Academic literature on the topic 'Leptin Physiological effect'

Leptin is a well-known hunger-sensing peptide hormone. The role of leptin in weight gain and metabolic homeostasis has been explored for the past two decades. In this review, we have tried to shed light upon the impact of leptin signaling on health and diseases. At low or moderate levels, this peptide hormone supports physiological roles, but at chronically higher doses exhibits detrimental effects on various systems. The untoward effects we observe with chronically higher levels of leptin are due to their receptor-mediated effect or due to leptin resistance and are not well studied. This review will help us in understanding the non-anorexic roles of leptin, including their contribution to the metabolism of various systems and inflammation. We will be able to get an alternative perspective regarding the physiological and pathological roles of this mysterious peptide hormone.

To elucidate the role of leptin in acute systemic inflammation, we investigated how its infusion at low, physiologically relevant doses affects the responses to bacterial lipopolysaccharide (LPS) in rats subjected to 24 h of food deprivation. Leptin was infused subcutaneously (0–20 μg·kg−1·h−1) or intracerebroventricularly (0–1 μg·kg−1·h−1). Using hypothermia and hypotension as biomarkers of systemic inflammation, we identified the phase extending from 90 to 240 min post-LPS as the most susceptible to modulation by leptin. In this phase, leptin suppressed the rise in plasma TNF-α and accelerated the recoveries from hypothermia and hypotension. Suppression of TNF-α was not accompanied by changes in other cytokines or prostaglandins. Leptin suppressed TNF-α when infused peripherally but not when infused into the brain. Importantly, the leptin dose that suppressed TNF-α corresponded to the lowest dose that limited food consumption; this dose elevated plasma leptin within the physiological range (to 5.9 ng/ml). We then conducted in vitro experiments to investigate whether an action of leptin on macrophages could parallel our in vivo observations. The results revealed that, when sensitized by food deprivation, LPS-stimulated peritoneal macrophages can be inhibited by leptin at concentrations that are lower than those reported to promote cytokine release. It is concluded that physiological levels of leptin do not exert a proinflammatory effect but rather an anti-inflammatory effect involving selective suppression of TNF-α via an action outside the brain. The mechanism of this effect might involve a previously unrecognized, suppressive action of leptin on macrophage subpopulations sensitized by food deprivation, but future studies are warranted.

Interleukin-1β (IL-1β) is synthesized in a variety of tissues, including the hypothalamus, where it is implicated in the control of food intake. The current studies were undertaken to investigate whether hypothalamic IL-1β gene expression is subject to physiological regulation by leptin and glucocorticoids (GCs), key hormones involved in energy homeostasis. Adrenalectomy (ADX) increased hypothalamic IL-1β mRNA levels twofold, measured by real-time PCR ( P < 0.05 vs. sham-operated controls), and this effect was blocked by subcutaneous infusion of a physiological dose of corticosterone. Conversely, hypothalamic IL-1β mRNA levels were reduced by 30% in fa/fa (Zucker) rats, a model of genetic obesity caused by leptin receptor mutation ( P = 0.01 vs. lean littermates), and the effect of ADX to increase hypothalamic IL-1β mRNA levels in fa/fa rats ( P = 0.02) is similar to that seen in normal animals. Moreover, fasting for 48 h (which lowers leptin and raises corticosterone levels) reduced hypothalamic IL-1β mRNA levels by 30% ( P = 0.02), and this decrease was fully reversed by refeeding for 12 h. Thus leptin and GCs exert opposing effects on hypothalamic IL-1β gene expression, and corticosterone plays a physiological role to limit expression of this cytokine in both the presence and absence of intact leptin signaling. Consistent with this hypothesis, systemic leptin administration to normal rats (2 mg/kg ip) increased hypothalamic IL-1β mRNA levels twofold ( P < 0.05 vs. vehicle), an effect similar to that of ADX. These data support a model in which expression of hypothalamic IL-1β is subject to opposing physiological regulation by corticosterone and leptin.

Leptin, the protein product of the ob/ obgene, is thought to have a central site of action, presumably within the hypothalamus, through which it regulates feeding behavior. The paraventricular nucleus (PVN) is one structure that has been implicated in regulating feeding behavior. Using patch-clamp recording techniques, this study examines the direct membrane effects of leptin on neurons in a coronal PVN slice. Bath application of the physiologically active leptin fragment (amino acids 22–56) elicited dose-related depolarizations in 82% of the type I cells tested ( n = 17) and 67% of the type II cells tested ( n = 9). By contrast, the physiologically inactive leptin fragment (amino acids 57–92) had no discernible effect on membrane potential ( n = 7). The effects of this peptide were unaffected following synaptic isolation of the cells by bath application of the sodium channel blocker tetrodotoxin ( n = 5). Voltage clamp recordings in six cells demonstrated that leptin increased a nonspecific cation conductance with a reversal potential near −30 mV. These findings suggest that neurons in PVN may play an important role in the central neuronal circuitry involved in the physiological response to leptin.

There is clear evidence of placental leptin production, as shown recently in trophoblast cultures and by dual in vitro placenta perfusion (median production of 225 pg/min per g of tissue; 98.4% released into the maternal and 1.6% into the fetal circulation). However, the physiological impact for the mother and the fetus is unclear. The classical role of leptin is to provide information about energy stores to the central nervous system, and to reduce appetite if the energy stores are full. In pregnancy, maternal plasma leptin concentrations are elevated, and lack the well established correlation with body fat energy stores that is observed in non-pregnant women, indicating an alternative function for leptin during pregnancy and fetal development. Maternal and fetal plasma leptin levels are dysregulated in pathological conditions such as gestational diabetes, pre-eclampsia and intra-uterine growth retardation, representing an effect or a cause of disturbances in the feto/placento/maternal unit.

