hagerp@iuvax.cs.indiana.edu (Paul Hager) (08/22/90)
I am interested in information/sources on common subtances/foods
which have long biological half-lives in the human body. This
can be either the substance itself or its metabolites. DDT,
for example, tends to concentrate in tissues. What I am interested
in is information on benign, common, everyday foods or substances
that exhibit the long half life.
Thanks in advance.
--
paul hager hagerp@iuvax.cs.indiana.edu
"I would give the Devil benefit of the law for my own safety's sake."
--from _A_Man_for_All_Seasons_ by Robert Boltrmhoward@peg.UUCP (10/26/90)
>I am interested in information/sources on common subtances/foods >which have long biological half-lives in the human body. This >can be either the substance itself or its metabolites. DDT, >for example, tends to concentrate in tissues. What I am interested >in is information on benign, common, everyday foods or substances >that exhibit the long half life. Although I'm no expert I read up aspects of this subject when researching on exotic chemicals such as DDT etc. The following general points seem to apply. (1) Liver metabolic processes such as conjugation, oxidation etc. are directed towards increasing water solubility of exotic compounds and hence increasing their excretion rate. (2) These processes don't always work and they can be inhibited or overwhelmed by the presence of non-degradable substances such as DDT, dioxin etc.Hence, literature talks about prolongation of phenobarbitone half-lifes in relation to these sort of substances. (3) Liver can metabolize by oxidation(say) but still produce a substance which has low water solubility and hence remains in the body until it is again attacked by the liver, possibly THC(Cannibis) and its relatives are long-lasting becuase of this (this is a guess, but the lit. will tell you definitely) (4) Fat soluble substances can't be excreted in general although they may be slowly metabolized by liver enzymes as they come out of solution .Hence: exotic lodges in fat -> redissolves in blood, possibly attached to albumin{this is a complication}-> is presented to the liver. Critical fact is the octanol/water coefficient which is a measure of relative solubility of a substance in water to fat. High coefficient(e.g.DDT = 1000 roughly) means only a small amount is being presented to the liver at one point in time, hence breakdown is slow. (5) Modern synthetic chemicals are refractory to liver metabol- ism because earth based life uses only a very small range of the possible small organic molecules that can be made. The variety comes from the way they are joined together(DNA uses only 4 molecules proteins use 18, etc). Thus, compounds with lots of chlorine, the infamous organo-chlorines, don't lose there chlorines in liver metabolism but (if possible) get oxidised at another point in the compound. Implication is that the very long half lives of synthetic chemicals are not mirrored by natural chemicals. (6) Fatty acids last for the longest of all natural substances, insofar as they are used as energy stores. If you overeat and don't exercise you'll keep them in obvious places - starvation or diabetes will cause them to be metabolized. (7) Nerve cell DNA lasts for as long as you live and still have nerve cells intact, since nerve cells don't reproduce.Although you could argue that DNA is immortal :-) In conclusion, half life depends on (a) fat solubility and (b) the state of your liver. ************************************************************* * * * 'But now we got weapons of chemical dust, * * If fire them we're forced to then fire them we must * * One push of the button and a shot the world wide * * And you never ask questions when God's on your side'* * B.D.'63 * * * ************************************************************* Bob Howard :-Peg:rmhoward ; Contact for A.C.F.South Coast Branch.Ph(098-413805);Address:19 Carlisle St, Albany,6330 WEST AUSTRALIA Sci.bio 41