Binding and neutralizing anti-AAV antibodies: Detection and implications for rAAV-mediated gene therapy

Assessment of anti-adeno-associated virus (AAV) antibodies in patients prior to systemic gene therapy administration is an important consideration regarding efficacy and safety of the therapy. Approximately 30%-60% of individuals have pre-existing anti-AAV antibodies. Seroprevalence is impacted by multiple factors, including geography, age, capsid serotype, and assay type. Anti-AAV antibody assays typically measure (1) transduction inhibition by detecting the neutralizing capacity of antibodies and non-antibody neutralizing factors, or (2) total anti-capsid binding antibodies, regardless of neutralizing activity. Presently, there is a paucity of head-to-head data and standardized approaches associating assay results with clinical outcomes. In addition, establishing clinically relevant screening titer cutoffs is complex. Thus, meaningful comparisons across assays are nearly impossible. Although complex, establishing screening assays in routine clinical practice to identify patients with antibody levels that may impact favorable treatment outcomes is achievable for both transduction inhibition and total antibody assays. Formal regulatory approval of such assays as companion diagnostic tests will confirm their suitability for specific recombinant AAV gene therapies. This review covers current approaches to measure anti-AAV antibodies in patient plasma or serum, their potential impact on therapeutic safety and efficacy, and investigative strategies to mitigate the effects of pre-existing anti-AAV antibodies in patients.

Durability of transgene expression after rAAV gene therapy

Recombinant adeno-associated virus (rAAV) gene therapy has the potential to transform the lives of patients with certain genetic disorders by increasing or restoring function to affected tissues. Following the initial establishment of transgene expression, it is unknown how long the therapeutic effect will last, although animal and emerging human data show that expression can be maintained for more than 10 years. The durability of therapeutic response is key to long-term treatment success, especially since immune responses to rAAV vectors may prevent re-dosing with the same therapy. This review explores the non-immunological and immunological processes that may limit or improve durability and the strategies that can be used to increase the duration of the therapeutic effect.

A Retrospective Study of Clinical and Economic Burden of Focal Segmental Glomerulosclerosis (FSGS) in the United States

Introduction

Information on the economic burden of focal segmental glomerulosclerosis (FSGS) is sparse. This study characterized health care resource utilization (HCRU) and costs in patients with FSGS, and evaluated the impact of nephrotic range proteinuria on these outcomes.

Methods

This retrospective, observational cohort study used administrative claims data from the Optum Clinformatics Data Mart Database from October 2015 to December 2019. Patients with FSGS (n = 844; first claim = index event) between April 2016 and December 2018 were matched on index date, age, sex, and race to non-FSGS controls (n = 1688). FSGS nephrotic range (urine protein/creatinine ratio >3000 mg/g or albumin/creatinine ratio >2000 mg/g) and non-nephrotic subpopulations were identified. Baseline comorbidities, 12-month post-index all-cause HCRU and costs (per patient per year [PPPY]), and immunosuppressant prescriptions were compared between matched cohorts and between FSGS subpopulations.

Results

Comorbidity burden was higher in FSGS. Of 308 patients with available urine protein/creatinine ratio/albumin/creatinine ratio results, 36.4% were in nephrotic range. All-cause HCRU was higher in FSGS across resource categories (all P < 0.0001); 50.6% of FSGS and 23.3% of controls were prescribed glucocorticoids (P < 0.0001). Mean total medical costs were higher in FSGS ($59,753 vs. $8431 PPPY; P < 0.0001), driven by outpatient costs. Nephrotic range proteinuria was associated with higher all-cause inpatient, outpatient, and prescription costs versus nonnephrotic patients (all P < 0.0001), resulting in higher total costs ($70,481 vs. $36,099 PPPY; P < 0.0001).

Conclusions

FSGS is associated with significant clinical and economic burdens; the presence of nephrotic range proteinuria increased the economic burden. New treatment modalities are needed to reduce proteinuria, help improve patient outcomes, and reduce HCRU and associated costs.

PODO: Trial Design: Phase 2 Study of PF-06730512 in Focal Segmental Glomerulosclerosis

Introduction

Focal segmental glomerulosclerosis (FSGS) is characterized by proteinuria and a histologic pattern of glomerular lesions of diverse etiology that share features including glomerular scarring and podocyte foot process effacement. Roundabout guidance receptor 2 (ROBO2)/slit guidance ligand 2 (SLIT2) signaling destabilizes the slit diaphragm and reduces podocyte adhesion to the glomerular basement membrane (GBM). Preclinical studies suggest that inhibition of glomerular ROBO2/SLIT2 signaling can stabilize podocyte adhesion and reduce proteinuria. This clinical trial evaluates the preliminary efficacy and safety of ROBO2/SLIT2 inhibition with the ROBO2 fusion protein PF-06730512 in patients with FSGS.

