Effects of chronic exposure to low-level cadmium on renal tubular function and CYP2A6-mediated coumarin metabolism in healthy human subjects

Inhibition and induction of CYP enzymes in humans: an update

The cytochrome P450 (CYP) enzyme family is the most important enzyme system catalyzing the phase 1 metabolism of pharmaceuticals and other xenobiotics such as herbal remedies and toxic compounds in the environment. The inhibition and induction of CYPs are major mechanisms causing pharmacokinetic drug–drug interactions. This review presents a comprehensive update on the inhibitors and inducers of the specific CYP enzymes in humans. The focus is on the more recent human in vitro and in vivo findings since the publication of our previous review on this topic in 2008. In addition to the general presentation of inhibitory drugs and inducers of human CYP enzymes by drugs, herbal remedies, and toxic compounds, an in-depth view on tyrosine-kinase inhibitors and antiretroviral HIV medications as victims and perpetrators of drug–drug interactions is provided as examples of the current trends in the field. Also, a concise overview of the mechanisms of CYP induction is presented to aid the understanding of the induction phenomena.

Heavy metal imaging in fibrotic human kidney tissue using the synchrotron X-ray fluorescence microprobe

Abnormally high exposure to heavy metals and their accumulation in some tissues are recognized as causes of many acute and chronic human diseases. Because of the roles many metals have in normal human physiology, proving cause and effect between exposure to heavy metals and pathogenesis of disease is problematic. Therefore, many illnesses that develop through occupational and environmental exposure are not considered directly related to heavy metal toxicity. The high sensitivity and spatial resolution of elements using the synchrotron X-ray fluorescence microprobe (XFM) may give a robust means to investigate spatial distribution of heavy metals in correlation with specific pathologies. For example, proven presence of different heavy metals may correlate spatially with kidney fibrosis, suggesting a mechanistic link between heavy metal-induced fibrosis and chronic kidney disease. One specific example that may benefit from such an analysis relates to a cluster of people with chronic kidney disease of unknown cause (CKDu), in a significant proportion of the population of the North Central Province of Sri Lanka. Here, it was postulated that heavy metal exposure, in particular of cadmium, in foods and agriculture may be one cause of end-stage kidney disease and premature death of patients with CKDu. Synchrotron methods had not been applied previously to this particular problem. This manuscript provides a brief review of the literature and reports some pilot data from an investigation of localization of kidney fibrosis in CKDu with selected heavy metals including cadmium.

The Diagnostic Role of Urinary N-Acetyl-β-D-glucosaminidase (NAG) Activity in the Detection of Renal Tubular Impairment

The kidney function can be assessed by a number of methods. The urinary excretion of enzymes, in particular N-acetyl-β-D-glucosaminidase (NAG), is considered a relatively simple, cheap, fast and non-invasive method in the detection and follow-up of renal tubular function under various conditions. The determination of urinary NAG provides a very sensitive and reliable indicator of renal damage, such as injury or dysfunction due to diabetes mellitus, nephrotic syndrome, inflammation, vesicoureteral reflux, urinary tract infection, hypercalciuria, urolithiasis, nephrocalcinosis, perinatal asphyxia, hypoxia, hypertension, heavy metals poisoning, treatment with aminoglycosides, valproate, or other nephrotoxic drugs. This paper gives an overview of the current use of urinary NAG in the detection of renal injury.

Kidney biomarkers associated with blood lead, mercury, and cadmium in premenopausal women: a prospective cohort study

Certain metals are harmful to the kidney and liver at high levels, but associations with functional biomarkers at low exposure levels among premenopausal women apparently has not been evaluated. Healthy, regularly menstruating women (n = 259) were followed for up to 2 menstrual cycles with up to 16 visits. Renal and liver biomarkers were measured in serum at each clinic visit. Cadmium (Cd), lead (Pb), and mercury (Hg) were measured in whole blood at baseline. Linear mixed models were adjusted for age, body mass index (BMI), race, average calories, alcohol intake, smoking, and cycle day. Median levels of Cd, Pb, and Hg were 0.31 μg/L, 0.88 μg/dl, and 1.1 μg/L, respectively. One-third of women had diminished glomerular filtration rate (eGFR) (<90 ml/min/1.73 m(2)). Each twofold increase in Cd was associated with a negative 4.9% change in blood urea nitrogen (BUN) and bilirubin. Each twofold rise in Pb was associated with decreased eGFR and increased creatinine. A twofold elevation in Hg was associated with higher protein and reduced alkaline phosphatase. In healthy, predominantly nonsmoking women, low levels of Cd, Pb, and Hg were associated with changes in select biomarkers of kidney and liver function.

