Xenotransplantation: just around the corner?

Grape Seed Proanthocyanidin Extract Alleviates AflatoxinB₁-Induced Immunotoxicity and Oxidative Stress via Modulation of NF-κB and Nrf2 Signaling Pathways in Broilers

Aflatoxin B₁ (AFB₁) is a widely spread mycotoxin contaminates food and feed, causing severe oxidative stress damages and immunotoxicity. Grape seed proanthocyanidin (GSPE), a natural antioxidant with wide range of pharmacological and medicinal properties. The goal of the present study was to investigate the protective effects of GSPE against AFB₁-induced immunotoxicity and oxidative stress via NF-κB and Nrf2 signaling pathways in broiler chickens. For the experiment, 240 one-day old Cobb chicks were allocated into four dietary treatment groups of six replicates (10 birds per replicate): 1. Basal diet (control); 2. Basal diet + AFB₁ 1mg/kg contaminated corn (AFB₁); 3. Basal diet + GSPE 250 mg/kg (GSPE); 4. Basal diet + AFB₁ 1 mg/kg + GSPE 250 mg/kg (AFB₁ + GSPE). The results showed that GSPE significantly decreased serum inflammatory cytokines TNF-α, IFN-γ, IL-1β, IL-10, and IL-6 induced by AFB₁. Similarly, GSPE + AFB₁ treated group revealed a significant decrease in mRNA expressions of pro-inflammatory cytokines (TNF-α, IFN-γ, IL-1β, and IL-6) in the splenic tissue compared to the AFB₁ treatment group. In addition, western blotting results manifested that GSPE treatment normalized the phosphorylation of nuclear factor kappa B (p65) and the degradation of IκBα protein induced by AFB₁. Furthermore, GSPE enhanced the antioxidant defense system through activating the nuclear factor-erythroid-2-related factor (Nrf2) signaling pathway. The mRNA and protein expression level of Nrf2 and its down streaming associated genes were noted up-regulated by the addition of GSPE, and down-regulated in the AFB₁ group. Taken together, GSPE alleviates AFB₁-induced immunotoxicity and oxidative damage by inhibiting the NF-κB and activating the Nrf2 signaling pathways in broiler chickens. Conclusively, our results suggest that GSPE could be considered as a potential natural agent for the prevention of AFB₁-induced immunotoxicity and oxidative damage.

Dual Role of Dietary Curcumin Through Attenuating AFB1-Induced Oxidative Stress and Liver Injury via Modulating Liver Phase-I and Phase-II Enzymes Involved in AFB1 Bioactivation and Detoxification

It is well understood that liver cytochrome p450 enzymes are responsible for AFB1 bioactivation, while phase-II enzymes regulated by the transcription factor nuclear factor-erythroid-2-related factor 2 (Nrf2) are involved in detoxification of AFB1. In this study, we explored the potential of curcumin to prevent AFB1-induced liver injury by modulating liver phase-I and phase-II enzymes along with Nrf2 involved in AFB1 bioactivation and detoxification. Arbor Acres broiler were divided into four groups including control group (G1; fed only basal feed), curcumin alone-treated group (G2; 450 mg/kg feed), AFB1-fed group (G3; 5 mg/kg feed), and curcumin plus AFB1 group (G4; 5 mg AFB1+450 mg curcumin/kg feed). After 28 days, liver and blood samples were collected for different analyses. Histological and phenotypic results revealed that AFB1-induced liver injury was partially ameliorated by curcumin supplementation. Compared to AFB1 alone-treated group, serum biochemical parameters and liver antioxidant status showed that curcumin supplementation significantly prevented AFB1-induced liver injury. RT-PCR and western blot results revealed that curcumin inhibited CYP enzymes-mediated bioactivation of AFB1 at mRNA and protein level. Transcription factor Nrf2, its downstream genes such as GSTA3, and GSTM2 mRNA, and protein expression level significantly upregulated via dietary curcumin. In addition, GSTs enzyme activity was enhanced with dietary curcumin which plays a crucial role in AFB1-detoxification. Conclusively, the study provided a scientific basis for the use of curcumin in broiler's diet and contributed to explore the multi-target preventive actions of curcumin against AFB1-induced liver injury through the modulation of phase-I and phase-II enzymes, and its potent anti-oxidative effects.

