Biotin uptake and cellular translocation in human derived retinoblastoma cell line (Y-79): A role of hSMVT system

The Importance of Biotinylation for the Suitability of Cationic and Neutral Fourth-Generation Polyamidoamine Dendrimers as Targeted Drug Carriers in the Therapy of Glioma and Liver Cancer

In this study, we hypothesized that biotinylated and/or glycidol-flanked fourth-generation polyamidoamine (PAMAM G4) dendrimers could be a tool for efficient drug transport into glioma and liver cancer cells. For this purpose, native PAMAM (G4) dendrimers, biotinylated (G4B), glycidylated (G4gl), and biotinylated and glycidylated (G4Bgl), were synthesized, and their cytotoxicity, uptake, and accumulation in vitro and in vivo were studied in relation to the transport mediated by the sodium-dependent multivitamin transporter (SMVT). The studies showed that the human temozolomide-resistant glioma cell line (U-118 MG) and hepatocellular carcinoma cell line (HepG2) indicated a higher amount of SMVT than human HaCaT keratinocytes (HaCaTs) used as a model of normal cells. The G4gl and G4Bgl dendrimers were highly biocompatible in vitro (they did not affect proliferation and mitochondrial activity) against HaCaT and U-118 MG glioma cells and in vivo (against Caenorhabditis elegans and Wistar rats). The studied compounds penetrated efficiently into all studied cell lines, but inconsistently with the uptake pattern observed for biotin and disproportionately for the level of SMVT. G4Bgl was taken up and accumulated after 48 h to the highest degree in glioma U-118 MG cells, where it was distributed in the whole cell area, including the nuclei. It did not induce resistance symptoms in glioma cells, unlike HepG2 cells. Based on studies on Wistar rats, there are indications that it can also penetrate the blood-brain barrier and act in the central nervous system area. Therefore, it might be a promising candidate for a carrier of therapeutic agents in glioma therapy. In turn, visualization with a confocal microscope showed that biotinylated G4B penetrated efficiently into the body of C. elegans, and it may be a useful vehicle for drugs used in anthelmintic therapy.

Biotin conjugates in targeted drug delivery: is it mediated by a biotin transporter, a yet to be identified receptor, or (an)other unknown mechanism(s)?

Conjugation of drugs with biotin is a widely studied strategy for targeted drug delivery. The structure-activity relationship (SAR) studies through H3-biotin competition experiments conclude with the presence of a free carboxylic acid being essential for its uptake via the sodium-dependent multivitamin transporter (SMVT, the major biotin transporter). However, biotin conjugation with a payload requires modification of the carboxylic acid to an amide or ester group. Then, there is the question as to how/whether the uptake of biotin conjugates goes through the SMVT. If not, then what is the mechanism? Herein, we present known uptake mechanisms of biotin and its applications reported in the literature. We also critically analyse possible uptake mechanism(s) of biotin conjugates to address the disconnect between the results from SMVT-based SAR and "biotin-facilitated" targeted drug delivery. We believe understanding the uptake mechanism of biotin conjugates is critical for their future applications and further development.

Recent advances in small-molecule fluorescent probes with the function of targeting cancer receptors

Cancer is "the sword of Damocles" that threatens human life and health. Therefore, the diagnosis and treatment of cancer have been receiving much attention. Many overexpressed receptors on the surface of cancer cells provide us with an effective way to specifically identify the cancer cells, and receptor targeting strategies are becoming one of the hot ideas to enhance the ability of fluorescent probes to target tumors. Fluorescent probes connected to ligands are targeted at cancer cell surfaces through receptor-mediated endocytosis. Receptor-targeting probes can image and track cancer cells, determine tumor boundaries, monitor deep lesions, and play a role in clinical medicine, such as fluorescent imaging-guided surgery. In this review, based on the perspective of small molecule fluorescent probes, we reviewed the design ideas, photophysical properties, and applications of receptor-targeting probes for detecting biomarkers in imaging and tracing cancer cells and prospected the future developmental direction of such probes. We hope that this review will provide more ideas for the design and development of active targeting probes for receptors and lead to more applications in the medical field.

