Hematological alterations in protein malnutrition.

Protein malnutrition is one of the most serious nutritional problems worldwide, affecting 794 million people and costing up to $3.5 trillion annually in the global economy. Protein malnutrition primarily affects children, the elderly, and hospitalized patients. Different degrees of protein deficiency lead to a broad spectrum of signs and symptoms of protein malnutrition, especially in organs in which the hematopoietic system is characterized by a high rate of protein turnover and, consequently, a high rate of protein renewal and cellular proliferation. Here, the current scientific information about protein malnutrition and its effects on the hematopoietic process is reviewed. The production of hematopoietic cells is described, with special attention given to the hematopoietic microenvironment and the development of stem cells. Advances in the study of hematopoiesis in protein malnutrition are also summarized. Studies of protein malnutrition in vitro, in animal models, and in humans demonstrate several alterations that impair hematopoiesis, such as structural changes in the extracellular matrix, the hematopoietic stem cell niche, the spleen, the thymus, and bone marrow stromal cells; changes in mesenchymal and hematopoietic stem cells; increased autophagy; G0/G1 cell-cycle arrest of progenitor hematopoietic cells; and functional alterations in leukocytes. Structural and cellular changes of the hematopoietic microenvironment in protein malnutrition contribute to bone marrow atrophy and nonestablishment of hematopoietic stem cells, resulting in impaired homeostasis and an impaired immune response.

Malnutrition suppresses cell cycle progression of hematopoietic progenitor cells in mice via cyclin D1 down-regulation.

OBJECTIVE: Protein malnutrition (PM) often is associated with changes in bone marrow (BM) microenvironment leading to an impaired hematopoiesis; however, the mechanism involved is poorly understood. The aim of this study was to compare the cell cycle progression of hematopoietic stem cells (HSC) and hematopoietic progenitor cells (HPC) and evaluate the cell cycle signaling in malnourished mice to assess the mechanism of cell cycle arrest. METHODS: C57Bl/6J mice were randomly assigned in control and malnourished groups receiving normoproteic and hypoproteic diets (12% and 2% protein, respectively) over a 5-wk period. Nutritional and hematologic parameters were assessed and BM immunophenotypic analysis was performed. Cell cycle of HPC (Lin(-)) and HSC (Lin(-)Sca-1(+)c-Kit(+)) were evaluated after 6 h of in vivo 5-bromo-2'-deoxyuridine (BrDU) incorporation. Cell cycle regulatory protein expression of HPC was assessed by Western blot. RESULTS: Malnourished mice showed lower levels of serum protein, albumin, glucose, insulin-like growth factor-1, insulin, and higher levels of serum corticosterone. PM also caused a reduction of BM myeloid compartment resulting in anemia and leukopenia. After 6 h of BrDU incorporation, malnourished mice showed G0-G1 arrest of HPC without changes of HSC proliferation kinetics. HPC of malnourished mice showed reduced expression of proteins that induce cell cycle (cyclin D1, cyclin E, pRb, PCNA, Cdc25a, Cdk2, and Cdk4) and increased expression of inhibitory proteins (p21 and p27) with no significant difference in p53 expression. CONCLUSION: PM suppressed cell cycle progression mainly of HPC. This occurred via cyclin D1 down-regulation and p21/p27 overexpression attesting that BM microenvironment commitment observed in PM is affecting cell interactions compromising cell proliferation.

Effects of selenium on Pteridium aquilinum and urethane-induced lung carcinogenesis.

The results of our previous study demonstrated that ptaquiloside, the main toxic agent found in Pteridium aquilinum, suppresses natural killer (NK) cell-mediated cytotoxicity. However, the ability of ptaquiloside to suppress the cytotoxicity of NK cells was prevented by selenium supplementation. NK cells play an important role in the innate immune response and have the ability to kill tumor cells. Therefore, we hypothesized that selenium may prevent the higher susceptibility to urethane-induced lung carcinogenesis that has been observed in mice treated with P. aquilinum. The immunosuppressive effects of ptaquiloside have been associated with a higher number of urethane-induced lung nodules in mice. Hence, we assessed the effects of P. aquilinum-induced immunosuppression on urethane-induced lung carcinogenesis in C57BL/6 mice that had been supplemented with selenium. For these experiments, mice were treated with both an aqueous extract of P. aquilinum (20 g/kg/day) and selenium (1.3 mg/kg) by gavage once daily for 14 days followed by a once-weekly intraperitoneal injection of urethane (1 g/kg) for 10 weeks that was accompanied by gavage 5 days a week. Lung adenomas in mice that had been treated with P. aquilinum plus urethane occurred with a frequency that was 44% higher than that in mice that had been treated with only urethane. In mice that had been supplemented with selenium and treated with P. aquilinum plus urethane, the occurrence of lung adenomas was reduced to 26%. These results suggest that selenium prevents the immunosuppressive effects of P. aquilinum on urethane-induced lung carcinogenesis.