Variability of metabolism and function of sterols in insects.
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Alkylation↗
Biomedical subjects
J A Svoboda
Publications and source records attributed to J A Svoboda.
The effect of some Solanum steroidal alkaloids and glycoalkaloids on larvae of the red flour beetle, Tribolium castaneum, and the tobacco hornworm, Manduca sexta.
Evaluation of the inhibitory effect of a series of secondary plant compounds including steroidal alkaloids and glycoalkaloids on larvae of the red flour beetle, Tribolium castaneum, was investigated. Larval growth was inhibited on artificial diets containing 1 mumol g-1 diet of the glycoalkaloids solamargine, solasonine and tomatine, whereas the corresponding aglycones solasodine and tomatidine, and also tomatidenol, were inactive. The inhibitory effect of solamargine and tomatine, but not of solasonine, was completely abolished by addition of 1 mumol g-1 diet cholesterol and/or sitosterol. Nonetheless, synthetic cholesteryl tomatide displayed significant activity at 2 mumol g-1 diet. Parallel studies with the tobacco hornworm, Manduca sexta, showed marked inhibitory activity of tomatine at a dietary concentration of 1 mumol g-1, whereas the other compounds did not affect sterol metabolism or larval development. An appraisal of the factors influencing the mode of action of the active steroidal glycoalkaloids is attempted.
Alkaloids↗
Effect of insect-growth-disrupting amines and amides on Schistosoma mansoni in vitro.
A series of nonsteroidal alkylamines and alkylamides, which apparently inhibit phytosterol dealkylation in insects and free-living nematodes, as well as steps in the ecdysteroid biosynthetic pathway of insects, are also known to affect growth and development of animal-parasitic nematodes. The effect of these compounds on the motility, pairing, and viability of the trematode, Schistosoma mansoni, maintained in vitro was examined by incorporating the potential inhibitors into the medium employed for parasite culture. The alkylamines were more active than their amide counterparts, killing all parasites within 18 hr when tested at 25 parts per million. At lower concentrations, reductions in schistosome pairing and motility were observed. The functional group of the amine compounds influenced the schistosomicidal activity, with N-ethylamines being more effective than N,N-dimethylamines of identical carbon chain-length. Of all the compounds tested, N-ethyldodecanamine appeared to be the most promising schistosomicidal agent, killing all parasites within 22 hr at 10 parts per million and preventing parasite pairing at 3 parts per million.
Amides↗
Degradation of pheromone biosynthesis-activating neuropeptide (PBAN) by hemolymph enzymes of the tobacco hornworm, Manduca sexta, and the corn earworm, Helicoverpa zea.
The tritium-labeled bis-norleucine analog of Helicoverpa zea pheromone biosynthesis-activating neuropeptide ([3H]NLPBAN) was incubated in vitro with hemolymph from Manduca sexta or H. zea adult females. The incubations resulted in the formation of several tritium-labeled degradation products. At a [3H]NLPBAN concentration of 0.9 microM the degradation proceeded at a very slow but physiologically plausible rate (2-10 fmol/min/microliters hemolymph). The primary [3H]NLPBAN degradation reaction in M. sexta hemolymph was not inhibited by 20 microM leupeptin, 0.1 mM amastatin, 1 mM EDTA, 1 mM EGTA, 1 mM 1,10-phenanthroline, or 2 mM 4-(2-aminoethyl)benzenesulfonyl fluoride; but secondary reactions may have been affected, as some of the inhibitors changed the radio-HPLC profile of the degradation products. It is concluded that hemolymph of M. sexta and H. zea contains peptidase(s) capable of inactivating circulating PBAN.
Amino Acid Sequence↗
Comparative studies of metabolism of 4-desmethyl, 4-monomethyl and 4,4-dimethyl sterols in Manduca sexta.
