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Biomedical subjects

R J Ho

Publications and source records attributed to R J Ho.

At least 19 recordsLinked to original sources
PubMed2001

Lipid association improves the therapeutic index of lomustine [1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea] to suppress 36B-10 tumor growth in rats.

The therapeutic efficacy and tumor accumulation of a liposome formulation of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), an effective agent used in the treatment of malignant brain tumors, was examined in an animal tumor model. Pharmacokinetic studies in normal and tumor-bearing rats indicated that a 2-fold greater plasma exposure was achieved with liposome-formulated CCNU compared with the free drug. In Fisher rats bearing s.c. tumors 36B-10, tumor growth was delayed substantially when liposomal CCNU was delivered compared with free-drug treatment. In single-dose treatments of 20, 35, and 50 mg/kg, tumor progression after each dose was reduced approximately 2-fold with liposomal compared with free CCNU (four animals in each treatment group). Multiple-dose treatments (given as three weekly doses with eight animals in each treatment group) with cumulative doses of 80 and 100 mg/kg of free and liposomal CCNU also resulted in a 2-fold reduction in tumor progression when compared with free-drug treatment. When drug levels in tumors relative to plasma were examined, it was observed that tumor drug concentrations did not exceed those found in plasma after administration of free CCNU; after administration of liposomal CCNU, however, tumor concentrations exceeded those in plasma by nearly 10-fold. These results suggest that the increased efficacy of liposome-formulated CCNU may be attributable to enhanced drug accumulation in tumor tissues.

Animals↗
PubMed2001

Trends and developments in liposome drug delivery systems.

Since the discovery of liposomes or lipid vesicles derived from self-forming enclosed lipid bilayers upon hydration, liposome drug delivery systems have played a significant role in formulation of potent drugs to improve therapeutics. Currently, most of these liposome formulations are designed to reduce toxicity and to some extent increase accumulation at the target site(s) in a number of clinical applications. The current pharmaceutical preparations of liposome-based therapeutics stem from our understanding of lipid-drug interactions and liposome disposition mechanisms including the inhibition of rapid clearance of liposomes by controlling size, charge, and surface hydration. The insight gained from clinical use of liposome drug delivery systems can now be integrated to design liposomes targeted to tissues and cells with or without expression of target recognition molecules on liposome membranes. Enhanced safety and heightened efficacy have been achieved for a wide range of drug classes, including antitumor agents, antivirals, antifungals, antimicrobials, vaccines, and gene therapeutics. Additional refinements of biomembrane sensors and liposome delivery systems that are effective in the presence of other membrane-bound proteins in vivo may permit selective delivery of therapeutic compounds to selected intracellular target areas.

Drug Carriers↗
PubMed2001

The role of drug-lipid interactions on the disposition of liposome-formulated opioid analgesics in vitro and in vivo.

UNLABELLED: Although liposome encapsulation prolongs the duration of action of epidurally administered drugs, little is known about how liposome encapsulation affects opioids differently, or about how lipid content of liposomes alters the bioavailability of epidurally-administered opioids. To address these issues, morphine, alfentanil, fentanyl, and sufentanil were loaded into D-alpha-dipalmitoyl phosphatidylcholine multilamellar liposomes, and incorporation efficiency and in vitro release rates were determined. We then determined epidural morphine and sufentanil liposomes, at two different lipid/opioid ratios, in vivo in a pig model in which epidural and intrathecal spaces were continuously sampled via microdialysis. Liposome encapsulation efficiency was significantly more for sufentanil (100%) than for the other opioids (25%-30%). The in vitro release rate was slowest for morphine, intermediate for fentanyl and alfentanil, and fastest for sufentanil. In vivo, morphine was released more slowly than sufentanil. It is most important to note that increasing the lipid content of morphine liposomes increased the proportion of drug reaching the intrathecal space. In contrast, increasing the lipid content of sufentanil liposomes did not alter intrathecal movement but did decrease movement into plasma. Therefore, increasing drug hydrophobicity and lipid content of the liposomes modulates drug distribution in vivo. IMPLICATIONS: The degree of interaction between opioids and lipid bilayers in liposome-formulated opioids dictates the rates at which epidurally-administered drugs distribute into the intrathecal compartment and blood in potentiating analgesic effects.

