Effect of statin treatment on metabolites, lipids and prostanoids in patients with Statin Associated Muscle Symptoms (SAMS).

BACKGROUND: Between 5-10% of patients discontinue statin therapy due to statin-associated adverse reactions, primarily statin associated muscle symptoms (SAMS). The absence of a clear clinical phenotype or of biomarkers poses a challenge for diagnosis and management of SAMS. Similarly, our incomplete understanding of the pathogenesis of SAMS hinders the identification of treatments for SAMS. Metabolomics, the profiling of metabolites in biofluids, cells and tissues is an important tool for biomarker discovery and provides important insight into the origins of symptomatology. In order to better understand the pathophysiology of this common disorder and to identify biomarkers, we undertook comprehensive metabolomic and lipidomic profiling of plasma samples from patients with SAMS who were undergoing statin rechallenge as part of their clinical care. METHODS AND FINDINGS: We report our findings in 67 patients, 28 with SAMS (cases) and 39 statin-tolerant controls. SAMS patients were studied during statin rechallenge and statin tolerant controls were studied while on statin. Plasma samples were analyzed using untargeted LC-MS metabolomics and lipidomics to detect differences between cases and controls. Differences in lipid species in plasma were observed between cases and controls. These included higher levels of linoleic acid containing phospholipids and lower ether lipids and sphingolipids. Reduced levels of acylcarnitines and altered amino acid profile (tryptophan, tyrosine, proline, arginine, and taurine) were observed in cases relative to controls. Pathway analysis identified significant increase of urea cycle metabolites and arginine and proline metabolites among cases along with downregulation of pathways mediating oxidation of branched chain fatty acids, carnitine synthesis, and transfer of acetyl groups into mitochondria. CONCLUSIONS: The plasma metabolome of patients with SAMS exhibited reduced content of long chain fatty acids and increased levels of linoleic acid (18:2) in phospholipids, altered energy production pathways (ß-oxidation, citric acid cycle and urea cycles) as well as reduced levels of carnitine, an essential mediator of mitochondrial energy production. Our findings support the hypothesis that alterations in pro-inflammatory lipids (arachidonic acid pathway) and impaired mitochondrial energy metabolism underlie the muscle symptoms of patients with statin associated muscle symptoms (SAMS).

Endothelial Nitric Oxide Synthase-Deficient Mice: A Model of Spontaneous Cerebral Small-Vessel Disease.

Age-related cerebral small-vessel disease (CSVD) is a major cause of stroke and dementia. Despite a widespread acceptance of small-vessel arteriopathy, lacunar infarction, diffuse white matter injury, and cognitive impairment as four cardinal features of CSVD, a unifying pathologic mechanism of CSVD remains elusive. Herein, we introduce partial endothelial nitric oxide synthase (eNOS)-deficient mice as a model of age-dependent, spontaneous CSVD. These mice developed cerebral hypoperfusion and blood-brain barrier leakage at a young age, which progressively worsened with advanced age. Their brains exhibited elevated oxidative stress, astrogliosis, cerebral amyloid angiopathy, microbleeds, microinfarction, and white matter pathology. Partial eNOS-deficient mice developed gait disturbances at middle age, and hippocampus-dependent memory deficits at older ages. These mice also showed enhanced expression of bone morphogenetic protein 4 (BMP4) in brain pericytes before myelin loss and white matter pathology. Because BMP4 signaling not only promotes astrogliogenesis but also blocks oligodendrocyte differentiation, we posit that paracrine actions of BMP4, localized within the neurovascular unit, promote white matter disorganization and neurodegeneration. These observations point to BMP4 signaling pathway in the aging brain vasculature as a potential therapeutic target. Finally, because studies in partial eNOS-deficient mice corroborated recent clinical evidence that blood-brain barrier disruption is a primary cause of white matter pathology, the mechanism of impaired nitric oxide signaling-mediated CSVD warrants further investigation.

Insulin-induced de novo lipid synthesis occurs mainly via mTOR-dependent regulation of proteostasis of SREBP-1c.