Thyroid hormones and leptin have effects on similar aspects of body homeostasis, such as energy expenditure, thermogenesis, and metabolic efficiency. Thus, the cross-talk between the thyrostat and the lipostat might play a crucial role in the maintenance of body homeostasis. To investigate the relationship between the hypothalamic-pituitary-thyroid (HPT) axis and leptin under physiological conditions, we evaluated the pulsatility and circadian rhythmicity and time-cross-correlated the 24-h secretory patterns of leptin and TSH in 12 short normal prepubertal children (6 girls and 6 boys). In both male and female subjects, leptin was secreted in a pulsatile and circadian fashion, with a nocturnal leptin surge that was more pronounced in males than in females. Mean 24-h leptin levels and total area under the curve were significantly higher in girls than in boys. This was mainly due to the nighttime mean leptin levels and total area under the curve, which were higher than those in boys. The cross-correlated 24-h leptin and TSH levels revealed significant positive and negative correlations. The positive one, of leptin over TSH, suggests a positive feedback regulation by leptin on the HPT axis, which might play an important role in triggering the neuroendocrine response to starvation, including decreased thyroid hormone levels. The negative correlation, of TSH over leptin, could explain the compensatory changes in adipocyte metabolism, and indirectly in circulating leptin levels, in response to alterations in thyroid status. In conclusion, we suggest that under baseline physiological conditions, the HPT axis has a prevailing inhibitory effect on leptin secretion, whereas leptin has a prevailing positive effect on the HPT axis. The sexual dimorphism in leptin levels does not seem to influence in a major way the interactions between the HPT axis and leptin.

We compared the estradiol/progesterone-induced luteinizing hormone [LH] and follicle-stimulating hormone [FSH] release between normally fed and leptin-supplemented starved ovariectomized female rats and studied also the effect of hyper-leptinaemia on the steroid-induced hormonal release in normally fed ovariectomized rats. Three days’ starvation completely abolished steroid-induced LH and FSH release. Significant recovery of the hormonal release was shown in the leptin-supplemented starved group. The magnitudes of LH and FSH release in the normally fed animals with a higher dose of leptin were statistically the same as those in the normally fed group without leptin. These observations indicate that physiological concentrations of circulating leptin exert a stimulatory effect on steroid-induced LH and FSH release.

Intracerebroventricular (ICV) administration of Neuromedin U (NMU), a hypothalamic neuropeptide, or leptin, an adipostat hormone released from adipose tissue, reduces food intake and increases energy expenditure. Leptin stimulates the release of NMU in vitro, and NMU expression is reduced in models of low or absent leptin. We investigated the role of NMU in mediating leptin-induced satiety. ICV administration of anti-NMU immunoglobulin G (IgG) (5 nmol) to satiated rats significantly increased food intake 4 h after injection, an effect seen for ≤8 h after injection. ICV administration of NMU (1 nmol) to fasted rats reduced food intake 1 h after injection compared with control, an effect attenuated by pretreatment with anti-NMU IgG. ICV administration of leptin (0.625 nmol) reduced 24-h food intake. This was partially attenuated by the administration of anti-NMU IgG [24 h after onset of dark phase: vehicle, 22.5 ± 2.0 g; leptin, 13.7 ± 2.3 g ( P < 0.005 vs. vehicle), leptin/NMU IgG, 19.4 ± 1.3 g ( P < 0.05 vs. leptin)]. Intraperitoneal administration of leptin (1.1 mg/kg body wt) reduced 24-h food intake. This was partially attenuated by ICV administration of anti-NMU IgG [24 h after onset of dark phase: vehicle, 31.4 ± 4.9 g; leptin, 20.8 ± 2.6 g ( P < 0.01 vs. vehicle); leptin/NMU IgG, 28.7 ± 1.1 g ( P < 0.01 vs. leptin)]. These results suggest that NMU plays a physiological role in the regulation of appetite and partially mediates the leptin-induced satiety.

There is increasing evidence that leptin is a physiological link between obesity and infertility. Although leptin receptors have been demonstrated in human ovaries, there is no information regarding the effects of leptin on cells from developing ovarian follicles. To test the direct effects of leptin on human ovarian cells, granulosa cells (GC) and theca cells were isolated from the ovaries of regularly cycling women. Serum was obtained at the time of surgery, and follicular fluid was aspirated from the follicles before isolation of the ovarian cells. Leptin concentrations were similar in follicular fluid and serum. RT-PCR analysis demonstrated that the long, signaling form of the leptin receptor was expressed in both theca and GC. In cultured GC, leptin had no effect on estradiol production, alone or in the presence of FSH, but caused a concentration-related inhibition of the insulin-like growth factor I (IGF-I) augmentation of FSH-stimulated estradiol production. The effect of leptin was specific, because there was no effect on progesterone production. In cultured theca cells, leptin did not alter androstenedione production, alone or in the presence of LH. Leptin caused a concentration-related inhibition of the IGF-I augmentation of LH-stimulated androstenedione production. These data demonstrate that leptin can directly inhibit IGF-I action in ovarian theca and GC at concentrations commonly present in obese women.

The ability to maintain core temperature within a narrow range despite rapid and dramatic changes in environmental temperature is essential for the survival of free-living mammals, and growing evidence implicates an important role for the hormone leptin. Given that thyroid hormone plays a major role in thermogenesis and that circulating thyroid hormone levels are reduced in leptin-deficient states (an effect partially restored by leptin replacement), we sought to determine the extent to which leptin’s role in thermogenesis is mediated by raising thyroid hormone levels. To this end, we 1) quantified the effect of physiological leptin replacement on circulating levels of thyroid hormone in leptin-deficient ob/ob mice, and 2) determined if the effect of leptin to prevent the fall in core temperature in these animals during cold exposure is mimicked by administration of a physiological replacement dose of triiodothyronine (T3). We report that, as with leptin, normalization of circulating T3 levels is sufficient both to increase energy expenditure, respiratory quotient, and ambulatory activity and to reduce torpor in ob/ob mice. Yet, unlike leptin, infusing T3 at a dose that normalizes plasma T3 levels fails to prevent the fall of core temperature during mild cold exposure. Because thermal conductance (e.g., heat loss to the environment) was reduced by administration of leptin but not T3, leptin regulation of heat dissipation is implicated as playing a uniquely important role in thermoregulation. Together, these findings identify a key role in thermoregulation for leptin-mediated suppression of thermal conduction via a mechanism that is independent of the thyroid axis.

