Lipoprotein(a) levels are associated with aortic valve calcification in asymptomatic patients with familial hypercholesterolaemia.

OBJECTIVES: Lipoprotein(a) [Lp(a)] is an independent risk factor for aortic valve stenosis and aortic valve calcification (AVC) in the general population. In this study, we determined the association between AVC and both plasma Lp(a) levels and apolipoprotein(a) [apo(a)] kringle IV repeat polymorphisms in asymptomatic statin-treated patients with heterozygous familial hypercholesterolaemia (FH). METHODS: A total of 129 asymptomatic heterozygous FH patients (age 40-69 years) were included in this study. AVC was detected using computed tomography scanning. Lp(a) concentration and apo(a) kringle IV repeat number were measured using immunoturbidimetry and immunoblotting, respectively. Univariate and multivariate logistic regression were used to assess the association between Lp(a) concentration and the presence of AVC. RESULTS: Aortic valve calcification was present in 38.2% of patients, including three with extensive AVC (>400 Agatston units). Lp(a) concentration was significantly correlated with gender, number of apo(a) kringle IV repeats and the presence and severity of AVC, but not with coronary artery calcification (CAC). AVC was significantly associated with plasma Lp(a) level, age, body mass index, blood pressure, duration of statin use, cholesterol-year score and CAC score. After adjustment for all significant covariables, plasma Lp(a) concentration remained a significant predictor of AVC, with an odds ratio per 10-mg dL(-1) increase in Lp(a) concentration of 1.11 (95% confidence interval 1.01-1.20, P = 0.03). CONCLUSION: In asymptomatic statin-treated FH patients, plasma Lp(a) concentration is an independent risk indicator for AVC.

HDL associates with insulin resistance and beta-cell dysfunction in South Asian families at risk of type 2 diabetes.

OBJECTIVE: Dyslipidemia precedes type 2 diabetes (T2D) and worsens with increasing glucose intolerance. First degree relatives of T2D patients have an increased risk to develop dyslipidemia and glucose intolerance. The aim of the present study was to assess the relation between the development of dyslipidemia and glucose intolerance in first-degree relatives of T2D patients. RESEARCH DESIGN AND METHODS: Fasting lipoprotein profiles were determined by density gradient ultracentrifugation in T2D patients and their first-degree relatives (42 Caucasians and 33 South Asians), and in 29 normoglycemic controls from non-T2D families. Glucose tolerance, insulin sensitivity index (ISI) and insulin disposition index (DI) were assessed by an extended, frequently sampled oral glucose tolerance test (OGTT), and fractional insulin synthesis rate (FSR) was measured by 13C-leucine enrichment in urinary C-peptide during the OGTT. RESULTS: Of the first-degree relatives, 40, 16 and 19 had NGT, prediabetes and T2D, respectively. NGT family members had lower plasma HDL-cholesterol (HDLC) (1.34 ± 0.07 vs 1.58 ± 0.06 mmol/L; p = 0.015), HDL2-C (0.41 ± 0.05 vs 0.57 ± 0.05 mmol/L; p = 0.021) and HDL3-C (0.62 ± 0.03 vs 0.72 ± 0.02 mmol/L; p = 0.043) than controls. HDL2-C levels tended to decrease with increasing glucose intolerance state. In South Asians, buoyant LDL-C levels decreased with increasing glucose intolerance state (p = 0.006). In South Asian families, HDL-C correlated with both ISI and DI (ß 0.42; p = 0.04 and ß 0.53; p = 0.01, respectively), whereas HDL2-C and HDL3-C levels correlated with DI (ß 0.64; p = 0.002 and ß 0.57; p = 0.005, respectively). HDL2-C and plasma triglyceride correlated with FSR (ß 0.48; p = 0.033 and ß -0.50; p = 0.029, respectively). CONCLUSIONS: Low HDL2-C and HDL3-C levels are present in NGT first-degree relatives of T2D patients, and HDL2-C tend to decrease further with increasing glucose intolerance. In South Asian families HDL2-C and HDL3-C levels linked predominantly to deteriorating beta cell function.

Breakfast partly restores the anti-inflammatory function of high-density lipoproteins from patients with type 2 diabetes mellitus.

