Control of androgen biosynthesis in the human through the interaction of Arg347 and Arg358 of CYP17 with cytochrome b5

The lyase activity of human CYP17 (17alpha-hydroxylase-17,20-lyase also P-450c17 or P-45017alpha) is greatly dependent on the presence of cytochrome b5, and this effect has been ascribed an important regulatory role [Lee-Robichaud, Wright, Akhtar and Akhtar (1995) Biochem. J. 308, 901-908]. This facet was further investigated by site-directed mutagenesis of selected basic residues of human CYP17. The purified mutant proteins were subjected to detailed kinetic analysis. It was found that the mutation of Lys83, Arg347 and Arg358 produced proteins that were deficient in their responsiveness to cytochrome b5, and the effect was most pronounced for the two arginine mutants (Arg347-->His and Arg358-->Gln) which have been found in male patients suffering from genital ambiguity. These residues are invoked to mediate protein-protein interaction between cytochrome b5 and CYP17, which 'awakens' the lyase activity of the enzyme required for androgen formation.

Spontaneous reinitiation of atrial fibrillation following transvenous atrial defibrillation

Spontaneous reinitiation of atrial fibrillation (AF) has not been systematically looked at in patients undergoing transvenous AF. This study involved 11 patients, the mean age 60 +/- 8 years, 3 male and 8 female, in whom transvenous atrial defibrillation successfully converted AF to sinus rhythm. Eight patients had paroxysmal AF and three patients had chronic persistent AF for 4 weeks or more. Four patients were taking antiarrhythmic medications at the time of testing. Multipolar transvenous catheters were positioned inside the coronary sinus, right atrium, and the right ventricle. Atrial defibrillation testing was performed using the METRIX atrial defibrillation system in nine patients and the Ventritex HVSO2 in the remaining two patients. A total of 64 therapeutic shocks (range 3-11) were delivered in the 11 patients, and 31 of these successfully converted AF to sinus rhythm. In four patients spontaneous AF was reinitiated following 12 successful transvenous atrial defibrillation episodes. The mean time to reinitiation of AF following shock delivery and restoration of sinus rhythm was 8.26 +/- 5.25 seconds, range 1.8-19.9 seconds. All 12 episodes of spontaneous AF were preceded by a spontaneous premature atrial complex. The coupling interval of the premature atrial complexes was 443 +/- 43 ms, range 390-510 ms. None of the patients taking antiarrhythmic medications or those demonstrating no premature atrial complexes had spontaneous reinitiation of AF. In conclusion, spontaneous reinitiation of AF can occur in a significant proportion of patients with AF undergoing transvenous atrial defibrillation. This phenomenon is preceded by the occurrence of atrial premature complex. Findings of this study may have significant clinical implications.

Paroxysmal nocturnal hemoglobinuria and renal failure

In this report we present two cases of acute renal failure in paroxysmal nocturnal hemoglobinuria (PNH) patients, who both eventually recovered their renal function. We also highlight some of the possible pathophysiological changes, which may contribute to renal failure in patients with PNH.

An analysis of the role of active site protic residues of cytochrome P-450s: mechanistic and mutational studies on 17alpha-hydroxylase-17,20-lyase (P-45017alpha also CYP17)

Certain cytochrome P-450s involved in the transformation of steroids catalyse not only the hydroxylation process associated with the group of enzymes, but also an acyl-carbon cleavage reaction. The hydroxylation occurs using an iron-monooxygen species while the acyl-carbon cleavage has been suggested to be promoted by an iron peroxide. In this paper we have studied the role of active site protic residues, Glu305 and Thr306, in modulating the two activities. For this purpose, the kinetic parameters for the hydroxylation reaction (pregnenolone-->17alpha-hydroxypregnenolone) and two different versions of acyl-carbon cleavage (17alpha-hydroxypregnenolone-->dehydroepiandrosterone and 3beta-hydroxyandrost-5-ene-17beta-carbaldehyde-->3beta-hydroxya ndrost -5,16-diene+androst-5-ene-3beta,17alpha-diol) were determined using the wild-type human CYP17 and its eight different single and double mutants. In addition the propensity of the proteins to undergo a subtle rearrangement converting the 450 nm active-form into an inactive counterpart absorbing at 420 nm, was monitored by measuring the t12 of the P-450-->P-420 conversion. The results are interpreted to draw the following conclusions. The functional groups of Glu305 and Thr306 do not directly participate in the two proton delivery steps required for hydroxylation but may be important participants for the provision of a net work of hydrogen bonds for 'activating' water that then acts as a proton donor. The loss of any one of these residues is, therefore, only partially debilitating. That the mutation of Thr306 impairs the hydroxylation reaction more than it does the acyl-carbon cleavage is consistent with the detailed mechanistic scheme considered in this paper. Furthermore attention is drawn to the fact that the mutation of Glu305 and Thr306 subtly perturbed the architecture of the active site, which affects the geometry of this region of the protein and therefore its catalytic properties.

Sinus tachycardia with atrioventricular block: an unusual presentation during neurocardiogenic (vasovagal) syncope

INTRODUCTION

Neurocardiogenic (vasovagal) syncope is characterized by hypotension and bradycardia. The presence of sinus tachycardia along with AV block during syncope in patients with neurocardiogenic syncope has not been described previously.

METHODS AND RESULTS

Two female patients (18 and 16 years old) with recurrent syncope and documented sinus tachycardia at the time of syncope are described. Patient 1 had recurrent episodes of syncope. During one of these episodes, which occurred while she was being monitored, sinus tachycardia along with high-grade AV block was seen at the time of syncope and hypotension. Patient 2 had a history of recurrent syncope and seizure. During one of these episodes, she was documented to have ventricular asystole lasting for about 39 seconds. The sinus rate was 480 msec at the beginning, before slowing down to 960 msec prior to restoration of sinus rhythm with 1:1 AV conduction. The same scenario was repeated during head-up tilt testing. Both patients were treated successfully with oral disopyramide and, during a follow-up of 28 months and 9 months, have remained symptom-free.

