A role for suppressed thermogenesis favoring catch-up fat in the pathophysiology of catch-up growth

Early-life origins of metabolic dysfunction: role of the adipocyte

More than 60% of adults in the US are classified as overweight, with most developing associated metabolic problems. It is increasingly clear that the origins of obesity and metabolic disease are early in life, yet the physiological basis for this is not well understood. We propose that perturbations to nutrient supply in utero affect adipocyte development, altering functional properties and promoting excess body fat accumulation after birth. We also propose that excessive body fat accumulation leads to leptin and insulin resistance in these individuals, rendering them more susceptible to further weight gain and metabolic deterioration. Finally, we propose that interventions that inhibit this early increase in fat deposition have the potential to interrupt the pathway to obesity.

Evaluation of body development, fat mass and lipid profile in rats fed with high-PUFA and -MUFA diets, after neonatal malnutrition

Neonatal malnutrition is associated with several features of the metabolic syndrome, later in life. Although the recovery of malnutrition was studied with different high-fat diets, few studies compare the effects of enriched vegetable oil diets, containing PUFA and MUFA, after weaning. Our aim was to evaluate the recovery with soya oil- or rapeseed oil-enriched diet, after malnutrition in rats whose mothers were food restricted (FR) during lactation. Dams were 50 % FR and compared to standard diet-fed dams (control, C). At 21 d, FR offspring had a lower body mass and length. After weaning C and FR offspring were fed a diet containing 7 % soya oil (7 %sC and 7 %sFR), or supplemented with 19 % soya oil (19 %sC or 19 %sFR) or 19 % rapeseed oil (19 %cC or 19 %cFR). The normal animals fed enriched vegetable oil diets had more visceral fat mass, but lower serum TAG and higher HDL-cholesterol. The 19 %FR groups showed significantly less food intake and body development compared to the 7 %sFR, and the same pattern was observed when this group was compared to the C groups. Absolute and relative mass of vital organs and body were lower in the FR groups. Visceral fat depot was lower in 19 %FR than 7 %FR and C groups. Serum glucose, albumin, TAG, cholesterol, leptin and triiodothyronine did not show significant changes. However, 19 %FR groups showed higher HDL-cholesterol and the 19 %sFR group showed lower serum thyroxine. The data suggest that a higher vegetable oil diet in the recovery of neonatal malnutrition ameliorates some features of the metabolic syndrome later in life.

Maternal undernutrition induces differential cardiac gene expression in pulmonary hypertensive steers at high elevation

Pulmonary hypertension, characterized by elevated pulmonary arterial pressure (PAP) and right ventricular hypertrophy, is caused by decreased atmospheric oxygen at high altitude. We hypothesized that maternal undernutrition programs right ventricle gene expression and sensitivity to increasing PAP at high altitude (2,183 m). On day 30 of gestation, forty Angus x Gelbvieh cows received diets to induce either gain (Control) or loss of body weight (Restricted) until day 125 of gestation. On day 126 of gestation, Restricted cows were realimented to achieve the same body weight as Controls by day 250. Parturition occurred naturally. PAP, which ranged from 40 to 114 mmHg, was determined in 15-mo-old steers from Control or Restricted cows before necropsy. At necropsy, hearts were collected from steers, separated into right and left ventricles, atria, and septa and weighed. Ventricular thickness was recorded. Eight Affymetrix bovine microarrays were screened [four high PAP (two Control and two Restricted) and four low PAP (two Control and two Restricted)] with right ventricle mRNA. This analysis revealed that pentraxin-related protein, interferon-related developmental regulator, and peroxisome proliferator-activated receptor-gamma coactivator-1alpha were differentially expressed (P < 0.05) in steer right ventricle from high-PAP cows compared with low-PAP cows. Also, activation peptide and pancreas cationic trypsinogen, alpha-actin, similar to ubiquitin carboxylesterase, were differently expressed (P < 0.05) in steers from Restricted cows compared with those from Control cows. Upregulated genes in high-PAP right ventricle have been associated with pathological cardiac hypertrophy. It is concluded that right ventricle gene expression may be differentially programmed by maternal undernutrition in the fetus during early gestation and may be detrimental to health and longevity of offspring, particularly at high altitude.

Regulation of fetal growth: consequences and impact of being born small

The first trimester of pregnancy is the time during which organogenesis takes place and tissue patterns and organ systems are established. In the second trimester the fetus undergoes major cellular adaptation and an increase in body size, and in the third trimester organ systems mature ready for extrauterine life. In addition, during that very last period of intrauterine life there is a significant increase in body weight. In contrast to the postnatal endocrine control of growth, where the principal hormones directly influencing growth are growth hormone (GH) and the insulin-like growth factors (IGFs) via the GH-IGF axis, fetal growth throughout gestation is constrained by maternal factors and placental function and is coordinated by growth factors. In general, growth disorders only become apparent postnatally, but they may well be related to fetal life. Thus, fetal growth always needs to be considered in the overall picture of human growth as well as in its metabolic development.

