Agouti regulation of intracellular calcium: role in the insulin resistance of viable yellow mice

Verapamil-loaded supramolecular hydrogel patch attenuates metabolic dysfunction-associated fatty liver disease via restoration of autophagic clearance of aggregated proteins and inhibition of NLRP3

BACKGROUND

Obesity, a serious threat to public health, is linked to chronic metabolic complications including insulin resistance, type-2 diabetes, and metabolic dysfunction-associated fatty liver disease (MAFLD). Current obesity medications are challenged by poor effectiveness, poor patient compliance, and potential side effects. Verapamil is an inhibitor of L-type calcium channels, FDA-approved for the treatment of hypertension. We previously investigated the effect of verapamil on modulating autophagy to treat obesity-associated lipotoxicity. This study aims to develop a verapamil transdermal patch and to evaluate its anti-obesity effects.

METHODS

Verapamil is loaded in biomimetic vascular bundle-like carboxymethyl pullulan-based supramolecular hydrogel patches cross-linked with citric acid and glycerol linkages (CLCMP). The investigation was then carried out to determine the therapeutic effect of verapamil-loaded CLCMP (Vera@CLCMP) on diet-induced obese mice.

RESULTS

Vera@CLCMP hydrogel patches with hierarchically organized and anisotropic pore structures not only improved verapamil bioavailability without modifying its chemical structure but also enhanced verapamil release through the stratum corneum barrier. Vera@CLCMP patches exhibit low toxicity and high effectiveness at delivering verapamil into the systemic circulation through the dermis in a sustained manner. Specifically, transdermal administration of this patch into diet-induced obese mice drastically improved glucose tolerance and insulin sensitivity and alleviated metabolic derangements associated with MAFLD. Furthermore, we uncovered a distinct molecular mechanism underlying the anti-obesity effects associated with the hepatic NLR family pyrin domain-containing 3 (NLRP3) inflammasome and autophagic clearance by the vera@CLCMP hydrogel patches.

CONCLUSION

The current study provides promising drug delivery platforms for long-term family treatment of chronic diseases, including obesity and metabolic dysfunctions.

Targeting the T-type calcium channel Cav3.2 in GABAergic arcuate nucleus neurons to treat obesity

OBJECTIVE

Cav3.2, a T-type low voltage-activated calcium channel widely expressed throughout the central nervous system, plays a vital role in neuronal excitability and various physiological functions. However, the effects of Cav3.2 on energy homeostasis remain unclear. Here, we examined the role of Cav3.2 expressed by hypothalamic GABAergic neurons in the regulation of food intake and body weight in mice and explored the underlying mechanisms.

METHODS

Male congenital Cana1h (the gene coding for Cav3.2) global knockout (Cav3.2KO) mice and their wild type (WT) littermates were first used for metabolic phenotyping studies. By using the CRISPR-Cas9 technique, Cav3.2 was selectively deleted from GABAergic neurons in the arcuate nucleus of the hypothalamus (ARH) by specifically overexpressing Cas9 protein and Cav3.2-targeting sgRNAs in ARH Vgat (Vgat^ARH) neurons. These male mutants (Cav3.2KO-Vgat^ARH) were used to determine whether Cav3.2 expressed by Vgat^ARH neurons is required for the proper regulation of energy balance. Subsequently, we used an electrophysiological patch-clamp recording in ex vivo brain slices to explore the impact of Cav3.2KO on the cellular excitability of Vgat^ARH neurons.

RESULTS

Male Cav3.2KO mice had significantly lower food intake than their WT littermate controls when fed with either a normal chow diet (NCD) or a high-fat diet (HFD). This hypophagia phenotype was associated with increased energy expenditure and decreased fat mass, lean mass, and total body weight. Selective deletion of Cav3.2 in Vgat^ARH neurons resulted in similar feeding inhibition and lean phenotype without changing energy expenditure. These data provides an intrinsic mechanism to support the previous finding on ARH non-AgRP GABA neurons in regulating diet-induced obesity. Lastly, we found that naringenin extract, a predominant flavanone found in various fruits and herbs and known to act on Cav3.2, decreased the firing activity of Vgat^ARH neurons and reduced food intake and body weight. These naringenin-induced inhibitions were fully blocked in Cav3.2KO-Vgat^ARH mice.

CONCLUSION

Our results identified Cav3.2 expressed by Vgat^ARH neurons as an essential intrinsic modulator for food intake and energy homeostasis, which is a potential therapeutic target in the treatment of obesity.

Role of dietary calcium and its possible mechanism against metabolic disorders: A concise review

The global prevalence of metabolic disorders including hypertension, dyslipidemia, insulin resistance, nonalcoholic fatty liver, and cardiovascular diseases seemed to affect people of all ages cutting across the national, economic, and demographic barrier. Therefore, the prevention of metabolic disorders is considered of paramount importance. The dietary role of nutrients including vitamins and minerals is one of the recommended preventive measures against metabolic disorders in modern society. Recently, dietary calcium, a common nutrient not only showed a beneficial effect against obesity through weight management, but also gained great attention against the risk of metabolic disorders. Though dietary calcium shows several beneficial effects against metabolic disorders but some inconsistent results were also reported. So, the present review aims to extract recent knowledge as well as their possible underlying mechanisms regarding the role of dietary calcium against metabolic disorders. The present review also discusses the negative impact as well as prospect of calcium intake on health issues. In summary, high calcium diet prevents the harmful consequences of metabolic disorders by regulating hormonal actions, alteration in intracellular calcium level, renin-angiotensin system, intestinal fat absorption, fecal fat excretion, lipid metabolism, carbohydrate metabolism, inflammation, and oxidative stress which together improve the metabolic health of an individual. PRACTICAL APPLICATIONS: Metabolic disorder is a global health issue across all sections of society and is growing rapidly in spite of several attempts by the scientific community to prevent it. Recently dietary calcium gained great attention in the last few years for its role in the management and treatment of metabolic disorders. The current review highlights the beneficial role of dietary calcium against several metabolic complications by exploring their underlying mechanisms at cellular level. This study will provide valuable information regarding the recommendation of dietary calcium in health policy as well as its inclusion in the dietary chart through calcium-rich foods and/or taking calcium supplements which can be a useful approach in preventing the risk of metabolic disorder depending on the health status of an individual.

Increased mitochondrial calcium uniporter in adipocytes underlies mitochondrial alterations associated with insulin resistance

Intracellular calcium influences an array of pathways and affects cellular processes. With the rapidly progressing research investigating the molecular identity and the physiological roles of the mitochondrial calcium uniporter (MCU) complex, we now have the tools to understand the functions of mitochondrial Ca²⁺ in the regulation of pathophysiological processes. Herein, we describe the role of key MCU complex components in insulin resistance in mouse and human adipose tissue. Adipose tissue gene expression was analyzed from several models of obese and diabetic rodents and in 72 patients with obesity as well as in vitro insulin-resistant adipocytes. Genetic manipulation of MCU activity in 3T3-L1 adipocytes allowed the investigation of the role of mitochondrial calcium uptake. In insulin-resistant adipocytes, mitochondrial calcium uptake increased and several MCU components were upregulated. Similar results were observed in mouse and human visceral adipose tissue (VAT) during the progression of obesity and diabetes. Intriguingly, subcutaneous adipose tissue (SAT) was spared from overt MCU fluctuations. Furthermore, MCU expression returned to physiological levels in VAT of patients after weight loss by bariatric surgery. Genetic manipulation of mitochondrial calcium uptake in 3T3-L1 adipocytes demonstrated that changes in mitochondrial calcium concentration ([Ca²⁺]_mt) can affect mitochondrial metabolism, including oxidative enzyme activity, mitochondrial respiration, membrane potential, and reactive oxygen species formation. Finally, our data suggest a strong relationship between [Ca²⁺]_mt and the release of IL-6 and TNFα in adipocytes. Altered mitochondrial calcium flux in fat cells may play a role in obesity and diabetes and may be associated with the differential metabolic profiles of VAT and SAT.

