Hepatocellular carcinoma tumour burden score to stratify prognosis after resection.

BACKGROUND: Although the Barcelona Clinic Liver Cancer (BCLC) staging system has been largely adopted in clinical practice, recent studies have emphasized the need for further refinement and subclassification of this system. METHODS: Patients who underwent hepatectomy with curative intent for BCLC-0, -A or -B hepatocellular carcinoma (HCC) between 2000 and 2017 were identified using a multi-institutional database. The tumour burden score (TBS) was calculated, and overall survival (OS) was examined in relation to TBS and BCLC stage. RESULTS: Among 1053 patients, 63 (6·0 per cent) had BCLC-0, 826 (78·4 per cent) BCLC-A and 164 (15·6 per cent) had BCLC-B HCC. OS worsened incrementally with higher TBS (5-year OS 77·9, 61 and 39 per cent for low, medium and high TBS respectively; P < 0·001). No differences in OS were noted among patients with similar TBS, irrespective of BCLC stage (61·6 versus 58·9 per cent for BCLC-A/medium TBS versus BCLC-B/medium TBS, P = 0·930; 45 versus 13 per cent for BCLC-A/high TBS versus BCLC-B/high TBS, P = 0·175). Patients with BCLC-B HCC and a medium TBS had better OS than those with BCLC-A disease and a high TBS (58·9 versus 45 per cent; P = 0·005). On multivariable analysis, TBS remained associated with OS among patients with BCLC-A (medium TBS: hazard ratio (HR) 2·07, 95 per cent c.i. 1·42 to 3·02, P < 0·001; high TBS: HR 4·05, 2·40 to 6·82, P < 0·001) and BCLC-B (high TBS: HR 3·85, 2·03 to 7·30; P < 0·001) HCC. TBS could also stratify prognosis among patients in an external validation cohort (5-year OS 79, 51·2 and 28 per cent for low, medium and high TBS respectively; P = 0·010). CONCLUSION: The prognosis of patients with HCC varied according to the BCLC stage but was largely dependent on the TBS.

ANTECEDENTES: Aunque el sistema de estadificación del Barcelona Clinic Liver Cancer (BCLC) ha sido adoptado en gran medida en la práctica clínica, estudios recientes han enfatizado la necesidad de un mayor refinamiento y subclasificación del sistema BCLC. MÉTODOS: Los pacientes con carcinoma hepatocelular (hepatocellular cancer, HCC) BCLC-0, A y B que se sometieron a una hepatectomía con intención curativa entre 2000 y 2017 fueron identificados utilizando una base de datos multi-institucional. Se calculó la puntuación de carga tumoral (tumour burden score, TBS) y se examinó la supervivencia global (overall survival, OS) en relación con la TBS y los estadios BCLC. RESULTADOS: En la serie de 1.053 pacientes, 63 (6%) tenían HCC BCLC-0, 826 (78,4%) HCC BCLC-A y 164 (15,6%) HCC BCLC-B. La OS disminuyó de forma incremental en función de la mayor TBS (OS a 5 años; TBS baja: 77,9% versus TBS media: 61% versus TBS alta: 39%, P < 0,001). No se observaron diferencias en la OS entre pacientes con una puntuación TBS similar, independientemente del estadio BCLC (BCLC-A/TBS media: 61,6% versus BCLC-B/TBS media: 58,9%, P = 0,93; BCLC-A/TBS alta: 45,1% versus BCLC-B/TBS alta: 12,8%, P = 0,175). Los pacientes con BCLC-B/TBS media tuvieron una mejor OS que los pacientes con BCLC-A/TBS alta (58,9% versus 45,1%, P = 0,005). En el análisis multivariable, la TBS se mantuvo asociada a la OS en el caso de BCLC-A (TBS media: cociente de riesgos instantáneos, hazard ratio, HR = 2,07, i.c. del 95%: 1,42-3,02, P < 0,001; TBS alta: HR = 4,05, i.c. del 95%: 2,40-6,82, P < 0,001) y BCLC-B pacientes (TBS alta: HR = 3,85, i.c. del 95%: 2,03-7,30, P < 0,001). La TBS también pudo estratificar el pronóstico entre pacientes en una cohorte de validación externa (OS a 5 años; TBS baja: 78,7% versus TBS media: 51,2% versus TBS alta: 27,6%, P = 0,01). CONCLUSIÓN: El pronóstico de los pacientes con HCC varió según el estadio BCLC, pero dependió en gran medida de la TBS.

