max_olivm@hotmail.com

mariasara_lc@hotmail.com

thais_tsosura@hotmail.com

fernando.chiba@unesp.br

renatoofp@hotmail.com

jessica_bonilha@hotmail.com

e.ervolino@unesp.br

biaelvirabelardi@gmail.com

rodrigoms13@hotmail.com

bruna_leonina@hotmail.com

nayaradourado@live.com

carolcarnevali05@gmail.com

juliasantelli@hotmail.com

heloisa_macedopf@hotmail.com

rakirafujii@gmail.com

doris.hissako@unesp.br

*Master in Physiology, Multicenter Graduate Program in Physiological Sciences

São Paulo State University (Unesp), School of Dentistry, Araçatuba, São Paulo

**Postdoctoral researcher, Multicenter Graduate Program in Physiological Sciences

School of Dentistry. Ph.D. in Physiology. Multicenter Graduate Program

in Physiological Sciences. São Paulo State University (Unesp), School of Dentistry

***Ph.D. student, Multicenter Graduate Program in Physiological Sciences

Master in Physiology, Multicenter Graduate Program in Physiological Sciences

São Paulo State University (Unesp), School of Dentistry

****Assistant Professor, Department of Preventive and Restorative Dentistry

Ph.D. in Preventive and Social Dentistry, São Paulo State University (UNESP),

School of Dentistry, Araçatuba, São Paulo

*****Ph.D. in Physiology, Multicenter Graduate Program in Physiological Sciences

Master in Physiology, Multicenter Graduate Program in Physiological Sciences

São Paulo State University (Unesp), School of Dentistry

******Biomedical, Paulista University (Unip), Araçatuba, São Paulo

*******Associate professor, Department of Basic Sciences

São Paulo State University (Unesp), School of Dentistry, Araçatuba

********Master's Degree student, Multicenter Graduate Program in Physiological Sciences

São Paulo State University (Unesp), School of Dentistry, Araçatuba, São Paulo

+Ph.D. student, Multicenter Graduate Program in Physiological Sciences

Master in Physiology, Multicenter Graduate Program in Physiological Sciences

São Paulo State University (Unesp), School of Dentistry, Araçatuba, São Paulo

++Master in Physiology, Multicenter Graduate Program in Physiological Sciences, 

São Paulo State University (Unesp), School of Dentistry, Araçatuba, São Paulo, Brazil.

+++Graduate student, São Paulo State University (Unesp), School of Dentistry, Araçatuba

++++Graduate student, Catholic Salesian Auxilium University Centre, Araçatuba

+++++Master's Degree student, Graduate Program in Public Health in Dentistry

Department of Preventive and Restorative Dentistry, São Paulo State University (Unesp)

School of Dentistry, Araçatuba, São Paulo

++++++Full Professor, Multicenter Graduate Program in Physiological Sciences

São Paulo State University (Unesp), School of Dentistry, Araçatuba, São Paulo

(Brazil)

Reception: 06/24/2020 - Acceptance: 12/28/2020

1st Review: 11/11/2020 - 2nd Review: 11/21/2020

Accessible document. Law N° 26.653. WCAG 2.0

Suggested reference: Mota, MS de O da, Mattera, MS de LC, Tsosura, TVS, Chiba, FY, Pereira, RF, Bonilha, JC, Ervolino, E., Belardi, BE, Santos, RM dos, Tavares, BS, Dourado, NG, Carnevalli, ACN, Santelli, JO, Sampaio, HM, Oliveira, RAF de, & Matsushita, DH (2021). The Resistance Training Reverses Insulin Resistance in Rats with Periodontitis. Lecturas: Educación Física y Deportes, 25(273), 97-113. https://doi.org/10.46642/efd.v25i273.2371

 

