Lipid-based delivery systems and intestinal lymphatic drug transport: a mechanistic update

Self-microemulsifying drug delivery system (SMEDDS)--challenges and road ahead

Self-microemulsifying drug delivery system (SMEDDS) has emerged as a vital strategy to formulate poor water soluble compounds for bioavailability enhancement. However, certain limitations are associated with SMEDDS formulations which include in vivo drug precipitation, formulation handling issues, limited lymphatic uptake, lack of predictive in vitro tests and oxidation of unsaturated fatty acids. These limitations restrict their potential usage. Inclusion of polymers or precipitation inhibitors within lipid based formulations helps to maintain drug supersaturation after dispersion. This, thereby, improves the bioavailability and reduces the variability on exposure. Also, formulating solid SMEDDS helps to overcome liquid handling and stability problems. Usage of medium chain triglycerides (MCT) and suitable antioxidants to minimize oxidation of unsaturated fatty acids are few of the steps to overcome the limitations associated with SMEDDS. The review discussed here, in detail, the limitations of SMEDDS and suitable measures that can be taken to overcome them.

Improved oral bioavalability of mebudipine upon administration in PhytoSolve and Phosal-based formulation (PBF)

The aim of this investigation was to examine the efficacy of PhytoSolve and Phosal-based formulation (PBF) to enhance the oral bioavailability of mebudipine, which is a poorly water-soluble calcium channel blocker. The solubility of mebudipine in various oils was determined. PhytoSolve was prepared with a medium-chain triglyceride (MCT) oil (20%), soybean phospholipids (5%), and a 70% fructose solution (75%). The influence of the weight ratio of Phosal 50PG to glycerol in PBF on the mean globule size was studied with dynamic light scattering. The optimized formulation was evaluated for robustness toward dilution, transparency, droplet size, and zeta potential. The in vivo oral absorption of different mebudipine formulations (PhytoSolve, PBF, oily solution, and suspension) were evaluated in rats. The optimized PBF contained Phosal 50PG/glycerol in a 6:4 ratio (w/w). The PBF and PhytoSolve formulations were miscible with water in any ratio and did not demonstrate any phase separation or drug precipitation over 1 month of storage. The mean particle size of PhytoSolve and PBF were 138.5 ± 9.0 and 74.4 ± 2.5 nm, respectively. The in vivo study demonstrated that the oral bioavailability of PhytoSolve and PBF in rats was significantly higher than that of the other formulations. The PhytoSolve and PBF formulations of mebudipine are found to be more bioavailable compared with suspension and oily solutions during an in vivo study in rats. These formulations might be new alternative carriers that increase the oral bioavailability of poorly water-soluble molecules, such as mebudipine.

Persistent HIV-1 replication is associated with lower antiretroviral drug concentrations in lymphatic tissues

Antiretroviral therapy can reduce HIV-1 to undetectable levels in peripheral blood, but the effectiveness of treatment in suppressing replication in lymphoid tissue reservoirs has not been determined. Here we show in lymph node samples obtained before and during 6 mo of treatment that the tissue concentrations of five of the most frequently used antiretroviral drugs are much lower than in peripheral blood. These lower concentrations correlated with continued virus replication measured by the slower decay or increases in the follicular dendritic cell network pool of virions and with detection of viral RNA in productively infected cells. The evidence of persistent replication associated with apparently suboptimal drug concentrations argues for development and evaluation of novel therapeutic strategies that will fully suppress viral replication in lymphatic tissues. These strategies could avert the long-term clinical consequences of chronic immune activation driven directly or indirectly by low-level viral replication to thereby improve immune reconstitution.

