Master of Science, Stanford University School of Medicine, Epidemiology and Clinical Research
Postdoctoral Research Fellowship, Stanford University School of Medicine, Endocrinology
Postbaccalaureate Premed. Prog., Columbia University, Premedical Studies (2001)
Bachelor of Arts, Tufts University, English (1995)
Role of GLP-1 in Hyperinsulinemic Hypoglycemia Post-bariatric Surgery
The purpose of this study is to evaluate the role of GLP-1 in causing extreme postprandial glucose reductions after bariatric surgery in a subset of patients who have severe symptomatic hypoglycemia.
Stanford is currently not accepting patients for this trial. For more information, please contact Colleen Craig, M.D., 650-350-2153.
Safety and Efficacy of Exendin 9-39 in Patients With Postbariatric Hypoglycemia
This clinical study will evaluate whether taking an investigational drug called exendin 9-39 is safe, well-tolerated, and helps to prevent low blood sugar in people who have had bariatric surgery and later develop a rare condition called postbariatric hypoglycemia (PBH).
Stanford is currently not accepting patients for this trial. For more information, please contact Aileen Muno, (650) 725-9890.
- Plasma FGF-19 Levels are Increased in Patients with Post-Bariatric Hypoglycemia OBESITY SURGERY 2019; 29 (7): 2092–99
Generating biosimilar therapeutic drugs through innovative technology and operational excellence
2019; 569 (7755)
View details for Web of Science ID 000467473600008
Longitudinal multi-omics of host-microbe dynamics in prediabetes.
2019; 569 (7758): 663–71
Type 2 diabetes mellitus (T2D) is a growing health problem, but little is known about its early disease stages, its effects on biological processes or the transition to clinical T2D. To understand the earliest stages of T2Dbetter, we obtained samples from 106 healthy individuals and individuals with prediabetes over approximately four years and performed deep profiling of transcriptomes, metabolomes, cytokines, and proteomes, as well as changes in the microbiome. This rich longitudinal data set revealed many insights: first, healthy profiles are distinct among individuals while displaying diverse patterns of intra- and/or inter-personal variability. Second, extensive host and microbial changes occur during respiratory viral infections and immunization, and immunization triggers potentially protective responses that are distinct from responses to respiratory viral infections. Moreover, during respiratory viral infections, insulin-resistant participants respond differently than insulin-sensitive participants. Third, global co-association analyses among the thousands of profiled molecules reveal specific host-microbe interactions that differ between insulin-resistant and insulin-sensitive individuals. Last, we identified early personal molecular signatures in one individual that preceded the onset of T2D, including the inflammation markers interleukin-1 receptor agonist (IL-1RA) and high-sensitivity C-reactive protein (CRP) paired with xenobiotic-induced immune signalling. Our study reveals insights into pathways and responses that differ between glucose-dysregulated and healthy individuals during health and disease and provides an open-access data resource to enable further research into healthy, prediabetic and T2D states.
View details for DOI 10.1038/s41586-019-1236-x
View details for PubMedID 31142858
Plasma FGF-19 Levels are Increased in Patients with Post-Bariatric Hypoglycemia.
BACKGROUND: Hypoglycemia is an increasingly recognized complication of bariatric surgery. Mechanisms contributing to glucose lowering remain incompletely understood. We aimed to identify differentially abundant plasma proteins in patients with post-bariatric hypoglycemia (PBH) after Roux-en-Y gastric bypass (RYGB), compared to asymptomatic post-RYGB.METHODS: Proteomic analysis of blood samples collected after overnight fast and mixed meal challenge in individuals with PBH, asymptomatic RYGB, severe obesity, or overweight recruited from outpatient hypoglycemia or bariatric clinics.RESULTS: The top-ranking differentially abundant protein at 120min after mixed meal was fibroblast growth factor 19 (FGF-19), an intestinally derived hormone regulated by bile acid-FXR signaling; levels were 2.4-fold higher in PBH vs. asymptomatic post-RYGB (mean + SEM, 1094±141 vs. 428±45, P<0.001, FDR<0.01). FGF-19 ELISA confirmed 3.5-fold higher concentrations in PBH versus asymptomatic (360±70 vs. 103±18, P=0.025). To explore potential links between increased FGF-19 and GLP-1, residual samples from other human studies in which GLP-1 was modulated were assayed. FGF-19 levels did not change in response to infusion of GLP-1 and PYY in overweight/obese individuals. Infusion of the GLP-1 receptor antagonist exendin 9-39 in recently operated asymptomatic post-RYGB did not alter FGF-19 levels after mixed meal. By contrast, GLP-1 receptor antagonist infusion yielded a significant increase in FGF-19 levels after oral glucose in individuals with PBH. While plasma bile acids did not differ between PBH and asymptomatic post-RYGB, these data suggest unique interrelationships between GLP-1 and FGF-19 in PBH.CONCLUSIONS: Taken together, these data support FGF-19 as a potential contributor to insulin-independent pathways driving postprandial hypoglycemia in PBH.
