Mercury-induced renal autoimmunity in the MAXX rat

Maternal exposure to mercury chloride during pregnancy and lactation affects the immunity and social behavior of offspring

Developmental HgCl2 exposures of F1 offspring (H-2(q/s)) from unsociable SJL/J (H-2(s)) dams with high susceptibility to Hg-induced autoimmunity (SFvF1) and from highly sociable FVB/NJ (FVB; H-2(q)) dams with lower susceptibility to Hg-induced autoimmunity (FvSF1) were investigated. Hg exposure increased the serum IgG levels of all offspring at postnatal day 21 (pnd21) and of SJL/J dams but not of FVB dams. Serum IgG anti-brain antibody (Ab) levels of pnd21 SFvF1 offspring and SJL dams were higher than those of the FvSF1 offspring and FVB dams, but Hg only increased the titers of the FVB dams and their offspring. Hg significantly elevated the presence of IgG in all brain regions of the pnd21 SFvF1 offspring, and the SFvF1 offspring had greater amounts of IgG in the brain than the FvSF1 offspring, which had Hg-induced increases in only two brain regions. Cytokine levels were elevated in the brain regions of Hg-treated pnd21 SFvF1 but not of FvSF1 offspring, and SFvF1 females had more brain regions expressing cytokines than the males. At pnd70, the serum IgG, serum antibrain Abs, amounts of brain IgG, and brain cytokine levels of all of the Hg-treated offspring were equivalent to those of their appropriate controls, suggesting that developmental Hg exposure did not induce chronic immunological effects. However, the social behaviors of Hg-exposed SFvF1 offspring at pnd70 were significantly impaired, and SFvF1 females displayed greater decline in social behaviors than males, suggesting that the higher neuroinflammation of SFvF1 females earlier in life is associated with the altered behavior. Thus, developmental Hg exposure induces long-lasting effects on social behavior of offspring, which is dependent on sex and genetics and the induction of neuroinflammation.

Phenotypic and gene expression differences between DA, BN and WOKW rats

BACKGROUND

Because inbred rat strains are widely used as laboratory models, knowledge of phenotypic and genetic variations between strains will be useful to obtain insight into the relationship between different strains.

METHODS AND RESULTS

We studied phenotypic traits: of each strain--BN/K, DA/K and WOKW--10 male rats were studied for body weight and serum constituents at an age of 10 and 30 weeks. In addition, a total of 95 rats were studied for life expectancy. At an age of 30 weeks, these male rats were killed by an overdose of anesthetic (Sevofluran, Abbott), and the subcutaneous and visceral adipose tissue as well as bone tissue were removed to study the expression of 20 genes. There were significant differences in body weight, serum lipids and leptin at an age of 30 weeks between strains. Regarding life expectancy, BN rats lived longest (1072±228d). The highest gene expression was found in bone of BN rats. In adipose tissues, Nfkb1 is only expressed in subcutaneous adipocytes, and 5 genes, Col2a1, Mmp9, Tnfa, Ins1 and Cyp24a1, are not expressed in adipocytes. The ranking BN = DA>WOKW was observed in only one gene in subcutaneous (Fto) and visceral adipocytes (Col6a1). There were no significant differences in gene expression of one gene in subcutaneous adipocytes and of 3 genes in visceral adipocytes. Comparing the gene expression in visceral and subcutaneous adipocytes, only one gene showed a comparable behavior (Bmp1).

CONCLUSION

From these results, it can be concluded that obvious phenotypic differences are caused by genetic differences between three rat strains, BN, DA and WOKW, as supported by gene expression studies in bone and adipose tissues. Especially BN rats can be used to study the genetic basis of long life.

Mercury in traditional medicines: is cinnabar toxicologically similar to common mercurials?

