The drive to replace synthetic dyes has never been more urgent. Common artificial colorants such as Allura Red, Tartrazine, Sunset Yellow, and Ponceau have been linked in various studies to oxidative damage in multiple organs, systemic inflammation, immune suppression, reduced male fertility, and allergic reactions affecting the skin, respiratory tract, and digestive system, particularly in children. Their environmental footprint is equally troubling: the same chemical stability that makes synthetic dyes attractive to manufacturers makes them poorly biodegradable, allowing them to persist and accumulate in water, soil, plants, and animals, with transformation products that may be toxic or potentially carcinogenic. Natural pigments from microalgae, lichens, plants, and bacteria have emerged as safer alternatives, and bacterial pigments in particular combine renewability, biocompatibility, and documented bioactivities ranging from antioxidant to anti-inflammatory and antimicrobial effects.

Indigoidine has long intrigued scientists because of its striking blue hue and its pharmacological promise, but producing it at industrially meaningful yields has been a persistent bottleneck. The new work began with a systematic comparison of culture media, screening Nutrient Broth, Tryptic Soy Broth, Peptone Glycerol Broth, and Luria-Bertani (LB) medium. Although Peptone Glycerol Broth supported the fastest bacterial growth, standard LB medium proved the most productive for pigment synthesis, yielding 75.8 milligrams of indigoidine per liter per 24 hours. The researchers then applied a two-stage statistical optimization strategy, first using a Plackett-Burman mixture design to identify the most influential nutritional and physicochemical variables, and then refining the three dominant factors with a central composite design implemented in Minitab software.

The results of that optimization were dramatic. Raising tryptone to 1.52 percent and yeast extract to 0.81 percent, introducing glucose at about 1 percent along with l-glutamine, magnesium sulfate, and potassium phosphate, and adjusting the culture to pH 7.8, 29 degrees Celsius, and 200 rpm agitation lifted indigoidine output to 177.4 milligrams per liter per 24 hours, a 2.34-fold increase over the standard medium. The response surface model predicted a maximum near 180 milligrams per liter, and the experimental value landed almost exactly on target, validating the statistical approach. The authors attribute the gains to a richer supply of amino acid and peptide precursors, improved ATP and cofactor availability, better oxygen transfer from increased agitation, and the metabolic support provided by magnesium and phosphate ions. Molecular oxygen is especially critical because it reoxidizes flavin mononucleotide during the enzymatic step catalyzed by the pigment-synthesizing enzyme BpsA.

Purification and characterization confirmed the quality of the product. Following ultrasonic disruption of the bacterial cells and a series of centrifugation and filtration steps, the pigment was recovered as a lyophilized powder with a purity of 92.3 percent, verified by LC-MS and by UV-visible spectroscopy showing the characteristic absorbance maximum at 612 nanometers. Stability testing then mapped how the pigment behaves under food-processing conditions. Indigoidine was most stable near neutral pH, with a half-life of about 150 hours at pH 7.8, but degraded rapidly at extremes, dropping to half-lives of just 3 hours at pH 1 and 10 hours at pH 12. Temperature told a similar story: the pigment endured for 240 hours at 4 degrees Celsius but lost half its content within 2 hours at 100 degrees Celsius. Darkness preserved it best, with a 220-hour half-life, while ultraviolet exposure cut that figure to 20 hours. These findings suggest that indigoidine is well suited to neutral-pH, refrigerated, light-protected applications.

Safety and bioavailability assessments added further credibility to the pigment’s industrial prospects. In a hemolysis assay using freshly isolated human erythrocytes, indigoidine caused less than 2 percent hemolysis at concentrations between 0.5 and 10 micrograms per milliliter, and even at the highest tested dose of 50 micrograms per milliliter hemolysis reached only 5.29 percent, within the generally accepted nontoxic threshold. A membrane distribution experiment showed that the pigment readily penetrates human cell membranes: at low concentrations more than 87 percent of the indigoidine was found inside the erythrocytes, indicating efficient cellular uptake, a property that could allow the molecule to reach intracellular targets in food and pharmaceutical contexts.

