Common variation in the C-terminal region of the fibrinogen beta-chain: effects on fibrin structure, fibrinolysis and clot rigidity.

Fibrinogen BbetaArg448Lys is a common polymorphism, positioned within the carboxyl terminus of the Bbeta-chain of the molecule. Studies suggest that it is associated with severity of coronary artery disease and development of stroke. The effects of the amino acid substitution on clot structure remains controversial, and the aim of this study was to investigate the effect(s) of this polymorphism on fibrin clot structure using recombinant techniques. Permeation, turbidity, and scanning electron microscopy showed that recombinant Lys448 fibrin had a significantly more compact structure, with thin fibers and small pores, compared with Arg448. Clot stiffness, measured by means of a novel method using magnetic tweezers, was significantly higher for the Lys448 compared with the Arg448 variant. Clots made from recombinant protein variants had similar lysis rates outside the plasma environment, but when added to fibrinogen-depleted plasma, the fibrinolysis rates for Lys448 were significantly slower compared with Arg448. This study demonstrates for the first time that clots made from recombinant BbetaLys448 fibrinogen are characterized by thin fibers and small pores, show increased stiffness, and appear more resistant to fibrinolysis. Fibrinogen BbetaArg448Lys is a primary example of common genetic variation with a significant phenotypic effect at the molecular level.

Genetic regulation of fibrin structure and function: complex gene-environment interactions may modulate vascular risk.

BACKGROUND: Polymorphisms in the fibrinogen and factor XIII genes are associated with atherothrombotic risk, but clinical studies have produced inconsistent results and laboratory studies have not explained these findings. We aimed to investigate interactions between polymorphisms in the factor XIII and fibrinogen genes, fibrinogen concentrations, and other cardiovascular risk factors in relation to fibrin structure and function. METHODS: We used permeation analysis and electron microscopy to investigate interactions between fibrin structure, factor XIII Val34Leu, fibrinogen Aalpha Thr312Ala, fibrinogen Bbeta Arg448Lys, and fibrinogen concentrations in plasma and purified systems. FINDINGS: Increased fibrinogen concentrations were associated with decreases in permeability, with tighter clot structures in the presence of factor XIII 34Val alleles compared with those in the presence of 34Leu alleles. Findings were confirmed by scanning electron microscopy of fibrin. Similar changes in permeability were noted for Aalpha fibrinogen 312Ala compared with that for 312Thr. INTERPRETATION: Our results show interactions between coding polymorphisms in fibrinogen and factor XIII and fibrinogen concentrations that modify fibrin and explain the apparent paradox between epidemiological studies of factor XIII 34Leu and reported in-vitro effects on fibrin structure and function. We suggest a potential complexity of gene-gene and gene-environment interactions in determining cardiovascular risk.

Methyl 4-hydroxy-3-(3'-methyl-2'-butenyl)benzoate, major insecticidal principle from Piper guanacastensis.

The CHCl3-soluble extract of Piper guanacastensis (Piperaceae) was found to have noteworthy insecticidal activity to Aedes atropalpus mosquito larvae (LC50 80.5 micrograms/mL). Bioassay-guided fractionation afforded methyl 4-hydroxy-3-(3'-methyl-2'-butenyl)benzoate (1) as the major bioactive constituent (LC50 20.5 micrograms/mL). The separation of compound 1 from its transesterification artifact (2), ethyl 4-hydroxy-3-(3'-methyl-2'-butenyl)benzoate, was achieved by recycling reversed-phase HPLC. The flavonoids acacetin, chrysin, and pinostrobin were also isolated from the active fraction but did not display insecticidal properties.

Insecticidal neolignans from Piper decurrens.

2,3-Dihydro-2-(4'-hydroxyphenyl)-3-methyl-5(E)-propenylbenzofuran (conocarpan) (1), 2-(4'-hydroxy-3'-methoxyphenyl)-3-methyl-5(E)- propenylbenzofuran (eupomatenoid-5) (2), and 2-(4'- hydroxyphenyl)-3-methyl-5(E)-propenylbenzofuran (eupomatenoid-6) (3), three known neolignans found for the first time in a species of the Piperaceae, were isolated from Piper decurrens via insecticidal bioassay-guided fractionation, along with a small quantity of a new related compound, 2,3-dihydro-5-formyl-2-(4'-hydroxyphenyl)-3-methylbenzofuran (decurrenal) (4), and 3,7,11,15-tetramethyl-2(E)-hexadecen-1-ol (trans-phytol).

Insecticidal defenses of Piperaceae from the neotropics.

Insecticidal and growth-reducing properties of extracts of 14 species of American neotropical Piperaceae were investigated by inclusion in diets of a polyphagous lepidopteran, the European corn borer,Ostrinia nubilalis. Nutritional indices suggested most extracts acted by postdigestive toxicity.Piper aduncum, P. tuberculatum, andP. decurrens were among the most active species and were subjected to bioassay-guided isolation of the active components. Dillapiol was isolated from the active fraction ofP. aduncum, piperlonguminine was isolated fromP. tuberculatum, and a novel neolignan fromP. decurrens. The results support other studies on Asian and AfricanPiper species, which suggest that lignans and isobutyl amides are the active defence compounds in this family.

Insecticide synergists: role, importance, and perspectives.

Synergists have been used commercially for about 50 years and have contributed significantly to improve the efficacy of insecticides, particularly when problems of resistance have arisen. In the current article we review the nature, mode of action, role in resistance management, natural occurrence, and significance in research of insecticide synergists. These natural or synthetic chemicals, which increase the lethality and effectiveness of currently available insecticides, are by themselves considered nontoxic. The mode of action of the majority of synergists is to block the metabolic systems that would otherwise break down insecticide molecules. They interfere with the detoxication of insecticides through their action on polysubstrate monooxygenases (PSMOs) and other enzyme systems. The role of synergists in resistance management is related directly to an enzyme-inhibiting action, restoring the susceptibility of insects to the chemical, which would otherwise require higher levels of the toxicant for their control. For this reason synergists are considered straightforward tools for overcoming metabolic resistance, and can also delay the manifestation of resistance. However, the full potential of these compounds may not have been realized in resistance management. Synergists have an important role to play in the ongoing investigation of insecticide toxicity and mode of action and the nature of resistance mechanism. They also can be used in understanding the effects of other xenobiotics in non-target organisms. The search for and the need of new molecules capable of synergizing existing or new pesticides has reactivated the identification and characterization of secondary plant compounds possessing such activity. Plants do possess and utilize synergists to overcome the damage produced by phytophages. This has to be exploited in pest management programs. Hopefully, it will lead to a new perspective on the nature and significance of synergism.