Consumption of a single serving of red raspberries per day reduces metabolic syndrome parameters in high-fat fed mice.

Using an animal model for diet-induced metabolic disease, we have shown previously that the addition of raspberry juice concentrate (RJC) and raspberry puree concentrate (RPC) at a level of 10% of kcal, equivalent to four servings per day, to an obesogenic high-fat, western-style diet (HF) significantly reduced body weight gain, serum resistin levels, and altered the expression of hepatic genes related to lipid metabolism and oxidative stress. This study was designed to examine the effect of a lower level of RJC or RPC consumption, at a level representing a single serving of food per day (2.5% of kcal). For ten weeks, four groups of C57BL/6J mice (n = 8 ea.) were fed: low fat (LF), HF, HF + RJC, or HF + RPC diets. Intake of RJC and RPC decreased final body weight. Hepatic lipid accumulation was significantly decreased in HF + RPC- and HF + RJC-fed mice, compared to HF-fed mice. Further, the relative expression of hepatic genes including Heme oxygenase 1 (Hmox1) and Hormone sensitive lipase (Lipe), were altered by RPC or RJC consumption. In this mouse model of diet-induced metabolic disease, consumption of the equivalent of a single daily serving of either RPC or RJC improved metabolism in mice fed HF diet. We hypothesize that the phytochemicals contained in raspberries, and/or their subsequent metabolites, may be acting to influence gene expression and other regulatory pathways, to produce the metabolic improvements observed in this study.

Zinc-deficient rats are insensitive to glucoprivation caused by 2-deoxy-D-glucose.

Three-choice macronutrient intake studies indicate that zinc-deficient (Zn-) rats selectively decrease intake of carbohydrate. Because glucoprivic stimuli increase food intake and selection for carbohydrate, the ability of Zn- rats to respond to glucoprivation induced by 2-deoxy-D-glucose (2-DG) was tested. Rats were fed a Zn-adequate (Zn+) or Zn- diet. In part 1, rats were challenged with 0, 250, or 400 mg 2-DG/kg BW (i.p.) after zinc deficiency was established. In part 2, rats received saline or 2-DG while zinc deficiency was being induced and then after deficiency was established. Food intake was increased after injection of 2-DG to Zn+ rats; however, food intake was not higher after 2-DG administration to Zn- rats. A dose-response test for 2-DG further confirmed these results. In part 2, it was found that Zn- rats lose the response to 2-DG administration when zinc deficiency-induced anorexia begins, after 3 days of consuming a zinc-deficient diet. It appears that the ability to sense blood glucose concentrations may be impaired during zinc deficiency, and this impairment could be a part of the anorexia that develops during zinc deficiency in the rat.

Zinc deficiency reduces leptin gene expression and leptin secretion in rat adipocytes.

The present study was conducted to measure ob mRNA abundance in the zinc-deficient (ZD) rats and the secretion of leptin from adipose tissue obtained from ZD, zinc-adequate (ZA), and pair-fed (PF) rats. It was found that ob mRNA abundance was greatest (P < 0.05) in adipose tissue obtained from ZA and PF rats. Ob mRNA abundance was similar in PF and ZD rats. To study leptin secretion from adipose tissue in a cell culture model, a method was developed to use excised epididymal adipose tissue from ZD, ZA, and PF rats. Tissue was incubated in Opti-modified Eagle's medium (MEM) cell culture medium in which concentrations of zinc and insulin were manipulated. It was observed that leptin secretion was higher (P < 0.05) in adipose tissue obtained from ZA than ZD and PF rats. Secretion of leptin was higher in adipose tissue of PF than ZD rats (P < 0.05). Surprisingly, media zinc content in this ex vivo model tended to suppress secretion of leptin. This suppression seems to be zinc specific and might be caused by the sequestration of insulin in the culture medium. Our results indicate that the reduction in serum leptin observed in ZD rats is likely caused by not only a reduction in body fat, but also by a decrease in leptin synthesis and secretion per gram of adipose tissue. Taking these results into account along with a prior study (1), it is possible that even a marginal zinc deficiency could affect leptin secretion and serum leptin concentrations. Impaired leptin secretion caused by zinc deficiency might be one factor contributing to hypogonadism observed in zinc deficiency.

