Analysis of "On/Off" Kinetics of a CETP Inhibitor Using a Mechanistic Model of Lipoprotein Metabolism and Kinetics.

RG7232 is a potent inhibitor of cholesteryl-ester transfer protein (CETP). Daily oral administration of RG7232 produces a dose- and time-dependent increase in high-density lipoprotein-cholesterol (HDL-C) and apolipoproteinA-I (ApoA-I) levels and a corresponding decrease in low-density lipoprotein-cholesterol (LDL-C) and apolipoproteinB (ApoB) levels. Due to its short plasma half-life (∼3 hours), RG7232 transiently inhibits CETP activity during each dosing interval ("on/off" kinetics), as reflected by the temporal effects on HDL-C and LDL-C. The influence of RG7232 on lipid-poor ApoA-I (i.e., pre-ß 1) levels and reverse cholesterol transport rates is unclear. To investigate this, a published model of lipoprotein metabolism and kinetics was combined with a pharmacokinetic model of RG7232. After calibration and validation of the combined model, the effect of RG7232 on pre-ß 1 levels was simulated. A dose-dependent oscillation of pre-ß 1, driven by the "on/off" kinetics of RG7232 was observed. The possible implications of these findings are discussed.

Pharmacokinetics and metabolism of a permeation-enhanced testosterone transdermal system in hypogonadal men: influence of application site- -a clinical research center study.

As part of a phase III multicenter study, the pharmacokinetics and metabolism of a permeation-enhanced testosterone (T) transdermal (TTD) system and the influence of application site were investigated in 34 hypogonadal men (21-65 yr of age). After an 8-week androgen washout period, two TTD systems were applied to the back for 24 h. Serum concentrations of total T, bioavailable testosterone (BT), dihydrotestosterone (DHT), and estradiol (E2) increased from hypogonadal levels into the respective normal physiological ranges and declined to baseline levels within 24 h after system removal. Peak concentrations occurred approximately 8 h after application for T and BT and at 13 h for DHT and E2. The baseline-subtracted time-average steady state concentrations (C'ss) for T and BT were 18.1 +/- 7.49 (+/- SD) and 9.08 +/- 3.99 nmol/L, respectively. DHT/T and E2/T ratios, derived from the C'ss values, were 0.063 +/- 0.018 and 0.0033 +/- 0.0018, comparable to the precursor-product conversion ratios reported in healthy men. The estimated half-lives of each hormone were: T, 1.29 +/- 0.71 h; BT, 1.21 +/- 0.75 h; DHT, 2.83 +/- 0.97 h; and E2, 3.53 +/- 1.93 h. The influence of application site was then evaluated by applying two TTD systems for 24 h to the abdomen, back, chest, shin, thigh, or upper arm, according to a sequential cross-over design. Hormone profiles were qualitatively similar at each site, but C'ss values showed significant differences (by ANOVA, P < 0.0001). Based on the BT levels, the rank ordering of the sites were: back > thigh > upper arm > abdomen > chest > shin. DHT/T and E2/T ratios showed negligible site to site variation and were comparable to the results from the initial study. Estimates of T input, based on hormone levels and analysis of the systems used, averaged 4-5 mg/day for the abdomen, back, thigh, and upper arm and were lower and more variable for the chest and shin. Individual C'ss values for T and BT increased linearly with the T input rates (derived from used system analysis) across all studies (n = 235; r = 0.564 for T and r = 0.754 for BT). From these data, T and BT clearance rates were estimated for each patient, averaging 1248 +/- 518 and 2435 +/- 778 L/day, respectively. T clearance rates were proportional to the BT/T ratio (nonsex hormone-binding globulin-bound fraction). On the basis of these studies, the optimal sites of TTD system application were identified as the back, thigh, upper arm, and abdomen

Enhanced transdermal delivery of testosterone across nonscrotal skin produces physiological concentrations of testosterone and its metabolites in hypogonadal men.