Exposure to permethrin promotes high fat diet-induced weight gain and insulin resistance in male C57BL/6J mice

Permethrin is a pyrethroid pesticide that was previously reported to promote fat accumulation and insulin resistance in vitro. A recent study in female mice also found that permethrin could promote high fat-induced insulin resistance. The effects of permethrin on glucose and lipid metabolisms in male mice, however, remain unknown. The purpose of this study was to investigate the effects and interactions of permethrin exposure (50, 500, and 5000 μg/kg body weight/day) and dietary fat (low fat, 4% w/w; high fat, 20% w/w) on development of obesity and insulin resistance in male C57BL/6J mice. Our results showed that permethrin treatment significantly increased body weight, fat mass, and insulin resistance with high fat diet, but not with low fat diet, without influencing energy intake. Permethrin treatment also significantly increased serum levels of insulin, glucose, leptin, triglycerides and cholesterol. Further results showed that permethrin inhibited AMP-activated protein kinase in white adipose tissue. These results suggest that permethrin interacts with dietary fat to alter lipid and glucose metabolisms in male C57BL/6J mice.

The effect of increasing dairy calcium intake of adolescent girls on changes in body fat and weight

Background: Overweight is epidemic in adolescents and is a major concern because it tracks into adulthood. Evidence supports the efficacy of high-calcium, high-dairy diets in achieving healthy weight in adults. However, no randomized controlled trials of the effect of dairy food on weight and body fat in adolescents have been reported to our knowledge.Objective: The aim was to determine whether increasing calcium intake to recommended amounts with dairy foods in adolescent girls with habitually low calcium intakes would decrease body fat gain compared with girls who continued their low calcium intake. Participants had above-the-median body mass index (BMI; in kg/m²).Design: We enrolled 274 healthy postmenarcheal 13- to 14-y-old overweight girls who had calcium intakes of ≤600 mg/d in a 12-mo randomized controlled trial. Girls were randomly assigned in a 1:1 ratio to 1 of 2 groups within each of 3 BMI percentiles: 50th to <70th, 70th to <85th, and 85th to <98th. The assignments were 1) dairy, which included low-fat milk or yogurt servings providing ≥1200 mg Ca/d or 2) control, which included the usual diet of ≤600 mg Ca/d.Results: We failed to detect a statistically significant difference between groups in percentage of body fat gain over 12 mo (mean ± SEM: dairy 0.40% ± 0.53% > control; P < 0.45). The effect of the intervention did not differ by BMI percentile stratum. There was no difference in weight change between the 2 groups.Conclusion: Our findings that the dairy group gained body fat similar to the control group provide no support for dairy food as a stratagem to decrease body fat or weight gain in overweight adolescent girls. This trial was registered at clinicaltrials.gov as NCT01066806.

Polymorphisms in PDLIM5 gene are associated with alcohol dependence, type 2 diabetes, and hypertension

The PDZ and LIM domain 5 (PDLIM5) gene may play a role in alcohol dependence (AD), bipolar disorder, and major depressive disorder; however, no study has identified shared genetic variants within PDLIM5 gene among AD, type 2 diabetes (T2D), and hypertension. This study investigated the association of 72 single nucleotide polymorphism (SNPs) with AD (1066 AD cases and 1278 controls) in the Study of Addiction - Genetics and Environment (SAGE) sample and 47 SNPs with T2D (878 cases and 2686 non-diabetic) and hypertension (825 cases and 2739 non-hypertensive) in the Marshfield sample. Multiple logistic regression models in PLINK software were used to examine the associations of genetic variants with AD, T2D, and hypertension and SNP x alcohol consumption interactions for T2D and hypertension. Twenty-five SNPs were associated with AD in the SAGE sample (p < 0.05); rs1048627 showed the strongest association with AD (p = 5.53 × 10^-4). Of the 25 SNPs, 5 SNPs showed associations with both AD in the SAGE sample and T2D in the Marshfield sample (top SNP rs11097432 with p = 0.00107 for T2D and p = 0.0483 for AD) while 6 SNPs showed associations with both AD in the SAGE sample and hypertension in the Marshfield sample (top SNP rs12500426 with p = 0.0119 for hypertension and p = 1.51 × 10^-3 for AD). SNP (rs6532496) showed significant interaction with alcohol consumption for hypertension. Our results showed that several genetic variants in PDLIM5 gene influence AD, T2D and hypertension. These findings offer the potential for new insights into the pathogenesis of AD, T2D, and hypertension.

Ion Channels in Obesity: Pathophysiology and Potential Therapeutic Targets

Obesity is a multifactorial disease related to metabolic disorders and associated with genetic determinants. Currently, ion channels activity has been linked to many of these disorders, in addition to the central regulation of food intake, energetic balance, hormone release and response, as well as the adipocyte cell proliferation. Therefore, the objective of this work is to review the current knowledge about the influence of ion channels in obesity development. This review used different sources of literature (Google Scholar, PubMed, Scopus, and Web of Science) to assess the role of ion channels in the pathophysiology of obesity. Ion channels present diverse key functions, such as the maintenance of physiological homeostasis and cell proliferation. Cell biology and pharmacological experimental evidences demonstrate that proliferating cells exhibit ion channel expression, conductance, and electrical properties different from the resting cells. Thereby, a large variety of ion channels has been identified in the pathogenesis of obesity such as potassium, sodium, calcium and chloride channels, nicotinic acetylcholine receptor and transient receptor potential channels. The fundamental involvement of these channels on the generation of obesity leads to the progress in the knowledge about the mechanisms responsible for the obesity pathophysiology, consequently emerging as new targets for pharmacological modulation.

Calcium Homeostasis and Organelle Function in the Pathogenesis of Obesity and Diabetes

A number of chronic metabolic pathologies, including obesity, diabetes, cardiovascular disease, asthma, and cancer, cluster together to present the greatest threat to human health. As research in this field has advanced, it has become clear that unresolved metabolic inflammation, organelle dysfunction, and other cellular and metabolic stresses underlie the development of these chronic metabolic diseases. However, the relationship between these systems and pathological mechanisms is poorly understood. Here we discuss the role of cellular Ca(2+) homeostasis as a critical mechanism integrating the myriad of cellular and subcellular dysfunctional networks found in metabolic tissues such as liver and adipose tissue in the context of metabolic disease, particularly in obesity and diabetes.

Permethrin alters adipogenesis in 3T3-L1 adipocytes and causes insulin resistance in C2C12 myotubes

Pyrethroids are a class of insecticides structurally derived from the naturally occurring insecticides called pyrethrins. Along with emerging evidence that exposure to insecticides is linked to altered weight gain and glucose homeostasis, exposure to pyrethroids has been linked to altered blood glucose levels in humans. Thus, the purpose of this study was to determine the role of permethrin on lipid and glucose metabolisms. Permethrin was treated to 3T3-L1 adipocytes and C2C12 myoblasts to determine its role in lipid and glucose metabolisms, respectively. Permethrin treatment resulted in increased expression of key markers of adipogenesis and lipogenesis in adipocytes. Permethrin significantly reduced insulin-stimulated glucose uptake in myotubes. This is the first report on the role of permethrin in altered lipid metabolism in adipocytes and impaired glucose homeostasis in myotubes. These results may help elucidate fundamental underlying mechanisms between insecticide exposure, particularly permethrin, and potential risk of developing obesity and its comorbidities.

Imidacloprid, a neonicotinoid insecticide, induces insulin resistance

Recently, scientific evidence supports a connection between environmental chemical exposures, which includes insecticides, and development of type 2 diabetes. However, there is limited information about the link between influences of neonicotinoid insecticides and incidence of type 2 diabetes. Thus, the purpose of the study was to determine effects of imidacloprid, a neonicotinoid insecticide, on glucose metabolism. Three different cell models were used; adipocytes (3T3-L1), hepatocytes (HepG2), and myotubes (C2C12). These cells were treated with imidacloprid (0, 10, and 20 μM) for 4-6 days followed by treatment with insulin for 15 min to determine responses. Insulin stimulated glucose uptake was reduced by imidacloprid in all three cell culture models. Treatment with imidacloprid reduced phosphorylation of protein kinase B (AKT), one of the major regulators of insulin signaling, without changing overall AKT expression. Subsequently, imidacloprid reduced phosphorylation of ribosomal S6 kinase (S6K), which is a downstream target of AKT and also a feed-back inhibitor of insulin signaling. These results suggest that imidacloprid could induce insulin resistance by affecting the insulin signaling cascade, particularly up-stream of AKT, in adipocytes, liver, and muscle.

