Effects of long-term dehydration on oxidative stress, apoptotic markers and neuropeptides in the gastric mucosa of the dromedary camel

Effects of long-term dehydration and quick rehydration on the camel kidney: pathological changes and modulation of the expression of solute carrier proteins and aquaporins

BACKGROUND

Recurrent dehydration causes chronic kidney disease in humans and animal models. The dromedary camel kidney has remarkable capacity to preserve water and solute during long-term dehydration. In this study, we investigated the effects of dehydration and subsequent rehydration in the camel's kidney histology/ultrastructure and changes in aquaporin/solute carrier proteins along with gene expression.

RESULTS

In light microscopy, dehydration induced few degenerative and necrotic changes in cells of the cortical tubules with unapparent or little effect on medullary cells. The ultrastructural changes encountered in the cortex were infrequent during dehydration and included nuclear chromatin condensation, cytoplasmic vacuolization, mitochondrial swelling, endoplasmic reticulum/ lysosomal degeneration and sometimes cell death. Some mRNA gene expressions involved in cell stability were upregulated by dehydration. Lesions in endothelial capillaries, glomerular membranes and podocyte tertiary processes in dehydrated camels indicated disruption of glomerular filtration barrier which were mostly corrected by rehydration. The changes in proximal tubules brush borders after dehydration, were accompanied by down regulation of ATP1A1 mRNA involved in Na + /K + pump that were corrected by rehydration. The increased serum Na, osmolality and vasopressin were paralleled by modulation in expression level for corresponding SLC genes with net Na retention in cortex which were corrected by rehydration. Medullary collecting ducts and interstitial connective tissue were mostly unaffected during dehydration. CKD, a chronic nephropathy induced by recurrent dehydration in human and animal models and characterized by interstitial fibrosis and glomerular sclerosis, were not observed in the dehydrated/rehydrated camel kidneys. The initiating factors, endogenous fructose, AVP/AVPR2 and uric acid levels were not much affected. TGF-β1 protein and TGF-β1gene expression showed no changes by dehydration in cortex/medulla to mediate fibrosis. KCNN4 gene expression level was hardly detected in the dehydrated camel's kidney; to encode for Ca +  + -gated KCa3.1 channel for Ca +  + influx to instigate TGF-β1. Modulation of AQP 1, 2, 3, 4, 9 and SLC protein and/or mRNAs expression levels during dehydration/rehydration was reported.

CONCLUSIONS

Long-term dehydration induces reversible or irreversible ultrastructural changes in kidney cortex with minor effects in medulla. Modulation of AQP channels, SLC and their mRNAs expression levels during dehydration/rehydration have a role in water conservation. Cortex and medulla respond differently to dehydration/rehydration.

Effects of long-term dehydration on stress markers, blood parameters, and tissue morphology in the dromedary camel (Camelus dromedarius)

Introduction

Dromedary camels robustly withstand dehydration, and the rough desert environment but the adaptation mechanisms are not well understood. One of these mechanisms is that the dromedary camel increases its body temperature to reduce the process of evaporative cooling during the hot weather. Stress in general, has deleterious effects in the body. In this study, we sought to determine the effects of dehydration and rehydration on stress parameters in the dromedary camels and how it pacifies these effects.

Methods

Nineteen male camels were randomly divided into control, dehydrated and rehydrated groups, and fed alfalfa hay ad-libitum. The dehydrated and rehydrated groups were water-restricted for 20 days after which the rehydrated camels were provided with water for 72 h. The control and dehydrated camels were slaughtered at day 20 from the start of experiment whereas the rehydrated group was killed 72 h later. Many biochemical, hematological histopathological parameters and gene analysis were performed in relevant tissues collected including blood, plasma, and tissues.

Results and discussion

It was observed that severely dehydrated camels lost body weight, passed very hard feces, few drops of concentrated urine, and were slightly stressed as reflected behaviorally by loss of appetite. Physiologically, the stress of dehydration elicited modulation of plasma stress hormones for water preservation and energy supply. Our results showed significant increase in cortisol, norepinephrine and dopamine, and significant decrease in epinephrine and serotonin. The significant increase in malondialdehyde was accompanied with significant increase in antioxidants (glutathione, retinol, thiamin, tocopherol) to provide tissue protection from oxidative stress. The physiological blood changes observed during dehydration serve different purposes and were quickly restored to normality by rehydration. The dehydrated/rehydrated camels showed reduced hump size and serous atrophy of perirenal and epicardial fat. The latter changes were accompanied by significantly increased expression of genes encoding proteins for energy production (ANGPTL4, ACSBG1) from fat and significantly decreased expression of genes (THRSP; FADS 1&2) encoding proteins enhancing energy expenditure. This process is vital for camel survival in the desert. Dehydration induced no major effects in the vital organs. Only minor degenerative changes were observed in hepatic and renal cells, physiological cardiomyocyte hypertrophy in heart and follicular hyperplasia in splenic but lipidosis was not depicted in liver hepatocytes. Ketone bodies were not smelled in urine, sweat and breathing of dehydrated animals supporting the previous finding that the ß hydroxybutyrate dehydrogenase, a key enzyme in ketone body formation, is low in the camel liver and rumen. Rehydration restored most of blood and tissues to normal or near normal. In conclusion, camels are adapted to combat dehydration stress and anorexia by increasing anti-stressors and modulating genes involved in fat metabolism.

