Mechanisms of antiviral action and toxicities of ipecac alkaloids: Emetine and dehydroemetine exhibit anti-coronaviral activities at non-cardiotoxic concentrations

The emergence of highly infectious pathogens with their potential for triggering global pandemics necessitate the development of effective treatment strategies, including broad-spectrum antiviral therapies to safeguard human health. This study investigates the antiviral activity of emetine, dehydroemetine (DHE), and congeneric compounds against SARS-CoV-2 and HCoV-OC43, and evaluates their impact on the host cell. Concurrently, we assess the potential cardiotoxicity of these ipecac alkaloids. Significantly, our data reveal that emetine and the (-)-R,S isomer of 2,3-dehydroemetine (designated in this paper as DHE4) reduce viral growth at nanomolar concentrations (i.e., IC50 ∼ 50-100 nM), paralleling those required for inhibition of protein synthesis, while calcium channel blocking activity occurs at elevated concentrations (i.e., IC50 ∼ 40-60 µM). Our findings suggest that the antiviral mechanisms primarily involve disruption of host cell protein synthesis and is demonstrably stereoisomer specific. The prospect of a therapeutic window in which emetine or DHE4 inhibit viral propagation without cardiotoxicity renders these alkaloids viable candidates in strategies worthy of clinical investigation.

Aristolochic acid-containing Chinese herbal medicine and upper urinary tract urothelial carcinoma in Taiwan: a narrative review

PURPOSE

The high incidence of upper urinary tract urothelial carcinoma (UTUC) in Taiwan is largely due to exposure to aristolochic acid (AA), a principal component of Aristolochia-based herbal medicines. Here we systematically review the molecular epidemiology, clinical presentation and biomarkers associated with AA-induced UTUC.

METHODS

This is a narrative review. Medline, Embase, and Web of Science were searched from inception to December 31, 2021. Studies evaluating the association, detection, and clinical characteristics of AA and UTUC were included.

RESULTS

A nationwide database revealed 39% of the Taiwanese population had been exposed to AA-containing herbs between 1997 and 2003. Epidemiological reports revealed AA posed a significantly higher hazard for renal failure and UTUC in herbalists and the general population who ingested AA-containing herbs. The presence of aristolactam-DNA adducts and a distinctive signature mutation, A:T to T:A transversions, located predominantly on the non-transcribed DNA strand, with a strong preference for deoxyadenosine in a consensus sequence (CAG), was observed in many UTUC patients. Clinically, AA-related UTUC patients were characterized by a younger age, female gender, impaired renal function and recurrence of contralateral UTUC. To date, there are no preventive measures, except prophylactic nephrectomy, for subjects at risk of AA nephropathy or AA-related UTUC.

CONCLUSION

AA exposure via Aristolochia-based herbal medicines is a problem throughout Taiwan, resulting in a high incidence of UTUC. Aristolactam-DNA adducts and a distinctive signature mutation, A:T to T:A transversions, can be used as biomarkers to identify AA-related UTUC. AA-related UTUC is associated with a high recurrence rate of contralateral UTUC.

Molecular profiles and urinary biomarkers of upper tract urothelial carcinomas associated with aristolochic acid exposure

Recurrent upper tract urothelial carcinomas (UTUCs) arise in the context of nephropathy linked to exposure to the herbal carcinogen aristolochic acid (AA). Here we delineated the molecular programs underlying UTUC tumorigenesis in patients from endemic aristolochic acid nephropathy (AAN) regions in Southern Europe. We applied an integrative multiomics analysis of UTUCs, corresponding unaffected tissues and of patient urines. Quantitative microRNA (miRNA) and messenger ribonucleic acid (mRNA) expression profiling, immunohistochemical analysis by tissue microarrays and exome and transcriptome sequencing were performed in UTUC and nontumor tissues. Urinary miRNAs of cases undergoing surgery were profiled before and after tumor resection. Ribonucleic acid (RNA) and protein levels were analyzed using appropriate statistical tests and trend assessment. Dedicated bioinformatic tools were used for analysis of pathways, mutational signatures and result visualization. The results delineate UTUC-specific miRNA:mRNA networks comprising 89 miRNAs associated with 1,862 target mRNAs, involving deregulation of cell cycle, deoxyribonucleic acid (DNA) damage response, DNA repair, bladder cancer, oncogenes, tumor suppressors, chromatin structure regulators and developmental signaling pathways. Key UTUC-specific transcripts were confirmed at the protein level. Exome and transcriptome sequencing of UTUCs revealed AA-specific mutational signature SBS22, with 68% to 76% AA-specific, deleterious mutations propagated at the transcript level, a possible basis for neoantigen formation and immunotherapy targeting. We next identified a signature of UTUC-specific miRNAs consistently more abundant in the patients' urine prior to tumor resection, thereby defining biomarkers of tumor presence. The complex gene regulation programs of AAN-associated UTUC tumors involve regulatory miRNAs prospectively applicable to noninvasive urine-based screening of AAN patients for cancer presence and recurrence.

Loss of proximal tubular transcription factor Krüppel-like factor 15 exacerbates kidney injury through loss of fatty acid oxidation

Loss of fatty acid β-oxidation (FAO) in the proximal tubule is a critical mediator of acute kidney injury and eventual fibrosis. However, transcriptional mediators of FAO in proximal tubule injury remain understudied. Krüppel-like factor 15 (KLF15), a highly enriched zinc-finger transcription factor in the proximal tubule, was significantly reduced in proximal tubule cells after aristolochic acid I (AAI) treatment, a proximal tubule-specific injury model. Proximal tubule specific knockout of Klf15 exacerbated proximal tubule injury and kidney function decline compared to control mice during the active phase of AAI treatment, and after ischemia-reperfusion injury. Furthermore, along with worsening proximal tubule injury and kidney function decline, knockout mice exhibited increased kidney fibrosis as compared to control mice during the remodeling phase after AAI treatment. RNA-sequencing of kidney cortex demonstrated increased transcripts involved in immune system and integrin signaling pathways and decreased transcripts encompassing metabolic pathways, specifically FAO, and PPARα signaling, in knockout versus control mice after AAI treatment. In silico and experimental chromatin immunoprecipitation studies collectively demonstrated that KLF15 occupied the promoter region of key FAO genes, CPT1A and ACAA2, in close proximity to transcription factor PPARα binding sites. While the loss of Klf15 reduced the expression of Cpt1a and Acaa2 and led to compromised FAO, induction of KLF15 partially rescued loss of FAO in AAI-treated cells. Klf15, Ppara, Cpt1a, and Acaa2 expression was also decreased in other mouse kidney injury models. Tubulointerstitial KLF15 independently correlated with eGFR, PPARA and CPT1A appearance in expression arrays from human kidney biopsies. Thus, proximal tubule-specific loss of Klf15 exacerbates acute kidney injury and fibrosis, likely due to loss of interaction with PPARα leading to loss of FAO gene transcription.

Additive Effects of Arsenic and Aristolochic Acid in Chemical Carcinogenesis of Upper Urinary Tract Urothelium

BACKGROUND

Aristolochic acids (AA) and arsenic are chemical carcinogens associated with urothelial carcinogenesis. Here we investigate the combined effects of AA and arsenic toward the risk of developing upper tract urothelial carcinoma (UTUC).

METHODS

Hospital-based (n = 89) and population-based (2,921 cases and 11,684 controls) Taiwanese UTUC cohorts were used to investigate the association between exposure to AA and/or arsenic and the risk of developing UTUC. In the hospital cohort, AA exposure was evaluated by measuring aristolactam-DNA adducts in the renal cortex and by identifying A>T TP53 mutations in tumors. In the population cohort, AA exposure was determined from prescription health insurance records. Arsenic levels were graded from 0 to 3 based on concentrations in well water and the presence of arseniasis-related diseases.

RESULTS

In the hospital cohort, 43, 26, and 20 patients resided in grade 0, 1+2, and 3 arseniasis-endemic areas, respectively. Aristolactam-DNA adducts were present in >90% of these patients, indicating widespread AA exposure. A>T mutations in TP53 were detected in 28%, 44%, and 22% of patients residing in grade 0, 1+2, and 3 arseniasis-endemic areas, respectively. Population studies revealed that individuals who consumed more AA-containing herbs had a higher risk of developing UTUC in both arseniasis-endemic and nonendemic areas. Logistic regression showed an additive effect of AA and arsenic exposure on the risk of developing UTUC.

