The Rare and Atypical Diabetes Network (RADIANT) Study: Design and Early Results

OBJECTIVE

The Rare and Atypical Diabetes Network (RADIANT) will perform a study of individuals and, if deemed informative, a study of their family members with uncharacterized forms of diabetes.

RESEARCH DESIGN AND METHODS

The protocol includes genomic (whole-genome [WGS], RNA, and mitochondrial sequencing), phenotypic (vital signs, biometric measurements, questionnaires, and photography), metabolomics, and metabolic assessments.

RESULTS

Among 122 with WGS results of 878 enrolled individuals, a likely pathogenic variant in a known diabetes monogenic gene was found in 3 (2.5%), and six new monogenic variants have been identified in the SMAD5, PTPMT1, INS, NFKB1, IGF1R, and PAX6 genes. Frequent phenotypic clusters are lean type 2 diabetes, autoantibody-negative and insulin-deficient diabetes, lipodystrophic diabetes, and new forms of possible monogenic or oligogenic diabetes.

CONCLUSIONS

The analyses will lead to improved means of atypical diabetes identification. Genetic sequencing can identify new variants, and metabolomics and transcriptomics analysis can identify novel mechanisms and biomarkers for atypical disease.

Abstract 368: Mechanisms of Arrhythmogenic Substrates in Lipotoxic Heart

Obesity is associated with dangerous pathologies including insulin resistance, hyperglycemia, and diabetes all of which are present as independent risks to developing fatal arrhythmias, which lead to sudden cardiac death. Cardiac lipotoxicity is a common mechanism that links these pathologies to cardiac dysfunction. The molecular mechanisms of cardiac lipotoxicity in obese heart are unknown. We investigated the effects of high-fat diet (HFD)-induced lipotoxicity on atrial electrical remodeling. Electrophysiology and rapid atrial pacing (RAP) were used to evaluate the effects of cardiac lipotoxicity in obese guinea pig hearts that show no signs of hyperglycemia or inflammation. HFD atria were associated with increased voltage-dependent potassium (I K ) and decreased L-type calcium current (I Ca,L ) densities, spontaneous beats, and increased vulnerability to atrial tachycardia with pacing. Further we see a marked reduction in I Kur and increased I K1 phenotype only after RAP. Human cardiac computer simulation studies underscore the translational relevance, as results were identical to data in lipotoxic guinea pig model. The data are the first to show that I K and I Ca,L underlie initiation of atrial arrhythmogenesis, while IK ur and IK 1 may act to sustain the arrhythmia. RNA sequencing assay in lipotoxic myocytes further revealed upregulation of PI3K and/or downregulation of AMPK as prime candidates for modulation of atrial ionic currents. The data provide a unique mechanism-based insight for targeted treatment options in patients.

Association Between Nitrate-Reducing Oral Bacteria and Cardiometabolic Outcomes: Results From ORIGINS

Background

The enterosalivary nitrate‐nitrite‐nitric oxide pathway is an alternative pathway of nitric oxide generation, potentially linking the oral microbiome to insulin resistance and blood pressure (BP). We hypothesized that increased abundance of nitrate‐reducing oral bacteria would be associated with lower levels of cardiometabolic risk cross‐sectionally.

Methods and Results

ORIGINS (Oral Infections, Glucose Intolerance, and Insulin Resistance Study) enrolled 300 diabetes mellitus–free adults aged 20 to 55 years (mean=34±10 years) (78% women). Microbial DNA was extracted from subgingival dental plaque (n=281) and V3–V4 regions of the 16S rRNA gene were sequenced to measure the relative abundances of 20 a priori–selected taxa with nitrate‐reducing capacity. Standardized scores of each taxon's relative abundance were summed, producing a nitrate‐reducing taxa summary score (NO₃TSS) for each participant. Natural log‐transformed homeostatic model assessment of insulin resistance, plasma glucose, systolic BP, and diastolic BP were regressed on NO₃TSS in multivariable linear regressions; prediabetes mellitus and hypertension prevalence were regressed on NO₃TSS using modified Poisson regression models. Nitrate‐reducing bacterial species represented 20±16% of all measured taxa. After multivariable adjustment, a 1‐SD increase in NO₃TSS, was associated with a −0.09 (95% CI, −0.15 to −0.03) and −1.03 mg/dL (95% CI, −1.903 to −0.16) lower natural log‐transformed homeostatic model assessment of insulin resistance and plasma glucose, respectively. NO₃TSS was associated with systolic BP only among patients without hypertension; 1‐SD increase in NO₃TSS was associated with −1.53 (95% CI, −2.82 to −0.24) mm Hg lower mean systolic BP. No associations were observed with prediabetes mellitus and hypertension.

