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Biomedical subjects

C Lim

Publications and source records attributed to C Lim.

At least 55 records · Page 3Linked to original sources
PubMed1996

Positive charge at position 549 is essential for phosphatidylinositol 4,5-bisphosphate-hydrolyzing but not phosphatidylinositol-hydrolyzing activities of human phospholipase C delta1.

Point mutagenesis, phosphatidylinositol (PI), and phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis assays and equilibrium centrifugation PIP2 assays were used to study the functional roles of four highly conserved arginine residues in the Y region of human phospholipase C delta1 (PLCdelta1) (Arg-527, -549, -556, -701). Most of the mutant enzymes were either partially defective or fully active in their abilities to catalyze the hydrolysis of PI or PIP2. However, upon substitution of Arg-549 by glycine or histidine, the mutant enzyme was defective in its ability to catalyze the hydrolysis of PIP2, but it is still able to hydrolyze PI. Replacing Arg-549 with lysine had little effect on the level of PI and PIP2 hydrolytic activities of the mutant enzyme. The residual PIP2 hydrolyzing activity of R549H is highly dependent on pH. R549H showed 5-10% of the PIP2-hydrolyzing activity of the native enzyme between pH 5 and 7 and nondetectable PIP2-hydrolyzing activity at pH 8. The PIP2-hydrolyzing activity of R549G was not detectable at all pH values. Kinetic analysis of PLCdelta1-catalyzed PIP2 hydrolysis revealed that the micellar dissociation constant Ks and interfacial Michaelis constant Km were similar in the native, R549K, and R549H enzymes; but the specific activity at the saturated substrate mole fraction and infinite level of substrate (Vmax) of the R549H mutant were reduced by a factor of 15. PIP2 competitively inhibits the native enzyme to hydrolyze PI at both pH 7 and 8. However, PIP2 inhibits R549H only at pH 7.0 and does not inhibit R549G at either pH. Taken together, these results suggest that positive charge at position 549 of PLCdelta1 protein is essential for the enzyme to recognize and catalyze the hydrolysis of PIP2 but not PI.

Calcium↗
PubMed1996

Significance of intermittency in men with lower urinary tract symptoms.

OBJECTIVES: To determine the relationship between the symptom of intermittency, objective evidence of intermittency on uroflow traces, benign prostatic enlargement, and bladder outlet obstruction (BOO) in men with lower urinary tract symptoms (LUTS). METHODS: The prevalence of the symptom of intermittency was determined from a symptom questionnaire in 165 men presenting with LUTS. Objective evidence of intermittency during voiding was assessed from uroflow traces, and prostate volume was measured by transrectal ultrasound. Combined pressure-flow studies were performed to determine the presence or absence of BOO. RESULTS: There was relatively poor agreement between the symptom of intermittency and objective evidence of its presence. Of the 35 patients who reported intermittency most or all of the time, 21 showed no objective evidence of intermittency on uroflowmetry. The symptom of intermittency was not significantly related to the presence of BOO (P = 0.42) and the group-specific urethral resistance factor (URA) did not differ significantly (P = 0.87) between those men who complained of intermittency and those who did not (median URA, 35 versus 32 cm H2O). However, objective evidence of intermittency on uroflow traces was significantly related to BOO (P = 0.016), and those patients with objective evidence of intermittency had higher URA values (median, 43 versus 32 cm H2O). Objective evidence of intermittency had a specificity of 98% and positive predictive value of 92% for the presence of BOO. Neither the symptom of intermittency nor objective evidence of its presence was significantly related to prostate size. CONCLUSIONS: Although the symptom of intermittency does not seem to be related to BOO or prostate size, objective evidence of intermittency on flow curve traces is specific for outflow obstruction, and as such its presence could potentially be of value in the assessment of men with lower urinary tract symptoms.

Aged↗
PubMed1996

The value of multiple free-flow studies in men with lower urinary tract symptoms.

