Scalable Generation of Pre-Vascularized and Functional Human Beige Adipose Organoids

Obesity and type 2 diabetes are becoming a global sociobiomedical burden. Beige adipocytes are emerging as key inducible actors and putative relevant therapeutic targets for improving metabolic health. However, in vitro models of human beige adipose tissue are currently lacking and hinder research into this cell type and biotherapy development. Unlike traditional bottom-up engineering approaches that aim to generate building blocks, here a scalable system is proposed to generate pre-vascularized and functional human beige adipose tissue organoids using the human stromal vascular fraction of white adipose tissue as a source of adipose and endothelial progenitors. This engineered method uses a defined biomechanical and chemical environment using tumor growth factor β (TGFβ) pathway inhibition and specific gelatin methacryloyl (GelMA) embedding parameters to promote the self-organization of spheroids in GelMA hydrogel, facilitating beige adipogenesis and vascularization. The resulting vascularized organoids display key features of native beige adipose tissue including inducible Uncoupling Protein-1 (UCP1) expression, increased uncoupled mitochondrial respiration, and batokines secretion. The controlled assembly of spheroids allows to translate organoid morphogenesis to a macroscopic scale, generating vascularized centimeter-scale beige adipose micro-tissues. This approach represents a significant advancement in developing in vitro human beige adipose tissue models and facilitates broad applications ranging from basic research to biotherapies.

Adipose tissue plasticity in pheochromocytoma patients suggests a role of the splicing machinery in human adipose browning

Adipose tissue from pheochromocytoma patients acquires brown fat features, making it a valuable model for studying the mechanisms that control thermogenic adipose plasticity in humans. Transcriptomic analyses revealed a massive downregulation of splicing machinery components and splicing regulatory factors in browned adipose tissue from patients, with upregulation of a few genes encoding RNA-binding proteins potentially involved in splicing regulation. These changes were also observed in cell culture models of human brown adipocyte differentiation, confirming a potential involvement of splicing in the cell-autonomous control of adipose browning. The coordinated changes in splicing are associated with a profound modification in the expression levels of splicing-driven transcript isoforms for genes involved in the specialized metabolism of brown adipocytes and those encoding master transcriptional regulators of adipose browning. Splicing control appears to be a relevant component of the coordinated gene expression changes that allow human adipose tissue to acquire a brown phenotype.

GDF11 inhibits adipogenesis and improves mature adipocytes metabolic function via WNT/β-catenin and ALK5/SMAD2/3 pathways

Objective

GDF11 is a member of the TGF‐β superfamily that was recently implicated as potential “rejuvenating” factor, which can ameliorate metabolic disorders. The main objective of the presented study was to closely characterize the role of GDF11 signaling in the glucose homeostasis and in the differentiation of white adipose tissue.

Methods

We performed microscopy imaging, biochemical and transcriptomic analyses of adipose tissues of 9 weeks old ob/ob mice and murine and human pre‐adipocyte cell lines.

Results

Our in vivo experiments employing GDF11 treatment in ob/ob mice showed improved glucose/insulin homeostasis, decreased weight gain and white adipocyte size. Furthermore, GDF11 treatment inhibited adipogenesis in pre‐adipocytes by ALK5‐SMAD2/3 activation in cooperation with the WNT/β‐catenin pathway, whose inhibition resulted in adipogenic differentiation. Lastly, we observed significantly elevated levels of the adipokine hormone adiponectin and increased glucose uptake by mature adipocytes upon GDF11 exposure.

Conclusion

We show evidence that link GDF11 to adipogenic differentiation, glucose, and insulin homeostasis, which are pointing towards potential beneficial effects of GDF11‐based “anti‐obesity” therapy.

Blood Sampling for Arteriovenous Difference Measurements Across Interscapular Brown Adipose Tissue in Rat

A classic physiological approach to assess the specific uptake or release of circulating factors in organs and tissues is to measure concentration differences between venous and arterial blood. For interscapular brown adipose tissue (iBAT), the anatomic distribution of its vascularization, which drains most of the blood into Sulzer's vein, allows for local measurement of arteriovenous differences. The use of this procedure to monitor oxygen concentration changes was fundamental for the recognition of BAT as the main site of adaptive non-shivering thermogenesis. More recently, this technique has regained importance as a means to identify BAT-secreted regulatory molecules, such as fibroblast growth factor-21 and the chemokine CXCL14. In this chapter, we provide a detailed description of an optimized and feasible protocol to determine arteriovenous differences across iBAT. We include tips and practical advice for using this powerful tool to study BAT metabolism and secretory activity in rats as an experimental model.

