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C L Alexander

Publications and source records attributed to C L Alexander.

12 recordsLinked to original sources
PubMed2000

Comparison of neuregulin-1 expression in olfactory ensheathing cells, Schwann cells and astrocytes.

Recently we demonstrated that a member of the neuregulin-1 (NRG-1) family of growth factors is a mitogen and survival factor for olfactory ensheathing cells (OECs). OECs are specialized glial cells within the olfactory system that are believed to play a role in the continual nerve re-growth of this tissue. OECs share properties with both astrocytes and Schwann cells but are likely to be a distinct glial cell type. NRG-1s have been found to be important regulators of Schwann cells in vivo, but the role of NRG-1 for OECs is less clear. The nrg-1 gene produces at least 12 different isoforms, that are likely to have different functions, due to alternative splicing of its mRNA. In this study, the expression of NRG-1 mRNAs in OECs was compared with other glial cells and their corresponding tissue sources. Cultured glial cells, unlike their tissue sources, expressed NRG-1 mRNAs containing the alpha EGF-like domain and expressed only the type 1beta isoform that lacks the glycosylated spacer domain. This correlated with expression of these isoforms during olfactory nerve degeneration in vivo. Although OECs expressed mRNA for all NRG-1 isoforms, the protein could not be detected in concentrated supernatant, or on the cell surface by immunofluorescence, but was detected in the nucleus or cytoplasm (depending on the isoform). These data support the hypothesis that NRG-1s play a functional role in OEC biology.

Animals↗
PubMed2000

Identification of a human olfactory ensheathing cell that can effect transplant-mediated remyelination of demyelinated CNS axons.

The olfactory ensheathing cell (OEC) has attracted much interest recently because of its potential for transplantation-based therapy of CNS disease. Rat OECs are able to remyelinate demyelinated axons and support regeneration of damaged axons. Although OECs can be grown readily from the rat, a macrosmatic species, it has been uncertain whether it would be similarly straightforward to obtain these cells from the human, a microsmatic species with a relatively poorly developed olfactory system. In this study, we have identified a human OEC which shares many properties with its rat counterpart, including expression of the low-affinity nerve growth factor receptor (L-NGFr) and similar growth factor requirements. Purified populations of human OECs obtained by selection with L-NGFr antibodies have extremely high viability in tissue culture, and are capable of remyelinating persistently demyelinated CNS axons following transplantation into experimentally induced demyelinating lesions in the rat spinal cord. Thus, the human OEC represents an important new cell for the development of transplant therapy of CNS diseases.

Animals↗
PubMed1999

The role of human melanoma cell ICAM-1 expression on lymphokine activated killer cell-mediated lysis, and the effect of retinoic acid.

Intercellular adhesion molecule (ICAM-1) exists as a membrane-associated form (mICAM-1) on the surface of tumour cells as well as a soluble form (sICAM-1). This study analyses the ability of all-trans retinoic acid (RA) to alter both sICAM and mICAM-1 expression in C8161 and Hs294T human melanoma cell lines and investigates the involvement of ICAM-1 in the interaction between tumour and lymphokine-activated killer (LAK) cells using the Cr-51 release assay. Our data showed that 4-day pretreatment of the tumour cells with 10(-7) M RA and 10(-6) M RA induced an increase in lysis of both cell lines and also increased mICAM-1 expression without having any effect on sICAM-1 levels. Addition of blocking ICAM-1 antibody (10 microg ml(-1)) to the C8161 cells at an effector:tumour cell ratio of 40:1 caused a 2.3-fold reduction in lysis of tumour cells and a 3-fold reduction in lysis of RA-treated cells. Blocking ICAM-1 antibody at optimum concentrations of 5 microg ml(-1) reduced lysis 1.8-fold in control Hs294T cells and 1.3-fold in RA-treated cells. Blocking the HLA-ABC complex had no effect on lysis. The more highly metastatic C8161 cells were found to secrete 4-fold greater levels of sICAM-1 than the poorly metastatic Hs294T cells and addition of sICAM-1 to the assay failed to affect lysis of either cell line but did induce a 2-fold decrease in lysis of RA-treated C8161 cells. Collectively, these data provide further evidence for ICAM-1 involvement in the tumour/LAK cell response and indicates that the RA-induced increase in mICAM-1 levels are partly responsible for the increase in susceptibility of the tumour cells. sICAM-1 appears to be unimportant in evasion of the tumour cells from LAK cell lysis, but may play a role in evasion of RA-treated C8161 cells.

Antibodies↗
PubMed1999

Pentoxifylline-induced modulation of melanoma cell growth, adhesion and lymphokine activated killer cell-mediated lysis.

