Absorption of a pharmacological dose of vitamin D3 from two different lipid vehicles in man: comparison of peanut oil and a medium chain triglyceride

Improvement and characterization of oral absorption behavior of clofazimine by SNEDDS: Quantitative evaluation of extensive lymphatic transport

Clofazimine, an anti-leprosy drug, has been anticipated for a candidate to treat tuberculosis, cryptosporidiosis, and coronavirus infection, but its low oral bioavailability is considered a reason for its limited activity. In the current study, we have tried to improve the oral bioavailability of clofazimine by several SNEDDS formulations and characterized the absorption behavior from various aspects. Among four SNEDDS formulations prepared, SNEDDS A, prepared with castor oil as an oil component, provided the highest bioavailability (around 61%) and SNEDDS D, prepared with Capryol 90, gave the second highest bioavailability. SNEDDS A formed the finest nanoparticles, which were maintained under gastric and intestinal luminal conditions. The comparison in oral bioavailability between the SNEDDS formulation and its corresponding preformed nanoemulsion suggested that SNEDDS A would efficiently form nanoemulsion in the gastrointestinal tract after oral administration. AUC of mesenteric lymph node concentration was the highest for SNEDDS A, which would be one of the reasons for SNEDDS A to reveal the highest oral bioavailability. A cycloheximide-treated oral absorption study and single-pass perfusion study by utilizing a vascular-luminal perfused small intestine-liver preparation clearly indicated that over 90% of clofazimine absorbed to systemic circulation should be derived from lymphatic transport for both SNEDDS A and D. Furthermore, the fraction of dose absorbed was around 65% for SNEDDS D, but SNEDDS A achieved around 94%, indicating the excellent performance of SNEDDS A.

Vitamin D deficiency and tumor aggressiveness in gastroenteropancreatic neuroendocrine tumors

PURPOSE

Data regarding vitamin D status in patients affected by gastroenteropancreatic (GEP) neuroendocrine tumor (NET) are limited and often showing contrasting results. The aim of the study was to evaluate the incidence of vitamin D deficiency (<20 ng/mL) in GEP-NET patients and compare the 25-hydroxyvitamin D (25(OH)D) levels with clinicopathological parameters and clinical outcome.

METHODS

A retrospective cross-sectional study including 75 low grade (G1-G2) GEP-NETs and 123 healthy controls matched for age, sex, and body mass index, was performed.

RESULTS

GEP-NET patients had significantly lower 25(OH)D levels compared to controls (17.9 ± 7.8 vs 24.2 ± 7.7 ng/mL, p < 0.0001). Ileal NETs were associated to lower 25(OH)D levels compared to other primary tumor sites (p = 0.049) and small bowel resection posed a significant increased risk of severe vitamin D deficiency (OR = 2.81, 95% CI = 1.25-3.37, p = 0.018). No correlation with somatostatin analogs treatment was found. 25(OH)D levels were significantly lower in G2 compared to G1 GEP-NETs (15.6 ± 7.8 vs 19.9 ± 7.4 ng/mL, p = 0.016) and in patients with progressive disease (12.6 ± 5.7 ng/mL) compared to those with stable disease (mean 21.5 ± 8.2 ng/mL, p = 0.001) or tumor free after surgery (19.6 ± 7.3 ng/mL, p = 0.002). Patients with vitamin D deficiency and insufficiency had shorter progression-free survival compared to those with sufficiency (p = 0.014), whereas no correlation was found with disease-specific survival.

CONCLUSIONS

Vitamin D deficiency is highly prevalent among GEP-NETs and could be associated with high tumor grade and disease progression. Therefore, the monitoring of 25(OH)D levels is relevant in these patients and vitamin D supplementation should be considered in the management of GEP-NET patients with vitamin D deficiency or insufficiency.

Vitamin D kinetics in nonpregnant and pregnant women after a single oral dose of trideuterated vitamin D3

