Age- and sex-related reference values for serum insulin concentration and its biological determinants in a French healthy population. The STANISLAS cohort

Salivary concentrations of cytokines and other analytes in healthy children

BACKGROUND

Blood has been the usual biological fluid for measuring analytes, but there is mounting evidence that saliva may be also useful for detecting cytokines in a noninvasive way. Thus, in this study we aimed to determine concentration of cytokines and other analytes in saliva from a population of healthy children.

METHODS

We collected un-stimulated whole saliva samples from clinically healthy children, and concentration of 17 cytokines and 12 other analytes were measured in supernatants. All values were adjusted by albumin content and were log-transformed before multivariate statistical analysis.

RESULTS

We included 114 children (53.5% females) between 6.0 and 11.9 years old. The highest concentrations (medians, pg/µg albumin) were seen for visfatin (183.70) and adiponectin (162.26) and the lowest for IL-13 and IL-2 (~0.003). Albumin concentration was associated with age (r_S = 0.39, p < 0.001). In the multivariate analysis, five analytes (C peptide, ghrelin, GLP-1, glucagon, leptin) inversely correlated with age and positively with height-for-age. Age was also positively associated with PAI-1, while height-for-age was also positively associated with insulin and visfatin. Finally, BMI-for-age had a positive correlation with GM-CSF and insulin.

CONCLUSIONS

Herein, we provided concentration values for 29 analytes in saliva from healthy children that may be useful as preliminary reference framework in the clinical research setting.

Metabolic actions of insulin in men and women

Insulin is an important regulator of glucose, lipid, and protein metabolism. It suppresses hepatic glucose and triglyceride production, inhibits adipose tissue lipolysis and whole-body and muscle proteolysis, and stimulates glucose uptake in muscle. In this review we discuss what is currently known about the control of substrate metabolism by insulin in men and women. The data available so far indicate that women are more sensitive to insulin with regards to glucose metabolism (both in the liver and in muscle), whereas there are no differences between men and women in insulin action on lipolysis. Potential differences exist in the regulation of plasma triglyceride concentration and protein metabolism by insulin and in changes in insulin action in response to stimuli (e.g., weight loss and exercise) that are known to alter insulin sensitivity. However, these areas have not been studied comprehensively enough to draw firm conclusions.

Lability landscape and protease resistance of human insulin amyloid: a new insight into its molecular properties

Amyloid formation is a universal behavior of proteins central to many important human pathologies and industrial processes. The extreme stability of amyloids towards chemical and proteolytic degradation is an acquired property compared to the precursor proteins and is a major prerequisite for their accumulation. Here, we report a study on the lability of human insulin amyloid as a function of pH and amyloid ageing. Using a range of methods such as atomic force microscopy, thioflavin T fluorescence, circular dichroism, and gas-phase electrophoretic mobility macromolecule analysis, we probed the propensity of human insulin amyloid to propagate or dissociate in a wide span of pH values and ageing in a low concentration regime. We generated a three-dimensional amyloid lability landscape in coordinates of pH and amyloid ageing, which displays three distinctive features: (i) a maximum propensity to grow near pH 3.8 and an age corresponding to the inflection point of the growth phase, (ii) an abrupt cutoff between growth and disaggregation at pH 8-10, and (iii) isoclines shifted towards older age during the amyloid growth phase at pH 4-9, reflecting the greater stability of aged amyloid. Thus, lability of amyloid strongly depends on the ionization state of insulin and on the structure and maturity of amyloid fibrils. The stability of insulin amyloid towards protease K was assessed by using real-time atomic force microscopy and thioflavin T fluorescence. We estimated that amyloid fibrils can be digested both from the free ends and within the length of the fibril with a rate of ca 4 nm/min. Our results highlight that amyloid structures, depending on solution conditions, can be less stable than commonly perceived. These results have wide implications for understanding the propagation of amyloids via a seeding mechanism as well as for understanding their natural clearance and dissociation under solution conditions unfavorable for amyloid formation in biological systems and industrial applications.

