Nitrite is the typical byproduct of nitric oxide (^•NO) autooxidation in biological systems. However, certain circumstances favor its reduction “back” to the signaling free radical, providing a non-enzymatic route for the synthesis of ^•NO. In pathophysiological conditions such as ischemia/reperfusion (I/R), where low oxygen availability limits nitric oxide synthase activity, nitrite reduction to ^•NO may allow protective modulation of mitochondrial oxidative metabolism and thus reduce the impact of I/R on brain tissue. In the current study, we used high-resolution respirometry to evaluate the effects of nitrite in an in vitro model I/R using hippocampal slices. We found that reoxygenation was accompanied by an increase in oxygen flux, a phenomenon that has been coined “oxidative burst”. The amplitude of this “oxidative burst” was decreased by nitrite in a concentration-dependent manner. These results support the notion that nitrite mediates a decrease in the hyper-reduction of the electron transport system during ischemia, decreasing the accelerated oxygen consumption that characterizes the reoxygenation phase of I/R that has been associated with an increase in oxidant production. Additionally, a pilot in vivo study in which animals received a nitrate-rich diet as a strategy to increase circulating and tissue levels of nitrite also revealed that the “oxidative burst” was decreased in the nitrate-treated animals. These results may provide mechanistic support to the observation of a protective effect of nitrite in situations of brain ischemia.

The physicochemical properties of nitric oxide (NO) as an intercellular messenger, in particular the way it conveys information via volume signaling, translate into advantages of communication in the brain. This becomes apparent when considering neurovascular coupling (NVC), the tightly temporal and spatial functional communication between active neurons and local blood microvessels. That the brain is energetically expensive given its mass and that increased neuronal activity in a region of the brain is associated with a local increase in blood flow (CBF) has been known since the XIX century. In turn, the association between CBF dysregulation and cognitive decline has been consistently established in older adults (brain aging, neurodegenerative diseases, type II DM) and lab rodent models but the neurobiological links are poorly understood. I will discuss the notion that neuronal-derived NO is the key mediator of NVC in the hippocampus and that impairment of NVC is an early and likely causative event leading to cognitive decline. The premise is that by rescuing the functionality of NVC then cognitive enhancement should be observed. This will be experimentally supported on basis of a diet-driven redox mechanism, involving the interaction of nitrite with ascorbate released from active neurons. Data suggest that an operational NVC, allocating energy resources according to neuronal activity, is a most fundamental biochemical process that underlines biological organization to support cognition.   

Supported by project 2022.05454.PTDC (https://doi.org/10.54499/2022.05454.PTDC).

Breast cancer is characterized by specific metabolic changes that support tumorigenesis, highlighting the emerging appreciation of cancer as a metabolic disease. These metabolic changes are simultaneous with redox reprogramming with nuclear factor erythroid 2-related factor 2 (Nrf2) representing their master integrator. Given that interscapular brown adipose tissue (IBAT) influences whole-body metabolism, our goal was to investigate the redox-metabolic crosstalk between the tumor and the host at the systemic level by exploring Nrf2-driven metabolic changes that occur in IBAT in the orthotopic model of breast cancer in wild-type (WT) and mice lacking functional Nrf2 (Nrf2KO). We analyzed the protein expression of key enzymes involved in glucose and lipid metabolism in control groups and at different points during tumor growth (10 mg, 50 mg, 100 mg, 200 mg, and 400 mg). In both WT and Nrf2KO mice, the results indicated a transient induction of hexokinase 2 expression during the early phase of tumor growth (<100 mg). Accordingly, pyruvate dehydrogenase expression followed the same profile. In Nrf2KO mice, a general decline in glyceraldehyde 3-phosphate dehydrogenase, phosphofructokinase-1, and glucose-6-phosphate dehydrogenase expression was detected during the late phase of tumor growth (>100 mg). Since no changes in WT mice occurred, these findings are considered Nrf2-dependent. Concomitantly, a decrease in protein expression of fatty acid synthase and acetyl-CoA carboxylase in Nrf2KO mice was observed. These observations correspond to decreased levels of 5'-AMP-activated protein kinase and hypoxia-inducible factor 1 during the late-phase (>100 mg) of tumor growth in Nrf2KO mice which suggests their involvement in transcriptional regulation. Our results revealed that IBAT metabolism responds to tumor growth and underscored that this communication is Nrf2-dependent giving implications for further understanding of breast cancer in the light of systemic metabolic disease.

This research was supported by the Science Fund of the Republic of Serbia, #7750238, Exploring new avenues in breast cancer research: Redox and metabolic reprogramming of cancer and associated adipose tissue - REFRAME.

The diverse uses of microalgae in ecological remediation, wastewater treatment, pharmaceutics, or food and biofuel production, have long kept these single-celled organisms in the spotlight. The focus of this study was on Chlamydomonas acidophila strain PM01, which thrives in acidic aquatic systems and is resistant to the presence of heavy metals in its environment. The redox metabolism of this microalga was assessed by its ability to reduce the EPR-active spin probe TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and compared to that of Chlorella sorokiniana strain CCAP 211/8K, a freshwater green microalga. The results showed that C. acidophila has a faster redox metabolic rate than C. sorokiniana, reducing 50% of TEMPO after 2.5, and 13 min, respectively. The addition of Mn²⁺ or Fe³⁺ to the culture medium of C. acidophila did not affect its reduction capacity, while it had a minor effect on C. sorokiniana. The faster rate in C. acidophila most likely represents the result of its adaptation to acidic environments. Namely, it has previously been suggested that acidophilic algae perform energy-demanding cellular processes in order to cope with the high pH gradient across the membrane. Moreover, the increased metabolic turnover requires an increased mitochondrial activity, resulting in a higher baseline production of superoxide and hydrogen-peroxide, subsequently compensated by an elevated baseline reduction capacity. Interestingly, the redox metabolic rate of C. sorokiniana was unaltered in suspensions that were kept in non-standard cultivation conditions (diurnal fluctuations of temperature and ambient lighting, absence of shaking) for five weeks. However, C. acidophila lost all of its reduction capacity in these conditions already after three days. These findings may be important when selecting the most appropriate microalgal strain for a specific application. Specifically, C. acidophila would likely be a good candidate for high-yield rapid production of endogenous products that are the result of its unique survival mechanism under extreme conditions.