The effect of Kupffer cell stimulation or depression on the development of liver metastases in the rat

Cells in the liver microenvironment regulate the process of liver metastasis

The research of liver metastasis is a developing field. The ability of tumor cells to invade the liver depends on the complicated interactions between metastatic cells and local subpopulations in the liver (including Kupffer cells, hepatic stellate cells, liver sinusoidal endothelial cells, and immune-related cells). These interactions are mainly mediated by intercellular adhesion and the release of cytokines. Cell populations in the liver microenvironment can play a dual role in the progression of liver metastasis through different mechanisms. At the same time, we can see the participation of liver parenchymal cells and nonparenchymal cells in the process of liver metastasis of different tumors. Therefore, the purpose of this article is to summarize the relationship between cellular components of liver microenvironment and metastasis and emphasize the importance of different cells in the occurrence or potential regression of liver metastasis.

The role of hepatic macrophages in liver metastasis

The liver is a major target organ for metastasis of both gastrointestinal and extra-gastrointestinal cancers. Due to its frequently inoperable nature, liver metastasis represents a leading cause of cancer-associated death worldwide. In the past years, the pivotal role of the immune system in this process is being increasingly recognised. In particular, the role of the hepatic macrophages, both recruited monocyte-derived macrophages (Mo-Mfs) and tissue-resident Kupffer cells (KCs), has been shown to be more versatile than initially imagined. However, the lack of tools to easily distinguish between these two macrophage populations has hampered the assignment of particular functionalities to specific hepatic macrophage subsets. In this Review, we highlight the most remarkable findings regarding the origin and functions of hepatic macrophage populations, and we provide a detailed description of their distinct roles in the different phases of the liver metastatic process.

Liver macrophages in healthy and diseased liver

Kupffer cells, the largest tissue resident macrophage population, are key for the maintenance of liver integrity and its restoration after injury and infections, as well as the local initiation and resolution of innate and adaptive immunity. These important roles of Kupffer cells were recently identified in healthy and diseased liver revealing diverse functions and phenotypes of hepatic macrophages. High-level phenotypic and genomic analysis revealed that Kupffer cells are not a homogenous population and that the hepatic microenvironment actively shapes both phenotype and function of liver macrophages. Compared to macrophages from other organs, hepatic macrophages bear unique properties that are instrumental for their diverse roles in local immunity as well as liver regeneration. The diverse and, in part, contradictory roles of hepatic macrophages in anti-tumor and inflammatory immune responses as well as regulatory and regenerative processes have been obscured by the lack of appropriate technologies to specifically target or ablate Kupffer cells or monocyte-derived hepatic macrophages. Future studies will need to dissect the exact role of the hepatic macrophages with distinct functional properties linked to their differentiation status and thereby provide insight into the functional plasticity of hepatic macrophages.

Enhanced performance of macrophage-encapsulated nanoparticle albumin-bound-paclitaxel in hypo-perfused cancer lesions

Hypovascularization in tumors such as liver metastases originating from breast and other organs correlates with poor chemotherapeutic response and higher mortality. Poor prognosis is linked to impaired transport of both low- and high-molecular weight drugs into the lesions and to high washout rate. Nanoparticle albumin-bound-paclitaxel (nAb-PTX) has demonstrated benefits in clinical trials when compared to paclitaxel and docetaxel. However, its therapeutic efficacy for breast cancer liver metastasis is disappointing. As macrophages are the most abundant cells in the liver tumor microenvironment, we design a multistage system employing macrophages to deliver drugs into hypovascularized metastatic lesions, and perform in vitro, in vivo, and in silico evaluation. The system encapsulates nAb-PTX into nanoporous biocompatible and biodegradable multistage vectors (MSV), thus promoting nAb-PTX retention in macrophages. We develop a 3D in vitro model to simulate clinically observed hypo-perfused tumor lesions surrounded by macrophages. This model enables evaluation of nAb-PTX and MSV-nab PTX efficacy as a function of transport barriers. Addition of macrophages to this system significantly increases MSV-nAb-PTX efficacy, revealing the role of macrophages in drug transport. In the in vivo model, a significant increase in macrophage number, as compared to unaffected liver, is observed in mice, confirming the in vitro findings. Further, a mathematical model linking drug release and retention from macrophages is implemented to project MSV-nAb-PTX efficacy in a clinical setting. Based on macrophage presence detected via liver tumor imaging and biopsy, the proposed experimental/computational approach could enable prediction of MSV-nab PTX performance to treat metastatic cancer in the liver.

Distribution profile of gadolinium in gadolinium chelate-treated renally-impaired rats: role of pharmaceutical formulation

While not acutely toxic, chronic hepatic effect of certain gadolinium chelates (GC), used as contrast agent for magnetic resonance imaging, might represent a risk in renally-impaired patients due to free gadolinium accumulation in the liver. To answer this question, this study investigated the consequences of the presence of small amounts of either a soluble gadolinium salt ("free" Gd) or low-stability chelating impurity in the pharmaceutical solution of gadoteric acid, a macrocyclic GC with high thermodynamic and kinetic stabilities, were investigated in renally-impaired rats. Renal failure was induced by adding 0.75% adenine in the diet for three weeks. The pharmaceutical and commercial solution of gadoteric acid was administered (5 daily intravenous injections of 2.5 mmol Gd/kg) either alone or after being spiked with either "free" gadolinium (i.e., 0.04% w/v) or low-stability impurity (i.e., 0.06 w/v). Another GC, gadodiamide (low thermodynamic and kinetic stabilities) was given as its commercial solution at a similar dose. Non-chelated gadolinium was tested at two doses (0.005 and 0.01 mmol Gd/kg) as acetate salt. Gadodiamide induced systemic toxicity (mortality, severe epidermal and dermal lesions) and substantial tissue Gd retention. The addition of very low amounts of "free", non-chelated gadolinium or low thermodynamic stability impurity to the pharmaceutical solution of the thermodynamically stable GC gadoteric acid resulted in substantial capture of metal by the liver, similar to what was observed in "free" gadolinium salt-treated rats. Relaxometry studies strongly suggested the presence of free and soluble gadolinium in the liver. Electron microscopy examinations revealed the presence of free and insoluble gadolinium deposits in hepatocytes and Kupffer cells of rats treated with gadoteric acid solution spiked with low-stability impurity, free gadolinium and gadodiamide, but not in rats treated with the pharmaceutical solution of gadoteric acid. The presence of impurities in the GC pharmaceutical solution may have long-term biological consequences.

