Pancreatic steatosis and its relationship to β-cell dysfunction in humans: racial and ethnic variations

A Systematic Review of Beta Cell Function in Adults of Black African Ethnicity

BACKGROUND

Understanding ethnic differences in beta cell function has important implications for preventative and therapeutic strategies in populations at high risk of type 2 diabetes (T2D). The existing literature, largely drawn from work in children and adolescents, suggests that beta cell function in black African (BA) populations is upregulated when compared to white Europeans (WE).

METHODS

A systematic literature search was undertaken in June 2018 to identify comparative studies of beta cell function between adults (>age 18 years) of indigenous/diasporic BA and WE ethnicity. All categories of glucose tolerance and all methodologies of assessing beta cell function in vivo were included.

RESULTS

41 studies were identified for inclusion into a qualitative synthesis. The majority were studies in African American populations (n = 30) with normal glucose tolerance (NGT)/nondiabetes (n = 25), using intravenous glucose stimulation techniques (n = 27). There were fewer studies in populations defined as only impaired fasting glucose/impaired glucose tolerance (IFG/IGT) (n = 3) or only T2D (n = 3). Although BA broadly exhibited greater peripheral insulin responses than WE, the relatively small number of studies which measured C-peptide to differentiate between beta cell insulin secretion and hepatic insulin extraction (n = 14) had highly variable findings. In exclusively IGT or T2D cohorts, beta cell insulin secretion was found to be lower in BA compared to WE.

CONCLUSIONS

There is inconsistent evidence for upregulated beta cell function in BA adults, and they may in fact exhibit greater deficits in insulin secretory function as glucose intolerance develops.

Ethnic differences in hepatic, pancreatic, muscular and visceral fat deposition in healthy men of white European and black west African ethnicity

AIMS

We aimed to assess ethnic differences in visceral adipose tissue (VAT), intrahepatic (IHL), intrapancreatic (IPL) and intramyocellular lipids (IMCL) between healthy white European (WE) and black west African (BWA) men.

METHODS

23 WE and 20 BWA men underwent Dixon-magnetic resonance imaging to quantify VAT, IHL and IPL; and proton-magnetic resonance spectroscopy to quantify IMCL. Insulin sensitivity and beta-cell function were determined using homeostasis model assessment (HOMA-2).

RESULTS

BWA men exhibited significantly lower VAT (P = 0.021) and IHL (P = 0.044) than WE men, but comparable IPL (P = 0.92) and IMCL (P = 0.87). VAT was associated with IPL in both ethnicities (WE: P < 0.001; BWA: P = 0.001) but the relationship with IHL differed by ethnicity (P_interaction = 0.018) and was only significant in WE men (WE: P < 0.001; BWA: P = 0.36). All ectopic fat depots inversely associated with insulin sensitivity and positively associated with beta-cell function in WE but not BWA men.

CONCLUSIONS

Lower VAT and IHL, and their lack of interrelation, in BWA men suggests ethnic differences exist in the mechanisms of ectopic fat deposition. The lack of association between ectopic fat with insulin sensitivity and beta-cell function in BWA men may indicate a lesser role for ectopic fat in the development of type 2 diabetes mellitus in black populations.

Understanding the mechanisms of reversal of type 2 diabetes

Clinical and pathophysiological studies have shown type 2 diabetes to be a condition mainly caused by excess, yet reversible, fat accumulation in the liver and pancreas. Within the liver, excess fat worsens hepatic responsiveness to insulin, leading to increased glucose production. Within the pancreas, the β cell seems to enter a survival mode and fails to function because of the fat-induced metabolic stress. Removal of excess fat from these organs via substantial weight loss can normalise hepatic insulin responsiveness and, in the early years post-diagnosis, is associated with β-cell recovery of acute insulin secretion in many individuals, possibly by redifferentiation. Collectively, these changes can normalise blood glucose levels. Importantly, the primary care-based Diabetes Remission Clinical Trial (DiRECT) showed that 46% of people with type 2 diabetes could achieve remission at 12 months, and 36% at 24 months, mediated by weight loss. This major change in our understanding of the underlying mechanisms of disease permits a reassessment of advice for people with type 2 diabetes.

Pancreatic steatosis: an update

PURPOSE OF REVIEW

Pancreatic steatosis is a clinical entity with emerging significance and impacts patient health in a multitude of ways. It has a high prevalence in the global population with predilections for different demographics by age, sex and ethnicity. Understanding the pathophysiology, clinical features and complications of this entity may be important to understanding the consequences of the ongoing obesity global epidemic.

RECENT FINDINGS

Obesity and metabolic syndrome contribute to metabolic derangements that result in lipid mishandling by adipocytes. Adipocytokine imbalances in circulation and in the pancreatic microenvironment cause chronic, low-grade inflammation. The resulting beta cell and acinar cell apoptosis leads to pancreatic endocrine and exocrine dysfunction. Furthermore, these adipocytokines regulate cell growth, differentiation, as well as angiogenesis and lymphatic spread. These consequences of adipocyte infiltration are thought to initiate carcinogenesis, leading to pancreatic intraepithelial neoplasia and pancreatic ductal adenocarcinoma.

SUMMARY

Obesity will lead to millions of deaths each year and pancreatic steatosis may be the key intermediate entity that leads to obesity-related complications. Enhancing our understanding may reveal strategies for preventing mortality and morbidity related to the global epidemic of obesity. Further research is needed to determine the pathophysiology, long-term complications and effective treatment strategies for this condition.

Ethnicity and Type 2 diabetes in the UK

Type 2 diabetes is a major UK public health priority. Among minority ethnic communities, the prevalence is alarmingly high, approximately three to five times higher than in the white British population. Particularly striking is the earlier onset of Type 2 diabetes, which occurs some 10-12 years younger, with a significant proportion of cases being diagnosed before the age of 40 years. This review focuses on the UK context and Type 2 diabetes in adult populations, exploring the available evidence regarding the complex interplay of biological, lifestyle, social, clinical and healthcare system factors that are known to drive these disparities.

Hyperinsulinemia: An Early Indicator of Metabolic Dysfunction

Hyperinsulinemia is strongly associated with type 2 diabetes. Racial and ethnic minority populations are disproportionately affected by diabetes and obesity-related complications. This mini-review provides an overview of the genetic and environmental factors associated with hyperinsulinemia with a focus on racial and ethnic differences and its metabolic consequences. The data used in this narrative review were collected through research in PubMed and reference review of relevant retrieved articles. Insulin secretion and clearance are regulated processes that influence the development and progression of hyperinsulinemia. Environmental, genetic, and dietary factors are associated with hyperinsulinemia. Certain pharmacotherapies for obesity and bariatric surgery are effective at mitigating hyperinsulinemia and are associated with improved metabolic health. Hyperinsulinemia is associated with many environmental and genetic factors that interact with a wide network of hormones. Recent studies have advanced our understanding of the factors affecting insulin secretion and clearance. Further basic and translational work on hyperinsulinemia may allow for earlier and more personalized treatments for obesity and metabolic diseases.

Ethnic distinctions in the pathophysiology of type 2 diabetes: a focus on black African-Caribbean populations

Type 2 diabetes (T2D) is a global public health priority, particularly for populations of black African-Caribbean ethnicity, who suffer disproportionately high rates of the disease. While the mechanisms underlying the development of T2D are well documented, there is growing evidence describing distinctions among black African-Caribbean populations. In the present paper, we review the evidence describing the impact of black African-Caribbean ethnicity on T2D pathophysiology. Ethnic differences were first recognised through evidence that metabolic syndrome diagnostic criteria fail to detect T2D risk in black populations due to less central obesity and dyslipidaemia. Subsequently more detailed investigations have recognised other mechanistic differences, particularly lower visceral and hepatic fat accumulation and a distinctly hyperinsulinaemic response to glucose stimulation. While epidemiological studies have reported exaggerated insulin resistance in black populations, more detailed and direct measures of insulin sensitivity have provided evidence that insulin sensitivity is not markedly different to other ethnic groups and does not explain the hyperinsulinaemia that is exhibited. These findings lead us to hypothesise that ectopic fat does not play a pivotal role in driving insulin resistance in black populations. Furthermore, we hypothesise that hyperinsulinaemia is driven by lower rates of hepatic insulin clearance rather than heightened insulin resistance and is a primary defect rather than occurring in compensation for insulin resistance. These hypotheses are being investigated in our ongoing South London Diabetes and Ethnicity Phenotyping study, which will enable a more detailed understanding of ethnic distinctions in the pathophysiology of T2D between men of black African and white European ethnicity.

