Biomedical subjects

D Baker

Publications and source records attributed to D Baker.

At least 73 records · Page 4Linked to original sources

PubMed2000

Endocannabinoids control spasticity in a multiple sclerosis model.

Spasticity is a complicating sign in multiple sclerosis that also develops in a model of chronic relapsing experimental autoimmune encephalomyelitis (CREAE) in mice. In areas associated with nerve damage, increased levels of the endocannabinoids, anandamide (arachidonoylethanolamide, AEA) and 2-arachidonoyl glycerol (2-AG), and of the AEA congener, palmitoylethanolamide (PEA), were detected here, whereas comparable levels of these compounds were found in normal and non-spastic CREAE mice. While exogenously administered endocannabinoids and PEA ameliorate spasticity, selective inhibitors of endocannabinoid re-uptake and hydrolysis-probably through the enhancement of endogenous levels of AEA, and, possibly, 2-arachidonoyl glycerol-significantly ameliorated spasticity to an extent comparable with that observed previously with potent cannabinoid receptor agonists. These studies provide definitive evidence for the tonic control of spasticity by the endocannabinoid system and open new horizons to therapy of multiple sclerosis, and other neuromuscular diseases, based on agents modulating endocannabinoid levels and action, which exhibit little psychotropic activity.

Amides↗

PubMed2000

A multivariate analysis of factors associated with depression: evaluating the role of health literacy as a potential contributor.

BACKGROUND: High rates of low health literacy among elderly populations along with a high prevalence of chronic conditions may lead to increased levels of depression symptomatology. We sought to determine whether older adults with inadequate health literacy were more likely to report depressive symptoms and whether health literacy was an independent predictor of depression symptomatology. METHODS: A total of 3260 new Medicare enrollees 65 years or older were interviewed in person between June and December 1997 from 4 managed care plans (853 in Cleveland, Ohio, 498 in Houston, Tex, 975 in South Florida, and 934 in Tampa, Fla). Depression symptoms were measured by the Geriatric Depression Scale. RESULTS: Overall, 13% of respondents were classified as depressed. Individuals with inadequate health literacy had 2.7 times the odds (95% confidence interval, 2.2-3.4) of being depressed compared with individuals with adequate health literacy skills. However, after controlling for health status with multiple logistic regression, individuals with inadequate health literacy were not more likely to be depressed (adjusted odds ratio, 1.2; 95% confidence interval, 0.9-1.7). Individuals who had less social support, exercised less than twice a week, drank alcohol heavily, or had poor health status (at least 3 health conditions, physical limitations, or fair or poor self-rated health) had significantly higher odds of depression symptomatology. CONCLUSIONS: Although individuals with inadequate health literacy were more than twice as likely to report depressive symptoms, this was mostly explained by their worse health status. The strong relation between depression symptoms and poor health status suggests the need to research interventions to improve mental and physical health concurrently. The influence of particular interventions on depression, such as referral to community support contacts and recommendations for an exercise program, needs to be further evaluated. Arch Intern Med. 2000;160:3307-3314.

Activities of Daily Living↗

PubMed2000

Sensory neuron-specific sodium channel SNS is abnormally expressed in the brains of mice with experimental allergic encephalomyelitis and humans with multiple sclerosis.

Clinical abnormalities in multiple sclerosis (MS) have classically been considered to be caused by demyelination and/or axonal degeneration; the possibility of molecular changes in neurons, such as the deployment of abnormal repertoires of ion channels that would alter neuronal electrogenic properties, has not been considered. Sensory Neuron-Specific sodium channel SNS displays a depolarized voltage dependence, slower activation and inactivation kinetics, and more rapid recovery from inactivation than classical "fast" sodium channels. SNS is selectively expressed in spinal sensory and trigeminal ganglion neurons within the peripheral nervous system and is not expressed within the normal brain. Here we show that sodium channel SNS mRNA and protein, which are not present within the cerebellum of control mice, are expressed within cerebellar Purkinje cells in a mouse model of MS, chronic relapsing experimental allergic encephalomyelitis. We also demonstrate SNS mRNA and protein expression within Purkinje cells from tissue obtained postmortem from patients with MS, but not in control subjects with no neurological disease. These results demonstrate a change in sodium channel expression in neurons within the brain in an animal model of MS and in humans with MS and suggest that abnormal patterns of neuronal ion channel expression may contribute to clinical abnormalities such as ataxia in these disorders.

Animals↗

PubMed2000

Topology, stability, sequence, and length: defining the determinants of two-state protein folding kinetics.

