Understanding the path to diagnosis and clinical presentation of patients with PIK3CA-related overgrowth spectrum (PROS) through an innovative patient-centered data platform

e18707

Background: PROS is a group of rare disorders driven by activating mutations in PIK3CA. Overactivation of the PI3K pathway, which regulates growth and proliferation, results in asymmetric malformations/overgrowths. Localized interventions are often not curative and no medical therapy for PROS is approved; however, mTOR inhibitors (ie sirolimus) are used off-label with modest success. Using a patient (pt)-focused approach, we seek to better understand the current path to diagnosis (dx), course of disease, interventions, and pt outcomes to optimize future therapies. Methods: Pts treated in the US are being actively recruited via interactions with pt advocacy groups, pt communities, social media, and allstripes.com. Following research and HIPAA authorization from each pt/guardian, AllStripes’ proprietary real-world evidence (RWE) platform collects pt medical records into a master medical record from which study data are abstracted. All activities are covered under AllStripes’ IRB-approved protocol. To enroll in the PROS cohort, pts must have a confirmed PROS dx via PIK3CA genetic testing. Data completeness and nomenclature are dependent on physician documentation. Results: To date 14 pts (7 female, 7 male) have enrolled; median age at enrollment was 10.5 y (range, 1-38). Of the 14 pts, 71.4% of pts (n = 10) had congenital onset. PIK3CA genetic testing was primarily (n = 12, 85.7%) completed as a part of a multigene panel. The most frequent specialties involved in dx were medical genetics (n = 4, 28.6%) and pediatric heme-oncology (n = 3, 21.4%). Clinical presentation commonly included vascular malformations (n = 8, 57.1%). Most pts were diagnosed with CLOVES (n = 12, 85.7%). Seven pts (50.0%) had documented lesions at dx, median of 2 (range, 1-13) lesions per pt, increasing after dx to 3 (range, 1-14). All pts reported PROS-related complications; 50.0% (n = 7) required hospitalization/ER visit. Musculoskeletal, neurological, and gastrointestinal related complications were each reported by ≥50% of pts. All pts required ≥1 surgery; ≥50% of pts had diagnostic, debulking, vascular, or other procedures. Median number of surgeries per pt was 7 (range, 1-28), corresponding to a median of 0.76 surgeries per pt per year. Eight pts (57.1%) received PROS related medications: 6 (42.9%) received alpelisib, 5 (35.7%) received sirolimus. Conclusions: While each pt is unique, similarities in the path to dx (eg, specialties involved) and disease history (eg, clinical presentation, symptoms experienced) exist. RWE abstracted from medical records rapidly provides data in an otherwise limited field, helping to address key questions. Preliminary results highlight the burden of PROS and the reliance on repetitive surgical interventions for management, suggesting there remains a high unmet medical need for effective therapeutic strategies.

Abstract PS10-29: Comparison of healthcare resource utilization and costs in women with HR+/HER2- metastatic breast cancer treated with ribociclib vs palbociclib or abemaciclib