Analgesics, Opioid↗
PubMed2001

Characterization of a maternal-fetal HIV transmission model using pregnant macaques infected with HIV-2(287).

To study mechanisms involved in mother-to-fetus transmission of human immunodeficiency virus (HIV) in utero, we have developed a chronically catheterized pregnant macaque model that permits simultaneous and sequential determination of virus in maternal and fetal blood and amniotic fluid during pregnancy. In this report, we have characterized this model using three groups of pregnant macaques designed to sample: (1) maternal blood, fetal blood, and amniotic fluid (n = 6); (2) maternal blood and amniotic fluid (n = 6); or (3) maternal blood only (n = 2). After inoculation with the highly pathogenic HIV-2(287), all pregnant macaques developed brief but intense viremias followed by precipitous CD4+ T-cell declines within 2-3 weeks. While all the infants born to dams of the three groups were HIV positive, the degree of infection and outcome of HIV infection varied. All infants were shown to be HIV-RNA-positive by reverse transcriptase-polymerase chain reaction (RT-PCR). However, HIV-infected cells were detected only in the blood of those born to dams enrolled in groups 1 and 2: most of these infants progressed to CD4+ T-cell depletion. The infants in group 3 exhibited HIV-RNA in plasma, although neither HIV-infected cells nor CD4+ T-cell depletion was detectable. However, all infants developed HIV-2-specific antibody at various levels by 2 months of age. Together, the data suggest that, while the degree of instrumentation may modulate intensity of virus transmission to fetus, the highly pathogenic HIV-2(287) exhibited a high frequency of virus transmission from the mother to fetus.

Amniotic Fluid↗
PubMed2000

Suppression of maternal virus load with zidovudine, didanosine, and indinavir combination therapy prevents mother-to-fetus HIV transmission in macaques.

Recently, we developed a maternal-fetal macaque model using a highly pathogenic HIV-2 strain, HIV-2287, to study the time course of HIV transmission in utero. Most pregnant macaques (Macaca nemestrina) infected with HIV-2287 (10-103 infective doses) transmitted HIV to their fetuses, as verified by positive identification of virus-infected mononuclear cells and free viral RNA in fetal blood. To determine whether an antiretroviral drug combination therapy composed of two dideoxynucleosides, azidothymidine (15 mg/kg) and dideoxyinosine (15 mg/kg), and a protease inhibitor, indinavir (25 mg/kg), could completely inhibit mother-to-fetus HIV transmission, we administered these drugs orally through gastric catheters to five pregnant macaques infected with 10 infective doses of HIV-2287. Beginning 30 minutes after HIV inoculation, the dams were given the combination antiviral therapy three times daily until delivery by cesarean section. Drug treatment reduced the maternal virus load to a minimally detectable level but did not prevent primary HIV-2287 infection. All fetal and infant blood samples were virus negative by internally controlled RNA polymerase chain reaction (QC-RNA-PCR) and virus coculture assays. Fetal and infant CD4+ T-cell levels remained normal throughout the experiment. These findings strongly suggest that combination chemotherapy with azidothymidine, dideoxyinosine, and indinavir can suppress maternal viral load enough to prevent mother-to-fetus transmission of HIV.

Animals↗
PubMed2000

Challenges in the development of an effective HIV vaccine: current approaches and future directions.