A Differential Pattern of Batokine Expression in Perivascular Adipose Tissue Depots From Mice

Depending on its anatomical placement, perivascular adipose tissue (PVAT) has been found to possess features more (e.g., aortic thoracic) or less (e.g., aortic abdominal) similar to brown/beige adipose tissue in mice, whereas PVAT surrounding the mesenteric arteries and the caudal part of abdominal aorta is similar to white fat. PVAT is thought to influence vascular function through the effects of adipose-secreted molecules on vessels. Brown adipose tissue was recently shown to play differential secretory role via secretion of the so-called batokines but the involvement of differential batokine production in PVAT brown/beige plasticity was unclear. The current study characterizes for the first time the expression of batokines at aortic thoracic PVAT (tPVAT) and aortic abdominal PVAT (aPVAT) in comparison with typical brown and white adipose depots, in basal and thermogenically activated conditions. We found that both PVAT depots increased their expression of genes encoding the batokines bone morphogenetic protein-8b (BMP8B), fibroblast growth factor-21 (FGF21), and kininogen-2 (KNG2) in response to cold, indicating that, under cold-induced thermogenic activation, both thoracic aorta and abdominal aorta would experience intense local exposure to these PVAT-secreted batokines. In contrast, the gene expression levels of growth/differentiation factor-15 and vascular endothelial growth factor-A were induced only in tPVAT. Under short-term high-fat diet-induced thermogenic activation, the thoracic aorta would be specifically exposed to a local increase in PVAT-originating BMP8B, FGF21, and KNG2. Our data support the notion that acquisition of a brown/beige phenotype in PVAT is associated with upregulation of batokines, mainly BMP8B, FGF21, and KNG2, that can differentially target the vascular system.

GDF11 induces mild hepatic fibrosis independent of metabolic health

Background & aims: Growth Differentiation Factor 11 (GDF11) is an anti-aging factor, yet its role in liver diseases is not established. We evaluated the role of GDF11 in healthy conditions and in the transition from non-alcoholic fatty liver disease (NAFLD) to non-alcoholic steatohepatitis (NASH).

Results: GDF11 mRNA levels positively correlated with NAFLD activity score and with CPT1, SREBP, PPARγ and Col1A1 mRNA levels, and associated to portal fibrosis, in morbidly obese patients with NAFLD/NASH. GDF11-treated mice showed mildly exacerbated hepatic collagen deposition, accompanied by weight loss and without changes in liver steatosis or inflammation. GDF11 triggered ALK5-dependent SMAD2/3 nuclear translocation and the pro-fibrogenic activation of HSC.

Conclusions: GDF11 supplementation promotes mild liver fibrosis. Even considering its beneficial metabolic effects, caution should be taken when considering therapeutics that regulate GDF11.

Methods: We analyzed liver biopsies from a cohort of 33 morbidly obese adults with NAFLD/NASH. We determined the correlations in mRNA expression levels between GDF11 and genes involved in NAFLD-to-NASH progression and with pathological features. We also exposed wild type or obese mice with NAFLD to recombinant GDF11 by daily intra-peritoneal injection and monitor the hepatic pathological changes. Finally, we analyzed GDF11-activated signaling pathways in hepatic stellate cells (HSC).

New insights into the secretory functions of brown adipose tissue

In recent years, an important secretory role of brown adipose tissue (BAT) has emerged, which is consistent, to some extent, with the earlier recognition of the important secretory role of white fat. The so-called brown adipokines or 'batokines' may play an autocrine role, which may either be positive or negative, in the thermogenic function of brown adipocytes. Additionally, there is a growing recognition of the signalling molecules released by brown adipocytes that target sympathetic nerve endings (such as neuregulin-4 and S100b protein), vascular cells (e.g., bone morphogenetic protein-8b), and immune cells (e.g., C-X-C motif chemokine ligand-14) to promote the tissue remodelling associated with the adaptive BAT recruitment in response to thermogenic stimuli. Moreover, existing indications of an endocrine role of BAT are being confirmed through the release of brown adipokines acting on other distant tissues and organs; a recent example is the recognition that BAT-secreted fibroblast growth factor-21 and myostatin target the heart and skeletal muscle, respectively. The application of proteomics technologies is aiding the identification of new members of the brown adipocyte secretome, such as the extracellular matrix or complement system components. In summary, BAT can no longer be considered a mere producer of heat in response to environment or dietary challenges; it is also an active secretory tissue releasing brown adipokines with a relevant local and systemic action. The identification of the major brown adipokines and their roles is highly important for the discovery of novel candidates useful in formulating intervention strategies for metabolic diseases.

Brown Adipokines

Brown adipokines are regulatory factors secreted by brown and beige adipocytes that exhibit endocrine, paracrine, and autocrine actions. Peptidic and non-peptidic molecules, including miRNAs and lipids, are constituents of brown adipokines. Brown adipose tissue remodeling to meet thermogenic needs is dependent on the secretory properties of brown/beige adipocytes. The association between brown fat activity and a healthy metabolic profile, in relation to energy balance and glucose and lipid homeostasis, is influenced by the endocrine actions of brown adipokines. A comprehensive knowledge of the brown adipocyte secretome is still lacking. Advancements in the identification and characterization of brown adipokines will facilitate therapeutic interventions for metabolic diseases, as these molecules are obvious candidates to therapeutic agents. Moreover, identification of brown adipokines as circulating biomarkers of brown adipose tissue activity may be particularly useful for noninvasive assessment of brown adipose tissue alterations in human pathologies.

