Biomedical subjects
Publications and source records attributed to A M Clark.
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BACKGROUND: We describe an in vitro tumour model for targeted radiotherapy and gene therapy that incorporates cell population heterogeneity. MATERIALS AND METHODS: Transfectant mosaic spheroids (TMS) and transfected mosaic monolayers (TMM) are composed of two cell populations derived from a single cell line. The cells of one population were transfected with the noradrenaline transporter gene (NAT), allowing active uptake of a radiolabelled targeting agent meta-[131I]iodobenzylguanidine ([131I]MIBG); the other population of cells was derived from the same parent line and transfected with a marker gene - green fluorescent protein (GFP). After treatment with [131I]MIBG, cell kill was determined in TMM by clonogenic assay and in TMS by clonogenic assay and spheroid growth delay. RESULTS: We have used the TMS model to assess the 'radiological bystander effect' (radiation cross-fire) conferred by the beta-emitting radiopharmaceutical [131I] MIBG whose cellular uptake is facilitated by the transfected gene encoding NAT. We show that cell killing by [131I]MIBG in both TMS and TMM cultures increased in direct proportion to the fraction of NAT-transfected cells and that the degree of cell killing against fraction transfected was greater in TMS, suggestive of a greater bystander effect in the three-dimensional culture system. CONCLUSIONS: TMS provide a useful model for assessment of the effectiveness of targeted radiotherapy in combination with gene therapy when less than 100% of the target cell population is expressing the NAT transgene. Further, this novel model offers the unique opportunity to investigate radiation-induced bystander effects and their contribution to cell cytotoxicity in radiotherapy and other gene therapy applications.
The potential for the use of microorganisms as tools in the study of drug metabolism appears to be unlimited. The selected examples cited here are only the beginning of what could develop into a widely accepted alternative in vitro model system for studying drug metabolism in humans. As with any other in vitro model system, it is not expected that microbial systems could ever replace animals in biomedical research. The acquisition of data regarding absorption, distribution, and excretion will still require whole animal systems. However, it is clear from the examples cited that microbial systems offer a reliable, reproducible alternative to small animal models for preliminary drug metabolism studies. Due to significant species variation, small animal models may, in many cases, be less reliable than microorganisms as predictive models of human metabolism. It has been estimated that approximately 70 million animals are used each year in the U.S. for biomedical research. The development of any techniques which curtail the sacrifice of such large numbers of animals is welcomed both by animal welfare groups who wish to ensure the humane treatment of laboratory animals and by researchers who additionally appreciate the more practical and economical benefits of such alternatives.
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Geometric isomers of pentamidine analogues were screened for antimicrobial activity in vitro. cis isomers demonstrated good antibacterial activity compared to their trans counterparts. Both isomers were moderately active against opportunistic pathogens that afflict AIDS patients with minimum inhibitory concentrations in the range of 3.12-12.5 microg/mL.
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EtOH extracts of the rhizomes and aboveground portion of Trillium grandiflorum showed significant antifungal activity. Bioassay directed fractionation has led to the identification of the active components as the saponin glycosides 1 and 3.
Bioactivity-guided fractionation of the hexane extract of the stems and leaves of Hypericum drummondii has afforded four new filicinic acid derivatives: drummondin D, isodrummondin D, drummondin E, and drummondin F. The structures of these compounds were established by spectroscopic methods. All compounds possessed strong antibiotic activity against the Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis and the acid fast bacterium Mycobacterium smegmatis.
The hexane-extracted resin of the roots of Croton sonderianus showed antimicrobial activity in standardized bioassays. Fractionation of the resin yielded two acid diterpenes, (-)-hardwickic acid [2] and the new 3,4-secotrachylobanoic acid [5] as major bioactive materials.
