End-organ damage in diabetes:Exploring innovative targets and therapies

Diabetes mellitus (DM) affects the function of blood vessels and various organs, eventually leading to life-threatening DM complications. The prediction of diabetic end-organ damage and exploring novel treatment strategies herein was the topic of this thesis. We first showed that intra-renal small artery function at pre-diabetes predicted an individual’s susceptibility to diabetic nephropathy. DM also increases the risk of brain damage and Alzheimer's disease via derailment of protein homeostasis. We showed that NaHS - a donor of H2S - is a powerful antioxidant compound which attenuated brain protein aggregation DM-rats. The results highlight the role of CBS system – which produces H2S in the brain – and the potential use of NaHS as a novel strategy against protein aggregation in diabetic brain. Anti-diabetic drugs may also exert beneficial effects independent of blood glucose control. Employing an animal model of hypertension, we found that metformin and vildagliptin both reduced blood pressure and improved vascular function. However, when hypertension was combined with insulin-dependent DM the beneficial effects remained after metformin, but not vildagliptin. The results suggest superior vascular pleiotropic effects of metformin compared to vildagliptin in DM. The immunosuppressant drug and sphingosine 1-phosphate (S1P) analog fingolimod – used in the treatment of multiple sclerosis - also exerts pleiotropic effects on vascular function but the mechanisms involved are relative unknown. Our present findings in normal rats now suggest a dual action of fingolimod treatment both on vascular smooth muscle and endothelial cell S1P-receptors; how this translates in DM conditions remains to be determined. This research may help to identify individuals at higher risk of diabetic end-organ damage and provide fuel for novel treatment strategies in DM

A Comparison between Shear Bond Strength of VMK Master Porcelain with Three Base-Metal Alloys (Ni-Cr-T3, Verabond, Super Cast) and One Noble Alloy (X-33) in Metal-Ceramic Restorations

Statement of Problem: The increase in the use of metal-ceramic restorations and a high prevalence of porcelain chipping entails introducing an alloy which is more compatible with porcelain and which causes a stronger bond between the two. This study is to compare shear bond strength of three base-metal alloys and one noble alloy with the common VMK Master Porcelain. Materials and Method: Three different groups of base-metal alloys (Ni-cr-T3, Super Cast, Verabond) and one group of noble alloy (x-33) were selected. The number of alloys in each group was 15. All the groups went through the casting process and change from wax pattern into metal disks. Then, VMK Master Porcelain was fired on each group. All the specimens were put in the UTM and a shear force was loaded until a fracture occurred. The fracture force was then recorded by the machine. The data was subjected to SPSS Version 16 and One-Way ANOVA was run to compare shear strength between the groups. Furthermore, the groups were compared two by two through running Tukey test. Results: The findings of this study revealed that shear bond strength of Ni-Cr-T3 alloy was higher than the three other alloys (94 Mpa or 330 N). Super Cast alloy had the second greatest shear bond strength (80. 87 Mpa or 283.87 N). Both Verabond (69.66 Mpa or 245 N) and x-33 alloys (66.53 Mpa or 234 N) took the third place. Conclusion: Ni-Cr-T3 with VMK Master Porcelain has the greatest shear bond strength. Therefore, the use of this low-cost alloy is recommended in metal-ceramic restorations

Metformin Improves Endothelial Function and Reduces Blood Pressure in Diabetic Spontaneously Hypertensive Rats Independent from Glycemia Control: Comparison to Vildagliptin

Metformin confers vascular benefits beyond glycemia control, possibly via pleiotropic effects on endothelial function. In type-1-diabetes-mellitus (T1DM-)patients metformin improved flow-mediated dilation but also increased prostaglandin(PG)-F-2 alpha, a known endothelial-contracting factor. To explain this paradoxical finding we hypothesized that metformin increased endothelial-vasodilator mediators (e.g. NO and EDHF) to an even larger extent. Spontaneously-hypertensive-rats (SHR) display impaired endothelium-dependent relaxation (EDR) involving contractile PGs. EDR was studied in isolated SHR aortas and the involvement of PGs, NO and EDHF assessed. 12-week metformin 300 mg/kg/day improved EDR by up-regulation of NO and particularly EDHF; it also reduced blood pressure and increased plasma sulphide levels (a proxy for H2S, a possible mediator of EDHF). These effects persisted in SHR with streptozotocin (STZ)-induced T1DM. Vildagliptin (10 mg/kg/day), targeting the incretin axis by increasing GLP-1, also reduced blood pressure and improved EDR in SHR aortas, mainly via the inhibition of contractile PGs, but not in STZ-SHR. Neither metformin nor vildagliptin altered blood glucose or HbA(1c). In conclusion, metformin reduced blood pressure and improved EDR in SHR aorta via up-regulation of NO and particularly EDHF, an effect that was independent from glycemia control and maintained during T1DM. A comparison to vildagliptin did not support effects of metformin mediated by GLP-1

Differential Effects of Long Term FTY720 Treatment on Endothelial versus Smooth Muscle Cell Signaling to S1P in Rat Mesenteric Arteries

The sphingosine-1-phosphate (S1P) analog FTY720 exerts pleiotropic effects on the cardiovascular system and causes down-regulation of S1P receptors. Myogenic constriction is an important mechanism regulating resistance vessel function and is known to be modulated by S1P. Here we investigated myogenic constriction and vascular function of mesenteric arteries of rats chronically treated with FTY720. Wistar rats received FTY720 1mg/kg/daily for six weeks. At termination, blood pressure was recorded and small mesenteric arteries collected for vascular studies in a perfusion set up. Myogenic constriction to increased intraluminal pressure was low, but a sub-threshold dose of S1P profoundly augmented myogenic constriction in arteries of both controls and animals chronically treated with FTY720. Interestingly, endothelial denudation blocked the response to S1P in arteries of FTY720-treated animals, but not in control rats. In acute experiments, presence of FTY720 significantly augmented the contractile response to S1P, an effect that was partially abolished after the inhibition of cyclooxygenase (COX-)-derived prostaglandins. FTY720 down regulated S1P1 but not S1P2 in renal resistance arteries and in cultured human endothelial cells. This study therefore demonstrates the endothelium is able to compensate for the complete loss of responsiveness of the smooth muscle layer to S1P after long term FTY720 treatment through a mechanism that most likely involves enhanced production of contractile prostaglandins by the endothelium

Acute effects of FTY720 on S1P mediated contraction.

<p>Mesenteric arteries of control animals were pre-incubated with 10μM FTY720 for 30 minutes before a dose effect curve to S1P (10nM-10μM) was constructed. S1P mediated contractions were normalized to maximal contractions to 60mM KCl. Pre-incubation with FTY720 (caused a leftward shift of the CR curve to S1P; this could be in part reversed by addition of indomethacin (10μM). n = 6 rats per group, 2 rings per rat. (*p<0.05 EC₅₀ FTY720 vs control).</p

Animal body weight and hemodynamic effects of FTY720.

<p>Animal body weight and hemodynamic effects of FTY720.</p