Dual role of Kupffer cell activation and endothelial cell damage in reperfusion injury to livers stored for transplantation surgery

Dimethyloxalylglycine pretreatment of living donor alleviates both donor and graft liver ischemia-reperfusion injury in rats

Background: Under the circumstance of the increasing waiting list for liver transplantation, living donor liver transplantation (LDLT) can alleviate the shortage of liver donors to some extent. However, how to reduce both donor and graft ischemia-reperfusion injury (IRI) is still an unsolved problem in LDLT. Hypoxia-induced transcription factor 1 (HIF1) activation is considered an important mechanism of cellular adaptation to hypoxia, and early activation of HIF1 may be a new way to alleviate liver IRI. Therefore, we aimed to investigate the impact of the HIF1 stabilizer dimethyloxalylglycine (DMOG) on IRI and the survival rate of donors and recipients of rat LDLT. Methods: Seventy percent partial liver resection and 30% partial liver transplantation were used to simulate donor and recipient of clinical LDLT. Rats were treated with DMOG (40 mg/kg) or with an equivalent amount of saline. The expression of HIF1 and downstream targets was analyzed after 2 h of reperfusion. Liver function and histopathology, apoptosis and oxidative stress levels were detected 6 h after reperfusion. At the same time, the 7-day survival rate of rats was calculated. Results: DMOG pretreatment significantly reduced IR-induced injury in the donor and recipient, which was manifested by reducing liver function damage and promoting tissue recovery. Meanwhile, compared with the untreated group, the oxidative stress level and the cell apoptosis rate were decreased in the group pretreated with DMOG. In addition, the transcription and expression of HIF1 target genes in the DMOG group were significantly enhanced. Remarkably, DMOG also increased the survival rate of the recipient. Conclusion: This study provides the first evidence that DMOG pretreatment of donors significantly alleviates liver IRI in both donors and recipients and increases the survival rate of recipients in LDLT. Therefore, DMOG may be a promising strategy for improving LDLT in the future.

Attenuation of Ischemia-Reperfusion Injury and Improvement of Survival in Recipients of Steatotic Rat Livers Using CD47 Monoclonal Antibody

BACKGROUND

Despite the efficacy of orthotopic liver transplantation in the treatment of end-stage liver diseases, its therapeutic utility is severely limited by the availability of donor organs. The ability to rehabilitate marginal organs, such as steatotic allografts, has the potential to address some of the supply limitations of available organs for transplantation. Steatotic livers are more susceptible to ischemia-reperfusion injury (IRI), which is exacerbated by the thrombospondin-1/CD47 pathway through inhibition of nitric oxide signaling. We postulated that CD47 blockade with a monoclonal antibody specific to CD47, clone 400 (CD47mAb400) may reduce the extent of IRI in steatotic liver allografts.

METHODS

Orthotopic liver transplantation was performed using steatotic liver grafts from Zucker rats transplanted into lean recipients. Control IgG or the CD47mAb400 was administered to the donor livers at procurement. Serum transaminases, histological changes, and animal survival were assessed. Hepatocellular damage, oxidative and nitrosative stress, and inflammation were also quantified.

RESULTS

Administration of CD47mAb400 to donor livers increased recipient survival and resulted in significant reduction of serum transaminases, bilirubin, triphosphate nick-end labeling staining, caspase-3 activity, oxidative and nitrosative stresses, and proinflammatory cytokine expression of TNF-α, IL-6 and IL-1β.

CONCLUSIONS

We conclude that administration of CD47mAb400 to donor grafts may reduce IRI through CD47 blockade to result in improved function of steatotic liver allografts and increased survival of recipients and represent a novel strategy to allow the use of livers with higher levels of steatosis.

Hyperbaric oxygen therapy reduces the severity of ischaemia, preservation and reperfusion injury in a rat model of liver transplantation

BACKGROUND

  Approaches to increase organ availability for orthotopic liver transplantation (OLT) often result in the procurement of marginal livers that are more susceptible to ischaemia, preservation and reperfusion injury (IPRI).

