Colonic malakoplakia in a liver transplant recipient.

Malakoplakia is a rare inflammatory condition seen in transplant patients. There are two previously reported cases of malakoplakia involving the gastrointestinal tract in liver transplant patients. The present paper reports a case of colonic malakoplakia in a 58-year-old woman, a liver transplant recipient who was receiving immunosuppressive drugs. She presented with chronic diarrhea while on tacrolimus. There was no history of antecedent infection. Colonoscopy showed patchy mucosal edema, but no discrete yellow plaques or nodules. The diagnosis was made by colon biopsies, which showed chronic inflammation with many histiocytes containing Michaelis-Gutmann bodies. Although rare, malakoplakia is one of many potential causes of diarrhea in a transplant patient. The present case indicates that malakoplakia may be associated with chronic diarrhea, even if there are no macroscopic lesions seen during colonoscopy.

Phosphorylation of Bad is not essential for PKB-mediated survival signaling in hemopoietic cells.

This study was designed to investigate Bad phosphorylation at several of its key regulatory Ser residues in cytokine-dependent hemopoietic cells. These studies were initiated in light of numerous studies that have reported a key role for phosphorylated Bad in preventing apoptosis. One key question is whether the survival signaling effect of the PI 3-kinase pathway is mediated by PKB phosphorylation of Bad. We confirm previous reports that if Bad is overexpressed or if active PKB is overexpressed, then the increased phosphorylation of Bad at Ser136 is apparent. However, we were unable to detect phosphorylation of endogenous Bad at Ser136 in the MC/9 mast cell line or in murine bone marrow-derived macrophages. On the other hand, phosphorylation of Bad at Ser112 and Ser155 was observed in response to IL-3 or GM-CSF, which activate the MEK/erk pathway, but not with IL-4, which activates the PI 3-kinase, but not the MEK/erk pathway, and also promotes cell survival. In contrast to previous reports, we found that ceramide had no effect on the phosphorylation status of Bad. In summary, our results suggest that Bad phosphorylation at any of the three major sites is not a required event for cytokine-dependent cell survival, and in particular, the activation of PI 3-kinase/PKB pathway can be dissociated from phosphorylation of Bad at Ser136.

Hepatic abscesses after liver transplantation secondary to traumatic intrahepatic bile duct injuries in a cadaveric allograft donor.

We report the case of an ultimately successful liver transplant recipient whose post-transplant course was complicated by the early development of multiple abscesses in the graft. Post-transplant cholangiography identified multiple shear injuries to the second and third order intrahepatic bile ducts, originating from blunt trauma to the donor liver. Treatment was non-operative following recent reports of the successful management of intrahepatic bile duct injury in the stable trauma patient. This discussion adds to the limited literature available on the transplantation of injured donor livers, despite this being a relatively common practice. Further experience is needed in determining the appropriate criteria for the use of traumatized donor livers. Cholangiography carried out on the back table may help to determine if such injured livers are suitable for transplantation.

Orthotopic liver transplantation in a patient with carbamyl phosphate synthetase deficiency and cystic fibrosis.

A 15-year-old female with carbamyl phosphate synthetase deficiency, cystic fibrosis, and cystic fibrosis-related diabetes underwent orthotopic cadaveric liver transplantation. Metabolic control was maintained during the procedure with nutritional support and the use of intravenous sodium phenylacetate and benzoate. Her postoperative course was complicated by seizures and a transient decline in her pulmonary function tests, which returned to preoperative levels within one year of the transplant. Now, four years post-transplant, her quality of life has dramatically improved. There are only four Canadian centres with paediatric liver transplantation programs. However, expert medical care for adults with inborn error of metabolism is even more limited, suggesting that access to adult medical care is one of the many factors to be considered when liver transplantation is contemplated for patients with metabolically unstable conditions.

Primary protein-losing enteropathy in anti-double-stranded DNA disease: the initial and sole clinical manifestation of occult systemic lupus erythematosus?

