PubMed Health⌕ Search

Biomedical subjects

D G Roberts

Publications and source records attributed to D G Roberts.

At least 19 recordsLinked to original sources
PubMed2001

Characterization of the EYE2 gene required for eyespot assembly in Chlamydomonas reinhardtii.

The unicellular biflagellate green alga Chlamydomonas reinhardtii can perceive light and respond by altering its swimming behavior. The eyespot is a specialized structure for sensing light, which is assembled de novo at every cell division from components located in two different cellular compartments. Photoreceptors and associated signal transduction components are localized in a discrete patch of the plasma membrane. This patch is tightly packed against an underlying sandwich of chloroplast membranes and carotenoid-filled lipid granules, which aids the cell in distinguishing light direction. In a prior screen for mutant strains with eyespot defects, the EYE2 locus was defined by the single eye2-1 allele. The mutant strain has no eyespot by light microscopy and has no organized carotenoid granule layers as judged by electron microscopy. Here we demonstrate that the eye2-1 mutant is capable of responding to light, although the strain is far less sensitive than wild type to low light intensities and orients imprecisely. Therefore, pigment granule layer assembly in the chloroplast is not required for photoreceptor localization in the plasma membrane. A plasmid-insertion mutagenesis screen yielded the eye2-2 allele, which allowed the isolation and characterization of the EYE2 gene. The EYE2 protein is a member of the thioredoxin superfamily. Site-directed mutagenesis of the active site cysteines demonstrated that EYE2 function in eyespot assembly is redox independent, similar to the auxiliary functions of other thioredoxin family members in protein folding and complex assembly.

Amino Acid Motifs↗
PubMed1999

Solid-phase synthesis of benzisothiazolones as serine protease inhibitors.

An efficient solid-phase synthesis of benzisothiazolone-1,1-dioxide-based serine protease inhibitors involving alkylation of carboxylic acids with N-(bromomethyl)benzisothiazolone-1,1-dioxide has been developed. An example using this procedure for preparation of a library of human mast cell tryptase inhibitors is described.

Chymases↗
PubMed1998

1,2-Benzisothiazol-3-one 1,1-dioxide inhibitors of human mast cell tryptase.

A library of compounds were prepared by reacting 2-(bromomethyl)-1, 2-benzisothiazol-3(2H)-one 1,1-dioxide (5) with commercially available carboxylic acids in the presence of potassium carbonate or a tertiary amine base. From this library, (1,1-dioxido-3-oxo-1, 2-benzisothiazol-2(3H)-yl)methyl N-[(phenylmethoxy)carbonyl]-beta-alanate (7b) emerged as a potent inhibitor of human mast cell tryptase (IC50 = 0.85 microM). Extension of the side chain of 7b by two carbons gave (1, 1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl 5-[[(phenylmethoxy)carbonyl]amino]pentanoate (7d) which was an 8-fold more potent inhibitor (IC50 = 0.1 microM). Further modification of this series produced benzoic acid derivative (1, 1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl 4-[[(phenylmethoxy)carbonyl]amino]benzoate (7n) which is the most potent inhibitor identified in this series (IC50 = 0.064 microM). These compounds exhibit time-dependent inhibition consistent with mechanism-based inhibition. For 7b, the initial enzyme velocity is not a saturable function of the inhibitor concentration and the initial Ki could not be determined (Ki > 10 microM). The steady-state rate constant, Ki, was determined to be 396 nM. On the other hand, compounds 7d and 7n are time-dependent inhibitors with a saturable initial complex. From these studies, an initial rate constant, Ki, for 7d and 7n was found to be 345 and 465 nM, respectively. The steady-state inhibition constants, Ki, for 7d and 7n were calculated to be 60 and 52 nM, respectively. Compound 7n is a 13-fold more potent inhibitor than 7b, and these kinetic studies indicate that the increase in inhibitory activity is due to an increase in initial affinity toward the enzyme and not an increase in chemical reactivity. These inhibitors generally show high selectivity for tryptase, being 40-fold weaker inhibitors of elastase, being 100-fold weaker against trypsin, and showing no inhibition against thrombin. These compounds are not inhibitors of thrombin, plasmin t-PA, urokinase, and factor Xa (IC50 > 33 microM). In the delayed-type hypersensitivity (DTH) mouse model, a model of skin inflammation, a 5% solution of 7d reduced edema by 69% compared to control animals.

Animals↗
PubMed1997

Severe burns resulting from an exploding teat on a bottle of infant formula milk heated in a microwave oven.

