Ceramide profiles in the brain of rats with diabetes induced by streptozotocin

Ceramides are fuel gauges on the drive to cardiometabolic disease

Ceramides are signals of fatty acid excess that accumulate when a cell's energetic needs have been met and its nutrient storage has reached capacity. As these sphingolipids accrue, they alter the metabolism and survival of cells throughout the body including in the heart, liver, blood vessels, skeletal muscle, brain, and kidney. These ceramide actions elicit the tissue dysfunction that underlies cardiometabolic diseases such as diabetes, coronary artery disease, metabolic-associated steatohepatitis, and heart failure. Here, we review the biosynthesis and degradation pathways that maintain ceramide levels in normal physiology and discuss how the loss of ceramide homeostasis drives cardiometabolic pathologies. We highlight signaling nodes that sense small changes in ceramides and in turn reprogram cellular metabolism and stimulate apoptosis. Finally, we evaluate the emerging therapeutic utility of these unique lipids as biomarkers that forecast disease risk and as targets of ceramide-lowering interventions that ameliorate disease.

Exploring the mechanisms of clozapine-induced blood-brain barrier dysfunction using untargeted metabolomics and cellular metabolism analysis

Brain microvascular endothelial cells (BMVECs) from the blood- brain barrier form a highly selective membrane that protects the brain from circulating blood and maintains a stable microenvironment for the central nervous system. BMVEC dysfunction has been implicated in a variety of neurological and psychiatric disorders. Clozapine, a widely used antipsychotics, has been demonstrated to alter the permeability of BMVECs, but the underlying mechanisms of this effect are not fully understood. In this study, we investigated the effects of clozapine in BMVECs using untargeted metabolomics analysis. Our results illustrated that treatment with clozapine led to significant changes in the metabolic profile of BMVECs, including alterations in amino acid and energy metabolism. These findings suggest that clozapine affects BMVEC permeability through its effects on cellular metabolism. Our study could inform the development of more targeted and effective treatments for understanding the relationships among clozapine, cellular metabolism, and BMVECs in more detail.

Lipid peroxidation and sphingolipid alterations in the cerebral cortex and hypothalamus of rats fed a high-protein diet

OBJECTIVES

High-protein diets (HPDs) are widely accepted to enhance satiety and energy expenditure and thus have become a popular strategy to lose weight and facilitate muscle protein synthesis. However, long-term high-protein consumption could be linked with metabolic and clinical problems such as renal and liver dysfunctions. This study verified the effects of 8-wk high-protein ingestion on lipid peroxidation and sphingolipid metabolism in the plasma, cerebral cortex, and hypothalamus in rats.

METHODS

Immunoenzymatic and spectrophotometric methods were applied to assess oxidation-reduction (redox) biomarkers and neutral sphingomyelinase activity, whereas gas-liquid chromatography and high-performance liquid chromatography were used to examine sphingolipid levels.

RESULTS

The vast majority of HPD-related alterations was restricted to the hypothalamus. Specifically, an increased rate of lipid peroxidation (increased lipid hydroperoxides, 8-isoprostanes, and thiobarbituric acid reactive substances) associated with ceramide accumulation via the activation of de novo synthesis (decreased sphinganine), salvage pathway (decreased sphingosine), and sphingomyelin hydrolysis (decreased sphingomyelin and increased neutral sphingomyelinase activity) was noted.

CONCLUSIONS

This study showed that HPD substantially affected hypothalamic metabolic pathways, which potentially alter cerebral output signals to the peripheral tissues.

