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R Ho

Publications and source records attributed to R Ho.

At least 37 records · Page 2Linked to original sources
PubMed1998

Hydration force in the atomic force microscope: A computational study.

Using a hard sphere model and numerical calculations, the effect of the hydration force between a conical tip and a flat surface in the atomic force microscope (AFM) is examined. The numerical results show that the hydration force remains oscillatory, even down to a tip apex of a single water molecule, but its lateral extent is limited to a size of a few water molecules. In general, the contribution of the hydration force is relatively small, but, given the small imaging force ( approximately 0.1 nN) typically used for biological specimens, a layer of water molecules is likely to remain "bound" to the specimen surface. This water layer, between the tip and specimen, could act as a "lubricant" to reduce lateral force, and thus could be one of the reasons for the remarkably high resolution achieved with contact-mode AFM. To disrupt this layer, and to have a true tip-sample contact, a probe force of several nanonewtons would be required. The numerical results also show that the ultimate apex of the tip will determine the magnitude of the hydration force, but that the averaged hydration pressure is independent of the radius of curvature. This latter conclusion suggests that there should be no penalty for the use of sharper tips if hydration force is the dominant interaction between the tip and the specimen, which might be realizable under certain conditions. Furthermore, the calculated hydration energy near the specimen surface compares well with experimentally determined values with an atomic force microscope, providing further support to the validity of these calculations.

Calibration↗
PubMed1998

Overexpression of transfected human ribonucleotide reductase M2 subunit in human cancer cells enhances their invasive potential.

The ribonucleotide reductase (RR) gene has been associated with malignant transformation and metastatic potential. In this report, the significance of the expression of RR mRNA and enzymatic activity to the invasive potential was examined by Boyden chamber invasion assay. Our results suggest that overexpression of RR M2 mRNA and RR enzymatic activity correlates to an increase in cell invasive potential. The drug-induced HURs clone expressed a higher level RR M2 mRNA and enzyme activity which contributes significantly to the 3-fold increase in invasive potential of the cells observed relative to the KB wild-type control. On the contrary, the HUr revertant clone decreased the RR M2 mRNA level and enzymatic activity, concomitantly decreasing their invasive potential. This phenomenon is most likely due to the return of RR to levels comparable to that of the KB wild-type cells. To confirm that this observation was not of a drug-resistance phenotype associated with multiple gene alterations, the panel of RR transfectants (M1-D transfected M1 subunit cDNA, M2-D transfected M2 subunit cDNA, X-D transfected M1/M2 cDNA) characterized in a previous study were also tested in the invasion assay. The M2-D clone expressed 6-fold higher RR M2 mRNA and RR activity and also demonstrated 6-fold higher invasive potential in vitro than either the parental or vector only transfected cell line (KB-V). The X-D clone demonstrated 3-fold higher M2 mRNA expression and revealed 4-fold higher invasive potential than control cells. The M1-D clone, in contrast, expressed a baseline level of RR M2 mRNA and higher M1 mRNA. In contrast to the X-D and M2-D cells, the invasive potential of M1-D reached an even lower level in the invasive assay than the control. These results, therefore, suggest that RR M2 overexpression plays an important role in a tumor's invasiveness.

Carcinoma↗
PubMed1998

The intention to give up smoking: disease versus social dimensions.

An expanded protection motivation model was used to investigate the intention to give up smoking. Because smoking has both physiological and social-psychological foundations, the model was expanded to include the social dimensions as well as the original disease dimensions as predictors of health behavior. The participants were 96 current smokers (35 male and 61 female) in Australia; 44 were young adults (age < 22 years), and 52 were adults (age > 34 years). Data were analyzed by multiple regression with hierarchical entry, first of disease dimensions, then of social dimensions. For both the young and the adult smokers, the disease dimensions contributed significantly to the results of the regression equations. Addition of the social dimensions yielded a significant F change only for young smokers and increased the amount of variance explained from 23% to 38%.

Adult↗
PubMed1997

Root reinforcement with a resin-bonded preformed post.

PURPOSE: This study evaluated the ability of resin-bonded posts to reinforce teeth that are structurally weak in the cervical area against fracture. MATERIAL AND METHODS: Forty canine roots were endodontically treated and randomly distributed into four groups of 10. Parallel-sided preformed posts were cemented into the roots of these teeth after their crowns were removed. The cervical third of the canals were flared to simulate teeth weakened in this area as a result of caries or endodontic therapy. Three resin cements and a zine-phosphate cement, which was used as the control, were used to secure the posts into the roots. Cemented posts were loaded in an Instron testing machine with a gradually increasing force at a 60-degree angle to the long axis of the root until the root fractured. RESULTS: Roots in which the posts were cemented with Panavia were significantly more resistant to fracture than those where zinc phosphate was used (p < 0.05). Because of the inability to determine exactly the point of failure of the zinc-phosphate cement, no statistically significant difference was found when compared with the other two resin cements (ANOVA and Student-Newman-Keuls test).

