Sir-dependent downregulation of various aging processes

Evaluation of free-radical quenching properties of standard Ayurvedic formulation Vayasthapana Rasayana

BACKGROUND

Cellular damage induced by free-radicals like Reactive Oxygen and Nitrogen Species (ROS and RNS) has been implicated in several disorders and diseases, including ageing. Hence naturally occurring anti-oxidant rich-herbs play a vital role in combating these conditions. The present study was carried out to investigate the in vitro free-radical quenching capacity of a known Ayurvedic poly-herbal formulation called Vayasthapana Rasayana.

METHODS

Methanol extracts of Vayasthapana Rasayana formulation (VRF) were studied for in vitro total antioxidant activity along with phenolic content and reducing power. In vitro assays like DPPH, FRAP, ABTS scavenging to evaluate radical quenching potential were performed.

RESULTS

The formulation has shown 94% at 0.1 mg/ml DPPH free-radical scavenging activity as against 84% at 0.1 mg/ml for standard ascorbic acid (IC₅₀ value 5.51 μg/ml for VRF and 39 μg/ml for standard). It has a significant higher ferric reducing potential also (OD 0.87 at 700 nm & 0.21 at 0.1 mg/ml for VRF and standard, respectively). The total phenolic content (gallic acid equivalent) of the VRF is 8.3 mg per g of dry mass. Total antioxidant capacity of the formulation, estimated by FRAP was 1150 ± 5 μM Fe(II)/g dry mass. ABTS radical scavenging activity of VRF was 69.55 ± 0.21% at 100 μg/ml concentration with a IC50 value of 69.87 μg/ml as against 9% and 95% by ascorbic acid and Trolox (at 70.452 μg/ml and 0.250 μg/ml concentrations, respectively).

CONCLUSION

In Indian traditional Ayurvedic system, use of VRF is in regular practice for mainly combating age-related disorders and diseases as many of the components of the Rasayana are known for their free-radical scavenging activity. This study has validated the potential use of VRF as an anti-oxidant to fight age-related problems.

A fitness-based interferential genetics approach using hypertoxic/inactive gene alleles as references

Genetics, genomics, and biochemistry have all been of immense help in characterizing macromolecular cell entities and their interactions. Still, obtaining an overall picture of the functioning of even a simple unicellular species has remained a challenging task. One possible way to obtain a comprehensive picture has been described: by capitalizing on the observation that the overexpression on a multicopy plasmid of apparently any wild-type gene in yeast can lead to some negative effect on cell fitness (referring to the concept of "gene toxicity"), the FIG (fitness-based interferential genetics) approach was devised for selecting normal genes that are in antagonistic (and potentially also agonistic) relationship with a particular gene used as a reference. Herein, we take a complementary approach to FIG, by first selecting a "hypertoxic" allele of the reference gene--which easily provides the general possibility of obtaining gene products with the remarkable property of being inactive without altering their macromolecular interactivity--and then looking for the genes that interact functionally with this reference. Thus, FIG and the present approach (Trap-FIG), both taking advantage of the negative effects on cell fitness induced by various quantitative modulations in cellular networks, could potentially pave the way for the emergence of efficient in situ biochemistry.

Function of Arabidopsis hexokinase-like1 as a negative regulator of plant growth

A recent analysis of the hexokinase (HXK) gene family from Arabidopsis revealed that three hexokinase-like (HKL) proteins lack catalytic activity, but share about 50% identity with the primary glucose (glc) sensor/transducer protein AtHXK1. Since the AtHKL1 protein is predicted to bind glc, although with a relatively decreased affinity, a reverse genetics approach was used to test whether HKL1 might have a related regulatory function in plant growth. By comparing phenotypes of an HKL1 mutant (hkl1-1), an HXK1 mutant (gin2-1), and transgenic lines that overexpress HKL1 in either wild-type or gin2-1 genetic backgrounds, it is shown that HKL1 is a negative effector of plant growth. Interestingly, phenotypes of HKL1 overexpression lines are generally very similar to those of gin2-1. These are quantified, in part, as reduced seedling sensitivity to high glc concentrations and reduced seedling sensitivity to auxin-induced lateral root formation. However, commonly recognized targets of glc signalling are not apparently altered in any of the HKL1 mutant or transgenic lines. In fact, most, but not all, of the observed phenotypes associated with HKL1 overexpression occur independently of the presence of HXK1 protein. The data indicate that HKL1 mediates cross-talk between glc and other plant hormone response pathways. It is also considered Whether a possibly decreased glc binding affinity of HKL1 could possibly be a feedback mechanism to limit plant growth in the presence of excessive carbohydrate availability is further considered.