The Kemp's ridley sea turtle (Lepidochelys kempi) is restricted to the warm temperate zone of the North Atlantic Ocean, whereas the olive ridley turtle (L. olivacea) is globally distributed in warm-temperate and tropical seas, including nesting colonies in the North Atlantic that nearly overlap the range of L. kempi. To explain this lopsided distribution, Pritchard (1969) proposed a scenario in which an ancestral taxon was divided into Atlantic and Pacific forms (L. kempi and L. olivacea, respectively) by the Central American land bridge. According to this model, the olive ridley subsequently occupied the Pacific and Indian Oceans and recently colonized the Atlantic Ocean via southern Africa. To assess this biogeographic model, a 470 bp sequence of the mtDNA control region was compared among 89 ridley turtles, including the sole L. kempi nesting population and 7 nesting locations across the range of L. olivacea. These data confirm a fundamental partition between L. olivacea and L. kempi (p = 0.052-0.069), shallow separations within L. olivacea (p = 0.002-0.031), and strong geographic partitioning of mtDNA lineages. The most divergent L. olivacea haplotype is observed in the Indo-West Pacific region, as are the central haplotypes in a parsimony network, implicating this region as the source of the most recent radiation of olive ridley lineage. The most common olive ridley haplotype in Atlantic samples is distinguished from an Indo-West Pacific haplotype by a single nucleotide substitution, and East Pacific samples are distinguished from the same haplotype by two nucleotide substitutions. These shallow separations are consistent with the recent invasion of the Atlantic postulated by Pritchard (1969), and indicate that the East Pacific nesting colonies were also recently colonized from the Indo-West Pacific region. Molecular clock estimates place these invasions within the last 300,000 years.
BACKGROUND AND OBJECTIVES: Nonoxynol-9, an intravaginal microbicide, is chlamydiacidal in vitro but also cytotoxic. This study examines the effects of nonoxynol-9 in vivo, using a pigtail macaque model of chlamydial cervicitis. GOALS: To establish a minimum infectious dose of Chlamydia trachomatis in the macaque, and to observe the effects of a single dose of nonoxynol-9 on efficiency of chlamydial infection, vaginal microflora, and cervicovaginal irritation. STUDY DESIGN: The effects of 4% nonoxynol-9, C. trachomatis (5,000 or 10,000 IFU) or both nonoxynol-9 application and chlamydial infection were studied in 17 macaques. RESULTS: Following a single application of nonoxynol-9, chlamydial infection was prevented in 4 of 6 monkeys infected with 10,000 IFU; there was a transient decrease in anaerobic gram-negative rods (P < 0.05) and Peptostreptococci (P > 0.05), but no change in Lactobacillus. Mild cervicovaginal irritation was observed in the monkeys. CONCLUSIONS: A single dose of nonoxynol-9 causes minimal vaginal flora and epithelial irritation, and may be useful for prevention of chlamydial infection.
Two novel fungal metabolites, N-benzoyl-L-phenylalaninol (1a) and asperphenamate (2) were isolated from the culture filtrate and mycelium of Aspergillus flavipes ATCC 11013. N-benzoyl-L-phenylalaninol was identified by direct comparison with an authentic sample. The structure of asperphenamate is proposed as (S)-N-benzoyl-phenylalanine-(S)-2-benzamido-3-phenyl propyl ester, based on chemical and spectroscopic evidence.
Clusterin is the major protein produced by rat Sertoli cells and is deposited onto sperm membranes; however, its function is unknown. In order to gain insight into the regulation of clusterin in Sertoli cells, the objective of the present study was to develop a model where the expression of clusterin could be affected in Sertoli cells in vitro. Rat Sertoli cells and mouse Sertoli cells (MSC1) were cultured under heat stress conditions (41 degrees C) for up to 48 hours. The mRNA for clusterin in Sertoli cells was compared to that in human epitheliod cancer cells (A431) to determine if clusterin expression was regulated in a lestis-specific manner. The mRNA for heat shock protein 70 (HSP70) was also examined as it is a known stress-regulated gene. Expression of HSP70 mRNA was increased in all three cell types by 4 hours after the start of heat stress. Clusterin mRNA was increased over that of controls by 4 hours in heat-stressed A431 cells but did not significantly increase in MSC1 or Sertoli cells until 12 hours (P < 0.05). The induction of clusterin mRNA in MSC1 cells continued for at least 48 hours and required the sustained exposure of cells to the 41 degrees C temperature. The increase in the amount of clusterin mRNA was not due to an increase in transcript half-life, as determined by the addition of actinomycin D to the media of control vs. heat-stressed MSC1 cells. From the development of this in vitro model, we have seen that the timing of induction of clusterin by heat stress is Sertoli cell specific and is different than that of HSP70. This response in surviving cells during heat stress may be protective in that clusterin would bind to toxic compounds or solubilize cellular debris released by degenerating cells.