Biomedical subjects

Andrew Jenner

Publications and source records attributed to Andrew Jenner.

10 recordsLinked to original sources

PubMed2006

Zinc supplementation decreases the development of atherosclerosis in rabbits.

Developing atherosclerotic plaques in cholesterol-fed rabbits are enriched in iron but depleted in zinc. In order to examine further the role of zinc, New Zealand White rabbits were fed a high-cholesterol 1% (w/w) diet with zinc (1 g/kg) supplementation for 8 weeks. After the 8-week period, the average atherosclerotic lesion cross-sectional areas in the aortas of the animals fed with the zinc supplement were significantly decreased (1.0 mm2) compared with lesion areas of the animals fed only on the high-cholesterol diet (3.1 mm2). Using nuclear microscopy, a technique for mapping and measuring trace elements in tissue sections, lesion zinc levels (24 ppm) were observed to be unchanged in the zinc-fed rabbits compared to controls. However, average lesion Fe levels in the zinc-fed group were measured at 32 ppm, whereas in the control group the average Fe levels were significantly higher at 43 ppm (P = 0.03). Our data support the concept that zinc may have an antiatherogenic effect by decreasing iron levels in the lesion, possibly leading to inhibition of iron-catalyzed free radical reactions.

Animals↗

PubMed2006

Potential artifacts in the measurement of DNA deamination.

Attack on DNA by some reactive nitrogen species results in deamination of adenine and guanine, leading to the formation of hypoxanthine and xanthine, respectively. Published levels of these products in cellular DNA have varied widely. Although these two deamination products are often measured by GC-MS analysis, the procedure of acid hydrolysis to release DNA bases for derivatization poses a risk of artifactual deamination of the DNA. In this study, we demonstrated the artifactual formation of these two deamination products during acid hydrolysis and hence developed a method for detecting and measuring 2'-deoxyinosine, the nucleoside of hypoxanthine. Our assay for 2'-deoxyinosine employs nuclease P1 and alkaline phosphatase to achieve release of the nucleosides from DNA, followed by HPLC prepurification with subsequent GC-MS analysis of the nucleosides. This assay detected an increase in the levels of 2'-deoxyinosine in DNA when commercial salmon testis DNA was treated with nitrous acid. We also used it to measure levels in various rat tissues of both normal and endotoxin-treated rats, but could not find increased 2'-deoxyinosine formation in tissues even though *NO production was substantially increased.

Amination↗

PubMed2005

Health promotion by flavonoids, tocopherols, tocotrienols, and other phenols: direct or indirect effects? Antioxidant or not?

Foods and beverages rich in phenolic compounds, especially flavonoids, have often been associated with decreased risk of developing several diseases. However, it remains unclear whether this protective effect is attributable to the phenols or to other agents in the diet. Alleged health-promoting effects of flavonoids are usually attributed to their powerful antioxidant activities, but evidence for in vivo antioxidant effects of flavonoids is confusing and equivocal. This may be because maximal plasma concentrations, even after extensive flavonoid intake, may be low (insufficient to exert significant systemic antioxidant effects) and because flavonoid metabolites tend to have decreased antioxidant activity. Reports of substantial increases in plasma total antioxidant activity after flavonoid intake must be interpreted with caution; findings may be attributable to changes in urate concentrations. However, phenols might exert direct effects within the gastrointestinal tract, because of the high concentrations present. These effects could include binding of prooxidant iron, scavenging of reactive nitrogen, chlorine, and oxygen species, and perhaps inhibition of cyclooxygenases and lipoxygenases. Our measurements of flavonoids and other phenols in human fecal water are consistent with this concept. We argue that tocopherols and tocotrienols may also exert direct beneficial effects in the gastrointestinal tract and that their return to the gastrointestinal tract by the liver through the bile may be physiologically advantageous.

Antioxidants↗

PubMed2005

Human fecal water inhibits COX-2 in colonic HT-29 cells: role of phenolic compounds.