Thrifty energy metabolism in catch-up growth trajectories to insulin and leptin resistance

Catch-up growth early in life (after fetal, neonatal or infantile growth retardation) is a major risk factor for later obesity, type-2 diabetes and cardiovascular diseases. These risks are generally interpreted alongside teleological arguments that environmental exposures which hinder growth early in life lead to programming of 'thrifty mechanisms' that are adaptive during the period of limited nutrient supply (or growth constraint), but which increase risks for diseases during improved nutrition and catch-up growth later in life. This paper addresses this notion of 'thrifty mechanisms' in the light of evidence that catch-up growth is characterized by a disproportionately higher rate of fat gain relative to lean tissue gain, and that such preferential catch-up fat is in part driven by energy conservation mechanisms operating via suppressed thermogenesis. It provides a molecular-physiological framework which integrates emerging insights into mechanisms by which this thrifty 'catch-up fat' phenotype cross-links with insulin and leptin resistance.

Thrifty metabolism that favors fat storage after caloric restriction: a role for skeletal muscle phosphatidylinositol-3-kinase activity and AMP-activated protein kinase

Energy conservation directed at accelerating body fat recovery (or catch-up fat) contributes to obesity relapse after slimming and to excess fat gain during catch-up growth after malnutrition. To investigate the mechanisms underlying such thrifty metabolism for catch-up fat, we tested whether during refeeding after caloric restriction rats exhibiting catch-up fat driven by suppressed thermogenesis have diminished skeletal muscle phosphatidylinositol-3-kinase (PI3K) activity or AMP-activated protein kinase (AMPK) signaling-two pathways required for hormone-induced thermogenesis in ex vivo muscle preparations. The results show that during isocaloric refeeding with a low-fat diet, at time points when body fat, circulating free fatty acids, and intramyocellular lipids in refed animals do not exceed those of controls, muscle insulin receptor substrate 1-associated PI3K activity (basal and in vivo insulin-stimulated) is lower than that in controls. Isocaloric refeeding with a high-fat diet, which exacerbates the suppression of thermogenesis, results in further reductions in muscle PI3K activity and in impaired AMPK phosphorylation (basal and in vivo leptin-stimulated). It is proposed that reduced skeletal muscle PI3K/AMPK signaling and suppressed thermogenesis are interdependent. Defective PI3K or AMPK signaling will reduce the rate of substrate cycling between de novo lipogenesis and lipid oxidation, leading to suppressed thermogenesis, which accelerates body fat recovery and furthermore sensitizes skeletal muscle to dietary fat-induced impairments in PI3K/AMPK signaling.

Perinatal circulating visfatin levels in intrauterine growth restriction

OBJECTIVE

The objective of this study was to investigate possible alterations in circulating levels of the adipocytokine visfatin in intrauterine growth-restricted and normal pregnancies, given that these groups differ considerably in fetal nutrition, body fat mass, and metabolic/endocrine mechanisms.

METHODS

Serum visfatin levels were prospectively measured by enzyme immunoassay in 40 mothers and their 40 singleton term fetuses and neonates on postnatal days 1 and 4. Twenty neonates had intrauterine growth restriction (birth weight < or = 3rd customized centile, adjusted for parameters that influence growth potential), and 20 were appropriate for gestational age.

RESULTS

Circulating maternal visfatin levels were significantly elevated in pregnancies with intrauterine growth restriction compared with control pregnancies with appropriate-for-gestational-age infants and negatively correlated with customized centiles in the group with intrauterine growth restriction. Postnatal day-1 and -4 visfatin levels were significantly higher in neonates with intrauterine growth restriction compared with neonates who were appropriate for gestational age. Postnatal-day-1 prefeeding insulin levels were significantly lower in neonates with intrauterine growth restriction.

CONCLUSIONS

Pathologic conditions in pregnancy that lead to intrauterine growth restriction could be responsible for elevated maternal visfatin levels. Higher visfatin levels in neonates with intrauterine growth restriction may serve as an early marker with prognostic value for later development of insulin resistance or type 2 diabetes, whereas lower insulin levels may indicate reduced beta-cell mass and/or impaired beta-cell function.

