Caigan Du

Metabolic syndrome (diabetes, hypertension, obesity and hypercholesteremia) increases the risk of high-mortality chronic diseases including chronic kidney disease, which accounts for 50% of end-stage renal disease (ESRD) in the developed world. Over 1/3 of the world’s adult population have metabolic syndrome. Oxidative stress plays a central role in metabolic syndrome pathophysiology. Grape is one of the broadly studied natural anti-oxidants. Literature demonstrates grape antioxidant’s significant protective effects on metabolic syndrome, however, not yet on metabolic syndrome-related kidney disease. This study evaluates the effect of whole grape on kidney disease associated with metabolic syndrome. Material and methods: Preclinical model of metabolic syndrome-related kidney disease, Obese ZSF-1 rats, ingested whole grape powder (5% of daily diet) for 6 months. Blood and urine samples were analyzed monthly to assess renal function parameters including 24-hour urine volumes, proteinuria, and urine protein to creatinine ratio (PCR). Rats’ kidney tissue histopathology and PCR array studies were conducted. In vitro kidney cell death was examined in cultured podocytes using flow cytometry. Results: Here, collective data from 6-month preclinical study showed chronic kidney disease consistent with an early stage diabetic nephropathy picture in both experimental and control groups. Renal function in rats of the experimental group was significantly enhanced compared with those of the control group, indicated by less 24-hour urine volumes (34.79 ± 15.77 mL vs. 55.8 ± 20.27 mL, p = 0.0147) and less proteinuria (8.56 ± 5.71 g vs. 24.01 ± 37.51 g, p = 0.0412) in the experimental group. Urine PCR was significantly lower in the experimental group versus control (3.42 ± 1.289 vs. 9.722 ± 9.156, p = 0.0084). Histopathology and PCR array analysis showed less oxidative stress picture in experimental group versus control. In vitro antioxidant assays showed significantly reduced H2O2-induced cell death in podocytes treated with grape extract versus control. Conclusion: This pilot study indicates that daily intake of whole grape powder has a protective effect on the kidney in obese ZSF-1 rats, suggesting the potential of grape antioxidants as a prevention strategy for reducing kidney disease progression in metabolic syndrome patients. Further investigations are required to support this preliminary study.

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Antifreeze proteins from natural sources have been discovered to have cryoprotective function against freezing temperature, and have been tested for the application for cryopreservation of biological materials. However, none has been shown to match the effectiveness of current chemical cryoprotectants, such as dimethyl sulfoxide. One potential limitation with the application of antifreeze proteins is that they may only stay in the extracellular space around cells whereas chemical cryoprotectants can be penetrative. In this thesis project, we have designed, purified and explored the function of antifreeze proteins that were engineered with an intracellular delivery signal peptide, known as iPTD. We showed that iPTD-engineered antifreeze proteins had effective cell surface coverage within 30 minutes of incubation as shown by flow cytometry; however no intracellular protein delivery was observed under multiphoton microscopy. The plasma membrane was protected by iPTD-engineered antifreeze proteins during cryopreservation as seen in Calcein dye release assay, but cell recovery or proliferation was not observed after thawing. Given these properties of iPTD-engineered antifreeze proteins, we used them as red blood cell cryopreservation additives. By adding these modified antifreeze proteins, we were able to reduce the amount of glycerol (used for RBC cryopreservation) necessary to control freeze-induced hemolysis. Furthermore, the quality of thawed red blood cells is higher as protein addition resulted in high retention of intracellular ATP.

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Peritoneal Dialysis (PD) is an effective method of renal replacement therapy for patients with end-stage renal disease. PD solution is instilled into the peritoneal cavity and water, solutes, and waste products are removed across the peritoneal membrane, which serves as a natural filter between the peritoneal cavity and the bloodstream. The current conventional PD solution uses hypertonic glucose as an osmotic agent to remove water – a process termed ultrafiltration (UF). Although effective, chronic daily exposure to glucose causes systemic metabolic complications for PD patients; it also directly damages the peritoneal membrane and eventually causes the filter to fail.Hyperbranched Polyglycerol (HPG) is a non-toxic, non-immunogenic synthetic polymer that contains no starch or glucose. HPG has shown very limited organ accumulation after intravenous injection. HPG offers many theoretical advantages over glucose-based PD including the ability to synthesize HPG over a range of molecular weights. This current thesis tests HPG as a glucose-sparing osmotic agent in PD solution.We used a rodent model of PD to evaluate solute and waste removal, ultrafiltration, and peritoneal biocompatibility over 0-8 hours of peritoneal exposure. We compared HPG solutions of molecular weights 0.5, 1, and 3 kDa with conventional glucose-based solution (Dianeal™ 2.5%) and buffered glucose-based solution (Physioneal™ 2.27%).We demonstrated that HPG solutions can induce superior and sustained UF for 8 hours, in contrast to glucose-based solutions that lose UF capacity after 4 hours. Sodium and urea removal was superior for HPG solutions, in part because HPG polymer acts as a colloid - as opposed to crystalloid - osmotic agent. We used neutrophil infiltration and peritoneal mesothelial cell detachment as markers of biocompatibility. We found that HPG solutions, particularly lower molecular weight polymers, demonstrate superior biocompatibility profiles when compared to glucose-based PD solutions.Taken together, these experiments support the proof-of concept of HPG as a promising novel osmotic agent in PD. Future studies are required to investigate the chronic effects of HPG exposure on the peritoneal membrane, as well as the metabolic and pharmacokinetic profiles of HPG PD solutions.

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No abstract available.