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Biomedical subjects

William Parker

Publications and source records attributed to William Parker.

At least 19 recordsLinked to original sources

An assessment of PTV margin definitions for patients undergoing conformal 3D external beam radiation therapy for prostate cancer based on an analysis of 10,327 pretreatment daily ultrasound localizations.

INTRODUCTION: We have assessed the planning target volume (PTV) margins required for adequate treatment of the prostate in the absence of daily localization imaging based on the statistical analysis of a large data set obtained from 5 years of use of a two-dimensional ultrasound pretreatment localization device. METHODS AND MATERIALS: Data from 387 prostate patients were analyzed retrospectively. Every patient in the study received daily pretreatment localization resulting in a total of 10,327 localizations, each comprising an isocenter displacement in three directions: anteroposterior, right-left lateral, and superior-inferior. The mean displacement for each direction for each patient was computed from daily treatment records, and a mean of the means was used in the analysis. RESULTS: The mean displacements required to shift the target to the required position were 6.1 mm posterior (4.4 mm SD), 2.1 mm superior (4.5 mm SD), and 0.5 mm right (3.6 mm SD). The 6.1-mm shift posterior is indicative of a systematic uncertainty. Differences in planning conditions between the computed tomography simulation and the treatment room may account for this discrepancy. CONCLUSION: Our study has revealed systematic intertreatment uncertainties that would have required a nonuniform PTV margin ranging in dimensions between 2.7 mm anterior, 14.9 mm posterior, 7.7 mm right, 6.7 mm left, 11 mm superior, and 7 mm inferior to encompass the prostate for 95% of our sample if the ultrasound localization system were not used. In the absence of systematic uncertainties, a uniform PTV margin of 9 mm would suffice.

Humans↗

Effect of an anti-C5a monoclonal antibody indicates a prominent role for anaphylatoxin in pulmonary xenograft dysfunction.

BACKGROUND: In contrast to renal or cardiac xenografts, the inhibition of complement using cobra venom factor (CVF) accelerates pulmonary xenograft failure. By activating C3/C5 convertase, CVF depletes complement while additionally generating C5a and other anaphylatoxins, to which pulmonary xenografts may be uniquely susceptible. The current study investigates the role of C5a in pulmonary xenograft failure in baboons. METHODS: Left orthotopic pulmonary xenografts using swine lungs expressing human CD46 were performed in baboons receiving: I) no other treatment (n=4), II) immunodepletion (n=5), and III) immunodepletion plus a single dose of mouse anti-human C5a monoclonal antibody (anti-C5a, 0.6 mg/kg administered intravenously) (n=3). The extent to which anti-C5a inhibits baboon C5a was assessed in vitro using a hemolytic reaction involving baboon serum and porcine red blood cells and by ELISA. RESULTS: Baboons in Group III exhibited significantly prolonged xenograft survival (mean=722+/-121 min, P=0.02) compared to baboons in Group I (mean=202+/-24 min) and Group II (mean=276+/-79 min). Furthermore, baboons in Groups I and II experienced pronounced hemodynamic compromise requiring inotropic support whereas those in Group III remained hemodynamically stable throughout experimentation without the need for additional pharmacologic intervention. CONCLUSIONS: These findings indicate that C5a exacerbates pulmonary xenograft injury and compromises recipient hemodynamic status. Moreover, blockade of anaphylatoxins, such as C5a, offers a promising approach for future investigations aimed at preventing pulmonary xenograft injury in baboons.

Animals↗

Depletion of pulmonary intravascular macrophages prevents hyperacute pulmonary xenograft dysfunction.

BACKGROUND: Recent years have brought dramatic progress in the field of xenotransplantation, with the development of transgenic swine and various other means of overcoming the rejection mediated by xenoreactive antibodies. Although progress has been rapid with kidney and heart xenografts, progress with pulmonary xenografts has lagged behind. Recent findings have suggested that donor pulmonary intravascular macrophages may play a critical role in the hyperacute dysfunction of pulmonary xenografts. METHODS: The function of pulmonary xenografts from pigs depleted of pulmonary intravascular macrophages was compared with the function of xenografts from normal pigs. RESULTS: Pulmonary xenografts from pigs from which pulmonary intravascular macrophages were depleted survived (23.5+/-0.9 hours) about five times longer than normal (macrophage sufficient) xenografts (4.4+/-1.41 hours) (P< 0.0001). At 21 hours post-reperfusion, the left pulmonary arterial flow was 225.0+/-34 ml/min in lungs depleted of pulmonary intravascular macrophages, whereas all normal xenografts had failed. CONCLUSIONS: These findings indicate that donor macrophages play a critical role in pulmonary xenograft dysfunction. This finding has broad implications for xenotransplantation, suggesting that porcine macrophages might pose a barrier to the engraftment and function of a variety of porcine organ xenografts.