The fastest simple, single domain proteins fold a million times more rapidly than the slowest. Ultimately this broad kinetic spectrum is determined by the amino acid sequences that define these proteins, suggesting that the mechanisms that underlie folding may be almost as complex as the sequences that encode them. Here, however, we summarize recent experimental results which suggest that (1) despite a vast diversity of structures and functions, there are fundamental similarities in the folding mechanisms of single domain proteins and (2) rather than being highly sensitive to the finest details of sequence, their folding kinetics are determined primarily by the large-scale, redundant features of sequence that determine a protein's gross structural properties. That folding kinetics can be predicted using simple, empirical, structure-based rules suggests that the fundamental physics underlying folding may be quite straightforward and that a general and quantitative theory of protein folding rates and mechanisms (as opposed to unfolding rates and thus protein stability) may be near on the horizon.

Amino Acid Sequence↗

PubMed2000

Native protein sequences are close to optimal for their structures.

How large is the volume of sequence space that is compatible with a given protein structure? Starting from random sequences, low free energy sequences were generated for 108 protein backbone structures by using a Monte Carlo optimization procedure and a free energy function based primarily on Lennard-Jones packing interactions and the Lazaridis-Karplus implicit solvation model. Remarkably, in the designed sequences 51% of the core residues and 27% of all residues were identical to the amino acids in the corresponding positions in the native sequences. The lowest free energy sequences obtained for ensembles of native-like backbone structures were also similar to the native sequence. Furthermore, both the individual residue frequencies and the covariances between pairs of positions observed in the very large SH3 domain family were recapitulated in core sequences designed for SH3 domain structures. Taken together, these results suggest that the volume of sequence space optimal for a protein structure is surprisingly restricted to a region around the native sequence.

Amino Acid Sequence↗

PubMed2000

HMMSTR: a hidden Markov model for local sequence-structure correlations in proteins.

We describe a hidden Markov model, HMMSTR, for general protein sequence based on the I-sites library of sequence-structure motifs. Unlike the linear hidden Markov models used to model individual protein families, HMMSTR has a highly branched topology and captures recurrent local features of protein sequences and structures that transcend protein family boundaries. The model extends the I-sites library by describing the adjacencies of different sequence-structure motifs as observed in the protein database and, by representing overlapping motifs in a much more compact form, achieves a great reduction in parameters. The HMM attributes a considerably higher probability to coding sequence than does an equivalent dipeptide model, predicts secondary structure with an accuracy of 74.3 %, backbone torsion angles better than any previously reported method and the structural context of beta strands and turns with an accuracy that should be useful for tertiary structure prediction.

Amino Acid Motifs↗

PubMed2000

NMR characterization of residual structure in the denatured state of protein L.

Triple-resonance NMR experiments were used to assign the (13)C(alpha), (13)C(beta), (15)N and NH resonances for all the residues in the denatured state of a destabilized protein L variant in 2 M guanidine. The chemical shifts of most resonances were very close to their random coil values. Significant deviations were observed for G22, L38 and K39; increasing the denaturant concentration shifted the chemical shifts of these residues towards theory random coil values. Medium-range nuclear Overhauser enhancements were detected in segments corresponding to the turn between the first two strands, the end of the second strand through the turn between the second strand and the helix, and the turn between the helix and the third strand in 3D H(1), N(15)-HSQC-NOESY-HSQC experiments on perdeuterated samples. Longer-range interactions were probed by measuring the paramagnetic relaxation enhancement produced by nitroxide spin labels introduced via cysteine residues at five sites around the molecule. Damped oscillations in the magnitude of the paramagnetic relaxation enhancement as a function of distance along the sequence suggested native-like chain reversals in the same three turn regions. The more extensive interactions within the region corresponding to the first beta-turn than in the region corresponding to the second beta-turn suggests that the asymmetry in the folding reaction evident in previous studies of the protein L folding transition state is already established in the denatured state.

Amino Acid Sequence↗

PubMed2000

Long-range order in the src SH3 folding transition state.

