Biomedical subjects

D Carroll

Publications and source records attributed to D Carroll.

At least 37 records · Page 2Linked to original sources

PubMed2001

Modulation of the human nociceptive flexion reflex across the cardiac cycle.

Carotid baroreceptor stimulation has been shown to dampen pain. This study tested, in 40 normotensive adults, the hypothesis that pain is lower during systole when arterial baroreceptor stimulation is maximal than diastole when stimulation is minimal. The sural nerve was stimulated electrocutaneously to obtain a nociceptive flexion reflex (NFR) threshold, and then stimulation was delivered for 28 trials at 100% NFR threshold at seven intervals after the R-wave. Nociceptive responding was indexed by electromyographic (EMG) activity elicited in the biceps femoris. Significant variations in EMG activity occurred across the cardiac cycle, with less activity midcycle, indicating that the NFR response was attenuated during systole compared to diastole. Stimulation of baroreceptors by natural changes in blood pressure during the cardiac cycle dampened nociception, and accordingly, the data support the arterial baroreflex mechanism of hypertensive hypoalgesia.

Adult↗

PubMed2000

Requirements for double-strand cleavage by chimeric restriction enzymes with zinc finger DNA-recognition domains.

This study concerns chimeric restriction enzymes that are hybrids between a zinc finger DNA-binding domain and the non-specific DNA-cleavage domain from the natural restriction enzyme FOK:I. Because of the flexibility of DNA recognition by zinc fingers, these enzymes are potential tools for cleaving DNA at arbitrarily selected sequences. Efficient double-strand cleavage by the chimeric nucleases requires two binding sites in close proximity. When cuts were mapped on the DNA strands, it was found that they occur in pairs separated by approximately 4 bp with a 5' overhang, as for native FOK:I. Furthermore, amino acid changes in the dimer interface of the cleavage domain abolished activity. These results reflect a requirement for dimerization of the cleavage domain. The dependence of cleavage efficiency on the distance between two inverted binding sites was determined and both upper and lower limits were defined. Two different zinc finger combinations binding to non-identical sites also supported specific cleavage. Molecular modeling was employed to gain insight into the precise location of the cut sites. These results define requirements for effective targets of chimeric nucleases and will guide the design of novel specificities for directed DNA cleavage in vitro and in vivo.

Amino Acid Sequence↗

PubMed2000

Anticonvulsant drugs for acute and chronic pain.

BACKGROUND: Anticonvulsant drugs have been used in the management of pain since the 1960s. The clinical impression is that they are useful for neuropathic pain, especially when the pain is lancinating or burning. OBJECTIVES: To evaluate the analgesic effectiveness of anticonvulsant drugs compared to either placebo or other drugs in order to provide evidence-based recommendations for pain management in clinical practice and to identify a clinical research agenda. Adverse effects are also considered. SEARCH STRATEGY: Randomised trials of anticonvulsants in acute, chronic or cancer pain were identified by Medline (Silver Platter 3.0, 3.1 and 3.11) from 1966 to February 1994. In addition, 40 medical journals were hand searched (published between 1950 and 1990). Additional reports were identified from the reference list of the retrieved papers, and contacting investigators. Date of the most recent searches: 1994. SELECTION CRITERIA: Randomised trials reporting the analgesic effects of anticonvulsant drugs in patients, with pain assessment as either the primary or a secondary outcome. DATA COLLECTION AND ANALYSIS: Data were extracted by two independent reviewers, and trials were quality scored. Numbers-needed-to-treat (NNTs) were calculated from dichotomous data for effectiveness, adverse effects and drug-related study withdrawal, for individual studies and for pooled data. MAIN RESULTS: Twenty trials of four anticonvulsants were considered eligible (746 patients). The only placebo-controlled study in acute pain found no analgesic effect of sodium valproate. Three placebo-controlled studies of carbamazepine in trigeminal neuralgia had a combined NNT for effectiveness of 2.6, for adverse effects 3.4, and for severe effects (withdrawal from study) 24. Three placebo-controlled studies of diabetic neuropathy had a combined NNT for effectiveness of 3, for adverse effects 2.5, and for severe effects 20. Three placebo-controlled studies of migraine prophylaxis had a combined NNT for effectiveness of 2.4, for adverse effects 2.4 and for severe effects 39. Phenytoin had no effect in irritable bowel syndrome, and carbamazepine little effect in post-stroke pain. Clonazepam was effective in one study of temporomandibular joint dysfunction. No study compared one anticonvulsant with another. Anticonvulsants fared poorly against other treatments. REVIEWER'S CONCLUSIONS: Although anticonvulsants are used widely in chronic pain surprisingly few trials show analgesic effectiveness. No trial compared different anticonvulsants. There is no evidence that anticonvulsants are effective for acute pain. In chronic pain syndromes other than trigeminal neuralgia anticonvulsants should be withheld until other interventions have been tried.