Background: Ribociclib, palbociclib, and abemaciclib are cyclin dependent kinase 4 and 6 (CDK4/6) inhibitors for the treatment of women with hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) advanced or metastatic breast cancer (mBC). The economic burden of women with HR+/HER2- mBC treated with different CDK4/6 inhibitors has not previously been compared. Objective: To describe and compare healthcare resource utilization (HRU) and healthcare costs in patients treated with CDK4/6 inhibitors in real-world clinical practice. Methods: Adult women with HR+/HER2- advanced or mBC who initiated treatment with ribociclib, palbociclib, or abemaciclib as the first CDK4/6 inhibitor (index therapy) were identified from IBM MarketScan Data (Q1 2000 - Q3 2018), a large US commercial claims database. HRU and healthcare costs were measured while patients were on treatment with their index CDK4/6 inhibitor. Total healthcare costs, measured from a payers' perspective, included medical (inpatient [IP], outpatient [OP], emergency room [ER]) and pharmacy costs, reported per-patient-per-month (PPPM). HRU and healthcare cost components were each separately compared between ribociclib and palbociclib cohorts, and between ribociclib and abemaciclib cohorts, using models adjusting for age, line of therapy, menopausal status, metastatic sites, and comorbidities. Results: A total of 4,320 women were included: 102 initiated ribociclib as first CDK4/6 inhibitor; 4,118 palbociclib; and 100 abemaciclib. The majority in each cohort were postmenopausal (ribociclib: 79%; palbociclib: 92%; abemaciclib: 92%), and received the index CDK4/6 inhibitor as either first-line (ribociclib: 40%; palbociclib: 31%; abemaciclib: 30%) or second-line therapy (ribociclib: 23%; palbociclib: 24%; abemaciclib: 22%). HRU was not statistically different between the ribociclib and palbociclib cohorts, whereas the ribociclib cohort had fewer IP days compared to the abemaciclib cohort (adjusted incidence rate ratio [IRR]: 0.25, 95% CI: 0.09; 0.67). Total healthcare costs were not statistically different between the ribociclib and palbociclib cohorts, although the ribociclib cohort had lower OP costs PPPM compared to the palbociclib cohort (-$1,339, 95% CI: -2,344; -209). Total healthcare costs were statistically lower for the ribociclib cohort compared to the abemaciclib cohort (-$6,519; 95% CI: -9,959; -2,984). IP costs, OP costs, and pharmacy costs (driven by CDK4/6 inhibitor costs) were all significantly lower for the ribociclib cohort vs the abemaciclib cohort (IP: -$3,398, 95% CI: -22,801; -768; OP: -$3,778, 95% CI: -6,502; -1,659; pharmacy costs: -$1,744, 95% CI: -2,881; -564).

Conclusions: HRU while on treatment was similar between ribociclib and palbociclib, while ribociclib had fewer IP days compared to abemaciclib, after adjusting for baseline covariates. Total healthcare costs while on treatment were higher in the abemaciclib cohort compared to the ribociclib cohort, while ribociclib and palbociclib cohorts tended to have similar total healthcare costs.

Ribociclib vs. PalbociclibRibociclib vs. AbemaciclibHRUAdjusted IRRConfidence intervalP-valAdjusted IRRConfidence intervalP-valIP admissions1.09(0.62; 1.91)0.760.67(0.29; 1.53)0.34IP days0.67(0.35; 1.28)0.220.25(0.09; 0.67)0.01*Days with ER services1.44(0.80; 2.57)0.220.76(0.37; 1.59)0.47Days with OP services1.01(0.91; 1.14)0.800.88(0.73; 1.04)0.14PPPM Healthcare costsAdjusted cost differenceConfidence intervalP-valAdjusted cost differenceConfidence intervalP-valTotal healthcare costs-1,013.82(-3,436; 1,924)0.48-6,519.18(-9,959; -2,984)<0.01*Medical costs-1,222.84(-3,275; 1,231)0.32-6,142.36(-9,907; -2,844)<0.01*IP costs-279.61(-1,516; 1,749)0.76-3,397.88(-22,801; -768)0.01*ER costs481.32(-87; 1,503)0.19577.82(-105; 2,449)0.16OP costs-1,338.92(-2,344; -209)0.03*-3,778.20(-6,502; -1,659)<0.01*Total pharmacy costs-28.95(-798; 917)0.91-1,743.98(-2,881; -564)<0.01*CDK4/6 costs120.08(-592; 1,053)0.83-1,631.39(-2,755; -464)0.01*

Citation Format: Sanjeev Balu, Rebecca Burne, Annie Guerin, Rebecca Bungay, Mary Lisha Paul, Roxana Sin. Comparison of healthcare resource utilization and costs in women with HR+/HER2- metastatic breast cancer treated with ribociclib vs palbociclib or abemaciclib [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-29.

Comparison of healthcare resource utilization and costs of patients with HR+/HER2- advanced breast cancer treated with ribociclib versus other CDK4/6 inhibitors

AIMS

To assess healthcare resource utilization (HRU) and healthcare costs among women with hormone receptor-positive and human epidermal growth factor receptor 2-negative advanced breast cancer (HR+/HER2- aBC) treated with cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors.

