Background and purpose: Recombinant human relaxin-2, serelaxin, is being proved as a novel drug with therapeutic efficacy in some cardiovascular diseases, especially heart failure, a disease whose physiopathology and course are firmly correlated with important alterations in cardiac metabolism. The aim of our present work was to investigate changes in the cardiac metabolome following relaxin-2 treatment.
Experimental approach: Sprague-Dawley rats were treated with human recombinant relaxin-2 using osmotic minipumps at a dose of 0.4 mg/kg/day for 2 weeks. Body composition was measured with a nuclear magnetic resonance imaging system seven days after surgery and on the final day of the experiment. The last two days of treatment, respiratory quotient, locomotor activity and energy expenditure were measured with a calorimetric system. The plasma levels of relaxin-2, total cholesterol, high- and low- density lipoproteins (HDL, LDL), triglycerides and the hepatic enzymes glutamic-pyruvic transaminase (GTP) and gamma-glutamyltransferase (GGT) levels were analyzed. The metabolic profiling of both atria from relaxin-2-treated and control rats was carried out using two separate ultra-high performance liquid chromatography (UHPLC)-Time of Flight-MS based platforms analyzing methanol and chloroform/methanol extracts combined with a UHPLC-single quadrupole-MS based platform used to analyze aminoacids and with a methanol/water extract platform that covered polar metabolites. Identified ion features in the methanol extract platform included fatty acids, acyl carnitines, bile acids, monoacylglycerophospholipids, monoetherglycerophospholipids, free sphingoid bases, and oxidized fatty acids. The chloroform / methanol extract platform provided coverage over glycerolipids, cholesterol esters, sphingolipids, diacylglycerophospholipids, and acyl-ether-glycerophospholipids. Gene expression levels of the adipokines adiponectin, leptin and nesfatin-1 in visceral adipose tissue and cardiac gene expression levels of key enzymes of desaturation and elongation of n-6 and n-3 PUFAs were assessed by Real Time-PCR.
Key results: Twenty-eight metabolites out of three hundred sixty-two were significantly altered by human relaxin-2. These included fifteen glycerophospholipids: three phosphatidylethanolamines (PE) and twelve phosphatidylcholines (PC); eight sphingolipids: three ceramides (Cer) and five sphingomyelins (SM); and also five aminoacids and one carboxylic acid. Interestingly, the majority of changes correspond to lipid classes, twelve of them polyunsaturated diacylglycerophosphatidylcholines with long acyl chains, containing mainly docosahexaenoic acid (22:6) and arachidonic acid (20:4). Atrial levels of Elovl5 (Elongation of very long chain fatty acids protein 5), Fads1 (Δ5-fatty acid desaturase) and Fads2 (Δ6-fatty acid desaturase), key enzymes of elongation and desaturation of n-6 and n-3 PUFAs like arachidonic acid and DHA, respectively, were significantly increased by relaxin-2 treatment. Atrial tissues from rats treated with relaxin-2 showed a significant increase in the mRNA levels of Srebf1, a transcription factor that activates the gene expression of Elovl5, Fads1 and Fads2. The treatment with relaxin-2 significantly decreased the visceral fat mRNA expression levels of adiponectin, leptin and nesfatin-1, adipokines known to exert an important influence on the regulation of cardiovascular function.
Conclusion and implications: Serelaxin (human recombinant relaxin-2) treatment induces significant changes in cardiac major components of the membrane lipid bilayer such as glycerophospholipids and sphingolipids, known to have structural roles but also very relevant regulatory effects in cardiac function. Serelaxin induced also modifications in several aminoacids of high influence in cardiac energy metabolism regulation. Our results highlight the need to further understand the role of relaxin-2 in the regulation of cardiac energy metabolism, in the context of the therapeutic strategies for the treatment of cardiometabolic pathologies as heart failure.
Keywords: Cardiovascular metabolism; Glycerophospholipids; Relaxin; Serelaxin; Serelaxin (PubChem CID:71300755); Sphingolipids.
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