Urinary excretion of L-carnitine and its short-chain acetyl-L-carnitine in patients undergoing carboplatin treatment

Uptake Transporters of the SLC21, SLC22A, and SLC15A Families in Anticancer Therapy-Modulators of Cellular Entry or Pharmacokinetics?

Solute carrier transporters comprise a large family of uptake transporters involved in the transmembrane transport of a wide array of endogenous substrates such as hormones, nutrients, and metabolites as well as of clinically important drugs. Several cancer therapeutics, ranging from chemotherapeutics such as topoisomerase inhibitors, DNA-intercalating drugs, and microtubule binders to targeted therapeutics such as tyrosine kinase inhibitors are substrates of solute carrier (SLC) transporters. Given that SLC transporters are expressed both in organs pivotal to drug absorption, distribution, metabolism, and elimination and in tumors, these transporters constitute determinants of cellular drug accumulation influencing intracellular drug concentration required for efficacy of the cancer treatment in tumor cells. In this review, we explore the current understanding of members of three SLC families, namely SLC21 (organic anion transporting polypeptides, OATPs), SLC22A (organic cation transporters, OCTs; organic cation/carnitine transporters, OCTNs; and organic anion transporters OATs), and SLC15A (peptide transporters, PEPTs) in the etiology of cancer, in transport of chemotherapeutic drugs, and their influence on efficacy or toxicity of pharmacotherapy. We further explore the idea to exploit the function of SLC transporters to enhance cancer cell accumulation of chemotherapeutics, which would be expected to reduce toxic side effects in healthy tissue and to improve efficacy.

Carnitine Profile Changes in Pediatric Hematopoietic Stem Cell Transplant: New Role for Carnitine?

Carnitine is an essential cofactor for mitochondrial import and oxidation of fatty acids. High-dose chemotherapy and radiation, often required for hematopoietic stem cell transplant (HSCT), leads to tissue damage, mitochondrial dysfunction, and alterations in carnitine metabolism. The aim of this pilot cohort study was to describe plasma and urinary carnitine profiles during pediatric HSCT and their relationships with clinical outcomes. Plasma and urinary carnitine samples were collected from 22 pediatric patients before and through day 180 post-HSCT. Associations were observed between graft-versus-host disease and an elevated plasma total carnitine (P=0.019), and also increased plasma acyl:free carnitine ratio with veno-occlusive disease (P=0.016). Mortality was observed in those with their highest urinary total carnitine losses on day 0 (P=0.005), and in those with an abnormal day 28 plasma ratio either above or below the reference range (P=0.007). Changes in carnitine profiles were more reflective of metabolic stress and negative outcomes than of inadequate dietary intake. Associations observed direct larger studies to assess the validity of carnitine profiles as a prognostic indicator and also to assess whether prophylactic carnitine supplementation pre-HSCT could reduce mitochondrial injury and urinary losses and help mitigate inflammatory and metabolic comorbidities of HSCT.

Efficacy and Effectiveness of Carnitine Supplementation for Cancer-Related Fatigue: A Systematic Literature Review and Meta-Analysis

Background: Carnitine deficiency has been implicated as a potential pathway for cancer-related fatigue that could be treated with carnitine supplementation. The aim of this systematic literature review and meta-analysis was to evaluate the literature regarding the use of supplemental carnitine as a treatment for cancer-related fatigue. Methods: Using the PRISMA guidelines, an electronic search of the Cochrane Library, MEDLINE, Embase, CINAHL and reference lists was conducted. Data were extracted and independently assessed for quality using the Academy of Nutrition and Dietetics evidence analysis by two reviewers. In studies with positive quality ratings, a meta-analysis was performed using the random-effects model on Carnitine and cancer-related fatigue. Results: Twelve studies were included for review with eight reporting improvement in measures of fatigue, while four reported no benefit. However, many studies were non-randomized, open-label and/or used inappropriate dose or comparators. Meta-analysis was performed in three studies with sufficient data. Carnitine did not significantly reduce cancer-related fatigue with a standardized mean difference (SMD) of 0.06 points ((95% CI −0.09, 0.21); p = 0.45). Conclusion: Results from studies with lower risk of bias do not support the use of carnitine supplementation for cancer-related fatigue.

