Linezolid absolute bioavailability and the effect of food on oral bioavailability.

Linezolid is a novel oxazolidinone antibiotic that has a spectrum of activity encompassing a variety of Gram-positive bacteria. The objectives of this study were twofold: (1) to compare the absorption of linezolid tablets given immediately following a high-fat meal with the absorption of tablets administered while fasting, and (2) to assess the bioavailability of a 375-mg oral dose given while fasting relative to a 375-mg dose of linezolid sterile solution given intravenously. Venous blood samples were taken over the 48 h following the single dose administration of both the oral and intravenous (IV) treatment. Samples were subsequently frozen for the determination of linezolid concentrations by HPLC. The only statistically significant difference between the fasted and the fed treatment was in peak plasma concentration, with the mean C(max) for fasted subjects being 23% greater than that for subjects after consumption of a high-fat meal. Comparable AUC(0-infinity) values were measured under both conditions, indicating that the overall extent of absorption is the same. Therefore, the difference in C(max), while statistically significant, should not affect the therapeutic efficacy of linezolid when it is administered with food. There were no statistically significant differences in AUC(0-infinity), CL or half-life between the fasted oral treatment and the intravenous treatment. As expected, C(max) was statistically different between the two treatments. However, the mean absolute bioavailability (F) of the tablet, using the IV sterile solution as the reference treatment, was 103% (+/-20%).

Pharmacokinetics, metabolism, and excretion of linezolid following an oral dose of [(14)C]linezolid to healthy human subjects.

Linezolid (Zyvox), the first of a new class of antibiotics, the oxazolidinones, is approved for treatment of Gram-positive bacterial infections, including resistant strains. The disposition of linezolid in human volunteers was determined, after a 500-mg (100-microCi) oral dose of [(14)C]linezolid. Radioactive linezolid was administered as a single dose, or at steady-state on day 4 of a 10-day, 500-mg b.i.d. regimen of unlabeled linezolid (n = 4/sex/regimen). Mean recovery of radioactivity in excreta was 93.8 +/- 1.1% (range 91.2-95.2%, n = 15), of which 83.9 +/- 3.3% (range 76.7-88.4%) was in urine and 9.9 +/- 3.4% (range 5.3-16.9%) was in feces. There was no major difference in rate or route of excretion of radioactivity by dose regimen. Linezolid was excreted primarily intact, and as two inactive, morpholine ring-oxidized metabolites, PNU-142586 and PNU-142300. Other minor metabolites were characterized by high-performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry and (19)F NMR spectroscopy. After the single radioactive dose, linezolid was the major circulating drug-related material accounting for about 78% (male) and 93% (female) of the radioactivity area under the curve (AUC). PNU-142586 (T(max) of 3-5 h) accounted for about 26% (male) and 9% (female) of the radioactivity AUC. PNU-142300 (T(max) of 2-3 h) accounted for about 7% (male) and 4% (female) of the radioactivity AUC. Overall, mean linezolid and PNU-142586 exposures at steady-state were similar across sex. In conclusion, linezolid circulates in plasma mainly as parent drug. Linezolid and two major, inactive metabolites account for the major portion of linezolid disposition, with urinary excretion representing the major elimination route. Formation of PNU-142586 was the rate-limiting step in the clearance of linezolid.

Linezolid: pharmacokinetic and pharmacodynamic evaluation of coadministration with pseudoephedrine HCl, phenylpropanolamine HCl, and dextromethorpan HBr.

Linezolid is a novel oxazolidinone antibiotic with mild reversible monoamine oxidase inhibitor (MAOI) activity. The potential for interaction with over-the-counter (OTC) medications requires quantification. The authors present data evaluating the pharmacokinetic and pharmacodynamic responses to coadministration of oral linezolid with sympathomimetics (pseudoephedrine and phenylpropanolamine) and a serotonin reuptake inhibitor (dextromethorphan). Following coadministration with linezolid, minimal but statistically significant increases were observed in pseudoephedrine and phenylpropanolamine plasma concentrations; a minimal but statistically significant decrease was observed in dextrorphan (the primary metabolite of dextromethorphan) plasma concentrations. Increased blood pressure (BP) was observed following the coadministration of linezolid with either pseudoephedrine or phenylpropanolamine; no significant effects were observed with dextromethorphan. None of these coadministered drugs had a significant effect on linezolid pharmacokinetics. Minimal numbers of adverse events were reported. Potentiation of sympathomimetic activity by linezolid was judged not to be clinically significant, but patients sensitive to the effects of increased BP due to predisposing factors should be treated cautiously. No restrictions are indicated for the coadministration of dextromethorphan and linezolid.