Animals↗

Increased IL-4 production and attenuated proliferative and pro-inflammatory responses of splenocytes from wild-caught rats (Rattus norvegicus).

Wild animals, unlike their laboratory counterparts, live amidst an abundance of pathogens and parasites. The presence of such immune stimulation from the time of birth likely has a profound effect on the development and stasis of the immune system. To probe potential differences between the immune systems of wild and laboratory animals, the response to mitogen (Con A) of splenocytes from wild rats was evaluated in vitro and compared with results from lab-rat-derived splenocytes. Although the response to mitogen is ubiquitous in splenocytes from laboratory animals regardless of strain or even species, splenocytes derived from wild rats were unresponsive to mitogen as judged by upregulation of activation markers and proliferation. Further, splenocytes from wild rats produced almost 10-fold less IL-2 and TNF-alpha in response to mitogen than did splenocytes from laboratory rats. In addition, mitogen stimulation resulted in an almost 100-fold greater production of IL-4 in wild-rat-derived splenocytes than in lab-rat-derived splenocytes. Perhaps surprisingly, these differences were observed in the absence of differences between wild and laboratory animals in the ratio of CD4+/CD8+ T cells or in the relative numbers of T cells, B cells and monocytes in the splenocyte population. These observations may have substantial implications for the hygiene hypothesis and provide considerable insight into the roles played by the environment during immune system development and modulation.

Animals↗

Adenosine regulation of cystic fibrosis transmembrane conductance regulator through prostenoids in airway epithelia.

Cystic fibrosis is caused by dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) protein, leading to altered ion transport, chronic infection, and excessive inflammation. Here we investigated regulation of CFTR in airway cell monolayers by adenosine, adenosine receptors, and arachidonic acid. Our studies demonstrate that the A2B adenosine receptor is expressed at high levels relative to the other adenosine receptor subtypes, with a characteristic low-affinity profile for adenosine-stimulated CFTR Cl- currents in both Calu-3 cells and CFBE41o- airway cell monolayers stably transduced with wild-type CFTR. The levels of adenosine found in sputum from patients with cystic fibrosis with moderate to severe lung disease stimulated apical prostaglandin release in Calu-3 and CFBE41o- cells, implicating adenosine regulation of phospholipase A2 (PLA2) activity. A2B adenosine receptor and arachidonic acid stimulation produced CFTR-dependent currents in airway monolayers and increased cAMP levels that were sensitive to cyclooxygenase inhibition. Arachidonic acid demonstrated dual regulation of CFTR, stimulating CFTR and Cl- currents in intact airway monolayers, and potently inhibiting PKA-activated Cl- currents in excised membrane patches. Cl- currents produced by arachidonic acid were sensitive to inhibition of PKA, cyclooxygenase, and 5-lipoxygenase. Together, the results provide a converging mechanism to link regulation of CFTR and airway cell inflammation through adenosine and adenosine receptors.

Adenosine↗

Secretory IgA and mucin-mediated biofilm formation by environmental strains of Escherichia coli: role of type 1 pili.

Recent studies suggest the importance of secretory IgA (SIgA) and mucin in the mediation of biofilm formation by commensal bacteria within the mammalian gut. Studies using a variety of strains of Escherichia coli have indicated that the interaction between E. coli and SIgA is dependent on the type 1 pilus. In this study, the importance of the pilus in SIgA-mediated biofilm formation by a laboratory strain (MG1655) and environmental (fecal) strains of E. coli was evaluated. Transient expression of the type 1 pilus by the laboratory strain of E. coli failed to facilitate SIgA-mediated biofilm formation, whereas constitutive expression of the type 1 pilus by the laboratory strain was sufficient. In contrast, transient expression of the type 1 pilus was sufficient to facilitate SIgA-mediated biofilm formation by environmental isolates. The "threshold" for mucin-mediated biofilm formation appeared to be lower than that for SIgA-mediated biofilm formation, perhaps reflecting disparate roles of mucin and SIgA in mediating biofilm formation in the gut. These studies also provide the first procedures for the growth of bacterial biofilms on live epithelial cells in vitro, an important development that may facilitate future studies on the effects of bacterial biofilms on epithelial cells.

