Arachidonic acid release: an in vitro alternative for dermal irritancy testing

Validated in vitro alternatives are being utilized extensively for mutagenicity and ocular irritancy testing. However, validation of alternative assays for dermal irritancy is progressing more slowly. As the irritant response in human skin is mediated, at least in part, by eicosanoids derived from arachidonic acid, the effect of relatively pure anionic surfactants (AS, n=8) and surfactant-containing finished products (FP, n=25) on the release of [3H]arachidonic acid from a prelabelled murine fibroblast cell line (C3H-10T1/2 cells) in vitro was examined. Test substances were administered at various non-lethal concentrations, in triplicate, to 12- and 24-well plates containing preconfluent monolayers (80-90% confluence) of C3H-10T1/2 cells. Because it is impossible to test all concentrations of each test substance in a single assay, statistical techniques were developed to 'standardize' in vitro assay results. In each assay, radiolabel release due to a positive control was also measured, using 0.04, 0.05 and 0.06 mM concentrations of sodium dodecyl sulfate (SDS). Test substance releases were then transformed into 'SDS equivalent' responses, significantly reducing both inter- and intra-assay variability. A straight line was fitted to the test substance responses and compared with that for SDS to calculate the relative potency in vitro for individual AS and FP. Relative potencies correlated with in vivo responses, that is primary dermal irritation indices obtained in rabbits, with Spearman p=0.408 (P<0.03) for 32 tested agents, and p=0.976 (P<0.001) for the eight AS. Exclusion of extremely alkaline or acidic FP (pH>11 or <2, n=4) and those which were insoluble in the aqueous cell culture media at the 1% stock dilution (n=5), improved the overall in vivo-in vitro correlation significantly (p=0.683, P<0.001, n=23) and produced a significant correlation for FP alone (p=0.539, P<0.05, n=15). These results suggest that release of [3H]arachidonic acid from cultured skin cells represents a novel, mechanistically based in vitro screen for dermal irritancy testing.

Early experience with homograft aortic root replacement for complex aortic pathology

BACKGROUND

Complex aortic valve and root pathology presents a serious operative challenge.

METHODS

During the last 45 months 21 cryopreserved homograft root replacements have been performed in 19 patients. The ages of the patients ranged from 28 to 77 years; there were 15 men and four women. Six patients had endocarditis, four prosthetic and two native valve endocarditis. One patient underwent homograft aortic root replacement twice; one underwent concomitant homograft right ventricular outflow tract reconstruction for pulmonic endocarditis. Causes of aortic pathology in the other 13 patients included ascending aortic aneurysm with valvular regurgitation in seven, Marfan syndrome in two, and four aortic dissections with aortic regurgitation. Ten of the nineteen patients were undergoing reoperative procedures.

RESULTS

There were three hospital deaths and one death at home of unknown cause. Two of the three patients who died in hospital had undergone redo cardiac procedures. Dramatic functional class improvement was seen in all survivors.

CONCLUSIONS

Follow-up from 2 to 45 months in the fifteen survivors revealed no clinical or significant echocardiographic evidence of valvular regurgitation or recurrent infection. We believe homograft root replacement provides an excellent method of reconstruction with several advantages unique to human valved conduits, including ease of handling, lack of synthetic nidus for recurrent infection, and absence of thrombogenic materials. Homografts should be considered the approach of choice in complex valvular and root infectious processes.

Prognostic value of dipyridamole thallium-201 scintigraphy in patients with stable chest pain

The usefulness of dipyridamole testing with planar thallium-201 scintigraphy for assessing risk of subsequent cardiac events was evaluated in 373 patients with stable chest pain. Follow-up information was complete in 362 patients (mean age 64 +/- 9 years). During an average follow-up period of 18 months, cardiac events occurred in 59 patients--unstable angina in 27, nonfatal acute myocardial infarction in 11, and death from cardiac causes in 21. A history of previous myocardial infarction, congestive heart failure, or coronary bypass surgery before the study, or the presence of an abnormal scan or one with a fixed perfusion defect was associated with a significantly increased frequency of subsequent cardiac events (p less than 0.05). However, the presence of a reversible perfusion defect was not associated with increased risk (p = 0.1872). Stepwise logistic regression showed that a history of coronary artery bypass surgery before the study and the presence of a fixed perfusion defect were the only variables with independent predictive value for occurrence of a subsequent cardiac event (p less than 0.05). Survival analysis revealed a significantly increased cardiac event rate in patients with abnormal scans compared with those with normal scans over a 30-month follow-up period (p less than 0.01). We conclude that dipyridamole testing with thallium-201 scintigraphy can provide prognostic information concerning risk of future cardiac events in patients with stable chest pain. The presence of a fixed perfusion defect in particular identifies patients at increased risk.

