Causes of failure in acute respiratory distress syndrome modeling and treatment in animal research and new approaches

Acute respiratory distress syndrome (ARDS) is a major cause of morbidity, death and cost in intensive care units. Despite intensive research, pharmacotherapy has not passed the experimental stage and mortality rates are still high. Animal models provide a bridge between patients and the laboratory bench. Different animal models have been developed in order to mimic human ARDS, but they have limitations. The purpose of this review was to summarize the properties of the most commonly used experimental animal models mimicking the causes and pathology of human ARDS, the limitations of ARDS models, treatment failure and new therapeutic approaches.

Experimental models of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a major cause of morbidity, death and cost in intensive care units. ARDS was first described in 1967, and the new definition was determined as the Berlin definition in 2011 in Berlin. ARDS is a syndrome of inflammation and increased permeability of the blood-gas barrier. Despite intensive research, treatments remain limited and supportive therapies represent the mainstay of the treatment of ARDS. This inability of therapeutic modalities largely depends on the complex pathogenesis of this syndrome with multiple overlapping signaling pathways activated depending on the type of lung injury. Today, this syndrome is still associated with a high morbidity and mortality. Animal models provide us a bridge between bench and bedside. Numerous different models have been developed in order to establish the properties of ARDS, but, to date, no single animal model that mimics all of the characteristics of ARDS in humans has been developed, and most of the existing animal models are relevant only for limited aspects of human ARDS. Furthermore, each animal model has unique features that affect responses to treatment. Therefore, when choosing an animal model of ARDS, to take into account the key feature of ARDS as a working hypothesis to be tested and then create the most appropriate model to exhibit those features is important. The goal of this review is to summarize the properties of the most commonly used experimental animal models of ARDS after mentioning briefly the causes and pathophysiology.

Effects of montelukast and zileuton on testicular torsion/detorsion injury in rats

The aim of this study was to evaluate and compare the effects of 5-lipoxygenase enzyme (5-LO) inhibitor zileuton and cysteinyl leukotriene receptor (CysLT1R) antagonist montelukast in testicular torsion/detorsion (T/D) injury model in rats. Rats were anaesthetised with 75 mg kg(-1) ketamine hydrochloride and 8 mg kg(-1) xylazine intraperitoneal before the operation. Torsion was created by rotating the right testis 720° clockwise and maintained by fixing the testis. The rats were treated with CysLT1R antagonist montelukast (10 mg kg(-1); i.p.), 5-LO inhibitor zileuton (3 mg kg(-1); i.p.), and vehicle, at 30 min prior detorsion. After 1 h of torsion, the testis was counter-rotated to the natural position and replaced into the scrotum. Malondialdehyde (MDA) level was measured in testicular tissue after 3 h of reperfusion. Histological examination was performed after 24 h of reperfusion. T/D caused a significant increase in MDA level and histopathological injury in testes. Montelukast and zileuton treatments prevented the T/D-induced augmentation in MDA levels. Only zileuton treatment significantly reduced the T/D-induced histopathological injury. In this study, we demonstrated for the first time that zileuton had protective effects on testicular T/D injury. We have also found that zileuton is more effective than montelukast on histopathological injury.

The presence of oxidized low-density lipoprotein and inducible nitric oxide synthase expression in renal damage after intestinal ischemia reperfusion

Intestinal ischemia/reperfusion (I/R) is a complex phenomenon that causes destruction of both local and remote tissues. The objective of this study was to investigate the possible participation of oxidized low-density lipoproteins (oxLDLs) and inducible nitric oxide synthase (iNOS) expression in renal tissue damage after intestinal I/R. The superior mesenteric artery was blocked for 30 minutes, followed by 24 hours of reperfusion. At the end of the reperfusion period, renal tissues were removed; the presence of oxLDL, superoxide dismutase enzyme activity, malondialdehyde levels, and iNOS expression were evaluated. I/R resulted in positive oxLDL staining in renal tissue. Compared with control rats, tissue from the I/R group showed significantly higher malondialdehyde levels and lower superoxide dismutase enzyme activity. Strong and diffuse iNOS expression was present in the I/R group. Our findings support the hypothesis that I/R of intestinal tissue results in oxidative and nitrosative stress and enhances lipid peroxidation in the end organ. These data show that oxLDL accumulates in rat renal tissue after intestinal I/R. Antioxidant strategies may provide organ protection in patients with reperfusion injury, at least by affecting interactions with free radicals, nitric oxide, and oxLDL. This study demonstrates for the first time that oxLDL may play a role in renal tissue damage after intestinal I/R. Antioxidant strategies may be beneficial for protection from reperfusion injury.

Low-density lipoproteins oxidized after intestinal ischemia/reperfusion in rats

BACKGROUND

Intestinal ischemia/reperfusion (I/R) is a complex phenomenon causing destruction of both local and remote tissues, as well as multiple-organ failure. We investigated the role of lipid peroxidation in damage to intestinal, liver, and lung tissues in this pathology.

