Formaldehyde activation factor, tetrahydromethanopterin, a coenzyme of methanogenesis

An oxygen-labile formaldehyde activation factor (FAF) was isolated in highly purified form by use of anoxic fractionation procedures. The molecular weight of FAF was determined to be 776 and that of methanopterin (MPT) 772 by fast-atom-bombardment mass spectrometry (FABMS). High-resolution FABMS measurements on MPT and FAF indicated molecular formulas of C(30)H(41)N(6)O(16)P and C(30)H(45)N(6)O(16)P, respectively. The presence of phosphorus was confirmed by 100-MHz (31)P NMR. The 360-MHz (1)H NMR spectrum of FAF in deuterium oxide was similar to that of MPT. A functional relationship between MPT and FAF was documented; both compounds stimulated the reductive demethylation of 2-(methylthio)ethanesulfonic acid (CH(3)-S-CoM) to CH(4) when formaldehyde oxidation provided a source of electrons, and FAF replaced MPT in the CH(3)-S-CoM-stimulated conversion of CO(2) to CH(4) under H(2) (the RPG effect). MPT was enzymically converted to FAF during the reduction of CH(3)-S-CoM, and HCHO to CH(4) under H(2). Evidence indicates that FAF is tetrahydromethanopterin.

Secondary metabolites from marine organisms

Marine macroorganisms and microorganisms, like terrestrial species, produce a dizzying array of secondary metabolites, including terpenes, steroids, polyketides, peptides, alkaloids and porphyrins. Most of the marine metabolites are found in terrestrial species as such or have close counterparts in land-based species, but some are sufficiently unusual to constitute a separate class (e.g. marine sterols). Although in many cases the functions of these secondary metabolites in the marine species themselves are unclear, other compounds play well-defined roles-for example as trail markers, sexual attractants, antifouling substances or antifeedants. What is clear is that many of the most interesting marine secondary metabolites have potent activities largely unrelated to their in situ roles. Examples abound of antitumour, antiviral, immunosuppressive and antimicrobial agents, as well as neurotoxins, hepatotoxins and cardiac stimulants. Relatively few biosynthetic studies of marine secondary metabolites have been done because of the logistical problems of working under water and the primitive state of techniques for growing marine invertebrates in culture. However, recent studies indicate that many compounds isolated from marine macrospecies (e.g. sponges) may instead be produced by microorganisms (e.g. bacteria or phytoplankton). Studies of these symbionts may facilitate efforts to understand the biosyntheses of these metabolites.

Hamigerols A and B, unprecedented polysulfate sterol dimers from the Mediterranean sponge Hamigera hamigera

Two novel polysulfate sterol dimers, hamigerols A (1) and B (2), have been isolated from the Mediterranean sponge Hamigera hamigera. Their structures and stereochemistry have been assigned from the analysis of spectroscopic data.

Myriaporones 1-4, cytotoxic metabolites from the Mediterranean bryozoan Myriapora truncata

Four novel polyketide-derived metabolites, myriaporones 1, 2, 3, and 4, have been isolated from the Mediterranean bryozoan Myriapora truncata. Their structures and stereochemistry have been assigned from the analysis of spectroscopic data. The inseparable equilibrium mixture of myriaporones 3 and 4 showed 88% inhibition of L1210 murine leukemia cells at 0.2 microg/mL.

Fate of tritiated didemnin B in mice: excretion and tissue concentrations after an intraperitoneal dose

Didemnin B has undergone trials in cancer patients, and has antiviral and immunosuppressive properties. [(3)H]didemnin B was administered intraperitoneally (i.p.) to mice at 320 or 1280 microg/kg. Urine and feces were collected until 168 h, at which time the mice were killed and tissues collected. Additionally, [(3)H]didemnin B was given i.p. at 320 microg/kg, and mice were killed at 1-120 h post-dosing. Radiolabel increased rapidly in blood then rapidly declined. Most radiolabel in urine, feces and tissues represented parent compound. Concentrations of [(3)H]didemnin B were greatest in the liver > gallbladder > lower digestive tract congruent with pancreas > spleen > kidney congruent with adipose tissue congruent with urinary bladder with urine. The pancreas had the longest terminal half-life of the tissues and the highest radioactivity at 7 days. Intermediate concentrations were in the duodenum congruent with jejunum > lung > iliopsoas > stomach congruent with testes congruent with skin > heart. Low concentrations were in the humerus congruent with femur congruent with quadriceps congruent with triceps >> brain. Fecal excretion accounted for 45.9%-58.3% of the dose and declined after 24 h, followed by an increase, suggesting possible enterohepatic recycling or an impact of circadian rhythms. Urinary excretion accounted for 18.4%-25.2% of the dose, but was minimal after 24 h. The concentrations were highest in organs previously found to be sensitive in animals and humans. Didemnin B should be evaluated in animal models for treatment of pancreatic cancer.