Phlebotomy resulting in controlled hypovolaemia to prevent blood loss in major hepatic resections (PRICE-1): a pilot randomized clinical trial for feasibility.

BACKGROUND: Major liver resection is associated with blood loss and transfusion. Observational data suggest that hypovolaemic phlebotomy can reduce these risks. This feasibility RCT compared hypovolaemic phlebotomy with the standard of care, to inform a future multicentre trial. METHODS: Patients undergoing major liver resections were enrolled between June 2016 and January 2018. Randomization was done during surgery and the surgeons were blinded to the group allocation. For hypovolaemic phlebotomy, 7-10 ml per kg whole blood was removed, without intravenous fluid replacement. Co-primary outcomes were feasibility and estimated blood loss (EBL). RESULTS: A total of 62 patients were randomized to hypovolaemic phlebotomy (31) or standard care (31), at a rate of 3·1 patients per month, thus meeting the co-primary feasibility endpoint. The median EBL difference was -111 ml (P = 0·456). Among patients at high risk of transfusion, the median EBL difference was -448 ml (P = 0·069). Secondary feasibility endpoints were met: enrolment, blinding and target phlebotomy (mean(s.d.) 7·6(1·9) ml per kg). Blinded surgeons perceived that parenchymal resection was easier with hypovolaemic phlebotomy than standard care (16 of 31 versus 10 of 31 respectively), and guessed that hypovolaemic phlebotomy was being used with an accuracy of 65 per cent (20 of 31). There was no significant difference in overall complications (10 of 31 versus 15 of 31 patients), major complications or transfusion. Among those at high risk, transfusion was required in two of 15 versus three of nine patients (P = 0·326). CONCLUSION: Endpoints were met successfully, but no difference in EBL was found in this feasibility study. A multicentre trial (PRICE-2) powered to identify a difference in perioperative blood transfusion is justified. Registration number: NCT02548910 ( http://www.clinicaltrials.gov).

ANTECEDENTES: La resección hepática mayor se asocia con pérdida de sangre y necesidad de transfusión. Datos observacionales sugieren que la flebotomía hipovolémica (hypovolaemic phlebotomy, HP) puede reducir estos riesgos. Este ensayo clínico aleatorizado (randomised clinical trial, RCT) de factibilidad comparó HP con el tratamiento estándar con el fin de proporcionar información para un futuro ensayo multicéntrico. MÉTODOS: Se reclutaron pacientes sometidos a resecciones hepáticas mayores entre junio 2016 y enero 2018. La aleatorización se realizó durante el intraoperatorio y los cirujanos eran ciegos al resultado de la asignación. Para la HP, se extrajeron 7-10 mL/kg de sangre total, sin reposición de líquidos intravenosos. Los resultados primarios fueron la factibilidad y la pérdida de sangre estimada (estimated blood loss, EBL). RESULTADOS: Un total de 62 pacientes se aleatorizaron a HP (n = 31) y a tratamiento estándar (n = 31), a un ritmo de 3,1 pacientes/mes, cumpliendo el co-objetivo primario de la factibilidad. La mediana de la diferencia de EBL fue 11 mL (P = 0,46). Entre los pacientes con alto riesgo de transfusión, la mediana de la diferencia de EBL fue 448 mL (P = 0,069). Los objetivos secundarios de factibilidad se consiguieron: reclutamiento (89%), cegamiento (98%), y objetivo de la flebotomía (7,6 ± 1,9 mL/kg). Los cirujanos que fueron cegados percibieron que la resección fue más fácil con la HP (52% versus 32%) y acertaron el uso de HP con una exactitud del 65%. No hubo diferencia significativa en las complicaciones globales (32% versus 48%), complicaciones mayores y transfusión. Entre aquellos pacientes de alto riesgo, la trasfusión se realizó en un 13% versus 33% (P = 0,33). CONCLUSIÓN: Se cumplieron los objetivos, pero no se identificó diferencia en EBL en este estudio de factibilidad. Ello justifica un ensayo multicéntrico (PRICE-2) con poder estadístico para identificar una diferencia en la transfusión de sangre perioperatoria.