CONCLUSIONS

Exposure to both AA and arsenic acts additively to increase the UTUC risk in Taiwan.

IMPACT

This is the first study to investigate the combined effect of AA and arsenic exposure on UTUC.

Proximal Tubular Vacuolization and Hypersensitivity to Drug-Induced Nephrotoxicity in Male Mice With Decreased Expression of the NADPH-Cytochrome P450 Reductase

The effect of variations in the expression of cytochrome P450 reductase (CPR or POR) is determined in mice with decreased POR expression to identify potential vulnerabilities in people with low POR expression. There is an age-dependent appearance of increasing vacuolization in the proximal tubules of the renal cortex in 4- to 9-month-old male (but not female) Cpr-low (CL) mice. These mice have low POR expression in all cells of the body and upregulation of lysosome-associated membrane protein 1 expression in the renal cortex. Vacuolization is also seen in extrahepatic CL and extrarenal CL male mice, but not in mice with tissue-specific Por deletion in liver, intestinal epithelium, or kidney. The occurrence of vacuolization is accompanied by increases in serum blood-urea-nitrogen levels. Male CL mice are hypersensitive to cisplatin- and gentamicin-induced renal toxicity at 3 months of age, before proximal tubular (PT) vacuoles are detectable. At doses that do not cause renal toxicity in wild-type mice, both drugs cause substantial increases in serum blood-urea-nitrogen levels and PT vacuolization in male but not female CL mice. The hypersensitivity to drug-induced renal toxicity is accompanied by increases in circulating drug levels. These novel findings demonstrate deficiency of renal function in mice with globally reduced POR expression and suggest that low POR expression may be a risk factor for drug-induced nephrotoxicity in humans.

Exploring the epidemiology of gastric cancer in a Tibetan population

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Background: Gastric cancer is the 3rd leading cause of death from cancer and the 5th most common cancer world-wide. It is the primary cause of death for people of Tibetan origin in the Himalayan belt, with incidence (and death) rates between 60-140/100,000 people per year. Despite such a high disease burden, the epidemiology of gastric cancer has not been studied in this population. In this study, we explore gastric cancer risk factors among Tibetan refugees residing in India. Methods: Patients diagnosed with gastric cancer were identified by reviewing admission, discharge and out-patient endoscopy records between 2013-2019 at the Tibetan Delek hospital in Dharamshala, India. Risk factors not captured in the records were collected through interviews of patients or their relatives. Results: A total of 52 gastric cancer cases were identified, mostly males (77%). Median age was 78 (range: 30-91 years). Of the gastric cancer cases, 32% (n = 12/37) were retired military, 19% (n = 7/37) were monks or nuns, and 95% (n = 36/38) were born in Tibet. Sixty-five percent (n = 34/52) of the cases had histories of dyspepsia, 49% (n = 21/43) had used alcohol, and 40% (n = 17/43) were past smokers. Ninety-five percent (n = 20/21) of cases had been treated with traditional Tibetan medicines for various reasons in the past. Of the 17 patients (or relatives) interviewed for dietary risk factors, 76% (n = 13) reported frequent ingestion of stale and unrefrigerated food, 30% (n = 5) did not eat fresh fruit, and 47% (n = 8) reported intake of fresh fruit < 3 times per month. Most (83%, n = 24/29) patients had non-cardia cancers located in the fundus/body (n = 12) and antrum/pylorus (n = 12). Fifty-two percent (n = 16/31) had been treated with either chemotherapy, radiotherapy, or surgery, and 34% (n = 11/32) of the patients were receiving traditional Tibetan medicine as treatment for gastric cancer. Conclusions: Tibetan people have socio-cultural, behavioral and dietary risk factors that may be associated with gastric cancer. Investigations of causal factors (genetic, infective ( Helicobacter pylori), environmental) with possible synergistic interactions could inform clinical and public health practice for this population and globally.

Non-invasive detection of urothelial cancer through the analysis of driver gene mutations and aneuploidy

Current non-invasive approaches for detection of urothelial cancers are suboptimal. We developed a test to detect urothelial neoplasms using DNA recovered from cells shed into urine. UroSEEK incorporates massive parallel sequencing assays for mutations in 11 genes and copy number changes on 39 chromosome arms. In 570 patients at risk for bladder cancer (BC), UroSEEK was positive in 83% of those who developed BC. Combined with cytology, UroSEEK detected 95% of patients who developed BC. Of 56 patients with upper tract urothelial cancer, 75% tested positive by UroSEEK, including 79% of those with non-invasive tumors. UroSEEK detected genetic abnormalities in 68% of urines obtained from BC patients under surveillance who demonstrated clinical evidence of recurrence. The advantages of UroSEEK over cytology were evident in low-grade BCs; UroSEEK detected 67% of cases whereas cytology detected none. These results establish the foundation for a new non-invasive approach for detection of urothelial cancer.

Recurrence pattern and TP53 mutation in upper urinary tract urothelial carcinoma

TP53 mutation patterns are associated with prognosis of various cancers. This study was designed to investigate the association between TP53 mutation patterns and recurrence patterns in upper urinary tract urothelial carcinoma (UTUC) patients. A total of 165 consecutive UTUC patients who underwent nephroureterectomies were enrolled for measuring mutation patterns of TP53 gene from exome 2 to 11. Bladder recurrence, contralateral UTUC recurrence, and metastases were compared among groups by using log-rank test and Cox proportional hazard model. Single base substitution as an A:T to T:A transversion was noted in 55 (33.3%) patients (AT group). Forty-two (25.5%) patients had TP53 mutations with only other than A:T to T:A transversion (NAT group), and 68 patients (41.2%) had wide-type TP53 (WT group). AT group was predominately female (64%, 52%, 29%, respectively), had a higher incidence of end-stage renal disease (24%, 14%, 10%, respectively), and had more high-grade tumors (82%, 74%, 62%, respectively) compared to NAT and WT groups. With adjustment of tumor grade/stages, bladder and contralateral UTUC recurrence-free survival duration was shortest in NAT (p < 0.001) and AT group (p < 0.001), respectively. NAT group had a shorter metastasis-free survival duration than the other two groups combined (p = 0.018). As a result, A:T to T:A transversion increased contralateral UTUC recurrence risk, but other mutations in TP53 raised the hazard of bladder recurrence and metastases. Therefore, TP53 mutation pattern may be a useful biomarker to predict recurrence patterns of UTUC patients.

A Rapid Throughput Method To Extract DNA from Formalin-Fixed Paraffin-Embedded Tissues for Biomonitoring Carcinogenic DNA Adducts

Formalin-fixed paraffin-embedded (FFPE) tissues are rarely used for screening DNA adducts of carcinogens because the harsh conditions required to reverse the formaldehyde-mediated DNA cross-links can destroy DNA adducts. We recently adapted a commercial silica-based column kit used in genomics to manually isolate DNA under mild conditions from FFPE tissues of rodents and humans and successfully measured DNA adducts of several carcinogens including aristolochic acid I (AA-I), 4-aminobiphenyl (4-ABP), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) (Yun et al. (2013) Anal. Chem. 85, 4251-8, and Guo et al. (2016) Anal. Chem. 88, 4780-7). The DNA retrieval methodology is robust; however, the procedure is time-consuming and labor intensive, and not amenable to rapid throughput processing. In this study, we have employed the Promega Maxwell 16 MDx system, which is commonly used in large scale genomics studies, for the rapid throughput extraction of DNA. This system streamlines the DNA isolation procedure and increases the sample processing rate by about 8-fold over the manual method (32 samples versus 4 samples processed per hour). High purity DNA is obtained in satisfactory yield for the measurements of DNA adducts by ultra performance liquid chromatography-electrospray-ionization-ion trap-multistage scan mass spectrometry. The measurements show that the levels of DNA adducts of AA-I, 4-ABP, and PhIP in FFPE rodent and human tissues are comparable to those levels measured in DNA from matching tissues isolated by the commercial silica-based column kits and in DNA from fresh frozen tissues isolated by the conventional phenol-chloroform extraction method. The isolation of DNA from tissues is one major bottleneck in the analysis of DNA adducts. This rapid throughput methodology greatly decreases the time required to process DNA and can be employed in large-scale epidemiology studies designed to assess the role of chemical exposures and DNA adducts in cancer risk.