None of the current or experimental androgen treatment modalities for male hypogonadism has been reported to produce physiological concentrations or circadian variations in testosterone (T) and its metabolites, dihydrotestosterone (DHT) and estradiol (E2). This investigation describes a novel transdermal dosage form designed to enhance the delivery of native T across nonscrotal skin. The main objective was to determine whether the nightly application of two experimental transdermal patches to different sites on the body (e.g. back, chest, arms, etc.) would result in normal plasma levels of T, DHT, and E2 for men and mimic the normal circadian variation. Six hypogonadal males (aged 24-66 yr) were studied 4 weeks after stopping T ester treatment. After single application of two patches, T levels increased from a pretreatment baseline of 5.8 +/- 0.94 nmol/L (mean +/- SE; 167 +/- 27 ng/dL) to an average peak concentration of 44.1 +/- 4.8 nmol/L (1273 +/- 138 ng/dL) 5.7 +/- 0.6 h after application and reached a 24-h level of 16.9 +/- 2.9 nmol/L (488 +/- 85 ng/dL). DHT and E2 levels exhibited parallel variations within the normal reference ranges. During 4 weeks of daily evening application to various sites on the torso, the mean delivery of T from two patches was 5.2 +/- 0.1 mg/day (approximately 20% of the patch content), and morning T levels were within the normal limits. On day 28 of treatment, the 24-h plasma profiles of T, DHT, and E2 (obtained with two patches on the back) approximately mimicked the normal circadian variations reported in healthy young men. The time-averaged T level was 21.8 +/- 2.9 nmol/L (629 +/- 84 ng/dL), and the plasma concentration ratios of DHT/T (0.07 +/- 0.01) and E2/T (0.005 +/- 0.001) were within the normal range. SHBG concentrations were not significantly altered over the 4 weeks of treatment. The patches were well tolerated, except for one patient who developed a local reaction to an excipient during the third week of treatment. Two of the patients (one with Klinefelter's syndrome) completed several months of continuous therapy. T, DHT, and E2 have remained in the range of normal, and plasma LH levels in the patient with Klinefelter's syndrome became normal. Subjective improvement in symptoms has continued, and tolerability has been good in both patients. These results indicate that the enhanced transdermal delivery of T across nonscrotal skin is a patient-friendly androgen replacement modality and produces physiological concentrations of T and its metabolites, which are unattainable with other treatment modalities.

Interrelationships among lipoprotein levels, sex hormones, anthropometric parameters, and age in hypogonadal men treated for 1 year with a permeation-enhanced testosterone transdermal system.

Serum lipoproteins and cardiovascular risk are affected by endogenous and exogenous sex hormones. As part of a multicenter evaluation of a permeation-enhanced testosterone transdermal system (TTD), the interrelationships among serum lipoproteins, hormone levels, anthropometric parameters, and age were investigated in 29 hypogonadal men. Subjects (aged 21-65 yr) were first studied during prior treatment with im testosterone esters (IM-T), then during an 8-week period of androgen withdrawal resulting in a hypogonadal state (HG), and finally during a 1-yr treatment period with the TTD. Compared with treatment with IM-T, the HG period produced increases in high density lipoprotein [HDL; 12.0 +/- 1.6% (+/-SEM); P<0.001] and total cholesterol (4.2 +/- 1.9%; P: = 0.02) and a decrease in the cholesterol/HDL ratio (-9.7 +/- 2.8%; P = 0.02). Compared with the HG period, TTD treatment produced decreases in HDL (-7.6 +/- 2.5%; P = 0.002) and increases in the cholesterol/HDL ratio (9.0 +/- 2.5%; P = 0.01) and triglycerides (20.7 +/- 6.4%; P: = 0.03). Small decreases in total cholesterol (-1.2 +/- 1.8%; P: = 0.1) and low density lipoprotein (-0.8 +/- 2.6%; P = 0.07) were also observed during TTD, but did not reach statistical significance. Likewise, there were no significant differences between the IM-T and TTD treatments. Serum HDL levels showed a strong negative correlation with body mass index and other obesity parameters in all three study periods (r < -0.45; P < 0.02). During treatment with TTD, serum testosterone levels also correlated negatively with body mass index (r = -0.621; P < 0.001). As a consequence of these relationships, a positive trend was observed between HDL and testosterone levels during TTD treatment (r = 0.336; P = 0.07). Interestingly, the changes in lipoprotein levels during TTD treatment indicated a more favorable profile (decrease in cholesterol and low density lipoprotein levels) with increasing age of the patients. In hypogonadal men the effects of transdermal testosterone replacement on serum lipoproteins appear consistent with the physiological effects of testosterone in eugonadal men.

Pharmacokinetics of a novel testosterone matrix transdermal system in healthy, premenopausal women and women infected with the human immunodeficiency virus.

