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G Hoyt

Publications and source records attributed to G Hoyt.

18 recordsLinked to original sources
PubMed2002

Regulation of matrix metalloproteinases and effect of MMP-inhibition in heart transplant related reperfusion injury.

PURPOSE: Metalloproteinases (MMPs) regulate extracellular matrix turnover and degrade basal lamina. Aim of the study was to examine the regulation of MMPs and the effect of an MMP inhibitor in transplant related ischemia/reperfusion injury. METHODS: Heterotopic cardiac transplantation was performed after 4 h of ischemia in three groups of six rats: allografts (black hooded inbred strain, PVG donor/August Copenhagen Irish inbred strain recipient); allografts treated with a competitive MMP-inhibitor (Batimastat) 15 mg/kg every 24 h; isografts (PVG donor and recipient). Normal PVG hearts served as a control. Hearts were explanted after 72 h of reperfusion. Expression of MMP-2 and -9 was measured using gelatin zymography. Proteolytic activity was measured using a gelatinase activity assay. Myeloperoxidase activity and tumor necrosis factor-alpha (TNF-alpha) were measured as markers of inflammatory response. Immunostaining for collagen IV and laminin was used to study degradation of basal lamina. RESULTS: There was a significant increase of MMP-2 expression in allografts (2271+/-571 microg/ml) as compared to normal (683+/-139 microg/ml) and the Batimastat-treated (259+/-140 microg/ml, P<0.05) groups. Although pro-MMP-2 expression was equally high in the untreated iso- and allograft group (75+/-23 versus 62+/-30 microg/ml) MMP-2 expression in the isograft hearts was significantly lower (359+/-267 microg/ml) suggesting activation of the pro-form by an immunologic mechanism. Pro-MMP-9 levels were significantly higher in the untreated iso- and allograft groups as opposed to normal hearts and MMP-inhibited hearts. MMP-9 was completely inhibited by Batimastat treatment. Collagenolytic activity was lower in the treated group as compared to untreated allografts (538+/-140 versus 384+/-97 microg/ml, P<0.05), demonstrating effective inhibition of MMPs by Batimastat. In the treated group a lesser extent of basement membrane component alterations could be demonstrated by laminin and collagen IV staining. There was a significant reduction in myeloperoxidase activity (P=0.027) as well as lower TNF-alpha levels (ns) in the in the Batimastat treated group. CONCLUSION: Ischemia leads to an increase in MMP expression and degradation of basal lamina. This process is enhanced in allografts as compared to isografts suggesting additional activation of MMPs by immunologic mechanisms. MMP-inhibition is effective in preventing the proteolytic activity of MMPs and may alter the host rejection response by preserving extracellular matrix components and basement membranes.

Animals↗
PubMed2001

Photodynamic therapy with motexafin lutetium (Lu-Tex) reduces experimental graft coronary artery disease.

BACKGROUND: Motexafin lutetium (Lu-Tex) is a photodynamic therapy (PDT) agent that localizes in atheromatous plaque in which it can be activated by far-red light. Lu-Tex biolocalization was examined in graft coronary artery disease (GCAD) with a rodent allograft model. After photoactivation, the effect on intimal proliferation was assessed. METHODS: A PVG to ACI rat heterotopic heart transplantation model was used. Lu-Tex (10 mg/kg) was intravenously administered 90 days after transplantation. Photoactivation was performed 24 hr after Lu-Tex administration. A light-emitting diode, central wavelength of 742 nm, was used to illuminate the intraperitoneally placed allografts via a laparotomy (light fluence of 75 J/cm2 at a power density of 75 mW/cm2). Animals were divided into four groups according to postoperative treatments: PDT with Lu-Tex injection and light illumination (n=21), Lu-Tex injection and laparotomy (n=14), laparotomy with light only (n=14), and laparotomy only (n=16). GCAD was quantitatively assessed 14 days after treatments. RESULTS: Lu-Tex localized in atherosclerotic plaque in vessels with GCAD. PDT significantly reduced both the percent of affected vessels and intimal proliferation compared to all other control study groups. alpha-Smooth muscle cell actin and anti-rat macrophage antibody-positive areas were significantly reduced within the neointima in allografts treated with PDT compared to all other study groups. CONCLUSIONS: PDT significantly reduced atherosclerotic lesions of GCAD. Lu-Tex-mediated PDT may, therefore, be a potential method for treating accelerated atherosclerosis associated with transplantation.

Actins↗
PubMed2001

Pre-transplant blood transfusion induces tolerance to hamster cardiac xenografts in athymic nude rats.

