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A J Brown

Publications and source records attributed to A J Brown.

At least 37 records · Page 2Linked to original sources
PubMed2001

Genetic drift and within-host metapopulation dynamics of HIV-1 infection.

Most HIV replication occurs in solid lymphoid tissue, which has prominent architecture at the histological level, which separates groups of productively infected CD4(+) cells. Nevertheless, current population models of HIV assume panmixis within lymphoid tissue. We present a simple "metapopulation" model of HIV replication, where the population of infected cells is comprised of a large number of small populations, each of which is established by a few founder viruses and undergoes turnover. To test this model, we analyzed viral genetic variation of infected cell subpopulations within the spleen and demonstrated the action of founder effects as well as significant variation in the extent of genetic differentiation between subpopulations among patients. The combination of founder effects and subpopulation turnover can result in an effective population size much lower than the actual population size and may contribute to the importance of genetic drift in HIV evolution despite a large number of infected cells.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Residual human immunodeficiency virus (HIV) Type 1 RNA and DNA in lymph nodes and HIV RNA in genital secretions and in cerebrospinal fluid after suppression of viremia for 2 years.

Residual viral replication persists in a significant proportion of human immunodeficiency virus (HIV)-infected patients receiving potent antiretroviral therapy. To determine the source of this virus, levels of HIV RNA and DNA from lymphoid tissues and levels of viral RNA in serum, cerebrospinal fluid (CSF), and genital secretions in 28 patients treated for < or =2.5 years with indinavir, zidovudine, and lamivudine were examined. Both HIV RNA and DNA remained detectable in all lymph nodes. In contrast, HIV RNA was not detected in 20 of 23 genital secretions or in any of 13 CSF samples after 2 years of treatment. HIV envelope sequence data from plasma and lymph nodes from 4 patients demonstrated sequence divergence, which suggests varying degrees of residual viral replication in 3 and absence in 1 patient. In patients receiving potent antiretroviral therapy, the greatest virus burden may continue to be in lymphoid tissues rather than in central nervous system or genitourinary compartments.

Cohort Studies↗
PubMed2001

Enhancement of macrophage survival and DNA synthesis by oxidized-low-density-lipoprotein (LDL)-derived lipids and by aggregates of lightly oxidized LDL.

Human atherosclerotic plaque contains a partially characterized range of normal and oxidized lipids formed mainly from free and esterified cholesterol and phospholipids, some of which can be located in macrophage-derived "foam" cells. Oxidation of low-density lipoprotein (LDL) is often considered as an important event leading to subsequent foam-cell development, which may also include enhanced cell survival and/or proliferation. The active component(s) in oxidized LDL (ox.LDL) causing macrophage proliferation is debated. We report here that the lipid component of ox.LDL can promote macrophage survival and DNA synthesis, the latter response showing a synergistic effect in the presence of low concentrations of macrophage colony-stimulating factor. 7-Ketocholesterol showed some stimulation of macrophage DNA synthesis whereas hypochlorite-oxidized (i.e. apolipoprotein B-oxidized) LDL did not. Plaque-derived lipids could enhance macrophage survival. It has not been proven that LDL in lesions is oxidized sufficiently to be the dominant source of sterols in vivo or to be able to induce macrophage growth in vitro or in vivo; it has been suggested that aggregation of modified LDL in vivo is an important step in the deposition of intracellular lipid. We found that aggregation of lightly oxidized LDL potentiated dramatically its ability to stimulate macrophage DNA synthesis, indicating that extensive oxidation of LDL is not required for this response in vitro and perhaps in vivo.

Animals↗
PubMed2001

Fungal virulence studies come of age.

Sophisticated molecular biological research has revealed many virulence attributes in at least four pathogenic fungi, but the future study of fungal virulence requires investigators to distinguish between molecules that directly interact with the host, molecules that regulate these, and molecules that are always required for fungal growth and survival, independent of the host.

Animals↗
PubMed2001

7-Ketocholesterol delivered to mice in chylomicron remnant-like particles is rapidly metabolised, excreted and does not accumulate in aorta.