METHODS

Women with HR+/HER2- aBC, initiating CDK4/6 inhibitor treatment were identified using IBM MarketScan Commercial and Medicare Supplemental databases (Q1/2000-Q3/2018). Based on the first CDK4/6 inhibitor patients received (index therapy), three cohorts were identified: abemaciclib, palbociclib, and ribociclib. The baseline period (six months preceding treatment initiation) was used to describe patient characteristics. All-cause HRU and direct total healthcare costs (medical and pharmacy) from treatment initiation until the earliest of the end of index therapy, continuous health plan enrollment, or data availability, were compared for the ribociclib cohort versus the abemaciclib and palbociclib cohorts, separately, using weighted regression analyses balanced on baseline covariates.

RESULTS

Average age at treatment initiation was ∼60 years and the majority of patients were postmenopausal (abemaciclib: 92%; palbociclib: 92%; ribociclib: 79%). Average follow-up duration was 3.9, 8.8, and 5.9 months for the abemaciclib, palbociclib, and ribociclib cohorts, respectively. After reweighting, HRU was not statistically different between the ribociclib and abemaciclib cohorts, however, the ribociclib cohort incurred significantly lower total healthcare costs (-$5,452; 95% CI: -$8,726; -$1,139, p = .01). Medical costs (driven by outpatient costs) and pharmacy costs (driven by CDK4/6 inhibitor costs) were significantly lower for the ribociclib cohort. Among the reweighted ribociclib and palbociclib cohorts, HRU and total healthcare costs were not statistically different, although the ribociclib cohort had lower outpatient costs per-patient-per-month (-$1,245, 95% CI: -$2,349; -$37, p = .04).

LIMITATIONS

Due to the retrospective, observational design, treatment cohorts were not randomly assigned.

CONCLUSIONS

During CDK4/6 inhibitor therapy, ribociclib patients tended to incur lower medical and pharmacy costs than abemaciclib patients. Among ribociclib and palbociclib patients, HRU and healthcare costs were similar.

EARLY real-world treatment and dosing patterns of ribociclib for metastatic breast cancer (mBC): A retrospective observational study

e13059

Background: Ribociclib and abemaciclib in combination with endocrine therapy have demonstrated survival benefit in women with HR-positive/HER2-negative mBC. This study assessed early real-world treatment and dosing patterns of ribociclib for mBC in a US community oncology setting. Methods: This was a retrospective, observational, descriptive study of female mBC patients initiating treatment with ribociclib between March 1, 2017 and September 30, 2018 within the US Oncology Network (USON) and followed through December 31, 2018. USON’s iKnowMed (iKM) EHR database was used to identify patients and medical chart data review was conducted to abstract treatment information. Descriptive analyses were performed to assess patient and treatment characteristics. Results: A total of 161 patients were selected for chart review, of which 116 patients who received ribociclib were confirmed as eligible. The mean age of patients at initiation of treatment was 66 (SD 14) years. Among patients with documented menopausal status, 90% were post-menopausal, and 10% were pre-menopausal. Among patients with documented receptor status, 99% were ER+/HER2-. Patients most commonly initiated ribociclib in the first-line setting (1L n = 52, 2L n = 30, 3L n = 9, 4L+ n = 25) and in combination with letrozole (n = 33, 28.4%). Eastern Cooperative Oncology Group (ECOG) performance score at time of ribociclib initiation was 0-1 in 60.4% of patients. Documented metastatic sites were present in bone (35.3%), lung (8.6%), and liver (6%). The most common comorbidities documented within 6 months of treatment initiation were cardiovascular disease (53.4%), diabetes (19%), and depression (18.1%). Overall, 46.6% (n = 54) of patients received prior neoadjuvant or adjuvant chemotherapy and 32.8% patients (n = 38) received prior neoadjuvant or adjuvant endocrine therapy. 95% of patients started at the full dose of 600mg. One-fourth of patients (n = 29) had a dose-hold and 27.6% (n = 32) patients experienced a dose reduction with ribociclib therapy. Conclusions: This study represents early ribociclib uptake in a real-world setting in the US. Early utilization demonstrates patients receiving ribociclib are older and sicker than those in pivotal clinical trials. Substantial heterogeneity in ribociclib initiation by LOT was observed.

