Pulmonary Absorption of Insulin Mediated by Tetradecyl-β-Maltoside and Dimethyl-β-Cyclodextrin

Purpose. To determine if tetradecyl--maltoside (TDM) and dimethyl--cyclodextrin (DMCD) enhance pulmonary absorption of insulin and to investigate if they do so by a reversible action on respiratory epithelium. Methods. Insulin formulated with saline, TDM, or DMCD was administered intratracheally, after laryngoscopic visualization, as a spray to anesthetized rats. Reversibility studies were conducted in intact rats by administering insulin at different time points after administration of TDM or DMCD. The pharmacodynamics and pharmacokinetics of insulin formulations were assessed by measuring plasma glucose and plasma insulin concentrations. Results. When insulin formulated with increasing concentrations (0.06-0.25%) of TDM or DMCD were administered to anesthetized rats, there was a concentration-dependent decrease in plasma glucose and increase in plasma insulin concentrations. The relative bioavailability of insulin formulations containing TDM was higher (0.34-0.84%) than that of formulations containing DMCD (0.19-0.48%). When insulin was administered 120 min after an agent was administered, in the reversibility study, no significant change in plasma glucose and insulin levels occurred compared to control. Conclusions. Both TDM and DMBCD enhance pulmonary absorption of insulin, with TDM being more efficacious than DMCD in enhancing insulin absorption via pulmonary administration. The effects of TDM and DMCD on respiratory epithelium are reversible, and the epithelium reestablishes its normal physiologic barrier 120 min after exposure to these agents.     

Characterization of the Oral Absorption of β-Lactam Antibiotics. I. Cephalosporins: Determination of Intrinsic Membrane Absorption Parameters in the Rat Intestine In Situ

The oral absorption of five cephalosporin antibiotics, cefaclor, cefadroxil, cefatrizine, cephalexin, and cephradine, has been studied using a single-pass intestinal perfusion technique in rats. Intrinsic membrane absorption parameters, unbiased by the presence of an aqueous permeability (diffusion or stagnant layer), have been calculated utilizing a boundary layer mathematical model. The resultant intrinsic membrane absorption parameters are consistent with a significant carrier-mediated, Michaelis-Menten-type kinetic mechanism and a small passive component in the jejunum. Cefaclor colon permeability is low and does not exhibit concentration dependent behavior. The measured carrier parameters (±SD) for the jejunal perfusions are as follows: cefaclor, J _max ^* = 21.3 (±4.0), K _m = 16.1 (±3.6), P _m ^* = 0, and P _c ^*= 1.32 (±0.07); cefadroxil, J _max ^* = 8.4 (±0.8), K _m = 5.9 (±0.8), P _m ^* = 0, and P _c ^* = 1.43 (±0.10); cephalexin, J _max ^* = 9.1 (±1.2), K _m = 7.2 (±1.2), P _m ^* = 0, and P _c ^* = 1.30 (±0.10); cefatrizine, J _max ^* = 0.73 (±0.19), K _m = 0.58 (±0.17), P _m ^* = 0.17 (±0.03), and P _c ^* = 1.25 (±0.10); and cephradine, J _max ^* = 1.57 (±0.84), K _m = 1.48 (±0.75), P _m ^* = 0.25 (±0.07), and P _c ^* = 1.06 (±0.08). The colon absorption parameter for cefaclor is P _m ^* = 0.36 (±0.06, where J _max ^* (mM) is the maximal flux, K _m (mM) is the Michaelis constant, P _m ^* is the passive membrane permeability, and P _c*is the carrier permeability. Aminocephalosporin perfusion results indicate that jejunal absorption in the rat occurs by a nonpassive process, with some of the compounds possessing a small but statistically significant passive component, while the colon permeability is low and follows a simple passive absorption mechanism.     

