Anabolic and catabolic mediators

Dangers, and benefits of the cytokine mediated response to injury and infection

The inflammatory response is essential for survival in an environment where continuous exposure to noxious events threaten the integrity of the organism. However, the beneficial effects of the response are influenced by factors, which disadvantage individuals within a population. These factors include malnutrition, infection, genotype, gender, pre-existing inflammation, and chronic intoxication. Although the inflammatory response is generally successful in dealing with noxious events, life-long exposure to these events takes its toll on the integrity of the body and becomes apparent as chronic disease, atherosclerosis, organ failure, and frailty. Progress in ameliorating the consequences of lifetime exposure to inflammatory events can only occur if a fuller understanding can be obtained of the factors, which influence the persistence and outcome of the inflammatory response at an individual level. A multitude of studies has shown that specific nutrients, diets, and dietary restriction are able to modulate the inflammatory response in the population as a whole. To advance in this area, precise knowledge is needed of how the disadvantageous factors, mentioned above, affect the individual's response to anti-inflammatory nutrients.

Cirrhosis and endotoxin decrease urea synthesis in rats

AIM

In patients with cirrhosis, endotoxemia is frequent and the vitally important capacity for urea synthesis is impaired. The patients' mortality of infection is markedly increased, which could be related to adverse metabolic effects of endotoxins. The effects of endotoxins on in vivo urea synthesis and on urea cycle genes during cirrhosis are unknown.

METHODS

We examined the effects of a low dose of 0.5 mg/kg ip lipopolysaccharide (LPS) on the basal urea nitrogen synthesis rate (UNSR), the capacity of urea nitrogen synthesis (CUNS), liver tissue mRNA levels of urea cycle enzyme genes, and on the metabolic liver function measured by the galactose elimination capacity (GEC) in rats with cirrhosis induced by bile duct ligation and in control animals.

RESULTS

LPS and cirrhosis + LPS decreased UNSR by 40% (P < 0.05). Cirrhosis and LPS each tended to decrease CUNS and cirrhosis + LPS decreased CUNS by 40% (P < 0.05). Cirrhosis and LPS each decreased the mRNA level of the gene for the flux-generating urea cycle enzyme carbamoyl phosphate synthetase (CPS) and the mRNA for the rate-limiting urea cycle enzyme arginine succinate synthetase (ASS) (P < 0.05). Cirrhosis + LPS left the mRNA level of CPS unchanged and decreased that of ASS (P < 0.05). The GEC did not differ among the study groups.

CONCLUSION

Endotoxemia in rats with experimental cirrhosis markedly impaired the ability of the animals' livers to synthesize urea, suggesting a pathophysiological mechanism underlying the severe consequences of endotoxemia in human cirrhosis.

Activation of Ca(2+)-dependent proteolysis in skeletal muscle and heart in cancer cachexia

Cachexia is a syndrome characterized by profound tissue wasting that frequently complicates malignancies. In a cancer cachexia model we have shown that protein depletion in the skeletal muscle, which is a prominent feature of the syndrome, is mostly due to enhanced proteolysis. There is consensus on the views that the ubiquitin/proteasome pathway plays an important role in such metabolic response and that cytotoxic cytokines such as TNFalpha are involved in its triggering (Costelli and Baccino, 2000), yet the mechanisms by which the relevant extracellular signals are transduced into protein hypercatabolism are largely unknown. Moreover, little information is presently available as to the possible involvement in muscle protein waste of the Ca(2+)-dependent proteolysis, which may provide a rapidly activated system in response to the extracellular signals. In the present work we have evaluated the status of the Ca(2+)-dependent proteolytic system in the gastrocnemius muscle of AH-130 tumour-bearing rats by assaying the activity of calpain as well as the levels of calpastatin, the natural calpain inhibitor, and of the 130 kDa Ca(2+)-ATPase, both of which are known calpain substrates. After tumour transplantation, total calpastatin activity progressively declined, while total calpain activity remained unchanged, resulting in a progressively increasing unbalance in the calpain/calpastatin ratio. A decrease was also observed for the 130 kDa plasma membrane form of Ca(2+)-ATPase, while there was no change in the level of the 90 kDa sarcoplasmic Ca(2+)-ATPase, which is resistant to the action of calpain. Decreased levels of both calpastatin and 130 kDa Ca(2+)-ATPase have been also detected in the heart of the tumour-bearers. These observations strongly suggest that Ca(2+)-dependent proteolysis was activated in the skeletal muscle and heart of tumour-bearing animals and raise the possibility that such activation may play a role in sparking off the muscle protein hypercatabolic response that characterizes cancer cachexia.