Controlled release of modified insulin glargine from novel biodegradable injectable gels

Injectable systems for long-lasting insulin therapy

Insulin therapy is the mainstay to treat diabetes characterizedd by hyperglycemia. However, its short half-life of only 4-6 min limits its effectiveness in treating chronic diabetes. Advances in recombinant DNA technology and protein engineering have led to several insulin analogue products that have up to 42 h of glycemic control. However, these insulin analogues still require once- or twice-daily injections for optimal glycemic control and have poor patient compliance and adherence issues. To achieve insulin release for more than one day, different injectable delivery systems including microspheres, in situ forming depots, nanoparticles and composite systems have been developed. Several of these delivery systems have advanced to clinical trials for once-weekly insulin injection. This review comprehensively summarizes the developments of injectable insulin analogs and delivery systems covering the whole field of injectable long-lasting insulin technologies from prototype design, preclinical studies, clinical trials to marketed products for the treatment of diabetes.

Formulation and characterization of insulin nanoclusters for a controlled release

The growing interest in biopharmaceuticals combined with the challenges regarding formulation and delivery continues to encourage the development of new and improved formulations of this class of therapeutics. Nanoclusters (NCs) represent a type of formulation strategy where the biopharmaceutical is clustered in a reversible manner to function as both the therapeutic and the vehicle. In this study, insulin NCs (INCs) were formulated by a new methodology of first crosslinking proteins followed by desolvation. Crosslinking of the protein with the reducible DTSSP crosslinker improved control of the INC synthesis process to give INCs with a mean size of 198 ± 7 nm and a mean zeta potential of -39 ± 1 mV. Crosslinking and clustering of insulin did not induce cytotoxicity or major differences in the biological activity compared to the free unmodified protein. The potency of the crosslinked insulin and the INCs appeared slightly lower than that of the unmodified protein, and significantly higher doses of the INCs compared to the free protein were applied to achieve similar blood sugar lowering effects in vivo. Interestingly, the INCs allowed for high doses to be subcutaneously delivered with prolonged efficacy without being lethal in rats.

Biomarker monitoring and long-acting insulin treatment in a stress model to facilitate personalized diabetic control

Diabetes is a chronic disease involving elevated blood glucose levels. Controlled insulin delivery is an ideal method to achieve glycemic control. However, glucose levels vary as a result of changes in the body's physiological conditions resulting from different daily events, such as meals, exercise and stress. It is essential to develop and to monitor appropriate biomarkers for these natural physiological perturbations in order to achieve a holistic understanding of metabolic changes in diabetic patients to facilitate optimal glucose management and make possible personalized medicine for this very debilitating disease. The novel aspects of the current research include the combination of the tail suspension stress animal model and microdialysis for stress biomarker monitoring. A tail suspension test was optimized and used as a stress inducer for different groups of model rats (normal, untreated diabetic and insulin-treated diabetic rats). The levels of multiple metabolic analytes in the subcutaneous tissue were monitored continuously using subcutaneous microdialysis analysis. Different analytes, including pH, glucose and lactate were monitored and analyzed. Another important and original aspect of the reported work is that revelation that the pH, lactate and glucose levels increased under the stress conditions and the changes tended to be more pronounced in diabetic rats (both untreated and long-acting insulin-treated) compared to normal rats. Long-acting insulin treatment was shown to shorten the duration of the pH and glucose changes in response to stress when compared to the untreated diabetic rats. An additional novel aspect of the research is that subcutaneous pH was shown to be a sensitive stress biomarker for diabetic rats as pH changes rapidly after stress initiation. This research provides insight into the importance of accurate glycemic control and diabetes management for individual patients through highlighting stress management and appropriate biomarker monitoring, especially the value of combining pH and lactate monitoring with typical glucose monitoring. This research will pave the way for individualized medicine for diabetic patients through helping to obtain a holistic understanding of the various important biomarkers, rather than solely depending on glucose monitoring to determine appropriate insulin dosing.

Pharmacokinetics and Bioavailability of the GnRH Analogs in the Form of Solution and Zn2+-Suspension After Single Subcutaneous Injection in Female Rats

BACKGROUND AND OBJECTIVES

Although many synthetic gonadoliberin analogs have been developed, only a few of them, including buserelin, were introduced into clinical practice. Dalarelin, which differs from buserelin by just one aminoacid in the position 6 (D-Ala), is not widely used so far. Gonadotropin-releasing hormone (GnRH) analogs are used to treat many different illnesses and are available in different forms like solution for injection, nasal spray, microspheres, etc. Unfortunately, none of the above drug formulations can release the hormones for 24 h. We assumed that classical suspension could solve this problem.

METHODS

Two sets of experiments were performed. In the first one, buserelin and dalarelin were injected into mature female rats in two forms: suspension, in which the analogs are bounded by Zn²⁺ ions and solution. The pharmacokinetic parameters and bioavailability of the analogs were calculated, based on their concentration in the plasma measured by high-performance liquid chromatography method (HPLC). In the second experiment, the hormones in two different forms were injected into superovulated immature female rats and then the concentration of Luteinizing hormone (LH), Follicle-stimulating hormone (FSH) and 17β-estradiol in the serum was measured by radioimmunological method.

RESULTS

The Extent of Biological Availability (EBA), calculated on the base of AUC_0-∞, showed that in the form of solution buserelin and dalarelin display, respectively, only 13 and 8 % of biological availability of their suspension counterparts. Comparing both analogs, the EBA of dalarelin was half (53 %) that of buserelin delivered in the form of solution and 83 % when they were delivered in the form of suspension. The injection of buserelin or dalarelin, in the form of solution or suspension, into superovulated female rats increased LH, FSH and estradiol concentration in the serum. However, after injection of the analogs in the form of suspension, the high concentration of LH and FSH in the serum persisted longer.

CONCLUSION

Performed studies indicate that GnRH analogs in the form of suspension have higher bioavailability than their solution counterparts. It influences the effects of their action, especially in relation to LH and FSH.