Karla S. Ritter

The effects of cholesterol on the development of Heliothis zea

Heliothis zea was reared on an artificial diet, which lacked supplementation with plant materials, in order to determine the effects of cholesterol on the development of this insect. A number of parameters of larval development were found to be dependent upon the concentration of dietary sterol including: the number of moults which the larvae completed within a particular time interval, the ability of the larvae to pupate and the survival of the larvae. The number of moults which a larva completed prior to pupation, though, was independent of the concentration of sterol.

The effects of the structure of sterols on the development of Heliothis zea

Abstract Heliothis zea was reared on artificial diets which lacked supplementation with plant materials but were supplemented with different sterols in order to determine how certain structural features of a sterol molecule affect the development of this insect. We found that sitosterol and cholesterol supported a more rapid rate of growth than did campesterol. Larvae did not moult when they ingested 5-pregnen-3β-ol. Larvae utilized spinasterol more efficiently than lathosterol. Such a pronounced effect was not observed in the Δ 5 -series. The substitution of a Δ 7 -bond (spinasterol, dihydrospinasterol, lathosterol) for the Δ 5 -bond (stigmasterol, sitosterol, cholesterol) in the 24-ethyl- and desalkylsterols reduced the rate of growth of the larvae. Although larvae developed normally on cholesterol, the addition of a Δ 7 -bond to give the Δ 5,7 -diene system apparently altered the functionality of the molecule because 7-dehydrocholesterol did not support larval development. The growth of larvae was also inhibited, although not prevented, when they consumed diets which contained ergosterol. In contrast, the larvae completed their development more rapidly on brassicasterol which lacked the Δ 7 -bond. Cholestanol supported the complete development of the insect. H. zea is unusual among investigated insects because it develops both on cholestanol and lathosterol but does not utilize ergosterol efficiently and fails to grow on 7-dehydrocholesterol.

Identification of Δ5,7-24-methylene- and methylsterols in the brain and whole body of Atta cephalotes isthmicola

Abstract 1. 1. The principal sterol of both the brain and the whole body of the leaf-cutting ant, Atta cephalotes isthmicola, was identified as 24-methylcholesta-5,7,24(28)-trien-3β-ol (7-dehydro-24-methylenecholesterol, 5-dehydroepisterol). 2. 2. Smaller amounts of 24β-methylcholesta-5,7-dien-3β-ol (22-dihydroergosterol) and 24β-methylcholesta-5,7,22-trans-trien-3β-ol (ergosterol) were also present, but cholesterol was not detected. 3. 3. This demonstrates that a functional nervous system can exist in the absence of cholesterol.

Steinernema feltiae (=Neoaplectana carpocapsae): Effect of sterols and hypolipidemic agents on development

The structure and concentration of sterol in a lipid-defined artificial medium affected the development of the entomogenous nematode, Steinernema feltiae (= Neoaplectana carpocapsae). The nematode grew normally in vitro when the medium was supplemented with delta 5-desalkylsterol (cholesterol) or delta 5-desalkylsteryl ester (cholesterol oleate). The minimum amount of cholesterol in the medium that was necessary to support the development of S. feltiae to the climax population (i.e., dauer stage) was 0.0025%. The nematode also completed its life cycle normally when delta 0- or delta 7-desalkylsterols (cholestanol and lathosterol) were substituted for cholesterol. In contrast, development was inhibited when the medium contained delta 5,7-desalkylsterol (7-dehydrocholesterol); however, the nematode population reached the climax stage, in medium containing this sterol, when cholesterol was also present. S. feltiae was able to utilize delta 5- and delta 0-24 alpha-ethylsterols (sitosterol and sitostanol) as dietary sterols; however, when a delta 22-bond was introduced into the side chain (stigmasterol) the rate of development of the nematode slowed significantly. The growth of the nematode was also retarded when the medium contained delta 5,7,22-24 beta-methylsterol (ergosterol). The nematode population reached the climax stage in medium containing delta 8,24-4,14 alpha-trimethylsterol (lanosterol) only when cholesterol was also present. When S. feltiae was exposed to certain hypolipidemic agents, which are known to lower the level of lipids in human plasma (clofibrate, cholestyramine resin, niacin, and D-thyroxine), all but D-thyroxine affected the growth and development of the nematode in vivo (in Heliothis zea) and/or in vitro. Therefore further studies are warranted to determine how these drugs affect the lipid biochemistry of this nematode.

