Neuropsychological deficits in human immunodeficiency virus type 1 clade C-seropositive adults from South India

Most studies of cognitive functioning in human immunodeficiency virus type 1 (HIV-1)-seropositive (HIV-1+) subjects have been done in the United States and Europe, where clade B infections predominate. However, in other parts of the world such as South India, where clade C HIV is most common, the prevalence of HIV-1 is increasing. Standardized neuropsychological tests were used to assess cognitive functioning in a sample of 119 adults infected with clade C HIV-1 who were not on antiretroviral medications. The subjects did not have neurological or psychiatric illness and were functioning adequately. Neuropsychological test performance was compared with gender-, age-, and education-matched normative data derived from a sample of 540 healthy volunteers and a matched cohort of 126 healthy, HIV-1-seronegative individuals. Among the seropositive subjects, 60.5% had mild to moderate cognitive deficits characterized by deficits in the domains of fluency, working memory, and learning and memory. None of the subjects had severe cognitive deficits. The HIV-1+ sample was classified into groups according to the level of immune suppression as defined by CD4 count (< 200, 201-499, and > 500 cells/mm3) and viral load (< 5000, 5001-30,000, 30,001-99,999, 100,000-1,000,000, and > 1,000,001 copies). Although the most immunosuppressed group (CD4 count < 200 cells/mm3 or viral load > 1,000,001 copies) was small, their rate of impairment in visual working memory was greater when compared to groups with better immune functioning. Mild to moderate cognitive deficits can be identified on standardized neuropsychological tests in clade C-infected HIV-1+ adults who do not have any clinically identifiable functional impairment. The prevalence of cognitive deficits is similar to that reported in antiretroviral treatment-naïve individuals infected with clade B virus in the western world.

Quantitation of Indian krait (Bungarus caeruleus) venom in human specimens of forensic origin by indirect competitive inhibition enzyme-linked immunosorbent assay

An indirect competitive inhibition enzyme-linked immunosorbent assay was reported to detect krait venom in human specimens of forensic origin. Polyclonal anti-krait venom antibodies were characterized by indirect antibody capture assay. The calibration plot was constructed based on linear regression analysis (y = 72.85 - 12.29x, r(2) = 0.98) with concentration ranges from 0.013 to 1000 ng/well of krait venom with a limit of detection of 0.2 ng/mL in the assay system. The IC50 (inhibitory concentration at 50% displacement) value of krait venom was observed to be 70 ng. Spiking studies indicated recoveries of 95-100% and 94-100% when various concentrations of krait venom were spiked to rat tissues (skin, liver, and kidneys) and pooled human serum, respectively. Polyclonal anti-krait venom antibodies showed no cross-reactivity with cobra and viper venom when tested in the assay system. The coefficient of variation of various concentrations of working range in intra-assay (n = 6) was <5%, whereas in interassay (n = 6) it was observed to be < or 7%. Further, the method was used to quantitate krait venom in human autopsy and biopsy specimens of forensic origin. Concentration of krait venom was found to be in the range of 4-172 ng/100 mg skin or skin scrapings and 64-378 ng/mL blood or serum. The methodology may find application in forensic laboratories to assess the cause of death in the cases of krait-bite victims.

Conventional slow freezing, vitrification and open pulled straw (OPS) vitrification of rabbit embryos

Three different methods of cryopreservation viz., conventional slow freezing, vitrification and open pulled straw vitrification were compared for their ability to support post thaw in vitro and in vivo development of rabbit embryos. Morula stage rabbit embryos were collected from super-ovulated donor does. They were randomly allocated to different freezing methods and stored up to 3 months in liquid nitrogen. After thawing and removal of cryoprotectants, embryos exhibiting intact zona pellucida and uniform blastomeres were considered suitable for in vitro culture and/or transfer. Three to five cryopreserved embryos placed in approximately 1 ml of culture medium (TCM 199 supplemented with foetal calf serum and antibiotics) were incubated for up to 72 h under humidified atmosphere of 5% CO2 in air at 39 degrees C. Development to hatched blastocyst stage was considered the initial indicator of success of cryopreservation of embryos. Of the embryos cryopreserved by programmed freezing, open pulled straw vitrification, vitrification-55 h pc and vitrification-72 h pc 55, 71, 17 and 48%, respectively, developed into hatched blastocysts. Similarly 19, 29, and 4% of embryos cryopreserved by programmed freezing, open pulled straw vitrification and vitrification -72 h pc developed into live offspring on transfer to recipient does. This is the first report on open pulled straw vitrification of rabbit embryos. Present results, suggest that (a) open pulled straw vitrification supports better in vitro survival of frozen thawed rabbit morulae; (b) both programmed freezing and OPS are similar but superior to vitirification in supporting in vivo survival of frozen thawed rabbit embryos.

