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Biomedical subjects

D Johnston

Publications and source records attributed to D Johnston.

At least 73 records · Page 4Linked to original sources
PubMed1999

Elevation of the epidermal growth factor receptor and dependent signaling in human papillomavirus-infected laryngeal papillomas.

Laryngeal papillomas are benign tumors caused by human papillomaviruses types 6 and 11. This study addressed alterations in levels of signal transduction from the epidermal growth factor receptor (EGFR) in papillomas and cultured papilloma cells compared to normal tissue and cells. Mitogen-activated protein kinase (MAPK) was activated to a greater extent, phosphotyrosine was more abundant, and EGFR was overexpressed in laryngeal papillomas compared to normal laryngeal epithelium by Western blot analysis. The EGFR was 3 times more abundant in cultured papilloma cells than in normal laryngeal cells by Scatchard analysis and Western blot, without gene amplification or an increase in steady-state levels of mRNA. Following stimulation with EGF, a significant portion of the EGFR was recycled to the surface in papilloma cells, whereas in normal cells, it was not. Tyrosine kinase activity and activation of MAPK was more responsive to epidermal growth factor stimulation in papilloma cells than in uninfected primary laryngeal cells. PD153035, a specific inhibitor of the EGFR, and an EGFR-specific antibody that blocks ligand binding completely abrogated basal MAPK activation by endogenous ligands in laryngeal papilloma cells. These results demonstrated that infection of laryngeal epithelium by low-risk human papillomaviruses elevates the EGFR by posttranslational mechanisms, increasing its responsiveness to ligand-mediated activation. They also showed that MAPK activation in laryngeal papillomas depends upon ligand-mediated EGFR stimulation.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1999

Superimposed histologic and genetic mapping of chromosome 9 in progression of human urinary bladder neoplasia: implications for a genetic model of multistep urothelial carcinogenesis and early detection of urinary bladder cancer.

The evolution of alterations on chromosome 9, including the putative tumor suppressor genes mapped to the 9p21-22 region (the MTS genes), was studied in relation to the progression of human urinary bladder neoplasia by using whole organ superimposed histologic and genetic mapping in cystectomy specimens and was verified in urinary bladder tumors of various pathogenetic subsets with longterm follow-up. The applicability of chromosome 9 allelic losses as non-invasive markers of urothelial neoplasia was tested on voided urine and/or bladder washings of patients with urinary bladder cancer. Although sequential multiple hits in the MTS locus were documented in the development of intraurothelial precursor lesions, the MTS genes do not seem to represent a major target for p21-23 deletions in bladder cancer. Two additional tumor suppressor genes involved in bladder neoplasia located distally and proximally to the MTS locus within p22-23 and p11-13 regions respectively were identified. Several distinct putative tumor suppressor gene loci within the q12-13, q21-22, and q34 regions were identified on the q arm. In particular, the pericentromeric q12-13 area may contain the critical tumor suppressor gene or genes for the development of early urothelial neoplasia. Allelic losses of chromosome 9 were associated with expansion of the abnormal urothelial clone which frequently involved large areas of urinary bladder mucosa. These losses could be found in a high proportion of urothelial tumors and in voided urine or bladder washing samples of nearly all patients with urinary bladder carcinoma.

Chromosome Aberrations↗
PubMed1999

Does loss of gray- and white-matter contrast in injured spinal cord signify secondary injury? In vivo longitudinal MRI studies.

Longitudinal in vivo magnetic resonance imaging (MRI) of moderately injured rat spinal cord was performed to investigate the transient loss in gray matter (GM) and white matter (WM) contrast. In addition, neurobehavioral scores (based on open field walking, inclined plane test, and grid walking) and tissue cholesterol concentrations at pre-determined time points were measured. On MRI, a loss in contrast between GM and WM in sections 2-4 mm caudal to the site of injury was consistently observed 2 days after injury. A substantial recovery in the contrast was observed within 1 week after injury. A strong correlation between the loss of GM-WM contrast and the cholesterol concentration was also observed. The neurobehavioral scores improved with the return of the GM-WM contrast. These serial MRI studies indicate that the loss of contrast in the cord is mainly due to edema accumulated in the WM. The resolution of edema seems to occur around the same time as the restoration of cholesterol in the cord tissue. It is speculated that the compromised membrane stability due to the loss of cholesterol may be one of the factors leading to the accumulation of edema in WM.

