葛根素固体自微乳制剂的制备及其质量评价

目的:制备葛根素固体自微乳制剂,并评价其质量。方法:通过改变处方组成、稀释倍数、介质、温度等考察影响自微乳化效率和粒径大小的因素,采用激光粒度分析仪测定成乳后粒径,并通过透射电镜对成乳后的微乳进行形态学观察;通过3个月的加速试验考察葛根素固体自微乳的稳定性。结果:处方组成、温度等因素对自微乳化效率和粒径大小都有影响;稀释倍数、分散介质等在一定范围内影响不大。葛根素固体自微乳成乳后为圆球形,平均粒径为30nm。结论:葛根素固体自微乳粒径小,稳定性好。     

9-硝基喜树碱自微乳化给药系统研究

以Maisine 35-1为油相,Cremophor EL、Labrasol为表面活性剂,Transcutol P为助表面活性剂,制得9-硝基喜树碱(1)负电荷自微乳化制剂;在此基础上加入油胺作为正电荷剂可得1正电荷自微乳化制剂.用HPLC法测定大鼠体内1含量.结果表明含药的负、正电荷自微乳化制剂经水稀释10倍时,粒径分别为(24.7±7.9)和(25.0±8.3)nm,电位分别为-(4.8±0.5)和(2.4±0.9)mV.大鼠分别以6mg/kg的剂量灌胃给予1溶液和负、正电荷自微乳化制剂后,三者的Cmax分别为(93.8±72.8)、(176.4±93.4)和(128.9±49.1)ng/ml;AUC分别为(127.6±51.6)、(331.9±261.1)和(595.1±42.0)ng·ml-1·h;MRT分别为(1.6±0.9)、(1.2±0.6)和(4.3±2.4)h.正、负电荷自微乳化制剂的相对生物利用度分别是溶液的4.7和2.6倍,表明前者提高药物的口服吸收作用优于后者(P＜0.05).     

ESR和CLSM技术用于促渗剂作用机制及亲水性大分子跨鼻黏膜转运途径的研究

采用电子自旋共振(ESR)和共聚焦激光扫描显微镜(CLSM)技术研究促渗剂作用机制及促渗剂对亲水性大分子跨鼻黏膜转运途径的影响。比较重组水蛭素-2(rHV2)与促渗剂联合鼻腔用药前后大鼠的生物利用度；采用以5-噁唑烷氮氧自由基硬脂酸、16-噁唑烷氮氧自由基硬脂酸和马来酰亚胺作为自旋标记物的电子自旋共振技术，考察促渗剂对家兔鼻黏膜脂质和蛋白的影响；采用共聚焦显微镜光学切片结合荧光探针标记技术探讨促渗剂对大鼠鼻黏膜上皮细胞骨架肌动蛋白的作用，同时观察在各种促渗剂作用下rHV2的转运途径。壳聚糖(chitosan,CS),羟丙基-β-环糊精(hydroxyl-propyl-beta-cyclodextrin,HP-β-CD),甘草酸单胺盐(ammonium glycyrrhizinate,AMGZ)均能显著改善rHV2的鼻黏膜吸收；CS主要通过细胞旁路途径增加rHV2鼻黏膜转运，这一结果可能与其对细胞骨架肌动蛋白微丝的影响从而打开细胞间紧密连接有关；HP-β-CD可同时增加跨细胞和经细胞旁路两种途径的转运，可能与其既能改变膜质流动性又能影响膜蛋白构象的特性有关；AMGZ主要增加亲水性大分子跨细胞途径的转运，实验观察到其对膜蛋白有作用，但未观察到其对膜质的作用，确切的机制尚有待研究。本实验可为促渗剂及亲水大分子跨细胞膜转运途径的研究提供借鉴。     

