Mohamed Lemdani

Daily melatonin supplementation in mice increases atherosclerosis in proximal aorta.

Considerable evidence supports the hypothesis that LDL oxidation plays an important role in atherosclerosis. Even though high melatonin doses inhibit LDL oxidation in vitro, the effect of melatonin on atherosclerosis has never been studied. We have demonstrated that the feeding of hypercholesterolemic mice with an atherogenic diet supplemented with melatonin highly increases the surface of atherosclerotic lesions in the proximal aorta. These observations occur without detectable lipidic or glucidic phenotype alteration. Melatonin treatment increased highly the sensitivity of atherogenic lipoprotein to Cu(2+) and gamma-radiolysis generated oxyradical ex vivo oxidation during the fasting period. Moreover, these altered lipoproteins were less recognized by the LDL receptor metabolic pathway of murine fibroblasts while they transferred many more cholesteryl esters to murine macrophages. This study suggests that caution should be taken as regards high melatonin dosage in hypercholesterolemic patients.

Body mass index and childhood obesity classification systems: A comparison of the French, International Obesity Task Force (IOTF) and World Health Organization (WHO) references

AIMnThis study aims to compare three body mass index (BMI)-based classification systems of childhood obesity: the French, the International Obesity Task Force (IOTF) and the World Health Organization (WHO) references.nnnMETHODSnThe study involved 1382 schoolchildren, recruited from the Lille Academic District in France in May 2009 aged 8.4±1.7 years (4.0-12.0 years). Their mean height and body mass were 131.5±10.9cm and 30.7±9.2kg, respectively, resulting in a BMI of 17.4±3.2kg/m(2). The weight status was defined according to the three systems considered in this study. The agreement between these references was tested using the Cohens kappa coefficient.nnnRESULTSnThe prevalence of overweight was higher with the WHO references (20.0%) in comparison with the French references (13.8%; P<0.0001) and the IOTF (16.2%; P≤0.01). A similar result was found with obesity (WHO: 11.6% vs. IOTF: 6.7%; or French references: 6.7%; P<0.0001). Agreement between the three references ranged from moderate to perfect (0.43≤κ≤1.00; P<0.0001). Kappa coefficients were higher when the three references were used to classify children as obese (0.63≤κ≤1.00; P<0.0001) as compared to classification in the overweight (obesity excluded) category (0.43≤κ≤0.94; P<0.0001). When sex and age categories (4-6 years vs. 7-12 years) were considered to define the overweight status, the lowest kappa coefficient was found between the French and WHO references in boys aged 7-12 years (κ=0.28; P<0.0001), and the highest one in girls aged 7-12 years between the French references and IOTF (κ=0.97; P<0.0001). As for obesity, agreement between the three references ranged from 0.60 to 1.00 (P<0.0001), with the lowest values obtained in the comparison of the WHO references against French references or IOTF among boys aged 7-12 years (κ=0.60; P<0.0001).nnnCONCLUSIONnOverall, the WHO references yield an overestimation in overweight and/or obesity within this sample of schoolchildren as compared to the French references and the IOTF. The magnitude of agreement coefficients between the three references depends on of both sex and age categories. The French references seem to be in rather close agreement with the IOTF in defining overweight, especially in 7-12-year-old children.

Asymptotic properties of a conditional quantile estimator with randomly truncated data

Let Y be a response variable that is subject to left-truncation by a variable T. We consider the problem of estimating its conditional quantile function given a vector of covariates X. We derive almost sure (a.s.) consistency and asymptotic normality results for a kernel estimate of the conditional quantile function. Simulations are drawn to illustrate the results for finite samples.

Increased susceptibility of low-density lipoprotein to ex vivo oxidation in mice transgenic for human apolipoprotein B treated with 1 melatonin-related compound is not associated with atherosclerosis progression.

Considerable evidence supports the hypothesis that LDL oxidation has an important role in atherosclerosis. It has been demonstrated that the feeding of hypercholesterolemic mice on an atherogenic diet supplemented with melatonin highly increases the surface of atherosclerotic lesions in aorta and the sensitivity of atherogenic lipoprotein to ex vivo oxidation even though high melatonin doses inhibit lipoprotein oxidation in vitro. A melatonin-related compound (DTBHB: N-[2-(5-methoxy-1H-indol-3-yl)ethyl]-3,5-di-tert-butyl-4-hydroxybenzamide) has been reported to strongly inhibit lipid peroxidation in vitro. In the present study, DTBHB treatment considerably increased the sensitivity of atherogenic lipoproteins to ex vivo oxidation but did not modify atherosclerotic lesion development in mice. Moreover, DTBHB treatment did not induce detectable lipidic alteration. These data confirm that the capacity of molecules to inhibit atherogenic lipoprotein oxidation in vitro offers no prediction of their capacity to inhibit in vivo atherosclerosis development.

Asymptotic behavior of the hazard rate kernel estimator under truncated and censored data

In this article, we give the asymptotic mean integrated squared error and the mean squared error for the kernel estimator of the hazard rate from truncated and censored data. Martingale techniques and combinatory calculus are used to obtain these results. A probability bound and the optimal bandwidth choice are also given.

Exact asymptotic -error of a kernel density estimator under censored data

In this paper, we give the exact asymptotic -error for the kernel estimator of the density function from censored data. We also give asymptotically optimal bandwidths. Strong approximation of the product-limit estimator by a Gaussian process is used to obtain the result.

On residual empirical processes of GARCH-SM models: application to conditional symmetry tests

Considering the generalized autoregressive conditionally heteroskedastic with stochastic mean (GARCH-SM) model, we establish in this article the consistency and the weak representation of a functional of its residual empirical process. Based on this result, a symmetry test for GARCH-SM model is developed. Simulations are given to show the asymptotic behaviour and normality of the test statistic. Copyright 2008 The Authors. Journal compilation 2008 Blackwell Publishing Ltd

-deficiency of the Kaplan-Meier estimator

Let X1,...,Xn,... be a sequence of independent and identically distributed random variables with distribution function F subject to random right censoring. Considering the classical Kaplan-Meier estimator and a smoothed kernel-type estimate , we prove that and (mean integrated absolute error) tend to the same constant as n goes to infinity. However, we establish that the smoothed estimator has a performance better than (for some bandwidths) what relative -deficiency is of interest. The optimal choice of the bandwidth hn, with respect to MIAE sense, is also obtained.

Exact asymptotic errors of the hazard rate kernel estimator under truncated and censored data

Abstract In this Note, we give the exact asymptotic mean integrated squared error and the mean squared error for the kernel estimator of the hazard rate from truncated and censored data. Martingale techniques and combinatory calculus are used to obtain these results. Axa0probability bound and the optimal bandwidth choice are also given.

On the Central Limit Theorem for a Conditional Mode Estimator of a Randomly Censored Time Series

In this article, we consider a kernel estimator of the conditional density function from which we derive an estimator of the conditional mode. We address the case of a randomly right-censored model when the data exhibit some kind of dependency. The conditional mode estimator is defined as the random variable that maximizes the conditional density estimator. Under classical conditions we establish a central-limit theorem for this estimator. We carry out a simulation study to illustrate our results.