Mechanism-based isocoumarin inhibitors for trypsin and blood coagulation serine proteases: new anticoagulants

Trypsin, porcine pancreatic kallikrein, and several blood coagulation enzymes, including bovine thrombin, bovine factor Xa, human factor Xa, human plasma factor XIa, human plasma factor XIIa, and human plasma kallikrein, were inactivated by a number of substituted isocoumarins containing basic functional groups (aminoalkoxy, guanidino, and isothiureidoalkoxy). 3-Alkoxy-4-chloro-7-guanidinoisocoumarins were found to be the most potent inhibitors for the coagulation enzymes tested with kobsd/[I] values in the range of 10(3)-10(5) M-1 s-1. 4-Chloro-3-isothiureidoalkoxyisocoumarins show high inhibitory potency toward porcine pancreatic kallikrein, human plasma kallikrein, human factor XIa, human factor XIIa, and trypsin with kobsd/[I] values of the order of 10(4)-10(5) M-1 s-1. The inhibition of these serine proteases by the substituted isocoumarins are time dependent, and the inactivation of trypsin by 3-alkoxy-4-chloro-7-guanidinoisocoumarins and 7-amino-4-chloro-3-(3-isothiureidopropoxy)isocoumarin occured concurrently with the loss of the isocoumarin absorbance. The complex formed from inactivation of trypsin by these two types of inhibitors was very stable and regained less than 4% activity in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (pH 7.5) after 1 day at 25 degrees C and regained 8-45% activity upon addition of buffered 0.29 M hydroxylamine. Trypsin inactivated by other inhibitors regained full activity upon standing or addition of hydroxylamine. Thrombin inactivated by 3-alkoxy-4-chloro-7-guanidinoisocoumarins was also quite stable and only regained 9-15% activity under similar conditions. These results are consistent with a proposed mechanism, where serine proteases inactivated by aminoalkoxyisocoumarins or isothiureidoalkoxyisocoumarins form acyl enzymes that will deacylate upon standing or addition of hydroxylamine. However, the acyl enzymes formed from 3-alkoxy-4-chloro-7-guanidinoisocoumarins or 7-amino-4-chloro-3-(3-isothiureidopropoxy)-isocoumarin will decompose further, probably through a quinone imine methide, to give an irreversibly inactivated enzyme by reaction with an active-site nucleophile such as His-57. The quinone imine methide intermediate may also react with a solvent nucleophile to give an acyl enzyme that can be reactivated by hydroxylamine. The inhibitors 4-chloro-7-guanidino-3-methoxyisocoumarin and 4-chloro-3-ethoxy-7-guanidinoisocoumarin have been tested as anticoagulants in human plasma and were effective at prolonging the prothrombin time. However, they are unstable in plasma (t1/2 = 4-8 min), and their in vivo utility may be limited.     

Overexpression of epidermal growth factor receptor in NIH-3T3- transfected cells slows its lateral diffusion and rate of endocytosis

Interactions between membrane proteins are believed to be important for the induction of transmembrane signaling. Endocytosis is one of the responses which is regulated by both intracellular and extracellular signals. To study such interactions, we have measured the lateral mobility and rate of endocytosis of epidermal growth factor receptor in three transfected NIH-3T3 cell lines (HER84, HER22, and HER82) expressing 2 X 10(4), 2 X 10(5) and 1.5 X 10(6) EGF-receptors per cell, respectively. Using rhodamine-labeled EGF (Rh-EGF) and rhodamine-labeled monoclonal anti-EGF-receptor antibody (Rh-mAb-108), we measured twofold decreases in the lateral diffusion coefficients for each approximately 10-fold increase in EGF-receptor concentration. Since steric effects cannot account for such dependence, we propose that protein mobility within the membrane, which is determined by the rate of motion between immobile barriers, decreases due to aggregate formation. The rate of endocytosis also decreases twofold between the HER84 (2 X 10(4) receptors/cell) and HER22 (2 X 10(5) receptors/cell) cell lines, suggesting that it is diffusion limited. The comparable rates of endocytosis of the HER82 and HER22 cell lines suggest that at high receptor density endocytosis may be limited by the total number of sites for receptors in coated-pits and by their rate of recycling.     

