Monogenic disorders of obesity and body fat distribution

MD, Eckel-Passow J, Acosta A. Precision Medicine for Obesity

Obesity is a multifactorial disease with a variable and underwhelming weight loss response to current treatment approaches. Precision medicine proposes a new paradigm to improve disease classification based on the premise of human heterogeneity, with the ultimate goal of maximizing treatment effectiveness, tolerability, and safety. Recent advances in high-throughput biochemical assays have contributed to the partial characterization of obesity's pathophysiology, as well as to the understanding of the role that intrinsic and environmental factors, and their interaction, play in its development and progression. These data have led to the development of biological markers that either are being or will be incorporated into strategies to develop personalized lines of treatment for obesity. There are currently many ongoing initiatives aimed at this; however, much needs to be resolved before precision obesity medicine becomes common practice. This review aims to provide a perspective on the currently available data of high-throughput technologies to treat obesity.

Accounting for a quantitative trait locus for plasma triglyceride levels: utilization of variants in multiple genes

Background

For decades, research efforts have tried to uncover the underlying genetic basis of human susceptibility to a variety of diseases. Linkage studies have resulted in highly replicated findings and helped identify quantitative trait loci (QTL) for many complex traits; however identification of specific alleles accounting for linkage remains elusive. The purpose of this study was to determine whether with a sufficient number of variants a linkage signal can be fully explained.

Method

We used comprehensive fine-mapping using a dense set of single nucleotide polymorphisms (SNPs) across the entire quantitative trait locus (QTL) on human chromosome 7q36 linked to plasma triglyceride levels. Analyses included measured genotype and combined linkage association analyses.

Results

Screening this linkage region, we found an over representation of nominally significant associations in five genes (MLL3, DPP6, PAXIP1, HTR5A, INSIG1). However, no single genetic variant was sufficient to account for the linkage. On the other hand, multiple variants capturing the variation in these five genes did account for the linkage at this locus. Permutation analyses suggested that this reduction in LOD score was unlikely to have occurred by chance (p = 0.008).

Discussion

With recent findings, it has become clear that most complex traits are influenced by a large number of genetic variants each contributing only a small percentage to the overall phenotype. We found that with a sufficient number of variants, the linkage can be fully explained. The results from this analysis suggest that perhaps the failure to identify causal variants for linkage peaks may be due to multiple variants under the linkage peak with small individual effect, rather than a single variant of large effect.

Equine metabolic syndrome

The concept of an equine metabolic syndrome (EMS) was first proposed in 2002. This concept has developed over time, and EMS was recently described in a consensus statement released by the American College of Veterinary Internal Medicine. In human medicine, metabolic syndrome (MetS) refers to a set of risk factors that predict the risk of cardiovascular disease, including obesity, glucose intolerance and insulin resistance (IR), dyslipidemia, microalbuminuria, and hypertension. EMS shares some of the features of MetS, including increased adiposity, hyperinsulinemia, IR, but differs in that laminitis is the primary disease of interest.

Unconventional wisdom about the obesity epidemic

Diet and sedentary lifestyle, interacting with "thrifty" genes, are widely accepted as the principal cause of the current global obesity epidemic. However, a number of alternative etiologies for obesity have been proposed, including "drifty" genes, viruses, bacteria, environmental toxins, social network effects, maternal imprinting, sleep deprivation, and others. These Grand Rounds reviews the background of some of these unconventional ideas and evidence for or against their roles in the obesity epidemic.

Effects of the dominant lethal yellow mutation on reproduction, growth, feed consumption, body temperature, and body composition of the Japanese quail

Wild-type Japanese quail were compared with full-sibs with a yellow plumage color determined by an autosomal dominant mutation (Y), which is lethal when homozygous. These quail have wheat-straw yellow-colored feathers. Early growth was slower in yellow quail that had 2.4% lower BW than wild-type quail (149.3 g vs. 153.0 g) at 28 d of age. The BW, however, was similar for yellow and wild-type males at 35 d, and it remained so throughout the last part of the growth of the quail monitored until the age of 120 d, as indicated by the very close parameters of the monomolecular growth curve [BW= A - B exp(-kt)] obtained for the 2 groups. Yellow plumage color was also associated with a more difficult adaptation to housing (measured by temporary BW loss) in individual cages and to a significantly 0.2 degrees C lower body temperature at 42 d, but feed consumption and residual feed intake were similar for the 2 plumage color phenotypes. Breast and liver weights were similar in the 2 groups, but abdominal fat was 24% higher (4.66 vs. 3.76 g) in yellow quail. There is some association between the correlated effects of the Y gene in quail and those of the lethal mutation A(y) at the agouti locus in the mouse.