Management of antitubercular drugs-induced hepatotoxicity and therapy reintroduction strategy in a TB clinic of Nepal

BACKGROUND

PZA, INH and R have potential for hepatotoxic side effects. Although anti-tuberculosis drug-induced hepatotoxicity is well known, there is no agreement on the clinical approach for cases in whom hepatotoxicity has developed.

OBJECTIVE

To study the management of anti-TB drugs induced hepatotoxicity and the standard anti-TB drugs therapy reintroduction procedure.

DESIGN

In prospective cohort analysis, 4 patients with active TB infection had developed anti-TB drugs induced hepatotoxicity. Retreatment of therapy was done on the basis of severity of hepatitis. If damage is mild, all the drugs were reintroduced at once in a tapering dose and if patient's condition is worse, INH and E is introduced in lower dose, later increasing the dose and the number of drugs.

RESULTS

All the patients tolerated anti-TB drugs well after reintroduction. There was no incidence of recurrence. All the patients completed their 8 months treatment regimen and all are cured.

CONCLUSION

Timely detection and temporary withdrawal of the offending agent can completely cure anti-TB drugs induced hepatotoxicity. The recurrence of hepatotoxicity is rare if reintroduction in done in a well planned manner.

Determination of diazepam in cream biscuits by liquid chromatography

An analytical procedure was developed for the detection and quantitation of diazepam in cream biscuits, which were used to commit crime. The method involves the extraction of diazepam with ethanol at room temperature, and the extract is filtered, evaporated to dryness, and redissolved in the mobile phase, methanol-acetonitrile-tetrahydrofuran-water (15 + 55 + 4 + 26, v/v). The separation is achieved on a C18 reversed-phase column with the mobile phase and diode array detection (lambda(max)) at 230 nm. Medazepam is used as the internal standard is for quantification. The calibration plot for the determination of diazepam is based on linear regression analysis (y = 0.6687x + 0.0372; r2 = 0.995). The limit of detection for diazepam in the biscuit samples was estimated as 600 ng/mL. The limit of quantitation for diazepam was estimated as 1.75 microg/mL. The diazepam detected per piece of biscuit was found to be in the range of 0.27-0.45 mg. Pure diazepam was added to biscuit samples at 3 levels (100 and 500 microg/g, and 1 mg/g), and the recoveries were found to be 95%. The mean retention time of diazepam was 2.7 min and that of medazepam (IS) was 4 min. The relative standard deviations of the diazepam level in the biscuit samples were estimated to be 0.4% for retention time and 1.02% for peak area in intraday analysis, whereas the corresponding values were and 0.61 and 2.34% in interday analysis. The method is rapid and reliable for qualitative and quantitative analysis of cream biscuits laced with diazepam, and it can be used by law enforcement laboratories for routine analysis.

Dependence of the expression of the radiation-induced gene conversion to arginine independence in diploid yeast on the amino acid concentration: effect on allelic mapping

The yield of radiation-induced gene conversion to arginine independence in diploid yeast depended on the concentration of the amino acid both in the plating medium and in the intracellular pool. By depletion of the level of arginine in the intracellular pool of amino acid or by provision of arginine at 0.4 mg/l of the plating medium the yield was varied by a factor as high as 20. This may be important in studies of the genetic mapping of alleles based on the slope of conversion frequency versus dose line.

