Wesley R. Anderson

Chronic weight loss in lean and obese rats with a brain-enhanced chemical delivery system for estradiol

Studies were undertaken to determine the effects on body weight and food intake of a chemical delivery system which preferentially delivers estradiol (E2) to the brain and there serves as a source for the sustained release of the steroid. We injected intravenously various doses of this estradiol-chemical delivery system (E2-CDS), E2-valerate (E2-VAL) or the dimethyl sulfoxide (DMSO) vehicle to young lean male rats and monitored body weight and 24 hr food intake for 39 days postinjection. E2-VAL caused a transient reduction in food intake and body weight gain. By contrast, a single injection of E2-CDS caused a chronic, dose-dependent reduction in the rate of body weight gain. In these lean rats, the duration of reduced body weight gain was not correlated with the observed transient reduction in food intake. In aged, obese male rats, E2-CDS caused a marked and chronic dose-dependent reduction in body weight. In contrast to lean rats, E2-CDS caused a long-term reduction in food intake in obese rats. To evaluate the importance of the E2-CDS-induced reduction in food intake in the observed persistent weight loss in obese rats, E2-CDS was administered to a group of obese rats and a second group which received the DMSO vehicle was pair-fed an equivalent amount of food daily. The resulting weight loss in both groups was equivalent. These results show that the enhanced delivery of E2 to the brain with the E2-CDS causes sustained reduction in the rate of body weight gain in lean rats and persistent weight loss in obese animals.

Effects of a Brain-Enhanced Chemical Delivery System for Estradiol on Body Weight and Food Intake in Intact and Ovariectomized Rats

Studies were undertaken to determine the effects on body weight of a brain-enhanced chemical delivery system for estradiol. This estradiol-chemical delivery system (E2-CDS) has a long half-life in the brain, where it slowly releases estradiol but is quickly cleared from peripheral tissues. We administered, by a single iv injection, E2-CDS (0.2, 1.0, or 5.0 mg/kg), equimolar doses of another 17-hydroxy-substituted estrogen, estradiol valerate (E2-VAL), or the dimethyl sulfoxide (DMSO) vehicle to female rats. Daily food intake and body weight was determined for 24 days thereafter. E2-CDS caused an initial dose-dependent suppression in body weight for up to 8 days and a suppression in food intake for up to 4 days. In response to E2-VAL, the initial declines in body weight and food intake were lower in magnitude, were shorter in duration, and showed no dose dependency. Following this period of weight loss, E2-CDS-treated rats gained weight at a rate greater than that of the DMSO controls, and at the 0.2- and 1.0-mg/kg doses, body weights achieved were greater than control levels. To determine the role of the ovaries on this biphasic response to E2-CDS, long-term ovariectomized rats were treated with E2-CDS (1.0 mg/kg) or the vehicle and parameters of body weight regulation were determined for 25 days. Ovariectomized rats responded to E2-CDS with a prompt and sustained decrease in body weight which did not recover over the 25-day course of the study. The body-weight loss in ovariectomized rats was associated with a marked reduction in food intake for 8 days. Finally, when intact female rats were administered the E2-CDS on the day of diestrus I, rats exhibited cornified vaginal epithelial lavages for 3.5 days, during which weight loss was observed, followed by a 7.8-day period of pseudopregnancy during which animals rapidly gained weight. Collectively, these data indicate that delivery of E2 to the brain with E2-CDS causes a marked decline in body weight and food intake in female rats. The phase of increased body weight which follows this drug-induced weight loss appears to be ovarian dependent, since in ovariectomized rats this phase of response to the drug is not observed.

Effect of Sustained Estradiol Release in the Intact Male Rat: Correlation of Estradiol Serum Levels with Actions on Body Weight, Serum Testosterone, and Peripheral Androgen-Dependent Tissues

The differential effect of increasing serum estradiol on various parameters in the intact male rat was assessed through the use of subcutaneously implanted, hormone-laden pellets. The delivery systems were designed to release drug through bioerosion at a zero-order rate over a 12-day time-course. Male Sprague-Dawley rats (190 to 220 g) were given estrogen pellets at increasing labeled strenghts (0, 0.001, 0.01, 0.1, 1.0, 10, 50, and 100 mg). Animals were weighed at various intervals before and after implantation. At Day 6, 12, and 26 after drug administration, rats were examined for 4 additional parameters, including serum estradiol and testoterone concentrations and accessory organ weights (i.e., ventral prostate and seminal vesicles). Serum estradiol levels were consistent with pellet potency and lifetime. Increases in body weight were suppressed 50% by circulating estradiol levels of approximately 200 pg/mL at Day 6,250 pg/mL at Day 12, and 285 pg/mL at Day 26. On the other hand, suppression of serum testosterone was more sensitive and was decreased 50% by peripheral estrogen levels of 36, 43, and 51 pg/mL at Days 6, 12, and 26, respectively. Accessory organ weights essentially reflected serum testosterone levels as indicated by their similar ED50 values: 50.5, 50.5, and 44.3 pg/mL for the ventral prostate at Day 6, 12, and 26, respectively, and 48, 56, and 51.5 pg/mL for the seminal vesicle regression at Day 6, 12, and 26, respectively. The data indicate the pellet used provided sustained plasma levels of hormone and these constant peripheral levels exerted potent pharmacological action. Initial body weight changes seemed to be less sensitive to the action of estradiol than serum testosterone or derivative properties, such as accessory organ weight.