Cholesterol oxidation products (oxysterols) have been implicated in atherogenesis due to their presence in atherosclerotic tissue and their potent effects in vitro. One of the major oxysterols currently of interest is 7-ketocholesterol (7K) and it has been suggested that the diet is an important source of this oxysterol. This investigation tested the hypothesis that 7K, delivered in a physiologically relevant vehicle, chylomicron remnant-like emulsion (CMR), would be metabolised and excreted by mice in a similar manner and to a similar extent as previously observed in rats when delivered in a chemically modified lipoprotein, acetylated low-density lipoprotein (acLDL). Indeed, the metabolism of 14C-7K delivered in CMR mirrored that of acLDL and was much more rapid than (3)H-cholesterol delivered simultaneously. The 7K-derived (14)C was cleared from the liver, appeared in the intestine and was excreted in the faeces. A substantial proportion of the 7K-derived (14)C in the intestine and faeces was aqueous-soluble, indicating metabolism to polar products, presumably bile acids. Moreover, while cholesterol-derived (3)H increased in the aorta, (14)C appeared transiently and there was no observable accumulation within 24 h. The data confirm our previous findings of rapid hepatic metabolism of 7K when delivered in acLDL and demonstrate that 7K delivered in a vehicle of dietary significance is similarly metabolised and excreted. Indeed, the data encourage further investigation into the contribution that dietary oxysterols may or may not make to atherogenesis.

Animals↗
PubMed2001

Metabolism of an oxysterol, 7-ketocholesterol, by sterol 27-hydroxylase in HepG2 cells.

7-Ketocholesterol (7K) is a quantitatively important oxysterol in both atherosclerotic lesions and macrophage foam cells. We reported recently that radiolabeled 7K delivered to rodents in a modified lipoprotein or chylomicron remnant-like emulsion, both cleared predominantly by the liver, was rapidly excreted into the intestine as water-soluble products, presumably bile acids. Herein, we aimed to elucidate the early or initial reactions in 7K metabolism. The hypothesis was tested that sterol 27-hydroxylase, a mitochondrial cytochrome P450 and the first enzyme of the acidic bile acid pathway, is responsible for the initial metabolism of 7K by HepG2 cells, a human hepatoblastoma cell-line. The 27-hydroxylated product of 7K (27OH-7K) was shown to be the initial, lipid-soluble product of 7K metabolism. It was produced in mitochondrial incubations and whole cells and was readily released into the media from cells. Intact cells generated metabolites of 7K that had undergone conversion from lipid-soluble precursors to water-soluble products rapidly and extensively. Their production was ablated with cyclosporin A, a sterol 27-hydroxylase inhibitor. Furthermore, we demonstrated the effectiveness of two novel selective inhibitors of this enzyme, GW273297X and GI268267X. These inhibitors also ablated the production of water-soluble products by cells; and the inhibitor of choice, GW273297X, decreased the production of 27OH-7K in mitochondrial preparations. This is the first study to demonstrate that sterol 27-hydroxylase plays an important role in the metabolism of oxysterols such as 7K in liver cells.

Cholestanetriol 26-Monooxygenase↗
PubMed2001

Clinical and biochemical features, molecular diagnosis and long-term management of a case of cerebrotendinous xanthomatosis.

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal recessive sterol storage disease characterised clinically by juvenile bilateral cataracts, progressive neurological dysfunction, and formation of tendon xanthomata. We describe the clinical and biochemical features, molecular diagnosis and long-term management of the first reported Australasian case of CTX. Molecular analysis confirmed the diagnosis of CTX and demonstrated that the patient was homozygous for a G-->A transition in the splice donor site of intron 4 of the sterol 27-hydroxylase gene. Serum cholestanol concentrations were decreased with the HMG-CoA reductase inhibitor simvastatin alone and greater reductions were achieved after the addition of the bile acid chenodeoxycholic acid; suggesting a synergistic effect of this combination. Despite serum cholestanol concentrations remaining within the low-normal range, there has been no significant improvement in mental and physical abilities or in EEG abnormalities with 5 years of treatment. Metabolism of radiolabeled 7-ketocholesterol to aqueous soluble products was absent in CTX-derived macrophages. Consistent with this finding, plasma 7 alpha-hydroxycholesterol, 7 beta-hydroxycholesterol, and 7-ketocholesterol concentrations were increased in the CTX subject compared with controls.

Achilles Tendon↗
PubMed2001

Interaction of caveolin with 7-ketocholesterol.

Caveolin is an integral membrane protein that interacts with cholesterol in glycosphingolipid-rich rafts at the cell surface. We have examined the interaction of recombinant His-tagged caveolin-1 with cholesterol and 7-keto cholesterol, the most abundant non-enzymatically formed oxysterol found in oxidised LDL and atheromatous plaque. Our data show that caveolin-1 is able to interact with both sterols. This might have consequences for sterol transport and the signalling properties of cells during atherosclerosis.