The plasma pool of the hormone 1,25-dihydroxyvitamin D (1,25(OH)₂D) is increased throughout most of human pregnancy. Mechanisms behind this adaptation are unclear, in part due to limited data on vitamin D kinetics during pregnancy. Stable isotopes make it possible to study vitamin D kinetics in vulnerable study populations like pregnant women. We conducted a pilot study of vitamin D kinetics in nonpregnant and pregnant women. We evaluated a clinical protocol and developed analytical methods to assess the serum appearance and disappearance of trideuterated vitamin D₃ (d3-vitamin D₃) and trideuterated 25-hydroxyvitamin D₃ (d3-25(OH)D₃) after a single oral dose of 25 μg of [6,19,19-²H]-vitamin D₃ (d3-vitamin D₃). Blood was collected at baseline and 2, 4, 6, 24, 168, 264, and 456 hours post-dosing. We then described the serum kinetic profiles of d3-vitamin D₃ and d3-25(OH)D₃ in nonpregnant and pregnant women. Serum kinetic profiles of d3-vitamin D₃ and d3-25(OH)D₃ followed a time course in line with previous pharmacokinetic studies. There was marked variability between participants in the area under the concentration-time curve (AUC) of d3-25(OH)D₃ over the 20-day study period. This AUC of d3-25(OH)D₃ was positively correlated with the serum vitamin D binding protein (DBP) concentration, which was higher in pregnant compared with nonpregnant women. The mean serum half-life of 25(OH)D₃ was longer but not significantly different in pregnant women (18.8 days) compared with nonpregnant women (13.6 days). Our pilot study demonstrated that a single oral dose of 25 μg of d3-vitamin D₃ can be used to study vitamin D kinetics. Serum DBP concentration is an important predictor of vitamin D kinetics, and more research is needed to fully understand the significance of elevated DBP concentration during pregnancy.

Drug delivery to the intestinal lymph by oral formulations

Oral drug delivery systems (DDS) targeting lymphocytes in intestinal lymphatic vessels, ducts, and nodes are useful for treating diverse diseases. The intestinal lymph harbors numerous lymphocyte subsets, and DDS containing lipids such as triglycerides and fatty acids can deliver drugs to the lymph through the chylomicron pathway. DDS are efficient, thus allowing the administration of reduced drug doses, which mitigate systemic adverse effects. Here we review orally administered lipid formulations comprising oil solutions, suspensions, micro/nanoemulsions, self-micro/nano emulsifying DDS, liposomes, micelles, solid lipid nanoparticles, and nanostructured lipid carriers for targeting drugs to the lymph. We first describe the structures of lymphatic vessels and lymph nodes and the oral absorption of lipids and drugs into the intestinal lymph. We next summarize the effects of the properties and amounts of lipids and drugs delivered into the lymph and lymphocytes, as well as their effects on drug delivery ratios of lymph to blood. Finally, we describe lymphatic DDS containing saquinavir, tacrolimus, and methotrexate, and their potency that reduce drug concentrations in blood, which are associated with systemic adverse effects.

Novel bioemulsomes for baicalin oral lymphatic targeting: development, optimization and pharmacokinetics

Aim: The aim of this study was to elaborate on 'bioemulsomes,' novel biocompatible lipoprotein analogs for effective lymphatic transport of baicalin (BCL). Methods: BCL bioemulsomes were developed and optimized and in vitro physicochemical characterization performed. The bioavailability of BCL bioemulsomes compared with free BCL was investigated using in vivo pharmacokinetics studies. Finally, BCL lymphatic transport was assessed via cycloheximide blockade assay. Results: Optimized BCL-loaded nanoemulsomes showed promising in vitro characteristics that favor lymphatic targeting. In vivo pharmacokinetics showed a significant improvement in bioavailability over free BCL. A significant decrease in BCL emulsome absorption (33%) was exhibited after chemical blockage of the lymphatic pathway, confirming the lymphatic transport potential. Conclusion: Bioemulsomes could be a promising tool for bypassing BCL oral delivery hurdles as well as lymphatic transport, paving the way for potential treatment of lymphoma.

Effects of an Omega-3 and Vitamin D Supplement on Fatty Acids and Vitamin D Serum Levels in Double-Blinded, Randomized, Controlled Trials in Healthy and Crohn's Disease Populations

Two trials separately measured the bioavailability and impact on inflammation of a supplement taken daily containing 510 mg Docosahexaenoic acid (DHA), 344 mg Eicosapentaenoic acid (EPA), and 1000 IU of vitamin D (25-hydroxyvitamin D; 25(OH)D), for healthy and Crohn’s disease (CD) populations. Both trials were double blinded, randomized, placebo-controlled with cross-over. Participants were randomly allocated to groups A (placebo then supplement) or B (supplement then placebo). Both included a washout. Fatty acid (N-3 PUFAs) and vitamin D serum levels, plasma C-reactive protein (CRP), and stool calprotectin were measured before and after each treatment period. Outcome measures were analyzed using generalized linear mixed models, including terms for treatment, period, and a treatment-by-period interaction. The supplement significantly increased serum levels in healthy and CD groups for EPA (p < 0.001 and p < 0.001, respectively), Docosapentaenoic acid (p < 0.001 and 0.005), DHA (p < 0.001 and 0.006), the omega-3 index (p < 0.001 and 0.001), and (vitamin D (p < 0.001 and 0.027). CRP and calprotectin measures showed no evidence of a treatment effect on inflammation; however, model estimation was imprecise for both outcomes, hence further research is required to elucidate potential inflammation effects. The nutrient supplement increased serum levels of key N-3 PUFAs and vitamin D in both populations, showing the preparation was readily bioavailable.

