Background DPP-4 inhibitors are increasingly used to accomplish glycemic targets in patients with Type II diabetes (T2DM). Since DPP-4 is expressed in inflammatory cells, we hypothesized that its inhibition will exert favorable effects in atherosclerosis. Methods and Results Male LDLR-/- mice (6 weeks) were fed with a high fat diet (HFD) or normal chow diet (NCD) for 4 weeks and then randomized to vehicle or Alogliptin, a high affinity DPP-4 inhibitor (40 mg/kg/day) for 12 weeks. Metabolic parameters, blood pressure, vascular function, atherosclerosis burden and indices of inflammation were obtained in target tissues including the vasculature, adipose and bone marrow with assessment of global and cell specific inflammatory pathways. In-vitro and in-vivo assays of DPP-4 inhibition (DPP-4i) on monocyte activation/migration were conducted in both human and murine cells and in a short-term ApoE-/- mouse model. DPP-4i improved markers of insulin resistance and reduced blood pressure. DPP-4i reduced visceral adipose tissue macrophage content (ATMs; CD11b+, CD11c+, Ly6Chi) concomitant with up-regulation of CD163. DPP-4 was highly expressed inbone-marrow derived CD11b+ cells with DPP-4i down-regulating pro-inflammatory genes in these cells. DPP-4i decreased aortic plaque with a striking reduction in plaque macrophages. DPP-4i prevented monocyte migration and actin polymerization in in-vitro assays via Rac dependent mechanisms and prevented in-vivo migration of labeled monocytes to the aorta in response to exogenous TNFα and DPP-4. Conclusion DPP-4i exerts anti-atherosclerotic effects and reduces inflammation via inhibition of monocyte activation/chemotaxis. These findings have important implications for the use of this class of drugs in atherosclerosis.

Rationale Chronic exposure to ambient air-borne particulate matter <2.5 µm (PM2.5) increases cardiovascular risk. The mechanisms by which inhaled ambient particles are sensed and how these effects are systemically transduced remain elusive. Objective To investigate the molecular mechanisms by which PM2.5 mediates inflammatory responses in a mouse model of chronic exposure. Methods and Results Here we show that chronic exposure to ambient PM2.5 promotes Ly6Chigh inflammatory monocyte egress from bone-marrow and mediates their entry into tissue niches where they generate reactive oxygen species via NADPH oxidase. Toll-like receptor-4 (TLR4) and Nox2 (gp91phox) deficiency prevented monocyte NADPH oxidase activation in response to PM2.5 and was associated with restoration of systemic vascular dysfunction. TLR4 activation appeared to be a prerequisite for NAPDH oxidase activation as evidenced by reduced p47phox phosphorylation in TLR4 deficient animals. PM2.5 exposure markedly increased oxidized phospholipid derivatives of 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine (oxPAPC) in bronchioalveolar lavage fluid. Correspondingly, exposure of bone-marrow derived macrophages to oxPAPC but not PAPC recapitulated effects of chronic PM2.5 exposure while TLR4 deficiency attenuated this response. Conclusions Taken together, our findings suggest that PM2.5 triggers an increase in oxidized phospholipids in lungs that then mediates a systemic cellular inflammatory response through TLR4/NADPH oxidase dependent mechanisms.

Vitamin A metabolite retinoic acid (RA) regulates life-sustaining differentiation processes and metabolic homeostasis. The aldehyde dehydrogenase-1 (Aldh1) family of enzymes (Aldh1a1, a2, and a3) catalyzes RA production from retinaldehyde and thereby controls concentrations of this transcriptionally active metabolite. The hierarchy of Aldh1 functions in adipose tissue has not been elucidated. We hypothesized that Aldh1 enzymes produce endogenous RA and regulate adipogenesis and fat formation in a fat depot-specific manner. We demonstrate that adipogenesis in vitro is accompanied by RA production generated primarily by Aldh1a1. In Aldh1a1-deficient adipocytes, adipogenesis is impaired compared with wild-type adipocytes due to markedly reduced expression of PPARγ regulated through zinc-finger protein 423 (ZFP423)-dependent mechanisms. These effects were recovered to some extent either by RA stimulation or overexpression of any of the Aldh1 enzymes in Aldh1a1(-/-) cells arguing that Aldh1a1 plays a dominant role in autocrine RA production. In vivo studies in C57/BL6 and Aldh1a1(-/-) mice on a regular diet revealed that multiple Aldh1 enzymes regulate differences in the formation of sc and visceral fat. In Aldh1a1(-/-) mice, visceral fat essentially lacked all Aldh1 expression. This loss of RA-producing enzymes was accompanied by 70% decreased expression of ZFP423, PPARγ, and Fabp4 in visceral fat of Aldh1a1(-/-) vs. wild-type mice and by the predominant loss of visceral fat. Subcutaneous fat of Aldh1a1(-/-) mice expressed Aldh1a3 for RA production that was sufficient to maintain expression of ZFP423 and PPARγ and sc fat mass. Our data suggest a paradigm for regulation of fat depots through the concerted action of Aldh1 enzymes that establish RA-dependent tandem regulation of transcription factors ZFP423 and PPARγ in a depot-specific manner.

Evidence from both clinical and experimental studies indicates that Di-peptidyl peptidase-IV (DPP-4) inhibition may mediate favorable effects on the cardiovascular system. The objective of this study was to examine the acute effects of DPP-4 inhibition on vascular responses and to study the underlying mechanisms of alteration in tone. Aortic segments from C57BL/6 mice were treated with vasoconstrictors and exposed to various doses of alogliptin, a selective DPP-4 inhibitor. Vasodilator responses were evaluated using pathway specific antagonists to elucidate mechanisms of response. In parallel experiments, cultured human umbilical vein endothelial cells (HUVEC) were exposed to varying concentrations of alogliptin to evaluate the effects on candidate vasodilator pathways. Alogliptin relaxed phenylephrine and U46619 pre-constricted aortic segments in a dose dependent manner. Relaxation responses were not affected by the glucagon-like peptide-1 (GLP-1) receptor antagonist, exendin fragment 9–39 (88±6 vs. 91±2, p<0.001). Vascular relaxation to alogliptin was significantly decreased by endothelial denudation, L-NG-monomethyl-arginine citrate (L-NMMA) and by the soluble guanylate cyclase inhibitor ODQ. DPP-4 inhibition induced relaxation was completely abolished by a combination of L-NMMA, charybdotoxin and apamin. Incubation of HUVECs with alogliptin resulted in eNOS and Akt phosphorylation (Ser1177 and Ser473 respectively) paralleled by a rapid increase in nitric oxide. Inhibition of Src kinase decreased eNOS and Akt phosphorylation, in contrast to a lack of any effect on insulin mediated activation of the eNOS-Akt, suggesting that alogliptin mediates vasodilation through Src kinase mediated effects on eNOS-Akt. DPP-4 inhibition by alogliptin mediates rapid vascular relaxation via GLP-1 independent, Src-Akt-eNOS mediated NO release and the activation of vascular potassium channels.