Response durability after cessation of immune checkpoint inhibitors in patients with metastatic Merkel cell carcinoma: a retrospective multicenter DeCOG study.

BACKGROUND: Immune checkpoint inhibitors (ICI) have led to a prolongation of progression-free and overall survival in patients with metastatic Merkel cell carcinoma (MCC). However, immune-mediated adverse events due to ICI therapy are common and often lead to treatment discontinuation. The response duration after cessation of ICI treatment is unknown. Hence, this study aimed to investigate the time to relapse after discontinuation of ICI in MCC patients. METHODS: We analyzed 20 patients with metastatic MCC who have been retrospectively enrolled at eleven skin cancer centers in Germany. These patients have received ICI therapy and showed as best overall response (BOR) at least a stable disease (SD) upon ICI therapy. All patients have discontinued ICI therapy for other reasons than disease progression. Data on treatment duration, tumor response, treatment cessation, response durability, and tumor relapse were recorded. RESULTS: Overall, 12 of 20 patients (60%) with MCC relapsed after discontinuation of ICI. The median response durability was 10.0 months. Complete response (CR) as BOR to ICI-treatment was observed in six patients, partial response (PR) in eleven, and SD in three patients. Disease progression was less frequent in patients with CR (2/6 patients relapsed) as compared to patients with PR (7/11) and SD (3/3), albeit the effect of initial BOR on the response durability was below statistical significance. The median duration of ICI therapy was 10.0 months. Our results did not show a correlation between treatment duration and the risk of relapse after treatment withdrawal. Major reasons for discontinuation of ICI therapy were CR (20%), adverse events (35%), fatigue (20%), or patient decision (25%). Discontinuation of ICI due to adverse events resulted in progressive disease (PD) in 71% of patients regardless of the initial response. A re-induction of ICI was initiated in 8 patients upon tumor progression. We observed a renewed tumor response in 4 of these 8 patients. Notably, all 4 patients showed an initial BOR of at least PR. CONCLUSION: Our results from this contemporary cohort of patients with metastatic MCC indicate that MCC patients are at higher risk of relapse after discontinuation of ICI as compared to melanoma patients. Notably, the risk of disease progression after discontinuation of ICI treatment is lower in patients with initial CR (33%) as compared to patients with initial PR (66%) or SD (100%). Upon tumor progression, re-induction of ICI is a feasible option. Our data suggest that the BOR to initial ICI therapy might be a potential predictive clinical marker for a successful re-induction.

Enhancement of electron-phonon coupling in Cs-overlayered intercalated bilayer graphene.

We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on cesium (Cs) intercalated bilayer graphene with a Cs overlayer (Cs-C8CsC8). Low-energy electron diffraction shows a (2 × 2) pattern consistent with intercalation of a Cs layer similar to bulk C8Cs, in addition to the signature of a nearly commensurate superstructure created by the Cs overlayer. ARPES results reveal folding of the π bands due to the periodic (2 × 2) potential of the intercalated Cs atoms, together with a free-electron-like state at the [Formula: see text] point. Significant mass renormalization is observed in the band dispersion near the Fermi level, indicative of strong electron-phonon coupling. Based on analysis of the self-energy, we find anisotropic electron-phonon coupling with an estimated strength of [Formula: see text] ± 0.02 in the K-[Formula: see text] direction, and [Formula: see text] in the K-M direction. This coupling is much larger than that of other doped graphenes, and comparable to superconducting bulk GICs. We attribute this large electron-phonon coupling constant to the presence of the Cs overlayer, which highly dopes [Formula: see text] bands, and creates a structure similar to stage-I graphite intercalation compounds.

Sustained nitric oxide production in macrophages requires the arginine transporter CAT2.