MicroRNAs transfer from human macrophages to hepato-carcinoma cells and inhibit proliferation

Recent research has indicated a new mode of intercellular communication facilitated by the movement of RNA between cells. There is evidence that RNA can transfer between cells in a multitude of ways, including in complex with proteins or lipids or in vesicles, including apoptotic bodies and exosomes. However, there remains little understanding of the function of nucleic acid transfer between human cells. In this article, we report that human macrophages transfer microRNAs (miRNAs) to hepato-carcinoma cells (HCCs) in a manner that required intercellular contact and involved gap junctions. Two specific miRNAs transferred efficiently between these cells--miR-142 and miR-223--and both were endogenously expressed in macrophages and not in HCCs. Transfer of these miRNAs influenced posttranscriptional regulation of proteins in HCCs, including decreased expression of reporter proteins and endogenously expressed stathmin-1 and insulin-like growth factor-1 receptor. Importantly, transfer of miRNAs from macrophages functionally inhibited proliferation of these cancerous cells. Thus, these data led us to propose that intercellular transfer of miRNA from immune cells could serve as a new defense against unwanted cell proliferation or tumor growth.

The renin angiotensin system regulates Kupffer cells in colorectal liver metastases

Blockade of the renin angiotensin system (RAS) can inhibit tumor growth and this may be mediated via undefined immunomodulatory actions. This study investigated the effects of RAS blockade on liver macrophages (Kupffer cells; KCs) in an orthotopic murine model of colorectal cancer (CRC) liver metastases. Here we showed that pharmacological targeting of the RAS [ANG II (31.25 µg/kg/h i.p.), ANG-(1-7) (24 µg/kg/h i.p.) or the ACE inhibitor; captopril (750 mg/kg/d i.p.)] altered endogenous KC numbers in the tumor-bearing liver throughout metastatic growth. Captopril, and to a lesser extent ANG-(1-7), increased KC numbers in the liver but not tumor. KCs were found to express the key RAS components: ACE and AT1R. Treatment with captopril and ANG II increased the number of AT1R-expressing KCs, although total KC numbers were not affected by ANG II. Captopril (0.1 µM) also increased macrophage invasion in vitro. Additionally, captopril was administered with KC depletion before tumor induction (day 0) or at established metastatic growth (day 18) using gadolinium chloride (GdCl 3; 20 mg/kg). Livers were collected at day 21 and quantitative stereology used as a measure of tumor burden. Captopril reduced growth of CRC liver metastases. However, when captopril was combined with early KC depletion (day 0) tumor growth was significantly increased compared with captopril alone. In contrast, late KC depletion (day 18) failed to influence the anti-tumor effects of captopril. The result of these studies suggests that manipulation of the RAS can alter KC numbers and may subsequently influence progression of CRC liver metastases.

Bimodal role of Kupffer cells during colorectal cancer liver metastasis

Kupffer cells (KCs) are resident liver macrophages that play a crucial role in liver homeostasis and in the pathogenesis of liver disease. Evidence suggests KCs have both stimulatory and inhibitory functions during tumor development but the extent of these functions remains to be defined. Using KC depletion studies in an orthotopic murine model of colorectal cancer (CRC) liver metastases we demonstrated the bimodal role of KCs in determining tumor growth. KC depletion with gadolinium chloride before tumor induction was associated with an increased tumor burden during the exponential growth phase. In contrast, KC depletion at the late stage of tumor growth (day 18) decreased liver tumor load compared with non-depleted animals. This suggests KCs exhibit an early inhibitory and a later stimulatory effect. These two opposing functions were associated with changes in iNOS and VEGF expression as well as T-cell infiltration. KC depletion at day 18 increased numbers of CD3 (+) T cells and iNOS-expressing infiltrating cells in the tumor, but decreased the number of VEGF-expressing infiltrating cells. These alterations may be responsible for the observed reduction in tumor burden following depletion of pro-tumor KCs at the late stage of metastatic growth. Taken together, our results indicate that the bimodal role of KC activity in liver tumors may provide the key to timing immunomodulatory intervention for the treatment of CRC liver metastases.

The renin-angiotensin system and malignancy

The renin-angiotensin system (RAS) is usually associated with its systemic action on cardiovascular homoeostasis. However, recent studies suggest that at a local tissue level, the RAS influences tumour growth. The potential of the RAS as a target for cancer treatment and the suggested underlying mechanisms of its paracrine effects are reviewed here. These include modulation of angiogenesis, cellular proliferation, immune responses and extracellular matrix formation. Knowledge of the RAS has increased dramatically in recent years with the discovery of new enzymes, peptides and feedback mechanisms. The local RAS appears to influence tumour growth and metastases and there is evidence of tissue- and tumour-specific differences. Recent experimental studies provide strong evidence that drugs that inhibit the RAS have the potential to reduce cancer risk or retard tumour growth and metastases. Manipulation of the RAS may, therefore, provide a safe and inexpensive anticancer strategy.

Role of Kupffer cells in the pathogenesis of liver disease

Kupffer cells, the resident liver macrophages have long been considered as mostly scavenger cells responsible for removing particulate material from the portal circulation. However, evidence derived mostly from animal models, indicates that Kupffer cells may be implicated in the pathogenesis of various liver diseases including viral hepatitis, steatohepatitis, alcoholic liver disease, intrahepatic cholestasis, activation or rejection of the liver during liver transplantation and liver fibrosis. There is accumulating evidence, reviewed in this paper, suggesting that Kupffer cells may act both as effector cells in the destruction of hepatocytes by producing harmful soluble mediators as well as antigen presenting cells during viral infections of the liver. Moreover they may represent a significant source of chemoattractant molecules for cytotoxic CD8 and regulatory T cells. Their role in fibrosis is well established as they are one of the main sources of TGFβ1 production, which leads to the transformation of stellate cells into myofibroblasts. Whether all these variable functions in the liver are mediated by different Kupffer cell subpopulations remains to be evaluated. In this review we propose a model that demonstrates the role of Kupffer cells in the pathogenesis of liver disease.

Patterns of heat shock protein (HSP70) expression and Kupffer cell activity following thermal ablation of liver and colorectal liver metastases

