A comparative study of multi and single post labeling delay pseudocontinuous arterial spin labeling in patients with carotid artery stenosis

PURPOSE

Arterial Spin Labeling (ASL) allows for the non-invasive visualization of brain perfusion to detect abnormalities. In unilateral carotid artery stenosis, one hemisphere is less supplied with blood which results in a lower cerebral blood flow (CBF) compared to the healthy side. ASL can be performed time-resolved using multiple post labeling delay (PLD) times after labeling or static with a single delay, the latter allowing for a faster and more robust acquisition while bearing the risk of a falsely set delay resulting in unusable images. The purpose of this study is to compare the performance of multi-PLD and single-PLD ASL in patients with unilateral carotid artery stenosis both as means of diagnosis and therapeutic follow-up examination.

METHODS

ASL perfusion data of 17 patients with known unilateral carotid artery stenosis was used to compare the diagnostic performance of the multi-PLD and single-PLD approach. Comparisons were made based on the CBF values and the added benefit of arrival time maps showing slower blood flow in multi-PLD ASL which might be overlooked in the individual delay images both before and after therapy.

RESULTS

Both the multi-PLD and the single-PLD data could identify the side of the stenosis with hemispheric differences in each approach (p < 0.001) and depict the normalization of CBF after therapy (p > 0.05). There were no differences between the individual methods (p > 0.05).

CONCLUSION

In this work, we could show that multi-PLD ASL in patients with unilateral carotid artery stenosis is beneficial as it provides both CBF and arrival time maps, however when only a single-PLD acquisition is available, this appears sufficient in a clinical setting to investigate the presence of a unilateral stenosis.

Bone Turnover Marker for the Evaluation of Skeletal Remodelling in Autosomal Recessive Osteopetrosis after Haematopoietic Stem Cell Transplantation: A Case Report

Background: Autosomal recessive osteopetrosis (ARO) is a rare genetic disorder of bone metabolism, primarily affecting the remodelling function of osteoclasts. Haematopoietic stem cell transplantation (HSCT) is the first-line treatment for ARO. Traditional tools for the assessment of therapeutic response, such as measuring donor chimerism, do not provide information on bone remodelling. The use of bone turnover markers (BTMs) might be ideal. Here, we report a case of a paediatric ARO patient undergoing successful HSCT. Methods: For the evaluation of donor-derived osteoclast activity and skeletal remodelling throughout the transplantation, the bone resorption marker β-CTX (β-C-terminal telopeptide) was used. Results: The low baseline level of β-CTX markedly increased after transplantation and remained in the elevated range even after 3 months. Donor-derived osteoclast activity reached its new baseline level around the 50th percentile range after 5 months and proved to be stable during the 15-month follow-up time. The apparent increase of the baseline osteoclast activity after HSCT was in consonance with the radiographic improvement of the disease phenotype and the correction of bone metabolic parameters. Despite the successful donor-derived osteoclast recovery, craniosynostosis developed, and reconstructive surgery had to be performed. Conclusions: The use of β-CTX may be of aid in assessing osteoclast activity throughout the transplantation. Further studies could help to establish the extended BTM profile of ARO patients using the available osteoclast- and osteoblast-specific markers.

Anti-N-methyl-D-aspartate receptor encephalitis and drug abuse - the probable role of molecular mimicry or the overstimulation of CB receptors in a 17-year-old adolescent - case report

Anti-N-methyl-D-aspartate encephalitis is an autoimmune disorder characterized by autoantibodies produced against NMDA receptors. We report the case of a 17-year-old drug user teenager who presented with altered mental scale, psychiatric symptoms and autonomic dysfunction. In the background we diagnosed NMDA encephalitis. We supposed that synthetic cannabinoids/drugs may have lead to the of trigger NMDA encephalitis via the altered activation of the immune system and molecular mimicry mechanism.

Effects of PACAP on oxidative stress-induced cell death in rat kidney and human hepatocyte cells

