Prevention of vascular and neural dysfunction in diabetic rats by C-peptide.

C-peptide, a cleavage product from the processing of proinsulin to insulin, has been considered to possess little if any biological activity other than its participation in insulin synthesis. Injection of human C-peptide prevented or attenuated vascular and neural (electrophysiological) dysfunction and impaired Na+- and K+-dependent adenosine triphosphate activity in tissues of diabetic rats. Nonpolar amino acids in the midportion of the peptide were required for these biological effects. Synthetic reverse sequence (retro) and all-D-amino acid (enantio) C-peptides were equipotent to native C-peptide, which indicates that the effects of C-peptide on diabetic vascular and neural dysfunction were mediated by nonchiral interactions instead of stereospecific receptors or binding sites.

(S)-13-[(dimethylamino)methyl]-10,11,14,15-tetrahydro-4,9:16, 21-dimetheno-1H, 13H-dibenzo[e,k]pyrrolo[3,4-h][1,4,13]oxadiazacyclohexadecene-1,3(2H)-d ione (LY333531) and related analogues: isozyme selective inhibitors of protein kinase C beta.

Protein kinase C (PKC) is a family of closely related serine and threonine kinases. Overactivation of some PKC isozymes has been postulated to occur in several diseases states, including diabetic complications. Selective inhibition of overactivated PKC isozymes may offer a unique therapeutic approach to disease states such as diabetic retinopathy. A novel series of 14-membered macrocycles containing a N-N'-bridged bisindolylmaleimide moiety is described. A panel of eight cloned human PKC isozymes (alpha, beta I, beta II, gamma, delta, epsilon, sigma, eta) was used to identify the series and optimize the structure and associated activity relationship. The dimethylamine analogue LY333531 (1), (S)-13-[(dimethylamino)methyl]-10,11,14,15-tetrahydro-4,9:16, 21-dimetheno-1H, 13H-dibenzo[e,k]pyrrolo[3,4-h][1,4,13]oxadiazacyclohexadecene++ +-1,3(2H)-dione, inhibits the PKC beta I (IC50 = 4.7 nM) and PKC beta II (IC50 = 5.9 nM) isozymes and was 76- and 61-fold selective for inhibition of PKC beta I and PKC beta II in comparison to PKC alpha, respectively. The additional analogues described in the series are also selective inhibitors of PKC beta. LY333531 (1) exhibits ATP dependent competitive inhibition of PKC beta I and is selective for PKC in comparison to other ATP dependent kinases (protein kinase A, calcium calmodulin, caesin kinase, src tyrosine kinase). The cellular activity of the series was assessed using bovine retinal capillary endothelial cells. Retinal endothelial cell dysfunction has been implicated in the development of diabetic retinopathy. Plasminogen activator activity stimulated by a phorbol ester (4 beta-phorbol 12,13-dibutyrate) in endothelial cells was inhibited by the compounds in the series with ED50 values ranging from 7.5 to 0.21 microM. A comparison of the PKC isozyme and related ATP dependent kinase inhibition profiles is provided for the series and compared to the profile for staurosporine, a nonselective PKC inhibitor. The cellular activity of the series is compared with that of the kinase inhibitor staurosporine.

Amelioration of vascular dysfunctions in diabetic rats by an oral PKC beta inhibitor.

The vascular complications of diabetes mellitus have been correlated with enhanced activation of protein kinase C (PKC). LY333531, a specific inhibitor of the beta isoform of PKC, was synthesized and was shown to be a competitive reversible inhibitor of PKC beta 1 and beta 2, with a half-maximal inhibitory constant of approximately 5 nM; this value was one-fiftieth of that for other PKC isoenzymes and one-thousandth of that for non-PKC kinases. When administered orally, LY333531 ameliorated the glomerular filtration rate, albumin excretion rate, and retinal circulation in diabetic rats in a dose-responsive manner, in parallel with its inhibition of PKC activities.

LY290181, an inhibitor of diabetes-induced vascular dysfunction, blocks protein kinase C-stimulated transcriptional activation through inhibition of transcription factor binding to a phorbol response element.