Human liver-kidney model elucidates the mechanisms of aristolochic acid nephrotoxicity

Environmental exposures pose a significant threat to human health. However, it is often difficult to study toxicological mechanisms in human subjects due to ethical concerns. Plant-derived aristolochic acids are among the most potent nephrotoxins and carcinogens discovered to date, yet the mechanism of bioactivation in humans remains poorly understood. Microphysiological systems (organs-on-chips) provide an approach to examining the complex, species-specific toxicological effects of pharmaceutical and environmental chemicals using human cells. We microfluidically linked a kidney-on-a-chip with a liver-on-a-chip to determine the mechanisms of bioactivation and transport of aristolochic acid I (AA-I), an established nephrotoxin and human carcinogen. We demonstrate that human hepatocyte-specific metabolism of AA-I substantially increases its cytotoxicity toward human kidney proximal tubular epithelial cells, including formation of aristolactam adducts and release of kidney injury biomarkers. Hepatic biotransformation of AA-I to a nephrotoxic metabolite involves nitroreduction, followed by sulfate conjugation. Here, we identify, in a human tissue-based system, that the sulfate conjugate of the hepatic NQO1-generated aristolactam product of AA-I (AL-I-NOSO3) is the nephrotoxic form of AA-I. This conjugate can be transported out of liver via MRP membrane transporters and then actively transported into kidney tissue via one or more organic anionic membrane transporters. This integrated microphysiological system provides an ex vivo approach for investigating organ-organ interactions, whereby the metabolism of a drug or other xenobiotic by one tissue may influence its toxicity toward another, and represents an experimental approach for studying chemical toxicity related to environmental and other toxic exposures.

Abstract 5241: Using affinity probes to explore the nephrotoxicity of aristolochic acid

Aristolochic acid, AA, is a natural compound found in Aristolochia plants used in Chinese Traditional Medicine and is a component of many herbal remedies used worldwide. In humans, exposure to AA is associated with kidney toxicity and otherwise rare upper urinary tract cancer (UTUC). AA undergoes bioactivation creating reactive species of AA that bind covalently to proteins and DNA. Formation of mutagenic AA-DNA adducts leads to AA-induced cancers. We identified the mutational signature associated with AA exposure in patients with UTUC in Taiwan, as well as in AA-initiated cancers in liver, bladder and kidneys. Meanwhile, the mechanism of AA nephrotoxicity remained a mystery, with covalent and non-covalent binding of AA or its metabolites to proteins hypothesized to be involved in its nephrotoxic effects. As millions of people in Asia have ingested AA and no effective therapies are known, establishing the molecular mechanism(s) of AA nephrotoxicity is a topic of major importance. A series of AA analogs were used to design affinity probes for target identification. Structure activity relationship studies in human cells aided in identifying a position in AA suitable for introducing biotinylated, aminopropyl and alkyne linkers. In addition, we have developed and validated monoclonal antibodies against AA-bovine serum albumin and/or AA-DNA covalent adducts. Combined with proteomics techniques, AA-affinity probes and monoclonal antibodies provide powerful tools for defining AA targets in human kidneys. We attached the aminopropyloxy derivative of AA to magnetic beads coated with N-hydroxysuccinimido acyl linkers. These probes, in parallel with unmodified, “control” beads were incubated with renal cortex lysates obtained from C3H mice selected for their sensitivity to the effects of AA. Bound proteins were digested "on bead", then identified by mass spectroscopic peptide analysis, with a total of 316 bound proteins detected. Spectral counts for 128 proteins bound to AA-beads were higher than those for control beads. After correction for nonspecific binding, 18 of these proteins had spectral counts of 10 or higher. These proteins are localized to various organelles, indicating high coverage of the major subcellular compartments. Among these proteins, Cryzl2, quinone oxidoreductase-like 2, was the leading candidate. Based on homology, Cryzl2 belongs to the family of the quinone oxidoreductase-like protein and bears a mitochondrial localization sequence. This protein retains conserved domains for both quinone oxidoreductase activity and NAD(P) binding sites, which is of particular interest since other oxidoreductases, such as NQO1, are known to catalyze nitroreduction, the initial step in the bioactivation of AA. In summary, our studies provide guidelines for design of AA-affinity probes and reveal an enzyme that may be responsible for AA activation in mitochondria, by generating active intermediates and inducing mitochondrial damage in renal tissue.

Citation Format: Viktoriya S. Sidorenko, Kathleen G. Dickman, Thomas Rosenquist, Radha Bonala, Sivaprasad Attaluri, Irina Zaitseva, Charles Iden, Francis Johnson, Arthur P. Grollman. Using affinity probes to explore the nephrotoxicity of aristolochic acid [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5241. doi:10.1158/1538-7445.AM2017-5241

Aristolochic Acid in the Etiology of Renal Cell Carcinoma

BACKGROUND

Aristolochia species used in the practice of traditional herbal medicine contains aristolochic acid (AA), an established human carcinogen contributing to urothelial carcinomas of the upper urinary tract. AA binds covalently to genomic DNA, forming aristolactam (AL)-DNA adducts. Here we investigated whether AA is also an etiologic factor in clear cell renal cell carcinoma (ccRCC).

METHODS

We conducted a population-based case-control study to investigate the linkage between Aristolochia prescription history, cumulative AA consumption, and ccRCC incidence in Taiwan (5,709 cases and 22,836 matched controls). The presence and level of mutagenic dA-AL-I adducts were determined in the kidney DNA of 51 Taiwanese ccRCC patients. The whole-exome sequences of ccRCC tumors from 10 Taiwanese ccRCC patients with prior exposure to AA were determined.

RESULTS

Cumulative ingestion of more than 250 mg of AA increased risk of ccRCC (OR, 1.25), and we detected dA-AL-I adducts in 76% of Taiwanese ccRCC patients. Furthermore, the distinctive AA mutational signature was evident in six of 10 sequenced ccRCC exomes from Taiwanese patients.

CONCLUSIONS

This study strongly suggests that AA contributes to the etiology of certain RCCs.

IMPACT

The current study offers compelling evidence implicating AA in a significant fraction of the RCC arising in Taiwan and illustrates the power of integrating epidemiologic, molecular, and genetic data in the investigation of cancer etiology. Cancer Epidemiol Biomarkers Prev; 25(12); 1600-8. ©2016 AACR.

Low-Coverage Exome Sequencing Screen in Formalin-Fixed Paraffin-Embedded Tumors Reveals Evidence of Exposure to Carcinogenic Aristolochic Acid

BACKGROUND

Dietary exposure to cytotoxic and carcinogenic aristolochic acid (AA) causes severe nephropathy typically associated with urologic cancers. Monitoring of AA exposure uses biomarkers such as aristolactam-DNA adducts, detected by mass spectrometry in the kidney cortex, or the somatic A>T transversion pattern characteristic of exposure to AA, as revealed by previous DNA-sequencing studies using fresh-frozen tumors.

METHODS

Here, we report a low-coverage whole-exome sequencing method (LC-WES) optimized for multisample detection of the AA mutational signature, and demonstrate its utility in 17 formalin-fixed paraffin-embedded urothelial tumors obtained from 15 patients with endemic nephropathy, an environmental form of AA nephropathy.

RESULTS

LC-WES identified the AA signature, alongside signatures of age and APOBEC enzyme activity, in 15 samples sequenced at the average per-base coverage of approximately 10×. Analysis at 3 to 9× coverage revealed the signature in 91% of the positive samples. The exome-wide distribution of the predominant A>T transversions exhibited a stochastic pattern, whereas 83 cancer driver genes were enriched for recurrent nonsynonymous A>T mutations. In two patients, pairs of tumors from different parts of the urinary tract, including the bladder, harbored overlapping mutation patterns, suggesting tumor dissemination via cell seeding.

CONCLUSIONS

LC-WES analysis of archived tumor tissues is a reliable method applicable to investigations of both the exposure to AA and its biologic effects in human carcinomas.

IMPACT

By detecting cancers associated with AA exposure in high-risk populations, LC-WES can support future molecular epidemiology studies and provide evidence-base for relevant preventive measures.