The clinical consequences of androgen deficiency in human immunodeficiency virus (HIV)-infected women remain underappreciated. The pharmacokinetics of transdermally administered testosterone in premenopausal women and HIV-infected women have not been studied. In this study we compared the pharmacokinetics of a novel testosterone matrix transdermal system (TMTDS) in healthy premenopausal women and women infected with HIV. Eight menstruating HIV-infected women, 18-50 yr of age, who had been receiving stable antiretroviral therapy, including a protease inhibitor, for at least 12 weeks and nine healthy, menstruating women of comparable age were enrolled. After baseline sampling during a 24-h control period in the early follicular phase (days 1-6), two TMTDS patches were applied with an expected delivery rate of 300 microg testosterone daily over an application period of 3-4 days. After 72 h, the patches were removed, a second set of two patches was applied, and blood samples were drawn over 96 h. Baseline serum total and free testosterone levels were lower in HIV-infected women than in healthy women. A diurnal rhythm of testosterone secretion, with higher levels in the morning and lower levels in the late afternoon, was apparent in both groups of women. Free testosterone levels were in the midnormal range at baseline in healthy women and increased above the upper limit of normal during TMTDS application. In HIV-infected women, free testosterone levels were in the low normal range at baseline and rose into the upper normal range during patch application. Serum total testosterone levels increased into the midnormal range in HIV-infected women and into the upper normal range in healthy women during patch application. The mean increments in free and total testosterone levels were significantly lower in HIV-infected women than in healthy women. Testosterone bioavailability, expressed as the mean +/- SEM baseline-subtracted area under the total testosterone curve, was significantly greater in healthy women than in HIV-infected women [3323 +/- 566 ng/dL x h (115 +/- 20 nmol/L x h) vs. 1506 +/- 316 ng/dL x h (52 +/- 11 nmol/ L x h); P = 0.016]. Assuming a daily testosterone delivery rate of 300 microg/day, the apparent plasma clearance was significantly higher in HIV-infected women than in healthy women (2531 +/- 469 vs. 1127 +/- 217 L/day1 P = 0.022), respectively. There was no significant change from baseline in serum LH, sex hormone-binding globulin, and estradiol levels in either group. Serum FSH levels showed a greater decrease from baseline in healthy women. A regimen of two testosterone patches applied twice a week can maintain serum total and free testosterone levels in the mid- to upper normal range, respectively, in HIV-infected women with low testosterone levels. During TMTDS application, the increments in serum total and free testosterone levels are lower in HIV-infected women than in healthy women, presumably due to increased plasma clearance or decreased absorption. Further studies are needed to assess the effects of physiological androgen replacement in HIV-infected women.

The use of a sensitive equilibrium dialysis method for the measurement of free testosterone levels in healthy, cycling women and in human immunodeficiency virus-infected women.

Measurements of total and free testosterone levels in women have lacked precision and accuracy because of limited assay sensitivity. The paucity of normative data on total and free testosterone levels in healthy women has confounded interpretation of androgen levels in women with human immunodeficiency virus (HIV) infection and other disease states. Therefore, the objectives of this study were to develop sensitive assays for the measurement of the low total and free testosterone levels in women to define the range for these hormones during the normal menstrual cycle and assess the total and free testosterone levels in HIV-infected women. By using a larger volume of serum, increasing the incubation time, and reducing the antibody concentration, the sensitivity of the total testosterone assay was increased to 0.008 nmol/L, and that of the free testosterone assay was increased to 2 pmol/L. The mean percent free testosterone was 1.0 +/- 0.1% of the total testosterone. Serum total and free testosterone levels in the follicular and luteal phases were not significantly different, but both demonstrated a modest preovulatory increase, 3 days before the LH peak. Serum total [0.50 +/- 0.32 (14.60 +/- 9.22) vs. 1.2 +/- 0.7 nmol/L (34.3 +/- 21.0 ng/dL); P < 0.0001] and free testosterone levels (5.56 +/- 2.70 (1.58 +/- 0.80) vs. 12.8 +/- 5.5 pmol/L (3.4 +/- 1.7 pg/mL); P < 0.0001) were significantly lower in HIV-infected women (n = 37) than in healthy women (n = 34). Serum total and free testosterone levels were also significantly lower in HIV-infected women who were menstruating normally. There were no significant differences in serum total and free testosterone levels between those who had lost weight and those who had not. Testosterone levels correlated inversely with plasma HIV ribonucleic acid copy number. Serum FSH, but not LH, levels were significantly higher in HIV-infected women than in controls. Using assays with sufficient sensitivity, we defined the range for total and free testosterone levels during the normal menstrual cycle. Serum total and free testosterone levels are lower in HIV-infected women and correlate inversely with plasma HIV ribonucleic acid levels. The hypothesis that androgen deficiency contributes to wasting in HIV-infected women remains to be tested.

Pharmacokinetics, efficacy, and safety of a permeation-enhanced testosterone transdermal system in comparison with bi-weekly injections of testosterone enanthate for the treatment of hypogonadal men.