To investigate the metabolism and possible deleterious effects of 4-methyl and 4,4-dimethyl steroids in Manduca sexta, the 4,4-dimethyl sterols lanosterol and cycloartenol, the 4-methyl sterol obtusifoliol and the 4,4-dimethyl pentacyclic triterpenoid alpha-amyrin were fed in an artificial agar-based diet at various concentrations. Utilization and metabolism of these four compounds were compared with sitosterol, stigmasterol, brassicasterol, ergosterol and 24-methylenecholesterol, 24-alkyl sterols that are readily dealkylated and converted to cholesterol in Manduca and in most phytophagous insects. None of the 4-methylated compounds significantly inhibited development except at very high dietary concentrations. The delta 24-bonds of lanosterol and cycloartenol were effectively reduced by the Manduca delta 24-sterol reductase enzyme, as is the delta 24-bond of desmosterol which, in most phytophagous insects, is an intermediate in the conversion of sitosterol, stigmasterol and other C28 and C29 phytosterols to cholesterol. On the other hand, the 24-methylene substituent of obtusifoliol was not dealkylated. Each of the 4-desmethyl C28 and C29 sterols was readily converted to cholesterol, and a significant amount of 7-dehydrocholesterol was derived from ergosterol metabolism. The reason for the differences in substrate specificity of these sterols is not clear, but the information may be useful in the development of new, specific, mechanism-based inhibitors of sterol metabolism.
Animals↗
Sterol metabolism in the tobacco hornworm, Manduca sexta--a review.
A number of intermediates involved in the dealkylation and conversion of the major C28 and C29 phytosterols to cholesterol in insects were first isolated and identified in studies with the tobacco hornworm, Manduca sexta, carried out in our laboratory. We also investigated the effects of a variety of known sterol metabolism inhibitors in Manduca, particularly those affecting the delta 24-sterol reductase enzyme, and synthesized and tested a number of new inhibitors as well. In-depth studies of ecdysteroids in Manduca during embryogenesis and during pupal-adult development provided new information on molting hormone content, biosynthesis, and metabolism. In addition, this insect has been utilized in the study of three specific enzyme systems of ecdysteroid metabolism, namely 20-monooxygenase, 3-epimerase, and phosphotransferase, which are critical to activation and deactivation of molting hormones in insects.
Animals↗
Ecdysteroid production in Drosophila melanogaster reared on defined diets.
Larvae of Drosophila melanogaster were reared aseptically on defined diets containing either cholesterol, campesterol or sitosterol as the only dietary sterol. Sterol analyses of pupae revealed that insects reared on campesterol and sitosterol diets contained 3.3 and 8.1% cholesterol, indicative of an ability to accumulate this sterol. Ecdysone and 20-hydroxyecdysone were the predominant ecdysteroids in insects from all diet studies, though makisterone A was detected in pupae reared on campesterol and sitosterol.
Animals↗
Liquid scintillation counting of tritium-labeled neuropeptide in the subnanomole range: quantitative study of adsorption to vials.
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Adsorption↗
Steroid metabolism as a target for insect control.
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Amides↗
Effects of potential inhibitors on Brugia pahangi in vitro: macrofilaricidal action and inhibition of microfilarial production.
A series of compounds that apparently disrupt hormonally regulated processes in insects have been examined for effects on the viability and microfilarial production of adult Brugia pahangi cultured in vitro. The azasteroids, 25-azacoprostane and 25-azacholestane, inhibited the production of microfilariae at 5 ppm, the former also exhibiting macrofilaricidal activity at this concentration. The brassinosteroids examined inhibited microfilarial production at 5 ppm but did not affect worm viability. Azadirachtin also proved to be a significant inhibitor of microfilarial release without effect on worm motility or viability. Of all the compounds tested, the non-steroidal amines appeared to be the most promising as potential filaricides, several of them proving to be macrofilaricidal at 1 ppm and affecting microfilarial production at even lower concentrations.
Amines↗
Use of temporary intraluminal shunts in selected peripheral arterial injuries.
