Adipose tissue development "in utero". Relationships between some nutritional and hormonal factors and body fat mass enlargement in newborns

Human Placental Lactogen in Relation to Maternal Metabolic Health and Fetal Outcomes: A Systematic Review and Meta-Analysis

Human placental lactogen (hPL) is a placental hormone which appears to have key metabolic functions in pregnancy. Preclinical studies have putatively linked hPL to maternal and fetal outcomes, yet-despite human observational data spanning several decades-evidence on the role and importance of this hormone remains disparate and conflicting. We aimed to explore (via systematic review and meta-analysis) the relationship between hPL levels, maternal pre-existing and gestational metabolic conditions, and fetal growth. MEDLINE via OVID, CINAHL plus, and Embase were searched from inception through 9 May 2022. Eligible studies included women who were pregnant or up to 12 months post-partum, and reported at least one endogenous maternal serum hPL level during pregnancy in relation to pre-specified metabolic outcomes. Two independent reviewers extracted data. Meta-analysis was conducted where possible; for other outcomes narrative synthesis was performed. 35 studies met eligibility criteria. No relationship was noted between hPL and gestational diabetes status. In type 1 diabetes mellitus, hPL levels appeared lower in early pregnancy (possibly reflecting delayed placental development) and higher in late pregnancy (possibly reflecting increased placental mass). Limited data were found in other pre-existing metabolic conditions. Levels of hPL appear to be positively related to placental mass and infant birthweight in pregnancies affected by maternal diabetes. The relationship between hPL, a purported pregnancy metabolic hormone, and maternal metabolism in human pregnancy is complex and remains unclear. This antenatal biomarker may offer value, but future studies in well-defined contemporary populations are required.

Transferred maternal fatty acids stimulate fetal adipogenesis and lead to neonatal and adult obesity

The prevalence of adult and childhood obesity are increasing. Most of the human newborn's body fat accumulates in the last half of intrauterine life. Fat in the fetus was thought to be mostly synthesized from glucose, but now it is commonly accepted that the bulk of it is the product of placental transfer of maternal fatty acids. Transported fatty acids originate in maternal plasma "free" fatty acids, fatty acids hydrolyzed from maternal plasma triglycerides, and the poly-unsaturated fatty acid component of maternal phospholipids. Glucose remains an important precursor of alpha-glycerol phosphate, to which most transported fatty acids are eventually esterified. Maternal plasma lipids are elevated in late pregnancy and even more in obese and diabetic pregnant women. This accelerates the placental transport of fatty acids. The hypothesis presented in this paper rests on the observations that the exponential increase in fat tissue in the human embryo's body occurs in time to parallel the increase of lipids in the mother's blood and depends on the chemical affinity of the transcription factor PPAR gamma to fatty acids and on fatty acid stimulation of adipocyte generation from precursor cells. The hypothesis asserts that transported maternal fatty acids activate the transcription factors in the fetus and initiate conversion of the mesenchymal stem cells into adipocytes. In obese and diabetic mothers, the higher plasma lipids facilitate increased placental fatty acid transfer. This will increase adipocyte generation and, through this, the prevalence of babies with increased fat cell size and number. Babies born with increased adipose tissue cellularity will have greater probability of growing up to become obese adolescents and adults. These newborns, whose obesity is hyperplastic as well as hypertrophic, as adults will have difficulty losing weight through diet and exercise or will regain the lost weight more quickly than others without these characteristics. Accordingly, increased placental fatty acid transfer and accelerated adipocyte generation may explain not only neonatal obesity, but some aspects of the adult obesity epidemic also. It is therefore recommended that prevention of fetal fat cell hyperplasia, by lowering maternal plasma lipids in mid and late pregnancy, should be attempted in pregnancies at risk for macrosomia.

