Biomedical subjects

J A Williams

Publications and source records attributed to J A Williams.

At least 73 records · Page 4Linked to original sources

PubMed1999

Comparison of ion release from a glass ionomer cement as a function of the method of incorporation of added ions.

The addition of potassium and fluoride ions to a water-admixed glass ionomer cement initially free from either ion was accomplished either by addition via the mixing water or by immersing mixed set cement in a solution of the ions in water. In both cases the aqueous concentration of ions was the same. The release of both potassium and fluoride was measured for 500 days. Ion release from immersed specimens was some 20-fold higher than from the other method indicating enhanced concentration of ions inside the cement. This calculation assumes that the ions resided in the aqueous phase. Ions added by mixing appeared to follow the release pattern shown by glass ionomers containing intrinsic fluoride; ions added by immersion did not. As specimens matured the amount which could be taken up by immersion was reduced. Potassium release was still continuing at 500 days whereas fluoride release was complete.

Aluminum Oxide↗

PubMed1999

The influence of sample dimensions on fluoride ion release from a glass ionomer restorative cement.

The fluoride release from a commercial, restorative glass ionomer cement was found to be strongly dependent on sample surface area rather than volume. This was noted for disc, cylindrical- and bar-shaped specimens over periods ranging from 1 day to 3 yr. Release from all shapes of specimen followed the established pattern of an initial non-linear region followed by one where release was proportional to the square root of time. If fluoride levels in the cement matrix of specimens were artificially increased by incorporation during the mixing then the release pattern during the first few months was altered. The initial release increased for some specimen sizes and decreased for others. The dependency on surface area was greatly reduced for several months. By the time a year had elapsed the correlation between fluoride ion release and surface area had been re-established. The influence of additional fluoride during setting can therefore act to perturb the normal release pattern and may in some instances reduce the initial fluoride release. Release should be quoted in terms of, or with measurements of, the surface area of specimens under investigation.

Drug Stability↗

PubMed1999

Adenovirus-mediated wild-type p53 expression induces apoptosis and suppresses tumorigenesis of experimental intracranial human malignant glioma.

Adenoviral-mediated gene transfer for the treatment of experimental intrinsic malignant brain neoplasms holds promise. The role, however, of intracellular, adenoviral-mediated p53 expression to inhibit growth of experimental human intracranial malignant gliomas remains largely unexplored. Using the AdCMV.p53 vector we measured the in vitro expression of p53 and the resultant effect upon U251 human malignant glioma cellular proliferation. We further measured the survival of nude mice after intracranial injection of the infected vs. control U251 cells. The growth of the infected U251 cells was inhibited when compared to both the uninfected cells and cells infected with the control vector (AdCMV.Null). Agarose gel electrophoresis confirmed the AdCMV.p53-dependent cellular apoptosis. Nude mice having intracranial injections of the U251 cells infected with the control (AdCMV.Null) vector showed diminished survival. In contrast, mice having intracranial injections of the cells infected with the AdCMV.p53 vector showed 100% survivorship measured 100 days after treatment. Gene therapy via the AdCMV.p53 viral vector holds promise for the clinical treatment of human malignant gliomas.

Adenoviridae↗

PubMed1999

Good outcome from surgery for ampullary tumour.

BACKGROUND: Ampulla of Vater tumours are rare but usually resectable. There is debate as to the better surgical approach between the standard radical procedure, which provides adequate resection margins, and local resection, which may carry a lower mortality. This study reports the 16-year experience of a specialist unit with these tumours, and compares our results with that of recently published series. METHOD: A retrospective review of patients admitted with an ampullary tumour to the Hepatobiliary and Pancreatic Surgery Unit, Royal Adelaide Hospital, Adelaide, Australia, between January 1981 and April 1997. RESULTS: Twenty-five patients (13 men, 12 women) of median age 65 years were admitted with an ampullary tumour to the unit during this period. The most common presentation was obstructive jaundice. Multiple endoscopic biopsy was found to be very reliable in distinguishing between benign and malignant tumours. Five patients, all male, had benign neoplasms: three adenomas, one carcinoid and one gangliocytic paraganglioma. Transduodenal local excision was performed in four patients. One patient had a Whipple procedure resulting in the only in-hospital death at 3 months. Twenty patients had adenocarcinoma, of which 13 patients had a pancreaticoduodenectomy, two local excisions, two palliative bypasses, two were unfit for surgery and one declined surgery. The resectability rate was 88%, with no operative mortalities. The 5-year actuarial survival of patients who underwent radical resection was 49%. CONCLUSIONS: Proximal pancreaticoduodenectomy, preferably a pylorus-preserving procedure, is safe and effective in the treatment of ampullary carcinoma, with low operative mortality and good long-term survival. Local resection is only recommended for small benign tumours and for patients who may be unfit for radical surgery.