Evolution and developmental expression of the sodium-iodide symporter (NIS, slc5a5) gene family: Implications for perchlorate toxicology

The vertebrate sodium-iodide symporter (NIS or SLC5A5) transports iodide into the thyroid follicular cells that synthesize thyroid hormone. The SLC5A protein family includes transporters of vitamins, minerals, and nutrients. Disruption of SLC5A5 function by perchlorate, a pervasive environmental contaminant, leads to human pathologies, especially hypothyroidism. Perchlorate also disrupts the sexual development of model animals, including threespine stickleback (Gasterosteus aculeatus) and zebrafish (Danio rerio), but the mechanism of action is unknown. To test the hypothesis that SLC5A5 paralogs are expressed in tissues necessary for the development of reproductive organs, and therefore are plausible candidates to mediate the effects of perchlorate on sexual development, we first investigated the evolutionary history of Slc5a paralogs to better understand potential functional trajectories of the gene family. We identified two clades of slc5a paralogs with respect to an outgroup of sodium/choline cotransporters (slc5a7); these clades are the NIS clade of sodium/iodide and lactate cotransporters (slc5a5, slc5a6, slc5a8, slc5a8, and slc5a12) and the SGLT clade of sodium/glucose cotransporters (slc5a1, slc5a2, slc5a3, slc5a4, slc5a10, and slc5a11). We also characterized expression patterns of slc5a genes during development. Stickleback embryos and early larvae expressed NIS clade genes in connective tissue, cartilage, teeth, and thyroid. Stickleback males and females expressed slc5a5 and its paralogs in gonads. Single-cell transcriptomics (scRNA-seq) on zebrafish sex-genotyped gonads revealed that NIS clade-expressing cells included germ cells (slc5a5, slc5a6a, and slc5a6b) and gonadal soma cells (slc5a8l). These results are consistent with the hypothesis that perchlorate exerts its effects on sexual development by interacting with slc5a5 or its paralogs in reproductive tissues. These findings show novel expression domains of slc5 genes in stickleback and zebrafish, which suggest similar functions across vertebrates including humans, and provide candidates to mediate the effects of perchlorate on sexual development.

Penetration of Carbon Nanotubes into the Retinoblastoma Tumor after Intravitreal Injection in LH BETA T AG Transgenic Mice Reti-noblastoma Model

Purpose

To evaluate the penetration of carbon nanotubes (CNTs) throughout retinoblastoma in a transgenic mice model.

Methods

CNTs functionalized with fluorescein isothiocyanate and targeting ligands biotin (CTN-FITC-Bio, 0.5mg/ml), or folic acid (CNT-FITC-FA, 0.5mg/ml) were injected into the vitreous of one eye of LH BETA T AG transgenic mice. Other eye did not receive any injection and was used as control. Three mice were sacrificed at days 1, 2, and 3. Eyes were enucleated and stained with 4,6-diamidino-2-phenylindole. The sections were imaged by fluorescent microscope. The images were transformed into grey-scale in MATLAB for intensity analysis. Background intensity was normalized by marking squares outside the eyeball and using the mean intensity of these squares. Fluorescent intensity (FI) for each image was measured by calculating the intensity of a same-sized square within retinoblastoma.

Results

Nine eyes of nine mice were included in each CNT-FITC-Bio and CNT-FITC-FA groups. The mean FI in CNT-FITC-Bio was 52.08 ± 6.33, 53.62 ± 9.00, and 65.54 ± 5.14 in days 1, 2, and 3, respectively. The mean FI in CNT-FITC-FA was 50.28 ± 7.37, 59.21 ± 6.43, and 58.38 ± 2.32 on days 1, 2, and 3, respectively. FI was significantly higher in eyes injected with CNT-FITC-Bio and CNT-FITC-FA compared to the control eyes (P = 0.02). There was no difference in FI between eyes with CNT-FITC-Bio and CNT-FITC-FA, and FI remained stable on days 1–3 in CNT-FITC-Bio, CNT-FITC-FA, and control eyes (P> 0.05).

