The effect of maternal prolactin infusion during pregnancy on fetal adipose tissue development

Neuroendocrine control of brown adipocyte function by prolactin and growth hormone

Growth hormone (GH) is fundamental for growth and glucose homeostasis, and prolactin for optimal pregnancy and lactation outcome, but additionally, both hormones have multiple functions that include a strong impact on energetic metabolism. In this respect, prolactin and GH receptors have been found in brown, and white adipocytes, as well as in hypothalamic centers regulating thermogenesis. This review describes the neuroendocrine control of the function and plasticity of brown and beige adipocytes, with a special focus on prolactin and GH actions. Most evidence points to a negative association between high prolactin levels and the thermogenic capacity of BAT, except in early development. During lactation and pregnancy, prolactin may be a contributing factor that limits unneeded thermogenesis, downregulating BAT UCP1. Furthermore, animal models of high serum prolactin have low BAT UCP1 levels and whitening of the tissue, while lack of Prlr induces beiging in WAT depots. These actions may involve hypothalamic nuclei, particularly the DMN, POA and ARN, brain centers that participate in thermogenesis. Studies on GH regulation of BAT function present some controversies. Most mouse models with GH excess or deficiency point to an inhibitory role of GH on BAT function. Even so, a stimulatory role of GH on WAT beiging has also been described, in accordance with whole-genome microarrays that demonstrate divergent response signatures of BAT and WAT genes to the loss of GH signaling. Understanding the physiology of BAT and WAT beiging may contribute to the ongoing efforts to curtail obesity.

Metabolic-endocrine disruption due to preterm birth impacts growth, body composition, and neonatal outcome

Despite optimized nutrition, preterm-born infants grow slowly and tend to over-accrete body fat. We hypothesize that the premature dissociation of the maternal-placental-fetal unit disrupts the maintenance of physiological endocrine function in the fetus, which has severe consequences for postnatal development. This review highlights the endocrine interactions of the maternal-placental-fetal unit and the early perinatal period in both preterm and term infants. We report on hormonal levels (including tissue, thyroid, adrenal, pancreatic, pituitary, and placental hormones) and nutritional supply and their impact on infant body composition. The data suggest that the premature dissociation of the maternal-placental-fetal unit leads to a clinical picture similar to panhypopituitarism. Further, we describe how the premature withdrawal of the maternal-placental unit, neonatal morbidities, and perinatal stress can cause differences in the levels of growth-promoting hormones, particularly insulin-like growth factors (IGF). In combination with the endocrine disruption that occurs following dissociation of the maternal-placental-fetal unit, the premature adaptation to the extrauterine environment leads to early and fast accretion of fat mass in an immature body. In addition, we report on interventional studies that have aimed to compensate for hormonal deficiencies in infants born preterm through IGF therapy, resulting in improved neonatal morbidity and growth. IMPACT: Preterm birth prematurely dissociates the maternal-placental-fetal unit and disrupts the metabolic-endocrine maintenance of the immature fetus with serious consequences for growth, body composition, and neonatal outcomes. The preterm metabolic-endocrine disruption induces symptoms resembling anterior pituitary failure (panhypopituitarism) with low levels of IGF-1, excessive postnatal fat mass accretion, poor longitudinal growth, and failure to thrive. Appropriate gestational age-adapted nutrition alone seems insufficient for the achievement of optimal growth of preterm infants. Preliminary results from interventional studies show promising effects of early IGF-1 supplementation on postnatal development and neonatal outcomes.

Comparative pathophysiology, toxicology, and human cancer risk assessment of pharmaceutical-induced hibernoma

In humans, hibernoma is a very rare, benign neoplasm of brown adipose tissue (BAT) that typically occurs at subcutaneous locations and is successfully treated by surgical excision. No single cause has been accepted to explain these very rare human tumors. In contrast, spontaneous hibernoma in rats is rare, often malignant, usually occurs in the thoracic or abdominal cavity, and metastases are common. In recent years, there has been an increased incidence of spontaneous hibernomas in rat carcinogenicity studies, but overall the occurrence remains relatively low and highly variable across studies. There have only been four reported examples of pharmaceutical-induced hibernoma in rat carcinogenicity studies. These include phentolamine, an alpha-adrenergic antagonist; varenicline, a nicotine partial agonist; tofacitinib, a Janus kinase (JAK) inhibitor; and hydromorphone, an opiod analgesic. Potential non-genotoxic mechanisms that may contribute to the pathogenesis of BAT activation/proliferation and/or subsequent hibernoma development in rats include: (1) physiological stimuli, (2) sympathetic stimulation, (3) peroxisome proliferator-activated receptor (PPAR) agonism, and/or (4) interference or inhibition of JAK/Signal Transducer and Activator of Transcription (JAK/STAT) signaling. The evaluation of an apparent increase of hibernoma in rats from 2-year carcinogenicity studies of novel pharmaceutical therapeutics and its relevance to human safety risk assessment is complex. One should consider: the genotoxicity of the test article, dose/exposure and safety margins, and pathophysiologic and morphologic differences and similarities of hibernoma between rats and humans. Hibernomas observed to date in carcinogenicity studies of pharmaceutical agents do not appear to be relevant for human risk at therapeutic dosages.

