Ecological Biochemistry

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Define ecological biochemistry. • Explain biochemical adaptation and the roles of secondary compounds. • Describe detoxification and the primary metabolic pathways in plants and animals. • Explain the key processes and factors involved in biotransformation & biodegradation. • Explain the concepts of sequestration, bioaccumulation, and biomagnification. • Contrast different forms of ecological biochemical interaction.

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Nội dung Text: Ecological Biochemistry

Principles of Environmental Toxicology Learning Objectives • Define ecological biochemistry. • Explain biochemical adaptation and the roles of secondary compounds. • Describe detoxification and the primary metabolic Ecological Biochemistry pathways in plants and animals. • Explain the key processes and factors involved in Principles of Environmental Toxicology biotransformation & biodegradation. Instructor: Gregory Möller, Ph.D. • Explain the concepts of sequestration, bioaccumulation, and biomagnification. University of Idaho • Contrast different forms of ecological biochemical interaction. 2 Principles of Environmental Toxicology Principles of Environmental Toxicology Ecological Biochemistry, 2 Ecological Biochemistry • Coupling of the observational science of ecology with • Synthesis and transformation of chemicals in the the molecular science of biochemistry. environment, as the result of biochemical • Ecological interaction. processes in an organism, to aid in species survival. • Includes: Animals 1. Biochemical adaptation. • Biosynthesis. 2. Detoxification. Plants Fungi • Biodegradation, biomineralization. 3. Bioaccumulation, biomagnification. Protists Monera 4. Ecological biochemical interaction. 3 4 Principles of Environmental Toxicology Principles of Environmental Toxicology Competitive, Symbiotic Interactions Biochemical Adaptation • Plant ↔ Plant ↔ Animal… • The metabolic flexibility of a living organism to fit into a changing environment, improving chances for – Secondary plant compounds. • Animal ↔ Animal… survival and reproduction. – Evolution – Venoms, toxins. • Many generations. – Acclimatization. • Lifetime of an individual. • Challenge: decipher the strategy of the natural world. – Example: THC 5 6 Harborne 1
Principles of Environmental Toxicology Principles of Environmental Toxicology Toxins and Survival Strategy Secondary Plant Compounds • Organisms often synthesize or use toxins in their survival • Hypothesis: strategy. developed in plants as survival mechanism. – “The most conspicuous non-event in the history of the – Offensive and defensive biosynthesis. angiosperms is the failure of insects and other herbivores to attack plants on a wide-scale.” (Feeny, 1975). • Plants dominate the landscape, hence plants must be “broadly repellent” to animals as food and “toxic” in the widest sense. • Overcoming the defense strategy of plants by insects and herbivores is a part of their survival strategy. 7 8 Harborne Principles of Environmental Toxicology Principles of Environmental Toxicology Nitrogen Compounds Terpenoids Number of Physiological activity Number of Physiological activity structures structures Monoterpenes 1,000 Pleasant smells Alkaloids 6,500 Toxic, bitter Sesquiterpene 1,500 Some bitter & toxic Amines 100 Repellent, hallucinogenic lactones Diterpenoids 2,000 Some toxic Amino acids 400 Many toxic Liminoids 100 Bitter Cyanogenic 30 Poisonous Cucurbitacins 50 Bitter & toxic glycosides (as HCN) Cardenolides 150 Toxic & bitter Glucosinolates 75 Acrid, bitter Carotenoids 500 Color 9 10 Harborne Harborne Principles of Environmental Toxicology Principles of Environmental Toxicology Phenolics Example: The Walnut Tree Number of Physiological activity • Allelopathy: “biochemical interactions between all structures types of plant” (Molisch, 1937). Simple phenols 200 Anti-microbial • Since the time of ancient Greece, the walnut tree (Juglans nigra) has been observed to kill nearby Flavinoids 4,000 Often colored vegetation. Quinones 800 Colored, sometimes toxic – Moderately toxic to some insects, horses, dogs, humans. • Produces a bound form of a toxin, which deposits in nearby soil through leaves, stems and roots. 11 Harborne 12 2
