Nicholas A. Tritos

Mice lacking melanin-concentrating hormone are hypophagic and lean

Feeding is influenced by hypothalamic neuropeptides that promote (orexigenic peptides) or inhibit feeding. Of these, neuropeptide Y (NPY) in the arcuate nucleus and melanin-concentrating hormone (MCH) and orexins/hypocretins, in the lateral hypothalamus have received attention because their expression is increased during fasting and because they promote feeding when administered centrally. Surprisingly, absence of the orexigenic neuropeptide NPY fails to alter feeding or body weight in normal mice. As deficiency of a single component of the pathway that limits food intake (such as leptin or receptors for melanocortin-4), causes obesity, it has been suggested that orexigenic signals are more redundant than those limiting food intake,. To define further the physiological role of MCH and to test the redundancy of orexigenic signals, we generated mice carrying a targeted deletion of the MCH gene. MCH-deficient mice have reduced body weight and leanness due to hypophagia (reduced feeding) and an inappropriately increased metabolic rate, despite their reduced amounts of both leptin and arcuate nucleus pro-opiomelanocortin messenger RNA. Our results show that MCH is a critical regulator of feeding and energy balance which acts downstream of leptin and the melanocortin system, and that deletion of a gene encoding a single orexigenic peptide can result in leanness.

Chemically defined projections linking the mediobasal hypothalamus and the lateral hypothalamic area

Recent studies have identified several neuropeptide systems in the hypothalamus that are critical in the regulation of body weight. The lateral hypothalamic area (LHA) has long been considered essential in regulating food intake and body weight. Two neuropeptides, melanin‐concentrating hormone (MCH) and the orexins (ORX), are localized in the LHA and provide diffuse innervation of the neuraxis, including monosynaptic projections to the cerebral cortex and autonomic preganglionic neurons. Therefore, MCH and ORX neurons may regulate both cognitive and autonomic aspects of food intake and body weight regulation. The arcuate nucleus also is critical in the regulation of body weight, because it contains neurons that express leptin receptors, neuropeptide Y (NPY), α‐melanin‐stimulating hormone (α‐MSH), and agouti‐related peptide (AgRP). In this study, we examined the relationships of these peptidergic systems by using dual‐label immunohistochemistry or in situ hybridization in rat, mouse, and human brains. In the normal rat, mouse, and human brain, ORX and MCH neurons make up segregated populations. In addition, we found that AgRP‐ and NPY‐immunoreactive neurons are present in the medial division of the human arcuate nucleus, whereas α‐MSH‐immunoreactive neurons are found in the lateral arcuate nucleus. In humans, AgRP projections were widespread in the hypothalamus, but they were especially dense in the paraventricular nucleus and the perifornical area. Moreover, in both rat and human, MCH and ORX neurons receive innervation from NPY‐, AgRP‐, and α‐MSH‐immunoreactive fibers. Projections from populations of leptin‐responsive neurons in the mediobasal hypothalamus to MCH and ORX cells in the LHA may link peripheral metabolic cues with the cortical mantle and may play a critical role in the regulation of feeding behavior and body weight. J. Comp. Neurol. 402:442–459, 1998.

Melanin-concentrating hormone overexpression in transgenic mice leads to obesity and insulin resistance

Several lines of investigation suggest that the hypothalamic neuropeptide melanin-concentrating hormone (MCH) regulates body weight in mammals. Obese mice lacking functional leptin overexpress the MCH message in the fed or fasted state. Acute intracerebroventricular injection of MCH increases energy intake in rats. Mice lacking the MCH gene are lean. To test the hypothesis that chronic overexpression of MCH in mice causes obesity, we produced transgenic mice that overexpress MCH (MCH-OE) in the lateral hypothalamus at approximately twofold higher levels than normal mice. On the FVB genetic background, homozygous transgenic animals fed a high-fat diet ate 10% more and were 12% heavier at 13 weeks of age than wild-type animals, and they had higher systemic leptin levels. Blood glucose levels were higher both preprandially and after an intraperitoneal glucose injection. MCH-OE animals were insulin-resistant, as demonstrated by markedly higher plasma insulin levels and a blunted response to insulin; MCH-OE animals had only a 5% decrease in blood glucose after insulin administration, compared with a 31% decrease in wild-type animals. MCH-OE animals also exhibited a twofold increase in islet size. To evaluate the contribution of genetic background to the predisposition to obesity seen in MCH-OE mice, the transgene was bred onto the C57BL/6J background. Heterozygote C57BL/6J mice expressing the transgene showed increased body weight on a standard diet, confirming that MCH overexpression can lead to obesity.