METHODS

  The effects of post-OLT hyperbaric oxygen (HBO) therapy on IPRI in a syngeneic rat OLT model were examined at various time-points. The effects of IPRI and HBO on hepatocyte necrosis, apoptosis, proliferation, and sinusoidal morphology and ultrastructure were assessed.

RESULTS

  Post-OLT HBO therapy significantly reduced the severity of IPRI; both apoptosis [at 12 h: 6.4 ± 0.4% in controls vs. 1.6 ± 0.7% in the HBO treatment group (p < 0.001); at 48 h: 2.4 ± 0.2% in controls vs. 0.4 ± 0.1% in the HBO treatment group (p < 0.001)] and necrosis [at 12 h: 18.7 ± 1.8% in controls vs. 2.4 ± 0.4% in the HBO treatment group (p < 0.001); at 48 h: 8.5 ± 1.3% in controls vs. 3.4 ± 0.9% in the HBO treatment group (P= 0.019)] were decreased. Serum alanine transaminase was reduced [at 12 h: 1068 ± 920 IU/l in controls vs. 370 ± 63 IU/l in the HBO treatment group (P= 0.030); at 48 h: 573 ± 261 IU/l in controls vs. 160 ± 10 IU/l in the HBO treatment group (P= 0.029)]. Treatment with HBO also promoted liver regeneration [proliferation at 12 h: 4.5 ± 0.1% in controls vs. 1.0 ± 0.3% in the HBO treatment group (p < 0.001); at 48 h: 8.6 ± 0.7% in controls vs. 2.9 ± 0.2% in the HBO treatment group (p < 0.01)] and improved sinusoidal diameter and microvascular density index.

CONCLUSIONS

  Hyperbaric oxygen therapy has persistent positive effects post-OLT that may potentially transfer into clinical practice.

Glycine and taurine equally prevent fatty livers from Kupffer cell-dependent injury: an in vivo microscopy study

BACKGROUND

IRI still is a major problem in liver surgery due to warm ischemia and organ manipulation. Steatosis is not only induced by diabetes, hyperalimentation, alcohol and toxins, but also chemotherapy given before resection. Since steatotic livers are prone to Kupffer cell-dependent IRI, protection of steatotic livers is of special interest. This study was designed to compare the effect of taurine and glycine on IRI in steatotic livers.

MATERIALS AND METHODS

Steatosis was induced with ethanol (7 g/kg b.w.; p.o.) in female SD rats. Ten minutes after inactivation of Kupffer cells with taurine or glycine (300 mM; i.v.), left liver lobes underwent 60 minutes of warm ischemia. Controls received the same volume of valine (300 mM; i.v.) or normal saline. After reperfusion, white blood cell-endothelial interactions and latex-bead phagocytosis by Kupffer cells were investigated. Liver enzymes were measured to estimate injury. For statistical analysis, ANOVA and Student's t-test were used.

RESULTS

Glycine and taurine significantly decreased leukocyte- and platelet-endothelium interactions and latex-bead phagocytosis (p < 0.05). Liver enzymes were significantly lower after glycine and taurine (p < 0.05).

CONCLUSIONS

This study shows that preconditioning with taurine or glycine is equally effective in preventing injury to fatty livers most likely via Kupffer cell-dependent mechanisms.

Biological modulation of liver ischemia-reperfusion injury

PURPOSE OF REVIEW

This review gives a broad overview of the key factors of ischemic injury to the liver and presents the current modifications of preservation solutions and the few strategies of biological modulation in clinical use today.

RECENT FINDINGS

Protective effects in human-liver transplantation were shown by methylprednisolone treatment in decreased donors, and by inhalation of a nontoxic dose of nitric oxide in recipients. In addition, recent results showed rescue of pig livers, donated after cardiac death by application of a cocktail of substances addressing several previously identified mechanisms of ischemia-reperfusion injury.