Carnitine deficiency and oxidative stress provoke cardiotoxicity in an ifosfamide-induced Fanconi Syndrome rat model

In addition to hemorrhagic cystitis, Fanconi Syndrome is a serious clinical side effect during ifosfamide (IFO) therapy. Fanconi syndrome is a generalized dysfunction of the proximal tubule which is characterized by excessive urinary excretion of glucose, phosphate, bicarbonate, amino acids and other solutes excreted by this segment of the nephron including L-carnitine. Carnitine is essential cofactor for β-oxidation of long-chain fatty acids in the myocardium. IFO therapy is associated with increased urinary carnitine excretion with subsequent secondary deficiency of the molecule. Cardiac abnormalities in IFO-treated cancer patients were reported as isolated clinical cases. This study examined whether carnitine deficiency and oxidative stress, secondary to Fanconi Syndrome, provoke IFO-induced cardiomyopathy as well as exploring if carnitine supplementation using Propionyl-L-carnitine (PLC) could offer protection against this toxicity. In the current study, an animal model of carnitine deficiency was developed in rats by D-carnitine-mildronate treatment Adult male Wistar albino rats were assigned to one of six treatment groups: the first three groups were injected intraperitoneally with normal saline, D-carnitine (DC, 250 mg/kg/day) combined with mildronate (MD, 200 mg/kg/day) and PLC (250 mg/kg/day), respectively, for 10 successive days. The 4^th, 5^th and 6^th groups were injected with the same doses of normal saline, DC-MD and PLC, respectively for 5 successive days before and 5 days concomitant with IFO (50 mg/kg/day). IFO significantly increased serum creatinine, blood urea nitrogen (BUN), urinary carnitine excretion and clearance, creatine phosphokinase isoenzyme (CK-MB), lactate dehydrogenase (LDH), intramitochondrial acetyl-CoA/CoA-SH and thiobarbituric acid reactive substances (TBARS) in cardiac tissues and significantly decreased adenosine triphosphate (ATP) and total carnitine and reduced glutathione (GSH) content in cardiac tissues. In carnitine-depleted rats, IFO induced dramatic increase in serum creatinine, BUN, CK-MB, LDH, carnitine clearance and intramitochondrial acetyl-CoA/CoA-SH, as well as progressive reduction in total carnitine and ATP in cardiac tissues. Interestingly, PLC supplementation completely reversed the biochemical changes-induced by IFO to the control values. In conclusion, data from the present study suggest that: Carnitine deficiency and oxidative stress, secondary to Fanconi Syndrome, constitute risk factors and should be viewed as mechanisms during development of IFO-induced cardiotoxicity. Carnitine supplementation, using PLC, prevents the development of IFO-induced cardiotoxicity through antioxidant signalling and improving mitochondrial function.

Uptake carriers and oncology drug safety

Members of the solute carrier (SLC) family of transporters are responsible for the cellular influx of a broad range of endogenous compounds and xenobiotics in multiple tissues. Many of these transporters are highly expressed in the gastrointestinal tract, liver, and kidney and are considered to be of particular importance in governing drug absorption, elimination, and cellular sensitivity of specific organs to a wide variety of oncology drugs. Although the majority of studies on the interaction of oncology drugs with SLC have been restricted to the use of exploratory in vitro model systems, emerging evidence suggests that several SLCs, including OCT2 and OATP1B1, contribute to clinically important phenotypes associated with those agents. Recent literature has indicated that modulation of SLC activity may result in drug-drug interactions, and genetic polymorphisms in SLC genes have been described that can affect the handling of substrates. Alteration of SLC function by either of these mechanisms has been demonstrated to contribute to interindividual variability in the pharmacokinetics and toxicity associated with several oncology drugs. In this report, we provide an update on this rapidly emerging field.

Potential nephroprotective effects of l-carnitine against drug-induced nephropathy: a review of literature

INTRODUCTION

Drug-induced nephrotoxicity (DIN) has been reported with a great number of medications and contributes to ∼ 20% of hospital admissions. l-carnitine owing to its antioxidant, anti-inflammatory and antiapoptotic properties has been proposed as a candidate for nephroprotection against DIN. Increasing need to use nephrotoxic therapeutic agents necessitated this review.