Bone Remodeling and Energy Metabolism: New Perspectives

Bone mineral, adipose tissue and energy metabolism are interconnected by a complex and multilevel series of networks. Calcium and phosphorus are utilized for insulin secretion and synthesis of high energy compounds. Adipose tissue store lipids and cholecalciferol, which, in turn, can influence calcium balance and energy expenditure. Hormones long-thought to solely modulate energy and mineral homeostasis may influence adipocytic function. Osteoblasts are a target of insulin action in bone. Moreover, endocrine mediators, such as osteocalcin, are synthesized in the skeleton but regulate carbohydrate disposal and insulin secretion. Finally, osteoblasts and adipocytes originate from the same mesenchymal progenitor. The mutual crosstalk between osteoblasts and adipocytes within the bone marrow microenvironment plays a crucial role in bone remodeling. In the present review we provide an overview of the reciprocal control between bone and energy metabolism and its clinical implications.

Calcium supplementation prevents obesity, hyperleptinaemia and hyperglycaemia in adult rats programmed by early weaning

It is known that Ca therapy may have anti-obesity effects. Since early weaning leads to obesity, hyperleptinaemia and insulin resistance, we studied the effect of dietary Ca supplementation in a rat model. Lactating rats were separated into two groups: early weaning (EW) - dams were wrapped with a bandage to interrupt lactation in the last 3 d of lactation and control (C) - dams whose pups had free access to milk during the entire lactation period (21 d). At 120 d, EW and C offspring were subdivided into four groups: (1) C, received standard diet; (2) CCa, received Ca supplementation (10 g of calcium carbonate/kg of rat chow); (3) EW, received standard diet; (4) EWCa, received Ca supplementation similar to CCa. The rats were killed at 180 d. The significance level was at P < 0·05. Adult EW offspring displayed hyperphagia (28 %), higher body weight (9 %) and adiposity (77 %), hyperleptinaemia (twofold increase), hypertriacylglycerolaemia (64 %), hyperglycaemia (16 %), higher insulin resistance index (38 %) and higher serum 25-hydroxyvitamin D₃ (fourfold increase), but lower adiponectinaemia:adipose tissue ratio (44 %). In addition, they showed Janus tyrosine kinase 2 and phosphorylated signal transducer and activator of transcription 3 underexpression in hypothalamus (36 and 34 %, respectively), suggesting leptin resistance. Supplementation of Ca for 2 months normalised these disorders. The EW group had no change in serum insulin, thyroxine or triiodothyronine, and Ca treatment did not alter these hormones. In conclusion, we reinforced that early weaning leads to late development of some components of the metabolic syndrome and leptin resistance. Dietary Ca supplementation seems to protect against the development of endocrine and metabolic disorders in EW offspring, maybe through vitamin D inhibition.

VDR haploinsufficiency impacts body composition and skeletal acquisition in a gender-specific manner

The vitamin D receptor (VDR) is crucial for virtually all of vitamin D's actions and is thought to be ubiquitously expressed. We hypothesized that disruption of one allele of the VDR gene would impact bone development and would have metabolic consequences. Body composition and bone mass (BMD) in VDR heterozygous (VDR HET) mice were compared to those obtained in male and female VDR KO and WT mice at 8 weeks of age. Male mice were also evaluated at 16 weeks, and bone marrow mesenchymal stem cell (MSC) differentiation was evaluated in VDR female mice. Additionally, female VDR HET and WT mice received intermittent PTH treatment or vehicle (VH) for 4 weeks. BMD was determined at baseline and after treatment. MRI was done in vivo at the end of treatment; μCT and bone histomorphometry were performed after killing the animals. VDR HET male mice had normal skeletal development until 16 weeks of age but showed significantly less gain in fat mass than WT mice. In contrast, female VDR HET mice showed decreased total-body BMD at age 8 weeks but had a normal skeletal response to PTH. MSC differentiation was also impaired in VDR HET female mice. Thus, female VDR HET mice show early impairment in bone acquisition, while male VDR HET mice exhibit a lean phenotype. Our results indicate that the VDR HET mouse is a useful model for studying the metabolic and skeletal impact of decreased vitamin D sensitivity.

Calcium supplementation reverts central adiposity, leptin, and insulin resistance in adult offspring programed by neonatal nicotine exposure

Obesity is a worldwide epidemic. Calcium influences energy metabolism regulation, causing body weight loss. Because maternal nicotine exposure during lactation programs for obesity, hyperleptinemia, insulin resistance (IR), and hypothyroidism, we decided to evaluate the possible effect of dietary calcium supplementation on these endocrine dysfunctions in this experimental model. Osmotic minipumps containing nicotine solution (N: 6 mg/kg per day for 14 days) or saline (C) were s.c. implanted in lactating rats 2 days after giving birth (P2). At P120, N and C offspring were subdivided into four groups: 1) C - standard diet; 2) C with calcium supplementation (CCa, 10 g calcium carbonate/kg rat chow); 3) N - standard diet; and 4) N with calcium supplementation (NCa). Rats were killed at P180. As expected, N offspring showed higher visceral and total body fat, hyperleptinemia, lower hypothalamus leptin receptor (OB-R) content, hyperinsulinemia, and higher IR index. Also, higher tyrosine hydroxylase (TH) expression (+51%), catecholamine content (+37%), and serum 25-hydroxyvitamin D(3) (+76%) were observed in N offspring. Dietary calcium supplementation reversed adiposity, hyperleptinemia, OB-R underexpression, IR, TH overexpression, and vitamin D. However, this supplementation did not reverse hypothyroidism. In NCa offspring, Sirt1 mRNA was lower in visceral fat (-37%) and higher in liver (+42%). In conclusion, dietary calcium supplementation seems to revert most of the metabolic syndrome parameters observed in adult offspring programed by maternal nicotine exposure during lactation. It is conceivable that the reduction in fat mass per se, induced by calcium therapy, is the main mechanism that leads to the increment of insulin action.

Ingestão do cálcio na obesidade de mulheres atendidas pelo Sistema Único de Saúde

OBJETIVOS: Verificar a associação entre consumo de cálcio e obesidade em uma amostra de mulheres obesas ou eutróficas. MÉTODOS: Por meio de inquéritos alimentares, estimou-se a ingestão de cálcio de 177 mulheres hipertensas e/ou diabéticas mediante recordatórios de 24h e frequência de consumo alimentar. Estudo caso-controle teve o grupo-estudo composto por 102 mulheres obesas e o grupo-controle por 75 mulheres eutróficas. Os dados de ingestão foram comparados às recomendações dietéticas e às porções de alimentos de origem animal, recomendados pela pirâmide alimentar brasileira, que são fontes de cálcio. Na análise estatística dos dois grupos segundo faixa etária, utilizou-se o coeficiente de correlação linear simples de Pearson com nível de significância de até 5% de probabilidade de erro experimental. RESULTADOS: A ingestão quantitativa de cálcio foi semelhante entre os grupos e igualmente insuficiente para atingir as recomendações nutricionais. A análise da frequência de consumo de fontes de cálcio revelou que os dois grupos apresentavam consumo inferior a três porções/dia, merecendo destaque o grande número que referiu "raramente" consumir tais alimentos. CONCLUSÃO: Não foi observada nessa população a associação entre obesidade e ingestão de cálcio. Seu consumo foi insuficiente para atingir as quantidades recomendadas, um achado relevante. Considerando a idade das mulheres estudadas e o diagnóstico de hipertensão e diabetes, é evidente a necessidade de atividades de educação nutricional para estimular o consumo de fontes alimentares de cálcio com o intuito de auxiliar no controle da hipertensão e de prevenir agravos importantes, como a obesidade e a osteoporose.