Molecular epidemiology of Burkholderia cepacia in two Australian cystic fibrosis centres

Forty individual patient sputum isolates of Burkholderia cepacia from two Australian cystic fibrosis (CF) centres more than 100 km apart were genotyped using pulsed-field gel electrophoresis (PFGE) with XbaI restriction enzyme digestion. Hospital 1 had an endemic strain with 19 of 20 isolates being closely related. This centre does not implement an inpatient segregation policy for its paediatric patients who constitute the majority of those colonized with B. cepacia. Hospital 2 did not have a single endemic strain; there were two different sibling clusters and a third cluster involving a cohabiting couple, but all other patients had unique isolates. One patient at Hospital 2 carried an organism closely related to the endemic strain from Hospital 1. Hospital 2 practises segregation of colonized inpatients and also segregation external to the hospital. It would appear that no nosocomial spread of infection is occurring with this policy.

Priming of a D1 dopamine receptor behavioural response is dissociated from striatal immediate-early gene activity

Repeated administration of direct-acting (apomorphine, SKF-38393, quinpirole) or indirect-acting (amphetamine, cocaine) dopaminergic agonists can produce enhancement of locomotor and sterotypic behaviours in response to subsequent dopamine agonist challenge. This sensitization of dopamine receptors, known as priming or reverse tolerance, is long-lasting and appears to be dependent upon the participation of the N-methyl-D-asparate excitatory amino acid receptor. The mechanism underlying dopamine receptor sensitization is not understood. Mounting evidence suggests that immediate-early genes may provide a link whereby extracellular stimuli are converted into long-term changes in neuronal activity. In the present study, behavioural measurements and immunohistochemical techniques were used to determine whether induction of the immediate-early gene c-fos is critical to the mechanism underlying priming of a D1-mediated behavioural response. It was demonstrated that in drug-naive rats bearing unilateral 6-hydroxydopamine lesions of the dopaminergic nigrostriatal pathway, the mixed D1/D2 agonist apomorphine produced a dramatic increase in the expression of Fos-like immunoreactivity in the ipsilateral caudoputamen, nucleus accumbens and globus pallidus, and was a potent primer of SKF-38393-mediated rotational behaviour. In contrast, saline administration did not increase Fos expression and did not prime SKF-38393-elicited rotation. Preadministration of MK-801 at 0.5 mg/kg significantly reduced apomorphine's effect on Fos expression and prevented apomorphine priming of SKF-38393-induced rotation. However, at a lower dose of 0.1 mg/kg, MK-801 had little effect on apomorphine-mediated Fos expression but did block the priming response. In another experiment, the D2 family-selective agonist quinpirole was found to be an affective primer of SKF-38393-mediated rotation, and to produce increase Fos expression in the ipsilateral globus pallidus only. Preadministration of MK-801 at 0.1 mg/kg blocked quinpirole priming of SKF-38393-mediated rotation and significantly reduced the number of Fos-positive neurons in the ipsilateral globus pallidus. Administration of the indirect dopamine agonist amphetamine increased Fos expression in the intact striatum, but not in the ipsilateral (lesioned) striatum or globus pallidus, and did not sensitize (prime) animals to behavioural effects of SKF-38393. In a separate group of animals. Northern blot analysis demonstrated that a priming dose of apomorphine significantly increased the messenger RNA signals for c-fos, c-jun, ngfi-A and jun-B in denervated striatum. Administration of 0.1 mg/kg MK-801 prior to apomorphine had no significant effect on signal intensities.(ABSTRACT TRUNCATED AT 400 WORDS)

Listeriosis--a review of eighty-four cases

OBJECTIVE

To review the epidemiology, risk factors for acquisition, clinical features and outcomes of Listeria monocytogenes infection in Sydney.

DESIGN

A retrospective study over the period 1983-1992 at four university teaching hospitals in Sydney. Cases were identified from microbiology laboratory records of the isolation of L. monocytogenes from sterile sites.

