Global Self-Organization of the Cellular Metabolic Structure

Background: Over many years, it has been assumed that enzymes work either in an isolated way, or organized in small catalytic groups. Several studies performed using "metabolic networks models'' are helping to understand the degree of functional complexity that characterizes enzymatic dynamic systems. In a previous work, we used "dissipative metabolic networks'' (DMNs) to show that enzymes can present a self-organized global functional structure, in which several sets of enzymes are always in an active state, whereas the rest of molecular catalytic sets exhibit dynamics of on-off changing states. We suggested that this kind of global metabolic dynamics might be a genuine and universal functional configuration of the cellular metabolic structure, common to all living cells. Later, a different group has shown experimentally that this kind of functional structure does, indeed, exist in several microorganisms. Methodology/Principal Findings: Here we have analyzed around 2.500.000 different DMNs in order to investigate the underlying mechanism of this dynamic global configuration. The numerical analyses that we have performed show that this global configuration is an emergent property inherent to the cellular metabolic dynamics. Concretely, we have found that the existence of a high number of enzymatic subsystems belonging to the DMNs is the fundamental element for the spontaneous emergence of a functional reactive structure characterized by a metabolic core formed by several sets of enzymes always in an active state. Conclusions/Significance: This self-organized dynamic structure seems to be an intrinsic characteristic of metabolism, common to all living cellular organisms. To better understand cellular functionality, it will be crucial to structurally characterize these enzymatic self-organized global structures.Supported by the Spanish Ministry of Science and Education Grants MTM2005-01504, MTM2004-04665, partly with FEDER funds, and by the Basque Government, Grant IT252-07

The α-ketoglutarate dehydrogenase complex in cancer metabolic plasticity

Deregulated metabolism is a well-established hallmark of cancer. At the hub of various metabolic pathways deeply integrated within mitochondrial functions, the α-ketoglutarate dehydrogenase complex represents a major modulator of electron transport chain activity and tricarboxylic acid cycle (TCA) flux, and is a pivotal enzyme in the metabolic reprogramming following a cancer cell’s change in bioenergetic requirements. By contributing to the control of α-ketoglutarate levels, dynamics, and oxidation state, the α-ketoglutarate dehydrogenase is also essential in modulating the epigenetic landscape of cancer cells. In this review, we will discuss the manifold roles that this TCA enzyme and its substrate play in cancer

Cannabinoid Receptors Are Overexpressed in CLL but of Limited Potential for Therapeutic Exploitation

<div><p>The cannabinoid receptors 1 and 2 (CNR1&2) are overexpressed in a variety of malignant diseases and cannabinoids can have noteworthy impact on tumor cell viability and tumor growth. Patients diagnosed with chronic lymphocytic leukemia (CLL) present with very heterogeneous disease characteristics translating into highly differential risk properties. To meet the urgent need for refinement in risk stratification at diagnosis and the search for novel therapies we studied CNR expression and response to cannabinoid treatment in CLL. Expression levels of CNR1&2 were determined in 107 CLL patients by real-time PCR and analyzed with regard to prognostic markers and survival. Cell viability of primary CLL cells was determined in suspension and co-culture after incubation in increasing cannabinoid concentrations under normal and reduced serum conditions and in combination with fludarabine. Impact of cannabinoids on migration of CLL cells towards CXCL12 was determined in transwell plates. We found CNR1&2 to be overexpressed in CLL compared to healthy B-cells. Discriminating between high and low expressing subgroups, only high CNR1 expression was associated with two established high risk markers and conferred significantly shorter overall and treatment free survival. Viability of CLL primary cells was reduced in a dose dependent fashion upon incubation with cannabinoids, however, healthy cells were similarly affected. Under serum reduced conditions, no significant differences were observed within suspension and co-culture, respectively, however, the feeder layer contributed significantly to the survival of CLL cells compared to suspension culture conditions. No significant differences were observed when treating CLL cells with cannabinoids in combination with fludarabine. Interestingly, biologic activity of cannabinoids was independent of both CNR1&2 expression. Finally, we did not observe an inhibition of CXCL12-induced migration by cannabinoids. In contrast to other tumor entities, our data suggest a limited usability of cannabinoids for CLL therapy. Nonetheless, we could define CNR1 mRNA expression as novel prognostic marker.</p></div

High CNR1 mRNA expression (≥ 1.52) confers significantly shorter survival in CLL patients (n = 107).

<p>(A) High expressing patients had a mean overall survival (OS) of 153 months compared to 277 months in low expressing patients (p = 0.001). (B) The mean treatment free survival (TFS) was 75 months in the CNR1 high group vs. 150 months in the CNR1 low group (p<0.0001).</p

Cytotoxic impact of cannabinoids on primary cells from healthy individuals.

<p>PBMC from 3 healthy donors were incubated in triplicates in suspension culture in increasing concentrations of compounds. Viability was determined after 48h, mean values and standard deviations are shown. (A) (R)-(+)-methanandamide. (B) (-)-cannabidiol. (C) ACEA. (D) JWH133. (E) AM251. (F) AM630. Note different scale on x-axis in A and D, note different scale on y-axis in D.</p

Impact of cannabinoids on CLL cell migration.

<p>B-cell enriched primary cells of 7 CLL patients (97.7% ± 1.04 CD19+CD5+) were incubated in transwell plates for 4h before the number of migrated cells was determined. Control experiments included CXCL12 alone (control), no CXCL12 (control w/o CXCL12), incubation with vehicle (DMSO, ethanol), and incubation with the CXCR4 inhibitor AMD3100. CLL cells were incubated either with agonist (ACEA, JWH133), antagonist (AM251, AM630), or a combination of antagonist plus agonist before migration (CB1: AMS251&ACEA; CB2: AM630&JWH133). Bars represent the mean values of migration indices + standard deviations, hatched lines indicate experimental blocks. *p = 0.0006; **p<0.0001.</p

P-values of the pairwise comparison of IC₅₀ values between suspension and co-culture in serum reduced experiments.

<p>P-values of the pairwise comparison of IC₅₀ values between suspension and co-culture in serum reduced experiments.</p

Comparison of patient characteristics between CNR1 high and low mRNA expressing groups.

<p>Comparison of patient characteristics between CNR1 high and low mRNA expressing groups.</p