Background and aims: High-density lipoproteins (HDL) of patients with type 2 diabetes mellitus (T2DM) have impaired anti-inflammatory activities. The anti-inflammatory activity of HDL has been determined ex vivo after isolation by different methods from blood mostly obtained after overnight fasting. We first determined the effect of the HDL isolation method, and subsequently the effect of food intake on the anti-inflammatory function of HDL from T2DM patients. Methods: Blood was collected from healthy controls and T2DM patients after an overnight fast, and from T2DM patients 3 h after breakfast (n = 17 each). HDL was isolated by a two-step density gradient ultracentrifugation in iodixanol (HDLDGUC2), by sequential salt density flotation (HDLSEQ) or by PEG precipitation (HDLPEG). The anti-inflammatory function of HDL was determined by the reduction of the TNFα-induced expression of VCAM-1 in human coronary artery endothelial cells (HCAEC) and retinal endothelial cells (REC). Results: HDL isolated by the three different methods from healthy controls inhibited TNFα-induced VCAM-1 expression in HCAEC. With apoA-I at 0.7 µM, HDLDGUC2 and HDLSEQ were similarly effective (16% versus 14% reduction; n = 3; p > 0.05) but less effective than HDLPEG (28%, p < 0.05). Since ultracentrifugation removes most of the unbound plasma proteins, we used HDLDGUC2 for further experiments. With apoA-I at 3.2 µM, HDL from fasting healthy controls and T2DM patients reduced TNFα-induced VCAM-1 expression in HCAEC by 58 ± 13% and 51 ± 20%, respectively (p = 0.35), and in REC by 42 ± 13% and 25 ± 18%, respectively (p < 0.05). Compared to preprandial HDL, postprandial HDL from T2DM patients reduced VCAM-1 expression by 56 ± 16% (paired test: p < 0.001) in HCAEC and by 34 ± 13% (paired test: p < 0.05) in REC. Conclusions: The ex vivo anti-inflammatory activity of HDL is affected by the HDL isolation method. Two-step ultracentrifugation in an iodixanol gradient is a suitable method for HDL isolation when testing HDL anti-inflammatory function. The anti-inflammatory activity of HDL from overnight fasted T2DM patients is significantly impaired in REC but not in HCAEC. The anti-inflammatory function of HDL is partly restored by food intake.

156Pro-->Gln substitution in the light chain of cytochrome b558 of the human NADPH oxidase (p22-phox) leads to defective translocation of the cytosolic proteins p47-phox and p67-phox.

Src homology 3 (SH3) domains have been suggested to play an important role in the assembly of the superoxide-forming nicotinamide adenine dinucleotide phosphate (NADPH) oxidase upon activation of phagocytes, which involves the association of membrane-bound and cytosolic components. We studied the translocation of the cytosolic proteins to the plasma membrane in neutrophils of a patient with a point mutation in the gene encoding the light chain of cytochrome b558. This mutation leads to a substitution at residue 156 of a proline into a glutamine in a putative SH3 binding domain of p22-phox (Dinauer, M., E. A. Pierce, R. W. Erickson, T. Muhlebach, H. Messner, R. A. Seger, S. H. Orkin, and J. T. Curnutte. 1991. Proc. Natl. Acad. Sci. 88:11231). In PMA-stimulated neutrophils and in a cell-free translocation assay with neutrophil membranes and cytosol, association of the cytosolic proteins p47-phox and p67-phox with the membrane fraction of the patient's neutrophils was virtually absent. In contrast, when solubilized membranes of the patient's neutrophils were activated with phospholipids in the absence of cytosol (Koshkin, V., and E. Pick. 1993. FEBS [Fed. Eur. Biochem. Soc.] Lett. 327:57), the rate of NADPH-dependent oxygen uptake was observed at a rate similar to that of control membranes. We suggest that the binding of an SH3 domain of p47-phox to p22-phox, and thus activation of the oxidase, does not occur in the neutrophils of this patient, although under artificial conditions, electron flow from NADPH to oxygen in cytochrome b558 is possible.

Disturbed interaction of p21-rac with mutated p67-phox causes chronic granulomatous disease.