Targeted delivery of a model immunomodulator to the lymphatic system: comparison of alkyl ester versus triglyceride mimetic lipid prodrug strategies

A lipophilic prodrug approach has been used to promote the delivery of a model immunomodulator, mycophenolic acid (MPA), to the lymphatic system after oral administration. Lymphatic transport was employed to facilitate enhanced drug uptake into lymphocytes, as recent studies demonstrate that targeted drug delivery to lymph resident lymphocytes may enhance immunomodulatory effects. Two classes of lymph-directing prodrugs were synthesised. Alkyl chain derivatives (octyl mycophenolate, MPA-C8E; octadecyl mycophenolate, MPA-C18E; and octadecyl mycophenolamide, MPA-C18AM), to promote passive partitioning into lipids in lymphatic transport pathways, and a triglyceride mimetic prodrug (1,3-dipalmitoyl-2-mycophenoloyl glycerol, 2-MPA-TG) to facilitate metabolic integration into triglyceride deacylation-reacylation pathways. Lymphatic transport, lymphocyte uptake and plasma pharmacokinetics were assessed in mesenteric lymph and carotid artery cannulated rats following intraduodenal infusion of lipid-based formulations containing MPA or MPA prodrugs. Patterns of prodrug hydrolysis in rat digestive fluid, and cellular re-esterification in vivo, were evaluated to examine the mechanisms responsible for lymphatic transport. Poor enzyme stability and low absorption appeared to limit lymphatic transport of the alkyl derivatives, although two of the three alkyl chain prodrugs - MPA-C18AM (6-fold) and MPA-C18E (13-fold) still increased lymphatic drug transport when compared to MPA. In contrast, 2-MPA-TG markedly increased lymphatic drug transport (80-fold) and drug concentrations in lymphocytes (103-fold), and this was achieved via biochemical incorporation into triglyceride deacylation-reacylation pathways. The prodrug was hydrolysed rapidly to 2-mycophenoloyl glycerol (2-MPA-MG) in the presence of rat digestive fluid, and 2-MPA-MG was subsequently re-esterified in the enterocyte with oleic acid (most likely originating from the co-administered formulation) prior to accessing the lymphatics and lymphocytes. Importantly, after administration of 2-MPA-TG, the concentrations of free MPA in the mesenteric lymph nodes were significantly enhanced (up to 28 fold) when compared to animals administered equimolar quantities of MPA, suggesting the efficient conversion of the esterified prodrug back to the pharmacologically active parent drug. The data suggest that triglyceride mimetic prodrugs have potential as a means of enhancing immunotherapy via drug targeting to lymphocytes and lymph nodes.

Demonstration of ATP-dependent, transcellular transport of lipid across the lymphatic endothelium using an in vitro model of the lacteal

PURPOSE

The lymphatic system plays crucial roles in tissue fluid balance, trafficking of immune cells, and the uptake of dietary lipid from the intestine. Given these roles there has been an interest in targeting lymphatics through oral lipid-based formulations or intradermal delivery of drug carrier systems. However the mechanisms regulating lipid uptake by lymphatics remain unknown. Thus we sought to modify a previously developed in vitro model to investigate the role of ATP in lipid uptake into the lymphatics.

METHODS

Lymphatic endothelial cells were cultured on a transwell membrane and the effective permeability to free fatty acid and Caco-2 cell-secreted lipid was calculated in the presence or absence of the ATP inhibitor sodium azide.

RESULTS

ATP inhibition reduced Caco-2 cell-secreted lipid transport, but not dextran transport. FFA transport was ATP-dependent primarily during early periods of ATP inhibition, while Caco-2 cell-secreted lipid transport was lowered at all time points studied. Furthermore, the transcellular component of transport was highly ATP-dependent, a mechanism not observed in fibroblasts, suggesting these mechanisms are unique to lymphatics. Total transport of Caco-2 cell-secreted lipid was dose-dependently reduced by ATP inhibition, and transcellular lipoprotein transport was completely attenuated.

CONCLUSION

The transport of lipid across the lymphatic endothelium as demonstrated with this in vitro model occurs in part by an ATP-dependent, transcellular route independent of passive permeability. It remains to be determined the extent that this mechanism exists in vivo and future work should be directed in this area.