Abstract

    The present study, aimed to evaluate the effects of resistance training (RT) on glycemia, insulinemia, insulin sensitivity, insulin signaling (IS), and tumor necrosis factor-α (TNF-α) levels in rats with periodontitis. 40 male Wistar rats were distributed into 4 groups: sedentary control group (SCN), exercised control group (ExCN), sedentary ligature-induced periodontal disease group (SPD), and exercised ligature-induced periodontal disease group (ExPD). 28 days after inducing periodontitis the RT started (14-week). Glycemia, insulin, TNF-α levels, and insulin sensitivity were analyzed using various methods. IS was evaluated by measuring tyrosine phosphorylated pp185 in insulin-sensitive tissues (western blot method). Higher levels of insulin, HOMA-IR, and TNF-α, and a decrease in insulin sensitivity were observed in the SPD group, which also had decreased levels of insulin-stimulated tyrosine phosphorylated pp185 in muscle and adipose tissue, when compared to the other groups. The ExPD group had increased levels of insulin-stimulated tyrosine phosphorylated pp185 compared to the SPD group, but showed no significant difference when compared to the SCN and ExCN groups. RT reversed both the insulin resistance (IR) and the IS alterations in rats with induced periodontitis, and decreased the insulin and TNF-α levels. Therefore, the results of show the importance of RT in preventing or reversing IR in rats with periodontitis.

    Keywords: Periodontitis. Diabetes Mellitus. Insulin resistance. Tumor necrosis factor-alpha. Resistance training.

 

Resumo

    O objetivo do presente estudo foi avaliar os efeitos do treinamento de resistência (TR) na glicemia, insulinemia, sensibilidade à insulina, sinalização à insulina (SI) e níveis de fator de necrose tumoral-α (TNF-α) em ratos com periodontite. 40 ratos Wistar machos foram distribuidos em 4 grupos: grupo controle sedentário (SCN), grupo controle exercitado (ExCN), grupo doença periodontal induzida por ligadura sedentária (SPD) e grupo doença periodontal induzida por ligadura exercitada (ExPD). 28 dias após a indução da periodontite iniciou a RT (14 semanas). Glicemia, insulina, níveis de TNF-α e sensibilidade à insulina foram analisados ​​usando vários métodos. IS foi avaliado medindo pp185 com tirosina fosforilada em tecidos sensíveis à insulina (método de western blot). Níveis mais elevados de insulina, HOMA-IR e TNF-α e diminuição da sensibilidade à insulina foram observados no grupo SPD, que também apresentou diminuição dos níveis de tirosina fosforilada por insulina estimulada em pp185 no músculo e tecido adiposo, quando comparado aos outros grupos. O grupo ExPD apresentou níveis aumentados de pp185 tirosina fosforilada estimulada por insulina em comparação ao grupo SPD, mas não apresentou diferença significativa quando comparado aos grupos SCN e ExCN. A RT reverteu as alterações de RI e SI em ratos com periodontite induzida e também diminuiu os níveis de insulina e TNF-α. Portanto, os resultados mostram a importância do TR na prevenção ou reversão da RI em ratos com periodontite.

    Unitermos: Periodontite. Diabetes mellitus. Resistência à insulina. Fator de necrose tumoral alfa. Treinamento de resistência.

 

Resumen

    El presente estudio tuvo como objetivo evaluar los efectos del entrenamiento de resistencia (RT) sobre la glucemia, insulinemia, sensibilidad a la insulina, señalización de insulina (IS) y niveles de factor de necrosis tumoral-α (TNF-α) en ratas con periodontitis. 40 ratas Wistar macho se dividieron en 4 grupos: grupo de control sedentario (SCN), grupo de control con ejercicio (ExCN), grupo de periodontitis inducida por ligadura sedentaria (SPD) y grupo de periodontitis inducida por ligadura con ejercicio (ExPD). 28 días después de inducir la periodontitis se inició la RT (14 semanas). Se analizaron la glucemia, la insulina, los niveles de TNF-α y la sensibilidad a la insulina utilizando varios métodos. La IS se evaluó midiendo pp185 fosforilada en tirosina en tejidos sensibles a la insulina (Western). Se observaron niveles más altos de insulina, HOMA-IR y TNF-α, y una disminución en la sensibilidad a la insulina en el grupo SPD, que también tuvo niveles disminuidos de pp185 fosforilada en tirosina estimulada por insulina en el músculo y el tejido adiposo, en comparación con los otros grupos. El grupo ExPD tenía niveles aumentados de pp185 fosforilada con tirosina estimulada por insulina en comparación con el grupo SPD, pero no mostró diferencias significativas en comparación con los grupos SCN y ExCN. La RT invirtió tanto las alteraciones de resistencia a la insulina (IR) como las de IS en ratas con periodontitis inducida y disminuyó insulina y TNF-α. Los resultados muestran la importancia de la RT para prevenir o revertir la IR en ratas con periodontitis.