SUMMARY

The future of a pharmacological approach attenuating or preventing ischemia-reperfusion injury lies in a combination of drugs acting simultaneously on several steps of the injury cascades. Applying these substances during flush, before, and during implantation appears as an attractive strategy to protect extended criteria liver grafts.

Graft preconditioning with low-dose tacrolimus (FK506) and nitric oxide inhibitor aminoguanidine (AGH) reduces ischemia/reperfusion injury after liver transplantation in the rat

Ischemia/reperfusion (I/R) injury is a main cause of primary dysfunction or non-function after liver transplantation (LTx). Recent evidence indicates that an increase in nitric oxide (NO) production after LTx is associated with I/R injury. The aim of this study was to demonstrate that low-dose FK506 in combination with aminoguanidine (AGH), which leads to a reduction of NO levels, has a protective effect by reducing I/R associated injury after LTx. Fortyone DA-(RT1av1) rats served as donors and recipients for syngenic orthotopic arterialised LTx. They were divided into 4 groups: controls without pre-/treatment (I), pre-/treatment with high-dose FK506 (II), pre-/treatment with AGH only (III), and pre-/treatment with low-dose FK506 in combination with AGH (IV). After LTx the laboratory parameters and liver biopsy were performed. The levels of transaminase (ALT) in groups I, II and III were significantly higher on day 3 after LTx compared to group IV (p = 0.001, p = 0.001, p = 0.000). In group IV the I/R-associated liver necrosis rate was reduced significantly. Our results demonstrated that a combined dual pharmacological pretreatment (group IV) reduced I/R injury of the graft after LTx in a rat model.

Augmenter of liver regeneration promotes hepatocyte proliferation induced by Kupffer cells

AIM

To observe the effects of augmenter of liver regeneration (ALR) on Kupffer cells and to determine whether ALR promotes hepatocyte proliferation induced by Kupffer cells.

METHODS

Kupffer cells and hepatocytes were cultured in vitro and various concentrations of recombinant rat ALR (rrALR) were added. 3H-thymidine, BrdU and 3H-leucine incorporation was determined in cultured Kupffer cells and hepatocytes, in hepatocytes conditioned by Kupffer cells, and in associated medium. rrALR was labeled by iodination and used to determine its binding activity by Scatchard analysis in Kupffer cells and primarily cultured rat hepatocytes.

RESULTS

rrALR stimulated DNA replication in Kupffer cells and protein synthesis both in cells and in medium in a non-concentration-dependent manner. The effect was significant at the concentration of 1 microg/L ALR. However, rrALR had no effect on primarily cultured hepatocytes, when hepatocytes were cultured with the Kupffer cell medium conditioned by ALR, DNA replication and protein synthesis in hepatocytes increased significantly at the concentration of 1 microg/L ALR. When the ALR concentration was increased, its effect on hepatocyte proliferation decreased to the basal level. Scatchard analysis indicated the presence of a single class of high affinity receptors with a dissociation constant (Kd) of 0.883 nmol/L and a maximum binding capacity (Bmax) of 126.1 pmol/g protein in the rat Kupffer cells.

CONCLUSION

ALR can promote hepatocyte proliferation induced by Kupffer cells, which is associated with the concentration of ALR, suggesting that Kupffer cells play a dual role in liver regeneration.

Prometheus' challenge: molecular, cellular and systemic aspects of liver regeneration

The fascinating aspect of the liver is the capacity to regenerate after injury or resection. A variety of genes, cytokines, growth factors, and cells are involved in liver regeneration. The exact mechanism of regeneration and the interaction between cells and cytokines are not fully understood. There seems to exist a sequence of stages that result in liver regeneration, while at the same time inhibitors control the size of the regenerated liver. It has been proven that hepatocyte growth factor, transforming growth factor, epidermal growth factor, tumor necrosis factor-alpha, interleukins -1 and -6 are the main growth and promoter factors secreted after hepatic injury, partial hepatectomy and after a sequence of different and complex reactions to activate transcription factors, mainly nuclear factor kappaB and signal transduction and activator of transcription-3, affects specific genes to promote liver regeneration. Unraveling the complex processes of liver regeneration may provide novel strategies in the management of patients with end-stage liver disease. In particular, inducing liver regeneration should reduce morbidity for the donor and increase faster recovery for the liver transplantation recipient.

