Effects of estradiol in the heart of rats with fructose-rich diet-induced insulin resistance

Fruktoza je prirodni šećer, ĉiji se unos poslednjih decenija dramatiĉno povećao, najvećim delom zbog povećane upotrebe kukuruznog sirupa sa visokim sadrţajem fruktoze. Povećan unos fruktoze vodi ka razvoju metaboliĉkog sindroma kod ljudi i eksperimentalnih ţivotinja. Pored promena u jetri, adipoznom tkivu i skeletnim mišićima, ishrana bogata fruktozom je praćena i razvojem insulinske rezistencije u srcu. Poznato je da insulin ostvaruje svoje efekte na ćelije srca i da u stanju insulinske rezistencije u srcu dolazi do poremećaja u signalnom putu Akt/eNOS i balansu korišćenja energetskih supstrata. Posledice povećanog unosa fruktoze su polno zavisne, pri ĉemu je protektivni efekat pripisan estrogenim hormonima. Fiziološke koncentracije estrogena poboljšavaju osetljivost na insulin i deluju kardioprotektivno. TakoĊe, estradiol utiĉe na specifiĉno delovanje insulina u srcu. Cilj ove studije bio je analiza efekta estradiola na procese u srcu regulisane insulinom u stanju insulinske rezistencije izazvane ishranom bogatom fruktozom. Ţenke pacova su podvrgnute standardnoj ishrani ili ishrani obogaćenoj 10% rastvorom fruktoze tokom 9 nedelja i ovarijektomisane 2 nedelje pre ţrtvovanja, pri ĉemu je polovina ţivotinja na fruktoznoj ishrani dan nakon ovarijektomije podvrgnuta tretmanu estradiolom. U cilju izuĉavanja efekata ishrane bogate fruktozom i estradiola na insulinom regulisanu fosforilaciju i unutarćelijsku lokalizaciju ispitivanih molekula, polovina ţivotinja je tretirana insulinom 40 minuta pre ţrtvovanja. Analizirani su molekuli iz insulinskog signalnog puta (IRS-1, Akt i ERK1/2), kao i efektorni molekuli ĉiju funkciju reguliše insulin, kao što su eNOS, Na+/K+-ATP-aza i molekuli ukljuĉeni u transport i metabolizam energetskih supstrata u srcu (GLUT1, GLUT4, CD36, lipin 1 i CPTI) i lipidni profil srca. Ispitivana je ekspresija ovih molekula na nivou proteina, kao i njihova fosforilacija ili unutarćelijska lokalizacija. Ishrana bogata fruktozom je povećala unos teĉnosti i smanjila unos hrane, dok je povećala ukupan kalorijski unos i koncentraciju leptina u plazmi. Estradiol je većim delom poništio štetne efekte ishrane na regulaciju apetita, verovatno preko povećanja centralne osetljivosti na leptin. Ţivotinje na fruktoznoj ishrani su imale povišene koncentracije triglicerida i insulina u plazmi i povećan HOMA indeks, smanjenu koncentraciju slobodnih masnih kiselina, dok je koncentracija glukoze bila nepromenjena...Fructose is natural sugar whose intake has increased dramatically over the past decades, mostly due to increased consumption of high-fructose corn syrup. Increased intake of fructose initiates development of metabolic syndrome phenotype in humans and experimental animals. In addition to changes in liver, adippose tissue and skeletal muscle, fructose-rich diеt is accompanied by cardiac insulin resistance. Cardiac muscle is a target of insulin. Insulin resistance is accompanied by disturbances in Akt/eNOS signalling and altered cardiac usage of energetic substrates. Consequences of enhanced fructose intake are shown to be sex-dependent and the protective effect is attributed to estrogens. Physiological concentrations of estrogens improve insulin sensitivity and they are cardioprotective. Also, estrogens affect specific cardiac insulin action. The aim of the present study was to analyze effects of estradiol on insulin-regulated processes in the heart in insulin resistance state. Female rats were subjected to standard diet or diet containing 10% fructose in drinking water during 9 weeks. Two weeks before sacrifice, all animals were bilaterally ovariectomized and half of the fructose-fed animals were subjected to estradiol replacement treatment, day after ovariectomy. In order to study fructose-rich diet and estradiol effects on the insulin regulated phosphorylations and subcellular localization of analyzed molecules, half of the animals were treated with insulin, 40 min before killing. Insulin signaling molecules (IRS-1, Akt i ERK1/2) were analyzed, as well as insulin regulated effector molecules, such as eNOS, Na+/K+-ATPase and molecules involved in the transport and metabolism of energetic substrates in the heart (GLUT1, GLUT4, CD36, lipin 1 i CPTI), as well as profile of cardiac lipids. We examined the protein exppression of the molecules, as well as their phosphorylation or subcellular localization. Fructose-rich diet increased liquid intake and decreased food intake, while it increased total caloric intake and plasma leptin concentration. Estradiol abolished most of the detrimental effects of diet on appetite regulation, probably through increase in central leptin sensitivity. The fructose-fed rats had increased plasma triglycerides and insulin levels and increased HOMA index, decreased plasma free fatty acid level, while glucose concentration was unaltered..