Alterations in Gut Microbiota and Immunity by Dietary Fat

Gut microbiota play critical physiological roles in energy extraction from the intestine and in the control of systemic immunity, as well as local intestinal immunity. Disturbance of gut microbiota leads to the development of several diseases, such as colitis, inflammatory bowel diseases, metabolic disorders, cancer, etc. From a metabolic point of view, the gut is a large metabolic organ and one of the first to come into contact with dietary fats. Interestingly, excessive dietary fat has been incriminated as a primary culprit of metabolic syndrome and obesity. After intake of high-fat diet or Western diet, extensive changes in gut microbiota have been observed, which may be an underlying cause of alterations in whole body metabolism and nutrient homeostasis. Here, we summarize recent data on changes in the gut microbiota and immunity associated with dietary fat, as well as their relationships with the pathogenesis of metabolic syndrome. These findings may provide insight into the understanding of the complex pathophysiology related to the development of metabolic diseases and offer an opportunity to develop novel candidates for therapeutic agents.

Gut Microbiota and Metabolic Disorders

Gut microbiota plays critical physiological roles in the energy extraction and in the control of local or systemic immunity. Gut microbiota and its disturbance also appear to be involved in the pathogenesis of diverse diseases including metabolic disorders, gastrointestinal diseases, cancer, etc. In the metabolic point of view, gut microbiota can modulate lipid accumulation, lipopolysaccharide content and the production of short-chain fatty acids that affect food intake, inflammatory tone, or insulin signaling. Several strategies have been developed to change gut microbiota such as prebiotics, probiotics, certain antidiabetic drugs or fecal microbiota transplantation, which have diverse effects on body metabolism and on the development of metabolic disorders.

Role of Innate Immunity in the Pathogenesis of Type 1 and Type 2 Diabetes

The importance of innate immunity in host defense is becoming clear after discovery of innate immune receptors such as Toll-like receptor or Nod-like receptor. Innate immune system plays an important role in diverse pathological situations such as autoimmune diseases. Role of innate immunity in the pathogenesis of metabolic disorders such as type 2 diabetes, metabolic syndrome or atherosclerosis that has not been previously considered as inflammatory disorders, is also being appreciated. Here, the role of innate immunity in the development of type 1 diabetes, a classical organ-specific autoimmune disease, and type 2 diabetes will be discussed, focusing on the role of specific innate immune receptors involved in these disease processes.

Using Growth Hormone Levels to Detect Macroadenoma in Patients with Acromegaly

BACKGROUND: The aim of this study was to assess the clinical differences between acromegalic patients with microadenoma and patients with macroadenoma, and to evaluate the predictive value of growth hormone (GH) levels for early detection of macroadenoma. METHODS: We performed a retrospective analysis of 215 patients diagnosed with a GH-secreting pituitary adenoma. The patients were divided into two groups: the microadenoma group and the macroadenoma group, and the clinical parameters were compared between these two groups. The most sensitive and specific GH values for predicting macroadenoma were selected using receiver operating characteristic (ROC) curves. RESULTS: Compared with the microadenoma group, the macroadenoma group had a significantly younger age, higher body mass index, higher prevalence of hyperprolactinemia and hypogonadism, and a lower proportion of positive suppression to octreotide. However, there were no significant differences in the gender or in the prevalence of diabetes between the two groups. The tumor diameter was positively correlated with all GH values during the oral glucose tolerance test (OGTT). All GH values were significantly higher in the macroadenoma group than the microadenoma group. Cut-off values for GH levels at 0, 30, 60, 90, and 120 minutes for optimal discrimination between macroadenoma and microadenoma were 5.6, 5.7, 6.3, 6.0, and 5.8 ng/mL, respectively. ROC curve analysis revealed that the GH value at 30 minutes had the highest area under the curve. CONCLUSION: The GH level of 5.7 ng/mL or higher at 30 minutes during OGTT could provide sufficient information to detect macroadenoma at the time of diagnosis.