Solute Absorption from the Airways of the Isolated Rat Lung. IV. Mechanisms of Absorption of Fluorophore-Labeled Poly-α,β-[N(2-Hydroxyethyl)-DL-Aspartamide]

The pulmonary absorption kinetics of a single molecular weight distribution (MWD) of fluorophore-labeled poly-,-[N(2-hydroxyethyl)-DL-aspartamide] (F-PHEA), a hydrophilic and biocompatible synthetic polypeptide, were studied in the isolated, perfused rat lung (iprl) as functions of administered polymer concentration, dose, vehicle, and presence and absence of fluorophore. The MWD was characterized before and after absorption by measurement of weight- and number-averaged molecular weights (M _wand M _n, respectively) using high-performance gel-permeation chromatography. Values for M _w and M _n were 8.6 and 5.3 kD before, and 6.7 and 4.7 kD after, absorption into the perfusate; there was no significant metabolism and the MWD of the absorbed polymer was independent of both dose and sampling time over a 3-hr period. F-PHEA failed to show any evidence of aggregation in solution or changes in dose distribution within the airways as functions of increasing polymer concentration and dose. A concentration ranging study indicated the presence of a saturable, carrier-mediated transport process for F-PHEA with a maximum absorption rate, V _max, of approximately 180 µg or 0.027 µmol/hr. Coadministration of fluorophore-free PHEA was capable of depressing the absorption of F-PHEA. The transport process for F-PHEA appeared to have a molecular weight limit of about 7 kD for this hydrophilic polymer.     

Bile Salt–Fatty Acid Mixed Micelles as Nasal Absorption Promoters of Peptides. I. Effects of Ionic Strength,Adjuvant Composition,and Lipid Structure on the Nasal Absorption of [D-Arg2]Kyotorphin

Bile salts and synthetic surfactants have been used to promote nasal absorption of peptide drugs. Although a marked increase in nasal absorption has been achieved, this may not be adequate and the possibility of adjuvant-induced membrane toxicity exists. The present study employs a rat in situ nasal perfusion technique and mixed micelles between sodium glycocholate (NaGC) and various lipids as potential nasal absorption enhancers of a stable model dipeptide, [D-Arg²]kyotorphin. NaGC alone enhanced the nasal absorption of the dipeptide in a concentration-dependent manner. When linoleic acid was added to form mixed micelles with NaGC, the absorption was further enhanced (P < 0.01). The effect of mixed micelles was synergistic and much greater than with single adjuvants. Increasing ionic strength was found to increase the adjuvant activity of both NaGC and NaGC–lipid mixed micelles. Structure of the lipid component of the mixed micelles also affected the adjuvant potency. Oleic acid, a cis-unsaturated fatty acid, was more effective than elaidic acid, the trans-isomer, whereas cis-linoleic acid and trans-linolelaidic acid were equally effective ( = 0.05). Mixed micelles of mono-glycerides such as monoolein and monolinolein were also more effective than NaGC alone ( = 0.05). Micellar solubilization of these polar lipids by NaGC appears to be important for nasal absorption enhancement to occur. Reversal of the membrane permeability was also observed within approximately 20–40 min after removal of the adjuvants from the rat nasal cavity. These observations are similar to the effects of mixed micelles on the rectal mucosa and may involve the same mechanism.     

Differential Effects of Anionic,Cationic, Nonionic,and Physiologic Surfactants on the Dissociation, α-Chymotryptic Degradation,and Enteral Absorption of Insulin Hexamers