    Palabras clave: Periodontitis. Diabetes mellitus. Resistencia a la insulina. Factor de necrosis tumoral alfa. Entrenamiento de resistencia.

 

Lecturas: Educación Física y Deportes, Vol. 25, Núm. 273, Feb. (2021)

---

 

Introduction 

 

    Diabetes is a group of metabolic diseases characterized by chronic hyperglycemia, resulting from defects in insulin secretion, insulin action, or both. Type 2 diabetes mellitus (T2DM) is the most prevalent form, accounting for approximately 90-95% of all cases of diabetes (Association, 2020). T2DM is characterized by insulin resistance (IR), a state in which the physiological concentration of insulin promotes a subnormal response to glucose uptake by cells, especially in muscle and adipose tissue. (Carvalho-Filho, 2007)

 

    Obesity is associated with the accumulation of activated macrophages that express several proinflammatory genes, including cytokines such as tumor necrosis factor-α (TNF-α), that locally impair insulin signaling (IS) (Lauterbach, & Wunderlich, 2017). These cytokines, in addition to reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress markers are increased in obese patients (Chen, 2020). The activation of Toll-like receptors (TLRs) by free fatty acids can lead to the activation of inflammatory pathways, which in turn activate transcription factors, causing further production of proinflammatory cytokines. When the production of these cytokines is sufficient, they are released into circulation, where they can act at distant sites, such as liver and skeletal muscle, to worsen IR. (Shoelson, 2006)

 

    Periodontal disease (PD) is considered to be a predisposing factor for the development of IR and T2DM because of the release of inflammatory mediators, such as TNF-α (Mattera, 2019; Mealey, & Ocampo, 2007). In fact, some studies have demonstrated that chronic periodontitis is associated with elevated levels of TNF-α in the plasma of subjects with T2DM (Engebretson, 2007), as well as in rats with induced PD. (Colombo, 2012)

 

    The proinflammatory cytokine TNF-α is related to IR in obese animals, and to the suppression of IS in vivo (Feinstein, 1993) and in vitro (Hotamisligil, 1994), by reducing the tyrosine phosphorylation of the insulin receptor and its substrates. Colombo et al. (2012) showed that induced PD caused alterations to both IS and sensitivity with the elevation of TNF-α levels in plasma. Additionally, it has been demonstrated that periodontal treatment reduces TNF-α levels (Dağ, 2009; Hayashi, 2017) and improves glycemic control in patients with T2DM. (Bharti, 2013)

 

    Previous studies have demonstrated that resistance training (RT) improves IR in association with T2DM and obesity (Mavros, 2013), and it is widely known that exercise can improve insulin sensitivity by decreasing visceral fat (Campos, 2014) and inflammatory markers (Phillips, 2010), and increasing GLUT4 translocation. (Ferrari, 2019; Kennedy, 1999)

 

    Considering that PD can promote alterations in insulin signal transduction and sensitivity, and that RT can improve such parameters in obese animals. The present study, therefore, aimed to evaluate the effects of RT on glycemia, insulinemia, insulin sensitivity, IS, and TNF-α levels in rats with PD.

 

Methods 

 

Animals 

 

    A total of 40, 2-month old male Wistar rats were housed under a light on a 12 hour light/12 hour dark cycle (lights on 7:00 am), with a temperature of 21°C ± 2°C, and food and water available ad libitum. The present study followed the ethical principles and guidelines for animal experimentation, and was approved by the local ethics committee as protocol no. 00510-2012.