CONCLUSION

Sinus acceleration along with high-grade AV block during syncope and hypotension can occur in some patients with neurocardiogenic syncope. The exact mechanism of this phenomenon is unclear.

Catheter ablation of atrial flutter using radiofrequency current: cumulative experience in 61 patients

We present our experience with radiofrequency catheter ablation of common atrial flutter.

METHODS

Radiofrequency ablation of atrial flutter was performed utilizing percutaneous techniques and the anatomic approach under conscious sedation or general anesthesia.

RESULTS

Sixty-one consecutive patients (51 men, and 10 women) aged 59 +/- 12 years with medically refractory atrial flutter underwent catheter ablation. Thirty-eight patients (62%) had structural heart disease, including complex congenital anomalies in one patient. Atrial flutter ablation was successfully accomplished in 55 patients (90%) in one session. There were no complications, and all patients were discharged within 24-hours of the procedure. During a mean follow-up of 10 +/- 9 months, recurrent atrial flutter occurred in 11 patients (18%), eight of which successfully underwent repeat atrial flutter ablation.

CONCLUSIONS

Catheter ablation of atrial flutter using radiofrequency current is safe and has a high success rate. This nonpharmacologic approach should be considered as the first line of therapy for common atrial flutter prior to the institution of antiarrhythmic drugs.

Lack of genetic changes at specific genomic sites separates renal oncocytomas from renal cell carcinomas

Morphological similarities between renal oncocytomas and 'oncocytic' renal cell carcinomas (RCCs) make a differential diagnosis in many cases difficult. A series of 41 renal oncocytomas has been analysed by microsatellite markers from chromosomes 1, 2, 3p, 6q, 8p, 9, 10, 13q, 14q, 17, and 21, alterations of which are known to be involved specifically in non-papillary and chromophobe RCCs. Only eight of the 41 renal oncocytomas showed loss of heterozygosity (LOH). LOH at chromosomes 1 and 14 occurred in four tumours each and at chromosomes 2, 8, and 9 in one tumour each. Combined LOH at chromosomes 1, 9, and 14 and also at chromosomes 1 and 14 occurred in one case each. No LOH was seen at any other genomic sites. The lack of combination of LOH at specific chromosomal sites differentiates renal oncocytomas from other renal cell tumours with overlapping phenotypes. Applying the microsatellite assay described here, the diagnosis can be established within 2 days, from fresh as well as from paraffin-embedded material.

Ventricular tachycardia in valvular heart disease: facilitation of sustained bundle-branch reentry by valve surgery

BACKGROUND

The clinical characteristics of sustained monomorphic ventricular tachycardia (SMVT), when it develops after valve surgery, have not been described.

METHODS AND RESULTS

Between 1985 and 1996, 31 patients (30 men and 1 woman) who had undergone valve surgery were found to have inducible SMVT. Nine patients (29%) had sustained VT due to bundle-branch reentry (BBR) (group 1). Four of these patients had normal left ventricular function, and VT with a right bundle-branch morphology was inducible in 4 patients. Group 2 included 20 patients with inducible myocardial (ie, non-BBR) VT. Coronary artery disease was present in 15 group 2 patients (75%) due to atherosclerotic (n=12) and nonatherosclerotic (n=3) causes. Two patients had both inducible sustained BBR and myocardial VT (group 3). Sustained BBR VT occurred significantly earlier after valve surgery (median, 10 days) than the onset of postoperative myocardial VT (median, 72 months; P<.005).

CONCLUSIONS

Myocardial VT was the most common type of inducible SMVT in patients with valvular heart disease. The majority of these patients had underlying coronary artery disease and significant left ventricular dysfunction. However, in almost one third of the patients, sustained BBR VT was the only type of inducible SMVT. This type of VT was facilitated by the valve procedure occurring within 4 weeks after surgery in most patients. In these patients, left ventricular function was relatively well preserved, and the right bundle-branch block type of BBR was frequently induced. Because a curative therapy can be offered to these patients (ie, bundle-branch ablation), BBR should be seriously considered as the mechanism of VT in patients with valvular heart disease, particularly if the arrhythmia occurs soon after valve surgery.

Comparison of outcome of implantable cardioverter defibrillator implantation in patients with severe versus moderately severe left ventricular dysfunction secondary to atherosclerotic coronary artery disease

This study was undertaken to assess the feasibility and clinical outcome of implantable cardioverter-defibrillators (ICDs) among patients with coronary artery disease and left ventricular ejection fraction (LVEF) of <20%. The morbidity, mortality, and the long-term survival of 117 patients with LVEF of <20% (group 1) were compared with 321 patients with LVEF of 20% to 40% (group 2). Mortality in the first 30 days after ICD implantation was 0% for group 1 and 0.6% in group 2. Actuarial survival (all cause) at the end of 2, 4, and 5 years were 83%, 70%, and 62%, respectively, in group 1 and 90%, 80%, and 71% in group 2 (p = 0.05). Fifty-five patients (47%) in group 1 and 126 patients (39%) in group 2 received appropriate shocks during follow up. Among the patients in group 1, the overall survival at 2 years after an appropriate shock from an ICD was 92% for patients <60 years of age, 77% for patients ages 60 to 69, and 53% for patients >70 years old. Although the overall survival of patients in group 1 was slightly lower compared with those in group 2, in a multivariate analysis, the EF was not an independent predictor of poor survival. The ICD can be implanted with acceptable operative morbidity and mortality in selected patients with LVEF of <20%.

Catheter ablation for atrioventricular nodal reentrant tachycardia

The current status of catheter ablation techniques for the management of atrioventricular nodal reentry tachycardia is outlined in this article. Some pertinent aspects of the atrioventricular nodal anatomy and physiology are discussed, to the extent that they are essential for understanding of the mechanism of this arrhythmia and the technique of catheter ablation.

