphabeta TCR(-/-)]. In addition, mucus production in naive NJ.1726 was inhibited by >90% after administration of the soluble anti-IL-4 receptor alpha-subunit antagonist. The loss of mucus production in NJ.1726/CD4(-/-), NJ.1726/alphabeta TCR(-/-), and anti-IL-4 receptor alpha-subunit antagonist-treated mice occurred notwithstanding the significant pulmonary eosinophilia and expansion of airway B cells induced by ectopic IL-5 expression. Furthermore, the loss of mucus accumulation occurred in these mice despite elevated levels of airway and peripheral IL-5, indicating that IL-5 does not directly induce goblet cell metaplasia and mucus production. Thus pulmonary expression of IL-5 alone is capable of inducing CD4(+) T cell-dependent goblet cell metaplasia, apparently mediated by IL-4 receptor alpha-subunit-ligand interactions, and represents a previously unrecognized novel pathway for augmenting allergen-induced mucus production.

The Scottish doctor--learning outcomes for the medical undergraduate in Scotland: a foundation for competent and reflective practitioners

This paper describes a set of learning outcomes that clearly define the abilities of medical graduates from any of the five Scottish medical schools. The outcomes are divided into 12 domains that fit into one of three essential elements for the competent and reflective medical practitioner.

beta-carboline binding to imidazoline receptors

A series of beta-carbolines were prepared and their affinities for imidazoline (I(1) and I(2)) sites evaluated. Selected compounds were also examined at alpha(2)-adrenoceptors. Some of the beta-carbolines were found to bind with high affinity to I(2)-sites and this affinity was dependent on both the planarity of the molecule and the presence of the aryl ring substituents. Good I(1)-affinity was observed with two of the compounds but none of the tested compounds bound to alpha(2)-adrenoceptors. The hallucinogenic properties of beta-carbolines have been linked to activity at 5-HT receptors, in particular 5-HT(2), however, it is apparent from this study that many of these compounds display substantially higher affinity for the imidazoline sites. This finding, and those showing modulation of some behavioural effects of morphine by I(2)-ligands, suggests that imidazoline sites may be interesting new targets in drug abuse research.

Intrinsic AHR in IL-5 transgenic mice is dependent on CD4(+) cells and CD49d-mediated signaling

Overexpression of interleukin (IL)-5 by the airway epithelium in mice using the rat CC10 promoter (NJ.1726 line) leads to several histopathologies characteristic of human asthma, including airway hyperreactivity (AHR). We investigated the contribution of B and T cells, as well as CD4 expression, to the development of AHR in IL-5 transgenic mice. NJ.1726 mice on a T cell or CD4 knockout background, but not on a B cell knockout background, lost intrinsic AHR. These effects occurred without decreases in IL-5 or eosinophils. We further investigated the contribution of alpha(4)-integrin signaling to the development of AHR in IL-5 transgenic mice through the administration of anti-CD49d (alpha(4)-integrin) antibody (PS/2). Administration of PS/2 resulted in immediate (16-h) inhibition of AHR. The inhibition of AHR was not associated with a decrease in airway eosinophils. These studies demonstrate that, despite the presence of increased levels of IL-5 and eosinophils in the lungs of NJ.1726 mice, CD4(+) cells and alpha(4)-integrin signaling are necessary for the intrinsic AHR that develops in IL-5 transgenic mice.

What do master surgeons think of surgical competence and revalidation?

BACKGROUND

There has been on-going debate and public interest in surgical competence in recent years.

METHODS

A Delphi reiterative opinion survey was conducted among master surgeons on selection of surgical trainees, methods of assessment of progress of surgical trainees, and revalidation of established consultant surgeons.

RESULTS

Selection-the current methods of trainee selection were considered inadequate and in need of revision. The important attributes recognized by group are cognitive factors, innate dexterity, and personality. Important aspects of personality include decision-making ability, insight, team spirit, and emotional stability. Assessment during training-the majority view was that this should be based on clinical judgement/skills, operative skills, and cognitive ability. Assessment of technical ability should be based on standardized checklists. Research within training programs was encouraged but academic achievement does not reflect surgical competence. There was a majority verdict for an exit clinical examination. Revalidation-the group agreed on the need for competence checks during the professional career of surgeons. These should cover knowledge, clinical, operative, and humanistic skills; but expressed concern on the feasibility of a revalidation system that can reliably assess the range of skills needed for surgical competence. There was a majority vote against an internal appraisal system. External assessment by nationally appointed 'assessors' was considered preferable.

CONCLUSIONS

Both selection and assessment of surgical trainees require changes and standardization. Although revalidation is necessary, concern was expressed on the reliability and validity of existing and proposed systems.

