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D W Russell

Publications and source records attributed to D W Russell.

At least 109 records · Page 6Linked to original sources
PubMed1992

Four-amino acid segment in steroid 5 alpha-reductase 1 confers sensitivity to finasteride, a competitive inhibitor.

The 4-azasteroid 17 beta-(N-t-butyl)carbamoyl-4-aza-5 alpha-androst-1-en-3-one (finasteride) is 100-fold more potent as a competitive inhibitor of the rat NADPH:delta 4-3-oxosteroid-5-alpha- oxidoreductase (steroid 5 alpha-reductase) type 1 enzyme (Ki = 3-5 nM) than of the human type 1 enzyme (Ki greater than or equal to 300 nM). In this study, we exploit this differential sensitivity to map a major determinant of finasteride sensitivity in steroid 5 alpha-reductase. Chimeric steroid 5 alpha-reductase cDNAs composed of different combinations of rat and human exon sequences were created by genetic engineering, expressed in human embryonic kidney 293 cells, and assayed for their sensitivity to finasteride. Hybrid proteins containing sequences encoded by rat exon 1 were found to be as sensitive to finasteride as the parental enzyme. The exchange of progressively smaller protein segments encoded within exon 1 identified a tetrapeptide sequence (Val-Ser-Ile-Val) in the rat enzyme that conferred sensitivity to finasteride. The analogous sequence in the human enzyme (Ala-Val-Phe-Ala) conferred partial resistance to the drug. Finasteride was a competitive inhibitor of the native and all chimeric enzymes tested, suggesting that the tetrapeptide segments form a portion of the substrate-binding domain of steroid 5 alpha-reductase.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1992

The localization, partial purification and regulation of pea plastid HMG-CoA reductase.

HMG-CoA reductase was located to the envelope membranes of pea etioplasts, the first report of the suborganelle localization of this key enzyme in isoprenoid synthesis. The enzyme was purified 156 fold from isolated envelope membranes. Purification was achieved by detergent solubilization, hydroxylapatite chromatography and glycerol gradient centrifugation. Membrane-bound etioplast HMG-CoA reductase was activated 4 to 5 fold by high concentrations of inorganic phosphate, this activation was prevented by arsenate, a structural analog of phosphate.

Arsenates↗
PubMed1992

Cholesterol biosynthesis and metabolism.

Cholesterol plays an essential role in cell membrane synthesis and in cell growth and differentiation. In mammalian cells, cholesterol can be synthesized from acetate precursors or taken up from dietary or exogenous sources. The major catabolic route for disposal of cholesterol involves conversion into excretable bile acids. The maintenance of cholesterol homeostasis is influenced and carefully controlled by multiple feedback mechanisms. The key regulatory targets of these feedback mechanisms are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in cholesterol biosynthesis, the low-density lipoprotein (LDL) receptor in cholesterol uptake, and cholesterol 7 alpha-hydroxylase in cholesterol catabolism. The elucidation of regulatory mechanisms in cholesterol metabolism has been greatly facilitated by the discovery of a new class of lipid-lowering drugs, the HMG-CoA reductase inhibitors. In addition to proving therapeutically useful in the treatment of hypercholesterolemia, these drugs have revealed novel regulatory steps in cholesterol metabolism and several new targets for future drug development. This manuscript reviews recent developments in the cholesterol biosynthetic pathway and the regulatory mechanisms that maintain cholesterol homeostasis.

Acyl Coenzyme A↗
PubMed1992

Researching and evaluating model geriatric mental health programs. Part III: Statistical analysis issues.

The third and final article in this three-part series on researching and evaluating geriatric mental health programs focuses on statistical analysis issues. Analysis of data from experimental and quasi-experimental studies is discussed involving inferential statistical techniques such as t test, analysis of variance, chi-square, and analysis of covariance, and interrupted time series techniques.

Aged↗
PubMed1992

Social support and depression in men during alcoholism treatment.

Psychiatric comorbidities have been shown to be important predictors of the outcome of alcoholism treatment. This study examines whether perceived lack of social support can be identified as an independent predictor of symptoms of depression experienced during alcoholism treatment over and above the effects of personality characteristics and the severity of alcohol and psychiatric history. We studied 189 alcoholic men in treatment at a rural midwestern Department of Veterans Affairs medical center. Multiple regression analyses found that reduced social support significantly predicted depression (measured by the Beck Depression Inventory) during treatment while controlling for personality characteristics and the alcoholism and psychiatric subscales of the Addiction Severity Index. Although self-esteem, neuroticism, and psychiatric severity also were significantly associated with depression in the hierarchical regression model, social support demonstrated the strongest unique contribution to depression of any of the predictors. These results suggest that social support has an independent association with depression and perhaps may play an important role in improving treatment compliance and the outcome of alcoholism treatment.

