Preparation and Evaluation of Self-nanoemulsifying Tablets of Carvedilol

The purpose of this study was to combine the advantages of self-nanoemulsifying drug delivery systems and tablets as a conventional dosage form emphasizing the excipients’ effect on the development of a new dosage form. Systems composed of HCO-40, Transcutol® HP, and medium-chain triglyceride were prepared. Essential properties of the prepared systems regarding carvedilol solubility, a model drug, and self-emulsification time were determined. In order to optimize self-nanoemulsifying drug delivery systems (SNEDDS), formulation dispersion–drug precipitation test was performed in the absence and presence of cellulosic polymers. Furthermore, SNEDDS was loaded onto liquisolid powders. P-glycoprotein (P-gp) activity of the selected SNEDDS was tested using HCT-116 cells. Carvedilol showed acceptable solubility in the selected excipients. It also demonstrated improvement in the stability upon dilution with aqueous media in the presence of cellulosic polymers. Use of granulated silicon dioxide improved the physical properties of liquisolid powders containing SNEDDS. It improved the compressibility of the selected powders and the tested SNEDDS showed marked P-gp inhibition activity. Prepared self-nanoemulsifying tablet produced acceptable properties of immediate-release dosage forms and expected to increase the bioavailability of carvedilol.     

Rates of Dissolution of Tolbutamide Tablets

An investigation was made of the pharmaceutical properties and the in vitro dissolution rates of 18 commercially available brands of tolbutamide tablets, all of which met the limits set by the Food and Drug Regulations for tablets sold in Canada.A marked variation in dissolution rates was found, which bore no relation to the official disintegration time. These wide variations in dissolution rate point to a need for (a) a comprehensive study of the in vivo effects of different tolbutamide tablets, and (b) an official test that sets limits for the rate of dissolution of tolbutamide tablets, in addition to the one that places limits on disintegration time.     

Development and Evaluation of Artemether Taste Masked Rapid Disintegrating Tablets with Improved Dissolution Using Solid Dispersion Technique

The purpose of this research was to mask the intensely bitter taste of artemether (ARM) and to formulate a rapid-disintegrating tablet (RDT) of the taste-masked drug. Taste masking was done by solid dispersion with mono amino glycyrrhyzinate pentahydrate (GLY) by solvent evaporation method. To characterize and formulate taste masked rapid disintegrating tablets (RDTs) of ARM, the 1:1M solid dispersion was selected based on bitterness score. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and X-ray powder diffraction (XRPD) were performed to identify the physicochemical interaction between drug and carrier, hence its effect on dissolution. RDTs were evaluated for weight variation, disintegration time, hardness and friability. In vitro drug release studies were performed for RDTs at pH 1.2 and 6.8. Bitterness score was evaluated using mini-column method and compared with gustatory sensation test. FTIR spectroscopy and DSC showed no interaction while XRPD showed amorphization of ARM in GLY solid dispersion. RDTs prepared using solid dispersion, (RDT3), showed faster disintegration (within 28 s) and complete bitter taste masking of ARM. In addition, RDT3 exhibited better dissolution profile at both pH 1.2 and 6.8, than RDTs prepared from pure ARM (RDT5). Taste evaluation of RDTs in human volunteers rated tasteless with a score of 0 to RDT3 and 3 to RDT5. Mini-column revealed that RDT5 showed increase in number of persons who sensed bitterness with increased amount of ARM release while RDT3 sensed no bitterness. Thus, results conclusively demonstrated successful masking of taste and rapid disintegration of the formulated tablets in the oral cavity with improved dissolution.     