Sarcomatoid renal cell carcinoma: the chromophobe connection

Eleven cases of sarcomatoid renal cell carcinoma were studied to determine the relative frequency of various subtypes of renal cell carcinoma that may be associated with sarcomatoid transformation. The epithelial components in these tumors were subcategorized according to established histologic criteria into chromophobe carcinoma (n = 6 cases), clear cell carcinoma (n = 3), papillary carcinoma (n = 1), and indeterminate (n = 1). In nine cases, material was available for immunohistochemical and DNA ploidy studies. The sarcomatoid component in all cases showed positivity for epithelial membrane antigen cytokeratin, indicating an epithelial derivation of these cells. Staining for mesenchymal markers was mostly negative, except for vimentin, which reacted strongly in all cases. DNA ploidy studies using flow cytometry and cell image analysis provided very similar results. Five of five chromophobe sarcomatoid carcinomas showed hypodiploid cell lines in the epithelial areas, whereas the sarcomatoid components mostly showed aneuploid peaks. In the remaining cases, DNA ploidy pattern was more variable. These findings indicate that chromophobe carcinoma may be the most frequent epithelial component associated with sarcomatoid renal cell carcinoma.

The Heidelberg classification of renal cell tumours

This paper presents the conclusions of a workshop entitled 'Impact of Molecular Genetics on the Classification of Renal Cell Tumours', which was held in Heidelberg in October 1996. The focus on 'renal cell tumours' excludes any discussion of Wilms' tumour and its variants, or of tumours metastatic to the kidneys. The proposed classification subdivides renal cell tumours into benign and malignant parenchymal neoplasms and, where possible, limits each subcategory to the most commonly documented genetic abnormalities. Benign tumours are subclassified into metanephric adenoma and adenofibroma, papillary renal cell adenoma, and renal oncocytoma. Malignant tumours are subclassified into common or conventional renal cell carcinoma; papillary renal cell carcinoma; chromophobe renal cell carcinoma; collecting duct carcinoma, with medullary carcinoma of the kidney; and renal cell carcinoma, unclassified. This classification is based on current genetic knowledge, correlates with recognizable histological findings, and is applicable to routine diagnostic practice.

Safety of atrial defibrillation shocks synchronized to narrow and wide QRS complexes during atrial pacing protocols simulating atrial fibrillation in dogs

BACKGROUND

The potential ventricular proarrhythmic effect of atrial defibrillation shocks (ADS) remains a concern with automatic internal atrial defibrillation. Optimal R-wave synchronization alone may not be sufficient to prevent the induction of ventricular fibrillation (VF).

METHODS AND RESULTS

The proarrhythmic effect of ADS synchronized to normally conducted QRS complexes (NQRS) and to supraventricular complexes with left or right bundle-branch block (L/RBBB) was investigated in a canine atrial pacing study. Short-long-short, single premature, and burst pacing protocols from the high right atrium were performed at baseline, during isoproterenol infusion, and after intravenous procainamide. The ADS were delivered between decapolar catheters in the coronary sinus and lateral right atrium. They were initially delivered 20 milliseconds (ms) after the end of the last conducted QRS complex and then scanned decrementally through that complex until VF was induced. For NQRS complexes, VF occurred only when the ADS were delivered at or before the onset of the QRS complex and never during the complex itself. In the presence of LBBB or RBBB, VF was induced by ADS delivered at the onset of or within the first 45 ms of the QRS complex in 16 animals. The longest RR (VV) intervals preceding ADS-induced VF were 345 ms at baseline and 380 ms after procainamide.

CONCLUSIONS

In this study, ADS synchronized to NQRS complexes appeared to be safe regardless of the preceding RR interval. In the presence of LBBB or RBBB, RR intervals preceding the ADS of >345 ms at baseline and >380 ms in the presence of procainamide would have been required to avoid VF. Alternatively, ADS delivered 50 ms after the onset of the RV electrogram appeared to be safe in all circumstances regardless of the preceding RR interval.

Evaluation and treatment strategies in patients at high risk of sudden death post myocardial infarction

Over 50 percent of deaths in patients who survive an acute myocardial infarction are due to fatal ventricular tachyarrhythmias. Patients who survive an episode of sustained ventricular arrhythmia are at highest risk of recurrent cardiac arrest. Electrophysiologic studies have been found to be useful in guiding therapy and reducing mortality in these patients and in patients with syncope due to arrhythmic etiology. Evaluation and treatment of nonsustained ventricular tachycardia post infarction remains somewhat controversial. A recently published trial (MADIT), however, showed improved survival with an implanted defibrillator in patients with coronary disease and asymptomatic nonsustained ventricular tachycardia. Asymptomatic patients post infarction at high risk include those who have significant left ventricular dysfunction, late potentials, high-grade ventricular ectopy, and abnormal heart rate variability. These tests individually, however, have a low positive predictive accuracy. This, combined with the fact that antiarrhythmic drugs are frequently not effective and can be proarrhythmic, leaves the best treatment for these patients uncertain. It is known, however, that beta-adrenoreceptor blocking agents do reduce mortality after an acute myocardial infarction. Early studies have shown mixed results relating to sudden death and total mortality with amiodarone. To date, no other antiarrhythmic drug has shown benefit, while several have been shown to be harmful. Recent studies have also shown some beneficial effects of angiotensin-converting enzyme inhibitors, carvedilol, a third-generation beta-blocking agent with vasodilator properties, and the angiotensin II receptor antagonist losartan. However, their precise role in reducing sudden death needs to be defined further.

Right side implant of the unipolar single lead defibrillation system

The active can defibrillator has been designed for implantation in the left prepectoral region. Whether this system can be successfully implanted on the right side is unknown. We describe six cases in which placement of the unipolar single lead defibrillation system was successfully attempted in the right prepectoral region due to impediments on the left side. The mean age of the patients was 62 +/- 12 years. Five patients had ischemic heart disease and one idiopathic dilated cardiomyopathy. The endocardial defibrillation electrode was placed in the right ventricle through the right subclavian vein and positioned at the apex in two patients and in the septal position in four patients. Defibrillation threshold testing was performed using a step-up/step-down protocol beginning at 12 J with 3-J increments or decrements. Defibrillation threshold was defined as the lowest energy of the first shock able to terminate ventricular fibrillation. The generator models used were the Medtronic 7218C in 1 patient, the Medtronic 7219C in 3 patients, and the Ventritex Cadet 115 AC in 2 patients. The mean defibrillation threshold was 15 +/- 3 J. The defibrillation thresholds were retested at 1, 3, and 6 months, and showed no significant change in five patients but decreased from 15 J to 12 J in one patient. The presence of impediments on the left side should not preclude attempts to place the unipolar active can system in the right prepectoral region.