Conclusion

We observed higher FI in eyes with CNT-FITC-Bio and CNT-FITC-FA compared to control eyes, showing penetration of CNTs throughout retinoblastoma. CNTs can be a carrier candidate for imaging or therapeutic purposes in retinoblastoma.

Biotinylation enhances the anticancer effects of 15d‑PGJ2 against breast cancer cells

15-Deoxy-∆12,14-prostaglandin J2 (15d‑PGJ2) is a natural agonist of peroxisome proliferator-activated receptor γ (PPARγ) that displays anticancer activity. Various studies have indicated that the effects of 15d‑PGJ2 are due to both PPARγ-dependent and -independent mechanisms. In the present study, we examined the effects of a biotinylated form of 15d‑PGJ2 (b‑15d‑PGJ2) on hormone-dependent MCF‑7 and triple‑negative MDA‑MB‑231 breast cancer cell lines. b‑15d‑PGJ2 inhibited cell proliferation more efficiently than 15d‑PGJ2 or the synthetic PPARγ agonist, efatutazone. b‑15d‑PGJ2 was also more potent than its non-biotinylated counterpart in inducing apoptosis. We then analyzed the mechanisms underlying this improved efficiency. It was found not to be the result of biotin receptor-mediated increased incorporation, since free biotin in the culture medium did not decrease the anti-proliferative activity of b‑15d‑PGJ2 in competition assays. Of note, b‑15d‑PGJ2 displayed an improved PPARγ agonist activity, as measured by transactivation experiments. Molecular docking analyses revealed a similar insertion of b‑15d‑PGJ2 and 15d‑PGJ2 into the ligand binding domain of PPARγ via a covalent bond with Cys285. Finally, PPARγ silencing markedly decreased the cleavage of the apoptotic markers, poly(ADP-ribose) polymerase 1 (PARP‑1) and caspase‑7, that usually occurs following b‑15d‑PGJ2 treatment. Taken together, our data indicate that biotinylation enhances the anti-proliferative and pro-apoptotic activity of 15d‑PGJ2, and that this effect is partly mediated via a PPARγ-dependent pathway. These results may aid in the development of novel therapeutic strategies for breast cancer treatment.

Targeted tumor detection: guidelines for developing biotinylated diagnostics

We highlight the prominent role of hydrophilicity in the preferential cellular uptake process of biotinylated fluorescent probes.

Inhibition of hypoxia inducible factor 1α by siRNA-induced apoptosis in human retinoblastoma cells

Hypoxia, which activates the hypoxia inducible factor 1α (HIF-1α), is an essential feature of retinoblastoma (RB) and contributes to poor prognosis and resistance to conventional therapy. In this study, the effect of HIF-1α knockdown by small interfering RNA (siRNA) on cell proliferation, apoptosis, and apoptotic pathways of human Y-79 RB cells was first investigated. Exposure to hypoxia induced the increased expression of HIF-1α both in mRNA and protein levels. Then, knockdown of HIF-1α by siRNAHIF-1α resulted in inhibition of cell proliferation and induced cell apoptosis in human Y-79 RB cells under both normoxic and hypoxic conditions, with hypoxic conditions being more sensitive. Furthermore, knockdown of HIF-1α could enhance hypoxia-induced slight increase of Bax/Bcl-2 ratio and activate caspase-9 and caspase-3. These results together indicated that suppression of HIF-1α expression may be a promising strategy for the treatment of human RB in the future.