The aberrant production of nitric oxide (NO) contributes to the pathogenesis of diseases as diverse as cancer and arthritis. Sustained NO production via the inducible enzyme, nitric-oxide synthase 2 (NOS2), requires extracellular arginine uptake. Three closely related cationic amino acid transporter genes (Cat1-3) encode the transporters that mediate most arginine uptake in mammalian cells. Because CAT2 is induced coordinately with NOS2 in numerous cell types, we investigated a possible role for CAT2-mediated arginine transport in regulating NO production. The complexity of arginine transport systems and their biochemically similar transport properties called for a genetic approach to determine the role of CAT2. CAT2-deficient mice were generated and found to be healthy and fertile in contrast to Cat1(-/-) animals. Analysis of cytokine-activated macrophages from Cat2(-/-) mice revealed a 92% reduction in NO production and a 95% reduction in l-Arg uptake. The reduction in NO production was not due to differences in NOS2 protein expression, NOS2 activity, or intracellular l-arginine content. In conclusion, our results show that sustained abundant NO synthesis by macrophages requires arginine transport via the CAT2 transporter.

Normal reproductive and macrophage function in Pem homeobox gene-deficient mice.

Interaction between germ cells and the supporting somatic cells guides many of the differentiative processes of gametogenesis. The expression pattern of the Pem homeobox gene suggests that it may mediate specific inductive events in murine reproductive tissues. During gestation, Pem is expressed in migrating and early postmigratory primordial germ cells, as well as in all embryo-derived extraembryonic membranes. Pem expression ceases in the germline after Embryonic Day 14 in both sexes and then reappears postnatally in the supporting cells of the gonad. In mature mice, Pem is produced by testicular Sertoli cells during stages VI-VIII of spermatogenesis and transiently by ovarian granulosa cells lining periovulatory follicles. Despite this tightly regulated reproductive expression pattern, mice with a targeted mutation in Pem have normal fecundity, with no detectable alteration in extraembryonic testicular or ovarian development or function. We also show that Pem is expressed throughout embryonic and adult development in a subset of a tissue-specific class of macrophages, Kupffer cells, as well as in a localized fraction of cells in macrophage cell lines. Although the number of Pem-positive Kupffer cells increases in mice treated with lipopolysaccharide, loss of Pem does not detectably interfere with the cells' ability to induce iNOS expression, demonstrating this Kupffer cell function does not require Pem. No differences were observed between Pem-knockout mice in 129, C57BL6/J, or mixed genetic backgrounds. Together, these data show that Pem is dispensable for embryonic and postnatal development, gonadal function, and Kupffer cell activation, perhaps due to compensatory expression of a similar homeobox gene.

Effect of a new rifamycin derivative, rifalazil, on liver microsomal enzyme induction in rat and dog.

1. The effect of a new rifamycin derivative, rifalazil (KRM-1648), on liver microsomal enzyme induction was studied in rat and dog with repeated oral administration of the compound. Relative liver weight, cytochrome b5 and P450 contents, enzyme activities of NADPH-cytochrome c reductase, aniline hydroxylase, p-nitroanisole O-demethylase, aminopyrine N-demethylase, and erythromycin N-demethylase were measured. 2. In rat, rifalazil treatment at 300 mg/kg/day for 10 days increased cytochrome b5 content but it did not affect liver weight, P450 content or enzyme activities. In contrast, rifampicin and rifabutin increased relative liver weights, cytochrome contents and enzyme activities under similar conditions. 3. In dog, rifalazil did not affect any parameters at 30 or 300 mg/kg/day for 13 weeks. 4. These findings indicate that rifalazil is not an enzyme inducer in rat and dog. This property differs from other rifamycin derivatives such as rifampicin and rifabutin.

Recurrent toxin-mediated perineal erythema.

BACKGROUND: Important new diseases due to bacterial toxins functioning as superantigens have been described with increasing frequency within recent years. Toxic shock syndrome, recalcitrant erythematous desquamating disorder, streptococcal toxic shock-like syndrome, and, most recently, mucocutaneous lymph node syndrome (Kawasaki disease) have been etiologically linked with certain staphylococcal and streptococcal toxins. We describe two patients with a novel clinical presentation of toxin-mediated disease, which shares certain clinical features with mucocutaneous lymph node syndrome. OBSERVATIONS: Two otherwise healthy young male adults developed recurrent erysipelaslike perineal erythema, which regularly erupted within 1 to 2 days of the onset of acute pharyngitis. Accompanying signs included mucosal changes and acral erythema with desquamation. Throat cultures obtained during the acute episodes yielded toxin-producing Staphylococcus aureus from one patient and toxin-producing Streptococcus pyogenes from the other. CONCLUSION: The recurrent nature, age predilection, and clinical presentation suggest that our patients display a unique clinical syndrome due to toxin-producing bacteria.

