Kidney derived apolipoprotein M and its role in acute kidney injury

Aim: Apolipoprotein M (apoM) is mainly expressed in liver and in proximal tubular epithelial cells in the kidney. In plasma, apoM associates with HDL particles via a retained signal peptide and carries sphingosine-1-phosphate (S1P), a small bioactive lipid. ApoM is undetectable in urine from healthy individuals but lack of megalin receptors in proximal tubuli cells induces loss of apoM into the urine. Besides this, very little is known about kidney-derived apoM. The aim of this study was to address the role of apoM in kidney biology and in acute kidney injury. Methods: A novel kidney-specific human apoM transgenic mouse model (RPTEC-hapoMTG) was generated and subjected to either cisplatin or ischemia/reperfusion injury. Further, a stable transfection of HK-2 cells overexpressing human apoM (HK-2-hapoMTG) was developed to study the pattern of apoM secretion in proximal tubuli cells. Results: Human apoM was present in plasma from RPTEC-hapoMTG mice (mean 0.18 μM), with a significant increase in plasma S1P levels. In vitro apoM was secreted to both the apical (urine) and basolateral (blood) compartment from proximal tubular epithelial cells. However, no differences in kidney injury score was seen between RPTEC-hapoMTG and wild type (WT) mice upon kidney injury. Further, gene expression of inflammatory markers (i.e., IL6, MCP-1) was similar upon ischemia/reperfusion injury. Conclusion: Our study suggests that kidney-derived apoM is secreted to plasma, supporting a role for apoM in sequestering molecules from excretion in urine. However, overexpression of human apoM in the kidney did not protect against acute kidney injury.

A randomised trial comparing weaning from CPAP alone with weaning using heated humidified high flow nasal cannula in very preterm infants: the CHiPS study

OBJECTIVE

To determine whether weaning from nasal continuous positive airway pressure (nCPAP) using heated humidified high flow nasal cannula (nHF) was non-inferior to weaning using nCPAP alone in relation to time on respiratory support.

STUDY DESIGN

Single-centre, non-inferiority, randomised controlled trial.

SETTING

Neonatal Intensive Care Unit, Middlemore Hospital, Auckland, New Zealand.

PATIENTS

120 preterm infants, <30 weeks' gestation at birth, stable on nCPAP for at least 48 hours.

INTERVENTIONS

Infants underwent stratified randomisation to nHF 6 L/min or bubble CPAP 6 cm water. In both groups, stepwise weaning of their respiratory support over 96 hours according to a strict weaning protocol was carried out.

MAIN OUTCOME MEASURES

Time on respiratory support from randomisation to 72 hours off respiratory support or 36 weeks' postmenstrual age. The non-inferiority threshold was set at 15%.

RESULTS

59 infants were randomised to weaning using nHF and 61 using nCPAP. The groups were well balanced in regards to baseline demographics. The restricted mean duration of respiratory support following randomisation for the nCPAP group, using per-protocol analysis was 401 hours (upper boundary, mean plus 0.15, was 461 hours) and 375 hours in the nHF group (upper 95% CI 413 hours). nHF weaning was, therefore, non-inferior to nCPAP weaning at the non-inferiority threshold. There was no significant difference in time to discharge.

CONCLUSION

For infants ready to wean from nCPAP, the CHiPS study found that nHF was non-inferior to discontinuing nCPAP at 5 cm water.

TRIAL REGISTRATION NUMBER

Australia and New Zealand Clinical Trials Registry (ACTRN12615000077561).

MO339KIDNEY DERIVED APOM AND ITS ROLE IN ACUTE KIDNEY INJURY

Background and Aims

Acute kidney injury is a severe disease with detrimental outcomes. The underlying ethiology is still elusive and besides dialysis, treatment options are poor.

