Tackling Non-Small Cell Lung Cancer in Young Adults: From Risk Factors and Genetic Susceptibility to Lung Cancer Profile and Outcomes

Lung cancer has traditionally been associated with advanced age; however, its increasing incidence among young adults raises concerning questions regarding its etiology and unique considerations for this population. In contrast to the older population, the onset of lung cancer at younger age may be attributed to a complex interplay of incompletely understood individual susceptibility and prevalent environmental risk factors beyond tobacco smoke exposure, such as radon gas and air pollution, which are widespread globally. Consequently, this leads to distinct clinical and molecular profiles, requiring a tailored approach. Furthermore, a diagnosis of cancer represents a threatening event during the prime years of a young person's life, prompting concern about career development, social aspects, fertility aspirations, and physical independence. This poses significant additional challenges for health care professionals in a field that remains underexplored. This comprehensive review recognizes lung cancer in young adults as a distinct entity, exploring its clinical and molecular characteristics, diverse predisposing factors, and priorities in terms of quality of life, with the aim of providing practical support to oncologists and enhancing our understanding of this under-researched population.

Incidental pathogenic germline alterations detected through liquid biopsy in patients with solid tumors: prevalence, clinical utility and implications

Liquid biopsy, a minimally invasive approach for detecting tumor biomarkers in blood, has emerged as a leading-edge technique in cancer precision medicine. New evidence has shown that liquid biopsies can incidentally detect pathogenic germline variants (PGVs) associated with cancer predisposition, including in patients with a cancer for which genetic testing is not recommended. The ability to detect these incidental PGV in cancer patients through liquid biopsy raises important questions regarding the management of this information and its clinical implications. This incidental identification of PGVs raises concerns about cancer predisposition and the potential impact on patient management, not only in terms of providing access to treatment based on the tumor molecular profiling, but also the management of revealing genetic predisposition in patients and families. Understanding how to interpret this information is essential to ensure proper decision-making and to optimize cancer treatment and prevention strategies. In this review we provide a comprehensive summary of current evidence of incidental PGVs in cancer predisposition genes identified by liquid biopsy in patients with cancer. We critically review the methodological considerations of liquid biopsy as a tool for germline diagnosis, clinical utility and potential implications for cancer prevention, treatment, and research.

Rethinking strategies in SCLC: Lessons learned from tiragolumab in the SKYSCRAPER-02 study

The addition of tiragolumab, an anti-TIGIT inhibitor, to chemotherapy plus atezolizumab demonstrated promising early results for lung cancer. Unfortunately, the phase 3 study SKYSCRAPER-02 did not confirm the anticipated benefit of tiragolumab combination in recalcitrant small-cell lung cancer,1 reiterating the need for a more accurate population selection in clinical trials.

Characterisation and Outcomes of Patients with Solid Organ Malignancies Admitted to the Intensive Care Unit: Mortality and Impact on Functional Status and Oncological Treatment

BACKGROUND

Despite the increasing number of ICU admissions among patients with solid tumours, there is a lack of tools with which to identify patients who may benefit from critical support. We aim to characterize the clinical profile and outcomes of patients with solid malignancies admitted to the ICU.

METHODS

Retrospective observational study of patients with cancer non-electively admitted to the ICU of the Hospital Clinic of Barcelona (Spain) between January 2019 and December 2019. Data regarding patient and neoplasm characteristics, ICU admission features and outcomes were collected from medical records.

RESULTS

97 ICU admissions of 84 patients were analysed. Lung cancer (22.6%) was the most frequent neoplasm. Most of the patients had metastatic disease (79.5%) and were receiving oncological treatment (75%). The main reason for ICU admission was respiratory failure (38%). Intra-ICU and in-hospital mortality rates were 9.4% and 24%, respectively. Mortality rates at 1, 3 and 6 months were 19.6%, 36.1% and 53.6%. Liver metastasis, gastrointestinal cancer, hypoalbuminemia, elevated basal C-reactive protein, ECOG-PS greater than 2 at ICU admission, admission from ward and an APACHE II score over 14 were related to higher mortality. Functional status was severely affected at discharge, and oncological treatment was definitively discontinued in 40% of the patients.

CONCLUSION

Medium-term mortality and functional deterioration of patients with solid cancers non-electively admitted to the ICU are high. Surrogate markers of cachexia, liver metastasis and poor ECOG-PS at ICU admission are risk factors for mortality.

Geographic differences in lung cancer: focus on carcinogens, genetic predisposition, and molecular epidemiology

Lung cancer poses a global health challenge and stands as the leading cause of cancer-related deaths worldwide. However, its incidence, mortality, and characteristics are not uniform across all regions worldwide. Understanding the factors contributing to this diversity is crucial in a prevalent disease where most cases are diagnosed in advanced stages. Hence, prevention and early diagnosis emerge as the most efficient strategies to enhance outcomes. In Western societies, tobacco consumption constitutes the primary risk factor for lung cancer, accounting for up to 90% of cases. In other geographic locations, different significant factors play a fundamental role in disease development, such as individual genetic predisposition, or exposure to other carcinogens such as radon gas, environmental pollution, occupational exposures, or specific infectious diseases. Comprehensive clinical and molecular characterization of lung cancer in recent decades has enabled us to distinguish different subtypes of lung cancer with distinct phenotypes, genotypes, immunogenicity, treatment responses, and survival rates. The ultimate goal is to prevent and individualize lung cancer management in each community and improve patient outcomes.

Adipose Tissue Protects against Hepatic Steatosis in Male Rats Fed a High-Fat Diet plus Liquid Fructose: Sex-Related Differences

Non-alcoholic fatty liver disease is a sexual dimorphic disease, with adipose tissue playing an essential role. Our previous work showed that female rats fed a high-fat high-fructose diet devoid of cholesterol (HFHFr) developed simple hepatic steatosis dissociated from obesity. This study assessed the impact of the HFHFr diet on the male rat metabolism compared with data obtained for female rats. A total of 16 Sprague Dawley (SD) male rats were fed either a control (standard rodent chow and water) or HFHFr (high-fat diet devoid of cholesterol, plus 10% fructose in drinking water) diet for 3 months. Unlike female rats, and despite similar increases in energy consumption, HFHFr males showed increased adiposity and hyperleptinemia. The expression of hormone-sensitive lipase in the subcutaneous white adipose tissue was enhanced, leading to high free fatty acid and glycerol serum levels. HFHFr males presented hypertriglyceridemia, but not hepatic steatosis, partially due to enhanced liver PPARα-related fatty acid β-oxidation and the VLDL-promoting effect of leptin. In conclusion, the SD rats showed a sex-related dimorphic response to the HFHFr diet. Contrary to previous results for HFHFr female rats, the male rats were able to expand the adipose tissue, increase fatty acid catabolism, or export it as VLDL, avoiding liver lipid deposition.