Conclusions

A higher relative abundance of oral nitrate‐reducing bacteria was associated with lower insulin resistance and plasma glucose in the full cohort and with mean systolic BP in participants with normotension.

Subgingival Microbiota and Longitudinal Glucose Change: The Oral Infections, Glucose Intolerance and Insulin Resistance Study (ORIGINS)

Microbial communities along mucosal surfaces throughout the digestive tract are hypothesized as risk factors for impaired glucose regulation and the development of clinical cardiometabolic disease. We investigated whether baseline measures of subgingival microbiota predicted fasting plasma glucose (FPG) longitudinally. The Oral Infections, Glucose Intolerance and Insulin Resistance Study (ORIGINS) enrolled 230 diabetes-free adults (77% female) aged 20 to 55 y (mean ± SD, 34 ± 10 y) from whom baseline subgingival plaque and longitudinal FPG were measured. DNA was extracted from subgingival plaque, and V3 to V4 regions of the 16S rRNA gene were sequenced. FPG was measured at baseline and again at 2 y; glucose change was defined as follow-up minus baseline. Multivariable linear models regressed 2-y glucose change onto baseline measures of community diversity and abundances of 369 individual taxa. A microbial dysbiosis index (MDI) summarizing top individual taxa associated with glucose change was calculated and used in regression models. Models were adjusted for age, sex, race/ethnicity, education, smoking status, body mass index, and baseline glucose levels. Statistical significance was based on the false discovery rate (FDR; <0.05) or a Bonferroni-corrected P value of 1 × 10^-4, derived from the initial 369 hypothesis tests for specific taxa. Mean 2-y FPG change was 1.5 ± 8 mg/dL. Baseline levels of 9 taxa predicted FPG change (all FDR <0.05), among which Stomatobaculum sp oral taxon 097 and Atopobium spp predicted greater FPG change, while Leptotrichia sp oral taxon 498 predicted lesser FPG change (all 3 P values, Bonferroni significant). The MDI explained 6% of variation in longitudinal glucose change (P < 0.001), and baseline glucose levels explained 10% of variation (P < 0.0001). FPG change values ± SE in the third versus first tertile of the MDI were 4.5 ± 0.9 versus 1.6 ± 0.9 (P < 1 × 10^-4). Subgingival microbiota predict 2-y glucose change among diabetes-free men and women.

The subgingival microbiome, systemic inflammation and insulin resistance: The Oral Infections, Glucose Intolerance and Insulin Resistance Study

BACKGROUND

Inflammation might link microbial exposures to insulin resistance. We investigated the cross-sectional association between periodontal microbiota, inflammation and insulin resistance.

METHODS

The Oral Infections, Glucose Intolerance and Insulin Resistance Study (ORIGINS) enrolled 152 diabetes-free adults (77% female) aged 20-55 years (mean = 34 ± 10). Three hundred and four subgingival plaque samples were analysed using the Human Oral Microbe Identification Microarray to measure the relative abundances of 379 taxa. C-reactive protein, interleukin-6, tumour necrosis factor-α and adiponectin were assessed from venous blood and their z-scores were summed to create an inflammatory score (IS). Insulin resistance was defined via the HOMA-IR. Associations between the microbiota and both inflammation and HOMA-IR were explored using multivariable linear regressions; mediation analyses assessed the proportion of the association explained by inflammation.