Blockade of CD49d inhibits allergic airway pathologies independent of effects on leukocyte recruitment

Lymphocyte and/or eosinophil recruitment is dependent on the sequential interactions between adhesion molecules expressed on activated endothelial cells and both leukocyte subtypes. Endothelial P- and E-selectins mediate tethering and rolling of leukocytes through interactions with P-selectin glycoprotein ligand-1 (PSGL-1), and diapedesis subsequently occurs by engagement of endothelial vascular cell adhesion molecule-1 and CD49d (alpha(4)-integrins). The anti-inflammatory potential of interfering with these adhesive interactions was assessed with an ovalbumin challenge mouse model of asthma. Administration of a soluble form of PSGL-1 reduced eosinophils (80%) and lymphocytes (50%) in bronchoalveolar lavage fluid without affecting epithelial changes or airway hyperreactivity (AHR). In contrast, although administration of anti-CD49d monoclonal antibodies (PS/2) resulted in similar reductions in eosinophils (75%) and lymphocytes (50%), PS/2 reduced and abolished mucous cell metaplasia and AHR, respectively. Administration of both PSGL-1 and PS/2 had the additive effect of eliminating eosinophils from the airways (96% decrease), with few or no additional reductions (relative to PS/2 administration alone) in lymphocyte recruitment, mucous cell metaplasia, or AHR. These data show that eosinophils and lymphocytes differentially utilize adhesive interactions during recruitment and that the inhibition of AHR is independent of this recruitment.

Solid phase synthesis of 4-hydroxycinnamic acid and its derivatives for potential use in combinatorial chemistry: a novel route for the synthesis of 4-hydroxycinnamoyl coenzyme A and NMDA receptor antagonists

Synthesis of 4-hydroxycinnamic acid 6 and its N-hydroxysuccinimide ester 8 has been carried out in high yield on solid support. Further development allowed the synthesis of 4-hydroxycinnamoyl CoA 1 in excellent overall yield. The utility of solid phase as a method for the synthesis of 4-hydroxycinnamic acid derivatives was demonstrated by the synthesis of a number of compounds including the NMDA receptor antagonists, N-(phenylalkyl)cinnamides 9 and 10.

Task-based learning: the answer to integration and problem-based learning in the clinical years

INTRODUCTION

Integrated teaching and problem-based learning (PBL) are powerful educational strategies. Difficulties arise, however, in their application in the later years of the undergraduate medical curriculum, particularly in clinical attachments. Two solutions have been proposed - the use of integrated clinical teaching teams and time allocated during the week for PBL separate from the clinical work. Both approaches have significant disadvantages. Task-based learning (TBL) is a preferred strategy. In TBL, a range of tasks undertaken by a doctor are identified, e.g. management of a patient with abdominal pain, and these are used as the focus for learning. Students have responsibility for integrating their learning round the tasks as they move through a range of clinical attachments in different disciplines. They are assisted in this process by study guides.

METHOD

The implementation of TBL is described in one medical school. One hundred and thirteen tasks, arranged in 16 groups, serve to integrate the student learning as they rotate through 10 clinical attachments.

RESULTS

This trans-disciplinary approach to integration, which incorporates the principles of PBL offers advantages to both teachers and students. It recognizes that clinical attachments in individual disciplines can offer rich learning opportunities and that such attachments can play a role in an integrated, as well as in a traditional, curriculum. In TBL, the contributions of the clinical attachments to the curriculum learning outcomes must be clearly defined and tasks selected which will serve as a focus for the integration of the students' learning over the range of attachments.

Isolation of RP-HPLC pure clonidine-displacing substance from NG108-15 cells

A crude extract of clonidine-displacing substance (CDS) has previously been extracted from the NG108-15 cell line. This study aimed to purify CDS extracted from this cell line further, by the technique of reverse phase-HPLC (RP-HPLC), and subsequently determine whether this refined CDS bears any similarity to CDS's extracted from other tissues. Crude CDS was extracted from NG108-cells and fractionated by RP-HPLC eluting with a linear gradient of methanol (5-65%; 1 ml min(-1) flow rate) over 50 min., and collected at 1 min. intervals. The pharmacological activities of the CDS fractions were determined by their abilities to displace bound [3H]clonidine to alpha(2)-adrenoceptors in rat brain membranes. RP-HPLC analysis of CDS revealed a pharmacologically active fraction distinct from agmatine, eluting at 24 min, corresponding to an absorbance peak observed at this time. Collectively, these results confirmed that CDS was present in the NG108-15 cell line. However, the RP-HPLC analysis showed the pharmacological activity to elute at a more hydrophobic gradient than previously observed with CDS's extracted from bovine tissues. These results support the notion of the existence of several CDS's.

