Scientists probe Aging's effect on key enzymes in blood and colon

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. English speaking male or female volunteers between the ages of 18-50 for younger adults or 65-80 for older adults 2. Willing to provide written informed consent 3. Willing to abstain from insertion of anything in rectum for 72 hours before and 72 hours after the endoscopic procedure for colorectal tissue collection. 4. Not currently participating in other research studies involving drugs and/or medical devices. For participants not infected with HIV (Control Cohort A) 1. No known risk for HIV exposure or a documented negative HIV-1/HIV-2 Ag/Ab test in the past 3 months (HIV risk, but not on PrEP) 2. Documented negative HBsAg in those taking study TFV (i.e. cohort B) For participants not infected with HIV, but taking or willing to take TFV (PrEP Cohort B) 1. Currently taking TFV-based oral PrEP daily or willing to take oral TFV-containing PrEP for one week 2. Documented negative HIV-1/HIV-2 Ag/Ab test in the past 3 months 3. Documented negative HBsAg For participants infected with HIV (ARV Cohort C) 1. Virologically suppressed HIV for at least 6 months prior to screening. 2. Taking tenofovir disoproxil fumarate or tenofovir alafenamide containing regimen to treat HIV Exclusion Criteria: 1. History of inflammatory bowel disease or active inflammatory condition of the GI tract 2. History of significant gastrointestinal bleeding 3. Current medically-indicated use of warfarin or heparin or other anticoagulant medications associated with increased risk for bleeding following mucosal biopsy (e.g., daily high dose aspirin \[\>81 mg\], non-steroidal anti-inflammatory drugs \[NSAIDs\], or Pradaxa®) 4. Use of systemic immunomodulatory medications within 4 weeks of enrollment 5. Use of rectally administered medications within 4 weeks of enrollment 6. Use of product containing nonoxynol-9 within 4 weeks of enrollment 7. Use of any investigational products within 4 weeks of enrollment 8. Any other clinical condition or prior therapy that, in the opinion of the investigator, would make the participant unsuitable for the study or unable to comply with the study requirements. Such conditions may include, but are not limited to, current or recent history of severe, progressive, or uncontrolled renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, neurological, or cerebral disease. 9. Active rectal infection (GC, Chlamydia, HSV). Participants screening positive for GC/CT at the time of endoscopy will be excluded from analysis (and replaced). For participants not undergoing a concurrent endoscopic procedure for indication unrelated to this study: 10. Hct \<36% 11. Platelet count \<150/mm3 12. International normalised ratio blood test \> 1.2