Immunotoxicological effects of streptozotocin and alloxan: in vitro and in vivo studies.

Streptozotocin (STZ) and alloxan (ALX), widely used to induce diabetes in experimental animals, have different structures and mechanisms of action. We investigated those effects of these drugs on the immune system that might influence engraftment efficiency and graft survival in transplantation models, and their cytotoxicity on hematopoietic cell lines. We used the minimum dose to induce diabetes in a mouse, i.e. 180 mg/kg i.v. STZ and 75 mg/kg i.v. ALX. Both groups exhibited significant decrease in body weight during 4 days post-treatment as compared to controls. We found that blood glucose in ALX-injected mice increased faster than in STZ-injected mice. The total number of recovered splenocytes was lower in STZ-injected animals than in ALX-injected animals. The survival periods of rat islet grafts in recipient mice were longer and more diverse in STZ-injected recipients (7-24 days) compared to ALX-injected recipients (6-7 days). The in vitro study showed that ALX was less cytotoxic in cell lines with IC50 values of 2809, 3679 and >4000 µg/ml for HL60, K562 and C1498 cells respectively. STZ was more toxic, especially in HL60 cells, with IC50 values of 11.7, 904 and 1024 µg/ml for HL60, K562 and C1498 cells respectively. Furthermore, in response to concanavalin A (Con-A), splenocytes from STZ-injected mice produced higher amounts of interferon-gamma (IFN-γ) than those from ALX-injected mice. In conclusion, STZ was more cytotoxic than ALX in vitro and in vivo. STZ caused lymphocytopenia, which may result in longer graft survival in STZ-treated animals than in ALX-treated animals.

Activation of peritoneal macrophages during the evolution of type 1 diabetes (insulitis) in streptozotocin-treated mice.

The effects of lipopolysaccharide (LPS) and desArg9Bradykinin (DBK) on the release of nitric oxide (NO) from macrophages of mice 8, 12 and 18 days after having been treated with low doses of streptozotocin (STZ; 5 × 45 mg/kg) were studied. The results showed that LPS stimulated the release of NO from macrophages of untreated animals by 50% whereas the bradykinin B(1) agonist desArg9Bradykinin (DBK) increased the level of NO by 20%. This increased NO production was totally abolished by incubating the cells with R-954, a selective bradykinin B(1) antagonist. The release of NO from macrophages of STZ-treated mice incubated in the presence of LPS was more marked and reached approximately 220, 300 and 270% respectively from cells collected 8, 12 and 18 days after the STZ treatment. These significant increases were completely blocked by R-954 and were even below control values. Similarly the results showed that DBK stimulated by 50-75% the release of NO from macrophages of STZ-treated mice. The most marked stimulation was noted when the cells were collected 18 days after the treatment of the animals with STZ. Again in this set of experiments the B(1) antagonist completely blocked the release of NO which went even below control values. The results clearly suggest the upregulation of bradykinin B(1) receptors in mouse macrophages in the early phase of STZ-induced diabetes, an event that could even precede the onset of the diabetic hyperglycemia.

Differential requirement for CD28/CTLA-4-CD80/CD86 interactions in drug-induced type 1 and type 2 immune responses to trinitrophenyl-ovalbumin.

The use of mAbs to abrogate costimulatory interactions has attracted much attention with regard to prevention and modulation of adverse (auto)immune-like reactions. However, the role of costimulatory molecules and possible therapeutic use of Ab-treatment in drug-induced immunostimulation is poorly elucidated. In the present studies, we show that CD28/CTLA-4-CD80/CD86 costimulatory interactions differently regulate drug-induced type 1 and type 2 responses to an identical bystander Ag, TNP-OVA, in BALB/c mice using the reporter Ag popliteal lymph node assay. The antirheumatic drug D-Penicillamine, which may induce lupus-like side-effects, stimulated type 2 responses against TNP-OVA, characterized by the production of IL-4 and TNP-specific IgG1 and IgE. These responses were abrogated in CD80/CD86-deficient mice and in wild-type mice that were treated with anti-CD80 and anti-CD86, or CTLA-4-Ig. Anti-CTLA-4 intensively enhanced the D-Penicillamine-induced effects. In contrast, the type 1 response (IFN-gamma, TNF-alpha, IgG2a) to TNP-OVA induced by the diabetogen streptozotocin still developed in the absence of CD80/CD86 costimulatory signaling. In addition, it was demonstrated that coadministration of anti-CD80 and anti-CD86 mAbs slightly enhanced streptozotocin-induced type 1 responses, whereas the CTLA-4-Ig fusion protein completely abrogated this response. In conclusion, different drugs may stimulate distinct types of immune responses against an identical bystander Ag, which are completely dependent on (type 2) or independent of (type 1) the CD28/CTLA-4-CD80/CD86 pathway. Importantly, the effects of treatment with anti-CD80/CD86 mAbs and CTLA-4-Ig may be considerably different in responses induced by distinct drugs.

