CARTIZ is a prospective observational clinical registry of adults in Mexico receiving tirzepatide (a dual GLP-1/GIP receptor agonist) under an independent clinical indication - typically type 2 diabetes, insulin resistance, obesity, renal protection, metabolic hypertension, or associated off-label metabolic use. The registry is entirely observational: CARTIZ does not initiate, modify, interrupt, or supply tirzepatide, and does not dictate dose, route, or duration. All pharmacological exposure decisions are made by the treating physician independently of study participation. The registry is operationalized through a four-institute architecture integrating three Mexican National Institutes of Health and one national imaging laboratory. Core 1 (Knee Cartilage Imaging, Ci3M UAM-Iztapalapa) performs bilateral 3T MRI with quantitative T2 mapping at Week 0 and Week 52. Core 2 (Cardiac Imaging, Instituto Nacional de Cardiología Ignacio Chávez) performs non-contrast cardiac computed tomography for radiomic phenotyping of epicardial adipose tissue at Week 0 and Week 52 under cardiovascular Co-Principal Investigator Dr. Erick Alexánderson Rosas. Core 3 (HLA Typing, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Transplant Department) performs Class I and Class II HLA typing by PCR-SSO Reverse Luminex. Core 4 (Body Composition, Universidad La Salle México) performs multi-frequency bioelectrical impedance analysis (seca mBCA) at six longitudinal timepoints capturing visceral adipose tissue trajectory, phase-angle trajectory, appendicular skeletal muscle mass, and hydration ratios at zero marginal cost. The registry enrolls n=30 patients across three clinical sites with identical protocol (IMSS Clínica Río Magdalena, INCMNSZ outpatient clinic, and a private practice site in Mexico City), generating 60 evaluable knees and 30 paired cardiac CT studies. The primary co-endpoints address a mechanistic question no other tirzepatide study is positioned to answer: whether the articular response to tirzepatide in inflammatory arthropathy precedes and mechanistically precedes weight loss, through formal mediation analysis of Week-4 ACR20 response via high-sensitivity C-reactive protein, SERPINB2, and dipeptidyl peptidase-4 activity, restricted to the Mechanistic Analysis Set of patients with tirzepatide exposure ≤16 weeks at Week 0 and delta-BMI \<1.0 kg/m² through Week 4. A prespecified Surgical Tissue Subcohort is declared at initial registration to establish public scientific priority on direct human epicardial adipose tissue transcriptomic characterization under dual GIP/GLP-1 receptor agonism. Subcohort participants who undergo clinically indicated cardiac surgery at INCar during follow-up (coronary artery bypass grafting, valve replacement, or combined procedures) are invited to provide specific additional informed consent for collection of epicardial adipose tissue fragments routinely excised during operative access and otherwise discarded as surgical waste. Operational launch is contingent on separate INCar tissue-specific approvals and will proceed via PRS record amendment when ready
