Protection against carbon tetrachloride-induced hepatotoxicity by protein A

Studies of the safety, pharmacokinetics and immunogenicity of repeated doses of intravenous staphylococcal protein A in cynomolgus monkeys

Three Good Laboratory Practice safety studies were performed with intravenous injections of highly purified staphylococcal protein A (SPA) in cynomolgus monkeys, in support of a clinical development programme utilizing this protein as an immunomodulator. These studies established a no-observable-adverse-effect level (NOAEL) for up to 12 weekly doses of SPA, as well as toxicokinetic profiles for SPA, evaluation of antiproduct antibodies and biomarkers to better characterize the pharmacodynamic response to SPA. Biomarkers included neopterin, C-reactive protein (CRP), troponin I and the change in the blood absolute lymphocyte count (ALC) 24 hr after SPA dosing. The transient decrease in ALC noted at 24 hr after dosing was similar to that seen in human Phase 1 trials. The majority of active-treated monkeys developed antibodies against SPA. Cmax was not affected by development of antidrug antibodies (ADAs), and after the first dose was 87 (SD 19) ng/mL, 330 (SD 84) ng/mL and 1191 (SD 208) ng/mL for 5, 25 and 100 μg/kg doses, respectively. The development of ADAs increased plasma clearance of SPA. By the sixth weekly dose, the AUC was decreased by 76%, 54% and 66% for the 5, 25 and 100 μg/kg dose groups, respectively. These results indicate that SPA can be administered intravenously to non-human primates without observable toxicity at weekly doses of up to 100 μg/kg.

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.

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.

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.

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.

Protection against 7,12-dimethylbenzanthracene-induced tumour initiation by protein A in mouse skin

Protein A is an immunostimulating glycoprotein obtained from Staphylococcus aureus Cowan I. Its antitumour activity is proven in various tumour models. Its ability to provide protection against tumour initiation by the chemical carcinogen 7,12-dimethylbenzanthracene (DMBA) has been investigated in the present study using a mouse skin model of two-stage carcinogenesis. Protein A was administered intraperitoneally (1 microgram/animal 20 g body wt.) twice a week for 2 weeks, prior to initiation by DMBA. The promotion was performed by twice weekly applications of 12-O-tetradecanoyl phorbol-13-acetate (TPA) (3 or 5 micrograms/animal in 100 microliters acetone). Protein A provided significant protection to animals from DMBA-induced tumour initiation as was observed by the decrease in cumulative number of tumours, percent of animals developing tumours, number of tumours per animal and rate of tumour growth. Our data indicate that protein A has anticarcinogenic properties.

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.

Metabolic zonation of the liver: regulation and implications for liver function

Liver parenchyma shows a remarkable heterogeneity of the hepatocytes along the porto-central axis with respect to ultrastructure and enzyme activities resulting in different cellular functions within different zones of the liver lobuli. According to the concept of metabolic zonation, the spatial organization of the various metabolic pathways and functions forms the basis for the efficient adaptation of liver metabolism to the different nutritional requirements of the whole organism in different metabolic states. The present review summarizes current knowledge about this heterogeneity, its development and determination, as well as about its significance for the understanding of all aspects of liver function and pathology, especially of intermediary metabolism, biotransformation of drugs and zonal toxicity of hepatotoxins.

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.

Protection against carbon-tetrachloride-induced lymphoid organotoxicity in rats by protein A

In a previous study we described protection of rats from carbon tetrachloride (CCl4)-induced hepatotoxicity by protein A (PA). In the present report we described protection against CCl4-induced lymphoid organotoxicity in rats by PA. Our data indicate that CCl4 administration produced a significant increase in the number of total leukocytes and polymorphs in blood, a significant decrease in leukocyte count in bone marrow, and a significant loss in weight of spleen and adrenals. In the animals receiving PA prior to and after CCl4, these values were found to be near those of controls. Histological examination revealed thymocyte depletion in thymic lobe and degenerative changes of tissue in spleen of CCl4-exposed animals. PA treatment to CCl4-exposed animals exhibited improvement and recovery from the damage caused by CCl4. These observations throw a new light on the field of CCl4 toxicity to lymphoid organs and their protection by PA.