Objective— The dyslipidemia of type 2 diabetes mellitus has multiple etiologies and impairs lipoprotein functionality, thereby increasing risk for cardiovascular disease. High-density lipoproteins (HDLs) have several beneficial effects, notably protecting the heart from myocardial ischemia. We hypothesized that glycation of HDL could compromise this cardioprotective effect. Approach and Results— We used in vitro (cardiomyocytes) and ex vivo (whole heart) models subjected to oxidative stress together with HDL isolated from diabetic patients and nondiabetic HDL glycated in vitro (methylglyoxal). Diabetic and in vitro glycated HDL were less effective ( P <0.05) than control HDL in protecting from oxidative stress. Protection was significantly, inversely correlated with the degree of in vitro glycation ( P <0.001) and the levels of hemoglobin A1c in diabetic patients ( P <0.007). The ability to activate protective, intracellular survival pathways involving Akt, Stat3, and Erk1/2 was significantly reduced ( P <0.05) using glycated HDL. Glycation reduced the sphingosine-1-phosphate (S1P) content of HDL, whereas the S1P concentrations of diabetic HDL were inversely correlated with hemoglobin A1c ( P <0.005). The S1P contents of in vitro glycated and diabetic HDL were significantly, positively correlated (both <0.01) with cardiomyocyte survival during oxidative stress. Adding S1P to diabetic HDL increased its S1P content and restored its cardioprotective function. Conclusions— Our data demonstrate that glycation can reduce the S1P content of HDL, leading to increased cardiomyocyte cell death because of less effective activation of intracellular survival pathways. It has important implications for the functionality of HDL in diabetes mellitus because HDL-S1P has several beneficial effects on the vasculature.

Enzymatic and homogeneous catalysis have evolved independently to address the challenges in the synthesis of enantiopure products. With the aim of complementing these fields, artificial metalloenzymes, which combine the structural diversity of biocatalysts with the wealth of metal-catalyzed reactions, have attracted increasing attention.[1] In homogeneous catalysis the cis-selective, OsO 4 -dependent asymmetric dihydroxylation (AD) of olefins ranks among the most powerful methods for the synthesis of vicinal diols. Ligands for homogeneous catalysis have been largely developed by Sharpless and co-workers, and are, with few exceptions, almost exclusively based on quinidine or quinine derivatives.[2] Although most classes of prochiral olefins are dihydroxylated with good activity and selectivity, the cissubstituted olefins are problematic. Nature relies on nonheme iron dioxygenases such as naphthalene dioxygenase (NDO) to perform a related reaction. These enzymes display broad substrate scope.[3] It is believed that both the OsO 4 -and NDO-catalyzed dihydroxylations proceed by an outer sphere [3+2] mechanism in which the substrate is not bound to the metal in the transition state (Figure 1). [2a,f, 3c] Considering a biomimetic approach, we hypothesized that anchoring a catalytically competent Os VIII center within a protein might afford an artificial metalloenzyme for the AD of olefins. Encouraged by a report by Kokubo et al., [2d] we set out to screen various proteins and to test whether the resulting dihydroxylases could be optimized by genetic means.Five proteins were evaluated as hosts for the AD of amethylstyrene: Wild-type streptavidin (SAV) clearly performed best. In contrast, bovine serum albumin (BSA) yielded the opposite enantiomer, albeit with a low turnover number (Table 1). In view of the size of the proteins (66 kDa for BSA and 16 kDa for the SAV monomer), the difficult recombinant production of BSA, [4] and the number of Figure 1. Postulated transition-state structure for the dihydroxylation of olefins: a) for the naphthalene dioxygenase; b) for the osmium-catalyzed AD of prochiral olefins; and c) for an artificial cis-dihydroxylase resulting from anchoring of OsO 4 within a host protein. TON [c]

BackgroundNew evidence shows that high density lipoproteins (HDL) have protective effects beyond their role in reverse cholesterol transport. Reconstituted HDL (rHDL) offer an attractive means of clinically exploiting these novel effects including cardioprotection against ischemia reperfusion injury (IRI). However, basic rHDL composition is limited to apolipoprotein AI (apoAI) and phospholipids; addition of bioactive compound may enhance its beneficial effects.ObjectiveThe aim of this study was to investigate the role of rHDL in post-ischemic model, and to analyze the potential impact of sphingosine-1-phosphate (S1P) in rHDL formulations.Methods and ResultsThe impact of HDL on IRI was investigated using complementary in vivo, ex vivo and in vitro IRI models. Acute post-ischemic treatment with native HDL significantly reduced infarct size and cell death in the ex vivo, isolated heart (Langendorff) model and the in vivo model (-48%, p<0.01). Treatment with rHDL of basic formulation (apoAI + phospholipids) had a non-significant impact on cell death in vitro and on the infarct size ex vivo and in vivo. In contrast, rHDL containing S1P had a highly significant, protective influence ex vivo, and in vivo (-50%, p<0.01). This impact was comparable with the effects observed with native HDL. Pro-survival signaling proteins, Akt, STAT3 and ERK1/2 were similarly activated by HDL and rHDL containing S1P both in vitro (isolated cardiomyocytes) and in vivo.ConclusionHDL afford protection against IRI in a clinically relevant model (post-ischemia). rHDL is significantly protective if supplemented with S1P. The protective impact of HDL appears to target directly the cardiomyocyte.

Our findings demonstrate that localized immunosuppression with TAC hydrogel is a long-term safe and reliable treatment. It may reduce the burden of systemic immunosuppression in vascularized composite allotransplantation, potentially boosting the clinical application of this surgical intervention.