Orthogonal End Labelling of Oligonucleotides through Dual Incorporation of Click-Reactive NTP Analogues

Post-synthetic modification of nucleic acid structures with clickable functionality is a versatile tool that facilitates many emerging applications, including immune evasion, enhancements in stability, fluorescent labelling, chemical 5'-RNA-capping and the development of functional aptamers. While certain chemoenzymatic approaches for 3'-azido and alkynyl labelling are known, equivalent 5'-strategies are either inefficient, complex, or require harsh chemical conditions. Here, we present a modular and facile technology to consecutively modify DNA and RNA strands at both ends with click-modifiable functional groups. Our approach using γ-modified ATP analogues facilitates T4 PNK-catalysed 5'-modification of oligonucleotides, a process that is compatible with TdT-catalysed 3'-elongation using 3'-azido-2',3'-ddGTP. Finally, we demonstrate that our approach is suitable for both oligo-oligo ligations, as well ssDNA circularization. We anticipate that such approaches will pave the way for the synthesis of highly functionalised oligonucleotides, improving the therapeutic and diagnostic applicability of oligonucleotides such as in the realm of next-generation sequencing.

Divergent Synthesis of Ultrabright and Dendritic Xanthenes for Enhanced Click-Chemistry-Based Bioimaging

Biorthogonal labelling with fluorescent small molecules is an indispensable tool for diagnostic and biomedical applications. In dye-based 5-ethynyl-2'-deoxyuridine (EdU) cell proliferation assays, augmentation of the fluorescent signal entails an overall enhancement in the sensitivity and quality of the method. To this end, a rapid, divergent synthetic procedure that provides ready-to-click pH-insensitive rhodamine dyes exhibiting outstanding brightness was established. Compared to the shortest available synthesis of related high quantum-yielding rhodamines, two fewer synthetic steps are required. In a head-to-head imaging comparison involving copper(I)-catalyzed azide alkyne cycloaddition reactions with in vitro administered EdU, our new 3,3-difluoroazetidine rhodamine azide outperformed the popular 5-TAMRA-azide, making it among the best available choices when it comes to fluorescent imaging of DNA. In a further exploration of the fluorescence properties of these dyes, a set of bis-MPA dendrons carrying multiple fluorescein or rhodamine units was prepared by branching click chemistry. Fluorescence self-quenching of fluorescein- and rhodamine-functionalized dendrons limited the suitability of the dyes as labels in EdU-based experiments but provided new insights into these effects.

Isoxazole Nucleosides as Building Blocks for a Plausible Proto-RNA

The question of how RNA, as the principal carrier of genetic information evolved is fundamentally important for our understanding of the origin of life. The RNA molecule is far too complex to have formed in one evolutionary step, suggesting that ancestral proto-RNAs (first ancestor of RNA) may have existed, which evolved over time into the RNA of today. Here we show that isoxazole nucleosides, which are quickly formed from hydroxylamine, cyanoacetylene, urea and ribose, are plausible precursors for RNA. The isoxazole nucleoside can rearrange within an RNA-strand to give cytidine, which leads to an increase of pairing stability. If the proto-RNA contains a canonical seed-nucleoside with defined stereochemistry, the seed-nucleoside can control the configuration of the anomeric center that forms during the in-RNA transformation. The results demonstrate that RNA could have emerged from evolutionarily primitive precursor isoxazole ribosides after strand formation.

Click Chemistry Enables Rapid Amplification of Full-Length Reverse Transcripts for Long-Read Third Generation Sequencing

Here we describe the development of a novel click chemistry-based method for the generation and amplification of full-length cDNA libraries from total RNA, while avoiding the need for problematic template-switching (TS) reactions. Compared with prior efforts, our method involves neither random priming nor stochastic cDNA termination, thus enabling amplification of transcripts that were previously inaccessible via related click chemistry-based RNA sequencing techniques. A key modification involving the use of PCR primers containing two overhanging 3'-nucleotides substantially improved the read-through compatibility of the 1,4-disubstituted 1,2,3-triazole-containing cDNA, where such modifications typically hinder amplification. This allowed us to more than double the possible insert size compared with the state-of-the art click chemistry-based technique, PAC-seq. Furthermore, our method performed on par with a commercially available PCR-cDNA RNA sequencing kit, as determined by Oxford Nanopore sequencing. Given the known advantages of PAC-seq, namely, suppression of PCR artifacts, we anticipate that our contribution could enable diverse applications including improved analyses of mRNA splicing variants and fusion transcripts.