New Approaches for Biomonitoring Exposure to the Human Carcinogen Aristolochic Acid

Aristolochic acids (AA) are found in all Aristolochia herbaceous plants, many of which have been used worldwide for medicinal purposes for centuries. AA are causal agents of the chronic kidney disease entity termed aristolochic acid nephropathy (AAN) and potent upper urinary tract carcinogens in humans. AAN and upper urinary tract cancers are endemic in rural areas of Croatia and other Balkan countries where exposure to AA occurs through the ingestion of home-baked bread contaminated with Aristolochia seeds. In Asia, exposure to AA occurs through usage of traditional Chinese medicinal herbs containing Aristolochia. Despite warnings from regulatory agencies, traditional Chinese herbs containing AA continue to be used world-wide. In this review, we highlight novel approaches to quantify exposure to AA, by analysis of aristolactam (AL) DNA adducts, employing ultraperformance liquid chromatography-electrospray ionization/multistage mass spectrometry (UPLC-ESI/MSⁿ). DNA adducts are a measure of internal exposure to AA and serve as an important end point for cross-species extrapolation of toxicity data and human risk assessment. The level of sensitivity of UPLC-ESI/MSⁿ surpasses the limits of detection of AL-DNA adducts obtained by ³²P-postlabeling techniques, the most widely employed methods for detecting putative DNA adducts in humans. AL-DNA adducts can be measured by UPLC-ESI/MS³, not only in fresh frozen renal tissue, but also in formalin-fixed, paraffin-embedded (FFPE) samples, an underutilized biospecimen for assessing chemical exposures, and in exfoliated urinary cells, a non-invasive approach. The frequent detection of AL DNA adducts in renal tissues, combined with the characteristic mutational spectrum induced by AA in TP53 and other genes provides compelling data for a role of AA in upper urothelial tract cancer.

Adipose tissue insulin resistance due to loss of PI3K p110α leads to decreased energy expenditure and obesity

Adipose tissue is a highly insulin-responsive organ that contributes to metabolic regulation. Insulin resistance in the adipose tissue affects systemic lipid and glucose homeostasis. Phosphoinositide 3-kinase (PI3K) mediates downstream insulin signaling in adipose tissue, but its physiological role in vivo remains unclear. Using Cre recombinase driven by the aP2 promoter, we created mice that lack the class 1A PI3K catalytic subunit p110α or p110β specifically in the white and brown adipose tissue. The loss of p110α, not p110β, resulted in increased adiposity, glucose intolerance and liver steatosis. Mice lacking p110α in adipose tissue exhibited a decrease in energy expenditure but no change in food intake or activity compared with control animals. This low energy expenditure is a consequence of low cellular respiration in the brown adipocytes caused by a decrease in expression of key mitochondrial genes including uncoupling protein-1. These results illustrate a critical role of p110α in the regulation of energy expenditure through modulation of cellular respiration in the brown adipose tissue and suggest that compromised insulin signaling in adipose tissue might be involved in the onset of obesity.

Formalin-fixed paraffin-embedded tissue as a source for quantitation of carcinogen DNA adducts: aristolochic acid as a prototype carcinogen

DNA adducts are a measure of internal exposure to genotoxicants. However, the measurement of DNA adducts in molecular epidemiology studies often is precluded by the lack of fresh tissue. In contrast, formalin-fixed paraffin-embedded (FFPE) tissues frequently are accessible, although technical challenges remain in retrieval of high quality DNA suitable for biomonitoring of adducts. Aristolochic acids (AA) are human carcinogens found in Aristolochia plants, some of which have been used in the preparation of traditional Chinese herbal medicines. We previously established a method to measure DNA adducts of AA in FFPE tissue. In this study, we examine additional features of formalin fixation that could impact the quantity and quality of DNA and report on the recovery of AA-DNA adducts in mice exposed to AA. The yield of DNA isolated from tissues fixed with formalin decreased over 1 week; however, the levels of AA-DNA adducts were similar to those in fresh frozen tissue. Moreover, DNA from FFPE tissue served as a template for PCR amplification, yielding sequence data of comparable quality to DNA obtained from fresh frozen tissue. The estimates of AA-DNA adducts measured in freshly frozen tissue and matching FFPE tissue blocks of human kidney stored for 9 years showed good concordance. Thus, DNA isolated from FFPE tissues may be used to biomonitor DNA adducts and to amplify genes used for mutational analysis, providing clues regarding the origin of human cancers for which an environmental cause is suspected.

Bioactivation of the human carcinogen aristolochic acid

Aristolochic acids are potent human carcinogens; the role of phase II metabolism in their bioactivation is unclear. Accordingly, we tested the ability of the partially reduced metabolites, N-hydroxyaristolactams (AL-NOHs), and their N-O-sulfonated and N-O-acetylated derivatives to react with DNA to form aristolactam-DNA adducts. AL-NOHs displayed little or no activity in this regard while the sulfo- and acetyl compounds readily form DNA adducts, as detected by (32)P-post-labeling analysis. Mouse hepatic and renal cytosols stimulated binding of AL-NOHs to DNA in the presence of adenosine 3'-phosphate 5'-phosphosulfate (PAPS) but not of acetyl-CoA. Using Time of Flight liquid chromatography/mass spectrometry, N-hydroxyaristolactam I formed the sulfated compound in the presence of PAPS and certain human sulfotransferases, SULT1B1 >>> SULT1A2 > SULT1A1 >>> SULT1A3. The same pattern of SULT reactivity was observed when N-hydroxyaristolactam I was incubated with these enzymes and PAPS and the reaction was monitored by formation of aristolactam-DNA adducts. In the presence of human

NAD(P)H

quinone oxidoreductase, the ability of aristolochic acid I to bind DNA covalently was increased significantly by addition of PAPS and SULT1B1. We conclude from these studies that AL-NOHs, formed following partial nitroreduction of aristolochic acids, serve as substrates for SULT1B1, producing N-sulfated esters, which, in turn, are converted to highly active species that react with DNA and, potentially, cellular proteins, resulting in the genotoxicity and nephrotoxicity associated with ingestion of aristolochic acids by humans.

Mutational signature of aristolochic acid exposure as revealed by whole-exome sequencing

In humans, exposure to aristolochic acid (AA) is associated with urothelial carcinoma of the upper urinary tract (UTUC). Exome sequencing of UTUCs from 19 individuals with documented exposure to AA revealed a remarkably large number of somatic mutations and an unusual mutational signature attributable to AA. Most of the mutations (72%) in these tumors were A:T-to-T:A transversions, located predominantly on the nontranscribed strand, with a strong preference for deoxyadenosine in a consensus sequence (T/CAG). This trinucleotide motif overlaps the canonical splice acceptor site, possibly accounting for the excess of splice site mutations observed in these tumors. The AA mutational fingerprint was found frequently in oncogenes and tumor suppressor genes in AA-associated UTUC. The AA mutational signature was observed in one patient's tumor from a UTUC cohort without previous indication of AA exposure. Together, these results directly link an established environmental mutagen to cancer through genome-wide sequencing and highlight its power to reveal individual exposure to carcinogens.

Human formalin-fixed paraffin-embedded tissues: an untapped specimen for biomonitoring of carcinogen DNA adducts by mass spectrometry

DNA adducts represent internal dosimeters to measure exposure to environmental and endogenous genotoxicants. Unfortunately, in molecular epidemiologic studies, measurements of DNA adducts often are precluded by the unavailability of fresh tissue. In contrast, formalin-fixed paraffin embedded (FFPE) tissues frequently are accessible for biomarker discovery. We report here that DNA adducts of aristolochic acids (AAs) can be measured in FFPE tissues at a level of sensitivity comparable to freshly frozen tissue. AAs are nephrotoxic and carcinogenic compounds found in Aristolochia herbaceous plants, many of which have been used worldwide for medicinal purposes. AAs are implicated in the etiology of aristolochic acid nephropathy and upper urinary tract carcinoma. 8-Methoxy-6-nitrophenanthro-[3,4-d]-1,3-dioxole-5-carboxylic acid (AA-I) is a component of Aristolochia herbs and a potent human urothelial carcinogen. AA-I reacts with DNA to form the aristolactam (AL-I)-DNA adduct 7-(deoxyadenosin-N(6)-yl) aristolactam I (dA-AL-I). We established a method to quantitatively retrieve dA-AL-I from FFPE tissue. Adducts were measured, using ultraperformance liquid chromatography/mass spectrometry, in liver and kidney tissues of mice exposed to AA-I, at doses ranging from 0.001 to 1 mg/kg body weight. dA-AL-I was then measured in 10-μm thick tissue-sections of FFPE kidney from patients with upper urinary tract cancers; the values were comparable to those observed in fresh frozen samples. The limit of quantification of dA-AL-I was 3 adducts per 10(9) DNA bases per 2.5 μg of DNA. The ability to retrospectively analyze FFPE tissues for DNA adducts may provide clues to the origin of human cancers for which an environmental cause is suspected.