Zinc has an insulin-like effect on glucose transport mediated by phosphoinositol-3-kinase and Akt in 3T3-L1 fibroblasts and adipocytes.

Zinc has insulin-like effects on cells, including promotion of both lipogenesis and glucose transport. The relationship between zinc and the stimulation of glucose transport is unclear. We hypothesize that zinc affects the insulin-signaling pathway. In this study, the effect of zinc on glucose transport and insulin signaling was examined in 3T3-L1-preadipocytes and -adipocytes. Treatment of cells with up to 200 micromol/L zinc significantly increased glucose transport (P < 0.05). The effect of zinc on adipocytes was greater than on preadipocytes, and the effect of zinc plus insulin was greater than that of either insulin or zinc alone. Cytochalasin D, which disrupts actin filaments, attenuated the increase of glucose transport induced by zinc or insulin (P < 0.05). At 100 nmol/L, wortmannin, the phosphoinositide (PI) 3-kinase inhibitor, decreased basal glucose transport and blocked zinc-stimulated glucose transport in both cell types (P < 0.05). H7, an inhibitor of protein kinase C, did not reduce basal glucose transport but decreased zinc-induced glucose transport (P < 0.05). Zinc increased tyrosine phosphorylation of the insulin receptor beta subunit of both preadipocytes and adipocytes after 5-10 min of treatment (P < 0.05). Zinc at 200 micromol/L did not affect tyrosine phosphorylation of insulin receptor substrate (IRS)-1 or -2; further, there was no effect of zinc on the association of the p85 subunit of PI 3-kinase and IRS-1. Zinc significantly increased serine-473 phosphorylation of Akt in both preadipocytes and adipocytes (P < 0.05). The PI 3-kinase inhibitor, wortmannin, totally blocked the effect of zinc on Akt activation. Hence, it appears that zinc can induce an increase in glucose transport into cells and potentiate insulin-induced glucose transport, likely acting through the insulin-signaling pathway.

Increased protein intake during recovery from zinc deficiency is accompanied by alterations in hypothalamic growth hormone releasing factor and somatostatin.

To determine if alterations in growth hormone releasing factor (GRF) and somatostatin (SRIF) occur during recovery from zinc deficiency and to examine the relationship between these peptides and the increased protein intake observed during zinc repletion, both the hypothalamic release and mRNA levels of GRF and SRIF were measured during zinc deficiency and zinc repletion. Groups of male rats (n = 4-8 each) were provided 3-choice macronutrient diets made either zinc adequate (Zn+) or deficient (Zn-; 30 vs. 1 mg Zn/kg diet). Pair fed, calorie restricted (PF) rats were also maintained. After 28 days, Zn- rats were repleted with Zn+ diets for 2 days and one PF group was allowed free access to the same Zn+ diets for 2 days. Additionally, groups of Zn- and PF rats were repleted 2 days with Zn+ carbohydrate and fat diets but no protein. Hypothalamic GRF and SRIF release was measured in vitro. Basal GRF secretion was not significantly different between Zn-, PF, or Zn+ groups although there was a significant increase (P<0.05) during zinc repletion. PF and Zn- rats repleted 2 days with diets devoid of protein had highest GRF secretion (P<0.01) compared to other groups. There were no differences in GRF mRNA levels among groups. Basal SRIF secretion was significantly lower in Zn- and PF groups compared to Zn+, and SRIF mRNA levels were significantly higher in zinc repleted groups compared to Zn-. These results demonstrate that during zinc repletion, GRF and SRIF secretion and SRIF gene expression are altered concomitantly with protein intake. The present data support involvement of GRF in protein intake changes during zinc repletion.

Growth hormone-releasing factor affects macronutrient intake during the anabolic phase of zinc repletion: total hypothalamic growth hormone-releasing factor content and growth hormone-releasing factor immunoneutralization during zinc repletion.