Obesity has risen 75% in the United States since 1980 and an estimated 80 million American adults are considered obese. Obesity activates the sympathetic nervous system and is associated with neurogenic hypertension. Leptin is an obesity-related neuropeptide released from fat cells which reduces appetite and increases metabolism. Leptin activates metabolic and cardiovascular responsive pre‑sympathetic neurons within the hypothalamus. Although leptin increases metabolism and curbs appetite, it also increases blood pressure. Considering that one main goal of obesity treatments is to diminish the cardiovascular-related co-morbidities this is an unacceptable side effect for potential treatments. Thus, a better understanding of the role hypothalamic sites involved in obesity-related hypertension is necessary for successful treatments. Our hypothesis is that leptin activates hypothalamic neurons that control metabolic (raphe pallidus) and cardiovascular activity (RVLM, rostroventrolateral medulla) within the brainstem. To test our hypothesis we created a line of transgenic mice using the cre-lox recombination system to express the reporter gene tdTomato under the control of the leptin (ObRb) receptor gene. First, we performed a behavioral study to verify the physiological effect and optimal dose of daily leptin treatment. To do this we implanted mini-osmotic pumps for continuous subcutaneous leptin (400 ng/hr) administration and measured food intake and body weight over 4 weeks. To determine if leptin activates pre‑sympathetic hypothalamic neurons we performed neuroanatomical tracer studies in these mice. At the end of the 4-week period, we injected fluorescent retrograde tracers into the raphe pallidus (green, metabolic center) and RVLM (magenta, cardiovascular). We then performed fluorescence immunohistochemical labelling to identify leptin-induced neuronal activation cFos a marker of neuronal activation of these neurons. Data from this behavioral, neurophysiological and neuroanatomical study will provide a better understanding of the role of the hypothalamus in controlling blood pressure and metabolism in obesity. Information from this study will provide groundwork for a better understanding of central autonomic mechanisms of cardiovascular risk as well as risk introduced by drugs intended to treat obesity.