Disintegration of Highly Soluble Immediate Release Tablets: A Surrogate for Dissolution

The purpose of the work was to investigate correlation between disintegration and dissolution for immediate release tablets containing a high solubility drug and to identify formulations where disintegration test, instead of the dissolution test, may be used as the acceptance criteria based on International Conference on Harmonization Q6A guidelines. A statistical design of experiments was used to study the effect of filler, binder, disintegrating agent, and tablet hardness on the disintegration and dissolution of verapamil hydrochloride tablets. All formulation variables, i.e., filler, binder, and disintegrating agent, were found to influence tablet dissolution and disintegration, with the filler and disintegrating agent exerting the most significant influence. Slower dissolution was observed with increasing disintegration time when either the filler or the disintegrating agent was kept constant. However, no direct corelationship was observed between the disintegration and dissolution across all formulations due to the interactions between different formulation components. Although all tablets containing sodium carboxymethyl cellulose as the disintegrating agent, disintegrated in less than 3 min, half of them failed to meet the US Pharmacopeia 30 dissolution criteria for the verapamil hydrochloride tablets highlighting the dependence of dissolution process on the formulation components other than the disintegrating agent. The results identified only one formulation as suitable for using the disintegration test, instead of the dissolution test, as drug product acceptance criteria and highlight the need for systematic studies before using the disintegration test, instead of the dissolution test as the drug acceptance criteria. The opinions expressed in this work are only of authors and do not necessarily reflect the policy and statements of the FDA.     

Investigating the Use of Liquisolid Compacts Technique to Minimize the Influence of pH Variations on Loratadine Release

Loratadine is a class II water-insoluble drug and its dissolution rate and, consequently, absorption are dependent on the gastrointestinal pH. The resulting very high variability in bioavailability and related inter- and intra-subject absorption variations present a major challenge that hinders the realization of an effective and uniform therapy. Among the several techniques that have been used to minimize pH dependency of dissolution rate, liquisolid compacts technique can be suggested as a promising solution. In this study, it was hypothesized that the formulation of loratadine using liquisolid compacts technique may reduce the effect of pH variation on the drug dissolution rate. Solubilities of loratadine in propylene glycol, Tween 80, and polyethylene glycol 400 were first measured and propylene glycol was selected as for producing the highest solubility among the tested solvents. Several liquisolid tablet formulations containing various ratios of drug: propylene glycol (5%, 10%, and 20% w/w) were prepared. The ratio of microcrystalline cellulose (carrier) to silica (coating powder material) was kept constant in all formulations. The dissolution behavior of loratadine from liquisolid compacts was investigated in several buffered media with different pH values (pH 1.2, 2.5, and 5). The results showed that the drug release rates produced by liquisolid compacts were significantly higher and less affected by pH variation compared with conventionally made (direct compression) and commercial (Clarityn) tablets. In conclusion, liquisolid compacts technique may be used as a tool to minimize the effects of pH variation on the dissolution rate of drugs with poor water solubility.     

Application of Carrier and Plasticizer to Improve the Dissolution and Bioavailability of Poorly Water-Soluble Baicalein by Hot Melt Extrusion

The objective of this study was to develop a suitable formulation for baicalein (a poorly water-soluble drug exhibiting high melting point) to prepare solid dispersions using hot melt extrusion (HME). Proper carriers and plasticizers were selected by calculating the Hansen solubility parameters, evaluating melting processing condition, and measuring the solubility of obtained melts. The characteristic of solid dispersions prepared by HME was evaluated. The dissolution performance of the extrudates was compared to the pure drug and the physical mixtures. Physicochemical properties of the extrudates were characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and Fourier transform infrared spectroscopy (FTIR). Relative bioavailability after oral administration in beagle dogs was assessed. As a result, Kollidon VA64 and Eudragit EPO were selected as two carriers; Cremophor RH was used as the plasticizer. The dissolution of all the extrudates was significantly improved. DSC and PXRD results suggested that baicalein in the extrudates was amorphous. FTIR spectroscopy revealed the interaction between drug and polymers. After oral administration, the relative bioavailability of solid dispersions with VA64 and EPO was comparative, about 2.4- and 2.9-fold greater compared to the pure drug, respectively.