Methods

The Study to Evaluate PF-06730512 in Adults With FSGS (PODO; ClinicalTrials.gov identifier NCT03448692), an open-label, phase 2a, multicenter trial in adults with FSGS, will enroll patients into 2 cohorts (n = 22 per cohort) to receive either high- or low-dose PF-06730512 (intravenous) every 2 weeks for 12 weeks. Key inclusion criteria include a confirmed biopsy diagnosis of FSGS, an estimated glomerular filtration rate (eGFR) ≥45 ml/min/1.73 m² based on the Chronic Kidney Disease Epidemiology Collaboration formula (30–45 with a recent biopsy), and urinary protein-to-creatinine ratio (UPCR) >1.5 g/g. Key exclusion criteria include collapsing FSGS, serious/active infection, ≥50% tubulointerstitial fibrosis on biopsy, and organ transplantation. The primary endpoint is change from baseline to week 13 in UPCR; secondary endpoints include safety, changes in eGFR, and PF-06730512 serum concentration.

Results

This ongoing trial will report the efficacy, safety, pharmacokinetics, and biomarker results of PF-06730512 for patients with FSGS.

Conclusion

Findings from this proof-of-concept study may support further development and evaluation of PF-06730512 to treat FSGS and warrant assessment in phase 3 clinical trials.

Incremental health care resource utilization and expenditures associated with autosomal-dominant polycystic kidney disease

Purpose

Incremental health care resource utilization and expenditures associated with autosomal dominant polycystic kidney disease (ADPKD) were estimated.

Methods

Study data were from a large administrative claims database. Individuals aged 18 years or older enrolled in tracked health plans for 12 months from April 1, 2011 through March 31, 2012, and with an International Classification of Disease, Ninth Revision, Clinical Modification diagnosis code for "polycystic kidney, autosomal dominant" (753.13) or for "polycystic kidney, unspecified type" (753.12) were identified as having ADPKD, and linked one-to-one with individuals without ADPKD based on age and gender. Zero-inflated negative binomial models estimated incremental health care resource utilization and expenditures, adjusting for risk factors.

Results

A total of 3,844 individuals with ADPKD who satisfied selection criteria were linked one-to-one with 3,844 individuals without ADPKD. Multivariate, regression models adjusting for risk factors revealed incremental mean (standard error) resource use associated with ADPKD of 0.68 (0.090) hospital days, equal to 68 additional hospital days per 100 ADPKD patients, and 6.9 (0.28) outpatient visits, equal to 690 additional visits per 100 ADPKD patients. Mean (standard error) incremental total expenditures associated with ADPKD were US$8,639 ($470). Mean incremental expenditures were largest for outpatient expenditures at US$4,918 ($198), followed by mean incremental hospital expenditures of US$2,603 ($263), and mean incremental medication expenditures of US$1,589 ($77). Based on sub-group analysis, mean incremental total expenditures were US$2,944 ($417) among ADPKD patients without end-stage renal disease and US$38,962 ($6,181) for those with end-stage renal disease.

Conclusion

ADPKD was associated with considerable incremental health care resource utilization and expenditures. Significant illness burden was found even before patients reached end-stage renal disease.

Kcne4 deletion sex- and age-specifically impairs cardiac repolarization in mice

Myocardial repolarization capacity varies with sex, age, and pathology; the molecular basis for this variation is incompletely understood. Here, we show that the transcript for KCNE4, a voltage-gated potassium (Kv) channel β subunit associated with human atrial fibrillation, was 8-fold more highly expressed in the male left ventricle compared with females in young adult C57BL/6 mice (P < 0.05). Similarly, Kv current density was 25% greater in ventricular myocytes from young adult males (P < 0.05). Germ-line Kcne4 deletion eliminated the sex-specific Kv current disparity by diminishing ventricular fast transient outward current (Ito,f) and slowly activating K(+) current (IK,slow1). Kcne4 deletion also reduced Kv currents in male mouse atrial myocytes, by >45% (P < 0.001). As we previously found for Kv4.2 (which generates mouse Ito,f), heterologously expressed KCNE4 functionally regulated Kv1.5 (the Kv α subunit that generates IKslow1 in mice). Of note, in postmenopausal female mice, ventricular repolarization was impaired by Kcne4 deletion, and ventricular Kcne4 expression increased to match that of males. Moreover, castration diminished male ventricular Kcne4 expression 2.8-fold, whereas 5α-dihydrotestosterone (DHT) implants in castrated mice increased Kcne4 expression >3-fold (P = 0.01) to match noncastrated levels. KCNE4 is thereby shown to be a DHT-regulated determinant of cardiac excitability and a molecular substrate for sex- and age-dependent cardiac arrhythmogenesis.