Acute Disease↗

PubMed2000

Single dose paracetamol (acetaminophen), with and without codeine, for postoperative pain.

BACKGROUND: Patient surveys have shown that postoperative pain is often not managed well, and there is a need to assess the efficacy and safety of commonly used analgesics as newer treatments become available. Paracetamol (acetaminophen) is an important non-opiate analgesic, commonly prescribed, as well as being available for retail sale. This review seeks to examine the efficacy of paracetamol alone and in combination with codeine, and also considers adverse effects. OBJECTIVES: To assess the analgesic efficacy and adverse effects of a single dose of oral paracetamol (acetaminophen) alone and in combination with codeine for moderate to severe postoperative pain. SEARCH STRATEGY: Published trials were identified from: Medline (1966 to May 1996), Embase (1980 to 1996), Cochrane Library (Issue 2 1996) and the Oxford Pain Relief Database (1950 to 1994). Additional trials were identified from reference lists of retrieved studies. Date of most recent searches: July 1998. SELECTION CRITERIA: Inclusion criteria were: full journal publication, postoperative pain, postoperative oral administration, adult patients, baseline pain of moderate to severe intensity, double-blind design, and random allocation to treatment groups which compared paracetamol with placebo or a combination of paracetamol and codeine with either placebo or the same dose of paracetamol alone. DATA COLLECTION AND ANALYSIS: Data were extracted by two independent reviewers, and trials were quality scored. Summed pain intensity and pain relief data were extracted and converted into dichotomous information to yield the number of patients with at least 50% pain relief. This was used to calculate the relative benefit and number-needed-to-treat (NNT) for one patient to achieve at least 50% pain relief over 4 to 6 hours compared with placebo. Adverse effects were used to calculate relative risk and number-needed-to-harm (NNH). MAIN RESULTS: We found 40 trials of paracetamol against placebo (4171 patients), 22 trials of paracetamol plus codeine against placebo (1407 patients) and 12 trials of paracetamol plus codeine against the same dose of paracetamol (794 patients). In postoperative pain paracetamol 1000 mg had an NNT of 4.6 (3.8-5.4) for at least 50% pain relief when compared with placebo, and paracetamol 600/650 mg had an NNT of 5.3 (4.1-7.2). Paracetamol 600/650 mg plus codeine 60 mg had an NNT of 3. 6 (2.9-4.5). Comparing paracetamol plus codeine 60 mg with the same dose of paracetamol alone gave an NNT of 7.7 (5.1-17) for at least 50% pain relief. Adverse effects: Relative risk estimates for paracetamol 600/650 mg plus codeine 60 mg versus placebo showed a significant difference for 'drowsiness'/somnolence (NNH 11 (7.5- 0)) and dizziness (NNH 27 (15-164)) but no significant difference for nausea/vomiting. REVIEWER'S CONCLUSIONS: Paracetamol is an effective analgesic with a low incidence of adverse effects. The addition of codeine 60 mg to paracetamol produces additional pain relief even in single oral doses, but may be accompanied by an increase in drowsiness and dizziness.

Acetaminophen↗

PubMed2000

Radiotherapy for the palliation of painful bone metastases.