Mercury is a major toxic metal ranked top in the Toxic Substances List. Cinnabar, which contains mercury sulfide, has been used in Chinese traditional medicines for thousands of years as an ingredient in various remedies, and 40 cinnabar-containing traditional medicines are still used today. Little is known about toxicology profiles or toxicokinetics of cinnabar and cinnabar-containing traditional medicines, and the high mercury content in these Chinese medicines raises justifiably escalations of public concern. This minireview, by searching the available database of cinnabar and by comparing cinnabar with common mercurials, discusses differences in their bioavailability, disposition, and toxicity. The analysis showed that cinnabar is insoluble and poorly absorbed from the gastrointestinal tract. Absorbed mercury from cinnabar is mainly accumulated in the kidneys, resembling the disposition pattern of inorganic mercury. Heating cinnabar results in release of mercury vapor, which in turn can produce toxicity similar to inhalation of these vapors. The doses of cinnabar required to produce neurotoxicity are 1000 times higher than methyl mercury. Following long-term use of cinnabar, renal dysfunction may occur. Dimercaprol and succimer are effective chelation therapies for general mercury intoxication including cinnabar. Pharmacological studies of cinnabar suggest sedative and hypnotic effects, but the therapeutic basis of cinnabar is still not clear. In summary, cinnabar is chemically inert with a relatively low toxic potential when taken orally. In risk assessment, cinnabar is less toxic than many other forms of mercury, but the rationale for its inclusion in traditional Chinese medicines remains to be fully justified.

Activation profiles of HSPA5 during the glomerular mesangial cell stress response to chemical injury

Environmental injury has been associated with endoplasmic reticulum (ER) stress, a response characterized by activation of the unfolded protein response, proteasomal degradation of proteins, and induction of HSPA5, also known as GRP78 or BiP. Although HSPA5 has been implicated in the stress response to environmental injury in several cell types, its role in the glomerular ER stress response is unknown. In this study, we evaluated HSPA5 activation profiles in rat glomerular mesangial cells (rGMCs) challenged with heavy metals (HgCl2 or Pb2+ acetate) or polycyclic aromatic hydrocarbons (PAHs, ie, benzo(a)pyrene [BaP]). Challenge of rGMCs with 1 or 10 microM HgCl2 or Pb2+ acetate increased HSPA5 mRNA and protein levels. The induction response was sensitive to transcriptional and translational inhibition by actinomycin D (AD) and cyclohexamide, respectively. HSPA5 mRNA was induced by 3 microM BaP in an AD-sensitive manner, but this response was unaffected by the presence of heavy metals. A promoter construct containing sequences that mediate thapsigargin (TH) inducibility of the HSPA5 promoter was refractory to both heavy metals and BaP. The HSPA5 induction response in rGMCs is conserved because it was reproduced with fidelity in immunolocalization experiments of HSPA5 protein in M15 and HEK293 cells in embryonic lines of murine and human origin, respectively. Collectively, these findings identify HSPA5 in the stress response of rGMCs and implicate regulatory mechanisms that are distinct from those involved in TH inducibility.

Lack of graft-versus-host-like pathology in mercury-induced autoimmunity of Brown Norway rats

The repeated administration of mercury to Brown Norway (BN) rats induces the production of autoantibodies to laminin 1 and other autoantigens, accompanied by renal deposition of immunoglobulins and a membranous glomerulonephropathy. A graft-versus-host-like (GVHL) syndrome, characterized by widespread necrotizing leukocytoclastic vasculitis of the bowel, skin, and other tissues, has also been observed after mercury treatment of BN rats. These findings have suggested that the autoimmunity caused by the administration of mercury to BN rats may result as a xenobiotic-induced GVHL effect under the control of OX22+ T lymphocytes. However, previous studies of mercury-induced autoimmunity have never reported any evidence of GVHL lesions. Therefore, we have carefully examined various tissues from a large group of BN rats injected with HgCl₂ to identify possible areas of inflammatory reactions that may have been unnoticed in previous investigations. In addition, we have determined by flow cytometry whether exposure to mercury results in percentage and numerical alterations of OX22+ or other lymphocyte subpopulations in lymphoid organs of HgCl₂-treated BN rats. The present article confirms that mercury induces autoimmune responses to laminin 1 but does not corroborate the hypothesis of a GVHL syndrome regulated by OX22+ lymphocytes. First, changes in OX22+ cells during treatment with HgCl₂ were infrequent and had no significant correlation with the kinetics of autoimmune responses to laminin 1. Second, we detected no GVHL lesions in skin and intestine of mercury-treated BN rats.