Adult↗

PubMed1999

Synthetic, implantable, biodegradable polymers for controlled release of radiosensitizers.

INTRODUCTION: Synthetic, implantable, biodegradable polymers offer the sustained local release of disparate therapeutic agents for the treatment of human malignant brain tumors. The role of polymeric devices for the local delivery of radiosensitizers remains unexplored, however. We therefore quantified the release of the representative radiosensitizers IUdR (5-iodo-2'-deoxyuridine), tirapazamine (3-amino-1,2,4-benzotriazine-1,4-dioxide) and etanidazole [N-(2-hydroxyethyl)-2-nitro-1-imidazole-1-acetamide] from the [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) (PCPP:SA ratio 20:80)] polymer. METHODS: For measurements of controlled release, triplicate polymer discs were incubated for known intervals in 2 ml 0.1 phosphate-buffered saline, pH 7.4, 37 degrees C. Using a predefined schedule, the supernatant fractions were systematically removed and replaced with fresh solution. The supernatant fractions were measured. The cumulative percentage of the loaded drug that appeared in these serial supernatant fractions was plotted vs. time. The percentage of the drug that was loaded into each polymer and that was released vs. time was fit to the power function of the form y = (a) x tb, where y is the cumulative released agent, a and b are constants and t is time (days). RESULTS: The IUdR was released over an interval of approximately one week, while the release of the tirapazimine persisted for over 100 days. The etanidazole was released most rapidly, over a period of hours. Modeling of release showed that regardless of percentage loading of the drug, the monoexponential function showed high correlation of the fit of the plot of the release vs. time. CONCLUSIONS: These results suggest that the hydrophilicity and percentage loading of the drug predominantly determine the rate of release. Based upon these results, IUdR and tirapazamine warrant preclinical testing for radiosensitization of human malignant brain tumors via the synthetic, implantable, biodegradable polymeric devices.

Biocompatible Materials↗

PubMed1999

Synthetic, implantable polymers for IUdR radiosensitization of experimental human malignant glioma.