三七总皂苷油包水微乳的处方筛选及体内外评价

筛选口服油包水(W/O)微乳处方以提高三七总皂苷(panax notoginsenoside，PNS)中人参皂苷Rb₁的体内肠吸收，分别采用大鼠体内肠吸收、脂质体和平行人工膜(parallel artificial membrane permeability assay，PAMPA)等模型分别研究微乳的体内药代动力学及体外对膜流动性和药物膜转运性质的影响。主要以磷脂/乙醇(SP/EtOH)为表面活性剂，与PNS水溶液(400 mg·mL^-1)和不同油相分别制备11个W/O微乳处方。多数微乳处方可提高药物的大鼠体内肠吸收，其吸收促进作用除与所含表面活性剂有关外，不同油相的选用也会产生一定影响，其吸收促进作用大小为月桂酸甘油酯≈肉蔻豆酸异丙脂>棕榈酸异丙脂>棕榈酸异辛酯。长链(>C₁₄)脂肪酸酯的吸收促进作用低于中链脂肪酸酯(C₈~C₁₄)。多数微乳处方可不同程度的提高脂质体的膜流动性。PAMPA研究中，稀释后微乳(D-ME)中药物的有效透过系数(P_e)多数高于PNS对照溶液，表明微乳中的组分可以提高药物的膜透过能力，稀释前微乳(ME)的P_e与大鼠体内肠吸收具有相对较好的直线相关性(r=0.774 0)。W/O微乳可以促进人参皂苷Rb₁的肠吸收，吸收促进作用与其提高生物膜流动性有一定关系。PAMPA可以尝试引入制剂处方研究(如吸收促进剂等)的某些领域中。     

靛玉红自乳化释药系统的跨膜转运及其在犬体内的药动学过程

目的:考察靛玉红自乳化释药系统的跨膜转运及其在犬体内的药动学过程。方法:采用高效液相色谱法测定靛玉红的含量;通过缚管翻转肠囊实验、离体肠黏膜透过实验和Caco-2细胞透过实验考察靛玉红及其自乳化释药系统的跨膜转运作用;同时,考察靛玉红自乳化释药系统在Beagle犬体内的药动学过程。结果:靛玉红自乳化释药系统的转运速度和表观渗透系数均明显高于靛玉红(P<0.05);以靛玉红市售片为对照,靛玉红自乳化释药系统在犬体内的相对生物利用度为(162.05±15.68)%。结论:自乳化释药系统可以促进靛玉红的跨膜转运,并可提高其口服生物利用度。     

尼莫地平自微乳化颗粒的研制及质量评价

摘 要 目的:制备尼莫地平固体自微乳化颗粒,并对其进行质量评价。方法: 通过综合考察不同处方比例的成型率、重分散性及体外溶出度,筛选尼莫地平固体自微乳化颗粒的最佳处方,并对最佳处方的粒径、Zeta电位、溶出度进行考察,同时用差示扫描量热法（DSC）、X-衍射考察尼莫地平在制剂存在状态。结果:最佳处方为尼莫地平-油酸乙酯-Tween 80-PEG400-糊精-乳糖-甘露醇的质量比为0.03∶0.2∶0.55∶0.25∶1∶1∶2,其自微乳化后平均粒径(28.8±0.71) nm,30 min溶出度达80.7%。结论:尼莫地平固体自微乳化颗粒制备简单,质量稳定,可提高药物溶出度。     

通过体外自乳化性能及体内药代动力学评价优化葛根素自乳化制剂

本文将水不溶性药物葛根素制备成自乳化制剂。测定了葛根素在不同油相及表面活性剂的溶解度，结果表明葛根素在油酸、Tween 80中的溶解度较好，1，2-丙二醇不但能增加药物的溶解度，而且能够提高自乳化能力。以油酸为油相，Tween 80为表面活性剂，1，2-丙二醇为助表面活性剂，配制一系列混合物，通过绘制三元相图得到自乳化区，考察不同自乳化处方的自乳化性质，采用激光粒度散射仪测定乳化后粒子大小，在体外评价基础上选择较好的3个处方进行比格犬体内药动学研究，比较不同处方自乳化制剂在比格犬体内的生物利用度包括药代动力学参数Cmax， Tmax， AUC0-t。结果表明处方2和处方3的AUC0-t值［(5.201±0.511) ng·mL^-1·h， (5.174±0.498) ng·mL^-1·h］和Cmax值［(1.524±0.125) ng·mL^-1， (1.513±0.157) ng·mL^-1］显著高于处方4［(3.013±0.623) ng·mL^-1·h， (0.939±0.089) ng·mL^-1］，通过体内研究结果获得较优处方为油酸(17.5%)、Tween 80(34.5%)、1，2-丙二醇(34.5%)。自乳化释药系统提供了水不溶性药物口服给药的新途径。     