Oxidative stress plays an important role in various renal and hepatic pathologies, and reduction of oxidative stress-induced processes is an important protective strategy in tissues of diverse origins against harmful stimuli. Pituitary adenylate cyclase activating polypeptide (PACAP) is a well-known cytotrophic and cytoprotective peptide. PACAP promotes cell survival in numerous cells and tissues exposed to various stimuli. Protective effects of PACAP have been shown in the kidney, but it is not known whether PACAP is protective against oxidative stress in renal cells. Little is known about the effects of PACAP in the liver. The aim of the present study was to investigate whether PACAP is protective against oxidative stress in primary rat kidney cell culture and whether PACAP has any effect on cell survival in human WRL-68 hepatocytes and HEP-G2 hepatocellular carcinoma cells subjected to oxidative stress. Cells were exposed to various concentrations of H(2)O(2) with or without PACAP co-treatment and cell viability was evaluated with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide test (MTT). We found that oxidative stress induced a significant decrease in cell viability in both cell lines. PACAP could dose-dependently increase the percentage of living cells in kidney cells, but it failed to do so in hepatocytes. Given the survival-promoting effects of PACAP against oxidative stress in rat kidney, we conducted a further experiment to determine whether PACAP influences the markers of oxidative stress in vivo. We have proven earlier that PACAP was effective in kidney ischemia/reperfusion injury in vivo. In the present study, we determined the levels of the oxidative stress marker malondialdehyde and the activity of the scavenger molecules glutathione (GSH) and superoxide dismutase (SOD) following kidney ischemia/reperfusion in rats. We found that PACAP significantly increased the level of GSH and counteracted the marked reduction of SOD activity after ischemia/reperfusion in vivo. In summary, the present study showed that while PACAP was able to significantly increase the cell survival in primary kidney cell cultures exposed to oxidative stress, possibly involving interaction with the endogenous scavenger system, it failed to influence the viability of normal or cancerous hepatocytes.

Binding of activated protein C to a specific receptor on human mononuclear phagocytes inhibits intracellular calcium signaling and monocyte-dependent proliferative responses

Upon activation, mononuclear phagocytes (Mphi) play key roles in the development of septic shock and multiple host immune responses, but details of the regulation of Mphi activation are little understood. We recently showed that the physiologic anticoagulant molecule, activated protein C (APC), blocks responses of human blood Mphi, alveolar Mphi, or THP-1 cells induced by LPS, IFN-gamma, or PMA, including TNF-alpha production and down-regulation of several LPS binding-related proteins. We now report a possible mechanism of action through inhibition of the rapid intracellular calcium signaling that occurs at the onset of Mphi activation, and characterization of a specific Mphi receptor for APC. Flow cytometry studies using Fluo-3 showed that Mph activation by Fc-receptor cross-linking or rIFN-gamma caused a rapid increase in free intracellular calcium, a primary event in multiple signal transduction pathways, which was blocked by pretreatment with APC. Consistent with this, addition of APC inhibited PHA-induced T cell proliferation in a dose- and time-dependent manner. Peak suppression (> 70%) required addition of APC within the first hour of 72 hr cocultures of Mphi and lymphocytes, and proliferative responses were not restored by addition of IL-2 or TNF-alpha. Biochemical studies showed that 125I-labeled APC bound specifically to M phi in a time-dependent and saturable manner. Scatchard analysis indicated there were 180,690 binding sites for APC per cell, which were of high affinity (Kd value of 12.9 mM). Binding of 125I-APC was doubled by activation of Mphi with LPS, and bound APC was not displaced by the zymogen, protein C (PC), or by enzymatically inactive (diisopropyl fluorophosphate- or PPACK-treated) APC, indicating an absolute requirement for the active site of APC in its binding to Mphi. APC binding was blocked by a polyclonal Ab to human PC/APC, but not by protein S, factor Va or Xa, or a polyclonal antithrombomodulin antibody. When 125I-APC was crosslinked to its receptor, immunoprecipitated and analyzed by SDS-PAGE under reducing conditions, a covalent complex (110-115 kD) of 125I-APC (62 kD) and its receptor was seen. In addition, a Mphi membrane protein of 50-55 kD, as determined by SDS-PAGE, was affinity-purified using an APC-Affigel column, and confirmed by ligand binding. Taken together, our findings document the presence of a M phi surface receptor for APC, which appears distinct from a recently described endothelial receptor for PC and APC, and which may be involved in the inhibitory effects of APC on activation of human Mphi, including Mphi-dependent T cell proliferation.

Protein S negates the activated protein C inhibitory activity of plasma

The inactivation of factor Va by the natural anticoagulant, activated protein C (APC) is subject to a number of regulatory mechanisms. This report examines the efficacy of APC in plasma and evaluates the role of the APC cofactor protein S in this milieu. The ability of protein S to enhance the anticoagulant effects of activated protein C was demonstrated using a factor Xa recalcification time of Al(OH)3 adsorbed plasma. At a set concentration of APC, increasing concentrations of protein S resulted in a linear and saturable potentiation of the activity of APC. This result was not reflected in a purified component assay, where the extent of factor Va inactivation by APC was only marginally augmented by protein S. The efficacy of the cofactor was not affected by variations in the concentration of factor Va. Similarly, increasing the protein S:APC molar ratio of 200:1 resulted in only a trivial enhancement of APC activity. To directly examine the proteolysis of factor Va by APC in plasma, a novel assay system containing Al(OH)3 adsorbed, factor V deficient plasma supplemented with purified human factor Va was developed. The addition of APC in varying concentrations to this system consistently yielded factor Va inactivation rates inferior to those seen in a purified component assay. This finding is consistent with the presence of APC inhibitory activity in plasma. When protein S was added to the plasma system, factor Va inactivation by APC was restored to a similar level to that observed in the purified system.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of activated protein C by factor Xa

