The Invisible Shield
How Zeljko Bosnjak's Research Reveals Why Anesthetics Sometimes Fail to Protect Diabetic Hearts
Introduction: The Scientist and the Mystery
When Zeljko J. Bosnjak, Ph.D. received the 2008 Excellence in Research Award from the American Society of Anesthesiologists, it represented far more than just personal achievement—it recognized a career dedicated to solving one of medicine's most perplexing puzzles: why do life-saving anesthetic protections sometimes fail in patients with diabetes? This question has driven decades of research that has fundamentally changed how we understand the intersection of metabolic disease and cardiovascular health.
Bosnjak's journey to this prestigious award is as remarkable as his science. Born in post-World War II Croatia, his family eventually emigrated to the United States in 1970, settling in Milwaukee, Wisconsin 4 . Despite early hardships, Bosnjak pursued science with determination, earning a doctorate in physiology from the Medical College of Wisconsin and establishing himself as a leading researcher. His work has bridged continents, fostering scientific collaboration between the United States and Croatia, training numerous scientists, and contributing significantly to our understanding of cardiovascular pharmacology 4 .
2008 Excellence in Research Award
American Society of Anesthesiologists
The Heart of the Matter: When Protection Fails
The Anesthetic Cardioprotection Phenomenon
For decades, anesthesiologists have observed that certain anesthetic agents, particularly volatile gases like isoflurane, provide an unexpected benefit: they protect heart tissue from damage during periods of oxygen deprivation and subsequent restoration (ischemia-reperfusion injury). This protective effect works through complex cellular mechanisms that essentially make heart cells more resilient to stress.
The Diabetes Paradox
However, this protective phenomenon has a crucial exception—it consistently fails in patients with diabetes and hyperglycemia (high blood sugar). This medical paradox has serious implications: diabetic patients undergoing surgery face significantly higher risks of cardiovascular complications when the very agents meant to protect them become less effective.
Bosnjak and his team dedicated themselves to uncovering why this failure occurs and how it might be prevented. Their research revealed that the answer lies deep within our cells, in the tiny power plants called mitochondria, and their intricate relationship with blood sugar levels 2 6 .
A Revolutionary Model: Stem Cells and Human Hearts
The Limitations of Animal Models
Much early research on anesthetic cardioprotection relied on animal models. While valuable, these models couldn't fully replicate human physiology, particularly the complex metabolic disruptions of human diabetes. Scientists needed a better system to study these interactions in human cells.
The process involves reprogramming ordinary human cells (like skin cells) back to an embryonic-like state, then redirecting them to become heart muscle cells. These cells beat rhythmically in culture dishes and respond much like native heart cells, providing an ethical, accurate, and manipulable model for studying human heart function and disease 5 .
Human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) in culture
The Pivotal Experiment: Glucose, Anesthetics, and Heart Cells
Methodology: Tracing a Cellular Mystery
In their crucial 2016 study published in Anesthesia & Analgesia, Bosnjak's team designed an elegant experiment to unravel the glucose-anesthetic interaction 2 6 :
1. Cell Culture Preparation
Human iPSC-derived cardiomyocytes were cultured under three different glucose conditions: normal (5 mM), moderately elevated (11 mM), and high (25 mM) for 24 hours.
2. Anesthetic Exposure
Cells were exposed to isoflurane (a common volatile anesthetic) at approximately one minimum alveolar concentration (0.5 mM) for 30 minutes.
3. Stress Simulation
Researchers then subjected the cells to oxidative stress using hydrogen peroxide (H₂O₂) to simulate the damaging effects of ischemia-reperfusion injury.
4. Measurements
Multiple endpoints were assessed:
- Cell viability using fluorescence-based live/dead assays
- Reactive oxygen species (ROS) production measured with fluorescent probes
- Mitochondrial fission visualized through confocal microscopy
- Key protein expression (Drp1 activation) analyzed via Western blot
- Mitochondrial permeability transition pore (mPTP) opening assessed with fluorescent dyes
Revelations from the Petri Dish
The results were striking:
- Isoflurane provided significant protection against oxidative stress in normal (5 mM) and moderately elevated (11 mM) glucose conditions
- This protective effect was completely lost in high glucose (25 mM) conditions
- High glucose environments dramatically increased reactive oxygen species production and induced mitochondrial fission (fragmentation of the mitochondrial network)
- The mitochondrial fission protein Drp1 showed increased activation in high glucose conditions
Most importantly, when researchers administered compounds that scavenge ROS (Trolox) or inhibit mitochondrial fission (mdivi-1), the cardioprotective effects of isoflurane were restored even in high glucose conditions 2 6 .
