Oral delivery of mouse [D-Leu-4]-OB3, a synthetic peptide amide with leptin-like activity, in male Swiss Webster mice: A study comparing the pharmacokinetics of oral delivery to intraperitoneal, subcutaneous, intramuscular, and intranasal administration

Pramlintide an Adjunct to Insulin Therapy: Challenges and Recent Progress in Delivery

Dysregulation of various glucoregulatory hormones lead to failure of insulin monotherapy in patients with diabetes mellitus due to various reasons, including severe hypoglycemia, glycemic hypervariability, and an increased risk of microvascular complications. However, pramlintide as an adjunct to insulin therapy enhances glucagon suppression and thereby offers improved glycemic control. Clinical studies have shown that pramlintide improves glycemic control, reduces postprandial glucose excursions, and promotes weight loss in patients with type 1 and type 2 diabetes. Although clinical benefits of pramlintide are well reported, there still exists a high patient resistance for the therapy, as separate injections for pramlintide and insulin must be administered. Although marketed insulin formulations generally demonstrate a peak action in 60-90 minutes, pramlintide elicits its peak concentration at around 20-30 minutes after administration. Thus, owing to the significant differences in pharmacokinetics of exogenously administered pramlintide and insulin, the therapy fails to elicit its action otherwise produced by the endogenous hormones. Hence, strategies such as delaying the release of pramlintide by using inorganic polymers like silica, synthetic polymers like polycaprolactone, and lipids have been employed. Also, approaches like noncovalent conjugation, polyelectrolyte complexation, and use of amphiphilic excipients for codelivery of insulin and pramlintide have been explored to address the issues with pramlintide delivery and improve patient adherence to the therapy. This approach may usher in a new era of diabetes management, offering patients multiple options to tailor their treatment and improve their quality of life. SIGNIFICANCE STATEMENT: To our knowledge, this is the first report that summarizes various challenges in insulin and pramlintide codelivery and strategies to overcome them. The paper also provides deeper insights into various novel formulation strategies for pramlintide that could further broaden the reader's understanding of peptide codelivery.

Harnessing the Power of Leptin: The Biochemical Link Connecting Obesity, Diabetes, and Cognitive Decline

In this review, the current understanding of leptin’s role in energy balance, glycemic regulation, and cognitive function is examined, and its involvement in maintaining the homeostatic “harmony” of these physiologies is explored. The effects of exercise on circulating leptin levels are summarized, and the results of clinical application of leptin to metabolic disease and neurologic dysfunction are reviewed. Finally, pre-clinical evidence is presented which suggests that synthetic peptide leptin mimetics may be useful in resolving not only the leptin resistance associated with common obesity and other elements of metabolic syndrome, but also the peripheral insulin resistance characterizing type 2 diabetes mellitus, and the central insulin resistance associated with certain neurologic deficits in humans.

Oral delivery of [D-Leu-4]-OB3 and MA-[D-Leu-4]-OB3, synthetic peptide leptin mimetics: Immunofluorescent localization in the mouse hypothalamus

This study describes the localization of [D-Leu-4]-OB3 and MA-[D-Leu-4]-OB3, synthetic peptide leptin mimetics, in the hypothalamus of Swiss Webster and C57BL/6J wild-type mice, leptin-deficient ob/ob mice, and leptin-resistant diet-induced obese (DIO) mice. The mice were given [D-Leu-4]-OB3 or MA-[D-Leu-4]-OB3 in 0.3% dodecyl maltoside by oral gavage. Once peak serum concentrations were reached, the mice received a lethal dose of pentobarbital and were subjected to intracardiac perfusion fixation. The brains were excised, post-fixed in paraformaldehyde, and cryo-protected in sucrose. Free-floating frozen coronal sections were cut at 25-µm and processed for imaging by immunofluorescence microscopy. In all four strains of mice, dense staining was concentrated in the area of the median eminence, at the base and/or along the inner wall of the third ventricle, and in the brain parenchyma at the level of the arcuate nucleus. These results indicate that [D-Leu-4]-OB3 and MA-[D-Leu-4]-OB3 cross the blood-brain barrier and concentrate in an area of the hypothalamus known to regulate energy balance and glucose homeostasis. Most noteworthy is the localization of [D-Leu-4]-OB3 immunoreactivity within the hypothalamus of DIO mice via a conduit that is closed to leptin in this rodent model, and in most cases of human obesity. Together with our previous studies describing the effects of [D-Leu-4]-OB3 and MA-[D-Leu-4]-OB3 on energy balance, glucose regulation, and signal transduction pathway activation, these findings are consistent with a central mechanism of action for these synthetic peptide leptin mimetics, and suggest their potential usefulness in the management of leptin-resistant obesity and type 2 diabetes in humans.

