Biological effects of essential oils - A review

Free radicals are common outcome of normal aerobic cellular metabolism. In-built antioxidant system of body plays its decisive role in prevention of any loss due to free radicals. However, imbalanced defense mechanism of antioxidants, overproduction or incorporation of free radicals from environment to living system leads to serious penalty leading to neuro-degeneration. Neural cells suffer functional or sensory loss in neurodegenerative diseases. Apart from several other environmental or genetic factors, oxidative stress (OS) leading to free radical attack on neural cells contributes calamitous role to neuro-degeneration. Though, oxygen is imperative for life, imbalanced metabolism and excess reactive oxygen species (ROS) generation end into a range of disorders such as Alzheimer's disease, Parkinson's disease, aging and many other neural disorders. Toxicity of free radicals contributes to proteins and DNA injury, inflammation, tissue damage and subsequent cellular apoptosis. Antioxidants are now being looked upon as persuasive therapeutic against solemn neuronal loss, as they have capability to combat by neutralizing free radicals. Diet is major source of antioxidants, as well as medicinal herbs are catching attention to be commercial source of antioxidants at present. Recognition of upstream and downstream antioxidant therapy to oxidative stress has been proved an effective tool in alteration of any neuronal damage as well as free radical scavenging. Antioxidants have a wide scope to sequester metal ions involved in neuronal plaque formation to prevent oxidative stress. In addition, antioxidant therapy is vital in scavenging free radicals and ROS preventing neuronal degeneration in post-oxidative stress scenario.

Oxidative stress and neurodegenerative diseases: a review of upstream and downstream antioxidant therapeutic options.

Privileged substructures are of potentially great importance in medicinal chemistry. These scaffolds are characterized by their ability to promiscuously bind to a multitude of receptors through a variety of favorable characteristics. This may include presentation of their substituents in a spatially defined manner and perhaps also the ability to directly bind to the receptor itself, as well as exhibiting promising characteristics to aid bioavailability of the overall molecule. It is believed that some privileged substructures achieve this through the mimicry of common protein surface elements that are responsible for binding, such as β- and gamma;-turns. As a result, these structures represent a promising means by which new lead compounds may be identified.

The combinatorial synthesis of bicyclic privileged structures or privileged substructures

Antioxidant activity and phenolic compounds of 112 traditional Chinese medicinal plants associated with anticancer.

The biochemistry and medical significance of the flavonoids.

In this review recent publications are cited for a number of antimutagens. The molecules surveyed are potential or proven "desmutagens" or "interceptors." These are biologically prevalent or synthetic molecules that are most often small metabolites proficient in binding to, or reacting with, mutagenic chemicals and free radicals. Many of this class of "blocking agents" are "soft" and "hard" nucleophiles with consequently varying abilities to react with particular classes of electrophiles, the major classes of direct-acting mutagens. Although they serve as a first line of defense against mutagens and carcinogens, many interceptor molecules are under-investigated with regard to their spectra of activity and their possible relevance to prophylaxis or treatment of human disease states.

Antimutagens and anticarcinogens: a survey of putative interceptor molecules.

Chemoprotection: a review of the potential therapeutic antioxidant properties of green tea (Camellia sinensis) and certain of its constituents.

Multiple drug resistance to antibacterial agents, antifungals, antivirals, antiprotozoals, and antitumor agents has risen spectacularly in the last decade or so and presently threatens eventually to put an end to successful chemotherapy in all of the above fields. This review summarizes the known origins of the problem, its present dimensions, the means employed to combat the phenomenon and promising avenues for future developments.

Multiple drug resistance.

Following a brief review of recent discoveries in the field of natural antimutagenic and tumor chemopreventive agents, contemporary findings in the author's laboratories employing the direct acting mutagen, ethyl methanesulfonate, in modified Ames tests and eukaryotic murine FM3A mammary tumor cells modified to be subject to thymidine-less death are described to illustrate the underlying principles. The EMS studies are illustrated with the isolation of the novel antimutagen, plicatin B, from the medicinal plants, Psoralea juncaea and P. plicata. The FM3A studies are carried out with extracts of Styrax asiatica, a plant previously studied extensively with the EMS system. The FM3A findings closely parallel the earlier work with EMS showing that the responsible agents, cinnamic acid, cinnamoyl ricinoleate and cinnamoyl cinnamate are effective both in prokaryotic and eukaryotic tests and that the new FM3A assay system has useful properties for screening and assay of novel antimutagenic agents.

Natural antimutagenic agents.

Certain chemical compounds increase mutation frequency of Escherichia coli B/r significantly when used in conjunction with nonlethal ultraviolet (UV) dosages. Studies were done to elucidate the mechanism of this enhancing mutational effect. Dark survival curves showed that 500 μg of caffeine per ml in the postirradiation medium markedly decreased survival to 60 ergs/mm2 of UV in strain B/r. Caffeine did not markedly decrease survival to UV in strain B/r WP-2 hcr−. At least 90% of the mutations induced to streptomycin resistance by UV and 85% of those induced by UV with caffeine could be photoreversed. Experiments with thymine analogues suggested that thymine dimerization at the streptomycin locus was the primary premutational photoproduct induced by sublethal UV dosages. Caffeine did not interfere with the photoreversal of induced mutants, indicating that it probably does not bind to the photoreactivating enzyme or to a UV-induced lesion in the DNA. Addition of DNA or irradiated DNA with 500 μg of caffeine per ml resulted in no loss of the caffeine activity. The excision of UV-induced thymine-containing dimers from E. coli B/r T− was investigated in the presence and absence of caffeine. Our results indicated that caffeine prevents excision of thymine dimers, presumably by binding to the excising enzyme. This binding results in an impairment of repair, which produces the increase in mutant numbers.

Delbert M. Shankel

Papers

Antimutagens and anticarcinogens: a survey of putative interceptor molecules.

Chemoprotection: a review of the potential therapeutic antioxidant properties of green tea (Camellia sinensis) and certain of its constituents.

Multiple drug resistance.

Natural antimutagenic agents.

Mechanism of Caffeine Enhancement of Mutations Induced by Sublethal Ultraviolet Dosages