Blotting, Western↗
PubMed2001

Mating in mushrooms: increasing the chances but prolonging the affair.

Finding a compatible mating partner is an essential step in the life cycle of most sexually reproducing organisms. Fungi have two or more mating types, and only cells of different mating type combine to produce diploid cells. In mushrooms, this is taken to extremes, with the occurrence of many thousands of mating types. But, having gone to such extraordinary lengths to ensure that almost any two mushroom mycelia in the wild can mate, cell fusion is not followed by nuclear fusion and true diploidy. Instead, the fused cells form a characteristic mycelium, known as the dikaryon, in which haploid nuclei are paired but actively prevented from fusing. The mating-type genes, which encode pheromones, pheromone receptors and homeodomain transcription factors, have crucial roles in regulating the complex developmental programme by which the dikaryon is formed.

Basidiomycota↗
PubMed2001

Chs1 of Candida albicans is an essential chitin synthase required for synthesis of the septum and for cell integrity.

CaCHS1 of the fungal pathogen Candida albicans encodes an essential chitin synthase that is required for septum formation, viability, cell shape and integrity. The CaCHS1 gene was inactivated by first disrupting one allele using the ura-blaster protocol, then placing the remaining allele under the control of the maltose-inducible, glucose-repressible MRP1 promoter. Under repressing conditions, yeast cell growth continued temporarily, but daughter buds failed to detach from parents, resulting in septumless chains of cells with constrictions defining contiguous compartments. After several generations, a proportion of the distal compartments lysed. The conditional Deltachs1 mutant also failed to form primary septa in hyphae; after several generations, growth stopped, and hyphae developed swollen balloon-like features or lysed at one of a number of sites including the hyphal apex and other locations that would not normally be associated with septum formation. CHS1 therefore synthesizes the septum of both yeast and hyphae and also maintains the integrity of the lateral cell wall. The conditional mutant was avirulent under repressing conditions in an experimental model of systemic infection. Because this gene is essential in vitro and in vivo and is not present in humans, it represents an attractive target for the development of antifungal compounds.

Animals↗
PubMed2001

Transcript profiling in Candida albicans reveals new cellular functions for the transcriptional repressors CaTup1, CaMig1 and CaNrg1.

The pathogenic fungus, Candida albicans contains homologues of the transcriptional repressors ScTup1, ScMig1 and ScNrg1 found in budding yeast. In Saccharomyces cerevisiae, ScMig1 targets the ScTup1/ScSsn6 complex to the promoters of glucose repressed genes to repress their transcription. ScNrg1 is thought to act in a similar manner at other promoters. We have examined the roles of their homologues in C. albicans by transcript profiling with an array containing 2002 genes, representing about one quarter of the predicted number of open reading frames (ORFs) in C. albicans. The data revealed that CaNrg1 and CaTup1 regulate a different set of C. albicans genes from CaMig1 and CaTup1. This is consistent with the idea that CaMig1 and CaNrg1 target the CaTup1 repressor to specific subsets of C. albicans genes. However, CaMig1 and CaNrg1 repress other C. albicans genes in a CaTup1-independent fashion. The targets of CaMig1 and CaNrg1 repression, and phenotypic analyses of nrg1/nrg1 and mig1/mig1 mutants, indicate that these factors play differential roles in the regulation of metabolism, cellular morphogenesis and stress responses. Hence, the data provide important information both about the modes of action of these transcriptional regulators and their cellular roles. The transcript profiling data are available at http://www.pasteur.fr/recherche/unites/RIF/transcriptdata/.

Candida albicans↗
PubMed2001

Parathyroid hyperplasia in uremic rats precedes down-regulation of the calcium receptor.