RESULTS

Eighty-four cases were reviewed, with 72 patients (86%) having a predisposing underlying condition, including 13 perinatal patients (15%). Septicaemia (56%) and central nervous system disease (41%) were the major clinical presentations. Nineteen patients (23%) had hospital-associated infection. A mortality of 21% (18 patients) was directly attributable to L. monocytogenes infection, with another 10% (nine patients) dying of their underlying disease during admission. The 84 cases represented 80% of all L. monocytogenes cases occurring in Sydney during the study period.

CONCLUSIONS

Listeriosis is predominantly a disease of the elderly or of immunosuppressed individuals, pregnant women and neonates. The presentation and outcome in these groups are similar to those reported in other Western countries. A significant feature of this study was the number of cases occurring in already hospitalised patients, suggesting that L. monocytogenes may be an important hospital-associated pathogen in immunocompromised patients.

Proton magnetic resonance spectroscopy of polymorphonuclear leukocytes from patients with serious bacterial infections

Triacylglycerols in human neutrophils exposed to proinflammatory stimuli generate a high-resolution proton magnetic resonance (1H MR) spectrum. Lipid cross-peak F volumes in neutrophils from patients with inflammatory conditions were measured. Values in patients hospitalized with localized infections (14.4 +/- 9.0; mean +/- SD) or bacteremia (19.3 +/- 9.7) were significantly higher than in patients with noninflammatory conditions (6.2 +/- 5.3) and healthy controls (2.0 +/- 3.0; P < .001). The positive predictive value of F volumes > 10 was 93% for all infection; the negative predictive value of volumes < or = 10 was 68% for all infection and 92% for bacteremia. Plasma lipopolysaccharide (LPS) concentrations were highest in bacteremic patients but did not correlate with levels of tumor necrosis factor-alpha (TNF alpha) or interleukin-6. In vitro, LPS increased F volumes of control neutrophils from 2.0 +/- 3.0 to 37.2 +/- 6.7 (P < .001); TNF alpha had no effect. F volumes in 1H MR spectra may be useful clinically to discriminate between serious bacterial infection and other inflammatory conditions. TNF alpha is not the stimulus for generation of lipid spectra in vivo.

Susceptibility of Legionella species to antimicrobial agents

Thirty-five clinical isolates of Legionella species were tested against 7 antimicrobial agents using an agar dilution technique. Results obtained on charcoal-supplemented (BCYE) and charcoal-free agar (BSYE) were compared. On BCYE, the most active agent was rifampicin; the minimal inhibitory concentration inhibiting 90% of the strains (MIC90) was 0.008 mg/L. Imipenem was the next most active in vitro (MIC90 0.06 mg/L). The macrolide antibiotics and ciprofloxacin also inhibited the organisms at low concentrations (MIC90 < or = 2 mg/L). In general, MIC's obtained on BCYE agar were at least twofold higher than on BSYE agar except for that of imipenem. BSYE agar is a suitable alternative medium for susceptibility testing of most Legionella species. Erythromycin and rifampicin continue to demonstrate good in vitro activity against legionellae in Australia. On the basis of in vitro susceptibility tests, the other macrolides and ciprofloxacin are likely to be suitable alternatives for the treatment of legionellosis.

Improving the delivery of clinic care

There has been an increasingly widespread movement toward the delivery of health care in outpatient settings. Hospitals must start to prepare for the shift from inpatient to outpatient services. Reductions in reimbursement and increasing costs will force hospitals to collect and obtain more data on outpatient services. Projecting future demands and assessing current utilization rates are two of the key factors in maintaining stability. This article is a case study of a major urban medical center's outpatient clinic. It includes a summary of observations on the clinic's daily operations and several recommendations for improvement. While the original analysis was highly specific to the actual facility observed, this article has been structured so that it may be applied to other institutions.

