SULFUR AS A PROTECTIVE AGENT AGAINST RADIATION DAMAGE

This is an excerpt from an article published on the Weston Price Foundation website. Link to full article and references are found HERE.

SULFUR AS A PROTECTIVE AGENT AGAINST RADIATION DAMAGE

 

Sulfur-containing biological molecules like glutathione and the amino acids cysteine and methionine play an important role in redox (oxidation/reduction) reactions by tempering the damaging effects of reactive oxygen species (ROS); that is, by acting as potent antioxidants.1 Closely related to this role in protecting from oxidation damage associated with aerobic metabolism is the potential role of sulfur in protection from radiation damage due to sun exposure, radiation treatments for cancer, or radiation exposure following a nuclear reactor meltdown.

An awareness that sulfur protects against ionizing radiation dates back to at least 1949.10 An enlightening article from 19835 showed, via experiments conducted at very low temperatures, that sulfur’s reaction to radiation is a secondary effect. The associated primary effect is ionization of oxygen, producing the highly reactive species, O2¯, Sulfur then responds by binding to the O2¯ and thus preventing other molecules from reacting adversely with it.

Through an extensive review of the research literature on the response of human skin to the radiation in sunlight, I have come up with a theory for how sulfur could be intimately involved not just in preventing harm from sunlight, but rather by contrast in harnessing the sun’s energy and putting it to good use. I propose that sulfur, readily available from the active cysteines in an enzyme called (inappropriately) endothelial nitric oxide synthase (eNOS), reacts with two O2¯ ions produced by sunlight exposure to produce the highly stable and useful anion, sulfate. This reaction would take place in a cavity formed by two abutting molecules of eNOS (that is, an eNOS dimer). A positively charged zinc atom centered in the cavity8 draws in the two O2¯ ions to combine them with a nearby sulfur atom attached to a cysteine residue, to form a sulfate anion SO4 −2. The sulfate, then, in a subsequent reaction, combines with cholesterol to form cholesterol sulfate, a prominent component of the outer layers of the skin (and also of hair, feathers, fur and fingernails).

An article that appeared in 2002 on the effects of irradiation treatment on aortic endothelial cells4 revealed that irradiation induces expression of another “inducible” nitric oxide synthase, iNOS. My belief is that the purpose of the iNOS in this case is identical to the purpose of eNOS in the skin: to mop up anticipated O2¯ radicals produced by the radiation, and to convert them to sulfate. The authors showed that if the cells are supplied with the substrate to produce nitric oxide, L-arginine, then this causes them to initiate a programmed cell death reaction called apoptosis. What happens is that the L-arginine binds to the iNOS (and the eNOS as well) and deflects these enzymes towards producing nitric oxide rather than sulfur dioxide. Unfortunately, under the right circumstances, nitric oxide can turn into the highly reactive species ONOO − (known in the vernacular as “oh, no!”)9and this can make the cell non-viable.

A highly significant fact that supports a primary role for the NOS’s in producing sulfate is that red blood cells have an abundance of eNOS, but they are very careful to keep out its substrate L-arginine.6 This act has puzzled researchers, but the answer becomes clear when you realize that red blood cells are strong producers of cholesterol sulfate,11as well as major carriers of oxygen. This makes them a prime candidate for using eNOS to convert oxygen to sulfate (taking advantage of sunlight as a catalyst), and then shipping it to the tissues via the carrier molecule cholesterol sulfate. This action would both protect the red blood cell from oxidative damage and reduce the risk of damage due to oxygen exposure in other cells, as the oxygen supply contained in the sulfate constitutes safe transport of oxygen to these cells. I have little doubt that this is a productive (but overlooked) mode of oxygen transport in the body.

The sulfur in cysteine plays a crucial role in protecting proteins from radiation damage. In experiments conducted in the late 1950s3, it was shown that proteins needed to contain only half a percent of cysteine by weight to be immune to any damage to the other amino acids in the protein. Proteins containing no cysteine produced complex irradiation spectra indicating that diverse chemical reactions had taken place.

An article from Nature in 19622showed that sulfur has a remarkable ability to protect macromolecules in colloidal suspensions against cross-linking upon exposure to radiation. The effect was much larger than what the authors would have expected, given their understanding of possible mechanisms, so there is still something mysterious about sulfur’s protective role. Since molecules in the blood serum are in some sense a colloidal suspension, this behavior has relevance to protection from ionizing radiation of proteins like serum albumin, which contains significant amounts of cysteine.

The best source of sulfur is the protein from animal products such as meat, fish and eggs. Sulfur is becoming depleted from the soil, so vegetables contain even less sulfur than they used to. It is therefore highly likely that vegetarians suffer from sulfur deficiency, which could affect their susceptibility to damage from radiation exposure.

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