Nitric oxide-induced downregulation of leptin production by 3T3-L1 adipocytes

Effects of co-incubation of LPS-stimulated RAW 264.7 macrophages on leptin production by 3T3-L1 adipocytes: a method for co-incubating distinct adipose tissue cell lines

BACKGROUND

Adipose tissue is a major endocrine organ capable of releasing inflammatory adipokines that are linked to changes occurring in the overfed state, where tissue remodeling results in hypertrophic adipocytes that recruit monocytes to infiltrate the tissue and take on an inflammatory phenotype. Increases in macrophage-specific inflammatory mediator levels contribute to the inflamed state and worsen the inflammatory loop between the macrophages and adipocytes. Although most inflammatory adipokines are released by macrophages, adipocytes can also release immunomodulatory adipokines, such as leptin. The objective of this research was to determine if co-incubation of activated macrophages with mature adipocytes, using transwell inserts, affected adipocyte leptin release. We also examined if there were differences in levels of cell-secreted products quantified in cell-conditioned media collected from macrophage-containing (transwell insert) and adipocyte-containing (well) compartments.

METHODS

Mature adipocytes were co-incubated with control and lipopolysaccharide-stimulated (0.01 mg/ml) murine macrophages, and nitric oxide, interleukin-6, and leptin levels were quantified in the cell-conditioned media from both compartments.

RESULTS

Activation status of the macrophages did not affect leptin release by the adipocytes. We observed higher amounts of leptin in wells compared to transwells. Nitric oxide and interleukin-6 levels were similar between transwells and wells, suggesting that these adipokines travel through the transwell inserts and are reaching equilibrium between the two compartments.

CONCLUSION

Our results suggest that co-incubating activated macrophages and adipocytes using transwell inserts can result in distinct microenvironments in the different cellular compartments and that separate sampling of these compartments is required to detect the subtle signaling dynamics that exist between these cells.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s42269-022-00747-7.

iNOS as a metabolic enzyme under stress conditions

Nitric oxide (NO) is a free radical acting as a cellular signaling molecule in many different biochemical processes. NO is synthesized from l-arginine through the action of the nitric oxide synthase (NOS) family of enzymes, which includes three isoforms: endothelial NOS (eNOS), neuronal NOS (nNOS) and inducible NOS (iNOS). iNOS-derived NO has been associated with the pathogenesis and progression of several diseases, including liver diseases, insulin resistance, obesity and diseases of the cardiovascular system. However, transient NO production can modulate metabolism to survive and cope with stress conditions. Accumulating evidence strongly imply that iNOS-derived NO plays a central role in the regulation of several biochemical pathways and energy metabolism including glucose and lipid metabolism during inflammatory conditions. This review summarizes current evidence for the regulation of glucose and lipid metabolism by iNOS during inflammation, and argues for the role of iNOS as a metabolic enzyme in immune and non-immune cells.

Anti-diabetic activities of Gegen Qinlian Decoction in high-fat diet combined with streptozotocin-induced diabetic rats and in 3T3-L1 adipocytes

Gegen Qinlian Decoction (GGQLD) is one of the well-known traditional Chinese medicines. Recently, it was reported that GGQLD had good clinical effects on type 2 diabetes mellitus. However, few studies have confirmed in detail the anti-diabetic activities of GGQLD in vivo and in vitro. In the present study, we investigated the anti-diabetic effects of GGQLD in high-fat diet combined with streptozotocin-induced diabetic rats and in 3T3-L1 adipocytes. The present results suggested GGQLD (4.95, 11.55 and 18.15 g/kg) decreased significantly fasting blood glucose, glycosylated serum protein, and glycosylated hemoglobin of diabetic rats (p<0.05), and GGQLD (4.95 and 18.15 g/kg) decreased significantly fasting serum insulin levels of diabetic rats (p<0.05); in 3T3-L1 adipocytes, Gegen Qinlian Decoction-containing serum (GGQLD-CS) (4%, 8% and 16%) enhanced glucose consumption, triglyceride (TG) content, adiponectin protein concentration and the mRNA expression of adiponectin. Adiponectin contributes to the regulation of lipid and glucose metabolism, and can play a critical role in the development of diabetes mellitus; the mechanisms of action of GGQLD might be related to augmentation of adiponectin protein concentration and up-regulation of the mRNA expression of adiponectin. However, the multi-target mechanisms of action of GGQLD need to be clarified further. The present study further validated the beneficial effects of GGQLD as an anti-diabetic agent. These findings provide a new insight into the anti-diabetic application for GGQLD in clinic and display the potential of GGQLD as a new drug candidate for the treatment of diabetes mellitus.