Epidemiology and risk factors for recurrence in biliary source bloodstream infection episodes in oncological patients

We aimed to describe the characteristics and outcomes of biliary source bloodstream infections (BSIs) in oncological patients. Secondarily, we analyzed risk factors for recurrent BSI episodes. All episodes of biliary source BSIs in oncological patients were prospectively collected (2008-2019) and retrospectively analyzed. Logistic regression analyses were performed. A rule to stratify patients into risk groups for recurrent biliary source BSI was conducted. Four hundred biliary source BSIs were documented in 291 oncological patients. The most frequent causative agents were Escherichia coli (42%) and Klebsiella spp. (27%), and 86 (21.5%) episodes were caused by multidrug-resistant Gram-negative bacilli (MDR-GNB). The rates of MDR-GNB increased over time. Overall, 73 patients developed 118 recurrent BSI episodes. Independent risk factors for recurrent BSI episodes were prior antibiotic therapy (OR 3.781, 95% CI 1.906-7.503), biliary prosthesis (OR 2.232, 95% CI 1.157-4.305), prior admission due to suspected biliary source infection (OR 4.409, 95% CI 2.338-8.311), and BSI episode caused by an MDR-GNB (OR 2.857, 95% CI 1.389-5.874). With these variables, a score was generated that predicted recurrent biliary source BSI with an area under the receiver operating characteristic (ROC) curve of 0.819. Inappropriate empirical antibiotic treatment (IEAT) was administered in 23.8% of patients, and 30-d mortality was 19.5%. As a conclusion, biliary source BSI in oncological patients is mainly caused by GNB, with high and increasing MDR rates, frequent IEAT, and high mortality. Recurrent BSI episodes are frequent. A simple score to identify recurrent episodes was developed to potentially establish prophylactic strategies. IMPORTANCE This study shows that biliary source bloodstream infections (BSIs) in oncological patients are mainly caused by Gram-negative bacilli (GNB), with high and increasing rates of multidrug resistance. Importantly, recurrent biliary source BSI episodes were very frequent and associated with delays in chemotherapy, high rates of inappropriate empirical antibiotic therapy, and high 30-d mortality (19.5%). Using the variable independently associated with recurrent BSI episodes, a score was generated that predicted recurrent biliary source BSI with high accuracy. This score could be used to establish prophylactic strategies and lower the risk of relapsing episodes and the associated morbidity and mortality.

Bempedoic acid for nonalcoholic fatty liver disease: evidence and mechanisms of action

PURPOSE OF REVIEW

Nonalcoholic fatty liver disease (NAFLD) is a highly prevalent progressive condition that lacks a specific pharmacological treatment. ATP-citrate lyase (ACLY) is one of the emergent targets for the treatment of NAFLD. This review aims to summarize the role of ACLY in NAFLD, provide evidences of the beneficial effects of the ACLY inhibitor bempedoic acid (BemA) in NAFLD and discuss the mechanisms involved.

RECENT FINDINGS

BemA is effective in reducing hepatic steatosis in several animal models that recapitulate different stages of the disease. Thus, in a dietary model of simple hepatic steatosis in female rats, BemA abrogates the accumulation of liver fat. Apart from ACLY inhibition, BemA has several functions in the liver that contribute to the antisteatotic effect: inhibition of ketohexokinase, induction of patatin-like phospholipase domain-containing protein 3 and increases in both fatty acid β-oxidation activity and hepatic H2S production. In models of the advanced phases of NAFLD, BemA reduces not only steatosis, but also ballooning, lobular inflammation and hepatic fibrosis, by mechanisms involving both hepatocytes and hepatic stellate cells.

SUMMARY

BemA, an ACLY inhibitor currently approved for the treatment of hypercholesterolemia, may be a useful drug to treat NAFLD through its antisteatotic, anti-inflammatory and antifibrotic effects.

Biomarkers of response to immunotherapy in early stage non-small cell lung cancer

Immunotherapy with immune-checkpoint inhibitors (ICIs) targeting programmed cell death 1 or programmed death-ligand 1 has revolutionised the treatment of advanced non-small cell lung cancer (NSCLC) and has been investigated in early NSCLC, alone or in combination with chemotherapy, anti-CTLA-4 antibodies and radiotherapy. Although more mature data are needed before setting a change of paradigm in early stages, reports of pathological response rates and disease-free survival are promising, especially with neoadjuvant multimodality approaches. Nevertheless, major pathological response rates for neoadjuvant anti-PD-(L)1 monotherapy rarely exceed 40%, and biomarkers for characterising patients who may benefit the most from ICIs are lacking. These biomarkers have a distinct value from the metastatic setting, with highly different tumour biologies. Among the most investigated so far in this context, programmed death-ligand 1 expression and, to a lesser extent, tumour mutational burden seem to correlate better with higher pathological response rates and survival. Epidermal growth factor receptor, Serine/Threonine Kinase 11and Kelch-like ECH-associated protein 1 mutations rise as essential determinations for the treatment selection in early-stage NSCLC. Emerging and promising approaches comprise evaluation of blood-based ratios, microbiota, and baseline intratumoural TCR clonality. Circulating tumour DNA will be of great help in the near future when selecting best candidates for adjuvant ICIs, monitoring the tumour response to the neoadjuvant treatment in order to improve the rates of complete resections in the early stage.

KHK, PNPLA3 and PPAR as Novel Targets for the Anti-Steatotic Action of Bempedoic Acid

Bempedoic acid (BemA) is an ATP-citrate lyase (ACLY) inhibitor used to treat hypercholesterolemia. We studied the anti-steatotic effect of BemA, and the mechanisms involved, in a model of fatty liver in female rats obtained through the administration of a high-fat diet supplemented with liquid fructose (HFHFr) for three months. In the third month, a group of rats was treated with BemA (30 mg/kg/day) by gavage. Plasma analytes, liver histology, adiposity, and the expression of key genes controlling fatty acid metabolism were determined, and PPAR agonism was explored by using luciferase reporter assays. Our results showed that, compared to HFHFr, BemA-treated rats exhibited lower body weight, higher liver/body weight, and reduced hepatic steatosis. In addition to ACLY inhibition, we found three novel mechanisms that could account for the anti-steatotic effect: (1) reduction of liver ketohexokinase, leading to lower fructose intake and reduced de novo lipogenesis; (2) increased expression of patatin-like phospholipase domain-containing protein 3, a protein related to the export of liver triglycerides to blood; and (3) PPARα agonist activity, leading to increased hepatic fatty acid β-oxidation. In conclusion, BemA may represent a novel approach to treat hepatic steatosis, and therefore to avoid progression to advanced stages of non-alcoholic fatty liver disease.

PBRM1 genomic alterations as a predictive biomarker to immune checkpoint inhibitors (ICI) and/or anti-angiogenic therapies (anti-VEGF) in metastatic renal cell carcinoma (mRCC): A systematic review and meta-analysis

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Background: Combination therapy with ICI and anti-VEGF has become the standard first-line (1L) therapy for metastatic clear cell RCC (mccRCC). However, about 25% of patients (pts) are long responders to anti-VEGF monotherapy. PBRM1 genomic alterations (ga) are present in around 40% mccRCC pts and contradictory results have been reported about its role as a predictive biomarker. We performed a systemic review and meta-analysis to assess the role of PBRM1 ga as a predictive biomarker of response to ICI, anti-VEGF, or its combination. Methods: A systematic review of PubMed, EMBASE, Cochrane, and Web of Science databases was performed (February 2022) to identify studies involving mRCC pts who received systemic therapy and had PBRM1 status and clinical outcomes reported. Study design, baseline characteristics, treatment data, and hazard ratios (HRs) with 95% confidence intervals (CI) for each clinical outcome were extracted. HRs were combined across studies using a random effect model. The primary endpoint was to correlate PBRM1 status with progression-free survival (PFS) to anti-VEGF, ICI, or its combination. Results: The systematic review included 12 out of 892 publications (n = 6528 pts), 98% (n = 6372) mccRCC; 3297 pts (51%) treated with anti-VEGF monotherapy, 1574 (24%) ICI (PD-L1 (n = 1019, 65%) or CTLA4 + anti PD-L1 (n = 555, 35%)), 997 pts (15%) anti-VEGF + ICI, and 660 pts (10%) with other therapies (e.g., mTORi or INF). PBRM1 status was assessed by NGS in 3841 pts (59%) and detected in 1595 (41%). Nine out of 12 publications were considered for the meta-analysis; excluding those with duplicated pts or lack of information. Six studies (n = 2593 pts) evaluated PBRM1 status in first-line (1L) therapies, including anti-VEGF in monotherapy (n = 1487, 57%) and ICI (n = 1106, 43%; combined w/anti-VEGF (n = 773), w/CTL4 (n = 262) or in monotherapy (n = 71)). In 1L setting, PBRM1 ga pts had longer PFS under monotherapy with anti-VEGF ( PBRM1 ga 44%; HR = 0.74 (95% CI, 0.62 - 0.88), p < 0.01) but not under ICI ( PBRM1 ga = 42%; HR = 1 (95% CI, 0.85 - 1.17), p = 0.38) nor ICI + anti-VEGF treatment ( PBRM1 ga = 33.5%; HR = 0.93 (95% CI, 0.73 - 1.18), p = 0.56). Two studies evaluated PBRM1 status in second line (2L) ICI-treated mRCC pts (n = 517 pts). PBRM1 ga pts had longer PFS under ICI in 2L ( PBRM1 ga = 36%, HR = 0.64 (95% CI, 0.49 - 0.83), p = 0.0007). Conclusions: mRCC pts with PBRM1 ga showed longer PFS to 1L anti-VEGF and 2L ICI therapy, supporting its role as a predictive biomarker. Anti-VEGF + ICI combination de-escalation strategies merits further investigation in PBRM1 ga mRCC patients.