Apolipoprotein M (apoM) is mainly expressed in liver and in proximal tubular epithelial cells in the kidney. In plasma, apoM associates with HDL particles via a retained signal peptide. ApoM is a carrier of sphingosine-1-phosphate (S1P), a small bioactive lipid involved in e.g. angiogenesis, lymphocyte trafficking, and vascular barrier function. Recently, it was shown that apoM/S1P protects against development of liver and lung fibrosis. In urine, apoM is normally undetectable in both wild type mice and healthy humans. However, lack of megalin receptors in proximal tubuli induces loss of apoM into the urine. The biological function of kidney-derived apoM is unknown, but it has been hypothesized that apoM might be secreted to the pre-urine to sequester molecules, such as S1P, from secretion.

The aim of this study was to unravel the role of apoM in kidney biology and in acute kidney injury.

Method

A novel kidney specific human apoM transgenic mouse (RPTEC-hapoMTG), was generated by expressing human apoM under the control of the proximal tubular epithelial cell specific Sglt2 promoter. The effect of kidney specific apoM overexpression on acute kidney injury was accessed by inducing either cisplatin or ischemia/reperfusion injury. Further, a stable cell line of HK-2 cells overexpressing hapoM (HK-2hapoM-TG) was generated and the cells were cultured on transwells to assess the secretion of apoM to respectively the apical and basolateral site.

Results

hapoM was present in plasma from RPTEC-hapoMTG mice (mean 0.18 μM), indicating that kidney-derived apoM can be secreted to plasma. When assessing the secretion of hapoM from proximal tubular epithelial cells in vitro, studies support that apoM can be secreted to both the apical (urine) and basolateral (blood) compartment. No differences in kidney injury markers (plasma urea and creatinine) between RPTEC-hapoMTG and wild type (WT) mice subjected to cisplatin injections, or in kidney injury score determined by histological evaluation was found. Similar, we could not detect any histological difference between RPTEC-hapoMTG and WT mice after ischemia/reperfusion injury, and overexpression of hapoM did not affect kidney gene expression of inflammatory markers (i.e. IL6, MCP-1) compared to WT mice.

Conclusion

Our study suggests that apoM can be secreted to both the apical and basolateral compartment, supporting a role for apoM in sequestering molecules from secretion in urine.

Transgenic overexpression of apoM in proximal tubular epithelial cells of mice did not protect against acute kidney injury.

Radial-probe endobronchial ultrasound outcomes in the investigation of peripheral pulmonary lesions: a New Zealand perspective

BACKGROUND

Radial-probe endobronchial ultrasound (radial-EBUS) is becoming an important investigation for peripheral pulmonary lesions (PPL). A key advantage of radial-EBUS is the favourable risk profile compared with current gold-standard computerised tomography-guided biopsy.

AIM

To investigate the diagnostic yield, predictors of positive yield and radial-EBUS safety in a New Zealand institution. We also determined whether molecular analysis was possible on the same tissue samples.

METHODS

We performed a retrospective analysis of all patients (n = 68) from Middlemore Hospital, Auckland, undergoing radial-EBUS with guide-sheath for PPL from March 2015 to August 2016. Clinical, radiological and procedural data were collected. Radial-EBUS diagnostic yield was determined for malignant and benign diagnoses, and molecular analysis yield was determined on appropriate malignant samples. Logistic regression was used to determine factors predicting successful radial-EBUS.

RESULTS

Overall diagnostic yield of radial-EBUS was 55.9% (95% confidence interval (CI): 44.3-67.9). Malignant diagnostic sensitivity was 60.8% (95% CI: 46.1-74.2) and benign diagnostic sensitivity was 50% (95% CI: 23-77). Lesions close to the hilum (P = 0.039), concentric radial-probe positioning (P = 0.008) and the use of forceps as first instrument (P = 0.0049) significantly predicted successful diagnostic yield. Of the malignant cases 81.0% (95% CI: 58.1-94.6) were sufficient for molecular analysis. Pneumothorax occurred in 4.4% (95% CI: 0.9-12.4), none required chest drain intervention. There were no cases of significant pulmonary haemorrhage.

CONCLUSION

Radial-EBUS was shown to be safe with diagnostic yield similar to international reports. Important predictors of success include distance from hilum, probe position and forceps as first instrument. We also demonstrated that molecular analysis is possible in radial-EBUS obtained samples.