FGF21 as a Stress Hormone: The Roles of FGF21 in Stress Adaptation and the Treatment of Metabolic Diseases

Fibroblast growth factor 21 (FGF21) is an endocrine hormone that is primarily expressed in the liver and exerts beneficial effects on obesity and related metabolic diseases. In addition to its remarkable pharmacologic actions, the physiological roles of FGF21 include the maintenance of energy homeostasis in the body in conditions of metabolic or environmental stress. The expression of FGF21 is induced in multiple organs in response to diverse physiological or pathological stressors, such as starvation, nutrient excess, autophagy deficiency, mitochondrial stress, exercise, and cold exposure. Thus, the FGF21 induction caused by stress plays an important role in adaptive response to these stimuli. Here, we highlight our current understanding of the functional importance of the induction of FGF21 by diverse stressors as a feedback mechanism that prevents excessive stress.

Treatment of Autoimmune Diabetes by Inhibiting the Initial Event

Recent papers have shown that the initial event in the pathogenesis of autoimmune type 1 diabetes (T1D) comprises sensing of molecular patterns released from apoptotic beta-cells by innate immune receptors such as toll-like receptor (TLR). We have reported that apoptotic beta-cells undergoing secondary necrosis called 'late apoptotic' beta-cells stimulate dendritic cells (DCs) and induce diabetogenic T cell priming through TLR2. The role of other innate immune receptors such as TLR7 or TLR9 in the initiation of T1D has also been suggested. We hypothesized that TLR2 blockade could inhibit T1D at the initial step of T1D. Indeed, when a TLR2 agonist, Pam3CSK4 was administered chronically, the development of T1D in nonobese diabetic (NOD) mice was inhibited. Diabetogenic T cell priming by DCs was attenuated by chronic treatment with Pam3CSK4, indicating DC tolerance. For the treatment of established T1D, immune tolerance alone is not enough because beta-cell mass is critically reduced. We employed TLR2 tolerance in conjunction with islet transplantation, which led to reversal of newly established T1D. Dipeptidyl peptidase 4 (DPP4) inhibitors are a new class of anti-diabetic agents that have beneficial effects on beta-cells. We investigated whether a combination of DPP4 inhibition and TLR2 tolerization could reverse newly established T1D without islet transplantation. We could achieve normoglycemia by TLR2 tolerization in combination with DPP4 inhibition but not by TLR2 tolerization or DPP4 inhibition alone. beta-cell mass was significantly increased by combined treatment with TLR2 tolerization and DPP4 inhibition. These results suggest the possibility that a novel strategy of TLR tolerization will be available for the inhibition or treatment of established T1D when combined with measures increasing critically reduced beta-cell mass of T1D patients such as DPP4 inhibition or stem cell technology.

Role of Autophagy in the Control of Body Metabolism

Autophagy plays a crucial role in the maintenance of cellular nutrient balance and the function of organelles such as mitochondria or the endoplasmic reticulum, which are important in intracellular metabolism, insulin release, and insulin sensitivity. In the insulin-producing pancreatic beta-cells, autophagy is important in the maintenance of beta-cell mass, structure, and function. Mice with deficiencies in beta-cell-specific autophagy show reduced beta-cell mass and defects in insulin secretion that lead to hypoinsulinemia and hyperglycemia but not diabetes. However, these mice developed diabetes when bred with ob/ob mice, suggesting that autophagy-deficient beta-cells have defects in dealing with the increased metabolic stress imposed by obesity. These results also imply that autophagy deficiency in beta-cells could be a factor in the progression from obesity to diabetes. Another important function of autophagy is in hypothalamic neurons for the central control of energy expenditure, appetite, and body weight. In addition, mice with autophagy deficiencies in the target tissues of insulin have yielded diverse phenotypes. Taken together, these results suggest that autophagy is important in the control of whole body energy and nutrient homeostasis, and its dysregulation could play a role in the development of metabolic disorders and diabetes.