Prevalence of incidental pathogenic germline variants detected in cfDNA in patients with oncogene-driven non-small cell lung cancer

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Background: Preliminary data has highlighted inherited predisposition to lung cancer (LC) related to certain pathogenic germline variant (PGV) in cancer predisposing genes, including patients (pts) with tumors harboring somatic driver oncogene alterations (alt); however, the frequency of PGV in LC is unknown. Liquid biopsy assays may be able to identify incidental PGV (iPGV) in pts with solid tumors at scale. Here, we report the prevalence of iPGV in genes predisposing to cancer in pts with advanced non-small cell LC (aNSCLC) relative to driver alt status. Methods: Genomic results were retrospectively queried from 31126 pts with aNSCLC who had Guardant360 testing as part of routine clinical care from 10/2020-12/2021. iPGVs were defined as being non-synonymous, non-VUS alt in selected genes known to increase lifetime cancer risk (Table) with variant allele frequency (VAF) >30% and pathogenicity defined by a proprietary bioinformatics pipeline. Clinical factors such as age, gender, histology, and diagnosis status (new/progressing) were extracted from test requisition forms. The driver group included guideline-recommended and emerging somatic mutations (m) in EGFR/KRAS/BRAF/MET/HER2, fusions (f) in ALK/ROS1/RET/NTRK1-3 and amplifications (a) in HER2/MET. Results: Out of 31126, 720 (2.3%) of pts had predicted iPGV, of whom 54% were female, with a median age of 64 (22-100); most pts were newly diagnosed (66%). Among them, 92% of pts had iPGVs identified in the homologous recombination and repair (HRR) pathway, 3% in mismatch repair (MMR) pathway and 5% EGFR iPGVs. A total of 335 (47%) pts with iPGVs had somatic driver alt (Table): 20% of pts with iPGV had KRASm (n=144/720; 67 G12C), 12% EGFRm (n=87; 28 ex19del, 35 ex21(L858R)), 2.5% BRAFm (n=18), 2.5% METm ex14 skip (n=18), 0.1% HER2m (n=1), 0.8% ALKf (n=6), 0.1% ROS1f (n=1), 0.1% RETf (n=1), 0.1% HER2a (n=1), and 0.4% METa (n=3). ATM iPGVs were enriched in pts with driver alt. (45% driver vs 27% non-driver, p<0.0001) while BRCA1 iPGVs were more frequently observed in pts without driver alt. (17% vs 8%, p<0.0001). Distribution of other iPGVs was similar across driver/non-driver groups. Conclusions: In this large cohort, 2.3% of pts with aNSCLC were iPGV-carriers; 47% of pts had oncogene-driven tumors, particularly with KRAS, EGFR, BRAF and MET alt. iPGV and lung carcinogenesis need further evaluation to define the role of genetic predisposition in LC risk and to determine the highest risk individuals to explore screening and therapeutic strategies, such as in pts with other solid tumors. [Table: see text]

Bempedoic acid as a PPARα activator: new perspectives for hepatic steatosis treatment in a female rat experimental model

INTRODUCTION

In its initial stages, nonalcoholic fatty liver disease presents hypertriglyceridemia and accumulation of lipids in the liver (hepatic steatosis). Bempedoic acid is an ATP:citrate lyase inhibitor that promotes a dual inhibition of the synthesis of cholesterol and fatty acids. However, its effect in the prevention / treatment of hepatic steatosis and hypertriglyceridemia has not been investigated. The aim of our work has been to elucidate whether bempedoic acid, through a mechanism other than ATP:citrate lyase inhibition, reverses these metabolic alterations.

EXPERIMENTAL DESIGN

The study was carried out in female Sprague-Dawley rats fed, for three months, with a high fat diet supplemented with fructose (10% w/v) in drinking water. During the last month, bempedoic acid (30mg/kg/day) was administered to a group of animals. Zoometric and plasmatic parameters were analyzed, gene and protein expression analysis were performed in liver samples and PPAR-PPRE binding activity was determined.

RESULTS

Our interventional model developed hepatic steatosis and hypertriglyceridemia. Despite an increase in total caloric intake, there was no increase in body weight of the animals. The administration of bempedoic acid significantly reduced hepatic steatosis and promoted a marked hepatocyte hypertrophy. There was a 66% increase in the liver weight of the animals treated with the drug that was not accompanied by modifications in the markers of inflammation, oxidative stress, or endoplasmic reticulum stress. Bempedoic acid activated the peroxisome proliferator activated nuclear receptor (PPARα) and its target genes.

CONCLUSIONS

Bempedoic acid could be an effective therapy for the treatment of fatty liver and associated cardiovascular risk. Bempedoic acid has other mechanisms of action besides the inhibition of ATP: citrate lyase, such as the activation of PPARα, which could explain the reduction in hepatic steatosis and the increase in liver weight observed in animals treated with the drug.

ChREBP‐driven DNL and PNPLA3 Expression Induced by Liquid Fructose Are Essential in the Production of Fatty Liver and Hypertriglyceridemia in a High‐fat Diet‐fed Rat Model

Scope

The aim of this study is to delineate the contribution of dietary saturated fatty acids (FA) versus liquid fructose to fatty liver and hypertriglyceridemia.

Methods and Results

Three groups of female rats are maintained for 3 months in standard chow (CT); High‐fat diet (46.9% of fat‐derived calories, rich in palmitic and stearic FA, HFD); and HFD with 10% w/v fructose in drinking water (HFHFr). Zoometric parameters, plasma biochemistry, and liver Oil‐Red O (ORO) staining, lipidomics, and expression of proteins involved in FA metabolism are analyzed. Both diets increase ingested calories without modifying body weight. Only the HFHFr diet increases liver triglycerides (x11.0), with hypertriglyceridemia (x1.7) and reduces FA β‐oxidation (x0.7), and increases liver FA markers of DNL (de novo lipogenesis). Whereas HFD livers show a high content of ceramides, HFHFr samples show unchanged ceramides, and an increase in diacylglycerols. Only the HFHFr diet leads to a marked increase in the expression of enzymes involved in DNL and triglyceride metabolism, such as carbohydrate response element binding protein β (ChREBPβ, x3.2), a transcription factor that regulates DNL, and patatin‐like phospholipase domain‐containing 3 (PNPLA3, x2.6), a lipase that mobilizes stored triglycerides for VLDL secretion.

Conclusion

The addition of liquid‐fructose to dietary FA is determinant in liver steatosis and hypertriglyceridemia production, through increased DNL and PNPLA3 expression, and reduced FA catabolism.

Chronic liquid fructose supplementation does not cause liver tumorigenesis but elicits clear sex differences in the metabolic response in Sprague-Dawley rats

Background

Non-alcoholic fatty liver disease (NAFLD) has increased over the last decades and may evolve into hepatocellular carcinoma (HCC). As HCC is challenging to treat, knowledge on the modifiable risk factors for NAFLD/HCC (e.g. hyper caloric diets rich in fructose) is essential.

