Dietary restriction: effects of short-term fasting on protein uptake and cell death/proliferation in the rat liver

Dietary restriction (DR) is known to prolong life in laboratory animals. Intermittent (alternate-day) fasting or short-term repeated fasting has also been reported to increase the life span of animals. In the present study, we investigated the changes or induction of abnormalities of protein metabolism in rats during fasting, and measured asialoglycoprotein uptake and cell death/proliferation in the liver of rats receiving fasting and refeeding. In the results, liver weight decreased significantly after 48 h of fasting and increased during the refeeding period, returning to the pre-fasting level by 12 h of refeeding. Cell death, determined by single stranded DNA (ssDNA) staining method, increased during the fasting period, and returned to the pre-fasting level during the refeeding period. Cell proliferation, determined using antibodies (Ab) against proliferating cell nuclear antigen, decreased during the fasting period, and increased during the refeeding period. Changes in cell death and cell proliferation were inversely related. However, there was no significant difference in asialoglycoprotein uptake by the whole liver between the ad libitum (AL)-fed rats and 48 h fasted rats. Thus, neither the changes in liver weight nor cell death/proliferation affected asialoglycoprotein uptake on a living body. These results suggest that episodes of 48 h fasting do not induce protein metabolism abnormalities in the liver.

Targeted delivery of DNA encoding herpes simplex virus type-1 glycoprotein D enhances the cellular response to primary viral challenge

Intravenous injection of plasmid DNA encoding herpes simplex virus type-1 glycoprotein D (gD-1) complexed with asialoorosomucoid-poly-L-lysine (gD-ASOR) targets foreign DNA to the liver, leading to hepatic expression of gD-1. BALB/c mice were given two intravenous injections of gD-ASOR, pBK-ASOR (plasmid lacking the gD-1 gene but complexed with ASOR), or PBS. The skin was inoculated with 1 x 10(4) PFU of HSV-1 or sham-inoculated, and analyzed for infectious virus and cellular infiltration 1, 3, and 5 days after inoculation. Prior immunization with gD-ASOR led to significantly lower (P < 0.05) viral titers in the skin 5 days after inoculation compared with controls. Infiltration of the skin at the site of inoculation by polymorphonuclear neutrophils (PMNs), T cells, B cells, dendritic cells, and macrophages was monitored immunohistochemically. Significantly higher numbers (P < 0.05) of CD4+ and CD8+ T cells, dendritic cells, and macrophages responded to HSV-1 challenge in mice immunized with gD-ASOR than in mice immunized with pBK-ASOR or PBS. The response by PMNs and B cells was indistinguishable among the treatment groups. These results suggest that BALB/c mice sensitized to gD-1 following gD-ASOR immunization develop an enhanced T-cell response to primary HSV-1 infection.

Murine response to DNA encoding herpes simplex virus type-1 glycoprotein D targeted to the liver

Plasmid DNA encoding herpes simplex virus type-1 glycoprotein D (gD-1) was complexed with asialoorosomucoid conjugated to poly-L-lysine. Following its intravenous injection into BALB/c mice, this complex was targeted to the liver. Liver cells expressing gD-1 were detected immunohistochemically through day 6 post-immunization, while gD-1 DNA was detectable through 14 days post-immunization. Decline of gD-1 expression and detectable gD-1 DNA in the liver correlated with influx of T cells, predominantly CD4(+). The ASOR-poly-L-lysine DNA carrier system promotes hepatic expression of gD-1 and may be useful in vaccination against herpes simplex virus type-1.

Non-viral gene delivery: vehicle and delivery characterization

The development of non-viral gene therapy has been hampered by an inability to reproducibly manufacture and characterize delivery system components and final formulations. Formation of interpolyelectrolyte complexes as the basis of various gene delivery methods has been approached as the first step towards development of synthetic viruses. We have found that preparation of interpolyelectrolyte complexes from disperse reagents gives a more homogeneous gene delivery vehicle than other methods. Methods which increase homogeneity also result in higher transfection efficiency in vivo. Expression levels of human growth hormone and other reporter proteins in mice confirm the potential of parenteral non-viral gene delivery for some therapeutic applications. Serum is demonstrated to inhibit transfection efficiency in vivo. Our results suggest that further development of methods to manufacture homogeneous disperse non-viral delivery vehicles with stealth characteristics may enhance both the potency and reproducibility of gene transfer in vivo.

Covalent protein-oligonucleotide conjugates for efficient delivery of antisense molecules

Antisense oligonucleotides have been covalently attached to asialoglycoprotein (ASGP) via disulfide bond conjugation chemistry. These conjugates were characterized extensively by an array of chemical, chromatographic, and spectroscopic means. Multiple (approximately six) oligonucleotides can be conjugated to each ASGP molecule. The molecular conjugates were used to deliver antisense oligonucleotides complementary to the mRNA of the interleukin 6 signal transduction protein (gp130) to modulate the acute phase response of hepatoma (HepG2) cells in vitro. These conjugates were biologically active, as measured by inhibition of the cytokine-stimulated up-regulation of the acute phase protein haptoglobin. The level of inhibition was comparable to that found with previous technology featuring noncovalent complexes of ASGP-poly(L-lysine) and oligonucleotide. Because of the ability to control the stoichiometry of the conjugate and its unimolecular nature (as opposed to bimolecular for the noncovalent conjugates), this methodology holds great promise for further development and application.