The time course and extent of thermal ablative injury differs in liver compared to tumour tissue. This may be influenced by differences in the expression of heat shock proteins (HSP) and the response of Kupffer cells to thermal injury. This study determines the expression and response of HSP70 and Kupffer cells to thermal ablative injury in a Murine model of colorectal liver metastases. Thermal ablation by laser (Nd-YAG wavelength 1064 nm) was induced in liver and colorectal cancer liver metastases in CBA strain mice. Laser energy was applied at 2 W for 50 s and produced incomplete tumour ablation. Established tissue injury was assessed in separate groups of animals at time points ranging from 12 h to 21 days following therapy. HSP70 and Kupffer cell expression at the margins of coagulated tissue was determined by immunohistochemical staining for HSP70 and F4/80 antigens, respectively. HSP70 was faintly expressed in the cytoplasm of all tumour cells, with distinct clusters exhibiting intense cytoplasmic and nuclear HSP70 staining (130+/-19 cells mm-2). Comparatively, HSP70 expression was uncommon in untreated control liver specimens (2+/-2 cells mm-2, p<0.001). Thermal ablation increased expression of HSP70 at coagulated tissue margins. The peak response in tumours occurred at 2 days post-ablation and was significantly greater than the peak response in liver, occurring at 12 h (809+/-80 cells mm-2 vs. 454+/-52 cells mm-2, p<0.001). HSP70 expression remained significantly elevated for 7 days following therapy in tumour tissue, compared to 3 days in liver. Kupffer cell numbers in untreated control tumours were significantly lower than in untreated control livers (285+/-23 cells mm-2 vs. 451+/-30 cells mm-2, p<0.001). Following thermal ablation, there was an initial decrease in Kupffer cell numbers at the margin of coagulation with subsequent persistent increases thereafter. In liver tissue, the peak Kupffer cell response occurred at 5 days post-therapy and was significantly greater than the peak response in tumour tissue 3 days post-thermal ablation (1074+/-34 cells mm-2 vs. 860+/-53 cells mm-2, p=0.007). Thermal ablation produces a greater and more prolonged HSP70 response in colorectal liver metastases than in liver tissue. It also induces persistent increases in Kupffer cell activity in liver and tumour tissue.

Mechanisms of Focal Heat Destruction of Liver Tumors

BACKGROUND

Focal heat destruction has emerged as an effective treatment strategy in selected patients with malignant liver tumors. Radiofrequency ablation, interstitial laser thermotherapy, and microwave treatment are currently the most widely applied thermal ablative techniques. A major limitation of these therapies is incomplete tumor destruction and overall high recurrences. An understanding of the mechanisms of tissue injury induced by focal hyperthermia is essential to ensure more complete tumor destruction. Here, the currently available scientific literature concerning the underlying mechanisms involved in the destruction of liver tumors by focal hyperthermia is reviewed.

METHODS

Medline was searched from 1960 to 2004 for literature regarding the use of focal hyperthermia for the treatment of liver tumors. All relevant literature was searched for further references.

RESULTS

Experimental evidence suggests that focal hyperthermic injury occurs in two distinct phases. The first phase results in direct heat injury that is determined by the total thermal energy applied, tumor biology, and the tumor microenvironment. Tumors are more susceptible to heat injury than normal cells as the result of specific biological features, reduced heat dissipating ability, and lower interstitial pH. The second phase of hyperthermic injury is indirect tissue damage that produces a progression of tissue injury after the cessation of the initial heat stimulus. This progressive injury may involve a balance of several factors, including apoptosis, microvascular damage, ischemia-reperfusion injury, Kupffer cell activation, altered cytokine expression, and alterations in the immune response. Blood flow modulation and administration of thermosensitizing agents are two methods currently used to increase the extent of direct thermal injury. The processes involved in the progression of thermal injury and therapies that may potentially modulate them remain poorly understood.

CONCLUSION

Focal hyperthermia for the treatment of liver tumors involves complex mechanisms. Evidence suggests that focal hyperthermia produces both direct and indirect tissue injury by differing underlying processes. Methods to enhance the effects of treatment to achieve complete tumor destruction should focus on manipulating these processes.

Inhibition of experimental hepatic metastasis by targeted delivery of catalase in mice

Bovine liver catalase derivatives possessing diverse tissue distribution properties were synthesized, and their effects on hepatic metastasis of colon carcinoma cells were examined in mice. An intraportal injection of 1 x 10(5) colon 26 cells resulted in the formation of more than 50 metastatic colonies on the surface of the liver at 14 days after injection. An intravenous injection of catalase (CAT; 35000 units/kg of body weight) significantly (P < 0.001) reduced the number of the colonies in the liver. Galactosylated (Gal-), mannosylated (Man-) and succinylated (Suc-) CAT were also tested in the same system. Of these derivatives, Gal-CAT showed the greatest inhibitory effect on hepatic metastasis, and the number of colonies was significantly (P < 0.001) smaller than following treatment with catalase. High activities of matrix metalloproteinases (MMPs), especially MMP-9, were detected in the liver of mice bearing metastatic tumor tissues, which was significantly (P < 0.05) reduced by Gal-CAT. These results, combined with our previous finding that Gal-CAT can be efficiently delivered to hepatocytes, indicate that the targeted delivery of catalase to the liver by galactosylation is a promising approach to suppress hepatic metastasis. Decreased MMP activity by catalase delivery seems to be involved in its anti-metastatic effect.

Influence of TNFA on the formation of liver metastases in a syngenic mouse model

The level of TNFalpha expression is increased after partial hepatectomy, and experimental evidence exists that TNFalpha plays a key role in liver regeneration. Contradictory results are reported about the influence of TNFalpha on tumor growth: on the one hand, stimulation of tumor growth in various animal models and, on the other hand, intraperitoneally administered TNFalpha leads to reduced metastasis formation. TNFalpha may be one responsible factor for increased metastasis formation after surgical trauma. The objective of our study was to clarify the influence of TNFalpha on the formation of liver metastases in a syngenic mouse model in vivo. We used a novel marker system, EGFP transfected C26 tumor cells for in vivo observation of metastasis formation by intravital microscopy. We analyzed the effect of intraperitoneal TNFalpha-injection on tumor cell adhesion, extravasation and tumor development. The expression of ICAM-1, VCAM-1 and E-Selectin was measured by Western blot and immunohistochemical staining. Tumor load was assessed by determining EGFP in Western blots. GdCl(3) was employed 24 and 48 hr before tumor cell injection to selectively deplete the liver of functioning Kupffer cells. We observed significantly more extravasated tumor cells in the TNFalpha-pre-treated animals at early time points with increased expression of adhesion molecules. Measurement of the EGFP levels showed fewer liver metastases in the TNFalpha-pretreated animals at day 8. After GdCl(3) pretreatment even lower levels of EGFP, i.e., fewer metastases and also lower expression levels of ICAM-1, VCAM-1 and E-Selectin could be observed. TNFalpha, acts in a bidirectional manner: whereas TNFalpha facilitates tumor cell adhesion and extravasation of C26 tumor cells by inducing the expression of adhesion molecules, at later time points, TNFalpha seems to hinder the formation of liver metastases.