The association between pancreas steatosis and metabolic syndrome: A systematic review and meta-analysis

OBJECTIVES

Pancreas steatosis is the description of fat accumulation in the pancreatic gland. The prevalence and development mechanisms of pancreatic steatosis in patients with metabolic disorders still remain unclear. The aim of this study is to systematically review the association between pancreatic steatosis and metabolic co-morbidities.

METHODS

We performed a systematic search strategy using three electronic databases (MEDLINE, Scopus, and Embase) for relevant studies concerning the associations of pancreatic steatosis with metabolic syndrome (MetS) and its clinical relevance from inception until 30 September 2018.

RESULTS

One thousand three hundred fifty one references were identified in the initial search, and a total of 13 studies involving 49 329 subjects were included. This analyses elucidated the presence of non-alcoholic fatty pancreas disease (NAFPD) and was associated with a significant increased risk of metabolic syndrome (RR = 2.25; 95% CI, 2.00-2.53; P < 0.0001; I²  = 42.8%; eight studies included), hypertension (RR = 1.43; 95% CI, 1.08-1.90; P = 0.013; I²  = 94.7%; nine studies included), non-alcoholic fatty liver disease (NAFLD) (RR = 2.49; 95% CI, 2.06-3.02; P < 0.0001; I²  = 96.9%; nine studies included), diabetes mellitus (RR = 1.99; 95% CI, 1.18-3.35; P = 0.01; I²  = 97.6%; 10 studies included), and central obesity (RR = 1.91; 95% CI, 1.67-2.19; P < 0.0001; I²  = 95.9%; six studies included). The association between NAFPD and hyperlipidaemia was not statistically significant (RR = 1.33; 95% CI, 0.82-2.17; P = 0.249; I²  = 97%; five studies included).

CONCLUSIONS

The existing evidence indicates that NAFPD is significantly associated with an increased risk of metabolic syndrome and its components. Well-designed prospective cohort studies between pancreatic steatosis and MetS are needed to elaborate the causality in the future.

Associations Between Pancreatic Lipids and β-Cell Function in Black African and White European Men With Type 2 Diabetes

CONTEXT

Intrapancreatic lipid (IPL) has been linked to β-cell dysfunction. Black populations disproportionately develop type 2 diabetes (T2D) and show distinctions in β-cell function compared with white populations.

OBJECTIVE

We quantified IPL in white European (WE) and black West African (BWA) men with early T2D and investigated the relationships between IPL and β-cell insulin secretory function (ISF).

DESIGN, SETTING, AND PARTICIPANTS

We performed a cross-sectional assessment of 18 WE and 19 BWA middle-age men with early T2D as part of the South London Diabetes and Ethnicity Phenotyping study.

MAIN OUTCOME MEASURES

The participants underwent Dixon MRI to determine IPL in the pancreatic head, body, and tail and subcutaneous and visceral adipose tissue volumes. Modeled first- and second-phase ISFs were comprehensively determined using C-peptide measurements during a 3-hour meal tolerance test and a 2-hour hyperglycemic clamp test.

RESULTS

The WE men had greater mean IPL levels compared with BWA men (P = 0.029), mainly owing to greater IPL levels in the pancreatic head (P = 0.009). The mean IPL level was inversely associated with orally stimulated first-phase ISF in WE but not BWA men (WE, r = -0.554, P = 0.026; BWA, r = -0.183, P = 0.468). No association was found with orally stimulated second-phase ISF in either WE or BWA men. No associations were found between the mean IPL level and intravenously stimulated ISF.

CONCLUSIONS

The IPL levels were lower in BWA than WE men with early T2D, and the lack of inverse association with first-phase ISF in BWA men indicates that IPL might be a less important determinant of the development of T2D in BWA than in WE men.

Pancreatic fat content is associated with β-cell function and insulin resistance in Chinese type 2 diabetes subjects

The pathogenesis of type 2 diabetes mellitus (T2DM) is characterized by insulin resistance and β-cell dysfunction. Earlier studies reported that increased levels of pancreatic fat may lead to the development of β-cell dysfunction and insulin resistance. The present study aimed to demonstrate the relationship between pancreatic fat content (PFC) and insulin secretion and insulin resistance in Chinese subjects with T2DM. Seventy-eight T2DM subjects and 35 non-diabetic volunteers were recruited in this study. All subjects were subjected to an oral glucose tolerance test (OGTT). We also measured PFC and liver fat content (LFC) by three-point Dixon method (3p-Dixon), and we examined the relations between PFC and OGTT-derived parameters. T2DM subjects had higher PFC than non-diabetic subjects (p < 0.01). PFC was correlated with body mass index (BMI), liver fat content (LFC) and age in two groups, however, it was only positively associated with insulin secretion, insulin resistance, early- and late-phase insulin secretion in male T2DM subjects, but not in non-diabetic and female T2DM subjects. After adjusting for BMI, LFC and age, the association still existed (all p < 0.05). Furthermore, the relationship was more obvious in male T2DM subjects with a shorter course of disease. PFC was associated with β-cell dysfunction and insulin resistance in subjects with T2DM and was more obvious in male T2DM subjects with shorter duration of diabetes. Therefore, PFC might represent a potential risk factor for the development of T2DM.

Association of Pancreatic Steatosis With Chronic Pancreatitis, Obesity, and Type 2 Diabetes Mellitus

OBJECTIVE

The aim of this study was to determine the association of the pancreatic steatosis with obesity, chronic pancreatitis (CP), and type 2 diabetes mellitus.

METHODS

Patients (n = 118) were retrospectively identified and categorized into no CP (n = 60), mild (n = 21), moderate (n = 27), and severe CP (n = 10) groups based on clinical history and magnetic resonance cholangiopancreatography using the Cambridge classification as the diagnostic standard. Visceral and subcutaneous compartments were manually segmented, and fat tissue was quantitatively measured on axial magnetic resonance imaging.

RESULTS

Pancreatic fat fraction showed a direct correlation with fat within the visceral compartment (r = 0.54). Patients with CP showed higher visceral fat (P = 0.01) and pancreatic fat fraction (P < 0.001): mild, 24%; moderate, 23%; severe CP, 21%; no CP group, 15%. Patients with type 2 diabetes mellitus showed higher pancreatic steatosis (P = 0.03) and higher visceral (P = 0.007) and subcutaneous fat (P = 0.004). Interobserver variability of measuring fat by magnetic resonance imaging was excellent (r ≥ 0.90-0.99).

CONCLUSIONS

Increased visceral adipose tissue has a moderate direct correlation with pancreatic fat fraction. Chronic pancreatitis is associated with higher pancreatic fat fraction and visceral fat. Type 2 diabetes mellitus is associated with higher pancreatic fat fraction and visceral and subcutaneous adiposity.

Pancreatic Cancer Following Incident Diabetes in African Americans and Latinos: The Multiethnic Cohort

Background

Diabetes has been proposed to be a risk factor for and a consequence of pancreatic cancer (PC). The relationship between recent-onset diabetes and PC is not well understood, and data in minorities are sparse. We examined the relationships between recent-onset diabetes and PC incidence in African Americans and Latinos in the Multiethnic Cohort.

Methods

A total of 48 995 African Americans and Latinos without prior diabetes and cancer at baseline (1993-1996) were included in the study. Questionnaires, Medicare data, and California hospital discharge files were used to identify new diabetes diagnoses. Cox regressions were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for cancer associated with diabetes and with diabetes duration.

Results

A total of 15 833 (32.3%) participants developed diabetes between baseline and 2013. A total of 408 incident PC cases were identified during follow-up. Diabetes was associated with PC (HRage75 = 2.39, 95% CI = 1.91 to 2.98). Individuals with recent-onset diabetes (within three or fewer years of PC diagnosis) had a greater risk compared with those with long-term diabetes across all ages. The HRage75 for recent-onset diabetes was 4.08 (95% CI = 2.76 to 6.03) in Latinos and 3.38 (95% CI = 2.30 to 4.98) in African Americans.

