Constitutional delay in growth and puberty (CDGP) is associated with hypoleptinaemia

PI3K signalling in leptin receptor cells: Role in growth and reproduction

Nutrition and growth are important signals for pubertal development, although how they are perceived and integrated in brain circuits has not been well defined. Growth hormones and metabolic cues both recruit phosphatidylinositol 3-kinase (PI3K) signalling in hypothalamic sites, although whether they converge into the same neuronal population(s) is also not known. In this review, we discuss recent findings from our laboratory showing the role of PI3K subunits in cells directly responsive to the adipocyte-derived hormone leptin in the coordination of growth, pubertal development and fertility. Mice with deletion of PI3K p110α and p110β catalytic subunits in leptin receptor cells (LR^Δα+β ) have a lean phenotype associated with increased energy expenditure, locomotor activity and thermogenesis. The LR^Δα+β mice also show deficient growth and delayed puberty. Deletion of a single subunit (ie, p110α) in LR cells (LR^Δα ) causes a similar phenotype of increased energy expenditure, deficient growth and delayed pubertal development, indicating that these functions are preferably controlled by p110α. The LR^Δα mice show enhanced leptin sensitivity in metabolic regulation but, remarkably, these mice are unresponsive to the effects of leptin on growth and puberty. PI3K is also recruited by insulin and a subpopulation of LR neurones is responsive to i.c.v. insulin administration. Deletion of insulin receptor in LR cells causes no changes in body weight or linear growth and induces only a mild delay in pubertal completion. Our findings demonstrate that PI3K in LR cells plays an essential role in growth and reproduction. We will also discuss the potential neural pathways underlying these effects.

Genes underlying delayed puberty

The genetic control of pubertal timing has been a field of active investigation for the last decade, but remains a fascinating and mysterious conundrum. Self-limited delayed puberty (DP), also known as constitutional delay of growth and puberty, represents the extreme end of normal pubertal timing, and is the commonest cause of DP in both boys and girls. Familial self-limited DP has a clear genetic basis. It is a highly heritable condition, which often segregates in an autosomal dominant pattern (with or without complete penetrance) in the majority of families. However, the underlying neuroendocrine pathophysiology and genetic regulation has been largely unknown. Very recently novel gene discoveries from next generation sequencing studies have provided insights into the genetic mutations that lead to familial DP. Further understanding has come from sequencing genes known to cause GnRH deficiency, next generation sequencing studies in patients with early puberty, and from large-scale genome wide association studies in the general population. Results of these studies suggest that the genetic basis of DP is likely to be highly heterogeneous. Abnormalities of GnRH neuronal development, function, and its downstream pathways, metabolic and energy homeostatic derangements, and transcriptional regulation of the hypothalamic-pituitary-gonadal axis may all lead to DP. This variety of different pathogenic mechanisms affecting the release of the puberty 'brake' may take place in several age windows between fetal life and puberty.

Review of the role of leptin in the regulation of male reproductive function

Since discovered in 1994, leptin has been thought to be a pleiotropic hormone that regulates food intake, controls energy balance in the body and influences multiple tissues in the body. Leptin plays an important mediating role in the regulation of neuroendocrine and can transmit the nutritional status signals to the reproductive-related central nervous system. Many studies have shown that leptin may play an important role in the control of reproductive function. Leptin can act on all levels of the hypothalamus-pituitary-gonadal (HPG) axis and may have local effects on the function of testis and spermatogenesis. Leptin is critical for puberty initiation and can also modulate testosterone synthesis by downregulating cAMP-dependent activation of steroidogenic genes expressions. Leptin is found to be higher in infertile men than in normal subjects. Yet, the exact role of leptin in the regulation of male reproductive function remains incomplete. The purpose of this review was to summarise the recent research about the biological effects of leptin on male reproductive system. In-depth study of leptin in reproductive system will help to reveal the pathogenesis of infertility and provide new treatment ideas for human assisted reproductive technology.

Contributions of Function-Altering Variants in Genes Implicated in Pubertal Timing and Body Mass for Self-Limited Delayed Puberty

CONTEXT

Self-limited delayed puberty (DP) is often associated with a delay in physical maturation, but although highly heritable the causal genetic factors remain elusive. Genome-wide association studies of the timing of puberty have identified multiple loci for age at menarche in females and voice break in males, particularly in pathways controlling energy balance.

OBJECTIVE/MAIN OUTCOME MEASURES

We sought to assess the contribution of rare variants in such genes to the phenotype of familial DP.

