Erika Nohara

Stage-specific effects of a thiazolidinedione on proliferation, differentiation and PPARγ mRNA expression in 3T3-L1 adipocytes

To clarify the target phase of thiazolidinediones, which are ligands for peroxisome proliferator-activated receptor (PPAR)gamma, during adipocyte differentiation, the effects of a thiazolidinedione, pioglitazone, on every stage during the course of adipocyte differentiation were investigated. Pioglitazone did not affect the cellular protein content and [3H]thymidine incorporation into preconfluent 3T3-L1 preadipocytes. Induction of differentiation of confluent 3T3-L1 preadipocytes with insulin, dexamethasone and isomethylbutylxanthine for 48 h resulted in 30% inhibition of [3H]thymidine incorporation into the cells and 354% increase in cellular protein content. Pioglitazone at 1 microM accelerated the increase in cellular protein content by 33% and the inhibition in the [3H]thymidine incorporation by 12%. Pioglitazone, when added from the start of the induction stage, dose-dependently enhanced cellular triglyceride accumulation, and both basal and insulin-stimulated glucose transporting activity producing only a slight increase in the ratio of insulin stimulation to basal glucose transporting activity. In mature adipocytes, however, pioglitazone did not enhance either of the transporting activities. PPARgamma messenger RNA (mRNA) levels estimated by a semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) increased during the course of adipocyte differentiation. Although pioglitazone dose-dependently up-regulated PPARgamma mRNA levels in postconfluent preadipocytes without induction, it down-regulated them in mature adipocytes. Thus, a PPARgamma agonist, pioglitazone, arrested the growth, and increased protein content and PPARgamma mRNA levels in postconfluent preadipocytes, followed by commitment and hypertrophy of 3T3-L1 cells without changing insulin sensitivity, whereas it failed to stimulate glucose transporting activities and down-regulated PPARgamma mRNA expression in mature adipocytes.

Variation of the Fatty Acid Binding Protein 2 Gene Is Not Associated With Obesity and Insulin Resistance in Japanese Subjects

An alanine to threonine substitution at codon 54 of the fatty acid binding protein 2 (FABP2) gene has been associated with insulin resistance in Pima Indians and with obesity in aboriginal Canadians. We investigated whether this polymorphism contributes to obesity and insulin resistance in 258 Japanese subjects. Thirty-six subjects (13.9%) were homozygous for the Thr54 allele, 106 (41.1%) were heterozygous for the Ala54/Thr54 allele, and 116 (45.0%) were homozygous for the Ala54 allele. The frequency of the Thr54 allele was 0.34 and did not differ significantly between men and women. The incidence of non-insulin-dependent diabetes mellitus (NIDDM) was not different among the three genotypes. The variation at codon 54 of the FABP2 gene was not associated with obesity, hypertension, dyslipidemia, hyperuricemia, or hyperinsulinemia. These results suggest that the polymorphism at codon 54 of the FABP2 gene is not a major contributing factor to obesity and insulin resistance in Japanese subjects.

Pioglitazone prevents mice from multiple low-dose streptozotocin-induced insulitis and diabetes.

Macrophage infiltration into pancreatic islets is thought to be an initial event inducing insulitis in the development of type 1 diabetes. Thiazolidinedione is a direct ligand for peroxisome proliferator-activated receptor-gamma, recently reported to inhibit macrophage activation, including cytokine production and type 2 nitric oxide synthase expression. We investigated the effect of pioglitazone, a thiazolidinedione compound, on the development of multiple low-dose streptozotocin (MLDS)-induced autoimmune diabetes in mice. CD-1 mice intraperitoneally injected with five daily sub-diabetogenic doses (30 or 40 mg/kg body weight) of streptozotocin developed mononuclear cell infiltration in and around islets, followed by hyperglycemia. Oral administration of pioglitazone (0.01% food admixture) from 7 days before the first streptozotocin injection prevented or delayed the development of diabetes induced by MLDS. Histologically, pioglitazone blocked the infiltration of mononuclear cells into islets in MLDS mice. Peritoneal macrophages from MLDS mice at day-7 produced significantly large amount of nitric oxide compared with those from control mice. Such activation of peritoneal macrophages was not observed in pioglitazone-treated MLDS mice. These findings suggest that pioglitazone blocks the autoimmune process in the development of MLDS diabetes, partly by inhibiting the macrophage activation.