BACKGROUND: Radiotherapy is used commonly to provide pain relief for painful bone metastases, and there is a perception that of the three-quarters of patients who achieve pain relief, half of these stay free from pain. However, the precise contribution from radiotherapy may be unclear because of difficulties in assessing the numbers of people achieving relief, the extent of relief and its duration, and the influence of other contemporaneous interventions, such as analgesics. OBJECTIVES: To assess pain relief from: 1. localised bone metastases achieved by radiotherapy, comparing the efficacy of different fractionation schedules 2. more generalised metastatic disease achieved by radiotherapy or radioisotopes. SEARCH STRATEGY: Studies were identified by searching Medline (1966 to August 1998), Embase (1980 to 1998), the Cochrane Library (1998 Issue 3) and the Oxford Pain Relief Database (1950 to 1994). SELECTION CRITERIA: The inclusion criteria used were: full journal publication, patients with pain due to bone metastases, and random allocation to a radiotherapeutic intervention (either external irradiation or administration of radioisotopes). DATA COLLECTION AND ANALYSIS: The number of patients achieving complete pain relief and at least 50% at one month were compared with an assumed natural history of 1 in 100 patients achieving pain relief without treatment to obtain the number-needed-to-treat (NNT). Summed pain relief or pain intensity difference over four to six hours was extracted, converted into dichotomous information yielding the number of patients with at least 50% pain relief, and used to calculate the relative benefit and the NNT for one patient to achieve at least 50% pain relief. MAIN RESULTS: Twenty trials reported on 43 different radiotherapy fractionation schedules and eight studies of radioisotopes. Radiotherapy produced complete pain relief at one month in 395/1580 (25%) patients, and at least 50% relief in 788/1933 (41%) patients at some time during the trials. There were no differences in the proportions of patients achieving these outcomes between single or multiple fraction schedules. The number-needed-to-treat (NNT) to achieve complete relief at one month (compared with an assumed natural history of 1 in 100 patients whose pain resolved without treatment) was 4.2 (95% CI 3.7-4.7). No pooled estimates of speed of onset of relief, or of its duration, could be obtained. In the largest trial (759 patients) 52% of those who had complete relief had achieved it within four weeks, and the median duration of complete relief was 12 weeks. For more generalised disease, radioisotopes produced similar analgesic results to external irradiation. Adverse effect reporting was poor. There were no obvious differences between the various fractionation schedules in the incidence of nausea and vomiting, diarrhoea or pathological fractures. REVIEWER'S CONCLUSIONS: Radiotherapy is clearly effective at reducing pain from painful bone metastases. There was no evidence of any difference in efficacy between different fractionation schedules, nor indeed of a dose-response with total dose of radiation. For treatment of generalised bone pain both hemibody irradiation and radioisotopes can reduce the number of painful new sites.

Bone Neoplasms↗

PubMed2000

Single dose oral aspirin for acute pain.

BACKGROUND: Aspirin has been known to be an effective analgesic for many years and is commonly used throughout the world for many different pain conditions. It is important for both prescribers and patients to have the best possible information about the efficacy and safety of analgesics, and this need is reflected in patient surveys which show that postoperative pain is often poorly managed. We also need to benchmark relative efficacy and safety of current analgesics so that we can compare them with new analgesics. OBJECTIVES: To quantitatively assess the analgesic efficacy and adverse effects of a single-dose of aspirin in acute pain of moderate to severe intensity. SEARCH STRATEGY: Randomised trials were identified by searching Medline (1966 to March 1998), Embase (1980 to January 1998), the Cochrane Library (Issue 1,1998) and the Oxford Pain Relief Database (1950 to 1994). SELECTION CRITERIA: The inclusion criteria used were: full journal publication, postoperative pain or a mixture of postoperative and acute trauma pain, oral administration, adult patients, baseline pain of moderate to severe intensity, double-blind design, and random allocation to treatment groups which compared aspirin with placebo. DATA COLLECTION AND ANALYSIS: Summed pain relief or pain intensity difference over four to six hours was extracted, and converted into dichotomous information yielding the number of patients with at least 50% pain relief. This was then used to calculate the relative benefit and the number-needed-to-treat (NNT) for one patient to achieve at least 50% pain relief. MAIN RESULTS: Seventy-two randomised single-dose trials met our inclusion criteria, with 3253 patients given aspirin, and 3297 placebo. Significant benefit of aspirin over placebo was shown for aspirin 600/650 mg, 1000 mg and 1200 mg, NNTs for at least 50% pain relief of 4.4 (4.0 to 4.9), 4.0 (3.2 to 5.4) and 2.4 (1.9 to 3.2) respectively. Single-dose aspirin 600/650 mg produced significantly more drowsiness and gastric irritation than placebo, with a number-needed-to-harm (NNH) of 28 (19 to 52) and 38 (22 to 174) respectively. Type of pain model, pain measurement, sample size, quality of study design, and study duration had no significant impact on the results. REVIEWER'S CONCLUSIONS: Aspirin is an effective analgesic for acute pain of moderate to severe intensity with a clear dose-response. Drowsiness and gastric irritation were seen as significant adverse effects even though the studies were single-dose. The pain relief achieved with aspirin was very similar milligram for milligram to that seen with paracetamol.

