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Biomedical subjects

C A Lang

Publications and source records attributed to C A Lang.

At least 55 records · Page 3Linked to original sources
PubMed1986

Dietary nordihydroguaiaretic acid increases the life span of the mosquito.

Our previous findings indicated that a major characteristic of aging organisms is a decrease in reducing capacity. Our objectives were to correct this impairment by administration of nordihydroguaiaretic acid (NDGA), a potent reducing agent, and to determine the effect on adult longevity of the mosquito. NDGA supplements were included in the axenic larval medium or adult diet of mosquitoes of different ages. The mean adult life spans of both sexes increased 42-64% over controls (P less than 0.025), and the most effective doses were 0.001% for females and 0.005% for males. This NDGA effect was dependent on the age when feeding was initiated, since only biosynthetically active larvae and young adults were responsive. Also the effect was not due to dietary restriction. These results confirm the life span-enhancement effect of NDGA using defined conditions and establish the importance of redox status in the aging process.

Aedes↗
PubMed1985

Glutathione peroxidase and reductase activities in the aging mouse.

Previous results from this laboratory demonstrated that glutathione concentrations decrease in aging mouse tissues. In this investigation glutathione (GSH) peroxidase and glutathione (GSSG) reductase activities were measured in tissues of standardized aging mice. Methods were validated for the quantitative determination of both enzymes in liver, kidney and heart tissues. GSH peroxidase activities were 27-53% lower in liver, kidney and heart of very old (36 months) mice compared to mature (10 months) mice (P less than 0.01). The same aging decreases were found with either hydrogen peroxide or cumene hydroperoxide as substrate. In a similar way GSSG reductase activities in liver and kidney were 25-28% lower in the old versus mature mice (P less than 0.01), but heart levels were unchanged. Further the lower GSSG reductase levels were unaffected by FAD supplementation in vitro. The changes in specific activity for both enzymes were not due to changes in organ weights and total protein contents, which were constant from 10 to 36 months of age. These decreases in GSH peroxidase and GSSG reductase do not account for the lower GSH levels in aging. Of special importance, however, is that these decreases indicate that detoxification via glutathione peroxidase and glutathione reductase could be impaired in senescence.

Aging↗
PubMed1984

The verification of a mammalian toxicant classification using a mosquito screening method.

Routine toxicity screening of substances using rodents can be time consuming and expensive. For these reasons various alternative methods have been developed, but many lack standardization and acceptance. It was hypothesized that a satisfactory classification of mammalian toxicants could be obtained using a simple mosquito (Aedes aegypti) screening method. To this end, median lethal concentration (LC50) values were determined for a wide variety of mammalian toxicants representing a range of toxicity classes. Each substance was assayed in aqueous solution by incubation for different times, up to 24 hr, using at least 30 individual larvae and six different concentrations, for valid statistical analysis. With few exceptions, the resultant toxicity classes were the same as those determined using mammalian models. This classification was validated further by the very high correlation (r = 0.97) determined between the mosquito LC50 values and the rat LD50 values. These results suggest that this mosquito method can be used to rapidly screen compounds of potential mammalian toxicity.

Aedes↗
PubMed1984

Glutathione levels during the mosquito life span with emphasis on senescence.

Glutathione levels were determined in mosquitoes of all ages of the life span. Specific analyses for reduced (GSH) and oxidized (GSSG) glutathione were used and validated to ensure minimal autoxidation of GSH and conversion of these forms. Indeed GSH accounted for greater than 97% of the total glutathione (GSH + GSSG) content in all samples. Marked changes occurred during the life span, and the highest levels of GSH and total glutathione were found during larval growth and metamorphosis (P less than 0.001). Thereafter the levels decreased in the early adult, plateaued in the mature, and decreased 46% in the old and very old mosquito (P less than 0.001). This aging-specific decrease was a general phenomenon, for it occurred in all body regions of both sexes. Starvation up to 3 days did not affect the GSH levels. The importance of these changes in glutathione is its relationship to the reducing and biosynthetic capacities of different life span stages. Of special interest is the senescence decrease which can lead to lower biosynthetic activity and also impaired detoxification capacity.