A mammalian arginine/lysine transporter uses multiple promoters.

The mCAT-2 gene encodes a Na(+)-independent cationic amino acid (AA) transporter that is inducibly expressed in a tissue-specific manner in various physiological conditions. When mCAT-2 protein is expressed in Xenopus oocytes, the elicited AA transport properties are similar to the biochemically defined transport system y+. The mCAT-2 protein sequence is closely related to another cationic AA transporter (mCAT-1); these related proteins elicit virtually identical cationic AA transport in Xenopus oocytes. The two genes differ in their tissue expression and induction patterns. Here we report the presence of diverse 5' untranslated region (UTR) sequences in mCAT-2 transcripts. Sequence analysis of 22 independent mCAT-2 cDNA clones reveals that the cDNA sequences converge precisely 16 bp 5' of the initiator AUG codon. Moreover, analysis of genomic clones shows that the mCAT-2 gene 5'UTR exons are dispersed over 18 kb. Classical promoter and enhancer elements are present in appropriate positions 5' of the exons and their utilization results in regulated mCAT-2 mRNA accumulation in skeletal muscle and liver following partial hepatectomy. The isoform adjacent to the most distal promoter is found in all tissues and cell types previously shown to express mCAT-2, while the other 5' UTR isoforms are more tissue specific in their expression. Utilization of some or all of five putative promoters was documented in lymphoma cell clones, liver, and skeletal muscle. TATA-containing and (G+C)-rich TATA-less promoters appear to control mCAT-2 gene expression. The data indicate that the several distinct 5' mCAT-2 mRNA isoforms result from transcriptional initiation at distinct promoters and permit flexible transcriptional regulation of this cationic AA transporter gene.

Toxicity of the protein kinase C inhibitor safingol administered alone and in combination with chemotherapeutic agents.

Safingol [(2S,3S)-2-amino-1,3-octadecanediol] potentiates the toxicity of doxorubicin (DOX) and cisplatin (CIS) against tumor cells in vitro and in vivo. The present studies were conducted in rats and dogs to evaluate safingol toxicity when administered i.v. as a single agent and to evaluate safingol's ability to potentiate the toxicity of established chemotherapeutic agents to normal tissues in vivo. In an escalating dose study, dogs were administered safingol i.v. at 5, 10, 20, 30, 40, and 75 mg/kg on Days 1 through 6. Necropsies were performed on Day 7. Red urine was observed at 10 mg/kg and higher. Icterus was observed following 40 mg/kg with additional signs of hypoactivity and anorexia occurring after 75 mg/kg. Clinical and microscopic pathology revealed marked hepatotoxicity, venous degeneration and necrosis at injection sites, and evidence of intravascular hemolysis. Doses of 5, 20, or 40 mg safingol/kg were utilized in single i.v. dose rat and dog studies. No evidence of adverse systemic toxicity was seen up to 20 mg/kg in either species [for rats: Cmax = 12,600 (males) or 17,133 (females) ng/ml, AUC = 3853 (males) or 4365 (females) ng x hr/ml; for dogs: Cmax = 2533 ng/ml, AUC = 2851 ng x hr/ml (no sex differences)]. Local effects of venous irritation or intravascular hemolysis were observed at all doses in rats and at 20 and 40 mg/kg in dogs. A dose of 40 mg/kg [for rats: Cmax = 31,233 (males) or 91,300 (females) ng/ml, AUC = 11,519 (males) or 18,620 (females) ng x hr/ml; for dogs: Cmax = 9033 ng/ml, AUC = 11,094 ng x hr/ml (combined sex)] was associated with clinical pathologic and renal histomorphologic changes considered consequent to intravascular hemolysis in both species, lethality and testicular toxicity in rats, and clinical biochemical changes indicative of hepatobiliary injury in dogs. Studies indicated that hemolysis occurred during infusion, was not caused by circulating levels of safingol, and was a function of dose concentration and vein of delivery. Safingol at 10 or 20 mg/kg was administered i.v. to rats 30-60 min prior to myelosuppressive i.v. doses of DOX, CIS, or cyclophosphamide (CYP). Hematology, plus renal function and morphology for CIS-treated animals, was assessed 4 and 14 days later.(ABSTRACT TRUNCATED AT 400 WORDS)

The Pem homeobox gene is X-linked and exclusively expressed in extraembryonic tissues during early murine development.