Current status of selected oral peptide technologies in advanced preclinical development and in clinical trials

The development of oral dosage forms that allows absorption of therapeutic peptides to the systemic circulation is one of the greatest challenges for the pharmaceutical industry. Currently, a number of technologies including either mixtures of penetration enhancers or protease inhibitors and/or nanotechnology-based products are under clinical development. Typically, these formulations are presented in the form of enteric-coated tablets or capsules. Systems undergoing preclinical investigation include further advances in nanotechnology, including intestinal microneedle patches, as well as their combination with regional delivery to the colon. This review critically examines four selected promising oral peptide technologies at preclinical stage and the twelve that have progressed to clinical trials, as indicated in www.clinicaltrials.gov. We examined these technologies under the criteria of peptide selection, formulation design, system components and excipients, intestinal mechanism of action, efficacy in man, and safety issues. The conclusion is that most of the technologies in clinical trials are incremental rather than paradigm-shifting and that even the more clinically advanced oral peptide drugs examples of oral bioavailability appear to yield oral bioavailability values of only 1-2% and are, therefore, only currently suitable for a limited range of peptides.

Intestinal permeation enhancers for oral peptide delivery

Intestinal permeation enhancers (PEs) are one of the most widely tested strategies to improve oral delivery of therapeutic peptides. This article assesses the intestinal permeation enhancement action of over 250 PEs that have been tested in intestinal delivery models. In depth analysis of pre-clinical data is presented for PEs as components of proprietary delivery systems that have progressed to clinical trials. Given the importance of co-presentation of sufficiently high concentrations of PE and peptide at the small intestinal epithelium, there is an emphasis on studies where PEs have been formulated with poorly permeable molecules in solid dosage forms and lipoidal dispersions.

High efficiency intranasal drug delivery using Intravail® alkylsaccharide absorption enhancers

A new class of alkylsaccharide transmucosal delivery enhancement agents are described that overcome the principal limitations preventing broad acceptance of intranasal administration for many potential applications in systemic drug delivery, namely, poor transmucosal absorption and damage to the nasal mucosa. This review will describe recent developments in use of these excipients in human clinical trials and preclinical studies along with their chemical and pharmacological properties and explore commercial implications of the use of these excipients in introduction of new intranasal formulations of peptidic and nonpeptidic drugs.

Myristic acid conjugation of [D-Leu-4]-OB3, a biologically active leptin-related synthetic peptide amide, significantly improves its pharmacokinetic profile and efficacy

We have previously described the pharmacokinetics of mouse [D-Leu-4]-OB3, a synthetic peptide amide with leptin-like activity, following delivery by subcutaneous (SC), intraperitoneal (IP), and intramuscular (IM) injection, and by oral gavage and intranasal instillation. These profiles suggested that the observed efficacy of [D-Leu-4]-OB3 on energy balance, glycemic control, and bone turnover in ob/ob and db/db mice might be improved by efforts directed toward improving its bioavailability, i.e., increasing maximum uptake (Cmax), extending serum half-life (t½), and reducing plasma clearance (CL). To address these issues, myristic (tetradecanoic) acid was conjugated to the N-terminal of [D-Leu-4]-OB3 (designated MA-[D-Leu-4]-OB3), and the pharmacokinetics of MA-[D-Leu-4]-OB3 in male Swiss Webster mice following SC, IP, and IM injection in PBS, and by oral and intranasal delivery in dodecyl maltoside (DDM, trade name Intravail®), a transmucosal absorption enhancing agent, were compared to those of [D-Leu-4]-OB. At a dose of MA-[D-Leu-4]-OB3 10-fold lower than that used previously for [D-Leu-4]-OB3 (0.1 mg vs.1.0 mg, respectively), Cmax of MA-[D-Leu-4]-OB3 was 11.1-, 7.5-, 1.9-, and 1.7-fold higher, t1/2 was 3.5-, 5.0-, 9.1-, and 86.7-fold longer, and CL was 17.0-, 11.6-, 5.7-, and 5.0-fold slower than [D-Leu-4]-OB3 following SC, IP, IM, and oral delivery, respectively. Furthermore, in leptin-resistant obese male db/db mice, oral delivery of MA-[D-Leu-4]-OB3 in DDM at concentrations up to 10-fold lower than those used with [D-Leu-4]-OB3 reduced fasting blood glucose levels in a dose-related manner.