Aedes↗
PubMed1983

Glutathione S-transferase activities in the yellow-fever mosquito [Aedes aegypti (Louisville)] during growth and aging.

Our previous findings [Hazelton & Lang (1978) Fed. Proc. Fed. Am. Soc. Exp. Biol. 37(6), 2378 (abstr.)] demonstrated aging-specific changes in glutathione concentrations in the yellow-fever mosquito [Aedes aegypti (Louisville)]. A possible mechanism could be increased utilization via glutathione S-transferase. Thus glutathione S-transferase activities were measured in mosquito samples from the entire life span, including growth, maturity and senescence. Methods were validated for the quantitative determination of transferase activities with 1,2-dichloro-4-nitrobenzene (DCNB) and 1-chloro-3,4-dinitrobenzene (CDNB) as second substrates. Marked changes occurred during the life span, and the profiles for both DCNB and CDNB activities were identical. The activities increased throughout larval development and reached a maximum in the metamorphosis stage. The activities decreased at the end of metamorphosis in the 5-day-old adult, reached a plateau during maturity (5-20 days), and then decreased 31% (P less than 0.007) during senescence (after 33 days). This senescence-specific decrease occurred in both sexes and was localized in the abdominal region. Further kinetic analyses indicated that the lower enzyme activities were most likely due to lower amounts of active enzyme rather than a change in kinetic properties. These findings indicate that the capacity for GSH utilization via glutathione S-transferase is diminished with aging. This does not explain our previously observed decreases in GSH, but the results suggest that GSH-linked detoxification would be impaired during senescence.

Aedes↗
PubMed1983

Glutathione biosynthesis in the aging adult yellow-fever mosquito [Aedes aegypti (Louisville)].

Our previous findings [Hazelton & Lang (1978) Fed. Proc. Fed. Am. Soc. Exp. Biol. 37(6), 2378 (abstr.)] demonstrated a senescence-specific decrease in glutathione (GSH) concentration in the yellow-fever mosquito Aedes aegypti (Louisville)]. As a possible mechanism for this change, GSH biosynthesis was investigated in adult mosquitoes of different ages through the life-span. Biosynthesis was measured as the incorporation rate of [14C]glycine or [14C]cystine into glutathione. Essential information to validate the procedure was also obtained on the precursor-amino-acid pool sizes and kinetic parameters such as lag-time and time course of incorporation. Also, synthesis de novo rather than exchange was verified using buthionine sulphoximine, a specific inhibitor of GSH biosynthesis. The synthetic rates with either amino acid precursor varied throughout the adult life-span, but the patterns for both precursors were essentially identical. Biosynthesis was high in the newly emerged adult and decreased 62-70% (P less than 0.005) to a plateau during maturity. From the mature value there was a decrease of 36-41% (P less than 0.005) to a new plateau during senescence. Glutathione biosynthesis and concentration were correlated throughout maturity and senescence (r = 0.982) and thus biosynthesis was proportional to glutathione content. On this basis we concluded that impaired biosynthesis is the major and perhaps sole mechanism for the aging decrease in glutathione content.

Aedes↗
PubMed1981

Effect of zinc deficiency on blood glutathione levels.

The specific effect of zinc deficiency on blood glutathione (GSH) concentrations has not been clearly demonstrated, for earlier results could have been due to differences in dietary intake. To clarify this, we determined blood GSH concentrations over a 17-day period in young, mature rats fed a zinc-deficient diet and compared them with pair-fed controls. Glutathione concentrations based on hemoglobin content increased in both groups but a different rates. After 17 days, the GSH levels increased 20% in deficient rats and 29% in control rats (P less than 0.005). The GSH levels in deficient rats were 11% lower than in controls by 10 days (P less than 0.025) and remained significantly lower thereafter. These results indicate that the decrease in blood GSH levels was a specific result of zinc deficiency.