Intestinal absorption of vitamin D: a systematic review

Context

Vitamin D is frequently prescribed as a supplement, yet its absorption remains poorly understood.

Objective

This systematic review was performed to evaluate data on mechanisms involved in the intestinal absorption of vitamin D.

Data Sources

PubMed, Embase, and Cochrane Library databases were searched.

Study Selection

The following studies were included: experimental laboratory studies of vitamin D absorption through the enterocyte brush-border membrane; absorption tests that used radiolabeled vitamin D; and clinical trials in adults that investigated a single dose of cholecalciferol or ergocalciferol and reported at least 2 measurements of serum cholecalciferol, ergocalciferol, or 25-hydroxyvitamin D.

Data Extraction

From 2069 articles identified, 46 met the inclusion criteria.

Results

Different methods were employed to evaluate vitamin D absorption. Recent research suggests that vitamin D absorption is not an exclusive simple diffusion process. Vitamin D was better absorbed when it was consumed with fat-containing meals, but absorption also occurred without fat or oily vehicles. Factors that modified cholesterol absorption also altered vitamin D absorption.

Conclusion

Vitamin D is probably absorbed through passive diffusion and a mechanism involving membrane carriers, especially cholesterol transporters, although data remain scarce. Some data suggest that fat, when consumed concomitantly with vitamin D, improves vitamin D absorption.

Correlating in Vitro Solubilization and Supersaturation Profiles with in Vivo Exposure for Lipid Based Formulations of the CETP Inhibitor CP-532,623

Lipid based formulations (LBFs) are a promising formulation strategy for many poorly water-soluble drugs and have been shown previously to enhance the oral exposure of CP-532,623, an oral cholesteryl ester transfer protein inhibitor. In the current study, an in vitro lipid digestion model was used to probe the relationship between drug solubilization and supersaturation on in vitro dispersion and digestion of LBF containing long chain (LC) lipids and drug absorption in vivo. After in vitro digestion of LBF based on LC lipids, the proportion of CP-532,623 maintained in the solubilized state in the aqueous phase of the digest was highest in formulations containing Kolliphor RH 40, and in most cases outperformed equivalent formulations based on MC lipids. Subsequent administration of the LC-LBFs to beagle dogs resulted in reasonable correlation between concentrations of CP-532,623 measured in the aqueous phase of the in vitro digest after 30 min digestion and in vivo exposure (AUC); however, the LC-LBFs required greater in vitro drug solubilization to elicit similar in vivo exposure when compared to previous studies with MC-LBF. Although post digestion solubilization was enhanced in LC-LBF compared to MC-LBF, equilibrium solubility studies of CP-532,623 in the aqueous phase isolated from blank lipid digestion experiments revealed that equilibrium solubility was also higher, and therefore supersaturation lower. A revised correlation based on supersaturation in the digest aqueous phase and drug absorption was therefore generated. A single, linear correlation was evident for both LC- and MC-LBF containing Kolliphor RH 40, but this did not extend to formulations based on other surfactants. The data suggest that solubilization and supersaturation are significant drivers of drug absorption in vivo, and that across formulations with similar formulation composition good correlation is evident between in vitro and in vivo measures. However, across dissimilar formulations, solubilization and supersaturation alone are not sufficient to explain drug exposure and other factors also likely play a role.

Factors influencing the absorption of vitamin D in GIT: an overview

Vitamin D refers to a group of secosteroid compounds and recognized as the antirachitic vitamin, as it counters rickets, mineral desorption from fully-grown bones (Osteodistrophy), bone, joint disorders, and fragility of bones. On one hand, there is scarcity of vitamin D rich food while on other hand a number of factors negotiate its absorption efficiency in human gastrointestinal tract (GIT). These factors include variations in the physiochemical state of the vitamin D (molecular forms, potency and their physiological linkages), the complexity of food matrix (the amount and type of fatty acids, dietary fibers and presence/absence of vitamin D enhancer and inhibitor), and its interaction of other fat soluble compounds with vitamin D as well as the host-associated factors (age, disease, surgery, obesity, genetic variation etc.). It is hypothesized that the bioavailability of vitamin D in GIT is compromised if there changes within these factors. Present article is intended to review the contribution of these factors anticipated to be influencing vitamin D absorption in GIT.