The role of lymphatic transport on the systemic bioavailability of the Bcl-2 protein family inhibitors navitoclax (ABT-263) and ABT-199

Navitoclax (ABT-263), a Bcl-2 family inhibitor and ABT-199, a Bcl-2 selective inhibitor, are high molecular weight, high logP molecules that show low solubility in aqueous media. While these properties are associated with low oral bioavailability (F), both navitoclax and ABT-199 showed moderate F in preclinical species. The objective of the described study was to determine if lymphatic transport contributes to the systemic availability of navitoclax and ABT-199 in dogs. The intravenous pharmacokinetics of navitoclax and ABT-199 were determined in intact (noncannulated) dogs. In oral studies, tablets (100 mg) of navitoclax and ABT-199 were administered to both intact and thoracic lymph duct-cannulated (TDC) dogs. The clearance of navitoclax and ABT-199 was low; 0.673 and 0.779 ml/min per kilogram, respectively. The volume of distribution of both compounds was low (0.5-0.7 l/kg). The half-lives of navitoclax and ABT-199 were 22.2 and 12.9 hours, respectively. The F of navitoclax and ABT-199 were 56.5 and 38.8%, respectively, in fed intact dogs. In fed TDC dogs, 13.5 and 4.67% of the total navitoclax and ABT-199 doses were observed in lymph with the % F of navitoclax and ABT-199 of 21.7 and 20.2%, respectively. The lower lymphatic transport of ABT-199 corresponds to the lower overall % F of ABT-199 versus navitoclax despite similar systemic availability via the portal vein (similar % F in TDC animals). This is consistent with the higher long chain triglyceride solubility of navitoclax (9.2 mg/ml) versus ABT-199 (2.2 mg/ml). In fasted TDC animals, lymph transport of navitoclax and ABT-199 decreased by 1.8-fold and 10-fold, respectively.

Nanoemulsion-based oral delivery systems for lipophilic bioactive components: nutraceuticals and pharmaceuticals

Nanoemulsions have considerable potential for encapsulating, protecting and delivering lipophilic bioactive components via the oral route, such as pharmaceuticals (drugs) and nutraceuticals (food components with specific health benefits). These systems can be fabricated from generally recognized as safe ingredients using relatively simple processing operations, such as mixing and homogenization. Some of the potential advantages of nanoemulsions over conventional emulsions include higher bioaccessibility, higher physical stability and higher optical clarity. An overview of the current status of nanoemulsion fabrication, stability, properties and biological fate is given, with special emphasis on the suitability of nanoemulsions for the oral delivery of hydrophobic bioactive components, such as drugs and nutraceuticals.

Binary lipids-based nanostructured lipid carriers for improved oral bioavailability of silymarin

The main purpose of this study was to prepare binary lipids-based nanostructured lipid carriers to improve the oral bioavailability of silymarin, a poorly water-soluble liver protectant. Silymarin-loaded nanostructured lipid carriers were prepared by the method of high-pressure homogenization with glycerol distearates (Precirol ATO-5) and oleic acid as the solid and liquid lipids, respectively, and lecithin (Lipoid E 100) and Tween-80 as the emulsifiers. The silymarin-nanostructured lipid carrier prepared under optimum conditions was spherical in shape with mean particle size of ∼78.87 nm, entrapment efficiency of 87.55%, loading capacity of 8.32%, and zeta potential of −65.3 mV, respectively. In vitro release of silymarin-nanostructured lipid carriers was very limited even after 12 h, while in vitro lipolysis showed fast digestion of nanostructured lipid carriers within 1 h. Relative oral bioavailability of silymarin-nanostructured lipid carriers in Beagle dogs was 2.54- and 3.10-fold that of marketed Legalon® and silymarin solid dispersion pellets, respectively. It was concluded that nanostructured lipid carriers were potential drug delivery systems to improve the bioavailability of silymarin. Other than improved dissolution, alternative mechanisms such as facilitated absorption as well as lymphatic transport may contribute to bioavailability enhancement.

