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Biomedical subjects

J W Allen

Publications and source records attributed to J W Allen.

At least 19 recordsLinked to original sources
PubMed2006

Orbitally driven spin-singlet dimerization in S=1 La4Ru2O10.

Using x-ray absorption spectroscopy at the Ru-L2,3 edge we reveal that the Ru4+ ions remain in the S=1 spin state across the rare 4d-orbital ordering transition and spin-gap formation. We find using local spin density approximation + Hubbard U band structure calculations that the crystal fields in the low-temperature phase are not strong enough to stabilize the S=0 state. Instead, we identify a distinct orbital ordering with a significant anisotropy of the antiferromagnetic exchange couplings. We conclude that La4Ru2O10 appears to be a novel material in which the orbital physics drives the formation of spin-singlet dimers in a quasi-two-dimensional S=1 system.

Journal Article↗
PubMed2006

New Luttinger-liquid physics from photoemission on Li0.9M06O17.

Temperature dependent high resolution photoemission spectra of quasi-one-dimensional Li(0.9)Mo(6)O(17)evince a strong renormalization of its Luttinger-liquid density-of-states anomalous exponent. We trace this new effect to interacting charge neutral critical modes that emerge naturally from the two-band nature of the material. Li(0.9)Mo(6)O(17) is shown thereby to be a paradigm material that is capable of revealing new Luttinger physics.

Journal Article↗
PubMed2006

Ambulatory photodynamic therapy: a new concept in delivering photodynamic therapy.

BACKGROUND: Photodynamic therapy (PDT) has been shown to be effective in treating Bowen's disease, superficial basal cell carcinoma and actinic keratosis. OBJECTIVES: To investigate the feasibility of delivering PDT using a portable light-emitting diode device. METHODS: A prototype diode array, comprising 37 AlGaInP diodes cast in epoxy with a diffuser, and driven by a battery pack, was designed and constructed. A pilot study was carried out in five patients with histologically proven Bowen's disease who were referred for PDT with 5-aminolaevulinic acid. They were all treated in the hospital-based dermatology PDT suite such that each received the same level of supervision as patients receiving PDT with nonambulatory light sources. Patients recorded pain levels. In accordance with our usual practice, patients received two treatments at a 4-week interval. RESULTS: Four of five patients were clear at follow-up (range 6-13 months, median 9). Pain was classified as none or mild in 80% of treatments and moderate in the remainder. CONCLUSIONS: There are many potential benefits of ambulatory PDT, including the possibility of a much higher patient throughput, and allowing effective treatment at home. This pilot study provides early promising data of the safety and efficacy of this approach.

Ambulatory Care↗
PubMed2004

Filling of the mott-hubbard gap in the high temperature photoemission spectrum of (V0.972Cr0.028)2O3.

Photoemission spectra of the paramagnetic insulating phase of (V0.972Cr0.028)2O3, taken in ultrahigh vacuum up to the unusually high temperature (T) of 800 K, reveal a property unique to the Mott-Hubbard (MH) insulator that has not been observed previously. With increasing T the MH gap is filled by spectral weight transfer, in qualitative agreement with high-T theoretical calculations combining dynamical mean field theory and band theory in the local density approximation.

Journal Article↗
PubMed2004

Favorable early results of gastric banding for morbid obesity: the American experience.

BACKGROUND: In 2001 a new device for surgical weight loss was approved by the Food and Drug Administration (Lap-Band, Inamed Health). We describe initial results of laparoscopic gastric banding for morbid obesity in two American academic centers. METHODS: Prospective data was collected on consecutive morbidly obese patients undergoing laparoscopic adjustable gastric banding, and evaluated retrospectively. RESULTS: Four hundred forty-five consecutive patients underwent Lap-Band from May 2001 through December 2002. The 103 men and 341 women had an average age of 42.1 years (range 17-72 years) and an average body mass index (BMI) of 49.6 kg/m2 (range 35.2-92.2 kg/m2). One operation required conversion to laparotomy due to bleeding; the rest were completed laparoscopically. Mean length of stay was 1.1 days (range 1-10 days). There was one death. Additional complications included band slippage in 14 patients (3.1%), gastric obstruction without slip in 12 (2.7%), port migration in 2 (0.4%), tubing disconnections in 3 (0.7%), and port infection in 5 (1.1%). Two bands (0.4%) were removed due to intraabdominal abscess 2 months after placement. There was one band erosion (0.2%) and no clinically significant esophageal dilation. Ninety-nine patients have 1-year follow-up and have lost an average of 44.3% excess body weight. CONCLUSION: Laparoscopic gastric banding has much to offer the morbidly obese. We present data showing weight loss rivaling gastric bypass and acceptably low complications. These results parallel success with this device outside America.