Chronic granulomatous disease (CGD) is characterized by the failure of phagocytic leukocytes to generate superoxide, needed for the intracellular killing of microorganisms. This is caused by mutations in any one of the four subunits of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. In a rare, autosomal recessive form of CGD, a 67-kD cytosolic component of this enzyme (p67-phox) is missing. We here report on a patient with a mutation in the p67-phox gene that leads to expression of a nonfunctional p67-phox protein. The purified granulocytes of this patient failed to produce superoxide and contained about half of the normal amount of p67-phox. Analysis of the cDNA and genomic DNA of this patient showed that the patient is a compound heterozygote for a triplet nucleotide deletion in the p67-phox gene, predicting an in-frame deletion of lysine 58 in the p67-phox protein and a larger deletion of 11-13 kb in the other allele. Interestingly, the 58Lys deletion in p67-phox disrupts the interaction with p21-rac1, a ras-related protein involved in the activation of the NADPH oxidase. In contrast to normal neutrophils, in which p47-phox and p67-phox translocate to the plasma membrane upon cell activation, the cells of the patient did not show this translocation, indicating that an interaction between p67-phox and p21-rac1 is essential for translocation of these cytosolic proteins and activation of the NADPH oxidase. Moreover, this CGD patient represents the first case of disease caused by a disturbed binding of a ras-related protein to its target protein.

NADPH-oxidase expression and in situ production of superoxide by osteoclasts actively resorbing bone.

Recent reports have suggested that production of superoxide or other reactive oxygen species by activated osteoclasts may play a role in the complex process of bone resorption; however, the enzyme responsible for production of superoxide by osteoclasts has not been characterized. To determine if osteoclasts express NADPH-oxidase, a superoxide-generating enzyme found in phagocytic leukocytes, immunohistochemical studies were performed on tibia from 1-5-d-old rats using mAbs 449 and 48 and an antiserum specific for p47-phox. These antibodies recognize epitopes on the alpha and beta subunits of cytochrome b558, respectively, and the p47 cytosolic component of NADPH-oxidase. We found that osteoclasts attached to bone surfaces in tibia expressed all three components, as did mature polymorphonuclear and some mononuclear leukocytes in the bone marrow. In many adherent osteoclasts, the cytochrome b558 subunits were localized to the ruffled-border and bone interfaces. Studies were also performed on mature rat tibia that had undergone controlled fracture. By two weeks the healing fractures develop a callus rich in actively resorbing osteoclasts. Osteoclasts within the calluses, and attached to bone surface, also expressed the cytochrome b558 proteins. In addition to demonstrating the expression of NADPH-oxidase, the active production of superoxide by osteoclasts was also demonstrated in situ in freshly isolated tibia using 3,3'-diaminobenzidine (DAB)-Mn2+, a histochemical method specific for superoxide localization. Osteoclasts attached to bone surfaces contained deposits of oxidized DAB which were observed by light microscopy. Nonstimulated polymorphonuclear and mononuclear leukocytes in the bone marrow did not contain DAB deposits unless stimulated with phorbol myristate acetate, a known activator of NADPH-oxidase. These findings indicate that osteoclasts contain NADPH-oxidase, and during the process of resorbing bone, are actively producing superoxide.

Activation of LFA-1 through a Ca2(+)-dependent epitope stimulates lymphocyte adhesion.

The leukocyte function-associated molecule-1 (LFA-1) plays a key role in cell adhesion processes between cells of the immune system. We investigated the mechanism that may regulate LFA-1-ligand interactions, which result in cell-cell adhesion. To this end we employed an intriguing anti-LFA-1 alpha mAb (NKI-L16), capable of inducing rather than inhibiting cell adhesion. Aggregation induced by NKI-L16 or Fab fragments thereof is not the result of signals transmitted through LFA-1. The antibody was found to recognize a unique Ca2(+)-dependent activation epitope of LFA-1, which is essentially absent on resting lymphocytes, but becomes induced upon in vitro culture. Expression of this epitope correlates well with the capacity of cells to rapidly aggregate upon stimulation by PMA or through the TCR/CD3 complex, indicating that expression of the NKI-L16 epitope is essential for LFA-1 to mediate adhesion. However, expression of the NKI-L16 epitope in itself is not sufficient for cell binding since cloned T lymphocytes express the NKI-L16 epitope constitutively at high levels, but do not aggregate spontaneously. Based on these observations we propose the existence of three distinct forms of LFA-1: (a) an inactive form, which does not, or only partially exposes the NKI-L16 epitope, found on resting cells; (b) an intermediate, NKI-L16+ form, expressed by mature or previously activated cells; and (c) an active (NKI-L16+) form of LFA-1, capable of high affinity ligand binding, obtained after specific triggering of a lymphocyte through the TCR/CD3 complex, by PMA, or by binding of NKI-L16 antibodies.

