Exploring the Obesity Paradox in A Murine Model of Sepsis: Improved Survival Despite Increased Organ Injury in Obese Mice.

ABSTRACT: Despite the known deleterious effects of obesity, clinical data indicate that overweight or obese patients experience higher rates of sepsis survival compared to normal and underweight patients; a phenomenon called the obesity paradox. Results from preclinical sepsis studies have not been able to replicate these findings. The objective of this study was to test the existence of the obesity paradox in a murine model of cecal slurry (CS)-induced sepsis with insulin-resistant diet-induced obese mice. Male C57BL/6 mice were provided high-fat (HFD) or low-fat (LFD) diets for 20 weeks. HFD-fed mice experienced higher rates of survival compared to LFD-fed mice after septic challenge induced by CS injection (66% vs. 25%, P = 0.01, survival assessed for 14 days). Despite the survival advantage, HFD-fed mice had higher rates of positive bacterial cultures and increased markers of kidney injury. Circulating levels of IL-6, IL-1ß, TNFα, and IL-23 were equivalent 24 h after CS-injection; however, IL-17A was uniquely increased in HFD-fed mice. While LFD-fed mice maintained euglycemia, HFD-fed mice were hyperglycemic 6 and 12 h after CS-injection. Stable isotope resolved metabolomics analysis of liver tissue showed diverging pathways of glucose utilization during sepsis, with LFD-fed mice significantly upregulating glycolytic activity and HFD-fed mice decreasing glucose entry into the TCA cycle. This murine study corroborates clinical data that obesity confers a survival benefit in sepsis, albeit at the expense of more significant organ injury. The mechanisms promoting survival in the obese remain unknown; however, this model appears to be well-poised to begin answering this question. Differences in glucose utilization are a novel target to investigate this paradox.

Lactate supports a metabolic-epigenetic link in macrophage polarization.

Lactate accumulation is a hallmark of solid cancers and is linked to the immune suppressive phenotypes of tumor-infiltrating immune cells. We report herein that interleukin-4 (IL-4)­induced M0 → M2 macrophage polarization is accompanied by interchangeable glucose- or lactate-dependent tricarboxylic acid (TCA) cycle metabolism that directly drives histone acetylation, M2 gene transcription, and functional immune suppression. Lactate-dependent M0 → M2 polarization requires both mitochondrial pyruvate uptake and adenosine triphosphate­citrate lyase (ACLY) enzymatic activity. Notably, exogenous acetate rescues defective M2 polarization and histone acetylation following mitochondrial pyruvate carrier 1 (MPC1) inhibition or ACLY deficiency. Lastly, M2 macrophage­dependent tumor progression is impaired by conditional macrophage ACLY deficiency, further supporting a dominant role for glucose/lactate mitochondrial metabolism and histone acetylation in driving immune evasion. This work adds to our understanding of how mitochondrial metabolism affects macrophage functional phenotypes and identifies a unique tumor microenvironment (TME)­driven metabolic-epigenetic link in M2 macrophages.

Non-estrogenic Xanthohumol Derivatives Mitigate Insulin Resistance and Cognitive Impairment in High-Fat Diet-induced Obese Mice.

Xanthohumol (XN), a prenylated flavonoid from hops, improves dysfunctional glucose and lipid metabolism in animal models of metabolic syndrome (MetS). However, its metabolic transformation into the estrogenic metabolite, 8-prenylnaringenin (8-PN), poses a potential health concern for its use in humans. To address this concern, we evaluated two hydrogenated derivatives, α,ß-dihydro-XN (DXN) and tetrahydro-XN (TXN), which showed negligible affinity for estrogen receptors α and ß, and which cannot be metabolically converted into 8-PN. We compared their effects to those of XN by feeding C57BL/6J mice a high-fat diet (HFD) containing XN, DXN, or TXN for 13 weeks. DXN and TXN were present at higher concentrations than XN in plasma, liver and muscle. Mice administered XN, DXN or TXN showed improvements of impaired glucose tolerance compared to the controls. DXN and TXN treatment resulted in a decrease of HOMA-IR and plasma leptin. C2C12 embryonic muscle cells treated with DXN or TXN exhibited higher rates of uncoupled mitochondrial respiration compared to XN and the control. Finally, XN, DXN, or TXN treatment ameliorated HFD-induced deficits in spatial learning and memory. Taken together, DXN and TXN could ameliorate the neurocognitive-metabolic impairments associated with HFD-induced obesity without risk of liver injury and adverse estrogenic effects.

Amelioration of Metabolic Syndrome-Associated Cognitive Impairments in Mice via a Reduction in Dietary Fat Content or Infusion of Non-Diabetic Plasma.