Pharmaco-Economic Aspects of Antibiotic Prescriptions in Clinics of Kathmandu

Antibiotics (AB) are the most widely prescribed group of drugs and their use is associated with increasingrate of AB resistance. Nearly one third of prescriptions of physicians for colds, upper respiratory tractinfections and bronchitis are of AB as documented in previous studies. Antibiotic use is associated withincreased cost of financial burden, which may be difficult to be borne by the patients in developing countrieslike Nepal.The objective was study the prescribing pattern of Antibiotic preparations in various diseases and to findout how the treatment could become more pharmaco-economic without compromising the quality of service.A cross sectional study of prescription pattern of antibiotics/drugs in which antibiotics were used fromrandomly selected 20 private clinics of four major specialties in Kathmandu valley.Total No. of prescriptions audited were 386, average number of drugs/per prescription was 2.74.Maximum antibiotics were prescribed for age group 21-40 years in gynecological, surgical and medicalproblems, in Pediatrics maximum AB were prescribed between 1-12 years.Minimum antibiotics were prescribed between 13-20 years for gynecological and Pediatric problems. Inmedical and surgical problems, minimums AB were administered between 41-60 years. Above 60 yearsalmost no AB were used.Males were prescribed more AB than females (73% for surgical, 62% for medical and 53% for Pediatricproblems)Only in 20.25% patients, AB were prescribed after proper diagnosis and sensitivity testsMaximum cost of prescription was 510 Nepali rupees (NR) for treatment of STD in Gynecology.Key Words: Antibiotics, Cost, Human Immune deficiency Virus, Kathmandu, Private Clinics, Pharmacoeconomic, Sexually Transmitted Diseases.

Pharmaco-Economic Aspects and Pattern of Antibiotic Precriptions in Four Major Hospitals in Kathmandu

Background: Antibiotics are extensively prescribed drugs and their use is associated with increasing rateof antibiotic resistance. Nearly one third of prescriptions of physicians for colds, upper respiratory tractinfections and bronchitis are of anticiotics as documented in previous studies. Antibiotic use is associatedwith higher cost of prescriptions, which is impracticable to low socioeconomic groups in Nepal. Besidesthis patients have little knowledge about the use of antibiotics as shown by previous study of antibiotics usedin randomly selected 20 private clinics of Kathmandu valley.13To study the prescribing pattern of Antibiotic preparations in various diseases and to find out how thetreatment could become more pharmaco-economic in government hospitals, without compromising thequality of service.The results were as under Total No. of prescriptions audited were 522, average numbers of drugs/perprescription were 2.61.Maximum antibiotics were received in age group 21-41 y in gynecological, surgical and medical problems,in Pediatrics maximum antibiotics were prescribed between 1-12 years.Minimum antibiotics were prescribed between 13-20 y for gynecological and Pediatric problems. In medicaland surgical problems, minimum antibiotics was administered between 41-60 years. Above 60 years almostno antibiotics were used.Males were prescribed more antibiotics then females (73% for surgical, 62% for medical and 53% forPediatric problems)Only in 24.5% patients, antibiotics were prescribed after proper diagnosis and sensitivity testsMaximum cost of Prescription was 638 Nepali Rupees for treatment of sexually transmitted infection inGynecology.Key Words: Antibiotics, Cost, Private Clinics, Pharmacoeconomic, Sexually Transmitted Diseases.

Application of capillary zone electrophoresis in the separation and determination of the principal gum opium alkaloids

We describe the use of capillary zone electrophoresis (CZE) for the qualitative and quantitative determination of major alkaloids (i.e., thebaine, codeine, morphine, papavarine and narcotine) in gum opium involving the analysis of alkaloids without derivatization or purification. Three extractions with 2.5% w/v aqueous acetic acid quantitatively extracted major alkaloids. The separation was carried out by CZE using a 7:3 mixture of methanol and sodium acetate (100 mM, pH 3.1) at a potential of 15 kV, with UV detection at 224 nm. Spiking of pure reference alkaloid standards in the opium extract was used for peak identification. The influences of buffer composition, pH and voltage on the separation of alkaloids were studied. The detection limit of each alkaloid dissolved in methanol was found to be 850 ng/mL (morphine), 450 ng/mL (thebaine), 500 ng/mL (codeine), 550 ng/mL (papaverine), and 500 ng/mL (narcotine) at an injection pressure of 300 mbar (injection volume, 4 nL) with a signal-to-noise ratio of 3:1. The external standard method was used for the quantification of alkaloids. The calibration plot was based on linear regression analysis. The relative standard deviation (RSD) for peak area and migration time was in the range of 1.03-3.56% and 0.34-0.69%, respectively. Percentage compositions (g%) of opium alkaloids in five gum opium samples were found to be in the range of 14.45-15.95 (morphine), 2.0-3.45 (codeine), 1.32-2.73 (thebaine), 0.92-2.37 (papavarine), and 3.85-5.77 (narcotine). The method developed is suitable for the routine analysis of major gum opium alkaloids in samples of forensic importance.

