Protein A protects mice from depletion of biotransformation enzymes and mortality induced by Salmonella typhimurium endotoxin

Cysteine Supplementation Mitigates the Toxicity Associated with Antitumor Therapy of Ehrlich's Ascites Fluid Adsorbed over Protein A Containing Staphylococcus aureus Cowan I

Introduction:

Previously, we have reported the amelioration of ad-AF induced hepatotoxicity with the exogenous supplementation of glutathione (GSH) without compromising the anti-tumor effect of ad-AF in ascites tumor model of mice with transplantable Ehrlich’s Ascites Tumor cells. Cellular uptake of glutathione (GSH) has its own limitations, therefore exogenous supplementation of L-cysteine (Cys) was tried to reduce the toxicity of ad-AF by providing –SH contents without compromising the anti-tumor property of adsorbed ascites fluid (ad-AF).

Results:

A significant increase in mean survival time (MST) of tumor bearing mice from 18.1 days to 32.9 days with exogenous supplementation of Cys was observed. Cys supplementation did not alter decline in body-weight gain, tumor cell counts as well as decrease in the viability of tumor cells in ascites tumor bearing animals. Similarly, Cys has been helpful to restore the hepatic –SH contents upto the levels of –SH content in tumor control group. The exogenous supplementation of Cys along with ad-AF has been helpful to restore the decline in the activities of phase-I and enhanced levels of glutathione-S-transferase (GST). The changes in the activities of different enzymes of phase-I and phase-II indicate the reduction in toxic insult induced by the therapeutic material (ad-AF). However, ad-AF treatment could not prevent tumor bearers from natural death due to tumor progression but significantly reduced the rate of tumor progression.

Conclusions:

Our study suggests that exogenous supplementation of Cys alongwith ad-AF could have a potential to be developed as a modality for the treatment of ascites tumor at least at experimental level.

Exogenous supplementation of N-acetylcysteine Can Reduce Hepatotoxicity Induced by Ascites Fluid (Cell-Free) Adsorbed Over Protein-A-Containing Staphylococcus aureus Cowan-I Without Compromising Its Antitumor Effect

Introduction:

Hepatotoxicity along with enhanced mortality has remained a major concern during the development of antitumor therapy with the use of cell-free ascites fluid adsorbed (ad-AF) over Protein-A-containing Staphylococcus aureus Cowan I (SAC). Major issue with ad-AF inoculation is the significant depletion of hepatic glutathione (GSH). Exogenous supplementation of –SH contents to the host has offered an encouraging hope to explore the possibilities to use ad-AF as a therapeutic material due to its antitumor effects. GSH and l-cysteine have shown a promise with the recovery of –SH contents as well as the recovery of phase I and phase II biotransformation enzymes. Aforementioned observations prompted us to try other –SH donors.

Materials and Methods:

Therefore, in this study, N-acetylcysteine (NAC) was used as an exogenous source to provide –SH contents to reduce hepatotoxicity and mortality induced by ad-AF treatment.

Results:

Exogenous supplementation of NAC along with ad-AF treatment to ascites tumor bearers has shown a significant protection against hepatotoxicity and mortality caused by ad-AF. NAC substitution along with ad-AF has significantly enhanced the mean survival time (MST), without altering the antitumor effect of ad-AF as evident from tumor cell counts and viability.

Discussion:

NAC supplementation has been successful to recover hepatic –SH contents along with the significant recovery of phase I and phase II biotransformation enzymes. Marker enzymes for liver injury have also given clear-cut indications for the recovery of tumor bearers from hepatotoxicity induced by ad-AF.

Conclusion:

This study has shown that exogenous supplementation of NAC protects the host from the enhanced mortality and hepatotoxicity induced by ad-AF. These observations offer a hope to develop ad-AF as one of the probable treatment strategies for ascites tumors at least at experimental levels.

