Endocrine disruptors: Challenges and future directions in epidemiologic research.

Public concern about the impact of endocrine disrupting chemicals (EDCs) on both humans and the environment is growing steadily. Epidemiologic research provides key information towards our understanding of the relationship between environmental exposures like EDCs and human health outcomes. Intended for researchers in disciplines complementary to epidemiology, this paper highlights the importance and challenges of epidemiologic research in order to present the key elements pertaining to the design and interpretation of an epidemiologic study on EDCs. The conduct of observational studies on EDCs derives from a thoughtful research question, which will help determine the subsequent methodological choices surrounding the careful selection of the study population (including the comparison group), the adequate ascertainment of exposure(s) and outcome(s) of interest, and the application of methodological and statistical concepts more specific to epidemiology. The interpretation of epidemiologic results may be arduous due to the latency occurring between EDC exposure and certain outcome(s), the complexity in capturing EDC exposure(s), and traditional methodological and statistical issues that also deserve consideration (e.g., confounding, effect modification, non-monotonic responses). Moving forward, we strongly advocate for an integrative approach of expertise in the fields of epidemiology, exposure science, risk assessment and toxicology to adequately study the health risks associated with EDCs while tackling their challenges.

Yeast Ku as a regulator of chromosomal DNA end structure.

During telomere replication in yeast, chromosome ends acquire an S-phase-specific overhang of the guanosine-rich strand. Here it is shown that in cells lacking Ku, a heterodimeric protein involved in nonhomologous DNA end joining, these overhangs are present throughout the cell cycle. In vivo cross-linking experiments demonstrated that Ku is bound to telomeric DNA. These results show that Ku plays a direct role in establishing a normal DNA end structure on yeast chromosomes, conceivably by functioning as a terminus-binding factor. Because Ku-mediated DNA end joining involving telomeres would result in chromosome instability, our data also suggest that Ku has a distinct function when bound to telomeres.

LKB1 deficiency in T cells promotes the development of gastrointestinal polyposis.

Germline mutations in STK11, which encodes the tumor suppressor liver kinase B1 (LKB1), promote Peutz-Jeghers syndrome (PJS), a cancer predisposition syndrome characterized by the development of gastrointestinal (GI) polyps. Here, we report that heterozygous deletion of Stk11 in T cells (LThet mice) is sufficient to promote GI polyposis. Polyps from LThet mice, Stk11+/- mice, and human PJS patients display hallmarks of chronic inflammation, marked by inflammatory immune-cell infiltration, signal transducer and activator of transcription 3 (STAT3) activation, and increased expression of inflammatory factors associated with cancer progression [interleukin 6 (IL-6), IL-11, and CXCL2]. Targeting either T cells, IL-6, or STAT3 signaling reduced polyp growth in Stk11+/- animals. Our results identify LKB1-mediated inflammation as a tissue-extrinsic regulator of intestinal polyposis in PJS, suggesting possible therapeutic approaches by targeting deregulated inflammation in this disease.

Chronic PMA treatment of Jurkat T lymphocytes results in decreased protein tyrosine phosphorylation and inhibition of CD3- but not Ti-dependent antibody-triggered Ca2+ signaling.