Vitamin D bioavailability: state of the art

There has been renewed interest in vitamin D since numerous recent studies have suggested that besides its well-established roles in bone metabolism and immunity, vitamin D status is inversely associated with the incidence of several diseases, e.g., cancers, cardio-vascular diseases, and neurodegenerative diseases. Surprisingly, there is very little data on factors that affect absorption of this fat-soluble vitamin, although it is acknowledged that dietary vitamin D could help to fight against the subdeficient vitamin D status that is common in several populations. This review describes the state of the art concerning the fate of vitamin D in the human upper gastrointestinal tract and on the factors assumed to affect its absorption efficiency. The main conclusions are: (i) ergocalciferol (vitamin D2), the form mostly used in supplements and fortified foods, is apparently absorbed with similar efficiency to cholecalciferol (vitamin D3, the main dietary form), (ii) 25-hydroxyvitamin D (25OHD), the metabolite produced in the liver, and which can be found in foods, is better absorbed than the nonhydroxy vitamin D forms cholecalciferol and ergocalciferol, (iii) the amount of fat with which vitamin D is ingested does not seem to significantly modify the bioavailability of vitamin D3, (iv) the food matrix has apparently little effect on vitamin D bioavailability, (v) sucrose polyesters (Olestra) and tetrahydrolipstatin (orlistat) probably diminish vitamin D absorption, and (vi) there is apparently no effect of aging on vitamin D absorption efficiency. We also find that there is insufficient, or even no data on the following factors suspected of affecting vitamin D bioavailability: (i) effect of type and amount of dietary fiber, (ii) effect of vitamin D status, and (iii) effect of genetic variation in proteins involved in its intestinal absorption. In conclusion, further studies are needed to improve our knowledge of factors affecting vitamin D absorption efficiency. Clinical studies with labeled vitamin D, e.g., deuterated or (13)C, are needed to accurately and definitively assess the effect of various factors on its bioavailability.

Stability of Vitamin D3 in fortified yoghurt and yoghurt drink (Doogh)

Background:

Vitamin D deficiency and insufficiency are recognized as a worldwide problem with serious consequences. Fortification of foods with Vitamin D is a certain approach to improve serum Vitamin D status if the stability of vitamin in the foodstuffs was controlled. The purpose of this study was to examine the stability of Vitamin D₃ added to low-fat yogurt and yogurt drink “Doogh” during the products shelf-life.

Materials and Methods:

Two kinds of Vitamin D₃, water- and oil-dispersible forms, suitable for food fortification, were compared to find out whether they show different stability in the products. The products were packed in opaque or translucent containers. The content of Vitamin D₃ was determined by high performance liquid chromatography method.

Results:

Vitamin D was not affected by the heat treatment (pasteurization) and other processes (homogenization and fermentation). Both water- and oil-dispersible forms were stable during the shelf-life of yogurt samples packed in opaque containers. The Vitamin D₃ content of yogurt fortified with water-dispersible form and packed in translucent containers was not stable during the shelf-life and significantly reduced after 1, 2, and 3 weeks of storage compared to the day 0. The Vitamin D₃ content of samples fortified with the oil-dispersible form packed in the same container was only stable after 1-week and significantly reduced after 2 and 3 weeks of storage. The Vitamin D₃ content of Doogh packed in the opaque containers remained stable during the shelf-life while it was not stable in the samples packed in translucent containers.

Conclusion:

The results suggested that both forms of Vitamin D are suitable for fortification, and opaque container is a better choice for packaging of the product.

Intestinal absorption of vitamin D: from the meal to the enterocyte

Vitamin D plays key roles in bone, infectious, inflammatory and metabolic diseases. As most people get inadequate sun exposure for sufficient vitamin D status, they need adequate intake of dietary vitamin D. Many studies see optimizing vitamin D status as a public health priority. It is thus vital to gain deeper insight into vitamin D intestinal absorption. It was long assumed that vitamin D intestinal absorption is a passive process, but new data from our laboratory showed that it is actually far more complex than previously thought. This review describes the fate of vitamin D in the human upper gastrointestinal lumen during digestion and focuses on the proteins involved in the intestinal membrane and cellular transport of vitamin D across the enterocyte. Although recent data significantly improve our understanding of vitamin D intestinal absorption, further studies are still needed to increase our knowledge of the molecular mechanisms underlying this phenomenon.

Improvement of Oral Bioavailability of N-251, a Novel Antimalarial Drug, by Increasing Lymphatic Transport with Long-Chain Fatty Acid-Based Self-Nanoemulsifying Drug Delivery System

PURPOSE

The objective of this study was to improve the absorption behavior of N-251, a novel antimalarial drug, by preparing an appropriate self-nanoemulsifying drug delivery system (SNEDDS).

METHODS

Two different types of SNEDDS formulations, medium-chain fatty acid-based SNEDDS (MC-SNEDDS) and long-chain fatty acid-based SNEDDS (LC-SNEDDS), were prepared based on pseudo-ternary phase diagram, and examined for their in vivo oral absorption behavior in rats.