DESIGN/PATIENTS

We performed whole-exome sequencing in 67 pedigrees (125 individuals with DP and 35 unaffected controls) from our unique cohort of familial self-limited DP. Using a whole-exome sequencing filtering pipeline one candidate gene [fat mass and obesity-associated gene (FTO)] was identified. In silico, in vitro, and mouse model studies were performed to investigate the pathogenicity of FTO variants and timing of puberty in FTO+/- mice.

RESULTS

We identified potentially pathogenic, rare variants in genes in linkage disequilibrium with genome-wide association studies of age at menarche loci in 283 genes. Of these, five genes were implicated in the control of body mass. After filtering for segregation with trait, one candidate, FTO, was retained. Two FTO variants, found in 14 affected individuals from three families, were also associated with leanness in these patients with DP. One variant (p.Leu44Val) demonstrated altered demethylation activity of the mutant protein in vitro. Fto+/- mice displayed a significantly delayed timing of pubertal onset (P < 0.05).

CONCLUSIONS

Mutations in genes implicated in body mass and timing of puberty in the general population may contribute to the pathogenesis of self-limited DP.

A link between hypothyroidism, obesity and male reproduction

Hypothyroidism is a condition in which the serum levels of thyroid hormones are below that necessary to carry out physiological functions in the body. Hypothyroidism is related to obesity as an increase in body weight gain is seen in hypothyroid patients. Moreover, an inverse correlation between free thyroxine values and body mass index has been reported. Leptin, a polypeptide hormone produced by adipocytes, was originally thought to be an antiobesity hormone due its anorexic effects on hypothalamic appetite regulation. However, nowadays it is known that leptin conveys information about the nutritional status to the brain being considered a crucial endocrine factor for regulating several physiological processes including reproduction. Since the identification of thyroid hormone and leptin receptors on the testes, these hormones are being recognized as having important roles in male reproductive functions. A clear link exists among thyroid hormones, leptin and reproduction. Both hormones can negatively affect spermatogenesis and consequently may cause male infertility. The World Health Organization (WHO) estimates the overall prevalence of primary infertility ranging from 8 to 15%. The fact that 30% of couples' inability to conceive is related to a male factor and that the longer hypothyroidism persisted, the greater the damage to the testes, strongly suggest that more studies attempting to clarify both hormones actions directly in the testes need to be conducted specially in cases of congenital hypothyroidism. Therefore, the goal of this review is to highlight the relationship of such hormones in the reproductive system.

From Placenta to Polycystic Ovarian Syndrome: The Role of Adipokines

Adipokines are cytokines produced mainly by adipose tissue, besides many other tissues such as placenta, ovaries, peripheral-blood mononuclear cells, liver, muscle, kidney, heart, and bone marrow. Adipokines play a significant role in the metabolic syndrome and in cardiovascular diseases, have implications in regulating insulin sensitivity and inflammation, and have significant effects on growth and reproductive function. The objective of this review was to analyze the functions known today of adiponectin, leptin, resistin, and visfatin from placenta throughout childhood and adolescence. It is well known now that their serum concentrations during pregnancy and lactation have long-term effects beyond the fetus and newborn. With regard to puberty, adipokines are involved in the regulation of the relationship between nutritional status and normal physiology or disorders of puberty and altered gonadal function, as, for example, premature pubarche and polycystic ovarian syndrome (PCOS). Cytokines are involved in the maturation of oocytes and in the regular progression of puberty and pregnancy.

Elevated phthalates' exposure in children with constitutional delay of growth and puberty

BACKGROUND

Phthalates have been proven to be antiandrogenic, which may interfere with the timing of puberty. Children with Constitutional Delay of Growth and Puberty (CDGP) typically display short stature and pubertal delay. This study investigated whether phthalate's exposure was associated with CDGP, and evaluated the potential mediator role of testosterone.

METHODS

In this case-control study, a total of 167 boys, including 57 boys with CDGP (cases) and 110 controls were enrolled. We measured six major phthalate metabolites in urine samples using high-performance liquid chromatography and tandem mass spectrometry (LC-MS/MS). The serum testosterone level was determined by radioimmunoassay.