Various surfactants were investigated to compare their effects on insulin dissociation, -chymotryptic degradation, and rat enteral absorption. With a circular dichroism technique, sodium dodecyl sulfate (SDS) at a 5 mM concentration was found to completely dissociate procine-zinc insulin hexamers (0.5 mg/ml) into monomers. The catalytic activity of -chymotrypsin (0.5 µM) was also abolished by 5 mM SDS. When insulin was injected into the distal jejunum/ proximal ileum segment of the rat, 5 mM SDS greatly enhanced its pharmacological availability, from a negligible value to 2.8%. Being a cationic surfactant, hexadecyl trimethylammonium bromide (CTAB) also efficiently dissociated insulin hexamers at concentrations of 1–5 mM. However, extensive charge–charge interaction was observed below a CTAB concentration of 0.6 mM, leading to insulin precipitation at a molar CTAB:insulin ratio of 1:1 to 2:1. An -chymotryptic degradation study also revealed near-complete dissociation of insulin hexamers at 1 mM CTAB. Above 1 mM, however, CTAB acted as an enzyme inhibitor, most likely by means of charge repulsion. Enteral absorption studies showed a much lower pharmacological availability, only 0.29%. Nonionic surfactants such as Tween 80 and polyoxyethylene 9 lauryl ether were ineffective in dissociating insulin hexamers. Tween 80, at 5 mM, neither significantly altered the -chymotryptic degradation pattern nor enhanced the enteral absorption of insulin. The relative effectiveness of different species of bile salts on insulin hexamer dissociation appeared to be similar. Sodium glycocholate at a 30 mM concentration also significantly increased insulin pharmacological availability, to 2.3%. A morphological study did not reveal any significant alteration of the rat intestinal mucosal integrity after exposure to 5 mM SDS for 30 min. The results further emphasize the importance of the degree of insulin aggregation on its enteral transport.     

FTIR Characterization of the Secondary Structure of Insulin Encapsulated within Liposome

Aim:To determine the secondary structure of insulin encapsulated within liposome.Methods:The secondary structure of native insulin,mixture of insulin with liposome(sample I) and insulin encapsulated within liposome(sample Ⅱ) were determined by FTIR(Fourier Transform Infrared) spectroscopy.Results:The secondary structure of insulin encspsulated within liposome(Ⅱ） are similar with the secondary structure of native insulin.The difference existed in the amount of α-helices (from 36% of insulin to 31% of sample Ⅱ）and β-sheet(from 48% of insulin to 51% of sample Ⅱ).The content of α-helices and β-sheet of insulin in sample I was found to be very close to that of sample Ⅱ.The results revealed that the insulin encapsulated within liposome possibly spread on the surface of liposome,without inserting into the liposome membrane.Coclusion:The secondary structure of insulin encapsulated within liposome is similar with the native insulin.     

Absorption of 5′-Deoxy-5-fluorouridine from Colon

Rectally administered 5-deoxy-5-fluorouridine (dFUR) is active against transplanted dimethylhydrazine-induced colon tumor in rats. This study investigated the disposition of dFUR in normal non-tumor-bearing rats after rectal administration (350 or 700 mg/kg). An intravenous (iv) bolus injection of [5-³H]dFUR (28.2 µCi, 0.43 µg) was given 5 min after the rectal dose (700 mg/kg) to determine the dFUR clearance (CL). Blood and fecal samples were analyzed by high-pressure liquid chromatography and liquid scintillation. After the iv tracer dose, the CL was 19 ml/min/kg and the terminal half-life was 50 min. After a 700-mg/kg rectal dose, the terminal half-life was 430 min, the bioavailability was 30%, and the fraction of the dose recovered in 24-hr feces was 34%. After a 350-mg/kg dose, absorption was apparently not completed at 12 hr, as indicated by a lack of decline in blood concentration. The bioavailability of the 350-mg/kg dose exceeded 16%. The absorption of dFUR (700 mg/kg) from the colon was analyzed by the Loo–Riegelman method; the absorption half-life was 550 min. The terminal half-life after the rectal dose was much slower than that after the iv tracer dose but similar to the absorption half-life. These data indicate that dFUR was absorbed from the colon, that the absorption process was the rate-limiting step of its disposition after rectal administration, and that the slow absorption gave a sustained drug concentration in blood.     

Does the Intake of Ethanol Affect Oral Absorption of Poorly Soluble Drugs?

The presence of ethanol in gastrointestinal (GI) fluids may increase the solubility of poorly water-soluble drugs. This suggests that intake of ethanol with such compounds could result in increased drug absorption in the stomach and duodenum because of the greater concentration gradient present. To test this hypothesis, in vitro dissolution of 2 poorly soluble compounds (indomethacin and felodipine) was studied in simulated GI rat fluids in the presence or absence of ethanol. Results were used to predict plasma exposure of the compounds using the software PK-Sim. Finally, in vivo plasma exposure in rats was investigated after oral dosing followed by immediate administration of water or ethanol. Despite increased solubility in GI fluids in the presence of ethanol, simulations predicted a negligible effect on absorption. This was confirmed in the rat study where oral intake of indomethacin or felodipine with ethanol did not increase in vivo plasma exposure. A possible explanation for the lack of an effect may be that dilution, absorption, and transfer of ethanol upon arrival in the stomach resulted in intragastric and intraduodenal ethanol concentrations that did not reach the levels required to affect local solubility.     