Aristolochic acid-induced upper tract urothelial carcinoma in Taiwan: clinical characteristics and outcomes

Aristolochic acid (AA), a component of all Aristolochia-based herbal medicines, is a potent nephrotoxin and human carcinogen associated with upper urinary tract urothelial carcinoma (UUC). To investigate the clinical and pathological characteristics of AA-induced UUC, this study included 152 UUC patients, 93 of whom had been exposed to AA based on the presence of aristolactam-DNA adducts in the renal cortex. Gene sequencing was used to identify tumors with A:T-to-T:A transversions in TP53, a mutational signature associated with AA. Cases with both aristolactam-DNA adducts and A:T-to-T:A transversions in TP53 were defined as AA-UUC, whereas patients lacking both of these biomarkers were classified as non-AA-UUC. Cases with either biomarker were classified as possible-AA-UUC. Forty (26%), 60 (40%), and 52 (34%) patients were classified as AA-UUC, possible-AA-UUC and non-AA-UUC, respectively. AA-UUC patients were younger (median ages: 64, 68, 68 years, respectively; p=0.189), predominately female (65%, 42%, 35%, respectively; p=0.011), had more end-stage renal disease (28%, 10%, 12%, respectively; p=0.055), and were infrequent smokers (5%, 22%, 33%, respectively; p=0.07) compared to possible-AA-UUC and non-AA-UUC patients. All 14 patients who developed contralateral UUC had aristolactam-DNA adducts; ten of these also had signature mutations. The contralateral UUC-free survival period was shorter in AA-UUC compared to possible- or non-AA-UUC (p=0.019 and 0.002, respectively), whereas no differences among groups were observed for bladder cancer recurrence. In conclusion, AA-UUC patients tend to be younger and female, and have more advanced renal disease. Notably, AA exposure was associated with an increased risk for developing synchronous bilateral and metachronous contralateral UUC.

Biomonitoring of aristolactam-DNA adducts in human tissues using ultra-performance liquid chromatography/ion-trap mass spectrometry

Aristolochic acids (AAs) are a structurally related family of nephrotoxic and carcinogenic nitrophenanthrene compounds found in Aristolochia herbaceous plants, many of which have been used worldwide for medicinal purposes. AAs have been implicated in the etiology of so-called Chinese herbs nephropathy and of Balkan endemic nephropathy. Both of these disease syndromes are associated with carcinomas of the upper urinary tract (UUC). 8-Methoxy-6-nitrophenanthro-[3,4-d]-1,3-dioxolo-5-carboxylic acid (AA-I) is a principal component of Aristolochia herbs. Following metabolic activation, AA-I reacts with DNA to form aristolactam (AL-I)-DNA adducts. We have developed a sensitive analytical method, using ultraperformance liquid chromatography-electrospray ionization/multistage mass spectrometry (UPLC-ESI/MS(n)) with a linear quadrupole ion-trap mass spectrometer, to measure 7-(deoxyadenosin-N(6)-yl) aristolactam I (dA-AL-I) and 7-(deoxyguanosin-N(2)-yl) aristolactam I (dG-AL-I) adducts. Using 10 μg of DNA for measurements, the lower limits of quantitation of dA-AL-I and dG-AL-I are, respectively, 0.3 and 1.0 adducts per 10(8) DNA bases. We have used UPLC-ESI/MS(n) to quantify AL-DNA adducts in tissues of rodents exposed to AA and in the renal cortex of patients with UUC who reside in Taiwan, where the incidence of this uncommon cancer is the highest reported for any country in the world. In human tissues, dA-AL-I was detected at levels ranging from 9 to 338 adducts per 10(8) DNA bases, whereas dG-AL-I was not found. We conclude that UPLC-ESI/MS(n) is a highly sensitive, specific and robust analytical method, positioned to supplant (32)P-postlabeling techniques currently used for biomonitoring of DNA adducts in human tissues. Importantly, UPLC-ESI/MS(n) could be used to document exposure to AA, the toxicant responsible for AA nephropathy and its associated UUC.

Aristolochic acid I metabolism in the isolated perfused rat kidney

Aristolochic acids are natural nitro-compounds found globally in the plant genus Aristolochia that have been implicated in the severe illness in humans termed aristolochic acid nephropathy (AAN). Aristolochic acids undergo nitroreduction, among other metabolic reactions, and active intermediates arise that are carcinogenic. Previous experiments with rats showed that aristolochic acid I (AA-I), after oral administration or injection, is subjected to detoxication reactions to give aristolochic acid Ia, aristolactam Ia, aristolactam I, and their glucuronide and sulfate conjugates that can be found in urine and feces. Results obtained with whole rats do not clearly define the role of liver and kidney in such metabolic transformation. In this study, in order to determine the specific role of the kidney on the renal disposition of AA-I and to study the biotransformations suffered by AA-I in this organ, isolated kidneys of rats were perfused with AA-I. AA-I and metabolite concentrations were determined in perfusates and urine using HPLC procedures. The isolated perfused rat kidney model showed that AA-I distributes rapidly and extensively in kidney tissues by uptake from the peritubular capillaries and the tubules. It was also established that the kidney is able to metabolize AA-I into aristolochic acid Ia, aristolochic acid Ia O-sulfate, aristolactam Ia, aristolactam I, and aristolactam Ia O-glucuronide. Rapid demethylation and sulfation of AA-I in the kidney generate aristolochic acid Ia and its sulfate conjugate that are voided to the urine. Reduction reactions to give the aristolactam metabolites occur to a slower rate. Renal clearances showed that filtered AA-I is reabsorbed at the tubules, whereas the metabolites are secreted. The unconjugated metabolites produced in the renal tissues are transported to both urine and perfusate, whereas the conjugated metabolites are almost exclusively secreted to the urine.

17β-estradiol protects the lung against acute injury: possible mediation by vasoactive intestinal polypeptide

Beyond their classical role as a class of female sex hormones, estrogens (e.g. 17β-estradiol) exert important biological actions, both protective and undesirable. We have investigated the ability of estradiol to protect the lung in three models of acute injury induced by 1) oxidant stress due to the herbicide paraquat; 2) excitotoxicity, caused by glutamate agonist N-methyl-d-aspartate; and 3) acute alveolar anoxia. We also assessed the role of estrogen receptors (ER) ERα and ERβ and the neuropeptide vasoactive intestinal peptide (VIP) in mediating this protection. Isolated guinea pig or rat lungs were perfused in situ at constant flow and mechanically ventilated. The onset and severity of lung injury were monitored by increases in pulmonary arterial and airway pressures, wet/dry lung weight ratio, and bronchoalveolar lavage fluid protein content. Estradiol was infused into the pulmonary circulation, beginning 10 min before induction of injury and continued for 60-90 min. Lung injury was marked by significant increases in the above measurements, with paraquat producing the most severe, and excitotoxicity the least severe, injury. Estradiol significantly attenuated the injury in each model. Both ER were constitutively expressed and immunohistochemically demonstrable in normal lung, and their selective agonists reduced anoxic injury, the only model in which they were tested. As it protected against injury, estradiol rapidly and significantly stimulated VIP mRNA expression in rat lung. Estradiol attenuated acute lung injury in three experimental models while stimulating VIP gene expression, a known mechanism of lung protection. The up-regulated VIP expression could have partially mediated the protection by estrogen.

Physiological and molecular characterization of aristolochic acid transport by the kidney

Consumption of herbal medicines derived from Aristolochia plants is associated with a progressive tubulointerstitial disease known as aristolochic acid (AA) nephropathy. The nephrotoxin produced naturally by these plants is AA-I, a nitrophenanthrene carboxylic acid that selectively targets the proximal tubule. This nephron segment is prone to toxic injury because of its role in secretory elimination of drugs and other xenobiotics. Here, we characterize the handling of AA-I by membrane transporters involved in renal organic anion transport. Uptake assays in heterologous expression systems identified murine organic anion transporters (mOat1, mOat2, and mOat3) as capable of mediating transport of AA-I. Kinetic analyses showed that all three transporters have an affinity for AA-I in the submicromolar range and thus are likely to operate at toxicologically relevant concentrations in vivo. Structure-activity relationships revealed that the carboxyl group is critical for high-affinity interaction of AA-I with mOat1, mOat2, and mOat3, whereas the nitro group is required only by mOat1. Furthermore, the 8-methoxy group, although essential for toxicity, was not requisite for transport. Mouse renal cortical slices avidly accumulated AA-I, achieving slice-to-medium concentration ratios >10. Uptake by slices was sensitive to known mOat1 and mOat3 substrates and the organic anion transport inhibitor probenecid, which also blocked the production of DNA adducts formed with reactive intracellular metabolites of AA-I. Taken together, these findings indicate that OAT family members mediate high-affinity transport of AA-I and may be involved in the site-selective toxicity and renal elimination of this nephrotoxin.

