CAMP is a key regulatory molecule that controls many important processes in the retina, including phototransduction, cell development and death, growth of neural processes, intercellular contacts, retinomotor effects, and so forth. The total content of cAMP changes in the retina in a circadian manner following the natural light cycle, but it also shows local and even divergent changes in faster time scales in response to local and transient changes in the light environment. Changes in cAMP might also manifest or cause various pathological processes in virtually all cellular components of the retina. Here we review the current state of knowledge and understanding of the regulatory mechanisms by which cAMP influences the physiological processes that occur in various retinal cells.

Due to the oncoming climate changes, various environmental stresses (drought, salinity, heavy-metals, low or high temperatures, etc.) might dramatically affect crop yields and the quality of produced foods. Therefore, to meet the growing food demand of the human population, improvement of stress tolerance of the currently cultured crops is required. The knowledge of the molecular underlying mechanisms provides a versatile instrument to correct plant metabolism via chemical tools and to thereby increase their adaptive potential. This will preserve crop productivity and quality under abiotic stress conditions. Endogenously produced nitric oxide (NO) is one of the key signaling factors activating stress tolerance mechanisms in plants. Thus, the application of synthetic NO donors as stress-protective phytoeffectors might support maintaining plant growth and productivity under stressful conditions. Sydnone imines (sydnonimines) are a class of clinically established mesoionic heterocyclic NO donors which represent a promising candidate group for such phytoeffectors. Therefore, here, we provide an overview of the current progress in the application of sydnone imines as exogenous NO donors in plants, with a special emphasis on their potential as herbicides as well as herbicide antidotes, growth stimulants and stress protectors triggering plant tolerance mechanisms. We specifically address the structure–activity relationships in the context of the growth modulating activity of sydnone imines. Growth stimulating or antidote effects are typical for 4-α-hydroxybenzyl derivatives of sydnone imines containing an alkyl substituent in position N-3. The nature of the substituent of the N-6 atom has a significant influence on the activity profile and the intensity of the effect. Nevertheless, further investigations are necessary to establish reliable structure–activity relationships (SAR). Consequently, sydnone imines might be considered promising phytoeffector candidates, which are expected to exert either protective effects on plants growing under unfavorable conditions, or herbicidal ones, depending on the exact structure.

The phototransduction cascade enables the photoreceptor to detect light over a wide range of intensities without saturation. The main second messenger of the cascade is cGMP and the primary regulatory mechanism is calcium feedback. However, some experimental data suggest that cAMP may also play a role in regulating the phototransduction cascade, but this would require changes in cAMP on a time scale of seconds. Currently, there is a lack of data on the dynamics of changes in intracellular cAMP levels on this timescale. This is largely due to the specificity of the sensory modality of photoreceptors, which makes it practically impossible to use conventional experimental approaches based on fluorescence methods. In this study, we employed the method of rapid cryofixation of retinal samples after light stimulation and subsequent isolation of outer segment preparations. The study employed highly sensitive metabolomics approaches to measure levels of cAMP. Additionally, PKA activity was measured in the samples using a western blot. The results indicate that when exposed to near-saturating but still moderate light, cAMP levels increase transiently within the first second and then return to pre-stimulus levels. The increase in cAMP activates PKA, resulting in the phosphorylation of PKA-specific substrates in frog retinal outer segments.

Diabetes mellitus is a chronic metabolic disorder characterized by persistent hyperglycemia, insulin dysfunction, and a substantial global health burden. Current pharmacological therapies often bring undesired side effects and limited long-term efficiency. These factors drive interest in the direction of preventive and complementary strategies. Plant-derived secondary metabolites – phenolics, alkaloids, terpenes, organosulfur compounds and polyacetylenes, demonstrate promising anti-diabetic activities. These compounds can modulate key molecular targets involved in glucose metabolism, insulin signaling, and development of oxidative stress, thereby improving glycemic control and reducing the risk of complications. Also, natural products can inhibit carbohydrate-digesting enzymes, enhance insulin secretion and sensitivity, regulate glucose transporters, and suppress pathways associated with inflammatory responses and the formation of advanced glycation end products (AGEs). Many of them also demonstrate pronounced antioxidant and antiglycative properties with all accompanying features - metal-chelating effects, α-dicarbonyl trapping properties, and interference with the AGE-RAGE axis, collectively mitigating vascular damage and attenuating diabetic complications such as nephropathy, neuropathy, and retinopathy. Recent studies highlight that certain plant metabolites can stabilize Nrf2, inhibit NF-κB activation, improve pancreatic β-cell function, and reduce protein tyrosine phosphatase activity. In this review we comprehensively address all this aspects with a special emphasis on the antiglycative properties as one of the central component of the overall anti-diabetic activity. Further, we discuss the further prospective in the biochemistry of plant-derived natural products in terms of antidiabetic, antiglycative and antioxidant agents. Although further research is needed to clarify their pharmacokinetics, safety, and efficacy in humans, the emerging evidence underscores the potential of plant secondary metabolites as natural, multifaceted agents for the prevention and management of diabetes and its associated complications.

The phototransduction cascade allows the photoreceptor to avoid saturation and retain the ability to detect light over a very wide range of intensities. The main second messenger of the cascade is cGMP and the main regulatory mechanism is calcium feedback, however some experimental data suggest that cAMP may also be involved in the regulation of the phototransduction cascade. For this to be the case, cAMP would have to change on a time scale of seconds. Currently, there are no data on the dynamics of changes in intracellular cAMP levels on this time scale, largely due to the specificity of the sensory modality of photoreceptors, where it is practically impossible to use conventional experimental approaches based on fluorescence methods. In the present work, we used the method of rapid cryofixation of retinal samples after light stimulation and subsequent isolation of outer segment preparations. Levels of cAMP were measured using highly sensitive metabolomics approaches. PKA activity was also measured in these samples by Western blot. We show that when illuminated with near-saturating but still moderate light, cAMP levels rise transiently within approximately the first second and then return to pre-stimulus levels. The increase in cAMP activates PKA, leading to phosphorylation of PKA-specific substrates in frog retinal outer segments.