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This study is evaluating whether a dual glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist, tirzepatide, can affect the function, structure and metabolism of skeletal muscles in adults with obesity. Participants, premenopausal females with obesity, will receive either tirzepatide or placebo over 24 weeks. Researchers will assess body weight, body composition, muscle strength and functional performance, neuromuscular function and will perform muscle biopsies before and after treatment to study molecular and histological changes following treatment. The goal of this study is to investigate the effects of tirzepatide on skeletal muscle function, quantity, quality and metabolism in adults with obesity as well as clarify the molecular and structural adaptations in skeletal muscle during tirzepatide-induced weight loss, addressing an important gap in understanding the impact of incretin-based therapies on muscle health.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Tirzepatide | Experimental |
| |
| Placebo | Placebo Comparator |
|
| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| Tirzepatide | Drug | Tirzepatide is a dual glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist. It will be administered via subcutaneous injection once weekly in a dose-titration scheme: starting at 2.5 mg and increased every 4 weeks by 2.5 mg up to a maximum of 15 mg, based on tolerability. |
| Measure | Description | Time Frame |
|---|---|---|
| Change in Body Mass and Composition | Measured primarily as changes in body weight and body composition measured by dual-energy X-ray absorptiometry (DXA). | Baseline to Week 24 |
| Change in Quadriceps Muscle Strength | Change in maximal knee extensor torque normalized to body mass (Nm/kg) will be evaluated using an isokinetic dynamometer. | Baseline to Week 24 |
| Measure | Description | Time Frame |
|---|---|---|
| Change in MRI-derived Skeletal Muscle Composition and Myosteatosis | Muscle volume and muscle fat fraction will be quantified using magnetic resonance imaging (MRI). | Baseline to Week 24 |
| Change in Molecular Markers in Vastus Lateralis Muscle: Gene-level Differential Expression |
| Measure | Description | Time Frame |
|---|---|---|
| Change in Handgrip Strenght | Change in maximal handgrip strength, normalized to body mass, will be assessed using a handheld dynamometer. | Baseline to Week 24 |
| Changes in Lower-Limb Functional Performance |
Inclusion Criteria:
Exclusion Criteria:
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| Name | Role | Phone | Extension | |
|---|---|---|---|---|
| Prof. Mojca Jensterle Sever, MD, PhD | Contact | 0038631312977 | mojca.jensterlesever@kclj.si | |
| Andrijana Koceva, MD | Contact | 0038630248963 | andrijana_koceva@yahoo.com |
| Name | Affiliation | Role |
|---|---|---|
| Mojca Jensterle Sever, Prof.MD, PhD | Department of Endocrinology, Diabetes and Metabolic Diseases, University Medical Centre Ljubljana | Principal Investigator |
| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| Department of Endocrinology, Diabetes and Metabolic Diseases, University Medical Centre Ljubljana | Recruiting | Ljubljana | 1000 | Slovenia |
De-identified individual participant data (IPD) to be shared will include demographic data, basic clinical measurements, body composition assessment, laboratory results, muscle strength and function assessment data, molecular data and histological features from skeletal muscle biopsies. All shared data will be fully de-identified, and no directly identifiable personal information will be included.
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| ID | Term |
|---|---|
| D009765 | Obesity |
| ID | Term |
|---|---|
| D050177 | Overweight |
| D044343 | Overnutrition |
| D009748 | Nutrition Disorders |
| D009750 | Nutritional and Metabolic Diseases |
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| ID | Term |
|---|---|
| D000098860 | Tirzepatide |
| ID | Term |
|---|---|
| D000067757 | Glucagon-Like Peptide-1 Receptor |
| D000067756 | Glucagon-Like Peptide Receptors |
| D043562 | Receptors, G-Protein-Coupled |
| D011956 | Receptors, Cell Surface |
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|
| Placebo | Drug | Placebo (saline solution) will be administered via subcutaneous injection once weekly with dose escalation following the same schedule (2.5 mg equivalent increments every 4 weeks) to preserve blinding integrity. |
|
Transcriptome-wide RNA-sequencing will be performed on vastus lateralis muscle biopsies from all participants (depending on sample quality and RNA integrity) before and after the intervention to identify differentially expressed genes associated with tirzepatide treatment. Differential gene expression will be reported as log2 fold change (log2FC) between post and pre-intervention, derived from normalized RNA-sequencing read counts. Statistical significance will be summarized using false discovery rate (FDR)-adjusted p-values. |
| Baseline to Week 24 |
| Change in Molecular Markers in Vastus Lateralis Muscle: Pathway-level Enrichment Analysis | Pathway-level changes will be reported using normalized enrichment scores (NES) derived from gene set enrichment analysis (GSEA), together with false discovery rate (FDR)-adjusted q-values for biological processes including mitochondrial function, lipid metabolism, insulin signaling, inflammation, muscle atrophy, and myogenesis. | Baseline to Week 24 |
| Change in Intramyocellular Lipid Content (IMCL) in Vastus Lateralis Muscle | Assessed by Oil Red O staining using a standard protocol. IMCL will be quantified as the proportion of Oil Red O-positive area per fibre and averaged across available fibres per section per time point. Microscopy imaging and analysis settings will be kept consistent across time points, and assessors will be blinded to group/time. | Baseline to Week 24 |
| Change in the Muscle Fiber Diameter of Type I and Type II Fibers | Muscle fiber diameter will be measured on the biopsy section using routine light microscopy. Fiber typing (type 1 vs type 2) will be performed by standard immunohistochemistry for myosin heavy chain isoforms. The metric is mean minimal Feret diameter in micrometers, averaged across available fibers of same type. | Baseline to Week 24 |
Change in lower-limb functional performance assessed using standardized sit-to-stand testing.
| Baseline to Week 24 |
| Change in 6-Minute Walk Test (6MWT) | The six-minute walk test (6MWT) will be used to assess functional exercise capacity. The outcome will be the total distance walked (meters) over 6 minutes on a flat corridor, following standardized guidelines. | Baseline to Week 24 |
| Spatial Transcriptomics Analysis of Vastus Lateralis Muscle Biopsy Samples | Potential exploratory: Feasibility-dependent analysis of spatial transcriptomic profiles in skeletal muscle biopsy. The objective is to identify treatment-related changes in spatial gene expression patterns in skeletal muscle tissue sections. A subset of approximately 8 patients (paired pre- and post-treatment muscle biopsy samples) will be selected for downstream analyses based on transcriptomic profiles obtained from the full RNA-seq dataset. | Baseline to Week 24 |
| Electrophysiological Assessment of Motor Responses in Skeletal Muscles | Potential exploratory: Electrophysiological recordings of motor responses (compound muscle action potentials, CMAP) will be assessed to evaluate potential changes in peripheral motor nerve excitability and neuromuscular function. | Baseline to Week 24 |
| D001835 |
| Body Weight |
| D012816 | Signs and Symptoms |
| D013568 | Pathological Conditions, Signs and Symptoms |
| D008565 | Membrane Proteins |
| D011506 | Proteins |
| D000602 | Amino Acids, Peptides, and Proteins |
| D011964 | Receptors, Gastrointestinal Hormone |
| D018000 | Receptors, Peptide |