RESULTS

The IS was inversely associated with Actinobacteria and Proteobacteria and positively associated with Firmicutes and TM7 (p-values < 0.05). Proteobacteria levels were associated with insulin resistance (p < 0.05). Inflammation explained 30-98% of the observed associations between levels of Actinobacteria, Proteobacteria or Firmicutes and insulin resistance (p-values < 0.05). Eighteen individual taxa were associated with inflammation (p < 0.05) and 22 with insulin resistance (p < 0.05). No findings for individual taxa met Bonferroni-adjusted statistical significance.

CONCLUSION

Bacterial measures were related to inflammation and insulin resistance among diabetes-free adults.

A differential dielectric affinity glucose sensor

A continuous glucose monitor with a differential dielectric sensor implanted within the subcutaneous tissue that determines the glucose concentration in the interstitial fluid is presented. The device, created using microelectromechanical systems (MEMS) technology, consists of sensing and reference modules that are identical in design and placed in close proximity. Each module contains a microchamber housing a pair of capacitive electrodes residing on the device substrate and embedded in a suspended, perforated polymer diaphragm. The microchambers, enclosed in semi-permeable membranes, are filled with either a polymer solution that has specific affinity to glucose or a glucose-insensitive reference solution. To accurately determine the glucose concentration, changes in the permittivity of the sensing and the reference solutions induced by changes in glucose concentration are measured differentially. In vitro characterization demonstrated the sensor was capable of measuring glucose concentrations from 0 to 500 mg dL(-1) with resolution and accuracy of ~1.7 μg dL(-1) and ~1.74 mg dL(-1), respectively. In addition, device drift was reduced to 1.4% (uncontrolled environment) and 11% (5 °C of temperature variation) of that from non-differential measurements, indicating significant stability improvements. Preliminary animal testing demonstrated that the differential sensor accurately tracks glucose concentration in blood. This sensor can potentially be used clinically as a subcutaneously implanted continuous monitoring device in diabetic patients.

A MEMS differential viscometric sensor for affinity glucose detection in continuous glucose monitoring

Micromachined viscometric affinity glucose sensors have been previously demonstrated using vibrational cantilever and diaphragm. These devices featured a single glucose detection module that determines glucose concentrations through viscosity changes of glucose-sensitive polymer solutions. However, fluctuations in temperature and other environmental parameters might potentially affect the stability and reliability of these devices, creating complexity in their applications in subcutaneously implanted continuous glucose monitoring (CGM). To address these issues, we present a MEMS differential sensor that can effectively reject environmental disturbances while allowing accurate glucose detection. The sensor consists of two magnetically driven vibrating diaphragms situated inside microchambers filled with a boronic-acid based glucose-sensing solution and a reference solution insensitive to glucose. Glucose concentrations can be accurately determined by characteristics of the diaphragm vibration through differential capacitive detection. Our in-vitro and preliminary in-vivo experimental data demonstrate the potential of this sensor for highly stable subcutaneous CGM applications.

Continuous monitoring of glucose in subcutaneous tissue using microfabricated differential affinity sensors

OBJECTIVE

We describe miniaturized differential glucose sensors based on affinity binding between glucose and a synthetic polymer. The sensors possess excellent resistance to environmental disturbances and can potentially allow wireless measurements of glucose concentrations within interstitial fluid in subcutaneous tissue for long-term, stable continuous glucose monitoring (CGM).

METHODS

The sensors are constructed using microelectromechanical systems (MEMS) technology and exploit poly(N-hydroxy-ethyl acrylamide-ran-3-acrylamidophenylboronic acid) (PHEAA-ran-PAAPBA), a glucose-binding polymer with excellent specificity, reversibility, and stability. Two sensing approaches have been investigated, which respectively, use a pair of magnetically actuated diaphragms and perforated electrodes to differentially measure the glucose-binding-induced changes in the viscosity and permittivity of the PHEAA-ran-PAAPBA solution with respect to a reference, glucose-unresponsive polymer solution.

