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Currently, clinical trials in patients are required by most regulatory authorities for the assessment of bioequivalence of topical products where the drug is not intended for systemic absorption. Hence there is a dire need for suitable methods for the assessment of bioavailability and bioequivalence of such products since clinical safety and efficacy studies are expensive, time-consuming and require very large numbers of patients. Except for topical corticosteroid products where the human skin blanching assay/vasoconstrictor assay has been approved by the US FDA for bioequivalence assessment of those products, no other method has been “officially” approved for use in those investigations. However, a few alternative methods such as tape stripping and microdialysis have been pursued and considered to have the potential for use in ioequivalence/bioavailability studies. The human skin blanching assay was used to assess the bioequivalence of commercially available topical products containing 0.05% clobetasol propionate. Both visual and chromameter data were obtained and a commercially available topical corticosteroid product, Dermovate® cream was used as both the “Test” and the “Reference” product. The results indicated that both visual and chromametric assessments were comparable to each other and that either could be used for the assessment of the bioequivalence of topical products containing clobetasol propionate. The screening procedure was optimized to identify potential “detectors” for inclusion in the bioequivalence studies. This resulted in fewer subjects being required in a bioequivalence pivotal study, still having the necessary power to confirm bioequivalence using the human skin blanching assay. Another objective of this research was to re-visit tape stripping and other possible alternative methods such as dermal microdialysis and to optimize these procedures for bioequivalence assessment of topical formulations where the drug is not intended for systemic absorption. In the past few decades, tape stripping has been used to investigate bioavailability/bioequivalence of various topical formulations. This technique involves the removal of the stratum corneum to assess drug penetration through the skin. A draft FDA guidance for tape stripping was initially published but was subsequently withdrawn due to high variability and poor reproducibility. This research project used an optimized tape stripping procedure to determine bioavailability and establish bioequivalence between three commercially available formulations containing 0.05 % m/m clobetasol propionate. Furthermore, tape stripping was validated by undertaking a study to assess the bioequivalence of a 0.05% topical cream formulation (Dermovate® cream) using the same cream as both the “Test” and “Reference” product, in which bioequivalence was confirmed. The findings highlight the potential of tape stripping as an alternative method for the assessment of bioequivalence of clobetasol propionate formulations and may possibly be extended for use in other topical products. Microdialysis is another useful technique that can assess the penetration of topically applied substances which diffuses through the stratum corneum and into the dermis. Microdialysis has previously been successfully used for in vivo bioavailability and bioequivalence assessments of topical formulations. However, the drugs which were under investigation were all hydrophilic in nature. A major problem with the use of microdialysis for the assessment of lipophilic substances is the binding/adherence of the substance to the membrane and other components of the microdialysis system. As a result, this necessitates the development of a microdialysis system which can be used to assess lipophilic drugs. Intralipid® 20% was investigated and successfully utilized as a perfusate to recover a lipophilic topical corticosteroid, clobetasol propionate, in microdialysis studies. Hence, the bioavailability of clobetasol propionate from an extemporaneous preparation was determined in healthy human volunteers using microdialysis. These findings indicate that in vivo microdialysis can be used to assess lipophilic drug penetration through the skin. A novel approach to investigate drug release from topical formulations containing 0.05% clobetasol propionate using in vitro microdialysis was also undertaken. The in vitro findings were found to be in agreement with the results obtained using tape stripping to assess bioequivalence of the same commercially available products, namely Dermovate® cream, Dovate® Cream and Dermovate® ointment. These results indicate the potential to correlate in vitro with in vivo data for bioequivalence assessment of such topical dosage forms.

No description available.