Redefining Lipodystrophy Syndrome

Lipodystrophy syndrome comprises several conditions (lipoatrophy; lipohypertrophy; mixed syndrome, often associated with dyslipidemia; and insulin resistance). These conditions, though sometimes occurring together, may occur independently, suggesting a complex, multifactorial cause. To elucidate the relative contribution of risk factors of drug, disease, and host to fat redistribution, large epidemiologic studies using multivariate analysis were reviewed. In studies assessing lipoatrophy, the most common statistically significant risk factors were use of specific nucleoside analogues, increasing age, presence of markers of disease severity (CD4/HIV RNA), duration of therapy, and white race. In studies assessing lipohypertrophy, the most common statistically significant risk factors were duration of therapy, markers of disease severity, and protease inhibitor use. The pathogenesis of these disorders is complex, but recent hypotheses and evidence suggest that impairment to adipocyte differentiation, impairment of adipokine regulation, unopposed production of proinflammatory cytokines, dysregulation of 11-beta-hydroxysteroid dehydrogenase, and mitochondrial toxicity may play a role.

A time-series study of sick building syndrome: chronic, biotoxin-associated illness from exposure to water-damaged buildings

The human health risk for chronic illnesses involving multiple body systems following inhalation exposure to the indoor environments of water-damaged buildings (WDBs) has remained poorly characterized and the subject of intense controversy. The current study assessed the hypothesis that exposure to the indoor environments of WDBs with visible microbial colonization was associated with illness. The study used a cross-sectional design with assessments at five time points, and the interventions of cholestyramine (CSM) therapy, exposure avoidance following therapy, and reexposure to the buildings after illness resolution. The methodological approach included oral administration of questionnaires, medical examinations, laboratory analyses, pulmonary function testing, and measurements of visual function. Of the 21 study volunteers, 19 completed assessment at each of the five time points. Data at Time Point 1 indicated multiple symptoms involving at least four organ systems in all study participants, a restrictive respiratory condition in four participants, and abnormally low visual contrast sensitivity (VCS) in 18 participants. Serum leptin levels were abnormally high and alpha melanocyte stimulating hormone (MSH) levels were abnormally low. Assessments at Time Point 2, following 2 weeks of CSM therapy, indicated a highly significant improvement in health status. Improvement was maintained at Time Point 3, which followed exposure avoidance without therapy. Reexposure to the WDBs resulted in illness reacquisition in all participants within 1 to 7 days. Following another round of CSM therapy, assessments at Time Point 5 indicated a highly significant improvement in health status. The group-mean number of symptoms decreased from 14.9+/-0.8 S.E.M. at Time Point 1 to 1.2+/-0.3 S.E.M., and the VCS deficit of approximately 50% at Time Point 1 was fully resolved. Leptin and MSH levels showed statistically significant improvement. The results indicated that CSM was an effective therapeutic agent, that VCS was a sensitive and specific indicator of neurologic function, and that illness involved systemic and hypothalamic processes. Although the results supported the general hypothesis that illness was associated with exposure to the WDBs, this conclusion was tempered by several study limitations. Exposure to specific agents was not demonstrated, study participants were not randomly selected, and double-blinding procedures were not used. Additional human and animal studies are needed to confirm this conclusion, investigate the role of complex mixtures of bacteria, fungi, mycotoxins, endotoxins, and antigens in illness causation, and characterize modes of action. Such data will improve the assessment of human health risk from chronic exposure to WDBs.

Aetiology of obesity: a striving after wind?