Previous studies have shown that high glucose levels and diabetes induce an elevation in protein kinase C (PKC) activity in vascular cells and tissues susceptible to diabetic complications. In addition, PKC activation has been shown to modulate vascular cell growth, permeability, and gene expression, processes thought to be involved in the development of vascular complications. Using two in vivo model systems, we have identified a novel inhibitor of diabetic vascular dysfunction, LY290181. LY290181 prevented glucose-induced increases in blood flow and permeability in rat granulation tissue and corresponding vascular changes in the retina, sciatic nerve, and aorta of diabetic rats. Tested for its ability to inhibit PKC-regulated processes, LY290181 inhibited phorbol ester-stimulated plasminogen activator activity in a dose-dependent manner in bovine retinal endothelial cells and in human dermal fibroblasts. In addition, LY290181 inhibited phorbol ester-stimulated activation of the porcine urokinase plasminogen activator (uPA) promoter (-4600/+398) linked to the chloramphenicol acetyltransferase (CAT) reporter gene (p4660CAT). More detailed analysis of the uPA promoter revealed that LY290181 inhibited phorbol ester-stimulated activation of the uPA phorbol response element (-2458/-2349) located upstream of the thymidine kinase promoter (puPATKCAT). LY290181 appears to inhibit uPA promoter activation by blocking phorbol ester-stimulated binding of nuclear proteins to the uPA PEA3/12-0-tetradecanoylphorbol 13-acetate responsive element (TRE). These results suggest that LY290181 may inhibit diabetes-induced vascular dysfunction by inhibiting transcription factor binding to specific PKC-regulated genes involved in vascular function.

Correlation of diacylglycerol level and protein kinase C activity in rat retina to retinal circulation.

The increases in diacylglycerol (DAG) level and protein kinase C (PKC) activity have been characterized biochemically and functionally in the retina and the brain of diabetic rats as well as in cultured vascular cells. PKC specific activities were increased in the membraneous fraction of retina from streptozotocin (STZ)-induced diabetic rats and the genetically determined diabetic BB rats, respectively, after 1 or 2 wk of diabetes, compared with control. The ratio of total PKC activities from membraneous and cytosol fractions was also increased in the retina of diabetic rats. With diabetes, all the isoenzymes and the total DAG level were increased in the rat retina, whereas no changes were found in the rat brain. Insulin treatment normalized plasma glucose levels and partially prevented the increases in the membraneous PKC activity and all the isoenzymes in the retina. In the retinal endothelial cells, the total DAG level and PKC specific activities are increased by 36 and 22%, respectively, in the membraneous pool when the glucose levels are changed from 5.5 to 22 mM. Activation of PKC activity and isoform beta II by the vitreal injection of phorbol dibutyrate mimicked the abnormal retinal blood circulation observed in diabetic rats (2.22 +/- 0.24 vs. 1.83 +/- 0.40 s). Thus diabetes and elevated glucose levels will increase DAG level and PKC activities and its isoenzyme specifically in vascular cells and may affect retinal hemodynamics.

Correlation of molecular shape with GPIIb-IIIa receptor antagonist activity in RGD peptides.

Arg-Gly-Asp-Ser (RGDS) 1, Arg-Val-Asp-Ser (RVDS) 2, Arg-dVal-Asp-Ser (R[d]VDS) 3, and a cyclic RGD peptide, cyclo S,R [H-Pen-Arg-Gly-Asp-Pen-Gly-OH] 4, were tested for their ability to antagonize GPIIb-IIIa function. The activities were found to fall in the order 4 >> 1 >> 3 > 2. Simulated annealing and molecular dynamics studies were carried out to estimate the most populated conformations of each molecule. The acyclic molecules 1-3 were found to populate a much wider range of conformations than the cyclic molecule 4. The backbones of all four molecules were found to approximate beta-turn structures in the most populated conformations. In 4 the beta-turn intramolecular hydrogen bond between C = O of the i residue (Arg) and NH of the i + 3 residue (Ser) did not appear to be present. The distance between the beta-carbons of the critical Arg and Asp groups was found to be shorter in 4 (average 7.98 A) than in the less active acyclic molecules (averages of 8.65-9.33 A).

Design and implementation of a particle concentration fluorescence method for the detection of HIV-1 protease inhibitors.