Trends in use of lymphadenectomy in surgery with curative intent for intrahepatic cholangiocarcinoma.

BACKGROUND: The role of routine lymph node dissection (LND) in the surgical treatment of intrahepatic cholangiocarcinoma (ICC) remains controversial. The objective of this study was to investigate the trends of LND use in the surgical treatment of ICC. METHODS: Patients undergoing curative intent resection for ICC in 2000-2015 were identified from an international multi-institutional database. Use of lymphadenectomy was evaluated over time and by geographical region (West versus East); LND use and final nodal status were analysed relative to AJCC T categories. RESULTS: Among the 1084 patients identified, half (535, 49·4 per cent) underwent concomitant hepatic resection and LND. Between 2000 and 2015, the proportion of patients undergoing LND for ICC nearly doubled: 44·4 per cent in 2000 versus 81·5 per cent in 2015 (P < 0·001). Use of LND increased over time among both Eastern and Western centres. The odds of LND was associated with the time period of surgery and the extent of the tumour/T status (referent T1a: OR 2·43 for T2, P = 0·001; OR 2·13 for T3, P = 0·016). Among the 535 patients who had LND, lymph node metastasis (LNM) was noted in 209 (39·1 per cent). Specifically, the incidence of LNM was 24 per cent in T1a disease, 22 per cent in T1b, 42·9 per cent in T2, 48 per cent in T3 and 66 per cent in T4 (P < 0·001). AJCC T3 and T4 categories, harvesting of six or more lymph nodes, and presence of satellite lesions were independently associated with LNM. CONCLUSION: The rate of LNM was high across all T categories, with one in five patients with T1 disease having nodal metastasis. The trend in increased use of LND suggests a growing adoption of AJCC recommendations in the treatment of ICC.

Early versus late recurrence of intrahepatic cholangiocarcinoma after resection with curative intent.

BACKGROUND: The objective of this study was to investigate the characteristics, treatment and prognosis of early versus late recurrence of intrahepatic cholangiocarcinoma (ICC) after hepatic resection. METHODS: Patients who underwent resection with curative intent for ICC were identified from a multi-institutional database. Data on clinicopathological characteristics, initial operative details, timing and sites of recurrence, recurrence management and long-term outcomes were analysed. RESULTS: A total of 933 patients were included. With a median follow-up of 22 months, 685 patients (73·4 per cent) experienced recurrence of ICC; 406 of these (59·3 per cent) developed only intrahepatic disease recurrence. The optimal cutoff value to differentiate early (540 patients, 78·8 per cent) versus late (145, 21·2 per cent) recurrence was defined as 24 months. Patients with early recurrence had extrahepatic disease more often (44·1 per cent versus 28·3 per cent in those with late recurrence; P < 0·001), whereas late recurrence was more often only intrahepatic (71·7 per cent versus 55·9 per cent for early recurrence; P < 0·001). From time of recurrence, overall survival was worse among patients who had early versus late recurrence (median 10 versus 18 months respectively; P = 0·029). In multivariable analysis, tumour characteristics including tumour size, number of lesions and satellite lesions were associated with an increased risk of early intrahepatic recurrence. In contrast, only the presence of liver cirrhosis was independently associated with an increased likelihood of late intrahepatic recurrence (hazard ratio 1·99, 95 per cent c.i. 1·11 to 3·56; P = 0·019). CONCLUSION: Early and late recurrence after curative resection for ICC are associated with different risk factors and prognosis. Data on the timing of recurrence may inform decisions about the degree of postoperative surveillance, as well as help counsel patients with regard to their risk of recurrence.