The pharmacokinetics, efficacy, and safety of the Androderm testosterone (T) transdermal system (TTD) and intramuscular T enanthate injections (i.m.) for the treatment of male hypogonadism were compared in a 24-week multicenter, randomized, parallel-group study. Sixty-six adult hypogonadal men (22-65 years of age) were withdrawn from prior i.m. treatment for 4-6 weeks and then randomly assigned to treatment with TTD (two 2.5-mg systems applied nightly) or i.m. (200 mg injected every 2 weeks); there were 33 patients per group. Twenty-six patients in the TTD group and 32 in the i.m. group completed the study. TTD treatment produced circadian variations in the levels of total T, bioavailable T, dihydrotestosterone, and estradiol within the normal physiological ranges. i.m. treatment produced supraphysiological levels of T, bioavailable T, and estradiol (but not dihydrotestosterone) for several days after each injection. Mean morning sex hormone levels were within the normal range in greater proportions of TTD patients (range, 77-100%) than i.m. patients (range, 19-84%). Both treatments normalized LH levels in approximately 50% of patients with primary hypogonadism; however, LH levels were suppressed to the subnormal range in 31% of i.m. patients vs. 0% of TTD patients. Both treatments maintained sexual function (assessed by questionnaire and Rigiscan) and mood (Beck Depression Inventory) at the prior treatment levels. Prostate-specific antigen levels, prostate volumes, and lipid and serum chemistry parameters were comparable in both treatment groups. Transient skin irritation from the patches was reported by 60% of the TTD patients, but caused only three patients (9%) to discontinue treatment. i.m. treatment produced local reactions in 33% of patients and was associated with significantly more abnormal hematocrit elevations (43.8% of patients) compared with TTD treatment (15.4% of patients). Gynecomastia resolved more frequently during TTD treatment (4 of 10 patients) than with i.m. treatment (1 of 9 patients). Although both treatments seem to be efficacious for replacing T in hypogonadal men, the more physiological sex hormone levels and profiles associated with TTD may offer possible advantages over i.m. in minimizing excessive stimulation of erythropoiesis, preventing/ameliorating gynecomastia, and not over-suppressing gonadotropins.

The brief index of sexual functioning for women (BISF-W): a new scoring algorithm and comparison of normative and surgically menopausal populations.

OBJECTIVE: To develop a new scoring algorithm for the Brief Index of Sexual Functioning for Women (BISF-W) and to compare results from a normative population with those from a clinical sample of surgically menopausal women with impaired sexual function. DESIGN: The scoring algorithm provided an overall composite score and seven dimension scores: D1 (thoughts/desires), D2 (arousal), D3 (frequency of sexual activity), D4 (receptivity/initiation), D5 (pleasure/orgasm), D6 (relationship satisfaction), and D7 (problems affecting sexual function). The normative population consisted of 225 healthy women between the ages of 20 and 55 years; 187 had regular sexual partners and 38 did not. The clinical sample comprised 104 women in the same age range (with partners), who reported that their sex lives had become less active or less satisfying after surgery (bilateral oophorectomy and hysterectomy), despite standard estrogen replacement therapy. RESULTS: The BISF-W composite and dimension scores for healthy women with partners were significantly greater (p < 0.001) than for women without partners, except for D1, which was comparable in both groups. For healthy women with partners, the composite and dimension scores (D1, D3, and D5) decreased significantly with increasing age (p < 0.05). In comparison, surgically menopausal women had significantly lower composite and dimension scores (p < 0.001), with the exception of D7, which was significantly higher (more problems). As a percent of the normative means for healthy women with partners, the dimension scores for surgically menopausal women were lowest for D1--47.2%, D3--46.9%, and D5--46.1%. CONCLUSIONS: This research provides further validation of the BISF-W as an instrument for evaluating female sexual function and quantifies the nature and degree of impaired sexual function in surgically menopausal women.

Pharmacokinetics of testosterone in hypogonadal men after transdermal delivery: influence of dose.

To assess the pharmacokinetics of testosterone after application of one, two, or three testosterone transdermal delivery systems to hypogonadal patients, 12 hypogonadal men (mean age 46.6 +/- 10.5 years) were enrolled in an open-label, randomized, crossover study. Each application period comprised 4 days: a 2-day washout period with no exogenous testosterone therapy followed by 2 days of therapy with one, two, or three transdermal systems applied daily to the patient's back. On day 4 of each period, serial blood samples were collected for determination of total and non-sex hormone binding globulin (non-SHBG) bound serum testosterone concentrations. Serum concentrations of testosterone were determined using validated radioimmunoassay methods. Residual testosterone analysis of used transdermal systems was used to estimate testosterone delivery through the skin. In general, serum concentrations of testosterone rose in accordance with an increase in dose. Using a strict bioequivalence approach to dose proportionality, the increases in area under the concentration-time curve (AUC) and morning concentrations were proportional to the increase in dose from two to three transdermal systems, but somewhat less than proportional with an increase from one to two transdermal systems. Results from the non-SHBG bound serum testosterone concentrations closely paralleled those of total serum testosterone. Use of three transdermal systems yielded serum concentrations of testosterone that tended to be above the upper limit of the normal range. The AUC and cumulative release of testosterone were linearly related to the number of applied systems. If necessary, the standard recommended dose of two testosterone transdermal delivery systems can be modified to accommodate interindividual differences in testosterone requirements of hypogonadal men.