RESULTS

Children in the CDGP group were determined to have significantly elevated urinary phthalates concentration compared with control subjects (total phthalates median: case, 107.00 ng/ml; control, 62.22 ng/ml, p = 0.001). After adjustment for BMI and other confounding factors: mono-n-butyl phthalate (MBP), monoethyl phthalate (MEP) and total phthalate concentrations were significantly negatively associated with serum testosterone level (MBP: β = -45.7, p = 0.017; MEP: β = -31.6, p = 0.022; total phthalates: β = -24.6, p = 0.011); MBP, MEP, mono (2-ethylhexyl) phthalate (MEHP) and total phthalates were significantly associated with CDGP (odds ratio: MBP: 8.30, p = 0.002; MEP: 5.43, p = 0.002; MEHP: 3.83, p = 0.017; total phthalates: 9.09, p = 0.001). Serum testosterone level acted as a mediator of the association between phthalates' exposure and CDGP (p = 0.002) (proportion mediated: 34.4%).

CONCLUSIONS

In this case-control study, elevated phthalates' level was detected in children with CDGP in Shanghai, China and phthalate level was associated with CDGP, which appeared to be mediated by circulating testosterone level.

Thyroid hormone and leptin in the testis

Leptin is primarily expressed in white adipose tissue; however, it is expressed in the hypothalamus and reproductive tissues as well. Leptin acts by activating the leptin receptors (Ob-Rs). Additionally, the regulation of several neuroendocrine and reproductive functions, including the inhibition of glucocorticoids and enhancement of thyroxine and sex hormone concentrations in human beings and mice are leptin functions. It has been suggested that thyroid hormones (TH) could directly regulate leptin expression. Additionally, hypothyroidism compromises the intracellular integration of leptin signaling specifically in the arcuate nucleus. Two TH receptor isoforms are expressed in the testis, TRa and TRb, with TRa being the predominant one that is present in all stages of development. The effects of TH involve the proliferation and differentiation of Sertoli and Leydig cells during development, spermatogenesis, and steroidogenesis. In this context, TH disorders are associated with sexual dysfunction. An endocrine and/or direct paracrine effect of leptin on the gonads inhibits testosterone production in Leydig cells. Further studies are necessary to clarify the effects of both hormones in the testis during hypothyroidism. The goal of this review is to highlight the current knowledge regarding leptin and TH in the testis.

Leptin in pediatrics: A hormone from adipocyte that wheels several functions in children

The protein leptin, a pleiotropic hormone regulates appetite and energy balance of the body and plays important roles in controlling linear growth, pubertal development, cardiovascular function, and immunity. Recent findings in the understanding of the structure, functional roles, and clinical significance of conditions with increased and decreased leptin secretion are summarized. Balance between leptin and other hormones is significantly regulated by nutritional status. This balance influences many organ systems, including the brain, liver, and skeletal muscle, to mediate the essential adaptation process. The aim of this review is to summarize the possible physiological functions of leptin and its signaling pathways during childhood and adolescence including control of food intake, energy regulation, growth and puberty, and immunity. Moreover, its secretion and possible roles in the adaptation process during different disease states (obesity, malnutrition, eating disorders, delayed puberty, congenital heart diseases and hepatic disorders) are discussed. The clinical manifestations and the successful management of patients with genetic leptin deficiency and the application of leptin therapy in other diseases including lipodystrophy, states with severe insulin resistance, and diabetes mellitus are discussed.

Leptin signaling and circuits in puberty and fertility

Leptin is an adipocyte-derived hormone involved in a myriad of physiological process, including the control of energy balance and several neuroendocrine axes. Leptin-deficient mice and humans are obese, diabetic, and display a series of neuroendocrine and autonomic abnormalities. These individuals are infertile due to a lack of appropriate pubertal development and inadequate synthesis and secretion of gonadotropins and gonadal steroids. Leptin receptors are expressed in many organs and tissues, including those related to the control of reproductive physiology (e.g., the hypothalamus, pituitary gland, and gonads). In the last decade, it has become clear that leptin receptors located in the brain are major players in most leptin actions, including reproduction. Moreover, the recent development of molecular techniques for brain mapping and the use of genetically modified mouse models have generated crucial new findings for understanding leptin physiology and the metabolic influences on reproductive health. In the present review, we will highlight the new advances in the field, discuss the apparent contradictions, and underline the relevance of this complex physiological system to human health. We will focus our review on the hypothalamic circuitry and potential signaling pathways relevant to leptin’s effects in reproductive control, which have been identified with the use of cutting-edge technologies of molecular mapping and conditional knockouts.