The reactive D-glucopyranose moiety of streptozotocin is responsible for activation of macrophages and subsequent stimulation of CD8+ T cells.

The antitumor drug streptozotocin (STZ) is commonly used as a diabetogenic compound in animal models. At relatively low doses, STZ-induced beta cell destruction is associated with Th1-driven type 1 immune reactions, including macrophages (MPhi) and IFN-gamma-producing CD8(+) T cells. STZ induces similar Th1-dependent effects in the popliteal lymph node assay (PLNA), and because this assay allows straightforward examination of early immunostimulating processes, the PLNA was used to further examine the importance of MPhi and structural properties of STZ in relation to the induction of type 1 immune responses. Results show that elimination of MPhi with clodronate-containing liposomes prior to exposure to STZ prevents the occurrence of some (CD8(+) T cell activation, IFN-gamma production, and tissue destruction) but not all (IgG2a formation) type 1 immune responses. It appeared that stimulation of MPhi depends on the d-glucopyranose moiety of STZ, as well as on the intact reactive N-methyl-N-nitrosourea (MNU) moiety. However, the MNU moiety suffices to induce IgG2a formation. In addition, STZ-derived nitric oxide may have modulating effects on the elicitation of STZ-induced immune responses. Present results support the idea that MPhi activation is indispensable for the STZ-induced tissue destructive type 1 responses and that various STZ-induced type 1 immune responses are differently regulated.

Tritiated thymidine incorporation does not enhance sensitivity of the popliteal lymph node assay.

The popliteal lymph node (PLN) assay has been proposed as a tool to predict drugs and chemicals with the potential to induce systemic autoimmune reactions in man. In this assay, weight and cellularity indices typically are the measured endpoints. The present study was conducted to test whether incorporation of tritiated thymidine could improve sensitivity of the PLN assay. Male and female Balb/c mice were injected with 20 microCi of [3H]-methyl-thymidine intravenously 7 days after receiving 0.5, 1 or 2 mg of diphenylhydantoin, streptozotocin, sulfamethoxazole, ofloxacin, phenobarbital, or metformin intradermally. Results obtained with incorporation of tritiated thymidine were compared to weight indices. No consistent or marked differences in these endpoints were noted whatever the compound used. This study shows that incorporation of tritiated thymidine does not improve sensitivity of the PLN assay.

Increased production of interferon-gamma, but not IL-4 mRNA, by streptozotocin in the popliteal lymph node assay.

The popliteal lymph node (PLN) assay has been proposed as a tool to predict systemic autoimmune reactions induced by medicinal products and chemicals, the mechanisms of which are poorly understood. To determine whether PLN responses involved Th1 or Th2 cell control, or both, the effects of streptozotocin (STZ), a prototypic immunotoxic compound, were analysed on the production of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) mRNA by lymph node cells after injection into the hind footpad of C57 BL/6 mice. Streptozotocin induced a dramatic increase in IFN-gamma mRNA production, which correlated with PLN responses as evidenced by augmented weight and cellularity indices. No effect on IL-4 mRNA synthesis was noted. These results suggest that a Th1 response is involved in the PLN response to STZ.

The popliteal lymph node response to streptozotocin is under type 1, MHC class-I restricted, CD8(+) T-cell control.