The effects of pre-transplant blood transfusion vary from induction of antibodies and accelerated graft rejection, to prolonged survival and even tolerance. The beneficial 'transfusion effect' in allotransplantation is believed to be merely T-cell mediated. In xenotransplantation, T-cell independent mechanisms form a major hurdle. In this study we investigated the effects of pre-transplant hamster blood transfusion on the survival of hamster cardiac xenografts in T-cell deficient athymic nude rats. Nude rats rejected xenografts after 3.8 +/- 0.5 d (n = 8), and immunocompetent Lewis rats after 4.0 +/- 0.5 d (n = 8), following a similar IgM response (P = NS). Hamster blood transfusion 3 d before transplantation in nude rats led to an IgM response and long-term xenograft survival in 17/20. Timing was of importance: blood transfusion 7 d before transplantation resulted in 45% long-term xenograft survival (n = 20). Injection of purified hamster erythrocytes, leukocytes or minced heart also led to survival of xenografts for > 100 d in nude rats, but not in all cases. Second xenografts transplanted to long-term survivors did not provoke an IigM response, and were accepted for > 100 d (n = 4). Transfer of serum from long-term survivors to untreated nude rats resulted in survival of xenografts for > 100 d (n = 4). In Lewis rats pre-transplant blood transfusion induced hyperacute rejection of xenografts after 158 +/- 128 min (n = 8, P < 0.01). We conclude that pre-transplant hamster blood transfusion can induce long-term survival of hamster cardiac xenografts in T-cell deficient athymic nude rats. This blood transfusion effect is mediated by humoral factors and can be transferred by serum. Elucidation of underlying mechanisms might provide some insight into xenotransplantation nonresponsiveness of T-cell independent immunefactors.

Animals↗
PubMed2001

Hamster cardiac xenografts are protected against antibody mediated damage, early after transplantation to Lewis rats.

Antibodies play a crucial role in the rejection of xenografts. We tested the hypothesis that xenografts are protected against antibody-mediated attack early after transplantation in a concordant model. We investigated the role of xenoreactive antibodies as a stimulus for protection and the effects of a total blockade of the antibody response by the leflunomide analog malononitrilamide 279. Hamster cardiac xenografts were transplanted to Lewis rat recipients. Second transplants and retransplants of xenografts were performed to untreated rats that had a xenograft in place for 3 d. Untreated rats rejected hamster cardiac xenografts after 4.0 +/- 0.0 d. Significant levels of anti-donor IgM, as measured by flowcytometry, were present on day 3 after transplantation (11.2% +/- 2.8 vs. 1.2% +/- 0.0 on day 0, P < 0.001). 'Fresh' second xenografts transplanted to rats that had a first xenograft in place for 3 d and had anti-hamster antibodies, underwent hyperacute rejection. The first xenografts remained functioning. Xenografts that were removed on day 3 from untreated rats and then retransplanted remained functioning. Xenografts that were removed on d 3 from rats that had been treated with malononitrilamide 279, 15 mg/kg/d and were retransplanted underwent hyperacute rejection. IgM levels at the time of removal were 1.1% +/- 0.5 in these rats and not different from baseline (P = 0.96). We conclude that xenografts are protected against antibody-mediated damage early after transplantation. The presence of anti-donor antibodies might be an essential stimulus for the induction of protection. There seems to be a delicate balance between the injurious and protective effects of antibodies. Treatment strategies that are designed to block antibody formation completely might prevent the induction of protection.

Abdomen↗
PubMed2000

Zinc-mediated reduction of apoptosis in cardiac allografts.