Objective and design

We used a model of diethyl nitrosamine-induced hepatocarcinogenesis to investigate the liver cancer-promoting effects of a diet supplemented with 10% liquid fructose, administered to male and female rats for 11 months. A subset of the fructose-supplemented rats received resveratrol (RVT) in the last 4 months of treatment.

Results and discussion

Rat livers showed no de visu or histological evidence of liver tumorigenesis. However, we observed metabolic abnormalities that could be related to cancer development mainly in the female fructose-supplemented rats, such as increases in weight, adiposity and hepatic triglyceride levels, as well as hyperglycaemia, hyperuricemia, hyperleptinemia and a reduced insulin sensitivity index, which were partially reversed by RVT. Therefore, we performed a targeted analysis of 84 cancer-related genes in the female liver samples, which revealed expression changes associated with cancer-related pathways. Analysis of individual genes indicated that some changes increased the risk of hepatocarcinogenesis (Sfrp2, Ccl5, Socs3, and Gstp1), while others exerted a protective/preventive effect (Bcl2 and Cdh1).

Conclusion

Our data clearly demonstrate that chronic fructose supplementation, as the sole dietary intervention, does not cause HCC development in rats.

Nicotinamide Protects Against Diet-Induced Body Weight Gain, Increases Energy Expenditure, and Induces White Adipose Tissue Beiging

SCOPE

Interventions that boost NAD+ availability are of potential therapeutic interest for obesity treatment. The potential of nicotinamide (NAM), the amide form of vitamin B3 and a physiological precursor of nicotinamide adenine dinucleotide (NAD)+ , in preventing weight gain has not previously been studied in vivo. Other NAD+ precursors have been shown to decrease weight gain; however, their impact on adipose tissue is not addressed.

METHODS AND RESULTS

Two doses of NAM (high dose: 1% and low dose: 0.25%) are given by drinking water to C57BL/6J male mice, starting at the same time as the high-fat diet feeding. NAM supplementation protects against diet-induced obesity by augmenting global body energy expenditure in C57BL/6J male mice. The manipulation markedly alters adipose morphology and metabolism, particularly in inguinal (i) white adipose tissue (iWAT). An increased number of brown and beige adipocyte clusters, protein abundance of uncoupling protein 1 (UCP1), mitochondrial activity, adipose NAD+ , and phosphorylated AMP-activated protein kinase (P-AMPK) levels are observed in the iWAT of treated mice. Notably, a significant improvement in hepatic steatosis, inflammation, and glucose tolerance is also observed in NAM high-dose treated mice.

CONCLUSION

NAM influences whole-body energy expenditure by driving changes in the adipose phenotype. Thus, NAM is an attractive potential treatment for preventing obesity and associated complications.

Effects of a Low Dose of Caffeine Alone or as Part of a Green Coffee Extract, in a Rat Dietary Model of Lean Non-Alcoholic Fatty Liver Disease without Inflammation

Non-alcoholic fatty liver disease is a highly prevalent condition without specific pharmacological treatment, characterized in the initial stages by hepatic steatosis. It was suggested that lipid infiltration in the liver might be reduced by caffeine through anti-inflammatory, antioxidative, and fatty acid metabolism-related mechanisms. We investigated the effects of caffeine (CAF) and green coffee extract (GCE) on hepatic lipids in lean female rats with steatosis. For three months, female Sprague-Dawley rats were fed a standard diet or a cocoa butter-based high-fat diet plus 10% liquid fructose. In the last month, the high-fat diet was supplemented or not with CAF or a GCE, providing 5 mg/kg of CAF. Plasma lipid levels and the hepatic expression of molecules involved in lipid metabolism were determined. Lipidomic analysis was performed in liver samples. The diet caused hepatic steatosis without obesity, inflammation, endoplasmic reticulum stress, or hepatic insulin resistance. Neither CAF nor GCE alleviated hepatic steatosis, but GCE-treated rats showed lower hepatic triglyceride levels compared to the CAF group. The GCE effects could be related to reductions of hepatic (i) mTOR phosphorylation, leading to higher nuclear lipin-1 levels and limiting lipogenic gene expression; (ii) diacylglycerol levels; (iii) hexosylceramide/ceramide ratios; and (iv) very-low-density lipoprotein receptor expression. In conclusion, a low dose of CAF did not reduce hepatic steatosis in lean female rats, but the same dose provided as a green coffee extract led to lower liver triglyceride levels.

mTOR is a Key Protein Involved in the Metabolic Effects of Simple Sugars

One of the most important threats to global human health is the increasing incidences of metabolic pathologies (including obesity, type 2 diabetes and non-alcoholic fatty liver disease), which is paralleled by increasing consumptions of hypercaloric diets enriched in simple sugars. The challenge is to identify the metabolic pathways affected by the excessive consumption of these dietary components when they are consumed in excess, to unravel the molecular mechanisms leading to metabolic pathologies and identify novel therapeutic targets to manage them. Mechanistic (mammalian) target of rapamycin (mTOR) has emerged as one of the key molecular nodes that integrate extracellular signals, such as energy status and nutrient availability, to trigger cell responses that could lead to the above-mentioned diseases through the regulation of lipid and glucose metabolism. By activating mTOR signalling, excessive consumption of simple sugars (such as fructose and glucose), could modulate hepatic gluconeogenesis, lipogenesis and fatty acid uptake and catabolism and thus lipid deposition in the liver. In the present review we will discuss some of the most recent studies showing the central role of mTOR in the metabolic effects of excessive simple sugar consumption.

Chronic fructose intake does not induce liver steatosis and inflammation in female Sprague-Dawley rats, but causes hypertriglyceridemia related to decreased VLDL receptor expression

PURPOSE

Sugar-sweetened beverage intake is a risk factor for insulin resistance, dyslipidemia, fatty liver, and steatohepatitis (NASH). Sub-chronic supplementation of liquid fructose, but not glucose, in female rats increases liver and plasma triglycerides without inflammation. We hypothesized that chronic supplementation of fructose would cause NASH and liver insulin resistance.

METHODS

We supplemented female Sprague-Dawley rats with water or either fructose or glucose 10% w/v solutions under isocaloric conditions for 7 months. At the end, plasma analytes, insulin, and adiponectin were determined, as well as liver triglyceride content and the expression of key genes controlling inflammation, fatty acid synthesis and oxidation, endoplasmic reticulum stress, and plasma VLDL clearance, by biochemical and histological methods.

RESULTS

Although sugar-supplemented rats increased their energy intake by 50-60%, we found no manifestation of liver steatosis, fibrosis or necrosis, unchanged plasma or tissue markers of inflammation or fibrosis, and reduced liver expression of gluconeogenic enzymes, despite both sugars increased fatty acid synthesis, mTORC1, and IRE1 activity, while decreasing fatty acid oxidation and PPARα activity. Only fructose-supplemented rats were hypertriglyceridemic, showing a reduced expression of VLDL receptor and lipoprotein lipase in skeletal muscle and vWAT. Glucose-supplemented rats showed increased adiponectinemia, which would explain the different metabolic outcomes of the two sugars.

CONCLUSIONS

Chronic liquid simple sugar supplementation, as the sole risk factor, is not enough for female rats to develop NASH and increased liver gluconeogenesis. Nevertheless, under isocaloric conditions, only fructose induced hypertriglyceridemia, thus confirming that also the type of nutrient matters in the development of metabolic diseases.