Conclusions

Diabetes was associated with a more than twofold higher risk of PC in African Americans and Latinos, but recent-onset diabetes was associated with a 2.3-fold greater increase in risk of PC than long-standing diabetes. Our findings support the hypothesis that recent-onset diabetes is a manifestation of PC and that long-standing diabetes is a risk factor for this malignancy.

The Association between Pancreatic Steatosis and Diabetic Retinopathy in Type 2 Diabetes Mellitus Patients

BACKGROUND

Whether pancreatic steatosis has a local or systemic effect, like ectopic fat of other major organs, remains unknown. Data on the influence of pancreatic steatosis on microvascular complication are rare. Therefore, we investigated the relationship between pancreatic steatosis and diabetic retinopathy (DR) in patients with type 2 diabetes mellitus (T2DM).

METHODS

The attenuation of three pancreatic regions (head, body, and tail) and the spleen (S) in 186 patients with T2DM was measured using non-enhanced computed tomography imaging. We used three parameters for the assessment of pancreatic steatosis ('P' mean: mean attenuation of three pancreatic regions; P-S: difference between 'P' mean and 'S'; P/S: the 'P' mean to 'S' ratio). The presence of DR was assessed by an expert ophthalmologist using dilated fundoscopy.

RESULTS

The average P mean was 29.02 Hounsfield units (HU), P-S was -18.20 HU, and P/S was 0.61. The three pancreatic steatosis parameters were significantly associated with the prevalence of DR in non-obese T2DM patients. In the non-obese group, the odds ratios of P mean, P-S, and P/S for the prevalence of DR, after adjustment for age, sex, and glycosylated hemoglobin level, were 2.449 (P=0.07), 2.639 (P=0.04), and 2.043 (P=0.02), respectively.

CONCLUSION

In this study, pancreatic steatosis was significantly associated with DR in non-obese patients with T2DM. Further studies are necessary to clarify the causal relationship between pancreatic steatosis and the development of DR.

No Correlation of Pancreatic Fat and β-Cell Function in Young Women With and Without a History of Gestational Diabetes

CONTEXT

Pancreatic steatosis may contribute to β-cell dysfunction in type 2 diabetes (T2D), but data are controversial. Women who had gestational diabetes mellitus (GDM) are at high risk for developing T2D.

OBJECTIVE

To examine the association of pancreatic fat content with early/first-phase insulin secretion (as markers of β-cell function).

DESIGN

Cross-sectional analysis of a subcohort of the monocentric, prospective cohort study titled Prediction, Prevention, and Subclassification of Type 2 Diabetes.

SETTING

Ludwig Maximilians University Hospital, Munich, Germany.

PARTICIPANTS

Ninety-seven women, 3 to 16 months after pregnancy [41 normoglycemic women post-GDM, 19 women post-GDM with pathological glucose metabolism, and 37 normoglycemic women after a normoglycemic pregnancy (controls)].

MAIN OUTCOME MEASURES

Correlation of MRI-measured pancreatic fat content with early insulin release in an oral glucose tolerance test (OGGT) [insulin increment within the first 30 minutes of the OGTT (IR30)] and first-phase insulin response (FPIR) in an intravenous glucose tolerance test (n = 65), both adjusted for insulin sensitivity index (ISI).

RESULTS

Pancreatic fat content did not correlate with IR30 and FPIR adjusted for ISI. It correlated positively with body mass index, waist circumference, liver fat, and intraabdominal fat volume.

CONCLUSION

Pancreatic fat content does not correlate with β-cell function in a cohort of young women with different degrees of T2D risk.

Obesity, metabolic disease and the pancreas-Quantitative imaging of pancreatic fat

The association between pancreatic fat, obesity and metabolic disease is well-documented, and although a potentially exciting target for novel therapies, remains poorly understood. Non-invasive quantitative imaging-derived biomarkers can provide insights into pathophysiology and potentially provide robust trial endpoints for development of new treatments. In this review, we provide an overview of the pathophysiology of non-alcoholic fatty pancreas disease and associations with metabolic factors, obesity and diabetes. We then explore approaches to pancreatic fat quantification using ultrasound, CT and MRI, reviewing the strengths, limitations and current published evidence in the assessment of pancreatic fat. Finally, we explore the broader challenges of pancreatic fat quantification as we move toward translating these methods into the clinical setting.

Circulating triacylglycerols but not pancreatic fat associate with insulin secretion in healthy humans

BACKGROUND

Loss of adequate insulin secretion for the prevailing insulin resistance is critical for the development of type 2 diabetes and has been suggested to result from circulating lipids (triacylglycerols [TG] or free fatty acids) and/or adipocytokines or from ectopic lipid storage in the pancreas. This study aimed to address whether circulating lipids, adipocytokines or pancreatic fat primarily associates with lower insulin secretion.

SUBJECTS/METHODS

Nondiabetic persons (n=73), recruited from the general population, underwent clinical examinations, fasting blood drawing to measure TG and adipocytokines and oral glucose tolerance testing (OGTT) to assess basal and dynamic insulin secretion and sensitivity indices. Magnetic resonance imaging and ¹H-magnetic resonance spectroscopy were used to measure body fat distribution and ectopic fat content in liver and pancreas.

RESULTS

In age-, sex- and BMI-adjusted analyses, total and high-molecular-weight adiponectin were the strongest negative predictors of fasting beta-cell function (BCF; β=-0.403, p=0.0003 and β=-0.237, p=0.01, respectively) and adaptation index (AI; β=-0.210, p=0.006 and β=-0.133, p=0.02, respectively). Circulating TG, but not pancreatic fat content, related positively to BCF (β=0.375, p<0.0001) and AI (β=0.192, p=0.003). Similar results were obtained for the disposition index (DI).

CONCLUSIONS

The association of serum lipids and adiponectin with beta-cell function may represent a compensatory response to adapt for lower insulin sensitivity in nondiabetic humans.

From Sea to Shining Sea and the Great Plains to Patagonia: A Review on Current Knowledge of Diabetes Mellitus in Hispanics/Latinos in the US and Latin America

The past two decades have witnessed many advances in the prevention, treatment, and control of diabetes mellitus (DM) and its complications. Increased screening has led to a greater recognition of type 2 diabetes mellitus (type 2 DM) and prediabetes; however, Hispanics/Latinos, the largest minority group in the US, have not fully benefited from these advances. The Hispanic/Latino population is highly diverse in ancestries, birth places, cultures, languages, and socioeconomic backgrounds, and it populates most of the Western Hemisphere. In the US, the prevalence of DM varies among Hispanic/Latino heritage groups, being higher among Mexicans, Puerto Ricans, and Dominicans, and lower among South Americans. The risk and prevalence of diabetes among Hispanics/Latinos are significantly higher than in non-Hispanic Whites, and nearly 40% of Hispanics/Latinos with diabetes have not been formally diagnosed. Despite these striking facts, the representation of Hispanics/Latinos in pharmacological and non-pharmacological clinical trials has been suboptimal, while the prevalence of diabetes in these populations continues to rise. This review will focus on the epidemiology, etiology and prevention of type 2 DM in populations of Latin American origin. We will set the stage by defining the terms Hispanic, Latino, and Latin American, explaining the challenges identifying Hispanics/Latinos in the scientific literature and databases, describing the epidemiology of diabetes-including type 2 DM and gestational diabetes mellitus (GDM)-and cardiovascular risk factors in Hispanics/Latinos in the US and Latin America, and discussing trends, and commonalities and differences across studies and populations, including methodology to ascertain diabetes. We will discuss studies on mechanisms of disease, and research on prevention of type 2 DM in Hispanics/Latinos, including women with GDM, youth and adults; and finalize with a discussion on lessons learned and opportunities to enhance research, and, consequently, clinical care oriented toward preventing type 2 DM in Hispanics/Latinos in the US and Latin America.

Metabolic crosstalk between fatty pancreas and fatty liver: effects on local inflammation and insulin secretion

AIMS/HYPOTHESIS

Obesity-linked ectopic fat accumulation is associated with the development of type 2 diabetes. Whether pancreatic and liver steatosis impairs insulin secretion is controversial. We examined the crosstalk of human pancreatic fat cells with islets and the role of diabetogenic factors, i.e. palmitate and fetuin-A, a hepatokine released from fatty liver.

