Cholesterol is an essential component of membranes and serves as precursor for a variety of products with specific biological activities, including steroid hormones.
In hematophagous insects steroid absorption from food is an essential event, since they are unable to synthesize cholesterol via de novo synthesis. Thus, for a normal development, insects require a dietary source of cholesterol. Some of the unique features of sterol metabolism in insects could provide potential targets for control.
This study focuses on absorption, transport and tissue distribution of dietary cholesterol in blood-feeding insect Rhodnius prolixus.
To characterize the cholesterol distribution, R. prolixus females were fed on blood enriched with radioactive cholesterol, insects were dissected on different days after blood meal, lipids were extracted and analyzed by TLC. Cholesterol and cholesterol ester were identified and counted by liquid scintillation. There was a decline of radioactive on food bolus during the days after blood meal, followed by an increase of radioactivity associated to free cholesterol in the anterior midgut and in the posterior midgut. So, dietary cholesterol was absorbed by anterior and posterior midgut. An increase of radioactive cholesterol was observed in the haemolymph during the days after blood meal, and the radioactivity was associated to lipophorin. This data indicate that lipophorin is the major cholesterol transporter in R. prolixus haemolymph. On the fifth day after blood meal there was a peak of non sterified cholesterol in the fat body that declined on seventh day. Ovaries accumulated increasing amounts of cholesterol through the days after feeding.
Injection of lipophorin containing radioactive cholesterol into females showed that radioactivity decreased in the haemolymph. On the other hand, radioactivity was found associated to fat body and ovaries. So, these tissues incorporated cholesterol from lipophorin.
These data suggest that R. prolixus uses the dietary cholesterol, which is absorbed by anterior and posterior midgut, and lipophorin transports it to different tissues, where there is some esterification of cholesterol. Other experiments are in course to better understand cholesterol metabolism in R. prolixus.