Genetic differences in methylcholanthrene-mediated suppression of cutaneous delayed hypersensitivity in mice

The flavonolignan-silymarin protects enzymatic, hematological, and immune system against γ-radiation-induced toxicity

The main focus of this study is evaluation of radioprotective efficacy of silymarin, a flavonolignan, against γ-radiation-induced damage to hematological, vital organs (liver and intestine), and immune system. Survival studies revealed that silymarin (administered orally for 3 days) provided maximum protection (67%) at 70 mg/kg body weight (b.wt.) against lethal 9 Gy γ-irradiation (dose reduction factor = 1.27). The study revealed significant (p < 0.05) changes in levels of catalase (12.57 ± 2.58 to 30.24 ± 4.89 units), glutathione peroxidase (6.23 ± 2.95 to 13.26 ± 1.36 µg of reduced glutathione consumed/min/mg protein), glutathione reductase (0.25 ± 5.6 to 11.65 ± 2.83 pM NADPH consumed/min/mg protein), and superoxide dismutase (11.74 ± 0.2 to 16.09 ± 3.47 SOD U/mg of protein) activity at 30th day. Silymarin pretreated irradiated group exhibited increased proliferation in erythrocyte count (1.76 ± 0.41 × 10(6) to 9.25 ± 0.24 × 10(6) ), hemoglobin (2.15 ± 0.48g/dL to 14.77 ± 0.25g/dL), hematocrit (4.55 ± 0.24% to 37.22 ± 0.21%), and total leucocyte count (1.4 ± 0.15 × 10(6) to 8.31 ± 0.47 × 10(6) ) as compared with radiation control group on 15th day. An increase in CD4:CD8 ratio was witnessed (0.2-1%) at 30th day time interval using flow cytometry. Silymarin also countered radiation-induced decrease (p < 0.05) in regulatory T-cells (Tregs ) (11.23% in radiation group at 7th day versus 0.1% in pretreated silymarin irradiated group at 15th day). The results of this study indicate that flavonolignan-silymarin protects enzymatic, hematological, and immune system against γ-radiation-induced toxicity and might prove useful in management of nuclear and radiological emergencies. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 641-654, 2016.

Chemical carcinogens increase IL-1 alpha and IL-6 gene transcripts in human keratinocytes

Using reverse transcriptase-linked polymerase chain reaction, the effect of polycyclic aromatic hydrocarbons (PAHs) on IL-1 alpha, IL-1 beta and IL-6 gene expression in cultured human keratinocytes was studied. Exposure to beta-naphthoflavone and benz(a)anthracene resulted in a higher copy number of IL-1 alpha and IL-6 mRNA while lower level of IL-1 beta mRNA was detected in these cells. These data suggest that, like ultraviolet B (UVB) radiation, ubiquitous environmental carcinogenic PAHs are potent inducers of IL-1 alpha and IL-6 cytokines and, unlike UVB, they downregulate IL-1 beta in human keratinocytes.

Pedigree analysis of aryl hydrocarbon hydroxylase inducibility in acute leukemia of childhood

We determined lymphocyte aryl hydrocarbon hydroxylase (AHH) inducibility for members of 13 families with one or more children with acute lymphoblastic leukemia (ALL) and 12 control families. Pedigree analysis suggested that aromatic hydrocarbon responsiveness (i.e. inducibility) is a codominant trait. Heterozygotes were found to be moderately responsive with IR values intermediate between homozygous minimally responsive and homozygous highly responsive individuals. Homozygous recessive and heterozygous genotypes accounted for 54% and 36% of ALL children respectively. The risk of ALL among minimally aromatic hydrocarbon responsive children was twice that of highly responsive children.

Alteration of methylcholanthrene-mediated suppression of cutaneous delayed hypersensitivity by benzoflavone treatment of C57BL/6J mice

The potential role of the cytochromes P-450 in methylcholanthrene (MC)-mediated suppression of cutaneous delayed hypersensitivity (CDH) in C57BL/6J (B6) mice was evaluated indirectly by treating mice with agents known to induce or inhibit hepatic cytochromes P-450 prior to contact sensitization. Subsequent alterations in aryl hydrocarbon hydroxylase (AHH) activity and CDH, as measured by suppression of 2,4-dinitrofluorobenzene (DNFB)-induced ear swelling, were measured. MC administration resulted in a dose-dependent suppression of ear swelling and a concomitant dose-dependent induction of hepatic AHH activity. Treatment of B6 mice with phenobarbital (PB), 80 mg/kg daily X 3, a broad spectrum inducer of P-450, resulted in a 2.5-fold increase in benzo[a]pyrene (B[a]P) hydroxylase activity without affecting CDH. Animals treated with the same PB protocol prior to an ED20 dose of MC showed no difference in suppression of CDH compared to animals treated with MC alone. In contrast, successive treatment with the selective P1-450 inducer, 5,6-benzoflavone (beta NF), prior to and following an ED20 dose of MC significantly increased suppression of CDH (p less than 0.001) usually seen at this MC dose. Treatment with a known inhibitor of cytochrome P1-450 activity, 7,8-benzoflavone (alpha NF), did not prevent AHH induction when administered prior to and following MC (ED100) nor did it suppress CDH when administered alone. However, this alpha NF treatment completely prevented suppression of CDH usually seen at this MC dose. These data provide evidence suggesting that metabolic activation by cytochrome P1-450 is required for the expression of the immunosuppressive activity of MC.