Adult↗
PubMed1992

Cloning of the human cholesterol 7 alpha-hydroxylase gene (CYP7) and localization to chromosome 8q11-q12.

Cholesterol 7 alpha-hydroxylase (7 alpha-hydroxylase) is a microsomal cytochrome P450 that catalyzes the first step in bile acid synthesis. In this paper, we describe the cloning, characterization, and chromosomal mapping of the human 7 alpha-hydroxylase gene (CYP7). The gene spans 10 kb and contains six exons and five introns. The exon-intron boundaries are completely conserved between the human and rat genes. Sequencing of the 5' flanking region revealed consensus recognition sequences for a number of liver-specific transcription factors. The human CYP7 gene was mapped to chromosome 8q11-q12 using both mouse-human somatic cell hybrids and in situ chromosomal hybridization studies. A total of four single-stranded conformation-dependent DNA polymorphisms and an Alu sequence-related polymorphism were identified. Of the individuals analyzed, 80% were heterozygous for at least one of these five polymorphisms. The localization and characterization of the human 7 alpha-hydroxylase gene, as well as the identification of polymorphisms, provide the molecular tools necessary to investigate the role of this gene in disorders of cholesterol and bile acid metabolism.

Amino Acid Sequence↗
PubMed1992

Genetic and pharmacological evidence for more than one human steroid 5 alpha-reductase.

The enzyme steroid 5 alpha-reductase catalyzes the conversion of testosterone into the more potent androgen, dihydrotestosterone, and impairment of this reaction causes a form of male pseudohermaphroditism in which genetic males differentiate predominantly as phenotypic females. We previously isolated cDNA clones that encode a human steroid 5 alpha-reductase enzyme. Here, we report molecular and genetic studies demonstrating that the gene encoding this cDNA is normal in subjects with the genetic disease steroid 5 alpha-reductase deficiency. We further show that in contrast to the major steroid 5 alpha-reductase in the prostate and cultured skin fibroblasts, the cDNA-encoded enzyme exhibits a neutral to basic pH optima and is much less sensitive to inhibition by the 4-aza steroid, finasteride (MK-906). The results provide genetic, biochemical, and pharmacological support for the existence of at least two steroid 5 alpha-reductase isozymes in man.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1992

Molecular genetics of steroid 5 alpha-reductase 2 deficiency.

Two isozymes of steroid 5 alpha-reductase encoded by separate loci catalyze the conversion of testosterone to dihydrotestosterone. Inherited defects in the type 2 isozyme lead to male pseudohermaphroditism in which affected males have a normal internal urogenital tract but external genitalia resembling those of a female. The 5 alpha-reductase type 2 gene (gene symbol SRD5A2) was cloned and shown to contain five exons and four introns. The gene was localized to chromosome 2 band p23 by somatic cell hybrid mapping and chromosomal in situ hybridization. Molecular analysis of the SRD5A2 gene resulted in the identification of 18 mutations in 11 homozygotes, 6 compound heterozygotes, and 4 inferred compound heterozygotes from 23 families with 5 alpha-reductase deficiency. 6 apparent recurrent mutations were detected in 19 different ethnic backgrounds. In two patients, the catalytic efficiency of the mutant enzymes correlated with the severity of the disease. The high proportion of compound heterozygotes suggests that the carrier frequency of mutations in the 5 alpha-reductase type 2 gene may be higher than previously thought.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1992

Social support and outcome of alcoholism treatment: an exploratory analysis.

Social support is becoming recognized as a positive influence on health and health maintenance. Forms of support which bolster the patient's sense of personal efficacy should enhance the alcoholic's ability to cope with a specific stressor (i.e., overcoming his or her addiction). Patients reporting higher levels of social support during alcoholism treatment, especially support that enhances his or her self-esteem, should therefore demonstrate improved outcome compared to patients with lower levels. Sixty-one consecutive admissions to an inpatient alcoholism treatment program at a rural midwestern medical center completed an assessment of six forms of social support (Guidance, Reliable Alliance, Reassurance of Worth, Opportunity for Nurturance, Attachment, and Social Integration) in terms of support obtained from family and friends and from the treatment environment. For each patient, additional information concerning age, marital status, financial support, and previous alcohol-related hospitalizations was also obtained. Outcome of treatment was measured by readmission for an alcohol-related diagnosis within 1 year of discharge. Survival analysis found that reassurance of worth from family and friends and number of previous hospitalizations were independent and significant predictors of time to readmission. Higher levels of reassurance of worth or esteem support significantly lengthened time to readmission, with the reverse relationship found for number of previous hospitalizations. These results suggest that specific sources (family and friends) and forms (reassurance of worth) of social support are important to the recovering alcoholic and that the effect of social support on treatment outcome is independent of the alcoholic's history of prior treatment failure. Interventions or program modifications should be designed specifically to bolster these facets of social support rather than addressing more general forms of support.