RESULTS

Oral dosing of MC-SNEDDS formulations significantly improved the bioavailability (BA) of N-251 compared with N-251 powders. However, its high hepatic extraction limited the BA of N-251 to only 0.49 for MC-SNEDDS B, the best formulation of MC-SNEDDS. LC-SNEDDS formulations, especially LC-SNEDDS F provided the highest BA, 0.65, and successfully attenuated the inter-individual difference in the absorption behavior. Furthermore, it was confirmed that lymphatic transport of N-251 for LC-SNEDDS F was significantly increased up to around 3.19 times larger than that for MC-SNEDDS B. Simulation study suggested that 20 to 39% of N-251 uptaken by the small intestine would be delivered to lymphatic system after oral administration of LC-SNEDDS F.

CONCLUSIONS

SNEDDS formulations significantly improved the absorption behavior of N-251 and long-chain fatty acid-based lipid further improved it by avoiding the hepatic first-pass elimination.

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.

Vitamin D3 fortification, quantification, and long-term stability in Cheddar and low-fat cheeses

Considering the widespread insufficiency of vitamin D, the fortification of additional foods with vitamin D is warranted. The objective of this research was to assess the feasibility of vitamin D3 fortification in natural hard cheeses. We examined the recovery, distribution, long-term retention, and heat stability of the vitamin in industrially made fortified Cheddar and low-fat cheeses. The results indicated that the vitamin D3 did not degrade during processing, over 1 year of ripening (3-8 degrees C), or after thermal treatment at 232 degrees C for 5 min. Vitamin D3 recovery in the fortified Cheddar and low-fat cheeses were, respectively, 91 and 55% of the vitamin D3 added to the milk used to make each cheese. The remaining vitamin D3 was entrained in the whey. The vitamin D3 was uniformly distributed throughout the blocks of cheese. The fortification process did not alter the yield, chemical composition, or flavor of the Cheddar cheese. We conclude that industrially manufactured Cheddar and low-fat cheeses are suitable for vitamin D3 fortification.

Vitamin D: a growing perspective

Vitamin D deficiency has been widely reported in all age groups in recent years. Rickets has never been eradicated in developed countries, and it most commonly affects children from recent immigrant groups. There is much evidence that current vitamin D guidelines for the neonatal period, 5-10 microg (200-400 IU)/day, prevent rickets at the typical calcium intakes in developed countries. The annual incidence of vitamin D-deficiency rickets in developed countries ranges between 2.9 and 7.5 cases per 100,000 children. The prevalence of vitamin D deficiency in mothers and their neonates is remarkable, and the results of one study suggest that third-trimester 25-hydroxyvitamin D (25(OH)D) is associated with fetal bone mineral accrual that may affect prepubertal bone mass accumulation. Beyond infancy, the evidence indicates that 5 microg (200 IU)/day of vitamin D has little effect on vitamin D status as measured by the serum 25(OH)D concentration. Two randomized clinical trials show that higher vitamin D intake improves one-year gain in bone density in adolescent girls. The functions of vitamin D extend beyond bone to include immune system regulation and anti-proliferative effects on cells. Early life vitamin D inadequacy is implicated in the risk of bone disease, autoimmune disease, and certain cancers later in life; however, long-term interventional studies do not exist to validate the widespread implementation of greater vitamin D consumption. Here we review the available data concerning vitamin D status and health effects of vitamin D in pregnancy through to and including adolescence.

The bioavailability of vitamin D from fortified cheeses and supplements is equivalent in adults

There is a need to increase the options for vitamin D fortification. We have developed a method to fortify hard cheese with vitamin D. Our aim was to characterize the bioavailability of vitamin D from fortified cheeses. Eighty adults were randomized to weekly servings of fortified cheddar cheese (DC) (34 g; n = 20); fortified low-fat cheese (DLF) (41 g; n = 10); liquid vitamin D supplement (1 mL), taken with food (DS+) (n = 20) or without food (DS-) (n = 10); placebo cheddar cheese (n = 10); or placebo supplement (n = 10). The treatments contained 28,000 IU cholecalciferol (vitamin D3), equivalent to 4000 IU (100 microg/d). The primary outcome was the comparison of vitamin D bioavailability, as measured by the serum 25-hydroxyvitamin D [25(OH)D] response, between fortified cheeses and supplement. In the placebo groups, initial 25(OH)D, 55.0 +/- 25.3 nmol/L, declined over the 8-wk winter protocol, to 50.7 +/- 24.2 nmol/L (P = 0.046). In the vitamin D-treated groups, the mean increases in 25(OH)D over 8 wk were: 65.3 +/- 24.1 (DC), 69.4 +/- 21.7 (DLF), 59.3 +/- 23.3 (DS+), and 59.3 +/- 19.6 nmol/L (DS-); these changes differed from the placebo groups (P < 0.0001) but not from one another (P = 0.62). Compared with baseline, serum parathyroid hormone decreased with both fortification (P = 0.003) and supplementation (P = 0.012). These data demonstrate that vitamin D is equally bioavailable from fortified hard cheeses and supplements, making cheese suitable for vitamin D fortification.