Thesis (PhD (Biomedical Sciences. Medical Physiology))--University of Stellenbosch, 2009.
ENGLISH ABSTRACT: In recent years there has been an increase in obesity and diabetes mellitus (DM). These conditions have for a long time been associated with infertility. Obesity is characterized by high levels of circulating leptin and cytokines as well as insulin resistance. Type I DM is associated with low or no insulin whereas, Type II DM is characterised by insulin resistance. As the prevalence of obesity and DM continues to rise, it is likely that the incidence of infertility associated with these pathological conditions will likewise increase. The effects of insulin and leptin on male reproductive function have been reported on the endocrine and spermatogenesis level, but their effects on cellular level of human ejaculated spermatozoa are yet to be elucidated. This study presents data on the role of insulin and leptin on human ejaculated spermatozoa and their interaction with cytokines and nitric oxide. In the first part of the study, we established the suitable concentrations of glucose, insulin and leptin that could be administered to human spermatozoa in vitro. Glucose concentration of 5.6 mM was chosen as the suitable concentration to be administered to human spermatozoa because it has previously been reported in the literature; furthermore, it is within the range of the physiological glucose levels found in the blood of fasting humans. Insulin and leptin concentrations of 10 μIU and 10 nmol were chosen respectively because they gave much improved sperm function and this was within the range of insulin and leptin levels previously measured in human ejaculated spermatozoa. This was followed by investigating the signalling pathway of insulin and its beneficial effects on human spermatozoa function. Endogenous insulin secretion from human ejaculated spermatozoa was blocked by nifedipine and its receptor tyrosine phosphorylation effects were inhibited by erbstatin while phosphatidylinositol 3-kinase (PI3K) phosphorylation activity was inhibited by wortmannin. Exogenous insulin administration significantly increased human sperm motility parameters as well as the sperm ability to acrosome react. The inhibition of endogenous insulin release from spermatozoa as well as the inhibition of the insulin receptor substrate (IRS) tyrosine phosphorylation significantly decreased motility parameters and the ability of spermatozoa to acrosome react. The study also investigated the effects of insulin and leptin on human sperm motility, viability, acrosome reaction and nitric oxide (NO) production. Both insulin and leptin significantly increased sperm motility parameters, acrosome reaction and NO production. The NO production induced by insulin and leptin was via PI3K signalling as evidenced by a reduction in NO levels when PI3K activity was inhibited by wortmannin. To investigate whether insulin and leptin could improve motility parameters of asthernozoospermic and teratozoospermic spermatozoa, the spermatozoa were separated into two fractions by means of a double density gradient technique. The gradient system was able to separate spermatozoa into high morphologically abnormal and less motile spermatozoa similar to that of asthernozoospermic and teratozoospermic patients as well as a more motile fraction. Insulin and leptin significantly increased the motility parameters of spermatozoa from the immature and less motile fraction. The fourth part of the study was aimed at investigating the effects of the cytokines, tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6), on human sperm motility, viability, acrosome reaction and NO production. The study shows that TNF-α and IL-6 significantly reduced motility parameters and acrosome reaction in a dose4 and time-dependent manner. These cytokines were also shown to significantly increase NO production from human spermatozoa. The decreased motility parameters induced by these cytokines could be attributed to their ability to induce excessive NO production. It is not yet clear how they inhibit spermatozoa to undergo the acrosome reaction. The fifth part of the study was to investigate the expression and localization of glucose transporter 8 (GLUT8) in human spermatozoa. This study shows that GLUT8 is constitutively expressed and located in the midpiece region of the human spermatozoa. The study also showed that stimulating spermatozoa with insulin led to an increase in GLUT8 expression as well as translocation to the acrosomal region. In the last part of the study we wanted to investigate why the increase in NO generation by spermatozoa due to insulin and leptin stimulation is accompanied with increased sperm function whereas NO increased due to TNF-α and IL-6 stimulation is accompanied with decreased sperm function. We observed that TNF-α and IL-6 not only increased NO production but also ROS production. This study speculates that the decrease in sperm motility and acrosome reaction when TNF-α and IL-6 were administered was due to the concomitant high increase in NO and ROS they induced. In conclusion, this study has established in vitro beneficial effects of insulin and leptin in normozoospermic and asthernozoospermic human sperm function. These hormones influence sperm function via the PI3K signalling pathway in two ways. Firstly, by increasing GLUT8 expression and translocation thereby possibly increasing glucose uptake and metabolism and secondly, by increasing NO production. The study has also established that TNF-α and IL-6 have detrimental effects on human spermatozoa in a dose and time dependent manner. These effects are mediated via their ability to stimulate both NO and ROS production in human spermatozoa. This study reports that GLUT8 is expressed in the midpiece region of human spermatozoa and that insulin stimulation upgrades its expression and leads to its translocation to the acrosomal region.