Mechanism of Absorption of the Dipeptide α-Methyldopa-phe in Intestinal Brush-Border Membrane Vesicles

Pharmaceutical Research -     

A ‘Rule of Unity’ for Human Intestinal Absorption

The ability to predict the passive intestinal absorption of organic compounds can be a valuable tool in drug design. Although Lipinski's ‘rule of 5’ is commonly used for this purpose, it does not routinely give reliable results. An alternative ‘rule of unity’ is proposed to predict the absorption efficiency of orally administered drugs that are passively transported. The rule of unity based upon the theoretical principals that govern passive transport. The ‘rule of 5’ and the ‘rule of unity’ are compared using experimentally determined passive human intestinal absorption data for 155 drugs. Absorption values which are >50% of the dose are classified as well absorbed and absorption values which are ≤50% of the dose are classified as classified as poorly absorbed. Comparison of the two models using a receiver operating characteristic (ROC) plot and McNemar's test reveal striking differences in absorption predictability. The ‘rule of 5’ gives twice as many false predictions than the ‘rule of unity.’     

Percutaneous Absorption of 2′,3′-Dideoxyinosine in Rats

This study explored the topical route for administering of 2,3-dideoxyinosine (ddI), a nucleoside analog used for treating patients with acquired immunodeficiency syndrome. A dose of ddI (180 mg/kg) dispersed in ~1 g ointment base was applied, with or without occlusion, to the back of high follicular density (HFD) and low follicular density (LFD) rats. The systemic ddI clearance was determined using a concomitant administration of an intravenous tracer dose of [³H]ddI. At 24 hr, the experiment was terminated and skin sections at the application site were removed. After topical application, average plateau plasma levels of about 0.6 µg/ml were achieved within 1 to 2 hr and maintained for 24 hr. Occlusion gave a more uniform plasma profile but did not increase the bioavailability. The systemic bioavailability in HFD and LFD rats was about the same at 33%. In addition, a depot of about 16% of the dose was recovered by rinsing the application area and extracting the drug from the excised application site. These data indicate that about 50% of the dermal dose penetrated the skin barrier in 24 hr. The similar bioavailability in the HFD and LFD rats further suggests an unimportant role for the transfollicular absorption route for ddI. The effect of a mixture of penetration enhancers, Azone and propylene glycol (5:95), was studied in HFD rats. Coadministration of ddI with the enhancers did not increase the ddI bioavailability. However pre-treatment and coadministration with the enhancers significantly increased the bioavailability to 62%, which is a conservative estimate because the plasma drug level was still at a plateau when the experiment was terminated at 24 hr. In summary, the transdermal bioavailability of ddI exceeded the 15% oral bioavailability found in previous studies by more than 3 folds and was further increased by the pretreatment with absorption enhancers. These data indicate the topical route as an attractive administration route.     

Absorption of ranolazine in a rat model of in-situ single-pass intestine perfusion 

目的：研究不同浓度雷诺嗪在大鼠肠段的吸收特征,并比较Beagle犬经口给予国外雷诺嗪缓释片(参比制剂)和国产雷诺嗪缓释片(受试制剂)的药动学。方法：以酚红为标示物,采用在体单向灌流法进行大鼠肠吸收研究,高效液相法测定灌流液中雷诺嗪和酚红的浓度并计算吸收参数。采用双交叉实验设计,6只Beagle犬分别经口给予受试制剂和参比制剂,高效液相法测定血药浓度,BAPP 3.0程序处理药动学参数。结果：10～40 mg&#8226;L-1的雷诺嗪在大鼠各肠段的表观通透系数(Papp)、吸收速率常数(Ka)的差异均无显著性意义(P>0.05)。Beagle犬经口给予单剂量国产雷诺嗪缓释片的相对生物利用度为(104.5±30.1)%。结论：在10～40 mg&#8226;L-1内雷诺嗪在大鼠肠道的吸收机制以被动吸收为主。国产和进口雷诺嗪缓释片在Beagle犬体内的药时曲线相似,2种缓释制剂均无突释现象。     