Maternal diets affected ceramides and fatty acids in brain regions of neonatal rats with prenatal ethanol exposure

Objectives: Ceramide (Cer), known as apoptotic markers, increases with prenatal ethanol (EtOH) exposure, resulting in neuroapoptosis. Whether maternal nutrition can impact Cer concentrations in brain, via altering plasma and brain fatty acid compositions have not been examined. This study compared a standard chow with a formulated semi-purified energy dense (E-dense) diet on fatty acid composition, Cer concentrations, and apoptosis in plasma and brain regions (cortex, cerebellum, and hippocampus) of pups exposed to EtOH during gestation. Methods: Pregnant Sprague-Dawley rats were randomized into four groups: chow (n = 6), chow + EtOH (20% v/v) (n = 7), E-dense (n = 6), and E-dense + EtOH (n = 8). At postnatal day 7, representing the peak brain growth spurt in rats, lipids, and apoptosis were analyzed by gas chromatography and a fluorometric caspase-3 assay kit, respectively. Results: Maternal E-dense diet increased total fatty acid concentrations (p < 0.0001), including docosahexaenoic acid (DHA) (p < 0.0001) in plasma, whereas DHA concentrations were decreased in the cerebellum (p < 0.03) of pups than those from chow-fed dams. EtOH-induced Cer elevations in the hippocampus of pups born to dams fed chow were reduced by an E-dense diet (p < 0.02). No significant effects of maternal diet quality and EtOH were observed on caspase-3 activity. No significant correlations existed between plasma/brain fatty acids and Cer concentrations. Discussions: Maternal diet quality affected fatty acid compositions and Cer concentrations of pups with prenatal EtOH exposure, differently. Maternal nutrition has the potential to prevent or alleviate some of the adverse effects of prenatal EtOH exposure.

Contribution of specific ceramides to obesity-associated metabolic diseases

Ceramides are a heterogeneous group of bioactive membrane sphingolipids that play specialized regulatory roles in cellular metabolism depending on their characteristic fatty acyl chain lengths and subcellular distribution. As obesity progresses, certain ceramide molecular species accumulate in metabolic tissues and cause cell-type-specific lipotoxic reactions that disrupt metabolic homeostasis and lead to the development of cardiometabolic diseases. Several mechanisms for ceramide action have been inferred from studies in vitro, but only recently have we begun to better understand the acyl chain length specificity of ceramide-mediated signaling in the context of physiology and disease in vivo. New discoveries show that specific ceramides affect various metabolic pathways and that global or tissue-specific reduction in selected ceramide pools in obese rodents is sufficient to improve metabolic health. Here, we review the tissue-specific regulation and functions of ceramides in obesity, thus highlighting the emerging concept of selectively inhibiting production or action of ceramides with specific acyl chain lengths as novel therapeutic strategies to ameliorate obesity-associated diseases.

Sphingomyelin profiling in patients with diabetes could be potentially useful as differential diagnostics biomarker: A pilot study

PURPOSE

Autoimmune diabetes (AD) in adults includes both the classical form of type 1 diabetes mellitus (T1DM) and latent autoimmune diabetes in adults (LADA). LADA shares clinical and metabolic features with type 1 and type 2 diabetes mellitus (T2DM). Ceramide (Cer) levels negatively correlate with insulin sensitivity in humans and animal models. However, only a few studies have focused on other sphingolipids, including sphingomyelin (SM). Therefore, we determined sphingolipids in patients with newly diagnosed diabetes as possible diagnostic biomarkers.

MATERIALS AND METHODS

We evaluated sphingolipids in a cohort of 59 adults with newly diagnosed diabetes without prior hypoglycemic pharmacotherapy to distinguish diabetes mellitus types and for precise LADA definition. All patients with newly diagnosed diabetes were tested for the concentrations of individual Cer and SM species by gas-liquid chromatography. The study included healthy controls and patients with T1DM, T2DM and LADA.

RESULTS

SM species were significantly altered in patients with newly diagnosed diabetes compared to healthy controls. SM-C16:0, C16:1, -C18:0, -C18:1, -C18:2, -C18:3, -C20:4, and -C22:6 species were found to be significantly elevated in LADA patients. In contrast, significant differences were observed for Cer species with saturated acyl chains, especially Cer-C14:0, -C16:0, -C18:0 (AD and T2DM), -C22:0, and -C24:0 (T1DM). Following ROC analysis, SM-C16:0, and particularly -C18:1, and -C20:4 may be supportive diagnostic markers for LADA.