View details for PubMedID 30976983
- High-frequency actionable pathogenic exome variants in an average-risk cohort COLD SPRING HARBOR MOLECULAR CASE STUDIES 2018; 4 (6)
High Frequency Actionable Pathogenic Exome Variants in an Average-Risk Cohort.
Cold Spring Harbor molecular case studies
Exome sequencing is increasingly utilized in both clinical and non-clinical settings, but little is known about its utility in healthy individuals. Most previous studies on this topic have examined a small subset of genes known to be implicated in human disease and/or have used automated pipelines to assess pathogenicity of known variants. In order to determine the frequency of both medically actionable and non-actionable but medically relevant exome findings in the general population we assessed the exomes of 70 participants who have been extensively characterized over the past several years as part of a longitudinal integrated multi-omics profiling study. We analyzed exomes by identifying rare likely pathogenic and pathogenic variants in genes associated with Mendelian disease in the Online Mendelian Inheritance in Man (OMIM) database. We then used American College of Medical Genetics (ACMG) guidelines for the classification of rare sequence variants. Additionally, we assessed pharmacogenetic variants. Twelve out of 70 (17%) participants had medically actionable findings in Mendelian disease genes. Five had phenotypes or family histories associated with their genetic variants. The frequency of actionable variants is higher than that reported in most previous studies and suggests added benefit from utilizing expanded gene lists and manual curation to assess actionable findings. A total of 63 participants (90%) had additional non-actionable findings, including 60 who were found to be carriers for recessive diseases and 21 who have increased Alzheimer's disease risk due to heterozygous or homozygous APOE e4 alleles (18 participants had both). Our results suggest that exome sequencing may have considerable more utility for health management in the general population than previously thought.
View details for PubMedID 30487145
Efficacy and pharmacokinetics of subcutaneous exendin (9-39) in patients with post-bariatric hypoglycaemia
DIABETES OBESITY & METABOLISM
2018; 20 (2): 352–61
To evaluate the efficacy, pharmacokinetic (PK) profile and tolerability of subcutaneous (s.c.). exendin 9-39 (Ex-9) injection in patients with post-bariatric hypoglycaemia (PBH).Nine women who had recurrent symptomatic hypoglycaemia after undergoing Roux-en-Y gastric bypass were enrolled in this 2-part, single-blind, single-ascending-dose study. In Part 1, a single participant underwent equimolar low-dose intravenous (i.v.) vs s.c. Ex-9 administration; in Part 2, 8 participants were administered single ascending doses of s.c. Ex-9 during an oral glucose tolerance test (OGTT). Glycaemic, hormonal, PK and symptomatic responses were compared with those obtained during the baseline OGTT.Although an exposure-response relationship was observed, all doses effectively prevented hyperinsulinaemic hypoglycaemia and improved associated symptoms. On average, the postprandial glucose nadir was increased by 66%, peak insulin was reduced by 57%, and neuroglycopenic symptoms were reduced by 80%. All doses were well tolerated with no treatment-emergent adverse events observed.Injection s.c. of Ex-9 appears to represent a safe, effective and targeted therapeutic approach for treatment of PBH. Further investigation involving multiple doses with chronic dosing is warranted.
View details for PubMedID 28776922
Integrative Personal Omics Profiles during Periods of Weight Gain and Loss.
Advances in omics technologies now allow an unprecedented level of phenotyping for human diseases, including obesity, in which individual responses to excess weight are heterogeneous and unpredictable. To aid the development of better understanding of these phenotypes, we performed a controlled longitudinal weight perturbation study combining multiple omics strategies (genomics, transcriptomics, multiple proteomics assays, metabolomics, and microbiomics) during periods of weight gain and loss in humans. Results demonstrated that: (1) weight gain is associated with the activation of strong inflammatory and hypertrophic cardiomyopathy signatures in blood; (2) although weight loss reverses some changes, a number of signatures persist, indicative of long-term physiologic changes; (3) we observed omics signatures associated with insulin resistance that may serve as novel diagnostics; (4) specific biomolecules were highly individualized and stable in response to perturbations, potentially representing stable personalized markers. Most data are available open access and serve as a valuable resource for the community.