Hypoalbuminemia and generalized edema is a common clinical problem and the etiology is usually clear: cirrhosis, nephrotic syndrome, primary gastrointestinal disorders, malnutrition, etc. We present a 23-year-old previously healthy woman of Korean background who presented with generalized edema and a serum albumin of 9 g/L (normal, 35-45 g/L). Intensive investigations failed to reveal liver, renal, or inflammatory gastrointestinal mucosal disease. The antinuclear antibody was positive at a titer of 1:80, and extractable nuclear antigens were positive for SSA/anti-Ro. Anti-double-stranded DNA was markedly elevated at 4.6 kU/L (normal, 0-2.0 kU/L). A technetium 99M-labeled albumin study revealed a protein-losing enteropathy, despite normal histologic full-thickness jejunal biopsies. A diagnosis of occult systemic lupus erythematosus resulting in increased intestinal vascular permeability was made. The hypoalbuminemia remained in long-term remission after the initiation of induction and maintenance immunosuppression.

Analysis of causes of death in liver transplant recipients who survived more than 3 years.

Few studies have examined causes of death in long-term survivors of orthotopic liver transplantation (OLT). We reviewed causes of death among 299 adult liver transplant recipients who survived more than 3 years after OLT at 2 centers. Thirty-eight of the 299 patients subsequently died. Nonhepatic causes accounted for 22 of 38 late deaths (58%). Death caused by malignancies occurred in 9 patients between 3.3 and 8.0 years after OLT. Eight patients died of cardiovascular complications. The 6 patients who died of myocardial infarction had risk factors for coronary artery disease. Hepatic failure caused by recurrent liver disease or chronic rejection accounted for 16 of 38 late deaths (42%). These 16 patients were younger than patients who died of nonhepatic complications (mean ages, 50.7 v 62.1 years; P =.001). However, the mean interval between OLT and death was similar among patients who died of nonhepatic versus hepatic causes. Nine patients had recurrent liver disease leading to death, and 8 of 9 patients had recurrent chronic hepatitis C virus (HCV) infection. Chronic rejection resulting in graft failure and death occurred in 7 patients. In summary, de novo malignancies and cardiovascular complications accounted for more than half the late deaths. Patients who died of nonhepatic causes were significantly older than patients who died of hepatic causes. Chronic rejection and recurrent HCV infection accounted for the majority of hepatic causes of death. With longer follow-up, graft failure resulting from recurrent HCV infection will become the major cause of death in late survivors.

5-Aminosalicylate stimulates phospholipase D activity in macrophages.

5-Aminosalicylate, which is considered to be the active moiety of sulfasalazine, is one of the most widely used agents for treatment of inflammatory bowel disease. However, its mechanism of action is unclear. In this report, we provide evidence that the phospholipase D pathway is a target for this drug in macrophages. Activation of phospholipase D leads to the generation of important second messengers such as phosphatidic acid, lysophosphatidic acid and diacylglycerol, all of which can regulate cellular responses involved in inflammation. Murine peritoneal macrophages were labeled with [(3)H]myristate, incubated with various drugs, agonists, or inhibitors, and phospholipase D activity was assayed. 5-Aminosalicylate or sulfasalazine stimulated phospholipase D in a time- and concentration-dependent manner. Chelation of extracellular Ca(2+) inhibited phospholipase D activation by either of these drugs whereas pretreatment of macrophages with the tyrosine kinase inhibitor genistein had no effect. Downregulation of protein kinase C by prolonged incubation with phorbol ester completely blocked the activation of phospholipase D. Pertussis toxin decreased the activation of phospholipase D. The levels of inositol 1,4,5-trisphosphate increased by 260% after treatment of macrophages with 5-aminosalicylate. A phosphoinositide-specific phospholipase C inhibitor U73122 blocked phospholipase D activation completely. Interestingly, long-term preincubation of the macrophages with a relatively low concentration of 5-aminosalicylate that did not stimulate phospholipase D activity by itself, potentiated the effect of phorbol ester-induced activation of phospholipase D. Taken together, these results show that 5-aminosalicylate activates phospholipase D via a pathway involving inositol 1,4,5-trisphosphate generation, calcium fluxes, and Gi/Go. Although the mechanisms by which phospholipase D activation by 5-aminosalicylate or sulfasalazine might attenuate inflammatory responses in the intestine remain to be defined, these results highlight a novel potential mechanism of action for these drugs.

