Location-dependent sensing of nitric oxide and calcium ions in living rat kidney using an amperometric/potentiometric dual microsensor

Electrochemical Detection of Gasotransmitters: Status and Roadmap

Gasotransmitters, including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S), are a class of gaseous, endogenous signaling molecules that interact with one another in the regulation of critical cardiovascular, immune, and neurological processes. The development of analytical sensing mechanisms for gasotransmitters, especially multianalyte mechanisms, holds vast importance and constitutes a growing area of study. This review provides an overview of electrochemical sensing mechanisms with an emphasis on opportunities in multianalyte sensing. Electrochemical methods demonstrate good sensitivity, adequate selectivity, and the most well-developed potential for the multianalyte detection of gasotransmitters. Future research will likely address challenges with sensor stability and biocompatibility (i.e., sensor lifetime and cytotoxicity), sensor miniaturization, and multianalyte detection in biological settings.

Ion-selective electrodes based on laser-induced graphene as an alternative method for nitrite monitoring

Nitrite is an important food additive for cured meats; however, high nitrite levels pose adverse health effects to humans. Hence, monitoring nitrite concentration is critical to comply with limits imposed by regulatory agencies. Laser-induced graphene (LIG) has proven to be a scalable manufacturing alternative to produce high-performance electrochemical transducers for sensors. Herein, we expand upon initial LIG studies by fabricating hydrophilic and hydrophobic LIG that are subsequently converted into ion-selective sensors to monitor nitrite in food samples with comparable performance to the standard photometric method (Griess method). The hydrophobic LIG resulted in an ion-selective electrode with improved potential stability due partly to a decrease in the water layer between the electrode and the nitrite poly(vinyl) chloride-based ion-selective membrane. These resultant nitrite ion-selective sensors displayed Nernstian response behavior with a sensitivity of 59.5 mV dec-1, a detection limit of 0.3 ± 0.1 mg L-1 (mean ± standard deviation), and a broad linear sensing range from 10-5 to 10-1 M, which was significantly larger than currently published nitrite methods. Nitrite levels were determined directly in food extract samples of sausage, ham, and bacon for 5 min. These sensor metrics are significant as regulatory agencies limit nitrite levels up to 200 mg L-1 in finished products to reduce the potential formation of nitrosamine (carcinogenic compound). These results demonstrate the versatility of LIG as a platform for ion-selective-LIG sensors and simple, efficient, and scalable electrochemical sensing in general while demonstrating a promising alternative to monitor nitrite levels in food products ensuring regulatory compliance.

Ferroptosis: A Potential Therapeutic Target in Acute Kidney Injury

Ferroptosis is a recently recognized form of nonapoptotic cell death that is triggered by reactive oxidative species (ROS) due to iron overload, lipid peroxidation accumulation, or the inhibition of phospholipid hydroperoxidase glutathione peroxidase 4 (GPX4). Recent studies have reported that ferroptosis plays a vital role in the pathophysiological process of multiple systems such as the nervous, renal, and pulmonary systems. In particular, the kidney has higher rates of O₂ consumption in its mitochondria than other organs; therefore, it is susceptible to imbalances between ROS and antioxidants. In ischemia/reperfusion (I/R) injury, which is damage caused by the restoring blood flow to ischemic tissues, the release of ROS and reactive nitrogen species is accelerated and contributes to subsequent inflammation and cell death, such as ferroptosis, as well as apoptosis and necrosis being induced. At the same time, I/R injury is one of the major causes of acute kidney injury (AKI), causing significant morbidity and mortality. This review highlights the current knowledge on the involvement of ferroptosis in AKI via oxidative stress.