Three-point transfusion risk score in hepatectomy.

BACKGROUND: Perioperative red blood cell transfusions are required in up to 23 per cent of patients undergoing hepatectomy. Previous research has developed three transfusion risk scores to assess risk of perioperative red blood cell transfusion. Here, the performance of these transfusion risk scores was evaluated in a multicentre cohort of patients who underwent hepatectomy and compared with that of a simplified transfusion risk score. METHODS: A database of patients undergoing hepatectomy at four specialized centres between 2008 and 2012 was developed. External validity was assessed by discrimination and calibration. Discrimination was evaluated using the area under the receiver operating characteristic (ROC) curve (AUC). Calibration was evaluated by the degree of agreement between predicted and actual red blood cell transfusion probabilities. A simplified transfusion risk score using variables common to the three models was created, and discrimination and calibration were evaluated. RESULTS: There were 1287 patients included in this study, with 341 (26·5 per cent) receiving a red blood cell transfusion. Discriminative ability was similar between the three transfusion risk scores, with AUCs of 0·66-0·68 and good calibration. A new three-point risk score was developed based on factors present in all models: haemoglobin 12·5 g/dl or less, primary liver malignancy and major resection (at least 4 segments). Discriminative ability and calibration of the three-point model were similar to those of the three existing models, with an AUC of 0·66. CONCLUSION: The three-point transfusion risk score simplifies assessment of perioperative transfusion risk in hepatectomy without sacrificing predictive ability.

Eastern Canadian Gastrointestinal Cancer Consensus Conference 2016.

The annual Eastern Canadian Gastrointestinal Cancer Consensus Conference 2016 was held in Montreal, Quebec, 5-7 February. Experts in radiation oncology, medical oncology, surgical oncology, and infectious diseases involved in the management of patients with gastrointestinal malignancies participated in presentations and discussion sessions for the purpose of developing the recommendations presented here. This consensus statement addresses multiple topics: ■ Follow-up and survivorship of patients with resected colorectal cancer■ Indications for liver metastasectomy■ Treatment of oligometastases by stereotactic body radiation therapy■ Treatment of borderline resectable and unresectable pancreatic cancer■ Transarterial chemoembolization in hepatocellular carcinoma■ Infectious complications of antineoplastic agents.

Use of chemotherapy and radiofrequency ablation to treat colorectal cancer metastases: a retrospective review of The Ottawa Hospital Cancer Centre over 7 years.

BACKGROUND: Almost 40% of people diagnosed with colorectal cancer will die from their disease, most with metastatic spread. When feasible, hepatic resection offers the greatest probability of cure for isolated liver metastases, but there are barriers to curative resection. Those barriers include the extent and distribution of lesions within the liver, extrahepatic disease, comorbidities, and age. Chemotherapy is often administered before or after resection with the intention of improving disease-free and overall survival. The timing of chemotherapy (adjuvant vs. neoadjuvant vs. perioperative) for patients undergoing potentially curative hepatic resection of metastasis of colorectal cancer origin is controversial. METHODS: Colorectal cancer patients with liver metastases resected at The Ottawa Hospital between January 1, 2003, and December 31, 2009, were identified, and their clinical records were retrospectively reviewed. Patients receiving intraoperative radiofrequency ablation (rfa) as part of their management were included. Factors associated with overall and disease-free survival were evaluated. RESULTS: The 168 identified patients (57% men, 43% women) had a median age of 63 years (range: 31-84 years). After hepatectomy, 10% had positive resection margins. Intraoperative rfa was used in 25 patients (15%). Chemotherapy was administered in the neoadjuvant (19%), adjuvant (31%), or "perioperative" (both neoadjuvant and adjuvant, 50%) setting. Use or omission of intraoperative rfa was not associated with a difference in overall survival (hazard ratio: 0.99; 95% confidence interval: 0.53 to 1.84; p = 0.97). CONCLUSIONS: Compared with patients who did not receive chemotherapy, those who received chemotherapy, regardless of timing, experienced improved overall survival and disease-free survival. Use of rfa where required as an adjunct to hepatic resection appears to be effective and is not associated with worse overall survival.

