Sian Astley

The effect of β-carotene supplementation on the immune function of blood monocytes from healthy male nonsmokers

Although there is strong epidemiologic evidence that diets rich in carotenoids such as beta-carotene are associated with a reduced incidence of cancer, the cellular mechanisms underlying this phenomenon remain unknown. This article describes the effect of dietary beta-carotene supplementation on both the expression of functionally associated surface molecules on human monocytes and on the secretion of the cytokine tumor necrosis factor-alpha (TNF-alpha) by monocytes, all of which are involved in the initiation and regulation of immune responses involved in tumor surveillance. A double-blind, placebo-controlled, crossover study was undertaken in which 25 healthy, adult male nonsmokers were randomly assigned to receive beta-carotene (15 mg daily) or placebo for 26 days, followed by the alternative treatment for a further 26 days. The expression of functionally related monocyte surface molecules was quantified by flow cytometry, and ex vivo secretion of TNF-alpha was quantified by an enzyme-linked immunosorbent assay, before and after each treatment period. After dietary supplementation there were significant increases in plasma levels of beta-carotene and in the percentages of monocytes expressing the major histocompatibility complex class II molecule HLA-DR and the adhesion molecules intercellular adhesion molecule-1 and leukocyte function-associated antigen-3. In addition, the ex vivo TNF-alpha secretion by blood monocytes was significantly increased after supplementation. These findings suggest that moderate increases in the dietary intake of beta-carotene can enhance cell-mediated immune responses within a relatively short period of time, providing a potential mechanism for the anticarcinogenic properties attributed to beta-carotene.

Effects of Lycopene and Lutein Supplementation on the Expression of Functionally Associated Surface Molecules on Blood Monocytes from Healthy Male Nonsmokers

It has been suggested that dietary carotenoids can enhance immune function. Supplementation with beta-carotene (15 mg daily) was previously shown to enhance human monocyte function. To examine the effect of other dietary carotenoids, two similar independent studies were done. Healthy adult male nonsmokers were randomly assigned to receive lycopene (study 1), lutein (study 2), or placebo for 26 days, followed by the alternative treatment for another 26 days. The expression of functionally related monocyte surface molecules was quantified by laser flow cytometry before and after each treatment period. There was a significant increase in plasma levels of each carotenoid following dietary supplementation, but the effects on monocyte surface molecule expression were not as striking as those observed after beta-carotene supplementation. These findings emphasize that it cannot be assumed that the effect of one carotenoid will be the same as another, even at the same level of intake.

Paraoxonase-1 (PON-1) genotype and activity and in vivo oxidized plasma low-density lipoprotein in Type II diabetes.

The HDL (high-density lipoprotein)-associated enzyme PON (paraoxonase)-1 protects LDL (low-density lipoprotein) from oxidative modification in vitro, although it is unknown if this anti-atherogenic action occurs in vivo. In a cross-sectional study of 58 Type II diabetic subjects and 50 controls, we examined the fasting plasma LDL basal conjugated diene concentration [a direct measurement of circulating oxLDL (oxidatively modified LDL)], lipoprotein particle size by NMR spectroscopy, PON-1 polymorphisms (coding region polymorphisms Q192R and L55M, and gene promoter polymorphisms -108C/T and -162G/A), PON activity (with paraoxon or phenyl acetate as the substrates) and dietary antioxidant intake. Plasma oxLDL concentrations were higher in Type II diabetic patients (males, P = 0.048; females, P = 0.009) and unrelated to NMR lipoprotein size, PON-1 polymorphisms or PON activity (with paraoxon as the substrate) in any group. In men with Type II diabetes, however, there was a direct relationship between oxLDL concentrations and PON activity (with phenyl acetate as the substrate; r = 0.611, P = 0.0001) and an atherogenic NMR lipid profile in those who were PON-1 55LL homozygotes. Circulating oxLDL concentrations in vivo were unrelated to PON-1 genotypes or activity, except in male Type II diabetics where there was a direct association between PON activity (with phenyl acetate as the substrate) and oxLDL levels. These in vivo data contrast with in vitro data, and may be due to confounding by dietary fat intake. Male Type II diabetic subjects with PON-1 55LL homozygosity have an atherogenic NMR lipid profile independent of LDL oxidation. These data do not support an in vivo action of PON on LDL oxidation.