Two important systems in energy homeostasis: melanocortins and melanin-concentrating hormone

Our understanding of the regulation of appetite and energy balance has advanced significantly over the past decade as several peptides, centrally or peripherally expressed, have been characterized and shown to profoundly influence food intake and energy expenditure. (1)The growing number of putative appetite-regulating neuropeptides includes peptides that are orexigenic (appetite-stimulating) signals and anorectic peptides. Neuropeptide Y (NPY), melanin concentrating hormone (MCH), orexins A and B, galanin, and agouti -related peptide (AgRP) all act to stimulate feeding while alpha-melanocyte stimulating hormone (alphaMSH), corticotropin releasing hormone (CRH), cholecystokinin (CCK), cocaine and amphetamine regulated transcript (CART), neurotensin, glucagon-like peptide 1 (GLP 1), and bombesin have anorectic actions.(1) Leptin, expressed in the periphery in white adipose tissue, acts in the CNS to modulate the expression of several of these hypothalamic peptides.(1) This creates a functional link between the adipose tissue and the brain that translates the information on body fat provided by leptin to input into energy balance regulating processes. In the current review we examine the significant role of the melanocortin system (alphaMSH, agouti and AgRP peptides, and their receptors and mahogany protein) and melanin concentrating hormone in the regulation of energy balance.

Management of Cushing disease

Cushing disease is caused by a corticotroph tumor of the pituitary gland. Patients with Cushing disease are usually treated with transsphenoidal surgery, as this approach leads to remission in 70–90% of cases and is associated with low morbidity when performed by experienced pituitary gland surgeons. Nonetheless, among patients in postoperative remission, the risk of recurrence of Cushing disease could reach 20–25% at 10 years after surgery. Patients with persistent or recurrent Cushing disease might, therefore, benefit from a second pituitary operation (which leads to remission in 50–70% of cases), radiation therapy to the pituitary gland or bilateral adrenalectomy. Remission after radiation therapy occurs in ∼85% of patients with Cushing disease after a considerable latency period. Interim medical therapy is generally advisable after patients receive radiation therapy because of the long latency period. Bilateral adrenalectomy might be considered in patients who do not improve following transsphenoidal surgery, particularly patients who are very ill and require rapid control of hypercortisolism, or those wishing to avoid the risk of hypopituitarism associated with radiation therapy. Adrenalectomized patients require lifelong adrenal hormone replacement and are at risk of Nelson syndrome. The development of medical therapies with improved efficacy might influence the management of this challenging condition.

Ipilimumab-Induced Hypophysitis: A Detailed Longitudinal Analysis in a Large Cohort of Patients With Metastatic Melanoma

CONTEXT Ipilimumab (Ipi) is approved by the Food and Drug Administration for the treatment of unresectable or metastatic melanoma. Little is known about Ipi-induced hypophysitis (IH), an important treatment complication. OBJECTIVE The objectives of the study were as follows: 1) to examine the prevalence of IH, 2) to characterize the clinical course and treatment outcomes in IH, 3) to identify the risk factors for the development of IH, and 4) to determine optimal strategies for the management of IH. DESIGN This was a retrospective review. SETTING The study was conducted at a tertiary referral center. SUBJECTS One hundred fifty-four adult patients with metastatic melanoma were evaluated at Massachusetts General Hospital and were treated with Ipi between March 2008 and December 2013. INTERVENTION(S) The intervention included treatment with Ipi. MAIN OUTCOME MEASURE(S) Pituitary magnetic resonance imaging, pituitary hormone assessment, and patient survival were measured. RESULTS IH was diagnosed in 17 patients (11%). Male gender (P = .02) and older age (P = .005), but not the cumulative dose of Ipi, were risk factors for IH. All patients with IH had anterior hypopituitarism (none had diabetes insipidus). Hypopituitarism was persistent in most individuals (76%). Diffuse pituitary enlargement was observed exclusively in all cases of IH and, upon retrospective review of magnetic resonance imaging scans, this finding preceded the clinical diagnosis of hypophysitis in eight patients. Pituitary enlargement resolved rapidly (within 40 d in seven of seven patients). Median survival in patients with IH was 19.4 vs 8.8 months (P = .05) in the remainder of the cohort. CONCLUSIONS Male gender and older age are risk factors for IH. Pituitary enlargement is sensitive and specific for IH in the appropriate setting, can precede the clinical diagnosis, and resolves rapidly. Anterior pituitary function recovery is uncommon. The incidence of hypophysitis may positively predict survival in melanoma patients treated with Ipi.