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

After oral administration, the majority of drug molecules are absorbed across the small intestine and enter the systemic circulation via the portal vein and the liver. For some highly lipophilic drugs (typically log P > 5, lipid solubility > 50 mg/g), however, association with lymph lipoproteins in the enterocyte leads to transport to the systemic circulation via the intestinal lymph. The attendant delivery benefits associated with lymphatic drug transport include a reduction in first-pass metabolism and lymphatic exposure to drug concentrations orders of magnitude higher than that attained in systemic blood. In the current review we briefly describe the mechanisms by which drug molecules access the lymph and the formulation strategies that may be utilised to enhance lymphatic drug transport. Specific focus is directed toward recent advances in understanding regarding the impact of lipid source (both endogenous and exogenous) and intracellular lipid trafficking pathways on lymphatic drug transport and enterocyte-based first-pass metabolism.

Enhancing intestinal drug solubilisation using lipid-based delivery systems

Lipid-based delivery systems are finding increasing application in the oral delivery of poorly water-soluble, lipophilic drugs. Whilst lipidic dose forms may improve oral bioavailability via several mechanisms, enhancement of gastrointestinal solubilisation remains argueably the most important method of absorption enhancement. This review firstly describes the mechanistic rationale which underpins the use of lipid-based delivery systems to enhance drug solubilisation and briefly reviews the available literature describing increases in oral bioavailability after the administration of lipid solution, suspension and self-emulsifying formulations. The use of in vitro methods including dispersion tests and more complex models of in vitro lipolysis as indicators of potential in vivo performance are subsequently described, with particular focus on recent data which suggests that the digestion of surfactants present in lipid-based formulations may impact on formulation performance. Finally, a series of seven guiding principles for formulation design of lipid-based delivery systems are suggested based on an analysis of recent data generated in our laboratories and elsewhere.

Use of a Dynamic in Vitro Lipolysis Model to Rationalize Oral Formulation Development for Poor Water Soluble Drugs: Correlation with in Vivo Data and the Relationship to Intra-Enterocyte Processes in Rats

PURPOSE

To examine the correlation between the in vitro solubilization process of lipophilic compounds from different lipid solutions and the corresponding in vivo oral bioavailability data. In particular, to assess the influence of intra-enterocyte processes (metabolism and lymphatic absorption) on this correlation.

MATERIALS AND METHODS

The dissolution of progesterone and vitamin D3 in long (LCT), medium (MCT) and short (SCT) chain triglyceride solutions were tested in a dynamic in vitro lipolysis model. The absolute oral bioavailability of the drugs from the tested formulations was investigated in rats. Vitamin D3 bioavailability was also examined following lymphatic transport blockage induced by cycloheximide (3 mg/kg).

RESULTS

The dynamic in vitro lipolysis experiments indicated a rank order of MCT > LCT > SCT for both progesterone and vitamin D3. The bioavailability of progesterone correlated with the in vitro data, despite its significant pre-systemic metabolism. For vitamin D3, an in vivo performance rank order of LCT > MCT > SCT was obtained. However, when the lymphatic transport was blocked the bioavailability of vitamin D3 correlated with in vitro data.

CONCLUSIONS

The in vitro lipolysis model is useful for optimization of oral lipid formulations even in the case of pre-systemic metabolism in the gut. However, when lymphatic transport is a significant route of absorption, the in vitro lipolysis data may not be predictive for actual in vivo absorption.

Bioavailability of seocalcitol I: Relating solubility in biorelevant media with oral bioavailability in rats--effect of medium and long chain triglycerides

Simulated intestinal media (SIM) containing bile salt (BS) and phospholipids (PL) with and without medium chain lipolytic products (MC-LP) or long chain lipolytic products (LC-LP) were developed to study the solubility of seocalcitol. Both MC-LP and LC-LP were studied in order to investigate the influence of fatty acid chain length on the in vitro solubility of seocalcitol. The same solubility of seocalcitol was found in media containing either MC-LP or LC-LP. The bioavailability after oral administration of seocalcitol dissolved in medium chain triglyceride (MCT), long chain triglyceride (LCT), and a reference formulation containing propylene glycol (PG) was studied in vivo in rats. The lipid formulations showed a twofold increase in bioavailability compared with the reference formulation, indicating positive effects of lipids on the bioavailability reflecting a better solubility in the intestine and protection against precipitation of seocalcitol in the gastro intestinal tract. There was no difference in the in vivo bioavailability of seocalcitol between the MCT and the LCT solutions, which correlates with the identical in vitro solubility of seocalcitol in SIM containing MC-LP or LC-LP.