CONCLUSION

SM profiling in patients with newly diagnosed diabetes could be potentially helpful for differential diagnosis of LADA, T1DM, and T2DM in more challenging cases.

Small Molecule Inhibitors Targeting Biosynthesis of Ceramide, the Central Hub of the Sphingolipid Network

Ceramides are composed of a sphingosine and a single fatty acid connected by an amide linkage. As one of the major classes of biologically active lipids, ceramides and their upstream and downstream metabolites have been implicated in several pathological conditions including cancer, neurodegeneration, diabetes, microbial pathogenesis, obesity, and inflammation. Consequently, tremendous efforts have been devoted to deciphering the dynamics of metabolic pathways involved in ceramide biosynthesis. Given that several distinct enzymes can produce ceramide, different enzyme targets have been pursued depending on the underlying disease mechanism. The main objective of this review is to provide a comprehensive overview of small molecule inhibitors reported to date for each of these ceramide-producing enzymes from a medicinal chemistry perspective.

Low basal metabolic rate as a risk factor for development of insulin resistance and type 2 diabetes

INTRODUCTION

Identification of physiological factors influencing susceptibility to insulin resistance and type 2 diabetes (T2D) remains an important challenge for biology and medicine. Numerous studies reported energy expenditures as one of those components directly linked to T2D, with noticeable increase of basal metabolic rate (BMR) associated with the progression of insulin resistance. Conversely, the putative link between genetic, rather than phenotypic, determination of BMR and predisposition to development of T2D remains little studied. In particular, low BMR may constitute a considerable risk factor predisposing to development of T2D.

RESEARCH DESIGN AND METHODS

We analyzed the development of insulin resistance and T2D in 20-week-old male laboratory mice originating from three independent genetic line types. Two of those lines were subjected to divergent, non-replicated selection towards high or low body mass-corrected BMR. The third line type was non-selected and consisted of randomly bred animals serving as an outgroup (reference) to the selected line types. To induce insulin resistance, mice were fed for 8 weeks with a high fat diet; the T2D was induced by injection with a single dose of streptozotocin and further promotion with high fat diet. As markers for insulin resistance and T2D advancement, we followed the changes in body mass, fasting blood glucose, insulin level, lipid profile and mTOR expression.

RESULTS

We found BMR-associated differentiation in standard diabetic indexes between studied metabolic lines. In particular, mice with low BMR were characterized by faster body mass gain, blood glucose gain and deterioration in lipid profile. In contrast, high BMR mice were characterized by markedly higher expression of the mTOR, which may be associated with much slower development of T2D.

CONCLUSIONS

Our study suggests that genetically determined low BMR makeup involves metabolism-specific pathways increasing the risk of development of insulin resistance and T2D.

Selected elements of extracellular matrix of the skin in diabetes and insulin resistance

PURPOSE

Reconstruction of the skin extracellular matrix is a physiological phenomenon occurring on a continuous basis. The aim of this study is to evaluate the content of basic enzymes preventing oxidative stress: superoxide dismutase 2 and 3 as well as catalase, the content of hyaluronic acid, and the activity of N-acetyl-β-d-hexosaminidase and β-d-glucuronidase in the skin of rats used as animal models of diabetes and insulin resistance, before and after the treatment.

MATERIALS AND METHODS

The study was conducted on a group of sexually mature male Wistar rats divided into 7 groups of 10 animals. Insulin resistance was induced by feeding the rats with a high-fat diet, and diabetes was induced by a single injection of streptozotocin. Chosen groups of rats were treated with insulin or metformin. After 8 weeks, we excised a fragment of shaved dorsal skin from anesthetized rats in each group.