CXCL14, a Brown Adipokine that Mediates Brown-Fat-to-Macrophage Communication in Thermogenic Adaptation

The beneficial effects of brown adipose tissue (BAT) are attributed to its capacity to oxidize metabolites and produce heat, but recent data suggest that secretory properties of BAT may also be involved. Here, we identify the chemokine CXCL14 (C-X-C motif chemokine ligand-14) as a novel regulatory factor secreted by BAT in response to thermogenic activation. We found that the CXCL14 released by brown adipocytes recruited alternatively activated (M2) macrophages. Cxcl14-null mice exposed to cold showed impaired BAT activity and low recruitment of macrophages, mainly of the M2 phenotype, into BAT. CXCL14 promoted the browning of white fat and ameliorated glucose/insulin homeostasis in high-fat-diet-induced obese mice. Impairment of type 2 cytokine signaling, as seen in Stat6-null mice, blunts the action of CXCL14, promoting adipose tissue browning. We propose that active BAT is a source of CXCL14, which concertedly promotes adaptive thermogenesis via M2 macrophage recruitment, BAT activation, and the browning of white fat.

The Lives and Times of Brown Adipokines

Brown adipose tissue (BAT) is responsible for adaptive non-shivering thermogenesis. Moreover, brown fat secretes regulatory factors, so-called brown adipokines, that have autocrine, paracrine, and endocrine actions. Brown adipokines are either polypeptides or nonpeptidic molecules including lipid molecules and microRNAs. The secretory properties of brown fat are essential for tissue remodeling adaptations to thermogenic necessities. The endocrine properties of brown adipokines are thought to contribute to the association between BAT activity and a healthy metabolic profile in relation to glucose and lipid homeostasis. The identification and characterization of brown adipokines may allow the discovery of circulating biomarkers of BAT activity in humans, and will lead to the development of candidate tools for therapeutic interventions in metabolic diseases.

Oncostatin m impairs brown adipose tissue thermogenic function and the browning of subcutaneous white adipose tissue

OBJECTIVE

Since oncostatin m (OSM) is elevated in adipose tissue in conditions of obesity and type 2 diabetes in mice and humans, the aim of this study was to determine whether this cytokine plays a crucial role in the impairment of brown adipose tissue (BAT) activity and browning capacity that has been observed in people with obesity.

METHODS

C57BL/6J mice rendered obese by high-fat diet, their lean controls, and C57BL/6J mice fed a standard diet and implanted subcutaneously with a mini pump through a surgical procedure to deliver OSM or placebo were used. Preadipocytes or fully differentiated brown adipocytes were treated with OSM or vehicle with or without norepinephrine before harvesting. RNA was extracted and processed for qPCR analysis. Media from mature adipocytes was also collected to measure glycerol levels.

RESULTS

Studies demonstrated that OSM gene expression was increased in BAT of mice fed a high-fat diet. In addition, exogenous OSM impaired BAT activity and the browning capacity of white adipose tissue in vitro and in vivo.

CONCLUSIONS

Overall, the results reveal a negative role for OSM on BAT and on the browning of white adipose tissue. Therefore, further studies are necessary to demonstrate whether OSM inhibition is a potential treatment for metabolic disorders.

The lipid sensor GPR120 promotes brown fat activation and FGF21 release from adipocytes

The thermogenic activity of brown adipose tissue (BAT) and browning of white adipose tissue are important components of energy expenditure. Here we show that GPR120, a receptor for polyunsaturated fatty acids, promotes brown fat activation. Using RNA-seq to analyse mouse BAT transcriptome, we find that the gene encoding GPR120 is induced by thermogenic activation. We further show that GPR120 activation induces BAT activity and promotes the browning of white fat in mice, whereas GRP120-null mice show impaired cold-induced browning. Omega-3 polyunsaturated fatty acids induce brown and beige adipocyte differentiation and thermogenic activation, and these effects require GPR120. GPR120 activation induces the release of fibroblast growth factor-21 (FGF21) by brown and beige adipocytes, and increases blood FGF21 levels. The effects of GPR120 activation on BAT activation and browning are impaired in FGF21-null mice and cells. Thus, the lipid sensor GPR120 activates brown fat via a mechanism that involves induction of FGF21.

GPR120 is a G-protein-coupled receptor that binds polyunsaturated fatty acids. Here, the authors show that GPR120 is upregulated in brown fat in cold-exposed mice, and mediates thermogenic activation of brown fat via a mechanism that, at least in part, depends on the release of the adipokine FGF21.