Pentoxifylline (PX) is a phosphodiesterase inhibitor which effectively increases overall cAMP levels within the cell. This study analyses the ability of PX to alter growth, adhesion and lymphokine activated killer (LAK) cell-mediated lysis of the C8161 and Hs294T human melanoma cell lines, and investigates the role of intercellular adhesion molecule-1 (ICAM-1) in the tumour/LAK cell interaction. We have demonstrated that 4 days' pretreatment with PX (100-250 microg/ml) significantly reduces cell numbers in a dose- and time-dependent manner, with cell numbers decreasing by 67.5% in the C8161 cell line and by 65.4% in the Hs294T cell line with 250 microg/ml PX. Adherence of both cell lines to a range of extracellular matrix components is not affected by PX, with the exception of the C8161 cells, where 4 days' pretreatment with 250 microg/ml PX causes a 24.2% reduction in adherence to fibronectin. Four days' pretreatment of the tumour cells with 250 microg/ml PX leads to increased lysis of the C8161 cells and decreased lysis of the Hs294T cells. The addition of blocking ICAM-1 antibody (10 microg/ml) to the C8161 cells at an effector:tumour cell ratio of 40:1 causes a 2.3-fold reduction in lysis of both control and PX-treated cells. Addition of blocking ICAM-1 antibody (5 microg/ml) to Hs294T cells reduces lysis of control cells 1.8-fold. In PX-treated Hs294T cells, 10 microg/ml of blocking ICAM-1 antibody significantly reduces lysis 1.5-fold. The more aggressive C8161 cells produce 5-fold greater levels of soluble ICAM-1 (sICAM-1) than the poorly metastatic Hs294T cells. PX (10-250 microg/ml) causes a dose-dependent increase in sICAM-1 expression in both cell lines, with maximum increases of 4.7-fold and 4.3-fold in the Hs294T and C8161 cell lines, respectively, following 4 days' pretreatment with 250 microg/ml PX. Collectively, these data demonstrate the ability of PX to alter tumour cell growth, adhesion and LAK cell-mediated lysis and also support a role for the involvement of ICAM-1 in the tumour/LAK cell interaction.

Cell Adhesion↗
PubMed1999

Effect of retinoic acid on plasminogen activator expression in human melanoma cells.

The plasminogen activation system comprises various proteases that contribute to the invasive potential and metastatic spread of the tumour cell. Two such proteases are tissue-type (tPA) and urokinase-type (uPA) plasminogen activators. Both these enzymes convert plasminogen into the active zymogen plasmin, which has a broad substrate specificity and is capable of degrading a wide range of extracellular matrix molecules. In this study, we examined the effect of retinoic acid (RA) on uPA and tPA secretion in the highly metastatic C8161 and the poorly metastatic Hs294T human melanoma cell lines using a specific enzyme-linked immunosorbent assay (ELISA) detection system, and correlated this production with RA receptor (RAR) expression. Over a range of dilutions, we were able to show that the highly metastatic C8161 cells secreted 0.95 ng of uPA/cell compared with 4.41 fg/cell for the Hs294T cells, whereas the Hs294T cells secreted 24.5 fg of tPA/cell compared with 4.35 fg/cell for the C8161 cells. On exposure of the cells to RA (10(-10)-10(-5) M) for 4 days, uPA secretion was increased 3.4-fold in the C8161 cell line and 1.6-fold in the Hs294T cell line using 10(-8) M RA. In addition, tPA expression was increased in both cell lines by 3.7-fold in the C8161 cells and 3.8-fold in the Hs294T cells with 10(-6) M RA treatment. Increases in PA expression by RA have been reported to involve RAR alpha and RAR beta expression. We were able to detect RAR beta and gamma expression in both cell lines, with and without RA treatment, but were unable to detect expression of RAR alpha. This suggests that another mechanism must exist to regulate the RA modulation of tPA and uPA secretion in these cell lines that does not require RAR alpha expression.

Blotting, Southern↗
PubMed1997

Effect of retinoic acid on melanoma cell-derived factor stimulation of fibroblast glycosaminoglycan synthesis.

The hyaluronan-rich matrix that surrounds many tumours and facilitates tumour cell growth and invasion is thought to be predominantly synthesized by normal stromal cells stimulated by tumour cell-derived factors. This study examines the possibility that the production of tumour cell-derived factors that stimulate fibroblast glycosaminoglycan (GAG) synthesis may be blocked by exposure to differentiation-inducing agents such as retinoic acid. We have demonstrated that Hs294T, C8161 and A375 human melanoma cell lines release factors into their medium that stimulate normal fibroblast GAG synthesis. Exposure of these melanoma cells to retinoic acid failed to mediate any significant reduction in growth over a 7-day period. Retinoic acid failed to block the tumour cell production of GAG-stimulating activities and even enhanced the activities produced by the C8161 cell line, particularly at low retinoic acid concentrations (48% stimulation at 10(-9) M retinoic acid; P < 0.02). Addition of retinoic acid directly to fibroblast cultures exposed to fibroblast-conditioned medium resulted in an inhibition of GAG synthesis with a 33% inhibition observed at 10(-5) M. Addition of retinoic acid to fibroblast cultures exposed to the tumour cell-conditioned medium failed to inhibit the stimulation of GAG synthesis. Other differentiation-inducing agents, such as hexamethylene-bis-acetamide and butyrate, also failed to block the production of tumour cell-derived GAG-stimulating activities. These results demonstrate that retinoic acid and other differentiation-inducing agents fail to inhibit melanoma cell production of fibroblast GAG synthesis-stimulating factors or their action upon fibroblasts.