Adolescent↗
PubMed2003

Prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3.

We present the first observation of a prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3 and report new spectral calculations that combine the local-density approximation with the dynamical mean-field theory (using quantum Monte Carlo simulations) to show the development of such a distinct peak with decreasing temperature. The experimental peak width and weight are significantly larger than in the theory.

Journal Article↗
PubMed2003

Laparoscopic management of Meckel's diverticulum in adults.

BACKGROUND: Meckel's diverticulum is an uncommon entity. A high index of suspicion is necessary for opportune diagnosis and prompt treatment. Technetium (TC) 99m pertechnetate scintigraphy is a sensitive and specific test for Meckel's diverticulum. In adults, the scan contributes little to clinical decision making and often will not change the need for surgical intervention. We describe our experience with four patients. METHODS: Between August 2000 and August 2001, four patients were seen with Meckel's diverticula. Three were male and one was female. The mean age was 39 years (range, 18-64). Three patients presented with anemia and one with an acute abdomen. A 99mTc pertechnetate scan was performed at a cost of 900 dollars in the three anemic patients after other endoscopic and radiographic tests were nondiagnostic. Only one patient had a positive scan. All four patients underwent exploratory laparoscopy and small bowel resection. In one patient, a minilaparatomy had to be performed. RESULTS: All patients had a satisfactory outcome without complications. Three patients were discharged within 3 days of surgery. The remaining patient had a prolonged hospital stay because of ongoing chemotherapy for small cell lung cancer. In the three anemic patients who underwent enterectomy, ulcerated small bowel outside the diverticulum was found by the pathologist. CONCLUSION: Laparoscopy is safe, cost-effective, and efficient for the diagnosis and definitive management of Meckel's diverticulum. Technetium 99m pertechnetate scintigraphy scanning adds considerable time and expense to the care of the patient without significant benefits in adults. The practice of exploratory laparoscopy rather than scintigraphy is recommended.

Adult↗
PubMed2002

Totally laparoscopic management of gallstone ileus.

Gallstone ileus is an uncommon disease of elderly patients who present with bowel obstruction. Mortality and severe complications are common, even in modern series, due to the comorbidities in the affected patient population. A number of less invasive ways to treat this disease are described. We report on a case where enterolithotomy was performed laparoscopically. The patient is a 60-year-old diabetic woman who presented with a bowel obstruction and pneumobilia on abdominal radiographs. She underwent exploratory laparoscopy using three reusable ports, an enterolithotomy, and her remaining bowel was examined. The benefits to a minimal access approach to this rare disorder are discussed. The ability to suture laparoscopically is emphasized.

Cholelithiasis↗
PubMed2002

Laparoscopic choledochojejunostomy and gastrojejunostomy in a porcine model.