Proposed role of calcium and dairy food components in weight management and metabolic health

Dietary calcium and dairy foods have demonstrated an antiobesity effect in animal studies, observational and population studies, and randomized clinical trials. Moreover, there is a strong theoretical framework to explain the effects of dietary calcium on energy metabolism. The supporting mechanisms include dietary calcium-correcting suboptimal calcium intakes, thereby preventing the endocrine response (parathyroid hormone [PTH] and calcitriol), which favors adipocyte energy storage and inhibits adipocyte loss via apoptosis. Dietary calcium appears to further promote energy loss via formation of calcium soaps in the gastrointestinal tract and thereby modestly reduces net energy absorption. Dietary calcium appears to be responsible for approximately 50% of the antiobesity bioactivity of dairy foods. The additional dairy bioactivity has not been fully identified, but is primarily localized in whey protein. The major components are the angiotensin-converting enzyme (ACE) inhibitor activity of whey proteins and the high concentration of leucine in whey. This high leucine content appears to be primarily responsible for the repartitioning of dietary energy from adipose tissue to skeletal muscle during weight loss, resulting in greater preservation of skeletal muscle and accelerated loss of adipose tissue during negative energy balance. Finally, high-calcium diets suppress obesity-induced oxidative and inflammatory stress independently from its role in modulating adiposity; these effects are similarly augmented by other dairy food components. However, the number of randomized clinical trials conducted is still modest, and a small number have not confirmed significant effects in weight management. Thus, the protective effects of dairy foods against obesity and its comorbidities are promising, but warrant further large-scale studies.

Insulin sensitivity increase after calcium supplementation and change in intraplatelet calcium and sodium-hydrogen exchange in hypertensive patients with Type 2 diabetes

AIMS/HYPOTHESIS

To investigate the effect of oral calcium (Ca(2+)) supplementation on insulin sensitivity measured by the euglycaemic hyperinsulinaemic clamp, intraplatelet cationic concentration of Ca(2+) ([Ca(2+)](i)) and the transmembrane sodium-hydrogen exchanger (NHE) activity in erythrocytes in subjects with Type 2 diabetes and hypertension.

PATIENTS AND METHODS

In this parallel randomized controlled single-blinded trial, 31 patients were allocated to receive either 1500 mg of Ca(2+) orally, daily (n = 15) or no treatment (n = 16) for 8 weeks. At baseline and at the end of the 8-week period insulin sensitivity, [Ca(2+)](i) and the first isoform of NHE (NHE-1) activity were measured.

RESULTS

At the end of the study, subjects who received Ca(2+) supplementation showed higher insulin sensitivity (Delta M-value 0.32 +/- 0.5 mmol/min P < 0.05) and lower [Ca(2+)](i) (125.0 +/- 24.7 to 80.4 +/- 10.6 nmol/l, P < 0.05, mean +/- sem) and NHE-1 activity (79.5 +/- 10.0 to 52.1 +/- 6.4 mmol Na/l red cell/h, P < 0.05). None of the above parameters were changed in the control group. Simple regression analysis demonstrated the change in [Ca(2+)](i) significantly determined insulin sensitivity change (beta = -0.36, P < 0.05).

CONCLUSIONS/INTERPRETATION

Oral Ca(2+) supplementation improves insulin sensitivity in patients with Type 2 diabetes and hypertension. These changes are likely to be mediated by changes in intracellular ionic Ca(2+). NHE-1 activity was also reduced after Ca(2+) supplementation but its role in insulin sensitivity requires further investigation.

Calcitriol and energy metabolism

Calcitriol, a calcitrophic hormone that can be suppressed by high dietary calcium, favors fatty acid synthesis and inhibits lipolysis via non-genomic modulation of Ca(2+) influx. Calcitriol also suppresses UCP2 expression via the nVDR and thereby increases energy efficiency. Calcitriol exerts a dose-dependent impact on adipocyte apoptosis and regulates adipose tissue fat depot location and expansion by promoting glucocorticoid production and release. Recent data also demonstrate a pivotal role of calcitriol in the modulation of cytokines, with potential roles in energy metabolism in adipocytes, macrophages, and skeletal muscle.

Mechanisms and outcomes of drug- and toxicant-induced liver toxicity in diabetes

Increase dincidences of hepatotoxicity have been observed in diabetic patients receiving drug therapies. Neither the mechanisms nor the predisposing factors underlying hepatotoxicity in diabetics are clearly understood. Animal studies designed to examine the mechanisms of diabetes-modulated hepatotoxicity have traditionally focused only on bioactivation/detoxification of drugs and toxicants. It is becoming clear that once injury is initiated, additional events determine the final outcome of liver injury. Foremost among them are two leading mechanisms: first, biochemical mechanisms that lead to progression or regression of injury; and second, whether or not timely and adequate liver tissue repair occurs to mitigate injury and restore liver function. The liver has a remarkable ability to repair and restore its structure and function after physical or chemical-induced damage. The dynamic interaction between biotransformation-based liver injury and compensatory tissue repair plays a pivotal role in determining the ultimate outcome of hepatotoxicity initiated by drugs or toxicants. In this review, mechanisms underlying altered hepatotoxicity in diabetes with emphasis on both altered bioactivation and liver tissue repair are discussed. Animal models of both marked sensitivity (diabetic rats) and equally marked protection (diabetic mice) from drug-induced hepatotoxicity are described. These examples represent a remarkable species difference. Availability of the rodent diabetic models offers a unique opportunity to uncover mechanisms of clinical interest in averting human diabetic sensitivity to drug-induced hepatotoxicities. While the rat diabetic models appear to be suitable, the diabetic mouse models might not be suitable in preclinical testing for potential hepatotoxic effects of drugs or toxicants, because regardless of type 1 or type2 diabetes, mice are resistant to acute drug-or toxicant-induced toxicities.

Ingestão de cálcio e indicadores antropométricos entre adolescentes

OBJETIVO: Este estudo teve como objetivo investigar a relação da ingestão de cálcio com indicadores antropométricos de adolescentes. MÉTODOS: Foram avaliados 507 alunos de duas escolas públicas e uma particular de Ouro Preto, Minas Gerais, por meio de questionário sobre condições socioeconômicas, avaliação da maturação sexual, antropometria, composição corporal e consumo alimentar. RESULTADOS: A ingestão média de cálcio foi 703,7 (396,0) mg/dia, sendo a maior ingestão verificada na escola de maior nível socioeconômico. Apenas 8% dos adolescentes apresentavam ingestão superior à ingestão adequada. Houve associação negativa do cálcio, ajustado para o índice de massa corporal (r=-0,203, p=0,001), na escola de médio nível socioeconômico e nos adolescentes com ingestão desse mineral entre 400 e 800mg/dia (r=-0,134, p=0,044). CONCLUSÃO: Verificou-se ingestão insuficiente de cálcio entre os adolescentes de Ouro Preto, evidenciando a necessidade de estimular o consumo de alimentos fontes desse mineral nesta população.

Low dairy intake in early childhood predicts excess body fat gain

OBJECTIVE

To estimate the effect of dairy intake in early childhood on the acquisition of body fat throughout childhood.

RESEARCH METHODS AND PROCEDURES

Ninety-nine of the original 106 families enrolled in the Framingham Children's Study with a child age to 6 years at baseline were followed into adolescence through yearly clinic visits and periodic data collection throughout each year. Dairy intake for these analyses was derived from a mean of 15 days of diet records per subject collected before age 6. A trained examiner took two measurements each year of height, weight, and triceps, subscapular, suprailiac, and abdominal skinfolds using a standardized protocol. Yearly change in body fat was estimated as the slope of these anthropometry measures from ages 5 to 13 years. Early adolescent body fat was estimated as the mean of all available measurements from 10 to 13 years of age.

