Dose-response effect of elevated plasma free fatty acid on insulin signaling.

The dose-response relationship between elevated plasma free fatty acid (FFA) levels and impaired insulin-mediated glucose disposal and insulin signaling was examined in 21 lean, healthy, normal glucose-tolerant subjects. Following a 4-h saline or Liposyn infusion at 30 (n = 9), 60 (n = 6), and 90 (n = 6) ml/h, subjects received a 2-h euglycemic insulin (40 mU . m(-2) . min(-1)) clamp. Basal plasma FFA concentration ( approximately 440 micromol/l) was increased to 695, 1,251, and 1,688 micromol/l after 4 h of Liposyn infusion and resulted in a dose-dependent reduction in insulin-stimulated glucose disposal (R(d)) by 22, 30, and 34%, respectively (all P < 0.05 vs. saline control). At the lowest lipid infusion rate (30 ml/h), insulin receptor and insulin receptor substrate (IRS)-1 tyrosine phosphorylation, phosphatidylinositol (PI) 3-kinase activity associated with IRS-1, and Akt serine phosphorylation were all significantly impaired (P < 0.05-0.01). The highest lipid infusion rate (90 ml/h) caused a further significant reduction in all insulin signaling events compared with the low-dose lipid infusion (P < 0.05-0.01) whereas the 60-ml/h lipid infusion caused an intermediate reduction in insulin signaling. However, about two-thirds of the maximal inhibition of insulin-stimulated glucose disposal already occurred at the rather modest increase in plasma FFA induced by the low-dose (30-ml/h) lipid infusion. Insulin-stimulated glucose disposal was inversely correlated with both the plasma FFA concentration after 4 h of lipid infusion (r = -0.50, P = 0.001) and the plasma FFA level during the last 30 min of the insulin clamp (r = -0.54, P < 0.001). PI 3-kinase activity associated with IRS-1 correlated with insulin-stimulated glucose disposal (r = 0.45, P < 0.01) and inversely with both the plasma FFA concentration after 4 h of lipid infusion (r = -0.39, P = 0.01) and during the last 30 min of the insulin clamp (r = -0.43, P < 0.01). In summary, in skeletal muscle of lean, healthy subjects, a progressive increase in plasma FFA causes a dose-dependent inhibition of insulin-stimulated glucose disposal and insulin signaling. The inhibitory effect of plasma FFA was already significant following a rather modest increase in plasma FFA and develops at concentrations that are well within the physiological range (i.e., at plasma FFA levels observed in obesity and type 2 diabetes).

Parathyroid carcinoma: a 22-year experience.

PURPOSE: Because parathyroid carcinoma is rare, clear consensus is not available regarding the optimal management of patients with this condition. Treatment strategies generally derive from clinical and anecdotal experiences. We report our experience with this entity. METHODS: We included all patients with parathyroid carcinoma seen at The University of Texas M. D. Anderson Cancer Center since January 1, 1980. The medical records and pathology specimens were reviewed and verified in all cases. RESULTS: Since 1980, 27 patients (16 men and 11 women) registered at M. D. Anderson Cancer Center with parathyroid carcinoma and a minimum follow-up of 2 years. The age at initial diagnosis (mean +/- SD) was 46.7 +/- 15.3 years. All patients were seen with hypercalcemia (mean calcium, 13.4 +/- 1.5 mg/dL). Eighteen patients had locally invasive disease, eight had localized disease, and one had distant metastasis. Parathyroid cancer was treated with complete surgical excision with curative intent in 18 patients. In the other nine patients, who had clinical and/or radiographic evidence of soft tissue extension, the tumor was treated by comprehensive "en bloc" soft tissue resection. Of six patients who received adjuvant radiotherapy after initial surgery, only one had a local relapse. In contrast, of 20 patients who did not receive adjuvant radiotherapy, 10 had a local relapse, excluding the one patient who had distant metastases. The 5-year survival was 85%, and the 10-year survival was 77%. Five patients died of parathyroid carcinoma; all deaths were hypercalcemia related. CONCLUSIONS: Parathyroid carcinoma can be an indolent disease with morbidity and mortality related to hypercalcemia. Adjuvant radiotherapy may improve local control and limit the occurrence of local relapse. A comprehensive multidisciplinary approach with surgery, radiation therapy, and medical treatment for hypercalcemia is needed to optimize patient outcome.