The current global epidemic of obesity is fuelled by a constant, unidirectional adverse effect on energy balance that exceeds the adaptive capacity of the system. The individual response to this environmental pressure is under the control of a variety of genes, which not only interacts with environmental factors but also with one another. Since the discovery that adipocytes may produce and secrete hormones, the adipose tissue has taken on increasing importance in the regulation of energy balance. Indeed, the pathogenesis of obesity, once regarded as so obvious and simple, is becoming one of the most complex in medical practice. From a clinical perspective, obesity is associated with a remarkably broad spectrum of health complications and, over the years, obesity-related mortality has consistently increased. From a theoretical viewpoint, the growing complexity of factors affecting the liability to obesity, the inconsistency of scientific results, the lack of consensus among scientists, and so forth, obstruct our efforts to unravel the aetiology of obesity. Is the field of obesity research merely a striving after wind, and nothing more?

Adipocyte biology and adipocytokines

Adipose tissue actively participates in regulation of food intake, energy expenditure, fuel metabolism, and a variety of other physiologic processes through its endocrine, paracrine, and autocrine secretory products (Table 4). Abnormal synthesis of these secretory products may be related to the pathogenesis of insulin resistance and its complications in patients who have adipose tissue disorders, such as obesity and lipodvstrophies.

Binge eating as a major phenotype of melanocortin 4 receptor gene mutations

BACKGROUND

Obesity, a multifactorial disease caused by the interaction of genetic factors with the environment, is largely polygenic. A few mutations in these genes, such as in the leptin receptor (LEPR) gene and melanocortin 4 receptor (MC4R) gene, have been identified as causes of monogenic obesity.

METHODS

We sequenced the complete MC4R coding region, the region of the proopiomelanocortin gene (POMC) encoding the alpha melanocyte-stimulating hormone, and the leptin-binding domain of LEPR in 469 severely obese white subjects (370 women and 99 men; mean [+/-SE] age, 41.0+/-0.5 years; body-mass index [the weight in kilograms divided by the square of the height in meters], 44.1+/-2.0). Fifteen women and 10 men without a history of dieting or a family history of obesity served as normal-weight controls (age, 47.7+/-2.0 years; body-mass index, 21.6+/-0.4). Detailed phenotypic data, including information on body fat, resting energy expenditure, diet-induced thermogenesis, serum concentrations of leptin, and eating behavior, were collected.

RESULTS

Twenty-four obese subjects (5.1 percent) and one control subject (4 percent) had MC4R mutations, including five novel variants. Twenty of the 24 obese subjects with an MC4R mutation were matched for age, sex, and body-mass index with 120 of the 445 obese subjects without an MC4R mutation. All mutation carriers reported binge eating, as compared with 14.2 percent of obese subjects without mutations (P<0.001) and 0 percent of the normal-weight subjects without mutations. The prevalence of binge eating was similar among carriers of mutations in the leptin-binding domain of LEPR and noncarriers. No mutations were found in the region of POMC encoding alpha melanocyte-stimulating hormone.

CONCLUSIONS

Binge eating is a major phenotypic characteristic of subjects with a mutation in MC4R, a candidate gene for the control of eating behavior.

Diurnal rhythm of agouti-related protein and its relation to corticosterone and food intake

In the present study we examined the diurnal patterns of agouti-related protein (AGRP) and proopiomelanocortin (POMC) mRNA expression in the arcuate nucleus and their relation to circulating glucocorticoids and food intake. Animals were killed at 4-h intervals throughout the 24-h diurnal cycle, and the expression of AGRP and POMC mRNA was evaluated by semiquantitative in situ hybridization analysis. We observed a significant diurnal rhythm in AGRP mRNA expression, with a marked peak at 2200 h (4 h after lights off) and a trough at 1000 h (4 h after lights on), consistent with the overall day-night rhythm of food intake. In contrast, POMC mRNA levels did not show a significant fluctuation across the diurnal cycle, although there was a tendency for levels to decrease after the onset of the dark cycle. Corticosterone secretion temporally coincided with the rising phase of AGRP mRNA expression. Depletion of corticosterone by adrenalectomy abolished the AGRP diurnal rhythm by suppressing the nighttime expression, but did not alter the feeding rhythm. Exposure of adrenalectomized rats to constant corticosterone replacement (10 or 50 mg continuous release corticosterone pellet) resulted in fixed AGRP mRNA expression throughout the 12-h light, 12-h dark cycle. A relatively high level of corticosterone (50 mg) significantly increased AGRP mRNA expression, with a positive correlation between these two measures. These results indicate that 1) the diurnal expression of AGRP mRNA is regulated by corticosterone independently of the light/dark cue; and 2) a normal endogenous corticosterone rhythm is required for generating the diurnal AGRP rhythm.