Anti-smoking legislation and its effects on urinary cotinine and cadmium levels

Anti-smoking legislation has been associated with an improvement in health indicators. Since the cadmium (Cd) body burden in the general population is markedly increased by smoke exposure, we analyzed the impact of the more restrictive legislation that came into force in Spain in 2011 by measuring Cd and cotinine in first morning urine samples from 83 adults in Madrid (Spain) before (2010) and after (2011) introduction of this law. Individual pair-wise comparisons showed a reduction of creatinine corrected Cotinine and Cd levels for non-active smokers, i. e. those which urinary cotinine levels are below 50 μg/L. After the application of the stricter law, cotinine levels in urine only decreased in non-active smokers who self-reported not to be exposed to second-hand smoke. The reduction in second hand smoke exposure was significantly higher in weekends (Friday to Sunday) than in working days (Monday to Thursday). The decrease in U-Cd was highly significant in non-active smokers and, in general, correlated with lower creatinine excretion. Therefore correction by creatinine could bias urinary Cd results, at least for cotinine levels higher than 500 μg/L. The biochemical/toxicological benefits detected herein support the stricter application of anti-smoking legislation and emphasize the need to raise the awareness of the population as regards exposure at home.

Low serum zinc is associated with elevated risk of cadmium nephrotoxicity

BACKGROUND

Despite animal evidence suggests that zinc modulates cadmium nephrotoxicity, limited human data are available.

OBJECTIVE

To test the hypothesis that low serum zinc concentrations may increase the risk of cadmium-mediated renal dysfunction in humans.

METHODS

Data from 1545 subjects aged 20 or older in the National Health and Nutrition Examination Survey (NHANES), 2011-2012 were analyzed. Renal function was defined as impaired when estimated glomerular filtration rate (eGFR) fell below 60 ml/min/1.73 m(2) and/or the urinary albumin-to-creatinine ratio surpassed 2.5 in men and 3.5mg/mmol in women.

RESULTS

Within the study cohort, 117 subjects had reduced eGFR and 214 had elevated urinary albumin. After adjusting for potential confounders, subjects with elevated blood cadmium (>0.53 μg/L) were more likely to have a reduced eGFR (odds ratio [OR]=2.21, 95% confidence interval [CI]: 1.09-4.50) and a higher urinary albumin (OR=2.04, 95% CI: 1.13-3.69) than their low cadmium (<0.18 μg/L) peers. In addition, for any given cadmium exposure, low serum zinc is associated with elevated risk of reduced eGFR (OR=3.38, 95% CI: 1.39-8.28). A similar increase in the odds ratio was observed between declining serum zinc and albuminuria but failed to reach statistical significance. Those with lower serum zinc/blood cadmium ratios were likewise at a greater risk of renal dysfunction (p<0.01).

CONCLUSIONS

This study results suggest that low serum zinc concentrations are associated with an increased risk of cadmium nephrotoxicity. Elevated cadmium exposure is global public health issue and the assessment of zinc nutritional status may be an important covariate in determining its effective renal toxicity.

Modeling cadmium exposures in low- and high-exposure areas in Thailand

BACKGROUND

Previous U.S. population modeling studies have reported that urinary cadmium (Cd) excretion patterns differ with age, sex, and dietary exposure; associations between Cd exposures and health outcomes also have differed by age and sex. Therefore, it is important to test models used to estimate Cd exposures across an expanded Cd-exposure range.

OBJECTIVES

We estimated relative Cd exposures from both diet and smoking in low- and high-exposure scenarios to provide data for improving risk assessment calculations.

METHODS

We used a Cd toxicokinetic-based model to estimate Cd exposures based on urinary Cd levels measured for 399 persons in a low-exposure area (Bangkok) and 6,747 persons in a high-exposure area (Mae Sot) in Thailand.

