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PubMed1990

Phospholipase activation and arachidonic acid release in intestinal epithelial cells from patients with Crohn's disease.

A method for studying the mobilization of free arachidonic acid (AA) in viable isolated human intestinal epithelial cells has been developed and applied to the study of patients with Crohn's disease. Cells were isolated from morphologically unaffected parts of the distal ileum and incubated with 14C-AA; most of the incorporated 14C-AA was then found in phospholipids (mainly phosphatidylcholine) and in a pool of neutral lipids (mainly triacylglycerols). Cells from patients with Crohn's disease incorporated more 14C-AA into their neutral lipids than did cells from control patients. When the labeled cells were stimulated with phospholipase C from Clostridium perfringens or with the calcium ionophore A23187, they released significant amounts of AA, mainly from phosphatidylcholine. There was no difference between cells from Crohn patients and controls in the 14C-AA amounts released, but unstimulated and phospholipase C-stimulated cells from prednisolone-treated Crohn patients released less AA than cells from control patients. The A23187-stimulated AA release was completely inhibited by the phospholipase A2 inhibitor 4-bromophenacyl bromide, whereas the phospholipase C-stimulated release was not. These findings suggest that AA release in human small-intestinal epithelial cells may be caused by calcium-mediated phospholipase A2 activation or by products of microbial phospholipase C activity and that prednisolone reduces the mobilization of free AA in intestinal epithelial cells. They also illustrate the potential use of isolated epithelial cells for revealing mechanisms underlying AA release in the intestinal mucosa in different disease states.

Adult↗

PubMed1990

Phospholipase A2 activation and autoinduction of tumor necrosis factor gene expression by tumor necrosis factor.

Tumor necrosis factor (TNF) acts via a cell surface receptor to induce a variety of cellular events including cytolysis, differentiation, and mitogenesis. The mechanisms underlying the cell specific actions of TNF are not known. In the present study, postreceptor events associated with the autoinduction of TNF expression were examined in HL-60 cells. There was no detectable alteration in phospholipase C activity as measured by inositol phosphate generation or release of choline metabolites following TNF stimulation. However, TNF increased the release of arachidonic acid metabolites from HL-60 cells. This increase in arachidonic acid metabolism was associated with a 40% increase in phospholipase A2 activity. Furthermore, the release of arachidonic acid metabolites was blocked by inhibitors of phospholipase A2. Taken together, these findings indicated that TNF stimulates phospholipase A2 and arachidonic acid metabolism in HL-60 cells. The results also demonstrate that TNF expression is induced 15-30 min after stimulation with TNF and that this effect is associated with an increase in the rate of TNF transcription. This autoinduction of TNF mRNA was blocked by inhibitors of phospholipase A2. While the cyclooxygenase inhibitor indomethacin had no detectable effect, ketoconazole and nordihydroguaiaretic acid, inhibitors of lipoxygenase, also blocked the induction of TNF expression by TNF. These findings suggest that phospholipase A2 and lipoxygenase activity are required for the transcriptional activation of TNF gene expression associated with TNF stimulation of HL-60 cells.

Acetophenones↗

PubMed1990

Identification and purification of a very high affinity binding protein for toxic phospholipases A2 in skeletal muscle.

Oxyuranus scutellatus toxin 1 (OS1) and toxin 2 (OS2) are two monochain phospholipases A2 isolated from the venom of Taipan. Their iodinated derivatives have been used to characterize phospholipase A2 receptors on rabbit skeletal muscle cells in culture. Both ligands recognize one family of binding sites on myotube membranes with a Bmax of 1.9 to 2.2 pmol/mg of protein and dissociation constant values of 7.4 pM for 125I-OS2 and 38 pM for 125I-OS1. Other snake venom phospholipases A2 are able to inhibit 125I-OS2 binding to the muscle receptor. Competition experiments with these unlabeled phospholipases A2 define a pharmacological profile of the muscle receptor very different from the previously described pharmacological profile of the neuronal phospholipase A2 receptors. The number of 125I-OS2 receptors in skeletal muscle cells increases during in vitro cell maturation but there is no clear relation between the increase of Bmax and the fusion of myoblasts into myotubes. The phospholipase A2 binding protein from myotubes has been identified both by cross-linking experiments and by purification studies. It is composed of only one subunit of Mr 180,000.

