DPP-4 inhibitors in diabetic complications: role of DPP-4 beyond glucose control

Dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) are an emerging class of antidiabetic drugs that constitutes approximately fifty percent of the market share of the oral hypoglycemic drugs. Its mechanism of action for lowering blood glucose is essentially via inhibition of the rapid degradation of incretin hormones, such as glucagon-like peptide (GLP)-1 and gastric inhibitory polypeptide (GIP), thus the plasma concentration of GLP-1 increases, which promotes insulin secretion from the pancreatic β cells and suppresses glucagon secretion from the α cells. In addition to the direct actions on the pancreas, GLP-1 exhibits diverse actions on different tissues through its action on GLP-1 receptor, which is expressed ubiquitously. Moreover, DPP-4 has multiple substrates besides GLP-1 and GIP, including cytokines, chemokines, neuropeptides, and growth factors, which are involved in many pathophysiological conditions. Recently, it was suggested that DPP-4 is a new adipokine secreted from the adipose tissue, which plays an important role in the regulation of the endocrine function in obesity-associated type 2 diabetes. Consequently, DPP-4 inhibitors have been reported to exhibit cytoprotective functions against various diabetic complications affecting the liver, heart, kidneys, retina, and neurons. This review outlines the current understanding of the effect of DPP-4 inhibitors on the complications associated with type 2 diabetes, such as liver steatosis and inflammation, dysfunction of the adipose tissue and pancreas, cardiovascular diseases, nephropathy, and neuropathy in preclinical and clinical studies.

DPP4 in Diabetes

Dipeptidyl-peptidase 4 (DPP4) is a glycoprotein of 110 kDa, which is ubiquitously expressed on the surface of a variety of cells. This exopeptidase selectively cleaves N-terminal dipeptides from a variety of substrates, including cytokines, growth factors, neuropeptides, and the incretin hormones. Expression of DPP4 is substantially dysregulated in a variety of disease states including inflammation, cancer, obesity, and diabetes. Since the incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide (GIP), are major regulators of post-prandial insulin secretion, inhibition of DPP4 by the gliptin family of drugs has gained considerable interest for the therapy of type 2 diabetic patients. In this review, we summarize the current knowledge on the DPP4–incretin axis and evaluate most recent findings on DPP4 inhibitors. Furthermore, DPP4 as a type II transmembrane protein is also known to be cleaved from the cell membrane involving different metalloproteases in a cell-type-specific manner. Circulating, soluble DPP4 has been identified as a new adipokine, which exerts both para- and endocrine effects. Recently, a novel receptor for soluble DPP4 has been identified, and data are accumulating that the adipokine-related effects of DPP4 may play an important role in the pathogenesis of cardiovascular disease. Importantly, circulating DPP4 is augmented in obese and type 2 diabetic subjects, and it may represent a molecular link between obesity and vascular dysfunction. A critical evaluation of the impact of circulating DPP4 is presented, and the potential role of DPP4 inhibition at this level is also discussed.

The ins and outs of hematopoietic stem cells: studies to improve transplantation outcomes

Deciphering the mechanisms of hematopoietic stem/progenitor cell (HSPC) mobilization and homing is important for the development of strategies to enhance the efficacy of HSPC transplantation and achieve the full potential of HSPC-based cellular therapy. Investigation of these mechanisms has revealed interdependence among the various molecules, pathways and cellular components involved, and underscored the complex nature of these two processes. This review summarizes recent progress in identifying the specific factors implicated in HSPC mobilization and homing, with emphasis on our own work. Particularly, we will discuss our studies on stromal cell-derived factor-1 and its interaction with its receptor CXCR4, proteases (matrix metalloproteinases and carboxypeptidase M), complement proteins (C1q, C3a, C5a, membrane attack complex), sphingosine-1-phosphate, and pharmacologic agents such as the histone deacetylase inhibitor valproic acid and hyaluronic acid.

Clozapine mobilizes CD34+ hematopoietic stem and progenitor cells and increases plasma concentration of interleukin 6 in patients with schizophrenia

The blood of 8 European patients with schizophrenia without manifest comorbidity was studied whether the classical atypical antipsychotic drug clozapine altered the amount of circulating CD34(+) hematopoietic cells. As assessed by flow cytometry, the number of CD34(+) cells increased by 433% (from 1.49 ± 1.07 × 10(6)/L, mean ± SD pretreatment, to a peak of 6.45 ± 3.47 × 10(6)/L) following first-time therapy with clozapine for 12 weeks. The increase of CD34(+) cell, neutrophil, and leukocyte counts was statistically significant (P = 0.012). A transversal investigation of 23 long-term patients and 58 controls showed elevated neutrophil counts in the clozapine-monotreated group, whereas CD34(+) cell numbers were unaltered. A transversal investigation of 12 clozapine-monotreated long-term patients and 10 controls revealed a 1.3-fold elevation of plasma interleukin 6 levels in patients on clozapine (P = 0.017). In conclusion, clozapine treatment results in an initial mobilization of CD34(+) stem and progenitor cells into the peripheral blood and in a slight long-term elevation of interleukin 6.