View details for PubMedID 29361466
Metabolic markers, regional adiposity, and adipose cell size: relationship to insulin resistance in African-American as compared with Caucasian women.
International journal of obesity (2005)
African-American women have the greatest prevalence of obesity in the United States, and higher rates of type 2 diabetes than Caucasian women, yet paradoxically lower plasma triglycerides (TG), visceral fat and intrahepatic fat, and higher high-density lipoprotein (HDL)-cholesterol. Visceral fat has not been evaluated against insulin resistance in African-American women, and TG/HDL-cholesterol has been criticized as a poor biomarker for insulin resistance in mixed-sex African-American populations. Adipocyte hypertrophy, reflecting adipocyte dysfunction, predicts insulin resistance in Caucasians, but has not been studied in African-Americans. Our goal was to assess whether traditional correlates of insulin resistance, measures of adiposity and adipocyte characteristics similarly predict peripheral insulin resistance in African-American and Caucasian women.Thirty-four healthy African-American (n = 17) and Caucasian (n = 17) women, matched for age (mean = 53.0 yrs) and body mass index (BMI) (mean = 30 kg/m2), underwent a steady-state plasma glucose test to measure insulin sensitivity; computed tomography (fat distribution); and a periumbilical scalpel biopsy (adipocyte characterization). By-race analyzes utilized analysis of covariance; linear regressions evaluated relationships between metabolic/adipose variables. All analyses adjusted for BMI and menopausal status.Insulin sensitivity did not differ between groups (p = 0.65). Neither BMI, nor %body fat or thigh fat predicted insulin resistance in African-American women. Fasting TG (p = 0.046), HDL-cholesterol (p = 0.0006) and TG/HDL-cholesterol ratio (p = 0.009) strongly predicted insulin resistance in African-American women. Despite being lower in African-American women, hepatic fat and visceral adipose tissue (VAT) correlated with insulin resistance in both groups, as did fasting glucose, VAT/SAT (subcutaneous adipose tissue) ratio, and %SAT (inverse).Total adiposity measures and adipocyte hypertrophy did not predict insulin resistance in African-American women, but did in Caucasian women. Plasma TG and HDL-cholesterol were significant predictors of insulin resistance in African-American women. Our findings demonstrate the need to identify race and sex-specific biomarkers for metabolic risk profiling.
View details for PubMedID 30127463
T-Cells in Human Subcutaneous Adipose Tissue
AMER DIABETES ASSOC. 2017: A90
View details for Web of Science ID 000408064100339
Critical role for GLP-1 in symptomatic post-bariatric hypoglycaemia.
2017; 60 (3): 531-540
Post-bariatric hypoglycaemia (PBH) is a rare, but severe, metabolic disorder arising months to years after bariatric surgery. It is characterised by symptomatic postprandial hypoglycaemia, with inappropriately elevated insulin concentrations. The relative contribution of exaggerated incretin hormone signalling to dysregulated insulin secretion and symptomatic hypoglycaemia is a subject of ongoing inquiry. This study was designed to test the hypothesis that PBH and associated symptoms are primarily mediated by glucagon-like peptide-1 (GLP-1).We conducted a double-blinded crossover study wherein eight participants with confirmed PBH were assigned in random order to intravenous infusion of the GLP-1 receptor (GLP-1r) antagonist. Exendin (9-39) (Ex-9), or placebo during an OGTT on two separate days at the Stanford University Clinical and Translational Research Unit. Metabolic, symptomatic and pharmacokinetic variables were evaluated. Results were compared with a cohort of BMI- and glucose-matched non-surgical controls (NSCs).Infusion of Ex-9 decreased the time to peak glucose and rate of glucose decline during OGTT, and raised the postprandial nadir by over 70%, normalising it relative to NSCs and preventing hypoglycaemia in all PBH participants. Insulin AUC and secretion rate decreased by 57% and 71% respectively, and peak postprandial insulin was normalised relative to NSCs. Autonomic and neuroglycopenic symptoms were significantly reduced during Ex-9 infusion.GLP-1r blockade prevented hypoglycaemia in 100% of individuals, normalised beta cell function and reversed neuroglycopenic symptoms, supporting the conclusion that GLP-1 plays a primary role in mediating hyperinsulinaemic hypoglycaemia in PBH. Competitive antagonism at the GLP-1r merits consideration as a therapeutic strategy.ClinicalTrials.gov NCT02550145.
View details for DOI 10.1007/s00125-016-4179-x
View details for PubMedID 27975209
View details for PubMedCentralID PMC5300915
Adipose tissue macrophages impair preadipocyte differentiation in humans.
