Peripheral chemoreceptors tune inspiratory drive via tonic expiratory neuron hubs in the medullary ventral respiratory column network.

Models of brain stem ventral respiratory column (VRC) circuits typically emphasize populations of neurons, each active during a particular phase of the respiratory cycle. We have proposed that "tonic" pericolumnar expiratory (t-E) neurons tune breathing during baroreceptor-evoked reductions and central chemoreceptor-evoked enhancements of inspiratory (I) drive. The aims of this study were to further characterize the coordinated activity of t-E neurons and test the hypothesis that peripheral chemoreceptors also modulate drive via inhibition of t-E neurons and disinhibition of their inspiratory neuron targets. Spike trains of 828 VRC neurons were acquired by multielectrode arrays along with phrenic nerve signals from 22 decerebrate, vagotomized, neuromuscularly blocked, artificially ventilated adult cats. Forty-eight of 191 t-E neurons fired synchronously with another t-E neuron as indicated by cross-correlogram central peaks; 32 of the 39 synchronous pairs were elements of groups with mutual pairwise correlations. Gravitational clustering identified fluctuations in t-E neuron synchrony. A network model supported the prediction that inhibitory populations with spike synchrony reduce target neuron firing probabilities, resulting in offset or central correlogram troughs. In five animals, stimulation of carotid chemoreceptors evoked changes in the firing rates of 179 of 240 neurons. Thirty-two neuron pairs had correlogram troughs consistent with convergent and divergent t-E inhibition of I cells and disinhibitory enhancement of drive. Four of 10 t-E neurons that responded to sequential stimulation of peripheral and central chemoreceptors triggered 25 cross-correlograms with offset features. The results support the hypothesis that multiple afferent systems dynamically tune inspiratory drive in part via coordinated t-E neurons.

[Grey zone lymphomas: limitations of the classification of aggressive B-cell lymphomas]. / Grauzonenlymphome : Grenzbereiche der Klassifikation aggressiver B-Zell-Lymphome.

Grey zone lymphomas are lymphatic tumors that cannot be assigned to a defined lymphoma entity due to morphological, clinical or genetic reasons. As a defining criterion they present with features of two overlapping entities or features that are intermediate. Such lymphomas may represent a grey zone in the differentiation between indolent and aggressive lymphomas. Often they may show morphological features of one entity but be more related to another entity with respect to the immunophenotype and/or genetic constitution, such as lymphomas in the grey zone between primary mediastinal large B-cell lymphoma and primary nodal diffuse large B-cell lymphoma. The B-cell lymphoma, unclassified, with features intermediate between diffuse large B-cell lymphoma and Burkitt lymphoma has recently been recognized as a provisional category in the updated WHO 2008 classification of malignant lymphomas. This corresponds to a practical lymphoma category that obviously contains several entities with a Burkitt-like appearance and aggressive clinical behavior. Genetically, tumors in this category are frequently characterized by an atypical MYC translocation and complex karyotypic alterations. As yet, no adequate therapy concept exists.

[Diagnostics of acute leukemias: interaction of phenotypic and genetic methods]. / Diagnostik akuter Leukämien: Interaktion phänotypischer und genetischer Methoden.

Due to the heterogeneity of these disorders, the diagnosis of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) requires a broad spectrum of laboratory techniques: cytomorphology, immunophenotyping, chromosome banding analysis, fluorescence in situ hybridization, and molecular genetics. The cytomorphological leukemia subtypes can be indicative for distinct genetic alterations and contribute to the guidance of the further diagnostic process. Immunophenotyping allows to define the hematological lineage and to characterize the leukemia-associated immunophenotype as basis for follow up investigation. Cytogenetic alterations and molecular mutations are essential for the correct classification of cases and for prognostication. Molecular markers are helpful to define the minimal residual disease load after the achievement of hematological complete remission. In cases of hypocellular AML or in case of bone marrow necrosis, histopathology in combination with immunohistochemistry is of importance. Hierarchies between the different techniques catalyze the workflow in the laboratory and allow a rapid diagnosis and classification of the leukemia cases.

[Splenic marginal zone B cell lymphomas]. / Splenische Marginalzonen-B-Zell-Lymphome.