Acute Disease↗

PubMed2000

The effects of an oral multivitamin combination with calcium, magnesium, and zinc on psychological well-being in healthy young male volunteers: a double-blind placebo-controlled trial.

RATIONALE: Vitamin and mineral supplements may be associated with improved psychological status. OBJECTIVE: The present study tested the effects of a multivitamin and mineral supplement (Berocca) on psychological well-being. METHODS: In a double-blind randomised-control trial, 80 healthy male volunteers were assigned to either Berocca or placebo. Questionnaires measuring psychological state were completed and a blood sample taken to determine plasma zinc concentration on day 1 (pre-treatment) and again on day 28 (post-treatment), following 28 days of treatments, which were administered at a dosage of one tablet daily. At the end of the study, the acceptability of the treatment and participants' awareness of treatment condition were assessed, as was habitual dietary behaviour. RESULTS: Relative to placebo, treatment with Berocca was associated with consistent and statistically significant reductions in anxiety and perceived stress. Participants in the Berocca group also tended to rate themselves as less tired and better able to concentrate following treatment. In addition, participants registered more somatic symptoms following placebo than following Berocca. These effects cannot be attributed to differences in the acceptability of the two treatments or to participants guessing what treatment they received. CONCLUSION: These findings demonstrate that Berocca significantly reduces anxiety and perceived stress.

Adolescent↗

PubMed2000

Effects of depression and anxiety on mortality and quality-of-life 4 months after myocardial infarction.

OBJECTIVE: The purpose of this study was to determine the impact of depression and anxiety on mortality and quality-of-life in patients hospitalized for an acute myocardial infarction (MI). METHODS: Questionnaire measures of depression and anxiety were completed during hospitalization by 288 MI patients. The main outcomes were mortality and quality-of-life, assessed by the Dartmouth COOP charts, at 4 months. RESULTS: A total of 25 patients died, 22 from cardiac causes, during the 4-month follow-up. Symptoms of depression and anxiety did not predict either cardiac or all-cause mortality. Severity of infarction, extent of heart failure, and a longer stay in hospital predicted mortality. Symptoms of depression and anxiety predicted 4-month quality-of-life among survivors, as did gender, partner status, occupational status, living alone, previous exercise behaviour, length of hospital admission, and Peel Index scores. In a multiple regression model, depression emerged as the strongest predictor of quality-of-life. State anxiety, severity of infarction, and partner status also entered the model. CONCLUSION: Neither depression nor anxiety predicted mortality 4 months after MI. Both depression and anxiety predicted quality-of-life at 4 months among survivors.

Adult↗

PubMed2000

Secretory immunoglobulin A and cardiovascular activity during mental arithmetic: effects of task difficulty and task order.

Secretory immunoglobulin A (sIgA) in saliva and cardiovascular activity were measured at rest and during mental arithmetic. Task difficulty was manipulated by presenting easy, hard, and impossible versions of the mental arithmetic task in counterbalanced order, while task novelty was operationalised as order of presentation (i.e. first, second, third). Mental arithmetic elicited significant increases in sIgA concentration and sIgA secretion rate, as well as significant cardiovascular effects. Performance decreased and rated difficulty increased with increasing task difficulty. However, sIgA and cardiovascular activity, with the exception of diastolic blood pressure, were insensitive to variations in task difficulty. In contrast, sIgA concentration and a broad range of cardiovascular variables were influenced by task novelty, with more pronounced activity characterising the task version presented first, irrespective of its level of difficulty. Task novelty would seem to be a more important determinant of sIgA and cardiovascular activity than task difficulty.

Adult↗

PubMed2000

Cardiovascular and secretory immunoglobulin A reactions to humorous, exciting, and didactic film presentations.