S179D prolactin: antagonistic agony!

The aims of this review are three-fold: first, to collate what is known about the production and activities of phosphorylated prolactin (PRL), the latter largely, but not exclusively, as illustrated through the use of the molecular mimic, S179D PRL; second, to apply this and related knowledge to produce an updated model of prolactin-receptor interactions that may apply to other members of this cytokine super-family; and third, to promote a shift in the current paradigm for the development of clinically important growth antagonists. This third aim explains the title since, based on results with S179D PRL, it is proposed that agents which signal to antagonistic ends may be better therapeutics than pure antagonists-hence antagonistic agony. Since S179D PRL is not a pure antagonist, we have proposed the term selective prolactin receptor modulator (SPeRM) for this and like molecules.

Timing of nutrient restriction and programming of fetal adipose tissue development

It is apparent from epidemiological studies that the timing of maternal nutrient restriction has a major influence on outcome in terms of predisposing the resulting offspring to adult obesity. The present review will consider the extent to which maternal age, parity and nutritional restriction at defined stages of gestation can have important effects on fat deposition and endocrine sensitivity of adipose tissue in the offspring. For example, in 1-year-old sheep the offspring of juvenile mothers have substantially reduced fat deposition compared with those born to adult mothers. Offspring of primiparous adult mothers, however, show increased adiposity compared with those born to multiparous mothers. These offspring of multiparous ewes show retained abundance of the brown adipose tissue-specific uncoupling protein 1 at 1 month of age. A stimulated rate of metabolism in brown fat of these offspring may act to reduce adipose tissue deposition in later life. In terms of defined windows of development that can programme adipose tissue growth, maternal nutrient restriction targetted over the period of maximal placental growth results in increased adiposity at term in conjunction with enhanced abundance of mRNA for the insulin-like growth factor-I and -II receptors. In contrast, nutrient restriction in late gestation, coincident with the period of maximal fetal growth, has no major effect on adiposity but results in greater abundance of specific mitochondrial proteins, i.e. voltage-dependent anion channel and/or uncoupling protein 2. These adaptations may increase the predisposal of these offspring to adult obesity. Increasing maternal nutrition in late gestation, however, can result in proportionately less fetal adipose tissue deposition in conjunction with enhanced abundance of uncoupling protein 1.

Prolactin, prolactin receptor and uncoupling proteins during fetal and neonatal development

Uncoupling proteins (UCP) 1 and 2 are members of the subfamily of inner mitochondrial membrane carriers. UCP1 is specific to brown adipose tissue (BAT), where it is responsible for the rapid production of heat at birth. In fetal sheep UCP1 is first detectable at approximately 900d of gestation; its abundance increases with gestational age and peaks at the time of birth. The mRNA and protein for both the long and short form of the prolactin (PRL) receptor (PRLR) are also highly abundant in BAT. Enhanced PRLR abundance in late gestation is associated with an increase in the abundance of UCP1. This relationship between PRLR and UCP is not only present in BAT. Similar findings are now reported in the pregnant ovine uterus, where PRLR abundance reaches a maximum just before that of UCP2. However, the role of PRLR in BAT remains undetermined. Rat studies have shown that PRL administration throughout pregnancy results in offspring with increased UCP1 at birth. Studies in newborn lambs have shown that administration of PRL (20mg/d) causes an acute response, increasing colonic temperature in the first hour by 1°. This increased colonic temperature is maintained for the first 240h of life, in conjunction with enhanced lipolysis. After 70d of treatment there is no difference in the abundance of UCP1 but an increase in UCP1 activity; this effect may be mediated by an increase in lipolysis. Taken together these findings suggest that PRL could be an important endocrine factor during pregnancy and early postnatal life.