Effect of a labile methyl donor on the transformation of 5-demethyltangeretin and the related implication on bioactivity

Polymethoxyflavones (PMFs) belong to a subgroup of flavonoids that particularly exist in the peels of citrus fruits. Despite their many health-beneficial biofunctionalities, the lipophilic nature of PMFs limits their water solubility and oral bioavailability. To investigate the effect of the delivery system on the improvement of PMF bioavailibility, a lecithin-based emulsion was formulated for the delivery of two PMF compounds, tangeretin and 5-demethyltangeretin. While the emulsion system improved the digestion kinetics and the total solubilized PMF concentrations in in vitro lipolysis studies, the concentration of 5-demethyltangeretin decreased due to chemical transformation to its permethoxylated counterpart, tangeretin. The emulsifier lecithin used in this emulsion formulation contained a choline headgroup as a labile methyl group donor. The presence of a methyl donor potentially caused the transformation of 5-demethyltangeretin and reduced its anti-cancer-cell-proliferation activities. Moreover, this is the first report in the literature of the transformation from 5-demethyltangeretin to tangeretin in a lecithin-based emulsion during lipolysis, and the mechanism underlying this phenomenon has also been proposed for the first time.

Advanced drug delivery to the lymphatic system: lipid-based nanoformulations

The delivery of drugs and bioactive compounds via the lymphatic system is complex and dependent on the physiological uniqueness of the system. The lymphatic route plays an important role in transporting extracellular fluid to maintain homeostasis and in transferring immune cells to injury sites, and is able to avoid first-pass metabolism, thus acting as a bypass route for compounds with lower bioavailability, ie, those undergoing more hepatic metabolism. The lymphatic route also provides an option for the delivery of therapeutic molecules, such as drugs to treat cancer and human immunodeficiency virus, which can travel through the lymphatic system. Lymphatic imaging is useful in evaluating disease states and treatment plans for progressive diseases of the lymph system. Novel lipid-based nanoformulations, such as solid lipid nanoparticles and nanostructured lipid carriers, have unique characteristics that make them promising candidates for lymphatic delivery. These formulations are superior to colloidal carrier systems because they have controlled release properties and provide better chemical stability for drug molecules. However, multiple factors regulate the lymphatic delivery of drugs. Prior to lymphatic uptake, lipid-based nanoformulations are required to undergo interstitial hindrance that modulates drug delivery. Therefore, uptake and distribution of lipid-based nanoformulations by the lymphatic system depends on factors such as particle size, surface charge, molecular weight, and hydrophobicity. Types of lipid and concentration of the emulsifier are also important factors affecting drug delivery via the lymphatic system. All of these factors can cause changes in intermolecular interactions between the lipid nanoparticle matrix and the incorporated drug, which in turn affects uptake of drug into the lymphatic system. Two lipid-based nanoformulations, ie, solid lipid nanoparticles and nanostructured lipid carriers, have been administered via multiple routes (subcutaneous, pulmonary, and intestinal) for targeting of the lymphatic system. This paper provides a detailed review of novel lipid-based nanoformulations and their lymphatic delivery via different routes, as well as the in vivo and in vitro models used to study drug transport in the lymphatic system. Physicochemical properties that influence lymphatic delivery as well as the advantages of lipid-based nanoformulations for lymphatic delivery are also discussed.

Pharmaceutical nanotechnology for oral delivery of anticancer drugs

Oral chemotherapy is an important topic in the 21st century medicine, which may radically change the current regimen of chemotherapy and greatly improve the quality of life of the patients. Unfortunately, most anticancer drugs, especially those of high therapeutic efficacy such as paclitaxel and docetaxel, are not orally bioavailable due to the gastrointestinal (GI) drug barrier. The molecular basis of the GI barrier has been found mainly due to the multidrug efflux proteins, i.e. P-type glycoproteins (P-gp), which are rich in the epithelial cell membranes in the GI tract. Medical solution for oral chemotherapy is to apply P-gp inhibitors such as cyclosporine A, which, however, suppress the body's immune system either, thus causing medical complication. Pharmaceutical nanotechnology, which is to apply and further develop nanotechnology to solve the problems in drug delivery, may provide a better solution and thus change the way we make drug and the way we take drug. This review is focused on the problems encountered in oral chemotherapy and the pharmaceutical nanotechnology solutions such as prodrugs, nanoemulsions, dendrimers, micelles, liposomes, solid lipid nanoparticles and nanoparticles of biodegradable polymers. Proof-of-concept in vitro and in vivo results for oral delivery of anticancer drugs by the various nanocarriers, which can be found so far from the literature, are provided.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Toward the establishment of standardized in vitro tests for lipid-based formulations, part 3: understanding supersaturation versus precipitation potential during the in vitro digestion of type I, II, IIIA, IIIB and IV lipid-based formulations

PURPOSE

Recent studies have shown that digestion of lipid-based formulations (LBFs) can stimulate both supersaturation and precipitation. The current study has evaluated the drug, formulation and dose-dependence of the supersaturation - precipitation balance for a range of LBFs.