Principles of Environmental Toxicology Principles of Environmental Toxicology Example: The Walnut Tree, 2 Harnessing Biosynthesis • Numerous secondary chemical compounds from • Leaching causes hydrolysis and oxidation, releasing nature have been used throughout the ages by jugalone, a powerful herbicide. humans in their own survival. – Medicines. OH O – Hunting, warfare. Hydrolysis Juglans sp. TAMU – Pesticides. – Flavors. Oxidation VMNH OH OGlc OH O Jugalone Bound form (5-Hydroxynaphthoquinone) of toxin Phyllobates terribilis, Poison dart frog Harborne 13 14 Batrachotoxin – a steroidal alkaloid Principles of Environmental Toxicology Principles of Environmental Toxicology Insecticide Biosynthesis: Spinosad Spinosyn Macrolides CH3 • Spinosad is a mixture of Dow N spinosyn A and spinosyn D H3C factors that are produced H3C H3C O by the soil actinomycete, O S. Spinosa H3C Saccharopolyspora spinosa. O CH3 Dow O CH3 O • Causes rapid excitation of O O the insect nervous system. H H H3C O – Effects chewing worms. • Off target: non-toxic to O O H mod. toxic (e.g. fish LD50 5 mg/L). H H R • Rapid biodegradation. Spinosyn A: R = H Spinosyn D: R = CH3 15 16 Principles of Environmental Toxicology Principles of Environmental Toxicology Detoxification Phase I & II • In animals, primary PII pathways include glucuronide • Adaptation of organisms to natural and “unnatural” or sulfate formation. chemicals which threaten their survival. • In plants, glucoside formation is the key detoxification – Both evolutionary and acclimatization processes. reaction. • Includes the pathways for metabolism and biotransformation of toxicants. – Carried out by glucosyltransferase enzyme and uridinediphosphateglucose as a co-factor. – Phase I & II; immune system. – More water soluble; pushed into the – Microbial biodegradation cell vacuole. and biomineralization. – Highly phytotoxic phenols. – Phase change; sequestration. • Glucosylation. – Systemic fungicidal agrichemicals. • Often “antimetabolite” glucoside forms with systemic activity. 17 18 Harborne 3
Principles of Environmental Toxicology Principles of Environmental Toxicology Detoxification of Herbicides Plant Metabolism of 2,4-D O OH • Selective ability and rate of certain plants to detoxify herbicides is a primary weed management strategy. Glc O OH O • e.g. 2,4-dichlorophenoxyacetic acid (2,4-D). In wheat Cl Cl Cl and peas – Extremely active auxin (growth hormone). – Causes plant to grow too fast; Cl Cl Cl upsets growth cycle. – Some crop plants degrade it In weeds and do so at a fast rate. Not detoxified immediately. Abnormal growth, plant death. 19 20 Harborne Harborne Principles of Environmental Toxicology Principles of Environmental Toxicology Microbial Processes Fluorocitrate and Kangaroos • Fluorocitrate found in legume • Microbial biotransformation/biodegradation: microbe pasture plants induced change or breakdown of natural and of Western Australia. synthetic chemical compounds. – Gastrolobium and Oxylobium. – In the natural world, some of these are higher trophic level • Highly lethal (TD 1 mg/1080 kg). xenobiotics or contaminants, some are not. – Leaf concentrations can be 2.6 g/kg. • Scale is important (dose). WACALM • The rat and gray kangaroo • Causes. of Western Australia have – Detoxification. evolved resistance. – Nutrition. – In vivo defluorination w/ glutathione. – Respiration. – Other kangaroos from areas w/o these plants are not tolerant. Harborne 21 22 Principles of Environmental Toxicology Principles of Environmental Toxicology Factors in Microbial Activity Microbial Processes • Key processes are enzymatic or respiratory in the • Evolutionary diversification. microbially induced changes of the chemical. • High specific surface area. • Enzyme processes: catalytic reactions. Hurst • High rate of population turnover. • Respiratory process: thermodynamic reactions. • Survival of tolerant and – Aerobic. acclimatized organisms. • Use O2 as terminal electron • Heritable change in acceptor in respiration. population characteristics. – Anaerobic. • Use NO32-, Mn4+, Fe3+, SO42-, CO2 as terminal electron acceptor. – Modulates biogeochemical redox rxns. • Fungi: enzymatic. 23 24 4
Principles of Environmental Toxicology Principles of Environmental Toxicology Bacteria Processes Bioremediation • Intrinsic bioremediation. • Metabolism of a bacterium can detoxify a chemical – Natural process, typically in situ. using PI & PII type processes for its own survival, rendering it less- or non-toxic to itself and sometimes • Biostimulation. higher life forms. – Addition of nutrients. • Biomineralization takes the process all the way to • Bioaugmentation. inorganic chemicals (e.g. CO2, H2O). – Inoculation. • Co-metabolism is the • Enzymatic processes can “gratuitous” oxidation allow “harvesting” of the of a chemical by an enzyme from culture for organism (no energy recovery). engineered treatments of chemical waste. – Also: the pooled action of a community. 25 26 Principles of Environmental Toxicology Principles of Environmental Toxicology Sequestration, Bioaccumulation Phase Change • Detoxification strategy of an organism sometimes • Often, an important process for management uses a phase change to assist in reducing toxicity and of some toxicants by an organism. increasing elimination. • Inorganic examples: • Example: – Mammalian incorporation of Pb into bone. – Volatilization of bioalkylated – Plant incorporation of Se into seleno-amino acids. metals and metalloids by – Microbial reduction of selenate/selenite microbes and plants. to Se0 and incorporation of the • As, Se, Pb, Hg, Sb… solid into the cell. • Can be exploited in hazardous waste clean-up. – Phytoremediation. 