Figure

Open in a separate windowᅟKEY WORDS: baicalein, carrier, high melting point, hot melt extrusion, plasticizer, solid dispersion     

Development and Validation of a Discriminative Dissolution Method for Atorvastatin Calcium Tablets using in vivo Data by LC and UV Methods

A dissolution method to analyze atorvastatin tablets using in vivo data for RP and test pilot (PB) was developed and validated. The appropriate conditions were determined after solubility tests using different media, and sink conditions were established. The conditions used were equipment paddle at 50 rpm and 900 mL of potassium phosphate buffer pH 6.0 as dissolution medium. In vivo release profiles were obtained from the bioequivalence study of RP and the generic candidate PB. The fraction of dose absorbed was calculated using the Loo–Riegelman method. It was necessary to use a scale factor of time similar to 6.0, to associate the values of absorbed fraction and dissolved fraction, obtaining an in vivo–in vitro correlation level A. The dissolution method to quantify the amount of drug dissolved was validated using high-performance liquid chromatography and ultraviolet spectrophotometry, and validated according to the USP protocol. The discriminative power of dissolution conditions was assessed using two different pilot batches of atorvastatin tablets (PA and PB) and RP. The dissolution test was validated and may be used as a discriminating method in quality control and in the development of the new formulations.     

The Development of Macrophage-Mediated Cell Therapy to Improve Skeletal Muscle Function after Injury

Skeletal muscle regeneration following acute injury is a multi-step process involving complex changes in tissue microenvironment. Macrophages (MPs) are one of the key cell types involved in orchestration and modulation of the repair process. Multiple studies highlight the essential role of MPs in the control of the myogenic program and inflammatory response during skeletal muscle regeneration. A variety of MP phenotypes have been identified and characterized in vitro as well as in vivo. As such, MPs hold great promise for cell-based therapies in the field of regenerative medicine. In this study we used bone-marrow derived in vitro LPS/IFN-y-induced M1 MPs to enhance functional muscle recovery after tourniquet-induced ischemia/reperfusion injury (TK-I/R). We detected a 15% improvement in specific tension and force normalized to mass after M1 (LPS/IFN-γ) MP transplantation 24 hours post-reperfusion. Interestingly, we found that M0 bone marrow-derived unpolarized MPs significantly impaired muscle function highlighting the complexity of temporally coordinated skeletal muscle regenerative program. Furthermore, we show that delivery of M1 (LPS/IFN-γ) MPs early in regeneration accelerates myofiber repair, decreases fibrotic tissue deposition and increases whole muscle IGF-I expression.     

Development and Evaluation of Avanafil Self-nanoemulsifying Drug Delivery System with Rapid Onset of Action and Enhanced Bioavailability

Utilization of lipid-based drug delivery systems has recently gained focus for drugs characterized by poor aqueous solubility. The improved aqueous solubility overcomes one of the main barriers that limit their bioavailability. The objective of this work was to improve the solubility and oral bioavailability of Avanafil (AVA), a recently approved second generation type 5 phospodiesterase inhibitor used for erectile dysfunction.AVA was formulated as self-nanoemulsifying drug delivery system (SNEDDS) utilizing various oils, surfactants, and cosurfactants. The solubility of AVA in various oils, surfactants, and cosurfactants was determined. Ternary phase diagram was constructed to identify stable nanoemulsion region. The prepared AVA loaded SNEDDS were assessed for optical clarity, droplet size, conductivity, and stability studies. In vitro drug release and in vivo pharmacokinetic parameters using animal model were also investigated. Results revealed that stable AVA (SNEDDS) were successfully developed with a droplet size range of 65 to 190 nm. SNEDDS composed of 25% dill oil, 55% Tween 80, and 20% propylene glycol successfully improved solubilization of AVA (over 80% within 30 min) vis-a-vis the powder AVA (35% within 30 min). In vivo pharmacokinetic showed a significant (P < 0.05) increase in C_max, reduction in T_max, and SNEDDS enhanced the bioavailability in the rats by 1.4-fold when compared with pure drug.Key words: avanafil, erectile dysfunction, dill oil, self-nanoemulsifying, SNEDDS     