Splenic marginal zone B cell lymphomas (SMZBCL) are rare, organotypic, lymphoid neoplasms with distinct clinicopathological features. At initial presentation, the spleen, bone marrow and peripheral blood are usually involved, while generalized lymphadenopathy is only rarely observed. Molecularly, somatic hypermutation of IgVH genes can be detected in roughly half of the cases, and deletions in 7q are present in 45% of tumors. Approximately 10%-15% of SMZBCL do occur in the setting of chronic hepatitis C. This association underlines the importance of antigenic stimulation in the proliferation of the tumor cells in HCV-associated SMBCL, if not also in their classical counterparts. More recently, gene profiling studies using cDNA microarrays revealed a homogeneous expression profile in SMZBCL, thus further confirming the notion of a distinct tumor entity. The clinical course is indolent in the majority of cases; however, some patients follow a more aggressive clinical course, usually associated with some particular molecular features in these tumors, such as unmutated IgVH genes and 7q deletions.

The t(11;18)(q21;q21) chromosome translocation is a frequent and specific aberration in low-grade but not high-grade malignant non-Hodgkin's lymphomas of the mucosa-associated lymphoid tissue (MALT-) type.

Primary extranodal malignant non-Hodgkin's lymphoma arising from the mucosa-associated lymphoid tissue (MALT-type lymphoma) represents a subtype of B-cell lymphoid malignancies with distinct clinicopathological features and is often associated with a favorable prognosis. Unlike the situation in nodal non-Hodgkin's lymphoma of B-cell lineage, few data are still available concerning the chromosomal constitution of MALT-type lymphomas. Until now, cytogenetic data from 29 low-grade MALT lymphomas with karyotypic alterations have been reported from different institutions, and virtually no data were available for high-grade MALT-type lymphomas. We have analyzed the cytogenetics of 44 MALT lymphomas arising in the stomach, parotid gland, thyroid gland, lung, breast, and conjunctiva. Clonal chromosome aberrations have been detected in 13 of 20 (65%) low-grade and 20 of 24 (83%) high-grade tumors. More than half of the low-grade lymphomas with abnormal karyotypes (7 of 13 cases, 53%) displayed clonal t(11;18)(q21;q21), thus specifically associating this translocation with MALT-type lymphomas for the first time in a larger series. In contrast, t(11;18) was not found in a single case of 20 high-grade MALT-type lymphomas with abnormal karyotypes, nor were translocations t(14;18) or t(3;14), characterizing about 10-35% of primary nodal large cell lymphomas. Instead, these lymphomas were associated with t(8;14)(q24;q32) in three cases, frequent deletions in the long arm of chromosome 6, and partial or whole gains of chromosomes 3, 7, 17, 18, and 21.

Localized gastric non-Hodgkin's lymphoma of high-grade malignancy in patients with pre-existing chronic lymphocytic leukemia or immunocytoma.

Analyses for clonality in cases of Richter's syndrome have provided evidence for a clonal evolution of high-grade lymphoma in most patients, while in others an independent cellular clone seems to exist in the secondary neoplasm. Richter's syndrome with an isolated high-grade lymphoma of the stomach has been rarely reported in patients with pre-existing B cell chronic lymphocytic leukemia (CLL). We investigated four cases of CLL or lymphoplasmacytoid immunocytoma (LPIC) with development of a localized high-grade B cell lymphoma in the stomach. Southern blotting showed different rearrangements of the immunoglobulin light and heavy chain genes in the tumor cells of the low-grade lymphoma and the gastric tumor in two cases. Comparison of the DNA sequences of the CDR3 region of the immunoglobulin genes revealed different clones in another case. By means of chromosomal in situ hybridization, trisomy 3 was detected in two cases of high-grade lymphoma of the stomach, but not in the cells of the associated low-grade tumor. Our findings indicate that high-grade non-Hodgkin's lymphomas arising localized in the stomach of patients with CLL or immunocytoma are not clonally related to the pre-existing low-grade lymphoma and, therefore indeed, present true secondary neoplasms.

Structure of Bcl-1 and IgH-CDR3 rearrangements as clonal markers in mantle cell lymphomas.