Prevention of diet-induced obesity and impaired glucose tolerance in rats following administration of leptin to their mothers

Absence of leptin is known to disrupt the development of energy balance regulatory mechanisms. We investigated whether administration of leptin to normally nourished rats affects energy balance in their offspring. Leptin (2 mg·kg−1·day−1) was administered from day 14 of pregnancy and throughout lactation. Male and female offspring were fed either on chow or on high-fat diets that elicited similar levels of obesity in the sexes from 6 wk to 15 mo of age. Treatment of the dams with leptin prevented diet-induced increases in the rate of weight gain, retroperitoneal fat pad weight, area under the intraperitoneal glucose tolerance curve, and fasting plasma insulin concentration in female offspring. In the male offspring, the diet-induced increase in weight gain was prevented and increased fat pad weight was reduced. Energy intake per rat was higher in response to the obesogenic diet in male offspring of saline-treated but not leptin-treated dams. A similar trend was seen in 3-mo-old female offspring. Energy expenditure at 3 mo of age was higher for a given body weight in female offspring of leptin-treated compared with saline-treated dams when these animals were fed on the obesogenic diet. A similar trend was seen for male rats fed on the obesogenic diet. Thus leptin levels during pregnancy and lactation can affect the development of energy balance regulatory systems in their offspring.

To catch up or not to catch up: is this the question? Lessons from animal models

PURPOSE OF REVIEW

Low birth weight and accelerated postnatal catch-up growth during early life are independent risk factors for adult disease, including diabetes, obesity, and cardiovascular disease. As they are intimately linked, it is difficult to determine the independent contributions of birth weight and catch-up growth per se. This review focuses on evidence derived from animal models of disease, in which it is possible to dissect more clearly the independent roles of intrauterine growth retardation, low birth weight, and catch-up growth in mediating disease risk.

RECENT FINDINGS

Recent data from rats, mice and birds show that accelerated postnatal growth is a trigger for the development of adult disease and, ultimately, can affect longevity.

SUMMARY

Understanding the mechanisms and relative contribution of low birth weight and early postnatal catch-up growth to late onset of disease is critical to establish appropriate interventions to prevent or delay adult disease.

Adrenarche in Prader-Willi syndrome appears not related to insulin sensitivity and serum adiponectin

Prader-Willi syndrome (PWS) is a genetic disorder characterized by dysmorphic features, obesity, hypogonadism, hypotonia and mental retardation. Obesity has been linked to insulin resistance and the latter has also been associated with premature adrenarche. Since up to date a controlled study to investigate adrenarche and its hormonal regulation was lacking in PWS, our aim was to assess whether prepubertal PWS patients develop premature adrenarche and its relationship with markers of insulin sensitivity. Fourteen prepubertal children with PWS (6 M, 8 F) and 10 non-syndromal simple obese matched controls (5 M, 5 F) participated (mean age: 7.62 +/- 1.84 years). A fasting blood sample was obtained for adrenal and ovarian androgens, sex hormone binding globulin, insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-1, leptin, adiponectin and a lipid profile. Thereafter an oral glucose tolerance test was performed. PWS patients were smaller at birth and a higher proportion displayed premature pubarche. No differences were found in testosterone, androstenedione, sex hormone binding globulin, free androgen index, homeostatic model assessment-IR, 2-hour insulin, leptin or adiponectin levels. 17-hydroxyprogesterone and DHEAS levels however, were significantly higher in PWS. IGF-I levels were significantly lower in PWS and correlated significantly with height SDS (p < 0.05). In conclusion, a higher proportion of premature adrenarche in our PW patients was observed, which was not explained by differences in insulin sensitivity or plasma levels of adipokines and IGF-I.

Intrauterine ethanol exposure results in hypothalamic oxidative stress and neuroendocrine alterations in adult rat offspring

Prenatal ethanol (EtOH) exposure is associated with low birth weight, followed by increased appetite, catch-up growth, insulin resistance, and impaired glucose tolerance in the rat offspring. Because EtOH can induce oxidative stress, which is a putative mechanism of insulin resistance, and because of the central role of the hypothalamus in the regulation of energy homeostasis and insulin action, we investigated whether prenatal EtOH exposure causes oxidative damage to the hypothalamus, which may alter its function. Female rats were given EtOH by gavage throughout pregnancy. At birth, their offspring were smaller than those of non-EtOH rats. Markers of oxidative stress and expression of neuropeptide Y and proopiomelanocortin (POMC) were determined in hypothalami of postnatal day 7 (PD7) and 3-mo-old (adult) rat offspring. In both PD7 and adult rats, prenatal EtOH exposure was associated with decreased levels of glutathione and increased expression of MnSOD. The concentrations of lipid peroxides and protein carbonyls were normal in PD7 EtOH-exposed offspring, but were increased in adult EtOH-exposed offspring. Both PD7 and adult EtOH-exposed offspring had normal neuropeptide Y and POMC mRNA levels, but the adult offspring had reduced POMC protein concentration. Thus only adult offspring preexposed to EtOH had increased hypothalamic tissue damage and decreased levels of POMC, which could impair melanocortin signaling. We conclude that prenatal EtOH exposure causes hypothalamic oxidative stress, which persists into adult life and alters melanocortin action during adulthood. These neuroendocrine alterations may explain weight gain and insulin resistance in rats exposed to EtOH early in life.