Accidental injury to infants can result from the use of home microwave ovens. The spectrum of injury includes scald burns of the trachea, palate oropharynx and oesophagus due to aspiration and ingestion of foods that have been overheated. There is one previous case report of a child with second-degree burns of 6 per cent of his body area due to explosion of the plastic liner and nipple on a feeding bottle top. We present a case report of an infant who suffered 7 per cent full-thickness burns following explosion of the bottle teat and subsequent splattering with hot milk. He required mid-palmar amputation of his left hand including thumb, index and middle fingers. The full-thickness burns of left cheek and left shoulder were grafted but will result in significant scarring. It is common practice in many homes to heat infant feeds in the microwaves. We suggest that health professionals dealing with children need to be aware of the potential hazards so that appropriate education of parents can take place.

Accidents, Home↗
PubMed1996

Crystallographic determination of the structures of human alpha-thrombin complexed with BMS-186282 and BMS-189090.

The crystallographic structures of the ternary complexes of human alpha-thrombin with hirugen (a sulfated hirudin fragment) and the small-molecule active site thrombin inhibitors BMS-186282 and BMS-189090 have been determined at 2.6 and 2.8 A. In both cases, the inhibitors, which adopt very similar bound conformations, bind in an antiparallel beta-strand arrangement relative to the thrombin main chain in a manner like that reported for PPACK, D-Phe-Pro-Arg-CH2Cl. They do, however, exhibit differences in the binding of the alkyl guanidine moiety in the specificity pocket. Numerous hydrophilic and hydrophobic interactions serve to stabilize the inhibitors in the binding pocket. Although PPACK forms covalent bonds to both serine and the histidine of the catalytic triad of thrombin, neither BMS-186282 nor BMS-189090 bind covalently and only BMS-186282 forms a hydrogen bond to the serine of the catalytic triad. Both inhibitors bind with high affinity (Ki = 79 nM and 3.6 nM, respectively) and are highly selective for thrombin over trypsin and other serine proteases.

Amino Acid Chloromethyl Ketones↗
PubMed1995

Structure of a retro-binding peptide inhibitor complexed with human alpha-thrombin.

The crystallographic structure of the ternary complex between human alpha-thrombin, hirugen and the peptidyl inhibitor Phe-alloThr-Phe-O-CH3, which is acylated at its N terminus with 4-guanidino butanoic acid (BMS-183507), has been determined at 2.6 A resolution. The structure reveals a unique "retro-binding" mode for this tripeptide active site inhibitor. The inhibitor binds with its alkyl-guanidine moiety in the primary specificity pocket and its two phenyl rings occupying the hydrophobic proximal and distal pockets of the thrombin active site. In this arrangement the backbone of the tripeptide forms a parallel beta-strand to the thrombin main-chain at the binding site. This is opposite to the orientation of the natural substrate, fibrinogen, and all the small active site-directed thrombin inhibitors whose bound structures have been previously reported. BMS-183507 is the first synthetic inhibitor proved to bind in a retro-binding fashion to thrombin, in a fashion similar to that of the N-terminal residues of the natural inhibitor hirudin. Furthermore, this new potent thrombin inhibitor (Ki = 17.2 nM) is selective for thrombin over other serine proteases tested and may be a template to be considered in designing hirudin-based thrombin inhibitors with interactions at the specificity pocket.

Amino Acid Sequence↗
PubMed1995

Resolution of middle ear effusion in newborns.

OBJECTIVES: To determine the natural history of middle ear effusion (MEE) in newborns and compare the results of pneumatic otoscopy with tympanometry and acoustic reflex measurements in the evaluation of the middle ear of neonates. DESIGN: A descriptive natural history study with comparison of three evaluation methods for MEE. SETTING: County hospital nursery and pediatric clinic. PARTICIPANTS: Sixty-eight full-term, healthy neonates were studied on day 1 of life; 65 on day 2; and 24 on day 3. Thirty-eight infants returned at 2 weeks of age, and from this group, 23 returned at 2 months of age. INTERVENTIONS: Two independent observers performed otoscopy. An audiologist performed tympanometry and ipsilateral acoustic reflex measurements. Infants were evaluated daily from birth by all three methods for up to 3 days. MAIN OUTCOME MEASURE: The time to resolution of MEE as determined by three methods. RESULTS: In the first 3 hours of life, all babies examined had MEE diagnosed in both ears. By the third day, MEE apparently had resolved in 73% of ears by otoscopy, 88% by acoustic reflex measurements, and 92% by tympanometry. At 2 weeks, MEE was present by otoscopy in 13% (10/75 of ears). These were primarily newly acquired MEEs. Interobserver agreement by otoscopy as determined by kappa scores was moderate on days 1 and 3, poor on day 2, and excellent at 2 weeks and 2 months. CONCLUSIONS: Middle ear effusion diagnosed by otoscopy apparently resolves in 72 hours in most neonates. Interobserver agreement of otoscopists was excellent after babies were discharged from the nursery, suggesting that pneumatic otoscopy can be used to diagnose MEE in neonates this age. Most MEEs that are diagnosed 2 weeks and 2 months after birth are new and asymptomatic.