Activation of Kupffer cells inhibits tumor growth in a murine model system

Kupffer cells, a liver organ-specific macrophage, play an important role in preventing the development of malignant tumors. The mechanism responsible for their tumoricidal activities is not completely known. In our study, we established in vivo models involving a rat malignant cell line, rat Kupffer cells and tumor implantation in nude mice. A series of relevant in vitro experiments were also carried out to determine possible pathways. LPS-activated Kupffer cells produced significant amounts of NO, TNFalpha and IFNgamma. Malignant cells treated with either Kupffer cells or culture supernatant of the activated Kupffer cells had an increase in caspase-8 activity. Implanted tumors originated from malignant cells treated with either Kupffer cells or culture supernatant of the activated Kupffer cells grew much smaller than those from malignant cells without treatment or treated with control supernatants. The alteration of anti-apoptotic Bcl-2 was inversely associated with the change of pro-apoptotic caspase-8 and their levels in the tumor tissues matched the size of the tumors and treatments they received. It appeared that the above changes resulted in an increase in cellular DNA damage and apoptosis seen in malignant cells. Therefore, Kupffer cells execute their anti-tumor effect via increasing the production of NO, TNFalpha and IFNgamma and these cytotoxic molecules inhibit the growth of tumor by damaging cellular DNA and inducing apoptosis that was featured by downregulation of Bcl-2 but upregulation of caspase-8.

Inhibition of liver metastasis by targeting of immunomodulators using mannosylated liposome carriers

Mannosylated liposomes were prepared by incorporating cholesten-5-yloxy-N-(4-((1-imino-2-beta-D-thiomannosylethyl)amino)butyl)formamide (Man-C4-Chol) into small unilamellar liposomes consisting of cholesterol and distearoyl phosphatidylcholine (DSPC). The biodistribution of liposomes labeled with [3H]cholesteryl hexadecyl ether was examined in mice. The rate and extent of the hepatic uptake of those [3H]liposomes increased proportionally on increasing the mixing ratio of Man-C4-Chol. Their hepatic uptake was reduced by increasing the administered dose due to the limited number of mannose receptors. The liver uptake of [3H]Man-liposomes was preferentially mediated by liver non-parenchymal cells (NPC) and significantly inhibited by co-injection with an excess of Man-BSA, indicating the involvement of a mannose receptor-mediated mechanism in the hepatic uptake of Man-liposomes. Muramyl dipeptide (MDP), an immunomodulator, was also incorporated into the liposomes and its inhibitory effect in an experimental liver metastasis model was examined. In contrast to free MDP treatment, which showed little effect on the inhibition of metastasis, liposomal MDP significantly reduced the number of metastatic colonies in the liver. Active targeting of MDP to liver NPC by Man-liposomes resulted in more effective inhibition than delivery of MDP by liposomes without mannose. Treatment with MDP/Man-liposomes further increased the survival of the tumor-bearing mice. These results suggest that Man-liposomes are effective carriers for targeted delivery of bioactive compounds to liver NPC.

Induction of Fas and Fas ligand expression on malignant glioma cells by Kupffer cells, a potential pathway of antiliver metastases

Kupffer cells play an important role in controlling the growth and development of liver metastases. However, the pathway of Kupffer cells against tumor metastases is not clear. In the present study, we set up an experimental model to investigate the mechanisms on how Kupffer cells kill tumor cells which metastasize to the liver. Malignant glioma cells were cocultured with Kupffer cells or treated with culture medium collected from lipopolysaccharide (LPS)-activated Kupffer cells. The results showed that the interaction between Kupffer cells and malignant glioma cells significantly stimulated the generation of tumor necrosis factoralpha (TNFalpha). TNFalpha was mainly produced by Kupffer cells, as its level in culture medium obtained from LPS-treated Kupffer cells was not significantly different from that of malignant glioma cells treated with the same medium. Both Kupffer cells and LPS/Kupffer cell-conditioned supernatants induced expression of Fas and Fas ligand on malignant glioma cells. Subsequently a significant proportion of malignant glioma cells became apoptotic, as evidenced by positive staining of annexin V and propidium iodine and an increase in cellular DNA fragmentation. Therefore, this study supports a novel pathway of Kupffer cells against liver metastases, in which tumor cells were apoptotic via the Fas-Fas ligand system induced by TNFalpha released from Kupffer cells.

Regional muramyl tripeptide phosphatidylethanolamine administration enhances hepatic immune function and tumor surveillance

BACKGROUND

Immune status of the liver may affect growth of liver metastases. We analyzed the ability of muramyl tripeptide phosphatidylethanolamine (MTP-PE), an immunomodulatory bacterial cell wall analog, to stimulate Kupffer cells (KCs) and protect against tumor growth, with or without an immunosuppressive partial hepatectomy (PH). Impact of MTP-PE's route of administration on KC function was assessed.

METHODS

Buffalo rats (n = 7 to 12/group) were treated with saline, 40 microg MTP-PE intraportally (portal) or intravenously (IV) and challenged with 5 x 10(5) hepatoma cells, and tumors counted on day 21. To assess MTP-PE's impact on KC stimulation in animals undergoing PH, a known stimulant of tumor cell growth, groups were treated with saline or MTP-PE and challenged with tumor and underwent 30% PH. KCs were harvested and analyzed for superoxide production. Statistical analysis was performed with Mann-Whitney U test or chi-square test.

RESULTS

MTP-PE-treated animals had fewer tumor nodules than control animals (19 vs 184, P <.005). MTP-PE-portal animals had fewer nodules than MTP-PE-IV (2 vs 36, P <.05). MTP-PE treatment before PH resulted in fewer tumor nodules compared with control animals (192 vs 276, P <. 05). MTP-PE administration increased macrophage superoxide production (20.6 +/- 2 vs 11.9 +/- 1.1 nmol/10(6) cells, P <.005).

CONCLUSIONS

MTP-PE improved KC function and decreased growth of microscopic tumor cells. MTP-PE's effects persist after an immunosuppressive hepatectomy. Portal administration was the most effective. MTP-PE administration may be useful as a neoadjuvant therapy for patients undergoing resection of liver malignancies.

Early events of hepatic metastasis formation in mice: role of Kupffer and NK-cells in natural and interferon-gamma-stimulated defense

Surgical manipulation of a tumor may result in increased influx of tumor cells into the systemic and portal circulation and give rise to formation of metastases. In addition, major surgery has been reported to cause profound immunosuppression. In an attempt to increase the host-antitumor immune mechanisms following surgery we have studied the effect of preoperative administration of interferon-gamma, related to the antimetastatic effects of Kupffer cells (KC) and natural killer cells (NK-cells) in the early phase of liver metastasis formation. Colon carcinoma cells were injected into the superior mesenteric vein of syngeneic mice and after 17 days metastases were quantified by weight, number, and uptake of [125I]iododeoxyuridine. Unstimulated control mice developed 10.5 surface nodules per liver 17 days following injection of colon carcinoma cells into the superior mesenteric vein of syngeneic mice. This figure was only 2.6 in mice stimulated with a single dose of 1000 IU IFN-gamma 4 h prior to inoculation of tumor cells. Administration of GdCl3, which is reported to deplete and block the function of Kupffer cells, 24 h prior to tumor cell inoculation resulted in a 5-fold tumor mass increase relative to control. Injection of anti-asiolo-GM1 antiserum, which eliminates the hepatic NK-cells, induced a 10-fold increase in tumor mass. These results indicate an important early antimetastatic function of hepatic NK-cells and KC and that presurgical administration of IFN-gamma may be important for eliminating circulating tumor cells and inhibiting development of residual tumors.