AREAS COVERED

The present review covers all published clinical and animal researches on nephroprotective effects of l-carnitine against DIN. l-carnitine significantly ameliorates DIN in animal studies especially against cisplatin-induced renal damage. Inhibition of reactive oxygen species generation, lipid peroxidation, matrix remodeling and apoptosis, anti-inflammatory properties and improvement in carnitine deficiency has been suggested as probable nephroprotective mechanisms of l-carnitine.

EXPERT OPINION

In spite of the evidences that support the nephroprotective effect of l-carnitine, the main problems in this area are inadequacy of reliable studies in humans and difficulty of translating the experimental results into clinical practice. In most of the described studies, l-carnitine treatment is prophylactically given. Use of l-carnitine as a prophylactic agent in clinical situations with an indication for nephrotoxic therapies is rarely possible except for contrast-induced nephrotoxicity. Development of validated early biomarkers to detect DIN may provide the opportunity to use prophylactic nephroprotective agents at golden time.

Urinary excretion of L-carnitine, acetyl-L-carnitine, propionyl-L-carnitine and their antioxidant activities after single dose administration of L-carnitine in healthy subjects

The urine excretion of L-carnitine (LC), acetyl-L-carnitine (ALC) and propionyl-Lcarnitine (PLC) and their relations with the antioxidant activities are presently unknown. Liquid L-carnitine (2.0 g) was administered orally as a single dose in 12 healthy subjects. Urine concentrations of LC, ALC and PLC were detected by HPLC. Superoxide dismutase (SOD), total antioxidative capacity (T-AOC), malondialdehyde (MDA) and nitrogen monoxidum (NO) activities were measured by spectrophotometric methods. The 0~2 h, 2~4 h, 4~8 h, 8~12 h, 12~24 h excretion of LC was 53.13±31.36 µmol, 166.93±76.87 µmol, 219.92±76.30 µmol, 100.48±23.89 µmol, 72.07±25.77 µmol, respectively. The excretion of ALC was 29.70±14.43 µmol, 80.59±32.70 µmol, 109.85±49.21 µmol, 58.65±18.55 µmol, and 80.43±35.44 µmol, respectively. The urine concentration of PLC was 6.63±4.50 µmol, 15.33±12.59 µmol, 15.46±6.26 µmol, 13.41±11.66 µmol and 9.67±7.92 µmol, respectively. The accumulated excretion rate of LC was 6.1% within 24h after its administration. There was also an increase in urine concentrations of SOD and T-AOC, and a decrease in NO and MDA. A positive correlation was found between urine concentrations of LC and SOD (r = 0.8277) or T-AOC (r = 0.9547), and a negative correlation was found between urine LC excretions and NO (r = -0.8575) or MDA (r = 0.7085). In conclusion, a single oral LC administration let to a gradual increase in urine L-carnitine excretion which was associated with an increase in urine antioxidant enzymes and the total antioxidant capacities. These data may be useful in designing therapeutic regimens of LC or its analogues in the future.

L-Carnitine-supplementation in advanced pancreatic cancer (CARPAN)--a randomized multicentre trial

Background

Cachexia, a >10% loss of body-weight, is one factor determining the poor prognosis of pancreatic cancer. Deficiency of L-Carnitine has been proposed to cause cancer cachexia.

Findings

We screened 152 and enrolled 72 patients suffering from advanced pancreatic cancer in a prospective, multi-centre, placebo-controlled, randomized and double-blinded trial to receive oral L-Carnitine (4 g) or placebo for 12 weeks. At entry patients reported a mean weight loss of 12 ± 2,5 (SEM) kg. During treatment body-mass-index increased by 3,4 ± 1,4% under L-Carnitine and decreased (−1,5 ± 1,4%) in controls (p < 0,05). Moreover, nutritional status (body cell mass, body fat) and quality-of-life parameters improved under L-Carnitine. There was a trend towards an increased overall survival in the L-Carnitine group (median 519 ± 50 d versus 399 ± 43 d, not significant) and towards a reduced hospital-stay (36 ± 4d versus 41 ± 9d,n.s.).

Conclusion

While these data are preliminary and need confirmation they indicate that patients with pancreatic cancer may have a clinically relevant benefit from the inexpensive and well tolerated oral supplementation of L-Carnitine.