Therapeutic Non-equivalence of Digoxin Tablets in United Kingdom: Correlation with Tablet Dissolution Rate

Seven types of digoxin 0·25 mg tablet in common use in the United Kingdom were administered to a total of 38 patients. Significant differences were found in the mean plasma digoxin levels and in the control of atrial fibrillation achieved with these brands. There was a close correlation between the dissolution rate of the tablets and the plasma digoxin levels. Measurement of in-vitro dissolution rate appears to be a valid method of ensuring that different tablets of digoxin are of equal efficacy. However, in some patients absorption of the drug is markedly sensitive to changes in dissolution rate and new pharmacopoeal standards should not be defined until very rapidly-dissolving formulations have been studied.     

Application of Pharmaceutical QbD for Enhancement of the Solubility and Dissolution of a Class II BCS Drug using Polymeric Surfactants and Crystallization Inhibitors: Development of Controlled-Release Tablets

The aim of this study was to apply quality by design (QbD) for pharmaceutical development of felodipine solid mixture (FSM) containing hydrophilic carriers and/or polymeric surfactants, for easier development of controlled-release tablets of felodipine. The material attributes, the process parameters (CPP), and the critical quality attributes of the FSMs were identified. Box–Behnken experimental design was applied to develop space design and determine the control space of FSMs that have maximum solubility, maximum dissolution, and ability to inhibit felodipine crystallization from supersaturated solution. Material attributes and CPP studied were the amount of hydroxypropyl methylcellulose (HPMC; X ₁), amount of polymeric surfactants Inutec®SP1 (X ₂), amount of Pluronic®F-127 (X ₃) and preparation techniques, physical mixture (PM) or solvent evaporation (SE; X ₄). There is no proposed design space formed if the Pluronic® content was below 45.1 mg and if PM is used as the preparation technique. The operating ranges, for robust development of FSM of desired quality, of Pluronic®, Inutec®SP1, HPMC, and preparation technique, are 49–50, 16–23, 83–100 mg, and SE, respectively. The calculated value of f2 was 56.85, indicating that the release profile of the controlled-release (CR) tablet (CR-6) containing the optimized in situ-formed FSM was similar to that of the target release profile. Not only did the ternary mixture of Pluronic®, HPMC with Inutec®SP1 enhance the dissolution rate and inhibit crystallization of felodipine, but also they aided Carbopol®974 in controlling felodipine release from the tablet matrix. It could be concluded that a promising once-daily CR tablets of felodipine was successfully designed using QbD approach.     

The Development of Transgenic Crops to Improve Human Health by Advanced Utilization of Seed Storage Proteins

Seed storage proteins are a major component of mature seeds. They are utilized as protein sources in foods. We designed seed storage proteins containing bioactive peptides based on their three-dimensional structures. Furthermore, to create crops with enhanced food qualities, we developed transgenic crops producing seed storage proteins with bioactive peptides. This strategy promises to prevent lifestyle-related diseases by simple daily food consumption. In this review, we discuss a strategy to develop transgenic crops to improve human health by advanced utilization of seed storage proteins.     