Bile Salt–Fatty Acid Mixed Micelles as Nasal Absorption Promoters. III. Effects on Nasal Transport and Enzymatic Degradation of Acyclovir Prodrugs

The absorption enhancement and presystemic degradation kinetics of a homologous series of acyclovir 2-ester prodrugs were investigated in rats using the in situ nasal perfusion technique in the presence of bile salt–fatty acid mixed micells. In vitro incubation studies indicated that nasal perfusate containing a mixed micellar solution generated higher ester-cleaving activity than isotonic phosphate buffer washings. Inhibitor screening and substrate specificity studies demonstrated the enzyme to be most likely carboxylesterase rather than true cholinesterase. The extent of prodrug cleavage by the carboxylesterase appears to correlate well with the substrate li-pophilicity for esters with linear acyl chains. On the other hand, branching of the acyl side chain significantly retards acyclovir pro-drug breakdown. To estimate the nasal epithelial membrane and cytoplasmic damaging effect caused by sodium glycocholate (NaGC)–linoleic acid (15 mM:5 mM) mixed micelles, the release profiles of 5-nucleotidase (5-ND), lactate dehydrogenase (LDH), and carboxylesterase in the nasal perfusate were measured as a function of time. The results indicated that the activities of all three enzymes resulting from the mixed micellar solution appeared to be significantly higher than those caused by 15 mM NaGC alone. The apparent nasal absorption rate constants of acyclovir and its butyrate, valerate, pivalate, and hexanoate ester prodrugs in mixed micellar solutions containing an esterase inhibitor (1 mM phenylmethylsulfonyl fluoride) were individually calculated. Without an inhibitor, lengthening of the linear acyl side chain of the prodrug resulted in greatly accelerated degradation coupled with moderate absorption improvement. The solubilities and micellar binding constants of acyclovir prodrugs were also determined. Mixed micelles composed of 15 mM NaGC and 5 mM linoleic acid are incapable of incorporating these esters into the micellar cavity, although NaGC micelle alone can actively solubilize them in a concentration-dependent manner.     

Nasal Insulin Delivery with Dimethyl-β-Cyclodextrin as an Absorption Enhancer in Rabbits: Powder More Effective than Liquid Formulations

The nasal absorption of insulin using dimethyl--cyclodextrin (DMCD) as an absorption enhancer in rabbits was studied. The nasal administration of insulin/DMCD liquid formulations did not result in significant changes in serum insulin and blood glucose concentrations. In contrast, previous experiments in rats showed that the addition of DMCD to the liquid nasal formulation resulted in an almost-complete insulin absorption, with a concomitant strong hy-poglycaemic response. Apparently, the effect of the cyclodextrin derivative on insulin absorption differs between animal species following nasal delivery of insulin/DMCD solutions. On the other hand, nasal administration of the lyophilized insulin/DMCD powder dosage form in rabbits resulted in increased serum insulin concentrations, and a maximum decrease in blood glucose of about 50%. The absolute bioavailability of the nasally administered insulin/DMCD powder was 13 ± 4%, compared to 1 ± 1% for both an insulin/ DMCD liquid and an insulin/lactose powder formulation. It is concluded that insulin powder formulations with DMCD as an absorption enhancer are much more effective than liquid formulations.     