We previously reported the isolation of a cDNA clone for a homeobox-containing gene designated Pem, shown by Northern analysis of Day 7 through Day 16 mouse embryos to be expressed in extraembryonic tissues. In this study, Pem gene expression was further examined using in situ hybridization and immunocytochemistry to determine the spatial distribution of Pem transcripts and protein in peri-implantation embryos and in embryoid bodies (EBs). Low amounts of Pem mRNA were detected in undifferentiated EBs. When EBs were induced to differentiate, the outer cell layer of visceral or parietal endoderm expressed both Pem mRNA and protein. In developing embryos, no Pem protein was detectable in the uncompacted morula; 12% of the nuclei in compacted morulae were Pem positive, while 25% of the blastocyst trophectoderm and 15% of inner cell mass cells expressed Pem protein. Shortly after implantation, in 5.5 and 6.5 d.p.c. embryos, Pem expression was limited to extraembryonic tissues and was present in distal and proximal visceral endoderm, parietal endoderm, and ectoplacental cone. By 7.5-8.5 d.p.c. neither Pem RNA nor protein was found in the distal squamous visceral endoderm, which surrounds the embryonic region of the egg cylinder, nor in the parietal endoderm. Expression was retained in the proximal columnar epithelium of the visceral endoderm. Prominent Pem expression was observed in the chorion, in trophoblast-derived cells of the ectoplacental cone, and in secondary giant cells, localized in the nuclear compartment. Pem was localized to the X chromosome and found to be expressed in cell lineages where only the maternal X chromosome is active. The data indicate a possible role for Pem in regulating genes involved in the differentiation of extraembryonic tissues.

A novel oncofetal gene is expressed in a stage-specific manner in murine embryonic development.

A novel cDNA clone obtained from a murine T-lymphoma library hybridizes to transcripts expressed in placenta and embryos (Pem) in a stage-specific manner. The Pem cDNA sequence predicts an intracellular hydrophilic protein with no significant sequence similarity to other DNA or protein sequences. Pem transcripts are abundant in 7- and 8-day mouse embryos, but decrease precipitously thereafter. On Day 9 they become abundant in placenta and yolk sac, persisting there until parturition. Although Pem transcripts are present in immortalized and tumorigenic cell lines from several different cell lineages, they are not detectable in any of 15 adult tissues tested. The expression of Pem during fetal development and its presence in immortalized and neoplastic cell lines is consistent with the properties expected of an "oncofetal" gene.

Inhibition of testicular steroidogenesis in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated rats: evidence that the key lesion occurs prior to or during pregnenolone formation.

The mechanism by which 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) treatment decreases testosterone (T) secretion without significantly altering plasma luteinizing hormone (LH) concentrations was investigated. Testes from sexually mature Sprague-Dawley rats dosed 7 days earlier with 100 micrograms TCDD/kg secreted 30-75% less T than did testes from control rats when perfused in vitro with the LH analog human chorionic gonadotropin (hCG). This decrease confirms that testicular responsiveness to LH, the hormone which regulates T secretion in vivo, is impaired by TCDD treatment. Because TCDD also reduced intratesticular T content, the decrease in T secretion is due to an inhibition of T synthesis rather than to a failure of the secretion process. These effects of TCDD are not secondary to undernutrition, because perfused testes from feed-restricted control rats were fully hCG responsive. TCDD treatment neither increased the hCG-stimulated secretion of any T precursor nor significantly decreased the efficiency with which testes converted the pregnenolone (PREG) they synthesized into T (PREG is the initial steroidogenic intermediate). In addition, TCDD did not inhibit T secretion when steroidogenesis was supported by exogenous PREG at approximately the in vivo rate. We conclude that TCDD does not inhibit the conversion of PREG to T. The inhibition of T biosynthesis must instead result from an inhibition of PREG formation. The finding that TCDD treatment substantially decreased the rate at which hCG-perfused testes secreted PREG and its metabolites (a decrease seen across all hCG concentrations) confirms this conclusion. This inhibition of LH/hCG-stimulated PREG formation by TCDD must be due to a reduction in the activity of the enzyme which converts cholesterol to PREG (cytochrome P450scc), and/or an impairment in the multistep process responsible for mobilizing cholesterol to this enzyme.