Prostate size in hypogonadal men treated with a nonscrotal permeation-enhanced testosterone transdermal system.

OBJECTIVES: This study examined the effects of testosterone replacement using a nonscrotal testosterone transdermal (TTD) system on prostate size and prostate-specific antigen (PSA) levels in hypogonadal men. METHODS: As part of an open-label, multicenter study, prostate volume as measured by transrectal ultrasound and PSA were assessed in 29 hypogonadal men during treatment with intramuscular testosterone enanthate (+TE), followed by 8 weeks of androgen withdrawal (-T), and then during 1 year of therapy with Androderm Testosterone Transdermal System, a nonscrotal permeation-enhanced TTD system (+TTD). RESULTS: Mean prostate volume decreased significantly from the +TE period (17 g) compared with the -T period (14 g) (P < 0.001). Prostate volume increased significantly from the -T period compared with the +TTD period (18 g) (P < 0.001). Maximum prostate size, comparable to that measured during +TE (P = 0.125), was reached by month 3 of +TTD therapy; prostate volume did not increase further during the remaining 9 months of +TTD therapy. Prostate volume correlated with age (P < 0.01) during all three periods of observation (+TE: r = 0.69; -T: r = 0.64; and +TTD: r = 0.55). No patient developed symptomatic benign prostatic hyperplasia during the treatment period. PSA levels decreased during androgen withdrawal compared with levels measured during +TE treatment (P < 0.001) and rose with resumption of androgen therapy with TTD (P < 0.006). However, PSA levels during +TTD replacement remained significantly lower (P < 0.001) than during +TE replacement. CONCLUSIONS: Physiologic testosterone replacement in hypogonadal men was achieved using the TTD system. Prostate size during therapy with TTD was comparable to that reported for normal men. In these men treated with TTD, PSA levels were also within the normal range.

New clinical applications of transdermal testosterone delivery in men and women.

This paper reviews recent progress in the development and clinical application of testosterone transdermal delivery systems designed for physiological replacement therapy in men and women. The biopharmaceutic goal of physiologic replacement therapy is to produce serum levels and circadian patterns of testosterone and its active metabolites that mimic the normal physiology of testosterone in the particular target population. For the treatment of adult hypogonadal men, the nightly 24 h application of the Androderm testosterone transdermal system (5 mg per day) achieves this goal - as demonstrated in a series of clinical pharmacokinetic studies. For the treatment of adolescent males, physiologic replacement can be approximated by modifying the dose and duration of Androderm application so as to mimic the patterns of nocturnal testosterone secretion observed during puberty. With the objective of providing physiological replacement for women with diminished testosterone production, an experimental testosterone matrix transdermal system (TMTDS) has been developed and is currently undergoing clinical evaluation. In parallel with the development of testosterone transdermal systems, physicians have been investigating a number of conditions, in both males and females, where testosterone production is diminished and replacement therapy may be beneficial. Three of these new clinical applications will be illustrated - the use of Androderm for the treatment of adolescent males with beta-thalassemia, the use of Androderm for the treatment of HIV+ men, and the use of the TMTDS for the treatment of HIV+ women. From the biopharmaceutic and clinical perspectives, the development of testosterone transdermal systems represents an important achievement in controlled drug delivery.

Androgen replacement in the treatment of Klinefelter's syndrome: efficacy and safety of a nonscrotal permeation-enhanced testosterone transdermal system.

