Search

Background: We have previously demonstrated an early and potent antiinflammatory effect of troglitazone and rosiglitazone. Hypothesis: Because inflammatory mediators interfere with insulin signal transduction, we have now hypothesized that rosiglitazone exerts an initial antiinflammatory effect independently of its metabolic actions including the suppression of the plasma concentration of free fatty acids (FFAs), insulin, and glucose after which insulin sensitization occurs. Patient and Methods: Fourteen patients with type 2 diabetes were included in the study. Eight patients were given 2 mg daily of rosiglitazone for 6 wk, whereas the other six patients were given a placebo for the same period. Results: After a 2-mg dose of rosiglitazone, plasma FFAs, insulin, and glucose concentrations and homeostasis model assessment of insulin resistance did not change. Plasma C-reactive protein, serum amyloid A, and matrix metalloproteinase concentrations fell significantly at wk 1 and continued to be significantly lower than the baseline levels by 25, 29, and 24%, respectively, at wk 6. Leukocyte count was significantly lower at wk 6 after rosiglitazone, whereas there was no change in the control group. Plasma adiponectin concentrations increased significantly at wk 2 and continued to increase during the treatment period with rosiglitazone. Resistin concentrations fell significantly by 10% at wk 6 only. There were no changes in any of these indices in the placebo group. Conclusions: A low dose of rosiglitazone exerts an early and potent antiinflammatory effect with an increase in adiponectin and a fall in resistin concentrations without causing any metabolic changes (fall in plasma glucose, FFAs, and insulin concentrations) over a 6-wk period. The increase in adiponectin and the decrease in resistin after rosiglitazone are thus related primarily to its antiinflammatory effects rather than its metabolic actions. These observations have implications in relation to the mode of action of this drug as an insulin-sensitizing agent and also its use as a potential antiinflammatory and antiatherogenic drug in the future.

Objective: Elevation of free fatty acids (FFAs) by the infusion of triglyceride-heparin emulsion infusion (TG-Hep) causes insulin resistance (IR). We examined the effect of insulin sensitizer (rosiglitazone) on FFA-induced IR. Design: Nine obese subjects underwent a 6-h infusion of TG-Hep before and after 6 wk of rosiglitazone (8 mg/d) treatment. Hyperinsulinemic euglycemic clamps were performed during 0–2 and 4–6 h of TG-Hep. Results: After rosiglitazone for 6 wk, fasting FFA concentration fell, but not significantly (489 ± 63 at 0 wk; 397 ± 58 μmol/liter at 6 wk; P = 0.16), whereas C-reactive protein (4.26 ± 0.95 at 0 wk; 2.03 ± 0.45 μg/ml at 6 wk) and serum amyloid A (17.36 ± 4.63 at 0 wk; 8.77 ± 1.63 μg/ml at 6 wk) decreased significantly. At 0 wk, TG-Hep infusion caused a decrease in glucose infusion rate (GIR) from 4.49 ± 0.95 mg/kg·min to 3.02 ± 0.59 mg/kg·min (P = 0.018). Rosiglitazone treatment resulted in an increase in baseline GIR to 6.29 ± 0.81 mg/kg·min (P = 0.03 vs. 0 wk), which decreased to 4.52 ± 0.53 mg/kg·min (P = 0.001) after 6 h of TG-Hep infusion. The decrease in GIR induced by TG-Hep infusion was similar before and after rosiglitazone therapy [1.47 ± 0.50 vs. 1.77 0.3 mg/kg·min (28.9 ± 6.5 vs. 26.4 ± 3.7%); P = 0.51]. The rise in FFAs and triglycerides after TG-Hep infusion was significantly lower at 6 wk (P = 0.006 for FFAs; P = 0.024 for triglycerides). Conclusions: We conclude that rosiglitazone: 1) causes a significant increase in GIR; 2) induces a decrease in inflammatory mediators, C-reactive protein, and serum amyloid A; 3) decreases the rise in FFAs and triglycerides after TG-Hep infusion; and 4) does not prevent FFA-induced IR.