Oxidized low density lipoprotein inhibits macrophage apoptosis through activation of the PI 3-kinase/PKB pathway.

Oxidized LDL (oxLDL) is known to induce endothelial adhesion molecule and monocyte chemoattractant protein 1 expression and this is thought to be involved in monocyte recruitment into atherosclerotic lesions. oxLDL has also been found to induce macrophage proliferation. The purpose of the present study was to determine whether oxLDL might also have the ability to increase macrophage populations by inhibiting apoptosis. We found that oxLDL caused a dose-dependent inhibition of the apoptosis that occurs in cultured bone marrow-derived macrophages after macrophage colony-stimulating factor (M-CSF) withdrawal without inducing proliferation. Incubation of macrophages with either native LDL or acetylated LDL had no effect on apoptosis. The prosurvival effect of oxLDL was not inhibited by neutralizing antibodies to granulocyte-macrophage colony-stimulating factor, was maintained in mice homozygous for a mutation in the M-CSF gene, and was not due to other secreted cytokines or growth factors. oxLDL caused activation of the mitogen-activated protein kinases ERK1/2 (extracellular signal-regulated kinases 1 and 2) as well as protein kinase B (PKB), a target of phosphatidylinositol 3-kinase (PI 3-kinase). Furthermore, there was phosphorylation of two important prosurvival PKB targets, I-kappaBalpha(Ser-32) and Bad(Ser-136). The MEK inhibitors PD 98059 and U0126 blocked ERK1/2 activation but did not diminish survival. Conversely, the PI 3-kinase inhibitors LY 294002 and wortmannin blocked PKB activation, and the ability of oxidized LDL to promote macrophage survival. Taken together, these results indicate that oxLDL can directly activate a PI 3-kinase/PKB-dependent pathway that permits macrophage survival in the absence of growth factors.

De novo acute hepatitis B infection in a previously vaccinated liver transplant recipient due to a strain of HBV with a Met 133 Thr mutation in the "a" determinant.

UNLABELLED: De novo HBV infection post-liver transplantation (LT) from an anti-HBc seropositive donor rarely presents as acute failure. We report a 42-year-old Caucasian female, HBsAg and anti-HBc seronegative, with primary biliary cirrhosis who received an allograft from a HBsAg negative, anti-HBc seropositive donor. The patient, previously vaccinated years pre-LT, was re-vaccinated against HBV and 1 year post-LT had an anti-HBs titre of 256 IU/l. Two years post-LT, elevated serum aminotransferases and worsening liver function with an INR of 2.0 developed. The HBsAg became positive, anti-HBs undetectable and serum HBV-DNA >2000 pg/ml by hybridisation assay. Liver biopsy revealed significant ballooning degeneration, piecemeal necrosis and positive immunostaining for HBsAg. Progressive liver failure developed followed by sepsis and terminal multi-organ failure. Subsequent analysis of the predominant HBV strain revealed mutations in the "a" determinant: Met 133 Thr (codon change ATG to ACG) and Asn 131 Thr. CONCLUSION: ' Acute de novo HBV infection from an anti-HBc sero-positive donor may occur long after LT despite protective anti-HBs titres post-vaccination secondary to the emergence of "a" determinant mutated strains of HBV.

Indications for liver transplantation in British Columbia's Aboriginal population: a 10-year retrospective analysis.

OBJECTIVES: To study the indications for liver transplantation among British Columbia's First Nation population. MATERIALS AND METHODS: A retrospective analysis of the British Columbia Transplant Society's database of Aboriginal and non-Aboriginal liver transplant recipients from 1989 to 1998 was undertaken. For primary biliary cirrhosis (PBC), the transplant assessment database (patients with and without transplants) was analyzed using a binomial distribution and compared with published census data regarding British Columbia's proportion of Aboriginal people. RESULTS: Between 1989 and 1998, 203 transplantations were performed in 189 recipients. Fifteen recipients were Aboriginal (n=15; 7.9%). Among all recipients, the four most frequent indications for liver transplantation were hepatitis C virus (HCV) infection (n=57; 30.2%), PBC (n=34; 18.0%), alcohol (n=22; 11.6%) and autoimmune hepatitis (n=14; 7.4%). Indications for liver transplantation among Aboriginal people were PBC (n=8; 53.3%; P<0.001 compared with non-Aboriginal people), autoimmune hepatitis (n=4; 26.67%; P=0.017), acute failure (n=2; 13.3%) and HCV (n=1). Among all patients referred for liver transplantation with PBC (n=43), 29 (67.44%) were white and 11 (25.6%) were Aboriginal. A significant difference was found between the proportion of Aboriginal people referred for liver transplantation and the proportion of Aboriginal people in British Columbia (139,655 of 3,698,755 [3.8%]; 1996 Census, Statistics Canada) (P<0.001). CONCLUSIONS: Aboriginal people in British Columbia are more likely to be referred for liver transplantation with a diagnosis of PBC but are less likely to receive a liver transplant because of HCV or alcohol than are non-Aboriginal people.