Association of ghrelin and leptin with reproductive hormones in constitutional delay of growth and puberty

BACKGROUND

Constitutional delay of growth and puberty (CDGP) is a variation of the onset and timing of pubertal development without a defined endocrine abnormality. Recently published studies indicate that leptin and ghrelin play a role in puberty initiation and progress. They have been implicated in regulation of GnRH secretion, with ghrelin having inhibitory and leptin, facilitatory effects. We hypothesized that elevated ghrelin and reduced leptin concentrations could be implicated in altering the tempo of puberty in adolescents with CDGP. So in the current study we evaluate variations in leptin and ghrelin levels in adolescent boys with CDGP, the relationships between both hormones and reproductive hormones including LH, FSH and testosterone were also evaluated.

METHODS

The study enrolled 23 adolescent boys with CDGP and 20 healthy controls matched for age and sex. Weight, height, BMI, testicular volume, bone age, bone age delay, serum FSH, LH, testosterone, leptin and ghrelin were assessed.

RESULTS

Adolescent boys with CDGP had significantly lower leptin and higher ghrelin than normal controls. Leptin was positively correlated with BMI, bone age, testicular volume, FSH, LH and testosterone and negatively correlated with delayed bone age and ghrelin. Ghrelin was negatively correlated with BMI, bone age, testicular volume, FSH, LH and testosterone. With multiple regression analysis BMI, FSH, LH, testosterone and ghrelin remained independently correlated with leptin while BMI, LH and testosterone remained independently correlated with ghrelin.

CONCLUSION

Elevated serum ghrelin and decreased leptin concentrations and their associations with reproductive hormones may explain the sexual immaturity in adolescent boys with CDGP.

Pubertal development and menarche

Puberty is the developmental process that culminates in reproductive capability and is the result of a complex series of molecular and physiological events. The release of gonadotropin-releasing hormone from specialized neurons of the hypothalamus begins the hormonal cascade that causes gonadal activation and the physical changes of puberty. Several factors have been proposed to influence the activation of the hypothalamus to trigger puberty, but the involved pathways have not been fully elucidated. The recent observations that the age of pubertal onset may be lowering in American girls calls attention to the lack of knowledge of modulating factors that affect the pubertal process. Genes necessary for puberty have been found by studying persons who do not achieve puberty; such studies have provided insights into the pathways necessary for pubertal development. A multidisciplinary focus is required to elucidate the complex mechanisms involved in the initiation and progression of puberty.

The genetic basis for the timing of human puberty

Puberty is a complex, coordinated biological process with multiple levels of regulation. Epidemiological observations suggest that the timing of pubertal events is a heritable trait, although environmental factors can modulate such genetic influence. The study of pathological states of early and late puberty has provided valuable insight into those genes that regulate gonadotrophin-releasing hormone (GnRH) activity. The development of pulsatile release of GnRH secretion mediated through kisspeptin-1 activation of G-protein coupled receptor-54 appears to be a central event at the onset and during progression of puberty. Stimulating and restraining influences (e.g. in the form of glutamatergic and GABAergic neuronal inputs) are likely to influence the timing of this process. The study of extreme variants of 'normality', such as constitutional delay of growth and puberty and early puberty, may lead to the recognition of additional genes and pathways that can modulate both the timing of pubertal onset and its tempo.

The Relationship between Nocturnal Urinary Leptin and Gonadotrophins as Children Progress towards Puberty

BACKGROUND/AIMS

Leptin is necessary for normal human pubertal development but its exact role in the period leading up to the onset of puberty has not been defined. This study has assessed the relationship between leptin and gonadotrophin secretion over time as children progress into puberty.

SUBJECTS AND METHODS

Twenty children (13 boys and 7 girls) judged to be close to the initiation of puberty were recruited. Three consecutive first morning urine samples were collected from each subject each month over 6 months. At the end of the study, the children were classified into those who remained physically prepubertal (n = 7) and those that had advanced in puberty (n = 13). Leptin and gonadotrophins were measured by immunoradiometric and immunofluorometric assay, respectively.

RESULTS

Total urinary leptin excreted over 6 months was higher in girls than in boys, both prepubertally and in early puberty, and in both sexes, was higher in those advancing into puberty than in those remaining prepubertal (girls 8.0 vs. 3.4 ng/l and boys 3.6 vs. 1.7 ng/l; both p < 0.05). In the whole group, when controlling for gender, there was a significant correlation between both leptin and luteinizing hormone (LH; r = 0.43, p < 0.001) and leptin and follicle-stimulating hormone (FSH; r = 0.32, p = 0.001). The possibility of a lead relationship was explored by pairing leptin values with the gonadotrophin values in the following month. Leptin was significantly correlated with FSH but not LH in both pre- and peripubertal children (prepubertal r = 0.45, p = 0.01; peripubertal r = 0.32, p = 0.01).