Transcriptional regulation of the uncoupling protein-1 gene

Regulated transcription of the uncoupling protein-1 (UCP1) gene, and subsequent UCP1 protein synthesis, is a hallmark of the acquisition of the differentiated, thermogenically competent status of brown and beige/brite adipocytes, as well as of the responsiveness of brown and beige/brite adipocytes to adaptive regulation of thermogenic activity. The 5' non-coding region of the UCP1 gene contains regulatory elements that confer tissue specificity, differentiation dependence, and neuro-hormonal regulation to UCP1 gene transcription. Two main regions-a distal enhancer and a proximal promoter region-mediate transcriptional regulation through interactions with a plethora of transcription factors, including nuclear hormone receptors and cAMP-responsive transcription factors. Co-regulators, such as PGC-1α, play a pivotal role in the concerted regulation of UCP1 gene transcription. Multiple interactions of transcription factors and co-regulators at the promoter region of the UCP1 gene result in local chromatin remodeling, leading to activation and increased accessibility of RNA polymerase II and subsequent gene transcription. Moreover, a commonly occurring A-to-G polymorphism in close proximity to the UCP1 gene enhancer influences the extent of UCP1 gene transcription. Notably, it has been reported that specific aspects of obesity and associated metabolic diseases are associated with human population variability at this site. On another front, the unique properties of the UCP1 promoter region have been exploited to develop brown adipose tissue-specific gene delivery tools for experimental purposes.

Efficacy and epigenetic interactions of novel DNA hypomethylating agent guadecitabine (SGI-110) in preclinical models of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a deadly malignancy characterized at the epigenetic level by global DNA hypomethylation and focal hypermethylation on the promoter of tumor suppressor genes. In most cases it develops on a background of liver steatohepatitis, fibrosis, and cirrhosis. Guadecitabine (SGI-110) is a second-generation hypomethylating agent, which inhibits DNA methyltransferases. Guadecitabine is formulated as a dinucleotide of decitabine and deoxyguanosine that is resistant to cytidine deaminase (CDA) degradation and results in prolonged in vivo exposure to decitabine following small volume subcutaneous administration of guadecitabine. Here we found that guadecitabine is an effective demethylating agent and is able to prevent HCC progression in pre-clinical models. In a xenograft HCC HepG2 model, guadecitabine impeded tumor growth and inhibited angiogenesis, while it could not prevent liver fibrosis and inflammation in a mouse model of steatohepatitis. Demethylating efficacy of guadecitabine on LINE-1 elements was found to be the highest 8 d post-infusion in blood samples of mice. Analysis of a panel of human HCC vs. normal tissue revealed a signature of hypermethylated tumor suppressor genes (CDKN1A, CDKN2A, DLEC1, E2F1, GSTP1, OPCML, E2F1, RASSF1, RUNX3, and SOCS1) as detected by methylation-specific PCR. A pronounced demethylating effect of guadecitabine was obtained also in the promoters of a subset of tumor suppressors genes (CDKN2A, DLEC1, and RUNX3) in HepG2 and Huh-7 HCC cells. Finally, we analyzed the role of macroH2A1, a variant of histone H2A, an oncogene upregulated in human cirrhosis/HCC that synergizes with DNA methylation in suppressing tumor suppressor genes, and it prevents the inhibition of cell growth triggered by decitabine in HCC cells. Guadecitabine, in contrast to decitabine, blocked growth in HCC cells overexpressing macroH2A1 histones and with high CDA levels, despite being unable to fully demethylate CDKN2A, RUNX3, and DLEC1 promoters altered by macroH2A1. Collectively, our findings in human and mice models reveal novel epigenetic anti-HCC effects of guadecitabine, which might be effective specifically in advanced states of the disease.

Phosphatase and tensin homolog is a differential diagnostic marker between nonalcoholic and alcoholic fatty liver disease

AIM: To investigate the protein expression of phosphatase and tensin homolog (PTEN) in human liver biopsies of patients with alcoholic and non-alcoholic liver disease.

METHODS: PTEN protein expression was assessed by immunohistochemistry in formalin-fixed, paraffin-embedded liver sections of patients with non-alcoholic fatty liver disease (NAFLD) (n = 44) or alcoholic liver disease (ALD) (n = 25). Liver resections obtained from 3 healthy subjects candidate for partial liver donation served as controls. Histological evaluations were performed by two experienced pathologists, and diagnoses established based on international criteria. The intensity of the PTEN staining in nuclei was compared between steatotic and non-steatotic areas of each liver fragment analyzed. For each liver specimen, the antibody-stained sections were examined and scored blindly by three independent observers, who were unaware of the patients’ clinical history.

RESULTS: In healthy individuals, PTEN immunostaining was intense in both the cytoplasm and nuclei of all hepatocytes. However, PTEN was strongly downregulated in both the nucleus and the cytoplasm of hepatocytes from steatotic areas in patients with NAFLD, independently of the disease stage. In contrast, no changes in PTEN protein expression were observed in patients with ALD, regardless of the presence of steatosis or the stage of the disease. The degree of PTEN downregulation in hepatocytes of patients with NAFLD correlated with the percentage of steatosis (r = 0.3061, P = 0.0459) and the BMI (r = 0.4268, P = 0.0043). Hovewer, in patients with ALD, PTEN expression was not correlated with the percentage of steatosis with or without obesity as a confounding factor (P = 0.5574). Finally, PTEN expression level in steatotic areas of ALD patients was significantly different from that seen in steatotic areas of NAFLD patients (P < 0.0001).