Cholesterol delivered to macrophages by oxidized low density lipoprotein is sequestered in lysosomes and fails to efflux normally.

Oxidized low density lipoprotein (LDL) has been found to exhibit numerous potentially atherogenic properties, including transformation of macrophages to foam cells. It is believed that high density lipoprotein (HDL) protects against atherosclerosis by removing excess cholesterol from cells of the artery wall, thereby retarding lipid accumulation by macrophages. In the present study, the relative rates of HDL-mediated cholesterol efflux were measured in murine resident peritoneal macrophages that had been loaded with acetylated LDL or oxidized LDL. Total cholesterol content of macrophages incubated for 24 h with either oxidized LDL or acetylated LDL was increased by 3-fold. However, there was no release of cholesterol to HDL from cells loaded with oxidized LDL under conditions in which cells loaded with acetylated LDL released about one-third of their total cholesterol to HDL. Even mild degrees of oxidation were associated with impairment of cholesterol efflux. Macrophages incubated with vortex-aggregated LDL also displayed impaired cholesterol efflux, but aggregation could not account for the entire effect of oxidized LDL. Resistance of apolipoprotein B (apoB) in oxidized LDL to lysosomal hydrolases and inactivation of hydrolases by aldehydes in oxidized LDL were also implicated. The subcellular distribution of cholesterol in oxidized LDL-loaded cells and acetylated LDL-loaded cells was investigated by density gradient fractionation, and this indicated that cholesterol derived from oxidized LDL accumulates within lysosomes. Thus impairment of cholesterol efflux in oxidized LDL-loaded macrophages appears to be due to lysosomal accumulation of oxidized LDL rather than to impaired transport of cholesterol from a cytosolic compartment to the plasma membrane.

Stimulation of phospholipase D activity by oxidized LDL in mouse peritoneal macrophages.

Oxidation of LDL is an important factor in the development of atherosclerosis. However, the mechanisms by which oxidized LDL exerts its atherogenic actions are poorly understood. In the present work, we show that oxidized LDL stimulates phospholipase D (PLD) activity in mouse peritoneal macrophages and that this effect increases with the degree of LDL oxidation. Oxidative modification of LDL results in the production of lipid peroxides and the conversion of phosphatidylcholine to lysophosphatidylcholine. Although we found that lysophosphatidylcholine alone activates PLD, the stimulation of this enzyme activity by oxidized LDL is independent of lysophosphatidylcholine formation. Also, 7-ketocholesterol, the major oxysterol in oxidized LDL, failed to stimulate PLD activity. To determine the mechanism(s) whereby oxidized LDL activates PLD, the possible involvements of protein kinase C and tyrosine phosphorylation were investigated. Pretreatment of macrophages with the protein kinase C inhibitor Ro-32-0432 or downregulation of protein kinase C activity by prolonged incubation with 100 nmol/L 4beta-phorbol 12-myristate 13-acetate did not alter the stimulatory effect of oxidized LDL on PLD activation. However, oxidized LDL stimulated tyrosine phosphorylation of several macrophage proteins, and preincubation of the macrophages with genistein, a tyrosine kinase inhibitor, blocked the activation of PLD by oxidized LDL. In addition, pretreatment with orthovanadate, which inhibits tyrosine phosphatases, enhanced basal and oxidized LDL-stimulated PLD activity. Pretreatment of macrophages with pertussis toxin decreased the stimulatory effect of oxidized LDL, indicating that GTP-binding proteins may also be involved in the activation of PLD by oxidized LDL. We also found that the platelet-activating factor receptor antagonists WEB 2086 and L-659,989 inhibit the oxidized LDL stimulation of PLD, suggesting a role for platelet-activating factor receptor in this process. The stimulation of the PLD pathway by oxidized LDL may be of importance in atherogenesis, because PLD activation leads to generation of important second messengers such as phosphatidate, lysophosphatidate, and diacylglycerol, which are known to regulate many cellular functions.

