Defective inflammatory response in interleukin 6-deficient mice.

Systemic and localized inflammation elicit a number of host responses which include fever, cachexia, hypoglycemia, and major changes in the concentration of liver plasma proteins. Interleukin 6 (IL-6) is considered an important mediator of the inflammatory response, together with IL-1 and tumor necrosis factor alpha (TNF-alpha). The purpose of this study was to unequivocally determine the role of IL-6 in these phenomena making use of IL-6-deficient mice that we have recently generated by gene targeting. We report here that in the absence of IL-6, mice are unable to mount a normal inflammatory response to localized tissue damage generated by turpentine injection. The induction of acute phase proteins is dramatically reduced, mice do not lose body weight and only suffer from mild anorexia and hypoglycemia. In contrast, when systemic inflammation is elicited through the injection of bacterial lipopolysaccharide (LPS), these parameters are altered to the same extent both in wild-type and IL-6-deficient mice, demonstrating that under these conditions IL-6 function is dispensable. Moreover, we show that LPS-treated IL-6-deficient mice produce three times more TNF-alpha than wild-type controls, suggesting that increased TNF-alpha production might be one of the compensatory mechanisms through which a normal response to LPS is achieved in the absence of IL-6. We also show that corticosterone is normally induced in IL-6-deficient mice, demonstrating that IL-6 is not required for the activation of the hypothalamic-pituitary-adrenal axis. Our results reinforce the idea that different patterns of cytokines are involved in systemic and localized tissue damage, and identify IL-6 as an essential mediator of the inflammatory response to localized inflammation.

Italian translation and cross-cultural comparison with the Childhood Attachment and Relational Trauma Screen (CARTS).

Background: The Childhood Attachment and Relational Trauma Screen (CARTS) is a computer-administered survey designed to assess retrospectively the socio-ecological context in which instances of child abuse may have occurred. To date, studies supporting the validity of the CARTS have only been undertaken in English-speaking North American populations. Validation projects in other countries and cross-cultural comparisons are therefore warranted. Objective: Develop and preliminarily evaluate the psychometric properties of an Italian version of the CARTS on college students and compare such observations to data acquired from Canadian students. Method: Seventy-nine undergraduate students from the University of Padua (Italy) completed an Italian translation of the CARTS as well as measures of childhood experiences, mental health and attachment, responses to which were compared to those obtained in 288 Canadian students who completed the CARTS in English. Results: Internal consistency and convergent validity with the Childhood Trauma Questionnaire and Parental Bonding Instrument were found to be acceptable for the Italian translation. Within the Italian sample, correlation analyses suggested that CARTS Mother ratings referring to attachment and abuse were associated with romantic attachment, whereas CARTS Father ratings were significantly correlated to PTSD symptoms and other symptoms of psychopathology-distress. Significant differences between Italian and Canadian students across the relationship types for the CARTS abuse and attachment scales were found, indicating that Italian students rated their mothers and fathers as simultaneously less abusive, but also less as a source of secure attachment. Conclusions: The results of this preliminary study seem to suggest convergent validity of the Italian CARTS and the association between childhood attachment-related experiences and romantic attachment. Cultural variations were identified between Canadian and Italian students in both attachment and abuse scales. Future studies to investigate cross-cultural variations in the relational context of childhood abuse and in order to boost Italian CARTS psychometric features are warranted.