BACKGROUND: Recently, polymeric controlled delivery of chemotherapy has been shown to improve survival of patients with malignant glioma. We tested the delivery of IUdR via polymers for radiosensitization of experimental intracranial human malignant glioma. To assess efficacy, we measured the in vitro release, the in vivo delivery of IUdR and the resultant radiosensitization of experimental human U251 glioblastoma xenografts. METHODS: In vitro: To measure release, increasing (10%, 30%, 50%) proportions of IUdR in synthetic [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) polymer discs were serially incubated in buffered saline and the supernatant fractions were assayed. In vivo: To compare local vs. systemic delivery, mice bearing flank xenografts had intratumoral or contralateral flank IUdR polymer (50% loading) treatments. Mice bearing intracranial (i.c.) xenografts had i.c. vs. flank IUdR polymer treatments. Four or 8 days after implantation of polymers, mice were sacrificed and the percentage tumor cells that were labeled with IUdR was measured using quantitative microscopic immunohistochemistry. For comparisons of radiosensitization, mice bearing i.c. xenografts had i.c. vs. flank IUdR polymers and cranial fractionated external beam irradiation (2 Gy BID x 4 days). RESULTS: In vitro: Increasing percentage loadings of IUdR resulted in higher percentages of release: 43.7 +/- 0.1, 70.0 +/- 0.2, and 90.2 +/- 0.2 (p < 0.001 ANOVA) for the 10, 30, and 50% loadings, respectively. In vivo: For the flank tumors, both the ipsilateral and contralateral IUdR polymers resulted in similarly high percentages labeling of the tumors vs. time. For the ipsilateral IUdR polymers, the percentages of tumor cellular labeling after 4 vs. 8 days were 45.8 +/- 7.0 vs. 40.6 +/- 3.9 (p = NS. For the contralateral polymer implants, the percentages tumor cellular labeling were 43.9 +/- 10.1 vs. 35.9 +/- 5.2 (p = NS) measured 4 vs. 8 days after implantation. For the i.c. tumors treated with extracranial IUdR polymers, the percentages of tumor cellular labeling were low: 13.9 +/- 8.8 and 11.2 +/- 5.7 measured 4 and 8 days after implantation. For the i.c. tumors having the i.c. IUdR polymers, however, the percentages labeling were comparatively much higher: 34.3 +/- 4.9 and 35.3 +/- 4.0 on days 4 and 8, respectively. For the i.c. tumors, examination of the percentage cellular labeling vs. distance from the implanted IUdR polymer showed labeling was highest closest to the polymer disc. Radiosensitization: For mice bearing i.c. tumors and receiving flank vs. intracranial IUdR polymer treatments, the survival after external beam irradiation was significantly higher for the intracranial treatments: 49 + 8.9 vs. 80 + 4.1 (p = 0.03) days, respectively. CONCLUSIONS: Implantable biodegradable polymers provide the local, controlled release of IUdR and result in the high, local delivery of IUdR to experimental intracranial human malignant glioma. The local delivery and labeling result in improved survival following radiotherapy. This technique holds promise for the local delivery of IUdR for radiosensitization of human brain tumors.

Animals↗

PubMed1999

Intracellular regulatory mechanisms in pancreatic acinar cellular function.

The intracellular mechanisms regulating pancreatic acinar cell function are more complex than previously realized. This is probably due in part to the need to match the biosynthetic and secretory functions of the cells. Much information is available on how secretagogue receptors acutely couple through heterotrimeric G proteins to increase intracellular messengers, particularly cytoplasmic free Ca(2+), although details are still being worked out. Less is known about how Ca(2+) signals to induce fusion of zymogen granules with the apical plasma membrane. Investigation has focused on the proteins of the zymogen granule membrane, and several novel proteins have recently been identified. In addition, understanding of the three MAP kinase cascades, the mTOR-p70S6 kinase pathway, and the focal adhesion kinase pathway in acinar cells is increasing. The functions of these pathways in acini have been linked to mitogenesis, protein synthesis, and regulation of the cytoskeleton.

Journal Article↗

PubMed1999

HSP27 expression regulates CCK-induced changes of the actin cytoskeleton in CHO-CCK-A cells.

We investigated how heat shock protein 27 (HSP27) and its phosphorylation are involved in the action of cholecystokinin (CCK) on the actin cytoskeleton by genetic manipulation of Chinese hamster ovary (CHO) cells stably transfected with the CCK-A receptor. In these cells, as in rat acini, CCK activated p38 mitogen-activated protein (MAP) kinase and increased the phosphorylation of HSP27. This effect could be blocked with the p38 MAP kinase inhibitor SB-203580. Examination by confocal microscopy of cells stained with rhodamine phalloidin showed that CCK dose-dependently induced changes of the actin cytoskeleton, including cell shape changes, which were coincident with actin cytoskeleton fragmentation and formation of actin filament patches in the cells. To further evaluate the role of HSP27, CHO-CCK-A cells were transfected with expression vectors for either wild-type (wt) or mutant (3A, 3G, and 3D) human HSP27. Overexpression of wt-HSP27 and 3D-HSP27 inhibited the effects on the actin cytoskeleton seen after high-dose CCK stimulation. In contrast, overexpression of nonphosphorylatable mutants, 3A- and 3G-HSP27, or inhibition of phosphorylation of HSP27 by preincubation of wt-HSP27 transfected cells with SB-203580 did not protect the actin cytoskeleton. These results suggest that phosphorylation of HSP27 is required to stabilize the actin cytoskeleton and to protect the cells from the effects of high concentrations of CCK.