Liver transplantation for chronic hepatitis B infection with the use of combination lamivudine and low-dose hepatitis B immune globulin.

Current protocols for prophylaxis against allograft reinfection after liver transplantation for chronic hepatitis B virus (HBV) infection include the administration of large doses of hepatitis B immune globulin (HBIG), with considerable associated economic costs. Monotherapeutic prophylaxis with lamivudine has been complicated by the development of resistant strains of HBV. We studied the effectiveness of a posttransplantation prophylaxis protocol using combination lamivudine and low-dose HBIG in 7 consecutive patients with chronic HBV infection, 4 of whom were serum HBV DNA positive before pretransplantation lamivudine therapy. All patients were serum HBV DNA negative at transplantation and received lamivudine, 100 mg/d, posttransplantation. HBIG, 2170 IU, was administered intramuscularly intraoperatively and daily for 14 days. Maintenance HBIG therapy consisted of 2170 IU intramuscularly twice weekly, tapered to every 2 to 4 weeks by 12 months posttransplantation. Target serum HBIG (HBV surface antibody) titers were less than 500 IU/L for 6 months, then greater than 300 IU/L until 12 months posttransplantation. Induction serum HBIG titers were determined daily in 5 patients, and both serum HBIG and hepatitis B surface antigen were determined every 4 weeks in all patients. One patient died 61 days posttransplantation; the surviving patients (n = 6) were followed up for a mean of 532 days (range, 395 to 648 days). No patient has developed allograft reinfection. In the induction period, a target HBIG titer of greater than 500 IU/L was not achieved until a mean of 6.8 days (range, 5 to 10 days). In the maintenance period, all patients achieved the target HBIG titer. This suggests combination lamivudine and low-dose HBIG is effective in preventing allograft reinfection by HBV.

Scavenger receptors and oxidized low density lipoproteins.

Oxidized LDL has been shown to exhibit a number of potentially proatherogenic actions and properties, including receptor-mediated uptake and lipid accumulation within macrophages. It has been postulated that rapid, unregulated uptake of oxidatively modified LDL could account for the transformation of monocyte-derived macrophages to foam cells in atherosclerotic lesions. In support of this hypothesis, oxidized LDL and lipid peroxidation products have been shown to exist in atheromas in vivo. Furthermore, a number of cell membrane proteins that can bind oxidized LDL with high affinity have been identified on the surface of macrophages, endothelial cells and smooth muscle cells. One characteristic that almost all of these 'scavenger receptors' share is the ability to bind with high affinity to a broad spectrum of structurally unrelated ligands. Of all of the different classes of scavenger receptors that have been identified, the scavenger receptor class A type I/II (SR-AI/II) has received the most attention. Studies with macrophages from mice deficient in the gene for SR-AI/II provide direct evidence that a receptor other than the SR-AI/II is responsible for most of the uptake of oxidized LDL in murine macrophages. This article provides an overview of the characterization and functions of the scavenger receptors that have been shown to interact with oxidized LDL, including SR-AI/II, CD36, SR-BI, macrosialin/CD68, LOX-1, and SREC. Isolation and characterization of these and other scavenger receptors has increased our understanding of their role in the uptake of oxidized LDL and the pathogenesis of atherosclerosis.

Assessment of immunologic status of liver transplant recipients by peripheral blood mononuclear cells in response to stimulation by donor alloantigen.