Mantle cell lymphoma represent a clinicopathologically distinct entity of malignant non-Hodgkin's lymphoma (NHL) and are characterized by a specific chromosomal translocation t(11;14)(q13;q32) involving the cyclin D1 gene also designated as bcl-1/PRAD1 gene on chromosome 11 and the heavy chain immunoglobulin joining region on chromosome 14. We have established a PCR method to amplify t(11;14) junctional sequences in DNA from fresh frozen and paraffin-embedded tissue by bcl-1-specific primers in combination with a consensus immunoglobulin JH primer. A total of 65 cases histologically classified as mantle cell lymphoma (MCL) were analyzed for the presence of a t(11;14) translocation and monoclonal IgH-CDR3 rearrangements. From 26 patients with classical MCL and three cases with the anaplastic variant of MCL fresh frozen biopsy material was available for DNA extraction. We detected a bcl-1/JH rearrangement in 12 out of 29 samples (41%). In 36 cases paraffin-embedded lymph node tissue was the only source of DNA. In this material we found a bcl-1/JH rearrangement in six out of 31 samples with intact DNA (20%). To confirm the specificity of the PCR and to determine the bcl-1/JH junctional region sequences as clone-specific marker in individual patients we characterized the junctional DNA sequences by direct PCR sequencing in 16 cases. Interestingly we found that six bcl-1/JH junctions harbored DH segments in their N regions indicating that bcl-1/JH rearrangements can occur in a later stage of B cell ontogeny during which the complete VH to DH-JH joining or VH-replacement takes place. To investigate the suitability of IgH-CDR3 as sensitive molecular marker for those MCL patients in which a t(11;14) translocation can not easily be amplified, we additionally analysed 60 cases for the presence of monoclonally rearranged IgH genes by IgH-CDR3-PCR. A monoclonal IgH-CDR3 PCR product could be identified in 24 out of 29 fresh frozen samples (79%) whereas only 11 out of 31 samples (36%) with paraffin-derived DNA were positive. We demonstrate that automated fluorescence detection of monoclonal IgH-CDR3 PCR products allows the rapid and sensitive monitoring of minimal residual disease also in cases that lack a PCR amplifiable t(11;14) translocation. In combination with allele-specific primers the procedure may improve current experimental approaches for detection of occult MCL cells at initial staging and residual disease during and after therapy.

Differential diagnosis between classic Hodgkin's lymphoma, T-cell-rich B-cell lymphoma, and paragranuloma by paraffin immunohistochemistry.

There are significant difficulties in the differential diagnosis of lymphomas at the interface between classic Hodgkin's lymphoma and both paragranuloma and T-cell-rich B-cell lymphoma as well as at the interface between T-cell-rich B-cell lymphoma and paragranuloma. We therefore investigated 197 cases (155 classic Hodgkin's lymphomas, 32 T-cell-rich B-cell lymphomas, and 10 paragranulomas) by paraffin immunohistochemistry. Special interest was given to cases with a B-cell phenotype of tumor cells. The reactive inflammatory infiltrate in both classic Hodgkin's lymphoma and T-cell-rich B-cell lymphoma was rich in TIA-1-positive cytolytic lymphocytes, and CD57-positive cells were rarely encountered. In contrast, in paragranuloma CD57-positive cells and small B-lymphocytes predominated the background infiltrate. The tumor cells in cases of classic Hodgkin's lymphoma were positive for CD30 in 95%, for CD15 in 75%, and for CD20 in 22%. Apart from this, vimentin was expressed in >95% of the cases. All cases of T-cell-rich B-cell lymphoma were negative for vimentin, CD30, and CD15. The reactivity of the tumor cells for CD30, CD15, CD20, and vimentin together with the background reactivity for CD57 and TIA-1 seem to reliably discriminate between the entities and should therefore help to increase the interobserver reproducibility of diagnoses in the gray zone around Hodgkin's lymphoma.

Abdominal T-cell non-Hodgkin's lymphoma of the gamma/delta type in a patient with selective immunoglobulin A deficiency.

A 28-year-old man presented with selective immunoglobulin A deficiency and severe diarrhea responding to a gliadin-free diet. Biopsy samples of the small intestine showed dense T-cell infiltrations in the lamina propria and a slight increase of intraepithelial T-lymphocytes. No clonal rearrangement of the T-cell receptor c-beta chain genes was detectable by Southern blotting. Four years later, at the age of 32, the patient was hospitalized again with liver failure, abdominal lymphadenopathy, pancytopenia, and recurrent bacterial infections. Retrospective polymerase chain reaction analysis of formalin-fixed tissues of the intestinal biopsy samples obtained 4 years earlier showed monoclonal T-cell receptor gamma-chain gene rearrangement. Lymphoid cells of the peripheral blood showed an immunophenotype of CD3-positive gamma/delta T cells with a negativity for CD4 and CD8. A clonally rearranged T-cell receptor delta chain gene and a germline configuration of the c-beta chain genes was found by Southern blotting. Cytogenetics showed an abnormal karyotype with unbalanced translocations t(1;5) and t(9;13). The patient died of extensive lung infiltrations by gamma/delta T cells; autopsy showed a peripheral T-cell lymphoma of the gamma/delta type in the enlarged abdominal lymph nodes. This is the first report of an abdominal T-cell lymphoma of the gamma/delta type in a patient with selective immunoglobulin A deficiency.