Adipocytes and adipose tissue

An epidemic of obesity is taking place in most societies around the world. Overall obesity substantially increases the risk of subsequent morbidity. In children and adolescents the degree of body fat mass depends upon ethnic background, gender, developmental stage and age. Obesity is characterized by increases in the number or size of fat cells, or a combination of both. It is generally believed that the number of fat cells depends on age of onset and degree of obesity. This chapter provides information on intrauterine growth of fetal adipose tissue, the earliest period of onset of proliferation, and some of the factors that interact to enhance or suppress development. Fetal adipose tissue development is regulated by the complex interaction of transcription factors, nutrients and adipocytokines. Maternal, endocrine, and paracrine factors also influence specific changes in angiogenesis, adipogenesis, and metabolism. During embryogenesis and in fetal life, leptin and adiponectin, two important adipocytokines, are present at high concentrations in the circulation and in tissues. Developmental stages and metabolic processes influenced by specific hormones and paracrine factors have been identified through examination of the offspring of obese and diabetic pregnancies, hormonal manipulation during late pregnancy in animal models, and the use of cell cultures. Collectively, the results of the studies cited herein delineate the basis for imprinting or conditioning of fetal pre-adipocytes at the paracrine/autocrine level, and of fetal adipose tissue development and metabolism.

Role of the prenatal environment in the development of obesity

Establishing that prenatal life is a critical or sensitive period for the development of obesity may focus basic research and clinical prevention efforts on this period. This review summarizes evidence that the intrauterine environment influences the risk of later obesity and considers the mechanisms by which this may occur. The association between birth weight and adult weight suggests that there are enduring effects of the intrauterine environment on later obesity risk. We examine whether the maternal factors of diabetes, obesity, and pregnancy weight gain alter the intrauterine environment and thereby increase the risk of later obesity in the offspring. Of these maternal factors, evidence is strongest for the role of maternal diabetes. No single mechanism explains how these maternal factors could change the intrauterine environment to increase obesity risk. However, all potential mechanisms involve an altered transfer of metabolic substrates between mother and fetus, which may influence the developing structure or function of the organs involved in energy metabolism.

The fate of hypodermis after liposuction surgery

Liposuction surgery can be viewed as a trauma to the hypodermis. With histologic, morphometric, and autoradiographic examination and the use of tritiated thymidine, uridine, and proline, we have studied the fate of adipose tissue at various intervals after liposuction; however, we have never seen a reparative proliferation of the residual lipocytes. Moreover, the metabolic activity of adipocytes apparently is not increased. Inflammatory reaction is minimal in the early weeks, but fibrosis takes place in some lobules of the hypodermis. Our data support the view that liposuction has a long-term effect on the structure of the hypodermis, without any stimulation in the proliferative and biosynthetic activity of residual adipocytes.

Postnatal development of adipose tissue in normal children on strictly controlled calorie intake

The relations between adipose tissue development at birth, later expansion of fat mass and the behavior of fat mass and fat cell growth from birth to 12 mo of age have been studied in normal children born to normal, obese or diabetic mothers and maintained on strictly controlled calorie intake. A simple method for fat cell size determination on microsamples of fat tissue, specifically designed for small children, is reported. In the first 3 mo of life, a marked increase of fatty tissue from 13.4 +/- 0.4 to 20.3 +/- 0.8 percent of total body mass was observed. Subsequently, a sharp decrease in the relative amount of fat mass occurs, probably related to an increased energy expenditure or to a slightly higher protein content in the diet. No sex related differences in body weight, body fat mass, sum of skinfold thickness or fat cell weight were found throughout the study. No significant differences in body fat mass, sum of skinfold thickness and body fat mass as percent of body weight was observed at birth and at 3 or 6 mo of age in children of obese or gestational diabetic mothers, in comparison with children of normal mothers, and no significant correlation was found between maternal adiposity (sum of skinfold thickness or pre-gravidic overweight) or glucose tolerance (blood glucose area after OGTT) and adipose tissue development in the first 6 mo of life. Thus, in children on strictly controlled intake, obesity or diabetes in the mother do not relate to the rate of fat accumulation. Moreover, no relations were found between adipose tissue development at birth and subsequent rate of fat enlargement in the first year of life. Thus, when the interference of a different calorie intake is excluded, adiposity at birth has no predictive value for possible fatness later in infancy.