Browsing by Author "Els, W J"

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    The foramen magnum and its contents : a magnetic resonance imaging study of the normal spatial relationships
    (1994) Lotz, Jan Willem; Els, W J
    The well-known neurological disturbances associated with caudal displacement of the cerebellar tonsils through the fora men magnum (Chiari malformation) have lead to many radiological studies of the region. With MRI, routine sagittal and parasagittal views of the craniovertebral junction have shown that the position of the cerebellar tonsils is variable, and in many otherwise healthy individuals, the inferior tonsillar margins lie within the fora men magnum itself. In some cases, this topography is associated with little signal from the surrounding cerebra-spinal fluid (CSF), indicating reduction of the cerebellomedullary cistern and, therefore, crowding of neural structures within the confines of the fora men. The objective of this study has been to examine the spatial relationship between the contents of the foramen magnum ie. the medulla and cerebellar tonsils, using a normal sample comprising 120 volunteers. Instead of the conventional measurements of distance, a ratio, the Foramen Magnum Index (FMI), has been determined, derived from the relative surface areas (pixels) of neural parenchyma and CSF, over axially and sagittaly-defined boundaries of the fora men. The FMI, with a 95th centile of 0.77, exhibits appropriate statistical correlation with tonsillar position below the level of the foramen, and is therefore considered specific. As a quantitative means of assessing the cerebellomedullary cistern, the FMI also identifies certain subjects whose tonsils are at the foramen, in whom the cistern is small with resultant neural crowding.
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    Immunospecific albumin microspheres as a drug delivery system for cisplatin and 5-fluorouracil for the treatment of ovarian adenocarcinoma
    (1999) Truter, Ernest John; Els, W J
    Ovarian carcinoma is considered to be the most deadly of the gynaecological malignancies which in its earliest stages is usually asymptomatic. The unsatisfactory survival rates of patients on conventional chemotherapy regimens, necessitates vehicles capable of carrying cytotoxic agents directly to the malignant cells. This mode of targeted delivery allows for efficient tumour cell kill whilst sparing surrounding normal tissue and substantially reducing side-effects. This project examined the possible therapeutic role of a targetable sustained drug delivery system, albumin immunomicrospheres containing the chemotherapeutic agents, cisplatin and 5-fluorouracil, for the treatment of ovarian adenocarcinoma. A rodent cell line, as a model, has proved to be similar to its human counterpart and also has shown to be transplantable from one animal to another. Such a model could therefore be useful for performing experiments relating to drug delivery targetability and therapeutic trials, as well as survival studies, in cases of ovarian adenocarcinoma. In particular, this project examines the efficacy of the immunospecific microspheres containing the drugs in a highly concentrated form, administered intraperitoneally and targeted to an ovarian adenocarcinoma, in an attempt to enhance tumour cell kill whilst largely sparing surrounding normal tissue. It is widely recognized that the effectiveness of most chemotherapeutic drugs would be enhanced if they were to act selectively where they are needed. In order to achieve a therapeutically relevant dose in tumour cells, the amount of drug required usually proves also to be highly toxic to normal tissues. It was postulated that, to overcome the above, it may be feasible to develop a sustained immunospecific drug delivery system to optimize the action of cisplatin and 5-fluorouracil at the target site. With the attainment of the above, it was further postulated that higher doses of drugs could be delivered to the target area effecting higher tumour cell kill, that less normal tissue damage should occur and that toxic side effects of the drugs should be reduced. The rationale for selecting combination therapy of cisplatin and 5-fluorouracil is that, although it has been inferred that DNA intrastrand and interstrand cross-links produced by the cisplatin often repair, this repair can be blocked by 5-fluorouracil by inhibition of thymidylate synthetase, thus preventing DNA strand repair. Albumin immunomicrospheres are relatively innocuous in terms of toxicity, non-antigenic and are capable of accommodating chemotherapeutic agents in a non-specific fashion. We showed that they were capable of a 0. 94% entrapment of 5-fluorouracil and 1.23% cisplatin. Delivery of these drugs at a target site, and at these concentrations, should effect extensive cell kill. As the microspheres are chemically stable and can be manipulated to offload the entrapped drugs satisfactorily, in vitro drug release profiles were performed employing immunospecific microspheres directed towards its target cells. Slow degradation of the drug- containing albumin immunomicrospheres showed that 0.283 μg cisplatin/ml plasma and 0. 