Mesoscopic models of neurotransmission as intermediates between disease simulators and tools for discovering design principles

Two grand challenges have been declared as premier goals of computational systems biology. The first is the discovery of network motifs and design principles that help us understand and rationalize why biological systems are organized in the manner we encounter them rather than in a different fashion. The second goal is the development of computational models supporting the investigation of complex systems, in particular, as simulation platforms in personalized medicine and predictive health. Interestingly, most published systems models in biology contain between a handful and a few dozen variables. They are usually too complicated for systemic analyses of organizing principles, but they are at the same time too coarse to allow reliable simulations of diseases. While it may thus appear that the modeling efforts of the past have missed the declared targets of systems biology, we argue in this article that midsized mesoscopic models are excellent starting points for pursuing both goals in computational systems biology.

Baifuzi reduces transient ischemic brain damage through an interaction with the STREX domain of BKCa channels

Stroke is a long-term disability and one of the leading causes of death. However, no successful therapeutic intervention is available for the majority of stroke patients. In this study, we explored a traditional Chinese medicine Baifuzi (Typhonium giganteum Engl.). We show, at first, that the ethanol extract of Baifuzi exerts neuroprotective effects against brain damage induced by transient global or focal cerebral ischemia in rats and mice. Second, the extract activated large-conductance Ca(2+)-activated K(+) channel (BK(Ca)) channels, and BK(Ca) channel blockade suppressed the neuroprotection of the extract, suggesting that the BK(Ca) is the molecular target of Baifuzi. Third, Baifuzi cerebroside (Baifuzi-CB), purified from its ethanol extract, activated BK(Ca) channels in a manner similar to that of the extract. Fourth, the stress axis hormone-regulated exon (STREX) domain of the BK(Ca) channel directly interacted with Baifuzi-CB, and its deletion suppressed channel activation by Baifuzi-CB. These results indicate that Baifuzi-CB activated the BK(Ca) channel through its direct interaction with the STREX domain of the channel and suggests that Baifuzi-CB merits exploration as a potential therapeutic agent for treating brain ischemia.

Effects of dopamine and glutamate on synaptic plasticity: a computational modeling approach for drug abuse as comorbidity in mood disorders

Major depressive disorder (MDD) affects about 16% of the general population and is a leading cause of death in the United States and around the world. Aggravating the situation is the fact that "drug use disorders" are highly comorbid in MDD patients, and VICE VERSA. Drug use and MDD share a common component, the dopamine system, which is critical in many motivation and reward processes, as well as in the regulation of stress responses in MDD. A potentiating mechanism in drug use disorders appears to be synaptic plasticity, which is regulated by dopamine transmission. In this article, we describe a computational model of the synaptic plasticity of GABAergic medium spiny neurons in the nucleus accumbens, which is critical in the reward system. The model accounts for effects of both dopamine and glutamate transmission. Model simulations show that GABAergic medium spiny neurons tend to respond to dopamine stimuli with synaptic potentiation and to glutamate signals with synaptic depression. Concurrent dopamine and glutamate signals cause various types of synaptic plasticity, depending on input scenarios. Interestingly, the model shows that a single 0.5 mg/kg dose of amphetamine can cause synaptic potentiation for over 2 h, a phenomenon that makes synaptic plasticity of medium spiny neurons behave quasi as a bistable system. The model also identifies mechanisms that could potentially be critical to correcting modifications of synaptic plasticity caused by drugs in MDD patients. An example is the feedback loop between protein kinase A, phosphodiesterase, and the second messenger cAMP in the postsynapse. Since reward mechanisms activated by psychostimulants could be crucial in establishing addiction comorbidity in patients with MDD, this model might become an aid for identifying and targeting specific modules within the reward system and lead to a better understanding and potential treatment of comorbid drug use disorders in MDD.

Unacceptable side-effects associated with a hyperosmolar vaginal microbicide in a phase 1 trial

We carried out a phase 1 trial of a candidate vaginal microbicide gel against HIV-1 and other sexually transmitted diseases, which contained cellulose acetate 1,2-benzenedicarboxylate (also known as cellulose acetate phthalate) in a glycerol-based vehicle. We had to terminate the study after five women had completed dosing, due to all women experiencing unacceptable vulvo-vaginal side-effects. Further investigations showed that the gel had a very high osmolality, which we believe led to excessive fluid transudation across the vaginal mucosa and acute mucosal dysfunction. We also showed that the rheology of the gel changed dramatically on fluid dilution. The osmolality and rheology of candidate microbicides and other genital mucosal products should therefore be analysed and considered at an early stage of product development.

Monoclonal antibody treatment to prolong the secondary cardiac allograft survival in alloantigen-primed mice

We have previously shown that costimulation blockade using a combination of monoclonal antibodies (mAbs) - CTLA4Ig, antibodies to CD154, LFA-1, and OX40L - can induce tolerance of cardiac allografts in mice with adoptively transferred CD4(+) memory T cells [1]. However, the effect of costimulatory blockade in secondary allograft rejection has not been studied. B6 mice that rejected BALB/c skin grafts for more than 4 weeks (defined as alloantigen-primed mice) were used as recipients. The recipient mice were treated with the mAbs to CD154, LFA-1, OX40L, and CD122 on days 0, 2, 4, and 6 after the secondary transplantation of BALB/c heart. The mean survival time (MST) of secondary cardiac allografts in rats treated with antibodies to CD154 and LFA-1 (2-antibodies approach) and those treated with antibodies to CD154, LFA-1, OX40L, and CD122 (4-antibodies approach) was greater than that of the controls (MST = 6.7 days, 22.2 days, and 3.2 days, respectively). The 4-antibodies approach prevented lymphocytic infiltration in the grafts, inhibited memory T-cells proliferation in the spleen, increased IL-10 secretion in the serum, and enhanced the expression of CD4(+) Foxp3(+) regulatory T cells (Tregs) in spleen. Expression levels of alloreactive antibodies were high in the recipient mice of experimental and control groups. Inhibiting the memory T cells by costimulation blockade extended allograft survival in secondary transplant models but could not induce tolerance of graft. Alloreactive antibodies may participate in alloresponse and play an important role in secondary cardiac allograft rejection.

Novel sulfated glucomannan-barium-alginate microcapsules in islet transplantation: significantly decreased the secretion of monocyte chemotactic protein 1 and improved the activity of islet in rats

The sulfated glucomannan can be used to filter the heparin-binding properties of cytokines. In this study, novel sulfated glucomannan-barium-alginate (SGA) microcapsules were prepared to encapsulate islets with barium-alginate (ABa) and calcium alginate-poly-l-lysine (APA) microcapsules as controls. SD rat islets were purified as donor cells to Lewis rats that had been treated with streptozotocin. Intraperitoneal transplantation was performed with about 3000 islet equivalent (IEQ) rat. At week three after transplantation, the concentrations of monocyte chemotactic protein-1 (MCP-1), interleukin (IL)-1 beta, interferon (IFN)-gamma, and tumor necrosis factor (TNF)-alpha in intraperitoneal fluid were determined using ELISA. At week 8, the islet cell mass in the abdominal microcapsules was excised to test insulin release. The EB-FDA fluorescence staining method was used to observe the functional activity of the islet cells. Compared with ABa and APA microcapsules, SGA microcapsules showed significantly decreased MCP-1 secretion by beta-cells. Also, the concentrations of cytokines IL-1beta, IFN-gamma, and TNF-alpha were decreased significantly. The activity of the transplanted islets was significantly improved in SGA microcapsules, which shielded against cytokines better than ABa or APA microcapsules and may serve as novel method.