We have treated Jurkat T lymphocytes with a concentration (160 nM) of phorbol myristyl acetate (PMA) that down-regulates conventional and novel protein kinase C (PKC) isozymes and we have investigated the effects on Ca2+ signaling and protein tyrosine phosphorylation using mAb (C305) directed against the beta-subunit of the Ti heterodimer or the epsilon/delta-component of the CD3 complex (mAb Leu 4 or OKT 3). The levels of expression of PKC alpha, betaI, betaII, and delta were reduced by 90% or more in PMA-treated cells, whereas the expression of PKCtheta decreased by approximately 30%. In contrast, the chronic treatment with PMA increased the expression of PKCepsilon and PKCzeta. There was a lack of Ca2+ response and myo-inositol trisphosphate (IP3) production in PMA-treated cells when they were exposed to mAb Leu 4 but the cells responded to mAb C305. The treatment with PMA did not affect the surface expression of Ti or CD3. The overall levels of tyrosine-phosphorylated proteins were markedly reduced in PMA-treated cells. We investigated whether these observations were related to defects in signal transduction related to protein tyrosine kinase (PTK) of the src and syk families. The electrophoretic mobilities of p59(fyn) or ZAP-70 were not changed in PMA-treated cells but p56(Ick) migrated as a large band of M(r) 60-62 kDa. The decreased mobility of p56(Ick) was related to a state of hyperphosphorylation. The activity of modified p56(Ick) was not up-regulated in activated Jurkat cells. Our data suggest that clonotypic Ti can trigger Ca2+ mobilization independently of conventional PKC isoforms. Our observations further suggest that conventional PKC isoforms are involved early in the cascade of events associated with Jurkat T lymphocyte activation.

[Migration, ethics and public health in Quebec]. / Migration, éthique et santé publique au Québec.

This article analyses the ethical issues of migration in relation to public health in Quebec. There are two objectives: to describe the progression of analysis of the migration phenomenon in public health over the last thirty years and to state the ethical debate it raises. The progression of analysis of the migration phenomenon has been characterised by various approaches: intercultural, acculturation, transcultural, and migratory journey. Although these approaches have contributed to the development of knowledge about the reality of immigration, they have also, in spite of themselves, generated stigmatisation, discrimination and the proliferation of prejudices. Generally, findings that have emerged when migration is taken into account indicate an imbalance of power. For some, to focus on the phenomenon of migration promotes the power imbalance while for others, to disregard it masks the issue.

[Cultural diversity in Montreal: a range of public health challenges]. / La diversité culturelle montréalaise: une diversité de défis pour la santé publique.

Increasing immigration to Quebec has brought to the surface the need for adapting its public health systems and services, particularly in the area of primary care. The challenge is to take the heterogeneous nature of the population into account and to integrate diverse values, experience and know-how into the development of programmes and delivery of services, whilst simultaneously respecting the values of the various care providers and the norms of the institutions in the host country. This article addresses the question of adaptation strategies for health services, and namely the development of prevention and heath promotion programmes in public health within the framework of primary health care services within the intercultural context of Montreal. The issue of adaptation falls within the perspective and mandate of the Quebec government's policy on health and well-being (La politique de santé et du bien-être, 1992). Furthermore, it is a response to frequent demands from various health professionals and groups concerned with the adaptation of public services with respect to intercultural relationships confronted with the emerging realities associated with immigration. The article provides a reflection on specific ways of adapting prevention and health promotion initiatives targeting cultural communities and those who are undergoing immigration procedures or transitions. It also examines the development of ethno-cultural or other indicators which make it possible to capture migration experiences and their health impact. Since the Quebec health and social services system is currently in the process of major reform, it is hoped that it will seize this opportunity in order to make health and social service centres accountable for the adaptation of their programmes and services to the diversity of the populations they serve.

Cytological and functional aspects of telomere maintenance.

The fact that eukaryotic chromosomes are linear poses a special problem for their maintenance: the natural ends of chromosomes must be distinguished from ends generated by chromosomal breakage and somehow, the chromosome ends must also be fully replicated to maintain their integrity. Telomeres, the complex structures at the ends of chromosomes are thought to be instrumental for both of these functions. However, recent insights in telomere biology suggest that these terminal structures do much more than just fulfill these two basic functions. Cytological data demonstrate that telomeres may play leading roles in chromatin organization and nuclear architecture during mitosis and meiosis. Moreover, non-functional telomeres may lead to genetic instability, a common prelude to cancer. Here, we review the basic functions of telomeres during chromosome replication and discuss the cytological aspects of telomere function during mitosis and meiosis.

The origin of forebrain afferents to the habenula in rat, cat and monkey.