Sunscreen protection against cis-urocanic acid production in human skin

Commercial sunscreens may offer some protection from immunosuppression induced by ultraviolet (UV) radiation, but agreement concerning the degree of protection is lacking. Cis-urocanic acid, formed by the photoisomerization of transurocanic acid is considered an important mediator of the cutaneous immunomodulation resulting from exposure to UV radiation. We investigated the effect of sunscreens on the isomerization of urocanic acid in 17 human subjects. Two sunscreens containing chemical filters, sun protection factor (SPF) 4 and SPF 10, and a SPF 10 sunscreen with a physical filter were applied at a thickness of 2 mg/cm2. The effect of a thin layer (0.5 mg/cm2) of the chemical SPF 10 sunscreen was also evaluated, as the amount of sunscreen applied in practice may be considerably less than recommended. All areas were irradiated with a single UV dose of 3.6 SED (standard erythema doses). In irradiated unprotected skin the median net production of cis-urocanic acid was 52% (relative amount). In the sites treated with the chemical sunscreens, the production of cis-urocanic acid was 7.4% (SPF 4) and 3.5% (SPF 10), and isomerization was thus reduced more efficiently at a higher SPF (p<0.01). The physical sunscreen reduced the formation of cis-UCA to 15%, and was significantly less effective than both the chemical SPF 10 sunscreen (p<0.01) and the SPF 4 sunscreen (p<0.01). The production of cis-urocanic acid in the area treated with the thin layer of the chemical SPF 10 sunscreen was 22%. The protection against the production of cis-urocanic acid was therefore reduced significantly (p<0.01) when the sunscreen was applied in an amount lower than recommended.

A chain initiation factor common to both modular and aromatic polyketide synthases

Antibiotic-producing polyketide synthases (PKSs) are enzymes responsible for the biosynthesis in Streptomyces and related filamentous bacteria of a remarkably broad range of bioactive metabolites, including antitumour aromatic compounds such as mithramycin and macrolide antibiotics such as erythromycin. The molecular basis for the selection of the starter unit on aromatic PKSs is unknown. Here we show that a component of aromatic PKS, previously named 'chain-length factor', is a factor required for polyketide chain initiation and that this factor has decarboxylase activity towards malonyl-ACP (acyl carrier protein). We have re-examined the mechanism of initiation on modular PKSs and have identified as a specific initiation factor a domain of previously unknown function named KSQ, which operates like chain-length factor. Both KSQ and chain-length factor are similar to the ketosynthase domains that catalyse polyketide chain extension in modular multifunctional PKSs and in aromatic PKSs, respectively, except that the ketosynthase domain active-site cysteine residue is replaced by a highly conserved glutamine in KSQ and in chain-length factor. The glutamine residue is important both for decarboxylase activity and for polyketide synthesis.

Extraction of active clonidine-displacing substance from bovine lung and comparison with clonidine-displacing substance extracted from other tissues

Crude methanolic clonidine-displacing substance (CDS) extracted from bovine lung competed for radioligand binding from alpha2-adrenoceptors and I2-sites present in rat brain membranes, and from I1-sites present in rat brain and kidney membranes. There was no difference in the competition of [3H]clonidine binding to alpha2-adrenoceptors present in either rat or rabbit brain membranes by the crude CDS extract and therefore either tissue could be used to estimate the number of units of CDS present in extracts. Further purification by reverse phase high performance liquid chromatography (RP-HPLC), with UV detection, of extracts obtained from bovine lung, brain and rat brain exhibited similar three-peak profiles, previously reported. Corresponding fractions competed for radioligand binding to alpha2-adrenoceptors present in rat brain membranes, eluting between 19 and 23 min, which corresponded with the middle peak of the three-peaks. Therefore, we propose the CDS-like material eluting from all these tissues to be similar. Interestingly, CDS extracted from bovine adrenal glands under the same conditions showed a similar three-peak profile, but did not repeat the displacement of binding just at 19-23 min, but at every time point after 4 min. This suggests this tissue could represent a source of CDS in this species.