Overgrowth

The predominant influences on fetal growth are maternal and placental factors. Post-natal growth is regulated by a complex interaction between genetic, environmental and hormonal influences. The role of the growth hormone insulin-like growth factor (GH-IGF) system is explored, including the emerging role of IGF-2 in fetal growth. Increasing understanding of the genetics of overgrowth and short stature syndromes is contributing greatly to basic understanding of growth regulation. A range of prenatal overgrowth syndromes is discussed, including those associated with neonatal hyperinsulinism and hypoglycaemia.Post-natal overgrowth may be caused by a diverse range of normal variant conditions, endocrine disorders, chromosomal abnormalities and other genetic syndromes. An approach to diagnosis is presented and major conditions discussed in detail. Sex-steroid therapy for height limitation continues to be a controversial area with uncertainty about height prediction, benefits achieved and possible long-term side-effects.

Early decline in the catecholamine release-inhibitory peptide catestatin in humans at genetic risk of hypertension

BACKGROUND

Hypertension is a complex trait with an ill-defined genetic predisposition, in which adrenergic mechanisms seem to be involved even at the early stages. Chromogranin A is a pro-hormone stored and released with catecholamines by exocytosis; its fragment catestatin, formed in vivo, inhibits further catecholamine release as an antagonist at the physiologic trigger for secretion, the neuronal nicotinic cholinergic receptor.

METHODS

We measured catestatin by radioimmunoassay in n = 277 subjects stratified by blood pressure (n = 61 hypertensive, n = 216 normotensive), and if normotensive by genetic risk of developing hypertension: family history positive (n = 176) versus negative (n = 40). Maximum likelihood analysis tested for bimodality. Involvement of catestatin in pathophysiology was probed by measurements of catecholamines and leptin, and the hemodynamic responses to environmental (cold) stress.

RESULTS

The normotensive offspring of patients with hypertension already had diminished catestatin (P = 0.024), and family history was a better predictor of catestatin than age, ethnicity or gender (P = 0.014). Greater catestatin variance among family history-positive individuals (P = 0.021) suggested heterogeneity in this group, and a bimodal distribution (P < 0.001) identified 4.3% of individuals in a lower mode of catestatin values, all with positive family histories (P = 0.05). Catestatin correlated inversely with body mass index (r = -0.215, r(2) = 0.046, n = 276, P < 0.001) and plasma leptin (r = -0.203, r(2) = 0.041, n = 212, P = 0.003), while body mass index and leptin correlated directly (r = 0.59, r(2) = 0.350, n = 212, P < 0.001). Family history-positive individuals had greater epinephrine excretion (P = 0.037) in addition to diminished catestatin, suggesting an inhibitory effect of catestatin on chromaffin cells in vivo. Low plasma catestatin predicted enhanced pressor response to a sympathoadrenal stressor (cold stress; r = -0.184, r(2) = 0.034, n = 211, P = 0.007), suggesting an adrenergic mechanism whereby diminished catestatin might predispose to later development of hypertension. In white subjects, diminished catestatin also predicted greater systemic vascular resistance responses to cold stress (r = -0.307, r(2) = 0.094, n = 75, P = 0.007), a relationship not found in Blacks (r = 0.122, r(2) = 0.015, n = 94, P = 0.243).

CONCLUSIONS

We conclude that catestatin is diminished early in the course of development of hypertension, even in the normotensive offspring of patients with the disease. Low catestatin predicts augmented adrenergic pressor responses, suggesting a mechanism whereby diminished catestatin might increase the risk for later development of hypertension.