AFRIKAANSE OPSOMMING: Oor die afgelope jare was daar `n toename in obesiteit en diabetes mellitus (DM). Hierdie toestande word reeds vir ’n geruime tyd geassosieer met onvrugbaarheid. Obesiteit word gekenmerk deur verhoogde sirkulerende vlakke van leptiene en sitokiene sowel as insulien weerstandigheid. Tipe I DM word geassosieer met lae of geen insulien terwyl Tipe II DM gekenmerk word deur insulien weerstandigheid. Soos wat die voorkoms van obesiteit en DM toeneem, is dit waarskynlik dat die insidensie van onvrugbaarheid wat met hierdie patologiese toestande geassosieer word, gevolglik ook sal toeneem. Die effek van insulien en leptien op die manlike voortplantingsfunksie is alreeds aangetoon op endokriene en spermatogenese vlak, maar hul effekte op sellulêre vlak van menslike geëjakuleerde spermatosoë is nog onduidelik. Die studie vertoon data oor die rol van insulien en leptien op die menslike geëjakuleerde spermatosoë en hul interaksie met sitokiene en stikstofoksied (NO). In die eerste gedeelte van die studie, het ons ’n toepaslike konsentrasie van insulien en leptien bepaal wat aan menslike spermatosoë in vitro toegedien kan word. Glukose konsentrasies van 5,6 mM is bepaal as die gepaste konsentrasie om aan menslike spermatosoë toe te dien, omdat dit beter resultate tot gevolg het; verder is dit vergelykbaar met fisiologiese glukose vlakke in die bloed van `n vastende persoon. Insulien en leptien konsentrasies is op 10 μIU en 10 nm onderskeidelik vasgestel, aangesien dit tot beter resultate gelei het, en omdat dit vergelykbaar was met insulien en leptien vlakke wat reeds voorheen in menslike geëjakuleerde spermatosoë gemeet is. Dit was gevolg deur `n ondersoek na die insulien seintransduksie pad en sy voordelige effekte op menslike spermatosoë funksie. Endogene insulien afskeiding deur menslike geëjakuleerde spermatosoë was deur nifedipien geïnhibeer en sy reseptor tirosien fosforilasie effekte was deur erbstatin geïnhibeer terwyl fosfatidielinositol 3-kinase (PI3K) fosforilasie deur wortmannin geïnhibeer is. Eksogene insulien toediening het menslike sperm-motiliteit parameters betekenisvol laat toeneem asook die vermoë van sperme om die akrosoomreaksie te ondergaan. Die inhibisie van endogene insulien afskeiding deur spermatosoë sowel as die inhibisie van die insulien reseptor substraat (IRS) tirosien fosforilasie het die motiliteit parameters en die akrosoomreaksievermoë van spermatosoë verlaag. Die studie het ook die effekte van insulien en leptien op menslike sperm-motiliteit, -lewensvatbaarheid, -akrosoomreaksie en -NO produksie nagevors. Beide insulien en leptien het sperm-motiliteit parameters, -akrosoomreaksie en -NO produksie betekenisvol verhoog. NO produksie is deur insulien en leptien via PI3K seintransduksie geïnduseer, soos bewys deur die verlaging waargeneem in NO vlakke toe PI3K aktiwiteit deur wortmannin geïnhibeer was. Om vas te stel of insulien en leptien die motiliteit parameters van asthenozoospermiese en teratozoospermiese spermatosoë kon verbeter, het ons spermatosoë in twee fraksies met ’n dubbel digtheid gradiënt geskei. Die gradiënt sisteem was daartoe instaat om die spermatosoë in ’n onvolwasse, (morfologies abnormaal en minder motiel - soortgelyk aan dié van asthenozoospermiese en teratozoospermiese pasiënte), sowel as ’n volwasse meer motiele fraksie te skei. Insulien en leptien het die motiliteit parameters van spermatosoë van die onvolwasse en minder motiele fraksie verhoog. Die vierde gedeelte van die studie was daarop gemik om die effekte van die sitokiene tumor nekrose faktor alfa (TNF-α) en interleukin-6 (IL-6) op menslike sperm-motiliteit, -lewensvatbaarheid, -akrosoomreaksie en -NO produksie, te ondersoek. Die studie het getoon dat TNF-α en IL-6 motiliteit parameters en akrosoomreaksie in ’n tyd- en dosis-afhanklike wyse betekenisvol verlaag het. Hierdie sitokiene was ook in staat om NO produksie in menslike spermatosoë te verhoog. Die verlaging in motiliteit parameters wat deur hierdie sitokiene geïnduseer is, kan toegeskryf word aan hul vermoë om die produksie van oormatige hoeveelhede NO te stimuleer. Dit is nog nie duidelik hoe hulle die akrosoomreaksie in spermatosoë kan inhibeer nie. Die vyfde gedeelte van die studie het dit ten doel gehad om die uitdrukking en lokalisering van die glukose transporter 8 (GLUT8) in menslike spermatosoë te ondersoek. Hierdie studie kon aantoon dat GLUT8 konstitutief uitgedruk is en in die middelstuk van die menslike spermatosoë voorkom. Die studie bewys ook dat stimulering van die spermatosoë met insulien tot `n toename in GLUT8 uitdrukking sowel as translokasie na die akrosomale area, lei. In die finale gedeelte van die studie wou ons ondersoek waarom die toename in NO produksie in spermatosoë (as gevolg van insulien en leptien stimulasie) deur `n toename in spermfunksie gekenmerk word, terwyl die toename in NO produksie (as gevolg van TNF-α en IL-6 stimulasie) deur ’n afname in spermfunksie gekenmerk word. Ons het waargeneem dat TNF-α en IL-6 nie alleen NO produksie nie, maar ook reaktiewe suurstof spesies (ROS) produksie verhoog het. Ons vermoed dat die afname in sperm motiliteit en akrosoomreaksie met TNF-α en IL-6 toediening, die gevolg van die gelyktydige verhoging in NO en ROS was. In gevolgtrekking kan ons sê dat hierdie studie die voordelige in vitro effekte van insulien en leptien op asthenozoospermiese en teratozoospermiese menslike spermfunksie aangetoon het. Hierdie hormone beïnvloed spermfunksie via die PI3K seintransduksie pad op twee maniere. Eerstens, deur `n toename in GLUT8 uitdrukking en translokasie, met die gevolg dat glukose opname en metabolisme moontlik verhoog is, en tweedens, deur die toename in NO produksie. Die studie het ook vasgestel dat TNF-α en IL-6 nadelige effekte op menslike spermatosoë in `n dosis- en tyd-afhanklike wyse het. Hierdie effekte vind plaas a.g.v. hul vermoë om beide NO en ROS produksie in menslike spermatosoë te induseer. Die studie toon aan dat GLUT8 uitdrukking in die middelstuk van die menslike spermatosoon voorkom en dat insulien stimulasie GLUT8 uitdrukking opreguleer en tot translokasie na die akrosomale area lei.