RESULTS

Children in the lowest sex-specific tertile of dairy intake during preschool (i.e., <1.25 servings per day for girls and <1.70 servings per day for boys) had significantly greater gains in body fat during childhood. These children with low dairy intakes gained more than 3 additional mm of subcutaneous fat per year in the sum of four skinfold measures. By the time of early adolescence, those in the lowest tertile of dairy intake had a BMI that was approximately two units higher and an extra 25 mm of subcutaneous fat.

DISCUSSION

Suboptimal dairy intakes during preschool in this cohort were associated with greater gains in body fat throughout childhood.

PKC-mediated modulation of L-type calcium channels may contribute to fat-induced insulin resistance

Increased intracellular free calcium [Ca2+]i has been noted in adipocytes, platelets, and leukocytes of subjects with insulin resistance syndrome or allied disorders. In rodent studies, measures which increase [Ca2+]i in adipocytes and skeletal muscle are associated with impaired insulin signaling, attributable at least in part to diminished ability of insulin to activate phosphoserine phosphatase-1 (PP-1). In fat-fed insulin resistant rats, pre-treatment with a drug that selectively chelates intracellular calcium eliminates about half of the decrement in insulin-stimulated glucose uptake induced by fat feeding; since this chelator does not influence the insulin sensitivity of chow-fed rats, it is reasonable to suspect that fat feeding boosts [Ca2+]i in skeletal muscle, and that this effect is partially responsible for the associated reduction in insulin sensitivity. Clinical insulin resistance is associated with increased levels of triglycerides and other fatty acid metabolites in muscle fibers; this can give rise to diacylglycerol-mediated activation of PKC, which in turn compromises insulin signaling by triggering kinase cascades that phosphorylate IRS-1 on key serine residues. Yet there is also evidence that, in skeletal muscle, PKC activity up-regulates the function of L-type calcium channels, increasing their maximal conductance while left-shifting their voltage dependence. Thus, the PKC activation associated with fat overexposure might be expected to boost basal [Ca2+]i in skeletal muscle, potentially impeding insulin-mediated activation of PP-1. This hypothesis is consistent with several clinical studies demonstrating that long-acting inhibitors of L-type calcium channels can improve insulin sensitivity in overweight hypertensives; it should be readily testable in rodent models of fat-induced insulin resistance. Since parathyroid hormone can act on adipocytes and muscle to boost [Ca2+]i, mild secondary hyperparathyroidism associated with low calcium intakes and poor vitamin D status may contribute to insulin resistance, consistent with certain clinical and epidemiological findings. Magnesium, often thought of as a mild calcium antagonist, appears to have favorable effects on insulin sensitivity and risk for diabetes, and recent evidence indicates that increases of intracellular magnesium within the physiological range can diminish calcium influx through phosphorylated L-type calcium channels. It will be of interest to determine whether calcium antagonism does indeed underlie the favorable influence of good magnesium status on insulin function. A report that chromium picolinate can induce the plasmalemmal Ca2+-ATPase in smooth muscle cells, raises the possibility that modulation of calcium transport might play a role in the insulin-sensitizing efficacy of bioactive chromium.

The Role of Dairy Foods in Weight Management

Dietary calcium appears to play a pivotal role in the regulation of energy metabolism and obesity risk. High calcium diets attenuate body fat accumulation and weight gain during periods of over-consumption of an energy-dense diet and to increase fat breakdown and preserve metabolism during caloric restriction, thereby markedly accelerating weight and fat loss. This effect is mediated primarily by circulating calcitriol, which regulates adipocyte intracellular Ca(2+). Studies of human adipocyte metabolism demonstrate a key role for intracellular Ca(2+) in regulating lipid metabolism and triglyceride storage, with increased intracellular Ca(2+) resulting in stimulation of lipogenic gene expression and lipogenesis and suppression of lipolysis, resulting in adipocyte lipid filling and increased adiposity. Moreover, the increased calcitriol produced in response to low calcium diets stimulates adipocyte Ca(2+) influx and, consequently, promotes adiposity, while higher calcium diets inhibit lipogenesis, promote lipolysis, lipid oxidation and thermogenesis and inhibit diet-induced obesity in mice. Notably, dairy sources of calcium exert markedly greater effects in attenuating weight and fat gain and accelerating fat loss. This augmented effect of dairy products versus supplemental calcium has been localized, in part, to the whey fraction of dairy and is likely due to additional bioactive compounds, such as angiotensin converting enzyme (ACE) inhibitors in dairy, as well as the rich concentration of branched chain amino acids, which act synergistically with calcium to attenuate adiposity; however, these compounds do not fully account for the observed effects, as whey has significantly greater bioactivity than found in these compounds. These concepts are confirmed by epidemiological data as well as recent clinical trials which demonstrate that diets which include at least three daily servings of dairy products result in significant reductions in body fat mass in obese humans in the absence of caloric restriction and markedly accelerates the weight and body fat loss secondary to caloric restriction compared to low dairy diets. These data indicate an important role for dairy products in both the ability to maintain a healthy weight and the management of overweight and obesity.

C-terminal part of AgRP stimulates insulin secretion through calcium release in pancreatic beta Rin5mf cells

Agouti-related protein (AgRP) is an orexigenic peptide which is composed of three parts; the amino (N)-terminus, the middle part, and the carboxyl (C)-terminus. AgRP has been implicated in various cell signaling, but the precise role of each parts are currently unclear. In this study, we have attempted to determine which part of AgRP was critical for insulin secretion. We have found that the C-terminus of AgRP specifically increases the intracellular calcium concentration in pancreatic beta Rin5mf cells in a PLC-dependent manner, whereas the middle part and C-terminus have little effects on calcium release. This calcium response can be observed in the freshly isolated primary beta cells also. Moreover, amperometric measurement reveals that the C-terminus of AgRP increases the rate of exocytosis in Rin5mf cells. We further show that this region of AgRP is responsible for insulin secretion in a PLC-dependent manner. Taken together, these results indicate that the C-terminus of AgRP can participate in the insulin secretion in pancreatic beta cells, through the modulation of calcium release.

Adrenocorticotropin evokes transient elevations in intracellular free calcium ([Ca2+]i) and increases basal [Ca2+]i in resting chondrocytes through a phospholipase C-dependent mechanism

Both clinical and in vitro evidence points to the involvement of the melanocortin peptide, ACTH, in the terminal differentiation of chondrocytes. Terminal differentiation along the endochondral pathway is responsible for linear growth, but also plays a role in osteoarthritic cartilage degeneration. Chondrocyte terminal differentiation is associated with an incremental increase in chondrocyte basal intracellular free calcium ([Ca(2+)](i)), and ACTH agonism of melanocortin receptors is known to mobilize [Ca(2+)](i.) Using differentiated resting chondrocytes highly expressing type II collagen and aggrecan, we examined the influence of both ACTH and dexamethasone treatment on matrix gene transcription and [Ca(2+)](i). Resting chondrocytes treated concurrently with dexamethasone and ACTH expressed matrix gene transcripts in a pattern consistent with that of rapid terminal differentiation. Using the fluorescent Ca(2+) indicator, fura-2, we determined that ACTH evokes transient increases in [Ca(2+)](i) and elevates basal Ca(2+) levels in resting chondrocytes. The transient increases were initiated intracellularly, were abrogated by the phospholipase C-specific inhibitor, U73122, and were partly attenuated by myo-inositol 1,4,5-triphosphate receptor inhibition via 10 mm caffeine. The initial intracellular release also resulted in store-operated calcium entry, presumably through store-operated channels. Dexamethasone priming increased both the initial ACTH-evoked [Ca(2+)](i) release and the subsequent store-operated calcium entry. These data demonstrate roles for ACTH and glucocorticoid in the regulation of chondrocyte terminal differentiation. Because the actions of ACTH are mediated through known G protein-coupled receptors, the melanocortin receptors, these data may provide a new therapeutic target in the treatment of growth deficiencies and cartilage degeneration.