METHODS

Human pancreatic resections were immunohistochemically stained for insulin, glucagon, somatostatin and the macrophage/monocyte marker CD68. Pancreatic adipocytes were identified by Oil Red O and adiponectin staining. Primary pancreatic pre-adipocytes and differentiated adipocytes were co-cultured with human islets isolated from organ donors and the metabolic crosstalk between fatty liver and fatty pancreas was mimicked by the addition of palmitate and fetuin-A. Insulin secretion was evaluated by ELISA and RIA. Cytokine expression and secretion were assessed by RT-PCR and multiplex assay, respectively. Subcellular distribution of proteins was examined by confocal microscopy and protein phosphorylation by western blotting.

RESULTS

In human pancreatic parenchyma, highly differentiated adipocytes were detected in the proximity of islets with normal architecture and hormone distribution. Infiltration of adipocytes was associated with an increased number of CD68-positive cells within islets. In isolated primary pancreatic pre-adipocytes and differentiated adipocytes, palmitate and fetuin-A induced IL6, CXCL8 and CCL2 mRNA expression. Cytokine production was toll-like receptor 4 (TLR4)-dependent and further accentuated in pre-adipocytes when co-cultured with islets. In islets, IL6 and CXCL8 mRNA levels were also increased by fetuin-A and palmitate. Only in macrophages within the isolated islets, palmitate and fetuin-A stimulated the production of the cytotoxic cytokine IL-1β. Palmitate, but not fetuin-A, exerted pro-apoptotic effects in islet cells. Instead, fetuin-A impaired glucose-induced insulin secretion in a TLR4-independent, but c-Jun N-terminal kinase- and Ca²⁺-dependent, manner.

CONCLUSIONS/INTERPRETATION

These results provide the first evidence that fetuin-A-mediated metabolic crosstalk of fatty liver with islets may contribute to obesity-linked glucose blindness of beta cells, while fatty pancreas may exacerbate local inflammation.

Pancreas Fat and β Cell Mass in Humans With and Without Diabetes: An Analysis in the Japanese Population

CONTEXT

The mechanisms by which β cell mass is reduced in patients with type 2 diabetes remain unclear. It has been postulated that ectopic fat deposits in the pancreas induce β cell apoptosis, leading to the development of diabetes.

OBJECTIVE

The aim of this study was to clarify the effects of intrapancreatic fat on β and α cell mass in humans with and without diabetes.

DESIGN AND SUBJECTS

Using our tissue database, pancreas sections of 72 Japanese nondiabetic (NDM) autopsy cases and 50 diabetic and 49 age- and body mass index (BMI)-matched NDM patients who underwent pancreatic surgery were analyzed. In addition to histological grading, intrapancreatic fat area (IPFA) was quantified as fractional intralobular, but not interlobular, fat area to the whole pancreas area.

RESULTS

Although IPFA was positively correlated with age and BMI, there was no significant difference in IPFA between cases with and without diabetes. Moreover, no association was found between IPFA and either β or α cell area, or glycated hemoglobin.

CONCLUSION

These findings suggest that pancreatic fat deposits have little effect on β cell mass and the development of diabetes in humans.

Pancreatic fat content assessed by 1 H magnetic resonance spectroscopy is correlated with insulin resistance, but not with insulin secretion, in Japanese individuals with normal glucose tolerance

AIMS/INTRODUCTION

Whereas some clinical studies have shown that excessive fat accumulation in the pancreas is associated with impairment of insulin secretion, others have not found such an association. 1 H magnetic resonance spectroscopy allows quantitative fat analysis in various tissues including the pancreas. The pathological relevance of pancreatic fat content (PFC) in Japanese individuals remains unclear, however.

MATERIALS AND METHODS

We analyzed PFC in 30 Japanese individuals with normal glucose tolerance by 1 H magnetic resonance spectroscopy, and then investigated the relationships between PFC and indexes of insulin secretion and insulin sensitivity-resistance determined by an oral glucose tolerance test. We also measured hepatic fat content and intramyocellular lipid content by 1 H magnetic resonance spectroscopy, as well as visceral fat area and subcutaneous fat area by magnetic resonance imaging, and we examined the relationships between these fat content measures and oral glucose tolerance test-derived parameters.

RESULTS

PFC was correlated with indexes of insulin sensitivity-resistance, but not with those of insulin secretion. Hepatic fat content and visceral fat area were correlated with similar sets of parameters as was PFC, whereas subcutaneous fat area was correlated with parameters of insulin secretion, and intramyocellular lipid content was not correlated with any of the measured parameters. The correlation between PFC and homeostasis model assessment of insulin resistance remained significant after adjustment for age, body mass index and sex. Among fat content measures, PFC was most highly correlated with hepatic fat content and visceral fat area.

CONCLUSIONS

PFC was correlated with indexes of insulin resistance, but not with those of insulin secretion in non-obese Japanese individuals with normal glucose tolerance.

Non-alcoholic fatty liver disease: A sign of systemic disease

Non-alcoholic fatty liver disease (NAFLD) is the most common form of liver disease and leading cause of cirrhosis in the United States and developed countries. NAFLD is closely associated with obesity, insulin resistance and metabolic syndrome, significantly contributing to the exacerbation of the latter. Although NAFLD represents the hepatic component of metabolic syndrome, it can also be found in patients prior to their presentation with other manifestations of the syndrome. The pathogenesis of NAFLD is complex and closely intertwined with insulin resistance and obesity. Several mechanisms are undoubtedly involved in its pathogenesis and progression. In this review, we bring together the current understanding of the pathogenesis that makes NAFLD a systemic disease.

Risk of Obesity-Related Cardiometabolic Complications in Special Populations: A Crisis in Asians

The prospect of a significant increase in global health-related costs associated with high cardiometabolic complications of obesity in Asians has encouraged more attention to be focused on the problem of growing obesity prevalence in these populations. Although these studies have shown that cardiometabolic complications occur more frequently and at a lower body mass index (BMI) in Asians than in European populations, the mechanisms involved have yet to be discovered. Ethnic/racial differences in body composition and fat distribution have been studied extensively. Although these studies have shown that increasing BMI is associated with larger increases in body fat content in Asians, growing evidence points to factors other than body fat content and fat distribution in determining a higher prevalence of cardiometabolic complications in these populations. Here, we provide support to our view that earlier onset of adipocyte maturation arrest/insulin resistance during weight gain could be a major factor in increasing the cardiometabolic risk of Asian populations at a lower BMI.

Quantification of intrapancreatic fat in type 2 diabetes by MRI

OBJECTIVES

Accumulation of intrapancreatic fat may be important in type 2 diabetes, but widely varying data have been reported. The standard quantification by MRI in vivo is time consuming and dependent upon a high level of experience. We aimed to develop a new method which would minimise inter-observer variation and to compare this against previously published datasets.

METHODS

A technique of 'biopsying' the image to minimise inclusion of non-parenchymal tissues was developed. Additionally, thresholding was applied to exclude both pancreatic ducts and intrusions of visceral fat, with pixels of fat values of <1% or >20% being excluded. The new MR image 'biopsy' (MR-opsy) was compared to the standard method by 6 independent observers with wide experience of image analysis but no experience of pancreas imaging. The effect of the new method was examined on datasets from two studies of weight loss in type 2 diabetes.

RESULTS

At low levels of intrapancreatic fat neither the result nor the inter-observer CV was changed by MR-opsy, thresholding or a combination of the methods. However, at higher levels the conventional method exhibited poor inter-observer agreement (coefficient of variation 26.9%) and the new combined method improved the CV to 4.3% (p<0.03). Using either MR-opsy alone or with thresholding, the new methods indicated a closer relationship between decrease in intrapancreatic fat and fall in blood glucose.

CONCLUSION

The inter-observer variation for quantifying intrapancreatic fat was substantially improved by the new method when pancreas fat levels were moderately high. The method will improve comparability of pancreas fat measurement between research groups.

Ectopic fat accumulation in the pancreas and its clinical relevance: A systematic review, meta-analysis, and meta-regression

OBJECTIVE

Growing evidence suggests that individuals with excessive fat in the pancreas are at an increased risk of chronic metabolic disorders. The aim was to systematically review studies on non-alcoholic fatty pancreas disease (NAFPD) with a view to determine its prevalence, associations with metabolic co-morbidities, and to suggest normal pancreatic fat percentage threshold.

