Insulin effect on glucose transport in thymocytes and splenocytes from rats with metabolic syndrome

Abstract

Metabolic syndrome (MS) may comprise several clinical conditions such as obesity, diabetes and inflammatory disorders, which are characterized by metabolic imbalances. The study of glucose transport and regulation by insulin in lymphocytes is important, since the way they increase inflammation and susceptibility to infections are common in MS. We studied glucose internalization in isolated thymocytes and splenocytes, its regulation by insulin, and the role of three glucose transporters (Gluts) in control and in MS rats. Control glucose internalization and insulin responses were lower in splenocytes than in thymocytes. Control and insulin-induced glucose internalization in thymocytes declined with age, while transport by splenocyte continued to respond to insulin. Control thymocyte glucose internalization was blocked by antibodies against Glut 1 and 4, while the insulin response also was blocked by an anti-Glut 3 antibody. On four month old control and insulin-induced response, splenocyte transport was only blocked by Glut 1 and 4 antibodies. At six months splenocyte glucose internalization depended on Glut 1 and was less sensitive to the effects of an anti-Glut 4 antibody. In MS splenocytes the capacity of anti-Glut 1 antibodies to inhibit control and insulin-dependent glucose transport was less significant, and we found that in MS rats, glucose internalization was dependent on Glut 3 and Glut 4. In summary, the altered metabolic state present in MS rats shows signs of modulation of glucose internalization by the Glut1, Glut 3 and Glut 4 transporters, compared with its own age control.

Figure 1

Insulin effect on glucose internalization of control and MS rat lymphocytes. A) Comparative glucose transport in control and MS thymocytes and splenocytes, with and without insulin. B) Experiments with TPZ as a control of the possible pathway of the insulin effect. * p < 0.05 comparing the two types of cells; ^♦ p < 0.05 insulin effect when compared to control values incubated with Tyrode; ^♥ p < 0.05 comparing between ages; ^× p < 0.05 MS effect of the MS compared to its 6 months control; ⊕ p < 0.05 compared with its insulin control.

Figure 2

Glucose transporter participation in basal and insulin-induced glucose internalization of young rat lymphocytes. A) Effect of the three different antibodies against the glucose transporter on glucose transport of young (4 months) control cells and the insulin effect. B) Experiments in the presence of an unspecific serum without antibodies against the glucose transporters and in the presence of cytochalasin B (Cyto B), a non-selective glucose transporter blocker, * p < 0.05 comparing the two type of cells; ^♦ p < 0.05 insulin effect when compared to control values incubated with Tyrode; ▲ p < 0.05 compared to its own Tyrode control.

Figure 3

Splenocyte glucose transporter participation in basal and insulin-induced glucose internalization at two ages. A) Changes on the effect of the three different antibodies, against the glucose transporter, on glucose transport at 4 and 6 months with and without insulin. B) Given the different response to the anti Glut 4 antibodies there was the need to use a different antibody concentration (1:500); ^◆ p < 0.05 insulin effect when compared to control values incubated with Tyrode; ▲ p < 0.05 compared to its own control; ^♥ p < 0.05 comparison between ages.

Figure 4

Splenocyte glucose transporter participation in glucose internalization with and without insulin on the MS model. A) Changes on the effect of the three different glucose transporter antibodies, on control and MS glucose transport are shown. Anti-Glut 3 antibodies responded in the MS splenocytes only. B) Given the different response to the anti Glut 1 antibodies there was also the need to use a different antibody concentration (1:500). Anti Glut 4 concentration used in the MS was the same (1:500) as in the previous experiments in control of six months old animals. ^◆ p < 0.05 insulin effect when compared to control values incubated with Tyrode; ▲ p < 0.05 compared with its own control; ^× p < 0.05 MS effect compared with its 6 months control.