A murine model for studying endotoxemia and the efficacy of anti-LPS agents in an immunocompromised host

In most murine models of endotoxemia, an exogenous agent is injected to increase the sensitivity of the mouse to endotoxin (lipopolysaccharide, LPS). Here, a clinically encountered event, a bum, was found to reproducibly decrease the amount of LPS required to kill half of the mice (LD50). In this more clinically relevant model, the anti-LPS agents, monophosphoryl lipid A and polymyxin B sulfate, each increased the LD50 of burned mice challenged with LPS from Klebsiella pneumoniae, while the LPS-directed monoclonal antibody E5 did not. However, E5 did protect burned mice challenged with smooth or rough LPS from Salmonella typhimurium and S. minnesota, respectively. Hence, in vivo protection was dependent upon both the anti-LPS agent and the chemical composition of the LPS used for intoxication. The differences in protection observed in this intoxication model may explain some protection discrepancies reported when these anti-LPS agents have been tested for protection against Gram negative sepsis.

Activities of conjugating and antioxidant enzymes following endotoxin exposure

Endotoxin exposure elicits various responses in mammals including the acute phase response that has been shown to cause changes in the activity of several forms of cytochrome P450s and other enzymes. Therefore, the hepatic conjugating enzyme, glutathione S-transferase (GST), and UDP-glucuronosyltransferase (UDPGT), the antioxidant enzymes, glutathione peroxidase (GSHPx), catalase, and superoxide dismutase (SOD), as well as lipid peroxidation were investigated following the administration of endotoxin to male Sprague-Dawley rats (8 mg/kg body weight). Rats were euthanized at various times following endotoxin administration and the livers removed and processed to assess various enzyme activities. Glutathione S-transferase, UDPGT, and GSHPx activity showed statistically significant decreases after 24 hours and remained lower than controls for the duration of the study. Decreases in total SOD and catalase activities were seen at 24, 48, and 72 hours following endotoxin administration; however, only catalase activity showed statistically significant differences between control and treated samples at those time points, and total SOD activity showed a statistically significant decrease at 24 hours. No statistically significant changes were seen in the level of lipid peroxidation in the liver microsomes from endotoxin-treated animals. Changes in the conjugative enzymes and the free-radical scavenging enzymes following endotoxin exposure may alter the host's metabolism and response to free radicals.

Protein A-activated rat splenic lymphocyte proliferation involves tyrosine kinase-phospholipase C-protein kinase C pathway

Protein A (PA) of Staphylococcus aureus was long been known for its affinity towards the Fc domain of immunoglobulin G. It is now well established that PA is a potent biological response modifier showing simultaneously antitumor, antitoxic, and anticarcinogenic properties. This bacterial protein was also observed to stimulate production of cytokines. But the molecular mechanism(s) of immunocyte activation by PA still remained essentially unknown. In this report, we demonstrate a hitherto undescribed role of PA as a signal inducer in rat splenic lymphocytes. Our studies describe that PA induces transition of G0/G1 to S and G2/M phases of cell cycle, thus ultimately stimulating splenic lymphocyte proliferation. It has also been revealed that PA binds to rat splenic lymphocytes in a dose dependent manner and stimulates proliferation via tyrosine kinase-phospholipase C (PLC)-Ca2+-dependent protein kinase C (PKC) pathway. These observations will be of valid help in correlating the immunostimulatory activities of PA with the molecular mechanism(s) of its action.

Protein-A activates membrane bound multicomponent enzyme complex, NADPH oxidase in human neutrophils

Protein-A, 42KD cell wall glycoprotein of S. aureus Cowan I enhance mononuclear and polymorphonuclear cell counts in vivo and possesses antitoxic, antitumor, properties. In order to explain the mechanism of its function, the respiratory burst phenomenon in cell and cell free system was studied using lucigenin-dependent chemiluminescence technique. A dose dependent increase in protein A-mediated generation of superoxide radical was observed in resting and PMA stimulated neutrophils. Superoxide dismutase (SOD) was used to confirm the production of superoxide radicals (O2-). To understand the mechanism of protein-A induced O2- generation; NADPH oxidase activity was measured in cell free system using NADPH as a substrate. A significant increase in NADPH oxidase activity was observed in the membrane and post-nuclear supernatant fraction of activated human neutrophils. Cytosolic fraction showed slight enzyme activation. Protein A (SpA)-induced NADPH oxidase activation in the membrane fraction was observed even in the absence of the substrate NADPH. These data indicate that protein A attenuate the NADPH oxidase system to produce O2- radicals.