One of the outstanding questions in protein folding concerns the degree of heterogeneity in the folding transition state ensemble: does a protein fold via a large multitude of diverse "pathways," or are the elements of native structure assembled in a well defined order? Herein, we build on previous point mutagenesis studies of the src SH3 by directly investigating the association of structural elements and the loss of backbone conformational entropy during folding. Double-mutant analysis of polar residues in the distal beta-hairpin and the diverging turn indicates that the hydrogen bond network between these elements is largely formed in the folding transition state. A 10-glycine insertion in the n-src loop (which connects the distal hairpin and the diverging turn) and a disulfide crosslink at the base of the distal beta-hairpin exclusively affect the folding rate, showing that these structural elements are nearly as ordered in the folding transition state as in the native state. In contrast, crosslinking the base of the RT loop or the N and C termini dramatically slows down the unfolding rate, suggesting that dissociation of the termini and opening of the RT loop precede the rate-limiting step in unfolding. Taken together, these results suggest that essentially all conformations in the folding transition state ensemble have the central three-stranded beta-sheet formed, indicating that, for the src homology 3 domain, there is a discrete order to structure assembly during folding.

Animals↗

PubMed2000

A breakdown of symmetry in the folding transition state of protein L.

The 62 residue IgG binding domain of protein L consists of a central alpha-helix packed on a four-stranded beta-sheet formed by N and C-terminal beta-hairpins. The overall topology of the protein is quite symmetric: the beta-hairpins have similar lengths and make very similar interactions with the central helix. Characterization of the effects of 70 point mutations distributed throughout the protein on the kinetics of folding and unfolding reveals that this symmetry is completely broken during folding; the first beta-hairpin is largely structured while the second beta-hairpin and helix are largely disrupted in the folding transition state ensemble. The results are not consistent with a "hydrophobic core first" picture of protein folding; the first beta-hairpin appears to be at least as ordered at the rate limiting step in folding as the hydrophobic core.

Amino Acid Substitution↗

PubMed2000

Molecular chaperone properties of serum amyloid P component.

The selective binding of serum amyloid P component (SAP) to proteins in the pathological amyloid cross-beta fold suggests a possible chaperone role. Here we show that human SAP enhances the refolding yield of denatured lactate dehydrogenase and protects against enzyme inactivation during agitation of dilute solutions. These effects are independent of calcium ions and are not inhibited by compounds that block the amyloid recognition site on the B face of SAP, implicating the A face and/or the edges of the SAP pentamer. We discuss the possibility that the chaperone property of SAP, or its failure, may contribute to the pathogenesis of amyloidosis.

Binding Sites↗

PubMed2000

A surprising simplicity to protein folding.

The polypeptide chains that make up proteins have thousands of atoms and hence millions of possible inter-atomic interactions. It might be supposed that the resulting complexity would make prediction of protein structure and protein-folding mechanisms nearly impossible. But the fundamental physics underlying folding may be much simpler than this complexity would lead us to expect folding rates and mechanisms appear to be largely determined by the topology of the native (folded) state, and new methods have shown great promise in predicting protein-folding mechanisms and the three-dimensional structures of proteins.

Amino Acid Sequence↗

PubMed2000

Evolutionary conservation in protein folding kinetics.

The sequence and structural conservation of folding transition states have been predicted on theoretical grounds. Using homologous sequence alignments of proteins previously characterized via coupled mutagenesis/kinetics studies, we tested these predictions experimentally. Only one of the six appropriately characterized proteins exhibits a statistically significant correlation between residues' roles in transition state structure and their evolutionary conservation. However, a significant correlation is observed between the contributions of individual sequence positions to the transition state structure across a set of homologous proteins. Thus the structure of the folding transition state ensemble appears to be more highly conserved than the specific interactions that stabilize it.

Animals↗

PubMed2000

Efficacy and safety of sertraline treatment of posttraumatic stress disorder: a randomized controlled trial.