OBJECTIVE: To assess the variability of free-flow studies in men presenting with lower urinary tract symptoms (LUTS) suggestive of benign prostatic obstruction (BPO) and to determine the sensitivity, specificity and predictive values of consecutive measurements of maximum flow rate for the presence of bladder outlet obstruction (BOO) at several threshold values. PATIENTS AND METHODS: The value of multiple free-flow studies was assessed in 165 men presenting with LUTS suggestive of BPO. Each patient was requested to void four times into a uroflowmeter and the voided volume and post-void residual urine volume (PVR) were also measured. The variability of the maximum flow rate (Qmax), voided volume and PVR between consecutive voids was assessed. In addition, the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of various thresholds of Qmax for the presence of BOO were calculated for each consecutive void. RESULTS: The mean Qmax on void 1 was 10.2 mL/s and the mean maximum value for Qmax between voids 1 and 2 was 12.5 mL/s. For voids 1, 2 and 3, the mean maximum Qmax was 13.9 mL/s and for voids 1 to 4 it was 15.2 mL/s. There were no significant changes in PVR among any of these voids. There was a statistically significant, although small, decrease in voided volume between voids 1 to 3 and voids 1 to 4. The specificity and PPV of Qmax for BOO increased with each subsequent void, such that using a threshold value for Qmax of 10 mL/s on the fourth void, the specificity and PPV for BOO were 96% and 93%, respectively. CONCLUSIONS: There was a significant increase in Qmax with each successive void when men with LUTS suggestive of BPO performed multiple free-flow measurements and consequently, single free-flow measurements substantially underestimated the maximum Qmax that these patients achieved. The specificity and PPV of Qmax for BOO can be improved considerably by performing multiple free-flow studies and by carefully selecting an appropriate threshold value (although whether pressure-flow studies are unnecessary will depend on what level of specificity and PPV is deemed acceptable in clinical practice). These findings should be considered if free-flow studies are to be used as the basis for deciding the clinical management of men with LUTS and may be particularly useful for urologists with limited facilities for pressure-flow studies.

Aged↗
PubMed1996

The significance of terminal dribbling in men with lower urinary tract symptoms.

OBJECTIVE: To determine the relationship between the symptom of terminal dribbling, objective evidence of terminal dribbling on recordings of uroflow, benign prostatic enlargement (BPE) and bladder outlet obstruction (BOO) in men with lower urinary tract symptoms (LUTS). PATIENTS AND METHODS: The prevalence of the symptom of terminal dribbling was determined from a symptom questionnaire completed by 165 men presenting with LUTS. Objective evidence of terminal dribbling during voiding was assessed from uroflow recordings and prostate volume was measured by transrectal ultrasonography. Combined pressure-flow studies were performed to determine the presence or absence of BOO. RESULTS: There was relatively poor agreement between the symptom of terminal dribbling and objective evidence of its presence; 48% of the patients who reported terminal dribbling most or all of the time showed no objective evidence of terminal dribbling on uroflowmetry. The symptom of terminal dribbling was not significantly related to the presence of BOO (P = 0.74) and the group-specific urethral resistance factor (URA) did not differ significantly (P = 0.79) between those men who complained of terminal dribbling and those who did not (median URA 33 and 31 cmH2O, respectively). However, objective evidence of terminal dribbling on uroflow traces was significantly related to BOO (P < 0.001) and those patients with objective evidence of terminal dribbling had higher values of URA (median 39 compared with 28 cmH2O). Objective terminal dribbling had a specificity of 92% and positive predictive value of 88% for the presence of BOO. Neither the symptom of terminal dribbling nor objective evidence of its presence were significantly related to prostatic enlargement. CONCLUSION: While the symptom of terminal dribbling is probably not related to BOO or prostatic enlargement, objective evidence of terminal dribbling on flow curve recording is specific for BOO and as such, its presence could potentially be of value in the assessment of men with LUTS.

Aged↗
PubMed1996

The binding mode of an E-64 analog to the active site of cathepsin B.