Effects of HgCl2 on the expression of autoimmune responses and disease in diabetes-prone (DP) BB rats

Repeated exposure of Brown Norway (BN) rats to relatively low doses of HgCl2 induces autoantibodies to renal antigens (e.g., laminin) and a membranous glomerulonephropathy characterized by proteinuria. In contrast, Lewis (LEW) rats are "resistant" to the autoimmune effects of mercury and, when exposed to this metal, are protected against experimental autoimmune encephalomyelitis (EAE) and Heymann's nephritis. To date, there is no information on "suppressive" effects of mercury in naturally occurring (so-called "spontaneous") rat models of autoimmune disease. Therefore, we have administered HgCl2 to diabetes-prone (DP) BB rats, animals that spontaneously develop both insulin-dependent diabetes mellitus (IDDM) and thyroiditis. We found that DP rats treated with mercury or water for a period of 40-125 days developed autoantibodies to thyroglobulin, with a higher incidence in HgCl2-injected animals (92% vs. 56% in H2O-injected controls). A novel finding of our study was the detection of autoantibodies to laminin in the same rats, again with an increased incidence after HgCl2 treatment (83% vs. 44%). IgG2a was the most frequently detected isotype of antibodies to laminin, followed by IgG1, IgG2b and IgG2c. The IgG isotype profile suggests that treatment with HgCl2 may activate both Th1 and Th2 lymphocytes in BB rats. In spite of these stimulatory effects on autoantibody responses, we found that there was no difference in the incidence of IDDM and thyroiditis between HgCl2-treated and control animals. We conclude that the suppressive effects of mercury previously observed in EAE and Heymann's nephritis of LEW rats do not occur in "spontaneous" autoimmune IDDM and thyroiditis of BB rats. Therefore, immune suppression caused by HgCl2 cannot be considered a common phenomenon, but may be a genetically determined characteristic of LEW rats, possibly related to a specific or unique cytokine profile of this particular rat strain. In contrast, while mercury does not seem to recruit, induce or rescue regulatory T cell function in DP rats, it does stimulate autoantibody responses in these animals.

Abnormal antioxidant system in erythrocytes of mercury-exposed workers

To investigate the effects of chronic exposure to mercury we studied the red cell antioxidant system in mercury-exposed workers through the evaluation of reduced glutathione, catalase and superoxide dismutase systems. Of these workers, some were being exposed at the time and had presented urinary mercury levels considered safe for occupational exposure for at least 3 months prior to the initiation of this study, and others had been on leave for at least 6 months because of intoxication symptoms. Reduced glutathione levels were lower and catalase activity was higher in the workers which were still being exposed, compared to those on leave and controls. No differences were observed between the workers on leave and controls.

T lymphocytes in mercury-exposed workers

In this work we have investigated the changes in T-helper and T-suppressor cells and T-cell proliferative response to phytohemagglutinin (PHA) in mercury-exposed workers. The study group consisted of 33 workers from a mercury-producing plant with a mean age of 29 years and a mean exposure period of 19 months. At the time of testing, and for the three previous months, the exposed population had urinary mercury levels below the currently accepted limit of 50 micrograms/g creatinine. A reverse CD4+/CD8+ ratio was observed in the mercury-exposed individuals which was characterized by a reduction in the number of CD4+ lymphocytes. No changes were observed in the proliferative response of lymphocytes from exposed individuals to PHA. Similarly, no proliferative response was observed when lymphocytes from normal individuals were cultivated in the presence of serum from the exposed workers. We found no correlations between lymphocytes changes and urinary mercury concentrations, time of exposure or the age of the workers.

B lymphocytes in mercury-exposed workers

We have investigated the number of B lymphocytes in mercury-exposed workers. The study group consisted of 33 workers from a mercury-producing plant, mean age 27 years and a mean exposure period 19 months. At the time of testing and for the three previous months, the exposed persons had urinary mercury levels below the currently accepted limit of 50 micrograms g creatinine. A significant reduction in the number of B lymphocytes was observed in the mercury-exposed individuals. We found no correlation between B lymphocytes changes and urinary mercury concentrations, length of exposure or age of the workers.