Aflatoxin B1 invokes apoptosis via death receptor pathway in hepatocytes

The fungal metabolites produced by Aspergillus flavus and Aspergillus parasiticus cause detrimental health effects on humans and animals. Particularly aflatoxin B1 (AFB1) is the most studied and a well-known global carcinogen, producing hepatotoxic, genotoxic and immunotoxic effects in multiple species. AFB1 is shown to provoke liver dysfunctioning by causing hepatocytes apoptosis and disturbing cellular enzymatic activities. In liver, AFB1 causes apoptosis via extrinsic mechanism because of high expression of death receptor pathway. The detailed mechanism of AFB1 induced hepatocytes apoptosis, via death receptor pathway still remains elusive. So the present study was conducted to explore apoptotic mechanism initiated by death receptors and associated genes in aflatoxin B1 induced liver apoptosis in chickens fed with AFB1 for 3 weeks. Results from the present study displayed histopathological and ultrastructural changes in liver such as hydropic degeneration, fatty vacuolar degeneration and proliferation of bile duct in hepatocytes in AFB1 group, along with imbalance between reactive oxygen species (ROS) and antioxidant defense system upon AFB1 ingestion. Moreover, AFB1 intoxicated chickens showed upregulation of death receptors FAS, TNFR1 and associated genes and downregulation of inhibitory apoptotic proteins XIAP and BCL-2. The results obtained from this novel and comprehensive study including histopathological, ultrastructural, flow cytometrical and death receptor pathway gene expression profiles, will facilitate better understanding of mechanisms and involvement of death receptor pathway in hepatocytes apoptosis induced by AFB1 and ultimately may be helpful in bringing down the toxigenic potential of AFB1.

Aflatoxin B1 Induced Systemic Toxicity in Poultry and Rescue Effects of Selenium and Zinc

Among many challenges, exposure to aflatoxins, particularly aflatoxin B₁ (AFB₁), is one of the major concerns in poultry industry. AFB₁ intoxication results in decreased meat/egg production, hepatotoxicity, nephrotoxicity, disturbance in gastrointestinal tract (GIT) and reproduction, immune suppression, and increased disease susceptibility. Selenium (Se) and zinc (Zn), in dietary supplementation, offer easy, cost-effective, and efficient ways to neutralize the toxic effect of AFB₁. In the current review, we discussed the impact of AFB₁ on poultry industry, its biotransformation, and organ-specific noxious effects, along with the action mechanism of AFB₁-induced toxicity. Moreover, we explained the biological and detoxifying roles of Se and Zn in avian species as well as the protection mechanism of these two trace elements. Ultimately, we discussed the use of Se and Zn supplementation against AFB₁-induced toxicity in poultry birds.

Transplantation of immortalized human fetal hepatocytes prevents acute liver failure in 90% hepatectomized mice

AIM

The aim of this study was to investigate whether human fetal hepatocytes are amenable to simian virus 40 large T-antigen (SV40Tag) mediated immortalization and whether the immortalized cells rescue mice with acute liver failure induced by 90% hepatectomy.

METHODS

We constructed a retroviral vector expressing a thermolabile mutant SV40Tag for transfer into primary human fetal hepatocytes. We quantitatively detected the synthetic ability for albumin and urea by the immortalized cells, which were subcutaneously inoculated into mice with severe combined immunodeficiency (SCID) to evaluate tumorigenzcity. The immortalized cells were also transplanted into the spleens of mice with acute liver failure.

RESULTS

One clone resulting after selection, referred to as HepCL, was highly differentiated, growing steadily in a chemically defined serum-free medium. HepCL cells were positive for albumin, cytokeratin 18, and cytokeratin 19 immunocytochemical staining. The average synthetic efficacies of HepCL cells for albumin and urea were comparable to that of unmodified primary human fetal hepatocytes. The population doubling time of HepCL cells in the logarithmic growth phase was approximately 17 hours. HepCL cells showed no oncogenicity in immunodeficient mice at 16 months. Mice receiving HepCL cells (G1) and primary human fetal hepatocytes (G2) showed significantly lower blood ammonia levels after 90% hepatectomy. Pairwise comparisons between the 4 groups showed that xenotransplantation of HepCL (G1) or primary fetal hepatocytes (G2) significantly improved survivals of recipient mice.

CONCLUSIONS

HepCL may be useful as a source of hepatic function for cell-based therapeutics in acute liver failure.

Treatment of fulminant liver failure by transplantation of microencapsulated primary or immortalized xenogeneic hepatocytes

BACKGROUND

The aim of this study was to evaluate the in vitro and in vivo function of hepatocytes after immortalization, cryopreservation, encapsulation, and xenotransplantation into mice with fulminant liver failure (FLF).

METHODS

Rat and human hepatocytes were isolated by collagenase digestion. Human hepatocytes were immortalized using lentiviral vectors. Rat and immortalized human hepatocytes (IHH) were encapsulated in 400 microm of alginate-poly-L-lysine (PLL; Sigma, Buchs, Switzerland)-alginate membranes and cryopreserved using a computerized device. In vitro, encapsulated hepatocytes (cryopreserved or noncryopreserved) were cultured; albumin secretion was measured by enzyme-linked immunosorbent assay. Microencapsulated (cryopreserved or noncryopreserved) hepatocytes were transplanted intraperitoneally to mice with FLF: group 1 (n = 10) transplantation of empty capsules; group 2 (n = 12) transplantation of free primary rat hepatocytes; group 3 (n = 12) transplantation of cryopreserved encapsulated rat hepatocytes; group 4 (n = 10) transplantation of encapsulated rat hepatocytes; group 5 (n = 9) transplantation of cryopreserved encapsulated IHH; group 6 (n = 10) transplantation of encapsulated IHH.