Increased fatty acid re-esterification by PEPCK overexpression in adipose tissue leads to obesity without insulin resistance

Adipose tissue glyceroneogenesis generates glycerol 3-phosphate, which could be used for fatty acid esterification during starvation. To determine whether increased glyceroneogenesis leads to increased fat mass and to explore the role of obesity in the development of insulin resistance, we overexpressed PEPCK, a regulatory enzyme of glyceroneogenesis in adipose tissue. Transgenic mice showed a chronic increase in PEPCK activity, which led to increased glyceroneogenesis, re-esterification of free fatty acids (FFAs), increased adipocyte size and fat mass, and higher body weight. In spite of increased fat mass, transgenic mice showed decreased circulating FFAs and normal leptin levels. Moreover, glucose tolerance and whole-body insulin sensitivity were preserved. Skeletal muscle basal and insulin-stimulated glucose uptake and glycogen content were not affected, suggesting that skeletal muscle insulin sensitivity is normal in transgenic obese mice. Our results indicate the key role of PEPCK in the control of FFA re-esterification in adipose tissue and, thus, the contribution of glyceroneogenesis to fat accumulation. Moreover, they suggest that higher fat mass without increased circulating FFAs does not lead to insulin resistance or type 2 diabetes in these mice.

Biological influences on obesity

Severely obese children are even more likely to have mutations in obesity genes than are severely obese adults. Thus, investigators searching for obesity genes commonly focus on children, with the result that many human obesity genes were first identified in studies of children. Although the development of obesity depends on living in an obesity-promoting environment, it also is influenced strongly by individual genetic composition. Thus, the discovery of new obesity genes provides new opportunities to identify causes of severe obesity. Finally, identification of individual causes of obesity may, in the future, provide for a safe, effective, and individualized treatment recommendation for each obese person.

The role of leptin and hypothalamic neuropeptides in energy homeostasis: update on leptin in obesity

Leptin is an adipocyte-secreted hormone the serum levels of which reflect the amount of energy stored in adipose tissue as well as short-term energy imbalance. Serum levels of many cytokines and hormones also influence circulating leptin levels. Leptin binding to specific receptors in the hypothalamus results in altered expression of orexigenic and anorexigenic neuropeptides that regulate neuroendocrine function and energy homeostasis, and recent experimental evidence suggests that leptin plays an important role in the pathogenesis of obesity and eating disorders. Research that followed the discovery of leptin is significantly broadening our understanding of the mechanisms underlying energy homeostasis, the elucidation of which is expected to result soon in the development of new therapeutic approaches for obesity and eating disorders.

Biological activities of glucagon-like peptide-1 analogues in vitro and in vivo

Studies support a role for glucagon-like peptide 1 (GLP-1) as a potential treatment for diabetes. However, since GLP-1 is rapidly degraded in the circulation by cleavage at Ala(2), its clinical application is limited. Hence, understanding the structure-activity of GLP-1 may lead to the development of more stable and potent analogues. In this study, we investigated GLP-1 analogues including those with N-, C-, and midchain modifications and a series of secretin-class chimeric peptides. Peptides were analyzed in CHO cells expressing the hGLP-1 receptor (R7 cells), and in vivo oral glucose tolerance tests (OGTTs) were performed after injection of the peptides in normal and diabetic (db/db) mice. [D-Ala(2)]GLP-1 and [Gly(2)]GLP-1 showed normal or relatively lower receptor binding and cAMP activation but exerted markedly enhanced abilities to reduce the glycemic response to an OGTT in vivo. Improved biological effectiveness of [D-Ala(2)]GLP-1 was also observed in diabetic db/db mice. Similarly, improved biological activity of acetyl- and hexenoic-His(1)-GLP-1, glucagon((1-5)-, glucagon((1-10))-, PACAP(1-5)-, VIP(1-5)-, and secretin((1-10))-GLP-1 was observed, despite normal or lower receptor binding and activation in vitro. [Ala(8/11/12/16)] substitutions also increased biological activity in vivo over wtGLP-1, while C-terminal truncation of 4-12 amino acids abolished receptor binding and biological activity. All other modified peptides examined showed normal or decreased activity in vitro and in vivo. These results indicate that specific N- and midchain modifications to GLP-1 can increase its potency in vivo. Specifically, linkage of acyl-chains to the alpha-amino group of His(1) and replacement of Ala(2) result in significantly increased biological effects of GLP-1 in vivo, likely due to decreased degradation rather than enhanced receptor interactions. Replacement of certain residues in the midchain of GLP-1 also augment biological activity.