Amino Acid Modified RNA Bases as Building Blocks of an Early Earth RNA-Peptide World

Fossils of extinct species allow us to reconstruct the process of Darwinian evolution that led to the species diversity we see on Earth today. The origin of the first functional molecules able to undergo molecular evolution and thus eventually able to create life, are largely unknown. The most prominent idea in the field posits that biology was preceded by an era of molecular evolution, in which RNA molecules encoded information and catalysed their own replication. This RNA world concept stands against other hypotheses, that argue for example that life may have begun with catalytic peptides and primitive metabolic cycles. The question whether RNA or peptides were first is addressed by the RNA‐peptide world concept, which postulates a parallel existence of both molecular species. A plausible experimental model of how such an RNA‐peptide world may have looked like, however, is absent. Here we report the synthesis and physicochemical evaluation of amino acid containing adenosine bases, which are closely related to molecules that are found today in the anticodon stem‐loop of tRNAs from all three kingdoms of life. We show that these adenosines lose their base pairing properties, which allow them to equip RNA with amino acids independent of the sequence context. As such we may consider them to be living molecular fossils of an extinct molecular RNA‐peptide world.

Unified prebiotically plausible synthesis of pyrimidine and purine RNA ribonucleotides

Theories about the origin of life require chemical pathways that allow formation of life's key building blocks under prebiotically plausible conditions. Complex molecules like RNA must have originated from small molecules whose reactivity was guided by physico-chemical processes. RNA is constructed from purine and pyrimidine nucleosides, both of which are required for accurate information transfer, and thus Darwinian evolution. Separate pathways to purines and pyrimidines have been reported, but their concurrent syntheses remain a challenge. We report the synthesis of the pyrimidine nucleosides from small molecules and ribose, driven solely by wet-dry cycles. In the presence of phosphate-containing minerals, 5'-mono- and diphosphates also form selectively in one-pot reactions. The pathway is compatible with purine synthesis, allowing the concurrent formation of all Watson-Crick bases.

Proto-Urea-RNA (Wöhler RNA) Containing Unusually Stable Urea Nucleosides

The RNA world hypothesis assumes that life on Earth began with nucleotides that formed information-carrying RNA oligomers able to self-replicate. Prebiotic reactions leading to the contemporary nucleosides are now known, but their execution often requires specific starting materials and lengthy reaction sequences. It was therefore proposed that the RNA world was likely proceeded by a proto-RNA world constructed from molecules that were likely present on the early Earth in greater abundance. Herein, we show that the prebiotic starting molecules bis-urea (biuret) and tris-urea (triuret) are able to directly react with ribose. The urea-ribosides are remarkably stable because they are held together by a network of intramolecular, bifurcated hydrogen bonds. This even allowed the synthesis of phosphoramidite building blocks and incorporation of the units into RNA. Investigations of the nucleotides' base-pairing potential showed that triuret:G RNA base pairs closely resemble U:G wobble base pairs. Based on the probable abundance of urea on the early Earth, we postulate that urea-containing RNA bases are good candidates for a proto-RNA world.

Rethinking the tools of the RNA world

An artificially evolved ribozyme can catalyse the synthesis of RNA by using trinucleotide triphosphates as building blocks.

Noncanonical RNA Nucleosides as Molecular Fossils of an Early Earth-Generation by Prebiotic Methylations and Carbamoylations

The RNA-world hypothesis assumes that life on Earth started with small RNA molecules that catalyzed their own formation. Vital to this hypothesis is the need for prebiotic routes towards RNA. Contemporary RNA, however, is not only constructed from the four canonical nucleobases (A, C, G, and U), it also contains many chemically modified (noncanonical) bases. A still open question is whether these noncanonical bases were formed in parallel to the canonical bases (chemical origin) or later, when life demanded higher functional diversity (biological origin). Here we show that isocyanates in combination with sodium nitrite establish methylating and carbamoylating reactivity compatible with early Earth conditions. These reactions lead to the formation of methylated and amino acid modified nucleosides that are still extant. Our data provide a plausible scenario for the chemical origin of certain noncanonical bases, which suggests that they are fossils of an early Earth.