The STANISLAS Cohort: a 10-year follow-up of supposed healthy families. Gene-environment interactions, reference values and evaluation of biomarkers in prevention of cardiovascular diseases

The description of this familial longitudinal cohort was published in this journal 10 years ago, in 1998. To date, 117 publications on the STANISLAS Cohort (SC) have appeared, corresponding to five main categories of results: familial resemblance and heritability; genetics and gene-environment interactions; mRNA and proteins as gene products; reference values and biological variations of proteins; and finally preventive medicine and prepathological epidemiological data. More than 600 data values on demographic and laboratory data have been collected on each individual taking part out of the 1006 families at the beginning and for all three recruitments. Serum and plasma are stored in liquid nitrogen for all participants for all three recruitments. DNA has been extracted from all participants and mRNA from 357 families. They are stored at -80 degrees C. Owing to the SC study, heritability and many gene-environment interactions have been described. The expression of 166 genes related to cardiovascular diseases was measured in peripheral blood mononuclear cells RNA. Reference values for proteins and vitamins have been established in addition to reference values for the carotid and femoral intima media thickness in adults and children. The data obtained contribute to a better understanding of the relation between the studied polymorphisms (161 polymorphic sites) and health, and predisposition to obesity, high blood pressure and metabolic syndrome. To the best of our knowledge, the SC study is internationally the only longitudinal family cohort of subjects who are presumed to be healthy, which enables the study of the chain DNA-RNA-proteins.

Assay-dependent variability of serum insulin levels during oral glucose tolerance test: influence on reference intervals for insulin and on cut-off values for insulin sensitivity indices

BACKGROUND

The oral glucose tolerance test (oGTT) is the most common method to estimate indices of insulin sensitivity in clinical as well as in epidemiological studies. The aim of this study was to investigate the variability of insulin levels for reference intervals and of insulin sensitivity indices during oGTT by three different insulin immunoassays.

METHODS

Serum insulin levels were determined during oGTT of randomly selected adult subjects (total n=101, with n=68 with normal glucose tolerance) by the LIAISON (LIA), the Elecsys (EL) and the AutoDELFIA (AD) method.

RESULTS

Sensitivity and precision of all three insulin assays were comparable. Insulin levels demonstrated a close (p<0.001) interassay correlation (LIA vs. EL: r=0.987, LIA vs. AD: r=0.966, EL vs. AD: r=0.965). Insulin levels and insulin sensitivity indices (n=68) of the AD method were significantly different compared to the LIA or EL assay (p<0.001). Basal insulin levels demonstrated an assay-dependent significant body mass index (BMI) dependency (LIA: r=0.24, p=0.05; AD: r=0.44, p<0.001; EL: r=0.36, p<0.01) in the regression analysis. At 120 min post glucose, gender was the relevant influencing factor on insulin levels of the LIA (r=0.40, p<0.001), AD (r=0.37, p<0.01) and EL (r=0.40 p<0.001) method.

CONCLUSIONS

We conclude that assay-dependent reference intervals should be used for the clinical interpretation of insulin levels from oGTT and of insulin sensitivity indices. Moreover, BMI and gender have to be considered as influencing factors.

[The HOMA and QUICKI indexes, and insulin and C-peptide levels in healthy children. Cut off points to identify metabolic syndrome in healthy children]

OBJECTIVE

The aim of this study was to establish the reference values of the Homeostasis Model Assessment (HOMA) and Quantitative Insulin Sensitivity Check (QUICKI) indexes, as well as those of insulin and C-peptide levels in healthy children and adolescents with a view to determining reference percentiles to detect those at cardiovascular risk.

MATERIAL AND METHODS

A total of 372 children boys and girls of different ages and at distinct pubertal stages with normal body mass index participated in the study. Fasting glucose, insulin and C-peptide values were measured by chemiluminescence and the HOMA and QUICKI indexes were calculated.