Growth hormone-releasing factor (GRF) is thought to perform two distinct functions within the brain. GRF synthesized in the median eminence (ME) stimulates the release of growth hormone (GH) from the pituitary, while GRF in the suprachiasmatic nucleus and median preoptic area (SCN/MPOA) may stimulate selection of dietary protein. These two functions may be coupled to regulate and enhance growth. During zinc repletion, a period characterized by increased protein intake and accelerated growth, we examined this coupling by measuring GRF peptide content in hypothalamic sites and neutralizing GRF function by infusing anti-GRF antibody into the hypothalamus during zinc repletion. Total GRF content and GRF content in the ME and SCN/MPOA were decreased in zinc-deficient (Zn-) rats compared to zinc-adequate (Zn+) rats (P < 0.05). There were no differences in GRF content during zinc repletion in either nuclei. Subsequently, we investigated the macronutrient feeding patterns of rats chronically infused with anti-GRF IgG into the lateral ventricle of the brain during zinc repletion. All Zn- and Zn+ rats administered anti-GRF IgG exhibited a reduction in protein intake during zinc repletion. The Zn- rats receiving anti-GRF-IgG consumed equal amounts of total diet compared to those receiving vehicle during the repletion period however they consumed less carbohydrate (P < 0.05) and considerably more fat (P < 0.02). There were no significant differences in carbohydrate or fat intake in Zn+ rats receiving anti-GRF antibody. These results suggest that GRF likely directs protein intake during normal growth, but may interact with additional appetite-controlling neuropeptides during zinc repletion.

Neurobiology of zinc-influenced eating behavior.

Zinc is an essential nutrient that is required in humans and animals for many physiological functions, including immune and antioxidant function, growth and reproduction. Many aspects of zinc deficiency-induced anorexia have been well studied in experimental animals, most notably the laboratory rat. There is evidence that suggests zinc deficiency may be intimately involved with anorexia in humans: if not as an initiating cause, then as an accelerating or exacerbating factor that may deepen the pathology of the anorexia. The present review describes recent research investigating the relationship between zinc deficiency and the regulation of food intake, along with advances in the understanding of the food intake and body weight regulation systems. For more comprehensive reviews of zinc nutrition and zinc deficiency, readers are referred to the other reviews in this volume and the review text of Mills (1989). An excellent review focused solely on zinc status and food intake has been presented by O'Dell and Reeves (1989).

Dietary thiamin level influences levels of its diphosphate form and thiamin-dependent enzymic activities of rat liver.

This study was prompted by our incomplete understanding of the mechanism responsible for the clinical benefits of pharmacological doses of thiamin in some patients with maple syrup urine disease (MSUD) and the question of whether thiamin diphosphate (TDP), a potent inhibitor of the activity of the protein kinase that phosphorylates and inactivates the isolated branched-chain alpha-ketoacid dehydrogenase (BCKDH) complex, affects the activity state of the complex. Rats were fed a chemically-defined diet containing graded levels of thiamin (0, 0.275, 0.55, 5.5, and 55 mg thiamin/kg diet). Maximal weight gain was attained over a 3-wk period only in rats fed diets with 5.5 and 55 mg thiamin/kg. Feeding rats the thiamin-free diet for just 2 d caused loss of nearly half of the TDP from liver mitochondria. Three more days caused over 70% loss, an additional 3 wk, over 90%. Starvation for 2 d had no effect, suggesting a mechanism for conservation of TDP in this nutritional state. Mitochondrial TDP was higher in rats fed pharmacological amounts of thiamin (55 mg thiamin/kg diet) than in rats fed adequate thiamin for maximal growth. Varying dietary thiamin had marked but opposite effects on the activities of alpha-ketoglutarate dehydrogenase (alpha-KGDH) and BCKDH. Thiamin deficiency decreased alpha-KGDH activity, increased BCKDH activity, and increased the proportion of BCKDH in the active, dephosphorylated, state. Excess dietary thiamin had the opposite effects. TDP appears to be more tightly associated with alpha-KGDH than BCKDH in thiamin-deficient rats, perhaps denoting retention of alpha-KGDH activity at the expense of BCKDH activity. Thus, thiamin deficiency and excess cause large changes in mitochondrial TDP levels that have a major influence on the activities of the keto acid dehydrogenase complexes.

Soy protein and isoflavones: their effects on blood lipids and bone density in postmenopausal women.