The most striking results, however, concerned metabolism. In what the study describes as a first, indigoidine was tested against key enzymes implicated in obesity and diabetes. The pigment inhibited alpha-amylase, the enzyme that breaks down starch and drives postprandial glucose spikes, with an IC50 of 0.69 micrograms per milliliter, close to the 0.36 micrograms per milliliter of the clinical drug acarbose. Molecular docking supported the finding, with a binding energy of minus 7.4 kilocalories per mole versus minus 7.7 for acarbose, and hydrogen bonds to ASP197, ASP300, and GLN63 plus pi-pi interactions with TRP59 stabilizing the complex. Against pancreatic lipase, the fat-digesting enzyme targeted by the anti-obesity drug orlistat, indigoidine actually outperformed the reference compound, achieving an IC50 of 0.37 micrograms per milliliter compared with 0.62 for orlistat, and a stronger docking score of minus 8.1 versus minus 6.9 kilocalories per mole.

Beyond blocking digestion, indigoidine activated the two master switches of cellular energy handling. AMPK, the cellular fuel gauge and a major therapeutic target for diabetes and insulin resistance, was stimulated in a dose-dependent manner up to 65.1 percent activation, with an EC50 of 1.36 micrograms per milliliter, near the 0.98 micrograms per milliliter of the reference activator A-769662. AKT, or protein kinase B, the linchpin of insulin signaling, glucose transport, and glycogen synthesis, was activated up to 65.6 percent with an EC50 of 4.59 micrograms per milliliter and a docking affinity almost identical to that of the standard activator SC79. To test these effects in a living, highly metabolic human cell system, the researchers exposed spermatozoa to the pigment. Glucose consumption rose to 133.4 percent of control at 20 micrograms per milliliter, AMPK activity peaked at 128.9 percent, and AKT activity reached 121.4 percent, all while showing less toxicity at high doses than either A-769662 or SC79, which suppressed metabolism sharply at elevated concentrations.

The convergence of enzyme inhibition, signaling activation, membrane penetration, and low hemotoxicity positions indigoidine as a rare multitarget natural compound, one that could serve simultaneously as a food colorant and a functional bioactive ingredient. The authors caution, however, that several hurdles remain before the pigment can move toward therapeutic use. In vivo studies are needed to confirm the metabolic effects observed in vitro, comprehensive toxicity and safety evaluations must be completed, pharmacokinetics and bioavailability in the body remain uncharacterized, and the precise molecular mechanisms of AMPK and AKT modulation require deeper investigation. Formulation optimization and scale-up of production will also be essential for any commercial application.

Even with those caveats, the study marks a significant advance on two fronts at once. It demonstrates that rational, statistics-guided fermentation can more than double the yield of a bacterial pigment without genetic manipulation of the production strain, and it reveals that the same molecule coloring our foods may also help regulate the digestive enzymes and metabolic pathways implicated in two of the world’s most widespread chronic diseases. As pressure mounts to phase out synthetic dyes and to find gentler, multifunctional alternatives, the deep blue chemistry of indigoidine may prove to be one of microbiology’s most colorful contributions to human health.

Subject of Research: Sustainable fermentation overproduction of the bacterial pigment indigoidine and its inhibitory and activating effects on enzymes involved in obesity, diabetes, and insulin signaling

Article Title: Sustainable Overproduction of the Bacterial Pigment Indigoidine as a Natural Colorant: Stability Evaluation, Inhibition of Obesity‐Diabetes‐Related Digestive Enzymes, and Activation of AMPK–AKT

Article References: Sustainable Overproduction of the Bacterial Pigment Indigoidine as a Natural Colorant: Stability Evaluation, Inhibition of Obesity‐Diabetes‐Related Digestive Enzymes, and Activation of AMPK–AKT. (n.d.). https://doi.org/10.1002/mbo3.70429