Systematic review and meta-analysis of liver resection for metastatic melanoma.

BACKGROUND: The multidisciplinary management of metastatic melanoma now occasionally includes major hepatic resection. The objective of this work was to conduct a systematic review of the literature on liver resection for metastatic melanoma. METHODS: MEDLINE, Embase, the Cochrane Library and Scopus were searched (1990 to December 2012). Studies with at least ten patients undergoing liver resection for metastatic melanoma were included. Data on the outcomes of overall survival (OS) and/or disease-free survival (DFS) were abstracted and synthesized. Hazard ratios (HRs) were derived from survival curves and subjected to meta-analysis using random-effects models. RESULTS: Twenty-two studies involving 579 patients (13 per cent weighted resection rate) who underwent liver resection were included. Study quality was poor to moderate. Median follow-up ranged from 9 to 59 months. Median DFS ranged from 8 to 23 months, and median OS ranged from 14 to 41 months (R0, 22-66 months, R2, 10-16 months; R0 versus R1/R2: HR 0.52, 95 per cent confidence interval (c.i.) 0.37 to 0.73). The OS rate was 56-100 per cent at 1 year, 34-53 per cent at 3 years and 11-36 per cent at 5 years. Median OS with non-operative management ranged from 4 to 12 months. Comparison of OS with resection and non-operative management favoured resection (HR 0.32, 95 per cent c.i. 0.22 to 0.46). CONCLUSION: Radical resection of liver metastases from melanoma appears to improve overall survival compared with non-operative management or incomplete resection, but this observation requires future confirmation as selection bias may have confounded the results.

Complications in laparoscopic intestinal surgery: prevention and management.

Laparoscopic surgery is rapidly becoming the standard of care for many intestinal disorders. Intraoperative complications of laparoscopic intestinal surgery have been described to occur in 4-16% of procedures, although definitions vary widely across reports. Complications associated with first trocar insertion, although rare, can be fatal. The use of an open insertion technique is strongly recommended. Other intraoperative complications associated with laparoscopic intestinal surgery include cautery injuries, vascular injuries and hemorrhage, bowel injuries, bladder and ureteric injuries as well as missed or delayed injuries. Physiolo-gical complications of laparoscopy include pneumoperitoneum-specific complications, cardiopulmonary complications, and position-related complications. Finally, injury to the surgeon can occur, from which the field of surgical ergonomics has been derived.

Laparoscopy influences hiring practices within academic surgical departments.