Species differences in 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity and biotransformation in fish.

Rainbow trout, yellow perch, carp, bluegill, largemouth bass, and bullhead were treated with graded doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 1, 5, 25, or 125 micrograms/kg) or vehicle, ip. The lethal potency of TCDD tended to be greater in yellow perch, carp, and bullhead than in the other three species (LD50 80 days post-treatment, 3-5 versus 10-16 micrograms/kg, respectively). All species treated with the highest dose of TCDD (125 micrograms/kg) displayed a latency period of 1-4 weeks prior to death; longer latency periods were produced by lower lethal doses. Effects of TCDD treatment on body weight were both species-dependent and dose-dependent. Fin necrosis was observed in all fish species; however, cutaneous hemorrhage was observed only in TCDD-treated perch, carp, and bluegill, and cutaneous hyperpigmentation only in TCDD-treated carp and largemouth bass. Gallbladder bile was analyzed for TCDD and its metabolites 7 days after fish were injected with [14C]TCDD (60 micrograms/kg, ip). At least three TCDD metabolites in addition to the parent compound were found in the gallbladder bile of all six species. In addition, the retention time of the major biliary TCDD metabolite (determined by HPLC) was similar in all species except yellow perch. Beta-Glucuronidase treatment of the bile from largemouth bass and bluegill suggested that at least two of the TCDD metabolites were glucuronide conjugates. Thus, species differences exist in the lethal potency, signs of overt toxicity, and biotransformation of TCDD among freshwater fish.

Morphologic lesions and acute toxicity in rainbow trout (Salmo gairdneri) treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin.

To determine effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on growth, mortality, and morphologic lesions in rainbow trout, juvenile Shasta or Wytheville strain fish, obtained from 4 hatcheries, were administered graded single doses of TCDD, 0.1-125 micrograms/kg, ip. TCDD doses of 25 and 125 micrograms/kg caused 85% lethality 2-4 wk after treatment. At these high doses, death occurred before body weight loss could be detected. A lower dose of 5 micrograms/kg caused decreased growth and cumulative mortality of 20% after 11 wk. Stress associated with netting and weighing the fish at weekly intervals significantly shortened the delay period prior to TCDD-induced lethality. Gross and microscopic lesions were evident in rainbow trout treated with 10 micrograms TCDD/kg, but not in fish treated with 1 or 0.1 microgram/kg. Morphologic lesions occurred consistently in epithelial and lymphomyeloid tissues of TCDD-treated fish. Lymphomyeloid lesions included thymic involution, splenic lymphoid depletion, and hypocellularity of hematopoietic tissues in the head kidney and trunk kidney. In association with decreased hematopoiesis, peripheral leukopenia and thrombocytopenia occurred in Shasta strain yearling trout treated with 1 microgram/kg or more TCDD. Regarding epithelial lesions, all 4 hatchery strains treated with 10 micrograms/kg or more TCDD showed multifocal necrosis of gastric cardiac glandular mucosa, 3 of 4 hatchery strains showed vacuolar inclusions in exocrine pancreatic cells, and 2 of 4 hatchery strains showed fin necrosis. The severity and character of lesions in the liver and gastric mucosa varied markedly between hatchery strains of trout. One hatchery strain showed no hepatic lesions, two showed mild hepatocyte lesions, and one exhibited severe diffuse hepatopathy. In this severely affected hatchery strain, hyaline intracytoplasmic inclusions occurred in hepatocytes at 14 and 34 d after TCDD exposure, and bile-duct hyperplasia occurred at 34 d following TCDD exposure. One of 4 hatchery strains showed atrophy of serous gastric glands and 1 of 4 hatchery strains showed hyperplasia of these same glands at 25 and 34 d, respectively, following TCDD treatment. Thus, lymphomyeloid and epithelial tissues are the primary targets for TCDD-induced pathologic lesions in rainbow trout, and the incidence and severity of these lesions is influenced by the strain of trout used and the hatchery from which the trout were obtained.