Actin Cytoskeleton↗

PubMed1999

Immunolocalization of CRHSP28 in exocrine digestive glands and gastrointestinal tissues of the rat.

The 28-kDa (on SDS-PAGE) Ca2+-regulated heat stable protein (CRHSP28) was recently purified as novel phosphoprotein in exocrine pancreas, since it undergoes an immediate increase in serine phosphorylation when acini are stimulated with Ca2+-mobilizing agonists. Examination of CRHSP28 protein expression in rat revealed that most was highly expressed in pancreas and other morphologically related exocrine tissues, including the parotid, lacrimal, and submandibular glands. Immunofluorescence staining in pancreas indicated that CRHSP28 was specifically concentrated in zymogen granule-rich areas in the apical cytoplasm of acinar cells. Lack of colocalization with pancreatic lipase in dual immunofluorescence studies confirmed localization of CRHSP28 to the area immediately surrounding the granules. Western analysis of pancreatic zymogen granule membrane proteins indicated CRHSP28 was not associated with the granules following their purification. A similar pattern of apical cytoplasmic secretory granule staining was noted in lacrimal and submandibular glands. CRHSP28 protein was also expressed at relatively high levels in mucosal epithelial cells of the stomach and small intestine. CRHSP28 was found in the supranuclear apical cytoplasm of cells lining the small intestinal crypts, including Paneth cells, and was abundant in the cytoplasm of goblet cells. In the stomach, strong CRHSP28 staining was seen in mucus-secreting cells in the upper portion of the gastric glands and in the apical, granule-rich cytoplasm of chief cells located in the lower portions of the glands. Dual labeling with anti-H+-K+-ATPase demonstrated a comparatively lower expression of CRHSP28 in parietal cells. Collectively, the high relative expression of CRHSP28 in various secretory cell types within the digestive system, together with its intracellular localization surrounding the acinar cell secretory granules, strongly supports a role for CRHSP28 in Ca2+-mediated exocrine secretion.

Animals↗

PubMed1999

Calcium signaling in rat pancreatic acinar cells: a role for Galphaq, Galpha11, and Galpha14.

Stimulus-secretion coupling in the pancreatic acinar cell is initiated by the secretagogues CCK and ACh and results in the secretion by exocytosis of the contents of zymogen granules. A key event in this pathway is the G protein-activated production of second messengers and the subsequent elevation of cytosolic-free Ca2+. The aim of this study was therefore to define the heterotrimeric G protein alpha-subunits present and participating in this pathway in rat pancreatic acinar cells. RT-PCR products were amplified from pancreatic acinar cell mRNA with primers specific for Galphaq, Galpha11, and Galpha14 but were not amplified with primers specific for Galpha15. The sequences of these PCR products confirmed them to be portions of the rat homologues of Galphaq, Galpha11, and Galpha14. The pancreatic-derived cell line AR42J similarly expressed Galphaq, Galpha11, and Galpha14; however, the Chinese hamster ovary (CHO) cell line only expressed Galpha11 and Galphaq. These data indicate that caution should be exercised when comparing signal transduction pathways between different cell types. The expression of these proteins in acinar cells was confirmed by immunoblotting samples of acinar membrane protein using specific antisera to the individual G protein alpha-subunits. The role of these proteins in Ca2+ signaling events was investigated by microinjecting a neutralizing antibody directed against a homologous sequence in Galphaq, Galpha11, and Galpha14 into acinar cells and CHO cells. Ca2+ signaling was inhibited in acinar cells and receptor-bearing CHO cells in response to both physiological and supermaximal concentrations of agonists. The inhibition was >75% in both cell types. These data indicate a role for Galphaq and/or Galpha11 in intracellular Ca2+ concentration signaling in CHO cells, and in addition to Galphaq and Galpha11, Galpha14 may also fulfill this role in rat pancreatic acinar cells.

Animals↗

PubMed1999

Fractionated stereotactic radiosurgery for treatment of acoustic neuromas.