RESULTS

In vivo characterization of the MEMS affinity sensors were performed by controlling blood glucose concentrations of laboratory mice by exogenous glucose and insulin administration. The sensors experienced an 8-30 min initialization period after implantation and then closely tracked commercial capillary glucose meter readings with time lags ranging from 0-15 min during rapid glucose concentration changes. Clarke error grid plots obtained from sensor calibration suggest that, for the viscometric and dielectric sensors, respectively, approximately 95% (in the hyperglycemic range) and 84% (ranging from hypoglycemic to hyperglycemic glucose concentrations) of measurement points were clinically accurate, while 5% and 16% of the points were clinically acceptable.

CONCLUSIONS

The miniaturized MEMS sensors explore differential measurements of affinity glucose recognition. In vivo testing demonstrated excellent accuracy and stability, suggesting that the devices hold the potential to enable long-term and reliable CGM in clinical applications.

DNA methylation as a risk factor in the effects of early life stress

Epigenetic marks (e.g., DNA 5-methylcytosine [5mC] content or CpG methylation) within specific gene regulatory regions have been demonstrated to play diverse roles in stress adaptation and resulting health trajectories following early adversity. Yet the developmental programming of the vast majority of the epigenome has not yet been characterized, and its role in the impact of early stress largely unknown. In the present study, we investigated the relationships among early life stress, whole-epigenome and candidate stress pathway gene (serotonin transporter, 5-HTT) methylation patterns, and adult behavioral stress adaptation in a non-human primate model. Early in life, experimental variable foraging demand (VFD) stress or control conditions were administered to two groups each of 10 female bonnet macaques (Macaca radiata) and their mothers. As adults (3-13 years of age), these females were assessed for behavioral adaptation to stress across four conditions of increasing intensity. Blood DNA 5-HTT 5mC status was determined using sodium bisulfite pyrosequencing and total 5mC content was determined using ELISA. Neither stress reactivity nor DNA methylation differed based on early life stress. However, we found that both greater 5-HTT and whole-genome 5mC was associated with enhanced behavioral stress reactivity following early life stress, but not control conditions. Therefore, regardless of developmental origin, greater DNA methylation conferred a genomic background of "risk" in the context of early stress. We suggest that this may arise from constrained plasticity in gene expression needed for stress adaptation early in development. This risk may have wider implications for psychological and physical stress adaptation and health.

Epigenetic regulation of serotonin transporter expression and behavior in infant rhesus macaques

Epigenetic mechanisms may moderate genetic and environmental risk (GxE) for mood disorders. We used an experimental rhesus macaque model of early life stress to test whether epigenetic regulation of serotonin transporter (5-HTT) may contribute to GxE interactions that influence behavior and emotion. We hypothesized that peripheral blood mononuclear cell (PBMC) DNA methylation within an 800 bp cytosine-phosphate-guanosine (CpG) island that overlaps with the 5-HTT transcription initiation start site, a hypothesized model of the same genomic region in brain tissue, would mediate or moderate the effects of early life stress and a functional 5-HTT promoter polymorphism (rh5-HTTLPR) on two outcomes: PBMC 5-HTT expression and behavioral stress reactivity. Eighty-seven infant rhesus macaques (3-4 months of age) were either mother reared in large social groups (n = 70) or nursery reared (n = 17). During a maternal/social separation, infants' blood was sampled and behavioral stress reactivity recorded. PBMC DNA and RNA samples were used to determine rh5-HTTLPR genotype, 5-HTT mRNA expression using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and 5-HTT CpG methylation status using sodium bisulfite pyrosequencing. Consistent with human data, carriers of the low-expressing rh5-HTTLPR alleles exhibited higher mean 5-HTT CpG methylation, which was associated with lower PBMC 5-HTT expression. Higher 5-HTT CpG methylation, but not rh5-HTTLPR genotype, exacerbated the effects of early life stress on behavioral stress reactivity in infants. 5-HTT CpG methylation may be an important regulator of 5-HTT expression early in development and may contribute to the risk for mood disorders observed in 'high-risk'5-HTTLPR carriers.