A phosphoprotein of Mr 47,000, defective in autosomal chronic granulomatous disease, copurifies with one of two soluble components required for NADPH:O2 oxidoreductase activity in human neutrophils.

The NADPH:O2 oxidoreductase (NADPH oxidase) of human neutrophils is converted from a dormant to an active state upon stimulation of the cells. We have studied the soluble fraction that is required for NADPH oxidase activation in a cell-free system. Human neutrophils were separated in a membrane-containing and a soluble fraction. The soluble fraction was separated on carboxymethyl (CM) Sepharose in 10 mM 4-morpholino-ethanesulfonic acid buffer of pH 6.8. Reconstitution of the NADPH oxidase activity, measured as O2 consumption, was only found when the membrane fraction was combined with the flowthrough of the CM Sepharose column as well as with a fraction that eluted at 125 mM NaCl. This result indicates that at least two soluble components are necessary for reconstitution of the NADPH oxidase activity: one that does not bind to CM Sepharose and one that does bind. These components were designated soluble oxidase component (SOC) I and SOC II, respectively. Boiling destroyed the activity in both fractions. In the soluble fraction of human lymphocytes and thrombocytes neither SOC I nor SOC II activity was found. SOC II copurified with a 47-kD phosphoprotein, previously found defective in patients with the autosomal form of chronic granulomatous disease (CGD). Inactive soluble fractions of cells from autosomal CGD patients were reconstituted with a SOC II fraction from control cells. The result of this experiment indicates that autosomal CGD patients are normal in SOC I but defective in SOC II.

Recombinant C1 inhibitor P5/P3 variants display resistance to catalytic inactivation by stimulated neutrophils.

Proteolytic inactivation of serine protease inhibitors (serpins) by neutrophil elastase (HNE) is presumed to contribute to the deregulation of plasma cascade systems in septic shock. Here, we report a supplementary approach to construct serpins, in our case C1 inhibitor, that are resistant to catalytic inactivation by HNE. Instead of shifting the specificity of alpha 1-antitrypsin towards the proteases of the contact activation and complement systems, we attempted to obtain a C1 inhibitor species which resists proteolytic inactivation by HNE. 12 recombinant C1 inhibitor variants were produced with mainly conservative substitutions at the cleavage sites for HNE, 440-Ile and/or 442-Val. Three variants significantly resisted proteolytic inactivation, both by purified HNE, as well as by activated neutrophils. The increase in functional half-life in the presence of FMLP-stimulated cells was found to be 18-fold for the 440-Leu/442-Ala variant. Inhibitory function of these variants was relatively unimpaired, as examined by the formation of stable complexes with C1s, beta-Factor XIIa, kallikrein, and plasmin, and as determined by kinetic analysis. The calculated association rate constants (k(on)) were reduced twofold at most for C1s, and appeared unaffected for beta-Factor XIIa. The effect on the k(on) with kallikrein was more pronounced, ranging from a significant ninefold reduction to an unmodified rate. The results show that the reactive centre loop of C1 inhibitor can be modified towards decreased sensitivity for nontarget proteases without loss of specificity for target proteases. We conclude that this approach extends the possibilities of applying recombinant serpin variants for therapeutic use in inflammatory diseases.

A point mutation in gp91-phox of cytochrome b558 of the human NADPH oxidase leading to defective translocation of the cytosolic proteins p47-phox and p67-phox.

The superoxide-forming NADPH oxidase of human phagocytes is composed of membrane-bound and cytosolic proteins which, upon cell activation, assemble on the plasma membrane to form the active enzyme. Patients suffering from chronic granulomatous disease (CGD) are defective in one of the following components: p47-phox and p67-phox, residing in the cytosol of resting phagocytes, and gp91-phox and p22-phox, constituting the membrane-bound cytochrome b558. In an X-linked CGD patient we identified a novel missense mutation predicting an Asp-->Gly substitution at residue 500 of gp91-phox, associated with normal amounts of nonfunctional cytochrome b558 in the patient's neutrophils. In PMA-stimulated neutrophils and in a cell-free translocation assay with neutrophil membranes and cytosol, the association of the cytosolic proteins p47-phox and p67-phox with the membrane fraction of the patient was strongly disturbed. Furthermore, a synthetic peptide mimicking domain 491-504 of gp91-phox inhibited NADPH oxidase activity in the cell-free assay (IC50 about 10 microM), and the translocation of p47-phox and p67-phox in the cell-free translocation assay. We conclude that residue 500 of gp91-phox resides in a region critical for stable binding of p47-phox and p67-phox.