Affinity Labels↗

PubMed1990

[The effect of calmodulin and chlorpromazine on the activity of phospholipases A2 from various sources].

The effects of calmodulin and chlorpromazine on purified phospholipase A2 preparations from snake venoms: cobra (Naja naja oxiana), echis (Ehis multisquamatus) and Agkistrodon halys halys, as well as on phospholipases A2 from rat liver mitochondria and human platelets were studied. It was shown that within the concentration range of 1-5 microM calmodulin stimulates the phospholipase activity. Chlorpromazine inhibits the activity of these enzymes, the degree of inhibition being different for various phospholipases. Calmodulin was shown to interact with the phospholipases in the absence of exogenous Ca2+. The results obtained indicate that all phospholipases tested are calmodulin-dependent enzymes.

Animals↗

PubMed1985

Effects of phospholipase A2 inhibitors on ruthenium red-induced Ca2+ release from mitochondria.

The pharmacologic agents verapamil, nifedipine, diltiazem, prenylamine, N-oleoylethanolamine, R 24571, trifluoperazine, dibucaine, and quinacrine are examined as potential inhibitors of rat liver mitochondrial phospholipase A2 acting on endogenous phospholipid. Their potency as inhibitors of the enzyme is compared to their activities as inhibitors of phospholipase A2-dependent swelling and ruthenium red-induced Ca2+ release in intact mitochondria. For verapamil, diltiazem, trifluoperazine, dibucaine, and quinacrine, there is complete agreement between the relative potencies as inhibitors of phospholipase A2 and the two other processes. Nifedipine and prenylamine, which are weak inhibitors of phospholipase A2, produce a permeable inner membrane, provided that the mitochondrial have accumulated Ca2+. R 24571, which strongly inhibits the enzyme, disrupts mitochondria by a Ca2+-independent mechanism. N-Oleoylethanolamine, which is an effective inhibitor of swelling, does not inhibit phospholipase A2 or ruthenium red-induced Ca2+ release. The results support a proposed scheme wherein ruthenium red-induced Ca2+ release is viewed as reverse activity of the Ca2+-uptake uniporter occurring subsequent to decline in the proton motive force. The latter effect is proposed to arise from a specific phospholipase A2-dependent increase in inner-membrane H+ conductance of mitochondrial subpopulations. It is further shown that mitochondrial membranes display cyclic oscillations in free fatty acid content which are not dependent on the presence of Ca2+ or on the capacity to generate acylcoenzyme A.

Animals↗

PubMed1989

Receptor-stimulated phospholipase A2 activation is coupled to influx of external calcium and not to mobilization of intracellular calcium in C62B glioma cells.

