Association of free fatty acids (FFA) and tumor necrosis factor-alpha (TNF-alpha) and insulin-resistant metabolic disorder

Latest advances in STAT signaling and function in adipocytes

Adipocytes and adipose tissue are not inert and make substantial contributions to systemic metabolism by influencing energy homeostasis, insulin sensitivity, and lipid storage. In addition to well-studied hormones such as insulin, there are numerous hormones, cytokines, and growth factors that modulate adipose tissue function. Many endocrine mediators utilize the JAK-STAT pathway to mediate dozens of biological processes, including inflammation and immune responses. JAKs and STATs can modulate both adipocyte development and mature adipocyte function. Of the seven STAT family members, four STATs are expressed in adipocytes and regulated during adipogenesis (STATs 1, 3, 5A, and 5B). These STATs have been shown to play influential roles in adipose tissue development and function. STAT6, in contrast, is highly expressed in both preadipocytes and mature adipocytes, but is not considered to play a major role in regulating adipose tissue function. This review will summarize the latest research that pertains to the functions of STATs in adipocytes and adipose tissue.

The role of pro-inflammatory cytokines in lipid metabolism of metabolic diseases

Adipose tissue has been considered as a crucial source of certain pro-inflammatory cytokines; conversely, these pro-inflammatory cytokines are involved in regulating the proliferation and apoptosis of adipocytes, promoting lipolysis, inhibiting lipid synthesis and decreasing blood lipids, etc. In recent decades, extensive studies have indicated that pro-inflammatory cytokines play important roles in the development of lipid metabolism of metabolic diseases, including obesity, atherosclerosis, steatohepatitis and hyperlipoproteinemia. However, the involved pro-inflammatory cytokines types and the underlying mechanisms remain largely unknown. The "re-discovery" of cancer as a metabolic disorder largely occurred in the last five years. Although pro-inflammatory cytokines have been intensively investigated in cancer research, there are very few studies about the roles of pro-inflammatory cytokines in the lipid metabolism of cancer. In the current review, we provide an overview of the progress that has been made in the roles of different pro-inflammatory cytokines in lipid metabolism of metabolic diseases including cancer.

An ethanolic extract of Artemisia scoparia inhibits lipolysis in vivo and has antilipolytic effects on murine adipocytes in vitro

An ethanolic extract of Artemisia scoparia (SCO) has metabolically favorable effects on adipocyte development and function in vitro and in vivo. In diet-induced obese mice, SCO supplementation significantly reduced fasting glucose and insulin levels. Given the importance of adipocyte lipolysis in metabolic health, we hypothesized that SCO modulates lipolysis in vitro and in vivo. Free fatty acids and glycerol were measured in the sera of mice fed a high-fat diet with or without SCO supplementation. In cultured 3T3-L1 adipocytes, the effects of SCO on lipolysis were assessed by measuring glycerol and free fatty acid release. Microarray analysis, qPCR, and immunoblotting were used to assess gene expression and protein abundance. We found that SCO supplementation of a high-fat diet in mice substantially reduces circulating glycerol and free fatty acid levels, and we observed a cell-autonomous effect of SCO to significantly attenuate tumor necrosis factor-α (TNFα)-induced lipolysis in cultured adipocytes. Although several prolipolytic and antilipolytic genes were identified by microarray analysis of subcutaneous and visceral adipose tissue from SCO-fed mice, regulation of these genes did not consistently correlate with SCO's ability to reduce lipolytic metabolites in sera or cell culture media. However, in the presence of TNFα in cultured adipocytes, SCO induced antilipolytic changes in phosphorylation of hormone-sensitive lipase and perilipin. Together, these data suggest that the antilipolytic effects of SCO on adipose tissue play a role in the ability of this botanical extract to improve whole body metabolic parameters and support its use as a dietary supplement to promote metabolic resiliency.

An integrated metabolomic strategy for the characterization of the effects of Chinese yam and its three active components on septic cardiomyopathy

This integrated metabolomic approach interpreted the effects of Chinese yam on septic cardiomyopathy and the roles of its major active components.

Sex difference of hyperinsulinemia in the C57BL/6J-Daruma (obese) mouse

The C57BL/6J-Daruma mouse is an animal model of obesity derived from the original genetically obese ICR-Daruma mouse by transfer of the phenotype into the C57BL/6J background by backcrossing into the C57BL/6J strain. Although, like the original ICR-Daruma mouse model, both male and female C57BL/6J-Daruma mice develop obesity, the latter strain shows sex differences in several phenotypes. A sex difference in plasma insulin levels was especially notable in C57BL/6J-Daruma mice; only males showed hyperinsulinemia. Orchiectomy suppressed this hyperinsulinemia completely, whereas testosterone supplementation restored it. Glucose administration increased the plasma glucose level in both male and female Daruma mice to a greater extent than in wild-type control mice. Orchiectomy, but not ovariectomy, decreased the plasma glucose level to that seen in wild-type controls. On the other hand, this effect of orchiectomy was abrogated by testosterone supplementation. The expression of mRNAs for several genes related to insulin resistance was significantly changed in white adipose tissue and liver of C57BL/6J-Daruma mice, especially males, as early as 4 weeks of age. The present results suggest that testosterone may be involved in the hyperinsulinemia shown by male C57BL/6J-Daruma mice and that this strain may be an appropriate animal model for examining the relationship between obesity and sex hormones.