The Addition of Liquid Fructose to a Western-Type Diet in LDL-R-/- Mice Induces Liver Inflammation and Fibrogenesis Markers without Disrupting Insulin Receptor Signalling after an Insulin Challenge

A high consumption of fat and simple sugars, especially fructose, has been related to the development of insulin resistance, but the mechanisms involved in the effects of these nutrients are not fully understood. This study investigates the effects of a Western-type diet and liquid fructose supplementation, alone and combined, on insulin signalling and inflammation in low-density lipoprotein (LDL) receptor-deficient mice (LDL-R^−/−). LDL-R^−/− mice were fed chow or Western diet ±15% fructose solution for 12 weeks. Plasma glucose and insulin, and the expression of genes related to inflammation in the liver and visceral white adipose tissue (vWAT), were analysed. V-akt murine thymoma viral oncogene homolog-2 (Akt) activation was measured in the liver of the mice after a single injection of saline or insulin. None of the dietary interventions caused inflammation in vWAT, whereas the Western diet induced hepatic inflammation, which was further enhanced by liquid fructose, leading also to a significant increase in fibrogenesis markers. However, there was no change in plasma glucose or insulin, or insulin-induced Akt phosphorylation. In conclusion, hepatic inflammation and fibrogenesis markers induced by a Western diet supplemented with liquid fructose in LDL-R^−/− mice are not associated with a significant impairment of hepatic insulin signalling.

Liquid fructose in Western-diet-fed mice impairs liver insulin signaling and causes cholesterol and triglyceride loading without changing calorie intake and body weight

BACKGROUND/OBJECTIVES

Liquid fructose associates with prevalence of type 2 diabetes mellitus and obesity. Intervention studies suggest that metabolically unfit individuals are more responsive than healthy individuals to liquid fructose. We determined whether mice consuming an obesogenic Western diet were more responsive than chow-fed mice to the alterations induced by liquid fructose supplementation (LFS).

METHODS

C57BL/6N mice were fed chow or Western diet±ad libitum 15% fructose solution for 12 weeks. Food and liquid intake and body weight were monitored. Plasma analytes and liver lipids, histology and the expression of genes related to lipid handling, endoplasmic reticulum stress, inflammation and insulin signaling were analyzed.

RESULTS

Western diet increased energy intake, visceral adipose tissue (vWAT), body weight, plasma and liver triglycerides and cholesterol, and inflammatory markers in vWAT vs. chow-fed mice. LFS did not change energy intake, vWAT or body weight. LFS significantly increased plasma and liver triglycerides and cholesterol levels only in Western-diet-fed mice. These changes associated with a potentiation of the increased liver expression of PPARγ and CD36 that was observed in Western-fed mice and related to the increased liver mTOR phosphorylation induced by LFS. Furthermore, LFS in Western-diet-fed mice induced the largest reduction in liver IRS2 protein and a significant decrease in whole-body insulin sensitivity.

CONCLUSIONS

LFS in mice, in a background of an unhealthy diet that already induces fatty liver visceral fat accretion and obesity, increases liver lipid burden, hinders hepatic insulin signaling and diminishes whole-body insulin sensitivity without changing energy intake.

Suppressor of cytokine signaling-3 (SOCS-3) and a deficit of serine/threonine (Ser/Thr) phosphoproteins involved in leptin transduction mediate the effect of fructose on rat liver lipid metabolism

There is controversy regarding whether fructose in liquid beverages constitutes another dietary ingredient of high caloric density or introduces qualitative changes in energy metabolism that further facilitate the appearance of metabolic diseases. Central to this issue is the elucidation of the molecular mechanism responsible for the metabolic alterations induced by fructose ingestion. Fructose administration (10% wt/vol) in the drinking water of Sprague-Dawley male rats for 14 days induced hyperleptinemia and hepatic leptin resistance. This was caused by impairment of the leptin-signal transduction mediated by both janus-activated kinase-2 and the mitogen-activated protein kinase pathway. The subsequent increase in activity in the liver of the unphosphorylated and active form of the forkhead box O1 nuclear factor, which transrepresses peroxisome proliferator-activated receptor alpha activity, and a lack of activation of the adenosine monophosphate-activated protein kinase, led to hypertriglyceridemia and hepatic steatosis. These alterations are attributable to two key events: (1) an increase in the amount of suppressor of cytokine signaling-3 protein, which blocks the phosphorylation and activation of janus-activated kinase-2 and Tyr(985) on the long form of the leptin receptor; and (2) a common deficit of phosphorylation in serine/threonine residues of key proteins in leptin-signal transduction pathways. The latter is probably produced by the early activation of protein phosphatase 2A, and further sustained by the accumulation in liver tissue of ceramide, an activator of protein phosphatase 2A, due to incomplete oxidation of fatty acids.

CONCLUSION

Our data indicate that fructose ingestion as a liquid solution induces qualitative changes in liver metabolism that lead to metabolic diseases.

Hypertriglyceridemia and hepatic steatosis in senescence-accelerated mouse associate to changes in lipid-related gene expression

Aged rodents show increasing plasma and tissue triglycerides, and reductions in liver peroxisome proliferator-activated receptor alpha (PPARalpha) and its target genes. We determined whether a similar situation is present in a model of accelerated aging, the senescence-accelerated prone (SAM-P8) mouse. Five-month-old SAM-P8 mice were hypertriglyceridemic, and exhibited hepatic steatosis and reduced fatty acid oxidation versus control 5-month-old senescence-accelerated resistant (SAM-R1) mice, with no differences in PPARalpha expression and binding activity; in fact, fenofibrate administration to SAM-P8 mice induced a clear PPARalpha-driven response. Complementary DNA (cDNA) microarray analysis (Affymetrix Mouse Genome 430A 2.0 GeneChip array), Western blot, and electrophoretic mobility shift assay (EMSA) experiments indicated, among other changes, a deficit in farnesoid X receptor (FXR) expression and binding activity in the livers of SAM-P8 mice with respect to SAM-R1 controls. Triglyceride accretion and a deficit in hepatic fatty acid oxidation, features of the aging process in mammals, associate to a deficit in hepatic FXR activity in the SAM-P8 mice.

Impairment of hepatic Stat-3 activation and reduction of PPARalpha activity in fructose-fed rats

Fructose makes up a significant proportion of energy intake in westernized diets; its increased consumption has paralleled the growing prevalence of obesity and metabolic syndrome over the past two decades. In the current study, we demonstrate that fructose administration (10% wt/vol) in the drinking water of rats reduces the trans-activating and trans-repressing activity of the hepatic peroxisome proliferator-activated receptor alpha (PPARalpha). As a consequence, fructose decreases hepatic fatty oxidation and increases pro-inflammatory transcription factor nuclear factor kappaB (NF-kappaB) activity. These changes were not observed in glucose-administered rats (10% wt/vol), although both carbohydrates produced similar changes in plasma adiponectin and in the hepatic expression of transcription factors and enzymes involved in fatty acid synthesis. Fructose-fed, but not glucose-fed, rats were hyperleptinemic and exhibited increased tyrosine phosphorylation of the signal transducer and activator of transcription-3 (STAT-3) transcription factor, although they did not present a similar increase in the serine phosphorylation of nuclear STAT3. Thus, an impairment in the hepatic transduction of the leptin signal could be responsible for the observed alterations in PPARalpha activity in fructose-fed rats. Because PPARalpha activity is lower in human than in rodent liver, fructose ingestion in humans should cause even worse effects, which would partly explain the link between increased consumption of fructose and widening epidemics of obesity and metabolic syndrome.

CONCLUSION

Hypertriglyceridemia and hepatic steatosis induced by fructose ingestion result from a reduction in the hepatic catabolism of fatty acids driven by a state of leptin resistance.