CONCLUSIONS

This study has shown that in children approaching and progressing into puberty, leptin is associated with LH and FSH over the same time frame, and with FSH when leptin is acting as the lead hormone. These data imply that leptin is an important facilitator of the early phases of human puberty.

Longitudinal study of the simultaneous secretion of melatonin and leptin during normal puberty

BACKGROUND/AIMS

Pubertal changes are a consequence of the activation of the hypothalamic-pituitary-gonadal axis due to an increase in the frequency and magnitude of pulses of gonadotropin-releasing hormone (GnRH), which may depend on the intrinsic properties of the neurons of the hypothalamic arcuatus nucleus, or on the influence of neurotransmitters and/or neuromodulators. We evaluated the serum concentrations of melatonin and leptin in healthy prepubertal and adolescent subjects of both sexes, to define their participation at the initial stages and during the progression of pubertal development.

METHODS

80 pediatric subjects (47 females and 33 males), aged 6-18 years, were divided into 2 groups, prepubertal (n = 25) and adolescent (n = 55), according to the absence or presence, respectively, of physical signs of pubertal development. The subjects were assessed on two occasions: at the time of their inclusion in the study, and 12-18 months later when the subject had advanced one pubertal stage according to the Tanner classification. Blood was obtained in fasting for clinical purposes and for the hormonal study. Melatonin and leptin were measured by radioimmunoanalysis.

RESULTS

As described previously, melatonin decreases at the onset of puberty and during pubertal development. Both the absolute melatonin value and the decrease between evaluations tended to be greater in females; the variations were correlated with neither an increase in body weight nor with the degree of pubertal development. The concentration of leptin increased in both sexes with the progression of puberty, this value being 40% greater in women, and correlated with the indicators of an increase in body volume and fat accumulation. Although its concentration remained stable between evaluations for both sexes, among the males the association between leptin and pubertal development took place at the start of the process, while for the females we observed a significant overall association between pubertal stage and leptin concentration, this association being stronger at more advanced Tanner stages. Neither at the onset of puberty nor during its course did we observe any significant relation between melatonin concentration and any of the Tanner stages, whether for males or for females. Neither was there any correlation between the absolute values or rates of modification of melatonin and leptin.

CONCLUSION

According to the evolutionary dynamics of their respective concentrations, both initially and during pubertal progress, melatonin and leptin do not interact in the initiation or progression of human pubertal development, and do not seem to play a key role in this process.

Gluten-free diet impact on leptin levels in asymptomatic coeliac adolescents: one year of follow-up

Coeliac disease, daily more frequently diagnosed in our population, involves many organs also in oligosymptomatic patients and with an adequate nutritional regime. Possible endocrine implications include failure to thrive, pubertal delay and reproduction diseases due to deregulation of GH, FSH and LH secretion. Leptin, an adipose tissue hormone, can be decreased as well and its deficiency could be related to growth and puberty anomalies. We studied 14 asymptomatic coeliac patients in peripubertal age (7.5-13.8 years) and tested their leptin levels in order to correlate them with endocrine and anthropometric data. Before the diet was started leptinaemia (M+/-DS) was: 4.94+/-5.53 ng/ml. In 10/14 patients (71%) leptinaemia was<or=2 DS for gender and age. In all the patients, after a period of 6-12 months of gluten-free diet, Leptin levels appreciably raised to 10.8+/-7.9 ng/ml, with a significant correlation to the time of the diet. Leptinaemia was actually lower in patients with a severe mucosal atrophy, and in these patients it increased more significantly after the diet was started. The removal of gluten itself may reduce immunological hit to adipose tissue and the 'malnutrition' of adipocytes: leptin can hence increase despite no significant increase of body mass index occurs. This study could partially explain the correlation between body mass index, Coeliac disease and the deregulation of puberty and fertility, mainly in patients who started the diet late. It could also explain the reversibility of this alteration if the cause is removed.