Protection by protein A of apoptotic cell death caused by anti-AIDS drug zidovudine

Zidovudine, the anti-AIDS drug, caused inhibition of mitogen-induced proliferation and perturbation of cell-cycle progression of cultured bone marrow cells of mice. There was significant hypoploidy observed in flow cytometric analysis of AZT-treated bone marrow cells. In apo-direct analysis, cells showed apoptosis in G0/G1 phase. In DNA gel analysis, characteristic laddering of apoptosis was observed in AZT-treated bone marrow cells. We demonstrated that, when the animals were pretreated with protein A (PA) of Staphylococcus aureus, the apoptotic changes could be prevented in bone marrow cells of AZT-treated animals. There is a significant (p < 0.05) increase in proliferation of bone marrow cells subjected to mitogen treatment in PA+AZT-treated animals, compared to only AZT-treated animals. However, cell-cycle phase distribution was not hampered and no laddering in DNA gel analysis was also observed in this group. In apo-direct analysis, PA treatment showed significant (p < 0.001) inhibition of AZT-induced apoptosis. These observations indicate that by using a suitable agent such as protein A the toxic side effects of AZT could be minimized.

Functional mimicry of protein A of Staphylococcus aureus by a proteolytically cleaved fragment

Protein A (PA) of Staphylococcus aureus has an array of biological functions, such as antitumor, antitoxic, anticarcinogenic, immunomodulatory, antifungal, and antiparasitic properties. We have already established that a theoretical trypsin-digested peptide fragment of protein A (20-mer) mimics immunomodulatory and IgG binding property of PA. In the present report we have concentrated on a 16-mer chymotryptic fragment of protein A, which has a sequence of 13 amino acids in common with the previously studied 20-mer peptide. Molecular modeling study qualitatively predicted that both 20-mer and 16-mer peptides retain Fc binding ability from an interaction energy point of view. In the present study our aim was to understand whether this theoretically predicted 16-mer chymotryptic fragment could be formed in a real experiment and also to understand its biological activities. Chymotrypsin cleavage of PA at 37 degrees C for 24 h produced four major fragments on reverse-phase HPLC. The amino acid analyses of each fragment show the absence of cysteine residue from all fragments, which justifies the absence of cysteine in PA. We also observed high content of aspartic acid and glutamic acid residues in all fragments. On gel-filtration chromatography the chymotrypsin cleavage of PA shows five peaks, one of which overlaps with our theoretically selected 16-mer peptide on superimposition. We verified the IgG binding capacity of 16-mer peptide by capillary electrophoresis. The 16-mer peptide also induces the production of TNFalpha and IL-1alpha in serum of mice. The above observations suggest that the 16-mer peptide may be produced by chymotrypsin cleavage and also that this peptide possesses some of the major biological properties of PA, such as IgG binding, TNFalpha and IL-1alpha elicitation, etc.

A minimized Fc binding peptide from protein A induces immunocyte proliferation and evokes Th1-type response in mice

It is now well established that PA is a potent biological response modifier, showing simultaneously antitumor, antitoxic, anticarcinogenic, antifungal, antiparasitic and immunomodulatory properties. Since PA is a foreign protein, it is quite logical to assume that it may be cleaved into smaller peptide fragments in vivo which may be responsible for biological activities of whole PA molecule. The present study was undertaken to dissect out the structural entities of PA responsible for its biological properties. Protein A (PA) of Staphylococcus aureus has a unique property of binding with immunoglobulins. On the basis of molecular modeling and energy minimization studies a 20-mer tryptic fragment (theoretical) was predicted to retain IgG binding capacity which has been verified by immunoblot. This peptide sequence was selected to carry out experimental studies to show its functional mimicry of PA. We observed in the sera of 20-mer peptide treated mice that the concentrations of IFNgamma, TNFalpha and IL1alpha increase to a peak level by 4 h; on the other hand, there was a decrease in IL4, IL6 and IL10 concentrations at the same time (4 h). The ratio of IFNgamma to IL4 showed Th1 type of response with the peptide as well as with that of PA. The nitric oxide concentration in sera also increases and the peak increase was in 6 h with both the peptide and PA. Cell cycle analysis using FACS shows that 20 micrograms dose of peptide was non-toxic to thymocytes and spleenocytes; on the other hand, it was immunoproliferative, shifting the thymocytes and spleenocytes from G0/G1 to S phase of the cell cycle. Further studies are in progress to evaluate other biological properties of the peptide, to evaluate if this peptide could be used as a substitute of PA to mimic at least some of its biological activities.

