Table 2 Overview of preclinical studies for GLP-1 analogs.

1

Exenatide

In vitro and In vivo (C57BL/6 N mice).

Subcutaneous injection in mice

Optimized porous silicon microparticles (pSiMP) exhibited excellent peptide loading and sustained release kinetics. Additionally, the formulation demonstrated an 83 ± 5% peptide recovery after enzyme challenge, indicating significant protection of exenatide from proteolytic degradation.

-

Exenatide from pSiMPs was detectable for up to 14 days, with sustained plasma levels ranging from 1 to 3 ng/mL.

The formulation represents a promising delivery system for GLP-1R agonists in type 2 diabetes.

[121]

2

Liraglutide

In vitro and in vivo (Type 2 diabetic rat model [Sprague Dawley rats induced via high-fat diet over 6 months]).

-

Liraglutide-loaded microspheres demonstrated sustained drug release profile. In addition, a comparable hypoglycaemic efficacy between microsphere groups and injection group from days 10 to 25 was observed. The HbA1c and insulin levels after 30 days showed no significant difference between the microsphere and injection groups.

-

-

The formulations exhibited comparable efficacy and safety to daily liraglutide injections.

[122]

3

Semaglutide

In vivo (Diet-Induced Obese [DIO] Mice)

Subcutaneous injection

Microspheres (MS) encapsulating semaglutide resulted in nearly 20% body weight loss over one month compared to twice-daily dosing. Furthermore, it also reduced blood glucose levels and food intake in a dose-dependent manner.

-

Single injections of 400 nmol/kg and 2000 nmol/kg of MS-semaglutide produced a t_1/2 of approximately 36 days. The C_max and the AUC_inf, normalized to a dose of 1 nmol/kg, were found to be 1.2 nM and 1080 nM h, respectively. Additionally, a relative bioavailability of 92% was observed when compared to free semaglutide.

MS-semaglutide is an optimal formulation.

[123]

4

Exenatide

In vitro and in vivo (Male Sprague Dawley rats)

Transdermal

A single administration of exenatide (EXT)-loaded two-layer sustained-release microneedles (EXT-TS-MNs) in diabetic rats demonstrated a sustained hypoglycemic effect lasting nearly 24 h, compared to only 8 hours with subcutaneous (SC) administration. Furthermore, multiple administrations of the microneedles maintained their efficacy for 6 days without causing drug resistance.

No specific systemic or local toxicity reported.

EXT was detected in plasma for up to 48 h in the MN group. The relative bioavailability (RB) of the TS-MNs was 83.04% compared to SC injection. The maximum concentration (C_max) was 13.60 ± 2.95 ng/mL for the MN group, compared to 16.68 ± 4.87 ng/mL for the SC group. The area under the curve (AUC_0–t) was 55.17 ng h/mL for the MN group, while it was 28.01 ng h/mL for the SC group.

TS-MNs show great potential as a delivery system for EXT in the treatment of type 2 diabetes mellitus.

[111]

5

Lixisenatide

In vivo (db/db mice)

Transdermal

A subcutaneous injection reduced blood glucose levels to 24.97% of the baseline within 2 h. In comparison, the microneedles (MN) group demonstrated a sustained-release profile, with glucose levels decreasing to 34.64% at 6 h after application. Additionally, the MN group significantly reduced glucose excursions following a glucose challenge in both db/db and Kunming mice.

Mild erythema resolved within 72 h, with no signs of tissue necrosis, inflammation, or lesions observed.

-

The MN effectively delivered Lixisenatide transdermally with minimal skin irritation and significant hypoglycemic effects in db/db diabetic mice.

[124]

6

Liraglutide

In vivo (Rats and pigs)

Transdermal

The liraglutide-loaded microneedle (MN) patch showed faster drug absorption compared to subcutaneous (SC) injection, achieving a relative bioavailability of 69.8% in rats and 46.3% in minipigs. Additionally, the MN patch produced hypoglycemic effects in diabetic rat models that were comparable to those observed with SC injection.

Aside from mild erythema that developed within 4 h after daily administration for 7 days at the same site, no skin irritation was observed in minipigs.

MN patches displayed optimal Pharmacokinetic properties.

Liraglutide-loaded MN patch offers a feasible, effective, and safe alternative to conventional SC injections.

[125]

7

Lixisenatide

In vivo (male Sprague Dawley [SD] rats and diabetic db/db mice)

Subcutaneous injection

A single injection of Lixisenatide hydrogel provided glycemic control equivalent to twice-daily injections of free Lixisenatide for nine days. Additionally, its monthly administration led to increased plasma insulin levels and a reduction in HbA1c.

-

The formulation demonstrated a 14-fold increase in the half-life (t_1/2z) and a 7.6-fold higher area under the curve (AUC) for free Lixisenatide.

The formulation demonstrated optimal glycemic control in the management of type 2 diabetes.

[116]