Serum ghrelin, IGF-I and IGFBP-3 levels in children with normal variant short stature

This study is planned to investigate the role of ghrelin in normal variant short stature. Serum ghrelin, IGF-I and IGFBP-3 levels were measured in 17 children with constitutional delay of growth, 19 children with familial short stature and 11 age matched healthy children. Mean bone age of the constitutional delay of growth group was lower compared to other groups. Constitutional delay of growth group had lower mean weight compared to the controls. Serum IGF-I values were lower in the constitutional delay of growth group compared to the familial short stature and control groups. IGFBP-3 levels of the groups were similar. Ghrelin levels were higher in the short stature groups compared to the controls. In the multiple regression analyses, weight (beta = -.54, p < 0.0001) and height SDS (beta = -.33, p = 0.01) were the independent determinants of ghrelin. The results of this study, the first one in which ghrelin levels are investigated in normal variant short stature, suggest that ghrelin does not play a role as a cause, but as a consequence in these patients because it is negatively correlated with weight and height standard deviation score. These negative correlations can be attributed to the compensatory response of ghrelin, which deserves further attention in future studies.

Somatotropic and gonadotropic axes linkages in infancy, childhood, and the puberty-adult transition

Integrative neuroendocrine control of the gonadotropic and somatotropic axes in childhood, puberty, and young adulthood proceeds via multiple convergent and divergent pathways in the human and experimental animal. Emerging ensemble concepts are required to embody independent, parallel, and interacting mechanisms that subserve physiological adaptations and pathological disruption of reproduction and growth. Significant advances in systems biology will be needed to address these challenges.

Regulation and disorders of pubertal timing

Disorders of pubertal timing are common and challenging problems for pediatric endocrinologists. Early or late puberty can have immediate effects on a child's psychosocial well-being and may have long-term effects on adult stature. Much is known about the regulation of the hypothalamic-pituitary-gonadal axis, but the triggers of pubertal onset in the general population remain elusive. This article reviews recent data suggesting a possible shift in the age of pubertal onset; current knowledge regarding factors that regulate the onset of puberty; and the etiologies, diagnosis, and treatment of precocious and delayed puberty.

Children with idiopathic short stature are poor eaters and have decreased body mass index

OBJECTIVE

In children with idiopathic short stature (ISS), studies investigating body mass index (BMI) or parameters of satiety regulation are scarce, and studies analyzing eating behavior are lacking.

METHODS

We recruited 214 children (123 index cases and 91 siblings) with ISS from 123 families. Affected children had to have a body height <5th percentile, or, in the case of siblings, the body height of 1 child had to be <5th percentile and the other <15th percentile. Medical histories were recorded by using structured and standardized interviews. Eating behavior was assessed by using the Child Eating Behavior Questionnaire. Percent energy intake as fat was assessed by using the Leeds Food Frequency Questionnaire. Endocrine markers of body weight regulation (leptin, ghrelin) were determined in serum.

RESULTS

Compared with population norms, BMI was significantly lower (mean: -0.33 standard deviation score). Furthermore, there was decreased food responsiveness (mean Child Eating Behavior Questionnaire score: 1.9; population mean: 2.4), reduced enjoyment of food (3.2 vs 3.9), emotional undereating (2.6 vs 3.0), lower desire to drink (2.0 vs 2.8), and increased fussiness over food (3.2 vs 2.9). When the sample was subdivided into the 2 groups of "good" and "poor" eaters according to the mothers' assessment of the current eating behavior, reduction in BMI as well as the behavioral characteristics already delineated in the total sample were found to be even more consistent in the subgroup of poor eaters. In the total sample of our children, as well as in both subgroups, serum leptin (adjusted for gender, BMI, and Tanner stage) was found to be moderately raised but did not differ between poor and good eaters. Total serum ghrelin was not different between poor and good eaters.

CONCLUSIONS

Our clinical, behavioral, and endocrinologic findings in patients with ISS point to an altered eating behavior that possibly contributes to their short stature.

The role of falling leptin levels in the neuroendocrine and metabolic adaptation to short-term starvation in healthy men

To elucidate the role of leptin in regulating neuroendocrine and metabolic function during an acute fast, six to eight healthy, lean men were studied under four separate conditions: a baseline fed state and three 72-hour fasting studies with administration of either placebo, low-dose recombinant-methionyl human leptin (r-metHuLeptin), or replacement-dose r-metHuLeptin designed to maintain serum leptin at levels similar to those in the fed state. Replacement-dose r-metHuLeptin administered during fasting prevents the starvation-induced changes in the hypothalamic-pituitary-gonadal axis and, in part, the hypothalamic-pituitary-thyroid axis and IGF-1 binding capacity in serum. Thus, in normal men, the fall in leptin with fasting may be both necessary and sufficient for the physiologic adaptations of these axes, which require leptin levels above a certain threshold for activation. In contrast to findings in mice, fasting-induced changes in the hypothalamic-pituitary-adrenal, renin-aldosterone, and growth hormone-IGF-1 axes as well as fuel utilization may be independent of leptin in humans. The role of leptin in normalizing several starvation-induced neuroendocrine changes may have important implications for the pathophysiology and treatment of eating disorders and obesity.