D1-like and D2-like dopamine receptors synergistically activate rotation and c-fos expression in the dopamine-depleted striatum in a rat model of Parkinson's disease

Selective agonists for D1-like and D2-like dopamine receptors can interact synergistically to enhance each other's actions on locomotion and behavior in experimental animals. Clinically, the combination of the D2 agonist bromocriptine with L-dopa (which has pronounced D1 effects) is a highly effective treatment for Parkinson's disease. The mechanisms underlying this important receptor interaction are poorly understood and are the subject of intense study in vitro. In rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway, D1-selective (but not D2-selective) dopamine agonists produce a marked increase in expression of the immediate-early gene c-fos in the striatum ipsilateral to the 6-OHDA lesion. In the experiments reported here, we have used this in vivo model to explore the possibility that combinations of D1-selective and D2-selective agonists might have effects on c-fos transcription that are different from those exhibited by D1 or D2 agonists administered alone. We examined the effects of the D1-selective agonist SKF-38393 and the D2-selective agonist quinpirole (LY 171555) on the expression of Fos-like protein and c-fos mRNA in the caudoputamen and made parallel behavioral observations in the same animals. A low dose of SKF-38393 produced little contraversive rotation and little induction of Fos-like immunoreactivity in the striatum. A low dose of quinpirole elicited contralateral rotation but little or no induction of Fos-like immunoreactivity in the caudoputamen; there was, however, induction of Fos in the globus pallidus ipsilateral to the 6-OHDA lesion. Combination of the low dose of SKF-38393 and quinpirole produced a synergistic effect on rotation and elicited, in the dopamine-depleted caudoputamen, a striking pattern of Fos-like protein expression in which Fos-positive neurons were concentrated in striosomes and in the dorsolateral caudoputamen. Northern blot analysis showed that c-fos mRNA was expressed following combined agonist treatment but was not detectable after the single-agonist treatments. Both the contraversive rotation and the induction of Fos-like immunoreactivity were blocked by the preadministration of the D1-preferring antagonist SCH-23390 and the D2-selective antagonist raclopride in combination. Pretreatment with the glutamate NMDA receptor antagonist MK-801 also blocked the induction of Fos-like immunoreactivity, and it reversed the rotation. These findings suggest a D1/D2 synergistic mechanism that involves the participation of D1-responsive striatonigral and D2-responsive striatopallidal output pathways, and that is sensitive to glutamatergic modulation.

Effect of pressure on the release of endogenous dopamine from rat striatum and the role of sodium-calcium exchange

Exposure to environmental pressures in excess of 20 atm abs can precipitate a hyperexcitability state known as high pressure neurologic syndrome (HPNS). Little is known about the underlying neurochemical basis of this syndrome. An in vitro model of the synthesis and release of endogenous dopamine (DA) from rat striatal slices has been used to examine the mechanism underlying the effects of high pressures of He. He at 100 atm abs produced changes in DA release which were strikingly similar to those of the cardiac glycoside, ouabain. Neither pressure nor ouabain (1-10 microM) had any significant effects on the spontaneous (nonevoked) release of DA or its metabolite 3,4-dihydroxyphenylacetic acid, but both pressure and ouabain significantly enhanced the stimulated release of DA which was evoked by a 6-min exposure to 35 mM KCl (P less than 0.05 and P less than 0.001). In both cases, this effect was dependent on the presence of extracellular Ca2+. Augmentation of evoked DA release by both ouabain and He pressure was reversed (P less than 0.05) by 3,4-dichlorobenzamil, a selective antagonist of the membrane Na+/Ca2+ exchange mechanism. The results suggest that pressure exerts its effects on DA release by increasing intracellular-free Ca2+ exchange after pressure-inhibition of the activity of the membrane Na,K-ATPase.

Expression of the immediate early gene c-fos in basal ganglia: induction by dopaminergic drugs

Expression of the immediate early gene c-fos is increased in mammalian neurons by a number of stimuli and the usefulness of this gene as a marker of neuronal activation has been demonstrated in several systems. Directly-acting dopamine agonists of the D1-type (SKF 38393, CY 208-243) and indirectly-acting dopamine agonists (amphetamine, cocaine) all produce a rapid and transient increase in Fos protein levels in varying patterns in striatum and cerebral cortex. Directly-acting dopamine agonists only produce c-fos activation in denervated (supersensitive) striatum whereas cocaine and amphetamine activate c-fos in striatum in naive animals. Remarkably, D2 selective antagonists such as haloperidol, albeit in high doses, also activate c-fos expression. Activation of c-fos and other immediate early genes may play a part in the development of such long-term dopamine-related effects as dyskinetic movements and addiction.