Wet-dry cycles enable the parallel origin of canonical and non-canonical nucleosides by continuous synthesis

The molecules of life were created by a continuous physicochemical process on an early Earth. In this hadean environment, chemical transformations were driven by fluctuations of the naturally given physical parameters established for example by wet-dry cycles. These conditions might have allowed for the formation of (self)-replicating RNA as the fundamental biopolymer during chemical evolution. The question of how a complex multistep chemical synthesis of RNA building blocks was possible in such an environment remains unanswered. Here we report that geothermal fields could provide the right setup for establishing wet-dry cycles that allow for the synthesis of RNA nucleosides by continuous synthesis. Our model provides both the canonical and many ubiquitous non-canonical purine nucleosides in parallel by simple changes of physical parameters such as temperature, pH and concentration. The data show that modified nucleosides were potentially formed as competitor molecules. They could in this sense be considered as molecular fossils.

Why do we choose rheumatology? Implications for future recruitment--results of the 2006 UK Trainee Survey

OBJECTIVES

Against changes to junior doctor career structure under MMC (Modernizing Medical Careers), and uncertainty about the future place of rheumatology, we explored critical factors in choice of rheumatology as a speciality, and asked what factors might govern choices of prospective trainees. Using these data, we developed suggestions to enhance future recruitment.

METHODS

A postal survey was sent to rheumatology specialist registrars (SpRs) on the Joint Committee for Higher Medical Training (JCHMT) database between December 2005 and January 2006, and concurrently by e-mail to the Rheumatologists at Training e-mail list.

RESULTS

Seventy-three percent (165/227) of trainees responded. Of them, 89.1% had previous senior house officer (SHO) experience in rheumatology and 81.8% made a career decision in favour of rheumatology during their SHO post. The top four ranked factors influencing choice of rheumatology were SHO experience, subject matter, inspirational consultants and lifestyle aspects; 89.1% would still choose rheumatology now. Factors felt to be negatively influencing future trainees came under three key themes: poor student or postgraduate exposure, employment and service delivery issues (including concern over the future place of rheumatology in primary vs secondary care), and perceived poor profile of rheumatology. Factors positively influencing future candidates were subject matter, work/life balance and prior exposure to the speciality.

CONCLUSIONS

Early postgraduate experience is key to choice of speciality. An overwhelming majority of trainees decide speciality during SHO experience. With ongoing changes in career structure, it is critical that rheumatology is incorporated into foundation and speciality training programmes and essential that continued measures are taken to improve the image of rheumatology.

Anorexia nervosa and social class

OBJECTIVES

(1) To examine social class status of female patients with anorexia nervosa presenting over a 33-year period; (2) to identify any differences in clinical features between the social classes.

METHOD

Retrospective survey using comprehensive clinical database of patients referred to a national specialist center for the assessment and treatment of anorexia nervosa. Social class was defined using UK Registrar General's classification of father's occupation. Statistical methods included initial univariate analyses and subsequent ordinal logistic regression.

RESULTS

(1) Social class distribution was consistently weighted toward social classes 1/2. (2) Possible clinical indicators examined included low body weight, binge eating, and consequent weight-regulatory behaviors such as vomiting and laxative and diuretic misuse. These clinical features and their distribution proved to be similar across the social groups. Clinically rated quality of family relationships and types of family constellations were also consistent across the social classes. (3) Dieting prodromata and onset of the disorder occurred at younger ages in social classes 1/2. (4) A modest shift in social class distribution over time was apparent, with slightly more patients presenting post-1985 likely to come from lower social classes. Claims that the social class distribution is a product of referral patterns and acceptances are disputed.

CONCLUSION

We suggest that the social class bias reflects a sociocultural influence; a product of the disorder significantly often arising as an avoidant response to the conflict between social class-related family values/attitudes and adolescent turbulence within that family.

Effect of early intervention with sumatriptan on migraine pain: retrospective analyses of data from three clinical trials

OBJECTIVE

This study assessed the efficacy of sumatriptan 50- and 100-mg tablets in the treatment of migraine attacks while the pain is mild rather than moderate/severe.