Influence of cumulative number of marginal donor criteria on primary organ dysfunction in liver recipients

BACKGROUND

The aim of this cohort study was to assess the cumulative effect of marginal donor criteria on initial graft function and patient survival after liver transplantation.

METHODS

We included 734 consecutive patients who underwent orthotopic liver transplantation at the Vienna General Hospital between January 1993 and December 2003. We employed the local registry of the Department of Transplant Surgery, where variables of all patients are routinely and prospectively recorded. Primary outcome was initial graft function, secondary outcome was patient survival.

RESULTS

Cumulative number of marginal donor criteria was significantly and linearly associated with an increased rate of primary dysfunction (PDF; p = 0.005). In patients with more than three cumulative marginal donor criteria the rate of PDF was 36%. Patient survival was not influenced by the cumulative number of donor criteria (log-rank test, p = 0.81). Independent marginal donor criteria to predict PDF were cold ischemia time >10 h [odds ratio (OR) 0.56; 95% CI 0.32-0.98] and donor peak serum sodium >155 mEq/L (OR 0.44; 95% CI 0.26-0.77), as assessed in a multivariate regression model.

CONCLUSIONS

The use of marginal liver donors with more than three marginal donor criteria shows deleterious effects on initial graft function. Noteworthy, patient survival was not associated with marginal donor criteria, which may be explained by early and successful retransplantation of liver recipients with primary non-function.

In vitro interleukin-6 treatment prevents mortality associated with fatty liver transplants in rats

BACKGROUND & AIMS

Orthotopic liver transplantation is currently the only curative therapy for chronic end-stage liver disease and acute liver failure. However, a scarcity of cadaveric donors has led to a critical shortage of organs available for transplant. This is further complicated by the prevalence of steatosis in about 13%-50% of donor livers, which is associated with a high risk of dysfunction and primary nonfunction.

METHODS

Steatotic Zucker rat livers and livers from alcohol-fed rats were transplanted into lean control rats. Liver injury, activation of survival signals, and hepatic microcirculation were compared in nontreated and interleukin-6 (IL-6)-treated steatotic isografts.

RESULTS

IL-6 pretreatment of steatotic Zucker rat liver isografts dramatically reduces mortality and liver injury following transplantation. Reperfusion after transplantation induces significant sinusoidal endothelial cell necrapoptosis in steatotic Zucker rat liver isografts, which is prevented by in vitro IL-6 pretreatment. IL-6 treatment activates cell survival signal transducer and activator of transcription factor 3 (STAT3) in hepatocytes and sinusoidal endothelial cells. Laser Doppler imaging and microsphere analyses demonstrate that IL-6 treatment markedly improves hepatic microcirculation, which is impaired in steatotic Zucker rat liver transplants. Finally, in vitro IL-6 treatment of donor livers also markedly reduces mortality associated with fatty liver transplants from alcohol-fed rats.

CONCLUSIONS

IL-6 induces hepatoprotection of steatotic liver isografts via preventing sinusoidal endothelial cell necrapoptosis and consequent amelioration of hepatic microcirculation, and protecting against hepatocyte death. IL-6 pretreatment of steatotic livers may render such allografts useable for clinical transplantation.