Single dose pharmacokinetics of linezolid in infants and children.

BACKGROUND: Linezolid is an oxazolidinone antibiotic with excellent in vitro activity against a number of Gram-positive organisms including antibiotic-resistant isolates. The safety and pharmacokinetics of intravenously administered linezolid were evaluated in children and adolescents to examine the potential for developmental dependence on its disposition characteristics. METHODS: Fifty-eight children (3 months to 16 years old) participated in this study; 44 received a single 1.5-mg/kg dose and 14 received a single 10-mg/kg dose of linezolid administered by intravenous infusion. Repeated blood samples (n = 10 in children > or = 12 months; n = 8 in children 3 to 12 months) were obtained during 24 h after drug administration, and linezolid was quantitated from plasma by high performance liquid chromatography with mass spectrometry detection. Plasma concentration vs. time data were evaluated with a model independent approach. RESULTS: Linezolid was well-tolerated by all subjects. The disposition of linezolid appears to be age-dependent. A significant although weak correlation between age and total body clearance was observed. The mean (+/- SD) values for elimination half-life, total clearance and apparent volume of distribution were 3.0 +/- 1.1 h, 0.34 +/- 0.15 liter/h/kg and 0.73 +/- 0.18 liter/kg, respectively. Estimates of total body clearance and volume of distribution were significantly greater in children than historical values of adult data. As such maximum achievable linezolid plasma concentrations were slightly lower in children, and concentrations 12 h after a single 10-mg/kg dose were below the MIC90 for selected pathogens with in vitro susceptibility to the drug. CONCLUSION: Based on these data a linezolid dose of 10 mg/kg given two to three times daily would appear appropriate for use in pediatric therapeutic clinical trials of this agent.

Pharmacokinetics of oral glyburide in subjects with non-insulin-dependent diabetes mellitus and renal failure.

To test the hypothesis that renal failure has no effect on the pharmacokinetics of glyburide, five subjects with non-insulin-dependent diabetes mellitus (NIDDM) and end-stage renal disease requiring hemodialysis, and four NIDDM subjects with normal renal function were studied. On days 0, 1, and 15, subjects consumed 33 carbohydrate grams, and glucose, insulin, and C-peptide were measured for 4 hours. On day 1, subjects received 3 mg glyburide and measured plasma concentrations for 48 hours. On day 3, multiple dosing on 3 mg glyburide daily began. On day 15, plasma concentrations were measured for 48 hours. The pharmacokinetics and pharmacodynamics of glyburide, glucose, insulin, and C-peptide were determined as well as daily fasting blood glucose. Glucose area under the curve (AUC) and daily fasting glucose levels did not change in either controls or hemodialysis subjects. The mean serum glyburide blood levels and pharmacokinetics did not differ after initial or chronic glyburide administration in NIDDM subjects with end-stage renal disease treated with hemodialysis compared with controls. Glyburide half-life averaged 3.3 hours in control subjects and 5.0 hours in hemodialysis subjects. Hemodialysis subjects had increased C-peptide and insulin AUC with chronic dosing. Renal failure does not affect the pharmacokinetics of 3.0 mg oral glyburide.

Pharmacokinetics and pharmacodynamics of glyburide in young and elderly patients with non-insulin-dependent diabetes mellitus.