Gadolinium blocks rat Kupffer cell calcium channels: relevance to calcium-dependent prostaglandin E2 synthesis and septic mortality

Hepatic Kupffer cells (KC), the major tissue macrophage population, produce the septic response mediators, tumor necrosis factor alpha (TNF-alpha) and prostaglandin E2 (PGE2), and have been shown to internalize gadolinium chloride (GD), a rare earth metal of the lanthanide series. Because GD pretreatment of rats has been shown to inhibit the mortality of sepsis, we studied the secretory response to lipopolysaccharide (LPS) by KC isolated from rats injected with either saline or GD (7 mg/kg, intravenously) on the 2 days before KC isolation. Using culture conditions modified to reflect the intrasinusoidal milieu of arginine (RPMI-1640 media with 10 or 100 micromol/L arginine), KC from GD-treated rats responded to LPS (0. 0025 microg/mL) with significantly (P <.01) reduced PGE2 release. In contrast, TNF-alpha release by treated KC was significantly (P <.05) enhanced, consistent with the loss of PGE2 autocoid inhibition of TNF-alpha. Calcium flux is an early signaling event in eicosanoid synthesis, and GD is known to block calcium channels. Therefore, KC were loaded with fura-2-AM to study the effect of GD on KC calcium flux. GD prevented ionomycin and platelet-activating factor (PAF)-mediated [Ca++]i increase and calcium-dependent PGE2 synthesis, while GD did not affect PGE2 synthesis when protein kinase C (PKC) was directly activated with tetradecanoylphorbolacetate (TPA). The inhibition of calcium flux and calcium-dependent PGE2 synthesis in the major cell of the monocytic phagocytic system by GD may explain the previously reported ability of this lanthanide to prevent the mortality of endotoxemia.

The effects of hepatic cryosurgery on tumor growth in the liver

BACKGROUND

The effects of hepatic cryosurgery on residual hepatic tumor growth, and on tumor immunity, have not been determined.

MATERIALS AND METHODS

Two experiments were performed. In both, animals (n = 10 per group) had solitary left lobe hepatomas established, and underwent left lobectomy, cryoablation, or control laparotomy. Experiment I: immediately after tumor treatment, intraportal challenge of hepatoma cells was performed to evaluate for the effects of treatment on residual hepatic tumor growth. Experiment II: animals were challenged 14 days after tumor treatment, and splenocyte cytotoxicity assays were performed to evaluate for tumor immunity. Hepatic tumor nodules were counted 3 weeks after challenge in both experiments.

RESULTS

In animals challenged immediately after tumor treatment, the mean number of liver nodules at 3 weeks was similar between control and cryoablation groups (65 +/- 13 vs 115 +/- 38, P = 0.17). Animals that had undergone resection, however, had a significant increase in the mean number of nodules as compared to cryoablation (278 +/- 74 vs 115 +/- 38, P = 0. 04) and control (278 +/- 74 vs 65 +/- 13, P = 0.002) animals. In addition, only resection animals had elevation in serum levels of the growth factor FGF-basic, 48 h after treatment (mean = 30 +/- 14 pg/ml). In animals challenged 14 days following treatment, all groups had similar numbers of nodules (resection vs cryoablation, P = 0.8). Splenocyte cytotoxicity was not increased after cryosurgical treatment.

CONCLUSIONS

Unlike partial hepatectomy, cryoablation of hepatomas in rats does not accelerate residual tumor growth in the liver or result in production of the growth factor FGF-basic. We did not find evidence for the development of tumor immunity following cryosurgery.

Prevention of hepatic tumor metastases in rats with herpes viral vaccines and gamma-interferon

Previous studies showed that gammaIFN decreases metastatic hepatic tumor growth by stimulating Kupffer cells (KC). The present studies examine whether lymphocyte stimulation via cells engineered to secrete GM-CSF or IL-2 decreases hepatic tumor growth, and whether stimulation of both macrophages and lymphocytes is more effective than either individually. Rats were immunized with irradiated hepatoma cells transduced by herpes viral amplicon vectors containing the genes for GM-CSF, IL-2 or LacZ. On day 18, half of each group was treated with 5 x 10(4) U gammaIFN, or saline intraperitoneally for 3 d. On day 21, all rats received 5 x 10(5) hepatoma cells intrasplenically. On day 41, rats were killed and tumor nodules were counted. Separate rats underwent splenocyte and KC harvest for assessment of lymphocyte- and macrophage-mediated tumor cell kill in vitro. GM-CSF or IL-2 vaccines or gammaIFN decreased tumor nodules significantly (GM-CSF 13+/-4, IL-2 14+/-6 vs. control 75+/-24, P < 0.001). Combination therapy was more effective, and completely eliminated tumor in 4 of 12 IFN-GM-CSF and 8 of 11 IFN-IL-2 animals. Additional rats underwent partial hepatectomy, an immunosuppressive procedure known to accelerate the growth of hepatic tumor, following tumor challenge. Therapy was equally effective in this immunosuppressive setting. Vaccination is associated with enhancement of splenocyte-mediated tumoricidal activity, whereas the effect of gammaIFN is mediated by KC. GM-CSF and IL-2 vaccine therapy and pretreatment with gammaIFN represent effective strategies in reducing hepatic tumor. Combination therapy targets both lymphocytes and macrophages, and is more effective in reducing tumor than either therapy alone.

In vivo assessment of hepatic alterations following gadolinium chloride-induced Kupffer cell blockade

BACKGROUND/AIMS

In recent years, Gadolinium chloride (GdCl3), a rare earth metal, has frequently been used to study the role and function of Kupffer cells under physiological and pathological conditions. This study was performed to elucidate the consequences of GdCl3-induced Kupffer cell blockade for hepatic microcirculation, hepatocellular function and integrity.

METHODS/RESULTS

Using intravital fluorescence microscopy, we studied the hepatic microcirculation of rats pretreated with either GdCl3 (n = 12; 10 mg/kg; 1 ml i.v. for 2 d) or saline (n = 9; 1 ml). The GdCl3-treated animals revealed a significantly lower phagocytic activity of Kupffer cells when compared to controls. Concomitantly, GdCl3-treatment resulted in a pronounced rise of serum cytokine activity (tumor necrosis factor-alpha; interleukin-6). The hepatic microvascular perfusion was characterized by a moderate increase in the number of non-perfused sinusoids accompanied by a reduction of bile flow. In addition, GdCl3-treatment caused a slight increase in liver enzyme activity (< 200 U/l) (aspartate aminotransferase and alanine aminotransferase) with no substantial parenchymal tissue injury (light microscopy). The groups did not differ in concentrations of circulating endotoxin (GdCl3-treatment: 0.044 +/- 0.042 ng/ml; controls: 0.052 +/- 0.014 ng/ml).