RESULTS

In Bangkok, we estimated dietary Cd exposures of 50-56 µg/day for males and 21-27 µg/day for females 20-59 years of age who never smoked. In Mae Sot, we estimated dietary Cd exposures of 188-224 µg/day for males and 99-113 µg/day for females 20-59 years of age who never smoked. In Bangkok, we estimated Cd exposures from smoking to be 5.5-20.4 µg/day for male smokers 20-59 years of age. In Mae Sot, we estimated Cd exposures from smoking to be 9.8-26 µg/day for male heavy smokers and 26 µg/day for female heavy smokers.

CONCLUSION

This study provides estimates of Cd exposures from diet and smoking in low- and high-exposure scenarios. Our findings suggest a relatively small safety margin between the established tolerable Cd reference exposure of 62 µg/day and exposure levels previously associated with evidence of kidney and bone effects in Mae Sot residents, where dietary Cd exposures among women were only 1.6-2.1 times the reference value.

Onion (Allium cepa) extract prevents cadmium induced renal dysfunction

Cadmium (Cd), a heavy metal, is known for its adverse effects on the body. In this study, the lowering effect of Cd on renal clearance (RC) was investigated, and Allium cepa extract (AcE) (an antioxidant) was pre-administered orally to prevent Cd's adverse effects. Seventy-two Wistar rats, grouped into three (n = 24), were used for this study. While Group C was given 1.0 ml of AcE daily (orally), Group A and Group B were given distilled water. AcE administration was done for eight weeks. Afterwards B and C were then given 1.5 ml/kg BW of 0.3 mg/L 3CdSO(4).8H(2)O intraperitoneally for three consecutive days. The results obtained showed that Cd causes significant reduction in the 24 hour urine volume (from 3.017 +/- 0.125 to 2.433 +/- 0.118 ml), RC (from 3.258 +/- 0.114 to 1.357 +/- 0.104 ml/h for creatinine; and from 0.350 +/- 0.057 to 0.185 +/- 0.055 ml/h for urea), plasma and tissue SOD and CAT activity (form 1.644 +/- 0.036 to 1.307 +/- 0.056 u/g protein for plasma SOD; 0.391 +/- 0.029 to 0.2692 +/- 0.031 u/protein for plasma CAT; 1.695 +/- 0.034 to 1.327 +/- 0.049 u/g protein for tissues SOD; and from 0.350 +/- 0.027 to 0.273 +/- 0.043 u for tissue CAT), and significant MDA increased in plasma (from 1496.79 +/- 1.321 to 1679.48 +/- 143.29 mug/g protein) and tissue (from 1265.22 +/- 2.285 to 1669.87 +/- 14.61 mug/dL). AcE, however, prevents these Cd's adverse effects. This findings lead to the conclusion Cd exposure causes renal dysfunction, but oral administration of onion could prevent it.

Human CYP2A6 is regulated by nuclear factor-erythroid 2 related factor 2

Human CYP2A6 is responsible for the metabolism of nicotine and coumarin as well as the metabolic activation of tobacco-related nitrosamines. Earlier studies revealed that CYP2A6 activity was increased by dietary cadmium or cruciferous vegetables, but the underlying mechanisms remain to be clarified. In the present study, we investigated the possibility that Nrf2 might be involved in the regulation of CYP2A6. Real-time RT-PCR analysis revealed that the CYP2A6 mRNA level in human hepatocytes was significantly (P<0.01, 1.4-fold) induced by 10μM sulforaphane (SFN), a typical activator of Nrf2. A computer-based search identified three putative antioxidant response elements (AREs) in the 5'-flanking region of the CYP2A6 gene at positions -1212, -2444, and -3441, termed ARE1, ARE2, and ARE3, respectively. Electrophoretic mobility shift assays demonstrated that Nrf2 bound only to ARE1. Luciferase assays using HepG2 cells revealed that the overexpression of Nrf2 significantly increased the reporter activities of the constructs containing a 30-bp fragment that included ARE1. However, the activity of the construct containing the intact 5'-flanking region (-1 to -1395) including ARE1 was not increased by the overexpression of Nrf2. In contrast, when the reporter construct was injected into mice via the tail vein, the reporter activity in the liver was significantly (P<0.05, 1.9-fold) increased by SFN (1mg/head) administration. In conclusion, we found that human CYP2A6 is regulated via Nrf2, suggesting that CYP2A6 is induced under oxidative stress.