尼索地平自微乳制剂稳定性的影响因素

目的：研究影响尼索地平自微乳制剂稳定性的因素。方法：以温度、稀释倍数、稀释递质种类、絮凝剂及反絮凝剂为主要影响因素，采用测定微乳粒子大小及其分布、Zeta电位进行综合评价。结果：本自微乳制剂对稀释倍数、稀释递质种类、絮凝剂及反絮凝剂敏感，但对温度不敏感，且粒径稳定。结论：本自微乳制剂质量稳定，但稀释后的微乳稳定性下降。     

罗红霉素自乳化制剂的制备及体外评价

目的制备罗红霉素自乳化制剂,并初步探讨其体外质量评价。方法通过测定药物在不同油相中的溶解度,确定油相与各种乳化剂(助乳化剂)的配伍对自乳化效率的影响;通过绘制伪三相图,筛选罗红霉素自乳化制剂的最佳处方;考察该制剂水稀释液的微乳外观、粒径和乳化时间。结果自乳化制剂处方为罗红霉素:肉豆蔻酸异丙酯:Tween80(甘油)为3∶3∶4,该制剂稀释50倍后仍为澄清透明液体,粒径约75nm,呈正态分布,乳化时间约10min。结论罗红霉素自乳化制剂制备简单,质量稳定,能显著提高药物的溶解度。     

芍药苷抑制肌球蛋白轻链激酶缓解肠上皮细胞屏障功能紊乱

目的考察芍药苷对肿瘤坏死因子α(TNF-α)所致Caco-2模拟的肠上皮细胞屏障功能紊乱的保护作用及相关机制。方法体外培养Caco-2细胞,采用MTT法研究芍药苷对Caco-2细胞活性的影响;建立TNF-α所致Caco-2细胞的屏障功能紊乱模型,研究芍药苷对屏障功能的影响。结果TNF-α孵育Caco-2细胞,明显降低了Caco-2细胞屏障的跨膜电阻,肌球蛋白轻链激酶(MLCK)表达明显增加,紧密连接蛋白occludin和ZO-1表达明显下降,提示Caco-2细胞屏障功能紊乱;芍药苷明显逆转TNF-α所造成的Caco-2细胞屏障功能紊乱,即抑制MLCK的表达,促进紧密连接蛋白occludin和ZO-1的表达,芍药苷的这种保护细胞屏障的作用可被MLCK的小分子干扰RNA(small interfering RNA,siRNA)所阻断。结论芍药苷可明显缓解TNF-α诱导的肠上皮屏障功能紊乱,该作用与降低MLCK,促进紧密连接蛋白表达有关。     

Effect of self-microemulsifying drug delivery systems containing Labrasol on tight junctions in Caco-2 cells

The aim of this study was to investigate the effect of two novel self-microemulsifying drug delivery systems (SMEDDS) containing Labrasol with different dilutions on tight junctions. Changes in barrier properties of Caco-2 cell monolayers, including transepithelial electrical resistance (TEER) and permeability to the paracellular marker, i.e., mannitol, were assessed in response to dilutions and surfactants contents within formulations. The cytotoxicity of SMEDDS and the effect of surfactants on Caco-2 cells were evaluated by the MTT. Changes in subcellular localization of the tight junction proteins, ZO-1 and F-actin, were examined by confocal laser scanning microscopy. Results demonstrated that negatively charged SMEDDS with different dilutions had no effect on the TEER, but significantly increased the permeability of mannitol. In contrast, the positively charged formulation showed a dilution-dependent reduction in TEER. A corresponding increase in mannitol permeability of up to 29.4-fold to 64.7-fold greater than the control was also observed across the monolayer. Labrasol with the concentration of 0.1 and 1% was shown to increase the permeability of mannitol by 4.6-fold and 33.8-fold, respectively. The mechanism of opening of tight junctions was found to involve F-actin-related changes and redistribution of ZO-1.     

