Alterations in enzymatic functions in hepatocytes and hepatocellular carcinomas from Ras-transduced livers resemble the effects of insulin.

An understanding of how oncogenes affect differentiated liver functions might lead to improved treatments for liver cancer or other disorders where liver-specific functions are compromised. A retroviral vector that coexpressed beta-galactosidase (beta-gal) and activated Ras genes (Ras-gal) was transduced into a small fraction of adult rat hepatocytes in vivo. Hepatocytes from Ras-gal-transduced diethylnitrosamine-untreated livers and hepatocellular carcinomas (HCC) from Ras-gal-transduced diethylnitrosamine-treated rats were analyzed for liver functions by performing histochemical assays on liver sections. Ras-gal-transduced hepatocytes failed to express gluconeogenic, ketogenic, and urea pathway enzymes. In contrast, several enzymes involved in fat synthesis were strongly activated, and microvesicular fat accumulated. These metabolic changes are induced in normal livers by insulin, a hormone that activates p21-ras. The deregulation of p21-ras may inhibit these liver-specific functions and may induce fat synthesis in both malignant and nonmalignant liver diseases. Furthermore, treatment with drugs that inhibit the attachment of p21-ras to the plasma membrane might reverse these changes. The alterations in enzymatic functions in the HCCs were similar to those observed in the hepatocytes, although each of the two cancers had a region that abruptly lost its expression of liver-specific enzymes and acquired the expression of genes that are more characteristic of oval or bile ductule cells. This suggests that a single genetic event in a malignant cell may dramatically alter its apparent phenotype. The identification of this putative gene might lead to insights into the regulation of the phenotype of normal cells in the liver.

Ras-transduced diethylnitrosamine-treated hepatocytes develop into cancers of mixed phenotype in vivo.

The cell of origin of hepatocellular carcinoma (HCC) is controversial. A method for marking cells of different lineages in vivo and then determining their carcinogenic potential should resolve this issue. A retroviral vector expressing activated ras and beta-gal genes (Ras-gal) was transferred into adult rat hepatocytes in vivo, and some animals were treated with diethylnitrosamine (DEN). Bile ductule cells and the putative stem cells of the liver (the oval cells) did not appear to be transduced by this method. At 1 month after transfer, 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside staining was performed on transduced rat livers to determine the blue cluster size. Eight % of the clusters in Ras-gal-transduced, DEN-treated livers contained at least twice as many cells as the largest cluster in Ras-gal-transduced, DEN-untreated rats, demonstrating that they had acquired markedly abnormal growth properties. When the retroviral vector containing beta-gal without ras (Gal-509) was transferred into DEN-treated rats, 2.5% of the cells were present in clusters containing at least twice as many cells as the largest cluster in Gal-509-transduced, DEN-untreated animals. Thus, p21-ras may increase the percentage of cells that acquire mutations in response to DEN, or it may behave synergistically with other mutations to increase the replication rate of cells. Occasional foci in Ras-gal-transduced, DEN-treated rats had extramedullary hematopoiesis. Forty % of the Ras-gal-transduced, DEN-treated rats developed unifocal HCC, mixed HCC/cholangiocarcinoma (CC), or CC at 3-6 months after transduction, suggesting that hepatocytes can develop into HCC or CC if sufficient genetic alterations occur.

Endotoxin tolerance alters phospholipase C-gamma 1 and phosphatidylinositol-3'-kinase expression in peritoneal macrophages.

