Role of isovaleroyl lipids in channeling of sound in the porpoise melon

Physical properties (e.g. specific gravity, adiabatic compressibility and sound velocity) of lipids isolated from tissues from contiguous areas of the fatty melon of an echo-locating porpoise (Delphinus delphis) were determined to elucidate relations between lipid composition and structure, and sound transmission in the head. Lipid content varied greatly within the melon (13.6–77.6% of the tissue weight) and triacylglycerols (80–100%) were the major lipid components. This lipid class was composed of diisovaleroylglycerides (triacylglycerols containing two isovaleroyl moieties and a long-chain acyl moiety), monoisovaleroyldiacylglycerols and triacylglycerols consisting of long-chain acids. The lipid-rich (>45%) areas in the melon contained a high proportion (>45% of total triacylglycerols) of diisovaleroylglycerides. There were gradations of sound velocities within the melon; the lowest sound velocities were associated with high concentrations of diisovaleroylglycerides (<1400 m/s) and the highest with high concentrations of long-chain triacylglycerols. Assuming an average sound frequency of 75 kHz, and considering dimensions of melon (path length and width of 12–14 cm and 5 cm, respectively), a forward radiating lobe of 15–25 degrees is produced. Thus, the deposition of lipids of different acoustic properties in a three-dimensional matrix within the porpoise melon results in a lens for the projection of sound into the marine environment.     

Quantitative studies of hydroperoxide reduction by prostaglandin H synthase. Reducing substrate specificity and the relationship of peroxidase to cyclooxygenase activities

The peroxidase activity of prostaglandin H (PGH) synthase catalyzes reduction of 5-phenyl-4-pentenyl hydroperoxide to 5-phenyl-4-pentenyl alcohol with a turnover number of approximately 8000 mol of 5-phenyl-4-pentenyl hydroperoxide/mol of enzyme/min. The kinetics and products of reaction establish PGH synthase as a classical heme peroxidase with catalytic efficiency similar to horseradish peroxidase. This suggests that the protein of PGH synthase evolved to facilitate peroxide heterolysis by the heme prosthetic group. Comparison of an extensive series of phenols, aromatic amines, beta-dicarbonyls, naturally occurring compounds, and nonsteroidal anti-inflammatory drugs indicates that considerable differences exist in their ability to act as reducing substrates. No correlation is observed between the ability of compounds to support peroxidatic hydroperoxide reduction and to inhibit cyclooxygenase. In addition, the resolved enantiomers of MK-410 and etodolac exhibit dramatic enantiospecific differences in their ability to inhibit cyclooxygenase but are equally potent as peroxidase-reducing substrates. This suggests that there are significant differences in the orientation of compounds at cyclooxygenase inhibitory sites and the peroxidase oxidation site(s). Comparison of 5-phenyl-4-pentenyl hydroperoxide reduction by PGH synthase and horseradish peroxidase reveals considerable differences in reducing substrate specificity. Both the cyclooxygenase and peroxidase activities of PGH synthase inactivate in the presence of low micromolar amounts of hydroperoxides and arachidonic acid. PGH synthase was most sensitive to arachidonic acid, which exhibited an I50 of 0.6 microM in the absence of all protective agents. Inactivation by hydroperoxides requires peroxidase turnover and can be prevented by reducing substrates. The I50 values for inactivation by 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid are 4.0 and 92 microM, respectively, in the absence and presence of 500 microM phenol, a moderately good reducing substrate. The ability of compounds to protect against hydroperoxide-induced inactivation correlates directly with their ability to act as reducing substrates. Hydroquinone, an excellent reducing substrate, protected against hydroperoxide-induced inactivation when present in less than 3-fold molar excess over hydroperoxide. The presence of a highly efficient hydroperoxide-reducing activity appears absolutely essential for protection of the cyclooxygenase capacity of PGH synthase. The peroxidase activity is, therefore, a twin-edged sword, responsible for and protective against hydroperoxide-dependent inactivation of PGH synthase.(ABSTRACT TRUNCATED AT 400 WORDS)     

1-Methyl-4-phenylpyridine (MPP+) induces oxidative stress in the rodent

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) produces an irreversible parkinsonism in primates. Recent evidence suggests metabolism of MPTP to 1-methyl-4-phenylpyridine (MPP+) is required for toxicity. We have proposed that MPP+ may play a central role in the toxicity of MPTP, but direct assessment of the effects of MPP+ in brain is difficult. Therefore, we have sought to define the mechanism of peripheral MPP+ toxicity in the rat and mouse. Systemically administered MPP+ produced its major pathology in the lung and was typified by perivascular edema. An increase in plasma glutathione disulfide concentrations also resulted, suggesting that MPP+ in analogy to paraquat produces oxidative stress. In addition, the lethality of MPP+ in the mouse was increased by dietary selenium deficiency. These results define in both pathological and chemical terms the potent systemic toxicity of MPP+ and suggest that MPP+, because of its high concentration in primate brain, has the potential to play an important role in the CNS toxicity of MPTP.     