C62B rat glioma cells respond to muscarinic cholinergic stimulation with transient inositol phosphate formation and phospholipase A2-dependent arachidonic acid liberation. Since phospholipase A2 is a Ca2+-sensitive enzyme, we have examined the role of the agonist-stimulated Ca2+ response in production of the arachidonate signal. The fluorescent indicator fura-2 was used to monitor changes in cytoplasmic Ca2+ levels ([Ca2+]i) of C62B cells following acetylcholine treatment. In the presence of extracellular Ca2+, acetylcholine induces a biphasic [Ca2+]i response consisting of an initial transient peak that precedes arachidonate liberation and a sustained elevation that outlasts the phospholipase A2 response. The initial [Ca2+]i peak is not altered by the absence of external Ca2+ and therefore reflects intracellular Ca2+ mobilization. The sustained elevation phase is dependent on the influx of external Ca2+; it is lost in Ca2+-free medium and restored on the addition of Ca2+. Pretreating cells with phorbol dibutyrate substantially inhibits acetylcholine-stimulated inositol phosphate formation and the peak [Ca2+]i response without affecting the sustained elevation in [Ca2+]i. This suggests that the release of internal Ca2+ stores by inositol 1,4,5-trisphosphate can be blocked without interfering with Ca2+ influx. Pretreatment with phorbol also fails to affect acetylcholine-stimulated arachidonate liberation, demonstrating that phospholipase A2 activation does not require normal intracellular Ca2+ release. Stimulated arachidonate accumulation is totally inhibited in Ca2+-free medium and restored by the subsequent addition of Ca2+. Pretreatment with verapamil, a voltage-dependent Ca2+ channel inhibitor, also blocks both the sustained [Ca2+]i elevation and arachidonate liberation without altering peak intracellular Ca2+ release. We conclude that the influx of extracellular Ca2+ is tightly coupled to phospholipase A2 activation, whereas large changes in [Ca2+]i due to mobilization of internal Ca2+ stores are neither sufficient nor necessary for acetylcholine-stimulated phospholipase A2 activation.

Acetylcholine↗

PubMedDate not supplied

[Effect of phospholipases A2 from bee and cobra venom on the phospholipid composition and Na+-,K+-ATPase activity of synaptosomes].

The bee and cobra venom phospholipases A2 as well as partially acetylated cobra venom phospholipase A2 are studied for their effect on phospholipid composition of synaptosomes and their Mg2+- and Na+,K+-ATPase activity. It is established that these phospholipases induce the splitting of phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine, inhibition of the Na+,K+-ATPase activity and activation of Mg2+-ATPase. Bee venom phospholipase A2 is more effective than cobra venom phospholipase A2, the both phospholipases splitting phosphatidylethanolamine most intensively. The ATPase activity may be partially or completely restored by exogenic phosphatidylcholine and phosphatidylserine; exogenic phosphatidylethanolamine is not efficient in this respect.

Animals↗

PubMed1987

Characterization of lipocortin I and an immunologically unrelated 33-kDa protein as epidermal growth factor receptor/kinase substrates and phospholipase A2 inhibitors.

Reversible calcium-dependent association with a particulate fraction from human placenta was used as the first step in the purification of substrates for the epidermal growth factor-stimulated protein kinase. A protein with apparent Mr of 35,000 was purified to homogeneity, and the sequence was determined for approximately one-fourth of the protein. These residues could be aligned exactly with the previously published sequence of lipocortin I derived from the cDNA from a human lymphoma. Two other proteins that appear to be formed by proteolytic removal of 12 or 26 of the amino acids from the NH2 terminus of the protein also were isolated. Placental lipocortin I was phosphorylated in Tyr-21 in an epidermal growth factor-dependent manner by the kinase activity in a particulate fraction from A431 cells; half-maximal phosphorylation occurred at 50 nM lipocortin I. Lipocortin I phosphorylated on Tyr-21 was approximately 10-fold more sensitive to tryptic cleavage at Lys-26 than was the native protein. Placental lipocortin I and its two truncated forms were potent inhibitors of pancreatic phospholipase A2 activity. Another 33-kDa protein that was not related immunologically to lipocortin I or lipocortin II (calpactin I) also was purified from the EGTA extract of placenta. The unidentified protein inhibited phospholipase A2 but was not a substrate for the epidermal growth factor-stimulated kinase. The mechanism by which these proteins inhibit phospholipase A2 activity was investigated. Attempts to detect direct interaction between these proteins and the enzyme were unsuccessful. However, both the unidentified protein, lipocortin I, and 32P-labeled lipocortin I bound in a Ca2+-dependent manner to the [3H]oleic acid-labeled Escherichia coli membranes used as substrate in the phospholipase A2 assay. Heparin, which is known to block lipocortin I inhibition of phospholipase A2, also blocked binding of lipocortin I to E. coli membranes. The results of these and other experiments raise the possibility that placental lipocortin I inhibits phospholipase A2 activity in this assay by coating the phospholipid and thereby blocking interaction of enzyme and substrate.