PLA2G16 promotes osteosarcoma metastasis and drug resistance via the MAPK pathway

The prognosis of metastatic osteosarcoma is dismal and a better understanding of the mechanisms underlying disease progression is essential to improve treatment options and patient outcomes. We previously demonstrated Pla2g16 overexpression in mouse osteosarcoma contributes to metastasis phenotypes and increased expression of PLA2G16 is associated with metastasis and poor prognosis in human tumors. To further examine the mechanisms through which PLA2G16 contributes to human osteosarcoma metastasis and explore the potential of PLA2G16 as a therapeutic target in osteosarcoma, we generated a panel of human osteosarcoma cell lines expressing different levels of PLA2G16. The functional analyses of these cell lines demonstrated high levels of PLA2G16 expression increased osteosarcoma cell migration, invasion, clonogenic survival, and anchorage-independent colony formation. Importantly, this activity was dependent on the phospholipase activity of PLA2G16. Additionally, PLA2G16 overexpression decreased the sensitivity of cells to a panel of chemotherapeutic agents. Analysis of downstream pathways revealed the pro-metastasis functions of PLA2G16 were mediated through the MAPK pathway, as knockdown of PLA2G16 decreased ERK1/2 phosphorylation and pharmacological inhibition of MEK significantly repressed PLA2G16 mediated cell migration and clonogenic survival. Furthermore, PLA2G16 overexpression promoted xenograft tumor growth in vivo, and these tumors exhibit increased ERK1/2 phosphorylation. Lastly, the expression of PLA2G16 is strongly correlated with the increased ERK1/2 phosphorylation in human osteosarcoma samples, and the combined lesions are associated with reduced overall and metastasis-free survival. Collectively, these results demonstrate increased PLA2G16 expression activates the MAPK pathway to enhance osteosarcoma metastasis and may be a novel therapeutic target for these cancers.

Insulin resistance and its consequences in chronic hepatitis C

Chronic hepatitis C (CHC) is generally a slowly progressive disease, but some factors associated with rapid progression have been identified. Hepatitis C virus (HCV) may contribute to a broad spectrum of metabolic disturbances - namely, steatosis, insulin resistance (IR), increased prevalence of impaired glucose tolerance, type 2 diabetes mellitus (T2DM), lipid metabolism abnormalities and atherosclerosis. HCV can directly or indirectly cause both IR and steatosis, but it is still not resolved whether this viral impact bears the same prognostic value as the metabolic counterparts. As the population exposed to HCV ages, the morbidity due to this disease is increasing. The rising epidemic of obesity contributes to higher prevalence of IR and T2DM. Our understanding of the mutual association between both disease states continues to grow, but is still far from complete. This review briefly discusses the most probable mechanisms involved in IR development in the course of CHC. Molecular mechanisms for the direct and indirect influence of HCV on intracellular insulin signaling are described. Subsequently, the consequences of IR/T2DM for disease progression and management are summarized.

Combined elevated midpregnancy tumor necrosis factor alpha and hyperlipidemia in pregnancies resulting in early preterm birth

OBJECTIVE

The objective of the study was to determine whether pregnancies resulting in early preterm birth (PTB) (<30 weeks) were more likely than term pregnancies to have elevated midtrimester serum tumor necrosis factor alpha (TNF-α) levels combined with lipid patterns suggestive of hyperlipidemia.

STUDY DESIGN

In 2 nested case-control samples drawn from California and Iowa cohorts, we examined the frequency of elevated midpregnancy serum TNF-α levels (in the fourth quartile [4Q]) and lipid patterns suggestive of hyperlipidemia (eg, total cholesterol, low-density-lipoproteins, or triglycerides in the 4Q, high-density lipoproteins in the first quartile) (considered independently and by co-occurrence) in pregnancies resulting in early PTB compared with those resulting in term birth (n = 108 in California and n = 734 in Iowa). Odds ratios (ORs) and 95% confidence intervals (CIs) estimated in logistic regression models were used for comparisons.