Solid-State Stability of Human Insulin I. Mechanism and the Effect of Water on the Kinetics of Degradation in Lyophiles from pH 2–5 Solutions

Purpose. Previous studies have established that in aqueous solution at low pH human insulin decomposition proceeds through a cyclic anhydride intermediate leading to the formation of both deamidated and covalent dimer products. This study examines the mechanism and kinetics of insulin degradation in the amorphous solid state (lyophilized powders) as a function of water content over a similar pH range. Methods. Solutions of 1.0 mg/mL insulin were adjusted to pH 2–5 using HC1, freeze-dried, then exposed to various relative humidities at 35°C. The water content within the powders was determined by Karl Fischer titration, and the concentrations of insulin and its degradation products were determined by HPLC. Degradation kinetics were determined by both the initial rates of product formation and insulin disappearance. Results. Semi-logarithmic plots of insulin remaining in lyophilized powders versus time were non-linear, asymptotically approaching non-zero apparent plateau values, mathematically describable by a reversible, first-order kinetic model. The rate of degradation of insulin in the solid state was observed to increase with decreasing apparent pH (pH) yielding, at any given water content, solid-state pH-rate profiles parallel to the solution pH-rate profile. This pH dependence could be accounted for in terms of the fraction of the insulin A21 carboxyl in its neutral form, with an apparent pKa of 4, independent of water content. Aniline trapping studies established that the mechanism of degradation of human insulin in lyophilized powders between pH 3–5 and at 35°C involves rate-limiting intramolecular nucleophilic attack of the Asn_A21 C-terminal carboxylic acid onto the side-chain amide carbonyl to form a reactive cyclic anhydride intermediate, which further reacts with either water or an N-terminal primary amino group (e.g., Phe_B1, and Gly_Al) of another insulin molecule to generate either deamidated insulin (Asp_A21) or an amide-linked covalent dimer (e.g., [Asp_A21-Phe_B1] or [Asp_A21-Gly_A1]), respectively. The rate of insulin degradation in lyophilized powders at 35°C increases with water content at levels of hydration well below the suspected glass transition and approaches the rate in solution at or near the water content (20–50%) required to induce a glass transition. Conclusions. The decomposition of human insulin in lyophilized powders between pH 3–5 is a water induced solid-state reaction accelerated by the plasticization effect of sorbed water. The formation of the cyclic anhydride intermediate at A21 occurs readily even in the glassy state, presumably due to the conformational flexibility of the A21 segment even under conditions in which the insulin molecules as a whole are largely immobile.     

Absorption of 2′, 3′-Dideoxyinosine from Lower Gastrointestinal Tract in Rats and Kinetic Evidence of Different Absorption Rates in Colon and Rectum

This study explored the rectal route of administration for 2,3-dideoxyinosine (ddI). Rats were given a rectal infusion of nonradiolabeled ddI (200 mg/kg in 0.7 mL saline) over 35 min along with an intravenous (iv) bolus injection of [8-³H]ddI (20 µCi, equivalent to 2.1 µg), which was used to calculate the absolute rectal bioavailability of ddI. Maximal plasma concentrations of rectally administered unlabeled ddI were 5.4 ± 2.2 µg/mL and were reached at the end of the infusion. The rectal bioavailability averaged 15.6 ± 4.4% (n = 9). The second aim of this study was to examine the kinetics of ddI absorption from the colorectal region. Analyses of the absorption rate–time profiles by the Loo–Riegelman and deconvolution methods showed biphasic absorption: a rapid phase during infusion and a slow phase postinfusion. These profiles were inconsistent with a mammillary model with absorption from a single site with one apparent rate constant. The model which gave the best fit for infusion and postinfusion data consisted of two different sites (colon and rectum) with different apparent absorption rate constants. The two sites were connected by a first-order transfer of drug solution from rectum to colon. The apparent absorption rate constant in the rectum was 39-fold higher than that in the colon. In conclusion, these results show absorption of ddI from the colorectal region and suggest the rectal route as an alternative to the oral route. The data further suggest different absorption sites in the colorectal region, with a more rapid absorption in the rectum than in the colon.     

Über kristallinisches Insulin

Ohne ZusammenfassungDie I. bis VIII. Mitteilung wurde veröffentlicht in diesem Archiv:173, 431, 439, 452 (1933);174, 118, 130 (1933);178, 270, 282, 396 (1935);182, 550 (1936).Angemeldet zum Reichspatent am 4. Mai 1936.