Glossary: peptides, biomarkers and longevity terms

Most explanations of this vocabulary are either a research abstract or a product page. This is neither. Each entry says what the term means, what the human evidence does and does not cover, and whether Baseline offers anything related to it. Where the honest answer is that nobody knows yet, the entry says that.

  • SS-31 A short synthetic peptide that concentrates in the inner mitochondrial membrane, studied as a drug for mitochondrial disease rather than as a wellness compound.
  • 5-Amino-1MQ A small molecule that blocks the enzyme NNMT, sold widely as a metabolic capsule despite having no published human trials.
  • Dihexa An angiotensin IV derived peptide that promoted synapse formation in rodent models of cognitive impairment, with no human data at all.
  • Thymosin alpha-1 A 28 amino acid thymic peptide that modulates T cell responses, licensed as a medicine in some countries and not approved in the United States.
  • Thymosin beta-4 An actin sequestering protein present in most human cells that promotes cell migration and tissue repair in animal models, and the source of the fragment sold as TB-500.
  • Pentadeca arginate A marketed variant of BPC-157 in arginate salt form, promoted as more stable, with no peer-reviewed human or animal studies of the variant itself.
  • GLP-1 receptor agonist A class of injectable medicines that mimic the gut hormone GLP-1, slowing gastric emptying and reducing appetite signaling, with the largest outcome trial base in modern metabolic medicine.
  • Retatrutide An investigational triple agonist at the GIP, GLP-1 and glucagon receptors that produced the largest weight reductions yet reported in a phase 2 obesity trial.
  • NAD+ precursors Oral compounds such as nicotinamide riboside and NMN that raise blood NAD+ levels reliably, with human functional outcomes that remain small and inconsistent.
  • Cystatin C A protein filtered by the kidneys that estimates kidney function without depending on muscle mass, which makes it more reliable than creatinine in lean or very muscular people.
  • GDF-15 A stress-responsive cytokine that rises with cellular and mitochondrial stress, tracks mortality risk across many conditions, and drives appetite suppression through a brainstem receptor.
  • Homocysteine An amino acid intermediate that accumulates when B12, folate or B6 handling falters, associated with cardiovascular and cognitive risk, though lowering it with B vitamins has not reduced events in trials.
  • Ferritin The main iron storage protein, and the first test for iron deficiency, with the important catch that inflammation raises it independently of iron status.
  • SHBG A liver protein that binds most circulating testosterone and estradiol, so it determines how much of a total hormone reading is actually available to tissue.
  • HbA1c The share of hemoglobin with glucose attached, reflecting average blood glucose over roughly the previous two to three months.
  • Fasting insulin The amount of insulin circulating after an overnight fast, which usually rises years before fasting glucose does.
  • Omega-3 index The percentage of EPA and DHA in red blood cell membranes, a stable measure of long term omega-3 intake rather than what you ate yesterday.
  • Serum albumin The most abundant protein in blood, made by the liver, and one of the strongest single predictors of mortality on an ordinary blood panel.
  • Red cell distribution width A measure of how variable red blood cell size is, originally used to classify anemia, now recognized as a broad predictor of mortality risk.
  • Creatinine A waste product of muscle metabolism cleared by the kidneys, used to estimate filtration rate, and therefore sensitive to how much muscle you carry.
  • Autophagy The cell's recycling process, in which damaged proteins and organelles are packaged and broken down for reuse, upregulated by fasting and exercise.
  • mTOR A protein kinase that senses nutrients and growth signals and decides whether a cell builds or recycles, and the target of the best validated lifespan extending drug in mammals.
  • AMPK The cell's low energy sensor, activated when ATP falls, which switches metabolism from building to burning and turns on repair processes.
  • Sirtuins A family of enzymes that remove chemical tags from proteins using NAD+ as a substrate, linking cellular energy status to gene regulation and repair.
  • Cellular senescence A state in which a damaged cell permanently stops dividing but stays alive and secretes inflammatory signals that affect the tissue around it.
  • Senolytics Drugs that selectively kill senescent cells, promising in mice and still at the stage of small early phase human trials.
  • Biological age An estimate of how old your body appears to be based on measured markers rather than your birth date, useful as a summary and often oversold as a verdict.
  • Epigenetic clocks Age estimates built from DNA methylation patterns at specific sites in the genome, accurate across populations and still unreliable for tracking one person over months.
  • Visceral fat Fat stored around the abdominal organs, metabolically active and far more strongly linked to cardiometabolic risk than fat stored under the skin.
  • Sarcopenia Age related loss of muscle mass and strength, defined clinically by low strength first, with mass and physical performance used to confirm and stage it.