Evidence for Prolonged Suppression of Stress-Induced Release of Adrenocorticotropic Hormone and Corticosterone with a Brain-Enhanced Dexamethasone-Redox Delivery System

We have developed a redox system for brain-enhanced delivery of dexamethasone based on an interconvertible dihydropyridine in equilibrium pyridinium salt carrier. Dexamethasone, when combined with the lipoidal carrier, readily crosses the blood-brain barrier. The carrier, when oxidized, reduces its rate of exit from the brain. The aim of the study was to evaluate the capacity of a dexamethasone-chemical delivery system (DX-CDS) and dexamethasone (DEX) to suppress stress-induced elevations of plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT). Adult male Sprague-Dawley (CD) rats were administered either DX-CDS (10 mg/kg), an equimolar dose of DEX or the drug vehicle (2-hydroxypropyl-beta-cyclodextrin) by a single tail vein injection. Rats then received either no stress or a restraint stress for a 5- or 15-min duration on days 1, 3, 5 or 7 after drug administration and trunk blood was rapidly collected. To assess peripheral effects of DX-CDS and DEX, 1 ml of blood was removed via orbital puncture and evaluated for total and differential leukocyte counts in a separate group of animals. Both DX-CDS and DEX were effective on day 1 in suppressing, by greater than 95%, ACTH secretion induced by a 5-min stress. However, DX-CDS was effective through day 5 (44% suppression) while DEX was not effective after 24 h. When 15 min of stress was applied, DX-CDS effected a significant ACTH suppression through 7 days while DEX was effective for only 3 days. DX-CDS was effective through day 7 (55%) in suppressing CORT after a 15-min stress while DEX was effective for 3 days only.(ABSTRACT TRUNCATED AT 250 WORDS)

Redox targeting of LY231617, an antioxidant with potential use in the treatment of brain damage

Abstract Several brain-targeting chemical delivery systems (CDS) based on a dihydropyridine ⇌ pyridinium salt-type targetor were synthesized and evaluated for LY231617 (1), a di-tert-butylated phenolic amine antioxidant with potential use in the treatment of brain injuries. The dihydropyridine moiety was chemically attached to the amine (by either amide or various substituted carbamate linkages) or to the phenolic hydroxyl (by carboxylic ester linkage) functionalities of LY231617. In vitro stability and in vivo tissue distribution studies (in the rat) were performed with the novel derivatives. The results indicated that a simple amide-type CDS demonstrated efficient delivery of LY231617-targetor conjugate to the CNS. This derivative which contains the intact pharmacophore might possess intrinsic pharmacological antioxidant activity. Favorable in vitro properties suggested that a substituted carbamate-type CDS might be a better delivery modality for LY231617.

Evidence for suppression of serum LH without elevation in serum estradiol or prolactin with a brain-enhanced redox delivery system for estradiol

We developed a redox system for brain-enhanced delivery of estradiol based on an interconvertible dihydropyridine in equilibrium pyridinium salt carrier. Estradiol (E2), when combined with the lipoidal carrier, readily crosses the blood-brain barrier. The carrier, when oxidized, reduces the rate of exit of the estradiol-carrier complex from the brain. Subsequent hydrolysis of the carrier provides sustained production of estradiol in the brain. The aim of the study was to evaluate the effects of single vs. multiple injections of the estradiol-chemical delivery system (E2-CDS) on both central and peripheral estrogen-responsive tissues. Ovariectomized Sprague-Dawley rats received an intravenous injection of E2-CDS at 10, 33, 100 or 333 micrograms/kg BW or the drug vehicle, dimethyl sulfoxide (DMSO; 0.5 ml/kg) every 2 days for 7 injections (2 weeks) or a single injection only at 2 days before sacrifice. With a single injection, E2-CDS did not affect serum luteinizing hormone (LH) levels at the 10 micrograms/kg dose but caused a dose-dependent reduction in serum LH of 39-52% at the dose range of 33 to 333 micrograms/kg. By contrast, multiple injections of E2-CDS caused a 32 to 76% reduction in serum LH levels at doses ranging from 10 micrograms/kg to 333 micrograms/kg. Additionally, multiple doses of E2-CDs caused a dose-dependent reduction in body weight at the 10 and 33 micrograms/kg doses with the higher doses causing no further weight reduction. For both single and multiple dosage groups, serum E2 levels remained unchanged after doses of E2-CDS of 10 and 33 micrograms/kg, then increased to 21 pg/ml for the single dosage group and to 23 pg/ml for the multiple dosage group at the 100 micrograms/kg dose, and to 59 pg/ml for singly-injected rats and 60 pg/ml for multiply-injected rats at the 333 micrograms/kg dose. Serum prolactin concentrations were closely correlated with serum E2 levels for both the single and multiple dose groups. These data reveal that a single or multiple doses of E2-CDS can reduce serum LH levels without elevating serum E2 or prolactin concentrations, supporting the concept of brain-enhanced delivery of estradiol with an estradiol chemical delivery system.