Impaired endothelial barrier function in apolipoprotein M-deficient mice is dependent on sphingosine-1-phosphate receptor 1

Apolipoprotein M (ApoM) transports sphingosine-1-phosphate (S1P) in plasma, and ApoM-deficient mice (Apom(-/-)) have ∼50% reduced plasma S1P levels. There are 5 known S1P receptors, and S1P induces adherens junction formation between endothelial cells through the S1P1 receptor, which in turn suppresses vascular leak. Increased vascular permeability is a hallmark of inflammation. The purpose of this study was to explore the relationships between vascular leakage in ApoM deficiency and S1P1 function in normal physiology and in inflammation. Vascular permeability in the lungs was assessed by accumulation of dextran molecules (70 kDa) and was increased ∼40% in Apom(-/-) mice compared to WT (C57Bl6/j) mice. Reconstitution of plasma ApoM/S1P or treatment with an S1P1 receptor agonist (SEW2871) rapidly reversed the vascular leakage to a level similar to that in WT mice, suggesting that it is caused by decreased plasma levels of S1P and reduced S1P1 stimulation. In a carrageenan-induced model of inflammation, Apom(-/-) mice had increased vascular leakage compared with that in WT mice. Adenoviral overexpression of ApoM in Apom(-/-) mice decreased the vascular leakage compared to adenoviral overexpression of green fluorescent protein. The study suggests that vascular leakage of albumin-sized particles in ApoM deficiency is S1P- and S1P1-dependent and this dependency exacerbates the response to inflammatory stimuli.-Christensen, P. M., Liu, C. H., Swendeman, S. L., Obinata, H., Qvortrup, K., Nielsen, L B., Hla, T., Di Lorenzo, A., Christoffersen, C. Impaired endothelial barrier function in apolipoprotein M-deficient mice is dependent on sphingosine-1-phosphate receptor 1.

Comparison between two assessment methods for exercise-induced laryngeal obstructions

Exercise-induced laryngeal obstructions (E-ILOs) are important differential diagnoses to exercise-induced asthma and are diagnosed by the continuous laryngoscopy exercise (CLE) test. There are two different methods for evaluating the severity of E-ILOs using recordings from the CLE test; the CLE score and EILOMEA. The aim of this study was to investigate the consistency between these methods. Using their respective method, the developers of each method evaluated 60 laryngoscopic recordings from patients with different subtypes and various levels of severity of E-ILOs. The CLE score evaluates glottic and supraglottic obstructions on a 4-grade scale. EILOMEA uses software to calculate the obstruction severity on continuous scales from a still frame of the larynx during maximal obstruction giving three parameters reflecting glottic and supraglottic obstruction. The means of the EILOMEA measures differed significantly for CLE score 1 vs. 2 and 2 vs. 3, but not for 0 vs. 1 for glottic as well as supraglottic obstructions. The EILOMEA method does not distinguish between CLE score 0 and 1, but otherwise the methods correlate. Since previous studies have suggested that only CLE scores of 2 and 3 reflect a severity of E-ILOs of clinical importance, this lack of the EILOMEA method is not crucial for a correct medical evaluation.

ERS/ELS/ACCP 2013 international consensus conference nomenclature on inducible laryngeal obstructions

Individuals reporting episodes of breathing problems caused by re-occurring variable airflow obstructions in the larynx have been described in an increasing number of publications, with more than 40 different terms being used without consensus on definitions. This lack of an international consensus on nomenclature is a serious obstacle for the development of the area, as knowledge from different centres cannot be matched, pooled or readily utilised by others. Thus, an international Task Force has been created, led by the European Respiratory Society/European Laryngological Society/American College of Chest Physicians. This review describes the methods used to reach an international consensus on the subject and the resulting nomenclature, the 2013 international consensus conference nomenclature.

Apolipoprotein M in lipid metabolism and cardiometabolic diseases

PURPOSE

This review will address recent findings on apolipoprotein M (apoM) and its ligand sphingosine-1-phosphate (S1P) in lipid metabolism and inflammatory diseases.