Secretory immunoglobulin A (sIgA) in saliva and cardiovascular activity were measured at rest and in response to three film extracts varying in affective content. Subjective ratings of film impact confirmed a priori assumptions; the humorous film was rated as funnier than the other two films, the didactic film as more boring than the other two films, and the exciting film as more exciting and more stressful than the other two films. The films elicited distinct patterns of cardiovascular autonomic activity. The exciting film provoked changes characteristic of beta-adrenergic activation: increased systolic blood pressure (SBP); heart rate (HR); cardiac output (CO); and shortened pre-ejection period (PEP). The didactic film had little impact on cardiovascular activity. While an increase in total peripheral resistance (TPR) occurred, the humorous film was largely notable for a reduction in beta-adrenergic drive, as evidenced by reduced CO and a lengthening of PEP. In contrast to previous research reporting a rise in sIgA particular to humorous exposures, the sIgA secretion rate, although enhanced by exposure to the films, did not vary with film content.

Adult↗

PubMed2000

Motor cortex stimulation for chronic neuropathic pain: a preliminary study of 10 cases.

There is growing evidence to support the use of motor cortex stimulation (MCS) in the management of patients with chronic neuropathic pain. A prospective audit of ten patients using a modified staged technique for motor cortex implantation provides further evidence for the analgesic effectiveness of this technique. Ten patients suffering from phantom limb pain (n=3), post stroke pain (n=5), post traumatic neuralgia secondary to gunshot injury to the brain stem (n=1) and brachyalgia secondary to neuro-fibromatosis (n=150% pain relief) and long-term benefit in 4/5 of patients who initially responded to intermittent cortical stimulation (longest follow up 31 months after implantation). Of those patients who benefited two had post stroke pain, two phantom limb pain and one post-traumatic neuralgia. We conclude that motor cortex stimulation is an effective analgesic intervention in some patients with chronic neuropathic pain, but it is difficult if not impossible to predict those patients who may respond to treatment prior to implantation. Randomised controlled trials are now urgently needed to test the effectiveness of motor cortex stimulation under double-blind conditions.

Adult↗

PubMed2000

Comparative studies of the endonucleases from two related Xenopus laevis retrotransposons, Tx1L and Tx2L: target site specificity and evolutionary implications.

In the genome of the South African frog, Xenopus laevis, there are two complex families of transposable elements, Tx1 and Tx2, that have identical overall structures, but distinct sequences. In each family there are approximately 1500 copies of an apparent DNA-based element (Tx1D and Tx2D). Roughly 10% of these elements in each family are interrupted by a non-LTR retrotransposon (Tx1L and Tx2L). Each retrotransposon is flanked by a 23-bp target duplication of a specific D element sequence. In earlier work, we showed that the endonuclease domain (Tx1L EN) located in the second open reading frame (ORF2) of Tx1L encodes a protein that makes a single-strand cut precisely at the expected site within its target sequence, supporting the idea that Tx1L is a site-specific retrotransposon. In this study, we express the endonuclease domain of Tx2L (Tx2L EN) and compare the target preferences of the two enzymes. Each endonuclease shows some preference for its cognate target, on the order of 5-fold over the non-cognate target. The observed discrimination is not sufficient, however, to explain the observation that no cross-occupancy is observed - that is, L elements of one family have never been found within D elements of the other family. Possible sources of additional specificity are discussed. We also compare two hypotheses regarding the genome duplication event that led to the contemporary pseudotetraploid character of Xenopus laevis in light of the Tx1L and Tx2L data.

Amino Acid Sequence↗

PubMed2000

Single-dose ketorolac and pethidine in acute postoperative pain: systematic review with meta-analysis.

