Sulfonylureas exert antidiabetic action on adipocytes by inhibition of PPARγ serine 273 phosphorylation.

OBJECTIVE: Sulfonylureas (SUs) are still among the mostly prescribed antidiabetic drugs with an established mode of action: release of insulin from pancreatic ß-cells. In addition, effects of SUs on adipocytes by activation of the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) have been described, which might explain their insulin-sensitizing potential observed in patients. However, there is a discrepancy between the impact of SUs on antidiabetic action and their rather moderate in vitro effect on PPARγ transcriptional activity. Recent studies have shown that some PPARγ ligands can improve insulin sensitivity by blocking PPARγ Ser-273 phosphorylation without having full agonist activity. It is unknown if SUs elicit their antidiabetic effects on adipocytes by inhibition of PPARγ phosphorylation. Here, we investigated if binding of SUs to PPARγ can interfere with PPARγ Ser-273 phosphorylation and determined their antidiabetic actions in vitro in primary human white adipocytes and in vivo in high-fat diet (HFD) obese mice. METHODS: Primary human white preadipocytes were differentiated in the presence of glibenclamide, glimepiride and PPARγ ligands rosiglitazone and SR1664 to compare PPARγ Ser-273 phosphorylation, glucose uptake and adipokine expression. Transcriptional activity at PPARγ was determined by luciferase assays, quantification of PPARγ Ser-273 phosphorylation was determined by Western blotting and CDK5 kinase assays. In silico modelling was performed to gain insight into the binding characteristics of SUs to PPARγ. HFD mice were administered SUs and rosiglitazone for 6 days. PPARγ Ser-273 phosphorylation in white adipose tissue (WAT), body composition, glucose tolerance, adipocyte morphology and expression levels of genes involved in PPARγ activity in WAT and brown adipose tissue (BAT) were evaluated. RESULTS: SUs inhibit phosphorylation of PPARγ at Ser-273 in primary human white adipocytes and exhibit a positive antidiabetic expression profile, which is characterized by up regulation of insulin-sensitizing and down regulation of insulin resistance-inducing adipokines. We demonstrate that SUs directly bind to PPARγ by in silico modelling and inhibit phosphorylation in kinase assays to a similar extend as rosiglitazone and SR1664. In HFD mice SUs reduce PPARγ phosphorylation in WAT and have comparable effects on gene expression to rosiglitazone. In BAT SUs increase UCP1 expression and reduce lipid droplets sizes. CONCLUSIONS: Our findings indicate that a part of SUs extra-pancreatic effects on adipocytes in vitro and in vivo is probably mediated via their interference with PPARγ phosphorylation rather than via classical agonistic activity at clinical concentrations.

Systemic therapy of Cushing's syndrome.

Cushing's disease (CD) in a stricter sense derives from pathologic adrenocorticotropic hormone (ACTH) secretion usually triggered by micro- or macroadenoma of the pituitary gland. It is, thus, a form of secondary hypercortisolism. In contrast, Cushing's syndrome (CS) describes the complexity of clinical consequences triggered by excessive cortisol blood levels over extended periods of time irrespective of their origin. CS is a rare disease according to the European orphan regulation affecting not more than 5/10,000 persons in Europe. CD most commonly affects adults aged 20-50 years with a marked female preponderance (1:5 ratio of male vs. female). Patient presentation and clinical symptoms substantially vary depending on duration and plasma levels of cortisol. In 80% of cases CS is ACTH-dependent and in 20% of cases it is ACTH-independent, respectively. Endogenous CS usually is a result of a pituitary tumor. Clinical manifestation of CS, apart from corticotropin-releasing hormone (CRH-), ACTH-, and cortisol-producing (malign and benign) tumors may also be by exogenous glucocorticoid intake. Diagnosis of hypercortisolism (irrespective of its origin) comprises the following: Complete blood count including serum electrolytes, blood sugar etc., urinary free cortisol (UFC) from 24 h-urine sampling and circadian profile of plasma cortisol, plasma ACTH, dehydroepiandrosterone, testosterone itself, and urine steroid profile, Low-Dose-Dexamethasone-Test, High-Dose-Dexamethasone-Test, after endocrine diagnostic tests: magnetic resonance imaging (MRI), ultra-sound, computer tomography (CT) and other localization diagnostics. First-line therapy is trans-sphenoidal surgery (TSS) of the pituitary adenoma (in case of ACTH-producing tumors). In patients not amenable for surgery radiotherapy remains an option. Pharmacological therapy applies when these two options are not amenable or refused. In cases when pharmacological therapy becomes necessary, Pasireotide should be used in first-line in CD. CS patients are at an overall 4-fold higher mortality rate than age- and gender-matched subjects in the general population. The following article describes the most prominent substances used for clinical management of CS and gives a systematic overview of safety profiles, pharmacokinetic (PK)-parameters, and regulatory framework.