Hyperbaric He but not N2 augments Ca2+-dependent dopamine release from rat striatum

Endogenous dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured by high performance liquid chromatography with electrochemical detection in perfusate from continuously superfused rat brain striatal slices, and the effects of various pressures of He and N2 were determined. He at 24 and 100 atmospheres absolute (ATA) significantly (P less than 0.01 and less than 0.05) increased the release of DA evoked by a 6-min exposure to 35 mM K+, whereas He at 48 ATA did not. Experiments conducted in a Ca2+-free medium showed that only the extracellular Ca2+-dependent component of release was affected by pressure. Similar increases in DA release were observed when DA reuptake and metabolism were blocked with cocaine and pargyline, although statistical significance was not achieved. N2 did not significantly affect DA release at 12, 24, 48, or 100 ATA. The results indicate that He (= hydrostatic pressure) augments Ca2+-dependent DA release and that substitution of N2 negates this effect. The relevance of these observations to the phenomena of high pressure neurologic syndrome in divers and the anesthetic reversal of pressure effects is discussed.

Salicylate antagonism of acetylsalicylic acid inhibition of platelet aggregation in male and female subjects: influence of citrate concentration

Platelets from volunteers were exposed for 1 min to sodium salicylate (SA) before and after the addition of acetylsalicylic acid (ASA) to produce greater than or equal to 50% inhibition of aggregation induced by arachidonic acid (AA) or collagen. SA:ASA concentrations = 20:1. SA protection against ASA inhibition was always observed even if ASA exposure time was 15 min, whereas reversal could not be demonstrated once exposure of platelets to ASA exceeded a minimum of 3-10 min with AA as the stimulus. Reversal was even less effective when collagen was the stimulus. An apparent, increased sensitivity to SA reversal of ASA inhibition in females disappeared when citrate concentration was adjusted to compensate for lower packed cell volume. The proposed male dependency for protection in ASA treatment of thromboembolic disorders cannot be explained on the basis of differences in the SA-ASA competition at platelet cyclooxygenase and, if collagen is an important in vivo stimulus of platelet interaction with damaged vessel wall, the antagonism of ASA by SA may not be important.

Effects of aspirin dosage and time of administration on arterial prostacyclin production and platelet aggregation in rats

Previously we reported that electrically-induced carotid artery thrombosis in anesthetized rats was prevented by 3.3 or 10 mg/kg aspirin (ASA) given i.v. 10 min before injury but not by 1.7, 20 or 100 mg/kg and protection was lost by delaying injury to 20 min (Haemostasis 13:42, 1983). Here, collagen-induced platelet aggregation and arterial prostacyclin-generating activity, measured by RIA for 6 keto-PGF1 alpha and by human platelet aggregation bioassay, were studied ex vivo after i.v. ASA to anesthetized rats. In all cases where platelet aggregation was inhibited less than 50%, no protection had been observed (1.7 mg/kg at 10 min, 3.3 at 20 min, 20 at 10 min). In the two cases where protection had been observed, platelet aggregation was inhibited by about 75% or more and in one, prostacyclin activity was about 50% of normal (3.3 mg/kg at 10 min). Thus in five of six dose-time combinations tested, antithrombotic protection could be explained by a requirement for about 50% of normal prostacyclin activity and about 75% of inhibition of collagen aggregation. Aberrant findings are discussed in the light of knowledge of salicylate/aspirin competition for cyclooxygenase.

