Chromium, like many transition metal elements, is essential to life at low concentrations yet toxic to many systems at higher concentrations. In addition to the overt symptoms of acute chromium tox...

Mechanisms of Chromium Carcinogenicity and Toxicity

Citrulline (Cit, C6H13N3O3), which is a ubiquitous amino acid in mammals, is strongly related to arginine. Citrulline metabolism in mammals is divided into two fields: free citrulline and citrullinated proteins. Free citrulline metabolism involves three key enzymes: NO synthase (NOS) and ornithine carbamoyltransferase (OCT) which produce citrulline, and argininosuccinate synthetase (ASS) that converts it into argininosuccinate. The tissue distribution of these enzymes distinguishes three “orthogonal” metabolic pathways for citrulline. Firstly, in the liver, citrulline is locally synthesized by OCT and metabolized by ASS for urea production. Secondly, in most of the tissues producing NO, citrulline is recycled into arginine via ASS to increase arginine availability for NO production. Thirdly, citrulline is synthesized in the gut from glutamine (with OCT), released into the blood and converted back into arginine in the kidneys (by ASS); in this pathway, circulating citrulline is in fact a masked form of arginine to avoid liver captation. Each of these pathways has related pathologies and, even more interestingly, citrulline could potentially be used to monitor or treat some of these pathologies. Citrulline has long been administered in the treatment of inherited urea cycle disorders, and recent studies suggest that citrulline may be used to control the production of NO. Recently, citrulline was demonstrated as a potentially useful marker of short bowel function in a wide range of pathologies. One of the most promising research directions deals with the administration of citrulline as a more efficient alternative to arginine, especially against underlying splanchnic sequestration of amino acids. Protein citrullination results from post-translational modification of arginine; that occurs mainly in keratinization-related proteins and myelins, and insufficiencies in this citrullination occur in some auto-immune diseases such as rheumatoid arthritis, psoriasis or multiple sclerosis.

Almost all about citrulline in mammals.

The sections in this article are:


1
Manifestations of Skin Permeability

2
Structure of the Skin
2.1
Relevant Structural Features of the Whole Skin




3
The Stratum Corneum
3.1
Regional Variations in Structure




4
Human Versus Other Mammalian Skin

5
Biophysics of Skin Permeability
5.1
Mathematical Analysis of Skin Permeability

5.2
Steady-State Permeability of Skin—Fick's Law

5.3
Appendageal Diffusion

5.4
Concentration Levels in the Skin

5.5
Regional Variations in Permeability




6
Effect of Solvents and Surfactants
6.1
Water

6.2
Aprotic Solvents

6.3
Surfactants

6.4
Organic Solvents

Permeability of the Skin

: Selective review and synthesis of the technical literature on copper and copper salts in the environment and their effects primarily on fishes, birds, mammals, terrestrial and aquatic invertebrates, and other natural resources. The subtopics include copper sources and uses; chemical and biochemical properties; concentrations of copper in field collections of abiotic materials and living organisms; effects of copper deficiency; lethal and sublethal effects on terrestrial plants and invertebrates, aquzatic organisms, birds, and mammals, including effects on survival, growth, reproduction, behavior, metabolism, carcinogenicity, mutagenicity, and teratogenicity; proposed criteria for the protection of human health and sensitive natural resources; and recommendations for additional research.

Copper Hazards to Fish, Wildlife, and Invertebrates : A Synoptic Review

Studies on contact sensitivity to chromium in the guinea pig. The role of valence in the formation of the antigenic determinant.

Sensitization of Guinea Pigs to Chromium Salts

The interactions of chromium and proteins have been studied by various investigators. By tagging proteins with radioactive chromium, Grey and Stirling (1) demonstrated that plasma proteins bound tri valent chromium. Hexa valent chromium combined with hemoglobin only after reduction to the tri valent state. After undergoing reduction hexavalent chromium also interfered with nucleic acid determinations by combining with proteins (2). With an electrophoretic technic, no binding of hexavalent chromium to proteins could be detected; binding was postulated if the metal were converted to the trivalent form (3). Baetjer, Damron and Budacz (4) investigated the interactions of both tri- and hexavalent chromium with lung tissue. They found that only trivalent chromium was bound to the tissue; again hexavalent chromium had to undergo reduction to the trivalent state before it could combine with the lung tissue. Anderson (5) reported that skin, when treated with either tri- or hexavalent chromium bound considerable amounts to chromium. The blocking of certain functional groups in the skin had little effect on the amount of chromium bound. In these studies the oxidation state of the bound chromium was not determined; it was assumed that in the course of the reaction chromium remained in the original oxidation state.

A Study of the Chemical Reactions Between Chromium and Skin

(1965). Protection Against Inhalation of Chromic Acid Mist. Archives of Environmental Health: An International Journal: Vol. 11, No. 6, pp. 770-772.

Protection against inhalation of chromic acid mist. Use of filters impregnated with ascorbic acid.

In this study, we have demonstrated that hexavalent chromium is reduced by skin and chromium is bound to skin. The chemical findings were corroborated with tracer methods. The chromium bound to the skin was in the trivalent state, indicating a chemical reduction of the hexavalent species before binding.

M.H. Samitz

Papers

Sensitization of Guinea Pigs to Chromium Salts

A Study of the Chemical Reactions Between Chromium and Skin

Protection against inhalation of chromic acid mist. Use of filters impregnated with ascorbic acid.

Preliminary Studies on the Reduction and Binding of Chromium With Skin

Inactivation of chromium ion in allergic eczematous dermatitis.