BACKGROUND: Surgical extirpation remains the only known curative treatment for cancer of the pancreas. Because of locally advanced or metastatic tumor, up to 80% of patients are unresectable at the time of initial diagnosis [13]. Other investigators previously have suggested that laparoscopy before laparotomy aids in the diagnosis of unresectable pancreatic cancer in a fair number of patients even after negative computed tomography scans [3, 17]. Many surgeons are reluctant to incorporate laparoscopy into the workup of patients with cancer of the pancreas because of the frequent need for surgical bypass in the management of either biliary tract obstruction or gastric outlet obstruction [9, 13]. Previous studies have demonstrated the feasibility of laparoscopic cholecystojejunostomy combined with gastrojejunostomy in a porcine model, as well as the individual accomplishment of laparoscopic choledochojejunostomy. The purpose of this study was to document the feasibility of performing laparoscopic choledochojejunostomy with gastrojejunostomy. METHODS: Under general anesthesia, seven pigs underwent laparoscopic choledochojejunostomy and gastrojejunostomy using an intracorporeal hand-sutured technique. RESULTS: The mean operating time ranged from 150 to 450 min. All the animals recovered completely from the operation and had patent anastomoses at the time of necropsy. One pig died of gastric bleeding on postoperative day 13, and two animals had intraabdominal fluid collections discovered at the time of necropsy. CONCLUSIONS: These results suggest that synchronous laparoscopic bypass of biliary and gastric outlet obstruction is feasible, and can be performed in a manner similar to that used in open operations. We believe this lends support to the argument promoting laparoscopy in the evaluation of pancreatic cancer.

Animals↗
PubMed2002

Bulk band gaps in divalent hexaborides.

Complementary angle-resolved photoemission and bulk-sensitive k-resolved resonant inelastic x-ray scattering of divalent hexaborides reveal a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. This semiconducting gap implies that carriers detected in transport measurements arise from defects, and the measured location of the bulk Fermi level at the bottom of the conduction band implicates boron vacancies as the origin of the excess electrons. The measured band structure and X-point gap in CaB6 additionally provide a stringent test case for many-body quasiparticle band calculations.

Journal Article↗
PubMed2002

Totally laparoscopic feeding jejunostomy.

BACKGROUND: A feeding jejunostomy should be used for nutritional support in a small subset of patients. Minimal-access approaches for the placement of jejunal tubes have been described, but they often require special equipment not common to all operating theaters. We describe a technique of totally laparoscopic jejunostomy tube (LJT) placement using equipment found in most operating theaters. METHODS: Thirty-five patients underwent LJT over a 12-month period. Indications included gastroparesis, anorexia nervosa, oral cancer, cerebral palsy, and Huntington's chorea. The technique involved three incisions for trocars (one for a 10-mm camera and two for 5-mm working ports) and one small incision for the tube. A 16-Fr T-tube was passed transabdominally under direct vision, and a jejunotomy was made approximately 20 cm distal to the ligament of Trietz. Each limb of the T-tube was passed into the lumen of the bowel, and a purse-string suture was placed around the enterotomy and tied intracorporeally. After insertion, the serosa surrounding the insertion site is tacked to the anterior abdominal wall in four places with a reusable stainless steel suture passer. To test whether the tube was watertight, we injected methylene blue solution into the tube. RESULTS: All of the patients tolerated the procedure well. There were no operative deaths. Five LJTs were electively removed in the office. One patient was reoperated on 10 days postoperatively because of intractable pain, but the source of pain was not found and the LJT was intact. CONCLUSIONS: LJT may be placed safely using the described technique. No significant morbidity or mortality occurred in our series. The results of this study have prompted us to consider LJT for any patient requiring access to the jejunum for feeding.

Anorexia Nervosa↗
PubMed2002

Effects of heat shock protein 70 (Hsp70) on arsenite-induced genotoxicity.

Arsenic, a human carcinogen, is genotoxic, although its mechanism(s) of action for tumorigenesis is not well understood. Among the toxicity-related properties of this chemical are its clastogenic and aneugenic activities, as well as its capacity for inducing stress-response in the form of elevated heat shock protein (HSP) expression. In the present study, we evaluated the effects of Hsp70 expression on arsenite (As)-induced structural and numerical chromosome anomalies in human cells. Human MCF-7 Tet-off cells stably transfected with a pTRE/Hsp70-1 transgene construct were used to regulate Hsp70 levels prior to in vitro As exposures. Separate cultures of relatively high vs. low Hsp70-expressing cells were established. A cytokinesis block micronucleus assay with kinetochore immunostaining was used to detect micronuclei (MN) derived from chromosome breakage (K-MN) or loss (K+MN). These studies demonstrated significant increases in micronucleus frequencies in response to As following either a long exposure (5 or 10 microM for 46 hr), or short exposure (10 or 40 microM for 8 hr) protocol. Overall, the long protocol was more efficient in producing K+MN and cells with multiple MN. Overexpressing Hsp70 resulted in significant reductions in the percent of cells positive for MN for both the long and short As exposure protocols. Both K+ and K- types of As-induced MN were lower in cells with elevated Hsp70 as compared to cells without overexpression of Hsp70. We conclude that the dose and duration of As exposure influence the type as well as amount of chromosomal alteration produced and that inducible Hsp70 protects against both the clastogenic and aneugenic effects of this chemical.