Function of the hypothalamo-hypophyseal-adrenal system in mice with ectopic hyperproduction of the agouti protein

The agouti protein is known to compete with the melanocortin hormones (ACTH, melanocyte-stimulating hormone) at melanocortin receptors, which in turn are involved in controlling the central and peripheral components of the hypothalamo-hypophyseal-adrenal system. The aim of the present work was therefore to assess the effects of the dominant mutation Agouti yellow (A(y)/a), which induces ectopic hyperproduction of the agouti protein and yellow coat color, on the function of the hypothalamo-hypophyseal-adrenal system. Experiments were performed on male A(y)/a mice of the C57BI/6J line. Controls consisted of mice of the same line bearing the recessive mutation nonagouti (a/a), which leads to the absence of agouti protein and black coat color. The experimental results showed that mice with different agouti genotypes had identical basal corticosterone levels, though yellow mice, as compared with black mice, had increased corticosterone levels after restriction stress (p < 0.02), along with decreased stress reactivity after treatment with dexamethasone (p < 0.0007), and increased adrenal sensitivity to small doses of activity, both in vitro and in vivo.

Dietary calcium and dairy modulation of adiposity and obesity risk

Dietary calcium plays a key role in the regulation of energy metabolism and obesity risk. This appears to be mediated primarily by dietary calcium modulation of circulating calcitriol, which in turn regulates adipocyte intracellular calcium ([Ca2+]i). Increased [Ca2+]i stimulates lipogenic gene expression and activity and inhibits lipolysis, resulting in increased adipocyte lipid accumulation. Since calcitriol stimulates adipocyte Ca2+ influx, low calcium diets promote adiposity, while dietary calcium-suppression of calcitriol reduces adiposity. These concepts are confirmed in controlled rodent studies as well as by epidemiological and clinical trial data, all of which confirm protection from obesity with high calcium intakes. Moreover, dairy sources of calcium exert markedly greater effects which are most likely attributable to additional bioactive compounds in dairy which act synergistically with calcium to attenuate adiposity.

Role of calcium and dairy products in energy partitioning and weight management

Dietary calcium plays a pivotal role in the regulation of energy metabolism because high-calcium diets attenuate adipocyte lipid accretion and weight gain during the overconsumption of an energy-dense diet and increase lipolysis and preserve thermogenesis during caloric restriction, which thereby markedly accelerates weight loss. Intracellular Ca(2+) plays a key regulatory role in adipocyte lipid metabolism and triacylglycerol storage; increased intracellular Ca(2+) results in the stimulation of lipogenic gene expression and lipogenesis and the suppression of lipolysis, which results in increased lipid filling and increased adiposity. Moreover, the increased calcitriol produced in response to low-calcium diets stimulates adipocyte Ca(2+) influx and, consequently, promotes adiposity, whereas higher-calcium diets inhibit lipogenesis, inhibit diet-induced obesity in mice, and promote lipolysis, lipid oxidation, and thermogenesis. Notably, dairy sources of calcium markedly attenuate weight and fat gain and accelerate fat loss to a greater degree than do supplemental sources of calcium. This augmented effect of dairy products relative to supplemental calcium is likely due to additional bioactive compounds, including the angiotensin-converting enzyme inhibitors and the rich concentration of branched-chain amino acids in whey, which act synergistically with calcium to attenuate adiposity. These concepts are confirmed by epidemiologic data and recent clinical trials, which indicate that diets that include > or =3 daily servings of dairy products result in significant reductions in adipose tissue mass in obese humans in the absence of caloric restriction and markedly accelerate weight and body fat loss secondary to caloric restriction compared with diets low in dairy products. These data indicate an important role for dairy products in both the prevention and treatment of obesity.

Effects of an intracellular Ca(2+) chelator on insulin resistance and hypertension in high-fat-fed rats and spontaneously hypertensive rats

We explored the possibility that a sustained elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) may be a cellular abnormality common to both insulin resistance and hypertension. In high-fat diet (HFD) fed rats, the steady-state glucose infusion rate (GIR) during the euglycemic hyperinsulinemic clamp was reduced by 40% (P <.05) and mean arterial pressure (MAP) was elevated by 20 mm Hg (P <.01) in comparison to the normal chow-fed rats. Intravenous injection of 5,5'-dimethyl derivative of bis(o-aminophenoxy)ethane-N,N,N',N' tetraacetic acetoxymethyl ester (dimethyl-BAPTA/AM), an effective intracellular Ca(2+) chelator, 90 minutes before the clamp not only restored about 50% of the reduced GIR, but also normalized MAP in the HFD rats. The chelator injection also significantly increased GIR by 25% (P <.01) and reduced MAP about 30 mm Hg (P <.01) in the spontaneously hypertensive rats (SHR). In addition, we have recently shown in the HFD rats that an injection of dimethyl-BAPTA/AM normalizes elevated [Ca(2+)](i) in adipocytes. These results together demonstrate that lowering [Ca(2+)](i) simultaneously ameliorates both insulin resistance and hypertension and provide presumptive evidence that sustained high levels of [Ca(2+)](i) may play a common pathophysiologic role in these 2 diseases.

No effect of dietary calcium on body weight of lean and obese mice and rats

Recent epidemiological and animal studies have led to the hypothesis that low dietary calcium intakes contribute to obesity. Here, we evaluated whether calcium influenced the body weight of normal-weight and obese rodents. All experiments involved female C57BL/6J mice or Sprague-Dawley rats fed normal- or high-energy-density diets (3.8 o 4.7 kcal/g). Calcium intake was manipulated by allowing mice to drink sweetened 30 mM CaCl(2) solution or feeding mice and rats diets differing in calcium content (0.2%, 0.6%, o 1.8% Ca(2+)). Blood samples were taken from rats to confirm that the diets had their intended effects on metabolism. There were no effects of the calcium manipulations on energy intake, body weight, or carcass fat content and no simple elation between calciotropic hormones and body weight. One experiment found a significant decrease in body weight gain of lean and obese rats fed the 1.8% Ca(2+) diet, but we suspect that this was due to forced consumption of the unpalatable diet, reducing growth. These studies provide little support for the hypothesis that dietary calcium contributes to the etiology or maintenance of obesity.

Regulation of PPARgamma and obesity by agouti/melanocortin signaling in adipocytes

To study the potential biological role of agouti/melanocortin signaling in human adipose tissue, we engineered transgenic mice to overexpress agouti in adipose tissue. The aP2-agouti transgenic mice become significantly heavier than littermates. The increased body weight is maintained at approximately 15% above nontransgenic mice through 20 weeks and is caused by increased fat mass. The obesity is increased by a high-fat diet. There is no change in food intake in the aP2-agouti mice suggesting changes in energy utilization. A possible mechanism is that the agouti/melanocortin signaling regulates levels of PPARgamma. PPARgamma functions as a major regulator of adipocyte differentiation and as a receptor for the antidiabetic thiazolidinediones. Agouti increases PPARgamma protein levels in differentiated 3T3-L1 adipocytes, and PPARgamma expression is elevated in the fat pads of the aP2-agouti transgenic mice. The modest weight gain observed in the transgenic mice suggests that hypothalamic pathways regulating food intake are intact and the observed adiposity is within ranges that can be achieved by a paracrine mechanism at the adipocyte level.

Role of dietary calcium and dairy products in modulating adiposity

Dietary calcium plays a pivotal role in the regulation of energy metabolism. High-calcium diets attenuate adipocyte lipid accretion and weight gain during overconsumption of an energy-dense diet and increase lipolysis and preserve thermogenesis during caloric restriction, thereby markedly accelerating weight loss. Our studies of the agouti gene demonstrate a key role for intracellular Ca2+ in regulating adipocyte lipid metabolism and TG storage. Increased intracellular Ca2+ resulting in stimulation of lipogenic gene expression, and lipogenesis and suppression of lipolysis resulting in adipocyte lipid filling and increased adiposity. Moreover, we recently demonstrated that the increased calcitriol produced in response to low-calcium diets stimulates adipocyte Ca2+ influx and, consequently, promotes adiposity. Accordingly, suppressing calcitriol levels by increasing dietary calcium is an attractive target for obesity intervention. In support of this concept, transgenic mice expressing the agouti gene specifically in adipocytes (a human-like pattern) respond to low-calcium diets with accelerated weight gain and fat accretion, whereas high-calcium diets markedly inhibit lipogenesis, accelerate lipolysis, increase thermogenesis, and suppress fat accretion and weight gain in animals maintained at identical caloric intakes. Further, low-calcium diets impede body fat loss, whereas high-calcium diets markedly accelerate fat loss in transgenic mice subjected to caloric restriction. Dairy sources of calcium exert markedly greater effects in attenuating weight and fat gain and accelerating fat loss. This augmented effect of dairy products is likely due to additional bioactive compounds in dairy that act synergistically with calcium to attenuate adiposity. These concepts are confirmed by both epidemiological and clinical data, which demonstrate that increasing dietary calcium results in significant reductions in adipose tissue mass in obese humans in the absence of caloric restriction and markedly accelerates the weight and body fat loss secondary to caloric restriction, whereas dairy products exert significantly greater effects. These data indicate an important role for dairy products in both the prevention and treatment of obesity.