Long-term evaluation of analytical methods used in sirolimus therapeutic drug monitoring

Results of therapeutic monitoring of sirolimus blood concentrations are assay and laboratory dependent. This study compared performance over time of the IMx microparticle enzyme immunoassay (MEIA), Architect chemiluminescent microparticle immunoassay (CMIA), and liquid chromatography with mass spectrometric detection (LC/MS/MS) as part of a proficiency testing scheme. Pooled samples from sirolimus-treated patients and whole-blood samples spiked with known quantities of sirolimus were assayed monthly between 2004 and 2012. When results of pooled patient samples were compared with LC/MS/MS, the MEIA assay showed an overall mean percent bias of -2.3% ± 11.2% that, although initially positive, became increasingly negative from 2007 through 2009. The CMIA, which replaced the MEIA assay, had a mean percent bias of 21.9% ± 12.3%, remaining stable from 2007 through 2012. Similarly, for spiked samples, the MEIA showed an increasingly negative bias over time vs. LC/MS/MS, whereas CMIA maintained a stable positive bias. Based on comparison of immunoassay measurements on individual patient samples, CMIA values were more than 25% higher than MEIA values. These results highlight the importance of continued proficiency testing and regular monitoring of sirolimus assay performance. Clinicians must be aware of the methodology used and adjust target levels accordingly to avoid potential effects on efficacy and toxicity.

The membrane protein MiRP3 regulates Kv4.2 channels in a KChIP-dependent manner

MiRP3, the single-span membrane protein encoded by KCNE4, is localized by immunofluorescence microscopy to the transverse tubules of murine cardiac myocytes. MiRP3 is found to co-localize with Kv4.2 subunits that contribute to cardiac transient outward potassium currents (I(to)). Whole-cell, voltage-clamp recordings of human MiRP3 and Kv4.2 expressed in a clonal cell line (tsA201) reveal MiRP3 to modulate Kv4.2 current activation, inactivation and recovery from inactivation. MiRP3 shifts the half-maximal voltage for activation (V(1/2)) approximately 20 mV and slows time to peak approximately 100%. In addition, MiRP3 slows inactivation approximately 100%, speeds recovery from inactivation approximately 30%, and enhances restored currents so they 'overshoot' baseline levels. The cytoplasmic accessory subunit KChIP2 also assembles with Kv4.2 in tsA201 cells to increase peak current, shift V(1/2) approximately 5 mV, slow time to peak approximately 10%, slow inactivation approximately 100%, and speed recovery from inactivation approximately 250% without overshoot. Simultaneous expression of all three subunits yields a biophysical profile unlike either accessory subunit alone, abolishes MiRP3-induced overshoot, and allows biochemical isolation of the ternary complex. Thus, regional heterogeneity in cardiac expression of MiRP3, Kv4.2 and KChIP2 in health and disease may establish the local attributes and magnitude of cardiac I(to).

MiRP3 acts as an accessory subunit with the BK potassium channel

MinK-related peptides (MiRPs) are single-span membrane proteins that assemble with specific voltage-gated K+ (Kv) channel alpha-subunits to establish gating kinetics, unitary conductance, expression level, and pharmacology of the mixed complex. MiRP3 (encoded by the KCNE4 gene) has been shown to alter the behavior of some Kv alpha-subunits in vitro but its natural partners and physiologic functions are unknown. Seeking in vivo partners for MiRP3, immunohistochemistry was used to localize its expression to a unique subcellular site, the apical membrane of renal intercalated cells, where one potassium channel type has been recorded, the calcium- and voltage-gated channel BK. Overlapping staining of these two proteins was found in rabbit intercalated cells, and MiRP3 and BK subunits expressed in tissue culture cells were found to form detergent-stable complexes. Electrophysiologic and biochemical evaluation showed MiRP3 to act on BK to reduce current density in two fashions: shifting the current-voltage relationship to more depolarized voltages in a calcium-dependent fashion ( approximately 10 mV at normal intracellular calcium levels) and accelerating degradation of MiRP3-BK complexes. The findings suggest a role for MiRP3 modulation of BK-dependent urinary potassium excretion.

Analysis of complex framing coil stability in a wide-necked aneurysm model

Appropriately sized 0.010- and 0.018-inch complex framing coils were placed in a wide-necked silicone aneurysm replica, and their stability was evaluated at variable physiologic flow rates using video recording. After detachment, the 0.010-inch coils demonstrated instability/prolapse that was proportional to flow rate. In contrast, 0.018-inch coils held their 3D configuration regardless of flow rate. The findings support the use of 0.018-inch coils (when possible) in aneurysms with unfavorable geometry, particularly in circulations with higher flow rates.