VMAT2 quantitation by PET as a biomarker for beta-cell mass in health and disease

The common pathology underlying both type 1 and type 2 diabetes (T1DM and T2DM) is insufficient beta-cell mass (BCM) to meet metabolic demands. An important impediment to the more rapid evaluation of interventions for both T1DM and T2DM lack of biomarkers of pancreatic BCM. A reliable means of monitoring the mass and/or function of beta-cells would enable evaluation of the progression of diabetes as well as the monitoring of pharmacologic and other interventions. Recently, we identified a biomarker of BCM that is quantifiable by positron emission tomography (PET). PET is an imaging technique which allows for non-invasive measurements of radioligand uptake and clearance, is sensitive in the pico- to nanomolar range and of which the results can be deconvoluted into measurements of receptor concentration. For BCM estimates, we have identified VMAT2 (vesicular monoamine transporter type 2) as a biomarker and [(11)C] DTBZ (dihydrotetrabenazine) as the transporter's ligand. VMAT2 is highly expressed in beta-cells of the human pancreas relative to other cells of the endocrine and exocrine pancreas. Thus measurements of [(11)C] DTBZ in the pancreas provide an indirect measurement of BCM. Here we summarize our ongoing efforts to validate the clinical utility of this non-invasive approach to real-time BCM measurements.

Dietary curcumin significantly improves obesity-associated inflammation and diabetes in mouse models of diabesity

Obesity is a major risk factor for the development of type 2 diabetes, and both conditions are now recognized to possess significant inflammatory components underlying their pathophysiologies. We tested the hypothesis that the plant polyphenolic compound curcumin, which is known to exert potent antiinflammatory and antioxidant effects, would ameliorate diabetes and inflammation in murine models of insulin-resistant obesity. We found that dietary curcumin admixture ameliorated diabetes in high-fat diet-induced obese and leptin-deficient ob/ob male C57BL/6J mice as determined by glucose and insulin tolerance testing and hemoglobin A1c percentages. Curcumin treatment also significantly reduced macrophage infiltration of white adipose tissue, increased adipose tissue adiponectin production, and decreased hepatic nuclear factor-kappaB activity, hepatomegaly, and markers of hepatic inflammation. We therefore conclude that orally ingested curcumin reverses many of the inflammatory and metabolic derangements associated with obesity and improves glycemic control in mouse models of type 2 diabetes. This or related compounds warrant further investigation as novel adjunctive therapies for type 2 diabetes in man.

Whole body [11C]-dihydrotetrabenazine imaging of baboons: biodistribution and human radiation dosimetry estimates

PURPOSE

Vesicular monoamine transporter type 2 abundance quantified using the radiotracer [(11)C]-dihydrotetrabenazine (DTBZ) has been used to study diagnosis and pathogenesis of dementia and psychiatric disorders in humans. In addition, it may be a surrogate marker for insulin-producing pancreatic beta cell mass, useful for longitudinal measurements using positron emission tomography to track progression of autoimmune diabetes. To support the feasibility of long-term repeated administrations, we estimate the biodistribution and dosimetry of [(11)C]-DTBZ in humans.

METHODS

Five baboon studies were acquired using a Siemens ECAT camera. After transmission scanning, 165-210 MBq of [(11)C]-DTBZ were injected, and dynamic whole body emission scans were conducted. Time-activity data were used to obtain residence times and estimate absorbed radiation dose according to the MIRD model.

RESULTS

Most of the injected tracer localized to the liver and the lungs, followed by the intestines, brain, and kidneys. The highest estimated absorbed radiation dose was in the stomach wall.

CONCLUSIONS

The largest radiation dose from [(11)C]-DTBZ is to the stomach wall. This dose estimate, as well as the radiation dose to other radiosensitive organs, must be considered in evaluating the risks of multiple administrations.

