3,5-Diiodo-L-Thyronine (T2) Administration Affects Visceral Adipose Tissue Inflammatory State in Rats Receiving Long-Lasting High-Fat Diet

Abstract

3,5-diiodo-thyronine (T2), an endogenous metabolite of thyroid hormones, exerts beneficial metabolic effects. When administered to overweight rats receiving a high fat diet (HFD), it significantly reduces body fat accumulation, which is a risk factor for the development of an inflammatory state and of related metabolic diseases. In the present study, we focused our attention on T2 actions aimed at improving the adverse effects of long-lasting HFD such as the adipocyte inflammatory response. For this purpose, three groups of rats were used throughout: i) receiving a standard diet for 14 weeks; ii) receiving a HFD for 14 weeks, and iii) receiving a HFD for 14 weeks with a simultaneous daily injection of T2 for the last 4 weeks. The results showed that T2 administration ameliorated the expression profiles of pro- and anti-inflammatory cytokines, reduced macrophage infiltration in white adipose tissue, influenced their polarization and reduced lymphocytes recruitment. Moreover, T2 improved the expression of hypoxia markers, all altered in HFD rats, and reduced angiogenesis by decreasing the pro-angiogenic miR126 expression. Additionally, T2 reduced the oxidative damage of DNA, known to be associated to the inflammatory status. This study demonstrates that T2 is able to counteract some adverse effects caused by a long-lasting HFD and to produce beneficial effects on inflammation. Irisin and SIRT1 pathway may represent a mechanism underlying the above described effects.

Altered Mitochondrial Quality Control in Rats with Metabolic Dysfunction-Associated Fatty Liver Disease (MAFLD) Induced by High-Fat Feeding

“…In a previous study, we demonstrated that rats receiving an HFD for 6 weeks exhibited an alteration in mitochondrial oxidative stress parameters, such as an increase in H 2 O 2 production and an inhibition of aconitase and superoxide dismutase activity [ 49 , 50 ]. In a more recent study, we have demonstrated that rats fed an HFD for 14 weeks showed markedly increased serum levels of 8-OHdG, indicating a condition of increased systemic oxidative stress [ 27 , 51 , 52 ]. In line with the previous literature, data obtained in the present study show an increase in mitochondrial ROS production and an imbalance of antioxidant defense enzymes in the set-up model of the MAFLD ( Figure 3 ).…”

“…Every effort was made to minimize animal pain and suffering. At the start of the study (day 0), and after seven days of acclimatization to thermoneutrality, the rats were divided into two groups, as follows: The first group, control group (N), received a standard diet ad libitum (total metabolizable percentage of energy: 60.4 carbohydrates, 29 proteins, and 10.6 fat J −1 ; 15.88 kJ gross energy g −1 ) (Muscedola, Milan, Italy) for fourteen weeks; The second group, MAFLD group (HFD) received a high-fat diet (HFD) ad libitum (280 g diet supplemented with 395 g of lyophilized lamb meat (Liomellin, Milan, Italy), 120 g cellulose (Sigma-Aldrich, St. Louis, MO, USA), 20 g mineral mix (ICN Biomedical, Solon, OH, USA), 7 g vitamin mix (ICN), and 200 g low-salt butter (Lurpak, Denmark); total metabolizable percentage of energy: 21 carbohydrates, 29 proteins, and 50 fat J −1 ; 19.85 kJ gross energy g −1 ) for fourteen weeks to reproduce a model of overweight recently characterized for visceral adipose tissue inflammation [ 27 ]. …”

“…The second group, MAFLD group (HFD) received a high-fat diet (HFD) ad libitum (280 g diet supplemented with 395 g of lyophilized lamb meat (Liomellin, Milan, Italy), 120 g cellulose (Sigma-Aldrich, St. Louis, MO, USA), 20 g mineral mix (ICN Biomedical, Solon, OH, USA), 7 g vitamin mix (ICN), and 200 g low-salt butter (Lurpak, Denmark); total metabolizable percentage of energy: 21 carbohydrates, 29 proteins, and 50 fat J −1 ; 19.85 kJ gross energy g −1 ) for fourteen weeks to reproduce a model of overweight recently characterized for visceral adipose tissue inflammation [ 27 ].…”

“…Oxygen consumption (VO2) and carbon dioxide production (CO2) measurements were made using a four-chamber, indirect open-circuit calorimeter (Columbus Instrument), with one rat per chamber at a room temperature of 28 °C to evaluate basal metabolic parameters, as previously described [ 27 ].…”

“…Total RNA liver was isolated using TRIzol reagent (Invitrogen) according to the manufacturer’s protocol as previously described [ 27 ]. A quantity of 1 µg of RNA was used to synthesize cDNA strands in 20 µL reaction volume, according to the Quanti Tect Reverse Transcription Kit instructions (Qiagen, Hilden, Germany).…”