Acoustic Impedance Tests↗
PubMed1991

Cefixime compared with amoxicillin for treatment of acute otitis media.

Cefixime was compared with amoxicillin for treatment of acute otitis media in a randomized trial. Results of tympanocentesis on day 3 to 5 of therapy were used as the major outcome. Total daily doses were 8 mg/kg of cefixime and 40 mg/kg of amoxicillin. One hundred twenty-six patients were randomly assigned to receive treatment; 64 cultures grew pathogens. Pathogens were eradicated from the middle ear after 3 to 5 days of therapy in 27 (79.4%) of 34 children given amoxicillin and 26 (86.7%) of 30 children given cefixime (p = 0.47). When Streptococcus pneumoniae cases were analyzed, bacteriologic cure occurred in 14 (93.3%) of 15 children given amoxicillin and 12 (75%) of 16 given cefixime (p = 0.333). When cases of Haemophilus influenzae infection were analyzed, significantly more cures occurred with cefixime (10/10, 100%) than amoxicillin (8/13, 62%) (p = 0.046). Pathogens associated with failure of amoxicillin therapy were H. influenzae (five cases, two beta-lactamase-positive), S. pneumoniae (one case), and Moraxella catarrhalis (one case, beta-lactamase-positive). The four failures with cefixime therapy were all in patients infected with S. pneumoniae. Rates of rash, diarrhea, and vomiting were the same in both groups and did not necessitate stopping therapy. We conclude the following: (1) Cefixime and amoxicillin were equivalent in overall clinical and bacteriologic efficacy for otitis media. (2) Cefixime was more efficacious than amoxicillin in treating H. influenzae otitis media and should be preferred when H. influenzae is the suspected etiologic agent. (3) Side effects of both drugs were mild and equivalent.

Acute Disease↗
PubMed1991

Gamma globulin prophylaxis to reduce post-transfusion non-A, non-B hepatitis after cardiac surgery with cardiopulmonary bypass.

A prospective, randomized study of immune serum globulin (ISG) for prevention of post-transfusion hepatitis was performed on 196 patients (100 controls without gammaglobulin or placebo and 96 who received ISG) undergoing valve replacement or coronary artery bypass with extracorporeal circulation. The dose of ISG was 2 ml i.m. at premedication and 2 ml i.m. on postoperative day 3. Probable non-A, non-B hepatitis developed postoperatively in ten of the 100 controls and two of the 96 in the ISG group. Two ISG patients and three controls with non-A, non-B hepatitis still have increased serum aminotransferase values after 3-5 years, but liver biopsy revealed hepatitis, which histologically was very mild, in only two control and two ISG patients. Low-dose gamma globulin thus reduced the incidence of acute, probable non-A, non-B hepatitis in cardiac surgery with cardiopulmonary bypass.

Alanine Transaminase↗
PubMed1989

Long-term follow-up of operative treatment for pulmonary metastases.

From 1954 onwards, 132 patients underwent 165 resections for pulmonary metastases. No other forms of therapy were adopted. The operative mortality was 7.6% (10 patients). After a minimum follow-up of 5 years, the overall survival rate was 20%. The 10- and 15-year survival rates were 6% and 3%, respectively. The major cause of late death was recurrence or spread of the primary disease in 102 patients (83.6%) while 5 patients died of reasons not related to cancer. Fifteen patients (12.3%) are still alive, 13 of whom have no clinical cancer. The presence of symptoms, the disease-free interval of less than 1 year and the number of metastases showed a statistically significant detrimental influence on survival (P less than 0.001, P less than 0.05 and P less than 0.046, respectively). The best 5-year survivals of 42%, 24%, 23% and 23% were noted for metastases from malignancies in the body of the uterus, kidney, bone and colon, respectively. Longterm survival or clinical cure can be achieved with surgery alone by an aggressive approach in selected malignancies.