Effect of exercise level on the ability of thallium-201 tomographic imaging in detecting coronary artery disease: analysis of 461 patients

This study examined the effect of the level of exercise on the ability of thallium-201 imaging with single photon emission computed tomography (SPECT) to detect coronary artery disease. Patients in group 1 (n = 164) achieved adequate exercise end points, defined as positive exercise electrocardiograms or greater than or equal to 85% of maximal predicted heart rate. Patients in group 2 (n = 108) had submaximal exercise. The SPECT thallium-201 images showed perfusion defects in 74%, 88%, and 98%, respectively, of patients with one, two and three vessel coronary artery disease in group 1, compared with 52%, 84% and 79%, respectively, of such patients in group 2 (p less than 0.05). Perfusion defects showed partial or complete redistribution consistent with ischemia in 56%, 80% and 88%, respectively, of patients with one, two and three vessel coronary artery disease in group 1 compared with 35%, 58% and 56%, respectively, of such patients in group 2 (p = 0.08, less than 0.03 and less than 0.001, respectively). Of 58 patients with normal coronary angiograms or less than 50% diameter stenosis, 36 (62%) had normal SPECT images. In a separate group of 131 patients with less than 5% pretest probability of coronary artery disease, the specificity was 93%. The sensitivity of exercise SPECT imaging in group 1 was higher than that of ST segment depression (p less than 0.001). Thus, the level of exercise affects the results of SPECT thallium imaging in the localization and evaluation of the extent of coronary artery disease and the detection of ischemia.

Use of oral dipyridamole SPECT thallium-201 imaging in detection of coronary artery disease

This study examined the merits of oral dipyridamole SPECT thallium-201 imaging in detecting CAD and multivessel CAD. The 65 patients included in this study (aged 62 +/- 11 years) were not candidates for exercise testing (for the usual reasons). Coronary arteriography revealed no significant CAD in 17 patients and greater than or equal to 50% narrowing of one or more vessels in 48 patients; 12 had one-vessel and 36 had multivessel CAD (high-risk group). Thallium-201 was injected intravenously 45 minutes after an oral dose of 375 mg of dipyridamole, and SPECT imaging was performed within 10 minutes and 4 hours after injection. There were no serious side effects; only six patients (8%) had ST segment depression and 18 patients (28%) had chest pain. The heart rate increased from 74 +/- 15 beats/min at rest to 84 +/- 14 beats/min at peak effect (p = 0.001); the systolic blood pressure did not change (130 +/- 18 and 128 +/- 20 mm Hg, respectively, p = NS). The thallium images were abnormal in 6 of 17 patients (35%) with no CAD, in 7 of 12 patients with one-vessel disease (58%), and in 34 of 36 patients with multivessel CAD (94%) (p = 0.001). Twenty-one of 25 patients (84%) with a perfusion abnormality in more than one vascular territory had multivessel CAD assessed by angiography. Thus oral dipyridamole SPECT thallium-201 imaging is a safe and inexpensive method for the detection of CAD in patients who are otherwise not candidates for exercise testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of technetium-99m isonitrile (RP-30A) in assessing left ventricular perfusion and function at rest and during exercise in coronary artery disease, and comparison with coronary arteriography and exercise thallium-201 SPECT imaging

This study compared the results of stress and rest single-photon emission computed tomography imaging of myocardial perfusion using technetium-99m isonitrile (RP-30A) with the results of stress and redistribution tomographic thallium imaging and the results of coronary arteriography in 39 patients, 11 without and 28 with coronary artery disease (CAD). Each patient underwent 2 exercise studies at identical workload, heart rate and double product. In a subset of 13 patients, concomitant evaluation of left ventricular (LV) function using first-pass radionuclide angiography with a multi-crystal camera also was performed with bolus injections of isonitrile. Isonitrile had similar sensitivity (82 vs 82%, difference not significant), a slightly--but not significantly--higher specificity (100 vs 82%) and similar predictive accuracy (87 vs 82%) to thallium-201. The tracer uptake was assessed in 20 segments/study. There was concordance between the isonitrile and thallium-201 images in 723 of the 780 segments (93%) (kappa = 0.83 +/- 0.02). In general, the isonitrile images were considered of better quality than the thallium-201 images. All 10 patients with CAD who underwent concomitant first-pass radionuclide angiography had either perfusion abnormalities or an abnormal ejection fraction response to exercise. Thus, technetium-99m isonitrile provides a reliable method of assessment of CAD with a sensitivity, specificity and predictive accuracy comparable to that of exercise thallium-201 imaging. Additional advantages include better image quality and the ability to obtain concomitant assessment of LV function with the use of first-pass radionuclide angiography.

Elimination of amphotericin B in impaired renal function

The influence of impaired renal function on the steady-state plasma clearance of amphotericin B was determined in seven patients with creatinine clearances ranging from zero to normal. Contrary to previous reports, steady-state plasma concentrations of total drug were lower in uremic patients than in patients with normal renal function. Total plasma clearance of amphotericin B ranged from 16.7 to 39.9 ml/min, correlated directly with the plasma creatinine concentration, and correlated inversely with the creatinine clearance. Urinary excretion of unchanged drug accounted for less than 10% of the dose. In 10 healthy subjects, mean percent of amphotericin B unbound in plasma was 3.55 +/- 0.32 (SD). Binding was determined in a further group of 10 uremic patients. Mean unbound percent (4.15 +/- 0.73, SD) was higher than in the healthy subjects, and the binding ratio (molar concentration of bound to unbound drug) correlated weakly with the creatinine clearance. This suggests that plasma clearance of unbound amphotericin B and, therefore, steady-state plasma concentrations of unbound drug are not affected by renal impairment, and that dosage requirements will be overestimated if based on measurements of total drug plasma concentration.