BACKGROUND: Apoptosis is thought to occur during immune-mediated acute rejection of cardiac allografts. In vitro studies have shown that zinc inhibits the activity of the proapoptotic enzyme caspase-3. We hypothesized that ZnCl(2) would reduce acute cardiac rejection in vivo via the blockade of caspase-3-dependent apoptosis. (99m)Tc-labeled annexin V was used to measure apoptosis in cardiac allografts through nuclear imaging. Annexin V binds to phosphatidylserines, which are externalized to the outer membrane of apoptotic cells. METHODS AND RESULTS: Twenty-seven PVG rat hearts were transplanted heterotopically into the abdomen of untreated ACI rats as controls (group 1). Fifteen were scanned and euthanized on postoperative day 4, and 12 were assessed for graft survival. Group 2 and 3 rats (n=15 each) received 1 and 5 mg/kg ZnCl(2) BID IP, respectively. Nine of each of these groups were scanned and euthanized on postoperative day 4, and 6 were studied for allograft survival. Group 4 rats (n=3) received isografts. Region-of-interest analysis demonstrated a dose-dependent reduction in (99m)Tc annexin uptake in ZnCl(2)-treated allografts: 2.43+/-0.37% for group 1, 1. 97+/-0.41% for group 2, 1.21+/-0.47% for group 3, and 0.55+/-0.19% for group 4 (ANOVA, P:=0.001). Graft survival times of 6.4+/-1.7, 9. 3+/-3.0, and 11.5+/-3.4 days for groups 1, 2, and 3, respectively, were also observed (ANOVA, P:=0.001). Caspase-3 activity in the allografts showed a 3.7-fold reduction in group 3 animals compared with group 1 animals (P:=0.004). CONCLUSIONS: Apoptosis that occurs in acute cardiac allograft rejection is reduced with ZnCl(2) in a dose-dependent manner via caspase-3 inhibition.

Animals↗
PubMed1997

Perinatal induction of immunotolerance to cardiac and pulmonary allografts.

OBJECTIVES: Tolerance appears to be more easily induced in the fetus before full immunocompetence is established, but elucidation of this process is needed. A model of perinatal tolerance induction to neonatal skin allografts followed by cardiac and pulmonary allografts is described. METHODS: Sixty Lewis (RT11) rat fetuses were inoculated intraperitoneally at 18 days gestation with 1 x 10(7) ACI (RT1a) rat fetal liver cells (group I); 20 Lewis fetuses were inoculated with 2 x 10(7) ACI fetal liver cells (Group II). control groups consisted of Lewis fetuses inoculated with saline solution (n = 25, group III) and fetuses that were not inoculated (n = 25, group IV). Twenty-five of the 50 surviving group I rats received ACI skin (< 24 hours old) and heart (8 to 10 weeks old) allografts (group IA); the remaining 25 rats received only ACI heart grafts (group IB). Groups II, III, and IV received ACI skin and cardiac allografts. Recipients tolerant to both skin and cardiac grafts received orthotopic ACI lung grafts and third-party skin grafts. Tolerance was indicated by graft survival for more than 100 days. Limiting dilution and flow cytometric analyses were performed. RESULTS: Abortion rates in groups I, II, III, and IV were 17% (10/60), 65% (13/20), 8% (2/25), and 4% (1/25), respectively. Specific tolerance to skin, cardiac, and lung allografts was observed in seven of 25 group IA recipients (28%) and seven of seven group II recipients (100%) compared with no tolerance in any group IB, III, or IV recipients (p = 0.03, chi 2 test). A 100-fold reduction of precursor cytotoxic T lymphocytes and significant splenocyte and bone marrow chimerism in tolerant versus nontolerant rats were noted (p = 0.0001, Student's t test). CONCLUSIONS: Using donor-strain fetal liver cells and neonatal skin grafts, we achieved higher frequencies of tolerance to solid organ grafts in adulthood with lower cell inocula and abortion rates than previously described. Chimerism and depressed precursor cytotoxic T lymphocyte frequencies in tolerant recipients suggest that hematopoietic stem cell engraftment and clonal deletion/anergy are involved in induction of perinatal tolerance.

Animals↗
PubMed1997

A rodent model of in utero chimeric tolerance induction.