CONCLUSION: PTEN protein expression is downregulated early in NAFLD, but not in ALD. PTEN immunohistochemical detection could help in the differential diagnosis of NAFLD and ALD.

Hepatic PTEN deficiency improves muscle insulin sensitivity and decreases adiposity in mice

BACKGROUND & AIMS

PTEN is a dual lipid/protein phosphatase, downregulated in steatotic livers with obesity or HCV infection. Liver-specific PTEN knockout (LPTEN KO) mice develop steatosis, inflammation/fibrosis and hepatocellular carcinoma with aging, but surprisingly also enhanced glucose tolerance. This study aimed at understanding the mechanisms by which hepatic PTEN deficiency improves glucose tolerance, while promoting fatty liver diseases.

METHODS

Control and LPTEN KO mice underwent glucose/pyruvate tolerance tests and euglycemic-hyperinsulinemic clamps. Body fat distribution was assessed by EchoMRI, CT-scan and dissection analyses. Primary/cultured hepatocytes and insulin-sensitive tissues were analysed ex vivo.

RESULTS

PTEN deficiency in hepatocytes led to steatosis through increased fatty acid (FA) uptake and de novo lipogenesis. Although LPTEN KO mice exhibited hepatic steatosis, they displayed increased skeletal muscle insulin sensitivity and glucose uptake, as assessed by euglycemic-hyperinsulinemic clamps. Surprisingly, white adipose tissue (WAT) depots were also drastically reduced. Analyses of key enzymes involved in lipid metabolism further indicated that FA synthesis/esterification was decreased in WAT. In addition, Ucp1 expression and multilocular lipid droplet structures were observed in this tissue, indicating the presence of beige adipocytes. Consistent with a liver to muscle/adipocyte crosstalk, the expression of liver-derived circulating factors, known to impact on muscle insulin sensitivity and WAT homeostasis (e.g. FGF21), was modulated in LPTEN KO mice.

CONCLUSIONS

Although steatosis develops in LPTEN KO mice, PTEN deficiency in hepatocytes promotes a crosstalk between liver and muscle, as well as adipose tissue, resulting in enhanced insulin sensitivity, improved glucose tolerance and decreased adiposity.

Safety, tolerability, and pharmacokinetics of 6-month daily dosing of an oral formulation of cyclosporine (ATOPICA for cats®) in cats

Cyclosporine was proven efficacious in the treatment of feline hypersensitivity dermatitis. This target animal study was conducted to evaluate the safety, tolerability, and pharmacokinetics of ATOPICA for Cats® (cyclosporine oral solution, USP) MODIFIED following 6-month daily dosing in cats. Forty healthy cats (four cats/sex/group) received 0, 8 (1×), 16 (2×), 24 (3×), or 40 (5×) mg/kg cyclosporine once daily for 6 months (183 days). Body weight, food consumption, ophthalmoscopic, physical examinations including neurological assessments, blood pressure, electrocardiography, clinical pathology (hematology, coagulation, clinical chemistry, urinalysis), organ weights, and macroscopic and microscopic examinations were performed and assessed. In addition, blood concentrations of cyclosporine were measured at the pretreatment trough on Days 1, 2, 7, 14, 31, 91, 154, and 182, and post-treatment on Days 1, 31, and 182. Adverse effects possibly related to treatment included prolonged APTT and one report each of bone marrow hypocellularity and lymphoma; all occurred in cats treated with doses more than 16 mg/kg. There was no significant accumulation of cyclosporine beyond the first week of treatment. Results confirm that ATOPICA for Cats is safe and well tolerated in cats without unexpected accumulation beyond the first week of treatment when administered as directed.

PTEN protein phosphatase activity regulates hepatitis C virus secretion through modulation of cholesterol metabolism

BACKGROUND & AIMS

Hepatitis C virus (HCV) infection is dependent on lipid metabolism. Hepatocyte steatosis occurs frequently in HCV infection, but the relationship between steatosis and HCV life cycle is unclear. We showed that HCV induces steatosis via the downregulation of the phosphatase and tensin homolog deleted on chromosome 10 (PTEN). We here investigated how PTEN may affect HCV production.

METHODS

The effect of overexpression or silencing of PTEN on HCV secretion was assessed in genomic-length Jc1 infected HuH7 cells. The role of PTEN protein and lipid phosphatase activities on lipid metabolism and infectious viral particle secretion was investigated using dominant-negative PTEN mutants. The importance of cholesterol metabolism for PTEN-dependent lipid droplet biogenesis and viral particle secretion was examined using statins.

RESULTS

PTEN silencing in Jc1 infected HuH7 cells stimulated HCV particle secretion, while PTEN overexpression decreased virus egress. Viral secretion was also increased by overexpression of protein phosphatase-deleted (PTENY138L), but not lipid phosphatase-deleted (PTENG129E), PTEN mutant, thus indicating that the protein phosphatase activity of PTEN controls viral secretion. Similarly, PTENY138L, but not PTENG129E mutant induced the formation of large lipid droplets. PTENY138L mutant did not affect biosynthesis of triglycerides, but promoted the biosynthesis of cholesterol esters. Consistently, statins prevented the increased cholesterol ester production, large lipid droplet formation, and viral secretion in cells expressing the PTENY138L mutant.