BACKGROUND

Results from The Spectrum Study suggested that early treatment of migraine attacks with sumatriptan 50-mg tablets while the pain is mild might enhance pain-free response and reduce headache recurrence.

METHODS

Retrospective analyses of headaches treated during mild pain were performed using data from 3 studies of sumatriptan tablets (protocols S2CM09, S2BT25, and S2BT26). Our primary interest was pain-free response 2 and 4 hours after dosing; secondary interests were use of a second dose of medication, clinical disability (as measured on a 4-point disability scale), migraine-associated symptoms, meaningful pain relief (patient defined), time to meaningful relief, sustained pain-free response, and proportion of attacks in which pain had worsened 2 and 4 hours after dosing, all of which were compared in headaches treated during mild versus moderate/severe pain.

RESULTS

In S2CM09, 92 patients treated 118 headaches during mild pain. Rates of pain-free response were higher 2 hours after dosing with sumatriptan 50 mg (51%) or 100 mg (67%; P < 0.05) compared with placebo (28%), and were higher with early treatment of mild pain compared with treatment of moderate/severe pain at 2 hours (sumatriptan 50 mg: mild pain, 51%; moderate/severe pain, 31%; P < 0.05; sumatriptan 100 mg: mild pain, 67%; moderate/severe pain, 36%) and 4 hours (50 mg: 75% vs 56%; 100 mg: 90% vs 61%; P < 0.05). Early intervention also resulted in less redosing than when moderate/severe pain was treated (50 mg: 21% vs 32%; 100 mg: 20% vs 29%). More attacks treated early with sumatriptan 50 or 100 mg were associated with normal function 4 hours after dosing compared with placebo (70% and 93% vs 46%, respectively). Sustained pain-free response rates 2 to 24 hours after early dosing with sumatriptan 50 or 100 mg were also higher (34% and 53%, respectively) compared with treatment of moderate/severe pain (19% and 24%, respectively). Early treatment with sumatriptan 100 mg produced significantly higher pain-free rates at 2 hours after dosing (P < 0.001) than did ergotamine plus caffeine (S2BT25: 69% vs 34%, respectively) or aspirin plus metoclopramide (S2BT26: 73% vs 25%, respectively).

CONCLUSIONS

Sumatriptan 50- and 100-mg tablets are effective whether pain is mild or moderate/severe. However, treatment with sumatriptan while pain is mild provides high pain-free response rates while reducing the need for redosing, benefits not seen with ergotamine plus caffeine or aspirin plus metoclopramide.

Comparison of naratriptan and sumatriptan in recurrence-prone migraine patients. Naratriptan International Recurrence Study Group

OBJECTIVE

This randomized, double-blind, crossover study was undertaken to compare the incidence of headache recurrence after treatment with naratriptan or sumatriptan in migraine patients with a history of frequent headache recurrence (recurrence in > or =50% of successfully treated attacks).

BACKGROUND

Although the selective 5-hydroxytryptamine, (5-HT1) agonist sumatriptan is effective and well tolerated for acute treatment of migraine in most patients, headache recurrence within 24 hours of initial successful treatment with sumatriptan and other medications has been reported in approximately 35% of patients. The novel 5-HT1 agonist naratriptan possesses pharmacologic and pharmacokinetic characteristics that may address the issue of headache recurrence.

METHODS

Men and women aged 18 to 65 years with a > or =1-year history of migraine with or without aura were randomly assigned to treat 1 moderate or severe migraine attack in a nonclinical setting with one 2.5-mg naratriptan tablet and 1 attack with one 100-mg sumatriptan tablet. A pain-free interval of > or =24 hours was required between attacks. At 4 hours, patients not using rescue medication and experiencing headache recurrence could take a second, identical dose of study medication to treat recurrence. No more than 2 tablets of study medication were permitted in any 24-hour period.