Acetamides↗
PubMed1997

An experimental study of airbag impact to the orbit using an instrumented Hybrid III headform.

This paper provides the results from an experimental study intended to assess airbag impact to the orbit. Twenty-seven airbags were deployed onto an instrumented Hybrid III headform. Seven different types of airbags were used that included tethered and nontethered, light to heavy nylon weaves, and different coating types. The airbags were deployed via a pneumatic deployment system. Seven individual force transducers, each having a 2.25 cm2 contact area, were placed on the right orbital region to evaluate the force patterns. The midpoint of the two ocular regions of the headform was positioned 12.5 cm above and 15.0 cm away from the center of the airbag, a position determined from previous airbag deployments to yield the highest leading edge velocity. The average maximum force per sensor ranged from 15.4 N to 63.6 N, and peak pressure ranged from 68 kPa to 282 kPa. The upper center of the orbit presented the highest values while the center of the orbit recorded the lowest values, a comparison that was proven to be statistically significant. For this configuration, the maximum force on the ocular region was found to be independent of the presence of a tether or the maximum internal airbag pressure.

Air Bags↗
PubMed1997

Airbag-induced eye injuries: experiments with in situ cadaver eyes.

In an attempt to investigate eye injuries from airbags, a set of experiments was performed that involved the deployment of several types of airbags onto thirteen unembalmed, previously frozen cadaver heads. The airbags differed in the material, coating, presence of a tether, and folding pattern, and were deployed via a pneumatic deployment system. The eyes were impacted in situ after being repressureized with saline injected through a 30-gauge needle. Injury determination was achieved by ophthalmic ultrasound imaging, staining with fluorescein dye, and dissection. All twenty-six eyes revealed detached retinas, as shown by the ultrasound, before impact as a result of decaying tissue and the freezing process. High speed video and film were used to capture the events. The impact velocities of the airbags were recorded from the digitized film at the first contact location with the eye and ranged from 30 m/s to 66 m/s. Eyeglasses were placed on four of the specimens, and the presence of eyeglasses seemed to provide protection to the eye because of the lack of contact between the airbag and ocular region. Minimal ocular damage was recorded for all experiments.

Air Bags↗
PubMed1995

Rapid desensitization of the thyrotropin-releasing hormone receptor expressed in single human embryonal kidney 293 cells.

This study uses fluorescence microscopy combined with dynamic video imaging to examine the events associated with the rapid desensitization of the thyrotropin-releasing hormone receptor (TRH-R). In single non-pituitary human embryonic kidney 293 (HEK-293) cells, expressing either the rat or human TRH-Rs, TRH produced a rapid dose-dependent monophasic rise in [Ca2+]i. This Ca2+ transient was completely abolished by pretreatment of cells with the intracellular Ca2+ antagonists thapsigargin or cyclopiazonic acid, but not EGTA, the voltage-operated Ca2+ channel (VOCC) antagonist nifedipine or the second-messenger-operated Ca2+ channel antagonist SK&F 96365. These results suggest that TRH causes the mobilization of Ca2+ from thapsigargin/cyclopiazonic acid-sensitive intracellular Ca2+ stores but not the influx of extracellular Ca2+. HEK-293 cells also failed to respond to KCl or the slow Ca(2+)-channel activator BAY K 8644, suggesting that they lack L-type VOCCs. Rat and human TRH-Rs are highly conserved except at the C-terminus where the sequence differs. The C-terminus is believed to be important in receptor desensitization. Despite differences in this region, rat and human TRH-Rs expressed in HEK-293 cells underwent rapid (within 1 min) desensitization. This desensitization was dose-dependent and did not involve receptor loss. Similarly the bradykinin receptor endogenous to HEK-293 cells also displays a rapid desensitization. We conclude that in TRH-R-expressing non-pituitary HEK-293 cells, TRH mobilizes intracellular Ca2+ resulting in a monophasic Ca2+ transient. The rat and human TRH-Rs as well as the endogenous bradykinin receptor also displayed rapid receptor desensitization.

Animals↗
PubMed1979

Keynote address.

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Humans↗