ABSTRACT
Liraglutide is a glucagon-like peptide-1 (GLP-1) analog developed for type 2 diabetes. Long-term liraglutide exposure in rodents was associated with thyroid C-cell hyperplasia and tumors. Here, we report data supporting a GLP-1 receptor-mediated mechanism for these changes in rodents. The GLP-1 receptor was localized to rodent C-cells. GLP-1 receptor agonists stimulated calcitonin release, up-regulation of calcitonin gene expression, and subsequently C-cell hyperplasia in rats and, to a lesser extent, in mice. In contrast, humans and/or cynomolgus monkeys had low GLP-1 receptor expression in thyroid C-cells, and GLP-1 receptor agonists did not activate adenylate cyclase or generate calcitonin release in primates. Moreover, 20 months of liraglutide treatment (at >60 times human exposure levels) did not lead to C-cell hyperplasia in monkeys. Mean calcitonin levels in patients exposed to liraglutide for 2 yr remained at the lower end of the normal range, and there was no difference in the proportion of patients with calcitonin levels increasing above the clinically relevant cutoff level of 20 pg/ml. Our findings delineate important species-specific differences in GLP-1 receptor expression and action in the thyroid. Nevertheless, the long-term consequences of sustained GLP-1 receptor activation in the human thyroid remain unknown and merit further investigation.
Subject(s)
Calcitonin/metabolism , Cell Proliferation/drug effects , Glucagon-Like Peptide 1/analogs & derivatives , Receptors, Glucagon/metabolism , Thyroid Gland/drug effects , Animals , Blotting, Western , Calcitonin/genetics , Cell Line , Cells, Cultured , Cyclic AMP/metabolism , Diabetes Mellitus, Type 1/genetics , Diabetes Mellitus, Type 1/metabolism , Dose-Response Relationship, Drug , Enzyme-Linked Immunosorbent Assay , Gene Expression/drug effects , Glucagon-Like Peptide 1/pharmacology , Glucagon-Like Peptide-1 Receptor , Humans , Immunohistochemistry , In Situ Hybridization , Liraglutide , Macaca fascicularis , Mice , Mice, Knockout , Obesity/genetics , Obesity/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Radioimmunoassay , Rats , Rats, Sprague-Dawley , Receptors, Glucagon/genetics , Reverse Transcriptase Polymerase Chain Reaction , Species Specificity , Thyroid Gland/cytology , Thyroid Gland/metabolismABSTRACT
A maltogenic amylase produced by a genetically engineered Bacillus subtilis was studied to evaluate its safety in the food industry. First, the safety of the component parts used in the cloning process, i.e. the host organism ( B. subtilis ), the donor organism ( Bacillus stearothermophilus ) and the construction process, were evaluated. This evaluation indicated that the final construct should be regarded as a safe source for maltogenic amylase when manufactured according to current Good Manufacturing Practices. Additional experimental safety testing was carried out to confirm this conclusion. In a 13-week oral toxicity study rats tolerated the maltogenic amylase at dietary levels of 5% without toxicologically significant adverse reaction. Lack of mutagenic potential was confirmed in bacterial mutagenic as-says with Salmonella typhimurium and in an in vivo cytogenetic study in rat bone marrow cells. In an acute inhalation study with 4 h of exposure to rats, no death occurred at the highest dose level, i.e, 1.59 mg/L. The test material was non-irritating to skin and did not product eye injury in rabbits. A skin sensitization study in guinea pigs was negative. Antibiotic activity tests indicated that the microorganism did not produce antibiotics. Results indicated that maltogenic amylase should be generally recognized as safe for use in production of maltose syrups, and confirmed the conclusion drawn from the safety evaluation of the component parts used in the cloning process.