 

Experimental design 

 

    Initially, the animals were randomly divided into two groups: control (CN) and periodontal disease (PD). The PD group animals were anesthetized using ketamine hydrochloride, 10% at 80 mg/kg intraperitoneally (Ketamina, Agener, Embu-Guaçu, Brazil) with xylazine, 2% at 10 mg/kg intraperitoneally (Xilasina, Dorcipec®, Monte Carlos, Brazil), and PD was induced by ligating 4-0 silk thread on the cervical area of the lower first molars, bilaterally. The first insulin tolerance test (ITT) was administered in both groups 28 days after the induction of PD, after which the animals were divided into four groups: sedentary control group (SCN), exercised control group (ExCN), sedentary periodontal disease group (SPD), and exercised periodontal disease group (ExPD). At this point, the RT protocol was started. After 14 weeks, the animals made to fast for 14 hours, and received intraperitoneal sodium thiopental anesthetization, 3% at 50 mg/kg body weight (Thiopentax®, Cristália, Itapira, Brazil). Experimentation commenced after the administration of anesthesia.

 

Radiographic evaluation of alveolar bone loss and periodontal bone support 

 

    The animals were euthanized 28 days after the induction of PD. The right and left hemimandibles were dissected and fixed for 24 hours in 4% formaldehyde. Radiographic images were acquired using an exposure technique of 70 kVp and 10mA, at 0.10 seconds. The source-to-film distance was consistently set at 40 cm. Images were obtained directly with an optical digital plate (Digora, Soredex Orion Corporation, Helsinki, Finland).

 

Resistance training 

 

    RT was performed according to the protocol described by Hornberger and Farrar (2004). Initially, the rats were subjected to a 2 week adaptation program, and then the RT program started. During the RT period, training was performed 3 days a week on an alternate day basis, with the rats climbing a ladder with a gradual load increase during the 12-week training period.

 

Determination of glucose, insulin, and TNF-α levels 

 

    Plasma samples were used to determine glucose levels using the glucose oxidase method (Enzymatic glucose, ANALISA Diagnóstica, Belo Horizonte, Brazil), and insulin levels were determined by radioimmunoassay (Coat - A - Count, DPC Diagnostics Products, Los Angeles, CA). IR was evaluated using the homeostatic model assessment of IR (HOMA-IR), where HOMA-IR = (fasting glucose [mmol/L] x fasting insulin [mIU/mL])/22.5. TNF-α plasma levels were quantified using an enzyme-linked immunosorbent assay kit (ELISA; Invitrogen, Camarillo, CA).

 

Short intravenous insulin tolerance test 

 

    ITTs were performed before and after the training period, following the protocol described by Chehoud et al. (2008). Insulin (0.75 U/kg body weight) was administered through the penile vein to animals in all groups. Blood samples (≈ 50 mL) were collected from nicked tails at 0 (before insulin administration), 4, 8, 12, and 16 minutes (after insulin administration), and glucose was measured using a glucose monitor (Accu-Chek Advantage, Roche Diagnostics, Indianapolis, IN). The results were analyzed by comparing the constant rate for glucose disappearance (Kitt value) from 0 to 16 minutes of the test. The Kitt value was calculated using the equation 0.693/t1/2. The glucose half-life (t1/2) was calculated from the slope of the least squares analysis of the plasma glucose concentrations during the linear decay phase.

 

Assessment of the IRS (pp185 – IRS-1/IRS-2) tyrosine phosphorylation status 

 

    Samples from the liver, gastrocnemius muscle, and periepididymal white adipose tissue were collected from six animals in each group, before and after the administration of 1.5 U of regular insulin (intravenously through the portal vein) at variable times (30 seconds for liver, 90 seconds for gastrocnemius, and 120 seconds for white adipose tissue). Tissue samples were prepared using the method described by Carvalho et al. (1996), and were analyzed via western blotting for the quantification of tyrosine phosphorylated pp185 (IRS-1/IRS-2) using anti-phosphotyrosine antibody (Santa Cruz Biotechnology, Santa Cruz, CA). Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) antibody (Santa Cruz Biotechnology, Santa Cruz, CA) was used as a control. Immunoreactive bands were detected using a chemiluminescent substrate autoradiography system (GE Healthcare, Buckinghamshire, UK), according to the manufacturer’s instructions. Quantitative analysis of the blots was performed using Scion Image Release beta 3b software (National Institute of Health, Frederick, MD, USA).