Overnourishing pregnant adolescent ewes preserves perirenal fat deposition in their growth-restricted fetuses

Overnourishing the adolescent sheep promotes rapid maternal growth at the expense of the gravid uterus. The growth of the placenta is impaired and results in the premature delivery of low-birthweight lambs. The present study details fetal adipose tissue development in these growth-restricted pregnancies. Singleton pregnancies were established by embryo transfer and, thereafter, adolescent ewes were offered a high (H; n = 12) or moderate (M; n = 14) level of a complete diet until necropsy on Day 131 of gestation. Fetal weight was lower (P < 0.001) in H compared with M groups. High maternal intake preserved brain and perirenal fat weight (P < 0.003), whereas relative weights of the heart, lungs, spleen and liver were unaltered. High nutrient intake resulted in significantly elevated maternal plasma concentrations of insulin, leptin, prolactin and glucose, no significant changes in fetal insulin, leptin or non-esterified fatty acids and attenuated fetal prolactin concentrations. Irrespective of nutritional intake, maternal plasma leptin, prolactin and glucose concentrations were negatively correlated with fetal weight and were positively correlated with fetal perirenal fat proportion (all P < 0.01). The mRNA expression for leptin, prolactin receptor and uncoupling protein (UCP) 1 in fetal perirenal fat was equivalent between groups, but, irrespective of maternal nutrition, UCP1 mRNA levels were negatively correlated with fetal weight (P < 0.01). Thus, overnourishing pregnant adolescent sheep preserves fat deposition in their growth-restricted fetuses, which may have implications for neonatal thermogenesis and for programming of postnatal adiposity.

Evaluation of maternal infusion therapy during pregnancy for fetal development

The aim of this project was to study the possible association between maternal infusion treatments during pregnancy and variables of fetal development as well as the occurrence of congenital abnormalities (CA) in a case-control design. The large population-based data set of the Hungarian Case-Control Surveillance of Congenital Abnormalities (HCCSCA) was evaluated based on the medically recorded infusion treatment during pregnancy. Of 22,843 case pregnant women who had newborns or fetuses with congenital abnormalities, 112 (0.5%), while of 38,151 control pregnant women who had newborn infants without any defects, 262 (0.7%), had infusion treatment during pregnancy. Infusion treatment was more frequent in the control group than in the case group with congenital abnormalities (adjusted POR with 945 95% CI: 0.7, 0.6-0.9) and there was no higher rate of maternal infusion treatments in any congenital abnormality group. Mean gestational age was shorter and mean birth weight was smaller in control newborn infants without CA born to mothers with infusion treatment during pregnancy than in the babies of mothers without infusion treatment. The prevalence of mild intrauterine growth retardation was more frequent in the fetuses of pregnant women with hyperemesis gravidarum treated with infusion. The results of the study suggest that infusion treatment of pregnant women did not associate with a higher risk of congenital abnormalities. In addition, the intravenous infusion of drugs has some, but limited efficacy to prevent the adverse effects of hyperemesis gravidarum and threatened preterm delivery.

Leptin distribution and metabolism in the pregnant rat: transplacental leptin passage increases in late gestation but is reduced by excess glucocorticoids

Leptin is essential for the establishment of pregnancy and appears to promote fetal growth, but the mechanisms regulating fetal leptin exposure remain unclear. In rodents, indirect evidence suggests that fetal leptin is partly derived from the maternal circulation via transplacental passage. Indeed, the placenta expresses mRNA for Ob-Ra, one of the short forms of the leptin receptor (Ob-R(S)) important in leptin transport, and this expression increases markedly in late pregnancy. Therefore, we determined the transplacental passage of maternal leptin to the fetus in the rat and whether this transport increases near term in association with a rise in placental expression of Ob-R(S) protein. Because of the proposed role of leptin in promoting fetal growth, we also assessed the effect of glucocorticoid-induced fetal growth retardation on placental leptin transport. Anesthetized rats received a constant infusion of (125)I-leptin via a jugular cannula before and at d 16 and 22 of pregnancy (term = d 23); plasma samples were obtained at 10, 20, 40, 60, 80, and 100 min, and fetuses and placentas were collected at the time of the final sample. The metabolic clearance rate of leptin fell (P < 0.01) from 3.08 +/- 0.23 ml/min per kg in nonpregnant rats to 2.36 +/- 0.13 ml/min per kg by d 22. Transplacental passage of (125)I-leptin, estimated from its concentration in the whole fetus relative to maternal plasma, increased 10-fold (P < 0.005) between d 16 and d 22 of pregnancy. Over this same period, Ob-R(S) protein expression in the placental labyrinth zone increased by almost 2-fold. Transplacental leptin passage was reduced (P < 0.05) by 77% after maternal dexamethasone treatment, whereas suppression of endogenous glucocorticoid synthesis (by metyrapone) increased (P < 0.05) the transfer of maternal leptin to the fetus by 55%. These data show that transplacental passage of maternal leptin is a significant source of fetal leptin and increases markedly during late pregnancy. Consistent with the proposed role of leptin as a fetal growth factor, transplacental leptin passage is reduced in association with glucocorticoid-induced fetal growth retardation.