METHODS

Three electronic databases (MEDLINE, Scopus, and Embase) were queried. Studies in humans were eligible for inclusion if they provided data on NAFPD and/or pancreatic fat percentage. Where possible, data were pooled using random-effects meta-analysis and the effect of covariates analysed using meta-regression.

RESULTS

Pooling data on pancreatic fat percentage from nine studies (1209 healthy individuals who underwent magnetic resonance imaging), yielded the weighted mean and weighted standard deviation of 4.48% and 0.87%, respectively. Pooling data on NAFPD from eleven studies (12,675 individuals), yielded the pooled prevalence of 33% (95% confidence interval, 24% - 41%). Meta-regression analysis showed that the prevalence of NAFPD was independent of age and sex. The presence of NAFPD was associated with a significantly increased risk of arterial hypertension (risk ratio 1.67; 95% confidence interval, 1.32-2.10; p<0.0001), diabetes mellitus (risk ratio 2.08; 95% confidence interval, 1.44-3.00; p=0.0001), and metabolic syndrome (risk ratio 2.37; 95% confidence interval, 2.07-2.71; p<0.0001).

CONCLUSION

The findings indicate that NAFPD is a frequent clinical entity, associated with significantly increased risk of metabolic syndrome and its components. The normal pancreatic fat cut-off point of 6.2% may be recommended for use in future prospective studies.

Exploring the metabolic syndrome: Nonalcoholic fatty pancreas disease

After the first description of fatty pancreas in 1933, the effects of pancreatic steatosis have been poorly investigated, compared with that of the liver. However, the interest of research is increasing. Fat accumulation, associated with obesity and the metabolic syndrome (MetS), has been defined as "fatty infiltration" or "nonalcoholic fatty pancreas disease" (NAFPD). The term "fatty replacement" describes a distinct phenomenon characterized by death of acinar cells and replacement by adipose tissue. Risk factors for developing NAFPD include obesity, increasing age, male sex, hypertension, dyslipidemia, alcohol and hyperferritinemia. Increasing evidence support the role of pancreatic fat in the development of type 2 diabetes mellitus, MetS, atherosclerosis, severe acute pancreatitis and even pancreatic cancer. Evidence exists that fatty pancreas could be used as the initial indicator of "ectopic fat deposition", which is a key element of nonalcoholic fatty liver disease and/or MetS. Moreover, in patients with fatty pancreas, pancreaticoduodenectomy is associated with an increased risk of intraoperative blood loss and post-operative pancreatic fistula.

Pancreas Volume and Fat Deposition in Diabetes and Normal Physiology: Consideration of the Interplay Between Endocrine and Exocrine Pancreas

The pancreas is comprised of exocrine and endocrine components. Despite the fact that they are derived from a common origin in utero, these two compartments are often studied individually because of the different roles and functions of the exocrine and endocrine pancreas. Recent studies have shown that not only type 1 diabetes (T1D), but also type 2 diabetes (T2D), is characterized by a deficit in beta-cell mass, suggesting that pathological changes in the pancreas are critical events in the natural history of diabetes. In both patients with T1D and those with T2D, pancreas mass and exocrine function have been reported to be reduced. On the other hand, pancreas volume and pancreatic fat increase with obesity. Increased beta-cell mass with increasing obesity has also been observed in humans, and ectopic fat deposits in the pancreas have been reported to cause beta-cell dysfunction. Moreover, neogenesis and transdifferentiation from the exocrine to the endocrine compartment in the postnatal period are regarded as a source of newly formed beta-cells. These findings suggest that there is important interplay between the endocrine and exocrine pancreas throughout life. This review summarizes the current knowledge on physiological and pathological changes in the exocrine and endocrine pancreas (i.e., beta-cell mass), and discusses the potential mechanisms of the interplay between the two compartments in humans to understand the pathophysiology of diabetes better.

Mesenchymal Stem Cells and Metabolic Syndrome: Current Understanding and Potential Clinical Implications

Metabolic syndrome is an obesity-based, complicated clinical condition that has become a global epidemic problem with a high associated risk for cardiovascular disease and mortality. Dyslipidemia, hypertension, and diabetes or glucose dysmetabolism are the major factors constituting metabolic syndrome, and these factors are interrelated and share underlying pathophysiological mechanisms. Severe obesity predisposes individuals to metabolic syndrome, and recent data suggest that mesenchymal stem cells (MSCs) contribute significantly to adipocyte generation by increasing the number of adipocytes. Accordingly, an increasing number of studies have examined the potential roles of MSCs in managing obesity and metabolic syndrome. However, despite the growing bank of experimental and clinical data, the efficacy and the safety of MSCs in the clinical setting are still to be optimized. It is thus hoped that ongoing and future studies can elucidate the roles of MSCs in metabolic syndrome and lead to MSC-based therapeutic options for affected patients. This review discusses current understanding of the relationship between MSCs and metabolic syndrome and its potential implications for patient management.

Overnutrition, ectopic lipid and the metabolic syndrome

The metabolic syndrome is a constellation of metabolic risk factors including atherogenic dyslipidemia (elevated serum triglycerides, reduced high-density lipoprotein (HDL) cholesterol), elevated blood pressure, dysglycemia (insulin resistance and elevated serum glucose), a pro-inflammatory state, and a prothrombotic state. Most persons with metabolic syndrome are obese, and usually have abdominal obesity. Generally, obesity is a reflection of overnutrition. A current view is that when adipose tissue fails to store all excess nutrients as triglyceride, lipid begins to accumulate in various tissues (eg, muscle, liver, pancreas, and heart). This accumulation is called ectopic lipid. Various mechanisms have been proposed whereby ectopic lipid is detrimental in different tissues; these derangements induce metabolic risk factors. The foundation of the metabolic syndrome thus appears to be overnutrition, that is, more nutrient intake than can be safely disposed by lipid oxidation. Excess dietary carbohydrate also induces ectopic lipid. Of interest, less than half of obese individuals develop metabolic syndrome. Through various mechanisms they adapt to overnutrition so as to minimize lipid overload in tissues, and consequently, prevent the syndrome.

Mechanisms of Action of Liraglutide in Patients With Type 2 Diabetes Treated With High-Dose Insulin

CONTEXT

The mechanisms of action of incretin mimetics in patients with long-standing type 2 diabetes (T2D) and high insulin requirements have not been studied.

OBJECTIVE

To evaluate changes in β-cell function, glucagon secretion, and fat distribution after addition of liraglutide to high-dose insulin.

DESIGN

A single-center, randomized, double-blind, placebo-controlled trial.

SETTING

University of Texas Southwestern and Parkland Memorial Hospital clinics.

PATIENTS

Seventy-one patients with long-standing (median, 17 years) T2D requiring high-dose insulin treatment (>1.5 U/kg/d; average, 2.2 ± 0.9 U/kg/d).

INTERVENTION

Patients were randomized to liraglutide 1.8 mg/d or matching placebo for 6 months.

MAIN OUTCOME MEASURES

We measured changes in insulin and glucagon secretion using a 4-hour mixed-meal challenge test. Magnetic resonance-based techniques were used to estimate sc and visceral fat in the abdomen and ectopic fat in the liver and pancreas.

RESULTS

Glycosylated hemoglobin improved significantly with liraglutide treatment, with an end-of-trial estimated treatment difference between groups of −0.9% (95% confidence interval, −1.5, −0.4%) (P = .002). Insulin secretion improved in the liraglutide group vs placebo, as measured by the area under the curve of C-peptide (P = .002) and the area under the curves ratio of C-peptide to glucose (P = .003). Insulin sensitivity (Matsuda index) and glucagon secretion did not change significantly between groups. Liver fat and sc fat decreased in the liraglutide group vs placebo (P = .0006 and P = .01, respectively), whereas neither visceral nor pancreatic fat changed significantly.

CONCLUSIONS

Treatment with liraglutide significantly improved insulin secretion, even in patients with long-standing T2D requiring high-dose insulin treatment. Liraglutide also decreased liver and sc fat, but it did not alter glucagon secretion.

