In humans, prediabetes is characterized by marked increases in plasma insulin and near normal blood glucose levels as well as microvascular dysfunction of unknown origin. Using the extensor digitorum longus muscle of 7-wk inbred male Zucker diabetic fatty rats fed a high-fat diet as a model of prediabetes, we tested the hypothesis that hyperinsulinemia contributes to impaired O(2) delivery in skeletal muscle. Using in vivo video microscopy, we determined that the total O(2) supply to capillaries in the extensor digitorum longus muscle of prediabetic rats was reduced to 64% of controls with a lower O(2) supply rate per capillary and higher O(2) extraction resulting in a decreased O(2) saturation at the venous end of the capillary network. These findings suggest a lower average tissue Po(2) in prediabetic animals. In addition, we determined that insulin, at concentrations measured in humans and Zucker diabetic fatty rats with prediabetes, inhibited the O(2)-dependent release of ATP from rat red blood cells (RBCs). This inability to release ATP could contribute to the impaired O(2) delivery observed in rats with prediabetes, especially in light of the finding that the endothelium-dependent relaxation of resistance arteries from these animals is not different from controls and is not altered by insulin. Computational modeling confirmed a significant 8.3-mmHg decrease in average tissue Po(2) as well as an increase in the heterogeneity of tissue Po(2), implicating a failure of a regulatory system for O(2) supply. The finding that insulin attenuates the O(2)-dependent release of ATP from RBCs suggests that this defect in RBC physiology could contribute to a failure in the regulation of O(2) supply to meet the demand in skeletal muscle in prediabetes.

Increases in the second messenger cAMP are associated with receptor-mediated ATP release from erythrocytes. In other signaling pathways, cAMP-specific phosphodiesterases (PDEs) hydrolyze this second messenger and thereby limit its biological actions. Although rabbit and human erythrocytes possess adenylyl cyclase and synthesize cAMP, their PDE activity is poorly characterized. It was reported previously that the prostacyclin analog iloprost stimulated receptor-mediated increases in cAMP in rabbit and human erythrocytes. However, the PDEs that hydrolyze erythrocyte cAMP synthesized in response to iloprost were not identified. PDE3 inhibitors were reported to augment increases in cAMP stimulated by prostacyclin analogs in platelets and pulmonary artery smooth muscle cells. Additionally, PDE3 activity was identified in embryonic avian erythrocytes, but the presence of this PDE in mammalian erythrocytes has not been investigated. Here, using Western blot analysis, we determined that PDE3B is a component of rabbit and human erythrocyte membranes. In addition, we report that the preincubation of rabbit and human erythrocytes with the PDE3 inhibitors milrinone and cilostazol potentiates iloprost-induced increases in cAMP. In addition, cilostamide, the parent compound of cilostazol, potentiated iloprost-induced increases in cAMP in human erythrocytes. These findings demonstrate that PDE3B is present in rabbit and human erythrocytes and are consistent with the hypothesis that PDE3 activity regulates cAMP levels associated with a signaling pathway activated by iloprost in these cells.

Objectives The purpose of this study was to establish that the prostacyclin (PGI2) receptor (IP receptor) is present on rabbit and human erythrocytes and that its activation stimulates cAMP synthesis and ATP release. Methods The effect of incubation of erythrocytes with the active PGI2 analogues, iloprost or UT-15C, on cAMP levels and ATP release was determined in the absence and presence of the IP receptor antagonist, CAY10441. Western analysis was used to determine the presence of the IP receptor on isolated membranes. To establish that effects of PGI2 analogues were not due to prostaglandin E2 (PGE2) receptor activation, the effect of PGE2 on cAMP levels and ATP release was determined. Results Rabbit and human erythrocytes possess IP receptors. Iloprost and UT-15C stimulated increases in cAMP and ATP release that were prevented by the IP receptor antagonist, CAY10441. PGE2 did not stimulate cAMP accumulation or ATP release and did not inhibit iloprost-induced increases in cAMP. Conclusions This study establishes that the IP preceptor is present on rabbit and human erythrocytes and that its activation results in increases in cAMP and ATP release. These results suggest a novel mechanism by which PGI2 and its active analogues, when administered pharmacologically, could produce vasodilation.

In the preceding article, a method for measuring total marrow cellularity was described (1). The purpose of this report is to relate numerically (a) the erythroid marrow to the circulating red cell mass, and (b) the granulocytic marrow to the circulating granulocytic leukocytes. Results in three animal species and in man are reported, and are compared with data obtained by other methods. MATERIALS AND METHODSStudies were performed on Sprague-Dawley rats weighing between 200 to 300 Gm., New Zealand white rabbits weighing 2 to 33/ Kg., and 2 to 3 Kg. male Rhesus monkeys. All animals were given approximately 15 mg. per Kg. of iron as iron dextran2 at least two weeks before the study to insure adequate iron stores. Only those animals with hemoglobin levels above 13 Gm. were used. Reticulocyte counts in rabbits were required to be below 4 per cent and those of monkeys and rats below 3 per cent before the animals were considered suitable for study.Clinical studies were performed on male patients with controlled tuberculosis who were being subjected to thoracotomy. Prior to operation, these patients had normal leukocyte counts and were afebrile, but plasma iron values were usually subnormal. On the morning of operation their red counts were above 4.5 X 106; their reticulocyte counts were less than 2 per cent. They had not been transfused during the previous six months. I. Erythrocytic seriesA. Studies of the circulating erythrocytes. A red count was performed by enumerating a minimum of 1,000 cells from two or more pipettes in two counting chambers. Reticulocyte counts were performed on dried

High mobility group box 1 (HMGB1) is a chromatin-binding protein that maintains DNA structure. On cellular activation or injury, HMGB1 is released from activated immune cells or necrotic tissues and acts as a damage-associated molecular pattern to activate Toll-like receptor 4 (TLR4). Little is known concerning HMGB1 release and TLR4 activity and their role in the pathology of inflammation of sickle cell disease (SCD). Circulating HMGB1 levels were increased in both humans and mice with SCD compared with controls. Furthermore, sickle plasma increased HMGB1-dependent TLR4 activity compared with control plasma. HMGB1 levels were further increased during acute sickling events (vasoocclusive crises in humans or hypoxia/reoxygenation injury in mice). Anti-HMGB1 neutralizing antibodies reduced the majority of sickle plasma-induced TLR4 activity both in vitro and in vivo. These findings show that HMGB1 is the major TLR4 ligand in SCD and likely plays a critical role in SCD-mediated inflammation. (Blood. 2014;124(26):3978-3981)