Dose rate effect on micronuclei induction in cytokinesis blocked human peripheral blood lymphocytes

The effect of dose rate on the induction of micronuclei (MN) in human peripheral blood lymphocytes was investigated over a range of dose rates from 0.125 Gy h(-1) to 178.2 Gy h(-1). The response of MN induction was fitted with a linear quadratic model and the alpha and beta coefficients were estimated. It was found that beta values decrease with decreasing dose rate as in the case of chromosomal aberration. At the dose rate of 0.125 Gy h(-1), pure linear response of MN induction was observed. An attempt was made to simulate the calibration curve for the purpose of biological dosimetry at different dose rates and exposure times. The yields when simulated with the exposure time or the dose rate are in agreement with experimental results.

Selective .beta.3-adrenergic agonists of brown adipose tissue and thermogenesis. 2. [4-[2-[(2-Hydroxy-3-phenoxypropyl)amino]ethoxy]phenoxy]acetamides

The ester methyl [4-[2-[(2-hydroxy-3-phenoxypropyl)amino]ethoxy]phenoxy]acetate (1) (R1 = OMe) had previously been identified as the most interesting member of a series of selective beta 3-adrenergic agonists of brown adipose tissue and thermogenesis in the rat. In vivo it acts mainly via the related acid 1 (R1 = OH). Amides have been examined to determine whether they have advantages over the ester. In particular, in the rat and dog the half-lives of amides of appropriate potency were no longer than those of the ester. The amide (S)-4-[2-[(2-hydroxy-3-phenoxypropyl)amino]ethoxy]-N-(2- methoxyethyl)phenoxyacetamide [S-27, ICI D7114] was selected as having properties consistent with a sustained-release formulation should that prove necessary. Unlike the ester it is resistant to hydrolysis in the gut lumen. Further testing of ICI D7114 has shown that in the rat, cat, and dog it stimulates the beta 3-adrenergic receptor in brown adipose tissue at doses lower than those at which it affects beta 1- and beta 2-adrenergic receptors in other tissues. Slimming effects were observed in the dog. ICI D7114 may be a selective thermogenic agent in man and may be useful in the treatment of obesity and diabetes.

Selective .beta.3-adrenergic agonists of brown adipose tissue and thermogenesis. 1. [4-[2-[(2-Hydroxy-3-phenoxypropyl)amino]ethoxy]phenoxy]acetates

The ester methyl [4-[2-[(2-hydroxy-3-phenoxypropyl)amino]ethoxy]phenoxy]acetate (8) has been identified as the most interesting member of a series of selective beta 3-adrenergic agonists of brown adipose tissue and thermogenesis in the rat. In vivo it acts mainly via the related acid 10. Potency was generally markedly reduced by placing substituents on the phenyl ring of the phenoxypropanolamine unit of 8; only the 2-fluoro analogue 16 had comparable potency to 8. Other structure-activity relationships are discussed. Further testing of 8 (ICI 198157) has shown that in the rat it stimulates the beta 3-adrenergic receptor in brown adipose tissue at doses lower than those at which it affects beta 1 and beta 2 adrenergic receptors in other tissues. It increases metabolic rate, as judged by an increase in oxygen consumption, and in the genetically obese Zucker rat it causes a reduced rate of weight gain. This class of compound may be useful in the treatment of obesity in man.

Synthesis of some new biologically active bis-(thiadiazolotriazines) and bis-(thiadiazolotriazinyl) alkanes

4-Amino-3-mercapto-1,2,4-triazin-5(4H)-ones (1) were condensed with dicarboxylic acids 2 to yield bis-(4-oxo-4H-1,3,4-thiadiazolo[2,3-c]-1,2,4-triazin-7-yl)alkanes (3b-d,f-h,j-l,n-p) and bis-thiadiazolotriazines (3a,e,i,m). All the newly synthesised compounds were characterised by analytical, IR, NMR and mass spectral studies. Some of the newly synthesised compounds were screened for their antibacterial and antifungal properties. Among the tested compounds, compound 7,7'-(1,4-butanediyl)-his-(3-t-butyl-4-oxo-4H-1,3,4-thia-diazolo[2,3-c]-1,2,4-triazine (3p) exhibited highest degree of antifungal activity.

