Regulation of LDL receptor expression by luminal sterol flux in CaCo-2 cells

Novel surface-engineered solid lipid nanoparticles of rosuvastatin calcium for low-density lipoprotein-receptor targeting: a Quality by Design-driven perspective

AIM

The present studies describe Quality by Design-oriented development and characterization of surface-engineered solid lipid nanoparticles (SLNs) of rosuvastatin calcium for low density lipoprotein-receptor targeting.

MATERIALS & METHODS

SLNs were systematically prepared employing Compritol 888 and Tween-80. Surface modification of SLNs was accomplished with Phospholipon 90G and DSPE-mPEG-2000 as the ligands for specific targeting to the low density lipoprotein-receptors. SLNs were evaluated for size, potential, entrapment, drug release performance and gastric stability. Also, the formulations were evaluated for cellular cytotoxicity, uptake and permeability, pharmacokinetic, pharmacodynamic and biochemical studies.

RESULTS & CONCLUSION

Overall, the studies ratified enhanced biopharmaceutical performance of the surface-engineered SLNs of rosuvastatin as a novel approach for the management of hyperlipidemia-like conditions.

Regulation of the proprotein convertase subtilisin/kexin type 9 in intestinal epithelial cells

Proprotein convertase subtilisin/kexin type 9 (PCSK9) posttranslationally promotes the degradation of the low-density lipoprotein receptor (LDLr) in hepatocytes and increases plasma LDL cholesterol. It is not clear, however, whether PCSK9 plays a role in the small intestine. Here, we characterized the patterns of variations of PCSK9 and LDLr in fully differentiated Caco-2/15 cells as a function of various potential effectors. Cholesterol (100 microM) solubilized in albumin or micelles significantly downregulated PCSK9 gene (30%, P<0.05) and protein expression (50%, P<0.05), surprisingly in concert with a decrease in LDLr protein levels (45%, P<0.05). Cells treated with 25-hydroxycholesterol (50 microM) also displayed significant reduction in PCSK9 gene (37%, P<0.01) and protein (75% P<0.001) expression, whereas LDLr showed a decrease at the gene (30%, P<0.05) and protein (57%, P<0.01) levels, respectively. The amounts of PCSK9 mRNA and protein in Caco-2/15 cells were associated to the regulation of 3-hydroxy-3-methylglutaryl-CoA reductase and sterol regulatory element binding protein-2 (SREBP-2) that can transcriptionally activate PCSK9 via sterol-regulatory elements located in its proximal promoter region. On the other hand, depletion of cholesterol content by hydroxypropyl-beta-cyclodextrin upregulated PCSK9 transcripts (20%, P<0.05) and protein mass (540%, P<0.001), in parallel with SREBP-2 protein levels. The addition of bile acids (BA) taurocholate and deoxycholate to the apical culture medium lowered PCSK9 gene expression (25%, P<0.01) and raised PCSK9 protein expression (30%, P<0.01), respectively, probably via the modulation of farnesoid X receptor. Furthermore, unconjugated and conjugated BA exhibited different effects on PCSK9 and LDLr. Altogether, these data indicate that intestinal PCSK9 is highly modulated by sterols and emphasize the distinct effects of BA species.

The human intestinal epithelial cell line Caco-2; pharmacological and pharmacokinetic applications

The gastrointestinal tract remains the most popular and acceptable route of administration for drugs. It offers the great advantage of convenience and many compounds are well absorbed and thereby provide acceptable plasma concentration-time profiles. Currently there is considerable interest from the pharmaceutical industry in development of cell culture systems that would mimic the intestinal mucosa in order to evaluate strategies for investigating and/or enhancing drug absorption. The intestinal epithelial cells of primary interest, from the standpoint of drug absorption and metabolism, are the villus cells, which are fully differentiated cells. An in vitro cell culture system consisting of a monolayer of viable, polarized and fully differentiated villus cells, similar to that found in the small intestine, would be a valuable tool in the study of drug and nutrient transport and metabolism. The Caco-2 cell line, which exhibits a well-differentiated brush border on the apical surface and tight junctions, and expresses typical small-intestinal microvillus hydrolases and nutrient transporters, has proven to be the most popular in vitro model (a) to rapidly assess the cellular permeability of potential drug candidates, (b) to elucidate pathways of drug transport (e.g., passive versus carrier mediated), (c) to assess formulation strategies designed to enhance membrane permeability, (d) to determine the optimal physicochemical characteristics for passive diffusion of drugs, and (e) to assess potential toxic effects of drug candidates or formulation components on this biological barrier. Since differentiated Caco-2 cells express various cytochrome P450 isoforms and phase II enzymes such as UDP-glucuronosyltransferases, sulfotransferases and glutathione-S-transferases, this model could also allow the study of presystemic drug metabolism.

Effect of chronic incubation of CaCo-2 cells with eicosapentaenoic acid (20:5, n-3) and oleic acid (18:1, n-9) on triacylglycerol production

CaCo-2 monolayers, cultured for 1 week after reaching confluence, were incubated with micellar solutions of fatty acids for up to 7 days. These conditioned cells were incubated acutely (5 h) with eicosapentaenoic acid and oleic acid, and the levels of cell-associated and secreted triacylglycerol were determined. With acute addition of oleic acid, both cell-associated and secreted triacylglycerol were decreased in cells chronically exposed to eicosapentaenoic acid. This effect was observed after as little as 2 days of chronic incubation with eicosapentaenoic acid. A further decrease was found when these cells were incubated acutely with eicosapentaenoic acid, regardless of which radioisotopes were used to label precursors in the incubation media. The secretion of both labelled and total triacylglycerol and apolipoprotein B was reduced approximately 50% in cells incubated chronically with eicosapentaenoic acid. The amounts of triacylglycerol and apolipoprotein B within the cells were not decreased by chronic exposure to eicosapentaenoic acid. Our data indicate that CaCo-2 cells chronically incubated with eicosapentaenoic acid secrete significantly less triacylglycerol than cells incubated chronically with oleic acid. When eicosapentaenoic acid was also included acutely, triacylglycerol secretion was reduced even more. We conclude that chronic exposure of eicosapentaenoic acid to this intestinal cell type reduces the rate of chylomicron secretion and may help explain the decreased postprandial lipaemia observed in humans taking fish oil supplements.