S. aureus superantigen protein A expands CD4(+)/CD8(+)/CD19(+)/CD34(+) cells in mice: a potential immunorestorer

Protein A (PA) of Staphylococcus aureus is known for its immunostimulatory, anti-cancer, and anti-toxic properties. The present study revealed that PA stimulates specific immunocytes to act as a potential immunorestorer. It has also been shown that the percentage of various cell types bearing different clusters of differentiation markers, e.g., CD4(+), CD8(+), CD19(+), increases considerably after inoculation with PA. It has also been observed that CD34(+) progenitor cells of bone marrow also increased significantly (P < 0.05) upon PA treatment. PA significantly elevated Th-1 cytokines, e.g., IFN-gamma, TNF-alpha, and IL-1alpha. The increased percentages of CD4(+), CD8(+), CD19(+), CD34(+) cells and elevated cytokine levels in PA treated animals may contribute to the reported anti-tumor, anti-fungal, anti-parasitic, and anti-toxic properties of PA. Since in various diseased conditions and during toxic drug therapy lymphocytes bearing such differentiation markers get suppressed, this type of approach could help in immunorestoration of the host. These findings might help in designing therapeutic approaches toward various diseases which cause immunosuppression.

Antitumour activity of protein A in a mouse skin model of two-stage carcinogenesis

Protein A (PA) is an immunostimulating glycoprotein (mol. wt. 43,000 kDa) obtained from Staphylococcus aureus cowan I. The antitumour property of PA is well documented in the literature in various transplantable tumours of rats and mice. In the present set of investigations, the antitumour property of PA was tested in Swiss albino mice in a two-stage initiation-promotion mouse skin carcinogenesis model. The animals were initiated topically with a single subcarcinogenic dose (52 microgram) of 7,12-dimethylbenzanthracene (DMBA). PA was administered intraperitoneally (1 microgram/animal), twice weekly for 2 weeks. Promotion was performed by twice weekly applications of 12-O- tetradecanoyl phorbol-13-acetate (TPA) at a dose of 5 microgram/animal for 32 weeks. The result showed that the treatment schedule can effectively check the onset of tumorigenesis, the cumulative number of tumours and the average number of tumours per mouse. In the PA administered group, 30% of the animals remained tumour free until the termination of the experiments (i.e. 32 weeks of promotion). Thus the present study proves that protein A can effectively inhibit DMBA initiated and TPA promoted mouse skin carcinogenesis.

Modulation of primary antibody response by protein A in tumor bearing mice

Protein A (PA) is a cell wall glycoprotein of Staphylococcus aureus Cowan I, which possess a number of immunomodulatory and antitumor properties. We have previously shown that PA suppresses the anti-sheep erythrocyte primary antibody response in normal mice. The present investigation evaluates the effect of protein A on the anti-sheep erythrocyte primary antibody response in tumor-bearing mice. The primary antibody response in tumor-bearing mice immunized with sheep red blood cells (SRBC) was suppressed by the intraperitoneal administration of PA in a dose-dependent fashion. The plaque forming cell (PFC) assay was used to assess this response. Maximum suppression of the PFC response was observed at 12 micrograms PA/animal (p < 0.001) and could be observed at doses as low as 1 microgram PA/animal (p < 0.01). The amount of suppression was proportional to the number of PA doses administered. In addition this effect was critically dependent on the timing of PA administration. PA showed no significant effect on PFC when injected after immunization, but it produced pronounced suppression when injected prior to the immunization with SRBC. Maximum suppression of the PFC response was observed when PA was administered one day before the antigen challenge. PA also reduced splenic localization of 51Cr labeled SRBC to 42% (p < 0.01). The altered localization of antigen in spleen may be responsible for reduced PFC response in tumor-bearing mice. Depletion of B-lymphocyte is reported to exhibit tumor inhibition. Therefore, we propose that the suppression of the primary antibody response by PA helps in tumor regression by reducing the soluble immunosuppressive immune complexes.