Cytochrome P450 1A2 detoxicates aristolochic acid in the mouse

Aristolochic acids (AAs) are plant-derived nephrotoxins and carcinogens responsible for chronic renal failure and associated urothelial cell cancers in several clinical syndromes known collectively as aristolochic acid nephropathy (AAN). Mice provide a useful model for study of AAN because the renal histopathology of AA-treated mice is strikingly similar to that of humans. AA is also a potent carcinogen in mice with a tissue spectrum somewhat different from that in humans. The toxic dose of AA in mice is higher than that in humans; this difference in susceptibility has been postulated to reflect differing rates of detoxication between the species. Recent studies in mice have shown that the hepatic cytochrome P450 system detoxicates AA, and inducers of the arylhydrocarbon response protect mice from the nephrotoxic effects of AA. The purpose of this study was to determine the role of specific cytochrome P450 (P450) enzymes in AA metabolism in vivo. Of 18 human P450 enzymes we surveyed only two, CYP1A1 and CYP1A2, which were effective in demethylating 8-methoxy-6-nitro-phenanthro-(3,4-d)-1,3-dioxolo-5-carboxylic acid (AAI) to the nontoxic derivative 8-hydroxy-6-nitro-phenanthro-(3,4-d)-1,3-dioxolo-5-carboxylic acid (AAIa). Kinetic analysis revealed similar efficiencies of formation of AAIa by human and rat CYP1A2. We also report here that CYP1A2-deficient mice display increased sensitivity to the nephrotoxic effects of AAI. Furthermore, Cyp1a2 knockout mice accumulate AAI-derived DNA adducts in the kidney at a higher rate than control mice. Differences in bioavailability or hepatic metabolism of AAI, expression of CYP1A2, or efficiency of a competing nitroreduction pathway in vivo may explain the apparent differences between human and rodent sensitivity to AAI.

Akt and c-Myc differentially activate cellular metabolic programs and prime cells to bioenergetic inhibition

The high glucose consumption of tumor cells even in an oxygen-rich environment, referred to as the Warburg effect, has been noted as a nearly universal biochemical characteristic of cancer cells. Targeting the glycolysis pathway has been explored as an anti-cancer therapeutic strategy to eradicate cancer based on this fundamental biochemical property of cancer cells. Oncoproteins such as Akt and c-Myc regulate cell metabolism. Accumulating studies have uncovered various molecular mechanisms by which oncoproteins affect cellular metabolism, raising a concern as to whether targeting glycolysis will be equally effective in treating cancers arising from different oncogenic activities. Here, we established a dual-regulatable FL5.12 pre-B cell line in which myristoylated Akt is expressed under the control of doxycycline, and c-Myc, fused to the hormone-binding domain of the human estrogen receptor, is activated by 4-hydroxytamoxifen. Using this system, we directly compared the effect of these oncoproteins on cell metabolism in an isogenic background. Activation of either Akt or c-Myc leads to the Warburg effect as indicated by increased cellular glucose uptake, glycolysis, and lactate generation. When cells are treated with glycolysis inhibitors, Akt sensitizes cells to apoptosis, whereas c-Myc does not. In contrast, c-Myc but not Akt sensitizes cells to the inhibition of mitochondrial function. This is correlated with enhanced mitochondrial activities in c-Myc cells. Hence, although both Akt and c-Myc promote aerobic glycolysis, they differentially affect mitochondrial functions and render cells susceptible to the perturbation of cellular metabolic programs.

Abstract B96: Akt and c-Myc differentially activate cellular metabolic programs and prime cells to bioenergetic inhibition

The high glucose consumption of tumor cells even in oxygen rich environments, referred to as the Warburg effect, has been noted as a nearly universal biochemical characteristic of cancer cells. Targeting the glycolysis pathway has been explored as an anti-cancer therapeutic strategy to eradicate cancer based on this fundamental biochemical property of cancer cells. Oncogenes such as Akt and c-Myc regulate cell metabolisms. Accumulating studies have uncovered various molecular mechanisms by which oncoproteins affect cellular metabolism, raising a concern as to whether targeting glycolysis will be equally effective in treating cancers arisen from different oncogenic activities. To address this issue, we establish a dual-regulatable FL5.12 pre-B cell line in which myrAkt is expressed under the control of doxycycline, and c-Myc, fused to the hormone-binding domain of the human estrogen-receptor (ER), is activated by tamoxifen. Using this system we directly compare the effect of these oncoproteins on cell metabolism in an isogenic background. Activation of either Akt or c-Myc leads to the Warburg effect as indicated by increased cellular glucose uptake, glycolysis, and lactate generation. When cells are treated with glycolysis inhibitors, Akt sensitizes cells to apoptosis whereas c-Myc does not. In contrast, c-Myc but not Akt sensitizes cells to the inhibition of mitochondrial function. This is correlated with enhanced mitochondrial activities in c-Myc cells. Hence, while both Akt and c-Myc promote aerobic glycolysis, they differentially affect mitochondrial functions and render cells susceptible to the perturbation of cellular metabolic programs.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B96.

Moderate Pulmonary Arterial Hypertension in Male Mice Lacking the Vasoactive Intestinal Peptide Gene

Background— Vasoactive intestinal peptide (VIP), a pulmonary vasodilator and inhibitor of vascular smooth muscle proliferation, has been reported absent in pulmonary arteries from patients with idiopathic pulmonary arterial hypertension (PAH). We have tested the hypothesis that targeted deletion of the VIP gene may lead to PAH with pulmonary vascular remodeling.

Methods and Results— We examined VIP knockout (VIP −/− ) mice for evidence of PAH, right ventricular (RV) hypertrophy, and pulmonary vascular remodeling. Relative to wild-type control mice, VIP −/− mice showed moderate RV hypertension, RV hypertrophy confirmed by increased ratio of RV to left ventricle plus septum weight, and enlarged, thickened pulmonary artery and smaller branches with increased muscularization and narrowed lumen. Lung sections also showed perivascular inflammatory cell infiltrates. No systemic hypertension and no arterial hypoxemia existed to explain the PAH. The condition was associated with increased mortality. Both the vascular remodeling and RV remodeling were attenuated after a 4-week treatment with VIP.

Conclusions— Deletion of the VIP gene leads to spontaneous expression of moderately severe PAH in mice during air breathing. Although not an exact model of idiopathic PAH, the VIP −/− mouse should be useful for studying molecular mechanisms of PAH and evaluating potential therapeutic agents. VIP replacement therapy holds promise for the treatment of PAH, and mutations of the VIP gene may be a factor in the pathogenesis of idiopathic PAH.

Clues to VIP function from knockout mice

We have taken advantage of the availability of vasoactive intestinal polypeptide (VIP) knockout (KO) mice to examine the possible influence of deletion of the VIP gene on: (a) airway reactivity and airway inflammation, as indicators of bronchial asthma; (b) mortality from endotoxemia, a model of septic shock; and (c) the pulmonary circulation. VIP KO mice showed: (a) airway hyperresponsiveness to the cholinergic agonist methacholine, as well as peribronchial and perivascular inflammation; (b) a greater susceptibility to death from endotoxemia; and (c) evidence suggestive of pulmonary hypertension.

Mice lacking the VIP gene show airway hyperresponsiveness and airway inflammation, partially reversible by VIP

The mechanisms leading to asthma, and those guarding against it, are yet to be fully defined. The neuropeptide VIP is a cotransmitter, together with nitric oxide (NO), of airway relaxation, and a modulator of immune and inflammatory responses. NO-storing molecules in the lung were recently shown to modulate airway reactivity and were proposed to have a protective role against the disease. We report here that mice with targeted deletion of the VIP gene spontaneously exhibit airway hyperresponsiveness to the cholinergic agonist methacholine as well as peribronchiolar and perivascular cellular infiltrates and increased levels of inflammatory cytokines in bronchoalveolar lavage fluid. Immunologic sensitization and challenge with ovalbumin generally enhanced the airway hyperresponsiveness and airway inflammation in all mice. Intraperitoneal administration of VIP over a 2-wk period in knockout mice virtually eliminated the airway hyperresponsiveness and reduced the airway inflammation in previously sensitized and challenged mice. The findings suggest that 1) VIP may be an important component of endogenous anti-asthma mechanisms, 2) deficiency of the VIP gene may predispose to asthma pathogenesis, and 3) treatment with VIP or a suitable agonist may offer potentially effective replacement therapy for this disease.