METHODS

Type I, II, IIIA/B LBFs containing medium-chain (MC) or long-chain (LC) lipids, and lipid-free Type IV LBF incorporating different doses of fenofibrate or tolfenamic acid were digested in vitro in a simulated intestinal medium. The degree of supersaturation was assessed through comparison of drug concentrations in aqueous digestion phases (APDIGEST) during LBF digestion and the equilibrium drug solubility in the same phases.

RESULTS

Increasing fenofibrate or tolfenamic acid drug loads (i.e., dose) had negligible effects on LC LBF performance during digestion, but promoted drug crystallization (confirmed by XRPD) from MC and Type IV LBF. Drug crystallization was only evident in instances when the calculated maximum supersaturation ratio (SR(M)) was >3. This threshold SR(M) value was remarkably consistent across all LBF and was also consistent with previous studies with danazol.

CONCLUSIONS

The maximum supersaturation ratio (SR(M)) provides an indication of the supersaturation 'pressure' exerted by formulation digestion and is strongly predictive of the likelihood of drug precipitation in vitro. This may also prove effective in discriminating the in vivo performance of LBFs.

Nonlinear absorption kinetics of self-emulsifying drug delivery systems (SEDDS) containing tocotrienols as lipophilic molecules: in vivo and in vitro studies

Self-emulsifying drug delivery systems (SEDDS) have been broadly used to promote the oral absorption of poorly water-soluble drugs. The purpose of the current study was to evaluate the in vivo oral bioavailability of vitamin E isoforms, δ-tocotrienol (δ-T3) and γ-tocotrienol (γ-T3) administered as SEDDS, as compared to commercially available UNIQUE E® Tocotrienols capsules. Results from studies in rats showed that low dose treatment with δ-T3 (90%) and γ-T3 (10%) formulated SEDDS showed bioavailability of 31.5% and 332%, respectively. However, bioavailability showed a progressive decrease with increased treatment dose that displayed nonlinear absorption kinetics. Additional in vitro studies examining cellular uptake studies in Caco 2 cells revealed that the SEDDS formulation increased passive permeability of δ-T3 and γ-T3 by threefold as compared to the commercial capsule formulation. These studies also showed that free surfactants decreased δ-T3 and γ-T3 absorption. Specifically, combined treatment cremophor EL or labrasol with tocotrienols caused a 60-85% reduction in the cellular uptake of δ-T3 and γ-T3 and these effects appear to result from surfactant-induced inhibition of the δ-T3 and γ-T3 transport protein Niemann-Pick C1-like 1 (NPC1L1). In summary, results showed that SEDDS formulation significantly increases the absorption and bioavailability δ-T3 and γ-T3. However, this effect is self-limiting because treatment with increasing doses of SEDDS appears to be associated with a corresponding increase in free surfactants levels that directly and negatively impact tocotrienol transport protein function and results in nonlinear absorption kinetics and a progressive decrease in δ-T3 and γ-T3 absorption and bioavailability.