Peripheral T-cell lymphoma with distinct perifollicular growth pattern: a distinct subtype of T-cell lymphoma?

Nine cases of peripheral T-cell lymphoma were identified in this study showing a distinctive growth pattern with partial distortion of the lymph node structure and prominent infiltration predominantly of marginal zones by medium-sized cells with clear cytoplasm and significant nuclear atypia. In the paracortical T-zone, there was a marked proliferation of high endothelial venules. Plasmocytosis and capsular fibrosis were other distinctive features. On immunohistochemistry, the lymphomas proved to be of T-helper cell origin (CD3+, CD4+, CD5+/-, CD8-, TIA1-) and proliferation was most prominent in the marginal zone of the regressive B-cell follicles. These cases have a characteristic morphology that may be sufficient to differentiate them as a variant from other peripheral T-cell lymphomas of the "not otherwise specified" group and to include them in the list of currently recognized lymphomas. Because of the distinct perifollicular growth pattern and incomplete effacement of the lymph node architecture, the differential diagnosis consists mainly of marginal zone B-cell lymphoma and reactive lesions.

Large cell anaplastic (KI-1) brain lymphoma of T-cell genotype.

Three cerebral lesions were neuroradiologically detected in a 63-year-old man without evidence of an extracranial neoplasm. The biopsy specimen from one lesion showed a large cell anaplastic lymphoma (LCAL). Immunohistochemically, tumor cells were positive for CD3, CD30, CD45RO, and HLA-DR. The polymerase chain reaction (PCR) of the rearranged T-cell receptor beta chain genome (TcR beta) derived from paraffin sections showed monoclonality. This case shows that primary cerebral T-cell lymphomas genotypically correspond to nodal T-cell lymphomas, a correspondence that has previously been demonstrated for the more common brain lymphomas of B-cell lineage.

Vaginal clear cell carcinoma in a young patient with ectopic termination of the left ureter in the vagina.

The association of clear cell adenocarcinoma of the vagina and vaginal adenosis with prenatal exposure to diethylstilbestrol (DES) is well-documented in the United States. In Europe, however, DES was never used in the therapy of threatened abortion and, therefore, clear cell adenocarcinoma and vaginal adenosis remained rare diseases. We report on the clinical and pathological features of a case of clear cell adenocarcinoma of the upper vagina in a 17-year-old German girl, who had a history of hypoplasia of the left kidney with an ectopic termination of the ureter in the upper vagina, removed surgically 2 years before. No previous report of a similar coincidence of vaginal clear cell carcinoma and a congenital disorder of the genitourinary tract exists. Congenital anomaly of the ureter interfering with the development and the differentiation of the distal Müllerian tract and its epithelium might have provided a similar histological basis for carcinogenesis in our patient to that in those provided exposed to DES.

The Epstein-Barr virus in malignant non-Hodgkin's lymphoma of the upper aerodigestive tract.

Sixty malignant non-Hodgkin's lymphomas originating in the upper aerodigestive tract have been analyzed for their cytologic type, immunophenotype and association with the Epstein-Barr virus (EBV). The majority of these tumors were B-cell lymphomas of blastic cytology (78%) with the exception of lymphomas in the parotid gland. Large B-cell lymphomas were the most frequent encountered in the sinonasal region and Waldeyer's ring. Twelve lymphomas were of T- or T/NK (natural killer)-cell lineage. They were in the nasal cavity and the paranasal sinuses (4), the tonsil (5), and the oral cavity (3). Epstein-Barr sequences were detected in five angiocentric T/NK-lymphomas, one peripheral T-cell lymphoma, one lymphoma of lymphomatoid granulomatosis type, one large B-cell lymphoma, and in a lymphoroliferative disorder in an HIV-positive patient. These results suggest that EBV is not involved in lymphomagenesis of B-cell tumors, but is associated with angiocentric T/NK-cell lymphoma in the upper aerodigestive tract.

Jumping translocation of 1q as the sole aberration in a case of follicular lymphoma.