Amino Acid Sequence↗

PubMed1987

The purification and characterization of a phospholipase A in hamster heart cytosol for the hydrolysis of phosphatidylcholine.

Phospholipases A1 and A2 catalyze the hydrolysis of acyl groups of phospholipids at C-1 and C-2, respectively. These phospholipases are important in phospholipid catabolism and the remodeling of the acyl groups of phospholipids. Phospholipase A from hamster heart cytosol was purified by a combination of ion-exchange and gel filtration chromatography. The purity of the enzyme was assessed by nondenaturing polyacrylamide gel electrophoresis, two-dimension polyacrylamide gel electrophoresis, and immunological studies. The purified enzyme exhibited both phospholipase A1 and A2 activities toward phosphatidylcholine and had the ability to hydrolyze the acyl groups of phosphatidylethanolamine. However, the enzyme was not active toward lysophosphatidylcholine, diacylglycerol, or triacylglycerol. By Sepharose 6B chromatography, the molecular weight of the purified enzyme was estimated to be 140,000. Analysis of the purified enzyme by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the enzyme was composed of identical Mr 14,000 subunits. At least six subunits in the native enzyme could be cross-linked by dimethyl suberimidate. Both phospholipase A1 and A2 activities showed similar pH profiles, exhibited no absolute requirements for divalent metallic cations, but displayed a high degree of specificity for the acyl groups of phosphatidylcholine at both C-1 and C-2. The Km of phospholipases A1 and A2 for 1-palmitoyl-2-arachidon-ylglycerophosphocholine was found to be identical (0.5 mM).

Animals↗

PubMed1988

Functional interaction between Cerebratulus lacteus cytolysin A-III and phospholipase A2. Implications for the mechanism of cytolysis.

A study on the interaction between bee venom phospholipase A2 and Cerebratulus lacteus cytolysin A-III, a major hemolysin secreted by this organism has been carried out. The hemolytic activity of A-III in phosphate-buffered saline is increased 5-fold in the presence of phospholipase A2 from bee venom. Dansylphosphatidylethanolamine (DPE) labeled, phosphatidylcholine-containing liposomes and human erythrocyte membranes were employed to study the interaction between these two proteins. In DPE-liposomes, A-III alone had no effect on DPE fluorescence nor did it enhance either the phospholipase A2-dependent fluorescence increase or blue shift in emission maximum, indicating that the cytolysin is not a major phospholipase A2-activator. However, when DPE was incorporated into erythrocyte membranes, A-III alone induced a 40% fluorescence increase and a 5 nm blue shift, implying a transient activation of an endogenous phospholipase A2. Further studies using synthetic lysophosphatidylcholine and free fatty acids demonstrated that the hemolytic activity of A-III is potentiated by free fatty acids, a product of phospholipid degradation catalyzed by phospholipase A2. Together, sublytic concentrations of A-III and nonlytic concentrations of oleic acid cause extensive cell lysis. Subsequent analysis of this phenomenon by gel filtration chromatography, analytical ultracentrifugation, chemical cross-linking, and measurement of [14C]oleic acid binding by the cytolysin demonstrated that binding of oleic acid to A-III causes aggregation of the toxin molecules to a tetrameric form which has a higher alpha-helix content and a greater activity than the monomer.

Bee Venoms↗

PubMed1982

Differential inhibitory effects by phospholipase A2 on guanylate and adenylate cyclases of Tetrahymena plasma membranes.