2,3,7,8-Tetrachlorodibenzo-p-dioxin toxicity in yellow perch (Perca flavescens).

Growth, mortality and morphologic lesions in juvenile, hatchery-reared yellow perch, Perca flavescens, were studied after treatment with graded single doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 1-125 micrograms/kg, intraperitoneally). TCDD doses of 25 and 125 micrograms/kg caused 95% mortality by 28 d after treatment, without decreasing body weight. A TCDD dose of 5 micrograms/kg resulted in progressive loss of body weight with cumulative mortality of 80% by 80 d posttreatment. Periodic handling stress did not affect the time course of mortality or cumulative percent lethality in TCDD-treated perch. Fin necrosis, petechial cutaneous hemorrhage, and ascites occurred in perch treated with 5 micrograms/kg or more of TCDD. Thymic atrophy, decreased hematopoiesis in the head kidney, fibrinous pericarditis, focal myocardial necrosis, submucosal gastric edema, and hyperplasia of the epithelium of gill filaments and lamellae occurred in perch dosed with 25 or 125 micrograms/kg. Dose-related splenic lymphoid depletion occurred in perch receiving 5 micrograms/kg or more TCDD, and hepatocyte lipidosis occurred in groups treated with doses of 1 microgram/kg or more TCDD. Thus yellow perch are as responsive to the acute toxic effects of TCDD as some of the more sensitive mammalian species, and neither loss of body weight nor histologic lesions in TCDD-treated perch are sufficient to explain mortality.

Effect of membrane cholesterol depletion on the immunoreactivity of the D antigen and IgG anti-D.

The immunoreactivity of the main Rh antigen (D) and its corresponding antibody, as determined by a ti-IgG to IgG combining ratio, antibody dissociation and antigen accessibility to antibody, was examined in cholesterol depleted human red cells and ghost membranes. The anti-IgG reactivity of IgG anti-D bound to cholesterol depleted red cells and ghosts was demonstrably enhanced in vitro and in electron microscopy studies, particularly in ghosts. Dissociation of cell bound anti-D during buffer incubation was greater after cholesterol depletion, especially in ghosts. There was also reduced binding of anti-D to cholesterol-depleted cells as previously reported. All these effects appeared to be independent of endogenous or exogenous proteolysis in either cholesterol-depleted membranes or controls as judged from membrane electrophoretic analyses. A2C, an agent which increases membrane fluidity, had no effect on anti-D binding or the antiglobulin reactivity of cell bound IgG. A reduction in anti-D binding also was observed in red cells depleted of cholesterol following immobilization of membrane proteins by glutaraldehyde crosslinking. The findings show that cholesterol depletion not only affects the antigen but also Rh antibody reactivity. They also suggest that factors other than vertical antigen movement in a fluid bilayer may influence the behavior of the D antigen in cholesterol-modified erythrocytes.

Interactions of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with immune responses of rainbow trout.

Chlorinated dioxins, as typified by the most potent isomer, TCDD, are immunosuppressive in mammalian species and can enhance the susceptibility to a number of diseases. In recent years chlorinated dioxins have been detected in fish in many freshwater and marine habitats. Thus far, the effects of these chemicals on the immune responses of fish have not been examined. We studied the influence of TCDD on the defense mechanisms of rainbow trout. Yearling trout were injected intraperitoneally with the vehicle, 0.1, 1.0 or 10 micrograms/kg of TCDD. Interactions with the humoral immune response to sheep red blood cells (SRBC) were assessed by the Jerne plaque assay using head kidney and spleen leukocytes. Serum antibody was measured by complement-mediated lysis of SRBC in a chromium release assay. Effects of TCDD on the cellular immune responses were evaluated by the response of thymic and splenic lymphocytes to Con A and PWM. In addition, the phagocytic activity of peritoneal macrophages was examined in vitro. Trout which received 0.1 or 1.0 micrograms/kg TCDD remained clinically normal, and defense mechanisms were unaltered in these fish. Trout which received 10 micrograms/kg of TCDD became hypophagic and exhibited fin necrosis, ascites and suppression of hematopoiesis. In this treatment group, Con A-induced blastogenesis of thymic and splenic lymphocytes was not significantly changed, however, suppression of the PWM-induced response of splenic lymphocytes occurred. No statistically significant alterations occurred in humoral immune responses, and phagocytic activity of peritoneal macrophages was not decreased. The dose-response curve for various biologic effects of TCDD in the rainbow trout appears different from that in sensitive mouse strains. The 30-day, single-dose, parenteral LD50 for TCDD in the C57BL mouse is 100 micrograms/kg, and TCDD suppresses both cell-mediated and humoral immune responses at 1-2 micrograms/kg in this mouse strain. In the rainbow trout, however, immunosuppression was evident only at doses of TCDD approaching the 80-day, single-dose, parenteral LD50 of 20 micrograms/kg.

