Organotins are a group of chemical compounds that have a tin atom covalently bound to one or more organic groups. The best-studied organotin is tributyltin chloride, which is an environmental pollutant and an endocrine disruptor. Tributyltin chloride has been shown to bind to PPARγ/RXRα and induces adipogenesis in different mammalian cells. However, there are few studies with other organotin compounds, such as dibutyltins. The aim of this study was to investigate the effect of dibutyltins diacetate, dichloride, dilaurate, and maleate on the transcriptional activity of the nuclear PPARγ and RXRα receptors, and on adipogenesis and inflammation. Analogous to tributyltin chloride, in reporter gene assay using HeLa cells, we observed that dibutyltins diacetate, dichloride, dilaurate, and maleate are partial agonists of PPARγ. Unlike tributyltin chloride, which is a full agonist of RXRα, dibutyltins dichloride and dilaurate are partial RXRα agonists. Additionally, the introduction of the C285S mutation, which disrupts tributyltin chloride binding to PPARγ, abrogated the dibutyltin agonistic activity. In 3T3-L1 preadipocytes, all dibutyltin induced adipogenesis, although the effect was less pronounced than that of rosiglitazone and tributyltin chloride. This adipogenic effect was confirmed by the expression of adipogenic markers Fabp4, Adipoq, and Glut4. Exposure of 3T3-L1 cells with dibutyltin in the presence of T0070907, a specific PPARγ antagonist, reduced fat accumulation, suggesting that adipogenic effect occurs through PPARγ. Furthermore, dibutyltins dichloride, dilaurate, and maleate inhibited the expression of proinflammatory genes in 3T3-L1 cells, such as Vcam1, Dcn, Fn1, S100a8, and Lgals9. Additionally, in RAW 264.7 macrophages, tributyltin chloride and dibutyltin dilaurate reduced LPS-stimulated TNFα expression. Our findings indicate that dibutyltins diacetate, dichloride, dilaurate, and maleate are PPARγ partial agonists and that dibutyltins dichloride and dilaurate are also partial RXRα agonists. Furthermore, dibutyltins induce adipogenesis in a PPARγ-dependent manner and repress inflammatory genes in 3T3-L1 and RAW 264.7 cells. Although dibutyltins display some partial PPARγ/RXRα agonistic effects, the translation of cell-based results assays into in vivo effects on inflammation and insulin resistance is not entirely known. Nevertheless, further studies are necessary to address their effects in different periods of life and to elucidate the actions of organostanic compounds in whole-body context.

Organotins are endocrine disruptors and a widely distributed environmental chemical. The best‐studied organotin is tributyltin (TBT), which has been shown to bind to PPAR gamma/RXR alpha and induces adipogenesis in different mammalian cells. Dibutyltin (DBT) is another organotin used as a stabilizer in the production of polyvinyl chloride plastics, and it is also the major metabolite formed from TBT in vivo. Recently, we demonstrated that DBTs are PPARγ partial agonists and that DBT chloride and dilaurate are also partial RXRα agonists. Additionally, DBTs induce adipogenesis in a PPARγ‐dependent manner and repress inflammatory genes in preadipocyte cell culture. However, the role of DBTs on PPAR alpha is still unknown. In the present study, we investigate the effect of dibutyltins pharmacological effects on PPAR alpha in mammalian cells. In reporter gene assay using HeLa cells, we observed that dibutyltins do not display an agonist effect on PPAR alpha. Therefore, we decided to explore the antagonistic effects on PPARα. In the cell‐based reporter gene assay, treatment with PPAR alpha agonist (bezafibrate) induced a 3.3‐fold activation on PPAR alpha. On the other hand, DBT dilaurate and DBT dichloride produced a dose‐dependently inhibition of the PPAR alpha transcription transactivation induced by bezafibrate. These effects were not due to the cytotoxicity. Next, we compared the antagonistic results of DBT dilaurate and DBT dichloride to GW6471, a well‐known synthetic specific PPAR alpha antagonist. Transfected cells were treated with vehicle, an increasing concentration of DBT dilaurate, DBT dichloride or GW6471 in the presence of Bezafibrate (10μM). Bezafibrate activation in the absence of antagonist was considered as 100%. The percentage of GW6471, DBT dilaurate, and DBT dichloride were calculated in comparison to bezafibrate. DBT dilaurate and DBT dichloride showed a dose‐dependent inhibition of bezafibrate induced PPARα transcriptional activity. The median inhibitory concentration (IC50) of DBT dilaurate (4.1μM) was significantly higher than GW647, which displayed an IC50 value of 0.13μM. However, IC50 of DBT dichloride upon PPAR alpha was significantly lower (0.26μM) and similar to GW647. Therefore, DBT dilaurate was considered as a weak antagonist, while the dibutyltin dichloride displayed a potent antagonist effect on PPAR alpha. Next, to further characterize these effects on a physiological assay, we analyzed the catalase activity induced by WKY14643, a PPAR alpha agonist in the presence and absence of DBT dilaurate and DBT dichloride in HepG2 and HFF‐1 cells. As was observed with GW647, DBT dilaurate and DBT dichloride inhibited the catalase activity induced by WKY14643 in a dose‐dependent manner. These results showed for the first time that DBT dilaurate and dichloride display a PPAR alpha antagonist effect.Support or Funding InformationNational Council for Scientific and Technological Development–Grant number: CNPq 486613/2013‐5 and Fundacao de Apoio a Pesquisa do Distrito Federal ‐ FAPDF ‐ Edital 04/2017.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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