Weight Loss Decreases Excess Pancreatic Triacylglycerol Specifically in Type 2 Diabetes

OBJECTIVE

This study determined whether the decrease in pancreatic triacylglycerol during weight loss in type 2 diabetes mellitus (T2DM) is simply reflective of whole-body fat or specific to diabetes and associated with the simultaneous recovery of insulin secretory function.

RESEARCH DESIGN AND METHODS

Individuals listed for gastric bypass surgery who had T2DM or normal glucose tolerance (NGT) matched for age, weight, and sex were studied before and 8 weeks after surgery. Pancreas and liver triacylglycerol were quantified using in-phase, out-of-phase MRI. Also measured were the first-phase insulin response to a stepped intravenous glucose infusion, hepatic insulin sensitivity, and glycemic and incretin responses to a semisolid test meal.

RESULTS

Weight loss after surgery was similar (NGT: 12.8 ± 0.8% and T2DM: 13.6 ± 0.7%) as was the change in fat mass (56.7 ± 3.3 to 45.4 ± 2.3 vs. 56.6 ± 2.4 to 43.0 ± 2.4 kg). Pancreatic triacylglycerol did not change in NGT (5.1 ± 0.2 to 5.5 ± 0.4%) but decreased in the group with T2DM (6.6 ± 0.5 to 5.4 ± 0.4%; P = 0.007). First-phase insulin response to a stepped intravenous glucose infusion did not change in NGT (0.24 [0.13-0.46] to 0.23 [0.19-0.37] nmol ⋅ min(-1) ⋅ m(-2)) but normalized in T2DM (0.08 [-0.01 to -0.10] to 0.22 [0.07-0.30]) nmol ⋅ min(-1) ⋅ m(-2) at week 8 (P = 0.005). No differential effect of incretin secretion was observed after gastric bypass, with more rapid glucose absorption bringing about equivalently enhanced glucagon-like peptide 1 secretion in the two groups.

CONCLUSIONS

The fall in intrapancreatic triacylglycerol in T2DM, which occurs during weight loss, is associated with the condition itself rather than decreased total body fat.

Myocardial steatosis as a possible mechanistic link between diastolic dysfunction and coronary microvascular dysfunction in women

Women with coronary microvascular dysfunction (CMD) and no obstructive coronary artery disease (CAD) have increased rates of heart failure with preserved ejection fraction (HFpEF). The mechanisms of HFpEF are not well understood. Ectopic fat deposition in the myocardium, termed myocardial steatosis, is frequently associated with diastolic dysfunction in other metabolic diseases. We investigated the prevalence of myocardial steatosis and diastolic dysfunction in women with CMD and subclinical HFpEF. In 13 women, including eight reference controls and five women with CMD and evidence of subclinical HFpEF (left ventricular end-diastolic pressure >12 mmHg), we measured myocardial triglyceride content (TG) and diastolic function, by proton magnetic resonance spectroscopy and magnetic resonance tissue tagging, respectively. When compared with reference controls, women with CMD had higher myocardial TG content (0.83 ± 0.12% vs. 0.43 ± 0.06%; P = 0.025) and lower diastolic circumferential strain rate (168 ± 12 vs. 217 ± 15%/s; P = 0.012), with myocardial TG content correlating inversely with diastolic circumferential strain rate (r = -0.779; P = 0.002). This study provides proof-of-concept that myocardial steatosis may play an important mechanistic role in the development of diastolic dysfunction in women with CMD and no obstructive CAD. Detailed longitudinal studies are warranted to explore specific treatment strategies targeting myocardial steatosis and its effect on diastolic function.

Pancreatic adipose tissue infiltration, parenchymal steatosis and beta cell function in humans

AIMS/HYPOTHESIS

This study aimed to perform a comprehensive analysis of interlobular, intralobular and parenchymal pancreatic fat in order to assess their respective effects on beta cell function.

METHODS

Fifty-six participants (normal glucose tolerance [NGT] (n = 28), impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) (n = 14) and patients with type 2 diabetes (n = 14)) underwent a frequent-sampling OGTT and non-invasive magnetic resonance imaging (MRI; whole-body and pancreatic) and proton magnetic resonance spectroscopy ((1)H-MRS; liver and pancreatic fat). Total pancreatic fat was assessed by a standard 2 cm(3) (1)H-MRS method, intralobular fat by 1 cm(3) (1)H-MRS that avoided interlobular fat within modified DIXON (mDIXON) water images, and parenchymal fat by a validated mDIXON-MRI fat-fraction method.

RESULTS

Comparison of (1)H-MRS techniques revealed an inhomogeneous distribution of interlobular and intralobular adipose tissue, which increased with decreasing glucose tolerance. mDIXON-MRI measurements provided evidence against uniform steatosis, revealing regions of parenchymal tissue void of lipid accumulation in all participants. Total (r = 0.385, p < 0.01) and intralobular pancreas adipose tissue infiltration (r = 0.310, p < 0.05) positively associated with age, but not with fasting or 2 h glucose levels, BMI or visceral fat content (all p > 0.5). Furthermore, no associations were found between total and intralobular pancreatic adipose tissue infiltration and insulin secretion or beta cell function within NGT, IFG/IGT or patients with type 2 diabetes (all p > 0.2).

CONCLUSIONS/INTERPRETATION

The pancreas does not appear to be another target organ for abnormal endocrine function because of ectopic parenchymal fat storage. No relationship was found between pancreatic adipose tissue infiltration and beta cell function, regardless of glucose tolerance status.

Pancreatic lipid content is not associated with beta cell dysfunction in youth-onset type 2 diabetes

OBJECTIVE

To determine whether pancreatic lipid content is associated with type 2 diabetes and beta cell function in Indigenous and Caucasian adolescents.

METHODS

This was a cross-sectional study comparing (1)H-magnetic resonance spectroscopy-derived pancreatic triglyceride content in adolescents 13 to 18 years of age with type 2 diabetes (n=20) and body mass index-matched normoglycemic controls (n=34). Beta cell function was measured by the acute insulin response and disposition index derived from intravenous glucose tolerance tests.

RESULTS

Pancreatic lipid content was not significantly different in youth with type 2 diabetes and their normoglycemic body mass index-matched peers (2.41 [95% CI: 0.63, 5.60] vs. 1.22 [0.08, 5.93]; p=0.27). Pancreatic triglyceride levels were not associated with measures of beta cell function in the cohort. In subgroup analyses, pancreatic lipid content was ∼4-fold higher in youth with type 2 diabetes who were carriers of the G319S mutation in the HNF-1alpha gene (7.45 [2.85, 26.8] vs. 2.20 [0.350, 3.30] % Fat to Water Ratio F/W; p=0.032).

CONCLUSIONS

Pancreatic lipid content is not elevated in Indigenous or Caucasian youth with type 2 diabetes compared to normoglycemic youth, nor is it associated with beta cell function. The presence of the G319S mutation in the HNF-1alpha gene in Indigenous youth with type 2 diabetes is associated with higher pancreatic lipid content. Further research is needed to understand the mechanisms that explain beta cell failure in overweight youth with type 2 diabetes.

Altered volume, morphology and composition of the pancreas in type 2 diabetes

Objective

Although impairment in pancreatic insulin secretion is known to precede the clinical diagnosis of type 2 diabetes by up to a decade, fasting blood glucose concentration only rises abnormally once the impairment reaches a critical threshold. Despite its centrality to the pathogenesis of type 2 diabetes, the pancreas is the least studied organ due to its inaccessible anatomical position. Previous ultrasound and CT studies have suggested a possible decrease in pancreatic volume in type 2 diabetes. However, ultrasound techniques are relatively insensitive while CT uses ionizing radiation, making these modalities unsuitable for precise, longitudinal studies designed to explore the underlying mechanisms of type 2 diabetes. Hence there is a need to develop a non-invasive, safe and precise method to quantitate pancreas volume.

Methods

We developed and applied magnetic resonance imaging at 3.0T to obtain balanced turbo field echo (BTFE) structural images of the pancreas, together with 3-point Dixon images to quantify pancreatic triglyceride content. Pancreas volume, morphology and triglyceride content was quantified in a group of 41 subjects with well-controlled type 2 diabetes (HbA_1c ≤ 7.6%) taking only metformin (duration of T2DM 5.7±0.7years), and a control group of 14 normal glucose tolerance subjects matched for age, weight and sex.