Two binding modes of the isobutyl-NH-Eps-Leu-Pro inhibitor to cathepsin B have been proposed. Molecular docking using an empirical force field was carried out to distinguish between the two modes. The search began with manual docking, followed by random perturbations of the docking conformation and cycles of Monte Carlo minimization. Finally, molecular dynamics was carried out for the most favorable docking conformations. The present calculations predict that the isobutyl-NH-Eps-Leu-Pro inhibitor preferentially binds to the S' rather than the S subsites of cathepsin B. The S' binding mode prediction is supported by the X-ray crystal structure of cathepsin B bound to a closely related ethyl-O-Eps-Ile-Pro inhibitor, which was found to bind in the S'subsite with the C-terminal epoxy ring carbon making a covalent bond to the sulfur atom of Cys29. This agreement, in turn, validates our docking strategy. Furthermore, the calculations provide evidence that the dominant contribution to the total stabilization energy of the enzyme-inhibitor complex stems from the strong electrostatic interaction between the negatively charged C-terminal carboxylate group of the ligand and the positively charged imidazolium rings of His110 and His111. The latter are stabilized and held in an optimal orientation for interactions with the C-terminal end of the ligand through a salt bridge between the side chains of His110 and Asp22. By comparison with the crystal structure, some insight into the specificity of the epoxyldipeptide family towards cathepsin B inhibition has been extracted. Both the characteristics of the enzyme (e.g. subsite size and hydrophobicity) as well as the nature of the inhibitor influence the selectivity of an inhibitor towards an enzyme.

Binding Sites↗
PubMed1996

The obstructive effect of a urethral catheter.

PURPOSE: The effect of a urethral catheter on pressure-flow relationships of the urethra has important implications for the practice to this question in the past in men with benign prostatic hyperplasia. We assessed the obstructive effect of an 8 Ch. urethral catheter in men who presented with lower urinary tract symptoms due to benign prostatic hyperplasia. MATERIALS AND METHODS: During combined pressure-flow studies 59 men completed 2 voids of similar volume with and without a urethral catheter in situ. Maximum flow rate, detrusor pressure at maximum flow and the group of specific urethral resistance factor were measured and compared between these 2 voids. RESULTS: There was no significant difference in maximum flow rate between voids (with catheter 9.1 ml. per second versus without catheter 8.6 ml. per second). Although detrusor pressure was significantly greater with the urethral catheter in situ (80 versus 67 cm. water), voids (with catheter 42.1 cm, water versus without catheter 36.6 cm water). CONCLUSIONS: A 8 Ch. catheter does not appear to have a significant obstructive effect in the urethra. This finding has important implications for the practice and interpretation of pressure-flow studies.

Aged↗
PubMed1996

Gestational diabetes in Singaporean women: use of the glucose challenge test as a screening test and identification of high risk factors.

In this study, 1141 antenatal women attending 9 Government polyclinics were screened between 24 and 28 weeks of gestation for gestational diabetes mellitus (GDM) using the glucose challenge test (GCT). An attempt was made to determine whether 7.2 mmol/l or 7.8 mmol/l was an effective cut-off point as an indicator for GDM. The women with GCT levels of > or = 7.2 mmol/l had an oral glucose tolerance test (OGTT) for confirmation of GDM. The results showed that 420 (36.8%) had GCT levels > or = 7.2 mmol/l, including 299 (26.2%) with GCT levels of > or = 7.8 mmol/l. Of the 190 OGTT carried out, 8 (4.2%) were confirmed to have GDM, all of whom had GCT levels of > or = 7.8 mmol/l, indicating that a GCT level of 7.8 mmol/l was the effective cut-off point. Univariate analysis showed that epidemiological features associated with a raised GCT > or = 7.8 mmol/l were, older age that is 30 years and above, Chinese ethnic group, maternal obesity (body mass index > or = 25) and history of > or = 4 pregnancies. Multivariate analysis using stepwise logistic regression, showed that factors significantly and independently associated with raised GCT levels were older age, Chinese ethnic group and maternal obesity. All antenatal women should be screened for GDM using the GCT, and those with levels of > or = 7.8 mmol/l should be subjected to the OGTT for confirmation.

Adult↗
PubMed1995

Molecular dynamics simulation of E. coli ribonuclease H1 in solution: correlation with NMR and X-ray data and insights into biological function.