Immunostimulating effects of protein A in immunosuppressed aflatoxin-intoxicated rats

Aflatoxin B1, the potent carcinogenic compound produced by the Aspergillus flavus group of fungi on food and feed, induces immunosuppressive effects in rodents. In this communication, we report an immunomodulatory approach to abrogate aflatoxin B1-induced immunotoxicity in rats using protein A of Staphylococcus aureus Cowan 1. We have earlier demonstrated that protein A can protect the animals from toxicities induced by a number of drugs, chemicals and toxins. In the present study various combinations of aflatoxin B1 exposure and protein A treatment in animals were used. It was observed that protein A could provide protection to animals from aflatoxin B1-induced immunotoxicity, as measured by a battery of tests assessing cell-mediated immunity (CMI) profile of the host. Various parameters showing suppression of CMI following aflatoxin B1 exposure were reverted back towards normalcy in protein A-treated animals. It is concluded that protein A may prove to be a useful agent to protect the host from aflatoxin immunotoxicity, in view of its stimulatory effects on various immune functions even after their initial depression due to aflatoxin B1.

Acrylamide induced immunosuppression in rats and its modulation by 6-MFA, an interferon inducer

In the present communication, we describe acrylamide (ACR) induced immunotoxicity and its modulation by an interferon inducer, the 6th mycelial fraction acetone (6-MFA) of Aspergillus ochraceus ATCC 28706. ACR administration to rats produced a significant decrease in the weight of spleen (p < 0.001), thymus (p < 0.001) and mesenteric lymph nodes (p < 0.05). A decrease in cellularity of spleen (p < 0.001), thymus (p < 0.001), bone marrow (p < 0.001) and circulating blood lymphocyte population (p < 0.001) was also recorded. ACR suppressed the humoral as well as cell mediated immunity as assessed by erythrocyte antibody complement (EAC)-rosettes (p < 0.001), hemagglutination titre (p < 0.001), PFC (p < 0.001) and the delayed type hypersensitivity response against sheep red blood cells (SRBC, p < 0.001). ACR treated immunosuppressed rats when treated with 6-MFA restored the circulating lymphocyte number to the normal level and a partial recovery in the weight of spleen and thymus. Potentiation of EAC-rosettes, hemagglutination titre, IgM-PFC and DTH response against SRBC was observed. It is concluded that 6-MFA ameliorate the ACR induced toxicity. This study may be of significance in prevention of ACR toxicity.

Modulation of anti-sheep erythrocyte primary antibody response by protein A in normal mice

Protein A (PA), a cell wall glycoprotein of Staphylococcus aureus Cowan I, is known to possess immunomodulatory and antitumor activities. In the present study the effect of protein A on the anti-sheep erythrocyte primary antibody response in normal mice has been investigated. Intraperitoneal administration of PA resulted in suppression of primary antibody response in mice immunized with sheep red blood cells (SRBC) as assessed by plaque forming cell (PFC) assay. The suppressive effect was dose dependent. Maximum suppression in PFC response was observed at 12 micrograms PA/animal and could be observed as low as 1 microgram PA/animal. The suppression at 6 and 12 micrograms PA/animal was significant when compared with control values (p < 0.02 and p < 0.001, respectively). However, no significant suppression was recorded at 1 microgram dose. The suppression was proportional to the numbers of administrations of PA to the mice and critically dependent on the timing of inoculation of PA. PA produced pronounced suppression when injected prior to the immunization of animals with SRBC. PA reduced splenic localization of 51Cr labelled SRBC to 55%. It is proposed that the altered localization of antigen (SRBC) in spleen may be responsible for reduced plaque forming cells in normal mice.

Modulation of benzene induced toxicity by protein A

Administration of benzene (i.p. 1.0 mL/kg body weight) for 3 consecutive days produced leucopenia and lymphocytopenia in female albino rats. In addition, the total iron content, lipid peroxidation and superoxide dismutase activity of the liver and bone marrow were significantly (P < 0.001) increased. Low molecular weight (LMW) bleomycin-detectable iron accumulated only in bone marrow. Prior administration of Protein A (PA), a multipotent immunostimulant and interferon inducer (60 micrograms/kg body weight, i.v. twice weekly for 2 weeks), ameliorated most of the adverse effects of benzene. PA restored the changes in hepatic histological architecture, reversed leucopenia and superoxide dismutase activity, lipid peroxidation, total iron content and LMW iron content of bone marrow were normalized. Isozymes of glutathione-S-transferase (alpha, pi, mu) which decreased following benzene exposure increased in PA pretreated benzene exposed rats. This study suggests that pretreatment with PA modulates the toxicity of benzene.

