Microscopic FT-IR/DSC combined system used to investigate the thermotropic behavior of lipid in porcine stratum corneum after pretreatment with skin penetration enhancers

A finasteride patch for the treatment of androgenetic alopecia: A study of promoting permeability strategy using synthetic novel O-acylmenthols combined with ion-pair

Currently, finasteride (FIN) is approved to treat androgenetic alopecia only orally, and the application of FIN in transdermal drug delivery system (TDDS) has introduced a new approach for treating the disease. This study was aimed to develop a FIN transdermal patch for the treatment of androgenetic alopecia（AGA） by combing ion-pair and O-acylmenthols (AM) as chemical permeation enhancers (CPEs). The formulation of patch was optimized though single-factor investigation and Box-Behnken design. The pharmacokinetics and androgenetic alopecia pharmacodynamics of the patch were evaluated. Additionally, the permeability enhancement mechanisms of ion-pair and AMs were explored at both the patch and skin levels. The effects of ion-pair and AMs on the patch were characterized by rheology study, FTIR, and molecular docking, and the effects on the skin were assessed through ATR-FTIR, Raman study, DSC, CLSM and molecular dynamics. The finalized formulation of FIN patches was consisted of 5 % (w/w) synthetic FIN-CA (Citric Acid), 6 % MT-C6 as CPEs, 25-AAOH as a pressure-sensitive adhesive (PSA), with a patch thickness of 80 ± 5 μm. The final Q24 h is 78.22 ± 5.18 μg/cm2. Based on the high FIN permeability, the pharmacokinetic analysis revealed that the FIN patch group exhibited a slower absorption rate (tmax = 7.3 ± 2.7 h), lower peak plasma concentration and slower metabolic rate (t1/2 = 6.2 ± 0.8 h, MRT0-t = 26.0 ± 7.8 h) compared to the oral group. Moreover, the FIN patch also demonstrated the same effect as the oral group in promoting hair growth in AGA mice. The results indicated that both FIN-CA and AMs could enhance the fluidity of the PSA and weaken the interaction between FIN-CA and PSA, thereby promoting the release of the FIN from the patch. The interaction sites on the skin for ion-pair and the four AMs were found in the stratum corneum (SC) of the skin, disrupting the tight arrangement of stratum corneum lipids. This study serves as a reference for the multi-pathway administration of FIN and the combination of ion-pair with AMs to enhance drug permeation.

Advances in simultaneous DSC-FTIR microspectroscopy for rapid solid-state chemical stability studies: some dipeptide drugs as examples

The solid-state chemistry of drugs has seen growing importance in the pharmaceutical industry for the development of useful API (active pharmaceutical ingredients) of drugs and stable dosage forms. The stability of drugs in various solid dosage forms is an important issue because solid dosage forms are the most common pharmaceutical formulation in clinical use. In solid-state stability studies of drugs, an ideal accelerated method must not only be selected by different complicated methods, but must also detect the formation of degraded product. In this review article, an analytical technique combining differential scanning calorimetry and Fourier-transform infrared (DSC-FTIR) microspectroscopy simulates the accelerated stability test, and simultaneously detects the decomposed products in real time. The pharmaceutical dipeptides aspartame hemihydrate, lisinopril dihydrate, and enalapril maleate either with or without Eudragit E were used as testing examples. This one-step simultaneous DSC-FTIR technique for real-time detection of diketopiperazine (DKP) directly evidenced the dehydration process and DKP formation as an impurity common in pharmaceutical dipeptides. DKP formation in various dipeptides determined by different analytical methods had been collected and compiled. Although many analytical methods have been applied, the combined DSC-FTIR technique is an easy and fast analytical method which not only can simulate the accelerated drug stability testing but also at the same time enable to explore phase transformation as well as degradation due to thermal-related reactions. This technique offers quick and proper interpretations.

Correlation of the penetration enhancement with the influence of an alcohol/tocopheryl polyethylene glycol succinate (TPGS) cosolvent system on the molecular structure of the stratum corneum of nude mouse skin as examined by microscopic FTIR/DSC

Tocopheryl polyethylene glycol succinate (TPGS) is a water-soluble derivative of natural source of vitamin E, which possesses a dual nature of lipophilicity and hydrophilicity, similar to a surface-active agent. The penetration enhancement of estradiol by an ethanol and TPGS cosolvent system (EtOH/TPGS) has been confirmed. In this study, the correlation of the penetration enhancement with the influence of the EtOH/TPGS cosolvent system on biophysical changes of the stratum corneum (SC) as examined by Fourier transformation infrared spectrometry differential scanning calorimetry (FTIR/DSC) was investigated. Thermotropic changes in the asymmetrical and symmetrical C-H stretching of hydrocarbon chains of lipids, and amide I and II bands that characterize the protein structure of the SC treated with different concentrations of the EtOH/TPGS cosolvent were examined in this investigation. Results demonstrated that a strong correlation of the influence on biophysical changes of the SC treated with the EtOH/TPGS cosolvent system with the penetration enhancement of estradiol by the corresponding cosolvent system was not evident. It was concluded that the incorporation of TPGS in the cosolvent system seemed only to have insignificantly modified the structural features of the SC. It was not obvious that the penetrant had encountered these modifications resulting in an improvement in the penetration of estradiol by TPGS.