pH-dependent modulation of Kv1.3 inactivation: role of His399

The Kv1.3 K(+) channel lacks N-type inactivation, but during prolonged depolarized periods it inactivates via the slow (P/C type) mechanism. It bears a titratable histidine residue in position 399 (equivalent of Shaker 449), a site known to influence the rate of slow inactivation. As opposed to several other voltage-gated K(+) channels, slow inactivation of Kv1.3 is slowed when extracellular pH (pH(o)) is lowered under physiological conditions. Our findings are as follows. First, when His399 was mutated to a lysine, arginine, leucine, valine or tyrosine, extracellular acidification (pH 5.5) accelerated inactivation reminiscent of other Kv channels. Second, inactivation of the wild-type channel was accelerated by low pH(o) when the ionic strength of the external solution was raised. Inactivation of the H399K mutant was also accelerated by high ionic strength at pH 7.35 but not the inactivation of H399L. Third, after the external application of blocking barium ions, recovery of the wild-type current during washout was slower in low pH(o). Fourth, the dissociation rate of Ba(2+) was pH insensitive for both H399K and H399L. Furthermore, Ba(2+) dissociation rates were equal for H399K and the wild type at pH 5.5 and were equal for H399L and the wild type at pH 7.35. These observations support a model in which the electric field of the protonated histidines creates a potential barrier for potassium ions just outside the external mouth of the pore that hinders their exit from the binding site controlling inactivation. In Kv1.3, this effect overrides the generally observed speeding of slow inactivation when pH(o) is reduced.

Functional Polymorphism in the Carboxyl Terminus of the α-Subunit of the Human Epithelial Sodium Channel

A common human epithelial sodium channel (ENaC) polymorphism, alphaT663A, is present in the cytoplasmic C terminus of the alpha-subunit, although it is unclear whether this polymorphism segregates with blood pressure. We examined whether this polymorphism was associated with differences in functional Na(+) channel expression. Whole cell amiloride-sensitive currents in Xenopus oocytes expressing wild type channels (alphaT663betagamma) were significantly approximately 1.3-2.0-fold higher than currents measured in oocytes expressing channels with an Ala, Gly or Leu, or Lys at position alpha663. In contrast, differences in functional human ENaC expression were not observed with oocytes expressing channels having Thr (wild type), Ser, or Asp at this position. The surface expression of channels, measured using an epitope-tagged beta-subunit, was significantly reduced in oocytes expressing alphaT663Abetagamma when compared with oocytes expressing alphaT663betagamma. The corresponding polymorphism was generated in the mouse alpha-subunit (malphaA692T) and was not associated with differences in functional alphabetagamma-mouse ENaC expression. The polymorphism is present in a region that is not well conserved between human and mouse. We generated a mouse/human chimera by replacement of the distal C terminus of the mouse alpha-subunit with the distal C terminus of the human alpha-subunit. Co-expression of this m(1-678)/h(650-669)T663A chimera with mouse betagamma led to a significant reduction in whole cell Na(+) currents and surface expression when compared with m(1-678)/h(650-669)T663-mbetagamma. Our results suggest that halphaT663A is a functional polymorphism that affects human ENaC surface expression.

Segment-specific expression of 2P domain potassium channel genes in human nephron

BACKGROUND

The 2P domain potassium (K2P) channels are a recently discovered ion channel superfamily. Structurally, K2P channels are distinguished by the presence of two pore forming loops within one channel subunit. Functionally, they are characterized by their ability to pass potassium across the physiologic voltage range. Thus, K2P channels are also called open rectifier, background, or leak potassium channels. Patch clamp studies of renal tubules have described several open rectifier potassium channels that have as yet eluded molecular identification. We sought to determine the segment-specific expression of transcripts for the 14 known K2P channel genes in human nephron to identify potential correlates of native leak channels.

METHODS

Human kidney samples were obtained from surgical cases and specific nephron segments were dissected. RNA was extracted and used as template for the generation of cDNA libraries. Real-time polymerase chain reaction (PCR) (TaqMan) was used to analyze gene expression.

RESULTS

We found significant (P < 0.05) expression of K2P10 in glomerulus, K2P5 in proximal tubule and K2P1 in cortical thick ascending limb of Henle's loop (cTAL) and in distal nephron segments. In addition, we repeatedly detected message for several other K2P channels with less abundance, including K2P3 and K2P6 in glomerulus, K2P10 in proximal tubule, K2P5 in thick ascending limb of Henle's loop, and K2P3, K2P5, and K2P13 in distal nephron segments.

CONCLUSION

K2P channels are expressed in specific segments of human kidney. These results provide a step toward assigning K2P channels to previously described native renal leaks.

Balloon-assisted coil embolization of wide-necked aneurysms of the internal carotid artery: medium-term angiographic and clinical follow-up in 22 patients

BACKGROUND AND PURPOSE

The management of broad-necked cerebral aneurysms by Guglielmi detachable coils (GDCs) is technically challenging owing to a variety of factors, including difficulty in defining the aneurysm/parent vessel interface angiographically and problems in achieving complete occlusion, later predisposing the aneurysm to regrowth/recanalization. We sought to determine whether the use of intraluminal balloons to remodel the parent vessel/aneurysm interface during GDC embolization would provide a safe means of improving the efficacy of endovascular treatment of broad-necked aneurysms.

METHODS

Twenty-two saccular aneurysms of the internal carotid artery were treated with GDCs by using balloon remodeling techniques. All aneurysms were characterized by wide necks or were small with unfavorable neck/fundus ratios and required balloon assistance for coil embolization. Patients were followed up both clinically and angiographically.