Ionotropic glutamate receptors in lungs and airways: molecular basis for glutamate toxicity

We earlier showed that the ionotropic glutamate receptor agonist N-methyl D-aspartate (NMDA) induces excitotoxic pulmonary edema, and that endogenous activation of NMDA receptors (NMDAR) could mediate lung injury caused by oxidative stress. In this study, we searched for evidence of NMDAR expression in the rat lung and in the alveolar macrophage (AM) cell line NR8383, and for possible regulation of receptor expression by NMDA. The presence of mRNA for NMDAR 1 and the four known NMDAR 2 subtypes (A, B, C, and D) was examined by reverse transcriptase-polymerase chain reaction using isoform-specific primers. NMDAR 1 was expressed in all lung regions examined (peripheral, midlung, and mainstem), as well as in trachea and the AMs. Expression of NMDAR 2A and 2B subtypes was not detected, whereas NMDAR 2C was present only in peripheral and mid-lung samples. NMDAR 2D was the dominant subtype expressed in the peripheral, gas-exchange zone of lung and in alveolar macrophages, and this expression was upregulated in lungs treated with NMDA. Western blot confirmed the presence of NMDAR 1 protein in all lung regions and in AMs. These findings provide a molecular-biological basis for the excitotoxic actions of glutamate in rat lungs and airways, and raise the question of a possible physiologic role for NMDAR in lung and airway function.

Rotavirus alters paracellular permeability and energy metabolism in Caco-2 cells

Rotaviruses infect epithelial cells of the small intestine, but the pathophysiology of the resulting severe diarrhea is incompletely understood. Histological damage to intestinal epithelium is not a consistent feature, and in vitro studies showed that intestinal cells did not undergo rapid death and lysis during viral replication. We show that rotavirus infection of Caco-2 cells caused disruption of tight junctions and loss of transepithelial resistance (TER) in the absence of cell death. TER declined from 300 to 22 Omega. cm(2) between 8 and 24 h after infection and was accompanied by increased transepithelial permeability to macromolecules of 478 and 4,000 Da. Distribution of tight junction proteins claudin-1, occludin, and ZO-1 was significantly altered during infection. Claudin-1 redistribution was notably apparent at the onset of the decline in TER. Infection was associated with increased production of lactate, decreased mitochondrial oxygen consumption, and reduced cellular ATP (60% of control at 24 h after infection), conditions known to reduce the integrity of epithelial tight junctions. In conclusion, these data show that rotavirus infection of Caco-2 intestinal cells altered tight junction structure and function, which may be a response to metabolic dysfunction.

Pathways of inflammation and cell death in the lung: modulation by vasoactive intestinal peptide

The pathogenesis of tissue injury in disease is a complex process that is only partially understood. We have investigated different models of acute lung injury, representing the clinical entity known as the acute respiratory distress syndrome, and tested their possible modulation by the neuropeptide vasoactive intestinal peptide (VIP). Three major mechanisms of injury appear to be involved in many of these models as common denominators: (1) activation of nuclear transcriptions factor NFkappaB; (2) apoptotic cell death; and (3) excitotoxic phenomena, due to activation of N-methyl-D-aspartate glutamate receptors. These pathogenetic mechanisms and pathways are logical targets of therapeutic intervention. Protection by VIP against lung injury, and against related forms of injury/cell death of neuronal cells and heart muscle, is attributable, in large measure, to the ability of VIP to suppress these mechanisms, and to additional anti-inflammatory and anti-oxidant actions. Finally, a hypothesis is presented for survival-promoting pathways that can be augmented by VIP and the related pituitary adenylyl cyclase-activating peptide.

Enhanced Na+ transport in an air-liquid interface culture system

Use of the air-liquid interface culture technique has produced improved morphological differentiation of rodent, canine, and human tracheal epithelia. We have investigated the effect of this culture technique on ion transport activities of cultured canine bronchial epithelia. These cells were isolated from excised airways by enzymatic digestion and plated on permeable collagen membrane substrates. All cultures were maintained utilizing standard culture techniques, by bathing both apical and basolateral sides with hormone supplemented, serum-free media until confluent (days 4-6). Half of the cultures were converted to air-liquid interface cultures (ALIC) by gentle aspiration of the apical medium and half were continued under standard technique culture (STC) conditions. After three additional days, preparations cultured under both conditions were mounted in modified Ussing chambers where bioelectric properties were measured under short-circuit conditions. Mean short-circuit current (Isc) was significantly greater in ALIC (-91.3 +/- 7.84 microA/cm2) than in STC (-54.8 +/- 5.03 microA/cm2). The sodium channel blocker, amiloride, reduced Isc by 68.4 +/- 5.0% in STC and by 84.8 +/- 3.0% in ALIC. 22Na and 36Cl fluxes confirmed the presence of enhanced sodium absorption in ALIC when compared with STC. The depth of the apical fluid, measured by microelectrodes during ALIC, was approximately 15 microns. Studies of cellular metabolism demonstrated a shift in metabolism from an anaerobic to an oxidative pattern in ALIC. This change in the pattern of metabolism suggests that the ALIC technique enhanced sodium transport in canine bronchial epithelia by increasing oxygen delivery to the epithelium.

Relationship between HCO3- transport and oxidative metabolism in rabbit proximal tubule

HCO3-/CO2 can affect proximal tubule energy metabolism directly by serving as a substrate for metabolic reactions and indirectly through ATP utilization by HCO3(-)-coupled Na+ reabsorption and proton secretion. In this study, metabolic and transport roles of HCO3-/CO2 were examined by measuring the effects of HCO3-/CO2 removal and transport inhibitors on oxygen consumption (QO2) in suspensions of rabbit proximal tubules. Removal of medium HCO3-/CO2 inhibited ouabain-sensitive, ouabain-insensitive, and uncoupled QO2. Consistent with metabolic inhibition, the absence of HCO3-/CO2 also reduced tubule ATP content and stimulated lactate production. Analysis of the dependence of mitochondrial state 3 respiration on HCO3-/CO2 in digitonin-permeabilized tubules traced the metabolic inhibition to limitations in tricarboxylic acid cycle intermediate supply. Energy requirements for HCO3- transport were examined by measuring QO2 in response to acetazolamide, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), and the H(+)-adenosinetriphosphatase (H(+)-ATPase) inhibitor bafilomycin A. Acetazolamide had no effect on QO2, whereas DIDS-SITS and bafilomycin A reduced ouabain-insensitive QO2, consistent with inhibition of active proton secretion. DIDS-SITS did not affect ouabain-sensitive respiration, suggesting that HCO3(-)-dependent Na+ reabsorption may not be mediated through the Na(+)-K(+)-ATPase in this preparation.

Streptomycin toxicity in primary cultures of flounder renal proximal tubule cells

The aminoglycoside antibiotic streptomycin is a known nephrotoxin in vivo and a common component of cell culture media. The effects of streptomycin (100 micrograms/ml) on transepithelial electrical properties, glucose transport, glycolytic metabolism, and morphology were examined in primary proximal tubule cell cultures from winter flounder (Pseudopleuronectes americanus) kidney. Streptomycin treatment on either Days 2 to 12 or Days 8 to 13 abolished the transepithelial potential difference and short-circuit current across the monolayer but had no effect on transepithelial resistance in confluent 12 to 13-d cultures, suggesting the loss of active transepithelial transport. Consistent with these findings, mucosal-to-serosal glucose fluxes were greatly reduced in streptomycin-treated cultures and insensitive to the transport inhibitor phlorizin, indicating the absence of the apical Na-dependent glucose transport system associated with net glucose reabsorption. In addition to transport processes, antibiotic treatment also interfered with cellular energy metabolism as judged by the rapid reduction in glycolytic lactate production observed in the presence of streptomycin. Scanning and transmission electron microscopy revealed that streptomycin-treated cultures were composed of cuboidal-to-columnar shaped cells which maintained intact tight junctions similar to control cultures. However, apical microvilli, the presumed sites of mucosal transport systems, were severely reduced in number in streptomycin-treated cultures. We concluded that streptomycin, at a dose commonly used in cell culture, inhibited the expression of differentiated function by flounder proximal tubule cell cultures. These cell cultures may provide a suitable model system for examination of the mechanisms of aminoglycoside nephrotoxicity.