OBJECTIVE: To determine whether there is a role for assessing peripheral blood mononuclear cell (PBMC) cytokine patterns as a means of measuring the immunologic and clinical status of liver transplant recipients. SUMMARY BACKGROUND DATA: The role of assessing cytokine patterns in the prediction of clinical graft rejection or acceptance remains unclear. The purpose of this study was to examine the cytokine profiles of PBMC stimulated in vitro with donor alloantigen and to correlate prospectively the data with clinical assessment of graft status in orthotopic liver transplant (OLT) recipients. METHODS: PBMCs from OLT recipients were examined for proliferation and cytokine mRNA expression after stimulation by donor alloantigen, third-party alloantigen, or phytohemagglutinin (PHA). mRNA extracted from PBMC was amplified by reverse transcriptase-polymerase chain reaction with oligospecific primer pairs for interleukin (IL)-2, IL-4, IL-6, IL-10, interferon (IFN) gamma, tumor necrosis factor (TNF) alpha and transforming growth factor (TGF) beta. Results were prospectively correlated with each patient's allograft status. RESULTS: Increased IL-4 and TGF-beta and decreased IL-2, IFNgamma, and TNF-alpha mRNA expression by PBMCs in response to donor alloantigen stimulation predicted immunologic graft stability over a minimum 60-day interval compared with mRNA expression of PBMCs from patients with established rejection or those who experienced a rejection episode within a 30-day period (p < 0.05). Stimulation of recipient PBMCs with third-party alloantigens or PHA yielded similar but less specific results. PBMC proliferation to varying antigenic stimulation did not correlate with clinical graft status, nor did cytokine production by unstimulated PBMC. CONCLUSIONS: Prospective assessment of cytokine expression by PBMC from OLT recipients in response to stimulation by donor alloantigen is helpful for predicting the clinical status of the allograft and may be useful in the development of more precise immunologic monitoring protocols.

Uptake of oxidized LDL by macrophages differs from that of acetyl LDL and leads to expansion of an acidic endolysosomal compartment.

Accumulation of cholesterol by macrophage foam cells in atherosclerotic lesions is thought to involve the uptake of modified low density lipoproteins (LDLs). Previous studies have shown that there is impaired degradation of oxidized LDL in macrophages. The present study was done to determine whether the differences in intracellular metabolism of oxidized LDL and acetyl LDL were associated with delivery to different intracellular compartments. Mouse peritoneal macrophages were incubated with 1,1'-dioctadecyl-3, 3,3',3'-tetramethylindocarbocyanine perchlo- rate-labeled oxidized LDL or 3,3'-dioctadecyloxacarbocyanine perchlorate-labeled acetyl LDL and examined by fluorescence microscopy. Deconvolution image analysis showed <10% colocalization of the 2 lipoproteins at incubation times ranging from 30 minutes to 6 hours. Subcellular fractionation of macrophages after incubation with (99m)Tc-labeled oxidized LDL revealed accumulation of the tracer in a compartment with a d=1.042 g/mL, consistent with endosomes. Surprisingly, there was a concurrent dramatic shift of the density of lysosomal marker enzymes from d=1.1 g/mL to the same fractions that contained (99m)Tc, indicating that this compartment was formed after fusion with primary lysosomes. Parallel experiments in J774 cells, a murine macrophage-like cell line, did not show a similar density shift, perhaps because of the slower rate of accumulation of oxidized LDL by these cells. Fluorescence microscopy of macrophages labeled with a lysosomotropic dye revealed a marked expansion of the acidic compartment after exposure of cells to oxidized LDL. We conclude that oxidized LDL and acetyl LDL are internalized by morphologically distinct pathways. Furthermore, because of its impaired lysosomal degradation, oxidized LDL causes expansion of and a decrease in the density of the lysosomal compartment in macrophages.

Lysophosphatidylcholine stimulates phospholipase D activity in mouse peritoneal macrophages.