Obesity, metabolic syndrome (MetS) and type 2 diabetes (T2D) are associated with decreased cognitive function. While weight loss and T2D remission result in improvements in metabolism and vascular function, it is less clear if these benefits extend to cognitive performance. Here, we highlight the malleable nature of MetS-associated cognitive dysfunction using a mouse model of high fat diet (HFD)-induced MetS. While learning and memory was generally unaffected in mice with type 1 diabetes (T1D), multiple cognitive impairments were associated with MetS, including deficits in novel object recognition, cued fear memory, and spatial learning and memory. However, a brief reduction in dietary fat content in chronic HFD-fed mice led to a complete rescue of cognitive function. Cerebral blood volume (CBV), a measure of vascular perfusion, was decreased during MetS, was associated with long term memory, and recovered following the intervention. Finally, repeated infusion of plasma collected from age-matched, low fat diet-fed mice improved memory in HFD mice, and was associated with a distinct metabolic profile. Thus, the cognitive dysfunction accompanying MetS appears to be amenable to treatment, related to cerebrovascular function, and mitigated by systemic factors.

Immediate and lasting effects of chronic daily methamphetamine exposure on activation of cells in hypothalamic-pituitary-adrenal axis-associated brain regions.

RATIONALE: Chronic methamphetamine (MA) abuse leads to dependence and symptoms of withdrawal after use has ceased. Negative mood states associated with withdrawal, as well as drug reinstatement, have been linked to drug-induced disruption of the hypothalamic-pituitary-adrenal (HPA) axis. However, effects of chronic MA exposure or acute MA exposure following withdrawal on neural activation patterns within brain regions that regulate the HPA axis are unknown. OBJECTIVES: In this study, neural activation patterns were assessed by quantification of c-Fos protein in mice exposed to different regimens of MA administration. METHODS: (Experiment 1) Adult male mice were treated with MA (5 mg/kg) or saline once or once daily for 10 days. (Experiment 2) Mice were treated with MA or saline once daily for 10 days and following a 10-day withdrawal period were re-administered a final dose of MA or saline. c-Fos was quantified in brains after the final injection. RESULTS: (Experiment 1) Compared to exposure to a single dose of MA (5 mg/kg), chronic MA exposure decreased the number of c-Fos expressing cells in the paraventricular hypothalamus, dorsomedial hypothalamus, central amygdala, basolateral amygdala, bed nucleus of the stria terminalis (BNST), and CA3 hippocampal region. (Experiment 2) Compared to mice receiving their first dose of MA, mice chronically treated with MA, withdrawn, and re-administered MA, showed decreased c-Fos expressing cells within the central and basolateral amygdala, BNST, and CA3. CONCLUSIONS: HPA axis-associated amygdala, extended amygdala, and hippocampal regions endure lasting effects following chronic MA exposure and therefore may be linked to stress-related withdrawal symptoms.

Sex differences in activation of the hypothalamic-pituitary-adrenal axis by methamphetamine.

Dysregulation of hypothalamic-pituitary-adrenal (HPA) axis activation is associated with changes in addiction-related behaviors. In this study, we tested whether sex differences in the acute effects of methamphetamine (MA) exposure involve differential activation of the HPA axis. Male and female mice were injected with MA (1 mg/kg) or saline for comparison of plasma corticosterone and analysis of the immediate early gene c-Fos in brain. There was a prolonged elevation in corticosterone levels in female compared to male mice. C-Fos was elevated in both sexes following MA in HPA axis-associated regions, including the hypothalamic paraventricular nucleus (PVN), central amygdala, cingulate, and CA3 hippocampal region. MA increased the number of c-Fos and c-Fos/glucocorticoid receptor (GR) dual-labeled cells to a greater extent in males than females in the cingulate and CA3 regions. MA also increased the number of c-fos/vasopressin dual-labeled cells in the PVN as well as the number and percentage of c-Fos/GR dual-labeled cells in the PVN and central amygdala, although no sex differences in dual labeling were found in these regions. Thus, sex differences in MA-induced plasma corticosterone levels and activation of distinct brain regions and proteins involved in HPA axis regulation may contribute to sex differences in acute effects of MA on the brain. Methamphetamine induces a prolonged plasma corticosterone response in females compared to males. This may be mediated by increased neural activation, involving a greater activation of glucocorticoid receptor-positive cells, in males in the CA3 and cingulate brain regions, which are involved in negative feedback functions. These findings indicate a sex difference in the neural regulation of methamphetamine-induced plasma corticosterone release.

Diabetic atherosclerosis in APOE*4 mice: synergy between lipoprotein metabolism and vascular inflammation.