For a systematic review of postoperative analgesic efficacy and adverse effects of single doses, injected or oral, of pethidine and ketorolac compared with placebo, we sought published randomized studies in moderate to severe postoperative pain. Information on summed pain intensity or pain relief outcomes over 4-6 h was extracted and converted to dichotomous information to produce the number of patients with at least 50% pain relief. This was used to calculate the relative benefit and number-needed-to-treat (NNT) for one patient to achieve at least 50% pain relief. Minor and major adverse effect data were extracted and summarized. For pethidine 100 mg i.m., eight randomized, controlled studies met the inclusion criteria, with 203 patients given pethidine and 161 placebo. The NNT to produce at least 50% pain relief was 2.9 (95% confidence interval 2.3-3.9). At this dose, pethidine produced significantly more drowsiness and dizziness than placebo, with numbers-needed-to-harm (NNH) of 2.9 (2.2-4.4) and 7.2 (4.8-14), respectively. For ketorolac, 14 reports met the inclusion criteria (six i.m. and eight oral). Most i.m. information (176 patients) was available for the 30 mg dose, which had an NNT of 3.4 (2.5-4.9). Most oral information was available for the 10 mg dose, which had an NNT of 2.6 (2.3-3.1). Oral ketorolac 10 mg was consistently at least as effective as ketorolac 30 mg i.m. Only with oral ketorolac 10 mg were there significantly more adverse effects than with placebo, with an NNH for any adverse effect of 7.3 (4.7-17).

Acute Disease↗

PubMed2000

Do depression and anxiety predict recurrent coronary events 12 months after myocardial infarction?

We examined the association between depression and anxiety and recurrent coronary heart disease events during the first 12 months subsequent to myocardial infarction. The Beck Depression Inventory and the State-Trait Anxiety Inventory were completed during hospitalization by 288 myocardial infarction patients. Peel Index score and Killip class were used as indices of disease severity. The 12-month incidence of recurrent coronary heart disease events (fatal and non-fatal) was determined. Eighty-two patients experienced recurrent coronary heart disease events, including 27 cardiac fatalities, during follow-up. Whereas the Peel Index differentiated patients who experienced recurrent events from those who did not (OR 3.00, 95% CI 1.46-6.20), symptoms of depression (OR 0.97, 95% CI 0. 55-1.70) and anxiety (OR 1.00, 95% CI 0.98-1.02) were unrelated to outcome. Depression and anxiety did not predict subsequent coronary heart disease events and were not associated with either Peel Index scores or Killip class.

Anxiety↗

PubMed2000

Expression, purification, and structural analysis of the trimeric form of the catalytic domain of the Escherichia coli dihydrolipoamide succinyltransferase.

The dihydrolipoamide succinyltransferase (E2o) component of the alpha-ketoglutarate dehydrogenase complex catalyzes the transfer of a succinyl group from the S-succinyldihydrolipoyl moiety to coenzyme A. E2o is normally a 24-mer, but is found as a trimer when E2o is expressed with a C-terminal [His]6 tag. The crystal structure of the trimeric form of the catalytic domain (CD) of the Escherichia coli E2o has been solved to 3.0 A resolution using the Molecular Replacement method. The refined model contains an intact trimer in the asymmetric unit and has an R-factor of 0.257 (Rfree = 0.286) for 18,699 reflections between 10.0 and 3.0 A resolution. The core of tE2oCD (residues 187-396) superimposes onto that of the cubic E2oCD with an RMS difference of 0.4 A for all main-chain atoms. The C-terminal end of tE2oCD (residues 397-404) rotates by an average of 37 degrees compared to cubic E2oCD, disrupting the normal twofold interface. Despite the alteration of quaternary structure, the active site of tE2oCD shows no significant differences from that of the cubic E2oCD, although several side chains in the active site are more ordered in the trimeric form of E2oCD. Analysis of the available sequence data suggests that the majority of E2 components have active sites that resemble that of E. coli E2oCD. The remaining E2 components can be divided into three groups based on active-site sequence similarity. Analysis of the surface properties of both crystal forms of E. coli E2oCD suggests key residues that may be involved in the protein-protein contacts that occur between the catalytic and lipoyl domains of E2o.

Acyltransferases↗

PubMed2000

Triple-helix formation induces recombination in mammalian cells via a nucleotide excision repair-dependent pathway.