引言: 青少年突發性脊柱側彎(Adolescent Idiopathic Scoliosis, AIS)是一種複雜的脊柱三維畸形，而目前病因未明。這病主要出現於11-14歲的青少年女性，罹患率約為四個百分比。未經治療的側彎可能逐漸加重並導致明顯的外觀畸形，嚴重者可導致心肺功能異常等其他併發症。目前對AIS的治療方法包括觀察，支具和手術內固定矯形。然而因為這些治療並非針對病因而仍然存在一定缺陷，如支具治療失敗和手術的併發症等。因此明確AIS的發病機制仍然是制定有效治療的關鍵。
根據過往研究報告，AIS患者有低體重、身形高大、臂展增加、低體重指數，月經初潮推遲與低骨量，這顯示AIS患者或有全身性生長異常。因為瘦素的重要生理功能如影響骨骼發育、開始青春期，能量消耗和身體成分，所以瘦素被假設為AIS的病因之一。之前的研究報告指出，AIS患者對比相同年齡和性別的人擁有較低水平的循環瘦素。然而，瘦素信號的強度不僅由瘦素水平所決定的，它也有可能受到可溶性瘦素受體(sOB-R)所影響。sOB-R是循環系統中瘦素的結合蛋白，可以調節血清瘦素水平，並影響對目標組織的生物活性游離瘦素之生物利用度。游離瘦素指數(FLI)的開發是為了幫助數據的詮釋，並提供游離瘦素水平的估計。
瘦素對骨代謝的影響是間接地由中央神經系統和直接地由周緣組織來施加的。瘦素被發現通過下丘腦神經系統對骨形成有分解效果。而瘦素的周緣作用被證實對骨形成有直接的合成作用，例如促進成骨細胞和軟骨細胞的增殖，刺激成骨細胞的分化和礦化，及抑制破骨細胞的生長和活性。根據先前對AIS患者的骨髓間充質幹細胞(MSCs)之研究，AIS患者對瘦素有較低的反應和在成脂和成骨幹細胞有較低的瘦素受體。這提供了在AIS患者的骨細胞和瘦素相關異常的初步證據。
當前研究的目的是:
1）通過測量在AIS患者和正常對照組的血清總瘦素，sOB-R和FLI的水平來調查AIS患者是否有任何異常的游離瘦素生物利用度，及是否和異常的人體測量參數有關聯。
2）通過研究AIS患者和對照組之身體成分及與血清總瘦素，sOB-R和FLI的相互關係來調查游離瘦素生物利用度與AIS患者與對照組之關聯。
3）通過利用高分辨率周邊定量電腦斷層來研究與AIS患者與對照組的骨質量差異及與血清總瘦素，sOB-R和FLI的相互關系來調查游離瘦素生物利用度與AIS患者與對照組之關聯。
4）通過研究AIS患者與對照組對瘦素與成骨細胞增殖，分化和礦化的影響, 與成骨細胞上的瘦素受體來調查AIS患者是否對瘦素有異常反應和瘦素受體的異常表現。
方法: 1）游離瘦素的生物利用度和人體測量參數的研究包括了207名AIS女孩和155名年齡和性別匹配的正常對照組。因超重/肥胖者有比較高的血清瘦素水平，為避免來自於超重/肥胖者的影響，身體質量指數(BMI)大於23.0的實驗對象被排除。評估包括人體和性成熟的測量：如體重、身高、臂展、坐高，體重指數和坦納階段。血清總瘦素和sOB-R水平測定採用ELISA法，而游離瘦素指數(FLI)的計算為總血清瘦素/sOB-R的比值。
2）游離瘦素的生物利用度和身體成分的研究包括了148名AIS女孩和116名正常對照。身體成分的評估採用了生物電阻抗分析(BIA)。
3）游離瘦素的生物利用度和骨質量參數的研究包括了207名AIS女孩和155名正常對照。非優勢的遠端橈骨質量以高分辨率周邊定量電腦斷層(HR-pQCT)進行評估。體內骨骼強度以有限元分析(FEA)進行了評估。
4）對成骨細胞功能反應和瘦素受體表達的研究包括了12名接受矯正脊椎手術的AIS女孩和6名接受與側彎無關之手術的對照組。成骨細胞是從手術中拿取的骨活檢中分離，並進行培養和評估瘦素對細胞增殖，分化和礦化的影響(0，10，100，1000毫微克/毫升)，而分別採用MTT法，鹼性磷酸酶活性測定, 骨鈣素酶聯免疫吸附和von Kossa染色。瘦素受體（LEP-R）在基礎和成骨條件下的蛋白表達以Western blot檢測來進行AIS和對照組之間的比較。
結果: 1）在游離瘦素的生物利用度和人體測量參數的研究中，AIS女孩在調整了年齡和體重後有較高的sOB-R和較低的FLI，也和較低的體重和較低的BMI有關聯。AIS女孩還有在血清總瘦素，FLI和人體測量參數之間顯著較弱的相關性。
2）在游離瘦素的生物利用度和身體成分的研究中，AIS女孩有較低的骨骼肌質量，較低的身體脂肪和較低的身體脂肪百分比，以及在血清總瘦素，FLI和所有身體成分參數之間較弱的相關性。
3）在游離瘦素的生物利用度和骨質量的研究中，AIS女孩有較低的皮質體積骨密度，較低的骨小梁數量，較高的骨小梁分離度以及更高的結構模型指數（SMI）。在相關性分析中, AIS女孩在血清總瘦素和FLI與骨小梁參數的相關性有特殊的相關模式，這相關性沒有在正常對照組中出現。
4）在對成骨細胞的功能反應和瘦素受體的表達之研究中，對照組隨瘦素濃度升高而有增加的代謝信號，然而，AIS組沒有對瘦素出現增殖反應。在第六天和第十四天的分化實驗中，對照組的鹼性磷酸酶活性隨著瘦素濃度升高而表現出清晰而強烈的趨勢，而AIS組的鹼性磷酸酶活性沒有出現趨勢也沒有顯著差異。在骨鈣素酶聯免疫吸附實驗中, 對照組隨著瘦素濃度升高而表現出清晰而強烈的趨勢, 而AIS組沒有出現顯著差異。在礦化實驗中，對照組隨瘦素濃度升高而呈輕度上升的礦化趨勢, AIS組再次地沒有出現趨勢和差異。在基礎和成骨條件下, 瘦素受體的表達並沒有出現顯著差異。
討論：這是對AIS中瘦素的生物利用度與身體成分和骨質量之關係的第一個研究。本研究的結果表示，AIS女孩可能存在異常的游離瘦素生物利用度，並可能導致異常表型，例如較低的BMI，異常的身體成分和較差的骨質量。低骨量在AIS中的重要性和骨小梁參數與血清總瘦素和FLI的不正常的關係，使我們進一步研究瘦素對AIS的成骨細胞的影響。當與對照組相比,來自AIS女孩的成骨細胞對瘦素有非常低的反應。這異常反應可能是由於瘦素信號轉導途徑的功能障礙，其中可能包括異常的瘦素受體和下游信號分子。這是一個重要的發現，並可能有助於解釋與AIS相關的低骨量和較差的骨質量。這項研究提供了AIS發病機理的新見解和新的研究方向。未來的研究不妨包括瘦素信號轉導途徑中可能受到AIS影響的下游信號分子和動物模型來證實瘦素和瘦素生物利用度與AIS之間的因果關係。總而言之，這一系列的研究結果表示了瘦素和瘦素生物利用度在骨骼發育、體格，骨骼質量和AIS的發病機制中的重要性。
Introduction: Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional structural deformity of the spine and its etiology remains unknown. It mainly occurs in girls between 11 to 14 years old with a prevalence rate of 4%. This common spinal deformity can be associated with significant cosmetic, psychological, and clinical morbidities in severe cases. Current treatments for AIS are unsatisfactory, mainly because they are merely treating the phenotype of the spinal deformity but not the underlying etiology. Therefore, it is crucial to understand the etiopathogenesis of AIS so that effective therapeutic and preventive measures can be devised.
Previous studies have reported the association between AIS and low body weight, tall stature, increased arm span, low body mass index, delayed onset of menarche and low bone mass, which indicated abnormal systemic growth in patients with AIS. Leptin has been postulated as one of the etiologic factors of AIS because of its important physiological functions in neuro-osseous development affecting skeletal growth, the onset of puberty, energy expenditure and body composition. A previous study had reported lower circulating leptin in AIS girls than age- and sex-matched controls. However, the strength of leptin signal is not only determined by the leptin level, it could also be affected by soluble leptin receptor (sOB-R), its binding protein in circulation. sOB-R could modulate the serum leptin level, and affect the bioavailability of free leptin, the biologically active form, to its target tissues. Free leptin index (FLI) was developed to aid interpretation of data and provide an estimation of free leptin level.
The effects of leptin on bone metabolism are exerted indirectly through the central nervous system and directly on the peripheral tissues. Leptin was shown to have a catabolic effect on bone formation through the hypothalamus and the sympathetic nervous system (SNS). While the peripheral effects of leptin was shown to be anabolic to bone formation, promoting the proliferation of osteoblasts and chondrocytes, stimulating osteoblastic differentiation, mineralization, and inhibiting osteoclastogenesis and osteoclast activity. With regards to AIS, a previous study on bone marrow derived mesenchymal stem cells (MSCs) showed lower responses to leptin, and lower leptin receptor expressions in adipogenic and osteogenic MSCs. This study provided initial evidence that leptin related pathways might be abnormal in the bone cells of AIS patients.
This study aimed to:
1) Investigate if there is any abnormality in free leptin bioavailability by measuring the serum total leptin, sOB-R levels, and FLI in AIS and control subjects, and if it is associated with abnormal anthropometric parameters in AIS.
2) Investigate if free leptin bioavailability in AIS is associated with abnormal body composition by studying the difference in body composition and its correlations with serum total leptin, sOB-R, and FLI between AIS and control subjects.
3) Investigate if free leptin bioavailability in AIS is associated with abnormal bone quality by studying the difference in bone quality as measured by high resolution pQCT and its correlations with serum total leptin, sOB-R, and FLI between AIS and control subjects.