The utility of marginal donors in liver transplantation

The shortage of organs has led centers to expand their criteria for the acceptance of marginal donors. The combination of multiple marginal factors seems to be additive on graft injury. In this review, the utility of various marginal donors in patients requiring liver transplantation will be described, including older donors, steatotic livers, non-heart-beating donors, donors with viral hepatitis, and donors with malignancies. The pathophysiology of the marginal donor will be discussed, along with strategies for minimizing the ischemia reperfusion injury experienced by these organs. Finally, new strategies for improving the function of the marginal/expanded donor liver will be reviewed.

Pretransplant rinse of hearts preserved with colloid-free UW solution and more effective heart preservation: studies in a rat abdominal heart transplant model

BACKGROUND

University of Wisconsin solution (UW) provides effective heart preservation under hypothermic conditions, but it can be deleterious at warmer temperatures. Re-warming during the implantation of the graft may be a problem. This study examined the damaging effect of peri-operative warm ischemia in a transplant setting and recovery from such damage. The amelioration of damage by rinsing the graft before re-warming and transplantation was also examined.

METHODS

Rat donor hearts were preserved for 2 hr (0 degrees C) as follows: Series A was preserved with colloid-free UW (MUW), St. Thomas' solution (ST), or calcium-supplemented MUW (MUW+Ca) followed by either transplantation or warming (22 degrees C) for 10 min before transplantation. Series B was preserved with MUW, rinsed with fresh MUW, ST, MUW+Ca, or low-potassium MUW before warming and transplantation. All heart isografts were transplanted heterotopically with an indwelling left intraventricular balloon-tipped catheter. Graft function was measured 1 and 7 days after transplantation.

RESULTS

Grafts re-warmed rapidly during implantation. Function (left ventricular developed pressure, contractility, and relaxation) was significantly and persistently diminished in MUW-preserved grafts subjected to additional warming before transplantation. Preservation with ST was less effective than MUW despite being unaffected by warming. Preservation with MUW+Ca and rinsing with fresh MUW or ST before re-warming allowed recovery of function within 7 days despite significantly diminished function on day 1.

CONCLUSION

This study demonstrated that an increase in the peri-transplant warm ischemic period was detrimental when hearts were preserved with MUW. Preservation with calcium-supplemented MUW or rinsing the heart with fresh MUW or ST before transplantation ameliorated this damage.

Intrahepatic expression and release of vascular endothelial growth factor following orthotopic liver transplantation in the rat

BACKGROUND

Morphological and functional changes to sinusoidal endothelial cells mediated by soluble factors released from activated Kupffer cells, including cytokines, are considered pivotal events in ischemia/reperfusion injury (IRI) to liver grafts. Vascular endothelial growth factor (VEGF) is an endothelial cell-specific cytokine with potent pro-inflammatory and mitogenic effects. We investigated the possible role of VEGF in IRI to liver grafts using a syngeneic rat orthotopic liver transplantation model.

METHODS

Transplantation was performed in Lewis rats using livers preserved for various periods of time (24-48 hr) in University of Wisconsin solution at 4 degrees C. Systemic VEGF levels were measured by enzyme-linked immunosorbent assay (ELISA). Intrahepatic VEGF expression was analyzed by Northern blotting and in situ hybridization. The effects of anti-VEGF neutralizing antibody treatment on the extent of IRI were assessed by measuring liver function tests, lipid peroxidation, and metalloproteinase activity.

RESULTS/CONCLUSION

VEGF is expressed and released in a biphasic pattern during the early postoperative period after liver transplantation. Anti-VEGF antibody treatment, administered during reperfusion, decreased the degree of damage, suggesting that VEGF may have a role in IRI to liver grafts.

Endotoxin-induced aggravation of preservation-reperfusion injury of rat liver and its modulation

BACKGROUND/AIMS

In clinical transplantation, exposure of donors to gut-derived endotoxin occurs frequently and may adversely affect liver transplantation therapy. The aim of this study was to investigate: 1) whether brief exposure of rats to endotoxin before liver procurement aggravates the early phase of reperfusion injury of hepatic explants; and if so 2) whether Kupffer cell activation is a contributing factor to liver injury; and 3) whether heparin and pentoxifylline could minimize this effect.