Longitudinal noninvasive PET-based beta cell mass estimates in a spontaneous diabetes rat model

Diabetes results from an absolute or relative reduction in pancreatic beta cell mass (BCM) leading to insufficient insulin secretion and hyperglycemia. Measurement of insulin secretory capacity is currently used as a surrogate measure of BCM. However, serum insulin concentrations provide an imprecise index of BCM, and no reliable noninvasive measure of BCM is currently available. Type 2 vesicular monoamine transporters (VMAT2) are expressed in human islet beta cells, as well as in tissues of the CNS. [11C]Dihydrotetrabenazine ([11C]DTBZ) binds specifically to VMAT2 and is a radioligand currently used in clinical imaging of the brain. Here we report the use of [11C]DTBZ to estimate BCM in a rodent model of spontaneous type 1 diabetes (the BB-DP rat). In longitudinal PET studies of the BB-DP rat, we found a significant decline in pancreatic uptake of [11C]DTBZ that anticipated the loss of glycemic control. Based on comparison of standardized uptake values (SUVs) of [11C]DTBZ and blood glucose concentrations, loss of more than 65% of the original SUV correlated significantly with the development of persistent hyperglycemia. These studies suggest that PET-based quantitation of VMAT2 receptors provides a noninvasive measurement of BCM that could be used to study the pathogenesis of diabetes and to monitor therapeutic interventions.

Genetic variability in responses to caloric restriction in animals and in regulation of metabolism and obesity in humans

Panel 5 focused on genetic factors that might mediate or moderate the effects of caloric restriction (CR) on longevity. Panel members stated that currently there is limited information directly addressing these issues. Therefore, they focused attention on what studies could be done. In addition, the panel believed that certain conceptual issues merited clarification and focused attention on this issue. Human studies and studies of nonhuman model organisms were discussed. The panel found at least three reasons why it would be valuable to find genes that influence the (putative) longevity-promoting effect of CR in humans. Such knowledge would offer: (a) the ability to predict individual responses to CR; (b) increased understanding of physiological mechanisms; and (c) the potential to develop mechanism-based interventions to promote longevity or healthy aging. In addition, the panel emphasized several macro-level recommendations regarding research strategies to avoid, research strategies to emphasize, and resources needing development.

Mechanisms for LEPR-mediated regulation of leptin expression in brown and white adipocytes in rat pups

To investigate the underlying mechanisms for leptin receptor (LEPR)-mediated regulation of leptin gene (Lep) expression in brown (BAT) and white (WAT) adipose tissue and resultant effects on plasma leptin concentrations (plasma-LEP), we examined effects of sympathetic nervous system (SNS) activity, caloric balance, and body fat content on leptin mRNA levels in BAT and WAT in 10-day-old rat pups segregating for Lepr(fa). In mother-reared pups, Lep mRNA levels were fa/fa > +/fa = +/+ in BAT and was fa/fa > +/fa > +/+ in WAT. The genotype effects on Lep expression in BAT and plasma-LEP were virtually eliminated when the differences in SNS activity between fa/fa and +/fa pups were equalized by artificial rearing of pups under thermoneutral conditions with or without oral norepinephrine (NE) administration. NE administration alone had little effect on the Lepr(fa)-dependent stratification of Lep expression in WAT. BAT-Lep mRNA was the main determinant of plasma-LEP. Metabolic rate, a surrogate indicator of SNS activity, explained 87% of the variation in BAT-Lep mRNA (R(2) = 0.93), whereas caloric balance (40%) and body fat mass (6%) accounted for most of the variation in WAT-Lep mRNA (R(2) = 0.53). We conclude that feedback regulation of Lep expression in BAT is primarily via central nervous system-mediated effects of leptin on SNS activity, whereas the control of leptin expression in WAT is more likely via mechanisms not directly dependent on SNS activity.

