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D Prasa

Publications and source records attributed to D Prasa.

14 recordsLinked to original sources
PubMed2003

Blood coagulation and fibrinolysis after extreme short-term exercise.

INTRODUCTION: Maximal exercise may be a trigger for cardiovascular events. The aim of the study was to investigate changes in blood coagulation and fibrinolysis following maximal short-term exercises with different durations up to 90 s. METHODS: A total of 15 healthy nonsmokers underwent three isokinetic maximal tests on an SRM cycle ergometry system with durations of 15, 45, and 90 s. Blood samples were taken after a 30-min rest, immediately before and after exercise, 15 min, and 1 h after completion of exercise. For the investigation of blood coagulation, prothrombin fragment 1+2 (F1+2), thrombin-antithrombin III complex (TAT), intrinsic and extrinsic total (TTPin+ex), and endogenous thrombin potential (ETPin+ex) were measured. For testing fibrinolysis, determinations of plasmin-alpha(2)-antiplasmin complex (PAP), tissue-type plasminogen activator (tPA)-antigen, plasminogen activator inhibitor (PAI)-1-antigen and D-dimer were used. RESULTS: Immediately after the exercise tests, only F1+2 (15- and 90-s test) and TTPin (45 and 90 s) showed a moderate increase (p<0.05), while TAT and ETP was unchanged. In contrast, a clear increase in PAP and tPA-antigen already after 15 s maximal exercise in relation to the exercise duration time could be investigated. These effects were not totally reversed to baseline 15 min after exercise; D-dimer and PAI-1-antigen still remained unchanged after these types of exercise. CONCLUSIONS: Maximal short-term exercise does not lead to a relevant activation of blood coagulation in healthy young subjects, it is only slightly altered within the normal range. In contrast, fibrinolysis is clearly activated, and the increase is directly dependent on exercise duration. Additionally, it could be shown for the first time that fibrinolysis is already activated after 15 s maximal exercise duration.

Adult↗
PubMed2002

Thrombin potential and thrombin generation after exhaustive exercise.

Exhaustive exercise leads to an activation of blood coagulation, but the implications of this activation are still unclear. The aim of this study was to investigate if a hypercoagulant stage exists after exhaustive treadmill- or cycle exercise; intrinsic and extrinsic endogenous thrombin potential (ETP) were measured by using the method of Hemker et al. Thirteen healthy male subjects underwent an exhaustive treadmill (TR) or cycle (CY) ergometer test and a control-day in random order. Blood samples were taken, repeatedly, after a 30 min rest, immediately before and after, and 1 h after exercise for measuring intrinsic and extrinsic total thrombin potential (TTPin, TTPex) (including free and alpha 2 -macroglobulin-bound thrombin) and endogenous thrombin potential (ETPin, ETPex), aPTT, PT, F1 + 2 and TAT. In comparison to the pre-value taken immediately before the exercise, the intrinsic TTP was significantly (p < 0.05) increased directly after exercise (TR-TTPin, + 11.6 %; CY-TTPin, + 11.5 %). In contrast, ETPin remained unchanged after both exercises. Additionally for TTPex and ETPex, no changes after exercise were detectable. aPTT was significantly (p < 0.05) shorter after exercise (TR-aPTT, - 16.2 %; CY-aPTT - 17.5 %), F1 + 2-concentrations were higher (p < 0.05) (TR-F1 + 2, + 21.2 %; CY-F1 + 2, + 9.8 %), but TAT remained unchanged. Differences between TR or CY could not be determined. These results show the expected shortening of aPTT and the increase of F1 + 2 indicating an activation of the coagulation system during exercise. However, the unchanged intrinsic and extrinsic ETP lead to the conclusion that in healthy young male subjects the potential for thrombin generation is insignificant, is directly counterbalanced by alpha 2-macroglobulin and is independent of the type of exhaustive exercise done.

Adult↗
PubMed2002

[Inhibitors of factor XIIIa].

