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.

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.

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.