Biomedical subjects

Ken Karasawa

Publications and source records attributed to Ken Karasawa.

6 recordsLinked to original sources

PubMed2006

Clinical aspects of plasma platelet-activating factor-acetylhydrolase.

Plasma platelet-activating factor (PAF)-acetylhydrolase (PAF-AH), which is characterized by tight association with plasma lipoproteins, degrades not only PAF but also phospholipids with oxidatively modified short fatty acyl chain esterified at the sn-2 position. Production and accumulation of these phospholipids are associated with the onset of inflammatory diseases and preventive role of this enzyme has been evidenced by many recent studies including prevalence of the genetic deficiency of the enzyme in the patients and therapeutic effects of treatment with recombinant protein or gene transfer. With respect to the atherosclerosis, however, it is not fully cleared whether this enzyme plays an anti-atherogenic role or pro-atherogenic role because plasma PAF-AH also might produce lysophosphatidylcholine (LysoPC) and oxidatively modified nonesterified fatty acids with potent pro-inflammatory and pro-atherogenic bioactivities. These dual roles of plasma PAF-AH might be regulated by the altered distribution of the enzyme between low density lipoprotein (LDL) and high density lipoprotein (HDL) particles because HDL-associated enzymes are considered to contribute to the protection of LDL from oxidative modification. This review focuses on the recent findings which address the role of this enzyme in the human diseases especially including asthma, septic shock and atherosclerosis.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed2005

Adenovirus-mediated gene transfer and lipoprotein-mediated protein delivery of plasma PAF-AH ameliorates proteinuria in rat model of glomerulosclerosis.

Oxidative stress has been proposed to play a crucial role in glomerulosclerosis, although its in vivo demonstration has proved taxing given the difficulty of inducing gene expression in specific renal cells. In this study, we examined whether the liver-directed expression of plasma platelet-activating factor acetylhydrolase (PAF-AH) would affect the glomerular pathophysiology in Imai rats, an animal model for glomerulosclerosis. Adenovirus-mediated liver-directed gene delivery of human PAF-AH resulted in a significant increase in plasma PAF-AH activity, which was detected almost exclusively on HDL. Histological examination of rats overexpressing PAF-AH showed not only the deposition of PAF-AH in mesangial cells, but also a reduction in hydroxynonenal and matrix protein content in the glomeruli. In situ hybridization analysis was negative for human PAF-AH mRNA in the kidney, while injection of HDL abundant in PAF-AH resulted in the deposition of PAF-AH in mesangial cells. Urine protein levels did not increase in rats overexpressing PAF-AH, while those of control rats increased significantly with age. This study provides direct evidence of the in vivo role of an enzyme that degrades lipid peroxides during the progression of glomerulosclerosis. Adenovirus-mediated extrarenal gene expression and lipoprotein-mediated glomeruli-targeted protein delivery promise to be a novel therapeutic approach to glomerulosclerosis.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed2005

Local expression of platelet-activating factor-acetylhydrolase reduces accumulation of oxidized lipoproteins and inhibits inflammation, shear stress-induced thrombosis, and neointima formation in balloon-injured carotid arteries in nonhyperlipidemic rabbits.

BACKGROUND: Platelet-activating factor (PAF) and PAF-like phospholipids are inactivated by PAF-acetylhydrolase (PAF-AH). Using nonhyperlipidemic animals, we tested whether local expression of PAF-AH into injured arteries might induce antithrombotic and antiinflammatory effects.Method and Results- Balloon-injured rabbit carotid arteries were infected at the time of injury with an adenovirus expressing either human plasma PAF-AH (AdPAF-AH) or bacterial beta-galactosidase (AdLacZ) or infused with saline. Seven days later, shear stress-induced thrombosis was observed in all AdLacZ-infected and saline-infused arteries (controls) but eliminated in AdPAF-AH-treated contralateral arteries, even in the presence of epinephrine or an inhibitor of NO production. Injury-induced expression of tissue factor was also significantly suppressed. In AdPAF-AH-treated arteries compared with controls, the expressions of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 and macrophage infiltration were decreased by 66%, 66%, and 71%, respectively (P<0.01), and intimal area and intima/media ratio were decreased on day 21 by 43% and 52%, respectively (P<0.05). Within 1 week after injury, oxidized lipoproteins (OxLDL) had readily accumulated in the arterial wall. However, this was markedly reduced in the AdPAF-AH-treated arteries. No differences in the titers of autoantibodies to OxLDL or total cholesterol in blood were found between controls and AdPAF-AH-treated rabbits. CONCLUSIONS: Our results show for the first time that OxLDL accumulates in arteries in nonhyperlipidemic animals within 1 week after injury and that local expression of PAF-AH reduces this accumulation and exerts antiinflammatory, antithrombotic, and antiproliferative effects without changing the plasma levels of PAF-AH activity or titers of autoantibodies to OxLDL.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed2005

Red blood cells highly express type I platelet-activating factor-acetylhydrolase (PAF-AH) which consists of the alpha1/alpha2 complex.

