Drug in focus is rapamycin, which functions by inhibiting mTOR pathway. Similar drugs include everolimus. Normally when over-activated by nutrients and insulin, mTOR acts via S6K to inhibit insulin signaling, thereby causing insulin resistance.
The evidence in preclinical and animal suggests that rapamycin is a universal anti-aging drug that is, it extends lifespan in all tested models from yeast to mammals, suppresses cell senescence and delays the onset of age-related diseases, which are manifestations of aging
Author lists advantages of rapamycin which include immunomodulator and anti inflammatory effects in addition to anti aging effects. Also it is know that rapamycin reduces viral replication. Some of the notable side effects include stomatitis and mucositis, non-infectious interstitial pneumonitis and nuetrophil inhibition which can lead to severe bacterial infections.
In addition to rapamycin/everolimus, other conventional drugs with anti-aging effect include metformin, aspirin, ACE inhibitors, angiotensin receptor blockers and PDE5 inhibitors such as Sildenafil and Tadalafil, can prevent or treat more than one age-related disease. In addition to above drugs calorie restriction and intermittent fasting has been shown to extend both the lifespan and healthspan in diverse species.
Dramatic calorie restriction have long been known to boost healthy lifespan and reduce the risk of heart attack, diabetes and other age-related conditions. In animal studies it is shown to extend life span in most animal species examined. Further research has shown that animals fed restricted-calorie diets are also better able to regenerate numerous tissues after injury.
When mice were allowed to eat without limit and were then exposed to radiation, their intestinal cells’ (in red) regeneration was limited (left). Mice fed a calorie-restricted diet showed a greatly enhanced regenerative capacity in their intestinal tissue (right). Credit: University of Pennsylvania.
A new study led by University of Pennsylvania researchers pinpoints the cell responsible for these improved regenerative abilities in the intestines. According to the scientists’ work, when a calorie-restricted mouse is subjected to radiation, a particular type of stem cell in the intestines, known as reserve stem cells, can survive and quickly rebuild intestinal tissues. The findings align with observations by oncologists that short-term fasting prior to chemotherapy can mitigate the severity of gastrointestinal destruction.
Christopher Lengner, an associate professor in Penn’s School of Veterinary Medicine collaborated on the work with lead author Maryam Yousefi, a graduate student in the Cell and Molecular Biology program at Penn Medicine and a Howard Hughes Medical Institute International Student Fellow, and other colleagues from Penn and China Agricultural University. Their work appears in the journal Stem Cell Reports.
One theory has been that calorie restriction slows age-related degeneration and enables more efficient tissue function by influencing the integrity and activity of adult stem cells, the precursor cells that dwell within specific tissues and give rise to the diversity of cell types that compose that tissue.
In prior work, Lengner’s lab has studied how certain stem cells in the intestines resist DNA damage. Perhaps, the researchers reasoned, calorie restriction is somehow targeting these stem cells to enhance their ability to resist damage.
Recent studies focused on the effects of calorie restriction on the active intestinal stem cells. While these active stem cells bear the burden of daily tissue turnover and act as the workhorses of intestinal function, they are also known to be highly susceptible to DNA damage, such as that induced by radiation exposure, and thus are unlikely to be the cells mediating the enhanced regeneration seen under calorie restriction, the Penn team reasoned.
Instead of looking at these active stem cells, Lengner’s group examined a second population of intestinal stem cells known as reserve stem cells. Lengner’s group and others had previously shown that these reserve stem cells normally reside in a dormant state and are protected from chemotherapy and radiation. Upon a strong injury that kills the active cells, these reserve stem cells “wake up” to regenerate the tissue.
To investigate this hypothesis, the scientists focused on how a subpopulation of mouse intestinal stem cells responded under calorie restriction and then when the animals were exposed to radiation. When mice were fed a diet reduced in calories by 40 percent from normal, the researchers observed that reserve intestinal stem cells expanded five-fold. Paradoxically, these cells also seemed to divide less frequently, a mystery the researchers hope to follow up on in later work.
When the research team selectively deleted the reserve stem cells in calorie-restricted mice, their intestinal tissue’s regeneration capabilities were cut in half, implicating these cells as having an important role in carrying out the benefits of calorie restriction.
“These reserve stem cells are rare cells,” Lengner said. “In a normal animal they may make up less than half a percentage of the intestinal epithelium and in calorie restricted animals maybe slightly more. Normally, in the absence of injury, the tissue can tolerate the loss, due to the presence of the active stem cells, but, when you injure the animal, the regeneration is compromised and the enhanced regeneration after calorie restriction was compromised in the absence of the reserve stem cell pool.”
To tease out the mechanism by which these cells were acting, the researchers compared the genes that were turned on in normal versus calorie-restricted animals. “It was very obvious,” Lengner said. “These reserve stem cells that we had shown were important for the beneficial effects of calorie restriction, were repressing many pathways that are all known to be regulated by the protein complex mTOR, which is most well known as being a nutrient-sensing complex.”
The finding made intuitive sense; researchers studying other tissue types had shown that activating mTOR can drive dormant cells out of quiescence, a necessary step for regeneration. Here, researchers found that reserve stem cells had low mTOR activity, and this was even lower upon calorie restriction. Lower mTOR activity correlated with resistance to injury. Yet in order to regenerate after the injury was over, these cells would need mTOR again.
“Curiously, we see that, when they’re injured, the calorie-restricted mice were actually better able to activate mTOR than their counterparts,” Lengner said. “So somehow, even though mTOR is being suppressed initially, it’s also better poised to become activated after injury. That’s something we don’t fully understand.”