Animals↗
PubMed1999

The incidence of occult nipple-areola complex involvement in breast cancer patients receiving a skin-sparing mastectomy.

BACKGROUND: Surgical treatment of breast cancer traditionally has included resection of the nipple-areola complex (NAC), in the belief that this area had a significant probability of containing occult tumors. The purpose of this study was to investigate the true incidence of NAC involvement in patients who underwent a skin-sparing mastectomy (SSM) and to determine associated risk factors. METHODS: A retrospective chart review was conducted of 326 patients who had a SSM at our institution from 1990 to 1993. NAC involvement was reviewed in 286 mastectomy specimens. The charts were analyzed for tumor size, site, histology, grade, nodal status, recurrence, survival, and NAC involvement. RESULTS: Occult tumor involvement in the NAC was found in 5.6% of mastectomy specimens (16 patients). Four patients would have had NAC involvement identified on frozen section if they had been undergoing a skin-sparing mastectomy with preservation of the NAC. There were no significant differences between NAC-positive (NAC+) and NAC-negative (NAC-) patients in median tumor size, nuclear grade, histologic subtype of the primary tumor, or receptor status. There were significant differences in location of the primary tumor (subareolar or multicentric vs. peripheral) and positive axillary lymph node status. NAC involvement was not a marker for increased recurrence or decreased survival. CONCLUSIONS: Occult NAC involvement occurred in only a small percentage of patients undergoing skin-sparing mastectomies. NAC preservation would be appropriate in axillary node-negative patients with small, solitary tumors located on the periphery of the breast.

Breast Neoplasms↗
PubMed1999

Prostate cancer detection: relationship to prostate size.

OBJECTIVES: It has been suggested that the lower detection rate for cancer in large prostates is due to the smaller proportion of tissue sampled. To examine this hypothesis, we evaluated whole-mount radical prostatectomy specimens in which the volume of cancer had been determined. We correlated cancer volume to overall gland volume. In addition, we performed stochastic computer simulations of parasagittal sextant biopsies on the same group of radical prostatectomy specimens. We correlated the likelihood of a positive cancer biopsy simulation with tumor volume and gland size. METHODS: Six hundred seven tumor foci from 180 serially sectioned whole-mount prostatectomy specimens were mapped and digitized. Tumor volume was calculated by a step-section planimetry algorithm. Before sectioning, each gland was weighed. Systematic parasagittal sextant biopsies were computer simulated for each case. For each prostate, 40 simulations were performed, with random variations in biopsy location programmed for each run. Overall cancer detection by biopsy was considered positive if 90% of the 40 simulation runs were positive for cancer. Chi-square tests were used to evaluate statistical significance. RESULTS: Small-volume cancers (0.5 cc or less) were twice as frequent in large glands greater than 50 g (P = 0.03). These small-volume tumors comprised 33% (13 of 40) of cancers in prostates greater than 50 g, 16% (5 of 31) in glands less than 30 g, and 14% (15 of 109) in glands 30 to 50 g. The rate of positive sextant biopsy simulation was lower in glands greater than 50 g than in glands 50 g or less (48% versus 67%, P<0.03). Smaller cancers were much less likely to be detected in the simulations. The simulation detection rate for cancers 0.5 cc or less was 18% (6 of 33), compared with a detection rate of 73% (107 of 147) for cancers greater than 0.5 cc (P<0.00001). CONCLUSIONS: The observed lower cancer detection rate in large glands is a result of the higher proportion of low-volume cancers in these glands. This suggests that large prostates are more likely to be biopsied because of an elevated prostate-specific antigen value resulting from benign elements of the gland and not from a significant cancer. Increasing the number of cores solely to compensate for increased prostate size risks a disproportionate increased detection of small-volume tumors with a low clinical likelihood of progression.