The objective of the study was to determine whether plasma migration inhibitor factor (MIF) concentration and mononuclear cell (MNC) mRNA are elevated in obesity and whether treatment with metformin reduces plasma MIF concentration. Forty obese subjects [body mass index (BMI), 37.5 +/- 4.9 kg/m(2)] and 40 nonobese healthy subjects (BMI, 22.6 +/- 3.4 kg/m(2)) had their plasma MIF, glucose, insulin, free fatty acids (FFAs) and C-reactive protein (CRP) concentrations measured. Sixteen obese patients and 16 nonobese healthy subjects had RNA prepared from MNCs. Eight obese subjects with normal glucose concentration were treated with metformin 1 g (Glucophage XR; 1000 mg twice daily) twice daily for 6 wk. Eight obese subjects were used as controls. Plasma concentration of glucose, insulin, FFAs, and MIF was measured by appropriate assays. mRNA for MIF was measured by real-time PCR. Forty obese subjects had a fasting concentration of MIF of 2.8 +/- 2.0 ng/ml, whereas 40 nonobese subjects had a fasting MIF concentration of 1.2 +/- 0.6 ng/ml (P < 0.001). Plasma MIF concentrations were significantly related to BMI (r = 0.52; P < 0.001). mRNA for MIF was correlated to plasma FFAs (r = 0.40; P < 0.05) and plasma CRP (r = 0.42; P < 0.05) concentrations. Eight obese subjects had their fasting blood samples taken before and after taking a slow-release preparation of metformin at 1, 2, 4, and 6 wk. The mean plasma concentration fell from 2.3 +/- 1.4 to 1.6 +/- 1.2 ng/ml at 6 wk (P < 0.05). Obese subjects not on treatment with metformin showed no change. During the period of treatment with metformin, the body weight did not change and the plasma concentration of glucose, insulin, and FFAs did not alter. We conclude that: 1) plasma MIF concentrations and MIF mRNA expression in the MNCs are elevated in the obese, consistent with a proinflammatory state in obesity; 2) these increases in MIF are related to BMI, FFA concentrations, and CRP; 3) metformin suppresses plasma MIF concentrations in the obese, suggestive of an antiinflammatory effect of this drug; and 4) this action of metformin may contribute to a potential antiatherogenic effect, which may have implications for the reduced cardiovascular mortality observed with metformin therapy in type 2 diabetes mellitus.

The rationale for the treatment of diabetes has hitherto been directed to the correction of hyperglycemia because hyperglycemia is known to be responsible for the symptoms of polyuria and polydipsia in the short term and microangiopathic complications of diabetes in the long term. The correction of hyperglycemia leads to immediate resolution of polydipsia and polyuria and the prevention of microvascular complications in the long term (1, 2). The relationship between the decline in glycosylated hemoglobin (HbA1c) and the reduction in the rate of complications is well established, and a fall in HbA1c can reasonably predict a fall in the rate of microangiopathic complications (1, 2). In view of this close relationship between glycemia and the microangiopathic complications of diabetes, it is now accepted that any means used to decrease blood glucose concentrations will result in a reduction in microangiopathic complications. Thus, glycemic control is the cardinal measure required to prevent microangiopathic complications. Whereas microangiopathic complications lead to blindness (retinopathy) and renal failure (nephropathy) and may contribute to neuropathy, the most important complication leading to mortality in type 2 diabetes is macroangiopathy or atherosclerosis (3). Hyperglycemia may contribute to macrovascular disease, but the evidence related to its prevention by the control of hyperglycemia is limited (2, 4, 5). Whereas observational studies demonstrate a relationship between HbA1c and cardiovascular events, prospective interventional studies do not demonstrate an impressive reduction in cardiovascular events with a fall in HbA1c (2, 4, 5). In both Kumamoto (5) and UKPDS studies (2), the reduction in cardiovascular events was just short of statistical significance. Although the Kumamoto study results and correlations are based on a fall in HbA1c by more than 2%, the number of patients included was small. On the other hand, the UKPDS study was large, but the overall HbA1c fall was less than 1% (0.9%; Ref. 2). The Diabetes Control and Complications Trial, which was carried out over a period of 10 yr, achieved a consistent reduction in HbA1c of 2% and showed a decrease in cardiovascular events, but the reduction was again short of being statistically significant (1). In this case, the relative youth of the patients with type 1 diabetes may have contributed to a low overall rate of macrovascular events. It would thus appear that at best, glycemia levels do contribute to atherogenic complications of heart attack and stroke but that their contribution is small. These considerations are important because we need to develop a rational strategy for the control/prevention of macrovascular complications. Macrovascular disease (atherosclerosis) accounts for 70% of the mortality in type 2 diabetes, making heart attacks and strokes two to four times more frequent in these patients when compared with controls (6). Thus, a type 2 diabetic patient without a history of coronary heart disease (CHD) carries the same risk of having a heart attack as a nondiabetic with a previous history of a heart attack (7). It is important that several epidemiological studies have shown that fasting hyperinsulinemia predicts cardiovascular events (8). This was initially interpreted as evidence that insulin is atherogenic. However, because hyperinsulinemia is a reflection of an insulin-resistant state, it is now increasingly accepted that insulin resistance rather than hyperinsulinemia is proatherogenic. Furthermore, there are recent data that insulin has a potent antiinflammatory effect that may inhibit atherogenesis in the long term (9). This action of insulin may also explain why insulin-resistant states may be proinflammatory and proatherogenic.