Palmitate-mediated downregulation of peroxisome proliferator-activated receptor-gamma coactivator 1alpha in skeletal muscle cells involves MEK1/2 and nuclear factor-kappaB activation

The mechanisms by which elevated levels of free fatty acids cause insulin resistance are not well understood. Previous studies have reported that insulin-resistant states are characterized by a reduction in the expression of peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1, a transcriptional activator that promotes oxidative capacity in skeletal muscle cells. However, little is known about the factors responsible for reduced PGC-1 expression. The expression of PGC-1 mRNA levels was assessed in C2C12 skeletal muscle cells exposed to palmitate either in the presence or in the absence of several inhibitors to study the biochemical pathways involved. We report that exposure of C2C12 skeletal muscle cells to 0.75 mmol/l palmitate, but not oleate, reduced PGC-1alpha mRNA levels (66%; P < 0.001), whereas PGC-1beta expression was not affected. Palmitate led to mitogen-activated protein kinase (MAPK)-extracellular signal-related kinase (ERK) 1/2 (MEK1/2) activation. In addition, pharmacological inhibition of this pathway by coincubation of the palmitate-exposed cells with the MEK1/2 inhibitors PD98059 and U0126 prevented the downregulation of PGC-1alpha. Furthermore, nuclear factor-kappaB (NF-kappaB) activation was also involved in palmitate-mediated PGC-1alpha downregulation, since the NF-kappaB inhibitor parthenolide prevented a decrease in PGC-1alpha expression. These findings indicate that palmitate reduces PGC-1alpha expression in skeletal muscle cells through a mechanism involving MAPK-ERK and NF-kappaB activation.

Leptin down-regulates peroxisome proliferator-activated receptor gamma (PPAR-gamma) mRNA levels in primary human monocyte-derived macrophages

Increased leptin levels are associated with cardiovascular disease in obesity although the mechanism is unknown. Peroxisome proliferator-activated receptor gamma (PPARgamma) is a key regulator of macrophage lipid metabolism and its activation by thiazolidinediones protects against atherosclerosis. The aim of this study was to assess the effects of human recombinant leptin on PPARgamma mRNA levels in primary human macrophages and macrophage-derived foam cells. Leptin treatment (100 ng/ml) for 24 h caused a 41% reduction (p < 0.01) in PPARgamma transcript levels in human-derived macrophages. This fall was accompanied by a reduction in the mRNA expression of carnitine palmitoyltransferase (CPT-I) (36%, p < 0.05) and ABCA1 (62%, p < 0.05), whereas CD36 mRNA reduction (34%) was not significant. In macrophage-derived foam cells, leptin at 20 ng/ml reduced PPARgamma mRNA levels by 33% (p < 0.01) and CPT-I by 27% (p < 0.05). At this concentration, leptin did not modify the expression of either ABCA1 or CD36. In agreement with these results, intracellular cholesterol ester accumulation was not altered in macrophage-derived foam cells by leptin at 20 ng/ml. We propose that the reduction in PPARgamma expression in both macrophages and foam cells may be one of the factors linking high leptin levels and cardiovascular disease.

Palmitate induces tumor necrosis factor-alpha expression in C2C12 skeletal muscle cells by a mechanism involving protein kinase C and nuclear factor-kappaB activation

The mechanisms responsible for increased expression of TNF-alpha in skeletal muscle cells in diabetic states are not well understood. We examined the effects of the saturated acid palmitate on TNF-alpha expression. Exposure of C2C12 skeletal muscle cells to 0.75 mm palmitate enhanced mRNA (25-fold induction, P < 0.001) and protein (2.5-fold induction) expression of the proinflammatory cytokine TNF-alpha. This induction was inversely correlated with a fall in GLUT4 mRNA levels (57% reduction, P < 0.001) and glucose uptake (34% reduction, P < 0.001). PD98059 and U0126, inhibitors of the ERK-MAPK cascade, partially prevented the palmitate-induced TNF-alpha expression. Palmitate increased nuclear factor (NF)-kappaB activation and incubation of the cells with the NF-kappaB inhibitors pyrrolidine dithiocarbamate and parthenolide partially prevented TNF-alpha expression. Incubation of palmitate-treated cells with calphostin C, a strong and specific inhibitor of protein kinase C (PKC), abolished palmitate-induced TNF-alpha expression, and restored GLUT4 mRNA levels. Palmitate treatment enhanced the expression of phospho-PKCtheta, suggesting that this PKC isoform was involved in the changes reported, and coincubation of palmitate-treated cells with the PKC inhibitor chelerythrine prevented the palmitate-induced reduction in the expression of IkappaBalpha and insulin-stimulated Akt activation. These findings suggest that enhanced TNF-alpha expression and GLUT4 down-regulation caused by palmitate are mediated through the PKC activation, confirming that this enzyme may be a target for either the prevention or the treatment of fatty acid-induced insulin resistance.

Palmitate-induced interleukin 6 production is mediated by protein kinase C and nuclear-factor kappaB activation and leads to glucose transporter 4 down-regulation in skeletal muscle cells

The mechanisms by which elevated levels of free fatty acids cause insulin resistance are not well understood. In addition, accumulating evidence suggests a link between inflammation and type 2 diabetes. Here, we report that exposure of C2C12 skeletal muscle cells to 0.5 mm palmitate results in increased mRNA levels (3.5-fold induction; P < 0.05) and secretion (control 375 +/- 57 vs. palmitate 1129 +/- 177 pg/ml; P < 0.001) of the proinflammatory cytokine IL-6. Palmitate increased nuclear factor-kappaB activation and coincubation of the cells with palmitate and the nuclear factor-kappaB inhibitor pyrrolidine dithiocarbamate prevented both IL-6 expression and secretion. Furthermore, incubation of palmitate-treated cells with calphostin C, a strong and specific inhibitor of protein kinase C, and phorbol myristate acetate, that down-regulates protein kinase C in long-term incubations, abolished induction of IL-6 production. Finally, exposure of skeletal muscle cells to palmitate caused a fall in the mRNA levels of glucose transporter 4 and insulin-stimulated glucose uptake, whereas in the presence of anti-IL-6 antibody, which neutralizes the biological activity of mouse IL-6 in cell culture, these reductions were prevented. These findings suggest that IL-6 may mediate several of the prodiabetic effects of palmitate.

Increased Akt protein expression is associated with decreased ceramide content in skeletal muscle of troglitazone-treated mice

Although it is generally believed that thiazolidinediones ameliorate insulin resistance by lowering circulating free fatty acids, direct effects of these drugs in skeletal muscle may also contribute to their antidiabetic action. We report that troglitazone administration to mice for 1 day increased the protein expression of Akt (two-fold induction, P<0.001) in skeletal muscle without significant changes in the levels of free fatty acids in plasma. Increased Akt protein expression was associated with reduced phospho-AMP-activated protein kinase abundance and with a fall in the phosphorylation of acetyl-CoA carboxylase, which in turn resulted in an increase in the content of muscular malonyl-CoA (2.4-fold, P<0.05) and lactate (1.4-fold, P<0.05). Troglitazone treatment did not affect the mRNA levels of either Akt1 or Akt2, suggesting that a transcriptional mechanism was not involved, but caused a dramatic reduction in the content of muscular ceramides (76%, P<0.001), lipid-derived second messengers known to increase Akt degradation. Our data indicate that troglitazone treatment inhibited de novo ceramide synthesis, since the content of its precursor, palmitoyl-CoA, was reduced (55%, P=0.05). These results were confirmed in C2C12 myotubes, where troglitazone treatment increased Akt protein expression and prevented the reduction of this protein and the increase in ceramide levels caused by palmitate. These findings implicate ceramide as an important intermediate in the regulation of Akt after troglitazone treatment.

Sexual dimorphism in lipid metabolic phenotype associated with old age in Sprague-Dawley rats

PURPOSE

Aged male rats show a decrease in liver PPARalpha. We aimed to determine if the sexual dimorphism in lipid metabolism observed in the PPARalpha-/- mouse is also present in senescent rats.