Formulation development for a zidovudine chemical delivery system 1. Parenteral dosage forms

Abstract A chemical delivery system for zidovudine (AZT-CDS) has been shown to increase brain levels of the parent antiretroviral agent while at the same time reducing blood concentrations. Such selectivity may improve the therapeutic index for AZT. Unfortunately, the AZT-CDS is lipophilic and labile to oxidative and hydrolytic degradation thereby complicating the development of a convenient formulation. The configuration of several potentially acceptable parenteral dosage forms using cyclodextrin-based systems are described herein. A prototype formulation was developed using the AZT-CDS potassium salt in an aqueous matrix of 2-hydroxypropyl-β-cyclodextrin (HPβCD) (15% w/v) and Na 3 PO 4 (0.005 M). While alkaline, the formulation was associated with a low buffering capacity and was not irritating in a rat tail model of extravasation. Systemic administration of this dosage form provided for, in addition to improved brain levels of AZT and an increased brain to blood ratio, improved bioavailability compared to a dimethyl sulfoxide (DMSO) vehicle.

Formulation development for a zidovudine chemical delivery system 2. Towards oral and non-parenteral dosage forms

Steps toward the development of an oral dosage form for a dihydronicotinate chemical delivery system for zidovudine (AZT-CDS) were examined. Administration of the AZT-CDS by gavage to rats indicated poor bioavailability consistent with the acid lability of the CDS. Furthermore, administration of the AZT-CDS in dimethyl sulfoxide (DMSO) intraintestinally did not result in therapeutically relevant brain or blood levels of the AZT-CDS or its metabolites. Use of a liposome formulation, however, did provide for significant uptake with administration to the jejunum more effective than AZT-CDS administration to the ileum or colo-caecum. Invasive administration of AZT-CDS complexed with various chemically modified cyclodextrins to the intestine also resulted in good bioavailability. Perfusion of a section of jejunum with a solution of AZT-CDS in 2-hydroxypropyl-β-cyclodextrin (HPβCD) resulted in demonstrable AZT-CDS uptake and pre-liver/post-liver blood concentration ratio of approx. 0.5. These results suggest that an enterically coated AZT-CDS tablet may provide for pharmacologically useful oral bioavailability. A second route of administration considered was rectal dosing. AZT was significantly bioavailable from prototype suppositories in the rat and although AZT-CDS could be detected after AZT-CDS treatment, the absolute bioavailability for AZT after such treatment was low.

Intravenous and Buccal 2-Hydroxypropyl-β-Cyclodextrin Formulations of E2-CDS — Phase I Clinical Trials

Intravenous and buccal dosage forms were configured for E2-CDS, a brain-targeting estrogen delivery system, using 2-hydroxypropyl-β-cyclodextrin (HPβCD) and examined in a Phase I clinical protocol. Eighteen post-menopausal volunteers were administered a single oral dose of Progynova (estradiol valerate, 1.0 mg). Four days later the group was randomized to receive either i.v. E2-CDS (n=9, 0.6 to 2.5 mg in 20% HPβCD) or buccal i.v. E2-CDS (n=9, 2.0 to 16.0 mg in HPβCD administered as a solution). Subsequent to the rising dose study, nine of the volunteers were treated with estradiol (equimolar to 2.5 mg E2-CDS in HPβCD). All treatments were well tolerated. Both i.v. and buccal treatment lead to dose-dependent decreases in serum LH consistent with brain-targeted delivery. In the case of the buccal treatments, bioavailability was estimated at 20-25%.

Effect of 2-Hydroxypropyl-β-Cyclodextrin Complexes of the Neurosteroids, Alfaxalone, Pregnanolone and Pregnenolone, on Various Convulsant Stimuli in the Mouse

Water-soluble complexes of the progesterone derivatives, alfaxalone, pregnanolone and pregnenolone were prepared and characterized. The complexes were tested in vivo in the mouse using two administration routes (i.v. and i.p.) and six convulsant stimuli. Intravenous administration of alfaxalone and pregnanolone inhibited convulsions associated with electrical and pentylenetetrazole treatment but not after picrotoxin, bicuculline or strychnine treatment. Pregnenolone was only effective in pentylenetetrazole threshold seizures and only at higher doses. On the other hand, i.p. treatment with the steroids revealed that both alfaxalone and pregnanolone were active against picrotoxin- and bicuculline-induced seizures while manifesting poor action against maximum electroconvulsive shock.