Biopsy↗
PubMed1999

Comparison of prostate biopsy schemes by computer simulation.

OBJECTIVES: To compare the ability of different biopsy schemes to detect cancer and predict tumor volume using our previously described prostate biopsy simulation system. In addition, we used the simulation system to evaluate the optimal location of transition zone biopsies. METHODS: Digital reconstructions of 180 radical prostatectomy specimens were used. Forty simulations were performed on each prostate for 10 biopsy schemes, including a previously reported five-region peripheral zone biopsy pattern and a new 11-core multisite-directed scheme consisting of sextant, two transition zone, one midline, and two anterior horn biopsies. For simulation of the transition zone biopsies, paired near-midline biopsies were simulated, with needle insertion points from the apex to the base of the prostate and with needle advances of 1 to 4 cm before firing. A total of 1,180,800 individual biopsy tracks were simulated. RESULTS: The 11-core multisite-directed biopsy scheme had the highest detection rate for cancers greater than 0.5 cc. This scheme reliably detected cancer in 94% (138 of 147) of the cases. These results were significantly better than those of the sextant biopsy scheme (P <0.001) and the five-region 18-core peripheral zone scheme (P = 0.03). Compared with other schemes, there were increases in small-volume (0.5 cc or less) cancer detection by both the 11-core multisite-directed and five-region schemes, but they were not statistically significant. The multisite and the sextant plus four transition zone biopsy schemes had the best correlation of mean total core cancer length with total cancer volume. In the simulation of the transition zone biopsies, the highest detection rate was observed when the biopsies were initiated at the most apical section and inserted for a depth of 3 cm before firing. CONCLUSIONS: Our simulation results suggest that the detection rate of prostate biopsies is not related solely to the number of cores taken. Core placement (the regions of the prostate from which samples are taken) is also important. The 11-core multisite-directed biopsy scheme performed the best, with improved cancer detection rates and tumor volume correlation over other schemes. On the basis of our simulations, this scheme has been chosen for clinical evaluation.

Biopsy↗
PubMed1999

Regulation of back-propagating action potentials in hippocampal neurons.

Protein kinase C has recently been shown to modulate the slow recovery from inactivation of Na+ channels in apical dendrites of hippocampal CA1 pyramidal neurons. Moreover, dendritic, A-type K+ channels have been found to be modulated by protein kinases A and C and by mitogen-activated protein kinase. The electrical signalling ability of these dendrites is thus highly regulated by a number of neurotransmitters and second-messenger systems.

Action Potentials↗
PubMed1999

Multiple forms of LTP in hippocampal CA3 neurons use a common postsynaptic mechanism.

We investigated long-term potentiation (LTP) at mossy fiber synapses on CA3 pyramidal neurons in the hippocampus. Using Ca2+ imaging techniques, we show here that when postsynaptic Ca2+ was sufficiently buffered so that [Ca2+]i did not rise during synaptic stimulation, the induction of mossy fiber LTP was prevented. In addition, induction of mossy fiber LTP was suppressed by postsynaptic injection of a peptide inhibitor of cAMP-dependent protein kinase. Finally, when ionotropic glutamate receptors were blocked, LTP depended on the postsynaptic release of Ca2+ from internal stores triggered by activation of metabotropic glutamate receptors. These results support the conclusion that mossy fiber LTP and LTP at other hippocampal synapses share a common induction mechanism involving an initial rise in postsynaptic [Ca2+].

Animals↗
PubMed1999

Neuromodulation of dendritic action potentials.

