Soluble CD4 and CD4-Mimetic Compounds Inhibit HIV-1 Infection by Induction of a Short-Lived Activated State

Binding to the CD4 receptor induces conformational changes in the human immunodeficiency virus (HIV-1) gp120 exterior envelope glycoprotein. These changes allow gp120 to bind the coreceptor, either CCR5 or CXCR4, and prime the gp41 transmembrane envelope glycoprotein to mediate virus–cell membrane fusion and virus entry. Soluble forms of CD4 (sCD4) and small-molecule CD4 mimics (here exemplified by JRC-II-191) also induce these conformational changes in the HIV-1 envelope glycoproteins, but typically inhibit HIV-1 entry into CD4-expressing cells. To investigate the mechanism of inhibition, we monitored at high temporal resolution inhibitor-induced changes in the conformation and functional competence of the HIV-1 envelope glycoproteins that immediately follow engagement of the soluble CD4 mimics. Both sCD4 and JRC-II-191 efficiently activated the envelope glycoproteins to mediate infection of cells lacking CD4, in a manner dependent on coreceptor affinity and density. This activated state, however, was transient and was followed by spontaneous and apparently irreversible changes of conformation and by loss of functional competence. The longevity of the activated intermediate depended on temperature and the particular HIV-1 strain, but was indistinguishable for sCD4 and JRC-II-191; by contrast, the activated intermediate induced by cell-surface CD4 was relatively long-lived. The inactivating effects of these activation-based inhibitors predominantly affected cell-free virus, whereas virus that was prebound to the target cell surface was mainly activated, infecting the cells even at high concentrations of the CD4 analogue. These results demonstrate the ability of soluble CD4 mimics to inactivate HIV-1 by prematurely triggering active but transient intermediate states of the envelope glycoproteins. This novel strategy for inhibition may be generally applicable to high–potential-energy viral entry machines that are normally activated by receptor binding

Porcine islet function: effects of arginine, leucine, and butyrate

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Successful cryopreservation of porcine pancreatic islets

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Automated large-scale isolation, in vitro function and xenotransplantation of porcine islets of Langerhans

Abstract: To evaluate the potential of utilizing porcine islet tissue as an alternative to human islet tissue for transplantation, we developed a method for the isolation of large amounts of highly purified porcine islets, and assessed the in vitro and in vivo function of the isolated islets after 1, 4, and 7 days of culture. The pancreatic duct of the splenic lobe was cannulated and distended by, injection of Hanks' balanced salt solution containing 1.5 mg/ml collagenase. The pancreas was then processed by a modification of the automated digestion-filtration method developed in this laboratory, and with purification accomplished by Euro-Ficoll gradients (dialyzed Ficoll in Eurocollins solution), consisting of two layers of 1.108 and 1.091 g/cm3 density, topped with a layer of HBSS. The postpurification yield was 5203 +/- 645 (mean +/- SEM) islets per gram of pancreas with a number of islet equivalents (IE) per gram pancreas (islet equivalence: 150-mu-m-sized islets) of 3551 +/- 305, and a volume of 6.27 +/- 1.7 mm3 islet tissue per gram of pancreas. The islet purity exceeded 90%. Overnight-cultured, perifused porcine islets released 53.1 +/- 8.2 pM insulin/200 IE at 3.3 mM glucose, and 114.9 +/- 25.4 p.M insulin/200 IE at 16.7 mM glucose (P < 0.001 vs. basal output). When theophylline was added, insulin secretion increased to 264.2 +/- 63.2 pM/200 IE (P < 0.001 vs. basal secretion and P < 0.005 vs. secretion at 16.7 mM glucose). After 4 days of culture, the islets still responded to secretagogues. The functional integrity of the isolated islets was confirmed by reversal of diabetes in aL3T4 antibody-treated C57B/B6 diabetic mice: normoglycemia was promptly restored by transplanting 1000 over-night- or 7-day-cultured (24-degrees-C) islets under the kidney capsule. These results suggest that continued improvements of porcine islet isolation and culture could permit the use of porcine islets in immunoalteration and immunoisolation studies that may lead to eventual human transplantation

In vitro function and xenotransplantation of long-term (3 weeks) cultured porcine islets of Langerhans

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