Reductions in caloric intake and early postnatal growth prevent glucose intolerance and obesity associated with low birthweight

AIMS/HYPOTHESIS

Low birthweight (LBW) and rapid postnatal weight gain, or catch-up growth, are independent risk factors for the development of obesity and diabetes during adult life. Individuals who are both small at birth and have postnatal catch-up growth are at the highest risk. We hypothesised that dietary interventions designed to attenuate catch-up growth in LBW subjects may have long-term beneficial consequences.

MATERIALS AND METHODS

We used our previously described mouse model of LBW-associated diabetes, created by restricting maternal food intake to 50% during the last week of gestation. Control (C) dams and dams that had been subjected to undernutrition (U) were then provided either chow ad libitum after delivery or 50% food restriction on a per-day basis from delivery until weaning. We designated the resulting four groups control-control (CC), undernutrition-control (UC), control-undernutriton (CU) and undernutrition-undernutrition (UU), indicating the prenatal and postnatal experimental conditions, respectively. Carbohydrate metabolism and adiposity were assessed prospectively in offspring until age 6 months.

RESULTS

Males that were small at birth and exhibited early postnatal catch-up growth developed glucose intolerance and obesity by age 6 months. In contrast, LBW mice without catch-up growth (UU) remained smaller than controls (CC), and glucose intolerance and obesity was prevented. Similarly, mice with normal birthweight that had blunted catch-up growth (CU) were leaner and had better tolerance test than CC mice. Catch-up growth during the first week of life correlated better than birthweight with glucose, fat mass and glucose tolerance up to 6 months of age.

CONCLUSIONS/INTERPRETATION

Prevention of early catch-up growth reversed the development of glucose intolerance and obesity in our mouse model of LBW-associated diabetes.

Altered skeletal muscle subsarcolemmal mitochondrial compartment during catch-up fat after caloric restriction

An accelerated rate of fat recovery (catch-up fat) and insulin resistance are characteristic features of weight recovery after caloric restriction, with implications for the pathophysiology of catch-up growth and weight fluctuations. Using a previously described rat model of weight recovery in which catch-up fat and skeletal muscle insulin resistance have been linked to suppressed thermogenesis per se, we investigated alterations in mitochondrial energetics and oxidative stress in subsarcolemmal (SS) and intermyofibrillar (IMF) skeletal muscle mitochondria. After 2 weeks of semistarvation followed by 1 week of refeeding, the refed rats show persistent and selective reductions in SS mitochondrial mass (assessed from citrate synthase activity in tissue homogenate and isolated mitochondria) and oxidative capacity. Furthermore, the refed rats show, in both SS and IMF muscle mitochondria, a lower aconitase activity (whose inactivation is an index of increased reactive oxygen species [ROS]), associated with higher superoxide dismutase activity and increased proton leak. Taken together, these studies suggest that diminished skeletal muscle mitochondrial mass and function, specifically in the SS mitochondrial compartment, contribute to the high metabolic efficiency for catch-up fat after caloric restriction and underscore a potential link between diminished skeletal muscle SS mitochondrial energetics, increased ROS concentration, and insulin resistance during catch-up fat.

Postnatal growth, neurodevelopment and altered adiposity after preterm birth--from a clinical nutrition perspective

Evidence reveals a dilemma that under-nutrition and growth retardation during brain growth are associated with neurodevelopmental deficits, and nutritional supplement resulting in catch-up growth and relative visceral adiposity leads to metabolic/cardiovascular morbidities. Hyperinsulinaemia secondary to insulin resistance appears to play a central role in the development of visceral adiposity through its action on adipocyte beta3-adrenoceptor.

CONCLUSION

Optimal nutritional management to minimize hyperinsulinaemia and insulin resistance may potentially improve neurodevelopment and facilitate catch-up growth with normal body composition.