Diabetes is a major risk factor for cardiovascular disease. To examine how diabetes interacts with a mildly compromised lipid metabolism, we introduced the diabetogenic Ins2(C96Y/+) (Akita) mutation into mice expressing human apoE4 (E4) combined with either an overexpressing human LDL receptor gene (hLDLR) or the wild-type mouse gene. The hLDLR allele caused 2-fold reductions in plasma HDL-cholesterol, plasma apoA1, and hepatic triglyceride secretion. Diabetes increased plasma total cholesterol 1.3-fold and increased apoB48 secretion 3-fold, while reducing triglyceride secretion 2-fold. Consequently, diabetic E4 mice with hLDLR secrete increased numbers of small, cholesterol-enriched, apoB48-containing VLDL, although they have near normal plasma cholesterol (<120 mg/dl). Small foam cell lesions were present in the aortic roots of all diabetic E4 mice with hLDLR that we analyzed at six months of age. None were present in nondiabetic mice or in diabetic mice without hLDLR. Aortic expression of genes affecting leukocyte recruitment and adhesion was enhanced by diabetes. ApoA1 levels, but not diabetes, were strongly correlated with the ability of plasma to efflux cholesterol from macrophages. We conclude that the diabetes-induced proinflammatory changes in the vasculature and the hLDLR-mediated cholesterol accumulation in macrophages synergistically trigger atherosclerosis in mice with human apoE4, although neither alone is sufficient.

Pro- and antiatherogenic effects of a dominant-negative P465L mutation of peroxisome proliferator-activated receptor-γ in apolipoprotein E-Null mice.

OBJECTIVE: The dominant-negative mutation, P467L, in peroxisome proliferator-activated receptor-γ (PPARγ) affects adipose tissue distribution, insulin sensitivity, and blood pressure in heterozygous humans. We hypothesized that the equivalent mutation, PPARγ-P465L, in mice will worsen atherosclerosis. METHODS AND RESULTS: Apolipoprotein E-null mice with and without PPARγ-P465L mutation were bred in 129S6 inbred genetic background. Mild hypertension and lipodystrophy of PPARγ-P465L persisted in the apolipoprotein E-null background. Glucose homeostasis was normal, but plasma adiponectin was significantly lower and resistin was higher in PPARγ-P465L mice. Plasma cholesterol and lipoprotein distribution were not different, but plasma triglycerides tended to be reduced. Surprisingly, there were no overall changes in the atherosclerotic plaque size or composition. PPARγ-P465L macrophages had a small decrease in CD36 mRNA and a small yet significant reduction in very-low-density lipoprotein uptake in culture. In unloaded apolipoprotein E-null macrophages with PPARγ-P465L, cholesterol uptake was reduced whereas apolipoprotein AI-mediated efflux was increased. However, when cells were cholesterol loaded in the presence of acetylated low-density lipoprotein, no genotype difference in uptake or efflux was apparent. A reduction of vascular cell adhesion molecule-1 expression in aorta suggests a relatively antiatherogenic vascular environment in mice with PPARγ-P465L. CONCLUSIONS: Small, competing pro- and antiatherogenic effects of PPARγ-P465L mutation result in unchanged plaque development in apolipoprotein E-deficient mice.

Absence of hyperlipidemia in LDL receptor-deficient mice having apolipoprotein B100 without the putative receptor-binding sequences.

OBJECTIVE: To examine the effects of apoB100 structure, specifically a mutation in the LDLr binding region, on the production of LDL and development of atherosclerosis in vivo. METHODS AND RESULTS: Ldlr(-/-)Apobec1(-/-) mice lacking the LDLR and apoB editing enzyme accumulated LDL in plasma and developed severe atherosclerosis when they had wild-type apoB100. In marked contrast, in Ldlr(-/-)Apobec1(-/-) mice carrying the Apob100-beta mutation, in the 2 putative LDLR-binding domains of apoB prevented both LDL accumulation and atherosclerosis. Intestinal absorption of lipids and triglyceride secretion from the liver were not affected. However, the VLDL particles with apoB100-beta were larger in volume by about 70%, and carried approximately four times as much apoE per particle. ApoB100-beta synthesis rate in the primary hepatocytes was normal, but its intracellular degradation was enhanced. Additionally, mutant apoB100 VLDL cleared from the circulation more quickly in vivo through apoE-LRP-mediated mechanism than VLDL with wild-type apoB100. In contrast, uptake of the 2 VLDL by macrophages were not different. CONCLUSIONS: While conformational change to apoB100 during conversion of VLDL to LDL exposes LDLR binding domains and facilitates LDLR-mediated lipoprotein clearance, it may also inhibit LRP-mediated VLDL uptake and contribute to LDL accumulation in familial hypercholesterolemia.