Metabolism and disposition of 2,3,7,8-tetrachlorodibenzo-p-dioxin in rainbow trout.

Accumulation, tissue distribution, and depuration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-derived 3H were studied in fingerling rainbow trout fed a diet containing 494 ppt [3H]TCDD for 13 weeks followed by the same diet without TCDD for 13 weeks. This exposure did not cause fin rot, cutaneous hemorrhage, reduced growth rate, or an increase in relative lethality in TCDD-exposed fish. Visceral fat, carcass, skin, and pyloric caeca and all fatty tissues, accounted for greater than 90% of the TCDD-derived 3H in the fish after the 13-week exposure period. The remaining TCDD-derived radioactivity was distributed to skeletal muscle, gill, gastrointestinal tract, liver, kidney, heart, and spleen. High-pressure liquid chromatographic analysis of 3H in skeletal muscle, liver, kidney, carcass, and visceral fat showed that it was primarily due to TCDD (greater than or equal to 98%) and not metabolites (less than or equal to 2%). The t1/2 for whole-body depuration of TCDD-derived 3H was 15 weeks, and individual organ t1/2 values ranged from 8 to 19 weeks. To determine if rainbow trout metabolize TCDD, adult fish were injected with [14C]TCDD (60 micrograms/kg, ip), and gallbladder bile, liver, skeletal muscle, and kidney were analyzed 1 week later. While only the parent compound was found in the tissues, bile contained at least three TCDD metabolites and the parent compound. beta-Glucuronidase treatment of the bile suggested that at least one TCDD metabolite was a glucuronide conjugate.

2,3,7,8-Tetrachlorodibenzo-p-dioxin metabolism and disposition in yellow perch.

Accumulation, tissue distribution, and depuration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-derived 3H were examined in fingerling yellow perch fed a diet containing 494 ppt of [3H]TCDD for 13 weeks followed by the same diet without TCDD for 13 weeks. None of the TCDD-exposed perch showed any signs of overt toxicity such as reduced growth rate, fin necrosis, cutaneous hemorrhage, or lethality. At the end of the 13-week exposure period, 78% of the total body burden of TCDD-derived 3H was contained in the carcass and visceral fat while the remaining 22% was distributed among the liver (9%), gill (5%), skin (3%), skeletal muscle (2%), gastrointestinal tract (1%), pyloric caeca (1%), kidney (less than 1%), spleen (less than 1%), and heart (less than 1%). High-performance liquid chromatographic analysis of organic extracts of visceral fat, carcass, liver, skeletal muscle, and skin showed that 96-99% of the tritium extracted from these tissues was due to the parent compound. The estimated t1/2 for whole-body depuration of TCDD-derived 3H was 18 weeks, and individual organ t1/2 values ranged from 6 to 19 weeks for the gastrointestinal tract, pyloric caeca, liver, gill, and carcass, and from 24 to 49 weeks for the visceral fat, kidney, skin, skeletal muscle, and spleen. To determine if yellow perch metabolize TCDD, a single dose of [14C]TCDD was administered to adult yellow perch (60 micrograms/kg, ip), and, 1 week later, gallbladder bile, liver, skeletal muscle, and kidney were removed, extracted, and analyzed by high-performance liquid chromatography. In contrast to the liver, muscle, and kidney where the parent compound accounted for 96-99% of the extractable 14C, the gallbladder bile contained almost entirely TCDD metabolites. At least four TCDD metabolites were detected in yellow perch bile and beta-glucuronidase treatment of the bile suggested that at least one was a glucuronide conjugate.