BACKGROUND: Microsurgery and single-fraction radiosurgery for acoustic neuromas are associated with high rates of control, but can result in facial palsy and trigeminal neuropathy. To reduce the morbidity of treatment for acoustic neuromas while maintaining efficacy, we explored fractionated stereotactic radiosurgery (FSR). METHODS: We reviewed data for 31 acoustic neuromas in 30 patients treated with 25 Gy (linear accelerator) given in 5 consecutive daily fractions. The minimum follow-up was 6 months (6-44 months). The mean tumor volume was 1.1 cm(3) (0.1-8.74 cm(3)). RESULTS: All tumors remain controlled (9 smaller, 22 unchanged). No patient has experienced post-radiosurgery facial motor dysfunction. Two patients developed new trigeminal neuropathy; 2 patients with preexisting trigeminal nerve symptoms had improvement after FSR. Balance improved in 3 patients, was unchanged in 20 and worsened in 7 patients. Of the 12 patients with useful hearing (PTA < or = 50 dB) prior to treatment, 9 patients retained useful hearing following FSR. Subjectively, of 25 patients with any hearing prior to treatment, 2 had improvement, 10 remained unchanged and 13 had worsening. CONCLUSIONS: Short course FSR for acoustic neuromas results in acceptable toxicity and may provide high control of tumors. Longer follow-up is needed to assess outcomes.

Adult↗

PubMed1999

Regulation of hypothalamic proopiomelanocortin by leptin in lean and obese rats.

The mechanisms by which leptin influences energy homeostasis are not entirely understood. Several observations indicate that proopiomelanocortin (POMC) is involved in the regulation of food intake and may be a mediator of leptin action. To further study this interaction, a sensitive solution hybridization assay was used to compare the levels of POMC mRNA in the medial basal hypothalamus (MBH) of lean (+/+, +/fa(f)) and obese leptin receptor-deficient (fa(f)/fa(f)) rats. POMC peptide products were also measured by RIA in the same animals. Cytoplasmic POMC RNA levels were significantly reduced by 53% in obese rats as compared with lean controls: 0.30 +/- 0.04 vs. 0.64 +/- 0.07 pg/microgram total RNA (p < 0.02). Significant reductions in mean concentrations of hypothalamic POMC-derived peptides from the same dissections were detected in the obese rats vs. lean controls: alpha-MSH 1.77 +/- 0.07 vs. 2.34 +/- 0.10; beta-EP 4.06 +/- 0.24 vs. 5.86 +/- 0.36; gamma(3)-MSH 5.32 +/- 0. 20 vs. 6.52 +/- 0.12 ng/mg protein (p < 0.001). To determine whether leptin stimulates POMC gene transcription, the acute effect of an intracerebroventricular (i.c.v.) injection of leptin (5 microgram) on POMC primary transcript was quantified in the MBH of lean rats after a 16-hour fast. There was a significant 167% increase in mean POMC hnRNA levels 3 h after i.c.v. leptin injection (1.15 +/- 0.22 pg/MBH; p < 0.02), but not after 1 h (0.76 +/- 0.08 pg/MBH), compared to saline controls (0.69 +/- 0.08 pg/MBH). 4 h after the injection of leptin, POMC hnRNA was still increased, but to a lesser extent (140%), as compared with control animals (p = 0.006). These studies demonstrate for the first time in the leptin receptor-deficient rat that there is an associated decrease in POMC gene expression and peptide levels in the MBH. Furthermore, the acute increase in the levels of POMC primary transcript in non-obese rats after a single i.c.v. injection of leptin supports a role for leptin in the regulation of POMC gene transcription. Taken together, these studies provide further evidence that POMC is an important mediator of the effects of leptin on food intake and energy expenditure.

Animals↗

PubMed1999

Effect of AMPA receptor blockade on the control of cerebral O2 supply/consumption balance in newborn pigs.