Plasmodium vivax merozoite surface protein-3 contains coiled-coil motifs in an alanine-rich central domain

Plasmodium merozoites are covered with a palisade layer of proteins that are arranged as organized bundles or appear as protruding spikes by electron microscopy. Here we present a third Plasmodium vivax merozoite surface protein, PvMSP-3, which is associated with but not anchored in the merozoite membrane. Serum from a P. vivax immune squirrel monkey was used to screen a lambdagt11 P. vivax genomic DNA (gDNA) library. Plaque-selected antibodies from clone no. 6.1, and rabbit antisera against its encoded protein, produced a pattern in immunofluorescence assays (IFAs) that is consistent with a localization at the surface of mature schizonts and free merozoites. Specific antisera also agglutinated merozoites and recognized a protein of 150 000 Da by SDS-PAGE. The complete msp-3 gene and flanking sequences were cloned from a P. vivax lambda Dash II gDNA library and also partly characterized by RACE (rapid amplification of cDNA ends). The immediate upstream sequence contains non-coding repeats and a putative protein encoding open reading frame (ORF), which are also present on the msp-3 5'RACE gene product. Pvmsp-3 encodes a protein with a calculated mass of 89 573 Da, which has a potential signal peptide and a major central alanine-rich domain (31%) that exhibits largely alpha-helical secondary structure and is flanked by charged regions. The protein does not have a putative transmembrane domain or a consensus sequence for a glycosylphosphatidylinositol (GPI) anchor modification. However, the alanine-rich domain has heptad repeats that are predicted to form coiled-coil tertiary structures, which mediate protein-protein interactions. PvMSP-3 is structurally related to P. falciparum MSP-3 and the 140000 Da MSP of P. knowlesi. Characterization of PvMSP-3, thus, also begins to define a new interspecies family of evolutionarily related Plasmodium merozoite proteins.

The role of urocanic acid in UVB-induced suppression of immunity to Trichinella spiralis infection in the rat

The naturally occurring trans-isomer of urocanic acid (trans-UCA), found in the stratum corneum, absorbs ultraviolet light (UV) and isomerizes to the cis-form. Cis-UCA has been shown to impair some cellular immune responses, and has been proposed as an initiator of the suppression that follows UV irradiation. UVB exposure leads to an increase in cis-UCA in the skin of rats from about 10% to 40% of the total UCA. Previously it has been demonstrated that UVB lowers immune responses to Trichinella spiralis after oral infection of rats with the parasitic worm. In the present study we investigated the role of cis-UCA in the control of this parasitic infection. Rats were infected orally with T. spiralis and injected with different doses of cis- or trans-UCA subcutaneously. Mitogenic responses and the mixed lymphocyte reaction were not affected by either isomer. In contrast, the number of T. spiralis larvae in muscle tissue of infected rats was increased significantly in the cis-UCA-treated animals compared with the trans-UCA-treated animals. In addition, delayed-type hypersensitivity (DTH) to T. antigen in infected rats was significantly impaired by cis-UCA but not by trans-UCA. If rats were injected with a monoclonal antibody with specificity for cis-UCA 2 hr prior to UVB exposure, the UVB-induced suppression in DTH to T. spiralis and the increase in larvae counts were significantly inhibited compared with rats that were similarly injected with a control antibody. Thus cis-UCA can inhibit the specific resistance to parasitic infections and acts as an important mediator of UVB-induced suppression of immunity to T. spiralis in the rat.

Isomerization of urocanic acid after ultraviolet radiation is influenced by skin pigmentation

Exposure to ultraviolet (UV) radiation may induce erythema, DNA damage and suppression of immune responses. Melanin pigmentation offers protection against the first two of these effects, but immunosuppression seems to occur irrespective of the subject's pigmentation. Cis-urocanic acid (cis-UCA), produced by isomerization of trans-UCA in the stratum corneum on UV exposure, initiates some of the immunomodulatory effects of UV radiation. In the present study the relationship between skin pigmentation and UCA isomerization has been examined in 28 healthy individuals of skin types I-IV. Pigmentation is measured in five areas of not recently exposed back skin before irradiation with 0, 0.45, 0.9, 1.8 and 3.6 standard erythema dose (SED) of filtered broadband UV-B (1 SED = 10 mJ cm-2 at 298 nm). The concentration of UCA isomers is measured immediately after the irradiation. With 3.6 SED, the relative production of cis-UCA is close to the maximum obtainable, irrespective of skin type. A significant negative correlation is found between pigmentation and relative production of cis-UCA at 0.45 and 1.8 SED, and between pigmentation and absolute production of cis-UCA at 0.45 SED. At doses of 0.45 and 0.9 SED the relative and absolute production of cis-UCA are higher in the group with skin types I and II when compared with the group with skin types III and IV. The higher isomerization in the lightly pigmented subjects than in the more pigmented ones may indicate that people with fair skin are at a relatively higher risk of immunosuppression when exposed to low doses of UV radiation.

MCAT is not required for in vitro polyketide synthesis in a minimal actinorhodin polyketide synthase from Streptomyces coelicolor

BACKGROUND

It has been proposed that Streptomyces malonyl CoA: holo acyl carrier protein transacylases (MCATs) provide a link between fatty acid and polyketide biosynthesis. Two recent studies have provided evidence that the presence of MCAT is essential for polyketide synthesis to proceed in reconstituted minimal polyketide synthases (PKSs). In contrast to this, we previously showed that the holo acyl carrier proteins (ACPs) from type II PKSs are capable of catalytic self-malonylation in the presence of malonyl CoA, which suggests that MCAT might not be necessary for polyketide biosynthesis.