Inhibitory effect of troglitazone on TNF-α-induced expression of monocyte chemoattractant protein-1 (MCP-1) in human endothelial cells

Insulin resistance is one of the risk factors for the progression of atherosclerosis. Recently, the new oral insulin-sensitizing drug troglitazone is thought to offer potential in the treatment of diabetes. If adopted for such use, this drug might be helpful in protecting against the development of atherosclerosis and microvascular complications via its improvement of insulin resistance. However, it has not yet been clarified whether troglitazone acts directly on the vascular cells and inhibits the progression of atherosclerosis. Meanwhile, Monocyte chemoattractant protein-1 (MCP-1) is known to play an important role in the pathogenesis of atherosclerosis by inducing monocyte migration. Therefore, we investigated the effect of troglitazone on the expression of MCP-1 in human umbilical vein endothelial cells (HUVECs). HUVECs were treated with or without troglitazone (1 or 10 microM) in the presence or absence of various concentrations of tumor necrosis factor-alpha (TNF-alpha) (5, 50 or 500 ng/ml), and then the amounts of MCP-1 secreted from the HUVECs were measured. We found that TNF-alpha increased the secretions of MCP-1 119-fold vs. control, and that troglitazone significantly inhibited this TNF-alpha-induced increase in MCP-1 secretions (19.4%). Moreover, Northern blot analysis revealed that troglitazone decreased the MCP-1 mRNA level in HUVECs. Our present studies indicated that troglitazone may prevent the progression of atherosclerosis by inhibiting MCP-1 expression in endothelial cells.

Inhibitory effect of troglitazone on tumor necrosis factor alpha—induced expression of monocyte chemoattractant protein-1 in human mesangial cells

Insulin resistance is one of the risk factors for the progression of atherosclerosis and glomerulosclerosis. Recently, the new oral insulin-sensitizing agent troglitazone has been thought to offer potential in the treatment of diabetes. If adopted for this use, it might be helpful in protecting against the development of atherosclerosis and microvascular complications via its improvement of insulin resistance. However, it has not yet been clarified whether troglitazone acts directly on the vascular cells and inhibits the progression of atherosclerosis, including glomerulosclerosis. Meanwhile, monocyte chemoattractant protein-1 (MCP-1) is known to play an important role in the pathogenesis of atherosclerosis and glomerulosclerosis through the induction of monocyte migration. Therefore, we investigated the effect of troglitazone on the expression of MCP-1 in human mesangial cells (HMCs). HMCs were treated with or without troglitazone (1 or 10 micromol/L) in the presence or absence of tumor necrosis factor alpha (TNF-alpha) at various concentrations (50 or 500 ng/mL), and then MCP-1 secretion from the HMCs was measured. We found that TNF-alpha increased the secretion of MCP-1 by 55-fold versus the control and troglitazone significantly inhibited this TNF-alpha-induced increase in MCP-1 secretion (49.3%). Moreover, Northern blot analysis showed that troglitazone decreased the MCP-1 mRNA level in HMCs. We demonstrated that alpha-tocopherol also inhibited TNF-alpha-induced MCP-1 production in HMCs, although its effects were not as strong as troglitazone. The present study indicates that troglitazone may prevent the progression of atherosclerosis by inhibiting MCP-1 expression in mesangial cells.

Extramedullary plasmacytoma in the adrenal incidentaloma

High‐resolution imaging has led to the increasingly frequent discovery of adrenal incidentalomas. Most are nonfunctioning tumours and adenomas, but it is difficult to distinguish benign from malignant tumours using only morphological and laboratory data, and the diagnosis often remains uncertain without histological examination. Here we report the case of a 52‐year‐old Japanese man who had a right adrenal incidentaloma 4 cm in diameter. The tumour was removed by laparoscopic adrenalectomy. The pathology specimen revealed the typical histology of plasmacytoma. Extramedullary plasmacytoma is a very rare type of plasma cell proliferative disorder. This is the first documented case of an extramedullary plasmacytoma in the adrenal gland.