799 μg 5-fluorouracil/ml plasma could be made available at the target site over a 14-day period. These concentrations could be maintained over at least another 14 days and effect tumour cell kill satisfactorily. In order to assess the tumour cell kill, we performed clonogenic assays, cell survival growth curves, MTT cytotoxicity assays and assessed the induction of micronuclei in the tumour cells. The synergism between 5-fluorouracil and cisplatin showed a modulation of cisplatin cytotoxicity and total tumour cell kill was achieved at concentrations of 0.5 μg/ml 5-fluorouracil and 0.1 μg/ml cisplat in at the target site. The above-mentioned evidence of effective targeting of the drugs was then investigated in female Wistar rats with ovarian adenocarcinoma to assess comparative survival times when treated with free drugs or immunospecific albumin microspheres containing the drugs. Animals given a free drug dose of 5 mg/kg cisplatin and 20mg/kg 5-fluorouracil, followed by a repeat dose at the same concentrations 7 days later showed that only 14% of the animals survived a 90-day trial period. Animals given an intraperitoneal bolus dose of immunomicrospheres at a dose of 1 O mg/kg cisplatin and 40 mg/kg 5-fluorouracil showed that 60% of the animals survived the 90-day trial period. This data indicated to us that the survival probability of animals treated with drug-containing immunomicrospheres was substantially superior to other protocols employed in this study.
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    Sodium channel regulatory mechanisms : current fluctuation analysis on frog skin epithelium
    (1994) Chou, Kuang-Yi; Els, W J
    This project examined the role of the cytoskeleton in regulatory mechanisms of the amiloride-sensitive Na⁺ channels in isolated frog skin epithelium. The epithelium from ventral frog skin is a model tissue which has proved significant in our understanding of the basic principles involved in water and Na⁺ homeostasis. In particular, this project examines ways in which local (non-hormonal) and hormonal regulatory mechanisms adjust the Na⁺ permeability of apical membranes of frog skin epithelium. Both mechanisms contain factors that are known to increase the apical membrane Na⁺ permeability mainly by increases in the number of open channels. The origin of these new open channels is unknown but, it is postulated that they could arise either by activation of quiescent channels already present in the apical membrane, or by recruitment of channels from cytoplasmic stores. Regarding the latter hypothesis, we also examined the idea that the cytoskeleton might somehow be involved in the insertion of Na⁺ channels within vesicles, into the apical membrane. This is based on the fact that the cytoskeleton is involved in a similar mechanism whereby, in the toad urinary bladder, anti-diuretic hormone (ADH) causes the insertion of aggregates with water channels. Much current interest focuses on the role of the cytoskeleton in the regulation of epithelial Na⁺ channels. To test this hypothesis, we used noise analysis to examine the effects of disrupting the cytoskeleton, on two different mechanisms which bring about changes in open channel densities. The mechanisms are: (1) lowering mucosal Na⁺ concentration (non-hormonal), and (2) addition of arginine-vasopressin (A VP) (hormonal). Non-hormonal, autoregulatory changes in apical membrane Na⁺ conductance were examined by investigating the effects of reducing the mucosal Na⁺ concentration. Our results showed that lowering the mucosal Na⁺ concentration induced large increases in the open channel density in order to stabilise the transport rate. In addition, we observed an average 55-60% increase in the open channel probability, which implies that in epithelium from Rana fuscigula, changes of channel open probability are also an important mechanism in the autoregulation of channel densities in response to a reduction in mucosal Na⁺. The hormonal control of Na⁺ channels by A VP has been intensively studied by noise analysis and the patch clamp. Our results confirmed previous reports that A VP increases the Na⁺ transport rate by increasing the number of open Na⁺ channels, primarily through large changes in the total number of channels, without a significant change in open probability. Regarding the role of the cytoskeleton in regulation of Na⁺ channels and/or its possible role in control of inserting putative vesicles with Na⁺ channels, we studied the effects of disrupting the cytoskeleton on the two regulatory mechanisms. Disrupting microtubules with colchicine had no, or very little effect on either of the regulatory mechanisms. On the other hand, the integrity of the microfilaments was very important for the autoregulatory changes in the number of open channels. After cytochalasin B treatment, lowering the mucosal Na⁺ concentration did not result in the usual compensatory changes in channel densities. There was no prior evidence that cytochalasin B had any actual effect on the F-actin network in the frog skin epithelium. Accordingly, modified cytochemical techniques were designed to demonstrate and localise F-actin in the epithelial granular cells. The direct immunofluorescent method proved useful, but did not allow sufficient resolution to examine the changes to different populations of actin in the cells. We then modified an immunogold method to suit our conditions, and the results demonstrated the localisation of different pools of F-actin and showed the effects of the cytochalasin B and vasopressin.
