Margaretha Viljoen

Ferritin and ferritin isoforms I: Structure–function relationships, synthesis, degradation and secretion

Abstract Ferritin is the intracellular protein responsible for the sequestration, storage and release of iron. Ferritin can accumulate up to 4500 iron atoms as a ferrihydrite mineral in a protein shell and releases these iron atoms when there is an increase in the cells need for bioavailable iron. The ferritin protein shell consists of 24 protein subunits of two types, the H-subunit and the L-subunit. These ferritin subunits perform different functions in the mineralization process of iron. The ferritin protein shell can exist as various combinations of these two subunit types, giving rise to heteropolymers or isoferritins. Isoferritins are functionally distinct and characteristic populations of isoferritins are found depending on the type of cell, the proliferation status of the cell and the presence of disease. The synthesis of ferritin is regulated both transcriptionally and translationally. Translation of ferritin subunit mRNA is increased or decreased, depending on the labile iron pool and is controlled by an iron-responsive element present in the 5′-untranslated region of the ferritin subunit mRNA. The transcription of the genes for the ferritin subunits is controlled by hormones and cytokines, which can result in a change in the pool of translatable mRNA. The levels of intracellular ferritin are determined by the balance between synthesis and degradation. Degradation of ferritin in the cytosol results in complete release of iron, while degradation in secondary lysosomes results in the formation of haemosiderin and protection against iron toxicity. The majority of ferritin is found in the cytosol. However, ferritin with slightly different properties can also be found in organelles such as nuclei and mitochondria. Most of the ferritin produced intracellularly is harnessed for the regulation of iron bioavailability; however, some of the ferritin is secreted and internalized by other cells. In addition to the regulation of iron bioavailability ferritin may contribute to the control of myelopoiesis and immunological responses.

The validity of melatonin as an oncostatic agent

ABSTRACT: The validity of melatonin as a prominent, naturally occurring oncostatic agent is examined in terms of its putative oncostatic mechanism of action, the correlation between melatonin levels and neoplastic activity, and the outcome of therapeutically administered melatonin in clinical trials. Melatonins mechanism of action is summarized in a brief analysis of its actions at the cellular level, its antioxidative functions, and its indirect immunostimulatory effects. The difficulties of interpreting melatonin levels as a diagnostic or prognostic aid in cancer is illustrated by referral to breast cancer, the most frequently studied neoplasm in trials regarding melatonin. Trials in which melatonin was used therapeutically are reviewed, i.e., early studies using melatonin alone, trials of melatonin in combination with interleukin‐2, and controlled studies comparing routine therapy to therapy in combination with melatonin. A table compiling the studies in which melatonin was used in the treatment of cancer in humans is presented according to the type of neoplasm. Melatonins suitability in combination chemotherapy, where it augments the anticancer effect of other chemotherapeutic drugs while decreasing some of the toxic side effects, is described. Based on the evidence derived from melatonins antiproliferative, antioxidative, and immunostimulatory mechanisms of action, from its abnormal levels in cancer patients and from clinical trials in which melatonin was administered, it is concluded that melatonin could indeed be considered a physiological anticancer substance. Further well‐controlled trials should, however, be performed in order to find the link between its observed effects and the underlying mechanisms of action and to define its significance as a therapeutic oncostatic agent.

Autonomic correlates at rest and during evoked attention in children with attention-deficit/hyperactivity disorder and effects of methylphenidate