Development of Approaches to Improve Cell Survival in Myoblast Transfer Therapy

Myoblast transplantation has been extensively studied as a gene complementation approach for genetic diseases such as Duchenne Muscular Dystrophy. This approach has been found capable of delivering dystrophin, the product missing in Duchenne Muscular Dystrophy muscle, and leading to an increase of strength in the dystrophic muscle. This approach, however, has been hindered by numerous limitations, including immunological problems, and low spread and poor survival of the injected myoblasts. We have investigated whether antiinflammatory treatment and use of different populations of skeletal muscle–derived cells may circumvent the poor survival of the injected myoblasts after implantation. We have observed that different populations of muscle-derived cells can be isolated from skeletal muscle based on their desmin immunoreactivity and differentiation capacity. Moreover, these cells acted differently when injected into muscle: 95% of the injected cells in some populations died within 48 h, while others richer in desmin-positive cells survived entirely. Since pure myoblasts obtained from isolated myofibers and myoblast cell lines also displayed a poor survival rate of the injected cells, we have concluded that the differential survival of the populations of muscle-derived cells is not only attributable to their content in desmin-positive cells. We have observed that the origin of the myogenic cells may influence their survival in the injected muscle. Finally, we have observed that myoblasts genetically engineered to express an inhibitor of the inflammatory cytokine, IL-1, can improve the survival rate of the injected myoblasts. Our results suggest that selection of specific muscle-derived cell populations or the control of inflammation can be used as an approach to improve cell survival after both myoblast transplantation and the myoblast-mediated ex vivo gene transfer approach.     

Contact Angle Measurements: an Alternative Approach Towards Understanding the Mechanism of Increased Drug Dissolution from Ethylcellulose Tablets Containing Surfactant and Exploring the Relationship Between Their Contact Angles and Dissolution Behaviors

The addition of surfactant in tablet was a well-defined approach to improve drug dissolution rate. While the selected surfactant played a vital role in improving the wettability of tablet by medium, it was equally important to improve the dissolution rate by permeation effect due to production of pores or the reduced inter-particle adhesion. Furthermore, understanding the mechanism of dissolution rate increased was significant. In this work, contact angle measurement was taken up as an alternative approach for understanding the dissolution rate enhancement for tablet containing surfactant. Ethylcellulose, as a substrate, was used to prepare tablet. Four surfactants, sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), dodecyltrimethylammonium bromide (DTAB), and sodium lauryl sulfonate (SLS), were used. Berberine hydrochloride, metformin hydrochloride, and rutin were selected as model drugs. The contact angle of tablet in the absence and presence of surfactant was measured to explore the mechanism. The dissolution test was investigated to verify the mechanism and to establish a correlation with the contact angle. The result showed that the mechanism was the penetration effect rather than the wetting effect. The dissolution increased with a reduction in the contact angle. DTAB was found to obtain the highest level of dissolution enhancement and the lowest contact angle, while SDS, SDBS, and SLS were found to be the less effective in both dissolution enhancement and contact angle decrease. Therefore, contact angle was a good indicator for dissolution behavior besides exploring the mechanism of increased dissolution, which shows great potential in formula screening.     

New Approach for the Application of USP Apparatus 3 in Dissolution Tests: Case Studies of Three Antihypertensive Immediate-Release Tablets

The USP Apparatus 3 is a compendial dissolution Apparatus that has been mainly used to assess the performance of modified-release drug products. However, this Apparatus can be applied to dissolution testing of immediate-release tablets as well, with several advantages such as lower consumption of dissolution media, reduced setup time in quality control routine, and minimized hydrodynamic issues. In this work, three immediate-release (IR) tablets containing antihypertensive drugs of different Biopharmaceutic Classification System (BCS) classes were evaluated in order to assess the possible interchangeability between the official dissolution method using typical USP Apparatus 1 or 2 and the proposed methods using USP Apparatus 3. Depending on the selection of the appropriate operational conditions, such as dip rate and sieve mesh size, it was observed that USP Apparatus 3 could provide similar dissolution profiles compared to USP Apparatus 1 or 2 to the drug products tested. In addition, USP Apparatus 3 avoided conning issues related to USP Apparatus 2. The successful application of USP Apparatus 3 in dissolution tests for IR drug products depends on the definition of specific test conditions for each product, considering all the equipment variables, as well as drug and formulation characteristics.     