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    Ultrastructural characterization of ultraviolet induced corneal disease : an animal model
    (1994) Schultes, Klaus; Els, W J; Hill, C J
    The majority of ancient people worshipped the sun and viewed it as a health - bringing deity. During the eighteenth and nineteenth century therapeutic benefits of sunlight exposure were beginning to be understood and by the end of the nineteenth century the importance of ultraviolet radiation was being realized. Danish physician Niels Finsen, whom many regard as the father of ultraviolet phototherapy, also stressed that it was ultraviolet radiation in the solar spectrum which cause sunburn. We now recognize that the small portion of ultraviolet radiation which reaches the earth's surface is not necessarily therapeutic, but in fact could be harmful to humans. There are numerous accounts of the harmful effects of UV radiation to the skin and the eye as a whole. These effects may be caused by either acute or chronic exposure to UV radiation. For example, some acute effects of UV-B radiation include conjunctivitis and photokeratitis. "Snow blindness" and "arc welders eye" are further examples of acute ultraviolet damage specifically to the surface of the cornea. On the other hand, chronic exposure to ultraviolet radiation is thought to be responsible for pterygia, climatic droplet keratopathy Hill and Maske (1989), cancers of the external eye, cataracts and various types of retinal diseases. The present study is an extension of ongoing studies on ultraviolet radiation damage to the cornea in the Department of Ophthalmology, University of Cape Town and Groote Schuur Hospital. Their specific interest lies in the causes and treatment of climatic droplet keratopathy. The aims of the present study are: 1) Establish a possible role of ultraviolet B radiation in human corneal diseases such as climatic droplet keratopathy and pterygium using the rabbit as an animal model. 2) Determine by means of SEM the initial effects and subsequent recovery of the epithelium after a 3-hour dose of ultraviolet B radiation. We refer to this study as "acute" response to ultraviolet B radiation. 3) To try and confirm the effects observed by SEM with ultrastructural studies using TEM. 4) In addition, we are also looking at the possible effects after exposing rabbit cornea to a daily dose of low level ultraviolet B radiation, over a long period of time. We refer to this as chronic exposure to ultraviolet B radiation. It is hoped that by exposing rabbits to ultraviolet light, principally ultraviolet B radiation, diseases similar to those found in humans could be simulated and disease progression studied. People are generally exposed to substantial amounts of UV radiation for a very long time. Since people generally live longer they will be exposed to an ever-increasing amount of solar UV radiation and subsequently, there is an increasing risk of developing corneal diseases. The possible threat to the ozone is also a real possibility and could lead to increased levels of ultraviolet radiation reaching the earth's surface. This will require a greater understanding of the very nature of corneal damage due to acute and chronic exposure. This study focusses mainly on the acute response to UV-B radiation since most studies have investigated effects of prolonged exposure to UV light. Accordingly, much less is known about acute exposure. Many people suffering from acute UV B radiation effects probably never visit the ophthalmologist or wait for a couple of days. This could also contribute to the fact that effects of short-term damage is not well documented.