Inhibition of gene expression of organic cation/carnitine transporter and antioxidant enzymes in oxazaphosphorines-induced acute cardiomyopathic rat models

It is well documented that high therapeutic doses of oxazaphosphorines, cyclophosphamide (CP) and ifosfamide (IFO), are associated with cardiomyopathy. This study investigated whether oxazaphosphorines alter the expression of organic cation/carnitine transporter (OCTN2) and antioxidant genes and if so, whether these alterations contribute to CP and IFO-induced cardiotoxicity. Adult male Wistar albino rats were assigned to one of six treatment groups namely, control, L carnitine, CP, IFO, CP plus L carnitine and IFO plus L carnitine. In cardiac and kidney tissues, CP and IFO significantly decreased mRNA and protein expression of OCTN2. Oxazaphosphorines significantly increased serum acyl-carnitine/free carnitine ratio and urinary carnitine excretion and significantly decreased total carnitine in cardiac tissues. Interestingly, carnitine supplementation completely reversed the biochemical and gene expression changes-induced by oxazaphosphorines to the control values, except OCTN2 expression remained inhibited by IFO. Data from this study suggest that: (1) Oxazaphosphorines decreased myocardial carnitine content following the inhibition of OCTN2 mRNA and protein expression in cardiac tissues. (2) Oxazaphosphorine therapy increased urinary loss of carnitine secondary to the inhibition of OCTN2 mRNA and protein expression in proximal tubules of the kidney. (3) Carnitine supplementation attenuates CP but not IFO-induced inhibition of OCTN2 mRNA and protein expression in heart and kidney tissues.

Inhibition of OCTN2-mediated transport of carnitine by etoposide

OCTN2 is a bifunctional transporter that reabsorbs filtered carnitine in a sodium-dependent manner and secretes organic cations into urine as a proton antiport mechanism. We hypothesized that inhibition of OCTN2 by anticancer drugs can influence carnitine resorption. OCTN2-mediated transport inhibition by anticancer drugs was assessed using cells transfected with human OCTN2 (hOCTN2) or mouse Octn2 (mOctn2). Excretion of carnitine and acetylcarnitine was measured in urine collected from mice and pediatric patients with cancer before and after administration of etoposide. Five of 27 tested drugs (50-100 μmol/L) inhibited hOCTN2-mediated carnitine uptake by 42% to 85% (P < 0.001). Of these inhibitors, etoposide was itself a transported substrate of hOCTN2 and mOctn2. Etoposide uptake by hOCTN2 was reversed in the presence of excess carnitine. This competitive inhibitory mechanism was confirmed in an in silico molecular docking analysis. In addition, etoposide inhibited the transcellular apical-to-basolateral flux of carnitine in kidney cells. Etoposide was also associated with a significant urinary loss of carnitine in mice (~1.5-fold) and in patients with cancer (~2.4-fold). Collectively, these findings indicate that etoposide can inhibit hOCTN2 function, potentially disturb carnitine homeostasis, and that this phenomenon can contribute to treatment-related toxicities.

A review of the logistic role of L-carnitine in the management of radiation toxicity and radiotherapy side effects

Radiation therapy is a key modality in the treatment of different cancer types. Fatigue is the most common side effect of radiotherapy, while others include nausea, hair loss, skin irritation, anemia, infertility, cardiovascular disease, cognitive impairment and even the development of second cancers. Studies in experimental animals have shown protective effects of carnitine against exposure of various organs to ionizing radiation, whereas carnitine deficiency is known to enhance radiation-induced toxicity. This report summarizes the recent literature on the adverse effects of radiotherapy and the impact of radiation on carnitine homeostasis. Although some studies have demonstrated the prophylactic benefits of carnitine against the toxic effects of chemotherapy, the role of carnitine in the prognosis and management of cancer patients receiving radiotherapy is not clear and needs to be explored.

