Effective Delivery of Endogenous Antioxidants Ameliorates Diabetic Nephropathy.

BACKGROUND: Diabetic nephropathy (DN) is thought to be partially due to the injury of renal cells and the renal micro-environment by free radicals. Free radial scavenging agents that inhibit free radical damage may well prevent the development of underlying conditions such as mesangial expansion (by inhibiting extracellular matrix expression) in these patients. METHODS: Using techniques for intra-cellular delivery of peptides, we made metallothionein (MT) and superoxide dismutase (SOD), potent endogenous antioxidants, readily transducible into cell membrane and tested their protective effect against the development of DN in OLETF rats. Herein, we study antioxidant peptides for their ability to prevent oxidative damage to primary rat mesangial cells (MCs), which are important constituents of renal glomeruli. RESULTS: Intraperitoneal administration of these antioxidants resulted in delivery to the kidney and decreased ROS and the expression of downstream signals in renal cells and postponed the usual progression to DN. In in vitro experiments, MT and SOD were efficiently transferred to MCs, and the increased removal of ROS by MT and SOD was proportional to the degree of scavenging enzymes delivered. MT and SOD decreased three major oxidative injuries (hyperglycemia, AGE and ROS exposure) and also injuries directly mediated by angiotensin II in MCs while changing downstream signal transduction. CONCLUSIONS: The protective effects of MT and SOD for the progression of DN in experimental animals may be associated with the scavenging of ROS by MT and SOD and correlated changes in signal transduction downstream. Concomitant administration of these antioxidant peptides may prove to be a new approach for the prevention and therapy of DN.

Amelioration of diabetic neuropathy by TAT-mediated enhanced delivery of metallothionein and SOD.

Because diabetic neuropathy (DN) appears to result from oxidative stress in neuronal tissues, antioxidant treatment should counteract the condition. Metallothionein (MT) and superoxide dismutase (SOD) are free-radical scavengers, but their ability to cross biological membranes is limited. Applying cell penetrating peptide technologies, we made Tat-MT and Tat-SOD constructs and tested their ability to protect PC12 cells, as surrogates of peripheral nerve cells, from various forms of oxidative damage. Tat-MT and Tat-SOD were successfully delivered to PC12 cells, and the intracellular activities of MT and SOD increased in line with the amount of protein delivered. These agents inhibited cellular damage and apoptotic signaling caused by three different types of injuries (high glucose, hypoxia, and advanced glycation end product injury). We also examined transduction of Tat-MT and Tat-SOD into Otsuka Long-Evans Tokushima fatty rats. A single ip injection of Tat-MT and Tat-SOD resulted in increased radical scavenging activity and decreased apoptosis, by inhibiting nuclear factor κB and MAPK signaling. Continuous treatment resulted in improved myelination of sciatic nerves and delayed the clinical development of DN. We conclude that effective delivery of a combination antioxidant treatment may facilitate the repair of damage in patients with DN.

The combination of metallothionein and superoxide dismutase protects pancreatic ß cells from oxidative damage.

BACKGROUND: Reactive oxygen species are considered an important cause of the death of pancreatic ß cells, thereby triggering the development of type 2 diabetes as well as failure of islet transplantation. The biological properties of metallothionein (MT) and superoxide dismutase (SOD) are likely to be related to their antioxidant and free-radical scavenging abilities, but their access across biological membranes is limited. METHODS: We investigated whether Tat-MT and Tat-SOD fusion protein could be introduced into islets by a novel protein transduction technology and protect them from oxidative damage. We used 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and Annexin V/propidium iodide assays to analyse cell viability, and assessed expression of apoptosis marker proteins by Western blotting. We examined the protective effect of Tat-MT and Tat-SOD on the development of diabetes and on graft failure after syngeneic islet transplantation into Otsuka Long Evans Tokushima Fatty (OLETF) rats and Imprinting Control Region (ICR) mice, respectively. RESULTS: Tat-MT and Tat-SOD were successfully delivered into the rat islets, and reactive oxygen species, nitric oxide, glucolipotoxicity-induced cell death, cytokine injury, and DNA fragmentation due to ischaemia-reperfusion in pancreatic ß cells were significantly reduced. In addition Tat-MT and Tat-SOD treatment protected OLETF rats from developing diabetes, and enhanced the survival of antioxidant-treated islets transplanted into the renal capsules of diabetic mice. CONCLUSIONS: Transduction of Tat-MT and Tat-SOD proteins offers a new strategy for protecting against the development of diabetes by relieving oxidative stress.

Tat-enhanced delivery of metallothionein can partially prevent the development of diabetes.

Metallothioneins (MTs) are intracellular low-molecular-weight, cysteine-rich proteins with potent metal-binding and redox functions, but with limited membrane permeativity. The aim of this study was to investigate whether we could enhance delivery of MT-1 to pancreatic islets or ß cells in vitro and in vivo. The second goal was to determine whether increased MT-1 could prevent cellular toxicity induced by high glucose and free fatty acids in vitro (glucolipotoxicity) and ameliorate the development of diabetes induced by streptozotocin in mice or delay the development of diabetes by improving insulin secretion and resistance in the OLETF rat model of type 2 diabetes. Expression of HIV-1 Tat-MT-1 enabled efficient delivery of MT into both INS-1 cells and rat islets. Intracellular MT activity increased in parallel with the amount of protein delivered to cells. The formation of reactive oxygen species, glucolipotoxicity, and DNA fragmentation due to streptozotocin decreased after treating pancreatic ß cells with Tat-MT in vitro. Importantly, in vivo, intraperitoneal injection resulted in delivery of the Tat-MT protein to the pancreas as well as liver, muscle, and white adipose tissues. Multiple injections increased radical-scavenging activity, decreased apoptosis, and reduced endoplasmic reticulum stress in the pancreas. Treatment with Tat-MT fusion protein delayed the development of diabetes in streptozotocin-induced mice and improved insulin secretion and resistance in OLETF rats. These results suggest that in vivo transduction of Tat-MT may offer a new strategy to protect pancreatic ß cells from glucolipotoxicity, may improve insulin resistance in type 2 diabetes, and may have a protective effect in preventing islet destruction in type 1 diabetes.