Mechanisms of dairy modulation of adiposity

Dietary calcium plays a pivotal role in the regulation of energy metabolism, in that we have found high calcium diets to attenuate adipocyte lipid accretion and weight gain during periods of overconsumption of an energy-dense diet and to increase lipolysis and preserve thermogenesis during caloric restriction, thereby markedly accelerating weight loss. Our studies of the agouti gene in obesity and insulin resistance demonstrate a key role for intracellular Ca(2+) in regulating adipocyte lipid metabolism and triglyceride storage, with increased intracellular Ca(2+), resulting in stimulation of lipogenic gene expression and lipogenesis, and suppression of lipolysis, resulting in adipocyte lipid filling and increased adiposity. Moreover, we have recently demonstrated that the increased calcitriol produced in response to low calcium diets stimulates Ca(2+) influx in human adipocytes and thereby promotes adiposity. Accordingly, suppressing calcitriol levels by increasing dietary calcium is an attractive target for the prevention and management of obesity. In support of this concept, transgenic mice expressing the agouti gene specifically in adipocytes (a humanlike pattern) respond to low calcium diets with accelerated weight gain and fat accretion, whereas high calcium diets markedly inhibit lipogenesis, accelerate lipolysis, increase thermogenesis and suppress fat accretion and weight gain in animals maintained at identical caloric intakes. Further, low calcium diets impede body fat loss, whereas high calcium diets markedly accelerate fat loss in transgenic mice subjected to caloric restriction. Notably, dairy sources of calcium exert markedly greater effects in attenuating weight and fat gain and accelerating fat loss. This augmented effect of dairy vs. supplemental calcium is likely attributable to additional bioactive compounds in dairy that act synergistically with calcium to attenuate adiposity; among these are angiotensin converting enzyme inhibitory peptides, which limit angiotensin II production and thereby limit angiotensin II stimulation of adipocyte lipogenesis. These concepts are confirmed by both epidemiological and clinical data, which similarly demonstrate that dairy products exert a substantially greater effect on both fat loss and fat distribution compared to an equivalent amount of supplemental calcium.

1alpha,25-dihydroxyvitamin D3 inhibits uncoupling protein 2 expression in human adipocytes

We recently demonstrated that suppressing 1alpha,25-(OH)2-D3 by increasing dietary calcium decreases adipocyte intracellular Ca2+ ([Ca2+]i), stimulates lipolysis, and inhibits lipogenesis. High calcium diets also increase core temperature and white adipose tissue uncoupling protein 2 (UCP2) expression in aP2-agouti transgenic mice. Accordingly, we have evaluated the role of 1alpha,25-(OH)2-D3 in regulating human adipocyte UCP2 expression. Treatment of human adipocytes for 48 h with 1 nM 1alpha,25-(OH)2-D3 inhibited UCP2 mRNA and protein levels by 50% (P<0.002) and completely blocked isoproterenol- or fatty acid-stimulated two- to threefold increases in UCP2 expression. However, a specific agonist for the membrane vitamin D receptor (mVDR), 1alpha,25-dihydroxylumisterol3, was unable to inhibit basal, isoproterenol-stimulated, or fatty acid-stimulated UCP2 expression, whereas a specific mVDR antagonist,1beta,25-dihydroxyvitamin D3, was unable to prevent the 1alpha,25-(OH)2-D3 inhibition of UCP2 expression. In contrast, nuclear vitamin D receptor (nVDR) knockout via antisense oligodeoxynucleotide (ODN) prevented the inhibitory effect of 1alpha,25-(OH)2-D3 on adipocyte UCP2 expression and protein levels. These data indicate that 1a,25-(OH)2-D3 exerts an inhibitory effect on adipocyte UCP2 expression via the nVDR. Thus, suppression of 1alpha,25-(OH)2-D3 and consequent up-regulation of UCP2 may contribute to our previous observation of increased thermogenesis in mice fed with high calcium diets.

Body mass index-related human adipocyte agouti expression is sex-specific but not depot-specific

OBJECTIVE

To determine if human adipocyte agouti signal protein (ASIP) mRNA expression is associated with obesity and is gender and/or depot specific.

RESEARCH METHODS AND PROCEDURES

Subjects included 8 men (64 +/- 3 years) and 14 women (56 +/- 15 years) undergoing elective abdominal surgery. ASIP mRNA levels in isolated omental and subcutaneous abdominal adipocytes were measured by quantitative reverse transcription polymerase chain reaction.

RESULTS

No significant depot difference was observed between genders; ASIP mRNA levels of omental and subcutaneous abdominal adipocytes were pooled for this analysis. BMI and ASIP gene expression were negatively correlated in men (rho = -0.70; p < 0.05), whereas a positive relationship was observed in women (rho = 0.48; p < 0.05). No significant difference was observed in age, body weight, body mass index (BMI), and waist circumference between groups. Hip circumference was significantly higher in women than in men (p < 0.05). Also, no significant difference in ASIP mRNA expression was observed between men and women, regardless of the fat depot.

DISCUSSION

These results show that men and women of similar age and BMI present similar ASIP mRNA levels in omental and subcutaneous abdominal adipocytes. However, a sexual dimorphism exists in the relationship between ASIP expression and BMI. If ASIP is involved in appetite regulation or energy homeostasis in humans, this observation may contribute to the recognized differences in these parameters between men and women.

Regulation of adiposity and obesity risk by dietary calcium: mechanisms and implications

Dietary calcium plays a pivotal role in the regulation of energy metabolism; high calcium diets attenuate adipocyte lipid accretion and weight gain during periods of overconsumption of an energy-dense diet and increase lipolysis and preserve thermogenesis during caloric restriction, thereby markedly accelerating weight loss. Intracellular Ca2+ has a key role in regulating adipocyte lipid metabolism and triglyceride storage, with increased intracellular Ca2+ resulting in stimulation of lipogenic gene expression and lipogenesis, suppression of lipolysis, and increased lipid filling and adiposity. Moreover, we have recently demonstrated that the increased calcitriol released in response to low calcium diets stimulates Ca2+ influx in human adipocytes and thereby promotes adiposity. Accordingly, suppressing calcitriol levels by increasing dietary calcium is an attractive target for the prevention and management of obesity. In support of this concept, transgenic mice expressing the agouti gene specifically in adipocytes (a human-like pattern) respond to low calcium diets with accelerated weight gain and fat accretion, while high calcium diets markedly inhibit lipogenesis, accelerate lipolysis, increase thermogenesis and suppress fat accretion and weight gain in animals maintained at identical caloric intakes. Further, low calcium diets impede body fat loss, while high calcium diets markedly accelerate fat loss in transgenic mice subjected to caloric restriction. These findings are further supported by clinical and epidemiological data demonstrating a profound reduction in the odds of being obese associated with increasing dietary calcium intake. Notably, dairy sources of calcium exert a significantly greater anti-obesity effect than supplemental sources in each of these studies, possibly due to the effects of other bioactive compounds, such as the angiotensin converting enzyme inhibitor found in milk, on adipocyte metabolism, indicating an important role for dairy products in the control of obesity.