Spectral properties of the higher oxidation states of prostaglandin H synthase

Prostaglandin H (PGH) synthase reacts with organic hydroperoxides and fatty acid hydroperoxides on a millisecond time scale to generate an intermediate that is spectrally similar to compound I of horseradish peroxidase. Compound I of PGH synthase is converted to compound II within 170 ms. Compound II decays to resting enzyme in a few seconds. Thus, the peroxidase reaction of PGH synthase appears to involve a cycle of native enzyme, compound I, and compound II, typical of heme-containing peroxidases. The Soret absorption maximum of compound I appears to occur at 412 nm but a small amount of compound II may be present. Soret maxima occur at 420, 433, and 419 for compound II, the ferrous enzyme, and the oxyferrous enzyme (compound III), respectively. Rapid scan analysis of the reaction of PGH synthase with arachidonic acid reveals the absorbance of compound II but no evidence for ferrous or oxyferrous enzyme.     

Development of catecholaminergic phenotypic characters in the mouse locus coeruleus in vivo and in culture

While abundant studies have begun to elucidate ontogeny of the peripheral nervous system, molecular mechanisms underlying brain development remain obscure. To approach this problem, we initiated parallel in vivo and in vitro studies of the mouse locus coeruleus (l.c.), a brainstem noradrenergic nucleus. The catecholaminergic enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) were used to monitor phenotype expression and development. TH catalytic activity and immunocytochemical reactivity were initially detectable on gestational Day 13 (E-13) in vivo, and adult levels of activity were approximately by the third postnatal week. Immunotitration studies indicated that the developmental increase was due to accumulation of enzyme molecules and not enzyme activation. The in vivo developmental profile of DBH approximated that of TH. To begin defining regulatory mechanisms, explants of embryonic brainstem were placed in culture. Explantation on E-12, prior to expression of TH or DBH, resulted in the de novo appearance of these phenotypic characters after 4 days. Explantation on E-18, after the enzymes are already expressed, was followed by a striking sixfold rise in TH activity. Immunotitration studies revealed that the increase in TH activity in E-18 cultures was attributable to increased molecule number, reproducing the in vivo results. Moreover, the E-18 explants, cultured for 3 weeks, attained higher plateau levels of TH activity than E-12 cultures, and this differences was due to increased molecule number. Morphometric analysis indicated that 3-week E-12 cultures actually had more l.c. cells than E-18 cultures, indicating that differences in TH were not due to increased cells in the E-18 l.c. Finally, systemic study revealed that the development of TH activity in culture increased progressively from E-11 to E-12 to E-13, suggesting that critical regulatory events occur at this time. Our studies suggest that the l.c. is an excellent model for the study of brain development in vivo and in vitro. Initial phenotypic expression and dramatic development occur in culture in the absence of normal targets, normal afferent innervation and, presumably, normal humoural milieu.     

Brain and Plasma Quinolinic Acid in Profound Insulin-Induced Hypoglycemia

Profound insulin-induced hypoglycemia is associated with early-onset neuronal damage that resembles excitotoxic lesions and is attenuated in severity by antagonists of N-methyl-D-aspartate receptors. Hypoglycemia increases L-tryptophan concentrations in brain and could increase the concentration of the L-tryptophan metabolite quinolinic acid (QUIN), an agonist of N-methyl-D-aspartate receptors and an excitotoxin in brain. Therefore, we investigated the effects of 40 min of profound hypoglycemia (isoelectric EEG) and 1-2 h of normoglycemic recovery on the concentrations of QUIN in brain tissue, brain extracellular fluid, and plasma in male Wistar rats. Plasma QUIN increased 6.5-fold by the time of isoelectricity (2 h after insulin administration). Regional brain QUIN concentrations increased two- to threefold during hypoglycemia and increased a further two- to threefold during recovery. However, no change in extracellular fluid QUIN concentrations in hippocampus occurred during hypoglycemia or recovery as measured using in vivo microdialysis. Therefore, the increases in brain tissue QUIN concentrations may reflect elevations of QUIN in the intracellular space or be secondary to the increases in QUIN in the vascular compartment in brain per se. L-Tryptophan concentrations increased more than twofold during recovery only. Serotonin decreased greater than 50% throughout the brain during hypoglycemia, while 5-hydroxyindoleacetic acid concentrations increased more than twofold during hypoglycemia and recovery. In striatum, dopamine was decreased 75% during hypoglycemia but returned to control values during recovery, while striatal 3,4-dihydroxyphenylacetic acid and homovanillic acid were increased more than twofold during both hypoglycemia and recovery.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prolonged changes in plasma concentrations of catecholamine metabolites following a single infusion of an MPTP analog