Lysophosphatidylcholine (lysoPC) is a bioactive phospholipid that is involved in atherogenesis and inflammatory processes. However, the present understanding of mechanisms whereby lysophosphatidylcholine exerts its pathophysiological actions is incomplete. In the present work, we show that lysoPC stimulates phospholipase D (PLD) activity in mouse peritoneal macrophages. PLD activation leads to the generation of important second messengers such as phosphatidic acid, lysophosphatidic acid, and diacylglycerol, all of which can regulate cellular responses involved in atherogenesis and inflammation. The activation of PLD by lysoPC was attenuated by down-regulation of protein kinase C activity with prolonged incubation with 100 nm of 4beta-phorbol 12-myristate 13-acetate (PMA). Preincubation of the macrophages with the tyrosine kinase inhibitor genistein also decreased the stimulation of PLD by lysoPC, while pretreatment with orthovanadate, which inhibits tyrosine phosphatases, enhanced basal and lysoPC-stimulated PLD activity. The activation of PLD by lysoPC was attenuated by the platelet activating factor (PAF) receptor antagonist WEB-2086, suggesting a role for PAF receptor activation in this process. Furthermore, acetylation of lysoPC substantially increased its potency in activating PLD, suggesting that a cellular metabolite of lysoPC such as 1-acyl 2-acetyl PC might be responsible for at least part of the effect of lysoPC on PLD.

The platelet-activating factor receptor antagonist L-659,989 inhibits phospholipase D activity.

The platelet-activating factor (PAF) receptor antagonist L-659,989 [(+/-)-trans-2-(3-methoxy-5-methylsulfonyl-4-propoxyphenyl)-5-(3,4, 5-trimethoxyphenyl)tetrahydrofuran)] has been reported to be a specific inhibitor of the PAF receptor and as such, it is widely used for assessment of PAF receptor mediated biological effects. We report here that L-659,989 may not be as specific as previously reported because it is also a potent inhibitor of phospholipase D activity. At concentrations of 30 micrograms/ml, L-659,989 inhibited basal and agonist-stimulated phospholipase D activity by about 55% and 70-100% respectively, through a mechanism that may involve the generation of intracellular ceramides. Another PAF receptor antagonist, WEB-2086, did not affect phospholipase D activity at concentrations up to 50 micrograms/ml. Either of these inhibitors when present at 20 micrograms/ml are reported to fully block the effects of PAF. Furthermore, L-659,989 directly inhibited the activity of bacterial PLD in vitro. These results indicate that caution is required in the interpretation of results derived from the use of L-659,989.

A modification of apolipoprotein B accounts for most of the induction of macrophage growth by oxidized low density lipoprotein.

It has recently been shown that macrophage proliferation occurs during the progression of atherosclerotic lesions and that oxidized low density lipoprotein (LDL) stimulates macrophage growth. Possible mechanisms for this include the interaction of oxidized LDL with integral plasma membrane proteins coupled to signaling pathways, the release of growth factors and autocrine activation of growth factor receptors, or the potentiation of mitogenic signal transduction by a component of oxidized LDL after internalization. The present study was undertaken to further elucidate the mechanisms involved in the growth-stimulating effect of oxidized LDL in macrophages. Only extensively oxidized LDL caused significant growth stimulation, whereas mildly oxidized LDL, native LDL, and acetyl LDL were ineffective. LDL that had been methylated before oxidation (to block lysine derivatization by oxidation products and thereby prevent the formation of a scavenger receptor ligand) did not promote growth, even though extensive lipid peroxidation had occurred. The growth stimulation could not be attributed to lysophosphatidylcholine (lyso-PC) because incubation of oxidized LDL with fatty acid-free bovine serum albumin resulted in a 97% decrease in lyso-PC content but only a 20% decrease in mitogenic activity. Similarly, treatment of acetyl LDL with phospholipase A2 converted more than 90% of the initial content of phosphatidylcholine (PC) to lyso-PC, but the phospholipase A2-treated acetyl LDL was nearly 10-fold less potent than oxidized LDL at stimulating growth. Platelet-activating factor receptor antagonists partly inhibited growth stimulation by oxidized LDL, but platelet-activating factor itself did not induce growth. Digestion of oxidized LDL with phospholipase A2 resulted in the hydrolysis of PC and oxidized PC but did not attenuate growth induction. Native LDL, treated with autoxidized arachidonic acid under conditions that caused extensive modification of lysine residues by lipid peroxidation products but did not result in oxidation of LDL lipids, was equal to oxidized LDL in potency at stimulating macrophage growth. Albumin modified by arachidonic acid peroxidation products also stimulated growth, demonstrating that LDL lipids are not essential for this effect. These findings suggest that oxidatively modified apolipoprotein B is the main growth-stimulating component of oxidized LDL, but that oxidized phospholipids may play a secondary role.