Planteamiento: La Encuesta de Apego Infantil y Trauma Relacional (CARTS) es una encuesta administrada por ordenador diseñada para evaluar retrospectivamente el contexto socio-ecológico en el que pueden haber ocurrido casos de abuso infantil. Hasta la fecha, los estudios que apoyan la validez de la CARTS sólo se han realizado en poblaciones norteamericanas de habla inglesa. Por lo tanto, se justifican los proyectos de validación en otros países y las comparaciones interculturales. Objetivos: Desarrollar y evaluar de manera preliminar las propiedades psicométricas de una versión italiana de CARTS en estudiantes universitarios y comparar dichas observaciones con datos obtenidos de estudiantes canadienses. Método: Setenta y nueve estudiantes de pre-grado de la Universidad de Padua (Italia) completaron una traducción al italiano de la CARTS, así como medidas de experiencias infantiles, salud mental y apego. Las respuestas fueron comparadas con las obtenidas en 288 estudiantes canadienses que completaron la CARTS en inglés. Resultados: Se encontró que la coherencia interna y la validez convergente con el Cuestionario de Trauma Infantil (Childhood Trauma Questionnaire) y el Instrumento de Vinculación Parental (Parental Bonding Instrument) eran aceptables para la traducción al italiano. Dentro de la muestra italiana, los análisis de correlación sugirieron que las puntuaciones de la CARTS-Madre que se refieren al apego y al abuso se asociaron con el apego romántico, mientras que las puntuaciones de la CARTS-Padre se correlacionaron significativamente con síntomas de TEPT y otros síntomas de trastorno psicopatológico. Se encontraron diferencias significativas entre los estudiantes italianos y canadienses entre los tipos de relación para las escalas de abuso y apego de la CARTS, lo que indica que los estudiantes italianos clasificaron a sus madres y padres simultáneamente como menos abusivos, pero también menos como fuente de apego seguro. Conclusiones: Los resultados de este estudio preliminar parecen sugerir la validez convergente de la CARTS italiana y la asociación entre las experiencias relacionadas con el apego infantil y el apego romántico. Se identificaron variaciones culturales entre estudiantes canadienses e italianos en las escalas de apego y abuso. Se justifican la realización de futuros estudios para investigar las variaciones interculturales en el contexto relacional del abuso infantil y con el fin de impulsar las características psicométricas de la CARTS italiana.

Bullous pemphigoid autoantibodies, HIV-1 infection and pruritic papular eruption.

Bullous pemphigoid (BP)-type autoantibodies were found by Western blot (WB) analysis of epidermal extracts in the serum of 38% of HIV-seropositive patients compared with 21% of HIV-seronegative patients with chronic pruritus and 76% of patients with BP. They were further identified as BP autoantibodies (BPab) by immunoprecipitation and immunoelectron microscopy. Their incidence increased from 21% in HIV infection stage II to 37% and 43% in stages III and IV, respectively. Of the patients suffering from HIV-related chronic pruritic papulovesicular eruption. 75% showed circulating BPab as compared with 29% in those without skin problems (P = 0.0066) and, among them, 30% met the diagnostic criteria for BP when histology, WB, immunofluorescence and immunoelectron microscopy techniques were used. In conclusion, this study identifies an autoimmune skin reaction that may account for, or be related to, the distressing pruritic eruptions occurring in HIV-infected patients.

Hepatic protoporphyria is associated with a decrease in ligand binding for the mitochondrial benzodiazepine receptors in the liver.

Protoporphyrin IX (PP) and N-methylprotoporphyrin IX (N-MePP) added in vitro to liver membranes reduced dose-dependently the affinity of [3H]PK 11195 for the mitochondrial benzodiazepine receptors (MBRs), the latter being about 20 times more potent (Ki 4.5 and 0.25 microM). Preincubation of these two porphyrins with liver homogenates for 120 min at 4 degrees resulted in significant inhibition of [3H]PK 11195 binding even after repeated washings of the membranes due to the residual presence in the membranes of about 35 and 5% of PP and N-MePP, respectively. Thus, the hypothesis that an in vivo increase in the hepatic porphyrin content modifies the binding of the isoquinoline PK 11195 to the MBRs was investigated in an experimental model of protoporphyria. PP and N-MePP were allowed to accumulate in vivo through treatment with 3,5-diethoxycarbonyl-1, 4-dihydrocollidine (DDC) (100 mg/kg i.p., once), and rats were killed 5 h after treatment when hepatic porphyrin accumulation was marked (10-fold increase), PP predominating. In the liver, treatment reduced the affinity (Kd) of [3H]PK 11195 for MBRs (from 3.56 to 15.37 nM, P < 0.01) and the maximum number of binding sites (Bmax) (55% decrease, P < 0.05); the affinity (Ki) of RO 5-4864 for [3H]PK 11195 binding sites was also reduced (from 23.9 to 72.99 nM, P < 0.05). No significant differences were found in the brain cortex. Liver and brain diazepam binding inhibitor levels and plasma corticosterone levels were unchanged. The reduction in [3H]PK 11195 binding to MBRs in the liver of DDC-treated rats thus appears to be attributable to a specific effect of the DDC-induced formation of the two protoporphyrins; this conclusion suggests that in hepatic protoporphyria processes modulated by MBRs may be altered.