The magnitude and duration of effects of a single intravenous injection of 4'-amino MPTP, an analogue of the dopamine neurotoxin, MPTP, on plasma levels of catechols and normetanephrine were examined in conscious dogs. Plasma samples were collected prior to treatment with intravenous saline or 4'-amino MPTP.2HCl (22.5 mg/kg) and at weekly intervals for six weeks following treatment. Saline treatment had no effect on plasma levels of any of the measured compounds. Following 4'-amino MPTP, plasma DHPG fell to 14% of the pre-injection value and remained decreased for the full 6-week test period, with partial recovery by week 6 to 42% of the pre-injection value. Plasma DOPAC levels fell to 28% of pre-injection values 1 week after treatment with 4'-amino MPTP and showed no evidence of recovery during the 6-week test period. Plasma DOPA fell to 58% of the pre-injection level, while concentrations of the catecholamines NE, EPI, and DA were generally unaffected. The plasma concentration of the O-methylated NE metabolite, normetanephrine, was also unchanged by 4'-amino MPTP treatment. There were no differences in the concentrations of DA, NE or EPI within the adrenal medulla between saline and 4'-amino MPTP treated groups. This pattern of changes in plasma levels of catechols, which is consistent with presynaptic inhibition of MAO within sympathetic terminals, may be a useful indicator of exposure to MPTP-like neurotoxins.     

Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves

A puzzling population-genetic phenomenon widely reported in allozyme surveys of marine bivalves is the occurrence of heterozygote deficits relative to Hardy-Weinberg expectations. Possible explanations for this pattern are categorized with respect to whether the effects should be confined to protein-level assays or are genomically pervasive and expected to be registered in both protein- and DNA-level assays. Anonymous nuclear DNA markers from the American oyster were employed to reexamine the phenomenon. In assays based on the polymerase chain reaction (PCR), two DNA-level processes were encountered that can lead to artifactual genotypic scorings: (a) differential amplification of alleles at a target locus and (b) amplification from multiple paralogous loci. We describe symptoms of these complications and prescribe methods that should generally help to ameliorate them. When artifactual scorings at two anonymous DNA loci in the American oyster were corrected, Hardy-Weinberg deviations registered in preliminary population assays decreased to nonsignificant values. Implications of these findings for the heterozygote-deficit phenomenon in marine bivalves, and for the general development and use of PCR-based assays, are discussed.      

Monocarbonyl Analogs of Curcumin with Potential to Treat Colorectal Cancer

Curcumin has a plethora of biological properties, making this compound potentially effective in the treatment of several diseases, including cancer. However, curcumin clinical use is compromised by its poor pharmacokinetics, being crucial to find novel analogs with better pharmacokinetic and pharmacological properties. Here, we aimed to evaluate the stability, bioavailability and pharmacokinetic profiles of monocarbonyl analogs of curcumin. A small library of monocarbonyl analogs of curcumin 1a–q was synthesized. Lipophilicity and stability in physiological conditions were both assessed by HPLC-UV, while two different methods assessed the electrophilic character of each compound monitored by NMR and by UV-spectroscopy. The potential therapeutic effect of the analogs 1a–q was evaluated in human colon carcinoma cells and toxicity in immortalized hepatocytes. Our results showed that the curcumin analog 1e is a promising agent against colorectal cancer, with improved stability and efficacy/safety profile.     

Sampling properties of DNA sequence data in phylogenetic analysis

We inferred phylogenetic trees from individual genes and random samples of nucleotides from the mitochondrial genomes of 10 vertebrates and compared the results to those obtained by analyzing the whole genomes. Individual genes are poor samples in that they infrequently lead to the whole-genome tree. A large number of nucleotide sites is needed to exactly determine the whole-genome tree. A relatively small number of sites, however, often results in a tree close to the whole-genome tree. We found that blocks of contiguous sites were less likely to lead to the whole-genome tree than samples composed of sites drawn individually from throughout the genome. Samples of contiguous sites are not representative of the entire genome, a condition that violates a basic assumption of the bootstrap method as it is applied in phylogenetic studies.