Serdar Dogan

Hepatic ischemia–reperfusion injury and therapeutic strategies to alleviate cellular damage

Warm hepatic ischemia–reperfusion injury is a significant medical problem in many clinical conditions such as liver transplantation, hepatic surgery for tumor excision, trauma and hepatic failure after hemorrhagic shock. Partial or, mostly, total interruption of hepatic blood flow is often necessary when liver surgery is performed. This interruption of blood flow is termed “warm ischemia” and upon revascularization, when molecular oxygen is reintroduced, the organ undergoes a process called “reperfusion injury” that causes deterioration of organ function. Ischemia reperfusion results in cellular damage and tissue injury associated with a complex series of events. Pathophysiological mechanisms leading to tissue injury following ischemia–reperfusion will be discussed and therapies targeted to reduce liver damage will be summarized within this review.

Oxidative stress and potential applications of free radical scavengers in glaucoma

Abstract Glaucoma is the leading cause of irreversible blindness in industrialized countries and comprises a group of diseases characterized by progressive optic nerve degeneration. Glaucoma is commonly associated with elevated intraocular pressure due to impaired outflow of aqueous humor resulting from abnormalities within the drainage system of the anterior chamber angle (open-angle glaucoma) or impaired access of aqueous humor to the drainage system (angle-closure glaucoma). Oxidative injury and altered antioxidant defense mechanisms in glaucoma appear to play a role in the pathophysiology of glaucomatous neurodegeneration that is characterized by death of retinal ganglion cells. Oxidative protein modifications occurring in glaucoma serve as immunostimulatory signals and alter neurosupportive and immunoregulatory functions of glial cells. Initiation of the apoptotic cascade observed in glaucomatous retinopathy can involve oxidant mechanisms and different agents have been shown to be neuroprotective. This review focuses on the molecular mechanisms of oxidant injury and summarizes studies that have investigated novel free radical scavengers in the treatment of glaucomatous neurodegeneration.

The effect of hemolysis on plasma oxidation and nitration in patients with sickle cell disease.

Abstract This study aimed to determine the effect of haemolysis on plasma oxidation and nitration in sickle cell disease (SCD) patients. Blood was collected from haemoglobin (Hb)A volunteers and homozygous HbSS patients who had not received blood transfusions in the last 3 months. Haemolysis was characterised by low levels of haemoglobin and haptoglobin and high levels of reticulocyte, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), plasma cell-free haemoglobin, bilirubin, total lactate dehydrogenase (LDH) and dominance of LDH-1 isoenzyme. Plasma 8-isoprostane, protein carbonyl and nitrotyrosine levels were measured to evaluate oxidised lipids, oxidised and nitrated proteins, respectively. Plasma nitrite–nitrate levels were also determined to assess nitric oxide (NO) production in both SCD patients and controls. Markers of haemolysis were significantly evident in SCD patients compared to controls. Plasma 8-isoprostane, protein carbonyl and nitrotyrosine levels were markedly elevated in SCD patients compared to controls. Linear regression analysis revealed a significant inverse correlation between haemoglobin and reticulocyte counts and a significant positive correlation of plasma cell-free haemoglobin with protein carbonyl and nitrotyrosine levels. The obtained data shows that increased haemolysis in SCD increases plasma protein oxidation and nitration.

Proteomic detection of nitroproteins as potential biomarkers for cardiovascular disease.

Increased levels of reactive oxygen and nitrogen species are linked to many human diseases and can be formed as an indirect result of the disease process. The accumulation of specific nitroproteins which correlate with pathological processes suggests that nitration of protein tyrosine represents a dynamic and selective process, rather than a random event. Indeed, in numerous clinical disorders associated with an upregulation in oxidative stress, tyrosine nitration has been limited to certain cell types and to selective sites of injury. Additionally, proteomic studies show that only certain proteins are nitrated in selective tissue extracts. A growing list of nitrated proteins link the negative effects of protein nitration with their accumulation in a wide variety of diseases related to oxidation. Nitration of tyrosine has been demonstrated in diverse proteins such as cytochrome c, actin, histone, superoxide dismutase, α-synuclein, albumin, and angiotensin II. In vitro and in vivo aspects of redox-proteomics of specific nitroproteins that could be relevant to biomarker analysis and understanding of cardiovascular disease mechanism will be discussed within this review.