The popliteal lymph node (PLN) assay has been proposed to predict the 'autoimmunogenic' potential of xenobiotics. A better understanding of the processes involved in PLN responses is needed to establish the value of this assay for preclinical safety evaluation. In order to determine whether PLN responses involve CD4(+) or CD8(+) T-cells, the effects of streptozotocin (STZ), a prototypic immunotoxic compound, were analyzed after injection into the hind footpad of C57 BL/6 mice and major histocompatibility complex (MHC) class I or II deficient mice. The involvement of type 1 or type 2 cell control on the production of cytokine mRNAs was analyzed in lymph node cells by quantitative RT-PCR, together with the analysis of a wide range of cytokine mRNAs after STZ injection (IL-1alpha, IL-1beta, TNF-alpha, IFN-gamma, IL-2, IL-2 receptor, IL-4, IL-5, IL-6, IL-10 and IL-12). We have found that mice depleted in CD8(+) T-cells did not respond to STZ, whereas mice depleted in CD4(+) T-cells exhibited the expected positive PLN responses, with increased weight and cellularity indices. STZ induced a low production of interleukin (IL)-2 mRNAs, a mild increase in IL-1alpha and IL-6 mRNAs production, and a dramatic increase in IFN-gamma, IL-1beta, TNF-alpha, IL-12 and IL-2 receptor mRNAs, which correlated with positive PLN responses. No effects on IL-4, IL-5 and IL-10 mRNAs synthesis were noted. In CD8(+) T-cell deficient mice, there was no production of IFN-gamma or IL-6 mRNAs. These results suggest that PLN responses to STZ are under the control of type 1, MHC class-I-restricted, CD8(+) T-cells. This is in accordance to the known physiopathology of STZ-induced diabetes. Additional studies are necessary to establish the mechanism of CD8+ T-cell activation.

Selective immunomodulation by the autoimmunity-inducing xenobiotics streptozotocin and HgCl2.

Exposure to certain drugs and environmental chemicals can provoke the onset of autoimmune disease in susceptible individuals by releasing (self) epitopes for which tolerance has not been established, while simultaneously providing the necessary adjuvant activity. The resulting response type is influenced by the genotype of exposed individuals and relates to susceptibility to the adverse immune effects of the chemicals. Here, we assessed the modulatory role of the chemical compounds themselves. A single injection of streptozotocin (STZ) increased the number of CD8+ cells, macrophages, apoptotic cells, and IFN-gamma-producing T helper and T cytotoxic cells, whereas the number of CD4+ cells and B cells was reduced in the draining lymph node. Coinjection with the reporter antigen TNP-OVA resulted in primary and secondary production of TNP-specific antibodies that were predominantly of IgG2a and IgG2b isotype, whereas STZ did not enhance priming for delayed-type hypersensitivity (DTH) responses to TNP-OVA. Injection of HgCl2 on the other hand, reduced the number of IFN-gamma-producing cells, induced accumulation of B cells and CD4+ and CD8+ T cells, enhanced IgG1 and IgE production to TNP-OVA, and primed for secondary IgG1 and IgE production as well as for DTH reactions. Together these results indicate that a single injection of STZ stimulates type-1 responses, whereas HgCl2 enhanced mixed type-1 and -2 responses in BALB/c mice. These response types match the (auto)immune effects elicited to unknown (auto)antigens following multiple injections of these chemicals.

CD28/B7 regulation of autoimmune diabetes.

The initiation and progression of autoimmune diseases, such as insulin-dependent diabetes mellitus (IDDM), are complex processes that depend on autoantigen exposure, genetic susceptibility, and secondary events that promote autoaggression. T-cell costimulation, largely mediated by CD28/B7 interactions, is a major regulatory pathway in the activation and differentiation of T-cells that cause IDDM in murine models. In this article, we summarize our results in two models of IDDM: the nonobese diabetic (NOD) mouse and diabetes induced with multiple low doses of streptozotocin (MDSDM). In both of these models, blockade of CD28/B7 costimulation regulates the development of disease. The effects of blockade vary with the intensity of cognate signal delivered to the T-cells, the timing of the costimulatory signal, and perhaps even the CD28 ligand expressed on antigen-presenting cells (APCs). Our results suggest that targeting CD28/B7 signals is a feasible approach for treatment and prevention of recurrence of autoimmune diabetes. However, the dynamic nature of these interactions highlights the importance of a clear understanding of their role in regulation of the disease.

Expression and immune response to islet antigens following treatment with low doses of streptozotocin in H-2d mice.