The extent to which regenerative action potentials invade hippocampal CA1 pyramidal dendrites is dependent on both recent activity and distance from the soma. Previously, we have shown that the amplitude of back-propagating dendritic action potentials can be increased by activating either protein kinase A (PKA) or protein kinase C (PKC) and a subsequent depolarizing shift in the activation curve for dendritic K+ channels. Physiologically, an increase in intracellular PKA and PKC would be expected upon activation of beta-adrenergic and muscarinic acetylcholine receptors, respectively. Accordingly, we report here that activation of either of these neurotransmitter systems results in an increase in dendritic action-potential amplitude. Activation of the dopaminergic neurotransmitter system, which is also expected to raise intracellular adenosine 3',5'-cyclic monophosphate (cAMP) and PKA levels, increased action-potential amplitude in only a subpopulation of neurons tested.

Action Potentials↗
PubMed1999

Voltage-dependent properties of dendrites that eliminate location-dependent variability of synaptic input.

We examined the hypothesis that voltage-dependent properties of dendrites allow for the accurate transfer of synaptic information to the soma independent of synapse location. This hypothesis is motivated by experimental evidence that dendrites contain a complex array of voltage-gated channels. How these channels affect synaptic integration is unknown. One hypothesized role for dendritic voltage-gated channels is to counteract passive cable properties, rendering all synapses electrotonically equidistant from the soma. With dendrites modeled as passive cables, the effect a synapse exerts at the soma depends on dendritic location (referred to as location-dependent variability of the synaptic input). In this theoretical study we used a simplified three-compartment model of a neuron to determine the dendritic voltage-dependent properties required for accurate transfer of synaptic information to the soma independent of synapse location. A dendrite that eliminates location-dependent variability requires three components: 1) a steady-state, voltage-dependent inward current that together with the passive leak current provides a net outward current and a zero slope conductance at depolarized potentials, 2) a fast, transient, inward current that compensates for dendritic membrane capacitance, and 3) both alpha amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid- and N-methyl-D-aspartate-like synaptic conductances that together permit synapses to behave as ideal current sources. These components are consistent with the known properties of dendrites. In addition, these results indicate that a dendrite designed to eliminate location-dependent variability also actively back-propagates somatic action potentials.

Action Potentials↗
PubMed1998

HLA-independent heterogeneity of CD8+ T cell responses to MAGE-3, Melan-A/MART-1, gp100, tyrosinase, MC1R, and TRP-2 in vaccine-treated melanoma patients.

An important element in melanoma vaccine construction is to identify peptides from melanoma-associated Ags that have immunogenic potential in humans and are recognized by CD8+ T cells in vivo. To identify such peptides, we evaluated HLA-A*02+ melanoma patients immunized to a polyvalent vaccine containing multiple Ags, including MAGE-3, Melan-A/MART-1, gp100, tyrosinase, melanocortin receptor (MC1R), and dopachrome tautomerase (TRP-2). Using a filter spot assay, we measured peripheral blood CD8+ T cell responses, before and after immunization, to a panel of 45 HLA-A*0201-restricted peptides derived from these Ags. The peptides were selected for immunogenic potential based on their strong binding affinity in vitro to HLA-A*0201. Vaccine treatment induced peptide-specific CD8+ T cell responses to 22 (47.8%) of the peptides. The most striking finding was the HLA-independent heterogeneity of responses to both peptides and Ags. All responding patients reacted to different combination of peptides and Ags even though the responding patients were all A*0201+ and the peptides were all A*0201-restricted. From 9 to 27% of patients developed a CD8+ T cell response to at least one peptide from each Ag, but no more than 3 (14%) reacted to the same peptide from the same Ag. This heterogeneity of responses to individual peptides and Ags in patients with the same haplotype points to the need to construct vaccines of multiple peptides or Ags to maximize the proportion of responding patients.

Alleles↗
PubMed1998

Genetic epidemiology study of idiopathic talipes equinovarus.