Insulin stimulates de novo lipid synthesis in the liver and in cultured hepatocytes via its ability to activate sterol regulatory element-binding protein 1c (SREBP-1c). Although PI3K-AKT-mTORC1-p70S6K-signaling kinases are known to drive feed-forward expression of SREBP-1c, the identity of the phosphorylated amino acid residue(s) putatively involved in insulin-stimulated de novo lipogenesis remains elusive. We obtained in silico and mass spectrometry evidence, that was combined with siRNA strategies, to discover that insulin-induced phosphorylation of serine 418, serine 419, and serine 422 in rat SREBP-1c was most likely mediated by p70S6 kinase. Here, for the first time, we show that insulin-induced phosphorylation of these 3 serine residues mainly impinged on the mechanisms of proteostasis of both full-length and mature SREBP-1c in the McArdle-RH7777 hepatoma cells. Consistent with this conclusion, nascent SREBP-1c, substituted with phosphomimetic aspartic acid residues at these 3 sites, was resistant to proteasomal degradation. As a consequence, endoplasmic reticulum to Golgi migration and proteolytic maturation of pSREBP-1c was significantly enhanced which led to increased accumulation of mature nSREBP-1c, even in the absence of insulin. Remarkably, aspartic acid substitutions at S418, S419 and S422 also protected the nascent SREBP-1c from ubiquitin-mediated proteasome degradation thus increasing its steady-state levels and transactivation potential in the nucleus. These complementary effects of p70S6K-mediated phosphorylation on proteostasis of pSREBP-1c were necessary and sufficient to account for insulin's ability to enhance transcription of genes controlling de novo lipogenesis in hepatocytes.

Phosphorylation dependent proteostasis of sterol regulatory element binding proteins.

Lipid homeostasis is critically dependent on the liver. Hepatic genes involved in lipid biosynthesis are controlled by combinatorial actions of multiple transcription factors that include three sterol regulatory element binding proteins (SREBPs), carbohydrate responsive element binding protein, liver X receptors, and others. SREBP-1c, a seminal regulator of de novo lipogenesis, resides in the endoplasmic reticulum as a transcriptionally inert precursor and must undergo a regulated intramembrane proteolysis (RIP) prior to its nuclear translocation as a bone fide transcription factor. The regulation of biosynthesis, turnover and actions of SREBP-1c and lipogenesis are mechanistically linked to signaling kinases, canonically induced by macronutrients and insulin. Here, we briefly review the evidence showing that phosphorylation of SREBP-1c and its interacting partners, catalyzed by phosphatidyl inositol-3-kinase, protein kinase B, mechanistic target of rapamycin complex 1 and 2, mitogen activated protein kinases, glycogen synthase kinase-3ß, protein kinase A and 5' adenosine monophosphate-activated protein kinase regulates the mechanisms of RIP and stability of SREBP-1c and de novo lipogenesis.

Circadian rhythms of hormone secretion and obesity.

The adipose tissue homeostasis is profoundly affected by circadian rhythms of corticosteroid secretion and chronic loss of hormonal oscillations is associated with obesity. How adipose tissue differentially responds to pulsatile vs continuous presence of glucocorticoids is poorly defined. To address this question, Bahrami-Nejad et al studied differentiation of pre-adipocytes, containing endogenously tagged CCAAT/enhancer binding protein and peroxisome proliferator-activated receptor (PPAR) γ (key regulators of adipocyte differentiation), in response to corticosteroids that were delivered either in an oscillatory fashion or continuously. The authors show that the bi-stable state of differentiation of pre-adipocytes and adipocytes was regulated by a combination of fast and slow positive feedback networks, that determined unique threshold of PPARγ in these cells. Evidently, pre-adipocytes used the fast feedback loop to reject differentiation cues of oscillating pulses of glucocorticoids and failed to differentiate into fat cells. In contrast, when glucocorticoids were delivered continuously, precursor cells exploited the slow feedback loop to embark on a path of maximal differentiation. This differential differentiation response of pre-adipocytes to pulsatile vs continuous exposure to glucocorticoids was corroborated in vivo. Thus, mice receiving non-oscillating doses of exogenous glucocorticoids, for 21 d, elicited excessive accumulation of visceral and subcutaneous fat. These data shed new light on the mechanisms of obesity caused by putative misalignment of circadian secretion of glucocorticoids or their persistently high levels due to chronic stress or Cushing's disease.