Update information on drug metabolism systems--2009, part II: summary of information on the effects of diseases and environmental factors on human cytochrome P450 (CYP) enzymes and transporters

The present paper is an update of the data on the effects of diseases and environmental factors on the expression and/or activity of human cytochrome P450 (CYP) enzymes and transporters. The data are presented in tabular form (Tables 1 and 2) and are a continuation of previously published summaries on the effects of drugs and other chemicals on CYP enzymes (Rendic, S.; Di Carlo, F. Drug Metab. Rev., 1997, 29(1-2), 413-580., Rendic, S. Drug Metab. Rev., 2002, 34(1-2), 83-448.). The collected information presented here is as stated by the cited author(s), and in cases when several references are cited the latest published information is included. Inconsistent results and conclusions obtained by different authors are highlighted, followed by discussion of the major findings. The searchable database is available as an Excel file, for information about file availability contact the corresponding author.

The influence of CYP2A6 polymorphisms and cadmium on nicotine metabolism in Thai population

We investigated the influence of genetic, cadmium exposure and smoking status, on cytochrome P450-mediated nicotine metabolism (CYP2A6) in 182 Thai subjects after receiving 2mg of nicotine gum chewing for 30min. The urinary excretion of cotinine was normally distributed over a 2h period (logarithmically transformed). Individuals with urinary cotinine levels in the ranges of 0.01-0.21, and 0.52-94.99μg/2h were categorized as poor metabolizes (PMs: 6.5%), and extensive metabolizers (EMs: 93.5%), respectively. The majority of EMs (45%) carried homozygous wild-type genotypes (CYP2A6*1A/*1A, CYP2A6*1A/*1B and CYP2A6*1B/*1B), whereas only 1% of PMs carried these genotypes. Markedly higher frequencies of EMs were also observed in all heterozygous defective genotypes including the null genotype (*4C/*4C; 1 subject). A weak but significant positive correlation was observed between total amounts of urinary cadmium excretion and total cotinine excretion over 2h. Our study shows generally good agreement between CYP2A6 genotypes and phenotypes. Smokers accumulated about 3-4-fold higher mean total amounts of 2-h urinary cadmium excretion (127.5±218.2ng/2h) than that of non-smokers (40.5±78.4ng/2h). Among the smokers (n=16), homologous wild-type genotype *1/*1 was significantly the predominant genotype (6/16) compared with other defective allele including *4C/*4C. In addition, 2h urinary excretion of cotinine in smokers of all genotypes was significantly higher than non-smokers. The proportion of smokers who smoked more than 5 cigarettes/day was significantly higher in EMs in all CYP2A6 genotypes (n=14) than in PMs (n=0).

Tubular marker excretion in children from families with Balkan nephropathy

Balkan nephropathy (BN) has not been described in children; however, some previous studies in children from families with BN have revealed abnormalities of the urinary tract. In this study, urinary excretion of beta2-microglobulin, N-acetyl-beta-D-glucosaminidase (NAG) and gamma-glutamyl transpeptidase (GGT) was studied three times a year: spring, autumn, and winter, during a 3-year period, in 703 healthy children, initial age 9-13, from endemic and nonendemic settlements around the South Morava River. Beta-2-microglobulin excretion in urine, in all three seasons, was highest in children from families with BN compared with the excretion in children from the city, nonendemic villages, and those from nonendemic families. Increased urinary GGT excretion in children from endemic villages in October was higher than in children from the city and control villages, being the same in both endemic and nonendemic families. However, in February, it was similar in children from the city, endemic, and control villages. In conclusion, children from families with BN excreted significantly more beta2-microglobulin in all three seasons (spring, autumn, winter) of the study, in multivariate analysis significant for family status, gender, and the season (p < 0.001). NAG emerged as a potentially useful marker for seasonal exposure to an environmental nephrotoxin.