Mutation in the leptin receptor (Leprfa) causes fat-storage-independent hyperleptinaemia in neonatal rats

The plasma leptin concentration adjusted for fat mass is affected by mutant gene dosage in older animals segregating for Leprfa. Because the plasma of neonatal rats contains leptin, although their adipocytes contain virtually no triglyceride, we determined whether mutation dose-dependent differences in plasma leptin concentration exist before the postnatal onset of triglyceride storage. Plasma samples were obtained 10 min after birth of each rat pup and leptin concentration determined by radioimmunoassay. Plasma leptin in homozygous wild-type (+/+) pups was 1.6 +/- 0.2 ng/ml (n = 20) and 2.4 +/- 0.2 ng/ml in +/fa (n = 32) littermates (least-square means +/- SE, P < 0.05, two-way ANOVA with litter and genotype as factors). The corresponding values for +/fa (n = 21) and fa/fa (n = 15) littermates were 2.4 +/- 0.2 and, 4.0 +/- 0.3 ng/ml respectively (P < 0.001). Leprfa gene dose-dependent elevations in plasma leptin are, therefore, present at birth and constitute the only Leprfa-related phenotypic trait presently known to precede the onset of increased fat storage.

Obesity solutions: report of a meeting

A workshop entitled "Obesity Solutions" was held on January 11, 1996, at St. Luke's-Roosevelt Hospital in New York City and was jointly sponsored by the St. Luke's-Roosevelt Obesity Research Center and the Nestlé R&D Center, Inc., of New Milford, Connecticut. The purpose of the workshop was to bring together experts from the research community and the pharmaceutical and food industries to address the epidemic of obesity in the United States and offer potential solutions. The following is a report of that meeting.

Molecular genetic analysis of a human neuropeptide Y receptor. The human homolog of the murine "Y5" receptor may be a pseudogene

Neuropeptide Y is a 36-amino-acid peptide amide with numerous biological activities. These functions are mediated through several pharmacologically distinct receptors. To date five receptor subtypes have been cloned. Here we report the isolation, by low stringency homology cloning from a hypothalamic library, of a cDNA encoding the human homolog of the murine neuropeptide Y receptor subsequently reported (). Translation of the human Y1-like receptor clone suggested that it encoded a receptor which is truncated in the third extracellular loop. Comparison of the human Y1-like sequence to that of the human Y1 receptor suggested that the truncated receptor could have resulted from a frameshift due to a single nucleotide deletion in the sixth transmembrane domain. Southern blot analysis suggested that the gene is single copy in the human genome. The gene is located on chromosome 5q. To test the hypothesis that allelic variation of nucleic acid length within the sixth transmembrane domain of the Y1-like receptor may exist to produce a functional receptor, genomic DNA from 192 individuals of various ages, ethnic backgrounds, and degrees of obesity were analyzed electrophoretically and by direct sequencing. No variation was detected in any of the subjects, indicating that this receptor subtype may be a transcribed pseudogene in humans.

Hyperleptinemia: an early sign of juvenile obesity. Relations to body fat depots and insulin concentrations

Leptin, the OB gene product, is an adipocyte-derived circulating protein. In several rodent models of obesity, such as the db/db mice, fa/fa rats, and ventromedial hypothalamus-lesioned mice, as well as adult obese subjects, leptin mRNA expression and the circulating levels are elevated, suggesting resistance to its action. However, it is unknown whether the rise in leptin concentration occurs early in the natural evolution of human obesity or is a chronic adaptation to the obese state. Moreover, whether the distribution of body fat (i.e., visceral vs. subcutaneous abdominal fat) influences circulating leptin levels has not been assessed. We have determined in a group of obese and nonobese children and young adults whether leptin levels 1) are increased early in the development of obesity, 2) are related to a specific fat depot measured by magnetic resonance imaging, 3) vary during hyperinsulinemic, euglycemic, and hyperglycemic clamp studies, and 4) are different in males vs. females. In the basal state, leptin levels were elevated in obese children. Children and adults demonstrated a strong positive correlation between leptin concentrations and the subcutaneous fat depot (r = 0.84, P < 0.001). Surprisingly, a weaker correlation was found with visceral fat mass (r = 0.59, P = 0.001). Leptin levels remained unchanged under both euglycemic and hyperglycemic hyperinsulinemic conditions in both obese and nonobese subjects. A pronounced effect of gender on leptin levels was also observed. We conclude that, early in the development of juvenile obesity, leptin concentrations are elevated and are more closely linked to subcutaneous than visceral fat mass. Acute increases in insulin concentrations do not affect circulating leptin levels.