Application of polymerase chain reaction to detect rearrangement of immunoglobulin heavy chain genes in lymphoproliferative disease

As part of our routine work-up in the diagnosis of lymphoproliferative disease, we used a rapid polymerase chain reaction (PCR) assay to amplify the DNA fragments of the framework 3 (FR3) region of the immunoglobulin heavy (IgH) chain genes. The assay does not involve hybridization, nested priming, or sequencing of the amplified PCR product. It was performed on 66 specimens of B-cell lymphoproliferative disease, including acute lymphoblastic leukemia, chronic lymphocytic leukemia, multiple myeloma, hairy cell leukemia and follicular lymphoma. Twenty-six specimens of negative controls, including acute myeloid leukemia, chronic myeloid leukemia in myeloid transformation and idiopathic thrombocytopenic purpura, were also analyzed. The assay was performed with 77% sensitivity and 100% specificity. The standard IgH chain gene rearrangement by Southern blot analysis is reserved for the remaining negative cases if clinically indicated.

The effect of biphasic waveform tilt in transvenous atrial defibrillation

Atrial defibrillation can be accomplished using low energy shocks and transvenous catheters. The biphasic waveform tilt required to achieve optimal atrial defibrillation thresholds (ADFTs) is, however, not known. The effect of single capacitor biphasic waveform tilt modification on ADFT was assessed in 20 patients. Following AF induction the defibrillation pulses were delivered between the catheters positioned in the coronary sinus and the right atrium. The single capacitor biphasic waveform shocks, delivered over the same pathways, consisted of 65% tilt (65/65 biphasic waveform) to produce an overall tilt of 88%, or 50% tilt (50/50 biphasic waveform) to produce an overall tilt of 75%. Although 65/65 biphasic waveform delivers more energy, the shorter duration 50/50 biphasic waveform reduced stored energy ADFT 21%, from 1.34 +/- 0.82 J with 65/65 biphasic to 1.06 +/- 0.81 J. These differences were not statistically significant. Nine patients had lower ADFT with 50/50 biphasic waveform while five patients had lower ADFT with 65/65 biphasic waveform. Equivalent reduction in ADFT was seen in the remaining six patients. The ADFT was 0.83 +/- 0.65 J when both tilts were considered. In conclusion, biphasic waveform tilt modification may affect the ADFT in an individual patient. The optimal biphasic waveform for ADFT is not known.

Rhodopsin phosphorylation in bovine rod outer segments is more sensitive to the inhibitory action of recoverin at the low rhodopsin bleaching than it is at the high bleaching

Recoverin, a calcium-binding protein, is supposed to have rhodopsin kinase as a target in the retinal rod cell. In the present work, we show that efficiency of recoverin as an inhibitor of rhodopsin phosphorylation in bovine rod outer segments is inversely proportional to the level of rhodopsin bleaching. These results, together with the data obtained previously in a reconstituted system (Senin et al. (1997) Biochem. J. 321, 551-555), allow us to hypothesize that recoverin might be responsible for a Ca2(+)-dependent regulation of the kinase in vivo, preventing it from participating in the phosphorylation of unbleached rhodopsin.

Yield and complications in percutaneous renal biopsy. A comparison between ultrasound-guided gun-biopsy and manual techniques in native and transplant kidneys

PURPOSE

To compare the yield and complications of ultrasound-guided gun-biopsy and manual Tru-Cut techniques in percutaneous renal biopsy.

MATERIAL AND METHODS

A total of 448 biopsies were reviewed. They comprised 124 manual and 131 gun-biopsies in native kidneys, and 111 manual and 82 gun-biopsies in transplant kidneys. The gun-biopsies were performed under real-time ultrasound (US) guidance. The manual technique used US mainly for marking the position of the kidney.

RESULTS

There was a significantly higher diagnostic yield and fewer complications in the gun-biopsy group. A total of 8 major complications were found, all in the manual group.

CONCLUSION

Provided that the operator is experienced in US scanning, a switch from the manual technique to real-time US-guided gun-biopsy will result in the improvement of diagnostic accuracy together with a reduced risk of complications.

Defibrillation efficacy of commercially available biphasic impulses in humans. Importance of negative-phase peak voltage

BACKGROUND

Recent studies have shown that specifically shaped biphasic waveforms can lower energy requirements for ventricular defibrillation. We prospectively compared the defibrillation efficacy of three different biphasic wave shapes incorporated in three commercially available implantable defibrillators. The results led to the development of a second protocol in which the importance of negative-phase peak voltage and duration was investigated.

METHODS AND RESULTS

Defibrillation threshold (DFT) testing using different biphasic waveforms was performed randomly on 42 patients undergoing implantation of a cardioverter-defibrillator for ventricular arrhythmias. In 23 patients (group 1), 3 waveforms were tested: a CPI waveform with 60% positive-phase (P1) tilt and 50% negative-phase (P2) tilt, a Medtronic waveform with 65% fixed tilt in both P1 and P2, and a Ventritex waveform with 60% P1 tilt and a P2 leading edge voltage equal to half of the P1 trailing edge voltage. In 19 patients (group 2), 3 biphasic waveforms with equal P1 tilt at 65% but shorter P2 duration or smaller P2 peak voltage were tested. The Endotak C 60 series lead system (CPI) was used in 11 patients in group 1 and 10 patients in group 2. A Transvene lead system (Medtronics) was used in the remaining patients. Stored energy required for defibrillation was significantly lower with the CPI waveform compared with the Ventritex waveform. In group 2, energy requirements were significantly increased for the waveform with a smaller P2 peak voltage, whereas a short P2 duration did not influence defibrillation success.