OBJECTIVE: To report the efficacy and safety of a permeation-enhanced nonscrotal testosterone transdermal (TTD) system for the treatment of Klinefelter's syndrome. METHODS: Fifteen male patients with Klinefelter's syndrome, including 12 patients who received previous intramuscular (IM) treatment with testosterone esters, were part of the study population from three phase III clinical studies; 13 completed the studies. Patients applied two TTD systems nightly for 6 months or more. Nocturnal erections were assessed by RigiScan monitoring; sexual function was evaluated by using the Watts and Davidson questionnaires. Hypogonadal symptoms were determined by direct patient questioning. RESULTS: Mean morning serum testosterone levels increased to within normal range in all 13 patients (from 5.9 +/- 3.2 nmol/L at hypogonadal baseline to 22.3 +/- 5.6 nmol/L at 6 months). Luteinizing hormone levels decreased to within normal range in six patients and showed clinically significant decreases in four of the other seven patients (from 25 +/- 12 IU/L at hypogonadal baseline to 17 +/- 11 IU/L at 6 months). Nocturnal erections improved significantly during TTD system therapy in comparison with the hypogonadal state. Patient self-reported measures of sexual functioning were comparable to those during prior IM testosterone treatment and better than during the hypogonadal state. Hypogonadal symptoms decreased during TTD therapy in comparison with hypogonadal baseline. No clinically significant changes were noted in prostate volume, prostate-specific antigen, or lipid values. Three patients experienced anxiety or depression during TTD treatment, requiring discontinuation of therapy in one case and use of antidepressants in the other two. CONCLUSION: The testosterone patches were generally well tolerated in all patients. The nonscrotal TTD system for testosterone replacement is a safe and effective treatment for patients with Klinefelter's syndrome.

Quasielastic light scattering studies of aqueous biliary lipid systems and native bile.

During the past 15 yr, the technique of quasielastic light scattering has been used by a number of laboratories to systematically investigate the aggregative behavior of model bile systems and more recently to characterize particles present in native bile. Quasielastic light scattering investigations of aqueous bile salt solutions have indicated important similarities and differences between the various bile salt species and have led to a quantitative model for the formation of globular and rodlike micelles, based on Small and Ekwall's primary-secondary micelle hypothesis. Studies of aqueous bile salt-lecithin systems have indicated three important aggregation regimens dependent on the lecithin/bile salt molar ratio and total solute concentration. Region I of the phase diagram, which includes the lecithin/bile salt and total solute concentration values found in most mammalian biles, corresponds to a population of "simple" bile salt micelles coexisting in equilibrium with a population of mixed bile salt-lecithin micelles. Region II contains only mixed micelles, whose apparent size and shape vary with lecithin/bile salt and total solute concentration in a manner consistent with a "mixed disc" model. In this model, bile salts not only coat the perimeter of the disc (as proposed in Small's original model) but are also incorporated within the lecithin bilayer, possibly as hydrogen-bonded dimers. Finally, in region III, where total solute concentration values are typically less than the critical micelle concentration of the pure bile salt, the systems contain mixed vesicles (spherical bilayer shells) whose size (approximately 130 to 500A) depends on lecithin/bile salt and total solute concentration in accordance with a simple partition equilibrium that determines the composition of the mixed vesicle bilayer.(ABSTRACT TRUNCATED AT 250 WORDS)

Quasi-elastic light-scattering studies of aqueous biliary lipid systems. Cholesterol solubilization and precipitation in model bile solutions.

We have employed quasi-elastic light-scattering methods to characterize micellar aggregates and microprecipitates formed in aqueous solutions containing sodium taurocholate (TC), egg lecithin (L), and cholesterol (Ch). Particle size and polydispersity were studied as functions of Ch mole fraction (XCh = 0-15%), L/TC molar ratio (0-1.6), temperature (5-85 degrees C), and total lipid concentration (3 and 10 g/dL in 0.15 M NaCl). For XCh values below the established solubilization limits (XChmax) [Carey, M. C., & Small, D. M. (1978) J. Clin. Invest. 61, 998], added Ch has little influence on the size of simple TC micelles (type 1 systems), on the coexistence of simple and mixed TC-L micelles (type 2 systems), or on the growth of "mixed disc" TC-L micelles (type 3 systems). For supersaturated systems (XCh/XChmax greater than 1), 10 g/dL type 1 systems (L/TC = 0) exist as metastable micellar solutions even at XCh/XChmax = 5.3. Metastability is decreased in type 2 systems (0 less than L/TC less than 0.6), and "labile" microprecipitation occurs when XCh/XChmax exceeds approximately 1.6. In 10 g/dL mixtures, the microprecipitates initially range in size from 500 to 20000 A and later coalesce to form a buoyant macroscopic precipitate phase. In 3 g/dL mixtures, the microprecipitates are smaller (200-400 A) and remain as a stable, noncoalesced microdispersion. Transmission electron microscopy of the microprecipitates formed at both concentrations indicates a globular noncrystalline structure, and lipid analysis reveals the presence of cholesterol and lecithin in a molar ratio (Ch/L) of approximately 2/1, suggesting that the microprecipitates represent a metastable cholesterol-rich liquid-crystalline phase. In supersaturated type 3 systems (0.6 less than L/TC less than 2.0), the precipitate phase is a lecithin-rich liquid-crystalline phase which likewise coalesces in a 10 g/dL system but forms stable vesicle (liposomal) structures (600-800 A radius) in 3 g/dL systems. In conjunction with these experimental data, we present a quantitative thermodynamic analysis of Ch solubilization in model bile systems from which rigorous deductions of the free energy and enthalpy change for solubilization of cholesterol monohydrate in type 1 and type 2 systems are obtained. In addition, we employ homogeneous nucleation theory to analyze the origin of the metastable/labile limit in supersaturated systems and to deduce the interfacial tension between microprecipitates and solution. On the basis of these experimental data and theoretical analyses, we offer new hypotheses on the structure and physiology of bile and the pathogenesis of Ch gallstones. In particular, it is suggested that the "stable" microprecipitates observed in 3 g/dL type 2 systems may provide a secondary vehicle (in addition to micelles) for cholesterol transport in supersaturated hepatic bile.