Factor XIIIa (FXIIIa) catalyzes the covalent crosslinking of fibrin polymers and incorporation of proteins into the fibrin network and thus confers on the thrombus additional structural stability and relative resistance to plasmin-mediated degradation. Moreover, FXIIIa is involved in other physiological and pathophysiological processes such as wound healing and arteriosclerosis. Selective FXIIIa inhibitors may be a valuable tool for evaluation of the various functions of FXIIIa and their pharmacological control. This paper presents an overview of the inhibitors of FXIIIa. Analogues of natural FXIIIa substrates - including glutamine containing peptides and low molecular weight substituted alkylamines - are incorporated into the fibrin network and thus prevent crosslinking of fibrin. Naturally occurring, direct inhibitors of FXIIIa have been isolated from a leech species and microorganisms. With effective concentrations in the nanomolar range the peptide tridegin is the most potent FXIIIa inhibitor up to now. The majority of the synthetic, low molecular Weight inhibitors bind covalently to Cys314 at the active site of FXIIIa. Besides the relatively nonspecific thiol reagents, azol derivatives, azolium salts and related substances are described as specific inhibitors of FXIIIa. They inhibit the activity of FXIIIa at nanomolar concentrations. Animal experiments have demonstrated improved thrombolysis by a plasminogen activator in combination with a FXIIIa inhibitor.

Arteriosclerosis↗
PubMed1997

Synthesis and structure-activity relationships of potent thrombin inhibitors: piperazides of 3-amidinophenylalanine.

Thrombin is the key enzyme in the blood coagulation system, and inhibitors of its proteolytic activity are of therapeutic interest since they are potential anticoagulants. The most potent inhibitor of the benzamidine type is N alpha-[(2-naphthylsulfonyl)glycyl]-4-amidinophenylalanylpiperid ide (NAPAP). However, NAPAP and other benzamidine derivatives do not show favorable pharmacological properties; above all, they have very low systemic bioavailability after oral administration. The goal of designing new compounds was to obtain potent inhibitors with improved pharmacokinetic properties. Piperazide derivatives of 3-amidinophenylalanine as the key building block were synthesized. The piperazine moiety opened the possibility to introduce quite different substituents on the second nitrogen using common synthetic procedures. Some of the newly synthesized compounds are potent inhibitors of thrombin and offer an approach to study structure-function relationships for inhibition of thrombin and related enzymes and for the improvement of their pharmacokinetic properties.

Animals↗
PubMed1997

Structural mapping of the active site specificity determinants of human tissue-type plasminogen activator. Implications for the design of low molecular weight substrates and inhibitors.

The recent structure determination of the catalytic domain of tissue-type plasminogen activator (tPA) suggested residue Arg174 could play a role in P3/P4 substrate specificity. Six synthetic chromogenic tPA substrates of the type R-Xaa-Gly-Arg-p-nitroanilide, in which R is an N-terminal protection group, were synthesized to test this property. Although changing the residue Xaa (in its L or D form) at position P3 from the hydrophobic Phe to an acidic residue, Asp or Glu, gave no improvement in catalytic efficiency, comparative analysis of the substrates indicated a preference for an acidic substituent occupying the S3 site when the S4 site contains a hydrophobic or basic moiety. The 2.9 A structure determination of the catalytic domain of human tPA in complex with the bis-benzamidine inhibitor 2, 7-bis-(4-amidinobenzylidene)-cycloheptan-1-one reveals a three-site interaction, salt bridge formation of the proximal amidino group of the inhibitor with Asp189 in the primary specificity pocket, extensive hydrophobic surface burial, and a weak electrostatic interaction between the distal amidino group of the inhibitor and two carbonyl oxygens of the protein. The latter position was previously occupied by the guanidino group of Arg174, which swings out to form the western edge of the S3 pocket. These data suggest that the side chain of Arg174 is flexible, and does not play a major role in the S4 specificity of tPA. On the other hand, this residue would modulate S3 specificity, and may be exploited to fine tune the specificity and selectivity of tPA substrates and inhibitors.

Arginine↗
PubMed1997

The ability of thrombin inhibitors to reduce the thrombin activity generated in plasma on extrinsic and intrinsic activation.

In a thrombin generation test with continuous registration of thrombin activity in plasma we studied the ability of a variety of thrombin inhibitors of different type and mechanism of action of influence the activity of thrombin after activation of the coagulation system. Depending on the inhibitor, the peak of thrombin activity is delayed and/or reduced. By blocking the active site of generated thrombin inhibitors cause a concentration dependent reduction of the thrombin peak and inhibit feed-back reactions of thrombin resulting in a delay of thrombin generation. Highly potent synthetic active-site directed inhibitors (Ki < or = 20 nM) reduce the thrombin activity formed in plasma after extrinsic or intrinsic activation with the same efficiency (IC50 0.1-0.6 microM) as hirudin. The delay and reduction of thrombin generation by inhibitors of the anion-binding exosite 1 of thrombin is only attributed to an inhibition of feed-back reactions of thrombin. For a 50% reduction of thrombin activity in plasma by this type of inhibitors relatively high concentrations were determined.