Biotin-conjugated tumour-targeting photocytotoxic iron(III) complexes

Iron(III) complexes [FeL(B)] (1-4) of a tetradentate phenolate-based ligand (H3L) and biotin-conjugated dipyridophenazine bases (B), viz. 7-aminodipyrido [3,2-a:2',3'-c]-phenazine (dppza in 1), (N-dipyrido[3,2-a:2',3'-c]-phenazino)amidobiotin (dppzNB in 2), dipyrido [3,2-a:2',3'-c]-phenazine-11-carboxylic acid (dppzc in 3) and 2-((2-biotinamido)ethyl) amido-dipyrido[3,2-a:2',3'-c]-phenazine (dppzCB in 4) are prepared, characterized and their interaction with streptavidin and DNA and their photocytotoxicity and cellular uptake in various cells studied. The high-spin iron(III) complexes display Fe(III)/Fe(II) redox couple near -0.7 V versus saturated calomel electrode in dimethyl sulfoxide-0.1 M tetrabutylammonium perchlorate. The complexes show non-specific interaction with DNA as determined from the binding studies. Complexes with appended biotin moiety show similar binding to streptavidin as that of free biotin, suggesting biotin conjugation to dppz does not cause any loss in its binding affinity to streptavidin. The photocytotoxicity of the complexes is tested in HepG2, HeLa and HEK293 cell lines. Complex 2 shows higher photocytotoxicity in HepG2 cells than in HeLa or HEK293, forming reactive oxygen species. This effect is attributed to the presence of overexpressed sodium-dependent multi-vitamin transporters in HepG2 cells. Microscopic studies in HepG2 cells show internalization of the biotin complexes 2 and 4 essentially occurring by receptor-mediated endocytosis, which is similar to that of native biotin and biotin fluorescein isothiocyanate conjugate.

Differential expression of folate receptor-alpha, sodium-dependent multivitamin transporter, and amino acid transporter (B (0, +)) in human retinoblastoma (Y-79) and retinal pigment epithelial (ARPE-19) cell lines

PURPOSE

The overall objective of this study was to investigate the differential expression of folate receptor-alpha (FR-α), sodium-dependent multivitamin transporter (SMVT), and amino acid transporter [B ((0, +))] in retinoblastoma (Y-79) and retinal pigment epithelial (ARPE-19) cells.

METHODS

Polymerase chain reaction (PCR) analysis was performed to confirm the existence of FR-α, SMVT, and B ((0, +)) in Y-79 and ARPE-19 cell lines. Quantitative real-time PCR was also performed to determine the relative expression of FR-α, SMVT, and B ((0, +)) at mRNA level in these cell lines. Quantitative uptake of [(3)H] Folic acid, [(3)H] Biotin, and [(14)C] Arginine was studied in Y-79 and ARPE-19 cells. Further, saturation kinetics of [(3)H] Folic acid, [(3)H] Biotin, and [(14)C] Arginine was performed in the presence of various concentrations of respective cold substrates to determine the kinetic parameters (K(m) and V(max)) in Y-79 and ARPE-19 cells.

RESULTS

PCR analysis had confirmed the existence of FR-α, SMVT, and B ((0, +)) in Y-79 and ARPE-19 cells. Quantitative real-time PCR analysis had shown significantly higher expression of FR-α, SMVT, and B ((0, +)) mRNA levels in Y-79 cells compared with ARPE-19 cells. Quantitative uptake of [(3)H] Folic acid, [(3)H] Biotin, and [(14)C] Arginine was found to be significantly higher in Y-79 cells relative to ARPE-19 cells. [(3)H] Folic acid uptake process followed saturation kinetics with apparent K(m) of 8.29 nM and V(max) of 393.47 fmol/min/mg protein in Y-79 cells and K(m) of 80.55 nM and V(max) of 491.86 fmol/min/mg protein in ARPE-19 cells. [(3)H] Biotin uptake process also displayed saturation kinetics with K(m) of 8.53 μM and V(max) of 14.12 pmol/min/mg protein in Y-79 cells and K(m) of 138.25 μM and V(max) of 38.85 pmol/min/mg protein in ARPE-19 cells. [(14)C] Arginine uptake process followed saturation kinetics with K(m) of 16.77 μM and V(max) of 348.27 pmol/min/mg protein in Y-79 cells and K(m) of 52.03 μM and V(max) of 379.21 pmol/min/mg protein in ARPE-19 cells.