Microdissection of proximal mouse chromosome 6: identification of RFLPs tightly linked to the ob mutation

In a previous report, the ob mutation was mapped to a position 5 cM distal to Met on murine Chromosome (Chr) 6 in tight linkage to Cpa. In order to identify additional RFLPs in the region of ob, we have made use of chromosome microdissection of a 6:16 Robertsonian chromosome. In total, 19 RFLPs were used to type 131 progency of a B6D2 ob/ + x B6 spretus ob/ + intercross. Fifteen of the RFLPs mapped to Chr 6, one of which, D6Rck13, was tightly linked to ob. For refinement of the genetic map around ob, 350 obese progency of a B6 Mus castaneus ob/ + intercross were characterized. DNAs from these animals were typed for microsatellite markers from Chr 6 that flank ob. Recombinants were then typed for D6Rck13. D6Rck13 was nonrecombinant among all the progency of both crosses corresponding to 831 meioses. This probe will be of use as an entry point for physical mapping of the ob mutation.

The effect of Escherichia coli endotoxin on the adrenergic control of lipolysis in the human adipocyte

We investigated the effect of Escherichia coli O127:B8 endotoxins on the adrenergic control of lipolysis in the human adipocyte. Adipose tissue was incubated in vitro with isoproterenol to stimulate the beta-1 receptors, clonidine to stimulate the alpha-2 receptors, and theophylline to stimulate the subreceptor mechanism. Using a dual radioisotope technique, a lipolysis factor was calculated for each sample. The basal lipolysis factor was significantly (P less than 0.006) decreased 31% with endotoxin. beta-1 adrenergic receptor stimulation (isoproterenol, 1 X 10(-8) to 1 X 10(-4) M) was significantly decreased an average of 31% with E. coli endotoxin. The beta-1 receptor responsiveness was also significantly (P less than 0.02) decreased but not the receptor sensitivity. This indicated an alteration in the post beta receptor mechanism. The various components of the post beta-1 adrenergic mechanism were stimulated including the beta-1 receptor, the G protein, adenylase cyclase, and the lipase phosphorylase. The results indicated a significant 24.2% reduction of the beta-1 receptor and a 25.4% reduction in G protein stimulation. Thus the E. coli endotoxin effect on the beta adrenergic mechanism is at the G protein. The endotoxin had no effect on the alpha-2 receptor stimulation nor the theophylline stimulation of the subreceptor lipolysis. This study indicates that E. coli endotoxin (O127:B8) decreases in vitro beta adrenergic stimulation of human adipocyte lipolysis, and this effect can be partially reversed by theophylline.

Adrenergic control of adipocyte lipolysis in trauma and sepsis

Adipocyte lipolysis and its adrenergic control were studied in vitro from normal patients and those with trauma and sepsis. The adrenergic receptors were studied in terms of their responsiveness, a measure of the postreceptor mechanism, and their sensitivity, a measure of the receptor number or affinity. With early trauma, beta-adrenergic responsiveness and receptor number were significantly decreased. This is desensitization of the beta-receptors with down regulation and indicates increased in vivo lipolysis in early injury. After 4 days these changes had returned to normal. Early sepsis resulted in a significant increase in beta- and alpha-receptor responsiveness with beta-upregulation. This indicated hypersensitivity of the adipocyte adrenergic receptors and suggests the presence of an in vivo block of the adrenergic receptors in early sepsis. This would decrease adipocyte lipolysis. After 4 days there was a decrease in beta-receptor responsiveness in the patients with sepsis, indicating that the adrenergic receptor block was no longer present and adipocyte adrenergic stimulated lipolysis was increased.