Injections of horseradish peroxidase (HRP) involving the entire habenular complex in rat, cat and squirrel monkey (Saimiri sciureus) label (1) numerous cells in anterior lateral hypothalamic area, (2) a moderate number of cells in lateral preoptic area, substantia innominata, nucleus of diagonal band and postcommissural septum, and (3) a few cells in medial hypothalamus, ipsilaterally, in all three species. Some labeled cells also occur in corresponding regions contralaterally. The contribution of these limbic structures to the innervation of habenula is thus strikingly similar in the three groups. In contrast, significant species variations are found in respect to pallidal afferents. Whereas the entopeduncular nucleus in rat stands out as the main source of forebrain habenular afferents, the same structure in cat appears to contribute less substantially than adjoining lateral hypothalamus to the innervation of habenula. In monkey habenular afferents also arise principally from lateral hypothalamic neurons. At pallidal levels, labeled cells are nevertheless abundant in the rostral pole of primate internal pallidum. More caudally, they are found in significant number along internal and accessory medullary laminae where they intermingle with acetylcholinesterase-containing neurons which do not themselves project significantly upon habenula. This heterogeneous distribution of labeled pallidal cells indicates that the pallidohabenular projections in primate may arise, at least in part, from specific neuronal subpopulations within internal pallidum.

[Adequacy of health care services for young immigrant families]. / Adéquation des services de santé aux jeunes familles immigrantes.

This article relates the results of descriptive exploratory research conducted through interviews with 297 young immigrant families and 40 health and social workers on the primary health problems encountered by the families and on how they resolved these problems. Families and workers rank problems in different orders of priority. While families give priority to the health problems of their children, workers give priority to the problems encountered by the mothers, and in particular, mental health problems. Families and workers alike express a desire for help from the health and social service system for these problems. For families, this help would come from family doctors and nurses. These health providers are subsequently consulted; when they are not, language is determined to be the main obstacle to accessibility. Difficulties related to cultural compatibility of services are seen as more numerous by workers than by families.

[Health promotion for immigrant women in Quebec]. / Promotion de la santé en faveur des femmes immigrant au Québec.

Over the past fifteen years, the Canadian population has undergone increasing cultural diversification. Many researchers have investigated the role of culture with respect to social and health services. Most studies confirm the fact that increased cultural diversification related to immigration challenges the public health system in many ways. Certain groups, such as economically challenged immigrant women, may pose even greater problems to the health system. While these individuals are in relatively good health upon arrival to Canada, there is a need to ensure that adequate health promotion as well as disease prevention strategies are instituted. It is important to examine the concepts of health promotion and disease prevention through a cultural perspective. Little research has been done in this area. Concepts of promotion and prevention as they are understood by immigrants may not always coincide with North American or European definitions. Therefore, it is essential to consider life conditions that surround potential health promotion and prevention behaviors of immigrants. Empowerment, economic integration and acculturation are among the many factors that need to be taken into account when studying immigrants' health promotion behavior. Here, we present a critical analysis of current knowledge in this field. This is followed by research recommendations aimed at facilitating the development of health promotion and prevention strategies that are appropriate to the needs of Canadian, and more specifically of immigrant women in Québec.

[Exposure to the risk of traffic accidents, a fundamental epidemiological parameter, and one difficult to measure]. / L'exposition au risque d'accident de la route, un paramètre épidémiologique fondamental et difficile à mesurer.

This is a review of the literature dealing with exposure to the risk of traffic accidents. We present the principal definitions of this concept, the different measures of risk exposure, indicators of the risk of traffic accidents, and the advantages and disadvantages of the methods used for the collection of data. The validity of the measure of exposure to risk is analyzed as well. We conclude that while distance travelled is the principal measure of exposure to risk accepted by the research community, it is necessary to use a composite measure which also takes into account the risk associated with the driver.

The mistreatment of older adults: perpetrator-victim relationships and interventions.

