Since 1980 we have performed the identical Greenville gastric bypass (GGB) procedure on 479 morbidly obese patients with an acceptable morbidity and a mortality rate of 1.2%. The weight loss in the series was well maintained over the follow-up period of 10 y. The GGB can control non-insulin-dependent diabetes mellitus (NIDDM) in most patients. The group of 479 patients included 101 (21%) with NIDDM and another 62 (13%) who were glucose impaired. Of these 163 individuals, 141 reverted to normal and only 22 (5%) remained with inadequate control of their carbohydrate metabolism. Those patients who were older or whose diabetes was of longer duration were less likely to revert to normal values. The gastric bypass operation is an effective approach for the treatment of morbid obesity. Along with its control of weight, the operation also controls the hyperglycemia, hyperinsulinemia, and insulin resistance of the majority of patients with either glucose impairment or frank NIDDM.

We have previously demonstrated that chronic exposure of 3T3-L1 adipocytes to tumour necrosis factor-alpha (TNF) resulted in a marked decrease (approximately 90%) in cellular GLUT4 (insulin-responsive glucose transporter) mRNA content as a result of a decreased transcription rate of the GLUT4 gene (approximately 75%) and a reduced half-life of its mRNA (9 to 4.5 h). Investigation of the signalling mechanism responsible for this regulation demonstrated that in the 3T3-L1 adipocytes, sphingomyelin levels decreased to 50% of control levels within 40 min of exposure to TNF, consistent with activation of a sphingomyelinase. In the same manner as with TNF, treatment of the adipocytes with 1-3 microM C6-ceramide, a membrane-permeable analogue of ceramide, decreased GLUT4 mRNA content by approximately 60%. Subsequent investigations revealed that transcription of the GLUT4 gene was reduced by approximately 65% in response to C6-ceramide, demonstrating that the decrease in mRNA content is mediated by a reduction in the transcription of the genc. No effect on GLUT4 mRNA stability was observed after exposure of the adipocytes to C6-ceramide. These observations are interesting in light of our previous data demonstrating that TNF affects both GLUT4 transcription and mRNA stability in the 3T3-L1 adipocytes. In conclusion, the effect of ceramide on GLUT4 gene expression is at the level of transcription, suggesting that another pathway controls mRNA stability. These data establish that ceramide-initiated signal transduction pathways exist within the adipocyte, and provide a potential mechanism for control of GLUT4 gene expression.

No abstract

To determine the cellular basis for insulin resistance observed in patients with uremia, we investigated insulin action in vivo and in vitro using skeletal muscle obtained from patients with chronic renal failure. Uremic subjects had significantly reduced rates of insulin-stimulated glucose disposal, as determined by a 3-h intravenous glucose tolerance test and using the hyperinsulinemic euglycemic clamp technique. Hepatic glucose production was similar before (control, 76.2 +/- 6.3 vs. uremic, 74.2 +/- 6.9 mg.kg-1.min-1) and during insulin infusion at 40 mU.m-2.min-1 (control, -60.9 +/- 6.6 vs. uremic, -53.9 +/- 6.3 mg.kg-1.min-1). In incubated human skeletal muscle fiber strips, basal 2-deoxy-D-glucose transport was unchanged in uremic subjects compared with controls. However, the increase in insulin-stimulated glucose transport was significantly reduced by 50% in muscles from uremic patients (P = 0.012). In partially purified insulin receptors prepared from skeletal muscle, 125I-labeled insulin binding, beta-subunit receptor autophosphorylation, and tyrosine kinase activity were all unchanged in uremic subjects. The abundance of insulin-sensitive (muscle/fat, GLUT-4) glucose transporter protein measured by Western blot using Mab 1F8 or polyclonal antisera was similar in muscles of control and uremic patients. These findings suggest that the insulin resistance observed in skeletal muscle of uremic patients cannot be attributed to defects in insulin receptor function or depletion of the GLUT-4 glucose transporter protein. An alternative step in insulin-dependent activation of the glucose transport process may be involved.

We have previously described the ability of arachidonic acid (AA) to regulate GLUT4 gene expression (Tebbey, P. W., McGowan, K. M., Stephens, J. M., Buttke, T. M., and Pekala, P. H. (1994) J. Biol. Chem. 269, 639 -644). Chronic exposure (48 h) of fully differentiated 3T3-L1 cells to AA resulted in an ϳ90% suppression of GLUT4 mRNA accumulation. This decrease was demonstrated to be due to a 50% decrease in GLUT4 gene transcription as well as a destabilization of the GLUT4 message (t1 ⁄2 decreased from 8.0 to 4.6 h). In the current study we have identified, at least in part, the mechanism by which AA exerts its effects on GLUT4 expression. Compatible with a cyclooxygenase mediated event, the AA-induced suppression of GLUT4 mRNA was abolished by pretreating the cells with the inhibitor, indomethacin. Consistent with this observation, exposure of the cells to 10 M PGE 2 mimicked the effect of AA, in contrast to products of the lipoxygenase pathway which were unable to suppress GLUT4 mRNA content. Quantification of the conversion of AA to PGE 2 demonstrated a 50-fold increase in PGE 2 released into the media within 7 h of AA addition. Cyclic AMP levels were also increased 50-fold with AA treatment consistent with PGE 2 activation of adenylate cyclase. Various long chain fatty acids, including the nonmetabolizable analog of AA, eicosatetraenoic acid (ETYA), also decreased GLUT4 mRNA levels. The effect of ETYA, a potent inhibitor of both lipo-and cyclooxygenases and a potent activator of peroxisome proliferator activated receptors (PPARs), suggested the presence of a second pathway where nonmetabolized fatty acid functioned to suppress GLUT4 mRNA levels. Further support for a PPAR-mediated mechanism was obtained by exposure of the cells to the classic PPAR activator, clofibrate, which resulted in a ϳ75% decrease in GLUT4 mRNA content. Nuclear extracts prepared from the adipocytes contained a protein complex that bound to the PPAR responsive element (PPRE) found in the promoter of the fatty acyl-CoA oxidase gene. When the adipocytes were treated with either AA or ETYA, binding to the PPRE was disrupted, consistent with an ability of these fatty acids to control gene expression by altering the occupation of a PPRE. However, a perfect PPRE has yet to be identified in the GLUT4 promoter, but this does not rule the possibility of a PPAR playing an indirect role in the AA-induced GLUT4 mRNA suppression.