Role of carnitine in cancer chemotherapy-induced multiple organ toxicity

In the last few years, cancer chemotherapy has been successfully employed in the treatment of different types of human tumours. Unfortunately, the optimal clinical usefulness of this important treatment modality is usually limited secondary to the development of life-threatening multiple organ toxicity. Cancer chemotherapy may cause these toxic effects by mechanisms not involved in their anticancer activity that can severely affect the life of patients and represent a direct cause of death. Several experimental and clinical studies have demonstrated that some important anticancer drugs interfere with the absorption, synthesis, and excretion of carnitine in non-tumour tissues, resulting in a secondary carnitine deficiency which is reversed by carnitine treatment without affecting anticancer therapeutic efficacy. Prototypes of anticancer drugs that alter carnitine system are doxorubicin, cisplatin, carboplatin, oxaliplatin, cyclophosphamide and ifosfamide. Furthermore, cachectic cancer patients are especially at risk for carnitine deficiency due to decreased oral intake and/or increased renal losses. Altered serum and urine carnitine levels have been reported in cancer patients with various forms of malignant diseases. Recent studies in our laboratory have demonstrated that carnitine deficiency constitute a risk factor and should be viewed as a mechanism during development of oxazaphosphorines-induced cardiotoxicity in rats. Similarly, inhibition of gene expression of heart fatty acid-binding protein and organic cation/carnitine transporter in doxorubicin cardiomyopathic rat model has been reported. In view of these facts and in view of irreplaceability of these important anticancer drugs, this review aimed to highlight the role of carnitine depletion and supplementation during development of chemotherapy-induced multiple organ toxicity.

Cisplatin-induced downregulation of OCTN2 affects carnitine wasting

PURPOSE

Carnitine is an essential cofactor for mitochondrial fatty acid oxidation that is actively reabsorbed by the luminal transporter Octn2 (Slc22a5). Because the nephrotoxic agent cisplatin causes urinary loss of carnitine in humans, we hypothesized that cisplatin may affect Octn2 function.

EXPERIMENTAL DESIGN

Excretion of carnitine and acetylcarnitine was measured in urine collected from mice with or without cisplatin administration. The transport of carnitine was assessed in cells that were transfected with OCT1 or OCT2. The effect of cisplatin treatment on gene expression was analyzed using a mouse GeneChip array and validated using quantitative reverse transcriptase-PCR.

RESULTS

In wild-type mice, urinary carnitine excretion at baseline was ∼3-fold higher than in mice lacking the basolateral cisplatin transporters Oct1 and Oct2 [Oct1/2(-/-) mice], indicating that carnitine itself undergoes basolateral uptake into the kidney. Transport of carnitine by OCT2, but not OCT1, was confirmed in transfected cells. We also found that cisplatin caused an increase in the urinary excretion of carnitine and acetylcarnitine in wild-type mice but not in Oct1/2(-/-) mice, suggesting that tubular transport of cisplatin is a prerequisite for this phenomenon. Cisplatin did not directly inhibit the transport of carnitine by Octn2 but downregulated multiple target genes of the transcription factor peroxisome proliferator activated receptor α, including Slc22a5, in the kidney of wild-type mice that were absent in Oct1/2(-/-) mice.

CONCLUSION

Our study shows a pivotal role of Oct1 and Oct2 in cisplatin-related disturbances in carnitine homeostasis. We postulate that this phenomenon is triggered by deactivation of peroxisome proliferator activated receptor α and leads to deregulation of carnitine-shuttle genes.

Urinary excretion of carnitine as a marker of proximal tubular damage associated with platin-based antineoplastic drugs

BACKGROUND

Patients treated with cisplatin or carboplatin show increased renal excretion of carnitine. It is currently unclear whether this is also the case for oxaliplatin and which are the responsible mechanisms.

METHODS

We investigated 22 patients treated either with a single dose of cisplatin, carboplatin or oxaliplatin. Carnitine and kidney function parameters were determined in plasma and urine. Inhibition and mRNA expression of OCTN2, the principle carnitine transporter, were assessed in L6 cells overexpressing OCTN2 and in 293-EBNA cells, respectively.

RESULTS

Renal excretion of free and short-chain acylcarnitine increased already at the day of administration was maximal the day after and had normalized 1 week after administration of cisplatin, carboplatin or oxaliplatin. The renal excretion fractions for free carnitine and acylcarnitines increased 4-10 times during treatment with platin derivatives. Renal excretions of alpha1-microglobulin and other proximal tubular markers were also increased, compatible with a proximal tubular defect. Direct inhibition of OCTN2 expressed in L6 cells by cisplatin, oxaliplatin or platinum(2+) could not be demonstrated, and experiments using urine from patients treated with cisplatin inhibited OCTN2 activity no more than expected from the carnitine content in the respective urine sample. Cisplatin was associated with a time- and concentration-dependent decrease of OCTN2 mRNA and protein expression in 293-EBNA cells.

