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Biomedical subjects

D H Johnson

Publications and source records attributed to D H Johnson.

At least 127 records · Page 7Linked to original sources

Carcinoid tumor and the nephrotic syndrome: a novel association between neoplasia and glomerular disease.

Various malignancies are associated with the paraneoplastic evolution of the nephrotic syndrome. Renal biopsy in these instances frequently shows membranous glomerulonephritis. We describe a patient who had metastatic bronchial carcinoid tumor with development of microscopic hematuria and subsequent nephrotic syndrome in conjunction with another paraneoplastic process, a malignancy-related neuropathy. A decline in actual glomerular filtration rate led to percutaneous renal biopsy, which revealed fine holes in the glomerular basement membrane and focal capillary corrugation. Electron microscopy showed numerous small subepithelial dense deposits and fusion of foot processes, confirming the diagnosis of stage I membranous nephropathy. We believe this is the first published case of true carcinoid tumor associated with the nephrotic syndrome and a specific paraneoplastic glomerular lesion. Carcinoid tumor should be considered in the spectrum of malignancies associated with paraneoplastic development of the nephrotic syndrome.

Basement Membrane↗

Fractal noise strength in auditory-nerve fiber recordings.

Discharge patterns recorded from single auditory-nerve fibers have demonstrated long-range dependence, with the count variance-to-mean ratio growing as a power of the counting time for times greater than 0.1-1 s. The intent of this study is to provide a large dataset to enable a more detailed investigation of this phenomenon. Based on 108 recordings from a cat, we conclude that the presence of the fractal noise in the discharge rate is independent of characteristic frequency and stimulus level, but does depend on discharge rate. We measured the low-frequency power of the fractal noise, finding its coefficient of variation to range between 6% and 26% and to decrease as firing rate increases. Such behavior is consistent with multiplicative fractal variations in models of the hair cell membrane permeability to neurotransmitter. Measured standard deviations of spike rate correspond to a sound-pressure level difference limen of approximately 1 dB.

Acoustic Stimulation↗

Identification of overlapping DNA-binding and centromere-targeting domains in the human kinetochore protein CENP-C.

The kinetochore in eukaryotes serves as the chromosomal site of attachment for microtubules of the mitotic spindle and directs the movements necessary for proper chromosome segregation. In mammalian cells, the kinetochore is a highly differentiated trilaminar structure situated at the surface of the centromeric heterochromatin. CENP-C is a basic, DNA-binding protein that localizes to the inner kinetochore plate, the region that abuts the heterochromatin. Microinjection experiments using antibodies specific for CENP-C have demonstrated that this protein is required for the assembly and/or stability of the kinetochore as well as for a timely transition through mitosis. From these observations, it has been suggested that CENP-C is a structural protein that is involved in the organization or the kinetochore. In this report, we wished to identify and map the functional domains of CENP-C. Analysis of CENP-C truncation mutants expressed in vivo demonstrated that CENP-C possesses an autonomous centromere-targeting domain situated at the central region of the CENP-C polypeptide. Similarly, in vitro assays revealed that a region of CENP-C with the ability to bind DNA is also located at the center of the CENP-C molecule, where it overlaps the centromere-targeting domain.

Amino Acid Sequence↗

Pulmonary hemodynamic response to exercise in subjects with prior high-altitude pulmonary edema.

Individuals with a prior history of (susceptible to high altitude pulmonary edema (HAPE-S) have high resting pulmonary arterial pressures, but little data are available on their vascular response to exercise. We studied the pulmonary vascular response to exercise in seven HAPE-S and nine control subjects at sea level and at 3,810 m altitude. At each location, both normoxic (inspired PO2 = 148 Torr) and hypoxic (inspired PO2 = 91 Torr) studies were conducted. Pulmonary hemodynamic measurements included pulmonary arterial and pulmonary arterial occlusion pressures. A multiple regression analysis demonstrated that the pulmonary arterial pressure reactivity to exercise was significantly greater in the HAPE-S group. This reactivity was not influenced by altitude or oxygenation, implying that the response was intrinsic to the pulmonary circulation. Pulmonary arterial occlusion pressure reactivity to exercise was also greater in the HAPE-S group, increasing with altitude but independent of oxygenation. These findings suggest an augmented flow-dependent pulmonary vasoconstriction and/or a reduced vascular cross-sectional area in HAPE-S subjects.

Adult↗

Exercise-induced VA/Q inequality in subjects with prior high-altitude pulmonary edema.