The inducible enzyme cyclooxygenase-2 (COX-2) plays a major role in the regulation of inflammation and possibly in the development of colon cancer. The aim of the present study was to screen for COX-2 inhibitors in samples of fecal water (the aqueous phase of feces) and investigate whether phenolic compounds are responsible for any observed effects on COX-2. Volunteers (n = 20) were recruited and asked to supply a 24-h stool sample. Fecal water samples were prepared and analyzed by GC-MS for their content of phenolic compounds. These samples were also evaluated for their effects on COX-2 protein levels (Western blot) and prostaglandin (PG)E2 production in tumor necrosis-alpha-stimulated HT-29 cells and pure enzymatic activity in a COX-2-catalyzed prostaglandin biosynthesis in vitro assay. The major phenolic compounds identified were phenylpropionic acid, phenylacetic acid, cinnamic acid, and benzoic acid derivatives. Of 13 fecal water samples analyzed, 12 significantly decreased PGE2 production (range 5.4-39.7% inhibition, P-value < 0.05) compared with control cells and 13 of 14 samples analyzed decreased COX-2 protein levels in HT-29 cells (19-63% inhibition). Of the 20 fecal water samples, 2 also weakly inhibited enzymatic activity of purified COX-2 (22-24% inhibition). Three compounds identified in fecal water, 3-phenylpropionic acid, 3-hydroxyphenylacetic acid, and 3-(4-hydroxyphenyl)-propionic acid, decreased the protein level at 250 micromol/L (15-62% inhibition). This study shows for the first time that human fecal water contains components that can affect both the COX-2 protein level and enzymatic activity.

Colonic Neoplasms↗

PubMed2005

Oxidative damage in mitochondrial DNA is not extensive.

Since 1988 several research groups have reported greater levels of oxidative damage in mitochondrial DNA than in nuclear DNA, while others have suggested that the greater damage in mtDNA might be due to artifactual oxidation. The popular theory that mtDNA is more heavily damaged in vivo than nDNA does not stand on firm ground. Using an improved GC-MS method and pure mtDNA, our analyses revealed that the damage level in mtDNA is not higher, and may be somewhat lower, than that in nDNA.

Animals↗

PubMed2004

Characterization of antioxidant and antiglycation properties and isolation of active ingredients from traditional chinese medicines.

There is considerable interest in the isolation of more potent antioxidant compounds to treat diseases involving oxidative stress. Thirty-three traditional Chinese medicine (TCM) extracts were examined for their antioxidant activity using the 2,2'-azinobis[3-ethylbenzothiazoline-6-sulfonate] (ABTS) assay. Five extracts with high activity (Cratoxylum cochinchinense, Cortex magnoliae officinalis, Psoralea corylifolia L, Curculigo orchioides Gaertn, and Glycyrrhiza uralensis Fisch.) were selected for further characterization. C. cochinchinense outperformed other extracts in most of the assays tested except phospholipid peroxidation inhibition, where P. corylifolia L showed higher activity. C. cochinchinense was particularly potent in inhibiting the formation of advanced glycation end products on proteins and strongly inhibited hypochlorous acid-induced DNA damage. We attempted to isolate the active ingredients from C. cochinchinense and obtained an extract (YCT) containing at least 90% mangiferin as identified by HPLC and mass spectrometry. However, YCT showed significantly higher activity in assays of phospholipid peroxidation, inhibition of protein glycation, and superoxide (O(2)(?-)) and peroxynitrite (ONOO(-)) scavenging, as compared with mangiferin, suggesting that the nonmangiferin constituents of YCT contribute to its additional antioxidant activities.

Antioxidants↗

PubMed2004

Mechanism of cell death induced by an antioxidant extract of Cratoxylum cochinchinense (YCT) in Jurkat T cells: the role of reactive oxygen species and calcium.

YCT is a semipurified extract from Cratoxylum cochinchinense that has antioxidant properties and contains mostly mangiferin. We show here that YCT is selectively toxic to certain cell types and investigate the mechanisms of this toxicity in Jurkat T cells. By flow cytometric analyses, we show that YCT causes intense oxidative stress and a rise in cytosolic Ca(2+). This is followed by a rise in mitochondrial Ca(2+), release of cytochrome c, collapse of Deltapsi(m), a fall in ATP levels, and eventually cell death. The mechanism(s) of intense oxidative stress may involve a plasma membrane redox system, as cell death is inhibited by potassium ferricyanide. Cell death has some features of apoptosis (propidium iodide staining, externalization of phosphatidylserine, limited caspase-3 and -9 activities), but there was no internucleosomal DNA fragmentation.