Molecular genetics of nicotine metabolism

The molecular genetics of nicotine metabolism involves multiple polymorphic catalytic enzymes. Variation in metabolic pathways results in nicotine disposition kinetics that differ between individuals and ethnic groups. Twin studies indicate that a large part of this variance is genetic in origin, although environmental influences also contribute. The primary aim of this chapter is to review the current knowledge regarding the genetic variability in the enzymes that metabolize nicotine in humans. The focus is on describing the genetic polymorphisms that exist in cytochromes P450 (CYPs), aldehyde oxidase 1 (AOX1), UDP-glucuronosyltransferases (UGTs), and flavin-containing monooxygenase 3 (FMO3). Genetic studies have demonstrated that polymorphisms in CYP2A6, the primary enzyme responsible for nicotine breakdown, make a sizable contribution to the wide range of nicotine metabolic capacity observed in humans. Thus, special attention will be given to CYP2A6, because slower nicotine metabolism requires less frequent self-administration, and accordingly influences smoking behaviors. In addition, the molecular genetics of nicotine metabolism in nonhuman primates, mice, and rats will be reviewed briefly.

Novel and established CYP2A6 alleles impair in vivo nicotine metabolism in a population of Black African descent

Cytochrome P450 2A6 (CYP2A6) is a human enzyme best known for metabolizing tobacco-related compounds, such as nicotine, cotinine (COT), and nitrosamine procarcinogens. CYP2A6 genetic variants have been associated with smoking status, cigarette consumption, and tobacco-related cancers. Our objective was to functionally characterize four nonsynonymous CYP2A6 sequence variants with respect to their haplotype, allele frequency, and association with in vivo CYP2A6 activity. In vivo, nicotine was administered orally to 281 volunteers of Black African descent. Blood samples were collected for kinetic phenotyping and CYP2A6 genotyping. In vitro, nicotine C-oxidation catalytic efficiencies of heterologously expressed variant enzymes were assessed. The four uncharacterized sequence variants were found in seven novel alleles CYP2A6(*)24A&B ; (*)25, (*)26, (*)27, and *28A&B, most were associated with impaired in vivo CYP2A6 activity. Nicotine metabolism groupings, based on the in vivo data of variant alleles, were created. Mean trans-3'-hydroxycotinine/cotinine (3HC/COT) differed (P<0.001) between normal (100%), intermediate (64%), and slow (40%) groups. Systemic exposure to nicotine following oral administration also differed (P<0.001) between normal (100%), intermediate (139%), and slow (162%) metabolism groups. In addition, alleles of individuals with unusual phenotype-genotype relationships were sequenced, resulting in the discovery of five novel uncharacterized alleles and at least one novel duplication allele. A total of 7% of this population of Black African descent had at least one of the eight novel characterized alleles and 29% had at least one previously established allele. These findings are important for increasing the accuracy of association studies between CYP2A6 genotype and behavioral, disease, or pharmacological phenotypes.

JWA gene is involved in cadmium-induced growth inhibition and apoptosis in HEK-293T cells

Cadmium (Cd) is widely dispersed in the environment due to occupational and personal (cigarette) emissions. Exposure of human embryonic kidney 293T (HEK-293T) cells to CdCl2 resulted in growth inhibition and apoptosis. Our previous studies demonstrated that JWA, a novel retinoic acid-inducible and cytoskeleton-associated gene, is a potential environmental-responsive gene with increased expression attributed to oxidative and heat-shock stresses. In the present study, JWA was also found to be responsive to Cd exposure. After treatment with 20 microM CdCl2 for 12 h, the expression level of JWA was increased with accompanied growth inhibition and apoptosis. In addition, knock-down JWA protein expression by using transient transfecting of HEK-293T cells with antisense JWA express vector showed a protective effect against Cd-induced apoptosis. To determine whether the upregulation of JWA by Cd involved regulation by transcriptional mechanisms, further reporter gene assays were employed, which demonstrated a marked increase in JWA promoter activity. In addition, elevated intracellular levels of ROS components (O2-* and H2O2) and activation of JNK, ERK, and MAPK were found with corresponding upregulation of JWA protein expression. These results suggest that Cd-induced growth inhibition and apoptosis may involve ROS generation and subsequent affect on MAPK signal pathway. JWA responsiveness to CdCl2 might be through both transcriptional and posttranslational mechanisms.