Previous genetic studies of idiopathic talipes equinovarus (ITEV) suggest an environmental and genetic component to the etiology of ITEV. The present study was undertaken to assess the role of causal factors in the development of ITEV. A total of 285 propositi were ascertained, with detailed family history information available in 173 cases and medical records on the remaining 112 propositi. Information was collected on specific prenatal, parental, and demographic factors. No racial heterogeneity was noted among any of the factors. The overall ratio of affected males to females was 2.5:1. The incidence of twinning among all propositi was significantly increased (P=0.006) above the expected population frequency. A family history of ITEV was noted in 24.4% of all propositi studied. These findings, in addition to the detailed analysis of 53 pedigrees with ITEV history, suggest the potential role of a gene or genes operating in high-risk families to produce this foot deformity.

Clubfoot↗
PubMed1998

Downregulation of transient K+ channels in dendrites of hippocampal CA1 pyramidal neurons by activation of PKA and PKC.

We have reported recently a high density of transient A-type K+ channels located in the distal dendrites of CA1 hippocampal pyramidal neurons and shown that these channels shape EPSPs, limit the back-propagation of action potentials, and prevent dendritic action potential initiation (). Because of the importance of these channels in dendritic signal propagation, their modulation by protein kinases would be of significant interest. We investigated the effects of activators of cAMP-dependent protein kinase (PKA) and the Ca2+-dependent phospholipid-sensitive protein kinase (PKC) on K+ channels in cell-attached patches from the distal dendrites of hippocampal CA1 pyramidal neurons. Inclusion of the membrane-permeant PKA activators 8-bromo-cAMP (8-br-cAMP) or forskolin in the dendritic patch pipette resulted in a depolarizing shift in the activation curve for the transient channels of approximately 15 mV. Activation of PKC by either of two phorbol esters also resulted in a 15 mV depolarizing shift of the activation curve. Neither PKA nor PKC activation affected the sustained or slowly inactivating component of the total outward current. This downregulation of transient K+ channels in the distal dendrites may be responsible for some of the frequently reported increases in cell excitability found after PKA and PKC activation. In support of this hypothesis, we found that activation of either PKA or PKC significantly increased the amplitude of back-propagating action potentials in distal dendrites.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1998

Expression of v-Ha-ras driven by the calcitonin/calcitonin gene-related peptide promoter: a novel transgenic murine model for medullary thyroid carcinoma.

v-Ha-ras has been demonstrated previously to induce neuroendocrine differentiation of medullary thyroid carcinoma (MTC, malignant C cell tumor) cell lines. The potential role of ras mediated signaling in neuroendocrine cells in vivo has been investigated by expressing v-Ha-ras under control of the neural/neuroendocrine specific calcitonin/calcitonin gene-related peptide (CGRP) promoter. Five independent mouse lineages were derived following germ line insertion of the transgene. Four of the five lineages consistently express the transgene; neuroendocrine expression is found in three of the five lineages as both spliced and full length messages. Phenotypically, the mice expressing rascal have shortened lifespans primarily due to the high incidence of MTCs between 6 months to a year of age. C-cell hyperplasia is demonstrated in several mice in the absence of gross evidence of tumor formation. Histopathological and ultrastructural analyses demonstrate typical features of MTCs including prominent immunohistochemical staining for calcitonin and dense-core neurosecretory-type granules. In addition, four of 22 tumors co-express thyroglobulin (a non-neuroendocrine follicular epithelial cell marker) and calcitonin (a neuroendocrine marker) in a subset of the tumor cells. The rascal transgenic mouse provides a unique model for investigating the sequential pathogenesis of MTC and possibly also for elucidating the relationship between MTC and mixed medullary-follicular carcinomas.

Animals↗
PubMed1998

Comparison of the skin tumor-promoting potential of different organic peroxides in SENCAR mice.