OBJECTIVE: The intent of this review is to investigate and discuss why developing a successful HIV vaccine has been so challenging, first by examining the molecular biology of the virus and how HIV interacts with the immune system, and then reviewing past viral vaccine successes as well as future directions for HIV vaccine research. BACKGROUND: Since HIV appeared in the United States in the early 1980s, an estimated 40 million people worldwide have been infected with the virus. Despite promising advances in the pharmacotherapy of HIV infection, it is apparent that the best, most cost-effective strategy for controlling the further spread of the virus is through synthesis of a protective vaccine. Almost 2 decades into the epidemic, there are few prospects for a truly effective vaccine entering the market in the foreseeable future. METHODS: MEDLINE was searched for articles written between 1966 and June 1999. Search terms used were AIDS, HIV vaccine, HIV-1, HIV-2, vaccines, and human immunodeficiency virus. RESULTS: Only 2 candidates for an HIV vaccine are currently in phase III clinical trials (1 in the United States and 1 in Thailand). The efficacy of these vaccines when applied to the population as a whole is widely questioned, largely because they induce protection by an antibody response only. Several studies have suggested that this approach will likely be ineffective in providing any real protection from viral infection. It appears that a strong cellular immune response is necessary in addition to a strong antibody response.

AIDS Vaccines↗
PubMed2000

The effects of intrathecal morphine encapsulated in L- and D-dipalmitoylphosphatidyl choline liposomes on acute nociception in rats.

UNLABELLED: Liposomes can serve as a sustained-release carrier system, permitting the spinal delivery of large opioid doses restricting the dose for acute systemic uptake. We evaluated the antinociceptive effects of morphine encapsulated in liposomes of two isomeric phospholipids, L-dipalmitoylphosphatidyl choline (L-DPPC) and D-dipalmitoylphosphatidyl choline (D-DPPC), in comparison with morphine in saline. Sprague-Dawley rats with chronic lumbar intrathecal catheters were tested for their acute nociceptive response using a hindpaw thermal escape test. Their general behavior, motor function, pinna reflex, and corneal reflex were also examined. The duration of antinociception was longer in both liposomal morphine groups than in the free morphine group. The peak antinociceptive effects were observed within 30 min after intrathecal morphine, L-DPPC or D-DPPC morphine injection. The rank order of the area under the effect-time curve for antinociception was L-DPPC morphine > D-DPPC morphine > morphine. The 50% effective dose was: 2.7 microg (morphine), 4.6 microg (L-DPPC morphine), and 6.4 microg (D-DPPC morphine). D-DPPC morphine had less side effects for a given antinociceptive AUC than morphine. In conclusion, L-DPPC and D-DPPC liposome encapsulation of morphine prolonged the antinociceptive effect on acute thermal stimulation and could decrease side effects, compared with morphine alone. IMPLICATIONS: Two isomers of liposome (L-dipalmitoylphosphatidyl choline and D-dipalmitoylphosphatidyl choline) encapsulation of morphine prolonged the analgesic effect on acute thermal-induced pain when administered intrathecally and could decrease side effects, compared with morphine alone.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2000

Development of a semi-quantitative assay to detect full-length CYP2C19 RNA.

Cytochrome P450 2C19 (CYP2C19) is the enzyme responsible for the metabolism of a number of drugs, including anticonvulsants and antidepressants. We have developed a semi-quantitative competitive RT-PCR assay to estimate the degree of expression of the full-length CYP2C19 message. This assay used a known quantity of internally deleted CYP2C19 RNA to quantitate the RT-PCR products of the CYP2C19 transcript in the RNA extracted from tissues. We determined that this method is sensitive and reproducible in assaying for CYP2C19 RNA in human livers. The lowest detectable amount of competitor RNA was 0.166 fg or 270 copies of CYP2C19 competitor RNA. Using human liver samples containing 3-23 x 10(5) copies of CYP2C19 RNA, we found the assay to be reproducible with a coefficient of intra- and interday variation of 11% and 20%, respectively. Using this assay, we measured full-length CYP2C19 RNA in 10 human livers. We found the CYP2C19 transcripts range from 0.1-23 x 10(5) copies/microgram liver total RNA. The analysis of CYP2C19 transcripts for liver of *1 and *2 genotypes, based on restriction enzyme digest analysis of RT-PCR products, suggests that only normal (*1), not the variant (*2) copy of full-length CYP2C19 RNA, was detectable in these livers. We report for the first time the quantification of full-length CYP2C19 RNA in livers.