RESULTS

In the course of diabetes and insulin resistance, an intensified defensive activity of cells against the oxidative stress was observed in the undamaged skin, expressed by an increase in the relative content of superoxide dismutase 2 and 3, catalase and the activity of N-acetyl-β-d-hexosaminidase and β-d-glucuronidase. Diabetes and insulin resistance cause similar skin damage, as there are no differences in the relative contents or specific activities of the examined parameters.

CONCLUSIONS

Insulin and metformin improve the quality of the skin in rats with diabetes and insulin resistance, by restoring the content of hyaluronic acid to the healthy skin level.

Feeding Stimulates Sphingosine-1-Phosphate Mobilization in Mouse Hypothalamus

Previous studies have shown that the sphingolipid-derived mediator sphingosine-1-phosphate (S1P) reduces food intake by activating G protein-coupled S1P receptor-1 (S1PR1) in the hypothalamus. Here, we examined whether feeding regulates hypothalamic mobilization of S1P and other sphingolipid-derived messengers. We prepared lipid extracts from the hypothalamus of C57Bl6/J male mice subjected to one of four conditions: free feeding, 12 h fasting, and 1 h or 6 h refeeding. Liquid chromatography/tandem mass spectrometry was used to quantify various sphingolipid species, including sphinganine (SA), sphingosine (SO), and their bioactive derivatives SA-1-phosphate (SA1P) and S1P. In parallel experiments, transcription of S1PR1 (encoded in mice by the S1pr1 gene) and of key genes of sphingolipid metabolism (Sptlc2, Lass1, Sphk1, Sphk2) was measured by RT-PCR. Feeding increased levels of S1P (in pmol-mg⁻¹ of wet tissue) and SA1P. This response was accompanied by parallel changes in SA and dihydroceramide (d18:0/18:0), and was partially (SA1P) or completely (S1P) reversed by fasting. No such effects were observed with other sphingolipid species targeted by our analysis. Feeding also increased transcription of Sptlc2, Lass1, Sphk2, and S1pr1. Feeding stimulates mobilization of endogenous S1PR1 agonists S1P and SA1P in mouse hypothalamus, via a mechanism that involves transcriptional up-regulation of de novo sphingolipid biosynthesis. The results support a role for sphingolipid-mediated signaling in the central control of energy balance.

Counter effects of Asiaticosids-D through putative neurotransmission on rotenone induced cerebral ganglionic injury in Lumbricus terrestris

Asiaticoside-D (AD) was shown to efficacy of ganglionic degenerated Lumbricus terrestris as a pioneering observation in our earlier research. Though, extract molecular mechanisms of AD for degenerative diseases (DDs) remains largely unknown. We investigated the neuroprotective effects of AD against ROT in cerebral ganglions (CGs) of degenerative L. terrestris. Worms were exposed to 0.4 ppm ROT for 7 days were subjected to co- treatment with 15 ppm of AD. After, CGs was removed. The levels oxidant, non-antioxidant, antioxidant status, ganglioside, ceramide and ceramide glycanase (CGase) were estimated. The m-RNA levels of dopamine transporter (DAT), octopamine transporter (OAT), innexins-9 (inx-9), ionotropic glutamate receptor 3 (iGlu3), heat shock proteins (hsp70), XPRLamide neuropeptide precursor, tyramine beta-hydroxylase (tbh-1) and β- adrenergic receptor kinase-2 (β-ARK2-3) by semi-qRT- PCR. The expression pattern of tyramine beta hydroxylase (TBH), glutamate receptor (iGluR), serotonin transporter (SERT), dopamine transporters (DAT), nerve growth factors (NGF), cytochrome C oxidase (COC), NADH dehydogenase subunit-1 (ND-1), neurotrophin receptor p75 (p75NTR), neuronal nitric oxiside synthase (nNOs) interleukin 1- beta (IL1-β) and tumor necrosis factor alpha (TNF-α) by western blotting. Glutaminergic, serotogenic and dopaminergic toxicity variations were also performed. The levels of oxidant, non-antioxidant, antioxidant status, lipids, proteins and m-RNAs were significantly altered (p < 0.001) on ROT-induced (group II) and their levels were significantly changes (p < 0.05) by ROT+AD in CGs. The sensitive study plan concluded the neuroprotective effects of AD against ROT induced degeneration in worms and suggest that the AD deserves future studies for its use as an effective alternative medicine that could minimize the morbidity of ganglionic degenerative diseases patients.