Analysis of adipose tissues and stromal vascular cells in a murine arthritis model

PURPOSE

Changes in body composition in rheumatoid arthritis (RA), including a reduction in skeletal muscle mass and the accumulation of visceral fat, have been identified, and the interaction between immune abnormality and metabolic disorders has received much attention. The effect of a high-fat (HF) diet and the role of adipose tissue in an arthritis model were investigated.

METHODS

The effect of an HF diet on the histopathology of joints in murine type II collagen-induced arthritis (CIA) was evaluated. The morphology and adipokine production of adipose tissues were analyzed, and macrophages in the stromal vascular fraction (SVF) were counted by flow cytometry. Serum adipokine levels were measured by ELISA.

RESULTS

Significant exacerbation of joint destruction and aggravated pathological conditions were observed in CIA mice that were fed an HF diet. However, the boundary length of adipose tissue tended to decrease and the levels of adipokines (leptin and adiponectin) were lowered by the induction of arthritis. In HF/CIA mice, nevertheless, the production of MCP-1 in adipose tissues and the accumulation of macrophages in the SVF were significantly higher than CON/CIA group. The serum leptin/adiponectin (L/A) ratio was positively correlated with the number of macrophages in the SVF and MCP-1 production by adipose tissue, particularly in the CIA group.

CONCLUSION

Functional alterations of adipose tissues could be originated from HF diet during developing arthritis. An abnormal activation of macrophages and an increased production of MCP-1 in adipose tissues might be both involved in joint destruction and inflammation.

Food additives such as sodium sulphite, sodium benzoate and curcumin inhibit leptin release in lipopolysaccharide-treated murine adipocytes in vitro

Obesity leads to the activation of pro-inflammatory pathways, resulting in a state of low-grade inflammation. Recently, several studies have shown that the exposure to lipopolysaccharide (LPS) could initiate and maintain a chronic state of low-grade inflammation in obese people. As the daily intake of food additives has increased substantially, the aim of the present study was to investigate a potential influence of food additives on the release of leptin, IL-6 and nitrite in the presence of LPS in murine adipocytes. Leptin, IL-6 and nitrite concentrations were analysed in the supernatants of murine 3T3-L1 adipocytes after co-incubation with LPS and the food preservatives, sodium sulphite (SS), sodium benzoate (SB) and the spice and colourant, curcumin, for 24 h. In addition, the kinetics of leptin secretion was analysed. A significant and dose-dependent decrease in leptin was observed after incubating the cells with SB and curcumin for 12 and 24 h, whereas SS decreased leptin concentrations after 24 h of treatment. Moreover, SS increased, while curcumin decreased LPS-stimulated secretion of IL-6, whereas SB had no such effect. None of the compounds that were investigated influenced nitrite production. The food additives SS, SB and curcumin affect the leptin release after co-incubation with LPS from cultured adipocytes in a dose- and time-dependent manner. Decreased leptin release during the consumption of nutrition-derived food additives could decrease the amount of circulating leptin to which the central nervous system is exposed and may therefore contribute to an obesogenic environment.

Involvement of iNOS and NO in TNF-alpha-downregulated resistin gene expression in 3T3-L1 adipocytes

OBJECTIVE

In order to characterize the regulation of resistin gene expression, we explore the effect of tumornecrosis factor-alpha (TNF-alpha) on resistin mRNA expression and its underlying mechanism in 3T3-L1 adipocytes.

METHODS AND PROCEDURES

Differentiated 3T3-L1 adipocytes were treated for 24 h with 0-10 ng/ml of TNF-alpha or with 2.5 ng/ml of TNF-alpha for 0-24 h, and then resistin mRNA levels were measured by northern blotting. To further explore the involvement of nitric oxide (NO) in TNF-alpha-regulated resistin expression, the effect of the NO donor, sodium nitroprusside (SNP), on resistin mRNA levels in adipocytes and the effect of the nitric oxide synthase (NOS) inhibitors, N(G)-nitro-L-arginine methyl ester (L-NAME), and S,S'-1,3-phenylene-bis(1,2-ethanediyl)-bis-isothiourea.2HBr (PBITU), on the TNF-alpha effect in adipocytes were examined. The effects of TNF-alpha on inducible NOS (iNOS) protein expression in adipocytes were also measured by western blotting.