CONTEXT: Despite the high prevalence, chronicity, and associated comorbidity of posttraumatic stress disorder (PTSD) in the community, few placebo-controlled studies have evaluated the efficacy of pharmacotherapy for this disorder. OBJECTIVE: To determine if treatment with sertraline hydrochloride effectively diminishes symptoms of PTSD of moderate to marked severity. DESIGN: Twelve-week, double-blind, placebo-controlled trial preceded by a 2-week, single-blind placebo lead-in period, conducted between May 1996 and June 1997. SETTING: Outpatient psychiatric clinics in 8 academic medical centers and 6 clinical research centers. PATIENTS: A total of 187 outpatients with a Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition diagnosis of PTSD and a Clinician Administered PTSD Scale Part 2 (CAPS-2) minimum total severity score of at least 50 at baseline (mean age, 40 years; mean duration of illness, 12 years; 73% were women; and 61.5% experienced physical or sexual assault). INTERVENTION: Patients were randomized to acute treatment with sertraline hydrochloride in flexible daily dosages of 50 to 200 mg/d, following 1 week at 25 mg/d (n=94); or placebo (n=93). MAIN OUTCOME MEASURES: Baseline-to-end-point changes in CAPS-2 total severity score, Impact of Event Scale total score (IES), and Clinical Global Impression-Severity (CGI-S), and CGI-Improvement (CGI-I) ratings, compared by treatment vs placebo groups. Results Sertraline treatment yielded significantly greater improvement than placebo on 3 of the 4 primary outcome measures (mean change from baseline to end point for CAPS-2 total score, -33.0 vs -23.2 [P =.02], and for CGI-S, -1.2 vs -0.8 [P=.01]; mean CGI-I score at end point, 2.5 vs 3.0 [P=.02]), with the fourth measure, the IES total score, showing a trend toward significance (mean change from baseline to end point, -16.2 vs -12.1; P=.07). Using a conservative last-observation-carried-forward analysis, treatment with sertraline resulted in a responder rate of 53% at study end point compared with 32% for placebo (P=.008, with responder defined as >30% reduction from baseline in CAPS-2 total severity score and a CGI-I score of 1 [very much improved], or 2 [much improved]). Significant (P<.05) efficacy was evident for sertraline from week 2 on the CAPS-2 total severity score. Sertraline had significant efficacy vs placebo on the CAPS-2 PTSD symptom clusters of avoidance/numbing (P=.02) and increased arousal (P=.03) but not on reexperiencing/intrusion (P=.14). Sertraline was well tolerated, with insomnia the only adverse effect reported significantly more often than placebo (16.0% vs 4.3%; P=.01). CONCLUSIONS: Our data suggest that sertraline is a safe, well-tolerated, and effective treatment for PTSD.

Adolescent↗

PubMed2000

Encephalitogenic and immunogenic potential of the stress protein alphaB-crystallin in Biozzi ABH (H-2A(g7)) mice.

The stress protein alphaB-crystallin is an immunodominant antigen in multiple sclerosis (MS)-affected myelin for human T cells and is expressed at elevated levels in MS lesions. Using bovine alphaB-crystallin and synthetic peptides based on mouse alphaB-crystallin the ability of this stress protein to induce experimental allergic encephalomyelitis (EAE) was screened in Biozzi ABH (H-2A(g7)) mice. While whole alphaB-crystallin and the immunodominant T cell epitopes (49-64, 73-88, 153-168) failed to induce disease the subdominant or cryptic epitope (1-16) was weakly encephalitogenic. The lack of encephalitogenicity of whole protein and dominant epitopes may be due to the low constitutive expression of alphaB-crystallin in the CNS combined with a state of peripheral tolerance suggested by the constitutive expression of alphaB-crystallin in secondary lymphoid tissues in ABH mice. Further evidence for a role of alphaB-crystallin in the progression of chronic relapsing neurological disease is suggested by the development of T cell responses to alphaB-crystallin during MOG-induced relapsing EAE as myelin damage accumulates. Together our data indicate that normal tolerising mechanisms in ABH mice prevent the induction of EAE by alphaB-crystallin while the subdominant or cryptic epitope is able to circumvent these mechanisms and contribute to pathogenic myelin-directed autoimmunity following T cell activation.

Animals↗

PubMed2000

Cannabinoids control spasticity and tremor in a multiple sclerosis model.

Chronic relapsing experimental allergic encephalomyelitis (CREAE) is an autoimmune model of multiple sclerosis. Although both these diseases are typified by relapsing-remitting paralytic episodes, after CREAE induction by sensitization to myelin antigens Biozzi ABH mice also develop spasticity and tremor. These symptoms also occur during multiple sclerosis and are difficult to control. This has prompted some patients to find alternative medicines, and to perceive benefit from cannabis use. Although this benefit has been backed up by small clinical studies, mainly with non-quantifiable outcomes, the value of cannabis use in multiple sclerosis remains anecdotal. Here we show that cannabinoid (CB) receptor agonism using R(+)-WIN 55,212, delta9-tetrahydrocannabinol, methanandamide and JWH-133 (ref. 8) quantitatively ameliorated both tremor and spasticity in diseased mice. The exacerbation of these signs after antagonism of the CB1 and CB2 receptors, notably the CB1 receptor, using SR141716A and SR144528 (ref. 8) indicate that the endogenous cannabinoid system may be tonically active in the control of tremor and spasticity. This provides a rationale for patients' indications of the therapeutic potential of cannabis in the control of the symptoms of multiple sclerosis, and provides a means of evaluating more selective cannabinoids in the future.