OBJECTIVE: To determine the influence of age on the pharmacokinetics and pharmacodynamics of glyburide after acute and chronic dosing in young and elderly subjects with non-insulin-dependent diabetes mellitus. DESIGN: Ten elderly (mean age 69.3 +/- 3.1 y) and 10 younger (mean age 45.6 +/- 4.5 y) patients received a glucose challenge test at baseline, with a 2.5-mg dose of glyburide at week 0 (acute dose) and again at weeks 6 and 12 of chronic glyburide therapy. Glyburide doses were titrated to a maximum daily dosage of 20 mg to achieve a glucose concentration of 7.8 mmol/L or less. During 24-h pharmacokinetic determinations at weeks 0, 6, and 12, serial blood samples were obtained for glyburide determination with HPLC. Serial blood samples for glucose, insulin, and C-peptide determinations were obtained at baseline (week -1) and at weeks 0, 6, and 12. RESULTS: All pharmacokinetic parameters assessed for glyburide were statistically comparable between the two age groups with the exception of a shorter time to peak concentration in the elderly at weeks 0 and 12. The glucose pharmacodynamic response to glyburide was not statistically different between the two groups. However, there was a statistically significant greater C-peptide response in the elderly group at all evaluation weeks. CONCLUSIONS: Aging appears to have no influence on the pharmacokinetics of glyburide. Observed pharmacodynamic differences indicate the necessity for dosage titration to a specified therapeutic response regardless of patient age.

Effects of aspirin and ibuprofen on the pharmacokinetics and pharmacodynamics of glyburide in healthy subjects.

OBJECTIVE: To determine the effects of aspirin and ibuprofen on the pharmacokinetics and pharmacodynamics of glyburide in healthy volunteers. DESIGN: Single-center, randomized, two-way, crossover design following an initial baseline evaluation phase. SETTING: Outpatient, university-based ambulatory care facility. PATIENTS: Sixteen healthy nonsmoking men aged 20-34 years. INTERVENTION: Three phases consisting of six treatments. Phase 1 began with treatment A, a baseline oral glucose tolerance test (GTT), followed by treatment B, glyburide 5 mg plus a GTT. The other two phases were administered in a crossover design. Phase 2 consisted of the administration of aspirin 975 mg qid for 4 days. On day 3 a GTT was administered (treatment C) and on day 4 glyburide 5 mg plus a GTT was administered (treatment E). Phase 3 consisted of the administration of ibuprofen 600 mg qid for 4 days with a GTT on day 3 (treatment D) and glyburide 5 mg plus a GTT on day 4 (treatment F). MAIN OUTCOME MEASURES: Serum glyburide concentrations after each treatment, as well as glucose and insulin, ibuprofen, and salicylate serum concentrations and glyburide free fractions. RESULTS: Aspirin administration resulted in an 85% increase in mean total glyburide oral clearance and a 29% increase in glyburide free fraction. Ibuprofen administration resulted in a slight increase in mean glyburide free fraction, but no significant changes in glyburide pharmacokinetic parameters were observed. Insulin concentrations were increased during the glyburide plus aspirin treatment. Conflicting results were observed in the glucose parameters. CONCLUSIONS: The potential for this glyburide-aspirin interaction resulting in a transient hypoglycemia should be considered in diabetic patients receiving glyburide therapy.

Comparison of pharmacokinetics and pharmacodynamics of short- and long-term glyburide therapy in NIDDM.

OBJECTIVE: To examine the pharmacokinetics and pharmacodynamics of glyburide after single- and multiple-dose administration in patients with type II diabetes. RESEARCH DESIGN AND METHODS: Twenty patients with type II diabetes between 40 and 70 years of age participated in the study. A 24-h pharmacokinetic evaluation including a 4-h Sustacal tolerance test was conducted before instituting glyburide therapy (baseline), after the first 2.5-mg test dose of glyburide and at weeks 6 and 12 of chronic glyburide therapy. Glyburide doses were titrated with a target goal of achieving a fasting plasma glucose of < or = 7.8 mmol/l or to reach maximum daily doses of 20 mg. RESULTS: A significant prolongation in the elimination half-life (t1/2: week 0, 4.0 +/- 1.9 h; week 6, 13.7 +/- 10.5 h; and week 12, 12.1 +/- 8.2 h) and an increased volume of distribution of glyburide was observed during chronic dosing. These results strongly suggest possible drug accumulation. No differences in pharmacokinetic parameters were noted between evaluations at week 6 or week 12. Changes in pharmacodynamic response of glucose, insulin, and C-peptide to chronic glyburide therapy were observed. Glyburide therapy significantly reduced plasma glucose levels at weeks 6 and 12 (percent changes in AUC0-->4. glucose from baseline: week 0, -3 +/- 11%; week 6, -29 +/- 13%; and week 12, -26 +/- 19%). Pancreatic insulin secretion was acutely enhanced and maintained during long-term therapy. Responsiveness to therapy as assessed by the ratio of AUC0-->4.glucose:AUC0-->4.C-peptide was significantly improved at all weeks compared with baseline. No pharmacodynamic response differences were observed between the week 6 and the week 12 evaluations. CONCLUSIONS: This study demonstrates that significant differences in glyburide pharmacokinetics and pharmacodynamics exist between single-dose and steady-state conditions. These differences support the need for careful dosage titration of glyburide to achieve a desired therapeutic response in patients with type II diabetes.