RESULTS

By using a microcatheter-mounted nondetachable balloon to provide a temporary barrier across the aneurysmal neck, we were able to deploy GDCs safely within a variety of aneurysms. Among the 22 patients treated, aneurysmal occlusion on follow-up angiography (mean, 19 months) was found in 17 of 20 patients (two patients died and no follow-up studies were available). Observed or suspected thromboembolic events occurred in four of 22 patients, resulting in one permanent deficit. Twenty of the 22 patients had good to excellent clinical outcomes.

CONCLUSION

Although balloon-assisted coiling of cerebral aneurysms requires manipulation of a second microcatheter and an inflatable balloon, increasing its technical complexity, we believe that this method has utility in treating broad-necked aneurysms and small aneurysms that are otherwise suboptimally managed by conventional GDC deployment.

Neurotopographic considerations in the microsurgical treatment of small acoustic neurinomas

OBJECT

The authors studied the relationships between tumor size, location, and topographic position relative to the intact facial nerve bundles in acoustic neurinomas to determine the influence of these factors on hearing preservation postoperatively. Consistent topographic relationships were found.

METHODS

Four hundred fifty-two patients with acoustic neurinoma treated via a retrosigmoid approach were analyzed with respect to hearing preservation and facial nerve function. One hundred fifteen tumors were identified as small and were categorized as Grades I and II. Patients with Grade I tumors, that is, purely intracanalicular lesions, all had good hearing preoperatively, defined by a less than 50-dB pure tone average and 50% speech discrimination score. All 14 Grade I tumors were removed, resulting in preservation of the patient's hearing by these criteria. There were no particular topographic anatomical relationships associated with these tumors that affected hearing preservation. Grade II tumors, defined as those protruding into the cerebellopontine angle without contacting the brainstem, were found in 101 patients and were divided by size into two grades: IIA (< 1 cm) and IIB (1-1.8 cm). In 90 patients with Grade IIA tumors, 72 (89%) of 81 who had preserved hearing preoperatively maintained it postoperatively, and in the 11 patients with Grade IIB tumors, six of whom had good hearing preoperatively, four (67%) had preserved hearing postoperatively. Six morphological types were identified based on their neurotopographic relationships to the elements of the vestibulocochlear nerve.

CONCLUSIONS

Hearing preservation postsurgery by tumor type was as follows: 1A, 92%; 1B, 88%; 1C, 100%; 2A, 83%; 2B, 92%; and 3, 57%. Combined, this represents a hearing preservation rate of 87% after surgical treatment of Grade II acoustic neurinomas. Full nerve function was maintained in 88% of patients with anatomically preserved facial nerves in both Grade I and II tumors. The remaining 12% of patients retained partial function of the facial nerve. Two patients in the series lost anatomical integrity of the nerve due to surgery.

Endovascular treatment of carotid artery occlusion in progressive stroke syndromes: technical note

OBJECTIVE AND IMPORTANCE

We describe two patients, with progressing neurological deficits, who showed improvement after revascularization of their carotid arteries using stents.

CLINICAL PRESENTATION

One patient presented clinically with the symptoms of a middle cerebral artery territory stroke. Angiography demonstrated total occlusion of the right internal carotid artery (ICA), with evidence of clot from the origin of the ICA to the middle cerebral artery trifurcation. The second patient presented with bilateral ICA occlusions and evidence of a progressing left hemispheric deficit; she was receiving therapeutic levels of heparin at the time of deterioration of her condition.

INTERVENTION

Thrombolysis and stenting successfully recanalized the occluded vessels, and the deficits of the first patient were reversed. With the second patient, a dissected carotid loop was encountered. Straightening of the loop with a wire and stenting of the carotid artery using two stents allowed revascularization of the left hemisphere and resolution of most of the deficits of this patient.

CONCLUSION

This report demonstrates the technical feasibility of placing stents in high-risk patients with carotid artery occlusions from either dissection or atherosclerosis. Both patients sustained much smaller infarctions than would have been expected if the carotid artery territory had been infarcted. We report on the technical feasibility of reopening acutely closed ICAs by using endovascular methods.

Embolization of wide-necked anterior communicating artery aneurysm: technical note

OBJECTIVE AND IMPORTANCE

Although surgical treatment of saccular aneurysms continues to be the gold standard of care, certain situations arise for which surgery may not be the best option. In these cases, electrically detachable coils have proven to provide superior outcomes in aneurysms left to medical management alone. An anterior communicating artery aneurysm with an anatomic neck wider than the fundus of the aneurysm failed to accommodate an initial attempt at Guglielmi detachable coil placement and was treated with an adjunctive balloon technique that allowed safe and effective aneurysm occlusion.

CLINICAL PRESENTATION

The patient presented with an asymptomatic anterior communicating artery aneurysm that was detected incidentally on angiography after rupture of a giant middle cerebral artery aneurysm.