Kidney Dysfunction and Hypertension: Role for Cadmium, P450 and Heme Oxygenases?

Cadmium (Cd) is a metal toxin of continuing worldwide concern. Daily intake of Cd, albeit in small quantities, is associated with a number of adverse health effects which are attributable to distinct pathological changes in a variety of tissues and organs. In the present review, we focus on its renal tubular effects in people who have been exposed environmentally to Cd at levels below the provisional tolerable intake level set for the toxin. We highlight the data linking such low-level Cd intake with tubular injury, altered abundance of cytochromes P450 (CYPs) in the kidney and an expression of a hypertensive phenotype. We provide updated knowledge on renal and vascular effects of the eicosanoids 20-hydroxyeicosatetraenoic acid (20-HETE) and eicosatrienoic acids (EETs), which are biologically active metabolites from arachidonate metabolism mediated by certain CYPs in the kidney. We note the ability of Cd to elicit "oxidative stress" and to alter metal homeostasis notably of zinc which may lead to augmentation of the defense mechanisms involving induction of the antioxidant enzyme heme oxygenase-1 (HO-1) and the metal binding protein metallothionein (MT) in the kidney. We hypothesize that renal Cd accumulation triggers the host responses mediated by HO-1 and MT in an attempt to protect the kidney against injurious oxidative stress and to resist a rise in blood pressure levels. This hypothesis predicts that individuals with less active HO-1 (caused by the HO-1 genetic polymorphisms) are more likely to have renal injury and express a hypertensive phenotype following chronic ingestion of low-level Cd, compared with those having more active HO-1. Future analytical and molecular epidemiologic research should pave the way to the utility of induction of heme oxygenases together with dietary antioxidants in reducing the risk of kidney injury and hypertension in susceptible people.

Renal and hepatic accumulation of cadmium and lead in the expression of CYP4F2 and CYP2E1

The present study examined accumulation of the metal toxins cadmium (Cd) and lead (Pb) in relation to the abundance of cytochrome P450 4F2 (CYP4F2), CYP2E1 and concentrations of zinc and copper in liver and kidney samples using immunoblotting coupled with metal analysis. The post mortem liver and kidney cortex samples were from 23 males and 8 females aged 3-89 years. All were Caucasians who had not been exposed to metals in the workplace. Average kidney cortex Cd load of 17.4 microg/g w.w. was 17 times greater than average liver Cd load (1.1 microg/g w.w.). In contrast, average kidney cortex Pb load of 0.09 microg/g w.w. was two times lower than liver Pb load of 0.19 microg/g w.w. Average Zn and Cu concentrations in the kidney cortex samples were 67% and 33% lower than those in the liver. Liver and kidney Cd loads, but not liver or kidney Pb loads, correlated positively with donors' age. After controlling for liver Cd load, an inverse correlation was seen between Zn and age (partial r=-0.39, P=0.02), suggesting reduction in liver Zn levels in old age. Liver CYP2E1 protein abundance correlated with age-adjusted Cd load (partial r=0.37, P=0.02) whereas kidney CYP4F2 protein abundance showed a positive correlation with age-adjusted Cd loads (partial r=0.40, P=0.02). These findings suggest that Cd may be an inducer of renal CYP4F2 and hepatic CYP2E1 and that increased renal CYP4F2 expression may implicate in Cd-linked renal tubular dysfunction and high blood pressure, involving CYP4F2-dependent arachidonic acid metabolism.

Metabolism and Disposition Kinetics of Nicotine

Nicotine is of importance as the addictive chemical in tobacco, pharmacotherapy for smoking cessation, a potential medication for several diseases, and a useful probe drug for phenotyping cytochrome P450 2A6 (CYP2A6). We review current knowledge about the metabolism and disposition kinetics of nicotine, some other naturally occurring tobacco alkaloids, and nicotine analogs that are under development as potential therapeutic agents. The focus is on studies in humans, but animal data are mentioned when relevant to the interpretation of human data. The pathways of nicotine metabolism are described in detail. Absorption, distribution, metabolism, and excretion of nicotine and related compounds are reviewed. Enzymes involved in nicotine metabolism including cytochrome P450 enzymes, aldehyde oxidase, flavin-containing monooxygenase 3, amine N-methyltransferase, and UDP-glucuronosyltransferases are represented, as well as factors affecting metabolism, such as genetic variations in metabolic enzymes, effects of diet, age, gender, pregnancy, liver and kidney diseases, and racial and ethnic differences. Also effects of smoking and various inhibitors and inducers, including oral contraceptives, on nicotine metabolism are discussed. Due to the significance of the CYP2A6 enzyme in nicotine clearance, special emphasis is given to the effects and population distributions of CYP2A6 alleles and the regulation of CYP2A6 enzyme.