RECENT FINDINGS

ApoM's likely role(s) in health and disease has become more diverse after the discovery that apoM functions as a chaperone for S1P. Hence, apoM has recently been implicated in lipid metabolism, diabetes and rheumatoid arthritis through in-vivo, in-vitro and genetic association studies. It remains to be established to which degree such associations with apoM can be attributed to its ability to bind S1P.

SUMMARY

The apoM/S1P axis and its implications in atherosclerosis and lipid metabolism have been thoroughly studied. Owing to the discovery of the apoM/S1P axis, the scope of apoM research has broadened. ApoM and S1P have been implicated in lipid metabolism, that is by modulating HDL particles. Also, the importance in regulating endothelial function is being investigated. Furthermore, both apoM and S1P have been linked to diabetes and glucose and insulin metabolism. Finally, genetic variations in the apoM gene are associated with lipid disturbances, diabetes and rheumatoid arthritis. These findings suggest not only diverse effects of apoM, but also the important question of whether apoM mainly acts as a S1P carrier, if apoM carries other substances with biological effects as well, or whether the apoM protein has effects on its own.

Can flow-volume loops be used to diagnose exercise induced laryngeal obstructions? A comparison study examining the accuracy and inter-rater agreement of flow volume loops as a diagnostic tool

Background:

Pre- and post-exercise flow-volume loops are often recommended as an easy non-invasive method for diagnosing or excluding exercise-induced laryngeal obstructions in patients with exercise-related respiratory symptoms. However, at present there is no evidence for this recommendation.

Aims:

To compare physician evaluated pre- and post-exercise flow-volume loops and flow data with laryngoscopic findings during exercise.

Methods:

Data from 100 consecutive exercise tests with continuous laryngoscopy during the test were analysed. Laryngoscopic images were compared with the corresponding pre- and post-exercise flow-volume loops assessed by four separate physicians and with data from the loops (forced inspiratory flow (FIF) at 25% vs. FIF at 75% of forced inspiratory vital capacity (FIVC), forced expiratory flow at 50% of forced expiratory volume vs. FIF at 50% of FIVC, and FIVC vs. FIF at 50% of FIVC).

Results:

There was no significant association between the laryngoscopic findings and the flow-volume data. There was no agreement between the four physicians in their assessment of the flow-volume loops (kappa <0.00), and none of the individual physician's assessments were significantly associated with the laryngoscopic findings.

Conclusions:

Exercise-induced laryngeal obstructions cannot be diagnosed or excluded by physician evaluated pre- and post-exercise flow-volume loops or flow data alone.

Eucapnic voluntary hyperventilation in diagnosing exercise-induced laryngeal obstructions

Exercise-induced laryngeal obstructions (EILOs) cause exercise-related respiratory symptoms (ERRS) and are important differential diagnoses to exercise-induced asthma. The diagnostic method for EILOs includes provocation to induce the obstruction followed by a verification of the obstruction and the degree thereof. The objective of the present study was to examine if a eucapnic voluntary hyperventilation (EVH) test could induce laryngeal obstructions laryngoscopically identical in subtypes and development as seen during an exercise test. EVH and exercise testing with continuous laryngoscopy were performed during a screening of two national athletic teams (n = 67). The laryngoscopic recordings were examined for usability, abnormalities and maximal supraglottic and glottic obstruction using two currently available methods (Eilomea and CLE-score). The participants were asked questions on ERRS, and whether the symptoms experienced during each provocation matched those experienced during regular training. A total of 39 completed both tests. There were no significant differences in subtypes and development thereof, the experience of symptoms, and specificity and sensitivity between the methods. Significantly more recordings obtained during the exercise test were usable for evaluation primarily due to resilient mucus on the tip of the fiber-laryngoscope in the EVH test. Only recordings of six athletes from both provocation methods were usable for evaluation using the Eilomea method (high-quality demand). Amongst these, a linear correlation was found for the glottic obstruction. EVH tests can induce EILOs. However, the present test protocol needs adjustments to secure better visualisation of the larynx during provocation.