CONCLUSIONS

Our results suggest that specifically shaped biphasic waveforms delivered from commercially available devices can affect energy requirements for defibrillation. More importantly, the amplitude of the P2 peak voltage may be a more critical determinant than the P2 duration for defibrillation success of biphasic waveforms in humans.

The impact of aromatase mechanism on other P450s

Experimental findings from a number of laboratories have converged to show that the conversion of androgens into oestrogen, catalysed by aromatase, involves three distinct reactions which occur at a single active site. That each one of these reactions belongs to a different generic type was revealed by chemical consideration, together with our (18)O-experiments. In particular, these findings highlighted the fact that the third reaction in the sequence occurs by a novel process for which a number of plausible mechanisms have been considered. The scrutiny of these mechanisms has involved either studies on aromatase itself, or on related enzymes which catalyse the aromatase type of cleavage reaction as generalized in equation 1: [equation: see text]. The acyl-carbon cleavage reaction of equation 1 is catalysed by sterol 14alpha-demethylases, accounts for several side-chain fission products formed by CYP17 (17alpha-hydroxylase-17,20-lyase), and constitutes a weak property of certain drug metabolizing P450s, when given aliphatic aldehydes as substrates. From cumulative studies on these enzymes, consensus is beginning to emerge that the acyl-carbon fission may be promoted by the FeIII-OOH intermediate, formed during the catalytic cycles of P450s. The precedent for the direct involvement of the FeIII-OOH species in the reaction of equation 1 is influencing our thinking regarding the mechanism of the conventional hydroxylation reaction. The status of knowledge surrounding the current debate on these issues will be reviewed.

Efficacy of the implantable cardioverter-defibrillator in the elderly

OBJECTIVES

We sought to assess the effect of advanced age on the outcome of patients with an implantable cardioverter-defibrillator (ICD).

BACKGROUND

ICDs are effective in preventing sudden cardiac death in susceptible patients, but their beneficial effect on survival is attenuated by the high rate of nonsudden cardiac death in those treated. Although advanced age is an important variable in determining cardiovascular mortality, its impact on the outcome of patients with an ICD has been inadequately studied.

METHODS

We performed multivariate analysis of a data base consisting of 769 consecutive patients with an ICD. Seventy-four patients > or = 75 years old at ICD implantation (Group 1) were compared with the remaining 695 patients (Group 2).

RESULTS

The two groups were similar in clinical presentation, left ventricular function and gender distribution. The mean follow-up time was 29 and 42 months, respectively, for patients in Group 1 and Group 2. Actuarial survival at 4 years was 57% in Group 1 versus 78% in Group 2 (p = 0.0001). This difference was primarily due to a higher rate of nonsudden cardiac death in Group 1. On multivariate analysis, age > or = 75 years, New York Heart Association functional class III, left ventricular ejection fraction < 30% and appropriate shocks during follow-up were independently associated with increased mortality (odds ratio 3.56, 1.8, 1.6 and 1.39, respectively).

CONCLUSIONS

Among patients with similar functional class and ejection fraction, the mortality risk is increased threefold in those > or = 75 years old at the time of ICD implantation. Extrapolation of results from younger patients is likely to overestimate ICD benefit in the elderly.

Delivery of noncommitted shocks for nonsustained ventricular arrhythmias by a new implantable cardioverter defibrillator with abortive shock capability

INTRODUCTION

To describe the delivery of noncommitted implantable cardioverter defibrillator (ICD) shocks despite self-termination of ventricular arrhythmias. Abortive shock capability should eliminate the delivery of shocks for self-terminating ventricular arrhythmias. The delivery of noncommitted shocks despite abortive shock capability is, therefore, unexpected and previously unreported.

METHODS AND RESULTS

Among 118 patients who received the Transvene nonthoracotomy lead system and the Jewel ICD (model 7219D), three patients (1.7%) experienced supurious, noncommitted shocks for self-terminating arrhythmias. Only one detection zone (i.e., ventricular fibrillation) had been programmed in the defibrillator in each patient. In all three patients, the ventricular arrhythmias self-terminated during the charging period. One patient received seven shocks during periods of asystole, and the other two patients received one shock each. Two different mechanisms for shock delivery in this setting were identified: one occurring in the absence of electrical activity at the end of the bradycardia escape interval (i.e., associated with bradyarrhythmias), and the other when two sensed electrical events (i.e., escape beats) occurred during the so-called "synchronization" window of the defibrillator.

CONCLUSIONS

In rare patients with the Jewel defibrillator, shocks may be delivered for self-terminating arrhythmias despite abortive shock capability. Patients who are dependent upon pacing from their implanted defibrillator are at particular risk for shock in the aftermath of self-terminating ventricular arrhythmias. Defibrillator programming strategies aimed at eliminating or diminishing the incidence of this problem are discussed.

The mutation T315A in Candida albicans sterol 14alpha-demethylase causes reduced enzyme activity and fluconazole resistance through reduced affinity

Sterol 14alpha-demethylase (P45051) is the target for azole antifungal compounds, and resistance to these drugs and agrochemicals is of significant practical importance. We undertook site-directed mutagenesis of the Candida albicans P45051 heterologously expressed in Saccharomyces cerevisiae to probe a model structure for the enzyme. The change T315A reduced enzyme activity 2-fold as predicted for the removal of the residue that formed a hydrogen bond with the 3-OH of the sterol substrate and helped to locate it in the active site. This alteration perturbed the heme environment, causing an altered reduced carbon monoxide difference spectrum with a maximum at 445 nm. The changes also reduced the affinity of the enzyme for the azole antifungals ketoconazole and fluconazole and after expression induced by galactose caused 4-5-fold azole resistance in transformants of S. cerevisiae. This is the first example of a single base change in the target enzyme conferring resistance to azoles through reduced azole affinity.