Differential effects of respiratory inhibitors on glycolysis in proximal tubules

The effects of inhibition of mitochondrial energy production at various points along the respiratory chain on glycolytic lactate production and transport function were examined in a suspension of purified rabbit renal proximal tubules. Paradoxically, partial blockage at site 3 by hypoxia (1% O2) induced lactate production, whereas total site 3 blockage by anoxia (0% O2) failed to stimulate glycolysis. Compared with anoxia, hypoxic tubules exhibited greater preservation of ATP and K+ contents during O2 deprivation and more fully recovered oxidative metabolism and transport function during reoxygenation. The mitochondrial site 1 inhibitor rotenone and the uncoupler carbonyl cyanide-p-trifluorome-thoxyphenylhydrazone (FCCP) were equipotent stimuli for lactate production, whereas the site 2 inhibitor antimycin A failed to stimulate glycolysis despite a 90% inhibition of O2 consumption. Compared with antimycin A, treatment with rotenone or FCCP resulted in less cell injury [measured by lactate dehydrogenase (LDH) release] and greater preservation of cell K+ and ATP contents. 2-Deoxyglucose blocked lactate production by 50% in the presence of rotenone and increased LDH release, suggesting that glycolytic ATP is partially protective. Addition of ouabain during rotenone treatment reduced lactate production by 50%, indicating that glycolytic ATP can be used to fuel the Na pump when mitochondrial ATP production is inhibited. We conclude that 1) proximal tubules can generate lactate during inhibition of oxidative metabolism by hypoxia, rotenone, or FCCP; 2) mitochondrial inhibition is not obligatorily linked to activation of glycolysis, since neither anoxia nor antimycin A stimulate lactate production; 3) when ATP can be produced through anaerobic glycolysis it serves to protect cell viability and transport function during respiratory inhibition.

Cell volume regulation by skate erythrocytes: role of potassium

The role of K transport during cell volume regulation in response to extracellular osmolality, protein kinase C activation, and cellular Ca was examined in skate (Raja erinacea) red blood cells (RBC). Reduction of medium osmolality from 960 to 660 mosmol/kgH2O had no effect on K uptake or efflux despite a 25% increase in cell volume. Further reduction to 460 mosmol/kgH2O caused K uptake to double and K efflux to triple resulting in net K loss. Net K efflux in 460 mosmol/kgH2O medium was correlated with the presence of a regulatory volume decrease, which was sensitive to the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and insensitive to chloride replacement. K-K exchange was absent in both isotonic and hypotonic media. Treatment with the Ca ionophore A23187 in the presence of Ca had no effect on either cell volume or K efflux in isotonic medium, indicating the absence of Ca-activated K transport. In contrast, phorbol ester treatment caused cell volume, Na content, and proton and K efflux to increase. Consistent with activation of Na-H exchange, phorbol ester effects were inhibited by dimethylamiloride. This study constitutes the first demonstration of volume-sensitive K transport in RBC from the most primitive vertebrate studied to date.

Glycolytic and oxidative metabolism in primary renal proximal tubule cultures

Cultured cells often exhibit alterations in energy metabolism (increased glycolytic activity and decreased oxidative metabolism) during adaptation to the culture environment. The role of hypoxia as a mediator of these effects was examined by comparison of metabolism in primary rabbit renal proximal tubule (RPT) cultures maintained in stationary culture dishes (DISH), shaking Erlenmeyer flasks (SHAKE), and DISH cultures transferred back to SHAKE conditions (RESHAKE). Both oxidative metabolism and transport capacity were fully preserved in SHAKE cultures over a 24-h period. In contrast, within 6 h, DISH cultures exhibited a continuous decline in transport-dependent and -independent oxygen consumption, respiratory capacity, and ATP and K+ contents. The loss of oxidative metabolism in DISH cultures was accompanied by stimulation of lactate production, detectable within 1 h after plating. Comparison of metabolic properties of DISH cultures to those of RPT exposed to graded levels of hypoxia suggested that medium oxygen tensions may be as low as 1-3% in DISH cultures. RESHAKE cultures exhibited metabolic properties comparable to those of SHAKE cultures, indicating reversibility of DISH culture metabolism on reoxygenation. We concluded that DISH cultures rapidly become hypoxic as a consequence of static culture conditions. Shaking suspension cultures may provide a more metabolically appropriate model for long-term in vitro studies.

Renal metabolism and acute renal failure

We briefly review what appear to be the most important elements responsible for renal cell injury during and after oxygen deprivation. Recent studies in numerous laboratories have vastly improved our understanding of the changes in cell function that occur during ischemia and yet, the underlying mechanisms by which tubule damage and cell death occur remain elusive. We attempt to separate the effects that occur during ischemia or anoxia from those occurring during reperfusion (reoxygenation). These are not always separable, especially because it appears that ischemia initiates a series of complex events that may only become manifested during reperfusion. Ischemia-induced renal dysfunctions are clearly multifactorial events that will require major efforts to unravel.

Primary culture of flounder renal tubule cells: transepithelial transport

Renal proximal tubule cells from the winter flounder (Pseudopleuronectes americanus) were maintained in a functionally differentiated state for up to 16 days in primary culture on floating collagen gels. The cells were confluent after 7-8 days in culture, contracted the collagen gels, and exhibited ciliary activity. Electron microscopy indicated that the cultures were composed of continuous sheets of columnar epithelial cells that had established structural polarity. When mounted in Ussing chambers, the cultures exhibited a small mucosa-negative potential difference (0.6 +/- 0.10 mV) and a low transepithelial resistance (23 +/- 2.3 omega X cm2). Short-circuit current averaged 24 microA/cm2. The cultured epithelium was four times more permeable to Na than to Cl and actively secreted sulfate and p-aminohippuric acid and reabsorbed hexoses. Glucose reabsorption was rheogenic and occurred via a high-affinity (Km = 0.16 mM), low-capacity (Vmax = 5 microA/cm2), phlorizin-sensitive transport system. We concluded that the cultured cells express many of the differentiated properties of the intact flounder proximal tubule and thus provide a suitable model system for studying renal transport processes.

Effect of Na+ and ATP on peritubular Ca transport by the marine teleost renal tubule

Ca uptake rates and efflux rate coefficients were determined in isolated renal tubules of the winter flounder, Pseudopleuronectes americanus. Na-free medium and 10(-4) M ouabain depressed while 0.2 mM dinitrophenol stimulated Ca efflux. The effects on Ca movement appeared to be associated with the adenosine triphosphate (ATP) concentration of the tubular fluid space (TFS), rather than the bath-to-tissue Na gradient. Elevation of the ATP concentration of TFS by incubation of tissue in external ATP more than doubled Ca uptake rate. Inhibition of Ca uptake by lanthanum and stimulation by Ca ionophore A23187 suggested that ATP altered plasma membrane Ca transport. Incubation in external phosphate had no effect. Plasma membrane vesicles (PMV) prepared from flounder tubules showed saturable Ca uptake inhibited by Mg, unaffected by Na gradients, and stimulated by intravesicular but not extravesicular ATP. ATP appeared to stimulate PMV Ca uptake by increasing membrane Ca binding. We concluded that Ca uptake across the peritubular membranes was not directly linked to the serosal Na gradient but was greatly influenced by the intracellular ATP concentration.

Sulfate transport across the peritubular surface of the marine teleost renal tubule

The uptake of sulfate across the peritubular surface of isolated renal tubules of seawater-acclimated winter flounder, Pseudopleuronectes americanus, consisted of two phases. The fast exchanging component appeared to be a small sulfate compartment with a saturable uptake rate; however, the Km was quite large (14.5 mM). The fast phase was partially inhibited by the anion transport inhibitor 4-acetamido-4'-isothiocyano-2,2'-disulfonic stilbene (SITS), but was unaffected by antimycin A, which indicated lack of ATP-dependence. The slowly exchanging compartment was fourfold larger than the fast, saturable with a low Km (0.65 mM), and inhibited by antimycin A, SITS, ouabain, and Na-free incubation medium. Phosphate appeared to be a noncompetitive inhibitor of this phase. These observations support the idea that the slow phase of sulfate uptake may be driven by the peritubular membrane Na gradient. This mediated, energy-dependent uptake may be part of the active sulfate secretory pump of the marine teleost renal tubule.