The skin tumor-promoting activities of three organic peroxides were evaluated and compared to the activity of benzoyl peroxide, a well-characterized tumor promoter. Two of the compounds (di-t-butyl peroxide and dicumyl peroxide) were dialkyl peroxides and the other (di-m-chlorobenzoyl peroxide) was a diacyl peroxide. These compounds were selected based on a previous study in which we evaluated their capacity to induce epidermal hyperplasia, ornithine decarboxylase activity, and dark basal keratinocytes, which have been reliable short-term markers of tumor promotion. Dicumyl peroxide was a weak tumor promoter despite its high activity in inducing hyperplasia. Like benzoyl peroxide, di-m-chlorobenzoyl peroxide generally had intermediate activity as an inducer of short-term markers of tumor promotion and was a moderately effective tumor promoter. However, compared to benzoyl peroxide, di-m-chlorobenzoyl peroxide was more toxic to the skin, which may have limited its tumor-promoting activity. The final compound, di-t-butyl peroxide, which was essentially inactive in short-term assays, was also totally inactive in promoting papillomas or carcinomas in initiated skin. Tumor-promoting efficacy generally showed an inverse association with thermal stability for the compounds tested, suggesting that the rate of formation of free radicals is a key factor contributing to tumor promotion by organic peroxides. However, a number of other factors can potentially affect the activity of different organic peroxides as tumor promoters. Each compound evaluated had a different spectrum of activities, and these compounds should be useful for studying mechanisms of organic peroxide-induced tumor promotion.

Animals↗
PubMed1998

Paradoxical high anal resting pressures in men with idiopathic fecal seepage.

PURPOSE: Fecal incontinence has been a matter of concern for many years, but seepage is poorly understood, especially in men. METHODS: We compared the results of anorectal physiologic tests in a group of 16 male patients who complained of fecal soiling but had no previous history of anorectal surgery or disease and had normal clinical examinations with findings of 16 normal male controls. Physical examination and proctosigmoidoscopy were normal in each patient. RESULTS: Maximum anal resting pressure (median interquartile range) was 136 (120-145) cm H2O in the "seepage" group and 104 (83-112) cm H2O in controls (P < 0.01). Inflation volumes at which patients and controls experienced rectal sensation were 45 (35-80) and 90 (75-100) ml of air, respectively (P < 0.01). Maximum tolerated volumes in the rectum were 130 (85-180) ml of air in the seepage group and 190 (140-240) ml of air in controls (P < 0.01). Median length of the anal sphincter was 3.75 (3.5-4) cm in patients and 3 (3-3.5) cm in controls (P < 0.01). Maximum squeeze pressures, sensation in the anal canal, and sphincter relaxation in response to rectal distention were similar in the two groups. CONCLUSION: Male patients with "idiopathic" fecal seepage have a long anal sphincter with abnormally high resting tone.

Adult↗
PubMed1998

Environmental effects of sodium Acetate/Formate deicer, ice sheartrade mark

The environmental impacts of Ice Sheartrade mark, an alternative highway deicer, have been evaluated using standard laboratory tests; biochemical oxygen demand (BOD) tests, chemical oxygen demand (COD) tests, acute rainbow trout bioassays, and phytotoxicity tests were used. Ice Shear consists of equimolar sodium acetate and sodium formate. The organic matter of the deicer can be readily degraded microbiologically in the natural environment with a slow rate of degradation at lower temperatures but an increased rate at higher temperatures. At elevated temperatures, highway runoffs of the deicer may reduce the level of dissolved oxygen in the receiving waters to cause an adverse impact. However, the apparent activation energy calculated for the BOD rate of Ice Shear is low (8.78 kcal mole-1), indicating that the temperature variation may not significantly influence the biodegradation of the deicer compound. Ice Shear appears relatively harmless to aquatic animals, showing a high 96-h LC50 value (16.1 g/L) derived for rainbow trout (Oncorhynchus mykiss). Ice Shear causes minimal toxicity to representative roadside vegetation; herbaceous (e.g., sunflowers, beans, and lettuce) and woody (e.g., pine seedlings) plants. Rather, the deicer at low concentrations (less than 2 g/kg soil) seems to work as a fertilizer, promoting the yield of biomass. The test results indicate that Ice Shear poses minimal environmental disturbance in both aquatic and terrestrial ecosystems.

Journal Article↗