Long chain lipid based tamoxifen NLC. Part I: preformulation studies, formulation development and physicochemical characterization

Tamoxifen citrate (Tmx) was formulated in nanostructured lipid carrier system (NLC) using long chain solid lipids (LCSL) and oils (LCO) with the aim to target lymphatic system to improve its bioavailability in plasma and lymphnode (initial sites for metastasis) and reduce its drug associated toxicity. Tamoxifen loaded NLC (Tmx-NLC) was formulated using solvent diffusion technique. Preformulation studies comprised evaluation of drug-excipients compatibility. Solubility of Tmx was screened in LCSL and LCO, surfactants and co-surfactants to identify NLC components. Surfactant co-surfactant combinations were studied for their ability to stabilize the system. Tmx-NLC was physicochemically characterized by TEM, DSC, XRD, and FTIR studies. Drug-excipients chemical compatibility study facilitated anticipation of excipients induced oxidative degradation of Tmx. Suitable storage condition below 30°C could stabilize Tmx. Tmx-NLC with >90% entrapment efficiency and 215.60 ± 7.98 nm particle size were prepared and freeze dried. Freeze dried Tmx-NLC could withstand various gastrointestinal tract (GI) media (pH 1.2, pH 3.5, pH 4.5, pH 6.8, pH 7.4). Dissolution profile of Tmx-NLC in various media showed sustained release pattern irrespective of pH of medium. No significant change in characteristics of Tmx-NLC was observed after 3 months of accelerated stability studies.

A mouse model to evaluate the impact of species, sex, and lipid load on lymphatic drug transport

PURPOSE

To establish a lymph-cannulated mouse model, and use the model to investigate the impact of lipid dose on exogenous and endogenous lipid recruitment, and drug transport, into the lymph of males versus females. Finally, lymphatic transport and drug absorption in the mouse were compared to other pre-clinical models (rats/dogs).

METHODS

Animals were orally or intraduodenally administered 1.6 mg/kg halofantrine in low or high (14)C-lipid doses. For bioavailability calculation, animals were intravenuosly administered halofantrine. Lymph or blood samples were taken and halofantrine, triglyceride, phospholipid and (14)C-lipid concentrations measured.

RESULTS

Lymphatic lipid transport increased linearly with lipid dose, was similar across species and in male/female animals. In contrast, lymphatic transport of halofantrine differed markedly across species (dogs>rats>mice) and plateaued at higher lipid doses. Lower bioavailability appeared responsible for some species differences in halofantrine lymphatic transport; however other systematic differences were involved.

CONCLUSIONS

A contemporary lymph-cannulated mouse model was established which will enable investigation of lymphatic transport in transgenic and disease models. The current study found halofantrine absorption and lymphatic transport are reduced in small animals. Future analyses will investigate mechanisms involved, and if similar trends occur for other drugs, to establish the most relevant model(s) to predict lymphatic transport in humans.

Monitoring gene expression: quantitative real-time rt-PCR

Two-step quantitative real-time RT-PCR (RT-qPCR), also known as real-time RT-PCR, kinetic RT-PCR, or quantitative fluorescent RT-PCR, has become the method of choice for gene expression analysis during the last few years. It is a fast and convenient PCR method that combines traditional RT-PCR with the phenomenon of fluorescence resonance energy transfer (FRET) using fluorogenic primers. The detection of changes in fluorescence intensity during the reaction enables the user to follow the PCR reaction in real time.RT-qPCR comprises several steps: (1) RNA is isolated from target tissue/cells; (2) mRNA is reverse-transcribed to cDNA; (3) modified gene-specific PCR primers are used to amplify a segment of the cDNA of interest, following the reaction in real time; and (4) the initial concentration of the selected transcript in a specific tissue or cell type is calculated from the exponential phase of the reaction. Relative quantification or absolute quantification compared to standards that are run in parallel can be performed.This chapter describes the entire procedure from isolation of total RNA from liver and fatty tissues/cells to the use of RT-qPCR to study gene expression in these tissues. We perform relative quantification of transcripts to calculate the fold-difference of a certain mRNA level between different samples. In addition, tips for choosing primers and performing analyses are provided to help the beginner in understanding the technique.