Plasma matrix metalloproteinases, low density lipoprotein oxidisability and soluble adhesion molecules after a glucose load in Type 2 diabetes

BackgroundAcute hyperglycaemia is an independent cardiovascular risk factor in Type 2 diabetes which may be mediated through increased oxidative damage to plasma low density lipoprotein, and in vitro, high glucose concentrations promote proatherogenic adhesion molecule expression and matrix metalloproteinase expression.MethodsWe examined these atherogenic risk markers in 21 subjects with Type 2 diabetes and 20 controls during an oral 75 g glucose tolerance test. Plasma soluble adhesion molecule concentrations [E-selectin, VCAM-1 and ICAM-1], plasma matrix metalloproteinases [MMP-3 and 9] and plasma LDL oxidisability were measured at 30 minute intervals.ResultsIn the diabetes group, the concentrations of all plasma soluble adhesion molecules fell promptly [all p < 0.0001] related principally to glycaemic excursions, but such changes also occurred in the control group. Plasma MMP-3 and -9 concentrations were lower [p < 0.05], and LDL oxidisability greater [p < 0.01] in the diabetes group but did not change in either group. There was a direct relationship between plasma MMP-9 and s ICAM-1 in the controls [r = 0.62; p = 0.006] perhaps suggesting a functional relationship between s ICAM-1 shedding and MMP-9.ConclusionsA glucose load leads to a rapid fall in plasma soluble adhesion molecule concentrations in Type 2 diabetes and controls, perhaps reflecting reduced generation of soluble from membrane forms during enhanced leukocyte – endothelial adhesion or increased hepatic clearance, without changes in plasma matrix metalloproteinase concentrations or low density lipoprotein oxidisability. These in vivo findings are in contrast with in vitro data.

Increased cellular carotenoid levels reduce the persistence of DNA single-strand breaks after oxidative challenge

Dietary antioxidants, such as the carotenoids, may protect DNA from oxidative damage. This has been proposed to explain the epidemiological association between higher consumption of fruits and vegetables, which are rich in antioxidants, and lower incidence of cancer. However, this remains to be demonstrated conclusively. The effects of carotenoid supplementation on 1) baseline DNA damage, 2) susceptibility of cellular DNA to oxidative attack, and 3) DNA repair were measured in the human lymphocyte cell line Molt-17. Baseline DNA damage, susceptibility to oxidant attack (100 μmol/l H2O2 for 5 min at 4°C), and disappearance of DNA single-strand breaks (SSB) after oxidative challenge were monitored by single-cell gel electrophoresis. DNA repair patch synthesis activity in cell extracts was determined using assays that measure nucleotide incorporation during repair of oxidative lesions in template DNA. Unlike single-cell gel electrophoresis, the parameters measured with these assays are not dependent on strand break religation. There was no evidence that β-carotene, lutein, or β-cryptoxanthin supplementation protected cellular DNA from oxidation under basal conditions or after oxidative challenge. However, only carotenoid-supplemented cells exhibited a significant decrease in numbers of SSB over a 2-h period after treatment with H2O2. Carotenoid supplementation did not provoke any detectable change in repair patch synthesis activity. We conclude that supplementation with carotenoids at 8 μmol/l does not provide significant antioxidant protection for DNA in Molt-17 lymphocytes but may enhance recovery of cells from oxidative challenge, as measured by loss of SSB. We argue that these data are most consistent with carotenoids acting to enhance DNA strand break repair.