Data Presentation: Understanding the Mechanisms
Effects of Glucose Concentration on Cellular Processes
| Glucose Concentration | ROS Production | Mitochondrial Fission | Drp1 Activation | Isoflurane Protection |
|---|---|---|---|---|
| 5 mM (Normal) | Baseline | Minimal | Baseline | Yes |
| 11 mM (Moderate) | Significantly increased | Minimal | Minimal change | Yes |
| 25 mM (High) | Dramatically increased | Pronounced fragmentation | Significantly increased | No |
Essential Research Reagent Solutions
| Reagent/Tool | Function | Research Application |
|---|---|---|
| Human iPSCs | Differentiate into human cardiomyocytes | Provides a relevant human model for study without ethical concerns of human subject research |
| Isoflurane | Volatile anesthetic agent | Testing cardioprotective properties under various conditions |
| Trolox | ROS scavenger | Reduces oxidative stress to test its role in cardioprotection |
| Mdivi-1 | Inhibitor of mitochondrial fission | Tests whether preventing fission restores anesthetic protection |
| TMRE dye | Mitochondrial membrane potential indicator | Assesses mitochondrial health and function |
Key Experimental Findings
| Experimental Condition | Cell Viability | ROS Levels | Mitochondrial Fission | mPTP Opening |
|---|---|---|---|---|
| Normal Glucose + Stress | Low | High | Moderate | Rapid |
| Normal Glucose + Isoflurane + Stress | High | Moderate | Minimal | Delayed |
| High Glucose + Stress | Low | Very High | Pronounced | Rapid |
| High Glucose + Isoflurane + Stress | Low (no protection) | Very High | Pronounced | Rapid (no delay) |
| High Glucose + Isoflurane + Trolox/mdivi-1 + Stress | High (protection restored) | Moderate | Minimal | Delayed |
Impact of Glucose Levels on Cell Viability with Isoflurane Treatment
Beyond the Laboratory: Implications for Patient Care
The implications of Bosnjak's work extend far beyond basic research. By identifying the specific mechanisms through which high glucose disrupts anesthetic cardioprotection, his team opened doors to potential clinical interventions:
Personalized Anesthesia Management
Patients with diabetes or hyperglycemia might receive tailored anesthetic protocols that include tight preoperative glucose control, adjunctive therapies like ROS scavengers, and selection of alternative anesthetic agents.
Therapeutic Targets
The research identifies specific molecular targets for drug development including Drp1 inhibition to prevent excessive mitochondrial fission and antioxidant therapies to reduce ROS burden.
Improved Surgical Outcomes
Ultimately, this research may lead to reduced cardiovascular complications in diabetic patients undergoing surgery, potentially saving lives and improving recovery experiences.
The Research Legacy: Beyond a Single Discovery
Bosnjak's contributions to science extend beyond this single line of investigation. His research has also explored:
Ketamine's Neurotoxic Effects
Studied ketamine's effects on developing human neurons derived from stem cells, revealing potential risks in pediatric anesthesia .
Mitochondrial Dynamics
Explored mitochondrial dynamics in various cell types and their role in health and disease.
International Scientific Collaboration
Fostered collaboration between U.S. and Croatian researchers, training dozens of scientists who have advanced biomedical research globally 4 .
Conclusion: Protection Restored
Zeljko Bosnjak's research journey demonstrates how scientific curiosity, pursued with rigor and creativity, can transform medical understanding and practice. His work has moved us from observing a clinical paradox to understanding its fundamental mechanisms and developing potential solutions.
The 2008 Excellence in Research Award recognized not just a single achievement, but a career of dedicated investigation that has made surgery safer for diabetic patients worldwide. As research continues to build on Bosnjak's foundational work, we move closer to personalized anesthetic approaches that account for each patient's metabolic profile, ensuring that the protective benefits of anesthetics are available to all, regardless of their blood sugar levels.
Through stem cell technology, meticulous experimentation, and interdisciplinary collaboration, Bosnjak and his team have shown that even when nature creates obstacles to protection, science can find pathways around them—offering hope for more equitable medical outcomes for patients with metabolic diseases.