Publications

Administration of the cytochrome P450 (P450) suicide inactivator allylisopropylacetamide (AIA) to phenobarbital (PB)-pretreated rats results in rapid and marked inactivation of several liver endoplasmic reticulum (ER)-bound P450s. A few of these such as CYP2B1, inactivated due to AIA-mediated prosthetic heme N-alkylation, can be structurally and functionally restored nearly completely by exogenous hemin in vivo or in vitro. Such in vitro hemin-mediated reassembly is unsuccessful with purified AIA-inactivated CYP2B1 and, as shown herein, is not very effective even when heme is incubated with just the corresponding liver microsomes that contain the reconstitutable CYP2B1 protein, thereby implicating a requirement for additional factors provided by the intact liver cell homogenates, ER, and/or cytosol. Using various approaches that include high-performance liquid chromatographic fractionation of the liver cytosolic subfraction as well as chemical and immunological probes such as the Hsp90/GRP94-specific inhibitor geldanamycin (GA) and polyclonal anti-GRP94 antibodies, respectively, we now demonstrate that the in vitro hemin-mediated reassembly of heme-stripped microsomal CYP2B1 requires GSH as well as the ER chaperone GRP94, but not the cytosolic chaperone heat shock protein 90. It remains to be determined whether GSH acts directly or indirectly, via a putative ER thiol reductase, to maintain the conserved active site cysteine-thiol (Cys436 in CYP2B1) in a reduced state, competent for heme binding and repair.

Inhibitors of cytochrome P450 3A4 (CYP3A4) were identified in crude extracts from the rhizomes of Piper methysticum G. Forst. (Kava-Kava) using bioassay-guided fractionation. After preliminary purification of an ethyl acetate extract with solid phase extraction, the eluate was further fractionated by means of HPLC and fractions were tested for inhibitory potency using cDNA expressed CYP3A4. Positive fractions were analysed with LC/MS using electrospray ionisation and kavapyrones could be identified as the main CYP3A4 inhibitory components of Piper methysticum.

OBJECTIVE

To compare and contrast methods and findings from two approaches to valuation used in the same survey: measurement of "attitudes" using simple rankings and ratings versus measurement of "preferences" using conjoint analysis. Conjoint analysis, a stated preference method, involves comparing scenarios composed of attribute descriptions by ranking, rating, or choosing scenarios. We explore possible explanations for our findings using focus groups conducted after the quantitative survey.

METHODS

A self-administered survey, measuring attitudes and preferences for HIV tests, was conducted at HIV testing sites in San Francisco in 1999-2000 (n = 365, response rate = 96 percent). Attitudes were measured and analyzed using standard approaches. Conjoint analysis scenarios were developed using a fractional factorial design and results analyzed using random effects probit models. We examined how the results using the two approaches were both similar and different.

RESULTS

We found that "attitudes" and "preferences" were generally consistent, but there were some important differences. Although rankings based on the attitude and conjoint analysis surveys were similar, closer examination revealed important differences in how respondents valued price and attributes with "halo" effects, variation in how attribute levels were valued, and apparent differences in decision-making processes.

CONCLUSIONS

To our knowledge, this is the first study to compare attitude surveys and conjoint analysis surveys and to explore the meaning of the results using post-hoc focus groups. Although the overall findings for attitudes and preferences were similar, the two approaches resulted in some different conclusions. Health researchers should consider the advantages and limitations of both methods when determining how to measure what people value.

OBJECTIVE

To examine preferences for HIV test methods using conjoint analysis, a method used to measure economic preferences (utilities).

DATA SOURCES

Self-administered surveys at four publicly funded HIV testing locations in San Francisco, California, between November 1999 and February 2000 (n = 365, 96 percent response rate).

STUDY DESIGN

We defined six important attributes of HIV tests and their levels (location, price, ease of collection, timeliness/accuracy, privacy/anonymity, and counseling). A fractional factorial design was used to develop scenarios that consisted of combinations of attribute levels. Respondents were asked 11 questions about whether they would choose "Test A or B" based on these scenarios.

DATA ANALYSIS

We used random effects probit models to estimate utilities for testing attributes. Since price was included as an attribute, we were able to estimate willingness to pay, which provides a standardized measure for use in economic evaluations. We used extensive analyses to examine the reliability and validity of the results, including analyses of: (1) preference consistency, (2) willingness to trade among attributes, and (3) consistency with theoretical predictions.

PRINCIPAL FINDINGS

Respondents most preferred tests that were accurate/timely and private/anonymous, whereas they had relatively lower preferences for in-person counseling. Respondents were willing to pay an additional $35 for immediate, highly accurate results; however, they had a strong disutility for receiving immediate but less accurate results. By using conjoint analysis to analyze new combinations of attributes, we found that respondents would most prefer instant, highly accurate home tests, even though they are not currently available in the U.S. Respondents were willing to pay $39 for a highly accurate, instant home test.

CONCLUSIONS

The method of conjoint analysis enabled us to estimate utilities for specific attributes of HIV tests as well as the overall utility obtained from various HIV tests, including tests that are under consideration but not yet available. Conjoint analysis offers an approach that can be useful for measuring and understanding the value of other health care goods, services, and interventions.