Development of an Electrochemical Dual H2S/Ca2+ Microsensor and Its In Vivo Application to a Rat Seizure Model

A dual electrochemical microsensor was fabricated for concurrent monitoring of hydrogen sulfide (H₂S) and calcium ions (Ca²⁺), which are closely linked important signaling species involved in various physiological processes. The dual sensor was prepared using a dual recessed electrode consisting of two platinum (Pt) microdisks (50 μm in diameter). Each electrode was individually optimized for the best sensing ability toward a target analyte. One electrode (WE1, amperometric H₂S sensor) was modified with electrodeposition of Au and electropolymerized polyaniline coating. The other electrode (WE2, all-solid-state Ca²⁺-selective electrode) was composed of Ag/AgCl onto the recessed Pt disk formed via electrodeposition/chloridation, followed by silanization and Ca²⁺-selective membrane loading. The current of WE1 and the potential of WE2 in a dual sensor responded linearly to H₂S concentration and logarithm of Ca²⁺ concentration, respectively, without a crosstalk between the sensing signals. Both WE1 and WE2 presented excellent sensitivity, selectivity (log⁡KH2S,iAmp≤-3.5, i = CO, NO, O₂, NO₂^-, AP, AA, DA, and GABA; and log⁡KCa2+,jPot≤-3.2, j = Na⁺, K⁺, and Mg²⁺), and fast response time with reasonable stability (during ca. 6 h in vivo experiment). Particularly, WE2 prepared using a mixture of two ionophores (ETH1001 and ETH129) and two plasticizers (2-nitrophenyl octyl ether and bis(2-ethylhexyl) sebacate) showed a very shortened response time (t_R to attain the ΔE/Δt slope of 0.6 mV/min = 3.0 ± 0.2 s, n ≥ 10), a critically required factor for real-time analysis. The developed sensor was utilized for simultaneous real-time monitoring of H₂S and Ca²⁺ changes at the brain cortex surface of a living rat during spontaneous epileptic seizures induced by a cortical 4-aminopyridine injection. The dynamic changes of H₂S and Ca²⁺ were clearly observed in an intimate correlation with the electrophysiological recording of seizures, demonstrating the sensor feasibility of in vivo and real-time simultaneous measurements of H₂S and Ca²⁺.

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).

Physiological and pathophysiological role of reactive oxygen species and reactive nitrogen species in the kidney

End‐stage renal disease is a leading cause of morbidity and mortality worldwide. The prevalence of the disease and the number of patients who receive renal replacement therapy are expected to increase in the next decade. Accumulating evidence suggests that chronic hypoxia in the tubulointerstitium represents the final common pathway to end‐stage renal failure, and that reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the key players in kidney injury. However, ROS and RNS that exceed the physiological levels associated with the pathophysiology of most kidney diseases. The molecules that comprise ROS and RNS play an important role in regulating solute and water reabsorption in the kidney, which is vital for maintaining electrolyte homeostasis and the volume of extracellular fluid. This article reviews the physiological and pathophysiological role of ROS and RNS in normal kidney function and in various kidney diseases.

Nitric oxide production by glomerular podocytes

Nitric Oxide (NO), a potent vasodilator and vital signaling molecule, has been shown to contribute to the regulation of glomerular ultrafiltration. However, whether changes in NO occur in podocytes during the pathogenesis of salt-sensitive hypertension has not yet been thoroughly examined. We showed here that podocytes produce NO, and further hypothesized that hypertensive animals would exhibit reduced NO production in these cells in response to various paracrine factors, which might contribute to the damage of glomeruli filtration barrier and development of proteinuria. To test this, we isolated glomeruli from the kidneys of Dahl salt-sensitive (SS) rats fed a low salt (LS; 0.4% NaCl) or high salt (HS; 4% NaCl, 3 weeks) diets and loaded podocytes with either a combination of NO and Ca²⁺ fluorophores (DAF-FM and Fura Red, respectively) or DAF-FM alone. Changes in fluorescence were observed with confocal microscopy in response to adenosine triphosphate (ATP), angiotensin II (Ang II), and hydrogen peroxide (H₂O₂). Application of Ang II resulted in activation of both NO and intracellular calcium ([Ca²⁺]_i) transients. In contrast, ATP promoted [Ca²⁺]_i transients, but did not have any effects on NO production. SS rats fed a HS diet for 3 weeks demonstrated impaired NO production: the response to Ang II or H₂O₂ in podocytes of glomeruli isolated from SS rats fed a HS diet was significantly reduced compared to rats fed a LS diet. Therefore, glomerular podocytes from hypertensive rats showed a diminished NO release in response to Ang II or oxidative stress, suggesting that podocytic NO signaling is dysfunctional in this condition and likely contributes to the development of kidney injury.