RESULTS

Fasting glucose levels were normal in all children. The mean values obtained for each variable were (mean (SD)): fasting glucose 87(7.75) mg/dL, insulin 7.74 (5.35) microU/mL, C-peptide: 1.76 (0.79) ng/mL, HOMA index 1.72 (1.27) and QUICKI index 0.72 (0.29). All the variables progressively increased with age, with statistically significant differences between prepubertal and pubertal children. The QUICKI index showed an inverse relationship. In addition, significant differences were found between sexes. The 90th percentile for all the variables was as follows: insulin 15.05 microU/mL, C-peptide: 2.85 ng/mL, HOMA index 3.43 and QUICKI index 1.10.

CONCLUSIONS

Values of fasting glucose, insulin, C-peptide and the HOMA index significantly increased with age and pubertal stage, while the QUICKI index decreased. We defined the 90th percentile for all the parameters studied as the cut-off point to identify children at cardiovascular risk in our population.

Insulin resistance: sex matters

PURPOSE OF REVIEW

This review summarizes recent advances in our understanding of the differences between the sexes in relation to insulin resistance. Alterations in the body's sensitivity to insulin cause a series of metabolic abnormalities representing essentially the metabolic syndrome (i.e. high fasting plasma triglyceride and glucose and low HDL-cholesterol concentrations, hypertension, abdominal obesity) and type 2 diabetes. Although our knowledge of the causes and consequences of impairments in the insulin signaling pathway at the metabolic, cellular and molecular level has progressed rapidly and continues to do so, serious attempts to discover whether and how sex affects the metabolic control by insulin has only recently started to evolve.

RECENT FINDINGS

The most significant recent findings include data that suggest that females are intrinsically more insulin resistant than males, possibly because of specific sex-linked gene expression and the resulting differences in metabolic control elements (e.g. signaling pathway and substrate shuttling elements, receptors). Sex hormones, environmental and life-style factors augment or improve the female 'genetic' disadvantage, in ways that are possibly also genetically predetermined.

SUMMARY

Women are distinctly different to men with regard to the actions of insulin, the susceptibility to develop insulin resistance, and the response to stimuli that are known to enhance or impair sensitivity to the effects of insulin. Therefore, sex has to be considered when investigating insulin action, metabolic pathways known to be affected by the actions of insulin and diseases that result from abnormalities in insulin action and their treatment.

A prospective study on the prevalence of metabolic syndrome among healthy french families: two cardiovascular risk factors (HDL cholesterol and tumor necrosis factor-alpha) are revealed in the offspring of parents with metabolic syndrome

OBJECTIVE

The purpose of this study was to estimate the longitudinal variation of prevalence of metabolic syndrome within French families and to observe biological parameters involved in cardiovascular disease among their offspring.

RESEARCH DESIGN AND METHODS

Three hundred seventy-one apparently healthy families (1,366 individuals) taken from the STANISLAS cohort were studied. The subjects were examined at two time points with a 5-year interval (t(0) and t(+5)). The crude prevalence of metabolic syndrome was assessed among parents according to the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP) definition.

RESULTS

The prevalence of metabolic syndrome was 5.9% in men and 2.1% in women at t(0), rising to 7.2 and 5.4% in men and women, respectively, at t(+5). Children of parents having metabolic syndrome showed higher levels of tumor necrosis factor-alpha (TNF-alpha), whereas their HDL cholesterol and apolipoprotein (apo) E concentrations were lower compared with those of age- and sex-matched control subjects (P </= 0.05). When applying NCEP ATP definitions that included either antihypertensive drugs only or all the drugs involved in metabolic syndrome, we found that the three parameters shared by the three different versions of the definition were TNF-alpha, HDL cholesterol, and an interaction between alcohol consumption and parental metabolic syndrome on HDL cholesterol concentration.

CONCLUSIONS

Metabolic syndrome increases with age in supposedly healthy families from the STANISLAS cohort. In offspring of affected people, it seems to be predictive of higher values of TNF-alpha and low HDL cholesterol levels, which are two major cardiovascular factors. Therefore, in terms of prevention, it is important to identify and follow subjects with metabolic syndrome as well as their offspring, even in apparently healthy populations, to enable early disease management.