Suppression of splenic lymphocyte function by 7,12-dimethylbenz[a]anthracene (DMBA) in vitro

The effects of the immunosuppressive polycyclic aromatic hydrocarbon (PAH) 7,12-dimethylbenz[a]anthracene (DMBA) were studied directly by in vitro exposure of splenic lymphocytes. On the basis of evidence from prior studies that DMBA immunotoxicity in vivo may not be dependent upon induction of the Ah locus in mice, splenocytes from Ah-responsive B6C3F1, Ah-nonresponsive DBA/2N, and in C57BL/6J Ah-congenic mice (responsive B6-Ah(b)Ah(d) and nonresponsive B6-Ah(d)Ah(d) were exposed to xenobiotic in culture. For some experiments, B6C3F1 mice were pretreated with 200 nmol 2,3,7,8-tetrachlorodibenzop-dioxin (TCDD) to induce Ah-associated enzymatic activity prior to in vitro splenocyte exposure to DMBA. Humoral immunity assessed as splenic antibody plaque-forming cells measured after a 5-day in vitro immunization to sheep erythrocytes (SRBC) was suppressed up to 99% by continuous exposure to 20 microM DMBA, and was comparable between control mice having basal levels of hepatic monooxygenase activity and Ah-induced mice (TCDD-treated) having elevated enzyme activity. Similarly, cytotoxic T-lymphocyte generation against P815 target cells was suppressed up to 88 and 86% in 40 microM DMBA-exposed splenocytes from Ah-induced and noninduced mice, respectively. The mixed lymphocyte responsiveness (MLR) of B6C3F1, DBA/2N, B6-Ah(b)Ah(d), and B6-Ah(d)Ah(d) splenocytes exposed in vitro to 40 microM DMBA was suppressed 54, 72, 51, and 29%, respectively. However, the degree of suppression was not significantly different between the strains. The secretion of interleukin 2 (IL2) was also suppressed in splenocytes from both strains exposed to 40 microM DMBA in vitro. Studies which included benzo[a]pyrene (BaP) as a control xenobiotic known to demonstrate Ah dependence showed that the MLR of splenic lymphocytes from Ah-congenic mice was comparably suppressed following 40 microM DMBA exposure, whereas exposure to 40 microM BaP resulted in suppression of the MLR only in B6-Ah(b)Ah(d) splenocytes. In addition, mitogen-stimulated proliferation was inhibited in both B6C3F1 and DBA/2N splenocytes exposed to 40 microM DMBA, whereas 40 microM BaP inhibited only B6C3F1 splenocyte proliferation to LPS. These data suggest that DMBA may act on immunocytes by mechanisms largely independent of the Ah locus and associated metabolic processes.

Persistent suppression of humoral immunity produced by 7,12-dimethylbenz(A)anthracene (DMBA) in B6C3F1 mice: correlation with changes in spleen cell surface markers detected by flow cytometry

The purpose of these studies was to examine the effects of DMBA on subpopulations of splenocytes obtained from B6C3F1 mice, using cell surface markers defined by monoclonal antibodies and multiparameter flow cytometry. Changes were correlated with alterations in humoral immune function assessed in vitro. Mice were treated for 10 days during a 2 week period by subcutaneous (s.c.) injections of DMBA in corn oil at doses of 0.5, 5 and 10 micrograms/g/day (5-100 micrograms/g total dose). Four mice from each exposure group and an additional corn oil control group of mice were studied at 4 and 8 weeks following the last injection with DMBA. These studies demonstrated a dose-dependent decrease in the total number and percentage of spleen cells expressing B-cell markers (mu heavy chain, kappa light chain and 14.8 antigen) as well as T-cell markers (Thy 1.2, Lyt-1 and Lyt-2). The percentage of splenocytes expressing Mac-1 was increased by DMBA. Helper T-cells appeared to be a very sensitive population of spleen cells to DMBA exposure, as suggested by a decrease in the number and percentage of Lyt-1 positive cells recovered from the spleen 4 weeks after exposure to DMBA. DMBA produced a dose-dependent suppression of the in vitro primary humoral immune responses to SRBC, TNP-Ficoll and TNP-LPS. The fact that a functional suppression of humoral immunity was accompanied by a decrease in the number of mature B-cells and T-cells in the spleen suggests that cell surface markers may be useful indicators of immunotoxicity in animals receiving DMBA in sub-chronic studies.