Amino Acid Chloromethyl Ketones↗
PubMed1997

Inhibition of thrombin generation in plasma by inhibitors of factor Xa.

A series of inhibitors of factor Xa (FXa) were investigated using the thrombin generation assay to evaluate the potency and specificity needed to efficiently block thrombin generation in activated human plasma. By inhibiting FXa the generation of thrombin in plasma is delayed and decreased. Inhibitor concentrations which cause 50 percent inhibition of thrombin generation (IC50) correlate in principle with the Ki values for inhibition of free FXa. Recombinant tick anticoagulant peptide (r-TAP) is able to inhibit thrombin generation with considerably low IC50 values of 49 nM and 37 nM for extrinsic and intrinsic activation, respectively. However, the potent synthetic, low molecular weight inhibitors of FXa (Ki values of about 20 nM) are less effective in inhibiting the generation of thrombin with IC50 values at micromolar concentrations. The overall effect of inhibitors of FXa in the thrombin generation assay was compared to that of thrombin inhibitors. On the basis of similar Ki values for the inhibition of the respective enzyme, synthetic FXa inhibitors are less effective than thrombin inhibitors. In contrast, the highly potent FXa inhibitor r-TAP causes a stronger reduction of the thrombin activity in plasma than the most potent thrombin inhibitor hirudin.

Animals↗
PubMed1997

Trypsin- and SLIGRL-induced vascular relaxation and the inhibition by benzamidine derivatives.

Serine proteinases are involved in several physiological processes and elicit profound cellular effects in a variety of tissues. Besides the thrombin receptor a second receptor, activated by trypsin, the proteinase-activated receptor 2 (PAR-2), was cloned and characterized. Both enzymes generate a new extracellular N-terminus by limited proteolytic cleavage which functions as tethered ligand to activate the receptor. Synthetic peptides corresponding to the sequences of the newly generated N-terminus are able to mimic the effects of the enzymes. In porcine pulmonary arteries trypsin and the receptor-derived peptide SLIGRL elicited an endothelium-dependent transient relaxation of PGF2alpha-precontracted vessels. The EC50 values for trypsin and SLIGRL amounted to 1.1 +/- 0.2 nM and 5.4 +/- 0.6 microM, respectively. Trypsin and SLIGRL caused a homologous desensitization but thrombin and the thrombin receptor-activating peptide SFLLRN were still able to elicit pronounced relaxant effects. The trypsin- and SLIGRL-induced relaxant responses were markedly diminished after blockade of the nitric oxide synthesis by N(G)-nitro-L-arginine methyl ester (200 microM) and were absent in endothelium-denuded vessels. Indomethacin and hirudin did not influence the relaxant effects. The effect of trypsin but not that of SLIGRL was blocked by the proteinase inhibitor aprotinin suggesting that only proteolytically active trypsin activates the receptor. Benzamidine derivatives of the 3-amidinophenylalanine type with different affinity for trypsin and thrombin inhibited the vascular effects of trypsin (IC50 0.007-0.7 microM) correlating with its antitrypsin activity. The data suggest that the vascular effects of trypsin and SLIGRL are mediated through activation of PAR-2 which differs from the thrombin receptor.

Animals↗
PubMed1995

Structure-activity relationships of inhibitors derived from 3-amidinophenylalanine.

Thrombin is the key enzyme in coagulation and its inhibitors are of therapeutic interest since they are potential anticoagulants. The most potent inhibitor of the benzamidine type is N alpha-(2-naphthylsulfonyl-glycyl)-4-amidinophenylalanine piperidide (NAPAP). However, NAPAP and other substances designed so far do not fulfill the pharmacological requirements. The goal of designing new compounds was to obtain potent inhibitors with improved pharmacokinetic properties, such as absorption after oral application and a sustained elimination. Novel derivatives of 3-amidinophenylalanine as key building block were synthesized. The amidino moiety and both the N alpha- and the C-terminal substituents were widely varied. Some of the newly synthesized compounds are potent inhibitors of thrombin and exert improved pharmacokinetic properties.