Adenocarcinoma↗

Chronic aspiration of gastric fluid accelerates pulmonary allograft dysfunction in a rat model of lung transplantation.

OBJECTIVE: Emerging clinical evidence suggests that gastroesophageal reflux disease is associated with pulmonary allograft dysfunction. In this study, we used a model of rat lung transplantation to test the hypothesis that chronic aspiration of gastric contents accelerates pulmonary allograft dysfunction. METHODS: We evaluated the effects of chronic aspiration on pulmonary isografts (strain F344) and pulmonary allografts (strain WKY to strain F344). Chronic aspiration consisted of 0.5 mL/kg of filtered gastric contents injected weekly into the left lung for 4 to 8 weeks beginning 1 week after transplantation. Seven days after the last aspiration, animals were killed, and grafts were evaluated grossly and by histologic and immunochemical analyses, including Masson trichrome staining for collagen and immunostaining for CD68+ and CD8+ cells. Serum cytokine concentrations were determined by bead-based immunoassays or enzyme-linked immunosorbent assay. RESULTS: Allografts without aspiration (n = 12) demonstrated a relatively normal architecture with diffuse International Society for Heart and Lung Transplantation grade 3 acute rejection; occasional grade 4 rejection was noted. In contrast, allografts with chronic aspiration (n = 7) demonstrated severe grade 4 acute rejection with significant monocyte infiltration, fibrosis, and loss of normal alveolar anatomy. Grossly, 8 (67%) of 12 allografts without aspiration seemed to inflate and perfuse normally, whereas all allografts exposed to chronic aspiration were firm and shrunken, without the ability to ventilate (P = .013; Fisher exact test). Aspiration was associated with increases in graft-infiltrating macrophages and CD8+ T cells and higher levels of serum transforming growth factor beta. CONCLUSIONS: Chronic aspiration of gastric contents promotes accelerated allograft failure and may promote a profibrotic environment.

Animals↗

Failure of cAMP agonists to activate rescued deltaF508 CFTR in CFBE41o- airway epithelial monolayers.

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cyclic AMP-regulated chloride channel. Mutations in the CFTR gene result in cystic fibrosis (CF). The most common mutation, deltaF508, results in endoplasmic reticulum-associated degradation (ERAD) of CFTR. DeltaF508 CFTR has been described as a temperature-sensitive mutation that can be rescued following growth at 27 degrees C. In order to study the processing and function of wild-type and rescued deltaF508 CFTR at the cell surface under non-polarized and polarized conditions, we developed stable cell lines expressing deltaF508 or wild-type CFTR. CFBE41o- is a human airway epithelial cell line capable of forming high resistance, polarized monolayers when cultured on permeable supports, while HeLa cells are normally grown under non-polarizing conditions. Immunoprecipitation, cell surface biotinylation, immunofluorescence, and functional assays confirmed the presence of deltaF508 CFTR at the cell surface in both cell lines after incubating the cells for 48 h at 27 degrees C. However, stimulators of wild-type CFTR such as forskolin, beta2-adrenergic or A2B-adenosine receptor agonists failed to activate rescued deltaF508 CFTR in CFBE41o- monolayers. Rescued deltaF508 CFTR could be stimulated with genistein independent of pretreatment with cAMP signalling agonists. Interestingly, rescued deltaF508 CFTR in HeLa cells could be efficiently stimulated with either forskolin or genistein to promote Cl- transport. These results indicate that deltaF508 CFTR, when rescued in CFBE41o- human airway epithelial cells, is poorly responsive to signalling pathways known to regulate wild-type CFTR. Furthermore, the differences in rescue and activation of deltaF508 CFTR in the two cell lines suggest that cell-type specific differences in deltaF508 CFTR processing are likely to complicate efforts to identify potentiators and/or correctors of the deltaF508 defect.