ABSTRACT The characteristics of the mistreatment of older adults were investigated in a sample of 128 older adults identified as potential mistreatment cases in three community-based agencies in Quebec. Practitioners completed questionnaires to collect quantitative and qualitative data. The study also examined: (1) difficulties in identifying mistreatment, (2) interventions and outcomes, and (3) reasons for the refusal of services. The major finding (with important implications for practice) was the association between type of treatment and perpetrator relationship to victim. The harm reduction model is suggested as a useful approach to guide interventions.

Single-cell analysis of the t(14;18)(q32;q21) chromosomal translocation in Hodgkin's disease demonstrates the absence of this translocation in neoplastic Hodgkin and Reed-Sternberg cells.

Using the polymerase chain reaction (PCR) technique and total DNA extracts of Hodgkin's disease (HD)-involved lymph nodes, the t(14;18)(q32;q21) translocation was detected in 37 of 115 (32.2%) cases studied. No correlation was found between the presence of this translocation and bcl-2 protein expression in Hodgkin and Reed-Sternberg (HRS) cells detected by immunohistochemistry in 58 of 96 (60.4%) cases. To identify the cells carrying the t(14;18) translocation, single-cell DNA from HRS cells isolated by micromanipulation from frozen tissue sections of lymph nodes was investigated by PCR amplification. Eleven cases showing a positive band of the same size in at least two of five PCR experiments performed on the same total DNA extract were selected for single-cell PCR. We postulated that this repeated successful amplification could be indicative of the presence of the t(14;18) translocation in the neoplastic HRS cells. Single cells from frozen tumor sections of the t(14;18)-positive OCI LY8 cell line grafted into nude mice served as a positive control. The bcl-2/JH rearrangement, involved in this translocation, could be amplified from single-cell DNA of the latter tumor, whereas, in all of the HD cases, HRS cells were found to be negative. We conclude that the t(14;18) translocation is not localized in HRS cells, but in nonmalignant B bystander lymphocytes, admixed with these neoplastic cells.

Phorbol myristate acetate stimulates the formation of 5-oxo-6,8,11,14-eicosatetraenoic acid by human neutrophils by activating NADPH oxidase.

We have shown previously that human neutrophil microsomes contain a highly specific dehydrogenase which, in the presence of NADP+, converts 5S-hydroxy-6,8,11,14-eicosatetraenoic acid (5S-HETE) to its 5-oxo metabolite, 5-oxo-ETE, a potent agonist of these cells. However, intact neutrophils convert 5S-HETE principally to its omega-oxidation product, 5,20-diHETE, and to only small amounts of 5-oxo-ETE. Phorbol myristate acetate (PMA) dramatically shifts the metabolism of 5S-HETE by intact cells so that 5-oxo-ETE is the major metabolite. The objective of this investigation was to determine the mechanism for the stimulatory effect of PMA on 5-oxo-ETE formation. The possibility that oxidants released in response to PMA nonenzymatically oxidized 5S-HETE was ruled out, since PMA did not appreciably stimulate the formation of 5-oxo-ETE from 5R-HETE. On the other hand, inhibition of NADPH oxidase either by diphenylene iodonium or by mild heating nearly completely prevented the stimulatory effect of PMA on the formation of 5-oxo-ETE. The possibility that this effect was mediated by superoxide seems unlikely, since it was still observed, although somewhat attenuated, in the presence of superoxide dismutase. Moreover, superoxide generated by another mechanism (xanthine/xanthine oxidase) did not appreciably affect the formation of 5-oxo-ETE by neutrophils. However, phenazine methosulfate, which can nonenzymatically convert NADPH to NADP+, mimicked the effect of PMA on 5-oxo-ETE formation by intact neutrophils. It is concluded that PMA acts by activating NADPH oxidase, resulting in conversion of NADPH to NADP+, which enhances the formation of 5-oxo-ETE and reduces the formation of 5,20-diHETE. Serum-treated zymosan has an effect on the metabolism of 5S-HETE similar to that of PMA in that it also stimulates the formation of 5-oxo-ETE and inhibits that of 5,20-diHETE.