INTERVENTION

Transarterial embolization of the patient's aneurysm was attempted with Guglielmi detachable coils. Although this procedure initially failed, it was then successfully performed when combined with a balloon angioplasty technique.

CONCLUSION

The Guglielmi detachable coils were able to be placed when a nondetachable balloon was used to occlude the neck of the aneurysm and allow for the coils to be deposited into the aneurysm while protecting the parent vessel.

Stenting: a new approach to carotid dissection

A patient with bilaterally occluded internal carotid arteries had a right hemispheric stroke followed by a left cerebral infarction, secondary to dissection from fibromuscular dysplasia, seen also in the vertebral arteries. The occluded left carotid was reopened and stents placed, with apparent reestablishment of left hemispheric blood flow. The speech and other deficits resolved. Although its use is under investigation, percutaneous balloon angioplasty with stents may be an appropriate intervention when other measures do not prevent progressive ischemic events.

Balloon-assisted coil placement in wide-necked aneurysms. Technical note

Saccular intracranial aneurysms are a common and often fatal lesion. Whereas surgical treatment of these aneurysms continues to be the gold standard of care, certain situations arise for which surgery may not be the best option. In some of these cases, electrolytically detachable coils have been proven to provide outcomes superior to those seen for medical management alone. The authors present two cases of ophthalmic artery aneurysms that would not hold the Guglielmi detachable coils on the initial attempt. One aneurysm was 7 mm and one 4 mm, both with wide necks relative to the aneurysm sac. By using a balloon-assisted technique and blocking the parent artery with a nondetachable balloon, the coils could be safely placed in these aneurysms without herniation when the balloon was deflated. Both patients exhibited embolic symptoms after the procedure, one with a mild but permanent deficit. Although this technique requires manipulation of a second microcatheter and balloon, which increases its technical difficulties and is a higher risk procedure than standard coil placement, it has utility in patients who are not candidates for surgery.

A voltage-dependent role for K+ in recovery from C-type inactivation

Recovery from C-type inactivation of Kv1.3 can be accelerated by the binding of extracellular potassium to the channel in a voltage-dependent fashion. Whole-cell patch-clamp recordings of human T lymphocytes show that Ko+ can bind to open or inactivated channels. Recovery is biphasic with time constants that depend on the holding potential. Recovery is also dependent on the voltage of the depolarizing pulse that induces the inactivation, consistent with a modulatory binding site for K+ located at an effective membrane electrical field distance of 30%. This K(+)-enhanced recovery can be further potentiated by the binding of extracellular tetraethylammonium to the inactivated channel, although the tetraethylammonium does not interact directly with the K(+)-binding site. Our findings are consistent with a model in which K+ can bind and unbind slowly from a channel in the inactivated state, and inactivated channels that are bound by K+ will recover with a rate that is fast relative to unbound channels. Our data suggest that the kinetics of K+ binding to the modulatory site are slower than these recovery rates, especially at hyperpolarized voltages.

Recovery from C-type inactivation is modulated by extracellular potassium

Extracellular potassium modulates recovery from C-type inactivation of Kv1.3 in human T lymphocytes. The results of whole-cell patch clamp recordings show that there is a linear increase in recovery rate with increasing [K+]o. An increase from 5 to 150 mM K+o causes a sixfold acceleration of recovery rate at a holding potential of -90 mV. Our results suggest that 1) a low-affinity K+ binding site is involved in recovery, 2) the rate of recovery increases with hyperpolarization, 3) potassium must bind to the channel before inactivation to speed its recovery, and 4) recovery rate depends on external [K+] but not on the magnitude of the driving force through open channels. We present a model in which a bound K+ ion destabilizes the inactivated state to increase the rate of recovery of C-type inactivation, thereby providing a mechanism for autoregulation of K+ channel activity. The ability of K+ to regulate its own conductance may play a role in modulating voltage-dependent immune function.

Controlled lumbar drainage in pediatric head injury

A retrospective study of external lumbar subarachnoid drainage in 16 pediatric patients with severe head injuries is presented. All patients had Glasgow Coma Scale scores of 8 or lower at 6 hours postinjury and were initially treated with ventriculostomy. Five patients required surgical evacuation of focal mass lesions. All patients manifested high intracranial pressures (ICPs) refractory to aggressive therapy, including hyperventilation, furosemide, mannitol, and in some cases, artificially induced barbiturate coma. After lumbar drainage was instituted, 14 patients had an abrupt and lasting decrease in ICP, obviating the need for continued medical management of ICP. In no patient did transtentorial or cerebellar herniation occur as a result of lumbar drainage. It was also noted retrospectively that the patients in this study had discernible basilar cisterns on computerized tomography scans. Fourteen patients survived; eight made good recoveries, three are functional with disability, and three have severe disabilities. Two patients died, most likely from uncontrolled ICP before the lumbar drain was placed. It is concluded that controlled external lumbar subarachnoid drainage is a useful treatment for pediatric patients with severe head injury when aggressive medical therapy and ventricular cerebrospinal fluid evacuation have failed to control high ICP. Selected patients with elevated ICP, which may be a function of posttraumatic cerebrospinal fluid circulation disruption and/or white matter cerebral edema, can be treated with this modality, which accesses the cisternal spaces untapped by ventriculostomy.