A 500 ps molecular dynamics simulation of Escherichia coli RNase H1 in the presence of explicit water molecules has been carried out to aid in the interpretation of NMR N-H backbone model free parameters and X-ray B-factor values of the free enzyme. Both experimental techniques have revealed unusual structural and dynamic features of the protein. Atomic fluctuations (B-factors) and re-orientational motions of the backbone heteronuclear bonds (order parameters) computed from the simulation are compared with results obtained from experiments. Qualitative agreement is obtained between the computed and X-ray B-factors, whereas the agreement between the computed and NMR generalized order parameters is as good as quantitative for most residues. Reasons for significant discrepancies, the physical basis and the plausible biological consequences of the observed protein dynamics are discussed.

Amino Acid Sequence↗
PubMed1995

Identifying the mechanism of protein loop closure: a molecular dynamics simulation of the Bacillus stearothermophilus LDH loop in solution.

The 'loop' involving residues 98-110 in Bacillus stearothermophilus lactate dehydrogenase (BSLDH) is of great interest as substrate-induced 'loop' closure is thought to be rate-limiting and essential in catalyzing the reaction and in determining substrate specificity. Consequently, we have explored the mechanism underlying 'loop' opening in BSLDH through a molecular dynamics simulation at high temperature (1000 K) in the presence of explicit solvent, starting from the X-ray structure of BSLDH complexed with the co-enzyme NAD+ and oxamate at 2.5 A. During the simulation, a significant conformational change occurred, as evidenced by sharp dihedral angle transitions, hydrogen bond breaking and formation and large root mean square deviations from the starting structure; these changes define the criteria for 'loop' opening. The mechanical elements responsible for 'loop' opening, i.e. 'loop' hinges and flap, are defined through a combination of order parameters, dihedral angle changes and their correlations and the dynamical cross-correlation map of atomic displacements for the 'loop' residues. The results indicate that the 'loop' consists of two flexible hinge regions on either side of a relatively rigid three-residue segment that undergoes a significant spatial displacement during 'loop' opening. 'Loop' opening is made possible through an array of correlated dihedral angle changes and intra-'loop' rearrangements of hydrogen-bond interactions. The present findings are compared to previous work related to 'loop' opening and site-directed mutagenesis experiments.

Amino Acid Sequence↗
PubMed1994

Cholinergic innervation in the human hippocampal formation including the entorhinal cortex.

The cholinergic innervation of the hippocampal formation is thought to play an important role in memory processes, but its organization in humans has not been described in detail. We studied the cholinergic innervation of the human hippocampal formation by means of immunohistochemistry with polyclonal antisera directed against acetylcholinesterase (AChE), choline acetyltransferase (ChAT), and the low-affinity (p75) nerve growth factor receptor (NGFR). The density of ChAT-like immunoreactive (ChAT-li) fibers differed substantially among the various regions, in general paralleling the pattern of AChE-li staining. One notable exception was the presence of AChE-li cell bodies. In contrast, ChAT immunoreactivity was associated only with fibers and terminals. NGFR-li staining corresponded closely to the ChAT-li fiber pattern. ChAT-li fibers in the CA fields diffusely filled the stratum pyramidale and extended into the stratum oriens and radiatum as well. The highest density was consistently observed in CA4 and CA3 subfields. Staining decreased from CA4 to CA1 and was substantially less dense in the subicular complex. In the entorhinal cortex, the ChAT- and NGFR-li fiber innervation displayed a laminar pattern, most intense over the nests of cells in layer II. There was a trend towards an age-related reduction in the density of ChAT- and AChE-li fibers and terminals. Nonetheless, we also found a surprisingly conserved NGFR-li innervation and the presence of occasional NGFR-li pyramidal cells, providing evidence of a plastic response in the brains of the elderly patients.

Acetylcholinesterase↗
PubMed1994

The double catalytic triad, Cys25-His159-Asp158 and Cys25-His159-Asn175, in papain catalysis: role of Asp158 and Asn175.