Effects of phorbol myristate acetate on the synthesis of 5-oxo-6,8,11,14-eicosatetraenoic acid by human polymorphonuclear leukocytes.

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a newly discovered chemotactic agent for human polymorphonuclear leukocytes (PMNL) which has potent stimulatory effects on cytosolic calcium levels in these cells. Although we have shown that it is synthesized from 5(S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) by a highly specific microsomal dehydrogenase, little is known about the synthesis of this substance by intact PMNL. In the present study we found that in contrast to PMNL microsomes, intact, unstimulated PMNL produced relatively small amounts of 5-oxo-ETE from 5-HETE, but instead converted 5-HETE primarily to its omega-oxidation product, 5,20-diHETE. However, preincubation of PMNL with phorbol myristate acetate (PMA; EC50, ca. 4 nM) dramatically increased the ratio of 5-oxo-ETE to 5,20-diHETE from 0.07 in its absence to 1.85 in the presence of 100 nM PMA. Both effects were completely reversed by staurosporine, indicated that they were mediated by a protein kinase. PMA also stimulated the formation of 5-oxo-ETE, 5-HETE, and leukotriene B4 (LTB4) from exogenous arachidonic acid. The greatest enhancement was observed for 5-oxo-ETE, which, under all conditions, was produced in greater quantities than LTB4. PMA stimulated the formation of 5-oxo-ETE by PMNL stimulated with either A23187 or zymosan. A23187-stimulated PMNL initially produced more LTB4 than 5-oxo-ETE, but at longer time points, 5-oxo-ETE predominated. These results demonstrate that PMA-activated human PMNL can synthesize substantial amounts of 5-oxo-ETE and raise the possibility that this substance may be an important inflammatory mediator.

Eotaxin and RANTES enhance 5-oxo-6,8,11,14-eicosatetraenoic acid-induced eosinophil chemotaxis.

BACKGROUND: The 5-lipoxygenase product 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a potent activator of human eosinophils and, among lipid mediators, is the most active chemoattractant for these cells. Studies have demonstrated the importance of 5-lipoxygenase products in allergen-induced pulmonary eosinophilia. Because CC chemokines such as eotaxin and RANTES also play critical roles in this phenomenon, it would seem likely that members of both classes of mediators contribute to this response. OBJECTIVE: The study was designed to directly compare the effects of 5-oxo-ETE on eosinophils with those of eotaxin and RANTES and to determine whether these chemokines could enhance the chemotactic response to 5-oxo-ETE. METHODS: Eosinophil chemotaxis was measured with microchemotaxis chambers. CD11b, L-selectin, and actin polymerization were measured by flow cytometry. Calcium mobilization was measured by fluorescence. RESULTS: 5-Oxo-ETE stimulated eosinophil chemotaxis with a potency between those of eotaxin and RANTES and a maximal response about 50% higher than that of eotaxin. Threshold concentrations of eotaxin and RANTES increased the chemotactic potency of 5-oxo-ETE by more than 4-fold. 5-Oxo-ETE and eotaxin were approximately equipotent in mobilizing cytosolic calcium in eosinophils. Eotaxin was more potent in inducing CD11b expression and actin polymerization, but the maximal responses to 5-oxo-ETE were about 50% higher. 5-Oxo-ETE strongly induced L-selectin shedding, whereas eotaxin elicited only a weak and variable response. CONCLUSION: 5-Oxo-ETE is a strong activator of human eosinophils with a chemotactic potency comparable to those of eotaxin and RANTES, both of wwhich enhance 5-oxo-ETE-induced chemotaxis. 5-Oxo-ETE and CC chemokines may combine to induce pulmonary eosinophilia in asthma.

Metabolism of 5(S)-hydroxyeicosanoids by a specific dehydrogenase in human neutrophils.