27 28 Principles of Environmental Toxicology Principles of Environmental Toxicology Sequestration, Bioaccumulation, 2 PCB Biomagnification • Organic examples: Lake Food Chain Concentration Magnification – Accumulation of non-polar compounds in adipose tissue (mg/kg) (e.g. DDT, dioxins). Phytoplankton 0.0025 1 • In both inorganic and organic cases, the organism can contain higher levels of a sequestered contaminant than the Zooplankton 0.123 49 surrounding environment by factors as high as 102-103 (BCF). Smelt 1.04 416 • Food chain implications: a contaminant can “magnify” Lake Trout 4.83 1930 up a multi-trophic level food chain. – Low dose at lower levels; high dose Gull Eggs* 124 49,600 and toxicity at upper levels. *Egg shell thinning, teratogenesis, immune dysfunction, death. 29 30 5
Principles of Environmental Toxicology Principles of Environmental Toxicology Ecological Biochemical Interaction Milkweed-Monarch-Blue Jay • Classic example of • Transfer of biosynthesized secondary compounds plant-animal co-evolution. between different organisms. – Insects using plants toxins – Food web interaction. against high predators. – Part of a survival strategy. – Plants. • Milkweed (Aslepias currassavica); Nerium oleander. – Insects. • Monarch butterfly (Danaus plexippus); others. – Bird. • Blue Jay (Cyanocitta Harborne cristata bromia). 31 32 Principles of Environmental Toxicology Principles of Environmental Toxicology Chain of Events Cardiac Glycosides O Calotropin 1. Milkweed produces bitter, O toxic cardiac glycosides as a passive defense. O 2. Feeding Monarch butterfly H OH C OH caterpillar adapts to O Encarta these toxins and stores them. OH O O O 3. Adult butterfly flies away H H with sequestered c. glycosides. O 4. Blue Jay tries feeding on Oleandrin the butterfly, vomits. H O 5. Blue Jay avoids brightly HO O colored Monarch butterflies. H OH O O O H 33 34 Harborne Principles of Environmental Toxicology Principles of Environmental Toxicology Ciguatera Fish Poisoning Ciguatoxin • The most commonly reported marine toxin disease in • The dinoflagellate, the world. NIEHS Gambierdiscus toxicus – Associated with consumption of contaminated reef fish produces ciguatoxin such as barracuda, grouper, and snapper (vector fish). throughout tropical • 50,000 people per year: debilitating neurologic regions of the world. symptoms, including Fukuyo profound weakness, temperature sensation changes, pain, and numbness in the extremities. 35 36 6
Principles of Environmental Toxicology Principles of Environmental Toxicology Ciguatoxin, 2 Ciguatoxin, 3 CH3 • The two most common toxins associated with Ciguatera are Ciguatoxin and Maitotoxin CH3 HO H3C O O – Some of the most lethal natural substances known (mice O 0.45 μg/kg ip). O O CH3 HO • Ciguatoxin, a lipid soluble substance, opens voltage O O O HO O O O HO O dependant sodium H3C channels in cell membranes O CH3 which induces membrane OH depolarization. – Lethality is usually seen with ingestion of the most toxic parts of fish. 37 38 Principles of Environmental Toxicology Principles of Environmental Toxicology Pyrrolizidine Alkaloids & Moths Senecio Alkaloids • Highly toxic pyrrolizidine alkaloids are • Plants. found in plant species of the genus – Groundsel Senecio. (Senecio vulgaris). • Poisonous to foraging wildlife and – Ragwort livestock. (S. jacobaea). Comfrey • Insects. – Strong hepatotoxins. • Also found in comfrey – Tiger moth (Arctia caja). (Symphonium officinale). – Cinnabar moth – Used in herbal medicines Poppenga; QED (Tyria jacobaeae). and tea (!). 39 40 Harborne Harborne Principles of Environmental Toxicology Principles of Environmental Toxicology Pyrrolizidine Alkaloid Metabolism Senecio-Moth Interaction Mammals • Pyrrolizidine alkaloids from the plants are Ester sequestered and stored by the moths. Retronecine HO H2C OH HO H2C OH O H2C O • The moths can biotransform one alkaloid Hydrolysis -2H in vivo, into another. N N N – Toxic alkaloids are even present in the insect eggs. Pyrrolizidine Alkoloid – Bright colors and patterns General Formula also present. OH • Moth will also feed on O foxglove (Digitalis purpuria), Bound To Liver a source of cardiac glycosides. (Toxic) 4-Hydroxy-hex-2-enal 41 42 Harborne Harborne 7
Principles of Environmental Toxicology Principles of Environmental Toxicology Pyrrolizidine Alkaloid Metabolism Pyrrolizidine Alkaloid Metabolism Lepidoptera • In mammals, PAs metabolize to a pyrrole. Harborne Harborne Ester Retronecine – Can bind to macromolecules (DNA). HO H2C OH O H2C O – Can breakdown to a more reactive metabolite. Pheromone Hydrolysis synthesis in • In lepidoptera, PAs can act as essential pheromone N Lepidoptera N precursors. Pyrrolizidine Alkoloid (Stored unchanged or as – Biotransformed into “love dust”. N-oxides in Lepidoptera) HC HO H HC O CH3 O O + + N N N Hydroxydanaidal Danaidal Danaidone 43 44 8