Disruption of Epithelial Tight Junctions by Yeast Enhances the Paracellular Delivery of a Model Protein

Purpose The aim of this study was to investigate the effect of heat-killed yeast cells on the integrity of epithelial tight junctions in vitro.Methods Changes in barrier potential of Caco-2 cell monolayers were assessed by transepithelial electrical resistance (TEER) measurements and by an increasing permeability to a marker protein, horse–radish peroxidase (HRP). Visualisation of tight junction disruption was carried out directly through electron microscopy and indirectly through fluorescence confocal microscopy and immunoblotting of the tight junction-associated proteins zonula occludens ZO-1, occludin and actin.Results Yeast cells opened tight junctions in a reversible dose- and time-dependent manner, as shown by a decrease in TEER and an increase in HRP permeability. These changes to barrier potential were shown not to be due to cytotoxic effects but due to modulation of the tight junctions. ZO-1, actin and occludin proteins were demonstrated to be involved in yeast-induced tight junction opening through the use of confocal microscopy and western blotting. Electron microscopy confirmed a direct opening of tight junctions after application of yeast.Conclusion Yeast modulated epithelial tight junctions in a reversible manner by contraction of the actin cytoskeleton and shift of ZO-1 and occludin tight junction proteins from the membrane to cytoskeletal areas of the cell.     

乙醇对肠上皮细胞紧密连接蛋白ZO-1表达的影响

目的探讨乙醇引起肠黏膜屏障的破坏以及这种破坏机制是否与紧密连接蛋白ZO-1相关。方法培养人结肠腺癌细胞株Caco-2,分别设正常对照组:不加刺激物及干预因素;实验组:加入不同体积分数(1%、2.5%、5%、7.5%、10%)乙醇分别刺激不同时间(0～3h),四甲基偶氮唑盐(MTT)比色法检测细胞生存率;测定跨上皮电阻(TEER)和荧光黄的透过量反映肠上皮细胞单层通透性;选定体积分数5%乙醇作为实验浓度,应用蛋白印迹法检测紧密连接蛋白ZO-1表达的动态变化。结果体积分数为5%的乙醇未影响到细胞的生存率。不同浓度乙醇作用20min后,细胞单层通透性增加,60min达高峰,TEER下降,荧光黄透过增加,以体积分数5%乙醇最明显。蛋白印迹法检测体积分数5%乙醇在1h内致Caco-2细胞表达ZO-1减少。结论乙醇可引起肠上皮黏膜屏障破坏,其机制可能和紧密连接蛋白ZO-1的破坏相关。     

Cyclodextrins in Nasal Delivery of Low-Molecular-Weight Heparins: In Vivo and in Vitro Studies

PURPOSE: To test the hypothesis that cyclodextrins reversibly enhance nasal absorption of low-molecular-weight heparins (LMWHs) and to investigate the mechanisms by which cyclodextrins enhance LMWH absorption via the nose. METHODS: Absorption of LMWHs was studied by measuring plasma anti-factor Xa activity after nasal administration of various LMWH formulations to anesthetized rats. In vivo reversibility studies were performed to investigate if the effects of cyclodextrins are reversible and diminish with time. The absorption-enhancing mechanisms of cyclodextrins were investigated in cell culture model. The transport of enoxaparin and mannitol, changes in transepithelial electrical resistance (TEER), and distribution of tight junction protein ZO-1 were investigated. RESULTS: Formulations containing 5% dimethyl-beta-cyclodextrin (DMbetaCD) produced the highest increase in the bioavailability of LMWH preparations tested. In vivo reversibility studies with 5% DMbetaCD showed that the effect of the absorption enhancer at the site of administration diminished with time. Transport studies using 16HBE14o(-) cells demonstrated that the increase in the permeability of enoxaparin and mannitol, reduction in TEER, and the changes in the tight junction protein ZO-1 distribution produced by 5% DMbetaCD were much greater than those produced by beta-cyclodextrin (betaCD) or hydroxyl-propyl-beta-cyclodextrin (HPbetaCD). CONCLUSIONS: Of the cyclodextrins tested, DMbetaCD was the most efficacious in enhancing absorption of LMWHs both in vivo and in vitro. The study also suggests that cyclodextrins enhance nasal drug absorption by opening of cell-cell tight junctions.     