Biologically active leptin-related synthetic peptides activate STAT3 via phosphorylation of ERK1/2 and PI-3K

The effects of leptin-related synthetic peptides [d-Leu-4]-OB3 and OB3 on energy balance and glucose homeostasis in ob/ob and db/db mice have been confirmed. The molecular basis of these effects, however, remains unclear. In the present study, we examined the ability of these peptides to activate signal transduction pathways known to be involved in transduction of the leptin signal. In a specific and concentration-dependent manner, [d-Leu-4]-OB3 induced phosphorylation of ERK1/2, PI-3K, Ser-727 STAT3, and Tyr-705 of STAT3. OB3 also induced activation of STAT3 via phosphorylation of ERK1/2, STAT3 Ser-727, STAT3 Tyr-705 and PI-3K p85, but to a lesser degree. Using PD98059 and LY294002, specific inhibitors of MEK and PI-3K, respectively, we were able to identify the signal transduction pathways involved in peptide-induced STAT3 activation. [d-Leu-4]-OB3 induced serine phosphorylation of STAT3 primarily through activation of ERK1/2. Tyrosine phosphorylation of STAT3, however, was induced primarily through activation of PI-3K. Our data suggest that in db/db mice, [d-Leu-4]-OB3 binding to short isoforms of the leptin receptor induces intracellular signaling cascades which do not require OB-Rb activation. These signals may ultimately result in peptide effects on transcriptional and translational events associated with energy balance and glycemic regulation. In summary, we have shown for the first time that, similar to leptin, bioactive leptin-related synthetic peptide analogs activate STAT3 via phosphorylation of serine and tyrosine residues by multiple signal transduction pathways.

Formulation strategies to improve oral peptide delivery

Delivery of peptides by the oral route greatly appeals due to commercial, patient convenience and scientific arguments. While there are over 60 injectable peptides marketed worldwide, and many more in development, most delivery strategies do not yet adequately overcome the barriers to oral delivery. Peptides are sensitive to chemical and enzymatic degradation in the intestine, and are poorly permeable across the intestinal epithelium due to sub-optimal physicochemical properties. A successful oral peptide delivery technology should protect potent peptides from presystemic degradation and improve epithelial permeation to achieve a target oral bioavailability with acceptable intra-subject variability. This review provides a comprehensive up-to-date overview of the current status of oral peptide delivery with an emphasis on patented formulations that are yielding promising clinical data.

Colonic absorption of salmon calcitonin using tetradecyl maltoside (TDM) as a permeation enhancer

Calcitonin is used as a second line treatment of postmenopausal osteoporosis, but widespread acceptance is somewhat limited by subcutaneous and intranasal routes of delivery. This study attempted to enable intestinal sCT absorption in rats using the mild surfactant, tetradecyl maltoside (TDM) as an intestinal permeation enhancer. Human Caco-2 and HT29-MTX-E12 mucus-covered intestinal epithelial monolayers were used for permeation studies. Rat in situ intestinal instillation studies were conducted to evaluate the absorption of sCT with and without 0.1 w/v% TDM in jejunum, ileum and colon. TDM significantly enhanced sCT permeation across intestinal epithelial monolayers, most likely due to combined paracellular and transcellular actions. In situ, TDM caused an increased absolute bioavailability of sCT in rat colon from 1.0% to 4.6%, whereas no enhancement increase was observed in ileal and jejunal instillations. Histological analysis suggested mild perturbation of colonic epithelia in segments instilled with sCT and TDM. These data suggest that the membrane composition of the colon is different to the small intestine and that it is more amenable to permeation enhancement. Thus, formulations designed to release payload in the colon could be advantageous for systemic delivery of poorly permeable molecules.

Water-in-oil-in-water double emulsions: an excellent delivery system for improving the oral bioavailability of pidotimod in rats

The aims of this study were to prepare fine pidotimod-containing water-in-oil-in-water (W/O/W) double emulsions and to investigate the possibility of those emulsions as a delivery system for promoting the oral bioavailability of pidotimod. A modified two-step emulsification procedure was applied to prepare the double emulsions using medium-chain triglyceride as the oil phase, Tween 80 as the hydrophilic emulsifier, and Span 80 alone or in combination with different amount of phospholipids as the lipophilic emulsifiers. A fine W/O/W emulsion, with the encapsulation efficiency of 82 ± 3.4%, mean oil-droplet diameter of 3.93 ± 0.25 μm, and viscosity of 36.4 ± 0.93 mPa · s at 25 °C and 300 s(-1), was stable for 1 month at 4 °C. In addition, the oral bioavailability of pidotimod in rats, after intragastric administration of W/O/W double emulsions, was significantly higher than that of pidotimod control solution. Moreover, the maximum uptake time was significantly prolonged, suggesting an extra absorption pathway for W/O/W emulsions: a lymphatic circulation pathway. Those results demonstrated that W/O/W emulsions could become a potential formulation for improving the oral bioavailability of poorly absorbable drugs and suggested an important technology platform for the oral administration of peptide and peptidomimetic drugs.