RESULTS

Compared with free primary hepatocytes, cryopreserved or noncryopreserved encapsulated rodent hepatocytes showed similar levels of continuous in vitro albumin secretion over 1 week. Cryopreserved or noncryopreserved encapsulated IHH showed minimal albumin secretion compared with free primary human hepatocytes. Fulminant liver failure, produced by a combination of acetaminophen and 30% hepatectomy, resulted in a 20% to 30% host survival. In groups 1 and 2, survival was unmodified, compared with untreated mice. For groups 3 and 4, transplantation of cryopreserved or noncryopreserved encapsulated rat hepatocytes significantly increased survival rates to 66% and 80%, respectively (P < .01). For groups 5 and 6, transplantation of cryopreserved or noncryopreserved encapsulated IHH improved host survival to 50% and 55%, respectively (P < .05).

CONCLUSIONS

Primary rodent hepatocytes maintained synthetic functions after encapsulation and cryopreservation. Immortalized human hepatocytes showed minimal albumin secretion in the absence of encapsulation and cryopreservation, suggesting that hepatocytes lose some specific functions after immortalization. After induction of FLF in mice, intraperitoneal transplantation of encapsulated (primary or immortalized, cryopreserved or noncryopreserved) xenogeneic hepatocytes significantly improved survival. These results indicate that naive and genetically modified hepatocytes can be successfully encapsulated, stored by cryopreservation, and transplanted into xenogeneic recipients with FLF to sustain liver metabolic functions.

Targeted deletion of Fgl-2/fibroleukin in the donor modulates immunologic response and acute vascular rejection in cardiac xenografts

BACKGROUND

Xenografts ultimately fail as a result of acute vascular rejection (AVR), a process characterized by intravascular thrombosis, fibrin deposition, and endothelial cell activation.

METHODS AND RESULTS

We studied whether targeted deletion of Fgl-2, an inducible endothelial cell procoagulant, (Fgl-2-/-) in the donor prevents AVR in a mouse-to-rat cardiac xenotransplantation model. By 3 days after transplant, Fgl-2+/+ grafts developed typical features of AVR associated with increased levels of donor Fgl-2 mRNA. Grafts from Fgl-2-/- mice had reduced fibrin deposition but developed cellular rejection. Treatment with a short course of cobra venom factor and maintenance cyclosporine resulted in long-term acceptance of both Fgl-2+/+ and Fgl-2-/- grafts. On withdrawal of cyclosporine, Fgl-2+/+ grafts developed features of AVR; in contrast, Fgl-2-/- grafts again developed acute cellular rejection. Rejecting Fgl-2+/+ hearts stained positively for IgG, IgM, C3, and C5b-9, whereas rejecting Fgl-2-/- hearts had minimal Ig and complement deposition despite xenoantibodies in the serum. Furthermore, serum containing xenoantibodies failed to stain Fgl-2-/- long-term treated hearts but did stain wild-type heart tissues. Treatment of Fgl-2-/- xenografts with mycophenolate mofetil and tacrolimus, a clinically relevant immune suppression protocol, led to long-term graft acceptance.

CONCLUSIONS

Deletion of Fgl-2 ameliorates AVR by downregulation of xenoantigens and may facilitate successful clinical heart xenotransplantation.

Comparison of in vivo lymphocyte proliferation between allogeneic and xenogeneic heart transplantation in mice

There are controversial in vitro data comparing the strength of the cellular immune response between allogeneic and xenogeneic stimulator/responder combinations. The present study therefore compares in vivo lymphocyte proliferation using heart transplantation (HTx) models in mice. Heterotopic HTx into BALB/c mice was performed using donor organs from mice (BALB/c and C57BL/6) or Lewis rats. Intraperitoneally given bromodeoxyuridine (BrdU) was incorporated into the DNA and was subsequently analyzed by flow cytometry. On postoperative days 3 and 5, proliferation of splenocytes, CD4(+) T-lymphocytes, and CD19(+) B-lymphocytes was significantly higher after xenogeneic than after allogeneic and isogeneic HTx. No significant difference was observed when proliferation of CD8(+) lymphocytes was determined. The increased in vivo proliferation after xenotransplantation may reflect an earlier and probably stronger cellular immune response compared to allogeneic transplantation. The higher CD4(+) lymphocyte proliferation underscores the importance of this cell population in xenograft rejection.