The 1.65 A X-ray structure of papain, which exhibits a Cys25-His159-Asn175 triad, does not correspond to the catalytically active ion pair state since Cys25 is oxidized to cysteic acid and His159 is predominantly neutral. Thus, stochastic boundary molecular dynamics simulations starting from the 1.65 A X-ray structure of papain have been performed for Cys25 and His159 in the SH-ImH+, SH-Im, S(-)-ImH+ and S(-)-Im states and for Asp158 mutated to Asn, Glu and Gly in the ion pair state. By comparing the resulting averaged structures and analyzing the trajectories of certain interatomic distances, important differences in the active-site geometry of papain have been found. In particular, the initial Cys25(S-)-His159(ImH+)-Asn175(C = O) triad found in the X-ray structure is retained in all the structures except the wild type and Asp158-->Asn ion pair states where there is a conformational transition to form the triad, Cys25(S-)-His159(ImH+)-Asp158(COO-). Both triads, Cys25(S-)-His159(ImH+)-Asp158(COO-) and Cys25(S-)-His159(ImH+)-Asn175(C = O) are postulated to participate in catalysis and their roles are discussed. Thus, catalysis does not take place from a single steric position but a two-state mechanism.

Amino Acid Sequence↗
PubMed1992

Effect of ethanol on prostaglandin E2 receptor in rat submandibular salivary glands.

The dose-dependent effects of acute ethanol treatment on the prostaglandin E2 (PGE2) receptor in submandibular salivary glands was investigated. Rat submandibular-gland segments were preincubated with Dulbecco's modified Eagle's medium in the absence and the presence of various concentrations of ethanol (0.1-5%). After incubation, membranes were prepared and assayed for PGE2 receptor binding using [3H]-PGE2. Ethanol had no effect on receptor binding at concentrations below 1%, but binding was stimulated by higher concentrations. A 30% increase in binding occurred with 2.5% ethanol and 50% with 5% ethanol. This increase was due to an alteration of the binding characteristics. Scatchard analysis of the data from the control and 5% ethanol groups revealed that the ethanol-induced increase in PGE2 receptor binding was mainly due to a 26 and 58% decrease in the dissociation constant (Kd) for the high- and low-affinity binding sites, respectively. A 31% decrease of binding capacity (Bmax) was also observed in the low-affinity binding sites. The results demonstrate that PGE2 receptor binding in submandibular glands is not altered by acute treatment with ethanol at physiological doses. The receptor binding is also relatively stable on pretreatment with 1% ethanol. It is suggested that the increase of receptor binding induced by high concentrations of ethanol may be a spontaneous response to the decrease of PGE2 synthesis in the tissues.

Animals↗
PubMed1992

Visual field differences for clockwise and counterclockwise mental rotation.

Geometric line drawings were presented to normal subjects in the left visual field (LVF) or right visual field (RVF) at various degrees of rotation from a centrally presented vertical standard. The task of the subject was to indicate with a reaction time (RT) response whether the laterally presented stimulus could be rotated into the vertical standard or if it was a rotated mirror image of the standard. In Study 1, an overall right hemisphere superiority was found for RT and accuracy on match trials. Most interestingly, interactions between Visual Field and Rotation Angle for the match accuracy data and between Visual Field and Direction of Rotation (clockwise or counterclockwise) for the match RT slopes were found. These interactions suggested that clockwise rotations were more readily performed in the LVF and counterclockwise rotations in the RVF, consistent with other literature for mental rotation. The purpose of Study 2 was to replicate this finding of visual field differences for rotation direction using a design in which direction and degree of rotation were varied orthogonally. No main effect of Visual Field was found. However, significant interactions between Visual Field and Rotation Angle were found for both RT and accuracy, confirming the presence of visual field differences for rotation direction in a new sample of subjects. These differences were discussed in terms of the possibly greater relevance of medially directed stimuli and a possible hemispheric bias for rotation direction, and in terms of interhemispheric transmission factors.

Adolescent↗
PubMed1992

Cigarette smoking reduces human salivary eicosanoids.