Bullous pemphigoid associated with acute graft-versus-host disease after allogeneic bone marrow transplantation.

A 47-year-old patient was treated with allogeneic bone marrow transplantation (BMT) for chronic myelogenous leukaemia in blast crisis. Three months after the procedure he developed bullous pemphigoid (BP) and symptoms suggestive of BP oesophageal involvement, associated with skin and liver acute graft-versus-host disease. The occurrence of BP is exceptional after BMT.

Effects of chlorinated organics on intermediates in the heme pathway and on uroporphyrinogen decarboxylase.

Experimental porphyria induced by PHAHs is characterized by a progressive reduction in the activity of UROD. After intoxication with TCDD, the most porphyrogenic compound known to date, the liver was the principal site of action, as regards both porphyrin accumulation (mostly uroporphyrin) and the degree of enzyme impairment; the kidney was the site of the second greatest accumulation; the brain and erythrocytes were unaffected. Additional modifications of the heme pathway involved induction of the activity of ALAS and, at least in HCB-induced porphyria after iron pretreatment, may have involved reduced activity of uroporphyrinogen III cosynthetase. These changes can alter the amount and the isomeric composition of uroporphyrinogens and uroporphyrins present in the liver in a way that is likely to help reduce formation of coproporphyrinogen III in porphyric animals. As in the human syndrome porphyria cutanea tarda, iron administration increased porphyrin accumulation and the degree of reduction of UROD activity in mice fed HCB. Mice fed HCB also presented an activation of the type O form of XO. This activation was independent of tissue injury derived from the lipid peroxidation that was concomitant with iron administration. The increase in activity of the type O form of XO may be a characteristic feature of the liver damage found in PHAH intoxication and, in intoxicated animals, could be a source in the liver of oxidant species involved in the mechanism of UROD inactivation--if this inactivation is in fact due to an oxidative reaction.

Peripheral benzodiazepine receptor ligands in rat liver mitochondria: effect on cholesterol translocation.

Peripheral benzodiazepine receptors mediate cholesterol translocation between the outer and inner mitochondrial membranes in steroidogenic tissues. They are found in many other tissues too, including liver. We studied the effect of the peripheral benzodiazepine receptor ligands PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)isoquinoline-3-carboxa mid e], Ro 5-4864 (4-chlorodiazepam), hemin, protoporphyrin IX and N-methyl protoporphyrin IX on cholesterol mitochondrial intermembrane transport of cholesterol in vitro in rat liver. Endogenous cholesterol translocation from outer to inner mitochondrial membranes was significantly increased by PK11195 and N-methyl protoporphyrin IX (140% and 150% increase, respectively, at 1 microM, P<0.01). 5 microM protoporphyrin IX, 1 microM Ro 5-4864 and 5 microM hemin was ineffective. When mitochondria were labeled with exogenous [4-14C]cholesterol, PK11195 and N-methyl protoporphyrin IX were the most effective in increasing total cholesterol incorporation and cholesterol translocation into inner membranes, and their effect was dose-dependent. These data suggest that in liver the binding to peripheral benzodiazepine receptors is related to cholesterol translocation and the interaction of ligands with these receptors may play a role in the complex mechanism of regulation of cholesterol traffic between liver mitochondrial membranes.

Peripheral benzodiazepine receptor ligands in rat liver mitochondria: effect on 27-hydroxylation of cholesterol.

The effect of peripheral benzodiazepine receptor ligands: PK11195 (1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)isoquinoline-3-carboxamid e), Ro 5-4864 (4-chlorodiazepam), hemin, N-methyl protoporphyrin IX and protoporphyrin IX on liver mitochondrial 27-hydroxylation of cholesterol was studied by adding them together with [4-14C]cholesterol. N-Methyl protoporphyrin IX, PK11195 and protoporphyrin IX stimulated mitochondrial 27-hydroxylation of [4-14C] cholesterol in vitro, the first two being the most potent (2-3-fold increase). Ro 5-4864 and hemin were not active. 27-Hydroxylation of [4-14C]cholesterol was reduced to below control levels (respectively 40 and 56% decrease compared to control, P < 0.01) when PK11195, N-methyl protoporphyrin IX or protoporphyrin IX were allowed to equilibrate in vitro with mitochondria for 20 min at 37 degrees C. Hepatic protoporphyria was induced using 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) (100 mg/kg, i.p.) to study the effect of in vivo accumulation of large amounts of dicarboxylic porphyrins, i.e. endogenous peripheral benzodiazepine receptor ligands, on cholesterol 27-hydroxylation. DDC treatment caused an increase in total porphyrin content in liver homogenate (10-fold) and mitochondria (2-fold). Mitochondrial 27-hydroxylation of [4-14C]cholesterol was depressed after treatment (60% decrease, P < 0.01). We suggest that peripheral benzodiazepine receptor ligands act on liver mitochondrial 27-hydroxylation of cholesterol by a mechanism coupled to these receptors and that the time of exposure of peripheral benzodiazepine receptors to ligands is a major factor. The modulation of 27-hydroxycholesterol production may have a physiological role in liver and possibly in other tissues.