Mutations in the small heterodimer partner gene are associated with mild obesity in Japanese subjects

Mutations in several genes encoding transcription factors of the hepatocyte nuclear factor (HNF) cascade are associated with maturity-onset diabetes of the young (MODY), a monogenic form of early-onset diabetes mellitus. The ability of the orphan nuclear receptor small heterodimer partner (SHP, NR0B2) to modulate the transcriptional activity of MODY1 protein, the nuclear receptor HNF-4alpha, suggested SHP as a candidate MODY gene. We screened 173 unrelated Japanese subjects with early-onset diabetes for mutations in this gene and found five different mutations (H53fsdel10, L98fsdel9insAC, R34X, A195S, and R213C) in 6 subjects as well as one apparent polymorphism (R216H), all present in the heterozygous state. Interestingly, all of the subjects with the mutations were mildly or moderately obese at onset of diabetes, and analysis of the lineages of these individuals indicated that the SHP mutations were associated with obesity rather than with diabetes. Therefore, an additional group of 101 unrelated nondiabetic subjects with early-onset obesity was screened for mutations in the SHP gene. Two of the previously observed mutations (R34X and A195S) and two additional mutations (R57W and G189E) were identified in 6 subjects, whereas no mutations were identified in 116 young nondiabetic lean controls (P = 0.0094). Functional studies of the mutant proteins show that the mutations result in the loss of SHP activity. These results suggest that genetic variation in the SHP gene contributes to increased body weight and reveal a pathway leading to this common metabolic disorder in Japanese.

LMNA R482Q mutation in partial lipodystrophy associated with reduced plasma leptin concentration

Mutations in LMNA, which encodes lamins A and C, have been found in patients with autosomal dominant Dunnigan-type familial partial lipodystrophy (FPLD). We analyzed the relationship between plasma leptin and the rare LMNA R482Q mutation in 23 adult FPLD subjects compared with 25 adult family controls with normal LMNA in an extended Canadian FPLD kindred. We found that the LMNA Q482/R482 genotype was a significant determinant of plasma leptin, the ratio of plasma leptin to body mass index (BMI), plasma insulin, and plasma C peptide (P= 0.015, P = 0.0007, P = 0.0004, and P < 0.0001, respectively), but not BMI (P = 0.67). Family members who were heterozygous for LMNA Q482/R482 had significantly lower plasma leptin and leptin:BMI ratio than unaffected R482/R482 homozygotes. Fasting plasma concentrations of insulin and C peptide were both significantly higher in LMNA Q482/R482 heterozygotes than in R482/R482 homozygotes. Multivariate regression analysis revealed that the LMNA R482Q genotype accounted for 40.9%, 48.2%, 86.9%, and 81.0%, respectively, of the attributable variation in log leptin, leptin:BMI ratio, log insulin, and log C peptide (P = 0.013, P = 0.0007, P = 0.0002 and P < 0.0001, respectively). The results indicate that a rare FPLD mutation in LMNA determines the plasma leptin concentration. It remains to be established whether the reduction in leptin results from the reduced adipose tissue mass in FPLD or from another subcellular effect of mutant LMNA. It also remains to be established whether the insulin resistance in FPLD is a consequence of the reduced plasma leptin or of another functional change resulting from mutant LMNA.

Lipodystrophy syndrome in HIV infection: what is it, what causes it and how can it be managed?

Since the introduction of HIV-1 protease inhibitors as components of antiretroviral drug combination regimens, the clinical course of HIV disease and opportunistic infections has changed dramatically. Besides the favourable virological, immunological and clinical impact of highly active antiretroviral therapy (HAART), several adverse drug reactions have been observed in patients with HIV receiving therapy. Particularly, peripheral lipodystrophy, central adiposity, dyslipidaemia and insulin resistance have been described with a prevalence of up to 80% in patients infected with HIV, and attributed to almost all components of HAART. Hyperlipidaemia is characterised by an increase of low and very low density lipoprotein-cholesterol as well as apolipoproteins B and E. Several studies strongly suggest that there are either multiple syndromes or a variety of factors inducing different changes that influence the ultimate phenotype. Similarities between HIV-associated fat redistribution and metabolic abnormalities with both inherited lipodystrophies and benign symmetric lipomatosis suggest the pathophysiological involvement of, for example, nuclear factors like lamin A/C and drug-induced mitochondrial dysfunction. Moreover, there is some evidence that cytokines and hormones impair fat and glucose homeostasis in patients with HIV receiving HAART. Three years after the first description of HIV therapy-associated abnormal fat redistribution, there is still an ongoing discussion about the case definition, diagnostic procedure and treatment options for both body shape changes and metabolic disturbances. Regarding therapy, there is a major concern about possible complex pharmacological interactions and overlapping adverse effects between HAART and, for example, lipid-lowering therapy. In addition, the likely contribution of both nucleoside analogue reverse transcriptase inhibitors and protease inhibitors to the development of abnormal fat redistribution in patients with HIV limits options of changing to alternative effective antiretroviral drug combinations. Thus, the occurrence of hyperlipidaemia, maturity onset diabetes mellitus, and marked changes in body habitus resulted in important social and clinical consequences such as an increased risk of atherosclerosis. It also sheds new light on the use of protease inhibitors regarding risk factors for the initial treatment decision. In this article, we discuss the features, pathogenesis and treatment options for body fat redistribution and metabolic disturbances associated with HAART in HIV-1 infection.