Mesenteric lymphatic absorption and the pharmacokinetics of naringin and naringenin in the rat

The hypothesis for this study was that flavanoids and their glycoside are absorbed mainly through the portal vein to enter the liver for biotransformation and are only partially absorbed through the lymphatic duct. To verify this hypothesis, an unconscious, mesenteric lymphatic/portal vein/jugular vein/bile duct/duodenum-cannulated rat model was developed. Naringin was administered at dosages of 600 and 1000 mg/kg, and naringenin was given at 100 and 300 mg/kg by intraduodenal administration. Blood samples collected from the portal vein and jugular vein as well as lymphatic fluid were prepared by protein precipitation and then analyzed by high-performance liquid chromatography with photodiode array detection (HPLC-DAD). Analyses of these samples were doubly confirmed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The results show that, after intraduodenal administration, both compounds were mainly absorbed into portal blood rather than mesenteric lymph, and most of the intact analyte would be eliminated through bile excretion. The area under the concentration (AUC) ratio was defined to represent the absorption ratio for portal vein [AUC(portal)/AUC((portal+lymph))] and lymph fluid [AUC(lymph)/AUC((portal+lymph))]. The results indicate that the portal and lymphatic absorptions for naringin were around 95 and 5.0%, respectively. The respective absorptions for naringenin were around 98 and 2%, respectively.

Impact of the pharmaceutical sciences on health care: a reflection over the past 50 years

During the last century, particularly the latter half, spectacular progress has been made in improving the health and longevity of people. The reasons are many, but the development of medicines has played a critical role. This report documents and reflects on the impressive contribution that those working in the pharmaceutical sciences have made to healthcare over the past 50 years. It is divided into six sections (drug discovery; absorption, distribution, metabolism, and excretion; pharmacokinetics and pharmacodynamics; drug formulation; drug regulation; and drug utilization), each describing key contributions that have been made in the progression of medicines, from conception to use. A common thread throughout is the application of translational science to the improvement of drug discovery, development, and therapeutic application. Each section has been coordinated by a leading scientist who was asked, after consulting widely with many colleagues across the globe, to identify "The five most influential ideas/concepts/developments introduced by 'pharmaceutical scientists' (in their field) over the past 50 years?" Although one cannot predict where the important breakthroughs will come in the future to meet the unmet medical needs, the evidence presented in this report should leave no doubt that those engaged in the pharmaceutical sciences will continue to make their contributions heavily felt.

Dual-channel in-situ optical imaging system for quantifying lipid uptake and lymphatic pump function

Nearly all dietary lipids are transported from the intestine to venous circulation through the lymphatic system, yet the mechanisms that regulate this process remain unclear. Elucidating the mechanisms involved in the functional response of lymphatics to changes in lipid load would provide valuable insight into recent implications of lymphatic dysfunction in lipid related diseases. Therefore, we sought to develop an in situ imaging system to quantify and correlate lymphatic function as it relates to lipid transport. The imaging platform provides the capability of dual-channel imaging of both high-speed bright-field video and fluorescence simultaneously. Utilizing post-acquisition image processing algorithms, we can quantify correlations between vessel pump function, lymph flow, and lipid concentration of mesenteric lymphatic vessels in situ. All image analysis is automated with customized LabVIEW virtual instruments; local flow is measured through lymphocyte velocity tracking, vessel contraction through measurements of the vessel wall displacement, and lipid uptake through fluorescence intensity tracking of an orally administered fluorescently labelled fatty acid analogue, BODIPY FL C16. This system will prove to be an invaluable tool for scientists studying intestinal lymphatic function in health and disease, and those investigating strategies for targeting the lymphatics with orally delivered drugs to avoid first pass metabolism.