The effects of soy protein (40 g/d) containing moderate and higher concentrations of isoflavones on blood lipid profiles, mononuclear cell LDL receptor messenger RNA, and bone mineral density and content were investigated in 66 free-living, hypercholesterolemic, postmenopausal women during a 6-mo, parallel-group, double-blind trial with 3 interventions. After a control period of 14 d, during which subjects followed a National Cholesterol Education Program Step I low-fat, low-cholesterol diet, all subjects were randomly assigned to 1 of 3 dietary groups: Step I diet with 40 g protein/d obtained from casein and nonfat dry milk (CNFDM), Step I diet with 40 g protein/d from isolated soy protein containing 1.39 mg isoflavones/g protein (ISP56), or Step I diet with 40 g protein/d from isolated soy protein containing 2.25 mg isoflavones/g protein (ISP90). Total and regional bone mineral content and density were assessed. Non-HDL cholesterol for both ISP56 and ISP90 groups was reduced compared with the CNFDM group (P < 0.05). HDL cholesterol increased in both ISP56 and ISP90 groups (P < 0.05). Mononuclear cell LDL receptor mRNA was increased in subjects consuming ISP56 or ISP90 compared with those consuming CNFDM (P < 0.05). Significant increases occurred in both bone mineral content and density in the lumbar spine but not elsewhere for the ISP90 group compared with the control group (P < 0.05). Intake of soy protein at both isoflavone concentrations for 6 mo may decrease the risk factors associated with cardiovascular disease in postmenopausal women. However, only the higher isoflavone-containing product protected against spinal bone loss.

Long-term intake of soy protein improves blood lipid profiles and increases mononuclear cell low-density-lipoprotein receptor messenger RNA in hypercholesterolemic, postmenopausal women.

The long-term clinical effects of soy protein containing various amounts of isoflavones on lipoproteins, mononuclear cell LDL receptor messenger RNA concentrations, and other selected cardiovascular risk factors are not well known. Sixty-six hypercholesterolemic, free-living, postmenopausal women were investigated during a 6-mo parallel-group, double-blind trial with 3 interventions. After a control period of 14 d, all subjects were randomly assigned to 1 of 3 dietary groups (all with 40 g protein): a National Cholesterol Education Program (NCEP) Step 1 diet with protein from casein and nonfat dry milk (control), an NCEP Step 1 diet with protein from isolated soy protein containing moderate amounts of isoflavones (ISP56), or an NCEP Step 1 diet with protein from isolated soy protein containing high amounts of isoflavones (ISP90). Non-HDL cholesterol in both the ISP56 and ISP90 groups was reduced compared with the control group (P < 0.05), whereas total cholesterol was not changed. HDL cholesterol increased in both the ISP56 and ISP90 groups (P < 0.05), whereas the ratio of total to HDL cholesterol decreased significantly in both groups compared with the control (P < 0.05). Mononuclear cell LDL receptor messenger RNA concentrations increased in subjects consuming ISP56 or ISP90 compared with the control (P < 0.05). These results indicate that soy protein, with different amounts of isoflavones, may decrease the risk of cardiovascular disease via improved blood lipid profiles, and that the mechanism by which apolipoprotein B-containing lipoproteins were depressed may be via alterations in LDL receptor quantity or activity.

Zinc deficiency increases hypothalamic neuropeptide Y and neuropeptide Y mRNA levels and does not block neuropeptide Y-induced feeding in rats.

Zinc deficiency reduces intake and produces an unusual approximately 3.5-d cycle of intake in rats. The mechanism underlying the anorexia and cycling has not yet been defined; current hypotheses suggest that alterations in amino acid metabolism and neurotransmitter concentrations may be a part of this anorexia. Recent reports indicate that appetite-stimulating neuropeptide Y (NPY) may be elevated during zinc deficiency. This suggests that a resistance to NPY may exist during zinc deficiency because NPY levels are high, yet appetite is low. The purpose of this study was to measure NPY peptide and mRNA concentrations during zinc deficiency in specific nuclei of the hypothalamus in which peptide and mRNA for NPY are known to be associated with appetite, and also to determine whether zinc-deficient rats are responsive to central infusions of NPY. Both NPY peptide levels in the paraventricular nucleus and NPY mRNA levels in the arcuate nucleus were higher (P < 0.05) in zinc-deficient rats than in zinc-adequate rats. When rats were administered exogenous NPY to the paraventricular nucleus, both zinc-deficient and zinc-adequate rats responded similarly by increasing food intake. These results suggest that NPY is elevated during zinc deficiency in an attempt to restore normal food intake levels, rather than being reduced and thereby contributing to the anorexia associated with zinc deficiency. During zinc deficiency, NPY receptors are able to bind NPY and initiate an orexigenic response.