Alleles↗
PubMed1999

Formulation of HIV-envelope protein with lipid vesicles expressing ganglioside GM1 associated to cholera toxin B enhances mucosal immune responses.

Taking advantage of the ability of pentameric cholera toxin B subunit (CTB) to bind selectively to GM1, we developed recently a CTB-mediated GM1 lipid vesicle delivery system to target drugs and proteins to mucosal tissues [1]. In this report, we present the use of such a strategy to deliver an HIV envelope protein (HIV-env) to mucosal tissues via intranasal route. Intranasal administration of a recombinant HIV envelope protein formulated in CTB-associated GM1 lipid vesicles enhanced mucosal IgA antibody responses detected in the nasal and gut tissues, compared to that of control animals immunized with antigen formulated in GM1-free vesicles with CTB or formulated in alum-associated vesicles with CTB. We found a nearly 2- to 3-fold enhancement in IgA antibody titers detected both in nasal and gut tissues using the CTB-GM1 lipid vesicle delivery system, compared to using the GM1-free lipid vesicle system. Intranasal administration of HIV-env formulated in the CTB-associated GM1 vesicles also induced a significant level of serum IgG and cellular immune responses against HIV-env. IgG isotype analysis indicates that CTB in GM1 vesicle delivery system enhanced both IgG1 and IgG2a while CTB in alum formulation enhanced only IgG1. However, IgA and IgG antibody responses against CTB were similar for GM1 vesicles regardless of whether HIV-env was present in the vaccine formulation. Collectively, these data indicate that delivery of HIV-env to mucosal epithelial cells with CTB-associated GM1 lipid vesicles enhanced mucosal and systemic immune responses against the HIV-envelope protein. It is possible that both the CTB-mediated targeted delivery of antigen-loaded GM1 lipid vesicles and mucosal adjuvanticity of CTB may be involved in enhancing the immune responses.

Adjuvants, Immunologic↗
PubMed1999

Lipid association increases the potency against primary medulloblastoma cells and systemic exposure of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in rats.

PURPOSE: To reduce the systemic toxicity and prolong the systemic presence of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), a lipid-based drug carrier was designed and characterized. METHODS: The degree of CCNU association with lipid vesicles composed of 1, 2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) (1:1, m/m) was characterized and the drug decomposition rates of lipid-drug complexes were monitored. Effects of lipid association on drug potency against medulloblastoma cells and total systemic drug exposure in rats were determined. RESULTS: At a CCNU:lipid molar ratio greater than 1:5, more than 90% of the drug was associated with the lipid vesicles. In aqueous suspensions, lipid association significantly reduced the first-order drug decomposition rate. In addition, lipid-associated CCNU exhibited a 4-fold increase in drug sensitivity with medulloblastoma cells. IC50 values for CCNU admixed and encapsulated with lipid vesicles were 18+/-4.9 and 14.0+/-2.2 microM, respectively, compared to 83+/-11.0 microM for free CCNU. When administered to rats, lipid-associated CCNU increased the AUC (area under the concentration-time curve) of CCNU by approximately 2-fold (20.46+/-2.15 compared to 39.59+/-1.87 microg x min/ml), and the terminal half-life (t1/2beta) by almost 9-fold (17+/-9 compared to 147+/-48 min) over free CCNU. Despite the increase in total systemic drug exposure, rats treated with lipid-associated CCNU exhibited a significantly lower frequency of acute neurotoxicity. CONCLUSIONS: These data indicate that CCNU associated with lipid vesicles may increase drug stability, potency, and systemic exposure in rats.

Animals↗
PubMed1999

Association with oleic acid vesicles enhances manganese III mesoporphyrin absorption and biliary elimination in rats.