Phospholipid composition of Tetrahymena plasma membranes was modified by phospholipase A2-treatment and its effects on the activities of the two membrane-bound cyclases (adenylate and guanylate) were studied. Phospholipase A2 from Crotalus adamanteus was found to hydrolyze preferentially phosphatidylethanolamine of isolated plasma membranes. In the phospholipase A2-treated membranes in which 45% of total phosphatidylethanolamine was converted to its lysolipid, adenylate cyclase activity was to a small extent reduced, whereas guanylate cyclase activity was decreased almost to a half. However, the stimulation rate of the guanylate cyclase activity by calmodulin was unaffected in phospholipase A2-treated plasma membranes. The apparent Km value for substrates was not different between phospholipase A2-untreated and -treated plasma membranes. The ESR analysis demonstrated that the phospholipase A2-treated plasma membranes showed an increased fluidity in the range above 25 degrees C as compared to the untreated control membranes. These results suggest that guanylate cyclase is more dependent on phospholipid environment than adenylate cyclase in Tetrahymena plasma membranes, presumably offering evidence for the different location of two enzymes in the membrane.

Adenylyl Cyclase Inhibitors↗

PubMed1983

Effect of membrane sterol content on the susceptibility of phospholipids to phospholipase A2.

The effects of membrane sterol level on the susceptibility of LM cell plasma membranes to exogenous phospholipases A2 has been investigated. Isolated plasma membranes, containing normal or decreased sterol content, were prepared from mutant LM cell sterol auxotrophs. beta-Bungarotoxin-catalyzed hydrolysis of both endogenous phospholipids and phospholipids introduced into the membranes with beef liver phospholipid exchange proteins was monitored. In both cases, phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were degraded at similar rates in normal membranes, while PC hydrolysis was specifically accelerated in sterol-depleted membranes. Additional data suggest that this preferential hydrolysis of PC is not a consequence of the phospholipid head group specificity of the phospholipase, nor of a difference in the accessibility of PC versus PE to the enzyme. Analysis of the reaction products formed during treatment of isolated membranes with phospholipase A2 showed almost no accumulation of lysophospholipids. This was found to be due to highly active lysophospholipase(s), present in LM cell plasma membranes, acting on the lysophospholipids formed by phospholipase A2 action. A soluble phospholipase A2 was partially purified from LM cells and found to behave as beta-bungarotoxin with regard to membrane sterol content. These results demonstrate that the nature of phospholipid hydrolysis, catalyzed by phospholipase A2, can be significantly affected by membrane lipid composition.

Animals↗

PubMed1981

[Phospholipase A in the semen. Occurrence, properties and possible physiological significance].

Phospholipase A2 activities have been detected in seminal plasmas of different vertebrates. These enzyme activities significantly correlate with the prostanoid contents. Considering these findings and the general regulatory function of phospholipase A2 in prostanoid biosynthesis, it is concluded that the seminal phospholipase A2 functions in triggering biosynthesis of seminal prostanoids, both being released predominantly by the vesicular and/or prostate glands. Phospholipase A2, which has been purified to homogeneity from human seminal plasma as the obviously richest enzyme source, clearly resembles pancreatic phospholipase A2 in many of its properties. In principle stimulatory as well as inhibitory effects of various drugs on fertility seem to be possible via alterations in the biosynthesis of seminal prostanoids as a consequence of drug effects on phospholipase A2 activities.

Fertility↗

PubMed1980

Isolation of anticoagulant proteins from cobra venom (Naja nigricollis). Identity with phospholipases A2.