A critical step in the replicative cycle of the human immunodeficiency virus HIV-1 involves the proteolytic processing of the polyprotein products Prgag and Prgag-pol that are encoded by the gag and pol genes in the viral genome. Inhibitors of this processing step have the potential to be important therapeutic agents in the management of acquired immunodeficiency syndrome. Current assays for inhibitors of HIV-1 protease are slow, cumbersome, or susceptible to interference by test compounds. An approach to the generation of a rapid, sensitive assay for HIV-1 protease inhibitors that is devoid of interference problems is to use a capture system which allows for isolation of the products from the reaction mixture prior to signal quantitation. In this paper, we describe a novel method for the detection of HIV-1 protease inhibitors utilizing the concept of particle concentration fluorescence. Our approach involves the use of the HIV-1 protease peptide substrate Ser-Gln-Asn-Tyr-Pro-Ile-Val which has been modified to contain a biotin moiety on one side and a fluorescein reporter molecule on the other side of the scissile Tyr-Pro bond. This substrate is efficiently cleaved by the HIV-1 protease and the reaction can be readily quantitated. Known inhibitors of the protease were readily detected using this new assay. In addition, this approach is compatible with existing instrumentation in use for broad screening and is highly sensitive, accurate, and reproducible.

Glucose transporter levels in tissues of spontaneously diabetic Zucker fa/fa rat (ZDF/drt) and viable yellow mouse (Avy/a).

We used antibodies to the fat/muscle glucose transporter (GLUT4) and the liver glucose transporter (GLUT2) to measure levels of these proteins in various tissues of two rodent models of non-insulin-dependent (type II) diabetes mellitus: the obese spontaneously diabetic male Zucker fa/fa rat (ZDF/drt) and the male viable yellow Avy/a obese diabetic mouse. The ZDF/drt strain generally develops overt diabetes associated with decreased plasma insulin levels. Depending on the age of the animals, the ZDF/drt rats can be arbitrarily segregated into age-matched obese, mildly diabetic (blood glucose less than 11 mM) and obese, and severely diabetic (blood glucose greater than 20 mM) groups. Avy/a mice are comparably hyperglycemic but unlike the ZDF/drt rats are severely hyperinsulinemic. In both groups of diabetic animals, GLUT4 in adipose tissue, heart, and skeletal muscle was reduced 25-55%, and GLUT2 in liver was increased 30-40%, relative to lean, age-matched controls. However, when the mildly diabetic ZDF/drt rats were compared to the lean controls, the only significant difference was a 25% reduction of GLUT4 in heart. Within all of the ZDF/drt rats (excluding the lean controls), GLUT2 in liver and GLUT4 in adipose tissue, heart, and skeletal muscle correlated significantly with glycemia. These data suggest that, in these two models of type II diabetes, glucose transporter levels in muscle, adipose tissue, and liver are regulated in a tissue-selective manner in response to changes in insulin and glucose. Furthermore, at least in the ZDF/drt rat, alterations in GLUT2 and/or GLUT4 protein levels appear not to be associated with obesity per se but appear to be secondary to the severely diabetic state.(ABSTRACT TRUNCATED AT 250 WORDS)

(A-C-B) human proinsulin, a novel insulin agonist and intermediate in the synthesis of biosynthetic human insulin.

The hormone insulin is synthesized in the beta cell of the pancreas as the precursor, proinsulin, where the carboxyl terminus of the B-chain is connected to the amino terminus of the A-chain by a connecting or C-peptide. Proinsulin is a weak insulin agonist that possesses a longer in vivo half-life than does insulin. A form of proinsulin clipped at the Arg65-Gly66 bond has been shown to be more potent than the parent molecule with protracted in vivo activity, presumably as a result of freeing the amino terminal residue of the A-chain. To generate a more active proinsulin-like molecule, we have constructed an "inverted" proinsulin molecule where the carboxyl terminus of the A-chain is connected to the amino terminus of the B-chain by the C-peptide, leaving the critical Gly1 residue free. Transformation of Escherichia coli with a plasmid coding for A-C-B human proinsulin led to the stable production of the protein. By a process of cell disruption, sulfitolysis, anion-exchange chromatography, refolding, and reversed-phase high-performance liquid chromatography, two forms of the inverted proinsulin differing at their amino termini as Gly1 and Met0-Gly1 were identified and purified to homogeneity. Both proteins were shown by a number of analytical techniques to be of the inverted sequence, with insulin-like disulfide bonding. Biological analyses by in vitro techniques revealed A-C-B human proinsulin to be intermediate in potency when compared to human insulin and proinsulin. The time to maximal lowering of blood glucose in the fasted normal rat appeared comparable to that of proinsulin. Additionally, we were able to generate fully active, native insulin from A-C-B human proinsulin by proteolytic transformation. The results of this study lend themselves to the generation of novel insulin-like peptides while providing a simplified route to the biosynthetic production of insulin.

Mutations in the heparin-binding domains of human basic fibroblast growth factor alter its biological activity.