Design of a synthetic leptin agonist: effects on energy balance, glucose homeostasis, and thermoregulation

We have previously reported that a synthetic peptide amide corresponding to amino acid residues 116-130 of mouse leptin, LEP-(116-130), reduces body weight gain, food intake, and blood glucose levels in ob/ob and db/db mice. In the present study we show that the activity of LEP-(116-130) resides in a restricted sequence between amino acid residues 116-122. A synthetic peptide corresponding to this sequence (Ser-Cys-Ser-Leu-Pro-Gln-Thr) has been named OB3. Single point D-amino acid substitution was used to study the structure-function relationship of each residue in OB3. D-Amino acid analogs of OB3 were synthesized by the solid phase method, purified to 98+%, and administered (1 mg/day, ip) for 7 days to female C57BL/6J ob/ob mice. The effects of the peptides on body weight gain, food and water intake, glucose homeostasis, and thermoregulation were assessed. In most cases, the efficacy of OB3 on all parameters tested was reduced by substitution of an L-amino acid with its corresponding D-isoform. A statistically significant increase (2.6-fold) in the weight-reducing effect of OB3, however, was observed by inversion of the configuration of the leucine residue at position 4 (Leu-4) of OB3 by substitution with its D-amino acid isoform [D-Leu-4]. Compared with OB3, mice treated with [D-Leu-4]-OB3 consumed 7.9% less food and 16.5% less water. Blood glucose was normalized to levels comparable to those in wild-type control mice within 2 days after initiation of [D-Leu-4]-OB3 treatment. Unlike native leptin, however, neither OB3 nor any of its D-amino acid-substituted analogs had any apparent effect on thermogenesis. Our results indicate that synthetic peptide strategies may be useful in the development of potent and stabile pharmacophores with potential therapeutic significance in the treatment of human obesity and its related metabolic dysfunctions.

A1 adenosine receptor activation increases adipocyte leptin secretion

A1 adenosine receptors (A1ARs) are heavily expressed in adipocytes and influence fat cell metabolism. Because increasing evidence suggests a role for leptin in mediating appetite and fat cell metabolism, we tested whether ALARs regulate leptin production. Rats were treated with the A1AR agonist N6-cyclopentyladenosine (CPA), and changes in circulating levels of leptin and leptin gene expression were examined. Serum leptin levels rose 2- to 10-fold, with peak increases seen 8-16 h after injection of CPA (P < 0.05). In contrast, CPA did not alter steady state levels of adipose tissue leptin mRNA. To assess the influence of endogenous adenosine on circulating leptin levels, rats were also injected with dipyridamole (DPY), an adenosine reuptake blocker. DPY induced 80% increases in serum levels at 8 h after injections (P < 0.05). Supporting the idea that stimulation of leptin production is A1AR mediated, pretreatment with the A1AR antagonist 8-cyclopentyl-1,3-dipropylxanthine completely blocked increases in leptin levels after DPY treatment. To complement in vivo studies, the effect of A1AR activation on leptin secretion was also studied in epididymal fat pad cultures. In cultures, CPA treatment increased leptin secretion by 37% (P < 0.05). Collectively, these data show that the adenosinergic system can increase leptin secretion by directly activating A1ARs in fat tissue.