Although the molecular signaling mechanisms underlying macrophage endotoxin (LPS) responsiveness are not fully understood, alterations in intracellular phosphatidylinositol (PI) metabolism appear to contribute. We evaluated the effects of endotoxin tolerance (ET) induction upon peritoneal macrophage (PM) expression of the principal PI enzymes phospholipase PLC-gamma 1 (PLC-gamma 1) and phosphatidylinositol 3'-kinase (PI-3-K). Rats received either 5 mg/kg LPS (ET) or phosphate-buffered saline (nontolerant, NT) which enabled 88% of ET and 25% of NT to survive a 25 mg/kg LPS dose 3 days later. PM were harvested by lavage on Day 3 from both ET and NT rats. Following overnight culture, 5 x 10(6) PM in serum-free media were stimulated with 5 ng/ml LPS for 0 to 30 min. Cell lysates fractionated by SDS-PAGE were transferred to nitro-cellulose and blotted with PLC-gamma 1, PI-3'-K, and phosphotyrosine (4G10) monoclonal antibodies. Western immunoblots were developed by enhanced chemiluminescence and quantitated by densitometry. Unlike NT cells in which PLC-gamma 1 was expressed constitutively and increased with LPS stimulation, PLC-gamma 1 expression in ET cells stimulated with LPS was markedly reduced in three separate experiments. In contrast, ET cells expressed considerably higher concentrations of PI-3'-K to NT cells. Patterns of protein tyrosine phosphorylation were similar in both NT and ET cells regardless of LPS stimulation. The development of endotoxin tolerance decreased PLC-gamma 1 expression and markedly amplified PI-3'-K expression in macrophages. PI-3'-K-generated second messengers may contribute to unique signaling pathways responsible for tempered cellular responses to LPS.

Quantitative evaluation of liver-specific promoters from retroviral vectors after in vivo transduction of hepatocytes.

Hepatic gene therapy could be used to treat a number of inherited blood diseases such as hemophilia or thrombophilia. Although liver-directed retroviral transduction can result in long-term gene expression in vivo, the low level of protein production has limited its clinical application. We reasoned that the insertion of liver-specific promoters into retroviral vectors would increase gene expression in vivo. The 347-bp human alpha 1-antitrypsin (hAAT), the 810-bp murine albumin (mAIb), the 490-bp rat phosphoenolpyruvate carboxykinase (rPECK), and the 596-bp rat liver fatty acid binding protein promoters were inserted into a Moloney murine leukemia retroviral backbone containing the hAAT reporter gene. Vectors that produced appropriately sized RNA and hAAT protein in vitro were tested in vivo by transducing regenerating rat livers. Long-term serum expression of the hAAT reporter gene was normalized to retroviral transduction efficiency as determined by using a polymerase chain reaction-based assay of genomic DNA from transduced rat livers. The hAAT, mAIb, and rPEPCK promoters were, respectively, 35-, 8-, and 0.02-fold as strong as the previously studied constitutive Pol-II promoter. We conclude that the hAAT promoter resulted in the highest expression from a retroviral vector and may result in therapeutically significant expression of other clinically significant blood proteins.

The Kupffer cell in endotoxin tolerance: mechanisms of protection against lethal endotoxemia.

Kupffer cells (KC) of the hepatic sinusoid respond to endotoxemia by producing mediators which promote or inhibit systemic inflammatory responses. Sublethal lipopolysaccharide (LPS) pretreatment confers tolerance to the lethality of a subsequent LPS exposure. However, the precise role of the KC in endotoxin tolerance (ET) remains unclear. This study evaluated the effect of ET induction upon the rat KC production of the mediators tumor necrosis factor-alpha (TNF-alpha), prostaglandin E2 (PGE2), and interleukin-6 (IL-6), and upon the in vivo phagocytic capacity of the KCs. 3 days prior to KC isolation, age-matched rats received either 5 mg/kg LPS (ET) or normal saline (nontolerant, NT), which protected 100% of the ET rats against an LPS dose 3 days later which was lethal in 72% of NT rats. On an in vitro LPS rechallenge, ET KC produced significantly lower amounts of TNF than NT KC (p < .01). In contrast, the ET KC produced significantly more PGE2 (p < .05) and IL-6 (p < .001) than the NT KC. The percentage of KC phagocytosing fluorescent latex spheres in vivo was increased 7-fold in the ET rats. Thus, ET induction, which protects rats against subsequent lethal endotoxemia, selectively alters KC mediator production and phagocytic capacity. These findings strongly implicate the KC in the mediation of early endotoxin tolerance.

Liver-directed gene therapy: evaluation of liver specific promoter elements.

