Efficacy and Safety of SP16 in Preventing Acute Kidney Injury in At-risk Subjects With Chronic Kidney Disease Undergoing Elective Cardiac Surgery Using the Heart-lung-machine

Inclusion Criteria: * Individual aged ≥18 years. * Male or female. * Scheduled for CABG OR aortic valve surgery (aortic valve replacement or repair alone, with or without aortic root repair) OR mitral valve surgery OR aortic/mitral valve surgery combined with CABG. * Use of the CPB during surgical intervention expected. * Written informed consent obtained from the participant. * Understanding of study procedures and willingness to abide by all procedures during the course of the clinical trial. * CKD Stage 2-3b with eGFR ≤90 and ≥30 ml/min/1.73 m2 (according to 2021 CKD-EPI equation) known for ≥ 3 months prior to enrollment * BMI ≥19 kg/m² to ≤40 kg/m². * Contraceptive measures: Female participants must fulfil at least one of the following criteria of highly effective contraception (according to CTFG recommendations v1.2) during and up to 3 months after the end of study participation: * Menopause (at least 12 months of natural amenorrhoea or 6 months of amenorrhoea with serum FSH \>40 mU/ml) OR * Condition after bilateral ovariectomy or hysterectomy for at least 6 weeks prior to the screening appointment (Visit 1a, Day 54 to -2) OR * Regular, correct and reliable use of a contraceptive method with an error rate ≤1% per year: 1. Inhibition of ovulation by estrogen and progesterone combination preparations (oral, intravaginal, or transdermal) or 2. Inhibition of ovulation by progesterone monopreparations (oral, per injectionem \[depot injections\], or implant) or 3. Intrauterine device, hormone coil OR * Bilateral tubal ligation OR * Vasectomy of all partners OR * Sexual abstinence. Male participants must fulfill at least one of the following contraceptive criteria during and up to 3 months after the end of participation in the study: * Vasectomy OR * Regular, correct, and reliable use of condoms Exclusion Criteria: * CKD stages 4-5 with eGFR \<30 ml/min/1.73 m2 pre-surgery as determined by CKD EPI. * Previous cardiac surgery. * Person has a kidney transplant or another solid organ transplant. * Person is scheduled for intermittent or continuous renal replacement therapy (dialysis). * Known diagnosis of dementia or other clinical signs of mental illness that will prevent full understanding. * Known diagnosis of severe COPD (Gold 3) and/or FEV1 \< 1 l/s. * Heart failure with severity of symptoms according to NYHA IV. * Heart failure with impaired cardiac pump function (LVEF \<35%). * Acute onset or ongoing sepsis - sepsis is defined as the presence of a confirmed or putative infection, along with a dysregulated systemic immune reaction leading to organ dysfunction. * Clinical signs of a currently active infection including endocarditis requiring antibiotic treatment. * Clinical signs of an acute viral infection. * Serious underlying disease(s) or very poor general medical condition, so that in the investigator's judgment the person is not expected to survive ICU or hospital stay. * Patient who has an active (requiring treatment) malignancy or history within 5 years prior to enrollment in the study, of solid, metastatic or hematologic malignancy with the exception of basal or squamous cell carcinoma of the skin that has been removed. * Administration of iodinated contrast agent within 24 hours prior to cardiac surgery * Recent (discontinued in the last 14 days before V1a or V1b) or current treatment with immunosuppressive drugs, including, but not limited to, high dose corticosteroids \[\> 1 mg/kg of prednisone equivalent\], tumour necrosis factor alpha blockers, or ciclosporin. * Current regular use of anti inflammatory drugs such as NSAID, with discontinuation not possible. (however, if these medications are discontinued in the last 10 days before V2, the participant is eligible to participate). ASA up to 100 mg per day is allowed. * Systemic corticosteroid therapy (any dose). * Known active chronic inflammatory disease (including, but not limited to, rheumatoid arthritis or systemic lupus erythematosus). * Known allergy to SP16 or to other ingredients of the IMP. * Person who is not willing to use highly effective contraceptive measures (according to CTFG recommendations v1.2). * Pregnant women. * Breastfeeding women. * Current participation in another interventional clinical study (register studies or non-interventional, observational studies excluded). * Employee or direct relative of an employee of the study site, the CRO, or the Sponsor.