Association between Serum Albumin, Insulin Resistance, and Incident Diabetes in Nondiabetic Subjects

BACKGROUND: Serum albumin has been suggested to be associated with insulin resistance. We evaluated the association between serum albumin concentration and insulin resistance. We also investigated whether serum albumin level has an independent effect on the development of diabetes. METHODS: In our study, 9,029 subjects without diabetes, who underwent comprehensive health check-ups annually for 5 years, were categorized into tertiles based on their serum albumin levels at baseline. The odds ratio (OR) for the prevalence of insulin resistance, defined as the top quartile of homeostasis model assessment of insulin resistance and the presence of impaired fasting glucose and nonalcoholic fatty liver disease, was evaluated cross-sectionally. Also, the hazard ratio (HR) for incident diabetes was estimated longitudinally, according to the baseline albumin tertiles using Cox proportional hazard analysis respectively. RESULTS: From the lowest to the highest tertile of albumin, the multivariable-adjusted ORs of insulin resistance increased significantly in both men and women. During the mean follow-up period of nearly 4 years, 556 (6.1%) subjects progressed to diabetes. The multivariable-adjusted HR (95% confidence interval [CI]) of diabetes in men were 1, 1.09 (95% CI, 0.86 to 1.40), and 1.10 (95% CI, 0.86 to 1.41), respectively, from the lowest to the highest tertiles of baseline albumin. Corresponding values for women were 1, 1.21 (95% CI, 0.66 to 2.21), and 1.06 (95% CI, 0.56 to 2.02), respectively. CONCLUSION: Our study showed that increased serum albumin level was associated with insulin resistance. However, serum albumin did not have an independent effect on the development of diabetes.

Apoptosis of Human Islet Cells by Cytokines

FasL, perforin, TNFalpha, IL-1 and NO have been considered as effector molecule(s) leading to beta-cell death in autoimmune diabetes. However, the real culprit(s) of beta-cell destruction have long been elusive despite intense investigation. Previously we have suggested IFNgamma/TNFalpha synergism as the final effector molecules in autoimmune diabetes of NOD mice. A combination of IFNgamma and TNFalpha but neither cytokine alone, induced classical caspase-dependent apoptosis in murine insulinoma and pancreatic islet cells. IFNgamma treatment conferred susceptibility to TNFalpha-induced apoptosis on otherwise resistant murine insulinoma cells by STAT1 activation followed by IRF-1 induction. Here we report that IFNgamma/TNFalpha synergism induces apoptosis of human pancreatic islet cells. We also observed STAT1 activation followed by IRF-1 induction by IFNgamma treatment in human islet cells. Taken together, we suggest that IFNgamma/TNFalpha synergism could be involved in human islet cell death in type 1 diabetes, similar to murine type 1 diabetes.

Role of autophagy in diabetes and endoplasmic reticulum stress of pancreatic beta-cells

Type 2 diabetes mellitus is characterized by insulin resistance and failure of pancreatic beta-cells producing insulin. Autophagy plays a crucial role in cellular homeostasis through degradation and recycling of organelles such as mitochondria or endoplasmic reticulum (ER). Here we discussed the role of beta-cell autophagy in development of diabetes, based on our own studies using mice with beta-cell-specific deletion of Atg7 (autophagy-related 7), an important autophagy gene, and studies by others. beta-cell-specific Atg7-null mice showed reduction in beta-cell mass and pancreatic insulin content. Insulin secretory function ex vivo was also impaired, which might be related to organelle dysfunction associated with autophagy deficiency. As a result, beta-cell-specific Atg7-null mice showed hypoinsulinemia and hyperglycemia. However, diabetes never developed in those mice. Obesity and/or lipid are physiological ER stresses that can precipitate beta-cell dysfunction. Our recent studies showed that beta-cell-specific Atg7-null mice, when bred with ob/ob mice, indeed become diabetic. Thus, autophagy deficiency in beta-cells could be a precipitating factor in the progression from obesity to diabetes due to inappropriate response to obesity-induced ER stress.