Sex-specific differences in hepatic steatosis in obese spontaneously hypertensive (SHROB) rats.

BACKGROUND: Patients with metabolic syndrome, who are characterized by co-existence of insulin resistance, hypertension, hyperlipidemia, and obesity, are also prone to develop non-alcoholic fatty liver disease (NAFLD). Although the prevalence and severity of NAFLD is significantly greater in men than women, the mechanisms by which gender modulates the pathogenesis of hepatic steatosis are poorly defined. The obese spontaneously hypertensive (SHROB) rats represent an attractive model of metabolic syndrome without overt type 2 diabetes. Although pathological manifestation caused by the absence of a functional leptin receptor has been extensively studied in SHROB rats, it is unknown whether these animals elicited sex-specific differences in the development of hepatic steatosis. METHODS: We compared hepatic pathology in male and female SHROB rats. Additionally, we examined key biochemical and molecular parameters of signaling pathways linked with hyperinsulinemia and hyperlipidemia. Finally, using methods of quantitative polymerase chain reaction (qPCR) and western blot analysis, we quantified expression of 45 genes related to lipid biosynthesis and metabolism in the livers of male and female SHROB rats. RESULTS: We show that all SHROB rats developed hepatic steatosis that was accompanied by enhanced expression of SREBP1, SREBP2, ACC1, and FASN proteins. The livers of male rats also elicited higher induction of Pparg, Ppara, Slc2a4, Atox1, Skp1, Angptl3, and Pnpla3 mRNAs. In contrast, the livers of female SHROB rats elicited constitutively higher levels of phosphorylated JNK and AMPK and enhanced expression of Cd36. CONCLUSION: Based on these data, we conclude that the severity of hepatic steatosis in male and female SHROB rats was mainly driven by increased de novo lipogenesis. Moreover, male and female SHROB rats also elicited differential severity of hepatic steatosis that was coupled with sex-specific differences in fatty acid transport and esterification.

Patients experiencing statin-induced myalgia exhibit a unique program of skeletal muscle gene expression following statin re-challenge.

Statins, the 3-hydroxy-3-methyl-glutaryl (HMG)-CoA reductase inhibitors, are widely prescribed for treatment of hypercholesterolemia. Although statins are generally well tolerated, up to ten percent of statin-treated patients experience myalgia symptoms, defined as muscle pain without elevated creatinine phosphokinase (CPK) levels. Myalgia is the most frequent reason for discontinuation of statin therapy. The mechanisms underlying statin myalgia are not clearly understood. To elucidate changes in gene expression associated with statin myalgia, we compared profiles of gene expression in skeletal muscle biopsies from patients with statin myalgia who were undergoing statin re-challenge (cases) versus those of statin-tolerant controls. A robust separation of case and control cohorts was revealed by Principal Component Analysis of differentially expressed genes (DEGs). To identify putative gene expression and metabolic pathways that may be perturbed in skeletal muscles of patients with statin myalgia, we subjected DEGs to Ingenuity Pathways (IPA) and DAVID (Database for Annotation, Visualization and Integrated Discovery) analyses. The most prominent pathways altered by statins included cellular stress, apoptosis, cell senescence and DNA repair (TP53, BARD1, Mre11 and RAD51); activation of pro-inflammatory immune response (CXCL12, CST5, POU2F1); protein catabolism, cholesterol biosynthesis, protein prenylation and RAS-GTPase activation (FDFT1, LSS, TP53, UBD, ATF2, H-ras). Based on these data we tentatively conclude that persistent myalgia in response to statins may emanate from cellular stress underpinned by mechanisms of post-inflammatory repair and regeneration. We also posit that this subset of individuals is genetically predisposed to eliciting altered statin metabolism and/or increased end-organ susceptibility that lead to a range of statin-induced myopathies. This mechanistic scenario is further bolstered by the discovery that a number of single nucleotide polymorphisms (e.g., SLCO1B1, SLCO2B1 and RYR2) associated with statin myalgia and myositis were observed with increased frequency among patients with statin myalgia.