The pharmacokinetics and pharmacodynamics of 12 weeks of glyburide therapy in obese diabetics.

We have studied the pharmacokinetics and pharmacodynamics of glyburide during long-term therapy in 20 patients with type II diabetes mellitus. The patients were divided according to body mass index (BMI) into an obese group [n = 12, age 55(13) y, BMI 36.2(9.2) kg.m-2, total body weight (TBW) 100(23) kg], and a non-obese group [n = 8, age 61(13) y, BMI 24.5(2.1) kg.m-2, TBW 73(7) kg]. The dosages of glyburide were titrated to achieve specified therapeutic goals based upon serum glucose concentrations or to a maximum dosage of 20 mg per day. The pharmacokinetics of glyburide were determined at week 12 of treatment. On the study day, the patients took a 2.5 mg liquid test dose of glyburide with a Sustacal meal challenge. The elimination rate constant (lambda z), clearance (CL), and apparent volume of distribution (Vz) were 0.08 h-1, 3.3 l.h-1, and 47.0 l in the obese group, and 0.07 h-1, 3.1 l.h-1, and 56.8 l in the non-obese group. These values were not statistically significantly different. However, there were differences between the groups when the volume and clearance were corrected by TBW or BMI but not by ideal body weight (IBW) or fat-free mass (FFM). Regression analysis between the pharmacokinetic variables and body weight status revealed statistically significant correlations between volume or clearance and body weight. However, due to large inter-patient variability, these relations were relatively weak and were considered to be non-predictive.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioavailability of medroxyprogesterone acetate from three oral dosage formulations.

The bioavailability of three formulations of medroxyprogesterone acetate (MPA) was assessed in 30 healthy male volunteers in a three-way, open-label, cross-over-designed trial. Each subject received one Provera 500-mg tablet, one Farlutal 500-mg tablet, and one Provera 500-mg granule packet according to a randomized schedule, with each treatment separated by a 21-day washout period. Serum MPA levels were determined using both radioimmunoassay (RIA) and high-performance liquid chromatography techniques. Based on the results of RIA analysis, Farlutal tablets produced significantly lower serum MPA concentrations compared with Provera tablets at most sampling times, resulting in statistically lower AUC0-144 for the Farlutal tablet (544 vs 768 ng.hr/ml; -29.2%). The Farlutal tablet also had a significantly lower maximum concentration than the Provera tablet (27.8 vs 47.4 ng/ml; -41.4%). However, there was no significant difference in time of maximum concentration between the tablet formulations (3.71 vs 3.41 hr), indicating that the rates of absorption of the two tablet formulations were comparable. Provera granules provided significantly higher serum MPA levels than Provera tablets at 0.5, 1, 1.5, 2, and 6 hours, and the AUC0-144 for Provera granules was higher by 5.47% (810 vs 768 ng.hr/ml). There were no differences in terminal elimination rate constants among the dosage forms. No significant adverse events were noted during the trial. The relative bioavailabilities of Provera granules and Farlutal tablets were 105% and 71.2%, respectively, compared with Provera tablets.

The effect of colestipol dose on postprandial serum bile acid concentration: assessment by an enzymic bioluminescence procedure.

