Chronic hyperglycemia has been associated with an increased prevalence of pathological conditions including cardiovascular disease, cancer, or various disorders of the immune system. In some cases, these associations may be traced back to a common underlying cause, but more often, hyperglycemia and the disturbance in metabolic balance directly facilitate pathological changes in the regular cellular functions. One such cellular function crucial for every living organism is cell cycle regulation/mitotic activity. Although metabolic challenges have long been recognized to influence cell proliferation, the direct impact of diabetes on cell cycle regulatory elements is a relatively uncharted territory. Among other “nutrient sensing” mechanisms, protein O-linked β-N-acetylglucosamine (O-GlcNAc) modification emerged in recent years as a major contributor to the deleterious effects of hyperglycemia. An increasing amount of evidence suggest that O-GlcNAc may significantly influence the cell cycle and cellular proliferation. In our present review, we summarize the current data available on the direct impact of metabolic changes caused by hyperglycemia in pathological conditions associated with cell cycle disorders. We also review published experimental evidence supporting the hypothesis that O-GlcNAc modification may be one of the missing links between metabolic regulation and cellular proliferation.

O‐linked β‐N‐acetlyglucosamine or O‐GlcNAc modification is a dynamic post‐translational modification occurring on the Ser/Thr residues of many intracellular proteins. The chronic imbalance between phosphorylation and O‐GlcNAc on tau protein is considered as one of the main hallmarks of Alzheimer's disease. In recent years, many studies also showed that O‐GlcNAc levels can elevate upon acute stress and suggested that this might facilitate cell survival. However, many consider chronic stress, including oxidative damage as a major risk factor in the development of the disease. In this study, using the neuronal cell line SH‐SY5Y we investigated the dynamic nature of O‐GlcNAc after treatment with 0.5 mM H2O2 for 30 min. to induce oxidative stress. We found that overall O‐GlcNAc quickly increased and reached peak level at around 2 hrs post‐stress, then returned to baseline levels after about 24 hrs. Interestingly, we also found that tau protein phosphorylation at site S262 showed parallel, whereas at S199 and PHF1 sites showed inverse dynamic to O‐Glycosylation. In conclusion, our results show that temporary elevation in O‐GlcNAc modification after H2O2‐induced oxidative stress is detectable in cells of neuronal origin. Furthermore, oxidative stress changes the dynamic balance between O‐GlcNAc and phosphorylation on tau proteins.

Our data suggest that the oxidative stress marker m-Tyr and physiologic p-Tyr may be handled differently in septic patients. The excretion of m-Tyr correlates with inflammation. m-Tyr may be actively secreted or produced in the kidney in some patients, whereas the decreased serum level of p-Tyr is a consequence of diminished renal production and not of renal loss.

Paclitaxel (taxol) is a chemotherapeutic agent frequently used in combination with other anti-neoplastic drugs. It is most effective during the M phase of the cell-cycle and tends to cause synchronization in malignant cells lines. In this study, we investigated whether timed, sequential treatment based on the cell-cycle characteristics could be exploited to enhance the cytotoxic effect of paclitaxel. We characterized the cell-cycle properties of a rapidly multiplying cell line (Sp2, mouse myeloma cells) by propidium-iodide DNA staining such as the lengths of various cell cycle phases and population duplication time. Based on this we designed a paclitaxel treatment protocol that comprised a primary and a secondary, timed treatment. We found that the first paclitaxel treatment synchronized the cells at the G2/M phase but releasing the block by stopping the treatment allowed a large number of cells to enter the next cell-cycle by a synchronized manner. The second treatment was most effective during the time when these cells approached the next G2/M phase and was least effective when it occurred after the peak time of this next G2/M phase. Moreover, we found that after mixing Sp2 cells with another, significantly slower multiplying cell type (Jurkat human T-cell leukemia) at an initial ratio of 1:1, the ratio of the two different cell types could be influenced by timed sequential paclitaxel treatment at will. Our results demonstrate that knowledge of the cell-cycle parameters of a specific malignant cell type could improve the effectivity of the chemotherapy. Implementing timed chemotherapeutic treatments could increase the cytotoxicity on the malignant cells but also decrease the side-effects since other, non-malignant cell types will have different cell-cycle characteristic and be out of synch during the treatment.

The aim of this study was to reveal whether increased reward dependence (RD) plays a role in the catecholamine neurotransmitter release and testosterone hormone regulation during physical activities among healthy trained participants. Twenty-two male participants (mean age: 40.27 ± 5.4 years) participated in this study. Two conditions were constructed, namely, a noncompetitive and a competitive running task (RT), which were separated by a 2-week interval. Urine and blood samples were collected prior to and following the running tasks. Noradrenaline (NA), adrenaline (A), dopamine (D), and their metabolites, vanillylmandelic acid (VMA) and homovanillic acid (HVA), were measured from urine, while testosterone levels were analyzed from blood samples. RD was assessed using the Cloninger’s Personality Inventory (PI). Mental health was evaluated using the WHO Well-Being, Beck Depression, and Perceived Life Stress Questionnaires. According to our findings, levels of NA, A, D, VMA, and testosterone released underwent an increase following physical exertion, independently from the competitive condition of the RT, while HVA levels experienced a decrease. However, we found that testosterone levels showed a significantly lower tendency to elevate in the competitive RT, compared with the noncompetitive condition (p = 0.02). In contrast, HVA values were higher in the competitive compared with the noncompetitive condition (p = 0.031), both before and after the exercise. Considering the factor RD, in noncompetitive RT, its higher values were associated with elevated NA levels (p = 0.007); however, this correlation could not be detected during the competitive condition (p = 0.233). Among male runners, the NA and testosterone levels could be predicted to the degree of RD by analyzing competitive and noncompetitive physical exercises.