BACKGROUND: This study aimed to determine whether the increasing emphasis on minimally invasive surgery (MIS) influences hiring practices within academic surgical departments. METHODS: A questionnaire was mailed to chairs of surgery departments and divisions of general surgery at the 16 Canadian academic institutions. Nonresponders were identified and contacted directly. The survey consisted of 34 questions, including Likert scales, single answers, and multiple-choice questions. Data were collected on demographics, perceptions of MIS, and recruitment/hiring. At the time of the survey, two department chair positions were vacant. RESULTS: A response rate of 87% (26/30) was obtained, with representation from 94% of departments (15/16). Of those surveyed, 88% intend to increase the importance of MIS at their institution within 5 years, and 87% intend to achieve this objective through new hirings. Networking (73%) and retention of recent graduates (89%) were cited most frequently as recruitment strategies. Strengthening the division, research, and education were considered important or extremely important by more than 90% of the respondents with respect to recruitment goals, whereas strengthening MIS was considered important or extremely important by 50%. Within 5 years, surgical departments intend to hire a median of four general surgeons, 50% of whom will have formal MIS training. In comparison, over the past 10 years, only 25% of new recruits had formal MIS training. More than 90% of the respondents considered formal MIS fellowship, MIS fellowship plus a second fellowship, and proctorship to be adequate training for performing advanced MIS, whereas traditional methods were considered inadequate. Lack of operative time and resource issues were considered most limiting in the hiring of new MIS surgeons. CONCLUSION: Minimally invasive surgery is growing in importance within academic surgical departments, but it remains an intermediate recruitment priority. Formal MIS training appears to be important in the recruiting of new surgeons, whereas traditional training methods are considered inadequate.

Hand-assisted laparoscopic colorectal surgery: an evidence-based review.

Despite its increasing use by practitioners, laparoscopic colorectal surgery remains technically challenging. Hand-assisted laparoscopic colorectal surgery may represent a viable hybrid alternative approach to standard laparoscopy. Although few high-quality studies have been carried out, hand-assistance appears to reduce operative time when compared to straight laparoscopy for both left-sided segmental colonic and total colorectal resections. Moreover, hand-assistance appears to maintain the short-term benefits of laparoscopy, while affording the surgeon with the ability to carry out complex cases in a minimally invasive fashion. Data pertaining to the use of hand-assistance for rectal cancer surgery are currently lacking. One the whole, hand-assisted laparoscopic colorectal surgery appears to be a useful tool for the minimally invasive surgeon, one that is perhaps best thought of as an adjunct to simple laparoscopy.

Muscle biopsy and muscle fiber hypercontraction: a brief review.

The percutaneous muscle biopsy technique is an important tool used in exercise and applied physiology to study human skeletal muscle structure, adaptation, and regeneration. One important use of this technique has been the assessment of ultrastructural muscle damage, especially in tissue samples obtained following strenuous exercise protocols, often involving eccentric muscle actions. In this brief review, we define and describe hypercontracted fibers, and outline how such fibers may adversely affect the interpretation of muscle damage from fixed tissue. Evidence suggests that hypercontracted fibers present in healthy skeletal muscle samples are likely to be artifacts related to the muscle biopsy procedure, as opposed to intrinsic degeneration present prior to the biopsy. When hypercontracted fibers are noted as being intrinsic to a muscle sample (e.g., in myopathy or following an extreme eccentric stimulus), such fibers are generally associated with the infiltration of inflammatory cells, indicative of a regenerative response. In contrast, hypercontracted fibers resulting from the biopsy procedure are not typically associated with an inflammatory response. The major sources of hypercontracted fibers are outlined and recommendations for their interpretation are discussed.

Mutations in the conserved regions of p53 are infrequent in betel-associated oral cancers from Papua New Guinea.