Ventilation-perfusion (VA/Q) mismatch has been shown to increase during exercise, especially in hypoxia. A possible explanation is subclinical interstitial edema due to high pulmonary capillary pressures. We hypothesized that this may be pathogenetically similar to high-altitude pulmonary edema (HAPE) so that HAPE-susceptible people with higher vascular pressures would develop more exercise-induced VA/Q mismatch. To examine this, seven healthy people with a history of HAPE and nine with similar altitude exposure but no HAPE history (control) were studied at rest and during exercise at 35, 65, and 85% of maximum 1) at sea level and then 2) after 2 days at altitude (3,810 m) breathing both normoxic (inspired Po2 = 148 Torr) and hypoxic (inspired Po2 = 91 Torr) gas at both locations. We measured cardiac output and respiratory and inert gas exchange. In both groups, VA/Q mismatch (assessed by log standard deviation of the perfusion distribution) increased with exercise. At sea level, log standard deviation of the perfusion distribution was slightly higher in the HAPE-susceptible group than in the control group during heavy exercise. At altitude, these differences disappeared. Because a history of HAPE was associated with greater exercise-induced VA/Q mismatch and higher pulmonary capillary pressures, our findings are consistent with the hypothesis that exercise-induced mismatch is due to a temporary extravascular fluid accumulation.

Adult↗

Paclitaxel plus carboplatin in advanced non-small-cell lung cancer: a phase II trial.

PURPOSE: Studies conducted by the Eastern Cooperative Oncology Group (ECOG) indicate both paclitaxel and carboplatin are associated with an improvement in 1-year survival in patients with stage IV non-small-cell lung cancer (NSCLC). Based on these findings, a phase II trial of these agents in combination was conducted in patients with advanced NSCLC. PATIENTS AND METHODS: Eligibility included previously untreated stage IIIB or IV NSCLC patients with a good performance status (PS). Paclitaxel (135 or 175 mg/m2) was administered by 24-hour infusion on day 1, followed by a 1-hour infusion of carboplatin on day 2 (300 mg/m2 or dosed to an area under the concentration-time curve [AUC] of 6 mg/mL.min). Treatment was repeated every 28 days for a total of six cycles. Hematopoietic growth factors were not routinely used. RESULTS: Among 51 eligible patients, there were no complete and 14 partial responses, for an overall response rate of 27% (95% confidence interval [CI], 17% to 41%). The median progression-free survival time was 23.8 weeks (range, 12.1 to 73.9) and median survival time, 38 weeks. The survival rate at 1 year was 32%. Grade 3 or 4 granulocytopenia and thrombocytopenia were observed in 47% and 3%, respectively, of the 184 treatment cycles administered. The most common nonhematologic toxicities included nausea and emesis, neuropathy, and arthralgia/myalgia. CONCLUSION: Paclitaxel plus carboplatin is a moderately active regimen in patients with advanced NSCLC and warrants comparison with existing cisplatin-based regimens in a prospective randomized trial. The toxicities of this regimen are well tolerated in patients with a good PS.

Adult↗

Effect of fixation pressure on juxtacanalicular tissue and Schlemm's canal.

PURPOSE: A quantitative study was performed to compare the effect of two commonly used fixation pressures, 0 mm Hg (immersion) and 10 mm Hg (perfusion), on the porosity of the juxtacanalicular tissue and the size of Schlemm's canal. METHODS: Twelve pairs of human eyes were studied by fixing one eye with perfusion fixation and the fellow eye with immersion fixation. Morphometric analysis of the juxtacanalicular tissue and Schlemm's canal was performed. Outflow resistance was calculated from these measurements and compared with the measured outflow resistance obtained in six eyes. RESULTS: Schlemm's canal was narrowed in perfusion-fixed eyes, with a 47% smaller cross-sectional area than in immersion-fixed eyes (P = 0.04). Juxtacanalicular tissue of perfusion-fixed eyes had a 13.4% increase in the relative amount of empty space when compared with immersion-fixed fellow eyes (P = 0.04). Solid tissue components were almost equally divided among amorphous basement membrane, tendon and sheath material, and cytoplasm. No obvious washout of extracellular material was noted in perfused tissue. Measured outflow resistance was 100 times larger than outflow resistance of the juxtacanalicular tissue calculated from histologic measurements. CONCLUSIONS: Perfusion fixation at physiologic intraocular pressure caused a 47% decrease in the area of Schlemm's canal and a mean increase of 13.4% in the relative amount of empty space in the juxtacanalicular tissue compared with immersion-fixed fellow eyes. Perfusion of fixative did not appear to cause washout of extracellular material. Perfusion-fixed tissue appears preferable for studies of Schlemm's canal and for ultrastructural studies of the aqueous outflow pathways within the juxtacanalicular tissue.