Leukocyte adhesion deficiency type 1 (LAD-1)/variant. A novel immunodeficiency syndrome characterized by dysfunctional beta2 integrins.

Leukocyte adhesion deficiency (LAD) is characterized by the inability of leukocytes, in particular neutrophilic granulocytes, to emigrate from the bloodstream towards sites of inflammation. Infectious foci are nonpurulent and may eventually become necrotic because of abnormal wound healing. LAD-1 is characterized by the absence of the beta2 integrins (CD11/CD18) on leukocytes. When expression is completely absent, patients often die within the first year. However, low levels of beta2 expression may result in a milder clinical picture of recurrent infection, which offers a better prognosis. In this paper, we describe the in vivo and in vitro findings on a patient with clinical features of a mild LAD-1 disorder, i.e., suffering from bacterial infections without apparent pus formation in the presence of a striking granulocytosis, showing no delayed-type hypersensitivity reaction upon skin testing, no specific antibody generation, but normal in vitro T cell proliferation responses after immunization. Expression levels of CD11/CD18 proteins were completely normal, but leukocyte activation did not result in CD11/ CD18 activation and high-avidity ligand-binding. In vitro chemotaxis and endothelial transmigration of the neutrophils as well as leukocyte aggregation responses were almost absent. On the other hand, beta1 and beta3 integrin-mediated adhesion functions were completely normal. During follow-up, a bleeding tendency related to decreased beta3 activation became clinically apparent, different from previously described cellular adhesion molecule variants. Therefore, this is the first well-documented case of a clinical combined immunodeficiency syndrome that results from nonfunctional CD11/CD18 molecules, and thus designated LAD-1/ variant.

Mitochondria in neutrophil apoptosis.

Central in the regulation of the short life span of neutrophils are their mitochondria. These organelles hardly contribute to the energy status of neutrophils but play a vital role in the apoptotic process. Not only do the mitochondria contain cytotoxic proteins that are released during apoptosis and contribute to caspase activation, but they also act as sensors of the metabolic and redox state of the cell and as scavengers of free Ca2+. The balance of the expression and activity of the proapoptotic and antiapoptotic members of the Bcl-2 family of proteins determines the life span of neutrophils, because these proteins are essential for the formation of a permeability transition pore in the mitochondria and also seem to control the release of Ca2+ from the endoplasmic reticulum and thereby mitochondrial energy metabolism.

Diet-induced weight loss and markers of endothelial dysfunction and inflammation in treated patients with type 2 diabetes.

BACKGROUND & AIMS: Overweight and obesity increase cardiovascular mortality in patients with type 2 diabetes (T2D). In a recent trial, however, diet-induced weight loss did not reduce the cardiovascular risk of patients with T2D, possibly due to the parallel intensive medical treatment. We investigated the effect of diet-induced weight loss on cardiovascular risk factors in overweight and obese patients with T2D, and whether this effect was influenced by the use of statins, ACE inhibitors, metformin and duration of T2D. METHODS: Patients with T2D and BMI >27 were subjected to an energy-restricted diet during 4 months. Before and after intervention, plasma levels of sICAM-1, sVCAM-1, hsCRP, vWF and classical biomarkers were measured. The association of the change in biomarker levels with medication use and T2D history, corrected for age, sex and change in insulin dose, was tested by matched linear regression analyses. RESULTS: In 131 patients, the diet resulted in weight loss of 10.2 kg (95%CI 9.2, 11.3; p < 0.001), improved median levels of HbA1c (-7.0 mmol/mol (95%CI -8.5, -5.0); p < 0.001), LDL cholesterol (-0.2 mmol/L (95%CI -0.4, -0.1); p < 0.001), sICAM-1 (-22.4 ng/mL (95%CI -37.1, -8.7); p = 0.001), vWF (-3.9 IU/mL (95%CI -6.4, -1.4); p = 0.003) and hs-CRP (-0.6 mg/L (95%CI -1.2, -0.2); p = 0.007), but did not affect sVCAM-1 levels (1.6 ng/mL (95%CI -41.5, 48.6); p = 0.949). Duration of T2D and medical treatment were not associated with these effects, except for an association between statin use and change in sVCAM-1, where statin users improved more. CONCLUSION: Diet-induced weight loss reduced the levels of biomarkers of endothelial dysfunction and inflammation in overweight and obese patients with T2D independently of medication use and T2D duration. Even on intensive medical drug treatment as well as after a long history of T2D, patients may still profit from diet-induced weight reduction.