Animals↗

PubMed2000

Gene therapy for chronic relapsing experimental allergic encephalomyelitis using cells expressing a novel soluble p75 dimeric TNF receptor.

In a murine relapsing experimental allergic encephalomyelitis (EAE) model, gene therapy to block TNF was investigated with the use of a retroviral dimeric p75 TNF receptor (dTNFR) construct. To effectively produce these TNF inhibitors in vivo, a conditionally immortalized syngeneic fibroblast line was established, using a temperature-sensitive SV40 large T Ag-expressing retrovirus. These cells were subsequently infected with a retrovirus expressing soluble dTNFR. CNS-injected cells could be detected 3 mo after transplantation and were shown to produce the transgene product by immunocytochemistry and ELISA of tissue fluids. These levels of dTNFR protein were biologically active and could significantly ameliorate both acute and relapsing EAE. This cell-based gene-vector approach is ideal for delivering proteins to the CNS and has particular relevance to the control of inflammatory CNS disease.

Acute Disease↗

PubMed2000

Factors predictive of bone mineral density in eating-disordered women: a longitudinal study.

OBJECTIVE: Osteoporosis in eating-disordered women is well established, but factors predictive of this condition have proved elusive. The roles of behavioral factors, weight, menstrual status, and the degree of bone mineral density change over the clinical course of the eating disorder were investigated METHOD: A cohort of 56 eating-disordered women was subjected to bone mineral density measurement at Scan 1 and were followed up between 9 and 51 months later for repeat measurement (n = 10) at Scan 2. RESULTS: High levels of reduced bone mineral density were observed. Total duration of amenorrhea, body mass index, frequency of vomiting, and cigarette and alcohol consumption accounted for 40% of the variance in spinal bone mineral density measurement at Scan 1. No significant changes in bone mineral density were observed at Scan 2 despite increases in body mass index. DISCUSSION: The results suggest that increases in weight appear not to be sufficient to increase bone mineral density.

Absorptiometry, Photon↗

PubMed2000

Bypass surgery for chronic lower limb ischaemia.

BACKGROUND: Surgical bypass of an occluded arterial segment is the mainstay of treatment for patients with critical limb ischaemia. As with many surgical interventions, however, it was introduced without formal evaluation. OBJECTIVES: The objective of this review was to determine the effects of bypass surgery in patients with chronic lower limb ischaemia. SEARCH STRATEGY: The reviewers searched the Cochrane Peripheral Vascular Diseases Group trials register, MEDLINE, EMBASE, reference lists of relevant articles, and contacted principal trial investigators. SELECTION CRITERIA: All randomised controlled trials of bypass surgery versus control, or versus any other form of treatment. DATA COLLECTION AND ANALYSIS: At least two reviewers extracted data and assessed trial quality independently. The reviewers contacted investigators to obtain information or data needed for the review that could not be found in published reports. Dichotomous data were analysed using the Peto odds ratio (OR), and continuous data with the weighted mean difference (fixed effect and random effects models). MAIN RESULTS: Eight trials were identified which appeared to meet the inclusion criteria, but two were subsequently excluded. The remaining six trials involved a total of just over 700 patients, two trials comparing bypass surgery with angioplasty (PTA), and one with each of thromboendarterectomy, thrombolysis, exercise, and spinal cord stimulation. Four trials included patients with a range of disease severity (intermittent claudication and critical limb ischaemia), one was restricted to claudicants only and another to only critical limb ischaemia. The type of bypass procedure performed in each trial was similar: vein grafts for distal reconstructions; synthetic prostheses for aorto-iliac or ilio-femoral bypasses. The outcome measures varied, but four of the six trials included mortality and operative failure. In general the quality of the trials was good, but none was blinded because of the nature of the intervention. There were no clear differences between bypass surgery and PTA. Mortality and amputation rates did not differ significantly, although primary patency was significantly higher in the bypass group after 12 months (Peto OR 1. 6, 95% CI 1.0, 2.6) but not after four years (p=0.14). Compared with thrombolysis, amputation rates were significantly lower in the bypass group (Peto OR 0.2, 95% CI 0.1, 0.6), but mortality rates did not differ. Compared with thromboendarterectomy, restoration of blood flow was significantly greater in the bypass patients (Peto OR 9.2, 95% CI 1.7, 50.6), but mortality and amputation rates did not differ. Bypass did not differ significantly from exercise or spinal cord stimulation. REVIEWER'S CONCLUSIONS: There is limited evidence for the effectiveness of bypass surgery and further large trials are required.

Angioplasty, Balloon↗