A role for skeletal muscle stearoyl-CoA desaturase 1 in control of thermogenesis

An enhanced metabolic efficiency for accelerating the recovery of fat mass (or catch-up fat) is a characteristic feature of body weight regulation after weight loss or growth retardation and is the outcome of an "adipose-specific" suppression of thermogenesis, i.e., a feedback control system in which signals from the depleted adipose tissue fat stores exert a suppressive effect on thermogenesis. Using a previously described rat model of semistarvation-refeeding in which catch-up fat results from suppressed thermogenesis per se, we report here that the gene expression of stearoyl-coenzyme A desaturase 1 (SCD1) is elevated in skeletal muscle after 2 wk of semistarvation and remains elevated in parallel to the phase of suppressed thermogenesis favoring catch-up fat during refeeding. These elevations in the SCD1 transcript are skeletal muscle specific and are associated with elevations in microsomal Delta9 desaturase enzyme activity, in the Delta9 desaturation index, and in the relative content of SCD1-derived monounsaturates in several lipid fractions extracted from skeletal muscle. An elevated skeletal muscle SCD1, by desaturating the products of de novo lipogenesis and diverting them away from mitochondrial oxidation, would inhibit substrate cycling between de novo lipogenesis and lipid oxidation, thereby leading to a state of suppressed thermogenesis that regulates the body's fat stores.

Prematurity and insulin sensitivity

Premature infants of low and extremely low birth weight represent a challenge for neonatal intensive care units and paediatricians. These neonates may be at increased risk of insulin resistance and diabetes perinatally and during childhood. During the first week of postnatal life, infants born prematurely are at risk of abnormalities in glucose homeostasis. Additionally, there are major differences in their glucose/insulin homeostasis compared with infants born at term. Preterm infants are at risk of hypoglycaemia, due to decreases in deposits of glycogen and fat that occur during the third trimester, and also to transient hyperinsulinaemia. Hyperglycaemia may also be observed in preterm infants during the perinatal period. These infants are unable to suppress glucose production within a large range of glucose and insulin concentrations, insulin secretory response is inappropriate, insulin processing is immature and there is an increased ratio of the glucose transporters Glut-1/Glut-2 in fetal tissues, which limits sensitivity and hepatocyte reaction to increments in glucose/insulin concentration during hyperglycaemia. In addition, increased concentrations of tumour necrosis factor alpha present in intrauterine growth retardation (IUGR) and induce insulin resistance. It has been proposed that the reduced insulin sensitivity may result from adaptation to an adverse in utero environment during a critical period of development. We have investigated postnatal insulin resistance in 60 children born with very low birth weight and either small for gestational age or at an appropriate size for gestational age. This study showed that IUGR, rather than low birth weight itself, was associated with increased fasting insulin levels. As poor fetal growth may be associated with the development of obesity, type 2 diabetes and the metabolic syndrome in later life, it is important that we continue to increase our understanding of the effects of IUGR on postnatal growth and metabolism.

Regulation of fat storage via suppressed thermogenesis: a thrifty phenotype that predisposes individuals with catch-up growth to insulin resistance and obesity

Catch-up growth during infancy and childhood is increasingly recognized as a major risk factor for later development of insulin-related complications and chronic diseases, namely abdominal obesity, type 2 diabetes and cardiovascular disease. As catch-up growth per se is characterized by insulin resistance, hyperinsulinaemia and an accelerated rate of fat storage (i.e., catch-up fat) even in the absence of hyperphagia, the possibility arises that suppressed thermogenesis in certain organs/tissues - for the purpose of enhancing the efficiency of catch-up fat - also plays a role in the pathophysiological consequences of catch-up growth. Here, the evidence for the existence of an adipose-specific control of thermogenesis, the suppression of which contributes to catch-up fat, is reviewed. Recent findings suggest that such suppression of thermogenesis is accompanied by hyperinsulinaemia, insulin resistance in skeletal muscle and insulin hyperresponsiveness in adipose tissue, all of which precede the appearance of excess body fat, central fat distribution and elevations in intramyocellular triglyceride or circulating lipid concentrations. These findings underscore a role for suppressed thermogenesis per se as an early event in the pathophysiology of catch-up growth. It is proposed that, in its evolutionary adaptive role to spare glucose for the rapid rebuilding of an adequate fat reserve (for optimal survival capacity during intermittent famine), suppressed thermogenesis in skeletal muscle constitutes a thrifty phenotype that confers to the phase of catch-up growth its high sensitivity to the development of insulin resistance and hyperinsulinaemia. In the context of the complex interactions between earlier reprogramming and a modern lifestyle characterized by nutritional abundance and low physical activity, this thrifty 'catch-up fat phenotype' is a central event that predisposes individuals with catch-up growth to abdominal obesity, type 2 diabetes and cardiovascular disease.

Insulin resistance in pre-school very-low-birth weight pre-term children

AIMS

To evaluate the metabolic pattern of a group of pre-school small- (SGA) and appropriate-for-gestational age (AGA) pre-term very-low-birthweight (VLBW) (<1500 gr) Italian children and retrospectively verify if the growth rate in the first years of life is associated to the laboratory and anthropometric characteristics of these children.