RESULTS

Early preterm pregnancies were 2-4 times more likely than term pregnancies to have a TNF-α level in the 4Q co-occurring with indicators of hyperlipidemia (37.5% vs 13.9% in the California sample (adjusted OR, 4.0; 95% CI, 1.1-16.3) and 26.3% vs 14.9% in the Iowa sample (adjusted OR, 2.7; 95% CI, 1.1-6.3). No differences between early preterm and term pregnancies were observed when TNF-α or target lipid abnormalities occurred in isolation. Observed differences were not explicable to any maternal or infant characteristics.

CONCLUSION

Pregnancies resulting in early PTB were more likely than term pregnancies to have elevated midpregnancy TNF-α levels in combination with lipid patterns suggestive of hyperlipidemia.

TNF-alpha, a potent lipid metabolism regulator

As a multifunctional cytokine, tumor necrosis factor alpha (TNF-alpha) exerts a series of biological actions in different cells, tissues, organs, and species and has been demonstrated to regulate and interfere with energy metabolism, especially lipid homeostasis. A large body of researches suggested that the effects of TNF-alpha on lipid metabolism mainly include five aspects: (1) suppresses free fatty acid (FFA) uptake and promotes lipogenesis; (2) induces lipolysis; (3) inhibits lipid-metabolism-related enzymes activity; (4) regulates cholesterol metabolism; (5) regulates other adipocyte-derived adipokines. The molecular mechanisms underlying these actions are complex and several signal transduction pathways might be involved. Regulation of metabolism-related gene expression at transcriptional and protein levels and impact on enzymes activity might be of importance. Identification and verification of these pathways might provide novel potential strategies and drug targets for dyslipidemia therapy. However, the inconsistent and even conflict conclusions on lipid profile drawn from human subjects after infliximab therapy poses the possibility that the effect of TNF-alpha on lipid metabolism might be more complicated than it appeared to be.

Serum fatty acid binding protein 4, free fatty acids, and metabolic risk markers

Fatty acid binding protein (FABP) 4 chaperones free fatty acids (FFAs) in the adipocytes during lipolysis. Serum FFA relates to metabolic syndrome, and serum FABP4 is emerging as a novel risk marker. In 36 overweight/obese women, serum FABP4 and FFA were measured hourly during 5-hour oral glucose tolerance test. Insulin resistance was determined using frequently sampled intravenous glucose tolerance test. Serum lipids and inflammation markers were measured at fasting. During oral glucose tolerance test, serum FABP4 decreased by 40%, reaching its nadir at 3 hours (from 45.3 +/- 3.1 to 31.9 +/- 1.6 ng/mL), and stayed below the baseline at 5 hours (35.9 +/- 2.2 ng/mL) (P < .0001 for both, compared with the baseline). Serum FFA decreased by 10-fold, reaching a nadir at 2 hours (from 0.611 +/- 0.033 to 0.067 +/- 0.004 mmol/L), then rebounded to 0.816 +/- 0.035 mmol/L at 5 hours (P < .001 for both, compared with baseline). Both fasting FABP4 and nadir FABP4 correlated with obesity. Nadir FABP4 correlated also with insulin resistance parameters from frequently sampled intravenous glucose tolerance test and with inflammation. Nadir FFA, but not fasting FFA, correlated with the metabolic syndrome parameters. In conclusion, fasting FABP4 related to metabolic risk markers more strongly than fasting FFA. Nadir FABP4 and nadir FFA measured after glucose loading may provide better risk assessment than the fasting values.

Hepatitis C virus infection: molecular pathways to metabolic syndrome

Chronic infection with hepatitis C virus (HCV) can induce insulin resistance (IR) in a genotype-dependent fashion, thus contributing to steatosis, progression of fibrosis and resistance to interferon therapy. The molecular mechanisms in genotype 1 patients that lead to metabolic syndrome are still ambiguous. Based on our current understanding, HCV proteins associate with mitochondria and endoplasmic reticulum and promote oxidative stress. The latter mediates signals involving the p38 mitogen-activated protein kinase and activates nuclear factor kappa B. This transcription factor plays a key role in the expression of cytokines, tumor necrosis factor alpha (TNF-alpha), interleukin 6, interleukin 8, tumor growth factor beta, and Fas ligand. TNF-alpha inhibits the function of insulin receptor substrates and decreases the expression of the glucose transporter and lipoprotein lipase in peripheral tissues, which is responsible for the promotion of insulin resistance. Furthermore, reduced adiponectin levels, loss of adiponectin receptors, and decreased anti-inflammatory peroxisome proliferator-activated receptor alpha in the liver of HCV patients may contribute to reduced fatty acid oxidation, inflammation, and eventually lipotoxicity. This chain of events may be initiated by HCV-associated IR and provides a direction for future research in the areas of therapeutic intervention.