CONCLUSIONS

We conclude that hepatic alterations following Kupffer cell blockade with GdCl3 may possibly be the consequence of cytokine release as a response to the phagocytic challenge of GdCl3-aggregates. If used for Kupffer cell blockade, the hepatic alterations following GdCl3-treatment described in the present study should be taken into consideration.

Kupffer cells and pit cells are not effective in the defense against experimentally induced colon carcinoma metastasis in rat liver

The present study was performed to investigate processes involved in circumvention of the immune system by advanced stages of tumor growth in the liver. The efficacy of Kupffer cells and pit cells against cancer cells was tested in vivo in an experimental model of colon carcinoma metastasis in rat liver. Liver tumors were induced by administration of CC531 colon cancer cells into the vena portae. After 3 weeks, livers were obtained and partly fixed for electron microscopic procedures or frozen in liquid nitrogen for enzyme and immunohistochemistry at the light microscope level. The activation status of Kupffer cells was studied by expression of Ia-antigen (MHC class II) and by measurement of glucose-6-phosphate dehydrogenase (G6PDH) activity in the cells in situ as a measure of production of reactive oxygen species. Large numbers of Kupffer cells were found in liver parenchyma surrounding colon carcinomas when compared with levels in control livers, but these cells were not activated. Large numbers of activated monocytes and macrophages, cytotoxic T cells but only a few pit cells were found to be recruited to the boundary between liver parenchyma and tumors or their stroma. In those areas where cancer cells invaded liver parenchyma, only newly recruited macrophages and some Kupffer cells were present but few cytotoxic T cells or pit cells were found. The low activation status of Kupffer cells both in terms of production of reactive oxygen species and Ia-antigen expression and the absence of significant numbers of pit cells at tumor sites suggest that Kupffer cells and pit cells do not play a significant role in advanced stages of tumor growth. High levels of prostaglandin E2 were detected in the parenchyma of livers containing tumors and transforming growth factor beta was detected in the stroma of the tumors, therefore suggest that cytotoxicity of newly recruited monocytes, macrophages and cytotoxic T cells may be limited in these stages because of local production of these immunosuppressive factors.

Effect of membrane free fatty acid alterations on the adhesion of human colorectal carcinoma cells to liver macrophages and extracellular matrix proteins

Epidemiologic studies have linked diets high in animal fat with colon carcinogenesis. A number of animal tumor models have shown that diets rich in omega-3 fatty acids inhibit colon carcinogenesis while diets rich in omega-6 fatty acids promote tumor growth. This study examines whether modification of the membrane fatty acid composition of both moderately (CX-1) and poorly differentiated (MIP-101 and Clone A) human colorectal carcinoma cells alters their interaction with Kupffer cells and extracellular matrix proteins (collagen type IV, fibronectin and laminin). The cells were treated with 15-16 micrograms/ml of docosahexanoic acid (22:6, omega 3) or linoleic acid (18:2,omega 6). Gas chromatography showed significant alterations in the membrane fatty acid composition of the human colorectal cancer cell lines. Binding assays were performed by measuring adherence of 51Cr-labelled tumor cells to Kupffer cell monolayers or to immobilized proteins. Omega-3 treatment significantly decreased the Kupffer cell binding of only the CX-1 line while omega-6 treatment decreased binding of all three cell lines. In contrast both omega-3 and omega-6 treatment of MIP-101 cells decreased binding to the extracellular matrix proteins with the omega-6 effect being more pronounced. These results indicate that the binding characteristics of the colon cancer cells to both Kupffer cells and extracellular matrix proteins may be determined in part by the membrane fatty acid composition. Decreased adherence to extracellular matrix proteins may lead to increased cell motility and invasiveness. Since Kupffer cell binding precedes tumor cell phagocytosis and killing, decreased binding may improve tumor cell survival.

Tumour growth stimulation after partial hepatectomy can be reduced by treatment with tumour necrosis factor alpha

This study investigated whether partial hepatectomy enhances the growth of experimental liver metastases of colonic carcinoma in rats and whether treatment with recombinant human tumour necrosis factor (TNF) alpha can reduce this increased growth. Resection of 35 or 70 per cent of the liver was performed in inbred WAG rats, with sham-operated controls (five to eight animals per group). Immediately after surgery 5 x 10(5) CC531 colonic tumour cells were injected into the portal vein. After 28 days the animals were killed and the number of liver metastases counted. A 35 per cent hepatectomy induced a significant increase in the median number of liver metastases (28 versus 3 in controls), whereas a 70 per cent resection provoked excessive growth, consistently leading to more than 100 liver metastases and a significantly increased wet liver weight in all animals. TNF-alpha was given intravenously to rats following 70 per cent hepatectomy or sham operation in a dose of 160 micrograms/kg three times per week. This had only a marginal effect on tumour development in sham-operated rats but was very effective following partial hepatectomy (median 45 liver metastases). These observations confirm previous findings that surgical metastasectomy may act as a 'double-edged sword' by provoking outgrowth of dormant tumour cells and suggest that adjuvant treatment with TNF-alpha may be of benefit in patients undergoing resection of metastases.

Kupffer cell/tumor cell interactions and hepatic metastasis in colorectal cancer

The degree of interaction with Kupffer cells of two moderately well differentiated cell lines, CX-1 and CCl-188 of high metastatic potential (61%) were compared to two poorly differentiated cell lines, MIP-101 and Clone A of low metastatic potential (6%) in the intrasplenic injection model for liver metastasis. MIP-101 and Clone A bound significantly better to mouse Kupffer cells in vitro than either CX-1 or CCL-188. We also identified specific cell surface proteins mediating attachment of colorectal carcinoma cells to murine Kupffer cells. Kupffer cells were radiolabelled and their surface proteins incubated with MIP-101 and CX-1. Two radiolabelled proteins from murine Kupffer cells of 14 and 34 kDa were identified consistently binding to the tumor cells. Binding of both proteins was inhibited by asialofetuin but not by fetuin. This suggests that the major binding proteins between Kupffer cells and colorectal cancer cells are galactose binding lectins.