Beta adrenoceptor blockade ameliorates impaired glucose tolerance and alterations of the cerebral ceramide metabolism in an experimental model of ischemic stroke

Background:

Sphingolipids are versatile signaling molecules derived from membrane lipids of eukaryotic cells. Ceramides regulate cellular processes such as proliferation, differentiation and apoptosis and are involved in cellular stress responses. Experimental evidence suggests a pivotal role of sphingolipids in the pathogenesis of cardiovascular diseases, including ischemic stroke. A neuroprotective effect has been shown for beta-adrenergic antagonists in rodent stroke models and supported by observational clinical data. However, the exact underlying pathophysiological mechanisms are still under investigation. We aimed to examine the influence of propranolol on the ceramide metabolism in the stroke-affected brain.

Methods:

Mice were subjected to 60 or 180 min transient middle cerebral artery occlusion (tMCAO) and infarct size, functional neurological deficits, glucose tolerance, and brain ceramide levels were assessed after 12, 24, and 72 h to evaluate whether the latter two processes occur in a similar time frame. Next, we assessed the effects of propranolol (10 mg/kg bw) at 0, 4 and 8 h after tMCAO and FTY720 (fingolimod; 1 mg/kg) on infarct size, functional outcome, immune cell counts and brain ceramide levels at 24 h after 60 min tMCAO.

Results:

We found a temporal coincidence between stroke-associated impaired glucose tolerance and brain ceramide accumulation. Whereas propranolol reduced ischemic lesion size, improved functional outcome and reduced brain ceramide accumulation without an effect on circulating immune cells, FTY720 showed the known neuroprotective effect and strong reduction of circulating immune cells without affecting brain ceramide accumulation.

Conclusions:

Propranolol ameliorates both stroke-associated impairment of glucose tolerance and brain ceramide accumulation which are temporally linked, strengthening the evidence for a role of the sympathetic nervous system in regulating post-stroke glucose metabolism and its metabolic consequences in the brain.

Myriocin treatment affects lipid metabolism in skeletal muscles of rats with streptozotocin-induced type 1 diabetes

PURPOSE

The aim of this work was to assess the effect(s) of de novo ceramide synthesis inhibition on lipid metabolism in skeletal muscle tissue of type 1 diabetic rats. The latter seems to be of vital importance, since previous works have shown its positive influence on lipid metabolism and glucose homeostasis in the case of its counterpart - type 2 diabetes.

MATERIALS/METHODS

The animals were randomly assigned to one of the following groups: C - control, M - myriocin (ceramide de novo synthesis inhibitor), D - diabetes (induced by streptozotocin injections); D+M - diabetes+myriocin. We have evaluated intracellular concentration of key sphingolipid species, via chromatography (GC and HPLC), and the activity of their most important enzymes, using radiometric approach. The aforementioned assessments were evaluated in respect to the three different types of muscle tissue representing different spectra of muscle metabolism (soleus - oxidative, red gastrocnemious - oxidative-glycolytic, white gastrocnemious - glycolytic).

RESULTS

Interestingly, our therapeutic intervention not only lowered the level of ceramide, its precursors (sphinganine) and derivatives (sphingosine and sphingosine-1-phosphate), but also reduced other lipid species (triacylglycerols, diacylglycerols and free fatty acids) content, thus improving glucose homeostasis in type 1 diabetic animals.