The ability to stimulate recombination in a site-specific manner in mammalian cells may provide a useful tool for gene knockout and a valuable strategy for gene therapy. We previously demonstrated that psoralen adducts targeted by triple-helix-forming oligonucleotides (TFOs) could induce recombination between tandem repeats of a supF reporter gene in a simian virus 40 vector in monkey COS cells. Based on work showing that triple helices, even in the absence of associated psoralen adducts, are able to provoke DNA repair and cause mutations, we asked whether intermolecular triplexes could stimulate recombination. Here, we report that triple-helix formation itself is capable of promoting recombination and that this effect is dependent on a functional nucleotide excision repair (NER) pathway. Transfection of COS cells carrying the dual supF vector with a purine-rich TFO, AG30, designed to bind as a third strand to a region between the two mutant supF genes yielded recombinants at a frequency of 0.37%, fivefold above background, whereas a scrambled sequence control oligomer was ineffective. In human cells deficient in the NER factor XPA, the ability of AG30 to induce recombination was eliminated, but it was restored in a corrected subline expressing the XPA cDNA. In comparison, the ability of triplex-directed psoralen cross-links to induce recombination was only partially reduced in XPA-deficient cells, suggesting that NER is not the only pathway that can metabolize targeted psoralen photoadducts into recombinagenic intermediates. Interestingly, the triplex-induced recombination was unaffected in cells deficient in DNA mismatch repair, challenging our previous model of a heteroduplex intermediate and supporting a model based on end joining. This work demonstrates that oligonucleotide-mediated triplex formation can be recombinagenic, providing the basis for a potential strategy to direct genome modification by using high-affinity DNA binding ligands.

Animals↗

PubMed2000

Target specificity of the endonuclease from the Xenopus laevis non-long terminal repeat retrotransposon, Tx1L.

Elements of the Tx1L family are non-long terminal repeat retrotransposons (NLRs) that are dispersed in the genome of Xenopus laevis. Essentially all genomic copies of Tx1L are found inserted at a specific site within another family of transposable elements (Tx1D). This suggests that Tx1L is a site-specific retrotransposon. Like many (but not all) other NLRs, the Xenopus element encodes an apparent endonuclease that is related in sequence to the apurinic-apyrimidinic endonucleases that participate in DNA repair. This enzyme is thought to introduce the single-strand break in target DNA that initiates transposition by the target-primed reverse transcription (TPRT) mechanism. To explore the issue of target specificity more fully, we expressed the polypeptide encoded by the endonuclease domain of open reading frame 2 from Tx1L (Tx1L EN) and characterized its cleavage capabilities. This endonuclease makes a specific nick in the bottom strand precisely at one end of the presumed Tx1L target duplication. Because this activity leaves a 5'-phosphate and 3'-hydroxyl at the nick, it has the location and chemistry required to initiate new insertion events by TPRT. Tx1L EN does not make a specific cut at a preferred target site for Tx1D elements, ruling out the alternative possibility that the composite Tx1L-Tx1D element moves as a unit under the control of functions encoded by Tx1L. Further characterization revealed that the endonuclease remains active for many hours at room temperature and that it is capable of enzymatic turnover. Scanning substitution mutagenesis located the recognition site for Tx1L EN within 10 bp surrounding the primary nick site. Implications of these features for natural transposition events are discussed.

Animals↗

PubMed2000

The pathological status of exercise dependence.

OBJECTIVES: This study was concerned with the concept of exercise dependence. Levels of psychological morbidity, personality profiles, and exercise beliefs were compared among subjects screened for exercise dependence and eating disorders. METHOD: Adult female exercisers were allocated on the basis of questionnaire screening to one of the following groups: primary exercise dependence (n = 43); secondary exercise dependence, where there was the coincidence of exercise dependence and an eating disorder (n = 27); eating disorder (n =14); control, where there was no evidence of either exercise dependence or eating disorder (n = 110). Questionnaire assessment was undertaken of psychological morbidity, self esteem, weight and body shape dissatisfaction, personality, and exercise beliefs. RESULTS: Aside from a higher incidence of reported menstrual abnormalities, the primary exercise dependence group was largely indistinguishable from the controls. In stark contrast, the secondary exercise dependence group reported higher levels of psychological morbidity, neuroticism, dispositional addictiveness, and impulsiveness, lower self esteem, greater concern with body shape and weight, as well as with the social, psychological, and aesthetic costs of not exercising than the controls, but differed little from the eating disorder group. CONCLUSIONS: In the absence of an eating disorder, women identified as being exercise dependent do not exhibit the sorts of personality characteristics and levels of psychological distress that warrant the construction of primary exercise dependence as a widespread pathology.

Adult↗