Radiosurgery in the treatment of cerebral AVMs

Radiosurgery of AVM's is gaining in popularity and is advocated by many for the treatment of lesions less than 3 cm in diameter. During a 17 month period 33 patients with cerebral AVM's were treated with radiosurgery. All regions of the brain were represented in the series including brain stem. A mean follow-up of 10.8 months revealed a 6% rebleed rate and a 9% total complication rate. Multimodality therapy including embolization and surgery is recommended for the treatment of AVM's and radiosurgery is seen as an important adjunctive treatment option.

Titanium dural clip testing. Technical note

Spinal dural lacerations can be a difficult part of spinal surgery. A dural tear can result in complications that include meningitis and pseudocyst formation. Appropriate treatment for these tears is generally suturing, using 4.0, 5.0, or 6.0 suture. For successful closure of dural lacerations, the authors have collaborated in the design of a titanium clip, which resembles an aneurysm clip in appearance and is applied with standard aneurysm clip appliers. The titanium clip was tested against suture and Weck hemostatic vascular clips and found to have excellent tissue-approximating capacity and a rapid application time. It is believed that this is an appropriate device for the repair of spinal dural lacerations.

Injuries resulting from bungee-cord jumping

A 19-year-old woman sustained a nonfatal hanging injury and a 28-year-old man sustained a unilateral locked facet with resultant quadriplegia as a result of bungee jumping. Injuries due to this sport have not been reported previously.

Diverse K+ channels in primary human T lymphocytes

We used patch clamp techniques to identify and characterize a variety of K+ channels in primary human peripheral T lymphocytes. The most common channel observed in cell-attached configuration was voltage gated and inactivating. In ensemble averages, the kinetics of its activation and inactivation were similar to those of the whole-cell, voltage-gated K+ current described previously (Cahalan, M. D., K. G. Chandy, T. E. DeCoursey, and S. Gupta. 1985. J. Physiol. [Lond.]. 358:197-237; Deutsch, C., D. Krause, and S. C. Lee. 1986. J. Physiol. [Lond.]. 372:405-423), suggesting that this channel underlies the major portion of the outward current in lymphocytes. A small fraction of the time, this or another very similar channel was observed to inactivate significantly more slowly. Another channel type observed in cell-attached recording was seen less frequently and was transient in its appearance. This channel has a unitary conductance of approximately 10 pS, similar to the voltage-gated channel, but its voltage-independent gating, lack of inactivation, and different kinetic parameters showed it to be distinct. In whole-cell recording there is often a significant plateau current during sustained depolarization. Experiments using whole-cell and excised outside-out configurations indicate that at least part of this residual current is carried by K+ and, as opposed to the predominant voltage-gated current, is charybdotoxin insensitive. These findings are consistent with evidence that implicates charybdotoxin-sensitive and -insensitive components in T lymphocyte proliferation and volume regulation.

Intradural extramedullary ganglioneuroma: case report and review of the literature

The authors present a unique case of an intradural extramedullary ganglioneuroma in the thoracic spine of an adult. Intraspinal ganglioneuromas are rare, benign tumors of sympathetic nervous tissue origin, but exclusively intradural ganglioneuromas have not been reported.

Glutathione prevents N-methyl-D-aspartate receptor-mediated neurotoxicity

N-methyl-D-aspartate(NMDA) antagonists afford possible therapeutic modalities for stroke, trauma, and various neurodegenerative conditions thought to be mediated by excessive stimulation of NMDA receptors in the brain. To date, however, no drug has been demonstrated to be a safe NMDA antagonist at a dosage necessary for neuroprotection. In the present study, we use an in-vitro preparation to show that glutathione is capable of attenuating neuronal damage mediated by NMDA receptor activation. Both oxidized and reduced glutathione are protective, and an extracellular mechanism of action on the NMDA receptor-channel complex is suggested.

Comparison of delayed administration of competitive and uncompetitive antagonists in preventing NMDA receptor-mediated neuronal death

Activation of N-methyl-D-aspartate (NMDA) receptors is thought to mediate toxic damage to central neurons due to hypoxia-ischemia, hypoglycemia, and trauma. We studied identified rat retinal ganglion cell neurons in vitro, a useful system for the study of excitotoxicity, and compared the protective effects of delayed administration of a competitive antagonist, 2-amino-5-phosphonovalerate (APV), and of an uncompetitive antagonist, MK-801, after glutamate-induced injury. We used maximally protective doses of the 2 antagonists. Under these conditions, both antagonists were able to prevent neuronal cell death if they were present within minutes of exposure to an endogenous glutamate-related toxin. In contrast, MK-801, but not APV, protected significantly against NMDA-mediated neurotoxicity when administered 1 to 4 hours after the initial insult. Thus, at least under certain conditions, an uncompetitive NMDA antagonist may offer a distinct advantage over a competitive antagonist when given several hours after a neurologic injury.