Specific genetic changes of diagnostic importance in chromophobe renal cell carcinomas

The histologic diagnosis of chromophobe renal cell carcinomas is often uncertain because of phenotype overlap among different types of kidney cancers. Recently, in a novel genetic classification of renal cell tumors, a combination of monosomies of chromosomes 1, 2, 3, 6, 10, 13, 17, and 21 have been suggested to have a diagnostic value for this unique type of tumor. Therefore, we have analyzed fresh and paraffin-embedded tissues obtained from 42 chromophobe renal cell carcinomas for allelic losses at the above-mentioned chromosomal regions by employing microsatellite markers. Loss of chromosomes 1, 2, 6, 10, 13, and 17 was detected in between 75% and 95% of tumors, and loss of chromosome 21 was observed in 54% of cases. All but one tumor showed a combination of monosomies at the specific chromosomes. Thus, applying the set of microsatellite markers used in this study, a PCR-based diagnosis of chromophobe renal cell carcinomas could be established within 1 to 2 days. The general applicability of this approach to fresh and paraffin-embedded tissues allows a correct genetic characterization in all cases where a diagnosis based on histopathology remains uncertain.

Human herpesvirus-8/Kaposi's sarcoma-associated herpesvirus in organ transplant patients with immunosuppression

Several recent studies have demonstrated Kaposi's sarcoma-associated herpes virus (KSHV), also known as putative human herpes virus-8 (HHV-8), DNA in various epidemiologic forms of Kaposi's sarcoma (KS), including AIDS-associated, classic, and endemic types. Risk of developing KS in non-HIV-infected immunosuppressed hosts, such as patients following solid organ transplantation, is also significantly higher compared to normal individuals. We have retrospectively evaluated 28 organ transplant patients with KS (23 cutaneous and five visceral) for the presence of KSHV genome by polymerase chain reaction (PCR) amplification of DNA isolated from formalin-fixed, paraffin-embedded archival tissue samples. 27/28 KS patients were positive for the presence of KSHV. In four KS patients, tissue samples with no histologic evidence of KS were also analysed for KSHV. No evidence of positivity in three samples was noted, but one patient had weak positive amplification products on DNA samples isolated from a gastric biopsy with chronic gastritis and lymph node with sinus histiocytosis. These data support the association of KSHV with KS developing in non-HIV-infected immunosuppressed patients, similar to other forms of KS, and suggest that KSHV may play a significant role in the development of all forms of KS.

Interaction of human CYP17 (P-450(17alpha), 17alpha-hydroxylase-17,20-lyase) with cytochrome b5: importance of the orientation of the hydrophobic domain of cytochrome b5

Human CYP17 (P-450(17alpha), 17alpha-hydroxylase-17,20-lyase)-catalysed side-chain cleavage of 17alpha-hydroxyprogestogens into androgens is greatly dependent on the presence of cytochrome b5. The native form of cytochrome b5 is composed of a globular core, residues 1-98, followed by a membrane insertable C-terminal tail, residues 99-133. In the present study the abilities of five different forms of cytochrome b5 to support the side-chain cleavage activity of CYP17 were compared. The five derivatives were: the native pig cytochrome b5 (native pig), its genetically engineered rat counterpart (core-tail), the soluble core form of the latter (core), the core with the secretory signal sequence of alkaline phosphatase appended to its N-terminal (signal-core) and the latter containing the C-terminal tail of the native rat protein (signal-core-tail). When examined by Edman degradation and MS, the engineered proteins were shown to have the expected N-terminal amino acid sequences and molecular masses. The native pig was found to be acetylated at the N-terminal. The native pig and core-tail enzymes were equally efficient at enhancing the side-chain cleavage activity of human CYP17 and the signal-core-tail was 55% as efficient. The core and signal-core constructs were completely inactive in the aforementioned reaction. All the five derivatives were reduced to varying degrees by NADPH:cytochrome P-450 (NADPH-P450) reductase and the relative efficiencies of this reduction were reminiscent of the behaviour of these derivatives in supporting the side-chain cleavage reaction. In the side-chain cleavage assay, however, NADPH-P450 reductase was used in large excess so that the reduction of cytochrome b5 derivatives was not rate-limiting. The results highlight that productive interaction between cytochrome b5 and CYP17 is governed not only by the presence of a membrane insertable hydrophobic region on the cytochrome b5 but also by its defined spatial orientation at the C-terminal.

The effect of polarity of the initial phase of a biphasic shock waveform on the defibrillation threshold of pectorally implanted defibrillators

The effect of initial phase polarity on the DFT of two pectorally implanted biphasic ICDs was tested in a randomized, prospective manner at the time of implantation. Twenty-two consecutive patients with VT-VF who received either the Medtronic PCD 7219C Jewel device (10 patients) or PCD 7219D Jewel device (12 patients) were studied. DFT testing was performed in a standard step-down manner. Both initial phase polarities--initial defibrillation current flowing from active can/SVC coil +/- subcutaneous patch) to the RV coil (RV coil to active can/SVC (RV+)--were tested in random order. The mean DFT achieved with RV+ compared with RV-was lower for the 7219C patient group (6.6 +/- 3.1 vs 10.8 +/- 5.5 J; P = 0.007). A similar trend was observed for the 7219D group, though the difference did not reach statistical significance (12.0 +/ 4.0 vs 16.3 +/- 7.3 J; P = 0.07). Seven of the 10 patients in the 7219C group had a lower DFT with RV+, while the initial phase polarity made no difference in 3. In the 7219D group, 7 patients had a lower DFT using RV+, 2 patients had a lower DFT using RV-, and the initial phase polarity made no difference in 3. In conclusion, this study demonstrates that changing the polarity of the initial phase of a biphasic shock waveform can have a significant impact on the DFT achieved at the time of ICD implantation.