 

Statistical analyses 

 

    All values are presented as the mean ± SEM. The normality of data was verified, and statistical analysis was performed by analysis of variance (ANOVA), followed by Tukey’s post hoc test when the analysis of variance suggested a significant difference between groups (P< 0.05).

 

Results 

 

Radiographic analysis of alveolar bone 

 

    Alveolar bone analysis revealed that animals in the PD group had more bone loss and less bone support than those in the CN group (Figure 1).

 

Note: Radiographic images showing normal alveolar bone (A) and bone loss in the interproximal 

and interradicular regions (B) (white arrowheads) 28 days after ligature-induced periodontitis.

 

Glucose, insulin, HOMA-IR indices, and TNF-α levels 

 

    The comparison of fasting glucose between the four groups showed no significant difference. Insulin and HOMA-IR index values were higher (P<0.05) in the SPD group than in the other groups, however, the ExPD insulin levels and HOMA-IR indices were higher only when compared to SCN. No significant difference was observed between the SPD and ExCN groups (Table 1).

 

	SCN	ExCN	SPD	ExPD
Glycemia (mmol/L)	5.07 ± 0.16	5.39 ± 0.59	5.48 ± 0.22	5.30 ± 0.11
Insulinemia (µIU/mL)	3.32 ± 0.40	4.49 ± 0.28	9.79 ± 6.93*	6.93 ± 0.92#
HOMA-IR	0.78 ± 0.07	1.08 ± 0.05	2.36 ± 0.22*	1.59 ± 0.18#
TNF-α (pg/mL)	6.95 ± 0.32	7.66 ± 0.33	9.56 ± 0.90+	7.24 ± 0.14

Source: Self made

 

ITT 

 

    Twenty-eight days after periodontal disease induction (before RT period), the Kitt of PD group was smaller (P<0.05) than CN group. A smaller value of Kitt shows greater insulin resistance due to impaired insulin sensitivity. After RT, SPD showed smaller Kitt value (P<0.05) when compared to SCN, ExCN, and ExPD groups (Figure 2).

 

Note: In Figure 2A, the Kitt value for the CN and PD groups (n=12).
In Figure 2B, the Kitt value for all groups (n=6)
Values are expressed as the mean ± SEM
*P < 0.0001 PD versus CN, #P< 0.05 SPD versus SCN, ExCN, and ExPD.

 

Insulin signal transduction 

 

    An increase in tyrosine phosphorylated pp185 was observed after insulin stimulation in relation to the baseline for all groups and tissues. After insulin stimulation, tyrosine phosphorylated pp185 was reduced (P<0.05) in muscle and white adipose tissues in the SPD group, when compared with the SCN, ExCN, and ExPD groups. However, this alteration in IS was not observed in the livers of all groups (Figure 3).

 

Note: Panels A, C, and E show typical autoradiography, in which similar quantities of protein (185 µg) were subjected to

sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). GAPDH was used as a control. Panels B, D, and F

show tyrosine phosphorylation status values (expressed in arbitrary units), which are presented as mean ± SEM, n = 6.

*P<0.05 for insulin (-) versus insulin (+); †P<0.05 for SPD (+) versus SCN (+), ExCN (+), and ExPD (+).

 

Discussion 

 

    Given that there is a relationship between PD, IR, and IS (Colombo, 2012), the present study aimed to verify the effects of RT on these parameters in adult rats with induced PD. The results of this study showed that induced PD promoted IR and a decrease in IS in adult rats, whereas RT improved these alterations.

 

    The existence of a bidirectional relationship between periodontal condition, T2DM, and IR has been demonstrated. Katagiri et al. (2013) showed that glycemic control ameliorated PD in subjects with T2DM without periodontal treatment. Other previous studies have shown that the presence of PD is related to elevated blood glucose levels in humans when compared to individuals with healthy periodontal conditions (Jung, 2015). However, in the present study, no significant difference in glucose levels were observed (Table 1), which is in agreement with the findings of Machado et al. (2005),who did not observe differences in glucose levels of humans with PD, and Pontes Andersen et al. (2006) and Colombo et al. (2012), who did not observe differences in glucose levels of rats with PD when compared to controls.