RESULTS

A total of 253 patients treated > or =1 migrane attack and were included in the safety analysis; the 225 patients who treated both attacks were included in the efficacy analysis. Of the 164 naratriptan-treated and 181 sumatriptan-treated patients experiencing headache relief after > or =1 attack, headache recurrence 4 to 24 hours after treatment was reported by 74 naratriptan-treated patients (45%) and 101 sumatriptan-treated patients (57%; not statistically significant). (One naratriptan- and 3 sumatriptan-treated patients who experienced headache relief did not record recurrence status and were not included in the denominator for the percentage calculation.) In a subset of patients experiencing headache relief after 2 attacks, headache recurrence 4 to 24 hours after initial dosing was reported by 55 naratriptan- and 77 sumatriptan-treated patients (41% and 57%, respectively; P = 0.005). The overall incidence of adverse events was 22% after treatment with naratriptan and 33% after treatment with sumatriptan. This incidence did not increase after use of a second dose of naratriptan (20%) or sumatriptan (31%).

CONCLUSION

These data suggest that naratriptan is a long-acting and well-tolerated addition to currently available medications for the treatment of acute migraine.

Effect of naratriptan on myocardial blood flow and coronary vasodilator reserve in migraineurs

BACKGROUND

Migraine drugs can produce adverse cardiac effects. The authors have demonstrated previously that ergotamine can lead to a significant reduction of hyperemic myocardial blood flow, but little is known about the effect of the newer serotonin analogues. Coronary artery constriction caused by serotonin or its analogues is mediated mainly by 5HT2 receptors. The selective 5HT1B/1D agonist naratriptan has no significant activity at 5HT2 receptors; however, like all 5HT1B/1D agonists developed for the acute treatment of migraine, naratriptan could potentially constrict coronary arteries by activation of 5HT1B receptors.

METHODS

The effects on myocardial blood flow of subcutaneous naratriptan 1.5 mg compared with placebo were assessed under resting and hyperemic conditions with PET using oxygen-15 labeled water during two separate visits. This study was a randomized, double-blind, placebo-controlled crossover trial in 34 migraine subjects with no evidence of ischemic heart disease, studied outside a migraine attack.

RESULTS

Naratriptan did not differ significantly from placebo in its effects on resting myocardial blood flow, but did evoke a small, significant fall in hyperemic myocardial blood flow (-13% versus placebo) and an increase in hyperemic coronary resistance (+19% versus placebo) without any signs or symptoms suggestive of myocardial ischemia. Naratriptan did not significantly affect the coronary vasodilator reserve (hyperemic/resting blood flow) compared with placebo.

CONCLUSIONS

These results show that at therapeutic doses, naratriptan exerts only a minor effect on myocardial blood flow, coronary vasodilator reserve, or coronary resistance among subjects with no evidence of ischemic heart disease. These results should not be extrapolated to patients with coronary artery disease, in whom all 5HT1 agonists for migraine are contraindicated.

Bone density of women who have recovered from anorexia nervosa

OBJECTIVE

To examine bone density in 19 women who had previously experienced classical anorexia nervosa from which they had been fully recovered for a mean of 21 years (current characteristics: median age 40.2 years; Eating Attitudes Test [EAT] score 2; body mass index [BMI] 21.1; average 1.8 offspring).

METHOD

Probands were compared, blindly, in respect of bone density, with 13 control subjects matched for age and sex and with no history of eating disorders. Dual energy X-ray absorptiometry (DXA) was used to evaluate the bone mineral density (BMD) of the lumbar spine and the head of the femur.

RESULTS

Femur BMD was still significantly less among ex-anorectic sufferers. Two subjects had experienced pathological fractures while anorectic, both having been strenuous exercisers. None appeared to have suffered post illness fractures. BMD at follow-up did not relate to the severity or chronicity of previous anorexia nervosa.

DISCUSSION

Full clinical recovery from anorexia nervosa does not quite confer full establishment of normal bone density. However, pathological fractures are not a feature thereafter, within middle life.

Porous alloplastic material encasement of gold weights for the treatment of paralytic lagophthalmos

PURPOSE

To determine if encasing gold weights in a porous alloplastic material would improve their longevity in situ.

METHODS

Gold weights used for passive eyelid reanimation in patients with paralytic lagophthalmos were wrapped in either expanded polytetrafluoroethylene (E-PTFE) or porous polyurethane (PPU) to allow cellular infiltration and ingrowth and increase the blood supply to the site of the implant. A total of 14 implants, six encased in E-PTFE, six encased in PPU, and two with no casings (controls), were tested for biocompatibility and stability in rabbit eyelids for 10 months.