OBJECTIVE: To determine whether the association of manganese III mesoporphyrin (MnMeso), an oral MR contrast agent, to oleic acid (OA) vesicles will improve absorption and delivery of MnMeso to the liver. METHODS: MnMeso or MnMeso-OA vesicle suspension was intraduodenally administered to rats and the time course of MnMeso concentration in plasma, bile, and intestinal solution was determined. Tissue concentrations of MnMeso in the liver were also determined. RESULTS: Association of MnMeso to OA reduced the time it took to reach one-half absorption maximum, TC50, and enhanced the rate and the extent of biliary elimination of this contrast agent. In addition, the results obtained from dose-titration studies indicate that MnMeso-OA vesicle complex may enhance MnMeso accumulation in the liver, observed as a lower dose required to reach equivalent tissue concentration. Taken together, complexion to OA vesicles may provide rapid absorption, enhanced liver accumulation, and efficient elimination of MnMeso. CONCLUSIONS: Association with OA vesicles may enhance the rate of MnMeso absorption and biliary excretion while promoting the extent of liver accumulation of MnMeso in rats. This strategy may provide a means to provide safe and effective use of MnMeso as an MR contrast medium.

Animals↗
PubMed1997

Augmentation of cell-mediated immunotherapy against herpes simplex virus by interleukins: comparison of in vivo effects of IL-2 and IL-7 on adoptively transferred T cells.

We investigated the ability of human recombinant interleukin-7 (IL-7) to enhance cytotoxic T lymphocyte (CTL) activity in vivo using mice infected with herpes simplex virus type-1 (HSV-1). IL-7 or interleukin-2 (IL-2) was administered twice daily to immune naive mice subjected to adoptive transfer of immune T cells after infection with HSV-1. The immunotherapeutic effect was measured by detecting the virus recovered from pinna. Administration of HSV-1 immune T cells to naive mice significantly increased their ability to clear the virus. Twice-daily injections of IL-7 at 200 IU provided an additional 20-fold reduction in virus load, compared with T cell therapy alone (P < 0.0005). Combining IL-2 and T cell therapy provided about a sevenfold reduction compared with T cell therapy alone (P < 0.0009). IL-7 also enhanced the antiviral effects of T cell therapy against HSV-1 through the enhancement of CD8+ CTLs, as observed with IL-2. These results indicate that IL-7 may be used adjunct to adoptive T lymphocyte therapy in modulating human viral diseases and cancer through enhanced immune T cell activities.

Adjuvants, Immunologic↗
PubMed1997

Intestinal absorption of Mn-mesoporphyrin in a small bowel sac system: effect of oleic acid.

RATIONALE AND OBJECTIVES: The authors investigated the effect of oleic acid (cis-9-octadecenoic acid) (OA), a lipidic carrier, on the intestinal absorption rate and T1 relaxation time of manganese (III) mesoporphyrin (Mn-mesoporphyrin), a prototype hepatobiliary contrast agent for magnetic resonance imaging. METHODS: Mn-mesoporphyrin was formulated with OA at various concentrations. Small bowel sacs were created in 36 rats and filled with complexed and free Mn-mesoporphyrin. Intestinal absorption of Mn-mesoporphyrin was measured with spectrophotometry at 364 nm. T1 relaxation times were measured in samples of Mn-mesoporphyrin solutions, bowel wall, liver, and bile. RESULTS: Absorption rates ranged from 4.2%/cm2/h to 13%/cm2/h. Absorption was greatest (13%/cm2/h) when a combination of 1 mmol/L Mn-mesoporphyrin and 26.5 mmol/L OA was used. The T1 of bile decreased from 2,480 to 248 msec (maximum decrease) in rats that received Mn-mesoporphyrin. CONCLUSION: Mn-mesoporphyrin is absorbed from the small bowel in both the lipid-associated and free form, resulting in substantial shortening of the T1 in bile.

Animals↗
PubMed1997

Cholera toxin B-mediated targeting of lipid vesicles containing ganglioside GM1 to mucosal epithelial cells.