Measurement of intracellular biomolecular oxidation in liver ischemia–reperfusion injury via immuno-spin trapping

Hepatic ischemia-reperfusion (I/R) can lead to liver failure in association with remote organ damage, both of which have significant rates of morbidity and mortality. In this study, novel spin trapping and histopathological techniques have been used to investigate in vivo free radical formation in a rat model of warm liver I/R injury. 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) was administered to rats via intraperitoneal injection at a single dose of 1.5g of pure DMPO/kg body wt 2h before the initiation of liver ischemia. Blood vessels supplying the median and left lateral hepatic lobes were occluded with an arterial clamp for 60min, followed by 60min reperfusion. The effects of DMPO on I/R injury were evaluated by assessing the hepatic ultrastructure via transmission electron microscopy and by histopathological scoring. Immunoelectron microscopy was performed to determine the cellular localization of DMPO nitrone adducts. Levels of nitrone adducts were also measured to determine in situ scavenging of protein and DNA radicals. Total histopathological scoring of cellular damage was significantly decreased in hepatic I/R injury after DMPO treatment. DMPO treatment significantly decreased the hepatic conversion of xanthine oxidase and 4-hydroxynonenal formation in I/R injury compared to the untreated I/R group. The distribution of gold-nanoparticle-labeled DMPO nitrone adducts was observed in mitochondria, cytoplasm, and nucleus of hepatocytes. The formation of protein- and DNA-nitrone adducts was increased in DMPO-treated I/R livers compared to DMPO controls, indicating increased in situ protein and DNA radical formation and scavenging by DMPO. These results suggest that DMPO reduces I/R damage via protection against oxidative injury.

The Role of Retinal Oxidative and Nitrative Injury in Glaucomatous Neurodegeneration

The mechanical compression theory explaining the origin of glaucoma considers elevated intraocular pressure as the most important risk factor for the disease. This theory gives support to the essential signs of glaucomatous optic neuropathy, such as increased cupping and neuroretinal rim thinning but does not explain the existence of normal tension glaucoma. Alternatively, the vascular ischemia theory supposes that vascular insufficiency in the optic nerve head results in decreased metabolic activity, which subsequently leads to increased glutamate accumulation and ganglion cell death. Indeed, a large number of studies have shown a high association between glaucomatous optic neuropathy and vascular disorders related to hypertension, diabetes and hypercholesterolemia. Oxidative stress has been implicated to cause increased intraocular pressure by triggering trabecular meshwork degeneration and thus contributing to alterations in the aqueous outflow pathway. It has also been demonstrated that oxidative DNA damage is significantly greater in trabecular meshwork cells of glaucoma patients compared with controls. Moreover, in vivo studies in humans have shown that both intraocular pressure increase and visual field damage are significantly related to the amount of oxidative DNA damage. Similarly, severity of optic nerve damage in eyes with primary open angle glaucoma is correlated with changes in the trabecular meshwork. Retinal oxidative injury occurring in models of elevated intraocular pressure or in normal tension glaucoma also directly damage the retinal ganglion cell layer, leading to glaucomatous optic neuropathy. Free radical injury has been reported to cause caspase independent cell death in retinal ganglion cells in vitro. Furthermore, many retinal proteins exhibit oxidative modifications in experimental glaucoma, which may lead to important structural and functional alterations. Ocular tissues and fluids contain antioxidants that play a key role in protecting against oxidative damage. However, specific activity of a major antioxidant enzyme, superoxide dismutase, demonstrates an age-dependent decline in normal human trabecular meshwork. Similarly, plasma glutathione levels assessed in patients with newly diagnosed primary open angle glaucoma and ageand gender-matched control subjects revealed that glaucoma patients exhibited significantly lower levels of reduced and total glutathione than did control subjects.