RESULTS

We reconstituted a homologous actinorhodin (act) type II minimal PKS in vitro. When act holo-ACP is present in limiting concentrations, MCAT is required by the synthase complex in order for polyketide biosynthesis to proceed. When holo-ACP is present in excess, however, efficient polyketide synthesis proceeds without MCAT. The rate of polyketide production increases with holo-ACP concentration, but at low ACP concentration or equimolar AC:KS:CLF (KS, ketosynthase; CLF, chain length determining factor) concentrations this rate is significantly lower than expected, indicating that free holo-ACP is sequestered by the KS/CLF complex.

CONCLUSIONS

The rate of polyketide biosynthesis is dictated by the ratio of holo-ACP to KS and CLF, as well as by the total protein concentration. There is no absolute requirement for MCAT in polyketide biosynthesis in vitro, although the role of MCAT during polyketide synthesis in vivo remains an open question. MCAT might be responsible for the rate enhancement of malonyl transfer at very low free holo-ACP concentrations or it could be required to catalyse the transfer of malonyl groups from malonyl CoA to sequestered holo-ACP.

Chemometric analysis of high performance liquid chromatography-diode array detection-electrospray mass spectrometry of 2- and 3-hydroxypyridine

Triply coupled high performance liquid chromatography using diode array detection and positive ion electrospray mass spectrometry of 2- and 3-hydroxypyridine is presented. Considerations of the physical method for coupling the two detectors, the influence of pH on retention times, the cone voltage of the mass spectrometer and the linear concentration ranges are described. Data from both detectors are aligned and interpolated. The analyte mass spectra are reduced to 20 significant masses. Principal components plots on the raw, normalised and standardised data, derivatives to determine composition 1 regions, deconvolution and procrustes analysis to compare data from both detectors are discussed. Common trends in both mass spectral and diode array chromatograms are interpreted. This paper represents a new approach to common processing of chromatographic data from two detectors.

Urocanic acid isomers and photosensitivity in healthy children

Episodes of intense sun exposure, particularly in childhood, seem to carry a risk for the development of malignant melanoma in later life. However, little is known about photosensitivity and natural photoprotection in children. In adult subjects, photoprotection is provided mainly by the epidermal content of melanin and the thickness of the stratum corneum, while the amount of urocanic acid (UCA), a major ultraviolet-absorbing component of the stratum corneum, is not thought to contribute significantly to photoprotection. The minimal erythema dose (MED) was determined in 22 healthy children aged 6-13 years and in 36 healthy adults (mean age 28.1 years). Pigmentation was measured at six body sites by use of reflectance spectroscopy and the concentration of UCA isomers was measured in a sun-exposed area (upper back) and in unexposed buttock skin. No significant differences between children and adults were found, either in pigmentation at exposed and unexposed body sites, or in MED. The concentration of total UCA was significantly higher in the children than in the adults on the buttock (median 22.2 vs. 13.6 nmol/cm2), but not on the back. On exposed back skin, the children had a significantly higher percentage of cis-UCA than the adults (median 60.1 vs. 28.3%), while no difference was found on the buttock. In both groups, a significant correlation was found between pigmentation and MED (children: Spearman correlation coefficient 0. 58, P = 0.006; adults: Spearman correlation coefficient 0.69, P < 0. 0001), indicating that pigmentation is of major importance in determining photosensitivity in children as well as in adults. The concentration of total UCA did not correlate with the MED in either group.

Acylation of Streptomyces type II polyketide synthase acyl carrier proteins

Acyl derivatives of type II PKS ACPs are required for in vitro studies of polyketide biosynthesis. The presence of an exposed cysteine residue prevented specific chemical acylation of the phosphopantetheine thiol of the actinorhodin PKS holo ACP. Acylation studies were further complicated by intramolecular disulphide formation between cysteine 17 and the phosphopantetheine. The presence of this intramolecular disulphide was confirmed by tryptic digestion of the ACP followed by ESMS analysis of the fragments. An act Cys17Ser ACP was engineered by site-directed mutagenesis. S-Acyl adducts of act C17S, oxytetracycline and griseusin holo ACPs were rapidly formed by reaction with hexanoyl, 5-ketohexanoyl and protected acetoacetyl imidazolides. Comparisons with type 11 FAS ACPs were made.