Treatment of recurrent attacks of supraventricular tachycardia during pregnancy causing complications in both mother and fetus

Cardiac arrhythmias including supraventricular tachycardia are commonly encountered during pregnancy. The case of a young Indian woman with recurrent attacks of supraventricular tachycardia during pregnancy which was managed with adenosine and verapamil is reported. The possible mechanisms of maternal and fetal complications are discussed.

Enzyme immunoassay for aflatoxin B1-lysine adduct and its validation

A simple procedure was developed for in vitro synthesis and characterization of aflatoxin B1-lysine adduct using aflatoxin B1, N-alpha-acetyl lysine and m-chloroperbenzoic acid (MCPBA). At a molar ratio of 1:16 (aflatoxin B1:N-alpha-cetyl lysine), the recovery of adduct was 62%. Analysis of the adduct by thin-layer chromatography showed a single spot (Rf = 0). Absorption spectra of the adduct showed 2 peaks at 275 and 335 nm. Liquid chromatographic (LC) analysis of the AFB1-lysine adduct showed a relative retention time of 2.1 min. Using the same epoxidation procedure, BSA-AFB1 adduct and ovalbumin-AFB1 adduct were synthesized for production of antibodies and as coating antigen, respectively. Control rat serum, spiked with AFB1-lysine adduct and subjected to LC analysis showed a retention time of 2.1 min, which is similar to that of AFB1-lysine reference standard, synthesized. Further, enzymatically hydrolyzed, control rat serum spiked with BSA-AFB1 adduct showed 2 peaks with retention times of 2.1 and 2.7 min. Based on the LC analysis, recovery of BSA-AFB1 in terms of AFB1-lysine adducts was 67 +/- 5%. The major peak (2.1 min) accounted for 72% of the adduct; the second minor peak (2.7 min) accounted for 28% of the total AFB1-lysine adducts formed. Stability studies on the AFB1-lysine adduct synthesized, indicated that it was stable for 1 month. Antibody capture assay showed an absorbance of 0.9 to 1.0 at a dilution of 1:50,000 when ovalbumin-AFB1 was used as a coating antigen. Indirect competitive ELISA showed 50% displacement (IC50) of the antibodies at a concentration of 13 ng AFB1-lysine, whereas the IC50 for AFB1 was 7 ng. The recovery of AFB1-lysine adduct spiked to control rat serum followed by enzymatic hydrolysis and immunoanalysis (indirect ELISA) was 93 +/- 6%. The enzyme immunoassay was validated by a rodent model, in which the animals were exposed to aflatoxin B1 (20 microg AFB1/kg body mass/day). The level of AFB1-lysine adduct in the rat serum was 27.3 +/- 4.37 microg/mg albumin.

Synthesis of some halogen-containing 1,2,4-triazolo-1,3,4-thiadiazines and their antibacterial and anticancer screening studies--part I

A series of 7-arylidene-6-(2,4-dichloro-5-fluorophenyl)-3-substituted-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines (3) were prepared by the condensation of 4-amino-5-mercapto-3-substituted-1,2,4-triazoles (1) and 3-aryl-1-(2,4-dichloro-5-fluorophenyl)-2-bromo-2-propen-1-one (2). An alternative route for the synthesis of the title compound 3 has been described. The newly synthesised compounds were characterised on the basis of N-analyses, IR, 1H NMR and mass spectral data. Some of the newly synthesised compounds were tested for their antibacterial activities against Gram + ve and Gram - ve bacteria. Among the tested compounds 3n showed the highest degree of antibacterial activity against S. aureus and evaluation of the LD50 value of this compound was carried out. Some of the newly synthesised compounds were also screened for their anticancer activities. Among these, compounds 3b, 3g, 3n and 3p are found to be active against NCI-H460 (lung), MCF7 (breast), SF 268 (CNS) in the preliminary anticancer screening studies. Further, 60-cell-line anticancer studies of these compounds were carried out. The results of such studies are discussed in this paper.