PURPOSE: To determine whether the non-toxic pentameric B subunit of Cholera toxin (CTB) binding to ganglioside GM1 on both the lipid vesicles and epithelial cells may provide a means to target lipid vesicles to mucosal cells expressing surface GM1. METHODS: Sonicated lipid vesicles containing ganglioside GM1 were prepared. Inter-vesicle cross-linking due to pentameric CTB binding to these GM1 vesicles was determined with a sub-micron particle analyzer. Association of CTB to GM1 vesicles was analyzed with continuous sucrose gradient centrifugation. CTB-mediated binding of GM1 vesicles to human mucosal epithelial cells (Caco-2 and HT-29), mucous membranes of mouse trachea, and nasal tissues were detected with fluorescent labeled vesicles. RESULTS: An increase in lipid particle size due to binding of CTB to lipid vesicles and inter-vesicles cross-linking was detected. At a 30-to-1 mole ratio of membrane-bound GM1-to-CTB, optimum increase in GM1 vesicle aggregation, was detected. Under such conditions, all the added CTB molecules were associated with GM1 vesicles. Time course analysis showed that inter-vesicles cross linking by CTB was detectable within 10 min. and reached a maximum value at 60 min. CTB associated GM1-vesicles bind to mucosal epithelial cells HT-29 and Caco-2 with similar affinity [Kd = 7.8 x 10(-4) M lipid (Caco-2) and 7.6 x 10(-4) M lipid (HT-29)]. GM1 mediated binding specificity was demonstrated by blocking with anti-GM1 antibody and the insignificant degree of CTB-associated GM1 vesicle binding to GM1 deficient C6 cells. CONCLUSIONS: The CTB-mediated GM1 binding to multiple membrane surfaces provides selective localization of GM1 vesicles to GM1 expressing mucosal cells and tissues. The strategy may be useful in localizing drugs and proteins to gut and respiratory tract mucosa.

Animals↗
PubMed1997

Development of a high-performance liquid chromatographic assay for G418 sulfate (Geneticin).

We have developed a chromatographic assay with high sensitivity and specificity to quantify G418 sulfate (Geneticin), an antibiotic used routinely in molecular genetics experiments for selecting eukaryotic transformants. With this method, G418 in tissues and plasma samples can be quantitated without the confounding factors often associated with biological assays. After removal of proteins in homogenized tissue or plasma samples with methanol (2:1, vol/vol), the amino group of G418 was derivatized with 1-fluoro-2,4-dinitrobenzene (DNFB) to form the UV-visible G418-DNFB product. The DNFB-derivatized G418 was separated on a reversed-phase C18 column with an acetonitrile and water gradient as the mobile phase. Under these assay conditions, the detection limit for G418 sulfate in buffer, plasma, and tissues was recorded at 78 ng/ml and the linearity was recorded for concentrations up to 100 micrograms/ml. The data obtained from this analysis indicate that this assay can be used for the quantitative determination of G418 sulfate in plasma and tissue samples.

Animals↗
PubMed1996

A deficiency in prothoracicotropic hormone transduction pathway during the early last larval instar of Bombyx mori.

The prothoracicotropic hormone (PTTH) is an insect cerebral peptide that stimulates the prothoracic glands to produce ecdysteroids that initiate moulting and metamorphosis. During the last larval instar of holometabolous insects, a reduction in the hemolymph juvenile hormone (JH) levels is a necessary step in initiating larval-pupal transformation. Recently we have demonstrated that very low ecdysteroid levels in the early last larval instar of Bombyx mori initiate the complete inactivation of corpora allata (CA). Results presented here further indicate that PTTH signal transduction pathways undergo specific developmental changes, with a deficiency in transduction in prothoracic gland cells occurring during the early last instar. Glands from the early last instar showed no increase in either cAMP levels or steroidogenesis to the stimulation of PTTH, indicating the absence of the PTTH receptors in gland cells. We propose that this absence of PTTH receptors plays a critical role in directing larval-pupal transformation.

Animals↗