Assessment of metals induced histopathological and gene expression changes in different organs of non-diabetic and diabetic rats

Abstract

Diabetes is a complex metabolic disorder and different environmental toxicants including heavy metals have been involved in diabetes induction. Therefore, assessment of the environmental risk factors and heavy metals induced toxicity have become critical for reducing the consequences of metals pollutants. Previously, we reported heavy metals induced nephrotoxicity in non-diabetic and diabetic rats. Here, we extended our analysis by examining the heavy metals induced organs (heart, kidney, liver, pancreas, and spleen) damage in diabetic and non-diabetic Wistar rats using histopathology and quantitative real-time PCR (qRT-PCR). Following the generation of the diabetic rat model, the animals were exposed to heavy metals including lead (Pb), arsenic (As), manganese (Mn) and cadmium (Cd). Both non-diabetic and diabetic rats were exposed to heavy metals for 30 days and subsequently, the heart, kidney, liver, pancreas and spleen tissues were examined. Heavy metal treatment resulted in irregularly arranged myofibrils and vacuolization in the heart tissue of metal treated groups as evident from hematoxylin and eosin (H & E) staining. The kidney tissue of rats treated with heavy metals showed tubular degeneration, fibrosis, hemorrhage, and vacuolation. The liver of the heavy metals treated rats exhibited cellular degeneration and necrosis. The pancreatic tissue of streptozotocin injected untreated and metal treated rats revealed severe degeneration, necrosis, degranulation, shrinkage, and depression in the islets of Langerhans. Increased red pulp area and congestion were observed in the spleen of the metal mixture treated non-diabetic and diabetic rats. In line with the histological data, the qRT-PCR analysis showed downregulated expression of Bcl 2 and upregulation of Caspase-3 in nondiabetic and diabetic metal treated rats as compared to the non-diabetic untreated rats. In conclusion, the present study revealed, diabetic rats are more prone to metal alone as well as metal mixture induced organ damage as compared to non-diabetic rats. Diabetes is a metabolic disorder, characterized by impaired insulin secretion, fasting hyperglycemia or insulin receptor insensitivity. The prevalence of diabetes is increasing all over the world and increased from 4.7% in 1980 to 8.5% in 2014 1. Diabetes is the 7 th leading cause of mortality in the United States and worldwide and results in serious complications including kidney disease, cardiovascular disease, blindness, etc. 1,2. It is well documented that environmental exposure to synthetic or naturally occurring chemical elements contribute to diabetes induction 3-5. Metals are essential components of biological functions, while their higher concentrations can be toxic 6,7. Cadmium (Cd), arsenic (As), cobalt (Co), mercury (Hg), manganese (Mn) and lead (Pb) are known as endocrine-disrupting chemicals 8,9. Importantly, Pb, As, Mn and Cd play a crucial role in public health issues 10 .

Effects of oral exposure to arsenite on arsenic metabolism and transport in rat kidney

“…According to these results, major renal damage could be ruled out. This is in contrast to some works clearly showing renal damage by arsenic in humans (Meliker et al, 2007, Robles-Osorio et al, 2015, even in rodents (Shahid et al, 2014, Riaz et al, 2020, but the experimental design and epidemiology in humans have, sometimes, provided conflicting results (Samelo et al, 2020). However, it is known that these classical endpoints are not sensitive enough to detect early renal damage (Sabbisetti and Bonventre, 2012), and several molecules occurring in urine in the very early stages of renal injury have been found to be useful as biomarkers, such as neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule 1 (KIM-1), N-acetyl-β-D-glucosaminidase (NAG), liver fatty acid binding protein (L-FABP), heart fatty acid binding protein (H-FABP, also known as FABP3), tissue inhibitor metalloproteinase-2 (TIMP-2), insulin-like growth factor binding protein 7 (IGFBP-7), clusterin, and netrin, among others (Griffin et al, 2019;Schaub, 2016).…”

Arsenic exposure and non-carcinogenic health effects

“…), and reduced activities of antioxidant enzymes, such as, SOD, CAT, and TrxR in pancreas tissue, compared with control rats. 122,133–137 Similarly, STZ-induced diabetic rats exposed to arsenic presented severe degeneration, vacuolation, necrosis, degranulation, and shrinkage in the islets of Langerhans 138 (Figure 2).

Figure 2.Molecular mechanisms of pancreas damage induced by arsenic.

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“…This iAs-associated diabetogenic toxicity might be related to molecular level with pro-oxidant properties of iAs that induces ROS overproduction, possibly through of elevated SIRT3 levels and decreased mitochondrial complex II activity in rats with deregulated glucose metabolism. 139,140 This oxidative environment in pancreatic β-cells promotes low protein levels of PPARγ-PINK1 axis associated with mitophagy inhibition, TrxR inactivation, and high ASK1 levels, favoring apoptosis induction characterized by mitochondrial membrane potential disruption, cytochrome c release, increased pro-apoptotic protein Bax, reduced anti-apoptotic Bcl-2 protein levels, caspase-3 activation, and DNA fragmentation 134,137,138,141,142 (Figure 2). In addition to apoptosis, in pancreas cells, iAs induces a ROS-dependent autophagic cell death accompanied with antioxidant Nrf2/ TrxR pathway inhibition.…”

Air Pollution, Oxidative Stress, and the Risk of Development of Type 1 Diabetes

“…In addition, these metals are classified as known or probable human carcinogens, according to the U.S. Environmental Protection Agency (EPA) and the International Agency for Research on Cancer (IARC) [ 52 ]. Cd, As, Co, Hg, Mn, and Pb are documented to be endocrine disruptors [ 46 , 53 ].…”