Desialylation of metastatic human colorectal carcinoma cells facilitates binding to Kupffer cells

Cell surface hypersialylation of human colorectal carcinoma (HCRC) cells correlates with increased metastatic potential after intrasplenic injection, while desialylation with various agents has been shown to inhibit hepatic metastases. In this study we examined the effects of desialylation of HCRC cell lines with a novel intracellular inhibitor of the CMP-sialic acid transport protein (KI-8110). HCRC cells, which are poorly differentiated and poorly metastatic in nude mice (Clone A and MIP-101) were compared to well-differentiated, highly metastatic cells (CX-1 and CCL-235). KI-8110 treatment has previously been shown to reduce sialic acid levels in each of these cell lines and to reduce hepatic metastases in CX-1 and CCL-235 cell lines. This study attempts to identify a mechanism by which desialylation inhibits hepatic metastases. After KI-8110 treatment, in vitro adhesion assays were performed with each cell line to examine binding to Kupffer cells and the extracellular matrix protein fibronectin. Binding of Clone A, CX-1, and CCL-235 to Kupffer cells was significantly increased after KI-8110 treatment. Desialylation had no significant effect on binding of HCRC cell lines to fibronectin. While the metastatic cascade involves many complex interactions, the cytotoxic effects of Kupffer cells in the hepatic sinusoid are known to be an important mechanism of host defense against tumor cells. Cell surface sialic acids may well mask Kupffer cell binding to HCRC cells, preventing their cytotoxic effects and enhancing the metastatic potential of circulating tumor cells.

Enhanced tumour growth in the rat liver after selective elimination of Kupffer cells

The evidence that Kupffer cells are capable of controlling metastatic growth in the liver in vivo is largely circumstantial. The best approach when studying natural cytotoxicity activities of Kupffer cells is to investigate the effect of Kupffer cell elimination on tumour growth. Until now it has not been possible to eliminate Kupffer cells without affecting other cell populations. We have recently developed a new method to eliminate Kupffer cells selectively: intravenous injection of liposome-encapsulated (dichloromethylene)bisphosphonate (Cl2MDP-liposomes) leads to effective elimination of all Kupffer cells, without affecting non-phagocytic cells. Wag/Rij rats were injected with Cl2MDP-liposomes. After 48 h, rats were inoculated with syngeneic CC531 colon carcinoma cells by injection in the portal system. The results show a strongly enhanced tumour growth in the liver of the Cl2MDP-liposome-treated rats. In these animals, livers were almost completely replaced by tumour and had increased in weight, whereas in the control groups only a few (four to eight) small (1-mm) tumour nodules were found. These data show that selective elimination of Kupffer cells results in enhanced tumour growth in the liver, implying that Kupffer cells play a crucial role in controlling tumour growth in the liver.

Human and murine Kupffer cell function may be altered by both intrahepatic and intrasplenic tumor deposits

The liver is the most common site of hematogenous metastases from colorectal carcinoma. Kupffer cells (KC), which line the hepatic sinusoids, may form the first line of defense against circulating tumor cells. The purpose of this study was to determine the effect of hepatic metastases and intra-abdominal tumor growth on KC binding of human colorectal carcinoma (HCRC) cells. MIP-101, a poorly metastatic cell line, and CX-1, a highly metastatic cell line, were injected intrasplenically into nude mice and KC were isolated by collagenase perfusion at varying intervals after injection. Conditioned media were collected from MIP-101, CCL 188 and CX-1 to determine their in vitro effect on KC function. KC from MIP-101 injected mice (14% liver metastases, 100% splenic tumors) bound a significantly greater number of MIP-101 and clone A cells than CX-1 cells in vitro. KC isolated from mice 5 weeks after CX-1 injection (100% liver metastases) also showed increased binding of MIP-101 and clone A cells compared to CX-1 cells. Similar results were obtained when tumor cell binding to normal human liver KC was compared to binding to KC from human livers from patients with hepatic metastasis from colorectal cancer. In contrast KC obtained from mice 3 weeks after CX-1 injection (44% liver metastases) showed significantly decreased binding of MIP-101 and clone A cells. The conditioned medium from CX-1 cells significantly decreased the in vitro binding of both MIP-101 and CX-1 by KC. These results indicate that the ability of KC to bind HCRC cells (which precedes phagocytosis and tumor cell killing) is a dynamic function and affected by concomitant tumor growth. HCRC cells may alter KC function via the production of specific tumor-derived soluble factors. In order to devise new and more effective therapeutic options in the treatment of liver metastases the nature of this tumor cell-KC interaction must be better understood.

Murine Kupffer cells and hepatic natural killer cells regulate tumor growth in a quantitative model of colorectal liver metastases

This investigation aimed to develop a biologically relevant murine model of colorectal liver metastases and determine if Kupffer cells (KC) and hepatic natural killer cells (hNKC) regulate tumor growth. The model involves the injection of murine colon adenocarcinoma 26 (MCA 26) tumor cells into the portal vein of female-specific pathogen-free BALB/c mice. Metastases developed in all animals, and the growth was limited entirely to the liver. To determine if KC and hNKC control the development of liver metastases, the in vivo function of these hepatic effector cells was modulated. Tumor growth was quantitated by the uptake of 125I into tumor DNA. Stimulation of the KC and hNKC produced a significant (P less than 0.01) dose-dependent decrease in 125I uptake in the liver in both treatment groups, which was associated with a significant improvement in survival (P less than 0.05). The in vivo cytotoxic function of the liver was inhibited with an intravenous injection of gadolinium chloride (for KC) or asialo GM1 antiserum (for hNKC). Inhibition of KC and hNKC cytotoxic function led to a significant (P less than 0.01) increase in 125I uptake in the liver and a significant decrease in survival (P less than 0.05).

Dormant liver metastases: an experimental study

Experimental work was undertaken to evaluate whether intrahepatic recurrences, observed after resection of colorectal liver metastases in humans, could be due to the activation of dormant cancer cells already present within the liver at liver resection. About 250 cell aggregates (DHDK12 colon carcinoma cell line) were injected into the portal vein of 70 BD IX rats. Eight weeks later, 43 rats with no apparent liver metastases were divided randomly into three groups: group 1 (n = 15) served as control; group 2 (n = 15) were given cyclosporin A (10 mg kg body-weight-1 day-1) for 28 days; and group 3 (n = 13) underwent a 70 per cent hepatectomy. Twelve weeks after the injection of cells, when the animals were killed, 20 per cent of rats in group 1 had liver metastases, 80 per cent in group 2 (P less than 0.01) and 62 per cent in group 3 (P less than 0.05). Undetectable liver micrometastases may have been present at 8 weeks and had not developed until stimulation by cyclosporin A-induced immunosuppression or by liver regeneration after hepatectomy. A similar mechanism may occur clinically and explain some of the recurrences observed after resection of liver metastases.