Using 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride (GYKI 52466), we tested the hypothesis that alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors are important controllers of cerebral O2 supply/consumption balance in newborn piglets during both normoxia and hypoxia. Twenty-seven 2- to 7-day-old piglets were anesthetized with alpha-chloralose and were divided into four groups: 1) normoxia (n = 7), 2) GYKI 52466 (10 mg/kg, n = 7), 3) hypoxia (n = 6), and 4) hypoxia + GYKI 52466 (n = 7). We used [14C]iodoantipyrine to measure regional cerebral blood flow (rCBF) in mL/min/100 g, and we determined O2 extraction by microspectrophotometry, calculating cerebral O2 consumption (VO2) in mL O2/min/100 g in the cortex, hypothalamus, and pons. GYKI 52466 had no effect on regional VO2 or rCBF in normoxic piglets compared with controls. Hypoxia resulted in an increase in local VO2 and rCBF in the cortex and hypothalamus compared with controls: rCBF from 50 +/- 10 to 97 +/- 16 and VO2 from 2.4 +/- 0.5 to 3.7 +/- 0.4 in the cortex, and rCBF from 41 +/- 9 to 99 +/- 17 and VO2 from 2.5 +/- 1 to 3.8 +/- 0.5 in the hypothalamus. GYKI 52466 abolished this hypoxic flow effect in both the cortex (68 +/- 14) and hypothalamus (73 +/- 12). GYKI 52466 also blocked the increased VO2 in the cortex (2.5 +/- 0.4) and hypothalamus (3.0 +/- 0.5) of the hypoxic group. These findings suggest that the AMPA receptor is an important controller of VO2 in the cortex and hypothalamus during hypoxia in this immature porcine model.

Animals↗

PubMed1999

Dynamic rearrangement of the spectrin membrane skeleton during the generation of epithelial polarity in Drosophila.

The origin of epithelial cell polarity during development is a fundamental problem in cell biology. Central to this process is the establishment of asymmetric membrane domains that will ultimately form the apical and basolateral surfaces. The spectrin-based membrane skeleton has long been thought to participate in the generation of this asymmetry. Drosophila melanogaster contains two known (beta)-spectrin isoforms: a conventional (beta)-spectrin chain, and the novel isoform (beta)(Heavy)-spectrin. These two proteins are restricted to the basolateral and apical membrane domains, respectively. To assay for the emergence of membrane asymmetry, we have characterized the distribution of these two (beta)-spectrins during the formation of the primary epithelium in the fly embryo. Our results show that the syncytial embryo contains a maternally established apical membrane skeleton containing (beta)(Heavy)-spectrin into which the basolateral (beta)-spectrin membrane skeleton is added. We have called this process basolateral interpolation. Although basolateral membrane skeleton addition begins during cellularization, it does not become fully established until the formation of a mature zonula adherens at mid to late gastrulation. The behavior of (beta)-spectrin is consistent with a primary role in establishing and/or maintaining the basolateral domain while the behavior of (beta)(Heavy)-spectrin suggests that its primary role is associated with a specialized DE-cadherin complex associated with the furrow canals and with the maturation of the zonula adherens. Thus, the apical spectrin membrane skeleton appears to play a distinct rather than analogous role to the basolateral spectrin membrane skeleton, during the emergence of cell polarity. We find that there are several parallels between our observations and previous studies on the establishment of primary epithelial polarity in vertebrates, suggesting that basolateral interpolation of the membrane skeleton may be a common mechanism in many organisms.

Animals↗

PubMed1998

Synthetic, implantable polymers for local delivery of IUdR to experimental human malignant glioma.