RESULTS

Two of the PPU-encased gold weights showed some anterior extrusion, one at 3 months and one at 5 months after implantation. All of the E-PTFE-encased gold weights and both control weights were well tolerated for the entire study period. Histology of the alloplastic casings and surrounding tissues showed good tissue compatibility and cellular ingrowth for both alloplastic materials.

CONCLUSIONS

Encasing the weights in a biocompatible alloplastic material, such as E-PTFE, may decrease micromovement and improve attachment to the eyelid tissue, as well as increase blood supply to the area, thereby reducing the rates of the major complications--infection and extrusion--associated with these implants.

Why may teenage girls persist in smoking?

Teenage girls often smoke cigarettes, recognizing that it protects them from the impulse to binge eat with its feared weight-gain consequences. Evidence is marshalled from our studies of a female eating-disordered population, teenage females (London, U.K. and Ottawa, Canada) and middle-aged women (London and rural England) in the general population. Teenage female data analysis reveals links between smoking and body-weight/shape concerns. Those who smoked were likely to be moderately overweight. Smoking was also related at all ages to being postmenarchal. Sensitivity to shape is largely and qualitatively prompted by the development of body fat in puberty. Smoking by the London schoolgirls in particular also independently revealed an association with greater weight loss since puberty. Smoking was powerfully linked with vomiting undertaken as another defence against weight gain and may also be further reinforced as a behaviour by it. The eating-disordered population showed these latter associations most strikingly. Since smoking amongst older women is associated with below average body-weight it may indeed be effective in curbing weight gain and therefore promoting desired weight loss. Our studies provide little evidence of association between smoking and generalized or social anxiety. We propose that preventative psychological approaches to teenage female smoking should include attention to these matters.

Zanamivir in the prevention of influenza among healthy adults: a randomized controlled trial

CONTEXT

The neuraminidase inhibitor zanamivir, a sialic acid analog administered directly to the respiratory tract, has been demonstrated in clinical studies to be effective in treatment of type A and B influenza. It has also been shown to prevent influenza infection and disease in an experimental model.

OBJECTIVE

To examine the efficacy of zanamivir, administered once daily, in the prevention of influenza infection and disease.

DESIGN

Double-blind, randomized, placebo-controlled trial.

SETTING

Two midwestern university communities.

PARTICIPANTS

A total of 1107 healthy adults (mean age [range], 29 [18-69] years) were recruited in November 1997, before the influenza season.

INTERVENTION

At the start of the influenza outbreak, 554 subjects were randomized to receive placebo and 553 to receive zanamivir. The drug, 10 mg once per day, or identical placebo was administered by oral inhalation for a 4-week period.

MAIN OUTCOME MEASURES

Illness occurrence was recorded by participants daily and records were evaluated weekly. Specimens were collected for viral isolation when symptoms were reported within 3 days of illness onset. Infection was also identified by testing paired serum samples for rise in antibody titer against the circulating influenza viruses.

RESULTS

Zanamivir was 67% efficacious (95% confidence interval [CI], 39%-83%; P<.001) in preventing laboratory-confirmed clinical influenza meeting the case definition and 84% efficacious (95% CI, 55%-94%; P=.001) in preventing laboratory-confirmed illnesses with fever. All influenza infections occurring during the season, with or without symptoms, were prevented with an efficacy of 31% (95% CI, 4%-50%; P=.03). The nature and incidence of adverse events in the zanamivir group did not differ from placebo. Compliance with the once-daily dosage was high.

CONCLUSIONS

Zanamivir administered once daily is efficacious and well tolerated in the prevention of influenza for a 4-week period in healthy adults.

Valacyclovir for the prevention of cytomegalovirus disease after renal transplantation. International Valacyclovir Cytomegalovirus Prophylaxis Transplantation Study Group

BACKGROUND

Cytomegalovirus (CMV) disease is a major complication of organ transplantation. We hypothesized that prophylactic treatment with valacyclovir would reduce the risk of CMV disease.

METHODS

A total of 208 CMV-negative recipients of a kidney from a seropositive donor and 408 CMV-positive recipients were randomly assigned to receive either 2 g of valacyclovir or placebo orally four times daily for 90 days after transplantation, with the dose adjusted according to renal function. The primary end point was laboratory-confirmed CMV disease in the first six months after transplantation.