Influence of nitrate supplementation on VO₂ kinetics and endurance of elite cyclists

The present study examined if an elevated nitrate intake would improve VO(2) kinetics, endurance, and repeated sprint capacity in elite endurance athletes. Ten highly trained cyclists (72 ± 4 mL O(2) /kg/min, mean ± standard deviation) underwent testing for VO(2) kinetics (3 × 6 min at 298 ± 28 W), endurance (120 min preload followed by a 400-kcal time trial), and repeated sprint capacity (6 × 20 s sprints, recovery 100 s) during two 6-day periods in randomized order with a daily ingestion of either 0.5 L beetroot (BR) juice to increase nitrate levels or a 0.5 L placebo (PLA) drink with blackcurrant juice. Plasma NOx (nitrate + nitrite) levels were higher (P < 0.01) in BR (147 ± 102 and 159 ± 103 μM after 4 and 6 days of beverage intake, respectively) compared with PLA (41 ± 10 and 40 ± 7 μM). VO(2) kinetics and exercise economy were the same in BR and PLA. Time-trial performance was similar with an average completion time of 18:20 and 18:37 min:s in BR and PLA, respectively, with average power outputs of 290 ± 43 W in BR and 285 ± 44 W in PLA. Peak and mean power during repeated sprinting were similar in BR and PLA. In contrast to observations in moderately trained subjects intake of BR juice had no effect on VO(2) kinetics and performance in elite cyclists.

The plasma concentration of HDL-associated apoM is influenced by LDL receptor-mediated clearance of apoB-containing particles

ApoM is mainly associated with HDL. Nevertheless, we have consistently observed positive correlations of apoM with plasma LDL cholesterol in humans. Moreover, LDL receptor deficiency is associated with increased plasma apoM in mice. Here, we tested the idea that plasma apoM concentrations are affected by the rate of LDL receptor-mediated clearance of apoB-containing particles. We measured apoM in humans each carrying one of three different LDL receptor mutations (n = 9) or the apoB3500 mutation (n = 12). These carriers had increased plasma apoM (1.34 ± 0.13 µM, P = 0.003, and 1.23 ± 0.10 µM, P = 0.02, respectively) as compared with noncarriers (0.93 ± 0.04 µM). When we injected human apoM-containing HDL into Wt (n = 6) or LDL receptor-deficient mice (n = 6), the removal of HDL-associated human apoM was delayed in the LDL receptor-deficient mice. After 2 h, 54 ± 5% versus 90 ± 8% (P < 0.005) of the initial amounts of human apoM remained in the plasma of Wt and LDL receptor-deficient mice, respectively. Finally, we compared the turnover of radio-iodinated LDL and plasma apoM concentrations in 45 normocholesterolemic humans. There was a negative correlation between plasma apoM and the fractional catabolic rate of LDL (r = -0.38, P = 0.009). These data suggest that the plasma clearance of apoM, despite apoM primarily being associated with HDL, is influenced by LDL receptor-mediated clearance of apoB-containing particles.

Effect of whey protein- and carbohydrate-enriched diet on glycogen resynthesis during the first 48 h after a soccer game

The effect of a whey protein- and carbohydrate (CHO)-enriched diet on the rate of muscle glycogen resynthesis after a soccer match was examined. Sixteen elite soccer players were randomly assigned to a group ingesting a diet rich in carbohydrates and whey protein [CHO, protein, and fat content was 71, 21, and 8E%, respectively; high content of carbohydrates and whey protein (HCP), n = 9] or a group ingesting a normal diet (55, 18, and 26E%; control [CON], n = 7) during a 48-h recovery period after a soccer match. CON and three additional players carried out a 90- and 60-min simulated match without body contacts (SIM90 and SIM60). Muscle glycogen was lowered (P < 0.05) by 54, 48, 53, and 38% after the matches in CON, HCP, SIM90, and SIM60, respectively. Glycogen resynthesis during the first 48 h after the match was not different between CON and HCP, whereas glycogen resynthesis was slower (P < 0.05) during the first 24 h after SIM60 than SIM90 (2.88 ± 0.84 vs 4.32 ± 0.54 mmol/kg dw/h). In HCP, glycogen content in type II muscle fibers was still lowered 48 h after the match. In conclusion, glycogen resynthesis 48 h after a soccer match is not elevated by ingestion of a HCP diet. Furthermore, glycogen resynthesis does not appear to be impaired by body contacts during a match.