Adenosine Triphosphate↗

Sensitization with xenogeneic tissues alters the heavy chain repertoire of human anti-Galalpha1-3Gal antibodies.

BACKGROUND: Antigen sensitization alters the use of genes encoding the variable and constant regions of immunoglobulin, changing avidity, and function. Alterations in variable region genes induced by carbohydrate antigens have been studied extensively in animals but are incompletely characterized in humans. We asked how sensitization with the carbohydrate Galalpha1-3Gal modifies antibody heavy chain use. METHODS: To overcome limited access to B cells, we analyzed anti-Galalpha1-3Gal antibodies from the serum of naïve and sensitized human subjects with anti-sera specific for VH families. RESULTS: We find that in preimmune subjects, heavy chains of IgM anti-Galalpha1-3Gal derived primarily from VH3 family members, whereas the heavy chains of IgG are from diverse VH families. After sensitization, heavy chains of IgM and IgG antibodies both derived from diverse VH families. CONCLUSIONS: The preimmune repertoire of IgM antibodies to Galalpha1-3Gal is thus more restricted than the antibody repertoire after sensitization, suggesting an antigen-induced shift in the repertoire.

Adult↗

Antihuman factor V antibodies after use of relatively pure bovine thrombin.

Although bovine thrombin is commonly used in the operating room, there is evidence that exposure to bovine thrombin can result in the development of autoimmune antibodies, usually against factor V, which can lead to a profound coagulopathy. It is thought that impurities in bovine thrombin preparations are responsible for the adverse reactions in patients. Here we describe a case in which exposure to a relatively pure bovine thrombin preparation resulted in the development of an antihuman factor V antibody-associated coagulopathy. This report calls into question the safety of even relatively pure bovine thrombin.

Aged↗

In pursuit of xenoreactive antibodies: where has it gotten us?

Numerous studies have aimed to overcome the barrier to xenotransplantation posed by xenoreactive antibodies and the antigens they recognize. Whether this work will eventually lead to the widespread clinical application of xenotransplantation remains unknown. However, the benefits of this research are already substantial, with research leading to dramatic new developments in fields other than xenotransplantation. Our understanding of natural immunity, particularly the nature and function of natural antibodies, has taken quantum leaps forward, with far-reaching implications. Our improved understanding of the immune response to xenografts has proven invaluable in the characterization of the human immune reaction to commonly used biological therapeutics of xenogeneic origin. Our understanding of cell surface carbohydrates and our ability to modify these carbohydrates in living animals has advanced substantially, with implications for diseases such as cancer and autoimmunity. With this in mind, it is argued that continued work in xenotransplantation is of great value, not only because of the great potential benefits of xenotransplantation, but also because of the more certain benefits that arise from setting our sights on a difficult challenge.

Animals↗

Treating the contents and not the container: dosimetric study of hair-sparing whole brain intensity modulated radiation therapy.

Hematogenous metastatases are the most common adult central nervous system malignancies. The standard treatment of these patients continues to include whole brain radiation. An unavoidable toxicity of this treatment is acute iatrogenic alopecia. This alopecia is a significant cause of patient distress. Our purpose was to quantify the sparing of the hair bearing skin that could be achieved by using a complex hair-sparing approach. To achieve this goal, we treat an anthropomorphic phantom with both conventional and inverse-planned intensity-modulated portals. The skin dose was evaluated through dose-volume histograms and thermo-luminescent dosimetry. The median calculated dose was reduced by 38%. The average measured dose at five surface points was reduced by 53%--from 95% of the prescription dose with the conventional plan, to 44%, with the IMRT plan. This sparing was achieved while maintaining adequate target coverage. Because of the low radiation tolerance of the hair follicle, this dose reduction is not expected, on its own, to eliminate radiation alopecia but bears promise in combination with other toxicity-sparing strategies.

Alopecia↗

Practical aspects of inverse-planned intensity-modulated radiation therapy for prostate cancer: a radiation treatment planner's perspective.