Three anticoagulant proteins were isolated from the venom of Naja nigricollis (spitting cobra). The peaks of anticoagulant activity co-chromatographed with phospholipase A2 activities. The three proteins were homogeneous by the criteria of electrophoresis in two acidic polyacrylamide gel systems. Electrophoresis in sodium dodecyl sulfate also yielded single protein bands with molecular weights of about 15,000. The amino acid compositions of the three anticoagulant proteins are reported. All three proteins have only one amino acid replacement in the first 25 to 30 amino acids of their NH2-terminal sequences, compared to the sequence of the basic phospholipase from N. nigricollis venom. Removal of Ca2+ from the crude venom caused loss of both anticoagulant and phospholipase activities, and restoration of Ca2+ caused partial recovery of both activities. Both activities were lost in parallel when the venom was heated between pH 6.0 and 8.5. The association of the anticoagulant effect with phospholipase activity contradicts the previous conclusion that phospholipase is not responsible for the anticoagulant action of cobra venom. The previous results might be explained by independence of the anticoagulant and phospholipase effects within the same protein molecule, or by different activity levels of monomer and dimer forms of the enzyme.

Amino Acid Sequence↗

PubMed1980

Snake venom phospholipases A2. A fluorescence study of their binding to phospholipid vesicles correlation with their anticoagulant activities.

The interaction of snake venom phospholipases A2 with phospholipids has been studied by intrinsic fluorescence. This has been performed in order to understand why some enzymes possess anticoagulant properties while others have no action on blood clotting. We show that phospholipases A2 can be distinguished according to their binding properties to phospholipid vesicles. Strong inhibitors of coagulation interact with phospholipids with a significant change of their fluorescence while poor inhibitors have little or no effect. Strong inhibitors have a great affinity toward phosphatidylserine and do not require Ca2+ for interaction. Similar results are obtained with phosphatidylcholine-phosphatidylserine 1:1 mixtures. The diether analogue of phosphatidylcholine shows that formation of the complex is promoted by Ca2+ and can occur whenever the lipids are in crystal or fluid phase. Inactivation of anticoagulant phospholipase A2 decreased the affinity of enzyme for the phospholipids. The change in the intrinsic fluorescence of the phospholipases A2 on binding indicates a modification of the environment of the tryptophan residues. This is discussed in terms of the so-called interface recognition site as seen in the case of pancreatic phospholipase A2. It is concluded that the phospholipases may inhibit coagulation by competing with clotting proteins for the lipid surface. Although not considered in this study, the consequence of the hydrolysis of lipids remains to be estimated.

Animals↗

PubMed2007

Impact of Phospholipase A2 group IIa gene polymorphism on phenotypic features of patients with familial adenomatous polyposis.

PURPOSE: Phospholipase A2 Group IIa has been suggested to be a possible disease modifier gene in familial adenomatous polyposis. This investigation was designed to elucidate possible association between phospholipase A2 Group IIa polymorphism and phenotypes of patients with familial adenomatous polyposis. METHODS: Phospholipase A2 Group IIa was examined by polymerase chain reaction-based single strand conformation polymorphism and direct sequencing in 55 patients from 45 families with familial adenomatous polyposis. The patients were examined by gastroduodenoscopy plus biopsy with respect to fundic gland polyposis and gastroduodenal adenomas. Helicobacter pylori status was determined by rapid urease test. Contributions of genetic alteration and Helicobacter pylori infection to intestinal and extraintestinal lesions were investigated. RESULTS: Four types of single nucleotide polymorphism were found in exon 3 of phospholipase A2 Group IIa, among which single nucleotide polymorphism in codon 32 was the most frequent. The prevalence of fundic gland polyposis was higher in patients positive for single nucleotide polymorphism of phospholipase A2 Group IIa than those negative for single nucleotide polymorphism (61 vs. 33 percent; P < 0.05). In contrast, positive rate of Helicobacter pylori infection was lower in the former than in the latter (22 vs. 52 percent; P < 0.05). The prevalence of the other phenotypes was not different significantly. Logistic regression analysis revealed a possibility toward single nucleotide polymorphism of phospholipase A2 Group IIa as an independent risk factor for fundic gland polyposis (95 percent confidence interval, 00.9-14.3; P = 0.06). CONCLUSIONS: Phospholipase A2 Group IIa may be a modifier gene for fundic gland polyposis in patients with familial adenomatous polyposis.

