Emerging from obscurity to challenge our fundamental understanding of how cells survive under stress
Simplified representation of a hydropersulfide molecule (RSSH)
In the intricate landscape of our cellular machinery, where countless molecules vie for attention, a group of unassuming compounds has emerged from obscurity to challenge our fundamental understanding of how cells survive under stress. Hydropersulfides—molecules characterized by a chain of sulfur atoms with a hydrogen atom attached—have been quietly existing in biological systems for eons, yet only recently have scientists begun to appreciate their profound significance.
What makes this story particularly fascinating is that while these molecules represent a frontier of modern biochemistry, their chemical foundations were actually laid down decades ago in forgotten laboratory notebooks. As researchers connect these historical dots, they're uncovering a sophisticated protection system that may have profound implications for understanding aging, degenerative diseases, and cellular resilience.
"What Is Old Is New Again" perfectly captures the paradoxical nature of this scientific quest 1 . Early chemists conducted extensive studies on persulfide chemistry more than sixty years ago, but this work proceeded before the biological significance was fully appreciated.
Today, armed with more sophisticated tools and a deeper understanding of cellular processes, scientists are returning to these early findings with fresh eyes, discovering that hydropersulfides likely represent an evolutionarily ancient mechanism for maintaining cellular health, one that predates and potentially complements more familiar antioxidant systems like glutathione.
Persulfide chemistry was studied over sixty years ago, but its biological significance is only now being fully appreciated 1 .
To understand the excitement surrounding hydropersulfides, we must first grasp their fundamental nature. At their simplest, hydropersulfides (chemical notation: RSSH) are sulfur-based molecules that can be visualized as cousins to the more familiar thiols (RSH)—compounds like cysteine and glutathione that play crucial roles in cellular function.
The critical difference lies in their atomic structure: where thiols possess a single sulfur atom bonded to hydrogen, hydropersulfides contain two sulfur atoms in sequence, with the terminal sulfur bonded to hydrogen. This seemingly minor structural variation translates into major differences in chemical behavior and biological function 1 5 .
The story of hydropersulfides is inextricably linked to that of hydrogen sulfide (H₂S), now recognized as an important signaling molecule in the body 1 4 .
H₂S is relatively unstable and reactive in cellular environments, yet it produces effects that suggest more precise and regulated activity than would be expected.
Researchers now hypothesize that RSSH may be responsible for at least part of the observed H₂S-mediated biology/physiology 1 .
Single sulfur atom bonded to hydrogen
Two sulfur atoms with terminal hydrogen
One of the most crucial functions of hydropersulfides appears to be their ability to protect critical cellular proteins from irreversible damage. Our cells are constantly bombarded by reactive oxygen species and electrophilic stressors—unstable molecules that can permanently disable essential enzymes and structural proteins by modifying their vulnerable sulfur-containing regions.
Traditional thinking held that glutathione, the most abundant cellular antioxidant, served as the primary defense against such threats. However, hydropersulfides may provide a more specialized and effective protection system 2 .
Perhaps the most groundbreaking discovery in recent years involves the role of hydropersulfides in preventing a specific type of cell death called ferroptosis. Unlike programmed cell death (apoptosis), ferroptosis is driven by a destructive chain reaction—lipid peroxidation—that ravages cellular membranes, ultimately causing them to fall apart.
In 2023, research published in Nature Chemical Biology revealed that hydropersulfides provide a potent parallel protection system against ferroptosis, one that operates independently of the GPX4 pathway 3 .
| Stress Type | Protective Mechanism | Biological Outcome |
|---|---|---|
| Oxidative Stress | Reacts with oxidants before they damage proteins | Preservation of enzyme function and cellular integrity |
| Electrophilic Stress | Scavenges toxic electrophiles that would modify DNA/proteins | Prevention of mutational damage and cellular dysfunction |
| Lipid Peroxidation | Terminates radical chain reactions through hydrogen atom transfer | Inhibition of ferroptosis and maintenance of membrane integrity |
| Heavy Metal Toxicity | Binds to toxic metal ions (e.g., mercury) | Protection against metal-induced autophagy and cell damage 6 |
The mechanism is both elegant and efficient. Hydropersulfides can preferentially react with oxidants and electrophiles, sacrificing themselves to spare more critical protein thiols. Even more remarkably, when hydropersulfides become modified in the process, they often form species that can be readily converted back to active thiols, unlike the irreversible damage that can occur when protein thiols are directly modified 2 .
This creates a protective buffer system—a molecular lightning rod that draws damaging strikes away from more essential cellular components.
Hydropersulfides act as sacrificial molecules, drawing damaging reactions away from critical cellular components 2 .
