Postnatal Changes in Pyridine Nucleotides in Rat Hepatocytes: Composition and O2 Dependence

Abstract

ABSTRACT. Postnatal changes in pyridine nucleotide concentration, composition, and oxidation-reduction characteristics were studied in liver cells from neonatal (newborn, d 4 and d 8) and adult rats to determine the development of hepatic pyridine nucleotide status and O2 dependence of oxidation of reducing equivalents. The results show that the total pyridine nucleotide concentrations in newborn and 4-d-old rat liver were low (30%) but increased to near adult values (80%) by d 8 postpartum. Analyses of the cellular distribution of NAD+, NADH, NADP", and NADPH reveal that the reduced forms (NADH plus NADPH) accounted for over 50% of the total in the newborn and 4-dold rats compared to 30% in adult animals. This relatively higher reductive capacity in hepatocytes of younger rats was largely the result of a significantly higher proportion of NADPH in these cells. Examination of the NADPH/ NADP+ and NADH/NAD+ ratios show that they occur in an inverse relationship with postnatal age; the NADPH/ NADPC ratio was high at birth and decreased with age, whereas the reverse pattern was found for the NADH/ NAD+ ratio. The result, that NADPH represents a significant percentage of the total pyridine nucleotides in neonatal cells in the early postnatal period, is consistent with a higher demand for NADPh for biosynthetic activities in association with tissue growth. A high NADPH concentration coupled with a low NADH concentration in these cells is further consistent with the finding that succinate is a preferred substrate for newborn respiratory function so as to spare NADH for transhydrogenation to NADPH. The half-maximal oxidation of pyridine nucleotides in cells from newborn rats occurred at 0.49 pM 0 2 , as compared to 1.2 and 4.0 pM O2 in cells from 4-d-old and adult rats, respectively. Direct comparison of the Oz dependencies of pyridine nucleotides at different ages with those of cytochrome c + el demonstrates that the oxidation of pyridine nucleotides occurs in concert with the expression of mitochondrial respiratory components during development. (Pediatr Res 30: 11 2-1 17, 1991) Abbreviations PS0, half-maximal associated greater demand for oxidizable substrates and reducing equivalents. In liver, the age-dependent increase in cellular respiration is attained by marked changes in the composition and contents of the enzymes of the respiratory systems (1-5) and by selective use of specific respiratory substrates (6, 7). We recently found that hepatocytes from newborn rats preferentially use succinate for cell respiration compared to a variety of other carbohydrate or amino acid substrates (6,7). These results suggest that oxidation of NADH is limited during the late fetal and early perinatal phases of development (8). The relatively slower ontogenic development of pyruvate dehydrogenase activity compared to other mitochondrial enzymes (9) is consistent with a limited utilization of glucose or lactate for energy production (8, 10). Together, the limitation of NADf-linked oxidations and the selective oxidation of succin...

Opposing Changes in 3α-Hydroxysteroid Dehydrogenase Oxidative and Reductive Activities in Rat Leydig Cells during Pubertal Development1

“…1). Northern blotting and reverse transcription-polymerase chain reaction analysis confirmed the expression of the mRNA encoding rat liver 3␣-HSD in Leydig cells [8,29]. Therefore, these studies indicate that the NADP(H)-dependent 3␣-HSD in Leydig cells is similar to the enzyme in rat liver.…”

“…This showed that the 3␣-HSD in progenitor Leydig cells was NADP(H)-dependent. The ratio of NADPH to NADP ϩ is known to be high in cells [28,29]; therefore, NADP(H)-dependent 3␣-HSD activities in intact Leydig cells were expected to be exclusively reductive, and this was confirmed by the data. Rates of NADP(H)-dependent oxidoreductase activity were equivalent in progenitor and immature Leydig cells, and the rates for both were higher than in adult Leydig cells.…”

“…However, the previously described NADPH-dependent 3␣-HSD is exclusively reductive in intact cells (in the present paper); this could account for all of the reductive activity observed in adult Leydig cells. Since the NAD/NADH ratio is normally high in intact cells [28,29], NADH-dependent 3␣-HSD reductive activity may not convert DHT to 3␣-DIOL in intact Leydig cells. We hypothesize that a microsomal NAD(H)-dependent 3␣-HSD catalyzes oxidative activity in vivo, which amplifies androgen action by generating the potent androgen, DHT, from the weak androgen, 3␣-DIOL.…”

Cytoplasmic and Mitochondrial NADPH-Coupled Redox Systems in the Regulation of Aging

“…NADPH is also required for steroid biosynthesis and protects cells from toxic metabolites by providing reducing power to cytochrome P450 enzymes. NADPH levels decrease with age [1,2] due to both aging-related loss of nicotinamide adenine dinucleotide (NAD + ) [3], a precursor for its synthesis, and to the aging related increase in the [NADP + ]/[NADPH] ratio that occurs as a result of oxidative stress due to increased mitochondrial electron transport chain dysfunction [4] and inflammation [5]. Therapies that increase NAD + levels combined with therapies that increase NADPH levels could greatly benefit subjects with aging-related disorders.…”

“…The NAD + /NADH and the NADP + /NADPH ratios oscillate over a 24 hour cycle [276,277] due in part to circadian regulation of NAMPT [278,279], NADK [280], and the PPP [281,282]. Therefore, loss of circadian rhythms could play an important role in the decreased NAD + [3] and NADPH [1,2] levels observed in aged tissues. Disruption of the PPP through the administration of 6-aminonicotinic acid was described to lengthen the circadian period in one study [282], while disruption of the PPP with the inhibitors diphenyleneiodonium (DPI) or dehydroepiandrosterone (DHEA) was described to alter the phase and amplitude of the circadian changes without affecting the period in another [281].…”