Cyp7b, a novel brain cytochrome P450, catalyzes the synthesis of neurosteroids 7α-hydroxy dehydroepiandrosterone and 7α-hydroxy pregnenolone

Steroids produced locally in brain (neurosteroids), including dehydroepiandrosterone (DHEA), influence cognition and behavior. We previously described a novel cytochrome P450, Cyp7b, strongly expressed in rat and mouse brain, particularly in hippocampus. Cyp7b is most similar to steroidogenic P450s and potentially could play a role in neurosteroid metabolism. To examine the catalytic activity of the enzyme mouse Cyp7b cDNA was introduced into a vaccinia virus vector. Extracts from cells infected with the recombinant showed NADPH-dependent conversion of DHEA (K_m, 13.6 μM) and pregnenolone (K_m, 4.0 μM) to slower migrating forms on thin layer chromatography. The expressed enzyme was less active against 25-hydroxycholesterol, 17β-estradiol and 5α-androstane-3β,17β-diol, with low to undetectable activity against progesterone, corticosterone, and testosterone. On gas chromatography and mass spectrometry of the Cyp7b metabolite of DHEA the retention time and fragmentation patterns were identical to those obtained with authentic 7α-hydroxy DHEA. The reaction product also comigrated on thin layer chromatography with 7α-hydroxy DHEA but not with 7β-hydroxy DHEA; when [7α-³H]pregnenolone was incubated with Cyp7b extracts the extent of release of radioactivity into the medium suggested that hydroxylation was preferentially at the 7α position. Brain extracts also efficiently liberated tritium from [7α-³H]pregnenolone and converted DHEA to a product with a chromatographic mobility indistinguishable from 7α-hydroxy DHEA. We conclude that Cyp7b is a 7α-hydroxylase participating in the synthesis, in brain, of neurosteroids 7α-hydroxy DHEA, and 7α-hydroxy pregnenolone.     

Impact of the basic skin cancer triage curriculum on providers’ skin cancer control practices

OBJECTIVE: To evaluate the effect of a 2-hour, multicomponent educational intervention on provider skin cancer control practices. DESIGN: Nonrandomized intervention study. The intervention was a 2-hour curriculum designed to augment provider skin cancer control practices through instruction in basic skin cancer triage (BSCT) and a brief summary of skin cancer epidemiology, prevention, and counseling. SETTING: Five staff-model health maintenance organizations in southeastern New England. PARTICIPANTS: Convenience sample of primary care providers. Providers older than age 75, individuals in practice for less than 1 year, or individuals planning to retire in the next 2 years were excluded from the study. Twenty-two of 28 participants completed the study. RESULTS: Providers completed preintervention and postintervention surveys asking them to rate their attitudes towards skin examination and skin cancer counseling and to rate the frequency of their skin cancer control practices, using 5-point Likert scales. We independently assessed provider behavior through surveys of their patients, eliciting information on provider practices before and after BSCT participation. Following participation in the curriculum, there was significant improvement in provider attitudes towards the total body skin examination but not towards skin cancer prevention counseling. Significant increases in provider self- reported skin cancer control practices during an initial visit with a new patient (2.17 to 3.21, P <.0001) and a routine visit with a patient at high risk for melanoma (2.15 to 3.00, P <.0001) were demonstrated. Analysis of the patient exit interviews independently confirmed these changes in practice patterns. CONCLUSIONS: The study results suggest that the BSCT curriculum may be a useful tool in increasing the practice of skin cancer control measures by primary care providers.