Objective: The aim of this study was to assess autonomic nervous system functioning in children with attention-deficit/hyperactivity disorder (ADHD) and to examine the effects of methylphenidate and focussed attention. Method: Children with ADHD (n = 19) were tested while they were stimulant free and during a period in which they were on stimulants. On both occasions, autonomic nervous system functioning was tested at baseline and during focussed attention. Autonomic nervous system functioning of control subjects was also tested at baseline and during focussed attention. Autonomic nervous system activity was determined by means of heart rate variability (HRV) and skin conductivity analyses. Attention was evoked by means of the BioGraph Infiniti biofeedback apparatus. HRV was determined by time domain, frequency domain and Poincaré analysis of RR interval data. Skin conductivity was determined by the BioGraph Infiniti biofeedback apparatus. Results: The main findings of this study were (a) that stimulant-free children with ADHD showed a sympathetic underarousal and parasympathetic overarousal of the sympathovagal balance relative to control subjects; (b) methylphenidate shifted the autonomic balance of children with ADHD towards normal levels; however, a normal autonomic balance was not reached, and (c) stimulant-free children with ADHD exhibited a shift in the sympathovagal balance towards the sympathetic nervous system from baseline to focussed attention; however, methylphenidate appeared to abolish this shift. Conclusions: Stimulant-free children with ADHD have a parasympathetic dominance of the autonomic balance, relative to control subjects. Methylphenidate attempts to restore the normal autonomic balance in children with ADHD, but inhibits the normal autonomic nervous system response to a cognitive challenge. Clinical Applications: These results indicate that methylphenidate may have a suppressive effect on the normal stress response. Although this may be of benefit to those who interact with children who suffer from ADHD, the implications for the physiological and psychological well-being of the children themselves are debatable. Further research is needed. Limitations of the Study: Only 19 children with ADHD and 18 control subjects were tested. Further studies should include prior testing in order to exclude children with possible co-existing learning disabilities. Cognitive function and emotional responses of children with ADHD were not tested.

Ferritin and ferritin isoforms II: protection against uncontrolled cellular proliferation, oxidative damage and inflammatory processes.

Abstract Ferritin is a major iron storage protein involved in the regulation of iron availability. Each ferritin molecule comprises 24 subunits. Various combinations of H-subunits and L-subunits make up the 24-subunit protein structure and these ferritin isoforms differ in their H-subunit to L-subunit ratio, as well as in their metabolic properties. Ferritin is an acute-phase protein and its expression is up-regulated in conditions such as uncontrolled cellular proliferation, in any condition marked by excessive production of toxic oxygen radicals, and by infectious and inflammatory processes. Under such conditions ferritin up-regulation is predominantly stimulated by increased reactive oxygen radical production and by cytokines. The major function of ferritin in these conditions is to reduce the bio-availability of iron in order to stem uncontrolled cellular proliferation and excessive production of reactive oxygen radicals. Ferritin is not, however, indiscriminately up-regulated in these conditions as a marked shift towards a predominance in H-subunit rich ferritins occurs. Preliminary indications are that, while the L-subunit primarily fulfils the conventional iron storage role, the H-subunit functions primarily as rapid regulator of iron availability, and perhaps indirectly as regulator of other cellular processes. It is suggested that the optimum differential expression of the two subunits differ for different cells and under different conditions and that the expression of appropriate isoferritins offers protection against uncontrolled cellular proliferation, oxidative stress and against side effects of infectious and inflammatory conditions.

Heart Rate Variability Assessment of the Effect of Physical Training on Autonomic Cardiac Control

Background: The effect of exercise interventions on autonomic nervous system (ANS) control of the heart by heart rate variability (HRV) is often investigated in just one position. It was hypothesized that results of exercise‐induced changes on ANS are dependent on body position and that it is possible to distinguish between exercise induced changes in vagal and sympathetic influence by taking measurements in different body positions.

Importance of Tachogram Length and Period of Recording during Noninvasive Investigation of the Autonomic Nervous System

Background: Various disciplines use quantification of heart rate variability (HRV) as an indicator of autonomic function without recognizing the importance of using standardized methodologies. The aim of this study was to assess the influence of tachogram length and period of recording on HRV indicator values.

