Inclusion Criteria:  Willing and able to give written informed consent for participation in the study. Part I and IIa: Healthy male or female subject aged 18-50 years inclusive. Part IIb: Healthy male or female subject aged ≥65 years inclusive. Body Mass Index (BMI) ≥ 18.0 and ≤ 30.0 kg/m2. Clinically normal medical history, physical findings, vital signs, ECG and laboratory values at the time of screening, as judged by the Investigator. WOCBP must practice abstinence (only allowed when this is the preferred and usual lifestyle of the subject) or must agree to use a highly effective method of contraception with a failure rate of < 1% to prevent pregnancy (combined [oestrogen and progestogen containing] hormonal contraception associated with inhibition of ovulation [oral, intravaginal, transdermal], progestogen-only hormonal contraception associated with inhibition of ovulation [oral, injectable, implantable], intrauterine device [IUD] or intrauterine hormone-releasing system [IUS]) from at least 4 weeks prior to dose to 4 weeks after last dose. Female subjects must refrain from donating eggs from the date of dosing until 3 months after dosing with the IMP. Their male partner must agree to use a condom during the same time frame if he has not undergone vasectomy.  Women of non-childbearing potential are defined as pre-menopausal females who are sterilised (tubal ligation or permanent bilateral occlusion of fallopian tubes); or females who have undergone hysterectomy or bilateral oophorectomy; or post-menopausal defined as 12 months of amenorrhea (in questionable cases a blood sample with detection of follicle stimulating hormone [FSH] 25-140 IE/L is confirmatory).  Male subjects must be willing to use condom or be vasectomised or practice sexual abstinence to prevent pregnancy and drug exposure of a partner and refrain from donating sperm from the date of dosing until 3 months after dosing with the IMP. Their female partner of child-bearing potential must use contraceptive methods with a failure rate of < 1% to prevent pregnancy (see above). -  Exclusion Criteria:  History of any clinically significant disease or disorder which, in the opinion of the Investigator, may either put the subject at risk because of participation in the study, or influence the results or the subject's ability to participate in the study. Any clinically significant illness, medical/surgical procedure or trauma within 4 weeks of the first administration of IMP. Current or history of gastrointestinal bleedings, inflammatory bowel disease, irritable bowel syndrome or coeliac disease, as judged by the Investigator. Malignancy within the past 5 years with the exception of in situ removal of basal cell carcinoma. Any planned major surgery within the duration of the study. Any positive result on screening for serum hepatitis B surface antigen, hepatitis C antibody and HIV. After 10 minutes supine rest at the time of screening, any vital signs values outside the following ranges: Part I, IIa: Systolic blood pressure <90 or >140 mmHg, or Diastolic blood pressure <50 or >90 mmHg, or Pulse <40 or >90 beats per minute (bpm) Part IIb: Systolic blood pressure <90 or >160 mmHg, or Diastolic blood pressure <50 or >100 mmHg, or Pulse <40 or >90 bpm Prolonged QTcF (>450 ms for men, >470 ms for women), cardiac arrhythmias or any clinically significant abnormalities in the resting ECG at the time of screening, as judged by the Investigator. History of severe allergy/hypersensitivity or ongoing allergy/hypersensitivity, as judged by the Investigator, or history of hypersensitivity to drugs with a similar chemical structure or class to CUR-N399. Regular use of any prescribed or non-prescribed medication including antacids, analgesics, herbal remedies, vitamins and minerals within 2 weeks prior to the (first) administration of IMP, at the discretion of the Investigator. NB. The use of a stable dose of levothyroxine is allowed for subjects in Part IIb. Any use of omeprazole products (or products of the same drug class) within 2 weeks prior to the (first) administration of IMP, at the discretion of the Investigator. Planned treatment or treatment with another investigational drug within 3 months prior to Day -1. Subjects consented and screened but not dosed in previous Phase I studies are not excluded. Current smokers or users of nicotine products. Irregular use of nicotine (e.g. smoking, snuffing, chewing tobacco) less than three times per week is allowed before screening visit. Positive screen for drugs of abuse or alcohol at screening or on admission to the unit prior to (first) administration of the IMP. History or presence of alcohol abuse or excessive intake of alcohol, as judged by the Investigator. Presence or history of drug abuse, as judged by the Investigator. History of, or current use of, anabolic steroids. Excessive caffeine consumption defined by a daily intake of >5 cups of caffeine containing beverages. Plasma donation within one month of screening or blood donation (or corresponding blood loss) during the three months prior to screening. Investigator considers the subject unlikely to comply with study procedures, restrictions and requirements.