Effect of host sterols on the sterol composition and virulence of a nuclear polyhedrosis virus ofHeliothis zea

The type of sterol in the diet ofHeliothis zea affected not only the sterol composition of the insect larva but also the virulence and/or sterol composition of a single-nucleocapsid nuclear polyhedrosis virus (HzSNPV). This baculovirus, which was purified by differential and sucrose density gradient centrifugation, had a sterol content of 40 ng per 106 polyhedra. When the sterol composition of HzSNPV was characterized by gas liquid chromatography, reversed phase-high performance liquid chromatography, mass spectrometry, proton nuclear magnetic resonance spectrometry and/or ultraviolet spectroscopy, the sterols in the virus were similar to those of the host. The HzSNPV isolated from larvae fed Δ5_, Δ0_ or Δ5,7-sterols contained primarily cholesterol, cholestanol or 7-dehydrocholesterol, respectively. Changes in the sterol composition of HzSNPV affected its LD50, but not LT50, in larvae containing Δ5-sterols. The LD50 of virus isolated from larvae containing Δ0_, Δ5_ and Δ7-sterols decreased from 275,423 to 32,359 to 5,012 polyhedra/larva, respectively. The latter virus was also more virulent than the one that was isolated from larvae containing Δ5,7-sterol and had an LD50 of 58,884 polyhedra/larva. In contrast, the LD50 of an HzSNPV (Sandoz, Inc.) containing Δ5-sterol was not affected by the presence of Δ5_, Δ0_ or Δ5,7-sterols in the tissues of the host (1,413; 1,288 and 355 polyhedra/larva, respectively). The results of this study indicate that the sterol composition ofH. zea can affect the sterol composition of HzSNPV and therefore may affect the ability of this biological control agent to control its economically important insect host.

Acyl coenzyme A: Cholesterol acyltransferase activity in fat body and intestinal microsomes of heliothis zea

Abstract 1. 1. Acyl coenzyme A: cholesterol acyltransferase (ACAT) activity was detected in the fat body and intestinal microsomes of prepupae of Heliothis zea and was consistent with the presence of steryl esters (principally cholesteryl) in these tissues. 2. 2. The formation of cholesteryl ester, by microsomes of the fat body, was linear to at least 20 min and over a range of protein concentrations from 25 to 200 μg. Under standard assay conditions, the average specific enzymatic activity in the fat body was 41.7 pmol/min/mg while in the intestine it was 59.5 pmol/min/mg. 3. 3. The tissue with the highest percentage of its sterol esterified was the intestine (10.2–11.9%), followed by the fat body (3.9–5.7%) and then the whole prepupa (1.0–1.5%).

A comparison of the biological properties of of androst-5-en-3β-ol, a series of (20R)-n-alkylpregn-5-en-3β-ols and 21-isopentylcholesterol with those of cholesterol

The Δ5-sterol, androst-5-en-3β-ol, which has no side chain at C-17, did not permit molting of the insectHeliothis zea, growth of either the protozoanTetrahymena pyriformis, or the yeastSaccharomyces cerevisiae adapted to anaerobic conditions, nor was the sterol esterified by a mammalian microsomal ACAT preparation. However, the sterol did form a liposome with egg lecithin and, when fed to mice, did inhibit hepatic cholesterol synthesis. 21-Isopentylcholesterol also formed a liposome but neither supported the growth of the yeast nor was metabolized by the protozoan. When sterols, 20(R)-n-alkylpregn-5-en-3β-ols, with side chains of varying lengths were added to the medium of the protozoan, maximal esterification with fatty acids occurred with the 20(R)-n-pentyl derivative, and maximal inhibition of tetrahymanol formation occurred with then-butyl,n-pentyl andn-hexyl derivatives. In all of the assays, cholesterol showed a positive response, either permitting molting or growth, being metabolized, inhibiting sterol or tetrahymanol synthesis, or forming a liposome.