CONCLUSIONS

This work demonstrated for the first time the higher expression and affinity of FR-α, SMVT, and B ((0, +)) mRNA levels in retinoblastoma (Y-79) cells compared with retinal pigment epithelial (ARPE-19) cells.

Loss of taste responds to high-dose biotin treatment

BACKGROUND AND OBJECTIVE

We saw 2 patients who lost their sense of taste, which was restored by pharmacologic doses of biotin. The key objective is to describe the 2 case reports and suggest a potential treatment for unexplained loss of taste.

METHODS AND DESIGN

The first patient was a 67-year-old woman who lost her sense of taste taking Juvenon, a dietary herbal supplement containing acyl-L-carnitine, lipoic acid, calcium, phosphorus, and biotin 300 μg per day. The second patient was a 60-year-old man who lost his sense of taste after a sleeve gastrectomy for obesity.

RESULTS

The first patient did not respond to 5 mg per day of biotin, but taste was restored with 10 mg of biotin per day. Biotin was prescribed based on information that lipoic acid bound to the biotin transporter. Baseline urine gave no evidence of a pre-existing biotin deficiency. The second patient did not have restoration of taste after taking biotin 5 mg per day for 7 weeks but did have taste restoration on biotin 20 mg per day. Neither subject had an abnormal biotinidase level.

CONCLUSIONS

Further research into the relationship of biotin to taste is clearly indicated. Loss of taste was very distressing and significantly altered the quality of life for both patients. Since biotin up to 40 mg per day has been shown to be safe, a therapeutic trial of pharmacologic doses of biotin should be considered as a potentially curative treatment in patients who present with a loss of taste that has no obvious cause.

New troglitazone derivatives devoid of PPARγ agonist activity display an increased antiproliferative effect in both hormone-dependent and hormone-independent breast cancer cell lines

Numerous recent studies indicate that most anticancer effects of PPARγ agonists like thiazolidinediones are the result of PPARγ-independent pathways. These conclusions were obtained by several approaches including the use of thiazolidinedione derivatives like Δ2-Troglitazone (Δ2-TGZ) that does not activate PPARγ. Since biotinylation has been proposed as a mechanism able to increase the specificity of drug delivery to cancer cells which could express a high level of vitamin receptor, a biotinylated derivative of Δ2-TGZ (bΔ2-TGZ) has been synthetized. In the present article, we have studied the in vitro effects of this molecule on both hormone-dependent (MCF-7) and hormone-independent (MDA-MB-231) breast cancer cells. In both cell lines, bΔ2-TGZ was more efficient than Δ2-TGZ to decrease cell viability. bΔ2-TGZ was also more potent than Δ2-TGZ to induce the proteasomal degradation of cyclin D1 in both cell lines and those of ERα in MCF-7 cells. However, in competition experiments, the presence of free biotin in the culture medium did not decrease the antiproliferative action of bΔ2-TGZ. Besides, other compounds that had no biotin but that were substituted at the same position of the phenolic group of the chromane moiety of Δ2-TGZ decreased cell viability similarly to bΔ2-TGZ. Hence, we concluded that the increased antiproliferative action of bΔ2-TGZ was not due to biotin itself but to the functionalization of the terminal hydroxyl group. This should be taken into account for the design of new thiazolidinedione derivatives able to affect not only hormone-dependent but also hormone-independent breast cancer cells in a PPARγ-independent pathway.