Effects of cigarette smoking and exposure to cadmium and lead on phenotypic variability of hepatic CYP2A6 and renal function biomarkers in men

Effects of cigarette smoking and exposure to dietary cadmium (Cd) and lead (Pb) on urinary biomarkers of renal function and phenotypic variability of cytochrome P450 2A6 (CYP2A6) were investigated in a group of 96 healthy Thai men with mean age of 36.7 year (19-57 years). In non-smokers, Cd burden increased with age (r = 0.47, P < 0.001). In current smokers, Cd burden increased with both age (r = 0.45, P = 0.01) and number of cigarettes smoked per day (r = 0.32, P = 0.05). Cd-linked renal tubular dysfunction was seen in both smokers and non-smokers, but Pb-linked glomerular dysfunction was seen in smokers only, possibly due to more recent exposure to high levels of Cd and Pb, as reflected by 30-50% higher serum Cd and Pb levels in smokers than non-smokers (P < 0.05). Exposure to dietary Cd and Pb appeared to be associated with mild tubular dysfunction whereas dietary exposure plus cigarette smoking was associated with tubular plus glomerular dysfunction. Hepatic CYP2A6 activity in non-smokers showed a positive association with Cd burden (adjusted beta = 0.38, P = 0.006), but it showed an inverse correlation with Pb (adjusted beta = -0.29, P = 0.003), suggesting opposing effects of Cd and Pb on hepatic CYP2A6 phenotype. In contrast, CYP2A6 activity in current smokers did not correlate with Cd or Pb, but it showed a positive correlation with serum ferritin levels (r = 0.45, P = 0.01). These finding suggest that Pb concentrations in the liver probably were too low to inhibit hepatic synthesis of heme and CYP2A6 and that the concurrent induction of hepatic CYP2A6 and ferritin was probably due to cigarette smoke constituents other than Cd and Pb.

Evidence for concurrent effects of exposure to environmental cadmium and lead on hepatic CYP2A6 phenotype and renal function biomarkers in nonsmokers

We examined the interrelationships between phenotype of hepatic cytochrome P450 2A6 (CYP2A6), nephropathy, and exposure to cadmium and lead in a group of 118 healthy Thai men and women who had never smoked. Their urinary Cd excretion ranged from 0.05 to 2.36 microg/g creatinine, whereas their urinary Pb excretion ranged from 0.1 to 12 microg/g creatinine. Average age and Cd burden of women and men did not differ. Women, however, on average showed a 46% higher urinary Pb excretion (p < 0.001) and lower zinc status, suggested by lower average serum Zn and urinary Zn excretion compared with those in men. Cd-linked nephropathy was detected in both men and women. However, Pb-linked nephropathy was seen only in women, possibly because of higher Pb burden coupled with lower protective factors, notably of Zn (p < 0.001), in women compared with men. In men, Pb burden showed a negative association with CYP2A6 activity (adjusted beta = -0.29, p = 0.003), whereas Cd burden showed a positive association with CYP2A6 activity (adjusted beta = 0.38, p = 0.001), suggesting opposing effects of Cd and Pb on hepatic CYP2A6 phenotype. The weaker correlation between Cd burden CYP2A6 activity in women despite similarity in Cd burden between men and women is consistent with opposing effects of Pb and Cd on hepatic CYP2A6 phenotypic expression. A positive correlation between Cd-linked nephropathy (urinary N-acetyl-beta-D-glucosaminidase excretion) and CYP2A6 activity in men (r = 0.39, p = 0.002) and women (r = 0.37, p = 0.001) suggests that Cd induction of hepatic CYP2A6 expression and Cd-linked nephropathy occurred simultaneously.