Arsenites↗
PubMed2001

The poor quality of information about laparoscopy on the World Wide Web as indexed by popular search engines.

BACKGROUND: This study was undertaken to determine the quality of information on the Internet regarding laparoscopy. METHODS: Four popular World Wide Web search engines were used with the key word "laparoscopy." Advertisements, patient- or physician-directed information, and controversial material were noted. RESULTS: A total of 14,030 Web pages were found, but only 104 were unique Web sites. The majority of the sites were duplicate pages, subpages within a main Web page, or dead links. Twenty-eight of the 104 pages had a medical product for sale, 26 were patient-directed, 23 were written by a physician or group of physicians, and six represented corporations. The remaining 21 were "miscellaneous." The 46 pages containing educational material were critically reviewed. At least one of the senior authors found that 32 of the pages contained controversial or misleading statements. All of the three senior authors (LKN, NAO, GAF) independently agreed that 17 of the 46 pages contained controversial information. CONCLUSION: The World Wide Web is not a reliable source for patient or physician information about laparoscopy. Authenticating medical information on the World Wide Web is a difficult task, and no government or surgical society has taken the lead in regulating what is presented as fact on the World Wide Web.

Abstracting and Indexing↗
PubMed2001

Methylmercury inhibits cysteine uptake in cultured primary astrocytes, but not in neurons.

The maintenance of adequate intracellular glutathione (GSH) concentrations is dependent on the availability and transport of the rate-limiting substrate, cysteine. A suggested mechanism of methylmercury (MeHg) neurotoxicity in brain involves the formation of oxygen radicals, and a decrease in intracellular levels of GSH. Recently, we have characterized various cysteine transport systems (both Na(+)-dependent and -independent) in cerebrocortical astrocytes and hippocampal neurons. The present study was carried out to investigate the effect of MeHg on cysteine uptake in both astrocytes and neurons, and to determine whether cysteine transport is differentially affected in the two cell types by MeHg treatment. Sixty-minute pretreatment with MeHg caused significant concentration-dependent inhibition in cysteine uptake in astrocytes, but not in neurons. As most of the cysteine transport is Na(+)-dependent (80-90% of total), additional studies focused on MeHg's effect on the Na(+)-dependent cysteine transporters X(AG(-)) and ASC. An additive inhibitory effect on cysteine uptake was observed in astrocytes treated with MeHg (5 microM) plus sub-maximal inhibitory concentrations (0.1 and 0.5 mM) of threo-beta-hydroxy-aspartate (THA), a specific inhibitor of the Na(+)-dependent transporter, X(AG(-)), compared to astrocytes treated with MeHg (P<0.001) or THA alone (P<0.05). There was no additive effect of MeHg and maximal inhibitory concentrations of THA (1.0 and 5.0 mM) on astrocytic cysteine uptake inhibition. Additional studies examined the sensitivity of the Na(+)-dependent ASC transport system to MeHg treatment. Maximal inhibitory concentration of L-serine (10 mM) alone had a rather modest inhibitory effect on cysteine uptake, and when applied in the presence of MeHg there was no additive effect. These results suggest that the inhibition of cysteine uptake by MeHg in astrocytes occurs through specific inhibition of both the X(AG(-)) as well as the ASC transport system.

Animals↗
PubMed2001

Methylmercury has a selective effect on mitochondria in cultured astrocytes in the presence of [U-(13)C]glutamate.