We have recently demonstrated that an infusion of a low dose of insulin reduces the intranuclear NF-κB (a pro-inflammatory transcription factor) content in MNC while also reducing the p;asma concentration of NF-κB dependent pro-inflammatory cytokines and adhesion molecules. We have now tested the effect of insulin on the pro-inflammatory transcription factor, early growth response-1 (Egr-1) and plasma concentration of tissue factor (TF) and plasminogen activator inhibitor-1 (PAI-1), two major proteins whose expression is modulated by Egr-1. Insulin was infused at the rate of 2 IU/h in 5% dextrose (100 mL/h) and KCI (8 mmol/h) for 4 h in the fasting state in ten obese subjects. Blood samples were obtained at 0, 2, 4 and 6 h. MNC were isolated and their total homogenates and nuclear fractions were prepared and Egr-1 was measured by electrophoretic mobility shift assay (EMSA). Plasma TF and PAI-1 were assayed by ELISA. There was a significant fall in Egr-1 at 2 (66 ± 14% of basal level) and 4 h (47± 17% of the basal level; P

To elucidate whether troglitazone exerts an antiinflammatory effect in humans, in vivo, we investigated the suppression of nuclear factor kappaB (NFkappaB) in mononuclear cells (MNC) by this drug. We measured intranuclear NFkappaB, total cellular NFkappaB, inhibitor kappaB (IkappaB)alpha, reactive oxygen species (ROS) generation, and p47(phox) subunit (a key component protein of nicotinamide adenine dinucleotide phosphate oxidase) in MNC. Plasma tumor necrosis factor (TNF)-alpha, soluble intercellular adhesion molecule-1 (sICAM-1), monocyte chemoattractant protein-1 (MCP-1), plasminogen activator inhibitor type 1 (PAI-1), C-reactive protein (CRP), and interleukin (IL)-10 (antiinflammatory cytokine) concentrations were also measured as mediators of inflammatory activity that are regulated by the proinflammatory transcription factor NFkappaB. Seven nondiabetic obese patients were given 400 mg troglitazone daily for 4 weeks. Blood samples were collected before and at weekly intervals thereafter. MNC were separated; and the levels of intranuclear NFkappaB, total cellular NFkappaB, IkappaBalpha, and p47 (phox) subunit and ROS generation were determined. Plasma was used to measure insulin glucose, TNFalpha, sICAM, MCP-1, PAI-1, CRP, and IL-10. Plasma insulin concentrations fell significantly at week 1, from 31.2 +/- 29.1 to 14.2 +/- 11.4 mU/L (P0.01) and remained low throughout 4 weeks. Plasma glucose concentrations did not alter significantly. There was a fall in intranuclear NFkappaB, total cellular NFkappaB, and p47 (phox) subunit, with an increase in cellular IkappaBalpha at week 2, which persisted until week 4. There was a parallel fall in ROS generation by MNC at week 1; this progressed and persisted until week 4 (P0.001). Plasma TNF-alpha, sICAM-1, MCP-1, and PAI-1 concentrations fell significantly at week 4. Plasma IL-10 concentration increased significantly, whereas plasma CRP concentrations decreased. We conclude that troglitazone has an antiinflammatory action that may contribute to its putative antiatherosclerotic effects.