Statins redux: A re-assessment of how statins lower plasma cholesterol.

Obesity associated dyslipidemia and its negative effects on the heart and blood vessels have emerged as a major healthcare challenge around the globe. The use of statins, potent inhibitors of hydroxyl-methyl glutaryl (HMG) Co-A reductase, a rate-limiting enzyme in cholesterol biosynthesis, has significantly reduced the rates of cardiovascular and general mortality in patients with coronary artery disease. How statins lower plasma cholesterol levels presents a mechanistic conundrum since persistent exposure to these drugs in vitro or in vivo is known to induce overexpression of the HMG Co-A reductase gene and protein. In an attempt to solve this mechanistic puzzle, Schonewille et al, studied detailed metabolic parameters of cholesterol synthesis, inter-organ flux and excretion in mice treated with 3 common statins, rosuvastatin, atorvastatin or lovastatin, each with its unique pharmacokinetics. From the measurements of the rates of heavy water (D2O) and [13C]-acetate incorporation into lipids, the authors calculated the rates of whole body and organ-specific cholesterol synthesis in control and statin-treated mice. These analyses revealed dramatic enhancement in the rates of hepatic cholesterol biosynthesis in statin-treated mice that concomitantly elicited lower levels of cholesterol in their plasma. The authors have provided strong evidence to indicate that statin treatment in mice led to induction of compensatory metabolic pathways that apparently mitigated an excessive accumulation of cholesterol in the body. It was noted however that changes in cholesterol metabolism induced by 3 statins were not identical. While sustained delivery of all 3 statins led to enhanced rates of biliary excretion of cholesterol and its fecal elimination, only atorvastatin treated mice elicited enhanced trans-intestinal cholesterol excretion. Thus, blockade of HMGCR by statins in mice was associated with profound metabolic adaptations that reset their cholesterol homeostasis. The findings of Schonewille et al, deserve to be corroborated and extended in patients in order to more effectively utilize these important cholesterol-lowering drugs in the clinic.

Gut-brain crosstalk regulates craving for fatty food.

Patients undergoing Roux-en-Y gastric bypass (RYGB) surgery elicit striking loss of body weight. Anatomical re-structuring of the gastrointestinal (GI) tract, leading to reduced caloric intake and changes in food preference, are thought to be the primary drivers of weight loss in bariatric surgery patients. However, the mechanisms by which RYGB surgery causes a reduced preference for fatty foods remain elusive. In a recent report, Hankir et al described how RYGB surgery modulated lipid nutrient signals in the intestine of rats to blunt their craving for fatty food. The authors reported that RYGB surgery restored an endogenous fat-satiety signaling pathway, mediated via oleoylethanolamide (OEA), that was greatly blunted in obese animals. In RYGB rats, high fat diet (HFD) led to increased production of OEA that activated the intestinal peroxisome proliferation activator receptors-α (PPARα). In RYGB rats, activation of PPARα by OEA was accompanied by enhanced dopamine neurotransmission in the dorsal striatum and reduced preference for HFD. The authors showed that OEA-mediated signals to the midbrain were transmitted via the vagus nerve. Interfering with either the production of OEA in enterocytes, or blocking of vagal and striatal D1 receptors signals eliminated the decreased craving for fat in RYGB rats. These studies demonstrated that bariatric surgery led to alterations in the reward circuitry of the brain in RYGB rats and reduced their preference for HFD.

An 'Omics' Perspective on Cardiomyopathies and Heart Failure.

Pathological enlargement of the heart, represented by hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM), occurs in response to many genetic and non-genetic factors. The clinical course of cardiac hypertrophy is remarkably variable, ranging from lifelong absence of symptoms to rapidly declining heart function and sudden cardiac death (SCD). Unbiased omics studies have begun to provide a glimpse into the molecular framework underpinning altered mechanotransduction, mitochondrial energetics, oxidative stress, and extracellular matrix in the heart undergoing physiological and pathological hypertrophy. Omics analyses indicate that post-transcriptional regulation of gene expression plays an overriding role in the normal and diseased heart. Studies to date highlight a need for more effective bioinformatics to better integrate patient omics data with their comprehensive clinical histories.