Redox modulation of NMDA receptor-mediated toxicity in mammalian central neurons

Acute neurological injury from hypoxia-ischemia, hypoglycemia, and trauma is thought to be predominantly mediated by activation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor in the brain and the subsequent influx of calcium ions through receptor-operated channels. Several chronic degenerative diseases, such as Huntington's disease and the amyotrophic lateral sclerosis-Parkinsonism-dementia complex found on Guam, may share a similar pathogenesis due to a glutamate-like toxin. This laboratory recently reported that exposure to a reducing agent, such as dithiothreitol (DTT), selectively increases ionic current flow through NMDA-activated channels in several types of central neurons; conversely, oxidizing agents reverse this effect. To investigate the novel influence of redox modulation on NMDA neurotoxicity, in the present in vitro study we monitored survival of an identified central neuron, the retinal ganglion cell, approximately 24 h after a brief exposure to DTT. To determine the degree of killing specifically related to activation of the NMDA receptor, 2-amino-5-phosphonovalerate (APV, a selective NMDA antagonist) was added to sibling cultures. APV-preventable, glutamate-induced death was increased 70 +/- 9% with DTT treatment. This effect was totally blocked by the concomitant addition of an oxidizing agent, 5,5-dithiobis-2-nitrobenzoic acid (DTNB). These findings suggest that the enhanced killing following chemical reduction with DTT is mediated at the NMDA receptor site, and that the redox state of the NMDA receptor is crucial for the survival of neurons facing glutamate-related injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Midbrain areas required for locomotion initiated by electrical stimulation of the lateral hypothalamus in the anesthetized rat

Locomotor stepping in the Nembutal-anesthetized rat was elicited by electrical stimulation of either of two sites in the right or left posterolateral hypothalamus. Essential midbrain loci were identified by reversibly blocking the elicited locomotion through local injections of the anesthetic procaine (15%, 0.5 microliter). Two types of critical midbrain sites were found. At ipsilateral block sites (n = 21), procaine blocked only that locomotion elicited by ipsilateral stimulation. These sites could be along the course of a direct descending ipsilateral pathway although a possible bidirectional pathway is not to be excluded. At bilateral block sites (n = 21), procaine blocked locomotion elicited by both ipsilateral and contralateral stimulation. These sites could be involved in functions prerequisite for the initiation of locomotion or in the generation of the stepping pattern. Procaine injections in 35 sites had no effect on locomotion. Ipsilateral and bilateral block sites were intermixed and generally located in regions ventral to the midbrain central gray: chiefly the anterior ventromedial midbrain, the pontis oralis nucleus and the pedunculopontine nucleus. Negative sites were located in both the dorsal and ventral midbrain. Ipsilateral block sites were relatively prevalent in the anterior midbrain, indicating that the locomotor initiation signals are lateralized at this level. Bilateral block sites were more prevalent in the posterior levels, suggesting that the initiation signals are proximal to, or interact with, circuits that have a bilateral influence on locomotion.

Discitis caused by the Centers for Disease Control microorganism Group Ve-1

An unusual case of discitis in a 60-year-old, insulin-dependent, diabetic man is presented. Radiographs of the lumbar spine demonstrated changes associated with infection of the intervertebral disc space. Cultures from the L5-S1 disc space grew the microorganism designated by the Centers for Disease Control as Group Ve-1, an organism that has had questionable clinical significance in the past, and has not been reported as a pathogen in an intervertebral disc space.

Some emerging principles underlying the physical properties, biological actions, and utility of vitrification solutions

Vitrification solutions are aqueous cryoprotectant solutions which do not freeze when cooled at moderate rates to very low temperatures. Vitrification solutions have been used with great success for the cryopreservation of some biological systems but have been less successful or unsuccessful with other systems, and more fundamental knowledge about vitrification solutions is required. The purpose of the present survey is to show that a general understanding of the physical behavior and biological effects of vitrification solutions, as well as an understanding of the conditions under which vitrification solutions are required, is gradually emerging. Detailed nonequilibrium phase diagram information in combination with specific information on the tolerance of biological systems to ice and to cryoprotectant at subzero temperatures provides a quantitative theoretical basis for choosing between vitrification and freezing. The vitrification behavior of mixtures of cryoprotective agents during cooling is predictable from the behavior of the individual agents, and the behavior of individual agents is gradually becoming predictable from the details of their molecular structures. Progress is continuing concerning the elucidation of mechanisms and cellular sites of toxicity and mechanisms for the reduction of toxicity. Finally, important new information is rapidly emerging concerning the crystallization of previously vitrified cryoprotectant solutions during warming. It appears that vitrification tendency, toxicity, and devitrification all depend on subtle variations in the organization of water around dissolved substances.