Results

The mean pancreatic volume was found to be 33% less in type 2 diabetes than in normal glucose tolerant subjects (55.5±2.8 vs. 82.6±4.8cm³; p<0.0001). Pancreas volume was positively correlated with HOMA-β in the type 2 diabetes subjects (r = 0.31; p = 0.03) and controls (r = 0.46; p = 0.05) considered separately; and in the whole population studied (r = 0.37; p = 0.003). In type 2 diabetes, the pancreas was typically involuted with a serrated border. Pancreatic triglyceride content was 23% greater (5.4±0.3 vs. 4.4±0.4%; p = 0.02) in the type 2 diabetes group.

Conclusion

This study describes for the first time gross abnormalities of the pancreas in early type 2 diabetes and quantifies the decrease in pancreas size, the irregular morphology and increase in fat content.

Thyroid dysfunction associated with follicular cell steatosis in obese male mice and humans

Adult thyroid dysfunction is a common endocrine disorder associated with an increased risk of cardiovascular disease and mortality. A recent epidemiologic study revealed a link between obesity and increased prevalence of hypothyroidism. It is conceivable that excessive adiposity in obesity might lead to expansion of the interfollicular adipose (IFA) depot or steatosis in thyroid follicular cells (thyroid steatosis, TS). In this study, we investigated the morphological and functional changes in thyroid glands of obese humans and animal models, diet-induced obese (DIO), ob/ob, and db/db mice. Expanded IFA depot and TS were observed in obese patients. Furthermore, DIO mice showed increased expression of lipogenesis-regulation genes, such as sterol regulatory element binding protein 1 (SREBP-1), peroxisome proliferator-activated receptor γ (PPARγ), acetyl coenzyme A carboxylase (ACC), and fatty acid synthetase (FASN) in the thyroid gland. Steatosis and ultrastructural changes, including distension of the endoplasmic reticulum (ER) and mitochondrial distortion in thyroid follicular cells, were uniformly observed in DIO mice and genetically obese mouse models, ob/ob and db/db mice. Obese mice displayed a variable degree of primary thyroid hypofunction, which was not corrected by PPARγ agonist administration. We propose that systemically increased adiposity is associated with characteristic IFA depots and TS and may cause or influence the development of primary thyroid failure.

Normal weight individuals who develop Type 2 diabetes: the personal fat threshold

Type 2 diabetes (T2DM) is frequently regarded as a disease of obesity and its occurrence in individuals of normal body mass index (BMI) is often regarded as indicating a non-obesity-related subtype. However, the evidence for such a distinct, common subtype is lacking. The United Kingdom Prospective Diabetes Study (UKPDS) cohort of people diagnosed with T2DM in the 1970s and 1980s had a median BMI of only 28 kg/m2. UKPDS data form the basis of current understanding of the condition even though one in three of those studied had a BMI of less than 25 kg/m2. BMI, though, is a population measure and not a rigid personal guide. Weight loss is considered de rigueur for treating obese diabetic individuals, but it is not usually considered for those deemed to have a normal BMI. Given the new evidence that early T2DM can be reversed to normal glucose tolerance by substantial weight loss, it is important to explain why non-overweight people respond to this intervention as well as obese individuals. We hypothesize that each individual has a personal fat threshold (PFT) which, if exceeded, makes likely the development of T2DM. Subsequent weight loss to take the individual below their level of susceptibility should allow return to normal glucose control. Crucially, the hypothesized PFT is independent of BMI. It allows both understanding of development of T2DM in the non-obese and remission of diabetes after substantial weight loss in people who remain obese by definition. To illustrate this concept, we present the distribution curve of BMI at diagnosis for the UKPDS cohort, together with a diagram explaining individual behaviour within the population. The concept of PFT is of practical benefit in explaining the onset of diabetes and its logical management to the non-obese majority of people with T2DM.

Obese first-degree relatives of patients with type 2 diabetes with elevated triglyceride levels exhibit increased β-cell function

BACKGROUND

Type 2 diabetes mellitus (T2DM) is characterized as a disease continuum that is marked by metabolic changes that are present for several years, sometimes well before frank diagnosis of T2DM. Genetic predisposition, ethnicity, geography, alterations in BMI, and lipid profile are considered important markers for the pathogenesis of T2DM through mechanisms that remain unresolved and controversial. The aim of this study was to investigate the relationship between triglycerides (TGs) and β-cell function, insulin resistance (IR), and insulin sensitivity (IS) in obese first-degree relatives of patients with T2DM (FDR-T2DM) among subjects from central Mexico with normal glucose tolerance (NGT).

METHODS

We studied 372 FDR-T2DM subjects (ages,18-65) and determined body mass index (BMI), fasting plasma glucose (FPG), oral glucose tolerance test (OGTT), insulin, and TGs levels. Subjects were categorized based on glycemic control [NGT, prediabetes (PT2DM), or T2DM]. NGT subjects were further categorized by BMI [normal weight (Ob-) or obese (Ob+)] and TGs levels (TG-, <150 mg/dL, or TG+, ≥150 mg/dL). β-cell function, IR, and IS were determined by the homeostasis model assessment of β-cell function (HOMA2-β), homeostasis model assessment of insulin resistance (HOMA2-IR), and Quantitative Insulin Sensitivity Check Index (QUICKI) indices, respectively.

RESULTS

The obese subjects with elevated TGs levels had 21%-60% increased β-cell function when compared to all groups (P<0.05). In addition, this group had insulin levels, IS, and IR similar to PT2DM. Furthermore, only in obese subjects did TGs correlate with β-cell function (ρ=0.502, P<0.001).

CONCLUSION

We characterized FDR-T2DM subjects from central Mexico with NGT and revealed a class of obese subjects with elevated TGs and β-cell function, which may precede PT2DM.

Leptin restores the insulinotropic effect of exenatide in a mouse model of type 2 diabetes with increased adiposity induced by streptozotocin and high-fat diet

Leptin may reduce pancreatic lipid deposition, which increases with progression of obesity and can impair β-cell function. The insulinotropic effect of glucagon-like peptide-1 (GLP-1) and the efficacy of GLP-1 receptor agonist are reduced associated with impaired β-cell function. In this study, we examined whether leptin could restore the efficacy of exenatide, a GLP-1 receptor agonist, in type 2 diabetes with increased adiposity. We chronically administered leptin (500 μg·kg⁻¹·day⁻¹) and/or exenatide (20 μg·kg⁻¹·day⁻¹) for 2 wk in a mouse model of type 2 diabetes with increased adiposity induced by streptozotocin and high-fat diet (STZ/HFD mice). The STZ/HFD mice exhibited hyperglycemia, overweight, increased pancreatic triglyceride level, and reduced glucose-stimulated insulin secretion (GSIS); moreover, the insulinotropic effect of exenatide was reduced. However, leptin significantly reduced pancreatic triglyceride level, and adding leptin to exenatide (LEP/EX) remarkably enhanced GSIS. These results suggested that the leptin treatment restored the insulinotropic effect of exenatide in the mice. In addition, LEP/EX reduced food intake, body weight, and triglyceride levels in the skeletal muscle and liver, and corrected hyperglycemia to a greater extent than either monotherapy. The pair-feeding experiment indicated that the marked reduction of pancreatic triglyceride level and enhancement of GSIS by LEP/EX occurred via mechanisms other than calorie restriction. These results suggest that leptin treatment may restore the insulinotropic effect of exenatide associated with the reduction of pancreatic lipid deposition in type 2 diabetes with increased adiposity. Combination therapy with leptin and exenatide could be an effective treatment for patients with type 2 diabetes with increased adiposity.

Ectopic fat storage in the pancreas using 1H-MRS: importance of diabetic status and modulation with bariatric surgery-induced weight loss

OBJECTIVES

Recent literature suggests that ectopic fat deposition in the pancreas may contribute to endocrine and exocrine organ dysfunction, such as type 2 diabetes (T2D), pancreatitis or pancreatic cancer. The aim of this study was to determine factors associated with pancreatic triglyceride content (PTGC), and to investigate the impact of bariatric surgery on ectopic fat pads, pancreatic fat (PTGC) and hepatic fat (HTGC).