Immunosuppression following exposure to 7,12-dimethylbenz[a]anthracene (DMBA) in Ah-responsive and Ah-nonresponsive mice

Recent reports suggest that the immunotoxicity of certain polycyclic aromatic hydrocarbons is associated with the Ah locus in mice. To test whether immunosuppression mediated by 7,12-dimethylbenz[a]anthracene (DMBA) is regulated by the Ah locus, several endpoints of immune function were measured in Ah-responsive B6C3F1 and Ah-nonresponsive DBA/2N and in Ah-congenic C57BL/6J (responsive B6-AhbAhd and nonresponsive B6-AhdAhd) mice dosed sc with up to 100 micrograms/g DMBA in corn oil. Some groups of B6C3F1 and DBA/2N mice were exposed to 100 micrograms/g benzo[a]pyrene (B(a)P) or 1 nmol 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for determination of hepatic microsomal monooxygenase activity. The body weights of all mice were unaffected by DMBA exposure, but thymus weights and spleen cellularity were decreased. Antibody plaque-forming cells (PFC) measured 4 days after iv sheep erythrocyte (SRBC) immunization were suppressed 99% in B6C3F1 and 96% in DBA/2 mice. Antibody PFC after in vitro immunization to SRBC were similarly suppressed 98% in both B6-AhbAhd and B6-AhdAhd Ah-congenic mice exposed to 100 micrograms/g DMBA. Responses to the T-cell mitogens concanavalin A and phytohemagglutinin were significantly suppressed in both B6C3F1 and DBA/2N strains, as was mitogenesis to bacterial lipopolysaccharide. The unidirectional mixed lymphocyte responses of the congenic strains were suppressed 76% in B6-AhbAhd and 85% in B6-AhdAhd, cytotoxic lymphocyte generation was suppressed 68% in B6-AhbAhd and 78% in B6-AhdAhd. The overall differences between immunosuppressive responses in splenocytes from B6-AhbAhd and B6-AhdAhd congenics were not significant. Induction of cytochrome P1-450, a marker of Ah responsiveness, was determined by 7-ethoxycoumarin O-deethylase monooxygenase activity in hepatic microsomes or splenocytes. This monooxygenase activity was not significantly increased in either B6C3F1 or DBA/2 mice exposed to DMBA, whereas B(a)P and TCDD exposure significantly induced enzyme activity in B6C3F1 hepatocytes. These data suggest that DMBA has an immunosuppressive action on murine splenocytes which is independent of the Ah locus and associated induction of cytochrome P1-450 xenobiotic-metabolizing enzymes.

Inhibition of murine interferon production following in vivo administration of benzo[a]pyrene

To investigate whether alteration in interferon (IFN) production might serve as a biomarker for certain toxic chemical exposures, an in vivo mouse model system was studied. Female C3H mice were injected intraperitoneally with varying doses of benzo[a]pyrene (BP), and at various times subsequent to this treatment, serum IFN levels, following Sendai virus induction, were determined by a cytopathic effect inhibition assay. Doses of 4.6 mg/mouse (180 mg/kg body weight) caused a significant depression in IFN production at 12, 48, and 120 h after BP administration. Doses of 0.46 mg also produced significant decreases at 48 h following exposure. At 48 h post-BP treatment, the reduction in serum IFN titers in treated animals relative to controls was: 62% for the 0.46-mg dose, and 94% for the 4.6-mg dose. These results indicate that systemic administration of BP can significantly depress the whole-animal IFN response to viral stimulation, and that such depression can persist for a rather extended period at certain dose levels.

Induction of immunotoxicity by polycyclic hydrocarbons: role of the Ah locus

We have employed the plaque forming cell (PFC) response to sheep erythrocytes as well as lymphocyte proliferation to study the induction of immunotoxicity in AHH-inducible (Ah Locus positive, C57BL/6N; B6C3F1) and AHH non-inducible (Ah Locus negative, DBA2/N) mice following administration of polycyclic aromatic hydrocarbons. When two potent carcinogenic polycyclic hydrocarbons which induce AHH activity, 3-methylcholanthrene (MCA) or 1,2,5,6-dibenzanthracene [DB(a,h)A] were administered IP, immunotoxicity was observed in both AHH-inducible and AHH non-inducible animals. However, the AHH-inducible animals appeared to be more sensitive, and substantial suppression of a PFC response toxicity could be induced with doses as low as 14 mg/kg methylcholanthrene. While suppression of a mitogen response required a dose of 43-125 mg/kg. Administration of the weak carcinogen 1,2,3,4-dibenzanthracene [DB(a,c)A], IP, which similarly induces AHH activity in inducible animals, failed to induce immunotoxicity in either C57B1/6N or DBA/2N mice. In contrast to the results obtained following IP administration, when MCA was administered repeatedly (4X) via an intragastric (IG) route we observed striking immunosuppression of a PFC response in Ah locus negative (DBA/2) animals but minimal effects in Ah locus positive animals (C57B1/6). We finally observed that a single IP dose of MCA (125 mg/kg) to Ah locus positive animals substantially inhibited Natural Killer Cell activity but had more limited effects on the ability of an animal to reject a challenge by an immunogenic syngeneic fibrosarcoma.