Biodisponibilidade de vitaminas lipossolúveis

O termo biodisponibilidade representa a parte do nutriente ingerido que tem o potencial de suprir as demandas fisiológicas em tecidos alvos; por definição, não corresponde, na maioria das vezes, à quantidade ingerida. Apesar da concordância entre alguns pesquisadores no que se refere ao conceito de biodisponibilidade, vários termos são comumente utilizados em trabalhos científicos como sinônimos desse, em função das peculiaridades dos métodos empregados na sua determinação. Estudos de balanço, relação dose-efeito e uso de isótopos são alguns dos métodos mais comumente utilizados para determinar a biodisponibilidade de vitaminas. Tais metodologias, além de avaliar a biodisponibilidade do nutriente, devem tanto quanto possível procurar elucidar ou levar em consideração os fatores que interferem na sua absorção e utilização. Dentre esses fatores, estão a interação com outros nutrientes ou componentes da dieta e as condições fisiológicas dos organismos submetidos ao estudo. As vitaminas lipossolúveis, devido ao seu metabolismo complexo, diversidade funcional e mecanismo de absorção relacionado a lipoproteínas, apresentam alguns problemas específicos no que se refere à avaliação de sua biodisponibilidade em alimentos ou dietas, necessitando, por ocasião dos ensaios, de um criterioso planejamento e análise de resultados. Dessa forma, ressaltaram-se, nesta revisão, alguns aspectos importantes com relação à biodisponibilidade das vitaminas lipossolúveis, como: diversidade de termos usados, metodologia para avaliação, fatores que interferem na absorção e utilização, entre outros, visto que a avaliação da biodisponibilidade de algumas vitaminas lipossolúveis ainda não possui métodos validados, gerando uma grande variação nos resultados obtidos nas pesquisas realizadas nesta área.

Influence of the intermediate digestion phases of common formulation lipids on the absorption of a poorly water‐soluble drug

The influence of different model intestinal phases (modelled on those likely to be produced in vivo after the digestion of commonly used formulation lipids) on the absorption profile of cinnarizine has been studied. Combinations of C8, C12, or C18:1 fatty acid and monoglyceride and simulated endogenous intestinal fluid were formulated to provide examples of liquid (L1), lamellar (L(alpha)), and cubic (C) liquid crystalline phases. Phases containing cinnarizine were dosed intraduodenally and absorption was assessed in an anesthetized rat model. Bile duct ligation was performed to inhibit the effects of digestion/dilution on the phase structure. Absorption from the L(alpha) phases (C8 and C12 lipids) was statistically higher (p < 0.05) than a cinnarizine suspension: however, a statistically significant difference was not observed from the L1 and C phases. The rigid C18:1 C phase showed evidence of providing for sustained drug absorption. Experiments in bile intact rats with the C8 L(alpha) and C18:1 C phase highlighted that the absorption-modifying properties of these phases were influenced by dilution in the endogenous bile milieu, with absorption from L(alpha) phase reducing (possibly through precipitation of solubilized drug) and increasing in the case of the C18:1 C phase, possibly through the coexistence of L1 and C upon dilution permitting more efficient transfer of solubilized drug.

Use of in vitro lipid digestion data to explain the in vivo performance of triglyceride-based oral lipid formulations of poorly water-soluble drugs: studies with halofantrine

The relative oral bioavailability (BA) of halofantrine base (Hf) was assessed in male beagle dogs after administration of a medium chain triglyceride (MCT), a long chain triglyceride (LCT), and a blended LCT/MCT lipid solution formulation of Hf (Study 1) and after administration of suspensions of Hf base and Hf. HCl in LCT (Study 2). A series of in vitro lipid digestion experiments were also performed in an attempt to clarify the data obtained. In vitro drug solubilization profiles were markedly dependent on the mass of lipid employed in lipid digestion experiments. At high lipid masses ( approximately 25 mg triglyceride/mL), MCT formulations gave maximal benefit, whereas at low lipid concentrations ( approximately 5 mg triglyceride/mL), LCT formulations provided improved solubilization capacity. The in vitro digestion and solubilization data at lower lipid masses were consistent with the in vivo data where the BA of Hf after oral administration of the LCT solution > LCT/MCT blend > MCT solution. The second BA study showed similar, albeit variable, exposure after oral administration of a suspension of Hf base or Hf. HCl in LCT and this trend was broadly consistent with in vitro results. This study demonstrates the potential utility of in vitro digestion models to assess and rank order the in vivo performance of lipid solution and suspension formulations of poorly water-soluble drugs such as Hf.