4) Investigate if there are abnormal functional responses to leptin and abnormal expression of leptin receptor in AIS by determining the effects of leptin on proliferation, differentiation, and mineralization of osteoblasts; and the expression levels of leptin receptor in osteoblasts isolated from intra-operative bone biopsies of AIS and control subjects.
Methods: 1) The study on free leptin bioavailability and anthropometric parameters included 207 AIS girls and 155 age- and gender-matched normal controls. Subjects with body mass index (BMI)>23.0 were excluded to avoid bias from the relatively high serum leptin level in overweight / obese subjects. Assessments included anthropometric and sexual maturity measurements: body weight, height, arm span, sitting height, BMI, and Tanner stages. Serum total leptin and sOB-R levels were measured with ELISA, and free leptin index (FLI) was calculated as the ratio of serum total leptin / sOB-R.
2) The study on free leptin bioavailability and body composition included 148 AIS girls and 116 normal controls, while anthropometric and sexual maturity parameters included 207 AIS girls and 155 normal controls. Body composition was assessed with bioelectrical impedance analysis (BIA).
3) The study on free leptin bioavailability and bone quality parameters included 207 AIS girls and 155 normal controls. Bone quality on the non-dominant distal radius was assessed with high resolution pQCT (HR-pQCT). In vivo bone strength was assessed with finite element analysis (FEA).
4) The study on functional responses and leptin receptor expression in osteoblasts included 12 AIS girls undergoing corrective spinal surgery and 6 control subjects undergoing unrelated surgery. Primary osteoblasts were isolated from intra-operative bone biopsies, and were cultured and assessed for the effects of leptin (0, 10, 100, 1000 ng/mL) on cell proliferation, differentiation, and mineralization by MTT assay, alkaline phosphatase activity assay and osteocalcin ELISA, and von Kossa staining respectively. Protein expressions of leptin receptor (LEP-R) under basal and osteogenic conditions were compared between AIS and controls by Western blot.
Results: 1) In the study on free leptin bioavailability and anthropometric parameters, AIS girls had higher sOB-R and lower FLI after adjusting for age and body weight, and these were associated with lower body weight and lower BMI. Significant correlation between serum total leptin and sOB-R was found in controls, but no correlation was observed in AIS girls. AIS girls also showed markedly weaker correlations between serum total leptin, FLI, and anthropometric parameters.
2) In the study on free leptin bioavailability and body composition, AIS girls had lower skeletal muscle mass, lower body fat, and percentage body fat, as well as weaker correlations between serum total leptin, FLI, and all body composition parameters.
3) In the study on free leptin bioavailability and bone quality, AIS girls had lower cortical volumetric bone mineral density (vBMD), lower trabecular number, higher trabecular separation, and higher structural model index (SMI) value. In correlation analysis with serum total leptin and FLI, AIS girls had distinctive correlation pattern with trabecular bone parameters that was not observed in the normal controls.
4) In the study on functional responses and leptin receptor expression in osteoblasts, control group showed increasing MTT signals to leptin in a dose dependent manner, while AIS group showed no proliferative response to leptin. For differentiation, control group showed strong and significant trend in ALP activity to increasing leptin concentrations in both day 6 and 14, but this trend was not observed in the AIS group. Osteoblasts from the control group secreted osteocalcin in an increasing dose dependent manner to leptin, but AIS group showed weak responses to leptin. For mineralization, the control group showed a mild increasing trend to increasing leptin concentrations, and again no trend was observed in the AIS group. No significant differences in the expression of leptin receptor under basal and osteogenic conditions were found between AIS and control group.
Discussion: This is the first study on the relationship of leptin bioavailability with body composition and bone quality in AIS. The results in this study suggested that abnormal free leptin bioavailability might exist in AIS girls and could lead to abnormal phenotypes such as lower BMI, abnormal body composition, and deranged bone quality that often manifested in AIS simultaneously. The importance of low bone mass in AIS and the presence of correlations between trabecular bone parameters and serum total leptin and FLI which were not observed in controls, have led us to further investigate the effects of leptin on primary osteoblasts in AIS. The osteoblasts isolated from AIS girls had no or very low response to leptin when compared with controls, which was shown to be independent of the difference in leptin receptor expression levels. This lack of response might be due to dysfunction of leptin signaling pathway, which might include structural or binding abnormalities in the leptin receptor or downstream signal molecules. This is an important finding and might serve to explain the low bone mass and deranged bone quality that is associated with AIS. This study provided new insights and new research directions on the etiopathogenesis of AIS. Future research could include studies on the downstream signal molecules along the leptin pathways that might be affected in AIS, and animal models to confirm the causal relationship of leptin and leptin bioavailability to AIS. In summary, the findings in this series of studies demonstrated the importance of leptin and leptin bioavailability in skeletal growth, body build, bone quality, and the etiopathogenesis of AIS.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Tam, Man Shan Elisa.
Thesis (Ph.D.) Chinese University of Hong Kong, 2014.
Includes bibliographical references (leaves 259-301).
Abstracts also in Chinese; appendixes includes Chinese.