In this study, the ability of factor Xa to protect factor Va from proteolysis by activated protein C (APC) was verified. Interestingly, factor X was found to exert a similar effect with a dose-dependence identical to that of factor Xa. The effects of factor X and Xa were abrogated in the presence of protein S. To further assess the interactions of factor Va with factors Xa, X and APC, direct binding studies were performed. Factor X and Xa bound to factor Va with equal efficacy. Both proteins displaced APC from its factor Va binding site. These interactions were calcium-dependent. Although the binding of factor Xa devoid of its principal calcium binding site (the Gla-domain) to factor Va was identical to that observed using the native protein, its APC inhibitory effects were significantly reduced. These findings suggest that the Gla-domain of factor X (Xa) is pivotal in the protection of factor Va from APC.

Arterial thrombosis associated with immune thrombocytopenia: presence of a platelet aggregating IgG synergistic with thrombin and adrenalin

We report the case of a 50-year-old lady who presented with arterial thrombosis in the setting of thrombocytopenia. Investigations confirmed the diagnosis of idiopathic thrombocytopenic purpura. A spontaneous platelet aggregating factor (SPAF) was isolated from the immunoglobulin fraction of the patient's plasma. The isolated IgG irreversibly aggregated platelet-rich plasma and washed platelets, an effect abolished by pretreating the platelets with aspirin. The activity of the IgG was greatly enhanced by subaggregatory concentrations of thrombin and adrenalin and was localized to the F(ab')2 of the molecule. Plasmapheresis in combination with anti-platelet therapy resulted in an increase in the patient's platelet count, reduced platelet aggregating activity of plasma and significant clinical improvement. We suggest that the presence of this platelet aggregating IgG contributed to the development of thrombosis in our patient and postulate that a similar factor may explain the paradox of thrombosis observed in a select group of thrombocytopenic patients.

Inhibition of activated protein C by platelets

Activated protein C (APC), an anticoagulant that acts by inactivating Factors Va and VIIIa, is dependent on a suitable surface for its action. In this study we examined the ability of human platelets to provide this surface and support APC-mediated anticoagulant effects. The activity of APC was examined in three systems: the Factor Xa recalcification time of Al(OH)3 adsorbed plasma, studies of thrombin generation in recalcified plasma, and assessment of the rate of inactivation of purified Factor Va. In comparison with phospholipid, intact platelets required significantly greater concentrations of APC to achieve a similar degree of anticoagulation. When washed platelet membranes were substituted for intact platelets, adequate support of APC was observed and the anticoagulant effect was similar to that obtained with phospholipid. Platelet releasate obtained by stimulation of platelets with thrombin and epinephrine contained an inhibitor that interfered with the ability of phospholipid and washed platelet membranes to catalyze the anticoagulant effects of APC. A noncompetitive inhibition was suggested by Dixon plot analysis of the interaction between platelet releasate and APC. The activity of the platelet APC inhibitor was immediate and was not enhanced by heparin, distinguishing it from the circulating protein C inhibitor. The presence of this inhibitor in the platelet and its release with platelet stimulation emphasizes the procoagulant role of this cell.

The effect of enzymatic removal of sialic acids on the functional properties of protein C

The effect of enzymatic removal of sialic acid residues on the functional properties of human protein C was examined. The rates of activation of native and asialo protein C were identical using either the thrombin thrombomodulin complex or the snake venom activator, protac. Desiaylated activated protein C (APC) was, two-three-fold more active than native protein C, both as an anticoagulant and in its ability to hydrolyze chromogenic substrates. The potentiating effect of the desialylation was confirmed by initially fully activating protein C followed by the desialylation process. In these studies, a two-three-fold enhancement in the activity of the protein was observed which paralleled the extent of the desialylation. The activity of asialo-protein C was completely abolished by monoclonal and polyclonal antiprotein C antibodies, confirming that the effect was mediated by APC. Our studies suggest that the sialic acid component of protein C is not essential for the expression of APC activity but may act to modulate the function of the protein.