Liver-directed gene therapy could dramatically alter the therapy of many inherited hematologic and metabolic diseases. We have developed a rapid, reliable, low-mortality method for the in vivo delivery in rats of retroviral vectors 24 hr after 70% hepatectomy by intraportal injection during hepatic in-flow occlusion (HIFO). Using the human alpha 1-antitrypsin (hAAT) reporter gene, we found in vivo that up to 10% of hepatocytes integrated the provirus, and serum hAAT protein levels were sustained for up to 1 year. Despite high in vivo transduction efficiencies, gene expression at the mRNA level is disappointingly low compared to in vitro transduced NIH 3T3 or Hepa A1 tissue culture cells. In this report, LNL-6-derived retroviral vectors (RV) were combined with one of two strong, liver-specific promoters, murine albumin or human alpha 1-antitrypsin, an upstream insertion of a trimer of hepatocyte nuclear factor-3 (HNF-3) binding sites, and the hAAT reporter gene. HNF-3 has been demonstrated to increase in vitro transcriptional activity [23]. Twenty-four hours after 70% hepatectomy, 10-fold concentrated (by methotrexate-resistant titer) RV-producing cell supernatant was given intraportally during a 3-min HIFO. Serum hAAT levels as quantitated with a human specific ELISA were sustained for over 40 weeks with all of the liver-specific promoter constructions. However, the hAAT protein production with the murine albumin promoter retroviral constructs decreased with time, but was sustained at levels approximately 80% of the initial serum peak levels with the constructs containing the hAAT promoter.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoregulation by eicosanoids of human Kupffer cell secretory products. A study of interleukin-1, interleukin-6, tumor necrosis factor-alpha, transforming growth factor-beta, and nitric oxide.

OBJECTIVE: Methods employed previously to analyze the secretory behavior of rodent Kupffer cells (KC) were used to examine the human KC's secretory response to lipopolysaccharide (LPS). SUMMARY BACKGROUND DATA: As the resident hepatic macrophage, the KC resides at the interface between the portal and systemic circulations. Consequently, this cell may play an integral role in the immune response to antigens and bacteria in the sinusoid. Study of cytokine production by the KC has relied predominantly on the rat as the source of these cells. Whether human KCs respond similarly to rat KCs after LPS stimulation has been a matter of speculation. METHODS: Kupffer cells obtained from seven human livers were tested under conditions identical to those used to study rat KCs. Kupffer cells rested for 12 hours after isolation were stimulated with LPS (2.5 micrograms/mL). Arginine concentration in the culture medium varied from 0.01 to 1.2 mM. To examine the role of eicosanoids, parallel culture wells received indomethacin (10 microM). Culture supernatants were assayed for interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), transforming growth factor-beta (TGF-beta), prostaglandin E2 (PGE2), and nitric oxide. RESULTS: Similar to the rat KC, LPS-stimulated human KCs released IL-1, IL-6, TNF-alpha, TGF-beta, and PGE2. However, unlike rat KCs, nitric oxide could not be detected, regardless of whether the human KCs were exposed to LPS, interferon-gamma (INF-gamma), or LPS + IFN-gamma. Similar to rat KCs, indomethacin prevented PGE2 release while significantly upregulating TNF-alpha, IL-1, and IL-6, but not TGF-beta, consistent with an autoregulatory control of eicosanoids over proinflammatory cytokines. As has been shown in the rat, physiologic levels of L-arginine (0.01 mM) significantly enhanced LPS-induced PGE2 secretion relative to the response in medium containing standard L-arginine concentration (1.2 mM); however, unlike the rat KC, the human's cytokine response to LPS was not downregulated by this enhanced PGE2 release. CONCLUSIONS: Although many functional features are shared by rat and human KCs, significant differences do exist. Such discrepancies reinforce the need to proceed with caution when generalizing from the results obtained in other species to human physiology.

Liver-directed gene therapy: quantitative evaluation of promoter elements by using in vivo retroviral transduction.