CONCLUSIONS

Downregulation of PTEN protein phosphatase activity by HCV affects cholesterol metabolism, thereby inducing the appearance of large lipid droplets and increasing virion egress.

Immunopositivity for histone macroH2A1 isoforms marks steatosis-associated hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. Prevention and risk reduction are important and the identification of specific biomarkers for early diagnosis of HCC represents an active field of research. Increasing evidence indicates that fat accumulation in the liver, defined as hepatosteatosis, is an independent and strong risk factor for developing an HCC. MacroH2A1, a histone protein generally associated with the repressed regions of chromosomes, is involved in hepatic lipid metabolism and is present in two alternative spliced isoforms, macroH2A1.1 and macroH2A1.2. These isoforms have been shown to predict lung and colon cancer recurrence but to our knowledge, their role in fatty-liver associated HCC has not been investigated previously.

Methods

We examined macroH2A1.1 and macroH2A1.2 protein expression levels in the liver of two murine models of fat-associated HCC, the high fat diet/diethylnistrosamine (DEN) and the phosphatase and tensin homolog (PTEN) liver specific knock-out (KO) mouse, and in human liver samples of subjects with steatosis or HCC, using immunoblotting and immunohistochemistry.

Results

Protein levels for both macroH2A1 isoforms were massively upregulated in HCC, whereas macroH2A1.2 was specifically upregulated in steatosis. In addition, examination of human liver samples showed a significant difference (p<0.01) in number of positive nuclei in HCC (100% of tumor cells positive for either macroH2A1.1 or macroH2A1.2), when compared to steatosis (<2% of hepatocytes positive for either isoform). The steatotic areas flanking the tumors were highly immunopositive for macroH2A1.1 and macroH2A1.2.

Conclusions

These data obtained in mice and humans suggest that both macroH2A1 isoforms may play a role in HCC pathogenesis and moreover may be considered as novel diagnostic markers for human HCC.

Challenges obtaining a biowaiver for topical veterinary dosage forms

Obtaining a biowaiver for topical drugs used in veterinary species faces many of the same challenges associated with human topicals. However, the skin of domestic animals varies anatomically and biochemically and experimental approaches to assess bioequivalence (BE) in veterinary species have challenges that are not often encountered with human skin. This is especially the situation with locally acting drugs. The focus of this paper is to address several of the challenges associated with (i) determining the BE of these locally acting drugs and (ii) critically examine the current technological advances that can act as a surrogate for clinical trials.

Chronic mTOR inhibition by rapamycin induces muscle insulin resistance despite weight loss in rats

BACKGROUND AND PURPOSE

mTOR inhibitors are currently used as immunosuppressants in transplanted patients and as promising anti-cancer agents. However, new-onset diabetes is a frequent complication occurring in patients treated with mTOR inhibitors such as rapamycin (Sirolimus). Here, we investigated the mechanisms associated with the diabetogenic effects of chronic Sirolimus administration in rats and in in vitro cell cultures.

EXPERIMENTAL APPROACH

Sirolimus was administered to rats fed either a standard or high-fat diet for 21 days. Metabolic parameters were measured in vivo and in ex vivo tissues. Insulin sensitivity was assessed by glucose tolerance tests and euglycaemic hyperinsulinaemic clamps. Rapamycin effects on glucose metabolism and insulin signalling were further evaluated in cultured myotubes.

KEY RESULTS

Sirolimus induced a decrease in food intake and concomitant weight loss. It also induced specific fat mass loss that was independent of changes in food intake. Despite these beneficial effects, Sirolimus-treated rats were glucose intolerant, hyperinsulinaemic and hyperglycaemic, but not hyperlipidaemic. The euglycaemic hyperinsulinaemic clamp measurements showed skeletal muscle is a major site of Sirolimus-induced insulin resistance. At the molecular level, long-term Sirolimus administration attenuated glucose uptake and metabolism in skeletal muscle by preventing full insulin-induced Akt activation and altering the expression and translocation of glucose transporters to the plasma membrane. In rats fed a high-fat diet, these metabolic defects were exacerbated, although Sirolimus-treated animals were protected from diet-induced obesity.

CONCLUSIONS AND IMPLICATIONS

Taken together, our data demonstrate that the diabetogenic effect of chronic rapamycin administration is due to an impaired insulin action on glucose metabolism in skeletal muscles.