METHODS

58 (16 SGA, 42 AGA) VLBW children, without major congenital malformations/conditions were enrolled; their anthropometric, clinical and (in 34 of them) laboratory characteristics were evaluated at pre-school age (> 2<6 years of corrected age).

RESULTS

Clinical, anthropometric and laboratory characteristics at pre-school age were similar in SGA and AGA. Sixty-nine percent of SGA and 51% of AGA children showed a significant weight centile crossing (CC) at 24 months. Fasting serum glucose, insulin and insulin resistance (evaluated by the Homeostasis Model Assessment -HOMA-IR-) were higher in AGA and SGA with CC. The increment in weight standard deviation scores from birth-to-24 months was significantly associated with pre-school BMI SDS, waist, fasting insulin, and HOMA-IR values, both in unadjusted and adjusted models. In a multiple regression model, after multiple adjustments, this increment is the only significant predictor of pre-school insulin (B = 0.19; 95%CI 0.07-0.31; P = 0.006) and HOMA-IR levels (B = 0.20; 95%CI 0.08-0.32; P = 0.004) both in SGA and AGA children.

CONCLUSIONS

The adverse metabolic pattern of pre-school VLBW children seems related to post-natal events (rapid weight growth) independently by their being small- or appropriate-for gestational age.

A role for suppressed skeletal muscle thermogenesis in pathways from weight fluctuations to the insulin resistance syndrome

An impressive body of epidemiological evidence suggests that a history of large perturbations in body weight earlier in life, independently of excess weight, is a risk factor for later development of insulin-related complications, namely central obesity, type 2 diabetes and cardiovascular disease. Such an increased risk has been reported in men and women who in young adulthood experienced weight fluctuations that involved weight recovery after weight loss caused by disease, famine or voluntary 'yoyo' dieting, and is particularly strong when the weight fluctuations occurred much earlier in life and are characterized by catch-up growth after foetal and/or neonatal growth retardation. As the phase of weight recovery/catch-up growth is associated with both hyperinsulinaemia and an accelerated rate for recovering fat mass (i.e. catch-up fat), the questions arise as to whether, why and how processes that regulate catch-up fat might predispose to hyperinsulinaemia and to insulin-related diseases. In addressing these issues, this paper first reviews evidence for the existence of an adipose-specific control of thermogenesis, whose suppression contributes to the phenomenon of catch-up fat during weight recovery/catch-up growth. It subsequently concentrates upon recent findings suggesting that: (i) such suppression of thermogenesis directed at catch-up fat is accompanied by a redistribution of glucose from skeletal muscle to white adipose tissue, and (ii) substrate cycling between de novo lipogenesis and lipid oxidation can operate as a thermogenic effector in skeletal muscle in response to signalling interactions between leptin and insulin - two key 'adiposity' hormones implicated in the peripheral control of substrate metabolism. These new findings are integrated into the proposal that, in its 'evolutionary adaptive' role to spare glucose for rapid rebuilding of the fat stores, suppressed thermogenesis in skeletal muscle - via inhibition of substrate cycling between de novo lipogenesis and lipid oxidation - confers to the phase of weight recovery/catch-up growth its high sensitivity towards the development of insulin resistance and hyperinsulinaemia, and hence towards diseases that are clustered around the insulin resistance syndrome.

Homeostatic responses to caloric restriction: influence of background metabolic rate

The biological responses to caloric restriction (CR) are generally examined in rats with elevated metabolic rates due to being housed at ambient temperatures (Ta) below the zone of thermoneutrality. We determined the physiological and behavioral responses to 2 wk of 30–40% CR in male FBNF1 rats housed in cool (Ta = 12°C) or thermoneutral (TMN; Ta = 30°C) conditions. Rats were instrumented with telemetry devices and housed continuously in home-cage calorimeters for the entire experiment. At baseline, rats housed in cool Ta had reduced rate of weight gain; thus a mild CR (5%) group at thermoneutrality for weight maintenance was also studied. Rats housed in cool Ta exhibited elevated caloric intake (cool = 77 ± 1; TMN = 54 ± 2 kcal), oxygen consumption (V̇o2; cool = 9.9 ± 0.1; TMN = 5.5 ± 0.1 ml/min), mean arterial pressure (cool = 103 ± 1; TMN = 80 ± 2 mmHg), and heart rate (cool = 374 ± 3; TMN = 275 ± 4 beats/min). Cool-CR rats exhibited greater CR-induced weight loss (cool = −62 ± 3; TMN = −42 ± 3 g) and reductions in V̇o2 (cool = −2.6 ± 0.1; TMN = −1.5 ± 0.1 ml/min) but similar CR-induced reductions in heart rate (cool = −59 ± 1; TMN= −51 ± 7 beats/min). CR had no effect on arterial blood pressure or locomotor activity in either group. Unexpectedly, weight maintenance produced significant reductions in V̇o2 and heart rate. At thermoneutrality, a single day of refeeding effectively abolished CR-induced reductions in V̇o2 and heart rate. The results reveal that rats with low or high baseline metabolic rate exhibit comparable compensatory reductions in V̇o2 and heart rate and suggest that Ta can be used to modulate the metabolic background on which the more prolonged effects of CR can be studied.