Cytogenetic and fluorescence in situ hybridization (FISH) studies in a case of follicular lymphoma grade III showed a "jumping translocation" of chromosome 1q21-qter to chromosomes Xq28 and 18q23, which resulted in a partial trisomy 1q as the only chromosome aberration. This case represents, to the best of our knowledge, the first report of a jumping translocation in a malignant lymphoma occurring as the sole aberration.

Inverse correlation of cell proliferation and expression of progesterone receptors in tumor spheroids and monolayer cultures of human meningiomas.

OBJECTIVE: The progesterone receptor (PgR) can be detected in 60 to 70% of meningiomas using immunohistochemistry] in situ. Whereas in monolayer tissue cultures the PgR is only rarely expressed, we were able recently to demonstrate the preservation of the PgR in fragment spheroid cultures of meningiomas. The aim of the present study was to evaluate the stability of PgR expression in meningioma spheroids in vitro and the correlation of PgR expression and cell proliferation in spheroids and whether meningioma cells reaggregated to spheroids from monolayer cultures to reexpress the PgR again. METHODS: Tumor fragment spheroids (Weeks 1-6) and cell monolayers (Passages 1 and 3) of 15 PgR-positive meningiomas were investigated by immunohistochemistry for the expression of PgRs and their proliferative activity, as demonstrated by positivity for the proliferation-related antigen Ki-67. To study PgR reexpression in reaggregated spheroids, Northern blots were performed. In addition, a reverse transcriptase-polymerase chain reaction technique was established and evaluated in combination with immunohistochemistry. Growth of meningioma spheroids was quantified in the presence of progesterone and the specific antagonist onapristone. RESULTS: The PgR remained stable in spheroids for 6 weeks in 9 of 13 cases that were able to be evaluated. All tumor fragment spheroids exhibited a proliferation index of 5 to 40% Ki-67-positive cells. Monolayer cell cultures, on the other hand, failed to express PgRs but revealed higher proliferation indices (40-90%) to a significant extent. The detection of PgR messenger ribonucleic acid in reaggregated spheroids by means of reverse transcriptase-polymerase chain reaction correlated to the nuclear expression of PgR in immunohistochemistry. Neither progesterone nor its antagonist onapristone altered spheroid growth in vitro. CONCLUSION: The expression of the PgR in meningiomas is preserved in spheroid cultures with low proliferation indices for at least 6 weeks, whereas monolayer cell cultures with a high proliferative activity lack PgR expression. The inverse pattern of Ki-67-positive cells in the outer regions of the spheroids and PgR-expressing tumor cells in the spheroid centers leads us to the conclusion that proliferating meningioma tumor cells do not express PgRs. This might also explain why tumor cell growth in vitro was neither affected by progesterone nor by onapristone. Monolayer cell cultures can be reaggregated to spheroids, the consequence being a reexpression of PgRs and, therefore, a down-regulation of proliferation.

Progesterone receptors are detectable in tumor fragment spheroids of meningiomas in vitro.

Progesterone receptors (PgR) are hardly to be found in monolayer tissue culture of meningiomas although 60-70% of native tissue specimens are PgR positive. Thus we examined whether RgR might be detectable in fragment spheroids of meningiomas in vitro. 25 meningiomas of 17 women and 8 men were investigated as native tissue, monolayer cell culture (primary passage and passage 3) and as fragment spheroid culture after 1 and 3 weeks. 18/25 native tissue samples revealed the PgR. There was no prevalence of sex or histological subtypes discernible. PgR was preserved in cell clumps of the primary passage but was completely lost when cells grew as monolayers (primary passage and passage 3). 21 meningiomas formed spheroids in vitro. In 8 out of 15 native PgR positive tumors the fragment spheroids showed PgR on cryosections after 1 and 3 weeks of culture. We conclude that PgR are preserved in a considerable amount of tumor fragment spheroids of meningiomas in contrast to monolayer culture. Thus spheroids seem to be a suitable tool to investigate progesterone/anti-progesterone effects in meningiomas in vitro.

Progesterone receptors in tumor fragment spheroids of human meningiomas.