Aged↗

Paclitaxel and 5-fluorouracil in metastatic breast cancer: the US experience.

Paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) is an effective drug in the treatment of metastatic breast cancer (MBC). In the salvage setting, 5-fluorouracil (5-FU) and folinic acid have proved to be effective against MBC as well. Recent preclinical data suggest that paclitaxel plus 5-FU has additive cytotoxicity. Given these observations, we initiated a phase II trial in which 38 women with MBC have been treated with a combination of all three drugs. All patients are currently evaluable for toxicity and 34 are evaluable for response. All women had histologically proven and assessable disease. Patients with prior exposure to paclitaxel were ineligible. Patient characteristics include a median age of 51 years (age range, 31 to 73 years) and a median performance status of 1 (range, 0 to 2). Thirty-three patients have received prior chemotherapy, of whom 23 had adjuvant chemotherapy only. Fifty-eight percent of the patients (22 of 38) had received prior doxorubicin or mitoxantrone; four patients had only hormonal therapy. Four patients had bone-only disease, and three patients had lymphangitic spread or cytologically positive pleural effusion as the only evaluable disease. Treatment consisted of paclitaxel 175 mg/m2 over 3 hours (day 1 only), followed by folinic acid 300 mg over 1 hour, followed by 5-FU 350 mg/m2 on days 1 to 3. Patients received standard paclitaxel premedications. To date, 175 cycles have been administered (median cycle length, 29 days; median number of cycles per patient, five). Toxicities included grade 3/4 infections in nine cycles (5%), grade 3/4 mucositis in three cycles, grade 3/4 nausea/vomiting in three cycles, grade 1 paresthesias in 12 patients (32%), alopecia 100%, and 17 cycles (10%) associated with dose reduction. Based on Cancer and Leukemia Group B toxicity criteria, arthralgia/myalgias were modest and graded mild (32 cycles), moderate (nine cycles), or severe (two cycles). There were two major hypersensitivity reactions, prompting removal of those patients from further protocol treatment. Four patients are unassessable for response due to hypersensitivity reactions (two) and unevaluable disease (two). Among the 34 patients evaluable for response, there were three complete responses, 18 partial responses, one minor response, nine stable disease, and three progressive disease (response rate, 62%). Responses were seen in patients who had received prior doxorubicin or mitoxantrone (11 of 22 patients) and in anthracycline/naive patients (10 of 16 patients). Responses were observed in all metastatic sites: soft tissue, viscera, and bone. Paclitaxel/5-FU/folinic acid appears to be an effective and well-tolerated outpatient regimen for women with MBC, even after failure of anthracycline-containing therapy.

Adult↗

Human trabecular meshwork cell survival is dependent on perfusion rate.

PURPOSE: To determine whether suppression of flow may be detrimental to trabecular cell survival and to the morphologic characteristics of the trabecular meshwork. METHODS: The anterior segments of normal human eye bank eyes were placed in perfusion organ culture. The effect of various perfusion rates of culture medium, and of the constant flow and constant pressure methods of delivery of culture medium, were studied. Trabecular cell survival was determined by quantitation of cell nuclei in histologic sections and by morphologic observation. RESULTS: Trabecular meshworks with perfusion rates of 1 microliter/minute and higher had significantly more trabecular cells than meshworks with lower perfusion rates. A significant loss of trabecular cells was found in meshworks cultured with the constant pressure technique when compared with fellow eyes cultured with the constant flow of medium. Those constant pressure cultured meshworks with surviving cells had higher flow rates than those with necrotic cells. CONCLUSIONS: A minimum perfusion rate of 1 microliter/minute is required for trabecular cell survival in perfusion organ culture. Constant pressure perfusion of medium is unsuccessful in maintaining trabecular cells in long-term culture if low perfusion rates occur. Constant flow appears to mimic the in vivo situation more closely.

Adult↗

Ifosfamide in non-small cell lung cancer.

Ifosfamide is an analogue of cyclophosphamide that is active against a variety of solid tumors, including non-small cell lung cancer. In preclinical studies, ifosfamide had yielded an average response rate of 20% to 25% and a median length of survival of 4 to 5 months. With the introduction of mesna, hematologic toxicity is the major toxicity associated with ifosfamide use. Response is not affected by the schedule of drug administration, nor is the response rate compromised by oral delivery of ifosfamide. Neurotoxicity is greater with oral administration, however. Ifosfamide has been used in combination with many different agents, including cisplatin and etoposide and newer drugs like vinorelbine and paclitaxel. The results of the combination studies indicate improved response rates. However, results of randomized phase II trials suggest there may be no survival benefit with the addition of ifosfamide to establish drug combinations. Further study of ifosfamide in combination with newer drugs is appropriate.

