Abdelouahed Khalil

Signal transduction and functional changes in neutrophils with aging.

It is well known that the immune response decreases during aging, leading to a higher susceptibility to infections, cancers and autoimmune disorders. Most widely studied have been alterations in the adaptive immune response. Recently, the role of the innate immune response as a first‐line defence against bacterial invasion and as a modulator of the adaptive immune response has become more widely recognized. One of the most important cell components of the innate response is neutrophils and it is therefore important to elucidate their function during aging. With aging there is an alteration of the receptor‐driven functions of human neutrophils, such as superoxide anion production, chemotaxis and apoptosis. One of the alterations underlying these functional changes is a decrease in signalling elicited by specific receptors. Alterations were also found in the neutrophil membrane lipid rafts. These alterations in neutrophil functions and signal transduction that occur during aging might contribute to the significant increase in infections in old age.

Study of factors influencing the decreased HDL associated PON1 activity with aging.

Paraoxonase (PON1) is principally complexed to HDL and is responsible, at least in part, for its antioxidant properties. PON1 activity decreases in several pathologies associated with atherosclerosis. The aim of this study was to investigate the PON1 activity and factors influencing its activity as a function of age. One hundred and twenty nine healthy subjects aged between 22 and 89 years were recruited for the study. We found that serum PON1 activity significantly decreased with age (r=-0.38, p<0.0001) while its arylesterase activity as well as its concentration in the serum did not change significantly. HDL concentrations remained unchanged with age, however, Apo A1 concentration showed a slight negative but significant correlation with age (r=-0.19, p<0.027). Moreover, the total cholesterol concentration was positively and significantly correlated with age (r=0.40, p<0.001). Thus, our results suggest that the decrease in PON1 activity cannot be explained by the decrease in Apo A1 concentrations with age. HDL from elderly subjects was more susceptible to oxidation than HDL from young subjects measured by higher lipid peroxidation rate. Thus, the decrease in PON1 activity may contribute to this increased susceptibility of HDL to oxidation with aging. Altogether our results suggest that the decrease in PON1 activity may be related to the development of oxidative stress conditions with aging and the increased HDL susceptibility to oxidation in elderly subjects.

Effect of sarcopenia on cardiovascular disease risk factors in obese postmenopausal women.

Objective: To compare sarcopenic‐obese and obese postmenopausal women for risk factors predisposing to cardiovascular disease (CVD) and determine whether there may be a relationship between muscle mass and metabolic risk in obese postmenopausal women.

Age‐associated alterations in the recruitment of signal‐transduction proteins to lipid rafts in human T lymphocytes

Aging is associated with a decline in T cell activation and proliferation, but the underlying mechanisms are not fully understood. Recent findings suggest that lipid rafts act as a platform in the initiation of T cell activation by selectively recruiting signaling proteins associated with formation of the initial complex of signal transduction. We tested the hypothesis that lipid raft properties are altered in T lymphocytes from elderly, healthy individuals in comparison with young subjects. Results showed that the cholesterol content of lipid rafts derived from these cells was consistently higher in the case of elderly donors and that membrane fluidity was decreased. In addition, lipid rafts coalescence to the site of T cell receptor engagement was impaired in T cells from elderly donors. The recruitment of p56lck, linker of activated T cells, and their tyrosine‐phosphorylated forms to lipid rafts was decreased in activated T cells from aged individuals. CD45 was not recruited to the lipid raft fractions in either group of subjects. Our data suggest that some properties of lipid rafts are altered in aging, and this finding may be part of the causes for the decline in T cell functions that are observed in elderly individuals.

A new insight into resveratrol as an atheroprotective compound: Inhibition of lipid peroxidation and enhancement of cholesterol efflux

Resveratrol, a polyphenolic constituent of red wine, is known for its anti-atherogenic properties and is thought to be beneficial in reducing the incidence of cardiovascular diseases (CVD). However, the mechanism of action by which it exerts its anti-atherogenic effect remains unclear. In this study, we investigated the relationship between the antioxidant effects of resveratrol and its ability to promote cholesterol efflux. We measured the formation of conjugated dienes and the rate of lipid peroxidation, and observed that resveratrol inhibited copper- and irradiation-induced LDL and HDL oxidation as observed by a reduction in oxidation rate and an increase in the lag phase (p<0.05). We used DPPH screening to measure free radical scavenging activity and observed that resveratrol (0-50microM) significantly reduced the content of free radicals (p<0.001). Respect to its effect on cholesterol homeostasis, resveratrol also enhanced apoA-1-mediated cholesterol efflux (r(2)=0.907, p<0.05, linear regression) by up-regulating ABCA-1 receptors, and reduced cholesterol influx or uptake in J774 macrophages (r(2)=0.89, p<0.05, linear regression). Incubation of macrophages (J774, THP-1 and MPM) with Fe/ascorbate ion, attenuated apoA-1 and HDL(3)-mediated cholesterol efflux whereas resveratrol (0-25microM) significantly redressed this attenuation in a dose-dependent manner (p<0.001). Resveratrol thus appears to be a natural antioxidant that enhances cholesterol efflux. These properties make it a potential natural antioxidant that could be used to prevent and treat CVD.

Effects of gliclazide versus metformin on the clinical profile and lipid peroxidation markers in type 2 diabetes.