Exercise-induced laryngeal obstructions: prevalence and symptoms in the general public

Respiratory difficulties caused by exercise-induced laryngeal obstructions (EILOs) are reported with increasing frequency. The aim of this study was to assess the prevalence and symptoms of EILOs and their relation to airway hyperresponsiveness (AHR). In total, 556 randomly selected youths in Copenhagen aged 14-24 years were invited over a 2-year period. The study included a mailed questionnaire and two visits: day 1 (an interview-based questionnaire, methacholine bronchial provocation test and physical exertion test); and day 2 [an exercise test with continuous laryngoscopic recordings (CLE test)]. The diagnosis of EILOs was based on the CLE test. In total, 237 answered the mailed questionnaire and 150 participated on day 1 whereof 98 participated on day 2 also. AHR was verified in 23 (4.1% of invitees) and EILOs in 42 (7.5% of invitees). Co-morbidity was verified in 6 cases (26.1% of verified AHR cases). No symptoms were found specific for either AHR or EILOs. The minimum prevalence of EILOs in this cohort was 7.5%. EILOs were verified in 26.1% of participants with AHR. Questionnaires could not differentiate between AHR and EILOs.

The sparteine/debrisoquine (CYP2D6) oxidation polymorphism and the risk of Parkinson's disease: a meta-analysis

The association between the sparteine/debrisoquine (CYP2D6) oxidation polymorphism and the risk of Parkinson's disease was examined in a meta-analysis of case-control studies. The odds ratio was calculated for the risk of Parkinson's disease among poor metabolisers compared with extensive metabolisers. Twenty-one studies were identified of which six were excluded because they were not reported as full papers (n = 3), used incomplete genotype analysis (n = 2) or used Parkinson patients as both control individuals and cases (n = 1). The overall odds ratio was 1.48 (95% confidence interval 1.10-1.99). The odds ratio was 1.05 (95% confidence interval 0.63-1.77) in studies discriminating extensive and poor metabolisers by phenotyping (n = 8) and 1.67 (95% confidence interval 1.11-2.50) in studies using genotyping (n = 7). This difference was caused by a single large study using genotyping. We conclude that there is no convincing evidence of an association between the debrisoquine/sparteine polymorphism and Parkinson's disease. However, it could prove worthwhile to perform another large study using genotyping.

[Evaluation of ear temperature measurements in a geriatric department]

We evaluated an infrared tympanic thermometer (Genius 3000A) by comparing it with parallel measurements with an electronic rectal thermometer (Philips HP 5316) on 121 patients admitted to a geriatric department. Rectal temperature was on average 0.14 degree C +/- (ISD) above the ear temperature. 95% of the differences are within the interval from -1.18 degrees C to 1.46 degrees C. The coefficient of determination was only 0.30. The tympanic thermometer, Genius 3000A, cannot be recommended for daily use on a geriatric ward.

The sparteine/debrisoquine (CYP2D6) oxidation polymorphism and the risk of lung cancer: a meta-analysis

OBJECTIVE

To examine the association between the sparteine/debrisoquine (CYP2D6) oxidation polymorphism and the risk of lung cancer.

METHOD

Meta-analysis of case-control studies using a random effects model. The "Main outcome measure" was the odds ratio for the risk of lung cancer, using extensive metabolisers as the reference group.

RESULTS

Thirteen studies were identified. The studies were too heterogeneous to be pooled the size of the odds ratio increased with the sample size. When the analysis was restricted to the largest studies, there was no difference in risk between poor and extensive metabolisers (odds ratio 0.95, 95% confidence interval 0.68-1.33).