Trichostatin A induces a unique set of microRNAs including miR-129-5p that blocks cyclin-dependent kinase 6 expression and proliferation in H9c2 cardiac myocytes.

The pan-histone deacetylase inhibitor (HDACI), trichostatin A (TSA), was shown to normalize interleukin-18-induced cardiac hypertrophy in vivo and in vitro; evidently, this occurred via epigenetic mechanisms that profoundly altered cardiac gene expression (Majumdar et al. in, Physiol Genom, 43: 1392, 2011; BMC Genom, 13: 709, 2012). Here, we tested the hypothesis that TSA-induced changes in chromatin architecture also led to altered expression of microRNAs that in turn, contributed to the unique transcriptome of cardiac myocytes exposed to the HDACI. Using miRCURY LNA™ Universal microRNA PCR system, we demonstrate that H9c2 cells exposed to TSA for 6 and 24 h elicited differential expression of 19 and 16 microRNAs, respectively. H9c2 cells incubated in medium-containing 100 nM of TSA elicited a rapid and robust induction of miR-129-5p. Enhanced expression of miR-129-5p was also observed in the hearts of TSA-treated mice. Induction of miR-129-5p in H9c2 cells was accompanied by reduced expression of its direct target, cyclin-dependent kinase 6 (CDK6) that is a key regulator of cell cycle. Using cell division-dependent dilution of Cell Trace™ violet measurements we showed that concomitant induction of miR-129-5p and reduced CDK6 expression were mechanistically involved in TSA-induced inhibition of proliferation of H9c2 cells. Consistent with this scenario, cells expressing an antagomiR of miR-129-5p were resistant to the anti-proliferative actions of TSA. These data indicate that although TSA treatment led to altered expression of several microRNAs, the overarching action of TSA (i.e., inhibition of cell division) in H9c2 cells was achieved via miR-129-5p.

Glycogen synthase kinase-3-mediated phosphorylation of serine 73 targets sterol response element binding protein-1c (SREBP-1c) for proteasomal degradation.

Sterol regulatory element binding protein-1c (SREBP-1c) is a key transcription factor that regulates genes involved in the de novo lipid synthesis and glycolysis pathways. The structure, turnover and transactivation potential of SREBP-1c are regulated by macronutrients and hormones via a cascade of signalling kinases. Using MS, we have identified serine 73 as a novel glycogen synthase kinase-3 (GSK-3) phosphorylation site in the rat SREBP-1c purified from McA-RH7777 hepatoma cells. Our site-specific mutagenesis strategy revealed that the turnover of SREBP-1c, containing wild type, phospho-null (serine to alanine) or phospho-mimetic (serine to aspartic acid) substitutions, was differentially regulated. We show that the S73D mutant of pSREBP-1c, that mimicked a state of constitutive phosphorylation, dissociated from the SREBP-1c-SCAP complex more readily and underwent GSK-3-dependent proteasomal degradation via SCF(Fbw7) ubiquitin ligase pathway. Pharmacologic inhibition of GSK-3 or knockdown of GSK-3 by siRNA prevented accelerated degradation of SREBP-1c. As demonstrated by MS, SREBP-1c was phosphorylated in vitro by GSK-3ß at serine 73. Phosphorylation of serine 73 also occurs in the intact liver. We propose that GSK-3-mediated phosphorylation of serine 73 in the rat SREBP-1c and its concomitant destabilization represents a novel mechanism involved in the inhibition of de novo lipid synthesis in the liver.

Docosahexaenoic acid inhibits proteolytic processing of sterol regulatory element-binding protein-1c (SREBP-1c) via activation of AMP-activated kinase.