Recoverin inhibits the phosphorylation of dark-adapted rhodopsin more than it does that of bleached rhodopsin: a possible mechanism through which rhodopsin kinase is prevented from participation in a side reaction

In its resting state rhodopsin kinase is present in an inactive from and is activated after interaction with light-activated rhodopsin (Rho*). The activated rhodopsin kinase then phosphorylates Rho* but is also able to catalyse the phosphorylation of dark-adapted rhodopsin. A consequence of the latter behaviour of the activated kinase is that at low levels of bleach a large number of phosphoryl groups are incorporated per mol of Rho*. Recoverin- and Ca2+-dependent inhibition of rhodopsin kinase was found to be inversely related to the extent of bleaching; the lower the fraction of rhodopsin bleached, the greater the inhibition. The IC50 of recoverin is approx. 1 microM at a 0.2% level of bleach and about 5 microM in a fully bleached sample. The inhibitory effect of recoverin was studied separately on the phosphorylation of rhodopsin and Rho*. The formation of phosphorylated rhodopsin was inhibited 4.5-fold more strongly than that of phosphorylated Rho*. These results are interpreted to suggest that one of the roles of the recoverin-dependent regulation of the activity of rhodopsin kinase is to prevent the enzyme from participating in the unwanted phosphorylation of dark-adapted rhodopsin, directing it to fulfil its 'correct' function of quenching the transduction activity of Rho*.

An overview of breast cancer

Breast cancer is a major health problem in many parts of the world. Its impact in Saudi Arabia will be more obvious when the national data is released from the National Cancer Registry (NCR) in the near future. It is the most common cancer referred to the King Faisal Specialist Hospital and Research Centre (KFSH&RC). This is a retrospective review of all female breast cancer cases treated at KFSH&RC over a 15-year period. Patients were divided into two groups at the time of their referral to KFSH&RC: metastatic and nonmetastatic. We describe the demographic data, cancer-related information and the treatments offered to all patients. Comparisons were made between Saudi and non-Saudi, and the Saudis were examined in relation to their region of referral and observed to see if any changes occurred during the study period. As well, we tried to compare our results with experience elsewhere. A total of 1584 female breast cancer patients were treated at KFSH&RC between 1975 and 1991. Early breast cancer (Stages I, II) represented 36%, while 64% presented with advanced or metastatic disease (Stages III, IV). The majority of patients were premenopausal (64%). For patients with Stages I-III (1005), mastectomy was performed in 85% and lymph node dissection in 93%. Only 30% had no pathologic lymph node involvement and in 49% of the patients, lymph node dissection was adequate (>/= 10 nodes removed). Estrogen and progesterone receptors were known in 30% of the patients. Sixty-two percent and 72% of patients referred from the central region and the northern region had Stages II and III, respectively. For the non-Saudis, we observed more premenopausal patients (76%) and fewer Stage III. At 15 years, the relapse-free survival in Stages I, II and III was 33%, 36% and 18%, and the overall survival was 80%, 64% and 45%, respectively. Breast cancer in this population affects younger patients (premenopausal) and a higher proportion present with metastatic or locally advanced disease. Management strategies should incorporate conservative surgery when appropriate, and adequate lymph node dissection. This should be coupled with increasing public awareness and education and institution of screening programs. Overall survival is clearly linked to the stage of the disease.

Is it feasible to diagnose germ-cell tumors by fine-needle aspiration biopsy?

Fine needle aspiration biopsy is an extremely useful procedure for the diagnosis of germ cell tumors. Most of the subtypes can be easily recognized and differentiated from other subtypes. For difficult cases clinical pathologic correlation may be extremely helpful in establishing a precise diagnosis. Mixed germ cell tumors may cause some difficulty if one of the components is predominant. Immunohistochemistry may also play an important role in arriving at a definitive diagnosis.

Efficacy of midodrine hydrochloride in neurocardiogenic syncope refractory to standard therapy

INTRODUCTION

Some patients with neurocardiogenic syncope continue to have recurrent syncope or presyncope despite the use of currently available drug therapy. The purpose of this study was to determine whether midodrine hydrochloride, a selective adrenergic agonist, could be effective in patients resistant to, or intolerant of, currently used medications in the treatment of neurocardiogenic syncope.

METHODS AND RESULTS

Eleven patients with a history of recurrent syncope or presyncope in whom hypotension with syncope or presyncope could be provoked during head-up tilt testing were included. There were 4 men and 7 women with a mean age (+/-SD) age of 34 +/- 13 years. In all patients, standard therapy with beta-adrenergic receptor blocking agents, ephedrine, theophylline, disopyramide, fludrocortisone, and sertraline hydrochloride, was either ineffective, poorly tolerated, or contraindicated. Midodrine was initially administered orally at a dose of 2.5 mg three times daily. After adjustment of dosage over 2 to 4 weeks, patients were followed-up clinically. Midodrine was discontinued in one patient because of side effects. Frequency of syncope or presyncope during the 3 months prior to starting treatment was compared during a mean follow-up of 17 +/- 4 weeks after starting treatment with midodrine. There was significant (P < 0.01) reduction in syncopal and presyncopal episodes on midodrine. Five patients had complete resolution of symptoms, while four patients had significant improvement. Symptoms did not improve in one patient.

CONCLUSIONS

Midodrine hydrochloride can be effective in preventing recurrent symptoms in selected patients with neurocardiogenic syncope unresponsive to, or intolerant of, standard drug therapy.

Idiopathic membranous nephropathy in identical twins

Familial idiopathic membranous nephropathy is rarely reported, despite the striking immunogenetic association of the disease with certain HLA antigens. This report describes a pair of identical male twins who contemporaneously developed idiopathic membranous nephropathy. HLA typing was carried out in the twins and in almost all members of their family. Interestingly, HLA antigens that have been reported to be associated with idiopathic membranous nephropathy, especially DR3, were found not only in the twins, but in the other family members as well. Due to similarities between Heymann nephritis and human membranous nephropathy, we performed a search for anti-brush border and antipodocyte antibodies. The inability to detect these antibodies suggests that they were probably not involved in the pathogenesis of these cases.