Mathematical model of biliary lipid secretion: a quantitative analysis of physiological and biochemical data from man and other species.

We propose a simple mathematical model to account for the coupling of secretion rates of bile salts, lecithin, and cholesterol into bile. The model assumes that: 1) molecules of "biliary" lecithin and cholesterol enter a functional compartment located in the endoplasmic reticulum of the hepatocyte from which they are secreted into bile, and in the case of cholesterol, also catabolized to bile salts; 2) the rates at which lecithin and cholesterol enter the "secretory" compartment are regulated independently by feedback loops that control their synthesis and/or uptake; 3) lecithin secretion is coupled by an unknown transport mechanism, possibly micellar or vesicular, to the flux of bile salts passing through the compartment; 4) cholesterol secretion is coupled by a similar mechanism to lecithin secretion and not to bile salt secretion directly; and 5) bile salt synthesis is proportional to the cholesterol content of the compartment. The model predicts that in the steady state the dependences, lecithin secretion vs bile salt secretion; cholesterol secretion vs lecithin secretion; and cholesterol secretion vs bile salt secretion, will all have the form of rectangular hyperbolae. Four independent parameters related to the postulated mechanisms of biliary lipid synthesis, uptake, and transport determine the quantitative features of these hyperbolae. These four "secretion parameters" also determine how the biliary lipid composition of hepatic and "fasting" gallbladder bile varies with bile salt secretion rate. A quantitative analysis of biochemical and physiological data on biliary lipid secretion in rat, dog, and man confirms the general predictions of the model. Deductions of the secretion parameters are made for each species and are compared with other relevant data on biliary lipid metabolism. From this analysis, we offer new insights into: i) the species differences in biliary lipid secretion and bile composition; ii) the influence of obesity on biliary lipid secretion in man; and iii) the causes of cholesterol super-saturation in fasting gallbladder bile.

Biliary lipid secretion in health and in cholesterol gallstone disease.

The secretory compartment for biliary lecithin and cholesterol secretion probably resides in the smooth endoplasmic reticulum of the hepatocyte. The secretory compartment for bile salts lies predominantly in the enterohepatic circulation which fluxes bile salts continuously through the smooth endoplasmic reticulum compartment and extracts lipids for secretion into bile. Most of bile lecithin is newly synthesized by the liver; most of bile cholesterol is derived from extrahepatic sources. Both cholesterol and lecithin secretion are coupled to bile salt secretion and describe output curves which can be fitted by rectangular hyperbolae: since bile salt secretion is a linear function of input, the relative proportions of cholesterol to bile salts plus lecithin in bile increase at low bile salt outputs. In health, an adequate bile salt (+ lecithin) secretion coupled with normal cholesterol secretion maintains the relative composition of bile in a stable state: fasting compositions usually lie within the micellar zone or metastable supersaturated zone of a triangular coordinate-phase diagram plot. In cholesterol gallstone disease, mean bile salt (+ lecithin) secretion rates are subnormal and/or mean cholesterol secretion rates are supranormal, especially in the fasting state. If individuals are obese there is also enhanced hypersecretion of biliary cholesterol. Either or both secretory defects lead to an elevation and persistence of cholesterol supersaturation of bile. The physical state of the secreted lipids in bile is complex and fluctuant, and probably involves vesicle structures and mixed micelles at high water and cholesterol concentrations and predominantly micellar structures at low water and cholesterol concentrations. In lithogenic bile, the physical state, proportions and nucleation potential of the lipid aggregates are probably different.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of interleukin 2 mRNA and protein produced in the human T-cell line Jurkat and effect of cyclosporin A.

