Lawrence S. Olanoff

Stereoselective binding of propranolol to human plasma, α1‐acid glycoprotein, and albumin

Our aim was to determine possible stereoselectivity in the plasma binding of propranolol. Equilibrium dialysis with plasma from seven healthy subjects and a deuterium‐labeled pseudoracemate of propranolol was used. Plasma binding of the propranolol enantiomers differed with the unbound fraction of (−)‐propranolol (22 ± 2%; mean ± SE) being smaller than that of (+)‐propranolol (25.3 ± 1.9%). The (−)/(+)‐propranolol ratio for the unbound fraction, a measure of the stereoselectivity, was 0.86 ± 0.02. There was an inverse correlation between the unbound (−)/(+)‐propranolol ratio in individual subjects and overall binding of (±)‐propranolol, indicating greater stereoselectivity at higher total binding. To assess the site of the stereoselective binding to plasma proteins, the binding of (+)‐ and (−)‐propranolol to human α1‐acid glycoprotein (AGP) and human serum albumin (HSA) was examined. The binding to AGP was stereoselective for (−)‐propranolol with a (−)/(+)‐propranolol ratio for the unbound fraction of 0.79 ± 0.01, whereas (+)‐propranolol was bound to a greater extent to HSA with a (−)/(+)‐propranolol ratio for the unbound fraction of 1.07 ± 0.01. Although these results demonstrate opposite stereoselectivity in the binding of (+)‐ and (−)‐propranolol to AGP and HSA, the stereoselective binding of (−)‐propranolol to AGP predominates in plasma. This stereoselective plasma binding of the (−)‐enantiomer of propranolol could limit the access of this more active enantiomer to β‐receptors or other active sites. The uptake of propranolol by red blood cells was not stereoselective.

Food effects on propranolol systemic and oral clearance: Support for a blood flow hypothesis

The influence of a high‐protein meal as compared to fasting on the disposition of simultaneous intravenous and oral doses of propranolol, as well as on indocyanine green clearance, was examined in six normal subjects. The intravenous dose (0.1 mg/kg) was unlabeled propranolol and the oral dose (80 mg) was a stereospecifically deuterium‐labeled pseudoracemate of propranolol. Systemic clearance of propranolol increased 38%, from 1005 ± 57 to 1384 ±115 ml/min (mean ± SE; P < 0.05) as a result of the meal, with no change in t1/2 or apparent volume of distribution. A 12% decrease in oral clearance occurred with the meal but was not statistically significant (3717 ± 185 ml/min, fasting; 3245 ± 498 after meal), whereas bioavailability increased 67% (27.2% ± 1.7% fasting; 45.5% ± 4.3% after meal; P < 0.01). Estimated hepatic blood flow, as measured by indocyanine green clearance, rose 34% 60 minutes after the meal (1719 ± 155 ml/min fasting; 2304 ± 218 ml/min after meal; P < 0.02). A difference was observed in the oral clearance of the propranolol enantiomers in the fasting state, but this difference was unaffected by the meal. These alterations in propranolol disposition, as the result of a high‐protein meal, are consistent with a transient increase in hepatic blood flow.

Stereoselective clearance and distribution of intravenous propranolol

Our objective was to determine the kinetics of (+)‐ and (–)‐propranolol after intravenous doses of racemic drug. Five normal subjects received 0.1 mg/kg of a pseudoracemate of propranolol that consisted of deuterium‐labeled (+)‐propranolol and unlabeled (–)‐propranolol. Plasma concentrations of (+)‐ and (–)‐propranolol as measured by gas chromatography‐mass spectrometry demonstrated enantiomeric differences in systemic clearance (Cls) [(+)‐propranolol, 1.21 ± 0.15 l/min; (–)‐propranolol, 1.03 ± 0.12 l/min; P < 0.01] and apparent volume of distribution (Vd) [(+)‐propranolol, 4.82 ± 0.34 l/kg; (‐)‐propranolol, 4.08 ± 0.33 l/kg; P < 0.001], but no difference in distribution or elimination t½s (t½β 3.5 hr). The higher Cls of (+)‐propranolol suggests stereoselective hepatic elimination. The higher apparent Vd of (+)‐propranolol is mainly related to its lower plasma binding [(–)‐propranolol, 20.3 ± 0.8% unbound; (–)‐propranolol, 17.6 ± 0.7% unbound; P < 0.001]. There was no stereoselective uptake by red blood cells. These findings demonstrate that multiple stereoselective mechanisms are involved in the disposition of propranolol and determine the access of the drug to active sites.

