Novel glimepiride derivatives with potential as double-edged swords against type II diabetes

Transfer of Proteins from Cultured Human Adipose to Blood Cells and Induction of Anabolic Phenotype Are Controlled by Serum, Insulin and Sulfonylurea Drugs

Glycosylphosphatidylinositol-anchored proteins (GPI-APs) are anchored at the outer leaflet of eukaryotic plasma membranes (PMs) only by carboxy-terminal covalently coupled GPI. GPI-APs are known to be released from the surface of donor cells in response to insulin and antidiabetic sulfonylureas (SUs) by lipolytic cleavage of the GPI or upon metabolic derangement as full-length GPI-APs with the complete GPI attached. Full-length GPI-APs become removed from extracellular compartments by binding to serum proteins, such as GPI-specific phospholipase D (GPLD1), or insertion into the PMs of acceptor cells. Here, the interplay between the lipolytic release and intercellular transfer of GPI-APs and its potential functional impact was studied using transwell co-culture with human adipocytes as insulin-/SU-responsive donor cells and GPI-deficient erythroleukemia as acceptor cells (ELCs). Measurement of the transfer as the expression of full-length GPI-APs at the ELC PMs by their microfluidic chip-based sensing with GPI-binding α-toxin and GPI-APs antibodies and of the ELC anabolic state as glycogen synthesis upon incubation with insulin, SUs and serum yielded the following results: (i) Loss of GPI-APs from the PM upon termination of their transfer and decline of glycogen synthesis in ELCs, as well as prolongation of the PM expression of transferred GPI-APs upon inhibition of their endocytosis and upregulated glycogen synthesis follow similar time courses. (ii) Insulin and SUs inhibit both GPI-AP transfer and glycogen synthesis upregulation in a concentration-dependent fashion, with the efficacies of the SUs increasing with their blood glucose-lowering activity. (iii) Serum from rats eliminates insulin- and SU-inhibition of both GPI-APs' transfer and glycogen synthesis in a volume-dependent fashion, with the potency increasing with their metabolic derangement. (iv) In rat serum, full-length GPI-APs bind to proteins, among them (inhibited) GPLD1, with the efficacy increasing with the metabolic derangement. (v) GPI-APs are displaced from serum proteins by synthetic phosphoinositolglycans and then transferred to ELCs with accompanying stimulation of glycogen synthesis, each with efficacies increasing with their structural similarity to the GPI glycan core. Thus, both insulin and SUs either block or foster transfer when serum proteins are depleted of or loaded with full-length GPI-APs, respectively, i.e., in the normal or metabolically deranged state. The transfer of the anabolic state from somatic to blood cells over long distance and its "indirect" complex control by insulin, SUs and serum proteins support the (patho)physiological relevance of the intercellular transfer of GPI-APs.

Glycosylphosphatidylinositol-anchored proteins coordinate lipolysis inhibition between large and small adipocytes

In response to palmitate, the antidiabetic sulfonylurea drug glimepiride, phosphoinositoglycans, or H(2)O(2), the release of the glycosylphosphatidylinositol-anchored and cyclic adenosine monophosphate-degrading phosphodiesterase Gce1 from adipocytes into small vesicles (adiposomes) and its translocation from adiposomes to cytoplasmic lipid droplets (LD) of adipocytes have been reported. Here the role of Gce1-harboring adiposomes in coordinating lipolysis between differently sized adipocytes was studied. Separate or mixed populations of isolated epididymal rat adipocytes of small and large size and native adipose tissue pieces from young and old rats were incubated with exogenous adiposomes or depleted of endogenous adiposomes and then analyzed for translocation of Gce1 and lipolysis in response to above antilipolytic stimuli. Large compared with small adipocytes are more efficient in releasing Gce1 into adiposomes but less efficient in translocating Gce1 from adiposomes to LDs. Maximal lipolysis inhibition by above antilipolytic stimuli, but not by insulin, was observed with mixed populations of small and large adipocytes (1:1 to 1:2) rather than with separate populations. In mixed adipocyte populations and adipose tissue pieces from young, but not old, rats, lipolysis inhibition by above antilipolytic stimuli, but not by insulin, was dependent on the function of Gce1-harboring adiposomes. Inhibition of lipolysis in rat adipose tissue in response to palmitate, glimepiride, and H(2)O(2) is coordinated via the release of adiposome-associated and glycosylphosphatidylinositol-anchored Gce1 from large "donor" adipocytes and their subsequent translocation to the LDs of small "acceptor" adipocytes. This transfer of antilipolytic information may be of pathophysiologic relevance.