CONCLUSIONS

In the light of the results ensuing from this study, it seems conceivable that the reduction of intramuscular ceramide production and accumulation could bestow an insulin-sensitizing effect. If so, then SPT inhibition could find potential future applications as a therapeutic intervention aimed to mitigate the effects of insulin resistance.

Changes in the Diaphragm Lipid Content after Administration of Streptozotocin and High-Fat Diet Regime

The diaphragm is a dome-shaped skeletal muscle indispensable for breathing. Its activity contributes up to 70% of the total ventilatory function at rest. In comparison to other skeletal muscles, it is distinguished by an oxidative phenotype and uninterrupted cyclic contraction pattern. Surprisingly, the research regarding diaphragm diabetic phenotype particularly in the light of lipid-induced insulin resistance is virtually nonexistent. Male Wistar rats were randomly allocated into 3 groups: control, streptozotocin-induced (STZ) type-1 diabetes, and rodents fed with high-fat diet (HFD). Additionally, half of the animals from each group were administered with myriocin, a robust, selective inhibitor of ceramide synthesis and, therefore, a potent agent ameliorating insulin resistance. Diaphragm lipid contents were evaluated using chromatography. Fatty acid transporter expression was determined by Western blot. The STZ and HFD rats had increased concentration of lipids, namely, ceramides (CER) and diacylglycerols (DAG). Interestingly, this coincided with an increased concentration of long-chain (C ≥ 16) saturated fatty acid species present in both the aforementioned lipid fractions. The CER/DAG accumulation was accompanied by an elevated fatty acid transporter expression (FATP-1 in HFD and FATP-4 in STZ). Surprisingly, we observed a significantly decreased triacylglycerol content in the diaphragms of STZ-treated rats.

Effect of streptozotocin-induced diabetes on lipids metabolism in the salivary glands

BACKGROUND

Diabetes is one of the most common metabolic diseases. Moreover, previous studies indicate that diabetes may cause changes in the salivary glands phenotype and in the composition of saliva itself. Therefore, the main objective of this study was to determine the effects of streptozotocin induced diabetes on lipid profile of the rat salivary glands.

METHODS

Male Wistar rats were divided into two groups: control and STZ-induced diabetes. At the end of the experiment all animals were sacrificed and samples of the parotid and submandibular salivary glands were excised. Major lipid fractions concentrations were determined by means of chromatography (TLC and GC).

RESULTS

We observed a significant increase (∼3.5 fold) in the level of triacylglycerol in both the parotid and submandibular salivary glands of diabetic rats. The abovementioned changes were accompanied by significant, although less dramatic (i.e. from -60% to -90%), decrements in the levels of other lipid classes (phospholipids, free fatty acids and diacylglycerol).

CONCLUSIONS

In our study we have showed, presumably for the first time, that streptozotocin induced diabetes causes decrement in PH content with subsequent atrophy and malfunction in both parotid and submandibular salivary glands. Another novel finding of our research is that diabetic rats were characterized by an increased TG accumulation in both parotid and submandibular salivary glands. The later one could be a clinical manifestation of diabetes.

Myriocin prevents muscle ceramide accumulation but not muscle fiber atrophy during short-term mechanical unloading