2017; 12 (2)
The physiologic mechanisms underlying the relationship between obesity and insulin resistance are not fully understood. Impaired adipocyte differentiation and localized inflammation characterize adipose tissue from obese, insulin-resistant humans. The directionality of this relationship is not known, however. The aim of the current study was to investigate whether adipose tissue inflammation is causally-related to impaired adipocyte differentiation.Abdominal subcutaneous(SAT) and visceral(VAT) adipose tissue was obtained from 20 human participants undergoing bariatric surgery. Preadipocytes were isolated, and cultured in the presence or absence of CD14+ macrophages obtained from the same adipose tissue sample. Adipocyte differentiation was quantified after 14 days via immunofluorescence, Oil-Red O, and adipogenic gene expression. Cytokine secretion by mature adipocytes cultured with or without CD14+macrophages was quantified.Adipocyte differentiation was significantly lower in VAT than SAT by all measures (p<0.001). With macrophage removal, SAT preadipocyte differentiation increased significantly as measured by immunofluorescence and gene expression, whereas VAT preadipocyte differentiation was unchanged. Adipocyte-secreted proinflammatory cytokines were higher and adiponectin lower in media from VAT vs SAT: macrophage removal reduced inflammatory cytokine and increased adiponectin secretion from both SAT and VAT adipocytes. Differentiation of preadipocytes from SAT but not VAT correlated inversely with systemic insulin resistance.The current results reveal that proinflammatory immune cells in human SAT are causally-related to impaired preadipocyte differentiation, which in turn is associated with systemic insulin resistance. In VAT, preadipocyte differentiation is poor even in the absence of tissue macrophages, pointing to inherent differences in fat storage potential between the two depots.
View details for DOI 10.1371/journal.pone.0170728
View details for PubMedID 28151993
View details for PubMedCentralID PMC5289462
Subcutaneous Exendin (9-39) Effectively Treats Postbariatric Hyper insulinemic Hypoglycemia
AMER DIABETES ASSOC. 2016: A7–A8
View details for Web of Science ID 000398372800028
Adipose Cell Size and Regional Fat Deposition as Predictors of Metabolic Response to Overfeeding in Insulin-Resistant and Insulin-Sensitive Humans
2016; 65 (5): 1245-1254
Obesity is associated with insulin resistance (IR), but significant variability exists between similarly-obese individuals, pointing to qualitative characteristics of body fat as potential mediators. To test the hypothesis that obese, insulin-sensitive (IS) individuals possess adaptive adipose cell/tissue responses, we measured subcutaneous adipose cell size, insulin-suppression-of lipolysis, and regional fat responses to short-term overfeeding in BMI-matched overweight/obese individuals classified as IS or IR. At baseline, IR subjects exhibited significantly-greater visceral adipose tissue(VAT), intrahepatic lipid(IHL), plasma FFAs , adipose cell diameter, and %small adipose cells. With weight gain (3.1+1.4 kg), IR subjects demonstrated no significant change in adipose cell size, VAT, or insulin-suppression-of lipolysis, and only 8% worsening of insulin-mediated glucose uptake (IMGU).Alternatively, IS subjects demonstrated significant adipose cell enlargement, decrease in %small adipose cells, increase in VAT, IHL, lipolysis, 45% worsening of IMGU, and decreased expression of lipid metabolism genes. Smaller baseline adipose cell size and greater enlargement with weight gain predicted decline in IMGU, as did increase in IHL, VAT, and decrease in insulin-suppression-of lipolysis. Weight gain in IS humans causes maladaptive changes in adipose cells, regional fat distribution, and insulin resistance. The correlation between worsening insulin resistance and changes in adipose cell size, VAT, IHL, and insulin-suppression-of lipolysis highlight these factors as potential mediators between obesity and insulin resistance.
View details for DOI 10.2337/db15-1213
View details for Web of Science ID 000375028000015
View details for PubMedID 26884438
Pasireotide Induced Adrenal Insufficiency.
We report the case of secondary adrenal insufficiency in a 56-year-old woman with a history of post-Roux-en-Y gastric bypass hyperinsulinemic hypoglycemia, undergoing experimental treatment with pasireotide. This article is protected by copyright. All rights reserved.
View details for PubMedID 26733356
In vivo 2H2O administration reveals impaired triglyceride storage in adipose tissue of insulin-resistant humans.