PURPOSE: Recently, polymeric controlled delivery of chemotherapy has been shown to improve survival of patients with malignant glioma. We evaluated whether we could similarly deliver halogenated pyrimidines to experimental intracranial human malignant glioma. To address this issue we studied the in vitro release from polymers and the in vivo drug delivery of IUdR to experimental human U251 glioblastoma xenografts. METHODS AND MATERIALS: In vitro: To measure release, increasing (10%, 30%, 50%) proportions of IUdR in synthetic [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) polymer discs were serially incubated in buffered saline and the supernatant fractions were assayed. In vivo: To compare local versus systemic delivery, mice bearing flank xenografts had intratumoral or contralateral flank IUdR polymer (50% loading) treatments. Mice bearing intracranial (i.c.) xenografts had i.c. versus flank IUdR polymer treatments. Four or 8 days after implantation of polymers, mice were sacrificed and the percentage tumor cells that were labeled with IUdR was measured using quantitative microscopic immunohistochemistry. RESULTS: In vitro: Increasing percentage loadings of IUdR resulted in higher percentages of release: 43.7 + 0.1, 70.0 + 0.2, and 90.2 + 0.2 (p < 0.001 ANOVA) for the 10%, 30%, and 50% loadings, respectively. In vivo: For the flank tumors, both the ipsilateral and contralateral IUdR polymers resulted in similarly high percentages labeling of the tumors versus time. For the ipsilateral IUdR polymers, the percentage of tumor cellular labeling after 4 days versus 8 days was 45.8 +/- 7.0 versus 40.6 +/- 3.9 (p = NS). For the contralateral polymer implants, the percentage of tumor cellular labeling were 43.9 +/- 10.1 versus 35.9 +/- 5.2 (p = NS) measured 4 days versus 8 days after implantation. For the i.c. tumors treated with extracranial IUdR polymers, the percentage of tumor cellular labeling was low: 13.9 +/- 8.8 and 11.2 +/- 5.7 measured 4 and 8 days after implantation. For the i.c. tumors having the i.c. IUdR polymers, however, the percentage labeling was comparatively much higher: 34.3 +/- 4.9 and 35.3 +/- 4.0 on days 4 and 8, respectively. For the i.c. tumors, examination of the percentage cellular labeling versus distance from the implanted IUdR polymer showed that labeling was highest closest to the polymer disc. CONCLUSION: Synthetic, implantable biodegradable polymers provide the local, controlled release of IUdR and result in the high, local delivery of IUdR to experimental intracranial human malignant glioma. This technique holds promise for the local delivery of IUdR for radiosensitization of human brain tumors.

Animals↗

PubMed1998

A role for the p38 mitogen-activated protein kinase/Hsp 27 pathway in cholecystokinin-induced changes in the actin cytoskeleton in rat pancreatic acini.

Cholecystokinin (CCK) and other pancreatic secretagogues have recently been shown to activate signaling kinase cascades in pancreatic acinar cells, leading to the activation of extracellular signal-regulated kinases and Jun N-terminal kinases. We now show the presence of a third kinase cascade activating p38 mitogen-activated protein (MAP) kinase in isolated rat pancreatic acini. CCK and osmotic stress induced by sorbitol activated p38 MAP kinase within minutes; their effects were dose-dependent, with maximal activation of 2.8- and 4.4-fold, respectively. The effects of carbachol and bombesin on p38 MAP kinase activity were similar to those of CCK, whereas phorbol ester, epidermal growth factor, and vasoactive intestinal polypeptide stimulated p38 MAP kinase by 2-fold or less. Both CCK and sorbitol also increased the tyrosyl phosphorylation of p38 MAP kinase. Using the specific inhibitor of p38 MAP kinase, SB 203580, we found that p38 MAP kinase activity was required for MAP kinase-activated protein kinase-2 activation in pancreatic acini. SB 203580 reduced the level of basal phosphorylation and blocked the increased phosphorylation of Hsp 27 after stimulation with either CCK or sorbitol. CCK treatment induced an initial rapid decrease in total F-actin content of acini, followed by an increase after 40 min. Preincubation with SB 203580 significantly inhibited these changes in F-actin content. Staining of the actin cytoskeleton with rhodamine-conjugated phalloidin and analysis by confocal fluorescence microscopy showed disruption of the actin cytoskeleton after 10 and 40 min of CCK stimulation. Pretreatment with SB 203580 reduced these changes. These findings demonstrate that the activation of p38 MAP kinase is involved not only in response to stress, but also in physiological signaling by gastrointestinal hormones such as CCK, where activation of Gq-coupled receptors stimulates a cascade in which p38 MAP kinase activates MAP kinase-activated protein kinase-2, resulting in Hsp 27 phosphorylation. Activation of p38 MAP kinase, most likely through phosphorylation of Hsp 27, plays a role in the organization of the actin cytoskeleton in pancreatic acini.