Adult↗
PubMed1991

Deletion of steroid 5 alpha-reductase 2 gene in male pseudohermaphroditism.

The conversion of testosterone into dihydrotestosterone by steroid 5 alpha-reductase is a key reaction in androgen action, and is essential both for the formation of the male phenotype during embryogenesis and for androgen-mediated growth of tissues such as the prostate. Single gene defects that impair this conversion lead to pseudohermaphroditism in which 46X,Y males have male internal urogenital tracts, but female external genitalia. We have described the isolation of a human 5 alpha-reductase complementary DNA from prostate. Subsequent cloning and genetic studies showed that this gene (designated 5 alpha-reductase 1) was normal in patients with 5 alpha-reductase deficiency. We report here the isolation of a second 5 alpha-reductase cDNA by expression cloning and the polymerase chain reaction. The biochemical and pharmacological properties of this cDNA-encoded enzyme (designated 5 alpha-reductase 2) are consistent with it being the major isozyme in genital tissue. A deletion in this gene is present in two related individuals with male pseudohermaphroditism caused by 5 alpha-reductase deficiency. These results verify the existence of at least two 5 alpha-reductases in man and provide insight into a fundamental hormone-mediated event in male sexual differentiation.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1991

Feed-forward control of prostate growth: dihydrotestosterone induces expression of its own biosynthetic enzyme, steroid 5 alpha-reductase.

Dihydrotestosterone, the primary mediator of prostate growth, is synthesized in target tissues from the circulating androgen testosterone through the action of steroid 5 alpha-reductase (EC 1.3.99.5). The expression of 5 alpha-reductase and the level of 5 alpha-reductase messenger RNA in rat ventral prostate are regulated by androgens. To determine whether this control is mediated by dihydrotestosterone or testosterone, we investigated the effect of finasteride, a potent inhibitor of steroid 5 alpha-reductase, on the expression of 5 alpha-reductase in the prostate. The administration of finasteride to intact rats for 7 days caused a 55% decrease in prostate weight and an 87% decrease in 5 alpha-reductase enzyme activity. Furthermore, the restoration of prostate growth after castration and the enhancement in 5 alpha-reductase enzyme activity and 5 alpha-reductase messenger RNA level by testosterone administration were blocked by finasteride, whereas the inhibitor had no effect on dihydrotestosterone-mediated increases in 5 alpha-reductase activity or messenger RNA level. These findings indicate that dihydrotestosterone itself controls prostate growth and 5 alpha-reductase activity. They further suggest that prostate growth is controlled by a feed-forward mechanism by which formation of trace amounts of dihydrotestosterone induces 5 alpha-reductase, thereby increasing dihydrotestosterone synthesis and triggering a positive developmental cascade.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1991

cDNA cloning and expression of the peptide-binding beta subunit of rat p21ras farnesyltransferase, the counterpart of yeast DPR1/RAM1.

Protein farnesyltransferase is a heterodimeric enzyme that attaches a farnesyl group to cysteine in ras proteins and other membrane-associated proteins. The beta subunit contains the recognition site for the peptide substrates, but is inactive in the absence of the alpha subunit. A cloned cDNA for the rat beta subunit predicts a protein of 437 amino acids whose mRNA is present in many tissues. Transfection of the beta subunit cDNA produced farnesyltransferase activity in human kidney cells, but only when it was transfected together with a cDNA encoding part of the alpha subunit. Each of the subunits appeared to be unstable in the transfected cells unless the other subunit was present. The rat beta subunit shows 37% sequence identity with the protein encoded by the yeast DPR1/RAM1 gene, indicating that DPR1/RAM1 is the yeast counterpart of the peptide-binding subunit of the mammalian farnesyltransferase.

Alkyl and Aryl Transferases↗
PubMed1991

Characterization of human sterol 27-hydroxylase. A mitochondrial cytochrome P-450 that catalyzes multiple oxidation reaction in bile acid biosynthesis.