Serum leptin and interleukin-6 levels in pediatric patients with HIV

Recent therapeutic approaches have improved the prognosis of children with HIV. Many new efforts could be involved in their quality of life and therefore could need additional diagnostic strategies. Leptin regulates pubertal development; furthermore a continuous immune stimulus, as in chronic infectious diseases, can enhance leptin's secretion by the action of cytokines such as interleukin (IL)-6. To clarify this role in patients infected with HIV, we assayed leptin and IL-6 and evaluated the influence of HIV severity on its secretion. IL-6 (380.5 +/- 257.6 pg/ml; range: 22-900 pg/ml) showed a significant correlation with leptinemia, HIV-1 RNA, and viremia related to the stage of HIV disease. The difference in leptinemia from a control group (3 +/- 3.2 ng/ml; range: 1-12 ng/ml in HIV patients; 6.72 +/- 8 ng/ml in the controls) did not reach statistical significance, nor did it correlate with pubertal stage, BMI, viremia, CD4 or anti-retroviral therapy. There was a statistically significant correlation between leptinemia and the stage of the HIV disease, and with IL-6 level. We want to stress the role of immunological factors in enhancing leptin secretion.

Diurnal leptin secretion is intact in male hypogonadotropic hypogonadism and is not influenced by exogenous gonadotropins

Circulating leptin shows a pulsatile secretory pattern along with a nocturnal rise. We have previously shown that circulating leptin concentrations are high in males with untreated idiopathic hypogonadotropic hypogonadism (IHH). However, circadian leptin secretion in IHH before and after gonadotropin treatment is not known. Thus, we studied 14 adult males with IHH who had no history of previous hormonal therapy, and 12 age- and body mass index-matched healthy men. Plasma leptin concentrations were measured with 1-h intervals for 24 h before and 6 months after gonadotropin treatment. The 24-h mean leptin concentration showed a significant decrease, from 11.78 +/- 1.908 microg/liter at baseline to 10.85 +/- 1.939 microg/liter after 6 months of therapy (z = 3.107; P = 0.002). Before and after treatment, 24-h mean leptin concentrations were also significantly higher in the patient group when compared with controls (4.275 +/- 0.711 microg/liter) (z = 5.938; P = 0.0001). Hourly leptin levels demonstrated a diurnal pattern in hypogonadal patients, a surge in the midday, and a peak just after midnight, and this pattern did not differ before and after treatment. We observed a similar diurnal pattern in the control subjects too. Leptin levels were negatively and significantly correlated with free testosterone and total testosterone levels both before (r = -0.656, P = 0.011; and r = -0.639, P = 0.014, respectively) and after (r = -0.537, P = 0.048; and r = -0.563, P = 0.036, respectively) gonadotropin administration. Our observations suggest that the diurnal rhythm of leptin is intact in males with IHH, and short-term gonadotropin treatment does not effect its diurnal rhythm. Moreover, testosterone produced under the influence of the gonadotropin treatment led to decreases in the leptin levels.

