Biren Zhao

Platelet-activating factor in surfactant preparations

Surfactant administration is used for treatment of neonatal respiratory distress syndrome. We studied whether currently used surfactant preparations contain platelet-activating factor (PAF), a potent lipid mediator produced by fetal lungs. Three surfactant preparations from animal sources contained between 36 and 218 pmol of PAF per mL, whereas PAF was undetectable in an artificial surfactant. Based on current recommendations, about 144-654 pmol PAF would be administered per dose of natural surfactant, sufficient to exert possible physiological effects on the lung. The action of PAF may be exacerbated by low activity of PAF-acetylhydrolase, which inactivates PAF, in tracheal fluid from infants with respiratory distress syndrome.

A chimeric Cfh transgene leads to increased retinal oxidative stress, inflammation, and accumulation of activated subretinal microglia in mice.

PURPOSE Variants of complement factor H (Cfh) affecting short consensus repeats (SCRs) 6 to 8 increase the risk of age-related macular degeneration. Our aim was to explore the effect of expressing a Cfh variant on the in vivo susceptibility of the retina and RPE to oxidative stress and inflammation, using chimeric Cfh transgenic mice (chCfhTg). METHODS The chCfhTg and age-matched C57BL/6J (B6) mice were subjected to oxidative stress by either normal aging, or by exposure to a combination of oral hydroquinone (0.8% HQ) and increased light. Eyes were collected for immunohistochemistry of RPE-choroid flat mounts and of retinal sections, ELISA, electron microscopy, and RPE/microglia gene expression analysis. RESULTS Aging mice to 2 years led to an increased accumulation of basal laminar deposits, subretinal microglia/macrophages (MG/MΦ) staining for CD16 and for malondialdehyde (MDA), and MDA-modified proteins in the retina in chCfhTg compared to B6 mice. The chCfhTg mice maintained on HQ diet and increased light showed greater deposition of basal laminar deposits, more accumulation of fundus spots suggestive of MG/MΦ, and increased deposition of C3d in the sub-RPE space, compared to controls. In addition, chCfhTg mice demonstrated upregulation of NLRP3, IP-10, CD68, and TREM-2 in the RNA isolates from RPE/MG/MΦ. CONCLUSIONS Expression of a Cfh transgene introducing a variant in SCRs 6 to 8 was sufficient to lead to increased retinal/RPE susceptibility to oxidative stress, a proinflammatory MG/MΦ phenotype, and a proinflammatory RPE/MG/MΦ gene expression profile in a transgenic mouse model. Our data suggest that altered interactions of Cfh with MDA-modified proteins may be relevant in explaining the effects of the Cfh variant.

Functional analysis of platelet-activating factor in the retinal pigment epithelial cells and choroidal endothelial cells.

Purpose: To investigate the function of platelet-activating factor (PAF) in cultured retinal pigment epithelial (RPE) and choroidal endothelial (CE) cells. Methods: The in vitro and in vivo expression of PAF-receptors (PAF-R) on both these cells was determined. The production of PAF by RPE cells was also determined. The effect of PAF on the proliferation, migration, permeability, and apoptosis of CE cells was examined, and the modulation of PAF on the VEGF level in RPE cells was assessed. Results: PAF-R was present in both types of cells in vitro, as well as in RPE and choroid in vivo. Cultured RPE cells synthesized PAF. PAF stimulated CE cell migration and permeability but not the proliferation. PAF also increased the VEGF level in RPE cells. Conclusions: Similar to VEGF, PAF stimulates CE cell migration and permeability. It also up-regulates VEGF level in RPE cells. PAF may be involved in the pathogenesis of choroidal neovascularization.

Effect of dexamethasone on rat plasma platelet activating factor acetylhydrolase during the perinatal period

It has been previously reported that the administration of dexamethasone (DEX) to adult rats increases the activity of plasma platelet-activating factor acetylhydrolase (PAF-AH) and prevents the development of intestinal necrosis caused by platelet activating factor (PAF) injection. In this report, we examined the effect of DEX administration on plasma PAF-AH activity during the perinatal period. Timed-pregnant rats received DEX (0.2-1.0 mg/kg/d) or normal saline (controls) on days 16-18 (early group) or days 18-20 (late group) of gestation. Maternal plasma PAF-AH activity was lower in late gestation than in postpartum period (P < 0.001). Fetal and neonatal plasma PAF-AH activity was higher than maternal values (P < 0.05). No changes of PAF-AH activity were seen in maternal, fetal or neonatal plasma after prenatal DEX administration at the aforementioned doses. A higher dose of DEX (1.3 mg/kg/d x 4d) or cortisone (200 mg/kg/d) produced an elevation of maternal plasma PAF-AH activity (DEX 79.2+/-3.0, cortisone 70.5+/-1.9 vs. controls 49.4+/-2.3 nmol/min/ml, P < 0.01), but resulted in a high fetal mortality. Treatment of newborn rats with DEX (0.5 mg/kg/d) on days 1-3 after birth, increased plasma PAF-AH activity on day 4 (DEX 292+/-5 versus controls 140+/-9 nmol/min/ml, P < 0.001) and day 6 (DEX 302+/-12 versus controls 136+/-6 nmol/min/ml, P < 0.001). Postnatal administration of DEX increases the plasma PAF-AH activity in the rat. Only high doses of prenatal corticosteroids that cause fetal death can elevate maternal plasma PAF-AH activity.

The Prevention of Necrotizing Enterocolitis

A disease similar, if not identical, to necrotizing enterocolitis (NEC) was first described in the last century in a 2 day-old infant who died of inflammation and perforation of the ileum.1 The incidence of NEC, a disease linked to prematurity, has increased recently due to innovative treatments of premature infants, particularly surfactant replacement. It has been estimated that premature infants suffering from this disease may have a mortality rate as high as 50%. Minimal basic information is known concerning the mechanism(s) involved in the development of NEC. Numerous hypotheses have been invoked as causative or modifying factors of this disease. These include hypothermia, hypoxia, infectious agents, ischemia, various feeding regimes,2 oxygen free radical generation, etc..

Role of Malondialdehyde in the Age-Related Macular Degeneration

The pathogenesis of age-related macular degeneration (AMD) is not clear. The most important risk factors for developing AMD are age, race, and smoking. Genetics, inflammation, and oxidative stress have all been suggested to play a role. The retina is rich in oxygen, free radicals, polyunsaturated fatty acid, and photoactive substances such as lipofuscin, and is exposed to high levels of visible irradiation. Aging is associated with increased oxidative injury. Lipid peroxidation and lipofuscin formation is also increased with aging. Malondialdehyde (MDA) is a product of lipid peroxidation and can be used as a biomarker for oxidative stress. In this chapter, we summarize the available evidence of oxidative stress in the pathogenesis of AMD. In addition, we have demonstrated that high levels of MDA were present in patients with AMD compared to patients without AMD. This suggests that lipid peroxidation-induced oxidative stress may play a role in the pathogenesis of AMD.

PLATELET ACTIVATING FACTOR (PAF) AND PAF-ACETYLHYDROLASE (PAF-AH) ACTIVITY IN NECROTIZING ENTEROCOLITIS (NEC). † 1200

PLATELET ACTIVATING FACTOR (PAF) AND PAF-ACETYLHYDROLASE (PAF-AH) ACTIVITY IN NECROTIZING ENTEROCOLITIS (NEC). † 1200