The enzyme sterol 27-hydroxylase catalyzes the first step in the oxidation of the side chain of sterol intermediates in the bile acid synthesis pathway. Human sterol 27-hydroxylase cDNAs were isolated from a liver cDNA library by cross-hybridization with a previously cloned rabbit cDNA probe. DNA sequence analysis of hybridization-positive clones predicted a human sterol 27-hydroxylase consisting of a 33-amino-acid mitochondrial signal sequence followed by a mature protein of 498 amino acids. RNA blotting experiments demonstrated sterol 27-hydroxylase mRNAs of approximately 1.8 to 2.2 kilobases in liver and fibroblast cells. The steady state levels of the mRNA did not change when cultured cells were grown in the presence or absence of sterols. Introduction of the sterol 27-hydroxylase cDNA into Simian COS cells resulted in the expression of active enzyme capable of catalyzing multiple oxidation reactions (R-CH3----R-CH2OH----R-COOH) at carbon 27 of sterol intermediates of the bile acid synthesis pathway.

Amino Acid Sequence↗
PubMed1991

Mutations in the bile acid biosynthetic enzyme sterol 27-hydroxylase underlie cerebrotendinous xanthomatosis.

The sterol storage disorder cerebrotendinous xanthomatosis (CTX) is characterized by abnormal deposition of cholesterol and cholestanol in multiple tissues. Deposition in the central nervous system leads to neurological dysfunction marked by dementia, spinal cord paresis, and cerebellar ataxia. Deposition in other tissues causes tendon xanthomas, premature atherosclerosis, and cataracts. In two unrelated patients with CTX, we have identified different point mutations in the gene (CYP27) encoding sterol 27-hydroxylase, a key enzyme in the bile acid biosynthesis pathway. Transfection of mutant cDNAs into cultured cells results in the synthesis of immunoreactive sterol 27-hydroxylase protein with greatly diminished enzyme activity. We have localized the CYP27 gene to the q33-qter interval of human chromosome 2, and to mouse chromosome 1, in agreement with the autosomal recessive inheritance pattern of CTX. These findings underscore the essential role played by sterols in the central nervous system and suggest that mutations in other sterol metabolizing enzymes may contribute to diseases with neurological manifestations.

Animals↗
PubMed1991

Caffeine, a naturally occurring acaricide.

Since caffeine is a plant alkaloid that has been described as a naturally occurring insecticide, its acaricidal effect on Dermatophagoides pteronyssinus (Dp) was investigated. Twelve cultures were established by adding 30 Dp to 200 mg of Tetramin fish food and brewer's yeast (8:2 ratio); six cultures were treated with 20 mg of finely ground caffeine. All 12 cultures were incubated at 75% relative humidity, 25 degrees C, and observed during 8 weeks. Live mites were then counted under a stereoscope, cultures were extracted, and supernatants were analyzed for Der p I and Der f I allergen content with a two-site monoclonal RIA. Live mite counts in untreated cultures varied from 146 to 274 (215 +/- 47.1), and in caffeine-treated cultures from 0 to 3 (1 +/- 1.2; p less than or equal to 0.0001). Der p I concentrations in untreated cultures varied from 588 to 9000 ng/gm (3138.3 +/- 2990.8 ng/gm), and in caffeine-treated cultures from 52 to 117 ng/gm (78 +/- 23.8 ng/gm; p less than or equal to 0.01). Der p I was not detected in the food media or caffeine; Der f I was not detected in any of the cultures. Results demonstrate that caffeine inhibits mite growth and allergen production.

Acari↗
PubMed1991

Researching and evaluating model geriatric mental health programs, Part I: Design of mental health evaluation studies.

The first article in this three-part series on researching and evaluating geriatric mental health programs focuses on issues related to the design of studies for summative evaluations of geriatric mental health programs. Experimental and quasi-experimental designs are discussed in terms of their advantages and disadvantages, and threats to internal validity are highlighted.

Aged↗
PubMed1991

Characterization and chromosomal mapping of a human steroid 5 alpha-reductase gene and pseudogene and mapping of the mouse homologue.

The enzyme steroid 5 alpha-reductase catalyzes the conversion of testosterone into the more powerful androgen, dihydrotestosterone. We previously described the cloning of rat and human cDNAs that encode steroid 5 alpha-reductase and their expression in oocytes and cultured cells. Here, we report the isolation, characterization, and chromosomal mapping of two human steroid 5 alpha-reductase genes. One gene (symbol SRD5A1) is functional, contains five exons separated by four introns, and maps to the distal short arm of chromosome 5. Two informative restriction fragment length polymorphisms are present in exons 1 and 2 of this gene. A second gene (symbol SRD5AP1) has all of the hallmarks of a processed pseudogene and was mapped to the q24-qter region of the X chromosome. In the mouse, a single steroid 5 alpha-reductase gene (Srd5 alpha-1) is linked to Xmv-13 on chromosome 13.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