Adenomatous Polyposis Coli↗

PubMed2006

Prostacyclin production in tryptase and thrombin stimulated human bladder endothelial cells: effect of pretreatment with phospholipase A2 and cyclooxygenase inhibitors.

PURPOSE: Thrombin and tryptase stimulation of human bladder microvascular endothelial cells (Cambrex Bioscience, Walkersville, Maryland) results in the production of multiple membrane phospholipid derived inflammatory mediators via the activation of a calcium independent phospholipase A2 that may have important implications in bladder inflammatory conditions, such as interstitial cystitis. We examined the effect of multiple phospholipase A2 and cyclooxygenase inhibitors on the immediate release of prostacyclin from human bladder microvascular endothelial cells. MATERIALS AND METHODS: We stimulated confluent human bladder microvascular endothelial cell monolayers with thrombin or tryptase and measured the immediate release of prostacyclin. Human bladder microvascular endothelial cells were pretreated with several selective phospholipase A2 and cyclooxygenase inhibitors before thrombin or tryptase stimulation to determine which combination of phospholipase A2/cyclooxygenase isoforms was involved in this process. Phospholipase A2 activity was measured using (16:0, [3H]18:1) plasmenylcholine substrate in the absence of calcium. [3H] arachidonic acid release was measured in the surrounding medium from prelabeled human bladder microvascular endothelial cell monolayers. Prostacyclin release into the surrounding medium was measured using a commercially available immunoassay kit. RESULTS: The immediate increase in prostacyclin release from thrombin or tryptase stimulated human bladder microvascular endothelial cells depended on the activation of membrane associated calcium independent phospholipase A2, resulting in an increase in arachidonic acid production. Constitutively active cyclooxygenase-1 was then responsible for further metabolism of free arachidonic acid to prostacyclin. CONCLUSIONS: These results show that the search for a suitable anti-inflammatory agent that selectively target specific phospholipase A2 isoforms requires rigorous testing in several cell types in response to various stimuli.

Arachidonic Acids↗

PubMed2005

Phospholipase B enzyme expression is not associated with other virulence attributes in Candida albicans isolates from patients with human immunodeficiency virus infection.

The extracellular phospholipases of Candida albicans are considered to play a significant role in the pathogenesis of human infections. Therefore 30 clinical isolates of C. albicans from human immunodeficiency virus (HIV)-infected individuals were screened for phospholipase production in vitro (using an egg-yolk-agar medium). Two groups of six isolates with positive (group A) or deficient (group B) phospholipase activity were then analysed for phospholipase B1 (PLB1) gene expression both in egg-yolk-agar and yeast extract/peptone/dextrose (YPD) broth media. A total of four virulence attributes of these two groups were in turn characterized, namely their germ-tube formation, cell-surface-hydrophobicity (CSH), adhesion to buccal epithelial cells (ABEC) and haemolysin production, and these factors were subsequently correlated with PLB1 expression. In the phospholipase-producing isolates (group A) a positive correlation was demonstrated between phospholipase production and the degree of PLB1 expression in YPD medium (r = 0.96, P < 0.01). No such association was observed in group A isolates for PLB1 expression in egg-yolk-agar medium. Further, PLB1 expression in egg-yolk agar was less than that in YPD medium, although a positive correlation was seen between the expression levels on regression analysis (r = 0.86, P = 0.026). Surprisingly, however, no significant associations were observed in either growth media between PLB1 expression and any of the four pathogenic attributes examined (P < 0.001). A significant correlation was seen between CSH and ABEC (r = 0.74) in group A isolates. The phospholipase-deficient group B, however, demonstrated a significant correlation between the latter parameters (r = +0.50) and also between germ-tube formation and ABEC (r = -0.59), and germ-tube formation and haemolysin production (r = +0.31). It appears that in oral C. albicans isolates in HIV infection there may be no significant association between the degree of PLB1 expression and other widely recognized major virulence attributes.

Bacterial Adhesion↗