Liver-directed gene therapy will be applicable to many inherited diseases. Although various protocols have been devised for in vivo delivery of retrovirus, comparison of hepatocyte transduction frequencies has been difficult due to variations in retroviral titer and a paucity of DNA data. We have previously reported an in vivo rat hepatocyte transduction technique which involves 70% hepatectomy followed 24 hr later by portal vein injection of retrovirus during hepatic in-flow occlusion. In this study, we employed this method and concentrated retroviral preparations to achieve transduction of up to 15% of hepatocytes as determined by a quantitative PCR assay. As an initial step toward identifying promoters which lead to high-level long-term expression of retroviral transduced genes, we used our in vivo delivery system to compare the Moloney murine leukemia virus long terminal repeat (LTR) promoter with the promoter for the large subunit of murine RNA polymerase II (Pol-II). Human alpha 1-antitrypsin (hAAT) was used as the reporter gene to facilitate long-term analysis of expression. Serum hAAT levels were higher for the Pol-II promoter (143 ng/ml) than for the LTR promoter (50 ng/ml). This difference was consistent with the higher transduction frequency observed for the Pol-II-hAAT vector. Although serum hAAT expression was sustained for up to 1 year in six of eight Pol-II-hAAT-transduced rats and three of five LTR-hAAT-transduced rats and was proportional to hAAT mRNA level and proviral DNA frequency, in vivo expression was significantly lower than in transduced tissue culture cells. We conclude that a high frequency of in vivo transduction can be achieved by using retroviral vectors and our rapid transduction protocol, but transduced gene expression remains a serious problem. The quantitative assays described herein will facilitate in vivo comparisons of gene regulatory elements.

Clinical diagnostic applications of the polymerase chain reaction. Infection and rejection.

In this review, we describe the power and sensitivity of the polymerase chain reaction and indicate areas of clinical medicine in which it is currently being applied. As this technology and automation improves and is simplified, its realm of application will expand, but its major impact will continue to be its facilitation of early, specific diagnoses in infectious disease, genetics, cancer, and transplantation. Polymerase chain reaction is currently most useful in the care of opportunistic infections in immunosuppressed hosts and in making the distinction between infection and rejection in transplant recipients. As the technique becomes more widely available and less costly, its application should minimize the need for broad-spectrum antibiotic therapy of infections, lower costs, and perhaps even shorten hospitalization. These potential beneficial effects of polymerase chain reaction will be particularly relevant in the current cost-conscious health-care environment.

In vivo hepatocyte transduction with retrovirus during in-flow occlusion.

Gene therapy research would be facilitated by a technically simple procedure for transducing hepatocytes in vivo. Previously reported methods have employed partial hepatectomy followed 24 hr later by asanguineous perfusion of the regenerating liver with retrovirus. We have developed a simpler method of in vivo transduction in which we deliver an intraportal bolus of retrovirus to the regenerating rodent liver during a brief period of hepatic in-flow occlusion. On Day 0, adult male Sprague-Dawley rats (N = 19) underwent 70% hepatectomy to induce hepatocyte replication. On Day 1, retroviral supernatant was harvested from an amphotropic retroviral packaging cell line that packaged an LNL6-derived vector containing the cytomegalovirus promoter driving expression of the Escherichia coli beta-galactosidase (beta gal) gene. Twenty-four hours after partial hepatectomy, experimental rats (N = 17) received 6 x 10(5) colony-forming units of retrovirus by intraportal injection during a 3-min occlusion of the hepatic artery and portal vein. Control rats (N = 2) received intraportal medium (without retrovirus), also during in-flow occlusion. The procedure required 20-25 min, and the survival rate was 84%. Cryostat sections were prepared from liver biopsies obtained on Post-transduction Days 8 and 15 and stained with 5-bromo-4-chloro-3-indolyl- beta-D-galactopyranoside to detect beta gal expression. Light microscopic examination of Day 8 sections from surviving experimental rats (N = 14) revealed 0.10-1.00% blue (i.e., transduced) hepatocytes per low power field, while sections from control rats (N = 2) exhibited no blue cells. Day 15 sections from experimental rats revealed a somewhat lower frequency of hepatocytes expressing beta gal.(ABSTRACT TRUNCATED AT 250 WORDS)