Control of thrombin mediated cleavage of protein S

Thrombin has been shown to cleave the vitamin K dependent cofactor protein S with subsequent loss of its cofactor activity. This study examines the control mechanisms for thrombin cleavage of protein S. The anticoagulant activity of activated protein C (APC) is enhanced fourteen fold by the addition of protein S. Thrombin cleaved protein S is seven fold less efficient than the native protein, and this loss of activity is due to reduced affinity of cleaved protein S for APC or the lipid surface compared to the intact protein. In the absence of Ca++, protein S is very sensitive to minimal concentrations of thrombin. As little as 1.5 nM thrombin results in complete cleavage of 20 nM protein S in 10 min and loss of cofactor activity. Ca++, in concentrations greater than 0.5 mM, will inhibit this cleavage and in the presence of physiological Ca++ concentrations, no cleavage of protein S could be demonstrated in spite of high concentrations of thrombin (up to 1 microM) and prolonged incubations (up to two hours). The endothelial surface protein thrombomodulin is very efficient in inhibiting the cleavage of protein S by thrombin suggesting that any thrombin formed on the endothelial cell surface is unlikely to cleave protein S, thus allowing the intact protein to act as a cofactor to APC. We conclude that the inhibitory effects of Ca++ and thrombomodulin on thrombin mediated cleavage of protein S imply that this event, by itself, is unlikely to represent a physiological control of the activity of protein S.

Binding of human thrombin to human factor VIII:RAg

The binding capacity of radiolabelled human alpha-thrombin (alpha-thrombin), inactivated with phenyl-methyl sulphonyl fluoride (PMSF), to factor VIII related antigen (VIII:RAg) multimers isolated by immune precipitation and resolved by sodium dodecyl sulphate (SDS) agarose gel electrophoresis has been examined. 125I-PMSF alpha-thrombin bound predominantly to four low molecular weight multimers (LMW) of VIII:RAg prepared from either normal or haemophilia A plasma. Two of these VIII:RAg multimers present in serum had lost the capacity to bind thrombin. No bands were observed when either plasma or serum from three patients with severe von Willebrand's disease (vWd) was processed in an identical manner. This binding was not dependent on the presence of an intact catalytic site on the thrombin molecule. A similar pattern of binding to VIII:RAg multimers was observed with 125I-labelled human anti-FVIII antibodies as 125I-alpha-thrombin and appears to involve the same multimers.

Variant von Willebrand's disease type B--revisited

Results of investigations of the factor VIII (FVIII) of a patient with an unusual variant form of von Willebrand's disease (vWD) are presented. A two-peak crossed-immunoelectrophoresis (CIE) pattern was seen when fresh plasma was electrophoresed, but the CIE pattern became normal by incubating the plasma at 37 degree C for more than 72 hr. The two peaks on CIE were separated by cryoprecipitation: the slow-moving peak precipitating and the fast-moving forms of FVIII remaining in the cryosupernate. An additional protein band was seen on multimeric analysis of FVIII. The platelet-rich plasma (PRP) from this patient did not respond to ristocetin, but agglutinated normally in response to botrocetin. Multimeric and CIE analysis of the FVIII post agglutination and 125I-FVIII binding studies to normal formalin-fixed platelets indicated that this patient's FVIII interacted normally with botrocetin but failed to interact with ristocetin. These data strongly suggest that the sites on the FVIII molecule or the multimeric forms involved for ristocetin and botrocetin are different and that the ristocetin reaction is more closely aligned to the physiologic function of FVIII.

Stimulation of glucose transport in rat adipocytes by calcium

Glucose transport in rat adipocytes was studied by monitoring the conversion of [1-14C]-glucose to 14CO2 in a system where glucose transport was made rate-limiting by increasing the flux through the pentose phosphate pathway with phenazine methosulphate, an agent which rapidly reoxidizes NADPH. Calcium increased both basal and insulin-stimulated apparent rates of glucose transport by approximately 40%. The maximum velocity of the apparent rate of glucose transport was increased by extracellular calcium both in the presence or absence of insulin. There was no change in the glucose concentration required for half-maximal rates of 14CO2 production. Calcium also enhanced the stimulation of apparent rates of glucose transport by insulin when examined over a range of hormone concentrations. Adipocyte cAMP concentrations were significantly lowered by calcium under conditions which led to increased apparent rates of glucose transport. In contrast, cobalt and nickel, antagonists of calcium action, elevated adipocyte cAMP levels and inhibited apparent rates of glucose transport. Agents which inhibit transmembrane calcium flux (verapamil, tetracaine, and procaine) inhibited apparent rates of glucose transport despite a reduction in adipocyte cAMP concentration.On the basis of the above data we suggest that calcium may increase apparent rates of glucose transport in rat adipocytes both by lowering intracellular cAMP concentration and by a further mechanism independent of changes in the level of cAMP. These results are consistent with the hypothesis that glucose transport in rat adipocytes may be controlled, in part, by a cAMP-induced phosphorylation mechanism.