Includes bibliographical references (leaves 165-225)
xx, 298 leaves : ill. ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, School of Molecular and Biological Sciences, Discipline of Physiology, 2004

Includes bibliographical references (leaves 165-225)
xx, 298 leaves : ill. ; 30 cm.
Thesis (Ph.D.)--University of Adelaide, School of Molecular and Biological Sciences, Discipline of Physiology, 2004

Adipose tissue (AT) in the body plays a very important role in the regulation of energy metabolism. AT regulates energy metabolism by secreting adipokines. Some of the adipokines released are vaspin, resistin, adiponectin, visfatin and omentin, and leptin. In addition to regulating energy metabolism, leptin plays a role in the regulation of many physiological functions of the body such as regulation of blood pressure, inflammation, nutrition, appetite, insulin and glucose metabolism, lipid metabolism, coagulation, and apoptosis. Among all these physiological functions, the relationship between leptin, oxidative stress, and apoptosis has gained great importance recently due to its therapeutic effect in various types of cancer. For this reason, in this study, the release of leptin, its cellular effects and its effect on oxidative stress, and apoptosis are discussed in line with current information.

As part of the biological rhythm, the human brain has a healthy functioning with the ability to differentiate between day and night hours in any given day (sleep rhythm, life rhythm). From the control of hormone levels to muscle tonus, from the regulation of respiratory rate to the content of our thoughts, sleep has an impact on all bodily and cognitive functions. It is not surprising to see such effects of sleep on the body as it leads to significant changes in the electrical activity of the brain in general. Electrical signal changes in the brain (sleep-wakefulness rhythm) are regulated by neurohormonal molecules and their receptors in the body. Neurotransmitters that control sleep and wakefulness can be listed as “Glutamate, Acetylcholine, Histamine, Norepinephrine and GABA”. Main hormones are: Melatonin, Corticotropin Releasing Hormone (CRH), cortisol, prolactin, Growth Hormone (GH), Insulin like Growth Factor (IGF-1, Somatomedin-C), Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH), progesterone, estrogen, testosterone, catecholamines, leptin and neuropeptide Y″. The effects of pharmacological agents on sleep and wakefulness cycles are materialized through the following molecules and their receptors: Hypnotics (GABA A agonists, benzodiazepines, gabapentin, tiagabine), sedative antidepressants (tricyclic antidepressants, trazadone, mitrazapine), antihistamines, medications used for the treatment of sleeplessness (melatonin and melatonin analogues), amphetamine (most commonly used stimulant), secretion of monoamines (dopamine), non-amphetamine stimulants used in the treatment of hypersomnia and narcolepsy (modafinil, bupropion, selegiline, caffeine) and other substances (alcohol, nicotine, anesthetics). To the extent we can conceptualize the physiological mechanisms of these basic molecules listed above and the regions they affect, we can appreciate the effects of these substances on sleep physiology and sleep disorders.

Objectives The original project had 2 major objectives: (1) To determine the effects of centrally administered leptin antagonist on appetite and adaptive metabolism in the sheep; (2) To develop and prepare second-generation leptin antagonists combining high binding affinity and prolonged in vivo half-life. Background Periods of suboptimal nutrition or exaggerated metabolic activity demands lead to a state of chronic energy insufficiency. Ruminants remain productive for a surprisingly long period of time under these circumstances by evoking adaptations sparing available energy and nutrients. The mechanism driving these adaptations in ruminant remains unknown, but could involve a reduction in plasma leptin, a hormone acting predominantly in the brain. In laboratory animals, reduced leptin signaling promotes survival during nutritional insufficiency by triggering energy sparing adaptations such as reduced thyroid hormone production and insulin resistance. Our overall hypothesis is that similar adaptations are triggered by reduced leptin signaling in the brain of ruminants. Testing of this hypothesis in ruminants has not been possible due to inability to block the actions of endogenous leptin and access to ruminant models where leptin antagonistic therapy is feasible and effective. Major achievements and conclusions The Israeli team had previously mutated 3 residues in ovine leptin, with no effect on receptor binding. This mutant was renamed ovine leptin antagonist (OLA) because it cannot activate signaling and therefore antagonizes the ability of wild type leptin to activate its receptor. To transform OLA into an effective in vivo antagonist, the Israeli made 2 important technical advances. First, it incorporated an additional mutation into OLA, increasing its binding affinity and thus transforming it into a super ovine leptin antagonist (SOLA). Second, the Israeli team developed a method whereby polyethylene glycol is covalently attached to SOLA (PEG-SOLA) with the goal of extending its half-life in vivo. The US team used OLA and PEG-SOLA in 2 separate animal models. First, OLA was chronically administered directly into the brain of mature sheep via a cannula implanted into the 3rdcerebroventricule. Unexpectedly, OLA had no effect of voluntary feed intake or various indicators of peripheral insulin action but reduced the plasma concentration of thyroid hormones. Second, the US team tested the effect of peripheral PEG-SOLA administration in an energy sensitive, rapidly growing lamb model. PEG-SOLA was administered for 14 consecutive days after birth or for 5 consecutive days before sacrifice on day 40 of life. Plasma PEG-SOLA had a half-life of over 16 h and circulated in 225- to 288-fold excess over endogenous leptin. PEG-SOLA administration reduced plasma thyroid hormones and resulted in a higher fat content in the carcass at slaughter, but had no effects on feed intake, body weight, plasma glucose or insulin. These results show that the team succeeded in developing a leptin antagonist with a long in vivo half-life. Moreover, in vivo results show that reduced leptin signaling promotes energy sparing in ruminants by repressing thyroid hormone production. Scientific and agricultural implications The physiological role of leptin in ruminants has been difficult to resolve because peripheral administration of wild type leptin causes little effects. Our work with leptin antagonists show for the first time in ruminants that reduced leptin signaling induces energy sparing mechanisms involving thyroid hormone production with little effect on peripheral insulin action. Additional work is needed to develop even more potent leptin antagonists, to establish optimal administration protocols and to narrow down phases of the ruminant life cycle when their use will improve productivity.