Animals↗
PubMed1981

Differences in blood glutathione levels of tumor-implanted or zinc-deficient rats.

Previously we found that blood glutathione (GSH) levels were decreased in rats that were both zinc-deficient and tumor-bearing. In this study the separate effects of zinc deficiency and tumor were investigated. Young, male rats were pair-fed either a complete, control diet or a zinc-deficient diet, and some of each group were implanted intramuscularly (i.m.) with Walker 256/Ml carcinosarcoma. Then half of the tumor-implanted, zinc-deficient rats were repleted with zinc. All rats were killed 7 days after tumor implantation. Zinc deficiency was validated by poor growth, low food efficiency and decreased concentrations of zinc in liver, kidney and plasma. Relative to controls rats, the blood GSH level increased 21% as a result of tumor alone (P less than 0.005) and decreased 19% with zinc-deficiency alone (P less than 0.025). In rats that were both tumor-bearing and zinc-deficient, the GSH level was 16% higher than the controls (P less than 0.005). Zinc repletion of the tumor-bearing rats restored GSH levels to control values. These results indicate that the marked and opposite changes in blood GSH levels as a result of tumor implantation or of zinc deficiency occur by different mechanisms.

Animals↗
PubMed1980

Glutathione contents of tissues in the aging mouse.

1. Previous results from this laboratory demonstrated that the erythrocyte content of reduced glutathione (GSH) decreased as a function of both increasing cell age and mouse age [Abraham, Taylor & Lang (1978) Biochem. J. 174, 819-825]. In the present investigation glutathione concentrations were determined in other tissues of the C57BL/6J mouse of different ages (6--31 months) throughout the life-span. 2. At all ages the total glutathione and the GSH concentrations in liver were 3 times that in kidney and 10 times that in heart. In the old (31 months) mouse the GSH contents were lower by 30% in the liver, 34% in the kidney and 20% in the heart than in the mature (17--23 months) animals. 3. The oxidized glutathione (GSSG) concentrations of the tissues did not vary with age and constituted less than 3% of the total glutathione. 4. The decreased in GSH concentrations were not due to changes in organ weights, which were constant from 10 to 36 months of age. 5. These findings extend our previous results and indicate that a general characteristic of aging tissues may be a decrease in GSH concentrations. Further, this is consistent with our hypothesis that the reducing potential of tissues decreases in senescence.

Aging↗
PubMed1978

Influence of mouse age and erythrocyte age on glutathione metabolism.

In order to determine whether the biological age of a mouse influences erythrocyte metabolism and erythrocyte aging in vivo, blood samples were collected from male C57/BL6J mice of different biological ages ranging from mature (10 months) to "very old" (37 months). In the very old mouse, compared with the mature mouse, the erythrocyte survival time was decreased, erythrocyte densities were increased, the concentrations of total free thiol and reduced glutathione, and glutathione reductase activity were decreased. Erythrocytes were separated into different density (age) groups by phthalate ester two-phase centrifugation or by albumin density-gradient centrifugation. The density-age relationship of erythrocytes was established by pulse-labelling with 59Fe in vivo and by subsequent determinations of specific radioactivity of erythrocyte fractions of different densities prepared during a chase period of 60 days. The age of erythrocytes in mice of all ages was directly related to density. Also, in older erythrocytes compared with younger erythrocytes, decreased concentrations of total free thiol and reduced glutathione, and decreased glutathione reductase activity were observed. These were the lowest in the old erythrocytes of very old mice. These results in aging erythrocytes from aging mice suggest that the glutathione status the erythrocyte may be an index of aging, not only of the cell but also of the organism.

Aging↗
PubMed1978

Purification and properties of mosquito DNA polymerase.