Vitreal pharmacokinetics of biotinylated ganciclovir: role of sodium-dependent multivitamin transporter expressed on retina

PURPOSE

The objective of this study was to investigate the role of sodium-dependent multiple vitamin transporter (SMVT) on Biotin-Ganciclovir (biotin-GCV) uptake on both human retinal pigmented epithelium cell line (ARPE-19) and rabbit retina. Study also aims to delineate the vitreal pharmacokinetics of biotin-GCV.

METHOD

ARPE-19 was employed to study the in vitro uptake experiments. New Zealand white albino rabbits were used to study in vivo retinal uptake and vitreal pharmacokinetics following intravitreal administration of biotin-GCV. In vitro uptake kinetics of [3H] biotin was determined at various initial concentrations. Competitive inhibition studies were conducted in the presence of unlabelled biotin, desthiobiotin, pantothenic acid, and lipoic acid. Various other uptake studies were performed to functionally characterize the transporter. To provide the molecular evidence of this transporter, Reverse Transcription-Polymerase Chain Reaction (RT-PCR) studies were also conducted. In vivo retinal/choroidal uptake studies were carried out with New Zealand albino rabbits. Unconscious animal ocular microdialysis studies were performed in order to evaluate intravitreal pharmacokinetics of GCV and Biotin-GCV.

RESULTS

Uptake of [3H] biotin into ARPE-19 was linear over 7 min, and found to be saturable with K(m) of 138.25 muM and Vmax of 38.85 pmol/min/mg protein. Both pantothenic acid and lipoic acid decreased significantly in uptake of biotin in the concentration-dependent manner. Uptake of biotin into ARPE-19 was found to be temperature, energy, and Na+ dependent but Cl(-)independent. Further, RT-PCR studies identified a band exhibiting presence of hSMVT on ARPE-19. Biotin-GCV is recognized by SMVT system present on the ARPE-19 and rabbit retina. Vitreal Pharmacokinetics profile reveals that most of the parameters were not significantly different for GCV and Biotin-GCV. However, use of Biotin-GCV may result in sustain levels of regenerated GCV in vitreous.

CONCLUSIONS

SMVT was identified and functionally characterized on ARPE-19 cells. Further, Biotin-GCV shares this transport system. Vitreal pharmacokinetics of the conjugate was determined in unconscious rabbit model.

Targeting cancer cells with biotin-dendrimer conjugates

Star-burst dendrimers represent a superior carrier platform for targeted drug delivery. Partially acetylated generation 5 (G5) polyamidoamine (PAMAM) dendrimer was conjugated with the targeting moiety (biotin) and the imaging moiety (fluoresceinisothiocyanate, FITC), and the resulting dendrimer-biotin conjugate was characterized by (1)H NMR, UV-vis spectrum. As revealed by flow cytometry and confocal microscopy, the bifunctional conjugate (dendrimer-biotin-FITC) exhibited much higher cellular uptake into HeLa cells than the conjugate without biotin. The uptake was energy-dependent, dose-dependent, and could be effectively blocked by dendrimer-conjugated biotin. Our results indicated that the biocompatible biotin-dendrimer conjugate might be a promising nano-platform for cancer therapy and cancer diagnosis.

Folic acid transport via high affinity carrier-mediated system in human retinoblastoma cells