A dose-response study was performed with three doses of colestipol, using postprandial serum bile acid levels to assess bile acid sequestering activity in 40 volunteers with asymptomatic hyperlipidaemia. Subjects who entered the study had total serum cholesterol concentrations greater than 220 mg/dl and triglyceride concentrations less than 200 mg/dl. They were randomly assigned to one of four parallel treatment groups: (a) placebo b.d., (b) colestipol (as Colestid hydrochloride granules) 2.5 g b.d., (c) colestipol 5 g b.d., and (d) colestipol 7.5 g b.d. Subjects were maintained on a constant repeating solid diet throughout the 6-day study period, and colestipol was ingested 30 min before breakfast and dinner. No drug was administered on Days 1-3; baseline (pre-treatment) serum bile acid concentration profiles were determined on Day 3. The above treatments were given on Days 4-6, and total serum bile acid concentrations were determined at 30- or 60-min intervals for 10 h on Days 4 and 6. Serum bile acids were measured using a bioluminescence procedure which enzymically measures total 3 alpha hydroxy bile acids. Serum bile acid concentrations were significantly decreased from the pretreatment period by 5.0 and 7.5 g/day as compared to 2.5 g/day or placebo. Differences from the pre-treatment period in the area under the serum bile acid time curve revealed the same trends in the data as analysis of percentage difference (Day 6 vs pre-treatment period) in serum bile acid concentrations. These results indicate that postprandial serum bile acid concentrations are influenced by colestipol in a dose-related manner, with doses of 5 and 7.5 g b.d. having a significantly greater effect than 2.5 g b.d. The dose of 7.5 g b.d. had an identical effect on serum bile acid patterns as a dose of 5.0 g t.d.s., which was previously reported. Our findings also show that changes in serum bile acid concentrations may be used to follow the immediate effects of bile acid sequestration in hypercholes terolaemic subjects, and that the bioluminescence enzyme technique is sufficiently sensitive to detect such changes.

The pharmacokinetics of 2.5- to 10-mg oral doses of minoxidil in healthy volunteers.

The dose proportionality of minoxidil was investigated by studying its pharmacokinetics after administration of single, oral doses of 2.5, 5.0, and 10.0 mg. The study, which was a Latin square cross-over design, was performed in 30 young, nonobese, normal subjects. Treatments were separated by a 4-day washout period. Serum and urine levels of minoxidil were determined by high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA). Supine blood pressure and pulse were monitored during each study phase. Minoxidil concentrations determined by RIA were highly correlated with concentrations determined by HPLC; only the HPLC data was used in the pharmacokinetic analyses. No significant effects were observed for dose normalized Cmax, tmax, volume of distribution, minoxidil renal clearance, or the percentage of the dose excreted as either minoxidil or minoxidil glucuronide. Significant differences in apparent oral clearance, dose normalized AUC, and terminal elimination rate constant (beta) were observed between the 2.5-mg dose and the higher doses, but no differences in these parameters between the 5.0- and 10.0-mg doses were apparent. Thus, the available data support dose-independent pharmacokinetics for minoxidil over this range of doses. Repeated measures analysis of variance detected significant time and treatment effects on supine blood pressure and pulse rate, but the effects were generally small and of little clinical significance. The results support the hypothesis that minoxidil has little effect on blood pressure in normotensive subjects.

Safety profile: fifteen years of clinical experience with ibuprofen.

Since its introduction in the United States in 1974, ibuprofen (Motrin, Upjohn) has been shown to be safe and effective for the treatment of pain, dysmenorrhea, inflammation, and fever. A careful review of pre-registration and postmarketing data from both patients and normal subjects clearly indicates ibuprofen's remarkable safety profile compared with that of aspirin and other commonly prescribed nonsteroidal anti-inflammatory agents. Continued safety can be anticipated on the basis of the past 15 years of review experience.

Mechanism of defective sterol synthesis in human leukocytes.