RESULTS

Eighteen-month old rats were obese and presented high plasma NEFA concentrations. Old male rats were more hypercholesterolemic and hyperleptinemic than females, presenting a higher content in hepatic triglycerides and cholesteryl esters, while 18-month old females were more hypertriglyceridemic than males. Although PPARalpha expression and binding activity was reduced in liver from old male and female rats, the mRNA for a PPARalpha target gene, such as CPT-I, was reduced in old males (-56%), while increased by 286% in old females. LXRalpha protein was increased, and its binding activity was decreased in livers of old males, while livers of old females showed an increase in DGAT1 (2.6-fold) and DGAT2 (4.9-fold) mRNA, with respect to 3-month old animals. The increases in DGAT1 and DGAT2 mRNAs matched in old females those of plasma (3.1-fold) and liver triglycerides (5.0-fold).

CONCLUSIONS

These features disclose a marked sexual dimorphism in lipid metabolism associated to old age in rats that can be partially attributed not only to an age-related decrease in liver PPARalpha expression, but also to changes in other hepatic transcription factors and enzymes, such as liver X receptor alpha (LXRalpha) and diacylglycerol acyltransferases (DGAT).

Aspirin increases CD36, SR-BI, and ABCA1 expression in human THP-1 macrophages

OBJECTIVE

CD36 is a receptor, whose expression increases during the differentiation of monocytes to macrophages, playing a key role in the phagocytosis of apoptotic cells and in the formation of foam cells during atherosclerosis. Recently, it has been described that ligands of PPARgamma induce CD36 expression and inhibit cyclooxygenase expression in macrophages. Our aim was to study whether the reduction of endogenous prostaglandin production could modify CD36 expression in macrophages and to outline the potential mechanism.

METHODS AND RESULTS

CD36 expression was measured by flow cytometry in THP-1 cells differentiated to macrophages that had been incubated with aspirin (ASA) alone or in combination with PGE(2), sulprostone (EP1/EP3 agonist), butaprost (EP2 agonist,) and PGE1 alcohol (EP2/EP4 agonist). Aspirin induced CD36 expression. Only PGE(2) and PGE1 alcohol completely abolished CD36 induction by aspirin, whereas butaprost strongly reduced it. BADGE (a PPARgamma antagonist) or diclofenac (a PPARgamma antagonist and a cyclooxygenase inhibitor) in aspirin-incubated cells did not reduce CD36 induction. On the other hand, aspirin also induced the expression of SR-BI and ABCA1, an HDL receptor and an HDL formation-related protein, respectively.

CONCLUSIONS

Aspirin produces an increase of CD36 expression in THP-1 macrophages by a PGE(2)-dependent mechanism. The PGE(2) receptors implicated in CD36 modulation by ASA are the EP2/EP4 subtypes. Further, we provide evidence of SR-BI and ABCA1 induction by aspirin treatment.

Peroxisome proliferator-activated receptors and the control of inflammation

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors which form a subfamily of the nuclear receptor gene family. This subfamily consists of three isotypes, alpha (NR1C1), gamma (NR1C3), and beta/delta (NRC1C2) with a differential tissue distribution. PPARalpha is expressed primarily in tissues with a high level of fatty acid catabolism such as liver, brown fat, kidney, heart and skeletal muscle. PPARbeta is ubiquitously expressed, and PPARgamma has a restricted pattern of expression, mainly in white and brown adipose tissues, whereas other tissues such as skeletal muscle and heart contain limited amounts. Furthermore, PPARalpha and gamma isotypes are expressed in vascular cells including endothelial and smooth muscle cells and macrophages/foam cells. PPARs are activated by ligands, such as naturally occurring fatty acids, which are activators of all three PPAR isotypes. In addition to fatty acids, several synthetic compounds, such as fibrates and thiazolidinediones, bind and activate PPARalpha and PPARgamma, respectively. In order to be transcriptionally active, PPARs need to heterodimerize with the retinoid-X-receptor (RXR). Upon activation, PPAR-RXR heterodimers bind to DNA specific sequences called peroxisome proliferator-response elements (PPRE) and stimulate transcription of target genes. PPARs play a critical role in lipid and glucose homeostasis, but lately they have been implicated as regulators of inflammatory responses. The first evidence of the involvement of PPARs in the control of inflammation came from the PPARalpha null mice, which showed a prolonged inflammatory response. PPARalpha activation results in the repression of NF-kappaB signaling and inflammatory cytokine production in different cell-types. A role for PPARgamma in inflammation has also been reported in monocyte/macrophages, where ligands of this receptor inhibited the activation of macrophages and the production of inflammatory cytokines (TNFalpha, interleukin 6 and 1beta), although part of the anti-inflammatory effects of these ligands seems to be mediated by a mechanism not involving PPARgamma. All these findings suggest a role of PPARs in the control of the inflammatory response with potential therapeutic applications in inflammation-related diseases.

Differential effects of peroxisome proliferator-activated receptor activators on the mRNA levels of genes involved in lipid metabolism in primary human monocyte-derived macrophages

Peroxisome proliferator-activated receptors (PPARs) are key regulators of macrophage lipid metabolism. We compared the effects of three PPAR activators (bezafibrate, fenofibrate, and troglitazone) on the mRNA levels of genes involved in lipid metabolism in primary human macrophages and macrophage-derived foam cells. Treatment of human macrophages for 24 hours with 100 micro mol/L bezafibrate, a nonselective drug that activates the 3 PPAR subtypes (PPARalpha, PPARbeta/delta, and PPARgamma), caused an 87% (P <.01) and a 230% rise in CD36 and adipocyte fatty acid-binding protein (aP2) mRNA levels, respectively, whereas the expressions of PPARgamma, PPARalpha, acyl-CoA oxidase, carnitine palmitoyltransferase I (CPT-I), adenosine triphosphate (ATP)-binding cassette transporter 1 (ABCA1), neutral cholesteryl ester hydrolase, and lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) were not modified. However, treatment with selective PPARalpha (fenofibrate at 100 micro mol/L) and PPARgamma (troglitazone at 5 micro mol/L) activators had different effects. Fenofibrate increased PPARalpha (62%, P <.05) and LOX-1 (180%, P <.05) mRNA levels; and troglitazone upregulated CPT-I expression (75%, P <.05). When the effects of these drugs were assessed in macrophage-derived foam cells, we found that troglitazone caused a 134% (P <.05) and a 66% (P <.01) rise in ABCA1 and CPT-I mRNA levels, respectively, whereas the 3 drugs significantly increased aP2 transcripts (about 100% induction). Given that troglitazone treatment resulted in the upregulation of genes involved in the mitochondrial beta-oxidation of fatty acids (CPT-I) and in the reverse-cholesterol-transport pathway (ABCA1), we subsequently determined whether these changes affected intracellular cholesterol ester accumulation. In macrophage-derived foam cells a significant reduction (32%, P <.01) was observed in intracellular cholesterol accumulation after troglitazone, but not after bezafibrate or fenofibrate treatment. Since CPT-I inhibition promotes cholesterol incorporation into cholesteryl esters in macrophages, study is now needed on whether CPT-I induction by troglitazone may reduce the availability of fatty acids for synthesizing cholesterol esters, leading to less foam cell formation.

Walnut-enriched diet increases the association of LDL from hypercholesterolemic men with human HepG2 cells

In a randomized, cross-over feeding trial involving 10 men with polygenic hypercholesterolemia, a control, Mediterranean-type cholesterol-lowering diet, and a diet of similar composition in which walnuts replaced approximately 35% of energy from unsaturated fat, were given for 6 weeks each. Compared with the control diet, the walnut diet reduced serum total and LDL cholesterol by 4.2% (P = 0.176), and 6.0% (P = 0.087), respectively. No changes were observed in HDL cholesterol, triglycerides, and apolipoprotein A-I levels or in the relative proportion of protein, triglycerides, phospholipids, and cholesteryl esters in LDL particles. The apolipoprotein B level declined in parallel with LDL cholesterol (6.0% reduction). Whole LDL, particularly the triglyceride fraction, was enriched in polyunsaturated fatty acids from walnuts (linoleic and alpha-linolenic acids). In comparison with LDL obtained during the control diet, LDL obtained during the walnut diet showed a 50% increase in association rates to the LDL receptor in human hepatoma HepG2 cells. LDL uptake by HepG2 cells was correlated with alpha-linolenic acid content of the triglyceride plus cholesteryl ester fractions of LDL particles (r(2) = 0.42, P < 0.05). Changes in the quantity and quality of LDL lipid fatty acids after a walnut-enriched diet facilitate receptor-mediated LDL clearance and may contribute to the cholesterol-lowering effect of walnut consumption.