Mechanisms of interleukin-2-induced depression of hepatic cytochrome P-450 in mice.

Interleukin-2 (15 micrograms/mouse, i.p. twice daily for 4 days and once on the 5th day) significantly lowered cytochrome P-450 and heme content and increased heme oxygenase mRNA accumulation; the activities of 7-ethoxycoumarin O-deethylase, ethoxy- and pentoxyphenoxazone O-dealkylases were decreased. The activity of the type O form of hepatic xanthine oxidase increased, but there was no increase in lipid peroxide, expressed in terms of microsomal malondialdehyde. In vivo inactivation of xanthine oxidase activity by feeding mice with tungstate did not substantially change the degree of interleukin-2-induced cytochrome P-450 depression, suggesting that the two processes are not causally linked. Induction of tolerance to endotoxin by a 4-day pretreatment with lipopolysaccharide resulted in 50% protection against this depression despite inhibition of the interleukin-2 induced formation of tumor necrosis factor. This suggests that the release of tumor necrosis factor per se does not fully account for the depression of cytochrome P-450. Dexamethasone, already used in patients to reduce the toxicity of interleukin-2 therapy, provided full protection against the cytochrome P-450 depression.

Frequency of bullous pemphigoid-like antibodies as detected by western immunoblot analysis in pruritic dermatoses.

BACKGROUND AND DESIGN: Ninety-seven patients suffering from a pruritic dermatosis were screened for the detection of bullous pemphigoid (BP) antibodies (ab) using the Western immunoblot (WB) analysis technique. RESULTS: Twenty-four patients (25%) reacted at least twice with the BP antigen on WB analysis at a 1/10 dilution: seven had typical BP, four had papular BP, 10 had pruritus and prurigo of unknown origin, two had eczema, and one had lichen planus. This corresponds to 13% of BP-type ab in patients who did not fulfill criteria for BP. Therefore, we did the following: (1) tested a control group of 24 subjects; (2) assessed the reproducibility of the WB method by retesting the same serum samples on different epidermal extracts; and (3) estimated the BP ab titer. None of the 24 control subjects had detectable BP ab, and reproducible results were obtained in all groups when serum samples were retested at the 1/10 dilution. Although 86% (6/7) of patients with BP had BP ab titers of 1/100 or greater, only 60% (6/10) of the group with pruritus and prurigo and 33% (1/3) of the group with eczema reached such titers. CONCLUSION: These results indicate that due to its sensitivity, the WB method can detect low titers of BP ab in patients with pruritic dermatoses who did not fulfill criteria for BP, and therefore we question the specificity of this method.

Mitochondrial dysfunction and death in motor neurons exposed to the glutathione-depleting agent ethacrynic acid.

This study investigated the mechanisms of toxicity of glutathione (GSH) depletion in one cell type, the motor neuron. Ethacrynic acid (EA) (100 microM) was added to immortalized mouse motor neurons (NSC-34) to deplete both cytosolic and mitochondrial glutathione rapidly. This caused a drop in GSH to 25% of the initial level in 1 h and complete loss in 4 h. This effect was accompanied by enhanced generation of reactive oxygen species (ROS) with a peak after 2 h of exposure, and by signs of mitochondrial dysfunction such as a decrease in 3-(4,5-dimethyl-2-thiazoyl)-2,5-diphenyltetrazolium bromide (MTT) (30% less after 4 h). The increase in ROS and the MTT reduction were both EA concentration-dependent. Expression of heme oxygenase-1 (HO-1), a marker of oxidative stress, also increased. The mitochondrial damage was monitored by measuring the mitochondrial membrane potential (MMP) from the uptake of rhodamine 123 into mitochondria. MMP dropped (20%) after only 1 h exposure to EA, and slowly continued to decline until 3 h, with a steep drop at 5 h (50% decrease), i.e. after the complete GSH loss. Quantification of DNA fragmentation by the TUNEL technique showed that the proportion of cells with fragmented nuclei rose from 10% after 5 h EA exposure to about 65% at 18 h. These results indicate that EA-induced GSH depletion rapidly impairs the mitochondrial function of motor neurons, and this precedes cell death. This experimental model of oxidative toxicity could be useful to study mechanisms of diseases like spinal cord injury (SCI) and amyotrophic lateral sclerosis (ALS), where motor neurons are the vulnerable population and oxidative stress has a pathogenic role.