MATERIALS AND METHODS

The superior mesenteric artery was blocked for 30 min followed by 24 h of reperfusion. Tissues were removed and the presence of oxidized LDL, the activities of the superoxide dismutase enzyme, malondialdehyde levels, and inducible nitric oxide synthase expression were each evaluated in the intestinal, liver, and lung tissues.

RESULTS

While there was no staining in the control group tissues, ischemia/reperfusion resulted in positive oxidized LDL staining in all of the I/R test group tissue samples. Inducible nitric oxide synthase expression was significantly increased in the ischemia/reperfusion group tissues. Compared with those of the control group rats, the ischemia/reperfusion group tissues showed significantly higher malondialdehyde levels and lower superoxide dismutase activities.

CONCLUSIONS

This study demonstrated for the first time that oxidized LDL accumulated in the terminal ileum, liver, and lung tissues after intestinal ischemia/reperfusion. This occurrence (or the presence of oxidized LDL) may be an indicator of ongoing oxidative stress and enhanced lipid peroxidation. Augmentation of inducible nitric oxide synthase expression may play a role in progression of inflammation and LDL oxidation. These data support the hypothesis that cellular oxidative stress is a critical step in reperfusion-mediated injury in both the intestine and end organs, and that antioxidant strategies may provide organ protection in patients with reperfusion injury, at least through affecting interaction with free radicals, nitric oxide, and oxidized LDL.

Accumulation of oxidized low-density lipoprotein in psoriatic skin and changes of plasma lipid levels in psoriatic patients

Background. Psoriasis is a chronic inflammatory skin disease characterized by an accelerated turnover of epidermal cells and an incomplete differentiation in epidermis with lesion. However, the exact etiology of psoriasis is unknown. Abnormalities in essential fatty acid metabolism, free radical generation, lipid peroxidation, and release of lymphokines have been proposed. Objective. Our purpose was to evaluate the plasma lipids and oxidized low-density lipoprotein accumulation in psoriatic skin lesion in order to ascertain the possible participation of oxidative stress and oxidative modification of lipids in pathogenesis of psoriasis. Methods. The study group included 84 patients with psoriasis, and 40 sex- and age-matched healthy volunteers. Blood lipid profile was determined. Psoriatic and nonlesional skin samples of psoriatic patients were evaluated for the presence of oxidized low-density lipoprotein by using an immune-fluorescent staining method. Results. The mean levels of lipids (total cholesterol, triglyceride, and LDL cholesterol) in patients with psoriasis were found to be significantly higher than those of healthy subjects. Psoriatic skins were shown positive oxidized low-density lipoprotein staining. There was no staining in nonlesional skin samples of the same individuals. Conclusion. Lipid peroxidation mediated by free radicals is believed to be one of the important causes of cell membrane destruction and cell damage. This study shows for the first time the accumulation of oxidized low-density lipoprotein in psoriatic skin lesion. We believe that accumulation of ox-LDL in psoriatic skin may have an important role in the immune-inflammatory events that result in progressive skin damage.

Plasma total homocysteine levels in a healthy Turkish population sample

OBJECTIVE

The objective of this study is to determine the reference values of homocysteine levels from a sample of healthy native Turks, and the relationship of these levels with gender, age and other risk factors.

METHODS AND RESULTS

Plasma homocysteine level was measured in 159 healthy Turkish individuals. Homocysteine levels were determined by the HPLC method and differences between sex and age groupings (20-40 years, 41-60 years, and 61 and older) were compared. Mean homocysteine levels were 8.91 +/- 1.41 micromol/l. The median homocysteine level was 8.35 micromol/l (men 8.80, women 7.0). Homocysteine levels significantly increased with age (r = 0.49) and higher in men than in women in each age group (p < 0.05) (men: 9.51 +/- 1.40; women 7.38 +/- 1.36; p < 0.001). The cut-off point for high homocysteine level is selected to be the value that marks the upper 20% of the control population distribution (12.26 micromol/l). Postmenopausal > 60-year-old women manifested significantly higher increases in total homocysteine concentrations than 20 to 40-year-old premenopausal women. There were no significant correlations between homocysteine and body mass index, glucose, total and lipoprotein lipids, C-reactive protein, creatinine, smoking and alcohol consumption except blood pressure and uric acid.

CONCLUSIONS

These data indicate the significance of sex- and age-associated differences of homocysteine levels in native Turkish subjects. Upper reference limits for the plasma total homocysteine concentration increased with age and were higher for men than for women at all ages. Focusing public health initiatives on this issue may reduce the high prevalence of cardiovascular disease in the Turkish population.