To understand how scientists established the connection between hydropersulfides and ferroptosis prevention, let's examine the groundbreaking 2023 study published in Nature Chemical Biology in detail 3 . The research team employed a multi-faceted approach:
| Genetic Manipulation | Effect on S⁰ Levels | Impact on Ferroptosis |
|---|---|---|
| CSE Overexpression | Increased | More resistant |
| CSE Knockdown | Decreased | More vulnerable |
| ETHE1 Overexpression | Decreased | More vulnerable |
| ETHE1 Knockdown | Increased | More resistant |
Based on data from 3
The experiments yielded compelling evidence for hydropersulfides as central players in ferroptosis protection:
When cells were treated with ferroptosis inducers, intracellular hydropersulfide levels significantly increased 3 .
Providing additional cysteine protected cells from ferroptosis even when GPX4 was completely absent 3 .
Hydropersulfides terminate radical chains through a unique autocatalytic regeneration mechanism 3 .
The researchers proposed that hydropersulfides terminate radical chain reactions through a unique autocatalytic cycle. When a hydropersulfide (RSSH) encounters a radical, it donates a hydrogen atom, becoming a perthiyl radical (RSS•). These perthiyl radicals then recombine to form tetrasulfides (RSSSSR), which can react with glutathione to regenerate hydropersulfides. This regeneration mechanism explains why relatively low concentrations of hydropersulfides (micromolar) can effectively protect against radical threats in an environment where glutathione is much more abundant (millimolar) 3 .
| Experimental Finding | Significance |
|---|---|
| Pro-ferroptotic conditions increase intracellular S⁰ levels | S⁰ biosynthesis is an adaptive cellular response to radical stress |
| Cysteine protects against ferroptosis independently of GPX4 | Reveals a new pathway for ferroptosis resistance beyond the classical GPX4 system |
| Manipulating S⁰ levels directly affects ferroptosis sensitivity | Establishes a causal relationship, not just correlation |
| Hydropersulfides terminate radical chains through H-atom transfer | Identifies a direct chemical mechanism for protection against lipid peroxidation |
| The autocatalytic regeneration of hydropersulfides | Explains how low concentrations can have potent effects |
Based on data from 3
As interest in hydropersulfides has grown, so too has the toolbox available for studying these elusive molecules.
These advanced detection tools (e.g., TP-Dise) allow scientists to monitor glutathione hydropersulfides (GSSH) in living cells and tissues with high spatial and temporal resolution 6 .
The "ratiometric" aspect means that measurements are self-calibrating, reducing artifacts and providing more reliable quantification.
To study the effects of hydropersulfides in biological systems, chemists have designed compounds that release RSSH under physiological conditions.
Recent innovations include alkylsulfenyl thiocarbonates—a class of RSSH precursors that efficiently generate hydropersulfides with tunable release kinetics .
Since specific enzymes control the balance of hydropersulfide production and degradation, researchers use both genetic and pharmacological approaches to manipulate this system.
For instance, inhibiting the persulfide-degrading enzyme ETHE1 increases endogenous persulfide levels, while activating CSE enhances production 3 .
Specialized mass spectrometry methods and chromatographic approaches have been developed to detect and quantify different hydropersulfide species in complex biological samples, though this remains technically challenging due to their reactivity.
Using advanced detection tools, researchers have determined that GSSH biosynthesis depends primarily on the sulfurtransferases CBS and CSE 6 .
Hydropersulfide donors have demonstrated protective effects against oxidative stress in cardiac myoblasts, providing experimental evidence for the cytoprotective roles of hydropersulfides .
The rediscovery of hydropersulfides represents a fascinating case study in how scientific understanding evolves—how clues from the past can merge with modern techniques to reveal profound biological truths. These molecules, once considered chemical curiosities or mere intermediates in metabolic pathways, are now recognized as central players in cellular defense with potentially far-reaching implications for human health and disease.
As research progresses, scientists are particularly excited about the therapeutic potential of hydropersulfides. Could compounds that enhance hydropersulfide production protect neurons in degenerative diseases like Alzheimer's and Parkinson's, where oxidative stress is a major contributor? Could they help prevent the cellular damage that occurs during heart attacks or strokes?
The ability of hydropersulfides to inhibit ferroptosis suggests possible applications in conditions where this form of cell death has been implicated, including certain cancers, neurodegenerative diseases, and ischemia-reperfusion injury 3 .
Perhaps the most compelling aspect of this story is how it exemplifies the nature of scientific discovery. As one review aptly notes, "What Is Old Is New Again" 1 . The early chemists who meticulously studied persulfide chemistry decades ago likely had little inkling that their work would eventually contribute to understanding fundamental cellular protection mechanisms.
Their foundational research, combined with modern insights, has revealed hydropersulfides as potentially "representing a primordial radical protection system" 3 —an ancient guardian that has been protecting our cells all along, waiting for science to appreciate its significance.
The story of hydropersulfides reminds us that sometimes, the most important scientific discoveries aren't just about finding something new—they're about looking with fresh eyes at what has been there all along.
Early chemical studies on persulfides
H₂S recognized as signaling molecule
Rediscovery of hydropersulfides
Link to ferroptosis established 3
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