Transcriptomic plasticity of the hypothalamic osmoregulatory control centre of the Arabian dromedary camel

Water conservation is vital for life in the desert. The dromedary camel (Camelus dromedarius) produces low volumes of highly concentrated urine, more so when water is scarce, to conserve body water. Two hormones, arginine vasopressin and oxytocin, both produced in the supraoptic nucleus, the core hypothalamic osmoregulatory control centre, are vital for this adaptive process, but the mechanisms that enable the camel supraoptic nucleus to cope with osmotic stress are not known. To investigate the central control of water homeostasis in the camel, we first build three dimensional models of the camel supraoptic nucleus based on the expression of the vasopressin and oxytocin mRNAs in order to facilitate sampling. We then compare the transcriptomes of the supraoptic nucleus under control and water deprived conditions and identified genes that change in expression due to hyperosmotic stress. By comparing camel and rat datasets, we have identified common elements of the water deprivation transcriptomic response network, as well as elements, such as extracellular matrix remodelling and upregulation of angiotensinogen expression, that appear to be unique to the dromedary camel and that may be essential adaptations necessary for life in the desert.

Purification and biochemical characterization of catalase that confers protection against hydrogen peroxide induced by stressful desert environment: the Camelus Dromedarius kidney catalase

Camel is continually exposed to stressful desert environment that enhances generation of reactive oxygen species, including hydrogen peroxide (H₂O₂). Catalase plays an important role in detoxification of H₂O₂. A highly active catalase from camel kidney was purified to homogeneity, with a specific activity of 1,774,392 U/mg protein, using ion exchange and metal chelate affinity chromatography. The molecular weight of the enzyme was 268 kDa consisting of four identical subunits of 63 kDa. The enzyme showed higher optimum temperature (45 °C) and higher activation energy (4.37 kJ mol^-1). The thermodynamic parameters, ΔH, ΔG and ΔS, were determined. The effect of various metal ions and chemicals on enzyme activity was investigated. K_m, V_max, k_cat and k_cat/K_m values for H₂O₂ were found to be 46 mM, 10,715,045 U/mg, 48,265,968 s^-1 and 2,966,562 s^-1mM^-1, respectively. Camel kidney catalase displayed higher affinity efficiency for H₂O₂ and can protect reduced glutathione (GSH) from oxidation by H₂O₂. Sodium azide was found to be a noncompetitive inhibitor of enzyme with K_i and IC₅₀ of 17.88 µM and 20.94 µM, respectively. Camel catalase showed unique biochemical properties. Interestingly, camel catalase can protect molecules (GSH) and organ functions (kidney) from the toxic effects of H₂O₂ induced by stressful desert environment.

Multiomic analysis of the Arabian camel (Camelus dromedarius) kidney reveals a role for cholesterol in water conservation

The Arabian camel (Camelus dromedarius) is the most important livestock animal in arid and semi-arid regions and provides basic necessities to millions of people. In the current context of climate change, there is renewed interest in the mechanisms that enable camelids to survive in arid conditions. Recent investigations described genomic signatures revealing evolutionary adaptations to desert environments. We now present a comprehensive catalogue of the transcriptomes and proteomes of the dromedary kidney and describe how gene expression is modulated as a consequence of chronic dehydration and acute rehydration. Our analyses suggested an enrichment of the cholesterol biosynthetic process and an overrepresentation of categories related to ion transport. Thus, we further validated differentially expressed genes with known roles in water conservation which are affected by changes in cholesterol levels. Our datasets suggest that suppression of cholesterol biosynthesis may facilitate water retention in the kidney by indirectly facilitating the AQP2-mediated water reabsorption.

The effect of long-term dehydration and subsequent rehydration on markers of inflammation, oxidative stress and apoptosis in the camel kidney

Background

Dehydration has deleterious effects in many species, but camels tolerate long periods of water deprivation without serious health compromise. The kidney plays crucial role in water conservation, however, some reports point to elevated kidney function tests in dehydrated camels. In this work, we investigated the effects of dehydration and rehydration on kidney cortex and medulla with respect to pro-inflammatory markers, oxidative stress and apoptosis along with corresponding gene expression.

Results

The cytokines IL-1β and IL-18 levels were significantly elevated in the kidney cortex of dehydrated camel, possibly expressed by tubular epithelium, podocytes and/or mesangial cells. Elevation of IL-18 persisted after rehydration. Dehydration induced oxidative stress in kidney cortex evident by significant increases in MDA and GSH, but significant decreases in SOD and CAT. In the medulla, CAT decreased significantly, but MDA, GSH and SOD levels were not affected. Rehydration abolished the oxidative stress. In parallel with the increased levels of MDA, we observed increased levels of PTGS1 mRNA, in MDA synthesis pathway. GCLC mRNA expression level, involved in GSH synthesis, was upregulated in kidney cortex by rehydration. However, both SOD1 and SOD3 mRNA levels dropped, in parallel with SOD activity, in the cortex by dehydration. There were significant increases in caspases 3 and 9, p53 and PARP1, indicating apoptosis was triggered by intrinsic pathway. Expression of BCL2l1 mRNA levels, encoding for BCL-xL, was down regulated by dehydration in cortex. CASP3 expression level increased significantly in medulla by dehydration and continued after rehydration whereas TP53 expression increased in cortex by rehydration. Changes in caspase 8 and TNF-α were negligible to instigate extrinsic apoptotic trail. Generally, apoptotic markers were extremely variable after rehydration indicating that animals did not fully recover within three days.

Conclusions

Dehydration causes oxidative stress in kidney cortex and apoptosis in cortex and medulla. Kidney cortex and medulla were not homogeneous in all parameters investigated indicating different response to dehydration/rehydration. Some changes in tested parameters directly correlate with alteration in steady-state mRNA levels.