Expression and evolutionary features of the hexokinase gene family in Arabidopsis

Arabidopsis hexokinase1 (HXK1) is a moonlighting protein that has separable functions in glucose signaling and in glucose metabolism. In this study, we have characterized expression features and glucose phosphorylation activities of the six HXK gene family members in Arabidopsis thaliana. Three of the genes encode catalytically active proteins, including a stromal-localized HXK3 protein that is expressed mostly in sink organs. We also show that three of the genes encode hexokinase-like (HKL) proteins, which are about 50% identical to AtHXK1, but do not phosphorylate glucose or fructose. Expression studies indicate that both HKL1 and HKL2 transcripts occur in most, if not all, plant tissues and that both proteins are targeted within cells to mitochondria. The HKL1 and HKL2 proteins have 6-10 amino acid insertions/deletions (indels) at the adenosine binding domain. In contrast, HKL3 transcript was detected only in flowers, the protein lacks the noted indels, and the protein has many other amino acid changes that might compromise its ability even to bind glucose or ATP. Activity measurements of HXKs modified by site-directed mutagenesis suggest that the lack of catalytic activities in the HKL proteins might be attributed to any of numerous existing changes. Sliding windows analyses of coding sequences in A. thaliana and A. lyrata ssp. lyrata revealed a differential accumulation of nonsynonymous changes within exon 8 of both HKL1 and HXK3 orthologs. We further discuss the possibility that the non-catalytic HKL proteins have regulatory functions instead of catalytic functions.

A potentially general method for the in vivo selection of inhibitory peptides targeted at a specific protein using yeast

Although invaluable for biology and medicine, general methods for the selection of inhibitors directed against any protein activity are still missing. To test whether the fitness-based interferential genetics (FIG) approach performed in yeast might contribute to changing this situation, we used this method for the selection of artificial-gene-encoded peptides targeted at firefly luciferase, a foreign protein which was expressed in yeast. Some of these peptides were shown to inhibit the light-producing activity of luciferase in vitro. These results obtained within a totally artificial setting provide a direct demonstration of FIG selection for antagonistic components. Moreover, they open the way for FIG as a simple and general approach for selecting peptides against any specific protein activity expressed in a cellular environment, thus yielding compounds of potential scientific, medical and therapeutic value. Conditions for the development of such valuable compounds in the future using FIG are discussed.

Direct in vivo access to potential gene targets of the RPD3 histone deactylase using fitness-based interferential genetics

Using the fitness-based interferential genetics (FIG) approach in yeast, potential in vivo gene targets of the Rpd3 histone deacetylase were selected. In agreement with previous studies using different methods, three genes were found to be involved in the translational machinery (MRPL27, FHL1 and RDN1). Moreover, other selected genes are linked to cell-cycle control (CSE4, AMN1, VAC17 and GRR1). In addition to playing a crucial role in cell cycle progression to the S phase and participating in the G(2)-M transition, GRR1 has important functions related to nutrient import to the cell via the the derepression of hexose transporters and the induction of amino acid permeases. Consistent with this, FIG selection also retrieved: the PMA1 gene, encoding the plasma H(+)-membrane ATPase; FOL2 and FOL3, involved in folic acid biosynthesis; and UBR2, which indirectly downregulates the proteasome genes. Finally, the other selected genes, ISU1, involved in the biosynthesis of the iron-sulphur cluster in mitochondria, and the less well functionally defined BSC5 and YBR270c, may participate in the cell's antioxidant and stress defence. The genes emerging from this FIG selection thus appear to be part of the downstream molecular mechanisms of the TOR signalling pathway, accounting for its effects on cell proliferation and longevity. From our results on gene expression under conditions of RPD3 overexpression, and by comparison with the available pharmacogenomics studies, it is proposed that FIG could be an invaluable approach for contributing to our understanding of complex cell regulatory systems.

Characterization of regulatory non-catalytic hexokinases in Aspergillus nidulans

Hexokinases catalyse the first step in glucose metabolism and play a role in glucose sensing in mammals, plants and fungi. We describe a new class of hexokinases that appear to be solely regulatory in function. The Aspergillus nidulans hxkD gene (formerly named xprF) encodes a hexokinase-like protein. We constructed hxkDDelta gene disruption mutants which showed increased levels of extracellular protease in response to carbon starvation. The hxkDDelta mutations are not completely recessive, indicating that the level of the gene product is critical. Transcript levels of hxkD increase during carbon starvation and this response is not dependent on functional HxkD. A gene encoding a second atypical hexokinase (HxkC) was identified. The hxkCDelta gene disruption mutant exhibits a phenotype similar, but not identical, to hxkDDelta mutants. As with hxkD, mutations in hxkC are suppressed by loss-of-function mutations in xprG, which encodes a putative transcriptional activator involved in the response to nutrient limitation. We show that GFP-tagged HxkD was found only in nuclei suggesting a regulatory role for HxkD. GFP-tagged HxkC was associated with mitochondria. Homologs of hxkC and hxkD are conserved in multi-cellular fungi. Genes encoding atypical hexokinases are present in many genome sequence databases. Thus, non-catalytic hexokinases may be widespread.