Image Credits: AI Generated

DOI: 10.1002/mbo3.70429

Keywords: indigoidine, bacterial pigment, natural colorant, fermentation optimization, alpha-amylase inhibition, pancreatic lipase, AMPK activation, AKT signaling, type 2 diabetes, obesity, Escherichia coli, food safety

AMPK sits at the very heart of cellular energy bookkeeping. When energy levels run low, the enzyme springs into action, switching on energy-producing processes and shutting down energy-consuming ones such as protein synthesis and cell growth. It is a heterotrimer, built from a catalytic alpha subunit and two regulatory partners, beta and gamma, and its sequence is strikingly conserved from fungi to humans. Maximal activity requires phosphorylation of a conserved threonine in the alpha subunit, a molecular switch that has been preserved across hundreds of millions of years of evolution. Decades of work in fruit flies, nematode worms and fission yeast have shown that genetic manipulations or dietary interventions that boost AMPK activity reliably produce longer-lived animals, making the enzyme one of the most compelling therapeutic targets in the biology of ageing.

The problem, until now, has been specificity. Metformin, the most famous AMPK-linked drug, activates the enzyme only indirectly, by perturbing the cellular AMP-to-ATP ratio and hitting mitochondrial and lysosomal targets along the way. Its effects in vivo are so tangled that studies in worms and flies have shown the drug’s lifespan-extending power actually flows through the gut microbiota rather than the host itself, and even in mammals there is evidence that bacteria mediate part of the response. That complexity has left the field with an uncomfortable question: is AMPK itself the pro-longevity target, or just one bystander among many? To answer it, the research team turned to 991, a synthetic molecule that binds in the so-called ADaM site, a pocket wedged between the alpha and beta subunits of AMPK, and locks the enzyme into its active state.

The first challenge was evolutionary. 991 had only ever been tested in mammalian systems, so the researchers built homology models of the fly, worm and yeast AMPK complexes against the known human crystal structure. The modelling revealed a high degree of overlap in the drug-binding pocket, including a key serine residue in the beta subunit that coordinates 991 binding, and conserved hydrophobic residues that stabilise the interaction between the beta subunit and the kinase domain. In the laboratory, the predictions held up beautifully. 991 allosterically activated AMPK purified from fruit fly cells in a dose-dependent manner, protected the enzyme from dephosphorylation by phosphatases, and boosted AMPK activity in extracts from wild-type worms but not from mutants lacking the AMPK alpha gene aak-2. Micromolar concentrations of 991 achieved what required millimolar doses of metformin or phenformin, a thousand-fold potency advantage that underscores the difference between direct and indirect activation.

Getting the drug into living organisms required some pharmaceutical finesse. In flies, 991 activated AMPK in vivo only when delivered in a chemically defined diet, which offers better drug bioavailability than standard yeast-based food, a reminder that in ageing research the medium can matter as much as the molecule. Western blotting confirmed that dietary 991 raised levels of phosphorylated, active AMPK in flies, worms and fission yeast alike. With the target engagement established across three phyla, the team moved to the question everyone wanted answered: does directly activating AMPK actually make animals live longer?

The answer was yes, and in a remarkably consistent pattern. Flies fed 991 in defined medium lived significantly longer than controls, with the effect highly statistically significant at both low and moderate doses. Fission yeast treated with 10 micromolar 991 showed extended chronological lifespan, a measure of how long stationary-phase cells survive. Nematode worms gained longevity on two different bacterial diets, the standard OP50 strain and the alternative BW25113, and the drug did not substantially alter bacterial growth, indicating that, unlike metformin, 991 acts on the worm host directly rather than through the microbes in its gut. The drug also reshaped metabolism in both animals: flies showed dose-dependent reductions in whole-body triglyceride stores without any change in feeding rate or glycogen content, while worms displayed altered lipid staining patterns. Fecundity in the flies was untouched, ruling out the classic trade-off in which reproduction is sacrificed for survival.