Journal of lipid research
2015; 56 (2): 435-439
Indirect evidence suggests that impaired triglyceride storage in the subcutaneous fat depot contributes to the development of insulin resistance via lipotoxicity. We directly tested this hypothesis by measuring, in vivo, TG synthesis, de novo lipogenesis (DNL), adipocyte proliferation, and insulin suppression of lipolysis in subcutaneous adipose tissue of BMI-matched individuals classified as insulin resistant (IR) or insulin sensitive (IS). Nondiabetic, moderately obese subjects with BMI 25-35 kg/m(2), classified as IR or IS by the modified insulin suppression test, consumed deuterated water ((2)H2O) for 4 weeks. Deuterium incorporation into glycerol, palmitate, and DNA indicated TG synthesis, DNL, and adipocyte proliferation, respectively. Net TG synthesis and DNL in adipose cells were significantly lower in IR as compared with IS subjects, whereas adipocyte proliferation did not differ significantly. Plasma FFAs measured during an insulin suppression test were 2.5-fold higher in IR subjects, indicating resistance to insulin suppression of lipolysis. Adipose TG synthesis correlated directly with DNL but not with proliferation. These results provide direct in vivo evidence for impaired TG storage in subcutaneous adipose tissue of IR as compared with IS. Relative inability to store TG in the subcutaneous depot may represent a mechanism contributing to the development of insulin resistance in the setting of obesity.
View details for DOI 10.1194/jlr.M052860
View details for PubMedID 25418322
View details for PubMedCentralID PMC4306696
The Use of Gastrostomy Tube for the Long-Term Remission of Hyperinsulinemic Hypoglycemia After Roux-en-y Gastric Bypass: A Case Report
AACE Clinical Case Reports: Spring 2015
2015; 1 (2): e84-e87
View details for DOI 10.4158/EP14218
The Integrative Human Microbiome Project: Dynamic Analysis of Microbiome-Host Omics Profiles during Periods of Human Health and Disease
CELL HOST & MICROBE
2014; 16 (3): 276-289
Much has been learned about the diversity and distribution of human-associated microbial communities, but we still know little about the biology of the microbiome, how it interacts with the host, and how the host responds to its resident microbiota. The Integrative Human Microbiome Project (iHMP, http://hmp2.org), the second phase of the NIH Human Microbiome Project, will study these interactions by analyzing microbiome and host activities in longitudinal studies of disease-specific cohorts and by creating integrated data sets of microbiome and host functional properties. These data sets will serve as experimental test beds to evaluate new models, methods, and analyses on the interactions of host and microbiome. Here we describe the three models of microbiome-associated human conditions, on the dynamics of preterm birth, inflammatory bowel disease, and type 2 diabetes, and their underlying hypotheses, as well as the multi-omic data types to be collected, integrated, and distributed through public repositories as a community resource.
View details for DOI 10.1016/j.chom.2014.08.014
View details for Web of Science ID 000342057000006
View details for PubMedID 25211071
Notch Oncoproteins depend on gamma-secretase/presenilin activity for processing and function
JOURNAL OF BIOLOGICAL CHEMISTRY
2004; 279 (29): 30771-30780
During normal development Notch receptor signaling is important in regulating numerous cell fate decisions. Mutations that truncate the extracellular domain of Notch receptors can cause aberrant signaling and promote unregulated cell growth. We have examined two types of truncated Notch oncoproteins that arise from proviral insertion into the Notch4 gene (Notch4/int-3) or a chromosomal translocation involving the Notch1 gene (TAN-1). Both Notch4/int-3 and TAN-1 oncoproteins lack most or all of their ectodomain. Normal Notch signaling requires gamma-secretase/presenilin-mediated proteolytic processing, but whether Notch oncoproteins are also dependent on gamma-secretase/presenilin activity is not known. We demonstrate that Notch4/int-3-induced activation of the downstream transcription factor, CSL, is abrogated in cells deficient in presenilins or treated with a pharmacological inhibitor of gamma-secretase/presenilins. Furthermore, we find that both Notch4/int-3 and TAN-1 accumulate at the cell surface, where presenilin-dependent cleavage occurs, when gamma-secretase/presenilin activity is inhibited. gamma-Secretase/presenilin inhibition effectively blocks cellular responses to Notch4/int-3, but not TAN-1, apparently because some TAN-1 polypeptides lack transmembrane domains and do not require gamma-secretase/presenilin activity for nuclear access. These studies highlight potential uses and limitations of gamma-secretase/presenilin inhibitors in targeted therapy of Notch-related neoplasms.
View details for DOI 10.1074/jbc.M309252200
View details for Web of Science ID 000222531900108
View details for PubMedID 15123653