Increase in hepatic expression of SREBP-2 by gemfibrozil administration to rats

It is well known that gemfibrozil increases the biliary output of cholesterol and phospholipids, but we have little knowledge about the impact these changes have on liver cholesterol and phospholipid biosynthetic pathways. In the present study, no changes were detected in liver lipids and CTP:phosphocholine cytidylyltransferase after gemfibrozil administration to rats. On the contrary, 3-hydroxy-3-methylglutaryl-CoA reductase mRNA (9.9-fold) and Rd activity (16.7-fold) and phosphatidate phosphohydrolase activity (1.7-fold) increased, while plasma apo B-cholesterol (40%) and triglyceride (43%) levels decreased. As a part of a compensatory homeostatic response, we report for the first time that gemfibrozil administration to rats increased the hepatic sterol regulatory element binding protein-2 (SREBP-2) mRNA (2.9-fold) and mature protein (2.2-fold) levels. An early increase in the transcriptional activity of SREBP-2 elicited by gemfibrozil administration might be responsible for the observed changes in HMG-CoA reductase, phosphatidate phosphohydrolase, and SREBP-2 expression.

Bezafibrate reduces mRNA levels of adipocyte markers and increases fatty acid oxidation in primary culture of adipocytes

The molecular mechanisms by which peroxisome proliferator-activated receptor (PPAR) activation by fibrates reduces fat deposition and improves insulin sensitivity are not completely understood. We report that exposure of a rat primary culture of adipocytes for 24 h to the PPAR activator bezafibrate increased the mRNA levels of crucial genes involved in peroxisomal and mitochondrial beta-oxidation. The mRNA levels of the peroxisomal beta-oxidation rate-limiting enzyme acyl-CoA oxidase and of the muscle-type carnitine palmitoyl transferase I (M-CPT-I), which determines the flux of mitochondrial beta-oxidation, increased by 1.6-fold (P < 0.02) and 4.5-fold (P = 0.001), respectively. These changes were accompanied by an increase in the transcript levels of the uncoupling protein-2 (UCP-2; 1.5-fold induction; P < 0.05) and UCP-3 (3.7-fold induction; P < 0.001), mitochondrial proteins that reduce ATP yield and may facilitate the oxidation of fatty acids. Furthermore, bezafibrate increased the mRNA levels of the fatty acid translocase (2-fold induction; P < 0.01), suggesting a higher fatty acid uptake into adipocytes. In agreement with these changes, bezafibrate caused a 1.9-fold induction (P < 0.02) in 9,10-[(3)H]palmitate oxidation. Moreover, bezafibrate reduced the mRNA expression of several adipocyte markers, including PPARgamma (30% reduction; P = 0.05), tumor necrosis factor-alpha (33% reduction; P < 0.05), and the ob gene (26% reduction). In contrast, adipocyte fatty acid binding protein mRNA levels increased (1.5-fold induction; P < 0.01), pointing to a mobilization of fatty acids to mitochondria and peroxisomes. The reduction of the adipocyte markers caused by bezafibrate was accompanied by an increase in the mRNA levels of the preadipocyte marker Pref-1 (1.6-fold induction; P < 0.01). Some of the changes observed in the primary culture of rat adipocytes also were studied in the epididymal white adipose tissue of bezafibrate-treated rats for 7 days. In vivo, M-CPT-I mRNA levels increased (4.5-fold induction; P = 0.001) in epididymal white adipose tissue of bezafibrate-treated rats. Similarly, fatty acid translocase (2.6-fold induction; P = 0.002) and Pref-1 (5.6-fold induction) mRNA levels increased, although differences in the latter were not significant because of huge individual variations. These results indicate that exposure of adipocytes to bezafibrate, independent of its hepatic effects, increases the degradation of fatty acids, reducing their availability to synthesize triglycerides. As a result, some degree of dedifferentiation of adipocytes to preadipocyte-like cells is achieved. These changes may be involved in the reduction in fat depots and in the improvement of insulin sensitivity observed after bezafibrate treatment.

Uncoupling protein-3 mRNA up-regulation in C2C12 myotubes after etomoxir treatment

Uncoupling proteins (UCPs) are mitochondrial membrane proton transporters that uncouple respiration from oxidative phosphorylation by dissipating the proton gradient across the membrane. Treatment of C2C12 myotubes for 24 h with 40 microM etomoxir, an irreversible inhibitor of carnitine palmitoyltransferase I (CPT-I), up-regulated uncoupling protein 3 (UCP-3) mRNA levels (2-fold induction), whereas UCP-2 mRNA levels were not modified. Etomoxir treatment also caused a 2.5-fold induction in M-CPT-I (muscle-type CPT-I) mRNA levels. In contrast, other well-known peroxisome proliferator-activated receptor alpha (PPAR alpha) target genes, such as acyl-CoA oxidase and medium-chain acyl-CoA dehydrogenase, were not affected, suggesting that this transcription factor was not involved in the effects of etomoxir. Since it has been reported that CPT-I inhibition by etomoxir leads to a further increase in ceramide synthesis, we test the possibility that ceramides were involved in the changes reported. Similarly to etomoxir, addition of 20 microM C(2)-ceramide to C2C12 myotubes for 3, 6 and 9 h resulted in increased UCP-3 and M-CPT-I mRNA levels. These results indicate that the effects on UCP-3 mRNA levels could be mediated by increased ceramide synthesis.

Differential induction of stearoyl-CoA desaturase and acyl-CoA oxidase genes by fibrates in HepG2 cells

We studied whether two typical effects of fibrates, induction of stearoyl-CoA desaturase (EC 1.14.99.5) and peroxisome proliferation, are related. The effect of bezafibrate on the activity and mRNA of stearoyl-CoA desaturase and acyl-CoA oxidase in the liver and epididymal white adipose tissue of male Sprague-Dawley rats was determined. The same parameters were measured in HepG2 cells, a cell line resistant to peroxisome proliferation, following incubation with ciprofibrate. Bezafibrate increased the hepatic mRNA levels (14.5-fold on day 7) and activity (9.3-fold on day 15) of acyl-CoA oxidase. Stearoyl-CoA desaturase mRNA levels were transiently increased (2.7-fold on day 7), while its activity remained increased at the end of the treatment (2.4-fold). In white adipose tissue, bezafibrate increased the mRNA (5-fold) and activity (1.9-fold) of acyl-CoA oxidase, while stearoyl-CoA desaturase was not modified. Ciprofibrate addition to HepG2 cells cultured in 7% fetal bovine serum (FBS) only increased the stearoyl-CoA desaturase mRNA (1.9-fold). When cells were cultured in 0.5% FBS, ciprofibrate increased acyl-CoA oxidase mRNA (2.2-fold), while the increase in stearoyl-CoA desaturase mRNA was identical (1.9-fold). Further, its activity was also increased (1.5-fold). Incubation of HepG2 cells in the presence of cycloheximide did not alter the capacity of ciprofibrate to induce stearoyl-CoA desaturase mRNA, whereas the presence of actinomycin abolished the induction. In addition, preincubation of HepG2 cells with ciprofibrate increased the rate of stearoyl-CoA desaturase mRNA degradation. The results presented in this study suggest that fibrates induce stearoyl-CoA desaturase activity and mRNA levels independently of peroxisome proliferation.