BACKGROUND: In utero tolerance induction has potential application in pediatric heart transplantation. Immunotolerance appears to be more easily induced in the fetus before full immunocompetence is established; however, the mechanisms behind this phenomenon are still undefined. METHODS: One hundred thirty Lewis (RT1l) rat fetuses from 10 litters were inoculated intraperitoneally at 18 days gestation with 1 x 10(7) ACI (RT1a) rat fetal liver cells. Fifty of the 100 viable neonates successfully brought to term were grafted with neonatal ACI skin within 24 hours of birth and heterotopic ACI hearts at 8 to 10 weeks of age (group 1A); the remaining 50 neonates only received heterotopic ACI heart grafts at 8 to 10 weeks (group 1B). Control groups consisted of 50 Lewis fetuses (five litters) inoculated in utero with phosphate-buffered saline solution (group 2) and 50 Lewis fetuses (five litters) that received no inoculum (group 3); all of these surviving progeny received both neonatal ACI skin and adult ACI cardiac allografts. Skin and cardiac grafts were monitored by daily visual inspection and palpation, respectively. Limiting dilution analysis was performed among all groups to assess precursor cytotoxic lymphocyte frequencies. Likewise, peripheral blood lymphocyte and splenocyte populations were analyzed with flow cytometry to detect allogeneic chimerism. RESULTS: Abortion rates among groups 1, 2, and 3 were 23% (30/130 abortions), 10% (5/50 abortions), and 6% (3/50 abortions), respectively. Tolerance to both ACI skin and cardiac allografts was induced in 14 of the 50 group 1A Lewis recipients (28%). Tolerance was not achieved in any of the recipients in groups 1B, 2, or 3. Limiting dilution analysis among all groups revealed a marked reduction of precursor cytotoxic T-lymphocytes in tolerant allograft recipients compared with recipients in the other groups. Flow cytometry detected significant splenocyte chimerism among tolerant rats; significant peripheral blood chimerism was not noted. CONCLUSIONS: We describe allogeneic tolerance induction in utero to both rat skin and heart tissue by use of donor-strain fetal liver cells. Compared with previous studies with adult splenocytes as the tolerogen, we achieved a higher frequency of tolerance with a markedly lower cell inoculum and lower abortion rate. Allogeneic chimerism was noted in the tolerant recipients, suggesting hematopoietic stem cell engraftment. Cytotoxic T-lymphocyte precursor frequencies were markedly depressed in tolerant animals. Interestingly, both donor-strain fetal liver cells and neonatal skin grafts were required to induce tolerance. These data suggest a period of hematopoietic "education" during and shortly after hematopoietic stem cell engraftment.

Animals↗
PubMed1996

Tolerance to cardiac allografts induced in utero with fetal liver cells.

BACKGROUND: Induction of immunological tolerance in utero has potential application in pediatric cardiac transplantation. We describe an inexpensive, reproducible, and well-characterized model of allogeneic tolerance induction in utero using donorstrain fetal liver cells. METHODS AND RESULTS: Each of 9 Lewis (LEW, RTl1) rat fetuses in one litter (group 1) and 10 LEW fetuses in another litter (group 2) were inoculated intraperitoneally at 17 to 18 days of gestation with 1 x 10(6) ACI (RTla) rat fetal liver cells. Ten LEW fetuses in a third litter inoculated with PBS (group 3) and 10 LEW noninoculated fetuses in a fourth litter (group 4) served as controls. The LEW rats were brought to term, and groups 1, 3, and 4 were grafted with neonatal ACI skin within 24 hours of birth and with heterotopic ACI hearts at 8 to 10 weeks of age; group 2 rats received only an ACI heart graft at 8 to 10 weeks. Skin and cardiac grafts were monitored by daily visual inspection and palpation, respectively. Peripheral blood lymphocyte (PBL) populations in all LEW recipients were analyzed with flow cytometry. All LEW fetuses survived to term and developed normally. The ACI skin and cardiac allografts on 3 of the 9 LEW rats in group 1 are viable to date (skin, > 170 days; cardiac, > 100 days). The remaining 6 recipients of this group and all animals in groups 2, 3, and 4 rejected their skin and cardiac grafts by postgrafting day 7. Significant PBL chimerism (1.57%) was observed in only 1 tolerant rat. CONCLUSIONS: We describe allogeneic tolerance induction in utero to both rat skin and cardiac tissue with donor-strain fetal liver cells. Compared with previous studies using adult splenocytes as the tolerogen, we achieved a higher frequency of tolerance with a markedly lower cell inoculum and no abortions. Interestingly, both donor-strain fetal liver cells and neonatal skin grafts were required to maintain tolerance into adulthood. Immunocompetence sufficient to reject allografts was noted in neonates, and PBL chimerism was not prominent in tolerant recipients.

Animals↗
PubMed1994

Induction of allograft tolerance in rats by an HLA class-I-derived peptide and cyclosporine A.

T cell recognition of MHC molecules initiates a cascade of events resulting in allograft rejection. CTLs damage the graft by targeting nonself-MHC class I molecules. We and others have previously shown that small synthetic peptides corresponding to regions of certain MHC class I molecules can inhibit the CTL response against MHC class I alloantigens in vitro. Here we report that rat heart allografts survived survived indefinitely when transplanted into recipients treated with a synthetic peptide corresponding to residues 75-84 of (B7.75-84) in combination with a subtherapeutic dose of cyclosporine A. Furthermore, this treatment induced long-term donor-specific tolerance that was mediated by anergic cells, indicating that such peptides may have potential as therapeutics for human organ transplantation.