Histidine availability alters glucagon gene expression in murine alphaTC6 cells.

Because individual amino acids (AA) stimulate glucagon release from pancreatic alpha-cells, the purpose of this study was to determine if individual AA could influence glucagon gene expression. Preproglucagon mRNA levels were 67% lower (P < 0.05) in mouse alphaTC6 cells incubated for 12 h in amino acid-free medium compared with cells incubated in complete medium containing all 20 AA. A time-course study indicated that alphaTC6 cells incubated in amino acid-free medium +/-1 micromol/L puromycin or amino acid-containing medium plus puromycin exhibited similar preproglucagon mRNA decreases over 12 h. When 1 micromol/L actinomycin was added to medium with or without AA, ppG mRNA concentrations decreased (P < 0.05) for 3h; however, values at 12 h were not different than those at 3 h. Deletions of single AA from complete medium demonstrated that only histidine removal or depletion reproduced the decrease in ppG mRNA observed in amino acid-free medium. We conclude that histidine is involved in the regulation of preproglucagon mRNA levels in alphaTC6 cells and that this regulation may be operative during both transcriptional and post-transcriptional events.

Intake of soy protein and soy protein extracts influences lipid metabolism and hepatic gene expression in gerbils.

The ability of alcohol extract of isolated soy protein to contribute to the hypochoesterolemic effect mediated by the intake of soy protein was tested in gerbils. Gerbils were assigned to five different groups (n = 8) and provided experimental diets for 28 d. Diets contained either casein or alcohol-washed isolated soy protein (ISP). The ISP diet was provided alone, or supplemented with one of three different levels of an alcohol extract of isolated soy protein contributing either 2.1, 3.6 or 6.2 mg isoflavones/g protein. Gerbils fed all of the soy-based diets had significantly lower (P < 0.05) total cholesterol, LDL + VLDL cholesterol, and apolipoprotein B concentrations than those fed casein. The addition of the alcohol extract to ISP did not reduce serum cholesterol concentrations any further, but reduced hepatic apolipoprotein A-I mRNA levels (P < 0. 05) compared with casein- and ISP-fed groups. Levels of apolipoprotein E mRNA were not affected by diet. These data suggest that in gerbils, consumption of an isoflavone-containing extract does not contribute to the hypocholesterolemic effect of alcohol-extracted soy, but may influence lipid metabolism by altering gene expression for lipid-related genes.

Zinc deficiency changes preferred macronutrient intake in subpopulations of Sprague-Dawley outbred rats and reduces hepatic pyruvate kinase gene expression.

Macronutrient selection patterns of male rats were analyzed using a 3-choice macronutrient selection system providing either adequate (+Zn) or deficient (-Zn) levels of zinc (30 or 1 mg Zn/kg). In study 1, rats were provided +Zn and -Zn diets for 28 d. All rats preferred carbohydrate (>50% carbohydrate intake) at the onset, consuming an average of 71% carbohydrate (cho), 17% protein (pro), and 12% fat. By the end of the study, 25% of the -Zn rats switched preference from cho to fat, whereas no +Zn rats changed. In study 2, -Zn rats preferring fat increased their total intake to normal levels, but only 50% reverted to carbohydrate preference after 35 d of zinc repletion. Hypothalamic concentrations of galanin were measured in groups of +Zn and -Zn cho- and fat-preferring rats. Galanin, which may be regulated with fat intake, was not different in -Zn rats preferring fat vs. -Zn rats preferring cho. Galanin concentrations were higher in +Zn than in -Zn rats (P < 0.05) and higher in +Zn rats preferring fat than in +Zn rats preferring cho (P < 0.05). Hepatic pyruvate kinase (PK) mRNA concentrations were related to cho preference, regardless of zinc status. When PK mRNA levels were measured in rats consuming a single AIN- 93-based diet, PK mRNA levels were significantly reduced by zinc deficiency (P < 0.05). Because PK is highly regulated by insulin, the effect of insulin may be reduced by zinc deficiency, making it more difficult for -Zn rats to catabolize dietary cho. This may explain why some -Zn rats switched from preferring cho to fat after developing zinc deficiency.

Food intake patterns are altered during long-term zinc deficiency in rats.