BACKGROUND: Recent evidence points to a relationship between the down-regulation of the calcium-sensing receptor (CaR) and parathyroid cell hyperplasia that is associated with chronic renal failure. It is not known, however, if down-regulation of the CaR precedes, and perhaps initiates, parathyroid cell proliferation, or if a decrease in the expression of the CaR occurs subsequently to hyperplasia or the conditions promoting it. The current study examined the temporal relationship of these two events. METHODS: Rats were made uremic by subtotal nephrectomy and were (1) placed immediately on a high phosphate (HP) diet that promotes parathyroid gland hyperplasia, or (2) maintained on a low phosphate (LP) diet that inhibits development of secondary hyperparathyroidism before being switched to the HP diet. Serum chemistries and parathyroid gland (PTG) weights were examined; CaR content and parathyroid cell proliferation (PCNA/Ki-67) were analyzed by immunohistochemistry. RESULTS: When rats were nephrectomized and placed immediately on a HP diet, parathyroid cell proliferation was significantly increased by day 2 and continued to increase at day 4. CaR content was unchanged at 1 and 2 days post-nephrectomy, but fell by day 4. When nephrectomized rats were maintained for 1 week on a LP diet, then switched to a HP diet, an increase in parathyroid cell proliferation was again seen at day 2; down-regulation of the CaR did not occur until after 7 days of uremia and the HP diet. CONCLUSION: These data indicate that parathyroid cell hyperplasia precedes down-regulation of CaR expression in the uremic rat model.

Animals↗
PubMed2001

p21(WAF1) and transforming growth factor-alpha mediate dietary phosphate regulation of parathyroid cell growth.

BACKGROUND: The parathyroid (PT) hyperplasia induced by renal failure can be further enhanced by high dietary phosphate (P) or completely abolished by P restriction. To identify potential mechanisms mediating these opposing effects of dietary P on PT growth, this study first focused on p21(WAF1) (p21) because high P reduces while low P enhances serum 1,25-dihydroxyvitamin D, whose potent antiproliferative properties result from the induction of p21. In addition to reducing p21, high P-induced PT growth could result from increased PT expression of the growth promoter transforming growth factor-alpha (TGF-alpha), known to be elevated in hyperplastic and adenomatous human PT glands. METHODS: The time course for dietary P regulation of PT expression of TGF-alpha and p21 was assessed for seven days after 5/6 nephrectomy in rats and correlated with the degree of PT hyperplasia and secondary hyperparathyroidism. RESULTS: In P-restricted 5/6 nephrectomized rats, PT-p21 mRNA and protein increased by day 2, independent of changes in serum 1,25-dihydroxyvitamin D, and remained higher than in the high P counterparts for up to seven days. The PT hyperplasia of the high P group could not be attributed to a reduction of PT-p21 expression from normal control values. Instead, PT-TGF-alpha protein was higher in uremic rats compared with normal controls and increased further with high dietary P intake. PT levels of proliferating cell nuclear antigen (PCNA), an index of cell mitoses, correlated inversely with p21 and directly with TGF-alpha. Consistent with these findings, PT gland size and serum PT hormone levels, similar in both dietary groups at day 2, were higher in the high P group by day 5. Induction of p21 by low P and of TGF-alpha by high P was specific for the PT glands. Dietary P had no effect either on intestinal growth or p21 or TGF-alpha protein content. CONCLUSIONS: These findings suggest that low P induction of p21 could prevent PT hyperplasia in early uremia, whereas high P enhancement of TGF-alpha may function as an autocrine signal to stimulate growth further.

Animals↗
PubMed2001

Therapeutic uses of vitamin D analogues.

The vitamin D endocrine system has been implicated in numerous biological activities throughout the body. The breadth and magnitude of vitamin D activity suggest potential therapeutic applications for the treatment of several diseases and disorders, including hyperproliferative diseases, immune dysfunction, endocrine disorders, and metabolic bone diseases. However, therapy using natural vitamin D hormone, 1,25-dihydroxyvitamin D(3) (1,25[OH](2)D(3)) has been precluded in most cases because of the potent calcemic activity shown by this hormone. Newly developed vitamin D analogues with lower calcemic activity have been shown to retain many therapeutic properties of 1,25(OH)(2)D(3). Molecular studies discussed in this article provide insights into the unique target cell specificity afforded by these analogues. In particular, the importance of the nuclear vitamin D receptor (VDR), serum vitamin D-binding protein, 24-hydroxylase, and membrane receptor is noted because analogue selectivity, specificity, and potency are afforded through their molecular interactions. The nuclear VDR has been isolated from a variety of target cells and tissues, suggesting that vitamin D compounds may have therapeutic potential throughout several body systems. Five vitamin D analogues have been approved for use in patients: calcipotriol (Dovonex; Leo Pharmaceuticals, Copenhagen, Denmark) for the treatment of psoriasis, 19-nor-1,25(OH)(2)D(2) (Zemplar; Abbott Laboratories, Abbott Park, IL) for secondary hyperparathyroidism, doxercalciferol (Hectorol; Bone Care Int, Madison, WI) for reduction of elevated parathyroid hormone levels, 22-oxacalcitriol (Maxacalcitol; Chugai Pharmaceuticals, Tokyo, Japan), and alfacalcidol. Several other analogues are currently being tested in preclinical and clinical trials for the treatment of various types of cancer and osteoporosis, as well as immunosuppression. Understanding how analogues exert their selective actions may allow for the design of more effective and safer vitamin D compounds for the treatment of a wide range of clinical disorders.