The kinetics of interleukin 2 mRNA accumulation in the leukemic T-cell line Jurkat, which can be induced with phytohemagglutinin and phorbol 12-myristate 13-acetate to produce large amounts of interleukin 2, was analyzed by a modified DNA-excess solution hybridization assay using a 5'-32P-labeled oligodeoxyribonucleotide 30 bases long as probe. Cyclosporin A was used as a valuable tool to gain more insight into the quantitative aspects of interleukin 2 production, on the basis of the assumption that transcription of the interleukin 2 gene is completely inhibited shortly after administration of cyclosporin A. The half-life of interleukin 2 mRNA was estimated to be approximately 2 h. With the aid of simple mathematical models, we have been able to relate the concentration of interleukin 2 protein in the supernatant to the interleukin 2 mRNA kinetics. This novel quantitative kinetic analysis revealed that, independent of the absence or presence of cyclosporin A, interleukin 2 protein is synthesized at a rate of approximately 1.3 molecules per molecule of interleukin 2 mRNA per second and secreted within 2 h after it is synthesized and that its half-life in the supernatant is approximately 10 h.

Cyclic neutropenia (CN): a clue to the control of granulopoiesis.

A simple quantitative feedback model of granulopoiesis is presented and discussed within the framework of existing data on granulopoiesis in both normals and patients with cyclic neutropenia (CN). The model assumes that the controlled compartment is the bone marrow pool of mature neutrophils (PMNs), which sends a negative feedback signal to the mitotic pool of early granulocyte precursors (i.e., CFU-C, myeloblasts, etc.) thus controlling the granulocyte production rate. Three parameters are found to play important roles in determining the response of the system to perturbations. These are: TM, the granulocyte maturation time; a, a parameter reflecting the strength of the negative feedback exerted by mature PMNs on the granulocyte production rate; and b, a parameter describing the leakiness of the bone marrow for PMN egress. It is shown that depending on the relative magnitudes of a and b, the system will either respond to perturbations with a damped oscillation (a less than b: the normal state) or with a sustained oscillation (a greater than b: the CN state). In both cases, the oscillation period is found to approximately equal 2TM. Deductions of the values of a, b, and TM from experimental data are consistent with the predictions of the model and show an increased value of a in CN relative to the normal state. This suggests an overly active feedback mechanism as the pathophysiologic basis of CN. In addition, the model can explain how various therapeutic agent correct CN and also provides insight into why other hematologic cell lines and CSA oscillate in CN.

Quasielastic light-scattering studies of aqueous biliary lipid systems. Mixed micelle formation in bile salt-lecithin solutions.

From measurements of the autocorrelation function and time-averaged intensity of light scattered from aqueous bile salt-lecithin solutions, we deduced the mean hydrodynamic radius (Rh), shape, and polydispersity of bile salt-lecithin mixed micelles as functions of bile salt species, lecithin to bile salt (L/BS) molar ratio, total lipid concentration (0.625-10 g/dL), temperature (20-60 degrees C), and NaCl concentration (0.15-0.6 M). Our data suggest that at low L/BS ratios (0 to approximately 0.6) simple bile salt micelles coexist in varying proportions with minimum-sized mixed micelles (Rh, 18-35 A). These solutions are highly polydisperse and display features dependent upon the particular bile salt species. At high L/BS ratios (greater than 0.6), only mixed micelles are present, and their sizes increase markedly (Rh, 20 leads to 300 A) with increases in L/BS ratio and appear to diverge as the lecithin-bile salt phase limit is approached. The shape of the mixed micelles as deduced from light-scattering measurements and confirmed by transmission electron microscopy is disklike. The radii of the disks, however, are not compatible with Small's model of mixed micellar structure [Small, D.M. (1967a) Gastroenterology 52, 607-a1 but are consistent with a new model proposed here in which bile salts and lecithin interact to form a mixed bilayer disk which is surrounded on its perimeter by bile salts. The inclusion of bile salts in a fixed stoichiometry within the interior of the bilayers is shown to provide a quantitative explanation for the divergence of the mixed micellar sizes, their temperature dependence, and the origin of the lecithin-bile salt phase limit. The influence of total lipid concentration on both mixed micellar size and the lecithin-bile salt phase limit is explained by the "mixed disk" model by taking account of the equilibrium between mixed micelles and bile salt monomers in the intermicellar solution. By use of this concept, deductions of the intermicellar bile salt concentration in taurocholate-lecithin solutions are made and are shown to vary as a function of mixed micellar size and temperature. The range of values obtained, 3-6 mM, is comparable in magnitude to the critical micellar concentration of the pure bile salt.