Determination of azadirachtin in agricultural matrixes and commercial formulations by enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) was developed for azadirachtin (aza), a biopesticide from the neem tree (Azadirachta indica A. Juss). The immunogen was synthesized by epoxidation using the furan ring in the aza molecule. Rabbits were immunized with either bovine serum albumin (BSA)-azadirachtin or ovalbumin (OA)-azadirachtin conjugate. Evaluation of the antisera by antibody capture assay showed that the antibody titer of antisera raised against OA-aza was 1:30,000. An indirect competitive ELISA was developed with BSA-azadirachtin as coating antigen and aza-specific antibodies raised against OA-aza immunogen. The immunoassay showed an inhibitory concentration (IC50) value of 75 ppb, with a range of detection from 0.5 to 1,000 ppb for azadirachtin [based on regression analysis, y= 85.87 (-18.89x); r2 = -0.97]. Cross-reactivity of the antibodies with 2 aza- derivatives (22,23-dihydro-23beta-methoxy azadirachtin and 3-tigloylazadirachtol) was 33 and 29%, respectively. The indirect competitive ELISA was validated and evaluated by quantitating aza in spiked agricultural commodities and from neem formulations. Azadirachtin was spiked into 5 different agricultural commodities: tomato, brinjal, coffee, tea, and cotton seed at 500 and 1,000 ppb and recovered at 62-100%. In samples drawn from 6 lots, the aza content in neem-seed kernels ranged from 0.1 to 0.15%; in commercial neem formulations the content ranged from 200 to 2,000 ppm. The method developed may be applied to environmental monitoring of aza and quality assurance studies of aza-based commercial formulations.

Chromium removal and reduction in COD of tannery effluents by actinomycetes

Tannery effluents are highly polluting and contain chroomium and high Cod and Bod. Alkalotolerant/alkalophilic actinomycetes NCIM 5080 and NCIM 5142 have been shown earlier to tolerate and accumulate chromium during growth also produce alkaline protease in presence of chromium ions, these properties of the isolates are suitable for treatment of tannery effluents which are alkaline and contain chromium and proteinaceous matter, both the actinomycetes are able to grow in undiluted tannery effluents and remove chromium almost completely and reduce the COD by 70%-80% during growth as well as by pregrown biomass.

Retrospective dosimetry based on cytogenetic study of individuals chronically exposed to ionizing radiation

Analysis of chromosomal aberrations (CAA) was carried out in 27 radiation workers with cumulative exposures of approximately 500 mSv received over a period of 2-3 decades. A similar study was carried out in 20 age- and gender-matched healthy individuals who served as controls. The average age of the exposed group was 50 years, and that of the controls was 51 years. The absorbed radiation dose was calculated by using the linear component of the in vitro dose response curve established for 60Co gamma-rays. In the controls we found only 3 dicentrics in 5,500 metaphases analyzed. In the exposed group, we detected 49 dicentrics and 1 centric ring in 13,900 metaphases analyzed. Because of the small number of dicentrics scored in each individual, the dose estimates of our method of study suffers from a large statistical uncertainty. The collective dose calculated from our data was 3.4 Sv. The difference in the physical dose based on personal monitoring and that from biological dosimetry may be attributed to the disappearance of lymphocytes carrying the aberrations from the living system. These results are consistent with the present knowledge of the kinetics of turnover of T-lymphocytes. Most residual damage appears to be from the long-lived component of T-lymphocytes with a mean life of 10 years.

Effect of caffeine on the genotoxic effects of gamma radiation and 4-NQO in diploid yeast

Caffeine is an environmental agent to which people are commonly exposed through medicines, drinks, food items, etc. It has been shown to be mutagenic in a number of test systems. In addition, it has also been shown to modify the mutagenic response of ionizing radiation, UV, and several chemical mutagens in a number of test systems. We have studied the effect of caffeine on gamma radiation and 4-Nitroquinoline 1-oxide (4-NQO)-induced gene conversion in the yeast Saccharomyces cerevisiae D7. Stationary phase cells were either exposed to 100-600 Gy of 60Co gamma radiation or treated with 0.15-0.3 microM 4-NQO (30 degrees C, 1 hour), after which they were plated on synthetic complete or minimal media with or without caffeine. Caffeine concentrations ranged from 5 to 15 mM. The results indicated that caffeine at 5 and 10 mM decreased gamma radiation-induced gene conversion frequencies significantly at 400 and 600 Gy. At 600 Gy, the decrease was about 30% and 50% with caffeine concentrations of 5 and 10 mM, respectively. In contrast, caffeine was found to increase the induced gene conversion frequency when cells treated with 0.15, 0.225, and 0.3 microM 4-NQO were plated on media containing caffeine. The increase with 5, 10, and 15 mM caffeine was approximately 1.5, 2, and 2.5, respectively, times the value of 4-NQO alone. The results indicate that the posttreatment repair processes following gamma irradiation or 4-NQO treatment are modified via different pathways.