RESULTS

Treatment with valacyclovir reduced the incidence or delayed the onset of CMV disease in both the seronegative patients (P<0.001) and the seropositive patients (P=0.03). Among the seronegative patients, the incidence of CMV disease 90 days after transplantation was 45 percent among placebo recipients and 3 percent among valacyclovir recipients. Among the seropositive patients, the respective values were 6 percent and 0 percent. At six months, the incidence of CMV disease was 45 percent among seronegative recipients of placebo and 16 percent among seronegative recipients of valacyclovir; it was 6 percent among seropositive placebo recipients and 1 percent among seropositive valacyclovir recipients. At six months, the rate of biopsy-confirmed acute graft rejection in the seronegative group was 52 percent among placebo recipients and 26 percent among valacyclovir recipients (P=0.001). Treatment with valacyclovir also decreased the rates of CMV viremia and viruria, herpes simplex virus disease, and the use of inpatient medical resources. Hallucinations and confusion were more common with valacyclovir treatment, but these events were not severe or treatment-limiting. The rates of other adverse events were similar among the groups.

CONCLUSIONS

Prophylactic treatment with valacyclovir is a safe and effective way to prevent CMV disease after renal transplantation.

Effects of ergotamine on myocardial blood flow in migraineurs without evidence of atherosclerotic coronary artery disease

The effects of intravenous ergotamine (0.25 mg) on basal and hyperemic (dipyridamole) myocardial blood flow (MBF), measured with positron emission tomography and H2(15)O, were assessed in 15 migraineurs in a double-blind, randomized, placebo controlled, crossover study. Ergotamine produced a 27% reduction in hyperemic MBF (2.62 +/- 0.11 vs 3.72 +/- 1.05 ml x min(-1) x g(-1); p <0.05), a 31% reduction in the coronary vasodilator reserve (1.81 +/- 0.50 vs 2.71 +/- 1.15; p <0.01), and a 55% increase in minimal coronary resistance (42.2 +/- 15 vs 26.7 +/- 8 mm Hg x min x ml(-1) x g(-1); p <0.001), suggesting vasoconstriction of the coronary microcirculation.

Effect of silicone oil viscosity on emulsification

Emulsification of intravitreal silicone oil has been observed as a late complication after its use as a retinal tamponade. We compared the emulsification potential of silicone oil of different viscosities (100 centistokes [cs], 1000 cs, and 12,500 cs) and molecular composition in an in vitro model using a commercial detergent (benzalkonium chloride) and physiologic surface-active agents (human serum and lysed red blood cells). We found that silicone oils that have low-molecular-weight contents emulsify more readily than those that do not. Moreover, the extent and susceptibility to emulsification increases with decreasing viscosity or with an increase in the proportion of low-molecular-weight constituents. Hence, higher-molecular-weight (viscosity) oils or removal of low-molecular-weight components from medical grade fluid may lessen the emulsification observed clinically.

Errors in measurements of CO2 with the use of drying agents

To assess the errors in measurements of CO2 concentration that arise from the widespread use of drying agents in clinical and physiological studies, continuous measurements of CO2 concentration were made with an infra-red analyser before and after standard gas mixtures were passed through a tube containing one of several drying agents: calcium chloride; calcium sulphate (Drierite); alumina; silica gel; and magnesium perchlorate. The response time of the infra-red analyser was independent of the concentration of CO2 used (0-1%), but it was related to flow rate, dead space and the amount and drying agent used. At a low rate of 1 litre/min, alumina (145 g anhydrous weight) trapped virtually all the CO2 (0.8% in air) passing over it; silica gel (145 g anhydrous weight, mesh 6-20) adsorbed approximately 2 mmol CO2 (38% of total) over a period of 15 min; calcium sulphate (Drierite) absorbed a variable amount, depending on the bath; and calcium chloride adsorbed virtually no CO2. Increasing hydration of the drying agents reduced their capacity to adsorb CO2. Nitrogen was found to elute CO2 from the drying agents at about the same rate as it had been adsorbed. It is concluded that awareness of these adsorption/elution phenomena by drying agents should prevent errors from being made in the calibration of CO2 analysers, in the analysis of CO2, and in the measurement of specific activity or isotopic enrichment of CO2.