Etudes theoriques et experimentales de structurations spatiales apparaissant dans un systeme biocatalytique compartimente

SIGLEINIST T 76380 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Multiple Steady States and Dissipative Structures in a Circular and Linear Array of Three Cells: Numerical and Experimental Approach

The steady-state behavior of a circular and linear array of three cells containing a substrate-inhibited-like kinetics catalyzed by immobilized thylakoids is studied. The photobiochemical reaction used to model the system is based on previous studies concerning a single and a two-cell system. In a general model all the cells in the array are considered to be continuously fed by the substrate and under diffusional relation with each others. Several models are then considered (circular and linear arrangements) depending upon the presence or the absence of these previous characteristics on each cell. The behavior of the various configurations is studied as a function of both the external substrate input concentration a 0, and the ratio between the transport terms λ. The results given by bifurcation analysis and limit point continuation allows to determine three domains of stable stationary behavior: I, monostability; II, bistability and multistability; III, multistability and occurrence of dissipative structures. The existence of domain III is strictly dependent on the existence of a topological and functional symmetry in the arrangement. The experimental occurrence of both stable symmetric and asymmetric steady states in a circular and linear array of cells is also illustrated. © 1991 American Institute of Physics.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Long-term ethanol consumption impairs reverse cholesterol transport function of high-density lipoproteins by depleting high-density lipoprotein sphingomyelin both in rats and in humans

Moderate alcohol consumption has been linked to lower incidence of coronary artery disease due to increased plasma high-density lipoprotein (HDL), whereas heavy drinking has the opposite effect. Because of the crucial role of HDL in reverse cholesterol transport and positive correlation of HDL sphingomyelin (SM) content with cholesterol efflux, we have compared HDL SM content with its reverse cholesterol transport capacity both in rats fed ethanol on long-term basis and alcoholic individuals. In rats, SM HDL content was decreased in the ethanol group (−15.4%, P < .01) with a concomitant efflux decrease (−21.0%, P < .01) compared to that in controls. Similarly, HDL from the ethanol group, when compared with HDL from the control group, exhibited 13.8% (P < .05) less cholesterol uptake with control-group hepatocytes and 35.0% (P < .05) less cholesterol uptake with ethanol-group hepatocytes. Conversely, hepatocytes from the ethanol group, when compared with hepatocytes from the control group, exhibited 31.0% (P < .01) less cholesterol uptake with control-group HDL and 48.0% (P < .01) less with ethanol-group HDL. In humans, SM content in plasma HDL was also decreased in chronically alcoholic individuals without liver disease (−51.5%, P < .01) and in chronically alcoholic individuals with liver disease (−51.3%, P < .01), compared with nondrinkers. Concomitantly, in alcoholic individuals without liver disease, both efflux and uptake were decreased by 83.0% and 54.0% (P < .01), respectively, and in chronically alcoholic individuals with liver disease by 84.0% and 61.0% (P < .01), respectively, compared with nondrinkers. Based on these findings, we conclude that long-term ethanol consumption significantly impairs not only cholesterol efflux function of HDL by decreasing its SM content but also cholesterol uptake by affecting presumably hepatocyte receptors for HDL

Inverse correlation of serum paraoxonase and homocysteine thiolactonase activities and antioxidant capacity of high-density lipoprotein with the severity of cardiovascular disease in persons with type 2 diabetes mellitus

Atherosclerotic risk is increased in diabetes partly because of increased plasma levels of the oxidized low-density lipoprotein and homocysteine, 2 independent and important cardiovascular disease (CVD) risk factors. Paraoxonase (PON) is a multifunctional antioxidant enzyme component of high-density lipoprotein (HDL), which can protect against low-density lipoprotein (LDL) oxidation. It also exhibits homocysteine thiolactonase (HCTL) activity that detoxifies homocysteine thiolactone, which can damage proteins by homocysteinylation of the lysine residues, thus leading to atherosclerosis. We conducted a cross-sectional study to correlate PON-1, HCTL activities, and the lag time of LDL oxidation in 15 healthy control subjects and in 55 subjects with type 2 diabetes mellitus with different degrees of CVD. Compared with healthy controls and diabetic subjects without evidence of overt CVD, we not only found 47% (P \u3c .005) decrease in PON-1 activity, but also for the first time, 30% (P = .019) decrease in HCTL activity in subjects with a prior coronary artery bypass surgery. There was corresponding decreased effectiveness of HDLs from diabetic groups (with and without CVD) in protecting against LDL oxidation. Moreover, the PON-1 activity was significantly inversely correlated to the extent of intracoronary lesions determined at catheterization (ie, a high Gensini score). These decreases in PON-1 and HCTL activity were not due to any bias in preferential distribution of low-activity QQ homozygotes in the diabetic groups compared with the control group because QQ allele was equally distributed in all the experimental groups, whereas RR allele tended to increase in the diabetic subjects with coronary artery bypass surgery compared with the other groups. Therefore, clinical intervention to restore the impaired antiatherogenic activities of HDL should be considered an important goal in the treatment of persons with diabetes. © 2006