A hepatocyte-targeted conjugate capable of delivering biologically active colchicine in vitro

A derivative of colchicine was synthesized, in a manner that preserved its important structural features, and conjugated to an asialoglycoprotein. The conjugate was characterized by ultraviolet-visible spectrophotometry and protein analysis. An average coupling ratio of 2 mol of colchicine per mole of asialoglycoprotein was achieved. The conjugate was stable to incubation in serum but was split into its separate components under chemically reducing conditions. Incubation with cells in culture revealed that the conjugate had antiproliferative activity similar to that of colchicine, but only in asialoglycoprotein receptor-containing cells. There was no effect at all on asialoglycoprotein receptor (-) cells. Furthermore, the antiproliferative effect of the conjugate on receptor (+) cells was blocked by addition of a large molar excess of free asialoglycoprotein. Immunofluorescence microscopy revealed disruption of microtubules in cell cultures that were pretreated with the conjugate. These results indicate that a colchicine conjugate that is taken up specifically into cells by asialoglycoprotein receptors and released intracellularly in a biologically active form can be prepared.

Targeted delivery of antisense DNA in woodchuck hepatitis virus-infected woodchucks

An asialoglycoprotein-based DNA delivery system containing an antisense oligo DNA against the polyadenylation region and adjacent upstream sequences of woodchuck hepatitis virus (WHV) was prepared. Experimental woodchucks were inoculated neonatally with the woodchuck virus 23 weeks before initiating the study, and all animals subsequently developed hepatitis as evidenced by the presence of measurable levels of circulating viral DNA. Animals were injected intravenously (i.v.) with asialoorosomucoid (AsOR)-poly-L-lysine complexes containing 0.1 mg kg-1 antisense DNA for five consecutive days. Levels of surface antigen did not differ substantially between treated and control animals. However, intravenous administration of complexed antisense DNA significantly decreased viraemia, as shown by a five- to 10-fold decrease in circulating viral DNA 25 days post treatment. The decline lasted for at least 2 weeks, after which there was a gradual increase in DNA levels. Antisense DNA alone or a complex containing a random oligo DNA of the same size and linkage failed to have any significant effect on viral DNA levels. We conclude that antisense oligo DNA can be targeted to the liver in vivo, resulting in a substantial and prolonged decrease in viral DNA levels in WHV-infected woodchucks.

Overexpression of human methylmalonyl CoA mutase in mice after in vivo gene transfer with asialoglycoprotein/polylysine/DNA complexes

Methylmalonic acidemia resulting from genetic deficiency of methylmalonyl CoA mutase (MCM) is an often fatal metabolic disease. Somatic gene therapy for this disorder may require gene replacement in the liver. We describe overexpression of MCM in the liver of mice after in vivo gene delivery using asialoglycoprotein/polylysine/DNA (ASO/PL/DNA) targeted delivery to the liver of plasmids expressing recombinant MCM. After intravenous administration of the ASO/PL/DNA complex, the vector sequences are cleared from the blood with t1/2 = 2.5 min and > 95% of the vector is taken up by the liver. Vector sequences are cleared from the liver with t1/2 = 1.0-1.3 hr. MCM enzyme activity in the liver increases to levels 30-40% over baseline 6-24 hr after injection. No acute or chronic toxicity was observed. This net level of expression is likely to be therapeutic for MCM if the complex could be administered repetitively to treat acute episodes of life-threatening acidosis or establish a steady-state level of MCM activity. Repetitive administration of the ASO/PL/DNA complexes in mice was associated with formation of antibodies against asialo-orosomucoid and the asialo-orosomucoid complex but not against DNA.

Delivery systems for gene therapy

Introduction of foreign genes into mammalian cells in vitro has been accomplished previously by a variety of methods. The few techniques that have been developed for transfection of mammalian cells in vivo, are technically difficult or lack cell specificity. We have developed a soluble, targetable DNA carrier system consisting of an asialoglycoprotein covalently coupled to a polycation. The strategy was based on: 1) the presence of unique receptors on hepatocytes which internalize galactose-terminal (asialo-)glycoproteins; 2) polycations can bind DNA in a non-covalent, non-damaging interaction. Using chloramphenicol acetyltransferase (CAT) as a marker gene, specific delivery and expression of CAT was demonstrated in vitro using asialoglycoprotein receptor (+) and (-) cell lines. Intravenous injection of conjugate-DNA complexes in rats resulted in detection of CAT DNA sequences in liver 10 min later by dot blots with a CAT cDNA probe. CAT enzyme activity 24 hrs later was found specifically in liver but no other tissues or control livers. Targeted hepatic CAT expression was transient, maximal at 24 hrs but declined to barely detectable levels by 96 hrs. Persistent foreign gene expression was achieved by injection of DNA complex followed by 67% partial hepatectomy. High levels of hepatic CAT activity were detected through 11 weeks post-hepatectomy. The data indicate that a targetable gene delivery system can permit in vivo expression of an exogenous gene after simple intravenous injection. The foreign gene expression can be enhanced and made to persist by induction of hepatocyte replication.