Lomitapide affects HDL composition and function.

BACKGROUND: Lomitapide reduces low-density lipoprotein-cholesterol (LDL-C) but also high-density lipoprotein-cholesterol (HDL-C) levels. The latter may reduce the clinical efficacy of lomitapide. We investigated the effect of lomitapide on HDL-C levels and on cholesterol efflux capacity (CEC) of HDL in patients with homozygous familial hypercholesterolemia (HoFH). METHODS AND RESULTS: Four HoFH patients were treated with increasing dosages of lomitapide. Lomitapide decreased LDL-C (range -34 to -89%). Total HDL-C levels decreased (range -16 to -34%) with a shift to buoyant HDL. ABCA1-mediated CEC decreased in all patients (range -39 to -99%). The changes of total, ABCG1- and SR-BI-mediated CEC were less consistent. CONCLUSION: Lomitapide decreased LDL-C and HDL-C levels. Our report raises the hypothesis that the anti-atherogenic potential of HDL seems to be unaffected as total CEC did not seem to change consistently. Combined with the reduction of atherogenic lipoproteins, the net effect of lomitapide appears to be beneficial in HoFH patients.

Secretion of liver lipase activity by periportal and perivenous hepatocytes.

Periportal and perivenous hepatocytes were separated by isopycnic centrifugation through Percoll, or selectively isolated by combined digitonin/collagenase perfusion. With either method, secretion of liver lipase activity was 2-2.5-fold higher in periportal than perivenous cells. This acinar heterogeneity parallels that of cholesterol de novo synthesis and bile formation reported previously.

Secretion-coupled increase in the catalytic activity of rat hepatic lipase.

Freshly isolated rat hepatocytes synthesize and secrete hepatic lipase (HL). Comparison of secreted HL with intracellular HL indicates a secretion-linked increase in the specific enzyme activity. (a) Immunotitration with polyclonal anti-HL showed a 3-5-fold lower specific enzyme activity of intracellular HL than of secreted HL. This was confirmed by ELISA using a mixture of monoclonal anti-HL's. (b) After isolation on Sepharose-heparin, a similar difference in specific enzyme activity was observed, whereas the apparent Km for glyceroltrioleate was not different. (c) HL activity secreted in the absence of protein de novo synthesis was 5-fold higher than was accounted for by the fall in intracellular activity, whereas HL protein lost from the cells was near-completely recovered in the extracellular medium. (d) The presence of inactive HL protein was demonstrated in cells treated with castanospermine, which inhibits secretion of newly synthesized HL by interfering with maturation at an early stage of N-linked oligosaccharide processing. Upon removal of castanospermine, secretion of HL activity recovered, even when protein de nove synthesis was inhibited, strongly suggesting that part of the inactive HL was mobilized and became activated. This secretion-coupled increase in HL activity in the absence of protein synthesis suggests the existence of inactive precursor within rat hepatocytes. The catalytic activity of HL becomes apparent upon maturation of the protein after oligosaccharide processing by the rough endoplasmic reticulum glucosidases.

Hepatic lipase mRNA is expressed in rat and human steroidogenic organs.

Rat and human steroidogenic organs contain an enzyme activity that is indistinguishable from hepatic lipase present in liver. Using primers that recognize exons 5 and 8 of the rat and human HL gene, a 596-bp product was found by RT-PCR in rat liver, adrenal, ovaries and testes, but not in heart and kidney. A similar product was also observed with human hyperplastic adrenocortical tissue. Identity of this product with part of the HL cDNA was confirmed by restriction mapping and internal re-amplification. Our results indicate that the HL gene is transcribed in steroidogenic tissues that also contain HL protein.