Although red blood cells account for about 30% of total PAF-AH activity found in the blood, the physiological function of this enzyme is unknown. To understand the role and regulatory mechanism of this enzyme, we purified it from easily obtainable pig red blood cells. PAF-AH activity was mainly found in the soluble fraction of the red blood cells. Two peaks of enzyme activity appeared with increasing concentration of imidazole on column chromatography on nickel-nitroacetic acid (Ni-NTA) resin. We called these peaks of small and large enzyme activities fractions X and Y, respectively, and then further purified the enzymes by sequential chromatofocusing on Mono P and gel filtration on TSK G-3000. In the final preparation from fraction Y, two proteins bands corresponding to 26 kDa and 28 kDa were related to enzyme activity. Determination of the partial amino acid sequences of the proteins of 26 kDa and 28 kDa revealed that these proteins were identical to alpha(1) and alpha(2), respectively, both of which are catalytic subunits of Type I intracellular PAF-AH. On Western analysis, the 26 kDa and 28 kDa protein bands cross-reacted with specific monoclonal antibodies to alpha(1) and alpha(2), respectively. Since the apparent molecular weight of the natural enzyme was estimated to be about 60 kDa, the enzyme activity in fraction Y was thought to be that of a heterodimer consisting of alpha(1) and alpha(2). On the other hand, the enzyme activity in fraction X was thought to be that of a homodimer consisting of alpha(2). Other blood cells such as polymorphonuclear leukocytes and platelets only contained the alpha(2)/alpha(2) homodimer. It has been reported that the alpha(1)/alpha(2) heterodimer is poorly expressed in adult animals except for in the spermatogonium. Taken altogether, these results suggest that high expression of the alpha(1)/alpha(2) heterodimer is important for the physiological function of mature red blood cells.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed2003

Human plasma platelet-activating factor acetylhydrolase binds to all the murine lipoproteins, conferring protection against oxidative stress.

OBJECTIVE: Plasma platelet-activating factor (PAF) acetylhydrolase (AH) is an enzyme bound with lipoproteins that degrades not only PAF but also PAF-like oxidized phospholipids that are proposed to promote atherosclerosis. In this study, we investigated the distribution of PAF-AH protein among lipoprotein classes by using adenovirus-mediated gene transfer in mice, and we examined its effects on lipoprotein oxidation and foam cell formation of macrophages. METHODS AND RESULTS: Adenovirus-mediated overexpression of PAF-AH in mice resulted in a 76- to 140-fold increase in plasma PAF-AH activity. Contrary to the previous report, overexpressed human PAF-AH protein was bound to very low density lipoprotein, intermediate density lipoprotein, low density lipoprotein, and high density lipoprotein (HDL). All the lipoproteins with overexpressed human PAF-AH revealed more resistance against oxidative stress, which was associated with lower levels in autoantibody against oxidized low density lipoprotein in the plasma. In addition, HDL with human PAF-AH inhibited foam cell formation and facilitated cholesterol efflux in macrophages. CONCLUSIONS: These results suggest that human plasma PAF-AH exerts an antiatherogenic effect by binding to all the lipoproteins and thereby protecting them from oxidation, producing less proatherogenic lipoproteins and preserving HDL functions.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed2003

Plasma platelet activating factor-acetylhydrolase (PAF-AH).

The platelet-activating factor-acetylhydrolase (PAF-AH) is an enzyme which catalyzes the hydrolysis of acetyl ester at the sn-2 position of PAF. The family of PAF-AHs consists of two intracellular isoforms (Ib and II), and one secreted isoform (plasma). These PAF-AHs show different biochemical characteristics and molecular structures. Plasma PAF-AH and intracellular isoform, II degrade not only PAF but also oxidatively fragmented phospholipids with potent biological activities. Among these PAF-AHs, plasma PAF-AH has been the target of many clinical studies in inflammatory diseases, such as asthma, sepsis, and vascular diseases, because the plasma PAF-AH activity in the patients with these diseases is altered when compared with normal individuals. Finding a genetic deficiency in the plasma PAF-AH opened the gate in elucidating the protecting role of this enzyme in inflammatory diseases. The most common loss-of-function mutation, V279F, is found in more than 30% of Japanese subjects (4% homozygous, 27% heterozygous). This single nucleotide polymorphism in plasma PAF-AH and the resulting enzymatic deficiency is thought to be a genetic risk factor in various inflammatory diseases in Japanese subjects. Administration of recombinant plasma PAF-AH or transfer of the plasma PAF-AH gene improves pathology in animal models. Therefore, substitution of plasma PAF-AH would be an effective in the treatment of the patients with the inflammatory diseases and a novel clinical approach. In addition, the detection of polymorphisms in the plasma PAF-AH gene and abnormalities in enzyme activity would be beneficial in the diagnosis of the inflammatory diseases.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