Insulin dependent diabetes mellitus (IDDM) is likely to be due to the immunologic destruction of the islets of Langerhans. However, the relative importance of expression of a unique set of islet antigens or of differences in immune responses to those antigens in determining susceptibility to auto-immune diabetes is unknown. To a large extent, the reason for this uncertainty is the difficulty in directly identifying islet antigens expressed in vivo. We have studied the relationship between islet antigen expression, immune responsiveness to islet antigens, and the development of diabetes in diabetes induced by multiple low-doses of streptozotocin (STZ) in mice of the H-2d haplotype. We identified the expression of relevant islet antigens by testing the ability of STZ treated islets to induce tolerance to diabetes in C57BL/KsJ mice after intrathymic transplantation. C57BL/KsJ but not BALB/cByJ mice developed hyperglycaemia and insulitis following STZ treatment. Interferon-gamma transcription was detected in intrapancreatic lymphocytes from C57BL/KsJ mice but at lower levels in cell from BALB/cByJ. IL-4 levels were higher in BALB/cByJ than C57BL/KsJ. Intrathymic STZ-treated islets from syngeneic mice induced tolerance to diabetes in C57BL/KsJ mice following transient depletion of mature peripheral T cells, but islets from resistant BALB/cByJ mice did not induce tolerance to disease in C57BL/KsJ mice even though they did cause tolerance to the alloantigens. (C57BL/KsJ x BALB/cByJ)F1 mice developed hyperglycaemia like the susceptible parent following STZ treatment, and islets from these mice induced tolerance to MDSDM when treated with STZ and transplanted intrathymically into C57BL/KsJ. We conclude the expression of islet antigens and the intrapancreatic responses to STZ treated islets differs between mice that are susceptible and resistant to multi-dose streptozotocin induced diabetes mellitus.

Specific immunity to streptozocin. Cellular requirements for induction of lymphoproliferation.

The mechanism(s) of the immunological reactions involved in the pathogenesis of hyperglycemia induced by multiple intraperitoneal injections of subdiabetogenic doses of streptozocin (STZ) in mice remains to be elucidated. We found that STZ can act as a hapten in vivo by using the popliteal lymph node (PLN) assay. With this assay a direct toxic effect of STZ on the pancreatic beta-cells was dissociated from the effects exerted on the immune system. Subcutaneous injections of STZ induced immune reactivity in the draining PLN as determined by increase in weight, cell number, and [3H]thymidine incorporation. T-lymphocytes were required to induce the PLN response to STZ, because athymic nu/nu mice completely failed to respond to STZ, in contrast to their euthymic +/nu counterparts (P less than .001). The STZ-induced PLN response was sex independent and unaffected by prior subcutaneous injections of 3-O-methylglucose known to protect pancreatic beta-cells against STZ. STZ-primed mice exhibited an accelerated and enhanced STZ-specific secondary PLN response on challenge with subimmunogenic doses of STZ. In adoptive transfer experiments, STZ-sensitized splenic lymphocytes enriched for T-lymphocytes induced an STZ-specific significant (P less than .005) PLN enlargement provided the syngeneic recipients had been pretreated with subimmunogenic doses of STZ. Presumably, such STZ-specific immune reactions enhance a subtoxic effect of STZ on the pancreatic beta-cells.

Effects of three new nitrosourea analogs (CNCC, RFCNU and chlorozotocin) on in vivo destruction of L 1210 leukemia cells and on the immune response.

Three new nitrosourea analogs (CNCC, RFCNU, and chlorozotocin) had comparable activities in vivo against L1210 leukemia cells. In addition to the antileukemia effect, these drugs also decreased both the humoral immune response to sheep red blood cells and the delayed hypersensitivity reaction to oxazolone. The immunodepression induced by these agents lasted at least 25 days, and could not be reversed by the transplantation of normal syngenic bone marrow cells into treated animals.

Islet implantation into diabetic mice with pancreatic insulitis.

Repeated injections of small doses of streptozotocin (s.z.) lead to a slowly-developing hyperglycemia with a concomitant infiltration of lymphocytes into the pancreatic islets. Similarly, intrasplenically islet-implanted but otherwise normal mice became diabetic when given the multi-s.z.-treatment, suggesting that the splenic location of the islets does not protect them from the toxic effects of s.z. or immune-reactions. Intrasplenic, syngeneic islet implantation normalized the elevated blood sugars of multi-s.z.-treated mice, irrespective of whether the transplantation was performed 8 or 15 days after the first injection of s.z. These findings suggest that s.z. has to be present in order to trigger the auto-immune process of this insulitis model. In support of this suggestion, we observed that hyperglycemic, multi-s.z.-treated mice cured by islet implantation reverted to a hyperglycemic state when treated repeatedly with small doses of s.z., suggesting the presence of a booster-dose phenomenon.