The Fate of Dietary Cholesterol in the Kissing Bug Rhodnius prolixus

Abstract

Insects are unable to synthesize cholesterol and depend on the presence of sterols in the diet for cell membrane composition and hormone production. Thus, cholesterol absorption, transport, and metabolism are potential targets for vector and pest control strategies. Here, we investigate the dietary cholesterol absorption and tissue distribution in the kissing bug Rhodnius prolixus using radiolabeled cholesterol. Both the anterior and posterior midguts absorbed cholesterol from the ingested blood, although the anterior midgut absorbed more. We also observed esterified cholesterol labeling in the epithelium, indicating that midgut cells can metabolize and store cholesterol. Only a small amount of labeled cholesterol was found in the hemolymph, where it was mainly in the free form and associated with lipophorin (Lp). The fat body transiently accumulated cholesterol, showing a labeled cholesterol peak on the fifth day after the blood meal. The ovaries also incorporated cholesterol, but cumulatively. The insects did not absorb almost half of the ingested labeled cholesterol, and radioactivity was present in the feces. After injection of 3H-cholesterol-labeled Lp into females, a half-life of 5.5 ± 0.7 h in the hemolymph was determined. Both the fat body and ovaries incorporated Lp-associated cholesterol, which was inhibited at low temperature, indicating the participation of active cholesterol transport. These results help describe an unexplored part of R. prolixus lipid metabolism.

Effect of Dietary Azasteroids on the Growth and Development of the Gram Pod Borer Helicoverpa armigera (Hubner)

“…Compounds such as azasteroids are known to inhibit the metabolism of sterols in plants (Darnet et al, 2020), nematodes (Choi et al, 2003) and insects either by acting directly on the enzyme Δ 24 -sterol reductase or at some other step in sterol metabolism, transport or utilization (Svoboda and Weirich, 1995). In insects, they block the formation of the moulting hormone or inhibit sterol transport and utilization which is essential for insect growth and development (Entringer et al, 2021;Toprak and Musselman, 2021). A retardation in growth and development due to azasteroids similar to that seen in our study on H. armigera has been reported in many insects (Al-Izzi and Hopkins, 1982;Kuthiala et al, 1987;Goel and Agarwal, 1987;Agarwal et al,1990) and nematode, Caenorhabditis elegans (Choi et al, 2003).…”

“…In some insects growth and development of the larvae was not inhibited even though the analyses of the sterols revealed that the Δ 24 -sterol reductase enzyme was inhibited considerably. It appears then that a significant limitation in availability of cholesterol was not sufficient in itself to disrupt normal development but in addition ecdysteroid biosynthesis or metabolism might also be affected (Svoboda et al, 1972;Tarlochan et al, 1998;Gilbert et al, 2002;Entringer et al, 2021). Larval-pupal intermediates and abnormal wing formation in adults due to azasteroid treatment also indicate that the growth, Figures 3 and 4 show the effect of the second azasteroid, 25-azacoprostane on growth in H. armigera.…”

“…Dominant plant sterols such as sitosterol, stigmasterol and campesterol are converted to cholesterol by the dealkylation pathway using several enzymes (Svoboda and Feldlaufer, 1991;Behmer et al, 1999). Cholesterol is essential for growth and development of insects being a constituent of cell membranes and as a precursor for ecdysteroid synthesis (Svoboda and Thompson, 1985;Tarlochan et al, 1998;Gilbert et al, 2002;Behmer and Nes, 2003;Toprak et al, 2020;Entringer et al, 2021;Goel et al, 2021). Azasteroids are known to inhibit the pathway of conversion of phytosterols to cholesterol, thereby affecting growth, moulting and development in some insects (Svoboda and Robbins, 1971;Svoboda et al, 1972;Thompson et al, 1975;Agarwal et al, 1990).…”

Deficiency of Acetyl-CoA Carboxylase Impairs Digestion, Lipid Synthesis, and Reproduction in the Kissing Bug Rhodnius prolixus

“…In R. prolixus, after feeding, Lp transports diacylglycerol, fatty acids, phospholipids, and cholesterol to the vitellogenic ovaries (Gondim et al, 1989;Santos et al, 2011;Entringer et al, 2021). These lipids are loaded onto circulating Lp at the midgut during blood digestion, but they may also be acquired from the fat body, where-except cholesterol-they may result from de novo lipogenesis (Saraiva et al, 2021).…”

Division of Labor among Worker Bees Is Associated with the Lipidomic Plasticity in Their Brains

“…Glycerolipids are carbohydrate-attached lipids that provide energy to all living things [19]. Moreover, cholesterol, although not present in insects, resides in the brain of mammals in the form of myelin [20].…”