Urocanic acid isomers in patients with basal cell carcinoma and cutaneous malignant melanoma

Urocanic acid (UCA) is a major chromophore for ultraviolet (UV) radiation in the skin. On UV exposure, the naturally occurring trans-isomer converts to the cis-isomer in a dose-dependent manner. Accumulating evidence indicates that cis-UCA acts as an initiator of the UV-induced suppression of certain skin immune functions. This immunomodulation is recognized as an important factor in the development of skin cancer. In this study, pigmentation and UCA isomers were measured in 29 patients with previous basal cell carcinoma (BCC), 23 patients with previous cutaneous malignant melanoma (MM), and 32 healthy controls. Measurements were performed on UV-exposed (forehead, upper back) and UV non-exposed (buttock) skin. No significant differences in pigmentation percentage, total UCA concentration, relative (%) or absolute (nmol/cm2) cis-UCA concentration were observed between the groups in any of the body sites studied. The net production of cis-UCA after irradiation with a single test UV dose was evaluated. The relative production of cis-UCA following irradiation was significantly higher in both cancer groups when compared with the control group, while no significant difference was found between the BCC and the MM patients.

Catalytic self-acylation of type II polyketide synthase acyl carrier proteins

BACKGROUND

Aromatic polyketides are synthesised in streptomycetes by the successive condensation of simple carboxylic acids, catalysed by multienzyme complexes--the polyketide synthases (PKSs). Polyketide assembly intermediates are covalently linked as thioesters to the holo-acyl carrier protein (ACP) subunit of these type II PKSs. The ACP is primed for chain elongation by the transfer of malonate from malonyl CoA. Malonylation of fatty acid synthase (FAS) ACPs is catalysed by specific malonyl transferase (MT) enzymes. The type II PKS gene clusters apparently lack genes encoding such MT proteins, however. It has been proposed that the MT subunit of the FAS in streptomycetes catalyses malonylation of both FAS and PKS ACPs in vivo.

RESULTS

We demonstrate that type II PKS ACPs catalyse self-malonylation upon incubation with malonyl CoA in vitro. The self-malonylation reaction of the actinorhodin C17S holo-ACP has a K(m) for malonyl CoA of 219 microM and a kcat of 0.34 min-1. Complete acylation of the PKS ACPs was observed with malonyl, methylmalonyl and acetoacetyl CoAs. No reaction was observed with acetyl and butyryl CoAs and FAS ACPs did not react with any of the substrates. Recombinant FAS MT from Streptomyces coelicolor did not accelerate the rate of malonylation.

CONCLUSIONS

The catalytic self-acylation of type II PKS ACPs is an unprecedented reaction. We propose a reaction mechanism in which conserved arginines form a salt bridge with the acyl moiety and sequester it from bulk solvent. This work suggests that the beta-ketoacyl synthase, chain length factor and ACP may constitute a truly minimal PKS in vivo.

Urocanic acid isomers: relation to body site, pigmentation, stratum corneum thickness and photosensitivity

Urocanic acid (UCA), present in the stratum corneum as trans-UCA, absorbs ultraviolet (UV) radiation and isomerizes to cis-UCA. Cis-UCA has been demonstrated to initiate suppression of selected immune responses in several experimental systems. Topical application of UCA-containing products reduces UV-induced erythema, but a role for endogenous UCA in photoprotection has not been reported. In this study the relationship between UCA isomers, pigmentation, minimal erythema dose (MED), and stratum corneum thickness was investigated. Pigmentation, concentration of total UCA, and the percentage present as the cis-isomer was measured in 36 healthy subjects, skin type I-IV, at six UV-exposed and nonexposed body sites: forehead, chest, back, outer upper arm, inner upper arm, and buttock. The MED was determined by phototesting on buttock skin, and a punch biopsy for measurement of stratum corneum thickness was taken adjacent to the site of the phototest. The percentage of cis-UCA was significantly higher in UV-exposed than on nonexposed areas. A small intraindividual variation in total UCA was found, being high on the buttock and the arm, lowest on the forehead. The subject to subject variation of total UCA was considerable at all body sites. No correlation was found between total UCA and MED, skin type, pigmentation, or stratum corneum thickness.

