Horm Res Paediatr. 2013;79(5):293-9. doi: 10.1159/000351012.
Indices of insulin resistance and dyslipidemia are correlated with lymphocyte proneness to apoptosis in obese or overweight low birth weight children.
Barg E, Szopa J, Pesz KA, Gąsiorowski K.
Department of Basic Medical Sciences, Wroclaw Medical University, Wroclaw Medical University, PL–50-556 Wroclaw, Poland. firstname.lastname@example.org
Aims: Our aim was to study the relationship between markers of cell proneness to apoptosis and indices of insulin resistance and dyslipidemia in children born with low birth weight (LBW).
Methods: The study comprised 177 prepubertal children stratified by birth weight and their nutritional status into LBW (n = 138) and normal birth weight (NBW; n = 39) groups. We analyzed DNA from peripheral blood lymphocytes, separated by pulsed-field gel electrophoresis (PFGE), as well as the serum levels of cholesterol, HDL-cholesterol, triglycerides, fasting insulin and glucose, caspase 3, and BCL2.
Results: LBW children with a BMI SDS >1.55 demonstrated increased content of the large fragments of the lymphocyte DNA [300-500 kb (DNA300-500 kb)] in electrophoretic slides (a marker of decreased chromatin stability and susceptibility of cells to apoptosis) compared to the NBW group. In these children the level of DNA300-500 kb exhibited a strong negative correlation with the serum level of antiapoptotic protein of BCL2 (r = -0.901). DNA300-500 kb significantly correlated with calculated indices of insulin resistance: HOMA-IR and QUICKI as well as with the indices of lipid homeostasis (Castelli and AIP).
Conclusions: Increased susceptibility of lymphocytes to apoptosis correlated with a higher risk of insulin resistance and lipid disturbance in overweight or obese LBW children. A comprehensive study of the proneness of cells to apoptosis should be implemented to further investigate the pathomechanism of the metabolic syndrome in these children.
Supplementary data and comments:
In the tested group of children born with low birth weight (<2.500g) we distinguished a subgroup of children (20.5%; n=32) who exhibited markedly higher content of the large DNA fragments (300-500 kb) in the pulsed field gel electrophoresis (PFGE) of DNA from venous blood-derived lymphocytes. In this subgroup, the indices of lipid and glucose metabolism, although did not exceed the normal rates accepted for the age range, were significantly shifted to the higher values . To quantify the shift of lipids and glucose levels we compared the median values estimated in the LBW children to those obtained in the control group (children with normal birth weight), according to the formula: τ = (Ei-Oi)2) × 100 / Ei; where Ei = median in control group NBW and Oi = median in LBW subgroup A or B; (LBW A – children without increase of the 300-500 kb fragments in PFGE, LBW B – children with increased content of the 300-500 kb fragments, higher than 35% of the total separated DNA). Calculated statistical distance (τ) of the results obtained in LBW subgroups to those estimated in the control group were given in Table 1.
In the subgroup of children who exhibited high content of DNA300-500 kb fragments in PFGE electrophoresis (LBW B) the results of lipid and glucose parameters were more distant to those obtained in the control group,, when compared with children who did not reveal elevated content of the DNA fragments (LBW A), and the total sum of the statistical distances was 3.05 times as high in LBW B as in LBW A subgroup. It suggests significantly higher probability for the LBW B children to expand future metabolic disturbances, which eventually could lead to development of the metabolic syndrome.
It should be indicated that the values of glucose metabolism indices were markedly distant to those in the control group, both in LBW A and LBW B subgroups, which indicates that both subgroups of children born with low birth weight could reveal future glucose metabolism disturbance. Nevertheless LBW B subgroup children were significantly (2.56 times) more prone to glucose metabolism disorders. In the case of serum lipid concentration the sum of the statistical distances in LBW B children showed that the median of the results was shifted to the higher values, whereas in LBW A subgroup the medians were shifted to slightly lower values when compared to the control group. It indicates that LBW B children exhibited moderately elevated susceptibility to expand future lipid metabolism disturbances. In contrast, LBW A children did not reveal such a risk, and their lipid values were even slightly lower than those estimated in the control group.
In conclusion, analysis of the content of the DNA300-500 kb fragments in PFGE electrophoresis of venous blood-derived lymphocytes let us distinguish in the group of children born with low birth weight the subpopulation LBW B, children with increased content of the fragments in PGFE and with significantly higher risk of future development of glucose metabolism disorders and also with slightly elevated risk of lipid metabolism disturbances.
Elevated content of the DNA300-500 kb fragments in pulsed field gel electrophoresis (PFGE) reflects decreased stability of chromatin. In such case the cells were more susceptible to damages caused by various unfavorable conditions, both endogenous and exogenous, such as free radical and metabolic stress. These large DNA fragments, although relatively quickly repaired, were precisely recognized by cellular systems of surveillance on genome stability. Among them the p53 protein is an important player in regulation of DNA synthesis, DNA repair, cell cycle regulation, and induction of cell death by apoptosis. Recently, the important function of p53 in modulation of cellular metabolic homeostasis has emerged . By activation of its target transcription genes, p53 contributes to the regulation of glycolysis, oxidative phosphorylation, insulin sensitivity, and fatty acid oxidation . Since the effect of p53 on glucose metabolism is opposite to the effects of insulin, it could be pointed out that p53 evokes insulin resistance condition . Also p53 plays a major role in transcriptional activation of genes that participate in lipid metabolism, thereby it leads to enhanced lipid catabolism while decreased anabolism of intracellular lipids . Importantly, p53 exerts significant impact on intracellular sphingolipid metabolism and conducts to elevated intracellular concentration of ceramide [4, 5]. Ceramide enhances insulin resistance by inhibition of insulin receptor and insulin receptor transduction pathways, and intracellular accumulation of ceramide could induce an apoptosis [4-6].
We previously noted significantly higher frequency of apoptosis in lymphocytes from venous blood of LBW children cultured in vitro in restricted nutritional conditions . Enhanced cell apoptosis probably had existed also in vivo, since lowered counts of lymphocytes were estimated in blood smears in LBW B children . The results of metabolic disturbances in LBW children were in accordance with the concept of moderate, frequent stimulation of the p53 expression and function by increased content of DNA300-500 kb fragments. This incrementally moves glucose and lipid metabolism to insulin resistance condition and ultimately turns the metabolic disturbances towards development of the metabolic syndrome.
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Table 1. Comparison of the median values of selected lipids concentration and glucose metabolism indices between children from LBW and NBW groups.
LBW – children born with low body weight
LBW A – children without increased content of the DNA300-500 kb fragments in pulsed
field electrophoresis of lymphocyte DNA
LBW B – children with increased content of the DNA300-500 kb fragments in pulsed
field electrophoresis of lymphocyte DNA.