Impact of Vibration and Agitation Speed on Dissolution of USP Prednisone Tablets RS and Various IR Tablet Formulations

Dissolution testing is an in vitro procedure which is widely used in quality control (QC) of solid oral dosage forms and, given that real biorelevant test conditions are applied, can also be used as a predictive tool for the in vivo performance of such formulations. However, if a dissolution method is intended to be used for such purposes, it has to deliver results that are only determined by the quality of the test product, but not by other variables. In the recent past, more and more questions were arising on how to address the effects of vibration on dissolution test results. The present study was performed to screen for the correlation of prednisone dissolution of USP Prednisone Tablets RS with vibration caused by a commercially available vibration source as well as to investigate how drug release from a range of immediate release formulations containing class 1–4 drugs of the biopharmaceutical classification scheme is affected by vibration when performing dissolution experiments at different agitation rates. Results of the present study show that the dissolution process of oral drug formulations can be affected by vibration. However, it also becomes clear that the degree of which a certain level of vibration impacts dissolution is strongly dependent on several factors such as drug properties, formulation parameters, and the design of the dissolution method. To ensure the establishment of robust and predictive dissolution test methods, the impact of variation should thus be considered in method design and validation.KEY WORDS: dissolution, USP prednisone calibrator tablets, variability, vibration meter, vibration source     

