A new general solid-phase method for the synthesis of backbone-to-backbone cyclized peptides

A model peptide with the sequences Ala-Pro-Lys(2ClZ)-Tyr(2BrZ) was synthesized on a 4-methylbenzhydryl amine (MBHA) polystyrene resin using conventional Boc/benzyl protective group strategy. The amino acid aldehyde Boc-valinal was coupled by reductive alkylation with NaCNBH₃ in acidified DMF for 1 h. The secondary amine in the peptide-resin Boc-Valψ[CH₂NH]Ala-Pro-Lys(2CIZ)-Tyr(2BrZ)-MBHA was reductively alkylated by 3(4-methylbenzylthio)-propanal at 40 °C for 6 h, resulting the peptide-resin Boc-Valψ[CH₂N(CH₂CH²CH₂-S-pMeBzl)]Ala-Pro-Lys(2ClZ)-Tyr(2BrZ)-MBHA. After the removal of the Boc group the synthesis was continued employing the above-mentioned methods, which led to the resin-bound peptide Leuψ[CH₂N(CH₂CH₂CH₂S-pMeBzl)]Ser-Pro-Gly-Lys(2ClZ)-Valψ[CH₂N(CH₂CH₂CH₂-S-pMeBzl)]Ala-Pro-Lys(2ClZ)-Tyr(2BrZ)-MBHA. The peptide was cleaved from the resin with hydrogen fluoride. Reversed-phase HPLC and plasma desorbtion mass spectrometry analysis showed that the expected peptide Leuψ[CHIN(CH₂CH₂CH₂SH)ISer-Pro-Gly-Lys-Valψ[CH₂N(CH₂CH₂CH₂-SH)]Ala-Pro-Lys-Tyr-NH₂ was obtained as the major product with low levels of side products. Intramolecular oxidation of the thiols gave the backbone to backbone cyclized peptide Leuψ[CH₂N(CH₂CH₂CH₂S)]Ser-Pro-Gly-Lys-Valψ[CH₂N(CH₂CH₂CH₂-S)]A1a-Pro-Lys-Tyr-NH₂.     

HEPATOTOXICITY AND ABSORPTION OF EXTRAHEPATIC ACETALDEHYDE IN RATS

Acetaldehyde, the first metabolite of ethanol oxidation, has been proposed as a major initiating factor in ethanol-induced liver injury. The aims of this study were to examine whether acetaldehyde is absorbable from the digestive tract and whether, when delivered chronically in drinking water, it is capable of inducing liver injury in rats. Acetaldehyde concentrations in the rat portal and peripheral blood were measured by head space gas chromatography after intragastric (5 ml) and intracolonic (3 ml) administration of 20 mM acetaldehyde solution. In the hepatotoxicity study, rats were exposed to acetaldehyde (20 and 120 mM ) delivered in drinking water for 11 weeks and histopathological changes in the liver were morphometrically assessed. Peak blood acetaldehyde levels were found at 5 min after acetaldehyde infusion and were 235±11 μμ (mean±SE) after intragastric and 344±83 μμ after intracolonic infusion of 20 mM acetaldehyde solution. The exposure of rats to 120 mM acetaldehyde solution for 11 weeks resulted in the development of fatty liver and inflammatory changes. Morphometric analysis showed significantly more fat accumulation in rats receiving 120 mM acetaldehyde solution (85±2 per cent of hepatocytes occupied by fat) than in rats receiving 20 mM acetaldehyde solution (38±11 per cent) or in controls (36±10 per cent). The dose of extrahepatic acetaldehyde (500 mg/kg per day) producing liver injury corresponds to only around 3 per cent of that derived from hepatic ethanol oxidation in animals receiving an ethanol-containing totally liquid diet (15 g/kg per day). These results indicate that acetaldehyde delivered via the digestive tract can reach the liver by the portal circulation and that acetaldehyde of extrahepatic origin appears to be more hepatotoxic than acetaldehyde formed during ethanol oxidation within the liver.     

Group IIA phospholipase A2 as a prognostic marker in prostate cancer: relevance to clinicopathological variables and disease‐specific mortality

Group IIA Phospholipase A₂ (PLA2‐IIA), a key enzyme in arachidonic acid and eicosanoid metabolism, participates in a variety of inflammatory processes but possibly also plays a role in tumor progression in vivo. Our aim was to determine the mRNA and protein expression of PLA2‐IIA during prostate cancer progression in localized and metastatic prostate tumors. We evaluated the prognostic significance of PLA2‐IIA expression in biochemical recurrence, clinical recurrence and disease‐specific survival after surgical treatment. The expression of PLA2‐IIA was examined by immunohistochemistry and chromogenic in situ hybridization in tissue microarrays of radical prostatectomy specimens and advanced/metastatic carcinomas. The expression data were analyzed in conjunction with clinical follow‐up information and clinicopathological variables. The mRNA and protein expression of PLA2‐IIA was significantly increased in Gleason pattern grade 2–4 carcinomas compared with benign prostate (p‐values 0.042–0.001). In metastases, the expression was significantly lower than in local cancers (p=0.001). The PLA2‐IIA expression correlated positively with Ki‐67 and α‐methylacyl CoA racemase (AMACR) expression. The prognostic evaluation revealed decreased PLA2‐IIA protein expression among patients who had died of prostate cancer. In conclusion, PLA2‐IIA expression is increased in carcinoma when compared with benign prostate. However, metastatic carcinoma showed decreased expression of PLA2‐IIA when compared with primary carcinomas. PLA2‐IIA may serve as a marker for highly proliferating, possibly poorly differentiated prostate carcinomas. The protein expression of PLA2‐IIA may be diminished in patients who consequently die of prostate cancer.