Antineoplastic Agents, Alkylating↗

Enzymes protective of oxidative damage present in all decades of life in the trabecular meshwork, as detected by two-dimensional gel electrophoresis protein maps.

Our purpose was to determine whether there are age-related differences in the presence of enzymes protective against oxidative damage in normal human trabecular meshwork (TM). The study was also done to determine whether there are significant changes in proteins related to age, gender, or position around the circumference of the meshwork. Human TM was dissected from both eyes of 16 normal donors ranging in age from 9 to 91 years. Proteins were mapped with two-dimensional (2D) gel electrophoresis. The microanalytical method used allowed analysis of samples as small as one fourth of a single meshwork. Selected proteins were identified by Western blot. Superoxide dismutase (SOD) and glutathione reductase were present in all ages on the 2D maps. Age-related changes in the TM were not apparent, although slight differences may exist between juvenile and adult TM, since differences in the relative intensities of some polypeptides were evident. In any single quadrant of the TM, > or = 160 protein spots could be counted visually. The 2D maps of the various quadrants were very similar, and the protein patterns were analogous between fellow eyes. Distinct differences were noted between maps from TM and adjacent cornea and sclera. Other protein spots identified included actin, albumin, transferrin, and vimentin. The TM samples had a mean cellular protein content of 66.3 +/- 15.4 micrograms.

Adolescent↗

Human and monkey trabecular meshwork accumulate alpha B-crystallin in response to heat shock and oxidative stress.

PURPOSE: Oxidative stress and other forms of injury to trabecular meshwork (TM) cells may contribute to changes seen with age and primary open-angle glaucoma. This study was designed to investigate if TM expresses alpha B-crystallin, a small heat-shock protein with chaperone activity, and whether it might be overexpressed under stress conditions. METHODS: The TM from human and monkey eyes, as well as organ and primary cell cultures derived from these eyes, were investigated for alpha B-crystallin by immunohistochemistry, two-dimensional gel electrophoresis, Northern and Western blot analysis. The TM cell cultures were stressed by heat shock (44 degrees C for 15 minutes) or hydrogen peroxide (200 mumol for 1 hour). Semiquantitation of alpha B-crystallin messenger RNA (mRNA) or protein was obtained by densitometry. RESULTS: In both species, alpha B-crystallin could be detected in fresh and cultured TM by two-dimensional gel electrophoresis in conjunction with Western blot analysis. Immunohistochemistry of fresh samples showed that alpha B-crystallin was expressed predominantly in the cribriform area. Protein expression was enhanced in 4- to 7-day organ cultures. Primary cultures from human TM cells expressed two sizes (approximately 0.8 and 1.1 kb) of alpha B-crystallin mRNA in Northern blots. In monkey TM cultures, a 0.8-kb band was observed, which comigrated with lens alpha B-crystallin. In both species, heat shock caused a significant increase in alpha B-crystallin mRNA with a peak after 4 hours. An increase in alpha B-crystallin mRNA also was observed after oxidative stress; however, the onset of mRNA induction was slower. After heat shock, but not after oxidative stress, a transient change in mRNA mobility was observed. Western dot blot analysis showed a 3.4-fold increase in protein 24 hours after heat shock and a 20-fold increase after 48 hours. No constitutive mRNA expression and only a minimal increase 4 hours after heat shock could be observed in simian virus 40 transformed cell lines from human TM. CONCLUSIONS: Overexpression of alpha B-crystallin might be an important mechanism for TM to prevent cellular damage associated with various stress conditions.

Aged↗

Paclitaxel plus carboplatin in the treatment of patients with advanced lung cancer: a Vanderbilt University Cancer Center phase II trial (LUN-46).