Rats experience anorexia and reduction or cessation in growth after being provided a zinc-deficient diet. While zinc deficient, intake levels may be reduced 50% or more compared to control rats. In the present report, diurnal food intake patterns of male Sprague-Dawley rats were measured during zinc deficiency. In Study 1, rats consuming a modified AIN-93 diet were tested during the dark phase using an automated food weighing system. In zinc-deficient animals (Zn-), the onset of the first meal of the dark phase was delayed compared to zinc-adequate rats (Zn+; 106+/-47 vs. 23+/-5 min; p<0.05) and the number of meals consumed during the dark phase was reduced in Zn- vs. Zn+ rats (3.9+/-0.5 vs 7.1+/-0.4; p<0.05). In Study 2, diurnal food intake patterns were tested using a three-choice macronutrient self-selection paradigm of carbohydrate-, protein-, and fat-containing diets made deficient or adequate in zinc (1 or 30 mg Zn/kg diet). Food intake was recorded in the early-, mid-, late-dark period (4 h each) and light period (12 h). Carbohydrate intake was 70% of total intake of both Zn+ and Zn- rats during the first 5 days, but decreased significantly to 50% in the Zn- group during the last 5 days. Fat intake increased significantly in the Zn- group during the last 5 days. This increase was the result of 4 of 15 Zn- rats increasing their intake of fat significantly. Results of this study indicate that zinc status alters dark phase and macronutrient selection patterns by delaying consumption of the initial meal of the dark phase, reducing the average meal number and by changing the dominant macronutrient preference of some Zn- rats.

Minimum thiamin requirement of weanling Sprague-Dawley outbred rats.

To determine the minimum thiamin requirement for maximal growth, two trials were conducted using male weanling Sprague-Dawley rats fed graded doses of thiamin from thiamin mononitrate as a component of a chemically defined diet. This diet included 16% amino acids, 72% sucrose and cornstarch and 5% soybean oil. Total weight gain and food intake were recorded over 2- (trial 1) or 3- (trial 2) wk periods. In trial 1, graded levels of thiamin were fed at 0, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 mg thiamin/kg diet, and growth rate reached a plateau in rats fed 0.50 mg thiamin/kg. In trial 2, lower doses of thiamin were fed (0, 0.25, 0.50, 0.75, 1.0, 4.0 and 5.0 mg/kg) to determine the minimum requirement for maximal growth. Using broken-line least-squares analysis, weight gain reached a plateau (6.8 g/d) at a thiamin concentration of 0.55 +/- 0.07 mg/kg. No differences (P > 0.05) in weight gain, food intake or gain:food ratio were observed at thiamin levels at or above 0.5 mg/kg, but food intake was substantially lower (P < 0.05) in rats fed 0 and 0.25 mg thiamin/kg (9.9 and 13.4 g/d, respectively) than in rats fed higher doses of thiamin (16.1 g/d). Hepatic transketolase, a measure of enzymatic thiamin status, increased with dietary thiamin in rats fed diets containing 0-5.0 mg/kg thiamin. However, an inflection point occurred at 0.53 mg thiamin/kg, with the slope being eight times greater below than above the inflection point. The data suggest that the thiamin requirement for maximal growth of weanling rats fed a chemically defined diet is approximately 0.55 mg thiamin/kg, which is substantially below the current National Research Council estimated requirement of 3.1 mg thiamin/kg diet.

Zinc status specifically changes preferences for carbohydrate and protein in rats selecting from separate carbohydrate-, protein-, and fat-containing diets.

This study examined how macronutrient intake preferences were specifically altered in the loss of appetite caused by experimentally produced zinc deficiency. Outbred female rats were allowed to freely select from simultaneously provided carbohydrate-, protein-, and fat-rich diets to provide themselves with an acceptable total diet. Rats were divided into two groups and provided the three diets containing either adequate (30 mg/kg; Zn+) or deficient (1 mg/kg; Zn-) levels of zinc (Zn). After 28 d, rats offered the Zn- diet were returned to a Zn+ diet (Zn repletion). Intakes from each of the three macronutrient diets were measured to determine macronutrient preferences of Zn-adequate, Zn-deficient, and Zn-repleted rats. In two 28-d studies involving a total of 66 rats, total metabolizable energy intake in Zn deficient rats was between 20 and 35% lower than in Zn+ rats, and carbohydrate intake accounted for essentially 100% of the lower energy intake. Fat and protein intakes were not affected by Zn deficiency. When Zn-deficient rats were repleted with Zn by providing diets containing adequate Zn, carbohydrate intake was restored to normal levels after 1 d of feeding. A transient difference in protein intake was noted during the repletion period, peaking during d 2-4 of repletion. Protein intake increased by more than 50% during this period. We hypothesize that specific changes in macronutrient intake patterns during development and recovery from Zn deficiency may be reflections, at least in part, of Zn-mediated changes in the central control of appetite.