Stereochemistry of kahalalide F

The stereochemistry of the amino acids in the marine-derived cyclic depsipeptide kahalalide F has been defined by a series of degradation reactions (hydrolysis, ozonolysis, Edman degradation, and Marfey derivatization), yielding smaller fragments of the marine natural product. The results from these reactions agree with the structure originally proposed by Hamann and Scheuer and with the same stereochemistry of most of the component amino acids more recently proposed by Goetz, Yoshida, and Scheuer. However, our assignments of d-Val(3) and l-Val(4) are the reverse of previous assignments made as l-Val(3) and d-Val(4). The present (reversed) stereochemistry is crucial for the antitumor activity of kahalalide F.

Illudin S, the sole antiviral compound in mature fruiting bodies of Omphalotus illudens

Crude extracts from the fruiting bodies of Omphalotus illudens displayed activity in the HSV-I/CV-1 antiviral assay. Bioactivity-guided isolation led to the known compound illudin S (1) as the sole antiviral component present in these extracts.

Human intoxication by microcystins during renal dialysis treatment in Caruaru-Brazil

In February 1996, an outbreak of illness occurred at a hemodialysis clinic in Caruaru, Pernambuco State-Brazil. At this clinic 116 (89%) of 131 patients experienced visual disturbances, nausea, vomiting, and muscle weakness, following routine haemodialysis treatment. Subsequently, 100 patients developed acute liver failure. As of December 1996, 52 of the deaths could be attributed to a common syndrome now called 'Caruaru Syndrome'. Examination of previous years' phytoplankton counts showed that cyanobacteria were dominant in the water supply reservoir since 1990. Analyses of carbon and other resins from the clinic's water treatment system plus serum and liver tissue of patients led to the identification of two groups of hepatotoxic cyanotoxins: microcystins (cyclic heptapeptides) in all of these samples and cylindrospermopsin (alkaloid hepatotoxic) in the carbon and resins. Comparison of victims symptoms and pathology with animal studies on these two cyanotoxins, leads us to conclude that the major contributing factor to death of the dialysis patients was intravenous exposure to microcystins, specifically microcystin-YR, -LR and -AR. In 2000, a review of the Brazilian regulation for drinking water quality, promoted by Brazilian Health Ministry with collaboration of PAHO, incorporated cyanobacteria and cyanotoxins into this new regulation as parameters that must to be monitored for water quality control.

Rat and human liver cytochrome P-450 isoform metabolism of ecteinascidin 743 does not predict gender-dependent toxicity in humans

Ecteinascidin 743 (ET743, NSC648766) is a marine natural product with potent in vivo activity in human xenograft models. Hepatotoxicity was the most prominent toxicity in preclinical studies and was greater in female rats than in male rats. To assess the potential implications for human toxicities, the in vitro metabolism of ET743 was characterized using rat and human preparations. NADPH-dependent ET743 metabolism was greater with male rat liver microsomal preparations than with preparations from female rats and was induced by pretreatment of rats with phenobarbital and dexamethasone but not by pretreatment with 3-methylcholanthrene. Rat and human microsomal metabolism of ET743 was reduced in the presence of chemical CYP3A inhibitors or antirat CYP3A2 antiserum and to a much lesser extent by CYP2E, CYP2C, and CYP2A inhibitors. In human liver panel studies, ET743 disappearance was highly correlated with CYP3A activities and to a lesser extent with CYP2C activities. ET743 was metabolized by a number of cDNA-expressed rat P-450 isoforms, including male-predominant CYP2A2 and CYP3A2. ET743 was metabolized by cDNA-expressed human CYP3A4 and to a much lesser extent by CYP2C9, CYP2D6, and CYP2E1 preparations. Three oxidative metabolites were detected in cDNA-expressed isoform incubations, including the N-demethylated metabolite ET729 and two additional products characterized by laser capture-mass spectrometry analyses. The plasma pharmacokinetics and biliary excretion of ET743 were characterized in rats. There were no gender-dependent differences in half-life or total body clearance values. Although very modest, the biliary excretion of ET743 in male rats (0.48%) was greater than in female rats (0.28%). In contrast, the biliary excretion of the cytotoxic N-demethylated metabolite ET729 was 5-fold greater in the female rat (1.05% of dose) than in the male rat (0.19% of dose). Biliary excretion of ET729 may contribute to the hepatic toxicity in rats. These data are consistent with a major role for CYP3A isoforms in ET743 rat and human metabolism. Although there are conflicting data in the literature, expression of CYP3A isoforms in human tissues and elimination of CYP3A substrates have not been shown to vary substantially by gender. There are no indications that the other CYP isoforms implicated in ET743 metabolism are expressed differently in males and females. Thus, although it is not possible to rule out gender differences in ET743 human toxicities, our data do not predict major gender-dependent differences in the toxicity of ET743 based on metabolism.