Education as Prescription for Patients with Type 2 Diabetes Mellitus: Compliance and Efficacy in Clinical Practice

BACKGROUND: Diabetes self-management education has an important role in diabetes management. The efficacy of education has been proven in several randomized trials. However, the status of diabetes education programs in real Korean clinical practice has not yet been evaluated in terms of patient compliance with the education prescription. METHODS: We retrospectively analyzed clinical and laboratory data from all patients who were ordered to undergo diabetes education during 2009 at Samsung Medical Center, Seoul, Korea (n=2,291). After excluding ineligible subjects, 588 patients were included in the analysis. RESULTS: Among the 588 patients, 433 received education. The overall compliance rate was 73.6%, which was significantly higher in the subjects with a short duration or living in a rural area compared to those with a long duration (85.0% vs. 65.1%, respectively; P<0.001) or living in an urban area (78.2% vs. 70.4%, respectively; P=0.037). The hemoglobin A1c decreased greater in the compliant group (from 7.84+/-1.54 at baseline to 6.79+/-1.06 at 3 months and 6.97+/-1.20 at 12 months after prescription in the compliant group vs. from 7.74+/-1.25 to 7.14+/-1.02 and 7.24+/-1.24 in the non-compliant group; P=0.001). The decrease in hemoglobin A1c was greater in the subjects with a short duration (P=0.032). CONCLUSION: In our study a large percent of patients refuse to get education despite having a prescription from their physician. This refusal rate was higher in the patients with long-standing diabetes or in urban residence. Furthermore, education was more effective in patients with a short duration of diabetes in clinical practice.

A Case of Congenital Adrenal Hyperplasia Mimicking Cushing's Syndrome

Congenital adrenal hyperplasia (CAH) is characterized by decreased adrenal hormone production due to enzymatic defects and subsequent rise of adrenocorticotrophic hormone that stimulates the adrenal cortex to become hyperplastic, and sometimes tumorous. As the pathophysiology is basically a defect in the biosynthesis of cortisol, one may not consider CAH in patients with hypercortisolism. We report a case of a 41-yr-old man with a 4 cm-sized left adrenal tumorous lesion mimicking Cushing's syndrome who was diagnosed with CAH. He had central obesity and acanthosis nigricans involving the axillae together with elevated 24-hr urine cortisol level, supporting the diagnosis of Cushing's syndrome. However, the 24-hr urine cortisol was suppressed by 95% with the low dose dexamethasone suppression test. CAH was suspected based on the history of precocious puberty, short stature and a profound suppression of cortisol production by dexamethasone. CAH was confirmed by a remarkably increased level of serum 17-hydroxyprogesterone level. Gene mutation analysis revealed a compound heterozygote mutation of CYP21A2 (I173N and R357W).

Korean Type 2 Diabetes Patients have Multiple Adenomatous Polyps Compared to Non-diabetic Controls

We tested the correlation between diabetes and aggressiveness of colorectal polyps in diabetic patients and matched non-diabetic controls. We retrospectively studied 3,505 type 2 diabetes (T2DM) patients without gastrointestinal symptoms who underwent colonoscopy for colorectal cancer at Samsung Medical Center, Seoul, Korea from August 1995 to August 2009. We matched 495 non-diabetic subjects with colon polyps to the diabetic patients in whom polyps were detected by year of colonoscopy, age, sex and body mass index (BMI). Among the 3,505 T2DM patients screened, 509 were found to have 1,136 colon polyps. Those with diabetes had a greater proportion of adenomatous polyps (62.8% vs 53.6%) compared to the control. Multivariate logistic regression analysis identified DM, male gender, age and BMI as independent risk factors for multiple polyps (more than three polyps). Polyp multiplicity in diabetic patients was significantly associated with male gender (OR 2.360, P = 0.005), age (OR 1.033, P = 0.005) and BMI (OR 1.077, P = 0.028). Neither aspirin nor metformin use affected either size or number of polyps in diabetic patients. Male patients older than 65 yr with T2DM and BMI greater than 25 have increased risk for multiple adenomatous polyps and should be screened with colonoscopy to prevent colorectal cancer.