Characterization of melanin concentrating hormone and preproorexin expression in the murine hypothalamus.

Melanin concentrating hormone (MCH) and the orexins (A and B) have been identified as neuropeptides localized to the lateral hypothalamic area (LHA) and are potential regulators of energy homeostasis. Potential factors regulating expression of both MCH and the orexins include fasting and leptin. Previous studies have generated conflicting data and, as there is little leptin receptor expressed in the lateral hypothalamus, it is likely that any observed leptin effects on these peptides are indirect. In this study, we examined MCH and preproorexin expression in mice in physiological states of starvation, with or without leptin administration, in addition to characterizing MCH and preproorexin expression in well-known obesity models, including ob/ob and UCP-DTA mice. Neuropeptide Y (NPY) expression in the arcuate nucleus was used as a positive control. After a 60-h fast, expression of both NPY and MCH mRNA was increased (by 148 and 33%, respectively) while preproorexin expression in the murine LHA did not change. Leptin administration to fasted mice blunted the rise in MCH and NPY expression towards control levels. In contrast, there was a 78% increase in preproorexin expression in fasted mice in response to peripheral leptin administration. MCH expression was increased (by 116%) in ob/ob mice at baseline, as we have previously reported. In addition, leptin treatment of ob/ob mice blunted the increase in MCH expression. In contrast, preproorexin expression did not differ in the leptin-deficient ob/ob mice or in the obese hyperleptinemic brown adipose tissue deficient (UCP-DTA) mice in comparison with controls. In summary, MCH expression is increased in two states of decreased leptin, fasting and ob/ob mice, and leptin replacement blunts MCH expression in both paradigms. Thus, MCH expression appears to be regulated by leptin. In contrast, preproorexin expression does not respond acutely to fasting, although it is acutely increased by leptin treatment during fasting. These preproorexin responses are in contrast to those seen with well-characterized orexigenic neuropeptides, such as NPY and AgRP, suggesting that appetite regulation may not be a significant physiological role of orexins. This conclusion is further supported by the observation that orexin ablated mice have arousal and not feeding deficits.

Comparison of aortic elasticity determined by cardiovascular magnetic resonance imaging in obese versus lean adults

The vascular properties of large vessels in the obese have not been adequately studied. We used cardiovascular magnetic resonance imaging to quantify the cross-sectional area and elastic properties of the ascending thoracic and abdominal aorta in 21 clinically healthy obese young adult men and 25 men who were age-matched lean controls. Obese subjects had greater maximal cross-sectional area of the ascending thoracic aorta (984 +/- 252 vs 786 +/- 109 mm(2), p <0.01) and of the abdominal aorta (415 +/- 71 vs 374 +/- 51 mm(2), p <0.05). When indexed for height the differences persisted, but when indexed for body surface area, a significant difference between groups was found only for the maximal abdominal aortic cross-sectional area. The obese subjects also had decreased abdominal aortic elasticity, characterized by 24% lower compliance (0.0017 +/- 0.0004 vs 0.0021 +/- 0.0005 mm(2)/kPa/mm, p <0.01), 22% higher stiffness index beta (6.0 +/- 1.5 vs 4.9 +/- 0.7, p <0.005), and 41% greater pressure-strain elastic modulus (72 +/- 25 vs 51 +/- 9, p <0.005). At the ascending thoracic aorta, only the pressure-strain elastic modulus was different between obese and lean subjects (85 +/- 42 vs 65 +/- 26 kPa, respectively; p <0.05), corresponding to a 31% difference-but arterial compliance and stiffness index were not significantly different between groups. In clinically healthy young adult obese men, obesity is associated with increased cross-sectional aortic area and decreased aortic elasticity.