For the first time, DNA polymerase in a postembryonic insect has been purified and characterized. This enzyme from mosquito larvae was purified 1700-fold and was free of deoxyribonuclease and protease activities, which hindered previous investigations of insect polymerases. The enzyme had a molecular weight of 132,000 by gen filtration and aggregated to higher molecular weights when concentrated. With an activated DNA template, the pH optimum was 7.2 in phosphate buffer, and the Mg2+ concentration optimum was 5 to 10 mM. Polymerase activity was inhibited by the antisulfhydryl reagents, N-ethylmaleimide and p-mercuribenzoate, and by KCl. These properties indicate that the mosquito enzyme resembles mammalian alpha-polymerase but differs in its lack of inhibition to low ethanol concentrations. There was no evidence of a beta-polymerase form in the mosquito.

Animals↗
PubMed1976

A deoxyribonucleic acid-replication intermediate in the growing mosquito.

In previous experiments on growth and aging in the yellow-fever mosquito, Aedes aegypti, a low mol. wt. (500000) DNA species was found in the supernatant fraction after ultracentrifugation of homogenates of rapidly-growing larvae. This DNA species, "sDNA", constituted 30-40% of total DNA in 2-4-day-old larvae, but was less than 5% in older larvae, pupae and adults. We have now isolated and characterized sDNA and initiated experiments to determine its metabolic role. Isolated sDNA has the same physical and chemical characteristics as bulk DNA, "pDNA", and differs only in size. In CsCl isopycnic centrifugation the buoyant densities of sDNA and pDNA were 1.700 and 1.697 g/cm3 respectively. The "melting" temperature of both DNA species was 84 degrees C. Base compositions calculated from these data and other methods were 38.9 mol% of guanine-plus-cytosine for sDNA, and 38.5 for pDNA. Also, the size of newly-synthesized DNA was investigated by pulse-labelling and pulse-chase experiments. In neutral sucrose gradients the labelled DNA component after a 2h pulse had a sedimentation coefficient of about 8S, but after a 4h pulse sedimented in a broad band from 10-19S. In alkaline sucrose gradients a single peak around 7S was observed for pulse times up to 4h. After a 6h pulse and a 1 day "chase", labelled DNA species had sedimentation coefficients ranging from 10-15S in alkaline sucrose, and after a 2-day chase the values were 17-31S, similar to those of pDNA under alkaline conditions. These results suggest that sDNA represents an intermediate form in the replication of DNA in mosquito larvae.

Aedes↗
PubMed1976

The biosynthesis of deoxyribonucleic acid during the life-span of the mosquito.

Previous results from this laboratory [Kao et al, (1976) Biochem. J. 154, 471-480] demonstrated that a low-molecular-weight DNA species, "sDNA", present in high concentrations during rapid larval growth of the yellow-fever mosquito, Aedes aegypti, may be an intermediate in DNA replication. We have now determined the life-span profiles of synthetic rates and the steady-state contents of sDNA and total DNA by radiometric and biochemical procedures and by using mosquitoes grown and maintained under defined and controlled conditions, including axenic culture and synchronization of stages. 2. Our results showed exponential increases in DNA contents and synthetic rates which paralleled the changes in weight during larval growth. Of special importance was the finding that in rapidly-growing larvae and newly-emerged adult mosquitoes high contents and rates of synthesis of sDNA were correlated with increases in total DNA/organism, which suggests that sDNA content may be an index of DNA replication. In senescent mosquitos a twofold increase in the synthetic rate of bulk DNA ("pDNA") without an increase in sDNA may reflect repair synthesis. 3. The significance of this investigation is that it may be the first quantitative and systematic description of the synthetic rates and contents of both DNA-replication intermediates and total DNA in an axenic, eukaryotic organism rather than a specific cell type. Equally important is that these findings describe DNA changes during growth and also during aging through senescence in an age-characterized organism.

Aedes↗