Fourier transform IR attenuated total reflectance spectroscopy studies of cysteine-induced changes in secondary conformations of bovine serum albumin after UV-B irradiation

Fourier transform IR spectroscopy equipped with attenuated total reflection was used to investigate the cysteine-induced alteration of the protein secondary structure of bovine serum albumin (BSA) in aqueous solution before and after UV-B irradiation. Several amino acids were also studied. The results indicate the unchanged IR spectra of BSA coincubated with amino acids, except cysteine, did not change after 72-h UV-B irradiation. There was no difference in the IR spectrum of the unirradiated BSA coincubated with cysteine. A shoulder at 1620 cm(-1) attributed to the intermolecular beta-sheet structure was observed for the IR spectrum of BSA coincubated with cysteine after 72-h UV-B irradiation. Moreover, the peak intensity at 1303 cm(-1) that is due the alpha-helix structure was reduced, but the peak intensity at 1247 cm(-1) corresponding to beta-sheet structures was increased. Longer UV-B exposure for a BSA solution coincubated with cysteine changed the BSA solution from clear to viscous to gel form in which a transparent gel and another white gel were simultaneously observed. A gradual IR spectral alteration was found for BSA coincubated with cysteine and subjected to increased UV-B irradiation. The longer UV-B irradiation yielded increased intensity at 1620 cm(-1). The second-derivative IR peaks at 1655, 1631, and 1548 cm(-1) were shifted to 1650, 1620, and 1544 cm(-1), respectively, by the increase of UV-B irradiation, suggesting a progressive transformation from an alpha-helix to an intermolecular beta-sheet structure for BSA coincubated with cysteine. This strongly implies that longer UV-B exposure time for the BSA solution in the presence of cysteine did alter the protein secondary structures of BSA more, thus inducing gel formation by protein aggregation.

Reaction kinetics of solid-state cyclization of enalapril maleate investigated by isothermal FT-IR microscopic system

To investigate the reaction kinetics of the solid-state degradation process of enalapril maleate, a Fourier transform infrared microspectroscope equipped with thermal analyzer (thermal FT-IR microscopic system) was used. The isothermal stability study was conducted at 120-130 degrees C for 1-2 h and changes in the three-dimensional plots of the IR spectra of enalapril maleate with respect to heating time were observed. The study indicates that the bands at 1649, 1728, and 1751 cm(-1) assigned to intact enalapril maleate gradually reduced in peak intensity with heating time. However, the peak intensities at 1672 and 1738 cm(-1) (due to enalapril diketopiperazine (DKP) formation) and at 3250 cm(-1) (corresponding to water formation) gradually increased with heating time. The solid-state diketopiperazine formation and the degradation process of enalapril maleate via intramolecular cyclization were found to be simultaneous. The isothermal decomposition curves were sigmoidal and were characterized by induction and acceleration periods, indicating the presence of autocatalytic solid-state decompositions. Moreover, the power-law equation (n = 1/4) was found to provide the best fit to the kinetics of decomposition. This isothermal FT-IR microscopic system was easily used to investigate the degradation of enalapril maleate and the concomitant formation of DKP. The solid-state reaction of enalapril maleate required an activation energy of 195+/-12 kJ/mol to undergo the processes of decomposition and intramolecular cyclization.

UV-B-induced secondary conformational changes in lens alpha-crystallin

The changes in turbidity and protein secondary structure of alpha-crystallin after a 72 h UV-B (302 nm) irradiation in aqueous solution have been determined by UV spectrophotometry and Fourier transform infrared (FT-IR) microspectroscopy with reflection mode. The relative transmission of alpha-crystallin aqueous solution gradually decreases with the exposure time, indicating that the transparent alpha-crystallin aqueous solution becomes opaque with prolonged UV-B irradiation. The turbidity induced by UV-B shows first-order kinetics due to the photo-induced aggregation. The modification of the secondary structure of the alpha-crystallin molecule in aqueous solution caused by this aggregation might enhance the alpha-helix and beta-turn structures from 8.14 to 14.92% and from 24.46 to 35.54%, respectively; reduce the beta-sheet structure from 60.20% to 43.77%; and leave the random coil structure almost unaltered. The secondary conformation of alpha-crystallin changes gradually but evidently with its increase of turbidity during UV-B exposure.