Liver biochemical functions

Le Page, KN., Cheeseman, K.H., Osman, N. and Slater, T.F. (1988). Lipid peroxidation in purified plasma membrane fractions of rat liver in relation to the toxicity of carbon tetrachloride. Cell Biochem. Function 6, 87-99. 

Kitamura S, Tatsumi K. Reduction of tertiary amine N-oxides by liver preparations function of aldehyde oxidase as a major N-oxide reductase. Biochem Biophys Res Commun 1984 121(3) 749-754. 

The liver is the body s largest organ and is central to metabolic processes. The liver performs a wider range of biochemical functions than any other organ. For this reason, the liver is one of the tissues most commonly used by biochemists studying metabolic pathways and their control mechanisms. For simplicity, the various functions to be described in this chapter have been arranged under a number of subheadings. 

Yamaguchi M, Kura M, Okada S (1982) Role of zinc as an activator of mitochondrial function in rat liver. Biochem Pharmacol 31 1289-1293... 

Liver damage from excessive ethanol consumption occurs in three stages. The first stage is the aforementioned development of fatty liver. In the second stage—alcoholic hepatitis—groups of cells die and inflammation results. This stage can itself be fatal. In stage three—cirrhosis—fibrous structure and scar tissue are produced around the dead cells. Cirrhosis impairs many of the liver s biochemical functions. The cirrhotic liver is unable to convert ammonia into urea, and blood levels of ammonia rise. Ammonia is toxic to the nervous system and can cause coma and death. Cirrhosis of the liver arises in about 25% of alcoholics, and about 75% of all cases of liver cirrhosis are the result of alcoholism. Viral hepatitis is a nonalcoholic cause of liver cirrhosis. 

The morphological and functional integrity of the liver is vital to the health of the human organism. This essentially depends upon constant maintenance of the numerous biochemical functions of the liver and the diverse metabolic processes occurring in the hepatocytes and sinusoidal cells. 

In the course of acute or chronic liver disease, the biochemical functions of the liver may be compromised indefinitely the outcome is decompensated liver insufficiency. (s. pp 277, 381) (s. tab. 20.4) The stage of decompensation is synonymous with the onset of life-threatening complications. These mainly take the form of hepatic encephalopathy with transition to hepatic coma (see chapter 15), oedema and ascites with imbalance of the electrolytes and the acid-base equilibrium (see chapter 16) through to the hepatorenal syndrome (see chapter... 

Vitamin A performs numenius biochemical functions. It promotes the production nf mucus by the basal cells of the epithelium, whereas in its absence keratin can be fonned. Vitamin A performs a function in the biosynthesis of glycogen and some steroids, and increased quantities nf coen/yme Q are found in the livers nf vitamin-deficicnt rats. Significantly. the best-known action of vitamin A is its function in the chemistry of vision. 

The chapter begins with a discussion of the anatomy and biochemical functions of the liver. The various disease states that involve the fiver are then discussed. The chapter concludes with a discussion of use of laboratory test results in recognizing and characterizing patterns of fiver injury. 

Early work on this vitamin was confusing because similar outcomes were seen with ingestion of "yellow" vegetables and colorless fish liver oils. It finally was shown that carotene (the yellow pigment) extracts Ifom vegetables were converted to colorless retinal. Because the retinoids are discussed in considerably more detail elsewhere, this chapter presents only a cursory overview of their biochemical functions. 

The fat-soluble vitamins share many properties despite their limited chemical similarity. They are absorbed into the intestinal lymphatics, along with other dietary lipids, after emulsification by bile salts. Lipid malabsorption accompanied by steatorrhea usually results in poor uptake of all the fat-soluble vitamins. Deficiency disease (except in the case of vitamin K) is difficult to produce in adults because large amounts of most fat-soluble vitamins are stored in the liver and in adipose tissue. The fat-soluble vitamins are assembled from isoprenoid units this fact is apparent from examination of the structures of vitamins A, E, and K cholesterol, the precursor of vitamin D, is derived from six isoprenoid units (Chapter 18). Specific biochemical functions for vitamins A, D, and K are known, but a role for vitamin E, other than as a relatively nonspecific antioxidant, remains elusive. 

Among its physiological and biochemical functions, tryptophan is a precursor of NAD (Figure 4.1).1 Tryptophan, ingested via the portal vein, affects many processes in the liver, RNA synthesis, gluconeogenesis, and the induction of many enzymes. These aspects of tryptophan s action are covered in other sections. 

Teleological Considerations of Cell Structure. It is apparent that the organized structures of the cell contain specific enzymes and carry out defined biochemical functions. Most of the conclusions discussed above were derived from studies with liver preparations. In general the same properties are found when fractions of other cells are studied, but there is not sufficient information to conclude that the enzyme distribution of cells necessarily follows a given pattern. 

The liver is the organ where very many of these interconversions and synthetic processes occur if we were to enumerate all the biochemical functions that are localized in the liver, the greater part of this book would have to be reprinted here. Liver cells are particularly rich in mitochondria (up to 2000 per cell) and for that reason are especially well equipped to carry out metabolic processes. 

Ritter CL, Malejka-Giganti D. 1982. Mixed function oxidase in the mammary gland and liver microsomes of lactating rats. Biochem Pharmacol 31 239-247. 

The above scientific information on rice bran phytochemicals indicates that a multitude of mechanisms are operating at the cellular level to bring about specific health effects. Several health benefits of rice bran appear to be the result of the synergistic function of the many phytochemicals, antioxidants, vitamins and minerals which operates through a specific immune response. Their role in the biochemical mechanisms at the cellular level which result in major health effects is shown in Fig. 17.1. A short overview summarizing the effect of the various phytochemicals on major health issues such as cancer, immune function, cardiovascular disease, diabetes, altered liver function and gastrointestinal and colon disease will be given below. 

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