Pro- and Anti-Inflammatory Cytokines during Immune Stimulation: Modulation of Iron Status and Red Blood Cell Profile

Forty-eight patients were subdivided according to C-reactive protein (CRP) levels, resulting in 19 patients with normal (2.8 ± 2.8 mg/L) and 29 with elevated (82.2 ± 76.2 mg/L) CRP levels. The elevated CRP group had iron and red blood cell (RBC) profiles characteristic of chronic immune stimulation (CIS), and the normal CRP group, profiles of true iron deficiency. Normal relationships between storage iron, bioavailable iron, and RBC indices were absent in the elevated CRP group—implying the role of iron as major determinant of the RBC profile to be diminished during CIS. The elevated CRP group had significant increases in proinflammatory cytokines (INF-γ, TNF-α, Il-1β, Il-6, and Il-8). Anti-inflammatory cytokine levels were normal, except for Il-10, supporting previous indications that Il-10 contributes to reducing bioavailable iron. Regression analysis suggested decreases in transferrin to be related to increases in Il-8 and an increase in ferritin to be related to a decrease in Il-12 levels. TGF-β levels were positively related to transferrin and negatively to ferritin.

Relationship between exercise capacity and heart rate variability : supine and in response to an orthostatic stressor

The study investigated whether supine-measured HRV indicators, and/or HRV indicators measured during orthostatic stress are related to conventional measures of exercise and performance ability such as VO(2max). Only two significant correlations (p<0.05) out of 30 tests were found between supine-determined HRV indicators and conventional measures. In contrast, fifteen of the 30 relationships calculated during orthostatic stress were significant. Relationships were at best low to moderate (0.2<|corr|<0.4). As expected, the relationships obtained during orthostatic stress were reversed from that obtained in the supine position. In summary, although HRV indicators are related to cardiovascular fitness, correlations between VO(2max) and these parameters are found only under very specific conditions. HRV parameters explain very little of the variance in VO(2max). In addition, estimating the exercise capacity from HRV indicators requires experience and extreme caution.

Associations between psychological profiles and diseases: examining hemispheric dominance and autonomic activation as underlying regulators

Personality profiles are often typical for specific illnesses, e.g., the type A personality and heart disease. We hypothesize that many more such patterns exist, and have developed a scheme in which many diseases can be classified, depending on hemispheric dominance (i.e., integrated, intellectualising or emotional) and type of autonomic control (i.e., dominance of either sympathetic or parasympathetic system, or an increase in both types of autonomic outflow). Our hypothesis is based on recent findings in neurophysiology, involving the early rearing environmental effects on the developing orbitofrontal cortex, and attachment theory. We conclude with implications for therapy, and a discussion of the limitations of our hypothesis.

Acute Phase Proteins: Ferritin and Ferritin Isoforms

Ferritin is a positive acute phase reactant, exhibiting increased levels in blood during the acute phase response. Nevertheless, the precise role of ferritin as an acute phase reactant remains to be clarified. As for other acute phase proteins, ferritin is produced and secreted by hepatocytes. However, ferritin is also produced and secreted by other cell types, including macrophages and cancer cells. Many isoforms of ferritin (isoferritins) are found in the body, depending on the H-subunit to L-subunit ratio in the ferritin protein shell. The subunit composition of ferritin molecules is a major determinant of the functional properties of the ferritin isoforms. Expression of ferritin and its subunits is governed by the amount of metabolically available iron, the presence of oxidative stress and both proand antiinflammatory cytokines. Ferritin as an acute phase reactant is well known for its intracellular iron sequestration and storage abilities during immune activation (Weiss & Goodnough, 2005). This function is of high importance for protection of the body against microbial proliferation, oxidative damage, inflammation and cancer. Although the regulation of iron appears to be a primary function of ferritin in both normal conditions and during the acute phase response, other functions, beyond the control of iron bio-availability, have also been described. Although more investigations are required in order to clarify the precise role of ferritin as an acute phase reactant, this chapter shows a synopsis on the present knowledge on ferritin during the acute phase response. In the first part of this chapter (2-4), the processes of iron sequestration, storage and release by the ferritin molecule, the significance of the presence of isoferritins, and the regulation of the expression of ferritin by iron are described. In the next section (5) changes with diseases, and possible significance of extracellular (plasma) ferritin is discussed. In the last section (6-11) the differential up-regulation of H-subunit rich ferritins during the acute phase response, the importance of H-subunit rich ferritins in the withholding of iron by the macrophage, as well as its role in immune modulation, its pro-apoptotic and anti-apoptotic activities, and variations in cancer are addressed.