The most convincing evidence came from the genetic controls. Because AMPK alpha-null flies do not survive to adulthood, the researchers tested the drug in yeast and worm mutants lacking the catalytic subunit. In both cases, the lifespan benefit vanished entirely. The ssp2 yeast mutant, which is hypersensitive to any stress, was actually harmed by the drug, and the aak-2 mutant worms showed no extension at all. That loss-of-effect in the absence of the target is exactly what a rigorous pharmacological study should show, and it distinguishes this work from much of the longevity literature, where compounds often extend lifespan through murky, multi-target mechanisms that resist genetic dissection. Higher doses of 991 shortened lifespan in flies and yeast, a dose-response caution that the authors emphasise as critical for any future therapeutic development.

To bridge the gap to mammals, the team delivered 991 to mice using biodegradable polymeric nanoparticles, injected intravenously three times a week for three weeks. Unbiased proteomic analysis of liver tissue from treated wild-type mice, and from a short-lived muscular dystrophy model, revealed a clear molecular signature of AMPK activation: increased ATP biosynthesis, inhibition of the pro-ageing mTOR pathway, and enhanced mitochondrial biogenesis. Phenotypic ontology analysis flagged survival-related processes as the most enriched category among the responding proteins. While these proteomic shifts fall short of a demonstrated lifespan extension in mammals, they are precisely the profile that pro-longevity interventions produce, and they suggest the machinery responds to direct AMPK activation in mice much as it does in the invertebrates.

There is also a pharmaceutical tailwind behind these findings. Several major companies, including Merck, Pfizer, Boehringer Ingelheim and Poxel, have developed second-generation direct AMPK activators that bind the same ADaM site as 991. These compounds have better bioavailability than 991, have activated AMPK in vivo across a range of rodent studies, improving glucose homeostasis, dyslipidemia and fatty liver disease, and have even been given to non-human primates. Most strikingly, PXL770 has already been through human clinical trials for metabolic liver disease, showing good safety and improved lipid profiles after just four weeks of treatment. The path from a worm surviving longer on a drug-laced agar plate to a human pill is long, but it is considerably shorter when the pill in question already has clinical safety data.

The authors are careful about the limits of their work. The mouse data are preliminary, delivered by injection rather than diet, and longer-term metabolic and longevity studies in mammals remain to be done, likely using the improved second-generation activators. The downstream mechanisms by which AMPK activation extends lifespan in vivo are still unknown, and additional healthspan measures will be needed to complement survival curves. Even so, the study delivers something the ageing field has rarely possessed: a direct activator of a single, evolutionarily conserved target that extends lifespan in three distantly related organisms, fails to do so when the target is genetically removed, and produces a pro-longevity molecular signature in mammals. If metformin’s tangled story taught researchers anything, it is that longevity drugs need clean mechanisms. With 991, they may finally have one.

Subject of Research: Direct pharmacological activation of AMP-activated protein kinase as a conserved mechanism for extending lifespan across species

Article Title: Direct Pharmacological Activation of AMPK Extends Lifespan in Yeast, Worms and Flies

Article References: dos Santos, E., Blickling, M., Leiper, F. C., Alao, J.-P., Lennicke, C., Foley, A., Wilson, J. R., Gamblin, S. J., Chazaud, B., Lollo, G., Mounier, R., Juban, G., Rallis, C., Carling, D., Cabreiro, F., & Cochemé, H. M. (2026). Direct Pharmacological Activation of AMPK Extends Lifespan in Yeast, Worms and Flies. Aging Cell, 25(10), Article e70721. https://doi.org/10.1111/acel.70721

Image Credits: AI Generated

DOI: 10.1111/acel.70721

Keywords: AMPK, ageing, lifespan extension, 991, metformin, Drosophila, C. elegans, fission yeast, ADaM site, geroprotectors, metabolism, proteomics