Short- and long-term effects of hyperlipidemia with elevated FFA on insulin secretion were investigated. Male Sprague-Dawley rats were fed ad libitum and additionally infused with Intralipid 10%, 1.0 ml/h. After 3 h of Intralipid the response to 27 mM glucose in isolated perfused pancreas was enhanced by 86%, P less than 0.02. After 6 h of Intralipid enhancement had subsided. After 48 h of Intralipid glucose-induced insulin release was inhibited by 49%, from 1950 +/- 177 microU/min after saline to 1003 +/- 232 microU/min after Intralipid, P less than 0.02. Inhibition was glucose-selective since responses to other secretagogues (1 mM 3-isobutyl-1 methylxanthine, 10 mM octanoate, or 5 mM alpha-ketoisocaproic acid) were unaffected as were pancreatic contents of insulin (2284 +/- 111 mU/pancreas after saline, 2566 +/- 131 mU/pancreas after Intralipid). In isolated islets from 48 h lipid infused rats production of [14-C]CO2 from D[U-14-C]glucose was decreased (P less than 0.02) in parallel with the insulin response to 27 mM glucose. Glucose-induced secretion was partially normalized by in vitro exposure to a carnitine palmitoyl-transferase I inhibitor (Etomoxir). Effects of a 48 h lipid infusion were also tested during hyperglycemia. Rats were infused with glucose, and hyperglycemia was enhanced by dexamethasone (25 micrograms/24 h). Hyperglycemia depressed glucose-induced secretion from perfused pancreas from 2072 +/- 22 microU/min after saline + dexamethasone to 1185 +/- 155 microU/min after glucose + dexamethasone, P less than 0.01). Intralipid, added to the latter protocol, further inhibited glucose-induced secretion to 437 +/- 87 microU/min, P less than 0.005. Hyperlipidemia is concluded to be associated with short term stimulation but long term inhibition of glucose-induced insulin secretion. Evidence indicates that inhibition depends on fatty acid oxidation, is coupled to decreased glucose oxidation and operates both during normo- and hyperglycemia.

Amyloid fibril formation is associated with protein misfolding disorders, including neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's diseases. Familial amyloid polyneuropathy (FAP) is a hereditary disease caused by a point mutation of the human plasma protein, transthyretin (TTR), which binds and transports thyroxine (T(4)). TTR variants contribute to the pathogenesis of amyloidosis by forming amyloid fibrils in the extracellular environment. A recent report showed that epigallocatechin 3-gallate (EGCG), the major polyphenol component of green tea, binds to TTR and suppresses TTR amyloid fibril formation. However, structural analysis of EGCG binding to TTR has not yet been conducted. Here we first investigated the crystal structure of the EGCG-V30M TTR complex and found novel binding sites distinct from the thyroxine binding site, suggesting that EGCG has a mode of action different from those of previous chemical compounds that were shown to bind and stabilize the TTR tetramer structure. Furthermore, EGCG induced the oligomerization and monomer suppression in the cellular system of clinically reported TTR variants. Taken together, these findings suggest the possibility that EGCG may be a candidate compound for FAP therapy.

Nascent secretory proteins are extensively scrutinized at the endoplasmic reticulum (ER). Various signatures of client proteins, including exposure of hydrophobic patches or unpaired sulfhydryls, are coordinately utilized to reduce nonnative proteins in the ER. We report here the cryptic N-glycosylation site as a recognition signal for unfolding of a natively nonglycosylated protein, transthyretin (TTR), involved in familial amyloidosis. Folding and ER-associated degradation (ERAD) perturbation analyses revealed that prolonged TTR unfolding induces externalization of cryptic N-glycosylation site and triggers STT3B-dependent posttranslational N-glycosylation. Inhibition of posttranslational N-glycosylation increases detergent-insoluble TTR aggregates and decreases cell proliferation of mutant TTR-expressing cells. Moreover, this modification provides an alternative pathway for degradation, which is EDEM3-mediated N-glycan-dependent ERAD, distinct from the major pathway of Herp-mediated N-glycan-independent ERAD. Hence we postulate that STT3B-dependent posttranslational N-glycosylation is part of a triage-salvage system recognizing cryptic N-glycosylation sites of secretory proteins to preserve protein homeostasis.

No abstract

The effects of a thiazolidinedione antidiabetic agent (CS-045) on diabetic metabolic abnormalities were studied in a double-blind clinical trial. Fourteen patients with Type 2 diabetes were selected according to study criteria. Eight were treated with oral CS-045 at 400 mg daily, and six were given placebo. A multi-step, hyperinsulinaemic, euglycaemic clamp study, with simultaneous plasma free fatty acid study, and glucagon tolerance test were performed before and after administration of drug. Following 3 months of treatment with CS-045, there were significant decreases in the mean levels of fasting plasma glucose (from 9.18 +/- 0.95 to 7.78 +/- 0.44 mmol l-1), postprandial plasma glucose (from 11.8 +/- 1.23 to 10.36 +/- 1.06 mmol l-1), and haemoglobin A1c (from 9.3 +/- 0.4 to 6.8 +/- 0.4%). Insulin sensitivity also improved (1st step: from 3.12 +/- 0.33 to 4.70 +/- 0.47 mg kg-1 min-1 (p < 0.01); 2nd step: from 5.61 +/- 0.63 to 7.54 +/- 0.58 mg kg-1 min-1 (p < 0.01); 3rd step: from 9.21 +/- 0.67 to 11.10 +/- 0.87 mg kg-1 min-1). The fasting free fatty acid level decreased significantly from 0.28 +/- 0.04 to 0.22 +/- 0.02 g l-1. The residual free fatty acid level (%) under insulin infusion clamp conditions decreased significantly from 63.7 +/- 9.7 to 45.0 +/- 9.2%. CS-045 treatment was associated with decrease in total cholesterol, total triglycerides, and increase in HDL cholesterol. Basal C-peptide immunoreactivity level decreased, but there was no change in the peak C-peptide immunoreactivity value.(ABSTRACT TRUNCATED AT 250 WORDS)

Nondiabetic rats were infused with glucose for 48 h to maintain moderate or marked hyperglycemia (mean blood glucose 13.2 +/- 0.7 or 22.8 +/- 0.3 mM, respectively). The two levels of hyperglycemia increased plasma insulin levels severalfold but decreased the insulin response to 27 mM glucose by 19 and 95%, respectively, versus saline infusion. Diazoxide (5 mg.kg-1.h-1), when continuously infused during the hyperglycemia protocols, completely inhibited the glucose-induced rise in plasma insulin levels. Diazoxide transformed beta-cell insensitivity to stimulation: glucose-induced insulin release was thus increased 318% after moderate hyperglycemia and 707% after marked hyperglycemia. These stimulatory effects of diazoxide were reversed by exogenous insulin infusion (8 or 2 U/24 h) in a dose-dependent manner. It is concluded that excessive beta-cell stimulation rather than glucotoxicity underlies hyperglycemia-induced beta-cell insensitivity. Effects of hyperinsulinemia can form part of the mechanisms whereby excessive stimulation affects beta-cell secretion.

No abstract

Insulin therapy-naive HCPs found FlexPen easier to handle and preferable to use compared to a conventional syringe and vial. Both insulin therapy-experienced and -naive HCPs were able to deliver insulin significantly more accurately with the FlexPen than with a syringe and vial (P < 0.001).