Cloning and initial characterization of the promoter region of the rat cysteine-rich intestinal protein gene.

Cysteine-rich intestinal protein (CRIP) is an intestinal Zn(2+)-binding protein containing a single copy of the double Zn(2+)-finger arrangement known as the LIM motif. CRIP is developmentally regulated and can be induced by glucocorticoid hormones during the early suckling period. In this report we show that CRIP mRNA levels are induced by dexamethasone in cultured rat intestinal epithelial cells (IEC-6). Analysis of the 2644 bp of the 5'-flanking region of the CRIP gene revealed that the CRIP promoter lacks classical CAAT and TATA boxes but contains GC-rich regions in the proximal end of the promoter that probably function in transcription initiation. In addition to binding sites for transcription factors such as Sp-1, AP-2, OCT and GATA-2, there are multiple glucocorticoid-response elements. CRIP promoter constructs fused to the chloramphenicol acetyltransferase reporter gene and transfected into IEC-6 cells confirmed glucocorticoid responsiveness and the presence of negative acting elements. Mobility-shift assays revealed the presence of nuclear factors that bind to the CRIP promoter as a result of dexamethasone treatment. These experiments provide the initial data required to explore further the regulation of this tissue-specific developmentally regulated Zn(2+)-finger protein.

Nuclear retention of the induced mRNA following amino acid-dependent transcriptional regulation of mammalian ribosomal proteins L17 and S25.

An amino acid starvation-induced mRNA, increased up to 4-fold in the absence of amino acids, was identified previously as rat 60 S subunit ribosomal protein L17. The data presented here demonstrate that among ribosomal proteins, L17, as well as the smaller subunit ribosomal protein S25, are uniquely regulated by amino acid deprivation of cells; the increase in L17 and S25 mRNA content in response to substrate starvation is not shared by the 11 other ribosomal proteins tested. When rat Fao hepatoma cells were incubated in the presence of actinomycin D, the L17 mRNA level decayed below the basal level, regardless of medium amino acid content, and nuclear run-off assays confirmed that nutrient starvation leads to enhanced transcription of the L17 ribosomal protein gene. Likewise, the induction of S25 mRNA also was prevented in the presence of actinomycin D. Furthermore, the induction of L17 and S25 mRNA content was blocked by cycloheximide, demonstrating the requirement for a newly synthesized protein in the signaling pathway. Northern analysis with RNA isolated from cytoplasmic, polysomal, and nuclear enriched fractions indicated that the starvation-dependent increase in the S25 and L17 mRNAs is retained within the nucleus and not is available for translation. Amino acid refeeding of the cells caused the translocation of the stored nuclear mRNAs to the polysomal fraction.

Expression of cysteine-rich intestinal protein in rat intestine and transfected cells is not zinc dependent.

The cysteine-rich intestinal protein (CRIP) is a member of a superfamily of proteins containing the LIM motif (a double zinc finger) that has been shown to bind zinc. The role of zinc in the regulation of CRIP was examined in adult rats, cultured intestinal epithelial cells and in a transient transfection system. When adult male rats were fed diets with various amounts of zinc, the amount of ileal CRIP mRNA was only 19% lower in rats fed a zinc-deficient diet (1 mg Zn/kg) and was not different in the zinc-supplemented group (180 mg Zn/kg) compared with the zinc-adequate group (30 mg Zn/kg). In contrast, metallothionein mRNA levels were 76% lower and 80% greater than control levels in the zinc-deficient and zinc-supplemented groups, respectively. Using the chloramphenicol acetyltransferase (CAT) reporter gene, 5'-deletion products of the CRIP genomic promoter were tested for basal and zinc-induced CAT activity in transiently transfected IEC-6 cells. Treatment of the cells with zinc did not alter CAT activity of any construct. These results suggest that CRIP is not directly regulated by zinc in the intestine of rats.