Analysis of Variance↗
PubMed1996

The National Cancer Data Base report on longitudinal observations on prostate cancer.

BACKGROUND: Data on 349,154 prostate cancer cases diagnosed since 1986 have been entered to the American College of Surgeons National Cancer Data Base (NCDB). Previous annual reports have examined subsets of these data. The present report highlights major trends in the presentation and treatment of prostate cancer in the United States evident from longitudinal analyses of the entire data. METHODS: NCDB data are collected following a computerized, standard format. Hospital participation is voluntary. RESULTS: Since the first year of data collection, the number of participating hospitals has increased from 496 to 996 and the number of prostate cancer patients reported to the NCDB increased from 19,531 to 84,408. The proportion of men diagnosed at ages younger than 70 years increased from 37.8% in 1986 to 46.9% in 1993. Completeness of reporting stage of disease and tumor grade has improved. The proportions of both the earliest (American joint Committee an Cancer [AJCC] Stage Groups 0 and I) and the most advanced (AJCC++ Stage Group IV) stages declined. The proportion of Grade 2 (moderately differentiated) tumors increased from 38.6% in 1986 to 57.5% in 1993. The proportion of AJCC Stage II prostate cancer increased from 19% in 1986 to 48.4% in 1993. The proportion of patients treated by prostatectomy increased from 9.9% in 1986 to 29.2% in 1993. The proportion of patients receiving no cancer directed treatment declined from 41.8% in 1986 to 21.6% in 1993. Less change was observed in the use of radiation and hormonal treatments. CONCLUSIONS: These data show that the clinical patterns of prostate cancer have changed markedly in recent years.

Age Factors↗
PubMed1996

High resolution surface structure of E. coli GroES oligomer by atomic force microscopy.

Using atomic force microscopy (AFM) in aqueous solution, we show that the surface structure of the oligomeric GroES can be obtained up to 10 angstroms resolution. The seven subunits of the heptamer were well resolved without image averaging. The overall dimension of the GroES heptamer was 8.4 +/- 0.4 nm in diameter and 3.0 +/- 0.3 nm high. However, the AFM images further suggest that there is a central protrusion of 0.8 +/- 0.2 nm high and 4.5 +/- 0.4 nm in diameter on one side of GroES which displays a profound seven-fold symmetry. It was found that GroEL could not bind to the adsorbed GroES in the presence of AMP-PNP and Mg2+, suggesting that the side of GroES with the central protrusion faces away from the GroEL lumen, because only one side of GroES was observed under these conditions. Based on the results from both electron and atomic force microscopy, a surface model for the GroES is proposed.

Bacterial Proteins↗
PubMed1996

Chaperonins GroEL and GroES: views from atomic force microscopy.

The Escherichia coli chaperonins, GroEL and GroES, as well as their complexes in the presence of a nonhydrolyzable nucleotide AMP-PNP, have been imaged with the atomic force microscope (AFM). We demonstrate that both GroEL and GroES that have been adsorbed to a mica surface can be resolved directly by the AFM in aqueous solution at room temperature. However, with glutaraldehyde fixation of already adsorbed molecules, the resolution of both GroEL and GroES was further improved, as all seven subunits were well resolved without any image processing. We also found that chemical fixation was necessary for the contact mode AFM to image GroEL/ES complexes, and in the AFM images. GroEL with GroES bound can be clearly distinguished from those without. The GroEL/ES complex was about 5 nm higher than GroEL alone, indicating a 2 nm upward movement of the apical domains of GroEL. Using a slightly larger probe force, unfixed GroEL could be dissected: the upper heptamer was removed to expose the contact surface of the two heptamers. These results clearly demonstrate the usefulness of cross-linking agents for the determination of molecular structures with the AFM. They also pave the way for using the AFM to study the structural basis for the function of GroE system and other molecular chaperones.

Adenylyl Imidodiphosphate↗
PubMed1996

Differential gene expression of transforming growth factors alpha and beta, epidermal growth factor, keratinocyte growth factor, and their receptors in fetal and adult human prostatic tissues and cancer cell lines.