Seasonal variation in urocanic acid isomers in human skin

Urocanic acid (UCA) is a major chromophore for UV in the skin and has been suggested to act as an initiator of UV-induced immunosuppression. It converts from the naturally occurring trans-isomer to the cis-isomer on UV exposure. Isomerization is dose dependent until the photostationary state is reached, and the seasonal variation in irradiance from the sun may lead to changes in the percentage of UCA present as cis-UCA throughout the year. Thirty young healthy subjects, skin types I-IV, were followed from early summer till spring. At each of six visits (June, July, August, October, December, March), pigmentation and the concentration of UCA isomers were measured at six body sites: forehead, upper chest, upper back, outer upper arm, inner upper arm and buttock. In exposed as well as unexposed regions a variation in pigmentation was found, peak values being recorded in August. Total UCA concentration was lower in July and August than in the rest of the year, irrespective of body site. In July, the percentage of cis-UCA was close to the maximal obtainable (50-60%) at all sites except the buttock. In the three winter months the percentage of cis-UCA was below 7% in all regions except for the forehead, where the mean cis-UCA was 18% in October and March. No consistent relationship was found between UCA isomers and pigmentation or skin type.

Solution structure of the actinorhodin polyketide synthase acyl carrier protein from Streptomyces coelicolor A3(2)

The solution structure of the actinorhodin acyl carrier protein (act apo-ACP) from the polyketide synthase (PKS) of Streptomyces coelicolor A3(2) has been determined using 1H NMR spectroscopy, representing the first polyketide synthase component for which detailed structural information has been obtained. Twenty-four structures were generated by simulated annealing, employing 699 distance restraints and 94 dihedral angle restraints. The structure is composed, principally, of three major helices (1, 2, and 4), a shorter helix (3) and a large loop region separating helices 1 and 2. The structure is well-defined, except for a portion of the loop region (residues 18-29), the N-terminus (1-4), and a short stretch (57-61) in the loop connecting helices 2 and 3. The RMS distribution of the 24 structures about the average structure is 1.47 A for backbone atoms, 1.84 A for all heavy atoms (residues 5-86), and 1.01 A for backbone atoms over the helical regions (5-18, 41-86). The tertiary fold of act apo-ACP shows a strong structural homology with Escherichia coli fatty acid synthase (FAS) ACP, though some structural differences exist. First, there is no evidence that act apo-ACP is conformationally averaged between two or more states as observed in E. coli FAS ACP. Second, act apo-ACP shows a disordered N-terminus (residues 1-4) and a longer flexible loop (19-41 with 19-29 disordered) as opposed to E. coli FAS ACP where the N-terminal helix starts at residue 3 and the loop region is three amino acids shorter (16-35). Most importantly, however, although the act apo-ACP structure contains a hydrophobic core, there are in addition a number of buried hydrophilic groups, principally Arg72 and Asn79, both of which are 100% conserved in the PKS ACPs and not the FAS ACPs and may therefore play a role in stabilizing the growing polyketide chain. The structure-function relationship of act ACP is discussed in the light of these structural data and recent genetic advances in the field.

Post-translational modification of heterologously expressed Streptomyces type II polyketide synthase acyl carrier proteins

Expression in Escherichia coli of Streptomyces acyl carrier proteins (ACPs) associated with polyketide biosynthesis using the pT7-7 expression system of Tabor and Richardson led to the production predominantly of inactive apo-proteins lacking the 4'-phosphopantetheinyl prosthetic group essential for polyketide synthase activity. Modification of growth conditions led to an increase of production of active holo-protein for the actinorhodin (act) ACP, but this technique was ineffective for oxytetracycline (otc) and griseusin (gris) ACPs. Labelling experiments revealed that a low level of otc ACP expressed prior to induction was produced mainly as active holo-protein, while post-induction 15N-labelled protein was almost exclusively in the apo-ACP form. Limiting endogenous holo-acyl carrier protein synthase (ACPS) concentration was implicated as responsible for low apo-ACP to holo-ACP conversion, rather than limiting substrate (coenzyme A) and cofactor (Mg2+) concentrations. Co-expression of act and gris ACPs with ACPS in E. coli led to high levels of production of active holo-ACPs and ACPS. We have also made the significant observation that ACPS is able to transfer acylated CoA moieties to act apo-ACP.

Conserved secondary structure in the actinorhodin polyketide synthase acyl carrier protein from Streptomyces coelicolor A3(2) and the fatty acid synthase acyl carrier protein from Escherichia coli

The acyl carrier protein (ACP) of Streptomyces coelicolor A3(2) functions as a molecular chaperone during the biosynthesis of the polyketide actinorhodin (act). Here we compare structural features of the polyketide synthase (PKS) ACP, determined by two-dimensional 1H-NMR, with the Escherichia coli fatty acid synthase (FAS) ACP. The PKS ACP contains four helices (residues 7-16 [A], 42-53 [B], 62-67 [C], 72-86 [D]), and a large loop (residues 17-41) having no defined secondary structure with the exception of a turn between residues 21 and 24. The act ACP shows 47% sequence similarity with the E. coli FAS ACP and the results demonstrate that the sequence homology is extended to the secondary structure of the proteins.