Progesterone receptors (PgR) are detectable in about 60-70% of tissue specimens of human meningiomas. Despite these data, PgR are hardly to be found in monolayer tissue culture of meningiomas. Aim of this study was to elucidate whether PgR might be preserved in tumor fragment spheroids of meningiomas maintained in organ culture since the morphological appearance of the original tumor is preserved by this culture technique. Aliquots of meningioma specimens of 25 patients (17 females) were snap frozen in liquid nitrogen immediately after removal. Additionally, monolayer tissue cultures of the same specimen were obtained as primary culture and passage #3. Tumor fragment spheroids were kept on medium-agar with liquid medium overlay and harvested after 1 and 3 weeks in culture. PgR were detected by immunohistochemistry using a rat monoclonal antibody. 18/25 meningioma tissue specimens were positive for PgR. In 8 out of 15 PgR-positive tumors which formed spheroids we could detect PgR in fragment spheroids after 1 and 3 weeks in culture. In contrast, none of the monolayers depicted PgR. PgR is preserved in a considerable amount of tumor fragment spheroids of PgR-positive meningiomas. They remain detectable after 3 weeks of culture whereas monolayer tissue cultures are PgR-negative. Thus, tumor fragment spheroids seem to be a suitable tool to investigate progesterone/antiprogesterone effects in vitro.

Pulmonary leiomyosarcoma mimicking glomus tumor at first biopsy and surgically treated with isolated left main bronchus resection: rare clinical documentation.

Soft tissue tumors originating within the endobronchial tree are extremely rare and most of them correspond to lipomas or leiomyomas. We here report a rare clinical presentation of leiomyosarcoma mimicking glomus tumor at initial biopsy arising from the left main bronchial trunk leading to left lower lobe atelectasis. Primary leiomyosarcoma of the lung is an unusual malignancy. Among this entity, the endobronchial form is very rare and the preoperative diagnosis is extremely difficult. We documented two different presentations and outcomes of primary endobronchial leiomyosarcoma of the lung. In this clinical presentation, histological study and immunohistochemical stain of the surgical resection provided the final diagnosis. Through the following we present the diagnostic and therapeutic difficulties encountered with endobronchial leiomyosarcoma.

Sex differences in hexachlorobutadiene biotransformation and nephrotoxicity.

Hexachlorobutadiene is nephrotoxic in rats, causing damage to the proximale tubules. Renal toxicity is presumed to be due to bioactivation by glutathione S-conjugate formation. Hexachlorobutadiene is conjugated with glutathione to S-(1,2,3,4,4-pentachlorobutadienyl)glutathione and further transformed to S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine (PCBC), which is N-acetylated in the liver to form N-acetyl-S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine (N-ac-PCBC). N-ac-PCBC is accumulated in the kidney. Renal acylases cleave N-ac-PCBC to PCBC, which is a substrate for renal cysteine conjugate beta-lyase and transformed to a reactive thioketene. Binding of this intermediate to renal macromolecules is most likely responsible for the nephrotoxicity of hexachlorobutadiene. In this study, we administered [14C]HCBD (200 mg/kg, per gavage) to male and female Wistar rats and compared the distribution and biotransformation. No significant differences in the disposition and rates of excretion of [14C]hexachlorobutadiene-derived radioactivity were observed between male and female rats. A portion of the dose (15.6 +/- 4.2) was excreted in the feces and 3.1% ( +/- 0.7) in the urine of male rats, and 11.1% ( +/- 3.8) of the dose was excreted in the feces and 4.5% ( +/- 1.5) in the urine of female rats. The major metabolite excreted by female rats was N-ac-PCBC, while small amounts of PCBC were also detected. In the urine of male rats, in addition to small amounts of PCBC and N-ac-PCBC, N-acetyl-S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine sulfoxide and [14C]hexachlorobutadiene were identified. Formation of the electrophile N-ac-PCBC sulfoxide must be considered as an alternative, beta-lyase-independent, bioactivation pathway for hexachlorobutadiene-derived S-conjugates. In isolated rat renal tubular cells, N-ac-PCBC sulfoxide induced a significantly more marked loss in cell viability than N-ac-PCBC. After identical doses of hexachlorobutadiene, the extent of necrosis to the pars recta of the proximal tubules was increased in male rats compared to the necrotic changes in female rats. While female animals showed a normal liver histology, male rats revealed slight toxic centrilobular liver changes in addition to the renal necroses. In vitro, only liver microsomes from male rats catalyzed the formation of N-ac-PCBC sulfoxide from N-ac-PCBC. Our results describe a new pathway of hexachlorobutadiene biotransformation in male rats, the formation of a mercapturic acid sulfoxide. The formation of this Michael acceptor may contribute to sex differences in hexachlorobutadiene nephrotoxicity.