Low-dose aspirin (ASA) renders human platelets more vulnerable to inhibition of aggregation by prostacyclin (PGI2)

Pre-treatment of human, platelet-rich plasma with concentrations of aspirin that produced 50% or less inhibition of aggregation induced by collagen, arachidonic acid or adenosine diphosphate, significantly increased the % inhibition of platelet aggregation by a low concentration of authentic prostacyclin or by prostacyclin-like activity generated by incubation of rat aorta rings in human platelet-poor plasma. Similarly a single aspirin tablet (325 mg) taken orally by human volunteers significantly increased the sensitivity of their platelets to inhibition of aggregation by authentic prostacyclin (8.1 X 10(-10) M) for 2-48 h after ingestion. Statistical significance was lost at 72 h but the trend was still evident. These results support the contention that low doses of aspirin may be efficacious in the therapy of arterial thromboembolism since this could preserve some arterial prostacyclin-generating activity which might be sufficient to inhibit adhesion and aggregation of the aspirin-treated platelets.

The influence of dose, time of administration, body temperature and salicylate kinetics on the antithrombotic action of acetylsalicylic acid in male rats

Acetylsalicylic acid (ASA), given i.v. to male rats 10 min before electrical injury to the carotid artery, was found to reduce rate and extent of thrombosis at 3.3 and 10.0 mg/kg but not at 1.7, 20 or 100 mg/kg, indicating a narrow, low-dose window for antithrombotic effect. ASA was more effective in rats in which body temperature was allowed to fall greater than 0.5 degrees C but protection was lost if injury was delayed 15 min or more after ASA administration. Serum salicylate studies did not support the view that loss of protection was due to competition between salicylate and ASA for cyclooxygenase-binding sites. ASA was also protective at 200 mg/kg i.v., possibly through non-specific toxic effects.

The influence of glucosidic conformation and charge distribution on activity of adenine nucleosides as presynaptic inhibitors of acetylcholine release

The electrically stimulated guinea-pig ileum preparation was used to establish the potency of adenosine and a series of nucleoside analogs as presynaptic inhibitors of acetylcholine output and a rank order was obtained. 2-Chloroadenosine was the most potent compound studied (pD2 = 7.74), whereas inosine yielded the lowest measurable efficacy (pD2 = 3.66). The 8-substituted nucleotides studied were either poorly active or inactive. The Iterative Extended Huckel Theory method was used to calculate the total conformational energy of each analog as well as the electronic properties at key positions in purine moiety. Spectra relating conformation energy to the dihedral angle of rotation of the purine base about the glycoside bond permitted the preferred glycosidic conformation of each analog to be determined. Comparison of this conformational data, which indicated few strong conformational differences, with the biological efficacy did not permit an association between potency and stability in the glycosidic high anti conformation to be drawn. however, the inactivity of the adenine nucleotides with bulky substituents at position 8 may suggest involvement of the entire anti-high anti range as essential conformations. A possible association between activity and charge density at the purine N1 atom, for a subset of the nucleosides investigated, was seen. It is suggested that the accessibility of nucleosides to the entire anti-high anti conformational region is a permissive condition in addition to which other molecular characteristics play a role in determining activity at the presynaptic locus.

Non-interference by salicylate with aspirin inhibition of arterial thrombosis in rats

Several authors have reported that salicylate blocks and reverses aspirin inhibition of prostaglandin synthesis by platelets and arterial wall. Male rats were given sodium salicylate 15 or 100 mg/kg i.v. 2 min before receiving aspirin, 10 mg/kg i.v. Right and left carotid arteries were injured electrically before and after drug administration and thrombus generation recorded by measuring downstream temperature. Significant antithrombotic effect of aspirin was observed in all cases regardless of prior salicylate administration and the results were similar to those obtained with aspirin alone. Thus competition between salicylate and aspirin as reported in vitro does not appear to significantly affect the in vivo antithrombotic action of aspirin in this model.

Lack of effect of botulinum toxin on nonadrenergic, noncholinergic inhibitory responses of the guinea pig fundus in vitro

The nonadrenergic, noncholinergic inhibitory (NAI) response of guinea pig fundic strip to electrical field stimulation was examined in the presence of botulinum toxin and tetrodotoxin. Tetrodotoxin completely abolished the NAI response while botulinum toxin did not alter it. It is concluded that the mediator of NAI responses is unlikely to be released with acetylcholine from cholinergic nerves or that such release would have to occur by a mechanism resistant to botulinum toxin.