Immunoglobulin E and autoantibodies in mercury-exposed workers

In this work we have studied the serum immunoglobulin E (IgE) levels and the concentration of anti-DNA and anti-nucleus antibodies in mercury-exposed workers. The study group consisted of 36 workers from a mercury producing plant, with a mean age of 27 years and a mean exposure period to mercury of 19 months. At the time of testing, and for the three previous months, the exposed population had urinary mercury levels below the currently accept limit of 50 ug/g creatinine. Significantly increased IgE levels was found in the mercury-exposed individuals. Moreover, a moderate negative correlation (r = -0.43 P < 0.05) between the length of exposure to mercury and IgE levels was observed. Anti-DNA and anti-nucleus antibodies were not detected in these workers. These results suggest that the humoral immune response is an indicator of cellular changes in workers chronically exposed to mercury, even in those with urinary mercury concentrations within levels considered safe in the occupational area.

Murine strain differences in response to mercuric chloride: antinucleolar antibodies production does not correlate with renal immune complex deposition

Mercuric chloride (HgCl2) induces the production of antinucleolar antibodies (ANucA) in susceptible strains of mice. Responder strains bearing the H-2(5) haplotype as well as several ANucA resistant strains have been shown to develop renal immune complex deposits after HgCl2 treatment. Sera obtained throughout 12 to 16 weeks of HgCl2 treatment from mice of four ANucA responder strains (A.SW/SnJ, A.CA/SnJ, DBA/1J, and P/J) and one ANucA-resistant strain (C57BL/10SnJ) were examined for ANucA production. Terminal sera were also tested for the presence of anti-glomerular basement membrane antibodies, and the kidneys were examined for the deposition of IgG and C3. Only one strain, A.SW, developed significant deposits of IgG in the renal glomeruli, although all four responder strains exhibited similar ANucA induction/production profiles. The differences seen by direct immunofluorescence assay (IFA) in renal immune complex deposition between the A.SW and histocompatibility congenic A.CA mice were corroborated by individually eluting and then quantitating the deposited IgG from renal tissues of Hg-treated A.SW and A.CA mice as well as control A.SW mice. The average amount of IgG eluted from A.SW renal tissue was significantly greater than that eluted from either A.CA or control A.SW renal tissues. All eluates from Hg-treated animals gave only a nucleolar fluorescence pattern when assayed by indirect IFA against a panel of rat organ tissues. In summary, no correlation was found between ANucA production and renal IgG deposition in response to treatment with HgCl2.

Measurement of the respiratory burst and chemotaxis in polymorphonuclear leukocytes from mercury-exposed workers

The chemotactic and nitroblue tetrazolium reducing activities of neutrophils from 48 mercury-exposed workers were examined and compared with those of non-exposed, age- and sex-matched individuals. At the time of testing, the exposed population had a mean (+/- s.d.) urinary mercury concentration of 24.0 +/- 20.1 micrograms g-1 creatinine and in 44 of these workers urinary mercury levels were below the accepted threshold level (TLV) of 50 micrograms g-1 creatinine. The two neutrophil functions were significantly reduced in the mercury-exposed workers compared with the controls. In 28 of these workers, chemotaxis was re-evaluated 6 months later. During the intervening 6 months, the level of hygiene was improved throughout the plant and urinary mercury concentrations were determined monthly in each worker. Despite a significant reduction in urinary mercury concentrations, neutrophil migration did not return to within the normal range. These results suggest that 'safe' level mercury exposure may lead to impairment of neutrophil function.

The in vitro effects of mercury on peritoneal leukocytes (PMN and macrophages) from inbred brown Norway and Lewis rats