In hyperinsulinemic states including obesity and T2DM, overproduction of fatty acid and triglyceride contributes to steatosis of the liver, hyperlipidemia and hepatic insulin resistance. This effect is mediated in part by the transcriptional regulator sterol responsive element binding protein-1c (SREBP-1c), which stimulates the expression of genes involved in hepatic fatty acid and triglyceride synthesis. SREBP-1c is up regulated by insulin both via increased transcription of nascent full-length SREBP-1c and by enhanced proteolytic processing of the endoplasmic reticulum (ER)-bound precursor to yield the transcriptionally active n-terminal form, nSREBP-1c. Polyunsaturated fatty acids of marine origin (n-3 PUFA) prevent induction of SREBP-1c by insulin thereby reducing plasma and hepatic triglycerides. Despite widespread use of n-3 PUFA supplements to reduce triglycerides in clinical practice, the exact mechanisms underlying their hypotriglyceridemic effect remain elusive. Here we demonstrate that the n-3 PUFA docosahexaenoic acid (DHA; 22:5 n-3) reduces nSREBP-1c by inhibiting regulated intramembrane proteolysis (RIP) of the nascent SREBP-1c. We further show that this effect of DHA is mediated both via activation of AMP-activated protein kinase (AMPK) and by inhibition of mechanistic target of rapamycin complex 1 (mTORC1). The inhibitory effect of AMPK on SREBP-1c processing is linked to phosphorylation of serine 365 of SREBP-1c in the rat. We have defined a novel regulatory mechanism by which n-3 PUFA inhibit induction of SREBP-1c by insulin. These findings identify AMPK as an important negative regulator of hepatic lipid synthesis and as a potential therapeutic target for hyperlipidemia in obesity and T2DM.

Ménage-à-trois of bariatric surgery, bile acids and the gut microbiome.

Bariatric surgeries have emerged as highly effective treatments for obesity associated type-2 diabetes mellitus. Evidently, the desired therapeutic endpoints such as rates of weight loss, lower levels of glycated hemoglobin and remission of diabetes are achieved more rapidly and last longer following bariatric surgery, as opposed to drug therapies alone. In light of these findings, it has been suspected that in addition to causing weight loss dependent glucose intolerance, bariatric surgery induces other physiological changes that contribute to the alleviation of diabetes. However, the putative post-surgical neuro-hormonal pathways that underpin the therapeutic benefits of bariatric surgery remain undefined. In a recent report, Ryan and colleagues shed new light on the potential mechanisms that determine the salutary effects of bariatric surgery in mice. The authors demonstrated that the improved glucose tolerance and weight loss in mice after vertical sleeve gastrectomy (VSG) surgery were likely to be caused by post-surgical changes in circulating bile acids and farnesoid-X receptor (FXR) signaling, both of which were also mechanistically linked to changes in the microbial ecology of the gut. The authors arrived at this conclusion from a comparison of genome-wide, metabolic consequences of VSG surgery in obese wild type (WT) and FXR knockout mice. Gene expression in the distal small intestines of WT and FXR knockout mice revealed that the pathways regulating bile acid composition, nutrient metabolism and anti-oxidant defense were differentially altered by VSG surgery in WT and FXR(-/-) mice. Based on these data Ryan et al, hypothesized that bile acid homeostasis and FXR signaling were mechanistically linked to the gut microbiota that played a role in modulating post-surgical changes in total body mass and glucose tolerance. The authors' data provide a plausible explanation for putative weight loss-independent benefits of bariatric surgery and its relationship with metabolism of bile acids.

A streamlined protocol for extracting RNA and genomic DNA from archived human blood and muscle.

We combined the TRIzol method of nucleic acid extraction with QIAamp columns to achieve coextraction of RNA and genomic DNA from peripheral blood mononuclear cells (PBMCs) and biopsied skeletal muscle, both stored at -80 °C for many months. Total RNA was recovered from the upper aqueous phase of TRIzol. The interphase and organic phases were precipitated with ethanol, digested with proteinase K, and filtered through QIAamp MinElute columns to recover DNA. The combined protocol yielded excellent quality and quantity of nucleic acids from archived human PBMCs and muscle and may be easily adapted for other tissues.

Phosphorylation of sterol regulatory element binding protein-1a by protein kinase A (PKA) regulates transcriptional activity.