Successful limb salvage following major peripheral arterial injury is now limited mainly by destruction of nerve, bone, and soft tissue. In some patients prolonged tissue ischemia may be a problem because of delays in treatment caused by associated injuries. In order to minimize tissue ischemia times, temporary arterial shunting was used in selected patients with injuries requiring fracture fixation or extensive debridement. Forty-two patients with major peripheral arterial injuries were seen in 27 months. Thirteen patients, including ten of the 12 with popliteal artery injuries, had placement of a temporary arterial shunt. All shunted patients had successful revascularization and no complications of the shunting occurred. In the total group of 42 there was one death and one below-knee amputation. In patients with extensive but salvageable injuries occurring with peripheral arterial injuries we feel that the use of a temporary arterial shunt is safe and may prevent prolonged severe ischemia.
Adolescent↗
Biosynthesis of a C21 steroid conjugate in an insect. The conversion of [14C]cholesterol to 5-[14C]pregnen-3 beta,20 beta-diol glucoside in the tobacco hornworm, Manduca sexta.
Following injection into Manduca sexta (L.) female pupae (day 16), [14C]cholesterol was converted to a C21 steroid conjugate, 5-[14C]pregnen-3 beta,20 beta-diol glucoside. The conjugate was isolated from ovaries and eggs and contained three glucose units at least one of which is attached to C-20. The distribution of the other two glucose units remains to be determined. Other than the dealkylation of C-24 alkane or alkene substituents, side-chain cleavage of sterols is uncommon to insects. Here we report the first definitive proof of the biosynthesis of a C21 steroid conjugate from cholesterol in an insect species. The capability of M. sexta to so readily convert cholesterol to a C21 steroid suggests a physiological role for 5-pregnen-3 beta,20 beta-diol in this species.
Animals↗
Inhibition of C28 and C29 phytosterol metabolism by N,N-dimethyldodecanamine in the nematode Caenorhabditis elegans.
Effects on the metabolism of campesterol and stigmasterol in Caenorhabditis elegans were investigated using N,N-dimethyldodecanamine, a known inhibitor of growth, reproduction and the delta 24-sterol reductase of this nematode. 7-Dehydrocholesterol was the predominant sterol (51%) of C. elegans grown in stigmasterol-supplemented media, whereas addition of 25 ppm amine resulted in a large decrease in the relative percentage of 7-dehydrocholesterol (23%) and the accumulation of a substantial proportion (33%) of delta 24-sterols (e.g., cholesta-5,7,24-trienol) and delta 22,24-sterols (e.g., cholesta-5,7,22, 24-tetraenol) but yielded no delta 22-sterols. Dealkylation of stigmasterol by C. elegans proceeded in the presence of the delta 22-bond; reduction of the delta 22-bond occurred prior to delta 24-reduction. Addition of 25 ppm amine to campesterol-supplemented media altered the sterol composition of C. elegans by increasing the percentage of unmetabolized dietary campesterol from 39 to 60%, decreasing the percentage of 7-dehydrocholesterol from 26 to 12%, and causing the accumulation of several delta 24-sterols (6%). C. elegans also was shown to be capable of dealkylating a delta 24 (28)-sterol as it converted 24-methylenecholesterol to mostly 7-dehydrocholesterol. The proposed role of 24-methylenecholesterol as an intermediate between campesterol and 7-dehydrocholesterol was supported by the results.
Amines↗
Ecdysteroids in developing ovaries and eggs of the tobacco hornworm.
Ecdysteroids of ovaries and newly-laid eggs (0- to 1-hour-old) of the tobacco hornworm are present mainly as conjugates (greater than 95%). Newly-laid eggs contain ecdysteroid conjugates equivalent to 21 micrograms of 26-hydroxyecdysone and 0.73 micrograms of ecdysone per gram of eggs. These levels are similar in ovaries of 93-hour-old adult females. In 1- to 18-hour-old eggs more than 63% of the ecdysteroids exist in the free form and the proportion is similar in 48- to 64-hour-old eggs. The ratio of 26-hydroxyecdysone to ecdysone in the conjugated form remains constant during oocyte maturation and embryogenesis. Though 26-hydroxyecdysone is without molting hormone activity in the house fly assay, the exceptionally high concentration of 26-hydroxyecdysone conjugate(s) in ovaries and newly-laid eggs, together with the fact that it is being released during embryogenesis, indicate some physiological role for 26-hydroxyecdysone.