Role of Innate Immunity in Diabetes and Metabolism: Recent Progress in the Study of Inflammasomes

Type 1 diabetes is one of the classical examples of organ- specific autoimmune diseases characterized by lymphocytic infiltration or inflammation in pancreatic islets called 'insulitis'. In contrast, type 2 diabetes has been traditionally regarded as a metabolic disorder with a pathogenesis that is totally different from that of type 1 diabetes. However, recent investigation has revealed contribution of chronic inflammation in the pathogenesis of type 2 diabetes. In addition to type 2 diabetes, the role of chronic inflammation is being appreciated in a wide variety of metabolic disorders such as obesity, metabolic syndrome, and atherosclerosis. In this review, we will cover the role of innate immunity in the pathogenesis of metabolic disorders with an emphasis on NLRP3.

Role of Innate Immunity in Diabetes and Metabolism: Recent Progress in the Study of Inflammasomes

Type 1 diabetes is one of the classical examples of organ- specific autoimmune diseases characterized by lymphocytic infiltration or inflammation in pancreatic islets called 'insulitis'. In contrast, type 2 diabetes has been traditionally regarded as a metabolic disorder with a pathogenesis that is totally different from that of type 1 diabetes. However, recent investigation has revealed contribution of chronic inflammation in the pathogenesis of type 2 diabetes. In addition to type 2 diabetes, the role of chronic inflammation is being appreciated in a wide variety of metabolic disorders such as obesity, metabolic syndrome, and atherosclerosis. In this review, we will cover the role of innate immunity in the pathogenesis of metabolic disorders with an emphasis on NLRP3.

Inhibition of NF-kappaB prevents high glucose-induced proliferation and plasminogen activator inhibitor-1 expression in vascular smooth muscle cells

Recent epidemiologic studies clearly showed that early intensive glucose control has a legacy effect for preventing diabetic macrovascular complications. However, the cellular and molecular processes by which high glucose leads to macrovascular complications are poorly understood. Vascular smooth muscle cell (VSMC) dysfunction due to high glucose is a characteristic of diabetic vascular complications. Activation of nuclear factor-kappaB (NF-kappaB) may play a key role in the regulation of inflammation and proliferation of VSMCs. We examined whether VSMC proliferation and plasminogen activator inhibitor-1 (PAI-1) expression induced by high glucose were mediated by NF-kappaB activation. Also, we determined whether selective inhibition of NF-kappaB would inhibit proliferation and PAI-1 expression in VSMCs. VSMCs of the aorta of male SD rats were treated with various concentrations of glucose (5.6, 11.1, 16.7, and 22.2 mM) with or without an inhibitor of NF-kappaB or expression of a recombinant adenovirus vector encoding an IkappaB-alpha mutant (Ad-IkappaBalphaM). VSMC proliferation was examined using an MTT assay. PAI-1 expression was assayed by real-time PCR and PAI-1 protein in the media was measured by ELISA. NF-kappaB activation was determined by immunohistochemical staining, NF-kappaB reporter assay, and immunoblotting. We found that glucose stimulated VSMC proliferation and PAI-1 expression in a dose-dependent manner up to 22.2 mM. High glucose (22.2 mM) alone induced an increase in NF-kappaB activity. Treatment with inhibitors of NF-kappaB such as MG132, PDTC or expression of Ad-IkappaB-alphaM in VSMCs prevented VSMC proliferation and PAI-1 expression induced by high glucose. In conclusion, inhibition of NF-kappaB activity prevented high glucose-induced VSMC proliferation and PAI-1 expression.

Modulation of Glial and Neuronal Migration by Lipocalin-2 in Zebrafish

BACKGROUND: Glial cells are involved in immune and inflammatory responses in the central nervous system (CNS). Glial cells such as microglia and astrocytes also provide structural and functional support for neurons. Migration and morphological changes of CNS cells are associated with their physiological as well as pathological functions. The secreted protein lipocalin-2 (LCN2) has been previously implicated in regulation of diverse cellular processes of glia and neurons, including cell migration and morphology. METHODS: Here, we employed a zebrafish model to analyze the role of LCN2 in CNS cell migration and morphology in vivo. In the first part of this study, we examined the indirect effect of LCN2 on cell migration and morphology of microglia, astrocytes, and neurons cultured in vitro. RESULTS: Conditioned media collected from LCN2-treated astrocytes augmented migration of glia and neurons in the Boyden chamber assay. The conditioned media also increased the number of neuronal processes. Next, in order to further understand the role of LCN2 in the CNS in vivo, LCN2 was ectopically expressed in the zebrafish spinal cord. Expression of exogenous LCN2 modulated neuronal cell migration in the spinal cord of zebrafish embryos, supporting the role of LCN2 as a cell migration regulator in the CNS. CONCLUSION: Thus, LCN2 proteins secreted under diverse conditions may play an important role in CNS immune and inflammatory responses by controlling cell migration and morphology.