Mechanism of action of ZOT-derived peptide AT-1002, a tight junction regulator and absorption enhancer

Tight junctions (TJs) are intercellular structures that control paracellular permeability and epithelial polarity. It is now accepted that TJs are highly dynamic structures that are regulated in response to exogenous and endogenous stimuli. Here, we provide details on the mechanism of action of AT-1002, the active domain of Vibrio cholerae's second toxin, zonula occludens toxin (ZOT). AT-1002, a hexamer peptide, caused the redistribution of ZO-1 away from cell junctions as seen by fluorescence microscopy. AT-1002 also activated src and mitogen activated protein (MAP) kinase pathways, increased ZO-1 tyrosine phosphorylation, and rearrangement of actin filaments. Functionally, AT-1002 caused a reversible reduction in transepithelial electrical resistance (TEER) and an increase in lucifer yellow permeability in Caco-2 cell monolayers. In vivo, co-administration of salmon calcitonin with 1 mg of AT-1002 resulted in a 5.2-fold increase in AUC over the control group. Our findings provide a mechanistic explanation for AT-1002-induced tight junction disassembly, and demonstrate that AT-1002 can be used for delivery of other agents in vivo.     

Evaluation of human nasal RPMI 2650 cells grown at an air-liquid interface as a model for nasal drug transport studies

This study tests the hypothesis that human nasal RPMI 2650 cells grown at an air-liquid interface is a feasible model for drug transport studies via the nasal route. RPMI 2650 cells were cultured in Eagle's minimal essential medium (MEM) at both air-liquid and liquid-liquid interfaces. For each culture regimen, monolayer integrity was tested by measuring the transepithelial resistance (TEER) as well as the transport of paracellular and transcellular markers across the monolayer. The expression of tight junction proteins-differentiation markers-in cells of the different monolayers was studied by western blot analysis and confocal microscopy. The highest TEER values (192 +/- 3 Omega . cm2) were observed for RPMI 2650 cells seeded onto collagen-coated permeable polytetrafluoroethylene inserts and grown at an air-liquid interface for 10 days; a seeding density of 4 x 10(5)/cm2 generated and maintained a cell monolayer with suitable barrier properties at days 9-12. Microscopic examination showed that RPMI 2650 cells grown on filter inserts formed a fully confluent monolayer. The apparent permeability coefficients of the paracellular marker, [14C] mannitol, and the transcellular marker, [3H] propranolol, were 5.07 +/- 0.01 x 10(-6) cm/s and 16.1 +/- 0.1 x 10(-6) cm/s, respectively. Western blot analysis indicated the presence of four tight junction proteins: ZO-1, occludin, claudin-1 and E-cadherin; and the quantities of ZO-1, occludin, and E-cadherin were significantly higher in cells grown at an air-liquid interface than in cells grown at a liquid-liquid interface. Confocal microscopic studies showed ZO-1, F-actin, occludin and claudin-1 proteins at cell-cell contacts and revealed significant differences in the distributions and densities of ZO-1 protein in cells grown at the two types of interface. The data indicate that RPMI 2650 cells grown at an air-liquid interface form polarized monolayers with the cells interconnected by tight junction proteins. This human nasal cell line model could provide a useful tool for in vitro screening of nasal drug candidates.     

Indication of transcytotic movement of insulin across human bronchial epithelial cells

This study was performed to evaluate insulin permeability across human bronchial epithelial cell lines and investigate if insulin is transported via the paracellular or transcellular pathway. The movement of insulin across two bronchial epithelial cells, 16HBE14o- and Calu-3, was studied in the presence or absence of octylmaltoside. Mannitol and propanolol have been used as paracellular and transcellular marker, respectively, and transepithelial electrical resistance (TEER) was determined to investigate the tight junctional integrity of the monolayers. The possible endocytotic mechanism of insulin across these two cell lines was studied by confocal laser scanning microscopy after incubating the cells with fluorescent-labeled insulin. The TEER values for both cell monolayers were >400 Omega cm2 at confluency. There was a decrease in the TEER values when octylmaltoside was added to the apical side of transwells. Similarly, the apparent permeability coefficient (P(app)) values of insulin, mannitol and propanolol, showed an increase with the rise in the concentration of octylmaltoside. In the absence of octylmaltoside, the P(app) values for insulin and the markers were in the following order: propanolol > mannitol > insulin. Confocal microscopic studies revealed that the uptake of insulin by the bronchial epithelial cells perhaps occurs via translocation across the cell. The data presented in this study demonstrate that insulin perhaps moves across the bronchial cells via both paracellular and transcellular pathways.     