OBJECTIVES: Recent studies have shown that growth factors may play a role in the etiology of benign prostatic hyperplasia (BPH) and prostatic carcinoma. Several growth factors have been reported to be expressed by prostatic tissues, but these growth factors have never been examined in human fetal prostate and compared with adult prostates and cancer cell lines. The present study was designed to investigate the messenger ribonucleic acid (mRNA) expression of transforming growth factor (TGF)-alpha, TGF-beta 1, TGF-beta 2, TGF- beta 3, keratinocyte growth factor (KGF), epidermal growth factor (EGF), EGF receptor (EGF-R), and KGF receptor (KGF-R) in human fetal and adult prostatic tissues and cancer cell lines by reverse-transcriptase-polymerase chain reaction-(RT-PCR) using specific oligonucleotide primers. METHODS: Total RNA was extracted from human fetal and adult prostates (BPH tissues) and cancer cell lines. The gene expression of these growth factors and their receptors was determined by RT-PCR using specific oligonucleotide primers. RESULTS: The results of these experiments suggest that: (1) human fetal prostate expressed mRNA transcripts for TGF-alpha, TGF-beta 1, TGF-beta 2, TGF-beta 3, and EGF. However, KGF, KGF-R, and EGF-R mRNA were not expressed by human fetal prostate; (2) human adult prostate (BPH tissues) showed mRNA transcripts for all growth factors and their receptors except KGF-R; (3) human BPH-1 cell lines expressed mRNA transcripts for TGF-alpha, TGF-beta 1, TGF-beta 2, TGF-beta 3, EGF, and KGF-R, but not for EGF-R and KGF growth factors; (4) human primary prostate cancer cell line (ND-1) showed mRNA transcripts for all growth factors except EGF and KGF; and (5) human prostate cancer cell lines (LNCaP, DU-145, PC-3) expressed mRNA transcripts for all growth factors except KGF, which was absent in all cell lines. However, KGF-R mRNA was absent in the PC-3 prostate cancer cell line. CONCLUSIONS: These results suggest that the differential gene expression for various growth factors and their receptors in human fetal and adult prostatic tissues and cancer cell lines may be important in understanding the role of these factors in the pathophysiology of prostatic diseases.

Adult↗
PubMed1995

Touch-evoked agitation produced by spinally administered phospholipid emulsion and liposomes in rats. Structure-activity relation.

BACKGROUND: Phospholipid-based liposomes can alter the kinetics of spinally administered agents. We have observed that spinal delivery of these preparations results in an unexpected touch-evoked agitation, a state in which light touch evokes vocalization by the rat. In the current study we characterized this agitated state induced by various liposome preparations. METHODS: Rats prepared with lumbar intrathecal catheters received a variety of phospholipids delivered spinally as emulsions or as liposomes. Before and after injection, the animal's hot-plate latency (52.5 degrees C surface), spontaneous mobility, and spontaneous and evoked pain behavior were assessed. RESULTS: Spinal delivery of L-alpha-phosphatidylcholine of egg yolk (L-EPC) and the phospholipase hydrolysis product (lyso-L-alpha-phosphatidylcholine [lyso-L-EPC]) produced dose-dependent touch-evoked agitation; the order of potency and rapidity of onset was lyso-L-EPC > L-EPC, with no difference in activity whether administered as an emulsion or as a liposome preparation. Examination of the activity of a series of pure phospholipids revealed the ordering of touch-evoked agitation potency (where PC = phosphatidylcholine) to be L-monopalmitoyl-PC (lyso product of L-dipalmitoyl-PC) > L-dipalmitoyl-PC > L-distearoyl-PC, L-dioleoyl-PC >> L-dilauroyl-PC > L-dimyristoyl-PC; D-dipalmitoyl-PC = 0. The effect of unsaturation on touch-evoked agitation cannot be predicted because dioleoyl-PC and dioleoyl phosphatidylglycerol produced touch-evoked agitation but dipalmitoleoyl-PC did not. Substitution of glycerol for choline as the head group had no influence on touch-evoked agitation. Spinal treatment with an inhibitor of phospholipase (mepacrine) or a cyclooxygenase (ketorolac) blocked the touch-evoked agitation of L-EPC but not that of lyso-L-EPC. CONCLUSIONS: These results emphasize that certain L-isomeric phospholipids with their gel-transition temperatures near body temperature can produce prominent touch-evoked agitation after spinal delivery, an effect likely mediated by a phospholipase hydrolysis product. This touch-evoked agitation, which is consistent with neurotoxicity reported in the early literature on lysophospholipids, suggests that the choice of lipids for the formulation of liposomes intended for spinal drug delivery should be carefully considered.