The Dissolution of Double Holliday Junctions

Double Holliday junctions (dHJS) are important intermediates of homologous recombination. The separate junctions can each be cleaved by DNA structure-selective endonucleases known as Holliday junction resolvases. Alternatively, double Holliday junctions can be processed by a reaction known as “double Holliday junction dissolution.” This reaction requires the cooperative action of a so-called “dissolvasome” comprising a Holliday junction branch migration enzyme (Sgs1/BLM RecQ helicase) and a type IA topoisomerase (Top3/TopoIIIα) in complex with its OB (oligonucleotide/oligosaccharide binding) fold containing accessory factor (Rmi1). This review details our current knowledge of the dissolution process and the players involved in catalyzing this mechanistically complex means of completing homologous recombination reactions.For decades, homologous recombination (HR) was defined as a mechanism for the production of new allelic combinations during meiosis because it can generate so-called crossing-over (see Mehta and Haber 2014). Crossovers are likely generated by the asymmetric cleavage of a key intermediate in HR, the dHJ, by the action of structure-selective endonucleases called “resolvases” (Fig. 1A) (see Wyatt and West 2014). In addition to its essential function during meiosis, HR has proven to be a crucial DNA repair pathway in mitotic cells. Precisely because it has the potential to generate crossing-over, the resolution of dHJ by resolvases affords a high risk of genomic instability in these circumstances. Indeed, when HR is engaged between two homologous chromosomes or two homeologous sequences, dHJ resolution could lead, respectively, to loss of heterozygosity or gross chromosomal rearrangements. Thus, an alternative mechanism allowing dHJ processing without crossing-over would appear essential when HR is used for DNA repair. Such a mechanism, termed dHJ dissolution, is thought to be a major route for dissipation of dHJs arising from HR repair (LaRocque et al. 2011; Krejci et al. 2012). During dHJ dissolution, the two HJs are branch migrated toward one another until they form a hemicatenated intermediate that can be decatenated by a topoisomerase (Fig. 1B). This sophisticated reaction is performed by the so-called “dissolvasome” complex composed of a specific RecQ helicase (BLM in humans/Sgs1 in budding yeast) and a type IA topoisomerase known as topoisomerase III (Fig. 2; for general reviews about RecQ helicases and topoisomerases, see Champoux 2001; Wang 2002; Bachrati and Hickson 2003; Viard and de la Tour 2007; Chu and Hickson 2009; Vindigni and Hickson 2009.Open in a separate windowFigure 1.Double Holliday junction processing pathways. (A) During HJ resolution, each HJ of a dHJ is cleaved by a structure-selective endonuclease (resolvase). Depending on the combination of cleavage orientations, which can be asymmetric or symmetric, this process can generate both crossover and noncrossover products. In contrast, during dissolution (B), each strand engaged in the dHJ is reassociated with its original complementary strand, preventing exchange of genetic material between the two homologous sequences (and hence generating exclusively noncrossover products). DHJ dissolution (B) is initiated by migration of the HJs toward one another. The fusion/collapse of the two HJs results in a hemicatenated intermediate. Decatenation of this intermediate regenerates the original DNA species present before the initiation of HR.Open in a separate windowFigure 2.Domain organization of RecQ helicases, topoisomerases IA, and RMI proteins. (A) Most of the RecQ helicase members share a superfamily 2 helicase domain (SF2), a RecQ conserved domain (RQC), and a helicase and RNase D carboxy-terminal domain (HRDC). Besides this “RecQ core” domain, some RecQ helicases contain amino-terminal and carboxy-terminal extensions that vary in size, sequence, and functionality (e.g., SLD2 homology domain in RECQ4, and a signature motif in the carboxy-terminal domain of RECQ5). The hatched boxes denote partially degenerate RQC domains. BLM/Sgs1 helicases share a common domain organization, including an amino-terminal extension that includes domains for interaction with both TopoIII/RMI1 (TR) and replication protein A (RPA), in addition to a region that has been proposed to be required for DNA strand exchange (SE) activity. (B) All type IA topoisomerases contain a conserved catalytic domain (topoisomerase IA). Some topoisomerase IA enzymes also exhibit a carboxy-terminal extension, frequently composed of zinc finger motifs (black boxes), which is believed to mediate protein–DNA and protein–protein interactions. The contribution of the carboxy-terminal extension to dissolution is unknown. The regions interacting with other components of the dissolvasome are unknown. (C) In RMI1 proteins, only the DUF1676 and the OB-fold domain 1 (OB1) are conserved from yeast to human. The OB1 associates with both BLM/Sgs1 and topoisomerase III (BT/ST). In addition, human RMI1 exhibits a carboxy-terminal extension, composed of a middle region, which mediates RPA binding, and a second OB fold (OB2), which is able to associate with RMI2. RMI2 is also an OB-fold protein (OB3) that stably associates with the dissolvasome in human cells. In total, therefore, the human RMI1/2 complex contains three OB folds.In this review, we first take a historical look at the experimental evidence that led some groups to formulate the proposal that a reaction akin to dissolution must exist, and which then led Wu and Hickson (2003) to confirm its existence by reconstitution of the dissolution reaction in vitro using purified proteins. Following that, we will review the individual and combined roles of the components of what we will term the dHJ dissolvasome. Although many mechanistic aspects of dHJ dissolution remain obscure, several biochemical studies have provided a general understanding of this conceptually simple, but mechanistically complex, reaction.     

Bovine Oocytes Cryoinjury and How to Improve Their Development Following Cryopreservation

Bovine oocytes are less likely to undergo successful cryopreservation than cleavage-stage embryos. Bovine oocytes characteristically contain high levels of lipids that represent one of the major obstacles limiting efficient cryopreservation. These droplets together with structures such as cumulus cells, zona pellucida, cytoplasm membrane, cortical granules, mitochondria, spindle, and cytoskeleton (microtubles and microfilaments) often incur serious damage during cooling and warming. The cryoinjury could, to some extent, be decreased by selection of proper permeable and non-permeable cryoprotectants, and of vitrification with high cooling and warming rates. Additionally, such measures may also enhance their cryotolerance as partial removal of cumulus cells, modification of oocyte membrane constituents, polarization of the cytoplasmic lipid droplets by centrifugation, and addition of cytoskeleton relaxants or ice blockers into vitrification solutions. The improvement in cryopreservation methodology for bovine oocytes will no doubt augment other technologies such as bovine cloning and the establishment of gene bank for transgenic cattle.