Humans↗
PubMed2001

Trans fatty acids and cholesterol metabolism: mechanistic studies in rats and rabbits fed semipurified diets.

Studies were conducted in rabbits and rats to investigate the effects of diets rich in oleic (CIS diet), palmitic (SAT diet) and trans fatty acids (TRANS diet) on plasma lipids and lipoprotein metabolism. An important difference between these species is that rabbits possess plasma cholesteryl ester transfer protein (CETP) activity while rats are devoid of transfer activity. In the presence of dietary cholesterol (0.2% w/w) the change in plasma low density lipoprotein-cholesterol (LDL-C) concentration from baseline was significantly higher in rabbits fed the TRANS diet compared with those fed the CIS diet (P < 0.01). Despite this difference, the hepatic LDL-receptor activity was similar in all groups. Also, the fatty acid composition of hepatic phospholipids was affected by diet with lower proportion of palmitic (11%) and higher (19%) linoleic acid despite a similar content in the diet. These effects may represent the maintenance of membrane fluidity within narrow limits to ensure optimal function. The studies in rats showed that the plasma total cholesterol concentration was 20% lower (P < 0.01) in TRANS-fed rats compared with those fed the CIS diet. The results of an in vivo assay of reverse cholesterol transport (RCT) suggested that the three diets gave rise to high density lipoprotein (HDL) particles with similar capacity to accept cellular cholesterol. The differential effects of dietary trans fatty acids in these animal models provide another line of evidence that reinforces the significant role of CETP activity in determining the distribution of plasma cholesterol in response to dietary trans fatty acids.

Animal Feed↗
PubMed2001

Dietary cosupplementation with vitamin E and coenzyme Q(10) inhibits atherosclerosis in apolipoprotein E gene knockout mice.

Intimal oxidation of LDL is considered an important early event in atherogenesis, and certain antioxidants are antiatherogenic. Dietary coenrichment with vitamin E (VitE) plus ubiquinone-10 (CoQ(10), which is reduced during intestinal uptake to the antioxidant ubiquinol-10, CoQ(10)H(2)) protects, whereas enrichment with VitE alone can increase oxidizability of LDL lipid against ex vivo oxidation. In the present study, we tested whether VitE plus CoQ(10) cosupplementation is more antiatherogenic than either antioxidant alone, by use of apolipoprotein E-deficient (apoE-/-) mice fed a high-fat diet without (control) or with 0.2% (wt/wt) VitE, 0.5% CoQ(10), or 0.2% VitE plus 0.5% CoQ(10) (VitE+CoQ(10)) for 24 weeks. None of the supplements affected plasma cholesterol concentrations, whereas in the VitE and CoQ(10) groups, plasma level of the respective supplement increased. Compared with control, plasma from CoQ(10) or VitE+CoQ(10) but not VitE-supplemented animals was more resistant to ex vivo lipid peroxidation induced by peroxyl radicals. VitE supplementation increased VitE levels in aorta, heart, brain, and skeletal muscle, whereas CoQ(10) supplementation increased CoQ(10) only in plasma and aorta and lowered tissue VITE: All treatments significantly lowered aortic cholesterol compared with control, but only VitE+CoQ(10) supplementation significantly decreased tissue lipid hydroperoxides when expressed per parent lipid. In contrast, none of the treatments affected aortic ratios of 7-ketocholesterol to cholesterol. Compared with controls, VitE+CoQ(10) supplementation decreased atherosclerosis at the aortic root and arch and descending thoracic aorta to an extent that increased with increasing distance from the aortic root. CoQ(10) significantly inhibited atherosclerosis at aortic root and arch, whereas VitE decreased disease at aortic root only. Thus, in apoE-/- mice, VitE+CoQ(10) supplements are more antiatherogenic than CoQ(10) or VitE supplements alone and disease inhibition is associated with a decrease in aortic lipid hydroperoxides but not 7-ketocholesterol.

Animals↗