When human lymphocytes, granulocytes and monocyte-enriched cell preparations were incubated with [2-14C]acetate, only 10-36% of the radioactivity incorporated into the nonsaponifiable lipid fraction was present as digitonin-precipitable sterols. This percentage is considerably less than that observed for rat hepatocytes (95%) or human liver slices (68%). Even though a marked increase in the incorporation of labeled acetate into both nonsaponifiable lipids and digitonin-precipitable sterols resulted from stimulation of lymphocytes with concananvalin A or granulocytes by phagocytosis, the proportion of nonsaponifiable lipid radioactivity that was digitonin-precipitable remained low. These findings suggest that rate-limiting steps beyond the 3-hydroxy-3-methylglutaryl coenzyme A reductase reaction exist in the sterol synthetic pathway of leukocytes. Pulse-chase experiments demonstrated a precursor product relationship in leukocytes between lanosterol and cholesterol, but some squalene appears to be in a pool that is not further metabolized. A subcellular fraction prepared from mixed leukocytes was incapable of converting appreciable amounts of [3H]squalene to lanosterol or cholesterol, suggesting an enzyme deficiency in this segment of the sterol synthetic pathway. With isolated liver microsomes, 50% of the nonsaponifiable lipid radioactivity synthesized from [3H]squalene was recovered in cholesterol when the system contained added liver cytosol. By contrast, if the liver cytosol was replaced by leukocyte cytosol, 14-fold less radioactivity was incorporated into nonsaponifiable lipids, and only 17% of the radioactivity was recovered in cholesterol. When sterol-carrier protein 1, partially purified from rat liver, was added to leukocyte cytosol, [3H]squalene incorporation into lanosterol increased more than 3-fold. With the addition of both sterol-carrier protein 1 and sterol-carrier protein 2, cholesterol synthesis increased 2-fold. These results suggest that the low cholesterol synthetic activity in human leukocytes is due to a defect in one or more of the microsomal enzymes that operate between squalene and cholesterol, as well as to a deficiency of sterol-carrier proteins in leukocyte cytosol.

Evidence for rate-limiting steps in sterol synthesis beyond 3-hydroxy-3-methylglutaryl-coenzyme A reductase in human leukocytes.

When human blood leukocytes are incubated with [2-14C]acetate only about 32% of the nonsaponifiable lipid radioactivity is recovered in digitonin-precipitable material. Using thin-layer chromatography and gas-liquid radiochromatography, we have determined that most of the label from [2-14C]acetate in the nonsaponifiable fractions is in lanosterol, squalene and an unidentified sterol. Only 11% of the acetate radioactivity is contained in cholesterol. This distribution does not change when cholesterol synthesis is depressed by the addition of lipoproteins to the medium. These findings are in marked contrast to studies with liver, where most of the nonsaponifiable radioactivity derived from acetate is recovered in digitonin-precipitable sterols. Furthermore, they suggest that rate-limiting steps beyond the 3-hydroxy-3-methylglutaryl coenzyme A reductase reaction exist in the sterol synthesis pathway of human leukocytes.

Fatty acid utilization by L1210 murine leukemia cells.

L1210 murine leukemia cells grow in an ascites plasma that contains lipids, including 0.62 +/- 0.046 (S.E.) MICRONEq free fatty acid per ml. in vitro incubations demonstrated that isolated L1210 cells readily utilize free fatty acid that is added to the incubation medium. When the cells were incubated with albumin-bound [1-14C]palmitate, about 12 times more radioactivity was incorporated into cell lipids than was oxidized to CO2. Triacylglycerols contained 1.5 to 4 times more radioactivity than phospholipids, and from 48 to 69% of the phospholipid radioactivity was recovered in the choline phosphoglycerides. [1-14C]Palmitate utilization increased as the fatty acid concentration of the medium was raised, the largest increase occurring in the triacylglycerol fraction. Palmitate utilization also was increased by the presence of carbohydrates in the medium, their effectiveness (in descending order) being glucose, mannose, galactose, fructose, and glycerol. By contrast, ribose did not produce any stimulatory effect. During a 1-hr incubation, between 82 and 87% of the [1-14C]palmitate that was taken up remained as palmitic acid. From 8 to 15% was elongated to stearate, and only 2 to 3% was desaturated to palmitoleate and oleate. Based upon the lipid content, growth rate, and palmitate utilization rate of the cells, it appears that a major portion of the lipid requirements of the L1210 cell may be supplied by the fatty acid contained in the ascites plasma. In addition, our results suggest that most of the saturated fatty acid taken up is incorporated into cell lipids without structural modification.

Utilization of long-chain free fatty acids and glucose by human leukemic blast cells.