The present paper demonstrates that HgCl2 can affect rat peritoneal polymorphonuclear leukocyte (PMN) and macrophage (M phi) functions in vitro. In addition, we have noticed that these effects of mercury vary according to the rat strain: for example, HgCl2 stimulates H2O2 release from Lewis (LEW) but not Brown Norway (BN) PMN. Similarly, LEW M phi produce high levels of H2O2 when exposed to HgCl2 in vitro, whereas BN M phi do not. Finally, mercury inhibits erythrophagocytosis of both LEW and BN "resident" peritoneal M phi. Preliminary experiments using M phi from other rat strains have also shown that MAXX M phi are stimulated by HgCl2 to release H2O2 in vitro, whereas Yoshida M phi are inhibited. Differences in lymphocyte responses (e.g. delayed-type hypersensitivity reactions and mitogen stimulation) between rats of various strains are well known. To these examples one may now add variations in PMN and M phi responses to mercury and possibly other metals. Our results suggest that caution should be exercised in interpreting the outcome of immunotoxicity studies in experimental animals. In particular, outbred rats may not provide appropriate models, that might be better obtained by comparative investigations of rats from various inbred strains.

Reduction of the RT6.2+ subset of T lymphocytes in brown Norway rats with mercury-induced renal autoimmunity

Chemically induced autoimmunity is a recently recognized environmental hazard that may affect individuals genetically predisposed to autoimmune disease and chronically exposed to certain chemicals. For example, moderate concentrations of mercury may lead to renal autoimmune disease in a small but significant percentage of the exposed population. Mercury also induces autoimmune glomerulonephritis in susceptible Brown Norway (BN) and MAXX inbred strain rats. Autoimmune responses, directed to epitopes of the renal glomerular basement membrane (GBM), are rapid in onset and have a self-limiting course in mercury-treated rats. Both regulatory T cells and idiotype-anti-idiotype network have been implicated in the resolution of this autoimmune process. In our investigations of immune regulation of mercury-induced autoimmune glomerulonephritis, we have used flow cytometry to quantitate lymphocyte subpopulations in the spleen and lymph nodes of mercury-treated and control BN rats. Of particular interest was the RT6+ T cell subset, that appears to have important immunoregulatory properties in a rat model of autoimmune insulin-dependent diabetes mellitus. Spleen and lymph nodes from control BN rats contained 22 and 52%, respectively, RT6+ cells. Spleens from mercury-treated animals contained 21% RT6+ cells on Day 10 of treatment, 13% on Day 17, 16% on Day 24 and 20% on Day 30. Lymph nodes from the same rats had 36% RT6+ cells on Day 10, 23% on Day 17, 29% on Day 24, and 28% on Day 30. The decrease in RT6+ cells correlated inversely with autoimmune responses to GBM, which peaked on Days 17-24 and declined by Day 30. Moreover, autoimmune responses were also associated with elevated RT6-:RT6+ T cell ratios. Similar results were obtained in two additional groups of BN rats, comprising both younger and older animals, sacrificed at Day 18 of mercury treatment. Analysis of other lymphocyte subpopulations demonstrated a decrease of CD4+ and CD5+ cells, whereas B cells as well as CD8+, IL-2 receptor+, and MHC class II+ subsets showed no consistent correlation with the onset or resolution of the autoimmune process. These findings suggest that mercury-induced changes in RT6+ T lymphocytes may be related to the development of renal autoimmune disease in genetically predisposed BN rats.

Epibodies in autoimmunity: antisera against autoantibodies to the renal glomerular basement membrane react with idiotypes as well as with autoantigens

The results reported here show that we have experimentally produced xenogeneic anti-idiotypic antibodies to rat autoantibodies specific for the renal GBM and one of its components, laminin. Cross-reactive idiotypes have been detected by anti-idiotypic antibodies (anti-Id) on autoantibodies to the GBM (anti-GBM) from rats of different strains, confirming the results obtained in other autoantibody systems. During the course of studies aimed at determining whether anti-Id were directed to the paratope of anti-GBM antibodies, we have observed the presence of anti-GBM (and anti-laminin) antibodies in rabbit sera with anti-Id. Affinity chromatography experiments suggest that anti-GBM reactions detected with our anti-Id sera may be caused by a heterogeneous combination of anti-Id. Thus, Ab2 alpha (and/or Ab2 gamma, all reacting with Ab1), Ab2 epsilon (epibodies, that bind to both Ab1 and GBM) and Ab3 (similar to Ab1 and therefore, reacting with GBM) may be present in our anti-Id sera. It has been suggested that antibodies displaying epibody properties may be involved in the mutual regulation of autoreactive clones and represent an important component of the autoimmune process.