In mammalian cells, the carnitine system is essential for glucose and lipid turnover and it plays a crucial role in maintaining the energy metabolism (
Breitkreutz et al, 2000;
Peluso et al, 2000). Chemotherapy causes dysfunction of enzymes involved in the transport and trafficking of carnitines (
Peluso et al, 2000) and, in addition, ifosfamide and cisplatin induce increased urinary excretion of these molecules (
Dodson et al, 1989;
Marthaler et al, 1999;
Heuberger et al, 1998). These effects may worsen the dysmetabolic syndrome associated with cancer (
Tisdale, 1997) and increase side-effects of chemotherapy, like fatigue (
Tisdale, 1997;
Portenoy and Itri, 1999).
Fatigue is a common symptom in patients with advanced cancer and it frequently occurs after anti-cancer therapies (
Stone et al, 2000). In patients with metastatic tumours, cancer-related fatigue is extremely prevalent and it is observed in 70 to 80% of patients receiving chemotherapy and up to 90% of radiotherapy patients (
Richardson and Ream, 1996;
Morrow et al, 1999;
Schwartz et al, 2000). On the basis of current experience, fatigue is considered primarily treatment-related when there is a clear relationship between the timing of fatigue and the therapeutic intervention. In these cases, chemotherapy-induced fatigue is an early side-effect which peaks within a few days after treatment and declines thereafter (
Morrow et al, 1999). Cancer-related fatigue and chemotherapy-related fatigue are multifactorial, however, anaemia seems to play a major role (
Portenoy and Itri, 1999). Recent experiences have demonstrated the relationship between mild-moderate anaemia, fatigue and quality of life (
Groopman and Itri, 1999). Treatment of anaemia with epoetin alpha resulted in significant improvements of energy levels, activity levels, functional status and overall quality of life (
Groopman and Itri, 1999). Current data suggest that patients with haemoglobin levels >12 gr dl
−1 show significantly less fatigue and better quality of life than patients with haemoglobin values less than 12 gr dl
−1 (
Cleeland et al, 1999). Epoetins are the mainstay of treatment for anaemia-associated fatigue, but other conditions and mechanisms may sustain fatigue and require a different approach to treatment (
Portenoy and Itri, 1999;
Tisdale, 1997). Exercise and education about fatigue may be beneficial in its relief (
Dimeo et al, 1999). Low-dose corticosteroids have shown some positive effects against fatigue but data remain scattered and unconfirmed in comparative trials (
Portenoy and Itri, 1999). It was postulated that antidepressant modulating serotonin may alleviate fatigue in patients treated with chemotherapy. Unfortunately, the serotonin re-uptake inhibitor paroxetine was unable to improve fatigue in a double-blind, placebo-controlled trial (
Morrow et al, 2001). Tumour-induced cytokines and host-produced pro-inflammatory cytokines may represent a possible mechanism contributing to a condition of fatigue. Current research is exploring these and other mechanisms which could be the target of future clinical trials for the treatment of fatigue (
McNeil, 2001).
In the present study, a selected population of non-anaemic patients, with good performance status and without significant comorbidities showed early fatigue after cisplatin or ifosfamide-based chemotherapy. In the majority of patients, this side-effect significantly improved after LC supplementation which was well tolerated and did not affect anti-cancer therapeutic efficacy. These data suggest that chemotherapy-induced damage of the carnitine system and secondary deficiency of the molecule (
Dodson et al, 1989;
Heuberger et al, 1998;
Marthaler et al, 1999;
Peluso et al, 2000) may cause fatigue due to impaired energy metabolism (
Peluso et al, 2000). It therefore follows that restoration of the carnitine pool may alleviate this symptom (
Brass et al, 2001). To the best of our knowledge, this is the first study which has explored the therapeutic intervention of the carnitine system for treating selected patients with chemotherapy-induced fatigue. Results are encouraging, but these data should be looked at with caution due to potential biases and limitations inherent to the study itself.
In non-anaemic cancer patients, carnitine deficiency may not be the primary cause of fatigue and concomitant disease-related or host-related conditions may contribute to this toxicity. Early chemotherapy-induced asthenia may improve spontaneously and independently from specific interventions (
Richardson and Ream, 1996;
Morrow et al, 1999). Also, reduction of tumour burden in response to the anticancer treatment may alleviate fatigue. The urinary excretion of carnitine persists for several days after chemotherapy and this clearance returns to normal values 7 days after the administration of cisplatin (
Heuberger et al, 1998). However, even in the presence of carnitine deficiency, patients may restore their carnitine pool by food intake or endogen production, and urinary loss may not be sufficient to cause a symptomatic deficiency. Finally, this prospective trial was performed in a population of patients with homogenous good physical status, but the effect of LC supplementation was not compared to a control group in a randomised fashion.
On the basis of these considerations, present data on LC as an ergogenic aid after cancer chemotherapy are not compelling. However, clinical trials which investigate putative therapies against chemotherapy-induced fatigue are almost lacking (
Portenoy and Itri, 1999), and despite its limitations, the findings of this early study are intriguing and open new perspectives for future clinical trials. Further analyses are required to clarify the potential role of LC and we are planning to verify the efficacy of this compound in a randomised, placebo-controlled study.