Down-regulation of phosphatase and tensin homolog by hepatitis C virus core 3a in hepatocytes triggers the formation of large lipid droplets

Hepatitis C virus (HCV) perturbs the host's lipid metabolism and often results in hepatic steatosis. In nonalcoholic fatty liver disease, the intrahepatic down-regulation of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a critical mechanism leading to steatosis and its progression toward fibrosis and hepatocellular carcinoma. However, whether an HCV infection triggers the formation of large lipid droplets through PTEN-dependent mechanisms is unknown. We assessed PTEN expression in the livers of patients infected with HCV genotype 1 or 3 with or without steatosis. The role of PTEN in the HCV-induced biogenesis of lipid droplets was further investigated in vitro with hepatoma cells transduced with the HCV core protein of genotype 1b or 3a. Our data indicate that PTEN expression was down-regulated at the posttranscriptional level in steatotic patients infected with genotype 3a. Similarly, the in vitro expression of the HCV genotype 3a core protein (but not 1b), typically leading to the appearance of large lipid droplets, down-regulated PTEN expression by a mechanism involving a microRNA-dependent blockade of PTEN messenger RNA translation. PTEN down-regulation promoted in turn a reduction of insulin receptor substrate 1 (IRS1) expression. Interestingly, either PTEN or IRS1 overexpression prevented the development of large lipid droplets, and this indicates that the down-regulation of both PTEN and IRS1 is required to affect the biogenesis of lipid droplets. However, IRS1 knockdown per se did not alter the morphology of lipid droplets, and this suggests that other PTEN-dependent mechanisms are involved in this process.

CONCLUSION

The down-regulation of PTEN and IRS1 is a critical event leading to the HCV genotype 3a-induced formation of large lipid droplets in hepatocytes.

PTEN in liver diseases and cancer

The phosphoinositide 3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/Akt axis is a key signal transduction node that regulates crucial cellular functions, including insulin and other growth factors signaling, lipid and glucose metabolism, as well as cell survival and apoptosis. In this pathway, PTEN acts as a phosphoinositide phosphatase, which terminates PI3K-propagated signaling by dephosphorylating PtdIns(3,4)P₂ and PtdIns(3,4,5)P₃. However, the role of PTEN does not appear to be restricted only to PI3K signaling antagonism, and new functions have been recently discovered for this protein. In addition to the well-established role of PTEN as a tumor suppressor, increasing evidence now suggests that a dysregulated PTEN expression and/or activity is also linked to the development of several hepatic pathologies. Dysregulated PTEN expression/activity is observed with obesity, insulin resistance, diabetes, hepatitis B virus/hepatitis C virus infections, and abusive alcohol consumption, whereas mutations/deletions have also been associated with the occurrence of hepatocellular carcinoma. Thus, it appears that alterations of PTEN expression and activity in hepatocytes are common and recurrent molecular events associated with liver disorders of various etiologies. These recent findings suggest that PTEN might represent a potential common therapeutic target for a number of liver pathologies.

PTEN in non-alcoholic fatty liver disease/non-alcoholic steatohepatitis and cancer

The tumor suppressor PTEN is a protein/phosphoinositide phosphatase regulating the PI3K/Akt signaling pathway and is mutated or deleted in a variety of human cancers, including hepatocellular carcinoma (HCC). Accumulating evidence indicates that alterations of PTEN expression and activity in hepatocytes are common and recurrent molecular events associated with liver disorders of various etiologies including obesity, the metabolic syndrome, hepatitis B virus/hepatitis C virus infection and abusive alcohol consumption. Genetic and molecular studies, particularly in the context of non-alcoholic fatty liver disease (NAFLD), support a critical role for PTEN in hepatic insulin sensitivity and the development of steatosis, steatohepatitis and fibrosis. PTEN mutations/deletion or low PTEN expression are also associated with diverse liver malignancies, suggesting a critical role for PTEN in hepatic cancers. This review provides an overview of the current knowledge on pathological dysregulations of PTEN expression/activity in the liver with obesity and the metabolic syndrome, and the role of this enzyme in the development of non-alcoholic fatty liver disease and hepatocellular carcinoma.

Fibrogenic potential of human multipotent mesenchymal stromal cells in injured liver

Multipotent mesenchymal stromal cells (MSC) are currently investigated clinically as cellular therapy for a variety of diseases. Differentiation of MSC toward endodermal lineages, including hepatocytes and their therapeutic effect on fibrosis has been described but remains controversial. Recent evidence attributed a fibrotic potential to MSC. As differentiation potential might be dependent of donor age, we studied MSC derived from adult and pediatric human bone marrow and their potential to differentiate into hepatocytes or myofibroblasts in vitro and in vivo. Following characterization, expanded adult and pediatric MSC were co-cultured with a human hepatoma cell line, Huh-7, in a hepatogenic differentiation medium containing Hepatocyte growth factor, Fibroblast growth factor 4 and oncostatin M. In vivo, MSC were transplanted into spleen or liver of NOD/SCID mice undergoing partial hepatectomy and retrorsine treatment. Expression of mesenchymal and hepatic markers was analyzed by RT-PCR, Western blot and immunohistochemistry. In vitro, adult and pediatric MSC expressed characteristic surface antigens of MSC. Expansion capacity of pediatric MSC was significantly higher when compared to adult MSC. In co-culture with Huh-7 cells in hepatogenic differentiation medium, albumin expression was more frequently detected in pediatric MSC (5/8 experiments) when compared to adult MSC (2/10 experiments). However, in such condition pediatric MSC expressed alpha smooth muscle more strongly than adult MSC. Stable engraftment in the liver was not achieved after intrasplenic injection of pediatric or adult MSC. After intrahepatic injection, MSC permanently remained in liver tissue, kept a mesenchymal morphology and expressed vimentin and alpha smooth muscle actin, but no hepatic markers. Further, MSC localization merges with collagen deposition in transplanted liver and no difference was observed using adult or pediatric MSC. In conclusion, when transplanted into an injured or regenerating liver, MSC differentiated into myofibroblasts with development of fibrous tissue, regardless of donor age. These results indicate that MSC in certain circumstances might be harmful due to their fibrogenic potential and this should be considered before potential use of MSC for cell therapy.