INTRODUCTION: From a radiation treatment planner perspective, in the treatment of prostate cancer, inverse-planned intensity-modulated radiation therapy (IMRT) differs considerably from conventional, conformal, and forward-planned IMRT. In this work we aim to discuss the rationale behind the use of inverse-planned IMRT for the treatment of prostate cancer, as well as some of the practical aspects, including the differences in planning strategies, dose fractionation and issues in plan evaluation. DISCUSSION: The primary motivation behind the use of inverse-planned IMRT for prostate cancer radiotherapy is to attempt further dose escalation while maintaining critical structure and healthy tissue sparing at an acceptable level. The sparing of normal tissues is largely dependent on the size of the planning target volume (PTV) defined, and if the PTV overlaps critical structures. Depending on how the PTV is defined it may be impossible to achieve the desired healthy tissue sparing even with IMRT. A second role for the use of IMRT in the treatment of prostate cancer may be to conform the isodose distribution to a complex PTV, such as one that includes the seminal vesicles or the pelvic lymph nodes in the treatment volume. Finally, inverse planned IMRT may be useful in the planning and delivery of simultaneous integrated boosts where different parts of the target structures receive different daily doses. This again has applications for the simultaneous treatment of pelvic lymph nodes with the prostate treatment volume, and presents interesting opportunities for hypo-fractionation. All of these options of course require careful plan evaluation with respect to isodose distributions and dose-volume constraints as well as the radiobiological consequences of using unconventional fractionation. CONCLUSION: IMRT seems to be the most effective modality for treating complex target geometries and for delivering simultaneous integrated boosts. In particular for prostate cancer, the simultaneous treatment of the prostate and pelvic lymph nodes lends itself perfectly to IMRT, allowing the prostate to receive a higher daily dose per fraction, as well as minimizing the amount of small bowel in the field, while at the same time sparing the rectum and bladder adequately. Inverse-planned IMRT is, however, a complex procedure, and to safely implement it, an extensive patient- and machine-specific quality assurance program is required.

Dose-Response Relationship, Radiation↗

The use of hypofractionated intensity-modulated irradiation in the treatment of glioblastoma multiforme: preliminary results of a prospective trial.

PURPOSE: Despite major advances in treatment modalities, the prognosis of patients with glioblastoma multiforme (GBM) remains poor. Exploring hypofractionated regimens to replace the standard 6-week radiotherapy schedule is an attractive strategy as an attempt to prevent accelerated tumor cell repopulation. There is equally interest in dose escalation to the gross tumor volume where the majority of failures occur. We report our preliminary results using hypofractionated intensity-modulated accelerated radiotherapy regimen in the treatment of patients with GBM. METHODS AND MATERIALS: Between July 1998 and December 2001, 25 patients with histologically proven diagnosis of GBM, Karnofsky performance status > or =60, and a postoperative tumor volume < or =110 cm3 were treated with a hypofractionated accelerated course of radiotherapy. The gross tumor volume (GTV) was defined as the contrast-enhancing lesion on the postoperative MRI T1-weighted images with the latter fused with computed tomography images for treatment planning. The planning target volume was defined as GTV + 1.5-cm margin. Using forward-planning intensity modulation (step-and-shoot technique), 60 Gy in 20 daily fractions of 3 Gy each were given to the GTV, whereas the planning target volume received a minimum of 40 Gy in 20 fractions of 2 Gy each at its periphery. Treatments were delivered over a 4-week period using 5 daily fractions per week. Dose was prescribed at the isocenter (ICRU point). Three beam angles were used in all of the cases. RESULTS: Treatments were well tolerated. Acute toxicity was limited to increased brain edema during radiotherapy in 2 patients who were on tapering doses of corticosteroids. This was corrected by increasing the steroid dose. At a median follow-up of 8.8 months, no late toxicity was observed. One patient experienced visual loss at 9 months after completion of treatment. MRI suggested nonspecific changes to the optic chiasm. On review of the treatment plan, the total dose to the optic chiasm was confirmed to be equal to or less than 40 Gy in 20 fractions. When Radiation Therapy Oncology Group recursive partitioning analysis was used, 10 patients were class III-IV, and 15 patients were class V-VI. To date, 21 patients have had clinical and/or radiologic evidence of disease progression, and 16 patients have died. The median survival was 9.5 months (range: 2.8-22.9 months), the 1-year survival rate was 40%, and the median progression-free survival was 5.2 months (range: 1.9-12.8 months). CONCLUSION: This hypofractionated accelerated irradiation schedule using forward planning (step-and-shoot) hypofractionated, intensity-modulated accelerated radiotherapy is feasible and seems to be a safe treatment for patients with GBM. A 2-week reduction in the treatment time may be of valuable benefit for this group of patients. However, despite this accelerated regimen, no survival advantage has been observed.