Oxidized low-density lipoproteins accumulate in rat lung after experimental lung edema induced by alpha- naphthylthiourea (ANTU)

Oxidation of the low-density lipoprotein (LDL) results in the production of modified LDLs. Oxidation of LDL cholesterol plays a role on the pathogenesis of endothelial dysfunction. This study was designed to investigate the possible participation of the oxidative modification of low density lipoprotein in the lung edema induced by alpha-naphthylthiourea (ANTU), which is a well-known noxious chemical agent on the lung endothelium. When ANTU injected intraperitoneally into rats (15 mg kg(-1)), it produced lung edema as indicated by an increase in lung weight/body weight (LW/BW) ratio and pleural effusion (PE) reaching a maximum within 4 h. A significant lung edema was observed 4 h after intraperitoneally injection of alpha-naphthylthiourea when compared with olive oil-injected control rats. On microscopic examination of alpha-naphthylthiourea-treated rats were shown to have severe lung injury, while no change was observed in olive oil-treated control rats. While there were no staining in control lungs, positive oxidized low-density lipoproteins immune-fluorescent staining were observed in lung edema group. Our study showed that oxidized low-density lipoprotein (oxLDL) accumulated in ANTU-induced lung damage. This is the first study in which accumulation of oxLDL molecules in the intact lung tissue were shown by fluorescent immune-staining method in experimental lung edema. The potential role of oxLDL in this pathology are still under investigation.

Morphine modulates inducible nitric oxide synthase expression and reduces pulmonary oedema induced by α-naphthylthiourea

This study was designed to investigate the possible participation of morphine in pulmonary oedema induced by alpha-naphthylthiourea (ANTU), which is a well-known noxious chemical agent in the lung. Injection of ANTU (15 mg/kg i.p.) produced pulmonary oedema as indicated by an increase in lung weight/body weight ratio and pleural effusion reaching a maximum within 4 h in rat. Administration of morphine prior to ANTU significantly inhibited to pulmonary oedema with a dose-dependent manner. The protective effect of morphine is prevented by peripheral opioid receptor antagonist, naloxone methiodide. ANTU-treated rats were shown positive by inducible nitric oxide synthase immunohistochemical staining. There was no staining in the control group. On the other hand, the degree of staining was markedly reduced in tissue sections by morphine. These results suggest that previous administration of subcutaneous morphine has preventive effect on ANTU-induced pulmonary inflammatory reaction and its effect mediated via peripheral opioid receptors. Application of naloxone with ANTU has no effect on the lung parameters indicating that endogenous opioids do not modulate ANTU-induced damage.

Nitric oxide and prostanoid-dependent relaxation induced by angiotensin II in the isolated precontracted mouse tracheal muscle and the role of potassium channels

In this study we examined the mechanism of the concentration-dependent relaxant effect of angiotensin II (A II) on mouse isolated tracheal rings precontracted by carbachol. The contractile effect of carbachol is increased while the relaxant effect of A II decreased by pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME). This finding suggests that the L-arginine nitric oxide (NO) pathway is activated by the peptide. The relaxing effect of A II was also mediated through the release of cyclo-oxygenase products of arachidonic acid, as evidenced by the inhibition of the response by lysine acetylsalicylic acid (ASA) pretreatment. A II also caused a relaxation in the isolated tracheal rings precontracted by K(+)(>60 m m). K(+)-channel blockers partially inhibited the relaxant effect of A II in carbachol-precontracted mouse tracheal rings. A non-selective blocker of K(+)channels, tetraethylammonium, completely abolished the relaxation induced by A II. Among the other channel blockers, the inhibitory effect of apamine and glibenclamide was higher than that of iberiotoxin, indicating the involvement of K(ATP)and small conductance K(Ca)channels in the relaxing response to the octapeptide. These results suggest that the mechanisms, involved in the relaxation induced by A II in the isolated mouse tracheal rings precontracted by carbachol, were firstly l -arginine NO and cyclo-oxygenase products of arachidonic acid, secondly K(+)channels.

Changes of arterial arachidonic acid metabolites in hypertensive patients during haemodialysis

It is well known that in haemodialysis patients suffering from oligoanuria, extracellular hypervolaemia develops and this hypervolaemia is the main reason for hypertension occurring in some of the patients. The absence of vasorelaxation during hypervolaemia may be secondary to an increased activity of vasoconstrictor systems and/or a decreased formation of vasodilator agents like prostaglandin E2(PGE2) and prostaglandin I2(PGI2). In the present study, arterial PGE2 and leukotriene C4(LTC4)-like activities and the effect of fluid removal on these arachidonic acid metabolites during haemodialysis were measured in normotensive and hypertensive patients. Plasma PGE2 and LTC4-like activities were significantly different between hypertensive and normotensive patients. PGE2/LTC4 ratio did not change in normotensive patients while it was increased in hypertensive patients after haemodialysis. These results indicate that haemodialysis alters the synthesis of arachidonic acid metabolites especially in hypertensive patients.