Intranasal delivery of mouse [D-Leu-4]-OB3, a synthetic peptide amide with leptin-like activity, improves energy balance, glycaemic control, insulin sensitivity and bone formation in leptin-resistant C57BLK/6-m db/db mice

BACKGROUND

We have recently shown that intranasal administration of mouse [D-Leu-4]-OB3 reconstituted in Intravail(®) to male Swiss Webster mice resulted in significantly higher uptake and bioavailability when compared with commonly used injection methods of delivery.

AIM AND METHODS

In this study, we examined the effects of intranasal delivery of mouse [D-Leu-4]-OB3 in Intravail(®) on energy balance, glucose regulation, insulin secretion and serum levels of osteocalcin, a specific and sensitive marker of bone formation. Genetically obese C57BLK/6-m db/db mice were allowed food and water ad libitum and given either Intravail(®) alone or mouse [D-Leu-4]-OB3 in Intravail(®) for 14 days by intranasal instillation.

RESULTS

Mouse [D-Leu-4]-OB3 reduced body weight gain, daily food intake, daily water intake and serum glucose by 11.5, 2.2, 4.0 and 61.9%, respectively. Serum insulin levels in db/db mice given mouse [D-Leu-4]-OB3 were approximately threefold lower than those in mice receiving Intravail(®) alone. Mouse [D-Leu-4]-OB3 elevated serum osteocalcin in db/db mice by 28.7% over Intravail(®) treated control mice.

CONCLUSIONS

The results of our study indicate that intranasal delivery of biologically active mouse [D-Leu-4]-OB3 in Intravail(®) is feasible and has significant effects on regulating body weight gain, food and water intake, serum glucose, insulin sensitivity and bone formation in leptin-resistant C57BLK/6-m db/db mice.

Oral delivery of mouse [d-Leu-4]-OB3, a synthetic peptide amide with leptin-like activity, in male C57BL/6J wild-type and ob/ob mice: effects on energy balance, glycaemic control and serum osteocalcin levels

BACKGROUND

We have recently shown that intranasal administration of mouse [d-Leu-4]-OB3 reconstituted in Intravail to male Swiss Webster mice resulted in significantly higher bioavailability than commonly used injections methods of delivery. The absorption profile associated with intranasal delivery of mouse [d-Leu-4]-OB3 showed an early peak representing absorption across the nasal mucosa, and a later peak suggesting a gastrointestinal site of uptake.

AIM AND METHODS

In the present study, we examined the effects of orally administered (by gavage) mouse [d-Leu-4]-OB3 on energy balance, glycaemic control and serum osteocalcin levels in male C57BL/6J wild-type and ob/ob mice allowed food and water ad libitum or calorie restricted by 40% of normal intake.

RESULTS

In wild-type mice fed ad libitum, oral delivery of mouse [d-Leu-4]-OB3 reduced body weight gain, food intake and serum glucose, by 4.4, 6.8 and 28.2% respectively. Serum osteocalcin levels and water intake were essentially the same in control and treated wild-type mice. In ob/ob mice fed ad libitum, mouse [d-Leu-4]-OB3 reduced body weight gain, food intake, water intake and serum glucose by 11.6, 16.5, 22.4 and 24.4% respectively. Serum osteocalcin in ob/ob mice treated with mouse [d-Leu-4]-OB3 was elevated by 62% over controls. Calorie restriction alone caused significant weight loss in both wild-type (9.0%) and ob/ob (4.8%) mice, and mouse [d-Leu-4]-OB3 did not further enhance this weight loss. As expected, serum glucose levels in wild-type and ob/ob mice were significantly reduced by calorie restriction alone. Mouse [d-Leu-4]-OB3 further reduced serum glucose in wild-type mice and normalized levels in ob/ob mice. Calorie restriction alone reduced serum osteocalcin levels by 44.2% in wild-type mice and by 19.1% in ob/ob mice. Mouse [d-Leu-4]-OB3 prevented this decrease in groups of mice.

CONCLUSIONS

The results of this study suggest that oral delivery of mouse [d-Leu-4]-OB3 in Intravail is possible and may have potential not only as an alternative therapy in the treatment of human obesity and some of its associated metabolic dysfunctions, but also may help to prevent and/or reverse at least some of the bone loss which accompanies osteoporosis, anorexia nervosa and other wasting diseases.