Adult↗

Pulmonary xenotransplantation: rapidly progressing into the unknown.

As one approach to circumventing the dire shortage of human lungs for transplantation, a handful of investigators have begun to probe the possibility of pulmonary xenotransplantation. The immunologic and perhaps physiologic barriers encountered by these investigators are considerable and progress in pulmonary xenotransplantation has lagged behind progress in cardiac and kidney xenotransplantation. However, during the last few years there have been substantial advances in the field of pulmonary xenotransplantation including, most noticeably, significant progress in attenuating hyperacute dysfunction. Progress has been made in understanding the barriers imposed by xenoreactive antibodies, complement, coagulation incompatibility and porcine pulmonary intravascular macrophages. Although our understanding of the barriers to pulmonary xenotransplantation is far from complete and the clinical application of pulmonary xenotransplantation is not yet in sight, current progress is fast paced. This progress provides a basis for future work and for a hope that the shortage of human lungs for transplantation will not always be a matter of life and death.

Animals↗

Immunoglobulin-mediated agglutination of and biofilm formation by Escherichia coli K-12 require the type 1 pilus fiber.

The binding of human secretory immunoglobulin A (SIgA), the primary immunoglobulin in the gut, to Escherichia coli is thought to be dependent on type 1 pili. Type 1 pili are filamentous bacterial surface attachment organelles comprised principally of a single protein, the product of the fimA gene. A minor component of the pilus fiber (the product of the fimH gene, termed the adhesin) mediates attachment to a variety of host cell molecules in a mannose inhibitable interaction that has been extensively described. We found that the aggregation of E. coli K-12 by human secretory IgA (SIgA) was dependent on the presence of the pilus fiber, even in the absence of the mannose specific adhesin or in the presence of 25 mM alpha-CH(3)Man. The presence of pilus without adhesin also facilitated SIgA-mediated biofilm formation on polystyrene, although biofilm formation was stronger in the presence of the adhesin. IgM also mediated aggregation and biofilm formation in a manner dependent on pili with or without adhesin. These findings indicate that the pilus fiber, even in the absence of the adhesin, may play a role in biologically important processes. Under conditions in which E. coli was agglutinated by SIgA, the binding of SIgA to E. coli was not increased by the presence of the pili, with or without adhesin. This observation suggests that the pili, with or without adhesin, affect factors such as cell surface rigidity or electrostatic repulsion, which can affect agglutination but which do not necessarily determine the level of bound immunoglobulin.

Adhesins, Bacterial↗

Prevention of acute lung injury in swine: depletion of pulmonary intravascular macrophages using liposomal clodronate.

BACKGROUND: Swine contain large numbers of pulmonary intravascular macrophages (PIMs) that mediate the physiological response observed in acute lung injury (ALI). As the hyperacute dysfunction observed in pulmonary xenotransplantation is similar to endotoxin-induced ALI, PIMs may play a critical role in pulmonary xenograft dysfunction. We used liposomal clodronate to eliminate the PIM population in a model of acute swine lung injury. MATERIALS AND METHODS: Experimental swine (n = 6) received liposomal clodronate (1.25 g/10 kg) and control swine (n = 5) received saline containing liposomes before infusion of lipopolysaccharide (450 ng/kg). RESULTS: Control swine demonstrated higher peak pulmonary artery pressures (41.8 +/- 2.2 versus 16.8 +/- 1.2 mm Hg; P < 0.0001) and higher peak pulmonary vascular resistances (1405 +/- 209 versus 353 +/- 81 dynes. s. cm(-5); P = 0.0016) in response to lipopolysaccharide infusion. Clodronate treated swine also had significantly lower serum levels of tumor necrosis factor-alpha, interleukin-6, and thrombin. CONCLUSIONS: Liposomal clodronate effectively attenuates acute swine lung injury induced by endotoxin. This method of depletion of the PIM population presents a promising new treatment of swine lungs before xenotransplantation.

Acute Disease↗