We have previously shown that human polymorphonuclear leukocytes (PMNL) convert 6-trans isomers of leukotriene B4 (LTB4) to 6,11-dihydro metabolites (Powell and Gravelle (1988) J. Biol. Chem. 263, 2170-2177). In the present study, we have shown that the first step in the formation of these dihydro metabolites is oxidation of the 5-hydroxyl group to a 5-oxo group, which is catalyzed by an NADP(+)-dependent microsomal dehydrogenase enzyme. All the dihydroxyeicosanoids we investigated which contained a 5(S)-hydroxyl group followed by a 6-trans double bond were good substrates for this reaction. However, LTB4, which contains a 6-cis double bond, was not metabolized to any detectable 5-oxo products. The preferred substrate for the dehydrogenase reaction is 5(S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5(S)-HETE), which has a Km of about 0.2 microM, compared to approx. 0.9 microM for 12-epi-6-trans-LTB4. In contrast to 5(S)-HETE, 5(R)-HETE as well as a variety of positional isomers of 5(S)-HETE are not metabolized to significant extents by the PMNL dehydrogenase. 5-Oxo-ETE and 5-oxo-15-hydroxy-ETE, which are formed from 5(S)-HETE and 5,15-diHETE, respectively, by this pathway, are potent chemotactic agents for human neutrophils, and raise intracellular calcium levels in these cells.

Formation of a 5-oxo metabolite of 5,8,11,14,17-eicosapentaenoic acid and its effects on human neutrophils and eosinophils.

We recently showed that human neutrophils convert arachidonic acid to its 5-oxo metabolite, 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE). 5-Oxo-ETE, which is synthesized by oxidation of 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) by a highly specific microsomal dehydrogenase, is a potent stimulator of human neutrophils and eosinophils. The objective of the current investigation was to determine whether neutrophils can convert 5,8,11,14,17-eicosapentaenoic acid (EPA) to its 5-oxo metabolite, 5-oxo-6,8,11,14,17-eicosapentaenoic acid (5-oxo-EPE) and, if so, to compare the biological activities of 5-oxo-EPE and 5-oxo-ETE. The two major eicosanoids formed by neutrophils incubated with EPA in the presence of A23187 were 5-hydroxy-6,8,11,14,17-eicosapentaenoic acid (5-HEPE) and 5-oxo-EPE. Smaller amounts of LTB5 and 20-hydroxy-LTB5 were also formed. Phorbol myristate acetate stimulated the formation of 5-oxo-EPE from both EPA and 5-HEPE. 5-HEPE and 5-HETE were equally good substrates for 5-hydroxyeicosanoid dehydrogenase (Km, ca. 0.85 microM; Vmax, ca. 1.4 pmol/min per microgram protein). 5-Oxo-EPE mobilized calcium in neutrophils with an EC50 of 36 nM, about 10 times higher than that of 5-oxo-ETE. 5-Oxo-EPE was also about one-tenth as active as 5-oxo-ETE in stimulating the migration of both human neutrophils and human eosinophils. It is concluded that 5-oxo-EPE is readily formed from EPA via 5-HEPE. However, it is only about one-tenth as potent as 5-oxo-ETE in stimulating human neutrophils and eosinophils. These results support the contention that EPA can alleviate certain inflammatory diseases by reducing the contribution of arachidonate-derived eicosanoids.

5-Oxo-6,8,11,14-eicosatetraenoic acid is a potent stimulator of human eosinophil migration.