The effect of cigarette smoking on salivary eicosanoid levels was investigated in 10 smoker and 10 non-smoker volunteers. The smokers consumed an average of 20 cigarettes/day for the past 5 years or longer. The smoking status was validated by salivary cotinine level. Eicosanoids were extracted from saliva with ethanol, and the radioimmunoassay was performed to determine the concentrations of four major eicosanoids, i.e. prostaglandin E2 (PGE2), PGF2 alpha, 6-sulphidopeptide-containing leukotrienes (LTs) and 12-hydroxyeicosatetraenoic acid (12-HETE). The levels of PGE2, PGF2 alpha, and LTs were significantly lower in the saliva of smokers as compared to that of the non-smokers (1.74 +/- 0.32 vs 2.41 +/- 0.64, p = 0.006; 0.36 +/- 0.12 vs 0.54 +/- 0.18, p = 0.04; 2.24 +/- 0.96 vs 4.92 +/- 1.29, p = 0.006; mean +/- SD, ng/ml saliva). No significant differences were found in the levels of 12-HETE between the two groups. The results suggest that cigarette smoking reduces the concentrations of both the cyclooxygenase and 5-lipoxygenase products in saliva.

Cotinine↗
PubMed1992

Hemodynamic effects of carvedilol after acute oral administration in hypertensive and normal subjects.

Forearm hemodynamics using pulsed Doppler flowmetry were studied in nine healthy volunteers and 12 patients with mild-to-moderate hypertension before and after acute oral administration of the beta-blocking and vasodilating agent carvedilol. Both the 25- and the 50-mg dose produced a significant blood pressure reduction by comparison with placebo in normotensive and hypertensive subjects. Only the 50-mg dose caused a decrease in forearm vascular resistance in hypertensive subjects. The decrease disappeared after wrist occlusion. Although brachial artery diameter did not change, a significant decrease in tangential tension was observed. This study provides evidence that carvedilol produced arteriolar dilation within the forearm of hypertensive subjects in association with a decrease in brachial artery tangential tension.

Administration, Oral↗
PubMed1991

Effect of electroconvulsive therapy on serum concentration of alpha-1-acid glycoprotein.

Recent studies have shown significant alterations in serum alpha-1-acid glycoprotein (AGP) concentration in epileptic patients, the major protein to which basic drugs bind in serum. To date, there have been no reports in the literature investigating the effects of generalized seizures as a result of repeatedly administered electroconvulsive therapy (ECT) on this serum protein. As the cyclic antidepressants are basic drugs that bind avidly to AGP, an alteration of AGP concentration by ECT could represent a mechanism of interaction between two somatic treatments for depression. We therefore determined the serial AGP concentrations of 10 patients undergoing repeated ECT. AGP concentrations were determined by radial immunodiffusion on serum samples obtained at each treatment session (course of treatment ranged from 4 to 12 sessions over 8 to 32 days). The mean (SD) AGP concentrations prior to and at the end of ECT were 88.7 (18.3) mg/dl and 97.8 (24.8) mg/dl, respectively. Variability in AGP concentration was observed over the course of treatments with no consistent trend (intrapatient coefficients of variation averaged 11.5%). These data suggest that serial ECT does not produce consistent, significant changes in serum AGP concentrations and should have limited effects on altering the serum protein binding and, therefore, pharmacological effects of concurrently administered cyclic antidepressants.

Adolescent↗
PubMed1991

Hippocampus and the blood supply to TE: parahippocampal pial section impairs visual discrimination learning in monkeys.

In the base of each temporal lobe in 4 monkeys (Macaca fascicularis) we sectioned the pia mater in an antero-posterior line along the most medial part of the inferior temporal visual association cortex (area TE), lateral to the parahippocampal cortex. This pial section interrupts the blood flow in branches of the posterior cerebral artery which cross the parahippocampal gyrus en route to area TE. Histologically, the brains of 2 of these animals did not show any abnormalities in cresyl violet stained material, apart from the small cortical damage along the line of the pial section itself. Of the remaining two animals, one had a small unilateral infarct in TE and one had bilateral infarcts in TE. All of these animals were impaired in visual discrimination learning, and the severity of impairment was correlated only imperfectly with the severity of infarction. These results show that pial section along the medial boundary of area TE can affect visual discrimination learning without producing large infarcts. Further, since aspiration lesions of the hippocampal formation require the pia mater to be sectioned in a similar way to that reported here, the effects of such aspiration lesions on visual learning and memory may be mediated in part by effects on TE.

Animals↗