Role of protein phosphorylation in the degranulation of electropermeabilized human neutrophils.

We have studied the role of protein phosphorylation in the degranulation response of human neutrophils by measuring the effect of ATP depletion and the addition of the protein kinase inhibitor staurosporine in electropermeabilized human neutrophils, activated with Ca2+ and/or GTP-gamma-S. Our studies were carried out in the presence of cytochalasin B to prevent inhibitory effects of actin polymerization on the degranulation response. It was found that protein phosphorylation plays an important role in the degranulation response in cells stimulated with the single stimuli Ca2+ or GTP-gamma-S. However, in neutrophils stimulated with the combination of these activators degranulation can occur without the apparent need for protein phosphorylation, albeit with a slower rate than with protein phosphorylation.

Phosphate turnover of phosphatidylinositol in resting and thrombin-stimulated platelets.

Human platelets were pulse-labelled with [32P]Pi and extracts were analyzed for masses and radioactivities of ATP and phosphoinositides. Immediately after pulse-labelling, the specific 32P radioactivity of phosphatidylinositol (PI) was only 3.4% of that of the gamma-phosphoryl of ATP. Upon incubation of the platelets at 37 degrees C, the specific 32P radioactivity of ATP (beta- and gamma-phosphoryls) remained constant. However, specific 32P radioactivity in PI increased continuously to 17% of specific [gamma-32P]ATP at 90 min of incubation. Stimulation with 0.5 U/ml of thrombin induced a 35% decrease in mass of PI which was unaffected by the time after the pulse-labelling. In contrast, the thrombin-induced changes in [32P]PI differed markedly at the various times after the [32P]Pi-pulse. Immediately after pulse-labelling, [32P]PI initially decreased but increased thereafter to 260% of control values after 180 s. With increasing specific 32P-radioactivity in PI before stimulation, the thrombin-induced increase in [32P]PI gradually disappeared. After 90 min of incubation, thrombin induced a continuous decrease in [32P]PI that almost parallelled mass. The data are explained by an initial breakdown of PI to diacylglycerol through the PI cycle or the polyphosphoinositide cycle, followed by resynthesis of PI through phosphatidic acid. In contrast to pre-existing PI, the resynthesized PI is in full isotopic equilibrium with ATP. This allowed us to estimate that 14% of the PI that is consumed between 30 and 180 s of stimulation, is recycles. From our data we calculate that the rate of PI resynthesis increased from 2.4 to 20 nmol/min per 10(11) cells upon thrombin stimulation of platelets.

Studies on the preferential incorporation of [3H]glycerol over [32P]phosphate into major phospholipids of human platelets.

It is well known that platelets readily incorporate radioactive glycerol, but not radioactive phosphate into phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in vitro, thus not in accordance with de novo synthesis according to the Kennedy pathway. In attempts to understand the reason for the discrepancy, gel-filtered platelets were incubated simultaneously with [32P]Pi and [3H]glycerol, and the specific and relative radioactivities of products and intermediates were determined. Both precursors were incorporated into phosphatidylinositol (PI) with a 32P/3H ratio similar to that in glycerol 3-phosphate (in accordance with the Kennedy pathway). However, PC and PE obtained a much lower ratio. The specific 32P radioactivity in phosphorylcholine was similar to that of the gamma-phosphoryl of ATP and 650-times higher than that of PC. The specific 32P radioactivity of phosphorylethanolamine was 20-times less than that of phosphorylcholine. Both mass and 32P labelling of CDP-choline were below the detection limits. It is concluded that the incorporation of [32P]Pi into PC via phosphorylcholine is insignificant while the preferential incorporation of [3H]glycerol could be explained by exchange of diacyl[3H]glycerol in the reversible choline phosphotransferase (CDP-choline: 1,2-diacylglycerol cholinephosphotransferase) reaction. The same mechanism would explain the preferential incorporation of 3H over 32P into PE, although dilution of 32P at the phosphorylethanolamine stage would account for part of the feeble 32P incorporation. Although other mechanisms are also possible, our results clearly show that the appearance of [3H]glycerol in PC and PE is not a reliable method of monitoring de novo synthesis of these phospholipids.