CONCLUSIONS

All platin derivatives investigated are associated with renal tubular damage in humans without significantly affecting glomerular function. The rapid onset and complete reversibility of this effect favour a functional mechanism such as impaired expression of OCTN2 in proximal tubular cells.

Effect of acetyl-l-carnitine on ovarian cancer cells' proliferation, nerve growth factor receptor (Trk-A and p75) expression, and the cytotoxic potential of paclitaxel and carboplatin

OBJECTIVES

The incidence of chemotherapy induced peripheral neuropathy (CIPN) is 15-25% with platinum and taxanes. CIPN can be permanent and often requires dose reduction or change in chemotherapy. Acetyl-l-carnitine (ALCAR), an ester of l-carnitine, is used to treat CIPN in humans and in animal models. The goals of this study are: 1) examine the effects of ALCAR on ovarian cancer cells, 2) determine if ALCAR affects the cytotoxicity of standard chemotherapy on ovarian cancer cells.

METHODS

OVCAR-3 and SKOV-3 ovarian cancer lines were incubated in ALCAR containing media. Viability, proliferation, and expression of the nerve growth factor receptors (NGFR) Trk-A and p-75 were determined by flow cytometry. Cytotoxicity assays examining ALCAR's effect on paclitaxel and carboplatin were done by flow cytometry and infrared plate-reader.

RESULTS

Flow cytometry showed no change in percent live (p = 0.87) or proliferation (p = 0.95) of OVCAR-3 cells when comparing controls with up to 100 microM ALCAR. However, there was a slight but significant decrease in the proliferation of SKOV-3 cells incubated at higher ALCAR concentrations (p = < 0.01). Flow cytometry showed no difference in the viability of OVCAR-3 cells when comparing ALCAR: +/- paclitaxel (p = 1), +/- carboplatin (p = 0.8), or both (p = 0.4). Proliferation assays indicated that paclitaxel's cytotoxicity on OVCAR-3 and SKOV-3 cells was unchanged at higher ALCAR concentrations (p = < 0.01-0.4). ALCAR did not affect the expression of NGFR on OVCAR-3 or SKOV-3 cells.

CONCLUSION

ALCAR does not affect the cytotoxicity of paclitaxel or carboplatin. There was no increase in proliferation, or NGFR of OVCAR-3 or SKOV-3 cells exposed to ALCAR.

Carnitine deficiency aggravates carboplatin nephropathy through deterioration of energy status, oxidant/anti-oxidant balance, and inflammatory endocoids

We have recently shown that carnitine deficiency could represent a risk factor in paracetamol hepatotoxicity. By the same token, d-carnitine-induced carnitine deficiency aggravated carboplatin nephropathy following challenge with a single dose (35mg/kg, IP) of the platinum drug in male Swiss albino rats. The combination modality induced marked degenerative changes and severe inflammation in kidney tissues that surpassed either carboplatin or d-carnitine given alone. The combined regimen synergistically increased the serum levels of creatinine, blood urea nitrogen (BUN), tumor necrosis factor alpha (TNF-alpha), palmitate, and kidney malondialdehyde (MDA), adenosine triphosphate (ATP), nitric oxide (NO) contents as well as kidney myeloperoxidase (MPO) activity. The only parameter that has been notably decreased was the kidney reduced glutathione (GSH) level. Exaggeration by carnitine deficit of the deleterious effects of carboplatin is most probably ascribed to energy starvation. The reduction in kidney content of ATP parcels was associated with elevation of serum palmitate level that reflected debilitated fatty acid oxidation, and this further deteriorated energy resources in kidney tissues. Compromising the oxidant/anti-oxidant balance and modulating the release of some inflammatory endocoids namely, TNF-alpha and NO could also possibly account for such combinatorial detrimental toxicity. The current study was further extended to elucidate any possible nephroprotective effects of l-carnitine. Interestingly, carnitine supplementation ahead of carboplatin challenge ameliorated and almost normalized all the biochemical parameters and also mitigated the injurious effects of the cytotoxic drug. Thus, one could conclude that carnitine deficiency, whether being a causative clue or a sequela, might represent a risk factor in carboplatin nephropathy.