Adolescent↗
PubMed1988

Association between bleeding and reduced red cell deformability following cardiopulmonary bypass.

In 56 patients undergoing open-heart surgery, red cell trauma during and following cardiopulmonary bypass (CPB) was monitored with a microfiltration method that estimated deformability of the cells. Red cell deformability was reduced by 38% during CPB and at a slower rate thereafter. The lowest filterability rate was reached on the second day, after which improvement began. In patients who had undergone coronary artery bypass grafting, preoperative values of red cell deformability were reached after 6 weeks. Following valve replacement, however, preoperative values were not regained during this period, which was attributed to continuous mechanical trauma by the artificial valves. A 50% reduction of red cell filterability from the end of CPB to 12 and 24 hours from the start of CPB was associated with heavy blood loss (greater than 1,000 ml) from drains. Reduced red cell deformability thus showed relationship with a bleeding tendency following use of CPB.

Cardiac Surgical Procedures↗
PubMed1988

Association between pulmonary dysfunction and reduced red cell deformability following cardiopulmonary bypass.

Fifty-six patients undergoing open-heart surgery were monitored for red cell trauma during cardiopulmonary bypass (CPB), using a standard red cell microfiltration method. The average red cell deformability was reduced by 38%. Respirator time was shorter in the patients with lesser degrees of red cell trauma, and vice versa. After extubation, the tendency to hypercapnia was greatest in the patients with most red cell trauma during CPB. Hypoxic tendencies in the first 24 postextubation hours were comparably distributed among all levels of red cell trauma.

Cardiac Surgical Procedures↗
PubMed1985

Sulindac is not renal sparing in man.

We investigated the claimed renal-sparing effect of the cyclooxygenase inhibitor sulindac. Fifteen normal women following a diet of 50 mEq salt a day were randomly assigned to 5 days of either placebo, sulindac, 200 mg b.i.d., or indomethacin, 25 mg q.i.d., after first serving as their own controls. Renal effects were assessed by the excretion rate of prostaglandin (PG) E2 (an index of renal PG synthesis), sodium balance, plasma renin activity (PRA), and the response to furosemide. Systemic effects were assessed by collagen-induced platelet aggregation and thromboxane B2 formation and by the urinary excretion of a systemically formed metabolite of PGF2 alpha (PGF-M). Both sulindac and indomethacin resulted in a positive sodium balance and a reduction in 24-hour urinary PGE2 excretion (range -49% to -86%). Basal PRA was decreased by indomethacin only, but the increases in PRA and in urinary PGE2 excretion in response to furosemide were inhibited by both sulindac and indomethacin. Sulindac reduced the natriuresis induced by furosemide, and indomethacin reduced the rise in inulin clearance after furosemide. Thus the two nonsteroidal anti-inflammatory drugs had similar effects on the kidney. Indomethacin had a greater effect than sulindac on the inhibition of collagen-induced platelet aggregation and thromboxane synthesis and the two drugs had equivalent effects on the reduction of PGF-M excretion. Peak plasma drug concentration of indomethacin (1.9 +/- 0.4 microgram/ml) and sulindac sulfide (7.7 +/- 1.9 microgram/ml) were those associated with clinical efficacy.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1985

Single dose pharmacokinetics of trimethoprim.

Single oral dose trimethoprim pharmacokinetics were determined in 18 children aged 3 months to 13 years. Trimethoprim suspension was rapidly absorbed and quickly and widely distributed. The mean clearance was considerably faster and the elimination half life considerably shorter than values reported in adults. Only one third of the administered drug dose was recovered from the urine within 24 hours which is considerably less than in adults, suggesting that children may metabolise a greater proportion of the dose given. Urine trimethoprim concentrations greatly in excess of minimum inhibitory concentrations for common pathogens were rapidly achieved and sustained for at least 16 hours.

Adolescent↗
PubMed1985

Re-evaluation of saliva for monitoring theophylline concentrations.

Variability of the mixed saliva/plasma theophylline relation was examined in seven children aged 2 to 13 years. Good correlation between plasma and saliva concentrations was found, but on the three occasions there was considerable inter- and intrapatient variability. There was no significant or consistent relation between unstimulated and stimulated saliva concentrations or between saliva concentrations and sample volumes. Plasma theophylline concentrations cannot be predicted accurately from saliva values.

Adolescent↗