Fetal origins of insulin resistance and obesity

A number of epidemiological studies worldwide have demonstrated a relationship between poor early growth and an increased susceptibility to insulin resistance, visceral obesity, type 2 diabetes and other features of the metabolic syndrome in adulthood. However, the mechanistic basis of this relationship and the relative roles of genes and the environment remain a subject of debate. The 'thrifty phenotype' hypothesis proposes that poor fetal nutrition leads to programming of metabolism and an adult phenotype that is adapted to poor but not plentiful nutrition. The maternal reduced-protein rat model has been used to examine the importance of the maternal environment in determining susceptibility to adult disease. Pregnant and lactating rat dams are fed a diet containing 80 g protein/kg as compared with 200 g protein/kg, which leads to growth restriction in utero. Offspring of low-protein dams have increased susceptibility to diabetes, insulin resistance and hypertension when fed a palatable high-fat diet that promotes obesity. Administration of leptin during pregnancy and lactation to these protein-restricted dams produces offspring that have increased metabolic rate and do not become obese or insulin resistant when fed on a high-fat diet. Increased glucocorticoid exposure, particularly during late gestation, has been linked with insulin resistance in adulthood. High levels of fetal glucocorticoids may result from a decreased activity of placental 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2, which normally protects the fetus from high maternal glucocorticoid levels. Leptin administration to protein-restricted dams inhibits the suppression of 11beta-HSD-2 and may be one mechanism by which the metabolic syndrome is prevented.

Lower resting metabolic rate and higher velocity of weight gain in a prospective study of stunted vs nonstunted girls living in the shantytowns of São Paulo, Brazil

OBJECTIVE

Previous studies have shown that stunting increases the risk of obesity in developing countries, particularly among girls and women, but the underlying reasons are not known. This study aimed to investigate the relationship between stunting, weight gain, and resting metabolic rate.

DESIGN AND SUBJECTS

A prospective study was conducted over 36 months with girls from shantytowns in São Paulo, Brazil. A total of 15 stunted girls (S) were compared with 15 nonstunted (N) ones of similar weight for height ratio.

INTERVENTIONS

Resting metabolic rate was measured using indirect calorimetry, and the socioeconomic status was determined by interviews in the household. In addition, body composition was measured by skinfold thickness, while the growth rate was calculated dividing the change in weight and the change in height by the follow-up period.

RESULTS

The results of the present study, when combined, revealed that the S group had a lower resting metabolic rate throughout the follow-up period with the differences being significant at 24 and 36 months of follow-up, associated with an increase in the rate of weight gain and a decrease in lean mass, when compared to the N group.

CONCLUSIONS

These changes are known to be risk factors for obesity and may help to explain the particularly higher prevalence of obesity in women in urban areas of developing countries.

Redistribution of glucose from skeletal muscle to adipose tissue during catch-up fat: a link between catch-up growth and later metabolic syndrome

Catch-up growth, a risk factor for later obesity, type 2 diabetes, and cardiovascular diseases, is characterized by hyperinsulinemia and an accelerated rate for recovering fat mass, i.e., catch-up fat. To identify potential mechanisms in the link between hyperinsulinemia and catch-up fat during catch-up growth, we studied the in vivo action of insulin on glucose utilization in skeletal muscle and adipose tissue in a previously described rat model of weight recovery exhibiting catch-up fat caused by suppressed thermogenesis per se. To do this, we used euglycemic-hyperinsulinemic clamps associated with the labeled 2-deoxy-glucose technique. After 1 week of isocaloric refeeding, when body fat, circulating free fatty acids, or intramyocellular lipids in refed animals had not yet exceeded those of controls, insulin-stimulated glucose utilization in refed animals was lower in skeletal muscles (by 20-43%) but higher in white adipose tissues (by two- to threefold). Furthermore, fatty acid synthase activity was higher in adipose tissues from refed animals than from fed controls. These results suggest that suppressed thermogenesis for the purpose of sparing glucose for catch-up fat, via the coordinated induction of skeletal muscle insulin resistance and adipose tissue insulin hyperresponsiveness, might be a central event in the link between catch-up growth, hyperinsulinemia and risks for later metabolic syndrome.