The sunscreening effect of urocanic acid

Urocanic acid (UCA), present in the stratum corneum, is a major absorber of ultraviolet (UV) radiation and, on UV exposure, is induced to isomerize from the naturally occurring trans-isomer to the cis-isomer. Cis-UCA has been shown to have immunosuppressive properties, while trans-UCA may act as a natural sunscreen due to its UV-absorbing properties. The photoprotective capacity of UCA was investigated in this study. Minimal erythema dose (MED) was determined on normal buttock skin in 36 healthy subjects and the concentration of UCA isomers was measured on the skin adjacent to the test site. On the contralateral buttock. MED was determined 20 min after application of trans-UCA 5% in a cream base. The UCA cream gave a sun protection factor of 1.58. The amount of UCA applied was, however, 20-200 times higher than the amount of UCA found in normal skin, making a sunscreening effect of naturally occurring UCA very low. This was further supported, by a lack of correlation between naturally occurring UCA and the UV sensitivity of each subject determined by the MED.

Investigating the red shift between in vitro and in vivo urocanic acid photoisomerization action spectra

Trans-urocanic acid (UCA) is found in the upper layer of the skin and UV irradiation induces its photoisomerization to cis-UCA. Cis-UCA mimics some of the immunosuppressive properties of UV exposure. The wavelength dependence for in vitro photoisomerization of trans-UCA (15 microM) over the spectral range 250 nm-340 nm (10 nm intervals) was determined. The action spectrum revealed that maximal cis-UCA production occurred at 280 nm, which is red-shifted by 10-12 nm from its absorption peak at 268 nm and differs markedly from the reported action spectra for cis-UCA production in mouse skin in vivo, which peaks at 300-310 nm. The reasons for the red shift between the in vitro and in vivo action spectra are not clear. There is limited evidence suggesting that the UV absorption maximum of trans-UCA red shifts from 268 nm in vitro to 310 nm on interaction with stratum corneum proteins in vivo. This phenomenon was investigated by applying trans-UCA (2.5 mg/cm2) in an oil emulsion to isolated human stratum corneum. After incubation at 37 degrees C for 1 h, the absorption spectra of stratum corneum with UCA and with oil only were compared using a Xe arc source and a spectroradiometer. A moderate red shift in trans-UCA absorption from approximately 268 nm to 280 nm was observed. In summary, we suggest that the 10-12 nm red shift between the UCA absorption spectrum peak and the action spectrum peak in vitro may be accounted for by the wavelength dependence of quantum yields reported over the 254-313 nm range. The red shift between the in vitro and in vivo photoisomerization action spectra may result from the 10 to 12 nm red shift in the absorption of UCA in association with stratum corneum proteins, combined with increasing quantum yields over the 254-313 nm range.

Urocanic acid isomers in human skin: analysis of site variation

Urocanic acid (UCA) is found in the stratum corneum as the trans-isomer and, on ultraviolet (UV) irradiation, photoisomerization into cis-UCA takes place. Cis-UCA has been suggested to play a part in UV-induced immunosuppression. In the present study, the concentration of UCA and the percentage as cis-UCA at 10 different body sites of 20 normal volunteers were analysed. A large interindividual variation in total UCA concentration was found, but the mean UCA concentration in each site was similar, other than at the sole of the foot. There was little variation in the UCA content between sites normally exposed, and not exposed, to light, but the percentage of UCA in the cis form was clearly higher at exposed areas.

Polyketide synthase acyl carrier proteins from Streptomyces: expression in Escherichia coli, purification and partial characterisation

Acyl carrier proteins (ACPs) of the type II polyketide synthases for the aromatic antibiotics actinorhodin, granaticin, frenolicin and oxytetracycline were expressed in Escherichia coli downstream of an inducible phage T7 promoter. For the act and otc genes, several of the first eight codons were changed to synonymous codons used in highly expressed E. coli genes. Correlated with these changes, the amounts of the act and otc ACPs purified from the recombinant E. coli cultures were an order of magnitude greater than for the gra and fren ACPs expressed from the unmodified genes. Electrospray mass spectrometry (ESMS) of the purified proteins confirmed their calculated M(r) based on the DNA sequences while also revealing that, in the act and gra ACP samples, some 2% and 30% of the holo-form of the protein was present (i.e., carrying the 4'-phosphopantetheine prosthetic group), with the remainder (and 100% of the otc and fren samples) being in the apo-form. Increasing incubation time post heat induction led to an increase in act holo-ACP. The recombinant act and gra ACPs could function in vitro as substrates for an S. coelicolor malonyl CoA:ACP acyl transferase, as measured by the coupling of a labelled malonyl unit to the ACP; their quantitative abilities to do so correlated with the proportions of deduced holo form in the two samples.