CONCLUSION

No association was found between the CYP2D6 oxidation polymorphism and lung cancer risk when sample size bias was taken into account.

Recombinant human extrinsic pathway inhibitor. Production, isolation, and characterization of its inhibitory activity on tissue factor-initiated coagulation reactions

Previous studies have shown that extrinsic pathway inhibitor (EPI) is an effective inhibitor of factor Xa alone or factor VIIa-tissue factor complex in the presence of factor Xa. Since tissue factor exposure is implicated in thrombogenesis, we hypothesized that EPI may be valuable in the treatment of some thromboembolic episodes. Furthermore, EPI may be an important factor in bleeding complications in hemophiliacs. In the present study, human EPI was expressed in baby hamster kidney cells using a mammalian expression vector. Transfected cells expressed 1-2 micrograms/ml of recombinant EPI (rEPI) which was purified to homogeneity by heparin-Sepharose chromatography, ion-exchange chromatography, and reverse phase high performance liquid chromatography. Purified rEPI exhibited a specific activity of 30,000 units/mg and migrated as a single band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent molecular weight of 42,000. In addition, the NH2-terminal sequence of rEPI was identical to that of HepG2 EPI and HeLa EPI. The ability of rEPI to inhibit factor X activation by a complex of factor VIIa-tissue factor was then examined in the presence and absence of plasma concentrations of human factors VIII and IX. Using relipidated human brain tissue factor apoprotein, rEPI inhibited the factor VIIa-mediated activation of factor X half-maximally at 2.5 and 1 nM in the presence and absence of factors VIII and IX, respectively. Using monolayers of a human bladder carcinoma cell line (J82) as the source of tissue factor, the activation of factor X by cell-bound factor VIIa was inhibited half-maximally by 5 nM rEPI in the presence of factors VIII and IX. The proteolytic activity of J82 cell-bound factor Xa toward prothrombin was inhibited half-maximally at approximately 5 nM rEPI, while the amidolytic activity of factor Xa in solution was inhibited by rEPI with a Ki of 130 pM. Recombinant EPI also inhibited the amidolytic activity of factor VIIa half-maximally at 10 nM rEPI in the presence of relipidated tissue factor apoprotein and calcium. These results indicate that, in the presence of plasma concentrations of factors VIII and IX, at least 10 times the plasma concentration of EPI is required to reduce factor VIIa-dependent factor X activation one order of magnitude in vitro. In the absence of functional factor VIII and IX, rEPI at plasma levels was a potent inhibitor of factor VIIa-mediated factor X activation, and this activity presumably accounts for the inability of hemophiliacs to initiate hemostasis via the extrinsic pathway.

Changing the insulin receptor to possess insulin-like growth factor I ligand specificity

To examine the role of the N-terminal part of the insulin-like growth factor I (IGF-I) receptor and insulin receptor in determining ligand specificity, we prepared an expression vector encoding a hybrid receptor where exon 1 (encoding the signal peptide and seven amino acids of the alpha-subunit), exon 2, and exon 3 of the insulin receptor were replaced with the corresponding IGF-I receptor cDNA (938 nucleotides). To allow direct quantitative comparison of the binding capabilities of this hybrid receptor with those of the human IGF-I receptor and the insulin receptor, all three receptors were expressed in baby hamster kidney (BHK) cells as soluble molecules and partially purified before characterization. The hybrid IGF-I/insulin receptor bound IGF-I with an affinity comparable to that of the wild-type IGF-I receptor. In contrast, the hybrid receptor no longer displayed high-affinity binding of insulin. These results directly demonstrate that it is possible to change the specificity of the insulin receptor to that of the IGF-I receptor and, furthermore, that the binding specificity for IGF-I is encoded within the nucleotide sequence from 135 to 938 of the IGF-I receptor cDNA. Since the hybrid receptor only bound insulin with low affinity, the insulin binding region is likely to be located within exons 2 and 3 of the insulin receptor.