Plasma and red blood cell phospholipids in chronic liver diseases.

The total phospholipid content and the individual phospholipids, phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine and phosphatidylserine, and sphingomyelin were determined in the plasma and red blood cells of 58 patients with chronic liver disease and 12 control subjects by quantitative extraction and thin-layer chromatography. The total phospholipids were significantly reduced in both the plasma and red blood cells of the patients with liver disease. For the individual phospholipids, plasma sphingomyelin was significantly decreased, in the red blood cells there was an increase in lysophosphatidylcholine and a decrease in phosphatidylethanolamine and phosphatidylserine compared to the control subjects. It is suggested that in chronic liver disease the red blood cell lipid disturbances follow more closely those of the hepatocyte than those in plasma.

Comparison of hexachlorobenzene-induced alterations of microsomal membrane composition and monooxygenase activity in male and female rats.

The effect of hexachlorobenzene (HCB) on microsomal cytochromes P-450 and b5, monooxygenase activity and membrane composition was examined in male and female Fischer rats. Cytochrome P-450 was induced more in male than in female animals while cytochrome b5 was induced only in males. Analysis of patterns of induction of microsomal monooxygenases showed that aminopyrine-N-demethylase activity doubled in both sexes after treatment while aryl hydrocarbon hydroxylase activity was 16 times the control value in the females and 1.5 times in the males. After HCB treatment the phospholipid content of microsomal membranes per gram of liver was increased in both sexes while cholesterol was unchanged. Analysis of the phospholipids (PL) pattern showed that the percentage of sphingomyelin (SPH) decreased significantly (50% of the control value) while phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidylethanolamine (PE) did not change. These changes resulted in a reduction of membrane microviscosity and indicate that HCB interferes with the biosynthesis of phospholipids containing choline. Free fatty acid (FFA) content also dropped in both sexes but females were more affected; free arachidonic acid rose in females. HCB induction of microsomal cytochromes and monooxygenases is thus accompanied by marked modifications of membrane composition. Comparing the 2 sexes, HCB showed more pronounced features of 'PB type' inducers in males.

Effects of iron overload on bile secretion and hepatic porphyrin metabolism in ethinyl estradiol-treated rats.

We investigated the effects of ethinyl estradiol (5 mg/kg body wt daily for 5 days, orally) and/or iron sorbitol (50 mg/kg body wt daily for 5 days, i.m.) on bile flow, bile salt independent fraction (BSIF), hepatic delta-aminolevulinate synthase (ALA-S) and uroporphyrinogen decarboxylase (URO-D) in female rats. Ethinyl estradiol administration was associated with a significant decrease of bile flow and BSIF and an increase in URO-D activity in comparison to control values. Iron alone did not modify biliary parameters, but significantly increased the activity of ALA-S. Combined treatment with ethinyl estradiol plus iron partially corrected the reduction of BSIF and restored the activity of ALA-S and URO-D to control levels. Thus iron appears to exert a partially protective effect against ethinyl estradiol-induced cholestasis. No porphyrinogenic effect was observed.

Bile secretion and liver microsomal mixed function oxidase system in mice with griseofulvin-induced hepatic protoporphyria.

Administration of 2.5% griseofulvin in the diet to male CD1 mice produced protoporphyria and cholestasis. Protoporphyria became evident as early as after 10 days of treatment, whereas cholestasis, expressed in terms of total bile flow reduction, developed only after 45 days of griseofulvin. Bile flow impairment was due both to the length of treatment and to the severity of liver protoporphyria. Griseofulvin administration was also associated with a significant modification of the relative amounts of hepatic microsomal cytochromes P-450 and b5, a loss in concentration/mg of protein of cytochrome P-450 and a concomitant increase of b5. Despite these changes, the activity of aniline hydroxylase expressed per mg of microsomal protein, assessed in vitro, was not modified.