Characterization of Expression of Hypothalamic Appetite-Regulating Peptides in Obese Hyperleptinemic Brown Adipose Tissue-Deficient (Uncoupling Protein-Promoter-Driven Diphtheria Toxin A) Mice1

Brown adipose tissue-deficient [uncoupling protein (UCP)-promoter-driven diphtheria toxin A (DTA)] mice develop obesity as a result of both decreased energy expenditure and hyperphagia. The hyperphagia occurs despite high serum leptin levels. Hence, this is a model of leptin-resistant obesity in which the mechanism driving hyperphagia is unknown. Leptin is a regulator of a number of hypothalamic neuropeptides involved in energy homeostasis. In ob/ob mice, leptin deficiency results in increased expression of neuropeptide Y (NPY), agouti-related protein (AGRP), and melanin-concentrating hormone (MCH), and decreased expression of POMC. We have previously shown that NPY is reduced in the UCP-DTA mouse, suggesting a normal NPY response to leptin. To define other potential sites of leptin resistance, we used in situ hybridization to evaluate the expression of messenger RNAs (mRNAs) encoding a number of peptides, including NPY, AGRP, MCH, and POMC. We confirmed that the decrease in NPY expression previously detected by Northern blots reflects a decrease in NPY expression in the arcuate nucleus. AGRP mRNA was also decreased, whereas POMC mRNA levels in the arcuate nucleus were the same as control. MCH mRNA levels in the lateral hypothalamic area were also decreased. In contrast, there was induction of NPY expression in the dorsomedial hypothalamic nucleus in the UCP-DTA animals but not in the controls. The results indicate that these neuropeptides generally respond to leptin and that the hyperphagia seen in the UCP-DTA mice is likely the result of dysregulated expression of other, as yet unexamined, hypothalamic peptides, or lies at sites distal to the hypothalamus. (Endocrinology 139: 4634–4641, 1998) W animal models of obesity have emerged and offer the hope of shedding light on the pathogenesis of human obesity, a condition associated with significant morbidity and mortality (1). One of these models, brown adipose tissue (BAT)-deficient [uncoupling protein (UCP)-promoter-driven diphtheria toxin A (DTA)] mice, develop obesity and hyperphagia (2), despite extreme hyperleptinemia (3). Unlike ob/ob mice, these animals have normal linear growth and fertility (2), and they represent a potentially valuable model for the study of the pathogenesis of leptin-resistant obesity (3, 4). Deficient BAT function is critical for the development of obesity in UCP-DTA mice (2), as suggested by the observation that raising these mice at thermoneutrality prevents the development of obesity (5). Under normal conditions, UCP-DTA mice exhibit not only deficient BAT thermogenesis, as predicted by their BAT deficiency, but they also have inappropriate hyperphagia (2), despite their increased body weight and high serum leptin (6, 7). This unexpected hyperphagia occurs in the setting of marked hyperleptinemia and resistance to exogenous leptin, and it exacerbates their obese phenotype (6, 7). A number of hypothalamic factors are known to be important regulators of feeding behavior in rodents. These include the orexigenic peptides neuropeptide Y (NPY) (8–14) and agouti-related protein (AGRP) (15), which are expressed in the arcuate nucleus (Arc) (11, 15); melanin-concentrating hormone (MCH) (16–18), which is expressed in the lateral hypothalamic area (LHA) and the zona incerta (ZI) (16, 17); and the appetite-inhibiting peptide, aMSH (19, 20), which is also expressed in the arcuate (19). In the ob/ob mouse, levels of messenger RNAs (mRNAs) of transcripts encoding the orexigenic peptides are elevated (11, 15, 18), and the level of POMC transcript (which is the precursor of aMSH) is reduced (21). These changes are presumably the result of the absence of leptin signaling. In the present study, we sought to examine the expression of these peptides, by in situ hybridization histochemistry, in UCP-DTA mice that are hyperleptinemic and are resistant to exogenous leptin, with respect to both body weight and food intake (6). We expected that the leptin resistance might map to the hypothalamus and that levels of transcripts of orexigenic neuropeptides normally lowered by leptin would be elevated and the level of POMC would be decreased, as seen in ob/ob mice. Unexpectedly, we found that in the Arc, NPY and AGRP mRNA levels were appropriately reduced and that POMC mRNA was not low. In the lateral hypothalamus, Received April 15, 1998. Address all correspondence and requests for reprints to: Eleftheria Maratos-Flier, M.D., Joslin Diabetes Center, Room 620, One Joslin Place, Boston, Massachusetts 02215. E-mail: emarat@joslab.harvard.edu. * This work was supported by a grant from Eli Lilly & Co. (to E.M.F.), NIH Grant DK-R37–28082 (to J.S.F.), and NIH Grant MH-56537 (to J.K.E.). 0013-7227/98/

Effects of Recombinant Human Growth Hormone Therapy in Obesity in Adults: A Metaanalysis

03.00/0 Vol. 139, No. 11 Endocrinology Printed in U.S.A. Copyright