METHODS

Male Wistar rats were injected with 0.2-4.0 mg/kg of Escherichia coli lipopolysaccharide 2 h prior to liver harvest. After preservation in University of Wisconsin cold-storage solution, the livers were reperfused using a blood-free perfusion model. To inactivate Kupffer cells, some rats were pretreated with gadolinium chloride or liposome-encapsulated dichloromethylene-diphosphonate before lipopolysaccharide administration. The other rats received lipopolysaccharide with heparin or pentoxifylline.

RESULTS

In a dose-independent fashion, lipopolysaccharide impaired portal flow during graft reperfusion. In a dose-dependent way, lipopolysaccharide increased lactate dehydrogenase release into the perfusate and decreased bile flow and bromosulfophthalein excretion. Gadolinium chloride, liposomal dichloromethylene-diphosphonate, heparin, and pentoxifylline reduced lactate dehydrogenase release by 34%, 43%, 59%, and 64%, respectively, and improved functional parameters of the liver. A 52-fold increased neutrophil infiltration in the liver sinusoids after lipopolysaccharide exposure was not affected significantly by the drugs studied; however, heparin reduced markedly neutrophil activation.

CONCLUSIONS

The results of this investigation provide direct evidence that aggravation of preservation-reperfusion injury of rat liver by endotoxin is mediated by Kupffer cell-dependent mechanism(s) and it can be minimized by heparin and pentoxifylline.

Kupffer cell-independent acute hepatocellular oxidative stress and decreased bile formation in post-cold-ischemic rat liver

The purpose of this study was to examine distribution and time history of oxidative stress during the hyperacute period of reperfusion in the liver grafts undergoing cold ischemia and to investigate roles of Kupffer cells as a potential oxidant source. Rat livers were harvested at 4 degrees C in University of Wisconsin solution and followed by reperfusion with Krebs-Henseleit buffer under monitoring bile excretion. To investigate oxidative changes, laser-confocal microfluorography was performed in reperfused livers preloaded with dichlorodihydrofluorescein diacetate succinimidyl ester, a fluorescence precursor sensing intracellular hydroperoxide generation. Livers undergoing the 16-hour cold storage displayed an impaired recovery of bile acid-dependent bile output concurrent with a marked increase in hydroperoxide generation in hepatocytes, which occurred as early as 5 minutes after the onset of reperfusion, whereas the status of lobular perfusion was well maintained. Pretreatment with liposome-encapsulated dichloromethylene diphosphonate, a Kupffer cell-depleting reagent, did neither alter the reperfusion-induced periportal oxidative changes nor improve the recovery of bile output in the graft. On the other hand, EPCK, a hepatotropic antioxidant composed of vitamin E phosphate ester bound to vitamin C, not only diminished the oxidative changes but also improved the reduction of bile acid-dependent bile output. Furthermore, the reagent was capable of inhibiting H(2)O(2)-induced oxidative stress in cultured hepatocytes. These results suggest that hepatocytes constitute a major site of the oxidative insult triggered through Kupffer cell-independent mechanisms and serve as an important cellular component to be protected by antioxidant therapeutics.

Differential in vivo recovery of sinusoidal endothelial cells, hepatocytes, and Kupffer cells after cold preservation and liver transplantation in rats

BACKGROUND

The injury resulting from cold preservation/reperfusion primarily affects sinusoidal endothelial cells, while hepatocytes are thought to be less vulnerable; morphological changes and increased cytokine release suggest that Kupffer cells are activated. We evaluated the extent of functional damage to the different cell types in the liver after cold preservation and transplantation. Additionally, we analyzed in vivo the patterns of functional recovery of all three cell types over the first week after transplantation in Lewis rats.

