Diabetic retinopathy is an important cause of blindness in the adult population1,2 and is characterized by a progressive loss of vascular cells and slow dissolution of inter-vascular junctions resulting in vascular leak and retinal edema3. Later stages of the disease are characterized by inflammatory cell infiltration, tissue destruction and neovascularization4,5. Here we identify the soluble epoxide hydrolase (sEH) as a key enzyme that initiates the pericyte “drop off” and loss of endothelial barrier function by generating a diol from docosahexaenoic acid (DHA) i.e. 19,20-dihydroxydocosapentaenoic acid (19,20-DHDP). The expression of the sEH and the accumulation of 19,20-DHDP were elevated in diabetic murine and human retinas as well as in human vitreous. Mechanistically, the diol targeted the cell membrane to alter the localisation of cholesterol-binding proteins, and interfered with the association of presenilin 1 (PS1) with N-cadherin and VE-cadherin to compromise pericyte-endothelial cell as well as inter-endothelial cell junctions. Treating diabetic mice with a specific sEH inhibitor prevented the pericyte loss and vascular permeability that are characteristic of non-proliferative diabetic retinopathy. Overexpression of the sEH in the retinal Müller glial cells of non-diabetic mice, on the other hand, resulted in vessel abnormalities similar to those seen in diabetic animals with retinopathy. Thus, increased expression of the sEH is a determinant event in the pathogenesis of diabetic retinopathy and sEH inhibition can prevent the progression of the disease.

Advances in the “omics” field bring about the need for a high number of good quality samples. Many omics studies take advantage of biobanked samples to meet this need. Most of the laboratory errors occur in the pre-analytical phase. Therefore evidence-based standard operating procedures for the pre-analytical phase as well as markers to distinguish between ‘good’ and ‘bad’ quality samples taking into account the desired downstream analysis are urgently needed. We studied concentration changes of metabolites in serum samples due to pre-storage handling conditions as well as due to repeated freeze-thaw cycles. We collected fasting serum samples and subjected aliquots to up to four freeze-thaw cycles and to pre-storage handling delays of 12, 24 and 36 hours at room temperature (RT) and on wet and dry ice. For each treated aliquot, we quantified 127 metabolites through a targeted metabolomics approach. We found a clear signature of degradation in samples kept at RT. Storage on wet ice led to less pronounced concentration changes. 24 metabolites showed significant concentration changes at RT. In 22 of these, changes were already visible after only 12 hours of storage delay. Especially pronounced were increases in lysophosphatidylcholines and decreases in phosphatidylcholines. We showed that the ratio between the concentrations of these molecule classes could serve as a measure to distinguish between ‘good’ and ‘bad’ quality samples in our study. In contrast, we found quite stable metabolite concentrations during up to four freeze-thaw cycles. We concluded that pre-analytical RT handling of serum samples should be strictly avoided and serum samples should always be handled on wet ice or in cooling devices after centrifugation. Moreover, serum samples should be frozen at or below -80°C as soon as possible after centrifugation.

-Hydrogen sulfide (HS), generated by cystathionine γ lyase (CSE), is an important endogenous regulator of vascular function. The aim of the present study was to investigate the control and consequences of CSE activity in endothelial cells under physiological and pro-atherogenic conditions. -Endothelial cell CSE knock out mice were generated and lung endothelial cells were studied (gene expression, protein sulfhydration and monocyte adhesion). Mice were crossed onto the ApoE background and atherogenesis (partial carotid artery ligation) was monitored over 21 days. CSE expression, HS bioavailability and amino acid profiling were also performed using human material. -The endothelial cell-specific deletion of CSE selectively increased the expression of CD62E and elevated monocyte adherence in the absence of an inflammatory stimulus. Mechanistically, CD62E mRNA was more stable in endothelial cells from CSE-deficient mice, an effect attributed to the attenuated sulfhydration and dimerization of the RNA-binding protein HuR. CSE expression was upregulated in mice following partial carotid artery ligation as well as in atheromas from human subjects. Despite the increase in CSE protein, circulating and intra-plaque HS levels were reduced, a phenomenon that could be attributed to the serine phosphorylation (on Ser377) and inhibition of the enzyme, most likely due to increased IL-1β. Consistent with the loss of HS, HuR sulfhydration was attenuated in atherosclerosis, and resulted in the stabilization of HuR-target mRNAs e.g. CD62E and cathepsin S, both of which are linked with endothelial cell activation and atherosclerosis. The deletion of CSE from endothelial cells was associated with the accelerated development of endothelial dysfunction and atherosclerosis, effects that were reversed upon treatment with a HS donor. Finally, in mice and humans, plasma levels of the CSE substrate; L-cystathionine, negatively correlated with vascular reactivity and HS levels indicating its potential use as a biomarker for vascular disease. -The constitutive S-sulfhydration of HuR (on Cys13) by CSE-derived HS prevents its homo-dimerization and activity which attenuates the expression of target proteins such as CD62E and cathepsin S. However, as a consequence of vascular inflammation the beneficial actions of CSE-derived HS are lost due to the phosphorylation and inhibition of the enzyme.

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