Autosomal Dominant Hypocalcemia Caused by an Activating Mutation of the Calcium-Sensing Receptor Gene: The First Case Report in Korea

Hypoparathyroidism is an abnormality of calcium metabolism characterized by low serum levels of parathyroid hormone in spite of hypocalcemia. The causes of hypoparathyroidism are numerous. Activating mutations in the calcium-sensing receptor (CaSR) gene are well-known causes of familial isolated hypoparathyroidism, also known as autosomal dominant hypocalcemia (ADH). Here we describe members of a Korean family with a heterozygous Pro221Leu mutation causing ADH. This case is the first report in Korea.

Clinicopathological Characteristics and Prognostic Factors of Medullary Thyroid Carcinoma

BACKGROUND: Studies on the clinicopathological characteristics and prognostic factors of medullary thyroid carcinoma (MTC) in Korea are very rare. METHODS: We enrolled 56 MTC patients who underwent surgery at Samsung Medical Center from 1995 to 2006. We analyzed their gender, age at diagnosis, the pathologic findings, the TNM stage, the association with multiple endocrine neoplasia (MEN), RET protooncogene mutation and the, serum basal calcitonin levels before and after the surgery. We investigated the overall survival and the prognostic factors. RESULTS: The mean age at diagnosis was 46 years and the male/female ratio was 1:2.7. Fine needle aspiration cytology detected 61% of the MTC. The mean tumor size was 2.6 cm (range: 0.2-9.0 cm). Fifty-two percent of patients had the TNM stage more than III at the time of diagnosis. Distant metastasis was found in 5.3% (3/56) of the patients, either at the time of diagnosis or during the follow-up period. Hereditary MTC comprised of 23% of the patients and the disease developed at a younger age (38 years vs. 48 years, respectively, P < 0.05) with more bilaterality. RET protooncogene mutations were found in 27% (9/33) of the patients and most of them were in codon 634. After the primary surgery, the serum basal calcitonin levels were persistently elevated over 13 ng/L in 49% of the patients. The overall 5-year survival rate was 95.5%. Tumor size and distant metastasis were the significant prognostic factors for survival by univariate analysis (P < 0.05). CONCLUSION: There were no significant differences in the clinicopathological characteristics of MTC and survival in Korea compared to those of the Western countries.

Pathogenesis of Type 1 Diabetes / 한양의대학술지

Type 1 diabetes mellitus (T1D) is a chronic autoimmune disease characterized by selective destruction of pancreatic islet betacells causing insulin deficiency. T1D has been shown to be a polygenic trait, associated with several loci, among which the human leukocyte antigen (HLA) region accounts for 40% of the genetic risk to develop T1D. The betacell autoimmune response is triggered by environmental or unknown events in the predisposing genetic background. The triggers of autoimmunity can lead to a localized imbalance between regulatory T cells and autoimmune effector T cells. The macrophages and autoreactive lymphocytes infiltrate the islets and the interaction of betacells and immune cells leads to inductionamplification of insulitis and loss of betacells. T cells destroy betacells in a direct cytotoxic manner or influence the induction of betacell apoptosis through the release of cytotoxic molecules, such as cytokines. The autoimmune process progresses subclinically for many years in the majority of patients, and clinical symptom do not appear until more than 80% of betacells have been destroyed. Although no current "cure" exists, there is a major effort to develop immunotherapies to prevent or halt the disorder that still requires much research to fully understand exact triggering events leading toautoimmune activation. Other strategies involve beta- cell replacement by islet transplantation, but researchs to enhance the islet mass transplanted and preserve beta-cell function are necessary.