The counter-regulatory hormone glucagon inhibits lipogenesis via downregulation of sterol regulatory element binding protein 1 (SREBP-1). The effect of glucagon is mediated via protein kinase A (PKA). To determine if SREBP-1 is a direct phosphorylation target of PKA, we conducted mass spectrometry analysis of recombinant n-terminal SREBP-1a following PKA treatment in vitro. This analysis identified serines 331/332 as bona-fide phosphorylation targets of PKA. To determine the functional consequences of phosphorylation at these sites, we constructed mammalian expression vector for both nSREBP-1a and 1c isoforms in which the candidate PKA phosphorylation sites were mutated to active phosphomimetic or non-phosphorylatable amino acids. The transcriptional activity of SREBP was reduced by the phosphomimetic mutation of S332 of nSREBP-1a and the corresponding serine (S308) of nSREBP-1c. This site is a strong candidate for mediating the negative regulatory effect of glucagon on SREBP-1 and lipogenesis.

Bariatric surgery-mediated weight loss and its metabolic consequences for type-2 diabetes.

The worldwide epidemic of obesity and its medical complications are being dealt with a combination of life style changes (e.g., healthier diet and exercise), medications and a variety of surgical interventions. The Roux-en Y gastric bypass (RYGB) and laparoscopic adjustable gastric banding (LAGB) are two of the most common weight loss surgeries for morbid obesity-associated metabolic syndrome and insulin resistance. A vast majority of patients that undergo RYGB and LAGB are known to experience marked weight loss and attenuation of diabetes. A number of recent studies have indicated that the rates of remission in glycemic control and insulin sensitivity are significantly greater in patients that have undergone RYGB. A plausible hypothesis to explain this observation is that the gastric bypass surgery as opposed to the gastric banding procedure impinges on glucose homeostasis by a weight loss-independent mechanism. In a recent paper, Bradley et al have experimentally explored this hypothesis. The authors compared several clinical and laboratory parameters of insulin sensitivity and ß-cell function in cohorts of RYGB and LAGB patients before and after they lost approximately 20% of their body mass. After weight loss, both groups of patients underwent similar changes in their intra-abdominal and total adipose tissue volume, hepatic triglyceride and circulating leptin levels. The RYGB patients who lost 20% body mass, manifested higher postprandial output of glucose, insulin and glucagon-like peptide-1; these laboratory parameters remained unchanged in LABG patients. Irrespective of the observed differences in transient responses of RYGB and LAGB patients to mixed meal, the overall glycemic control as judged by glucose tolerance, multi-organ insulin sensitivity and ß-cell function were nearly identical in the two groups. Both RYGB and LAGB patient cohorts also experienced similar changes in the expression of a number of pro- and anti-inflammatory markers. Based on these analyses, Bradley et al concluded that similar restoration of insulin sensitivity and b-cell function in non-diabetic obese patients that have undergone RYGB and LAGB were directly due to marked weight loss. These data have important implications for the risk/benefit analysis of weight loss therapy by bariatric procedures.

Betatrophin: A liver-derived hormone for the pancreatic ß-cell proliferation.

The pancreatic ß-cell failure which invariably accompanies insulin resistance in the liver and skeletal muscle is a hallmark of type-2 diabetes mellitus (T2DM). The persistent hyperglycemia of T2DM is often treated with anti-diabetic drugs with or without subcutaneous insulin injections, neither of which mimic the physiological glycemic control seen in individuals with fully functional pancreas. A sought after goal for the treatment of T2DM has been to harness the regenerative potential of pancreatic ß-cells that might obviate a need for exogenous insulin injections. A new study towards attaining this aim was reported by Yi et al, who have characterized a liver-derived protein, named betatrophin, capable of inducing pancreatic ß-cell proliferation in mice. Using a variety of in vitro and in vivo methods, Yi et al, have shown that betatrophin was expressed mainly in the liver and adipose tissue of mice. Exogenous expression of betatrophin in the liver led to dramatic increase in the pancreatic ß-cell mass and higher output of insulin in mice that also concomitantly elicited improved glucose tolerance. The authors discovered that betatrophin was also present in the human plasma. Surprisingly, betatrophin has been previously described by three other names, i.e., re-feeding-induced fat and liver protein, lipasin and atypical angiopoeitin-like 8, by three independent laboratories, as nutritionally regulated liver-enriched factors that control serum triglyceride levels and lipid metabolism. Yi et al demonstration of betatrophin, as a circulating hormone that regulates ß-cell proliferation, if successfully translated in the clinic, holds the potential to change the course of current therapies for diabetes.