METHODS

We evaluated the in vivo uptake of hyaluronic acid, indocyanine green, and radio-labeled sulphur colloid to assess the function of sinusoidal endothelial cells, hepatocytes, and Kupffer cells, respectively. Measurements were performed immediately after transplantation using syngeneic grafts preserved in University of Wisconsin solution for different periods. Functional recovery was monitored in animals receiving grafts preserved for 24 hr over the first postoperative week.

RESULTS

We found that hepatocyte were less affected compared with the profoundly damaged endothelial cells. The phagocytic ability of Kupffer cells was, however, also seriously compromised, which suggests a selective down-regulation. Functional recovery occurs in a differential manner during the first postoperative week starting with hepatocytes followed by sinusoidal endothelial cells. Phagocytic function further deteriorates after transplantation before showing improvement.

CONCLUSIONS

In viable liver grafts, all cell types recover from preservation/reperfusion injury by the end of the first week after transplantation. The differential time courses of the recovery suggest that successful sinusoidal endothelial cell recovery may depend upon prior hepatocyte regeneration and may involve a paracrine interaction, via cytokines and growth factors.

A short-term study of the effects of SBHAN, a novel compound, on gingival inflammation in the beagle dog

Unique hydroxyl ion-modulating compounds based on the amino acid glycine have been developed that possess both antimicrobial and pro-healing properties. The purpose of the present study was to determine the effects of one of these compounds, 8.5% (w/v) sodium N, N-bis-2 (hydroxylethyl) aminoacetate (SBHA) with 0.3% (w/v) NaOH (SBHAN) on ligature-induced gingival inflammation in the beagle dog. Fifteen purebred beagle dogs were subjected to a 14-day oral hygiene regimen, consisting of manual scaling and daily toothbrushing with plain pumice. Gingival inflammation was then initiated by tying ligatures around 12 study teeth per dog and by placing the dogs on water-softened dog chow. After 30 days, ligatures were removed, dogs were placed on a hard diet and randomly assigned to five treatment groups by the flip of two coins. The five treatments included: 1) distilled, pyrogen-free water; 2) 8.5% (w/v) SBHAN; 3) 4.3% (w/v) SBHAN; 4) 0.12% chlorhexidine; and 5) 8.5% SBHA (w/v) (SBHAN without added NaOH). Solutions were placed in opaque spray bottles to shield their identity from the examiner. Treatment consisted of a daily aerosol application of 2 ml of each solution in a calibrated spray bottle to the affected teeth. The following measures were taken from the dogs at baseline (after hygienic phase), 30 days after initiation of gingival inflammation (before ligature removal), and 2 weeks and 4 weeks after ligature removal: 1) plaque index (PI); 2) gingival index (GI); 3) probing depths (PD); 4) relative attachment levels (RAL); and 5) gingival crevicular fluid volume (GCF). Analysis of subgingival plaque for anaerobic and aerobic colony forming units/ml was also performed at each time point. Gingival biopsies were performed, sectioned and stained with hematoxylin and eosin to quantify the inflammatory cell infiltrate (ICI). After ligature placement, increases were observed in PI, GI, PD, RAL, GCF, aerobic and anaerobic subgingival microbial counts, and ICI. After ligature removal, spontaneous resolution of gingival inflammation and plaque accumulation around the teeth of all dogs was observed with any treatment. Statistical analysis (Tukey's pairwise comparisons) of the mean PI, GI, PD, RAL, ICI, and GCF after 4 weeks of treatment with each agent, however, revealed that 8.5% SBHAN was significantly (P < 0.05) more effective than water, 4.3% SBHAN, or 8.5% SBHA in reducing PI, GI, PD, and GCF, but not RAL or ICI. Moreover, 0.12% chlorhexidine was more effective than water, 4.3% SBHAN, or 8.5% SBHA at reducing GI, PD, and GCF, but not PI, RAL, or ICI. No adverse reactions to the SBHAN were observed visually or histologically in any of the dogs during the course of the investigation. These data suggest that further investigation in a larger study population of the potential of SBHAN as an anti-gingivitis compound is warranted.