Amidines↗
PubMed1994

Novel plasma kallikrein inhibitors of the benzamidine type.

Besides guanidino compounds and amines structurally related to arginine and lysine, compounds with an amidino moiety are inhibitors of trypsin-like enzymes. However, in most cases ordinary benzamidine derivatives are not selective inhibitors. Relatively selective inhibitors of some enzymes were found among amino acids containing a benzamidine moiety at the side chain. For example, derivatives of phenyl-alpha-aminobutyric acid with one or two amidino moieties such as the 4'-amidinoanilide of N alpha-[4-amidinophenylsulfonyl]-phenyl-alpha- aminobutyric acid are potent and selective inhibitors of plasma kallikrein (Ki = 0.15 microM). Using N alpha-arylsulfonylated 3-amidinophenylalanine as the key building block, novel inhibitors of plasma kallikrein were developed. Several esters and amides of the nipecotic acid derivative were synthesized which inhibit plasma kallikrein competitively with Ki values between 0.1 and 1.0 microM. The compounds prolonged aPTT in micromolar concentration, indicating an inhibition of the intrinsic coagulation pathway.

Benzamidines↗
PubMed1993

Inhibition of activated protein C by benzamidine derivatives.

In studies on the inhibition of activated protein C (APC) by benzamidine derivatives potent inhibitors of APC were found among anilides of 4-amidinophenyl-alpha-aminobutyric acid (Ki = 0.58 mumol/l). Several bis-benzamidine derivatives containing a cycloalkanone linking bridge inhibit APC with Ki values near the micromolar range. Potent and selective inhibitors of thrombin derived from 3- and 4-amidinophenylalanine do not inhibit APC. This is of great importance for further development of these inhibitors as potential anticoagulant drugs.

Benzamidines↗
PubMed1992

Inhibition of glandular and plasma kallikrein by benzamidine derivatives.

Besides guanidino compounds and amines structurally related to arginine and lysine, compounds with other cationic groups are inhibitors of trypsin-like serine proteinases. Particularly aromatic ring structures with an amidino moiety have high affinity for these enzymes. In most cases ordinary benzamidine derivatives are no selective inhibitors, however, among derivatives of N alpha-arylsulfonyl-omega-amidinophenyl-alpha-amino-alkylcarboxylic acids selective competitive inhibitors of several enzymes were found. Amides of phenyl-alpha-aminobutyric acid containing an amidino moiety are inhibitors of plasma kallikrein. The p-amidinoanilide of 2-tosylamino-4-phenylbutyric acid inhibits selectively plasma kallikrein with a Ki of 0.70 mumol/l. In contrast, potent and selective inhibitors of glandular kallikrein were hardly found among benzamidines.

Animals↗
PubMed1992

Inhibition of human mast cell tryptase by benzamidine derivatives.

Considerable circumstantial evidence has been provided by in vitro studies that tryptase (EC 3.4.21.59), a neutral serine proteinase stored in large amounts in mast cell granules, may play an important pathogenetic role in mast cell-dependent diseases. However, a definitive role has not yet been ascribed to this trypsin-like enzyme with restricted substrate specificity as natural or synthetic inhibitors of tryptase applicable for in vivo studies are not available so far. Therefore, we have studied structure-activity relationships for inhibition of tryptase by benzamidine derivatives, compounds known to be potent inhibitors of various trypsin-like enzymes. Among the benzamidine derivatives 4-amidinophenylpyruvic acid exerts a striking inhibitory activity with a Ki of 0.71 mumol/l. Several additional inhibitors of tryptase with Ki values in the micromolar range were found among bis-benzamidines. Derivatives of N alpha-arylsulfonyl-omega-amidinophenyl-alpha-aminoalkylcarboxylic acids are only weak inhibitors of tryptase, although members of this group are potent and selective inhibitors of several other trypsin-like enzymes. Comparison of the inhibition of tryptase and trypsin revealed that the affinities of the benzamidine derivatives to both proteinases are closely correlated (correlation coefficient r = 0.702; n = 37; p < 0.001). These results demonstrate that 4-amidinophenylpyruvic acid may be useful as a pharmacologic tool for the investigation of the (patho)physiological role of tryptase. In addition, benzamidine derivatives may be applicable to probe the active site topography of tryptase isoenzymes.

Benzamidines↗