Malondialdehyde and 4-hydroxynonenal adducts are not formed on cardiac ryanodine receptor (RyR2) and sarco(endo)plasmic reticulum Ca ²⁺-ATPase (SERCA2) in diabetes

Recently, we reported an elevated level of glucose-generated carbonyl adducts on cardiac ryanodine receptor (RyR2) and sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA2) in hearts of streptozotocin(STZ)-induced diabetic rats. We also showed these adduct impaired RyR2 and SERCA2 activities, and altered evoked Ca²⁺ transients. What is less clear is if lipid-derived malondialdehyde (MDA) and 4-hydroxy-2-nonenal (4-HNE) also chemically react with and impair RyR2 and SERCA2 activities in diabetes? This study used western blot assays with adduct-specific antibodies and confocal microscopy to assess levels of MDA, 4-HNE, N ^ε-carboxy(methyl) lysine (CML), pentosidine, and pyrraline adducts on RyR2 and SERCA2 and evoked intracellular transient Ca²⁺ kinetics in myocytes from control, diabetic, and treated-diabetic rats. MDA and 4-HNE adducts were not detected on RyR2 and SERCA2 from either control or 8 weeks diabetic rats with altered evoked Ca²⁺ transients. However, CML, pentosidine, and pyrraline adducts were elevated three- to five-fold (p < 0.05). Treating diabetic rats with pyridoxamine (a scavenger of reactive carbonyl species, RCS) or aminoguanidine (a mixed reactive oxygen species-RCS scavenger) reduced CML, pentosidine, and pyrraline adducts on RyR2 and SERCA2 and blunted SR Ca²⁺ cycling changes. Treating diabetic rats with the superoxide dismutase mimetic tempol had no impact on MDA and 4-HNE adducts on RyR2 and SERCA2, and on SR Ca ²⁺ cycling. From these data we conclude that lipid-derived MDA and 4-HNE adducts are not formed on RyR2 and SERCA2 in this model of diabetes, and are therefore unlikely to be directly contributing to the SR Ca²⁺ dysregulation.