Response to beta blockers in patients with neurocardiogenic syncope: how to predict beneficial effects

No definitive data are available about the possibility of predicting improvement in patients with neurocardiogenic syncope treated with beta blockers. Among 112 patients with syncope and a positive head-up tilt test (HUT), independent predictors for prevention of symptoms with beta blockers were determined using the Cox proportional hazards model. Each patient underwent HUT at 70 degrees for 20 minutes both in the drug-free state and during isoproterenol infusion given to increase the heart rate by at least 25%. Fifty-nine patients had a positive HUT during isoproterenol infusion and 53 in the drug-free state. All patients were then given esmolol infusion at 500 micrograms/kg per minute for 3 minutes followed by 300 micrograms/kg per minute maintenance dose. HUT was then repeated as previously described with or without isoproterenol, depending upon the initial positive response. Regardless of the response during esmolol, all patients were treated with metoprolol 50 to 100 mg twice daily. At follow-up, 36 patients experienced symptom relapse. Four of them had negative HUT on esmolol, whereas the remaining 32 did not respond to the acute infusion of esmolol. Only four patients with positive HUT on esmolol had a favorable response to metoprolol. Patients responding to metoprolol were older (55 +/- 12 years vs 42 +/- 15 years, P < 0.05). Response to metoprolol was predicted by a negative test on esmolol (P < 0.0001) and a positive HUT on isoproterenol (P < 0.001). Age older than 42 years was also associated with a higher likelihood of metoprolol success (P < 0.02).

CONCLUSION

Acute challenge with esmolol infusion appears to be an accurate predictor of response to chronic beta blockers, together with age and a positive HUT during low-dose isoproterenol infusion.

Feasibility of atrial fibrillation detection and use of a preceding synchronization interval as a criterion for shock delivery in humans with atrial fibrillation

OBJECTIVES

This study assessed the feasibility of detecting atrial fibrillation (AF) and delivery of appropriately timed R wave shocks using an implantable atrial defibrillator.

BACKGROUND

For atrial defibrillation therapy to be feasible in an implantable form, AF must be detected in a specific fashion, and the risk of ventricular proarrhythmia should be minimized.

METHODS

Eleven patients with AF underwent testing with an implantable atrial defibrillator (METRIX 3000 Automatic Atrial Defibrillator, InControl, Inc.). Wideband electrograms (EGMs) were recorded from the right ventricular (RV) bipolar catheter and from the multipolar catheters located in the right atrium (RA) and coronary sinus (CS). Atrial fibrillation detection was performed using two serial algorithms-quiet interval analysis and baseline crossing analysis-that detect atrial activity on the RA-CS channel. Ventricular sensing using a minimal preceding synchronization interval of 500 ms as a criterion for synchronous shock delivery was performed from filtered RV and RV-CS EGMs.

RESULTS

The AF detection algorithms were applied to 53 AF data segments and 18 normal sinus rhythm data segments. Atrial fibrillation was detected appropriately in 49 instances, and the specificity for detecting AF and normal sinus rhythm was 100%. Synchronization criterion efficacy was assessed by delivering shock markers and shocks. Of the 2,025 R waves processed, 557 (27.5%) were marked as suitable for shock delivery. In addition, 69 therapeutic and 11 test shocks were delivered during AF. All shock markers and shocks were delivered synchronously with the R wave, and the synchronization criterion was never violated.

CONCLUSIONS

Atrial fibrillation can be detected in a specific fashion using the RA-CS lead configuration and serial detection algorithms for atrial sensing. The delivery of properly timed shocks is feasible and should minimize the risk of ventricular proarrhythmia.

Sudden death in patients with implantable cardioverter-defibrillators

Of the 733 patients with implantable cardioverter-defibrillators (ICDs) from 1982 to 1995 in our center, 20 died suddenly while the ICD was activated. This number included 16 men and four women with a mean age of 60 +/- 8 years and ejection fractions of 24.2% +/- 8.6%. ICDs were implanted for drug refractory ventricular tachycardia (VT) in 13 patients and for resucitated cardiac arrest in seven patients. The clinical VT was associated with syncope in 7 of 13 patients. VT was induced in 18 patients and was hemodynamically unstable in 12 patients. Shock therapies associated with syncope were delivered in 7 of 15 patients during the follow-up. This subgroup of patients survived a median of only 18 months after ICD implant. Ventricular fibrillation-defibrillation was found to surround death in nine patients.

CONCLUSIONS

(1) Sudden death victims of the ICD population are characterized by poor left ventricular function and hemodynamically unstable ventricular tachyarrhythmias. (2) Ventricular tachyarrhythmias are the major cause of sudden death in ICD patients.

Cytogenetic findings in renal cell carcinoma

Cytogenetic characterization of 24 renal cell carcinomas (RCCs) was performed. The various RCC subtypes included 8 chromophobe RCCs, 12 nonpapillary RCCs, and 4 papillary RCCs. Loss of chromosomes 1, 2, 6, 10, and 17 were observed in 5 of 8 chromophobe RCCs. Five of the 12 nonpapillary RCCs showed abnormalities involving chromosome 3. These were deletion of the 3p13 region, loss of the whole chromosome 3, and unbalanced translocation resulting in a derivative. Of the 4 papillary RCCs, two showed trisomy 7 and 17 along with other abnormalities, one had trisomy for chromosomes 7, 12, and 13, along with loss of chromosome #5 and Y chromosomes, and another papillary RCC revealed trisomy 15 and trisomy 17. These results further show that specific cytogenetic abnormalities are associated with various subtypes of RCCs.

Effect of urea treatment on recovery of staphylococcal enterotoxin A from heat-processed foods

The effects of urea treatment on the potential reactivation of heat-damaged antigenic components of staphylococcal enterotoxin A (SEA) were examined with cooked foods, including mushrooms, ham, bologna, salami, and turkey. The thermal stability of purified SEA spiked into foods and native SEA produced by Staphylococcus aureus in foods was also examined. Food samples containing either spiked or native SEA were thermally processed by autoclaving or retorting. This was followed sequentially by toxin extraction, urea treatment, dialysis, reconstitution, and SE assays with the reversed passive latex agglutination and/or enzyme immunoassay kit. The results indicate that (i) urea treatment did not result in any reactivation of heat-inactivated antigenic components of SEA in any of the foods tested, (ii) the serological components of purified SEA were destroyed (> or = 96%) by autoclaving at 121.1 degrees C for 5 to 15 min or by retorting at an F0 of 4 to 18, and (iii) the immunological property of the native SEA was approximately threefold-more heat resistant than that of the purified SEA. The study suggested that the current urea method is not suitable for the detection of heat-denatured SEA in the thermally processed foods.