This thesis reports the results of studies on steroid metabolism in a subject with an adrenocortical carcinoma and hypoglycemia, in the testes obtained from a subject with virilizing male pseudohermaphroditism and in the testes of the normal rat. Incubations of cell-free homogenates of an adrenocortical carcinoma from a 51 year old female with severe hypoglycemia were performed using ³H-pregnenolone and ¹⁴C-progesterone as substrates. Transformation of ³H-pregnenolone to progesterone, dehydroepiandrosterone and androstenedione was observed; no metabolites of ¹⁴C-progesterone were detected. The excretion rate in urine of 3α ,17,21-trihydroxy-5β -pregnan-20-one, a metabolite of cortexolone, was elevated which suggests that a defect in 11β -hydroxylase activity was present. The excretion rates in urine of total 17-ketosteroids, 17-hydroxycorticoids and 17-ketogenic steroids were elevated; the excretion rates of testosterone, dehydroepiandrosterone, pregnandiol, pregnanetriol and free cortisol were not elevated. The etiology of the hypoglycemia that may accompany some adrenocortical tumors remains unknown. It was not possible to relate the results of the investigations of steroid metabolism reported herein to the hypoglycemia that was present. Steroid biosynthesis in vitro was investigated in testes obtained during puberty from a 14 year old subject with virilizing male pseudohermaphroditism. Cell-free homogenates of gonadal tissue efficiently metabolized ³H-pregnenolone, ¹⁴C-progesterone and ¹⁴C-androstenedione to testosterone; formation of estrone and estradiol-17β was not detected. 16α-Htdroxyprogesterone was formed from both ³H-pregnenolone and ¹⁴C-progesterone. The results are similar to those of others who have investigated the steroidogenic capacity of gonadal tissue in patients with male pseudohermaphroditism and feminization at puberty. A defect in the formation of progesterone from pregnenolone has been suggested to explain the results of a previous study in which the gonadal tissue obtained from a patient with virilizing male pseudohermaphroditism was incubated with ³H-pregnenolone as substrate. In the investigations reported herein, transformations of ³H-pregnenolone to testosterone and androstenedione occurred both via 17-hydroxypregnenolone and dehydroepiandrosterone and via progesterone and 17-hydroxyprogesterone. The failure of patients with virilizing male pseudohermaphroditism to masculinize during embryonic development contrasts with the virilization that occurs during puberty. A biochemical abnormality may exert a transient effect during embryonic development. Alternatively, the sensitivity to androgenic hormones may be subnormal in certain tissues and normal in other tissues of patients with virilizing male pseudohermaphroditism. The biosynthesis of testosterone from progesterone and pregnenolone was investigated in the rat testis. Time studies were performed using cell-free homogenates and ³H-progesterone and ¹⁴C-17-hydroxyprogesterone in combination as substrates. It was demonstrated that the side-chain cleavage of 17-hydroxyprogesterone is the rate-limiting reaction in the biosynthesis of testosterone from progesterone and the evidence suggested that 17-hydroxyprogesterone was present as a bound intermediate (at least in part). The progesterone 17-hydroxylase and the 17-hydroxyprogesterone side- chain cleavage enzyme of the rat testis can be solubilized by treatment of lyophilized microsomes with Triton N-101. Both enzymes displayed maximal activity at pH 6.8 and at 37°. Progesterone rather than pregnenolone is the preferred substrate for the 17α-hydroxylase. Either NADH or NADPH can serve as the reductant for active 17-hydroxylation of progesterone and for side-chain cleavage of 17-hydroxyprogesterone. The soluble fraction contains NADPH dehydrogenase, non-heme iron protein and cytochrome P-450. The presence of these compounds in association with the 17α-hydroxylase and the side-chain cleavage enzyme activities suggests that these reactions are catalyzed by elaborate enzymatic systems analogous to those required for 11β-hydroxylation and cholesterol side-chain cleavage in adrenal mitochondria / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

Gel filtration coupled with radioimmunoassay of fractions has demonstrated the existence of an 8000 dalton immunoreactive form of GIP (glucose-dependent insulinotropic polypeptide or gastric inhibitory polypeptide), which may be a precursor in the biosynthetic pathway. A monoclonal antibody to GIP has been shown to have highly suitable characteristics for affinity purification of different species of IR-GIP. An enzyme-linked immunosorbent assay (ELISA) was developed for GIP, employing the monoclonal antibody and was used for screening fractions for peptides with the same antigenic determinant i.e. IR-foras of GIP. Classical strategy used in peptide purification may result in loss of related peptides if they are sensitive to the pH or temperature conditions used. Tissue from hog duodenal and jejunal mucosa was boiled and extracted into acetic acid. Peptides were then adsorbed to alginic acid, eluted with 200 mM HC1, precipitated with NaCl and desalted on Sephadex G-25. The desalted material was adjusted to pH 7.0 with 200mM ammonia and extracted with methanol. The methanol insoluble fraction demonstrated the highest content of IR-GIP₈₀₀₀⋅ The overall acidic charge on the larger IR-GIP oUUU moiety suggested the possibility that it might not be adsorbed to alginic acid. The monoclonal antibody to porcine GIP₅₀₀₀ was coupled to cyanogen bromide activated Sepharose -4B. The peptide fraction which was not adsorbed to alginic acid was applied to the column and the fraction which bound to the ligand was eluted with 100 mM HC1. The immunoreactive material was rotary evaporated to dryness and further purified to a monocomponent by HPLC. A µBondapak C₁₈ column and a linear gradient of acetonitrile in water containing 0.1% TFA was used for HPLC. Amino acid analyses revealed the following composition: Asx (6), Thr (2), Ser (3), Glx (3), Pro (3), Gly (4), Ala (8), Val (5), Met (1), He (0), Leu (7), Tyr (1), Phe (3), His (4), Lys (5), Arg (3), Trp (+). The N-terminal residue was identified as valine using the dansylation method. Cleavage of the molecule with trypsin and separation of the tryptic peptides on HPLC showed 2 peptides with elution times similar to tryptic peptides of GIP. Application of monocomponent IR-GIP designated IR-LGIP C, and GIP to the HPLC system confirmed the two peptides to be separate entities. Biological activity was assessed in the isolated perfused rat pancreas, a model used for measurement of the insulin releasing effect of GIP. IR-LGIP C did not demonstrate insulinotropic activity. It is unlikely that this polypeptide is a proform of GIP. It shares common immunoreactivity but lacks the necessary common core of amino acid residues. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate