The effect of cyclodextrins on the stability of peptides in nasal enzymic systems

Complexation of exenatide and cyclodextrin: An approach for the stabilization and sustained release of exenatide in PLGA microsphere

The purpose of this study was to evaluate the effects of cyclodextrins (CyDs) to stabilize exnatide in the microencapsulation medium and influence on the pharmaceutical properties of exenatide loaded PLGA microsphere. Three CyDs interacted differently with exenatide by investigation using ultraviolet, fluorescence and circular dichroism spectroscopy. The binding affinities of CyDs to the hydrophobic tryptophan residues of exenatide increased in following order: α-CyD < β-CyD < γ-CyD. It was consistent with orders of W/O interface stabilizing and anti-adsorption effects. However, the stabilizing effect of β-CyD on liquid-state and freeze-drying of exenatide was greater than that of γ-CyD. The negative values of ΔH₀, ΔS₀, and ΔG₀ indicated that the exenatide-CyDs complex formation was a favorable exothermic and spontaneous processes that increased the order in the complex with structural rigidity. Furthermore, it was also shown that β-CyD improved encapsulation efficiency, in vitro extended release, and in vivo pharmacokinetic and pharmacodynamic properties of prepared PLGA microspheres.

Increased antibiotic efficacy and noninvasive monitoring of Staphylococcus epidermidis biofilms using per-cysteamine-substituted γ-cyclodextrin - A delivery effect validated by fluorescence microscopy

Limited and poor delivery of antibiotics is cited as one reason for the difficulty in treating antibiotic-resistant biofilms associated with chronic infections. We investigate the effectiveness of a positively charged, single isomer cyclodextrin derivative, octakis[6-(2-aminoethylthio)-6-deoxy]-γ-CD (γCys) to improve the delivery of antibiotics to biofilms. Using multiphoton laser scanning microscopy complemented with super-resolution fluorescence microscopy, we showed that γCys tagged with fluorescein (FITC) is uniformly distributed throughout live S. epidermidis biofilm cultures in vitro and results suggest it is localized extracellularly in the biofilm matrix. NMR spectroscopic data in aqueous solution confirm that γCys forms inclusion complexes with both the antibiotics oxacillin and rifampicin. Efficacy of γCys/antibiotic (oxacillin and rifampicin) was measured in the biofilms. While treatment with γCys/oxacillin had little improvement over oxacillin alone, γCys/rifampicin reduced the biofilm viability to background levels demonstrating a remarkable improvement over rifampicin alone. The strong synergistic effect for γCys/rifampicin is at this stage not clearly understood, but plausible explanations are related to increased solubility of rifampicin upon complexation and/or synergistic interference with components of the biofilm. The results demonstrate that designed cyclodextrin nanocarriers, like γCys, efficiently deliver suitable antibiotics to biofilms and that fluorescence microscopy offers a novel approach for mechanistic investigations.

Iron Oxide Nanoparticle Delivery of Peptides to the Brain: Reversal of Anxiety during Drug Withdrawal

Targeting neuropeptide systems is important for future advancements in treatment of neurological and psychiatric illnesses. However, many of the peptides and their analogs do not cross the blood-brain barrier (BBB) efficiently. Nanoparticles such as iron oxide can cross the BBB, and here we describe a novel method for the conjugation of a peptide antisauvagine-30 (ASV-30) to iron oxide nanoparticles. Previous research has shown that direct infusion of ASV-30 into the brain reduces anxiety-like behavior in animal models via actions on corticotropin releasing factor type 2 (CRF₂) receptors. Therefore, we tested whether iron oxide+ASV-30 complexes cross the BBB of rats and then determined whether iron oxide+ASV-30 nanoparticles are localized with CRF₂-expressing neurons. Finally we tested the hypothesis that systemic infusion of iron oxide+ASV-30 can reduce anxiety-like behavior. First we describe the synthesis and demonstrate the stability of iron oxide-peptide nanoparticle complexes. Next, nanoparticles (87.7 μg/kg Fe₂O₃) with or without ASV-30 (200 μg/kg, ip) were injected into male rats 30 min prior to transcardial perfusion and brain fixation for immunohistochemical analysis, or before testing on the elevated plus maze (EPM) in an amphetamine withdrawal model of anxiety. Systemically administered iron oxide+ASV-30 particles were present in the brain and associated with neurons, including those that express CRF₂ receptors, but did not localize with the iron storage protein ferritin. Furthermore, systemic administration of ironoxide+ASV-30 reduced amphetamine withdrawal-induced anxiety without affecting locomotion, suggesting that the anxiolytic effects of ASV-30 were preserved and the bioavailability of ASV-30 was sufficient. The findings demonstrate a novel approach to peptide delivery across the BBB and provide insight as to the neural distribution and efficacy of this nanotechnology.

Strategies to deliver peptide drugs to the brain

Neurological diseases such as neurodegeneration, pain, psychiatric disorders, stroke, and brain cancers would greatly benefit from the use of highly potent and specific peptide pharmaceuticals. Peptides are especially desirable because of their low inherent toxicity. The presence of the blood brain barrier (BBB), their short duration of action, and their need for parenteral administration limits their clinical use. However, over the past decade there have been significant advances in delivering peptides to the central nervous system. Angiopep peptides developed by Angiochem (Montreal, Canada), transferrin antibodies developed by ArmaGen (Santa Monica, USA), and cell penetrating peptides have all shown promise in delivering therapeutic peptides across the BBB after intravenous administration. Noninvasive methods of delivering peptides to the brain include the use of chitosan amphiphile nanoparticles for oral delivery and nose to brain strategies. The uptake of the chitosan amphiphile nanoparticles by the gastrointestinal epithelium is important for oral peptide delivery. Finally protecting peptides from plasma degradation is integral to the success of most of these peptide delivery strategies.

Nasal administration of a novel recombinant human parathyroid hormone (1-34) analog for the treatment of osteoporosis of ovariectomized rats

Synthetic human parathyroid (1-34) (hPTH (1-34)) is known to have the full biological activity of the holohormone for osteoporosis. This study is about designing a novel analog of hPTH (1-34) which is more suitable for intranasal administration. We likewise evaluate effectiveness of the nasal drops against osteoroporosis. Through fusion expression of combining gene, cell disruption, inclusion body washing, ethanol fraction precipitation, acid hydrolysis, and CM-52 ion exchange column chromatography Pro-Pro-[Arg¹¹] hPTH (1-34)-Pro-Pro was designed and produced. Nasal drops of Pro-Pro-[Arg¹¹] hPTH (1-34)-Pro-Pro were prepared and administrated to ovariectomized rats. After 12 weeks of raising, Bone Material Densities (BMD) of vertebrae were examined by Dual Energy X-Ray Absorptiometry (DEXA). The average BMD of these groups treated with nasal drops of the peptide were 28.0%-47.2% (P<0.01) higher than that of the group treated with normal saline (NS). The subchondral bone plates of the femoral heads were examined by scanning electron microscopy and a defined planar section was photographed. Percentage of the area of the cancellous bone was calculated. Percentages of the groups treated with nasal drops of the peptide increased; values were significantly different to that of the group treated with NS (P<0.001) and were even equivalent to that of normal groups. These results show that nasal drops of Pro-Pro-[Arg¹¹] hPTH (1-34)-Pro-Pro are effective against osteoporosis.

Nasal delivery of high molecular weight drugs

Nasal drug delivery may be used for either local or systemic effects. Low molecular weight drugs with are rapidly absorbed through nasal mucosa. The main reasons for this are the high permeability, fairly wide absorption area, porous and thin endothelial basement membrane of the nasal epithelium. Despite the many advantages of the nasal route, limitations such as the high molecular weight (HMW) of drugs may impede drug absorption through the nasal mucosa. Recent studies have focused particularly on the nasal application of HMW therapeutic agents such as peptide-protein drugs and vaccines intended for systemic effects. Due to their hydrophilic structure, the nasal bioavailability of peptide and protein drugs is normally less than 1%. Besides their weak mucosal membrane permeability and enzymatic degradation in nasal mucosa, these drugs are rapidly cleared from the nasal cavity after administration because of mucociliary clearance. There are many approaches for increasing the residence time of drug formulations in the nasal cavity resulting in enhanced drug absorption. In this review article, nasal route and transport mechanisms across the nasal mucosa will be briefly presented. In the second part, current studies regarding the nasal application of macromolecular drugs and vaccines with nano- and micro-particulate carrier systems will be summarised.

Intranasal Bioavailability of Insulin from Carbopol-Based Gel Spray in Rabbits

The purpose of this study was to investigate the nasal absorption of insulin from a carbopol-based nasal gel spray in rabbits. An insulin nasal gel was prepared by dispersing carbopol in distilled water, followed by the addition of insulin solution, then neutralization and viscosity adjustment. The nasal absorption of insulin from the gel, in conscious rabbits, was evaluated in comparison with absorption from an insulin solution. The absolute bioavailability of insulin from the nasal gel was studied using blood glucose level in comparison to intravenous injection. The insulin gel formulation produced a significant hypoglycemic response in rabbits, whereas no response was seen following administration of the insulin solution formulation. The bioavailability of insulin from the nasal gel formulation was 20.6% compared with the intravenous injection. The results of the present study suggest that the carbopol gel promotes the nasal absorption of insulin in rabbit model and due to its sprayability with commercially available spray pumps, could be considered as a preferred platform in nasal drug administration.

Effects of cucurbit[7]uril on enzymatic activity

The macrocyclic host cucurbit[7]uril exhibits highly specific inhibitory effects on the activity of proteases, which can be analyzed by a host-substrate complexation model.

Preparation of hydrophobic drugs cyclodextrin complex by lyophilization monophase solution

A novel method was evaluated for preparation of hydrophobic drugs cyclodextrin (CD) complex in this study. To obtain sterilized drug-CD complex lyophilized powder for injection or other purpose, the CD solution in water and the hydrophobic drug in tertiary butyl alcohol (TBA) were mixed in a suitable volume ratio, filtered through 0.22 microm millpores, and subsequently freeze-dried. A high drug concentration was obtained in the co-solvent due to the good solvency of TBA, which is miscible with water in any proportion, for hydrophobic drugs. Moreover, TBA could be removed rapidly and completely by freeze-drying because of its high vapor pressure and high melting point. The chemical stability of some labile active compounds was also improved in TBA-water co-solvent. Based on the data from differential scanning calormetry (DSC) and X-ray diffractometry (XRD), drug was amorphous in freeze-dried complex. The fourier transform infrared spectra indicated drug-CD interaction was present in drug-CD complex. An enhanced dissolution rate was also obtained in drug-CD complex. These results proved drug-CD complex had been formed after this technique. Thus, this report provided a simple, efficient, and economic technique for preparation of hydrophobic drugs CD complex, which may be useful practically in modifying hydrophobic drugs physicochemical properties and improving their absorption and pharmacodynamics.

Characterization of human nasal primary culture systems to investigate peptide metabolism

The objectives of this study were to validate and compare the suitability of different primary cell culture systems as models to investigate peptide enzymatic stability following nasal administration. The degradation kinetics of a model peptide, leucine enkephalin (Tyr-Gly-Gly-Phe-Leu, Leu-Enk), was determined in four nasal cell culture systems: immersion, air-liquid interface, sequential monolayer-suspension, floating collagen. The influence of enzyme inhibitors (bestatin, puromycin) and Leu-Enk metabolite analogs (Tyr-Gly, Phe-Leu, Tyr-Gly-Gly, Gly-Phe-Leu) on the Leu-Enk degradation profile was also investigated. The disappearance of Leu-Enk in all the cell culture systems followed first order kinetics. The specific activity in the cell culture systems followed the rank: sequential monolayer-suspension (32.60 microM min(-1) mg(-1)) >air-liquid interface (15.19 microM min(-1) mg(-1)) >immersion (11.49 microM min(-1) mg(-1)) >floating collagen (4.57 microM min(-1) mg(-1)). At equimolar concentration, bestatin had a higher inhibitory effect than puromycin. The rate of hydrolysis of Leu-Enk was reduced significantly by co-incubation with Leu-Enk metabolite analogs. This study showed that immersion, sequential monolayer-suspension and air-liquid interface culture systems may be potentially suitable for further studies on peptide enzymatic stability following nasal administration.

Nasal absorption enhancement strategies for therapeutic peptides: an in vitro study using cultured human nasal epithelium

This study examined the potential usefulness of cultured human nasal epithelium as a model to investigate nasal absorption enhancement strategies for therapeutic peptides. The transport of leucine enkephalin (Leu-Enk) in the presence of bestatin and puromycin, respectively and various combinations of these protease inhibitors with absorption enhancers capable of inhibiting proteases or protecting peptides against protease degradation (glycocholate, dimethyl-beta-cyclodextrin (DM beta CD)) was studied. Epithelial membrane perturbation, protein leakage, bestatin/puromycin absorption and rebound aminopeptidase activity were used as toxicological end-points. The combination of puromycin with glycocholate or DM beta CD resulted in a higher absorption enhancement of Leu-Enk (9-14%) than when the absorption enhancers were combined with bestatin (1-3%) or when the inhibitors were used alone (2-4%). The higher absorption enhancement resulting from the combination of protease inhibitors with absorption enhancers caused a significant reduction of epithelial resistance and increased sodium fluorescein transport. Although only puromycin permeated the human nasal epithelium, both protease inhibitors induced a significant rebound aminopeptidase activity (25-61%), which can be associated with protein leakage (21-46%). This study highlighted (i) the potential usefulness of cultured human nasal epithelium as a model to study nasal absorption enhancement of therapeutic peptides; (ii) further studies using in vivo nasal models are required to ascertain whether the membrane perturbation and cytotoxicity observed with various combinations of the protease inhibitors and absorption enhancers really raise safety concerns.

Quantitative relationship between the chemical structure of antisense nucleosides and their capacity to interact with cyclomalto-octaose

The interaction of twelve 8-substituted-2'-deoxyadenosine and seventeen 5-substituted-2'-deoxyuridine derivatives (antisense nucleosides) with cyclomalto-octaose (GCD) was determined by charge-transfer chromatography and the relative strength of the interaction was calculated. The majority of antisense nucleosides (14 deoxyuridine and 11 deoxyadenosine derivatives) interacted with GCD, which probably led to inclusion complex formation. Stepwise regression analysis proved that the strength of interaction was related to the length of the apolar alkyl chain of substituents and the bulkiness of the nucleoside ring structure. The effect of double or triple bonds in the chain was negligible.

Simultaneous interaction of steroidal drugs with gamma- and hydroxypropyl-beta-cyclodextrin studied by charge-transfer chromatography

The simultaneous interaction of 15 steroidal drugs with tau-cyclodextrin (tauCD) and hydroxypropyl-beta-CD (HPbetaCD) was determined by charge transfer chromatography and the relative strength of interaction was calculated for each drug-tauCD-HPbetaCD ternary complex. The mixture of CDs interacted with each steroidal drugs decreasing the lipophilicity of the guest molecules. The chemical structure of steroidal drugs markedly influenced their capacity to interact with the mixture of CDs, the more lipophilic compounds formed stronger complexes with CDs. In the overwhelming majority of cases the stability of drug-tauCD-HPbetaCD system was higher than those of binary (drug-tauCD and drug-HPbetaCD) system indicating the probability of ternary complex formation. The data indicated that the ternary complex formation has to be taken into consideration in pharmaceutical formulations containing more than one type of CD or CD derivatives.

Intranasal insulin delivery and therapy

Intranasal insulin delivery has been widely investigated as an alternative to subcutaneous injection for the treatment of diabetes. The pharmacokinetic profile of intranasal insulin is similar to that obtained by intravenous injection and, in contrast to subcutaneous insulin delivery, bears close resemblance to the 'pulsatile' pattern of endogenous insulin secretion during meal-times. The literature suggests that intranasal insulin therapy has considerable potential for controlling post-prandial hyperglycaemia in the treatment of both IDDM and NIDDM. However, effective insulin absorption via the nasal route is unlikely without employing the help of absorption enhancers or promoters which are able to modulate nasal epithelial permeability to insulin and/or prolong the residence time of the drug formulation in the nasal cavity. This article discusses the structure and function of the nasal cavity, the barriers which prevent nasal insulin absorption and through the use of absorption enhancers or promoters methods by which these barriers may be overcome.