Animals↗
PubMed1994

A high-sensitivity CCD system for parallel electron energy-loss spectroscopy (CCD for EELS).

A cooled frame transfer CCD camera system was developed and tested as a parallel detector in an electron energy-loss spectrometer mounted on a transmission electron microscope. The use of a shutterless camera with a frame transfer CCD collected virtually 100% of the photon signal with a reasonably fast acquisition time. The system detective quantum efficiency was over 90% under normal experimental conditions. Because of the low channel to channel gain variations in the CCD, the signal-to-noise ratio and the detection limit were substantially better than that obtained with a silicon intensified target (SIT) camera, and direct fitting to the standard data was feasible. Quantitation at the phosphorus L edge generated from a phosphoprotein, phosvitin, showed that, under identical experimental conditions, direct fitting of spectra obtained with this CCD system gave better sensitivity than that given by the SIT camera system. Because of its larger pixel charge well, the CCD system can also operate at a much higher beam current, resulting in a significant reduction in the time required for elemental mapping at a given sensitivity.

Image Processing, Computer-Assisted↗
PubMed1993

Thickness determination of biological thin sections by multiple-least-squares fitting of the carbon K-edge in the electron energy-loss spectrum.

We show that the local thickness of biological thin sections can be measured by fitting the electron energy-loss spectrum of the plurally scattered carbon K-edge, and that such measurements are consistent with the results obtained by a conventional method based on the relationship t/lambda alpha ln(It/I0). The new method allows the simultaneous measurement and/or mapping of both local thickness and core-level excitations (e.g. Ca L-edge) in this energy range (280-400 eV) without requiring the measurement of the zero-loss and the valence/plasmon excitations.

Animals↗
PubMed1992

Euthanasia and abortion: personality correlates for the decision to terminate life.

The study addresses three research questions: (a) How well do level of conservatism and religiosity predict attitudes toward passive and active euthanasia? (b) What is the relationship between attitudes toward abortion and attitudes toward euthanasia? (c) How do personality variables relate differentially to these attitudes? Subjects were 168 Australian adults (68 men, 100 women). Initial analysis indicated no sex differences in attitudes toward the study's criterion variables. Descriptive statistics indicated general support for active and passive euthanasia and for abortion, although the majority of the respondents were found to be more accepting of passive than of active euthanasia. Multiple regression analyses indicated that level of conservatism was the most consistent predictor of attitudes toward euthanasia and abortion, whereas religiosity was found significantly to predict attitudes toward abortion only.

Abortion, Induced↗
PubMed1990

Stimulatory role of substance P on gonadotropin release in ovariectomized rats.

Substance P (SP) has been shown to be present in the hypothalamus and anterior pituitary. To evaluate a possible physiological role of endogenous SP in the control of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release, specific antiserum against SP (anti-SP) was injected intraventricularly (3 microliters into the third ventricle) or intravenously (50 or 200 microliters) into conscious, ovariectomized (OVX) rats. Third ventricular injection of the antiserum induced a significant decrease in both plasma LH and FSH levels when compared to values in control animals injected with normal rabbit serum (p less than 0.01 and p less than 0.025, respectively). The effect was observed within 10 mi and levels remained suppressed for 60 min. In contrast, intravenous injection of large doses of anti-SP had no effect on the release of both hormones. In order to confirm the stimulatory effect of SP itself, synthetic SP was injected intravenously and intraventricularly into estrogen-primed (E-primed), OVX rats. Synthetic SP dramatically stimulated LH release, but not FSH release when injected either intravenously or intraventricularly at doses of 10 and 50 micrograms (p less than 0.001, p less than 0.005 vs. control, respectively). To investigate any direct action of SP on gonadotropin release from the anterior pituitary gland, synthetic SP was incubated with dispersed anterior pituitary cells harvested from E-primed OVX rats. SP did not affect the release of gonadotropins in vitro. These results indicate that endogenous hypothalamic SP exerts a tonic stimulatory hypothalamic control of basal gonadotropin release in OVX rats.

Animals↗
PubMed1989

Cerebrovascular disease and functional outcome after coronary artery bypass surgery.