Mechanism of enhanced phagocytic response in protein a treated rat macrophages

Protein A of S. aureus Cowan I has been shown to stimulate macrophage mediated phagocytosis. The present study was undertaken to understand the mechanism involved in the enhancement of phagocytosis of peritoneal macrophages by protein A. The lucigenin and luminol-dependent chemiluminescence (CL) of rat peritoneal macrophages, after incubation with various concentrations of protein A, flow-cytometric studies using DCFH-DA as a fluorescent compound and phagocytosis of sheep red blood cells (SRBCs) by rat peritoneal macrophages were studied. A significant increase in lucigenin dependent CL due to formation of superoxide anions (O2-.) and in luminol dependent CL due to formation of hydrogen peroxide (H2O2) was observed in protein A treated macrophages. A significant increase in intracellular hydrogen peroxide (H2O2) was also observed along with an increase in phagocytosis of SRBCs by protein A treated macrophages. The present findings indicate that protein A helps to increase phagocytosis and triggers respiratory burst of macrophages. Thus, both increased phagocytic response and respiratory burst of macrophages in protein A treated animals may be contributing to the antitumor property of protein A reported earlier.

Effect of zinc on immune functions and host resistance against infection and tumor challenge

The effect of zinc treatment on immune function and resistance against infection and tumor challenge was studied in mice. Swiss albino mice were treated with zinc acetate (3 mg/kg body weight) in one or two intraperitoneal injections. Various immune function assays were performed in treated animals. Zinc treatment to normal animals caused potentiation of T-lymphocyte and macrophage functions. Zinc treatment was also found to increase host resistance against Candida albicans and Semliki Forest virus infections. Increased resistance against endotoxin shock and Ehrlich's ascites tumor challenge was also observed in zinc treated animals. It can be stated from this study that zinc treatment potentiates the cell mediated immunity and host resistance against infection and tumor challenge.

Induction of glutathione-S-transferase isoenzymes by protein A in rat liver

The administration of Protein A, a cell wall protein of Staphylococcus aureus Cowan I cells, causes an induction of glutathione-s-transferase in rat liver. Proteins, cross reactive with anti human glutathione-s-transferase, acidic (pi), basic (alpha, and neutral (mu) isoenzymes, are induced by 5.8, 2.2 and 6.15 fold respectively. The induction of glutathione -s-transferases, at least in part, might play a role in manifestation of therapeutic properties of Protein A.

Protein A induced abrogation of cyclophosphamide toxicity is associated with concomitant potentiation of immune function of host

This report confirms our previous observation that protein A (PA) of Staphylococcus aureus Cowan I reduces the cyclophosphamide (Cy) induced toxicity. PA treated animals recover quickly from the toxic effects of Cy. We have exhaustively studied the role of specific and nonspecific immunity in the protection of the animals. It was observed that PA helped the animals in the accelerated regeneration of leukocytes of blood (p less than 0.001) and different lymphoid organs like thymus (p less than 0.001), spleen (p less than 0.01) and bone marrow (p less than 0.01). Increased number and function of macrophages was also observed in PA (p less than 0.001) and PA+Cy (p less than 0.001) groups. PA, on one hand enhanced the cell mediated immunity while suppressed the humoral immunity as was assessed by increase in delayed type hypersensitivity response (p less than 0.001) and decreased in plaque forming cells (p less than 0.001), EAC-rosettes (p less than 0.001), hemagglutination (p less than 0.001) and hemolysin titre (p less than 0.05). On the basis of above observations we propose that the immunomodulatory activity of PA helped the animals to remain alive in two ways- (1) by early generation of the cells depleted by the Cy thus helping animals to repair the damaged immune system and fast clearance of the toxic metabolites of Cy (2) by temporarily suppressing the cells responsible for humoral immunity which are more susceptible to Cy metabolites.