The primary objective of this study was to investigate the expression of a specialized carrier-mediated system for folic acid and to delineate its uptake mechanism and intracellular trafficking in a human derived retinoblastoma cell line (Y-79). Uptake of [3H]Folic acid was determined at various concentrations, pH, temperatures, in the absence of sodium and chloride ions and in the presence of structural analogs, methyltetrahydro folate (MTF) and methotrexate (MTX), vitamins, membrane transport and metabolic inhibitors to delineate the mechanism of uptake. Kinetics of uptake was studied in the presence of various intracellular regulatory pathways; protein kinases A and C (PKA and PKC), protein tyrosine kinase (PTK) and calcium-calmodulin modulators. Reverse transcription polymerase chain reaction (RT-PCR) was performed to confirm the molecular identity of folate carrier systems. The uptake was found to be linear up to 30min. The rate of uptake followed saturation kinetics with apparent Km of 8.29+/-0.74nM, 17.03+/-1.98nM and 563.23+/-115.2nM and Vmax of 393.47+/-9.33, 757.58+/-26.21 and 653.17+/-31.7fmol/(minmg) protein for folic acid, MTF and MTX, respectively. The process was chloride, temperature and energy dependent but sodium and pH independent; inhibited by the structural analogs MTF and MTX but not by structurally unrelated vitamins. Membrane transport inhibitors did not affect the uptake of [3H]Folic acid, however endocytic inhibitor, colchicine, significantly inhibited the [3H]Folic acid uptake indicating the involvement of receptor mediated endocytosis process. PKC, PTK and Ca2+/calmodulin pathways appeared to play important roles in the regulation of folic acid uptake. Molecular evidence of the presence of folate receptor (FR) precursor was identified by RT-PCR analysis. This research work demonstrated, for the first time, the functional and molecular existence of a specialized high affinity carrier-mediated system for folic acid uptake, in human retinoblastoma cells.

Novel approaches to retinal drug delivery

Research into treatment modalities affecting vision is rapidly progressing due to the high incidence of diseases such as diabetic macular edema, proliferative vitreoretinopathy, wet and dry age-related macular degeneration and cytomegalovirus retinitis. The unique anatomy and physiology of eye offers many challenges to developing effective retinal drug delivery systems. Historically, drugs have been administered to the eye as liquid drops instilled in the cul-de-sac. However retinal drug delivery is a challenging area. The transport of molecules between the vitreous/retina and systemic circulation is restricted by the blood-retinal barrier, which is made up of retinal pigment epithelium and endothelial cells of the retinal blood vessels. An increase in the understanding of drug absorption mechanisms into the retina from local and systemic administration has led to the development of various drug delivery systems, such as biodegradable and non-biodegradable implants, microspheres, nanoparticles and liposomes, gels and transporter-targeted prodrugs. Such diversity in approaches is an indication that there is still a need for an optimized noninvasive or minimally invasive drug delivery system to the eye. A number of large molecular weight compounds (i.e., oligonucleotides, RNA aptamers, peptides and monoclonal antibodies) have been and continue to be introduced as new therapeutic entities. However, for high molecular weight polar compounds the mechanism of epithelial transport is primarily through the tight junctions in the retinal pigment epithelium, as these agents undergo limited transcellular diffusion. Delivery and administration of these new drugs in a safe and effective manner is still a major challenge facing pharmaceutical scientists. In this review article, the authors discuss various drug delivery strategies, devices and challenges associated with drug delivery to the retina.

REVIEW: Vitamin transport and homeostasis in mammalian brain: focus on Vitamins B and E

With the application of genetic and molecular biology techniques, there has been substantial progress in understanding how vitamins are transferred across the mammalian blood-brain barrier and choroid plexus into brain and CSF and how vitamin homeostasis in brain is achieved. In most cases (with the exception of the sodium-dependent multivitamin transporter for biotin, pantothenic acid, and lipoic acid), the vitamins are transported by separate carriers through the blood-brain barrier or choroid plexus. Then the vitamins are accumulated by brain cells by separate, specialized systems. This review focuses on six vitamins (B(1), B(3), B(6), pantothenic acid, biotin, and E) and the newer genetic information including relevant 'knockdown' or 'knockout' models in mice and humans. The overall objective is to integrate this newer information with previous physiological and biochemical observations to achieve a better understanding of vitamin transport and homeostasis in brain. This is especially important in view of the newly described non-cofactor vitamin roles in brain (e.g. of B(1), B(3), B(6), and E) and the potential roles of vitamins in the therapy of brain disorders.