 

    Although hyperglycemia is a characteristic of diabetes, a compensatory increase in insulin secretion makes even the most obese insulin-resistant individuals normoglycemic (Malone, & Hansen, 2019; Wu, 2013). This was also observed in the present study. The analysis of insulin levels (Table 1) revealed that rats in the SPD group showed higher insulin levels when compared to the control groups (SCN and ExCN). This is in agreement with the results from Demmer et al. (2012) and Pontes et al. (2006), who observed higher levels of insulin in association with PD. Moreover, Sun et al. (2011) observed that after 3 months of treatment, insulin levels were reduced.

 

    We also observed that RT had an effect on the rats’ insulin levels, as a significant decrease in insulin levels was observed in the ExPD group as compared to the SPD group. However, no differences were observed between sedentary and exercised controls (SCN and ExCN). Whyte et al. (2013) verified that a single bout of intensive exercise decreased insulin levels in obese individuals. Chronic physical activity, such as RT, conducted for 8 weeks in obese rats has been found to cause a decrease in insulin levels (Marinho, 2012). Geirsdottir et al. (2012) also observed a reduction in insulin levels after 12 weeks of RT in elderly prediabetic and T2DM patients.

 

    The HOMA-IR index was calculated using the values obtained for glucose and insulin levels. This index expresses IR, therefore the higher the value of this index the higher the IR in the animal. The results of the present study indicated that rats in the SPD group had higher HOMA-IR values when compared to the other groups (Table 1). This result is in agreement with Colombo et al. (2012), who observed greater IR in rats 28 days after the induction of PD. The exercise reversed this alteration, so that the ExPD group had a decreased HOMA-IR index when compared to the SPD group.

 

    Besides the HOMA-IR indices, insulin sensitivity was evaluated using another parameter, the constant rate for glucose disappearance (Kitt value), an index that allows the evaluation of insulin sensitivity in vivo. The lower this index is, the greater the IR (Geloneze, & Tambascia, 2006). The results obtained using ITT confirm the data seen with HOMA-IR indices, that is, rats with PD were more resistant to insulin prior to RT when compared to the control group, but after RT, the ExPD group had insulin sensitivity similar to that of the control group. On the other hand, the SPD group was more resistant to insulin when compared to the other groups, showing again the beneficial effects of physical activity on IR.

 

    The relationship between physical exercise and insulin sensitivity has been previously studied numerous times, and it is known that exercise is important for glycemic control in diabetic subjects. (Dubé, 2012)

 

    Several studies have shown an increase in insulin sensitivity and improvement in glycemic control as the result of physical exercise. Panveloski et al. (2011) demonstrated an increase in insulin sensitivity as the result of RT in diet-induced obese rats. A similar result was observed by Oliveira et al. (2011), who showed that chronic exercise promoted improvement in insulin sensitivity in obese rats. Mackenzie et al. (2012) observed that continuous moderate exercise also promoted improvement of glycemic control in diabetic patients. Furthermore, progressive aerobic training promotes a reduction in HbA1c compared to non-progressive aerobic training in patients with T2DM. (Delevatti, 2019)

 

    The mechanisms by which physical exercise improves insulin sensitivity are still not completely understood; however, exercise does indeed improve glycemic control (Falcão-Tebas, 2020; Figueira, 2013). Glycemic control promoted by physical exercise may possibly be due to a higher peripheral glucose uptake. This is due to a higher translocation of glucose transporter protein (GLUT4) to the plasma membrane through an insulin-independent pathway (Kennedy, 1999), possibly mediated by the 5’ AMP-activated protein kinase (AMPK) (Hayashi,1998). Carvalho et al. (1996) demonstrated that a higher expression of GLUT4 in adipose tissue results in lower fasting glucose levels and an increase in glucose tolerance in transgenic mice that did not express GLUT4 in muscle.

 

    Previous studies have shown that physical exercise increases GLUT4 mRNA in skeletal muscle (Hussey, 2011), as well as GLU4 translocation to the plasma membrane of muscle cells, caused by AMPK. (Hayashi, 1998; Kennedy, 1999)

 

    Due to the known relationship between IR and TNF-α plasma levels, the concentration of this cytokine was evaluated in the present study. We observed that PD increased TNF-α levels, as seen by Colombo et al. (2012) in rats with PD, and by Engebretson et al. (2007) in humans with PD.