Efficacy, safety and mechanism of cyclodextrins as absorption enhancers in nasal delivery of peptide and protein drugs

Cyclodextrins are used in nasal drug delivery as absorption enhancing compounds to increase the intranasal bioavailability of peptide and protein drugs. The most effective cyclodextrins in animal experiments are the methylated derivatives, dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin, which are active at low concentrations ranging between 2% and 5%. However, large species differences between rats, rabbits and humans exist for the nasal absorption enhancement by cyclodextrins. Based on toxicological studies of the local effects of cyclodextrins on the nasal mucosa dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin are considered safe nasal absorption enhancers. Their effects were quite similar to controls (physiological saline), but smaller than those of the preservative benzalkonium chloride in histological and ciliary beat frequency studies. In these studies, and in a study of the release of marker compounds after nasal administration, methylated beta-cyclodextrins were less toxic than sodium glycocholate, sodium taurodihydrofusidate, laureth-9 and L-alpha-phosphatidylcholine. Systemic toxicity after nasal cyclodextrin administration is not expected, because very low doses of cyclodextrins are administered and only very small amounts are absorbed. The mechanism of action of cyclodextrins may be explained by their interaction with the nasal epithelial membranes and their ability to transiently open tight junctions.

Protection afforded by maltosyl-beta-cyclodextrin against alpha-chymotrypsin-catalyzed hydrolysis of a luteinizing hormone-releasing hormone agonist, buserelin acetate

PURPOSE

The present study addresses how maltosyl-beta-cyclodextrin (G2-beta-CyD) impacts upon the alpha-chymotrypsin-catalyzed hydrolysis of buserelin acetate, an agonist of luteinizing hormone-releasing hormone with emphasis upon the direct effect of G2-beta-CyD on the activity of the protease.

METHODS

Kinetic and solubility studies were performed in isotonic phosphate buffer (pH 7.4) at 25 degrees C and 37 degrees C. The interaction of alpha-chymotrypsin with G2-beta-CyD in the buffer solution was examined by differential scanning calorimetry.

RESULTS

G2-beta-CyD decelerated the alpha-chymotrypsin-catalyzed hydrolysis of buserelin acetate to give the 1-3 tripeptide and the 4-9 hexapeptide fragments. This deceleration can be explained solely by a non-productive encounter between a complex of the substrate with G2-beta-CyD and the protease at relatively low CyD concentrations, while the direct inhibitory effect of G2-beta-CyD on the proteolytic activity made a considerable contribution to the overall deceleration of the hydrolysis at higher CyD concentrations. Calorimetric studies indicate the presence of intermediate states in the thermal unfolding of alpha-chymotrypsin, simultaneously accompanied by the autolysis. By contrast, a two-state thermal unfolding of alpha-chymotrypsin was observed in the presence of G2-beta-CyD, suggesting reduced proteolytic activity upon binding to G2-beta-CyD.

CONCLUSIONS

These results suggest that G2-beta-CyD at higher concentrations inhibits the proteolytic action of alpha-chymotrypsin through direct interaction with the protease, as well as through the formation of a non-productive complex with the substrate.

Charge-transfer chromatographic study of the complex formation of some steroidal drugs with carboxymethyl-gamma-cyclodextrin

The interaction between 15 steroidal drugs and carboxymethyl-gamma-cyclodextrin (CM-gamma-CD) was studied by reversed-phase charge-transfer thin-layer chromatography and the relative strength of interaction was calculated. CM-gamma-CD formed inclusion complexes with each compound, the complex always being less hydrophobic than the uncomplexed drug. The inclusion-forming capacity of drugs differed considerably depending on their chemical structures. The linear correlation between the hydrophobicity and specific hydrophobic surface area of anticancer drugs indicated that they can be considered as a homologous series of compounds, although their chemical structures are different. Hydrophobicity of drugs significantly influenced the strength of interaction, indicating the involvement of hydrophobic forces in the binding of drugs to CM-gamma-CD. The marked influence of CM-gamma-CD on the hydrophobicity of drugs suggests that this interaction may modify the biological properties (adsorption, uptake, half-life, etc.) of drug-CM-gamma-CD complexes drug, resulting in modified efficacy.

Pharmaceutical applications of cyclodextrins. 2. In vivo drug delivery

The objective of this Review is to summarize and critique recent findings and applications of both unmodified and modified cyclodextrins for in vivo drug delivery. This review focuses on the use of cyclodextrins for parenteral, oral, ophthalmic, and nasal drug delivery. Other routes including dermal, rectal, and pulmonary delivery are also briefly addressed. This Review primarily focuses on newer findings concerning cyclodextrin derivatives which are likely to receive regulatory acceptance due to improved aqueous solubility and safety profiles as compared to the unmodified cyclodextrins. Many of the applications reviewed involve the use of hydroxypropyl-beta-cyclodextrins (HP-beta-CDs) and sulfobutylether-beta-cyclodextrins (SBE-beta-CDs) which show promise of greater safety while maintaining the ability to form inclusion complexes. The advantages and limitations of HP-beta-CD, SBE-beta-CD, and other cyclodextrins are addressed.