Tissue-specific regulation of junctional communication in the skin of mouse fetuses homozygous for the repeated epilation (Er) mutation

Mouse embryos homozygous for the repeated epilation (Er) gene have abnormally developed skin characterised by hyper-proliferation and incomplete differentiation of the epidermis. In this report, we have studied the patterns of junctional communication in the skin of these mutants to see if the loss of control of proliferation/differentiation is associated with any altered patterns of communication. Using the dye-injection technique we have shown that, compared to normal skin, junctional communication among dermal cells of Er/Er mutants is greatly reduced and the frequency of dermal-epidermal communication is, on the other hand, increased. These results support our previously proposed model, which suggests that selective regulation of junctional communication can be a component of proliferative control in a complex tissue.     

Cryopreservation of human cadaveric bone marrow cells

The viability of cryopreserved human cadaveric bone marrow cells was studied using methylcellulose clonal cell culture assays. This is the first study done to reveal the persistence of hemopoietic proliferative and differentiative functions using the methylcellulose clonal cell assay in cryopreserved human cadaveric bone marrow cells which are several hours postmortem. Studies of cryopreserved human cadaveric bone marrows corresponded with those of murine bone marrows. These results strongly suggest that several hours postmortem human cadaveric bone marrow cells can be cryopreserved and may be useful for transplantation.     

The reconstruction of structure from electron micrographs of randomly oriented particles

A new method for enhancing and reconstructing the three dimensional structure of randomly oriented particles from their electron micrographs is developed. The method requires as an input many pictures of randomly oriented identical particles. The analysis is based on the calculation and accumulation of the spatial correlation of the densities on the electron micrographs, from which the spherical harmonic coefficients of the structure can be found. The process of enhancement of the spatial correlation and the averaging out of background noise enables reconstructions by use of pictures with low signal-to-noise ratio. The theory is presented and implemented in a computer program package. Simulated electron micrographs of ellipses, rods and a model of hexameric glutamate dehydrogenase are analyzed to demonstrate reconstructions using the computer programs.     

Structural study of porcine pancreatic elastase complexed with 7-amino-3-(2-bromoethoxy)-4-chloroisocoumarin as a nonreactivatable doubly covalent enzyme-inhibitor complex

The complex of porcine pancreatic elastase (PPE) with 7-amino-3-(2-bromoethoxy)-4-chloroisocoumarin, a potent mechanism-based inhibitor, was crystallized and the crystal structure determined at 1.9-A resolution with a final R factor of 17.1%. The unbiased difference Fourier electron density map showed continuous density from O gamma of Ser 195 to the benzoyl carbonyl carbon atom and from N epsilon 2 of His 57 to the carbon atom at the 4-position of the isocoumarin ring in the inhibitor. This suggested unambiguously that the inhibitor was doubly covalently bound to the enzyme. It represents the first structural evidence for irreversible binding of an isocoumarin inhibitor to PPE through both Ser 195 and His 57 in the active site. The PPE-inhibitor complex is only partially activated in solution by hydroxylamine and confirms the existence of the doubly covalently bound complex along with the acyl enzyme. The benzoyl carbonyl oxygen atom of the inhibitor is not situated in the oxyanion hole formed by the amide (greater than NH) groups of Gly 193 and Ser 195. The complex is stabilized by the hydrogen-bonding interactions in the active site (from the N epsilon 2 of Gln 192 to the bromine atom in the inhibitor and the amino group at the 7-position of the isocoumarin ring to the carbonyl oxygen of Thr 41) and by van der Waals interactions. The inhibition rates of several 7-substituted 4-chloro-3-(bromoalkoxy)isocoumarins toward PPE were measured.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intraocular pressure in cats is lowered by drops of hornet venom

1. Nine cats were given an intravenous injection of the Oriental hornet (Vespa orientalis, Vespinae; Hymenoptera) venom sac extract (VSE) and seven cats had the same VSE administered as eye drops. 2. When injected intravenously, the hornet VSE decreased the intraocular pressure in both eyes sharply during the first 20 min and with a slower rate later on until the end of the 3 hr experiment. The intraocular pressure dropped to zero in some cases. 3. VSE eye drops decreased the intraocular pressure only in the treated eye, while in the second eye (left as a control) the intraocular pressure remained the same throughout the experiment. 4. The decrease in the intraocular pressure was sharp during the first 20 min and slowed down afterwards until the end of the experiment. 5. The intraocular pressure did not reduce to zero. 6. This study shows that the active components of the hornet venom which caused a decrease in the intraocular pressure can cross the cornea and exert a hypotensive effect in the eye.