BHLHB4 is a bHLH transcriptional regulator in pancreas and brain that marks the dimesencephalic boundary

We have cloned a basic helix-loop-helix (bHLH) factor gene, Bhlhb4, from a mouse beta-cell line. Fluorescence in situ hybridization (FISH) and genetic mapping place Bhlhb4 at the telomeric end of mouse chromosome 2 (H3-H4), syntenic to human chromosome 20q13. Based on phylogenetic analysis, BHLHB4 belongs to a new subgroup of bHLH factors including at least four previously identified mouse bHLH factors: BHLHB5, MIST1, OLIG1, OLIG2, and OLIG3. In the developing nervous system, Bhlhb4 was found to mark the dimesencephalic boundary, suggesting that Bhlhb4 may have a role in diencephalic regionalization. In the pancreas, Bhlhb4 is expressed in a transient fashion that suggests a role in the pancreatic endocrine cell lineage. Transfection experiments show that BHLHB4 can repress transcriptional activation mediated through the pancreatic beta-cell specific insulin promoter enhancer RIPE3. Together, these data suggest that BHLHB4 may modulate the expression of genes required for the differentiation and/or maintenance of pancreatic and neuronal cell types.

Agouti: from mouse to man, from skin to fat

The agouti protein regulates pigmentation in the mouse hair follicle producing a black hair with a subapical yellow band. Its effect on pigmentation is achieved by antagonizing the binding of alpha-melanocyte stimulating hormone (alpha-MSH) to melanocortin 1 receptor (Mc1r), switching melanin synthesis from eumelanin (black/brown) to phaeomelanin (red/yellow). Dominant mutations in the non-coding region of mouse agouti cause yellow coat colour and ectopic expression also results in obesity, type 11 diabetes, increased somatic growth and tumourigenesis. At least some of these pleiotropic effects can be explained by antagonism of other members of the melanocortin receptor family by agouti protein. The yellow coat colour is the result of agouti chronically antagonizing the binding of alpha-MSH to Mc1r and the obese phenotype results from agouti protein antagonizing the binding of alpha-MSH to Mc3r and/or Mc4r. Despite the existence of a highly homologous agouti protein in humans, agouti signal protein (ASIP), its role has yet to be defined. However it is known that human ASIP is expressed at highest levels in adipose tissue where it may antagonize one of the melanocortin receptors. The conserved nature of the agouti protein combined with the diverse phenotypic effects of agouti mutations in mouse and the different expression patterns of human and mouse agouti, suggest ASIP may play a role in human energy homeostasis and possibly human pigmentation.

Molecular and phenotypic analysis of 25 recessive, homozygous-viable alleles at the mouse agouti locus

Agouti is a paracrine-acting, transient antagonist of melanocortin 1 receptors that specifies the subapical band of yellow on otherwise black hairs of the wild-type coat. To better understand both agouti structure/function and the germline damage caused by chemicals and radiation, an allelic series of 25 recessive, homozygous-viable agouti mutations generated in specific-locus tests were characterized. Visual inspection of fur, augmented by quantifiable chemical analysis of hair melanins, suggested four phenotypic categories (mild, moderate, umbrous-like, severe) for the 18 hypomorphs and a single category for the 7 amorphs (null). Molecular analysis indicated protein-coding alterations in 8 hypomorphs and 6 amorphs, with mild-moderate phenotypes correlating with signal peptide or basic domain mutations, and more devastating phenotypes resulting from C-terminal lesions. Ten hypomorphs and one null demonstrated wild-type coding potential, suggesting that they contain mutations elsewhere in the > or = 125-kb agouti locus that either reduce the level or alter the temporal/spatial distribution of agouti transcripts. Beyond the notable contributions to the field of mouse germ cell mutagenesis, analysis of this allelic series illustrates that complete abrogation of agouti function in vivo occurs most often through protein-coding lesions, whereas partial loss of function occurs slightly more frequently at the level of gene expression control.

1alpha,25-Dihydroxyvitamin D3 modulates human adipocyte metabolism via nongenomic action

We reported recently that suppression of the renal 1alpha,25-dihyroxyvitamin D3 (1lpha,25-(OH)2-D3) production in aP2-agouti transgenic mice by increasing dietary calcium decreases adipocyte intracellular Ca2+ ([Ca2+]i), stimulates lipolysis, inhibits lipogenesis, and reduces adiposity. However, it was not clear whether this modulation of adipocyte metabolism by dietary calcium is a direct effect of inhibition of 1alpha,25-(OH)2-D3-induced [Ca2+]i. Accordingly, we have now evaluated the direct role of 1alpha,25-(OH)2-D3. Human adipocytes exhibited a 1alpha,25-(OH)2-D3 dose-responsive (1-50 nM) increase in [Ca2+]i (P<0.01). This action was mimicked by 1alpha,25-dihyroxylumisterol3 (1alpha,25-(OH)2-lumisterol3) (P<0.001), a specific agonist for a putative membrane vitamin D receptor (mVDR), and completely prevented by 1b,25-dihydroxyvitamin D3 (1beta,25-(OH)2-D3), a specific antagonist for the mVDR. Similarly, 1alpha,25-(OH)2-D3 (5 nM) caused 50%-100% increases in adipocyte fatty acid synthase (FAS) expression and activity (P<0.02), a 61% increase in glycerol-3-phosphate dehydrogenase (GPDH) activity (P<0.01), and an 80% inhibition of isoproterenol-stimulated lipolysis (P<0.001), whereas 1beta,25-(OH)2-D3 completely blocked all these effects. Notably, 1alpha,25-(OH)2-lumisterol3 exerted more potent effects in modulating adipocyte lipid metabolism, with 2.5- to 3.0-fold increases in FAS expression and activity (P<0.001) and a threefold increase in GPDH activity (P<0.001). Also 1alpha,25-(OH)2-lumisterol3 was approximately twice as potent in inhibiting basal lipolysis (P<0.025), whereas 1beta,25-(OH)2-D3 completely blocked all these effects. These data suggest that 1alpha,25-(OH)2-D3 modulates adipocyte Ca2+ signaling and, consequently, exerts a coordinated control over lipogenesis and lipolysis. Thus, a direct inhibition of 1alpha,25-(OH)2-D3-induced [Ca2+]i may contribute to an anti-obesity effect of dietary calcium, and the mVDR may represent an important target for obesity.

Mechanism of intracellular calcium ([Ca2+]i) inhibition of lipolysis in human adipocytes

We investigated the mechanisms responsible for the anti-lipolytic effect of intracellular Ca2+ ([Ca2+]i) in human adipocytes. Increasing [Ca2+]i inhibited lipolysis induced by b-adrenergic receptor activation, A1 adenosine receptor inhibition, adenylate cyclase activation, and phosphodiesterase (PDE) inhibition, as well as by a hydrolyzable cAMP analog, but not by a nonhydrolyzable cAMP analog. This finding indicates that the anti-lipolytic effect of [Ca2+]i may be mediated by the activation of adipocyte PDE. Consistent with this theory, [Ca2+]i inhibition of isoproterenol-stimulated lipolysis was reversed completely by the nonselective PDE inhibitor isobutyl methylxanthine and also by the selective PDE 3B inhibitor cilostamide, but not by selective PDE 1 and 4 inhibitors. In addition, phosphatidylinositol-3 kinase inhibition with wortmannin completely prevented insulin's anti-lipolytic effect but only minimally blocked [Ca2+]i's effect, which suggests that [Ca2+]i and insulin may activate PDE 3B via different mechanisms. In contrast, the antilipolytic effect of [Ca2+]i was not affected by inhibitors of calmodulin, Ca2+/calmodulin-dependent kinase, protein phosphatase 2B, and protein kinase C. Finally, [Ca2+]i inhibited significantly isoproterenol-stimulated increases in cAMP levels and hormone-sensitive lipase phosphorylation in human adipocytes. In conclusion, increasing [Ca2+]i exerts an antilipolytic effect mainly by activation of PDE, leading to a decrease in cAMP and HSL phosphorylation and, consequently, inhibition of lipolysis.