The researchers, led by Yousefi, conducted experiments using leucine, an amino acid that activates mTOR, and rapamycin, a drug -which inhibits mTOR, to confirm that mTOR acted within these reserve stem cells to regulate their activity. Reserve stem cells exposed to leucine proliferated, while those exposed to rapamycin were blocked.
Pretreating the animals with leucine make the reserve stem cells more sensitive to radiation and less able to regenerate tissue following radiation injury, while rapamycin protected the reserve stem cells as they were more likely to remain dormant.
Lengner cautions, however, that rapamycin cannot be used as a stand-in for calorie restriction, as it would linger and continue to block mTOR activation even following injury, hindering the ability of the reserve stem cells to spring into action and regenerate intestinal tissue.
In future work, the researchers hope to drill down deeper, looking beyond nutrient signaling to see what type of signaling molecules can modulate the activation of reserve stem cells.
Research funding: Howard Hughes Medical Institute, National Natural Science Foundation of China, National Institute of Diabetes and Digestive and Kidney Diseases, National Cancer Institute, and Center for Molecular Studies in Digestive and Liver Diseases.
Studies of different animal species suggest a link between eating less and living longer, but the molecular mechanisms by which caloric restriction affords protection against disease and extends longevity are not well understood. New clues to help solve the mystery are presented in an article published in the September issue of Aging Cell by scientists at the Center for Research on Redox Processes in Biomedicine (Redoxoma), one of the Research, Innovation and Dissemination Centers (RIDCs) funded by FAPESP.
The results of in vitro and in vivo experiments performed by the Redoxoma team included the finding that a 40% reduction in dietary caloric intake increases mitochondrial calcium retention in situations where intracellular calcium levels are pathologically high. In the brain, this can help avoid the death of neurons that is associated with Alzheimer’s disease, Parkinson’s disease, epilepsy and stroke, among other neurodegenerative conditions.
“More than promoting the advantages of eating frugally, we aim to understand the mechanisms that make not overconsuming calories better for health. This can point to new targets for the development of drugs against various diseases,” said Ignacio Amigo, lead author of the article. The investigation was conducted at the University of São Paulo’s Chemistry Institute (IQ-USP) in Brazil during Amigo’s postdoctoral research.
According to Amigo, calcium participates in the process of communication between neurons. However, Alzheimer’s disease and other neurological disorders can cause an excessive influx of calcium ions into brain cells due to overactivation of neuronal glutamate receptors. This condition, known as excitotoxicity, can damage and even kill neurons.
To verify the effect of caloric restriction on excitotoxicity, Redoxoma’s scientists compared two groups of mice and rats. The control animals were given food and water ad libitum for 14 weeks and were overweight at the end of the experiment. The other group received a 40% caloric restriction (CR) diet for the same period.
“We calculated the daily amount of calories consumed on average by the control group and offered the other group 40% less,” Amigo explained. “They didn’t become underweight and remained healthy, although we supplemented their diet with vitamins and minerals to avoid malnutrition due to the restricted amount of food.”
In the first test, the animals were injected with kainic acid, a glutamate analogue with a similar effect in terms of inducing neuronal calcium influx, albeit more persistent. In rodents, it can cause brain damage, seizures and neuronal cell death due to overactivation of glutamate receptors in the hippocampus. It is used in the laboratory to mimic epilepsy.
Because previous research had shown that increasing mitochondrial calcium uptake can afford protection against excitotoxicity, he continued, “we decided to verify in vitro whether this was the case in our model. We isolated brain mitochondria from rats and again compared those fed ad libitum with those on a 40% caloric restriction diet. As we added calcium to the medium, we observed higher levels of mitochondrial calcium uptake in the caloric restriction group.”
The next step was to see what happened when the mitochondria isolated from each group were treated with cyclosporin, a drug known to increase calcium retention. While calcium uptake did indeed increase in the mitochondria from the control group, it remained unchanged in the caloric restriction group, eliminating the difference observed in the previous test.
“Cyclosporin’s target in mitochondria is well known,” Amigo said. “The drug inhibits the action of a protein called cyclophilin D, leading to increased mitochondrial calcium retention.”
In this case, however, cyclophilin D levels were found to be the same in both groups. The researchers therefore decided to measure the levels of other proteins that might be interfering with cyclophilin D’s action in the organism.
“We discovered that caloric restriction induces an increase in levels of a protein called SIRT3, which is capable of modifying the structure of cyclophilin D. It removes an acetyl group from the molecule in a process known as deacetylation, and this inhibits cyclophilin D, so that the mitochondria retain more calcium and become insensitive to cyclosporin,” Amigo said.
Just as other research groups had already found, the Redoxoma team also observed an increase in the activity of antioxidant enzymes such as glutathione peroxidase, glutathione reductase and superoxide dismutase in the caloric restriction rodents’ mitochondria. According to the scientists, these results suggest an enhanced capacity to manage cerebral oxidative stress, a condition that contributes to the onset of several degenerative diseases.
Many studies on the effects of caloric restriction on metabolism and cell signaling have been conducted at IQ-USP. Preliminary data suggest the change in mitochondrial calcium transport induced by caloric restriction may also occur in other tissues besides the brain, with different repercussions.
For Amigo, the proteins with activity affected by nutritional intervention in this recent study are potential targets to be explored for treatment of diseases in which excitotoxicity causes loss of neurons.
Publication: Caloric restriction increases brain mitochondrial calcium retention capacity and protects against excitotoxicity.
Authors: Ignacio Amigo et.,al.
Journal: Aging Cell
Adapted from press release by Agência FAPESP