We have studied the utilization of free fatty acid and glucose by human leukemic blast cells. Palmitate was both incorporated into complex cellular lipids, primarily phospholipids and triglycerides, and oxidized to CO2. The predominant phospholipid synthesized was phosphatidylcholine. Only a small proportion of the incoming fatty acid was modified structurally before incorporation into lipid esters. After incubation with [1-14 C]palmitate, 91% of the radioactivity recovered in cell lipids remained in fatty acids containing 16 carbon atoms. Studies with labeled glucose revealed little de novo synthesis of fatty acid, and the majority of the radioactivity from glucose was located in the water-soluble fraction after saponification of the esters. We conclude that the free fatty acids contained in the extracellular fluid provide much of the fatty acid for required cellular lipid synthesis in human leukemic blast cells. Since there is little elongation of incoming palmitate before incorporation into cellular lipids, it may be possible to alter the fatty acid composition of membrane phospholipids by changing the proportion of the various free fatty acids available to the leukemic cells.

Differences in free fatty acid and glucose metabolism of human blood neutrophils and lymphocytes.

Comparison of isolated human neutrophils and lymphocytes in short-term tissue culture revealed marked differences in their rates of lipid biosynthesis. Ficoll-Hypaque gradients were used to separate lymphocytes and neutrophils from the blood of normal subjects. Neutrophils incorporated more palmitate into cell lipids (151.0 +/- 16.6 nmole/hr/10(8) cells) than lymphocytes (41.6 +/- 4.1). By contrast, the lymphocytes oxidized more palmitate (8.3 +/- 0.5 nmole/hr/10(8) cells) as compared to neutrophils (1.1 +/- 0.1). The greater fatty acid uptake by the neutrophils was due to a sixfold greater rate of incoporation of palmitate into their triglyceride fraction. Triglyceride synthesis by neutrophils increased as the molar ratio of free fatty acid to albumin was raised, whereas incorporation into phospholipids remained relatively constant; there was preferential labeling of neutrophil triglycerides throughout the physiologic range. Studies using linoleate and oleate gave similar results. The distribution of radioactivity into various phospholipids determined by thin-layer chromatography was similar for the two cell types. When labeled glucose was used as a substrate to measure incorporation primarily into the glycerol backbone of the cell lipids, neutrophils incorporated more radioactivity into total lipids and triglycerides than lymphocytes. These results indicate that neutrophils take up much more fatty acid than lymphocytes primarily because they synthesize much larger quantities of triglycerides, a storage form. Since cellular triglycerides may act as a source of fatty acid for lecithin synthesis during phagocytosis, the greater rate of fatty acid incorporation in the neutrophil may reflect a metabolic pattern that permits efficient phagocytosis.

Metabolism of glucose and fatty acid by leukocytes from patients with endogenous hypertriglyceridemia.

The metabolic abnormalities responsible for endogenous hypertriglyceridemia have not been defined. Some in vivo studies have suggested that excessive triglyceride production is the cause of this defect. In an attempt to obtain direct evidence concerning this mechanism, we have compared in vitro the metabolism of radioactive glucose and palmitate by leukocytes from patients with endogenous hypertriglyceridemia and normal subjects. Leukocytes from the patients incorporated 9.82 plus or minus 1.7 (S.E.M.) nanomoles of glucose into cellular lipid per 10-8 cells per hour. When the cell lipid extract was sugjected to mild alkaline hydrolysis, 92 per cent of the glucose radioactivity was recovered in the glycerol backbone of the lipid esters. Comparison of specific yields of CO2 from glucose labeled in the 1- or 6- position revealed that 0.53 plus or minus 0.02 per cent was metabolized via the pentose cycle. The leukocytes from hypertriglyceridemic persons incorproated 140 plus or minus 6.9 nanomoles of [1-14C]-palmitate per 10-8 cells per hour. Eighty-four per cent of the radioactivity was in triglycerides and 14 per cent in phospholipids. The major phospholipid into which palmitate was incorporated was phosphatidyl choline. The leukocytes oxidized palmitate at a rate of 2.88 plus or minus 0.23 nanomoles per 10-8 cells per hour. There were no differences in any of the above values between leukocytes from hypertriglyceridemic patients and normal subjects. Likewise, there was no correlation between the plasma triglyceride concentration and glucose or palmitate incorporation into triglycerides. To the extent that leukocytes reflect systemic metabolic processes, these data provide no support for the interpretation that the mechanism of the plasma triglyceride elevation is excessive biosynthesis.