Eleven structural analogues of human basic fibroblast growth factor (bFGF) have been prepared by site-directed mutagenesis of a synthetic bFGF gene to examine the effect of amino acid substitutions in the three putative heparin-binding domains on FGF's biological activity. After expression in Escherichia coli, the mutant proteins were purified to homogeneity by use of heparin-Sepharose chromatography and analyzed for their ability to stimulate DNA synthesis in human foreskin fibroblasts. Recombinant human bFGF 1-146 and [Ala69,Ser87]bFGF, an analogue where two of the four cysteines had been replaced by alanine and serine, were equipotent to standard bovine basic fibroblast growth factor. Substitution of aspartic acid-19 by arginine in the first heparin-binding domain yielded a molecule that stimulated a higher total mitogenic response in fibroblasts as compared to bFGF. In addition, replacement of either arginine-107 in the second domain or glutamine-123 in the third domain with glutamic acid resulted in compounds that were 2 and 4 times more potent than bFGF. In contrast, substitution of arginine-107 with isoleucine reduced the activity of the molecule by 100-fold. Combination of domain substitutions to generate the [Glu107,123]bFGF and [Arg19,Lys123,126]bFGF mutants did not show any additivity of the mutations on biological activity. Alterations in the biological activity of the analogues was dependent on both the site of and the type of modification. Increased positive charge in the first domain and increased negative charge in the second and third domains enhanced biological potency. The altered activities of the derivatives appear to be due in part to changes in the affinity of the analogues for heparin. We conclude that changes in all three of the putative heparin-binding domains result in altered mitogenic activity and heparin interaction of basic fibroblast growth factor.

Inhibition of protein kinase C by calphostin C is light-dependent.

Calphostin C, a secondary metabolite of the fungus Cladosporium cladosporioides, inhibits protein kinase C by competing at the binding site for diacylglycerol and phorbol esters. Calphostin C is a polycyclic hydrocarbon with strong absorbance in the visible and ultraviolet ranges. In characterizing the activity of this compound, we unexpectedly found that the inhibition of [3H]phorbol dibutyrate binding was dependent on exposure to light. Ordinary fluorescent light was sufficient for full activation. The inhibition of protein kinase C activity in cell-free systems and intact cells also required light. Light-dependent cytotoxicity was seen at concentrations about 5-fold higher than those inhibiting protein kinase C.

Presence of liver CGRP/amylin receptors in only nonparenchymal cells and absence of direct regulation of rat liver glucose metabolism by CGRP/amylin.

Human calcitonin gene-related peptide (hCGRP-1) and human amylin (hA) have been reported to increase hepatic glucose output in vivo and to bind with high affinity to rat liver plasma membranes, resulting in increased cAMP production. These observations have led to the hypothesis that CGRP or amylin may be physiological regulators of liver glucose metabolism. Liver plasma membranes are derived from several cell types, including parenchymal (hepatocyte), Kupffer, endothelial, lipid storage, and smooth muscle cells. Because the parenchymal cell is responsible for the contribution of the liver to whole-body glucose homeostasis, it is important to verify the location and activity of the CGRP/amylin receptor to this cell. These studies separate liver cells prepared by collagenase digestion into parenchymal and nonparenchymal fractions by metrizamide gradient and differential centrifugation. 125I-labeled [Tyr-0]hCGRP-1 bound with high affinity to nonparenchymal cell fraction and was displaced by both hCGRP-1 and hA. hCGRP-1 bound with greater affinity than hA (Kd = 2.1 +/- 1.6 x 10(-11) vs. 2.6 +/- 1.2 x 10(-8) M) in a manner similar to the binding reported for liver plasma membrane fraction. Linear regression of receptor concentration against nonparenchymal cell count per milliliter was significant (r = 0.999, P = 0.026), leading to an estimate of 3000 receptors/cell. The parenchymal cell fraction bound very little 125I-[Tyr-0]hCGRP-1, and regression of receptor concentration against parenchymal cell count per milliliter was not significant (r = -0.708, P = 0.29), suggesting that binding was not due to parenchymal cells but instead to contamination by nonparenchymal cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of mitogenic stimuli by angiogenin correlates with in vitro phosphatidylinositol bisphosphate synthesis.