 

    In addition to its negative effects on insulin sensitivity, it has also been demonstrated that TNF-α is related to impairment in IS (Hotamisligil, 1994). The decrease in tyrosine phosphorylated pp185 in skeletal muscle and adipose tissue observed in the present study may be due to the effects of TNF-α. Colombo et al. (2012) demonstrated that PD led to decreased tyrosine phosphorylated pp185 levels. The same was reported by Astolphi et al. (2013), who found impairment in IS associated with periapical lesions.

 

    It is known that both IRS-1 and IRS-2 tyrosine phosphorylation cause the insulin signal to increase, whereas in some insulin-resistant conditions, there is an increase in serine phosphorylation of these substrates, which attenuates the signal by decreasing the tyrosine phosphorylation capacity of the insulin receptor and its substrate after insulin stimulation (Hotamisligil, 1996). It has been demonstrated that TNF-α can act on the IS pathway, increasing phosphorylation of IRS-1 on multiple serine residues (Yaribeygi, 2019; Zhang, 2008). Thus, it can be assumed that the increase in TNF-α levels in the SPD group caused IR due to a decrease in tyrosine phosphorylated pp185. (del Aguila, 1999)

 

    No difference in tyrosine phosphorylated pp185 was observed in the liver was observed, as described by Colombo et al. (2012). This may explain the absence of glucose alteration in the PD rats, even with reduced tyrosine phosphorylated pp185 in muscle and adipose tissues, since Cho et al. (2006) suggested that the liver may compensate for IR in adipose and muscle tissues to prevent hyperglycemia.

 

    Sun et al. (2011) observed that after 3 months of PD treatment, plasma levels of TNF-α and HOMA-IR indices were significantly decreased, showing that this treatment reduced inflammation, improved glycemic control, decreased IR, and improved β-cell function in patients with T2DM. This shows that the presence of localized inflammation is related to IR pathogenesis and, consequently, toT2DM.

 

    In the present study, it was observed that animals in the SPD group had an increased concentration of TNF-α in the plasma than those in the ExPD group, indicating that physical activity can change the plasma concentration of this cytokine.

 

    Previous studies have shown that acute exercise increases levels of proinflammatory cytokines in the plasma, such as TNF-α, and that chronic exercise decreases the levels of this cytokine as well as its expression. (Cabral-Santos, 2019; Ho, 2013)

 

    The mechanisms by which exercise acts on TNF-α have not been completely elucidated; however, it is known that there is an increase in IL-6 levels (produced by muscle) due to physical activity, and that this cytokine inhibits TNF-α production (Petersen, & Pedersen, 2005). Another possible factor is that during physical activity, epinephrine is released (Petersen, & Pedersen, 2005), which decreases TNF-α production induced by lipopolysaccharide (LPS) (van der Poll, 1996). Thus, the inhibitory effect of physical activity on TNF-α production is an important mechanism that restores tyrosine phosphorylated pp185 levels and decreases IR, one of the main features of T2DM. In fact, Pauli et al. (2008) demonstrated that physical activity is related to an increase in IRS-1 tyrosine phosphorylation and the improvement of IR.

 

    In summary, in addition to corroborating the relationship between PD and IR, the present study demonstrated that RT has a positive effect on insulin sensitivity, IS, TNF-α, and insulin levels, showing that physical exercise may be an important factor for the prevention of IR in patients with PD.

 

Conclusions 

 

    Given that PD can promote impaired insulin sensitivity and signaling, likely due to the elevation of TNF-α levels, the present study showed that RT reversed IR and the alterations in IS, and decreased TNF-α and insulin levels.

 

Acknowledgments 

 

    This study was supported by São Paulo Research Foundation (FAPESP) [grants #2012/03688-0 and #2014/01964-6] and Pro-Rectory of Research of UNESP (PROPe-UNESP). The authors thank Devani Mariano Pinheiro for her help with the insulinemia assay.

 

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