Bedridden patients in intensive care unit or after surgery intervention commonly develop skeletal muscle weakness. The latter is promoted by a variety of prolonged hospitalization-associated conditions. Muscle disuse is the most ubiquitous and contributes to rapid skeletal muscle atrophy and progressive functional strength reduction. Disuse causes a reduction in fatty acid oxidation, leading to its accumulation in skeletal muscle. We hypothesized that muscle fatty acid accumulation could stimulate ceramide synthesis and promote skeletal muscle weakness. Therefore, the present study was designed to determine the effects of sphingolipid metabolism on skeletal muscle atrophy induced by 7 days of disuse. For this purpose, male Wistar rats were treated with myriocin, an inhibitor of de novo synthesis of ceramides, and subjected to hindlimb unloading (HU) for 7 days. Soleus muscles were assayed for fiber diameter, ceramide levels, protein degradation, and apoptosis signaling. Serum and liver were removed to evaluate the potential hepatoxicity of myriocin treatment. We found that HU increases content of saturated C16:0 and C18:0 ceramides and decreases soleus muscle weight and fiber diameter. HU increased the level of polyubiquitinated proteins and induced apoptosis in skeletal muscle. Despite a prevention of C16:0 and C18:0 muscle accumulation, myriocin treatment did not prevent skeletal muscle atrophy and concomitant induction of apoptosis and proteolysis. Moreover, myriocin treatment increased serum transaminases and induced hepatocyte necrosis. These data highlight that inhibition of de novo synthesis of ceramides during immobilization is not an efficient strategy to prevent skeletal muscle atrophy and exerts adverse effects like hepatotoxicity.

Chronic ethanol consumption profoundly alters regional brain ceramide and sphingomyelin content in rodents

Ceramides (CER) are involved in alcohol-induced neuroinflammation. In a mouse model of chronic alcohol exposure, 16 CER and 18 sphingomyelin (SM) concentrations from whole brain lipid extracts were measured using electrospray mass spectrometry. All 18 CER concentrations in alcohol exposed adults increased significantly (range: 25–607%); in juveniles, 6 CER decreased (range: −9 to −37%). In contrast, only three SM decreased in adult and one increased significantly in juvenile. Next, regional identification at 50 μm spatial resolution from coronal sections was obtained with matrix implanted laser desorption/ionization mass spectrometry imaging (MILDI-MSI) by implanting silver nanoparticulate matrices followed by focused laser desorption. Most of the CER and SM quantified in whole brain extracts were detected in MILDI images. Coronal sections from three brain levels show qualitative regional changes in CER-SM ion intensities, as a function of group and brain region, in cortex, striatum, accumbens, habenula, and hippocampus. Highly correlated changes in certain white matter CER-SM pairs occur in regions across all groups, including the hippocampus and the lateral (but not medial) cerebellar cortex of adult mice. Our data provide the first microscale MS evidence of regional lipid intensity variations induced by alcohol.

Central ceramide-induced hypothalamic lipotoxicity and ER stress regulate energy balance

Hypothalamic endoplasmic reticulum (ER) stress is a key mechanism leading to obesity. Here, we demonstrate that ceramides induce lipotoxicity and hypothalamic ER stress, leading to sympathetic inhibition, reduced brown adipose tissue (BAT) thermogenesis, and weight gain. Genetic overexpression of the chaperone GRP78/BiP (glucose-regulated protein 78 kDa/binding immunoglobulin protein) in the ventromedial nucleus of the hypothalamus (VMH) abolishes ceramide action by reducing hypothalamic ER stress and increasing BAT thermogenesis, which leads to weight loss and improved glucose homeostasis. The pathophysiological relevance of this mechanism is demonstrated in obese Zucker rats, which show increased hypothalamic ceramide levels and ER stress. Overexpression of GRP78 in the VMH of these animals reduced body weight by increasing BAT thermogenesis as well as decreasing leptin and insulin resistance and hepatic steatosis. Overall, these data identify a triangulated signaling network involving central ceramides, hypothalamic lipotoxicity/ER stress, and BAT thermogenesis as a pathophysiological mechanism of obesity.

Inhibition of ceramide de novo synthesis with myriocin affects lipid metabolism in the liver of rats with streptozotocin-induced type 1 diabetes

Nowadays diabetes is one of the most common metabolic diseases. Sphingolipids, which are vitally important constituents of intracellular signal transduction pathways, may be among the most pathogenic lipid moieties intermingled in the origin and development of diabetes. It is now well established that inhibition of de novo ceramide synthesis with myriocin exerts positive effects on lipid metabolism and glucose homeostasis in type 2 diabetes mellitus animal models. However, its influence on type I diabetes still remains unknown. Therefore, the scope of this paper is to fulfill that particular gap in our knowledge.