Targeted lipid based drug conjugates: a novel strategy for drug delivery

A majority of studies involving prodrugs are directed to overcome low bioavailability of the parent drug. The aim of this study is to increase the bioavailability of acyclovir (ACV) by designing a novel prodrug delivery system which is more lipophilic, and at the same time site specific. In this study, a lipid raft has been conjugated to the parent drug molecule to impart lipophilicity. Simultaneously a targeting moiety that can be recognized by a specific transporter/receptor in the cell membrane has also been tethered to the other terminal of lipid raft. Targeted lipid prodrugs i.e., biotin-ricinoleicacid-acyclovir (B-R-ACV) and biotin-12hydroxystearicacid-acyclovir (B-12HS-ACV) were synthesized with ricinoleicacid and 12hydroxystearicacid as the lipophilic rafts and biotin as the targeting moiety. Biotin-ACV (B-ACV), ricinoleicacid-ACV (R-ACV) and 12hydroxystearicacid-ACV (12HS-ACV) were also synthesized to delineate the individual effects of the targeting and the lipid moieties. Cellular accumulation studies were performed in confluent MDCK-MDR1 and Caco-2 cells. The targeted lipid prodrugs B-R-ACV and B-12HS-ACV exhibited much higher cellular accumulation than B-ACV, R-ACV and 12HS-ACV in both cell lines. This result indicates that both the targeting and the lipid moiety act synergistically toward cellular uptake. The biotin conjugated prodrugs caused a decrease in the uptake of [(3)H] biotin suggesting the role of sodium dependent multivitamin transporter (SMVT) in uptake. The affinity of these targeted lipid prodrugs toward SMVT was studied in MDCK-MDR1 cells. Both the targeted lipid prodrugs B-R-ACV (20.25 ± 1.74 μM) and B-12HS-ACV (23.99 ± 3.20 μM) demonstrated higher affinity towards SMVT than B-ACV (30.90 ± 4.19 μM). Further, dose dependent studies revealed a concentration dependent inhibitory effect on [(3)H] biotin uptake in the presence of biotinylated prodrugs. Transepithelial transport studies showed lowering of [(3)H] biotin permeability in the presence of biotin and biotinylated prodrugs, further indicating a carrier mediated translocation by SMVT. Overall, results from these studies clearly suggest that these biotinylated lipid prodrugs of ACV possess enhanced affinity towards SMVT. These prodrugs appear to be potential candidates for the treatment of oral and ocular herpes virus infections, because of higher expression of SMVT on intestinal and corneal epithelial cells. In conclusion we hypothesize that our novel prodrug design strategy may help in higher absorption of hydrophilic parent drug. Moreover, this novel prodrug design can result in higher cell permeability of hydrophilic therapeutics such as genes, siRNA, antisense RNA, DNA, oligonucleotides, peptides and proteins.

Strategies of targeting oral drug delivery systems to the colon and their potential use for the treatment of colorectal cancer

Colorectal cancer (CRC) is the third most common cause of cancer-related death in both men and women. Often, surgical intervention remains the choice in treating CRC. Traditional dosage forms used for treating CRC deliver drug to wanted as well as unwanted sites of drug action resulting in several adverse side effects. Targeted oral drug delivery systems are being investigated to target and deliver chemotherapeutic and chemopreventive agents directly to colon and rectum. Site-specific delivery of a drug to colon increases its concentration at the target site, and thus requires a lower dose with reduced incidence of side effects. The major obstacle to be overcome for successful targeting of drug to colon through oral route is that drug absorption/degradation must be avoided in stomach and small intestine before the dosage form reaches colon. The review includes discussion of physiological factors that must be considered when targeting drugs directly to colorectal region, an outline on drugs used for treatment and prevention of CRC, and a brief description of various types of colon-targeted oral drug delivery systems. The focus is on the assessment of various formulation approaches being investigated for oral colon-specific delivery of drugs used in the treatment and prevention of CRC.

Modification of physicochemical characteristics of active pharmaceutical ingredients and application of supersaturatable dosage forms for improving bioavailability of poorly absorbed drugs

New chemical entities are required to possess physicochemical characteristics that result in acceptable oral absorption. However, many promising candidates need physicochemical modification or application of special formulation technology. This review discusses strategies for overcoming physicochemical problems during the development at the preformulation and formulation stages with emphasis on overcoming the most typical problem, low solubility. Solubility of active pharmaceutical ingredients can be improved by employing metastable states, salt forms, or cocrystals. Since the usefulness of salt forms is well recognized, it is the normal strategy to select the most suitable salt form through extensive screening in the current developmental study. Promising formulation technologies used to overcome the low solubility problem include liquid-filled capsules, self-emulsifying formulations, solid dispersions, and nanosuspensions. Current knowledge for each formulation is discussed from both theoretical and practical viewpoints, and their advantages and disadvantages are presented.