RESULTS

Our results showed that TNF-alpha caused a dose-dependent reduction in resistin mRNA levels. This effect seemed to be associated with the TNF-alpha-induced expression of iNOS. The results showed that TNF-alpha induced iNOS expression and release of NO after 24-h treatment of differentiated 3T3-L1 adipocytes. Pretreatment with L-NAME and PBITU significantly reversed the TNF-alpha-induced downregulation of resistin expression, while treatment with SNP mimicked the inhibitory effect of TNF-alpha on resistin expression. In addition, pretreatment with protein tyrosine kinase (PTK) inhibitors, genistein and AG-1288, prevented TNF-alpha-induced iNOS expression and subsequent resistin downregulation.

DISCUSSION

Our data suggest that TNF-alpha suppresses resistin expression by inducing iNOS expression, thus causing overproduction of NO, which downregulates resistin gene expression.

Nitric oxide dysregulates adipocytokine expression in 3T3-L1 adipocytes

Obesity is associated with infiltration of macrophages into adipose tissue, and macrophages are an important source of nitric oxide (NO). Dysregulated production of fat-derived secretory factor, adipocytokine, leads to obesity-linked metabolic disorders. However, it has not been fully determined whether NO might have direct effects on adipocytokine expressions. Here, we show that NO donor treatment downregulated gene expression and secretion of adiponectin, and upregulated mRNA levels of PAI-1 and IL-6. NO donor reduced promoter activity of adiponectin through PPARgamma responsive element. Moreover, NO donor activated JNK and NF-kappaB pathways, and inhibitors of these pathways rescued NO-mediated upregulation of PAI-1 and IL-6. Analysis of adipose tissue of high-fat-fed obese mice showed upregulation of PAI-1 and IL-6 expression, increased synthesis of NO, and downregulation of adiponectin. Our results suggest that increased NO synthesis might be partly responsible for dysregulation of adipocytokines in adipose tissue.

Adiponectin and leptin up-regulate extracellular matrix production by dermal fibroblasts

Adipocytes were recently shown to secrete adipocytokines, such as adiponectin and leptin, which may have an endocrine role. Subcutaneous adipose tissue lies just beneath the dermis, and dermal condition is correlated with body mass index (BMI). However, it is not clear whether adipocytokines released by adipocytes in subcutaneous adipose tissue influence the adjacent dermis. We found that human dermal fibroblasts express genes encoding receptors for adiponectin and leptin, and that those cytokines both significantly increase production of hyaluronic acid (HA), a major extracellular matrix component (ECM) of dermis, by dermal fibroblasts. This effect is accompanied with up-regulation of HA synthase 2 gene expression. Moreover, adiponectin significantly increases production of collagen, the most abundant component of ECM in dermis, by dermal fibroblasts. These results suggest that subcutaneous adipocytes influence dermal condition by up-regulating collagen and HA production by dermal fibroblasts via secretion of adiponectin and leptin.

Relationship among nitric oxide, leptin, ACTH, corticosterone, and IL-1beta, in the early and late phases of adjuvant arthritis in male Long Evans rats

Leptin, a hormone regulating body weight, food intake, and metabolism, is associated with activation of immune cells and inflammation. In this study we analyzed levels of leptin, adrenocorticotropic hormone (ACTH), corticosterone, interleukin 1beta (IL-1beta), and nitric oxide (NO) production on days 10 and 22 of adjuvant arthritis (AA) in male Long Evans rats to ascertain possible relationship of leptin with its modulators during the early and late phases of chronic inflammation. The circulating leptin levels were significantly reduced already on day 10 of AA compared to controls (1.97+/-0.22 ng/ml vs. 3.08+/-0.25 ng/ml, p<0.05); on day 22 no significant further drop was observed (1.06+/-0.21 ng/ml). Leptin mRNA in epididymal fat tissue was reduced in arthritic animals compared to controls on day 22 (0.61+/-0.09 vs. 1.30+/-0.1 arbU/GAPDH (p<0.01). IL-1beta concentration in spleen was enhanced on day 10 of AA (24.55+/-4.67 pg/100 microg protein vs. 14.33+/-1.71 pg/100 microg protein; p<0.05); on day 22 it did not differ from controls. ACTH and corticosterone levels were significantly elevated only on day 22 of AA (ACTH: 306.17+/-42.22 pg/ml vs. 157.61+/-23.94 pg/ml; p<0.05; corticosterone: 5.24+/-1.38 microg/100 ml vs. 1.05+/-0.23 microg/100 ml; p<0.01). Nitrate levels were enhanced similarly on days 10 (49.86+/-1.83 microM) and 22 of AA (43.58+/-2.17 microM), compared to controls (23.42+/-1.39 microM, p<0.001). These results show that corticosterone does not stimulate leptin production during AA. The suppression of leptin may be a consequence of permanent activation of NO, IL-1beta, and of lower weight gain. Circulating leptin does not seem to play a key role in the progression of chronic arthritis.