Dazoxiben in human sepsis and adult respiratory distress syndrome

Levels of thromboxane B2 (TxB2), the stable metabolite of thromboxine A2, are elevated in human and experimental septic shock. The thromboxane synthetase inhibitor dazoxiben has improved survival and decreased pulmonary hypertension in experimental endotoxemia. A randomized prospective study of 10 patients with the clinical diagnosis of sepsis and early adult respiratory distress syndrome (hypoxemia, radiologic evidence of the syndrome, and intrapulmonary shunt >20%) was performed to test the efficacy of dazoxiben in ameliorating the effects of human sepsis. Five subjects received dazoxiben and five received placebo. Dazoxiben, 100 mg, or placebo was injected intravenously every 4 hours for a maximum of 72 hours. Plasma immunoreactive TxB2 (iTxB2) levels were determined by radioimmunoassay. Before dazoxiben, the plasma iTxB2 level was 752 ±261 pg/ml (n = 5) and was reduced within 1 hour to 333 ±137 pg/ml. The plasma levels of iTxB2 remained significantly decreased with subsequent doses of dazoxiben and it was 201 ± 67 pg/ml (n = 4) 60 hours after dosing. In contrast, placebo had no significant effect on plasma iTxB2 levels (n = 5) throughout the entire period of observation. Dazoxiben did not induce any significant changes in pulmonary or systemic vascular resistance, intrapulmonary shunting, clotting studies, or extravascular lung water. One of the five subjects in the placebo group died and two of the five subjects in the dazoxiben group died. We conclude that dazoxiben was safe and effectively lowered plasma iTxB2 levels in patients with sepsis and incipient adult respiratory distress symptom, but did not significantly alter the hemodynamic and pulmonary sequelae of established sepsis.

Protective effects of trans-13-APT, a thromboxane receptor antagonist, in endotoxemia

The effect of the thromhoxane A2prosta-glandin H2 (TxA2PGH2) receptor antagonist trans- 712-(p-hydroxyphenethylamino)-cyclopentyl]-heptanoic acid Trans-13-APT) on certain pathogenic sequelae of endotoxic shock and associated changes in araehidonic acid metabolism in the rat was investigated. trans-13-APT. an analog of 13-aprostanoic acid, was synthesized and found lo block human platelet aggregation induced by the thromboxane mimetic U46619. Pretreatment with iraus-13-APT did not significantly alter the elevations in plasma immunoreactive (i) TxB, or iPGE, 0.5 or 4 h after the intravenous administration of Salmonella enterilidis endotoxin. However, in the trans-13-APT-pretreated group, 4 h after administration of the endotoxin. plasma i6-keto-PGI was significantly (p < 0.05) reduced to 1.2 ± 0.3 ng/ml (n - 17) compared with vehicle-treated rats (2.4 ± 0.5 ng/ml: n - 18). The elevation in plasma i6-kelo-PGI seen 0.5 h (n 17/grottp) after endotoxin infusion was not altered by trans-13-APT. trans-13-APT also significantly (p < 0.05) attenuated the endotoxinindticed fall in platelet count (135 + 27 × 10/mm vs. 350 + 65 × 10/mm and hypoglycemia (73 9 vs. 97 + 7 mg/dl). but not the leukopenia. Since the reticulo-endothelial system may be an important source of iTxB2, and i6-keto-PGF during endotoxemia, in vitro studies were conducted with adherent peritoneal cells. High concentrations of trans-13-APT (50 and 100 μ) significantly reduced (p < 0.05) basal but not endotoxin-induced synthesis of iTxB2 and i6-keto-PGF by isolated adherent rat peritoneal cells. The attenuated rise in plasma i6-keto-PGF in the trans-13-APT-pretreated rats may be the result of lessened shock severity or may represent antagonism of a stimulatory effect of TxA2 on PGI2 synthesis. The results also raise the possibility that thromboxane receptor antagonists may be of benefit during endotoxemia.