Actins↗

PubMed1998

Dosimetric properties of a novel brachytherapy balloon applicator for the treatment of malignant brain-tumor resection-cavity margins.

PURPOSE: This paper characterizes the dosimetric properties of a novel balloon brachytherapy applicator for the treatment of the tissue surrounding the resection cavity of a malignant brain tumor. METHODS AND MATERIALS: The applicator consists of an inflatable silicone balloon reservoir attached to a positionable catheter that is intraoperatively implanted into the resection cavity and postoperatively filled with a liquid radionuclide solution. A simple dosimetric model, valid in homogeneous media and based on results from Monte Carlo photon-transport simulations, was used to determine the dosimetric characteristics of spherical geometry balloons filled with photon-emitting radionuclide solutions. Fractional depth-dose (FDD) profiles, along with activity densities, and total activities needed to achieve specified dose rates were studied as a function of photon energy and source-containment geometry. Dose-volume histograms (DVHs) were calculated to compare idealized balloon-applicator treatments to conventional 125I seed volume implants. RESULTS: For achievable activity densities and total activities, classical low dose rate (LDR) treatments of residual disease at distances of up to 1 cm from the resection cavity wall are possible with balloon applicators having radii between 0.5 cm and 2.5 cm. The dose penetration of these applicators increases approximately linearly with balloon radius. The FDD profile can be made significantly more or less penetrating by combining selection of radionuclide with source-geometry manipulation. Comparisons with 125I seed-implant DVHs show that the applicator can provide a more conformal therapy with no target tissue underdosing, less target tissue overdosing, and no healthy tissue "hot spots;" however, more healthy tissue volume receives a dose of the prescribed dosage or less. CONCLUSIONS: This device, when filled with 125I solution, is suitable for classical LDR treatments and may be preferable to 125I interstitial-seed implants in several respects. Manipulation of the dosimetric properties of the device can improve its characteristics for brain tumor treatment and may make it suitable for boosting the lumpectomy margins in conservative breast cancer treatment.

Brachytherapy↗

PubMed1998

Purification and characterization of a novel physiological substrate for calcineurin in mammalian cells.

Although the calcium/calmodulin-regulated protein phosphatase calcineurin has been shown to play a role in a number of intracellular processes, relatively few of the downstream phosphoproteins that are dephosphorylated by this enzyme in cells have been described. Calcineurin was previously shown to play a role in amylase secretion by rat pancreatic acinar cells and to specifically dephosphorylate a 24-kDa cytosolic protein. The present study describes the purification and characterization of this novel phosphoprotein, termed CRHSP-24 (calcium-regulated heat-stable protein with a molecular mass of 24 kDa). Microgram quantities of CRHSP-24 were purified from a large-scale rat pancreas preparation in a procedure involving heat and acid precipitation, anion-exchange chromatography, preparative electrophoresis, electroelution, and two-dimensional electrophoresis. Internal amino acid sequence was obtained from two peptides following trypsin digestion and high pressure liquid chromatography. Both sequences matched with 100% identity nucleotide sequences of expressed sequence tags from human placenta and rat PC-12 cells. Two CRHSP-24 transcripts of 0.7 and 2. 9 kilobases were detected in multiple rat tissues by Northern analysis, whereas a single 24-kDa protein was observed by Western blotting. The CRHSP-24 protein is 147 amino acids in length, is composed of nearly 14% proline, and is phosphorylated entirely on serine residues. Western analysis and 32P metabolic labeling of acini revealed CRHSP-24 to be maximally phosphorylated in control cells and to undergo a rapid sustained dephosphorylation on at least 3 serine residues in response to calcium-mobilizing stimuli. Dephosphorylation of CRHSP-24 was completely inhibited by pretreatment of acini with cyclosporin A or FK506. Furthermore, the inhibitory effects of FK506 were blocked by excess rapamycin. The ubiquitous expression of CRHSP-24 in rat tissues suggests that this novel calcineurin substrate plays a common role in calcium-mediated signal transduction.

Amino Acid Sequence↗