The sulfonylurea gliclazide and the biguanide metformin have different mechanisms to reduce glycemia. We performed a randomized study to compare these two agents with respect to glycemic control and effects on lipid peroxidation markers in 36 adult patients with type 2 diabetes. Both agents significantly decreased glycosylated hemoglobin ([HbA1c] P < .05), fructosamine (P < .05), and the glucose-excursion curve during the oral glucose tolerance test ([OGTT] P < .01). With regard to the insulin curve during this test, no significant change was observed with metformin and a significant increase was measured with gliclazide (P < .05). Considering the small number of events, no significant difference was detected in the number of hypoglycemic episodes between the two agents. More upper-gastrointestinal (GI) symptoms were observed with metformin compared with gliclazide (P < .05). Even with no change in the standard lipid profile, both agents increased serum vitamin E (P < .01 for gliclazide and P < .05 for metformin) and decreased the level of lipid peroxidation markers in low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles (P < .05). Despite different mechanisms of action, gliclazide and metformin demonstrated comparable levels of efficacy and complementary effects on lipid peroxidation markers.

Effect of 6 months of exercise and isoflavone supplementation on clinical cardiovascular risk factors in obese postmenopausal women: a randomized, double-blind study.

Objective:To investigate whether 6 months of exercise combined with isoflavone supplementation could improve clinical risk factors that predispose to cardiovascular disease in obese postmenopausal women. Design:This was a randomized, double-blind, controlled trial in which 50 healthy obese postmenopausal women were divided into two groups and assigned to isoflavone supplementation (n = 25) or a placebo (n = 25) for 1 year. For the last 6 months, both groups participated in an exercise program (three times per week), at the end of which cardiovascular disease risk factors were compared between groups. Body composition (using dual-energy x-ray absorptiometry), metabolic profile (blood lipids, fasting insulin, fasting glucose, sex hormone-binding globulin, C-reactive protein) were determined at baseline and at 6 and 12 months. Results:We observed a significant effect of exercise and isoflavone supplementation on body weight, total and abdominal fat mass (kilograms and percentage), body mass index, appendicular fat-free mass, fat-free mass/fat mass ratio, and sex hormone-binding globulin, but not with exercise alone. No difference was observed for other biochemical characteristics, although the quantitative insulin sensitivity check index increased equally in both groups. Conversely, although not significant, we observed a tendency for a treatment effect on body mass index (P = 0.07) and on absolute (kilograms) (P = 0.07) and percentage of (P = 0.053) abdominal fat mass, whereas no effect of treatment was found for other variables using the Mann-Whitney test. Conclusions:Compared to an aerobic exercise program alone, 70 mg/day of isoflavones combined with exercise may promote significant improvements in body composition parameters that are known to influence cardiovascular disease risk in postmenopausal women.

Dehydroepiandrosterone protects low density lipoproteins against peroxidation by free radicals produced by γ-radiolysis of ethanol–water mixtures

Oxidized low density lipoproteins (LDL) are believed to play a central role in the events that initiate atherosclerosis. Antioxidants have been shown to decrease the oxidation of LDL, leading to the diminution of atherosclerosis. Since it is well-known that decreased levels of dehydroepiandrosterone (DHEA) are linked to the development of atherosclerosis, we studied the modulation of the oxidation of LDL by DHEA. LDL were obtained from 10 healthy subjects and oxidized by free radicals produced by gamma-radiolysis of ethanol-water mixtures. The formation of conjugated dienes and thiobarbituric acid-reactive substances (TBARS), the vitamin E content, as well as the incorporation of 4-[14C]DHEA in LDL and the chemotactic effect of oxidized LDL in the presence of DHEA towards monocytes, were investigated. It was found that DHEA was able to inhibit the oxidation of LDL by reducing over 90% of the conjugated dienes and TBARS formation, as well as by reducing the vitamin E disappearance and significantly decreasing the chemotactic activity towards monocytes. Our results suggest that DHEA exerts its antioxidative effect by protecting the endogenous vitamin E of LDL.

Age-related impairment of HDL-mediated cholesterol efflux.

Our aim in this study was to investigate the effect of aging on the capacity of HDLs to promote reverse cholesterol transport. HDLs were isolated from plasma of young (Y-HDL) and elderly (E-HDL) subjects. HDL-mediated cholesterol efflux was studied using THP-1 and J774 macrophages. Our results show that E-HDLs present a lower capacity to promote cholesterol efflux than Y-HDLs (41.7 ± 1.4% vs. 49.0 ± 2.2%, respectively; P = 0.013). Reduction in the HDL-mediated cholesterol efflux capacity with aging was more significant with HDL3 than HDL2 (Y-HDL3, 57.3 ± 1% vs. E-HDL3, 50.9 ± 2%; P = 0.012). Moreover, our results show that ABCA1-mediated cholesterol efflux is the more affected pathway in terms of cholesterol-removing capacity. Interestingly, the composition and structure of HDL revealed a reduction in the phosphatidylcholine-sphingomyelin ratio (E-HDL, 32.7 ± 2.7 vs. Y-HDL, 40.0 ± 1.9; P = 0.029) and in the phospholipidic layer membrane fluidity in E-HDL compared with Y-HDL as well as an alteration in the apolipoprotein A-I structure and charge. In conclusion, our results shown that E-HDLs present a reduced capacity to promote cholesterol efflux, principally through the ABCA1 pathway, and this may explain the increase of the incidence of cardiovascular diseases observed during aging.

Increased susceptibility of low‐density lipoprotein (LDL) to oxidation by γ‐radiolysis with age

The susceptibility to oxidation of freshly isolated LDL from healthy normolipidemic individuals in three age groups was estimated by exposure of LDL to ionizing radiation followed by analyses of vitamin E, TBARS, conjugated dienes, and fluorescent products. The results clearly showed that LDL from elderly subjects was the most susceptible to oxidative damage in vitro. In particular, the greater susceptibility of LDL from elderly subjects in comparison to that from young subjects may be attributed to the much lower (4‐fold) concentration of LDL vitamin E in the elderly subjects. The present study reinforces the notion that the susceptibility of LDL to oxidation increases with age.