We have recently demonstrated that hydrocortisone and other glucocorticoids inhibit reactive oxygen species (ROS) generation by mononuclear (MNC) and polymorphonuclear leucocytes (PMNL). Since NF-kappaB/IkappaB system regulates the transcription of proinflammatory genes, including those responsible for ROS generation, we tested the hypothesis that hydrocortisone may stimulate IkappaB production thus inhibiting NF-kappaB translocation from the cytosol into the nucleus in MNC, in vivo. One hundred milligram of hydrocortisone was injected intravenously into 4 normal subjects. Blood samples were obtained prior to the injection and at 1, 2, 4, 8 and 24 hr after the injection. Nuclear extracts and total cell lysates were prepared from MNC by standard techniques. IkappaB levels in MNC homogenates increased at 1 hr, peaked at 2-4 hr, started to decrease at 8 hr, and returned to baseline levels at 24 hr. NF-kappaB in MNC nuclear extracts decreased at 1 hr, reached a nadir at 4 hr, gradually increased at 8 hr and returned back to baseline levels at 24 hr. The total protein content of NF-kappaB subunit (P65) in MNC lysates also showed a decrease following hydrocortisone injection. This decrease was observed at 2 hr, reached a nadir at 4 hr, and returned to baseline levels at 24 hr. ROS generation inhibition paralleled NF-kappaB levels in the nucleus. It was inhibited at 1 hr, reached a nadir at 2-4 hr, started to increase at 8 hr, and returned to basal levels at 24 hr. Our data demonstrate that hydrocortisone induces IkappaB and suppresses NF-kappaB expression in MNC in parallel. IkappaB further reduces the translocation of NF-kappaB into the nucleus thus preventing the expression of proinflammatory genes.

In view of the recent demonstration that obesity in animals and humans is associated with an increase in tumor necrosis factor-α (TNFα) expression, that this expression falls with weight loss, and that TNFα may specifically inhibit insulin action, the possibility that TNFα may be a mediator of insulin resistance has been raised. We have undertaken this study to investigate whether serum TNFα concentrations are elevated in obese subjects, whether they fall after weight loss, and whether this fall parallels the fall in insulin release after glucose challenge. Obese patients (age range: 25–54, weight mean ± sd: 96.4 ± 13.8 kg, body mass index: 35.7 ± 5.6 kg/m2) were started on a diet program. The mean weight fell to 84.5 ± 11.3 (P < 0.0001) and body mass index to 31.3 ± 4.9 (P < 0.0001). Plasma TNFα concentrations were markedly elevated in the obese (3.45 ± 0.16 pg/mL), when compared with controls (0.72 ± 0.28 pg/mL), and fell significantly (2.63 ± 1.40 pg/mL) after weight loss (P < 0.02). The magnitude of insulin release after glucose (75 g) challenge (area under the curve) also fell significantly (P < 0.01) after weight loss. The magnitude of weight loss and fall in TNFα were related to basal body weight (r = 0.57, P < 0.001) and basal TNFα (r = 0.55, P < 0.001) concentrations, respectively, but not to each other or to the glucose-induced insulin release (area under the curve). We conclude that obesity is associated with increased plasma TNFα concentrations, which fall with weight loss. Because circulating TNFα may mediate insulin resistance in the obese, a fall in TNFα concentrations may contribute to the restoration of insulin resistance after weight loss, Thus, TNFα may be an important circulating cytokine, which may provide a potentially reversible mechanism for mediating insulin resistance.