Liver macrophage-mediated cytotoxicity toward mastocytoma cells involves phagocytosis of tumor targets

Macrophage-mediated cytotoxicity toward tumor cells usually involves extracellular lysis of the targets. In this study, we report that liver macrophages from rats treated with lipopolysaccharide (5 mg/kg, intravenous) also kill certain tumor cell targets by phagocytosis. Liver macrophages were coincubated with P815 mouse mastocytoma cells for 24 to 72 hr at an effector/target ratio of 10:1. Macrophage phagocytosis was characterized by flow cytometry and by light and electron microscopy. For flow-cytometric studies, P815 cells were prelabeled with the fluorescent dye 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate. We found that coincubation of macrophages with labeled targets resulted in a time-dependent increase in macrophage-associated fluorescence, reaching a maximum at 72 hr. This correlated with light-microscopic observations of increased numbers of tumor cells in the macrophages and enhanced macrophage surface area and density. Electron microscopic studies revealed that the initial event in the phagocytic process involved the capture of P815 cells by the pseudopodia of the macrophages. Target cells were then surrounded by lamellipodia, internalized in phagosomes and destroyed. These data, together with previous studies, provide evidence for multiple mechanisms of cytotoxicity mediated by activated liver macrophages.

Interdependence of tumor necrosis factor, prostaglandin E2, and protein synthesis in lipopolysaccharide-exposed rat Kupffer cells

Kupffer cells are the main producers of tumor necrosis factor-alpha (TNF; cachectin) and eicosanoids in the liver exposed to lipopolysaccharide (endotoxin; LPS). A very rapid but transient release of TNF is followed by a slow, steady synthesis of prostaglandin E2 (PGE2). TNF itself is able to provoke eicosanoid synthesis in Kupffer cells; the rate and pattern of prostaglandin production are similar to those observed after treatment with LPS. Anti-TNF antibodies completely neutralize TNF action on Kupffer cells, thus ruling out any participation of contaminating LPS. LPS stimulation of PGE2 production in Kupffer cells is reduced by the antiserum to 50%, indicating an involvement of TNF in the stimulatory action of LPS. On the other hand, PGE2, a potent inhibitor of LPS-elicited TNF release, is able to suppress LPS- but not TNF-stimulated eicosanoid synthesis in rat Kupffer cells. In addition to this autocrine circuit, extrahepatic factors participate in the regulation of Kupffer cell activation: glucocorticoids not only inhibit TNF or prostaglandin production, they also reverse the LPS-specific changes in the prostaglandin pattern of Kupffer cells. LPS, TNF or cycloheximide when given alone in the concentration range applied in this study do not affect the viability of rat Kupffer cells. However, the combinations of cycloheximide and either LPS or TNF cause rapid death of the cultured cells. The cytolytic potential of either combination cannot be alleviated by treatment with glucocorticoids.

Experimental colorectal liver metastases. Influence of sex, immunological status and liver regeneration

The liver is the most frequent site of metastases from colon cancer. To improve our knowledge of liver metastases and to develop new adjuvant therapies, a good animal model is necessary. The aims of this study were to obtain a model of liver metastases with intraportal injection of colon adrenocarcinoma cell aggregates (DHDK12 cell line) and to study the effect of various factors, i.e., sex, liver regeneration and immunosuppression, on the development of liver metastasis. Cell aggregates were injected into the portal vein of 59 syngenic male and female BD IX rats following randomization into three groups. Group 1, (control 12 males and 10 females) received only cell aggregates; group 2 (12 males and 10 females) underwent a 70% hepatectomy before cell injection; group 3 (15 males and 10 females) received cyclosporin A injections at a dose of 10 mg/kg per day for 28 days following cell injection. Autopsy was performed at 10 weeks. Liver metastases were more frequent in the male rats in group 3 than in those in group 1 (80% vs. 30%, p less than 0.04). The rate of liver metastases in females was not increased by immunosuppression (22.2% vs. 12.5%, N.S.). Liver resection (group 2) did not significantly modify the incidence of liver metastasis. No female had liver metastases in this group. This relatively simple model rapidly produces liver metastasis with a high yield, but only in male rats. Besides sexual factors, immunosuppression also increased the rate of experimental liver metastasis, while liver regeneration failed to do so.

Kupffer cells and liver metastasis. Optimization and limitation of activation of tumoricidal activity

Kupffer cells, tissue-fixed macrophages located in the sinusoids of the liver, represent the highest concentration of mononuclear phagocytes in the body. Their ability to act as scavengers of particulate material in the blood has given rise to speculation that they play a role in controlling hepatic metastases derived from blood-borne tumor cells. Circumstantial evidence for such a role has been obtained from animal studies where Kupffer cell function has been compromised or inhibited, and from anecdotal clinical observations. Current evidence suggests that Kupffer cells are capable of nonspecifically eliminating some circulating tumor cells from the circulation via phagocytosis. This surveillance mechanism would appear to be limited in capacity, and subject to a number of external factors. Recent studies have demonstrated that Kupffer cells can be activated to a tumoricidal state via the administration of biological response modifiers such as gamma interferon or muramyl peptides. The localization of liposomes within Kupffer cells after systemic administration has provided a considerable stimulus for the efficient targeting of macrophage-activating compounds to these cells. Such therapeutic intervention, while capable of inducing Kupffer cell tumoricidal activity in situ and inhibiting tumor growth, is limited with respect to the location of the tumor cells (sinusoidal versus parenchymal) and to the size of the metastatic nodule. Therapeutic intervention using liposomes containing macrophage-activating agents may only be of benefit in patients with minimal tumor load who are at risk for hepatic metastases, rather than those patients who already have clinically detectable liver tumors.

The release of tumor necrosis factor from endotoxin-stimulated rat Kupffer cells is regulated by prostaglandin E2 and dexamethasone

Evidence is presented that upon stimulation with endotoxin (lipopolysaccharide, LPS), Kupffer cells, the body's largest pool of sessile macrophages, synthesize and liberate a factor whose immunological, cytotoxic and chemical properties are those described for tumor necrosis factor (TNF)-alpha. Hepatocytes and sinusoidal endothelial cells do not produce detectable amounts of this protein. Ten nanograms of LPS per ml medium are sufficient to stimulate a substantial release of this mediator. Recombinant interferon-gamma (rIFN gamma) per se is a poor inducer of TNF release. Costimulation with endotoxin and rIFN gamma shows only a slight increment in the release of this cytotoxic factor, relative to LPS alone. Exposure of Kupffer cells to the Ca2+ ionophore A23187 or to elicitors of the oxidative burst and superoxide production, e.g. zymosan or phorbol 12-myristate 13-acetate, stimulates only a fraction (20%) of the TNF release seen after endotoxin challenge. Prostaglandin E2, the synthesis of which is strongly enhanced after challenge of rat Kupffer cells with LPS, suppresses the release of TNF by these cells. This autoregulatory mechanism may explain the kinetics of TNF production by stimulated Kupffer cells. Dexamethasone is another important mediator capable of reducing the LPS-elicited TNF formation. An effect of the glucocorticoid hormone can still be provoked if it is added simultaneously with or shortly after LPS. This rapid action requires a mechanism that is different from the time-consuming one leading to the inhibition of prostaglandin synthesis in Kupffer cells.