Specific modulation of airway epithelial tight junctions by apical application of an occludin peptide

Tight junctions are directly involved in regulating the passage of ions and macromolecules (gate functions) in epithelial and endothelial cells. The modulation of these gate functions to transiently regulate the paracellular permeability of large solutes and ions could increase the delivery of pharmacological agents or gene transfer vectors. To reduce the inflammatory responses caused by tight junction-regulating agents, alternative strategies directly targeting specific tight junction proteins could prove to be less toxic to airway epithelia. The apical delivery of peptides corresponding to the first extracellular loop of occludin to transiently modulate apical paracellular flux has been demonstrated in intestinal epithelia. We hypothesized that apical application of these occludin peptides could similarly modulate tight junction permeability in airway epithelia. Thus, we investigated the effects of apically applied occludin peptide on the paracellular permeability of molecular tracers and viral vectors in well differentiated human airway epithelial cells. The effects of occludin peptide on cellular toxicity, tight junction protein expression and localization, and membrane integrity were also assessed. Our data showed that apically applied occludin peptide significantly reduced transepithelial resistance in airway epithelia and altered tight junction permeability in a concentration-dependent manner. These alterations enhanced the paracellular flux of dextrans as well as gene transfer vectors. The occludin peptide redistributed occludin but did not alter the expression or distribution of ZO-1, claudin-1, or claudin-4. These data suggest that specific targeting of occludin could be a better-suited alternative strategy for tight junction modulation in airway epithelial cells compared with current agents that modulate tight junctions.     

Indication of transcytotic movement of insulin across human bronchial epithelial cells

This study was performed to evaluate insulin permeability across human bronchial epithelial cell lines and investigate if insulin is transported via the paracellular or transcellular pathway. The movement of insulin across two bronchial epithelial cells, 16HBE14o- and Calu-3, was studied in the presence or absence of octylmaltoside. Mannitol and propanolol have been used as paracellular and transcellular marker, respectively, and transepithelial electrical resistance (TEER) was determined to investigate the tight junctional integrity of the monolayers. The possible endocytotic mechanism of insulin across these two cell lines was studied by confocal laser scanning microscopy after incubating the cells with fluorescent-labeled insulin. The TEER values for both cell monolayers were >400 Ω cm² at confluency. There was a decrease in the TEER values when octylmaltoside was added to the apical side of transwells. Similarly, the apparent permeability coefficient (P_app) values of insulin, mannitol and propanolol, showed an increase with the rise in the concentration of octylmaltoside. In the absence of octylmaltoside, the P_app values for insulin and the markers were in the following order: propanolol > mannitol > insulin. Confocal microscopic studies revealed that the uptake of insulin by the bronchial epithelial cells perhaps occurs via translocation across the cell. The data presented in this study demonstrate that insulin perhaps moves across the bronchial cells via both paracellular and transcellular pathways.     

Dodecylphosphocholine-mediated enhancement of paracellular permeability and cytotoxicity in Caco-2 cell monolayers

The intestinal epithelium is a significant barrier for oral absorption of hydrophilic drugs because they cannot easily traverse the lipid bilayer of the cell membrane and their passage through the intercellular space (paracellular transport) is restricted by the tight junctions. In this report we show that dodecylphosphocholine (DPC) can improve the paracellular permeability of hydrophilic compounds across Caco-2 cell monolayers by modulating the tight junctions. The results show that the alkyl chain as well as the zwitterionic head group of DPC are required for its activity. DPC appears to act by modulating the permeability of tight junctions as evidenced by the fact that treatment of Caco-2 cell monolayers by this agent results in a decreased transepithelial electrical resistance (TEER), increased permeability of paracellular markers (e. g., mannitol) with no change in the permeability of the transcellular marker testosterone, and redistribution of the tight junction-associated protein ZO-1. The effect of DPC on Caco-2 cells (e.g., decrease in TEER) is reversible, and is not caused by gross cytotoxicity (as indicated by the MTT test) or by nonspecific disruption of the cell membrane (as indicated by only slight nuclear staining due to the nonpermeable DNA-specific dye propidium iodide). We propose in the present study a parameter, potency index, that allows comparison of various enhancers of paracellular transport in relation to their cytotoxicity. The potency index is a ratio between the IC(50) value (concentration at which 50% inhibition of control mitochondrial dehydrogenase activity occurs in the MTT test) and the EC(50) value (concentration at which TEER drops to 50% of its control (untreated) value). By this parameter, DPC is significantly safer than the commonly used absorption enhancer palmitoyl carnitine (PC), which has the potency index of approximately 1 (i.e., no separation between effective and toxic concentration).