Unsaturated fatty acids promote hepatoma proliferation and progression through downregulation of the tumor suppressor PTEN

BACKGROUND/AIMS

The impact of dietary fatty acids on the development of cancers is highly controversial. We recently demonstrated that unsaturated fatty acids trigger the downregulation of the tumor suppressor PTEN through an mTOR/NF-kappaB-dependent mechanism in hepatocytes. In this study, we investigated whether unsaturated fatty acids promote hepatoma progression by downregulating PTEN expression.

METHODS

The effects of fatty acids and PTEN-specific siRNAs on proliferation, invasiveness and gene expression were assessed using HepG2 hepatoma cells. The tumor promoting activity of unsaturated fatty acids was evaluated in vivo using HepG2 xenografts in nude mice.

RESULTS

Incubation of HepG2 cells with unsaturated fatty acids, or PTEN-specific siRNAs, increased cell proliferation, cell migration and invasiveness, and altered the expression of genes involved in inflammation, epithelial-to-mesenchymal transition and carcinogenesis. These effects were dependent on PTEN expression levels and were prevented by mTOR and NF-kappaB inhibitors. Consistent with these data, the development and size of subcutaneous HepG2-derived tumors in nude mice xenografts were dramatically increased when mice were fed with an oleic acid-enriched diet, even in the absence of weight gain.

CONCLUSIONS

These data demonstrate that dietary unsaturated fatty acids promote hepatoma progression by reducing the expression of the tumor suppressor PTEN.

Enrofloxacin and marbofloxacin in horses: comparison of pharmacokinetic parameters, use of urinary and metabolite data to estimate first-pass effect and absorbed fraction

Enrofloxacin and marbofloxacin are two veterinary fluoroquinolones used to treat severe bacterial infections in horses. A repeated measures study has been designed to compare their pharmacokinetic parameters, to investigate their bioavailability and to estimate their absorbed fraction and first-pass effect by using plasma, urinary and metabolite data collected from five healthy mares. Clearance and V(d(ss)) were greater for enrofloxacin (mean +/- SD = 6.34 +/- 1.5 mL/min/kg and 2.32 +/- 0.32 L/kg, respectively) than for marbofloxacin (4.62 +/- 0.67 mL/min/kg and 1.6 +/- 0.25 L/kg, respectively). Variance of the AUC(0-inf) of marbofloxacin was lower than that for enrofloxacin, with, respectively, a CV = 15% and 26% intravenously and a CV = 31% and 55% after oral administration. Mean oral bioavailability was not significantly different between marbofloxacin (59%) and enrofloxacin (55%). The mean percentage of the dose eliminated unchanged in urine was significantly higher for marbofloxacin (39.7%) than that for enrofloxacin (3.4%). Absorbed fraction and first-pass effect were only determinable for enrofloxacin, whereas the percentage of the dose absorbed in the portal circulation was estimated to be 78% and the fraction not extracted during the first pass through the liver was 65%. Consequently, the moderate observed bioavailability of enrofloxacin appears to be mainly caused by hepatic first-pass effect.

Population pharmacokinetics of marbofloxacin in horses: preliminary analysis

Population pharmacokinetic of marbofloxacin was investigated on 21 healthy and 16 diseased horses to assess interindividual variability of drug exposure. Demographic, physiologic and disease covariables were tested using mixed effects models. As a preliminary analysis, this study has demonstrated that none of the tested covariables were significant in regression models for compartmental volumes or clearance of distribution, but the clinical status of the horse (healthy/diseased) was a significant covariable (P < 0.01) for systemic clearance. Clearance had a lower mean and a higher variance for diseased horses than healthy horses, with respectively a mean of 0.209 and 0.284 L/h/kg and a coefficient of variation of 52 and 15%. Consequently, variability of AUC was greater in diseased horses. Considering an AUC/MIC ratio below 60 h as a prediction of poor efficacy, a dosage regimen of 2 mg/kg intravenous was deemed to be inadequate for 19% of diseased horses if the MIC of the bacteria was 0.1 microg/mL. However 93% of diseased horses could achieve a ratio above 125 h, predicting a very good efficacy, for the MIC(90) of Enterobacteriacae (0.027 microg/mL).