Factors affecting intestinal absorption of highly lipophilic food microconstituents (fat-soluble vitamins, carotenoids and phytosterols)

Highly lipophilic food microconstituents (HLFMs) with octanol-water partition coefficients log10 P(c) > 8 include the fat-soluble vitamins (A, E, D and K) and phytochemicals with potential health benefits, the carotenoids and phytosterols. It has been assumed that these compounds have the same metabolism in the human upper gastrointestinal tract and that they follow the same fate as lipids. However, a literature review shows that the metabolism of HLFMs in the upper gastrointestinal tract depends on each HLFM species. For example, some HLFM esters are hydrolyzed mainly by pancreatic lipase, others by bile salt-stimulated lipase; some HLFMs are apparently absorbed by passive diffusion, others by a transporter. Also, although some factors (HLFM molecular species, fat, food matrix) affect absorption efficiency of most HLFMs, other factors (fibers, microconstituents) apparently affect absorption only of some HLFMs. The mnemonic acronym SLAMENGHI, previously proposed to list the factors affecting the bioavailability of carotenoids, was used here to review current knowledge of the factors suspected to affect the intestinal absorption of HLFMs. The available data reveal numerous gaps in the knowledge of the metabolism of HLFMs and the factors that affect their absorption. These gaps need to be filled to be able to formulate HLFMs so as to promote greater absorption efficiency.

Characterisation and quantification of medium chain and long chain triglycerides and their in vitro digestion products, by HPTLC coupled with in situ densitometric analysis

The development of new and simple high performance thin layer chromatography (HPTLC) assays for the quantification of medium chain triglycerides (MCT, tricaprylin) and long chain triglycerides (LCT, triolein) and their lipolytic products, bile salts (BS) and phospholipids (PL) are described. Different classes of lipids (PL, BS, fatty acids, monoglycerides, diglycerides, and triglycerides) were separated on a single silica gel 60 HPTLC plate by Automated Multiple Development (AMD) methods using a Camag AMD 2. Post-chromatographic staining of long chain lipids (triolein, diolein, monoolein, and oleic acid), PL and BS with a solution of copper sulphate-phosphoric acid and medium chain lipids (tricaprylin, dicaprylin, monocaprylin, and caprylic acid) with a solution of ammonium molybdate-perchloric acid allowed visualisation of the lipids. Lipids were quantified by in situ spectrodensitometric measurements using a Camag TLC scanner 3. The intra- and inter-assay accuracy was between 83 and 115% and the assay was precise to within a CV of less than 20% over a range of 0.1-1 and 5-50 microg for long chain lipids and medium chain lipids, respectively. The methods have been employed to study the kinetics of triolein and tricaprylin lipolysis in an in vitro lipid digestion model commonly used to assess the digestibility of novel oral lipid-based formulations.

Lipid microemulsions for improving drug dissolution and oral absorption: physical and biopharmaceutical aspects

PURPOSE

This review highlights the state-of-the-art in pharmaceutical microemulsions with emphasis on self-emulsifying systems, from both a physical and biopharmaceutical perspective. Although these systems have several pharmaceutical applications, this review is primarily focused on their potential for oral drug delivery and intestinal absorption improvement.

METHODS

Physicochemical characteristics and formulation design based on drug solubility and membrane permeability are discussed.

RESULTS

Case studies in which lipid microemulsions have successfully been used to improve drug solubilization/dissolution and/or intestinal absorption of poorly absorbed drugs/peptides are presented.

CONCLUSIONS

Drug development issues such as commercial viability, mechanisms involved, range of applicability, safety, scale-up and manufacture are outlined, and future research and development efforts to address these issues are discussed.

A simplified high-performance liquid chromatographic method for determination of vitamin D3, 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in human serum

Measurement of the serum level of 25-hydroxyvitamin D is the most useful parameter in evaluating vitamin D status. The serum level of vitamin D is a useful parameter in studying short time effects after exposure to ultraviolet light and absorption of the vitamin after oral administration. A method for simultaneous determinations of vitamin D3 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 is described. Serum or plasma was extracted by methanol-isopropanol (90:10, v/v) and hexane. The hexane layer was injected in to a reversed-phase (C18) high-performance liquid chromatographic (HPLC) system. 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 were eluted by methanol-water (85:15, v/v), and vitamin D3 by a linear gradient of methanol-water (85:15) and methanol-isopropanol-water (87.5:10:2.5), and detected by u.v. absorption. This method gave separate determinations of the D2 and D3 forms of 25-hydroxyvitamin D, but owing to an interfering peak the method does not measure vitamin D2. The assay was very sensitive with a detection limit of 5 nmol l-1 for 25-hydroxyvitamin D2 and D3 and vitamin D3 by using 0.5 ml serum or plasma for analysis, so that for low vitamin D3 levels more than 1 ml of serum is desirable.