Animals↗
Comparative effects of growth inhibitors on sterol metabolism in the nematode Caenorhabditis elegans.
An analogous series of dimethylalkyl compounds, consisting of four amines, an amide, and a phosphonate ester, inhibited motility and reproduction of the nematode Caenorhabditis elegans. Dimethylamines with straight-chain lengths of 12, 14, or 16 carbon atoms were equally active nematicides, causing greater than 80% population growth inhibition at a concentration of 25 ppm. The C12 straight-chain amine and its corresponding amide produced similar inhibition and were much more potent than either the corresponding C12 phosphonate or a C12 branched-chain amine. Inhibition of the delta 24-sterol reductase system was exhibited by all four amines, but not by the amide or phosphonate, in the following order of activity: C12 branched-chain amine greater than C12 straight-chain amine greater than C14 amine greater than C16 amine. The C12 branched amine also blocked the C-24(28)-dehydrogenase system in the conversion of sitosterol to fucosterol, the initial step in sitosterol dealkylation.
Amides↗
Novel nuclear methylation of sterols by the nematode Caenorhabditis elegans.
Caenorhabditis elegans possesses a unique sterol methylation pathway not reported to occur in any other organism and also removes the C-24 ethyl group of sitosterol (a plant sterol). This nematode produced substantial quantities of 4 alpha-methyl-5 alpha-cholest-8(14)-en-3 beta-ol and smaller amounts of lophenol from dietary cholesterol, desmosterol or sitosterol. When C. elegans was propagated in media containing sitosterol plus 25-azacoprostane hydrochloride (25-aza-5 beta-cholestane hydrochloride), an inhibitor of delta 24-sterol reductase in insects, its 4 alpha-methylsterol fraction largely consisted of equal amounts of 4 alpha-methyl-5 alpha-cholesta-7,24-dien-3 beta-ol and 4 alpha-methyl-5 alpha-cholesta-8(14),24-dien-3 beta-ol. Thus 25-azacoprostane hydrochloride inhibited both a delta 24-sterol reductase and a delta 7-sterol isomerase in C. elegans.
Animals↗
Utilization and metabolism of dietary sterols in the honey bee and the yellow fever mosquito.
The honey bee, Apis mellifera, does not convert C28 and C29 phytosterols to cholesterol as found in most previous studies of phytophagous or omnivorous insects, but instead the workers and queens selectively transfer 24-methylenecholesterol, sitosterol and isofucosterol from their endogenous sterol pools to the brood larvae regardless of the sterol in the worker diet. Administering radiolabeled sterols by feeding and injection has made it possible to trace this selective transfer through a second generation of the honey bee. In further comparative sterol metabolism studies, the yellow fever mosquito, Aedes aegypti, was shown to be capable of dealkylating and converting a radiolabeled C29 dietary sterol ([14C]sitosterol) to cholesterol. Metabolic studies with several radiolabeled dietary sterols and an inhibitor of steroid metabolism in the yellow fever mosquito further verified this capability.
Aedes↗
Severe liver trauma in the face of coagulopathy. A case for temporary packing and early reexploration.
Most liver injuries lend themselves to satisfactory hemostasis and drainage, with or without resectional debridement. A small number of injuries will necessitate massive blood transfusion with clinically significant coagulopathy developing in about half of these patients despite prophylactic infusion of fresh frozen plasma and platelet concentrates. In our experience, after major, discrete arterial and venous vessels are individually ligated, the diffuse ooze from the raw surfaces can be effectively controlled by temporary packing of the liver. Packing provides time for coagulopathy and hypothermia to be corrected and for urgent diagnostic maneuvers to be completed safely. Packs should be removed early (within 24 to 48 hours postoperatively), and surgery performed as indicated by the injury. No intraabdominal abscesses have been encountered among our 12 patients who underwent temporary packing of their liver injuries.
Adolescent↗