125I-labeled angiogenin binds rapidly to the plasma membrane of several cell lines at 37 degrees C (t1/2 less than 1 min) but in comparatively small amounts. Competition with unlabeled angiogenin varies markedly with different cell lines, being most effective in vascular smooth muscle and fibroblast cells. Angiogenin modulates mitogenic stimuli in bovine adrenal capillary endothelial (BACE), rat aortic smooth muscle (RASM), and fibroblast (3T3) cells. Thus, it enhances the mitogenic effect of certain conditioned media on RASM and 3T3 cells, but it inhibits the mitogenic effect on BACE cells. In RASM and 3T3 cells, mitogenesis is increased at low (less than 5 ng/ml) and high (greater than 100 ng/ml) but not at intermediate concentrations of angiogenin. Plasma membranes from RASM and 3T3 cells that have been treated with angiogenin show an enhanced in vitro synthesis of phosphatidylinositol bisphosphate (PtdInsP2) with an angiogenin concentration dependence similar to that of enhanced mitogenesis. PtdInsP2 synthesis arises by activation of a fatty acid (arachidonyl) coenzyme A synthetase and either a plasma membrane fatty acid acyltransferase or phosphatidylinositol kinase(s), or both. Increased PtdInsP2 or the derived second messengers (e.g., diacylglycerol) may mediate modulation of the mitogenic stimulus. The differential mitogenic interaction of angiogenin with several cell types, either stimulation or inhibition, probably reflects the multistep nature of angiogenesis.

A synthetic approach to structure-function relationships in the murine epidermal growth factor molecule.

Murine epidermal growth factor, a 53-amino acid peptide that is mitogenic for a number of cell types, has been synthesized by the solid-phase method. The synthetic peptide is identical to the natural material in amino acid composition, chromatographic behavior, receptor binding, and stimulation of DNA synthesis. Fragments of the EGF molecule corresponding to residues 42-53, 32-53, and 15-53 were constructed as well as the methionine sulfoxide derivative of EGF, [Met(O)21]EGF-(1-53), and a polymeric form of EGF. [Met(O)21]EGF-(1-53) was slightly less active than EGF in receptor binding and stimulation of DNA synthesis. Polymeric EGF was 1/100th as active as EGF, while EGF-(15-53) was less potent than EGF-(1-53) by a factor of 10(4). EGF-(32-53) was even less active and EGF-(43-53) was inactive.

SN 1 and SN 2 mechanisms for the deprotection of synthetic peptides by hydrogen fluoride. Studies to minimize the tyrosine alkylation side reaction.

Studies on the side reaction leading to ring alkylation during HF deprotection of tyrosine revealed that under SN 1 conditions the formation of by-product can be reduced by using protecting groups that either provide only weakly electrophilic carbocations or give rise to an intermediate that deactivates the tyrosine ring and allows scavengers to suppress the formation of 3-alkyltyrosine. The effectiveness of the scavenger can be qualitatively predicted by its pKa value. A new reagent (HF: dimethylsulfide, 1:3, v/v) provides an SN2 cleavage mechanism that removes the danger of carbocation formation and suppresses the electrophilic alkylation side reaction.

Structural significance of the amino-terminal residues of sperm whale myoglobin.

Following the development of a nondestructive synthetic procedure for rapid production of des-Val1-myoglobin in large quantities, the synthesis of a series of myoglobin derivatives varying in structure and charge in the NH2-terminal region was accomplished. In comparison to the untreated myoglobin, the des-Val1-myoglobin was found to possess at low pH a decreased stability and an increased net positive charge in the pH range 5.5-8.5. While the elevated net positive charge was no longer apparent after removal of the second residue, the instability of the molecule was found to be sharply increased. Substitutions of the first residue, directed toward elucidating its structural importance, included glutamic acid, lysine, and glycine. Addition of any of the three amino acids to the des-Val1-myoglobin was found to restore much of the acid stability, with the [Gly1]myoglobin appearing nearly identical with the native molecule. All three semisynthetic myoglobins showed potentiometric titration curves characteristic of their respective, substituted residue. Carbamylation of the NH2 terminal of myoglobin and des-Val1-myoglobin yielded two nearly identical molecules in terms of all physical properties examined. Consequently, it was concluded that the first residue primarily serves the function of maintaining the positively charged NH2 terminus a certain distance away from the beginning of the A helix and from the charge pair interaction of Lys-133 with Glu-6. In addition, through physical measurements of the des-Val1,Leu2-myoglobin prior and subsequent to carbamylation of the NH2 terminus, it was apparent that the stabilization conferred on the des-Val1-myoglobin by the second residue was dependent to a large degree upon the hydrophobic interactions of its side chain.