A series of patients undergoing coronary artery bypass surgery was studied prospectively to see if angiographic evidence of cerebrovascular disease proved predictive of the incidence of neuropsychological deficit 8 days or 8 weeks after surgery. In 47 patients, intravenous digital subtraction angiography was carried out preoperatively to assess the presence and severity of atheromatous changes in the carotid arteries; 51% had evidence of vessel wall disease and 17% had stenosis of at least one carotid artery in the neck, although only one patient had severe narrowing. Overall, 77% of these 47 patients showed a neuropsychological deficit as defined by a significantly reduced score in at least two of 10 tests administered 8 days after surgery. Eight weeks after surgery 36% still showed a deficit. The incidence of neuropsychological deficit was not significantly greater among those patients with angiographically visible carotid artery disease. The mechanism of surgery-related cognitive impairment is briefly discussed in the light of these findings.

Brain↗
PubMed1988

Peripheral neuropathy complicating pancreatitis and major pancreatic surgery.

Four cases of a polyneuropathy associated with pancreatitis and pancreatic pseudocyst formation are reported. Electrophysiological investigation showed the peripheral neuropathy to be predominantly axonal in type. These patients were all seriously ill and many factors may have been involved in the pathogenesis of their neuropathy. They had all received parenteral nutrition and multiple drug therapy including metronidazole, and all had severe sepsis. There was evidence that insufficient vitamin replacement had been given during total parenteral nutrition. It was not possible to decide whether the polyneuropathy resulted from the summation of these factors, is similar to what has been called the polyneuropathy of the critically ill, or is a new association with pancreatic disease.

Acute Disease↗
PubMed1987

Development of brainstem and cerebellar projections to the diencephalon with notes on thalamocortical projections: studies in the North American opossum.

The North American opossum is born in a very immature state, 12 days after conception, and climbs into an external pouch where it remains attached to a nipple for an extended period of time. We have taken advantage of the opossum's embryology to study the development of brainstem and cerebellar projections to the diencephalon as well as the timing of diencephalic projections to somatosensory motor areas of neocortex. The techniques employed included immunocytochemistry for serotonin, the retrograde and orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase, and the selective impregnation of degenerating axons. Our results suggest that serotoninergic axons, presumably from the dorsal raphe and superior central nuclei, are present in the diencephalon at birth. Axons from the bulbar reticular formation, the vestibular complex, the trigeminal sensory nuclei, and the dorsal column nuclei reach at least mesencephalic (and probably diencephalic) levels by postnatal day (PND) 3, whereas those from the cerebellar nuclei may not grow into comparable levels until PND 5. The dorsal column and cerebellar nuclei innervate the ventral nuclei of the thalamus by estimated postnatal day (EPND) 17 and all of the diencephalic nuclei supplied in the adult animal by EPND 26. Diencephalic axons enter ventrolateral (face) areas of presumptive somatosensory motor cortex by PND 12, but do not reach dorsomedial (limb) regions until EPND 21. At both ages, diencephalic axons are limited to the cortical subplate and marginal zone; they do not innervate an identifiable internal granular layer until considerably later. Our results suggest that axons from the brainstem and cerebellum grow into the diencephalon early in development, but that they do not influence the cerebral cortex until relatively late. When the results of the present study are compared with those reported previously on the development of ascending spinal (Martin et al., '83) and corticofugal (Martin et al., '80; Cabana and Martin, '85b,c) projections, it appears that specific components of major somatosensory and motor circuits develop according to different timetables.

Animals↗
PubMed1985

Tamoxifen alone or in combination with estradiol-17 beta inhibits the growth and malignant transformation of hepatic hyperplastic nodules.

Hepatic hyperplastic nodules (HHNs) induced by the 'resistant hepatocyte method' of Solt et al. were studied as an experimental prototype of oral contraceptive-related tumors. Cytoplasmic estrogen receptors were present in all HHNs harvested and their concentration was always less than that in normal liver. No specific cytoplasmic progestin receptors could be measured in the above tumor or liver specimens. The long-term administration of estradiol-17 beta (4.8-24.0 micrograms/day) resulted in the death of all but one of 20 animals prior to termination at 10 months. Tamoxifen (0.25-2.5 mg biweekly), which did not lead to excess mortality, decreased HHN grade (proportion of liver slice occupied by HHN) and inhibited malignant transformation. Combination therapy with single-dose estradiol-17 beta (4.8 micrograms/day) and various doses of tamoxifen (0.25-2.5 mg biweekly) in most cases reduced mortality, HHN grade and malignant transformation. Cytoplasmic progestin receptors were absent and estrogen receptors were either undetectable or present in low concentrations in hepatic tumors harvested at the time of termination. Our results indicated that HHNs are hormone-dependent and that malignant transformation can be inhibited by tamoxifen alone or in combination with estradiol-17 beta.

Animals↗