Pan-histone deacetylase inhibitors regulate signaling pathways involved in proliferative and pro-inflammatory mechanisms in H9c2 cells.

BACKGROUND: We have shown previously that pan-HDAC inhibitors (HDACIs) m-carboxycinnamic acid bis-hydroxamide (CBHA) and trichostatin A (TSA) attenuated cardiac hypertrophy in BALB/c mice by inducing hyper-acetylation of cardiac chromatin that was accompanied by suppression of pro-inflammatory gene networks. However, it was not feasible to determine the precise contribution of the myocytes- and non-myocytes to HDACI-induced gene expression in the intact heart. Therefore, the current study was undertaken with a primary goal of elucidating temporal changes in the transcriptomes of cardiac myocytes exposed to CBHA and TSA. RESULTS: We incubated H9c2 cardiac myocytes in growth medium containing either of the two HDACIs for 6h and 24h and analyzed changes in gene expression using Illumina microarrays. H9c2 cells exposed to TSA for 6h and 24h led to differential expression of 468 and 231 genes, respectively. In contrast, cardiac myocytes incubated with CBHA for 6h and 24h elicited differential expression of 768 and 999 genes, respectively. We analyzed CBHA- and TSA-induced differentially expressed genes by Ingenuity Pathway (IPA), Kyoto Encyclopedia of Genes and Genomes (KEGG) and Core_TF programs and discovered that CBHA and TSA impinged on several common gene networks. Thus, both HDACIs induced a repertoire of signaling kinases (PTEN-PI3K-AKT and MAPK) and transcription factors (Myc, p53, NFkB and HNF4A) representing canonical TGFß, TNF-α, IFNγ and IL-6 specific networks. An overrepresentation of E2F, AP2, EGR1 and SP1 specific motifs was also found in the promoters of the differentially expressed genes. Apparently, TSA elicited predominantly TGFß- and TNF-α-intensive gene networks regardless of the duration of treatment. In contrast, CBHA elicited TNF-α and IFNγ specific networks at 6 h, followed by elicitation of IL-6 and IFNγ-centered gene networks at 24h. CONCLUSIONS: Our data show that both CBHA and TSA induced similar, but not identical, time-dependent, gene networks in H9c2 cardiac myocytes. Initially, both HDACIs impinged on numerous genes associated with adipokine signaling, intracellular metabolism and energetics, and cell cycle. A continued exposure to either CBHA or TSA led to the emergence of a number of apoptosis- and inflammation-specific gene networks that were apparently suppressed by both HDACIs. Based on these data we posit that the anti-inflammatory and anti-proliferative actions of HDACIs are myocyte-intrinsic. These findings advance our understanding of the mechanisms of actions of HDACIs on cardiac myocytes and reveal potential signaling pathways that may be targeted therapeutically.

Metabolic balancing acts of vitamin A in type-2 diabetes and obesity.

Using mice that lack retinaldehyde dehydrogenase 1 gene (Raldh1-/- mice), Kierfer et al demonstrated that retinoids (metabolites of Vitamin A) play an important role in the regulation of cellular metabolisms and energetics. The Aldh1a1-/- mice were leaner and less prone to accumulate subcutaneous and visceral fat, and to acquire insulin resistance on high fat diet. Their lower fasting glucose levels concomitant with reduced hepatic expression of glucose 6-phosphatase and phosphoenol pyruvate carboxy kinase genes indicated that Aldh1a1-/- mice were defective in gluconeogenesis. These mice also had lower plasma levels of triglycerides, very low-density lipoprotein and low-density lipoprotein-triacylglycerol, while their skeletal muscles elicited higher expression of carnitine palmatoyl transferase, medium chain acyl-A dehydrogenase, peroxisome proliferation activated receptor (PPARα and PPARδ. Thus, the improved lipid and lipoprotein profiles of Raldh1a1-/- mice resulted from a combination of reduced lipogenesis and enhanced fatty acid oxidation by retinoids. The mechanistic details of how retinoids integrate fasting glucose, hepatic gluconeogenesis and adaptive thermogenesis independent of body mass deserve further study.