The effect of methylmercury on glutamate metabolism was studied by (13)C magnetic resonance spectroscopy. Cerebral cortical astrocytes were pretreated with methylmercury, either 1 microM for 24 h, or 10 microM for 30 min, and subsequently with 0.5 mM [U-(13)C]glutamate for 2 h. Labeled glutamate, glutamine, aspartate and glutathione were present in cell extracts, and glutamine, aspartate and lactate in the medium of all groups. HPLC analysis of these amino acids showed no changes in concentrations between groups. Surprisingly, the amounts of [U-(13)C]glutamate and unlabeled glucose taken up by the astrocytes were unchanged. Furthermore, the amounts of most metabolites synthesized from [U-(13)C]glutamate were also unchanged in all groups. However, formation of [U-(13)C]lactate was decreased in the 10 microM methylmercury group. This was not observed for labeled aspartate. It is noteworthy that both [U-(13)C]lactate and [U-(13)C]aspartate can only be derived from [U-(13)C]glutamate via mitochondrial metabolism. [U-(13)C]glutamate enters the tricarboxylic acid cycle (located in mitochondria) after conversion to 2-[U-13C]oxoglutarate and [U-(13)C]aspartate is formed from [U-(13)C]oxaloacetate, as is [U-(13)C]lactate. [U-(13)C]lactate can also be formed from [U-(13)C]malate. This differential effect on labeled aspartate and lactate indicates cellular compartmentation and thus selective vulnerability of mitochondria within the astrocytes to the effects of methylmercury. The decreased lactate production from glutamate might be detrimental to surrounding cells since lactate has been shown to be an important substrate for neurons.

Animals↗
PubMed2001

Multiple caspases are involved in beta-amyloid-induced neuronal apoptosis.

beta-amyloid peptide (Abeta) has been implicated in the pathogenesis of Alzheimer disease and has been reported to induce apoptotic death in cell culture. Cysteine proteases, a family of enzymes known as caspases, mediate cell death in many models of apoptosis. Multiple caspases have been implicated in Abeta toxicity; these reports are conflicting. We show that treatment of cerebellar granule cells (CGC) with Abeta25-35 causes apoptosis associated with increased activity of caspases-2, -3 and -6. Selective inhibition of each of these three caspases provides significant protection against Abeta-mediated apoptosis. In contrast, no change in caspase-1 activity was seen after Abeta25-35 application, nor was inhibition of caspase-1 neuroprotective. Similar to CGC, cortical neuronal cultures treated with Abeta25-35 demonstrate increased caspase-3 activity but not caspase-1 activity. Furthermore, significant neuroprotection is elicited by selective inhibition of caspase-3 in cortical neurons administered Abeta25-35, whereas selective caspase-1 inhibition has no effect. Taken together, these findings indicate that multiple executioner caspases may be involved in neuronal apoptosis induced by Abeta.

Amino Acid Chloromethyl Ketones↗
PubMed2001

The uptake of cysteine in cultured primary astrocytes and neurons.

One of the vitally important functions of glutathione (GSH) is to adequately protect cells against toxic chemicals, reactive oxygen metabolites and free radical species. The amino acid, cysteine, is the key rate-limiting substrate for the biosynthesis of GSH, and the maintenance of adequate intracellular GSH levels is dependent upon the extracellular availability and transport of cysteine into cells. In the present study, primary cultures of astrocytes and neurons were employed to characterize cysteine transport systems. Both astrocytes and neurons used Na(+)-dependent systems as the major route for cysteine uptake (80-90% of total), while Na(+)-independent uptake represented a minor component of total transport (10-20% of total). Among the Na(+)-dependent systems, X(AG(-)) was the major contributor (approx. 80-90%) for cysteine uptake in both neurons and astrocytes, with a minor contribution from the ASC transport system (Na(+)-dependent neutral amino acid transport system for alanine, serine, and cysteine). In the Na(+)-independent transport systems (10-20% of total cysteine transport), multifunctional ectoenzyme/amino acid transporter gamma-glutamyltranspeptidase (GGT), and the neutral amino acid L-system contributed approximately equally towards cysteine uptake, in both neurons and astrocytes. The present studies demonstrate that astrocytes and neurons accumulate cysteine by both Na(+)-dependent and Na(+)-independent uptake systems, with major uptake occurring through the X(AG(-)) system and minor uptake via the ASC, GGT and L-systems.

Amino Acid Transport System X-AG↗