Hippocampal lipoprotein lipase regulates energy balance in rodents

Brain lipid sensing is necessary to regulate energy balance. Lipoprotein lipase (LPL) may play a role in this process. We tested if hippocampal LPL regulated energy homeostasis in rodents by specifically attenuating LPL activity in the hippocampus of rats and mice, either by infusing a pharmacological inhibitor (tyloxapol), or using a genetic approach (adeno-associated virus expressing Cre-GFP injected into Lpl (lox/lox) mice). Decreased LPL activity by either method led to increased body weight gain due to decreased locomotor activity and energy expenditure, concomitant with increased parasympathetic tone (unchanged food intake). Decreased LPL activity in both models was associated with increased de novo ceramide synthesis and neurogenesis in the hippocampus, while intrahippocampal infusion of de novo ceramide synthesis inhibitor myriocin completely prevented body weight gain. We conclude that hippocampal lipid sensing might represent a core mechanism for energy homeostasis regulation through de novo ceramide synthesis.

Sphingolipid profiles are altered in prefrontal cortex of rats under acute hyperglycemia

Diabetes type 1 is a common autoimmune disease manifesting by insulin deficiency and hyperglycemia, which can lead to dementia-like brain dysfunctions. The factors triggering the pathological processes in hyperglycemic brain remain unknown. We reported in this study that brain areas with different susceptibility to diabetes (prefrontal cortex (PFC), hippocampus, striatum and cerebellum) revealed differential alterations in ceramide (Cer) and sphingomyelin (SM) profiles in rats with streptozotocin-induced hyperglycemia. Employing gas-liquid chromatography, we found that level of total Cer increased significantly only in the PFC of diabetic animals, which also exhibited a broad spectrum of sphingolipid (SLs) changes, such as elevations of Cer-C16:0, -C18:0, -C20:0, -C22:0, -C18:1, -C24:1 and SM-C16:0 and -C18:1. In opposite, only minor changes were noted in other examined structures. In addition, de novo synthesis pathway could play a role in generation of Cer containing monounsaturated fatty acids in PFC during hyperglycemia. In turn, simultaneous accumulation of Cers and their SM counterparts may suggest that overproduced Cers are converted to SMs to avoid excessive Cer-mediated cytotoxicity. We conclude that broad changes in SLs compositions in PFC induced by hyperglycemia may provoke membrane rearrangements in some cell populations, which can disturb cellular signaling and cause tissue damage.

Antioxidant profile of salivary glands in high fat diet-induced insulin resistance rats

OBJECTIVE

There is no study analyzing the salivary antioxidant profile in the course of the insulin resistance.

MATERIALS AND METHODS

Rats were divided into two groups. One group was fed with a normal diet, another one with a high fat diet for 5 weeks. The analysis included: catalase (CAT), superoxide dismutase, peroxidase activities, uric acid, and total antioxidant status concentrations.

RESULTS

The activity of peroxidase in both kind of glands of insulin resistance rats was significantly reduced than in the control rats. The protein concentration, total amount of total antioxidant status in the parotid glands of insulin resistance rats were significantly lower than in the control glands The total amount of superoxide dismutase, CAT, and uric acid in the parotid glands of insulin resistance rats were significantly elevated in comparison with the control rats. The median values of the total amount of superoxide dismutase, CAT, peroxidase, total antioxidant status were significantly higher in the parotid than in the submandibular glands of the insulin resistance and control rats.

CONCLUSION

Parotid and submandibular glands of rats react differently when exposed to insulin resistance condition; however, the parotid glands seem to be more affected. The main source of antioxidants is parotid glands of rats.