Suicidal oxidative stress induced by certain antioxidants

Well known antioxidants-coumarins (7,8-dihydroxy-4-methyl coumarin-DHMC and 7,8-diacetoxy-4-methyl coumarin-DAMC) and flavonoids (quercetin-Q and quercetin penta-acetate-QPA) were investigated for their pro-oxidant effects in two human tumor cell lines. The breast carcinoma cell line (MDA-MB-468) was found to be more sensitive to treatment by the drugs-DAMC, Q and QPA at 10 microM than the glioma cell line (U-87MG), while DHMC was non toxic in both cell lines at this concentration. In MDA-MB-468 distinct growth inhibition was observed by 48 hr post treatment. Paradoxically, an increase in the formazan production was revealed by MTT assay at this time indicating an increase in the production of free radicals. An increase in the levels of reactive oxygen species (ROS) was also confirmed by DCFH-DA assay. In cells treated with DAMC, Q and QPA an increase in the percentage of cells with the hypodiploid DNA content was suggestive of apoptotic cell death. Taken together, these results suggest that an increase in oxidative stress caused by the pro-oxidant action of these drugs is responsible for cell death.     

Prevention of cecitis in hamsters by certain prostaglandins

Acute inflammation of the colon (cecitis) was produced in hamsters by daily subcutaneous administration of an antibiotic for 3 days. The following prostaglandins completely prevented the cecitis: 16,16-dimethyl-PGE2, 15(R)-15-methyl-PGE2, and 2-acetyl-2-decarboxy-15(S)-15-methyl-PGF2 alpha. PGF2 beta was less active. The synthesis of 2-acetyl-2-decarboxy-15(S)-methyl-PGF2 alpha is described. Castor oil also prevented the cecitis and peanut oil exerted partial protection. Since these oils contain linoleic acid, a precursor of PGE1, protection may have been due to endogenous formation of that prostaglandin. A partial block of the protective effect of castor oil by treatment with indomethacin supports such mechanism. The tissue level of endogenous prostaglandins seems to exert protection since administration of cyclooxygenase inhibitors, indomethacin and aspirin, markedly increased the incidence of cecitis. Magnesium sulfate given orally and sodium salicylate given subcutaneously reduced the incidence of cecitis only partially. The following agents were inactive: loperamide, an antidiarrheic agent; carbachol, a cholinergic and diarrheogenic agent, atropine, an anticholinergic agent; and acetazolamide, a carbonic anhydrase inhibitor. These results, show that certain prostaglandins, which have been shown earlier to be cytoprotective for the stomach and the small intestine, are cytoprotective for the large intestine as well.     

Inhibition of enkephalin-degrading aminopeptidase activity by certain peptides

The degradation of Leu-enkephalin by an aminopeptidase in rat whole brain supernatant was inhibited by two brain peptides and two bacterial peptides. The bacterial peptides, amastatin and bestatin, were slightly more potent than somatostatin and substance P (SP). Amastatin and bestatin exhibited non-competitive kinetics; somatostatin and SP were competitive inhibitors. It is suggested that the known analgesic properties of somatostatin and SP when injected intraventricularly may be due to inhibition of degradation of endogenous opioid peptides.     

Ketogenic regulation by certain metabolites in rumen epithelium

In experiments with rumen epithelium incubated in vitro in the presence of butyrate, the ketogenic effect of glucose was shared by epimeric monosaccharides but not by non-metabolizable analogues. 14C from glucose was not incorporated into ketone bodies. Malate increased ketogenesis from butyrate and decreased its oxidation, pyruvate and NH4+ had the opposite effect, and malonate inhibited both processes. The ketogenic effect of glucose was also effective with isovalerate maintaining the high proportion of acetoacetate which is characteristic of this substrate. Rumen epithelium transformed added acetoacetate into 3-hydroxybutyrate. It is concluded that reducing equivalents produced from glucose and other metabolizable substrates are responsible regulators of ketogenesis from butyrate. The results are discussed in view of the functional role of ruminal ketogenesis.     

Prevention of cecitis in hamsters by certain prostaglandins

Acute inflammation of the colon (cecitis) was produced in hamsters by daily subcutaneous administration of an antibiotic for 3 days. The following prostaglandins completely prevented the cecitis: 16,16-dimethyl-PGE₂, 15(R)-15-methyl-PGE₂, and 2-acetyl-2-decarboxy-15(S)-15-methyl-PGE_2α. PGF_2β was less active. The synthesis of 2-acetyl-2-decarboxy-15(S)-15-methyl-PGF_2α is described.Castor oil also prevented the cecitis and peanut oil exerted partial protection. Since these oils contain linoleic acid, a precursor of PGE₁, protection may have been due to endogenous formation of that prostaglandin. A partial block of the protective effect of castor oil by treatment with indomethacin supports such mechanism. The tissue level of endogenous prostaglandins seems to exert protection since administration of cyclooxygenase inhibitions, indomethacin and aspirin, markedly increased the incidence of cecitis. Magnesium sulfate given orally and sodium salicylate given subcutaneously reduced the incidence of cecitis only partially. The following agents were inactive: loperamide, an antidiarrheic agent; carbachol, a cholinergic and diarrheogenic agent, atropine, an anticholinergic agent; and acetazolamide, a carbonic anhydrase inhibitor.These results show that certain prostaglandins, which have been shown earlier to be cytoprotective for the stomach and the small intestine, are cytoprotective for the large intestine as well.