Amino Acid Sequence↗
PubMed1993

Cellular mechanisms underlying differential rejection of sequential heart and lung allografts in rats.

As the simultaneous transplantation of two or more organs into a single recipient has become increasingly common, asynchronous allograft rejection has become an important clinical problem. To investigate the cellular and molecular mechanisms underlying differential organ rejection, we developed a rat model in which heart and lung allografts were transplanted sequentially. Heterotopic heart allografts transplanted into DA recipients from PVG donors survived indefinitely if the recipients were given a short course of rabbit antirat thymocyte globulin or cyclosporine at the time of transplantation. In contrast, orthotopic left lungs transplanted under the same conditions were rejected in ATG-treated recipients and accepted in most CsA-treated recipients. These animals were then given a second organ allograft from the same strain or a third party to assess whether they exhibited donor specific tolerance and whether the acceptance or rejection of the first allograft would influence the survival of the second transplant. Animals tolerized to a heart allograft with ATG rejected an orthotopic lung transplant from the same strain as the original allograft, whereas recipients treated with CsA at the time of their heart transplant accepted a subsequent lung graft. Surprisingly, animals treated with either ATG or CsA that had rejected a lung allograft accepted a subsequent heart transplant. Using limiting dilution analysis and adoptive transfer studies, we found that some recipients had developed suppressor cells while others demonstrated anergy. We conclude that major histocompatibility complex antigens as well as other antigens are involved in the differential rejection of heart and lung allografts.

Animals↗
PubMedDate not supplied

Leflunomide prolongs pulmonary allograft and xenograft survival.

BACKGROUND: Leflunomide, an isoxazole derivative, has been shown to effectively prolong rodent allograft and cardiac xenograft survival. In vitro studies suggest that leflunomide inhibits the production of donor-specific antibodies and is capable of blocking both T- and B-cell proliferation. In light of the significant role that humoral immunity is believed to play in chronic pulmonary allograft rejection as well as hyperacute and accelerated acute xenograft rejection, we examined the efficacy of leflunomide in prolonging pulmonary allografts and xenografts and its effect on donor-specific antibody production. METHODS: Lungs from Brown Norway rats or Golden Syrian hamsters were orthotopically transplanted into Lewis rat recipients. Allograft recipients were treated daily for 14 days with vehicle, leflunomide (15 mg/kg/day orally), or cyclosporine (7.5 mg/kg/day orally) starting on the day of grafting (day 0). In xenograft recipients, leflunomide (20 mg/kg/day orally) or cyclosporine (7.5 mg/kg/day orally) treatment initiated on day 0 was continued until complete graft rejection; the leflunomide dosage was reduced to 10 mg/kg/day after day 14 because of weight loss and leukopenia. Graft viability was assessed with chest radiography in conjunction with open lung biopsies. Toxicity was monitored with body weight measurements, complete blood counts, and serum chemistries. Flow cytometric analysis of serum samples taken from graft recipients on day 7 was used to measure donor-specific immunoglobulin M and immunoglobulin G antibody titers. RESULTS: Allograft and xenograft control animals receiving vehicle yielded graft survival times of 6.0 +/- 0.0 and 5.4 +/- 0.6 days, respectively. Although xenograft recipients treated with cyclosporine (7.5 mg/kg/day orally) showed no significant graft prolongation, pulmonary allograft survival in recipients receiving cyclosporine alone was significantly prolonged to 28.2 +/- 0.7 days. Leflunomide-treated allograft (15 mg/kg/day orally) and xenograft (20 mg/kg/day orally) recipients displayed significant graft prolongation to 28.2 +/- 0.7 days and 15.8 +/- 3.3 days, respectively. Cyclosporine (7.5 mg/kg/day orally) enhanced the effect of leflunomide (20 mg/kg/day orally) in xenograft recipients with a mean graft survival time of 36.0 +/- 3.0 days achieved when both drugs were administered concomitantly. Cyclosporine significantly suppressed donor-specific immunoglobulin G antibody titers in both pulmonary allograft and xenograft recipients while not affecting immunoglobulin M levels. Leflunomide markedly suppressed both immunoglobulin G and immunoglobulin M donor-specific antibody titers in allograft and xenograft recipients. Except for mild leukopenia and anemia, both cyclosporine- and leflunomide-treated allograft recipients showed no evidence of toxic side effects after 14 days of therapy. However, leflunomide-treated xenograft recipients displayed significant weight loss, anemia, and leukopenia after 14 days of treatment with one death in each treatment group.

Administration, Oral↗