Adenosine Triphosphate↗

PubMed2004

Increased iron staining in the cerebral cortex of cholesterol fed rabbits.

The link between hypercholesterolemia and neuronal damage is not clear. In the present study, we studied some of the possible effects of hypercholesterolemia on the brain, using the cholesterol fed New Zealand White rabbit as a model. An increase in the number of iron positive cells (i.e. oligodendrocytes) was observed in the brain parenchyma, in rabbits treated with a high cholesterol diet for 8 weeks. At this time, no neuronal death was observed, indicating that the increased iron did not occur as a consequence of neuronal injury. No heme oxygenase-1 (HO-1) or bilirubin immunoreactivity was observed in the brains in these rabbits, indicating that the iron accumulation did not occur as a consequence of increased breakdown of heme. It is postulated that cholesterol could have subtly damaged brain endothelial cells, resulting in increased iron transport across brain endothelial cells. Hypercholesterolaemia is known to be associated with increased plasma lipid peroxidation which might contribute to such damage.

Animals↗

PubMed2004

Do mitochondria make nitric oxide? no?

Several papers have claimed that mitochondria contain nitric oxide synthase (NOS) and make nitric oxide (NO*) in amounts sufficient to affect mitochondrial respiration. However, we found that the addition of L-arginine or the NOS inhibitor L-NMMA to intact rat liver mitochondria did not have any effect on the respiratory rate in both State 3 and State 4. We did not detect mitochondrial NO* production by the oxymyoglobin oxidation assay, or electrochemically using an NO* electrode. An apparent NO* production detected by the Griess assay was identified as an artifact. NO* generated by eNOS added to the mitochondria could easily be detected, although succinate-supplemented mitochondria appeared to consume NO*. Our data show that NO* production by normal rat liver mitochondria cannot be detected in our laboratory, even though the levels of production claimed in the literature should easily have been measured by the techniques used. The implications for the putative mitochondrial NOS are discussed.

Animals↗

PubMed2002

Loss of oxidized and chlorinated bases in DNA treated with reactive oxygen species: implications for assessment of oxidative damage in vivo.

Oxidative damage to DNA has been reported to occur in a wide variety of disease states. The most widely used "marker" for oxidative DNA damage is 8-hydroxyguanine. However, the use of only one marker has limitations. Exposure of calf thymus DNA to an .OH-generating system (CuCl(2), ascorbate, H(2)O(2)) or to hypochlorous acid (HOCl), led to the extensive production of multiple oxidized or chlorinated DNA base products, as measured by gas chromatography-mass spectrometry. The addition of peroxynitrite (ONOO(-)) (<200 microM) or SIN-1 (1mM) to oxidized DNA led to the extensive loss of 8-hydroxyguanine, 5-hydroxycytosine, 2,6-diamino-4-hydroxy-5-formamidopyrimidine, 2-hydroxyadenine, 8-hydroxyadenine, and 4,6-diamino-5-formamidopyrimidine were lost at higher ONOO(-) concentrations (>200 microM). Exposure of DNA to HOCl led to the generation of 5-Cl uracil and 8-Cl adenine and addition of ONOO(-) (<200 microM) or SIN-1 (1mM) led to an extensive loss of 8-Cl adenine and a small loss of 5-Cl uracil at higher concentrations (>500 microM). An .OH-generating system (CuCl(2)/ascorbate/H(2)O(2)) could also destroy these chlorinated species. Treatment of oxidized or chlorinated DNA with acidified nitrite (NO(2)(-), pH 3) led to substantial loss of various base lesions, in particular 8-OH guanine, 5-OH cytosine, thymine glycol, and 8-Cl adenine. Our data indicate the possibility that when ONOO(-), nitrite in regions of low pH or .OH are produced at sites of inflammation, levels of certain damaged DNA bases could represent an underestimate of ongoing DNA damage. This study emphasizes the need to examine more than one modified DNA base when assessing the role of reactive species in human disease.

Animals↗