Long-Evans and Sprague-Dawley rats exhibit divergent responses to refeeding after caloric restriction

Mature male Sprague-Dawley (SD) and Long-Evans (LE) rats were instrumented with telemetry transmitters for measurement of heart rate (HR) and housed in room calorimeters for assessment of food intake and oxygen consumption (Vo(2)) at standard laboratory temperatures (23 degrees C) to examine physiological responses to caloric restriction (CR; 60% of baseline ad libitum calories for 2 wk) and refeeding. Ad libitum controls had stable food intake (84-88 kcal/day) and gained weight at rates of 3-4 g/day. Groups from both strains assigned to CR exhibited similar patterns of weight loss and reductions in Vo(2) and HR. Upon refeeding, SD rats exhibited a mild, transient hyperphagic response (1 day) accompanied by sustained suppression of Vo(2) and HR that remained evident 8 days after refeeding. In contrast, LE rats exhibited sustained daily hyperphagia that persisted 8 days after refeeding and was accompanied by a complete restoration of HR and Vo(2). The lower HR and Vo(2) observed during refeeding in SD rats were not due to reduced locomotor activity. The results reveal a strain-dependent divergent response to recovery from CR. We conclude that during recovery from CR, homeostatic stimulation of appetite or suppression of energy expenditure may occur selectively to restore body weight.

Role of energy charge and AMP-activated protein kinase in adipocytes in the control of body fat stores

As indicated by in vitro studies, both lipogenesis and lipolysis in adipocytes depend on the cellular ATP levels. Ectopic expression of mitochondrial uncoupling protein 1 (UCP1) in the white adipose tissue of the aP2-Ucp1 transgenic mice reduced obesity induced by genetic or dietary manipulations. Furthermore, respiratory uncoupling lowered the cellular energy charge in adipocytes, while the synthesis of fatty acids (FA) was inhibited and their oxidation increased. Importantly, the complex metabolic changes triggered by ectopic UCP1 were associated with the activation of AMP-activated protein kinase (AMPK), a metabolic master switch, in adipocytes. Effects of several typical treatments that reduce adiposity, such as administration of leptin, beta-adrenoceptor agonists, bezafibrate, dietary n-3 polyunsaturated FA or fasting, can be compared with a phenotype of the aP2-Ucp1 mice. These situations generally lead to the upregulation of mitochondrial UCPs and suppression of the cellular energy charge and FA synthesis in adipocytes. On the other hand, FA oxidation is increased. Moreover, it has been shown that AMPK in adipocytes can be activated by adipocyte-derived hormones leptin and adiponectin, and also by insulin-sensitizes thiazolidinediones. Thus, it is evident that metabolism of adipose tissue itself is important for the control of body fat content and that the cellular energy charge and AMPK are involved in the control of lipid metabolism in adipocytes. The reciprocal link between synthesis and oxidation of FA in adipocytes represents a prospective target for the new treatment strategies aimed at reducing obesity.

Randomized controlled trial of nutritional supplementation in patients with newly diagnosed tuberculosis and wasting

BACKGROUND

Nutritional support is often recommended as part of the treatment of tuberculosis, but it has never been properly tested.

OBJECTIVE

We assessed the effects of early nutritional intervention on lean mass and physical function in patients with tuberculosis and wasting.

DESIGN

Patients who started antituberculous therapy within the previous 2 wk were randomly assigned to receive standard nutritional counseling (control group) or nutritional counseling to increase their intake through diet and high-energy supplements (nutritional supplement group) for 6 wk. Body composition was measured by dual-energy X-ray absorptiometry, and physical function was assessed by maximum grip strength.

RESULTS

Patients in the nutritional supplement group (n = 19) had a significantly greater increase in body weight (2.57 +/- 1.78 compared with 0.84 +/- 0.89 kg, P = 0.001), total lean mass (1.17 +/- 0.93 compared with 0.04 +/- 1.26 kg, P = 0.006), and grip strength (2.79 +/- 3.11 compared with -0.65 +/- 4.48 kg, P = 0.016) than did the control subjects (n = 17) at week 6. During subsequent follow-up, the increase in body weight remained greater in the nutritional supplement group, but this increase was due mainly to a greater gain in fat mass in the nutritional supplement group than in the control group.

CONCLUSIONS

Early intervention to increase nutritional intake increases lean mass and physical function. This adjunct to tuberculosis therapy could confer socioeconomic and survival benefits that deserve investigation in large-scale trials. Nutritional intervention after the initial phase of treatment could be less beneficial because it mainly increases fat.