Human neutrophils and monocytes contain a highly specific dehydrogenase which converts 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) to 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE). We have previously shown that 5-oxo-ETE is a potent stimulus of neutrophil calcium levels and migration and have now investigated its effects on human eosinophils. 5-Oxo-ETE is a potent stimulus of eosinophil migration, with significant effects being detected at concentrations as low as 1 nM and a maximal response at 1 microM. The responses elicited by 5-oxo-ETE were about two to three times greater than those to platelet-activating factor (PAF) and 5-oxo-15-hydroxy-6,8,11,13-eicosatetraenoic acid (5-oxo-15-hydroxy-ETE) at all concentrations tested between 10 nM and 1 microM. Leukotrienes B4 and D4 also significantly stimulated eosinophil migration, but the maximal responses to these agonists were only about 4% of the maximal response to 5-oxo-ETE. A low concentration of 5-oxo-ETE (1 nM) potentiated eosinophil migration in response to PAF. Eosinophils were capable of converting 5-HETE to 5-oxo-ETE, and this reaction was enhanced by phorbol myristate acetate. Stimulation of eosinophils with A23187 in the presence of low concentrations of arachidonic acid and phorbol 12-myristate 13-acetate led to the formation of 5-oxo-ETE and 5-oxo-15-hydroxy-ETE, but the amounts were considerably less than those of other eicosanoids such as leukotriene C4, cysteine-containing lipoxins, and 5,15-dihydroxy-6E,8Z,11Z,13E-eicosatetraenoic acid. In summary, of all the lipid mediators tested, 5-oxo-ETE was the most effective in stimulating migration of human eosinophils. Although eosinophils are capable of synthesizing 5-oxo-eicosanoids, the amounts detected were relatively small, and other leukocytes such as neutrophils, monocytes, or macrophages may be more important sites for the synthesis of this compound.

Metabolism of 5(S)-hydroxy-6,8,11,14-eicosatetraenoic acid and other 5(S)-hydroxyeicosanoids by a specific dehydrogenase in human polymorphonuclear leukocytes.

Human polymorphonuclear leukocytes (PMNL) convert 6-trans isomers of leukotriene B4 (LTB4) to dihydro metabolites (Powell, W.S., and Gravelle, F. (1988) J. Biol. Chem. 263, 2170-2177). In the present study we investigated the mechanism for the initial step in the formation of these products. We found that the 1,500 x g supernatant fraction from human PMNL converts 12-epi-6-trans-LTB4 to its 5-oxo metabolite which was identified by mass spectrometry and UV spectrophotometry. The latter compound was subsequently converted to the corresponding dihydro-oxo product, which was further metabolized to 6,11-dihydro-12-epi-6-trans-LTB4, which was the major product after longer incubation times. The 5-hydroxyeicosanoid dehydrogenase activity is localized in the microsomal fraction and requires NADP+ as a cofactor. These experiments therefore suggest that the initial step in the formation of dihydro metabolites of 6-trans isomers of LTB4 is oxidation of the 5-hydroxyl group by a microsomal dehydrogenase. Studies with a variety of substrates revealed that the microsomal dehydrogenase in human PMNL oxidizes the hydroxyl groups of a number of other eicosanoids which contain a 5(S)-hydroxyl group followed by a 6-trans double bond. There is little or no oxidation of hydroxyl groups in the 8-, 9-, 11-, 12-, or 15-positions of eicosanoids, or of the 5-hydroxyl group of LTB4, which has a 6-cis rather than a 6-trans double bond. The preferred substrate for this enzyme is 5(S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5(S)-HETE) (Km, 0.2 microM), which is converted to 5-oxo-6,8,11,14-eicosatetraenoic acid. Unlike 5(S)-HETE, 5(R)-HETE is a poor substrate for the 5(S)-hydroxyeicosanoid dehydrogenase, indicating that in addition to exhibiting a high degree of positional specificity, this enzyme is also highly stereospecific. In addition to 5(S)-HETE and 6-trans isomers of LTB4, 5,15-diHETE is also a good substrate for this enzyme, being converted to 5-oxo-15-hydroxy-6,8,11,13-eicosatetraenoic acid (5-oxo-15-hydroxy-ETE). The oxidation of 5(S)-HETE to 5-oxo-ETE is reversible since human PMNL microsomes stereospecifically reduce 5-oxo-ETE to the 5(S)-hydroxy compound in the presence of NADPH. 5-Oxo-ETE is formed rapidly from 5(S)-HETE by intact human PMNL, but because of the reversibility of the reaction, its concentration only reaches about 25% that of 5(S)-HETE.