In studies conducted by the Eastern Cooperative Oncology Group, treatment with either paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) or carboplatin was associated with an improvement in 1-year survival in patients with stage IV non-small cell lung cancer (NSCLC). Based on these findings, a phase II trial of carboplatin plus paclitaxel was conducted in patients with advanced NSCLC to determine the activity and toxicity of this regimen. Eligibility requirements included stage IIIB or IV histologically confirmed NSCLC, Eastern Cooperative Oncology Group performance status of 0 to 2, no prior chemotherapy, and adequate hematologic, renal, hepatic, and cardiac functions. Paclitaxel was administered intravenously over 24 hours at a dose of 135 mg/m2 (28 patients) or 175 mg/m2 (23 patients), followed by a 1-hour infusion of carboplatin on day 2. Carboplatin was administered at a dose of 300 mg/m2 (16 patients) or, using the Calvert formula, a dose calculated to achieve an area under the concentration-time curve of 6 mg/mL x min (35 patients). Treatment was repeated every 28 days for a total of six cycles. Among the 51 eligible patients, 34 were men and 17 were women; their median age was 60 years and their median Eastern Cooperative Oncology Group performance status was 1. Six patients had stage IIIB and 45 had stage IV disease. Grade 3 or 4 granulocytopenia and thrombocytopenia were observed in 47% and 3% of treatment cycles, respectively. The most common nonhematologic toxicities noted included nausea and emesis, neuropathy, and arthralgia and myalgia. There were no complete responses and 14 partial responses, for an overall response rate of 27% (95% confidence interval, 17% to 41%). Median survival was 38 weeks and the survival rate at 1 year was 32%. Paclitaxel plus carboplatin, as given in this study, was found to be a moderately active regimen in patients with advanced NSCLC. This regimen warrants comparison with existing cisplatin-based regimens in a prospective randomized trial.

Adult↗

Induction but not expression of behavioural sensitization to nicotine in the rat is dependent on glucocorticoids.

Behavioural sensitization has been implicated in the development of addictive behaviour, and several studies suggest that corticosteroids may be involved in this phenomenon. In the present study, the effects of adrenalectomy and steroid replacement treatments on the behavioural sensitization observed after daily injections of nicotine (0.4 mg/kg s.c.) were investigated in the rat. Adrenalectomy completely prevented sensitization to the locomotor stimulating effect of nicotine after repeated injections but did not influence the acute locomotor activating effect of the drug or an already established sensitization to nicotine. In adrenalectomized animals receiving replacement treatment with corticosterone or dexamethasone, but not aldosterone, repeated administration of nicotine produced behavioural sensitization. Repeated dexamethasone treatment per se failed, however, to sensitize rats to nicotine. Post mortem neurochemical studies showed that repeated administration of nicotine significantly increased homovanillic acid (HVA) levels, as well as the dihydroxyphenylacetic acid (DOPAC)/dopamine quotient, in the limbic forebrain. Adrenalectomy per se significantly increased HVA levels and tended to elevate the DOPAC/dopamine quotient. When repeatedly treated with nicotine, adrenalectomized rats displayed a higher DOPAC/dopamine quotient, but no significant difference in HVA levels, compared to nicotine-treated sham-operated controls. In the striatum and the cortex, no significant effects of nicotine treatment or adrenalectomy were observed on any of the neurochemical measures. The present results suggest that glucocorticoid (type II) receptor activation is required for induction of sensitization to the locomotor stimulatory effect of nicotine, whereas corticosteroids are not required for the expression of the behavioural sensitization once established. Provided that HVA levels and the DOPAC/dopamine quotient relatively well reflect the presynaptic dopamine activating effect of nicotine, it may be suggested that corticosteroid-related mechanisms associated with behavioural sensitization to nicotine are post- rather than presynaptically located in relation to mesolimbic dopamine neurons.

Adrenalectomy↗

Aztreonam.

Aztreonam is a monocyclic beta-lactam antibiotic that is active exclusively against the aerobic gram-negative bacilli. It is not ototoxic or nephrotoxic and so is used as an alternative to aminoglycosides in a variety of clinical situations. In polymicrobial infections or when used for empiric therapy, aztreonam must be combined with other antimicrobial agents active against gram-positive and anaerobic species. Aztreonam is often effective against resistant strains of gram-negative organisms, which are often involved in nosocomial infections. Overuse of aztreonam should be avoided to prevent the emergence of resistant P. aeruginosa strains. Except in the treatment of P. aeruginosa infections, aztreonam should not be added to beta-lactam regimens for additional gram-negative coverage.

Aztreonam↗

Future directions in the management of small cell lung cancer.

The treatment of small cell lung cancer (SCLC) has continued to evolve over the past 20 years and now consists primarily of combination chemotherapy with or without thoracic radiotherapy depending on stage at presentation. However, despite marked improvement in overall survival, a majority of patients continue to die of their disease. It is not likely that conventional chemotherapy agents will substantially alter this dismal fact but new agents are available with novel mechanisms of action some of which yield excellent response rates. The agents with greatest promise include the taxanes and drugs that target topoisomerase I. Real progress in the management of SCLC will come with the identification of methods for overcoming drug resistance, exploration of new treatment strategies including gene therapy and possibly through the use of biological agents. Chemoprevention trials are of the utmost importance given the high incidence of second primary tumors that arise in the few long term survivors of this disease. All these areas are fertile grounds for future investigation in the management of SCLC.

Antineoplastic Combined Chemotherapy Protocols↗