SUBJECTS

In all, 45 subjects (13 lean, 13 obese nondiabetics and 19 T2D, matched for age and gender) underwent 1H-magnetic resonance spectroscopy, computed tomography of the visceral abdominal fat, metabolic and lipidomic analysis, including insulin-resistance homeostasis model assessment (HOMA-IR), insulin-secretion homeostasis model assessment (HOMA-B) and plasma fatty-acid composition. Twenty obese subjects were reassessed 6 months after the bariatric surgery.

RESULTS

PTGC was significantly higher in type 2 diabetic subjects (23.8±3.2%) compared with obese (14.0±3.3; P=0.03) and lean subjects (7.5±0.9%; P=0.0002). PTGC remained significantly associated with T2D after adjusting for age and sex (β=0.47; P=0.004) or even after adjusting for waist circumference, triglycerides and HOMA-IR (β=0.32; P=0.04). T2D, C18:1n-9 (oleic acid), uric acid, triglycerides and plasminogen activator inhibitor-1 were the five more important parameters involved in PTGC prediction (explained 80% of PTGC variance). Bariatric surgery induced a huge reduction of both HTGC (-51.2±7.9%) and PTGC (-43.8±7.0%) reaching lean levels, whereas body mass index remained greatly elevated. An improvement of insulin resistance HOMA-IR and no change in HOMA-B were observed after bariatric surgery. The PTGC or HTGC losses were not correlated, suggesting tissue-specific mobilization of these ectopic fat stores.

CONCLUSION

Pancreatic fat increased with T2D and drastically decreased after the bariatric surgery. This suggests that decreased PTGC may contribute to improved beta cell function seen after the bariatric surgery. Further, long-term interventional studies are warranted to examine this hypothesis and to determine the degree to which ectopic fat mobilization may mediate the improvement in endocrine and exocrine pancreatic functions.

Lipotoxicity in the pancreatic beta cell: not just survival and function, but proliferation as well?

Free fatty acids (FFAs) exert both positive and negative effects on beta cell survival and insulin secretory function, depending on concentration, duration, and glucose abundance. Lipid signals are mediated not only through metabolic pathways, but also through cell surface and nuclear receptors. Toxicity is modulated by positive signals arising from circulating factors such as hormones, growth factors and incretins, as well as negative signals such as inflammatory mediators and cytokines. Intracellular mechanisms of lipotoxicity include metabolic interference and cellular stress responses such as oxidative stress, endoplasmic reticulum (ER) stress, and possibly autophagy. New findings strengthen an old hypothesis that lipids may also impair compensatory beta cell proliferation. Clinical observations continue to support a role for lipid biology in the risk and progression of both type 1 (T1D) and type 2 diabetes (T2D). This review summarizes recent work in this important, rapidly evolving field.

Age-associated changes of islet endocrine cells and the effects of body mass index in Japanese

AIMS/INTRODUCTION

Impaired growth and premature death of β-cells are implicated in the progression of islet pathology in type 2 diabetes. It remains unclear, however, how aging affects islet cells, or whether the islet change in diabetes is an augmented process of aging. We studied age-related changes of the islet structure in Japanese non-diabetic subjects and explored the underlying mechanism of the changes.

MATERIALS AND METHODS

A total of 115 non-diabetic autopsy cases were subjected to morphometric analysis for volume densities of islets, β- and non-β-cells, as well as their masses. Proliferation activity identified by Ki67, and expressions of pancreatic and duodenal homeobox (PDX)-1, cell cycle inhibitor P16, and oxidative stress marker γH2AX were also examined.

RESULTS

There was a gradual and marginal decline of volume densities of islets, β- and non-β-cells with aging, while masses of these components were increased during maturation and slowly decreased after the 40s. Islet density was high in the young, but reduced after maturation. There was only a minimal influence of increased body mass index (BMI) on the increase in β-cell mass, but not on the other variables. Ki67 positivity and PDX-1 expressions were high in the young, but low after maturation, whereas expressions of P16 and γH2AX were elevated in the aged.

CONCLUSIONS

Age-associated decline of β-cell mass is marginal after maturation, and the reduction of β-cell mass could be a specific process in diabetes. The impact of BMI on the islet structure is limited in Japanese with normal glucose tolerance.

Metabolic basis of ethnic differences in diabetes risk in overweight and obese youth

The global pandemic of childhood obesity has led to increased risk for prediabetes and type 2 diabetes mellitus (T2DM). Studies have shown decreased insulin sensitivity and/or secretion with increasing adiposity and consistently observed greater risk for T2DM in obese, non-Caucasian youth. In the current review we describe recent advances in understanding how obesity and metabolic status in children and adolescents confers various risk profiles for T2DM among Latinos, African Americans, Caucasians, Asians, and Native Americans. These possible determinants include ectopic fat distribution, adipose tissue inflammation and fibrosis, and elevated plasma levels of nonesterified free fatty acids. Future work should aim to elucidate the ethnic-specific pathophysiology of T2DM in order to develop and implement appropriate prevention and treatment strategies based on different ethnic profiles of diabetes risk.

Adiposity and insulin resistance in humans: the role of the different tissue and cellular lipid depots

Human adiposity has long been associated with insulin resistance and increased cardiovascular risk, and abdominal adiposity is considered particularly adverse. Intra-abdominal fat is associated with insulin resistance, possibly mediated by greater lipolytic activity, lower adiponectin levels, resistance to leptin, and increased inflammatory cytokines, although the latter contribution is less clear. Liver lipid is also closely associated with, and likely to be an important contributor to, insulin resistance, but it may also be in part the consequence of the lipogenic pathway of insulin action being up-regulated by hyperinsulinemia and unimpaired signaling. Again, intramyocellular triglyceride is associated with muscle insulin resistance, but anomalies include higher intramyocellular triglyceride in insulin-sensitive athletes and women (vs men). Such issues could be explained if the "culprits" were active lipid moieties such as diacylglycerol and ceramide species, dependent more on lipid metabolism and partitioning than triglyceride amount. Subcutaneous fat, especially gluteofemoral, appears metabolically protective, illustrated by insulin resistance and dyslipidemia in patients with lipodystrophy. However, some studies suggest that deep sc abdominal fat may have adverse properties. Pericardial and perivascular fat relate to atheromatous disease, but not clearly to insulin resistance. There has been recent interest in recognizable brown adipose tissue in adult humans and its possible augmentation by a hormone, irisin, from exercising muscle. Brown adipose tissue is metabolically active, oxidizes fatty acids, and generates heat but, because of its small and variable quantities, its metabolic importance in humans under usual living conditions is still unclear. Further understanding of specific roles of different lipid depots may help new approaches to control obesity and its metabolic sequelae.

Metabolic imaging of human kidney triglyceride content: reproducibility of proton magnetic resonance spectroscopy

Objective

To assess the feasibility of renal proton magnetic resonance spectroscopy for quantification of triglyceride content and to compare spectral quality and reproducibility without and with respiratory motion compensation in vivo.

Materials and Methods

The Institutional Review Board of our institution approved the study protocol, and written informed consent was obtained. After technical optimization, a total of 20 healthy volunteers underwent renal proton magnetic resonance spectroscopy of the renal cortex both without and with respiratory motion compensation and volume tracking. After the first session the subjects were repositioned and the protocol was repeated to assess reproducibility. Spectral quality (linewidth of the water signal) and triglyceride content were quantified. Bland-Altman analyses and a test by Pitman were performed.

Results

Linewidth changed from 11.5±0.4 Hz to 10.7±0.4 Hz (all data pooled, p<0.05), without and with respiratory motion compensation respectively. Mean % triglyceride content in the first and second session without respiratory motion compensation were respectively 0.58±0.12% and 0.51±0.14% (P = NS). Mean % triglyceride content in the first and second session with respiratory motion compensation were respectively 0.44±0.10% and 0.43±0.10% (P = NS between sessions and P = NS compared to measurements with respiratory motion compensation). Bland-Altman analyses showed narrower limits of agreement and a significant difference in the correlated variances (correlation of −0.59, P<0.05).

Conclusion

Metabolic imaging of the human kidney using renal proton magnetic resonance spectroscopy is a feasible tool to assess cortical triglyceride content in humans in vivo and the use of respiratory motion compensation significantly improves spectral quality and reproducibility. Therefore, respiratory motion compensation seems a necessity for metabolic imaging of renal triglyceride content in vivo.