Effects of oleic acid on pulmonary capillary leak and thromboxanes

The role of arachidonic acid metabolites in oleic acid-induced lung injury in anesthetized dogs was investigated. Oleic acid was administered as a bolus injection into the pulmonary artery in the following dose sequence: 0.05, 0.10, and 0.20 ml/kg at 30, 60, and 120 min, respectively, after either indomethacin (10 mg/kg iv) or vehicle. A control group (n = 3) received normal saline instead of oleic acid. Measurements of hemodynamic parameters, mean systemic (MAP), pulmonary capillary wedge, and pulmonary artery pressures (PAP), cardiac output, arterial blood gases, extravascular lung waters (EVLW) by thermaldye double indicator dilution techniques and plasma immunoreactive thromboxane B2 ( iTxB2 ), by radioimmunoassay were obtained at zero time (baseline) and 20 min following each oleic acid injection. A new noninvasive technique was employed to measure pulmonary capillary protein leak by the scintigraphic analysis of intravenously administered technetium-99m radiolabeled human serum albumin ( 99mTc -HSA) in the cardiac and lung regions. Oleic acid injection caused a significant dose related fall in MAP (P less than 0.0002), arterial pO2 (P less than 0.0001), and cardiac output (P less than 0.001), and increases in EVLW (P less than 0.003) and plasma iTxB2 (P less than 0.02) in the vehicle pretreated animals, while mean PAP remained unchanged. In contrast, in the indomethacin pretreated dogs, MAP, EVLW, cardiac output, and plasma iTxB2 levels did not change from baseline values and there was an increase in mean PAP. Pulmonary vascular resistance was significantly elevated (P less than 0.05) in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial effects of ibuprofen in oleic acid induced lung injury

Metabolites of arachidonic acid, particularly thromboxanes, have been implicated as mediators of lung injury. The formation of thromboxane A2 can be decreased by glucocorticoid steroids by inhibiting the enzyme phospholipase A2 or by ibuprofen which inhibits fatty acid cyclooxygenase. This study was performed to determine if ibuprofen, methylprednisolone, or a combination of both could improve the pulmonary injury induced by oleic acid. Five groups of dogs were instrumented with pulmonary artery and extravascular lung water (EVLW) catheters and ventilated with 100% O2. Serial determinations of hemodynamic and pulmonary parameters were performed before and after oleic acid infusion. Plasma immunoreactive thromboxane B2 (iTxB2) and ibuprofen levels were also determined. Oleic acid rapidly induced a significant pulmonary injury as evidenced by hypoxemia and increases in extravascular lung water. Plasma iTxB2 rose significantly in the control group receiving only oleic acid. Pulmonary function and hemodynamic parameters were not changed by ibuprofen infusion alone. Ibuprofen attenuated the oleic acid induced hypoxemia and increased EVLW but did not significantly reduce plasma iTxB2. Methylprednisolone did not prevent the increase in plasma iTxB2 and was less effective than ibuprofen in preventing hypoxemia and increases in EVLW. The combination of ibuprofen and methylprednisolone did significantly inhibit the production of iTxB2, however in combination they protected less against the hypoxemia and increased EVLW than either agent alone. These results indicate that ibuprofen may have a protective effect in oleic acid induced lung injury that is not mediated through the inhibition of fatty acid cyclooxygenase. The results are also further evidence that thromboxane is probably not a pathogenetic factor in oleic acid induced lung injury.

Acute chlordane intoxication.

This report describes a patient who accidentally ingested 215 g of chlordane in a liquid pesticide formulation. The patient experienced multiple acute clinical sequellae attributable to his acute intoxication, including vomiting, diarrhea, seizures, coma and respiratory failure. Upon initial presentation and during the recovery phase, blood and urine specimens were collected to measure the disposition and elimination of chlordane and its metabolites. Whole blood chlordane concentrations measured over the subsequent 49 days suggested a multicompartmental kinetic profile of chlordane distribution, with an approximate terminal elimination half-life of 34 days. Tissue samples obtained from this patient, during elective surgery 58 days post chlordane ingestion, revealed persistent high levels of chlordane related metabolites. This case illustrates the physiological distribution and elimination of chlordane and its related metabolite residues after acute intoxication in an adult patient. Such information is important to improve the clinical management of patients acutely exposed to potentially lethal levels of pesticides.

Sulindac does not preserve renal prostacyclin synthesis during endotoxemia.

Previous reports have suggested that sulindac is a unique non-steroidal anti-inflammatory (NSAID) agent, because it does not inhibit renal prostaglandin synthesis in doses that inhibit platelet thromboxane B2 synthesis when tested ex vivo. NSAIDS are of potential therapeutic benefit in the treatment of septic or endotoxic shock. Therefore, this study was designed to investigate the proposed unique action of sulindac in experimental endotoxemia. In the current study, the effect of sulindac on aortic, portal and renal venous immunoreactive (i) 6-keto-PGF1 alpha levels, the stable metabolite of prostacyclin, was investigated during endotoxemia in the rat. In doses sufficient to reduce the elevation in aortic and portal venous plasma i6-keto-PGF1 alpha levels, sulindac also significantly (p less than 0.05) attenuated the elevated renal venous plasma 6-keto-PGF1 alpha levels, compared to the vehicle group. Using lower doses, sulindac failed to reduce the endotoxin associated increase in either aortic or renal venous plasma i6-keto- PGF1 alpha levels. Thus, sulindac failed to demonstrate any selective sparing effect on renal prostacyclin generation during endotoxemia.