Presystemic bradykinin metabolism in sheep and rat nasal homogenates

Bradykinin (BK) and its fragments BK(1-8), BK(1-7), and BK(1-5) were incubated with sheep nasal homogenates to investigate the extent of peptide metabolism within the nasal mucosa. The products for both bradykinin and BK(1-8) degradation were found to be BK(1-7) and BK(1-5). BK(1-7) was metabolized to BK(1-5) alone. The patterns of degradation suggest that the Pro7-Phe8 bond of bradykinin was hydrolyzed first, then BK(1-7) was further hydrolyzed to form BK(1-5). The metabolism of bradykinin in rat nasal homogenates and plasma was also investigated. BK(1-5) was the only metabolite measurable in the rat nasal homogenates, likely due to the activity of an endopeptidase. The reduction in the bradykinin degradation rate resulting from the inhibition of angiotensin converting enzyme (ACE) or carboxypeptidase N indicates that these enzymes participate in mucosal bradykinin metabolism to some degree. In comparison, the products of bradykinin hydrolysis in rat plasma were found to be BK(1-8), BK(1-7), and BK(1-5). These results indicate that the enzyme populations or/and activities vary significantly between different species and between different tissues within the same species. Although significant aminopeptidase activities were detected in the sheep nasal homogenates, bradykinin was not affected by their presence, since the N-terminal sequence of bradykinin is not susceptible to hydrolysis by most aminopeptidases.

Bradykinin metabolism in rat and sheep nasal secretions

The nasal secretions are the first barrier that nasally administered drugs encounter. Therefore, the characterization of peptide metabolism in the nasal secretions is essential to predict nasal peptide bioavailability. Metabolism of bradykinin was measured in rat and sheep nasal secretions to estimate the extent of degradation of nasally administered peptide compounds. A single-pass, in situ nasal perfusion technique was employed to collect secretions for the investigation of peptide metabolism in rat nasal secretions. The protein content, mucin concentration, and degree of bradykinin metabolism in perfusate aliquots collected over a 2-h period showed that the early perfusate fractions contained most of the active secretory materials. Evidence of continuous mucus secretion and plasma extravasation was found in the nasal perfusate throughout the entire collection period. Sheep nasal secretions were collected with a cotton pledget inserted into the nasal cavity. Bradykinin and its fragments were degraded by carboxypeptidases and endopeptidases present in both rat and sheep nasal secretions. Hydrolysis of Phe5-Ser6 was the major metabolism pathway of bradykinin in the rat nasal perfusate, whereas in sheep nasal secretions, hydrolysis of the Pro7-Phe8 and Phe8-Arg9 bonds also occurred. Evidence of angiotensin converting enzyme, carboxypeptide N, and aminopeptidase activity was identified in the rat nasal perfusate with specific substrates and inhibitors. The activity of these and other enzymes in the nasal secretions may significantly limit the bioavailability of nasally administered peptide drugs prior to their exposure to the nasal mucosal tissues.

The effect of cyclodextrins on the stability of peptides in nasal enzymic systems

Leucine enkephalin (YGGFL) undergoes rapid degradation in sheep nasal mucosa to yield GGFL which is further degraded to FL. The activity of the nasal mucosal homogenate against YGGFL and GGFL (t1/2 12 and 7 min) was significantly greater than that observed with a nasal wash fluid (t1/2 40 and 13 min). The effect of cyclodextrins on the rate of degradation of FGG and YGGFL by leucine aminopeptidase (LAP) and of GGF by carboxypeptidase A (CPA) was monitored. Little effect was observed with FGG (with LAP) but the half-life of YGGFL (with LAP) was extended from approximately 44 min to approximately 75 min in the presence of a 25-fold excess of beta-cyclodextrin. The stability of GGF (with CPA) was also enhanced; an effect was observable with a 5-fold excess of cyclodextrin and the half-life could be extended by 40-75%. An equation is presented which allows the estimation of the concentration of free peptide in the peptide-cyclodextrin solutions.