Induction of mixed-function oxidase by chronic treatment with 2,3,7,8-tetrachloro-dibenzo-p-dioxin in female rats.

The effect of a 45-week treatment with different doses of 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) (0.01, 0.10 and 1.00 microgram/kg/week) was evaluated in female rat liver by determining cytochrome P-450 and b5 content and the activities of the enzymes cytochrome c reductase, aryl hydrocarbon hydroxylase (AHH) and 7-ethoxycoumarin O-deethylase (7-ECD); TCDD content in the liver was also measured. Cytochrome b5 and cytochrome c reductase were unaffected at any of the dose levels and cytochrome P-450 was significantly induced only at the highest TCDD dose, but marked induction of AHH and 7-ECD was apparent when the animals were treated with 0.01 microgram/kg/week; a clear dose-response relationship was present in the induction at the 2 lower doses (0.01 and 0.10 microgram/kg/week). The amount of TCDD found in liver tissue (1050, 4740 and 30 700 ppt, respectively, for 0.01, 0.10 an 1.00 microgram/kg/week) indicated a relatively higher accumulation of this compound at lower doses.

Intercalation with DNA is a prerequisite for daunomycin, adriamycin and its congeners in inhibiting DNAase I.

DNAase I from bovine pancreas is inhibited by Daunomycin, Adriamycin, Adriamycin-14-acetate and Adriamycin-14-octanoate, whereas it is not inhibited by N-trifluoroacetyladriamycin-14-valerate or N-trifluoroacetyl-adriamycin. The present study suggests that these inhibitors act not directly on the enzyme, but on DNA, forming stable complexes and thus interfering with enzyme activity. The correlation between DNA binding and enzyme inhibition is demonstrated by the fact that the compounds forming complexes with DNA inhibit DNAase I activity, whereas those which do not form complexes with DNA cause no inhibition.

Isolation and structure determination of enzymatically formed styrene oxide glutathione conjugates.

When styrene oxide was incubated with glutathione in the presence of rat liver cytosolic fraction, two conjugates were formed. Structural investigation by mass spectrometry (MS), proton magnetic resonance (PMR) analysis and chemical fragmentation showed the presence of two positional isomers, namely S-(1-phenyl-2-hydroxyethyl)glutathione and S-(2-phenyl-2-hydroxyethyl)glutathione in a ratio of approx. 60 : 40.

Different susceptibility of mouse tissues to porphyrogenic effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The porphyrogenic effect of chronic administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (25 micrograms/kg/week) to male C57BL/6 mice was evaluated through quantitative and qualitative analysis of the porphyrins accumulated and of porphyrinogen carboxylase activity in liver, kidney, spleen, brain and erythrocytes. The liver was the principal site of action, both for porphyrin accumulation and for enzyme inhibition, with kidney next, whereas brain and erythrocytes were unaffected. In the spleen, despite unchanged formation of total products of uroporphyrinogen III decarboxylation, both an increase and a decrease of coproporphyrinogen formation were observed, the decrease being concomitant with a higher accumulation of tissue porphyrins. When a response to TCDD was found, the formation of the products of decarboxylaction of uroporphyrinogen III were affected to different extents. The pattern of enzyme inhibition paralleled data reported in the literature regarding tissue distribution of TCDD and indicated that TCDD porphyria is a suitable experimental model for the human 'sporadic' type of porphyria cutanea tarda (PCT).

In vitro inhibitory effect on porphyrinogen carboxylyase of liver extracts from TCDD treated mice.

Marked inhibition of porphyrinogen carboxylyase was produced in vitro by cytosol fractions, deproteinized and free of porphyrins, obtained from livers of mice made porphyric by 9 weeks i.p. treatment with 25 micrograms/kg/week of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Inhibition was proportional to the amount of the fraction added, was increased by preincubation in the absence of the substrate and, once established, could not be reversed by dialysis. TCDD itself, added to the control enzyme in the incubation mixture, did not affect enzyme activity up to a concentration of 77 nM, which is 10 times higher than the liver TCDD concentration found after in vivo TCDD treatment.