Delayed puberty: analysis of a large case series from an academic center

Despite the clinical importance of delayed puberty, the understanding of this condition is hampered by the lack of studies evaluating etiologies and predisposing factors among large case series. We performed a retrospective study of clinical and laboratory data from adolescents (< or =18 yr of age) with delayed puberty who had been seen in our clinic between 1/96 and 7/99 (n = 232 subjects; 158 males and 74 females). Family histories of pubertal timing among primary relatives were classified as negative, having at least a tendency to pubertal delay (development > or =1 SD beyond the mean), or diagnostic of delay (development > or =2 SD beyond the mean). The most common cause of delayed puberty was constitutional delay of growth and maturation (CD), which affected 53% of the subjects (63% of males and 30% of females). The remaining subjects could be divided into four categories: those with an underlying condition associated with delayed, but spontaneous, pubertal development [functional hypogonadotropic hypogonadism (FHH)], 19% of subjects; those with permanent hypogonadotropic hypogonadism, 12% of subjects; those with permanent hypergonadotropic hypogonadism, 13% of subjects; and those without clearly classified disorders, 3% of subjects. Like CD, FHH was male predominant, whereas the other categories either affected both genders equally or were predominantly female. In total, 50 different etiologies led to pubertal delay within our case series. Data permitted classification of family histories of pubertal timing among primary relatives in 95 of 122 of the CD and in 25 of 45 of the FHH cases. Analysis revealed at least a tendency to pubertal delay in 77% of the CD and in 64% of the FHH families and a diagnosis of delay in 38% of the CD and 44% of the FHH families. Both parents contributed to the positive family histories. The rates of positive family histories among the CD and FHH groups were approximately twice those seen among the other subjects in our case series. Among all subjects, those with FHH had the most marked growth delay, and girls had the greater bone age delay. Among the boys and at comparable chronological ages, CD and FHH were characterized by greater delays in pubic hair development and bone age than in the other diagnostic groups. Although CD is typically associated with leanness, 22% of our subjects had a BMI SD score at the 85th percentile or above for chronological age. These overweight subjects differed from the rest of the CD group: bone age was less delayed, and height was less affected. Finally, our analysis suggested a possible association between attention deficit disorder with or without hyperactivity and pubertal delay in our CD and FHH subjects. Our study provides valuable data regarding the variety and frequency of diagnoses that lead to delayed puberty. The results underscore the importance of performing a thorough evaluation and family history in adolescents with delayed puberty. Moreover, the data from our case series provide clues for unraveling the mechanism(s) of idiopathic pubertal delay and lead to the hypothesis that the pubertal delay seen among some subjects with FHH and CD may stem in part from similar underlying physiology.

Leptin and puberty

Leptin is thought to relay metabolic information to the hypothalamic-pituitary- gonadal axis and to participate in the neuroendocrine control of puberty. To help elucidate the underlying mechanism, Cheung et al. recently performed a diverse series of experiments, the results of which undermine the prevailing hypothesis that leptin acts as a metabolic trigger for the initiation of puberty. Instead, their results suggest that leptin is one of many permissive metabolic factors that allow pubertal development to proceed.

Leptin and puberty: a review

Over the last few years, many studies have focused on leptin, the product of the LEP (ob) gene, searching for a possible link between energy balance and reproduction. The involvement of this peptide in the regulation of the hypothalamo-pituitary-adrenal, gonadal, thyroid and somatotroph axes suggests that leptin might play a pivotal role in coordinating the activity of these axes and their relationship with the body's energy balance. The effects of leptin on hypothalamic, pituitary and peripheral hormone levels, as well as the presence of the leptin receptor in a variety of tissues, suggest both an endocrine and a paracrine mode of action. Particular attention was paid to the effect of leptin on the gonadal axis as infertility, a characteristic feature of both the leptin deficient ob/ob mice and the leptin receptor mutant db/db mice, could be corrected in ob/ob mice by leptin administration. Considerable leptin level changes were observed during puberty both in animal and human studies. A matter of controversy is the precise role of leptin in the onset of puberty: is leptin the signal that initiates puberty and the accompanying hormonal changes, or has leptin only a permissive but key role for the onset of puberty, as likely seems to be the case for the maintenance of a functional gonadotroph axis? On current evidence, a mainly permissive role seems most probable.

Body fat mass, leptin and puberty

Leptin, the ob gene product, provides a molecular basis for the lipostatic theory of the regulation of energy balance. Leptin circulates as a monomeric 16 kDa protein in rodent and human plasma and is also bound to leptin binding proteins that may form large high molecular weight complexes. Initial models of leptin action included leptin-deficient ob/ob mice and leptin-insensitive db/db mice. Peripheral or central administration of leptin reduced body weight, adiposity, and food intake in ob/ob mice but not in db/db mice. In ob/ob mice leptin treatment restored fertility. Leptin interacts with many messenger molecules in the brain. For example, leptin suppresses neuropeptide Y (NPY) expression in the arcuate nucleus. Increased NPY activity has an inhibitory effect on the gonadotropin axis and represents a direct mechanism for inhibiting sexual maturation and reproductive function in conditions of food restriction and/or energy expenditure. By modulating the hypothalamo-pituitary-gonadal axis both directly and indirectly, leptin may thus serve as the signal from fat to the brain about the adequacy of fat stores for pubertal development and reproduction. Normal leptin secretion is necessary for normal reproductive function to proceed and leptin may be a signal allowing for the point of initiation of and progression toward puberty.