Seventy-five % of the world's oral cancers arise in developing countries. In high incidence areas of Southeast Asia such as Papua New Guinea (PNG) the major region-specific risk exposure is betel quid chewing. While it has been shown that p53 gene mutations in the conserved midregion (exons 5-9) are a common feature of oral cancers in the developed world, there is no information on this type of genetic lesion in betel quid-associated oral cancers. We examined 50 oral squamous cell carcinomas, 20 from Baltimore, MD and 30 from PNG, for mutations in exons 5-9 of the p53 gene. DNA extracted from frozen biopsies was amplified by polymerase chain reaction, the purified product was sequenced directly, and mutations were confirmed by repeating the entire procedure. Mutations were found in 3 of 30 tumors from PNG (10%), whereas 9 mutations were detected among the 20 tumors (45%) from Baltimore, MD. This difference in frequency is statistically significant (P < 0.01) by chi 2 analysis. Nuclear accumulation of p53 protein, determined by immunohistochemistry with the CM-1 antiserum, was observed in the PNG cases harboring a missense mutation of the p53 gene. In agreement with the low number of PNG cancers with mutations, only 17% of the cases from PNG were immunostain positive. To explore whether less conserved regions of the gene are preferential targets for alterations in this patient group, sequence analysis in tumors from PNG was extended to outlying regions of the gene (all of exons 4 and 10, and splice sites), but mutations in only two additional tumors were identified. The presence of human papillomavirus DNA in PNG cases was examined with a polymerase chain reaction-based procedure, and viral sequences (human papillomavirus strains 11/16) were detected in two tumors. Human papillomavirus-triggered degradation of the tumor suppressor protein is thus unlikely to be a typical pathway to p53 dysfunction in tumors from PNG.

Enhanced O6-methylguanine-DNA alkyltransferase activity in rat liver nodules.

The progression of chemical carcinogen induced hepatic lesions in the rat from altered enzyme foci to hepatocyte nodules and ultimately to hepatocellular carcinoma appears to be related to the evolution of new cell populations within these hepatic lesions. Initiator-promoter-initiator experiments in rat liver models using alkylating agents as the second genotoxic compound suggest accelerated progression toward malignancy could be the result of mutations caused by O6-alkylguanine formation in the DNA of preneoplastic liver cells. Since mutation frequency is believed to be related not only to the extent of O6-alkylguanine formation in DNA, but also to the rate of O6-alkylguanine repair, we measured the activity of the enzyme which repairs O6-alkylguanine, O6-alkylguanine-DNA alkyltransferase, in rat liver nodules. The activity of O6-methylguanine-DNA alkyltransferase in extracts of rat liver nodules 15 and 25 weeks post-initiation was approximately 1.4- and 1.8-fold greater, respectively, than comparable extracts from untreated-control and promoter only-treated rat liver tissues. Thus, the enhanced progression toward malignancy caused by treatment of rats bearing carcinogen-induced preneoplastic hepatic lesions with alkylating agents cannot be explained by a generalized deficiency of O6-alkylguanine-DNA alkyltransferase in hepatic preneoplastic lesions as a whole. These studies show that the distinctive xenobiotic resistant phenotype of rat hepatocyte nodules includes, in addition to the previously documented alterations in xenobiotic activation and detoxification enzyme activities, enhanced activity of a specific DNA repair system.

Modulation of repair of O6-methylguanine in parenchymal and nonparenchymal liver cells of rats treated with dimethylnitrosamine.

Previous studies have shown that chronic treatment of rats with dimethylnitrosamine (DMN) (2 mg/kg for 3 weeks) results in increased repair of O6-methylguanine (O6-mGua) in liver DNA. The experiments reported here try to determine if this increased repair is confined to one or more cell populations of the liver. Liver cells [parenchymal (PC) and nonparenchymal (NPC)] were separated by elutriation centrifugation at various times after the last administration of DMN. The in vivo alkylation studies show that at any time after a dose of [14C]DMN (2 mg/kg) the level of O6-mGua in PC cells of DMN pretreated rats was much lower than in the same cell population from control rats receiving only a single dose of DMN. In contrast, the pretreatment schedule resulted in no change in the levels of this DNA adduct in NPC cells. These results were confirmed by the determination of the levels of O6-methyldeoxyguanosine by radioimmunoassay in DNA from PC or NPC cells of rats similarly either pretreated for 3 weeks with DMN or receiving a single dose of DMN (2 mg/kg). The in vitro measurements of O6-mGua DNA alkyltransferase activity, using alkylated DNA as substrate, also show a higher activity of this repair enzyme in PC cells. The DMN pretreatment resulted in a 25-fold difference in O6-mGua DNA alkyltransferase activity between the two cell populations of the liver.